JP2019188517A - Curve surface tracing device - Google Patents

Abstract

To correctly detect an external force added to a movable part even if the movable part is suddenly accelerated/decelerated or changed in an attitude, and to perform a curve surface tracing work on the basis of said external force.SOLUTION: A curve surface tracing device comprises: an actuator 1; a move part 3 which moves the actuator 1; a position detection part 4 which detects a position of a movable part 12 with respect to a stationary part 11; an acceleration detection part 5 which detects an acceleration of the stationary part 11; an actuator control part 61 which adjusts a gain for a difference between the detected position and a reference position Pr, and outputs a driving circuit Ia on the basis of a current instruction value Irp as an adjustment result and the detected acceleration; an external force detection part 62 which detects an external force F added to the movable part 12 on the basis of the current instruction value Irp, or the detected acceleration and a current value of the driving circuit Ia; and a work control part 7 which controls the actuator control part 61 and the move part 3 on the basis of data which indicates a curve surface shape of an object 50 and the detected external force F.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a curved surface tracing apparatus that traces the curved surface of an object.

  2. Description of the Related Art Conventionally, industrial robots (hereinafter referred to as robots) and the like are often used in working apparatuses that perform operations such as assembly, pressing, and polishing. This robot has an end effector such as a hand attached to the tip of an arm, and performs work by gripping an object (part or workpiece).

  On the other hand, the operation of the robot is generally controlled by position control. Therefore, when the target position programmed in advance differs from the actual position due to dimensional error or gripping position error of the object, a large external force is generated when the object comes into contact with another object, and the object is scratched or damaged. May occur.

  As a countermeasure, there is a case where a jig (so-called “buffer”) that absorbs the force generated by the position error of the object is separately installed. However, since this buffer requires different characteristics depending on the shape or material of the object, it is necessary to prepare buffers that differ by the number of types of objects, which is designed each time. Therefore, there are problems that the cost is increased and the apparatus is enlarged.

  On the other hand, a force sensor is installed between the robot and the end effector, and when an excessive external force is likely to be generated when an object comes into contact, the detection result of the force sensor is fed back to the robot so that no excessive external force is generated. There is also. In this case, a buffer is not necessary. However, force sensors are expensive.

  Further, when the force sensor is used, there is a problem that it is difficult to shorten the working time for the following reason.

That is, if there is an error in the position where an object comes into contact with another object, a stop command is issued by detecting that an excessive external force has been generated at the time of contact, but a robot with a large and heavy moving part and a deceleration mechanism is suddenly I can't stop.
The external force generated at the time of contact is the sum of the impact force due to inertia and the force generated by the robot at the time of contact. Here, the impact force due to inertia is proportional to the product of the mass and moving speed of the object and the robot movable part. However, since the robot has a large and heavy mechanism, it is necessary to slow down the moving speed immediately before contact in order to reduce the impact force due to inertia.

  Also, even if a stop command is issued after detecting the occurrence of excessive external force, the robot will not stop suddenly, so even if it decelerates suddenly from the time when the stop command is issued, it will stop at a position that deviates from the contact position. , Crush the object. Since the overshoot amount of the position is proportional to the moving speed, the speed at which the object is brought closer to another object must be slowed down.

  For the above reasons, it is necessary to sufficiently reduce the moving speed of the robot in an area where the object may come into contact with another object. However, in order to shorten the cycle time, it is necessary to increase the speed of transferring the object. As a result, the speed is drastically reduced in the vicinity of the contact area.

However, the end effector is attached to the tip of the force sensor. Therefore, when the robot rapidly decelerates, a force proportional to the acceleration in the negative direction is generated in the force sensor due to the influence of the mass of the end effector.
However, it is difficult to distinguish between the force proportional to the acceleration and the external force generated by contact with the object, and the deceleration time of the robot has to be significantly increased in order to distinguish.

  In addition, when a force sensor is used, there is a problem that it is difficult to compensate for the influence of gravity in real time for the following reason.

That is, the posture that the robot can take when performing operations such as assembly, pressing, and polishing is not always constant, and is often changed according to the state of the operation. For example, in an operation of performing polishing or inspection while tracing a curved surface, the posture needs to be continuously changed.
However, as described above, the end effector is attached to the tip of the force sensor. Therefore, when the posture of the robot is not horizontal, the force sensor has a force corresponding to the posture of the robot and the mass of the end effector due to the influence of gravity acceleration. Occurs.

  On the other hand, as a gravity compensation means for compensating the influence of gravity acceleration, for example, a method disclosed in Patent Document 1 can be cited. In this patent document 1, the force generated in the force sensor due to the influence of gravity corresponding to the posture is learned offline in advance. The work force is calculated by subtracting the learned force from the force generated during actual work. However, in this method, it is necessary to perform learning every time the object changes. Further, learning must be performed before contact with an object, and gravity compensation cannot be performed when the robot continuously changes its posture.

  In the above, the external force applied to the movable part is shown as the force generated when the object and another object come into contact with each other. However, the force generated when the end effector and the object come into contact with each other is not limited to this. It is the same.

