Abstract:
A transmission for transmitting rotary power in forward and reverse directions from a programmable source of input motion such as an electric motor uses individually rotatable coaxially mounted lock plates each having a pawl receiving socket therein providing access to an arcuate slot of selected angular length permits engagement and disengagement of the transmission only when input torque is applied thereto in forward and reverse directions to rotate the transmission input gear through pre-defined angles. The pawl is part of a frictionally driven shift arm on which a driven shift gear is also mounted whereby the driven shift gear is pivotally moved into and out of engagement with the output gear or gears of the transmission when the pawl is pivotally moved out of or into the sockets in the lock plates. Rotation limit stops are provided on the lock plates at selected angular positions so that the transmission can be engaged or disengaged for transmission of torque in both forward and reverse directions only when the motor is rotated through a sequence of predetermined angles in predetermined directions.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
         [0001]    None.  
         BACKGROUND OF THE INVENTION  
         [0002]    The present invention relates to power transmissions in general and, more particularly, to transmissions useful for transmitting rotary power in forward and reverse directions to computer controlled printers, document scanners, automatic document feeders and other office machine applications. Even more particularly, the invention is applicable for use in applying rotary power to accurately position apparatus such as an inkjet printer service station, to operate a scanner drive, and to operation of a paper pick roller in an automatic document feeder capable of separating single sheets of media such as paper, vellum, transparencies, etc. from a stack thereof.  
           [0003]    Inkjet printers ordinarily have a printhead servicing station located at some point on the path of travel of a printhead carriage. The servicing station typically includes printhead wipers, a source of printhead servicing fluid and printhead caps, some or all of which may be mounted on a sled or other moveable support to bring the service station into and out of operating proximity to the printheads to be serviced. Automatic document processing apparatus such as scanners and desktop printers typically include a shelf or tray for holding a stack of one or more sheets of documents to be scanned or blank paper or other media to be fed, one sheet at a time, from the stack to the other portions of the document processing apparatus. In such arrangements a driven pick roller having a friction surface may be used to engage the uppermost sheet in a horizontally oriented or downwardly inclined stack to strip the top sheet from the stack and move it parallel to the surface of the stack. The present invention is particularly useful in printhead servicing apparatus and for driving paper pick rollers and in other applications.  
           [0004]    It is objective of the present invention to provide a transmission which can selectively couple and de-couple a source rotary drive power to a rotary output shaft only upon application of predetermined angles of rotation of an input shaft or gear in both forward and reverse directions. The design angles of forward and reverse rotation of the input shaft or gear for engaging the transmission need not be the same as the design angles of forward and reverse rotation for disengaging the transmission.  
         SUMMARY OF THE INVENTION  
         [0005]    The present invention therefore provides a transmission for transmitting rotary power in forward and reverse directions from a source of rotary power to a load comprising:  
           [0006]    a) a rotary input gear for coupling to said source of rotary power;  
           [0007]    b) a rotary output gear;  
           [0008]    c) a clutch shaft;  
           [0009]    d) a clutch gear rotatably mounted on said clutch and drivingly engaged with said input gear;  
           [0010]    e) at least one lock plate rotatably mounted on said clutch shaft in frictional engagement with said clutch gear, said lock plate having a socket therein including a radially extending gate and an arcuate slot of first selected angular length accessed by said gate;  
           [0011]    f) a shift arm pivotally mounted coaxially with said input gear and frictionally engaged with said input gear, said shift arm including a pawl arcuately moveable into and out of engagement with said lock plate socket; and  
           [0012]    g) a shift gear engaged with said input gear, said shift gear being mounted on said shift arm and arcuately moveable with said shift arm between positions of engagement and disengagement with said output gear as said pawl moves into and out of said socket. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 is a schematic exploded isometric view of a transmission according to the present invention.  
         [0014]    [0014]FIG. 2 is a top plan view of a clutch shaft.  
         [0015]    [0015]FIG. 3 is a left end elevation view of the shaft of FIG. 2.  
         [0016]    [0016]FIG. 4 is a right end elevation view of the shaft of FIG. 2.  
         [0017]    [0017]FIG. 5 is a right (outer) side elevation view of an inner lock plate.  
         [0018]    [0018]FIG. 6 is a left (inner) side elevation view of the inner lock plate.  
         [0019]    [0019]FIG. 7 is a right (outer) side elevation view of an outer lock plate.  
         [0020]    [0020]FIG. 8 is a left (inner) side elevation view of the outer lock plate.  
         [0021]    [0021]FIG. 9 is a right (outer) side elevation view of a shift arm.  
         [0022]    [0022]FIG. 10 is a left (inner) side elevation view of the shift arm.  
         [0023]    [0023]FIG. 11 is a top plan view of the shift arm.  
         [0024]    [0024]FIG. 12 shows the facing sides of output gears.  
         [0025]    [0025]FIG. 13 shows elevation views of the output gears.  
