GB2078593A

GB2078593A - Die Cutter

Info

Publication number: GB2078593A
Application number: GB8119278A
Authority: GB
Original assignee: Rengo Co Ltd
Current assignee: Rengo Co Ltd
Priority date: 1980-07-01
Filing date: 1981-06-23
Publication date: 1982-01-13
Also published as: NL189498C; AT382338B; ZA814226B; IT1137980B; NZ197502A; DE3125770C2; JPS5715699A; FR2485980A1; FR2485980B1; GB2078593B; SE444282B; CA1173938A; SE8104094L; AU7239981A; CH644052A5; NL8103104A; IT8122644A0; AU538016B2; DE3125770A1; ATA288281A

Abstract

A die cutter for die cutting a running web (1) continuously into blanks comprises a blade (3) and an anvil (4) interlocked with each other so that they will contact each other at a point moving from one end of the anvil to the other. Either the feed rolls (6) for the web or the cutting mechanism (3, 4) are electronically controlled so that a length of the web just sufficient for one cutting operation will be supplied to the cutting mechanism while it performs one cycle. The cutting mechanism is kept synchronised with the web speed at least during the period from the start of cutting to its end. <IMAGE>

Description

SPECIFICATION Die Cutter The present invention relates to a die cutter which continuously cuts a running web material such as corrugated fiberboard, cardboard and metal plate into blanks of a desired shape for producing boxes, cans or the like.

Among conventional die cutters, there are two types, the rotary type and the flat plate type, classified according to the manner of mounting of the blade. The former with a rotary blade has an advantage of higher productivity but has a poor cutting accuracy due to slip between the web and the cutter. The latter has advantages of easy blade mounting on a flat plate and good cutting accuracy. However, for cutting with the flat plate type, the running web had to be stopped on a fixed anvil and then a vertically movable blade had to be pressed against the web and the anvil. Such an intermittent operation means poor productivity.

The present invention seeks to provide a die cutter which obviates such shortcomings while maintaining inherent advantages of the flat plate type. In other words, an object of the present invention is to provide a die cutter which permits continuous operation without the necessity of stopping the material for cutting, thereby providing higher productivity.

This is accomplished by controlling the die cutter so that a sufficient length of the web just for one cutting will be supplied to the cutting unit having a blade and an anvil while the cutting unit performs one cycle of operation and so that at least during the period from start to completion of cutting, the cutting unit will be kept synchronized with the web speed.

The present invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a complete perspective view of one embodiment of die cutter according to this invention; Fig. 2 is an enlarged front view of the cutting unit; Fig. 3 is a similar view of a variant of the cutting unit; Fig. 4 is a block diagram of a first embodiment of the control circuit embodying this invention; Fig. 5 is a block diagram of a second embodiment thereof; and Fig. 6 is a block diagram of a third embodiment thereof.

Referring to Figs. 1 and 2, a running web 1 is cut into blanks by a cutting unit generally 'designated by numeral 2. The cutting unit 2 comprises a blade 3 and an anvil 4 opposed to each other with the web 1 therebetween, as well as gears and a crank mechanism 5 for interlocking the blade 3 with the anvil 4. Upstream of the cutting unit 2 there is provided a pair of feed rolls 6 for feeding the web 1 toward the cutting unit.

2.

The cutting unit 2 will now be described in detail. There are two pairs of driven shafts 7a, 7b and 8a, 8b spaced from each other with the shafts 7a, Sa above the web and the shafts 7b, 8, below it. Main gears 9a, 9b are fixedly mounted on the ends of the driven shafts 7a, 7b and driven gears 1 Oa, 1 Ob are fixedly mounted on the ends of the driven shafts 8a, 8b. Similarly, driving gears 12 are fixed on the ends of a driving shaft 11. The driving gears 12 mesh the upper gears 9a, 1 Oa which mesh the lower gears 9b, Ob, respectively.

Crank arms I 3a, 1 3b, 1 4a, 1 4b are mounted on the ends of the shafts 7a, 7b, 8a, 8b, respectively. The blade 3 and the anvil 4 are pivoted at one end thereof to the crank arms 1 3a and 13b, respectively, through pins 1 5. At their other end, the blade and the anvil each have a guide slot 16 extending axially to receive a slider 1 7 which is pivotally supported by a pin 1 5 on the respective crank arm 14a (14b). The upper surface of the anvil 4 facing the blade 3 is curved.

