JPH0469184A - Control method for hold of robot hand - Google Patents

Abstract

PURPOSE:To surely hold a robot hand and holding object without damaging them, by generating the holding power of the hext stage in order whenever the holding power of a finger having more than one joint reaches each stage of the holding power in plural stages teached in advance. CONSTITUTION:After moving an arm to a preteached position, plural fingers are actuated until a 1st holding power P0 in the preset holding powers in plutal stages is detected, while monitoring the output of a holding power detector which each finger receives and the holding motion is performed by changing over to the set value of the holding power P2 of the next stage, after all fingers reaching the 1st holding power P1. Therefore the finger brought into contact with a holding object first becomes standing by until the other finger detects the specified holding power and it can correctly hold the holding object in a preteached posture.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a grasping control method for a robot hand, and more specifically, when an object to be grasped by the robot hand is moved to a position different from a previously taught position. The present invention relates to a gripping control method for a robot hand that allows a robot hand to correctly grip an object even when the object is in a different position.

[Prior Art] When a robot is made to perform a certain action, it is common to teach the order and content of the action in advance, store it in a storage device in a control device, and then read out the stored content sequentially. . However, the location of the object of work performed by the robot is not necessarily the same as in the teaching stage;
It often has some deviation. Particularly in automated production lines, where work objects are brought in by adjacent robots or belt conveyors, it is important from the perspective of improving productivity to take into account some degree of deviation and use equipment that can handle it. It is.

In addition, robots are often used as so-called hand robots that grasp and move objects, and various types of multi-joint robot hands are used.

For example, Japanese Patent Application Laid-Open No. 62-124891 r Automatic Gripping Device discloses a robot hand that has three fingers arranged at each vertex of an isosceles triangle and is capable of grasping objects of various shapes. ing.

However, in the robot hand according to the present invention, if the position of the object to be grasped deviates from the previously taught position, the object cannot be grasped in an accurate position and posture, and the object and robot There is a possibility of damaging the hand itself.

As a method to enable reliable gripping even if the object to be gripped deviates from the previously taught position,
For example, JP-A-62-139006 "Robot control device"
There is.

According to this invention, as shown in FIG. 6, the robot hand is provided with a sensor that detects the relative position of the object and the robot hand, and the position of the robot hand is appropriately corrected based on the deviation in the position of the object. Accurate gripping becomes possible.

As another method, as shown in FIG. 7, it is also possible to measure the positions of the object and the robot hand using a television camera, and perform a corrective action of the robot hand.

[Problem M to be solved by the invention] However, in the above method, a sensor or a television camera and an image processing device are required, but in order to accurately measure minute positional deviations, the device not only becomes complicated. , economic problems arise.

Therefore, in view of the above-mentioned problems, the present invention aims to accurately grasp the robot hand and the object to be grasped using an inexpensive device even when the position of the object to be grasped deviates from a previously taught position. The purpose of this invention is to provide a grasping control method for a multi-fingered robot hand.

C Means for Solving the Problem] The present invention was made by focusing on the fact that in automatic production lines, the object to be grasped by the robot hand is often set up by an adjacent robot or a belt conveyor. As long as it is within the range of motion of the fingers, accurate gripping is possible even if the position of the object to be gripped deviates from a previously taught position.

That is, each time a finger having one or more joints of a multi-fingered robot hand having a plurality of fingers having one or more joints reaches each stage of the multiple stages of gripping force taught in advance, the gripping force of the next stage is sequentially increased. to occur.

[Function] In this grip control method for a robot hand, after the arm is moved to a pre-taught position, multiple fingers are moved to a predetermined position while monitoring the output of the grip force detector that each finger receives. It operates until the first gripping force is detected among the multiple levels of gripping force, and after all the fingers reach the first gripping force, the gripping force is switched to the set value of the next level of gripping force and the gripping operation is performed. Therefore, the finger that first contacts the gripping object waits until the other fingers detect a predetermined gripping force, and accurately grips the gripping object in the previously taught posture.

[Example] FIG. 1 is a diagram showing an example of a robot hand attached to the tip of arm A of a robot.

