Method of operating a machine tool with a sensing probe in order to gather positional data for the calculation of tool offset parameters

In a machine tool comprising a spindle for driving a rotary cutting tool, the spindle having an axis of rotation, means for rotating the spindle through predetermined angles of rotation, a table for support of a workpiece thereon, the table being movable relative to the spindle transversely to the spindle axis, a surface-sensing probe mounted on the spindle, means for generating a probe signal at the instant of said probe being brought into a sensing relationship with a surface defined on said table, the signal occurring when the spindle axis is at a distance, defined as a probe offset, from the surface being sensed, said probe offset being liable to be different for different radii about the spindle axis, means responsive to the occurrence of a said probe signal for producing an output defining the position of the spindle axis relative to a primary datum which is fixed in relation to the table, and a computer adapted to store information defining the position of the spindle axis relative to the primary datum and adapted to read said output:

• the method of determining the position of the spindle axis in relation to surfaces to be machined on a said workpiece comprising the steps of:
• a. providing on the table a datum means defined by a cylindrical surface (24) which has an axis defining a datum axis (24A) which is parallel to the spindle axis (16A) and of known relation to said surfaces to be machined, the cylidnrical surface (24) defining a first pair of two surface regions (-DX, +DX) spaced apart in the direction (X) of a first diameter and a second pair of two surface regions (+DY, -DY) spaced apart in the direction (Y) of a seocnd diameter perpendicular to the first diameter, the datum axis (24A) having an acutal position (CA) which may differ from a demanded position (CN) of the spindle axis (16A), by an error defining a work offsets (WOX, WOY) in respect of the directions (X, Y) of said first and second diameters, said demanded position (CN) being stored in the computer,
• b. operating the machine to bring the probe into sensing relationship with one (-DX) of the first surface regions to produce a first said output (AX1),
• c. operating the machine to bring the probe into sensing relationship with the other of the first surface regions to produce a second said output (AX2),
• d. between operations (b) and (c) above, operating the machine to rotate the spindle through 180 degrees thereby to ensure that said probe offset is the same for both said sensing relationships,
• e. operating the computer to read said outputs (AX1, AX2) and determine the value WOX=CNX-(AX1+AX2)/2 defining said error in respect of the direction X of said first diameter,
• f. operating the machine to bring the spindle axis to a position defined by the value (AX1+AX2)/2 and repeat operations (b) to (e) above in respect of said second set of surface regions (-DY, +DY) thereby to determine a corresponding value WOY=CNY-(AY1+AY2)/2 defining said error in repsect of the direction Y of said second diameter.

In a machine tool comprising a spindle for driving a rotary cutting tool, the spindle having an axis of rotation means for rotating the spindle through predetermined angles of rotation, a table for support of a workpiece thereon, the table being movable relative to the spindle transversely to the spindle axis, a surface-sensing probe mounted on the spindle, means for generating a probe signal at the instant of said probe being brought into a sensing relationship with a surface defined on said table, the signal occurring when the spindle axis is at a distance, defined as a probe offset, from the surface being sensed, said probe offset being liable to be different for different radii about the spindle axis, means responsive to the occurrence of a said probe signal for producing an output defining the position of the spindle axis relative to a primary datum which is fixed in relation to the table, and a computer adated to store information defining the position of the spindle axis relative to the primary datum and adapted to read said output;

• the method of determining a said probe offset (PO) comprising the steps of:
• a. providing on the table a datum means defined by two test surfaces (-DX, +DX) spaced apart in a given direction (X) and having therebetween a known distance (F) a corresponding value of which is stored in the computer,
• b. operating the machine to bring the probe into sensing relationship with the first test surface (-DX) and produce a first said output (A1),
• c. operating the machine to rotate the spindle through 180 degrees,
• d. operating the machine to bring the probe into sensing relationship with the second test surface (-DX) and produce a second said output (A2), the rotation of the spindle at step (C) above establishing that the probe offset (PO) is the same for both said sensing relationships and establishing that the probe offset (PO) pertaining to one of said radii about the spindle axis is a function of the difference between said first and second outputs,
• e. operating the computer to read said outputs (A1, A2) and determine the value PO1=[F-(A2-A1)]/2 wherein the position A2 is assumed to be further from said primary datum than the position A1.

