Abstract:
An electrically powered clamp has a housing, a motor attached to the housing, a ball screw driven by the motor via a belt, and a linkage driven at one end by the ball screw such that the linkage rotates an output shaft attached to the other end of the linkage. The motor and belt drive the ball screw between a fully extended position to rotate the shaft to a clamped position, and a fully retracted position to rotate the shaft to an unclamped position. A built-in computer monitors and controls the clamp. The clamp can also be controlled and monitored by a remote pendant. Indicator lights on the housing and remote pendant convey clamp status information. The clamp is programmable and can memorize the clamped and unclamped positions. The clamp uses velocity and position feedback to determine appropriate drive mode. Torque monitors and timers determine if the clamp becomes stuck.

Description:
[0001]    The present application is a continuation-in-part of U.S. patent application Ser. No. 09/887,293, filed Jun. 22, 2001, and entitled, Electric Clamp, and is hereby incorporated by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Technical Field  
           [0003]    This invention pertains to power clamps and more particularly to clamps driven by electric motors. Clamps are used to secure an object to aid assembly or to secure it during transport from one location to another.  
           [0004]    2. Description of the Related Art  
           [0005]    The robotics and automation industry heavily relies on power clamps for securing objects such as mechanical or electrical components so those components can be integrated into an assembly or moved from one assembly station to another. Clamps of various sizes, shapes, and configurations have been used to secure objects ranging in size from as small as electronic circuit boards to as large as entire automobile body panels. Clamps can be comprised of opposing members, but are more commonly mounted to a work surface and use one arm to pin the object against the work surface.  
           [0006]    The majority of clamps currently used in the automation industry are pneumatically powered. This is primarily due to the significantly greater power obtainable from a pneumatically powered clamp compared to existing electrical clamps of similar size. Disadvantages of prior versions of electric clamps include being large, complex, delicate, or expensive.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention uses an innovative design to produce an electric clamp with high clamping power in a small and relatively inexpensive package. In one embodiment, the clamp of the present invention comprises an electrically powered clamp having a housing, a motor attached to the housing, a ball screw driven by the motor via a belt, and a linkage driven at one end by the ball screw such that the linkage rotates an output shaft attached to the other end of the linkage. The motor and belt drive the ball screw between a fully extended position to rotate the output shaft to a clamped position, and a fully retracted position to rotate the output shaft to an unclamped position. A built-in controller monitors and controls the clamp. The clamp can also be controlled and monitored by a remote pendant. Indicator lights on the housing and remote pendant convey clamp status information. The clamp is programmable and can memorize the clamped and unclamped positions. The clamp uses velocity and position feedback to determine appropriate drive mode. Torque monitors and timers determine if the clamp becomes stuck.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    So that the manner in which the described features, advantages and objects of the invention, as well as others which will become apparent, are attained and can be understood in detail, more particular description of the invention briefly summarized above may be had by reference to the embodiments thereof that are illustrated in the drawings, which drawings form a part of this specification. It is to be noted, however, that the appended drawings illustrate only typical preferred embodiments of the invention and are therefore not to be considered limiting of its scope as the invention may admit to other equally effective embodiments.  
         [0009]    [0009]FIG. 1 is a side view of an electric clamp constructed in accordance with one embodiment of the present invention showing the clamp in its clamped position.  
         [0010]    [0010]FIG. 2 is a side view of the clamp of FIG. 1, but showing the clamp in its unclamped position.  
         [0011]    [0011]FIG. 3 is a section view along Section  3 - 3  of FIG. 2.  
         [0012]    [0012]FIG. 4 is a top view of the clamp of FIG. 1 with cover removed.  
         [0013]    [0013]FIG. 5 is a top view of the clamp of FIG. 1 with cover on and remote pendant attached.  
         [0014]    [0014]FIG. 6 is an end view of the clamp of FIG. 1.  
         [0015]    [0015]FIG. 7 is a schematic diagram of the electronics used in the clamp of FIG. 1.  
         [0016]    [0016]FIG. 8 is a side view of an electric clamp constructed in accordance with a second embodiment of the present invention showing the clamp in its clamped position.  
         [0017]    [0017]FIG. 9 is a partial isometric view of a drive system of the electric clamp of FIG. 8.  
         [0018]    [0018]FIG. 10 is a side view of an electric clamp constructed in accordance with a third embodiment of the present invention showing the clamp in its clamped position.  
