Abstract:
An electronic detent apparatus and method for simulating a mechanical detent comprises a sensor connected to a microprocessor. A servo-motor is connected to the microprocessor and has a motor drive connected to a clutch. The clutch may engage a wheel disposed upon a rail or surface to effect the simulation of a mechanical detent through the microprocessor controlled servo-motor. The method for simulating a mechanical detent comprises the steps of moving an axis and monitoring the position and velocity of the axis. The position and velocity of the axis is then compared to a pre-specified position threshold value and a pre-specified velocity threshold value using a microprocessor disposed on the axis. A servo-motor is activated to accelerate the axis to a pre-specified position using a clutch controlled by the servo-motor when the position and velocity of the axis exceed the pre-specified position and velocity threshold values. Prior to engaging the clutch, the servo-motor drive speed is adjusted to nearly match the speed of the axis. The clutch operates on a wheel that is connected to the clutch and that is disposed upon a rail. The step of monitoring the position and velocity of the axis may be limited to monitoring only the position or velocity of the axis depending on the desired control characteristics of the electronic detent.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    This invention is directed to an electronic detent apparatus and method for simulating the effect of a mechanical detent. The use of mechanical detents to position mechanical apparatus is well known in the art and are used in a variety of applications, including in conjunction with positioning radiographic equipment.  
           [0002]    In radiographic procedures it is frequently necessary for an operator to manually position an x-ray assembly (i.e., a movable axis or movable assembly) to a previously specified precise position or configuration. For example, it is common to position the focal spot of the x-ray device about 1 meter above the receptor plane, with the focal spot centered front to rear and side to side relative to the receptor plane and with the centerline of the collimating device aligned with a line from the center of the receptor to the focal spot. To do this, mechanical locating features have been previously used to provide the operator with an indication that he is approaching the previously specified location. These prior mechanical locating features hold the assembly or movable axis in the specified location and return the assembly or movable axis to the specified location if moved a small distance. These mechanical locating features were and are commonly referred to as detents. The assembly or movable axis can be fixed at multiple pre-specified locations through the use of multiple mechanical detents.  
           [0003]    Past mechanical detents came in many variations. The most common designs included the use of a spring-loaded roller (or plunger) which operated on a surface having grooves or recesses. Movement of the movable axis caused relative motion between the spring-loaded roller and the surface, with the spring-loaded roller engaging the groove or recess at a pre-specified position. Engaging the groove or recess brought the movable axis to a stop at the pre-specified location within the groove or recess. As the spring-loaded roller engaged the groove or recess, the operator experienced a “pull” as the roller accelerated into the groove or recess. The feel of being pulled into the detent provided the operator with tactile feedback as to whether the detent had been reached. This type of mechanical detent design is common to many other types of equipment, including automotive gear shift levers.  
           [0004]    Alternatively, prior detent designs could use magnets physically attached to a rail. A circuit board containing Hall effect sensors would activate an electronic switch to bring the movable assembly to a stop when the circuit board was passed by the magnet(s) physically attached to the rail. The magnets in this alternative prior mechanical detent design were physically affixed to the rail in the same manner as the previously discussed mechanical ramps.  
           [0005]    The disadvantages associated with these prior mechanical detents were numerous. For example, adjusting the detenting force was difficult because the detent was a physical object (e.g., a steel wedge), or had a fixed property (e.g., a fixed magnetic field) that was difficult to change. Adjusting or changing the detenting positions was difficult because the mechanical detent had to be physically moved. Adding or removing mechanical detenting positions was very difficult. Also, mechanical detents were unreliable, wore out, and cost money. Finally, it was often difficult to find enough space for multiple mechanical detents, which resulted in additional design time as well as designs that were bulkier than they would be otherwise.  
           [0006]    Therefore, a need has long existed for a new and improved detent apparatus and method that overcomes the difficulties associated with past mechanical detents.  
