U.S. patent application number 10/267185 was filed with the patent office on 2004-04-15 for electric motor with magnetic sensor wheel.
Invention is credited to Muszynski, Jerzy.
Application Number | 20040070391 10/267185 |
Document ID | / |
Family ID | 32030353 |
Filed Date | 2004-04-15 |
United States Patent
Application |
20040070391 |
Kind Code |
A1 |
Muszynski, Jerzy |
April 15, 2004 |
ELECTRIC MOTOR WITH MAGNETIC SENSOR WHEEL
Abstract
A magnetic position sensor wheel for an angular position
transducer of an electric motor is provided which includes a hub
with a flange, a first ring of magnetic material disposed on one
side of the flange between a hub axis and an outer periphery of the
flange, and a second ring of magnetic material extending axially
along the outer periphery of the flange.
Inventors: |
Muszynski, Jerzy; (Rochester
Hills, MI) |
Correspondence
Address: |
DYKEMA GOSSETT PLLC
39577 WOODWARD AVENUE
SUITE 300
BLOOMFIELD HILLS
MI
48304-5086
US
|
Family ID: |
32030353 |
Appl. No.: |
10/267185 |
Filed: |
October 9, 2002 |
Current U.S.
Class: |
324/207.22 ;
310/68B; 324/207.25 |
Current CPC
Class: |
G01D 2205/80 20210501;
G01D 5/145 20130101; G01D 5/2451 20130101; H02K 29/08 20130101 |
Class at
Publication: |
324/207.22 ;
324/207.25; 310/068.00B |
International
Class: |
G01B 007/30 |
Claims
I claim:
1. A magnetic position sensor wheel for an angular position
transducer of an electric motor comprising: a body defining a hub
disposed about an axis of rotation and a flange extending radially
from said hub; a first ring of magnetic material disposed on one
side of said flange between said axis and a radially outer
periphery of said flange; and a second ring of magnetic material
extending axially along said radially outer periphery of said
flange.
2. An apparatus as described in claim 1 wherein said body is
fabricated from a polymeric material.
3. An apparatus as described in claim 2 wherein said body holding
material is plastic.
4. An apparatus as described in claim 1 wherein said body is
fabricated from a metal.
5. An apparatus as described in claim 4 wherein said metal is
aluminum.
6. An apparatus as described in claim 1 wherein said ring has a
higher number of poles than said first ring.
7. An apparatus as described in claim 1 wherein said flange has a
generally flat face with a first pocket of said first ring of
magnetic material disposed therein.
8. An apparatus as described in claim 1 wherein said second ring of
magnetic material is axially spaced from said first ring of
magnetic material.
9. An angular position transducer, comprising: a magnetic position
sensor wheel having: a body defining a hub disposed about an axis
of rotation and a flange extending radially from said hub; a first
ring of magnetic material disposed on one side of said flange
between said axis and a radially outer periphery of said flange;
and, a second ring of magnetic material extending axially along
said radially outer periphery of said flange; a first sensor that
generates a first position indicative signal responsive to rotation
of said first ring of magnetic material; and, a second sensor that
generates a second position indicative signal responsive to
rotation of said second ring of magnetic material.
10. An apparatus as described in claim 9 wherein said body is
fabricated from a polymeric material.
11. An apparatus as described in claim 10 wherein said body holding
material is plastic.
12. An apparatus as described in claim 9 wherein said body is
fabricated from a metal.
13. An apparatus as described in claim 12 wherein said metal is
aluminum.
14. An apparatus as described in claim 9 wherein said second sensor
and said second ring of magnetic material have a higher power
resolution than said first ring of magnetic material in said first
sensor.
15. An apparatus as described in claim 9 wherein said flange has a
generally flat face with a first pocket of said first ring of
magnetic material disposed therein.
16. An apparatus as described in claim 9 wherein said second ring
of magnetic material is axially spaced from said first ring of
magnetic material.
