GB2071064A - Controlling sheet feed to a printing machine - Google Patents

Abstract

Sheet feed to a printing machine 5 is controlled by monitoring a sheet fed to a registration line 3 of the machine and evaluating the monitoring signals at two different evaluating times per machine cycle. On detection of a correct sheet at the first evaluating time, evaluation at the second evaluating time is withheld and the sheet is released to enter the printing press. If, however, a skewed sheet is detected at the first evaluating time the sheet conveying is interrupted for one cycle and evaluation at the second evaluating time is withheld. Thereafter, on detection of a correct sheet at the first evaluating time of the succeeding cycle, evaluation at second evaluating time is withheld and the sheet is released to enter the machine, or on detection of a skewed sheet at the first evaluating time of the succeeding cycle the sheet conveying is stopped. If no sheet is detected at the first evaluating time, evaluation is carried out at the second evaluating time and, on detection of a correct or skewed sheet, the sheet conveying is interrupted for one cycle and evaluation is carried out at the first evaluating time of the succeeding cycle. If a skewed or lacking sheet is detected in any subsequent cycle, any such sheet is prevented from entering the machine and sheet conveying is stopped. <IMAGE>

Description

SPECIFICATION Method of and control means for controlling a printing machine The present invention relates to a method of and control means for controlling a printing machine with reference to sheets fed to the machine.

A monitoring device for the automatic commencement of printing and subsequential monitoring of entry and feed in sheet-fed printing machines is disclosed in DE 2 202 851. This device comprises two measuring heads disposed in a line and operates with three measuring time points, two of the three measuring time points being introduced only during start-up of the press for detecting early and late sheets and the monitoring being carried out during the running of the machine only at one measuring time point. The printing machine is immediately stopped by the device if early sheets, late sheets, skewed sheets or fault sheets are detached.

A disadvantage with the know device is the high cost of the switching mechanisms in the device, its complexity, and its lack of compatibility for the further connection of auxiliary devices for automatic sheet travel control. In addition, the outage rate in the occurrence of incorrect sheets is extremely high, due to the immediate shutting-down of the machine.

There is accordingly a need for a method of control means for controlling a printing machine with reference to sheet feed, with repeated and/or auxiliary operations for increasing operating performance.

According to a first aspect of the present invention there is provided a method of controlling a cyclically operable printing machine, comprising the steps of monitoring a feed of sheets to registration means at a sheet inlet of the machine and providing monitoring signals indicative of sheet presence and position at the registration means, evaluating the monitoring signals at at least the first one of two discrete evaluating times in each operating cycle of the machine to detect presence of a sheet at the registration means at the time of evaluation and to determine whether any such sheet is correctly or incorrectly positioned, and so controlling the feed of sheets to and entry of the sheets into the machine in dependence on cyclic evaluation of the monitoring signals that if a correctly positioned sheet is detected at the first evaluation time in a first operating cycle then evaluation at the second time in that cycle is inhibited and the sheet is caused or allowed to enter the machine, that if an incorrectly positioned sheet is detected at the first evaluation time in the first operating cycle then evaluation at the second time in that cycle is inhibited, the sheet is prevented from entering the machine, the sheet feed is interrupted for one operating cycle, and evaluation is repeated at the first evaluation time in the immediately succeeding cycle, that if a correctly positioned sheet is then detected at the first evaluating time in said succeeding cycle, evaluation at the second time in that cycle is inhibited and the sheet is caused or allowed to enter the machine, but that if an incorrectly positioned sheet is detected at the first evaluating time in said succeeding cycle then the sheet feed is stoped, that if no sheet is detected at the first evaluating time in said first cycle then evaluation is repeated at the second time in that cycle, that if a correctly or incorrectly positioned sheet is then detected at the second time in the first cycle the sheet feed is interrupted for one operating cycle and evaluation is repeated at the first evaluating time in the immediately succeeding cycle, and that if an incorrectly positioned sheet is detected, or no sheet is detected, in any operating cycle subsequent to a cycle in which a sheet is caused or allowed to enter the machine then the sheet feed is stopped and any such detected incorrectly positioned sheet is prevented from entering the machine.

