GB2140230A - Electrical/electronic control circuit - Google Patents

Abstract

The control circuit comprises a "start" push-button P1 having first and second poles to open or close, respectively, first and second pairs of contacts C3, C4; a "stop" push-button P2 having a pole adapted to open or close a third pair of contacts C2, a diode pump circuit comprising a pump capacitor CA capable of discharging stored energy into a relay RA via, and upon closing of, the second contact pair C4, when the "start" push-button P1 is activated by the machine operator, and a contact RA/1, momentarily closable by a pulse from the relay RA, to energise a pilot relay (R) of a gate end box (B) and thereby make the main power supply available to the machine. Thus, activation by the machine operator of the "stop" push-button P2 is effective to stop the machine irrespective of the position of the "start" push-button P1. The machine may be a mining machine. <IMAGE>

Description

SPECIFICATION Electrical/electronic control circuit This invention relates to an electrical/electronic control circuit for detecting the condition of a "start" push-button of electrical machinery or electrically driven machinery, such control circuit forming part of a pilot circuit for connecting or disconnecting a main electrical power source to the machinery in question.

Such machinery may for instance be a mining machine, conveyor etc. Considering the mining machine example, a standard configuration is to locate certain elements of the pilot circuit remotely from the machine in what is known as a gate end box, these elements comprising inter alia, a relay and a capacitor, with pilot lines extending from the gate end box to the mining machine where there is located other elements of the pilot circuit comprising, inter alia, a "start" push-button and a "stop" push-button. In fact a standard circuit of the National Coal Board, operating as above described, is known as the P 1 30 pilot circuit and is used for controlling the start-up of mining machines, often incorporating electric motors of 400 H.P. or more, or a conveyor of the scraper chain or belt type.With this circuit, the pilot relay in the gate end box is energised by pressing the "start" push-button on the mining machine, and once energised, the pilot relay is maintained through a resistor, usually 30R, bridging the contacts of the "start" push-button and a diode. When the pilot relay has been energised in this manner, the main electrical power supply is available to the machine, and machine start-up will occur.

However, it is not uncommon for the "start" push-button to become stuck in the closed position. The result is that after initiating a stop sequence, by pushing the "stop" push-button to open a pair of contacts, the machine would stop, but would inadvertently re-start immediately the "stop" push-button was released and consequently returned to its contact closing position. It will be appreciated that this is a potentially difficult situation and a known solution is to incorporate a relatively complex prevention of inadvertent start (POIS) circuit within the gate end box. However, POIS circuits are not readily adaptable and are far from being in universal use in British coal mines, which is due in part to cost and to the complication that they introduce into the otherwise simple P 1 30 pilot circuit.

The object of the present invention is to provide an electrical/electronic control circuit for detecting the condition of a "start" push-button of an electrical machine, which circuit may be carried by the machine and which does not require any modification to a basic P 130 pilot control circuit.

According to the present invention, there is provided an electrical/electronic control circuit for detecting the condition of a "start" push-button of electrical machinery, comprising a "start" pushbutton having first and second poles to open or close, respectively, first and second pairs of contacts; a "stop" push-button having a pole adapted to open or close a third pair of contacts, a diode pump circuit comprising a pump capacitor capable of discharging stored energy into a relay via, and upon closing of, the second contact pair, when the "start" push-button is activated by the machine operator, and a contact, momentarily closable by a pulse from the relay, to energise the pilot relay of the gate end box and thereby make the main power supply available to the machine, with activation by the machine operator of the "stop" push-button being effective to stop the machine irrespective of the position of the "start" push-button.

Thus, by adopting the circuit in accordance with the invention, due to the momentary closing of the contacts, the pilot circuit is unable to remain energised through the "stuck in start" push-button contacts.

The invention will be described in greater detail with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic drawing of a standard P130 pilot circuit, and Figure 2 illustrates a circuit in accordance with the present invention.

Considering Figure 1, the pilot relay R in the gate end box B is energised by the machine operator pressing the "start" push-button P 1 to close the contacts Cl, with a 30R resistor R1 bridging the contacts Cl, so that once energised, the pilot relay R in the gate end box B is maintained through R1 and a diode D. The main electrical power supply is then available to the machine involved. The circuit also includes a "stop" pushbutton P2 normally closing contacts C2. When it is required to stop the machine, the machine operator presses P2, to open the contacts C2.However, if P1 is stuck in its start position i.e. closing the contacts Cl, then immediately the operator releases P2, this will revert to a position in which it closes contacts C2, thereby automatically causing re-start of the machine. This effect can be obviated in a simple manner by employing the circuit in accordance with the invention shown in Figure 2.

Considering Figure 2, the circuit incorporates a two-pole "start" push-button, with one pole being adapted to open or close contacts C3 and the other pole being adapted to open or close contacts C4. The circuit further incorporates a diode pump circuit comprising a resistor RX, a diode D1 and a pump capacitor PC. The circuit also incorporates a relay RA and a momentarily closable contact RA/1. Upon the machine operator pressing the "start" push-button Pl,energy stored in the pump capacitor PC is discharged via the contacts C4 after closure of their contacts by the second pole of P1. This action pulses in relay RA, momentarily closing contacts RA/1, which in turn with the closed condition of the first pole of P 1 closing the contacts C3, energises the pilot relay R in the gate end box B, as described with respect to Figure 1.

If the "start" push-button P1 malfunctions by sticking in its start condition, i.e. closing the contacts C3 and C4, then upon the machine operator pressing the "stop" push-button P2 to open the contacts C2 to stop the machine, then the release of P2 and the consequent closing the contacts C2 does not result in machine re-start, because the pilot circuit is unable to become reenergised due to contacts RA/1 being open, the effect of the 30R resistor, and the fact that the capacitor is discharged.

It will be appreciated that the components RX, D1 and PC, forming the diode pump circuit, derives power from the incoming pilot line and earth, and thus no additional power supply is required to obtain a fail safe method of detecting a "stuck in start" push-button condition.

Furthermore, the entire circuit in accordance with the invention can be manufactured to sufficiently small dimensions for mounting on a standard push-button unit.

Claims (3)

1. An electrical/electronic control circuit for detecting the condition of a "start" push-button of electrical machinery, comprising a "start" pushbutton having first and second poles to open or close, respectively, first and second pairs of contacts; a "stop" push-button having a pole adapted to open or close a third pair of contacts, a diode pump circuit comprising a pump capacitor capable of discharging stored energy into a relay via, and upon closing of, the second contact pair, when the "start" push-button is activated by the machine operator, and a contact, momentarily closable by a pulse from the relay, to energise the pilot relay of the gate end box and thereby make the main power supply available to the machine, with activation by the machine operator of the "stop" push-button being effective to stop the machine irrespective of the position of the "start" push-button.

2. A circuit substantially hereinbefore described with reference to Figure 2 of the accompanying drawings.

3. A mining machine provided with a circuit as defined in Claim 1 or Claim 2.