JP2019030931A - Robot control device, control method, and robot apparatus - Google Patents

Abstract

To provide an easy-to-operate simple-structure control device which, when a teaching person directly teaches a robot, can restrain a robot arm from moving unintentionally, and also allow the teaching person to operate the position and posture of the robot arm over a wide range.SOLUTION: When the position of the robot arm changes by an externally applied operation force from a preset reference position to another position within a first range, the control device generates a force control signal which acts in a direction of moving the robot arm toward the reference position, and of which value becomes larger as the amount of change from the reference position becomes larger. When the robot arm changes from the reference position to a position beyond the first range, the control device generates a force control signal of which value becomes smaller as the amount of change from the reference position becomes larger unless a second range is exceeded, and does not change to exceed a fixed value when the second range is exceeded.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a control device and a control method for controlling the operation of a robot, and more particularly to a device for teaching the operation of a robot arm by so-called direct teaching.

  Conventionally, when teaching an operation to a robot, an operation to move the tip of the end effector to a predetermined position using a remote controller such as a teaching pendant, and confirming the position visually, the teaching position is determined. It was made to memorize. In the teaching method using the teaching pendant, the coordinates are input numerically or the robot is moved by repeating a small movement (JOG operation), so it cannot be said that the work is complicated and operability is high, and teaching is efficient. Could not be done.

  Therefore, as one method for improving the operability of teaching work, a method called direct teaching or direct teaching is known. This is a method in which an external force is directly applied to the robot and guided by a teacher, and the robot arm is operated to a desired position and posture. The advantage of direct teaching is that teaching work can be easily performed because the teacher can directly operate the robot arm without complicated programming using a remote controller.

  In order to improve the workability of direct teaching, it is necessary to facilitate guidance operation by the teacher while suppressing the robot arm from being moved to an unintended position or posture due to gravity or the like. The position here is typically the position of the tip of the robot arm, and the posture is typically the direction of the tip of the robot arm. In order to suppress unintended movement due to gravity or the like, it is only necessary to apply a restoring torque for returning the robot arm to the original state when the robot arm changes from the reference state (reference position, reference position). Generally, the magnitude of the restoring torque is set so as to increase in accordance with the amount of change from the reference state.

  The instructor applies a force to the robot arm in the reference state to change the position and posture to perform the teaching work. When the position and posture of the robot arm changes by the teacher's operation, the robot arm is returned to the reference state. Therefore, the restoring torque acts on each joint. Since a large restoring torque is applied as the distance from the reference state increases, for example, if an attempt is made to directly teach a movement of a large distance, the teacher must guide the robot arm with a large force, which makes operation difficult. turn into.

  Therefore, Patent Document 1 discloses a direct teaching device in which a reference dedicated state can be switched by attaching a dedicated teaching handle near the tip of a robot arm and depressing a switch provided on the handle. Yes. When the robot arm is operated until the teacher feels that the restoring torque is too large, the position and posture of the robot arm at that time can be set to a new reference state by pushing down the switch. Can be returned to a small state.

  Further, Patent Document 2 discloses a method in which a force applied by a teacher to a robot arm is detected using a force sensor or a torque sensor attached to the robot arm, and the rigidity of the detected force vector is reduced by control. Is disclosed. Here, the rigidity is a proportional coefficient between the change amount of the position and the restoring force when the restoring force is applied in proportion to the change amount of the position of the robot arm.

JP 2009-78308 A US Patent Application Publication No. 2015/0081098

  However, in the robot direct teaching apparatus described in Patent Document 1, a dedicated handle having a switch for changing the reference position is necessary, and the structure becomes complicated. Further, in order to perform the teaching work, a work process for attaching the dedicated handle to the robot in advance is required, and the work becomes complicated.

  Further, Patent Document 2 discloses a method of detecting the operating force of a teacher and lowering the control rigidity in the detected direction. However, in this method, it is necessary to provide a sensor for detecting the operating force. The robot structure becomes complicated. In addition, components corresponding to the operator's operating force must be extracted from the sensor detection signal, but the robot arm has various component forces such as the contact force between the arm tip and the work workpiece and the torque generated by the motor. Works. In order to extract only the target operating force from these, it is presumed that a complex and sophisticated algorithm is necessary, but Patent Document 2 does not disclose any specific algorithm for this purpose. .

  As described above, a control device that can suppress unintended movement of the robot arm during direct teaching, can be easily operated by a teacher over a wide range of positions and postures of the robot arm, and has a simple configuration. Was not achieved.

  The present invention includes a position detection unit that detects the position of the robot arm, a speed detection unit that detects the speed of the robot arm, and a control unit that generates a drive control signal for controlling the drive unit of the robot arm. The control unit stores the detection result of the position detection unit when the robot arm is in the initial position as reference position information, and stores the position detected by the position detection unit after storing the reference position information. When a change in position from the reference position to a position within a first range is detected as compared with the reference position information, the position of the robot arm moves in the direction of moving the robot arm toward the reference position. A force control signal that increases as the change increases is generated, the drive control signal is generated using the force control signal, and a position from the reference position to a position that exceeds the first range. When the shift is detected, it acts in the direction in which the robot arm is moved toward the reference position, and the position change from the reference position decreases to the second range as the position change increases, but the second range A force control signal that does not change beyond a predetermined value from a constant value regardless of the magnitude of the position change, and generates the drive control signal using the force control signal, and generates the drive control signal from the reference position. If a position change to a position exceeding the first range is detected, and the speed detector detects a reversal of the speed direction of the robot arm, the position when the reversal is detected and the force when the reversal is detected. A robot control apparatus that determines a new reference position based on a value of a control signal, and updates and stores the reference position information.

