JPH01210288A - Wrist device for robot - Google Patents

Abstract

PURPOSE:To enhance the accuracy of determining the position and attitude of a finger part of a robot by providing a piezoelectric driving device directly to an output shaft of a power transmission member of an electric motor part or a belt, etc. CONSTITUTION:An alternating voltage of resonance frequency of piezoelectric driving devices 6, 9 including a piezoelectric body is applied to the piezoelectric body. By giving a motion having a locus of elliptical vibration to a driving end part of the piezoelectric device by the application of the alternating voltage, and by pressing a moving part (rotational moving part, linear moving part) against the driving end part to move it into contact with the driving end part, the moving part is moved into a rotational or linear motion. In this instance, since the driving frequency is an inaudible frequency of 20KHz or more, the noise level remains low, and the vibration amplitude is in a range of only some microns, a finger part 19 of the robot can be positioned with high accuracy by detecting the position of the finger part 19 using a high resolution position- detecting board, and by performing a position feedback control.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a wrist device for a robot, and more particularly to a wrist device suitable for a horizontal long-jointed assembly robot that performs high-speed and highly accurate position/posture determination.

[Conventional technology]

FIG. 3 shows an example of a horizontal articulated robot that has been conventionally used for assembly work and the like. Arms 1 and 36 are rotationally driven in the direction of the arrow by electric motors 37 and 35. Wrist device 38
(Dotted line) indicates the position and posture of the hand 19 at the tip (opening/closing operations of the hand are performed using air pressure, etc., but this mechanism is not illustrated or explained in this explanation). 1 Down/Rotation operation is required.

Next, FIG. 4 shows an example of a conventional wrist device for a robot having vertical and rotational movements (see FIG. 6 of JP-A-62-1.938Q) with additional functions. First, the vertical drive mechanism will be explained.

A ball screw 20 is rotationally driven by an electric motor 26 via a belt 24, and is connected to a spline shaft 7 via a bearing by a connecting plate 12 connected to a ball screw nut 1 to 1. Since the spline shaft 7 is connected to the hand 19, the rotation of the ball screw 20 causes the spline shaft 7 to move in the vertical direction.

Next, the rotational drive mechanism will be explained. A spline bearing 8, which is rotationally connected to a spline shaft 7 connected to the hand 19, is connected to the bearing 4 with respect to the member 2 connected to the arm 1. a, 4b, and is coupled to the electric motor 21 via the pulley 23b and the bell 1 25, so rotation of the electric motor 21 can realize rotational movement.

Although not shown in Japanese Patent Application Laid-open No. 62-1.9389, a mechanical brake 27 is provided since the vertical axis must have a holding function when not in operation. The rotational position of each electric motor 26.21 is detected by a position detector 1.0.11, and the vertical origin position and the vertical overrun are determined by a proximity switch] 5b.

15a and 1.5c. Also, the rotation axis is 3
Since the rotation is over 60 degrees, an overrun function is not required, but the origin position is detected using the proximity switch 16. Further, stoppers 18 are provided at the top and bottom to stop the operation after overrun in the vertical direction. The entire mechanism is covered with a cover 17.

Vertical drive mechanism 9 There are various types of rotary drive mechanism in addition to the ball screw indirect drive system and belt drive system shown in FIG. 4, and these are summarized in the table below.

Each method (excluding the aforementioned methods 3-ii and 5) will be briefly explained using the above-mentioned known examples. Method 1 is a method in which the vertical axis is operated by air pressure from an air cylinder. Method 2 is a blade length that realizes vertical movement by replacing the ball screw in FIG. 4 with a rack and rotating a pinion that meshes with the rack with an electric motor. Method 3-j is a method in which the ball screw part is used as the output shaft, the ball screw nut part is connected to the direct drive motor rotor, and power is supplied to and driven the direct drive motor stator provided outside the rotor. be. Method 4 is a method in which the vertical axis is driven by a linear motor. Method 6 uses gears instead of the belt in Method 5. There are no examples in which a direct drive system is used for the rotational drive mechanism. Further, conventional wrist devices use an electromagnetic motor as a driving motor.

