JP3439935B2 - Work holding device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention grasps a workpiece by making a pair of fingers attached to the tip of a robot arm parallel to each other and varying the separation distance. The present invention relates to a work gripping device adapted to perform such operations. 2. Description of the Related Art In a work holding apparatus of this type, in order to stably hold a work, a positioning jig for imaging a work with a camera and holding the work at a regular holding position is provided on a finger thereof. For example, a special shape is formed in accordance with the shape of the work, and the cost remains a problem. SUMMARY OF THE INVENTION In view of the foregoing, the present invention is to grasp a work of various shapes with a simple structure by a pair of fingers parallel to each other without difficulty. ,
It is an object of the present invention to provide a work holding device that can move with accurate positional accuracy. In order to achieve this object, according to the present invention, according to the first aspect, a workpiece is gripped by changing the distance between the ends of a robot arm in parallel with each other. In a work gripping device in which a pair of flat inner surfaces on both sides are attached via a driving mechanism driven by an associated actuator, the pair of fingers on both sides opposed to each other can slide in the facing direction. The work contact plate is supported in a state where it is urged outward by a spring, and a load sensor that detects the load applied to the work contact plate as a gripping force is separated from one of the work contact plates in the finger direction. One load sensor is provided on the other work contact plate to detect the load applied to the work contact plate as a gripping force. In addition to performing the opening / closing operation, actuator control means for driving a corresponding actuator in accordance with a deviation between the gripping force detected by the load sensor and the set gripping force set in the gripping force setting means, and detection of the load sensor In response to the signal, it is detected that one of the fingers first comes in contact with the work, and the actuator control means interrupts the closing operation of one of the associated actuators, and then the other finger touches the work. When the contact is detected, the interruption of the closing operation is released, and the gripping force control means for operating the actuator control means in accordance with the deviation, and the mutual detection signal levels of the two load sensors of one finger portion. The position change detecting means for detecting the change of the ratio and increasing the set gripping force by a predetermined amount to the gripping force setting means, Finger position detection means for detecting the position of the finger part, and grip position detection means for detecting the grip position of the finger part in the finger direction based on the ratio of the detection signal levels of the two load sensors of one finger part And coordinate data creating means for creating coordinate data of the grip position on the robot operation coordinates based on the detected position of the finger and the grip position of the finger. [0005] The work is held by a work contact plate in a biased state by a spring. The closing operation of one finger that first contacts the workpiece is interrupted, and the interruption is released when the other finger also contacts, and gripping is performed with the set gripping force. When a shift is detected due to a change in the mutual ratio of the detection signal levels of the two load sensors of one finger, the set gripping force is increased by a predetermined amount. The robot moves from the position of the pair of fingers on both sides detected by the position sensor attached to the actuator, and the gripping position in the finger direction detected based on the ratio of the detection signal levels of the two load sensors of one finger. The coordinate data of the grip position on the coordinates is created. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A basic configuration of a work holding device according to an embodiment of the present invention will be described with reference to FIG. In the figure, a pair of inner flat fingers 2 and 2a on both sides for holding a work 8 by opening and closing by changing a separation distance in a parallel state is provided at a distal end portion 1 of a robot arm with a motor 5 as an actuator. The associated drive mechanism 4 driven by 5a,
4a. These drive mechanisms
The proximal end of the finger is pivotally attached to the distal end, and the proximal end is a parallel link on both sides pivotally attached to the distal end 1, or a finger is attached to each of the two threaded rods provided along the opening and closing direction. For example, the screws 2 and 2a may be screwed together. One finger 2 is provided with a load sensor 3 for detecting a gripping force, and the other finger 2a is provided with two load sensors 3a and 3b separated in the finger direction A. I have. These load sensors are arranged over the range of the shape of the workpiece to be gripped so that the gripping force can be reliably detected. Reference numeral 10 designates a pair of finger portions 2 and 2a on both sides to perform opening and closing operations for gripping and releasing the work, and also detects the detection signal level of the load sensor 3 or the load sensors 3a and 3b.
Motor control means for driving the motors 5 and 5a in accordance with the deviation between the gripping force detected as an added value of the detection signal levels and the set gripping force preset in the gripping force setting means 11. The gripping force setting means 11 is configured to set and store a gripping force suitable for the work 8 and to step up the set gripping force as described later. Numeral 12 is a gripping force control means. The work 8 is first applied to one of the fingers 2, 2a in response to a rise in the level of the detection signal from the load sensors 3, 3a, 3b. Upon detecting the contact, the closing operation of one of the motors 5 and 5a is interrupted, and then the other finger 2, 2
a is detected to have contacted the work 8, the interruption of the closing operation is released, and the automatic balancing operation according to the set gripping force is performed. Reference numeral 13 denotes a displacement detecting means,
At the time of gripping the two load sensors 3, 3a of the finger 2a.
