GB2283189A - Three fingered chuck - Google Patents

Abstract

The chuck has three fingers 5 which are opened and closed by a piston 10 of an air cylinder mechanism. Three inclined cams 4 are formed in a radially spaced arrangement at an end of a cam shaft 4a coupled to the piston 10, these cams 4 being engaged in respective cam reception grooves 18 each formed in an inner portion of each finger and having the same inclination as each cam. Air is supplied to chamber 15, forcing piston 10 and cams 4 downward, the cams 4 thus pushing fingers 5 radially outward of body 2. The workpiece is positioned between the fingers and the air pressure is released thus causing the fingers to move inwards and grip the workpiece. <IMAGE>

Description

A THREE-FINGERED CHUCK This invention relates to chucks which are mounted in use on arms of industrial robots or the like, and more particularly, to a three-fingered chuck for holding a workpiece.

A three-fingered chuck is well known in the art, thus requiring no particular illustration. In this chuck, three fingers for holding a workpiece are provided in radially uniform spacing and for movement in radial direction, on the underside of a body which is mounted on a robot arm or the like, and they are opened and closed by an air cylinder mechanism provided inside the body.

In such a chuck, a transmission mechanism for transmitting the acting force of a piston in the air cylinder mechanism to each finger, is formed with a combination of links and cams. Therefore, the mechanism is complicated in structure and readily subject to troubles, so that it cannot ensure stable operation of opening and closing the fingers. It is thus desired to obtain reliable holding of the work by constructing the transmission mechanism for transmitting the acting force of the piston to the fingers such that it is simple in construction and reliable in operation.

In the chuck, it is important that the work can be held and released safely and reliably. Accordingly, a spring-biased pusher is provided in correspondence to the three fingers to provide a pushing force for preventing the work from being pushed against the body with an excessive force when the work is held by the fingers and also reliably push out the work to a predetermined position before the work is released from the fingers in that position.

However, the pusher comprises a single spring-biased push rod. Therefore, its pushing force is liable to be applied to a deviated position of the work, thus causing the work to be turned down or setting the work at a deviated position.

In another aspect, since the above chuck is assembled in a robot or like automatic machine, it is important that the chuck permits detection of the holding or releasing of the work by the fingers. However, if it is intended to be able to detect the position of the fingers directly to thereby detect the opening or closing thereof, sensors have to be mounted in the fingers which are small parts and also in narrow body interior. This dictates complicated structure and also cumbersome design and manufacture. It is thus desired to permit detection of the opening and closing of the fingers with as simple structure as possible.

An object of the invention is to permit stable finger opening and closing operations to be obtained by reliably transmitting the acting force of the air cylinder mechanism piston to the fingers with a simple transmitting mechanism utilizing cams.

Another object of the invention is to provide a chuck with three fingers like the one noted above, which has a pusher capable of pushing the work with uniform force, thus permitting safe and reliable opening and closing of the work.

A further object of the invention is to provide a chuck with three fingers like the one noted above, which permits reliable detection of the opening and closing of the fingers without direct detection thereof but with a simple detecting mechanism.

To attain the above objects, according to the invention there is provided a chuck with three fingers, which comprises a body capable of being mounted on an industrial robot arm, tee fingers in a radial arrangement and capable of being opened and closed for holding a work, an air cylinder mechanism for opening and closing the fingers, and transmitting means for transmitting an acting force of the air cylinder mechanism to the fingers, the transmitting means including three cams formed in a radial arrangement on an end of a camshaft coupled to a piston of the air cylinder mechanism, each of the three cams being associated with each of the three fingers, each cam having an end portion inclined toward the axis of the cam shaft and being engaged in a cam reception groove formed in an inner end portion of each finger in the same inclination as the cam inclination, the cams being capable of sliding along the cam reception grooves in response to the operation of the piston, thus causing the fingers to be moved radially outward and inward.

