Accurate rotor position sensor and method using magnet ring and hall effect sensors

• US 20030128026A1
• Filed: 02/14/2003
• Published: 07/10/2003
• Est. Priority Date: 07/20/1998
• Status: Active Grant

• Current Assignee: Jon F. Lutz
• Original Assignee: Jon F. Lutz
• Inventors: Lutz, Jon F.
• Granted Patent: US 6,693,422 B2
• Time in Patent Office: Days
• US Class Current: 324/207.2
• CPC Class Codes: G01B 7/30 for measuring angles or tapers; for testing the alignment of axes
• CPC Class Codes: G01D 5/145 influenced by the relative movement between the Hall device and magnetic fields see G01R33/06
• CPC Class Codes: G01D 5/2451 Incremental encoders G01D5/2454 takes precedence

Abstract

An inexpensive and accurate device for sensing rotor position and detecting rotational speed over a broad range of speeds in an electric motor includes a sense ring magnet and two analog Hall effect sensors. The sense ring is magnetized in an alternating north-south fashion with a number of poles that correspond to a number of motor field poles. The Hall effect sensors are placed so that they measure magnetic flux tangential to the sense ring. The Hall effect sensors are preferably located at a distance from the sense ring where the Hall effect sensor output waveforms are substantially triangular, with a highly linear portion centered at zero flux between the minimum and maximum waveform peaks. The linear portions of the waveforms are decoded using an A/D converter and control software to provide an accurate measure of the rotor position.

Claims

1. A method for controlling a brushless electric motor including a rotor, a sense element with a plurality of magnetic pole pairs, and first and second sensors mounted less than or equal to 120 electrical degrees apart b) with sensing planes oriented perpendicular to an adjacent surface of the sense element and perpendicular to a movement direction of the sense element relative to the sensors, wherein one of a) the sense element and b) the first and second sensors is mounted in a fixed relationship with the rotor, the method comprising:

measuring magnetic flux of the plurality of magnetic pole pairs using the first and second sensors and outputting a corresponding measurement signal for each at least one first and second sensor;

determining a rotational position of the rotor based on the measurement signals; and

controlling the motor based on the determined rotor position.

2. The method of claim 1, wherein the first and second sensors are Hall effect sensors.

3. The method of claim 1, wherein the determining comprises determining an absolute rotational position of the rotor within an electrical cycle based on the measurement signals.

4. The method of claim 1, wherein the first and second sensors are mounted at an interval different from 90 electrical degrees.

5. The method of claim 1, wherein one of the measurement signals of the first and second sensors indicates a region within an electrical cycle, and the other of the measurement signals of the first and second sensors indicates a location within the region.

6. The method of claim 1, wherein the first and second sensors are mounted less than 120 electrical degrees apart.

11. The method of claim 1, wherein the first and second sensors mounted with sensing planes oriented perpendicular to a movement direction of the sense element relative to the sensors.

7. A method for controlling a brushless electric motor including a rotor, a sense element with a plurality of magnetic pole pairs, and first and second sensors mounted with their sensing planes perpendicular to a surface of the sense element to measure magnetic flux from the magnetic poles, wherein one of a) the sense element and b) the first and second sensors is mounted in a fixed relationship with the rotor, and wherein the first and second sensors are spaced so that at each rotational position of the rotor, an output of at least one of the first and second sensors is linear, the method comprising:

measuring magnetic flux of the plurality of magnetic pole pairs via the first and second sensors and outputting a corresponding measurement signal for each of the first and second sensors;

determining an absolute rotational position of the rotor within an electrical cycle based on the measurement signals; and

controlling the motor based on the determined rotor position.

8. The method of claim 7, wherein the first and second sensors are mounted with their sensing planes oriented perpendicular to a rotation direction of the sense element relative to the sensors.

9. The method of claim 8, wherein the first and second sensors are Hall effect sensors.

10. The method of claim 7, wherein one of the measurement signals of the first and second sensors indicates a region within an electrical cycle, and the other of the measurement signals of the first and second sensors indicates a location within the region.