GB2192584A - Monitoring sheet feed in a printing machine - Google Patents

Abstract

A printing machine comprising at least one printing head has means (60) for monitoring the sequential progress of sheets of paper during operation of the printing machine, and shut-down means (94) for initiating automatic shut down of the printing machine consequent upon the monitor means (60) sensing the loss of a predetermined number of sheets of paper. The invention is particularly applicable to a multi- colour machine with a monitor associated with each printing head to follow the passage of sheets through the entire installation. It is preferred for shut down to be in response to the loss of three sheets. Shut- down involves tripping of printing cylinders, inking and damping rollers and stopping of main motor drive. <IMAGE>

Description

SPECIFICATION A printing machine This invention relates to a printing machine.

There are various types of printing machine available from relatively simple duplicator type printing machines to very complicated multicolour printing presses. All of these known printing machines suffer from the disadvantage that paper jams in the machines are time consuming to correct. This is usually because the machines have to be shut down manually when a paper jam occurs and often the manual shutting down takes such a long time that considerably more paper jaming with consequent adverse side effects takes place than if the machines were able to be shut down more quickly.

It is an aim of the present invention to reduce the above mentioned problem by providing a printing machine which is able to automatically shut down in the event of a paper jam.

Accordingly, this invention provides a printing machine comprising at least one printing head having monitor means for monitoring the sequential progress of sheets of paper during operation of the printing machine, and shutdown means for initiating automatic shut down of the printing machine consequent upon the monitor means sensing the loss of a predetermined number of sheets of paper.

Preferably, the monitor means includes transmitter means for transmitting a signal, and receiver means for receiving the signal from the transmitter means.

Usually, the transmitter means will transmit an infra red signal. Other types of transmitter means may however be employed.

The shut-down means may comprise logic circuit means for receiving information from the monitor means as to the presence or absence of sheets of paper passing through the printing head, the logic circuit means being operative to initiate the shut down of the printing machine consequent upon the monitor means sensing the loss of the predetermined number of sheets of paper.

The logic circuit means preferably initiates the shut down of the printing machine in response to the monitor means sensing the loss of three sheets of paper. The logic circuit could of course initiate the shut down of the printing machine in response to the monitor means sensing the loss of only one sheet of paper. However, this could lead to situations where the printing machine is prematurely shut down. For example, in the case where the printing machine may be provided with means for eliminating two sheets of paper passing through the printing head together, then it would not be desirable to shut the printing machine down because there would be no paper jam in the printing machine. The sensing of the loss of three sheets of paper as the number of sheets of paper that causes the automatic shut down is a practical number.

The shut-down means may automatically shut down the printing machine by lifting off the compression roller, lifting off the ink and damp rollers, and stopping the main motor of the printing machine.

The compression roller may be lifted off by a solenoid. The ink and damp rollers may be lifted off by a motor and a cam and latch arrangement. The main motor of the printing machine may be stopped by actuation of a switch.

The printing machine may also be such that the motors driving the damp and the ink rollers are shut down.

The shut-down means may also be effective to activate an audible and/or a visual warning.

The monitor means advantageously has a secondary function of enabling a counter to start to determine the time that a paper gate is to release after the monitor means has sensed a sheet of paper. The paper gate is located at an upstream part of the printing head.

The printing machine of the present invention may be generally any known type of printing machine that may for example print black and white reproductions or multicolour reproductions. Where multicolour, for example four colour reproductions are being printed, a separate head for each colour will normally be employed. Thus a four colour printing machine will usually have four of the printing heads.

With a printing machine having two or more printing heads, then the printing heads will be arranged to shut down in cascade so that paper still satisfactorily progressing through the printing machine can continue to progress through the printing machine and be correctly printed and stacked.

An embodiment of the invention will now be described solely by way of example and with reference to the accompanying drawings in which: Figure 1 shows in diagramatic form a printing machine having a single printing head; Figure 2 shows monitor means and shutdown means for use in the printing machine shown in Figure 1; and Figure 3 shows a logic control circuit forming part of the shut-down means shown in Figure 2.

