Abstract:
A robotic gripping apparatus includes one or more constraining plates each having a plurality of holes formed therethrough and a plurality of elongate members. The elongate members are independently movable relative to one another. Each elongate member extends through a respective hole or set of aligning holes in the constraining plate(s). A distal end portion of one or more of the elongate members is capable of exerting a force for drawing an object against the distal end portion to thereby hold or grip the object.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a robotic gripping apparatus. 
     BACKGROUND OF THE INVENTION 
     Industrial robots often employ an articulated mobile structure, commonly referred to as an arm, with mobility approximating that of a human arm. Such a robotic arm is equipped with a so-called end effector to enable the robot to perform its assigned task. 
     In some applications, the end-effector performs a grasping or gripping function. One class of gripping end-effectors uses a set of individual prehensile mechanical fingers (typically two or more) which curl around an object, tightening around it in order to grip the object. This action closely mimics the grasping action of the human hand. 
     A mechanically simpler gripping action can be obtained by employing an attractive force, such as a magnetic or electric field or fluid suction. The gripper is placed against the object to be grasped and the attractive force is energized (e.g., the magnetic field or suction force is turned on). The object is then grasped for subsequent manipulation. When the robot is finished with the object, the attractive force is turned off, and the object is released. 
     However, some objects to be grasped are bulky and/or offer no obvious flat space against which to exert an attractive force. Examples include paint brushes and many surgical instruments. If, for example, a conventional electromagnet is used to grip a metal surgical instrument, the pole piece of the electromagnet may rest against a high spot or sharp surface or other irregular surface on the instrument. When the electromagnetic field is energized, the resulting grip may be less than satisfactory and the object may dangle, twist, or even be dropped. 
     SUMMARY OF THE INVENTION 
     In order to solve the problem of gripping objects that are not well-suited to being held using an attractive force, an improved gripping end-effector is proposed which is able to achieve a significantly more secure grip on bulky or oddly or irregularly shaped objects using an attractive force supplied at the end of each of a plurality of elongate members. 
     According to the present invention, a robotic gripping apparatus is provided which comprises a plurality of elongate members which independently adjust to the shape of an object to be gripped and are each capable of exerting an attractive force on the object. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention, together with further objects and advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings, wherein like reference numerals identify like elements, and wherein: 
         FIG. 1  shows a perspective cross section of a basic structure of a prior art pin and plate structure interacting with an object. 
         FIG. 2  shows a perspective cross section of an apparatus of the present invention and a pin locking mechanism of the present invention in an unlocked configuration. 
         FIG. 3  shows a perspective cross section of an apparatus of the present invention and a pin locking mechanism of the present invention in a locked configuration. 
         FIG. 4  shows a release mechanism of the present invention. 
         FIG. 5A  shows an electromagnetic pin usable in the present invention. 
         FIG. 5B  shows several permanent magnet pins usable in the present invention. 
         FIG. 5C  shows a fluid suction pin usable in the present invention. 
         FIG. 5D  shows a van der Waals force pin usable in the present invention. 
         FIG. 6A  shows a fluid piston usable in the present invention for forcing a pin in either of two directions. 
         FIG. 6B  shows a solenoid usable in the present invention for forcing a pin in either of two directions. 
         FIG. 6C  shows a spring usable in the present invention for forcing a pin to a neutral position thereof. 
         FIG. 7  shows a cross section of a rounded tip of a pin usable in the present invention. 
         FIGS. 8A ,  8 B,  8 C and  8 D show cross sections of an alternative locking mechanism according to the present invention. 
         FIGS. 9A and 9B  show cross sections of another alternative locking mechanism according to the present invention. 
         FIG. 10  shows a cross section of a curved structure of a gripper device according to the present invention. 
