JP7553423B2 - Robot System - Google Patents

Description

This disclosure relates to a robot system for grasping an object.

A technology has been disclosed that improves the stability of an object's grip in a robot hand equipped with multiple contact elements equivalent to fingers, a drive mechanism that drives the contact elements, and a control device that controls the operation of the drive mechanism (for example, Patent Document 1). The control device in Patent Document 1 sets a target action force by solving simultaneous equations that must be satisfied by the action force acting on the object from the contact elements under friction constraint conditions. When the target action force is obtained, the control device controls the operation of the drive mechanism so that the action force from the contact elements on the object matches the target action force.

Patent No. 5829103

The friction constraint condition indicates that the contact element and the object do not slip relative to each other at the contact point where the contact element comes into contact with the object, and is generally expressed as a conditional equation that states that the vector representing the acting force is within the friction cone.

In the robot hand of Patent Document 1, the tips of the fingers are roughly hemispherical, making it difficult to grasp thin objects. Therefore, in order to expand the range of objects that can be grasped by the robot hand, the inventors of the present application came up with the idea of providing claws on the fingers. However, the shape of the claws is often more complex than the shape of the fingers, making it difficult to obtain the contact points. This makes it difficult to calculate the target action force that should be output when grasping an object with the claws, resulting in the problem that it is not easy to grasp with the claws.

In view of the above background, the present invention aims to expand the range of objects that can be grasped by a robot hand in a robot system that includes a robot hand having a finger mechanism with claws and a control device that controls the robot hand.

In order to solve the above-mentioned problems, one aspect of the present invention is a robot system (1) for grasping an object, comprising: a robot hand (2) having a plurality of finger mechanisms (24), force sensors (26) provided on each of the finger mechanisms, and drive units (28) for driving each of the finger mechanisms; and a control device (20) for controlling the driving of each of the drive units, wherein the finger mechanisms include a finger body (30) and a claw (32) provided on the finger body, and the control device acquires a contact point ( _Pt ) between the finger body and the object based on the acquisition result of the force sensor, calculates a target action force by changing at least a portion of a plurality of contact point grasping conditions that should be satisfied for an action force that should act on the object at the contact point by each of the finger bodies in order to grasp the object, by regarding the claw as being in contact with an outer surface of the object, and drives each of the drive units to apply the target action force to the object.

The inventors of the present application have found that if the finger mechanism is driven to output a target action force based on changed conditions assuming that the object can be grasped by the claws, there are cases where the object can be grasped by the claws. According to this aspect, the target action force is calculated by changing the conditions assuming that the object can be grasped by the claws. When the drive device drives the finger mechanism to output the target action force, there are cases where the object can be grasped by the claws. Therefore, the range of objects that can be grasped by the robot hand can be expanded compared to cases where the possibility of grasping by the claws is not taken into consideration.

In the above aspect, preferably, the control device sequentially executes a contact point acquisition step (ST11) of acquiring the position of the contact point based on the result of acquisition by the force sensor, a body action force search step (ST12) of setting a plurality of contact point gripping conditions that should be satisfied by the action force acting on the object by each of the finger bodies to enable gripping at the contact point, and searching for a solution that satisfies all of the contact point gripping conditions to acquire the target action force, and a claw action force search step (ST15) of setting claw gripping conditions by changing at least a part of the contact point gripping conditions by regarding the claw as being in contact with the outer surface of the object at the contact point, and searching for a solution that satisfies the claw gripping conditions to acquire the target action force, when a solution cannot be acquired in the body action force search step and the contact point satisfies a predetermined claw contact condition.

According to this aspect, when a solution cannot be obtained that must be satisfied by the acting force to grasp an object under conditions in which the object is grasped by the finger body, a solution is searched for by changing some of the conditions on the assumption that the object is grasped by the claw. In this way, even when a solution cannot be searched for under conditions in which the object is grasped by the finger body, a solution is searched for by taking into consideration the possibility that the object can be grasped by contacting the claw, so that the range of objects that can be grasped by the robot hand can be expanded.

In the above aspect, preferably, the control device determines that the contact point satisfies the claw contact condition when the contact point is within a predetermined surface area (R) of the finger body, and the surface area is set within the area where the claw contacts the outer surface of the object when the drive device is driven to output the target action force calculated by modifying at least a portion of the contact point gripping condition by regarding the claw as contacting the outer surface of the object.

According to this aspect, when the finger mechanism is driven to exert a target force, it is possible to determine whether the nail will come into contact with an object based on the position of the contact point, making the determination easy.

In the above aspect, preferably, the control device calculates the target action force by modifying the friction constraint condition, which is one of the contact point gripping conditions that the component of the action force that acts to slide the finger body against the object is equal to or less than the maximum static friction force, by regarding the nail as being in contact with the outer surface of the object.

This aspect makes it easy to set the conditions under which the claws can grasp an object.

In the above aspect, preferably, the control device changes the friction constraint condition to one of the following: a force vector corresponding to the acting force that the claw should apply to the object is contained within a cone (54) whose half apex angle (θ') is determined by the maximum static friction coefficient (μs _' ) between the claw and the object, and whose axis (52) extends in any of the following directions: horizontally, parallel to the support surface on which the object is placed, and perpendicular to the outer surface of the object; the force vector is contained within a polygonal pyramid (60) circumscribing the cone; or the force vector is contained within a polygonal pyramid (70) inscribing the cone.

This aspect makes it easy to set conditions under which the claws can grip an object without slipping on the object.

In the above aspect, preferably, the tip portion (38) of the finger body that can contact the object forms part of a sphere, an oblate spheroid, or a spherical surface.

This aspect makes it easy to obtain the contact point.

In the above aspect, preferably, when the object is placed on the top surface of a desk, the control device brings the finger mechanism into contact with the top surface of the desk, and then drives the drive device to move the finger mechanism toward the object while keeping it in contact with the top surface, and after the finger mechanism comes into contact with the object, obtains the contact point based on the results obtained by the force sensor.

This aspect makes it possible to properly determine whether or not the object is in a state where it can be grasped by the robot hand.

In the above aspect, preferably, when the control device is driving the drive device to move the finger mechanism toward the object, the control device determines that the finger mechanism has come into contact with the object when the magnitude of the contact force, which is the tangential component of the force vector applied to the finger mechanism acquired by the force sensor, becomes equal to or greater than a predetermined threshold value.

This aspect makes it possible to properly determine when the finger mechanism has come into contact with an object.

In the above aspect, preferably, the control device brings the claw of the finger mechanism into contact with the top surface of the desk, and then drives the drive device to move the claw of the finger mechanism toward the object while keeping it in contact with the top surface, and the coefficient of kinetic friction between the top surface of the desk and the claw is smaller than the coefficient of kinetic friction between the top surface of the desk and the finger body.

This aspect allows accurate detection of contact with an object.

In the above aspect, preferably, the rigidity of the nail is greater than the rigidity of the finger body.

This aspect allows the claws to stably grasp an object.

According to the above aspects, in a robot system including a robot hand having a finger mechanism with claws and a control device that controls the robot hand, it is possible to expand the range of objects that can be grasped by the robot hand.

FIG. 1 is a perspective view of a robot provided with a robot system according to the present invention; A perspective view of a robot hand and an enlarged view of the area enclosed by the two-dot chain line. Side view of the finger mechanism when the finger pad is in contact with an object Contact Processing Flowchart FIG. 13 is a side view showing the finger mechanism and the desk when a tracing operation is being performed; Calculation process flowchart FIG. 1 is an explanatory diagram for explaining condition (C); An example of the movement of the finger mechanism when the action force obtained by changing the friction constraint condition is output, taking into account the gripping by the claws. FIG. 1 is an explanatory diagram for explaining condition (D); FIG. 11 is an explanatory diagram for explaining condition (C) according to the second embodiment. FIG. 11 is an explanatory diagram for explaining a modification of condition (C) according to the second embodiment. A table showing the direction of the unit vector ni parallel to the axis direction of the cone and the deformation of the shape of the object corresponding to condition (D). A table showing the direction of the unit vector ni parallel to the axis direction of the cone and the deformation of the shape of the object corresponding to condition (D). A table showing the direction of the unit vector ni parallel to the axis direction of the cone and the modified shapes and arrangements of the objects corresponding to condition (D).