Referring to Figure 1, there is shown a printing machine 2 comprising a plate roller 4, a reservoir 6 for water 8, and å fount roller 10 for transferring water 8 from the reservoir 6 to the plate roller 4.

The reservoir 6 and the fount roller 10 form part of a water unit which also comprises a ductor roller 14, a nitrile roller 16, an osciliating roller 18 and a Moileton roller 20. The direction of rotation of the various rollers in the water unit 12 is shown by arrows in the water unit 12.

The plate cylinder 4 receives ink from an ink unit 22. The ink unit 22 co.mprises an ink fount roller 24, a ductor roller 26, a rubber roller 28, idler rollers 30,32, ink forme rollers 34,36, a main oscillating roller 38, a rubber roller 40, and a distribution roller 42. The direction of rotation of the various rollers in the ink unit 22 is shown by arrows. The passage of ink from the ink fount roller 24 to the ink forme rollers 34,36 is shown by two long arrows 44,46. In the ink unit 22, the roller 46 acts as an auxiliary oscillating roller.

Water which is placed on the plate roller 4 via the water fount roller 10 and ink which is placed on the plate roller 4 via the ink fount roller 24 are transferred to the blanket roller 48. Paper 50 passes in the direction of the arrow 52 through the nip 54 between the blanket roller 48 and an impression roller 56.

The impression roller 56 operates in conjunction with a transfer roller 58. An image on the plate roller 4 is thus transferred to the paper 50. As is well known, the rollers 4,48 and 56 are sometimes referred to in the art as cylinders.

The paper 50 will usually come from a pile (not shown) of the paper and, once the paper 50 is printed, it will be delivered to another pile (not shown).

It will be seen from the drawing that the water unit 12 and the ink unit 2 are separate from each other so that the water and the ink are separately applied to the plate roller 4.

The ductor rollers 14,26 move as indicated to be in driving engagement or non-driving engagement with the respective rollers 10,26 as will be understood. Obviously, as'the plate roller 4 with' its printing plate attached rotates, ink from the ink unit 22 will be picked up by the cloth covered Molleton roller 20. Thus, at the roller 20, some milling of the ink and water will occur and this may be effective to give better printing under some printing conditions. The fount roller 10 is advantageously.

constructed such that its direction of rotation can be reversed and this will obviously reverse the 'direction of rotation of the other rollers in the water unit 12, including the 'di- rection of rotation of the roller 20. This is effective to increase the milling action of the water and the ink and this increased milling may be effective to give yet further better quality printing.

The printing machine 2 shown in Figure 1 is a printing machine having only one printing head. The printing head may be duplicated for each colour to be printed so that the printing machine 2 may have as many printing heads as there are colours to be printed.

When sheets of paper 50 are being run through the printing machine 2, the transfer of each sheet of paper 50 through the or each printing head, is constantly monitored by monitor means as shown in Figure 2. Figure 2 shows monitor means for the single printing head shown in Figure 1 and the monitor means of Figure 2 will be repeated for each printing head employed.

In Figure 2, there is shown monitor means 60 comprising an infra red light transmitter 62 which is mounted on a bracket 64 which is appropriately designed to allow the transmission of an infra red signal 66. The infra red signal 66 is received by a receiver 68 which is mounted on a bracket 70. Obviously, if desired, the position of the transmitter 62 and the receiver 68 can be reversed. The transmitter 62 and the receiver 68 are mounted just in front of a gate 72 and a head lay device 74.

The gate 72 has a shoulder portion 76 against which the sheets of paper 50 abut when the gate 72 is in a downward position.

When the gate 72 is in a raised position, the sheets of paper 50 can pass under the gate 72, where they are adjusted for position by the head lay device 74. The head lay device 74 comprises a pivotable shaft 78 from which project a plurality of fingers 80. The fingers 80 are received in a series of recesses 82 formed along the impression roller 56.

