Abstract:
A retrofit pivot pin for positioning at a pivot joint between a pair of articulated arms including a Hall effect element secured to a first arm and a magnet secured to said second arm.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/900,654 filed Feb. 9, 2007 and incorporated by reference herein. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention is directed to a replacement pivot pin for a joint of an articulated system having at least a pair of arms that swing or rotate relative to each other wherein a sensor utilizing the Hall effect provides information to a remote location as to the angular position of one arm relative to the other. 
         [0003]    Articulated arms are utilized on many types of equipment including construction equipment such as backhoes, excavators, mechanical arms such as on undersea exploration vehicles and on space vehicles such as the space station. Most of such arms can be visualized by an operator who controls the arms from a master controller which may be very closely spaced relative to the arm or at a substantial distance in which case the arm may be viewed by video. When the user can see the position of the arms relative to each other and to their environment, the operator uses such visual information to control the relative position of the arms. 
         [0004]    However, in certain circumstances the operator cannot visually see the arms or the arm is to be controlled by a computer. In such a situation it is necessary for the operator or computer to be able to determine the relative position of the arms by some other method. Furthermore, even if the arms can be seen, it is sometimes helpful or important for the information to be transmitted elsewhere for use in conjunction with computer programs, for data storage or the like. 
         [0005]    As most articulated arm systems are not initially provided with some type of position sensor, it is also important that such a device be easily retrofitted to articulated systems. Some sensory devices also require substantial modification of the equipment or addition of parts such as shafts that extend outwardly and add complexity to the equipment and that may make the equipment subject to breakdown. 
         [0006]    Some types of position sensing devices utilize contacts that are located about an articulating joint. However, contact sensors are not a very viable solution for equipment that must operate under conditions that can foul the contacts or wear on the contacts. Contact sensors may also not have the sensitivity required for many uses of such a device. Many types of position sensors can not function in severe or hazardous service. 
         [0007]    It is also noted that some types of position sensors are placed in hydraulic cylinders that move the arms. Such sensors present problems because the leads must pass through a high pressure barrier and many hydraulic systems are converting from an oil to a water based system. While the oil does not cause conductivity problems, the water can short out such systems. 
         [0008]    Therefore, a position sensor that does not require major modification is desirable for use in determining relative positions of arms in an articulated device wherein the positions can be transmitted to remote locations and wherein the sensor can withstand rugged conditions and is highly sensitive to small changes in position. 
       SUMMARY OF THE INVENTION 
       [0009]    A positional sensor, especially for retrofit, into an articulated arm structure wherein one arm pivots about a pivot pin relative to a second arm. The sensor includes structure that replaces the original pivot axle or pin with minimal drilling or other structural modification to the arms or, alternatively, is provided as an original pivot pin. Such a sensor can be utilized at one or any number of the articulated joints of the system. 
         [0010]    The sensor includes an elongate pin sized and shaped to be located between and in pivoting support of two arms that swing or rotate relative to one another and a bushing or bearing that is operably positioned between the pin and one arm and replaces the original bearing. 
         [0011]    The bearing includes a pair of diagonally opposed magnet sets that have one or more high gauss magnets (preferably rare earth magnets such as neodymium magnets) that are operably positioned to be in close proximity to and rotate about the pin. The bearing is secured to a first of the arms. The bearing is generally non magnetic and constructed of bronze or the like. 
         [0012]    The pin is secured to the second arm and is generally completely non magnetic and constructed of stainless steel with a chrome finish or the like. Located near one end of the pin and at least partially aligned with the magnets in the bearing is a bore within which is received a Hall effect element. The Hall effect element is aligned relative to the magnets such that rotation of the magnets in conjunction with angular movement of first arm relative to the second arm, produces a ratiometric change in an electrical output from the Hall effect element that is related to the relative rotation between the first and second arms. Each different output represents an absolute or specific angular configuration. The output is directed to a remote user of the output that converts the output to positional data for storage or use and/or provides a comparative visual display on a monitor or the like of the angular position of the first arm relative to the second arm. 
         [0013]    As used herein the term Hall effect refers to a potential difference on opposite sides of a thin sheet or plate of conducting or semiconducting material (here the element) through which an electric current is flowing and created by a magnetic field applied perpendicular to the Hall element. 
       OBJECTS AND ADVANTAGES OF THE INVENTION 
       [0014]    Therefore, the objects of the present invention are: to provide a position sensor for sensing the angular position of one arm pivoting relative to a second arm; to provide such a sensor that can be retrofitted to devices with articulating arms; to provide such a sensor that can withstand use in hazardous or stressful conditions, while remaining accurate; to provide such a sensor that can easily be mounted on existing equipment with little or no modification to the equipment other than that the pivot pin and bushing that are replaced; to provide such a sensor that provides a remote output with respect to the relative position between two arms that can be utilized in a closed loop servo control system for robotic master/slave operation of the arms or to drive a visual display for an operator to use; and to provide such a sensor that is easy to use, comparatively inexpensive to produce and especially well adapted for the intended usage thereof. 
         [0015]    Other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention. 
         [0016]    The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a fragmentary side elevational view of a backhoe apparatus having three articulating arms and a bucket with a sensor and original pivot pin shown exploded from the arm. 
           [0018]      FIG. 2  is an enlarged cross sectional view of the backhoe and sensor, taken along line  2 - 2  of  FIG. 1 . 
           [0019]      FIG. 3  is an exploded and perspective view of the sensor. 
