CN109844477B

CN109844477B - External force detection method

Info

Publication number: CN109844477B
Application number: CN201780064853.3A
Authority: CN
Inventors: 川瀬茂
Original assignee: Azbil Corp
Current assignee: Azbil Corp
Priority date: 2016-10-28
Filing date: 2017-09-12
Publication date: 2020-10-30
Anticipated expiration: 2037-09-12
Also published as: JP6711536B2; WO2018079107A1; JP2018072135A; CN109844477A

Abstract

The invention provides an external force detection method, which is formed by the following steps: an acceleration detector (4) detects acceleration of a fixed part (101), a position detector (2) detects a position of a movable part (102) relative to the fixed part (101), a position control component outputs a current command value based on a difference between the position detected by the position detector (2) and a reference position, an acceleration compensation part (8) outputs an acceleration compensation value based on a multiplication result of the acceleration detected by the acceleration detector (4) and a total mass of the movable part (102), an end effector (12) and a workpiece (50), an adder-subtractor (9) adds the current command value and the acceleration compensation value, a constant current control part (10) makes a current value of a driving current coincide with the current command value, and an external force detection part (11) detects an external force based on a result of subtracting the acceleration compensation value from the current value of the driving current.

Description

External force detection method

Technical Field

The present invention relates to an external force detection method that detects an external force applied to a movable portion of an actuator.

Background

Conventionally, industrial robots (hereinafter, referred to as "robots") have been used in many working apparatuses for performing operations such as assembly, pressing, and polishing. In the robot, an end effector (end effector) such as a robot hand is attached to a tip end of a robot arm, and work is performed by holding an object to be worked (a part or a workpiece).

On the other hand, the operation of the robot is generally controlled by position control. Therefore, when the planned target position of the work object is different from the actual position due to a dimension error or a gripping position error of the work object, a large force (external force) may be generated when the work object comes into contact with another object, and the work object may be damaged or broken.

As a countermeasure, a jig (so-called "damper") for absorbing a force generated by a position error of the work object may be separately provided. However, since the characteristics required for each shape or material of the work object are different, it is necessary to prepare different buffers corresponding to the number of types of work objects and design the buffers each time. Therefore, there is a problem that the cost increases and the apparatus becomes large.

In this regard, the following method is also available: a force sensor (forcesensor) is provided between the robot and the end effector, and if an excessive force is to be generated upon contact of the work object, the detection result of the force sensor is fed back to the robot without generating the excessive force. In this case, no buffer is required. However, the force sensor is expensive.

In addition, 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 the work object and another object are in contact, it is detected that an excessive force is generated at the time of contact and a stop command is issued, but a robot having a large and heavy movable part and a deceleration mechanism cannot be stopped suddenly.

Further, the force generated at the time of contact becomes the sum of the impact force generated by inertia and the force generated by the robot at the time of contact. Here, the impact force generated by inertia is proportional to the product of the mass and the moving speed of the work object and the robot movable portion. However, since the robot has a large and heavy mechanism, the moving speed immediately before contact must be reduced in order to reduce the impact force generated by inertia.

Further, even if it is detected that an excessive force is generated and a stop command is issued, the robot cannot be stopped suddenly, and therefore, even if the robot is decelerated suddenly from the time point when the stop command is issued, the robot is stopped at a position deviated from the contact position and crushes the work object. Further, since the amount of overshoot of the position is proportional to the moving speed, the speed of moving the work object closer to another object has to be reduced.

For this reason, in a region where there is a possibility that the work target object may come into contact with another object, the moving speed of the robot must be sufficiently reduced. However, in order to shorten the cycle time, the speed of transferring the work object must be increased. As a result, the speed is rapidly decreased in the vicinity of the contact region.

However, the end effector is mounted at the front end of the force sensor. Therefore, when the robot is decelerated rapidly, 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 force generated by the contact of the work object, and the deceleration time of the robot has to be significantly extended for the distinction.