17. A brushless motor comprising: a multi poled rotor; a coiled
stator encircling said stator; a controller to commutate said
stator coils; an angular position transducer to signal said
controller of said rotor angular position, said transducer
including: a magnetic position sensor wheel having: a body defining
a hub disposed about an axis of rotation of said rotor and a flange
extending radially from said hub; a first ring of magnetic material
disposed on one side of said flange between said axis and a
radially outer periphery of said flange; and, a second ring of
magnetic material extending axially along said radially outer
periphery of said flange; a first sensor that generates a first
position indicative signal responsive to rotation of said first
ring of magnetic material; and, a second sensor that generates a
second position indicative signal responsive to rotation of said
second ring of magnetic material.
18. An apparatus as described in claim 17 wherein said second
sensor and said second ring of magnetic material have a higher
power resolution than said first ring of magnetic material in said
first sensor.
19. An apparatus as described in claim 17 wherein said flange has a
generally flat face with a first pocket of said first ring of
magnetic material disposed therein.
20. An apparatus as described in claim 17 wherein said second ring
of magnetic material is axially spaced from said first ring of
magnetic material.
21. An apparatus as described in claim 17 wherein said motor is an
AC motor.
22. An apparatus as described in claim 17 wherein said motor is a
DC motor.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a magnetic sensor wheel and
in particular to a sensor wheel using a rotor position transducer
for an AC or DC brushless motor.
[0003] 2. Discussion of Related Art
[0004] Most early electric motors had a rotor rotatively mounted
within a housing, often referred to as a stator. The rotor
typically included windings which were energized or commutated by
an electrical charge. The electrical charge was delivered to the
coils of the rotor via a slip ring brush arrangement. The brushes
were typically made from an electrically conductive carbon material
which slid along an outer diameter of the rotor shaft, commonly
referred to as the slip ring. The stator had permanent magnets
which completed the electromagnetic field which powered the
motor.
[0005] Although the slip ring arrangement of commutation is
satisfactory, and is still in common use today, the slip ring brush
arrangement of commutation requires that a motor periodically
undergo maintenance for replacement of the brushes or repair of the
slip ring. It is desirable to provide electric motors in which the
brush can be eliminated. Such motors are referred to as brushless
motors.
[0006] In the brushless motor, the permanent magnets of the motor
are established on the rotor. The stator has poles with windings.
The polarity of the pole windings is controlled by a controller
which controls not only the direction of the current, but also the
wave form of the current. The controller (sometimes called the
driver) must be cognizant of the rotor position to properly control
the current to the various windings of the stator. Two position
sensing rings are required. The first position sensing ring is a
coarse ring which is necessary primarily from motor start up until
the motor reaches operational rotational speed.
[0007] In high performance applications, it is often desirable that
the controls of the coils go beyond normal on/off control
(sometimes referred to as trapezoidal control), but that the
controller controls the current to the various stator coils in a
sinusoidal manner. Thus, after the motor has started, there is an
additional need for a fine resolution of rotor angular position.
Thus, many brushless motors additionally have a fine resolution
rotor shaft angular position sensors. To provide the positional
data, many brushless motors are provided with a sensor wheel having
two generally concentric position data indicating rings. The higher
resolution position data indicator ring is typically outboard of
the lower resolution or coarse position data indicator ring.
[0008] Often to achieve the resolution desired, the higher
resolution ring required an outer diameter that was larger than
desired, therefore requiring an enlargement of the motor casing.
The enlargement of the high resolution data ring was worsened by
the fact that when the sensors were Hall effect sensors there
occurred magnetic cross-talk between the two data rings. To
minimize the effect of cross-talk, typically a minimum spacing
between the data rings was mandated.
[0009] There is an option to eliminate the magnetic cross-talk by
the utilization of optical sensors. However, in most instances,
optical sensing provides a cost penalty as compared with Hall
effect sensors. Additionally, optical sensors are not as desirable
if the motor is to be utilized in the harsh, dirty or dusty
environment.
[0010] It is desirable to provide a sensor ring which provides
better separation of the magnetic fields for the lower resolution
data ring and the high resolution data ring by minimizing magnetic
cross-talk.
[0011] It is also desirable to provide such a sensor ring wherein
the costs are minimized.
SUMMARY OF THE INVENTION
[0012] To make manifest the above-noted desires a revelation of the
present invention is brought forth.
[0013] In a preferred embodiment, the present invention brings
forth a brushless motor having a multi poled rotor. Encircling the
rotor is a coiled stator. A controller is provided to commutate the
coils of the stator. The motor additionally has an angular position
transducer to signal the controller of said rotor's angular
position. The transducer includes a magnetic position sensor wheel.
