JPH0310786A - Gravity balancing device - Google Patents

Abstract

PURPOSE:To sharply reduce motor given torque by providing a second rotational and direct acting conversion element to perform direct acting conversion of rotation in a gravity exerting direction in which rotation of a motor is movable in a reverse direction to a direct acting element in a higher reduction ratio and a weight mounted to the direct acting element so as to effect press in the antigravity exerting direction of the moving body. CONSTITUTION:When the direct acting element moving direction of a first direct acting shaft is a gravity exerting direction, when a drive motor does not generate hold torque, a moving body is slipped off in a gravity exerting direction, and a second ball screw nut part 11 is about to move in a reaction direction. In this case, a weight 13 is mounted to the second ball screw part 11, and a balance force is generated in the antigravity exerting direction of the moving body. The generation of the balance force prevents slip off of the moving body and reduces hold torque of a drive motor to a microvalue. By applying a press force on the reduction action of direct acting movement of the moving body, the increase of the load inertia of a direct acting shaft drive motor can be reduced, and motor given torque can be reduced sharply.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a gravity balance device for reducing the holding torque of a motor that drives a linear shaft that moves a movable body in the direction of gravity action, and a water balance device. The present invention relates to a gravity action direction drive device equipped with the device and an industrial robot equipped with the gravity action direction drive device.

[Conventional technology]

Conventionally, as a balance device for reducing the load torque of a drive motor of a linear motion axis moving in the direction of gravity of a moving object,
As described in No. 1836, a small lead ball screw shaft is provided coaxially with a ball screw shaft for driving a direct-acting shaft, and the small lead ball screw nut is connected to a piston to form a cylinder structure, thereby achieving balance using fluid pressure. is stated.

In addition, as described in Japanese Patent Application Laid-Open No. 55-35735, the drive motor holding torque, which changes depending on the rotation angle, is fixed from the rotating shaft to the tip of a small arm connected to the final stage gear via a multi-stage gear with an appropriate gear ratio. A device is described in which gravity balance is achieved regardless of the rotation angle by providing a spring between the rotation angle and the rotation angle.

On the other hand, as a robot structure for reducing the load torque of the robot arm rotary drive motor, as described in Japanese Patent Application Laid-Open No. 63-2679, the wrist linear motion/rotary shaft drive motor is connected to the wrist with respect to the rotary drive shaft of the second arm. An example is described in which the device is installed on the opposite side of the section.

[Problem to be solved by the invention]

The above-mentioned first conventional technology regarding the gravity balance device actively generates the gravity balance force by fluid pressure control.
It is effective in that it can generate a balance force arbitrarily regardless of the size of the load, but it is too large to be attached to the linear motion axis that moves in the direction of gravity at the wrist at the tip of the robot arm.
There was a problem in that the fluid pressure control peripheral equipment was complicated.

In the second prior art related to the gravity balance device, the gravity balance of the rotary joint is configured only by passive mechanical elements such as gears and springs. This balance device is effective when the gravitational load moment changes sinusoidally depending on the rotation angle, but it is not suitable as a balance device for a device using rotary/linear exchange elements where the gravitational load moment does not change regardless of the rotation angle. There was a problem with it not being available.

The above-mentioned third conventional technology related to industrial robots does not take measures to reduce the gravity load torque of the wrist direct-acting shaft drive motor, and there is a problem that the wrist direct-acting shaft drive motor becomes large in capacity and size under heavy loads. there were.

The object of the present invention is to provide a gravity balance device that reduces the gravity balance torque of a linear shaft drive motor that moves in the direction of gravity using only passive mechanical elements, a gravity direction drive device equipped with the gravity balance device, and a gravity force direction drive device equipped with the gravity balance device. An object of the present invention is to provide an industrial robot equipped with a directional drive device and designed to reduce the load torque of a wrist direct-acting shaft drive motor and a base arm drive motor.

[Means to solve the problem]

In order to achieve the above object, the present invention is characterized by the configuration described below.

