EP0934221B1 - Method and devices for feeding sheetlike material into a printer or photocopier - Google Patents

Abstract

The invention relates to a method of feeding a sheetlike material (50-54) into a printer. An externally located cover sheet (50-54) is removed from a pile of sheets and conveyed towards a section (a10-a12) of the transport path at a transport speed (V0, V1). The lower limit (v0) of the transport speed is the same as or greater than the transport speed (v0) of the sheets (50-54) in section (a1-a12). Conveyance of the sheet (52,54) is delayed until section (a10-a12) has been reached. Identical predetermined spacing (AS) thus occurs between immediately successive transported sheets (52,54).

Description

The invention in a first aspect relates to a method of inputting sheet material into a printer or copier. In known methods for inputting sheet material, an outer cover sheet is withdrawn from a stack of sheets in response to a start signal and transported at a feed rate in the direction of a subsection of the transport path, in which it is transported at an approximately constant desired transport speed, which corresponds to the feed rate.

A disadvantage of the known method for inputting sheet material is that the distance between successive sheets varies. This is due to the fact that the frictional engagement between intake rollers or feeder belts and the leaves is not guaranteed one hundred percent, so that a so-called micro-slip occurs. The microslip that occurs depends on the paper properties, e.g. Paper thickness and surface roughness. Adjustment of the pull-in force, in particular when removing the sheets from the stack, also leads to a change in the distance between successive sheets. When removing the sheets from the stack, a minimal displacement of the leaves adjacent to the cover sheet can not be prevented, so that the exact position of the leading edge of the sheet in the transport direction is not known when pulling. The consequence, in turn, is that a change in the distance between successive sheets occurs.

High-performance printers print over 100 sheets per minute. Variations in the pitch between a lower and an upper limit inevitably lead to a loss of speed in printing compared to a Pressure with the lower limit. When specifying the printable number of sheets per time unit, the worst value must be assumed. The user wants but a predictable constant printing speed.

European patent application EP 0 428 922 A2 discloses a device for document processing. The conveying density is increased by adjusting the distance between the documents by means of a plurality of light barriers for detecting the position of the documents.

European Patent Application EP 0 167 091 A1 discloses a separating device for letter mail. By taking into account a default value for the acceleration path at the time of insertion, the distance between the letters can be set more accurately.

In the German patent application DE 27 58 007 A, a method for controlling the deduction process is explained in a device for dispensing individual shipments of different lengths. In order to increase the conveying density of letters of different length, the reference edge is selected automatically for setting the distance between successive correspondence.

The object of the first aspect of the invention is to provide a simple method for the input of sheet material, which allows an approximately constant pitch between the sheets entered one after the other.

This object is achieved by a method having the features of patent claim 1. The first aspect of the invention is based on the recognition that blade spacing can be most easily adjusted when the blades are retracted, as later correction of a distance would result in a change in the location of all subsequent blades. A setting of the distance should be both below and below be possible when exceeding a desired distance. Therefore, in the first aspect of the invention, the transport of the sheet is so delayed that results in a predetermined equal distance until reaching the portion between immediately successively transported leaves. Thus, adjusting the distance between the sheets when the sheets are fed into the printer. If the intake speed is relatively low, it is hardly or not delayed. However, if the intake speed is relatively high, it will be delayed for a longer time to set the target distance. Even if the drawing speed is lower than or equal to the transporting speed, a delay can be set by retarding the cover sheet when drawing in, when the sheets are peeled from the stack at a smaller distance than the predetermined same target distance.

Delaying the transport is a simple technical measure, for example, by stopping a collection device or by slowing down the same.

In the method according to the first aspect of the invention, the feed rate is in particular greater than the transport speed of the sheets within the subsection. By this measure, delay time for regulating the distance is obtained. Thus, the distance can be increased when removing the leaves and also exceed the target distance, whereby the removal is safer, since a driving of the sheets is avoided each other. Ultimately, the control range of the distance increases as the feed rate increases.

The number of printed sheets per unit time is not reduced by the first embodiment of the invention, since in the worst case the feed rate has the size of the transport speed, in which case no or only a very small delay occurs.

