JP2008087143A - Actuator control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform force control of sufficient output applicable to a robot/hand, etc. <P>SOLUTION: The force control of the sufficient output free to apply to the robot/hand, etc. is realized by doubly using an actuator high in responsiveness of an electric motor, etc. and an actuator low in responsiveness of an artificial muscle, a spring element, etc. The force control making use of the high responsiveness of the electric motor and high output characteristic of the artificial muscle and the spring element together is realized by simultaneously estimating the output of the artificial muscle, the spring element, etc. with disturbance of abrasion of a joint, etc. by making use of a disturbance observer and feeding it back to control of the electric motor. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an actuator control device that controls driving of an actuator, and more particularly, to an actuator control device that realizes sufficient output force control that can be applied to a robot hand or the like.

  Currently, various types of robots are actively developed. A robot is a machine or device that can automatically perform the intended work, and there are various types with different hardware configurations, such as legged, wheeled, or crawler-type mobile robots. Basically, it has a plurality of movable parts such as joints.

  For example, if it is a humanoid robot, it is comprised of 32 or a degree of freedom around it (for example, refer to Patent Document 1). Then, the position and posture of a control target such as a foot or a fingertip are realized by operating each joint with a predetermined displacement amount or displacement speed by an actuator. Further, when a robot performs a task while performing physical interactions with various external environments, it is desired that the robot be driven by a force control system instead of position control.

  Moreover, it is common to use an electric motor that is small, has high torque, and is excellent in responsiveness as a joint actuator for a robot. In particular, AC servo motors (or DC brushless motors) have no brushes and are maintenance-free, and therefore can be applied in unmanned work spaces.

  Electric motors are becoming smaller and higher in output year by year. On the other hand, when manufacturing a robot hand or the like, for example, there is a problem that it is necessary to configure a motor in a smaller size and a sufficient torque cannot be obtained.

  On the other hand, an artificial muscle has been developed as a drive source that replaces an electric motor. Artificial muscles include, for example, shape memory alloys (Ti—Ni, Cu—Zn—Al alloys, etc.), hydrogen storage alloy actuators (for example, see Non-Patent Document 1), ionic EAP (electrically driven polymer) Or the like (for example, see Non-Patent Document 2). Artificial muscles are used not only for actuators for robots but also for medical and welfare purposes such as auxiliary machines for humans with weak muscle strength, such as elderly people.

  An actuator composed of a spring element, an artificial muscle, or the like can obtain a relatively high output torque even if it is small. However, since the response speed is lower than that of an electric motor and the output cannot be accurately determined, it is difficult to realize highly accurate force control.

  Although the shape memory effect itself by the shape memory alloy is high, the heat exchange rate (especially the cooling rate) is slow and not effective. In the case of a hydrogen storage alloy actuator, the response speed depends on the thermal conductivity of the hydrogen storage alloy layer, and there is a delay of about 0.5 seconds from energization to the start of pressure increase. In addition, the response speed of the polymer actuator is generally as low as a second level (see Non-Patent Documents 1 and 2).

Japanese Patent Laid-Open No. 13-150371 "New edition of Robotics Handbook" (Corona, 2005) Yoshihito Nagata, “The Forefront of Software Actuator Development: Toward Realization of Artificial Muscle” (NTS, 2004)

  An object of the present invention is to provide an excellent actuator control apparatus capable of realizing sufficient output force control that can be applied to a robot hand or the like.

The present invention has been made in consideration of the above problems, and is an actuator control apparatus that controls an actuator for driving a predetermined control object,
A first actuator having a first response speed for driving the control object;
A second actuator that drives the object to be controlled and has a second response speed that is faster than the first response speed;
First actuator driving means for driving the first actuator in accordance with a target driving torque in the control target;
Output estimating means for estimating an output torque of the first actuator;
Second actuator driving means for driving the second actuator according to a difference between a target driving torque and the output torque estimated by the output estimating means;
It is an actuator control apparatus characterized by comprising. Here, the first actuator is composed of an artificial muscle or a spring element, and the second actuator is composed of an electric motor.

  An electric motor is generally used for driving a robot joint, but if a small different motor is configured for a robot hand or the like, sufficient torque cannot be obtained. On the other hand, artificial muscles have been developed as a drive source to replace electric motors and can be folded to obtain relatively high output torque even with a small size, but response speed is low compared to electric motors, and the output cannot be accurately determined. Therefore, it is difficult to realize highly accurate force control.