  Further, the present invention provides a method for controlling a robot including a robot arm and a computer, wherein the computer moves the reference position when the position of the robot arm is changed to a position within a first range from a reference position by an operation force. A force control signal that acts in the direction in which the robot arm is moved toward the head and increases as the position change from the reference position increases, and a drive control signal for the robot arm is generated using the force control signal. And when the position of the robot arm is changed from the reference position to a position exceeding the first range by an operating force, the robot arm acts in a direction to move the robot arm toward the reference position. The position change from the position becomes smaller as the position change increases until the second range, but if the position change exceeds the second range, the position changes. Generating a force control signal that does not change beyond a predetermined value from a constant value regardless of the magnitude of the control, and generating a drive control signal for the robot arm using the force control signal, When the position of the robot arm is changed from the reference position to the position exceeding the first range by the operation force and the direction of the speed of the robot arm is reversed, the position of the reversed position and the force control signal of the reversed position The robot control method is characterized by executing a process of updating the reference position based on a value.

  The present invention also includes a robot arm, a position detection unit that detects the position of the robot arm, a speed detection unit that detects the speed of the robot arm, a control unit that generates a drive control signal, and the drive control signal. A drive unit that drives the robot arm based on the control unit, and the control unit stores a detection result of the position detection unit when the robot arm is in an initial position as reference position information, and the reference position information The position detected by the position detection unit after storing the reference position information is compared with the reference position information, and when a position change from the reference position to a position within a first range is detected, the robot arm is moved toward the reference position. Generates a force control signal that acts in the direction of movement, and increases as the position change from the reference position increases, and generates the drive control signal using the force control signal. When the position change from the reference position to the position exceeding the first range is detected, the robot arm acts in a direction to move the robot arm toward the reference position, and the position change from the reference position is the second position. A force control signal that does not change beyond a predetermined value from a constant value regardless of the position change is generated when the position change exceeds the second range. Is used to generate the drive control signal, detect a change in position from the reference position to a position exceeding the first range, and the speed detector detects a reversal of the speed direction of the robot arm. A new reference position is determined based on the position information when the reversal is detected and the value of the force control signal when the reversal is detected, and the reference position information is updated and stored. That is a robotic device.

  The present invention provides a control device that can suppress unintentional movement of a robot arm during direct teaching, can be easily operated by a teacher over a wide range of positions and postures of the robot arm, and has a simple configuration. it can.

The perspective view which shows the external shape of the control apparatus of the robot of an Example. The fragmentary sectional view which shows the joint part of the robot arm of an Example. The perspective view which shows the coordinate system set to the robot of an Example. The functional block diagram of the control apparatus of an Example. The schematic diagram which shows the effect | action of the control apparatus of an Example. The flowchart of the operation | movement of the direct teaching of an Example. (A) The figure for demonstrating operation | movement of a 1st calculating part. (B) The figure for demonstrating operation | movement of a 2nd calculating part. The figure for demonstrating operation | movement of a relative position detection part. (A) Speed vs time graph. (B) A graph of position vs time. (C) Graph of force control signal vs time. The graph which shows the inclination of the function calculated in a 2nd calculating part. The figure for demonstrating the setting of a parameter (x, y, z, alpha, beta, gamma) and a coordinate system.

A robot control apparatus according to an embodiment of the present invention includes a position detection unit that detects position information of a robot arm, a speed detection unit that detects speed information of the robot arm, and a drive control signal that controls the drive unit of the robot arm. The control part which produces | generates is provided.
The control unit stores, as an initial reference state, the position and posture of the robot arm at the initial stage when the teacher has started teaching directly by grasping the robot arm or the like. When the direct teaching is started, the control unit calculates a force control signal according to the position information from the position detection unit and the speed information from the speed detection unit, transmits the force control signal to the drive unit, and drives the robot arm. Controls the force or torque of the actuator. When the actuator is a direct acting system, the force is controlled, and when the actuator is a rotating system, the torque is controlled. When the teacher applies a force to the robot arm to move it from the reference state, the control unit stores the position and orientation as the teaching value of the trajectory.

For the movement of the robot arm, that is, the movement within the first range from the reference state, the first calculation unit in the control unit generates a force control signal that increases or decreases in size according to the increase or decrease of the position information. This is used to generate a drive control signal to the drive unit. The operation to generate the force control signal is typically performed with a monotonically increasing function. By transmitting the drive control signal generated using this force control signal to the drive unit, control is performed so that a force in a direction to return the robot arm to the reference state is output with respect to slight fluctuation of the position information. . This action prevents the robot arm from moving unintentionally for the teacher. For example, even if the calculation accuracy of a self-weight compensation calculation unit, which will be described later, is not sufficient and the influence of gravity cannot be completely compensated, it is possible to suppress the occurrence of unintended movement for the teacher.
The first calculation unit has an effect of causing the drive unit to output a force similar to a static friction force that keeps the robot arm in the reference state.

  When the control unit detects that the robot arm has moved from the reference state to a position exceeding the first range based on the position information, the control unit operates the switching unit in the control unit to calculate the force control signal. To the second arithmetic unit. That is, when the robot arm moves beyond the first range, it is assumed that the teacher is intentionally operating the robot arm, and the force control is switched. Therefore, the size of the first range is set to a size suitable for determining whether or not the movement of the robot arm is an intentional operation of the teacher.

  The second arithmetic unit is a force control signal that decreases as the position change amount increases until the position change amount from the reference position reaches the second range, but becomes a substantially constant value after exceeding the second range. Is generated. Here, the substantially constant value means that the predetermined value does not change by a predetermined width or more. Typically, this calculation starts from a value equal to the maximum output (final output) of the first calculation unit, and transitions toward a constant value smaller than the start point as the size of the position information increases. It is executed using a simple function. By transmitting a drive control signal generated using this force control signal to the drive unit, control is performed so that a force in a direction to return the robot arm to the reference state is output.

