JP3937078B2 - Robot control apparatus and control method - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a robot control device, and more particularly to a robot control device and a control method for controlling the generated force of a servo motor that drives a joint based on force and torque set values in a work coordinate system.
[0002]
[Prior art]
A conventional robot is controlled by a position and speed state feedback system as shown in FIG. 6 for each joint axis of the robot. When performing spot welding or seam welding work that involves contact with the workpiece in such a control system, if there is a workpiece misalignment or workpiece gripping misalignment, it was set large to increase the rigidity. Due to the action of the gain and integrator, a large torque is generated, which makes it difficult to carry out the work due to the occurrence of poor welding or welding, and sometimes there is a risk of damage to the tool or robot.
In order to deal with such a problem, there is a method using a device that allows an acting force due to a positional deviation of a workpiece or the like with a coil spring provided on a jig base and a leg portion as disclosed in JP-A-9-314347.
[0003]
Also, as a method using force information, as shown in Japanese Patent Laid-Open No. 2000-061645, the pressure applied to the upper and lower roller electrodes is measured with a load cell during seam welding, and the robot is feedback-controlled based on the pressure difference. There is a method and a method of detecting an abnormality when the rotational torque or the applied pressure by the torque detector exceeds a limit as shown in Japanese Patent Laid-Open No. 2000-042752.
Further, as a method using distance information, there is a method in which a position sensor is corrected in advance using a template having the same shape as a workpiece, using a distance sensor during seam welding, as disclosed in JP-A-9-314351.
Further, in recent years, as a method for performing flexible control in the work coordinate system without adding a special device to the robot, each of the work coordinate systems as shown in JP-A-8-227320 and JP-A-2000-005881 There is a method in which the softness (spring constant) can be set with respect to the coordinate system direction and the degree of adaptability to external force can be specified for each direction in the space.
[0004]
[Problems to be solved by the invention]
However, the method disclosed in Japanese Patent Application Laid-Open No. 9-314347 lacks versatility because the device itself needs to be recreated in accordance with the workpiece when the workpiece is changed, and the direction of the acting force is known in advance. It was necessary to match the direction of spring contraction.
Further, as shown in Japanese Patent Application Laid-Open Nos. 2000-061645 and 2000-042752, the method of acquiring sensor information by adding a force sensor and a load cell has a problem that costs increase.
In addition, as shown in Japanese Patent Laid-Open No. 9-314351, the method using a distance sensor cannot cope with positional misalignment other than the direction of the distance sensor, and in the case of a work change, it is necessary to change peripheral devices such as a template. there were.
Also, as shown in Japanese Patent Application Laid-Open No. 8-227320 and Japanese Patent Application Laid-Open No. 2000-005881, the softness (spring constant) is set in the work coordinate system and the degree of adaptability to external force is specified for each direction in the space. In this method, if the position deviation increases, the generated torque of the servo motor increases proportionally, so it is not possible to cope with a large stroke, and the calculation relational expression that makes the force of the work coordinate system correspond to the torque of the joint coordinate system is complicated. There are problems such as heavy load and difficulty in real-time control.
Therefore, the present invention has versatility that can cope with workpiece changes without using a sensor, etc., is inexpensive because it does not use a sensor, can handle large displacements of the stroke, and has a simple calculation and a work coordinate system. It is an object of the present invention to perform flexible control of a work coordinate system that can operate flexibly in a specific direction, and that can operate with high trajectory accuracy in directions other than the specific direction.