         [0019]    [0019]FIG. 11 is a side view of the clamp of FIG. 10, but showing the clamp in its unclamped position.  
         [0020]    [0020]FIG. 12 is a side view of an electric clamp constructed in accordance with a fourth embodiment of the present invention showing the clamp in its clamped position.  
         [0021]    [0021]FIG. 13 is a side view of the clamp of FIG. 12, but showing the clamp in its unclamped position.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0022]    [0022]FIGS. 1 and 2 illustrate an electric clamp  10 . Electric clamp  10  has a housing  12  that serves as a base on and inside of which other structural elements are mounted. Housing  12  protects the housed components. Housing  12  can be made of any durable, lightweight material, but is preferably metal or another conductive material that can be electrically grounded. It is desirable that housing  12  be easily formed into complex shapes to allow for space-efficient integration of various components.  
         [0023]    Electric clamp  10  further comprises a motor  14 . Motor  14  is a conventional electrically driven motor that mounts to housing  12  and serves to drive motor gear  16 . The motor  14  can be virtually any type of electric motor. Different applications may dictate whether the motor is preferably an ac or dc motor, a stepper motor, an induction motor, a brushless motor, or other less common motor type. A dc motor offers the advantages of low cost and simple control requirements, but other requirements may dictate other motor types. Larger motors are generally required for larger clamps.  
         [0024]    Motor gear  16  is on the output shaft  17  of motor  14  and engages ball nut gear  18  (FIG. 3). Ball nut gear  18  attaches to and drives ball nut hub  20  in response to motor gear  16 . Hub  20  attaches to and drives ball nut  22 . As ball nut  22  is rotated in place by hub  20 , ball screw  24 , a threaded shaft going through ball nut  22 , advances or retreats depending on the direction of rotation of ball nut  22 . The gear ratios for motor gear  16  and ball nut gear  18  can be chosen to produce a desired torque or rotational rate for ball nut  22 . That determines the power or rate of advance/retreat of ball screw  24 .  
         [0025]    One end of ball screw  24  pivotally attaches to one end of link  26 . The opposite end of link  26  pivotally attaches to an end of link  28 . Clamp output shaft  30  is rigidly attached to the opposite end of link  28 . Clamp arm  31  (shown in phantom line) is mounted to clamp output shaft  30 . Clamp arms of various sizes can be attached, depending on a user&#39;s needs.  
         [0026]    In the embodiment of FIG. 1, slave motor  32  is used to provide additional torque. Slave motor  32  is wired in parallel with motor  14  to assist motor  14 . The same voltage is applied to both motors. Slave motor  32 , through its output shaft  33 , drives motor gear  34 , which drives ball nut gear  18 , each identical in operation to motor  14 , output shaft  17 , and motor gear  16 , respectively.  
         [0027]    In the basic operation of clamp  10  of FIG. 1, power is supplied to motors  14  and  32  to drive motor gears  16  and  34 . Those gears drive ball nut gear  18 , which drives hub  20 . Hub  20  rotates ball nut  22 . Ball nut  22  drives ball screw  24 , which drives links  26  and  28 , rotating clamp output shaft  30  to a fully clamped (FIG. 1) or fully released (FIG. 2) position, depending on the direction of rotation of ball nut  22 .  
         [0028]    [0028]FIG. 2 shows an optional brake  37  attached to the motor shaft  33  of slave motor  32  that can be used to stop slave motor  32 , and therefore stop the motion of clamp  10 . Brake  37  may be required if large clamp arms having high rotational inertia or significant weight are used. In those situations, the inertia or moment may cause clamp  10  to move toward the clamped or unclamped position even though no power is applied. Brake  37  prevents such drift.  
         [0029]    While the structural elements described above are sufficient to describe the basic configuration and operation of clamp  10 , there are many other elements that enhance its functionality. Encoder  38  mounts to motor  14 . The encoder  38  shown in FIG. 1 attaches to motor shaft  17  of motor  14 . Encoder  38  provides motor angle information for position feedback. The motor angle information tells how far motor  14  has rotated from the clamped or unclamped position, therefore determining the position of clamp arm  31 . An absolute or incremental encoder can be used, or another type of motor position sensor, such as a resolver, can be used.  
