U.S. patent application number 10/862563 was filed with the patent office on 2005-02-10 for rotation angle detector.
Invention is credited to Oike, Koji, Shimizu, Masaru.
Application Number | 20050030011 10/862563 |
Document ID | / |
Family ID | 33534616 |
Filed Date | 2005-02-10 |
United States Patent
Application |
20050030011 |
Kind Code |
A1 |
Shimizu, Masaru ; et
al. |
February 10, 2005 |
Rotation angle detector
Abstract
A rotation angle detector is simple in structure and is capable
of angle detection with a high resolution, First and second
detecting units detect rotations of first and second detecting
members rotating in association with a rotating member as detection
signals in which predetermined waveforms continue. A control unit
connected with the first and second detecting units detects a
difference between the waveforms output from first and second
detecting units as a gradually increasing detection signal and
detects a rotation angle of the rotating member from two signals:
the gradually increasing detection signal and the waveform output
from the first detecting unit.
Inventors: |
Shimizu, Masaru;
(Yawata-shi, JP) ; Oike, Koji; (Otokuni-gun,
JP) |
Correspondence
Address: |
RATNERPRESTIA
P O BOX 980
VALLEY FORGE
PA
19482-0980
US
|
Family ID: |
33534616 |
Appl. No.: |
10/862563 |
Filed: |
June 7, 2004 |
Current U.S.
Class: |
324/207.25 ;
324/174; 324/207.21 |
Current CPC
Class: |
G01D 2205/28 20210501;
G01D 5/145 20130101; G01D 2205/26 20210501; B62D 15/0215
20130101 |
Class at
Publication: |
324/207.25 ;
324/207.21; 324/174 |
International
Class: |
G01B 007/30; G01P
003/48 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 16, 2003 |
JP |
2003-170291 |
Claims
What is claimed is:
1. A rotation angle detector comprising: a rotating member; first
and second detecting members rotating in association with the
rotating member; a first detecting unit for detecting a rotation of
the first detecting member as a detection signal in which a
predetermined waveform continues; a second detecting unit for
detecting a rotation of the second detecting member as a detection
signal in which a predetermined waveform different in period from
the first detect on signal continues; and a control unit connected
with the first and second detecting unit, wherein the control unit
detects a difference between waveforms output from the first and
second detecting units as a gradually increasing or decreasing
detection signal, and the control unit detects a rotation angle of
the rotating member by using two signals, of which one is the
gradually increasing or decreasing signal and the other is one of
the waveforms output from the first and second detecting units.
2. The rotation angle detector according to claim 1, wherein the
first and second detecting units are each formed of a magnet and a
magnetism detecting element.
3. The rotation angle detector according to claim 2, wherein the
magnetism detecting element is a magnetoresistance element.
4. The rotation angle detector according to claim 1, wherein the
rotating member has an opening through which a shaft of a steering
wheel is inserted.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a rotation angle detector
for detecting a rotation angle of, for example, a steering wheel on
a vehicle.
BACKGROUND OF THE INVENTION
[0002] While higher performance vehicles have come into being in
recent years, there have been developed various apparatuses for
detecting the rotation angle of the steering wheel (hereinafter
called SWH) with use of rotation angle detectors (hereinafter
called RAD) for performing various types of control.
[0003] One of such conventional rotation angle detectors will be
described with reference to FIG. 4, FIG. 5A and FIG. 5B.
[0004] FIG. 4 is a perspective view of a main portion of the
conventional RAD and FIG. 5A and FIG. 5B are voltage waveforms
obtained from the RAD. Rotating member 1 in a disk form has, in its
center, engagement portion 1A engaging a shaft (not shown) of an
SWH inserted therein and opening portion 1C allowing the shaft of
the SWH to pass therethrough. On the circumference of rotating
member 1, there are provided a plurality of through holes 1B at a
predetermined pitch. Across through hole 1B formed in rotating
member 1, there are arranged photo-interrupters 2, 3, each made up
of a light emitting element and a photo sensing element opposing
each other. Further, the photo-interrupters are held by holding
member 4 in predetermined positions slightly offset with respect to
through hole 1B, so that detection signals output therefrom while
rotating member 1 rotates may have a predetermined phase difference
therebetween.
