JPS58120101A - Method for grasping displacement mode by using holographic interferometry - Google Patents

Abstract

PURPOSE:To grasp the dynamic displacement, by extracting only a dynamic elastic displacement component by an image processing manipulation, from both an interference fringe pattern of a regenerated image and a rigid body displacement component by a pickup. CONSTITUTION:A disk 4 is elastically resonated and a supporting table 5 is rigidly vibrated. Under this state, an appropriate light emitting timing signal is given from a trigger device 7, and a hologram is formed by double exposure recording. The regenerated image of said hologram is coded into a binary value by the image processing manipulation. The data of the interference fringes having fringe degrees is converted into a displacment quantity and it is stored in a memory. Light signal A emitted from a pulse laser and acceleration pickup signals B1-B3 of the table 5 are recorded, the relative displacement at the time of the double exposure is computed, and the results are stored in the memory. The rigid body displacement mode is subtracted from the displacement pattern of the holographic interference fringes in the memory. Thus only the elastic resonation mode of the disk 4 can be extracted.

Description

Detailed Description of the Invention The present invention provides a displacement mode grasping method using holographic interferometry for grasping a dynamic displacement pattern from an interference fringe pattern obtained by double exposure holographic interferometry and a rigid body displacement component detected by a pickup or the like. It is related to.

Pulsed laser holography interferometry provides an interference fringe pattern using a double exposure image, and it is difficult to identify clear nodal lines as seen in the steady vibration mode using continuous light holography interferometry. One of the methods for understanding dynamic displacement modes using pulsed laser holography interferometry is the method described above. The dynamic response signal of the object to be measured and the laser pulse emission timing control signal are set so that the first laser pulse is always emitted at a certain dynamic response signal level value at a certain time, and then the second laser pulse is By sequentially delaying the emission timing by a minute amount of time, we create a hologram that is multiplex recorded on the same dry plate using reference waves arranged so that the double exposure images are incident independently from different directions, and reproduced. In this method, observation is performed sequentially using the same reference wave as used during recording, and the node or antinode region is estimated from changes in the amount of movement of the interference fringes in an attempt to understand the displacement mode.

There is also a method of sequentially recording and reproducing double exposure images in a slit shape at different positions on a dry plate using a similar method, and similarly attempting to estimate all displacement modes from the moving state of the interference fringes.

Conventional methods are applicable when the dynamic phenomenon to be measured is always reproducible, and there are limits to their applicability to extremely high-speed transient phenomena such as impact phenomena. Furthermore, since many actual objects to be measured have structures in which several parts are coupled, several resonance modes generally become a problem in actual operation.

However, in each resonance mode, only specific parts exhibit elastic vibration behavior, and other structural parts often undergo rigid translational or rotational displacement.

The conventional grasping method grasps the displacement mode from the movement state of only the interference fringe pattern of the entire object to be measured, and has the disadvantage that when the structure is complex, the mode may be incorrectly grasped or it may be difficult to grasp.

The purpose of the present invention is to provide a method for separating and understanding the elastic vibration mode of a structural part that is a resonance source from an interference fringe pattern obtained by pulsed laser holography interferometry and a dynamic rigid body displacement component detected by a pickup or the like. There is a particular thing.

The present invention is characterized in that it uses pulsed laser holography interferometry to grasp the displacement mode accompanying dynamic phenomena of a measured object, and uses the dynamic response characteristics of the measured object to control laser pulse emission timing. At the same time, the dynamic rigid body displacement component of the object to be measured in the observation direction is recorded by picking up the dynamic rigid body displacement component of the object to be measured in the observation direction. By extracting only the dynamic elastic displacement component through image processing operations from both the interference fringe pattern of the detected and reproduced image and the rigid body displacement component caused by the pickup, it is possible to fully grasp the dynamic displacement mode.

The configuration and processing method of the embodiment of the present invention will be explained below.

Figure 1 shows a holographic optical system, where 1 is a pulsed laser light source that emits laser pulses, 2 is a reflecting mirror,
3 shows all the dry plate attachment points. 4 and 5 are examples of objects to be measured, 4 is a disk, and 5 is a support base supported by the disk 4.

Reference numeral 6 indicates an acceleration pickup, 7 indicates a trigger device for timing the emission of laser pulses, and 8 indicates a spring supporting the support base 5.

Now, as a simple example, measurement of the vibration behavior of the object to be measured will be explained. In a certain vibration process, as shown in FIG. 2, the disk 4 resonates elastically (FIG. 2(a)), and
When the support base 5 is undergoing rigid body vibration (Fig. 2(b)), an appropriate light emission timing signal is applied from the trigger device 7.
Create a hologram by double exposure recording. After directly recording the reproduced image of the hologram (Fig. 3), it is observed with a TV camera, binarized by image processing, and the interference fringe data with fringe order is converted into displacement amount and stored in memory. do. Pulsed laser emission signal A detected by a photodiode etc. at the same time as hologram creation and acceleration pickup signals B1, B2, Bs of support base 5
Record as shown in Figure 4, calculate the rigid body mode plane (Figure 2 (b)) from the relative displacement during double exposure (requires displacement at three independent points) (5), and store it in memory. do. The holographic interference fringes corresponding to FIG. 2(C) are shown in FIG. 3, and by subtracting the rigid body displacement mode from this displacement pattern in memory, the elastic resonance of the disk 4 shown in FIG. 2(a) is generated. Only the mode can be extracted,
For example, as shown in FIG. 5, the rigid body displacement pattern of the support base 5 is erased, and the result showing only the resonance mode of the disk 4 is displayed as an image.

By applying such devices and methods, it is possible to find structural parts exhibiting elastic resonance modes that are generally problematic, and it becomes possible to understand modes that are effective for vibration or noise countermeasures.

According to the present invention, it is possible to separate the elastic vibration mode of a structural part, which has been considered difficult in the past, from the complex interference fringe pattern obtained by pulsed laser holography interferometry, and to search for the source of vibration that is a problem in vibration countermeasures. can do.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of the object to be measured and the measurement optical system in the method of the present invention, Fig. 2 (a), (b), and (e) are schematic diagrams of the elastic mode (6) and rigid body mode, and Fig. 3 4 is a diagram showing interference fringes representing a displacement pattern, FIG. 4 is a diagram showing a pulsed light synchronized acceleration signal, and FIG. 5 is a diagram showing an elastic vibration mode. 1... Pulse laser light source, 2... Reflection mirror, 3...
・Reflection mirror, 4... Disc, 5... Support stand, 6...
Acceleration pickup, 7... Trigger circuit for pulse light emission control, 8... Support spring. Figure 3 (d)

Claims (1)

[Claims] When using pulsed laser holography interferometry to grasp the displacement mode associated with the dynamic phenomenon of a measured object, the dynamic response characteristics of the measured object are used as a signal for controlling the laser pulse emission timing, and a constant movement at a certain time is used as a signal for controlling the laser pulse emission timing. In the same way as recording a double exposure image with a state delayed by a minute time based on the response signal level value of the object, the dynamic rigid body displacement component of the object to be measured in the observation direction is detected by a pickup, etc., and the interference fringes of the reproduced image are detected. The dynamic displacement mode can be grasped by extracting only the dynamic elastic displacement component from both the pattern and the rigid body displacement component caused by the pickup through image processing operations. Method.