JP 2012-115912 A

  As described above, when an operation such as assembly is performed using a robot and a force sensor, the operation time becomes longer. On the other hand, if an attempt is made to shorten the work time, the object is damaged, crushed, and contact cannot be detected correctly. It is also difficult to perform gravity compensation in real time. As described above, when the force sensor is used, there is a problem that the external force cannot be detected correctly when the robot suddenly accelerates or decelerates or when the posture is changed. This problem also applies to a curved surface tracing apparatus that performs operations such as polishing or inspection while tracing a curved surface, and improvement is required.

  The present invention has been made to solve the above-described problems, and can correctly detect the external force applied to the movable portion even when the movable portion is suddenly accelerated or decelerated or the posture is changed. An object of the present invention is to provide a curved surface tracing apparatus capable of tracing a curved surface of an object based on the above.

  A curved surface tracing apparatus according to the present invention includes a fixed portion, an actuator having a movable portion that can be displaced with respect to the fixed portion, a moving portion that moves the actuator, and a position detection portion that detects the position of the movable portion with respect to the fixed portion. And an acceleration detection unit that detects the acceleration of the fixed unit, and a gain that is adjusted with respect to a difference between the position detected by the position detection unit and the reference position, and is detected by the current command value and the acceleration detection unit that are the adjustment results An actuator controller that outputs a drive current to the actuator based on the acceleration, and a current command value obtained by the actuator controller, an acceleration detected by the acceleration detector, and a drive current output by the actuator controller Based on the current value, the external force detector that detects the external force applied to the movable part, and the curved surface shape of the target object Characterized in that a working controller which controls the actuator control unit and a mobile unit based on the external force detected by to the data and the external force detecting unit.

  According to the present invention, since it is configured as described above, it is possible to correctly detect the external force applied to the movable portion even when the movable portion is suddenly accelerated or decelerated or the posture is changed, and based on the external force, the curved surface of the object Can be traced.

It is a figure which shows the structural example of the curved surface trace apparatus which concerns on Embodiment 1 of this invention. It is a figure which shows the structural example of the external force detection control part in Embodiment 1 of this invention. It is a figure which shows the structural example of the gain adjustment part in Embodiment 1 of this invention. It is a figure which shows the structural example of the work control part in Embodiment 1 of this invention. It is a flowchart which shows an example of the curved surface trace operation | work by the curved surface trace apparatus which concerns on Embodiment 1 of this invention. It is a figure explaining the influence of the gravity by the inclination of a movable part in the case of the curved surface trace operation | work by the curved surface trace apparatus which concerns on Embodiment 1 of this invention. It is a figure which shows an example of the curved surface trace operation | work by the curved surface trace apparatus which concerns on Embodiment 1 of this invention. It is a figure which shows an example of the change of the drive current in the case of the curved surface trace operation | work by the curved surface trace apparatus concerning Embodiment 1 of this invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
Embodiment 1 FIG.
1 is a diagram showing a configuration example of a curved surface tracing apparatus according to Embodiment 1 of the present invention.
The curved surface tracing apparatus is an apparatus for tracing an object having a curved surface and tracing the curved surface of the object. As the curved surface tracing device, for example, a polishing device that performs polishing while tracing a curved surface with respect to an object 50 such as an arc-shaped plate member, or a contact while tracing a curved surface with respect to an object 50 such as a curved touch panel. The present invention can be applied to an inspection apparatus for inspecting whether or not there is a response to force. As shown in FIG. 1, this curved surface tracing apparatus includes an actuator 1, an end effector 2, a moving unit 3, a position detecting unit 4, an acceleration detecting unit 5, an external force detection control unit 6, and a work control unit 7. The external force detection control unit 6 includes an actuator control unit 61 and an external force detection unit 62.

  The actuator 1 includes a fixed portion 11 and a movable portion 12 that can be displaced with respect to the fixed portion 11, and the current is supplied to a coil placed in a magnetic field so that the movable portion 12 is moved relative to the fixed portion 11. Displaceable in the linear motion direction or rotational direction. The actuator 1 is attached to the moving unit 3, and is transferred as a whole and its posture is changed. That is, in the curved surface tracing apparatus, when tracing a curved surface with respect to the object 50, the external force F is managed in a state where the posture of the movable portion 12 (end effector 2) is maintained in the normal direction of the contact point with respect to the object 50. It is necessary to change the posture because it is necessary. Further, this posture is changed, for example, when the work control unit 7 acquires in advance data indicating the curved surface shape of the object 50 measured or designed by the user.

  The end effector 2 is a mechanism that is attached to the movable portion 12 and can trace a curved surface by rotating in one axial direction with respect to the object 50. In FIG. 1, as the end effector 2, an end effector having a roller that can rotate in one axial direction at the tip is used.

  The moving unit 3 moves (transfers and changes the posture) the actuator 1. In FIG. 1, as the moving unit 3, a robot is shown in which an actuator 1 (fixed unit 11) is attached to the tip and the actuator 1 can be moved.

