JP2003025263A - Control device for parallel mechanism machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To spread an actual movable region of an end effecter and sufficiently display an essential function of the machine tool. SOLUTION: A plurality of movable regions are stored in a memory part 21 in each attitude of an end effecter. The movable region is fixedly drawn in columnar shape by a limit value of the end effecter. An arithmetic part 22 calculates the present attitude and position of the end effecter based on a signal of position detectors 14a to 14f. A comparison part 23 reads the movable region corresponding to the present attitude from the memory part 21, to compare this movable region with the present position. In the case of the present position exceeding the movable region, a control part 12 judges apprehension provided of interference or uncontrollable, a stop signal is output to servomotors 6a to 6f, the end effecter is immediately stopped.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a machine control device using a parallel mechanism.

[0002]

2. Description of the Related Art As a machine of this type, a conventional machine, for example, FIG.
A parallel-mechanism machine tool having 6 degrees of freedom in space is known as shown in FIG. In this machine tool, the workpiece on the table 1 is processed by a tool attached to the spindle 8 of the end effector 2. The end effector 2 is connected via a universal joint 3 to six ball screws 4 as actuators, and each ball screw 4 is supported on a ceiling portion of a frame 7 via a universal joint 5. A servomotor 6 for driving a ball screw 4 is attached to the universal joint 5, and by changing the length of the ball screw 4 between the universal joint 3 and the universal joint 5, the end effector 2 can be placed at any position in any posture. Driven.

As shown in FIG. 2, the universal joint 3 is constructed by combining three rotary joints 31, 33 and 35. The rotary joint 31 has a base 3 with respect to the end effector 2.
2 is rotatably connected around the Pa axis. Rotary joint 3
A rod 3 is connected to a base 32 so as to be rotatable about a Pb axis. The rotary joint 35 connects the rod 34 to the ball screw 4 rotatably around the Pc axis. Then, the three rotary joints 31, 33, and 35 have Pa axis and Pb.
The shaft and the Pc shaft are assembled so that they intersect at one point, whereby the universal joint 3 functions as a joint having three rotational degrees of freedom like a spherical joint.

However, according to the machine using the universal joint 3 of this type, for example, as shown in FIG. 3, when the rod 34 is rotated by a certain angle or more, the rod 34 comes into contact with the base 32. May cause interference. Also, as shown in FIG. 4, when the Pa axis and the Pc axis are coaxial, the joint does not function as a joint having three degrees of freedom of rotation, and when the ball screw 4 expands and contracts in this state, the rod 34 Regardless of the rotation about the Pb axis, the amount of expansion and contraction of the ball screw 4 is the same, which may lead to uncontrollability that the position and orientation of the end effector 2 cannot be uniquely determined. Therefore, conventionally, by previously limiting the command value of the servo motor 6 on the NC program,
A method of defining a movable region of the end effector 2 and thereby avoiding interference and uncontrollability has been adopted.

[0005]

By the way, in the case of the parallel mechanism machine tool as shown in FIG. 1, the movable region of the end effector 2 is substantially symmetrical about the Z axis. Here, FIG. 8 shows a cross section including the Z axis of the movable region of the end effector 2. The area 101 is a virtual area when the posture of the end effector 2 is parallel to the Z axis, and interference between the end effector 2 and the table 1 and the frame 7 is not considered. The region 102 is a virtual region when the end effector 2 is tilted by 25 ° in all directions with respect to the Z axis, and the interference and uncontrollability of the universal joints 3 and 5 are not considered. The area 103 is a movable area that eliminates the possibility of interference and uncontrollability, and theoretically, the end effector 2 is located in this area 103.
Can move freely.

However, since the movement of the end effector 2 during machining is very complicated, it is complicated to accurately predict which region of the machining space and in which posture the interference and control will occur. Calculation is required, and it is not easy. Therefore, according to the conventional control method, it is necessary to highly estimate the probability of such an abnormal situation and limit the command value of the servo motor 6 widely. As a result, the actual movable region 104 of the end effector 2 becomes considerably narrower than the theoretical movable region 103, and there is a problem that the parallel mechanism machine cannot fully exhibit its original capability. Further, according to the conventional method of limiting the command values of the three orthogonal axes, the movable region 104 has a cubic shape, so that there is a problem that the region which should originally be rotationally symmetrical about the Z axis is narrowed down to that size.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a control device which can expand the actual movable region of the end effector in a machine using a parallel mechanism so that the original capability of the machine can be fully exhibited.

[0008]

In order to solve the above problems, the control device according to the invention of claim 1 is a posture of an end effector in a parallel mechanism machine in which a plurality of actuators drive the end effector via a universal joint. A storage unit that stores a plurality of movable regions for each, a calculation unit that calculates the current posture and position of the end effector, a comparison unit that compares the movable region and the current position corresponding to the current posture, and a comparison result. And a control unit for controlling the actuator based on the above. Further, the control device according to the invention of claim 2 is characterized in that the storage unit stores a limit value that defines a cylindrical movable region.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 5 shows an embodiment of a control device in a parallel mechanism machine tool. In this machine tool, the end effector 2 is driven by six ball screws 4 as actuators via a universal joint 3 (see FIG. 1). The nuts of the ball screws 4 are individually rotated by the servomotors 6a to 6f, and signals related to the joint length of the ball screws 4 are transmitted to the motors 6a.
6f are attached to the control unit 12 of the control device 11.

The control unit 12 analyzes the NC program and controls the servomotors 6a-6f in accordance with the analysis. Then, by changing the inter-joint length of the ball screw 4 by the servo motors 6a to 6f, the end effector 2 is driven to an arbitrary position in an arbitrary posture. Note that the NC program sets the position of the end effector 2 as coordinate values of three orthogonal axes (X, Y, Z axes in FIG. 6) and sets the posture of the end effector 2 around each axis (A, B, C directions in FIG. 6). ) Command as the rotation angle.