In order to achieve gravitational balance against the gravitational force direction load using only passive mechanical elements, a second rotating shaft with a large reduction ratio is used.
A configuration in which a linear motion conversion element is used to obtain a linear motion in the direction of gravity action, which is a reduction of the linear motion of the moving body, and a weight is connected to the linear element to generate a pressing force in the anti-gravity direction of the moving body. And so. In addition, in order to reduce the load torque of the motor that drives the wrist direct-acting shaft installed at the end of the second arm in a series-connected two-arm robot, a gravity balance device is installed on the first arm.
In order to reduce the load torque of the arm drive motor, the wrist direct drive shaft/rotary shaft drive motor and gravity balance weight are installed on the second arm on the side opposite to the wrist with respect to the arm drive motor. This is made possible by setting the center of gravity of the second arm near the axis of the second arm drive motor.

[Effect]

In a gravity balance device, a case where a ball screw is used as a rotation/linear motion conversion element and a case where a rack/binion is used will be explained.

When the screw shaft of a ball screw is rotated, the nut portion, which is prevented from rotating, moves linearly in the direction of the screw shaft by the lead of the screw per rotation. In the first rotation/linear motion conversion element, a moving body is coupled to a ball screw nut portion, and the ball screw shaft is rotationally driven by a drive motor, so that the moving body performs linear motion due to rotation of the drive motor. The second rotation/linear motion conversion element is a ball screw coaxial with the first ball screw or provided in the direction of gravity through a power transmission member such as a gear. The second ball screw has a smaller lead than the first ball screw, and its movement direction in the direction of gravity is opposite, so that the second ball screw nut section performs a reduction operation of the linear motion of the first ball screw nut section.

When the direction of movement of the linear motion element of the first linear motion shaft is in the direction of gravity, if the drive motor does not generate holding torque, the moving body will slide down in the direction of gravity, and the second ball screw nut will move in the reaction direction. Moving. The mizutari balance device attaches a weight to the second ball screw nut and generates a balancing force in the anti-gravity direction of the moving body, which prevents the moving body from sliding down and reduces the holding torque of the drive motor. It can be made very small. The reason why the pressing force is applied to the reduction operation of the linear motion of the moving body is that the increase in the load inertia of the linear shaft drive motor can be reduced.

Next, a case will be described in which a rack and pinion mechanism is used as the rotation/linear motion conversion element. When the drive motor rotates the re-pinion, the first rack and the movable body coupled thereto are supported by bearings and perform linear motion. The second rotary/linear motion conversion element uses a gear to reduce the pinion or the gear between the motor and the pinion in a single stage or in multiple stages, and the second rotation/linear motion conversion element reduces the speed of the pinion or the gear between the motor and the pinion in a single stage or in multiple stages, and directly moves the gear in the opposite direction of motion (direction of gravity action) to the first rack that meshes with the final stage gear. It is composed of a second rack that moves dynamically. The second rack is bearing supported and provides a reduction in the linear motion of the first rack. By attaching a weight to the second rack, a balancing force can be generated in the direction opposite to the gravity of the first rack.

Next, the operation of an in-line two-arm robot using this gravity acting direction drive device as a wrist linear motion axis drive device for an industrial robot will be explained using FIGS. 6 to 8. FIG. 6 shows a structural diagram of an industrial robot without a heavy-coverage balance device, FIG. 7 shows a structural diagram of an industrial robot with a heavy-coverage balance device, and FIG. 8 shows a required motor torque characteristic diagram of the industrial robot. The following relationship holds true between each axis motor torque τ1, each axis motor angular velocity θJ, and angular acceleration θj.