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, when performing operations such as fitting, pressing, and polishing, the posture that the robot can take is not always fixed, and often varies depending on the state of the operation. For example, in a polishing operation while following a curved surface, it is necessary to change the attitude continuously.

However, since the end effector is attached to the tip of the force sensor as described above, when the posture of the robot is not horizontal, the force sensor generates a force corresponding to the posture of the robot and the mass of the end effector due to the influence of the gravitational acceleration.

On the other hand, as a gravity compensation method for compensating for the influence of the gravitational acceleration, for example, a method disclosed in patent document 1 is cited. In 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 working force is calculated by subtracting the learned force from the force generated during the actual work. However, in this method, learning is required every time the work object is changed. In addition, learning must be performed before contact with an object, and gravity compensation cannot be performed in a case where the robot changes its posture continuously.

In the above description, the external force applied to the movable portion is a force generated when the object is brought into contact with another object, but the present invention is not limited to this, and a force generated when the end effector is brought into contact with the object is the same.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open No. 2012-115912

Disclosure of Invention

Problems to be solved by the invention

As described above, when a work such as assembly is performed using the robot and the force sensor, the work time is long. On the other hand, if the work time is to be shortened, it is impossible to accurately detect the object to be worked, which has been scratched, crushed, or touched. In addition, it is also difficult to perform gravity compensation in real time. As described above, when the force sensor is used, there are the following problems: when the robot is rapidly accelerated or decelerated or the posture of the robot is changed, the external force cannot be accurately detected.

The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an external force detection method capable of accurately detecting an external force applied to a movable portion even when the movable portion is rapidly accelerated or decelerated or the posture of the movable portion is changed.

Means for solving the problems

The external force detection method of the present invention is characterized in that: an acceleration detecting means for detecting an acceleration of the fixed portion in an actuator that allows the movable portion to be displaced with respect to the fixed portion, a position detecting means for detecting a position of the movable portion with respect to the fixed portion, a position control means for outputting a current command value based on a difference between the position detected by the position detecting means and a reference position, an acceleration compensating means for outputting an acceleration compensation value based on a result of multiplying the acceleration detected by the acceleration detecting means by a mass on the movable portion side, an adding means for adding the current command value output from the position control means to the acceleration compensation value output from the acceleration compensating means, a constant current control means for matching a current value of a drive current for driving the actuator to the current command value to which the acceleration compensation value is added by the adding means, and an external force detecting means for detecting an external force based on a result of subtracting the acceleration compensation value from a current value of the drive current, an external force applied to the movable portion is detected.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, since the structure is as described above, even when the actuator is rapidly accelerated or decelerated or the posture is changed, the external force applied to the movable portion can be accurately detected.

Drawings

Fig. 1 is a diagram showing a configuration example of a working device including an external force detection device according to embodiment 1 of the present invention.

Fig. 2 is a diagram showing a configuration example of a gain adjustment unit in embodiment 1 of the present invention.

Fig. 3A and 3B are diagrams for explaining detection of an external force when the movable part contacts a workpiece in a state where the actuator is rapidly accelerated and decelerated in the external force detection device according to embodiment 1 of the present invention, fig. 3A is a diagram showing a drive current and an acceleration compensation value which are input to the subtractor in the external force detection unit, and fig. 3B is a diagram showing an external force detected by the external force detection unit.

Description of the symbols

1: actuator

2: position detector (position detecting component)

3: position/velocity conversion unit

4: acceleration detector (acceleration detecting component)

5: subtracter

6: gain adjustment unit

7: mass estimation unit

8: acceleration compensation part (acceleration compensation component)

9: adder-subtractor (addition component)

10: constant current control unit (constant current control component)

11: external force detecting part (external force detecting component)

12: end effector

50: workpiece

101: fixing part

102: movable part

601: loop gain measuring part

602: gain intersection point control unit

603: variable gain adjustment unit

801: multiplier and method for generating a digital signal

802: coefficient multiplying unit

1001: subtracter

1002: driver for driving

1003: current detector

1101: coefficient multiplying unit

1102: subtracter

1103: coefficient multiplying unit

6011: oscillator

6012: adder

6021: comparator with a comparator circuit

Detailed Description

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 working device including an external force detection device (contact control device) according to embodiment 1 of the present invention.