         FIG. 11  shows a control unit usable with the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     The elongate members of the present invention may be better understood by comparison with the action of a known children&#39;s toy called a PINPRESSIONS® 1000, a representation thereof being shown in  FIG. 1 . This known device comprises an array of several hundred metal pins  1020  oriented vertically and parallel to each other. (For clarity of understanding, only a few of the pins  1020  are shown.) The pins  1020  are constrained to move parallel to each other by two parallel plates  1010 , both of which are perpendicular to the plurality of pins. The plates  1010  are spaced about one inch apart with each plate  1010  having matching sets of holes  1019  of slightly larger diameter than the pins  1020 . The fit between the pins  1020  and the holes  1019  allows the pins  1020  to slide freely in a direction perpendicular to the plates  1010 . A collar  1022  at the top of each pin  1020  prevents the pins  1020  from falling out of the toy  1000  in one direction, while a cover plate  1012  fastened to the two parallel plates  1010  by fastening structures  1015  prevents the pins from falling out of the toy  1000  in the opposite direction. In use, the toy  1000  is placed down onto an object  1050  and the pins  1020  adjust themselves in the vertical direction under the force of gravity to produce a relief image of the object  1050 . 
     According to the present invention, the end-effector  100  as shown in  FIGS. 2 and 3  comprises a plurality of parallel, independently sliding or adjustable elongate members, hereinafter pins  120 . (For clarity of understanding, only a few of the pins  120  are shown.) Each pin  120  is movable or adjustable in an axial direction independent of the movement or adjustment of the other pins  120  in the axial direction and each pin  120  is also individually capable of exerting an attractive force on an object  50 . Various mechanisms to enable each pin  120  to exert such an attractive force may be applied, either the same mechanism for all pins in an end-effector  100  or different mechanisms for different pins in the end-effector  100 . For example, each pin  120  might comprise an electromagnet  120   a  as in a first embodiment shown in  FIG. 5A , a permanent magnet  120   b   1 ,  120   b   2  as in a second embodiment shown in  FIG. 5B , a tube  120   c  through which a fluid pressure suction may be exerted as in a third embodiment shown in  FIG. 5C , or a pad  120   d  with microscopic hairs  125   d  for increasing the surface area over which a van der Waals force acts as in a fourth embodiment shown in  FIG. 5D . 
     In the embodiment shown in  FIG. 5A , is provided by a wire  125   a  wound around the electromagnet  120   a . In the embodiment shown in  FIG. 5C , to enable exertion of the fluid pressure suction, a suction source  127   c  is coupled to an interior  125   c  of the tube  120   c  via a connecting conduit  126   c.    
     In the embodiment shown in  FIGS. 2 and 3 , there are three constraining plates  110 ; however, a single plate would be practicable in combination with pins  120  equipped with permanently attractive ends and a release plate  111  or in combination with pins  120  equipped with an attractive force which could be turned off. A locking mechanism utilizing the relative position of two or more constraining plates  110  would not be practicable with a single constraining plate. The number of constraining plates may therefore vary in different embodiments of the invention. 
     The constraining plates  110  each have a plurality of holes  119  through which the pins  120  are freely slidable, when the constraining plates  110  are not in a locking position described below. The pins  120  are prevented from falling through the constraining plates  110  by a collar  121  on each pin that is larger than the corresponding hole  119  in each plate  110 . Another form or construction may be provided, either in connection with the pins  120  and/or one or more of the constraining plates  110 , to maintain the pins  120  in the holes  119  in the constraining plate  110 . 
     The gripping process of the present invention comprises several operations. 
