FR2536340A1 - DEVICE FOR CARRYING A SHEET OF PAPER OR THE LIKE FOR PRINTING IN A PRINTER - Google Patents

Abstract

DEVICE FOR STEP-BY-STEP FEEDING A SHEET TO BE PRINTED INTO A PRINTER AND FOR CONTINUOUS EXPULSION. BEHIND A CONTINUOUSLY ROTATING 16 DRIVE MOTOR, TWO STEP-BY-STEP COUPLINGS ARE PROVIDED. THE FIRST STEP-BY-STEP COUPLING 26 TRANSMITS THE DRIVING MOVEMENT OF THE STEP-BY-STEP DRIVE MOTOR TO THE SECOND STEP-BY-STEP COUPLING 46, OF WHICH DRIVE SHAFT 44 TURNING CONTINUOUSLY DRIVES A FIRST GEAR 54 WHICH IS CONNECTED TO THE DRIVE WITH THE TRANSPORT ROLLER 86. THE OUTPUT SHAFT 80 TURNING WHEN THE SECOND STEP-BY-STEP COUPLING IS ENGAGED A SECOND GEAR CONNECTED TO THE SHEET TRANSPORTING ROLLER, BUT STILL IN THE DIRECTION REVERSE. A THIRD STEP-BY-STEP COUPLING 92 ACTIVATES A DISC-CAM 112 WHICH CONTROLS PRESSURE ROLLERS 126 WHICH SWITCH BETWEEN A POSITION WHERE THEY PRESS THE TRANSPORT ROLLER AND A POSITION WHERE THEY ARE RAISED. IN THIS WAY THE STEP-BY-STEP INTRODUCTION MOVEMENT AS WELL AS THE CONTINUOUS SHEET EXTRACTION MOVEMENT CAN BE PERFORMED BY ACTING THE THREE STEP-BY-STEP COUPLINGS.

Description

Device for transporting a sheet of paper or

  the analog intended to be printed in a printer.

  The invention relates to a device for transporting a sheet of paper or the like intended for printing in a printer, in particular for transporting the sheet.

  step by step in a first direction of movement and for trans-

  carry the sheet continuously in the opposite direction, comprising a drive motor rotating continuously in a

  sense, a step coupling mounted as a result: of this

  ci and comprising a drive shaft and a drive shaft

  output can be coupled to the latter by means of a mechanism

  mechanical step-by-step advance, respectively for predetermined angles of rotation, of the transmission means

  mounted following the coupling step & not for drive

  means for transporting the sheet in the first direction as well as in the opposite direction, as well as a control device for controlling the drive motor and

the coupling step by step.

  The printers in which the transport devices of the aforementioned type are used, are used, for example, to

  print receipt forms which, after intro

  duction in a slot for forms, is automatically drawn in the printer, is printed by lines and comes out in the opposite direction of the introduction It is desirable in this case that the transport of the form

  takes place quickly and precisely on the lines.

  There are already known printers in which the sheet to be printed is picked up and transported in the usual way between a transport roller and pressure rollers cooperating therewith. A drive motor is generally used as a drive for the transport roller. continuously in one direction throughout the printing process, the motor at which the printing roller can

  be coupled by being ordered each time temporarily.

  As couplings, couplings are generally used

  magnetic To allow the drive of the trans roller

  carrier in both directions for the movement of introduction as well as for the movement of expulsion of the form, -one must be provided, either two magnetic couplings, or a magnetic coupling with two effects by means of which the conveyor roller is connected to trains of different gears respectively causing opposite directions of rotation; another solution consists in providing in the gear train between the drive motor and the conveyor roller a reversible transmission The control of the transport path, and in particular also of line steps is carried out in all cases by the duration of coupling of the couplings The accuracy of such systems leaves something to be desired due to the initial start-up which cannot be determined with precision and which depends on the thickness of the paper and other accidental influencing factors. magnetic couplings as well as reversible transmissions are elements

complicated and expensive.

  Another device of the aforementioned type has already been proposed in which, following the drive motor rotating continuously in one direction, a stepping coupling has been mounted which in principle allows very precise control of the path.

of the form in the printer.

