DE20203617U1 - Stapelhubantrieb - Google Patents

Abstract

The drive includes a drive motor (3) with a control (4), which is in connection with a sensor (5) sensing the upper edge of a stack (1). A value is input to the control according to the thickness tolerance of the printing material. The speed for moving the stack is determined in dependency on the thickness tolerance by the control.

Description

[Utility model application]

MAN Roland Printing Machines AG Mühlheimer Strasse 341
63 075 Mühlheim
5

[Name of the invention] Stacking lift drive

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[Description]

The invention relates to a stack lifting drive according to the preamble of claim 1.

[State of the art]

In sheet-fed printing machines, the sheets to be printed are taken from the top of a feeder stack and fed to the machine via a feed table. The stack is placed on a stack support plate and is moved vertically by an associated drive. A control system is arranged upstream of the drive, which has a signal connection to a sensor that scans the top of the stack. The sensor can thus determine whether the top edge of the stack has sunk below a specified height level due to the sheet removal, whereupon the corresponding follow-up movements are carried out via the control system and the drive.

The top edge of the stack must be kept at the intended height level with a relatively high degree of accuracy, otherwise - especially in the case of high-speed printing machines - the elements that take the sheets away cannot work reliably and sheets may be lost during transfer to the feed table, which leads to machine stoppages.

Continuously operating stack lifting drives and timed or discontinuous stack lifting drives are known. With the latter stack lifting drives, the stack is moved with a predetermined stroke or up to 0 with a sensor signal when the top edge of the stack falls below a predetermined height. The drive then remains switched off again until the top edge of the stack falls below the predetermined height again due to the sheet removal.

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The disadvantage of such cyclical drives is that the elements that transmit the lifting forces to the stack are subjected to relatively high stress due to the frequent switching on and off. The high switching currents also generate electromagnetic waves, which must be shielded by suitable measures.

Ultimately, the intermittent movement of the stack also represents a disadvantage, since corresponding movements can be transmitted as the movements of, for example, the printing press system, which can possibly lead to incorrect systems and thus machine stoppages.

The problems described can be avoided by continuously controlling the stacking stroke. For this purpose, a motor with adjustable speed should be provided, which, in conjunction with an upstream control system and a sensor that detects the height of the stack, keeps the top edge continuously within the specified height range. 20

With such stack lifting drives, the substrate thickness (thickness) and the processing speed of the machine (printing speed) as well as the size of the specified height range in which the top edge of the stack should lie influence the speed at which the stack is to be moved. In other words, ultimately the speed of the lifting drive.

From DE 36 31 456 C2 a control system for a pile lifting drive that operates both continuously and intermittently is known. Switching between continuous and discontinuous pile lifting drive is carried out depending on the thickness of the printing material. With very thin printing materials, a continuous feed speed is required due to the otherwise low feed speed.

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speeds are preferably driven in a clocked manner. The disadvantage of this solution, however, is that an additional pulse generator is required to determine the size of the tracking path on the stack lifting drive.
5

DE 198 07 528 C2 discloses a control system for a continuously operating pile lifting device in which the time between the triggering at the upper and lower height thresholds is recorded in order to determine the required pile feed speed. The disadvantage here is that the determined ideal feed speed for the pile does not take into account substrate tolerances, which also occur with higher-quality substrate thicknesses.

[Task of the invention]

The object of the present invention is therefore to develop a stack lifting drive according to the preamble of claim 1 in such a way that the stack can be controlled exactly in the intended height range with a simple sensor, even with tolerances in the printing material thickness.

This object is achieved by the characterizing features of claim 1. Further developments of the invention emerge from the subclaims.

[Examples]

According to the invention, the control system determines a tracking speed for the stack from the printing speed, the printing material thickness and a printing material thickness tolerance. The assumed thickness tolerance can be entered by a user before each print job via an operating device or can be stored as a fixed value. In the sensor that scans the top edge of the stack

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It is a sensor that delivers a signal when the stack edge is in contact with it and does not deliver a signal when the stack edge is no longer in contact with the sensor. The sensor preferably has a switching hysteresis, i.e. the switching state of the sensor "stack at the sensor" is above the level at which the signal level "stack not at the sensor" is delivered.

As long as the sensor emits the "stack at sensor" signal, the stacking is carried out at a lower speed than the ideal speed calculated by the control system. This speed is lower by such an amount that a negative thickness tolerance of the printing material (thinner than the actual printing material value) is completely compensated.

If the individual sheets on the stack ideally have the target substrate thickness, the slightly reduced stacking speed means that after a certain time 0 the top edge of the stack moves out of the sensor's switching range, i.e. the sensor signal changes from "stack at the sensor" to "stack not at the sensor". If all or only some of the sheets have a thickness less than the target substrate thickness, the time until the sensor signal changes from "stack at the sensor" to "stack not present" increases accordingly. Ideally the top edge of the stack will then never leave the sensor's switching range, i.e. the stacking speed is optimally selected.

If the individual sheets are either all or only partially thicker than the specified substrate thickness, the stack loses height more quickly and the sensor signal changes more quickly from "stack is present" to "stack is not present".

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In all three of the possible cases described, the lower stacking speed selected according to the invention means that the top edge of the stack either never leaves the switching range (hysteresis) of the sensor or does so after a more or less long time interval, which means that the sensor emits the signal "stack not present" at the lower level. In this case, stacking then takes place at a speed that is selected to be slightly higher than the stacking speed resulting from the printing speed and the target substrate thickness.

In this signal range, too, a distinction must be made between cases in which the individual sheets are either thicker, as thick as specified, or partially or completely thinner than the target substrate thickness, which is specified as a value for the control system. This means that the switching threshold of the sensor is exceeded after a certain period of time - ideally never.