This robot hand has three joints 211.21 each.
The first finger 21 and the second finger 22 are arranged so that their central axes are parallel to each other, and the third finger 23 is sandwiched between them. The central axis is arranged at 20 to 60 degrees with the central axes of the first finger and the second finger, and the fingertips are arranged to face the fingertips of the first finger and the second finger.

In Fig. 2, each finger 21.22.2 of the above robot hand is shown.
3 shows the configuration of a control device for each joint 211, 212, and 213 of No. 3.

Also, 1I in Figure 3! 1 shows the configuration of the entire control device of the robot hand shown in FIG.

That is, the robot hand shown in Fig. 1 is composed of three fingers each having three joints, but the control device for each joint is modularized, and the joint control device shown in Fig. 2! The three finger control devices constitute a finger control device corresponding to one finger, and the three finger control devices and the robot hand control device constitute a control device for the entire robot hand.

As shown in FIG. 2, the control device for each joint is such that the driving force of the electric motor 70 is transmitted from a drive pulley 72 attached to the shaft of the electric motor 70 via a reducer 71 to a wire rope 73 serving as a driving force transmission means. The signal is transmitted to a joint pulley 74 fixed to a link mechanism 75 of the joint.

The gripping force received by the joint pulley 74 is
The torque is detected by a torque detector (not shown), such as a strain gauge, installed on a beam-shaped steel piece 77 that fixes the idler pulley 76, which is installed approximately halfway between the joint pulley 74 and the joint pulley 74. The rotation angle is determined by the angle sensor 7 attached to the joint pulley 74.
Detected at 8.

The output of this angle sensor 78 is compared with the angle target value 83, and the deviation between the two is multiplied by a virtual spring constant in a multiplier 84 to obtain a virtual torque command 92.

That is, in order to simultaneously control the angle and torque of the joint, a virtual spring constant is provided that adjusts the ratio of angle control and torque control.

The virtual torque command is added to a torque target value 85 to become a torque command 86, and a corrected torque command 87 is calculated from the deviation from the output of a torque detector attached to a beam-shaped steel piece 77, and is input manually to a compensator 88.

The compensator 88 adjusts the current command value 80 based on the corrected torque command 87 and the estimated motor rotational speed 91. Based on this current command value 80, the output current of the variable constant current source 79 is controlled, and the driving force of the electric motor is controlled.

The compensator 88 calculates the estimated motor rotation speed from the motor voltage 89 and the current command value 80 based on the following.

When the rotor inductance of the motor can be ignored, the following equation holds.

Nm = (Vg-Im-Rm)/Kv (1) where Nm: Estimated motor rotation speed Vg: Actual motor terminal voltage Im: Variable current source output current Rm: Motor rotor resistance Kv: Motor back electromotive force constant Since the variable current source 79 has constant current characteristics, the variable current source output current 1m is maintained at a constant current value proportional to the current command value 80 (Imt) even if the motor load fluctuates. Since the rotor resistance Rm and the back electromotive force constant KV of the motor are known, it is possible to calculate the estimated motor rotation speed from the sixth order equation.

Nm= (Vg-a ・Imt-Rm)/K (2) where α: proportional constant of variable constant current source By using this compensator 88, it is possible to use a rotation speed sensor such as a conventionally used tachometer. It becomes possible to configure a stable control system by applying damping to the joint control system.

In the gripping control device for a robot hand according to the present invention, the rotation angle command of each joint output from the robot hand control device 5 and, for example, a two-step torque target value, that is, a command for detecting contact with an object to be gripped. The first torque target value, the second torque target value for reliably gripping the object to be gripped, and the output of the torque detector attached to the beam-shaped steel piece 77 are input, and each of the above-mentioned joint control devices A gripping control device 16 that outputs a target angle value 83 and a target torque value 85 is additionally provided.

FIG. 4 is a diagram showing the principle of positioning of the robot hand according to the present invention.

That is, the initial position of the finger is P. , let P be the grasping position when the robot hand is taught the motion, then P before starting the motion to grasp the object to be grasped.

A virtual gripping position P is calculated based on P3.

For example, the position where the fingers are most closed on the straight line connecting Po and P3 can be set as P4.

In addition, if the deviation between the robot hand and the object to be grasped is large and the finger does not come into contact with the object to be grasped even if the fingers are moved, the Pa
It is also possible to replace other points on the bottom of the cone whose apex is with the straight line connecting Po and P3 as the virtual gripping position P4, and to move the finger from Po toward the virtual gripping position P again. .

