GB2141855A - Temperature monitoring system for hot-glueing equipment and installations - Google Patents

Abstract

In hot-glueing installations and equipment, the problem frequently arises that the adhesive or the commodity to be stuck is damaged by a faulty operation of the regulator which controls heating of the glue or faulty operation at another place in the closed-loop control. The invention therefore provides a monitoring system which ascertains the correct operation of the closed-loop control by monitoring the switching frequency of the regulator within certain periods of time and delivers an error signal if a certain minimum number of switching operations is not reached.

Description

SPECIFICATION Temperature monitoring system for hot-glueing equipment and installations The invention relates to a temperature monitoring system for hot-glueing equipment and installations, having a heating closed-loop control with a two-step regulator.

Such temperature monitoring systems are particularly important in hot-glueing equipment and installations because only when the temperature is kept within a preset range can the adhesive be applied in the optimum manner and a connection be achieved which is reliable in the long term.

In practically all temperature closed-loop controls, after the heating up, the required temperature is adjusted by reducing the average power to the value which is necessary to adhere to the required temperature. This is possible, for example by quasicontinuous voltage adjustment (for example operating-angle control in regulators with continuous output signal). Generally, however, the power reduction is effected by adjusting the period of switching on. This is done by electronic two-step regulators, bimetal switches, liquid expansion regulators and so on. These are used, in particular, for slow controlled systems, that is to say controlled systems with heating-up times from minutes to hours.

In conventional systems it is a disadvantage that if the regulator is switched through permanently, too high or too low temperatures may be set over periods of time, for example as a result of sticking of the contacts, detachment of the temperature sensor or a regulator defect or permanent switching off, for example as a result of sensor breakage, burning away of the contacts, line fracture etc., in which periods of time damage may occur to the adhesive or to the goods to be stuck.

The invention therefore provides a temperature monitoring system for hot-glueing equipment and installations having a closed-loop control comprising a two step regulator, whereby such damage can be largely avoided.

According to the invention, this is achieved by a device which monitors the number of switching operations of the two-step regulator in preset periods of time and delivers an error signal on a drop below a minimum number.

The solution according to the invention has the advantage, in particular, that the operation of the two-step switch is continuously monitored. During normal operation of the installation, with correct operation of the two-step regulator, a certain switching frequency can be presupposed. If an adequate number of switching operations does not appear in one period of time, then it can be assumed, in the first instance, that the two-step regulator is disturbed or that there is a disturbance in the whole system.

The period of time is timed according to the requirements of the particular equipment or installations. Particularly if the criterion is the dropping below a relatively high number of switching operations, the period must not be too long in order to avoid an erroneous averaging, for example in the event of numerous switching operations appearing at the beginning of the period and the complete absence of switching operations at the end of the period.

A plurality of such periods may appropriately follow directly one on the other in order to cover the regular operating time (possibly excluding the heatup time). The periods do not need to be equal in length, in particular, the length of a period may depend on the switching operations which have taken place in it but also on the length of the preceding periods.

The number preferably amounts to one and with the appearance of a switching operation in one period of time, the device allows another preset period of time to begin.

Here, therefore, there is a case where the length of the period depends on the switching pulses appearing in it. This further development has the advantage, in particular, that a fixed time of not switching is associated with the appearance of an error. If the periods of time were fixed and if the following period began each time only with the end of a complete period preceding it, then the response time to no switching could fluctuate between the length of a period and practically the lengths of two periods according to whether a signal, assumed to be single, in the immediately preceding period lay right at the beginning or right at the end. In addition, this solution permits a particularly favourable construction as regards circuitry.

Naturally, the length of the following period may again be determined depending, for example, on the length of the preceding period broken off by the appearance of a switching pulse.

Preferably, the device comprises a means for detecting a switching operation and a counter which can be reset and the means detecting a switching operation delivers a reset signal to the counter on detecting a switching operation and the counter delivers the error signal on reaching a preset number of its counting pulses.

In this manner, the operation according to the invention can be realized particularly simply. The error signal may appropriately be the capacityexceeding signal of the counter and the preset number may be the, possibly adjustable, maximum number which can be counted before the capacity is exceeded.

