Patent GB-1456150-A (GB)
Title: Feed rate changing device for grinding machine
IPC: B24B49/00
Filed: 1974-06-27
Abstract: 1456150 Grinding TOYODA-KOKI KK 27 June 1974 [17 July 1973] 28603/74 Heading B3D A grinding machine in which the feed rate of a grinding wheel is changed just before the wheel contacts the workpiece, or at the moment of contact of the wheel with the workpiece, comprises a grinding wheel G rotatably mounted on a wheel slide 4 slidably mounted on a bed 1 and movable by a feed device 11 towards and away from a workpiece W supported by a table 2. An electrode device 20 is mounted adjacent the grinding wheel and connected to an electric power source 25 for giving a potential to the surface of the grinding wheel. A detecting device 24 detects a difference in potential between the grinding wheel and workpiece to generate an output voltage which is memorized by a memory device when the wheel is distant from the workpiece. A setting device reduces the memorized output voltage at a predetermined rate to provide a reference voltage corresponding to a predetermined gap between the grinding wheel and workpiece. A comparator circuit compares the output voltage with the reference voltage to generate a feed rate changing signal when the output voltage attains the reference voltage, and a control device controls the feed device so as to change the feed rate of the wheel slide in accordance with the feed rate changing signal. The workpiece is rotatably supported between a headstock 3 and a tailstock on a work-table 2 slidable on the bed 1, and the slide 4 for the grinding wheel G, which is driven by a belt 6 from a motor 7, is movable towards and away from the workpiece by a hydraulic cylinder 11 connected by valve 14, 15 to a pump P. The grinding wheel is of conductive material and is in non-conductive relationship with its shaft 5. Alternatively, the wheel may be of non-conductive material. A coolant nozzle 8 is mounted on a guard 12 and connected by a valve 10 to a pump Pc. A conductive pipe 20 is electrically isolated from the wheel slide 4 and supplies conductive coolant, supplied through a restriction 23 from the pump Pc, through nozzles 21 to the periphery of the grinding wheel. The pipe 20 acts as an electrode to provide a potential to the grinding wheel periphery, and is connected to a non-conductive pipe 22 sufficient in length to prevent leaking of current through the coolant. The potential is supported to the pipe 20 from a variable resistance 26 and oscillator 25. An electrode 24, which detects the change in potential between the electrode 24 and pipe 20 as the grinding wheel approaches the workpiece, is electrically insulated from the guard adjacent a side surface of the grinding wheel and is connetted to a circuit (Fig. 4, not shown) including an amplifier, high pass filter circuit, a rectifier, a low pass filter circuit, a memory circuit, a setting circuit and a comparator, the output of which is connected to a switching transistor. An air nozzle 27 is fixed to the coolant nozzle 8 and connected by a valve 28 to a pump Pa. In operation, with the parts in their initial position as shown in Fig. 1, motor 7 is started to rotate the grinding wheel, pump Pc supplies coolant to the pipe 20 and nozzle 21, the throttle 23 being adjusted so that only the periphery of the wheel is wet, and pumps Pa and P are driven to supply air to nozzle 27 and to supply the operating fluid. Upon a start-signal being applied, the valve 28 is actuated so that air is supplied to nozzle 27 to prevent coolant from nozzle 21 scattering towards the workpiece. The oscillator 25 is operative to apply 30 volts to the pipe 20 and the electrode 24 acts as a condensor due to the wet periphery of the wheel. The potential from electrode 24 is passed to the amplifier, high pass filter, rectifier and low pass filter to produce an output voltage which varies as the grinding wheel approaches the workpiece from say 2 volts to 0À7 volts in a distance of 0À3 mm., 0À7 volts being the earth voltage. The output voltage from the low pass filter is input to one terminal of the memory circuit. The setting circuit reduces the voltage at a predetermined rate to a predetermined value corresponding to a predetermined gap between the wheel and workpiece to provide a reference voltage which is memorized and, as the wheel approaches the workpiece, is compared with the output from the low pass filter. When the voltage from the low pass filter is less than the reference voltage, a switching transistor activates valve 15 to reduce the feed rate of the grinding wheel just before it engages the workpiece. The voltages may be set so that the feed rate is changed at the moment of contact between the wheel and workpiece.