The robot system according to this embodiment of the present invention will be described below with reference to the drawings.

First Embodiment
As shown in Fig. 1, a robot system 1 is applied to a robot 3 equipped with a robot hand 2. In this embodiment, the robot system 1 is mounted on a humanoid robot equipped with a head 5, a torso 6, arms 7, and legs 8. The robot hand 2 is a multi-fingered, multi-jointed robot provided at the tip of the arm 7. The robot hand 2 has the function of grasping an object in the same manner as a human hand. However, the robot system 1 according to the present invention may also be applied to a work robot used in a factory or the like, which is similarly equipped with the robot hand 2.

The robot 3 is equipped with at least one external world acquisition device 10 in the head 5. The external world acquisition device 10 is a device that acquires information equivalent to human vision, and is composed of a camera that acquires an image in front of the head 5. In this embodiment, the robot 3 is equipped with two external world acquisition devices 10, each of which is provided at a position on the head 5 that corresponds to a human eye. The head 5 may also be equipped with a speaker that emits sound and a microphone that acquires external sound.

The robot 3 acquires information from the external environment acquisition device 10, and based on that information, moves the legs 8 to walk on two legs. The robot 3 can also acquire human voices via a microphone, emit sounds via a speaker, and converse with people. To perform these various movements, the robot 3 is configured with a system that supports the various movements.

The robot system 1 according to the present invention is a system for a robot 3 to grasp an object (hereinafter, the grasping system 1A). Here, the operation realized by the grasping system 1A, in particular the operation of grasping a square plate-shaped object 14 (e.g., a plastic plate) placed on the top surface 12A of a desk 12, will be described.

The gripping system 1A includes a robot hand 2 that forms part of the arm 7, and a control device 20.

As shown in FIG. 2, the robot hand 2 constitutes the tip portion of the arm 7. The robot hand 2 includes a palm portion 22, a plurality of finger mechanisms 24 extending from the palm portion 22, a plurality of force sensors 26 provided on each of the finger mechanisms 24, and a plurality of drive devices 28 each corresponding to one of the finger mechanisms 24.

As shown in FIG. 2, the palm portion 22 is a member having a substantially flat plate shape, and constitutes a portion corresponding to the palm of a human hand. In this embodiment, five finger mechanisms 24 are connected to the palm portion 22, but the number of finger mechanisms 24 connected may be two or more. Hereinafter, the finger mechanisms 24 corresponding to the thumb, index finger, middle finger, ring finger, and little finger will be referred to as the first finger mechanism 24A, the second finger mechanism 24B, the third finger mechanism 24C, the fourth finger mechanism 24D, and the fifth finger mechanism 24E, in the order of description.

Each finger mechanism 24 includes a finger body 30 and a claw 32.

The finger body 30 includes a first link 30A, a second link 30B, and a third link 30C. The first link 30A is rotatably connected to the palm portion 22 at its base end. The second link 30B is rotatably connected to the tip of the first link 30A at its base end. The third link 30C is rotatably connected to the tip of the second link 30B at its base end. The first link 30A, the second link 30B, and the third link 30C correspond to the proximal, middle, and distal phalanges of the fingers of a human hand, respectively.

In this embodiment, the first link 30A, except for the first finger mechanism 24A, is connected to the palm 22 so as to be rotatable around one axis. The rotation axis (hereinafter, the first axis L ₁ ) of the first link 30A, except for the first finger mechanism 24A, is set in a direction perpendicular to the extension direction of the first link 30A. The first link 30A of the first finger mechanism 24A is connected to the palm 22 so as to be rotatable around two axes, the first axis L ₁ and the axis L ₀ extending in the extension direction of the first link 30A. The second link 30B is connected to the first link 30A so as to be rotatable around one axis. The rotation axis (hereinafter, the second axis L ₂ ) of the second link 30B is set so as to be parallel to the first axis L ₁ and perpendicular to the extension direction of the first link 30A. The third link 30C is connected to the second link 30B so as to be rotatable around one axis. The rotation axis of the third link 30C (hereinafter, the third axis _L3 ) is set to be perpendicular to the first axis _L1 and also perpendicular to the extension direction of the second link 30B.

As shown in the enlarged view of FIG. 2 and FIG. 3, the third link 30C includes a base 36 connected to the second link 30B at the base end side, and a finger pad 38 provided at the tip of the base 36. The base 36 is cylindrical. The finger pad 38 has a shape (hereinafter, a quarter hemisphere) in which a sphere passes through its center (hereinafter, fingertip center _Pf ) and is cut by two planes, a plane _Π1 parallel to the extension direction of the third link 30C and a plane _Π2 perpendicular to the fingertip center _Pf . The finger pad 38 is connected to the base 36 at the end face on the third link 30C side. However, the finger pad 38 is not limited to a quarter hemisphere, and may be a hemisphere, a semi-spherical sphere, a semi-oblate sphere, or a semi-cylindrical sphere. Here, a semi-prolate spheroid means a shape obtained by dividing a prolate spheroid (a rotating body obtained by rotating an ellipse around its major axis) by a plane passing through its center and perpendicular to the major or minor axis. A semi-oblate spheroid means a shape obtained by dividing an oblate spheroid (a rotating body obtained by rotating an ellipse around its minor axis) by a plane passing through its center and perpendicular to the major or minor axis. However, the tip shape of third link 30C is not limited to these modes and may be any mode as long as it is known and its surface shape can be expressed by a simple mathematical formula.

The claw 32 is connected to the finger pad 38 or the base 36 at the base end side and extends in a direction away from the base 36. In this embodiment, the claw 32 is connected to the tip surface of the base 36 and a surface of the finger pad 38 parallel to the extension direction of the base 36. In this embodiment, the claw 32 is connected to the surface parallel to the extension direction of the base 36 and includes a claw body 32A extending in a direction away from the base 36 and an extension part 32B that is bent at the extension end of the claw body 32A and extends in a direction perpendicular to the extension direction of the base 36 and toward the finger pad 38. The point on the outer surface of the finger pad 38 that is not covered by the claw 32 and the third link 30C is located at the tip of the finger body 30, is a part that can contact the object 14, and forms a part of a sphere. In other words, the point on the outer surface of the finger pad 38 is located on a sphere centered on the fingertip center _Pf . However, for example, when the finger pad 38 is semi-oblong or semi-oblate, the points on the outer surface of the finger pad 38 that are not covered by the nail 32 and the third link 30C are located at the tip of the finger body 30, are parts that can come into contact with the object 14, and form part of a prolate or oblate spheroid.

The claw 32 is preferably made of a material that has a smaller coefficient of friction (specifically, kinetic coefficient of friction) between the claw 32 and the top surface 12A of the desk 12 than the coefficient of friction (kinetic coefficient of friction) between the finger pad 38 and the top surface 12A of the desk 12. In addition, the rigidity (bending rigidity and shear rigidity) of the claw 32 is set higher than that of the finger body 30.

The force sensor 26 is the finger body 30 of the corresponding finger mechanism 24, and is attached to the tip of the base 36 of the third link 30C. The force sensor 26 is a so-called six-axis force sensor (also called a six-axis force-moment sensor), and acquires the force components (i.e., force vectors) in the three orthogonal axis directions applied to the finger pad 38, and the moment components around each axis. The force sensor 26 may be based on, for example, a strain gauge type, a capacitance type, a piezoelectric type, or an optical type, or may be composed of a composite sensor of a known MEMS and a strain-generating body.

