Instrument for measuring curved surface variations

• US 3,911,257 A
• Filed: 05/23/1974
• Issued: 10/07/1975
• Est. Priority Date: 05/23/1973
• Status: Expired due to Term

• Current Assignee: Rank Taylor Hobson Limited
• Original Assignee: David John Whitehouse, Derek Gordon Chetwynd, Philip Ross Bellwood
• Inventors: Whitehouse, David John, Bellwood, Philip Ross, Chetwynd, Derek Gordon
• Primary Examiner(s): Botz, Eugene G.
• Application Number:
  US05/472,724
• Time in Patent Office: 502 Days
• Field of Search: 33/174Q 235/151.3
• US Class Current: 702/168
• CPC Class Codes: G01B 7/282 for measuring roundness
• CPC Class Codes: G01B 7/34 for measuring roughness or irregularity of surfaces

Abstract

A method of testing a curved surface of a body, which can be used on bodies having only partial arcs available for testing and apparatus for performing the method comprising drawing a sensor over the surface of the body between two end points at which the relative angular orientation of the sensor and the body are known, and calculating from the information signals from the sensor, and from signals representing the relative angular orientation of the body and the sensor during the traverse, the parameters of a best fit limacon from which data indicating the eccentricity between the centre of the partial arc on the body with respect to the centre of relative rotation can be obtained and also a signal can be generated representing a reference figure against which surface variations of the body over the partial arc can be compared.

Claims

1. A method of testing a body having at least a part-circular surface, comprising the steps of:

traversing a sensor over a limited arc, less than a full circle, of said surface by effecting relative rotation between said body and said sensor about a centre of relative rotation;

providing from said sensor amplified signals representative of the profile of the surface thereof, providing signals representative of the relative angular orientation of said body and said sensor, and conbining said sensor signals with said angular orientation signals to provide an output signal representative of a reference curve centred at the centre of said at least partcircular surface of said body.

2. The method of claim 1, wherein said reference curve produced from said sensor signals and said anguLar orientation signals has the form Rho ( theta ) R + xcos theta + ysin theta where R is the nominal radius of the reference line, x is the x coordinate of the centre of the workpiece with respect to the centre of the relative rotation of the workpiece and sensor, y represents the y coordinate of the centre of the workpiece with respect to the centre of relative rotation of the workpiece and sensor, and theta is a variable representing the relative angular orientation of the said body and said sensor at any instant during said traverse....

3. A method of determining the eccentricity of the centre of a body having an at least part-circular profile, comprising the steps of:

traversing a sensor over a limited arc, less than a full circle, over the surface of said body by effecting relative rotation between said body and said sensor, providing an amplified output signal from said sensor representing said profile of said surface between the end points of said traverse, providing signals representative of the relative angular orientation of said body and said sensor, and combining said sensor signal and said relative orientation signals to provide output signals representing the value of the parameters x and y as solutions of the set of equations obtained by minimising the integral in the equation;

4. The method of claim 3, wherein said signals representing said parameters x and y are demagnified and displayed to provide an output indication of the x and y coordinates of the centre of that part of said part circular surface traversed by said sensor with respect to the centre of relative rotation as origin.

5. Apparatus for testing the surface of a body having an at least part circular surface thereon comprising:

mounting means for said body, a sensor mounted with respect to said body mounting means wereby said sensor can be traversed over said body upon relative rotation between said sensor and said body mounting means, amplifier means connected to said sensor for providing amplified sensor signals upon traversing of said sensor over said surface of said body, means sensitive to the relative angular inclination between said sensor and said body mounting means for providing an output signal representative thereof, means connecting the output of said angular inclination sensitive means to a computing circuit and, means connecting the output of said amplifier to said computing circuit, said computing circuit operating, upon reception of said amplified sensor signals and said angular orientation signals to provide output signals representing the solutions x and y of the equation;

6. The apparatus of claim 5, wherein said computing circuit further includes means for deriving a signal representing the parameter R and for producing an output signal of the form:

Rho ( theta ) R + x cos theta + y sin theta to represent a reference line against which variations in said amplified sensor signal can be compared.

