JP2010142909A - Controller for robot - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a controller for a robot which can continuously control, teach and reproduce a non-contact state to a contact state of not only a position or posture of a robot but also a state of force by suitably using a position control and a force control in accordance with a decision of the contact state of the robot. <P>SOLUTION: In the controller for the robot, the robot 101 having an end to which an end effector is attached is guided by a teaching device 108 to teach the robot an operation with a contact and the teaching operation is reproduced. At the time of teaching the operation, when the end effector or an object to be gripped 103 does not contact with an object to be operated 104, the robot 101 is guided by the position control to store the position of the robot 101 at the time of registering a teaching point. When the end effector or the object to be gripped 103 comes into contact with the object to be operated 104, the robot 101 is guided by the force control to store a level of force at the time of registering a teaching point. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a robot control device, and more particularly to a control device that teaches and reproduces work involving contact with a work object.

As means for causing an industrial robot to perform a predetermined work, a teaching playback method is widely used in which an operation is first taught (teaching) and then the operation is reproduced (played back). However, teaching operations for operations involving contact between a robot and an object to be worked are often trial and error, and the teacher cannot easily teach the robots the operations.
Briefly describe the background that makes it difficult to teach contact work.
When teaching the position and posture of the robot without contact, the teaching work is relatively easy because the teacher can visually recognize the positional relationship with the work object.
However, in contact work such as assembly, it is necessary to appropriately control the force that acts when the robot and the work object come into contact in addition to the six degrees of freedom in the space such as position and posture. The force acting between the object and the object cannot be felt intuitively by the teacher, making the teaching work difficult.

On the other hand, a servo motor is generally used as a driving source for each joint of the robot, and each value of its position (angle), speed, or force (torque) can be controlled quantitatively. In particular, when there is a means to accurately measure physical quantities such as encoders and force sensors, the potential to accurately control the physical quantities of the robot hand in a short time using the good response and quantitative controllability of the servo motor. It can be said that it has.
However, even if an attempt is made to teach only an apparent motion to cause a robot to perform a contact operation such as assembly performed by a human being, the teacher cannot directly intervene in the motion of the robot. It is difficult to teach the work as a robot work even if the work has appropriate skills. These circumstances are similar to the fact that it is difficult for human beings to convey the skill of appropriately controlling power to others.

However, as mentioned earlier, robots have features that humans cannot measure in that they can accurately measure physical quantities with sensors and that they can be controlled with high response characteristics. If the same situation can be set each time for reproducibility, that is, force generation as an interaction with the robot, there is a tremendous possibility that ideal force control (contact) work can be repeated. It can be said.
However, in the teaching method using the conventional teaching pendant, there is no mechanism capable of teaching seamlessly continuously from a non-contact state to a contact state in teaching reproduction of a work in which non-contact work and contact work are mixed. Also, there has been no mechanism for smoothly transitioning from position / posture control to force control at the time of reproduction, or appropriately responding to a position shift of the work object at the time of teaching and at the time of reproduction.
Also, depending on the type of contact work, switching between the position control and the force control for each movement direction of the robot is appropriately switched to maintain the continuity of the robot operation when shifting from the non-contact state to the contact state. There was no method, and a mechanism for smoothly shifting the robot control method among the teaching playback methods was required.

In the background as described above, several techniques related to teaching of contact work have been disclosed.
For example, as disclosed in Patent Document 1, there is a method in which teaching of a robot contact operation is performed by actually bringing a robot into contact with an object in a state where the rigidity of the robot is lowered.
Further, as in Patent Document 2, there is a teaching method in which flexible control is performed on a robot and a point obtained by adding a constant value to a current value is used as a teaching point.
In addition, there is a teaching method in which a force sensor is provided in a robot as in Patent Document 3, the robot guidance direction can be selected from the detection result of the force sensor by direct teaching, and the direction is selected by a switch or the like.
Further, a master-slave method has been conventionally known as a method for maintaining good robot workability by feeding back the detected force to a human. In the master-slave system, a master device that can move in the same manner as a robot is prepared. If the control similar to that of the robot that performs the work is performed on the master device, a robot system that allows the teacher to operate while directly feeling the force acting on the robot can be configured.
Japanese Patent No. 3483675 (page 3-5, FIG. 1) JP 2002-52485 A (page 3, FIG. 1) JP-A-6-250728 (page 3, FIG. 1)

