Patent GB-172192-A (GB)
Title: Improvements relating to electrically driven planers and the like
IPC: B23D7/00
Filed: 1920-10-25
Abstract: 172,192. Miller, L., and Metropolitan- Vickers Electrical Co., Ltd. Oct. 25, 1920. Planing.-The table of a planing or like machine is driven by the motor unit of a reversible hydraulic transmission gear, the pump unit of which is normally rotated in one direction by a main driving electric motor and is provided with variable-speed mechanism operated by an auxiliary reversible electric motor. The table 1, Fig. 1, is reciprocated by the hydraulic motor unit B through gearing diagrammatically indicated at 5. The pump unit A, preferably of the kind comprising a multi-cylinder rotor with pistons of variable throw, is driven from the main electric motor 2 having a fly-wheel 3, and the operating-lever 6 of the variable-speed mechanism is controlled by an auxiliary or servomotor 7. The control circuits for the main and auxiliary motors are provided with push-button switches for " inching " the table in either direction. Dynamic braking of the motor 2 is obtained at the ends of the cut and return strokes, during " inching " in either direction and upon failure of the voltage supply. The control system for reversing the main driving- motor 2 is only employed for " inching " or for setting the machine. For ordinary working, the main motor runs at constant speed and the reversal of the table is effected by means of a double-throw master reversing-switch 9 which is operated by tappets 11, 12 on the planer table to reverse the direction of rotation of the servomotor. The latter drives through the bevelgearing shown in Fig. 1 a disc 52 carrying an adjustable switch-operating tappet 51 and a number of switch-carrying handles 50 which may be set in different angular positions. The arrangement is such that the position of the tappet 51 on a dial 8a graduated in feet per minute indicates the position of the variable-speed mechanism of the pumping unit. In operation the control handles 50, 50a are set in positions which correspond respectively to the cutting and return speeds of the table. The master switch 9 is positioned for the cutting-stroke, and the main motor is accelerated to a constant speed. The rotation of the servo-motor in the forward direction mcves the variable-speed mechanism 6 and accelerates the table until the tappet 51 opens a limit switch on the handle 50 and stops the servo motor, the table then continuing its travel at constant cutting speed until the master switch 9 is operated by one of the tappets 11, 12 to reverse the servo motor. The latter then rotates at constant speed in the reverse direction, thus operating the mechanism 6 to retard the table and finally to accelerate it in the reverse direction until the tappet 51 opens the limit switch on the handle 50<a>, whereupon the servo-motor is again stopped and the planer table continues at a constant return speed. At the end of the return stroke the second tappet on the table engages the master reversing-switch and again connects the servo-motor for operation in the cutting direction and the cycle of operations is repeated. The energy of the fly-wheel 9 is absorbed when the table is being accelerated and restored during the retardation of the table. If necessary the positions of the handles 50, 50<a> may be altered to change the cutting and return speeds without stopping the machine. In a modification, the speed of the table may be increased between two cutting operations in a forward stroke to give a speed curve as shown in Fig. 7, additional limit switches being provided on the control pillar 8 in conjunction with a rotary switch operated by tappets on the table. In a further modification the control switches may be arranged to cause the tool to enter and leave the work at a speed lower than the cutting speed to obtain a speed curve as shown in Fig. 10. In order to obtain greater precision in the speed variations of the table, an adjustable braking resistance may be connected across the brushes of the servo-motor. In a further modification a Wheatstone bridge may be employed in place of the limit switches for controlling the operations of the servo-motor. In this arrangement the servo-motor operates in accordance with the current in the zero diagonal arm of the bridge, the resistances in two of the arms of the bridge being adjustable according to the speed at which the table in desired to move at different parts of thestroke and the resistances of the proportional arms being varied by the rotation of the servomotor so that when the desired speed of the table is attained the current in the diagonal arm is reduced to zero and the servo-motor is stopped.-