  This constant value has the effect of causing the drive unit to output a force similar to the dynamic friction force that the teacher feels as a constant small load during the movement of the robot arm. By this action, the teacher can move the robot arm while feeling a certain small load even when operating the robot arm in a state greatly changed from the reference state. That is, it is possible to avoid the inconvenience that when the robot arm is largely moved from the reference state, the load felt by the teacher increases and it becomes difficult to continue the operation.

  The switching unit performs switching from a force similar to static friction to a force similar to dynamic friction. If the force control signal becomes discontinuous when the signal from the first operation unit is switched to the signal from the second operation unit, the force felt by the teacher near the boundary of the first range becomes discontinuous, and smooth operation is performed. May cause trouble. Therefore, the signal output from the first calculation unit and the signal output from the second calculation unit are set to be equal across the boundary of the first range. Then, the size of the second range is appropriately set so that the teacher does not feel unnatural because the switching from static friction to dynamic friction is too rapid.

  Note that the explanation using the terms “first computing unit”, “second computing unit”, and “switching unit” is for the convenience of explaining that the force control signal is computed using different algorithms inside and outside the first range. Therefore, it does not mean that each part must be constituted by a separate electric circuit. Of course, the functions of the respective units may be realized by separate electric circuits, but for example, a control program for processing different operations inside and outside the first range is prepared and stored in a computer, and these processes are performed by computer processing. A function may be realized. The control program can be provided to the computer via a computer-readable recording medium or a network.

While the instructor performs direct teaching, the operation direction of the robot arm may be reversed. In this embodiment, when the operation direction is reversed in a region exceeding the first range, the reference state is reset.
That is, when the position of the robot arm changes from the reference state to a position beyond the first range and the speed detection unit detects the reversal of the speed direction of the robot arm, the control unit returns to the previously stored reference state. Instead, a new reference state is stored. The update of the reference state will be described in detail later with reference to FIG. And a control part performs the above-mentioned control based on the reset reference state (position, attitude | position). At the time of resetting, the robot arm is in the first range from the reset reference state, but the calculation of the force control signal returns from the second calculation unit to the first calculation unit in synchronization with the reset of the reference state. Can be switched. Therefore, even when the calculation accuracy of the self-weight compensation calculation unit is not sufficient and the influence of gravity cannot be completely compensated, it is possible to prevent the robot arm from moving unintentionally after the reset. . When the direction of the speed is reversed, switching is performed from a force similar to dynamic friction during movement to a force similar to static friction.

  In the robot control apparatus of the present embodiment, the above-described force control is performed in accordance with a reference coordinate system fixed to the robot arm. The reference coordinate system is typically an XYZ coordinate system fixed to the base of the robot arm. The coordinate space expressed by the XYZ coordinate system is a six-dimensional space that combines the three translational components and the three rotational components. However, the control unit controls the force for each of these components, so that the translation direction can be changed. The rotation direction of the robot arm is also prevented from moving in an unintended direction. Since a certain low load that simulates dynamic friction acts in the direction in which the teacher moves the robot arm, the teacher can easily move the robot arm greatly.

  Further, with respect to the maximum value of the signal output from the first calculation unit, if the rotation direction is set to be larger than the translation direction, the robot arm posture or the robot arm tip direction is maintained substantially constant, It becomes easy to teach the position of. For example, if you want to teach while keeping the orientation of the tip of the robot arm perpendicular to the table so that the workpiece moves within one work table, direct teaching can be performed more easily. Become.

  In addition, the robot control apparatus according to the present embodiment can perform the above-described force control according to the coordinate axis of the tool coordinate system fixed to the work tool attached to the tip of the robot arm. The work tool is typically a robot hand for gripping a workpiece or a screw fastening machine for fastening a screw, but is not limited thereto. Each tool has an appropriate coordinate system for defining work, such as the gripping direction of the robot hand and the axial direction of the screw tightening machine. When setting the functions of the first calculation unit and the second calculation unit of the control unit, it is possible to perform appropriate force control according to the work content by setting the function according to the coordinate axis of the tool coordinate system of each tool. .

  In the robot control apparatus according to the present embodiment, the absolute value of the output gradient with respect to the input (position change) in the first calculation unit is greater than the absolute value of the output gradient with respect to the input (position change) in the second calculation unit. Set the function to be greater or equal. As described above, the second calculation unit executes a function that makes a transition from the final output of the first calculation unit to a substantially constant output while the robot arm is moving. The first calculation unit has an action similar to static friction, and the second calculation unit has an action similar to dynamic friction.

  If the transition curve has a large slope when transitioning to a dynamic friction force that is smaller than the static friction force, the teacher feels that the load has suddenly decreased during operation of the robot arm. When the teacher wants to move the robot arm at a relatively short distance, if the operation load is suddenly reduced, the robot arm may not be stopped at a desired position, and the robot arm may go too far. What the teacher feels when operating is the magnitude of the load and the rate of change. Compare the absolute value of the load increase rate at the start of movement with the absolute value of the load decrease rate when transitioning to a low load, and if the load decrease rate is equal or small, the teacher feels that the operation load suddenly decreases Can be suppressed. That is, when the teacher operates the robot arm at a relatively short distance, it is possible to prevent the robot arm from going too far at the desired position without being stopped.