         BRIEF SUMMARY OF THE INVENTION  
         [0007]    In a preferred embodiment of the invention, the electronic detent apparatus includes a sensor connected to a microprocessor. A servo-motor is connected to the microprocessor and has a motor drive connected to a clutch. The clutch may engage a wheel disposed upon a rail or surface to effect the simulation of a mechanical detent through the microprocessor controlled servo-motor.  
           [0008]    In a preferred embodiment of the invention, a method for simulating a mechanical detent comprises the steps of moving an axis and monitoring the position and velocity of the axis. The position and velocity of the axis is then compared to a pre-specified position threshold value and a pre-specified velocity threshold value using a microprocessor disposed on the axis. A servo-motor is activated to accelerate the axis to a pre-specified position using a clutch controlled by the servo-motor when the position and velocity of the axis exceed the prespecified position and velocity threshold values. The servo-motor drive speed is adjusted to nearly match the speed of the axis before the clutch is engaged. The clutch operates on a wheel connected to the clutch and disposed upon a rail. In an alternative embodiment of the invention, the step of monitoring the position and velocity of the axis may be limited to monitoring only the position or velocity of the axis depending on the desired control characteristics.  
           [0009]    The preferred embodiment of the electronic detent apparatus and method has a number of advantages. First, the number of detents can be easily changed by adding pre-specified position and/or velocity threshold values to the microprocessor. Second, the location of the detent(s) can be easily changed by altering the pre-specified position and/or velocity threshold values. Third, because the detent(s) are electronic they occupy negligible space, unlike mechanical detents, thereby reducing detent device size and design times. Fourth, the method of the present invention provides great flexibility in positioning and changing the number of detents. Sixth, the use of an electronic detent allows for numerous detent characteristics (such as, for example, detent length and “pull force” experienced) to be varied in a virtually limitless number of ways, e.g., either in a pre-specified manner or continuously. Other features and advantages of the invention will become apparent from the description that follows.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    Additional objects and features of the invention will appear from the following description in which the preferred embodiments are set forth in conjunction with the accompanying drawings.  
         [0011]    [0011]FIG. 1 illustrates one embodiment of the electronic detent apparatus of the present invention.  
         [0012]    [0012]FIG. 2 illustrates one embodiment of the electronic detent apparatus of the present invention.  
         [0013]    [0013]FIG. 3 illustrates the method of one embodiment of the electronic detent apparatus of the present invention.  
         [0014]    [0014]FIG. 4 illustrates the method of one embodiment of the electronic detent apparatus of the present invention.  
         [0015]    [0015]FIG. 5 illustrates the method of one embodiment of the electronic detent apparatus of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]    Turning to FIG. 1, one embodiment of an electronic detent apparatus  10  is illustrated. The electronic detent apparatus  10  includes a wheel  20  connected to a clutch  30 . A servo-motor  40  is attached to the clutch  30 . A programmable microprocessor  50  is connected to the servo-motor  40 . A sensor  60  is connected to the programmable microprocessor  50 . The wheel  20 , the clutch  30 , the servo-motor  40 , the programmable microprocessor  50 , and the sensor  60  comprise an electronic detent  10  which simulates electronically the properties and function of prior mechanical detents. A movable axis  70  is connected to the electronic detent  10  in a manner suitable for effecting the desired deceleration and immobilization characteristics. The physical arrangement or configuration of the clutch  30 , the servo-motor  40 , the programmable microprocessor  50  and the sensor  60  may be varied without detracting from the present invention so long as the ability to effect an electronic detent is maintained. The electronic detent apparatus  10  of the present invention is particularly suitable for use in conjunction with radiographic medical equipment. In one alternative embodiment, the clutch  30  may be connected to the movable axis  70  via the servo-motor  40  using a variety of alternative well known mechanical connections (i.e., besides a wheel), depending on the needs of the specific design implementation. These alternative mechanical connections include the use of a timing belt, a chain, a ball screw, a gear and rack, or a wheel and track.  