Each of the driving devices 28 is composed of one or more motors provided on the arm 7. The driving force of the driving device 28 is transmitted to the first link 30A, the second link 30B, and the third link 30C of the corresponding finger mechanism 24 via the power transmission mechanism 40. The driving device 28 generates a driving force to rotate the first link 30A relative to the palm 22, rotate the second link 30B relative to the first link 30A, and rotate the third link 30C relative to the second link 30B. This allows the driving device 28 to bend and extend (flex and extend) the corresponding finger body 30. The driving device 28 obtains the rotation angle of each link by accumulating the driving amount of the first link 30A, the second link 30B, and the third link 30C. However, this is not limited to the above embodiment, and a rotation angle sensor may be provided between the palm portion 22 and the first link 30A, between the first link 30A and the second link 30B, between the second link 30B and the third link 30C, etc., and the driving device 28 may acquire the detection results of the rotation angle sensor. The power transmission mechanism 40 may be composed of a wire, a pulley, etc., and may have any configuration as long as it can transmit the power of the driving device 28 to cause the finger mechanism 24 to bend and extend.

The control device 20 is composed of a computer equipped with a CPU 41 (Central Processing Unit, also called a processor), a main memory device 42 such as a RAM 42A (Random Access Memory) or a ROM 42B (Read Only Memory), and an auxiliary memory device 43 such as a HDD (Hard Disk Drive) or an SSD (Solid State Drive). In this embodiment, the control device 20 is provided in the torso 6 of the robot 3.

The control device 20 is connected to the external environment acquisition device 10, the force sensor 26, and the drive device 28.

The control device 20 acquires the position, size, and external shape of the object 14 based on the image acquired by the external world acquisition device 10. Furthermore, the control device 20 identifies the type of object 14 from the image acquired by the external world acquisition device 10 based on the learning model stored in the auxiliary memory device 43 (or the main memory device 42). For example, the control device 20 can identify and acquire from the image that the object 14 in front of the robot 3 is on the desk 12, and the type of object 14 placed on the desk 12, such as a book, coin, plastic plate, etc.

The control device 20 then estimates the position of the center of gravity, mass, and moment of inertia tensor of the object 14 based on the object information table stored in the auxiliary storage device 43 (or the main storage device 42) and the size of the object 14 acquired from an image. The object information table records the name of the object 14 and the corresponding standard size, mass, density, and material. Furthermore, the object information table may record the maximum static friction coefficient _μs and kinetic friction coefficient between the side of the object 14 and the surface of the finger pad 38, the maximum static friction coefficient μs' and kinetic friction coefficient between the side of the object 14 and the nail 32, the maximum load λ _max that can be applied to the object 14, the moment of inertia tensor, and the like.

The control device 20 further stores information related to the shape of each finger pad 38 of the finger body 30. The information related to the shape of the finger pad 38 may be, for example, a parameter included in a mathematical expression indicating the shape of the finger pad 38. In this embodiment, since the shape of the finger pad 38 is a quarter hemisphere, the control device 20 stores at least the radius r _d of the quarter hemisphere.

The control device 20 drives the drive device 28 to rotate each of the first link 30A, the second link 30B, and the third link 30C provided on the finger body 30. The control device 20 acquires the rotation angles of each of the first link 30A, the second link 30B, and the third link 30C from the drive device 28. The control device 20 acquires the position and posture of the finger pad 38 based on the acquired rotation angles.

In this embodiment, the control device 20 can obtain a vector _pfi indicating the position of the fingertip center Pfi of the i-th finger mechanism 24 (i=1 to 5) from the driving device 28. Furthermore, the control device 20 obtains unit vectors _π1i and _π2i indicating the normal directions of two planes _{Π1i and Π2i} cutting the sphere corresponding to the finger pad 38 from the driving device 28. However, the plane _Π1i is set to be parallel to the extension direction of the third link 30C, and the plane _Π2i is set to be perpendicular to the extension direction of the third link 30C. In addition, the unit vectors _π1i and _π2i are set to face the direction in which the finger pad 38 is provided. As shown in FIG. 1, each vector is expressed in an absolute coordinate system with the _X0 axis in the horizontal forward direction, the _Y0 axis to the left, and the _Z0 axis vertically upward, based on a predetermined position in the space in which the robot 3 is placed.

Using p _fi , π _1i , π _2i and radius r _d , the condition that must be satisfied by vector x _i indicating a point on the surface of the finger pad 38 of the i-th finger mechanism 24 (i=1, 2, 3) is expressed by equation (1).

In the above formula (1), ∩ indicates "and", and ||x _i - p _fi || indicates the distance between the point indicated by the vector x _i and the fingertip center P _f of the corresponding finger mechanism 24. The first and second formulas in formula (1) indicate that the point on the surface of the finger pad 38 is located on the side of the unit vectors π _1i and π _2i with respect to the surfaces Π _1i and Π _2i , respectively. The third formula in formula (1) indicates that the point on the surface of the finger pad 38 is located on a spherical surface of radius r _d centered on the fingertip center P _f .

Next, the process performed by the control device 20 will be described when a square plate-shaped object 14 placed on a desk 12 having a horizontal upper surface 12A is grasped with three finger mechanisms 24 (first to third finger mechanisms 24). When the control device 20 attempts to grasp the object 14, it first executes a contact process. The contact process is a process for driving each of the finger mechanisms 24 and bringing the finger mechanisms 24 into contact. The contact process will be described below with reference to the flowchart shown in FIG. 4.

As shown in FIG. 4, in the first step ST1 of the contact process, the control device 20 acquires the outline of the object 14 on the desk 12 based on the image acquired by the external environment acquisition device 10. The control device 20 then estimates the position of the center of gravity from the outline of the object 14 and sets a coordinate system (reference coordinate system) with the position of the center of gravity as the origin. In this embodiment, the control device 20 sets the X-axis and Y-axis of the reference coordinate system in directions parallel to the horizontal plane, and sets the Z-axis to face vertically upward. In this embodiment, since the top surface 12A of the desk 12 is horizontal, the X-axis and Y-axis are parallel to the top surface 12A of the desk 12. Since the reference coordinate system is a translation of the absolute coordinate system, formula (1) also holds in the reference coordinate system. When the control device 20 completes the acquisition of the outline and the position of the center of gravity of the object 14 and the setting of the reference coordinate system, the control device 20 executes step ST2.

In step ST2, the control device 20 drives the drive device 28 to bring the tips of the three finger mechanisms 24 into contact with the top of the desk 12. At this time, the control device 20 may also drive the legs 8, the torso, etc., as necessary. The control device 20 controls the finger mechanisms 24 so that the tips of the finger mechanisms 24 are positioned in positions that surround the object 14 (more specifically, the outer shape of the object 14).

In this embodiment, the tips of the finger mechanisms 24 are arranged to face parallel surfaces of the object 14. At this time, the claws 32 of each of the three finger mechanisms 24 are in contact with the top surface 12A of the desk 12. The control device 20 may determine whether the tips of the finger mechanisms 24 (i.e., the claws 32) have contacted the top surface 12A of the desk 12 based on the detection results of the force sensor 26.

When the tips of the three finger mechanisms 24 each come into contact with the top surface 12A of the desk 12, the control device 20 executes the processing of step ST2.

In step ST2, the control device 20 drives the drive device 28 to move each of the finger mechanisms 24 toward the side of the object 14. At this time, the control device 20 controls the drive device 28 so that the finger mechanism 24 performs a tracing motion in which the tip of the finger mechanism 24 (i.e., the claw 32) is maintained in contact with the top surface 12A of the desk 12 and the finger mechanism 24 moves toward the object 14. In this embodiment, the control device 20 controls the drive device 28 so that the finger mechanism 24 moves toward the center of gravity of the object 14. The control device 20 may control the drive device 28 so that, during the tracing motion, the generation of in-plane forces parallel to the top surface 12A of the desk 12 is minimized.

