US 6,279,248 B1Granted

Digital measuring system having a multi-row encoder disk

AssigneeCentral Purchasing, LLC

InventorGary W. Walters

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Abstract

The present invention is embodied in a hand held caliper with a hand movable slide, whose motion is transformed into rotation of an apertured multi-row encoder disk, a radiation source and a radiation detector. The present invention accurately measures a linear dimension using a simple, efficient, and durable digital measuring system. Accuracy of 0.0001″ is attained, greater than the 0.0005″ of the prior art, without encountering greater manufacturing costs, by utilizing well known fabrication techniques when producing the multi-row encoder disk, and otherwise using well known and inexpensive technology. The present invention does not require a motion dampening device, as errors may be determined and signal jitter are compensated for in the invention electronically or through the use of software, which adds little or no additional cost to the system and does not add mechanical complexity. Further, the present invention only requires a single rotatable disk to determine the direction of rotation, and no phase offset circuitry, through the use of dual rows of light emitting slots in the disk, the slots being offset between rows by 90° (in quadrature), but may be offset by as little as 10°.

Claims4

Dependent claims

A portable hand held linear distance measurement apparatus having a slide which is hand movable relative to a caliper body and an encoder wheel linked to linear motion of the slide, said apparatus comprising:

a pair of respective concentric circular rows of plural spaced slots in said encoder wheel, said pair of rows being radially offset from one another, the slots in one row being circumferentially offset from the slots in the other row;
a sensor associated with each of said rows capable of generating a signal which is a function of alignment between the sensor and successive ones of the slots in the respective row as the wheel rotates, whereby to generate one signal for each of said rows, wherein said apparatus has a pair of sensors corresponding to said pair of rows;
a signal processor for combining the signals generated for each of said rows and generating therefrom a count indicative of a distance measurement, whereby said count provides a distance resolution exceeding that obtainable from a single one of the signals generated for a single one of the rows of slots;
a human-readable visual display on said body, said display being controlled by said signal processor to display said distance measurement;
wherein said signal processor comprises a comparator connected to receive the signal corresponding to a respective one of said rows of slots, each said comparator comprising:
a pulse-generating circuit for generating a first pulse whenever said signal exceeds a first predetermined threshold and generating a second pulse after said first pulse whenever said signal falls below a second predetermined threshold;
a state machine for forming a two-element state from the concurrent outputs of said pair of comparators, whereby a sequence of different two-element states occurs upon rotation of said encoder wheels;
and
an error detection module for forming a sequence of successive ones of said two-element states and determining whether said sequence is a valid sequence, whereby to generate an error message on said display whenever an invalid sequence is detected.

6 more elements

a pair of respective concentric circular rows of plural spaced slots in said encoder wheel, said pair of rows being radially offset from one another, the slots in one row being circumferentially offset from the slots in the other row;
a sensor associated with each of said rows capable of generating a signal which is a function of alignment between the sensor and successive ones of the slots in the respective row as the wheel rotates, whereby to generate one signal for each of said rows, wherein said apparatus has a pair of sensors corresponding to said pair of rows;
a signal processor for combining the signals generated for each of said rows and generating therefrom a count indicative of a distance measurement, whereby said count provides a distance resolution exceeding that obtainable from a single one of the signals generated from a single one of the rows of slots;
a human-readable visual display on said body, said display being controlled by said signal processor to display said distance measurement;
and
wherein said signal processing module further comprises:
a state machine capable of storing a state of the encoder wheel, wherein said state is determined by the signals generated by said sensors.

4 more elements

Dependencies are inferred from the claim text.