JP2010069584A - Device and method for controlling manipulator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device and a method for controlling a manipulator in which a multi-finger hand can be suitably controlled for gripping or conveying an object by carrying out switching between position control and force control individually for each finger of the multi-finger hand in accordance with a moving state of an arm with the hand being attached to a distal end thereof. <P>SOLUTION: The device for controlling the manipulator includes the multi-finger hand having a plurality of the fingers respectively provided with a force sensor 18 at an end thereof, and the arm with the multi-finger hand being attached to the distal end thereof. An arm controlling part 1 outputs at least one of acceleration, a velocity and a moving distance of an end part of the arm as the moving state of the arm, and a position and posture of the end part of the arm to a multi-finger hand controlling part 2. The multi-finger hand controlling part 2 includes finger controlling parts 51, 52, 53 for performing the position control or the force control in accordance with an output from the force sensor for each finger, and a control mode selection part 4 for directing switching of control between the force control and the position control to the finger controlling parts 51, 52, 53 in accordance with the moving state of the arm. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to control of a manipulator, and more particularly to control of a manipulator that includes an arm and a multi-finger hand and performs an object gripping operation with the multi-finger hand.

Conventionally, an apparatus for gripping an object with a multi-fingered hand including a plurality of fingers has been disclosed.
As a method for controlling such a multi-fingered hand, there is a method in which position control and force control are switched according to the gripping state of an object by the multi-fingered hand (see, for example, Patent Document 1). In addition, when a target is gripped by cooperative control of a plurality of fingers, there is a case where the control mode of each finger is switched to compliance control or force control (see, for example, Patent Document 2).
In the conventional multi-finger hand control method, a procedure is adopted in which the object is gripped by switching the entire hand or the control mode of each finger according to the gripping state of the object or the operation state of the hand.
Japanese Patent Laid-Open No. 6-126684 (page 6, FIG. 3) JP-A-8-141951 (5th page, FIG. 2)

However, although the multi-fingered hand is often used by being attached to the tip of an arm or the like, the prior art has not considered the operating state of the arm to which the multi-fingered hand is attached. For this reason, optimal object gripping corresponding to the operating state of the arm has not been performed.
On the other hand, by force-controlling each finger of a multi-fingered hand, even if the shape and position of the object to be grasped are unknown, the finger can flexibly operate to grasp the object and maintain the grasping force it can. However, when acceleration is applied to the multi-fingered hand or the object to be grasped when moving or transporting the object once grasped by the movement of the arm, the finger whose force is controlled by its inertial force will be affected, and the grasping state Has the disadvantages of becoming unstable and the object in the hand moving.
The present invention has been made in view of such problems, and switches position control and force control for each finger of a multifingered hand according to the operating state of an arm with the hand attached to the tip, An object of the present invention is to provide a control method and apparatus capable of controlling a multi-fingered hand suitable for conveyance.

In order to solve the above problem, the present invention is as follows.
The invention according to claim 1 is a manipulator control device comprising a multi-finger hand having a plurality of fingers each provided with a force sensor at the tip, and an arm having the multi-finger hand attached to the tip. The apparatus includes an arm control unit that controls the arm and a multi-finger hand control unit that controls the multi-finger hand, and the arm control unit sets the arm as an operation state of the arm with respect to the multi-finger hand control unit. At least one of acceleration, speed, or moving distance of the tip of the arm and the position and orientation of the tip of the arm, and the multi-finger hand control unit responds to position control or output of the force sensor for each finger. Instructs the finger control unit to switch between force control and position control by comparing the finger control unit performing force control and the operating state of the arm with a predetermined threshold value for each. It is characterized in further comprising a control mode selection section.
The invention according to claim 2 is characterized in that the finger control unit outputs a position correction amount of the finger based on a target force command and the magnitude and direction of the force detected by the force sensor; The position control unit that controls the position of the finger based on the target position command and the position information detected by the position detector that detects the position of each joint of the finger, and the switching command from the control mode selection unit A control mode changeover switch for adding a position correction amount output from the force control unit to the target position command is provided.
According to a third aspect of the present invention, the control mode selection unit groups the plurality of fingers whose direction of the force detected by the force sensor is within a predetermined range, and sets the grip side and the support side. It is divided into two groups, and the switch to the force control is instructed to the finger control unit on the holding side, and the switch to the position control is instructed to the finger control unit on the support side.
According to a fourth aspect of the present invention, the arm is a vertical articulated robot having a plurality of joints.
According to a fifth aspect of the present invention, there is provided a manipulator control method comprising: a multi-finger hand having a plurality of fingers each provided with a force sensor at a tip portion; and an arm having the multi-finger hand attached to the tip. Position control for each finger and force control according to the output of the force sensor according to at least one of acceleration, speed or moving distance of the tip of the arm and the operating state of the arm including the position and orientation of the tip of the arm The control is performed by switching between and.
The invention according to claim 6 groups the fingers whose direction of the force detected by the force sensor is within a predetermined range, and divides them into two groups, a grip side and a support side, The gripping finger is operated by switching to force control, and the supporting finger is operated by switching to position control.