The crank arms are set so that the crank arms 13a, 13b will move not in phase with the crank arms 1 4a, 1 4b. As the shafts 7a, 7b, 8a, 8b turn, the point at which the blade 3 contacts the anvil 4 moves from one end thereof to the other end to cut the web 1.

A first motor 18 for driving the cutting unit 2 is connected to the driving shaft 11. To the first motor 18 are coupled a pulse generator PGA for generating a pulse signal FA proportional to the angle of revolution of the first motor and a tachometer generator 1 9 for generating a voltage VF proportional to the speed of the first motor.

The feed rolls 6 are driven by a second motor 21 through speed change gears 20. Similarly, to the motor 21 are coupled a pulse generator PG8 for generating a pulse signal bB proportional to the angle of revolution of the motor 21 and a tachometer generator 22 for generating a voltage VF proportional to the speed of the motor 21.

Adjacent to the cutting unit 2, a sensor 23 is provided which senses the crank arm 1 3a to give a detection signal each time the cutting unit 2 completes cutting. The sensor 23 may be photoelectric, magnetic or any other type.

Fig. 3 shows another example of the cutting unit 2. The anvil 4 is supported on sliding members 24 such as rollers. A rod 26 has one end pivoted to a pin 25 fixed on a stationary part such as a machine frame (not shown). The rod 26 has a slot 26a at its other end and another slot 26b midway of its length. A pin 27 fixed on the anvil 4 slidably fits in the slot 26a and a pin 28 fixed on the gear 9b at an eccentric position slidably fits in the slot 26b. As the driving shaft 11 rotates, the anvil 4 will reciprocate so that the contact point between the blade 3 and the anvil 4 will move from one end thereof to the other end to cut the web 1.

A first embodiment of the control circuit will be described below with reference to Fig. 4. It is adapted to control the motor 21 for the feed rolls 6 so as to be driven in synchronization with the cutting unit 2.

In response to a cutting complete signal from the sensor 23, values Lo and Bo set in a setter 31 are read in a computing unit 32, which also receives pulse signal A from the pulse generator PGA and pulse signal B from the pulse generator PGa and performs the computation, BOLO-A+(t?8. The result M of computation as a digital signal from the computing unit 32 is converted to an analog error voltage Vc by a digital/analog converter 33. The value Lo is a value proportional to the length into which the web is to be cut and Bo is a value proportional to the number of revolutions of the first motor 1 8, that is, the distance for which the tip of the crank arm 13a moves during one cycle of operation of the cutting unit 2.

A frequency/voltage converter 34 converts the pulse signal bA to a reference voltage VA proportional to the frequency of the pulse signal A. An operational amplifier 35 receives the reference voltage VA and the error voltage Vc and outputs a difference voltage VO(=VAVc) between these two voltages.

In response to a cutting complete signal from the sensor 23, a value Co set in the setter 31 is read in a counter 36 which subtracts the pulse signal XB from Co. The result of counting n(=Co-e) is given as a digital signal. The value Co is a preset value proportional to the angle for which the feed rolls 6 turn during the period from the completion of cutting to its stop. The value Co is determined so as the minimize the load on the motor. The value N is given to a digital/analog converter 37, which outputs a stop voltage VB.

The latter is set to a value equal to or larger than the maximum value of the reference voltage VA when the cutting complete signal is given. The stop voltage V8 is clipped in an input selector 38 by the reference voltage VA to obtain a clip voltage VD which is the smaller one of the reference voltage VA and the stop voltage VB. The input selector 38 selects and outputs the higher one of the clip voltage VD and the difference voltage Vo. A speed command unit 39 compares the voltage V8 from the input selector 38 with a feedback voltage VF from the tachometer generator 22 and adds or subtracts a difference, if any, between them to or from V, to control the motor 21 for the feed rolls 6 through a motor driving unit 40.

The first embodiment of the control circuit described above operates as follows: When the sensor 23 gives a cutting complete signal upon or after the completion of cutting, the computing unit 32 and the counter 36 read the values Lo and Bo, and Co, respectively, and start computation Bo-Lo-#A + #B and Co-#B, respectively. The input selector 38 compares the difference volatage Vo with the clip voltage VD and outputs a voltage V8. The voltage VE differs according to whether Bo-LosO or > O.

