Abstract:
The present invention provides a robotic gripper mechanism. The invention comprises gripping jaws and a wedge that moves along angled groove between the gripping jaws. The angled grooves are connected to the gripping jaws, and the wedge moves the gripping jaws together and apart as it slides backward and forward along the angled grooves. The wedge also keeps the gripper jaws parallel to each other as they open and close. A motor moves the wedge backward and forward, and guiding surfaces attached to the base prevent the jaws from moving horizontally relative to the base.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to robotic gripper mechanisms. 
     2. Background of the Invention 
     Typical robotic grippers (also known as end effectors) for automated data storage libraries are slow-speed electric pinching mechanisms for gripping onto a standard sized box-shaped modia cassette. The size of the data cassette usually dictates the range of movement of the gripper jaws. The simplest solution for proper movement of the jaws is to hinge them in the rear and provide an actuator to push them apart and pull them together in order to grip an object. Typically, a motor is used to drive a nut and linkage arrangement that moves the gripper fingers (jaws) together or apart. This typical gripper design has several limitations related to the variability of cassette size. 
     The first limitation is the finger of the gripper. Because of their pivot point, the jaws will not remain parallel to each other as the cassette size varies in its tolerance range, and certainly will not remain parallel for a non-standard or smaller form factor cassette. Parallelism is desirable to control the attitude and gripping surface friction of the jaws. 
     A second limitation of the prior art gripper design relates to the linkage arms that drive the jaws in a non-linear force relationship. As the finger pivot angle changes, the linkage angles change, and a small change in gripper pinch width could result in a large difference in pinch force applied to the cassette. 
     Therefore, it would be desirable to have a robot gripper that can grip onto several different shaped objects with consistent orientation in space to keep the objects aligned with the library structure, while retaining constant grip force. 
     SUMMARY OF THE INVENTION 
     The present invention provides a robotic gripper mechanism. The invention comprises gripping jaws and a wedge that moves along angled groove between the gripping jaws. The angled grooves are connected to the gripping jaws, and the wedge moves the gripping jaws together and apart as it slides backward and forward along the angled grooves. The wedge also keeps the gripper jaws parallel to each other as they open and close. A motor moves the wedge backward and forward, and guiding surfaces attached to the base prevent the jaws from moving horizontally relative to the base. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein: 
     FIG. 1 depicts a schematic diagram illustrating a typical hinged gripper robot in accordance with the prior art; 
     FIG. 2 depicts a diagram illustrating a solution to controlling gripper jaws movement in accordance with the prior art; 
     FIG. 3 depicts a diagram illustrating a simplified version of the linear sliding approach to controlling gripper finger movement in accordance with the prior art; 
     FIG. 4 depicts a schematic diagram illustrating a method for producing linear force application to the gripper jaws in accordance with the prior art; 
     FIG. 5 depicts another prior art design similar to FIG. 4, but substituting a grooved wedge driver block for gripper-biasing springs; 
     FIG. 6 depicts a schematic diagram illustrating a gripper with a parallel jaw mechanism and inertia driven wedge in accordance with the present invention; and 
     FIG. 7 depicts a schematic diagram illustrating internal details of the sliding wedge in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the figures, and more specifically to FIG. 1, a schematic diagram illustrating a typical hinged gripper robot is depicted in accordance with the prior art. Typical robotic grippers for automated data storage libraries are slow speed pinching mechanisms for gripping onto a standard sized box shaped media cassette. The size of the cassette usually dictates a range of movement of the gripper jaws and the simplest solution for proper movement of the jaws is to hinge them in the rear and provide an actuator to push them apart and pull them together to pinch an object. 
     FIG. 1 depicts a pair of hinged jaws  101  and  102  supported by a pivot  103  in the rear and a driving linkage  104  in the front. A motor  105  is connected to a screw  106  which, when rotated, drives a nut  107  connected to the linkage  104 . This typical gripper has several limitations relating to the variability of cassette size. 
     First, the jaws  101 - 102 , because of their pivot point  103 , will not remain parallel to each other as the cassette size varies in it&#39;s tolerance range, and certainly will not remain parallel for a non-standard or smaller form factor cassette. Parallelism would be desirable to control the attitude and griping surface friction of the jaws  101 - 102 . Several methods have been used in the prior art for dealing with this problem. 
     FIG. 2 depicts a diagram illustrating a solution to controlling gripper jaws in accordance with the prior art. The gripper in FIG. 2 uses a sliding ball type of linear guide for controlling the jaws  201  and  202  in a parallel fashion. In this design, the jaws  201 - 202  move together and apart along linear slide bearings  203 , which keep the jaws  201 - 202  parallel. 