[0005] Further, there are disposed wiring board 5 with a plurality
of wiring patterns (not shown) formed on both sides thereof and a
control unit (not shown) made of a microcomputer and the like. By
having photo-interrupters 2, 3 connected to the control unit, the
RAD is constructed.
[0006] In the described configuration, rotating member 1 is rotated
according as the SWH is rotated and, thereby, admission of light
and cut-out of light are repeated.
[0007] As a result, detection signals in which periodical
rectangular waveforms with a phase difference therebetween, as
shown in FIGS. 5A and 5B, continue are output from
photo-interrupters 2, 3 to the control unit.
[0008] The rotation angle of rotating member 1 is detected by
counting the number of waveforms in either of the detection signals
from photo-interrupters 2, 3. The rotating direction can also be
detected as follows. When, for example, the waveform of
photo-interrupter 2 shown in FIG. 5A is lagging behind the waveform
of photo-interrupter 3 shown in FIG. 5B, it is determined that the
rotation is in a clockwise direction, and, when in reverse the
waveform of photo-interrupter 2 is output faster than the waveform
of photo-interrupter 3, it is determined that the rotation is in a
counterclockwise direction. An example of RAD having the described
configuration is disclosed in U.S. Pat. No. 6,380,536.
[0009] At this time, if the pitch of through hole 1B of rotating
member 1 is set at 6.degree., the width of the hole set at
3.degree., and the phase difference between photo-interrupters 2, 3
set at 1/4 period, waveforms of FIG. 5A and FIG. 5B each become a
waveform having a period of 6.degree. and they become 1/4 period
shifted from each other. Thus, a RAD capable of detecting a
rotation angle down to as small an increment as
6.degree./4=1.5.degree., i.e., that having a resolution of
1.5.degree., can be structured.
[0010] The described conventional RAD detects a rotation angle with
use of two sets of photo-interrupters 2, 3, as well as rotating
member 1 provided with a plurality of through holes 1B formed
therein. Therefore, there arises such a problem that layout and
machining of the components become complicated and costly. Further,
since there are limits in reducing the pitch distance between
through holes 1B and the width of the hole, it is difficult to
perform angle detection with a high resolution.
[0011] The present invention addresses the above mentioned problems
in the prior art and, accordingly, it aims at the provision of a
RAD capable of angle detection at a high resolution with a simple
structure.
SUMMARY OF THE INVENTION
[0012] The present invention provides a rotation angle detector, in
which first and second detecting units detect rotations of first
and second detecting members rotating in association with a
rotating member as detection signals in which predetermined
waveforms continue, a control unit connected with the first and
second detecting units detects a difference between the waveforms
output from the first and second detecting units as a gradually
increasing or decreasing signal and, thereupon, detects a rotation
angle of the rotating member from two detection signals: (1) the
gradually increasing or decreasing detection signal; and (2) one of
the waveforms output from the first and second detecting units.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a perspective view of an important portion of a
rotation angle detector of a first embodiment of the present
invention.
[0014] FIG. 2A-FIG. 2C are voltage waveform diagrams output from
the rotation angle detector of the embodiment of the present
invention.
[0015] FIG. 3 is a perspective view of an important portion of
another rotation angle detector of the embodiment of the present
invention.
[0016] FIG. 4 is a perspective view of an important portion of a
prior art rotation angle detector.