In one embodiment of the first aspect of the invention is located between the sheet stack and subsection a Voreinzugsposition, at which the position of the sheet is determined. By this measure it is achieved that the position of the sheet can be used for further control operations. The varying position of the leaves in the leaf compartment has by detecting the exact position of the sheet and measures based on it no longer influence on a possible change in the blade spacing.

In a further embodiment of the first aspect of the invention, the sheet between the sheet stack and subsection is stopped and preferably transported at the retraction speed after a holding time has elapsed. Conveniently, the sheet is stopped exactly at the Voreinzugsposition. The holding time is such that, seen in the transport direction between the cover sheet and a previously withdrawn sheet of the sheet stack of the same predetermined distance during transport of the cover sheet to the subsection established. The hold time can be determined by simple path-time calculations. The distance between the holding position and the transport device, and the feed rate are known. The stopping can be realized eg via stepper motors and / or couplings.

The invention in a second aspect relates to a device for drawing sheet material into a printer or copier, in particular for carrying out a method according to one of the preceding claims. Thus, the above-mentioned technical effects are also transferred to the sheet material drawing apparatus according to the second aspect of the invention.

In one embodiment of the second aspect of the invention, a take-off roll acting on the cover sheet is used, with which the respective withdrawn sheet is fed to a draw-in belt, which then feeds the sheet to the transport device. Rolls and tapes are equivalent technical means that can be exchanged against each other. In order to ensure a safe collection, the transport device detects the withdrawn sheet before its rear edge is transported past the take-off roll. By this measure, it is ensured that the take-off roller, which is not usually located directly on the leading edge of the sheet stack, can be unlocked upon detection of the sheet by the transport device until the sheet is completely removed from the stack of sheets. Thus, it is prevented that further sheets are withdrawn from the sheet stack by the take-off roll, before the cover sheet is completely withdrawn from the sheet stack.

In one embodiment of the second aspect of the invention, the sheet position is detected with a first photocell immediately behind the retractor. Depending on a signal of the first light barrier, which, for example, when interrupting a light beam through the leading edge of the sheet is generated, the collection device is released, so that the sheet rests in a Voreinzugsposition. A second light barrier is preferably arranged approximately at the predetermined distance in the transport direction behind the first light barrier. The control unit switches, depending on a signal of the second light barrier, which is generated for example by the back edge of an already withdrawn sheet, the collection device again effective. Thus, the sheet located in the advancing position is further conveyed at the predetermined distance from the previous sheet. With the aid of the two light barriers, the feed rate can be measured by measuring the duration of the transport of a sheet between the two light barriers. From the feed speed, the time can be derived at which the sheet is detected by the transport device, so that the collection device can be unlocked at this time. In addition, it can be calculated using the feed rate, when the withdrawn sheet has a minimum distance to the stack. If the minimum distance is reached, the control unit switches the feeder again effectively, so that a next sheet is removed.

The invention in a third aspect relates to a method for inputting sheet material into a printer or copier, which can be used in combination with the method according to the first aspect of the invention or separately. The method according to the third aspect of the invention is intended to prevent multiple sheet feeding. In multiple sheet feeds, at least two sheets that are at least partially overlapping are peeled off the sheet stack at the same time. The result is an increased sheet consumption and possibly misprints. A misprint is inevitable if the sheets are printed on both sides. A known measure for preventing multiple sheet feeding is to increase the pressing force of a take-off device when peeling off the sheets from the sheet stack. By this measure, however, not all multiple or double sheet feeding can be prevented become. Double-sheet feeds arise, for example, with poor paper quality or with burred cut edges.

British Patent Application GB 2 012 727 A discloses a collection device with a vibrating motion. The shaking movement is performed transversely to the transport direction of the sheet material. This requires a complex mechanical vibrator.

The object of the third aspect of the invention is to prevent multiple feeds when inputting sheet material into a printer or copier.

This object is achieved by a method having the features of patent claim 18. This is based on the consideration that two adhering sheets can be separated by a kind of shaking movement. Therefore, in the third aspect of the invention, the cover sheet is transported in particular at the peeling off of the sheet stack with a repeatedly greatly varying feed speed. In extreme cases, the cover sheet is withdrawn from the stack of sheets for a defined period of time in the start / stop mode. By repeatedly varying the feed speed, sheets also detach from each other which, when the feed rate is varied once, e.g. when accelerating, would not solve each other. A method according to the third aspect of the invention thus achieves a reduction of multiple sheet feeds.

