GB2149149A - Printing press synchronization - Google Patents

Abstract

In a printing press in which a plurality of shafts in one or more printing units are each driven by individual electric motors each motor is controlled by a hybrid analogue/digital control including a pulse generator and a counter to eliminate rotational and surface speed errors between said plurality of shafts and the plate cylinders driven by said shafts. In addition to a conventional speed control loop, the counter counts up pulses from a reference pulse train and counts down pulses from an encoder driven by the motor shaft, the counter output being summed with an analogue reference. <IMAGE>

Description

SPECIFICATION Improved printing press This invention relates to an improved printing press.

It is well known that in a large printing press for the printing of newspapers and for gravure and flexo-printing a plurality of printing units is deployed and these individual units require to be locked together, in use, so that the printing onto multiple paper webs is very accurately synchronized, the individual webs each being controlled by an adjustment linearly of their web paths so that a desired registration is effected as said multiple webs enter the folder at which severance of the webs is effected.

The accuracy of adjustments is known to be very demanding and the inter-relationships of the individual printing units one to the other has generally been effected through dog clutches, solid shafts and co-acting gear trains. The shafts are often of great length and it is clearly desirable to dispense with these and their mechanical co-acting parts. It is clearly further desirable to have recourse to independent electrical motor drives and this has been known to those skilled in the art for many years but no single individual electrical control to each individual drive has, as far as we are aware from our study of the operation of these large presses, given the desired accuracy of control.Surprisingly we have now found from critical tests such a control that gives the desired accuracy for a printing press operating at high speed and with the high inertial effects experienced in the practical printing of a newspaper. Accordingly we provide a printing press in which a plurality of shafts, in one or more printing units are each provided with individual electric motor drives the control of each of the said drives being effected via a hybrid analogue digital control including pulse generators and high accuracy counting means substantially to eliminate rotational and surface speed errors between said shafts and means driven by said shafts.

The invention will be more fully understood from the following description of a known printing press and a press of the invention given by way of example only with reference to the figures of the accompanying drawing in which: Figure 1 is a known press shown schematically; Figure 2 is by direct comparison a press similar to Fig. 1 incorporating the present invention; and Figure 3 shows a block circuit diagram of one hybrid analogue digital control known under the trade name of QUADRALOC.

Referring now to Fig. 1 clutches 10 permit selection of combinations of press units (P,P2P3P4P5) to produce a variety of newspaper pagination and printing effects.

In conjunction with inching motors 11 (typically a 2kW, 3 phase A.C. motor), clutches 1 2 can be set to permit isolated slow speed turnover of a printing unit for the purposes of replacing blankets or printing plates or for normal cleaning and maintenance.

During changes of printing plates the inching demands skill and judgement, in order to expose the grooves in the plate cylinder which are used for attaching the plate in the correct rotational position, sequentially.

When re-engaging the press unit back into the main drive mode, timing (phasing) is necessary to ensure that the correct physical relationship to other units and to the folder (F) is re-established.

Main d.c. drive motors 1 4 can be inched as an entity, to enable initial webbing of the machine prior to production, or for plating if the press is not equipped with the unit inching feature.

Cut off register bars 1 5 permit change of the web length between the printing unit cylinders and the folding cylinder, so that the printing area of the web is correctly positioned in the direction of web travel, for assembly of the newspaper.

The unit/unit register permits changes of the web length between one printing unit and another, normally adjacent, so that the overprinting of one image onto another can be executed with precision, in the direction of web travel.

In Fig. 2 the units P,-P5 and Folder F are each provided with an individual electrical motor drive 101 102103104 105 and 106.

The precise phase (positional) control of the units (P,-P5) and folder (F) is effected from a hybrid analogue/digital d.c. drive control that can, during all operational modes, achieve the following: Normal drive:-- steady state, acceleration, deceleration, emergency fast stop, group and unit inching.

Resynchronisation of a unit with other ele ments of the press.

Automatic positioning of any printing drum or cylinder and sequencing for plating.

Unit phase shifting with respect to other press elements, being equivalent to web length changes for registration.