[0005]
[Means for Solving the Problems]
In order to solve the above problems, a robot control apparatus according to claim 1 of the present invention is a joint angle and joint obtained from an angle measuring instrument that measures a first joint angle related to a joint coordinate system of a robot based on a joint command. In a robot control apparatus that drives each joint by feeding back a state of speed, first forward conversion means for converting the first joint angle into position data of a work coordinate system, and the joint command as a position of the work coordinate system Second forward conversion means for converting to command data; first subtraction means for subtracting position command data of the work coordinate system from position data of the work coordinate system to calculate position deviation data of the work coordinate system; a deviation correction means for correcting a nonlimiting for flexible configuration axis inflexible set axis limited by preset threshold for the position deviation data of the work coordinate system, the polarization Adding means for calculating position data of the second work coordinate system by adding the position deviation data corrected by the correction means and position command data of the work coordinate system; and a joint from the position data of the second work coordinate system And an inverse conversion means for calculating a second joint angle of the coordinate system, and the second joint angle is used for the state feedback. According to the robot control apparatus according to claim 1, when a force is applied to the robot from the outside due to a positional deviation of a workpiece during handling work, the joint angle and the joint command obtained by the angle measuring device are respectively converted into forward conversion means. The position and orientation deviation in the work coordinate system generated by the external force is obtained by subtracting by the subtracting means, and the work coordinate is set for the direction of the axis that is set flexibly in the work coordinate system (hereinafter, flexible setting axis). The position and attitude deviation in the system is corrected to a smaller value by the deviation correction means, and the second position feedback value and attitude feedback value are created by adding the deviation limited by the adding means to the position command and attitude command of the work coordinate system. Then, the second position feedback and posture feedback are converted back into joint angles by the reverse conversion means, and the obtained joint angles are converted into positions. By using it for state feedback, each joint angle is not updated at all or is not fully updated, and even if an external force is applied, the position deviation is small or not, so the position deviation is allowed only in the flexible setting axis direction. Thus, it is possible to absorb the acting force from the outside. Similarly, with respect to an axis direction that is not set flexibly in the work coordinate system (hereinafter, non-flexible set axis) direction, the position and orientation deviation in the work coordinate system is not limited by the deviation correction means, and the position and orientation deviation is added by the addition means. Second position feedback and posture feedback are created by adding to the position command and posture command of the work coordinate system, and the second position feedback and posture feedback are inversely converted into joint angles by the inverse conversion means, and position state feedback is performed. Since each joint angle is updated in the same manner as in a normal position control system, the operation can be performed with high trajectory accuracy as before.
[0006]
According to a second aspect of the present invention, the robot control apparatus uses the second joint angle as the position and / or speed as the state feedback.
According to the robot control device of claim 2, even when a positional deviation occurs in the flexible setting direction by using the derivative of the second joint angle only in the flexible setting axis direction for speed state feedback. Since the component related to the flexible setting axis direction of the speed integral term becomes small, even when a positional deviation occurs in the flexible axis direction, generation of a large torque can be suppressed by the speed integral term.
[0007]
The robot control apparatus according to claim 3, wherein the deviation correction unit is a unit that limits the position deviation data of the work coordinate system to a threshold value , or a unit that multiplies the position deviation data of the work coordinate system by a gain. It is. According to the robot control device of the third aspect, as in the first aspect, the joint angle obtained by the angle measuring instrument when a force is applied to the robot from the outside due to a positional deviation of the workpiece during handling work. And the joint command are respectively forward-converted by the forward-converting means, and subtracted by the subtracting means to obtain the position and orientation deviation in the work coordinate system generated by the external force, and the axis to be flexibly set in the work coordinate system (hereinafter, flexible setting) For the (axis) direction, the position and orientation deviation in the work coordinate system is multiplied by a gain sufficiently smaller than 1 preset by the deviation correction means, and the deviation multiplied by the gain by the addition means is used as the position command of the work coordinate system. A second position feedback and attitude feedback are generated by adding to the attitude command, and the second position feedback and attitude feedback are generated by the inverse conversion means. By reversely converting back to joint angle and using the obtained joint angle for position status feedback, each joint angle is not updated at all or not fully updated, and even if an external force is applied, the positional deviation is small Since there is no such state, it is possible to absorb the acting force from the outside by allowing the positional deviation only in the flexible setting axis direction. Similarly, for an axis that is not set flexibly in the work coordinate system (hereinafter, non-flexible set axis) direction, the position and orientation deviation in the work coordinate system is not multiplied by the deviation correction means, and the position and orientation deviation is added by the addition means. Second position feedback and posture feedback are created by adding to the position command and posture command of the work coordinate system, and the second position feedback and posture feedback are inversely converted into joint angles by the inverse conversion means, and position state feedback is performed. Since each joint angle is updated in the same manner as in a normal position control system, the operation can be performed with high trajectory accuracy as before.
[0008]
According to a fourth aspect of the present invention, there is provided the robot control apparatus according to the fourth aspect, wherein a gravitational torque calculating unit that calculates a gravitational torque acting on each joint of the robot based on a joint angle from the angle measuring device;
Gravity compensation calculation means for compensating the gravitational torque in a motor control system is provided.
