JP7442053B2 - Robot control method and robot control device - Google Patents

Description

The present disclosure relates to a robot control method and a robot control device.

Patent Document 1 discloses that during position control, a robot is operated using a torque command signal obtained by adding an integral value to a proportional value, while during flexible control, a torque command signal obtained by adding a compensation value to a proportional value limited to a torque limit value is used. A robot control device has been disclosed that operates a robot by.

Japanese Patent Application Publication No. 2000-42957

However, as in the invention of Patent Document 1, simply setting the gravity change compensation value to a small limit value corresponding to the change in gravity during flexible control may not be able to relieve the collision force applied to the robot.

Specifically, when a hypoid gear, which is a type of worm reducer, is used as a motor reducer, when a collision force is applied from the output side of the motor, the robot arm becomes stretched and stops rotating, a so-called self-locking phenomenon. It is easy to get stuck.

The present disclosure has been made in view of this point, and its purpose is to enable the motor to rotate in a direction that releases the collision force even when a collision force is applied from the output side of the motor.

A first invention is a robot control method for controlling the operation of a robot arm having a plurality of motors, the gravitational torque (τge) applied to the motor to be compensated for based on the rotation angles of the plurality of motors. a step of calculating a gravity compensation current (Igc) that compensates for the gravity torque (τge), based on the gravity compensation current (Igc) and a predetermined gravity subtraction setting value (Igth), a step of calculating a gravity compensation current subtraction value (Igsub); a step of calculating an excitation sine wave (Igsin) based on a predetermined excitation sine wave amplitude (Igsa) and a predetermined frequency (Igsf); A step of calculating a gravity compensation current correction value (Igc4) based on the gravity compensation current (Igc), the gravity compensation current subtraction value (Igsub), and the excitation sine wave (Igsin). It is characterized by

In the first invention, the gravity compensation current correction value (Igc4) is calculated based on the gravity compensation current (Igc), the gravity compensation current subtraction value (Igsub), and the excitation sine wave (Igsin). The gravity compensation current (Igc) is a current applied to the motor to compensate for the gravity torque (τge) applied to the motor to be compensated. A gravity compensation current subtraction value (Igsub) is subtracted from the gravity compensation current (Igc). An excitation sine wave (Igsin) is added to the gravity compensation current (Igc).

As a result, the motor, which has been self-locked and is in a static friction stop state, can be vibrated from the input side to bring the motor into a dynamic friction state. As a result, even if a collision force is applied from the output side of the motor, the motor can be rotated in a direction that releases the collision force.

A second invention is based on the first invention, and includes a step of performing flexible control to drive the motor so as to follow a direction in which the collision force is applied when a collision force is applied to the robot arm, and the flexible control. The present invention is characterized by comprising a step of correcting the current command of the motor based on the gravity compensation current correction value (Igc4).

In the second invention, flexible control is performed when a collision force is applied to the robot arm, and during the flexible control, the motor current command is corrected based on the gravity compensation current correction value (Igc4).

Thereby, the flexibility of the robot arm can be ensured and the tension phenomenon can be alleviated.

A third invention is a robot control device for controlling the operation of a robot arm having a plurality of motors, the gravitational torque (τge) applied to the motor to be compensated for based on the rotation angles of the plurality of motors. a first calculation unit that calculates a gravity compensation current (Igc) that compensates for the gravity torque (τge); a second calculation unit that calculates a gravity compensation current (Igc) that compensates for the gravity torque (τge); ) and a third calculation unit that calculates a gravity compensation current subtraction value (Igsub) based on a predetermined excitation sine wave amplitude (Igsa) and a predetermined frequency (Igsf). (Igsin), a gravity compensation current correction value based on the gravity compensation current (Igc), the gravity compensation current subtraction value (Igsub), and the excitation sine wave (Igsin); (Igc4).