         [0030]    Ball nut  22  is supported by thrust bearing  40 . Thrust bearing  40  mounts between housing  12  and ball nut  22  and carries the thrust load generated during the clamping process. Similarly, ball screw  24  is supported by support bearing  42 . Bearing  42  mounts between housing  12  and ball screw  24  and prevents lateral loads from being transferred to ball screw  24  during extreme loading conditions. Bearing  42 , in conjunction with retainer ring  44 , also acts as a barrier to prevent grease from moving from links  26 ,  28  into the vicinity of ball nut  22 .  
         [0031]    Stop collar  46  is adjustably fixed to ball screw  24  and physically inhibits further retraction of ball screw  24  once stop collar  46  is pulled into contact with bearing  42 . This feature is useful to prevent clamp  10  from opening too far. The need for restriction commonly arises when objects in the vicinity of clamp  10  interfere with the full range of motion of clamp  10 , particularly when longer clamp arms are used.  
         [0032]    [0032]FIG. 4 shows thumb wheel  48  attached to the motor shaft of slave motor  32 . Wheel  48  allows clamp  10  to be moved without electrical power. This is useful when no power is available, such as during initial setup, or when the drive control electronics (described below) are unavailable. This can occur when clamp  10  becomes extremely stuck or the electronics themselves fail. Wheel  48  is normal concealed and protected by access cover  50 , as shown in FIG. 5.  
         [0033]    [0033]FIG. 5 also shows clamp buttons  52  and  54 . Buttons  52 ,  54  allow a user to drive clamp  10  to a clamped or unclamped position, respectively. The motion produced is relatively slow in both directions and clamp  10  moves only while a button is depressed. Buttons  52 ,  54  are located in recesses  56  (FIG. 1) in cover plate  58 . Recesses  56  are covered to prevent infiltration of contaminates and to prevent inadvertent engagement of buttons  52 ,  54 . A pointed tool, such as a screwdriver, is needed to actuate buttons  52 ,  54 .  
         [0034]    Also located on cover plate  58  are status lights  62 ,  64 . Clamped status light  62 , when lit, indicates clamp  10  is very close to the programmed clamped position. (The programmable aspects are discussed below.) Similarly, unclamped status light  64  lights up when clamp  10  is very close to the programmed unclamped position. In addition, there are indicator lights  66  (FIG. 6) on control circuit board  68  (FIG. 2) within housing  12 . Indicator lights  66  are viewed through window  70  (FIG. 1) and provide an operator information about the operational state of clamp  10 .  
         [0035]    Electrical power is primarily supplied to clamp  10  through control cable  72  (FIG. 6), which fastens to cover plate  58  and electrically connects a wire bundle to electronics within housing  12 . Power could be dc, ac, 24 volts, or 48 volts—a preferred embodiment uses 24 volts dc. Higher voltages, such as 110 or 220 ac voltages, could be used, but are generally considered unacceptable because of safety concerns. Electrical power is typically provided by an external power supply with enough current capacity to service several clamps.  
         [0036]    Other electrical signals, such as a command signal from the user or clamp status information, are also transmitted through control cable  72 . The electronics within housing  12  include control circuit board  68  (FIG. 1). Control board  68  has the circuitry necessary to control clamp  10 .  
         [0037]    [0037]FIG. 7 shows conceptually the electronic components comprising control board  68 . Power conditioner  74  is used to provide clean 5 and 15 volts dc signal to control board  68 . A CPU  76  mounted to control board  68  controls all aspects of the operation of clamp  10 . CPU  76  comprises timers, counters, input and output portals, memory modules, and programmable instructions to regulate motion algorithms, error recovery, status messaging, test display, limit adjustment, and pushbutton control. Indicator lights  66  are connected to CPU  76 .  
         [0038]    Clamp  10  has pushbuttons  79 ,  81 ,  83 ,  85  on the exterior of housing  12  to permit a user to adjust the position to which CPU  76  will command the motor to move upon receiving a clamp or unclamp command. There is also a pushbutton  78  allowing CPU  76  to learn and memorize the clamped position based on when the motor stalls. This is usually a quicker way to set the programmed clamp position than by using pushbuttons  79 ,  81 ,  83 ,  85 . All of those pushbuttons  78 ,  79 ,  81 ,  83 ,  85 , as well as clamp/unclamp buttons  52 ,  54 , are illustrated in FIG. 7.  
