METHOD OF, AND APPARATUS FOR GAUGING, INSPECTING OR MEASURING PHYSICAL PROPERTIES OF OBJECTS

• US 3,814,520 A
• Filed: 05/28/1971
• Issued: 06/04/1974
• Est. Priority Date: 05/28/1971
• Status: Expired due to Term

• Current Assignee: Barry John Biddles, Lionel Richard Baker, Thomas Llewellyn Williams
• Original Assignee: Barry John Biddles, Lionel Richard Baker, Thomas Llewellyn Williams
• Inventors: Baker, Lionel Richard, Biddles, Barry John, Williams, Thomas Llewellyn
• Primary Examiner(s): Wibert, Ronald L.
• Assistant Examiner(s): Clark, Conrad
• Application Number:
  US05/148,104
• Time in Patent Office: 1,103 Days
• Field of Search: 356/71,156,159,160,164-168,171 350/16SF 250/200,211
• US Class Current: 356/71
• CPC Class Codes: G01B 11/00 Measuring arrangements characterised by the use of optical techniques
• CPC Class Codes: G01B 11/08 for measuring diameters
• CPC Class Codes: G01M 11/0292 of objectives by measuring the optical modulation transfer function photometry G01J

Abstract

An apparatus for gauging inspecting or measuring properties of objects and employing a detecting device receiving light from an image of the object which light is influenced in accordance with the property under investigation. The detecting device has an array of photo-electric elements or sensors which are separated by the use of masks or other means into two units each exhibiting a sinusoidal variation in sensitivity to the light received along a particular direction. The sinusoidal variations of the units are mutually displaced by 90 electrical degrees so that the device can produce electrical signals corresponding to the real and imaginary parts of a Fourier transform of the distribution of intensity of light in the image. These signals are processed to extract information about the property under investigation.

Claims

1. A method of gauging, inspecting or measuring a physical property of an object comprising the steps of providing a detecting device having two units sensitive to electromagnetic radiation and each exhibiting a sinusoidal distribution in radiation sensitivity along a predetermined path with the sinusoidal distribution of one unit being effectively displaced by a quarter of the period thereof in relation to the other unit, forming an image of said object on said detecting device and producing from said detecting device first and second electrical signals indicative, respectively, of the real and imaginary parts of a Fourier transform of the spatial distribution of the intensity of radiation in said image.

2. A method according to claim 1, further comprising modulating an A.C. carrier wave with the outputs from the units and processing and demodulating the resultant waveform to produce said signals.

3. A method according to claim 1, further comprising feeding the outputs from the units into a combination of D.C. amplifiers to produce said signals.

4. A method according to claim 1, further comprising feeding the outputs from the units to potentiometers to produce said signals.

5. A method according to claim 1, further comprising charging the units to a high reference voltage and allowing the units to discharge according to the amount of radiation received thereby.

6. A method according to claim 5, further comprising charging each of two elongate units sensitive to said radiation and constituting part of said detecting device to a high reference voltage simultaneously with an associated one of said two units, allowing said elongate units to discharge according to the amount of radiation received thereby, and feeding the difference in the outputs from each of said two units and its associated elongate unit to a sample and hold means whenever the output from either of said units reaches a low reference voltage.

7. A method according to claim 1 further comprising applying said first and second electrical signals to the X and Y plates of an oscilloscope.

8. A method according to claim 1, further comprising modulating each of said signals with a carrier wave, one signal being modulated in a sinusoidal manner and the other signal being modulated in a co-sinusoidal manner, adding said modulated waveforms and demodulating the resultant waveform to produce a voltage proportional to the modulus of the Fourier transform.

9. A method according to claim 1, further comprising making the period of said sinusoidal distributions equal to the size of the image of a reference object to produce a zero modulus for the associated Fourier transform and gauging other objects by determining the change in modulus produced thereby.

10. A method according to claim 1, further comprising altering the period of said sinusoidal distribution to cover a range of spatial frequencies.

11. A method according to claim 1, further comprising forming an image of a reference object scanning the images across the device in the direction of said sinusoidal distribution, deriving a voltage proportional to the modulus of the Fourier transform for each image from the electrical signals associated therewith, and comparing the modulus of one image with that of the other image.