In the third invention, the gravity compensation current correction value (Igc4) is calculated based on the gravity compensation current (Igc), the gravity compensation current subtraction value (Igsub), and the excitation sine wave (Igsin). The gravity compensation current (Igc) is a current applied to the motor to compensate for the gravity torque (τge) applied to the motor to be compensated. A gravity compensation current subtraction value (Igsub) is subtracted from the gravity compensation current (Igc). An excitation sine wave (Igsin) is added to the gravity compensation current (Igc).

As a result, the motor, which has been self-locked and is in a static friction stop state, can be vibrated from the input side to bring the motor into a dynamic friction state. As a result, even if a collision force is applied from the output side of the motor, the motor can be rotated in a direction that releases the collision force.

A fourth aspect of the present invention is a flexible control section based on the third aspect, which performs flexible control to drive the motor so as to follow a direction in which the collision force is applied when a collision force is applied to the robot arm; The present invention is characterized by comprising a current command correction section that corrects the current command of the motor based on the gravity compensation current correction value (Igc4) during flexible control.

In the fourth invention, flexible control is performed when a collision force is applied to the robot arm, and during the flexible control, the motor current command is corrected based on the gravity compensation current correction value (Igc4).

Thereby, the flexibility of the robot arm can be ensured and the tension phenomenon can be alleviated.

A fifth invention according to the third or fourth invention is characterized in that the motor has a hypoid gear.

In the fifth invention, a motor having a hypoid gear is used. A hypoid gear has a ring-shaped gear. This allows the robot cable to be placed through the inside of the ring-shaped gear. Furthermore, even if the motor has a hypoid gear that is likely to self-lock, the motor can be rotated in a direction that releases collision force.

According to the present disclosure, even if a collision force is applied from the output side of the motor, the motor can be rotated in a direction that releases the collision force.

FIG. 1 is a diagram showing the configuration of a robot according to this embodiment. FIG. 2 is a perspective view showing the configuration of the hypoid gear. FIG. 3 is a perspective view showing the arrangement of hypoid gears and cables. FIG. 4 is a block diagram showing the configuration of the robot control device. FIG. 5 is a diagram showing the configuration of the flexible control block. FIG. 6 is a diagram showing the waveform of the gravity compensation current when the arm is rotated 360 degrees from the arm side in a flexible control state. FIG. 7 is a diagram showing the waveform of the gravity compensation current subtraction value when the arm is rotated 360 degrees from the arm side in the flexible control state. FIG. 8 is a diagram showing the waveform of an excitation sine wave when the arm is rotated 360 degrees from the arm side in a flexible control state. FIG. 9 is a diagram showing the waveform of the gravity compensation current correction value when the arm is rotated 360 degrees from the arm side in the flexible control state. FIG. 10 is a diagram showing the waveform of the gravity compensation current when the collision stop occurs at a position where the fourth axis has an operating angle of 60° in the flexible control state. FIG. 11 is a diagram showing the waveform of the gravity compensation current subtraction value when the collision stop occurs at the position of the fourth axis operating angle of 60° in the flexible control state. FIG. 12 is a diagram showing a waveform of an excitation sine wave when a collision stop occurs at a position of an operating angle of 60 degrees of the fourth axis in a flexible control state. FIG. 13 is a diagram showing the waveform of the gravity compensation current correction value when the collision stop occurs at a position where the fourth axis has an operating angle of 60° in the flexible control state.

Embodiments of the present disclosure will be described below based on the drawings. Note that the following description of preferred embodiments is essentially just an example, and is not intended to limit the present disclosure, its applications, or its uses.

《Embodiment》
As shown in FIG. 1, a vertically articulated robot 1 includes a robot arm 2 and a plurality of joints J1 to J6. A robot control device 10 is connected to the robot 1 .

The robot arm 2 is divided into a plurality of parts, and joints J1 to J6 are provided at the connecting parts of each part. The joints J1 to J6 have first to sixth axes. A servo motor 3 is connected to each of the joints J1 to J6 via a reduction gear.

The servo motor 3 is driven based on a position command θcom from the robot control device 10.

The servo motor 3 controls the motion and posture of the robot arm 2 by rotating each of the joints J1 to J6 by a desired amount.