  In the present embodiment, the teacher performs the above-described force control while directly teaching by applying force to the robot arm, and the control unit stores the taught trajectory. According to the apparatus of the present embodiment, since the instructor can directly teach while feeling a force similar to the frictional force, it is possible to operate the robot arm without excessive load with a natural feeling without discomfort. Yes, the accuracy of the trajectory to be taught can be improved. Further, even when the calculation accuracy of the self-weight compensation calculation unit is not sufficient and the influence of gravity cannot be completely compensated, it is possible to suppress the occurrence of unintended movement for the teacher due to the influence of gravity. According to the control device of the present embodiment, the above-described effects can be achieved with a simple configuration without providing an expensive force sensor for detecting the operating force of the teacher or a handle having a special switch.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a perspective view showing a robot 200 and a robot controller 300 according to an embodiment of the present invention. The robot 200 has a multi-axis vertical articulated robot arm 201 and a robot hand 202 as an end effector attached to the tip of the robot arm 201. In the robot arm 201, a base portion (base end link) 210 fixed to a work table and a plurality of links 211 to 216 that transmit displacement and force are connected to bend (turn) or rotate at joints J1 to J6. ing.

  In this embodiment, the robot arm 201 is composed of six joints J1 to J6, which are three axes that bend and three axes that rotate. Here, bending refers to bending at a point where the two links are connected, and rotation refers to relative rotation of the links on the rotational axis in the longitudinal direction of the two links. Call. The robot arm 201 includes six joints J1 to J6. The joints J1, J4, and J6 are rotating parts, and the joints J2, J3, and J5 are bending parts.

  The robot hand 202 has a plurality of fingers 220 and is attached to the tip of the robot arm 201, that is, the tip of a link (tip link) 216. The plurality of fingers 220 are supported by the hand base so as to move inward and outward in the radial direction around the central axis with respect to the hand base. The workpiece W1 can be gripped by closing the plurality of fingers 220 (moving radially inward), and the workpiece W1 is gripped and released by opening the plurality of fingers 220 (moving radially outward). can do.

  The robot arm 201 has six joint driving devices 230 for driving the joints J1 to J6, respectively. In FIG. 1, the joint drive device 230 is shown only for the joint J2 for convenience of illustration. Although the illustration of the other joints J1, J3 to J6 is omitted, the joint driving device 230 having the same configuration is also arranged in the other joints J1, J3 to J6.

FIG. 2 is a partial cross-sectional view showing the joint J2 of the robot arm 201. As shown in FIG. Hereinafter, the joint J2 will be described as an example, but the other joints J1, J3 to J6 have the same configuration, and thus the description thereof is omitted.
The joint drive device 230 includes a motor 231 that is an electric rotary motor and a speed reducer 233 that decelerates the rotation of the rotation shaft 232 of the motor 231. The joint J2 includes an encoder 235 that is a motor angle detection unit that detects the rotation angle of the rotation shaft 232 of the motor 231 (the input shaft of the speed reducer 233). The motor 231 is a servo motor, for example, a brushless DC servo motor or an AC servo motor. The encoder 235 is preferably an absolute rotary encoder, and includes an absolute angle encoder for one rotation, a counter for the total number of rotations of the absolute angle encoder, and a backup battery for supplying power to the counter. Even if the power supply to the robot arm 201 is turned off, if the backup battery is valid, the total number of rotations is held in the counter regardless of whether the power supply to the robot arm 201 is on or off. Therefore, the posture of the robot arm 201 can be controlled. The encoder 235 is attached to the rotary shaft 232, but may be attached to the input shaft of the speed reducer 233.

  Further, the link 211 and the link 212 are rotatably coupled via a cross roller bearing 237. The motor 231 is covered and protected by a motor cover 238. A brake unit (not shown) is provided between the motor 231 and the encoder 235. The main function of the brake unit is to maintain the posture of the robot arm 201 when the power is turned off.

  The reducer 233 is a wave gear reducer that is small and light and has a large reduction ratio. The speed reducer 233 includes a web generator 241 that is an input shaft coupled to a rotating shaft 232 of the motor 231, and a circular spline 242 that is an output shaft and is fixed to the link 212. The circular spline 242 is directly connected to the link 212, but may be formed integrally with the link 212. The speed reducer 233 includes a flex spline 243 that is disposed between the web generator 241 and the circular spline 242 and is fixed to the link 211. The flex spline 243 is decelerated at a reduction ratio N with respect to the rotation of the web generator 241 and rotates relative to the circular spline 242. Accordingly, the rotation of the rotating shaft 232 of the motor 231 is decelerated by the reduction gear 233 with a reduction ratio of 1 / N, and the link 212 with the circular spline 242 fixed relative to the link 211 with the flexspline 243 fixed is relative to the link 212. The joint J2 is bent.

  FIG. 3 is a perspective view showing a coordinate system set for the robot 200. The base coordinate system ΣB is fixed to the proximal link 210 and has an XB axis, a YB axis, and a ZB axis that are orthogonal to each other. The tool coordinate system ΣT is fixed to the robot hand 202 and has an XT axis, a YT axis, and a ZT axis that are orthogonal to each other. The operation of the robot 200 is represented by the relative position and orientation of the tool coordinate system ΣT with respect to the base coordinate system ΣB. There are three parameters (x, y, z) representing the position. There are three parameters (α, β, γ) representing the posture. That is, the robot motion is represented by six parameters (x, y, z, α, β, γ). On the other hand, as already described, the robot arm 201 has six joints J1 to J6. The angles and parameters (x, y, z, α, β, γ) of the joints J1 to J6 can be mutually converted.

  FIG. 4 is a functional block diagram showing main functional blocks of the control device 300 according to the embodiment of the present invention. Note that each functional block included in the control device 300 in the figure may be configured as hardware using an electric circuit capable of achieving each function, or configured as software using a program capable of achieving each function. May be.

  4, for the robot 200, only the drive part of the joint J1 of the robot arm 201 is shown as a block. For simplicity, the joints J2 to J6 are not shown, but are controlled by the control device 300 in the same manner as the joint J1. As described above, the joint J1 includes the joint driving device 230, the motor 231 and the encoder 235. The same applies to the joints J2 to J6.

