Patent GB-358516-A (GB)
Title: Improvements in electric control systems
IPC: H02P7/34
Filed: 1930-07-07
Abstract: 358,516. Lifts. STEVENS, R. J., Dunoon, Coombe Lane, Kingston Hill, Surrey. July 7, 1930, Nos. 20580 and 29298. [Class 78 (ii).] Electric plant.-In the control of lifts, a transformer having primary and secondary windings 6, 7, Fig 1, co-operates with a magnetizable shield 8, which by insertion between the windings reduces the voltage induced in the secondary. The transformer may be carried by the lift and the shield be arranged in the lift shaft, the shield having a profile such that the shielding action increases as a floor is approached and the lift retarded, a pronounced hump on the shield, located at floor level, causing definite stoppage at the floor. Such a system is shown in Fig. 3, the secondary 7 is connected to the grid of an amplifier 12, the output of which is coupled to the grid of a rectifier 14. The anode circuit of the rectifier includes the field 15 of an exciter 16 of a Ward-Leonard generator supplying the lift motor, or the field 15 may be that of the generator itself. As the shielding effect increases, the excitation of the machine 16 decreases. When the hump passes between the primary and secondary windings a valve 21 causes a switch 23 to operate and effect the definite stopping of the lift. A second transformer with a hand-operated shield 37 is located in the lift for the purpose of starting. Alternatively a signal relay or several graded relays may be included in the anode circuit of the valve 14. In a modified system, Fig. 5, the transformer, with two primaries 62, 63 is located in a control room, and two shields 71, 72 of spiral configuration are rotated by a pilot motor during acceleration and deceleration of the lift. When the lift controller 42 is moved from its " off " position, the motor 74 is connected to withdraw the shields, thereby increasing the grid-swing on the rectifier 54, and the current through the field 51 of the exciter 50. As the voltage generated by the exciter is added to that of the supply 49, a steepened characteristic of the valve is attained as disclosed in Specification 358,587. When the motor 74 has fully withdrawn the shields 71, 72, resulting in full speed of the lift, a cam 80 opens a switch 77 and stops this motor. The controller 42 is returned to its " off " position as a floor, at which stoppage is desired, is approached, this action causing switches 88, 89 to close and excite "inducers" 83, 85. As a " pick-up " 92 on the lift passes the " inducer " 83, a pulse is given to the valves 96, 97 causing contacts 99 to operate, these in turn cause the motor 74 to reverse, reinserting the shields between the transformer windings and retarding the lift. As the " pick-up " 92 arrives opposite the " inducer " 85 a second pulse is given to the valves 96, 97, and a second closure of contacts 99 results in opening a switch 53 and stoppage of the lift. During floor to floor operation, the lift does not accelerate to full speed before the controller is returned to its " off " position, with the result that cams 90, 91 cause switch 87 to close instead of switch 88; thus deceleration is not initiated until the " pick-up " 92 passes an " inducer " 84. The radii of the shield 72 are greater than the corresponding radii of the shield 71, and during acceleration both primaries 62, 63 are energized whilst during deceleration only primary 63 is energized. The " inducers and " pick-ups " and their action is described in Specification 356,788 and they may be replaced by transformers and shields.