JP7042594B2 - Actuator operation switching device - Google Patents

Description

The present invention relates to an actuator operation switching device that switches the operation of an actuator based on an external force applied to a movable portion of the actuator.

Conventionally, industrial robots (hereinafter referred to as robots) and the like are often used in work devices that perform operations such as assembly, pressing, and polishing. An end effector such as a hand is attached to the tip of the arm of this robot, and the work is performed by grasping an object (part or work).

On the other hand, the operation of the robot is generally controlled by position control. Therefore, if the target position programmed in advance and the actual position are different 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. It may occur.

As a countermeasure, a jig (so-called "buffer") that absorbs the force generated by the position error of the object may be installed separately. However, since this buffer has different characteristics required for each shape and material of the object, it is necessary to prepare buffers different by the number of types of the object, and the buffer is designed each time. Therefore, there is a problem that the cost increases and the size of the device increases.

On the other hand, a method of installing a force sensor between the robot and the end effector and feeding back the detection result of the force sensor to the robot when an excessive external force is likely to be generated when the object touches, so that the excessive external force is not generated. There is also. In this case, no buffer is needed. 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 reasons described below.

That is, if there is an error in the position where an object contacts another object, it detects that an excessive external force is generated at the time of contact and issues a stop command, but a robot with a large and heavy moving part and a deceleration mechanism is sudden. I can't stop.
Further, 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 of the object and the moving part of the robot and the moving speed. 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 an excessive external force is detected and a stop command is issued, the robot will not stop suddenly, so even if the robot suddenly decelerates from the time when the stop command is issued, it will stop at a position deviated from the contact position. , Crush the object. And since the amount of overshoot of the position is proportional to the moving speed, the speed at which the object approaches another object must be slowed down.

For the above reasons, it is necessary to slow down the movement speed of the robot sufficiently in the area where the object may come into contact with other objects. However, in order to shorten the cycle time, it is necessary to increase the speed at which the object is transferred. As a result, the speed drops sharply in the vicinity of the contact area.

However, the end effector is attached to the tip of the force sensor. Therefore, when the robot suddenly 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 the contact of the object, and in order to distinguish between them, the deceleration time of the robot must be significantly lengthened.

Further, 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 reasons described below.

That is, the posture that the robot can take when performing work such as assembly, pressing, or polishing is not always constant, and is often changed according to the work state. For example, in the work of polishing while tracing a curved surface, it is necessary to continuously change the posture.
However, as mentioned above, since the end effector is attached to the tip of the force sensor, if the robot's posture is not horizontal, the force sensor will be affected by the gravitational acceleration and the force will correspond to the robot's posture and the mass of the end effector. Occurs.

On the other hand, as a gravity compensating means for compensating for the influence of gravitational acceleration, for example, the method disclosed in Patent Document 1 can be mentioned. In Patent Document 1, the force generated in the force sensor due to the influence of gravity according to the posture is learned in advance offline. Then, the working force is calculated by subtracting the learned force from the force generated during the actual work. However, in this method, it is necessary to perform learning every time the object changes. In addition, 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 moving part is the force generated when an object and another object come into contact with each other, but the force is not limited to this, and the force generated when the end effector and the object come into contact with each other is also included. The same is true.

Japanese Unexamined Patent Publication No. 2012-115912

As described above, when performing work such as assembly using a robot and a force sensor, the work time becomes long. On the other hand, if an attempt is made to shorten the working time, the object will be damaged and crushed, and the 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 correctly detected when the robot suddenly accelerates or decelerates or the posture is changed. This problem is the same in the actuator operation switching device that switches the operation of the actuator based on the external force applied to the movable portion of the actuator, and improvement is required.

The present invention has been made to solve the above-mentioned problems, and can correctly detect an external force applied to a movable part even when the movable part is suddenly accelerated or decelerated or the posture is changed, and the external force can be applied to the external force. It is an object of the present invention to provide an actuator operation switching device capable of switching an actuator operation based on the above.

The actuator operation switching device according to the present invention has a fixed portion, an actuator having a movable portion that can be displaced with respect to the fixed portion, a position detecting portion for detecting the position of the movable portion with respect to the fixed portion, and an acceleration of the fixed portion. The gain is adjusted for the difference between the detected acceleration detection unit and the position detected by the position detection unit and the reference position, and the actuator is based on the current command value that is the adjustment result and the acceleration detected by the acceleration detection unit. It is detected based on the current command value obtained by the actuator control unit and the torque constant representing the ratio of the thrust generated by the actuator to the drive current , or by the acceleration detection unit. Acceleration , current value of drive current output by the actuator control unit , torque constant, and mass obtained by adding the mass of the movable part and the mass of the end effector attached to the movable part, or the mass of the movable part. Based on the sum of the mass of the end effector and the mass of the object held by the end effector, the external force detector that detects the external force applied to the movable part and the actuator control unit in the instructed operation mode. It is characterized by including a mode control unit for controlling and a mode switching unit for switching the operation mode of the mode control unit based on the external force detected by the external force detection unit.