If the intake speed varies periodically, then the intake speed can be varied in accordance with a clock signal with little outlay on software or software.

In another embodiment of the third aspect of the invention, the feed rate is varied only when multiple sheet feeds occur. Varying the feed speed can be effectively switched by both an operator and a sensor unit. Thus, the leading to increased wear variation of the Feeding speed is only performed if, due to the paper quality, an increased number of multiple or double-sheet feeds is to be expected. In addition, due to the varying intake speed, a loss of speed occurs during retraction of the leaves, which is justifiable only when the risk of multiple sheet feeds is actually present.

The invention relates in a fourth aspect to a device for drawing sheet material into a printer or copier, in particular for carrying out the method according to the third aspect of the invention. Thus, the technical effects mentioned in the third aspect of the invention also apply to the device according to the fourth aspect of the invention.

Figur 1

eine schematische Darstellung einer Einzugsvorrichtung zum Einziehen von Blattmaterial in einen Drucker,

Figur 2

ein Weg-Zeit-Diagramm zur Darstellung einer Abstandsregelung, und

Figur 3

ein Weg-Zeit-Diagramm zur Darstellung einer Abstandsregelung mit Rütteleinzug.

In the following the invention will be described by means of embodiments. Showing:

FIG. 1

a schematic representation of a collection device for drawing sheet material into a printer,

FIG. 2

a path-time diagram for representing a distance control, and

FIG. 3

a path-time diagram showing a distance control with Rütteleinzug.

Figure 1 shows the side view of a feeder 10 for feeding paper sheets 12, 14 of a sheet stack 16. The components of the feeder 10 are supported by a frame 18, to which a pivotable about one end of the lever 20 is attached. At the other end of the lever 20, a take-off roller 22 is arranged, which is pressed by means of a spring, not shown, against the sheet stack 16. Between two rotatably mounted on the frame 18 Transport rollers 24, 26, a conveyor belt 28 is tensioned. Immediately on the transport belt 28 is located near the transport roller 24, a non-rotatable stop roller 30 at which the conveyor belt is passed approximately at an angle of 170 °. A counter-rotating roller 32 is in contact with the conveyor belt 28 in the region of the transport roller 26. An unillustrated stepper motor is connected via a coupling device with the take-off roller 22, the transport roller 24 and the counter-rotating roller 32, so that the take-off roller 22 in the direction of a direction of rotation arrow 34, the conveyor belt 28 in the direction of arrow 36 and the counter-rotating roller 32 in the direction of Direction of rotation arrow 38 rotates. The surfaces of the take-off roller 22, the conveyor belt 28 and the counter-rotating roller 32 is made of a rubberized material with a very high coefficient of friction. When the feed device 10 is activated, the uppermost sheet 12 of the sheet stack 16 is thus fed to the conveyor belt 28 by the take-off roller 22. A baffle 40 ensures that only a very small number of sheets 12, 14 of the sheet stack 16 can reach the stop roll 30 at the same time.

Once the cover sheet 12 is detected by the conveyor belt 28, it moves in the transport direction 36 to the mating roller 32 to. Supported by the counter-rotating roller 32, the respectively transported sheet is transported from the feeder 10 in the direction of an arrow 42 to another transport device, which then transports the withdrawn sheets to a printing unit, and a fuser to a sheet delivery.

Figure 2 shows a path-time diagram for three retracted sheets 50, 52 and 54, wherein on the ordinate axis 55 of the transport path s and on the abscissa 57, the time t are removed. In addition, the path-time diagram with a representation of the collection device 10 according to Figure 1 is deposited. The take-off roller 22 is located at the zero point of the ordinate axis 55 at the beginning of the transport path s of the sheets.

In the transport direction 36 of a sheet 50, 52 and 54, positions a1 to a12 are to be distinguished, which are arranged in this order along the transport path. At the position a1 is the transport roller 24 and at the position a2 the stop roller 30. The difference of a position a3 and the position a2 indicates a minimum distance between two consecutive sheets in the retractor 10, wherein the minimum distance is selected so that an approach of the following sheet on the previous sheet is excluded. At a distance a4, the transport roller 26 and the counter-rotating roller 32 are arranged.