Is calculated, and when the value changes, the gripping force set by the gripping force setting means 11 is increased by a predetermined amount.
This detection may detect a change in the gripping position described later. Reference numeral 16 denotes finger position detecting means for detecting the positions of the pair of fingers 2 and 2a on both sides from the rotational position sensors 6 and 6a attached to the motors 5 and 5a when the work 8 is gripped. Reference numeral 17 denotes two load sensors 3a of the finger 2a,
A gripping position detecting means for detecting a workpiece gripping position in the finger direction A between the load sensors 3a and 3b from the sum of the detection signal levels of the load sensors 3b or the ratio of the detection signal levels of the load sensors 3a and 3b to the detection signal level of the load sensor 3; is there. 18
Is coordinate data creation means for creating coordinate data on the robot operation coordinates of the position of the workpiece 8 gripped based on the detected finger position and grip position. The operation of the gripping device thus configured is as follows. When the motor control means 10 moves the fingers 2, 2a from the open position to the work 8 in the closing direction in response to the detection signals of the rotational position sensors 6, 6a as the position sensors, the finger 2 or 2a 8, the finger portion 2 or 2
a stops, and when the other finger 2a or 2 also comes into contact, the fingers 2, 2a further approach each other slightly according to the deviation from the actual gripping force so as to reach the set gripping force. When the position deviation detecting means 13 reaches the set gripping force, the ratio between the detection levels of the load sensors 3a and 3b is changed to the finger direction A of the workpiece 8.
When the change is detected in accordance with the change in the gripping position, the set gripping force is increased by a predetermined amount. Optionally, the multi-step gripping force is increased in this way. The coordinate data creating means 18 sends the robot coordinate data of the gripping position of the work 8 to the control unit of the robot body when the gripping is completed, controls the movement of the robot arm, and moves the work 8 at a predetermined position with the finger. Release from 2, 2a. A more specific embodiment using a computer will be described with reference to FIGS. At the distal end 1 of the robot arm, the base ends of two parallel link arms 25 and 25a are pivotally mounted on both sides as a drive mechanism, and the proximal ends of the fingers 20 and 20a are pivotally mounted at the distal ends thereof. ing. Thus, the plate-like finger portions 20 and 20a open and close at intervals parallel to each other while holding the finger direction A with the rotation of the parallel link arms 25 and 25a. Concave portions 20c and 20d for guiding the flat workpiece contact plates 21 and 21a are formed on inner surfaces of the finger portions 20 and 20a facing each other so as to be slidable in an opposing direction orthogonal to the finger direction A. At the same time, between the bottom surface of the concave portion and the back surfaces of the work contact plates 21 and 21a, the loads applied to the springs 22 and 22a and the work contact plates 21 and 21a for urging the work contact plates outward are applied. Load sensors 23, 23a and 23b for detection are mounted. The parallel link arms 25, 25a are rotated by motors 26, 26a, and their rotation positions are indicated by attached rotation position sensors 27, 27a.
Is to be detected. Such an actuator is provided with a control unit 30 which is a computer which operates to constitute each means of the present invention. The control unit 30 transmits and receives signals via an interface unit 31 and stores an operation stored in a built-in memory. Operates according to the program. That is, for example, the detection signal of the load sensor 23 is digitized by the A / D converter 35 and taken in so that the motor control means is constituted by the drive circuits 32 and 32a.
A motor drive signal corresponding to a deviation from preset gripping force data is generated and sent to the drive circuits 32 and 32a. In order to constitute the gripping force control means, a signal level increase obtained by adding the detection signal of the load sensor 23 and the detection signals of the load sensors 23a and 23b is detected, and the driving circuit of the finger unit 20 or 20a belonging thereto is detected. The transmission of the drive signal to 32 or 32a is suspended until the level increase of the load signal due to the contact of the other finger 20a or 20 with the workpiece is detected. In order to constitute the displacement detecting means, the ratio itself of the detection signal levels digitized by the A / D converters 35a and 35b of the load sensors 23a and 23b of the finger portion 20a is calculated and the value is calculated. Is changed, the work 9 is determined to be displaced in the finger direction A, and the set gripping force data is increased by a predetermined amount. The grip position P1 of the workpiece 9 in the finger direction A with respect to the finger portion 20a is calculated according to the following equation (1) and FIG. F = R3 = R1 + R2 Therefore, P1 = {R2 / (R1 + R2)} × Lf (1) where R1, R2, R3: load sensor 2
3, 23a, 23b Detection signal level F: gripping force Lf: length of gripping surface in finger direction The following equations (2) and (3) and FIG. Parallel link arm 2 according to
The finger direction A (Y-axis direction) of the center point of the finger units 20 and 20a with respect to the origin O between the points 5 and 25a and the positions xw and yw in the opposing direction (X-axis direction) are calculated. X1 = Lx / 2 + Lk × cos θ1 x2 = −Lx / 2 + Lk × cos θ2 Lw = (Lx / 2 + Lk × cos θ1) − (− Lx / 2 + Lk × cos θ2) = Lx + Lk (cos θ1−cos θ2) Therefore, xw = x1−Lw / 2 = x2 + Lw / 2 = Lk (cos θ1 + cos θ2) / 2 (2) yw = L1 + Lk × sin θ1 (3) where x1, x2 are the positions θ1 of the fingers 20, 20a in the X-axis direction. , Θ2: the rotation angle Lw of the parallel link arms 25, 25a: the width Lx of the work 9: the distance Lk between the pivot points of the parallel link arms 25, 25a: the length L1: the finger portions 20a of the parallel link arms 25, 25a The distance from the base end to the gripping position P1 Further, these detected finger positions xw,
Based on yw and the grip position P1, coordinate data on the robot operation coordinates of the grip position is created. The operation of the gripping device thus configured is as follows. By taking in digital encoder signals from the rotational position sensors 27 and 27a, the motor 26,
The parallel link arms 2 are arranged so that the fingers 26, 20a approach each other in the closing direction from the open position where the fingers 20, 20a are separated from each other to the maximum.