In order to maintain and further improve the workability of the teaching of contact work, it is not efficient to switch the teaching at the time of non-contact and the teaching at the time of contact by an intentional means such as a switch. It is desirable to appropriately determine whether or not it is in a contact state at the time of teaching, to store appropriate information, and to reproduce an operation intended by the teacher at the time of reproduction. In addition, it is desirable that the work accuracy and the installation position accuracy of the work object are low and that the reproduction operation intended by the instructor can be performed even when some deviation is included.
The problems of the prior art will be described from the above viewpoint.
In Patent Documents 1 and 2, since the teacher does not recognize and control the force actually acting, a teaching point at which a very large force acts between the robot and the work object is registered. There is a problem that it is difficult to set an appropriate force for the work.
In Patent Document 3, there is no description regarding teaching from the non-contact state to the contact state that there is no discontinuous state of the control state. Further, there is no description on means for appropriately adjusting the force, and no description is given of a treatment in the case of non-reaching of the robot caused by the displacement of the work object, which is a problem during reproduction.
Also, the master / slave system requires twice as many systems such as a robot, a sensor, and a controller for the master and the slave, which is not a practical method in terms of cost performance. Further, since the master slave is not configured as a teaching playback robot, it is always suitable for human operation and is not suitable for automation.
The above prior art includes necessary elements in terms of contact state control, but at the teaching stage, the robot can be guided continuously from the non-contact state to the contact state, and at the same time, each degree of freedom of the robot Position and force can be taught, and the control method can be selected appropriately between force control and position control (appropriate selection of control method based on time transition and direction), providing an intuitive and simple method It wasn't something to do.
That is, in the prior art, there is no teaching reproduction means that can easily simulate the state at the time of reproduction and obtain necessary information at the teaching stage of the operation involving contact.

In view of the above problems, the present invention uses a teaching pendant that is often used for teaching work of conventional robots and uses only position control and force control based on the determination of the contact state of the robot. In addition, an object of the present invention is to provide a robot control apparatus that can continuously control, teach, and reproduce force adjustment from a non-contact state to a contact state.
It is another object of the present invention to provide a mechanism capable of reproducing not only the position and posture but also the force work as taught, even if there is a slight shift in the work object during reproduction.
This concept is to teach the robot to bring in a control method similar to human behavior, in which position control is performed in the free direction that does not contact the work object, and force control is performed in the direction that contacts the work object. It is.

In order to solve the above problem, the present invention is as follows.
The invention according to claim 1 teaches a work involving a contact between a work object and an object gripped by the end effector or the end effector by guiding a robot having an end effector attached to the tip by a teaching device. In the robot control apparatus that reproduces the taught work, when the work is taught, if the end effector or the gripping object is not in contact with the work object, the robot is guided by position control, When the teaching point is registered, the position of the robot is memorized. When the end effector or the gripping object is in contact with the work object, the robot is guided by force control to register the teaching point. It is characterized by memorizing the magnitude of force.

  According to a second aspect of the present invention, whether or not the end effector or the grasped object is in contact with the work object is determined by a detection value of a force sensor provided between the tip of the robot and the end effector. It is judged that when the detected value of the force sensor becomes a predetermined reference value or more, the control method of the robot is switched from position control to force control.

  The invention according to claim 3 is characterized in that a value obtained by performing gravity compensation on the detection value of the force sensor is compared with the reference value to determine whether or not it is in contact with the work object. To do.

  According to a fourth aspect of the present invention, the contact direction between the end effector or the gripping object and the work object is determined from the detection value of the force sensor, and the control method of the robot is force controlled only for the contact direction. It is characterized by switching to.

  The invention according to claim 5 is characterized in that at the time of teaching, the detection value of the force sensor is displayed on the screen of the teaching device by at least one of numerical display, graph display, and vector display.

