DIGITAL POSITION SENSOR

• US 3,810,136 A
• Filed: 02/15/1973
• Issued: 05/07/1974
• Est. Priority Date: 02/15/1973
• Status: Expired due to Term

• Current Assignee: Kearfott Guidance and Navigation Corporation
• Original Assignee: Charles W. Lang, Peter J O'Hara
• Inventors: Lang, Charles W., O'Hara, Peter J.
• Primary Examiner(s): Habecker, Thomas B.
• Application Number:
  US05/332,682
• Time in Patent Office: 446 Days
• Field of Search: 340/199,196
• US Class Current: 341/6
• CPC Class Codes: G01D 5/2013 by a movable ferromagnetic element, e.g. a core G01D5/2033 takes precedence
• CPC Class Codes: H03M 1/30 incremental

Abstract

A reliable digital shaft encoder capable of operating at high speeds is shown. A plurality of magnetic segments are embedded in the rotor of the encoder forming two staggered rows. The stator contains a plurality of E shaped magnetic strips through which excitation and pickup coils are wound. Magnetic coupling from the stator strips through the rotor segments induces a voltage in the pickup coils which is then demodulated to provide a position indication.

Claims

1. A digital position sensor comprising:

a. a plurality of magnetic elements arranged on a non-magnetic surface to form an upper and a lower row of spaced elements;

b. a pickup assembly in spaced relationship to said rows, said assembly comprising;

a support member having a plurality of shaped magnetic segments attached thereto with an upper portion of each segment aligned with said upper row and a lower portion aligned with said lower row;

a first excitation coil magnetically coupled to the upper portions of said segments;

a first pickup coil similarly coupled to said upper portions;

a second excitation coil magnetically coupled to the lower portions of said segments; and

a second pickup coil similarly coupled to said lower portions; and

c. means to effect relative motion between said rows and said assembly.

2. The invention according to claim 1 wherein said non-magnetic surface comprises a disk affixed to a shaft for rotation therewith, said elements being spaced about circles on said disk, and said support member is annular in shape.

3. The invention according to claim 2 wherein said shaped magnetic segments are E-shaped and said first excitation and first pickup coils are wound through the upper openings in the Es and said second excitation and second pickup coils are wound through the lower openings in the Es.

4. The invention according to claim 3 wherein said inserts and E-shaped segments are of a quantity and so spaced that when one insert in a row is radially aligned with an E-shaped segment, at least one other insert in the same row will also be aligned with an E segment, thereby permitting an averaging effect.

5. The invention according to claim 1 wherein each of said first and second excitation coils are coupled to a voltage source and further including means to sense the voltages induced in said first and second pickup coils to provide an output.

6. The invention according to claim 5 wherein one lead of said first pickup coil is connected to the lead of opposite polarity of said second pickup coil and further including:

a. a first resistor having one end coupled to the other side of said first coil; and

b. a second resistor having one end coupled to the other side of said second coil and its other side to the other side of said first resistor thereby forming a bridge circuit with said coils, whereby an output may be taken across the junction of said first and second coils and said first and second resistors.

7. The invention according to claim 6 wherein said voltage is an alternating voltage.

8. The invention according to claim 6 wherein one of said first and second resistors is variable to permit balancing the bridge.

9. The invention according to claim 6 and further including:

a. a demodulator obtaining its input from across said bridge; and

b. a detector to detect each half cycle of output from said demodulator whereby each output of said detector will represent an increment of rotor motion.

10. The invention according to claim 9 wherein said detector is a zero crossover detector.

11. The invention according to claim 9 wherein said detector is a peak detector.

12. The invention according to claim 9 and further including a pulse shaping circuit coupled to the output of said detector.

13. The invention according to claim 12 and further including a counter coupled to said shaping circuit to maintain a count indicative of shaft position.

14. The invention according to claim 13 and further including:

a. a second pickup system including a second set of shaped magnetic segments, third and fourth pickup coils, a second bridge circuit, a second demodulator, a second detector, and a second pulse shaping circuit, the segments of said second set arranged to provide outputs which are out of phase with the first set of shaped segments;

b. means sense the relative occurrence of outputs from the first and second pickup systems to provide an indication of direction of motion; and

c. wherein said counter is an up-down counter obtaining its up and down enabling inputs from said sensing means.

15. A digital position sensor comprising:

a. a rotor including a rotor shaft and a cylindrical disc of non-magnetic material affixed thereto;

b. a plurality of magnets arranged on said cylindrical disc to form an upper and a lower row of space elements;

c. a cylindrical stator assembly surrounding said disc said stator assembly comprising;

an annular support ring having a plurality of equally spaced slits about its circumference;

a plurality of E-shaped magnetic segments inserted into the slits with the upper opening of each aligned with said upper row and the lower opening of said E aligned with said lower row;

a first excitation coil wound about said support through the upper openings of said E segments;

a first pick up coil similarly wound through said upper opening;

a second excitation coil wound about said support through the lower opening of said E segment; and

a second pick up coil similarly wound through said lower openings; and

c. a case surrounding stator and rotor and including means to support said rotor for rotation within said stator.