Patent GB-1440245-A (GB)
Title: Control of grinding machines
IPC: G01N3/58
Filed: 1973-06-14
Abstract: 1440245 Grinding M POSSATI [trading as FINIKE ITALIANA MARPOSS Sas] 14 June 1973 [15 June 1972] 28252/73 Heading B3D [Also in Division G1] Apparatus, for determining when the grinding efficiency of a grinding wheel 52 is inadequate, includes a gauging head 12 providing an electrical signal indicative of the size of a workpiece 11 being machined by the wheel. This signal is fed via amplifier 14 to a unit 16 which provides in response to the signal, an output signal representing the feed speed of the carriage carrying the wheel in accordance with a predetermined programme. The signal from amplifier 14 is also fed to a unit 15 arranged to derive the instantaneous value of workpiece material removal rate from the signal value. Output signals from units 15, 16 are fed to a comparator 17 producing their difference which is gated through switch 18 to an integrating and memory unit 20. The switch 18 is arranged to be closed by threshold unit 50 during the time when the size of the workpiece is decreased from one predetermined value to a second predetermined value (e.g. the nominal final size of the workpiece) these predetermined values being set at the inputs 53, 54 of the threshold unit 50, and the input signal to the threshold unit is provided from the amplifier 14. The difference signal is also fed to a control unit 19 for comparison with a reference signal at 51 which is determined empirically from the signals appearing at the output of comparator 17 when the grinding efficiency of the wheel is high. When the difference signal from the comparator is greater than the reference signal at 51 the unit 19 provides an enabling signal to unit 20 whereby it integrates the signal from the comparator for a time #t and stores the integral in a memory. Further the unit 20 sums the integrals from a number n of successive integrations in accordance with U=# 1 <SP>n</SP>-(V A -V p ).#t where V A  is a voltage proportional to workpiece material removal rate and V p  is a voltage proportional to programmed speed. The output of unit 20 is fed to a unit 21 where it is compared with a pre-set value and, when the output exceeds the preset value, the unit 21 initiates dressing of the wheel 52 and at the same time, via unit 22, clears the memory circuit of the unit 20. Alternative embodiment, Figs. 4, 5.-An input amplifier 32 receives the output of the workpiece gauging head and applies signals to the threshold unit 57 which controls an oscillator 58 to provide oscillations only when the amplifier output is between two preset values. A counter 50 counts the number of oscillations fed to it from the oscillator which count is proportional to the time T during which the oscillator is enabled. With reference to Fig. 5, S 1  is the workpiece size corresponding to the start of the final machining phase which ends when the nominal workpiece size (S 0 ) is reached. Curve 55 represents the workpiece size S with respect to time t for a workpiece 11 machined by an efficient grinding wheel and curve 56 is representative of the effect of a grinding wheel with poor grinding efficiency. It can be seen that the required grinding time for removal of the last portion of workpiece material is greater for an efficient grinding wheel than for an inefficient grinding wheel. The apparatus of Fig. 4 is arranged to calculate the value of function f where f= (1/T-K) in which T is the time taken to remove a predetermined amount of material to reduce the measured workpiece dimension from S 1  to S 0  and K is an empirical constant. This function is determined in the processing unit 61 from which the output signal is passed to a threshold circuit 62 for comparison with a pre-set reference value and when the sum of the function determined for successive workpieces exceeds a reference value the circuit 62 initiates dressing of the wheel.