  Therefore, the actuator control device according to the present invention is an artificial muscle or spring element that outputs a sufficient driving torque with a slow response speed as a driving actuator to be controlled, such as a joint of a robot hand, and a high responsiveness. A hybrid system using an electric motor with

  Although it is not possible to directly measure the driving torque of the artificial muscle, the actuator control device according to the present invention can estimate the driving torque of the artificial muscle simultaneously with a disturbance such as friction using a disturbance actuator for an electric motor. it can.

  A target drive torque in a control target such as a joint is given to the electric motor as a command value required when it is generated only by the electric motor as the second actuator. At this time, the drive state (current joint angular velocity) of the controlled object is measured using a sensor or the like. Using the disturbance observer, the torque generated in the first actuator at that moment can be estimated together with the disturbance torque. Then, the estimation result of the disturbance torque is fed back to the command value of the electric motor as the second actuator.

  When the joint is driven only by the artificial muscle, the response speed may be slow. Further, when the joint is driven only by the electric motor, the joint torque may be insufficient. Therefore, a hybrid system is constructed in which one control object is driven by using both an artificial muscle and an electric motor. Based on the estimation result of the artificial muscle driving torque due to disturbance torque, the driving torque by the artificial muscle is driven by the electric motor. Assist or make the torque of the artificial muscle and electric motor antagonize each other.

  As a result, the hybrid system as a whole can obtain a sufficient driving torque and realize highly accurate force control.

  ADVANTAGE OF THE INVENTION According to this invention, the outstanding actuator control apparatus which can implement | achieve sufficient output force control which can be applied to a robot hand etc. using an artificial muscle can be provided.

  An electric motor typified by a servo motor has high responsiveness and can realize position control and force control with high accuracy. However, when manufacturing a small automatic machine such as a robot hand, for example, there is often no small and high-power electric motor that sufficiently satisfies the requirements. In contrast, in the present invention, a sufficient output force that can be applied to a robot hand or the like by using a highly responsive actuator such as an electric motor together with a low responsive actuator such as an artificial muscle or a spring element. Control can be realized.

  Artificial muscles and spring elements have a slower response than electric motors, and their characteristics are fundamentally different. In addition, since the force generated by the artificial muscle and the spring element cannot be measured directly and accurately, there is a problem that the force target value cannot be realized accurately. Therefore, the present invention is configured to estimate the outputs of artificial muscles and spring elements simultaneously with disturbances such as joint friction using a disturbance observer. Therefore, by feeding back to the control of the electric motor, it is possible to realize force control utilizing both the high responsiveness of the electric motor and the high output characteristics of the artificial muscle and the spring element.

  Other objects, features, and advantages of the present invention will become apparent from more detailed description based on embodiments of the present invention described later and the accompanying drawings.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  Generally, an electric motor is used as a robot joint actuator. However, when a robot hand or the like is manufactured, for example, it is necessary to configure the motor in a small size, and a sufficient torque cannot be obtained. In contrast, in the present invention, a sufficient output force that can be applied to a robot hand or the like by using a highly responsive actuator such as an electric motor together with a low responsive actuator such as an artificial muscle or a spring element. Realize control.

  FIG. 1A shows a configuration example of a hybrid system that performs joint drive using an electric motor and an artificial muscle in combination. Artificial muscles have a slower response speed than electric motors, and since the output is not accurately known, it is difficult to realize highly accurate force control. For this reason, even the whole hybrid system using both artificial muscles and electric motors has a slow response and cannot achieve the force target value.

  Note that pneumatic actuators, hydraulic actuators, and various engines can be applied as an alternative or equivalent means of artificial muscle.

  Also, as shown in FIG. 1B, a hybrid system using a spring element instead of an artificial muscle is also conceivable. However, since the output of the spring element is not accurately known, it is similarly difficult to realize highly accurate force control. It is. The spring element can be configured using the restoring force of various elastic materials.

  Therefore, in the present invention, the disturbance observer is used to estimate and feed back the output of the artificial muscle and the spring element at the same time as the disturbance such as the friction of the joint. Realized force control taking advantage of both high output performance.

  FIG. 2 shows a functional configuration of a hybrid system having a disturbance observer and feedback function for the output of the artificial muscle. FIG. 3 shows a processing procedure for driving and controlling the actuators of the electric motor and the artificial muscle in the system 10 in the form of a flowchart. The system 10 executes the processing procedure shown in FIG. 3 every predetermined control cycle (for example, 1 millisecond).

  The target joint torque determination unit 11 determines a target torque to be generated in the joint unit to be controlled based on, for example, a command from a higher-level application that manages the robot operation plan (step S1).