  The invention according to claim 6 teaches a work involving a contact between a work object and an object gripped by the end effector or the end effector by guiding a robot having an end effector attached to the tip by a teaching device. In the robot control apparatus that reproduces the taught work, when the work is taught, if the end effector or the gripping object is not in contact with the work object, the robot is guided by position control, When the teaching point is registered, the position of the robot is memorized. When the end effector or the gripping object is in contact with the work object, the robot is guided by flexible control to register the teaching point. In this case, the position command value is stored.

  The invention according to claim 7 determines whether or not the end effector or the grasped object and the work object are in contact with each other based on a position deviation of the robot, and when the position deviation exceeds a predetermined threshold value, The robot control system is switched from position control to flexible control.

  The invention according to claim 8 is characterized in that the position deviation is displayed on the screen of the teaching device by at least one of numerical display, graph display, and vector display at the time of teaching.

  The invention according to claim 9 determines the contact direction between the end effector or the grasped object and the work object from the position deviation, and switches the robot control method to flexible control only for the contact direction. It is characterized by.

  According to a tenth aspect of the present invention, the torque command value to the motor of the robot is limited to a predetermined torque upper limit value or less during teaching.

  According to the eleventh aspect of the present invention, at the time of teaching, the end effector or a position returned in the reverse direction by a predetermined amount along the taught path from the contact point between the gripping object and the work object, or a predetermined direction. The position moved by a predetermined amount is automatically registered as an approach point.

According to the first and sixth aspects of the invention, the end effector or the object held by the end effector can be used while performing specific work using the JOG operation key of the teaching device for teaching such as assembly work requiring contact. The acting force between the work object and the work object can be appropriately controlled and continuously performed from the non-contact to the contact work. Moreover, it is possible to teach and play back not only the position information but also the working force.
According to the inventions of claims 2 and 7, continuity of control is ensured by appropriately sensing the contact state between the end effector or the object gripped by the end effector and the work object and switching the control method. Is possible.
According to the invention of claim 3, it is possible to more accurately sense the contact between the robot and the work object by removing the influence of gravity from the detection value of the force sensor.
According to the fourth and ninth aspects of the present invention, it is possible to switch between the control methods by determining contact or non-contact for each movement direction of the robot, and cope with various operations such as deburring and fitting with contact. Is possible.
According to the fifth and eighth aspects of the invention, the magnitude of the force detected by the sensor and the deviation between the command value of the sensorless flexible control and the current value are displayed on the teaching device, so that the direction and magnitude of the force can be visually confirmed. Intuitive recognition is possible using the, and the force acting between the robot and the work object can be easily monitored.
According to the invention of claim 10, by providing a limit of the magnitude of the torque, an excessive force is not generated between the work object and the end effector or the object gripped by the end effector in the contact state, and the robot or work Damage to the object can be prevented.
According to the invention of claim 11, even in the case of playback, it is possible to prevent a problem that the robot does not reach the work object due to the deviation of the installation of the work object and cannot perform the work.

  Hereinafter, specific embodiments of the apparatus of the present invention will be described with reference to the drawings.

A system configuration to which the robot control apparatus of the present invention is applied is shown in FIG.
Reference numeral 101 denotes an articulated robot, and reference numeral 105 denotes a robot control device that controls the articulated robot 101. The multi-joint robot 101 has a built-in servo motor for driving each joint axis, and each servo motor is driven via a servo motor amplifier 107 in accordance with the output of the robot control arithmetic unit 106. Although omitted in FIG. 1, the robot control apparatus 101 includes a storage unit for teaching data and various parameters for control, a communication unit with the teaching pendant 108, and the like.
The multi-joint robot 101 includes a force sensor 102 at the hand, and the force sensor 102 can detect a force acting in each axis direction of the force sensor coordinate system. An end effector can be attached to the tip of the force sensor.
A grinder is mounted as an end effector to deburr the work object 104, or a gripper is mounted as an end effector and the gripping object 103 is gripped by the gripper, to a hole provided on the work object 104 Can be fitted together. FIG. 1 shows a state where a gripper is attached as an end effector and the grasped object 103 is grasped.
The instructor teaches the work to be performed by the robot 101 by operating the teaching pendant 108. The teaching pendant 108 is shown in FIG.
In FIG. 2, reference numeral 201 denotes a JOG operation key for guiding the robot to a desired position in teaching work. The teacher can operate the JOG operation key to move the position of the hand of the robot 101 in each axis direction of the robot coordinate system or change the posture of the hand. Here, the robot coordinate system is an orthogonal coordinate system set for the robot 101 as shown in FIG. It is also possible to individually operate each joint of the robot 101 by operating the teaching pendant 108 and changing the function of the JOG operation key 201.
Reference numeral 202 denotes a registration key, and the instructor presses this key to store the teaching data in the robot controller. FIG. 2 shows only keys used in the teaching relating to the present invention, and other keys are omitted.

