A fiber optic sensor probe system comprises an electromechanical arrangement system which enables a fiber optic probe to lock onto a null point relative to a target which null point represents an in focus condition for the probe relative to the target. A servomechanism feedback circuit maintains the probe in an in focus condition relative to the target if the target moves. A dithering motion is provided to the probe such that, when the electrical output of the probe has a frequency component which is the same frequency as that of the dither, an out of focus condition of the probe relative to the target exists and the servomechanism feedback system operates to correct it. A monochromatic light source is used to eliminate the problem of different spectral components of light having slightly different focal lengths. A second dither or oscillation of the servomechanism's motor drive voltage causes the motor to oscillate and thus enables it to avoid becoming stuck by static friction, therefore enabling the system to achieve its proper null point. Finally, the geometry of the probe is such that the lens face is not parallel to the target, so that flat regions in the area of the null response point of the output curve of the probe which might cause the probe to hunt excessively for the null point are eliminated.

A method of determining the displacement of a fiber optic sensor from a target in which a first lens is spaced from the target at a first distance an a second lens is spaced from said target at a second distance which provides the greatest intensity response at said first distance and thereafter spacing said first lens from said second lens to provide symmetrical slope values of response.

A displacement measuring instrument for measuring the displacement of a target including in combination a fiber optic lens assembly including means for maintaining said assembly in space relation with said target, dither means for vibrating said assembly toward and away from said target about the lens null along the axis of said assembly, first electronic means for providing a first output voltage proportional to displacement of said assembly from said target, second electronic means cancelling that portion of said first output voltage resulting from displacement due to said dither means and providing a second voltage resulting from displacement due to means other than said dither means, servo means receiving said second output voltage and moving said assembly with respect to said target to null said second output voltage and measurement means measuring the movement of said servo means.

Method and apparatus for optical inspection of transparent layers such as the wall of glass and plastic containers, using bifurcated fiber optic probes. One or more of such fiber optic probes are directed at the wall of a transparent container, and light emitted thereby is selectively reflected from both the inner and outer surfaces of the container wall. Each probe includes a pair of bifurcated fiber optic bundles which are disposed at different distances behind a 1:1 lens system, resulting in two focal points at different distances from the fiber optic probe. Relative motion of the inner and outer wall surfaces between these focal points results in measurable variations of the probe output signals, which variations may be interpreted to track wall thickness and concentricity. An alternative detection scheme uses a probe with a single bifurcated bundle, and reciprocates such probe relative to the container wall while measuring the separation of null points of the output signal.

An optical displacement sensor comprises a light source 2 coupled to an optical fiber 1 the end 5 of which is directed onto a reflector 3 the displacement of which is to be measured. A lens 4 of appropriate focal length is positioned between the end of the optical fiber and reflector 3 to focus the light emitted from fiber 1 onto reflector 3 so that the amount of light reflected back is a function of the position of reflector 3. A signal detector 6 is also coupled to fiber 1 to detect and measure the light reflected back from reflector 3. Additionally a further light source 8 optical fiber 7 and detector 10 are provided with the end 9 of fiber 7 positioned at the focus of lens 4 so that the light reflected back to detector 10 is independent of the position of reflector 3. The ratio of the measurements from the two detectors gives the position of the reflector 3 with compensation for the effects of the deterioration of its reflectance.