  The control device 300 includes an angle calculation unit 306a, an angular velocity calculation unit 307a, a tip position calculation unit 309, a tip speed calculation unit 310, a force control unit 301x and a damper calculation unit 308x for each axis parameter, a self-weight compensation calculation unit 311, and a joint torque calculation. Part 312 and torque control part 313a. Among these, the force control unit 301x includes a relative position detection unit 305x, a switching unit 302x, a first calculation unit 303x, and a second calculation unit 304x. In addition, the force control unit 301x and the damper calculation unit 308x, the self-weight compensation calculation unit 311, the joint torque calculation unit 312, and the torque control unit 313a for each axis parameter may be collectively referred to as a control unit.

  The angle calculation unit 306a calculates the value of the joint angle of the joint J1 based on the value indicating the angle detection result of the encoder 235 mounted on the joint J1. The angular velocity calculation unit 307a calculates the value of the joint angular velocity of the joint J1 by differential calculation based on the value indicating the angle detection result of the encoder 235 mounted on the joint J1. Similarly, the control device 300 includes angle calculation units 306b, 306c, 306d, 306e, and 306f that calculate joint angles of the joints J2 to J6 and angular velocity calculation units 307b, 307c, 307d, 307e, and 307f that calculate joint angular velocities. However, illustration is omitted.

  The tip position calculation unit 309 calculates parameters (x, y, z, α, β, γ) representing the position and posture of the robot arm based on the outputs of the angle calculation units 306a to 306f. The tip speed calculator 310 is a speed d (x, x, y) that is a time derivative of the parameters (x, y, z, α, β, γ) based on the outputs of the angular speed calculators 307a to 307f and the output of the tip position calculator 309. y, z, α, β, γ) / dt is calculated. It is known to those skilled in the art that the parameters (x, y, z, α, β, γ) output from the tip position calculation unit 309 are necessary to calculate this time derivative. The tip speed calculator 310 calculates the speed of the tip of the robot arm and detects the reversal of the speed direction.

  The force control unit 301x is a block corresponding to x among the six parameters. Similarly, force control units 301y, 301z, 301α, 301β, and 301γ are provided as blocks corresponding to parameters (y, z, α, β, and γ), respectively, but are not illustrated. The force control units 301x to 301γ generate a force control signal of a force similar to a static friction force or a force similar to a dynamic friction force according to the displacement from the reference position of the robot hand, and output the force control signal to the joint torque calculation unit 312. To do. The force control unit 301x includes a relative position detection unit 305x, a switching unit 302x, a first calculation unit 303x, and a second calculation unit 304x.

  The relative position detection unit 305x stores the reference state, detects the relative position of the current position with respect to the stored reference state, and outputs the relative position information to the first calculation unit or the second calculation unit via the switching unit 302x. . The current position is input from the tip position calculation unit 309 to the relative position detection unit 305x.

At the start of the direct teaching mode, the relative position detection unit 305x stores the output value of the tip position calculation unit 309 at that time as the initial value of the reference state. Then, the relative position detection unit 305x resets the stored reference state at a predetermined timing. The reset timing is when the direction of the speed dx / dt output by the tip speed calculator 310 is reversed after the robot hand moves beyond the first range. The time when the direction of the speed is reversed is the time when the movement of the robot 200 stops and the movement in the reverse direction is started as the next movement. At this time, the second calculation unit is switched to the first calculation unit, but in order to avoid the discontinuity of the force control signal, the same value as the force control signal output from the second calculation unit immediately before is set to the first value. Let the arithmetic unit output. This method will be described later with reference to FIG.
The force control units 301y to 301γ (not shown) perform the same operation as the force control unit 301x.

  The first calculation unit 303x calculates and outputs a force control signal based on the input relative position information so that it can be controlled with a force similar to the static friction force. The second calculation unit 304x calculates and outputs a force control signal based on the input relative position information so that it can be controlled with a force similar to the dynamic friction force.

  The switching unit 302x switches whether the first calculation unit 303x performs the calculation or the second calculation unit 304x executes the calculation at a predetermined timing. The timing for switching is the timing when the tip position moves out of the first range or out of the range, or the timing when the reference state is reset. In FIG. 4, the switching unit 302x is shown as a switch provided on both the input side and the output side of the first calculation unit 303x and the second calculation unit 304x. Since it is only necessary to switch the arithmetic unit to be operated, a switch only on the output side may be used.

  The self-weight compensation calculation unit 311 calculates and outputs a control value that cancels the influence of gravity. The damper operation unit 308x performs an operation of multiplying the speed dx / dt by a proportional constant and outputs the result. Similarly, the damper calculation units 308y to 308γ (not shown in FIG. 4) execute the calculation by multiplying the speed dy / dt to dγ / dt by a proportionality constant and output the result.

  The output signal of the self-weight compensation calculation unit 311, the output signals of the force control units 301 x to 301 γ, and the output signals of the damper calculation units 308 x to 308 γ are added and guided to the joint torque calculation unit 312. The joint torque calculator 312 converts a force control signal for each parameter (x, y, z, α, β, γ) into a torque command for each joint J1 to J6 and outputs the torque command to each joint torque controller.

The torque control unit 313a controls the torque of the motor 231 mounted on the joint J1 according to the torque command of the joint J1. For torque control, the current flowing through the motor 231 is controlled. Alternatively, a torque sensor may be mounted on the joint drive device 230, and the current of the motor 231 may be controlled so that the joint torque detected by the torque sensor matches the torque command.
Although illustration is abbreviate | omitted about the torque control parts 313b-313f, the torque of the motor 231 mounted in joint J2-J6 is controlled according to the torque command for every joint J2-J6.