The joints J1 to J3 are three main axes that determine the overall posture of the robot arm 2. The joint J1 is a pivot axis for rotating the robot arm 2. Joints J4 to J6 are three wrist axes that determine the direction of the tip of the robot arm 2.

As shown in FIGS. 2 and 3, the joint J4 of the RW axis (fourth axis) and the joint J6 of the TW axis (sixth axis) are equipped with a reduction gear made of a hypoid gear 5. The hypoid gear 5 has a ring gear 6 and a pinion gear 7. A cable 8 is inserted through a hole in the center of the ring gear 6. The cable 8 is, for example, a welding cable for a welding section attached to the tip of the robot 1. The pinion gear 7 is connected to the servo motor 3 via a belt or the like.

As shown in FIG. 4, the robot control device 10 has a position control block 12. Position control block 12 constitutes a feedback controller. The position control block 12 generates a current command for causing the actual motor rotation angle θfb to follow the motor rotation angle command θcom. A motor rotation angle command θcom and an actual motor rotation angle θfb are input to the position control block 12. In the position control block 12, the first current command Icom1 is calculated by performing PID calculation etc. from the motor rotation angle command θcom and the motor rotation angle θfb. The position control block 12 outputs a first current command Icom1 to the control mode switching block 15.

The current control block 13 generates a current command for causing the motor to generate torque in a direction opposite to the motor rotation. The actual motor angular velocity ωfb is input to the current control block 13. The current control block 13 outputs a second current command Icom2 to the control mode switching block 15.

The flexible control block 14 generates a current command for performing flexible control that follows the direction of the collision force. The flexible control block 14 receives the first current command Icom1, the actual motor rotation angle θfb, and the other axis motor rotation angle load mass information 29. The flexible control block 14 outputs the third current command Icom3 to the control mode switching block 15.

In addition to the first current command Icom1, second current command Icom2, and third current command Icom3, the control mode switching block 15 receives a motor deceleration determination signal Dth, a collision direction flag Dir, and a collision detection signal Dcol. The control mode switching block 15 selects one of the first current command Icom1, the second current command Icom2, and the third current command Icom3 based on the motor deceleration determination signal Dth, the collision direction flag Dir, and the collision detection signal Dcol. and outputs it as a motor current Im applied to the motor.

Specifically, when the motor rotation direction and the collision torque direction are opposite to each other, the control mode switching block 15 switches from the position control block 12 to the current control block 13 to reduce the motor rotation speed.

Further, the control mode switching block 15 switches to the flexible control block 14 that follows the direction of the collision force when the motor rotation speed becomes equal to or less than a set value.

Further, the control mode switching block 15 switches from the position control block 12 to the flexible control block 14 when the motor rotation direction and the collision torque direction are on the same axis.

A motor current Im is supplied to the motor+actual load 17 indicated by the dotted line frame in FIG. In the motor, a motor torque τmm is generated in the calculation block 18 by multiplying the motor current Im by a torque constant Kt. A torque obtained by subtracting the disturbance torque 20 from the motor torque τmm is applied to the motor transfer function 21.

The disturbance torque 20 is the sum of the friction torque τμ, the gravitational torque τg, the dynamic torque τdyn (the sum of inertial force, centrifugal force, and Coriolis force), and the collision torque τdis.

The motor transfer function 21 is described using motor inertia J. The motor transfer function 21 outputs a motor rotation angle θfb. Motor rotation angle θfb is detected by an optical or magnetic encoder. In the calculation block 115, a value obtained by multiplying the motor rotation angle θfb by the reciprocal of the gear ratio 1/Rg is output as the operating angle θax.

The motor angular velocity ωfb and the collision torque detection value τdisd are input to the collision direction determination block 23. The collision direction determination block 23 calculates a collision direction flag Dir by comparing the collision torque detection direction and the motor rotation direction. The collision direction determination block 23 outputs a collision direction flag Dir to the control mode switching block 15.

