Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1998-11-04
2001-06-12
Budd, Mark O. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
Reexamination Certificate
active
06246151
ABSTRACT:
This application is based on application Ser. No. Hei 9-304482 filed in Japan, the content of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to a drive device, and particularly to a drive device that employs an electromechanical transducer such as a piezoelectric element, electrostrictive element or magnetrostrictive element.
The present invention further pertains to an apparatus equipped with said device, such as an apparatus having an X-Y drive table, a camera, an overhead projector, binoculars, a microscope equipped with a movable object table, and a scanning tunneling electronic microscope having a probe.
2. Description of the Prior Art
Conventionally, various types of drive devices employing an electromechanical transducer such as a piezoelectric element have been proposed. For example, in the drive device
1
shown in
FIG. 1
, a drive circuit
4
is connected to a piezoelectric linear actuator
2
, and the piezoelectric linear actuator
2
is operated based on the prescribed output from the drive circuit
4
.
Incidentally, because the drive circuit
4
operates regardless of the state of the piezoelectric linear actuator
2
, when a problem occurs with regard to the piezoelectric linear actuator
2
, a problem also occurs with regard to the power supply to the piezoelectric linear actuator
2
. However, because the drive device cannot consider the state of the piezoelectric linear actuator
2
and the abnormality in the piezoelectric linear actuator
2
cannot be output externally, abnormal driving is continued. When abnormal driving is continued, damage to the drive device can result.
SUMMARY OF THE INVENTION
Therefore, the object of the present invention is to obtain a drive device in which continued abnormal driving may be prevented by detecting abnormalities occurring during the driving of the electromechanical transducer, as well as a mechanism equipped with said device.
One aspect of the present invention provides a drive device equipped with an electromechanical transducer that extends and contracts based on drive signals input from a drive pulse generator, a first member that is fixed to one end of the electromechanical transducer, a driving friction member that is fixed to the other end of the electromechanical transducer, and a second member that frictionally engages with the driving friction member. Either the first or second member is fixed, such that when the electromechanical transducer extends and contracts based on the drive signals, the member that is not fixed is driven in prescribed directions.
In addition, this drive device is equipped with a characteristic signal generator, a detector and a comparator. The characteristic signal generator outputs standard characteristic signals indicating the characteristic pertaining to one or more factors of the drive signals in the normal state. When the drive signals are input to the detector, the characteristic regarding the same factor as that used in generating the standard characteristic signals is detected and the detected characteristic signals that indicate the characteristic are output. The standard characteristic signals and the detected characteristic signals are input to the comparator, where they are compared, and if the difference in characteristic regarding the same factor exceeds a prescribed range, a control signal is output.
In the construction described above, the drive pulse generator extends and contracts the electromechanical transducer such that slipping occurs between the second member and the driving friction member that are engaged via friction, and the relative amounts of movement of the second member and of the driving friction member are different. The second member and the driving friction member may slip by different amounts when the electromechanical transducer extends and contracts, or when it extends or contracts only. Where the first member is fixed, the second member is driven in prescribed directions. Where the second member is fixed, the first member is driven in prescribed directions.
Using this construction, where there is an abnormality with the electromechanical transducer, the drive signals assume a pattern that is different from when the electromechanical transducer is in the normal state, and therefore, the characteristic of the drive signals regarding a factor differs from the one that is obtained when the electromechanical transducer is in the normal state. In other words, when an appropriate factor is selected, the difference between the detected characteristic signals regarding the drive signals actually supplied to the electromechanical transducer and the standard characteristic signals regarding the same drive signals in the normal state exceeds a prescribed range. Based on this, the abnormality can be detected.
Therefore, the abnormality during the driving of the electromechanical transducer can be detected and output externally.
The characteristic of the drive signals can be obtained using various factors as explained in the following examples.
a: The drive pulse generator drives the electromechanical transducer using a constant current. The characteristic regarding a factor is the time required for the voltage of the drive signal to rise and exceed a prescribed threshold after the constant current driving is started.
In this construction, where the electromechanical transducer is in the normal state, the drive signal voltage gradually increases and exceeds the threshold after a prescribed time. However, if the electromechanical transducer is open, i. e., if it is insulated, the voltage increases instantaneously to the maximum voltage after the constant current driving is started, whereby the time required for the voltage increase is essentially zero, which is much less than the time required for the voltage to increase to the threshold when the electromechanical transducer is in the normal state. In addition, if there is a short-circuit in the electromechanical transducer, the voltage does not increase even if the element is driven using a constant current. Consequently, an infinite time is required for the voltage increase, which is much longer than the time needed when the electromechanical transducer is in the normal state. Therefore, if the difference between the actual voltage increase time and the prescribed time exceeds a certain range, it can be determined that an abnormality exists.
b: The drive pulse generator drives the electromechanical transducer using a constant current. The characteristic regarding a factor is the drive signal voltage waveform.
Using this construction, when the wires, etc. of the electromechanical transducer are damaged and the element becomes insulated, or when the electromechanical transducer has experienced insulation breakdown and has a short-circuit, the waveform of the drive signals is clearly different from that of the drive signals when the electromechanical transducer is in its normal state, and it can therefore be determined that an abnormality exists.
c: The drive pulse generator drives the electromechanical transducer using a constant current. The characteristic regarding a factor is the gain of each frequency band by means of frequency analysis regarding the drive signal voltage waveform.
Using this construction, where the mounting of the electromechanical transducer becomes unstable and the drive signal voltage waveform essentially matches the waveform when the electromechanical transducer is in the normal state but includes a high frequency component, the gain of the high frequency band is different from that of the element in the normal state, and therefore, an abnormality can be detected.
These and other objects, advantages and features of the invention will become apparent from the following description thereof taken in conjunction with the accompanying drawings, which illustrate specific embodiments of the invention.
REFERENCES:
patent: 5225941 (1993-07-01), Saito et al.
patent: 5587846 (1996-12-01), Miyano et al.
patent: 558972
Budd Mark O.
Minolta Co. , Ltd.
Sidley & Austin
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