According to the robot control apparatus of the fourth aspect, by separately compensating for the gravitational component, the value integrated in the velocity integral term of each joint coordinate system can be suppressed to a small value. Even when it occurs, it is possible to suppress the generation of large torque due to the speed integral term.
[0009]
According to a fifth aspect of the present invention, the robot control device feedbacks the state of the joint angle and the joint speed obtained from the angle measuring device that measures the first joint angle with respect to the joint coordinate system of the robot based on the joint command. The position control data of the work coordinate system is calculated based on the first joint angle, the position command data of the work coordinate system is calculated based on the joint command, and the position data The position deviation data is calculated from the position command data, and the position deviation correction data for correcting the position deviation data with a preset threshold for the flexible setting axis direction but not for the non-flexible setting axis direction is calculated. Then, a second joint angle is calculated from the position deviation correction data and the position command data, and the second joint angle is used for the state feedback. According to the robot control apparatus according to claim 5, when a force is applied to the robot from the outside due to a positional deviation of a workpiece during handling work, the joint angle and the joint command obtained by the angle measuring device are respectively forward-converted. The position and orientation deviation in the work coordinate system generated by the external force is obtained by subtracting by the subtracting means, and the work coordinate is set for the direction of the axis that is set flexibly in the work coordinate system (hereinafter, flexible setting axis). The position and attitude deviation in the system is corrected to a smaller value by the deviation correction means, and the second position feedback value and attitude feedback value are created by adding the deviation limited by the adding means to the position command and attitude command of the work coordinate system. Then, the second position feedback and posture feedback are converted back into joint angles by the reverse conversion means, and the obtained joint angles are converted into positions. By using it for state feedback, each joint angle is not updated at all or is not fully updated, and even if an external force is applied, the position deviation is small or not, so the position deviation is allowed only in the flexible setting axis direction. Thus, it is possible to absorb the acting force from the outside. Similarly, with respect to an axis direction that is not set flexibly in the work coordinate system (hereinafter, non-flexible set axis) direction, the position and orientation deviation in the work coordinate system is not limited by the deviation correction means, and the position and orientation deviation is added by the addition means. Second position feedback and posture feedback are created by adding to the position command and posture command of the work coordinate system, and the second position feedback and posture feedback are inversely converted into joint angles by the inverse conversion means, and position state feedback is performed. Since each joint angle is updated in the same manner as in a normal position control system, the operation can be performed with high trajectory accuracy as before.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
As shown in the conventional example of FIG. 6, in the position / velocity control state in the normal joint coordinate system, the position control loop and the speed control loop cause the force acting from the outside to move in a specific direction on the work coordinate system. Only the working position of the tip is difficult to follow flexibly. This depends on the reduction ratio for each joint axis, the magnitude of the gain, and the posture of the robot. Therefore, only the position deviation component in the specific direction (non-flexible set axis direction) of the work coordinate system is used for position state feedback control, and the position error component in the flexible set axis direction is not sufficiently updated, so that the flexible set axis direction It is possible to shift the position, and it is possible to operate with a highly accurate trajectory in the non-flexible setting axis direction.
Hereinafter, a first specific embodiment of the present invention will be described with reference to FIG. 1, and an example applied to a robot with n degrees of freedom will be described (n ≧ 3). First, a control block diagram in which the flexible control of the present invention is applied to a position / velocity control system in a normal joint coordinate system is shown.
[0011]
(1) Forward conversion As described in claim 1, the first joint angle obtained by the angle measuring device 1 is operated by the first forward conversion means 2 in the position and velocity state feedback system in the joint coordinate system. Convert to coordinate system position data. The work coordinate system is a three-dimensional coordinate system composed of three orthogonal axes, and the position data is data composed of a position and a posture. Here, the conversion means is an arithmetic expression for obtaining the hand position of the robot from the angles of the joint axes of the robot, which is generally called forward kinematics.
The first joint angle of the joint coordinate system is expressed as θfb = θFB1 to θFBn (1)
here,
θfb: joint angle vector in the joint coordinate system θFBn: set as the joint angle of the n-th axis.
The position feedback and attitude feedback of the work coordinate system are expressed as Xfb = XFB, YFB, ZFB, αFB, βFB, γFB (2)
here,
Xfb: position and orientation feedback vector in the work coordinate system XFB: X-axis position feedback in the work coordinate system αFB: posture feedback around the X axis in the work coordinate system
Xfb = F (θfb) (3)
here,
F: Forward conversion formula.