  The position detection unit 4 is provided in the actuator 1 and detects the position (relative position) of the movable unit 12 with respect to the fixed unit 11. A signal (position signal) indicating the position detected by the position detection unit 4 is output to the actuator control unit 61.

  The acceleration detection unit 5 is provided in the fixed unit 11 and detects the acceleration of the fixed unit 11. At this time, the acceleration detection unit 5 detects an acceleration (αg + α1) obtained by adding one or both of the gravitational acceleration αg and the movement acceleration α1 of the fixed unit 11. FIG. 2 shows a case where the acceleration detection unit 5 detects acceleration (αg + α1). A signal (acceleration signal) indicating the acceleration detected by the acceleration detector 5 is output to the actuator controller 61.

  The actuator controller 61 adjusts the gain (loop gain) with respect to the difference between the position detected by the position detector 4 and the reference position Pr, and is detected by the current command value Irp and the acceleration detector 5 as the adjustment result. A drive current Ia for the actuator 1 is output based on the acceleration thus generated.

The external force detection unit 62 is movable based on the current command value Irp obtained by the actuator control unit 61 or the acceleration detected by the acceleration detection unit 5 and the current value of the drive current Ia output by the actuator control unit 61. An external force (reaction force) F applied to the portion 12 is detected.
Configuration examples of the actuator control unit 61 and the external force detection unit 62 will be described later.

  The work control unit 7 realizes a curved surface tracing work by the curved surface tracing apparatus. At this time, the work control unit 7 controls the actuator control unit 61 and the moving unit 3 based on the data indicating the curved surface shape of the target object 50 and the external force F detected by the external force detection unit 62, thereby Realize tracing work. The work control unit 7 controls the actuator control unit 61 by changing the reference position Pr or the gain. In addition to the external force F detected by the external force detection unit 62, the work control unit 7 manages the position detected by the position detection unit 4, the acceleration detected by the acceleration detection unit 5, and the work control unit 7. The curved surface tracing operation may be realized in consideration of the time required. A configuration example of the work control unit 7 will be described later.

Next, a configuration example of the external force detection control unit 6 will be described with reference to FIG. In FIG. 2, the actuator 1, the end effector 2, the position detection unit 4, and the acceleration detection unit 5 are also illustrated.
As shown in FIG. 2, the external force detection control unit 6 includes a position / velocity conversion unit 63, a subtractor 64, a gain adjustment unit 65, a mass estimation unit 66, an acceleration compensation unit 67, an adder / subtractor 68, a constant current control unit 69, and An external force detector 62 is provided. In the external force detection control unit 6 shown in FIG. 2, the function units (position / speed conversion unit 63, subtractor 64, gain adjustment unit 65, mass estimation unit 66, acceleration compensation unit 67, adder / subtractor 68, and the external force detection unit 62 are excluded. The constant current control unit 69) constitutes an actuator control unit 61.

  The position / velocity conversion unit 63 differentiates the position detected by the position detection unit 4 and converts it into a speed. This speed indicates the speed (relative speed) of the movable part 12 with respect to the fixed part 11. A signal (speed signal) indicating the speed converted by the position speed conversion unit 63 is output to the adder / subtractor 68.

  The subtracter 64 subtracts the position detected by the position detector 4 from the reference position Pr. A signal indicating the result of subtraction by the subtractor 64 is output to the gain adjustment unit 65.

  The gain adjusting unit 65 adjusts the gain with respect to the subtraction result (positional deviation) by the subtractor 64 and outputs a current command value Irp. The gain is a compliance value in the actuator 1, and the compliance is the reciprocal of the spring constant and is an index indicating hardness and softness. In the gain adjusting unit 65, the function indicating the relationship between the position deviation and the current command value Irp may be linear or non-linear. As shown in FIGS. 2 and 3, the gain adjustment unit 65 includes a loop gain measurement unit 651, a gain intersection control unit 652, and a variable gain adjustment unit 653.

  The loop gain measurement unit 651 measures the gain of the signal output from the subtracter 64. At this time, as shown in FIG. 3, the loop gain measuring unit 651 sets the signal output from the subtractor 64 to a reference frequency at which the gain should be 1 (0 dB) by the oscillator 654, that is, the gain intersection. The sine wave having the reference frequency is added via an adder 655. The signals before and after the addition of the sine wave by the loop gain measuring unit 651 are output to the gain intersection control unit 652.

  As shown in FIG. 3, the gain intersection control unit 652 compares the amplitude ratios of the signals before and after the addition of the sine wave by the loop gain measurement unit 651 by the comparator 656. A signal indicating the comparison result by the gain intersection control unit 652 is output to the variable gain adjustment unit 653.

  The variable gain adjustment unit 653 sets the gain of the signal output from the subtractor 64 as an adjustment value so that the magnification of the amplitude ratio compared by the gain intersection control unit 652 is 1, adjust. That is, the variable gain adjustment unit 653 has a higher amplitude level Eb of the signal after the addition of the sine wave than the amplitude level Ea of the signal before the addition of the sine wave by the loop gain measurement unit 651 (Ea <Eb). Increases the adjustment value and decreases the adjustment value when the amplitude level Eb of the signal after addition of the sine wave is lower than the amplitude level Ea of the signal before addition of the sine wave (Ea> Eb). Then, the gain is adjusted to be 1. The signal whose gain is adjusted by the variable gain adjusting unit 653 is output to the adder / subtractor 68 as a current command value Irp. In addition, a signal indicating the gain adjustment value by the variable gain adjustment unit 653 is output to the mass estimation unit 66.

