Abstract:
A transmission for transmitting power from a printing device drive to drive a media pick roller to pick individual sheets of print media from a supply tray through the printing device without the necessity of requiring a separate pick roller motor and controls. The transmission uses a sun gear and a planet gear with a cam track and follower to move the planet gear into and out of driving relationship with the pick roller.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS, IF ANY 
     None. 
     BACKGROUND OF THE INVENTION AND PRIOR ART 
     The present invention relates to automatic printing devices such as desktop printers, copiers and similar devices which have a media supply tray which holds a stack of sheets of media on which printing is to take place or which are already printed and are to be copied. Throughout the present disclosure reference will be generally made to a “printing device” which is understood to encompass various types of printing devices including printers, copiers, combination printers and copiers, etc. 
     In typical printing devices, a first motor is used for driving the printing or copying elements and for movement of the sheet of paper or other media through the device. A separate motor is used for driving the media sheet pick roller or rollers which pick single sheets of media from the top (or sometimes bottom) of the media stack in the feed tray or supply tray. The present invention is directed to a transmission for transmitting power from the main printing device drive to drive a media pick roller and move individual sheets of media from a media supply tray through the printing device without the necessity of requiring a separate motor and controls for this purpose. 
     SUMMARY OF THE INVENTION 
     The present invention accordingly provides a transmission for transmitting power from a printing device drive to drive a media pick roller to move media from a printing device media supply tray comprising: 
     a) a support chassis; 
     b) a transmission power input gear mounted on said chassis; 
     c) a sun gear mounted on said chassis for rotation about a first axis and driveably connected to said power input gear; 
     d) a media pick roller drive gear mounted for rotation on said chassis; 
     e) a planetary gear mounting arm mounted on said chassis for pivotal movement about said first axis; 
     f) a planet gear mounted for rotation on said mounting arm, said planet gear being driveably connectable to said pick roller drive gear; 
     g) a cam track mounted on said chassis centered on said first axis and arcuately extending from a first location to a second location proximate said media pick roller drive gear, said cam track having a transmission engagement cam surface which inclines from said first location to said second location, said cam track also having a transmission reset cam surface spaced from said engagement cam surface, said reset cam surface extending from said second location to said first location; 
     h) a swing arm mounted on said chassis for movement with said mounting arm about said first axis, said swing arm having a cam follower thereon engageable with said cam track surfaces and said cam follower when engaged with said inclined engagement cam surface being resiliently biased away from said mounting arm; whereby, 
     (1) during a transmission engagement phase, said power input gear may rotate said sun gear, said mounting arm and said swing arm together in a first direction to arcuately move said follower in engagement with said engagement cam surface from said first location to said second location to move said planet gear into driving relationship with said pick roller drive gear, 
     (2) during a drive phase, said swing arm and said mounting arm remain stationary while power may be transmitted by rotation of said input gear in a second direction to rotate said sun gear to rotate said planet gear to rotate said drive gear, 
     (3) during a transmission disengagement phase, said power input gear again may rotate said sun gear, said mounting arm and said swing arm together in said first direction to arcuately move said follower past an end of said cam track to disengage said follower from said engagement cam surface and to disengage said planet gear from driving relationship with said pick roller drive gear, and 
     (4) during a reset phase, said power input gear may rotate said sun gear, said mounting arm and said swing arm in a second direction with said follower engaged with said reset cam surface to return said mounting arm and said swing arm to said first position. 
     The present invention further provides a printing device having a chassis and a media input tray and media sheet pick roller for feeding individual sheets of media from said tray to a media travel path in said printing device, said printing device including a transmission transmitting power from a main drive gear ( 11 ) in said printing device drive to drive said media pick roller, said transmission comprising: 
     a) a transmission power input gear mounted on said chassis in engagement with said main drive gear; 
     b) a sun gear mounted on said chassis for rotation about a first axis and driveably connected to said power input gear; 
     c) a media pick roller drive gear mounted for rotation on said chassis in driving engagement with said pick roller; 
     d) a planetary gear mounting arm mounted on said chassis for pivotal movement about said first axis; 
     e) a planet gear mounted for rotation on said mounting arm, said planet gear being driveably connectable to said pick roller drive gear; 
     f) a cam track mounted on said chassis centered on said first axis and arcuately extending from a first location to a second location proximate said media pick roller drive gear, said cam track having a transmission engagement cam surface which inclines from said first location to said second location, said cam track also having a transmission reset cam surface spaced from said engagement cam surface, said reset cam surface extending from said second location to said first location; 
     g) a swing arm mounted on said chassis for movement with said mounting arm about said first axis, said swing arm having a cam follower thereon engageable with said cam track surfaces and said cam follower when engaged with said inclined engagement cam surface being resiliently biased away from said mounting arm; 
     whereby, (1) during a transmission engagement phase, said main drive gear may rotate said power input gear, said sun gear, said mounting arm and said swing arm together in a first direction to arcuately move said follower in engagement with said engagement cam surface from said first location to said second location to move said planet gear into driving relationship with said pick roller drive gear, (2) during a media pick phase, said swing arm and said mounting arm remain stationary while power may be transmitted by reverse rotation of said main drive gear in a second direction to rotate said input gear, sun gear and said planet gear to rotate said pick roller drive gear, (3) during a transmission disengagement phase, said main drive gear again may rotate said input gear, sun gear, said mounting arm and said swing arm together in said first direction to arcuately move said follower past an end of said cam track to disengage said follower from said engagement cam surface and to disengage said planet gear from driving relationship with said pick roller drive gear, and (4) during a reset phase, said main drive gear may rotate said power input gear, said sun gear, said mounting arm and said swing arm in a second direction with said follower engaged with said reset cam surface to return said mounting arm and said swing arm to said first position. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic partial perspective view of the transmission and its connection to a pick roller drive shaft and media pick rollers for a print media supply tray. 
