Abstract:
A sheet feeding device for printers and other machines comprises a movable support ( 17 ) whereon a stack of sheets may be arranged and resiliently urged against selection wheels ( 19 ). A retracting mechanism ( 50 ) is arranged so as to push back during one phase of a selection cycle the movable support ( 7 ) by a predetermined distance which is substantially constant and independent of the thickness of the stack of sheets. The retracting mechanism ( 50 ) for this purpose comprises a connecting rod ( 58 ) displaced by a cam wheel ( 66 ) following a backward and forward movement. The connecting rod ( 58 ) bears a pawl ( 57 ) cooperating with a ratchet wheel ( 56 ) suitable for driving a lever ( 51 ) integral with the movable support ( 17 ). Additionally an actuating mechanism permits the partial opening of the guiding channel ( 28 ) when the sheet arrives in a printing zone ( 35 ). Thanks to these characteristics, the movements of parts, and in particular of the movable support ( 17 ), may be kept to an optimal and constant minimum, which ensures fast, precise and noiseless operation. Printing of great precision is also obtained.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a device for the feeding of flat materials for processing, such as sheets and envelopes, for machines using these materials, such as printers, comprising a frame and a movable support upon which a stack of said materials may be arranged and from which these materials are extracted one by one during selection cycles by selecting means engaging with a feeding mechanism and suitable for displacing the top material of the stack for feeding it into the machine, elastic means being provided for urging the movable support in the direction of the selecting means. 
     PRIOR ART 
     Devices such as these are known wherein the top sheet selection mechanism, upon each selection, requires great movements of parts, the full stroke of which is in relation to the maximum thickness of the stack of sheets that the movable support can accommodate. These great movements of parts, and of the movable support in particular, considerably slow down operation of the feeding device and cause annoying noises and rapid wear. 
     Another drawback of the known devices lies in the fact that the sheet selected is still being braked by the selection mechanism when it has already been entered in the printer and is being fed by the latter. As a result, there are variations of the paper feed pitch, giving rise to clearly visible defects, especially in high resolution graphics printing. 
     SUMMARY OF THE INVENTION 
     The object of this invention is to overcome the drawbacks outlined above; to this end, the invention is characterized in that the device comprises a retracting mechanism adapted in such a way as to push, during at least one phase of a selection cycle, the movable support back against the action of the elastic means by a predetermined distance which is substantially constant and independent of the thickness of the stack of materials, in order to produce a predetermined gap between the top material and the selecting means and of a magnitude such that friction between the top material and the selecting means is eliminated. 
     Thanks to these characteristics, the movements of the parts, and in particular those of the movable support for the sheets, may be reduced to a minimum during the selection, thus ensuring rapid, precise and silent operation, while lowering wear of the parts to a minimum. With the top sheet being distanced from the selecting means in a precise and controlled way, printing of great precision is obtained even in high resolution graphic printing. 
     To advantage, the feeding mechanism is adapted in such a way as to actuate both the selecting means and the retracting mechanism. Operation is particularly sure, while the construction remains simple and economical. 
     According to a preferred embodiment, the retracting mechanism comprises kinematic linkage members linking the driving mechanism with the movable support in such a way that the latter, in said phase, effects a predetermined movement starting from a first position wherein said stack is resting against the selecting means to a second position wherein the top material is removed from the selecting means by said predetermined gap, said movement being substantially constant whatever the position occupied by the movable support member in said first position and whatever the thickness of said stack. These characteristics guarantee great operating precision. 
     Advantageously the linkage members comprise a ratchet member cooperating actively with an opposing member following a first direction to displace the support member from the first position to the second position and permitting a free relative displacement of the ratchet member in relation to the opposing member following a second direction, opposite the first direction. 
     In a favourable embodiment, the opposing member is a ratchet wheel coupled in movement with the movable support and the ratchet mechanism is a pawl borne by a part, the displacement of which is controlled by the driving mechanism. 
     Thanks to these characteristics, the mode of operation is very safe and the number of parts limited. Said part is to advantage a connecting rod adapted for cooperating with a cam put in action by the driving means through the action of a clutching member. Separation of the top sheet from the selecting means can thus be controlled precisely and reliably. 
     In the known devices, it has often been remarked that the sheet feeding pitch in high resolution printing mode is not absolutely constant, which gives rise to images of poor quality. This drawback was to be ascribed to the fact that the sheet was braked to a varying extent in the guiding channel by the selecting means. In order to overcome this significant drawback, the device according to this invention comprises an actuating mechanism intended to broaden and narrow at least a part of a guiding channel for said materials during a phase of each selection cycle. 
