Patent GB-863459-A (GB)
Title: Control systems particularly for machine tools
IPC: B23B5/00
Filed: 1957-03-28
Abstract: 863,459. Hydraulic transmission of power; fluid pressure servomotor control systems. CALOW, T., [trading as CALOW & CO., T.]. March 28, 1957 [March 28, 1956; Dec. 7, 1956 ; Feb. 10, 1957], No. 10213/57. Classes 69 (2) and 135. [Also in Groups XXII and XXVI] A control system for maintaining the driving speed of a machine tool or other rotary machine, such as a surface-finishing machine e.g. a centreless bar-turning, peeling or skinning machine, substantially constant under varying load at any value to which it has been set comprises adjusting means for varying the torque applied to the drive shaft of the tool, and means operable automatically in response to variations in the speed of the shaft for actuating the adjusting means in a sense to provide compensating variations in the torque applied to the shaft. The drive to the shaft 5, Fig. 1, of the motor may incorporate either a torque converter 3 which is driven by an electric motor 2 and has angularly adjustable vanes for varying the torque transmitted, or a turbine 37, Fig. 2, driven from a jet 40 having a nozzle, the cross-sectional area of which is adjustable. As shown in Fig. 1, the electric motor 2 drives the torque converter 3, the output shaft of which is connected by a belt 4 to the driven shaft 5 of the machine. The shaft 5 is rigidly connected to the stator 28 of a synchronous polyphase motor having a rotor 29 connected by a clutch 30 to a threaded spindle 31 ; during operation the motor is supplied with a frequency corresponding to the desired speed of the driven shaft 5, the rotor therefore remaining substantially stationary. A nut 33 on the spindle is connected by a lever 34 to a valve 12 which controls the pressure in the output line 9 of a pump 7 in response to small values of acceleration of the shaft 5, the pump 7 being driven by a non-slip drive 6 from the drive shaft 5. The pressure in the line 9 from the pump is also controlled by a needle valve 10, which can be set to correspond to the desired speed of the shaft 5, and a valve 23 which is responsive to the pressure in the line 9 and has a piston 24 movable against the tension of a spring adjustable by a hand wheel 26. The line 9 is connected to a cylinder having a piston 16 joined by a rod 17 to a lever 19 which is pivoted at 18 and movable against a spring 20 to vary the angle of the blades in the converter. In operation, the piston 16 is initially in its highest position and the vanes of the converter are consequently adjusted for maximum torque transmission and, as the drive is stationary, there is no pressure in the pipe 9 and the valve 23 is fully open. When the electric motor 2 is started, the maximum torque is transmitted by the converter. As the speed of the pump 7 increases, the piston 16 is gradually moved downwardly by the pressure in the pipe 9 to an intermediate position to reduce the torque transmitted by the converter and the valve 23 is also moved to an intermediate position. Small variations of speed from the desired value axially move the nut 33 on the spindle of the rotor 28 to adjust the valve 12 and vary the pressure in the pipe 9 leading to the control piston. In the event of a sudden change of torque, such as when a heavy load is put on the machine, resulting in the pump 7 reducing its output rapidly, the drop in pressure in pipe 9 permits the valve 23 to open resulting in a further drop in pressure in the pipe 9 to more rapidly adjust the piston 16, the vanes of the converter thus being rapidly adjusted to the maximum torque conversion position to quickly bring the speed of the shaft 5 back to the desired value. A similar control arrangement using a turbine 37, Fig. 2, in place of the converter may be employed, the piston 16 being urged by a spring 20 to one end of its cylinder if the fluid is supplied at a constant pressure, and to the other end of the cylinder by a spring 20<SP>1</SP> if the fluid is supplied at a constant rate. The control of the turbine may be effected by electrical means consisting of a shaft 41, Fig. 3, which is driven from the non-slip drive 6 and carries (1) a device having a weight 43 which upon slow acceleration or deceleration of the drive shaft is moved relative to a disc 42, to which it is connected by leaf springs 44, in one direction or the other to close one or other of a pair of contacts to energize one or other of a pair of solenoids 49, 50, Fig. 7, connected to a lever 52 which is pivoted at 51 and urged to a central position by springs 53, 54, the lever carrying a motor 63 joined to the nose piece 38 and movement of the lever varying the output from the nozzle 40; (2) a device having a weight 57 held lightly in a central position by a spring 58, a rapid acceleration or deceleration causing the weight to engage one or other of a pair of contacts 62 to drive the motor 63 carried by the lever 52 in one direction or the other to axially move the nose-piece relative to the motor to vary the output from the nozzle ; and (3) a device having a weight 67 which is movable by centrifugal force against an adjustable spring 76 to close one or other of a pair of contacts also controlling the motor 63. The combination of devices thus controls the adjusting means so that slow changes in velocity, rapid changes in velocity and changes in velocity over a considerable time are compensated. In another embodiment, a torque converter 84, Figs. 9 and 10, has its turbine blades 102, 103 connected to the shaft 82 of the machine, stationary guide vanes 99, 100, 101 and rotatable pump blades 98 which are mounted on the ends of shafts 97<SP>1</SP> having helical gears 97 at their other ends engaging a helical gear 94. The angle of the vanes is adjusted by axially moving the gear 94 by a lever 90 connected to a piston 85 in a cylinder 86. The ends of the cylinder are connected by pipes 105, 106 to a pipe 104 connected to a pump 107 driven from the output shaft of the converter and a pump 108 driven from a motor 112. The pipe 104 is also connected by one-way valves to an accumulator 122, charged by a pump 125, and a reservoir 119. In operation, the motor 112 is started and brought up to the desired speed of the shaft 82. At this time the pump 107 is stationary and the output from the pump moves the piston 85 to a position corresponding to maximum conversion ratio of the converter. When the motor 83 is started, the output from the pump 107 gradually moves the piston to an intermediate position to reduce the conversion ratio. Changes in the output speed of the shaft 82 will then adjust the speed of the pump 107 to move the piston 85 and vary the conversion ratio of the converter to compensate for the change. A valve 131, similar to the valve 10, 23, 24, shown in Fig. 1, is incorporated in the circuit to effect a rapid change of the conversion ratio in the event of rapid changes of acceleration. In another similar arrangement, an infinitely variable gear is interposed in the drive between the output shaft of the converter and the pump 107, and a device responsive to accelerations and similar to the device 42, 43, shown in Fig. 3, is mounted on the pump 107 and controls a reversible motor which during normal operation runs at a constant speed and drives the pump 108. Two separate control systems may be utilized for controlling forward and reverse strokes of a machine tool, such as a planing machine, or a pair of torque converters may be employed having their driving and driven sides connected to each other by gears and driven by single motors.