JP4637211B2 - Parallel mechanism - Google Patents

Description

  The present invention relates to a parallel mechanism.

  Conventionally, a parallel mechanism is known in which a base portion that is a support base and a bracket to which an end effector (hand effector) is attached are connected in parallel by a plurality of links (see, for example, Patent Documents 1 to 3). In the parallel mechanism, for example, actuators such as electric motors are arranged in parallel, and a plurality of links (arms) connected to the electric motors are finally configured to operate one end effector.

The parallel mechanism having such a configuration does not need to provide an electric motor or the like for each joint as compared to a joint mechanism such as a serial mechanism, and it is not necessary to swing the electric motor or the like provided in the joint. Can be made lightweight. Further, in the parallel mechanism, since the power of all the electric motors and the like is concentrated in one place, the output can be increased. Furthermore, since the parallel mechanism has a triangular pyramid structure, it has very high rigidity. As described above, since the parallel mechanism has the characteristics of light weight, high output, and high rigidity, the end effector can be moved at a very high speed. For this reason, the parallel mechanism, for example, repeatedly performs at high speed an operation of picking up the object to be transported, gripping the object to be transported by the end effector, and then transporting the object to be transported to a predetermined position while gripping the object to be transported. Is used for applications where
JP-A-6-270077 JP 2001-277164 A JP 2005-528993A

  However, when the parallel mechanism is reciprocated at a high speed, the end effector vibrates, and there is a problem that the position accuracy of the end effector deteriorates when the object to be conveyed is grasped or released at a predetermined position. Therefore, there is a desire to improve the position accuracy of the end effector when the end effector reaches the target position without increasing the time required for the reciprocating motion (that is, the positional deviation when grabbing or releasing the object to be conveyed). There was a request to reduce).

  The present invention has been made to solve the above problems, and can improve the position accuracy of the end effector when reaching the target position without increasing the time required to reach the target position. It aims to provide a possible parallel mechanism.

  As a result of intensive studies on the above problems, the present inventors have obtained the following knowledge. That is, when the parallel mechanism is moved to the target position at high speed, an excitation force acts on the parallel mechanism during sudden acceleration / stop (rapid deceleration), causing the parallel mechanism to roll. The roll is magnified at the tip, and the end effector vibrates. When the end effector reaches the target position, that is, when the vibration is not subtracted when the conveyance object is grasped or released, the end effector is displaced and the position accuracy is deteriorated.

Therefore, the parallel mechanism according to the present invention is a control mechanism for controlling a plurality of actuators in a parallel mechanism in which a plurality of actuators attached to a base portion and a bracket to which an end effector is attached are connected in parallel by a plurality of arms. the provided, said control means, when moving the end effector in the stopped state to the target position, acceleration when accelerating the end effector, so that greater than the deceleration at the time of deceleration, the elapsed time from the drive start A speed control pattern that defines the relationship between the target effector speed and the end effector target speed is set, and a target movement position of the end effector is obtained based on the speed control pattern. The target drive position is obtained and the target drive position Characterized in that the current position is to control the plurality of actuators to match.

  According to the parallel mechanism according to the present invention, when the end effector is moved to the target position, the excitation force acting at the time of deceleration is reduced by decreasing the deceleration at the time of deceleration to a slower speed. The vibration of the end effector when the target position is reached can be reduced. On the other hand, by increasing the acceleration at the time of acceleration, an increase in time required for the end effector to reach the target position is suppressed. As a result, it is possible to improve the position accuracy of the end effector when the target position is reached without increasing the time required to reach the target position.

In the parallel mechanism according to the present invention, when the control means moves the stopped end effector to the target position, the speed control pattern is set so that the time for accelerating the end effector is shorter than the time for decelerating. Is preferred.

  In this way, since the deceleration time can be made longer, vibration can be sufficiently reduced while the end effector is being decelerated. On the other hand, since the acceleration time is shortened, an increase in total time required to reach the target position can be suppressed. As a result, it is possible to further improve the position accuracy of the end effector when reaching the target position without increasing the time required to reach the target position.

  Here, the speed control pattern is set so that the time until the stopped end effector reaches the target position does not change compared to the case where the time for accelerating the end effector and the time for decelerating are the same. It is preferable.