  Next, the artificial muscle drive torque control unit 12 drives the hybrid joint unit 14 including the artificial muscle and the electric motor so as to realize the target torque determined in the preceding step S1 (step S2). However, since the artificial muscle has a slow response, it is assumed that the target torque cannot actually be output. Further, the torque output from the artificial muscle cannot be directly measured.

  In the hybrid joint section 14, the artificial muscle operates in response to the drive torque generation instruction from the artificial muscle drive torque control section 12, and the electric motor operates in response to the drive torque generation instruction from the electric motor drive torque control section 13. The joint to be controlled can be driven as a cooperative action.

  Here, the current command value of the electric motor and the accompanying motor rotation angular velocity can be measured by a rotation sensor or the like. In step S3, the current command value of the electric motor is measured.

  Further, the joint angular velocity measuring unit 15 measures the angular velocity of the joint driven by the cooperative action of the artificial muscle and the electric motor (step S4).

  The artificial muscle drive torque estimation unit 16 calculates the joint torque generated by the artificial muscle based on the current command value of the electric motor measured in step S3 and the current joint angular velocity measurement value in step S4, as a disturbance observer. (Step S5). At this time, the case where friction is generated in the joint, the influence of gravity, and the like are estimated at the same time.

  The joint torque generated by the artificial muscle cannot be directly measured. Therefore, the hybrid joint unit 14 gives, as a current command value for the electric motor, a current value required when the total of the torque desired to be generated by the electric motor and the torque desired to be generated by the artificial muscle is generated only by the electric motor. . Then, the artificial muscle drive torque estimating unit 16 uses the disturbance observer used for disturbance suppression control of the electric motor, so that the torque generated in the artificial muscle at that moment is combined with the disturbance torque caused by friction or the like. presume.

  The mechanism for estimating the driving torque output by the artificial muscle using a disturbance observer together with the disturbance torque caused by friction will be described later. The details of the disturbance observer are described in, for example, Yoichi Hori and Koji Onishi “Applied Control Engineering” (Maruzen Corporation 1998), “Motion Control” by Akira Shimada (Ohm Corporation, 2004) and the like.

  Then, the artificial muscle drive torque estimation unit 16 feeds back to the target torque command from the target joint torque determination unit 11.

  When the hybrid joint unit 14 drives the joint with only artificial muscles, the response speed may be slow. Further, when the hybrid joint portion 14 drives the joint only with the electric motor, the joint torque may be insufficient. Therefore, the hybrid joint unit 14 assists the driving torque by the artificial muscle with the electric motor based on the estimation result of the driving torque by the artificial muscle torque estimating unit 16, or the torques of the artificial muscle and the electric motor antagonize each other. To do.

  When the drive torque estimated by the artificial muscle drive torque estimating unit 16 is insufficient with respect to the target torque (Yes in step S6), the hybrid joint unit 14 determines the drive torque of the artificial muscle estimated in step S5. Then, the torque that is insufficient from the target joint torque is compensated by the electric motor (step S7).

  On the other hand, when the drive torque estimated by the artificial muscle drive torque estimation unit 16 exceeds the target torque (No in step S6), the hybrid joint unit 14 applies reverse torque to the joint with an electric motor. Thus, the torque that the driving torque of the artificial muscle estimated in step S5 exceeds the target joint torque is adjusted (step S8).

  FIG. 4 is a control block diagram for feedback control of the artificial muscle and the electric motor by estimating the output of the artificial muscle and the spring element simultaneously with the disturbance such as the friction of the joint using the disturbance observer. Yes.

Based on the determined target joint torque, the current command value i _aref (i _a ) is input to the electric motor and the artificial muscle, respectively. That is, the current value i _a needed when generating only an electric motor the joint torque desired is given as the current command value for the electric motor.

At this time, a torque T _M corresponding to the current command value i _a and the actual torque constant K _t is generated in the electric motor. The feedback control system can estimate the torque T _Mn according to the current command value i _a and the nominal value K _tn of the torque constant. In addition, the artificial muscle, the torque T _S in accordance with the current command value i _a generated.

The electric motor, the reality with the generated torque T _M of the corresponding to the current instruction value i _a, and the generated torque T _S by artificial muscles, joined by the disturbance torque T _D caused such friction, the electric motor by these total torque The actual machine model 1 / (Js + B) is driven, and the rotational angular velocity dθ / dt of the motor is observed by the sensor. Here, J is the moment of inertia of the electric motor, and B is the viscous resistance coefficient of the electric motor.

