JPH1110575A - Parallel link mechanism - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve positional precision of an end effector by improving a control method on a parallel link mechanism. SOLUTION: A marginal part of an end plate 6 and a marginal part of a base plate 3 are connected to each other by three expansible links 7. A head end of a mast 1 is fixed on a center of the end plate 6, and a rear end is connected to a center of the base plate 3 in a state where rotation is constrained and movement in the axial direction and biaxial tilting are free. An end effector 2 is fixed on the end plate 6. Expansion of each of the links 7 is carried out by using a ball screw 19, and its expansion quantity is detected by an encoder 10. Moving quantity of the mast 1 in the axial direction is detected by a linear scale 11, and a tilting angle is detected by encoders 12a, b. A three-dimensional position of the end effector 2 is controlled by constituting a feedback loop to take in the moving quantity of the mast 1 in the axial direction and the biaxial tilting angle in addition to expansion quantity of each of the links 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a parallel link mechanism, and more particularly to an improvement in a control method thereof.

[0002]

2. Description of the Related Art FIG. 5 shows an example of the configuration of a conventional parallel link mechanism. The parallel link mechanism includes a base plate 3, an end effector 2 such as a hand or a tool.
End plate 6 to which is attached, end plate 6
And three extendable links 7 connecting between the peripheral edge of the base plate 3 and the peripheral edge of the base plate 3, and one mast 1 connecting the central part of the end plate 6 and the central part of the base plate 3. Have been.

[0003] The tip of each link 7 is attached to the peripheral edge of the end plate 6 via a spherical bearing 8b, and the rear end of each link 7 is a ball screw 19 and a spherical bearing 8 respectively.
are attached to the peripheral portion of the base plate 3 in this order. The ball screw 19 is attached to the movable core of the spherical bearing 8a, and the link 7 is expanded and contracted by driving the servomotor 9. Each servo motor 9 is provided with an encoder 10, and the amount of expansion and contraction of each link 7 converted from the rotation angle is sent to the control device.
Note that, instead of the encoder 10, a linear sensor that directly measures the amount of expansion and contraction of each link 7 can be used.

On the other hand, the end of the mast 1 is an end plate 6
The rear end is connected to the center of the base plate 3 via the cylindrical slider 4 and the universal joint 5 in this order.

[0005] On the front side of the end plate 6, the end effector 2 is mounted. In the parallel link mechanism having the above-described configuration, the three-dimensional position of the end effector 2 is controlled by independently controlling the amount of expansion and contraction of each link 7 based on the output value of the encoder 10.

FIG. 6 is a block diagram showing an example of a control method in a conventional parallel link mechanism. The position command is represented by xr, yr, and zr coordinates. Calculate the length command values Ur, Vr, Wr for each link 7 from the coordinate values and send them to the servo control mechanism of each axis, and drive the servo motor 9 until each link 7 has a predetermined length. Then, the end effector 2 is moved to the command position. If the capability of the control device is low, up to the three-axis conversion is obtained in advance offline, and a three-axis command is directly sent to the servo control mechanism.

(Problems of the prior art) The amount to be finally controlled is the coordinate value (x, y, z) of the end effector 2, but in the above-described conventional control method, it is actually controlled. The amount of extension / contraction of each link (U, V, W axis values)
It is. The U, V, and W axes are feedback-controlled via the output value of the encoder 10, but do not guarantee the position of the end effector 2 accurately. In reality,
Due to the influence of the backlash of the parallel link mechanism, the position accuracy of the end effector 2 is limited.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the control method in the conventional parallel link mechanism, and an object of the present invention is to improve the control method in the parallel link mechanism. By doing so, the position accuracy of the end effector can be improved.

[0009]

According to the present invention, there is provided a parallel link mechanism comprising: an end plate to which an end effector is attached; a base plate disposed to face the end plate; a peripheral portion of the end plate and a peripheral portion of the base plate. At least three links that connect between the links and can control the distance between the connecting portions, and first detecting means for detecting the distance between the connecting portions of the respective links, and a space surrounded by the respective links. A mast connected to the central portion of the base plate, with one end fixed to the central portion of the end plate and the other end restricted in rotation and capable of tilting and axial movement around two axes; And the feedback control of the distance between the linking portions of the respective links independently based on the output value from the first detecting means, whereby In a parallel link mechanism for controlling the three-dimensional position of the effector, a second detecting means for detecting an axial movement amount of the mast and a tilt angle around two axes is provided, and an output from the second detecting means and the A three-dimensional position of the end effector is controlled by forming a feedback loop for taking in an output from the first detecting means.