     FIG. 3 depicts a diagram illustrating a simplified version of the linear sliding approach in accordance with the prior art. This design operates along the same lines as the design illustrated in FIG.  2 . However, in FIG. 3, the linear slide bearings are replaced with tongue-and-groove guides comprised of sliding mounts  301  moving in slots between fixed supports  302 . 
     In both FIGS. 2 and 3, the additional structures for ensuring parallel movement take up considerable extra room in addition to the actuator components. The structures also add cost to the robot. 
     The second major problem with typical prior art grippers is that the linkage arms, e.g., linkage  104  in FIG. 1, can drive the gripper jaws in a non-linear force relationship. As the finger pivot angle changes, the linkage angles change, and a small change in gripper pinch width could result in a large difference in pinch force applied to the cassette. 
     Referring to FIG. 4, a schematic diagram illustrating a method for producing linear force application to the gripper jaws is depicted in accordance with the prior art. The design shown in FIG. 4 illustrates a more linear design, wherein a wedging action is provided by a motor  403  connected to a screw  404  and moving wedge  405 , which in turn provides a nice linear force to the jaws  401 - 402 , even with variation in cassette thickness. 
     FIG. 5 depicts another prior art design similar to FIG. 4, but without the gripper-biasing springs. Instead, this design uses a grooved wedge driver block  501  with bi-directional force. However, the prior art solutions depicted in both FIGS. 4 and 5 do not address the problem of maintaining the gripper jaws in a parallel position to each other. 
     The present invention provides a robotic gripper that can grip several different shaped objects while retaining constant grip force. The mechanism grips with consistent force across all of the grip range and also grips the object with consistent orientation in space to keep the object in alignment with the library structure. 
     Referring now to FIG. 6, a schematic diagram illustrating a gripper with a parallel jaw mechanism and inertia driven wedge is depicted in accordance with the present invention. The jaws  601  and  602  are supported and guided by slots  603  and  604  that are tipped at an angle. The jaws  601 - 602  are moveable vertically to pinch an object  605  by simply sliding the wedge  606  along the angled guide slot structures  603 - 604  in a horizontal direction. In addition, optional guide pins or ball bearings  612  may be placed in slots  603 - 604 . 
     A motor  610  drives the wedge  606  by means of a leadscrew  611 . The wedge  606  and slots  603 - 604  create linear force on the jaws  601 - 602  as they spread apart or together. Thus the guide slots  603 - 604  also become the driver device. In addition, the wedge  606  and guide slots  603 - 604  keep the jaws  601 - 602  parallel as they open and close, even as the size of the gripped object  605  changes. Therefore, the present invention overcomes both limitations of the prior art but without the need for additional bulky structures. 
     The example depicted in FIG. 6 assumes that “ribs” on the wedge  606  fit into slots  603 - 604 . However, the design in FIG. 6 may also be switched so that guide slots are placed along the wedge  606 , and structures  603  and  604  become the ribs that fit in such slots. 
     The guide surfaces  607  and  608  provide a way to keep the jaws  601 - 602  locked horizontally to the gripper base plate  609  without moving left or right relative to the plate. With these guide surfaces  607 - 608  in place, the sliding wedge  606  with integrated driver nut (not shown) is a means of actuating the gripper jaws  601 - 602  while holding them parallel, as explained above. The sliding wedge  606  is also fixed in horizontal slots (not shown) in the base plate  609  to hold the wedge  606  in vertical alignment, while allowing it to.slide left and right. 
     Referring now to FIG. 7, a schematic diagram illustrating internal details of the sliding wedge is depicted in accordance with the present invention. FIG. 7 illustrates possible improvements that can be added to the design of the wedge  606  from FIG.  6 . One improvement is a spring  701  to provide a preload between the lead driver nut  702  and the wedge  606 . This allows the motor  610  to actually drive the sliding wedge  606  and hence the jaws into contact with the gripped objects at very high speeds. The spring  701  provides a mechanical damping to the collision between gripper jaws and objects to allow the motor  610  to be controlled more loosely by the servo electronics so that the motor  610  and screw  611  is not damaged by impact. 
     The spring  701  can be further utilized to control grip pinch forces if the screw  611  and nut  702  are used to collapse the spring  701  in increasing amounts to get more force to the jaws. The spring compression is directly related to gripper pinch force and can be measured or sensed by an electrical position sensor  703  that can turn off the gripper motor  610  at a given force value. 
     The features of the present invention allow the gripper to achieve unusual grip forces at unsurpassed speeds, as well as maintain a gasp on objects when power is lost. 
     The description of the present invention has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiment was chosen and described in order to best explain the principles of the invention, the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.