         [0026]    [0026]FIG. 14 comprises schematic views of sequential positions of the shift arm, lock plates and shift gear. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0027]    The transmission of the present invention preferably is comprised of molded plastic parts such as Nylon, Delrin/POM, polycarbonate and is preferably enclosed in a frame or housing of suitable configuration which may include spaced side plates  12 ,  14  as shown schematically in FIG. 1. In the orientation of the transmission seen in FIG. 1, the side plate  12  will be referred to as an “inner” side plate and the opposite side plate  14  will be referred to as an “outer” side plate as will various other parts of the transmission. The inner side plate  12  has an input gear shaft  18  extending therefrom to receive an input sun gear  20  which is freely rotatable on the shaft  18 , and a shift arm  30  which is also freely rotatable on the shaft  18  and is urged by a compression spring  32  seated against the outer side plate  14  into face-to-face frictional engagement with the outer side face of the input or sun gear  20 . Optionally, an input gear train comprised of additional input gears  22 ,  24  respectively supported on shafts  26 ,  28 , in driving relationship with the input sun gear  20  may also be present to receive input torque from a controllable drive motor, not shown.  
         [0028]    A specially configured non-rotatable generally cylindrical clutch shaft  40  receives an inner lock plate  50  and a clutch gear  60  which are freely rotatable on the shaft  40 , the inner lock plate  50  and clutch gear  60  having abutting surfaces which are urged into frictional engagement with each other by a spring  62 . The clutch shaft  40  has an inner end  41  of non-circular configuration received in a complementary configured aperture  42  in the inner side plate  12 . Extending from the outer end of the clutch shaft is a cylindrical pin  43  on which is received an outer lock plate  70 . The outer lock plate  70  is urged by a spring  72  seated against the outer side plate toward the outer end surface of a rotation limiter shown as a semi-circular disc  44  integrally formed on the clutch shaft  40 . As shown, the semi-circular disc  44  has stop shoulders  45 ,  46  spaced from each other at a selected angle which, as shown, is somewhat less than 180°.  
         [0029]    The inner lock plate  50  includes a C shaped socket  52  therein comprised of a radially extending gate  54  and an arcuate slot  56  of selected angular length. Similarly, the outer lock plate  70  also has a socket  72  therein including a radially extending gate  74  and an arcuate slot  76  of selected angular length. As seen in the drawing, the angular length of the outer lock plate slot  76  is significantly shorter than the angular length of the inner lock plate slot  56 ; however, the relative lengths of the slots  56 ,  76  in the lock plates  50 ,  70  are not critical and are selected to coact with programed forward and reverse rotation of the motor which supplies input power to the transmission as will be described below. The clutch gear  60  is continuously engaged with the input sun gear  20  and is thus continuously driven thereby whenever rotary power is supplied in forward or reverse directions to the input gear  20 .  
         [0030]    An output gear shaft  78  extends from the inner side plate  12  and receives at least one and preferably two mutually engageable output gears  80 ,  82 . When the transmission is engaged, the outer output gear  80  is engaged with a shift gear  90  rotatably supported on the shift arm  30  and the shift gear  90  is continuously engaged with and driven in forward and reverse directions by the sun gear  20 . The shift gear  90  is arcuately moved into and out of engagement with the outer output gear  80  as the shift arm  30  pivots on its support shaft  18 . The shift arm  30  also includes an integrally formed pawl  34  receivable in the radially extending gates  54 ,  74  of the inner and outer lock plates  50 ,  70 , the pawl  34  being captured in the arcuate slots  56 ,  76  of the lock plates when the transmission is engaged. The compression spring  32  seated against the outer side plate  14  urges the shift arm  30  into face-to-face frictional engagement with the input sun gear  20  as previously described.  
         [0031]    A designed-in lag in commencement of and cessation of transmission output may be provided by use of a second or inner output gear  82  which is driven by the outer output gear  80  through the use of axially extending mutually engageable stops  84 ,  86  of selected angular extent on the facing sides of the outer and inner output gears  80 ,  82  as best seen in FIGS. 12 and 13.  
         [0032]    As seen in FIGS. 6 and 8 which show the facing sides of the inner and outer lock plates  50 ,  70  respectively, two rotation limit stops  58  and  59  are provided on the outer side of the inner lock plate  50  and a single rotation limit stop  78  is formed on the inner side of the outer lock plate  70 . Rotation of the outer lock plate  70  is confined to the angle between the disc shoulders  45 ,  46  which are engaged by the outer lock plate stop  78  at the ends of travel of the outer lock plate. Rotation of the inner lock plate  50  relative to the outer lock plate  70  is confined to the angular spacing between the stops  58 ,  59  which are also engaged by the outer lock plate stop  78 . It will be noted that in the embodiment shown, rotation of the outer lock plate  70  relative to the inner lock plate  50  is defined by the excess by which the angular length of the slot  56  in the inner lock plate exceeds the angular length of the slot  76  in the outer lock plate.  
         [0033]    The facing sides of the inner lock plate  50  and outer lock plate  70  are also preferably also configured to define a generally cylindrical cavity or recess  59  in which the semi-circular disc  44  is received.  