[0017] FIG. 5A and FIG. 5B are voltage waveform diagrams output
from the prior art rotation angle detector.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] An embodiment of the present invention will be described
with reference to FIG. 1-FIG. 3. It is to be noted that the
drawings are all schematic drawings and they do not show dimensions
and positions of the components exactly. As a magnetism detecting
element, a magnetoresistance device such as that of InSb is
preferably used. Further, as a magnet, while any permanent magnet
can be used, a samarium magnet, neodymium magnet, or ferrite magnet
is preferably used.
[0019] In the indication of a rotation angle, a positive rotation
is that in a clockwise direction and a negative rotation is that in
a counterclockwise direction.
Exemplary Embodiment
[0020] Rotating member 11 has spur gear portion 11A on its
circumferential side and has, in its interior, an opening 11C for
allowing the shaft of an SWH to be passed therethrough and
engagement portion 11B for allowing the shaft of SWH to be engaged
therewith.
[0021] First detecting member 12 has, on its circumferential side,
spur gear portion 12A in meshing engagement with spur gear portion
11A of rotating member 11. In the center of first detecting member
12, there is mounted magnet 13 by insert molding or the like.
[0022] Second detecting member 42 has, on its circumferential side,
spur gear portion 42A in meshing engagement with spur gear portion
12A of first detecting member 12. In the center of second detecting
member 42, there is mounted magnet 43 by insert molding or the
like.
[0023] Second detecting member 42 is formed to be larger in
diameter than first detecting member 12 and number of gear teeth of
spur gear portion 42A is made greater than that of spur gear
portion 12A.
[0024] The numbers of the gear teeth of first detecting member 12
and second detecting member 42 are set at such numbers of teeth
that the detecting members return to their original meshing
position after a predetermined angle of rotation made by rotating
member 11, i.e., they return to their original meshing position
after, for example, two rotations of rotating member 11 in a
counterclockwise direction and after two rotations of the same in a
clockwise direction, from the neutral position.
[0025] There is disposed wiring board 17, having a plurality of
wiring patterns (not shown) formed on both sides thereof,
substantially parallel to first detecting member 12 and second
detecting member 42.
[0026] Further, there is mounted magnetism detecting element 14
made for example of an AMR element (anisotropic magnetoresistance
element) on the surface of wiring board 17 opposite to first
detecting member 12. Thus, first detecting unit 19 is constituted
of magnet 13-and magnetism detecting element 14 opposing each
other.
[0027] In like manner, second detecting unit 49 is constituted of
magnet 43 and magnetism detecting element 44 opposing each
other.
[0028] Control unit 20 formed of a microcomputer and the like is
connected with magnetism detecting element 14 of first detecting
unit 19 and magnetism detecting element 44 of second detecting unit
49. Further, control unit 20 is connected to electronic circuitry
(not shown) on board the vehicle body. Thus, the RAD is
constructed.
[0029] In the described configuration, when the SWH is rotated,
rotating member 11 is rotated accordingly and, first detecting
member 12, whose spur gear portion 12A is in meshing engagement
with spur gear portion 11A on the circumferential side of rotating
member 11, is also rotated.
[0030] According as first detecting member 12 is rotated, the
magnetic field around magnet 13 mounted in the center of the same
varies. The variation in the magnetic field is detected by
magnetism detecting element 14, and thereby a detection signal, in
which predetermined increasing and decreasing waveforms continue as
shown in the voltage waveform diagram of FIG. 2Cis output from
magnetism detecting element 14 of first detecting unit 19 to
control unit 20.
[0031] At this time, if, for example, the number of teeth of first
detecting member 12 is set at one-third the number of teeth of
rotating member 11 and magnetism detecting element 14 is adapted
only to detect the magnetic field strength (namely, to detect the
magnetic field strength every 180.degree. rotation of detecting
member 12), then detecting member 12 makes three rotations while
rotating member 11 makes one rotation and magnetism detecting
element 14 detects two changes in field strength for one rotation
of first detecting member 12. As a result, six voltage waveforms
are successively output as the detection signal.