According to the present invention, since it is configured as described above, the external force applied to the movable portion can be correctly detected even when the movable portion is suddenly accelerated or decelerated or the posture is changed, and the actuator operates based on the external force. Can be switched.

It is a figure which shows the structural example of the actuator operation switching 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 figure which shows the mode transition example in the mode control part in Embodiment 1 of this invention. It is a figure which shows the structural example of the connector used in the actuator operation switching apparatus which concerns on Embodiment 1 of this invention. It is a flowchart which shows an example of the assembly work of the connector by the actuator operation switching device which concerns on Embodiment 1 of this invention. 8A to 8E are diagrams showing an example of connector assembly work by the actuator operation switching device according to the first embodiment of the present invention. It is a figure which shows the external force detected by the external force detection control unit in the assembling work of the connector by the actuator operation switching device shown in FIG.

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 an actuator operation switching device according to the first embodiment of the present invention.
The actuator operation switching device is a device that switches the operation of the actuator 1 based on an external force (reaction force) F applied to the movable portion 12 of the actuator 1. As shown in FIG. 1, this actuator operation switching device includes an actuator 1, an end effector 2, a moving unit 3, a position detection unit 4, an acceleration detection unit 5, an external force detection control unit 6, and a work control unit 7. Further, the external force detection control unit 6 is composed of an actuator control unit 61 and an external force detection unit 62. Further, the work control unit 7 is composed of a mode switching unit 71 and a mode control unit 72.

The actuator 1 has a fixed portion 11 and a movable portion 12 that can be displaced with respect to the fixed portion 11, and the movable portion 12 is moved with respect to the fixed portion 11 by supplying an electric current to a coil placed in a magnetic field. It can be displaced in the linear motion direction or the rotation direction. The actuator 1 is attached to the moving portion 3, and the entire actuator 1 is transferred and the posture is changed. If the movable portion 12 or the end effector 2 has a degree of freedom in a plurality of directions and it is not necessary to transfer the entire actuator 1 or change the posture, the moving portion 3 may be omitted. In the following, a case where the moving unit 3 is used will be described.

The end effector 2 is attached to the movable portion 12 and has a function of directly acting on the object 50. In FIG. 1, a gripper (hand) capable of gripping an object 50 is used as the end effector 2. As the end effector 2, for example, an adsorbent capable of adsorbing an object 50 may be used in addition to the gripper.

The moving unit 3 moves (transfers and changes the posture) the actuator 1. FIG. 1 shows a robot in which an actuator 1 (fixing portion 11) is attached to the tip of the moving portion 3 and the actuator 1 can be moved.

The position detecting 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. The 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 the acceleration (αg + α1) obtained by adding one or both of the gravitational acceleration αg and the moving acceleration α1 of the fixed unit 11. FIG. 2 shows a case where the acceleration detection unit 5 detects acceleration (αg + α1). The signal (acceleration signal) indicating the acceleration detected by the acceleration detection unit 5 is output to the actuator control unit 61.

The actuator control unit 61 adjusts the gain (loop gain) with respect to the difference between the position detected by the position detection unit 4 and the reference position Pr, and detects it by the current command value Irp and the acceleration detection unit 5 which are the adjustment results. The drive current Ia for the actuator 1 is output based on the accelerated acceleration.

The external force detection unit 62 is movable based on the current command value Irp obtained by the actuator control unit 61, 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 unit 12 is detected.
A configuration example of the actuator control unit 61 and the external force detection unit 62 will be described later.

The work control unit 7 realizes work using the actuator 1 by the actuator operation switching device. The work control unit 7 is a dedicated controller for realizing work using the actuator 1 by the actuator operation switching device.

The mode switching unit 71 instructs the mode control unit 72 to switch the operation mode (control unit to be operated and its control content) based on the external force F detected by the external force detection unit 62 (mode switching instruction signal). ) Is output. The mode switching unit 71 instructs the external force F to switch the operation mode based on a comparison with a preset threshold value or a time-series pattern, a moving average, or the like. Further, the mode switching unit 71 is managed by the position detected by the position detecting unit 4, the acceleration detected by the acceleration detecting unit 5, and the mode switching unit 71 in addition to the external force F detected by the external force detecting unit 62. The switching of the operation mode may be instructed in consideration of the time spent.

The mode control unit 72 switches the operation mode based on the mode switching instruction signal output by the mode switching unit 71, and controls the actuator control unit 61 and the moving unit 3. The mode control unit 72 controls the actuator control unit 61 by changing the reference position Pr or the gain (loop gain). Further, the mode control unit 72 shown in FIG. 1 also has a function of controlling the end effector 2. A configuration example of this mode control unit 72 will be described later.