Note that Pl and P2 respectively indicate the current position of the finger and the position where the finger contacts the grasped object.

The output of the torque detector is monitored while moving the finger, and when the detected torque becomes equal to the first target torque value, it is determined that the object to be grasped has been contacted, and the target torque value is set to the second target torque value. to securely grip the object to be gripped.

FIG. 5 is a diagram showing a gripping control routine executed for one joint by the gripping control device 16.

In step 401, the initiality f of the robot hand! fP.

A virtual gripping position P is based on the gripping position P3 taught in advance.
Calculate the coordinates of 4. The coordinates of P4 are determined in the direction in which the robot hand is closed relative to the grasping position P3 taught in advance, and the object to be grasped is located in either the direction in which the fingers are opened or closed from the grasping position P3 taught in advance. It is designed so that it can be grasped even if it is displaced.

In step 402, the initial position P is set as the rotation angle target value 83 of the joint control system. A rotation angle corresponding to the movement from to the virtual gripping position P4 is set, a first torque target value predetermined as the torque target value 85 is given, and the fingers of the robot hand move in the closing direction. In step 403, the output of the torque detector installed on the beam-shaped steel piece 77 is read, and in step 404, it is determined whether the current torque detected by the torque detector is greater than a preset first torque target value. It will be judged. If a negative determination is made in step 404, it is determined that the robot hand is not in contact with the object to be grasped, and the process returns to step 402 to continue the movement of the fingers in the closing direction. If an affirmative determination is made in step 404, it is determined in step 405 whether all fingers have reached the first torque target value.

Steps 402 to 404 are executed for fingers that have not reached the first torque target value, and the closing direction movement of the fingers is stopped in step 406 for fingers that have reached the first torque target value. Then, in step 407, a second torque target value, which is predetermined in order to reliably grip the object to be gripped, is set as the torque target value, and gripping torque is generated.

Note that the first torque target value and the second torque target value are determined as follows.

That is, at the stage of teaching the robot hand how to operate, the torque required to reliably grip the object to be gripped is set as the second torque target value, and contact with this value can be reliably detected, and when contact is made, It is possible to determine the first torque target value by multiplying it by a certain percentage so as not to damage the grasped object, and it is also possible to modify this percentage while the robot hand is operating. Therefore, the time required for the teaching stage can be significantly shortened.

In this embodiment, the torque target value is switched to two levels, but it is also possible to sequentially switch to three or more levels of target values.

Further, the torque target value can be set to a different target value for each joint of each finger in relation to the center of gravity of the object to be grasped.

Further, in this embodiment, the gripping force applied to each joint of each finger is detected by a torque detector, but the gripping force can also be detected by a pressure sensor attached to the fingertip or a strain gauge that detects the stress in each part. The present invention can be similarly applied to this case as well.

[Effects of the Invention] According to the present invention, even if the object to be grasped is displaced from a previously taught position, the fingers of the robot hand are moved toward the virtual grasping position, and each part of the robot hand is moved to the virtual grasping position. By sequentially comparing the gripping force with target values set in multiple stages, and switching to the next target value each time each part reaches this target value, the gripping force is ensured without damaging the robot hand or the gripping target. It becomes possible to hold the

[Brief explanation of drawings]

1 is a diagram showing an example of a robot hand, FIG. 2 is a diagram showing the configuration of the joint control device of the embodiment, FIG. 3 is a diagram showing the configuration of the entire control device of the robot hand of the embodiment, and FIG. 5 is a flowchart showing the gripping control operation of the present invention, FIG. 6 is a diagram showing the first example of the conventional gripping control method, and FIG. 7 is the conventional gripping control method. FIG. 6 is a diagram illustrating a second example of the method.

Claims (1)

[Scope of Claims] 1. A gripping control method for each finger when gripping an object with a multi-fingered robot hand having a plurality of fingers each having one or more joints, the method comprising: A gripping control method for a multi-fingered robot hand, characterized in that each time the gripping force of the fingers reaches each of multiple stages of gripping force taught in advance, the gripping force of the next stage is sequentially generated. .