     Accordingly when the sheet is being printed, the guiding channel may be broadened so that the friction forces are very low during the printing and a highly regular feeding of the sheet may be guaranteed. On the other hand, while the sheet is being fed towards the printing zone the guiding channel is narrowed to permit a very effective guiding of this sheet. 
     Other advantages will become apparent from the characteristics set down in the adjoining claims and from the description provided below explaining the invention in greater detail with the aid of drawings which represent, schematically and by way of example, one embodiment and variants thereof. 
    
    
     LIST OF FIGURES 
     FIG. 1 is a side view of this embodiment. 
     FIG. 2 is a partial plan view of this embodiment. 
     FIGS. 3A,  3 B and  3 C are side views of a part in three different working positions. 
     FIG. 4 shows a partial side view of a variant. 
     FIG. 5 is a detailed view of this variant. 
     FIG. 6 shows a partial side view of another variant. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The feeding device  10  of flat materials for processing is here combined with a printer  12  using sheets  14  or envelopes. Generally speaking, the feeding device  10  may be integrated in the machine that uses the sheets or could also be separate from the latter. In the embodiment illustrated in FIGS. 1 through 3, the feeding device  10  is entirely integrated within the printer. The whole comprises a frame  15 . The sheets for printing  14  are stored in a receptacle  16  comprising a movable support  17 . Springs  18  urge the movable bottom  17  and the sheets  14  against selection wheels  19 . 
     The latter-named are mounted on a selection shaft  20  and driven in rotation by a motor  21  illustrated schematically in FIG. 2 through a gear train  22 . Counter-rotating rollers  25 ,  26  and  27  mounted freely turning on shafts are arranged along a guiding channel  28  bounded by a wall  29  surrounding the selection wheels  19 . 
     The printer  12  comprises a printing zone  35  with a printhead  30  borne by a carriage  31  which is mounted slidingly on a shaft  32 . The printing zone  35  is provided with its own driving device  36  for the sheets  14 . This driving device comprises at the entrance to the printing zone a transport roller  37  also driven by the motor  21  through the gear train  22  and cooperating with counter-rotating rollers  38 . At the exit of the printing zone, the driving device has sprocket wheels  39  cooperating with rollers  40 . The sheets  14  are thus maintained and fed with precision through the printing zone. They are then placed on a receiving tray  45  which is mounted pivotingly on the frame  15  thanks to pins  46 . The receiving tray  45  is integral with one or two cam-shaped lateral extensions  47  adapted for cooperating with projecting portions  48  of the movable support  17 . Accordingly, when the receiving tray  45  is raised by right-hand rotation in FIG. 1 to load sheets  14  in the receptacle  16 , the movable support  17  is lowered through the action of the extensions  47 , which permits easy access and loading. 
     In an original way, the feeding device  10  is provided with a retracting mechanism  50  adapted for pushing back during a phase of the selection cycle the movable support  17  against the action of the springs  18  by a predetermined distance which is substantially constant and independent of the thickness of the stack of sheets  14  arranged on the movable support  17 . The mechanism  50  therefore permits an essentially fixed given gap to be obtained between the top sheet and the selection wheels  19  and of which the magnitude is such that friction between the top sheet and the selection wheels is eliminated. This withdrawal distance could, for example, be fixed at between 1 and 8 mm, to advantage between 2 and 5 mm. 
     With reference to FIG. 1, the retracting mechanism  50  comprises a lever  51  which is integral with the movable support  17 . This lever is affixed to a shaft  52  mounted rotatingly on the frame  15  and integral with a part  53  of the movable support  17 , extends parallel to the support  17  and possesses a toothing  54  at its free end. This toothing  54  cooperates with a cogwheel  55  belonging to a ratchet wheel  56  mounted rotatingly on the frame  15  and which can be put into left-hand rotation by means of an hinged pawl  57  pivoting about a connecting rod  58  and urged against the ratchet wheel  56  by a spring  59 . 
     The connecting rod  58  is mounted slidingly at one end on a shaft  60  of the ratchet wheel  56  and at the other end on a shaft  65  of a cam wheel  66 . The shafts  60  and  65 , to this end, traverse the connecting rod  58  through longitudinal slits. 
     The cam wheel  66  is provided with a cam  67  cooperating with a cam follower  68  integral with the connecting rod  58 . This cam follower  68  is urged against the cam  67  thanks to the action of the spring  18  acting on the lever  51  which urges the ratchet wheel  56  into right-hand rotation so as to push the connecting rod  58  to the right in FIG.  1 . 