Specifically, the collision direction determination block 23 calculates the collision direction flag Dir based on the following conditions.

ωfb×τdisd＜0 (Dir=1)
ωfb×τdisd≧0 (Dir=0)
In this way, the collision direction flag Dir becomes "1" when the motor angular velocity ωfb and the detected collision torque value τdisd are in opposite directions, and becomes "0" otherwise.

The motor rotation angle θfb is input to the motor angular velocity detection block 24. The motor angular velocity detection block 24 calculates the motor angular velocity ωfb by differentiating the motor rotation angle θfb.

The collision determination block 25 receives the collision torque detection value τdisd and the other axis collision torque detection value 28 . The collision determination block 25 determines that a collision has occurred when even one axis of the robot arm 2 exceeds a predetermined collision torque detection threshold out of the collision torque detection value τdisd and the other axis collision torque detection value 28. . The collision determination block 25 outputs a collision detection signal Dcol to the control mode switching block 15.

The collision torque detection block 26 calculates a collision torque detection value τdisd that is applied to the motor 3 that drives the robot arm 2 by the collision force applied to the robot arm 2. The collision torque detection block 26 receives input of the other axis motor rotation angle load mass information 29, the actual motor rotation angle θfb, and the motor current Im.

The collision torque detection block 26 calculates the angular velocity and the angular acceleration by differentiating the motor rotation angle θfb and the other-axis motor rotation angle load mass information 29 with respect to time. In the collision torque detection block 26, the torque required for the motor under the condition that no collision torque τdis is generated is determined by inverse dynamics calculation using the information of the robot mechanical parameters. The collision torque detection block 26 calculates the collision torque detection value τdisd by subtracting the value obtained by multiplying the motor current Im by the torque constant Kt from the torque determined by the inverse dynamics calculation.

The motor angular velocity ωfb is input to the motor deceleration determination block 32. The motor deceleration determination block 32 compares the magnitude of the motor angular velocity ωfb with a set threshold value to confirm deceleration of the motor. Specifically, if the following conditions are met, it is determined that the motor has been decelerated.

|ωfb|<ωth (Dth=1)
The motor deceleration determination block 32 outputs a motor deceleration determination signal Dth to the control mode switching block 15 when the absolute value of the motor angular velocity ωfb becomes smaller than a predetermined deceleration determination threshold ωth.

The operation when a collision force is applied to the robot arm 2 will be described below.

In normal position control before collision detection, the control mode switching block 15 selects the first current command Icom1 as the motor current Im, and applies it to the motor+actual load 17.

The control mode switching block 15 switches the control mode based on the information of the collision direction flag Dir shown below at the time when the collision detection signal Dcol is input.

Dir=1 (Im=Icom2) Current control mode
Dir=0 (Im=Icom3) Flexible control mode Specifically, when the collision direction flag Dir is "1", the control mode switching block 15 selects the second current command Icom2 as the motor current Im, and switches to the current control mode. Transition.

On the other hand, when the collision direction flag Dir is "0", the control mode switching block 15 selects the third current command Icom3 as the motor current Im, and shifts to the flexible control mode.

Here, as the motor decelerates after transitioning to the current control mode, the absolute value of the motor angular velocity ωfb becomes smaller than the predetermined deceleration determination threshold ωth. In this case, the motor deceleration determination block 32 outputs the motor deceleration determination signal Dth to the control mode switching block 15.

When the motor deceleration determination signal Dth is input, the control mode switching block 15 selects the third current command Icom3 as the motor current Im, and shifts to the flexible control mode.

Note that when the absolute value of the motor angular velocity ωfb is smaller than a predetermined deceleration determination threshold ωth when a collision is detected, the control mode switching block 15 does not shift from the normal control mode to the current control mode, but shifts to the flexible control mode. do. In other words, the control mode switching block 15 shifts from the normal control mode to the flexible control mode without applying reverse torque to the motor to decelerate it.

