Patent GB-268918-A (GB)
Title: Improvements in control of electrically driven lifts and cranes
IPC: B66B1/08
Filed: 1926-02-05
Abstract: 268,918. Smith, Major, & Stevens, Ltd., and Stevens, P. H. Feb. 5, 1926. Electric plant. - In means for reducing the speed of a lift in accordance with the load before the actuation of the brake to stop it at any floor, the current passing through the armature of the motor operates means which on the operation of a switch connects mechanism with a moving part of the lift mechanism, the connected mechanism first adjusting a solenoid, or other selecting means, to a position proportionate to the load on the motor, secondly locking the selecting means in position and introducing resistances proportionate to the current,, and finally cutting off the current and applying a brake at a predetermined position before the floor. The lift is started by moving the switch arm C<1> on the cage to bridge the contacts C<2>, C<3>. This completes a circuit through the coil of the magnet D, the armature of which rises and brings contact plates D' against contacts D<2>, D<3>, thereby putting the motor B in circuit. When a floor is being approached at which it is desired to stop, the arm C<1> is moved to bridge the contacts C<4>, C<5>, thereby causing the current supplied to the motor to pass through the windings of a series of solenoids H - - H<4> and completing an additional circuit which includes the winding of an electromagnet E. When the magnet E is energized, the rod E<3> is raised thereby moving the actuating arm E<4> of a clutch to connect a drum E<5> with a gear E<6> driven continuously by the winding drum A<4>. As the drum E<5> rotates, it winds one of the chains F attached to it and rotates a drum F' fast on a shaft F<2> carrying a series of cams G, J, F<8> - - F<13>. As the cam G rotates, its face G<3>, Fig. 2, engages a projection G<4> of a switch G<5> and separates the contacts G<8>, G<9> through which current is supplied to the motor. The number of turns on the solenoids H - - H<4> increases progressively so that the number of cores H<5> - - H<9> which lift varies with the current. As the shaft F<2> continues to rotate, a cam J rocks a shaft J' carrying a series of arms J<3>, Fig. 4, and thereby permits the movement of locking bolts J' under spring action to engage the cores H<5> - - H<9>, thus locking some of them in the raised position and others in the lowered position. Assuming that the cores H<5>, H<6> have not been raised, the shaft F<2> will continue to turn until the core H<7> encounters the cam F<5> of a series of cams F<3> - - F<7> carried in stepped position on the shaft F<2>. Each of these cams has a second cam face which contacts with one of a series of arms K actuating switches K<2> - - K<7>. In the present case the switches K<2> - - K<4> will be opened and the current for the motor will pass through the resistances which these switches short circuit when closed. The voltage to the motor is thus reduced and its speed through the slowing-down distance so diminished that the lift arrives at the point where the current is cut off at a creeping speed which enables the brake to bring it to rest accurately at the stopping place. When the current is cut off, the magnet E is de-energized, the drum E<5> is released, and the mechanism returned to its original position by a weight E'‹. The lift is moved in the opposite direction by turning the arm C' to bridge the contacts C<6>, C<7>, thereby energizing the magnet D<4> and causing current to pass through the motor in the reverse direction. Specification 259,014, [Class 38 (iii), Electric motor control systems &c.], is referred to in the Provisional Specification.