  This makes it possible to reliably prevent the required time from increasing when the stopped end effector is moved to the target position as compared with the case where the acceleration time and the deceleration time are the same.

  In the parallel mechanism according to the present invention, an electric motor is preferably used as the actuator.

  According to the present invention, when the stopped end effector is moved to the target position, the actuator is controlled so that the acceleration when accelerating the end effector is larger than the deceleration when decelerating. It is possible to improve the position accuracy of the end effector when the target position is reached without increasing the time required to reach the target position.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the same element and the overlapping description is abbreviate | omitted.

  First, the overall configuration of the parallel mechanism according to the embodiment will be described using FIG. 1 and FIG. 2 together. FIG. 1 is a perspective view showing an overall configuration of a parallel mechanism 1 according to the embodiment. FIG. 2 is a diagram showing the parallel mechanism 1 viewed from the direction of the arrow A1 in FIG.

  The parallel mechanism 1 has a base portion 2 at the top. The parallel mechanism 1 is supported by fixing a flat mounting surface 2a formed on the lower surface side of the base portion 2 to, for example, a horizontal ceiling. On the other hand, three support members 3 are provided on the lower surface side of the base portion 2. Each support member 3 supports an electric motor 4. The electric motor 4 is supported so that the axis C2 of the motor shaft is parallel (that is, horizontal) to the mounting surface 2a of the base portion 2. Each support member 3 is arranged at an equal angle (120 degrees) around the vertical axis C1 of the base portion 2, and each electric motor 4 is also centered on the vertical axis C1 of the base portion 2. They are arranged at an equal angle (120 degrees) (see FIG. 2).

  A substantially hexagonal columnar arm support member 5 is fixed to the output shaft of each electric motor 4 coaxially with the axis C2. The arm support member 5 rotates about the axis C2 when the electric motor 4 is driven. Each electric motor 4 is connected to an electronic control device 30 including a motor driver, and the rotation of the output shaft of the electric motor 4 is controlled by the electronic control device 30. Details of the electronic control unit 30 will be described later.

  The parallel mechanism 1 has three arm bodies 6, and each arm body 6 includes a first arm 7 and a second arm 8. The first arm 7 is a long hollow cylindrical member formed of, for example, carbon fiber. The base end portion of the first arm 7 is attached to the side surface of the arm support member 5. The first arm 7 is fixed so that the axis thereof is orthogonal to the axis C2 described above.

  The free end portion of the first arm 7 is connected to the proximal end portion of the second arm 8 so that the second arm 8 can swing around the free end portion of the first arm 7. The 2nd arm 8 is comprised including a pair of elongate rods 9 and 9, and a pair of rods 9 and 9 are arrange | positioned so that it may mutually become parallel in the longitudinal direction. The rod 9 is also a long hollow cylindrical member formed of, for example, carbon fiber. The base end portion of each rod 9 is connected to the free end portion of the first arm 7 by a pair of ball joints 10 and 10. Since the axis C3 connecting the ball joints 10 and 10 at the base end portion of each rod 9 is parallel to the axis C2 of the electric motor 4, the second arm 8 swings about the axis C3. .

  One rod 9 and the other rod 9 are connected to each other by a connecting member 11 at the base end portion of the second arm 8, and one rod 9 and the other rod 9 are connected to each other at the free end portion of the second arm 8. Are connected to each other by a connecting member 12. The connecting member 11 and the connecting member 12 have, for example, a tension coil spring as an urging member, and urge the pair of rods 9 and 9 in a direction that attracts each other. The connecting member 11 and the connecting member 12 may have different structures, but the same structure is preferable from the viewpoint of low cost. Each of the connecting members 11 and 12 has a function of preventing each rod 9 from rotating around an axis parallel to the longitudinal direction of the rod 9.

  Moreover, the parallel mechanism 1 has the bracket 14 for attaching the end effector 13 so that rotation is possible. The bracket 14 is a plate-like member having a substantially equilateral triangular shape. The bracket 14 has three arm bodies 6 so that the mounting surface 14a of the end effector 13 of the bracket 14 (the lower surface of the bracket 14 in FIG. 1) is parallel (that is, horizontal) to the mounting surface 2a of the base portion 2. Retained.