On the other hand, the actual moment of inertia J and viscous resistance coefficient B of the electric motor are unknown, and only the nominal values J _{n and} B _n are known. Then, the nominal torque applied to the electric motor is calculated by back-calculating the nominal mechanical model 1 / (J _n s + B _n ) of the electric motor with respect to the measured motor rotation angular velocity. The nominal torque obtained here, the torque generated in the electric motor in accordance with a current command value i _a, and the disturbance torque T _D caused such friction include torque T _S by artificial muscles.

On the other hand, as described above, the torque T _Mn corresponding to the current command value i _a and the nominal value K _tn of the torque constant is estimated. From the applied nominal torque to the electric motor, by subtracting the nominal torque K _tn electric motor corresponding to the current command value i _a, and the disturbance torque T _D caused such friction, the torque generated by the artificial muscle T _S is estimated. In the illustrated control block diagram, a high-frequency component is removed through a low-pass filter (ω _C / (s + ω _C )) to obtain an estimated value of T _D + T _S (where ω _C is a cutoff frequency).

In this way, the disturbance observer can be used to estimate the output torque T _S of the artificial muscle simultaneously with the disturbance torque T _D such as joint friction. When the nominal value of the torque applied to the electric motor is insufficient to the nominal value of the target torque, the estimated value of T _D + T _S is a negative value. When the nominal value of the torque applied to the electric motor exceeds the nominal value of the target torque, the estimated value of T _D + T _S is a positive value.

Then, by calculating back the estimated value of T _D + T _S by the nominal value K _tn of the torque constant of the electric motor, a feedback current for the current command value i _aref determined from the target joint torque is obtained, and this feedback current is obtained as a current command. By subtracting from the value i _aref , the supply current i _a to the electric motor is obtained.

  As described above, the control feedback system shown in FIG. 4 is configured to achieve the target joint torque by the sum of the torque desired to be generated by the electric motor and the torque desired to be generated by the artificial muscle. A current value required when this target joint torque is generated only by the electric motor is given as a current command value for the electric motor. At this time, by using the disturbance observer used for disturbance suppression control of the electric motor, the torque generated in the artificial muscle at that moment is estimated as disturbance torque including disturbance torque caused by friction etc. Can do. Then, feedback control of the electric current supplied to the electric motor so as to cancel the estimated disturbance torque, the hybrid system as a whole obtains sufficient driving torque and realizes highly accurate force control. Can do.

  The electric motor operates so that the driving torque of the artificial muscle is assisted by the electric motor based on the estimation result of the joint driving torque by the disturbance observer, or the torques of the artificial muscle and the electric motor are antagonized.

  The response speed of the artificial muscle is extremely slow compared to the electric motor. When the joint is driven only by the artificial muscle, it takes a long time until the driving torque by the artificial muscle reaches the target torque after the control command is issued. For this reason, as shown in FIG. 5, in the transition period in which the output of the artificial muscle becomes steady, when the target torque and the drive torque of the artificial muscle are compared, the drive torque is insufficient.

  On the other hand, although the response speed of the electric motor is very fast, the torque is often insufficient when the space and weight are limited as in the case of manufacturing a robot hand. Therefore, as shown in FIG. 6, the electric motor outputs a steady torque as the target torque is determined. However, when the target torque is compared with the driving torque of the electric motor, the driving torque remains insufficient.

  In the hybrid system according to the present embodiment, a current value required when the target joint torque is generated only by the electric motor is given as a current command value for the electric motor. FIG. 7 shows the operation characteristics of the artificial muscle and the electric motor in this case. When the drive torque is insufficient due to the slow response of the artificial muscle, the electric motor is quickly operated to compensate for the shortage, as shown in FIG. Therefore, as shown in FIG. 8, the target torque can be realized by the sum of the driving torque obtained by adding the driving torque by the artificial muscle and the driving torque by the electric motor. In this case, the direction of the driving torque generated by the artificial muscle and the direction of the driving torque generated by the electric motor are the same as shown in FIG. 9, and the electric motor assists in driving the artificial muscle.

  On the other hand, when the overshoot occurs in the driving torque of the artificial muscle or the target torque suddenly decreases, the driving torque by the artificial muscle becomes excessive as shown in FIG. In the hybrid system according to the present embodiment, in order to cancel out the excessive drive torque generated by the artificial muscle, the reverse drive torque is generated by the electric motor as shown by the dotted line in FIG. As a result, as shown in FIG. 11, it is possible to control so that the sum of the drive torque by the artificial muscle and the drive torque by the electric motor matches the target torque. In this case, the direction of the driving torque generated by the artificial muscle and the direction of the driving torque generated by the electric motor are opposite to each other as shown in FIG. 12, and the electric motor is in competition with the driving of the artificial muscle. Control can be performed in a unified manner as in the case of assistance (see FIG. 9) without switching in the control system. The only difference between FIG. 9 and FIG. 12 is that the sign of current feedback is reversed in the block diagram shown in FIG.