According to the invention, there is also provided a chuck with three fingers, which further comprises a pusher for pushing out the work to the outside as soon as the work is released by the fingers, the pusher including three push rods disposed substantially in a uniform angular arrangement and capable of elongation and contraction, three springs each biasing each of the push rods in a direction that the push rod projects from the body, and a push plate having three radially spaced-apart branches each secured to each of the push rods, the springs being compressed by the push plate pushed by the work when the work is taken hold of by the fingers, the push plate functioning to push out the work with the biasing forces of the springs as soon as the work is released.

Further, according to the invention there is provided a chuck with three fingers, which further comprises a permanent magnet for position detection mounted in the piston in the air cylinder mechanism, and a magnetic sensor for detecting the permanent magnet, the magnetic sensor being mounted in a sensor mounting groove formed in the outer periphery of the body, the permanent magnet and the magnetic sensor cooperating with each other to detect the position of the piston so as to cause the fingers to be opened and closed for taking hold of and releasing the work.

Desirably, a plurality of sensor mounting grooves are formed in the outer periphery of the body at circumferentially different positions.

Brief Description of the Drawings Fig. 1 is a sectional view showing an embodiment of the chuck with three fingers according to the invention; q Fig. 2 is a bottom view showing the chuck shown in Fig. 1; Fig. 3 is a right side view showing the chuck shown in Fig. 1; and Fig. 4 is a broken-apart plan view showing the relationship of three cams and three fingers.

Detailed Description of the Embodiment Figs. 1 to 3 show an embodiment of the chuck with three fingers according to the invention. The illustrated chuck 1, comprises a cylindrical body 2 to be mounted on an industrial robot arm, an air cylinder 3 mechanism/provided as pneumatic pressure means inside the body 2, three fingers 5 mounted substantially in a uniform radial spacing on the underside of the body and driven forward and backward in the radial direction of the body 2 via cams 4 by the air cylinder mechanism 3 to hold and release a work, and a pusher 6 for pushing out the work to the outside as soon as the work is released by the fingers 5.

In the body 2, two, i.e., upper and lower, chambers are defined by an inner partitioning wall 8. The air cylinder mechanism 3 comprises a cylinder bore 9, which is constituted by the upper chamber noted above, and a piston 10 disposed in the cylinder bore 9 for sliding therealong in the axial direction of the body 2. The upper end of the cylinder bore 9 is closed by a cap 11, which is secured in position by a set ring 12. The body 2 has ports 13 and 14, through which compressed air or like pressurized fluid is supplied to and discharged from pressure bearing chambers 15 and 16 defined on the opposite sides of the piston 10.

Three cams 4 are disposed in the lower chamber noted above formed in the body 2. As is seen from Fig. 4, these cams 4 are formed in a uniform radial spacing at the lower end of a cam shaft 4a, which is secured by a bolt 17 to the piston 10. Each of these cams 4 is associated with each of the three fingers 5. Each cam has a cam face which is inclined toward the axis of the cam shaft 4a as one goes downward. Each finger 5 has its inner end portion formed with a cam reception groove 18 inclined in the same direction as the cam face. Each cam is engaged in each cam reception groove 18 such that it is slidable therealong.

The fingers 5 are engaged for sliding in the radial direction of the body 2 in radially spaced-apart in finger reception grooves 20 formed in the underside surface of the body 2 and a plate 19 mounted on the underside surface.

Each finger 5, which has its inner end portion formed with the can reception groove 18 noted above, has its lower surface formed with a boss 5a for mounting an attachment (not shown) for holding a work. As the cam shaft 4a is moved downward in unison with the piston 10 to the position shown in Fig. 1, the cams 4 push the fingers 5 in radially outward directions of the body 2, thus increasing the mutual spacing of the fingers 5. When upward movement of the can shaft 4a in unison with the piston 10 is caused, the cams 4 which are engaged in the cam reception grooves 18, pull the fingers 5 in radially inward directions of the body 5. Thus, the mutual spacing of the fingers 5 is reduced, so that the work is held by holding attachments provided on the lower surface of the fingers 5.

