GB2072384A - Sheet stack height control means - Google Patents

Abstract

Stacking control means for a sheet feeder of a sheet treating or processing machine comprises a cycled stack height scanning device (1) which emits a pulse when the stack is below a required height, a stack-raising motor (2) and timing control means connected to a control input of the motor (2) to control the duration of operation of the motor. The motor (2) is connected to the scanning device (1) by way of a 2:1 divider (3), a comparison timing stage (4), a comparator (5), which consists of two AND-gates (10, 11) connected to the output of the comparison timing stage (4) - one of the gates (11) by way of an inverted input - and to the output of a further AND-gate (12), which is connected with the output of the scanning device (1) and through an inverted input with the output of the divider (3), a reversible shift register (6), a plurality of timing stages (7), each having a different running time and each connected to a respective one of the outputs of the individual bits of the shift register (6), and an OR-gate connected to the outputs of the timing stages (7). The running time is stepped up or down by the shift register according to whether or not a second pulse from the scanner (1) arrives before or after a preset time determined at (4). Thus the running time continuously alternates between two steps. <IMAGE>

Description

SPECIFICATION Sheet stack height control means The present invention relates to stacking control means for a sheet feeder of a sheet treating or processing machine.

Stacking control means are known (DD 124786), in which the conditions for precise control of the stacking movement are achieved through automatic adaptation to the printing speed in several speed steps and manual adaptation to the sheet thickness to be processed. This control means has the disadvantage that adaptation to sheet thickness is not undertaken automatically, so that either the number of switchings-on per unit time are too high for the components or stack height deviations become too great, which leads to disturbances in the course of sheet processing.

There is accordingly a need for control means for automatically maintaining a stack height which is optimum for the sheet processing, with least possible constructional complication technique while keeping to a number of switchings-on per unit time which will not mitigate against a long operational life of the components.

According to the present invention there is provided sheet stack height control means comprising raising means operable to raise a sheet stack in steps, stack height scanning means for cyclically scanning the stack and providing a signal output indicative of whether the stack is at a requisite height, and timing control means controliable by the scanning means to determine the duration of operation of the raising means for each stack raising step, the timing control means comprising a 2::1 divider connected to the output of the scanning means, a timing element connected to the output of the divider, comparison means comprising three AND-gates, a first one of the gates being connected at a first input to the output of the scanning means and at an inverted second input to the output of the divider, a second one of the gates being connected at a first input of the output of the first gate and at an inverted second input to the output of the timing element, and the third gate being connected at is inputs to the output of the timing element and the output of the second gate, a reversible shift register controllable by the comparison means, a plurality of timing stages having respectively different running times and each connected to a respective output of the shift register, and an OR-gate connected at its input to the output of the timing stages and at its output to a control input of the raising means.

Preferably, a respective checking AND-gate is connected to the output of each of the second and third AND-gates of the comparison means, second inputs of the checking AND-gates being connected with a switch "stack up" and the outputs of the checking AND-gates being connected to shift pulse inputs of the shift register.

The information input of the shift register may be connected with a pulse transmitter "feeder on" and the resetting inputs of the shift register are connected with a pulse transmitter "feeder off".

An embodiment of the present invention will now be more particularly described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a schematic circuit diagram of stack control means according to the said embodiment, and Figure 2 is a pulse diagram showing pulse output trains from different stages of the control means of Fig. 1.

Referring now to the drawings, there is shown in Fig. 1 a sheet stack control means consisting of a cycled stack height scanning device 1, a stack-raising motor 2, and timing control means for controlling the duration for which the motor 2 is switched on.

The timing means for control of the duration of the switching-on consists of a 2:1 divider 3, a comparison timing stage 4 connected to the output of the divider, a comparator 5 and a reversible shift register 6. Respectively connected to the outputs of the individual bits of the shift register 6 are timing stages 7.1 to 7.5 the motor 2 being connected through an OR-member and an amplifier 9 to the outputs of all of the timing stages 7.1 to 7.5. The times of the stages are so related to each other that the time of each subordinate timing stage is shorter than the time of the immediately superior timing stages (tl > t2 > t3 > t4 > t5). The time of the timing stages are a measure for the duration of the switching-on of the motor 2.

The comparator 5 comprises an AND-member 10, the first input of which is connected to the output of the comparison stages 4 and the second input of which is connected to the output of an AND-member 1 2. One input of the AND-member 1 2 is connected to the output of the scanning device 1 and the other, inverted input of the AND-member 1 2 to the output of the 2:1 divider 3. Finally, an AND-member 11 is connected at one input to the output of the AND-member 1 2 and at another, inverted input to the output of the timing stage 4.

