Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2001-07-11
2003-01-21
Budd, Mark O. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S316010, C310S323020
Reexamination Certificate
active
06509673
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is based on and incorporates herein by reference Japanese Patent Application No. 2000-220214 filed on Jul. 21, 2000 and Japanese Patent Application No. 2000-397310 filed on Dec. 27, 2000.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ultrasonic motor, and more specifically to an ultrasonic motor capable of sensing a rotational position of its rotor.
2. Description of Related Art
In some previously proposed motors, such as DC motors, ultrasonic motors or the like, a sensor and a sensor target are required as a part of a sensing arrangement for determining a rotational position of a rotor.
One example of such a previously proposed ultrasonic motor is shown in FIG.
8
. In the ultrasonic motor
31
, a plurality of magnets
34
acting as the sensor target are secured along a circumferential surface of a shaft
33
of a rotor
32
at substantially equal angular intervals. A Hall element
37
acting as the sensor is mounted inside of a housing
35
through a support member
36
. The Hall element
37
is arranged to oppose each one of the magnets
34
in a radial direction of the rotor
32
when the magnet
34
comes in front of the Hall element
37
during rotation of the rotor
32
. The Hall element
37
is connected to an encoder (not shown).
When the shaft
33
is rotated together with the rotor
32
,
5
a position of each one of the magnets
34
that comes in front of the Hall element
37
is sensed through the Hall element
37
. Based on this, an amount of rotation of the rotor
32
relative to a reference position of the rotor
32
is determined to obtain a current rotational position of the rotor
32
. A voltage to be applied to the ultrasonic motor
31
is controlled based on the current rotational position of the rotor
32
, and thereby a rotational speed and the rotational position of the rotor
32
are controlled accordingly.
However, in this case, the dedicated sensor target needs to be provided to determine the rotational position of the rotor which is required in the rotational position control of the rotor. This causes an increase in the number of the components, resulting in an increase in a manufacturing cost of the ultrasonic motor. Furthermore, in order to detect a rotational direction of the rotor or to improve accuracy (resolution) in the position detection of the rotor, more than one sensor is required, disadvantageously causing a further increase in the number of the components.
SUMMARY OF THE INVENTION
The present invention addresses the above-described disadvantages. Thus, it is an objective of the present invention to provide an ultrasonic motor capable of detecting a rotational position of its rotor without requiring a dedicated sensor target.
It is another objective of the present invention to provide an ultrasonic motor capable of detecting a rotational direction of its rotor and also capable of providing improved accuracy in detection of a rotational position of the rotor without requiring a dedicated sensor target.
To achieve the objective of the present invention, there is provided an ultrasonic motor comprising a stator, a rotor and one or more sensors. The stator has a plurality of piezoelectric elements clamped between a plurality of blocks. The stator vibrates upon application of a voltage to the piezoelectric elements. The rotor is rotatably urged against the stator. The rotor has one or more slits formed in a peripheral surface of the rotor and is rotated by the vibrations of the stator. The one or more sensors are provided for sensing a position of at least one of the one or more slits.
REFERENCES:
patent: 5164629 (1992-11-01), Nakanishi
patent: 5739621 (1998-04-01), Atsuta et al.
patent: 5939847 (1999-08-01), Ashizawa et al.
patent: 6037701 (2000-03-01), Atsuta
patent: 6084335 (2000-07-01), Tamai
patent: 6300705 (2001-10-01), Komoda et al.
patent: A-10-285964 (1998-10-01), None
patent: A-11-46485 (1999-02-01), None
patent: A-2000-69770 (2000-03-01), None
patent: A-2000-350480 (2000-12-01), None
Asmo Co. Ltd.
Budd Mark O.
Law Offices of David G. Posz
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