GB2136990A - Lift door control circuits - Google Patents

Abstract

Safety apparatus for use in lift door control circuits includes means for sensing the current fed to the door motor from a power supply and acts to reverse the current to the motor when the current exceeds a preset value as a result of, for example, the door meeting an obstruction.

Description

SPECIFICATION Improvements in lift door control circuits This invention relates to safety apparatus for lift door control circuits.

In lift systems both the lift car doors and the landing doors are provided with safety devices whereby, should the doors meet an obstruction as they close, the door motor automatically reverses and the doors re-open.

Hitherto, these safety devices have been in the form of strips which project from the leading edges of the doors. Should the door meet an obstruction, as it closes, the strip is pushed back into the door and trips a switch which operates the door control circuit so as to reverse the motor and re-open the doors.

This type of safety apparatus has a number of disadvantages. It requires relative movement of the door and the strip to activate it. It is necessary to run wiring from the doors to the control unit. As the operation of the strip involves mechanical movement it can be tampered with. The strip itself has to be activated to operate the safety circuit, thus it is possible to jam the doors if the strip is not activated. Finally, in order that the circuit is nots tripped when the doors from opposite sides meet, the strips have to be de-activated during the last few inches of travel of the doors.

According to the present invention there is provided safety apparatus for use in lift door control circuits, comprising a door motor current sensing circuit, a door motor power supply and a power supply control circuit, the arrangement being such that when the door motor current increases above the preset level, due to the door meeting increased resistance to closing, the current sensing circuit is activated and triggers the power supply control circuit so as to reverse the polarity of the power supply and hence reverse the motor and re-open the doors.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a block diagram of one embodiment of a door control circuit safety apparatus made in accordance with the present invention: and Fig. 2 shows part of a circuit diagram of the apparatus of Fig. 1.

Referring to the drawings safety apparatus for use in lift door control circuits comprises a power supply for driving electric motor for opening and shutting the doors of a lift. Electric power from the power supply 1 is fed to a door control motor 10 through a power supply control circuit 20.

The current flowing from the power supply control circuit 20 to the door motor is sensed by a door motor current sensing circuit 30. The door motor circuit sensing circuit 30 monitors the current flowing to the door control motor and, when this current exceeds a preset value for example, due to the door meeting increased resistance to closing, the current sensing circuit 30 acts to reverse the current fed to the door motor 10 by the power supply circuit 20 thus to open the door, Having particular reference to Fig. 2, the signal under surveillance is fed through an isolating transformer to the door motor circuit, rectified to give a proportional d.c. voltage. This voltage is then compared to a preset reference voltage. The unit remains static under normal conditions.When the lift doors under drive conditions confront an obstruction the unit will operate so as to reverse the door direction.

Modifications and improvements may be incorporated without departing from the scope of the invention.

1. Safety apparatus for use in lift door control circuits, comprising a door motor current sensing circuit, a door motor power supply and a power supply control circuit, the arrangement being such that when the door motor current increases above a preset level, due to the door meeting increased resistance to closing, the current sensing circuit is activated and triggers the power supply control circuit so as to reverse the polarity of the power supply and hence reverse the motor and re-open the doors.

2. Safety apparatus for use in lift door control circuits substantially as hereinbefore described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (2)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Improvements in lift door control circuits This invention relates to safety apparatus for lift door control circuits. In lift systems both the lift car doors and the landing doors are provided with safety devices whereby, should the doors meet an obstruction as they close, the door motor automatically reverses and the doors re-open. Hitherto, these safety devices have been in the form of strips which project from the leading edges of the doors. Should the door meet an obstruction, as it closes, the strip is pushed back into the door and trips a switch which operates the door control circuit so as to reverse the motor and re-open the doors. This type of safety apparatus has a number of disadvantages. It requires relative movement of the door and the strip to activate it. It is necessary to run wiring from the doors to the control unit. As the operation of the strip involves mechanical movement it can be tampered with. The strip itself has to be activated to operate the safety circuit, thus it is possible to jam the doors if the strip is not activated. Finally, in order that the circuit is nots tripped when the doors from opposite sides meet, the strips have to be de-activated during the last few inches of travel of the doors. According to the present invention there is provided safety apparatus for use in lift door control circuits, comprising a door motor current sensing circuit, a door motor power supply and a power supply control circuit, the arrangement being such that when the door motor current increases above the preset level, due to the door meeting increased resistance to closing, the current sensing circuit is activated and triggers the power supply control circuit so as to reverse the polarity of the power supply and hence reverse the motor and re-open the doors. Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a block diagram of one embodiment of a door control circuit safety apparatus made in accordance with the present invention: and Fig. 2 shows part of a circuit diagram of the apparatus of Fig. 1. Referring to the drawings safety apparatus for use in lift door control circuits comprises a power supply for driving electric motor for opening and shutting the doors of a lift. Electric power from the power supply 1 is fed to a door control motor 10 through a power supply control circuit 20. The current flowing from the power supply control circuit 20 to the door motor is sensed by a door motor current sensing circuit 30. The door motor circuit sensing circuit 30 monitors the current flowing to the door control motor and, when this current exceeds a preset value for example, due to the door meeting increased resistance to closing, the current sensing circuit 30 acts to reverse the current fed to the door motor 10 by the power supply circuit 20 thus to open the door, Having particular reference to Fig. 2, the signal under surveillance is fed through an isolating transformer to the door motor circuit, rectified to give a proportional d.c. voltage. This voltage is then compared to a preset reference voltage. The unit remains static under normal conditions. When the lift doors under drive conditions confront an obstruction the unit will operate so as to reverse the door direction. Modifications and improvements may be incorporated without departing from the scope of the invention. CLAIMS

1. Safety apparatus for use in lift door control circuits, comprising a door motor current sensing circuit, a door motor power supply and a power supply control circuit, the arrangement being such that when the door motor current increases above a preset level, due to the door meeting increased resistance to closing, the current sensing circuit is activated and triggers the power supply control circuit so as to reverse the polarity of the power supply and hence reverse the motor and re-open the doors.

2. Safety apparatus for use in lift door control circuits substantially as hereinbefore described with reference to the accompanying drawings.