JPH03166083A - Wrist device for robot and industrial robot - Google Patents

Abstract

PURPOSE:To remarkably increase a wrist rotating rigidity, to shorten a positioning time and to improve a wrist axis motion accuracy by arranging a wrist rotating axis speed reducer at a wrist part. CONSTITUTION:A wrist axis 12 is made integral with a ball screw shaft and ball spline shaft, power transmission is performed via a belt 3 from a rotation driving motor 1 to the wrist part and the rotation power decelerated by the rotation speed reducer 6 provided at the wrist part is transmitted to an integral axis 12 via the spline bearing 8 subjected to spline fitting to the integral axis. In this case, a rotation type direction action driving motor is bound with the integral axis 12 coaxially to the rotation speed reducer output shaft, a direction driving motor rotor 9a is bound with the ball nut which screws with the integral axis 12 to drive the integral axis 12 via the ball and a direct action motion is performed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to a rotary/linear motion 2 installed at the end of a robot arm.
The object of the present invention is to provide a wrist device for a robot having a degree of freedom with a simple mechanism that has high rigidity and facilitates the generation of motion commands, and also to provide an industrial robot having the wrist mechanism. [Prior art] Conventionally, as a wrist device for a robot, Japanese Patent Application Laid-Open No. 62-5
As described in No. 4693, a ball screw shaft and a spline shaft are arranged in parallel, driven in each direction by a direct-acting/rotary drive motor, and a rotary reducer is installed in the wrist to increase wrist rotational rigidity. It was being done. Furthermore, as described in JP-A No. 61-173875, the wrist shaft is composed of one shaft (tile), a direct drive motor is installed on the arm concentrically with the quill, and the tile outer circumferential thread and ball Direct drive is achieved by rotating a drive nut that is threaded through the rotary drive motor, and power is transmitted from the rotary drive motor via a belt to a pulley placed concentrically with the wrist shaft. A device was described that transmitted rotational power to row grooves via balls. Furthermore, as described in Japanese Patent Application Laid-Open No. 64-71678, in order to eliminate interference between linear motion and rotational motion by using an integrated ball screw shaft and spline shaft, a rotary direct motion drive motor is connected to the rotor of the rotary drive motor. The method for installing it above was described. [Problems to be Solved by the Invention] Although the above-mentioned first prior art has high wrist rotational rigidity, it uses a two-axis coupling mechanism of a ball screw shaft and a spline shaft to perform rotational and linear motion, so it has mechanical problems. The problem was that the weight was increased by each axis support housing, and the absolute positioning accuracy in the direction of wrist translation was poor due to bending deformation of the two-axis connection bracket.

In addition, in the second conventional technology, the wrist mechanism is composed of concentrically arranged shafts, and although it is mechanically simple, reverse-wound spiral steel ball rolling grooves are machined on the inside and outside (hollow *Since the 4illlrJi interference was removed by the driving nut, there was a problem that required high-precision machining and high-precision assembly of the drive nut.

In addition, in the third conventional technology, the wrist mechanism is composed of concentrically arranged shafts and is mechanically simple, and eliminates interference between the shafts without using special mechanical components. Since power is transmitted through the wrist shaft, there is a problem in that there is a limit to the accuracy of wrist axis movement due to transmission errors caused by its low rigidity. An object of the present invention is to provide a wrist device for a robot that has high wrist rotational rigidity, is mechanically simple and lightweight, and has high accuracy in wrist axis movement, and an industrial robot equipped with the wrist device. [Means for solving the problem] In order to achieve the above objective, we adopted the technical means described below. (1) In order to increase wrist shaft rotational rigidity, the wrist shaft rotation reducer is arranged concentrically with the wrist shaft, and torque is transmitted from the wrist shaft rotation drive motor to the wrist shaft rotation reduction gear input shaft via a belt. Achieved high rigidity of the rotating shaft. (2) In order to simplify the wrist mechanism, an integrated ball screw shaft and spline shaft is used as the wrist shaft, the speed reducer output shaft is splined to the wrist shaft, and a hollow direct drive motor is attached to the speed reducer output shaft. A ball screw nut part that screws into the wrist shaft is connected to the direct drive motor.