     The cam wheel  66  is provided with a toothing  70  having a notched sector  71  without toothing. The toothing  70  is suitable for meshing with a cogwheel  72  integral with the selection shaft  20 . 
     The retracting mechanism  50  also comprises a pawl  75  (FIG. 2) mounted rotatingly on the frame  15 . This pawl  75  is urged by a spring  76  into a notched recess  77  provided on the rear face of the cam wheel  66 . The pawl  75  can be disengaged from the notched recess  77  by means of an actuating pin  78 , the free end  79  of which is suitable for cooperating with a part of the carriage  31  when the latter is displaced upwards in FIG.  2 . 
     In the initial position illustrated in FIG. 1, the connecting rod  58  urges the cam wheel  66  into right-hand rotation. However, this cam wheel is held back by the pawl  75  and its notched sector  71  is then in a position facing the cogwheel  72 . In this position, the top sheet is withdrawn by a predetermined distance from the selection wheels  19 . The latter-named and the driving device  36  may be put into action to effect the printing of a sheet without the top sheet of the stack touching the selection wheels  19 . 
     When a new sheet has to be fed into the printing zone  35 , the carriage  31  actuates the pawl  75  following a sheet feeding command. The cam wheel  66  is then freed and, under the action of the connecting rod  58  and the spring  18 , effects a rapid right-hand rotation until its toothing  70  engages with that of the cogwheel  72 . To avoid this sudden rotation from causing too great a sound effect, the cogwheel  72  is provided on its flat outer surface with a neoprene disk  80  which touches the toothing  70  laterally and which, by flattening out, dampens the impact of the toothing  70  on the toothing of the cogwheel  72 . 
     The cam wheel  66  is then driven into right-hand rotation and the connecting rod  58  moves to the right in FIG. 1, as a result of which the ratchet wheel  56  can turn in a right-hand direction. At the end of the stroke of the connecting rod  58 , when the cam wheel  66  has turned through an angle of roughly 90°, the pawl  57  in abutment against a pin  61  is away from the toothing of the ratchet wheel  56 . The lever  51  and the movable support  17  can now turn in a left-hand direction about the shaft  52  under the effect of the spring  18  until the top sheet comes into contact with the selection wheels  19 . The latter in this way drive the sheets in the guiding channel  28  to the transport roller  37  of the printing zone  35 . The movable support  17  can in this way be removed from the selection wheels  19 . 
     The connecting rod  58  is then pushed by the cam  67  to the left, with the result that the pawl  57  turns the ratchet wheel  56  through a predetermined angle in the left-hand direction. The latter drives the lever  51  and the movable support through a given angle in the right-hand direction so as to obtain the predetermined distance between the top sheet  14  and the selection wheels  19 . This therefore remains substantially constant within the limits of precision determined by the angular rotation between two teeth of the ratchet wheel  56 . When the stack of sheets  14  on the movable support  17  becomes thinner, the ratchet wheel  56  cooperates with the pawl  57  through teeth located more and more to the left. The tooth of the ratchet wheel  56  which cooperates with the pawl  57  is determined when the connecting rod  58  is in its right-hand position. 
     When it is wished to feed sheets on the movable support  17  and the receiving tray  45  is pivoted, the movable support  17  is lowered by the lateral extensions  47 . The ratchet wheel  56  is then driven by the lever  51  following a left-hand direction of rotation, whereas the movable support  17  is retained in the low position by the pawl  57 . During the next selection and movement of the connecting rod  58  to the right, the movable support  17  is freed and urges the top sheet against the selection wheels  19 . 
     With reference to FIGS. 3A,  3 B and  3 C, the feeding device  10  can be combined with an actuating mechanism  82  adapted for broadening and narrowing the rear part  83  of the guiding channel  28 . A rear movable wall  84  of the outer wall  29  of the guiding channel  28  is, to this end, mounted by means of a pin  85  on the frame  15 , see also the two positions illustrated in FIG.  1 . At its free end, it disposes of a bar  86  adapted for cooperating with a ratchet and pawl mechanism  87 . The latter disposes of a rocker  88  mounted on the frame  15  by way of a pin  89  and comprising a fork  90  engaged on a rod  91  integral with the connecting rod  58 . The rocker  88  possesses a lip  92  adapted for cooperating with the bar  86 . 