[Problem to be solved by the invention]

Method 1 of the above-mentioned prior art is based on the compressibility of air.

There is a problem in that sufficient accuracy cannot be obtained, and method 2 has a problem in that it is difficult to adjust backlash, so it is difficult to obtain sufficient accuracy. Methods 3-j and 4 have good accuracy, but because they use an electromagnetic direct drive motor, there is a problem that the output/self-weight ratio cannot be large and the motor part becomes heavy. Method 3-
, il has better accuracy than methods 1 and 2, but the play and backlash of the ball screw may adversely affect the positioning accuracy of the hand. Also, method 2.3-jj, 5
．． No. 5 has the problem that sufficient accuracy cannot be obtained because it is driven by a belt and gears.

The purpose of the present invention is to improve the accuracy of positioning and posture of the hand,
Another objective is to make the entire wrist mechanism smaller and lighter, increase the speed of the wrist and robot arm movements, and further simplify and lighten the mechanism by providing a holding function that does not use a mechanical brake.

[Means to solve the problem]

The above objective is achieved by a direct drive method in which a piezoelectric drive device, which has extremely large output and self-weight compared to an electromagnetic direct drive motor, is installed on the direct motor section of a conventional device or on the output shaft of a power transmission member such as a belt. Ru.

[Effect]

This wrist device utilizes the fact that by applying an AC voltage at the resonance frequency of the piezoelectric drive device containing the piezoelectric body to the piezoelectric body, the drive end of the piezoelectric drive device can move along an elliptical vibration locus. By pressing the piezoelectric actuator's drive end (linear moving part) against the drive end of the piezoelectric drive device, it rotates or linearly moves. Since the drive frequency is an inaudible frequency of 20 KHz or more, the noise is low, and the vibration amplitude is at most a few microns, so a high-resolution position detector is used to detect the position and perform position feedback control. This enables highly accurate positioning.

Further, since the piezoelectric drive device is installed so as to press against the moving portion, when the piezoelectric drive device is not in operation, even if an external force in the moving direction is applied to the moving portion, the piezoelectric drive device is held by static frictional force.

〔Example〕

Before describing each embodiment of the present invention, a structural example and operating principle of a piezoelectric drive device commonly used in each embodiment of the present invention will be explained based on FIG. 2.

First, the structure and operating principle of the piezoelectric drive device will be explained with reference to FIG. Piezoelectric body 29.31 arranged orthogonally to the base 28
However, there are two pairs of elastic hinges 30 that are rigid in the vertical direction and flexible in the horizontal direction.
,． 32, and the drive end 33 is provided with a sliding member (for example, a member made of silicon nitride). The piezoelectric body 29.degree. 31 is displaced in the direction of the arrow when a voltage is applied. When an alternating current voltage that matches the resonance frequency of the piezoelectric drive device is applied to the piezoelectric body, an extremely large vibrational displacement is obtained at the drive end 33. For example, if an AC voltage with a resonant frequency is applied only to the piezoelectric body 31, the operating locus of the drive end shown by the broken line in the figure will be obtained, and if an AC voltage with a resonance frequency is applied only to the piezoelectric body 29, The motion locus of the drive end shown by the dotted chain line is obtained. Therefore, by pressing and installing the driven body 34 (for example, made of hardened steel) on the drive end 33, the driven body 34 is moved in the directions shown by the dashed line and the dashed three-dot line in the figure, respectively. be able to.

Further, since the piezoelectric drive device is installed so as to be pressed against the driven body, there is an advantage that when the piezoelectric drive device is not in operation, it is held by static frictional force even if an external force is applied in the moving direction of the driven body 34. In addition, the piezoelectric drive device has a maximum output/self-weight ratio of 3
00W/kg, compared to the maximum output/self-weight ratio of conventional electromagnetic drive devices, which is about 100W/kg.
Since it is approximately twice as large (see Machine Design Vol. 31, No. 13 (1987), p. 56), it is possible to realize a small and lightweight drive device. From the above, by directly driving the wrist device using the piezoelectric drive device, it is possible to reduce the weight of the wrist device.