[0012]
Similarly, the position command and the posture command of the work coordinate system are obtained by the second forward conversion means 3 for the joint command of the robot.
The joint command of the joint coordinate system is set to θref = θREF1 to θREFn (4)
here,
θref: Joint command vector in the joint coordinate system θREFn: Placed as a joint command for the n-th axis.
The position command and orientation command of the working coordinate system are set to Xref = XREF, YREF, ZREF, αREF, βREF, γREF (5)
here,
Xref: Work coordinate system position / orientation command vector XREF: Work coordinate system X-axis position command αREF: Posture command around the X axis of the work coordinate system
Xref = F (θref) (6)
here,
F: Forward conversion formula.
[0013]
(2) Subtracting means Next, the subtraction means 4 subtracts the position command and the posture command from the position feedback and posture feedback of the work coordinate system to calculate the position deviation and posture deviation ΔX of the work coordinate system.
ΔX = Xfb−Xref (7)
[0014]
(3) With respect to the deviation correction means flexible setting axis direction, the deviation correction means 5 limits the position deviation and posture deviation ΔX of the work coordinate system with a preset threshold value , for example, 0 or a value set smaller than normal. For the non-flexible set axis direction, the deviation correction means does not limit the position deviation and the posture deviation ΔX of the work coordinate system, or limits them with normal values. The post-limit position deviation and posture deviation are represented by ΔXLIMIT.
[0015]
(4) The position deviation and posture deviation ΔXLIMIT after the adding means deviation correcting means are added to the position command and posture command Xref of the work coordinate system by the adding means 6 and are the second position feedback and posture feedback of the work coordinate system. Xfb2 in the equation (8).
Xfb2 = ΔXLIMIT + Xref (8)
[0016]
(5) Inverse conversion means The inverse position conversion means 7 reversely converts the second position feedback and posture feedback into joint angles, and uses the obtained joint angle θfb2 for position state feedback.
The second joint angle of the joint coordinate system is expressed as θfb2 = θFB21 to θFB2n (9)
here,
θfb2: second joint angle vector in the joint coordinate system θFB2n: second joint angle of the n-th axis θfb2 = B (Xfb2) (10)
here,
B: Inverse conversion formula.
By performing position control using the obtained second joint angle of the joint coordinate system for position state feedback, only the position deviation component in the non-flexible setting axis direction is used for control of position state feedback, and the flexible setting axis By not sufficiently updating the positional deviation component in the direction, it is possible to shift the position in the flexible setting axis direction, and it is possible to perform an operation with a highly accurate trajectory in the non-flexible setting axis direction.
[0017]
An example in which this control is used for an actual robot will be described with reference to a schematic diagram showing the operation of FIG. In this example, a two-axis horizontal articulated robot is used for the sake of brevity, but the same applies to a vertical articulated robot having three or more axes. Consider a case where an external force F acts on the tip of the robot as shown in FIG. At this time, the Y-axis direction of the work coordinate system is set to the flexible setting axis direction, and the X-axis direction is set to the non-flexible setting axis direction. Normally, the position command and position feedback of the robot have the same value. However, the robot moves to the position shown by the solid line in FIG. 5B due to the external force F, and a slight deviation ΔX and ΔY occurs in the position command and position feedback. Here, the high loop gain of the position and speed usually tries to return to the original position (the position shown by the dotted line), but the limit of the deviation correction means 5 works in the Y-axis direction. For example, the limit threshold is 0. In this case, ΔY is 0, and the difference between the position command and the position feedback is ΔY = 0 in the Y-axis direction. Since the limit of the deviation correction means 5 does not act in the X-axis direction, ΔX does not become 0, and the deviation between the position command and the position feedback remains ΔX in the X-axis direction. Therefore, the obtained ΔX and ΔY are added to the position command by the adding means 6, the second joint angle of the joint coordinate system is obtained by the inverse transform means 7, and the position control is performed using the position state feedback, As indicated by the solid line in FIG. 5C, the position of the robot tip returns to the original value because position control works in the X-axis direction, and the position of the robot tip returns to the original value because position control does not work in the Y-axis direction. Do not return to. That is, even when the external force F is applied, the position is shifted in the Y-axis direction, but the locus can be maintained without being shifted in the X-axis direction.