  The reason why the sine wave having the reference frequency that should be multiplied by 1 is added by the oscillator 654 is that Ea / Eb = 1 at the frequency at which the gain is multiplied by 1, so that Ea / Eb = 1. This is because the gain intersection can always be maintained at 1 by adjusting the gain.

  The subtractor 64 and the gain adjustment unit 65 constitute position control means (phase control loop) that outputs a current command value Irp based on the difference between the position detected by the position detection unit 4 and the reference position Pr.

The mass estimation unit 66 estimates the mass on the movable unit 12 side from the gain adjustment value by the variable gain adjustment unit 653. That is, the mass estimation unit 66 uses the principle that the change in the gain adjustment value is proportional to the change in the mass. Here, the mass on the movable portion 12 side is a mass (M1 + M2) obtained by adding the mass M1 of the movable portion 12 and the mass M2 of the end effector 2.
For example, if the mass on the movable part 12 side is twice the specified value, the gain is 1/2 of the reciprocal number, and Ea / Eb = 1/2. On the other hand, in order to make the gain 1 time, the variable gain adjustment unit 653 adjusts the gain with a double adjustment value. Then, the mass estimation unit 66 can estimate from the adjustment value of the variable gain adjustment unit 653 that the mass on the movable unit 12 side has changed to twice the specified value.
A signal indicating the mass estimated by the mass estimation unit 66 is output to the acceleration compensation unit 67.

  In addition, although the case where the mass by the mass estimation part 66 estimated the mass by the side of the movable part 12 was shown above, not only this but the information which shows the mass by the side of the movable part 12 may be acquired using another method. .

  The acceleration compensation unit 67 outputs an acceleration compensation value Irc for correcting the disturbance torque. The acceleration compensation unit 67 includes a multiplier 671 and a coefficient multiplication unit 672.

  The multiplier 671 multiplies the acceleration detected by the acceleration detection unit 5 and the mass estimated by the mass estimation unit 66. A signal indicating a multiplication result by the multiplier 671 is output to the coefficient multiplier 672 and the external force detector 62.

  The coefficient multiplication unit 672 multiplies the multiplication result by the multiplier 671 by a coefficient (1 / Kt). Kt is a torque constant that represents the ratio between the thrust generated by the actuator 1 and the drive current Ia. A signal indicating the multiplication result by the coefficient multiplier 672 is output to the adder / subtractor 68 as an acceleration compensation value Irc.

  The adder / subtracter 68 adds the acceleration compensation value Irc output from the acceleration compensation unit 67 to the current command value Irp output from the gain adjustment unit 65 and subtracts the velocity signal output from the position / velocity conversion unit 63. . A signal indicating the result of addition / subtraction by the adder / subtractor 68 is output to the constant current control unit 69 as a current command value Ir.

  The constant current control unit 69 controls the drive current Ia for driving the actuator 1 so as to coincide with the current command value Ir. The constant current control unit 69 includes a subtracter 691, a drive driver 692, and a current detection unit 693.

  The subtractor 691 subtracts the current value of the drive current Ia detected by the current detector 693 from the current command value Ir output from the adder / subtractor 68. A signal indicating the result of subtraction by the subtractor 691 is output to the drive driver 692.

  The drive driver 692 generates a drive current Ia corresponding to the result of subtraction by the subtractor 691. The drive current Ia generated by the drive driver 692 is output to the actuator 1 via the current detector 693.

  The current detection unit 693 detects the current value of the drive current Ia generated by the drive driver 692. A signal indicating the current value detected by the current detector 693 is output to the subtractor 691.

  The external force detection unit 62 is movable based on the current command value Irp obtained by the actuator control unit 61 or the acceleration detected by the acceleration detection unit 5 and the current value of the drive current Ia output by the actuator control unit 61. The external force F applied to the part 12 is detected. Specifically, the external force detection unit 62 detects the external force F applied to the movable unit 12 based on the current command value Irp or the result of subtracting the acceleration compensation value Irc from the current value of the drive current Ia. An example of the external force F applied to the movable portion 12 is a force generated when the end effector 2 comes into contact with the object 50. In FIG. 2, the external force detection unit 62 detects the external force F applied to the movable unit 12 based on the acceleration detected by the acceleration detection unit 5 and the current value of the drive current Ia output by the actuator control unit 61. Show. The external force detection unit 62 illustrated in FIG. 2 includes a coefficient multiplication unit 621, a subtracter 622, and a coefficient multiplication unit 623.

  The coefficient multiplication unit 621 multiplies the multiplication result by the multiplier 671 of the acceleration compensation unit 67 by a coefficient (1 / Kt). A signal indicating the multiplication result by the coefficient multiplier 621 is output to the subtractor 622.