A first photoelectric sensor 56 is disposed at a position a5 so that a light beam is interrupted by a sheet transported thereover. A position a6 is located between the light barrier 56 and a second light barrier 58 for detecting the sheet position at a position a7. Between the light barrier 58 and a first transport roller pair of transport rollers 60 and 62 of a transport device of the printer at a position a9 is a position a8. The meaning of the positions a6, a8 and a position a10 in the transport direction immediately behind the transport rollers 60, 62 will be explained below.

At a position a11 is a third light barrier 64 seen in the transport direction in front of a second transport roller pair of transport rollers 66, 68 at a position a12.

The sheet 50 is retracted by activating the feeder 10 starting at a time t0. The leading edge 70 of the sheet 50 moves from the position a1 at a drawing speed v1 indicated by a dotted line 70. The sheet 50 is the first drawn sheet of a group of sheets 50, 52, 54, etc. to be fed and is therefore transported without stop. Between the photocells 56 and 58, the drawing speed v1 is measured.

Once the leading edge 70 is at position a10, it can be assumed that the transport rollers 60, 62 have securely grasped the sheet 50. By the transport rollers 60, 62, the leading edge 70 is further transported at a transport speed v0, which is smaller than the drawing speed v1. The transport speed v0 of the front edge 70 and thus also of the sheet 50 is represented by a solid line. If the leading edge 70 passes the light barrier 58 at a time t2, a time t3 at which the leading edge 70 reaches the position a10 can be calculated according to the following formula: $$\mathrm{t}\mathrm{3}\mathrm{=}\mathrm{t}\mathrm{2}\mathrm{+}\left(\mathrm{a}\mathrm{10}\mathrm{-}\mathrm{a}\mathrm{7}\right)\mathrm{/}\mathrm{v}\mathrm{1}$$

At time t3, the rear edge of the sheet 50 is still in front of the feed roller 22 when viewed in the direction of transport 36. The feed device 10 is released at time t3, that is, the stepper motor, take-up roller 22, conveyor belt 28 and reverse roller 32 are no longer driven. The sheet 50 is thus transported only by the transport rollers 60, 62 at the transport speed v0, so that the rear edge 72 of the sheet 50 must have the transport speed v0.

wobei L die Länge der Blätter 50, 52 bzw. 54 in Transportrichtung 36 ist.The retraction device 10 is only activated again when the rear edge 72 of the sheet 50 reaches the position a3 at a time t4, which is calculated according to the following formula: $$\mathrm{t}\mathrm{4}\mathrm{=}\mathrm{t}\mathrm{3}\mathrm{+}\left(\mathrm{L}\mathrm{-}\left(\mathrm{a}\mathrm{10}\mathrm{-}\mathrm{a}\mathrm{3}\right)\right)\mathrm{/}\mathrm{v}\mathrm{0}$$

where L is the length of the sheets 50, 52 and 54 in the transporting direction 36.

At time t4, the leading edge 74 of the next sheet 52 begins to move at the pull-in speed v1.

The exact starting position of leading edge 74 can not be accurately predicted because it is between positions a1 and a2. In the worst case, however, the starting position of the leading edge 74, as shown in Figure 2, the position a2. However, the safety distance a3-a2 is selected such that, with the maximum pull-in speed v1, the leading edge 74 can not catch up with the rear edge 72 of the leading sheet 50 up to the position a5. At position a5, i. upon reaching the light barrier 56, the sheet 52 is then stopped in a pre-set position. The stopping in the Voreinzugsposition takes place whenever there is a leading sheet in the area of the light barrier 58.

As soon as the rear edge 72 passes the light barrier 58, the retracting device 10 is again activated effectively, so that the leading edge 74 continues to move at the retraction speed v1 at a time t5 (see arrow P1). At a time t6, the leading edge 74 reaches the photocell 58. According to formula (1), a time t7 can be calculated when t2 is replaced by t6 and t3 in the formula (1) by t7. At time t7, the collection device 10 is released again. The leading edge 74 is detected by the transport rollers 60, 62 and is transported at the transport speed v0. Between the rear edge 72 and the front edge 74, a distance A1 remains unchanged since both edges move at the same transport speed v0. The distance A1 is smaller than a desired distance AS. The distance A1 is measured with the light barrier 64 and is known at a time t9 at which the leading edge 74 reaches the position a11 of the light barrier 64.

