Abstract:
A sensor for measuring a clamp arm position in a power clamp provides a sensor wheel that may fit beneath the clamp arm. A low profile sensor body abuts an edge of the sensory wheel to detect the sensor position without undue change in the power clamp or clearance about the power clamp.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to power clamps used in industry, and in particular, to a sensor for sensing the position of a clamp arm of a power clamp.  
           [0002]    Power clamps provide a pneumatic and hydraulic cylinder that drives a rotating clamp arm. Depending on the application, the clamp arm may rotate in an arc ranging from 18 to 118 degrees between a clamped and unclamped position.  
           [0003]    When power clamps are used in automated processes, it is desirable to develop an electrical signal indicating the position of the clamp so that the clamping process may be monitored and verified. Traditionally this has been done by detecting a position of the piston in the cylinder of the power clamp. Monitoring the piston, however, is less than ideal, in part, because it only indirectly indicates the position of the clamp arm and cannot detect possible failure of the clamp arm rotating mechanism.  
           [0004]    U.S. Pat. No. 5,694,042 describes a sensor for a power clamp that senses the position of the clamp arm directly by attaching two sensing disks directly to a free end of the axle of the clamp arm opposite the clamp arm. The sensor described is relatively bulky and thus may not be suitable for applications requiring tight clearances. Further, the sensor requires special modification of that axle through the drilling of holes into the axle by which to mount the sensing disk.  
         BRIEF SUMMARY OF THE INVENTION  
         [0005]    The present invention provides a low profile sensor for directly sensing the clamp arm position. A single sensing ring is slipped around the axle of the clamp arm beneath the clamp arm to be received within a notched cutout of a sensor body attached to the power clamp housing. The sensing ring includes radially extending metallic targets that may be sensed by corresponding proximity sensors in the sensor body-directed toward the notch of the sensor body. Multiple targets may be placed in the sensing wheel and multiple sensors in the plane of the sensing body so that a single wheel may be used, making the system extremely compact.  
           [0006]    Specifically, the present invention provides a sensor for use with a clamp having a piston actuated rotary clamp arm. The sensor includes a sensing ring coaxially attached to an axle of the rotary clamp arm to rotate therewith about a rotation axis. The sensing ring has a circumferential wall, including at least one target exposed toward the circumferential wall. A sensing body has a notch opening on one side to receive the sensing ring with motion of the sensor body perpendicular to the rotation axis and to present a sensor body wall adjacent to a portion of the circumferential wall of the sensing ring. The sensor body holds at least one proximity detector directed at the sensing body wall and detecting the target as it rotates with the sensing ring and rotary clamp.  
           [0007]    Thus, it is one object of the invention to provide a sensor that may be easily assembled to a power clamp and maintained after assembly. The notch in the sensor body allows the sensor body to be installed and removed without removal of the clamp arm that retains the sensor ring.  
           [0008]    The sensor may have only one sensor ring with multiple coplanar targets exposed at the circumferential wall.  
           [0009]    Thus, it is another object of the invention to provide an extremely low-profile sensor that may fit between the clamp arm and the power clamp body.  
           [0010]    The thickness of the sensor may be substantially equal to the thickness of the sensing ring. An electrical connector and signal lights may be mounted on an overhang portion on the side of the power clamp. The overhang portion could be integral or a separate element.  
           [0011]    Thus, it is another object of the invention to provide a sensor that has minimal thickness so as to allow the clamp arm to be positioned close to the power clamp body.  
           [0012]    The sensor body may include two opposed mounting surfaces perpendicular to the rotation axis for mounting against a face of the power clamp. Alternatively, the sensor body may by symmetrical about a diameter of the sensing ring when installed, so as to be rotatable to mount against either of two faces of the power clamp.  
           [0013]    Thus, it is another object of the invention to provide a design that may be used on either side of the clamp housing for left- or rightward extending clamp arms.  
           [0014]    The targets may be metal targets extending radially toward the circumferential wall of the sensing ring.  
           [0015]    Thus, it is another object of the invention to produce a robust sensing system that may use passive components on the rotating portion.  
           [0016]    The sensing ring may include multiple targets.  
           [0017]    Thus, it is another object of the invention to allow the sensor to work with clamp rotations of different angles without substantial change to the sensor body, but simply by modification of the sensor ring or the location of the targets in the sensor ring.  