Preferably, the means detecting a switching operation comprises a rectifier to which the heater voltage of the monitored equipment is applied and which produces a rectangular signal, the higher level of which corresponds to a switched-on heater voltage and the lower level of which corresponds to a switched-off heater voltage, and a differentiating memberforthe rectangular signal, the signal of the differentiating member serving as a reset signal.

This form of embodiment is particularly advantageous because a conclusion regarding the operation of the closed-loop control, particularly of the two-step switch, can be drawn from the application or non-application of the heater voltage. The flanks formed during the switching on or off become brief pulses through the differentiation, which pulses can well be used as a reset signal.

Preferably connected between the rectifier and the differentiating member is an opto-coupler which prepares the signal from the rectifier as a potentialfree rectangular signal. This has the advantage, in particular, that the signal thus formed can be more easily further processed.

Preferably only the signal corresponding to the switching off of the heating is evaluated as a reset signal. This has the advantage, in particular, that no reversal of the one signal need be effected because the differentiation of the trailing edge of the rectangular signal supplies a signal with uniform polarity.

The use of the switching-off signal only is also sufficient because failure of the switching off alone indicates an error source.

Preferably, a plurality of installations and/or a plurality of places in an installation are monitored and the error signals of each installation and/or of each place are transmitted, via an OR element, to a mains switch for all the installations, to switch off the mains switch. This has the advantage, in particular, that all the installations and/or places are switched off until the fault is found and rectified and so further damage can be avoided.

Preferably, the preset number of counting pulses of the counter is selected different in different channels. As a result, an individual adaptation of the error indication to the circumstances of the individual installations or at various points of equipment can be achieved.

Preferably, the error signal is blocked until the first switching-off of the two step regulator or until the first switching off of the last of a plurality of two-step regulators. Since the response times are generally considerably longer than the following switching times for the adjustment, erroneous error signals are thus avoided.

The invention is explained in more detail below in a preferred form of embodiment with reference to the accompanying drawings in which: Figure 1 shows a diagrammatic block circuit diagram of a system according to the invention; and Figure 2 shows the pulse shapes at various parts of the circuit at different times.

In Figure 1,a monitored installation 1 is supplied with an alternating voltage through connection terminals 2 and 2'. The line 4, 4' can be separated from the mains by a mains circuitbreaker 6 by means of switch contacts 8, 8' illustrated diagrammatically.

The monitored installation 1 is connected, via a measuring lineiO,toatwo-stepregulatori2which can open or close the contacts 16, 16' through diagrammatically illustrated final control elements 14,14' and so can supply heater power to the monitored installation 1 or cut it off therefrom.

At the installation side, a current supply for other parts of the installation, for example conveyor belts or the like, can be taken off after the contacts 8, 8' controlled by the mains circuit-breaker 6 and before the contacts 16, 16' controlled by the two-step regulator 12. This is not shown here, however.

Nevertheless, the voltage for othertemperature monitored parts of the installation is taken off at this point, as will be explained below.

The voltage at the heating to be monitored in the installation 1 is applied to a rectifier 20, for example a diode, through a series resistor 18. Thus the signal A shown in Figure 2A appears at the rectifier 20.

As a result of the rectification by means of the rectifier 20, filtering by means of a filter section 22 and the transmission through an opto-coupler 24, a potential-free rectangular signal B results as can be seen from Figure 2B.

Signals C, such as are illustrated diagrammatically in Figure 2C, are produced by a differentiating member 26.

The signals are transmitted to the reset input Rs of a counter 28. The counter counts, through an input not shown, pulses of an oscillator not shown. If the counting of the counter reaches a predetermined value, a signal which acts as the error signal is delivered through a capacity-exceeding output U.

Only the negative signals C2 act on the reset input. The counter 28 is a 2-decade counter which, beginning from 0, counts upwards after each reset signal at the timing frequency of the oscillator (not shown). If the reset signal drops out as a result of one of the faults mentioned at the beginning, then the counter, on reaching 100 pulses, switches on a circuit with a thyristor and a light-emitting diode which is preferably red. The light-emitting diode serves as an error indication for the person monitoring the installation. At the same time, through an OR element, the mains circuit-breaker 6 is controlled which opens the contacts 8,8' and so separates the installations and/or places in an installation, connected behind the contacts 8, 8' seen from the terminals 2, 2', from the mains.The error indication 30 and the mains contact-breaker 6 may appropriately be provided with their own voltage supply (not shown) so that they can continue their operation even after the installation has been disconnected from the mains.