At a time t8, which is slightly before the time t9, the retraction device 10 is again activated, since according to formula (2), the rear edge 74 of the blade 52, the position a3 has reached. In the formula (2) t3 must be replaced by t7 and t4 by t8. The leading edge 78 of the sheet 54 moves at the pull-in speed v1 to the pre-feed position a5 at the light barrier 56. The feed device 10 is consequently released at a time t10.

wobei ΔA1 der Abstand ist, um den sich der Abstand A1 vergrößert.The activation of the intake device 10 does not take place at a time t12 at which the rear edge 76 passes the light barrier 58, but with a delay Δt1 with respect to the time t12 at a time t13 (see arrow P2a), which is calculated according to the following formula : $$\mathrm{.delta.t}1=\frac{\mathrm{AS}-\mathrm{al}}{\mathrm{vl}}=\frac{\mathrm{\Delta Al}}{\mathrm{vl}}$$

where ΔA1 is the distance by which the distance A1 increases.

If the leading edge 78 reaches the position a10 at a point in time t14, then again the collection device 10 is released. A distance A1 'between the rear edge 76 and the front edge 78 now corresponds exactly to the desired distance AS. Also between other leaves exactly the desired distance AS is set.

If the feed speed v1 is changed to a value v0 which corresponds to the transport speed v0, the control of the distances between the sheets 50, 52 and 54 is carried out in a similar manner. A change in the intake speed occurs, for example. when inserting a sheet stack with sheets of other quality, by increasing the pressing force of the feed belt 28 to the stop roller 30th

The sheet 50 is now started from the position a2 at time t0, with the leading edge 70 'moving at the feed speed v0. This speed is detected between the light barrier 56 and the light barrier 58, and replaced in the formulas (1) to (3), the value for the intake speed v1. Otherwise, the transport of the sheet 50 is carried out exactly as described above, whereby the control operations mentioned there are carried out.

The sheet 52 is started at time t4 with the leading edge at the position a2 and the drawing speed v0. The leading edge 74 'moves to position a5 where the light barrier 56 is located, i. to the pre-closing position. The rear edge 72 of the sheet 50 passes the light barrier 58 again at the time t5, so that at this time the retraction device 10 is again activated effectively and thus the sheet 52 with the feed speed v0 moves on (see arrow P1). At a time t7 ', the front edge 74' reaches the position a10, whereupon the collection device 10 is released. The light barrier 64 detects a distance A0 between the rear edge 72 and the leading edge 74 '. This distance A0 is greater than the desired distance AS. Analogously to the formula (3), instead of the delay time Δt1, a delay time Δt0 is determined, which has a negative sign. In formula (3), instead of A1, the distance A0 is used, and instead of v1 the new pull-in speed v0 is used. The negative sign of Δt0 means that the sheets must be started from the pre-feed position before the back edge, e.g. 76, the leading sheet passes the position a7 at the light barrier 58. The earlier starting from the advance position a5 results in a change in the distance ΔA0, which leads to a distance A0 'between the blade 52 and the blade 54 and is dimensioned so that the distance A0' is equal to the desired distance AS.

wobei die senkrechten Striche die Betragsoperation kennzeichnen.The earlier starting (see arrow P2b) can be carried out with the aid of the light barrier 56 by calculating a time t10 starting from a time t * at which the rear edge 76 passes the light barrier 56: $$\mathrm{t}\mathrm{10}\mathrm{=}\mathrm{t}\mathrm{*}\mathrm{+}\frac{\left(\left(\mathrm{a}\mathrm{7}\mathrm{-}\mathrm{a}\mathrm{5}\right)\mathrm{-}\left|\mathrm{.DELTA.A}\mathrm{0}\right|\right)}{\mathrm{v}\mathrm{0}}$$

where the vertical bars indicate the amount operation.

If the pull-in speed lies between its minimum value v0 and its maximum value v1, the setpoint distance AS between the leaves can be adjusted in an analogous manner with the aid of the control described with reference to FIG.

A constant distance at least between the sheets following the first sheet is of particular importance when the sheets are in groups of e.g. each six sheets are fed into a high-performance printer, which has two printing units and in which cross over transport routes between these two printing units. The transport routes can be made very short if the total length of a group of blades can be set within narrow limits. Short transport routes result in a compact design of the high-performance printer.