7. The apparatus of claim 5, wherein there are further provided means for demagnifying said signals representing said parameters x and y and display means for displaying the demagnified signals which thus represent the coordinates of the centre of said part-circular surface of the body, over the limited arc traversed by said sensor, with respect to said centre of relative rotation as origin.

8. The apparatus of claim 5, wherein said means for generating signals representing the relative angular orientation between said body mounting means and said sensor comprise sine and cosine potentiometers, means mechanically interconnecting said sine and cosine potentiometers with said sensor and said bodymounting means, and means connecting said sensor output and said sine and cosine potentiometers, whereby said sensor output signal is fed to said sine and cosine potentiometers.

9. The apparatus of claim 8, wherein the outputs from said sine and cosine potentiometers are connected to respective integrating circuits, means connecting the outputs of said integrating circuits to respective inverting circuits, a plurality of linear potentiometers connected between the outputs of said inverting circuits and the outputs of said integrating circuits, a further integrating circuit connected to the output of said amplifier, A further inverting circuit connected to the output of said further integrating circuit, and further linear potentiometers connected between the output of said further integrating circuit and the output of said further inverting circuit, said linear potentiometers and said further linear potentiometers operating to multiply the signals fed thereto from said integrators and said inverters by factors representing ratios of the contants A, B, C, D, E, F as follows:

10. The apparatus of claim 9, wherein there are further provided first and second summing circuits connected to the ouTputs of selected said potentiometers, the output of said first summing circuit representing the parameter x and the output from said second summing circuit representing the parameter y, first and second invertors connected to the outputs of said first and second summing circuits, first and second linear potentiometers connected respectively between the outputs of said first summing circuit and said first invertor, and between said second summing circuit, and said second invertor, the outputs from said first and second potentiometers being connected to the input of a third summing circuit, and the output from a selected one of said further potentiometers being connected to the input of said third summing circuit, whereby the output from said third summing circuit represents the parameter R as herein defined.

11. The apparatus of claim 10, wherein there is provided a further computing circuit connected to the outputs of said first and second potentiometers and to the output of said third summing circuit, the output signal from said further computing circuit being in the form Rho ( theta ) R + x cos theta + y sin theta and means for displaying said signal, said display means also being connected to the output of said amplifier whereby to receive signals representing said amplified sensor signals for display.

12. The apparatus of claim 5, wherein said means for producing signals representative of the relative angular orientation between said body and said sensor include means for determining the end points of the traverse of said sensor over said limited arc and means for controlling said computing circuit to operate only on sensor signals generated when said relative angular orientation of said body and said sensor lies between said end points.

13. The apparatus of claim 12, wherein said means for determining said end points includes first and second mechanically operated switches, and said means for controlling said computing circuit includes a bistable circuit and an electrically operated switch having a control input connected to the output of said bistable circuit, means connecting said first mechanically operated switch to the set input of said bistable circuit, means connecting said second mechanically operated switch to the reset input of said bistable circuit, mounting means for said first and second mechanically operated switches, switch operating means for said first and second mechanically operated switches, said switch operating means being mounted so that relative angular movement between said body and said sensor causes relative angular movement between said switches and said switch operating means whereby said set input of said bistable circuit is energised to open said electrically operated switch to pass sensor signals to said computing circuit only when said sensor lies between the end points of said traverse as determined by the positions of said first and second switches.

14. The apparatus of claim 13, wherein the relative angular positions of said mechanically operated switches are adjustable.

15. The apparatus of claim 13, wherein there is a third mechanically operated switch operable by said switch operating member and mounted on the side of said first mechanically operated switch remote from said second mechanically operated switch, a reset pulse generator connected to said third mechanically operated switch, and means connecting the output of said reset pulse generator to said reset input of said bistable circuit whereby, in operation, said third mechanically operated switch is operated by said switch operating means to energise said reset pulse generator to feed reset pulses to said bistable circuit to ensure this is in its reset state upon subsequent operation, during the same traverse of said first mechanically operated swtich to energise said set input of said bistable circuit.