  The subtractor 622 subtracts the multiplication result by the coefficient multiplication unit 621 from the current value of the drive current Ia generated by the constant current control unit 69. A signal indicating the result of subtraction by the subtractor 622 is output to the coefficient multiplier 623.

  The coefficient multiplying unit 623 obtains an external force F by multiplying the result of subtraction by the subtractor 622 by a coefficient (Kt). A signal indicating the external force F obtained by the coefficient multiplication unit 623 is output to the work control unit 7.

  When the external force detection unit 62 detects the external force F applied to the movable unit 12 based on the current command value Irp obtained in the actuator control unit 61, the external force detection unit 62 includes a coefficient multiplication unit. The coefficient multiplication unit obtains an external force F by multiplying the current command value Irp output from the gain adjustment unit 65 by a coefficient (Kt). A signal indicating the external force F obtained by the coefficient multiplication unit is output to the work control unit 7.

Next, a configuration example of the work control unit 7 will be described with reference to FIG.
As shown in FIG. 4, the work control unit 7 includes a contact control unit 71, a curved surface trace control unit 72, and a separation control unit 73.

  The contact control unit 71 moves the end effector 2 until it makes contact with the object 50 in the normal direction of the contact point with a force (first force) F1. At this time, the contact control unit 71 moves the end effector 2 in a state where the posture of the end effector 2 is directed to the normal direction of the contact point with respect to the object 50. Further, the force F1 is a force that can be recognized that the end effector 2 is in contact with the object 50, and is a sufficiently weak force that does not damage the end effector 2, the object 50, and peripheral devices.

  The curved surface trace control unit 72 slides the end effector 2 on the object 50 while maintaining the force F <b> 1 after the processing by the contact control unit 71. At this time, the curved surface trace control unit 72 slides the end effector 2 on the object 50 while maintaining the posture of the end effector 2 in the normal direction of the contact point with respect to the object 50.

In addition, the contact control part 71 and the curved surface trace control part 72 implement | achieve said operation | movement with a push-pull mode or a spring mode.
The push-pull mode is an operation mode in which the actuator 1 generates a positive or negative thrust while the position of the actuator 1 is fixed. In this push / pull mode, the actuator 1 can generate a thrust in the positive direction to realize the pressing operation of the movable part 12, and the actuator 1 can generate a negative direction of the thrust to realize the pulling-out operation of the movable part 12. In the push-pull mode, thrust is generated at a preset change rate from the operation start position. In the push-pull mode, when the thrust generated by the actuator 1 exceeds a preset threshold value or when the position of the movable portion 12 exceeds a preset position, the actuator 1 operates to maintain the thrust. (Constant force mode).
The spring mode is an operation in which the position of the movable portion 12 with respect to the fixed portion 11 can be changed according to the external force F applied to the movable portion 12 while the position of the actuator 1 can be moved by the moving portion 3. Mode. In this spring mode, when the thrust generated by the actuator 1 exceeds a preset threshold value or when the position of the movable portion 12 exceeds a preset position, the actuator 1 operates to maintain the thrust (force Constant mode).

  The separation control unit 73 moves the end effector 2 away from the object 50 after the processing by the curved surface trace control unit 72.

  Next, the operation principle of the external force detection control unit 6 will be described. In the following description, it is assumed that a linear actuator of a direct drive type in which the generated thrust is directly transmitted to the end effector 2 is used as the actuator 1 and the movable portion 12 is linearly moved with respect to the fixed portion 11. The actuator 1 is driven by the drive current Ia generated by the constant current control unit 69 according to the current command value Ir.

On the other hand, the position detection unit 4 detects the position of the movable unit 12 in the linear movement direction with respect to the fixed unit 11.
Further, the position / velocity conversion unit 63 differentiates the position detected by the position detection unit 4 and converts it into a speed. This speed indicates the speed of the movable part 12 with respect to the fixed part 11.

  Further, the acceleration detection unit 5 detects the acceleration of the fixed unit 11 in the linear movement direction. In the following, it is assumed that the acceleration detection unit 5 detects an acceleration (α1 + αg) obtained by adding the movement acceleration α1 in the linear motion direction component of the fixed unit 11 and the gravitational acceleration αg in the linear motion direction component of the fixed unit 11. .

  The position detected by the position detector 4 is compared with the reference position Pr by the subtractor 64, and the difference is a current command value that is one of the elements constituting the current command value Ir via the gain adjuster 65. It is given to the adder / subtractor 68 as Irp.

The current command value Ir is composed of an acceleration compensation value Irc for correcting disturbance torque in addition to the current command value Irp, and is represented by the following equation (1).
Ir = Irp + Irc (1)

  If the position is simply fed back, the control system becomes unstable. Therefore, in practice, the speed signal from the position / speed converter 63 is added as a minor loop to the minus output of the adder / subtractor 68 for stabilization.

  The gain adjustment unit 65 can change the compliance value in the actuator 1 by changing the gain of the position control loop.

