Patent Publication Number: US-2016223031-A1

Title: Clutch apparatus

Description:
BACKGROUND 
     The present invention relates to a clutch apparatus, and relates particularly, but not exclusively, to a clutch apparatus for use as a locking device for an arm holding a machine keyboard close to a machine operator. 
     It is known to provide a clutch apparatus acting between an arm and a support for supporting a keyboard for a machine operator, wherein the arm is pivotable relative to the support and maintains its position if a torque applied to the clutch apparatus is less than a predetermined threshold value, whereas the support can be pivoted relative to the arm if the torque applied exceeds the threshold value. In this way, if the keyboard is pushed hard, the arm can pivot to avoid damage. 
     Known clutch apparatus suffer from the drawback that it is difficult to adjust the position of a keyboard relative to a machine when the clutch apparatus has a sufficiently high threshold torque value. 
     SUMMARY 
     Preferred embodiments of the present invention seek to overcome the above disadvantage of the prior art. 
     According to an aspect of the present invention, there is provided a clutch apparatus comprising: 
     at least one first member; 
     at least one second member; 
     at least one clutch device acting between at least one said first member and at least one said second member, where said first member is pivotable relative to said second member when torque acting between said first and second members is greater than at least one threshold value, and said first member is not pivotable relative to said second member when said torque is less than said threshold value; and 
     clutch overriding device configured to selectively enable at least one said first member to pivot relative to at least one said second member. 
     According to another aspect of the present invention, there is provided a support apparatus comprising a support body, a connecting member, and at least one clutch apparatus as defined above acting between said support body and said connecting member for controlling pivotal movement of said support body relative to said connecting member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A preferred embodiment of the invention will now be described, by way of example only and not in any limitative sense, with reference to the accompanying drawings in which: 
         FIG. 1  is a perspective view of a keyboard support apparatus embodying the present invention; 
         FIG. 2  is an end view of the apparatus of  FIG. 1 ; 
         FIG. 3  is a sectional view along the line A-A in  FIG. 2 ; 
         FIG. 4  is a side view of a clutch apparatus and fixing components of the support apparatus of  FIG. 1 ; 
         FIG. 5  is an end view of the clutch apparatus of  FIG. 4 ; and 
         FIG. 6  is a sectional view along the line B-B in  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION 
     According to an aspect of the present invention, there is provided a clutch apparatus comprising: 
     at least one first member; 
     at least one second member; 
     at least one clutch device acting between at least one said first member and at least one said second member, where said first member is pivotable relative to said second member when torque acting between said first and second members is greater than at least one threshold value, and said first member is not pivotable relative to said second member when said torque is less than said threshold value; and 
     clutch overriding device configured to selectively enable at least one said first member to pivot relative to at least one said second member. 
     By providing the clutch overriding device configured to selectively enable at least one said first member to pivot relative to at least one said second member, this provides the advantage that the threshold torque value can be set higher than for known clutch apparatus, thereby ensuring a more secure connection between the first and second members between which the clutch apparatus acts, while enabling apparatus incorporating the clutch apparatus to be easily adjusted by use of the clutch overriding device. 
     The clutch device may be configured to transmit torque from at least one said first member to at least one said second member by means of friction. 
     This provides the advantage of enabling the apparatus to provide a large threshold torque value while enabling compact construction of the apparatus. 
     The clutch device may further comprise at least one friction member for transmitting torque from at least one said first member to at least one said second member. 
     At least one said friction member may contain at least one fluoropolymer. 
     This provides the advantage of providing a smooth slipping torque when the threshold value is exceeded, thereby reducing wear of the apparatus. 
     At least one said fluoropolymer may include polytetrafluoroethylene (PTFE). 
     At least one said friction member may contain carbon. 
     This provides the advantage of improving the wear resistance of the friction member. 
     The apparatus may further comprise a first biasing device for urging at least one said friction member into engagement with a pressure member. 
     At least one said threshold value may be adjustable. 
     At least one said threshold value may be adjustable by means of adjusting a biasing force of said first biasing device. 
     This provides the advantage of enabling the apparatus to be made more compact. 
     The clutch overriding device may comprise at least one third member moveable between a first position in which at least one said first member is pivotable relative to at least one said second member when torque acting between said first and second members is less than said threshold value, and a second position in which said first member is not pivotable relative to said second member when said torque is less than said threshold value. 
     The clutch overriding device may further comprise an actuator device for moving at least one said third member to a first position thereof. 
     The actuator device may comprise at least one electromagnet. 
     The clutch overriding device may further comprise a second biasing device for urging at least one said third member towards a second position thereof. 
     According to another aspect of the present invention, there is provided a support apparatus comprising a support body, a connecting member, and at least one clutch apparatus as defined above acting between said support body and said connecting member for controlling pivotal movement of said support body relative to said connecting member. 
     Referring to  FIGS. 1 to 3 , a support apparatus  2  embodying the present invention for supporting a keyboard (not shown) close to a machine operator has a support body  4  defining a keyboard support part pivotably mounted to a first end of a connector member in the form of a connector arm  6 . A second end of the connector arm  6  is pivotably mounted to a machine (not shown) such as a piece of medical apparatus. A clutch apparatus  8  according to a preferred embodiment of the present invention is located in a recess  10  between the support body  4  and the first end of the connector arm  6 . 