Next, a configuration example of the external force detection control unit 6 will be described with reference to FIG. Note that FIG. 2 also shows an actuator 1, an end effector 2, a position detection unit 4, and an acceleration detection unit 5. Further, FIG. 2 shows a state in which the end effector 2 holds the object 50.
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 a constant current control unit 69. It has an external force detection unit 62. In the external force detection control unit 6 shown in FIG. 2, the functional units (position / velocity 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 the 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 velocity. This speed indicates the speed (relative speed) of the movable portion 12 with respect to the fixed portion 11. The signal (speed signal) indicating the speed converted by the position / speed conversion unit 63 is output to the adder / subtractor 68.

The subtractor 64 subtracts the position detected by the position detection unit 4 from the reference position Pr. The signal indicating the subtraction result by the subtractor 64 is output to the gain adjusting unit 65.

The gain adjusting unit 65 adjusts the gain with respect to the subtraction result (positional deviation) by the subtractor 64, and outputs the current command value Irp. The gain is the value of compliance in the actuator 1, and the compliance is the reciprocal of the spring constant, which is an index indicating hardness and softness. Further, 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 adjusting unit 65 includes a loop gain measuring unit 651, a gain intersection control unit 652, and a variable gain adjusting unit 653.

The loop gain measuring unit 651 measures the gain of the signal output from the subtractor 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 times (0 dB) by the oscillator 654, that is, the gain intersection. The sine wave of the reference frequency is added via the adder 655. The signals before and after the addition of the sine wave by the loop gain measurement 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. The signal showing 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 reciprocal of the amplitude ratio magnification as an adjustment value so that the magnification of the amplitude ratio compared by the gain intersection control unit 652 becomes 1, and sets the gain of the signal output from the subtractor 64 as an adjustment value. adjust. That is, when the variable gain adjusting 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 measuring unit 651 (Ea <Eb). Increases the adjustment value and decreases the adjustment value when the amplitude level Eb of the signal after the addition of the sine wave is lower than the amplitude level Ea of the signal before the addition of the sine wave (Ea> Eb). Then, adjust so that the gain becomes 1 times. The signal whose gain has been adjusted by the variable gain adjusting unit 653 is output to the adder / subtractor 68 as a current command value Irp. Further, a signal indicating the gain adjustment value by the variable gain adjustment unit 653 is output to the mass estimation unit 66.

It should be noted that the addition of the sine wave of the reference frequency at which the gain should be 1 times in the oscillator 654 is such that Ea / Eb = 1 because Ea / Eb = 1 at the frequency where the gain is 1 times. This is because the gain intersection can always be maintained at 1 by adjusting the gain.

Further, the subtractor 64 and the gain adjusting unit 65 constitute a 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 the mass (M1 + M2) obtained by adding the mass M1 of the movable portion 12 and the mass M2 of the end effector 2 when the end effector 2 does not hold the object 50. When the end effector 2 holds the object 50, the mass (M1 + M2 + M3) is the sum of the mass M1 of the movable portion 12, the mass M2 of the end effector 2, and the mass M3 of the object 50. Note that FIG. 2 shows a case where the mass estimation unit 66 estimates the mass (M1 + M2 + M3) obtained by adding the mass M1 of the movable portion 12, the mass M2 of the end effector 2, and the mass M3 of the object 50.
For example, if the mass on the movable portion 12 side is twice the specified value, the gain is 1/2 of the reciprocal of the specified value, and Ea / Eb = 1/2. On the other hand, in order to make the gain 1 times, the variable gain adjusting unit 653 adjusts the gain with an adjusting value of 2 times. 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.
The signal indicating the mass estimated by the mass estimation unit 66 is output to the acceleration compensation unit 67.

In the above, the case where the mass on the movable portion 12 side is estimated by the mass estimation unit 66 is shown, but the present invention is not limited to this, and the mass on the movable portion 12 side may be acquired by using another method.

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

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

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

The adder / subtractor 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 speed signal output from the position / speed conversion unit 63. .. The signal indicating the addition / subtraction result by the addition / subtractor 68 is output to the constant current control unit 69 as the current command value Ir.

The constant current control unit 69 controls the drive current Ia that drives the actuator 1 so as to match the current command value Ir. The constant current control unit 69 includes a subtractor 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 detection unit 693 from the current command value Ir output from the adder / subtractor 68. The signal indicating the subtraction result by the subtractor 691 is output to the drive driver 692.

The drive driver 692 generates a drive current Ia according to the subtraction result by the subtractor 691. The drive current Ia generated by the drive driver 692 is output to the actuator 1 via the current detection unit 693.

The current detection unit 693 detects the current value of the drive current Ia generated by the drive driver 692. The signal indicating the current value detected by the current detection unit 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, 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 unit 12 is detected. Specifically, the external force detection unit 62 detects the external force F applied to the movable unit 12 based on the result of subtracting the acceleration compensation value Irc from the current command value Irp or the current value of the drive current Ia. The external force F applied to the movable portion 12 includes a force generated when the end effector 2 comes into contact with the object 50 and a force generated when the object 50 held by the end effector 2 comes into contact with another object. Can be mentioned. Further, in FIG. 2, the case where 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. Shows. The external force detecting unit 62 shown in FIG. 2 has a coefficient multiplying unit 621, a subtractor 622, and a coefficient multiplying 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). The signal indicating the multiplication result by the coefficient multiplication unit 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. The signal indicating the subtraction result by the subtractor 622 is output to the coefficient multiplication unit 623.