     First, conforming is performed, i.e., the end-effector  100  is conformed to the shape of the object  50 . Specifically, the pins  120  are pressed against the surface  51  of object  50  and they slide relative to constraining plates  110  to conform to the shape of the object  50 . Each pin  120  is equipped with a positioning member  131  (only one is shown for clarity of understanding) attached to an inside surface  106  of the main body  102 . As shown in  FIGS. 6A ,  6 B and  6 C, the positioning member  131  may comprise at least one of a spring  131   c , a solenoid  131   b , or a fluid-actuated piston  131   a  for forcing each pin  120  in an outward normal direction of the constraining plates  110 . When the pins  120  are forced into contact with the surface  51  of the object  50  to be gripped by the end-effector  100 , the pins  120  conform to the shape of the object  50  because either the end-effector  100  is held stationary while the pins  120  are forced outwardly therefrom, or the object  50  is stationary while the end-effector  100  is moved closer to the object  50  or the object  50  is moved closer to the end-effector  100 . The pins  120  are constrained to move parallel to each other, i.e., in an axial direction of each pin  120 , by constraining plates  110 . A control unit  160  modulates or controls a force applied by the solenoid  131   b  or the fluid piston  131   a , when present, on the pins  120  according to the nature of the object  50 . 
     Next, locking is performed. The pins  120  are locked in the positions obtained during the above-described conforming step by moving one or both of the constraining plates  110  relative to each other so that the pins  120  are locked in positions relative to the constraining plates  110 . Locking can be accomplished by translation and/or rotation of the constraining plates  110  by plate translating/rotating devices  112 . The plate translating/rotating devices  112  are attached to a main body  102  of the end-effector  100  by an attaching member  104 . If the fit between each pin  120  and its corresponding hole  119  in each constraining plate is a close one, only a small displacement by rotation and/or translation of one of the constraining plates  110  is necessary to exert a sufficient shear force on some or all of the pins  120  to lock the pins  120  in position. The required force could be provided by an actuator such as, for example, a solenoid, a fluid driven piston or other linear or arc actuator. Such an actuator would be preferably controlled by a control unit  160  shown in  FIG. 11  (described later). 
     If only a single constraining plate  110  is used, locking does not occur. 
     Each plate translating/rotating device  112  must be capable of slightly translating or rotating at least one of the constraining plates  110  to provide sufficient force to lock the pins  120  in position. Each plate translating/rotating device  112  may comprise, for example, any number of linear or angular electromagnetic or fluid actuators. 
     After the pins  120  are locked in position, the attractive force is activated, preferably by the control unit  160 , in a gripping step (see  FIG. 11 ). The object  50  can then be manipulated by the end-effector  100  during a manipulation step, and used for its intended purpose. Alternatively, the pins  120  can be locked in position after activating the attractive force. 
     Finally, the end-effector  100  may be operated to release the object  50  in a releasing step, e.g., after manipulation and/or use of the object  50 . One method of releasing the object  50  is to simultaneously de-energize the attractive force and release the locking mechanism. Alternatively, the pins  120  can be unlocked before the attractive force is deactivated or vice versa. After the object  50  is released, each pin  120  is returned to a neutral position by the positioning member  131  to the position it had before beginning the conforming step. 
     In some instances, it is advantageous to shape tips or ends  129  of the pins  120  with a shallow convex radius (see, for example,  FIG. 7 ) or crown portion on the end rather than a flat end. This will enable the pins  120  to slide more easily over the surface of the object  50  (especially an irregularly shaped object  50 ) during conforming and release operations and will make them less prone to leaving scratch marks on the surface  51  of the object  50 . 
     In the embodiments of the present invention which utilize a permanent attractive force, the attractive force is permanently active and is provided by, for example, permanent magnets  125   b   1  and  125   b   2  located at the end  129  of each pin  120 . Conforming and locking are similar to those operations in the other embodiments, except that conforming occurs at the same time as gripping. Unlocking is also the same as in the other embodiments. Releasing the object  50  from pins  120  equipped with a permanently active attractive force requires retracting the ends  129  of the pins  120  into an interior  108  of the main body  102  of the gripper  100  or at least far enough apart from the object  50  so that the end  129  of enough of the pins  120  are prevented from being in contact with the object  50  so that the object  50  will not be held by the end-effector  100 . 