During the tracing operation, the control device 20 continues to perform a determination process to determine whether or not the finger mechanism 24 has touched the object 14. In the determination process, as shown in Fig. 5, the control device 20 ignores a component Fdz of a force vector (detection force _Fd ) acquired by the force sensor 26 in the normal direction (i.e., Z direction) of the top surface 12A of the desk 12, and determines whether or not the finger mechanism 24 has touched the object 14 based on a component (contact force _Ft ) of the force _vector in the tangential direction (direction parallel to the top surface 12A of the desk 12, i.e., the horizontal plane; i.e., XY directions; see the solid arrow in Fig. 5) of the force vector.

Specifically, the control device 20 converts the force vector acquired by the force sensor 26 into a force vector in a reference coordinate system by appropriately performing coordinate conversion. After that, the control device 20 extracts only the force components in the XY directions (i.e., the contact force F _t ), squares and adds them, and calculates the square root to acquire the magnitude of the force in the XY plane (i.e., the contact force F _t ). When the magnitude of the acquired contact force F _t (the magnitude of the force in the XY plane) is equal to or greater than a predetermined threshold, the control device 20 determines that the corresponding finger mechanism 24 has contacted the object 14, and stops the movement of the corresponding finger mechanism 24. When the magnitude of the contact force F _t is less than the threshold, the control device 20 determines that the corresponding finger mechanism 24 has not yet contacted the object 14, and controls the drive device 28 to move the corresponding finger mechanism 24 toward the object 14. When all the finger mechanisms 24 have come into contact, the control device 20 ends the contact process.

After the contact of the finger mechanism 24 is confirmed, the control device 20 executes a calculation process. The calculation process is a process for calculating a target action force to be output by the finger mechanism 24. The calculation process executed by the control device 20 will be described below with reference to the flowchart shown in FIG. 6.

In the first step ST11 (contact point acquisition step) of the calculation process, the control device 20 acquires a force vector represented by components in the three axial directions and moments around each axis acquired by the force sensor 26. Next, the control device 20 sets a conditional expression that should be satisfied by the contact point Pt by a known calculation method based on the force vector and _moment acquired by the force sensor 26 and the shape of the finger pad 38 stored in the auxiliary storage device 43 (or the main storage device 42).

At this time, the control device 20 may assume that the contact between the finger pad 38 and the object 14 is a hard finger contact in which only force is transmitted and no rotation moment around the normal to the contact surface 44 is transmitted. The method of calculating the contact point _Pt may be based on, for example, Nagata et al., "Development of a Fingertip Force Sensor and Evaluation of Contact Point Detection Error," Journal of the Robotics Society of Japan, vol. 14, No. 8, pp. 1221-1228 (1996).

In this embodiment, the control device 20 uses the force vectors and moments acquired by the force sensors 26 of the first to third finger mechanisms 24 based on the method of Nagata et al. to search for vectors xi (i = 1, 2, 3) that are solutions that simultaneously satisfy equation (1) and equation (2) below.

In formula (2), f _i is a force vector acquired by the force sensor 26 provided on the i-th finger mechanism 24, and m _i is a moment acquired by the force sensor 26 provided on the i-th finger mechanism 24. Ki is an unknown quantity. The above formula (2) corresponds to formula (2) described on page 1224 of Nagata et al.

As in the method of Nagata et al., the control device 20 solves the unknowns K _{i by solving equations (1) and (2) simultaneously while taking into consideration that the force vector acts inward on the surface of the finger pad 38, and substitutes the obtained K i} into equation (2) to search for vectors x _i indicating the positions of contact points P _t for each of the first to third finger mechanisms 24.

When the control device 20 obtains a solution that simultaneously satisfies both equations (1) and (2), that is, when the control device 20 obtains the position of the contact point _Pt on the surface of the finger pad 38 (more specifically, the vector x _i indicating the position), the control device 20 executes the process of step ST12. When the control device 20 cannot obtain a solution for any of the first to third finger mechanisms 24, that is, when the control device 20 cannot obtain the vector x _i indicating the position of the contact point _Pt on the surface of the finger pad 38, the control device 20 ends the calculation process without calculating the target acting force.

In step ST12 (body acting force search step), the control device 20 sets the following three conditions (A) to ( _C ) that should be satisfied by the acting forces that should be applied to the object 14 at the contact point _Pt of each of the finger bodies 30 of the first to third finger mechanisms 24 in order to stably grasp the object 14 at the contact point Pt, and searches for a solution that satisfies all of the conditions. Hereinafter, the conditions (A) to (C) will be referred to as contact point grasping conditions, respectively, as necessary.

Condition (A) is a condition that, from the viewpoint of stable gripping, there is no change over time in the relative velocity and relative angular velocity between the object 14 and the finger pad 38. Condition (A) is expressed by the following equation (3). Condition (3) can also be derived by formulating an equation of motion for a general velocity vector whose elements are the relative velocity vector and the relative angular velocity vector, and setting the acceleration and angular acceleration to zero.

Here, F _ex in formula (3) indicates an external force (gravity, etc.) acting on the object 14 excluding forces (resistance, friction, etc.) from the desk 12. When calculating F _ex , the control device 20 may acquire the type of the object 14 based on the image acquired by the external world acquisition device 10, and acquire (or estimate) the mass, etc. of the object 14 by referring to the object information table based on the type.

In equation (3), λ ₁ , λ ₂ , and λ ₃ represent vectors (force vectors) indicating the acting forces applied to the object 14 from each of the finger pads 38 expressed in the coordinate system (hereinafter, contact point coordinate system) of each of the contact points _Pt of the first to third finger mechanisms 24. Hereinafter, the normal direction of the contact surface 44 in the contact point coordinate system, which is the direction toward the object 14, is defined as the positive z-axis direction, and the tangential directions of the contact surface 44 are defined as the x-axis and y-axis (see FIG. 3 ).

Furthermore, J ₁ , J ₂ , and J ₃ in formula (1) are Jacobian matrices related to contact of the first to third finger mechanisms 24, and ^t J ₁ , ^t J ₂ , and ^t J ₃ respectively indicate the transposes of the corresponding Jacobian matrices. ^t J ₁ , ^t J ₂ , and ^t J ₃ respectively convert force vectors indicating the acting forces in the contact point coordinate system of the first to third finger mechanisms 24 into force vectors indicating the acting forces in the reference coordinate system. For example, acting forces f ₁ , f ₂ , and f ₃ acting on the object 14 from the first to third finger mechanisms 24 in the reference coordinate system are respectively expressed as follows:

In formula (3), Λ indicates a vector in which λ ₁ , λ ₂ , and λ ₃ are arranged vertically, and ^t J indicates a matrix in which ^t J ₁ , ^t J ₂ , and ^t J ₃ are arranged horizontally. In formula (3), ^t JΛ indicates the sum of the acting forces expressed in the reference coordinate system, that is, f ₁ + f ₂ + f _3. Formula (3) indicates that the sum of the external force Fex applied to the object 14 and the sum of the acting forces is zero, that is, the external force and the acting force are balanced. The above formula (3) corresponds to formula 06 shown in Japanese Patent No. 5829103.

Condition (B) is a condition in which the finger pad 38 does not move in a direction away from the object 14 in contact with it, in other words, no force is applied to the finger pad 38 in a direction away from the object 14. Condition (B) is expressed by the following equation (5).