Here, focusing on the drive current Ia, the current value becomes zero when there is no disturbance torque, but the current value also changes in proportion to the disturbance torque when there is disturbance torque.
As a general disturbance torque, a reaction force F received from the end effector 2 during work, a force generated by the gravitational acceleration αg and the movement acceleration α1, a loss torque of the speed reducer, and the like can be considered. Here, since the actuator 1 is a linear actuator of a direct drive type, it does not have a speed reducer, and there is little need to consider loss torque. Therefore, the drive current Ia has a value proportional to the reaction force F received from the end effector 2 during work, the force generated by the gravitational acceleration αg, and the movement acceleration α1. Hereinafter, the reaction force F is a force generated when the end effector 2 comes into contact with the object 50.

Here, the driving current Ia of the actuator 1, the reaction force F received from the end effector 2 during work, the movement acceleration α1 in the linear motion direction component of the fixed portion 11, the gravitational acceleration αg in the linear motion direction component of the fixed portion 11, and the movable portion 12 From the mass M1 and the mass M2 of the end effector 2, the relationship of the following formula (2) is established.
F + (α1 + αg) · (M1 + M2) = Kt · Ir = Kt · (Irp + Irc)
(2)
Kt is a torque constant representing the ratio between the thrust generated by the actuator 1 and the drive current Ia.

Further, the acceleration compensation value Irc for correcting the disturbance torque in the equation (2) is set as the following equation (3).
(Α1 + αg) · (M1 + M2) = Kt · Irc (3)

When the acceleration compensation value Irc is set as in Expression (3), the terms α1, αg, M1, and M2 disappear from Expression (2) and are rearranged as in Expression (4) below.
F = Kt · Irp (4)

  As described above, when the acceleration compensation value Irc for correcting the disturbance torque is set as shown in the equation (3), the reaction force F received from the end effector 2 during the work and the current command value Irp have a proportional relationship. .

This is because when the reaction force F received from the end effector 2 during work is zero, that is, when the end effector 2 is not in contact with the object 50, the current command value Irp based on the difference between the reference position Pr and the actual position is also zero. Means no displacement.
The reaction force F generated when the end effector 2 comes into contact with the object 50 can be known by monitoring the current command value Irp.

The expression (4) includes items of the movement acceleration α1 in the linear motion direction component of the fixed portion 11, the gravitational acceleration αg in the linear motion direction component of the fixed portion 11, the mass M1 of the movable portion 12, and the mass M2 of the end effector 2. Is not included.
That is, even when the robot suddenly moves or stops and the movement acceleration α1 occurs, and even when the robot continuously changes its posture and the gravitational acceleration αg changes, the movable portion 12 of the actuator 1 does not shake. Force F can be detected correctly.
The compliance value can also be set freely.

As described above, the reaction force F generated when the end effector 2 suddenly collides with the object 50 can be known by monitoring the current command value Irp. Further, since an induced current is generated in the actuator 1 so as to antagonize the reaction force F, the reaction force F can be detected from the drive current Ia.
However, in the position control loop, the response of the current command value Irp to the reaction force F is generally not fast. On the other hand, the response of the drive current Ia to the reaction force F is relatively fast because it is due to the induced current generated by the movement of the movable portion 12. Therefore, the reaction force F is detected not by directly monitoring the current command value Irp but by monitoring the drive current Ia.

Here, Formula (2) is as follows.
F + (α1 + αg) · (M1 + M2) = Kt · Ir = Kt · (Irp + Irc)
(2)

On the other hand, the drive current Ia can be expressed by the following equation (5).
Ia = Ir = Irp + Irc (5)

Therefore, the following equation (6) is obtained from the equations (2) and (5).
F + (α1 + αg) · (M1 + M2) = Kt · Ia (6)

Then, by subtracting ((α1 + αg) · (M1 + M2)), which is the left side of equation (3), from both sides of equation (6), the following equation (7) is obtained.
F = Kt · (Ia− (α1 + αg) · (M1 + M2) / Kt) (7)

  As shown in the equation (7), the reaction force F can be obtained by subtracting the acceleration compensation value (α1 + αg) · (M1 + M2) / Kt from the drive current Ia and applying the torque constant Kt.

Next, effects of the external force detection control unit 6 will be described.
The operation of the robot is generally controlled by position control. Therefore, when the actual position differs from the pre-programmed target position due to a dimensional error or gripping position error of the object 50, a large external force F is generated when the end effector 2 comes into contact with the object 50, and the object 50 is damaged. Or damage may occur.

  As a countermeasure, a force sensor is installed between the robot and the end effector 2, and if an excessive external force F is likely to occur when the end effector 2 and the object 50 are in contact with each other, the detection result of the force sensor is fed back to the robot. A method for preventing the external force F from being generated can be considered.

  However, even if a stop command is issued after detecting the occurrence of excessive external force F, the robot does not stop suddenly, so even if it decelerates suddenly from the time when the stop command is issued, it stops at a position that deviates from the contact position. As a result, the object 50 is crushed. Since the amount of overshoot of the position is proportional to the moving speed, the speed at which the end effector 2 is brought closer to the object 50 must be slowed down.