Preferably, if skewed or lacking sheets are detected after the preventing of entry of a sheet into the printing press and stopping of the sheet feed in said subsequent cycle, the speed of the printing machine is reduced, a further evaluation cycle is initiated and, if a correctly positioned sheet is detected, the sheet feed is resumed.

Advantageously, the monitoring signals are evaluated at an evaluating time before the start and an evaluating time after the end of the theoretical period of time for arrival of a sheet at the registration means, so that if a sheet is detected at the evaluating time before the start of said theoretical period of time, then a signal indicating early arrival of a sheet is provided, such signals occurring in successive operating cycles are integrated over a number of cycles and, if early arrival of sheets persists over a predetermined number of cycles, a later feed of sheet is caused.If, on the other hand, a sheet is detected at the evaluating time after the end of said theoretical period of time, then a signal indicating late arrival of a sheet is provided, such signals occurring in successive operating cycles are integrated over a number of cycles and, if late arrival of sheets persists over a predetermined number of cycles, an earlier feed of sheet is caused.

According to another procedure, however, the monitoring signals may be evaluated at a plurality of times generated periodically and extending over the entire possible arrival region of the sheet by counting the evaluations up up to an evaluation where a sheet is detected, and, if early or late arrival of the sheets has occurred, a later or an earlier sheet feed is caused.

According to a second aspect of the present invention there is provided control means for controlling a printing machine by a method according to the first aspect of the invention, the control means comprising monitoring means for monitoring a feed of sheets by sheet feeding means to registration means at a sheet inlet of the machine and providing monitoring signals indicative of sheet presence and position at the registration means, cyclically operable signal generating means for providing an evaluating signal at each of two discrete evaluating times in each operating cycle of the machine, evaluating means for cyclically evaluating the monitoring signals by the evaluating signals and providing output signals indicative of whether a sheet is present at the registration means at an evaluating time and whether any such sheet is correctly or incorrectly positioned, sheet entry control means for controlling sheet entry means to allow or prevent entry into the machine of a sheet present at the registration means, the sheet entry control means being connected at an input thereof to the evaluating means and at an input and an output thereof to the signal generating means, cyclically controllable sheet feed control means for controlling feed of sheets to the machine by the feeding means, the sheet feed control means being connected at an input thereof to the sheet entry control means and at an input and an output thereof to the signal generating means, sheet feed switching means for switching the feeding means on and off, the sheet feed switching means being connected at an inputthereof to the sheet feed control means, and a cyclically controllable control device for so controlling feed of sheets to and entry of sheets into the machine as to cause, in response to an output signal from the evaluating means indicative of no sheet or an incorrectly positioned sheet being present at the registration means at an evaluating time, entry of sheets into the machine to be prevented and feed of sheets stopped for one operating cycle to allow re-evaluation of the monitoring signals to be carried out in the succeeding cycle, the control device being connected at inputs thereof to the evaluating means and the sheet feed control means and at outputs thereof to the sheet entry control means, the sheet feed control means and the sheet feed switching means.

Expediently, the sheet entry control means is connected at output means thereof to input means of a restarter device, which is connected to the sheet feed control means and enables switching back on of the feeding means and thus commencement of further sheet feeding.

An example of the method and an embodiment of the control means of the invention will now be more particularly described with reference to the accompanying drawings, in which: Figure 1 is a schematic elevation of a printing machine equipped with control means embodying the invention, Figure 2 is a schematic plan view of sensing heads in the control means of Figure 1, Figure 3 is a pulse diagram showing timing pulse outputs in the control means, Figure 4 is a block circuit diagram of the control means, Figure 5 is a circuit diagram of a sheet entry device of the control means, Figure 6 is a circuit diagram of a sheet feeder circuit of the control means, Figure 7 is a circuit diagram of a sheet feeder control unit of the control means, Figure 8 is a circuit diagram of a cyclic timing device of the control means, Figure 9 is a circuit diagram of a measuring or evaluating device of the control means, Figure 70 is a circuit diagram of a revolution feeder circuit of the control means, Figure 11 is a circuit diagram of a sheet feed restarter device of the control means, Figure 12 is a circuit diagram of a first indication and evaluation device of the control means, and Figure 13 is a circuit diagram of a second indication and evaluation device of the control means.