  The transmission mounted following the stepping coupling comprises a disc-cam with a closed control cam driven by this coupling, into which a

  control rod connected to an oscillating lever L'oscilla-

  tion of the oscillating lever is transmitted to a carriage which carries the form and moves in the direction of introduction and expulsion The greater precision thus obtained is offset by the disadvantage of relatively large masses to move and especially by the fact that with this device it is only possible to print a determined number of lines depending on the design of the control cam used In addition, this known solution is of construction

complicated and expensive.

  The object of the invention is to provide a device of the type

  mentioned above which ensures rapid and extremely pre-

  cis of the sheet to be printed, which also allows

  simply override different numbers of lines, and

  which is simple in construction and therefore economical.

  This object is achieved according to the invention by the fact that the output shaft of the first stepping coupling is in

  drive link with the drive shaft of a -

  second step-by-step coupling that can be controlled by the

  intermediate of the control device, following the second stepping coupling is mounted a gear disposed on a gear support, comprising an output shaft rotating in opposite direction to the direction of input rotation, and connected by a roller sheet conveyor, or the like, the drive shaft of the second stepping coupling is drive-connected with the input of the gear, and the gear carrier is mounted in the printer so that rotate about an axis coaxial with the output shaft of the gear and it is connected by drive to

  the output shaft of the second stepping coupling.

  The first step coupling is used in a known manner

  in itself, to transform the continuous movement of the engine of-

  dragging in the desired positioning steps The step-by-step mechanism here guarantees the highest precision

possible positioning steps.

  The second step coupling mounted after the first is used to some extent for gear selection since either the direction of rotation of the drive shaft of this step coupling or the direction of rotation of the output shaft which is coupled to it, using a gear mounted subsequently, to drive the sheet transport roller in one direction or the other,

  as will be described in more detail below.

  Stepper couplings of the aforementioned type are objects

  of commerce and exist in very simple and economical versions

  mics, for example in the form of wrapped spring couplings These are characterized above all by very high positioning precision as well as by their clutching and disengaging practically without delay. They can be very easily controlled electrically. For this reason, the transport routes, the number of line steps, etc., depend only on the control program

  to which the couplings are subjected step by step.

  The gear can also very simply be produced in the manner of a planetary gear in which, on the one hand when the gear carrier is stopped, the central gear is driven and transmits its rotational movement to the shaft of output turning in opposite direction; in the other case, the central gear and the entire gear support are rotated in the same direction

  so that the gear does not move forward

  loppement, and that the output shaft rotates in the direction of input rotation, as will be explained in more detail below. According to another characteristic of the invention, one associates

  to the transport roller of the sheet of the press rolls

  which can be moved between a trans-

  port in which they press against it and a

  rest position in which they are lifted This displa-

  cement is carried out by means of a simple disc-

  cam acting on the support of pressure rollers, which in turn is in drive connection with a third stepping coupling The three stepping couplings can be identical, to allow the use of as many identical elements as possible; it will suffice, if necessary, depending on the design of the device, to differentiate the couplings turning to the right from the couplings

turning left.

  In addition, according to the invention, stop means are provided, before the sheet transport roller in the direction of entry thereof, which can tilt on the path of the sheet. These stop means prevent the sheet inserted into the printer slides between the transport roller that is out of grip, and the

  pressure; on the contrary, it stops first against-

  stop means, which aligns it with precision and which is also important for the precision of the following transport movements. It is further provided according to the invention that when tilting, the stop means come into contact with the support of the rollers. pressure and move it into its rest position, the abutment means themselves being able to be moved by means of the cam-disc connected to the drive with the third step-by-step coupling. An exact coupling is thus obtained between the tilting in engagement and out of engagement of the stop means and the displacement of the pressure rollers between their transport position and their position

rest.

  Although the positioning accuracy of the stepping couplings is very high, it can occur during the drive between the first stepping coupling and the shaft

  gear output, inaccuracies due to elastic

  cited, at play between the teeth and the analog For this

  reason, according to another characteristic of the

  vention, on the gear support a ratchet wheel connected in drive to a gear wheel of the gear close to the output shaft and the pitch of which corresponds to the pitch of transport of the means of transport of the sheet This ratchet wheel cooperates with a pawl subject to a spring which allows rotation only in the direction of rotation of the gear determined by the stepwise transport of the sheet The ratchet wheel and the pawl have the role of

  compensate for the above inaccuracies in the information system

  tra Inement and to ensure a precise angular position of the output shaft in all positions They also pocket a backward movement of the output shaft in the case of operation in which the gear support

  rotates and the output shaft is loaded in the direction of rotation

  inverse tion In the case of step-by-step couplings, in particular

  In the case of coil spring couplings of the usual type, the drive shaft generally crosses the entire coupling body so that it also protrudes from the output side proper. The rotational movements of the drive shaft and the output shaft coaxial to it

  are therefore taken from the same side of the coupling body.