     FIG. 2 is a front elevation view of the transmission. 
     FIG. 3 is a perspective view of an arcuate cam track. 
     FIG. 4 is a bottom plan view of the cam track. 
     FIG.  4   a  is a right side elevation of the catch point end of the cam track. 
     FIG. 5 is a front elevation view of a swing arm. 
     FIG. 6 is an end view of the swing arm showing the follower end. 
     FIG. 7 is a top side view of the swing arm. 
     FIG. 8 is a perspective view of a mounting arm for a planet gear. 
     FIG. 9 is a front elevation view of the mounting arm. 
     FIG. 10 is a top view of the mounting arm. 
     FIG. 11 is an end view of the mounting arm showing a rotation limit stop and cam follower guide. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 is a schematic partial perspective view of the transmission of the present invention and its connection to a pick roller drive shaft and media pick roller for a print media supply tray. The transmission itself is mounted on a support chassis  10  which may comprise a side plate of the printing device. The transmission receives rotary input power from a main drive gear  11  of the printer and selectively transmits power to a pick shaft driven gear  31  which is in turn connected to a pick roller drive shaft  32  having one or more rotary pick rollers  34  thereon which have a surface suitable for frictionally engaging the top sheet of a stack of paper or other media to move it from the stack to the media path through the printing device. 
     As seen in FIG. 2, where the main printer drive gear  11  and the pick shaft driven gear  31  are shown in phantom, the transmission comprises a power input gear  12  mounted on the chassis  10  which, through a series of intermediate gears  14 ,  16 ,  18 , engages a sun gear  20  which is mounted for rotation with respect to the chassis  10  on a shaft  22 . Also mounted on shaft  22  is a planet gear mounting arm  40  having a pair of spaced legs  42 ,  44  best seen in FIGS. 8 and 10. A planet gear  50  having teeth engaged with the teeth of the sun gear  20  is mounted for rotation on the mounting arm  40  for planetary movement with respect to the sun gear  20 . 
     An arcuate cam track  60  is also mounted on the chassis  10  and is centered on the axis of shaft  22  and extends from a first location A proximate the power input gear  12  to a second location B proximate the media pick roller drive gear  30 . The cam track  60  has a transmission engagement cam surface  62  which inclines away from the plane of the chassis  10  in a counterclockwise direction as seen in FIG. 2 from the first location A near the power input gear  12  to the second location B near the media pick roller drive gear  30 . Preferably, the cam track  60  has an engagement cam surface  62  which continuously extends at an angle θ with respect to the base plane of the chassis  10  as seen in FIG.  4 . As shown, the transmission engagement cam surface  62  comprises a surface of a flange on the cam track which faces outwardly of the chassis  10  and also has a lower inwardly facing flange surface  64  which comprises a cam reset surface which extends in the reverse or counterclockwise location from the second location B proximate the media pick roller drive gear  30  back to the first location A proximate the power input gear  12 . The end of the cam track  60  proximate the paper pick drive gear  30  is stepped to provide a cam follower catch surface  66  and a tongue  68  seen in FIGS.  3  and  4   a  for a purpose to be described. 
     A swing arm  70  is also mounted on the chassis  10  for movement about the axis of the shaft  22  together with the mounting arm  40 . The swing arm has a cam follower  72  at its radially outermost end, the follower  72  having lower and upper surfaces respectively engageable with the upper and lower cam track surfaces  62 ,  64 . Movement of the cam follower  72  in the counterclockwise direction in engagement with the cam surface  62  past the catch surface  66  on the end of the cam track  60  prevents movement of the follower in the reverse or clockwise direction from the catch surface  66  back to the engagement cam surface  62 . Continued counterclockwise movement of the follower all the way past the end of the tongue  68  on the cam track results in engagement of the upper surface of the cam follower  72  with the underside of the tongue  68  to guide the cam follower  72  into engagement with the reset cam surface  64 . 
