Control Device for Paper Converting Apparatus

The present invention relates to a control device for paper converting apparatus, especially a printer, and more particularly, but not exclusively, to a feeding device for a printing machine used for mass producing stationery, such as computer stationery, for example.

Computer stationery supplied to a user for use with a computer print-out machine normally consists' of a single length of paper folded into a "zig-zag" pack of sheets along transverse perforations. Rolls of stationery for use with print-out machines are also known. Such lengths of stationery are usually provided with a series of regularly spaced holes along one or both edges along the length. These holes are used to feed the paper through the printer by means of rotary driven wheels which have radially directed spikes extending at regular intervals around their peripheries and arranged to engage with the holes in the paper. It is also known to use "tractor feeds" consisting of belts or metal bands with spikes or pins attached to feed the paper through the printer. Such stationery, before it is supplied to the user, commonly has matter already printed on it. Examples are gas and electricity bills. Such stationery can be produced by feeding

continuous lengths of plain paper at high speeds through printing machines. It is imperative in these machines that the speed at which the paper is fed through the machine is precisely correlated with the speed of the printing device for printing the matter on the sheet in order to ensure that the matter is retained in the correct position on each sheet. Also, over the great lengths of paper passed through the printing machine a variation in the pitch of the holes punched in the edge from the nominal pitch tends to occur. This variation should also be taken into account if stationery is to be produced on which matter is printed in the correct position on each sheet. It is desirable to monitor the relative speeds of the paper and the printing device and to provide means for maintaining them in correlation so that the paper remains in correct "registration", i.e. each stationery sheet produced is correctly printed.

Because the printing process may demand high paper tension due to the high speed with which the paper is fed through the machine (in the order of 500 feet per minute or more in some cases) the paper cannot be fed by means of holes punched at the edges, since the tension would distort or tear the holes.

In many cases, therefore, the paper is fed into the printing device by means of a roller (the "infeed roller"), against which the paper is held by means of gripper wheels.

It has been previously proposed to optically monitor the speed of the paper into the printing device by means of a light source and photoelectric sensor which operate through the punched holes in the edges of the paper. The signal obtained is compared with a

signal obtained from the printing device, indicative of its speed, by means of a correction device. The correction device adjusts the paper speed in accordance with the relative values of the two signals.

Since the holes in the edges of the paper are generally at 1.25 cm (_r inch) intervals, the best resolution which can be obtained by the optical device described above is 1.25 cm (^ inch). Also, in practice it is not desirable to take account of every hole since the edges of the hole may be ragged due to the punching process and individual holes may be out of position or apparently so due to distortion in their shape. Confetti may also adhere to the hole blocking it partly or completely.- It is also difficult to avoid artifical error reading appearing if the paper moves sideways, so that the punched holes are moved out of the line of the light source and photoelectric sensor. German Offenlegungsschrift No. 2830932 discloses a device for monitoring the length of a paper web passing through a rotary printing press for the purpose of maintaining correct pitch or "length" between holes which are punched in the edges of the paper web during the printing operation. After passing through the printing press the holes in the edges of the paper engage with the projections of a guide sprocket wheel, the wheel acting to monitor the rate at which the holes pass it. A further wheel is positioned to frictionally engage the paper web to monitor the speed of the paper. Signals from the guide sprocket wheel and further wheel are compared and the speed of the paper can be adjusted accordingly to maintain the correct length between the holes in the paper.

Although the device of DE 2830932 may maintain the correct pitch between the holes, it does nothing to control the printing operation to ensure correct positioning of the printed material on the paper in correct rejistration.

The present invention provides a control device for paper converting apparatus, said device comprising a first means arranged to monitor the rate of movement of a printing device, a second means arranged to monitor the rate of movement of a web to be printed upon by said printing device, and a control means arranged to compare a first signal indicative of the rate of movement of the web with a second signal indicative of the rate of movement of the printing device and to control the relative rates of movement of said printing device and web in accordance with said comparison, whereby correct •registration of printing on the web is produced, said second means comprising a body having projections arranged to engage with indentations or perforations in said web, whereby movement of said web is transmitted to said body via said projections. Features and advantages of the present- invention will become apparent from the following description of an embodiment thereof given by way

^• of example with reference to the accompanying drawing, in which the single Figure is a block diagram of a printing machine in accordance with the present invention. A main drive motor 1 drives a printing device 2 and a rotary infeed roller 3 , as well as other devices (not shown) in the printing machine. The infeed roller 3 is driven via a differential gear box 4, one input 9 of which is connected to the printing device 2.