  With such a configuration, in particular of the second coupling-

  step by step, in accordance with the invention, a very simple and appropriate configuration of the gear is obtained, characterized in that the gear support is produced in the form of a gear housing comprising an internal toothed crown produced on one side outside of the casing and which can be threaded on the output pinion of the second stepping coupling,

  that a hole is provided in the housing wall

  stick to the inner ring gear, for the passage of the drive shaft of the second step coupling coupled in rotation with an input pinion disposed in the gear housing, and that in the housing wall opposite to the casing wall carrying the internal toothed crown is mounted the output shaft rotatably connected to the output pinion of the gear, the output shaft being further mounted in the printer by its free end The support of gear in the form of a gear housing is mounted on the input side on the output pinion as well as on the drive shaft arranged concentric therewith, and on the output side on the output shaft There is no need for '' another positioning of the

gear case.

  The invention will be clearly understood on reading the description

  detailed description, given below by way of example only, of an embodiment shown diagrammatically in the drawing, in which

  Figure 1 is a top view of a transfer device

  port, on which, for clarity, some details have been left out; Figure 2 is a view of the gear housing in the direction of arrow II; and Figure 3 is a section through the device of the

Figure 1 along line 111-III.

  The device shown in FIG. 1 is intended to be mounted in a printer, in which the sheet to be

364 O

8.

  printing is introduced in a known manner by means of a roller

  the sheet transport water and is expelled in reverse.

  The various components are essentially arranged between several parallel ribs 4 to 12 fixed on a base plate 2 The base plate 2 can be placed in the casing of the printer so as to be able to tilt or slide outwards, so the device

  placed on it is easily accessible for maintenance.

  On the rib 6 is fixed a drive motor 16 which is connected to the drive by means of an assembly

  of toothed wheels 18 with a shaft 20 mounted in rotation-equal-

  on the rib 6 The shaft 20 drives an inter-

  medial 22 which is connected to it by a drive rod and which, for its part, is connected via another drive rod to the drive shaft 24 of a coil spring coupling 26 or to a flange 28 connected to the drive shaft The end 30 of the shaft

  drive 24 exiting on the output side of the coupling-

  Ment by coiled spring 26 is rotatably mounted on the rib 10 To engage the coupling by coiled spring 26, a pawl 32 is used which can penetrate by its bent end 34 into snap-fit spouts made on the outer surface of the coil spring coupling 26 In this state, the coupling is released To engage the coupling 26, the pawl 32 can be raised by a magnetic switch 36 against the force of a

  tension spring 38, from which it follows that the drive shaft

  drag 24 is coupled to an output shaft disposed in the housing of the coil spring coupling 26; the output pinion 40 is part of this output shaft or is made integral with it When the excitation of the magnetic switch 36 is interrupted, the pawl 32 snaps again under the effect of the tension spring 38 in the nozzles snap-in coupling by coiled spring

  26 and thereby the coupling between the drive shaft

  ment 24 and the output shaft or the output pinion 40 is again released The function of the step coupling will be explained in more detail below with reference to

  at the third coupling by coiled spring.

  The output shaft or pinion 40 is connected via an intermediate shaft 42 mounted on the rib 10 with the drive shaft 44 of a second coupling by

  coiled spring 46 or a flange 48 connected thereto.

  The end 50 exiting on the output side of the coupling housing-

  coiled spring 46 drives a gear 54 available

  dried in the gear housing 52 This gear comprises a toothed wheel 56 movably mounted on the drive shaft 44, an intermediate toothed wheel 58, a grooved roller 60, as well as the output toothed wheel 62 which is integral with the output shaft 64 of the gear The free end of the output shaft 64 is rotatably mounted in a rib 14 An output pinion 66 formed on the output shaft 64 is connected to the drive via other gear wheels (not shown) with the sheet transport roller (also not shown) The output gear wheel 62 further drives a drive pinion 68 mounted on the gear housing 52 and connected to a ratchet wheel 70 which is coaxial to it A ratchet 72

  subject to a spring and pivotally mounted on the crankcase

  grenage 52 cooperates with the ratchet wheel, as it will

  explained in more detail with reference to Figure 2.