FIG. 5 is a schematic diagram showing the operation of the control device 300 when direct teaching is performed. When the teacher operates the robot 200, a load as schematically shown in FIG. 5 acts on the robot hand 202 by the operation of the control device 300.
First, a damper force and a friction force act on the three translation directions indicated by x, y, and z. The damper force is a force proportional to the speed in the translation direction. As the friction force, a static friction force and a dynamic friction force are switched to act. The static frictional force is a frictional force that acts to keep the robot hand 202 in the initial position against the teacher's operation when the robot 200 starts to move. The dynamic friction force is a friction force that acts as a constant low load when the teacher applies a force exceeding the static friction force to the robot 200.

  In addition, damper torque and friction torque act in the three rotational directions indicated by α, β, and γ. The damper torque is a torque proportional to the angular velocity in the rotation direction. As the friction torque, like the friction force, the static friction torque and the dynamic friction torque are switched and act. The static friction torque is a friction torque that acts to keep the robot hand 202 in the initial posture against the operation of the teacher when the robot 200 starts moving. The dynamic friction torque is a friction torque that acts as a constant low load when the teacher applies a torque exceeding the static friction torque to the robot 200.

FIG. 6 is a flowchart showing the operation of the force control unit 301x. The force control units 301y to 301γ perform the same operation, but the description thereof is omitted.
When receiving an instruction to start teaching directly (S1), the force control unit 301x stores the position and orientation at that time as a reference state (S2). Thereafter, the current state of the robot hand and the stored reference state are sequentially compared to check whether they are within the first range from the reference state (S3).
When it is within the first range, the force control unit 301x outputs a force control signal calculated using the first calculation unit 303x to the joint torque calculation unit 312 (S4). While within the first range, (S3) and (S4) are repeated, and the force control by the first computing unit 303x is continued.

  On the other hand, when the robot hand moves beyond the first range by the teacher's operation, the force control unit 301x outputs a force control signal calculated using the second calculation unit 304x to the joint torque calculation unit 312. (S5). Then, it is detected whether the speed dx / dt output from the tip speed calculator 310 is reversed (S6). While the reversal of the speed direction, that is, the reset condition is not detected, (S5) and (S6) are repeated, and the force control by the second calculation unit 304x is continued.

  On the other hand, when the reset condition is detected, the stored reference state is reset and a new reference state is stored (S7). Then, the force control unit 301x checks whether an instruction to end teaching is directly input (S8). If the end instruction has not been input, the process returns to (S3), and the force control is continued based on the reset reference state. When the direct teaching end instruction is input, the direct teaching operation is ended (S9).

  FIG. 7A and FIG. 7B are diagrams for explaining the operation of the first calculation unit 303x and the second calculation unit 304x, respectively. When the absolute value of the position x shown on the horizontal axis of the graph is smaller than or equal to the threshold value P1x that determines the first range, the first calculation unit 303x is selected, and the calculation based on the characteristics of FIG. Done. When the absolute value of the position x shown on the horizontal axis of the graph is larger than the threshold value P1x that determines the first range, the second calculation unit 304x is selected, and the calculation based on the characteristics of FIG. 7B is performed. In other words, when the absolute value of the position x transitions from a state that is smaller than or equal to the threshold value P1x to a state that is larger than the threshold value P1x, switching from the first computing unit to the second computing unit is executed.

  FIG. 7A is a graph showing an input / output function of an operation executed by the first operation unit 303x. The absolute value of the input position x is smaller than or equal to the threshold value P1x that determines the first range. The output is a monotonically increasing function with a maximum absolute value of F1x. F1x simulates the maximum static friction force in static friction. Further, as indicated by the arrows, bidirectional input that allows repeated increase and decrease is allowed. The first calculation unit outputs the force control signal to the joint torque calculation unit 312 so that a slight force of the position information is applied with a force in a direction to return the robot arm to the reference state.

  FIG. 7B is a graph showing an input / output function of an operation executed by the second operation unit 304x. The absolute value of the input position x is larger than a threshold value P1x that determines the first range. The input / output function of the second calculation unit 304x is a function that transitions from F1x to F2x smaller than that, and thereafter takes a constant value. F2x simulates a dynamic friction force. The second calculation unit outputs such a force control signal to the joint torque calculation unit 312 so that a control is applied to apply a force in a direction to return the robot arm to the reference state with respect to a change in position information. When the input has the value P2x, the output is F2x. What is indicated by a dotted line in FIG. 7B for reference is an input / output function of the first arithmetic unit. The input / output functions of the first calculation unit and the second calculation unit are continuously connected at points (P1x, F1x) and (−P1x, −F1x). For this reason, the output is continuous during switching.

  Further, as indicated by the arrows, the second arithmetic unit only allows input in the direction in which the absolute value increases. The absolute value of the input position x decreases when the speed direction is reversed, but switching from the second calculation to the first calculation is performed when the speed dx / dt is reversed. The output F0x immediately before switching is stored so that the output is continuous when switching from the second calculation to the first calculation.

FIG. 8 is a diagram for explaining the operation of the relative position detector 305x at the time of reset. The function shown in FIG. 8 is an inverse function of the function of the first calculation unit shown in FIG.
When the tip speed calculation unit detects the reversal of the speed at a position exceeding the first range, the relative position detection unit 305x sets the position information and the value of the force control signal output by the second calculation unit at that time. Based on this, a new reference position is determined, and the reference position information is updated and stored. For example, as shown in FIG. 9C, which will be described later, when the force control signal output by the second calculation unit when executing the reset is F2x, the actual position at the time of reset is reversed from FIG. A position shifted by a distance corresponding to P0x obtained by the function is stored as a new reference state. Due to the action of the relative position detection unit 305x, the continuity of the force control signal output to the joint torque calculation unit 312 is maintained when the second calculation is switched to the first calculation.
Since the force control signal value is zero at the start of the direct teaching mode, the relative position detection unit 305x stores the position at the start of the direct teaching mode as a reference state.