The sheets of paper 50 are fed along a conveyor belt 84 which passes around a groove 86 in a belt driver roller 88. The conveyor belt 84 passes over a base plate 90.

The base plate 90 is provided with an aperture 92 through which the infra red signal 66 passes.

When there is no sheet of paper 50 present at the gate 72, then the signal 66 is uninterupted and it is continually detected by the receiver 68. The receiver 68 gives out a logic high signal to a logic circuit 94. The logic circuit 94 is shown schematically in Figure 2 and in detail in Figure 3. When a sheet of paper 50 arrives at the gate 72, the sheet of paper 50 interupts the signal 66 so that no infra red light is seen by the receiver 68. The receiver 68 is such that when it does not see any light, its output signal changes from logic high to logic low, thus indicating that a sheet of paper 50 is present at the gate 72.

During operation of the printing machine 2, as sheets of paper 50 are being run through the printing machine 2, the transfer of each sheet of paper 50 through each printing head is thus continuously monitored by the monitor means 60. If, for any reason, a single sheet of paper 50 fouls up in any part of the printing machine 2, this is detected and the printing machine 2 automatically goes into a shutdown mode. In the shut-down mode, the drive motor (not shown) for the printing machine, the feed pump motor (not shown) and a paper feed vacuum solenoid (not shown) switch off. The printing machine 2 thus immediately stops, thereby avoiding a potentially catastrophic pile up of sheets of paper 50 at the foul-up point. In addition, a signal is sent to the or each printing head in the printing machine 2 to lift all head lays 74, drop all gates 72 and disengage all impression rollers 56.The ink forme rollers 34,36 and the damp forme roller 20 lift off. Further, an audible and a visual alarm are initiated in order to alert the operator of the printing machine 2 to the shut down.

The only functional machine controls available to the operator whilst the printing machine 2 is in its shut down mode are inch forward and inch reverse functions. The operator can only use these two functions, via appropriate inch forward and inch reverse buttons, to enable the operator to clear the obstruction and restore the printing machine 2 to its correctly operating condition.

The logic control circuit 94 will maintain the shut down condition of the printing machine 2 until the operator has satisfactorily restored the printing machine 2 to its correctly operating condition. Then the operator must reset the printing machine 2 by first switching off the power to the printing machine 2, via an emergency stop button, and then switching the power back on again. -All controls to the printing machine 2 will then become functional and ready to run.

The precise operation of the monitor means 60 is such that when a sheet of paper 50 is detected at the gate 70, the gate 70 is raised to allow the sheet of paper 50 through the printing head. As soon as that-sheet of paper 50 has passed through the gate 72, the gate 72 drops ready for the next sheet of paper 50. It will thus be seen that for every sheet of paper 50 processed through the printing head, the gate 72 must lift and drop once. An accurate sheet count can thus be made from each printing head, by monitoring the rise and fall of the gate 72. Each printing head has an electronic sheet count register. The electronic sheet count register operates as follows, reference being made as necessary to Figure 3 and the explanatory wording shown on Figure 3.

On power up of the printing machine 2, the electronic sheet count register is loaded with the binary number four. The electronic sheet count register has two inputs, these being count down and count up. A single pulse on the count down input will decrement the stored number by one. Similarly, a pulse on the count up input will increment the number by one. Every time the gate 72 lifts, a single count down pulse is given to the electronic sheet count register. Thus, when the fir st sheet passes through the gate 72, the stored number is decremented from four to three.

Similarly, the second sheet decrements from three to two and the third sheet decrements from two- to one. It can thus be seen that, from power up, after three sheets have been passed through the gate, the electronic sheet count register will read one. Because of the mechanics of a printing machine 2 having more than one printing head, before the first printing head sees the fourth sheet, the second printing head should have seen the first sheet.