Here, λ _1z , λ _2z , and λ _3z in formula (5) are components of the acting force applied to the finger pads 38 of the first to third finger mechanisms 24 in the normal direction (z-axis direction) of the contact surface 44, and are set so that the direction toward the object 14 is positive. Formula (5) indicates that the components (z components) of the acting force applied to the finger pads 38 of the first to third finger mechanisms 24 in the normal direction of the contact surface 44 are each equal to or greater than 0. Furthermore, in this embodiment, in consideration of the application of an excessive acting force to the object 14 and the output limit of the drive device 28, the components of the acting force in the normal direction of the contact surface 44 are set to be equal to or less than the maximum load λ _max that can be applied to the object 14. The control device 20 may refer to the object information table and set the maximum load λ _max based on the type of the object 14.

Condition (C) is a condition under which the finger pad 38 does not slip relative to the object 14 at the contact point _Pt (i.e., a friction constraint condition). Condition (C) can be expressed as a component of the acting force that causes the finger pad 38 (finger body 30) to slide relative to the object 14 being equal to or less than the maximum static friction force. Specifically, the component (x, y components) of the acting force in the tangential direction of the contact surface 44 is equal to or less than the product of the maximum static friction coefficient _μs and the component of the acting force in the normal direction to the contact surface 44. That is, condition (C) is expressed by the following formula (6).

Equation (6) means that the force vector corresponding to the acting force applied from the finger pad 38 to the object 14 is inside a cone 50 (so-called friction cone) whose apex is the contact point _Pt and whose central axis is an axis 44A perpendicular to the contact surface 44. Here, the half apex angle θ of the cone 50 is determined by the maximum static friction coefficient _μs , and specifically, is expressed as θ=arctan( _μs ).

Condition (C) may be expressed by the following formula (7) instead of formula (6).

In formula (7), e _zi is a unit vector in the z-axis direction in the contact point coordinate system of the i-th finger mechanism 24 (i=1 to 3) (see FIG. 7). Formulas (6) and (7) are equivalent formulas that can be converted into each other by transformation. Formula (7) is the same as formula (14) in JP 2007-75929 A.

Next, the control device 20 searches for a solution Λ that satisfies all of the conditions (A) to (C) (all of the contact point gripping conditions). For example, as described in Japanese Patent No. 5829103, the control device 20 may obtain a solution to the simultaneous equations of Equation (3) using the Guss-Seidel method, which is a stationary iterative method. When the Guss-Seidel method is used, the control device 20 sequentially searches for a solution based on a simultaneous recurrence formula that converts the simultaneous equations. In this case, as described in Japanese Patent No. 5829103, if the deviation between the current solution and the previous solution falls within an allowable range, the control device 20 may obtain the current solution as the solution to the simultaneous equations of Equation (3).

However, the method of searching for the solution to the simultaneous equations of equation (3) is not limited to this method, and may be based on other steady-state iterative methods such as the Jacobi method or the SOR method, or on non-steady-state iterative methods such as the conjugate gradient method. Furthermore, when the component of the acting force normal to the contact surface 44 becomes negative (the acting force acts in a direction away from the fingertip to the object 14), the control device 20 may fix the acting force to zero and search for the solution to the simultaneous equations of equation (3).

When the control device 20 determines whether the solution of the simultaneous equations of formula (3) satisfies condition (C), it obtains a vector perpendicular to the contact surface 44 based on the shape of the finger pad 38 and sets a friction cone with the perpendicular vector as its central axis. At this time, the control device 20 may refer to the object information table to obtain the maximum static friction coefficient _μs between the side surface of the object 14 and the surface of the finger pad 38 and calculate the half apex angle θ.

When the control device 20 obtains a solution that satisfies all of conditions (A), (B), and (C), it executes the process of step ST13, and when the control device 20 cannot obtain a solution, it executes the process of step ST14.

In step ST13, the control device 20 sets the solution that satisfies all of conditions (A), (B), and (C) as the target action force, and ends the calculation process.

In step ST14, the control device 20 determines whether or not all of the contact points _Pt obtained in step ST11 satisfy the claw contact condition. The claw contact condition is a condition under which, when a solution is searched for in the same manner as in step ST12 by changing at least a part of the contact point gripping condition (specifically, the friction constraint condition) by assuming that the claw 32 is in contact with the side surface of the object 14 at the contact _{point Pt} obtained in step ST11, and an acting force corresponding to the solution is output, the finger mechanism 24 moves as shown in FIG. 8, and as a result, the claw 32 comes into contact with the outer surface of the object 14. The claw contact condition is a condition under which, as a result, at least the claw 32 comes into contact with the outer surface of the object 14, and in detail, includes a condition under which only the claw 32 comes into contact with the outer surface of the object 14 and a condition under which the claw 32 and the finger body 30 come into contact with the outer surface of the object 14 at the same time.

The inventors of the present application have found that the nail contact condition is satisfied when the contact point _Pt is located within a surface region (hereinafter, referred to as the nail contact region R, see the colored portion in FIG. 2) close to the tip of the nail 32 of the finger pad 38. In this embodiment, the control device 20 stores the nail contact region R in advance in the auxiliary storage device 43 (or the main storage device 42), and determines that the nail contact condition is satisfied when the contact point _Pt is within the nail contact surface region. The nail contact region R is not limited to a specific range or distribution as long as it is set within a region that satisfies the nail contact condition. The nail contact region R may be set, for example, as a range in which the distance between the finger pad 38 and the tip of the nail 32 is equal to or less than a predetermined value.

When the contact point _Pt satisfies the respective claw contact conditions, the control device 20 executes the process of step ST15.

In step ST15 (jaw action force search step), the control device 20 searches for a solution that results in the target action force by modifying at least a part of the multiple contact point gripping conditions by assuming that the claw 32 is in contact with the outer surface of the object 14 at the contact point _Pt .

Here, the control device 20 changes the friction constraint condition (condition (B)) among the contact point gripping conditions. Specifically, the control device 20 changes the friction constraint condition to condition (D) in which the claw 32 is assumed to be in horizontal contact with the outer surface of the object 14 at the contact point _Pt , and the claw 32 does not slip relative to the object 14 in this assumed state.

Condition (D) is a condition that the force vector corresponding to the force that the claw 32 should exert on the object 14 is contained within a cone centered on an axis extending horizontally.

Specifically, condition (D) is expressed by the following formula (8):

9, n _i in formula (8) represents a unit vector obtained by rotating, into a horizontal plane, a unit vector e _zi in the normal direction of the contact surface 44 at the contact point P _t of the i-th finger mechanism 24. l _i and m _i each represent a unit vector perpendicular to n _i . In addition, "·" in formula (8) represents an inner product, and for example, the inner product a·b of vector a and vector b is equal to tab (where ta represents the transpose of vector a). Condition (D) may be expressed by the following formula (9).

Equation (8) and equation (9) each mean that the force vector corresponding to the acting force applied from the finger pad 38 to the object 14 is contained within a cone 54 (see FIG. 9 ) having a horizontally extending axis 52 as its central axis. Here, the half apex angle θ' of the cone is defined by the maximum static friction coefficient μs' between the nail 32 and the object 14, and is specifically expressed as θ'=arctan( _μs '). The control device 20 may refer to the object information table to obtain the maximum static friction coefficient μs'.

The control device 20 searches for a solution that satisfies the conditions (A), (B), and (D) using the formulas (3), (5), and (8). However, the control device 20 may search for a solution by simultaneously solving the formulas ( ₃ ) and (5) in which f ₁ , f ₂ , and f ₃ in the formula (8) (or the formula (9)) are replaced with λ ₁ , λ ₂ , and λ ₃ by the Jacobian matrices J ₁ , J 2 , and J _3, respectively. The search for a solution to the simultaneous equations of the formula (3) may be based on the same method as in step ST2, for example, the Guss-Seidel method. The control device 20 may sequentially search for a solution based on simultaneous recurrence formulas obtained by converting the simultaneous equations of the formula (3). In this case, as described in Japanese Patent No. 5,829,103, if the deviation between the current solution and the previous solution falls within an allowable range, the control device 20 may obtain the current solution as the solution to the simultaneous equations of equation (3).