The flexible control block 14 realizes flexible control by limiting the current to the first current command Icom1 output from the position control block 12 and adding a gravity compensation current to prevent the robot from falling under its own weight. do.

As a result, even if the deviation between the motor rotation angle command θcom and the motor rotation angle θfb becomes large, the motor current is limited, thereby weakening the servo rigidity of position control and creating flexibility.

When the motor deceleration determination signal Dth becomes "1", the motor angular velocity ωfb is smaller than the predetermined deceleration determination threshold ωth. Therefore, the motor is in a substantially stopped state and its inertial energy is small, and by shifting to the flexible control mode, it is possible to eliminate distortion in the speed reducer or the like caused by the collision.

<Operation during flexible control>
By the way, when a hypoid gear 5, which is a type of worm reducer, is used as a reducer for the motor 3, when a collision force is applied from the output side of the motor 3, the robot arm 2 becomes stretched and does not rotate. It is easy to become self-locked.

Therefore, in this embodiment, by devising the control of the flexible control block 14, even if a collision force is applied from the output side of the motor 3 during flexible control, the motor 3 can be rotated in a direction to release the collision force. I made it.

Specifically, as shown in FIG. 5, the flexible control block 14 includes a gravity torque calculation block 101 (first calculation section). The gravitational torque calculation block 101 receives the motor rotation angle θfb and other-axis motor rotation angle load mass information 29 . The gravitational torque calculation block 101 calculates the gravitational torque τge applied to the motor 3 to be compensated by dynamic calculation from the motor rotation angle θfb and the other-axis motor rotation angle load mass information 29. The gravitational torque calculation block 101 outputs the gravitational torque τge. The gravitational torque τge is input to the calculation block 103 (second calculation unit).

In the calculation block 103, a gravity compensation current Igc that compensates for the gravity torque τge is calculated.

The gravity compensation current Igc is a value obtained by multiplying the gravity torque τge by the reciprocal of the torque constant 1/Kt. Arithmetic block 103 outputs gravity compensation current Igc.

FIG. 6 shows the waveform of the gravity compensation current Igc when the fourth axis joint J4 is rotated 360° (-180° to 180°) from the arm side (reducer output side) in the flexible control state. .

As shown in FIG. 6, for example, when the operating angle θax of the fourth axis is 0°, the maximum motor current ratio is 0%. Further, when the operating angle θax of the fourth axis is 90°, the maximum motor current ratio is 30%. At this time, torque due to gravity compensation current Igc is applied to the motor 3 in a clockwise direction in FIG. 6, so that the motor 3 is in a self-locking state. Therefore, the welded portion at the tip of the arm cannot be rotated counterclockwise in FIG. 6.

The gravity compensation current Igc is input to the gravity compensation current subtraction value block 107 (third calculation section). The gravity compensation current subtraction value block 107 reduces the gravity compensation current Igc for the purpose of alleviating the self-locking state of the motor 3. The gravity compensation current subtraction value block 107 calculates and outputs a gravity compensation current subtraction value Igsub based on the gravity compensation current Igc and a predetermined gravity subtraction setting value Igth. The gravity compensation current subtraction value Igc is determined by the following formula.

Igc > Igth (Igsub= Igth)
|Igc|≦Igth (Igsub=Igc)
Igc <-Igth (Igsub=-Igth)
Specifically, when the gravity compensation current Igc is larger than the gravity subtraction setting value Igth, the gravity compensation current subtraction value Igsub=Igth. When the absolute value of the gravity compensation current Igc is less than or equal to the gravity subtraction setting value Igth, the gravity compensation current subtraction value Igsub=Igc. If the gravity compensation current Igc is smaller than the negative value (-Igth) of the gravity subtraction setting value, the gravity compensation current subtraction value Igsub=-Igth.

As shown in FIG. 7, for example, when the gravity subtraction setting value Igth is 20%, the waveform of the gravity compensation current subtraction value Igsub is such that the motor current maximum ratio is higher than 20% in the gravity compensation current Igc shown in FIG. The shape is obtained by removing the mountain portion and the valley portion lower than -20%.