When the gate 72 on the second printing head lifts, a count up signal is sent to the first electronic sheet count register. This then increments the number held in the first electronic sheet count register, while decrementing the number held in the second electronic sheet count register which is for the second printing head. Before the time the gate 72 of the first printing head lifts for the fourth sheet of paper 50, the second printing head should have seen the first sheet of paper 50.

Thus, before the first electronic sheet count register is decremented from one to zero by the fourth sheet, it should have been incremented from one to two by the first sheet of paper 50 reaching the second printing head. If all is well, the first electronic sheet count register will read two before the fourth sheet is detected. If so, the fourth sheet will count it down to one, but then the second sheet through the second printing head counts it back up to two. The fifth sheet will count it down to one. If the third sheet has for some reason fouled up in between the first and the second printing head, then the electronic sheet count register will stand at one. Sheet three is not detected at the second printing head before sheet six appears at the first printing head. Sheet six decrements the register from one to zero.It can thus be seen that if any electronic sheet count register reaches zero, a sheet of paper 50 has been lost and the electronics will implement a shut down of the printing machine 2 as described above.

It is to be appreciated that the embodiment of the invention described above with reference to the accompanying drawings has been given by way of example only and that modifications may be effected. Thus, for example, the logic circuit 94 as shown in Figure 3 can be varied. As shown in the logic circuit of Figure 3, over-ride switches may be provided for over riding various functions of the printing machine 2, for example at start up conditions.

Generally, where the printing machine comprises a plurality of printing heads, the printing heads will operate in pairs for the above mentioned sheet counting via the electronic sheet count registers. Obviously, at the last printing head in the printing machine, there will be a down stream monitor means to count the last printing head back up in order to stop a shut down. If the printing machine 2 only has one printing head, then the down stream side of the single printing head will be provided with the monitor means to effect the counting up that is required in order to prevent the premature shut down. The three sheet gap that is allowed to be present prior to the automatic shut down of the printing machine 2 being initiated can be varied as desired although the three sheet gap is believed to be an optimum gap which allows the printing machine 2 to operate without premature shut downs and to also take into account the possibility of mistimed sheets, for example those that may be hanging on to the feeder mechanism longer than usual.

Claims (11)

1. A printing machine comprising at least one printing head having monitor means for monitoring the sequential progress of sheets of paper during operation of the printing machine, and shut-down means for initiating automatic shut-down of the printing machine consequent upon the monitor means sensing the loss of a predetermined number of sheets of paper.

2. A printing machine according to claim 1 in which the monitor means includes transmitter means for transmitting a signal, and receiver means for receiving the signal from the transmitter means.

3. A printing machine according to claim 2 in which the transmitter means is such that it is adapted to transmit an infra red signal.

4. A printing machine according to any one of the preceding claims in which the-shutdown means comprises logic circuit means for receiving information from the monitor means as to the presence or absence of sheets of paper passing through the printing head, the logic circuit means being operative to initiate the shut-down of the printing machine consequent upon the monitor means sensing the loss of the predetermined number of sheets of paper.

5. A printing machine according to claim 4 in which the logic circuit means initiates the shut-down of the printing machine in response to the monitor means sensing the loss of three sheets of paper.

6. A printing machine according to any one of the preceding claims in which the shutdown means automatically shuts down the printing machine by lifting off a compression roller, lifting off ink and damp rollers, and stopping a main motor of the printing machine.

7. A printing machine according to claim 6 in which the compression roller is lifted off by a solenoid, in which the ink and damp rollers are lifted off by a motor and a cam and latch arrangement, and in which the main motor is stopped by actuation of a switch.

8. A printing machine according to any one of the preceding claims in which the shutdown means is effective to shut down motors driving damp and ink rollers.

9. A printing machine according to any one of the preceding claims in which the shutdown means is effective to activate an audible and/or a visual warning.

10. A printing machine according to any one of the preceding claims in which the monitor means is effective to enable a counter to start to determine the time that a paper gate is to release after the monitor means has sensed a sheet of paper.

11. A printing machine substantially as herein described with reference to the accompanying drawings.