When the control device 20 acquires a solution Λ (λ ₁ , λ ₂ , and λ ₃ ) that satisfies all of the conditions (A), (B), and (D), it executes the process of step ST16, and when the control device 20 cannot acquire a solution Λ, it ends the calculation process.

In step ST16, the control device 20 sets the solution Λ obtained in step ST15 as the target action force. When the setting is complete, the calculation process ends.

When the target action force is acquired in the calculation process, the control device 20 executes the output process. In the output process, the control device 20 drives the drive devices 28 to apply the target action force to the object 14 at the contact point _Pt , and operates the finger mechanism 24. When the target action force cannot be acquired, the control device 20 may notify the outside that the target action force could not be acquired, for example, by generating a predetermined sound from a speaker, without operating the drive devices 28.

Next, we will explain the operation and effects of the robot system 1 configured in this way.

In step ST1, the control device 20 brings the claw 32 into contact with the top surface 12A of the desk 12, and then in step ST2, while maintaining the contact state, moves the finger mechanism 24 toward the object 14. While the finger mechanism 24 is being moved toward the object 14, the control device 20 continues to perform a determination process to determine whether the finger mechanism 24 has touched the object 14.

In the determination process, the control device 20 determines that the finger mechanism 24 has come into contact with the object 14 when the component of the force vector applied to the finger mechanism 24 in the tangential direction of the top surface 12A of the desk 12, i.e., the contact force _Ft, becomes equal to or greater than a threshold value. In this manner, in the determination process, the control device 20 can perform the determination process based on the force that the finger mechanism 24 receives from the object 14 placed on the top surface 12A of the desk 12 by ignoring the components of the force vector in the normal direction of the top surface 12A of the desk 12 (vertical component, component in the Z-axis direction), and can therefore appropriately determine that the finger mechanism 24 has come into contact with the object 14.

The tangential component of the force vector applied to the finger mechanism 24 to the top surface 12A of the desk 12 (component in the XY plane) includes the force received from the object 14 by contact and the kinetic friction force between the finger mechanism 24 and the top surface 12A of the desk 12. The kinetic friction coefficient between the nail 32 and the top surface 12A of the desk 12 is set to be smaller than the kinetic friction coefficient between the top surface 12A of the desk 12 and the finger body 30 (finger pad 38). Therefore, among the tangential components of the force vector applied to the finger mechanism 24 to the top surface 12A of the desk 12, the components other than the force received from the object 14 by contact are smaller. Therefore, for example, the influence of fluctuations in the kinetic friction force is reduced, and it is possible to accurately determine that the object 14 has been contacted.

When gripping the object 14 placed on the desk 12, the finger mechanism 24 may touch the object 14 and the top surface 12A of the desk 12. Therefore, since the force vector detected by the force sensor 26 includes the resistance and friction applied from the desk 12 to the finger mechanism 24, it is not easy for the force sensor 26 to separate only the load applied from the object 14 to the finger mechanism 24. Therefore, in the present invention, the control device 20 causes the first to third finger mechanisms 24 to contact the object 14 in step ST2 based on a change in the contact force F _t acquired by the force sensor 26. In this way, the contact of the finger mechanism 24 with the object 14 is confirmed based on the change in the contact force F _t , so that the detection accuracy of the contact of the finger mechanism 24 with the object 14 is improved compared to the case where the contact with the object 14 is determined based only on the value of the force vector acquired by the force sensor 26. Furthermore, after the contact confirmation, the control device 20 acquires the contact point P _t in step ST11 and sets the target action force using the contact point P _t . Therefore, it is possible to prevent the target action force from being set even when the finger mechanism 24 is not in contact.

In step ST12, the control device 20 sets a condition (contact point gripping condition) that must be satisfied by the acting force in order to grip the object 14 while the finger pad 38 is in contact with the object 14 at the contact point _Pt, and searches for a solution that satisfies the condition. If a solution cannot be acquired in step ST12, the control device 20 determines in step ST14 whether or not the condition (nail contact condition) under which the claw 32 can come into contact is satisfied. If it is determined that the claw contact condition is satisfied, the control device 20 assumes in step ST15 that the object will be gripped by the claw 32, changes the friction constraint condition among the contact point gripping conditions by regarding the object as being grippable by the claw 32, and searches for a solution again.

When a solution can be obtained in step ST15, the control device 20 sets a target action force. The finger mechanism 24 then operates to output the target action force. In this way, even if a solution that can be grasped by the finger pad 38 cannot be obtained, a solution is searched for taking into account the possibility that the claw 32 will come into contact and be able to grasp the object by the claw 32. This makes it easier for the object 14 to be grasped by the claw 32, and it is possible to expand the range of objects 14 that can be grasped by the robot hand 2 compared to when the possibility of grasping by the claw 32 is not considered.

Moreover, the control device 20 determines whether or not the pawl contact condition is satisfied based on whether or not the contact point _Pt is located within the pawl contact region R. Therefore, the determination is easy.

In step ST15, the control device 20 assumes that the friction constraint condition can be grasped by the claws 32, and changes the condition to one in which the force vectors are contained within a cone 54 with a horizontal axis 52 as its central axis. Therefore, the condition can be changed without using information such as how the tip surface of the claws 32 touches the object 14, and the condition can be changed easily.

In step ST16, a solution is searched for assuming that the nail 32 contacts the object 14 at the contact point _Pt on the finger pad 38. Therefore, even if the finger pad 38 is actually driven, there is a risk that a solution that does not allow the nail 32 to grip the object 14 may be acquired as the target acting force. In this embodiment, when the contact point _Pt is located within the nail contact region R, that is, when the contact point _Pt approaches the tip surface of the nail 32 (Yes in ST15), a solution is searched for (ST16) assuming that the nail 32 contacts the object 14 at the contact point _Pt . Therefore, even if a solution is searched for using the contact point _Pt on the finger pad 38 and the finger mechanism 24 is driven, the position where the nail 32 actually contacts does not deviate significantly from the contact point _Pt on the finger pad 38, so that a solution close to the case of a strict calculation assuming gripping with the nail 32 can be acquired, and gripping with the nail 32 can be performed.

In the above embodiment, the shape of the finger pad 38 is set to be a quarter hemisphere. Therefore, as shown in formula (1), the surface shape of the finger pad 38 can be expressed by a simple formula. This makes it easy to obtain the contact point _Pt . In addition, the rigidity (bending rigidity and shear rigidity) of the nail 32 is set to be higher than that of the finger body 30, so that an object can be stably grasped by the nail 32.

<<Second embodiment>>
The control device 20 according to the second embodiment judges conditions (C) and (D) differently, but other configurations are similar to those of the first embodiment, so description of the other configurations will be omitted.

In the first embodiment, the control device 20 determined whether condition (C) is satisfied based on whether the force vector corresponding to the acting force is contained within the friction cone whose axis is a perpendicular line perpendicular to the contact surface 44. In this embodiment, the control device 20 determines whether condition (C) is satisfied based on whether the force vector corresponding to the acting force is contained within the pyramid 60.

Specifically, the control device 20 determines that condition (C) is satisfied when the following formula (10) is satisfied:

10, formula (10) corresponds to the condition that the force vector corresponding to the acting force is included inside a pyramid 60 circumscribing the cone 50 shown in formula (6) (the pyramid 60 including the cone 50 and in contact with the cone 50). The x-axis direction may be set, for example, in the direction from the nail 32 to the finger pad 38 (the direction of the unit vector π _1i ).

In the first embodiment, the control device 20 determined whether condition (D) is satisfied based on whether the force vector corresponding to the acting force is included inside a cone centered on an axis extending horizontally. In this embodiment, the control device 20 determines whether condition (D) is satisfied based on whether the force vector corresponding to the acting force is included inside a quadrangular pyramid centered on an axis extending horizontally.