The sensor wheel has a body defining a hub disposed about an axis
of rotation of the rotor. The body also has a flange extending
radially from the hub.
[0014] A first ring of magnetic material is disposed on one side of
the flange between the rotor axis and a radially outer periphery of
the flange. A second ring of magnetic material extends axially
along a radially outer periphery of the flange. A first resolution
sensor generates a first position indicative signal responsive of
rotation of the first ring of magnetic material This first signal
is utilized during motor start up. A second sensor generates a
second high resolution position indicative signal responsive of
rotation of the second ring of magnetic material. The second signal
is utilized in controlling the wave form of the current which
energizes the coils of the stator.
[0015] It is an advantage of the present invention to provide a
sensor wheel which minimizes cross-talk between two magnetic wheels
on a sensor ring.
[0016] Other advantages of the present invention will be made
apparent to those skilled in the art as the invention is further
explained in the accompanying drawings and detailed
description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a front elevational view of a sensor ring
according to the present invention.
[0018] FIG. 2 is a sectional view of the sensor ring shown in FIG.
1.
[0019] FIG. 3 is a top plan view of the sensor ring shown in FIGS.
1 and 2.
[0020] FIG. 4 is a schematic view of a motor with a transducer
which utilizes the sensor ring of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0021] Referring now to FIGS. 1-4, a magnetic position sensor wheel
7 of the present invention has a body 10. The body 10 defines a hub
portion 12. The body 10 may be fabricated from a polymeric material
such as plastic. The body 10 can also be fabricated from a
non-magnetic metal such as aluminum. The hub 12 is disposed about
an axis 14 of rotation of a rotor 16 (shown in FIG. 4). The body 10
also has integrally joined with the hub a radially extending flange
18. The flange 18 has a front side face 22. An annular pocket 24 is
formed in the face 22. Disposed between the rotational axis 14 and
an outer peripheral edge 26 of the flange 18 is a first magnetic
ring 28. The first ring 28 is formulated from a polymeric material
having magnetic material mixed therein. The first ring 28 has
magnetically alternating poles 30, 32 to provide six poles. The
first ring 28 has a typical diameter of 30-40 mms. The amount of
poles is equal in the example shown to the magnetic poles of the
rotor 16.
[0022] The sensor wheel 7 also has a second ring 36 of magnetic
material. The second ring 36 extends axially along the radially
outer peripherial edge 26 of the flange 18. An axial forward edge
of the second ring 36 is axially spaced from a forward edge of the
first ring 22 by an axial dimension 38.
[0023] The second ring 36 has a greater resolution than the first
ring 28. The second ring 36 has a series of 72 magnetically
oppositely oriented poles 40, 42. In the example shown, the second
ring 36 has a diameter approximately between 50-60 mms with each of
the 72 poles representing a five degree arcuate segment.
[0024] Referring additionally to FIG. 4, a transducer 50 of the
present invention has a sensor holder 52. The sensor holder 52
supports a low resolution Hall effect sensor 54. The low resolution
sensor 54 generates a first angular position indicative signal
responsive to rotation of the first ring 28. The sensor holder 52
also supports a second high resolution sensor 56. The second high
resolution sensor 56 generates a second position indicative signal
responsive to rotation of the second ring 36.
[0025] The signals from the sensors 54, 56 are delivered to a
controller 58. The controller 58 is inclusive of a driver circuit
that controls the current delivered to stator coils 64, 66, which
are positioned within a stator housing 68 that encircles the rotor
16. It should be noted that only two stator coils are shown.
Typically there will be six or more stator coils which are, in like
manner, driven by controller 58.
[0026] Typically the controller 58 will provide the stator coils
64, 66 with a sinusoidal current wave form in order to have a more
constant torque output of the motor 51. The motor 51 in most
instances will be an AC motor; however, it can be a DC brushless
motor.
[0027] The present invention has been shown in various embodiments.
However, it will be apparent to those skilled in the art of the
various changes and modifications which can be made to the present
invention without departing from the spirit or scope of the
invention as it is encompassed by the following claims.
* * * * *