     Referring to  FIGS. 4 to 6 , the clutch apparatus  8  has a first member in the form of a torque limiter body  12  non-rotatably mounted to the support body  4  and a second member in the form of a solenoid brake magnet  14  non-rotatably mounted to the connector arm  6 . A third member in the form of a spring loaded toothed plate  16  is axially slidably mounted to the solenoid brake magnet  14  and is moveable between a first, rightmost position as shown in  FIG. 6 , in which teeth on the toothed plate  16  are disengaged from teeth on a toothed engaging plate  18  to allow rotation of the toothed plate  16  and engaging plate  18  relative to each other, and a second, leftmost position as shown in  FIG. 4 , in which the teeth on the toothed plate  16  engage teeth on the engaging plate  18  to prevent rotation of the toothed plate  16  and engaging plate  18  relative to each other. The toothed plate  16  is moveable from the second position to the first position by means of an electromagnet having a coil assembly  20 , against the action of the second biasing device in the form of one or more compression springs  22 . 
     The solenoid brake magnet  14  and toothed plate  16  are non-rotatably mounted to a mounting shaft  24  by means of set screw  26  and the mounting shaft  24  is non-rotatably mounted to the connector arm  6  by means of first shoulder screw  28  and second shoulder screw  30 , which are received in respective threaded recesses  32 ,  34  in the ends of the mounting shaft  24 . 
     A torque limiter bush  36  is rotatably mounted to the mounting shaft  24 , and the toothed engaging plate  18  is rotatably mounted to the torque limiter bush  36  such that a radially inner flange  38  on the toothed engaging plate  18  abuts a flange  40  at the right hand end of the torque limiter bush  36  as shown in  FIG. 6 . A thrust washer  42  of fluoropolymer such as polytetrafluoroethylene (PTFE), or other suitable material which will be familiar to persons skilled in the art, which also contains carbon for improving the wear resistance of the thrust washer  42 , is located between the toothed engaging plate  18  and a pressure plate  44  which is non-rotatably mounted to the torque limiter bush  36 , and the torque limiter body  12  applies pressure via a disc spring  46  to compress the thrust washer  42  between the pressure plate  44  and the engaging plate  18  by means of a torque limiter lock nut  48 . By adjustment of the axial position of the torque limiter lock nut  48  by mutual engagement of screw threads on the lock nut  48  and torque limiter bush  36 , the spring force of the disc spring  46  can be adjusted, which in turn adjusts the frictional force between the thrust washer  42  and the engaging plate  18  and pressure plate  44 . The carbon content of the thrust washer  42  is typically of the order of 25%. By using a fluoropolymer such as PTFE, for which the difference between the dynamic and static coefficients of friction is small, for the thrust washer  42 , there is a fairly smooth transition from holding to slipping of the thrust washer  42 , with little juddering or noise. 
     The solenoid brake magnet  14  is non-rotatably mounted to the mounting shaft  24  by means of set screw  26 , and the spring loaded toothed plate  16  is axially slidable out of engagement with the toothed engaging plate  18  against the action of compression spring  22  by means of energisation of coil assembly  20  located in a recess in the solenoid brake magnet  14  behind a body plate  50 . The torque limiter bush  36  is located in position on the mounting shaft  24  by means of a circlip  52 , and the solenoid brake magnet  14  is located in position on the mounting shaft  24  by means of a circlip  54 . An anti-rotation pin  56  prevents rotation of the torque limiter body  12  relative to the support body  4 . A pair of bushes  58 ,  60  provide extra support to the assembly. 
     The operation of the support apparatus  2  will now be described. 
     When the coil assembly  20  is not energized, the application of torque to the support body  4  so as to tend to cause the support body  4  to pivot relative to the connector arm  6  about pivot axis  62  applies a torque between the torque limiter body  12  and the mounting shaft  24 . This torque is applied via the disc spring  46 , pressure plate  44 , thrust washer  42  and toothed engaging plate  18  to the spring loaded toothed plate  16  which, when the coil assembly  20  is not energized, is in its second position as shown in  FIG. 4 . The teeth of the toothed plate  16  therefore engage the teeth of the engaging plate  18 , as a result of which the torque applied to the torque limiter body  12  is in turn applied to the toothed plate  16  and solenoid brake magnet  14 . Because the toothed plate  16  and solenoid brake magnet  14  are non-rotatably mounted to the mounting shaft  24 , this torque is also applied to the mounting shaft  24 , which is fixed in position relative to the connector arm  6 . 
     When the torque applied by the torque limiter body  12  exceeds the threshold torque, however, the maximum frictional force of the thrust washer  42  is overcome, as a result of which the toothed engaging plate  18  can rotate relative to the pressure plate  44  to enable rotation of the torque limiter body  12  relative to the mounting shaft  24 , which in turn enables rotation of the support body  4  relative to the connector arm  6 . 
     In order to adjust the position of the support body  4  relative to the connector arm  6 , the coil assembly  20  is energized by actuation of a suitable switch (not shown) to supply electrical power to the coil assembly  20 . Energisation of the coil assembly  20  retracts the spring loaded toothed plate  16  against the action of the compression spring or springs  22  out of engagement with the toothed engaging plate  18 , to allow rotation of the torque limiter body  12  relative to the solenoid brake magnet  14  and mounting shaft  24  on application of a torque less than the threshold torque corresponding to the maximum frictional force of the thrust washer  42 . 
     It will be appreciated by persons skilled in the art that the above embodiment has been described by way of example only and not in any limitative sense, and that various alterations and modifications are possible without departure from the scope of the invention as defined by the appended claims.