Figure 3 shows a path-time diagram for three retracted sheets 100, 102 and 104, wherein on the ordinate axis 106 of the transport path s and on the abscissa axis 108, the time t are removed. In addition, the path-time diagram with a representation of the collection device 10 according to Figure 1 is deposited. The explained with reference to Figure 2 positions a1 to a12 and there explained reference numerals 56 to 78 are also registered in the figure 3. The regulation of the sheet spacing between the sheets 100, 102 and 104 is analogous to the control of the sheet spacing of the sheets 50, 52 and 54 according to Figure 2 at the feed rate v1.

In contrast to FIG. 2, in FIG. 3, when pulling in a sheet, a vibratory feeder is used, whereas the leading edge 70, 74 or 78 between positions a1 and a5, ie moved between the transport roller 24 and the light barrier 56. If the front edge of the sheet to be picked is located at the beginning of the drawing-in operation between the position a1 and the position a2, then the shaker is moved by a correspondingly shortened distance starting from the rest position of the respective leading edge.

During the transport of the sheet 100 from the position a1 to position a5, the collection device 10 is activated seven times and released six times. The activation times are about half as large as the times in which the collection device 10 is activated. When a sheet with its front edge reaches the position a5 at the light barrier 56, the first sheet 100 continues to engage the feeding device 10, so that the sheet 100 does not stop in the preforming position. In the following sheets 102, 104, the retractor 10 is released as soon as the leading edge 74, 78 is in the advanced position so that the sheet 102, 104 is stopped in the advancing position.

In another embodiment, the turn-on time of the retractor 10 is 60 ms each, and the turn-off time is 10 ms each, while the leading edge of a sheet 100, 102, 104 is between positions a1 and a5.

Claims (21)

1. A method for the input of sheets (12, 14; 50, 52, 54) of a sheet stack (16) into a printer or copier, comprising the following steps:

   - a first outwardly lying sheet (12, 50) is respectively pulled from the sheet stack (16) and is transported via a first sub-section (a1 to a5) to a second sub-section (a10 to a12) of a transport path,

   - the second sheet (14, 52, 54) following the first sheet is respectively pulled from the sheet stack (16),

   - each of the second sheets (14, 52, 54) is transported in the first sub-section (a1 to a5) at a draw-in speed (v1) in the direction of the second sub-section (a10 to a12) of the transport path,
   each time, the transport of the second sheet (14, 52, 54) is delayed until the second sub-section (a10 to a12) is reached such that a predetermined desired spacing (AS) precisely derives with respect to the distance to the first sheet (12, 50, 52) and for sheets (12, 14, 50, 52) immediately transported following one another in the second sub-section (a10 to a12),