Referring now to the drawings, there is shown in Figures 1 and 2 a printing machine which may be controlled by a method exemplifying the invention, the printing machine comprising a sheet feeder 1 including a feeder circuit 9, a feeder control 12, a feed table 2 with two sensing heads 4 disposed at a registration line 3 for monitoring sheets 11, one or more printing mechanisms 5, the or the first printing mechanism being equipped with a sheet entry device 6 for preventing a sheet from entering, or allowing a sheet to enter, the printing machine, and a sheet delivery (not shown). The drive of the printing machine is provided by an electric motor 7, a speed control device 8 being associated with the motor.By means of the feeder control 9 and feeder switching circuit 12, sheet conveying is initiated and successive sheets 11 are conveyed via the feed table 2 as far as raisable and lowerable lay marks 10 and the registration line 3. In the region of the lay marks, the sheets are monitored by means of the sensing heads 4.

The sensing heads 4 detect lacking sheets (no sheets), early sheets, late sheets, skewed sheets and correct sheets, and signals from the sensing heads are evaluated at two different measuring times determined by cyclically issued pulses (Figures 3, 3.1).

The first measuring pulse is issued at the latest instant at which, during printing operation at maximum speed, releasing of sheets for entry or preventing entry of sheets into the printing machine and stopping of sheet conveying can still be satisfactorily carried out.

The second measuring pulse, which is used only for evaluating the signals of the sensing heads when monitoring the first sheet, is issued at the instant at which an exact measurement can still just be obtained. For this purpose, the sheet must be situated in the region of the lay marks 10 with the lay marks raised at the feed table 2 (in this position of the lay marks, the entry of sheets into the printing press is also prevented; in the lowered position of the lay marks, sheet entry is possible). The measuring pulses are produced by a cyclic timing device 13, which supplies a number of periodic pulses.

If the sensing heads 4, when checking the first sheet (commencement of sheet run), emit a signal indicating a correct sheet, the second measuring pulse is blocked and the sheet is released for entry into the printing press.

If the sensing heads 4, when the first sheet is monitored (commencement of sheet run), supply a signal indicating a skewed sheet at the first measuring pulse, the second measuring pulse is blocked and, in order to prevent the occurrence of double sheets, the sheet conveying is interrupted for one machine cycle. On the assumption that the skewed sheet has righted itself in the interim, a measurement is again carried out at the first measuring pulse of the succeeding cycle.

If, at the first measuring pulse of the succeeding measuring cycle, a correct sheet is now detected, blocking of the second measuring pulse and releasing of the sheet for entry into the printing machine are carried out. If, on the other hand, a skewed sheet is again detected, i.e. if the sheet has not aligned itself, the sheet feed is stopped.

If the sensing head 4, on monitoring of the first sheet, supply a signal indicating a lacking sheet (no sheet present at the lay marks) at the first measuring pulse, measurement is carried out again, at the second measuring pulse. If a signal indicating a correct or skewed sheet is now present, the sheet conveying is interrupted for one cycle and measurement is again carried out at the first measuring pulse of the succeeding cycle. The procedures on the measurement at the first measuring pulse of the succeeding cycle take place as already described.

If a signal indicating a lacking sheet is still present (sheet has not yet reached the lay marks), a new measuring cycle is again carried out at the next machine cycle.

If when the machine is running - the first sheet has entered the printing press correctly - the sensing heads 4 supply a signal indicating a skewed or lacking sheet at the first measuring pulse, the sheet is prevented from entering the printing press and sheet conveying is stopped.

Since experience has shown that the sheet, after the first reading, aligns itself, a renewed attempt at start-up is undertaken.

On stopping of sheet conveying and preventing entry of sheets into the printing machine, the machine is brought from the production speed to a lower speed which makes possible renewed resumption of sheet conveying, a further measuring cycle is initiated and, if correct sheets are detected, sheet conveying is again commenced.

