Control Apparatus For The Measurement And Folding Of Flat Workpieces

Abstract

A control apparatus for use with a machine for folding a flat workpiece comprising a first detector and transmitter unit arranged to detect and measure a dimension of a travelling workpiece and transmit a signal whose value is representative of said dimension to a first memory store arranged to accept said signal, means for transferring at least part of said signal in the first memory store from said first store to a second memory store, and a second transmitter arranged to transmit to said second memory store a further and cumulative signal representative of the passage of said workpiece relative to a folding station, said second memory store being arranged to initiate a folding operation when the required length of workpiece has passed said folding station.

Description

The present invention is concerned with the measurement and folding of flat workpieces.

According to the present invention a control apparatus for use with a machine for folding a flat workpiece comprises a first detector and transmitter unit arranged to detect and measure a dimension of a travelling workpiece and transmit a signal whose value is representative of said dimension to a first memory store arranged to accept said signal, means for transferring at least part of said signal in the first memory store from said first store to a second memory store, and a second transmitter arranged to transmit to said second memory store a further and cumulative signal representative of the passage of said workpiece relative to a folding station, said second memory store being arranged to initiate a folding operation when the required length of workpiece has passed said folding station.

According to one preferred feature of the invention each of the first and second memory stores is an electronic circuit and comprises at least one storage capacitor, each storage capacitor being connected to its associated transmitter through a resistance, the arrangement thus forming a resistance-capacitor circuit.

The means for transferring at least part of the signal originally stored in the first memory store to the second memory store may comprise a switch, arranged when in its closed position to connect the two stores in parallel, with or without the association of other circuit elements to govern the ratio of said sharing.

According to a further embodiment of the invention a third memory store may be provided together with means for dividing and transferring thereto any remaining signal stored in said first memory store after the original information has been transferred to the second memory store, whereby a further folding operation can be initiated by said third store for further folding of the workpiece.

According to another embodiment of the invention for initiating further folding operations, a third memory store may be provided together with means for dividing the original information transferred from the first memory store between the second and third memory stores whereby further folding operations can be initiated by said third memory store.

One object of the invention is to provide a simple, cheap and robust control apparatus for use with a folding machine for folding flat workpieces.

A further object of the invention is to provide a control apparatus for use with a folding machine for giving an accurate fold by the adjustment of a variable resistor as a capacitor supply voltage.

Other and further objects of the invention will become apparent by reference to the accompanying drawings wherein:

FIG. 1 is a schematic diagram of the control system of the invention;

FIG. 2 shows one preferred input circuit suitable for use with the invention;

FIG. 3 shows the resistance-capacitor circuit of the invention;

FIG. 4 shows one preferred output circuit suitable for use with the present invention;

FIG. 5 is a diagrammatic charge curve for DC charging of capacitor C1 of FIG. 3;

FIG. 6 is a diagrammatic charge curve for the DC charging of capacitor C2 of FIG. 3;

FIG. 7 is a schematic diagram of the folding operation;

FIG. 8 is a diagrammatic charge curve for both DC and pulsed charging of a capacitor, and

FIG. 9 shows a resistance capacitor circuit suitable for multiple folding of a workpiece.

In FIG. 1 there is shown a conveyor system comprising movable belts or tapes 10 and 12 arranged for movement in the direction of the arrows shown. A first transmitter 13, forming part of a detector and transmitter unit 14 is arranged above conveyor 10 the detector (not shown) being arranged for actuation by a travelling workpiece 16 being carried along on the upper run of endless conveyor formed by the belts or tapes 10.

The transmitter 13 comprises a toothed wheel arranged for rotation by the passage of a workpiece 16 therebeneath, the teeth of said toothed wheel being arranged to alternately interrupt and restore a light beam impinging on a photoelectric cell 15. The output waveform of this detector is in the form of a spaced sawtooth voltage 17 which is then fed to a first pulse-shaping circuit 11.

One form of pulse-shaping circuit 11 which may be used is shown in FIG. 2 and comprises a Schmitt trigger semiconductor circuit (shown on the left of the FIG.) followed be a semiconductor monostable multivibrator (shown on the right of the FIG.) equipped with a resistance-capacitance delay circuit arranged to set a constant pulse width.