According to the first aspect of the present invention, the control of each finger of the multi-fingered hand is appropriately switched to position control or force control according to the operating state of the arm, and the multi-fingered hand or the gripping object is received by the arm operation. It is possible to prevent the gripping state from being disturbed by the inertia force and to stabilize the gripping state.
According to the invention of claim 2, the control of each finger of the multi-fingered hand can be immediately switched between the force control and the position control, and a stable gripping state corresponding to the operating state of the arm is realized. be able to.
According to the third aspect of the present invention, the support-side finger is fixed by switching the support-side finger from the force control to the position control, and is based on the inertial force that the multi-finger hand or the gripping object receives as the arm moves. It can be made unaffected.
According to the fourth aspect of the present invention, it is possible to allow the multi-fingered hand and the object to be gripped to take various positions and postures in a stable gripping state.
According to the fifth aspect of the present invention, the control of each finger of the multi-fingered hand is appropriately switched to position control or force control according to the operating state of the arm, and the multi-fingered hand or the gripping object is received by the arm operation. It is possible to prevent the gripping state from being disturbed by the inertia force and to stabilize the gripping state.
According to the sixth aspect of the present invention, the support side finger is fixed by switching the support side finger from the force control to the position control, and the inertial force received by the multi-fingered hand or the gripping object in accordance with the operation of the arm. You can avoid being affected by.

  Hereinafter, specific examples of the method of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing an example of the appearance of a manipulator and its control device according to the present invention. The manipulator includes an arm and a multi-fingered hand having three fingers attached to the tip of the arm, and the arm and the hand are controlled by a control device.
The arm is an articulated robot. Furthermore, it must be a vertical articulated robot so that the position and posture of the multi-fingered hand can be adjusted freely when the multi-fingered hand approaches the gripping object or moves the gripping object while maintaining the gripping state. Is desirable.
FIG. 2 is an enlarged view of the hand portion of FIG. Each finger of the hand has a plurality of joint axes, and each joint is operated by a drive source such as a servomotor. By such a plurality of fingers operating in a coordinated manner, it is possible to grasp the grasped object or change the posture of the object while keeping the object grasped. FIG. 2 shows an example in which each finger has two joints.
Further, a force sensor 18 is provided at the tip of each finger, and the magnitude and direction of the force acting on the fingertip when the object to be grasped is grasped can be detected.
The number of fingers of the hand and the number of joints of each finger shown in FIGS. 1 and 2 are examples, and the number of fingers of the hand and the number of joints of each finger can be changed as appropriate.

