Measuring apparatus

• US 4,080,741 A
• Filed: 08/11/1975
• Issued: 03/28/1978
• Est. Priority Date: 08/07/1974
• Status: Expired due to Term

• Current Assignee: Rank Taylor Hobson Limited
• Original Assignee: The Rank Organisation Ltd.
• Inventors: Siddall, Graham John, Garratt, David
• Primary Examiner(s): Aegerter, Richard E.
• Assistant Examiner(s): Little, Willis
• Application Number:
  US05/603,582
• Time in Patent Office: 960 Days
• Field of Search: 33/174 L, 33/174 Q, 33/174 R, 33/178 E, 33/174 P, 33/180 R, 33/1 M
• US Class Current: 33/502
• CPC Class Codes: G01B 7/293 for measuring radius of curvature

Abstract

With stylus type measuring instruments for the measurement of surface roughness or form an improved method of setting up employs a reference body having a cylindrical or part-cylindrical surface. By probing the curved reference surface a datum point is established. The reference body is then moved by a predetermined amount with respect to this datum and acts as a secondary reference standard.

Claims

1. A method of setting the pick-up of an instrument of the type comprising:

a workpiece support table,

an X-Y coordinate table mounted on the support table,

a pick-up on a pick-up support mounted with respect to said workpiece support table such that at least one of said pick-up and said workpiece support table are rotatable about a fixed datum axis of the instrument,

adjustment means carried by said workpiece support table to rectilinearly displace said workpiece support table, and

means for measuring displacements of said coorindate table with respect to said workpiece support table,

whereby to position said pick-up at a selected radial position, said method comprises the steps of;

locating on said X-Y coordinate table a reference body having an at least partly cylindrical surface,

centering said reference body on said X-Y coordinate table with respect to said datum axis by causing said pick-up to traverse over the cylindrical surface of said reference body and adjusting said adjustment means of said workpiece support table until the pick-up output is substantially constant at a certain value,

adjusting said X-Y coordinate table to displace said reference body by a selected distance away from said datum axis,

adjusting the radial position of said pick-up until it contacts the surface of said reference body,

turning one of said reference body and said pick-up back and forth over a limited range about said datum axis to establish the relative angular position of said pick-up and said reference body corresponding to a turning point of the output signal from said pick-up, and

further adjusting the radial position of said pick-up while continuing to effect back and forth turning movement of one of said pick-up and said reference body, to adjust the value of the pick-up output signal at said turning point to a selected value.

2. The method of claim 1, wherein said further adjustment of the radial position of said pick-up adjusts said pick-up output signal to the same value as that upon centering of the reference body.

3. The method of claim 1, which comprises the step of displaying the output signal from the pick-up on a chart, and in which said further adjustment to the radial position of said pick-up moves the chart display line to a preselected position on said chart.

4. The method of claim 1, which comprises the step of utilizing as said reference body a body which has a closed semi-cylindrical surface and a flat surface and in which said adjustment to the radial position of said reference body moves said reference body to a position where said pick-up can be brought into contact with the flat face thereof.

5. The method of claim 1, which comprises the step of utilizing as said reference body a body which has a closed semi-cylindrical surface and in which said adjustment to the radial position of said reference body moves said reference body to a position where said pick-up can be brought into contact with the semi-cylindrical surface thereof.

7. A method of determining the radius of a component the nominal radius of which is known using an instrument of the type comprising:

a workpiece support table,

a pick-up on a pick-up support mounted with respect to said workpiece support table such that at least one of said pick-up and said workpiece support table are rotatable about a datum axis of the instrument,

an X-Y coordinate table carried by said workpiece support table, and

means for measuring displacements of said X-Y coordinate table with respect to said workpiece support table,

which method comprises the steps of utilizing the method of claim 1 to set the radial position of the pick-up to said nominal radius, substituting the component under test for said reference body, traversing said pick-up in contact with the component under test and determining the difference in the mean value of the output signal from the pick-up during the traverse of the component under test from selected value thereof to provide an indication of the mean value of the radius of the component under test.

8. The method of claim 7, which comprises the steps of displaying said pick-up output signal on a graduated chart during the traverse thereof around the component under test, and

using the reading on said chart to establish the radius of the component under test.

6. A method of setting the pick-up of an instrument of the type comprising:

a workpiece support table,

an X-Y coordinate table mounted on the workpiece support table,

a pick-up on a pick-up support mounted with respect to said workpiece support table such that at least one of said pick-up and said workpiece support table are rotatable about a fixed datum axis of the instrument, and

means for measuring displacements of said X-Y coordinate table with respect to said workpiece support table,

whereby to position said pick-up at a selected radial position, said method comprising the steps of;

locating on said X-Y coordinate table a reference body having an at least partly cylindrical surface,

rotating one of said pick-up and said workpiece table about said datum axis with said pick-up in contact with the surface of said reference body,

feeding the output from said pick-up to a computer which calculates from it the radius of the least squares reference circle as said pick-up and said workpiece are relatively rotated, storing a signal representing said radius and computing from it the required displacement of said pick-up to set it to said selected radial position,

adjusting said X-Y coordinate table to move said reference body away from said datum axis by said required displacement,

adjusting the radial position of said pick-up until it contacts the surface of said reference body,

turning one of said reference body and said pick-up back and forth about said datum axis over a limited range to establish the relative angular position of said pick-up and said reference body corresponding to a turning point of the output signal from said pick-up, and

further adjusting the radial position of said pick-up while continuing to effect back and forth turning movement of one of said pick-up and said reference body, to adjust the value of the pick-up output signal at said turning point to a selected value which is determined by said computer.

9. A method of determining the radius of a component the nominal radius of which is known using an instrument of the type comprising:

a workpiece support table,

a pick-up on a pick-up support mounted with respect to said workpiece support table such that at least one of said pick-up and said workpiece support table is rotatable about a datum axis of the instrument,

an X-Y coordinate table carried by said workpiece support table, and

means for measuring displacements of said X-Y coordinate table with respect to said workpiece support table,

which method comprises the steps of utilizing the method of claim 6 to set the radial position of the pick-up to said nominal radius by substituting the component under test for said reference body, traversing said pick-up in contact with the component under test and determining the difference in the mean value of the output signal from the pick-up during the traverse of the component under test from said selected value thereof to provide an indication of the mean value of the radius of the component under test.