A first embodiment of the present invention will be described below with reference to FIG. In this embodiment, piezoelectric drive devices 9 and 6 are applied in place of the electric motors 21 and 26 to a wrist device having almost the same mechanism as the conventional device shown in FIG. First, the rotational drive mechanism will be explained. The piezoelectric drive device 9 is fixed to the hollow cylindrical member 2 connected to the arm 1 and is pressed into contact with the disc-shaped member 5, and the contact pressure is applied by the nut 46. The piezoelectric drive device 9 is provided so that the circumferential direction of the disc-shaped member 5 coincides with the operating direction of the driven body 34 shown in FIG. A single number 9 or a plurality of numbers 9 are provided at equal intervals in the circumferential direction of the lower surface of the hollow cylindrical member 2. When a voltage is applied to the piezoelectric body, the disc-shaped member 5 rotates together with the spline shaft 7 connected to the hand 19. Its rotation speed is
It is determined by the applied voltage and does not depend on the number of piezoelectric drive devices. Further, the generated torque is determined by the applied voltage and the number of piezoelectric drive devices, and when a plurality of piezoelectric drive devices are provided, the total torque is multiplied.

Next, the vertical drive mechanism will be explained.

A single piezoelectric drive device 6 or a plurality of piezoelectric drive devices 6 are installed at equal intervals on the lower surface of the hollow cylindrical member 13 so that their operating directions coincide with each other in the circumferential direction, and are pressed into contact with the disk-shaped member 14 by a nut 47. When a voltage is applied to the piezoelectric body, the ball screw 20 rotates, and the connecting plate 12. which is connected to the ball screw nut part. The spline shaft 7 moves up and down.

In this example, a position detector was provided on each output rotating shaft, so
As compared with the conventional device shown in FIG. 4, more accurate position detection is possible. Additionally, the mechanism has been greatly simplified, making it smaller and lighter.

Next, a second embodiment of the present invention will be described using FIGS. 5 and 6. 1st. The same parts as those in the embodiment are indicated by the same numbers. Although the first embodiment shows a configuration in which the ball screw and the spline shaft are arranged in parallel, the configuration can be made even simpler if it can be configured with only the spline shaft. This embodiment is an example of this. FIG. 5 is a longitudinal sectional view of the wrist device of this embodiment, and the sixth
The figure is a sectional view taken along the line VI-VI in FIG. The mechanism of this embodiment will be explained based on FIG.

The rotational drive mechanism is the same as that of the first embodiment, and one or more piezoelectric drive devices 9 provided in the circumferential direction on the lower surface of the hollow cylindrical portion 2 are pressed against the disk-shaped member 5 by a nut 46 and come into contact with the disk-shaped member 5. The structure is such that the disc-shaped member 5 and the spline shaft 7 can be rotated by applying a voltage to the piezoelectric body.

In the vertical drive mechanism, the piezoelectric drive device 6 is a hollow cylindrical member 48
A plurality of piezoelectric drive devices (three in the example shown) are provided inside the piezoelectric drive device 6 as shown in the cross-sectional view in FIG. The structure is such that it is pressed into contact with the surface. When a voltage is applied to the piezoelectric body, the spline ili[ll 7 moves in the vertical direction. Since a plurality of piezoelectric drive devices 6 are provided in the circumferential direction, they also function to support the spline shaft 7 together with the spline bearing 8.

In this embodiment, position detection in the rotational direction is performed by the brushless resolver 11, and position detection in the vertical direction is performed by the vertical position detector 40 and the coat plate 39, which together with the detector 40 constitutes the vertical position detector.

According to this embodiment, it is possible to use a wrist device that is smaller and lighter than the first embodiment described above.

Next, a third embodiment of the present invention will be described using FIGS. 7 and 8. The same parts as in the first and second embodiments are indicated by the same numbers. In the second embodiment described above, the vertical and rotational drive mechanisms are coaxially realized using only the spline shaft, but there is a problem in that many members are required around the spline shaft. Therefore, in this embodiment, an example of a wrist device with a simple structure using a linear guide is shown. FIG. 7 is a longitudinal sectional view of the wrist device of this embodiment, and FIG. 8 is a sectional view taken along the line Mll-■ in FIG.