     In the case of permanent magnet equipped pins (see  FIG. 5B ), the use of a holder  126   b   1  and  126   b   2  for a magnetic slug  125   b   1  and  125   b   2  is preferred because the slug itself may be difficult to machine. Each slug  125   b   1  and  125   b   2  has a North and South magnetic pole. The design as shown in  FIG. 5B  uses an array of slugs  125   b   1  and  125   b   2  with pole polarities alternating North and South. Such alternation of polarities is preferred because it results in little or no tendency to magnetize a metallic object after repeated grip and release cycles. 
     One configuration of the present invention, shown in  FIG. 2  (see also  FIG. 6C ), uses compression springs  131   c  to drive the pins in an outward normal direction of the main body  102  of the end-effector  100 . A collar  121  on an interior end of each pin  120  interacts with a constraining plate  110  that can be moved by the plate translating/rotating device  112  to force all of the pins  120  entirely inside the main body  102  of the end-effector  100  so as to disconnect the pins  120  from the surface  51  of the object  50 . 
     An alternate configuration uses the pin positioning member  131  to retract the pins  120 . However, using a release plate  111  in combination with the pin collar  121  (see  FIG. 4 ) to retract the pins  120  is preferable when the permanent attractive force being supplied is very large. 
     The gripping process of the permanent magnet equipped embodiments of the present invention is identical to the gripping process of other embodiments, except that the conforming and gripping steps occur at the same time. Locking of the pins should always follows conforming and gripping in permanent magnet equipped embodiments. Furthermore, release of the object  50  can only be adequately achieved by drawing the pins  120  entirely inside the main body  102  of the end-effector  100 . 
       FIG. 10  shows an alternate embodiment in which pins  220  are not parallel to each other and constraining plates  210  and  211  are curved. The pins  220  in this embodiment of the present invention are preferably locked by the locking mechanism shown in  FIGS. 8A ,  8 B,  8 C and  8 D (described below), due to the curved shape of the constraining plates  210  and  211 . This embodiment of the present invention is compatible with both permanent and temporary attractive forces. It is particularly suited to very oddly shaped objects  250  ( FIG. 10 ) with specific holding requirements. As in the previously described embodiments, the pins  220  in this embodiment are equipped with both positioning members  231  and collars  221 . A main body, control unit, and other parts of this embodiment are not shown in  FIG. 10  for the sake of simplicity. All of the above-described pin and positioning mechanism designs are applicable to this embodiment. 
     As shown in  FIGS. 8A ,  8 B,  8 C and  8 D, the pair of constraining plates  110  may be movable closer together to compress a fluid chamber  141  (or alternatively a foam) between the two constraining plates  110  to cause flexible walls  142  of the chamber  141  to come into contact with the pins  120 . Alternatively, the fluid pressure in the chamber  141  may be increased by action of a pump or piston  146  connected to the chamber  141  which deforms the flexible walls  142  and cause them to come into contact with the sides of the pins  120 . The pump or piston  146  or the motion of the constraining plates  110  is preferably controlled by the control unit  160 . It is preferable that the flexible walls  142  be made of a high friction material such as rubber or coated with a high friction material  147 . Only a few pins are shown and the main body and other parts are omitted from  FIGS. 8A ,  8 B,  8 C and  8 D for the sake of clarity. The locking mechanism of  FIGS. 8A ,  8 B,  8 C, and  8 D can be used with all embodiments of the present invention. 
     As shown in  FIGS. 9A and 9B , an electromagnet  143  may be used to drive the pins  120  against an inside surface  144  of holes  119  in one of the constraining plate  110 . In this embodiment, a single constraining plate may be used if it has sufficient thickness to maintain the pins  120  in positions substantially parallel to the inside surface  144  of the holes  119 . In this case, it is preferable that the inside surface  144  of the hole and the side surface  145  of the pin  120  are either roughened or grooved to enhance the effectiveness of the locking force provided by the electromagnet  143 . A fluid flowing parallel to and between the plates  110  may provide the locking force. Only a single pin is shown in  FIGS. 9A and 9B  and the main body, the other pins  120 , and other parts are omitted from  FIGS. 9A and 9B  for the sake of clarity. 
     Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.