FIG. 3 is a schematic diagram of a portion related to a function of switching position control and force control for each finger of the multi-fingered hand in accordance with the operation state of the arm in the configuration in the control device. The inside of the manipulator control device is divided into an arm control unit 1 and a multi-finger hand control unit 2. The multi-finger hand control unit 2 is further divided into control units 51, 52, and 53 for the first finger, the second finger, and the third finger, which control the operations of the first finger, the second finger, and the third finger, respectively. ing.
In addition to the position and orientation of the arm tip based on the reference coordinate system of FIG. 1, the arm controller 1 periodically outputs the arm tip speed information as the arm operating state 3 to the multi-finger hand controller 2. . White arrows extending from the arm control unit 1 indicate exchange of signals with the drive sources and encoders of the joints of the arms.
The multi-finger hand control unit 2 receives information about the arm operating state at the control mode selection unit 4, and the control mode selection unit 4 selects either position control or force control for each finger control mode based on the information. Then, the control mode of the control unit of each finger is switched (arrow 24 in FIG. 3). The control units 51 to 53 of each finger drive the finger by one of the control modes selected by the control mode selection unit 4, that is, position control or force control. White arrows extending from each finger control unit indicate signal exchange with the drive source, encoder, and force sensor of each finger of the multi-finger hand. Details will be described with reference to FIG.

FIG. 4 is a schematic diagram showing the internal configuration of the first finger control unit 51 in FIG. In the figure, the position control unit 11 generates a command to the drive source 14 based on the feedback target position 12 obtained from the follow target position 12 and the encoder 15 which is a position detector provided in the drive source 14 of the first finger. Take control.
On the other hand, the force control unit 17 generates a position correction amount 21 on the basis of force information (magnitude, direction) 19 and target force command 20 detected by the force sensor 18 provided at the fingertip of the first finger. The force control is configured by adding the target position command 22 to the follow-up target position 12 described above. The target force command 20 and the target position command 22 are commands sent to the multi-finger hand control unit 2 from an operation program or the like (not shown) of a host device that determines the operation of the manipulator.
If the control mode changeover switch 23 is closed and the position correction amount 21 output from the force control unit 17 is added to the target position command 22, the first finger is operated by force control. If the control mode changeover switch 23 is opened, the first finger operates by position control.
The control mode selection unit 4 switches between position control and force control for the first finger by controlling opening and closing of the control mode changeover switch 23.
The second finger control unit 52 and the third finger control unit 53 have the same configuration as that of the first finger control unit 51, and the control mode selection unit 4 switches the control mode in 51, 52, and 53 of each finger control unit. Switching between position control and force control is performed for each finger by individually controlling the opening and closing of the switches.
When the multi-fingered hand tries to grasp an object while the arm is stationary or moves at a low speed in a narrow range, all the fingers of the multi-fingered hand may be operated by force control as in the past.

FIG. 5 is a conceptual diagram illustrating a method for determining a combination of a finger operated by position control and a finger operated by force control among the three fingers in the control mode selection unit 4. FIG. 5 shows a state in which a rectangular parallelepiped object is grasped with a multi-fingered hand as seen from the direction of the white arrow in FIG.
The control mode selection unit 4 sets a pair of opposing fingers when gripping an object to be gripped by a multi-fingered hand, selects force control as one control mode of the pair, and performs position control on the other opposing face. select.
In order to perform such control, the control mode selection unit 4 checks the direction of the force acting for each finger from the output of the force sensor 18 of each fingertip, and sets a pair of opposing fingers. Therefore, the control mode selection unit 4 acquires the value of the encoder 15 of each finger, performs forward conversion to obtain the position and posture of each fingertip, and further acquires force information from the force sensor.
By converting the direction of the force detected by the force sensor provided on the fingertip according to the posture of the fingertip, the direction of the force based on the reference coordinate system can be known as shown in FIG.