Specifically, the control device 20 determines that condition (D) is satisfied when the following formula (11) is satisfied:

Equation (10) corresponds to the condition that the force vector corresponding to the acting force is included inside a square pyramid (not shown) circumscribing the cone 54 represented by equation (8). For example, the unit vector l _i may be set to be parallel (or perpendicular) to the side surface of the object 14 that the finger mechanism 24 comes into contact with.

Next, we will explain the effects of the robot system 1 configured in this way.

The control device 20 uses equations (10) and (11) as equations showing condition (C) and condition (D). The square pyramids corresponding to condition (C) and condition (D) are respectively approximations of a circular cone (using a polygonal pyramid), and equations (10) and (11) do not contain square roots. In this way, by approximating a circular cone with a square pyramid (polygonal pyramid), the conditions for grasping the object 14 with the finger pad 38 or nail 32 can be easily set, making it easier to search for a solution.

<<Third embodiment>>
In the third embodiment, the setting of the reference coordinate system and the direction of the unit vector in the formula (8) are different from those in the first embodiment, but the other configurations are the same as those in the first embodiment, and therefore the description of the other configurations will be omitted.

In step ST1, the control device 20 captures an image of the top surface 12A of the desk 12 using the external environment acquisition device 10, and acquires the inclination of the top surface 12A of the desk 12 with respect to a horizontal plane from the acquired image. After that, the control device 20 sets the X-axis and Y-axis of the reference coordinate system in the direction along the top surface 12A of the desk, and sets the Z-axis in the normal direction of the top surface 12A. The control device 20 also sets n _i in formula (8) as a unit vector obtained by rotating the unit vector in the normal direction of the contact surface 44 at the contact point P _t of the i-th finger mechanism 24 into a plane parallel to the top surface 12A of the desk 12, and sets l _i and m _i as unit vectors perpendicular to n _i .

Next, the effect of the robot system 1 configured in this manner will be described. Since n _i in formula (8) is set to be parallel to the top surface 12A of the desk 12, the condition (D) is expressed by the condition that the force vector indicating the acting force is included in a cone centered on an axis extending in a direction parallel to the top surface 12A of the desk 12. However, the half apex angle θ' of the cone is determined by the maximum static friction coefficient μ _s ' between the claw 32 and the object 14, as in the first embodiment, and is expressed as θ' = arctan(μ _s '). As a result, as in the first embodiment, the control device 20 can easily set the condition (D) that there is no slippage between the claw 32 and the object 14 without obtaining the contact point P _t between the claw 32 and the object 14.

<<Fourth embodiment>>
In the fourth embodiment, the setting of the reference coordinate system and the direction of the unit vector in formula (11) are different from those in the second embodiment, but the other configurations are the same as those in the second embodiment. The setting of the reference coordinate system is the same as that in the third embodiment. The directions of the unit vectors l _i , m _{i , and} n _i in formula (11) are set to the same directions as the unit vectors l _i , m _i , and n _i in formula (8) in the third embodiment.

Next, the effect of the robot system 1 configured in this manner will be described. Since n _i in formula (8) is set to be parallel to the upper surface 12A (also referred to as the placement surface) of the desk 12, condition (D) is expressed by the condition that the force vector corresponding to the acting force is within a square cone that includes a cone whose axis extends in a direction parallel to the upper surface 12A (placement surface) of the desk 12 and is defined by the maximum static friction coefficient μ _s ' between the claw 32 and the object 14 and abuts on the outer surface of the cone. The half apex angle θ' is expressed as θ'=arctan(μ _s '). As a result, similar to the second embodiment, the control device 20 can easily set the condition (D) that there is no slip between the claw 32 and the object 14 without acquiring the contact point P _t between the claw 32 and the object 14.

<<Fifth embodiment>>
In the fifth embodiment, the setting of the reference coordinate system and the direction of the unit vector in the formula (8) are different from those in the first embodiment, but the other configurations are the same as those in the first embodiment, and therefore the description of the other configurations will be omitted.

In step ST1, the control device 20 acquires the inclination of the end face of the object 14 with respect to the vertical direction from the image of the object 14 on the desk 12 acquired by the external environment acquisition device 10. Thereafter, the control device 20 sets the X-axis and Y-axis of the reference coordinate system in a plane perpendicular to the end face, and sets the Z-axis parallel to the end face and in a direction away from the top surface 12A of the desk 12. The control device 20 also sets n _i in formula (8) as a unit vector obtained by rotating a unit vector in the normal direction of the contact surface 44 at the contact point P _t of the i-th finger mechanism 24 into a plane perpendicular to the end face, and sets l _i and m _i as unit vectors orthogonal to n _i .

Next, the effect of the robot system 1 configured in this manner will be described. Since n _i in formula (8) is set to be parallel to the top surface 12A of the desk 12, condition (D) is expressed by the condition that the force vector indicating the acting force is contained within a cone whose axis extends in a direction perpendicular to the end surface of the object 14. However, the half apex angle θ' of the cone is determined by the maximum static friction coefficient μ _s ' between the claw 32 and the object 14, as in the first embodiment, and is expressed as θ' = arctan(μ _s '). As a result, as in the first embodiment, the control device 20 can easily set condition (D) that there is no slippage between the claw 32 and the object 14 without obtaining the contact point P _t between the claw 32 and the object 14.

<<Sixth embodiment>>
In the sixth embodiment, the setting of the reference coordinate system and the direction of the unit vector in formula (11) are different from those in the second embodiment, but the other configurations are the same as those in the second embodiment. The setting of the reference coordinate system is the same as that in the fourth embodiment. The directions of the unit vectors n _i , l _i , and m _i in formula (11) are set to the same directions as the directions of the unit vectors n _i , l _i , and m _i in formula (8) in the fourth embodiment.

Next, the effect of the robot system 1 configured in this manner will be described. Since n _i in formula (7) is set to be parallel to the top surface 12A of the desk 12, condition (D) is expressed by the condition that the force vector corresponding to the acting force is within a square cone that includes a cone whose half apex angle θ′ is an axis extending in a direction perpendicular to the end surface of the object 14 defined by the maximum static friction coefficient _{μ s} ′ between the claw 32 and the object 14 and abuts on the outer surface of the cone. The half apex angle θ′ is expressed as θ′=arctan(μ _s ′). As a result, similar to the second embodiment, the control device 20 can easily set condition (D) that there is no slip between the claw 32 and the object 14 without obtaining the contact point P _t between the claw 32 and the object 14.

This concludes the explanation of the specific embodiment, but the present invention is not limited to the above embodiment or modified examples, and can be implemented in a wide variety of variations. For example, the above embodiment describes an example in which the robot system 1 is applied to a humanoid robot, but the present invention is not limited to this aspect.

In the above embodiment, under the condition that the top surface 12A of the desk 12 is horizontal and the end surface of the object 14 is vertical, the cone and pyramid shown in equations (7) and (10) are set to have their centers on axes that extend horizontally. However, even if the top surface 12A of the desk 12 is not horizontal or the end surface of the object 14 is not vertical, the control device 20 may search for a solution based on equations (7) and (10) in steps ST12 and ST15, respectively.

In the second, fourth, and sixth embodiments, condition (C) and condition (D) are each expressed by a condition that the force vector indicating the acting force is contained within a square pyramid circumscribing the cone, but this is not limited to a square pyramid, and may be expressed by a condition that the force vector is contained within a polygonal pyramid (more specifically, a convex polygonal pyramid, preferably a regular convex polygonal pyramid) circumscribing the cone.