Further sequences are analogous to the sequence at entry of the first sheet into the printing machine.

The periodic pulses are also utilized for recognition and indication of early and late sheets, and for consequent influencing of the sheet conveying device in respect of the supply instant of the sheets. For this purpose, according to a first procedure, the monitoring signals of the first or the second measuring head of the sensing head are evaluated with a measuring pulse occurring before the commencement and a measuring pulse occurring after the end of the predetermined arrival time of each sheet (Figure 3, 3.2).

If a sheet is present at the measuring pulse before commencement of the predetermined arrival time, i.e. an early sheet is present, this is indicated, signals indicating an early sheet are integrated over a number of machine cycles and, if early sheets continue to be present over a number of machine cycles, the sheet supply time is retarded. If a sheet is present at the measuring pulse after the end of the predetermined theoretical arrival time, i.e. a late sheet is present, this is indicated, signals indicating a late sheet are integrated over a number of machine cycles and, if late sheets continue to be present over a number of machine cycles, the sheet supply is advanced.

According to a second procedure, the monitoring signals of the first or second measuring head of the sensing head are evaluated with periodically produced measuring pulses extending over the entire arrival region of the sheet (Figure 3,3.3).

Evaluation is carried out in this case by counting the number of the measuring pulses in relation to the signals from the sensing head. The number of measuring pulse counted before the pulse which represents the arrival of a sheet at the sensing head serves as a measure for determining whether the sheet has arrived early, late or at the correct time. If an early or a late sheet is determined, this is indicated, and in the case of early sheets a later feed of sheets, and in the case of late sheets an earlier feed of sheets, is caused.

Referring nowto Figures4to 13, there is shown the circuit of a control means for carrying out the afore-described method, the control means comprising a measuring or evaluating device 14 connected to the outputs of the sensing heads, and connected at an input to a cyclic timing device 13. The measuring device is connected at one output 14.1 (Figures 5 and 9), for signalling a skewed or lacking sheet, with the device 6 for preventing or allowing the sheet entry, with the feeder control 12 and with a revolution feeder circuit 15, and at another output 14.2 (Figures 9 and 10), for signalling a skewed sheet, with the feeder circuit 15. The device 6 is also connected at its input side with the feeder circuit 15 and with an output 16.1 of a pulse generator 16 of the timing device 13.The output 16.1 supplies a measuring pulse according to Figure 3,3.1. At its output side, the device 6 is connected with a pulse processor 17 of the device 13 and the feeder circuit 15. In addition, the device 6 is connected at output 6.1 and 6.2 thereof with a feeder restarting device 18, the output 6.2 also being connected with the feeder control 12. The restarter device 18 is furthermore connected at its input side with the speed control 8 and at its output side with the feeder control 12. The feeder control 12 is also connected at its input side with the feeder cicuit 15 and the output 16.1 of the pulse generator 16, and at its output side with the feeder circuit 9, the feeder circuit 15 and the processor 17.

The feeder circuit 9 is also connected at its input side with the feeder circuit 15. The feeder circuit 15 is connected at its input side also with the output 16.1 of the generator 16 and with the processor 17.

The device 6 for preventing or allowing sheet entry (Figure 5) comprises a first AND-gate 26 and a second AND-gate 27, both gates being connected with the pulse output 16.1 of the pulse generator 16 and with the lacking sheet/skewed sheet output 14.1 of the measuring device 14, the connection with the last-named output being inverted for the second AND-gate 27. Each input of a flip-flop stage 28 is connected to a respective one of the outputs of the AND-gates 26 and 27. The output of the flip-flop stage 28 is connected with the feeder circuit 15 and the processor 17 and with a first input of a third AND-gate 29, the second input of which is inverted and is connected to the output of the feeder circuit 15. The output of the third AND-gate 29 is connected directly with the restarting device 18 and, via an amplifier 30, with a magnet 31 for actuating the device 6.The output of the gate 29 is also connected via a NOR-gate 32 and pulse shaper 33 with the restarting device 18 and the feeder control 12.