The working device is a device that performs operations such as assembly, pressing, or polishing. As shown in fig. 1, the working device includes: an actuator 1, a position detector (position detecting means) 2, a position-velocity converting section 3, an acceleration detector (acceleration detecting means) 4, a subtractor 5, a gain adjusting section 6, a mass estimating section (mass estimating means) 7, an acceleration compensating section (acceleration compensating means) 8, an adder-subtractor (adding means) 9, a constant current control section (constant current control means) 10, and an external force detecting section (external force detecting means) 11.

The position detector 2, the position/velocity conversion unit 3, the acceleration detector 4, the subtractor 5, the gain adjustment unit 6, the mass estimation unit 7, the acceleration compensation unit 8, the adder-subtractor 9, the constant current control unit 10, and the external force detection unit 11 constitute an external force detection device.

The actuator 1 supplies a current to a coil placed in a magnetic field, thereby allowing the movable portion 102 to be displaced in a linear movement direction or a rotational direction with respect to the fixed portion 101. The actuator 1 is attached to a tip of a robot (not shown) or the like, and is transferred as a whole and changed in posture.

Further, the end effector 12 is attached to the movable portion 102. In fig. 1, a gripper (manipulator) is mounted as an end effector 12. The gripping claw is configured to freely grip the work object. In addition, although the case of using the workpiece 50 as the work object is described below, a component may be used.

The position detector 2 is provided in the actuator 1 and detects a position (relative position) of the movable portion 102 with respect to the fixed portion 101. A signal (position signal) indicating the position detected by the position detector 2 is output to the position/velocity conversion unit 3 and the subtractor 5.

The position/velocity conversion unit 3 differentiates the position detected by the position detector 2 and converts the position into a velocity. The velocity indicates a velocity (relative velocity) of the movable portion 102 with respect to the fixed portion 101. A signal (velocity signal) indicating the velocity converted by the position/velocity conversion unit 3 is output to an adder-subtractor 9.

The acceleration detector 4 is provided on the fixed unit 101 and detects acceleration of the fixed unit 101. At this time, the acceleration detector 4 detects one of the gravitational acceleration α g and the movement acceleration α 1 of the fixed unit 101 or an acceleration (α g + α 1) obtained by adding the both. Fig. 1 shows a case where the acceleration detector 4 detects the acceleration (α g + α 1). A signal (acceleration signal) indicating the acceleration detected by the acceleration detector 4 is output to an acceleration compensation unit 8.

The subtractor 5 subtracts the position detected by the position detector 2 from the reference position Pr. A signal indicating the subtraction result obtained by the subtractor 5 is output to a gain adjustment unit 6.

The gain adjustment unit 6 adjusts the value of compliance (the reciprocal of the spring constant: an index of stiffness/softness) in the actuator 1. As shown in fig. 1 and 2, the gain adjustment unit 6 includes a loop gain measurement unit 601, a gain intersection control unit 602, and a variable gain adjustment unit 603.

The loop gain measuring section 601 measures the loop gain of the signal output from the subtractor 5. At this time, as shown in fig. 2, the loop gain measuring unit 601 adds a sine wave of a frequency that is 1 time (0dB) higher than the loop gain output from the subtractor 5 by the oscillator 6011, that is, a frequency set at the gain intersection, to each other by the adder 6012. The signals before and after the addition of the sine waves obtained by the loop gain measuring section 601 are output to the gain intersection point control section 602.

As shown in fig. 2, the gain intersection control unit 602 compares the amplitude ratio of the sinusoidal wave obtained by the loop gain measuring unit 601 with the amplitude ratio of the sinusoidal wave before and after addition by the comparator 6021. A signal indicating the comparison result obtained by the gain intersection control unit 602 is output to the variable gain adjustment unit 603.

