Digital sensor of relative position

• US 6,400,143 B1
• Filed: 09/25/1998
• Issued: 06/04/2002
• Est. Priority Date: 09/26/1997
• Status: Expired due to Term

• Current Assignee: The Torrington Company (The Timken Company)
• Original Assignee: The Torrington Company (The Timken Company)
• Inventors: Lyle, Stephen J., Travostino, Francis, LaCroix, Mark E., Santos, A. John
• Primary Examiner(s): PATIDAR, JAY M
• Application Number:
  US09/160,307
• Time in Patent Office: 1,348 Days
• Field of Search: 324/207.13, 324/207.15, 324/207.2, 324/207.22, 324/207.25, 324/178-179, 324/207.21, 324/173, 324/174, 340/671, 341/15, 338/32.R, 338/32.H
• US Class Current: 324/207.22
• 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 5/2457 Incremental encoders having reference marks

Abstract

The invention relates to a digital sensor of relative position, which has a circular multipolar magnetic ring which is mobile in rotation opposite a stationary magnetic sensor comprised of at least two sensitive elements, respectively positioned facing a main track and a “revolution tick” reference track, and a device for processing of the output signals, such that on the magnetic ring, a magnetic pattern is produced from a pair of north and south poles whose transition is different from the transition between the other north and south poles of the magnetic ring, and of which the angular width of the north pole is different at the site of the “revolution tick” reference track. The sensitive elements can be three in number, the first of which faces reference track and of which the other two face the main track, or they can be produced in the form of two parallel bars.

Claims

1. A digital sensor of relative position, comprising:

a circular multipolar magnetic ring, on which are magnetized a number of pairs of north and south poles, which are equally distributed, of constant determined angular width, mobile in rotation opposite a stationary magnetic sensor comprised of at least two sensitive elements, which are situated on a radius (r) of the magnetic ring and a length (d) apart, respectively positioned facing a main track and a “

revolution tick”

reference track; and

a device for processing of output signals emitted by the sensitive elements, for providing one reference pulse per revolution of a component in rotation connected with the magnetic ring;

wherein on the magnetic ring, a magnetic pattern is produced from a pair of north and south poles whose transition is different from the transition between the other north and south poles of the magnetic ring, and of which the angular width of the north pole is, on one hand, equal to that of the south pole at the main track, and on the other hand, different at the “

revolution tick”

reference track.

2. A digital sensor according to claim 1, wherein the transition between one pair of adjacent north and south poles of the magnetic pattern is a line segment, rotated by an angle (α

) with respect to the direction of the transitions between the north and south poles of the other poles of the magnetic ring, the angle (α

) being generated by rotating the line segment about an origin (R), occurring at the intersection of the main track and a radius of the magnetic ring, and lying equidistant between the two adjacent transitions, with angle (α

) being the acute angle between the radius and the line segment.

3. A digital sensor according to claim 1, wherein the transition between one pair of adjacent north and south poles of the magnetic pattern is comprised of two line segments, a first segment directed along a radius of the magnetic ring which divides the magnetic pattern into two equal parts, maintaining a constant angular pole width at the main track, and a second segment rotated by an angle (β

) with respect to the first segment at the reference track.

4. A digital sensor according to claim 1, wherein the transition between one pair of adjacent north and south poles of the magnetic pattern is comprised of two line segments, one of which is directed along the same radius (r) of the magnetic ring, dividing the magnetic pattern into two equal parts, and the other of which is directed along a radius (r′

), offset by an angle (δ

) with respect to the radius (r), dividing the magnetic pattern into two unequal parts.

5. A digital sensor according to claim 4, wherein the two line segments are connected by an arc of a circle.

6. A digital sensor according to claim 4, wherein the line segments, situated at the main track and the reference track, are connected at the middle of the magnetic ring by a curvilinear line segment for attenuating magnetic influences between the main track and the reference track.

7. A digital sensor according to claim 4, wherein the line segments, situated at the main track and the reference track, are connected at the middle of the magnetic ring by a curvilinear line segment in the shape of an S at the middle of the magnetic pattern.

8. A digital sensor according to claim 1, wherein the magnetic ring has a magnetization profile, along a radius at the center of a pole, having a plateau region and two decreasing regions towards the interior and exterior diameters of the magnetic ring, the length of the plateau region being at least equal to the sum of the distance (d), between the sensitive elements of the sensor respectively facing the main track and the reference track, and, because each of the sensitive elements may be placed a distance plus or minus T (known as tolerance) from its track along a radius of the magnetic ring, the length of the plateau region must then be at least equal to the distance between the sensitive elements plus 2T.

9. A digital sensor according to claim 1, wherein the magnetic sensor comprises three sensitive elements, a first sensitive element facing the reference track and second and third sensitive elements facing the main track in such a way that one of the second and third sensitive elements is on the same radius (r) of the magnetic ring as the first sensitive element a distance (d) from the first sensitive element, the second and third sensitive elements being offset with respect to one another along the main track so as to deliver respective signals in quadrature, namely when one of these sensitive elements faces a magnetic transition between adjacent north and south poles, the other sensitive element faces the middle of a magnetic pole.