[0010]

FIG. 1 shows an example of a configuration of a parallel link mechanism according to the present invention. Since the basic configuration of the parallel link mechanism is the same as that of the conventional apparatus shown in FIG. 5, the same reference numerals are used to denote the same elements, and a description thereof will be omitted. In addition to an encoder 10 (first detecting means) for detecting the amount of expansion and contraction of the mast 7, a linear scale 11 for detecting the amount of movement of the mast 1 in the axial direction, and a tilt angle of the mast 1 around the x axis and the y axis are detected. Two encoders 12a and 12b (second detecting means) are provided. End effector 2
Position control, in addition to the output value from the encoder 10,
This is performed by constructing a feedback loop taking in the output values from the linear scale 11 and the encoders 12a and 12b as follows.

FIG. 2 shows a block diagram of this feedback loop. When the position command of the end effector 2 is x,
Given by the coordinates zr, yr, zr of the three orthogonal axes of y and z,
The control device converts the three-axis link expansion / contraction amounts Ur, Vr, and Wr. The converted data is sent to each of the three-axis servo control mechanisms, and before that, the value U calculated from the output values from the linear scale 11 and the encoders 12a and 12b.
a, Va, and Wa are compared and calculated to obtain a more accurate axis command Ur.
It is converted to 0, Vr0, Wr0. Thereby, each link 7
Are feedback-controlled based on the output of the encoder 10, and the length of each link 7 is maintained at the command values Ur0, Vr0, Wr0.

When the length of each link 7 changes and the mast 1 moves, the output values of the linear scale 11 and the two encoders 12a and 12b attached to the mast 1 change. Ua, Va, W obtained by three-axis conversion of these output values
a and three-axis converted Ur from the command values xr, yr, zr
, Vr and Wr, and the difference is calculated for each axis. By adding the amount of expansion and contraction up to now to these differences, more accurate movement commands Ur0, Vr0, Wr0 are given to the respective servo control mechanisms. As a result, more accurate positioning accuracy can be obtained.

FIG. 3 shows another example of the parallel link mechanism according to the present invention. Three ball screws 7 are connected to the base plate 3 and the end plate 6 via spherical bearings. There is a nut 22 on the spherical bearing on the base plate side of the ball screw. By rotating the nut by rotating the servo motor 9, the length of the ball screw between the spherical bearings can be controlled by rotating the nut via the gear 21. Thus, by rotating the three ball screws, the distance between the spherical bearings can be changed, and the position of the end effector 2 attached to the end plate can be moved.

FIG. 4 shows another example of the parallel link mechanism according to the present invention. A servo motor is mounted on the spherical bearing of the base plate. An arm 25 is attached to this servomotor. Two links 23 are connected by pin joints 24 between the arm and the spherical bearing of the end plate. By controlling the angle of the servomotor, the distance between the spherical bearing of the three base plates and the axis of the servomotor can be changed, and the position of the end effector attached to the end plate can be moved.

[0015]

According to the parallel link mechanism of the present invention,
The amount of axial movement of the mast to which the end plate and end effector are fixed and the tilt angle around the two axes are directly detected, and these values are taken into the control system to form a feedback loop. Can be controlled.

[Brief description of the drawings]

FIG. 1 is a diagram showing an outline of a parallel link mechanism based on the present invention.

FIG. 2 is a control block diagram of a parallel link mechanism according to the present invention.

FIG. 3 is a diagram showing another example of the parallel link mechanism according to the present invention.

FIG. 4 is a diagram showing another example of the parallel link mechanism based on the present invention.

FIG. 5 is a diagram showing an outline of a conventional parallel link mechanism.

FIG. 6 is a control block diagram of a conventional parallel link mechanism.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Mast, 2 ... End effector, 3 ... Base plate, 4 ... Slider, 5 ... Universal joint, 6 ... End plate, 7 ... Link, 8a, 8b ...・ Spherical bearing, 9 ・ ・ ・ Servo motor, 10 ・ ・ ・ Encoder, 11 ・ ・ ・ Linear scale, 12a, 12b ・ ・ ・ Encoder, 19 ・ ・ ・ Ball screw, 21 ・ ・ ・ Gear, 22 ・ ・ ・ Nut, 23 ... link, 24 ... pin joint, 25 ... arm.

Claims (1)

[Claims] 1. An end plate to which an end effector is attached, a base plate disposed opposite to the end plate, a connection between a peripheral portion of the end plate and a peripheral portion of the base plate, and control of a distance between the connection portions. At least three links, and first detecting means for detecting a distance between connecting portions of the links, and a first detecting means disposed in a space surrounded by the links, and one end fixed to a central portion of the end plate A first mast connected to the center of the base plate in a state where the other end is restricted in rotation and capable of tilting and axial movement around two axes, and an output from the first detecting means. A parallel control for controlling the three-dimensional position of the end effector by independently performing feedback control on the distance between the connecting portions of the links based on the values. In the link mechanism, a second detecting means for detecting an axial movement amount of the mast and a tilt angle around two axes is provided, and an output from the second detecting means and an output from the first detecting means are taken in. A parallel link mechanism comprising a feedback loop for controlling a three-dimensional position of the end effector.