The variable gain adjustment unit 603 adjusts the gain of the signal output from the subtractor 5 so that the magnification of the amplitude ratio compared by the gain intersection control unit 602 becomes 1. The signal whose loop gain is adjusted by the variable gain adjustment unit 603 is output to the adder-subtractor 9 as the current command value Irp. Further, a signal indicating the adjustment value of the loop gain obtained by the variable gain adjustment unit 603 is output to the quality estimation unit 7.

The subtractor 5 and the gain adjustment unit 6 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 detector 2 and the reference position Pr.

The mass estimation unit 7 estimates the mass of the movable unit 102 side based on the adjustment value of the loop gain obtained by the variable gain adjustment unit 603. That is, the mass estimation unit 7 uses the principle that a change in loop gain is proportional to a change in mass. Here, when the end effector 12 does not grip the workpiece 50, the mass on the movable portion 102 side is a mass obtained by adding the mass M1 of the movable portion 102 to the mass M2 of the end effector 12 (M1+ M2), and when the end effector 12 grips the workpiece 50, the mass on the movable portion 102 side is a mass obtained by adding the mass M1 of the movable portion 102 to the mass M2 of the end effector 12 and the mass M3 of the workpiece 50 (M1+ M2+ M3). Fig. 1 shows a case where the mass estimation unit 7 estimates a mass (M1+ M2+ M3) obtained by adding the mass M1 of the movable unit 102 to the mass M2 of the end effector 12 and the mass M3 of the workpiece 50. A signal indicating the mass estimated by the mass estimation unit 7 is output to an acceleration compensation unit 8.

The operation principle of the gain adjustment unit 6 and the mass estimation unit 7 is the same as that of patent document 2 described below, and detailed description thereof is omitted.

In the above description, the mass estimation unit 7 estimates the mass of the movable unit 102 side, but the present invention is not limited to this, and the mass of the movable unit 102 side may be acquired by another method.

Patent document 2: japanese patent application laid-open No. 2010-182084

The acceleration compensation unit 8 outputs an acceleration compensation value Irc for correcting the disturbance torque (disturbance torque). The acceleration compensation unit 8 includes a multiplier 801 and a coefficient multiplication unit 802.

The multiplier 801 multiplies the acceleration detected by the acceleration detector 4 by the mass estimated by the mass estimation unit 7. A signal indicating the multiplication result obtained by the multiplier 801 is output to the coefficient multiplication unit 802 and the external force detection unit 11.

The coefficient multiplication unit 802 multiplies the multiplication result obtained by the multiplier 801 by a coefficient (1/Kt). Further, Kt is a torque constant indicating a ratio of the thrust force generated by the actuator 1 to the drive current Ia. A signal indicating the multiplication result obtained by the coefficient multiplication unit 802 is output to the adder-subtractor 9 as the acceleration compensation value Irc.

The adder-subtractor 9 adds the current command value Irp output from the gain adjustment unit 6 to the acceleration compensation value Irc output from the acceleration compensation unit 8, and subtracts the velocity signal output from the position/velocity conversion unit 3. A signal indicating the addition/subtraction result obtained by the adder/subtractor 9 is output to the constant current control unit 10 as a current command value Ir.

The constant current control unit 10 controls the drive current Ia for driving the actuator 1 so as to match the current command value Ir. The constant current control unit 10 includes a subtractor 1001, a driver 1002 for driving, and a current detector 1003.

The subtractor 1001 subtracts the current value of the drive current Ia detected by the current detector 1003 from the current command value Ir that has been output from the adder-subtractor 9. A signal indicating the subtraction result obtained by the subtractor 1001 is output to the driver 1002 for driving.

The driver 1002 for driving generates a driving current Ia corresponding to the subtraction result obtained by the subtractor 1001. The drive current Ia generated by the driver 1002 is output to the actuator 1 via the current detector 1003.

The current detector 1003 detects the current value of the drive current Ia generated by the drive driver 1002. A signal indicating the current value detected by the current detector 1003 is output to the subtractor 1001.