1) If Bo-Lo#0 When the cutting complete signal has been given, the signal M from the computing unit 32 is negative (because Bo-Lo < =O and bA and B are zero) and the error voltage Vc is negative.

Therefore, the difference voltage VO(=VAVc) will be higher than the reference voltage VA. Also, since the stop voltage V8 is set to be higher than the maximum value of the reference voltage VA at the point of time when the cutting complete signal is given, the clip voltage VD will be the reference voltage VA. Therefore, the input selector 38 will seiect and output the difference voltage, so that the motor 21 for the feed rolls will be always driven by the difference voltage Vo.

2) If Bo--Lo > O When the cutting complete signal is given, the signal M from the computing unit 32 is positive because Bo-Lo > O and bA and B are still zero. Thus the error voltage Vc is positive, too.

Therefore, the difference voltage VO(=VAVc) will be lower than the reference voltage VA. Since the clip voltage VD is the reference voltage, the input selector 38 selects the reference voltage. So the second motor 21 will be driven by the reference voltage VA. As time passes, the content N(=Co-#B) of the counter 36 and thus the stop voltage V8 will decrease until the latter becomes smaller than the reference voltage VA. So the clip voltage VD will be the stop voltage VB, not the reference voltage VA. Since the input selector 38 now selects the stop voltage V8, the second motor 21 will be decelerated.This causes decrease of the pulse signal bB from the pulse generator PGB and thus of the signal M(=Bo-Lo-#A + #B) from the computing unit.

Therefore, the error voltage Vc will decrease gradually so that the difference voltage Vo(=VAVc) will increase. If the difference voltage Vo does not become positive before the stop voltage V8 becomes zero, the second motor 21 will stop when VB becomes zero, but it will restart and be driven by the difference voltage Vo from the instant when Vo has become positive. If the difference voltage Vo becomes equal to or larger than the stop voltage V8 before V8 becomes zero, the second motor 21 will be driven by Vo from the instant when Vo has become equal to VB.

The control circuit described above ensures that with the second motor 21 controlled by the difference voltage Vo, the feed rolls 6 driven by the second motor 21 will be controlled so as to run in synchronization with the cutting unit 2.

Then M and thus Vc are equal to zero. The reason will be described below.

If the cutting unit 2 runs at a higher speed than the feed rolls 6, the pulse signal iA will be larger than the pulse signal XB so that the result of computation (M=BoL 5dA+0B) and thus the error voltage Vc will be smaller than zero.

Therefore, the difference voltage Vo will be larger than the reference voltage VA by the error voltage Ve (Vo=VA -(-|Vc|) = VA + |Vc|). As a result, the feed rolls 6 will be accelerated and the pulse signal XB increase so that the signal M will come back to zero. Therefore, the feed rolls 6 are brought back to synchronization with the cutting unit 2 in a moment.

Next, if the cutting unit 2 runs at a lower speed than the feed rolls 6, the pulse signal #A will be smaller than bB so that M and thus Vc will be larger than zero. Therefore, the difference voltage Vo(=VAVc) from the operational amplifier 35 will be smaller than the reference voltage VA. As a result, the feed rolls 6 will be decelerated. This decreases-the pulse signal #B so that M(=Bo-Lo-#A+#B) will be kept at zero.

Therefore, the feed rolls 6 are brought back to synchronization with the cutting unit 2.

When the cutting unit has finished one cutting operation while being kept synchronized with the feed rolls, another cutting complete signal is given by the sensor 23 and the control system will start operation for another cycle of cutting.

Fig. 5 shows another embodiment of the control circuit in which the motor 18 for the cutting unit 2 is controlled in relation to the motor 21 for the feed rolls 6.

The control circuit of Fig. 5 differs from that of Fig. 4 in that the counter 36 receives the pulse signal XA not 4iB, to perform computation, COA, that the F/V converter 34 receives the pulse signal 4iB not FA that the speed command unit 39 receives a feedback voltage VF from the tachometer generator 19, not 22, that the computing unit 32 receives bA and FB at different terminals and performs the computation expressed by LoBo bB+4A, and that the motor driving unit 40 drives the first motor 18, not the second motor 21. In this mode, Co is a preset value proportional to the angle for which the crank arm turns during the period from completion of cutting to its stop.

