Patent GB-835996-A (GB)
Title: Improvements in and relating to electric motor control systems
Inventor: WYNNE WALTER LEWIS LIFTON
IPC: B65H23/18
Filed: 1955-07-01
Abstract: 835,996. Control of two D.C. motors. ENGLISH ELECTRIC CO. Ltd. July 2, 1956 [July 1, 1955], No. 19078/55. Class 38 (3). [Also in Group XXXV] An electric control system comprises two D.C. dynamo-electric machines 16, 17, coupled to two material coiling machines 11, 12 operating in conjunction with a material treating machine 10, the dynamo-electric machines having independent constant armature current control means dependent on material tension regulator settings and each having field regulating means controlled by control means dependent directly or indirectly on the amount of material on one of the coiler reels and arranged to vary the regulating means of the two machines in opposite senses and in a manner tending to maintain constant the tension in the material. In the condition shown, with material travelling at constant speed in the direction A, the D.C. machine 16, having an armature 16a and series field winding 16b connected to a generator 18, is acting as a motor driving coiler reel 11 which takes up material from the treating machine. The D.C. machine 17 runs as a generator acting as a brake on the coiler reel 12 feeding the treating machine. As the diameter of the coiler reel 11 increases and that of the coiler reel 12 decreases the speed and torque of each D.C. machine must vary inversely to maintain constant tension in the material being treated. The speed of motor 16 must decrease and its torque increase. The armature currents in the circuits 16, 18 and 17, 19 are arranged to be constant by a control means, not specified, at a value determined by the setting of tension regulators for the two reels and so variation of motor speed and torque is achieved by controlling field excitation current. Field windings 16c, 17c are connected through regulators 29, 30 to constant-voltage bus-bars 28, the regulators being mechanically coupled to pilot motors 31, 32 one of which, depending on the direction of travel of the material, either A or B, is operated by the regulation system to vary the excitation of D.C. machines 16, 17 as required. Mechanically coupled to motors 31, 32 are selsyn motors 33, 34 which with connections 35 through contacts 36 comprise an electromechanical transmission system enabling the operative motor to operate the remote regulator; in the condition shown, these being motor 31 and regulator 30. Connected in parallel with either D.C. machine 16 or 17, through the change-over switch 23, 24, is a tacho-generator 14, mechanically coupled to the treating maehine driving motor 13, and in series with it resistances 20, 21 the values being such that the ratio of the total resistance of 14 and 20 with the resistance 21 is the same as the ratio of the armature resistance 16a and field winding resistance 16b. When the back E.M.F. of motor 16 tends to change from a predetermined E.M.F. is caused across the series circuit comprising contact 23b, rectifier 26 and control winding 25a of magnetic amplifier 25, causing current to flow in the control winding, the magnetic amplifier output being applied to motor 31 in such a manner as to vary the excitation of motor 16 to restore the original back E.M.F. With the variation of excitation of motor 16 and, via the selsyn system of generator 17, comes the required change of torque and speed. For a pass of material in direction B effected by change-over switch 23, 24 the functions of machines 16 and 17 are interchanged, the magnetic amplfier being operated by control winding 25b and the field regulators being operated by motor 32. Modifications described include the provision of a change-over switch to replace contacts 23c enabling the motor 31 to drive the field regulators in opposite senses for the alternative directions of travel A and B; also, omitting the selsyn system, the field regulator contacts 29a; 30a are mechanically coupled together to work in opposite senses, provision being made for independent adjustment; also a similar control system is described in which the magnetic amplifier responds to deviations from a reference value of the E.M.F. of the D.C. machine acting as a generator. A further control system described refers to mechanical control of the field excitation of the coiler motors, the mechanical means being responsive to the amount of material on one of the reels. Specification 834,785 is referred to.