     A pawl  95  is mounted by way of a sliding pivot  96  on the lip  92 . A spring  97  stretched between the lip  92  and the pawl  95  urges the latter-named in the left-hand direction of rotation in FIG. 3A against a fixed abutment  94 . The pawl  95  is provided with a rod  98  adapted for engaging in a notch  99  provided on the lip  92  so as to retain the pawl  95  in the closed position (FIG.  3 C). 
     The actuating mechanism  82  also possesses a spring  100 , called “torpedo”, wound in a right-hand spiral on the selection shaft  20  in such a way that a right-hand rotation of the latter-named renders the spiral integral with the shaft  20 , whereas a rotation in the opposite direction does not drive this spring into rotation. This spring  100  possesses a free portion  101  engaged in a slit  102  of the pawl  95 . When the selection shaft  20  turns towards the rear in a right-hand direction, the pawl  95  can thus be opened by disengaging the rod  98  from the notch  99 . The rear wall  84 , urged by a spring  103 , can thus turn about the pin  85  to open the rear part  83  of the channel  28  (FIG.  3 A). The closing of this rear part  83  of the channel is commanded by an out-and-return movement of the rocker  88  and of the connecting rod  58 . In the outward movement to the right (FIG.  3 B), the rod  98  of the pawl  95  engages in the notch  99  of the rocker and in the return movement of the rocker  88 , the pawl  95  closes this rear part  83  of the channel to ensure precise guiding of the sheet towards the printing zone  35 . 
     It should be observed that the backward rotation in a right-hand direction of the selection shaft is commanded by the passage of the sheet in front of a mechanical or opto-electronic sensor  105  arranged in the printing zone 10 mm downstream of the rollers  37 ,  38 . 
     With reference to FIG.  1  and to FIGS. 3A,  3 B,  3 C, a selection and printing cycle comprises the following steps: 
     a) On completion of the printing of a sheet, the position is that illustrated in FIG. 3A with the rear part of the channel open, the cam wheel  66  being retained by the pawl  75 . 
     b) Following a selection command, the carriage  31  actuates the pawl  75  and frees the cam wheel  66  which meshes with the cogwheel  72  turning in a left-hand direction. The connecting rod  58  moves to the right and permits rising of the movable support  17 . After a rotation of roughly 90°, the pawl  57  is freed of the ratchet wheel  56  and the movable support  17  freely urges the top sheet against the selection wheels  19  to drive it into the guiding channel  28 . At the same time, the rocker  88  is turned in a left-hand direction and the rod  98  engages in the notch  99  (FIG.  3 B). 
     c) When the cam wheel  66  turns between 90 and 180°, the connecting rod  58  is pushed back to the left, as a result of which the support  17  is pushed by a given angle in a right-hand direction removing the top sheet by a predetermined angle away from the selection wheels  19 . 
     At the same time, the rocker  88  turns in a right-hand direction and closes the rear part  83  of the guiding channel to obtain a precise guiding of the sheet towards the printing zone  35  (FIG.  3 C). 
     After a 360° rotation of the cam wheel  66 , the pawl  75  blocks the latter in the position in which the notched sector  71  is facing the cogwheel  72 . 
     d) When the sheet passes in front of the sensor  105  located 10 mm downstream of the rollers  37 ,  38 , the direction of rotation of selection shaft  20  is inverted for a short time, corresponding to a retraction by about 5 mm of the sheet. The torpedo spring  100  then opens the pawl  95  and the rear wall  84  (FIG.  3 A). The sheet is then fed by the rollers  37  to  40  of the printing zone  35  and by the selection wheels  19  cooperating with the counter-rotating rollers  25 ,  26  located at the start of the guiding channel. Advantageously, the peripheral speed of the selection wheels is very slightly greater than that of the rollers  37  to  40  so that the sheet does not touch the selection wheels in the rear part  83  of the guiding channel and may be moved very uniformly and without jerks, ensuring a very precise printing with an absolutely constant line feed. 
     It should be observed that selection of the paper is made very quickly, corresponding to one half-turn of the cam wheel  66 . Accordingly further sheets cannot be driven in the wake of the top sheet. When the latter arrives in the printing zone, the selection has been completed for a considerable time. There is therefore no jerking during printing. 
     The selection of the sheet and the closing of the channel  29  are commanded by an outward-and-return movement of the connecting rod  58 . The opening of channel  29  is obtained by the brief inversion of the direction of rotation of the selection shaft  20 . 
     2 nd  embodiment—The variant illustrated in FIGS. 4 and 5 is similar to the embodiment in FIG. 1, apart from the shape of the connecting rod  158  and the linking of the cogwheel  55  with the movable support  17 . Items that are identical or similar are therefore designated with identical reference numerals. 