...(1) Here, JIJ is a coefficient indicating the amount equivalent to inertia, and JIJ is a coefficient indicating the equivalent amount of inertia.
J(θ2) is an amount that changes depending on the angle of view θ2. Also, assuming arm length aa, arm center of gravity distance Qi, and arm mass mJ, J13=mza I Q z, and each axis motor is Figure 8(n) shows the required torque of each shaft motor and its torque components without a heavy coverage device when accelerating and decelerating in a cycloidal speed pattern.
Because the arm center of gravity distance Q2 is large (see Figure 6), (
1) There is a problem in that the centrifugal/Coriolis torque component in the third term of equations (2) increases in the high-speed range, and the torque required for the single-axis motor becomes extremely large. Therefore, if a gravity balance device is provided and its balance weight is installed in a position that reduces the arm center of gravity distance Q2 in Figure 2, the total weight of the second arm will increase, but as shown in Figure 8 (■), centrifugal and Coriolis There is an effect that the torque is reduced and the total torque required for the single-axis motor is reduced. Here, in the gravity balance device, the second linear motion element performs a deceleration operation of 172 of the first linear motion element, so in order to maintain the gravity balance, the balance weight provided on the second linear motion element is By setting the weight to twice the load weight of the element, it is possible to balance the gravity of the wrist direct motion axis, and the second
When setting the amount of overhang of the arm on the side opposite to the wrist part, if the distance from the arm drive shaft to the first linear motion element is a2, then the second straight line is set to the overhang distance of 5z=az/Z on the opposite side. By providing a dynamic element, the distance between the center of gravity of the second arm can be made almost zero, and there is no need to increase the amount of extension unnecessarily.When the wrist member load changes, the second arm can be adjusted by simply changing the weight of the balance weight. It becomes possible to maintain the center of gravity distance to almost zero.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a gravity balance device and a gravity action direction driving device according to the present invention will be described below with reference to FIGS. 1 to 5. 1st
Figure 2 is a structural diagram of a gravity acting direction drive device using a pole screw, Figure 3 is a structural diagram of a gravity acting direction driving device using a rack and pinion mechanism, and Figure 4 is A-A in Figure 3. A partial sectional view, FIG. 5 is an explanatory diagram of the principle of the gravity balance device section of FIG. 2. The gravity balance device of the present invention is a gravity action direction drive device that converts the rotational motion of a motor into linear motion via a rotational/linear motion conversion element to move a moving object, and is capable of converting the rotational motion of a motor into linear motion via a rotational/linear motion conversion element to move a moving body. This is a structure in which a weight is coupled to a second moving body that performs a reduced linear motion obtained through a conversion element, and presses the first moving body in an anti-gravity direction to achieve gravity balance.

First, using Figures 1, 2, and 5, An example of a gravity action direction drive device and a gravity balance device using a ball screw as the second rotational/linear conversion element will be described.

In FIGS. 1 and 2, rotational power is transmitted from the motor 8 to the pulley 15b, belt 16. The force is transmitted to the first pole screw shaft 1 provided in the direction of gravity action via the pulley 15a. A ball screw nut part 2 is engaged with the first ball screw shaft 1 via a steel ball, and the pole nut part 2 moves linearly with the rotation of the ball screw 1i111. A bracket 4 is coupled to the ball screw nut portion 2, and a spline shaft 5 is coupled to the bracket 4 in parallel with the ball screw shaft 1. A spline bearing 6 provided on the base 14 connects the first ball screw shaft The ball screw nut part 2 is prevented from rotating during one rotation, and the linear movement of the spline shaft 5 is guided. A tool 18 is provided at the tip of the spline shaft 5, and a load acts in the direction of gravity. If the first ball screw speed Px (m), the rotational speed of the first ball screw shaft 01 (rad/s), and the linear speed Z of the first ball screw nut part 2 (m/s), then the following equation is obtained: becomes true.