The output waveform of this pulse-shaping circuit 11 comprises a train of constant width, constant height pulses 19 supplied at a rate proportional to the velocity of the flat workpiece 16 as it drives the toothed wheel of the unit 14. This train of pulses (shown schematically on FIG. 1 emerging from circuit 11) is delivered to the left-hand side of the resistance-capacitance circuit R1-C1 of the R-C circuit 21 of FIG. 3 for the length of time that the detector associated with the unit 14 is actuated. This detector, which may be in the form of a feeler switch, is connected so that operation thereof opens contact 18 (FIG. 3) thus allowing capacitor C1 of the circuit of FIG. 3 to become charged by said train of pulses, as shown in FIG. 5. The charge acquired by capacitor C1 is thus proportional to the overall length of workpiece 16 because contact 18 is open for the full time that the workpiece is passing under the detector of unit 14.

When workpiece 16 has completely passed the unit 14 the detector associated with the unit senses this fact and opens contact 20, simultaneously closing contact 22 (FIG. 3) momentarily. Thus a capacitor C2 connected in parallel to C1 acquires a part of the charge of capacitor C1.

Contact 18 then closes, and in so doing discharges capacitor C1 so that the circuit R1-C1 is then ready for charging by any subsequent workpiece travelling along the conveyor 10. Capacitor C2 is left holding at least part of the original charge of C1.

A second transmitter 24, (FIG. 1) similar to transmitter 13 is connected to pulley wheel 28, over which the endless conveyor formed by belts or tapes 10 passes, by a rotatable shaft 26. Shaft 26 thus rotates at a speed proportional to the velocity of workpiece 16 at any particular time, After the workpiece 16 has passed beyond unit 14, the transmitter 24 output voltage is fed cumulatively to capacitor C2 through resistance R2 of the R-C circuit 21 via a second pulse-shaping circuit 30, which can be substantially the same as circuit 11 (FIG. 2).

The charge acquired by capacitor C2 from the second transmitter 24 is thus added to the charge stored on capacitor C2 from the previous charge transfer from capacitor C1. When capacitor C2 has been charged to a predetermined firing voltage Vp (FIG. 6) the output circuit of FIG. 4 conducts to produce an output causing the folding mechanism, indicated schematically by folding blade 32, to operate. At the same time, contact 20 closes to completely discharge capacitor C2 and thus prepare it for the following cycle, when it will accept a further charge from capacitor C1 being built up thereon by the passage of a succeeding workpiece beneath unit 14.

One preferred form of output circuit which may be used is shown in FIG. 4. This circuit comprises a low leakage unijunction transistor 23 which is used to provide an output pulse at the said firing voltage Vp followed by a thyristor 25 to give the required output signal to the machine for folding the workpiece.

By selecting suitable values for the time constants of circuits R1-C1 and R2-C2, for aiming voltage E1 and E2, and for firing voltage Vp (referred to hereafter with reference to FIG. 6) the system will enable folding of the workpiece in any desired ratio regardless of the length of the workpiece fed to the device.

The theoretical aspect of the invention will now be further described with reference to FIGS. 5, 6, 7 and 8 of the accompanying drawings.

The charge curve of capacitor C1 is shown in FIG. 5. T.sub.1 is the time constant for the first memory store R1-C1, and E1 is the aiming voltage of capacitor C1. S1 is the workpiece velocity at the first detector and transmitter unit 14.

The charge curve of capacitor C2 is shown in FIG. 6 in which E2 is the aiming voltage of capacitor C2 and Vp is that predetermined voltage at which capacitor C2 is arranged to discharge into the output circuit of FIG. 4. Also T.sub.2 is the time constant for the second memory store R2-C2, and S.sub.2 is workpiece velocity at the second transmitter 24.