  The operations of the first calculation unit 303x, the second calculation unit 304x, and the relative position detection unit 305x have been described above with reference to FIGS. 7A, 7B, and 8. Since the operations of the first calculation units 303y to 303γ, the second calculation units 304y to 304γ, and the relative position detection units 305y to 305γ related to other axes are the same, the description thereof is omitted.

FIG. 9A, FIG. 9B, and FIG. 9C are diagrams for explaining the operation of the force control unit 301x in the direct teaching, in order of a speed vs time graph, a position vs time graph, It is a graph of force control signal vs time.
When the speed dx / dt and the position x are input to the force control unit 301x during execution of the direct teaching, the force control signal as an output is as shown in FIG. Arrows A, B, and C indicate times when the switching unit 302x operates.

  An arrow A is when the position x exceeds a threshold value P1x that defines the first range, and switches from the first calculation unit to the second calculation unit. At the time of switching, the force control signal is F1x corresponding to the maximum static friction force. Thereafter, as the position x moves to P2x, the force control signal transitions to F2x similar to the dynamic friction force. An arrow B is a point in time when the direction of the speed dx / dt is reversed, the switching unit 302x switches from the second calculation unit to the first calculation unit, and the relative position detection unit 305x resets the reference state. The force control signal becomes zero when the position x is decreased by P0x from the time point of the arrow B, and then the second operation is again performed from the first calculation unit by the arrow C, which is a time point when the threshold value P1x defining the first range is exceeded. Switch to the calculation unit. In addition, although operation | movement of force control part 301x was demonstrated in Fig.9 (a), FIG.9 (b), FIG.9 (c), operation | movement is the same also about force control part 301y-301γ.

  FIG. 10 is a graph showing parameter settings of functions calculated by the second calculation unit 304x. While the input changes from P1x to P2x, the output transitions from an output F1x similar to the maximum static friction force to F2x similar to the dynamic friction force. In the figure, two transition states are shown when P2x is equal to 2P1x and when P2x is equal to 3P1x. The larger the P2x, the smaller the input / output change rate. For the teacher, it is preferable that there is no steep change in load in order to operate the robot 200 smoothly and as intended. By setting P2x to be equal to or larger than 2P1x, the teacher can perform direct teaching more preferably. That is, the absolute value of the slope of the change with respect to the position of the force control signal generated within the first range is the slope of the change with respect to the position of the force control signal generated within the second range after exceeding the first range. Compared to the absolute value, it should be greater or equal. In addition, although operation | movement of the 2nd calculating part 304x was demonstrated in FIG. 10, operation | movement is the same also about 2nd calculating parts 304y-304γ.

  FIG. 11 is a diagram for explaining setting of parameters (x, y, z, α, β, γ) and a coordinate system. In the above embodiment, the parameters (x, y, z, α, β, γ) are derived from the relative position and orientation when the robot hand is viewed from the base coordinate system ΣB fixed to the proximal link 210. It was. The embodiment of the present invention is not limited to this, and a work tool is attached to the tip of the robot hand, and a force control signal is generated for each coordinate axis of the tool coordinate system set by being fixed to the work tool. It may be. That is, the tool coordinate system ΣT fixed to the robot hand 202 may be associated with the parameters (x, y, z, α, β, γ). First, the tool coordinate system ΣT0 in the initial state is fixed in space. The tool coordinate system ΣT moves in space according to the operation of the robot 200. An arrow A indicates relative movement of ΣT as viewed from ΣT0. The parameters (x, y, z, α, β, γ) may be derived in correspondence with the relative position and orientation of ΣT viewed from ΣT0.

  In the present embodiment, the teacher directly applies the force to the robot arm while performing the above-described robot arm force control, and the controller 300 stores the taught trajectory. According to the apparatus of this embodiment, when teaching directly, the teacher can feel a force similar to the frictional force, so that the robot arm can be operated without excessive load with a natural feeling without discomfort. Thus, the positional accuracy of the trajectory to be taught can be improved. In addition, for example, even when the calculation accuracy of the self-weight compensation calculation unit is not sufficient and the influence of gravity cannot be completely compensated, it is possible to suppress the occurrence of unintended movement for the teacher due to the influence of gravity. According to the control apparatus of the present embodiment, the above-described effects can be achieved with a simple configuration without providing an expensive force sensor for detecting the operating force of the teacher or a handle having a special switch.

  The implementation of the present invention is not limited to the above-described embodiments and examples, and many modifications are possible within the scope of the technical idea of the present invention. For example, the number of axes of the robot to be controlled is not limited to the example of the embodiment. Moreover, there is no restriction | limiting in the tool fixed to a robot hand, The tool coordinate system according to the kind of tool can be set. Further, in addition to the force control unit, the self-weight compensation calculation unit, and the damper calculation unit, a functional block for performing another force calculation may be provided.

  200 ... Robot / 201 ... Robot arm / 202 ... Robot hand / 210 ... Base part (base end link) / 211 to 216 ... Link / 235 ... Encoder / 300 ... Control device / 301x ... force control unit / 302x ... switching unit / 303x ... first calculation unit / 304x ... second calculation unit / 305x ... relative position detection unit / 306a ... angle Calculation unit / 307a ... Angular velocity calculation unit / 308x ... Damper calculation unit / 309 ... Tip position calculation unit / 310 ... Tip speed calculation unit / 311 ... Self weight compensation calculation unit / 312 ... Joint torque calculator / 313a ... Torque controller

Claims (18)

