Patent GB-672964-A (GB)
Title: Improvements in or relating to horizontal boring, drilling and milling machines and similar machine tools
IPC: B23B39/02
Filed: 1947-07-29
Abstract: 672,964. Control of several motors. GIDDINGS & LEWIS MACHINE TOOL CO. July 29, 1947. [March 15, 1945], No. 20413/47. Class 38 (iii). [Also in Groups XXII and XXIV] A horizontal boring, drilling, and milling machine or similar machine tool includes two reversible variable speed motors,. each having an adjustable speed mechanism associated therewith to provide a total speed range which is a multiple of the motor speed range, and coupling means for selectively connecting the output shaft of one of said mechanisms either to a first movable machine part or to a second movable machine part and for selectively connecting the output shaft of the second one of said mechanisms either to said second machine part or to a third movable machine part, so that any one or any two of said machine parts may be independently moved in either direction and at a selected speed, (see Group XXII.) Power supply connections. Power is supplied by mains L1 L2 L3, Fig. 18, directly serving the boring spindle and oil pump motors 34 and 155 respectively, and direct current is used for the feed motors 119 and 120 derived from the same supply through electronic control means which enables a graduated speed variation to be obtained (see below). To condition the machine for operation it is necessary first to start the oil pump motor 155 so as to build up pressure in the hydraulic system. This motor is started by momentary closure of a pushbutton switch 172 to complete a circuit across lines L1 and L2 through a relay coil OP this establishes a holding circuit and closes contacts OP2 to start the motor. A push button stop switch 173 and master stop switch 174 are provided opening of either stopping the entire machine. Relay coil OP also connects line L1 through contacts OP1 to a secondary line L4 conditioning circuit for motors 34, 119 and 120. Before the spindle can be operated, however, pressure switch 175, depending on.the oil pressure in the system, has to be closed. The spindle motor 34 is started by momentarily closing the push-button switch 176 to complete the circuit through either forward or reverse relay, coils 1F and 1R as determined by the setting of a selector switch 177. The line L4 is connected to a secondary line L5 for supplying current to the starting circuits for the feed motors 119, 120. Switch circuits are provided for enabling the spindle motor circuits to be conditioned for continuous or intermittent "(inching") operation. When the electronic and power control circuits for the feed motors 119, 120 are operative contacts CR2<SP>1</SP> and FPR2<SP>1</SP> will be closed to condition the starting circuit for the motor 119. Similar contacts are provided for motor 120. Each of the feed motors is adapted to be conditioned selectively by switch mechanism similar to that described for motor 34 for either continuous or intermittent operation in either direction. Electronic control of feed motors. The electronic control circuits for the motors 119, 120 are identical and that for motor 119 only will be described. Current is supplied from a transformer 204, Fig. 19, having a primary 205 and centre tapped secondary 206, and the current for the motor armature 201 is rectified by a first pair of grid-controlled thyratrons 207, 208, that for the motor field 203 being obtained from a second pair of thyratrons 209, 210. The anodes of the valves 207, 209 are connected to one end terminal of the transformer secondary through line 211, while the anodes of the other thyratrons 208, 210, are connected to the opposite end through a line 212. The cathodes of thyratrons 207, 208 are connected to the mid-point of the transformer secondary through the motor armature 201, whereas the cathodes of the other pair of valves are connected through the field 203. Heating current is supplied from respective additional windings 213, 214, of transformer 204. The amount of current passed by the pairs of thyratrons is controlled by varying the phase of their grid bias relative to the phase of the anode or plate potentiometer. Saturable core reactors 215, 216 are provided in the bridges for the grid circuits for this purpose and current is supplied to the bridges from a potentiometer 217 connected across the supply lines L1 L2 and resistances 64R and 65R constitute the resistance legs of these bridges. Saturation of the core reactors 215, 216, and hence their inductances, is controlled by variations in direct current passed through associated saturation windings 221 and 222 respectively. A small amount of current passing through the saturation windings gives a large reactance in the winding 215 and thus the alternating current supplied to the transformer winding 218a is far out of phase with that supplied to the anodes of the thyratrons 207, 208. The winding 218a thus does not fire the latter valves until late in their respective half cycle and the voltage supplied to the motor armature is low resulting in low speed running of the motor. The other pair of thyratrons 209, 210 similarly produce changes in the motor field current, this, however, is only used to pre-set different speed levels, all normal regulation being accomplished by armature control. The motor speed is actually controlled by a pair of ganged potentiometers 223, 224, the control portion of each is compressed into half the range of adjustment and the other half is a conducting segment of negligible resistance. These are staggered so that the slide of one potentiometer is on its conductor segment while the other is on its control portion. The potentiometer control knobs are mounted at 243,247, Figs. 1 and 15, on a control pendant 145 arranged. for easy reach by the operator. The electronic control network also includes a potentiometer 225 for adjusting the minimum value of the motor speed range ; potentiometers 226 and 227 for adjusting the amount of 1R drop compensation and armature voltage respectively ; a potentiometer 228 for adjusting the field voltage ; a potentiometer 229 for adjusting the maximum value of the motor speed range; and a potentiometer 230 for adjusting the current limiting action of the controls. A twin diode full wave rectifier A supplies direct current for the electronic network to a pair of conductors 231, 232 supplied from a transformer 233 across the lines L1 L2. The voltages are regulated by valves B, G, which operate on the current arc-drop principle eliminating the effects of voltage variation. Current to the saturating winding 221 is supplied by the output of a triode D the potential of the control grid of this valve depends upon the voltage drop across resistor 7R to which this grid is connected through resistors 24R and 8R. The amount of voltage drop across 7R depends in turn upon how much current is passing through triode valves C and E. The valve C is employed for varying the drop across resistor 7R in accordance with the setting of the speed control potentiometer 223 whereas the triode E is part of a safety arrangement for limiting the current to the motor armature during starting. Automatic speed regulation is accomplished by comparing the armature voltage to a standard voltage the latter being derived from the regulated supply afforded by the valves B and G. The difference between these two voltages is amplified and applied to the grid of the triode D which saturates the reactor 215, the triode C is utilized in this connection. To effect accurate speed regulation compensation for changes in 1R drop is arranged for, a voltage being introduced into the armature control circuit proportional to the armature current and in such a direction as to hold a higher armature voltage as the load on the motor increases. A pair of coupling transformers with primary windings 238, 239 in the anode circuits of the thyratrons are utilized to derive a current proportional to the motor armature current, these are inductively coupled to secondary windings 240, 241, and a full wave rectifier Fl is used in this connection, the direct current voltage of F1 being applied to the network to subtract from that part of the armature voltage that is used as a feed back, thus causing a higher voltage to be maintained by the regulating action of the system. Provision is made in addition to the safety arrangement referred to above for voltage snubbin and preconditioning by the use of a triode J1 and duplex diode rectifier J which act to retard the application of field when the armature voltage exceeds a present amount as, for example, when speed control potentiometers are suddenly turned from the weak field condition to a speed calling for full field. Control pendant. The pendant 145, Fig. 15, is suspended at the operator's station and contains the switches 176, 177 and 179 for "run", "direction", and "inching" respectively, for spindle motor 34. Also carried on the pendant are similar switches for the motors 119 and 120 and the selector switches 182, 183, for the saddle and table or headstock and table respectively. A master stop switch 174 is located at the lower end which stops the entire machine operation. The speed control potentiometers 223, 224 and 244, 245, for motors 119 and 120 are carried within the pendant and operable by hand wheels 243, 247 which are geared so that one revolution thereof rotates the associated potentiometer shaft two rotations-one revolution for the slow-speed range after which a toggle switch 199 or 200 is opened to control the hydraulic valve solenoid for the high-speed range. On the descending scale of the latter the toggle switch is closed to switch again to the slow speed range.