  A mounting piece 15 is formed on each side of the bracket 14. Each mounting piece 15 is connected to the free end portion of each arm body 6 (the free end portions of the pair of rods 9, 9 constituting the second arm 8), so that the bracket 14 is attached to each arm body 6. Thus, it swings around the free end of each arm body 6. Specifically, each end of each mounting piece 15 of the bracket 14 is connected to the free end of each corresponding rod 9, 9 by each ball joint 16, 16. An axis C4 (see FIG. 2) connecting the pair of ball joints 16 and 16 is also parallel to the axis C2 of the electric motor 4. For this reason, the bracket 14 can swing with respect to each arm body 6 around the horizontal axis C4. The bracket 14 is supported by the three arm bodies 6 so that it can swing around the horizontal axis C4 on all sides of the substantially equilateral triangular bracket 14.

  The distance between the pair of ball joints 10 and 10 at the connection portion between the first arm 7 and the second arm 8 and the distance between the pair of ball joints 16 and 16 at the connection portion between each rod 9 and the bracket 14 of the second arm 8. Is set equal to the distance. Therefore, as described above, the pair of rods 9 constituting the second arm are arranged in parallel with each other over the entire length in the longitudinal direction. Since all of the axes C2, C3, and C4 are parallel to the mounting surface 2a of the base portion 2, how the first arm 7, the second arm 8, and the bracket 14 are centered on the axes C2, C3, and C4, respectively. Even if it swings, the parallel relationship between the mounting surface 14a of the end effector 13 of the bracket 14 and the mounting surface 2a of the base portion 2 is maintained.

  And according to the instruction | command from the electronic control apparatus 30, the position of the free end part of each 1st arm 7 is controlled by controlling the rotation position of the arm support member 5 fixed to the output shaft of each electric motor 4. Be controlled. The position of the free end of each second arm 8 follows the position of the controlled free end of each first arm 7, and as a result, the position of the mounting surface 14 a of the end effector 13 of the bracket 14 is determined. At this time, as described above, the bracket 14 moves while maintaining the horizontal posture.

  That is, the electronic control unit 30 controls the electric motors 4 to drive the arm main body 6 and move the end effector 13 to the target position, and functions as the control means described in the claims. As the electronic control device 30, for example, a programmable logic controller (PLC) or a dedicated control computer is preferably used. The electronic control unit 30 is configured by a microprocessor that performs calculations, a ROM that stores a program for causing the microprocessor to execute each process, a RAM that temporarily stores various data such as calculation results, and the like. The electronic control device 30 drives the electric motor 4 by executing a program stored in the ROM, and controls the movement of the parallel mechanism 1 (that is, the position of the end effector 13).

  Next, the operation of the parallel mechanism 1 will be described with reference to FIGS. Here, the operation when the end effector 13 goes to grasp the conveyance target will be described as an example. In addition, since the operation | movement at the time of conveying to a predetermined position, holding this conveyance target object after holding this conveyance target object is the same as or the same except that the operation | movement direction demonstrated below becomes reverse. The description is omitted here. FIG. 3 is a diagram showing a movement trajectory (on the x (y), z plane) of the end effector 13, and FIG. 4 shows an example of a speed control pattern in the horizontal direction (on the x, y plane) of the end effector 13. FIG. 3 and 4, the solid line indicates the movement trajectory of the end effector 13 and the speed control pattern in the parallel mechanism 1 according to the present embodiment, and the broken line indicates the conventional parallel mechanism (acceleration time = deceleration time). The movement track of the end effector and the speed control pattern are shown.