Further, the control device 11 is provided with a storage unit 21, a calculation unit 22 and a comparison unit 23. The storage unit 21 stores a plurality of movable regions for each posture of the end effector 2. The movable region is a region in which the movement range of the end effector 2 is limited in order to avoid interference of the universal joints 3 and 5 and out of control, and as shown in FIG. 7, the posture of the end effector 2, that is, the Z axis. The cylindrical regions 105 and 10 having different sizes according to the inclination angle with respect to
Defined as 6.

In FIG. 7, a region 105 shows a movable region when the posture of the end effector 2 is parallel to the Z axis, and a region 106 shows a case where the posture of the end effector 2 is tilted by 25 ° in all directions with respect to the Z axis. Shows the movable region of. Each of the regions 105 and 106 has a cylindrical shape that is rotationally symmetrical about the Z axis. As in FIG. 8, the area 101 is the table 1
The area 103 is a virtual area that does not consider interference with the frame 7 and the area 103 is a theoretical movable area that eliminates the possibility of interference and uncontrollability.

The storage unit 21 has a cylindrical movable region 105,
A limit value defining 106 is stored. As the limit value, the maximum value of the inclination angle θ of the end effector 2 with respect to the Z axis, the radius R of the movable region 106, and the reference position O (for example, the center point of the table 1) are used as the limit values, as illustrated in the region 106 in FIG. 6. To the maximum value Zmax and the minimum value Zmi in the Z-axis direction
n and n are included, these are combined into one set, and a plurality of sets having different maximum values of the inclination angle θ are stored in the storage unit 21.

The calculation unit 22 includes position detectors 14a to 14f.
The present attitude of the end effector 2, that is, the inclination angle θ of the end effector 2 with respect to the Z axis is calculated using a geometrical calculation formula based on the output of the end effector 2, and the current position of the end effector 2, that is, the end effector 2. The coordinate value Z of 2 in the Z-axis direction and the distance L (radius of the cylindrical motion region) from the Z-axis to the end effector 2 are calculated. The comparison unit 23 reads the movable area corresponding to the current posture from the storage unit 21 and compares the movable area with the current position.

Then, the control unit 12 controls the six ball screws 4 based on the comparison result of the comparison unit 23. Specifically, when the current position of the end effector 2 is within the movable area, the controller 12 outputs a drive signal to the servo motors 6a to 6f. When the current position exceeds the movable area, the control unit 12 determines that there is a risk of interference or uncontrollability, and outputs a stop signal to the servo motors 6a to 6f.
Alternatively, the end effector 2 is immediately stopped by executing processing such as cutting off the power supply to the servomotors 6a to 6f.

According to the control device 11 having the above-described structure, the end effector 2 is operated while the parallel mechanism machine tool is operating.
Since the movable area of each of the postures is checked in real time, the actual movable areas 105 and 106 of the end effector 2 can be expanded to near the theoretical movable area 103 as shown in FIG. It is possible to fully exert the function. Further, since the current position of the end effector 2 is checked with the limit value that defines the cylindrical region, there is an advantage that the movable regions 105 and 106 can be set wider with a rotationally symmetrical shape by taking advantage of the characteristics of the parallel mechanism machine tool. .

In the above embodiment, a machine tool having space 6 degrees of freedom is exemplified as the parallel mechanism machine.
The degree of freedom is not limited to 6 and can be applied to machine tools having more or less degrees of freedom. In addition to machine tools, it may be applied to various machines using parallel mechanisms such as robots, construction machines, amusement machines, and medical machines. In addition, it is also possible to appropriately change the shape and configuration of each part without departing from the scope of the present invention, such as using a rotary joint or a spherical joint in a combination different from that of FIG. 2 for the universal joint.

[0018]

As described in detail above, according to the invention of claim 1, since the actuator is controlled based on the movable region stored for each posture of the end effector, the actual movable region of the end effector is expanded. And, it has an excellent effect that the original ability of the machine can be fully exhibited.

According to the second aspect of the present invention, since the cylindrical movable region is stored, there is an effect that the movable region can be set wider with a rotationally symmetrical shape by utilizing the characteristics of the parallel mechanism machine.

[Brief description of drawings]

FIG. 1 is a perspective view of a parallel mechanism machine tool.

FIG. 2 is a mechanism diagram illustrating a universal joint.

FIG. 3 is a mechanism diagram for explaining interference of a universal joint.

FIG. 4 is a mechanism diagram for explaining inability to control an end effector.

FIG. 5 is a block diagram of a control device showing an embodiment of the present invention.

FIG. 6 is a schematic diagram illustrating a limit value of an end effector.

FIG. 7 is a schematic diagram showing a movable region of an end effector according to the present invention.

FIG. 8 is a schematic view showing a movable region of an end effector according to a conventional technique.

[Explanation of symbols]

2 ... End effector, 3,5 ... Universal joint, 4 ...
Ball screw, 6 ... Servo motor, 11 ... Control device,
12 ... Control unit, 21 ... Storage unit, 22 ... Computing unit, 2
3 ... Comparison section.

Claims (2)

[Claims] 1. In a parallel mechanism machine in which a plurality of actuators drive an end effector via a universal joint, a storage unit that stores a plurality of movable regions for each posture of the end effector, and a current posture and position of the end effector are calculated. A control device, comprising: a calculation unit that performs: a movable region that corresponds to a current posture and a current position; and a control unit that controls the actuator based on the comparison result. 2. The control device for a parallel mechanism machine according to claim 1, wherein a limit value that defines a cylindrical movable area is stored in the storage unit.