     In this variant, the connecting rod  158  is shorter. It also bears the pawl  57  and the cam follower  68  cooperating with the cam  67 . The receiving tray  45  is mounted pivotingly by way of a pin  146 , whereon a toothed sector  151  is also mounted pivotingly. The toothing  154  of the latter meshes with the cogwheel  55  integral with the ratchet wheel  56 . The toothed sector  151  possesses a curved slit  147  cooperating with a rod  148  integral with the movable support  17 . Accordingly, when the ratchet wheel  56  is turned through a given angle following a left-hand direction, the toothed sector  151  makes the movable support  17  pivot downwards through a given angle about the pin  52 . The shape of the curved slit  147  is chosen in such a way that the relationship between the angles of pivoting of the toothed sector  151  and of the movable support  17  is substantially constant whatever the position of the latter, and therefore whatever the thickness of the stack of sheets upon the latter-named. The mechanism therefore also permits a given, essentially fixed gap to be obtained between the top sheet and the selection wheels. During its pivoting about the pin  146 , the toothed sector  151  does not drive the receiving tray  45 . In point of fact, the toothed sector  151  comprises a pivoting bore  162  surrounding the pin  146  of the receiving tray  45 . This bore is provided with two projecting portions  163  penetrating into two hollowed portions  164  shaped so as to permit a rotation action between the toothed sector  151  and the receiving tray  45  (FIG.  5 ). However, when the receiving tray  45  is raised, the toothed sector  151  can be driven, when the movable support  17  is in a high position, to displace the latter downwards and permit the loading of a stack of blank sheets. 
     According to a variant not depicted, the pawl  57  is mounted on a lever turning about the shaft  60  of the ratchet wheel  56 . This lever may in this way be driven by a connecting rod, one end of which is linked to a wheel linked in turn by a clutching member to the selection wheels  79 . 
     In another variant illustrated in FIG. 6, a cam wheel  110  integral with a cam  111  and pulleys  112 ,  113 ,  114  and  115  are driven by a motor not depicted. The cam wheel  110  turns selection wheels  116  for the top sheet of a stack arranged on a pivoting movable support  117 . The sheet selected is transported to the printing zone  118  comprising a printhead  119  by means of a driving belt  120  tightened about the rollers  112  to  115 . 
     The movable support  117  is pulled upwards against the selection wheels  116  by the traction force of a wire  121  attached to the bottom part of the movable support  117  and which is wound on a hub  122  pivoting about a shaft  123 . 
     The hub  122  is integral with a ratchet wheel  124  and bears a helical spring  125  arranged so as to make the hub  122  pivot in a right-hand direction, the effect of which is to pull the movable support  117  upwards. 
     A retracting mechanism  130  adapted for pushing back the movable support  117  is made of a lever  131  mounted pivotingly on the shaft  123  and cooperating with the cam  111  integral with the wheel  110  under the action of a spring  134 . The lever  131  bears a pawl  132  meshing in the ratchet wheel  124  under the action of a spring  133 . In a selection cycle, the mechanism  130  actuated by the cam  111  makes the ratchet wheel  124  pivot through a given angle, which allows the movable support  117  to move away by a predetermined distance from the selection wheels  116 , whatever the thickness of the stack of sheets. It should be noted that the pawl  132  rests against a fixed abutment  136 , when the lever  131  comes towards its maximal position of right-hand rotation so that it disengages from the teeth of the ratchet wheel  124  and the movable support  117  and the sheets thereon are urged by the helical spring  125  against the selection wheels  116 . When the lever  131  turns in a left-hand direction under the action of the cam  111 , the pawl  132  meshes again between the teeth of the ratchet wheel  124 , which it turns through a substantially constant angle to lower the movable support by a predetermined distance in relation to the selection wheels  116 . 
     It is understood that the embodiments described above are in no way restrictive and all changes desired may be made thereto within the scope as defined in claim 1. In particular, the kinematic linkage members linking the feeding mechanism with the movable support may be of any other kind, such as for example a ratchet mechanism, in the form of a pawl, borne by a part linked to a movable element of a driving mechanism, respectively to the movable support adapted for cooperating with an opposite member in the form of a rack linked to the movable support, respectively to a movable element of the feeding mechanism. The actuating mechanism  82  may be constructed completely differently, for instance providing the full opening of the entire guiding channel. This opening could be obtained by a mechanism very different from that of the helical spring, for example by means of an electromagnet-based operation.