  In FIG. 3, point A is the initial stop position (current position), and point F is the position of the conveyance object (that is, the target position when going to grab the conveyance object). When the end effector 13 stopped at the point A goes to the point F, the end effector 13 is first lifted vertically upward from the point A to the point B. Since this section is moving vertically upward (z direction), the speed in the speed control pattern in the horizontal direction (x, y direction) shown in FIG. 3 is zero. Next, from the point B to the point C1, the end effector 13 is moved upward and horizontally while being accelerated in the horizontal direction. Subsequently, from the point C1 to the point C2, the end effector 13 is moved upward and horizontally while keeping the horizontal speed constant. Next, the end effector 13 is moved in the horizontal direction at a constant speed from the point C2 to the point D1. Further, the end effector 13 is moved in the horizontal direction while being decelerated from the point D1 to the point D2. Here, while moving from point C2 to point D2, the movement in the z direction is zero. Then, the end effector 13 is moved horizontally and downward while being decelerated in the horizontal direction from point D2 to point E (a position vertically above the target position). Thereafter, the end effector 13 is lowered vertically from point E to point F. Since this section also moves downward (z direction), the speed in the speed control pattern in the horizontal direction (x, y direction) shown in FIG. 3 is zero. When the end effector 13 is moved from point A to point F in this way, the electronic control unit 30 stores a speed control pattern that prestores the relationship between the elapsed time from the start of driving and the target speed of the end effector 13. Based on the above, the electric motor 4 is controlled. Hereinafter, the movement in the horizontal direction will be described more specifically.

  First, in the electronic control unit 30, the current position (point A) and the target position (point F) of the end effector 13 are read. Here, the current position of the end effector 13 can be obtained from the drive position of each electric motor 4. Further, the target position can be acquired by, for example, performing image processing or the like on a captured image captured by a camera attached to a predetermined position (coordinates) and recognizing the conveyance object. Next, in the electronic control unit 30, a distance from the current position and the target position to the target position is obtained, and a speed control pattern is applied to the obtained distance, and an acceleration time t1, a constant speed time t2, and a deceleration time t3. , And the maximum speed V is set.

  Here, the speed control pattern includes an acceleration region, a constant speed region, and an acceleration region, as indicated by a solid line in FIG. 4, and the acceleration when accelerating the end effector 13 is the deceleration when decelerating. It is set to be larger. The speed control pattern is set so that the time t1 for accelerating the end effector 13 is shorter than the time t3 for decelerating. Furthermore, in the speed control pattern, the time required to reach point F (target position) from point A is the same as the time (t1 ′) for accelerating the end effector 13 and the time (t3 ′) for decelerating (FIG. 4 (see the broken line in FIG. 4). For example, when the end effector 13 reciprocates at 120 cycles / minute, the required time (one way) between point A and point F is 0.25 seconds.

  After the acceleration time t1, the constant speed time t2, the deceleration time t3, and the maximum speed V are set, the electronic control device 30 sets the end effector 13 for each control cycle based on the speed control pattern in which each time is set. A target movement position is obtained. Subsequently, the target drive positions of the three electric motors 4 are obtained according to the obtained target movement positions. In each control cycle, a drive current is supplied to each electric motor 4 so that the target drive position and the current position coincide with each other, and each electric motor 4 is driven. When each electric motor 4 is driven, each arm body 6 is driven, and the end effector 13 is moved from point A to point F (target position).

  Here, a movement locus in the vicinity of the target position of the end effector 13 when the end effector 13 is moved from the point A to the point F is shown in FIG. FIG. 5 is a diagram showing a target locus of the end effector 13 and an actual movement locus. In FIG. 5, the alternate long and short dash line is the target locus (target movement position) of the end effector 13. A solid line is a movement locus of the end effector 13 of the parallel mechanism 1 according to the present embodiment. A broken line indicates the movement track of the end effector when the acceleration time t1 'and the deceleration time t3' are the same.

  As shown in FIG. 5, according to the present embodiment, when the end effector 13 in the stopped state is moved to the target position (point F), the deceleration at the time of deceleration is made smaller to reduce the speed gently. Since the excitation force acting at the time of deceleration is reduced, the vibration of the end effector 13 when the target position is reached can be reduced. On the other hand, by increasing the acceleration at the time of acceleration, an increase in time required for the end effector 13 to reach the target position is suppressed. As a result, it is possible to improve the position accuracy of the end effector 13 when the target position is reached without increasing the time required to reach the target position.