In a machine tool comprising a spindle for driving a rotary cutting tool, the spindle having an axis of rotation, means for rotating the spindle through pre-determined angles of rotation, a table for support of a workpiece thereon, the table being moveable relative to the spindle transversely to the spindle axis, a surface-sensing probe mounted on the spindle, means for generating a probe signal at the instant of said probe being brought into a sensing relationship with a surface defined on said table, the signal occuring when the spindle axis is at a distance, defined as a probe offset, from the surface being sensed, said probe offset being liable to be different for different radii about the spindle axis, means responsive to the occurrence of a said probe signal for producing an output defining the position of the spindle axis relative to a primary datum which is fixed in relation to the table, and a computer adapted to store information defining the position of the spindle axis relative to the primary datum and adapted to read said output;

• the method of determining a said probe offset (PO) comprising the steps of:
• a. providing on the table a datum means defined by a cylindrical surface which has an axis defining a datum axis which is parallel to the spindle axis and which is of known relation to said surfaces to be machine, the cylindrical surface defining a first pair of two surface regions (-DX, +DX) spaced apart in the direction (X) of a first diameter and a second pair of two surface regions (+DY, -DY) spaced apart in the direction (Y) of a second diameter perpendicular to the first diameter, the cylindrical surface having a known diameter a corresponding value of which is stored in the computer;
• b. operating the machine to bring the probe into sensing relationship with the first test surface (-DX) and produce a first said output (AX1);
• c. operating the machine to rotate the spindle through 180 degrees;
• d. operating the machine to bring the probe into sensing relationship with the second test surface (-DX) and produce a second said output (AX2), the rotation of the spindle at step (c) above establishing that the probe offset (PO) is the same for both said sensing relationships and establishing that the probe offset (PO) pertaining to one of the said radii about the spindle axis is a function of the difrerence between said first and second outputs;
• e. operating the computer to read said outputs (AX1, AX2) and determine the value POX1=[F-(AX2-AX1)]/2 wherein the position AX2 is assumed to be further from said primary datum that the position AX1;
• f. operating the machine to bring the probe again into sensing relationship with the first test surface (-DX) and produce a third said output (BX), there being no rotation of the spindle between the steps (d) and (e) above thereby establishing that another said radius, offset by 180 degrees from said one of the radii is a function of said third output (BX);
• g. operating the computer to read said third output (BX) and determine the value POX2=AX2+POX1-F-BX;
• h. operating the machine:
• (i) to bring the spindle axis to a position defined by the value (AX1+AX2)/2;
• and
• (ii) repeat operations (b) to (g) above in respect of said second set of surface regions (-DY, +DY) thereby to determine corresponding values (POY1, POY2) in respect of the direction Y of said diameter.

In a machine tool comprising a spindle having an axis of rotation, a table for support of a workpiece thereon, the machine being operable to effect relative movement between the table and the spindle transversely to said axis, a probe element mounted on the spindle, means for generating an output when, by a said relative movement, said element is engaged with a surface defined on said table, said output defining the instantaneous position of said axis relative to a datum which is fixed in relation to the table, and a computer adapted to read said output;

• the method of determining the position of said axis in relation to surfaces to be measured with aid of said element, comprising the steps of:
• a. providing on the table a datum means defined by a cylindrical surface defining a first pair of test surfaces spaced apart in the direction of a first diameter and a second pair of test surfaces spaced apart in the direction of a second diameter perpendicular to the first diameter, each surface of said pairs having associated therewith a said axis position, the cylindrical surface having a known diameter a corresponding value of which is stored in the computer;
• b. operating the machine to:
• (i) bring said axis into a position at least approximately on said first diameter;
• (ii) while holding the spindle against rotation, relatively move the spindle in the direction of the first diameter and engage said probe element sequentially into sensing relationship with the first test surfaces to produce a corresponding first pair of said outputs;
• c. operate the computer:
• (i) in accordance with at least one expression relating said outputs to said known diameter to determine the position of said axis in relation to at least one of said first test surfaces;
• (ii) in accordance with an expression relating said outputs one to the other to determine a center position of the spindle axis intermediate between said first test surfaces;
• d. operate the machine to:
• (i) bring the spindle axis to said probe center position;
• (ii) while holding the spindle against rotation, relatively move the spindle in the direction of the second diameter to engage said element sequentially with the second said test surfaces to produce a corresponding second pair of said outputs;
• and
• e. operate the computer to repeat operations b. (ii) and c. above in respect to said second pair of outputs thereby to determine the position of said axis in relation to at least one of said second test surfaces.