[0018]
Next, a second specific embodiment of the present invention will be described with reference to FIG.
In the position / velocity control state in the normal joint coordinate system, if the position shift occurs due to the force acting from the outside due to the action of the speed integral term of the speed control loop, the speed deviation becomes large and integration causes excessive torque. End up. Therefore, in this embodiment, as described in claim 2, the joint angular velocity is obtained by differentiating the joint angle with respect to the first specific embodiment, and is used for speed state feedback. As a result, even if a positional deviation occurs due to a force acting from the outside, the positional deviation is limited to zero or small in the direction in which the positional deviation is allowed. The value can be small and generation of large torque can be suppressed. Here, since the component of the speed integral term with respect to the non-flexible set axis direction is the same as that of a normal position speed control system, a control system capable of maintaining the trajectory accuracy without misalignment can be configured.
[0019]
Next, a third specific embodiment of the present invention will be described with reference to FIG. In this embodiment, as described in claim 3, the deviation correcting means 5 (the flexible setting axis direction is limited by a preset threshold value and the non-flexible setting axis direction is limited in the first specific embodiment. Instead of means), gain multiplication is performed. For the flexible set axis direction of the work coordinate system, the position deviation and the attitude deviation ΔX are multiplied by a gain sufficiently smaller than 1, and the position deviation and the attitude deviation ΔX are 1 for the non-flexible set axis direction. A means for multiplying or not multiplying anything is used. The addition means 6 is used for the post-multiplication position deviation and attitude deviation ΔXGAIN in the same manner as in the first specific embodiment to obtain the second position feedback and the attitude feedback Xfb2 of the work coordinate system.
Xfb2 = ΔXGAIN + Xref (11)
[0020]
Next, the inverse joint means 7 is used, and the second joint angle θfb2 of the joint coordinate system is used for position state feedback according to equations (9) and (10). Thus, by performing position control using the obtained second joint angle of the joint coordinate system for position state feedback, only the position deviation component in the non-flexible set axis direction is used for position state feedback control, By not sufficiently updating the position deviation component in the flexible setting axis direction, it is possible to shift the position in the flexible setting axis direction, and it is possible to perform an operation with a highly accurate trajectory in the non-flexible setting axis direction.
[0021]
Next, a fourth specific embodiment of the present invention will be described with reference to FIG. In this embodiment, as described in claim 4, the first specific embodiment is compensated separately for a force such as gravity that constantly acts, thereby causing a positional shift in the vertical direction due to the influence of gravity. It is what suppresses doing. As a method of calculating the gravity, for example, the gravitational torque calculating means 8 obtains the gravity compensation torque from the weight of each link of the robot, the center of gravity position, and each joint angle, and the gravity compensation calculating means 9 calculates the speed integral value. There is a method of adding to the torque command obtained by adding the speed proportional value. As a result, when the flexible set axis direction of the work coordinate system and the vertical direction are the same, it is possible to prevent the torque of the gravitational component from being integrated into the speed integral term of each joint coordinate system, and the speed integral value itself is It is possible to suppress the generation of a large torque due to the speed integral term even when the positional deviation occurs, by making the position smaller than that during the position / speed control.
[0022]
【The invention's effect】
As described above, according to the robot control apparatus of the first aspect, the axis that is flexibly set in the work coordinate system with respect to the force acting on the robot from the outside due to the positional deviation of the workpiece (hereinafter referred to as the flexible setting) The velocity and angular velocity are limited only in the (axis) direction, and then converted into a joint angle, and the joint angle, which is an integral value thereof, is used for position state feedback. For this reason, the position of each joint angle regarding the component relating to the flexible setting axis direction is not updated. Therefore, it is possible to allow a positional shift only in the flexible setting axis direction and to absorb the acting force from the outside. In addition, since the position of the component related to the direction that is not the flexible setting axis of each joint angle is not updated, the operation can be performed with the conventional high trajectory accuracy.
According to the robot control apparatus of claim 2, the component related to the flexible setting axis direction of the speed integral term is used by using the second joint angular velocity, which is the current speed changed only in the flexible setting axis direction, for speed state feedback. Therefore, even when a positional deviation occurs in the flexible axis direction, generation of a large torque can be suppressed by the speed integral term.