  The coiled spring coupling 46 can also be

  controlled by a ratchet 74 which is now

  bare engaged by a tension spring 46 with spouts

  snap fitted on the outside of the coupling

  plement by coiled spring To raise the pawl 74,

  a magnetic switch 78 is used.

  coiled spring 46 is disengaged, the drive shaft

  nement 44 driven by means of the coupling 26 rotates and it drives the toothed wheels 56 to 62 in the direction of the arrows indicated. As can be seen, the output shaft 64 with the output pinion 66 rotates in the opposite direction from the direction of rotation of the toothed wheel 56 When the coil spring coupling 46 is engaged by lifting the pawl 74, the output shaft, and the output pinion 80 which is connected to it rotates in the same direction as the shaft drive 44 The gear housing 52

  is threaded on the output pinion 80 with a crown

  inner tee 82 made on the wall of the turned housing

  to the coil spring coupling 46 When the coupling

  plement by coiled spring 46 is engaged, the drive shaft

  drag 44 and the output pinion 80 rotate in the

  same direction in the sense of the arrow shown in dashes.

  Figure 2 shows the gear case 52 with the

  shot 54 in a view according to arrow II We see there the gear 56 coaxial with the drive shaft 44 of

  the coiled spring coupling 46, the toothed wheel inter-

  medial 58 driven by the previous one, the grooved roller 60 which is connected to it as well as the output toothed wheel 62 driven by the grooved roller The arrows indicating the directions of rotation are shown in correspondence with FIG. that the output pinion 66 drives the conveyor roller of the

  sheet 86 by means of an internal gear wheel

diary 84.

  The ratchet wheel 70 is also driven by the wheel

  output tooth 62 via the gear

  mande 68 connected to the ratchet wheel The transmission between the stepping coupling 26 and the sheet-86 transport roller is chosen so that one control pitch corresponds to one line pitch At the same time, the ratchet wheel 70 advancing a tooth As seen in Figure 2, the pawl 72 subject to a spring allows rotation in the direction of arrow 88, but blocks the opposite direction The force of spring 90 is such that the wheel

* - 255634 O

  ratchet is always pressed by the ratchet 72 in an exact angular position determined by: the cooperation of the profiles of the ratchet and the ratchet wheel, which allows an exact control of the lines as already described.

  As shown in Figure 1, another delivery is planned.

  step by step, or coupling by coiled spring 92, which is used to control pressure rollers cooperating with the roll & transport of the sheet as well as stop means for the sheet to be printed These are driven by the intermediate shaft 22 by means of toothed wheels 94, 96, 98 as well as by another intermediate shaft 10 O The coil spring coupling 92 has the same structure as the coil spring coupling 26 A pawl 102 is engaged by a tension spring 104 with snap-fit spouts made on the coil spring coupling 92 and can be raised by a magnetic switch 106, whereby the drive shaft 108 is coupled with the output shaft or pinion 110 A cam disc 112 is secured to the pinion of

  output 110 The drive shaft 108 crosses this disc-

  cam 112 being able to turn there and it is mounted to rotate

in rib 10.

  As can be seen in FIG. 1 and in particular also in FIG. 3, four snap-fit nozzles 114 offset by 90 '

  are made on the outer periphery of the coupling body

  plement 116 of the coupling by coiled spring 92 The pawl 102 is held in engagement with a latching spout 114 by the tension spring 104 In this state, the coupling

  is disengaged, the cam disc 112 is not rotated

  tion although the drive shaft 108 rotates For clutch

  yer the coupling, the magnetic switch 106 is briefly

  strongly excited so that the pawl 102 is lifted from the coupling body 1160 The coupling body 116, which is connected to the drive shaft 108 via

-25634 O

  of a friction coupling, continues to turn a little bit in the direction of the arrow Meanwhile, the current flow to the magnetic switch 106 has been interrupted again, so that the pawl 102 rests again on the periphery outside of the coupling body 116. When the following snap-fit spout 114 located at 90

  comes into engagement with the pawl 102, the coupling body

  ment 116 is stopped again and the coupling is

again disengaged.