The vertical drive mechanism of this embodiment will be explained. As shown in FIG. 8, a linear guide rail 5] is fixed to the arm 1. The linear guide rail 42 is in contact with the linear guy block 51 via a ball (not shown), and the linear guide rail 42 is movable in the vertical direction with respect to the linear guide block 51. Linear guide rail 4
A sliding member 43 is provided on the end face of the plate 48, and the piezoelectric drive device 6 provided on the plate 49 moves between the plates 1 and 49.
It is pressed against the sliding member 43 by the fastening pressure of the nuts 1-50. When a voltage is applied to the piezoelectric body, the sliding member 43
And the linear guide rail 42 moves in the vertical direction. The sliding member 43 (for example, a member made of hardened steel) has a large friction coefficient with the piezoelectric drive device drive end 33 (for example, a member made of silicon nitride), and the material with a small amount of wear is used. selected.

Next, the rotational drive mechanism will be explained. A piezoelectric drive device 9 is provided on a member 52 coupled to the linear guide rail 42, and is pressed into contact with a rotor 53 by a bolt 54. When voltage is applied to the piezoelectric body, the rotor rotates. The position detection method of the vertical drive mechanism and rotary drive mechanism described in this embodiment is the same as in the second embodiment. According to this embodiment, a wrist device capable of vertical and rotational movements can be obtained using a simpler mechanism than the second embodiment.

〔Effect of the invention〕

According to the present invention, both the vertical drive mechanism and the 9-rotation drive mechanism of the wrist device are made lighter and more rigid, so it is possible to move the tip with good positioning and orientation accuracy, and the load inertia of the arm drive motor is reduced. It has the effect of being Also,
Since the piezoelectric drive device is pressed into contact with the driven body, it has a holding function due to static frictional force, and has the effect that the conventionally used mechanical brake is unnecessary.

[Brief explanation of the drawing]

Fig. 1 is a vertical cross-sectional view of the first embodiment of the present invention, Fig. 2 is a structural example of a piezoelectric drive device and an explanatory diagram of its operating principle, and Fig. 3 is an example of a horizontal articulated robot incorporating this wrist device. FIG. 4 is a vertical sectional view of a conventional wrist device, FIG. 5 is a vertical sectional view of a second embodiment of the present invention, and FIG. 6 is a view taken along VI-V in FIG.
7 is a longitudinal sectional view of the third embodiment of the present invention, and FIG. 8 is a sectional view taken along the line ■--■ in FIG. 7. 1.36...Arm, 6,9...Piezoelectric drive device, 7
... Spline shaft, 8... Spline bearing, 10.
11...Position detector, 15.16...Proximity switch, 17...Cover, 18...Stopper, 19...
・Hand, 21.26, 35.37...Electric motor, 22
．． 23...Pulley, 24.25...Belt, 27.
...Mechanical brake, 28...Base, 29.3
1... Piezoelectric body, 30.32... Elastic hinge, 33.
... Drive end portion, 34... Driven body, 38... Wrist mechanism, 39.40... Vertical position detector, 42... Linear guide rail, 43... Sliding member, 44... ...Detection plate, 51...Linear guide block. To drink

Claims (1)

[Scope of Claims] 1. A wrist device provided on the most advanced arm of a robot, including a first movable member provided on a member integral with the most advanced arm via a first support member; a first piezoelectric drive mounted on the most distal arm and pressed against the movable member to enable contact movement of the first movable member; and a second support for the first movable member; a second movable member provided via a member, or a fourth movable member provided via a third support member with respect to the first movable member; and a fourth movable member provided via a third support member, and the second movable member The first movable member or the fourth movable member is pressed by the second movable member or the fourth movable member to enable the movable member or the fourth movable member to move in contact with each other. A wrist device for a robot having a second piezoelectric drive mounted on a third movable member. 2. In the robot wrist device according to claim 1, the movement displacement of the first movable member and the second movable member or the fourth movable member, the origin position in each movement direction, and the overrun A wrist device for a robot, characterized in that a detector for detecting the presence or absence is provided on each arm and the first movable member or the third movable member.