  For the above reason, it is necessary to sufficiently reduce the moving speed of the robot in a region where the end effector 2 may come into contact with the object 50. However, in order to shorten the cycle time, the moving speed of the end effector 2 needs to be increased. As a result, the speed is drastically reduced in the vicinity of the contact area.

  On the other hand, in the first embodiment, the actuator 1 is attached to the tip of the robot (the moving unit 3), and the external force detection control unit 6 is configured to generate the movement acceleration α1 when the actuator 1 is suddenly moved or stopped. Even when the attitude of the actuator 1 is changed and the gravitational acceleration αg is changed, the reaction force F applied to the movable portion 12 can be correctly detected, and the compliance value can be arbitrarily changed. Therefore, the point that the robot cannot stop suddenly is the same, but the object 50 is not crushed due to excessive position. Therefore, it is not necessary to extremely slow the speed at which the end effector 2 is brought close to the object 50, and the work can be performed safely.

Further, when a force sensor is installed between the robot and the end effector 2, when the robot rapidly decelerates, a force proportional to the negative acceleration is generated in the force sensor due to the influence of the mass M2 of the end effector 2. .
However, it is difficult to distinguish between the force proportional to the acceleration and the external force F generated by the contact of the object 50 of the end effector 2, and in order to do so, the deceleration time of the robot must be significantly increased.

  On the other hand, the external force detection control unit 6 can correctly detect the external force F even when the actuator 1 is suddenly accelerated and decelerated, and detects the external force F only at the time of contact. Therefore, it is not necessary to lengthen the deceleration time of the actuator 1.

In addition, when a force sensor is used, there is a problem that it is difficult to compensate for the influence of gravity in real time.
That is, the posture that the robot can take when performing the curved surface tracing work is not always constant, and it is necessary to change the posture according to the working state.
However, when a force sensor is installed between the robot and the end effector 2, if the posture of the robot is not horizontal, the force sensor is affected by the gravitational acceleration αg to the posture of the robot and the mass M2 of the end effector 2. A corresponding force is generated.

  On the other hand, since the external force detection control unit 6 can correctly detect the external force F even when the attitude of the actuator 1 is changed and the gravitational acceleration αg changes, the influence of gravity can be compensated in real time.

Next, an operation example of the work control unit 7 will be described with reference to FIGS. Hereinafter, a case where the curved surface tracing apparatus traces a curved surface with respect to the object 50 that is an arc-shaped plate member as illustrated in FIG. 7 will be described. In addition, the work control unit 7 acquires data indicating the curved surface shape of the target object 50, and the end effector 2 is moved to a position facing the first contact point on the object 50 by the moving unit 3. And
In this case, the work control unit 7 controls the actuator control unit 61 and the moving unit 3 based on the data indicating the curved surface shape of the target object 50 and the external force F detected by the external force detection control unit 6. Then, the curved surface tracing operation is performed. The work control unit 7 controls the actuator control unit 61 by changing the reference position Pr or the gain. Here, the gain adjusting unit 65 outputs the current command value Irp based on the position deviation, but the change in the gain means a change in the relationship between the position deviation and the current command value Irp. The change in the relationship includes a change in linear or non-linear inclination.

  In the curved surface tracing work by the curved surface tracing device, as shown in FIG. 5, first, the contact control unit 71 moves the end effector 2 until it contacts the object 50 in the normal direction of the contact point with the force F1. (Step ST1). The force F1 is a force that can recognize that the end effector 2 has come into contact with the object 50, and is a sufficiently weak force that does not damage the end effector 2, the object 50, and peripheral devices. Moreover, since the contact control part 71 implement | achieves said operation | movement by the push-pull mode or the spring mode, the object 50 does not apply an excessive load.

  Next, the curved surface trace control unit 72 slides the end effector 2 on the object 50 while maintaining the force F1 (step ST2). At this time, since the pressing force by the end effector 2 is a minute force, the curved surface of the object 50 is kept in contact with the object 50 according to the data indicating the curved surface shape by controlling the force to maintain this force. It is possible to shift (slide) along. Thereby, the curved surface tracing apparatus can perform curved surface tracing on the object 50.

Here, as shown in FIG. 6, the gravitational acceleration αg in the linear motion direction component of the fixed portion 11 is g · cos θ. Note that θ is the angle of the actuator 1 and also the angle of the tangent at the contact point of the object 50. Further, the mass on the movable part 12 side is M (= M1 + M2), and the movement acceleration α1 in the linear motion direction component of the fixed part 11 is zero. In this case, the drive current Ia of the actuator 1 is expressed by the following equation (8).
Ia = (F + M · g · cos θ) / Kt (8)

  In FIG. 7, when the orientation of the actuator 1 is in the direction 601 (θ = 0), the external force F is (Kt · Ia) − (M · g). When the orientation of the actuator 1 is in the direction 602 (0 <θ <90), the external force F is (Kt · Ia) − (M · g · cos θ). Further, when the orientation of the actuator 1 is in the direction of reference numeral 603 (θ = 90), the external force F is Kt · Ia. Therefore, when the attitude of the actuator 1 changes from the direction of reference numeral 601 to the direction of reference numeral 603, the actuator control unit 61 outputs a drive current Ia as shown in FIG. In addition, the code | symbol 604 in FIG. 6 has shown the track | orbit of the front-end | tip of the moving part 3. FIG.