A respective one of AND-members 13.1 to 1 3.5 is connected between each of the shift register 6 and the input of the associated one of the timing stages 7.1 to 7.5. The second inputs of the AND-members 13.1 to 13.5 are connected to the output of a second ORmember 14, the inputs of which are connected to the AND-members 10 and 11.

Two checking AND-members 15.1 and 15.2 are each connected at one input to the output of a respective one of the AND-members 10 and 11 and at another input to a swich "stack up" 1 6. The outputs of the AND-members 15.1 and 15.2 are connected to shift pulse inputs of the shift register 6.

A pulse transmitter "feeder on" 1 7 is connected to the information input of the shift register 6 and a pulse transmitter 'feeder off" 18 is connected to the resetting inputs of the register.

In operation, the stack height scanning device 1, which is synchronized with the operating cycle of a machine incorporating the control means, generates a pulse each time the stack no longer has the required height (Fig.

2, 2:1). These pulses are fed one after the other to a comparator 5. The output signals of the divider 3 are illustrated in Fig. 2, 2.2, and the output signals of the comparison stage 4 in Fig. 2, 2.3. Each first pulse in an output cycle of the scanning device 1 triggers the comparison timing stage 4 to provide a pulse with a constant time, which results from the maximum possible switching frequency of the motor 2. The second pulse is then fed to the comparator 5, where it is compared to determine whether or not the timing stage at the instant of the second pulse has run down. If the timing stage has already run down, then this means that the previous stack raising step, the duration of which was determined by one of the timing stages 7.1 to 7.5 was too great and a pulse, which drives the shift register in the reverse direction, is present at the output of the AND-member 11.

Only one bit at a time is set to "L" in the shift register 6, the setting taking place on each occasion through a pulse with "feeder on". With "feeder off", the shift register 6 is set staticaliy to "O" (reset) and the control means is thus taken out of operation.

The setting of the "L" signal in the shift register 6 is decisive through the AND-members 1 3.1 to 13.5 and the timing stages 7.1 to 7.5 for the duration of a raising step of the motor 2, which is activated by the switchingover of the "L" signal in the shift register 6 to another bit, also another timing stage 7.1 to 7.5. When a pulse is present at the output of the AND-member 11, then the "L" signal in the shift register 6 is thereby switched over to the next lower bit, whereby a timing stage of lower time is activated (Fig. 2, 2.4). When the comparison timing stage 4 has not run down at the instant of the second pulse, a pulse is present at the output of the AND-member 10.

The "L" signal in the shift register 6 is thereby switched over to the next higher bit and a timing stage of greater time is activated as a result.

In continuous operation, the duration of the raising step thus oscillates between two respectively adjacent bits, whereby the deviation of the intended stack height from the actual stack height is optimally maintained independently of the sheet thickness and speed.

Claims (5)

1. Sheet stack height control means comprising raising means operable to raise a sheet stack in steps, stack height scanning means for cyclically scanning the stack and providing a signal indicative of whether the stack is at a requisite height, and timing control means controilable by the scanning means to determine the duration of operation of the raising means for each stack raising step, the timing control means comprising a 2::1 divider connected to the output of the scanning means, a timing element connected to the output of the divider, comparison means comprising three AND-gates, a first one of the gates being connected at a first input to the output of the scanning means and at an inverted second input to the output of the divider, a second one of the gates being connected at a first input to the output of the first gate and at an inverted second input to the output of the timing element, and the third gate being connected at its inputs to the output of the timing element and the output of the second gate, a reversible shift register controllable by the comparison means, a plurality of timing stages having respectively different running times and each connected to a respective output of the shift register, and an OR-gate connected at its inputs to the output of the timing stages and at its output to a control input of the raising means.

2. Control means as claimed in claim 1, wherein each of the timing stages is connected to the associated output of the shift register by way of a respective AND-gate, which is connected at one input thereof to the shift register output and at another input thereof to the outputs of the second and third AND-gates of the comparison means by way of a further OR-gate.

3. Control means as claimed in either claim 1 or claim 2, comprising two checking AND-gates each connected at one input thereof to the output of a respective one of the second and third AND-gates of the comparison means and at another input thereof with switching means for permitting raising of the stack, the outputs of the checking ANDgates being connected with shift control inputs of the shift register.

4. Control means as claimed in any one of the preceding claims, wherein the shift register is connected at a setting input thereof with pulse transmission means for supplying a setting pulse indicative of operation of an associated sheet feeder, and at resetting inputs thereof with pulse transmission means for supplying a resetting pulse indicative of nonoperation of the feeder.

5. Sheet stack height control means substantially as hereinbefore described with refer ence to the accompanying drawings.