[0032] More specifically, for every 60.degree. rotation of rotating
member 11, one predetermined voltage waveform increasing from
voltage value zero to voltage value V and then decreasing is output
from magnetism detecting element 14 to control unit 20 as the
detection signal.
[0033] Likewise, according as first detecting member 12 is rotated,
second detecting member 42 rotates and the magnetic field around
magnet 43 mounted in the center of second detecting member 42
varies, and the varying magnetic field is detected by magnetism
detecting element 44. Since, at this time, the number of teeth of
first detecting member 12 and that of second detecting member 42
are made different from each other, there is produced a difference
between the voltage waveforms detected by first detecting unit 19
shown in FIG. 2C and the voltage waveform detected by second
detecting unit 49 shown in FIG. 2B, i.e., in the range from the
point where rotating member 11 has rotated two rotations leftward
and to the point where it has rotated two rotations rightward, from
the neutral point, there is produced a slight deviation in the
direction of rotation as seen from the voltage waveform of FIG.
2B.
[0034] More specifically, a voltage waveform, increasing from
voltage value zero to voltage value V and then decreasing, having a
longer period than the voltage waveform from first detecting unit
19 is output from second detecting 49 to control unit 20.
[0035] Then, control unit 20, first, deducts the voltage value of
the detection signal from second detecting unit 49 shown in FIG. 2B
having a longer period from the voltage value of the detection
signal from first detecting unit 19 shown in FIG. 2C having a
shorter period, to thereby detect the difference between the
voltage values.
[0036] The difference between the voltage values provides a
gradually increasing detection signal as shown in FIG. 2A, namely,
the detection signal passes a point of the value 0 as the
difference between the voltage value 0 of FIG. 2C and the voltage
value 0 of FIG. 2B at the position corresponding to two leftward
rotations of rotating member 11, a point of V/2 as the difference
between the voltage value V of FIG. 2C and the voltage value V/2 of
FIG. 2B at the neutral position, and a point of V as the difference
between the voltage value V of FIG. 2C and the voltage value 0 of
FIG. 2B at the position corresponding to two rightward rotations of
rotating member 11.
[0037] Then, control unit 20 detects, based on the voltage
difference as the gradually increasing detection signal, an
approximate value of the rotation angle, i.e., it detects within
what range of the rotation angle in the voltage waveform of FIG.
2C, successively output from first detecting unit 19, the rotation
angle is.
[0038] For example, when the rotation angle is .theta., control
unit 20 detects, by reference to the difference between voltage
values of FIG. 2A, that the rotation angle corresponds to the
second waveform of FIG. 2C counted from the neutral point at an
angle of 0.degree..
[0039] In other words, it detects an approximate rotation angle
being between 60.degree. and 120.degree..
[0040] It, finally, detects a precise rotation angle of rotating
member 11 from the detected voltage waveform.
[0041] For example, it detects, from the voltage value of the
detected voltage waveform between 60.degree. and 120.degree., that
the precise rotation angle, for example, is 100.degree..
[0042] The waveform of difference between voltage values of FIG. 2A
shows a gradually increasing waveform from the rotation angle of
rotating member 11 attained by its two leftward rotations to the
rotation angle of rotating member 11 attained by its two rightward
rotations. Further, the direction of rotation of rotating member
11, i.e., of the SWH, can be detected by control unit 20 according
to whether the difference between voltage values has increased or
decreased, i.e., it is detected that the direction is toward the
right when the difference between voltage values has increased or
it is toward the left when the difference between voltage values
has decreased.
[0043] At the same time, the angles of rotation of the SWH while it
is rotated two rotations each to the left and right can be
detected.
[0044] Since the voltage waveform of FIG. 2C shows a waveform in
which the voltage is increasing and decreasing every 60.degree.
rotation of rotating member 11, if, for example, a computation is
performed in the microcomputer of control unit 20 with use of a
10-bit A/D converter, detection of the rotation angle with as high
a resolution as 60.degree./1024.congruent.0.06.degree. (where 1024
is 2.sup.10) can be attained.