16. The apparatus of claim 15, wherein said pulse generator is Also connected to reset inputs of said integrating circuits whereby to ensure these are cleared before the commencement of an operative part of a traverse upon operation of said first switch.

17. The apparatus of claim 12, wherein said means for determining said end parts of a traverse includes an optical encoder.

18. The apparatus of claim 17, wherein said optical encoder comprises a member mounted on said body mounting means having a plurality of alternate reflective and absorbent segments, a light source, means mounting said light source with said sensor whereby relative movement between said body mounting means and said sensor causes corresponding relative movement between said light source and said segmented member, a photo detector mounted with said light source for detecting light reflected from said reflective segments as said detector is traversed therepast and for producing output pulses in dependent thereon, counting means connected to the output of said detector for receiving and counting said detector output pulses to provide an output signal representative of the relative angular orientation of said body and said sensor.

19. The apparatus of claim 18, wherein a logic circuit is connected to the output of said counter, the output from said logic circuit being connected to the control input of an electrically operated switch connected in the output line from said sensor, said logic circuit operating to open said electrically operated switch only between two selected relative angular orientations of said body and said sensor.

20. The apparatus of claim 19, wherein said logic circuit is also connected to the reset inputs of said integrating circuits said logic circuit operating to apply reset pulses to said integrating circuits upon relative rotation of said body and said sensor toward one of said selected two relative angular positions when said body and said sensor are outside the range determined by said two selected relative angular orientations.

21. The apparatus of claim 5, wherein there are provided analogue-to-digital convertor means for connecting the output signals from said sensor into digital form, an optical encoder providing digital signals representative of the relative angular orientation of said body and said sensor, and special purpose digital computor means connected to the output of said optical encoder and said analogue-to-digital convertor means, said digital computer means operating to produce from the digital signals fed thereto ouput signals representing the parameters x, y and R.

22. The apparatus of claim 21, including sine and cosine lookup devices each fed with the output signal from said optical encoder, first and second multiplier circuits, means connecting the output from said sine potentiometer to said first multiplier, means connecting the output from said cosine potentiometer to said second multiplier, and means connecting the output from said analogue-to-digital connentor to both said first and said second multipliers.

23. The apparatus of claim 22, further comprising first and second accumulator registers, means connecting the output of said first multiplier to said first register, means connecting the output of said second multiplier to said second register, a third accumulator register, means connecting the output of said analogue-to-digital connector to said third accumulator register, timing control means, and means connecting the output of said timing control means to said first, second and third accumulator registers.

24. The apparatus of claim 23 further comprising:

a third multiplier circuit, memory storage means storing values of the constants A, B, C, D, E, and F, where

25. The apparatus of claim 24 further comprising:

a subtractor circuit, means connecting the output from said second accumulator register to said subtractor circuit, a forther multiplier circuit, means connecting the output from said memory storage circuit to said fourth multiplier means, means connecting the output of said third accumulator register to said fourth multiplier circuit, means connecting the output from said fourth multiplier circuit to said divider circuit, a fifth multiplier circuit, means connecting the output from said memory storage means to said fifth multiplier circuit, and means connecting the output from said subtractor circuit to said fifth multiplier circuit,

26. The apparatus of claim 25 further comprising a sixth multiplier circuit, means connecting the output from said fifth multiplier circuit to said sixth multiplier circuit, mean means connecting the output of said timing control circuit to said sixth multiplier circuit, a divider circuit, means connecting the output of said third accumulator register to said divider circuit, means connecting the output from said optical encoder to said divider circuit, an adder circuit, means connecting the output from said divider circuit to said adder circuit, and means connecting the output of said sixth multiplier circuit to said adder circuit.