The external force detection unit 11 detects an external force (reaction force) F applied to the movable unit 102 based on a result of subtracting the acceleration compensation value Irc from the current value of the drive current Ia. In addition, as the external force F applied to the movable portion 102, there are listed: a force generated when the workpiece 50 held by the end effector 12 is brought into contact with another object, or a force generated when the end effector 12 is brought into contact with the workpiece 50. The external force detection unit 11 includes a coefficient multiplication unit 1101, a subtractor 1102, and a coefficient multiplication unit 1103.

The coefficient multiplication unit 1101 multiplies the multiplication result obtained by the multiplier 801 of the acceleration compensation unit 8 by a coefficient (1/Kt). A signal indicating the multiplication result obtained by the coefficient multiplication unit 1101 is output to the subtractor 1102.

The subtractor 1102 subtracts the multiplication result obtained by the coefficient multiplication unit 1101 from the current value of the drive current Ia generated by the constant current control unit 10. A signal indicating a subtraction result obtained by the subtractor 1102 is output to a coefficient multiplication unit 1103.

The coefficient multiplying unit 1103 multiplies the subtraction result obtained by the subtractor 1102 by a coefficient (Kt), thereby obtaining an external force F.

Next, the operation principle of the external force detection device of embodiment 1 will be explained. In the following, a linear actuator of a direct drive type for directly transmitting the generated thrust to the workpiece 50 is used as the actuator 1, and the movable portion 102 is linearly moved with respect to the fixed portion 101. The actuator 1 is driven by a drive current Ia generated by the constant current control unit 10 in accordance with the current command value Ir.

On the other hand, the position detector 2 detects the position of the movable part 102 relative to the fixed part 101 in the linear movement direction.

The position/velocity conversion unit 3 differentiates the position detected by the position detector 2 and converts the position into a velocity. The velocity represents the velocity of the movable part 102 relative to the fixed part 101.

In addition, the acceleration detector 4 detects the acceleration of the fixed part 101 in the linear movement direction. Hereinafter, the acceleration detector 4 is configured to detect an acceleration (α 1+ α g) obtained by adding a moving acceleration α 1 of the fixed unit 101 in the linear motion direction component to a gravitational acceleration α g of the fixed unit 101 in the linear motion direction component.

The subtractor 5 compares the position detected by the position detector 2 with the reference position Pr, and the difference is supplied to the adder-subtractor 9 via the gain adjustment unit 6 as a current command value Irp, which is one of the elements constituting the current command value Ir.

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

Ir＝Irp+Irc (1)

Further, if the position is simply fed back, the control system becomes unstable. Therefore, the velocity signal from the position/velocity conversion unit 3 is actually added as a sub loop (minor loop) to the negative output of the adder-subtractor 9 to stabilize the velocity signal, but the following description is omitted.

In addition, the gain adjustment unit 6 can change the loop gain of the position control loop, thereby changing the value of the compliance in the actuator 1.

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 thereto when there is disturbance torque.

As a general disturbance torque, a reaction force received from the workpiece 50 during operation, a force generated by gravity and a movement acceleration, a loss torque of a reducer, and the like are conceivable. Here, since the actuator 1 is a linear actuator of a direct drive type, it does not have a speed reducer and is less necessary to consider a loss torque. Therefore, the drive current Ia has a value proportional to the reaction force, gravity, and force generated by the movement acceleration received from the workpiece 50 during the operation. In addition, hereinafter, the reaction force is a force generated when the workpiece 50 contacts another object.

Here, let Ia be the drive current of the actuator 1, F be the reaction force received from the workpiece 50 during operation, α 1 be the moving acceleration of the fixed part 101 in the linear motion direction component, α g be the gravitational acceleration of the fixed part 101 in the linear motion direction component, M1 be the mass of the movable part 102, M2 be the mass of the end effector 12, and M3 be the mass of the workpiece 50. In this case, the relationship of the following expression (2) is established.

F+(α1+αg)·(M1+M2+M3)

＝Kt·Ir＝Kt·(Irp+Irc) (2)

Further, Kt is a torque constant indicating a ratio of the thrust force generated by the actuator 1 to the drive current Ia.

