Direction detection sensor

• US 8,022,692 B2
• Filed: 01/19/2009
• Issued: 09/20/2011
• Est. Priority Date: 01/19/2009
• Status: Active Grant

• Current Assignee: Allegro Microsystems Incorporated (Sanken Electric Company Limited)
• Original Assignee: Allegro Microsystems Incorporated (Sanken Electric Company Limited)
• Inventors: Morris, Michael, Shoemaker, Eric, Scheller, P. Karl, Fernandez, Devon, Taylor, William P.
• Primary Examiner(s): Phan; Huy Q
• Assistant Examiner(s): LE, SON T
• Application Number:
  US12/355,882
• Publication Number:
  US 20100181993A1
• Time in Patent Office: 974 Days
• Field of Search: None
• 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 2205/772 Sawtooth profiles
• CPC Class Codes: G01D 2205/85 Determining the direction of movement of an encoder, e.g. of an incremental encoder
• 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
• CPC Class Codes: G01R 33/072 Constructional adaptation of the sensor to specific applications
• CPC Class Codes: G01R 33/091 Constructional adaptation of the sensor to specific applications

Abstract

A sensor responsive to movement of a detection target includes a magnetic field transducer operative to provide a magnetic field signal proportional to a magnetic field associated with the detection target, a peak detector for tracking positive and negative peaks of the magnetic field signal to generate a tracking signal, and a comparator having a first input responsive to the magnetic field signal, a second input responsive to an input signal related to the tracking signal, and an output at which is provided an output signal comprising first pulses having a first pulse width when the detection target moves in a first direction and second pulses having a second pulse width when the detection target moves in a second direction.

Claims

1. A sensor responsive to the movement of a detection target, comprising:

a back-bias magnet;

a magnetic field transducer operative to provide a magnetic field signal proportional to a magnetic field associated with the detection target and the back-bias magnet;

a peak detector for tracking positive and negative peaks of the magnetic field signal to generate a tracking signal; and

a comparator having a first input responsive to the magnetic field signal, a second input responsive to an input signal related to the tracking signal, and an output at which is provided an output signal comprising first pulses having a first pulse width when the detection target moves in a first direction and second pulses having a second pulse width when the detection target moves in a second direction, wherein the detection target is positioned in a target plane and the sensor is mountable in a mounting plane and wherein the mounting plane is substantially parallel to the target plane, and wherein the detection target affects the magnetic field only due to the passing of the detection target in the vicinity of the transducer.

2. The sensor of claim 1, wherein the detection target is rotatable about an axis of rotation, wherein a center of the transducer is positioned along a mounting axis and the sensor is at a mounting angle relative to the mounting axis and wherein the sensor is insensitive to the mounting angle.

3. The sensor of claim 1, wherein the detection target is rotatable about an axis of rotation and the first direction of movement is characterized by a clockwise rotation about the axis of rotation and the second direction of movement is characterized by a counter-clockwise rotation about the axis of rotation.

4. The sensor of claim 1, wherein the magnetic field transducer comprises only a single magnetic field sensing element.

5. The sensor of claim 1, wherein the transducer is a magnetic-field-to-voltage transducer.

6. The sensor of claim 1, wherein the transducer is a magnetic-field-to-current transducer.

7. The sensor of claim 1, wherein the transducer is a Hall effect element.

8. The sensor of claim 1, wherein the transducer is a magnetoresistance element.

9. The sensor of claim 1, wherein at least a portion of the magnetic field signal comprises a sawtooth waveform characterized by a plurality of cycles, each cycle having a first portion having a first slope and a second portion having a second slope different than the first slope.

10. The sensor of claim 9, wherein the first portion of each cycle represents a response of the magnetic field transducer to a first profile of the detection target, at least a portion of the first profile defined by a first sloped edge, and the second portion of each cycle represents a magnetic field response of the magnetic field transducer to a second profile of the detection target, at least a portion of the second profile defined by a second sloped edge, wherein the first sloped edge has a smaller slope than the second sloped edge.

11. The sensor of claim 10, wherein the detection target is rotatable about an axis of rotation, wherein a center of the transducer is positioned along a mounting axis and the sensor is at a mounting angle relative to the mounting axis and wherein the sensor is insensitive to the mounting angle.

12. The sensor of claim 1, wherein the input signal to the second comparator input is a threshold voltage at a first level that is a first percentage of the peak-to-peak voltage of the magnetic field signal or at a second level that is a second percentage of the peak-to-peak voltage of the magnetic field signal.

13. The sensor of claim 12, wherein the first percentage is approximately equal to 25% of the peak-to-peak voltage of the magnetic field signal and the second percentage is approximately equal to 75% of the peak-to-peak voltage of the magnetic field signal.

14. The sensor of claim 1, wherein the input signal to the second comparator input is the tracking signal and wherein the comparator has hysteresis of a predetermined offset amount so that the output signal becomes a first binary level when the magnetic field signal exceeds the tracking signal by the predetermined offset amount and becomes a second binary level when the magnetic field signal falls below the tracking signal by the predetermined offset amount.

15. A sensor responsive to the movement of a detection target, comprising:

a magnetic field transducer operative to provide a magnetic field signal proportional to a magnetic field associated with the detection target;

a peak detector for tracking positive and negative peaks of the magnetic field signal to generate a tracking signal; and

a comparator having a first input responsive to the magnetic field signal, a second input responsive to an input signal related to the tracking signal, and an output at which is provided an output signal comprising first pulses having a first pulse width when the detection target moves in a first direction and second pulses having a second pulse width when the detection target moves in a second direction,

wherein the detection target is positioned in a target plane and is rotatable about an axis of rotation and the sensor is mountable in a mounting plane, wherein the mounting plane is substantially parallel to the target plane, and wherein the detection target affects the magnetic field only due to the passing of features of the detection target in the vicinity of the transducer.