In the case of FIG. 5A, the direction of the force detected by the force sensor of the second finger and the third finger is the same, so the second finger and the third finger are put together and the remaining first finger is moved. It is determined that the finger is opposite to this.
When setting a pair of fingers, the direction of the force detected by the force sensor of the second finger and the third finger does not have to be exactly the same, as long as the difference in the direction of the force is within a preset range Consider the same direction.
When the object is held between the first finger and the second and third fingers opposed to the first finger as shown in FIG. 5A, the first finger is moved by position control, while the second finger and the third finger The finger is operated by force control, and a force is generated by the second and third fingers.
Since the first finger operates by position control that keeps its position even when it receives a force, it functions as a support finger that supports the force generated by the second and third fingers and generates a reaction force. As a result, the same effect is obtained as when the first finger to the third finger are force-controlled to generate a force of facing and balancing as shown in FIG. 5B.
In addition, in FIG. 5 (a), some fingers are position controlled, so even if the hand or gripping object receives acceleration due to the movement of the arm to which the hand is attached and the inertial force is generated, it operates with position control. There is an advantage that the finger that is functioning as a supporting finger can maintain a gripping state by generating a reaction force that opposes the inertial force. When force control is performed on all fingers as shown in FIG. 5B, when the inertial force is generated, the finger is moved by the force, but in the case of FIG. Absent.

In FIG. 5, a rectangular parallelepiped in which a pair of opposing fingers is easily set depending on the direction of the force acting on each finger has been described as the gripping object. However, in the present invention, the direction of the force acting on each finger is different. It can also be applied to.
When gripping a sphere (or cylinder) as shown in FIG. 6, one finger (for example, the first finger) is operated by position control, and the remaining fingertips (second finger, third finger) are Operate by force control.
At this time, the force detected by the force sensor of each fingertip of the second finger and the third finger is decomposed into a component orthogonal to a component parallel to the direction of the force detected by the force sensor of the first finger and parallel. Assuming these components as a pair as shown in FIG. 5, control can be performed in the same manner as in FIG.

In this way, for each finger of the multi-fingered hand that grips an object, the gripping force is increased by giving a different function to a finger that generates force by force control and a finger that functions as a support finger by position control. Even if the inertia force is generated by the movement of the arm, the grip state can be maintained while suppressing the disturbance of the grip state.
Further, the control mode selection unit 4 controls the finger on the support side again according to the operation state 3 of the arm even after the fingers opposed to each other across the object are divided into the grip side and the support side when gripping the object. The mode can also be switched between force control and position control.

FIG. 7 is a schematic diagram showing the internal configuration of the control mode selection unit 4.
As described above, in addition to the position and orientation of the arm tip based on the reference coordinate system of FIG. 1 as the arm operating state 3, speed information of the arm tip is periodically provided.
The control mode selection unit 4 obtains the movement direction and acceleration of the arm tip from the calculation unit 25 based on changes in the position and orientation and speed of the arm tip. Further, the movement distance may be obtained by the calculation unit 25. On the other hand, the coordinate conversion unit 26 obtains the position of each finger of the multi-finger hand based on the reference coordinate system based on the feedback position 16 obtained from the encoder 15 of each joint of the finger and the position and orientation of the arm tip.
The threshold value storage unit 27 stores a preset speed threshold value, acceleration threshold value, and movement distance threshold value, and the comparison unit 28 compares these threshold values with the speed of the arm tip and the acceleration obtained by the calculation unit 25. When the speed, acceleration, and movement distance related to the operation of the arm exceed the respective threshold values or become smaller than the threshold values, the comparison unit 28 outputs a command to the switching command unit 29 and receives the command. 29 switches the control mode of the finger operating by force control to position control, and conversely switches the control mode of the finger operating by position control to force control.
At this time, the switching command unit 29 acquires the movement direction of the arm tip based on the reference coordinate system from the calculation unit 25, and acquires the position of each finger of the multi-fingered hand viewed from the reference coordinate system from the coordinate conversion unit 26. Determine which finger control mode to switch.

In this embodiment, the arm control unit 1 outputs the speed of the arm tip part to the multi-finger hand control unit 2 in addition to the position and orientation of the arm tip part based on the reference coordinate system of FIG. However, by realizing the function of the calculation unit 25 in the control mode selection unit 4 in the arm control unit 1, the arm tip state acceleration may be output as the arm operation state.
The movement distance of the arm tip may also be output from the arm control unit 1 to the multi-finger hand control unit 2 as the arm operating state 3.
Further, as the arm operating state 3 other than the position and orientation of the arm tip outputted from the arm control unit 1 to the multi-finger hand control unit 2, the acceleration, speed, and movement distance of the arm tip may be used together. Only one of acceleration, speed, and movement distance of the tip may be output.