         [0039]    CPU  76  controls motor drive circuit  80  and enabling circuit  82 . Those circuits  80 ,  82  supply the drive current sent to slave motor  32  and motor  14 . Because motor drive circuit  80  is easily damaged by logically inconsistent electrical input, enabling circuit  82  is used to independently assure logically consistent input. If excess current is detected by current monitor  84 , such as may occur if clamp  10  is stalled or stuck, the output from motor drive circuit  80  is inhibited. A user may set an over-current threshold using over-current circuit  86 .  
         [0040]    All user interfaces described above are also found on remote pendant  88  (FIG. 5). Thus, remote pendant  88  allows a user to operate clamp  10  some short distance from clamp  10 . This can be useful if clamp  10  is placed deeply within an automation tool, making the interfaces on housing  12  inaccessible. Lights  90  equivalent to indicator lights  66  are found on remote pendant  88 , so clamp status information can be observed. Remote pendant power supply  91  (FIG. 5) provides electrical power to clamp  10  through remote pendant  88  via connector  93  on cover plate  58 . This is useful if conventional power is unavailable, as is often the case in the early stages of building an automation system. Pushbuttons  92 ,  94 ,  96 ,  98 ,  100 ,  102 , and  104 , provide the same functionality as pushbuttons  78 ,  54 ,  52 ,  85 ,  83 ,  81 , and  79 , respectively, using remote pendant  88 .  
         [0041]    Clamps used in the automation industry are commonly used in conjunction with hundreds of other clamps, each clamp performing a specific function in a carefully choreographed manner. Often the multitude of clamps is controlled by a central controller issuing commands to the various clamps at the proper time. Clamp  10  accepts such external control commands through interface  106  (FIG. 7). Clamp  10  is typically isolated from the external controller using optical isolators  108 , however simple lights or light emitting diodes (LEDs) may also be used. The lights or LEDs can convey essential status information such as clamped, unclamped, or a fault condition. This information can be passed to the central controller as well.  
         [0042]    Referring now to FIG. 8, an alternate embodiment of the present invention is depicted as clamp  210 . Like the preceding embodiment, the components of clamp  210  are located entirely within its housing  212 , other than the clamp arm  231  and the remote pendant (not shown). The primary difference between clamp  210  and clamp  10  of FIGS. 1 and 2 is the belt drive assembly  201  (FIG. 9) utilized by clamp  210 . Thus, clamp  210  is very similar to clamp  10 , but in this embodiment of the present invention, the direct gear-to-gear drive assembly of clamp  10  illustrated in FIGS.  1 - 3  is replaced by the belt drive assembly  201 . The belt drive assembly  201  uses at least one drive sprocket (two are shown:  216 ,  234 ), a drive belt  207 , and a center sprocket  218 . The sprockets  216 ,  234 , and  218  have external teeth that engage internal grooves on the drive belt  207 . The drive sprockets  216 ,  234  engage and drive the belt  207  which, in turn, drives the center sprocket  218 . The sprockets  216 ,  234  are mounted to drive shafts  217 ,  233 , which extend from motors  214 ,  232 , respectively. These components are similar or identical to the drive shafts  17 ,  33  and motors  14 ,  32 , described above for the previous embodiment.  
         [0043]    To maintain adequate separation, sprockets  216 ,  234  are sufficiently spaced apart in a radial direction (relative to their axes of rotation) so as to not make direct contact with the center sprocket  218  that is located between sprockets  216 ,  234 . Center sprocket  218  is mounted to and drives a ball nut hub  220  having internal threads. As ball nut hub  220  is rotated by center sprocket  218 , a ball screw  224  advances or retreats depending on the direction of rotation of ball nut  222 . Ball screw  224  is a threaded shaft going through ball nut hub  220 , and is otherwise identical in function to ball screw  24  as described above. The tooth ratios for sprockets  216 ,  234 ,  218 , and belt  207  are selected to produce a desired torque or rotational rate for ball nut hub  220 , which determines the power or rate of advance/retreat of ball screw  224 . Other than the components employed and operated by belt drive assembly  201 , clamp  210  utilizes the same elements and operates in an identical manner as the previously described embodiment including, for example, a sensor or encoder  238  on motor  214 . The ball screw  224  is coupled to a linkage  226  to manipulate an output shaft  230  and a clamp arm  231 .  