A procedure for teaching a contact operation for the robot configured as shown in FIG. 1 will be described.
However, in order to simplify the explanation, it is assumed that an end effector such as a grinder is attached to the tip of the robot instead of gripping the gripping object with a gripper as shown in FIG. The teaching method will be described by taking as an example the operation of moving the tip of the robot toward the wall as shown in FIG. 3 and applying a constant force to the wall by the end effector. Note that the direction in which the wall is pushed by the end effector is made to coincide with the X-axis direction of the robot coordinate system.

First, the registration key 202 is pressed to register the position of point A (303) in FIG. At point A, the robot tip is not yet in contact with the wall.
When the robot 101 is not in contact with the wall, the robot operates by position control. After registering the point A, when the teacher pushes the XOG direction JOG operation key on the teaching pendant 108, the position command Xref is increased and the tip of the robot is moved to the wall.
The teacher guides the robot 101 further toward the wall while visually confirming that the tip of the robot has approached the wall, and teaches the teaching point B (304) immediately before contacting the wall. Thereafter, the end effector is brought into contact with the wall at a low speed. The acting force at the time of contact is detected by a force sensor 102 disposed on the wrist of the robot.

  When the detected value by the force sensor becomes equal to or greater than a predetermined reference value, the robot controller determines that the wall has been touched, and the control method for the X direction is changed from position control to impedance control represented by the following equation (1). Transition.

    Fr−F = MX ″ + DX ′ + K (X−Xref) (1)

  Here, Fr is a force command, F is an actually measured value of the force by the force sensor, and M, D, and K are the mass, viscosity, and rigidity of the mechanical virtual impedance, respectively. X represents the position of the end effector attached to the tip of the robot, and Xref represents a position command.

After the control method is switched to the impedance control, the teacher adjusts the magnitude Fr of the force command by pressing the X + direction key among the JOG operation keys 201 on the teaching pendant 108.
In position control, when a JOG operation key is pressed, a position command in the direction of the pressed key is generated. After switching to impedance control, the magnitude of the force command Fr increases as the time for which the JOG operation key is continuously pressed increases. Becomes larger.
Further, by displaying the measurement value F of the magnitude of the force by the force sensor 102 on the screen 203 on the teaching pendant as a numerical value or a graph, the teacher can control the force through vision.
FIG. 8 shows one display example of the screen 203, which graphically represents the force acting in each axial direction of the force sensor coordinate system detected by the force sensor 102 as a vector on an orthogonal coordinate system. Fx, Fy, and Fz in FIG. 8 represent the respective axes of the force sensor coordinate system (FIG. 1) provided at the robot hand portion.
Since the magnitude and direction of the force are more likely to change than physical quantities such as position and speed, it is necessary for the instructor to present the information so as to capture it instantaneously and sensuously. For this reason, in this embodiment, the expression using the vector by the arrow 801 is used. Arrows and black dots indicate the direction and magnitude of the current force in the X, Y, and Z directions. In addition, an auxiliary line 802 indicating the coordinates of the tip of the vector is also displayed so that the magnitude of the force of each direction component can be easily grasped. Furthermore, a sphere having a radius as a reference value is simultaneously drawn as an auxiliary figure so that comparison can be performed. Although the value of the force detected by the force sensor changes from moment to moment depending on the contact state, the teacher can intuitively grasp the state of the acting force by the expression method as shown in FIG.
In FIG. 8, the auxiliary figure is a sphere, but if the size of the reference value differs depending on the direction of the robot coordinate system as described later, it may be displayed as an elliptic sphere. Moreover, you may display as a rectangular parallelepiped which connected the point corresponded to the reference value of each direction of a robot coordinate system.
Further, for each direction of movement of the robot, whether the current control method is position control or impedance control is also displayed on the screen 203, so that if the teacher checks the screen 203, the current control method and force The direction and size of action can be recognized.