(3) In order to improve the movement accuracy of the wrist shaft, the wrist shaft rotation drive unit and wrist shaft direct drive unit on the same axis as the wrist shaft are directly connected, and the power transmission member is removed, thereby transmitting the power transmission member. Reduced deterioration in wrist axis movement accuracy due to errors. [Effects] We will discuss the effects of individual technical means to achieve the above objectives. (1) By arranging the wrist rotating shaft reducer at the wrist, high rigidity can be achieved based on the following principle. In FIG. 3, the rotational power of the wrist rotation drive motor 1 described in the third prior art is transmitted to a reducer 29 coaxially arranged with the motor, and the output is transmitted to a rotating body including a belt 32 and a spline bearing. 31 to the wrist shaft 12. FIG. 4 shows a system in which the rotational power of the wrist rotation drive motor 1 is transmitted to the wrist via the belt 3, and transmitted to the wrist shaft 12 via the reducer 6 and spline bearing disposed in the wrist. The above-mentioned first prior art (adopted in the present invention) is shown. Here, the rotational rigidity of the wrist mechanisms shown in FIGS. 3 and 4 will be compared. Here, the pulley speed ratio is assumed to be 1. The rotational direction rigidity of the belts 32, 3 seen from the pulley is kθ, kθ
', the rotational direction rigidity of the reducer kr, the reduction gear reduction ratio n, and the servo rigidity of the wrist rotation drive motor as infinite, the rotational rigidity of each as seen from the wrist axis is expressed by the following formula. Reducer motor K
z) Considering that normally k r > kθ, kθ′, n″r5o, K 1 z kθ, Kzχn″kθ
′, and considering that kθ〉kθ′, iooo
It is possible to increase the rigidity by about twice as much, significantly reduce belt transmission errors, and improve static stability during positioning operations by increasing the natural frequency. (2) The operating principle of this wrist device will be explained using Fig. 4. FIG. 4 is an explanatory diagram of the operating principle of the robot wrist device of the present invention. The output shaft of the wrist reducer 6 is rotationally driven by the wrist rotation drive motor 1 via the belt 3, and the wrist shaft 12 is composed of a ball screw and spline integrated shaft (lighter than when the ball screw shaft and spline shaft are provided separately). Rotational power is transmitted through a spline bearing connected to the spline (which can be used), and the rotational movement of the wrist shaft 12 is realized.
Further, a wrist direct drive motor 9 whose rotor is coupled to a ball screw nut portion 11 which is threadedly engaged with a wrist shaft 12 is connected to the output shaft of the reducer 6, thereby realizing wrist direct drive motion. The wrist device of the third prior art is shown in FIG.
9 output shaft, and linearly moves and rotates the wrist shaft l2 via belts 33 and 32. Compared to this prior art, the wrist device of the present invention has one less belt and has a simpler mechanism.Furthermore, as shown in FIG. However, in the wrist device of the present invention shown in FIG. 4, the tension of the belt 3 can be adjusted only by adjusting the distance between the axes, which simplifies the mechanism and reduces weight. be able to. (3) In this wrist device, when the wrist rotation drive motor and the wrist direct drive motor 9 rotate by nθ4, θ8 (n: reduction ratio of reducer 6), the wrist shaft rotates by an angle θ, and the ball screw nut part rotates by (θ8+04). ) No. 10 = 03P Inter-axis interference is removed. Here, if an angle transmission error of Δθ occurs in belt 3, the transmission error of the belt will not have a large effect on the wrist axis movement accuracy. On the other hand, in the third prior art, the belt 33.
When an angle transmission error of Δθ8 and Δθ occurs in 32, the wrist axis rotation angle error becomes P, and the belt's angle transmission error interferes between the axes, resulting in deterioration of operational accuracy (Δθ8 and Δθ depend on the rotation direction of each axis. There is a problem that leads to the difference in sign. From the above, in the wrist device of the present invention, by arranging the speed reducer at the wrist and using only one belt, it is possible to reduce deterioration in wrist axis movement accuracy due to belt transmission errors.

〔Example〕

An embodiment of the present invention will be explained using FIGS. 1 and 2.
FIG. 1 is a longitudinal sectional view of the robot wrist device of the present invention, and FIG. 2 is a diagram showing the structure of a horizontal multi-joint direct drive robot equipped with the robot wrist device of FIG. First, the configuration and operation of an industrial robot equipped with a wrist device, which is the object of the present invention, will be explained using Fig. 2.
This robot is a type of robot that can operate at high speed in the horizontal plane and has variable horizontal rigidity, making it suitable for assembly work. Single-axis direct drive motor 21 installed on the base
rotates the first arm 22 as shown by the arrow 25,
A two-axis direct drive motor 23 provided at the tip of the first arm 22 rotates the second arm 24 as shown by an arrow 26, and a working tool 20 is attached to the bottom end of the second arm 24. A wrist shaft l2 is provided, and performs vertical movement (arrow 27) and rotational movement (arrow 28).