Returning to Figure 4, an output 16.2, which supplies pulse according to Figure 3,3.2, of the generator 16 is connected with the indication and evaluation device 19, and an output 16.3, which supplies pulse according to Figure 3,3.3, of the generator is connected with the indication and evaluation device 20. It should be noted here that the devices 19 and 20 are used alternatively. The devices 19 and 20 are also connected to the sensing heads 4.

The measuring device 14 (Figure 9) comprises two input AND-gates 21.1 and 21.2, the inputs of which are connected to the outputs of the sensing heads 4 and an output of the timing device 13. The ANDgates 21.1 and 21.2 are connected at their outputs to first inputs of, respectively, flip-flop stages 22.1 and 22.2, the second inputs of the stages being connected to an output of the timing device 13.

Connected to the outputs of the flip-flop stages 22.1 and 22.2 are, respectively, OR-gates 23.1 and 23.2 and indicator lamps 24.1 and 24.2. The output of the OR-gate 23.2 forms the lacking sheet/skewed sheet output 14.1 of the measuring device. The OR-gate 23.1 has inverted inputs and the outputs of both OR-gates 23.1 and 23.2 are connected to an AND-gate 25, the output of which forms the skewed sheet output 14.2 of the measuring device 14.

The restarting device 18 (Figure 11) comprises a flip-flop stage 34, the first input of which is connected with the second output 6.2 of the device 6 and the second input of which is connected to the output of an OR-gate 35. The inputs of the OR-gate 35 are connected to the first output 6.1 of the device 6 and to a switch 36, which is opened when a protective grid 41 (Figure 1) is opened. The grid is disposed above the feed table 2; for removing sheets which are notto enter the machine, the grid must be opened, i.e. by being swung upwards.

The output of the flip-flop stage 34 is connected directly with an indicator lamp 38, via a first input of an AND-gate 40 with the feeder control 12, and via a first input of an AND-gate 37 and a following pulse shaper 39 with the second input of the AND-gate 40.

The second input of the gate 37 is connected with an output of the speed control device 8 (Figure 1), the device 8 providing a signal at the least possible speed.

The feeder control 12 (Figure 7) comprises a first flip-flop stage 42, the first input of which is connected to the output of a first OR-gate 43 and the second input to a second OR-gate 44.

The first input of the OR-gate 43 is connected to the output of the restarting device 18 and the second input to a switch 45 for switching the feeder on.

A first input of the second OR-gate 44 is connected to a switch 46 for switching the feeder off and a second input to the second output 6.2 of the device 6. A first output of the flip-flop stage 42 is connected to the first input of a second flip-flop stage 47, the output of which is connected with the feeder circuit 9, the feeder circuit 15 and the processor 17.

The feeder control 12 also comprises a first AND-gate 48, a first input of which is connected to the output 16.1 of the generator 16, a second input to the lacking sheet/skewed sheet output 14.1 of measuring device 14, and a third input to the feeder circuit 15.

The output of the AND-gate 48 is connected with a third input of the OR-gate 44 and with a first input of a third OR-gate 49. A second input of the third OR-gate 49 is connected to the second output 6.2 of the device 6 and a third input of the gate 49 to the output of a second AND-gate 50, which is connected at its input to a second output of the flip-flop stage 42 and to the output 16.1. The output of the OR-gate 49 is connected with the second input of the flip-flop stage 47.

The feeder circuit 9 (Figure 6) comprises an OR-gate 51, the outputs of which are connected to the feeder control 12 and the feeder circuit 15.

Serially connected to the output of the OR-gate 51 are a NOR-gate 52, an amplifier 53 and a magnet 54 for on-and-off switching of the feeder.

The revolution feeder circuit 15 (Figure 10) comprises a flip-flop stage 55, the output of which is connected with the feeder control 12 and the device 6.