Referring now to FIG. 7 let x be the distance travelled by the workpiece after measuring but before folding, and y be the length of the workpiece protruding beyond the fold station then,

D+ y=L+x (1) where D is the distance between the unit 14 and fold station 32, and L is the overall length of the workpiece. For halfway folding,

L/2=Y (2)

Equations (1) and (2) give

L/2=L+x-D (3) let t.sub.1 be the time the workpiece takes to travel past the first transmitter, and t.sub.2 be the time taken for the workpiece to travel the distance x, then ##SPC1## ##SPC2##

make D a constant, and satisfy the conditions for the workpiece to be folded in half.

The foregoing mathematical treatment of the invention assumes a DC capacitor charging current, whereas in the particular description a pulsed charging current was assumed. It is therefore necessary to show the relationship between DC and pulsed charging currents.

Referring to FIG. 8 the curves for both DC and pulsed charging currents are shown. The DC charging curve is shown as 44 and the pulsed charging curve as 46. Let t.sub.1 be the time taken for the DC charging current to charge a capacitor to voltage Vp., and let t.sub.1 ' be the time for the pulsed charging current to charge the same capacitor to voltage Vp. then, on the pulse fed curve 46

t.sub.1 '=P(r.sub.1 +r.sub.2) where P is the number of pulses received (i.e. number of cycles)

r.sub.1 is the time duration of the pulse (i.e. mark duration)

r.sub.2 is the time duration before a subsequent pulse (i.e. space duration)

and P=Lp

where L is the length of the sheet to be folded p is the pulse rate

but charging voltage V=E.sub.1 (1-e ) for DC

and also v E.sub.1 (1-e ) for pulsed current

but if r.sub.2 =0 on the pulsed current, then the charging current is DC t.sub.1 =Lpr.sub.1

now, if the mark-space ratio is 1/1, then r.sub.1 =r.sub.2

and T.sub.1 '=2I.sub.1 but t.sub.1 '=Lp.sub.1+r.sub.2)=L/S.sub.1 where S.sub.1 is speed ##SPC3## S.sub.1 T.sub.1 ' is independent of speed substituting in equation 10

S.sub.1 I.sub.2 /S.sub.1 T.sub.1 is a constant and can be made equal to a half by suitable selection of T.sub.1, T.sub.2, p and t.sub.1.

From the foregoing it may thus be seen that with the detector and switch set this distance D from the fold position the circuit gives the required fold in any workpiece length within the range 0<L.ltoreq.2 D.

In the above description it has been assumed that the conveyor speed has not varied. If the conveyors travel at all times at a constant speed, then second transmitter 24 and pulse-shaping circuit 30 can be omitted and a constant DC voltage equivalent to the second pulse train previously mentioned can be fed into circuit R1-C2 when the workpiece has passed unit 14 and circuit R1-C2 has received its appropriate share of the charge from circuit R1-C1.

The description so far has been concerned with the provision of a single fold in workpiece 16. One method for obtaining second and subsequent folds can be achieved by passing the initially folded workpiece through the device and past the folding machine again. In such a case the charge remaining on C1 after some of it has been transferred to C2, can be further shared through a suitable switching device, with another actuating circuit say R3-C3, similar to R2-C2.

A still further embodiment for initiating further folding operations is shown in FIG. 9 in which a resistance-capacitor circuit similar to that shown in FIG. 3 is illustrated.

The difference between the circuit of FIG. 3 and that of FIG. 9 basically resides in the fact that in FIG. 9 the second capacitor C2, and second resistor R2 are replaced by tow capacitors C2' and C3' and two resistors R2' and R3' respectively.

The modes of operation of the two circuits are similar, inasmuch as the first capacitor becomes charged from the first detector and transmitter unit 14 (as hereinbefore described), but the charge acquired by the first capacitor is shared between the two additional capacitors C2' and C3', which may be of equal capacity.

Additional capacitor C2' is firstly charged from the second transmitter 24 and subsequently discharged into the output circuit of FIG. 4, by suitable operation of switches 34, 36, 38, 40 and 42, thereby causing a signal to be issued to the folding machine to fold the workpiece once.

The capacitor C3' is then charged, either from the second transmitter, or, from a further transmitter associated with a further folding machine. Subsequently the capacitor C3' discharges into the output circuit of FIG. 4 thereby causing a further fold signal to be issued which in turn causes the workpiece to be folded for a second time.

