GB2092755A - Detecting electrically the stopping of a moving element - Google Patents

Abstract

A system for detecting the stopping of a normally moving machine component, e.g. a flywheel (3) of a press, in which the like outputs of at least two pulse transmitters (1, 2) are connected together and after passing through separate channels (13, 14) are connected to an AND- gate 15 whose output indicates stopping of the flywheel. In Fig. 1 (not shown) the two channels (13, 14) terminate in relays whose contacts are connected in series to constitute an AND-gate. The two channels (13, 14) are used for the purposes of detecting any relative displacement of the transmitters (1, 2). <IMAGE>

Description

SPECIFICATION Monitoring of stoppages The invention relates to a circuit arrangement for detecting the stoppage of moved machine components and for the positional control of the pulse transmitter signalling the stoppage. The invention may be used in particular for the monitoring of the flywheel of presses.

A circuit arrangement for monitoring stoppages is known from the German Auslegeschrift 1 925 137, in which the rotary movement is converted into electrical square pulses and the oscillations of an oscillator stage break down in accordance in each case with the position of the gear wheel and then build up again.

In order to enable the required switching function, the pulses are converted into needle pulses in a differentiating element.

The needle pulses control a saw-tooth generator which comprises a capacitor and a charging device. In the case of stoppage the needle pulses cease and lead to maximum voltage at the capacitor, so that the subsequent trigger is connected through. The pulse transmitted in this respect directly or indirectly connects through a relay stage connected downstream. Between the oscillator stage and the remaining parts of the circuit there is provided an AND-network to which two additional lines are supplied from the oscillator device as a safety device.

In addition a stoppage monitoring circuit is known from the DD-WP 131 057, in which square pulses are produced from the rotary movement and the inverse pulse frequency is taken in each case from two timer elements connected downstream and supplied to two Z-diodes, i.e. L and 0 signals are alternately in contact with the timer elements and therefore the Z-diodes.

In the case of rotation the voltage at the capacitor adjacent to the timer elements is maintained below the Z-voltage of the Z-diodes. In the case of stoppage the capacitor is charged at the timer element connected via the L-signal via a resistance and triggers a switching function after reaching the Z-voltage of the Z-diodes via transistors by means of a electronic switch connected downstream.

In order to protect the machine a further transistor is provided, which is fully modulated in the case of a rotating shaft by the constantly flowing minimum current and which is cut off by discontinuation of the current flow in the case of interference.

In the case of error the output signal is cut off.

The known solutions do not take into account any error in the pulse detection, are very complicated in construction and do not detect any defective conditions arising through undesired positional variations of the transmitter and inductive initiator for the directional disc.

This could for example lead to a case in which the stoppage signal is transmitted, although the flywheel is still rotating. If in this case a creep drive is included, this may lead to its destruction.

The aim of the invention is to provide a reliable stoppage monitoring system the use of which, substantially reduces the risk of damage.

The object of the invention is to construct a stoppage monitoring circuit in such a way that the safety of the stoppage detection is ensured with the least expenditure cwjn in the case of undesired positional variations of the pulse transmitter.

In accordance with the invention equivalent outputs of at least two puise transmitters connected in parallel are in AND-connection with a dynamic monitoring circuit, the antivalent outputs of the same pulse transmitters being in AND-connection with a static monitoring circuit, these being used to control the machine. In a further embodiment the dynamic monitoring circuit comprises a pulse former, an integrating element, a threshold value switch, a signal delay and a relay and the static monitoring circuit comprises an integrating element and a relay.

In the case of connection of this stoppage monitoring to an electronically controlled machine the output is connected in each case with the input of an AND-gate in the case of the dynamic monitoring circuit comprising a pulse former, an integrating element, a threshold value switch and a signal delay and in the case of a static monitoring circuit comprising an integrating element. The machine is controlled via an electronic evaluation circuit connected to the AN D-gate.

The invention will now be described, by way of example only, with reference to the two preferred embodiments shown in the drawings, in which: Fig. 1: schematic illustration of a stoppage monitoring circuit with conventional evaluation.

Fig. 2: schematic illustration of a stoppage monitoring circuit with electronic evaluation.

FIRST EMBODIMENT Fig. 1 shows a circuit arrangement of the invention comprising two pulse transmitters 1, 2 and two different evaluation circuits, i.e. a dynamic monitoring circuit 13 and a static monitoring circuit 1 4. The dynamic monitoring circuit 13 comprises a pulse former 4, an integrating element 5, a threshold value switch 6, a signal delay 7 and a relay 8 with the closing contact 12.

The static monitoring circuit i 4 comprises an integrating element 10 and an output relay 9 with the closing contact 11.

The control disc 3 is rigidly fixed to the flywheel of a press for example. The number of control lugs on the control disc 3 is dependent on its dimensions, the minimum width of the control lugs and the maximum rotation of the flywheel to be monitored.

The arrangement of the pulse transmitter 1, 2 with respect to the control disc 3 is such that the spacing of the pulse transmitters 1, 2 with respect to one another and the dimensions of the control lug gaps is equal. In this way it is achieved that at least one of the pulse transmitters 1, 2 is activated by a control lug.

The equivalent outputs of the pulse transmitters 1, 2 are connected in parallel and are connected on the input side with the dynamic monitoring circuit 1 3 and the antivalent (opposed or non linked) outputs of the pulse transmitters 1, 2 are connected in parallel and are connected to the static monitoring circuit 14.