The underside surface of the body 2 is formed with three, substantially uniformly radially spaced-apart rod holder reception bores 22 each substantially at a mid position between adjacent fingers 5. Cylindrical rod holders are each mounted in each rod holder reception bore 22. Each rod holder 23 projects downward through the plate 19, and its detachment from the rod holder reception bore 22 is prevented by its flange 23a engaged with the plate 19. In each rod holder 23 a push rod 24 is slidably inserted and biased by a spring 25 provided between it and the bottom of the rod holder reception bore 22 in the direction of projecting from the rod holder 23a. The push rod 24 has a flange 24a formed at its inner end. The push rod 24 is prevented from its detachment from the rod holder reception bore 22 by the engagement of the flange 24a and the rod holder 23 with each other. A push plate 26 having three, radially uniformly spaced-apart branches 26a, is mounted by screws 27 adjacent the end of the individual branches 26a. The push rods 24, rod springs 25 and push plate 26 form the pusher 6 noted above.

The chuck 1 has a detecting mechanism for detecting the opening or closing of the fingers to take hold of or release a work. This detecting mechanism detects the movement of the fingers not directly but indirectly by detecting the operating position of the piston 10. More specifically, the piston 10 has its outer peripheral surface formed with an annular magnet mounting groove 30 for mounting a permanent magnet for position detection, while the body 2 has its outer peripheral surface formed with sensor mounting grooves 31 for mounting magnetic sensors for detecting the permanent magnet noted above.

The sensor mounting grooves 31a and 31b are elongate grooves extending in the axial direction of the body 2.

With a permanent magnet mounted in the magnet mounting groove 30 and magnetic sensors mounted in the sensor mounting grooves 31a and 31b, it is possible to permit detection of the operating position of the piston 10.

Where a magnetic sensor is mounted in each of the two sensor mounting grooves 31a and 31b, the position of the piston 10 can be detected in each of the reciprocal directions. Where a magnetic sensor is mounted in either one of the two sensor mounting grooves 31a and 31b, the position of the piston 10 can be detected in either of the reciprocal directions.

Desirably, as shown in Fig. 2, the sensor mounting grooves 31a and 31b are formed as a plurality of pairs in the body 2 at different positions thereof in the circumferential direction. By so doing, it is possible to mount magnetic sensors in a selected pair of sensor mounting grooves 31a and 31b at positions, at which the magnetic sensors are not obstructive with the chuck 1 mounted on a robot arm or the like.

In the chuck as described above, the method of detecting the movement of the fingers 5 indirectly by detecting the operating position of the piston 10, is extremely effective compared to the method of directly detecting the movement of the fingers 5. More specifically, the body 2 of the chuck should have a certain large wall thickness because of the necessity of provision of the ports 13 and 14 for the connection of tubing and mounting holes 32 for securing the chuck to a robot arm or the like. The former method permits effective utilization of the shape of the body 2 for the detection of position of the piston 10 by forming the outer periphery of the body 2 with the sensor mounting grooves 31a and 31b for detecting the permanent magnet in the piston 10 with the magnetic sensors provided in the sensor mounting grooves. Such a design is simple and optimal compared to, for instance, the case in which a permanent magnet is mounted in the finger 5, a small component, and detected by a magnetic sensor provided in a small or narrow inner space in the body 2.

Further, since the sensor mounting grooves 31a and 31b can be formed to be elongate in the axial direction of the body 2, it is possible to permit the detection of the piston 10 over the entire stroke thereof by appropriately adjusting the mounting position of the magnetic sensor.

The chuck 1 having the above construction is used by mounting it on an arm of an industrial robot or the like.

By supplying compressed air to the pressure chamber 15 above the piston 10 in the air cylinder mechanism 3 while opening the lower pressure chamber 6 to atmosphere, the piston 10 and cams 4 are lowered to their positions shown in Fig. 1. At this time, the cams 4 push the fingers 5 radially outward of the body 2 to increase the spacing of the three fingers 5. In this state, the work is positioned amongst the opened fingers 5 by moving the robot arm, and it is pushed against the chuck 1 with the necessary force.