[0045] According to the present embodiment, a rotation angle
detector is arranged such that rotations of the first and second
detecting members rotating in association with rotating member 11
rotating in association with SWH are detected as detection signals
in which predetermined waveforms continue by first and second
detecting units 19, 49, the difference between the waveforms output
from first and second detecting units 19, 49 is detected as a
gradually increasing detection signal by control unit 20 connected
with first and second detecting units 19, 49, and the rotation
angle of the rotating member is detected from the two detection
signals, i.e., the gradually increasing detection signal and the
waveform output from first detecting unit 19. Thus, by having the
difference between the above mentioned waveforms detected by
control unit 20, an approximate value of the rotation angle is
detected and, based on this detected approximate rotation angle, a
precise rotation angle is detected from the predetermined waveform
output from first detecting unit 19.
[0046] Rotating member 11 and detecting members 12, 42 are placed
in the same plane. As a result, a RAD capable of angle detection
with a high resolution can be provided by a simple structure
composed of first and second detecting members 12, 42.
[0047] Further, by having first and second detecting units 19, 49
constructed of magnets 13, 43 and magnetism detecting elements 14,
44, the RAD, while it is provided in a simple structure and at a
low cost, is enabled to perform noncontact and stable
detection.
[0048] Further, auxiliary detecting unit 56, in addition to first
detecting unit 19, may be provided as shown in FIG. 3 by arranging
spur gear portion 53A of auxiliary detecting member 53, having the
same number of teeth and shape as spur gear portion 12A of first
detecting member 12, in meshing engagement with spur gear portion
11A of rotating member 11 and by mounting magnet 54 in the center
of auxiliary detecting member 53 and magnetism detecting element 55
of an AMR element or the like on wiring board 17. Thus, by allowing
a detection signal from auxiliary detecting unit 56 to be also
detected by control unit 20, in a case where, for example, a
detection signal is not output from first detecting unit 19 while a
detection signal from auxiliary detecting unit 56 is output, it can
be known that some trouble has occurred in first detecting unit
19.
[0049] In other words, when there is present some difference
between waveforms from first detecting unit 19 and auxiliary
detecting unit 56, which should essentially be output as the same
waveforms, it can be detected that either of the detecting units is
out of order. Therefore, more reliable detection of the rotation
angle can be attained.
[0050] In the foregoing, there has been described such an
arrangement in which spur gear portion 12A of first detecting
member 12 is disposed in meshing engagement with spur gear portion
11A on the circumferential side of rotating member 11 and spur gear
portion 42A of second detecting member 42 is disposed in meshing
engagement with spur gear portion 12A. Also, it is possible to use
other types of gears, such as bevel gears, instead of spur gear
portions 11A, 12A, 42A, 53A, or to use other elements than gear
wheels that are in projected shapes and depressed shapes and can be
engaged with each other.
[0051] In the description given above, the difference between
waveforms output from first and second detecting units 19, 49 has
been described as a gradually increasing detection signal obtained
by deducting the voltage value of the detection signal having a
longer period output from second detecting unit 49 from the voltage
value of the detection signal having a shorter period output from
first detecting unit 19. It may also be arranged to detect a
gradually decreasing detection signal by deducting the voltage
value of the detection signal having a shorter period output from
first detecting unit 19 from the voltage value of the detection
signal having a longer period output from second detecting unit
49.
[0052] Further, even if the precise rotation angle of rotating
member 11 is detected based on the detection signal having a longer
period output from second detecting unit 49, detection of rotation
angle with a high l ution can be obtained though the resolution in
this case may be slightly deteriorated from that obtained when the
rotation angle is detected based on the detection signal having a
shorter period output from first detecting unit 19.
[0053] According to the present invention, as described in the
foregoing, a RAD capable of angle detection at a high resolution
can be provided by a simple configuration.
* * * * *