Measuring and testing – Vibration – Sensing apparatus
Reexamination Certificate
1999-10-28
2001-11-06
Larkin, Daniel S. (Department: 2856)
Measuring and testing
Vibration
Sensing apparatus
C073S649000, C073S653000, C073S657000
Reexamination Certificate
active
06311559
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a vibration measurement apparatus and a recording medium containing a vibration measurement program and in particular, to a vibration measurement apparatus of non contact type calculating a displacement of an object utilizing the Doppler effect of the laser beam and a recording medium containing such a vibration measurement program.
This vibration measurement apparatus can be applied to various experiment analyses of the automobile production technology or the like. More specifically, engine vibration analysis, body vibration, analysis of noise within an automobile, muffler vibration analysis, and the like. Since the vibration measurement apparatus is non-contact type and capable of accurately measuring vibration in a very small area, it can be applied to inspection in semiconductor production as well as inspection of a drill and other instruments. Furthermore, the vibration measurement apparatus can be used for detecting can be applied for detecting abnormal vibration in a production plant using a motor as well as leak from the water pipe and gas pipe. Furthermore, the vibration measurement apparatus can be employed for checking sweetness of watermelon other big fruits by knocking on the fruits to generate a sound. Here, an “object to be measured” includes a vast range from engines to watermelons.
2. Description of the Related Art
Conventionally, a speed indicator utilizing the laser beam Doppler effect has been used. The laser beam Doppler effect can also be used for measuring a displacement of an object to be measured as follows. That is, an oscillated laser beam is mixed with a reflected beam in a laser resonator. As a result, a beat wave of the laser beam can be detected by a photo detector (photodiode and the like). Here, if the object has moved a certain distance (half of the laser beam wavelength &lgr;), a chopping wave appears. Accordingly, by counting the number of the chopping waves, it is possible to calculate the displacement of the object.
However, a displacement smaller than the certain distance of one chopping wave cannot be accurately measured. Especially, when the object is vibrating, it is difficult to detect a turning point. That is, displacing object moves to the maximum point by vibration and then displacement becomes zero. After this, the object starts to displace in the opposite direction. Here, the chopping wave has a gentle slope and it becomes difficult to detect the turning point, i.e., the moment when the vibration direction has changed.
To cope with this, there is a method to calculate the turning point according to the highest speed position in on vibration cycle. The highest speed position can be detected in a comparatively stable state. However, if the object vibrates with a plurality of frequency components, a displacement in one direction is not symmetrical to a displacement in the other direction. This disables to calculate a turning point according to the highest speed position in one vibration cycle.
The vibration measurement apparatus utilizing the Doppler effect of the laser beam intends to perform in non-contact state the function of the acceleration pickup to be fixed on the object to be measured. Accordingly, it is desired to preferably measure the vibration characteristics of the object to be measured. However, If the turning point cannot be calculated or detected accurately, a displacement amount is added without turning. Thus, it is impossible to calculate with a high accuracy.
Moreover, when the vibrating plane contains a displacement of large highest speed and a small highest speed, a plurality of waves are overlapped and it is impossible to calculate a turning point for the small highest speed. Furthermore, it is difficult to identify a turning point of vibration which has once slowed down speed and then increases the speed in the same direction.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a non-contact type vibration method and apparatus capable of accurately calculating the vibration turning point.
Another object of the present invention is to preferably calculate a vibration turning point even if a plurality of vibrations are overlapped in the object to be measure.
Still another object of the present invention to identify a turning point even if the vibration plane moving speed has slowed down and then increases the moving speed in the same direction.
In the present invention, utilizing the general vibration characteristics and the relationships between a beat wave chopping wave and a displacement amount of the object to be measured, a turning point of the object to be measured is decided according to a continuous change of the chopping wave. When identifying a turning point according to a chopping waveform, there is an approach using differential and an approach using integral.
The differential approach identifies a turning point according to a continuous inclination change of the chopping wave in a beat wave. This differential approach also utilizes a relationship between the object displacement direction and the beat wave inclination.
The integral approach identifies a turning point according to a continuous change of the chopping wave area or wavelength. In this approach, a turning point is identified when the object speed is slowed down and then increases speed.
The differential approach extracts a change of displacement direction.
Firstly, the differential approach will be detailed. In a beat wave, a chopping wave has ascending portion and a descending portion, one of which has inclination almost 90 degrees and the other has a gentle slope. This gentle slope may be an ascending portion or a descending portion according to the movement direction of the object to be measured. The inclination itself is determined by the displacement speed of the vibrating plane. When the vibrating plane is coming nearer to the vibration measurement apparatus, the gentle slope is ascending; and when the vibrating plane is going away from the vibration measurement apparatus, the gentle slope is descending.
The chopping wave inclination changes according to the displacement speed but no change can be seen in the gentle slope. If the gentle slope is ascending, the inclination sign is plus and if the gentle slope is descending, the inclination sign is minus. When the vibrating plane displacement changes its direction, the ascending portion or descending portion having a gentle slope is reversed and the sign is reversed. According to the present invention, a turning point is identified before and after the sign is changed.
More specifically, the present invention includes steps of: applying a laser beam oscillated in a laser resonator, to an object to be measured; photo detecting the return laser beam; photo-electrically converting the mixture the return beam with the oscillated laser beam; and a signal processing for analyzing a waveform of the beat wave output from the photo-electrical conversion.
The signal processing step includes: an inclination calculating step for calculating the ascending inclination and a descending inclination of each beat wave; and identification of a turning point of the object to be measured, according to the inclination value changes along the time axis.
The inclination calculation step calculates an ascending inclination and a descending inclination. Then, it can be known which of the inclination is more gentle. The return point identification step identifies a return point of the object to be measured, according to the inclination value change along the time axis. Thus, the turning point is identified depending whether the gentle slope is ascending or descending. Accordingly, the direction change can be detected regardless of the vibrating plane moving speed. This assures to detect a turning point of the vibration even if the object to be measured exhibits a complicated vibration such as speed change in the middle.
The data on this beat wave inclination can be handled through a differ
Maruyama Tetsuro
Ohno Akiyoshi
Larkin Daniel S.
McGinn & Gibb PLLC
Saint-Surin Jacques
Suzuki Motor Corporation
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