Then, by reversing the compressed air supply/discharge relation with respect to the pressure chambers 34 and 35, the piston 10 and cam shaft 4a are raised, and the cams 4 engaged in the cam reception grooves 18 pull the fingers 5 radially inward of the body 2. The spacing of the three fingers 5 is thus reduced, and thus the work is held by holding attachments mounted on the lower surface of the fingers 5. At this time, in the pusher 6 the push plate 26 is pushed and retreated by the work. The three push rods 24 are thus contracted to compress the springs 25 so as to store biasing forces therein. Further, the biasing forces stored in the springs 25 at this time can prevent the work from being pushed against the body by excessive forces.

After the work has been transferred to a desired place by moving the robot arm, by reversing the compressed air supply/discharge relation with respect to the pressure chambers 15 and 16, the piston 10 and cams 4 are lowered to their positions shown in Fig. 1, and thus the fingers 5 are moved radially outward to release the work. At this time, the biasing forces of the springs 25 are acting on the push plate 26, and thus as soon as the work is released by the fingers 5, it is reliably pushed out to the outside to be placed in a desired position.

Thus, the push plate 26, via which the work is pushed by the three push rods 24 in a substantially uniform angular arrangement, can be moved in a stabilized attitude to allow the biasing forces of the springs 25 to be acted uniformly on the work. The pusher 6 thus provide impartial forces to push the work, so that the work can be placed at the desired position in a correct attitude.

Further, with the provision of the three springs the pusher as a whole can provide a great push-out force without need for each spring to provide a considerably great biasing force. Thus, compared to a pusher which has only a single spring, it is possible to reduce the axial dimension of each spring 25 so as to reduce the axial dimension of the chuck.

Claims (8)

CLAIMS:

1. A three-fingered chuck comprising a body capable of being mounted on an industrial robot arm, three radially arranged fingers movable between an open position and a closed position for holding a workpiece, an air cylinder mechanism for moving the fingers between the open and closed positions, three cams formed in a radial arrangement on an end of a camshaft coupled to a piston of the air cylinder mechanism, each of said cams being associated with one of the three fingers, each cam having an end portion inclined toward the axis of the cam shaft and being engaged in a cam reception groove formed in an inner end portion of a finger in the same inclination as the cam inclination, said cams being capable of sliding along the cam reception grooves in response to the operation of the piston, thus causing the fingers to be moved radially outward and inward between the open and closed positions.

2. A three-fingered chuck as claimed in Claim 1, further comprising a pusher having a number of radially arranged branches and spring means for urging the pusher in a direction to eject a workpiece for pushing out a workpiece once the workpiece is released by the fingers.

3. A three-fingered chuck as claimed in Claim 2 in which the pusher includes three push rods disposed substantially in a uniform angular arrangement around the axis of the chuck, the spring means resiliently urging the push rods in a direction outwardly from the chuck, each branch of the pusher member being secured to one of the push rods, the spring means being compressed by the push plate as the workpiece is moved to a position to be gripped, the push plate functioning to eject the workpiece from the fingers with the biasing forces of the spring means as soon as the workpiece is released by the fingers.

4. A three-fingered chuck as claimed in Claim 3 in which the spring means comprises compression springs, one biasing each of the push rods to a direction to eject a workpiece.

5. A three-fingered chuck as claimed in any preceding claim which further comprises a permanent magnet for position detection mounted in the piston of the air cylinder mechanism, and a magnetic sensor for detecting the position of permanent magnet and accordingly the positions of the fingers.

6. A three-fingered chuck as claimed in Claim 5 in which the magnetic sensor is mounted in a sensor mounting groove formed in the outer periphery of the body.

7. A three-fingered chuck as claimed in Claim 6 in which the outer periphery of the body has a plurality of sensor mounting grooves formed at circumferentially different positions.

8. A three-fingered chuck substantially as herein described with reference to the accompanying drawings.