         [0017]    Turning to FIG. 2, one embodiment of the electronic detent apparatus of the present invention is graphically illustrated. An item  80  (e.g., the movable axis  70 ) is moved toward a detent  90  over a flat surface  100  by applying a steady force to move the item  80  over the flat surface  100 . FIG. 2 illustrates the item  80  at four distinct locations of the detent  90 . When the item  80  reaches an approach zone  110 , the electronic detent apparatus  10  matches the servo-motor  40  drive velocity to the item  80  velocity and engages the clutch  30  to take over motion of the item  80 . The engaged electronic detent apparatus provides the operator with “a pulling feel” as the item  80  accelerates towards and comes to rest in the detent  90 . The pulling feel experienced by the operator is effected by programming the programmable microprocessor  50  in a manner well understood to those skilled in the art. More specifically, the programmable microprocessor  50  activates the servo-motor  40  and the clutch  30  of the electronic detent apparatus  10  in a pre-specified manner to simulate a detent.  
         [0018]    For example, the desired deceleration and immobilization characteristics may be achieved by programming the programmable microprocessor  50  with pre-specified position and velocity threshold values. If the actual velocity or position of the movable axis  70  exceeds the pre-specified position or velocity threshold values the servo-motor  40  is energized so that the servo-motor  40  drive speed nearly matches the speed of the movable axis  70 . The speed need not be matched exactly. The servo-motor  40  may be energized by applying a voltage to the servo-motor  40  which gives a speed which is close to the desired speed. The objective is to minimize the speed difference between the servo-motor  40  drive speed and the movable axis  70 . Once the servo-motor  40  is energized, the clutch  30  is engaged so that the servo-motor  40  drive is connected to the movable axis  70 . Current is applied to the servo-motor  40  in such a direction as to move the movable axis  70  toward the detent position  90 . The current will reverse direction if the movable axis  70  position passes through the detent  90 . Also, when the movable axis  70  is within some predetermined value of the detent position  90 , and the movable axis  70  velocity is below some threshold value (i.e., the movable axis  70  is “in” the detent  90 ), the current to the servo-motor  40  is reduced or turned off. Once the movable axis  70  is positioned in the detent  90  a brake or lock  75  may be applied to hold the movable axis  70  in position.  
         [0019]    In an alternative embodiment, when the movable axis  70  is moved away from the detent position  90  (either passing through or returning in the direction it came from), to the extent that it exceeds a predetermined position or velocity value the clutch  30  is disengaged and the servo-motor  40  is turned off. Other electronic logic conditions may be used to define when the movable axis  70  is “in” the detent position without detracting from the present invention. Moreover, other methods of keeping the movable axis  70  in the detent position  90  may be implemented (e.g., the servo-motor  40  may be left on or may turn off on a timer, the clutch  30  may be disengaged, etc.). The use of other types of motors or actuating devices will change the details for implementing the present invention only slightly in a manner well known to those skilled in the art.  
         [0020]    In an alternative embodiment, the programmable microprocessor  50  may have logic applied such that the electronic detent  10  is activated only if the movable axis  70  velocity is within a certain predetermined range. This would be useful to prevent the detent  90  from engaging if the movable axis  70  speed is greater than the maximum speed of the servo-motor  40  drive, or if the speed is such that it would be unreasonable to expect that the operator would wish to stop at the detent  90 .  
         [0021]    In an alternative embodiment, the programmable microprocessor  50  may be programmed such that programmable microprocessor  50  adjusts the predetermined position value relative to the detent position  90  based on the velocity of the movable axis  70 . This may be useful in giving the operator the proper feel for the detent  90 .  
         [0022]    In an alternative embodiment, the programmable microprocessor  50  may be programmed such that for a certain range of movable axis  70  velocities the servo-motor  40  drive applies a force which opposes the movable axis  70  motion as the movable axis  70  position approaches the detent position  90 . This creates the effect of a wider detent  90 .  