0 Due to the inventive post-stacking, which takes the substrate thickness tolerance into account, the top edge of the stack is always moved in a range corresponding to the hysteresis of the sensor. Only relatively small variations in the post-stacking speed are necessary, i.e. this will fluctuate with a relatively small amplitude around the ideal post-stacking speed value.

According to a further development of the invention, a self-learning optimization is carried out at a production start 0. This can be done in particular if information about the thickness of the printing material is not available or is incorrect. When the print job starts, the pile lift drive initially receives widely differing setpoint values. Depending on the duration of the signal level for the two

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The minimum and maximum speed of the stack lifting drive are increasingly approximated via the machine control system in the possible states (stack at the sensor / not at the sensor) until a stationary state is formed in the immediate vicinity of the ideal stack lifting speed.

According to a further development of the invention, the actual ideal stacking speed can be calculated by analyzing the temporal progression of the sensor signals and the resulting average speed over a longer period of time. The result can be used to optimize the stacking behavior with a view to smaller deviations. On the other hand, it can be determined by how much the actual printing material thickness differs from the specified printing material thickness.

The invention can be applied to both a feeder and a delivery stack.
■ Furthermore, an embodiment of the invention is explained using the drawing.

It shows:
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Fig. 1 a stack lifting drive with the corresponding

corresponding components,

Fig. 2 the temporal course of the sensor signal,

the stacking speed as well as the stack height and

Fig. 3 the temporal course of the sensor signal,

the stacking speed and the stacking height in one embodiment of the invention.

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The stack in a feeder or delivery unit (not shown) of a printing machine is placed on a stack support plate 2. The stack support plate 2 can be raised and lowered by a drive motor 3 via gear means (not shown) - for example chains and deflection wheels. A control system is arranged upstream of the drive motor 3, the speed of which is controllable. The control system 4 is connected to a sensor 5 in

10. Signal connection, whereby the sensor 5 senses the stack height. The sensor is designed as a digital signal generator. The sensor supplies two signal states, depending on whether the stack 1 is touching the sensor 5 with its upper edge or not. The two signal states "stack on the sensor" and "stack not on the sensor" are shown in Figures 2 and 3 with 1 and 0 respectively. The vertical mobility of the stack 1 on the stack support plate 2 is shown by the double arrow. The target stack height SSH is indicated by the dash-dotted line. Finally, the control 4 is in signal connection with 0 an input device 6, for example in the form of the control station of the printing press (not shown).

During printing, sheets are removed from the top of the stack 1. This causes the stack height SH to decrease over time t, as shown in the bottom diagram of Fig. 2. Depending on the switching threshold of the sensor 5, the signal S changes from 1 (stack at the sensor) to 0 (stack not at the sensor) at a certain time. The stack speed SG during the "stack at the sensor" phase was lower by a predetermined value than the ideal stack speed SSG, which is shown in dash-dotted lines in the middle diagram in Fig. 2.

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After the sensor signal S changes from 1 to 0, the stacking speed SG is now increased by a predetermined value above the ideal stacking speed SSG, so that the stacking height SH increases until the sensor signal S changes from 0 to 1 again.

Figure 2 shows that when the sensor signal S changes from 1 to 0 or from 0 to 1, the stacking speed SG fluctuates with the specified stroke around the ideal stacking speed SSG. Accordingly, the stacking height SH is always slightly below or above the target stacking height SSH.

At the start of printing, a self-learning parameter adaptation takes place as shown in Figure 3. Initially, the stack is not moved at all, i.e. the stacking speed SG is zero. Depending on the printing speed and the thickness of the printing material, the stack height SH decreases quickly and falls below the target stacking height value SSH. The sensor signal S changes from 1 to 0. This is followed by re-stacking at a high stacking speed SG. This leads to the stacking height SH increasing again in a relatively short time, namely with the target stacking height SSH being exceeded. After the sensor signal S changes from 0 to 1, re-stacking is now carried out at a value for the stacking speed that is significantly reduced compared to the ideal stacking speed SSG. This reduction in the stacking speed SG is smaller in magnitude than the first "overstroke" compared to the value of the ideal stacking speed SSG. This procedure 0 is continued, with the increases or reductions in the stacking speed SG becoming smaller and smaller in magnitude, so that the stacking speed SG alternately approaches the ideal stacking speed SSG.

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Accordingly, the stack height SH also approaches the target stack height SSH.

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[Reference list]

1 . Stack

2 stacking support plate

3 Drive motor

4 Control

5 Sensor

6 ■ Input device S Sensor signal

SG stacking speed

SH stack height

SSH target stack height

SSG ideal stacking speed

t time

1 "Stack on the sensor"

0 "Stack not at sensor"

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Claims (4)

1. Stack lifting drive for a sheet processing machine, in particular for a sheet-fed offset printing press, with a drive motor by means of which the stack can be moved vertically, a control arranged upstream of the drive motor, which is connected to a sensor which senses the upper edge of the stack and which moves the stack at a speed depending on the printing material thickness and the printing speed, characterized in that a value corresponding to the thickness tolerance of the printing material can be fed to the control ( 4 ), and that the value of the speed for moving the stack ( 1 ) can be determined by the control ( 4 ) depending on this thickness tolerance. 2. Stack lifting drive according to claim 1, characterized in that the sensor ( 5 ) is designed as a signal generator which has a switching hysteresis. 3. Stacking lift drive according to claim 1 or 2, characterized in that the ideal speed value of the stacking speed (SG) can be determined in a self-learning manner by the control ( 4 ) as a function of the signal from the sensor ( 5 ) by alternating over- and under-steering with decreasing amplitude. 4. Stack lifting drive according to one of the preceding claims, characterized in that a measure for the existing printing material thickness tolerance can be determined by the control ( 4 ) as a function of the signal from the sensor ( 5 ).