It is apparent that using the above-outlined procedure, any number of folds may be produced in a flat workpiece.

In order flat successive workpieces travelling along the conveyor 10 may readily be folded at different position along their length, it is envisaged that either the resistors and/or capacitors of the resistance-capacitance circuit may be made variable.

Claims

We claim:

1. A control apparatus for use with a machine for folding a flat workpiece at a folding station, the control apparatus comprising in combination, a first memory store, a first detector and transmitter unit arranged to detect and measure a dimension of a travelling workpiece and transmit a signal whose value is representative of said dimension to said first memory store, said first detector and transmitter unit comprising a photoelectric cell, a light source directing a light beam on said photoelectric cell, a toothed wheel, the teeth of which are arranged to alternately interrupt and restore impingement of said light beam on said photoelectric cell to create said signal at said photocell, means mounting said toothed wheel in cooperating relationship with a workpiece the dimension of which is to be measured and which is travelling along a conveyor in said folding apparatus, means connecting said photoelectric cell and said first memory store to transmit said signal to said first memory store, a second memory store, means for transferring at least part of the signal stored in said first memory store to said second memory store and for subsequently releasing said first memory store to receive subsequent signal from said first detector and transmitter unit in response to measurement of a subsequent travelling workpiece, and a second transmitter arranged to transmit to said second memory store a further and cumulative signal representative of the passage of said first travelling workpiece relative to a folding station, said second memory store having means for initiating a folding operation of said folding apparatus when the required length of workpiece has passed the folding station.

2. A control apparatus according to claim 1 further including tow pulse-shaping circuits each comprising a Schmitt trigger stage followed by a monostable multivibrator for producing a train of constant width, constant height pulses at a rate proportional to the velocity of the flat workpiece, the output of said transmitter units being fed to said pulse-shaping circuits respectively, and means respectively connecting said pulse-shaping circuits with said first and second memory store.

3. A control apparatus according to claim 1 wherein each of the first and second memory stores is an electronic circuit and comprises at least one storage capacitor, each storage capacitor being connected to its associated transmitter through a resistance, the arrangement thus forming a resistance-capacitor circuit.

4. A control apparatus according to claim 1 wherein the means for transferring at least part of the signal originally stored in the first memory store to the second memory store comprises a switch, arranged when in its closed position to connect the tow stores in parallel, with or without the association of other circuit elements to govern the ratio of said storing.

5. A control apparatus according to claim 1 wherein a third memory store is provided together with means for dividing or transferring any remaining signal stored in said first memory store after the original information has been transferred to the second memory store, whereby a can folding initiated be by said third store for further folding of the workpiece. transmitting

6. A control apparatus according to claim 1 wherein a third memory store is provided together with means for dividing the original information transferred from the first memory store between the second and third memory stores whereby further folding operations can be initiated by said third memory store.

7. A control apparatus for use with a machine for folding a flat workpiece which includes conveyor means for carrying a flat workpiece between a sensing station and a folding station, the control apparatus comprising, a detector and transmitter means including a feeler switch, a toothed wheel and a photocell for detecting and transmitting the length of a workpiece as it travels on the conveyor means and for transmitting a signal corresponding to the length of the workpiece, a pulse-shaping circuit means for receiving a signal from said detector and transmitter means, and R-C memory storage means for receiving a signal from said pulse-shaping circuit means, a second capacitor, a switch means for transferring at least part of said signal from capacitor, first capacitor to said second capacitor, a second transmitter means including rotatable shaft operatively connected to said conveyor means to transmit to said second capacitor a further and cumulative signal corresponding to part of the length of said workpiece after the workpiece has left said sensing station, and means including said second capacitor for initiating a folding operation on the workpiece when the workpiece is in proper position at the folding station.

8. A control apparatus as defined in claim 7 further including means for discharging said first capacitor after said part of said signal is transferred from said first capacitor to said second capacitor for permitting said first capacitor to receive subsequent signals from said pulse-shaping circuit in response to the passage of a subsequent workpiece by said sensing station.