Patent GB-693205-A (GB)
Title: Improvements in or relating to control systems for electric motors operating double skip hoists
IPC: B66B1/06
Filed: 1951-08-28
Abstract: 693,205. Control of D.C. motors; controllers. POWER-GAS CORPORATION, Ltd., HOLMES F. R., and STODDART, A. L. Aug. 28, 1951, No. 20230/51. Class 38 (iii) A cyclical control system for two direct-current motors operating a double-skip hoist has one switch means for connecting the armatures AA, AB, of the motors in series or parallel, a second switch means for controlling the excitation of the shunt field windings APF, BPF, of the motors, and a third switch means including a programme switch responsive in part to changes in skip-position during hoisting operation to initiate operation of the first and second switch means in a cyclic manner. The programme switch (Fig. 4) may comprise moving contacts disposed on four radial arms mutually at right angles and a number of fixed contacts, which are connected to relays in the control circuit Fig. 3 (not shown), of the motor, and are equiangularly disposed on concentric pitch circles, the arrangement being such that the fixed contacts of one set (such as a<SP>1</SP>-l<SP>1</SP> or a<SP>12</SP>-l<SP>12</SP>) are all engaged by the moving contacts at the same time. The eleventh contact in each set of fixed contacts is in the form of a continuous ring b. The moving contacts of the programme switch are driven by a reversible pilot motor SPSM which is under the control of a plurality of limit switches (Fig. 2, not shown) operated in sequence in accordance with changes in position of the skips, the movement of the programme switch also being responsive to correct operation of the first and second switch means. The pilot motor drives the moving contacts in a step-by-step manner through a notching device (Fig. 5, not shown). The automatic starting operation of the two motors, involving the use of the programme switch, may be interlocked with the operation of the bell of a blast furnace which is served by the double-skip hoist. The motors are first connected in series and are accelerated by removal of armature resistance and shunt field control, the bridge transition to parallel operation being dependent upon the actuation of a limit switch by the moving skip. The series field windings of the motors are introduced at the transition stage and are in circuit during parallel operation. The motors operate at maximum speed until a slow-down limit switch is operated to introduce resistance into the armature circuit of the hoist motors and reverse the direction of movement of the programme switch. The shunt field excitation is then increased and the motors are returned to the series connection, the operation of a second slow-down limit switch causing further deceleration. When the programme switch has reached a pre-determined position in its travel towards the "off" position and the appropriate point in the cycle of bell operation has not been reached, the hoist is stopped and the programme switch is returned to the "off" position to await the necessary operation of the bell. If the required bell operation is completed, however, the hoist motors continue to operate at low speed with full armature resistance and maximum field excitation until a third slow-down limit switch effects the connection of diverter resistors DR1, DR2, DR3, to the motor armatures. The operation of a final limit switch disconnects the motors from the supply, applies the brakes, and drives the programme switch to the "off" position, the diverter resistors affording a degree of dynamic braking. In the event of failure of one of the motors, or if the charges on the skips are unusually light, the hoist may be automatically operated under the control of the programme switch using one motor. Provision is made for the operation of the equipment by means of a manual master controller, Fig. 3 (not shown), the programme switch being rendered ineffective. Manual control may be adapted for single or double motor operation. Double or single motor operation may be afforded with manual starting control and subsequent automatic operation. The hoist motors have cooling fans driven by motors ACFM, BCFM, and electro-magnetically released brakes for the main motors have operating coils BA, BB, and are controlled by means of series coils 1SB, 2SB. Either single or double brake operation is obtainable. Pilot lights are associated with a panel adjacent to the manual master controller, and others are at positions associated with the control equipment. Specification 588,973 is referred to.