Digital measuring system having a multi-row encoder disk

• US 6,279,248 B1
• Filed: 09/22/1999
• Issued: 08/28/2001
• Est. Priority Date: 09/22/1999
• Status: Expired due to Fees

• Current Assignee: Harbor Freight Tools USA Incorporated (Central Purchasing LLC)
• Original Assignee: Central Purchasing Incorporated (Central Purchasing LLC)
• Inventors: Walters, Gary W.
• Primary Examiner(s): Gutierrez, Diego
• Assistant Examiner(s): Gonzalez, Madeline
• Application Number:
  US09/401,620
• Time in Patent Office: 706 Days
• Field of Search: 33/1.N, 33/1.PT, 337/83, 337/84, 337/92, 337/93, 337/94, 337/95, 337/62, 337/63, 337/73, 338/18, 338/19, 338/20, 250/231.14
• US Class Current: 33/784
• CPC Class Codes: G01B 3/205 provided with a counter for digital indication of the measured dimension
• CPC Class Codes: G01D 2205/14 by converting the linear movement into a rotary movement
• CPC Class Codes: G01D 5/24461 by redundancy or plausibility
• CPC Class Codes: G01D 5/2451 Incremental encoders G01D5/2454 takes precedence

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°.

Claims

1. 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.

2. 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 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.

3. The hand held digital measuring device of claim 2 wherein said state comprises a vector comprised of signals received from said sensors, wherein respective elements of the vector are comprised of respective ones of said signals generated by said sensors.

4. The hand held digital measuring device of claim 2 further comprising an error detection module wherein said error detection module detects errors by a means for comparing a present state with a previous state, and a means for determining if the present state is expected after the previous state;

and

a means for displaying an error message in human readable form on said display.