Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Electrical signal parameter measurement system
Reexamination Certificate
2001-02-13
2003-12-30
Hoff, Marc S. (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Electrical signal parameter measurement system
C356S005090
Reexamination Certificate
active
06671638
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an oscillation measurement method and a frequency measurement apparatus and in particular, to an oscillation measurement method and a frequency measurement apparatus for measuring an oscillation state of an object by using a self-mixing type laser Doppler oscillation meter.
The present invention can be applied to an inspection and calibration apparatus for an oscillation generating apparatus and to apparatus of an abnormal oscillation detection in a power apparatus operating for a long period of time. As the inspection/calibration apparatus, the present invention can be applied for inspection of a frequency of, for example, a crystal oscillator and an ultrasonic oscillator and for calibration of a function generator. Moreover, as the abnormal oscillation detection apparatus, the present invention can be applied to a detection apparatus for a frequency deviation caused by undesirable resonance in a semiconductor manufacturing equipment which utilizing a high frequency oscillation as well as a defect in a tool such as a drill.
The invention can also be applied for purpose of oscillation analysis. More specifically, analysis of engine oscillation, analysis of vehicle body oscillation, analysis of noise in a vehicle, analysis of muffler oscillation, and the like. The invention can also be applied to various production fields. The invention can also be applied for detection of oscillation of a plant using a motor, leak analysis of a water pipe and a gas pipe for maintenance. Furthermore, the invention can be applied to determine sugar content in a large-size fruit such as a watermelon through a hitting sound. Here, the “object” to be measured has a wide range from crystal oscillators to watermelons.
2. Description of the Related Art
Conventionally, as means for measuring a frequency of a vibrating object in non-contact way, there is a method for obtaining a frequency by using a laser displacement meter utilizing the trigonometrical survey.
However, in the aforementioned conventional example, it is impossible to detect a displacement in a short period of time because of the sampling time of the displacement meter and has a problem that an error is caused in the measured oscillation cycle because of the sampling time. This becomes especially remarkable when the object oscillation becomes greater to reduce the difference between the oscillation cycle and the sampling time. That is, a great error is caused unless the sampling cycle is more than twice the maximum oscillation cycle (sampling theorem). Moreover, since the trigonometric survey is used, there is a need of using a large sensor head whose position and direction should be adjusted so that a reflected beam will not be cut off. Accordingly, this cannot be used for measurement in a small space.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an oscillation measurement method and a frequency measurement apparatus capable of measuring a small oscillation of an object with a high accuracy.
The oscillation measuring method according to the present invention comprises: a laser beam emission step for emitting a laser beam to an object to be measured; a return beam reception step for receiving a return beam reflected by the object and having an object Doppler frequency according to a velocity of the object; a self-mixing step for mixing the return beam having the Doppler frequency with beam emitted itself upon reception of the return beam and generating a self-frequency according to a resonator change during a time from the emission to the reception of the return beam, so as to generate a beat wave containing the object Doppler frequency superposed with the self-frequency; and an oscillation information output step for outputting the beat wave or information obtained from signal processing of the beat wave as the object oscillation information.
The oscillation measuring method according to the present invention measures an oscillation utilizing self-mixing type laser Doppler effect. A return beam having a Doppler frequency according to a velocity change of an object to be measured is self-mixed with an emitted beam generating a self-frequency of the resonator itself. The self-frequency is generated, for example, by a method for driving with a drive current of a sinusoidal waveform having a frequency in the proximity to the self-frequency and a method for physically oscillating the laser block having the resonator. When the resonator is driven by a drive current of a sinusoidal waveform, the oscillated beam has a wavelength changing according to the drive current value, causing a difference between the emitted beam and the return beam. This difference generates a beat wave of the self-frequency in the resonator. When the laser block having the resonator is physically oscillated, a Doppler frequency is generated by the resonator velocity and the velocity of the object to be measured. The Doppler frequency of the self-frequency by the resonator velocity is superposed by the Doppler frequency of the object to be measured. The self-frequency can be considered to be an imaginary velocity of the resonator. In other words, two Doppler frequencies based on two velocity values are mixed. Here, a phrase “having a Doppler frequency” means that a returned beam has a frequency shifted by the Doppler effect and has the shifted component as the Doppler frequency.
When the self-frequency change is in the proximity to the Doppler frequency change, a beat wave is generated according to a difference between the two frequencies. This beat wave has an envelope having a longer cycle as compared to the cycle of the Doppler frequency. Since the frequency of the envelope is a difference between the two frequencies, for example, in a preferred embodiment, it is possible to use this envelope frequency to obtain a difference between a frequency of the object to be measured and a frequency of an imaginary velocity of the resonator. Since the envelope frequency is lower than the Doppler frequency of the object to be measured, the accuracy in obtaining the envelope frequency value is higher than the accuracy in obtaining the Doppler frequency. Accordingly, according to the present invention, it is possible to improve the effective figures of the detectable miunute frequency difference without increasing the accuracy of the A/D converter or the like.
In the laser emission step, a laser beam is emitted to the object to be measured. The laser beam is scattered and reflected by the surface of the object to change its frequency according to the velocity of the object. In the return beam reception step, this return beam is received. In the self-mixing step this return beam is self-mixed in the resonator, with an emitted beam (oscillated beam) emitted upon reception of the return beam. The emitted beam emitted upon reception of the return beam generates a self-frequency according to a resonated change during a period from the laser beam emission to the laser beam reception. Accordingly, in the present invention, a newly emitted beam generating a self-frequency is self-mixed with the return beam having the Doppler frequency of the object to be measured. The oscillation information output step outputs as the oscillation information of the object to be measured a beat wave generated by the mixture of the object Doppler frequency and the self-frequency or information of the beat wave subjected to a signal processing.
This beat wave is useful for detecting a change of the oscillation state of the object to be measured. Especially when the self-frequency is in the proximity to the object oscillation frequency, it is possible to obtain a beat wave characterized in the envelope waveform. From this envelope frequency, it is possible to calculate a fine frequency difference between the modulation-frequency and the object frequency.
Moreover, when the envelope value change is below a predetermined value, it is possible to determine that the self-frequency is ma
Kitazumi Hitoshi
Kodera Hiroshi
Maruyama Tetsuro
Nishimura Yoshimitsu
Sumi Masao
Charioui Mohamed
Hoff Marc S.
Suzuki Motor Corporation
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