Surface measurement instruments
First Claim
1. A method of determining the coordinates of the centre of curvature of the curved surface of a workpiece with respect to a predetermined frame of reference the origin of which coincides with the centre of relative rotation between the workpiece and a sensor of a surface measurement instrument of the type having a table on which a workpiece is mounted and a sensor which is drawn in contact with the surface of the workpiece to produce output signals representative of surface variations upon relative rotation of the sensor and the table on which the workpiece is mounted, comprising the steps of:
- traversing the sensor over the workpiece surface to provide an output signal representing said surface, electrically deriving from said sensor output signal three signals representing the value of the radial distance of said surface of said workpiece from said centre of relative rotation at three points along the traverse of said sensor, the middle point lying at the intersection of one of the axes of said predetermined frame of reference and the workpiece surface, and the other two points subtending at the centre of relative rotation an angle φ
with the middle point, and electrically deriving from said three signals two output signals representing the expressions ##EQU9## where x and y respectively represent the coordinates of the centre of the workpiece parallel to and perpendicular to said one axis and r1, r2, r3 respectively represent the radial distance determined at said three points in order along said traverse.
1 Assignment
0 Petitions
Accused Products
Abstract
A method of determining the coordinates of the center of curvature of the curved surface of a workpiece on a surface measurement instrument of the type having a workpiece table rotatably mounted on a main spindle, and a sensor for contacting the surface of a workpiece mounted on the table. The method comprises the steps of traversing the sensor over the workpiece surface and deriving three signals representing the value of the radial distance from the spindle to the workpiece surface at three points spaced along the traverse. From these values, and a knowledge of the angular separation of the three points an approximation for the coordinates of the center of the curved surface of the workpiece with respect to the spindle can be derived using the algorithm ##EQU1## WHERE X AND Y RESPECTIVELY REPRESENT THE COORDINATES OF THE CENTER OF THE WORKPIECE, R1, R2, R3 REPRESENT THE RADIAL DISTANCE FROM THE SPINDLE AXIS TO THE WORKPIECE SURFACE AT THE THREE POINTS ALONG THE TRAVERSE, AND φ REPRESENTS THE ANGULAR SEPARATION OF THE THREE POINTS.
Using a further algorithm derived from this an estimate of the radius of curvature of the surface can also be provided.
-
Citations
13 Claims
-
1. A method of determining the coordinates of the centre of curvature of the curved surface of a workpiece with respect to a predetermined frame of reference the origin of which coincides with the centre of relative rotation between the workpiece and a sensor of a surface measurement instrument of the type having a table on which a workpiece is mounted and a sensor which is drawn in contact with the surface of the workpiece to produce output signals representative of surface variations upon relative rotation of the sensor and the table on which the workpiece is mounted, comprising the steps of:
traversing the sensor over the workpiece surface to provide an output signal representing said surface, electrically deriving from said sensor output signal three signals representing the value of the radial distance of said surface of said workpiece from said centre of relative rotation at three points along the traverse of said sensor, the middle point lying at the intersection of one of the axes of said predetermined frame of reference and the workpiece surface, and the other two points subtending at the centre of relative rotation an angle φ
with the middle point, and electrically deriving from said three signals two output signals representing the expressions ##EQU9## where x and y respectively represent the coordinates of the centre of the workpiece parallel to and perpendicular to said one axis and r1, r2, r3 respectively represent the radial distance determined at said three points in order along said traverse.- View Dependent Claims (2, 3, 4, 5, 6, 7)
-
8. Apparatus for determining the coordinates of the centre of curvature of the curved surface of a workpiece with respect to a predetermined frame of reference the origin of which coincides with the centre of relative rotation between the workpiece and a sensor of a surface measurement instrument of the type having a table on which a workpiece is mounted and a sensor which is drawn in contact with the surface of the workpiece to produce output signals representative of surface variations upon relative rotation of the sensor and the table on which the workpiece is mounted,
said apparatus comprising: -
means for traversing the sensor over the workpiece surface whereby to provide an output signal representing said surface, means for deriving from said sensor output signal three signals representing the value of the radial distance of said surface of said workpiece from said centre of relative rotation at three points along the traverse of said sensor, the middle point lying at the intersection of one of the axes of said predetermined frame of reference and the workpiece surface, and the other two points subtending at the centre of relative rotation an angle φ
with the middle point, andmeans for deriving from said three signals two output signals representing the expressions ##EQU10## where x and y respectively represent the coordinates of the centre of the workpiece parallel to and perpendicular to said one axis and r1, r2, r3 respectively represent the radial distance determined at said three points in order along said traverse. - View Dependent Claims (9, 10, 11, 12, 13)
-
Specification