           [0018]    These particular objects and advantages may apply to only some embodiments falling within the claims and thus do not define the scope of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    [0019]FIG. 1 is a perspective view of a power clamp showing placement of the clamp arm on either side of the clamp head and the positioning of the sensor of the present invention under the clamp arm on the right side of the clamp head;  
         [0020]    [0020]FIG. 2 is an exploded, perspective view of the clamp arm and its axle such as may fit through a sensing ring, the sensing ring received by a notch in a sensor body attached to the clamp head;  
         [0021]    [0021]FIGS. 3 and 4 are front elevational views of the sensor of FIG. 2 showing alignment of targets in the sensor ring with proximity detectors in the sensor body for a first and second clamp position;  
         [0022]    [0022]FIG. 5 is a view similar to FIGS. 3 and 4 showing an alternative embodiment of the invention having a notch with a reduced arcuate extent;  
         [0023]    [0023]FIG. 6 is a side elevation of FIG. 5 showing the low profile of the sensor of FIG. 5 and the use of an overhang portion to carry light-emitting diodes and an electrical connector that would otherwise increase the sensor thickness under the clamp arm ; and  
         [0024]    [0024]FIG. 7 is a perspective view of an alternative overhang portion attached by wires to the sensor to be independently mounted to the clamp. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0025]    Referring now to FIG. 1, a power clamp  10  includes a cylinder  12  that may receive hydraulic or pneumatic fluid through supply hoses  14  to drive an internal piston (not shown) up or down. A shaft (also not shown) of the piston is received by a clamp head  16  that includes a mechanism for converting the reciprocating linear motion of the piston shaft into a rotary motion acting on an axle  18 . In the following example, the shaft is square in cross-section, but it will be understood that other shaft shapes may also be used. A clamp arm  24  may be placed on the axle  18  to rotate therewith about an axis  22  to provide a rotary clamping action  26 .  
         [0026]    The axle  18  may be repositioned to extend alternatively from a right face  20   a  or a left face  20   b  of the clamp head  16  so as to be positioned the clamp arm  24  on either side of the clamp head  16  as shown. A sensor  28  may likewise be attached to either face  20   a  or  20   b  of the clamp head to be adjacent to the clamp arm  24 , as will be described.  
         [0027]    Referring to FIGS. 1 and 2, the sensor  28  includes generally a sensor ring  30  and a sensor body  38 . The sensor ring  30  is positioned between the clamp arm  24  and a face  20  of the clamp head  16  and is constructed of a disc-shaped, non-metallic material having a circular bore  32  sized to receive the circular cross section of the axle  18  and to rotate therewith as keyed to the clamp arm by pins  31 . An outer circumferential wall  34  of the sensor ring  30  includes a series of radial bores  36 , which may receive one or more metallic targets  39  press fit into the sensor ring  30 . As will be described, movement of the targets  39  among the bore  36  allow changing the detected limits of the clamp arm  24 .  
         [0028]    The sensor body  38  includes a hemi-circular notch  40  that may receive the sensor ring  30  with lateral motion of the sensor body indicated by arrow  42 . Thus the sensor body may be located in proximity to the sensor ring  30  after the sensor ring  30  has been assembled onto the axle  18 . In this regard, the arc of the notch  40  is somewhat less than 180 degrees allowing sufficient clearance for this sideward engagement.  
         [0029]    The sensor body  38  includes a front face  44   a  and a rear face  44   b  sized to abut the faces  20   a  and  20   b  of the clamp head  16 . Mounting holes  46  receiving cap screws  48  to mount either surface  44   b  against face  20   a  or surface  44   a  against face  20   b . In this way, the sensor  28  may be used with the clamp arm  24  on either side of the clamp head  16 . The thickness  33  of the sensor ring  30  and sensor body  38  may be comparable and minimized so as to allow clamp arm  24  to be as close as possible to clamp head  16 .  
         [0030]    The notch  40  in the sensor body  38  defines a sensor body wall  52  having an arc generally conforming to the circumferential wall  34  of the sensor ring  30 . Directed toward the sensor body wall  52  are a first and second proximity sensor  54  of conventional design that may detect the targets  39  in the circumferential wall  34  as they move past the proximity sensors  54 . A variety of different types of proximity sensors  54  may be used, for example, those detecting eddy current resistance, inductive change, or magnetic hysteresis, according to methods well known in the art.  