Next, the gravity balance device section will be described. In FIG. 1, a second ball screw shaft 1o machined coaxially with the first ball screw shaft 1 has a screw winding direction in which its nut portion 11 moves in the direction of gravity acting opposite to the first ball screw nut portion 2 when the shaft rotates. It becomes. Second ball screw nut part 11
is connected to the movable part of the linear guide 12, and is prevented from rotating to perform linear motion. Therefore, when the first ball screw nut section 2 moves in the gravitational direction, the second ball screw nut section 11 moves in the anti-gravitational direction. By coupling the weight 13 to the second ball screw nut portion 11, it is possible to realize gravity balance against the load in the direction of gravity acting on the tool 18. Here, the second pole screw lead Pz (m), the load weight W of the first ball screw
Then, the weight BkWt of the weight coupled to the second ball screw nut portion can be set based on the following equation.

The 2π motor 8 is provided with a position holding mechanism brake 9° and a position detection encoder 7.

2 Although this figure shows an example in which the first and second ball screw shafts are machined coaxially, the first and second ball screw shafts are machined coaxially. The second ball screw shaft may be separate and connected by a shaft joint.

Next, the gravity balance device shown in FIG. 2 will be described.

A bevel gear 19b meshes with a bevel gear 19a connected to the first ball screw shaft 1, and the motor is connected to the second ball screw shaft 10 whose direction of gravity is in the axial direction via the shaft 20 and bevel gears 21a and 21b. 8 rotational power is transmitted. The first ball screw nut part 2 and the second ball screw nut part 11 are wound in such a manner that the movement direction of the gravity action direction is opposite to the rotation of the motor 8. By providing the weight 13 (weight W 1 ) on the second ball screw nut 11 so as to satisfy equation (4) when the load W in the sliding direction is applied, gravity balance can be achieved. Fig. 4 is an explanatory diagram of the principle of this type of cover balance device, and gravity balance is achieved by providing a dampness Wl that is twice the pole screw pitch ratio in the reduction linear motion of the first ball screw obtained by the second ball screw. It shows the principle. Also, when comparing the load inertia of a linear shaft drive motor with and without a gravity balance device, (1) Without a gravity balance device (2) With a gravity balance device... (6) JMJ is a ball screw Indicates the load inertia of the shaft, etc., W
The term containing the term was added by installing a six-fold balance device that indicates the hand load and the load inertia due to the weight (
6) The magnitude relationship between the third and fourth terms of the large tube and the first and second terms will be explained. If the reduction operation ratio of the second ball screw to the first ball screw is large, since Pz<Pz,
The third term in equation (6) is significantly smaller than the first term. Also,
In this case, since the second ball screw axial length is significantly smaller than the first ball screw axial length, (6) the fourth term of the large cylinder becomes significantly smaller than the second term, and the linear motion due to the provision of a gravity balance device The increase in the load torque of the shaft drive motor is slight, and as shown in Fig. 14, the average torque during direct drive shaft operation is reduced, and as shown in Fig. 15, the increase in the load torque of the encoder section connected to the motor and with a low allowable temperature is reduced. Temperature rise can be suppressed to a low level, and the operating duty ratio of the linear motion axis can be set high.

Next, a gravity action direction drive device using a rack and pinion mechanism will be explained with reference to FIGS. 3 and 4.

The bevel gear 25b, which is rotationally driven by the motor 8, transmits power to the rack 22 via the bevel gear 25a, and the spur gear 24 and spur gear 23 installed coaxially with the bevel gear 25a, so that the rotational motion of the motor is transmitted directly to the rack. converted into dynamic motion.

The rack 22 is mounted parallel to and connected to the spline shaft 5 via brackets 4a and 4b. The spline shaft 5 has a structure in which its linear motion is guided by a spline bearing 6 connected to a base 14, and the zero-order movement can be performed using a tool 18 provided at the tip of the spline shaft 5. Next, the gravity balance device of this gravity action direction drive device will be described. The spur gear 23 that meshes with the rack 22 is meshed with a spur gear 26a in addition to a spur gear 24 that transmits the power provided by the motor 8. Spur gear 26
The power transmitted to a is multi-stage reduced through a spur gear 26b provided coaxially with it, a spur gear 27a meshing with the spur gear 26b, and a spur gear 27b provided coaxially with the spur gear 27a. The signal is transmitted to the rack 28. The second rack 28 is coupled to the movable part of the linear guide 12,
A reduced translational movement of the first rack 22 in the direction opposite to the direction of gravity is performed.