         [0023]    Turning to FIG. 3, one embodiment of the method of the present invention for simulating a mechanical detent is illustrated. A user moves an item  120  and obtains position and velocity feedback  130 . If the item is within the zone for control  140  the motor is activated and the clutch engaged  150 . The item is controlled by a motor and control switch  160  and obtains position and velocity feedback  170 . If the item is at the edge of the detent  180  the motor is then briefly accelerated  190 . The item accelerates briefly as it approaches the detent  200  and obtains further position and velocity feedback  210 . If the item is near the bottom of the detent  220  the motor is decelerated to the detent position  230  and brings the item smoothly to a stop  240 .  
         [0024]    Turning to FIG. 4, one embodiment of the method of the present invention for simulating a mechanical detent is illustrated. The method comprises the steps of determining whether the movable axis is within a detent control range  250 . The detent control range refers to the region around the detent location  90  within which the servo-motor  40  drive will drive the movable axis  70  toward the detent position  90 . If the movable axis is within the detent control range  250 , the electronic detent  10  determines whether the movable axis speed is greater than V 2   260 . Speed V 2  is a speed which represents the highest speed at which the operator is expected to wish to stop in the detent  90 . If the movable axis speed is greater than V 2   260 , no further action is taken  265  and the electronic detent  10  continues to monitor whether the movable axis is within a detent control range  250 . If the movable axis speed is not greater than V 2   260  the electronic detent  10  applies power to the servo-motor  40  drive to approximately match the speed of the movable axis  270  and connects the servo-motor drive to the movable axis through the clutch  280  if not already engaged. The electronic detent  10  then determines whether the movable axis is centered in the detent within a tolerance “d”  290 . (When the movable axis position is within “d” of the pre-specified detent position, the electronic detent  10  is “in detent.” This tolerance may be arbitrarily small.) If it is within the tolerance “d”  290 , no further action is taken  295  and the electronic detent  10  continues to monitor whether the movable axis is within a detent control range  250 . If it is not, the electronic detent  10  applies a force to the movable axis to move it toward the center of the detent  300 . If the movable axis is within the detent control range  310  the electronic detent  10  determines whether the movable axis is centered within the detent within a tolerance “d”  290 . If the movable axis is centered within a tolerance “d”  290 , no further action is taken  295  and the electronic detent  10  continues to monitor whether the movable axis is within a detent control range  250 . If the movable axis is not centered within a tolerance “d”  290 , the electronic detent continues to apply a centering force to the movable axis  300  until it is appropriately centered.  
         [0025]    If the movable axis is not within a detent control range  250 , the electronic detent  10  determines whether the movable axis is within a detent approaching range  310 . The detent approaching range refers to a region around the detent location larger than the detent control range. While in the detent approaching range (e.g., between speeds V 1  and V 2 ), the servo-motor  40  drive attempts to slow the movable axis down. The detent approaching range is used to slow the movable axis down as the detent control range is approached. If the movable axis is not within a detent approaching range  310 , the electronic detent  10  removes power from the servo-motor  40  drive and disengages the clutch if not already disengaged  320 . The electronic detent  10  then continues to monitor whether the movable axis is within a detent control range  250 .  
         [0026]    If the movable axis is within a detent approaching range  310  the electronic detent  10  determines whether the movable axis is moving toward the detent  330 . If it is not, power is removed from the servo-motor  40  drive and the clutch  30  is disengaged if not already disengaged  340 . The electronic detent  10  then continues to monitor whether the movable axis is within a detent control range  250 .  
         [0027]    If the movable axis is moving toward the detent  330  the electronic detent  10  determines whether the movable axis speed is greater than V 2   350 . If it is, power is removed from the servo-motor  40  drive and the clutch  30  is disengaged if not already disengaged  340 . The electronic detent  10  then continues to monitor whether the movable axis is within a detent control range  250 .  