         [0031]    Referring now to FIG. 3, the proximity sensors  54  communicate with amplification circuitry  56 , which provides switch signals on lines  58  that may be forwarded to an industrial control device or the like. The proximity sensors  54  may be spaced at an angular range  55  along the notch  40  sufficient to exceed the angular operating range of the clamp arm  24 , for example, 120 to 135 degrees. While a single target  39   a  may be used and detected as it passes each proximity sensor  54 , this limits the detection of the clamp arm  24  to the limits defined by the separation of the proximity sensors  54 . Accordingly, multiple targets  39   a  and  39   b  may be used to define a subset of the angular range of the proximity sensors  54  at which clamp arm motion will be detected. Also, the sensor ring could be designed to exceed the angular operation range of clamp arm. (Greater than 135 degree but less then 270 degrees)  
         [0032]    For example, and referring to FIG. 3, with the clamp arm  24  in the horizontal position, target  39   a  will align with proximity sensor  54   a  producing a first limit signal via circuitry  56  (e.g., a clamp signal). Rotation of the clamp arm  24  to a vertical position as shown in FIG. 4 (90 degrees away from the position shown in FIG. 3) brings target  39   b  into alignment with proximity sensor  54   b  producing a separate limit signal (e.g. an unclamp signal). Despite the separation of the proximity sensors  54   a  and  54   b  by an amount greater than 90 degrees, 90-degree motion limits may be readily detected.  
         [0033]    Additional flexibility in setting detection limits may be provided by drilling multiple bores  36  in the sensor ring  30  so that the location of targets  39  may be moved on an application-by-application basis.  
         [0034]    The proximity sensors  54   a  and  54   b  and the circuitry  56  may be potted within an injection molding housing or may be molded in place during the injection molding processes (RIM molding).  
         [0035]    Referring now to FIGS. 5 and 6, in a second embodiment, the hemicircular notch  40  of the sensor body  38  may be reduced to an angular extent less than ninety degrees to support two proximity sensors  54   a  and  54   b  separated by the angular range  55  of approximately forty-five degrees. While a single target  39   a  may be used and detected as it passes each proximity sensor  54 , this limits the detection of the clamp arm  24  to the limits defined by the separation of the proximity sensors  54 . Accordingly, again, multiple targets  39   a  and  39   b  may be used but this time to define a superset of the angular range 55 of the proximity sensors  54  at which clamp arm motion will be detected.  
         [0036]    For example, with the clamp arm  24  in the horizontal position, target  39   b will align with proximity sensor  54   b  producing a first limit signal via circuitry  56  (e.g., a clamp signal). Rotation of the clamp arm  24  to a vertical position brings target  39   a  into alignment with proximity sensor  54   a  producing a separate limit signal (e.g. an unclamp signal). Despite the separation of the proximity sensors  54   a and  54   b  by an amount less than 90 degrees, 90-degree motion limits may be readily detected.  
         [0037]    As shown best in FIG. 6, the thickness  60  of the sensor body  38  is comparable to the thickness of the sensor ring  30  both of which may be less than approximately one-half inch so as to fit easily under the clamp arm  24  without interference. A overhang portion  62  of the sensor body  38  may extend over a side face  64  of the clamp head perpendicular to the face  20  allowing components requiring greater depth to be mounted on the overhang portion  62  while keeping the thickness  60  measured along an axis from the face  20  to the underside of the clamp arm  24  low. Among the components mounted on the overhang portion  62  can be a plug type electrical connecter  66  receiving a connecting plug (not shown). The plug type electrical connector  66  is oriented on the overhang portion  62  so that any cabling connected to the connector  66  is directed away from the path of the arm  24 .  
         [0038]    Light-emitting diode displays  70  may also be exposed on the overhang portion  62  so as to provide a larger indicator area. The light-emitting diode displays  70  may read signals from the proximity sensors  54  to display clamp state (e.g., open, closed, or moving) and/or diagnostic information about the sensor (e.g., presence of power, detection of targets  39 ).  
         [0039]    The symmetry of the sensor body  38  where it attached to the clamp head  16  and the symmetry of the proximity sensors  54  about a diametric axis  72  of the sensor wheel, allow the sensor body  38  to be rotated about the diametric axis  72  to be attached to the opposite side of the clamp head  16  as shown in FIG. 6 as sensor body  38 ′. Again any cable connected to the connector  66  is directed away from the clamp arm  24 .  
         [0040]    Referring now to FIG. 7, the overhang portion  62  need not be integral to the remainder of the sensor body  38  but may be joined only by flexible electrical lines  58  and the overhang portion  62  attached independently to the clamp head  16  on side face  64 . This configuration provides even greater flexibility in mounting the sensor body  38 , allowing the sensor body  38  excluding the overhang portion  62  to be rotated and the overhang portion  62  to remain unrotated or allowing movement between the two so that the overhang portion  62  may be mounted more convently.  
         [0041]    It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein, but include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims.