Patent GB-1283083-A (GB)
Title: Electro-chemical grinding process
IPC: B23H5/08
Filed: 1969-10-16
Abstract: 1283083 Electro-chemical grinding HAMMOND MACHINERY BUILDERS Inc 16 Oct 1969 [7 Nov 1968] 50913/69 Heading C7B [Also in Division G3] An electro-chemical grinding operation is controlled by a variable control parameter to maintain an optimum operating condition, the control parameter utilizing a varying performance parameter whose magnitude is proportional to that of the control parameter and whose range of variation includes an inflection point which defines the optimum condition, and the control operation comprising the steps of detecting the performance parameter, producing a signal proportional to its variation, analyzing the variation and altering the control parameter in response to such analysis to further alter the performance parameter as required to maintain it within a zone including the inflection point. The specification discusses empirically-determined characteristics relating typical control and performance parameters and explains how the inflection point may correspond to a peak or trough in the characteristic and how the control may maintain operation at the inflection point or a point adjacent thereto. The characteristics discussed, Figs. 1 to 6 (not shown) are all derived for various values of workpiece table feed force and relate gap voltage to gap current or gap resistance or work feedrate or the power required to drive the grinding member, and gap current to gap resistance or the power to drive the grinding member. The embodiment shown in Fig. 8 employs conventional electrochemical grinding apparatus 10 to which is added a control system to maintain the gap current performance parameter within a zone including the optimum condition by variation of the gap voltage control parameter. A second control parameter is obtained by varying the workpiece feed force in accordance with the variation of gap current, so that the zone forms part of a three-dimensional characteristic, Figs. 7 and 7A (not shown), relating current, voltage and force. Generally the control system operates to repetitively sample the performance parameter, compare each sampled value with its predecessor and vary the control parameter in accordance with the result of the comparison, so that the performance parameter is progressively brought from an initial value corresponding to the start of the grinding operation to a value within the zone, where it is maintained irrespective of changes in the position of the zone caused by changes in the grinding conditions. The current is measured by a senser 29 whose signal is fed to control apparatus 27 comprising a timing section for generating synchronized pulse trains, which control logic and analytical sections for determining the change of current produced by a predetermined change of voltage and for producing a subsequent change of voltage whose sign is dependent on this determination. Thus the output voltage from source S is progressively increased as long as the increase in current is above a predetermined minimum and vice versa. The apparatus 27 comprises known components such as AND, OR, NAND and NOR gates, relays, counters and amplifiers, Fig. 13A (not shown). Each value of current is used to charge a capacitor for comparison with the subsequent value, the resulting difference controlling saturable on/off amplifiers to vary the output of source S as described above, by means of seriesconnected resistors each bridged by the contacts of relays controlled through an up/down counter and gates connected to the amplifiers. The apparatus 27 also produces a signal on line 32 representative of the current to vary the workpiece feed force through the transducer 25 and valve 22 controlling the air-pressure in the piston-cylinder combination 21, 24. The timing section of the apparatus 27 is controlled by a magnetic sensor 39 co-operating with magnetic polepieces on the hub 41 of the grinder 11. A complete grinding operation is described including an analysis of the action of the apparatus (27), Fig. 14 (not shown) and the function of the starting and stopping controls, Fig. 13B (not shown) and the limit switch 19. The Specification envisages the sensing of a number of performance parameters to provide signals for joint or separate application to an analytical section or sections feeding the logic section. Mention is also made of sensing the ratios of current or work feedrate or work feed force to the power consumed by the motor 13 driving the grinder 11 Two modifications are described which are generally similar to the embodiment of Fig. 8 but sense the motor current or power, Fig. 15 (not shown) or the workpiece feedrate and feed force Fig. 16 (not shown).