According to the robot control apparatus of the third aspect, as in the case of the first aspect, the axis (hereinafter referred to as the axis) flexibly set in the work coordinate system against the force acting on the robot from the outside due to the displacement of the workpiece. Only in the direction of the flexible setting axis), the velocity and the angular velocity are multiplied by a small gain and then converted into a joint angle, and the joint angle, which is an integral value thereof, is used for position state feedback. For this reason, the position of each joint angle regarding the component relating to the flexible setting axis direction is not updated. Therefore, it is possible to allow a positional shift only in the flexible setting axis direction and to absorb the acting force from the outside. In addition, since the position of the component related to the direction that is not the flexible setting axis of each joint angle is not updated, the operation can be performed with the conventional high trajectory accuracy.
According to the robot control apparatus of the fourth aspect, by separately compensating for the gravitational component, the value integrated in the velocity integral term of each joint coordinate system can be suppressed to a small value. Even when it occurs, it is possible to suppress the generation of large torque due to the speed integral term.
According to the robot control apparatus of the fifth aspect, the speed is only in the direction of the axis (hereinafter referred to as the flexible setting axis) that is flexibly set in the work coordinate system with respect to the force acting on the robot from the outside due to the displacement of the workpiece. After the angular velocity is limited, it is converted into a joint angle, and the joint angle, which is an integral value thereof, is used for position state feedback. For this reason, the position of each joint angle regarding the component related to the flexible setting axis direction is not updated. Therefore, it is possible to allow a positional shift only in the flexible setting axis direction and absorb an external acting force. In addition, since the position of the component related to the direction that is not the flexible setting axis of each joint angle is not updated, the operation can be performed with the conventional high trajectory accuracy.
[Brief description of the drawings]
1 is a first specific embodiment of the present invention; FIG. 2 is a second specific embodiment of the present invention; and FIG. 3 is a third specific embodiment of the present invention. Fig. 5 is a schematic diagram showing the operation of the present invention. Fig. 6 is a diagram showing a conventional control system.
1: Angle measuring instrument
2: First forward conversion means
3: Second forward conversion means
4: Subtraction means
5: Deviation correction means
6: Addition method
7: Inverse conversion means
8: Gravitational torque calculation means
9: Gravity compensation calculation means

Claims (5)

In a robot control device that drives each joint by state-feedbacking a joint angle and a joint speed obtained from an angle measuring device that measures a first joint angle related to a joint coordinate system of the robot based on a joint command,
First forward conversion means for converting the first joint angle into position data of a work coordinate system;
Second forward conversion means for converting the joint command into position command data of a work coordinate system;
First subtraction means for subtracting the position command data of the work coordinate system from the position data of the work coordinate system and calculating position deviation data of the work coordinate system;
Deviation correction means for performing correction that limits the position deviation data of the working coordinate system with a preset threshold for the flexible setting axis direction and does not limit the non-flexible setting axis direction ;
Adding means for calculating the position data of the second work coordinate system by adding the position deviation data corrected by the deviation correction means and the position command data of the work coordinate system;
Inverse conversion means for calculating a second joint angle of a joint coordinate system from position data of the second work coordinate system;
The robot control apparatus using the second joint angle for the state feedback.   The robot control apparatus according to claim 1, wherein the control apparatus uses the second joint angle as a position and / or velocity for the state feedback. The deviation correcting means includes means for limiting the positional deviation data of the working coordinate system to the threshold or, according to claim 1, wherein the robot, which is a means for multiplying a gain to the position deviation data of the work coordinate system, Control device. Based on the joint angle from the angle measuring device, gravity torque calculating means for calculating the gravity torque acting on each joint of the robot;
2. The robot control apparatus according to claim 1 , further comprising gravity compensation calculation means for compensating the gravity torque in a motor control system. In a robot control device that drives each joint by state-feedbacking a joint angle and a joint speed obtained from an angle measuring device that measures a first joint angle related to a joint coordinate system of the robot based on a joint command,
Calculating position data of the working coordinate system based on the first joint angle;
Calculate position command data of the working coordinate system based on the joint command,
Calculating position deviation data from the position data and the position command data;
About the position deviation data , the flexible setting axis direction is calculated with position deviation correction data for performing correction that is limited by a preset threshold value and that is not limited for the non-flexible setting axis direction ,
Calculating a second joint angle from the position deviation correction data and the position command data;
A robot control method using the second joint angle for the state feedback.

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