Hereinafter, a case where teaching is performed using impedance control using a force sensor as a method of force control will be described. FIG. 5 shows a control block diagram during impedance control.
In the force control state, the robot generates a force that pushes the wall according to the force command. The teacher confirms on the screen 203 that the target force has been detected by the force sensor, and teaches the teaching point C using the registration key.
When teaching the robot to move the end effector along the wall, guide the robot in the Y or Z direction of the robot coordinate system with the JOG operation key while pressing the end effector against the wall. Stop and confirm the acting force at that time on the screen on the teaching pendant, and register the teaching point D with the registration key.
In a direction different from the wall direction (X direction in FIG. 3), the robot tip moves by position control by JOG operation.
When a force greater than the reference value is applied due to friction between the wall surface and the end effector when the end effector is pressed against the wall and is guided in a direction other than the X direction by the JOG operation, for example, the Z direction, The Z direction is also switched to impedance control. The reference value in the Z direction may be the same as the reference value in the X direction described above, or a different value may be set depending on the direction.
Intuitiveness is not lost by adjusting the force command value Fr to increase or decrease by pressing the JOG key in the X + direction or the X- direction, and adjusting the robot tip to the equilibrium point balanced with the actual force value F. The robot tip can be moved along the wall surface.
This time, the control method was switched to the impedance control only for the X direction. However, when the direction of the force does not match the specific axial direction of the coordinate system as shown in FIG. When a frictional force greater than the reference value acts, the control method is switched to impedance control for the omnidirectional operation of the end effector.
The JOG operation key on the teaching pendant 108 is for moving the position of the robot tip in the conventional teaching, but in the present invention, it is also used for controlling the magnitude of the force acting after contact. This is different from the use of the conventional teaching pendant.

Fig. 4 shows the flow of switching the control method between position control and force control focusing on one axis of the robot's movement direction, and shows the configuration of the control system when focusing on control switching between multiple axes. As shown in FIG.
As described above, whether or not the user touches the wall in the guidance process to the wall is determined based on a detection value by the force sensor, and the control method is switched when the contact force with the wall is equal to or higher than a reference value. However, the detection value of the force sensor is the resultant force of the contact force with the wall and the other acting force. Therefore, in order to perform switching more accurately, in FIG. 4, processing for correcting the detected value so as to exclude external force (mainly gravity) other than the contact force is added.
The gravity compensation value is a value determined by the gravity acting on the end effector attached to the hand part from the force sensor of the robot, and can be obtained by calculation from the posture of the robot and the mass of the end effector. The detection value of the sensor is corrected.
If the force detection value after gravity compensation is | force detection value after gravity compensation | ≧ Fmin, the control is switched to force control. Here, Fmin means a reference value of force for switching to impedance control.
In addition to gravity, when the robot accelerates or decelerates, a force corresponding to the mass and acceleration is applied. Therefore, strictly speaking, compensation for the force is necessary, but the robot and the work object (wall) are usually in contact with each other. In some cases, the moving speed and acceleration of the robot are ignored because they are kept small.
After switching to force control, induction is performed by impedance control of equation (1).
Although the control method changes before and after contact, the direction is the same even though there is a difference between position control and force control as the guidance method, so the teacher's sense is exactly the same as the guidance method with the normal teaching pendant. is there.
Note that the physical shock that occurs during contact with the work subject increases with the robot's operating speed. To ease the shock of time.
Similarly, in the direction of leaving the contact state (X-direction in this example), the force is continuously measured and the output of the force sensor 102 is measured. When the output is smaller than the reference value, the force control is switched to the position control. Control.