Paper 5 to be printed is fed towards the printing device by means of the infeed roller 3• A number of evenly spaced holes 6 which extend in a line are provided along at least one edge of the paper 5« pinwheel 7 - which is provided with a number of evenly spaced radially extending spikes 8 in its periphery, is positioned so that the spikes 8 engage with the holes 6 in the paper 5-

When the infeed roller 3 is being driven, i.e. it is rotating, and the paper 5 is being fed towards the printing device 2, the pinwheel 7 will be turned by the movement of the holes 6, the line of holes 6 extending along the direction of movement of the paper 5 ₃ and so the linear motion of the paper 5 is converted into rotary motion of the pinwheel 7 -

An encoder 10 is connected to the pinwheel 7 - The encoder is preferably a digital shaft encoder or resolver, and is arranged to provide an output indicative of the movement of the paper 5 _> via the rotary motion of the pinwheel 7 •

Another encoding device 12 is connected to the printing device 2 and provides an indication of the movement of the printing device 2.

The encoders 10 and 12 may be arranged to have a very high resolution. For the encoder 10 resolutions have been achieved as high as the production of a signal for every 0.0012 inch of paper 5 _> and it is possible to envisage higher resoloutions using appropriate encoders. The signals from both encoders 10 and 12 are fed into a differential counter 14 which compares the two signals and produces a continuous count of positive or negative error, i.e. it effectively compares the relative speeds of the paper 5 and printing device 2 to see if they are. in correct correlation.

The error count from the differential counter 14 is used to drive a correction motor control system 15, which controls a correction motor 16 which drives the differential gear box 4 in accordance with the error. The speed of rotation of the infeed roller 3 and consequently the speed of the paper 5 will therefore be adjusted according to the error signal, and the paper 5 will be main¬ tained in correct registration. • The correction motor control system 15 and correction motor 16 may include a device such as a stepper motor which is driven by the error count, or the count may be converted to a voltage which is used as the input to a servo-motor system which drives the differential gear box 4» Alternatively the roller may be driven from the machine through a variable ratio gear box controlled by the error signal.

In operation, if the paper 5 slows down relative to the printing device 2 for any reason, such as slippage of the paper on the printing device, an error signal will be produced by the differential counter 14 via the encoders 10 and 12 which will cause an increase in the speed of the infeed roller 3 , via the correction motor control system 15 _? correction motor 16, and differential gear box 4. so increasing the speed of the paper 5 to bring the paper 5 back into correct registration.

The printing device 2 is preferably a rotary device, such as a printing cylinder or cylinders.

Because the paper speed is monitored by a device which actually physically contacts indentation^ or perforationsin the paper, rather than optical encoding as in the prior art, this system has the advantage that a very high basic resolution can be

achieved, limited only the the design and resolution of the encoders.

It should be noted that the encoders 10 and 11 may themselves be optical encoders. Also, fewer problems arise due to certian. holes 6 being out of place- or having ragged edges, as a form of mechanical "averaging" takes place through the pinwheel 7 • This is achieved by more than one pin 8 being in engagement with the paper 5 at any one time. The fact that a pinwheel 7 is utilised also gives rise to the advantage that the paper 5 is automatically aligned in a transverse direction by the pins 8.

The paper 5 can be easily moved to make register adjustments by introducing artificial error signals into the system.

Preferably, all the sensing elements can be sealed so that they are not subject to external interference from dust or moisture. It should be noted that the control device according to the present invention is not limited for use in printing computer stationery, but can be used in any paper conversion machine for other suitable paper conversion applications. It should also be noted.that, although the embodiment described discloses the maintenance of the correct registration of the paper by means of the adjustment of the paper speed, the error signal and correction system could be equally as well applied to the printing device to regulate its speed, e.g. by effecting rotation of the printing roller 2 via the use of a differential gear box.

Further, the means for monitoring the paper speed need not necessarily be a pinwheel, but could be any body having projections arranged to

engage with indentations or holes in the web, the body being arranged to be moved in accordance with the movement of the web being transmitted to the projections e.g. the body could be in the form of a "tractor feed" having projections.