   - both sheets (12, 14, 50, 52, 54) are transported at the same transport speed (v0) in the second sub-section (a10 to a12).
2. The method according to claim 1, characterized in that the distance between the first sheet (12, 50, 52) and the second sheet (14, 52, 54) in the first sub-section (a1 to a5) is smaller than the desired spacing (AS) in the second sub-section (a10 to a12).
3. The method according to claim 1 or 2, characterized in that the draw-in speed (v1) in the first sub-section (a1 to a5) is higher than the transport speed (v0) of the sheets (50 to 54) within the second sub-section (a10 to a12).
4. The method according to claim 1 or 2, characterized in that the draw-in speed (v1) is smaller or equal to the transport speed (v0).
5. The method according to one of the claims 1 to 4, characterized in that the two sheets (12, 14; 50, 52) are pulled from the sheet stack (16) at a spacing that is smaller than the desired spacing (AS).
6. The method according to one of the preceding claims, characterized in that a point in time (t3) is calculated at which the front edge (70) of the first sheet (12, 50, 52) reaches the second sub-section (a10 to a12) and in that at another point in time (t4) lying after the calculated point in time (t3) the second sheet (14, 52, 54) is pulled off.
7. The method according to one of the preceding claims, characterized in that between the sheet stack (16) and a second sub-section (a10 to a12) a pre-draw-in position (a5) is located at which the position of the second sheet (14, 52, 54) is determined.
8. The method according to one of the preceding claims, characterized in that the second sheet (14, 52, 54) is stopped between the sheet stack (16) and the second sub-section (a10 to a12) and is further transported after a holding time, the holding time being dimensioned such that the desired spacing (AS) is set between the second sheet (14, 52, 54) and the first sheet (12, 50, 52) as viewed in transport direction.
9. An apparatus for drawing in of sheets (12, 14; 50, 52, 54) of a sheet stack (16) into a printer or copier, in particular for carrying out a method according to one of the preceding claims,
   comprising at least one sheet compartment for receiving the sheet stack (16),
   comprising a draw-in device (10) for pulling off the respective outwardly lying first sheet (12, 50) from the sheet stack (16),
   for transporting the first sheet (12, 50) via a first sub-section (a1 to a5) to a second sub-section (a10 to a12) of a transport path, and
   for pulling off the respective second sheet (14, 52, 54) following the first sheet (12, 50),
   comprising at least one transport device (60, 62) for the transport of the two sheets (12, 14, 50, 52, 54) in the second sub-section (a10 to a12) at the same transport speed (v0),
   and comprising a control unit for driving the draw-in device (10),
   wherein the control unit delays the transport of each second sheet (14, 52, 54) up to the reaching of the second sub-section (a10 to a12) such that a predetermined desired spacing (AS) results for the spacing to the first sheet (12, 50) and for sheets (12, 14, 50, 52) which are transported immediately following one another in the second sub-section (a10 to a12).
10. The apparatus according to claim 9, wherein the draw-in speed (v1) is higher than the transport speed (v0).
11. The apparatus according to one of the claims 9 or 10, characterized in that
    a first light barrier (56) for detecting the sheet position in the sheet transport direction (42) is preferably arranged closely behind the draw-in device (10),
    in that a second light barrier (58) is arranged behind the first light barrier (56) in transport direction,
    in that the control unit measures the draw-in speed (v0, v1) with the aid of at least one light barrier (56, 58),
    and in that the control unit activates the draw-in device (10) dependent on the measured draw-in speed (v0, v1), when the sheet (50 to 54) is detected by the transport device (60, 62).
12. The apparatus according to one of the claims 9 to 11, characterized in that the draw-in device (60, 62) has a haul-off roller (22) acting on the sheets (50 to 54) with which the respectively pulled-off sheet (50 to 54) is supplied to a draw-in belt (28) that then supplies the sheet (50 to 54) to the transport device (60, 62).
13. The apparatus according to one of the claims 9 to 12, characterized in that the transport device (60, 62) is arranged at a distance (a10) to the haul-off roller, which distance is preferably somewhat smaller than the length (L) of a sheet in transport direction (36).
14. The apparatus according to one of the claims 9 to 13, characterized in that the control unit activates the draw-in device (10) dependent on a signal from the first light barrier (56).
15. The apparatus according to one of the claims 9 to 14, characterized in that the control unit activates the draw-in device (10) dependent on a signal from the first light barrier (56) or the second light barrier (58).
16. The device according to one of the claims 9 to 15, characterized in that the control unit activates the draw-in device (10) when the pulled-off sheet (50 to 54) has reached a minimum distance (a3 minus a2) with respect to the sheet stack (16).
17. The device according to one of the claims 9 to 16, characterized in that a third light barrier (64) is arranged in the transport device (60, 62; 66, 68) for detecting the distance (A0, A1) between successive sheets (50 to 54),
    and in that the control unit determines a holding time dependent on the distance (A0, A1) and a previously measured draw-in speed (v0, v1), during which holding time the draw-in device (10) is activated during drawing-in of a sheet (52, 54),
    the holding time being dimensioned such that the predetermined distance (AS) is set between the sheets (50 to 54) in the transport device during activation of the draw-in device (10) after expiration of the holding time as viewed in transport direction.
18. The method according to one of the claims 1 to 8, characterized in that the first or the second sheet (12, 14, 50 to 52) is transported at a draw-in speed that varies strongly several times during pulling off of the sheet (50 to 54).
19. The method according to claim 18, characterized in that the draw-in speed is periodically varied.
20. The method according to claim 18 or 19, characterized in that the draw-in speed is only varied when multiple sheets are drawn in.
21. The apparatus for drawing in sheet material in a printer or copier according to one of the claims 9 to 17, characterized in that the control unit strongly varies the draw-in speed several times during pulling off of the sheet (50 to 54).

Images