The dynamic monitoring circuit 1 3 has the following function: in the case of movement of the flywheel to be monitored pulses are transmitted from the equivalent outputs Xl , X2 of the pulse transmitters 1, 2 to the pulse forming stage 4.

The square pulses produced in a known manner from the pulse forming stage 4 are supplied to an integrating element 5 which in turn controls a threshold value switch 6. The threshold value switch 6 cuts off the relay 8 connected downstream.

In the case of stoppage of the flywheel to be monitored no pulses are transmitted from the pulse transmitters 1, 2 to the pulse forming stage 4, the threshold value switch 6 moves into the output position and connects via the signal delay 7, which comprises an arrangement of capacitors with diodes and a trigger in a known manner, the relay 8 connected downstream with a time lapse.

The lower rotation limit at which the switching function is triggered is determined by the RC time constant of the integrating element 5.

The time delay of the switching function enables the transmission of a stoppage signal only after reaching stoppage.

Monitoring of the unchanged position of the pulse transmitters 1, 2 is carried out by the static monitoring circuit 14. The pulses of the antivalent outputs X1, X2 of the pulse transmitters 1, 2 are supplied to the integrating element 10 in order to prevent unreliable switching in the lower area of rotation.

The relay 9 is controlled by the integrating element 10 which leads to the desired static monitoring. As a result of the AND-connection of the contacts 11, 12 of the relay 8 and the relay 9 the switching function takes place. Both a static and a dynamic monitoring is therefore ensured.

SECOND EMBODIMENT The arrangement of the pulse transmitters 1, 2 with respect to the control disc 3 takes place analogously to the first embodiment. The output of the threshold value switch 6 is connected via the signal delay 7 to the input of an AND-gate 13 whose output controls an electronic evaluation switch 1 4.

As long as the portion to be monitored is still moving and the pulse transmitters 1, 2 are transmitting pulses to the pulse former 4, an 0signal is transmitted from the AND-gate 1 3 to the electronic evaluation switch 1 4.

In the case of stoppage of the portion to be monitored no pulses are transmitted from the pulse transmitters 1, 2 to the pulse forming stage 4, the threshold value switch 6 is not controlled by the integrating element 5 and moves back into its output position. After control by the signal delay 7 this L-signal is provided at the first input of the AND-gate.

In an unchanged position of the pulse transmitters 1, 2 one of the antivalent outputs Xl, X2 of the pulse transmitters 1, 2 supplies a further L-signal to the second input of the AND-gate 13 via the integrating element 10.

The output of the AND-gate 1 3 connected with the input of the electronic evaluation switch 14 supplies L-signals which leads to the desired switching function "stoppage".

The safety of the arrangement described with respect to the first embodiment is achieved in that in the case of defect at least one of the two relays 8, 9 is cut off and therefore the "stoppage-signal" disappears. The relay 9 is therefore cut off for example if an undesired positional change of the pulse transmitters 1, 2 has arisen.

The connection of the "stoppage signal" with the control of the machine must be constructed such that the activation of one or more drives is safely avoided in the case of defect.

The control of the evaluation switch 1 3 takes place in that the L-signal present in the case of stoppage of the flywheel to be monitored disappears after the activation of the drive or drives.

The connection of the "stoppage signal" with the machine must in addition also be such that the machine may only be operated after the disappearance of the "stoppage-signal".

The safety of the arrangement described with respect to the second embodiment is achieved in that in the case of defect at least one of the two inputs of the AND-gate 1 5 supplies Signal and therefore that an O-signal is also present at the input of the electronic evaluation switch 1 6.

The connection with the machine must be carried out in a similar manner to that illustrated for the first embodiment.

The described embodiments provide a circuit arrangement for the detection of the stoppage of moved machine components and for the positional control of the pulse transmitters signalling the stoppage, in particular for the monitoring of the flywheel of a press. The aim of providing reliable stoppage monitoring for the extensive prevention of damage is achieved by means of the AND-connection of the dynamic monitoring circuit 13 and the static monitoring circuit 1 4 which are controlled by at least the two pulse transmitters 1, 2 connected in parallel.

Claims (4)

1. A stoppage monitoring arrangement for detecting the stoppage of moved machine components and for the positional control of a pulse transmitter signalling the stoppage, in particular for monitoring the flywheel of a press, characterised in that equivalent outputs of at least two pulse transmitters connected in parallel are in AND-connection with a dynamic monitoring circuit and in that antivalent outputs of the same pulse transmitters are in AND-connection with a static monitoring circuit and control a machine via these.

2. A stoppage monitoring arrangement as claimed in claim 1, characterised in that the dynamic monitoring circuit comprises a pulse former, an integrating element, a threshold value switch, a signal delay and a relay and in that the static monitoring circuit comprises an integrating element and a relay.

3. A stoppage monitoring arrangement as claimed in claim 1, characterised in that the dynamic monitoring circuit comprises the pulse former, the integrating element, the signal delay, the threshold value switch and in that the static monitoring circuit comprises an integrating element, in that these are connected with two inputs of an AND-gate and in that the machine is controlled via an electronic evaluation circuit.

4. A stoppage monitoring arrangement substantially as herein described with reference to the accompanying drawings.