           [0020]      FIG. 4  is a fragmentary and partially schematic side elevational view of the backhoe and sensor with arms in a first configuration, taken along line  4 - 4  of  FIG. 2 . 
           [0021]      FIG. 5  is a view similar to  FIG. 4  with the arms in a second configuration. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. 
         [0023]      FIG. 1  shows an articulatable portion of a backhoe  1  with a sensor in accordance with the invention and generally identified by the reference numeral  5  shown prior to insertion in the backhoe  1 . 
         [0024]    The articulatable portion of the backhoe  1  has three arms  10 ,  11  and  12  and a scoop or bucket  13 . The arms  10  and  11  are joined at a pivot joint  14 . The arms  11  and  12  are joined at a pivot joint  15  and the bucket  13  is joined to the arm  12  at a pivot joint  16 . Each of the pivot joints  14 ,  15  and  16  initially include a pivot pin  26  shown being removed in  FIG. 1 . The angular position of the arm  10  relative to the arm  11  is controlled by a hydraulic cylinder  22 . The angular position of the arm  11  relative to the arm  12  is controlled by a hydraulic cylinder  23 . And the angular position of the bucket  13  relative to the arm  12  is controlled by a hydraulic cylinder  24 . 
         [0025]    In accordance with the invention, it is foreseen that many types of articulated devices may utilize the sensor  5  whether initially fitted with the sensor  5  or retrofitted with the sensor  5 . It is also foreseen that the sensor  5  may be used with any number of articulated arms on a device and with many different types of tools such as a clamshell scoop, a jackhammer, a robotic hand or the like. 
         [0026]    In the embodiment shown, the backhoe  1  has three pivot joints  14 ,  15  and  16  which each originally came with a conventional pivot pin  26  which are each carefully removed so as to not disturb the structure of the joint or paint about the pin  26  and replaced by the sensor  5 . 
         [0027]    The sensor  5  includes a bearing  30  and a replacement pin  31 . 
         [0028]    As seen in  FIG. 2 , the bearing  30  includes a perforated annular sleeve  35  that is sized and shaped to fit between an arm, such as arm  11  and an associated pin  31  while allowing relative rotation between the pin  31  and the arm  11 . A companion bearing  36  is located opposite the bearing  30 . The bearing  30  is press fit into the arm  11  and positively rotates with the arm  11 . 
         [0029]    Mounted on the end of the bearing sleeve  35  is a location positioning flange or ring  38 . The ring  38  positions the bearing  30  relative to the arm  11 . Mounted in groups of three on each side of the bearing  30  and diagonally opposed between groups are magnets  40 . The magnets are high gauss magnets. It is foreseen that magnets in any combination or type necessary to provide for the sensor  5  may be used, but high gauss rare earth magnets are preferred. 
         [0030]    The pin  31  is an elongate generally cylindrical rod with a Hall effect element receiver  42  at one end thereof. The receiver  42  includes a partially threaded bore  44  that extends radially and axially inward from one end  45 . The exterior of the pin  31  around the bore  44  is of a smaller diameter than a remainder of the pin  31 . 
         [0031]    A threaded surface  48  on the outside of the pin  31  receives a keeper nut  50  (see  FIG. 2 ). 
         [0032]    The pin  31  includes a hall effect element  55  that has a cylindrical shaped outer body  56  with an interior plate or sheets and an electrical lead  57 . The body  56  mounts snugly in the receiver  44  and radially in line with the magnets  40 , so that the magnets create a magnetic field that is perpendicular to the element  55  plate as the magnets and plate rotate relative to one another. The lead  57  carries a signal to a remote location to a sensor signal receiver  59 . 
         [0033]    A plug  61  is externally threaded to be treaded into the receiver  44  behind the Hall effect element  55 . A non magnetic spring washer  63  is located between the plug  61  and the element  55 . The plug  61  has a length so that, when fully seated in the receiver  44 , the plug  61  snugly holds the element  55  in place. The plug  61  has a front face  66  with three apertures  67 ,  68  and  69 . 
         [0034]    A grommet  70  mounts in aperture  68  and both are penetrated by the element lead  57 . The apertures  67  and  69  may be utilized to receive a tool to rotate the plug  61 . 
         [0035]    A placement pin  72  is received in the pin  31  and element  55  when joined to prevent relative rotation therebetween. 
         [0036]    A bolt  75  is received in a threaded bore in the pin  31  opposite the bore  44 . The bolt  75  secures the pin  31  to the arm  10  with the nut  50  and prevents relative rotation therebetween. 
         [0037]    In use the original pins  26  are removed and the pins  31  are inserted and secured as shown in  FIG. 2 . The bearings  31  are also inserted and secured to respective arms.  FIGS. 4 and 5  show relative rotation between arms such as arms  10  and  11 . As shown, the magnets  40  rotate with the arm  11  as it rotates relative to the arm  10 . The element  55  is stationary with respect to arm  10  and the magnets  40  rotate with respect to the element  55 . The “Hall effect” in the element  55  changes output for each position of arm  10  relative to arm  11  such that an output signal is produced and carried by the lead  57  to a receiver  59 . Each output different signal provides a specific angular position of arm  10  relative to arm  11  so as to allow a user or computer to receive the output at the receiver  59  and understand the relative position between the arms  10  and  11 . This is done for each pair of arms or arm and tool pairing on the backhoe  1 . 
         [0038]    It is to be understood that while certain forms of the present invention have been illustrated and described herein, it is not to be limited to the specific forms or arrangement of parts described and shown.