In the second, fourth, and sixth embodiments, condition (C) and condition (D) are each expressed by a condition that the force vector indicating the acting force is contained within a quadrangular pyramid circumscribing the cone, but this is not limited to a circumscribing quadrangular pyramid, and may be expressed by a condition that the force vector is contained within a polygonal pyramid 70 (more specifically, a convex polygonal pyramid, preferably a regular convex polygonal pyramid) inscribing the cone, as shown in FIG. 11.

In the above embodiment, the object 14 is described as being a square plate, but this is not limited to this. As shown in Figures 12 to 14, the object 14 may be in any shape, such as a circular plate, an elliptical plate, a triangular plate, a pentagonal plate, or the like, and may be arranged in any manner.

In the above embodiment, the unit vector n _i is configured by rotating the normal vector of the contact surface 44 to be in a horizontal plane, in a plane parallel to the top surface 12A of the desk 12, or in a plane perpendicular to the end surface of the object 14. However, the unit vector n _i may be in any direction as long as it extends horizontally and faces the object 14. For example, as shown in the first column from the left in the tables shown in Figs. 11 to 13, the unit vectors n _i (n 1 , n ₂ , n ₃ ) corresponding to the first to third finger mechanisms 24 (24A, 24B, 24C) may be set to be parallel to each other. Also, as shown in the second column from the left, the unit vectors n _i ( _{n 1 ,} n ₂ , n ₃ ) may be set to be directed toward the center or center of gravity of the object 14.

In the above embodiment, the maximum static friction coefficient _μs between the object 14 and the finger pad 38 in equations (6) and (7) and the maximum static friction coefficient μs' between the object 14 and the nail 32 in equations (8) and (9) are written with different letters, but the maximum static friction coefficient _μs and the maximum static friction coefficient μs _' may be set to the same value.

In addition, the specific configuration, arrangement, quantity, angle, material, etc. of each member or part can be changed as appropriate without departing from the spirit of the present invention. On the other hand, not all of the components shown in the above embodiment are necessarily required, and can be selected as appropriate.

1: Robot system 1A: Grip system 2: Robot hand 20: Control device 24: Finger mechanism 28: Driving device 30: Finger body 32: Claw 38: Finger pad 52: Axis 54: Cone R: Claw contact area θ': Half apex angle μs': Maximum static friction coefficient

Claims (8)

1. A robotic system for grasping an object, comprising:
a robot hand including a plurality of finger mechanisms, a force sensor provided in each of the finger mechanisms, and a drive device that drives each of the finger mechanisms;
A control device for controlling the driving of each of the driving devices,
The finger mechanism includes a finger body and a claw provided on the finger body,
the control device acquires contact points between the finger bodies and the object based on the results acquired by the force sensor, calculates a target action force by modifying at least a portion of a plurality of contact point gripping conditions that should be satisfied by the action force that each of the finger bodies should apply to the object at the contact point in order to grip the object, by regarding the claws as being in contact with an outer surface of the object, and drives each of the drive devices to apply the target action force to the object ;
The control device includes:
a contact point acquisition step of acquiring a position of the contact point based on an acquisition result of the force sensor;
a body action force search step of setting a plurality of contact point gripping conditions that should be satisfied by the action forces acting on the object by each of the finger bodies so as to enable gripping at the contact points, and searching for a solution that satisfies all of the contact point gripping conditions to obtain the target action force;
a claw action force search step in which, when a solution cannot be obtained in the body action force search step and the contact point satisfies a predetermined claw contact condition, at least a part of the contact point gripping condition is changed by regarding the claw as being in contact with the outer surface of the object at the contact point, thereby setting a claw gripping condition, and a claw action force search step in which a solution that satisfies the claw gripping condition is searched for to obtain the target action force . the control device determines that the contact point satisfies the nail contact condition when the contact point is within a predetermined surface area of the finger body;
2. The robot system according to claim 1, wherein the surface area is set within an area where the claw contacts the outer surface of the object when the drive unit is driven to output the target action force calculated by modifying at least a portion of the contact point gripping condition by assuming that the claw is in contact with the outer surface of the object. 1. A robotic system for grasping an object, comprising:
a robot hand including a plurality of finger mechanisms, a force sensor provided in each of the finger mechanisms, and a drive device that drives each of the finger mechanisms;
A control device for controlling the driving of each of the driving devices,
The finger mechanism includes a finger body and a claw provided on the finger body,
the control device acquires contact points between the finger bodies and the object based on the results acquired by the force sensor, calculates a target action force by modifying at least a portion of a plurality of contact point gripping conditions that should be satisfied by the action force that each of the finger bodies should apply to the object at the contact point in order to grip the object, by regarding the claws as being in contact with an outer surface of the object, and drives each of the drive devices to apply the target action force to the object;
the control device calculates the target acting force by modifying a friction constraint condition, among the contact point gripping conditions, that a component of the acting force that acts to slide the finger body against the object is equal to or less than a maximum static friction force, by regarding the nail as being in contact with the outer surface of the object;
The control device changes the friction constraint condition to one of the following: a force vector corresponding to the acting force that the claw should apply to the object is contained within a cone whose half apex angle is determined by the maximum static friction coefficient between the claw and the object, and whose axis extends in any of the following directions: horizontally, parallel to a support surface on which the object is placed, and perpendicular to the outer surface of the object; the force vector is contained within a polygonal pyramid circumscribing the cone; and the force vector is contained within a polygonal pyramid inscribing the cone. 1. A robotic system for grasping an object, comprising:
a robot hand including a plurality of finger mechanisms, a force sensor provided in each of the finger mechanisms, and a drive device that drives each of the finger mechanisms;
A control device for controlling the driving of each of the driving devices,
The finger mechanism includes a finger body and a claw provided on the finger body,
the control device acquires contact points between the finger bodies and the object based on the results acquired by the force sensor, calculates a target action force by modifying at least a portion of a plurality of contact point gripping conditions that should be satisfied by the action force that each of the finger bodies should apply to the object at the contact point in order to grip the object, by regarding the claws as being in contact with an outer surface of the object, and drives each of the drive devices to apply the target action force to the object;
A robot system in which a tip portion of the finger body capable of contacting the object constitutes a part of a sphere, a prolate spheroid, or an oblate spheroid. 1. A robotic system for grasping an object, comprising:
a robot hand including a plurality of finger mechanisms, a force sensor provided in each of the finger mechanisms, and a drive device that drives each of the finger mechanisms;
A control device for controlling the driving of each of the driving devices,
The finger mechanism includes a finger body and a claw provided on the finger body,
the control device acquires contact points between the finger bodies and the object based on the results acquired by the force sensor, calculates a target action force by modifying at least a portion of a plurality of contact point gripping conditions that should be satisfied by the action force that each of the finger bodies should apply to the object at the contact point in order to grip the object, by regarding the claws as being in contact with an outer surface of the object, and drives each of the drive devices to apply the target action force to the object;
When the object is placed on the top surface of the desk,
The control device brings the finger mechanism into contact with the top surface of the desk, and then drives the drive device to move the finger mechanism toward the object while keeping it in contact with the top surface, and after the finger mechanism comes into contact with the object, acquires the contact point based on the result acquired by the force sensor. 6. The robot system according to claim 5, wherein the control device determines that the finger mechanism has come into contact with the object when, while driving the drive device to move the finger mechanism toward the object, a magnitude of a contact force, which is a tangential component of a force vector applied to the finger mechanism and acquired by the force sensor , becomes equal to or greater than a predetermined threshold value. The robot system of claim 6, wherein the control device brings the claw of the finger mechanism into contact with the upper surface of the desk, and then drives the drive device to move the claw of the finger mechanism toward the object while keeping it in contact with the upper surface, and a dynamic friction coefficient between the upper surface of the desk and the claw is smaller than a dynamic friction coefficient between the upper surface of the desk and the finger body. 8. The robot system according to claim 1, wherein the claw has a rigidity higher than a rigidity of the finger body.

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