Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Electrical signal parameter measurement system
Reexamination Certificate
2002-01-29
2003-12-30
Bui, Bryan (Department: 2863)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Electrical signal parameter measurement system
C702S033000, C702S034000, C700S045000, C318S561000
Reexamination Certificate
active
06671637
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to apparatus and method of measuring characteristics of a linear motor, and more particularly, to apparatus and method of measuring a thrust constant and a thrust ripple in a linear motor.
2. Description of the Related Art
An example of a linear motor will be briefly described with reference to
FIGS. 1 and 2
. In the linear motor, a fixed yoke
10
having an approximately U-shaped cross section is disposed on a base (not shown) so as to extend in a traveling direction. A moving body, for example, a coupling member
20
, which is coupled with a stage, is disposed above the fixed yoke
10
so as to slide in the traveling direction. A movable coil section
21
is disposed under the coupling member
20
. Permanent magnets
11
are fixed on the two inner surfaces of the fixed yoke
10
in the traveling direction at intervals, respectively, so as to face the two main surfaces of the movable coil section
21
through gaps.
Note that, in the case of a three-phase linear motor, the linear motor includes coils for three phases, that is, a U-phase, a V-phase, and a W-phase.
In the linear motor, electromagnetic force is generated by the mutual action between the magnetic flux from the permanent magnets
11
and the current flowing in the movable coil section
21
and causes the coupling member
20
and the movable coil section
21
to travel together.
The linear motor arranged as described above is used as a drive source of an X-Y stage apparatus in place of a ball thread mechanism because the linear motor can make positioning more accurately and generate a high thrust.
Incidentally, in this type of linear motors, a thrust constant and a thrust ripple are measured in a manufacturing process as factors for measuring characteristics thereof to know their performance.
A conventional method of measuring the thrust constant and the thrust ripple of a three-phase linear motor will be described with reference to FIG.
3
. In
FIG. 3
, a load cell
41
is pressed against the movable section
31
(for example, the coupling member
20
in
FIG. 1
) of a linear motor as a subject to be measured. The load cell
41
is mounted on a stage
43
capable of measuring a moving distance by a micrometer
42
. Then, the movable section
31
of the linear motor is pulled in a direction where it is pressed against the load cell
41
by a spring
44
such as a coil spring. A yoke
30
corresponds to the fixed yoke
10
in FIG.
1
.
A given current is supplied to the coils of the respective phases (U-phase, V-phase, and W-phase) in the linear motor using the apparatus arranged as described above. At the time, a force necessary to prohibit the movement of the movable section
31
is repeatedly measured by the load cell
41
at the respective points of a plurality of permanent magnets disposed in a traveling direction. As a result, a thrust constant is obtained as an output signal from the load cell
41
. In contrast, a thrust ripple is a difference (variable component) between the value obtained by subjecting the thrust constants of the respective phases to sine excitation, that is, the value obtained by combining the thrust constants of the three phases and a predetermined thrust.
FIG. 4A
shows the thrust constants of the respective phases that are obtained as the output signals from the load cell
41
.
FIG. 4B
shows the value obtained by combining the thrust constants of the three phases in
FIG. 4A
as the thrust ripple.
Note that the thrust constant and the thrust ripple may be measured by the following method in place of the method performed using the apparatus shown in FIG.
3
.
With reference to
FIG. 5
, a linear motor as a subject to be measured is prepared as a slave linear motor
51
as well as a master linear motor
52
is used. The slave linear motor
51
is coupled with the master linear motor
52
through a contact type guide mechanism
53
such as a bearing mechanism.
The guide mechanism
53
can move along a guide rail
54
.
When the master linear motor
52
is actuated, voltages are induced in the coils of the respective phases in the slave linear motor
51
in correspondence to the moving speed thereof, and the voltages (hereinafter, referred to as “speed-induced-voltages”) and the moving speed are measured. Then, a per-phase induced voltage constant is calculated from the ratio of the measured speed- induced-voltage of each phase and the moving speed. Further, the thrust constant and the thrust ripple are calculated from the thus obtained per-phase induced voltage constant of each phase.
In the method of measuring the thrust constant and the thrust ripple using the apparatus of
FIG. 3
, however, an error is included in the thrust constant and the thrust ripple due to the accuracy of a sensor such as the micrometer
42
.
In contrast, the measuring method shown in
FIG. 5
also lacks accuracy in measurement because the guide mechanism
53
is arranged as the contact type. Further, the thrust ripple cannot be accurately evaluated quantitatively because the drive system employed in the method is different from an actual drive system.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to improve a measuring accuracy in apparatus and method of measuring a thrust constant and a thrust ripple that determine the performance of a linear motor used to drive a stage.
A thrust ripple measuring apparatus according to the present invention is used for a linear motor. According to an aspect of the present invention, the apparatus comprises a master linear motor for driving a slave linear motor as a subject to be measured. A non-contact type stage mechanism couples the slave motor with the master motor. A voltage detector detects speed-induced-voltages generated in coils of the respective phases of the slave linear motor and a speed detector detects a moving speed of a movable portion in the slave linear motor when the master linear motor is actuated. A processing unit is supplied with the detected speed-induced-voltages and the detected moving speed and calculates a per-phase induced voltage constant from the ratio of the detected speed-induced-voltage of each phase and the detected moving speed of the slave linear motor. The processing unit further calculates a thrust constant and a thrust ripple from the calculated per-phase induced voltage constant.
According to a thrust ripple measuring method of the present invention, an apparatus is prepared in which a slave linear motor as a subject to be measured is coupled with a master linear motor for driving the slave linear motor through a non-contact type stage mechanism. When the master linear motor is actuated, speed-induced-voltages generated in coils of the respective phases of the slave linear motor are detected. At this time, a moving speed of the slave linear motor is detected. A per-phase induced voltage constant is calculated from the ratio of the detected speed-induced-voltage of each phase and the detected moving speed of the slave linear motor. A thrust constant and a thrust ripple is further calculated from the calculated per-phase induced voltage constant.
REFERENCES:
patent: 5838079 (1998-11-01), Morohashi et al.
patent: 6584367 (2003-06-01), Makino et al.
patent: 2003/0097193 (2003-05-01), Makino et al.
Arent Fox Kintner Plotkin & Kahn
Bui Bryan
Sumitomo Heavy Industrie's, Ltd.
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