The excitation sine wave current calculation block 109 (fourth calculation unit) calculates an excitation sine wave Igsin for transitioning the motor in the self-locked state from the static friction stop state to the dynamic friction state.

The excitation sine wave current calculation block 109 calculates and outputs an excitation sine wave Igsin based on a predetermined excitation sine wave amplitude Igsa and a predetermined frequency Igsf. When the elapsed time is t, the excitation sine wave Igsin is obtained by the following formula.

Igsin=Igsa×sin(2π×Igsf×t)
In the example shown in FIG. 8, the excitation sine wave amplitude Igsa is set to 5%. Frequency Igsf is set to 20Hz. The elapsed time t is set to 2 seconds.

Then, in the flexible control state, when the joint J4 of the fourth axis is rotated 360° (-180° to 180°) in 2 seconds from the arm side (reducer output side), the excitation sine wave amplitude shown in FIG. Igsa waveform can be obtained.

The calculation block 116 (fifth calculation unit) calculates the gravity compensation current correction value Igc4 based on the gravity compensation current Igc, the gravity compensation current subtraction value Igsub, and the excitation sine wave Igsin. The gravity compensation current correction value Igc4 is obtained by the following formula.

Igc4＝Igc－Igsub＋Igsin
In the calculation block 116, the gravity compensation current subtraction value Igsub is subtracted from the excitation sine wave Igsin to calculate a subtraction value (Igsin−Igsub). The calculation block 116 calculates and outputs the gravity compensation current correction value Igc4 by switching the switch Swg and selectively adding the subtraction value (Igsin-Igsub) to the gravity compensation current Igc.

Then, in the flexible control state, when the joint J4 of the fourth axis is rotated 360° (-180° to 180°) in 2 seconds from the arm side (reducer output side), the gravity compensation current correction value shown in FIG. Igc4 waveform is obtained.

A first current command Icom1 for normal control is input to the current limiting block 105. The current limit block 105 calculates and outputs a current command limit value Ic1_lim based on a preset current limit setting value Icth. The current command limit value Ic1_lim is determined by the following formula.

Icom1 > Icth (Ic1_lim= Icth)
｜Icom1｜≦ Icth (Ic1_lim= Icom1)
Icom1 <-Icth (Ic1_lim=-Icth)
Then, the flexible control block 14 calculates the fourth current command Icom4 during flexibility control by adding the current command limit value Ic1_lim to the gravity compensation current correction value Igc4. The flexible control block 14 outputs a fourth current command Icom4. In this way, the flexible control block 14 constitutes a current command correction section that corrects the current command of the motor 3 based on the gravity compensation current correction value Igc4 during flexible control.

<When the collision stops at a position with an operating angle of 60°>
Hereinafter, a case will be described in which a collision stop occurs at a position where the fourth axis operating angle θax=60° during flexible control.

FIG. 10 shows the waveform of the gravity compensation current Igc when the fourth axis joint J4 is rotated 360° (-180° to 180°) from the arm side (reducer output side) in the flexible control state. .

As shown in FIG. 10, when the collision stops at a position where the operating angle θax of the fourth axis is 60°, the maximum motor current ratio of the gravity compensation current Igc is 26%.

As shown in FIG. 11, when the collision stops at the position of the fourth axis operating angle θax=60°, the motor current maximum ratio of the gravity compensation current subtraction value Igsub is 20%.

As described above, the excitation sine wave Igsin is determined by Igsin=Igsa×sin (2π×Igsf×t). Here, if the excitation sine wave amplitude Igsa is 5%, the frequency Igsf is 20 Hz, and the elapsed time t is 2 seconds, the waveform of the excitation sine wave amplitude Igsa shown in FIG. 12 is obtained. In FIG. 12, the horizontal axis is the time axis.