A wrist shaft drive mechanism 34 that moves the wrist shaft 12 in the vertical and rotational directions is provided in the robot arm. Tool 2
0 in the three-dimensional space is performed by the direct drive motors 21 and 23 for the l-axis and 2-axis and the vertical drive motor for the wrist shaft 12, and the posture is determined only by rotating the wrist shaft 12 around the axis. This is done by a rotational direction drive motor. Robots that use a direct drive motor to drive the arm transmit power directly to the arm without going through a low-rigidity reducer, so the rotational rigidity of the axis can be increased, and by changing the constants of the direct drive motor control circuit. It has the advantage of being able to have variable rigidity. What is desired for the wrist device in such a robot is that it be lightweight and have high rigidity. This is a technical item that reduces the acceleration/deceleration time of each arm and improves the movement accuracy of the robot as a whole. The first mechanism for a robot wrist device that meets these requirements is
Explain using a diagram. As mentioned in the (Function) section, this wrist device uses an integrated ball screw shaft and spline shaft to reduce weight, and uses a reduction gear wrist arrangement method and wrist direct drive motor to increase rigidity. The wrist-mounted reducer is directly connected to the output shaft. The wrist direct drive motor's wrist-mounted reducer output shaft direct connection method is a new method that has not been used previously. In Figure 1, the wrist rotation drive system is configured as follows. Support plate 1 connected to robot arm 5
The rotation of the wrist rotation drive motor 1 installed at the wrist shaft 12 is transmitted to the input shaft of the reducer 6 via the pulley 2, belt 3, and pulley 4, and the rotational power taken out from the output shaft is transmitted to the wrist shaft 12. The rotation of the wrist shaft 12 is transmitted through the spline bearing 8 whose splines are aligned with the ball screw shaft/spline shaft (integrated shaft of the spline shaft) and the spline bearing member 7 which is key-coupled to the spline bearing. Here, if the speed ratio of pulleys 2 and 4 is 1, the reduction ratio is determined by the reduction ratio of reducer 6,
If the pulley speed ratio is not l, the reduction ratio from the motor is determined by the product of the reduction ratio of the reducer 6 and the pulley speed ratio. Next, we will discuss the wrist vertical drive system. In the present invention, in order to avoid interference with the wrist rotation drive system, a wrist vertical drive system is provided after the output shaft of the reducer. An internal cylinder rotor type direct drive motor 9 is installed in the direct drive NljJ motor housing 35 which is connected to the spline bearing mounting member 7. In the motor 9, for example, a coil is wound around a motor stator 9b, and a permanent magnet is provided on a motor rotor 9a supported by the motor stator 9b via a bearing, and the coil cannot be energized. Due to the magnetic effect, the motor rotor 9a rotates relative to the motor stator 9b. The motor rotor 9a has a hollow structure, and is connected to a pulley 11 whose inner surface is threadedly engaged with the wrist shaft 12.
The rotation of the direct drive motor 9 causes the wrist shaft 12 to perform direct motion in the vertical direction. Direct drive motor 9 usually has a maximum of 300
It is a high-speed rotation type direct drive motor that rotates up to about 100 rpm, and when the screw lead P of the wrist shaft 12 is 20 (am), the wrist shaft performs direct motion at a maximum of 1-.

