US 4,375,921 AGranted

Dimension measuring apparatus

AssigneeSelective Electronic, Inc.

InventorKarl-Erik Morander

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Abstract

A device for accurately measuring a dimension associated with a remote object without contacting the object itself is disclosed. A beam of light is directed at a surface of the object and a reflected portion of the beam is detected at a photodetector element. The particular dimension of the object is determined mathematically by measuring the distance by which the reflected light signal is offset from a predetermined point on the photodetector which is aligned with a reference plane at the object. By the use of two heads and respective light beams and photodetectors, a remote object's thickness can also be measured. In order to compensate for the angular relationship between the object's surface and that of the photodetector, a linearizing calibration circuit is included in which preset corrections are recorded in programmable memory units. The calibration settings are determined during manufacture and correct for each normally non-linear reading at incremental distances within a prescribed measurement range. Further accuracy of the system is obtained by using a high frequency sampling circuit to modulate the light source, with a demodulating circuit serving to discriminate between the input light beam and extraneous ambient light signals.

Claims8

Dependent claims

Apparatus for measuring a dimension associated with a remote object having at least one reflective surface comprising in combination a source of controllable light directed at said surface at a first predetermined angle to generate a corresponding reflected light signal, detection means for receiving and measuring said reflected light signal at a second predetermined angle, means for developing a transmittable signal based on said reflected light signal for readout of said dimension, correction means for adjusting said transmittable signal to eliminate non-linear errors attributable at least to the lack of perpendicularity between said first and second predetermined angles, and output means for processing said adjusted transmittable signal to generate an output display signal corresponding to said dimension of said remote object, wherein said dimension represents the distance between a predetermined point and said reflective surface of said object, and wherein said correction means includes pre-calibrated control means for developing a group of linearizing signals dependent on at least said lack of perpendicularity and on the material comprising said object to adjust said transmittable signal in accordance with a comparison of said transmittable signal and a selected one of said linearizing signals, wherein said pre-calibrated control means includes a programmable memory unit for receiving periodically generated correction signals during a separate calibration cycle, wherein said correction means further includes guiding means for providing a fixed transport path, means movable along said guiding means for establishing a positionally controllable detecting surface, means mounted on said guiding means for generating calibration signals comparable to said controllable light source signal and said reflected light signal, means for determining the non-linear departure of said calibration signals corresponding to said reflected light signal, means for effectively cancelling said non-linear departure in said calibration signals corresponding to said reflected light signal and for delivering said correction signals to said memory unit, and control means included in said movable means for monitoring the movement of said detecting surface at discrete detectable positions along said transport path and for causing said correction signals to be generated and communicated to said memory unit for each of said discrete detectable position on said guiding means.

Apparatus for measuring the thickness of a remote object having reflective surfaces comprising in combination a source of controllable light directed at each of said surfaces at a first predetermined angle to generate corresponding reflected light signals, detection means for receiving and measuring said reflected light signals at a second predetermined angle, means for developing transmittable signals based on said reflected light signals for readout of said thickness, correction means for adjusting said transmittable signals to eliminate non-linear errors attributable at least to the lack of perpendicularity between said first and second predetermined angles, and output means for processing said adjusted transmittable signals to generate an output display signal corresponding to said thickness of said remote object, wherein said correction means includes pre-calibrated control means for developing a group of linearizing signals dependent on at least said lack of perpendicularity and on the material comprising said object to adjust said transmittable signals and a selected one of said linearizing signals, and wherein said pre-calibrated control means includes a programmable memory unit for receiving periodically generated correction signals during a separate calibration cycle, wherein said correction means further includes guiding means for providing a fixed transport path, means movable along said guiding means for establishing a positionally controllable detecting surface, means mounted on said guiding means for generating calibration signals comparable to said controllable light source signal and said reflected light signals, means for determining the non-linear departure of said calibration signals corresponding to said reflected light signals, means for effectively cancelling said non-linear departure in said calibration signals corresponding to said reflected light signals and for delivering said correction signals to said memory unit, and control means included in said movable means for monitoring the movement of said detecting surface at discrete detectable positions along said transport path and for causing said correction signals to be generated and communicated to said memory unit for each of said discrete detectable positions on said guiding means.

Dependencies are inferred from the claim text.