The coefficient multiplication unit 623 obtains an external force F by multiplying the subtraction result by the subtractor 622 by a coefficient (Kt). The 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 detecting unit 62 detects the external force F applied to the movable unit 12 based on the current command value Irp obtained by the actuator control unit 61, it has a coefficient multiplication unit. This 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). Then, the signal indicating the external force F obtained by this coefficient multiplication unit is output to the work control unit 7.

Next, a configuration example of the mode control unit 72 will be described with reference to FIG.
As shown in FIG. 4, for example, the mode control unit 72 includes an initialization unit 721, an origin return unit 722, a drive-off unit 723, a position speed control unit 724, a position control unit 725, a push-pull control unit 726, and a force control unit 727. It has a force reset unit (force change control unit) 728 and an offset cancel unit 729. Further, FIG. 5 is a diagram showing an example of a mode transition in the mode control unit 72. In FIG. 5, the functional unit indicated by a thick circle is a functional unit that is particularly characteristic of the conventional configuration.

The initialization unit 721 drives the actuator 1 to perform initialization. In the initialization, the initialization unit 721 moves the actuator 1 to the physical origin, resets the position detected by the position detection unit 4, and then moves the actuator 1 to a preset home position (for example, 3 mm from the physical origin). Move to position). The initialization unit 721 performs the above operation at least once after the power of the actuator operation switching device is turned on (after the main power is turned on). Further, the initialization unit 721 also performs the above operation when the actuator operation switching device is operated again after the drive of the actuator 1 is cut off by the drive-off unit 723.

The origin return unit 722 forcibly moves the actuator 1 to the home position.

The drive-off unit 723 cuts off the drive of the actuator 1. At this time, the drive-off unit 723 determines the posture of the actuator 1 based on the acceleration detected by the acceleration detection unit 5, moves the actuator 1 to a position where a shock does not occur due to the drive disconnection of the actuator 1, and then moves the actuator 1. The drive of the actuator 1 is cut off.

The position / speed control unit 724 moves the actuator 1 to a designated position while controlling the speed so that sudden acceleration does not occur.

Like the force sensor, the position control unit 725 is in a state where the position of the movable unit 12 with respect to the fixed unit 11 is not changed. Further, the position control unit 725 can move the actuator 1 to a designated position while controlling the speed so that sudden acceleration does not occur, similarly to the position speed control unit 724.

The push-pull control unit 726 generates a positive or negative thrust in the actuator 1 with the position of the actuator 1 fixed (push-pull mode). In the push-pull control unit 726, the actuator 1 generates a thrust in the positive direction to realize the pushing operation of the movable part 12, and the actuator 1 generates the thrust in the negative direction to realize the pulling operation of the movable part 12. can. Further, the push-pull control unit 726 generates thrust at a preset rate of change from the operation start position. Further, the push-pull control unit 726 maintains the thrust when the thrust generated by the actuator 1 exceeds a preset threshold value or when the position of the movable unit 12 exceeds a preset position. Operates in (constant force mode).

The force control unit 727 is in a state 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 (spring mode). Further, the force control unit 727 maintains the thrust when the thrust generated by the actuator 1 exceeds a preset threshold value or when the position of the movable unit 12 exceeds a preset position. Operates (constant force mode).
As described above, in the force control unit 727, since the movable portion 12 is in a soft state, even if the end effector 2 collides with the object 50, it is possible to prevent the object 50 from being crushed as long as it is within the effective stroke range.

Further, the mechanical characteristics (gain) in the spring mode of the force control unit 727 can be arbitrarily set. A fixed value may be set in advance for the value of this mechanical characteristic, or the state of the actuator 1 (external force F detected by the external force detecting unit 62, the position detected by the position detecting unit 4, or the acceleration detecting unit 5). It may be changed based on the detected acceleration, etc.). Further, for example, a pressure sensor may be attached to a portion in contact with the end effector 2, and the value of the mechanical characteristics may be changed based on the pressure detected by the pressure sensor.

The force reset unit 728 resets the thrust generated by the actuator 1 to near zero. As a result, it is possible to make a state in which almost no thrust is generated when the end effector 2 is in contact with the object 50. Further, the operation by the force reset unit 728 is effective when the force control unit 727 repeatedly controls the force continuously.
In the mode control unit 72, when the thrust generated by the actuator 1 exceeds a preset threshold value or the position of the movable unit 12 exceeds a preset position while the force control unit 727 is operating. In this case, the force reset unit 728 may be automatically switched to operate instead of the force control unit 727.