A weight 13 is coupled to the second rack 28, and a gravitational balance force is generated to prevent the first rack 22 from sliding down in the direction in which the power is applied.

Next, the motion of the gravity action direction drive device using this rack and pinion mechanism will be explained using equations. The rotation speed θ (rad/s) of the motor 8, the rotational reduction ratio Z1 from the motor 8 to the spur gear 23 that drives the first rack 22. When the pitch diameter of the spur gear 23 is dot (m), the moving speed vx (m/S) of the first rack 22 is expressed by the following equation.

2π Zl If the rotational reduction ratio from the spur gear 23 to the spur gear 27b is 22, and the pitch circle diameter of the spur gear 27b is doz (m), then the second
The moving speed vz (m/s) of the rack 28 is expressed by the following equation.

Gravity balance can be achieved by

Next, the change in load inertia due to the installation of the water drop balance device is as shown in the following equation.

(1) Without heavy coverage device (2) With heavy coverage device 2π ZIZ2 First rack 22. Brackets 4a, 4b, spline shaft 5. If the total weight W of the tool 18 is the gravity load torque of the motor 8, the direct force Fz of the second rank 28 is expressed by the following formula.

os Therefore, set the weight 13 to have the weight of formula (10)...
・(12) Also in this formula, Zz >1. Since JMt>JMz, the increase in the load inertia of the motor 8 due to the provision of the gravity balance device is slight, and the load torque does not increase significantly, and the average torque during operation is reduced as shown in Fig. 14. , it is possible to reduce the temperature rise of the encoder section shown in FIG. 15, and it is possible to improve the linear motion axis operation duty.

Next, an industrial robot using the gravity action direction drive device having the gravity balance device described above will be explained with reference to FIGS. 7 and 9 to 13. Figure 7 is a structural diagram of a horizontal multi-joint direct drive robot with a heavy coverage device, Figures 9 and 1o are the second diagram of the robot in Figure 7 when a ball screw is applied to the gravity action direction drive device. 11 to 13 show a structural diagram of the main part of the second arm of the robot shown in FIG. 7 when the rack and pinion mechanism is applied to the gravity acting direction drive device.

The structure of a horizontal articulated direct drive robot having a gravity balance device will be explained using FIG. The l# pole part 30, the first arm, and the first
The second arm 33 is rotationally driven (35) by a second direct drive motor 32 provided at the tip of the arm 31, and the wrist shaft (spline shaft) 5 is linearly driven by the wrist device 49 provided at the tip of the second arm 33. Movement 361 Rotation movement 37
This structure allows the tool 18 to perform the work. The motors 8 and 42 that supply power to the wrist device 49 are connected to the arm drive motor 3 on the second arm 33.
The weight 13 is installed on the opposite side of the wrist device 49 to suppress the increase in the second arm center of gravity distance Q2.
is shrinking. Here, the detailed structure of both ends of the second arm 33, excluding the power transmission section, will be described below.

First, an example in which a ball screw is used as a rotation/linear motion conversion element will be explained using FIGS. 9 and 10. Figures 9 and 10 are the wrist attachments for the second arm in Figure 7! 49. It shows the structure of the right end of the second arm.

The rotation function of the wrist shaft (spline shaft) 5 is to convert the power generated by the motor 42 into a reducer 43. Pulley 39b.

Belt 40. Pulley 39a, spline bearing mounting member 3
8. This is done by transmitting the signal via the spline bearing 6. The linear motion function of the wrist shaft 5 is controlled by the pulley 15 from the motor 8.
b. Belt 16. The first ball screw shaft 1 is rotated via the pulley 15a to rotate the ball screw nut portion 2. Bracket 4
This is achieved by performing direct motion. bracket 4
Since the wrist shaft 5 is restrained in the direction of linear movement and freely connected in the direction of one rotation, the linear movement and rotational movement of the wrist shaft 5 are realized independently by the motors 8 and 42.