The second embodiment of the control circuit operates as follows: In response to the cutting complete signal from the sensor 23, the computing unit 32 and the counter 36 read the values Lo and Bo, and Co, respectively, and start computation Lo-Bo-#B+#A and CoXAT respectively. the input selector 38 compares the difference voltage Vo with the clip voltage Vn to output a voltage VE, which differs according to whether Lo-Bo < O or Lo-Bo > O.

1) If io-Bo < O At the time when the cutting complete signal has been given, the signal M is negative (because Lo-Bo < O and #A and FB are zero) and the error voltage Vc is negative, too. Therefore, the :difference voltage VO(=VAVc) will be higher than the reference voltage VA. Since the clip voltage VD is the reference voltage VA, the motor 18 for the cutting unit will be always controlled by the difference voltage Vo.

2) If Lo-Bo#0 At the time when the cutting complete signal is given, the signal M and thus the error signal Vc are positive. Therefore, the difference voltage Vo(=VA-Vc) will be lower than the reference voltage VA. Since the clip voltage VD is the reference voltage VA, the input selector 38 seiects the reference voltage. So the motor 18 for the cutting unit will be driven by the reference voltage VA. As time passes, the content N(=COA) of the counter 36 and thus the stop voltage V8 will decrease until the latter becomes smaller than the reference voltage VA. Now the clip voltage VD will be the stop voltage VB, not VA. Since the input selector 38 selects the stop voltage Ve the motor 18 for the cutting unit will be decelerated.This causes decrease of the pulse signal #A from the pulse generator PGA and thus of the signal M(=Lo-Bo-#B+#A) from the computing unit.

Therefore, the error voltage Vc will decrease gradually and accordingly the difference voltage Vo(=VA-Vc) will increase. If the difference voltage Vo does not become positive before the stop voltage C8 becomes zero, the motor 18 will stop when V8 becomes zero, but it will restart and be driven by the difference voltage Vo from the instant when Vo has become positive. If the difference voltage Vo become equal to or larger than the stop voltage V8 before V8 becomes zero, the motor 18 will be controlled by the difference voltage Vo from the instant when Vo has become equal to V8.

The above-mentioned control circuit ensures that with the motor 18 controlled by the difference voltage Vo, the cutting unit 2 driven by the motor 18 will be controlled so as to operate in synchronization with the feed rolls 6. Then M and thus Vc are equal to zero. The reason will be described below.

If the feed rolls 6 run at a higher speed than the cutting unit 2, the pulse signal bB will become larger than the pulse signal A so that the result of computation (M=LoBo02+0A) and thus the error voltage Vc will be smaller than zero.

Therefore, the difference voltage Vo will be larger than the reference voltage VA by the error voltage Ve (VO=VA(-|VC|)=VA+|VC|). As a result, the cutting unit 2 will be accelerated so that the pulse signal #A will increase until the signal M comes back to zero. The result is that the cutting unit is brought back to synchronization with the feed rolls 6 in a moment.

If the feed rolls 6 run at a lower speed than the cutting unit 2, the pulse signal #B will become smaller than #A so that the signal M and thus Vc will be larger than zero. Therefore, the difference voltage VO(=VAVc) will be smaller than the reference voltage VA. As a result, the cutting unit will be decelerated. This decreases the pulse signal bA so that M(=LoBoFB+0A) will be kept at zero. Therefore, the cutting unit is brought back to synchronization with the feed rolls 6.

Fig. 6 shows a further embodiment of the control circuit in which either the motor 18 for the cutting unit or the motor 21 for the feed rolls may be controlled in relation to the other motor.

In this embodiment, a selector means is provided for selecting the mode of control, that is, either that of Fig. 4 or that of Fig. 5. Inputs to the computing unit 32, F/V converter 34, counter 36, and speed command unit 39, and the motor to be controlled can be selected by means of a selector switch 41.