In equation (2), an acceleration compensation value Irc for correcting the disturbance torque is set as in equation (3) below.

(α1+αg)·(M1+M2+M3)＝Kt·Irc (3)

When the acceleration compensation value Irc is set as in the formula (3), the items α 1, α g, M1, M2, and M3 are removed from the formula (2), and the arrangement is performed as in the formula (4).

F＝Kt·Irp (4)

In this way, it is understood that when the acceleration compensation value Irc for correcting the disturbance torque is set as in the formula (3), the reaction force F received from the workpiece 50 during the operation and the current command value Irp are in a proportional relationship.

This means that when the force received from the workpiece 50 during operation is zero, that is, the workpiece 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 is not displaced.

Further, the reaction force F generated when the workpiece 50 is in contact with another object can be known by monitoring the current command value Irp.

In equation (4), the moving acceleration α 1 of the fixed part 101 in the linear motion direction component, the gravitational acceleration α g of the fixed part 101 in the linear motion direction component, the mass M1 of the movable part 102, the mass M2 of the end effector 12, and the mass M3 of the workpiece 50 are not included.

That is, even when the robot moves or stops abruptly and a movement acceleration is generated, or when the robot changes its posture continuously and the gravitational acceleration changes, the movable portion 102 of the actuator 1 does not shake and the reaction force F can be detected accurately.

The compliance value can also be set freely.

As described above, the reaction force F generated when the workpiece 50 comes into contact with another object can be known by monitoring the current command value Irp.

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. Therefore, the reaction force F is detected by monitoring the drive current Ia without directly monitoring the current command value Irp.

Here, formula (2) is as follows.

F+(α1+αg)·(M1+M2+M3)

＝Kt·Ir＝Kt·(Irp+Irc) (2)

On the other hand, the drive current Ia is represented by the following formula (5).

Ia＝Ir＝Irp+Irc (5)

Therefore, the following formula (6) can be obtained from the formulas (2) and (5).

F+(α1+αg)·(M1+M2+M3)＝Kt·Ia (6)

Then, the left side of the formula (3) (. alpha.1 +. alpha.g. (M1+ M2+ M3)) is subtracted from both sides of the formula (6) to carry out collation, whereby the following formula (7) can be obtained.

F＝Kt·(Ia－(α1+αg)·(M1+M2+M3)/Kt) (7)

As shown in the above equation (7), the reaction force F can be obtained from Ia proportional to the reaction force F and having a fast response by subtracting the acceleration compensation value (α 1+ α g) · (M1+ M2+ M3)/Kt from the drive current Ia and multiplying the result by the torque constant Kt.

Fig. 3A and 3B show signal waveforms when the movable portion 102 moves linearly downward as shown in fig. 1 and the workpiece 50 contacts another object (not shown). Fig. 3A shows the drive current Ia and the acceleration compensation value Irc (((. alpha.1 + α g) · (M1+ M2+ M3))/Kt) that have been input to the subtractor 1102, and fig. 3B shows the reaction force F detected by the external force detector 11. As shown in fig. 3A and 3B, the reaction force F can be accurately detected by subtracting the acceleration compensation value Irc (((. alpha.1 + α g) ((M1 + M2+ M3))/Kt) from the drive current Ia and multiplying the result by the coefficient (Kt).

Next, the effect of the external force detection device according to embodiment 1 will be described.

As described above, the operation of the robot is generally controlled by position control. Therefore, when the planned target position of the work object is different from the actual position due to a dimension error or a gripping position error of the work object, a large force may be generated when the work object is brought into contact with another object, and the work object may be damaged or broken.

As a countermeasure, there is also a method of: a force sensor is provided between a robot and an end effector, and if an excessive force is to be generated upon contact of a work object, the detection result of the force sensor is fed back to the robot without generating the excessive force.

However, even if it is detected that an excessive force is generated and a stop command is issued, the robot cannot be stopped suddenly, and therefore, even if the robot is decelerated suddenly from the time point when the stop command is issued, the robot is stopped at a position deviated from the contact position and crushes the work object. Further, since the amount of overshoot of the position is proportional to the moving speed, the speed of moving the work object closer to another object has to be reduced.

