Patent GB-190426096-A (GB)
Title: Improvements in Controlling Systems for Electric Motors
Inventor: EASTWOOD ARTHUR CLARKE
Filed: 1904-11-30
Granted: 1905-03-30
Abstract: 26,096. Eastwood, A. C. March 21, [date applied for under Patents Act, A.D. 1901]. Driving machines by electromotors.-Motors for actuating printing-machines are controlled so as to be automatically reversed without at any moment taking excessive current, and by means of an adjustable speed regulator the motor may be made to accelerate up to any desired speed on either the forward or the return stroke. Compound-wound machipes are preferably, but not necessarily, used, the series field being used only during reversal and acceleration ; the motor is geared to the machine direct, and the latter carries at the ends of the reciprocating member adjustable devices for gearing with the spindle of, and reversing, the controller automatically at the end of each stroke. Speed variations may be obtained by adjusting a variable resistance in circuit with the shunt field, and so changing the strength thereof as shown in Fig. 1, in which C is the controller, A the armature, f the shunt field which is connected to the adjustable resistance r, R, R<1> are resistances, and S<1>, S<2> &c. are electromagnet switches connected as shown, the switch S' being arranged to short-circuit the series field F, and the switch S‹ to similarly short-circuit the resistance r. When the main switch Q is closed and the "forward'' contacts C' of the controller made to engage with the studs C' to C<9>, the switch S' closes, and starts the motor through the resistance R<1> and field F, the shunt field f being also excited through the normally-closed switch S<6>. The switches S<2>, S<3> are wound to close and cut-out the resistance R<1> at successively. increasing voltages, and hence, as the motor speeds up, the switch S<2> first closes, and the motor again accelerates till the switch S<3> closes, supplies the motor direct from the mains, and, completing the auxiliary circuit round the coil s', causes the switch S' to operate and cut-out the series field F, accelerates the motor again, closes the switch S<5> by the auxiliary circuit, and opens the switch S<6>. The closing of the switch S<5> cuts out resistance between the field f and the arm r<1>, and the opening of the switch S<6> puts the remainder of the resistance r in circuit, and the motor reaches its final speed. At the end of the working stroke, the controller reverses, and, as the contacts c<8>, c<9> are shorter than the others, arcing takes place at the switches S<1> to S<6>, and not at the controller, and, although the contacts c'‹, c<11> are momentarily joined, the time is too short to allow the switch S to close unless the controller be left in the median position, when the coil s is excited by the counterelectromotive force of the armature, and the motor is braked through the resistance R. The switch S' then closes, and the armature, sending current through the resistance R<1> comes to rest and then commences to rotate in the reverse direction, and the operations go on as before, except that, the contact c<9> not being in circuit, the switch S<5> is not closed, no part of the resistance r is short-circuited, and the motor reverses at top speed, after which the whole cycle is again repeated. By duplicating the adjustable resistance r and using an extra switch, controller contact, and stud, the return may be made at speeds other than the maximum, if desired. Fig. 3 shows a modification, wherein the speed variation is obtained by applying to the motor armature, with or without resistance, one of the two voltages available from an Edison three-wire system, and also using an adjustable and a non- adjustable resistance in the shunt field. The adjustable resistance and contacts are of the form shown at r, d, a', &c., the controller C is actuated as before and the controller D can be operated by hand. When the controller D is in its first position, if the switch Q<1> be closed and the contacts C' brought into circuit, the switch S<9> closes, and supplies the motor with current from the neutral main through the resistance R', switch S", controller C, and field F to the negative main ; as before, when the back electromotive force of the motor reduces the current sufficiently, the switch S'‹ closes and cuts out the resistance R<2>, and then the switch S<13> operates through the contacts c<13>, c<14>, d<6>, and d<8>, and, shortcircuiting the series fieid, causes the motor to accelerate to top speed on a shunt field at the voltage between the neutral and negative supply mains. On reversal, the switches S<9> to S<13> open, and the switch S<14> closes, the energy of the armature is spent on the resistance R<2>, and its connections are reversed ; as the motor speeds up, the switches S<10>, S", S<12>, and S<13> are successively operated, and then switch S<15> puts the resistance r<4> in circuit with the shunt field, so that the motor operates at maximum speed on the idle stroke. Further speed variations are obtained by moving the controller D, and, if the resistance r' is adjustable, speed variations may be obtained in both directions. The control may be obtained, as shown in Fig. 4, on a four-wire system by varying the small resistance in the field of a shunt-wound motor. In addition to the automatic controller C, a second controller E is introduced, and the two are connected as shown. If the controller E is in its second position and the contacts C<1> are brought into action, the coil s<20> of the switch S<20> is energized from the mains x, x<1> and the blades s<21>, s<22> are brought on to contacts s<25>, s<26> ; the armature then starts on the voltage between the mains x, x<1>, and then, as the switchbars s<21>, s<22> close, speeds up for the working stroke on the voltage from the mains x<1>, x'. On reversal, the switch S<20> opens, the coil s<28> then closes it on the contacts s<29>, s<30>, and, when the contacts C<2> are in action, the switch coil s<20>, although energized, cannot operate till the motor comes to rest. On accelerating again; the switches S<21> to S<25> close successively, and bring the motor to top speed. The motor may be stopped by opening the switch Q<2>, or leaving the controller in the 'off' position, to allow the armature to supply current through the resistance R.