Patent GB-1242760-A (GB)
Title: Automatically operating on a workpiece with a cutting or forming tool
IPC: G05B19/18
Filed: 1969-10-20
Abstract: 1,242,760. Programmed control of machine tools. SIEMENS A. G. Oct. 20, 1969 [Oct. 18, 1968; Dec. 5, 1968], No.51432/69. Heading G3N. [Also in Division B3] In a machining operation in which the tool or workpiece is mounted on a rotary spindle, a rapid traverse is employed to bring about contact between the tool and workpiece, a torque transducer coupled to the spindle produces an electrical output which represents the torque applied to the spindle, and is supplied to threshold value devices, and when the torque applied exceeds a first threshold value, the rate of traverse is reduced, and when the torque exceeds a second threshold value, which is higher than the first threshold value there is brought about movement of the tool or work, such that the depth of cut is reduced, and/or the rate of traverse is maintained at a lower value so long as the torque exceeds the second threshold value, and when the torque falls below a third threshold value the tool or workpiece is moved, so as to increase the amount of cutting. Several examples of milling and turning are described. In a milling operation Figs. 4, 9, the machine tool is programmed to produce a flat face P 0 -P 5  on a workpiece W. A control system 1 is provided which supplies  Œ Y and  Œ X pulses to the machine tool 2. Three threshold-value signalling devices 12, 13, 14, with response levels M max -# M max and M max +# are connected to the machine tool torque pick-up via an amplifier and smoothing element 17. The signals from these devices determine the value of the machining operation through changeover switches 6, control reversing counters 7, 9, and pulse generators 8, 10 for X and Y directions. Also connected to the torque pick-up is a threshold value signalling device 11 which responds to a quantity proportional to the torque M min, and effects switching from fast traverse to machining traverse. Milling cutter F moves up to the workpiece at a fast rate and the tool spindle torque M is less than a value M min. When the tool contacts the work at P 0 , M exceeds M min and the machining traverse is switched in. If M rises to a value such that M max -# <M max, the fast machining traverse is switched in. If M were to rise to a value greater than M max then the slow machining traverse would be switched in, and the depth of cut reduced. If M is between M max -#, and M max along section P 0 -P 1  the workpiece is machined at a fast traverse. At P 1 , M max is exceeded, the fast traverse is switched to slow traverse, and a command is issued to move the tool in the +Y direction so as to reduce the cutting depth. Threshold value signalling device 13 is driven by a pulse generator 8, and supplies +Y pulses to the machine tool. At the same time these pulses are supplied to reversing counter 7. If M max +# is exceeded device 14 responds, and stops the X feed, and the +Y pulses are supplied to reversing counter 9. Cutter F moves to P<SP>1</SP> 2 , and M drops to less than M max +#, and X pulses are supplied to the machine tool. Details of the distance P<SP>1</SP> 1 -P<SP>1</SP> 2  is stored in counter 7 and details of the X distance which the tool would have traversed if the X feed had not stopped, is stored in counter 9. The cutter moves to P<SP>1</SP> 3  where M<M max -#, and a command is issued to pulse generator 8, which produces -Y pulses, in order to increase the depth of cut. These pulses are also supplied to reversing counter 7 and cause the latter to count backwardly. When the cutter has reached P<SP>1</SP> 4 , distance P<SP>1</SP> 1 -P<SP>1</SP> 2  will have been compensated for, i.e. the count in counter 7 will be zero. Generator 8 is halted, and the cutter traverses to P 5 . The operation is repeated until the cutter moves across the workpiece at a fast traverse. It is possible to include additional data, such as temperature of the cutting tool, or stability, into the control function. More than one tool may be controlled, and the monitoring of the spindle torque may be carried out by strain gauges.