Patent GB-420989-A (GB)
Title: Improvements relating to gate-operating mechanism
IPC: E05F15/12
Filed: 1933-06-29
Abstract: 420,989. Door-operating mechanism. HAMILTON, W., Broadfield, Wadhurst, Sussex. June 29, 1933, No. 18548. [Class 65 (i)] [See also Group XXXVII] In mechanism for operating gates by means of a chain which is attached to the gate and is tensioned to move the gate against the action of a return spring, means are provided to displace the point from which the chain passes to the gate, when the chain is in tension, in such a way that the angle between chain and gate is increased towards 90‹ during the movement of the gate by the tensioned chain, during which the tension of the return spring also increases, so that the tension in the chain remains substantially constant. Mechanism for operating one of a pair of double doors is shown, the mechanism for the other door being identical except for the omission of limit switches. The door 1, hinged at 2, carries a pivoted rod 10 having at its free end a roller 12 engaging in a guide channel 9 ; a torsion spring is provided at the pivot 11 connecting the rod 10 to the door, tending to press the rod towards the door hinge and thus to close the door. The door is opened by a cable 14 wound on a drum 7 on an underground shaft 8 driven through irreversible gears by an electric motor, the cable passing round a pulley 15 at the outer end of the guide 9 and a pulley at the end of the rod 10 and thence to the door at 18. The guide 9 is formed at its inner end with a short portion perpendicular to the rod 10 when the door is closed, so that the door cannot be opened except by pulling on the cable 14, which first moves the roller 12 into the straight portion of the guide and then pulls the door open, the end of the rod 10 meanwhile moving along the guide. As the door opens, the cable makes an increasing angle with it, and the tension in the cable necessary to move the door consequently diminishes while the tension required to overcome the resistance of the spring 17 increases, so that the total tension in the cable does not vary greatly. To allow the spring to close the doors, the motor is reversed to pay out the cable, and thus controls the speed of closing. The end of the rod 10 opens a limit switch 54 when the door is closed, and the attachment bracket 18 opens a limit switch 65 when the door is fully open. The motor is controlled by a separate relay for each direction of running, each relay being controlled by a push-button or other switch in parallel with a stick relay and in series with the appropriate limit switch ; the circuit for the closing relay also contains a switch, contained in the cable attachment 18 on the door, which maintains the relay circuit closed while the cable 14 is in tension but, when the cable slackens owing to obstruction of the movement of the door, opens the relay circuit to stop the motor and closes a circuit through a resistance in order to maintain the stick relay energized, so that when the obstruction is removed the motor starts again automatically. The pushbuttons may be replaced by, or connected in parallel with, a switch adapted to be operated by a solenoid on a vehicle stopped above it. This switch, Fig. 5, comprises a light metal frame 78, supported on pivots 90 and a float 79 floating on paraffin, having at each corner an integral depending point 82 for engagement with a mercury cup 83. The frame 78 is balanced by adjustable weights 80, and carries two magnetic needles 91, having like poles at the same end, so that when the solenoid on the vehicle is energized the adjacent end of the frame 78 is caused to rise or fall, according to the polarity of the solenoid, to connect the mercury cups at one end or the other, thus completing the circuit for the opening or closing relay. The motor may be provided with abrake to prevent over-running. In modifications, the motor may be replaced by a handwheel, or the motor, shaft 8 and drum 7 may be replaced by an hydraulic ram connected directly to the cable 14, the ram also forming a fluid check for the closing movement.