GB2098769A - Constant attendance system - Google Patents

Abstract

This intention relates to a constant attendance system for use in the control of machinery. The invention provides a system which is necessary to operate a constant attendance switch 4 at regular time intervals. The switch must be operated when a signal such as a light 6 is active. If the switch is not operated and released the machinery is caused to stop by the action of timing devices TR2, TR3 whose actions are controlled by the switch. The system operation is initiated by actuation of a dead man handle 3 and with the switch 4 in a first position, a first timer TR1 is activated to close a relay contact 5 after a delay to activate a second timer TR2 and a lamp or an audible device 6. The switch 4 is then depressed to reset the timers TR1, TR2 and to extinguish the lamp. The switch 4 is alternately depressed and released before the respective timing period of TR2, TR3 to prevent system shutdown by respective relays 7, 8. <IMAGE>

Description

SPECIFICATION Constant attendance system The present invention relates to a constant attendance system, and in particular, but not exclusively, to such a system for use in conjunction with a dead man handle.

In the operation of many pieces of machinery, it is required that an operator should always be in control of the machinery so that it can be stopped if a hazardous situation arises. To ensure constant surveillance, such machinery is commonly fitted with a dead man handle which the operator is supposed to hold in its "on" position. If the operator leaves the control, the dead man handle should automatically return to the "off" position to stop the machinery. A well known example of the use of a dead man handle is on railway or underground trains. If the driver is taken ill or otherwise rendered unable to control the train, the dead man handle should go to the "off" position and bring the train to a halt. There are many other areas in which the use of dead man handles is common for the control of potentially dangerous machinery.

It has been known for some time that the effect of a dead man handle can be overcome, either accidentally or deliberately, by jamming the handle in the "on" position, thus enabling the machinery to operate unattended. It is an aim of the present invention to provide a constant attendance system which overcomes, at least in part, the disadvantages of the use of dead man handles.

Therefore, according to the present invention, there is provided a constant attendance system, for use in the control of machinery, comprising a first timing device and a signal which are activated when the machinery is started, a manually operable switch biased to remain in a first position, and a second timing device, the system being arranged such that when the switch is put manually into a second position the second timing device is activated and the first timing device and signal are deactivated, when the switch is allowed to return to its first position the first timing device and the lamp are reactivated and the second timing device is deactivated, and the timing devices deactivate the machinery if either of the timing devices is not deactivated before a time preset on the relevant device has elapsed.

Preferably, the first timing device and the signal are not activated immediately on starting the machinery. A delay may be introduced by including a third timing device which activates the first timing device and the signal. The system should be arranged such that placing the switch in its second position deactivates the third timer.

The timing devices must be reset either when they are deactivated or reactivated. They may be electrical or mechanical timers and should be associated with relays or switches which can cause the machinery to stop. Preferably the timing devices include transistorised or microchip circuitry, although they may also be a part of a computer system which mediates the operation of the other parts of the machinery. The timing device used should be selected to be compatible with the type of control system used. The machinery may be caused to stop by any appropriate means. For instance the system may cause a relay to interrupt electrical power to the machinery, or may cause a relay to operate a mechanical device which stops the machinery.

The signal may be an audible signal, a lamp, an illuminated display on a panel or liquid crystal display, or any combination of these. The signal may be continuous or interrupted. Preferably the signal is aflashing lamp.

The setting of the time intervals on the timing devices will need to be arranged to suit the particular machinery being operated, and may vary from a few seconds to a few minutes.

The system is preferably used in conjunction with a dead man handle so that the machinery is stopped immediately if the operator is incapacitated. However an advantage of the system is that it can be used in piace of a dead man handle. A control station may be provided with a constant attendance switch which is a part of the system and a manual "panic" button for operation by the person attending the control station. Thus, if the person observes a hazardous situation he can manually stop the machinery using the "panic" button but if he is taken ill or leaves his post, the system according to the present intention will stop the machinery automatically.

The present invention will now be illustrated by way of exampie only, with reference to the accompanying drawings, in which: Figure 1 shows a circuit diagram of a constant attendance system according to the present invention; and Figure 2 shows an alternative circuit diagram.