On the other hand, in embodiment 1, the actuator 1 is attached to the tip of the robot or the like, and even when the actuator 1 moves or stops abruptly and a movement acceleration is generated, or when the posture of the actuator 1 is changed and the gravitational acceleration is changed, the external force detection device can accurately detect the reaction force F applied to the movable portion 102, and can arbitrarily change the compliance value. Therefore, the robot cannot be stopped suddenly, but the object to be worked is not crushed by the overshoot of the position. Therefore, it is not necessary to extremely slow down the speed of bringing the work object close to another object, and the work can be performed safely.

In addition, conventionally, when the end effector is attached to the tip of the force sensor and the robot is decelerated rapidly, 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.

On the other hand, in the external force detection device of embodiment 1, even when the actuator 1 is rapidly accelerated or decelerated, the external force F can be accurately detected, and since the force is detected only at the time of contact, 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.

On the other hand, in the external force detection device according to embodiment 1, even when the attitude of the actuator 1 is changed and the gravitational acceleration is changed, the external force F can be accurately detected, and therefore the influence of the gravitational force can be compensated in real time.

In the above description, the actuator 1 is used in which the movable portion 102 is displaceable in the linear motion direction. However, the present invention is not limited to this, and the actuator 1 that can displace the movable portion 102 in the rotational direction may be used as long as the acceleration detector 4 can detect angular acceleration.

As described above, according to the above-described embodiment 1, the acceleration detector 4 detects the acceleration of the fixed part 101, the position detector 2 detects the position of the movable part 102 with respect to the fixed part 101, the position control means (the subtractor 5 and the gain adjustment unit 6) outputs the current command value Irp based on the difference between the position detected by the position detector 2 and the reference position Pr, the acceleration compensation unit 8 outputs the acceleration compensation value Irc based on the multiplication result of the acceleration detected by the acceleration detector 4 and the mass on the movable part 102 side, the adder-subtractor 9 adds the current command value Irp to the acceleration compensation value Irc, the constant current control unit 10 matches the current value of the driving current Ia with the current command value Ir, the external force detection unit 11 detects the external force F based on the result of subtracting the acceleration compensation value Irc from the current value of the driving current Ia, therefore, even when the movable portion 102 is rapidly accelerated or decelerated or the posture thereof is changed, the external force F applied to the movable portion 102 can be accurately detected.

In the present invention, any constituent elements of the embodiments may be modified or omitted within the scope of the present invention.

Industrial applicability

The external force detection method of the present invention is suitable for an external force detection method or the like for detecting an external force applied to a movable portion, by accurately detecting an external force applied to the movable portion even when the movable portion is rapidly accelerated or decelerated or the posture of the movable portion is changed.

Claims

1. A method for detecting an external force, characterized in that,

an acceleration detection means detects acceleration of the fixed portion in an actuator that enables the movable portion to be displaced relative to the fixed portion,

a position detecting member detects a position of the movable portion with respect to the fixed portion,

the position control means outputs a current command value based on a difference between the position detected by the position detection means and a reference position,

the mass inferring part infers the mass of the movable part side,

acceleration compensation means outputs an acceleration compensation value based on a result of multiplication of the acceleration detected by the acceleration detection means and the mass on the movable portion side estimated by the mass estimation means,

an adding means adds the current command value that has been output from the position control means to the acceleration compensation value that has been output from the acceleration compensation means,

the constant current control means matches a current value of a drive current for driving the actuator with a current command value to which an acceleration compensation value is added by the addition means,

the external force detection means detects an external force applied to the movable portion based on a result of subtracting the acceleration compensation value from a current value of the drive current.

2. The external force detection method according to claim 1,

the acceleration detection means detects one of a gravitational acceleration and a movement acceleration of the fixed portion, or an acceleration obtained by adding both of them.

3. The external force detection method according to claim 1,

the actuator is a linear actuator of a direct drive type.