| 摘要 |
<p>PURPOSE:To perform surely touch detection without being affected by the change in the electric resistance owing to the oil film of bearings by providing means for detecting the current flowing in a secondary current path and the voltage induced between a spindle and a spindle head, and comparing the combined value of both outputs with a set value. CONSTITUTION:The electric resistance between the inner and outer rings of bearings 13, 14 changes with the formation of the oil film. While the electric resistance is small, large contact current flows to a current path 40 for an induction coil 22 upon touching of a tool T and work W, and a large voltage signal is transmitted from a current detecting circuit 28 via a winding 24 and a resistor 27. On the other hand, when the electric resistance is large, a large induced voltage is generated between the inner and outer rings of the bearings 13, 14, and a large voltage signal is transmitted from a voltage detecting circuit 29. The outputs of the circuits 28, 29 are combined respectively through a level shift circuit 31 and a gain adjusting circuit 32 in an adder 34. The combined value is compared with a set value in a discriminating circuit 35, and when the value exceeds the set value, a touch detection signal TDS is outputted and the touch detection is surely accomplished irrespectively of the change in the electric resistance of the bearings.</p> |