Referring now to Figure 1, the constant attendance system is shown located between power supply 1 and power output 2. The system includes a dead man handle 3 and a constant attendance monitor switch 4. The dead man handle 3 is biased to remain in the "off" position and should be manually held in the "on" position against the bias. The switch 4 is biased to remain in a first position in which, when the dead man handle 3 is held in the "on" position, voltage is supplied to a first timer TR1. With the switch 4 in the first position voltage is also applied across a line including in series a first relay 5 operated by timer TR1, an indicator lamp 6 and a second timer TR2. With the switch 4 in its second position voltage is supplied to a third timer TR3.

Both relays 7 and 8 associated with timers TR2 and TR3 respectively are included in series with the power output 2.

The timer TR1 and its associated relay 5 are arranged such that after a preset time has elapsed from the manual operation of the dead man handle 3, the relay 5 is closed, thereby activating the lamp 6 and the second timer TR2. If the switch 4 is not operated after a preset time has elapsed from the activation of the lamp 6 the relay 7 disconnects the power output 2 from the power supply 1. If the switch 4 is operated before the preset time on the second timer TR2, timer TR3 is activated and timers TR1 and TR2 are reset and deactivated. If after a preset time has elapsed from the operation of the switch 4, the switch has not been released, the relay 8 disconnects the power output 2 from the power supply 1. If before the preset time has elapsed after the operation of the switch 4, the switch is released timer TR3 is reset and deactivated and timer TR1 is reactivated.

In a particular embodiment it is envisaged that the preset times should be 20 seconds for timers TR1 and TR2 and 10 seconds for timer TR3. In this case, the sequence of operations for continuous operation of machinery 9 will be as follows.

1. Activate machinery by operation of dead man handle 3 2. After 20 seconds lamp 6 is activated 3. Within the next 20 seconds switch 4 is operated 4. Within the next 10 seconds switch 4 is released 5. Back to step 2 Thus if the dead man handle 3 is released, the switch 4 is not operated or the switch 4 is jammed in its second position, the power supply is disconnected from the power output 2. Thus a person must be in constant attendance atthe control station in order to operate the switch 4 at regular intervals.

The above described embodiment is clearly only one of many possible circuits which use conventional timers and relays and that can fulfil the function of a constant attendance system according to the present invention. For instance, the dead man handle may be replaced by a normal switch with an emergency cut off switch in series.

Referring now to Figure 2, there is shown an alternative circuit which is designed to use transistorised components. This circuit may be embodied on a printed circuit board or may be incorporated into a microchip in conventional manner. The components used are not in themselves novel and so no particulay types of component has been specified since the choice of components will be made by a competent electronics engineer.

The main control line of the circuit comprises a dead-man handle 10, an inverter 11, a "nor" gate 12, an amplifier 13, a triac 14 and a safety contactor circuit 15. The circuit 15 mediates the operation of the machinery in such a manner as to stop the machinery if the dead-man handle 10 is released or if switch 16 is not operated correctly.

The action of the "nor" gate 12 is mediated by two timers 17 and 18, whose states are controlled by the switch 16 through a first contact anti-bounce filter 19. The switch 16 also controls, through a second contact anti-bounce filter 20 a third timer 21, a second amplifier 22 and a signal light 23.

The circuit is arranged such that when switch 16 is operated timers 17 and 21 are switched from high to low state and return to high state after a preset time.

The timer 18 is switched from low to high state and after a preset time switches back to high state. The time intervals set on the timers in the present embodiment are 15, 5 and 10 seconds for timers 17, 18 and 21 respectively. Thus if the switch 16 is not operated and released within a given period after the light 23 has been activated, the contactor circuit 15 stops the machinery.

The present invention therefore provides a constant attendance system which eliminates at least in part the possibility of jamming a dead man handle and enabling an operator to leave his control station.

Claims (4)

1. A constant attendance system, for use in the control of machinery, comprising (a) a first timing device and a signal which are activated when the machinery is started, (b) a manually operable switch biased to remain in a first position, and (c) a second timing device, the system being arranged such that when the switch is put manually into a second position the second timing device is activated and the first timing device and signal are deactivated, when the switch is allowed to return to its first position the first timing device and the lamp are reactivated and the second timing device is deactivated, and the timing devices deactivate the machinery if either of the timing deices is not deactivated before a time preset on the relevant device has elapsed.

2. A system according to claim 1, and including a third timing device which delays the activation of the signal and the first timing device following activation of the machinery.

3. A system according to either one of claim 1 and 2, and including a dead-man handle for use in activating the machinery.

4. A constant attendance system, substantialiy as hereinbefore described with reference to either one of Figures 1 and 2 of the accompanying drawings.