The present invention relates to a calibration tool for a Grinder machining for grinding an ophthalmic lens, the machine having two lens-carrier half-shafts carried by a carriage and means for displacing said half-shafts, and the invention also relates to a Grinder machining including such a calibration tool.
Nevertheless, such detection of loss of plunger contact is not very accurate, and is lacking in repeatability since the measurement is performed with the weight of the carriage resting on the calibration tool. Consequently, deformation of the carriage and of the lens-carrier half-shafts degrades the measurement taken. In addition, that method leads to substantial forces being applied to the surfaces of the grindwheels.
Nevertheless, that method generates large forces on the grindwheels, which grindwheels may be fragile. Furthermore, the loss of a step on the stepper motor gives rise to a measurement of accuracy that is no better than plus or minus two steps. Such measurement is not sufficient for adjusting the Grinder machining accurately.
To this end, the invention provides a calibration tool of the above-specified type, characterized in that it comprises a support adapted to be mounted on the lens-carrier half-shafts; at least one piezoelectric element fastened to the support; and at least one feeler member carried by the support, the feeler member having a feeler region and at least one bearing surface suitable, on contact being made between the feeler region and a surface of the Grinder machining , for applying a pressure on the piezoelectric element to cause it to generate a detection signal representative of said contact.
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