Since, as indicated by the separation in broken lines in Figure 2B, the heating-up time may take a longer period of time in comparison with the usual regulating times, a separate circuit 32 may appropriately be provided which, as indicated in Figure 1,for example through flip-flops 34, stores the first negative signal of the differentiating member 26 and transmits it to an AND element 36 to which the corresponding signals of other monitored places, which are likewise stored, are transmitted. After all the first switching-off signals have been received, the component 32 actuates a switch 40 which then connects the overflow U of the counter 28 to the input of the warning and switching-off circuit 30.

As indicated by the boxes 3,...9,11 in Figure 1, there may possibly be a plurality of installations or a plurality of places in an installation, which are connected behind the same mains switch 8,8', particularly if it is a question of a plurality of places in one installation. Each of the channels contains the components shown in detail for the monitored place 1. They transmit signals to the common OR element 36 and to a common AND circuit 32 which then controls the contacts after the counters in the particular channels 3,...9,11, beyond the contact 40 shown, or to AND circuits provided separately for each of the channels, but now shown, so that an error signal can only appear if the particular heating means for each monitored place have been switched off once.Greater security is, however, preferably achieved as a result of the fact that the counters in the particular channels can be switched over so that the period in which the first switching-off signal should fall is selected correspondingly longer in orderto make allowanceforthe heating-uptime.

In a practical example of embodiment, an overall monitoring system monitors six temperature closedloop controls. In this case, two closed-loop controls are controlled with monitoring times (periods of time) of five minutes and four closed-loop controls with monitoring times (periods of time) of two minutes. This is because a thermoplastic adhesive application system to be monitored has two temperature regions, namely the pre-melting zone and the main melting zone, with relatively long regulating cycles (because of the large volume and the satisfactory insulation) and four further regions, namely flexible pipes and nozzles, with relatively short regulating cycles.

A regular operation of the installation may possibly be indicated by green light-emitting diodes, not shown.

The operation of the system will now be explained with reference to the time lapse diagram of Figure 2.

With the switching on of the system through closing of the contacts 8,8', the regulator 12, supplied with current from the lines 4,4' through branches, detects too low a temperature through the measuring line 10 and, at the time ta, causes a closing of the contacts 16 and 16' by means of the final control elements 14, 14' and hence an application ofthe heater voltage to the heater voltage inputs of the monitored place 1.

At the time to, the counter 28, which is controlled by the pulses of an oscillator not shown and which is supplied from a separate current source, not shown, begins to count and the first counting period designated byT1 begins. At the moment ts, the regulator 12 detects a temperature which allows it to open the contacts 16. The heater voltage UN applied to the heating means of the place 1 to be heated, from the moment t1 to the moment t3, is converted, through the resistor 18, the rectifier 20, the filtersection 22 and the opto-coupler 24, into the rectangular pulse D shown in the corresponding period of time in Figure 2B. The differentiation of its edges leads to the signals shown in Figure 2C.

Since the heating-up time was, however, presupposed to be longer than the otherwise undisturbed period Tor, the counter 28 overflows during the heating-up time and produces the signal D shown in Figure 2D. This signal is not passed on to the warning and interrupting circuit 30 because of the switch 40 which is still open until the first switchingoff signal. At the same time, a new counting period T2 begins as a result of the overflow. The end of this period T2 would be between t4 and t5 as indicated in broken lines over the straight time lines in Figure 2.

The negative pulse of Figure 2C obtained from the descending edge of the rectangular pulse at the time t3 acts on the reset input Rs of the counter 28, however and allows a new counting period T3 to begin. Thus a switching-off pulse has been detected in the counting period T2 and this allows a new counting period to begin. This first reset pulse is transmitted, via a diode serving to suppress the positive pulses from Figure 2C, to the set input of a flip-flop of a series of flip-flops 34. Its positive output signal is transmitted to the AND gate 38 as are the output signals of the other flip-flops in the series 34, which flip-flops belong to other heated and temperature-monitored places in the installation. It will be assumed that the other flip-flops have already been set.Then the output of the AND gate 38 is switched to 1 by the negative signal C and closes the contacts 40.