The first input of the flip-flop stage 55 is connected to the output of a first OR-gate 56, the inputs of which are connected to the feeder control 12 and the device 6. The second input of the flip-flop stage 55 is connected to the output of a second OR-gate 57, the inputs of which are connected to the outputs of, respectively, two AND-gates 58 and 59. The first input of the AND-gate 58 is connected with the processor 17 and the second input with the output of a third OR-gate 60. The first input of the AND-gate 59 is connected with the output 16.1 of the generator 16 and the second input of the AND-gate 59, as well as one input of the third OR-gate 60, are connected with the skewed sheet output 14.2. The other inverting input of the OR-gate 60 is connected with the lacking sheet/skewed sheet output 14.1.

The output leading to the feeder circuit 9 is connected to the output of the OR-gate 57 via a pulse shaper 61.

The cyclic timing device 13 (Figure 8) comprises the pulse generator 16 and processor 17. The generator supplies, via its outputs 16.1 and 16.4 pulse signals in accordance with Figure 3,3.1, via its outputs 16.2 pulse signals according to Figure 3,3.2, and via its outputs 16.3 pulse signals according to Figure 3, 3.3.

The processor 17 comprises an OR-gate 62, the output of which is connected with the measuring device 14 and the inputs of which with the outputs of two AND-gates 63 and 64. The output of the AND-gate 64 is also connected to the feeder circuit 15. A first input of the gate 64 is connected with the output 16.4 of the generator 16, an inverted secnd input with the device 6, and an inverted third input with the output of a third AND-gate 65. The first input of the AND-gate 63 is connected with the output 16.1 of the generator 16 and the inverted second input with the output of the AND-gate 65. The first input of the AND-gate 65 is connected with the feeder control 12 and the inverted input with the device 6.

The indication and evaluation device 19 (Figure 12) comprises two AND-gates 66 and 67, the first input of the AND-gate 66 being connected to the outputs of the sensing heads 4 and the second input to the output 16.2 (starting signal). The first input of the AND-gate 67 is connected to the output 16.2 (end signal) and the inverted second input to the sensing heads 4.

The outputs of the gates 66 and 67 are connected to, respectively, inputs of two flip-flop stages 68 adn 69 and inputs of two integrating circuits 70 and 71.

Connected to the output of the two flip-flop stages 68 and 69 are, respectively, two indicator lamps 72 and 73, and connected to outputs of both integrating circuits 70 and 71 is a phase control device 74.

The indication and evaluation device 20 (Figure 13) comprises an OR-gate 75, the inputs of which are connected to the outputs 16.3 of the generator 16.

Connected to output of the OR-gate 75 is a first input of an AND-gate 76, the second input of which is connected to the sensing heads 4. Connected in series to the output of the AND-gate 76 are a shift register or counter 77 and an indication and/or phase control device 78.

The method of operation of the control means is as follows: By actuation of the switch 45, the flip-flop stages 42 and 47 of the feeder control 12 are set and the magnet 54 is de-energized so as to bring the feeder into operation and thus start sheet conveying.

The flip-flop stages 22.1,22.2,28 and 55 are not yet set. By means of the processor 17, the measuring pulse are issued according to Figure 3,3.1.

Various operating cases now arise, as follows: Operating case 1 (correct entry of first sheet) The sensing heads 4 detect a correct sheet, the flip-flop stages 22.1 and 22.2 are set, the indicator lamps 24.1 and 24.2 are extinguished, and the flip-flop stage 28 is set via the second AND-gate 27 of the device 6. The magnet 31 is de-energized via the third AND-gate 29, i.e. sheet entry into the printing press is permitted.

Operating case 2 (first sheet is a skewed sheet at first measuring pulse, Figure 3, 3.1) The flip-flop stage 22.1 and 22.2 is set. By means of the AND-gates 25 and 59, the flip-flop stage 55 is set and the pulse shaper 61 is impulsed, causing the magnet 54 to be briefly energized. As a result the feeder is stopped for one working cycle; double sheets cannot therefore be fed to the machine.

Afurther measurement of the sheet position is now carried out at the first measuring pulse of the next working cycle.

Operating case 2. 1 (sheet as aligned itself in the interim) A measurement is carried out at the first measuring pulse of the second working cycle of the machine. The output of the OR-gate 23.2 carries an L signal, and the flip-flop stage 28 is set through the AND-gate 27. by means of the OR-gate 56, resetting of the flip-flop stage 55 is carried out, and by means of the AND-gate 29, switching is effected to open the sheet entry into the machine.