The switching of the control method for the X direction has been described above. Since it is appropriate to perform force control for the X direction and position control for the direction other than the X direction in this example, the position control is not performed for each direction other than the X direction unless each force sensor detection value is equal to or greater than the reference value. Induced by
On the other hand, in the teaching of the contact work, if the force acting on the work object is too large, the work object or the robot may be deformed or damaged. Therefore, the acting force needs to be kept below a certain level. Therefore, if the detected value of the force sensor in a direction other than the X direction exceeds the reference value set for that direction, the force acting on the robot is kept below a certain level by controlling the force in that direction.
An upper limit is also set for the force command value Fr indicated by the JOG operation key or the torque command value of the motor control system, and control is performed so that the motor torque does not exceed the torque upper limit value during teaching. Keep the force acting between objects below a certain level.
In the example of FIG. 3, switching to force control is performed only in the contact direction. This is suitable for work such as deburring that interferes with the work object only when the end effector or the grasped object moves in a specific direction (the degree of freedom in the movement direction is high).
On the other hand, when the object to be gripped, such as fitting, interferes with the work object in a plurality of directions (the degree of freedom in the operation direction is low), the contact is judged and all the axial directions (X direction, Y direction) of the robot are determined. By switching to the force control in the Z direction, it is possible to teach the work while preventing an excessive force from acting.
Whether or not to permit switching to force control in each direction of the robot coordinate system can be set by changing the parameters of the robot control device in accordance with the work contents. This parameter setting can be performed by the teaching device 108.

In the first embodiment, a force sensor is used to detect the contact force at the time of teaching, but in this embodiment, an example in which teaching is performed by force sensorless flexible control is shown.
Unlike the first embodiment, it is not possible to perform the flexible control by directly detecting the acting force by the force sensor, so the deviation amount between the command value and the current value is taught as a value corresponding to the force acting on the robot. carry out.
As a method for realizing flexible control, there are a method of reducing a control gain of a robot control system and a method of limiting a torque limit. In both cases, a deviation occurs between the command value and the current value of the robot, and the generated force is controlled according to the amount of deviation, so even if the actual robot is in contact with the work surface, the position command is The position command value is registered as the registered value of the teaching, which is set inside the work object. In the example of FIG. 3, C ′ (307) and D ′ (308) inside the work target (wall) are registered as teaching points.

The relationship between guidance and control will be described with reference to FIGS. In the sensorless flexible control, there is friction of the speed reducer attached to each axis motor, so the command position does not match the current position when the robot is not in contact with the object. Therefore, as in the first embodiment, the robot is guided by position control until it touches the work object.
In the first embodiment, the force command value is used for controlling the contact force after the end effector contacts the wall. However, in the sensorless flexible control, the force command acting on the object is controlled using the position command value instead of the force target value. Control. In the first embodiment, a reference value is set for the force sensor detection value or an upper limit value is set for the torque command value in order to keep the force acting on the wall (work object) below a certain level. Also, the magnitude of the acting force is suppressed to a certain level or less by providing an upper limit value for the torque command value of the motor.