In the above, the case where the force reset unit 728 that resets the thrust generated by the actuator 1 to near zero is used as the force change control unit is shown. However, the present invention is not limited to this, and the force change control unit may be any control unit that changes the thrust generated by the actuator 1 to an arbitrary value.

The offset canceling unit 729 cancels the offset included in the external force F detected by the external force detection control unit 6. In the external force detection control unit 6, the detected external force F may be offset depending on the installation environment (temperature, etc.) of the actuator operation switching device. Therefore, the offset can be canceled by operating the offset canceling unit 729.

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

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

Further, the acceleration detection unit 5 detects the acceleration of the fixed unit 11 in the linear motion direction. In the following, the acceleration detection unit 5 shall detect the acceleration (α1 + αg) obtained by adding the moving acceleration α1 in the linear motion direction component of the fixed portion 11 and the gravitational acceleration αg in the linear motion direction component of the fixed portion 11. ..

Further, the position detected by the position detection unit 4 is compared with the reference position Pr by the subtractor 64, and the difference thereof is the current command value which is one of the elements constituting the current command value Ir via the gain adjustment unit 65. It is given to the adder / subtractor 68 as Irp.

The current command value Ir is composed of the current command value Irp and the acceleration compensation value Irc for correcting the disturbance torque, 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 reality, the speed signal from the position / speed conversion unit 63 is used as a minor loop to be added to the negative output of the adder / subtractor 68 for stabilization, but this will be omitted below.

Further, in the gain adjusting unit 65, the compliance value in the actuator 1 can be changed 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.
As a general disturbance torque, a reaction force F received from the end effector 2 during work, a force generated by a gravitational acceleration αg and a moving acceleration α1, a loss torque of a speed reducer, and the like can be considered. Here, since the actuator 1 is a direct drive type linear actuator, it does not have a speed reducer and it is not necessary to consider the loss torque. Therefore, the drive current Ia is a value proportional to the reaction force F received from the end effector 2 during work, the gravitational acceleration αg, and the force generated by the moving acceleration α1. In the following, it is assumed that the reaction force F is a force generated when the object 50 comes into contact with another object.

Here, the drive current Ia of the actuator 1, the reaction force F received from the end effector 2 during work, the moving 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 The relationship of the following equation (2) is established from the mass M1 of the above, the mass M2 of the end effector 2, and the mass M3 of the object 50.
F + (α1 + αg) ・ (M1 + M2 + M3) = Kt ・ Ir = Kt ・ (Irp + Irc)
(2)
Kt is a torque constant representing the ratio of the thrust generated by the actuator 1 to the drive current Ia.

Further, in the equation (2), the acceleration compensation value Irc for correcting the disturbance torque is set as in the following equation (3).
(Α1 + αg) · (M1 + M2 + M3) = Kt · Irc (3)

When the acceleration compensation value Irc is set as in the equation (3), the terms α1, αg, M1, M2, and M3 disappear from the equation (2), and the terms are arranged as in the following equation (4).
F = Kt · Irp (4)

In this way, if the acceleration compensation value Irc for correcting the disturbance torque is set as in the equation (3), it can be seen that the reaction force F received from the end effector 2 during work and the current command value Irp have a proportional relationship. ..

This is because the reaction force F received from the end effector 2 during work is zero, that is, when the object 50 is not in contact with another object, the current command value Irp based on the difference between the reference position Pr and the actual position is also zero, that is, the position. Means that is not displaced.
The reaction force F generated when the object 50 comes into contact with another object can be known by monitoring the current command value Irp.

Then, in the equation (4), the moving 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, the mass M2 of the end effector 2, and the object. The item of mass M3 of 50 is not included.
That is, even when the robot suddenly moves or stops and the moving acceleration α1 is generated, or when the robot continuously changes its posture and the gravitational acceleration αg changes, the movable portion 12 of the actuator 1 does not shake and reacts. The force F can be detected correctly.
And the value of compliance can be set freely.

As described above, the reaction force F generated when the object 50 suddenly collides with another object can be known by monitoring the current command value Irp. Further, since the 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 by monitoring the drive current Ia instead of directly monitoring the current command value Irp.

Here, the equation (2) is as follows.
F + (α1 + αg) ・ (M1 + M2 + M3) = 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) can be obtained from the equations (2) and (5).
F + (α1 + αg) ・ (M1 + M2 + M3) = Kt ・ Ia (6)

Then, the following equation (7) is obtained by subtracting ((α1 + αg) · (M1 + M2 + M3)), which is the left side of the equation (3), from both sides of the equation (6).
F = Kt ・ (Ia- (α1 + αg) ・ (M1 + M2 + M3) / Kt) (7)

As shown in this equation (7), the reaction force F can be obtained by subtracting the acceleration compensation value (α1 + αg) · (M1 + M2 + M3) / Kt from the drive current Ia and multiplying by the torque constant Kt.