  In this way, the disc can be rotated each time-

  cam 112 with exact pitch of 90 By the control cams 118 offset by 180, produced on the cam disc 112, an oscillating lever 120 is pivoted between the position shown

  in solid lines and the position shown in dashed lines.

  On the oscillating lever 120 are fixed stop means 122 which move between a position where they project on the path of the sheet 124 (solid lines) and a

  position set back from it (dashed lines).

  When the stop means switch to their active position, they come into contact with the support 128 carrying the pressure rollers 126 and move the latter so that the pressure rollers 126 come out of contact with

  the sheet transport roller 86.

  Since the coiled spring coupling 92 trav-

  worth in steps of 90, two control cams 118 are provided

  located 180 from each other The control cam respects

  opposite the swing lever 120 is used to

  operate a microswitch 130 In the position shown

  sensed, for example this sends a signal to a control device which indicates that the oscillating lever 120 and with it the stop means 122 assume their active position

  and that the pressure rollers 126 are raised.

  When the stop means 122 have again pivoted to their positions indicated in phantom, the pressure rollers 126 are applied to the sheet transport roller 86 At the same time, the sheet 124 can fall until that it is gripped by the sheet transport roller 124 and the pressure rollers 126 and that it is transported further away The sheet 124 is then guided along the writing head 132 and of a sheet support

  134, where it can be printed by lines in a known manner.

  The sheet 124 is preferably introduced step by step into the printer where it is printed in lines; then,

  it is ejected in the opposite direction in a movement of expulsion-

continuous.

  The sheet transport roller 86 and the means for

  stop 122 are arranged, with respect to FIG. 1, au-

  above it As seen, in this case, the sheet transport roller 86 is divided into two roller sections 86 a, 86 be the stop means 122 are also divided into individual sections 122 a, 122 b , 122 c and arranged on each side of the roll sections

86 a, 86 b, etc., between them.

  As can also be seen in FIG. 1, a signal transmitter 136 is provided which registers the passage of the edge of the sheet penetrating the device and signals it to an electronic control device 140 by a pipe 138 Another transmitter of signals 142

  records the passage of the rear edge of the sheet and-

  also signals it to the control device 140 by a pipe 144 The signal from microswitch 130 is

  also brought to the control device 140 by a channel

  reading 146 The control device 140 shown twice for clarity, controls the drive motor 16 as well as the magnetic switches

  36, 78 and 106 respectively through lines 148 to 154.

  To introduce the sheet, the drive motor 16 is activated by the signal transmitter 136 via the control device 140 This motor drives the drive shafts 24 and 108 of the two couplings by

  coiled spring 126 and 92 Then the magnetic switch

  tick 106 is activated, so that the coiled spring coupling 92 and the Carmine disc 112 which is connected to it bring back the stop means 122 and that the pressure rollers 126 are applied against the transport roller 86 By activating the magnetic switch 36 step by step, the output pinion 40 is also driven in step-by-step rotation; this step-by-step movement is transmitted by the drive shaft 44 of the coil spring coupling 46 as well as by the gear 54 to the output pinion 66 and therefore to the sheet transport roller 86, which brings in the sheet step by step, so that it can be printed in lines When the rear edge of the sheet passes the signal transmitter 142, the magnetic switch 78 is activated so that the direction of rotation of the pin of outlet 66 and therefore from the transport roller

  sheet 86 is reversed as described above.

  The magnetic switch 36 is no longer activated step by step, but continuously. In this way, the sheet transport roller is driven continuously in the opposite direction, so that the sheet is expelled continuously. When the sheet has been completely returned. , the drive motor 16 as well as the magnetic switches 36, 78 and 106 are deactivated by means of the control device so that the stop means 122 fall back into their active position and in doing so raise the pressure rollers and that , moreover, the roller drive

  sheet transport is stopped.

