Method of and apparatus for determining relative position of a tool member to a workpiece in a machine tool

Claim 3

The method defined in claim 1 wherein the step (a) is carried out upon interrupting a given machining operation.

Claim 4

The method defined in claim 2 wherein the step (a) is carried out with said tool member and said workpiece in said given relative position after completing a given machining operation, the method further comprising determining the machining accuracy of said operation from said relative position determined.

Claim 5

The method defined in claim 3 wherein said machining accuracy is determined by calculating a deviation in distance from a predetermined correct relative position between said tool member and said workpiece.

Claim 6

The method defined in claim 2 wherein said machine tool is an electroerosion machine tool and the step (a) is carried out upon interrupting an electroerosion machining current to establish a monitoring period and wherein the steps (a), (b) and (c) are carried out during said monitoring period and with a monitoring electrical signal independent of said electroerosion machining current.

Claim 7

The method defined in claim 5 wherein said electroerosion machine tool is an EDM machine tool and wherein said electroerosion machining current is applied between said tool member and said workpiece in the form of a succession of machining pulses and said monitoring signal is applied between said tool member and said workpiece in the form of at least one monitoring pulse during said monitoring period.

Claim 8

The method defined in claim 1, further comprising the step of correcting relative position of said tool member to said workpiece by calculating a deviation in distance of said one of the given and shifted relative positions from a predetermined correct relative position between said tool member and said workpiece and relatively displacing said tool member and said workpiece from said one of given and shifted relative positions by said deviation in distance.

Claim 9

The method defined in claim 1, further comprising the step of determining the specific resistivity of a gap between said tool member and said workpiece by calculating it from said first and second measurement values and said known distance.

Claim 10

The method defined in claim 8 wherein said machine tool is an electroerosion machine tool and said specific resistivity is of an electroerosion gap formed between said tool member and said workpiece and filled with a liquid machining medium, the method further comprising controlling the supply of said liquid machining medium in response to said specific resistivity determined.

Claim 11

The method defined in claim 7, further comprising the step of determining the specific resistivity of a gap between said tool member and said workpiece by calculating it from said first and second measurement values and said known distance, wherein said deviation is obtained from said specific resistivity determined.

Claim 12

The method defined in claim 10, further comprising the steps of calculating a particular electrical resistance value corresponding to said predetermined correct relative position from said specific resistivity determined, wherein said tool member and said workpiece are relatively displaced until said electrical resistance therebetween becomes said particular value.

Claim 13

The method defined in claim 7, claim 10 or claim 11, further comprising the step of numerically displaying said deviation determined.

Claim 14

The method defined in claim 1 wherein said tool member and said workpiece are relatively displaced by said known distance by imparting mechanical vibrations to one of said tool member and said workpiece with an amplitude equivalent to said known distance and the step (c) is carried out by measuring the electrical resistance between said tool member and said workpiece one of which is vibrated.

Claim 15

A machine tool comprising in combination: a tool member for machining a workpiece in a given machining operation; means for interrupting said machining operation with said machine tool; drive means for relatively displacing said tool member and said workpiece to hold them in a given relative position when said given machining operation is interrupted by said interrupting means and subsequently to place them in a relative position shifted by a known distance from said given relative position during a period of the said interruption of the machining operation, sensing means for measuring the electrical resistance between said tool member and said workpiece in said given relative position and subsequently the electrical resistance between said tool member and workpiece in said shifted relative position to give a first and second measurement values, respectively; and computing means for calculating at least one of said given and shifted relative positions from said first and second measurement values and said known distance.

Claim 16

A machine tool comprising in combination: a tool member for machining a workpiece in a given machining operation; means for interrupting said machining operation with said machine tool; drive means for relatively displacing said tool member and said workpiece to hold them in a given relative position when said given machining operation is interrupted by said interrupting means and subsequently to place them in a relative position shifted by a known distance from said given relative position during a period of the said interruption of the machining operation, sensing means for measuring the electrical resistance between said tool member and said workpiece in said given relative position and subsequently the electrical resistance between said tool member and workpiece in said shifted relative position to give a first and second measurement values, respectively; and computing means for calculating at least one of said given and shifted relative positions from said first and second measurement values and said known distance.

Claim 17

The machine tool defined in claim 14 wherein said computing means is adapted to calculate a deviation in distance of said one of the given and shifted relative position from a predetermined correct relative position between said tool member and said workpiece.

Claim 18

The machine tool defined in claim 15, further comprising control means in response to said computing means for acting on said drive means to relatively displace said tool member and said workpiece by said deviation in distance.

Claim 19

The machine tool defined in claim 15, further comprising display means connected with said computing means for numerically displaying said deviation in distance.

Claim 20

The machine tool defined in claim 14, further comprising display means connected with said computing means for numerically displacing said one of the given and shifted relative positions.

Claim 21

The machine tool defined in claim 14 wherein said computing means is adapted to calculate the specific resistivity of a gap between said tool member and said workpiece from said first and second measurement values and said known distance.

Claim 22

The machine tool defined in claim 14 wherein said drive means includes vibrator means for imparting to one of said tool member and said workpiece mechanical vibrations with an amplitude equivalent to said known distance.

Claim 23

The machine tool defined in claim 14 wherein said known distance is a length between 0.5 and 10 micrometers.

Claim 24

The machine tool defined in claim 21 wherein said length is 1 to 2 micrometers.