FIG. 9 is a diagram expressing the relationship between the position command value and the current value at the time of teaching and reproduction, taking as an example a fitting operation in which the gripping object gripped by the gripper is inserted into a hole on the work target. In flexible control, a certain amount of deviation occurs between the command position for the robot and the current position. The dotted line indicates the command position of the gripping object, and the solid line indicates the actual position of the gripping object. In FIG. 9, the robot and the gripper are omitted.
Similar to the teaching of FIG. 3, the fitting shaft is guided by position control up to the vicinity of the fitting hole. When the positional deviation amount between the command position and the current position exceeds a predetermined threshold value, it is determined that contact has occurred, the control method is switched from position control to sensorless flexible control, and the fitting operation is executed.
In the first embodiment, the state of the magnitude of the force is presented using the force detection value by the force sensor, but in the sensorless flexible control of the present embodiment, the deviation is displayed on the screen 203 on the teaching pendant by a numerical value or a graph. . For example, the position deviation in each axis direction of the robot coordinate system is displayed to the teacher instead of the force acting in each axis direction of the force sensor coordinate system in FIG.
Even when sensorless flexible control is performed instead of impedance control, the magnitude of force can be determined in the same manner as in the first embodiment by expressing the deviation amount of each component with three orthogonal axes in FIG. .
Before insertion, contact between the gripping object and the work object occurs, and when the deviation between the command position and the current position exceeds a threshold value, the contact is recognized, and the control method is switched to sensorless flexible control. The teacher can recognize the acting force from the deviation displayed on the screen 203, perform the work while adjusting the acting force by operating the JOG key, and teach a force command at an appropriate position.
As mentioned earlier, because the work object interferes with the gripping object in multiple directions in the mating work, if contact is recognized, the control method is changed to flexible control for all axis directions of the robot's degree of freedom. This makes it easier to work.
Although commands and position detection to the servo motors of each axis of the robot are managed by values based on the joint coordinate system, calculations and commands for force control and flexible control are performed based on the orthogonal coordinate system. Therefore, calculation for coordinate system conversion is performed, and the configuration is shown in FIG.
In FIG. 7, the Cartesian coordinate command value Xref instructed by the JOG operation key is converted into the angle command value θref of the servo motor that drives each joint of the robot by the inverse mechanism conversion 701 of the robot. The servo motor angle command θref is input to the motor servo system 702. When the robot is in contact with the work object due to the control by the sensorless flexible control system, the actual motor angle is the same as the angle command value. Have different values. The position of the robot tip at that time is calculated by the forward mechanics calculation 703 using the value of an angle detector such as an encoder connected to the motor, and the deviation from the Cartesian coordinate system command value Xref is obtained. If the deviation at that time is equal to or greater than the threshold value, it is considered that the robot is in contact with the work object, and the position command value is determined inside the work object.

At the time of playback, the value stored as position information in the teaching work is reproduced by position control, and the value stored as force information is reproduced by force control. When it is detected that the work object has been touched before reaching the target position, the control is switched to force control in the same manner as in teaching. Even after the contact determination, the movement in the direction stored as the position information is reproduced by the position control.
First, a robot control method focusing on one direction of the robot movement will be described. Here, the case where the operation | work of FIG. 3 used in Example 1 and Example 2 is reproduced | regenerated is shown. In the figure, points A, B, C, and D are teaching points taught in advance, A and B are teaching points in position control, and C and D are points taught in force control with respect to the wall direction. . Also, at the time of playback, it shall operate by linear interpolation from point A to point B, and from point A to point B, it will operate to points C and D taught by position control and then with respect to the wall direction by force control. To do.

Usually, the arrangement of the object is slightly shifted from the teaching point. For this reason, there are a case where the pattern touches the wall before the teaching point, and a case where the teaching point does not reach the wall and does not contact.
Regardless of whether the control by force sensor or flexible control without force sensor is used, the control method is switched at the teaching point (point B) before touching the wall during playback, and the robot is already in contact with the wall. Operates with force control or flexible control.
In addition, there may be a large difference in the positional relationship between the robot and the wall between teaching and reproduction, and the robot may be in contact with the wall before the control method is switched (before reaching the teaching point B). As with teaching, the control method is switched when the detection value of the force sensor exceeds the reference value or the position deviation exceeds the threshold value during playback. The regenerating operation can be performed without excessive force acting between the objects. By constantly monitoring the force or deviation, the control method is quickly switched to the control method corresponding to the contact so that no excessive force is generated.
When reproducing the work of the first and second embodiments, the impedance control rigidity K is set to 0 because the robot control method is switched to force control or flexible control at the teaching point B before contacting the wall. Even in this case, the problem that the robot does not reach the wall does not occur.
Also, a route from the contact judgment point at the time of teaching (point C in FIG. 3) to the contact is stored, and a position returning a predetermined amount along the route from point C is automatically registered as an approach point. If this is done, the teaching point corresponding to the point B is automatically generated without the teacher explicitly registering the approach point, and the control method is switched appropriately, so that the robot reaches the work object (wall) during playback. The problem of not doing does not occur.
As a method for determining the position for automatic registration, there is a method for setting a registered position to a position moved in a predetermined direction in a direction opposite to the contact direction from the contact determination point (point C) in addition to the method for storing the route. .