S By adopting such a structure, interference between axes can be eliminated, and a lightweight and highly rigid wrist device can be realized. In the drive control of the drive system described below, the position detectors 18 and 10 directly connected to the motors 1 and 9 detect data and rotational/vertical movement amount data θ, ? Torque commands for motors 1 and 9 are generated/output based on the P deviation of π ■ΔZ (=08) (ΔZ: vertical movement distance). In addition, when the vertical axis is under heavy load, the direct drive motor 9
Because the robot slides down when the power is turned off, causing positional deviation, it is necessary to install a mechanical brake (for example, a non-excitation type). However, if it is installed coaxially with the direct drive motor 9, the robot As the load inertia increases, the position is maintained by a mechanical brake consisting of a rotating disc 17, a stationary disc 16, and an actuator spring 15 via a ball screw nut (pulley) 11, belt 13, and pulley 14 as shown in the figure. This can prevent the load inertia of the robot's 1.2-axis drive motor from increasing. In this mechanical brake, when the power is off, the stationary disk 16 and the rotating disk 17 come into contact with each other due to the spring force, and braking torque is generated by friction, and when the power is on, the stationary disk 16 moves downward and the rotating disk 1
7 is in a free state and can rotate. In addition, by setting the speed increasing ratio to about 3 between pulley 11 and pulley 14, the belt wrap angle can be set sufficiently, and the motor 9
It becomes possible to prevent the wrist shaft 12 from slipping off with a braking torque that is 1/3 of the generated torque, and the capacity and weight of the mechanical brake can be reduced. Furthermore, the effect of the braking device having this configuration was detailed in Japanese Patent Application No. 87729/1983 by the present applicant. The mechanical brake and wrist rotation drive motor 1 is located near the two-axis direct drive motor 25 in the second arm 26 or at the wrist l with respect to the two-axis direct drive motor 25.
By providing it on the side opposite to 2, the load inertia of the single-axis direct drive motor can be reduced, and there is an advantage that the acceleration/deceleration time of the robot can be shortened.

〔Effect of the invention〕

Since the present invention is structured as described above, it produces the effects described below.

(1) Since the reduction gear for the wrist rotation axis is placed in the wrist, the rotational rigidity of the wrist can be significantly increased, the positioning time can be shortened, and the accuracy of wrist axis movement can be improved.

(2) By configuring the wrist device using an integrated ball screw shaft and spline shaft as the wrist shaft, the wrist mechanism can be simplified and the weight can be reduced, so the load on the robot arm drive motor can be reduced. Inertia can be reduced and acceleration/deceleration time can be shortened. (3) By directly connecting the wrist rotary reducer output shaft to the wrist direct drive motor, position transmission errors caused by low belt rigidity can be reduced and the operational accuracy of the wrist shaft can be improved.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal sectional view of the robot wrist device of the present invention, Fig.
The figure shows the structure of a horizontal multi-joint direct drive robot equipped with the robot wrist device shown in FIG. 1, FIG. It is an explanatory diagram of the operating principle of the wrist device. l...Wrist rotation motor, 2, 4, 14.31...
・Pulley, 3, 13, 32. 33...Belt, 5...
・Robot arm, 6, 29...Reducer, 7...Spline bearing mounting member, 8...Spline bearing, 9,
30... Wrist direct drive motor, 10, 18... Position detector, 1 work... Ball screw nut section, 12... Wrist shaft (ball screw/spline integral shaft), Work 5... Actuator. Spring, 16...stationary disk. 17・
... Rotating disk, 19... Support plate. 20... Tool, 21... 1-axis direct drive motor, 22... 1st arm, 23... 2-axis direct drive motor, 24... 2nd arm, 25, 26, 27, 28...Each axis movement direction, 34...Wrist axis plan

Claims (1)

[Claims] 1. In a wrist device for a robot that allows free translational and rotational movement of a tool attached to the end of a robot arm, the wrist axis is composed of an integrated ball screw axis and ball spline axis, and the rotation Power is transmitted from the drive motor to the wrist via a belt, and the rotational power reduced by a rotary reducer provided at the wrist is transmitted to the integral shaft via a spline bearing that is aligned with the spline of the integral shaft. A rotary direct drive motor is coupled to the output shaft of the rotary reducer concentrically with the integral shaft, and the direct drive motor rotor is coupled to a ball nut that is threaded onto the integral shaft, and the integral shaft is connected to the rotary reducer through a ball. A wrist device for a robot that is driven and performs linear motion. 2. In the wrist device for a robot according to claim 1, speed-up power is transmitted from a ball screw nut directly connected to the direct drive motor rotor to another rotating shaft via a belt, and A wrist device for a robot characterized by having a mechanical brake coaxially provided that can brake its rotation. 3. A first arm that is rotationally driven around an axis perpendicular to the base, and a second arm that is rotationally driven around an axis at the tip of the first arm.
An industrial robot comprising an arm, characterized in that the wrist shaft according to claim 1 or 2 is provided at the tip of the second arm, and a drive mechanism thereof is provided in the periphery thereof. .