Next, the effect of the external force detection control unit 6 will be described.
The movement of the robot is generally controlled by position control. Therefore, when the target position programmed in advance and the actual position are different due to a dimensional error or a gripping position error of the object 50, a large external force F is generated when the object 50 comes into contact with another object, and the object 50 or another. There is a risk of scratches or damage to the object.

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

However, even if an excessive external force F is detected and a stop command is issued, the robot does not stop suddenly. Therefore, even if the robot suddenly decelerates from the time when the stop command is issued, it stops at a position deviated from the contact position. And crushes the object 50 or other objects. Since the amount of excess position is proportional to the moving speed, the speed at which the object 50 approaches another object must be slowed down.

For the above reasons, it is necessary to sufficiently slow down the moving speed of the robot in the region where the object 50 may come into contact with another object. However, in order to shorten the cycle time, it is necessary to increase the speed at which the object 50 moves. As a result, the speed drops sharply 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 (moving unit 3), and the external force detection control unit 6 suddenly moves or stops the actuator 1 to generate a moving acceleration α1. Even when the posture 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 does not stop suddenly is the same, but the object 50 or another object is not crushed by the excessive position. Therefore, it is not necessary to extremely slow down the speed at which the object 50 is brought closer to another object, 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 suddenly decelerates, a force proportional to the acceleration in the negative direction 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 with another object, and in order to distinguish between them, the deceleration time of the robot must be significantly lengthened.

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 or decelerated, and detects the external force F only at the time of contact, so that it is not necessary to lengthen the deceleration time of the actuator 1.

Further, 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 bonding work is not always constant, and is often changed according to the state of the work.
However, when the 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, and the posture of the robot and the mass M2 of the end effector 2 are affected. The corresponding force is generated.

On the other hand, the external force detection control unit 6 can correctly detect the external force F even when the posture of the actuator 1 is changed and the gravitational acceleration αg changes, so that 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. 6 to 9. The following shows a case where the actuator operation switching device performs an assembly operation of fitting the connector 51 to the connector 52. As shown in FIG. 6, the connector 51 has a claw 511, and the connector 52 has an insertion hole 521 into which the connector 51 is inserted and an engagement hole 522 in which the claw 511 engages when the connector 51 is inserted. have. Further, it is assumed that the connector 51 is held by the end effector 2 and the connector 52 is fixed to a workbench or the like.

Then, the work control unit 7 controls the actuator control unit 61, the end effector 2 and the moving unit 3 based on the external force F or the like detected by the external force detection unit 62, thereby realizing the assembly work by the actuator operation switching device. do. 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, and the change in the gain means the change in the function indicating the relationship between the position deviation and the current command value Irp. ing. In addition, the change of the above function includes the change of the slope of the function. Further, the work control unit 7 is a dedicated controller for realizing work using the actuator 1 by the actuator operation switching device, and is within a high-speed control cycle of 1 kHz or more (1 ms or less) based on the external force F or the like. The operation of the actuator 1 can be switched.

Further, in FIG. 9, the horizontal axis represents the time [s], and the vertical axis represents the external force F (force signal [mV]) detected by the external force detection control unit 6. Further, the reference numerals a to e in FIG. 9 indicate the states in FIGS. 8A to 8E, respectively.

In the assembly work of the connectors 51 and 52 by the actuator operation switching device, first, as shown in FIG. 7, the mode switching unit 71 switches the operation mode of the mode control unit 72 to the position speed control unit 724, and the position speed control unit 724 The connector 51 is brought closer to the connector 52 while controlling the speed so that sudden acceleration does not occur (step ST1).

Next, as shown in FIGS. 7 and 8A, the mode switching unit 71 switches the operation mode of the mode control unit 72 to the force control unit 727, and the moving unit 3 keeps the connector 51 in contact with the connector 52 by force F1. The end effector 2 is moved in the direction of the connector 52 (step ST2). As shown in FIG. 9, the force F1 is a force capable of recognizing that the connector 51 has come into contact with the connector 52, and is a force sufficiently weak enough not to damage the connector 51, the connector 52, and peripheral devices.

In this step ST2, the movable portion 12 initially operates like a spring in which the thrust changes linearly with respect to the displacement (spring mode). After that, when the connector 51 comes into contact with the connector 52, the external force F applied to the movable portion 12 changes, and the information is transmitted from the external force detecting unit 62 to the mode switching unit 71. Then, the mode switching unit 71 issues an instruction to the mode control unit 72 so that when the external force F (thrust generated by the actuator 1) exceeds the threshold value, the mode is set to the constant force mode. As a result, the connectors 51 and 52 can be brought into contact with each other without applying an excessive force.

In the above, in step ST2, the case where the connector 51 is brought into contact with the connector 52 by the moving unit 3 by the force F1 is shown. However, not limited to this, in step ST2, the mode switching unit 71 switches the operation mode of the mode control unit 72 to the push-pull control unit 726, and the push-pull control unit 726 makes the connector 51 contact the connector 52 with a force F1. The end effector 2 may be pressed in the direction of the connector 52 until.