Further, since the gravity balance device has exactly the same structure as shown in FIG. 2, the explanation thereof will be omitted. With such a structure, it is possible to reduce the load torque and capacity of the linear shaft drive motor 8 and the first direct drive motor 29 in FIG. 7.

Next, an example in which a rack and pinion mechanism is used as a rotation/linear motion conversion element will be explained using FIGS. 11 to 13. 1st
Figure 1 is a structural diagram of the wrist device 49 of the second arm in Figure 7.
2 is a sectional view taken along the line A-A in FIG. 11, and FIG. 13 is a structural view of the right end of the second arm in FIG. 7. The rotation function of the wrist shaft (spline shaft) 5 is controlled by a motor 42 and a reducer 43. Pulley 39b.

Belt 40. Pulley 39a, spline bearing mounting member 3
8. The linear motion function of the wrist shaft 5, which is performed by transmitting power via the spline bearing 6, is performed by the motor 8 to the bevel gears 48b, 48a, the shaft 20, and the bevel gears 25b, 2.
5a, a spur gear 24 coaxially arranged with the bevel gear 25a;
This is done by further transmitting power to the first rack 22 via the spur gear 23. The first rack 22 is pressed from both sides by rubber rollers 50 to prevent it from rotating. The gravity balance device controls the rotation of the spur gear 23 that meshes with the first rack 22 through the spur gear 26a.

26b, 27a, bevel gears 44a, 44b, shaft 4
5. The force is transmitted to the second rack 28 via the bevel gears 46a, 46b and a spur gear 47 coaxially arranged with the bevel gear 46b, and gravity balance is achieved by the weight 13 provided on the second rank 28. With such a structure, the direct-acting shaft drive motor 8. It becomes possible to reduce the load torque and reduce the capacity of the first direct drive motor 29.

〔Effect of the invention〕

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

With a simple structure, it is possible to generate a uniform gravitational balance force regardless of the position of the drive shaft in the direction of gravity action, so a slight increase in the load inertia of the drive motor in the direction of gravity action can significantly reduce the required torque of the motor. The capacity can be reduced.

In addition, by arranging the gravity balance device and the wrist shaft drive motor so that the center of gravity of the second arm of the horizontal articulated two-arm robot approaches the shaft center position of the arm drive motor, the first arm drive motor The required torque is significantly reduced, and the capacity of the motor can be reduced.

A structural diagram of the action direction driving device, FIG. 4 is a sectional view taken along the line A-A in FIG. 3, FIG. 5 is a diagram explaining the principle of the gravity balance device of this embodiment, and FIG. A structural diagram of an articulated direct drive robot, Fig. 7 is a structural diagram of a horizontal articulated direct drive robot with a gravity balance device, and Fig. 8 (a) (a)' is a velocity pattern characteristic diagram. (b) (b)', (c) (c)' show the required torque characteristics of the motor during operation of the robot shown in Figs. motor,(
a)'(b)'(C)' indicates the case of a two-axis motor,
Figures 9 to 13 show the second robot shown in Figure 7, respectively.
A structural diagram of the main part of the arm, Figure 14 (d) is a speed pattern characteristic diagram of the device shown in Figures 1 and 2, (e) and (f) are the required torque of the gravity action direction drive motor with and without the gravity balance device. The characteristic diagram, FIG. 15, is a temperature rise characteristic diagram of the gravity action direction drive motor encoder section with and without the gravity balance device.