The pulse signal bB or XA is supplied to the computing unit 32 and the counter 36 through contact A, or B,, respectively, of the selector switch 41 The pulse signal XA or XB is supplied to the computing unit 32 and the F/V converter 34 through contact A2 or B2, respectively. To the speed command unit 39, the signal from the tachometer generator 1 9 or 22 is supplied through contact B3 or A3, respectively. The signal from the motor driving unit 40 is supplied to the motor 18 or 21 through contacts B4 or A4, respectively. On the selector switch 41, the contacts A1, A2, A3 and A4 are interlocked with one another.Similarly, the contacts B,, B2, B3 and B4 are interlocked.

When the contacts A or B of the switch 41 are selected, the third embodiment of the control circuit shown in Fig. 6 will operate in the same manner as the first or second embodiment, respectively.

Although in the second embodiment the pulse signal XB is supplied from the pulse generator PG8, the actial web speed may be picked up by a measuring wheel which is provided between the feed rolls and the cutting unit so as to rotate under friction with the running web.

In the above-mentioned control circuit, the values Lo and Bo are determined so that the cutting unit will be brought to synchronization with the web speed at latest before the next cutting is started.

Although in the preferred embodiment the cutting unit 2 is driven directly by the motor 1 8, it may be driven through speed change means such as a universal joint or the like to assure more precise cutting. Also, another sensor for sensing the start of cutting operation may be provided.

Further, a speed compensator may be provided before or behind the F/V converter 34 for more accurate cutting.

The present invention provides a die cutter having a higher productivity while maintaining the advantages of the flat plate type die cutter, i.e.

ease of blade mounting and high cutting accuracy.

Claims

1. A die cutter for cutting a running web into blanks of a desired shape, said die cutter comprising; cutting means having a blade and an anvil opposed to each other with said web running therebetween, and link and transmission means for driving said blade and said anvil interlocked with each other in such a manner that the blade will contact the anvil at a point moving from one end thereof to the other, feed rolls for feeding said web toward said cutting means, A first motor for driving said cutting means, A second motor for driving said feed rolls, control means for controlling either said first motor or said second motor in relation to the other motor so that a sufficient length of the web just for one cutting will be supplied to said cutting means during one full cycle of operation by said cutting means and so that said cutting means will be kept synchronized with the web speed at least during the period from the start of cutting to its end.

2. A die cutter as claimed in claim 1 wherein said control means controls said first motor in relation to said second motor.

3. A die cutter as claimed in claim 1 wherein said control means controls said second motor in relation to said first motor.

4. A die cutter as claimed in claim 1 , further comprising a selector means for selecting the motor to be controlled by said control means.

5. A die cutter as claimed in any of claim 2-4, wherein said control means comprise: a first transducer means for generating pulses (56A) the number thereof being proportional to the angle through which said first motor has rotated; a second transducer means for generating pulses zero the number there of being proportional to the length of the web which has been fed, a converter means for converting said pulses from said first or second transducer means to a reference voltage signal;; a setter means for setting a first value (Lo) proportional to the length into which the web is to be cut and a second value (Bo) proportional to the number of revolutions of said first motor during one cycle of operation by said cutting.means, a sensor for giving a signal each time said cutting means complete one cutting operation, a computing means which receives said first and second values from the setter means in response to the signal from said sensor and performs a computation expressed by either Bo Lo XA+0B or Lo-Bo-8+, to obtain a signal proportional to the result of computation, a differencing means which subtracts the signal from said computing means from the reference voltage signal from said converter means to obtain a signal proportional to the difference therebetween, an input selector means for selecting the higher one of the signal from said converter means and the signal from said differencing means, and motor control means responsive to the signal from said input selector means for controlling said second or first motor.

6. A die cutter as claimed in claim 5, wherein said setter means sets a third value (Co) proportional to the number of revolutions of said second or first motor during the period frown'the completion of cutting to the stop of said second or first motor and said control means further include a counter means which receives said third value in response to said signal from said sensor to perform a counting, Co-8 or Co-, to obtain a stop voltage signal (V8), said stop voltage signal being clipped by said reference voltage signal, said input selector means selecting the higher one of the signal from said differencing means and the stop voltage signal clipper by said reference voltage signal.

7. Die cutters substantially as hereinbefore described with reference to Figures 1 and 2 or Figures 1 and 3 in combination with Figure 4, or Figure 5, or Figure 6 of the accompanying drawings.