Further, the mode switching unit 71 switches the operation mode of the mode control unit 72 to the force reset unit 728 when the processing in step ST2 is completed, and the force reset unit 728 reduces the thrust generated by the actuator 1 to near zero. You may reset it to. As a result, it is possible to make a state in which almost no thrust is generated when the connectors 51 and 52 are in contact with each other.
When the processing in step ST2 is completed and the stroke of the movable portion 12 has a margin and the thrust generated by the actuator 1 is low, the processing by the force resetting unit 728 is unnecessary. FIG. 9 shows a case where the processing by the force reset unit 728 is not performed.

Next, as shown in FIGS. 7 and 8B, the moving portion 3 moves the end effector 2 in the direction in which the connector 51 and the connector 52 are fitted while maintaining the contact of the connector 51 with the connector 52 (step). ST3). At this time, since an excessive force is not applied when the connectors 51 and 52 are in contact with each other, it is possible to shift (slide) the relative positions of the connectors 51 and 52 while maintaining the contact between the connectors 51 and 52. FIG. 8B shows a case where the connector 51 is displaced in the height direction with respect to the connector 52 in FIG. 8A, and the connector 51 is moved downward. In practice, it is necessary to align all degrees of freedom in the direction perpendicular to the fitting direction, such as the lateral direction and the rotational direction, in addition to the height direction. As shown in FIG. 9, the mode switching unit 71 determines that the connector 51 faces the insertion hole 521 of the connector 52 when the force F1 is lost. Alternatively, the mode switching unit 71 determines from the position of the connector 51 whether the connector 51 faces the insertion hole 521 of the connector 52. Then, when the mode switching unit 71 determines that the connector 51 faces the insertion hole 521 of the connector 52, the mode switching unit 71 instructs the mode control unit 72 to stop the movement of the end effector 2.

The work control unit 7 may update the reference position Pr in the external force detection control unit 6 when the process in step ST3 is completed. At this time, the work control unit 7 sets the position of the insertion destination of the connector 51 as the reference position Pr. This enables compliance control even in the fitting process of the connector 51.

Next, as shown in FIGS. 7, 8C, and 8D, the mode switching unit 71 switches the operation mode of the mode control unit 72 to the push-pull control unit 726, and the push-pull control unit 726 has an external force F as a force F2. Until then, the end effector 2 is pressed in the mating direction so that the connector 51 is inserted into the insertion hole 521 of the connector 52 (step ST4). As a result, the connector 51 can be inserted into the connector 52 with an appropriate force. Further, when the connector 51 is inserted into the insertion hole 521 of the connector 52, the claw 511 of the connector 51 is engaged with the engagement hole 522 of the connector 52, and the connector 51 is fitted into the connector 52.

Next, as shown in FIGS. 7 and 8E, the push-pull control unit 726 moves the end effector 2 in the direction opposite to the fitting direction so as to pull out the connector 51 from the connector 52, and the mode switching unit 71 moves. It is determined whether the external force F reaches the force Fref (step ST5). As shown in FIG. 9, the force Fref is a force that can confirm that the connector 51 is normally fitted to the connector 52.

Here, if the connector 51 is pulled out from the connector 52 before the external force F becomes the force Fref, it can be determined that the assembly of the connectors 51 and 52 has failed. 8E and 9 show a case where the connector 51 is disconnected from the connector 52 with a force F3 weaker than the force Fref.
On the other hand, when the external force F reaches the force Fref, it can be determined that the connectors 51 and 52 have been successfully assembled. After that, the end effector 2 releases the holding of the connector 51, and the assembly work of the connectors 51 and 52 is completed.

In steps ST4 and ST5, the push-pull control unit 726 gradually changes the thrust generated by the actuator 1 to a predetermined thrust (push-pull mode). Then, the external force F applied to the movable portion 12 changes during that time, and the information is transmitted from the external force detecting unit 62 to the mode switching unit 71. Then, when the external force F (thrust generated by the actuator 1) exceeds the threshold value, the mode switching unit 71 stops the thrust change and gives an instruction to the mode control unit 72 so that the mode becomes a constant force mode.

In the above, in step ST4, the case where the connector 51 is fitted to the connector 52 by the push-pull control unit 726 is shown. However, not limited to this, in step ST4, the mode switching unit 71 switches the operation mode of the mode control unit 72 to the force control unit 727, and the moving unit 3 connects the connector 51 to the connector 52 until the external force F becomes the force F2. The end effector 2 may be moved in the mating direction so as to be inserted into the insertion hole 521.

Further, in the above, in step ST5, the case where the connector 51 is pulled out so as to be detached from the connector 52 by the push-pull control unit 726 is shown. However, not limited to this, in step ST5, the mode switching unit 71 switches the operation mode of the mode control unit 72 to the force control unit 727, and the moving unit 3 attaches / detaches the connector 51 from the connector 52 to the end effector 2. May be moved in the direction opposite to the mating direction.