5, 25a rotate. One finger 20 or 20 on the way
When a touches the work 9, the finger 20 or 20a temporarily stops, and the other finger 20a or 20 continues the closing operation. When the finger contacts the work 9, the closing operation is started. Instead, the motors 26 and 26a further rotate slightly in the closing direction according to the deviation between the detected gripping force and the set gripping force. When a predetermined gripping force is reached, the load sensor 2
When the ratio between the detection levels 3 and 23b changes, it is determined that the work 9 has changed, and the motors 26 and 26a rotate by a predetermined amount. Thus, when the gripping force is stabilized, the control body controls the movement of the robot arm based on the robot coordinate data, and releases the work 9 at a predetermined position. According to the present invention, the work can be gripped with elasticity by the work contact plates on both sides urged by the ridges facing each other. Also, with three load sensors,
When one of the fingers touches the workpiece, it stops once, and when the other finger also touches, it can be gripped with a predetermined gripping force without difficulty. With the increase in the number of workpieces, reliable gripping becomes possible irrespective of the shape of the workpiece, and the gripping position of the workpiece is easily converted to the coordinate position data of the robot operation coordinates, thereby moving the gripped workpiece to a predetermined place. The position can be set accurately.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing a configuration of a work holding device according to an embodiment of the present invention. FIG. 2 is a diagram showing a configuration of an embodiment using a computer of the work holding device of the present invention. FIG. 3 is a diagram illustrating the principle of detecting the position of a finger of the work holding device according to FIG. 2; FIG. 4 is a view for explaining the principle of detecting the position of a finger of the work holding device according to FIG. 2; [Description of Signs] 1 Tip part 2, 2a, 20, 20a of robot arm Finger part 3, 3a, 3b, 23, 23a, 23b Load sensor 4, 4a Driving mechanism 5, 5a, 26, 26a Motor 8, 9 Work 21, 21a Work contact plate 25, 25a Parallel link arm

──────────────────────────────────────────────────の Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B25J 15/08

Claims (1)

(57) [Claims 1] A driving mechanism driven by an actuator belonging to each of the robot arms so as to grip a workpiece by varying a separation distance in parallel with each other at a distal end of the robot arm. In a work gripping device in which a pair of flat inner surfaces on both sides are attached via a pair, a pair of opposing fingers on both sides is urged outward by a spring so as to be slidable in the opposite direction. In addition, two load sensors that detect the load applied to the work contact plate as a gripping force are provided on the one work contact plate at a distance in the finger direction, and the other work contact plate is One load sensor for detecting the load applied to the work contact plate as a gripping force is provided, and in addition to causing the pair of fingers on both sides to open and close the work for gripping, the load sensor detects the load. Actuator control means for driving an associated actuator in accordance with the deviation between the set gripping force and the set gripping force set in the gripping force setting means, and one of the finger portions in response to a detection signal of the load sensor. When the first contact with the work is detected and the closing operation of one of the actuators belonging to the actuator control means is interrupted, and then it is detected that the other finger touches the work. And the mutual ratio of the detection signal levels of the two load sensors of the one finger and the gripping force control means for releasing the interruption of the closing operation and operating the actuator control means according to the deviation changes. And a positional deviation detecting means for increasing the set gripping force by a predetermined amount to the gripping force setting means, and a position sensor attached to the actuator. Finger position detection means for detecting the position of the pair of finger portions on both sides, and a grip position of the finger portion in the finger direction based on a ratio of detection signal levels of the two load sensors of the one finger portion And a coordinate data generating means for generating coordinate data of a gripping position on the robot operating coordinates based on the detected position of the finger and the gripping position of the finger. Work holding device.