  Further, according to the present embodiment, when the stopped end effector 13 is moved to the target position (point F), the electric motor 4 is set such that the time t1 for accelerating the end effector 13 is shorter than the time t3 for decelerating. Is controlled. Therefore, since the deceleration time t3 can be made longer, vibration can be sufficiently reduced while the end effector 13 is being decelerated. On the other hand, since the acceleration time t1 is shortened, an increase in the total time required to reach the target position can be suppressed. As a result, the positional accuracy of the end effector 13 when reaching the target position can be further improved without increasing the time required to reach the target position.

  According to the present embodiment, the electric motor 4 is controlled based on the current position of the end effector 13, the target position, and the speed control pattern. Therefore, by detecting the current position and the target position of the end effector 13, it is possible to determine the target movement position of the end effector 13, that is, the command current value of the electric motor 4, based on the speed control pattern.

  Further, according to the present embodiment, the speed control pattern has a time until the end effector 13 in the stopped state reaches the target position as compared with the case where the time for accelerating the end effector 13 and the time for decelerating are the same It is set not to change. Therefore, when the stopped end effector 13 is moved to the target position, it is possible to reliably prevent the required time from increasing as compared with the case where the acceleration time and the deceleration time are the same.

  Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications can be made. For example, the speed control pattern may be set such that acceleration> deceleration and acceleration time <deceleration time, and the maximum speed may be set so that the total required time does not increase. The shape is not limited to the shape shown in FIG. Here, another example of the speed control pattern is shown in FIG. As shown in FIG. 6, the speed control pattern eliminates the inflection points between the acceleration area and the constant speed area and the inflection points between the constant speed area and the deceleration area, and smoothly connects the areas. It is good also as a simple shape. Furthermore, it is good also as a shape which makes the linear part in an acceleration area | region and / or a deceleration area | region zero, and connects with an S-shaped curve.

  In the above embodiment, the movement in the horizontal direction has been described. However, the present invention can be similarly applied to the movement in the vertical direction. In other words, the acceleration when raising the end effector 13 in the upward direction may be set larger than the deceleration when lowering in the downward direction, and the acceleration time may be set shorter than the deceleration time. Moreover, in the said embodiment, although the end effector 13 moved to the perpendicular direction and the horizontal direction, the structure which moves only to a horizontal direction may be sufficient.

It is a perspective view showing the whole parallel mechanism composition concerning an embodiment. It is a figure which shows the parallel mechanism seen from the arrow A1 direction in FIG. It is a figure which shows the movement locus | trajectory of an end effector. It is a figure which shows an example of the speed control pattern of the horizontal direction of an end effector. It is a figure which shows the target locus | trajectory of an end effector, and an actual movement locus | trajectory. It is a figure which shows the other example of the speed control pattern of a horizontal direction.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Parallel mechanism 2 Base part 3 Support member 4 Electric motor 5 Arm support member 6 Arm main body 7 1st arm 8 2nd arm 9 Rod 10, 16 Ball joint 11, 12 Connecting member 13 End effector 14 Bracket 15 Mounting piece 30 Electronic control apparatus

Claims (4)

In a parallel mechanism in which a plurality of actuators attached to a base part and a bracket to which an end effector is attached are connected in parallel by a plurality of arms,
Control means for controlling the plurality of actuators,
The control means, when moving the stopped end effector to a target position , an elapsed time from the start of driving so that an acceleration at the time of accelerating the end effector is larger than a deceleration at the time of deceleration. A speed control pattern that defines a relationship with the target speed of the end effector is set, a target movement position of the end effector is obtained based on the speed control pattern, and the plurality of actuators are determined according to the target movement position of the end effector A parallel mechanism characterized by obtaining each target drive position and controlling each of the plurality of actuators so that the target drive position and the current position coincide with each other . The control means sets the speed control pattern so that a time for accelerating the end effector is shorter than a time for decelerating when the stopped end effector is moved to a target position. Item 2. The parallel mechanism according to Item 1. The speed control pattern is set so that the time until the end effector in the stopped state reaches the target position does not change compared to the case where the time for accelerating and decelerating the end effector is the same. The parallel mechanism according to claim 1 , wherein the parallel mechanism is provided. The actuator parallel mechanism according to any one of claims 1 to 3, characterized in that an electric motor.

Images