Patent GB-620236-A (GB)
Title: Improvements in electric motor control systems for winding engines
IPC: B66B1/12
Filed: 1947-01-10
Abstract: 620,236. Control of D.C. motors. BRITISH THOMSON - HOUSTON CO., Ltd., and PETCH, T. H. Jan. 10, 1947, No. 920. [Class 38(iii)] In a control system for a winding engine having a Ward-Leonard drive in which cams driven by the winding drum have cam rockers associated therewith, the cam rockers being so coupled to a potentiometer rheostat that, when the winding engine is at the limits of its travel, the potentiometer rheostat is gradually forced into its neutral or zero position to bring the engine to rest without any dangerous accelerating or retarding currents being generated, means are provided for preventing the winding engine from being started too quickly when the engine has been stopped between the limits of its travel. The field controlling the speed of the winding engine is connected so that it can be adjusted by the potentiometer rheostat, the moving arm of which is mechanically coupled so as to have limited movement imparted to it, to a thruster, operating at a time-controlled rate, which is also mechanically coupled to the cam rockers of the cam gear so as to operate the rockers on the faces of the cams. When a hand lever HL is actuated for motor operation in a forward direction, a master controller MC is moved to adjust a rheostat Rh and to close contacts energizing a coil Ha and exciting a thruster T1. The thruster T1 rises to take up the clearance between a rocker 19 and a cam 15, (see Fig. 2), and to move the arm of a faceplate rheostat PR2. Contacts 41 and 43 on the master controller MC are also closed to energize an exciter field winding GEf1 which is connected across bus bars 1 and 2 in series with a potentometer PR, the rheostat Rh, and resistors R1 and R2. An exciter energizes a field winding Gf of a generator G supplying a motor M which operates at low speed. The lever HL may then be moved to cut out the rheostat Rh and the motor-driven cam 15 allows further upward movement of the thruster T1, so adjusting the potentometer PR to a higher speed position until full motor speed is reached. As the motor approaches the end of its travel a cam 16 engages a rocker 20 to force the thruster T1 downwardly and return the rheostat PR2 to the low-speed position. The lever HL is normally moved at the end of the wind to re-energize the thruster T1 and the field winding GEf1. During the motor acceleration period, whilst the resistor Rh is being removed, increased voltage is applied to the armature of a machine C, which is mechanically coupled to a flywheel and is connected across the potentometer resistor PR. If, in a position intermediate the normal limits of motor travel, the lever HL is moved towards neutral, the resistor Rh is re-inserted but the voltage between the ends of the resistor PR is not immediately reduced due to the fly-wheel machine connected thereacross. The excitation of the field winding GEf1 therefore decays, to a value corresponding to the final position of the lever HL, at a rate substantially independent of the rate of movement of the lever. Contacts 5 and 6, which are closed by movement of the member PR2 from the " off " position, are connected in parallel with the contacts 41 and 43, which are opened if the master controller is moved to the " off " position, so preventing the rapid opening of the circuit of the field winding GEf 1 if the controller is moved to the " off " position, so thruster TI is provided with a time delay in falling. On re-starting after a stop in such a mid-position, the control lever may be moved to the " full speed" position immediately, so providing operation similar to that for a normal start, except that the rate of rise of the thruster T1 is not controlled by a cam but by a time delay device. If the speed had merely been reduced and it is desired to increase it, the thruster T1 would not have been de-energized and its time delay effect is inoperative. The resistor R1 is, however, left in circuit and extra current flows through this and the machine C which is operating at low speed, the resistor PR taking only a small current. As the machine C accelerates. the resistor PR takes more current and the strength of the field winding GEf1 is gradually built up. The resistor R1 prevents the full voltage of the brass bars 1 and 2 being applied immediately across the resistor PR when the rheostat Rh is removed. When the rheostat PR is adjusted, by movement of the arm PR2, to vary the strength of the field winding GEf1, the flywheel machine C exerts a small forcing effect. The resistor R2 is provided so that, when the rheostat arm PR2 is at its bottom position, there is a voltage drop thereacross which is sufficient to excite the field winding GEf1 for manoeuvring the winding motor independently of the thruster TI. Main motor operation in the reverse direction similar to that described is provided by appropriate movement of the master controller. Closer control of the motor independently of the thruster T1. winding GEf2 which bucks the winding GEf1 and is connected across the generator G, or is connected to a motor-driven tachometer generator. For an emergency stop, a switch E may be opened to deenergize a thruster T1 or T2 under control of its time delay device. According to the Provisional Specification, oil servo devices may be used instead of the thrusters T1 and T2, in which case contactors Hc and Lc may be replaced by magneticallyoperated oil valves. The fly-wheel machine C may be replaced by a condenser.