10. A digital sensor according to claim 9, wherein the device for electronic processing of the signals coming from the three sensitive elements of the magnetic sensor includes:

a differentiating circuit, which executes the analog difference between signal (S₆₁) emitted by the first sensitive element facing the main track and signal (S₇) emitted by the second sensitive element facing the reference track and located on the same radius of the magnetic ring as the reference track, and delivering an analog “

revolution tick”

reference signal (S_TT);

a first comparator circuit, which compares the signal (S₆₂) of the third sensitive element in quadrature with the second sensitive element, with analog “

revolution tick”

signal (S_TT), in order to deliver digital signal (D₁) which is in logic state 1 when signal (S₆₂) is greater than signal (S_TT) and in logic state 0 when the opposite is true;

a second comparator, which compares this same signal (S₆₂) with signal (S₆₁) emitted by the second sensitive element, in order to deliver digital signal (D₂), which is in logic state 1 when signal (S₆₂) is greater than signal (S₆₁) and in logic state 0 when the opposite is true;

a descending front detector connected to the second comparator, whose output signal (D₃) generates a pulse with each descending front of the logic signal (D₂);

an AND logic gate, which receives, as input, binary signals (D₁ and D₃) in order to generate a digital signal (D₄) consisting of a single pulse per revolution of the magnetic ring, always appearing at the same position with respect to the magnetic ring; and

a synchronization circuit, which receives, as input, digital signal (D₄) as well as other signals (A and B) and which generates a digital “

revolution tick”

reference signal (C).

11. A digital sensor according to claim 1, wherein the magnetic sensor is comprised of two small bars of sensitive magnetic elements, facing the two magnetic tracks, the main track and the “

revolution tick”

reference track, the sensitive magnetic elements being parallel and a length (d) apart and each being comprised of a number of respective sensitive elements, the number being a positive whole number, each sensitive element of one bar facing a sensitive element of the other bar.

12. A digital sensor according to claim 11, wherein the device for electronic processing of the signals coming from the two sensitive bars includes:

first analog summing means for summing of the first half of the signals coming from the first bar, which are referenced, delivering an analog signal (E₁);

second analog summing means for summing of the second half of the signals coming from the first bar, referenced, delivering a second analog signal (E₂);

third analog summing means for summing of the signals coming from second bar, delivering a third analog signal (E₃);

a circuit for analog summing of the signals (E₁ and E₂), coming from summing means (22 and 23), which delivers analog signal (S_SIN);

a first analog differentiating circuit, which executes the difference of signals (E₁ and E₂) coming from first analog summing means in order to deliver analog signal (S_COS);

a second analog differentiating circuit, which executes the difference between signal (S_SIN) and signal (E₃) coming respectively from the third and second analog summing means in order to deliver analog “

revolution tick”

reference signal (S_TT);

a first comparator, which compares signal (S_COS) coming from the first analog differentiating circuit with analog “

revolution tick”

signal (S_TT) in order to deliver digital signal (D₁) which is in the logic state 1 when signal (S_COS) is greater than (S_TT) and in the logic state 0 in the case to the contrary;

a second comparator, which compares this same signal (S_COS) with signal (S_SIN) coming from circuit for analog summing in order to deliver digital signal (D₂), which is equal to 1 when signal (S_COS) is greater than (S_SIN) and equal to 0 in the case to the contrary;

a descending front detector, connected to the second comparator, generating pulse (D₃) at each descending front of logic signal (D₂);

an AND logic gate (14), which receives binary signals (D₁ and D₃), which generates digital signal (D₄) in the form of a single pulse per revolution of magnetic ring 1; and

a synchronization circuit which receives this single pulse per revolution, as well as other signals (A and B), in order to generate the “

revolution tick”

output signal (C).

13. A digital sensor according to claim 1, wherein the device for electronic processing of the signals (S₆ and S₇) coming from the two sensitive elements of the magnetic sensor includes:

a differentiating circuit, which executes the analog difference between input signals (S₆ and S₇), in order to deliver an analog “

revolution tick”

reference signal (S_TT); and

a comparator circuit, which compares the analog reference signal (S_TT) with a set reference threshold (S_SE), between upper and lower limits of signal (S_TT), and which generates a digital “

revolution tick”

reference signal (C), which is used as a reference pulse.

14. A digital sensor according to claim 1, wherein the sensitive elements of the sensor are of the Hall-effect probe type.

15. A digital sensor according to claim 1, wherein the sensitive elements of the sensor are of the amorphous magneto-resistant probe type.

16. A digital sensor according to claim 1, wherein the sensitive elements of the sensor are of the giant magneto-resistant probe type.