At the moment t4, which may still lie within the period ofT3, the temperature at the place 1 may have dropped to such an extent that the regulator 12 again applies the heater voltage. As a result of rectification and differentiation, the signal C in Figure 2C appears at the moment 4 and on the switching off, the signal C in Figure 2C at the moment t5, which still lies in the period T3 indicated in broken lines above the straight time line and beginning att3. This negative signal now resets the counter 28 and so allows a new counting period T4to begin at the momentt5. Within the counting period T4, another switching-on and a switching-off operation taken place at t5 and t7 respectively.The switching-off operation allows a fresh period T5 to begin at the moments7.

Now let it be assumed that no further switching-off signal appears within the total duration of this period T5. Thus the period T5, not being shortened by an switching-off signal, ends with the overflow of the counter at the moment t8. Thus a fresh signal D appears at the moment t8, as shown in Figure 2D, and now reaches the warning and interrupting circuit 30 via the closed contacts 40, as the disturbance signal shown in Figure 2E, at the moment t8.

There the signal controls a thyristor which opens and, through the current flowing through it, causes a red light-emitting diode indicated diagrammatically in the block 30, to light up. Furthermore, the signal is transmitted through the OR gate 36 to the switch 6 which opens the contacts and disconnects the regulator and the mointored place 1 of the installation as well as all further channels, that is to say the monitored places with their associated regulators etc., from the mains voltage. Naturally, the circuit 30 may appropriately remain supplied with voltage in order to be able to give an indication, through the light-emitting diode, of the place where a fault has arisen.

On switching-on or re-switching-on after elimination of a fault, suitable resetting devices ensure the resetting of the flip-flops 34 for example, as a result of which the contacts 40 are opened again.

Claims (10)

1. A temperature monitoring system for hotglueing equipment and installations having a heating closed-loop control with a two-step regulator, including a device which monitors the number of switching operations of the two-step regulator in preset periods of time and delivers an error signal on a drop below a minimum number.

2. A system as claimed in Claim 1, wherein the minimum number is one and with the appearance of a switching operation in a period of time, the device breaks this period of time off and allows a further preset period of time to begin.

3. A system claimed in Claim 1 or 2, wherein the device comprises a means for detecting a switching operation and a counter which can be reset, and the means for detecting a switching operation delivers a reset signal to the counter on detecting a switching operation and the counter delivers the error signal on reaching a preset number of counting pulses.

4. A system as claimed in Claim 3, wherein the means for detecting a switching operation comprises: a rectifier to which the heater voltage applied to monitored equipment or some part thereof is applied and which produces a rectangular signal, the higher level of which corresponds to a switched-on heater voltage and the lower level of which corresponds to a switched-off heater voltage, and a differentiating member for the rectangular signal, the output of which supplies the reset signal.

5. A system as claimed in Claim 4, wherein connected between the rectifier and the differentiating member is an opto-coupler which prepares the signal from the rectifier as a potential-free rectangular signal.

6. A system claimed in any one of the preceding claims, wherein only the signal corresponding to the switching off of the heating is evaluated as a reset signal.

7. A system as claimed in any one of the preceding claims, wherein a plurality of installations and/or a plurality of places in an apparatus or an installation are monitored and the error signals of each installation and/or each place are supplied via an OR element to a mains switch at leastforthe closed-loop control or controls of the equipment or the plants, to switch off the mains switch.

8. A system as claimed in Claim 7 when dependent on Claim 3, or on any one of Claims 4 to 6, wherein the preset number of counting pulses of the counters is selected differently in different channels.

9. A system as claimed in any one of the preceding claims, wherein the error signal is blocked until the first switching off of the two-step regulator, or until the first switching off of the last of a plurality of two-step regulators.

10. Atemperature monitoring system substantially as hereinbefore described with particular reference to the accompanying drawings.