With the setting of the flip-flop stage 28, the second measuring pulse (according to Figure 3, 3.1) for the further measurement is blocked via the AND-gate 64.

Operating case 2.2 (sheet has not aligned itself in the interim, i.e. it remains skewed).

A measurement is carried out at the first measuring pulse of the second working cycle. By means of the set flip-flop stage 55, resetting of the flip-flop stage 47 is effected via the AND-gate 48 and the OR-gate 49, thus leading to shutdown of the feeder.

Operating case 3 (lacking sheet) At the first measuring pulse, the lack of a sheet is detected. Measurement is then carried out at the second measuring pulse.

Independently of whether a correct sheet or a skewed sheet is detected at the second measuring pulse, the flip-flop stage 55 is set and the pulse shaper 61 is impulsed via the OR-gate 60, the AND-gate 58 and the OR-gate 57. As a result, in order to prevent double feed of sheets, the feeder is shut off for one working cycle, and a further measurement is carried out at the first measuring pulse of the next working cycle. Depending upon the result of the measurement (correct sheet or skewed sheet), the further sequence takes place as already described.

Operating case 4 (sheet running) The first sheet has been processed according to operating case 1, i.e. the flip-flop stages 22.1 and 22.2 are set and the magnet 31 is de-energized, allowing sheet entry into the machine. At the same time, the second measuring pulse is blocked, i.e.

only the first measuring pulse is suppiied to measuring device 14.

If during sheet running (sheet sequence after first sheet) a skewed or lacking sheet is detected at a first measuring pulse, the flip-flop stage 28 is reset and the device 6 is blocked, i.e. the sheet is prevented from entering the machine. To prevent feed of double sheets, on the setting of the flip-flop stage 28 a pulse is generated in the pulse shaper 33, and resets the flip-flop stages 42 and 47 so as to decouple the feeder.

As a consequence of the interruption of sheet running, the speed of the machine reduced to a lower level.

The pulse from the pulse shaper 33 also sets the flip-flop stage 34, causing the indicator lamp 38 to light up so as to signal that the machine has not yet been finally shut down.

If the machine is to be run up to a speed which makes it possible for the feeder to be brought into operation again, the pulse shaper 39 is excited via the first AND-gate 37 and thus the feeder is brought back into operation.

A further measurement ofthe sheet position is now carried out at the first measuring pulse of the next working cycle. Depending on the result of the measurement, further signal processing takes place as described for operating case 2.1 or 2.2.

Claims (8)

1. A method of controlling a cyclically operable printing machine, comprising the steps of monitoring a feed of sheets to registration means at a sheet inlet of the machine providing monitoring signals indicative of sheet presence and position at the registration means, evaluating the monitoring signals at at least the first one of two discrete evaluating times in each operating cycle of the machine to detect presence of a sheet at the registration means at the time of evaluation and to determine whether any such sheet is correctly or incorrectly positioned, and so controlling the feed of sheets to and entry of the sheets into the machine in dependence on cyclic evaluation of the monitoring signals that if a correctly positioned sheet is detected at the first evaluation time in a first operating cycle then evaluation at the second time in that cycle is inhibited and the sheet is caused or allowed to enter the machine, that if an incorrectly positioned sheet is detected at the first evaluation time in the first operating cycle then evaluation at the second time in that cycle is inhibited, the sheet is prevented from entering the machine, the sheet feed is interrupted for one operating cycle, and evaluation is repeated at the first evaluation time in the immediately succeeding cycle, that if a correctly positioned sheet is then detected at the first evaluating time in said succeeding cycle, evaluation at the second time in that cycle is inhibited and the sheet is caused or allowed to enter the machine, but that if an incorrectly positioned sheet is detected at the first evaluating time in said succeeding cycle then the sheet feed is stopped, that if no sheet is detected at the first evaluating time in said first cycle then evalution is repeated at the second time in that cycle, that if a correctly or incorrectly positioned sheet is then detected at the second time in the first cycle sheet feed is interrupted for one operating cycle and evaluation is repeated at the first evaluating time in the immediately succeeding cycle, and that if an incorrectly positioned sheet is detected, or no sheet is detected, in any operating cycle subsequent to a cycle in which a sheet is caused or allowed to enter the machine then the sheet feed is stopped and any such detected incorrectly positioned sheet is prevented from entering the machine.

