Micro-encoder with molded micro-magnet

• US 5,982,169 A
• Filed: 09/24/1997
• Issued: 11/09/1999
• Est. Priority Date: 09/24/1997
• Status: Expired due to Fees

• Current Assignee: Eastman Kodak Company
• Original Assignee: Eastman Kodak Company
• Inventors: Furlani, Edward P., Ghosh, Syamal K.
• Primary Examiner(s): PATIDAR, JAY M
• Application Number:
  US08/936,123
• Time in Patent Office: 776 Days
• Field of Search: 324/174, 324/207.2, 324/207.21, 324/207.25, 324/252, 324/251, 324/117 H, 338/32 H, 338/32 R, 365/170, 365/171, 365/174, 365/2, 365/9, 164/6, 29/607, 29/608, 264/272.19, 335/302
• US Class Current: 324/207.2
• CPC Class Codes: G01D 5/145 influenced by the relative movement between the Hall device and magnetic fields see G01R33/06
• CPC Class Codes: G01P 3/487 delivered by rotating magnets

Abstract

A micro-sized encoder which can be used to track the rotational position, angular velocity and acceleration of micro-sized rotating devices. The encoder includes an extrusion molded, micro-sized ceramic housing adapted to receive the radically micro-polarized, mullet-pole micro-magnet with an axially shaft. End plates with integral bearings are formed which mount to the housing and support the axially shaft. A thin film Hall sensor mounted on the surface of the housing in proximity to the ratable micro-magnet is used for sensing the radial field component of the micromagnet. The sensor is in communication with sensor electronics whereby, as the micromagnet rotates, the radially alternating north and south magnetic fields are sensed to the thin film Hall sensor and counted by the sensor electronics.

Claims

1. A microencoder comprising:

(a) a molded ceramic housing;

(b) a micromagnet rotatably supported in said housing, said micromagnet having a diameter in the range of from about 1 mm to about 3 mm, said micromagnet having at least one north pole region and at least one south pole region on an exterior surface thereof, said at least one north pole region and said at least one south pole region residing in an alternating pattern with one another, said exterior surface being parallel to an axis of rotation of said micromagnet; and

(c) a magnetic field sensor affixed to a surface of said molded ceramic housing.

2. A microencoder as recited in claim 1 further comprising:

a controller means electrically connected to said magnetic field sensor for tracking angular rotation, angular velocity and acceleration of said micromagnet.

3. A microencoder as recited in claim 1 wherein:

said micromagnet is cylindrical in cross section.

4. A microencoder as recited in claim 1 wherein:

each of said at least one north pole region and said at least one south pole region has a width in the range of from about 100 microns to about 500 microns.

5. A microencoder as recited in claim 1 wherein:

said magnetic field sensor is a thin film Hall effect sensor.

7. An encoder as recited in claim 2 wherein:

each of said at least one north pole region and said at least one south pole region has a width in the range of from about 100 microns to about 500 microns.

8. An encoder as recited in claim 2 wherein:

said magnetic field sensor is a thin film Hall effect sensor.

6. An encoder comprising:

(a) a molded ceramic housing;

(b) a magnet supported in said housing and having an axis of rotation, said magnet having a maximum dimension perpendicular to said axis of rotation in the range of from about 1 mm to about 3 mm, said magnet having at least one north pole region and at least one south pole region on a peripheral surface thereof, said at least one north pole region and said at least one south pole region residing in an alternating pattern with one another, said peripheral surface being parallel to said axis of rotation; and

(c) a magnetic field sensor affixed to a surface of said molded ceramic housing.

9. A microencoder comprising:

(a) a molded housing having a central bore therethrough, said molded housing having two open ends;

(b) an end cap affixed to each of said two open ends, each of said two end caps including an integrally formed journal bearing therein;

(c) a magnet residing in said housing, said magnet having a diameter in the range of from about 1 mm to about 3 mm, said magnet having at least two north pole regions and at least two south pole regions an exterior surface thereof, said at least two north pole regions and said at least two south pole regions residing in an alternating pattern with one another;

(d) an axial shaft extending through said magnet, said axial shaft rotatably supported in said journal bearings, said axial shaft having a diameter in the range of from about 0.1 mm to about 0.5 mm; and

(e) a magnetic field sensor affixed to a surface of said molded ceramic housing.

10. A microencoder as recited in claim 9 further comprising:

a controller means electrically connected to said magnetic field sensor for tracking angular rotation, angular velocity and acceleration of said magnet.

11. A microencoder as recited in claim 10 wherein:

each of said at least one north pole region and said at least one south pole region has a width in the range of from about 100 microns to about 500 microns.

12. A microencoder as recited in claim 9 wherein:

said molded housing in an extruded ceramic.

13. A microencoder as recited in claim 9 wherein:

said micromagnet is cylindrical in cross section.

14. A microencoder as recited in claim 9 wherein:

each of said at least two north pole regions and said at least two south pole regions has a width in the range of from about 10 microns to about 500 microns.

15. A microencoder as recited in claim 9 wherein:

said magnetic field sensor is a thin film Hall effect sensor.