         [0044]    Referring now to FIGS. 10 and 11, a third embodiment of the present invention is depicted as an electric clamp  310 . Electric clamp  310  has a housing  312  and a number of other components including a lead screw  324 , which are all entirely enclosed within housing  312 . Clamp  310  is similar to the preceding embodiments in many respects, but differs primarily in the manner in which it manipulates the output shaft  330  and clamp arm  331 . In particular, clamp  310  uses a single electric motor  314 , which is preferably a linear actuator, to advance and retreat a lead screw  324  extending axially through the motor  314 . Consequently, no separate ball nut hub or ball nut are required.  
         [0045]    The lead screw  324  is further coupled to the output shaft  330  through components such as a linkage  326  and a piston  333 . The piston  333  is mounted in a chamber  335  that is located within the housing  312 . In this disclosure, the terms piston and chamber are not necessarily used in the conventional sense to include a sealing relationship. Rather, these terms are used to denote the relative motion of the components, i.e., substantial restriction of radial motion of the piston by the chamber, while allowing the piston to move axially within the chamber. In the version shown, motor  314 , lead screw  324 , and piston  333  are coaxial. The piston  333  is coupled to the lead screw  324  and the output shaft  330 , such that axial movement of the lead screw  324  by the electric motor  314  moves the piston  333  axially within the chamber  335 , and moves the output shaft  330  and the clamp arm  331  through a range of motion. The other components described above and used in conjunction with the previous embodiments are likewise available for use with and employed by clamp  310 . In this version of the invention, the control circuit  368  of electric clamp  310  is located in an upper portion of the housing  312 .  
         [0046]    Referring now to FIGS. 12 and 13, a fourth embodiment of the present invention is depicted as an electric clamp  410 . Clamp  410  utilizes many of the components and features of the preceding embodiments, including a housing  412  and an electric motor  414  with a drive shaft  417  that is rotatable about an axis. In the depicted embodiment, motor  414  is mounted to an exterior of the housing  412 , and drive shaft  417  protrudes into the housing  412 . A helical coupling  415  is mounted to drive shaft  417  and is coupled to a ball nut hub (not shown). A ball screw  424  extends axially through the ball nut hub such that the ball screw  424  is axially advanced and retreated by rotation of the ball nut hub. The ball screw  424  is entirely enclosed within the housing  412 . The housing  412  also contains a chamber  435  that is coaxial with the drive shaft  417 . A piston  433  is located in the chamber  435 , and the piston  433  is coupled to the ball screw  424  such that movement of the ball screw  424  by the electric motor  414  moves the piston  433  axially within the chamber  435 .  
         [0047]    An output shaft  430  is also mounted to the housing  412 . The output shaft  430  has a linkage  426  coupled to the piston  433  for movement therewith, and a mounting portion for a movable element (clamp arm  431 ) to permit the movable element to at least partially extend from the housing  412 , and move the clamp arm  431  between clamped and unclamped positions. As described above for the previous embodiments, clamp  410  also has a control circuit  468  located within an upper portion of the housing  412  for controlling the motor  414 , and a sensor  438 , such as an encoder, that provides a signal to the control circuit indicative of a current position of the clamp arm  431 . The sensor  438  is coupled to the drive shaft  417  via a set of gears  444 , and the signal provided to the control circuit is indicative of a rotational position of the drive shaft  417 . The clamp  410  further comprises a remote pendant (not shown), which is identical to the one described above.  
         [0048]    The present invention offers many advantages over the prior art. Housing the electronics controlling the clamp internally is a significant advantage. Using two motors in tandem is a new and useful arrangement for making a more powerful electric clamp while staying within industry size standards. The remote control provided by the remote pendant is another novel advantage, as is the ability to drive the clamp with power supplied through the remote pendant when normal power is unavailable. The use of an encoder rather than limit switches allows for more intelligent, and more easily modified control. Being able to manually move the clamp using the thumb wheel allows for quick remedy for stuck or defective control condition. The ability to program a clamped and an unclamped position is new and useful, as is the ability to use software to command the clamp to stop when an unrecoverable stuck condition is sensed. The clamp allows for automatic learning of the programmed clamp and unclamped positions, and allows a user to fine tune those positions, if desired.  
         [0049]    While the invention has been particularly shown and described with reference to a preferred and alternative embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.