Patent GB-190823908-A (GB)
Title: Improvements in Electrical Apparatus for Working Planing Machines and other Reciprocating Tools.
Filed: 1908-11-07
Granted: 1909-06-24
Abstract: 23,908. Vickers, Sons, & Maxim, and Williamson, A. D. Nov. 7. Motor control systems.-Reversible variable-speed electric motors, used to drive the reciprocating table of a planing-machine so as to obtain a slow working-stroke and a quick return,.together with a braking-action near each extreme position, are regulated by an electric master-control system instead of by mechanically connecting the main switch mechanism to moving parts of the apparatus. A tappet operated by the planing-table is connected by a rod c<7>, Fig. 1, to the arm of a switch C, which energizes one of the solenoids B', B<2>, causing the main switch arm a to start up the motor F. The following cycle of operations is gone through:-At the beginning of the quickreturn stroke of the table, the main arm a is in the horizontal position, and bridges contacts f, d<5>, subsidiary bammer switches c, b, e<1>, e<2> in the operating-circuits being closed. The tappet first pulls over the contact c<4> to bridge contacts c<1>, c<3> in the master switch C, thereby energizing a solenoid B' and moving the arm a slowly against a dash-pot and resetting-spring into the position shown in Fig. 1. The circuit through the solenoid B<1> starts from the positive main and passes through the wire b<1>, the hammer switch b, the solenoid B<1>, the wire b3, the contacts c<1>, c<3>, c<x>, and the wires b<4>, b<5> to the negative main. In the full on position of the arm, the hammer switch b is raised, and a resistance b<0> is inserted into the solenoid circuit, establishing hold-on conditions. A full shunt field E has been already made through the wires e, ex, the hammer switches e', e<2>, and the wire b<5>. At the first left-hand contact d', a circuit is completed through the armature F from the positive main through the right-hand contacts d, f and the lefthand contacts f, d', and thence through sections D' ... D<4> of the series field and resistance D to a contact d<4>, which is connected to the negative main. The rotation of the arm cuts out in succession the sections D<1>, D<2>, the resistance D, and the sections D<3>, D<4>, and in the extreme position the arm a opens the hammer switch e<1> as well as the switch b. The shunt field circuit is thus deflected from the fixed contact of switch e<1> through a wire e<3>, a rheostat e<4>, the wire e<5>, and to the negative main through the still-closed hammer switch e<2>. The working stroke is made under these conditions, and the amount of resistance e<4> included in the circuit is adjusted according to the speed required. Towards the end of the stroke, the motor armature is shorted in a strong shunt field through the resistance D to produce a braking- effect on the table. To effect this, the tappet moves the bridging-contact c<4> to the mid ' or ' off ' position, breaking the holding-circuit through the solenoid B<1> and allowing the arm a at once to return to the horizontal position. The shortcircuiting is effected, in this position, by means of the connected contacts d<5>, d<2>, d<3> on each side of the main switch. The strong field is obtained through the now closed hammer switch e'. In the extreme position of the contact c<4>, it bridges stationary contacts c<2>, c<3>, energizing the solenoid B', and moving the arm a in the opposite direction to reverse the motor. The same sequence is followed in switching out the series windings and resistance D, and in the 'full on' position the switches b, e', e<2> are opened by the arm a, the switch c having previously been opened by an extension c<8> on the arm of the master switch. The simultaneous opening of switches e', e' produces a weak field by diverting its current through the whole of the rheostat resistance Ex through the wires e<3>, e<7>. Under the weak field, the motor runs at a high speed to return the table. Near the end of the return stroke, the tappet moves the extension o<8> to reclose the switch c, thereby shorting all the rheostat resistance except the part e<4>, which remains in circuit with wires e<5>, e<6>, the switch c, and the wires b<4>, b<5>. At the same movement, contact between the parts c<2>, c3 is broken and the arm a returns to the shortcircuiting position, a new cycle of operations being started by bridging the contacts c<1>, c<3>. Motor controllers; ; switches.-The switch mechanism for effecting the above connexions comprises a rotary arm a, Fig. 2, on the spindle of which is a pinion a<2> engaged by a rack on a core B, Fig. 3, common to two solenoids B', B<2>. Fig. 2 shows the short-circuiting position, which is made stable by biassing-springs g<1>, g<2>, which press rollers a<4> against cam-surfaces a<3> on the spindle. The sucking action of each solenoid is retarded by applying to each end of the core a cup leather B', working piston-tight in a casing B<3>. The air in the casing escapes slowly through a constricted opening B<10>, but on the resetting-stroke a valve B<8> opens and permits the ready return of the core. The air in the casing of the inactive solenoid escapes through a hole B<x>. Springs pulling at diametrically opposite points on the spindle reset the switch arm a. The hammer switches are lifted by stirrup extensions a<18> on a rock shaft a<17>. When the shaft is rocked in one direction, all the hammers b, e', e<2> are lifted, but when moved in the other direction, hammers b, e<1> only are lifted, these being provided with tails to engage the stirrups. The shaft a<17> is rocked through a crank a<16>, a connecting-rod a<15>, a crank a<12>, and a link a<11>, this link having a pin a<10> which engages in a slot a<9> made in a disk a<8> on the main switch spindle.