12. A method according to claim 1, further comprising defining said image with a slit and partially rotating the detecting device relative to the slit until the size of the defined image equals the period of the sinusoidal distribution.

13. An apparatus for gauging, inspecting or measuring some physical property of an object;

said apparatus comprising means for forming an image of the object, a detecting device for receiving said image of the object, said device having two units sensitive to electromagnetic radiation, each unit exhibiting a sinusoidal distribution in sensitivity to said radiation along a predetermined path, with the sinusoidal distribution of one unit being effectively displaced by a quarter of the period thereof in relation to the other unit, and means, including said detecting device, for producing separate electrical signals indicative of the real and imaginary parts of a Fourier transform of the distribution of intensity of radiation in said image at at least one spatial frequency.

14. An apparatus according to claim 13, further including a first pair of outputs connected to one of said two units and a second pair of outputs connected to the other of said two units and a first potentiometer coupled to said first pair of outputs and a second potentiometer coupled to said second pair of outputs.

15. An apparatus according to claim 13, wherein the detecting device further includes two additional units each formed from an elongate array of radiation sensitive elements, the output of each of said elongate units being operably connected to the output of one of said two units.

16. An apparatus according to claim 15, further including first and second potentiometers, the output of each elongate unit being connected to the output of its associated one of two units through one of said potentiometers, said first and second electrical signals being taken from the potentiometers.

17. An apparatus according to claim 15, wherein a plurality of D.C. amplifiers are provided to combine the outputs from said units and produce said signals.

18. An apparatus according to claim 15, further comprising means for charging the units to a high reference voltage, the units being thereafter allowed to discharge at a rate dependent upon the radiation received thereby, means for sensing whenever the output from the units reaches a low reference voltage, and means activated by said sensing means for sampling the difference between the outputs of one of the said two units and its associated elongate unit and for storage of the difference value.

19. An apparatus according to claim 13, further including means for modulating an a.c. carrier wave, means for producing said carrier wave, the outputs from said two units being connected to said modulating means to modulate the a.c. carrier wave and means for processing and demodulating the Resultant waveform to produce said first and second electrical signals.

20. An apparatus according to claim 13, wherein the detecting device is provided with a planar mask at least defining said two units.

21. An apparatus according to claim 20, further comprising radiation guides devices to couple radiation from the open areas of the mask to the photoelectric elements.

22. An apparatus according to claim 13, wherein the detecting device comprises a photo-etched silicon chip and a planar mask to delineate the areas forming the units.

23. An apparatus according to claim 22, further comprising radiation guides devices to couple radiation from the open areas of the mask to the photoelectric elements.

24. An apparatus according to claim 13, further comprising an oscilloscope the X and Y plates of said oscilloscope being responsive to said first and second electrical signals, respectively.

25. An apparatus according to claim 15, further comprising means for modulating each of said signals with a carrier wave, one signal being modulated in a sinusoidal manner and the other signal being modulated in a cosinusoidal manner, means for adding said modulated waveform and means for demodulating the resultant waveform to produce a voltage proportional to the modulus of the Fourier transform.

26. An apparatus according to claim 13, further comprising operational amplifiers receiving said signals and arranged to produce a voltage proportional to the modulus of the Fourier transform.

27. An apparatus according to claim 13, further including means for varying the period of the sinusoidal distribution in sensitivity of the units of the detecting device.

28. An apparatus according to claim 13, wherein there is additionally provided means for forming an image of a reference object on the device, means for scanning the images of the object under investigation and the reference object across the device in the direction of said sinusoidal distribution means for deriving from the signals associated with each image a voltage proportional to the modulus of the Fourier transform of the image, and means for comparing the modulus of one image with the modulus of the other image.

29. An apparatus according to claim 13, wherein the image forming means includes a source of radiation and one or more lenses.

30. An apparatus according to claim 29, further comprising means for chopping the radiation from said source.

31. An apparatus according to claim 13, wherein the image formed by the image-forming means is defined by a slit further including means for partially rotating the detecting device relative to said slit.

32. An apparatus according to claim 13 further comprising a linear elongate strip of radiation-sensitive elements extending along said predetermined path so as to receive said image and produce a reference signal thereform.