A position detector for detecting the position of the robot arm;
A speed detector for detecting the speed of the robot arm;
A control unit that generates a drive control signal for controlling the drive unit of the robot arm,
The controller is
Storing the detection result of the position detection unit when the robot arm is in the initial position as reference position information;
Comparing the position detected by the position detector after storing the reference position information with the reference position information;
When a position change from the reference position to a position within the first range is detected, a force that acts in a direction to move the robot arm toward the reference position and increases as the position change from the reference position increases. Generating a control signal, generating the drive control signal using the force control signal,
If a position change from the reference position to a position exceeding the first range is detected, it acts in a direction to move the robot arm toward the reference position, and the position change from the reference position is a second range. However, when the position change exceeds the second range, a force control signal that does not change from a constant value to a predetermined magnitude or more is generated regardless of the position change. And generating the drive control signal using,
When a position change from the reference position to a position exceeding the first range is detected and the speed detection unit detects a reversal of the speed direction of the robot arm, the position and reversal when the reversal is detected are detected. A new reference position is determined based on the value of the force control signal when updated, and the reference position information is updated and stored.
A robot control device characterized by that. The control unit generates the force control signal for each coordinate axis of a reference coordinate system fixedly set on the robot arm.
The robot control apparatus according to claim 1. The robot arm has a work tool attached to the tip, and the control unit generates the force control signal for each coordinate axis of a tool coordinate system fixed and set to the work tool.
The robot control apparatus according to claim 1. The absolute value of the slope of the change with respect to the position of the force control signal generated within the first range is a change with respect to the position of the force control signal generated between exceeding the first range and exceeding the second range. Is greater than or equal to the absolute value of the slope of
The robot control device according to claim 1, wherein the robot control device is a robot. The control unit includes a self-weight compensation calculation unit and a damper calculation unit, and uses the signal obtained by adding the output signal of the self-weight compensation calculation unit, the output signal of the damper calculation unit, and the force control signal. Generate
The robot control device according to claim 1, wherein the robot control device is a robot. In a robot control method comprising a robot arm and a computer,
The computer
When the position of the robot arm is changed to a position within the first range from the reference position by an operation force, the robot arm acts in a direction to move the robot arm toward the reference position, and the position change from the reference position is large. Generating a force control signal that increases as much as possible, and using the force control signal to generate a drive control signal for the robot arm,
When the position of the robot arm is changed from the reference position to the position beyond the first range by an operation force, the robot arm acts in a direction to move the robot arm toward the reference position, and the position change from the reference position. Is smaller as the position change is larger up to the second range, but when the second range is exceeded, a force control signal that does not change beyond a predetermined value from a constant value regardless of the magnitude of the position change is generated, Performing a process of generating a drive control signal for the robot arm using the force control signal;
When the position of the robot arm changes from the reference position to a position exceeding the first range by an operation force, and the direction of the speed of the robot arm is reversed, the position when reversed and the force when reversed Performing a process of updating the reference position based on the value of the control signal;
A robot control method characterized by the above. The computer generates the force control signal for each coordinate axis of a reference coordinate system fixedly set on the robot arm.
The robot control method according to claim 6. The robot arm has a work tool attached to the tip, and the computer generates the force control signal for each coordinate axis of a tool coordinate system fixedly set on the work tool.
The robot control method according to claim 6. The absolute value of the slope of the change with respect to the position of the force control signal generated within the first range is a change with respect to the position of the force control signal generated between exceeding the first range and exceeding the second range. Is greater than or equal to the absolute value of the slope of
The robot control method according to any one of claims 6 to 8, wherein: The computer performs processing for generating an output signal by performing a self-weight compensation operation, and processing for generating an output signal by performing a damper operation, and outputs the output signal of the self-weight compensation operation, the output signal of the damper operation, and the force Generating the drive control signal using a signal obtained by adding the control signal;
The robot control method according to claim 6, wherein:   11. A robot control program that causes the computer to execute processing of the robot control method according to claim 6.   The computer-readable recording medium which recorded the control program of the robot of Claim 11. The position and posture of the robot arm controlled by the robot control method according to any one of claims 6 to 10 is stored as a teaching value.
A robot teaching method characterized by the above. A robot arm,
A position detector for detecting the position of the robot arm;
A speed detector for detecting the speed of the robot arm;
A control unit for generating a drive control signal;
A drive unit that drives the robot arm based on the drive control signal,
The controller is
Storing the detection result of the position detection unit when the robot arm is in the initial position as reference position information;
Comparing the position detected by the position detector after storing the reference position information with the reference position information;
When a position change from the reference position to a position within the first range is detected, a force that acts in a direction to move the robot arm toward the reference position and increases as the position change from the reference position increases. Generating a control signal, generating the drive control signal using the force control signal,
If a position change from the reference position to a position exceeding the first range is detected, it acts in a direction to move the robot arm toward the reference position, and the position change from the reference position is a second range. However, when the position change exceeds the second range, a force control signal that does not change from a constant value to a predetermined magnitude or more is generated regardless of the position change. And generating the drive control signal using,
When a position change from the reference position to a position exceeding the first range is detected and the speed detector detects a reversal of the speed direction of the robot arm, the position information and reversal when the reversal is detected are displayed. A new reference position is determined based on the value of the force control signal when detected, and the reference position information is updated and stored.
A robot apparatus characterized by that. The control unit generates the force control signal for each coordinate axis of a reference coordinate system fixedly set on the robot arm.
The robot apparatus according to claim 14. The robot arm has a work tool attached to the tip, and the control unit generates the force control signal for each coordinate axis of a tool coordinate system fixed and set to the work tool.
The robot apparatus according to claim 14. The absolute value of the slope of the change with respect to the position of the force control signal generated within the first range is a change with respect to the position of the force control signal generated between exceeding the first range and exceeding the second range. Is greater than or equal to the absolute value of the slope of
The robot apparatus according to claim 14, wherein the robot apparatus is characterized in that The control unit includes a self-weight compensation calculation unit and a damper calculation unit, and uses the signal obtained by adding the output signal of the self-weight compensation calculation unit, the output signal of the damper calculation unit, and the force control signal. Generate
The robot apparatus according to claim 14, wherein the robot apparatus is characterized.

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