Claims (8)

Claims.   1 e Device for transporting a sheet of paper or the like intended to be printed in a printer, in particular for transporting the sheet step by step in a first direction of movement and for transporting the sheet continuously in the opposite direction, comprising a motor   continuously rotating in one direction, a coupling   step by step assembled after it and behaving   both a drive shaft and an output shaft which can be coupled to the latter by means of a feed mechanism   mechanical step by step respectively for rotation angles   tion predetermined, means of transmission mounted following the stepwise coupling to drive means of transporting the sheet in the first direction as well as in the opposite direction, as well as a control device for controlling the motor d training and mating   step by step, characterized in that -   the output shaft (40) of the first coupling not to   pitch (26) is in drive connection with the drive shaft   nement (44) of a second step coupling (46) controllable by the control device (40); following the second step coupling (46) is mounted a gear (54) disposed on a gear support (52), comprising an output shaft (64) rotating in direction   opposite of the input rotation direction and connected by drive-   with a sheet transport roller (86) or the like; the drive shaft (44) of the second coupling not to   step (46) is connected by drive with the input of the gear   swimming (toothed wheel 56), and that the gear support (52) -is rotatably mounted, -in the printer, around an axis coaxial with the output shaft (64) of the gear (54 ) and it is connected by drive with the output shaft (80) of the second coupling not to no (46) -   2 Device according to claim 1, characterized in that the sheet transport roller (86) are associated with pressure rollers (126) or the like, arranged on a support of pressure rollers (128), which can be moved between a transport position where they press against the sheet transport roller (86) under the action of pressure spring means and a rest position where they are lifted from this roller, and that to move the roll support pressure (128), a rotatable cam disc (112) is provided which is   connected to drive with the output shaft (110) of a three   the fifth step coupling (92) can be controlled via the control device (140), the drive shaft (108) of the third step coupling   (92) being connected to the drive with the drive motor ment (16).   3 e Device according to claim 2, characterized in that there is provided before the sheet transport roller (86) in the direction of introduction of the sheet (124) stop means (122) which can pivot in the path of the sheet which, during this pivoting, come into contact with the support of pressure rollers (128) and move it in its rest position, and that the stop means (122) can be moved using the disc- cam (112) connected to drive with the   third step-by-step coupling (92).   4 Device according to any one of claims 1 to   3, characterized in that the step-by-step couplings (26, 46, 92) are respectively produced as coiled spring couplings comprising a control pawl (32,   74, 102) can be actuated by a magnetic switch tick (36, 78, 106).   Device according to any one of claims 1   to 4, characterized in that provision is made on the support for   shot (52) a ratchet wheel (70) connected to the drive with a toothed wheel (62) of the gear close to the shaft   outlet (64) and having a corresponding snap pitch   in one of the transport steps of the sheet transport roller (86), which ratchet wheel cooperates with a pawl (72) subjected to a spring, which allows rotation of the ratchet wheel only in the direction of rotation of the gear (54) provided for the stepwise transport of the sheet (124).   6 Device according to any one of claims   1 to 5, comprising a second stepped coupling, in which the drive shaft exits the coupling body on the drive side as well as on the output side, and in which the output shaft comprises a pinion exit   arranged on the outlet side of the coupling body and   centered on the drive shaft, characterized in that the gear carrier is designed as   gear housing (52) having an internal gear ring   lower (82) produced on an outer side of the casing and capable of being threaded on the output pinion (80) of the second stepping coupling (46),   that a hole is provided in the housing wall   stick to the inner ring gear (82) for the passage of the drive shaft (44) of the second stepping coupling, connected in rotation with an input pinion (56) disposed in the gear housing (52 ); and that in the casing wall opposite the casing wall carrying the internal toothed crown (82) is mounted the output shaft (64) connected in rotation to the output pinion (62) of the gear (54), the output shaft (64) being further mounted in the printer by its free end. 7 Device according to claim 6, characterized in that the output pinion (62) of the gear (54) meshes with a control pinion (68) rotatably mounted on the gear housing (52), which carries the ratchet wheel (70), and the pawl (72) is also tiltable on the gear case (52).   8 Device according to any one of claims 2 to   7, in which the second step coupling is calculated for steps of 90, characterized in that the disc-cam (112) comprises two cams (118) located 1800 from one another and that the cam respectively opposite the support   of pressure rollers (128) cooperates with a micro-   switch (i 30) or the like to signal to the device   control (140) the position of the cam disc (112>.   9 Device according to any one of claims 1 to   8, characterized in that, on the sheet path (124), are arranged before the sheet transport roller   (86) a signal transmitter (136) actuated by the anterior edge   laughter of the sheet (124) entering first as well as a signal transmitter (142) actuated by the terminal edge of the sheet (124) when the latter is fully entered, these transmitters sending signals to the control (140).   Device according to any one of the claims   to 10, characterized in that the control device   (140) is produced in the form of an electronic control.