System configuration diagram of the present invention Diagram showing teaching pendant The figure explaining the teaching method when a robot contacts a control object Flow chart of control method switching focusing on one axis direction Diagram showing control system configuration for force control Flow chart of control method switching focusing on one axis direction Diagram showing the control system configuration for sensorless flexible control Illustration of force sensor detection value display example on the teaching pendant Conceptual diagram of mating work

Explanation of symbols

101 Robot 102 Force Sensor 103 Grasping Object 104 Work Object 105 Robot Control Device 106 Robot Control Arithmetic Device 107 Servo Motor Amplifier 108 Teaching Pendant 201 JOG Operation Key 202 Registration Key 203 Screen 303 to 308 Teaching Point 701 Inverse Mechanism Calculation 702 Motor servo system 703 Forward mechanics calculation 801 Vector display 802 Auxiliary line 901 Actual position 902 of work object A Command position of work object A

Claims (11)

A robot having an end effector attached to the tip is guided by a teaching device to teach a work involving contact between the end effector or a grasped object gripped by the end effector and the work object, and reproduce the taught work In the robot controller,
When teaching the work, if the end effector or the grasped object is not in contact with the work object, the robot is guided by position control, and the position of the robot is stored when registering the teaching point. And
When the end effector or the gripping object is in contact with the work object, the robot is guided by force control, and the magnitude of the force is stored when the teaching point is registered. Control device.   Whether the end effector or the gripping object is in contact with the work object is determined based on a detection value of a force sensor provided between the tip of the robot and the end effector, and the detection value of the force sensor 2. The robot control apparatus according to claim 1, wherein the control method of the robot is switched from position control to force control when becomes equal to or greater than a predetermined reference value.   3. The robot control according to claim 2, wherein a value obtained by performing gravity compensation on the detection value of the force sensor is compared with the reference value to determine whether or not the contact state with the work object is present. apparatus.   The control method of the robot is switched to force control only for the contact direction by determining a contact direction between the end effector or the grasped object and the work object from a detection value of the force sensor. 3. The robot control apparatus according to 2.   The robot control apparatus according to claim 2, wherein the detected value of the force sensor is displayed on the screen of the teaching apparatus by at least one of a numerical display, a graph display, and a vector display during teaching. A robot having an end effector attached to the tip is guided by a teaching device to teach a work involving contact between the end effector or a grasped object gripped by the end effector and the work object, and reproduce the taught work In the robot controller,
When teaching the work, if the end effector or the grasped object is not in contact with the work object, the robot is guided by position control, and the position of the robot is stored when registering the teaching point. And
When the end effector or the gripping object is in contact with the work object, the robot is guided by flexible control, and a position command value is stored when registering a teaching point. Control device.   Whether the end effector or the gripping object is in contact with the work object is determined based on the position deviation of the robot, and when the position deviation exceeds a predetermined threshold, the robot control method is flexibly changed from position control. 7. The robot control apparatus according to claim 6, wherein the control is switched to control.   The robot control apparatus according to claim 6, wherein the position deviation is displayed on the screen of the teaching apparatus by at least one of numerical display, graph display, and vector display at the time of teaching.   The control method of the robot is switched to flexible control only for the contact direction by determining a contact direction between the end effector or the grasped object and the work object from the position deviation. Robot control device.   7. The robot control apparatus according to claim 1, wherein a torque command value to the motor of the robot is limited to a predetermined torque upper limit value or less during teaching.   At the time of teaching, an approach point is a position returned in a reverse direction by a predetermined amount along a taught path from a contact point between the end effector or the grasped object and the work object, or a position moved by a predetermined amount in a predetermined direction. 7. The robot control device according to claim 1, wherein the robot control device is automatically registered.

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