As shown in FIG. 8, a case will be described as an example where the object to be grasped is moved from the bottom (point a in the figure) to the top (point b in the figure) by the operation of the arm while being grasped by the multi-finger hand. FIG. 9 shows a state in which a rectangular parallelepiped object is grasped with a multi-fingered hand as seen from the direction of the white arrow in FIG.
When the multi-fingered hand that grips the gripping object starts to move upward from the state of stopping at point a and the movement speed increases, a downward inertial force acts on the gripping object. Therefore, in order to realize a stable gripping state, it is desirable to support the gripping object by performing position control with the finger under the gripping object.
The control mode selection unit 4 acquires the position / attitude and speed of the arm tip based on the reference coordinate system of FIG. 1 as the arm operation state 3 from the arm control unit 1. Further, the position of each finger tip is acquired from the finger control sections 51 to 53 of each finger.
The control mode selection unit 4 faces which finger supports the object to be grasped from below and which finger supports the object to be grasped from below based on the position and orientation of the arm tip and the position of each finger tip. And the acceleration is obtained from the change in the speed of the arm tip. When the acceleration at the arm tip exceeds a preset first threshold, the control mode of the finger supporting the object to be gripped from below is switched to position control, and the control mode of the finger holding the object to be gripped from above is applied. Switch to control.
FIG. 9A shows this state. The control mode of the second finger and the third finger supporting the grasped object from below is position control, and the control mode of the first finger holding the grasped object from above is force control.

As the gripping object continues to move and approaches point b, the movement speed of the arm tip starts to decrease to stop. Then, an upward inertia force acts on the grasped object. Therefore, in order to realize a stable gripping state, it is desirable to support the gripping object by performing position control with a finger on the gripping object.
Similarly to the previous step, the control mode selection unit 4 obtains the position and orientation and speed of the arm tip based on the reference coordinate system of FIG. 1 as the arm operation state 3 from the arm control unit 1. Further, the position of each finger tip is acquired from the finger control sections 51 to 53 of each finger. Since this time the vehicle is decelerating, the acceleration at the arm tip is negative.
The control mode selection unit 4 faces which finger is holding the object to be grasped from above and which finger is holding the object to be grasped from above based on the position and orientation of the arm tip and the position of each finger. And the acceleration is obtained from the change in the speed of the arm tip. When the acceleration at the tip of the arm becomes smaller than a preset second threshold value, the control mode of the finger holding the grasped object from above is switched to position control, and the control mode of the finger supporting the grasped object from below is changed. Switch to force control.
This state is shown in FIG. 9 (b). The control mode of the first finger holding the grasped object from above is position control, and the control mode of the second and third fingers supporting the grasped object from below is force control.

In the above example, the direction of the inertial force was derived by obtaining the acceleration based on the speed of the arm tip from the information on the arm operating state, but the arm tip per unit time was derived from the information on the position of the arm tip. The inertial force can be derived in the same manner by obtaining the movement distance of the part and obtaining the change.
Further, if the acceleration, speed, and moving distance of the arm tip are used in combination, the inertial force acting on the grasped object can be derived more appropriately. As described above, if the speed of the arm tip is equal to or less than a predetermined value, the comparison unit does not give an instruction to the switching command unit and operates all fingers by force control without switching between force control and position control. You may do it.
Also, the movement in the vertical direction as shown in FIG. 8 is merely an example of the movement direction of the multi-fingered hand by the arm operation. It is suitable for various arm movements by identifying the finger on which the inertial force acts with the movement of the arm tip, switching the finger to position control, and switching the opposing finger to force control. Needless to say, the gripping state can be maintained.