  The present invention has been described in detail above with reference to specific embodiments. However, it is obvious that those skilled in the art can make modifications and substitutions of the embodiment without departing from the gist of the present invention.

  In the present specification, the embodiment of the present invention has been described by exemplifying a case where the present invention is applied to a robot hand. However, the gist of the present invention is not limited to this. The present invention can be similarly applied to various automatic machines in which it is necessary to perform force control with high accuracy with high responsiveness, and an electric motor cannot obtain sufficient torque.

  In short, the present invention has been disclosed in the form of exemplification, and the description of the present specification should not be interpreted in a limited manner. In order to determine the gist of the present invention, the claims should be taken into consideration.

FIG. 1A is a diagram illustrating a configuration example of a hybrid system that performs joint driving using an electric motor and an artificial muscle in combination. FIG. 1B is a diagram illustrating a configuration example of a hybrid system that performs joint driving using an electric motor and a spring element in combination. FIG. 2 is a diagram showing a functional configuration of a hybrid system having a disturbance observer and a feedback function for the output of the artificial muscle. FIG. 3 is a flowchart showing a processing procedure for driving and controlling the actuators of the electric motor and the artificial muscle in the system shown in FIG. FIG. 4 is a control block diagram for performing feedback control of the artificial muscle and the electric motor by estimating the output of the artificial muscle and the spring element simultaneously with the disturbance such as the friction of the joint using the disturbance observer. FIG. 5 is a diagram showing operation characteristics from when the artificial muscle receives the control command until the drive torque reaches the target torque. FIG. 6 is a diagram illustrating operating characteristics in which the electric motor outputs a driving torque according to the control command. FIG. 7 is a diagram showing the relationship between the artificial muscle and the electric motor when the current value required when the target joint torque is generated only by the electric motor is given as the current command value for the electric motor in the hybrid system according to the present invention. It is the figure which showed the operating characteristic. FIG. 8 is a diagram showing operating characteristics for realizing a target torque with high accuracy by compensating an insufficient driving torque with an electric motor due to a slow response of the artificial muscle in the hybrid system according to the present invention. FIG. 9 shows a state in which the direction of the drive torque generated by the artificial muscle is the same as the direction of the drive torque generated by the electric motor, and the electric motor assists in driving the artificial muscle. FIG. 10 is a diagram showing operating characteristics of the artificial muscle and the electric motor when the overshoot occurs in the driving torque of the artificial muscle or the target torque suddenly decreases in the hybrid system according to the present invention. is there. FIG. 11 is a diagram showing operating characteristics for realizing the target torque with high accuracy by canceling the excessive driving torque generated by the artificial muscle with the electric motor in the hybrid system according to the present invention. FIG. 12 is a diagram illustrating a state in which the direction of the driving torque generated in the artificial muscle is opposite to the direction of the driving torque generated in the electric motor, and the electric motor is antagonizing the driving of the artificial muscle.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Hybrid system 11 ... Target joint torque determination part 12 ... Artificial muscle drive torque control part 13 ... Electric motor drive torque control part 14 ... Hybrid joint part 15 ... Joint angular velocity measurement part 16 ... Artificial muscle drive torque estimation part

Claims (5)

An actuator control device for controlling an actuator for driving a predetermined control object,
A first actuator having a first response speed for driving the control object;
A second actuator that drives the object to be controlled and has a second response speed that is faster than the first response speed;
First actuator driving means for driving the first actuator in accordance with a target driving torque in the control target;
Output estimating means for estimating an output torque of the first actuator;
Second actuator driving means for driving the second actuator according to a difference between a target driving torque and the output torque estimated by the output estimating means;
An actuator control device comprising: The first actuator is composed of an artificial muscle or a spring element, and the second actuator is composed of an electric motor.
The actuator control apparatus according to claim 1. The output estimating means estimates an output torque of the first actuator by a disturbance observer;
The actuator control apparatus according to claim 1. It further comprises a state measuring means for measuring the drive state of the controlled object,
The output estimating means estimates an output torque of the first actuator based on a control command value to the second actuator by the second actuator driving means and a measurement result by the state measuring means;
The actuator control apparatus according to claim 1. The total of the torque desired to be generated by the second actuator and the torque desired to be generated by the first actuator is given to the second actuator as a command value required when the torque is generated only by the second actuator. The output estimating means estimates a torque generated by the first actuator at the moment together with a disturbance torque using a disturbance observer.
The actuator control apparatus according to claim 1.

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