         [0028]    If the movable axis speed is not greater than V 2   350  the electronic detent  10  engages the servo-motor  40  drive to approximately match the speed of the movable axis if not already matched  360 . The servo-motor  40  drive is connected to the movable axis through the clutch  30  if not already engaged  370 . The electronic detent then determines whether the movable axis is within the near detent range  380 . If it is not, no further action is taken  385  and the electronic detent  10  continues to monitor whether the movable axis is within a detent control range  250 . If the movable axis is within the near detent range  380 , the electronic detent  10  determines whether the movable axis speed is greater than V 1   390 . V 1  is a speed which represents an operator moving the movable axis  70  slowly so as to find the detent  90  without passing through it. If the movable axis speed is not greater than V 1   390 , no further action is taken  395  and the electronic detent continues to monitor whether the movable axis is within a detent control range  250 . If the movable axis speed is greater than V 1   390 , the electronic detent applies a force to the movable axis to reduce the speed of the axis  400 . The electronic detent  10  then continues to monitor whether the movable axis is within a detent control range  250 . In this manner, FIG. 4 illustrates diagrammatically how one embodiment of the method of the electronic detent of the present invention may be practiced.  
         [0029]    Turning to FIG. 5, one alternative embodiment of the method of the present invention for simulating a mechanical detent is illustrated. The electronic detent  10  determines whether the movable axis is within a detent control range  410 . If it is not, power is removed from the servo-motor  40  drive and the clutch  30  is disengaged if not already  420 . The electronic detent  10  then continues to monitor whether the movable axis is within a detent control range  410 .  
         [0030]    If the movable axis is within a detent control range  410 , the electronic detent  10  applies power to the servo-motor  40  drive to approximately match the speed of the movable axis  430 . The servo-motor  40  drive is then connected to the movable axis by engaging the clutch  30  if not already engaged  440 . The electronic detent  10  then determines whether the movable axis is centered in the detent with a tolerance “d”  450 . If it is, no further action is taken  455  and the electronic detent continues to monitor whether the movable axis is within a detent control range  410 . If the movable axis is not centered within a tolerance “d”  450 , the electronic detent  10  applies a force to the movable axis to move it toward the center of the detent  460 . The electronic detent  10  then determines whether the movable axis is within a detent control range  470 . If the axis is not within the detent control range  470 , power is removed from the servo-motor  40  drive and the clutch  30  is disengaged if not already  40 . The electronic detent  10  continues to monitor whether the movable axis is within a detent control range  410 .  
         [0031]    If the movable axis is within a detent control range  470  after a force is applied to the movable axis to move it toward the center of the detent  460 , the electronic detent  10  determines again whether the movable axis is centered in the detent within a tolerance “d”  450 . If it is, no further action is taken  455 . If it is not, force is applied to the movable axis to move it toward the center of the detent  460 . In this manner, the electronic detent  10  continues to apply a centering force to the movable axis until it is centered within the detent within a tolerance “d”  450  or until the movable axis is no longer within a detent control range  470 .  
         [0032]    In one embodiment, at speeds greater than V 2 , the electronic detent function does not affect the operation of the system. This is useful where it is clear based on the movable axis speed that the operator does not wish to use the detent functions, e.g., where the operator wishes to quickly move radiographic equipment in an emergency situation. In an alternative embodiment, the electronic detent  10  may be provided with a “detent” switch which when “OUT” or “OFF” disables the electronic detent function and which when “IN” or “ON” enables the electronic detent function.  
         [0033]    The present invention thereby provides an electronic detent  10  and method for simulating a mechanical detent. The invention uses a servo-motor  40  activated clutch  30  to alter the wheel  20  velocity in a manner that simulates the feel of engaging a mechanical detent. The servo-motor  40  is activated when a programmable microprocessor  50  determines, based on velocity and position information, that a pre-specified detent position  90  is being approached. The feel of approaching a detent location  90  is simulated by programming the programmable microprocessor  50  with threshold velocity and position values in a manner that is well known in the art. Prior limitations associated with mechanical detents are, thus, eliminated.  
         [0034]    While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its scope. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.