When the arm equipped with a multi-fingered hand is stationary, if the object to be grasped is gripped by the movement of the finger of the hand or is manipulated after gripping, all fingers are flexibly operated by force control However, if the gripping object is moved by the arm movement while holding the gripping object after gripping the gripping object, a force to keep the gripping state against the inertial force generated by the arm movement is generated. It is necessary to make it.
Therefore, as described above, changing the control mode of some fingers of the multi-fingered hand according to the operating state of the arm is an effective means for controlling the manipulator composed of the arm and the multi-fingered hand.

  The present invention can be widely applied to manipulators having a multi-finger hand provided with a force sensor at the tip.

The figure which shows the example of an external appearance of the manipulator of this invention, and its control apparatus The figure which expanded the hand part of FIG. Schematic which shows the structure in the manipulator control apparatus of this invention. Schematic showing the configuration of the finger control unit of the present invention The conceptual diagram explaining the method of determining the combination of the finger operated by position control and the finger operated by force control in the present invention Another conceptual diagram for explaining a method of determining a combination of a finger operated by position control and a finger operated by force control in the present invention Schematic showing the internal configuration of the control mode selector The figure which shows a mode that a gripping target object is moved while holding with a multi-fingered hand The conceptual diagram explaining the method of determining the combination of the finger operated by position control and the finger operated by force control according to the operating state of the arm in the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Arm control part 2 Multi-finger hand control part 3 Arm operation state 4 Control mode selection part 11 Position control part 12 Following target position 13 Drive part 14 Drive source 15 Encoder 16 Feedback position 17 Force control part 18 Force sensor 19 Force information 20 Target Force command 21 Position correction amount 22 Target position command 24 Control mode switching command 25 Calculation unit 26 Coordinate conversion unit 27 Threshold storage unit 28 Comparison unit 29 Switching command unit 51 First finger control unit 52 Second finger control unit 53 Third finger control Part

Claims (6)

In a control device for a manipulator comprising a multi-finger hand having a plurality of fingers each provided with a force sensor at the tip, and an arm with the multi-finger hand attached to the tip.
The control device includes an arm control unit that controls the arm and a multi-finger hand control unit that controls the multi-finger hand,
The arm control unit outputs to the multi-finger hand control unit at least one of an acceleration, a speed, or a moving distance of the tip of the arm as a movement state of the arm, and a position and orientation of the tip of the arm;
The multi-finger hand control unit includes a finger control unit that performs position control or force control according to the output of the force sensor for each finger, and the acceleration, speed, or speed of the tip of the arm among the operating states of the arm. Control of a manipulator comprising a control mode selection unit that commands the finger control unit to switch between force control and position control by comparing at least one of the movement distances with a predetermined threshold value for each. apparatus. The finger control unit outputs a finger position correction amount based on a target force command and the magnitude and direction of the force detected by the force sensor;
A position control unit that controls the position of the finger based on a target position command and position information detected by a position detector that detects the position of each joint of the finger;
2. The manipulator control device according to claim 1, further comprising a control mode switching switch that adds a position correction amount output from the force control unit to the target position command in response to a switching command from the control mode selection unit. The control mode selection unit groups the fingers whose direction of the force detected by the force sensor is within a predetermined range and divides them into two groups, a grip side and a support side,
Instruct the finger control unit on the grip side to switch to force control,
2. The manipulator control device according to claim 1, wherein the support side finger control unit is instructed to switch to position control.   The manipulator control device according to claim 1, wherein the arm is a vertical articulated robot having a plurality of joints. In a control method of a manipulator comprising a multi-finger hand provided with a plurality of fingers each provided with a force sensor at the tip, and an arm with the multi-finger hand attached to the tip.
According to the position control and the output of the force sensor for each finger according to at least one of the acceleration, speed or movement distance of the tip of the arm and the operating state of the arm including the position and orientation of the tip of the arm A control method for a manipulator characterized by switching between force control and control.   Of the plurality of fingers, those in which the direction of the force detected by the force sensor is within a predetermined range are grouped into two groups, a grip side and a support side, and the fingers on the grip side are switched to force control. 6. The manipulator control method according to claim 5, wherein the support side finger is operated by switching to position control.

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