DESCRIPTION OF SYMBOLS 1... First ball screw support, 2... First ball screw nut part, 3... First ball screw support part, 4...
・Bracket, 5... Spline shaft (wrist shaft), 6.
... Spline bearing, 7... Encoder, 8... Wrist direct-acting shaft drive motor, 9... Brake, 10... Second ball screw shaft, 11... Second ball screw nut part, 12 ... Linear guide, 13 ... Weight, 14
...Base, 15...Pulley, 16...Belt,
17 River stopper, 18... Tool, 19... Bevel gear, 20... Shaft, 21... Bevel gear, 22...
・First rack, 23° 24.26.27... Spur gear, 25... Bevel gear, 28... Second rank, 29
...first direct drive motor, 30...
- Single-axis ball part, 31... first arm, 32... second direct drive motor, 33... second arm, 34-37... each axis movement direction, 38... Spline bearing mounting member, 39... Pulley, 40... Belt, 41... Encoder, 42... Wrist rotation shaft drive motor, 43... Reducer, 44... Bevel gear, 4
5... Shaft, 46... Bevel gear, 47... Spur gear, 48... Bevel gear, 49... Wrist toe] Country 3 - Morph Iθ --- Ho? Ruun ° service + 7 --- So "bu ¥ 9P Fukoku planning - 1st 9 Figure 3'/1-m-7'-ri 1rho Figure 3) 3 Figure procedure amendment (method) Nona balance costume 1 1 Compensation with π cases Patent applicant Nei T51Q + Co., Ltd. is Hitachi representative representative & 6゜7゜Date of amendment order September 26, 1999 (Delivery mill) Target of amendment Specification Column for brief explanation of drawings and drawings.

Contents of amendment (1) From page 25, line 18 of the specification to page 26, line 2 of the specification
Row ``Figure 8 Kaya/4 Figure Heron 5 Figure ne

Claims (1)

[Scope of Claims] 1. In a gravity balance device for a device that converts and decelerates the rotation of a motor into linear motion and causes a moving body coupled to a linear motion element to move linearly in the direction of gravity action, the motor a second rotational/linear motion converting element that converts rotation into a direction of gravity acting in a direction opposite to that of the linear motion element at a larger reduction ratio; A gravity balance device characterized by having a weight attached to press the weight. 2. In the gravity balance device according to claim 1, the first rotation/linear motion conversion element is constituted by a ball screw, and the ball screw shaft rotates with the rotation of the motor, and the first The linear motion element (moving body) is configured to be prevented from rotating relative to the ball screw axis and performs linear motion, and the second rotational/linear motion conversion element is coaxial with the ball screw or via a rotary power transmission member such as a gear or a belt. a second ball screw having a smaller lead than the ball screw provided so that the direction of movement is the direction of gravity, and a second linear motion element connected to the ball screw nut part is prevented from rotating with respect to the ball screw axis. A gravity balance device, characterized in that the second linear motion element is equipped with a weight that presses the first linear motion element (moving body) in an anti-gravity direction. 3. In the gravity balance device according to claim 1, the first rotation/linear motion conversion element is constituted by a rack and pinion, and the pinion rotates with the rotation of the motor, and A moving element (moving body) is supported by a bearing, and a gear that decelerates the second rotation/linear conversion element in one or more stages meshing with the pinion or the gear between the motor and pinion, and the rotation of the final stage gear. a second rack and its support member, which converts the movement direction into the direction of gravity action, and a weight that presses the second rack in the direction opposite to the gravity of the first linear motion element (moving body). A gravity balance device characterized by being provided with. 4. Claims 1 to 3 for a gravity action direction drive device that converts the rotation of a motor into linear motion and causes a moving body coupled with a linear motion element to move linearly in the direction of gravity action. A gravity action direction drive device comprising the gravity balance device according to any one of the above. 5. A first arm provided on the base so as to be rotatable around an axis perpendicular to the base; a second arm provided at the tip of the first arm so as to be rotatable around an axis perpendicular to the base;
A wrist linear motion shaft drive device for an industrial robot having a wrist shaft that performs linear motion in an axial direction perpendicular to the base and rotational motion around the axis at the tip of the arm is constituted by the gravity action direction drive device according to claim 4. The second rotary/linear motion converting element of the gravity balance device and the wrist linear motion/rotary shaft drive motor are provided on the second arm on the side opposite to the wrist portion with respect to the arm drive motor. industrial robot.