Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
2001-04-09
2003-11-04
Snow, Walter E. (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S166000, C702S145000, C702S151000
Reexamination Certificate
active
06642712
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to position prediction devices and methods. The present invention particularly relates to a device and a method for predicting shaft rotational positions with the predictions being utilized to control a magnitude and a duration of current being applied to stator windings of a motor.
2. Description of the Related Art
A prior art motor shaft position prediction technique involves a course-resolution position sensor
16
, a course-resolution position sensor
17
, and a course-resolution position sensor
18
disposed in an equidistant of 60 degrees about a motor shaft
10
and a rotor
11
attached thereto as shown in
FIGS. 1A-1D
. Referring to
FIGS. 1A-1D
, a magnet
12
displaying a north surface N, a magnet
13
displaying a south surface S, a magnet
14
displaying a north surface N, and a magnet
15
displaying a south surface S are attached to rotor
11
.
Each magnet
12
-
15
extends a radial distance of 90 degrees whereby collectively magnets
12
-
15
extend over a 360-degree radius of rotor
11
.
FIG. 1A
illustrates shaft
10
and rotor
11
at a 0 degree or 360 degree position.
FIG. 1B
illustrates shaft
10
and rotor
11
at a 90 degree position whereby magnets
12
-
15
have been rotated 90 degrees in a clockwise direction as indicated by arrow A.
FIG. 1C
illustrates shaft
10
and rotor
11
at a 180 degree position whereby magnets
12
-
15
have been rotated an additional 90 degrees in a clockwise direction as indicated by arrow A.
FIG. 1D
illustrates shaft
10
and rotor
11
at a 270 degree position whereby magnets
12
-
15
have been rotated an additional 90 degrees in a clockwise direction as indicated by arrow A.
Sensor
16
provides a rotational positional signal RP
S1
at a logic high level LH whenever sensor
16
is predominately facing magnet
12
or magnet
14
, and provides rotational positional signal RP
S1
at a logic low level LL whenever sensor
16
is predominately facing magnet
13
or magnet
15
.
Sensor
17
provides a rotational positional signal RP
S2
at a logic high level LH whenever sensor
17
is predominately facing magnet
12
or magnet
14
, and provides rotational positional signal RP
S2
at a logic low level LL whenever sensor
17
is predominately facing magnet
13
or magnet
15
.
Sensor
18
provides a rotational positional signal RP
S3
at a logic high level LH whenever sensor
18
is predominately facing magnet
12
or magnet
14
, and provides rotational positional signal RP
S3
at a logic low level LL whenever sensor
18
is predominately facing magnet
13
or magnet
15
.
The following TABLE 1 illustrates the logic levels of rotational position signals RP
S1-S3
for each incremental rotational position of shaft
10
and rotor
11
:
TABLE 1
INCREMENTAL ROTATONAL
RP
S1
RP
S2
RP
S3
POSITIONS
LH
LH
LL
0°/360°
LL
LH
LL
30°
LL
LH
LH
60°
LL
LL
LH
90°
LH
LL
LH
120°
LH
LL
LL
150°
LH
LH
LL
180°
LL
LH
LL
210°
LL
LH
LH
240°
LL
LL
LH
270°
LH
LL
LH
300°
LH
LL
LL
330°
From TABLE 1, it is understood that, for every 30 degrees incremental position of motor shaft
10
and rotor
11
, only one of the rotational position signals RP
S1-S3
transitions from one of the logic levels to the other logic level. As such, a logic unit (not shown) is utilized to provide a rotational positional signal RP
S4
as a function of each logic level transition of rotational positional signals RP
S1-S3
, whereby, as known in the art, rotational positional signal RP
S4
is an indication of each 30-degree incremental rotation position of motor shaft
10
and rotor
11
as illustrated in FIG.
2
.
A graph illustrating time stamps t
0-12
of each transition of rotational positional signal RP
S4
over the 360 degree rotation of motor shaft
10
and rotor
11
with motor shaft
10
and rotor
11
experiencing a constant rotational speed as known in the art is shown in FIG.
3
A. Referring to
FIG. 3A
, each 30-degree incremental rotation of motor shaft
10
and rotor
11
occurs every time interval ti
1
.
A graph illustrating a prediction, as known in the art, of each position of motor shaft
10
and rotor
11
over the 360 degree rotation of motor shaft
10
and rotor
11
with motor shaft
10
and rotor
11
experiencing a constant rotational speed during time stamps t
0-12
is shown in FIG.
3
B. Referring additionally to
FIG. 3B
, the prediction of each position is based on a constant slope equal to 30 degrees divided by time interval ti
1
.
A graph illustrating time stamps t
1-12
of each transition of rotational positional signal RP
S4
over the 360 degree rotation of motor shaft
10
and rotor
11
with motor shaft
10
and rotor
11
experiencing an increase in rotational speed between time stamp t
6
and time stamp t
7
as known in the art is shown in FIG.
4
A. Referring to
FIG. 4A
, each 30 degree incremental rotation of motor shaft
10
and rotor
11
occurs every time interval ti
1
during a time period covering time stamps t
0-6
and occurs every time interval ti
2
during a time period covering time stamps time stamps t
7-12
.
A graph illustrating a discontinuous prediction as known in the art of each position of motor shaft
10
and rotor
11
over the 360 degree rotation of motor shaft
10
and rotor
11
with motor shaft
10
and rotor
11
experiencing an increase in rotational speed between time stamp t
6
and time stamp t
7
is shown in FIG.
4
B. Referring additionally to
FIG. 4B
, the discontinuous prediction of each position is based on a constant slope equal to 30 degrees divided by time interval ti
1
during a time period covering from time stamp to t
0
the moment of the speed increase and a constant slope equal to 30 degrees divided by time interval ti
2
during a time period covering from the moment of the speed increase to time stamp t
12
.
A discontinuous prediction as shown in
FIG. 4B
triggers a potentially harmful torque ripple throughout motor shaft
10
when motor shaft
10
is experiencing any magnitude of acceleration or deceleration. The torque ripple also reduces the economic operation of motor shaft
10
. Thus, prior to the present invention, there is a need for a method and device of providing a continuous prediction of the position of motor shaft
10
during an acceleration or deceleration of motor shaft
10
.
SUMMARY OF THE INVENTION
The present invention relates to a method and device for predicting motor shaft positions that overcomes the aforementioned disadvantages of the prior art. Various aspects of the invention are novel, non-obvious, and provide various advantages. While the actual nature of the present invention covered herein can only be determined with reference to the claims appended hereto, certain features, which are characteristic of the embodiments disclosed herein, are described briefly as follows.
One form of the present invention is a method for predicting a plurality of rotational positions of a rotating shaft upon a first detection of a change in a rotational speed of the shaft from a first speed to a second speed. First, a first rotational position of the rotating shaft as a function of the first speed in response to the first detection of the change in rotational speed of the rotating shaft is predicted. Second, a first incremental rotational position of the rotating shaft that succeeds the first rotational position as predicted is determined. Third, a time interval between the first rotational position as predicted and the incremental rotational position as determined is estimated. Fourth, a prediction slope is estimated as a function of the time interval as estimated, and a differential between the first rotational position as predicted and the incremental rotational position as determined. Finally, a continuous prediction of the plurality of rotational positions of the shaft rotating at the second speed is generated as a function of the prediction slope as estimated.
A second form of the present invention is a system comprising a shaft, two or more sensors, an
DeVries Christopher
General Motors Corporation
Snow Walter E.
LandOfFree
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