  Next, the separation control unit 73 moves the end effector 2 so as to separate from the object 50 (step ST3).

  With the above operation, the curved surface tracing apparatus can perform curved surface tracing work on the object 50 without damaging the object 50 or the actuator 1 and without reducing the work speed.

  In the above description, the case where the work control unit 7 acquires data indicating the curved surface shape of the target object 50 in advance is shown. However, the present invention is not limited to this, and the work control unit 7 may acquire data indicating the curved surface shape of the target object 50 in real time. In this case, an angle detector that detects the angle of the actuator 1 is added to the curved trace device, and the work controller 7 acquires data indicating the curved surface shape based on the angle detected by the angle detector. .

  In the above description, the case where the actuator 1 that allows the movable portion 12 to be displaced in the linear motion direction is used is shown. However, the present invention is not limited to this, and if the acceleration detection unit 5 can detect angular acceleration, the actuator 1 that can displace the movable unit 12 in the rotation direction can also be used.

  In the above description, the moving unit 3 is a robot. However, not limited to this, a linear motion mechanism or a rotation mechanism may be used as the moving unit 3.

  As described above, according to the first embodiment, the curved surface tracing apparatus includes the actuator 1 having the fixed portion 11 and the movable portion 12, the moving portion 3 that moves the actuator 1, and the movable portion 12 with respect to the fixed portion 11. The position detection unit 4 that detects the position, the acceleration detection unit 5 that detects the acceleration of the fixed unit 11, and the adjustment of the gain with respect to the difference between the position detected by the position detection unit 4 and the reference position Pr Based on the current command value Irp as a result and the acceleration detected by the acceleration detection unit 5, the actuator control unit 61 that outputs the drive current Ia to the actuator 1, and the current command value Irp obtained in the actuator control unit 61, or Based on the acceleration detected by the acceleration detector 5 and the current value of the drive current Ia output by the actuator controller 61. Based on the external force detection unit 62 that detects the external force F applied to the moving unit 12, the data indicating the curved surface shape of the target object 50, and the external force F detected by the external force detection unit 62, the actuator control unit 61 and the moving unit 3 are And a work control unit 7 for controlling. Thereby, the curved surface tracing apparatus according to the first embodiment can correctly detect the external force F applied to the movable portion 12 even when the movable portion 12 is suddenly accelerated or decelerated or the posture is changed, and based on the external force F. Curved surface tracing work.

  In the present invention, any constituent element of the embodiment can be modified or any constituent element of the embodiment can be omitted within the scope of the invention.

DESCRIPTION OF SYMBOLS 1 Actuator 2 End effector 3 Moving part 4 Position detection part 5 Acceleration detection part 6 External force detection control part 7 Work control part 11 Fixed part 12 Movable part 50 Object 61 Actuator control part 62 External force detection part 63 Position speed conversion part 64 Subtractor 65 Gain adjustment unit 66 Mass estimation unit 67 Acceleration compensation unit 68 Addition / subtraction unit 69 Constant current control unit 71 Contact control unit 72 Curved trace control unit 73 Departure control unit 621 Coefficient multiplication unit 622 Subtraction unit 623 Coefficient multiplication unit 651 Loop gain measurement unit 652 Gain Intersection control unit 653 Variable gain adjustment unit 654 Oscillator 655 Adder 656 Comparator 671 Multiplier 672 Coefficient multiplier 691 Subtractor 692 Drive driver 693 Current detector

Claims (3)

An actuator having a fixed part and a movable part displaceable with respect to the fixed part;
A moving unit for moving the actuator;
A position detection unit for detecting the position of the movable unit with respect to the fixed unit;
An acceleration detector for detecting the acceleration of the fixed part;
The gain is adjusted with respect to the difference between the position detected by the position detection unit and the reference position, and the drive current for the actuator is calculated based on the current command value as the adjustment result and the acceleration detected by the acceleration detection unit. An actuator controller to output,
The external force applied to the movable part is detected based on the current command value obtained in the actuator control unit, or the acceleration detected by the acceleration detection unit and the current value of the drive current output by the actuator control unit. An external force detector;
A curved surface tracing apparatus comprising: data indicating a curved surface shape of a target object and a work control unit that controls the actuator control unit and the moving unit based on an external force detected by the external force detection unit. An end effector attached to the movable part and capable of tracing a curved surface;
The work control unit
A contact control unit that moves the end effector until it contacts the object with a first force in the normal direction of the contact point;
A curved surface trace control unit that slides the end effector on the object while maintaining the first force after the processing by the contact control unit;
The curved surface tracing apparatus according to claim 1, further comprising a separation control unit that moves the end effector away from the object after the processing by the curved surface tracing control unit. An angle detector for detecting the angle of the actuator;
The curved surface tracing apparatus according to claim 1, wherein the work control unit acquires data indicating the curved surface shape based on an angle detected by the angle detection unit.

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