By the above operation, the assembly work for the connectors 51 and 52 can be performed without damaging the connectors 51 and 52 or the actuator 1 and without slowing down the working speed.

In the above, 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 the angular acceleration, an actuator 1 that allows the movable unit 12 to be displaced in the rotational direction can also be used.

Further, in the above, the case where the moving unit 3 is a robot is shown. However, the present invention is not limited to this, and a linear motion mechanism or a rotation mechanism may be used as the moving portion 3.

As described above, according to the first embodiment, the actuator 1 having the fixed portion 11 and the movable portion 12, the position detecting portion 4 for detecting the position of the movable portion 12 with respect to the fixed portion 11, and the acceleration of the fixed portion 11. The gain is adjusted with respect to the difference between the position detected by the position detection unit 4 and the position detected by the acceleration detection unit 5 and the current command value Irp and the acceleration detection unit 5 which are the adjustment results. The actuator control unit 61 that outputs the drive current Ia to the actuator 1 based on the acceleration, the current command value Irp obtained by the actuator control unit 61, or the acceleration and the actuator control unit 61 detected by the acceleration detection unit 5. An external force detection unit 62 that detects an external force F applied to the movable unit 12 based on the output current value of the drive current Ia, a mode control unit 72 that controls the actuator control unit 61 in the instructed operation mode, and an external force detection unit. Since the mode switching unit 71 for switching the operation mode of the mode control unit 72 based on the external force F detected by the unit 62 is provided, the movable unit 12 can be moved even when the movable unit 12 is suddenly accelerated or decelerated or the posture is changed. The external force F applied to the unit 12 can be correctly detected, and the operation of the actuator 1 can be quickly switched based on the external force F.

In the present invention, within the scope of the invention, it is possible to modify any component of the embodiment or omit any component of the embodiment.

1 Actuator 2 End effector 3 Moving unit 4 Position detection unit 5 Acceleration detection unit 6 External force detection control unit 7 Work control unit 11 Fixed unit 12 Moving unit 50 Object 51, 52 Connector 61 Actuator control unit 62 External force detection unit 63 Position speed conversion unit 64 Subtractor 65 Gain adjustment unit 66 Mass estimation unit 67 Acceleration compensation unit 68 Addition / subtractor 69 Constant current control unit 71 Mode switching unit 72 Mode control unit 511 Claw 521 Insertion hole 522 Engagement hole 621 Coefficient multiplier 622 Subtractor 623 Coefficient multiplication Section 651 Loop gain measurement section 652 Gain intersection control section 653 Variable gain adjustment section 654 Oscillator 655 Adder 656 Comparer 671 Multiplier 672 Coefficient multiplier 691 Subtractor 692 Drive driver 693 Current detection section 721 Initialization section 722 Origin return section 723 Drive Off unit 724 Position speed control unit 725 Position control unit 726 Push-pull control unit 727 Force control unit 728 Force reset unit (force change control unit )
729 Offset cancel section

Claims (7)

An actuator having a fixed portion and a movable portion that can be displaced with respect to the fixed portion,
A position detection unit that detects the position of the movable portion with respect to the fixed portion,
An acceleration detection unit that detects the acceleration of the fixed unit, and
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 which is the adjustment result and the acceleration detected by the acceleration detection unit. Actuator control unit to output and
Based on the current command value obtained in the actuator control unit and the torque constant representing the ratio of the thrust generated by the actuator to the drive current , or the acceleration detected by the acceleration detection unit , the actuator control unit The current value of the output drive current , the torque constant, and the mass obtained by adding the mass of the movable part and the mass of the end effector attached to the movable part, or the mass of the movable part and the end effector. Based on the mass obtained by adding the mass of the object and the mass of the object held by the end effector, the external force detection unit that detects the external force applied to the movable unit, and the external force detection unit.
A mode control unit that controls the actuator control unit in the instructed operation mode,
An actuator operation switching device including a mode switching unit that switches the operation mode of the mode control unit based on the external force detected by the external force detection unit. The mode control unit
The actuator operation switching device according to claim 1, further comprising a push-pull control unit that generates thrust in a positive direction or a negative direction in the actuator in a state where the position of the actuator is fixed. The actuator operation switching device according to claim 2, wherein the push-pull control unit maintains the thrust when the thrust generated by the actuator exceeds a preset threshold value. The mode control unit
The actuator according to any one of claims 1 to 3, wherein the actuator has a force control unit that can change the position of the movable portion with respect to the fixed portion according to an external force applied to the movable portion. Operation switching device. The actuator operation switching device according to claim 4, wherein the force control unit maintains the thrust when the thrust generated by the actuator exceeds a preset threshold value. The mode control unit
The actuator operation switching device according to claim 4 or 5, further comprising a force change control unit that changes the thrust generated by the actuator to an arbitrary value. The mode control unit operates the force change control unit in place of the force control unit when the thrust generated by the actuator exceeds a preset threshold value while the force control unit is operating. The actuator operation switching device according to claim 6, wherein the actuator operation is switched.

Images