     A resilient cushion or spring  90  seen in FIG. 10 extends between facing surfaces of the mounting arm leg  44  and the swing arm  70  which in turn are preferably formed as an integral unit interconnected by a flexible tab  82 . The spring or resilient cushion  90  thus biases the swing arm away from the chassis  10  in an axial plane extending through the axis of shaft  22  toward the reset cam surface  64  and in a direction to engage the engagement cam surface  62  during reset of the transmission when the cam follower is at the first end of the cam track at location A. 
     The mounting arm  40  is preferably provided with a guide surface  46  thereon which engages a side edge of the swing arm  70  as seen in FIG. 2 to guide movement of the swing arm in the axial plane extending through the axis of shaft  22 . 
     Operation of the transmission in a complete cycle of operation which comprises four separate phases will now be described. As seen in FIG. 2, in the first or transmission engagement phase of operation, the transmission input gear  12  is first driven in a counterclockwise direction by the main drive gear  11 . This, via gears  14 - 18  causes rotation of the sun gear  20 , the mounting arm  40  and the swing arm  70  as a unit from the first location A where the cam follower  72  engages the engagement cam surface  62  of the cam track. Continued movement of the sun gear  20 , mounting arm  40  and swing arm  70  in a counterclockwise direction causes the cam follower  72  to gradually move away from the plane of the chassis  10  as it follows the inclined engagement surface  62  of the cam track until it reaches location B where the follower  72  passes the catch surface  66  but is still in engagement with the cam track  60 . At this location B the planet gear  50  moves into driving relationship with the pick roller drive gear  30  due to engagement of the teeth of the planet gear  50  with the teeth of an intermediate speed reducing gear  80 . 
     In the second phase of operation which comprises a media pick roller drive phase, the swing arm  70  and mounting arm  40  remain stationary while power is transmitted by reverse rotation of the input gear  12  in a second direction (clockwise caused by reverse rotation of the main drive gear  11  whereby the sun gear  20  and planet gear  50  rotate the media pick roller drive gear  30  in the sheet picking direction (counterclockwise as shown). 
     The third phase of the complete cycle of operation of the transmission comprises a transmission disengagement phase in which rotary power is no longer transmitted from the planet gear  50  to the pick roller drive gear  30  via the speed reducing gear  80 . Disengagement of the transmission is caused by again rotating the power input gear  12  in the original counterclockwise direction to arcuately move the cam follower  72  past the end of the tongue  68  of the cam shaft to disengage the follower from the tongue  68  and to disengage the planet gear  50  from driving relationship with the pick roller drive gear  30 . 
     The fourth or reset phase of the cycle of operation involves returning of the interconnected mounting arm  40  and swing arm  70  in the clockwise direction from position B to position A as the follower  72  is engaged with the reset cam surface  64 . 
     The transmission thus described is a purely mechanical solution for controlling and powering a media pick roller. 
     The transmission is configured to mate with existing gears  11 ,  31  on the printer chassis. Initial reverse and subsequent forward motion of the main drive gear  11  results in media being picked from the tray. Under rotation or over rotation of the transmission elements do not result in transmission engagement. Once engaged, the transmission can be rotated indefinitely and will continuously drive the paper media pick roller or rollers  34 . A small reverse rotation of the power input gears will disengage (reset) the transmission from the engaged state and large reverse rotations from the printer drive while in the engaged state will not cause any difficulty and will also reset the transmission. During the engagement phase of rotation (reverse rotation) the swing arm  70  follows the inclined engagement cam track surface  62  resulting in engagement of the planet gear  50  with the pick roller drive gear  30  via the speed reducing gear  80 . Once the transmission is engaged, further rotation can be controlled accurately even with fluctuating torque loads. The swing arm  70  can now be accurately rotated the remainder of the way past the catch surface  66  and end of tongue  68  of the cam track. The catch surface thus permits the swing arm  70  to rotate only in the reverse (counterclockwise) direction like a ratchet or pawl. At this point, the swing arm pivots back to its relaxed position and disengages the face of the sun gear  20 . The transmission is now engaged and ready for forward rotation. Once the desired forward rotation is complete, a small reverse rotation disengages the transmission by sliding the swing arm  70  off the end of the tongue  68  of the cam allowing it to rotate back under the cam surface  62  against the cam surface  64 . 
     Persons skilled in the art will appreciate that various 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. For example, the various gears  14 ,  16 ,  18  and  80  are not essential. Additionally, the mounting arm  40  and swing arm  70  need not be constructed as a single piece. Other changes can be made in the transmission as will be appreciated by persons skilled in the art without departing from the teachings of the invention.