Fig. 3 shows one hybrid analogue/digital control in which the control loop is interfaced with a conventional speed controlled motor drive. The original drive loop remains unmodified retaining the d.c. tachometer in a standard speed feedback mode. Provision is made for simultaneous ratio adjustment of the original analogue reference and the digital reference. Actuating signals generated by the difference counter plus associated P + I network are summed in with the ratioed analogue reference at a few percent strength. This is desirable because it allows the system to retain the dynamic performance of the original analogue loop and the security of a passive secondary feedback element. Control of the counter is effected by user trim inputs (serial input) load input (parallel input) and reset.In practical systems these inputs are provided with suitable conditioning logic to allow selective use of index markers from appropriate encoders or other sources.

A further advantage of this loop configuration is the ease with which it can be appiied to printing installations from a conceptual and practical point of view. With the inclusion of i 1 switches on the main signal paths, the loop can be closed with the minimum of disturbance to existing signal polarities.

The modus operandi of the control is as follows: Any error in the position counter (also referred to as a position error counter or difference counter) is forced to zero through the appropriate loop action on the controlled shaft.

Consider a system with a shaft encoder of 360 pulses per revolution. If the position counter were parallel loaded with the number 360,270 this would cause shaft rotation until the counter equalled zero i.e. 1000.75 revolutions. Loading - 360,270 would cause reverse rotation to the original position. In speed applications the counter is being continuously incremented by the reference pulse train. The loop action causes the controlled shaft to decrement the counter by an identical amount thus the loop maintains the net error count at zero. Hence, the reference and controlled shafts stay effectively in position lock.

Relative shaft positioning whilst running is easily achieved by extra inputs to the counter allowing one shot or packets of counts to be added to subtracted from the error via desk mounted pushbuttons or processor actions.

The error counter in certain units is j 1.5 million count capacity, this is very large by conventional standards. It allows great flexibility in certain applications where the controlled shaft is required to be temporarily rotated away from the reference position by external influence.

By perfroming a division of say two on the reference pulse train the controlled shaft will rotate by half the original distance. Using a unit that possesses a frequency divider of 6 decade resolution is effectively one million gear ratios. This facility plus the effective position control in all quadrants allows applications involving ultra low speed and defined operation through the zero speed boundary.

The applications of such a digital control are extremely widespread and they offer inter alia 1) Absolute speed control against a quartz reference.

2) Coupled shaft speed control.

3) Position control single shaft and coupled shaft.

4) Hybrid speed and position control; these include motion sequences involving stationary position and controlled speed in both directions either single or coupled shafts.

5) Computer control. Digital control units provide the tripartheid interface between the host computer, accuracy and power.

6) Low speed control.

Clearly such a control enables inter alia the linear speed of a paper sheet or web from two or more different drums of different diameters to be adjusted to great precision. This is of considerable importance in for example web tension control where hitherto drums of great inertia and size had to be machined to tight tolerances to give an accurate circumference and a commensurate peripheral speed involving high tooling charges; now the circumferential differences can be adjusted by the precise rotational speed to the passing paper web.

Claims (6)

1. A printing press in which a plurality of shafts in one or more printing units is each provided with an individual electric motor drive the control of which is effected via a hybrid analogue/digital control including a pulse generator and high accuracy counting means substantially to eliminate rotational and surface speed errors between said plurality of shafts and means driven by said shafts.

2. The printing press as claimed in Claim 1 wherein the hybrid analogue digital control is a dc drive control.

3. The printing press as claimed in Claim 2 wherein the hybrid analogue digital control provides normal drive: steady state, acceleration, deceleration, emergency fast stop, group and unit inching; resynchronisation of a unit with other elements of the press; automatic positioning of any printing drum or cylinder and sequencing for plating; unit phase shifting with respect to other press elements, being equivalent to web length changes for registration.

4. The printing press of any preceding claim wherein any error in a position error counter or difference counter of the control is forced to zero through a loop action on the shaft that is controlled.

5. The printing press of any preceding claim wherein the hybrid/analogue digital control is that known under the trade name QUADRALOC.

6. A printing press substantially as hereinbefore described and as shown in the Figs. 2 and 3 of the accompanying drawings.