As described above, the gravity compensation current correction value Igc4 is obtained by Igc4=Igc−Igsub+Igsin. Here, since the maximum motor current ratio of the gravity compensation current Igc is 26% and the maximum motor current ratio of the gravity compensation current subtraction value Igsub is 20%, Igc-Igsub=26-20=6%. As a result, the waveform of the gravity compensation current correction value Igc4 shown in FIG. 13 is obtained. In FIG. 13, the horizontal axis is the time axis.

As described above, according to the robot control device 10 according to the present embodiment, the flexibility of the robot arm 2 is improved by correcting the current command of the motor 3 based on the gravity compensation current correction value Igc4 during flexible control. can be ensured to alleviate the tension phenomenon.

Specifically, the motor 3, which has been self-locked and is in a static friction stop state, can be vibrated from the input side to bring the motor 3 into a dynamic friction state. As a result, even if a collision force is applied from the output side of the motor 3, the motor 3 can be rotated in a direction that releases the collision force.

As explained above, the present disclosure is extremely useful and industrially effective because even when a collision force is applied from the output side of the motor, the motor can be rotated in a direction to release the collision force, which is a highly practical effect. possibility of use is high.

2 Robot arm 3 Motor 5 Hypoid gear 10 Robot control device 14 Flexible control block (flexible control section, current command correction section)
101 Gravity torque calculation block (first calculation section)
103 Arithmetic block (second arithmetic unit)
107 Gravity compensation current subtraction value block (third calculation section)
109 Excited sine wave current calculation block (4th calculation section)
116 Arithmetic block (5th arithmetic unit)
τge Gravity torque
IGC gravity compensation current
Igth Gravity subtraction setting value
Igsub Gravity compensation current subtraction value
Igsa Excited sine wave amplitude
Igsf frequency
Igsin excitation sine wave
Igc4 gravity compensation current correction value

Claims (5)

A robot control method for controlling the operation of a robot arm having a plurality of motors, the method comprising:
a step of calculating a gravitational torque (τge) applied to the motor to be compensated based on the rotation angles of the plurality of motors;
a step of calculating a gravity compensation current (Igc) that compensates for the gravity torque (τge);
a step of calculating a gravity compensation current subtraction value (Igsub) based on the gravity compensation current (Igc) and a predetermined gravity subtraction setting value (Igth);
a step of calculating an excitation sine wave (Igsin) based on a predetermined excitation sine wave amplitude (Igsa) and a predetermined frequency (Igsf);
A step of calculating a gravity compensation current correction value (Igc4) based on the gravity compensation current (Igc), the gravity compensation current subtraction value (Igsub), and the excitation sine wave (Igsin). A robot control method characterized by: In claim 1,
When a collision force is applied to the robot arm, performing flexible control to drive the motor so as to follow the direction in which the collision force is applied;
A robot control method comprising the step of correcting a current command for the motor based on the gravity compensation current correction value (Igc4) during the flexible control. A robot control device for controlling the operation of a robot arm having a plurality of motors, the robot control device comprising:
a first calculation unit that calculates a gravitational torque (τge) applied to the motor to be compensated based on the rotation angles of the plurality of motors;
a second calculation unit that calculates a gravity compensation current (Igc) that compensates for the gravity torque (τge);
a third calculation unit that calculates a gravity compensation current subtraction value (Igsub) based on the gravity compensation current (Igc) and a predetermined gravity subtraction setting value (Igth);
a fourth calculation unit that calculates an excitation sine wave (Igsin) based on a predetermined excitation sine wave amplitude (Igsa) and a predetermined frequency (Igsf);
a fifth calculation unit that calculates a gravity compensation current correction value (Igc4) based on the gravity compensation current (Igc), the gravity compensation current subtraction value (Igsub), and the excitation sine wave (Igsin); A robot control device characterized by: In claim 3,
a flexible control unit that performs flexible control to drive the motor so as to follow the direction in which the collision force is applied when a collision force is applied to the robot arm;
A robot control device comprising: a current command correction section that corrects a current command of the motor based on the gravity compensation current correction value (Igc4) during the flexible control. In claim 3 or 4,
A robot control device, wherein the motor has a hypoid gear.

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