2. A method as claimed in claim 1, wherein, following stopping of the sheet feed and prevention of a sheet from entering the machine in said subsequent operating cycle, the operating speed of the machine is reduced, evaluation in the next operating cycle is carried out, and the sheet feed is resumed in response to detection in said next operating cycle of a correctly positioned sheet.

3. A method as claimed in either claim 1 or claim 2, comprising the further step of so evaluating the monitoring signals in each operating cycle at an evaluating time preceding and an evaluating time following a predetermined period for arrival of a sheet at the registration means that if in any operating cycle a sheet is detected at said preceding or said following evaluating time in that cycle then an early arrival signal or a late arrival signal, respectively, is provided to indicate early or late arrival of a sheet, early or late arrival signals provided in successive operating cycles are integrated to determine whether early or late sheet arrivals occur over a predetermined number of cycles, and the sheet feed is adjusted to delay arrival times of sheets at the registration means in the case of determined early arrivals orto advance the arrival time in the case of determined late arrivals.

4. A method as claimed in either claim 1 or claim 2, comprising the further step of evaluating the monitoring signals in each operating cycle at a plurality of evaluating times extending over the entire possible time period for arrival of a sheet at the registration means in that cycle, counting the number of evaluations carried out in each cycle before detection of a sheet, determining from the counted number of evaluations whether or not the sheet has arrived at the registration means before or after a predetermined arrival time, and adjusting the sheet feed to delay arrival times of the sheets at the registration means in the case of a determined arrival before the predetermined time orto advance arrival times in the case of a determined arrival after the predetermined time.

5. A method of controlling a printing machine, the method being substantially as hereinbefore describer with reference to the accompanying drawings.

6. Control means for controlling a cyclically operable printing machine by a method as claimed in claim 1, the control means comprising monitoring means for monitoring a feed of sheets by sheet feeding means to registration means at a sheet inlet of the machine and providing monitoring signals indicative of the sheet presence and position at the registration means, cyclically operable signal generating means for providing an evaluating signal at each of two discrete evaluating times in each operating cycle of the machine, evaluating means for cyclically evaluating the monitoring signals by the evaluating signals and providing output signals indicative of whether a sheet is present at the registration means at an evaluating time and whether any such sheet is correctly or incorrectly positioned, sheet entry control means for controlling sheet entry means to allow or prevent entry into the machine of a sheet present at the registration means, the sheet entry control means being connected at an input thereof to the evaluating means and at an input and an output thereof to the signal generating means, cyclically controllable sheet feed control means for controlling feed of sheets to the machine by the feeding means, the sheet feed control means being connected at an input thereof to the sheet entry control means and at an input and an output thereof to the signal generating means, sheet feed switching means for switching the feeding means on and off, the sheet feed switching means being connected at an input thereof to the sheet feed control means, and a cyclically controllable control device for so controlling feed of sheets to and entry of sheets into the machine as to cause, in response to an output signal from the evaluating means indicative of no sheet or an incorrectly positioned sheet being present at the registration means at an evaluating time, entry of sheets into the machine to be prevented and feed of sheets stopped for one operating cycle to allow re-evaluation of the monitoring signals to be carried out in the succeeding cycle, the control device being connected at inputs thereof to the evaluating means and the sheet feed control means and at outputs thereof to the sheet entry control means, the sheet feed control means and the sheet feed switching means.

7. Control means as claimed in claim 6, further comprising restarting means for initiating restarting of the sheet feeding means after stopping thereof, the restarting means being connected at input means thereof to the sheet entry control means and at output means thereof to the sheet feed control means.

8. Control means for controlling a printing machine, the control means being substantially as hereinbefore described with reference to the accompanying drawings.