         [0034]    Operation of the transmission will now be described with reference to the sequence of positions schematically shown in FIG. 14 starting with FIG. 14 a  which shows the transmission after disengagement with the radial gates  75 ,  74  in the lock plates remaining aligned and the pawl  34  positioned externally of the lock plate sockets. Counterclockwise rotation of the sun gear  20  will be assumed to be the forward direction of rotation and clockwise rotation of gear  20  will be reverse. Forward rotation urges the pawl  34  radially toward the lock plates due to frictional engagement of the sun gear  20  and shift arm  30 , causing the pawl  34  to enter the gates  54 ,  74  when the gates are aligned. Conversely, reverse rotation causes the pawl  34  to exit the sockets  52 ,  72  when the pawl  34  is aligned with the gates  54 ,  74  and when the gates  54 ,  74  are aligned with each other.  
         [0035]    The transmission is engaged by first rotating the input gear  20  by a programmed motor through a selected angle in a reverse direction to ensure that the pawl  34  has been pivoted out of the lock plate sockets  52 ,  72  and then rotating the input gear  20  in the forward direction to cause the pawl  34  to enter the sockets in the lock plates to permit the shift gear  90 , driven by the input gear  20 , to pivot into engagement with the output gear  80 . The lock plate  50  then rotates clockwise due to frictional engagement with the clutch gear  60  and the lock plate  70  is rotated clockwise due to engagement of the inner lock plate stop  58  with the outer lock plate stop  78  until the pawl  34  contacts the left ends of the gate slots  56 ,  76  as seen in FIG. 14 b.  At this time the outer lock plate stop  78  also contacts the right side disc shoulder  46  to prevent further clockwise rotation of the outer lock plate  70 . When the motor is driven in the reverse direction, the pawl  36  hits the right ends of the slots  56 ,  76  as seen in FIG. 13 c,  reverse torque then being applied to the output gears  80 ,  82 .  
         [0036]    The transmission is disengaged after forward drive by first rotating the input gear  20  in reverse which frictionally rotates the inner lock plate  50  counterclockwise and the outer lock plate counterclockwise due to engagement of the stops  59  and  78  until rotation of the outer lock plate  70  is terminated by engagement of the stop  78  with the left shoulder  45  of the disc  44 . The inner lock plate  50  continues to rotate counterclockwise for only the necessary angular distance under programmed control of the motor for a selected angle until the gates  54 ,  74  are aligned. The motor then drives the transmission forward until gates align with the pawl  36  which then permits the pawl  34  to exit the sockets  52 ,  72  under frictional urging by the face to face contact of the shift arm  30  with the sun gear  20 .  
         [0037]    The transmission is disengaged after reverse drive by rotating the motor forwardly for the precise angle until the gates align with the pawl  36  which then exits the sockets  52 ,  72 .  
         [0038]    The transmission can only be engaged with precise controlled reverse rotation and can only be disengaged by programmed precise forward and then reverse rotation. If the reverse rotation angle is shorter or longer than the prescribed amount, then the transmission will not engage. Likewise, if the angles of rotation in the forward and reverse directions are incorrect the transmission will not disengage. The precise angles of rotation of the input gear  20  to cause engagement or disengagement of the transmission as desired are accurately controllable through programming of the input motor which applies torque to the input gear  20  or gear train  20 ,  22 ,  24 .  
         [0039]    Two lock plates  50 ,  70  are shown in the described embodiment but it will be appreciated that a transmission can be constructed with more than two lock plates such that multiple programmed reverse and forward rotations of the input gear  20  by a motor are required to cause engagement and disengagement.  
         [0040]    When the transmission is disengaged, i.e., when the pawl  34  is clear of the lock plate sockets  52 ,  72 , the lock plate  50  is permitted to freely rotate on the clutch shaft since the inner lock plate  50  is friction coupled to the clutch gear  60  and turns with the gear  60  since the pawl  34  is clear of the sockets. Rotation of the outer lock plate  70  is caused and the angles of rotation thereof are limited by engagement of the stops  58  or  59  with stop  78  and by engagement of stop  78  with the disc shoulders  45 ,  46  which create a hysteresis or dead band of rotation of selected arcuate length. Only one particular sequence of forward and reverse input motions is required to engage the transmission and a second and different sequence is used to disengage the transmission. The sequences can be designed to be equal to each other but in this implementation are not the same.  
         [0041]    The preferred embodiment therefore allows selective engagement or disengagement of the transmission with merely the proper programmed forward and reverse rotation of the input motor. The transmission can be used to transmit torque in both the forward and reverse directions without disengagement and can be disengaged when not in use to reduce parasitic power consumption. Adjustment of the angular extent of the lock plate slots  56 ,  76  and angular spacing between the stop shoulders  45 ,  46  on the clutch shaft disc  44  and the spacing and configuration of the mutually engageable stops  84 ,  86  on the inner and outer output gears  80 ,  82  (if two output gears are provided), permits variation of the engagement and disengagement sequences and optionally designed motion lag thus allowing for a single motor to selectively power a number of devices independently or simultaneously. The design is entirely mechanical requiring no external input, either mechanical, electrical or otherwise beyond the easily programmable rotational power input of the torque of drive torque.  
         [0042]    Persons skilled in the art will also appreciate that various additional modifications can be made in the preferred embodiment shown and described above and that the scope of protection is limited only by the wording of the claims which follow.