JPH09318328A - Laser non-contact extensometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid hazard to a human body by utilizing scattered light from a test piece to automatically detect presence of fracture of the test piece at a measurement part, and reducing the output level of irradiation laser light to a specified level or less. SOLUTION: For example, under the condition where a test piece W is not held between holding tools Ca and Cb, a measurement laser light is emitted from a semiconductor laser 11. In that case, the scattered light from the test piece W does not enter and image sensor 21, so, the average value level of each channel output is significantly lower compared with the case where the test piece W is present at the position, therefore in this case, a control signal is supplied from a test piece fracture/presence detecting part 33 to a laser power source circuit 10, for lowering a driving current of the semiconductor laser 11. Thereby, an irradiation laser light immediately drops to a low level.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention utilizes a speckle pattern obtained by irradiating the surface of a test piece with a laser beam to measure the elongation or contraction of the test piece without contacting the so-called laser. Regarding non-contact extensometer.

[0002]

2. Description of the Related Art There is known a method of obtaining displacement information of an object by utilizing a speckle pattern obtained by irradiating the surface of the object with laser light.

When the displacement information is obtained by using the speckle pattern, basically, the scattered light of the laser light from the surface to be measured of the object is photoelectrically converted by an image sensor and an electric signal corresponding to the speckle pattern is obtained. And the amount of movement of the speckle pattern is obtained by obtaining the cross-correlation function of the signals at each moment, and the displacement information of the object is obtained from the amount of movement of the speckle pattern.

Using this principle, a laser non-contact extensometer for measuring the elongation (or contraction, hereinafter the same) between two points (standard points) of a test piece used for a material test in a non-contact manner. Has already been proposed (for example, JP-A-8-4306).
In such a laser non-contact extensometer, the scattered light from the test piece is formed into an image on the light receiving surface of the image sensor by the image forming optical system, and among the channel outputs of the image sensor, it is preset on the test piece. 2 places (marks)
Using the output of each of the plurality of channels corresponding to the above, the amount of movement of the speckle pattern at each location is individually calculated, and the difference between them is calculated to obtain the extension between the two gauge marks on the test piece.

[0005]

By the way, in the laser non-contact extensometer as described above, in a normal measurement state, the laser light is irradiated toward the test piece set at the measurement site and is blocked by the test piece. However, when the test piece breaks in a tensile test, or when the extensometer is accidentally activated when the test piece is not present at the measurement site, the laser light is emitted backwards beyond the measurement site. . If there is no screen or other shield behind the measurement site,
The laser light may pose a danger to the human body.

Even if a partition is provided behind the measurement site to block the laser light as described above, in order to completely remove the influence of the reflected light due to the partition, the shape and material of the partition, etc. Need to be considered, which leads to cost increase.

Here, the breakage of the test piece during the tensile test or the like can be detected from the load detection signal of the material testing machine or the like, and it is possible to take measures such as turning off the laser light source based on the detection output. In that case, the following problems occur.

That is, in order to control the laser output of the laser non-contact extensometer by the signal from the material testing machine,
It is necessary to connect the material testing machine and the extensometer with a signal line,
Especially when the laser non-contact extensometer is installed on an existing material testing machine, it is necessary to modify the material testing machine so that such output can be obtained. Even if it is a tester, not only will it be necessary to perform matching so that the laser output is controlled by the output signal supplied from the material tester on the laser non-contact extensometer side, but also for one form of connector, It requires troublesome work such as unifying the two.

The present invention has been made in view of the above circumstances, and an object of the present invention is to eliminate the need for a detection signal such as breakage of a test piece from a material testing machine or the like, and
When a test piece is ruptured without providing a partition for blocking,
Another object of the present invention is to provide a laser non-contact extensometer that does not pose a danger to the human body even if the laser non-contact extensometer is accidentally activated in the absence of a test piece.

[0010]

In order to achieve the above object, a laser non-contact extensometer of the present invention comprises a laser irradiation optical system for irradiating a test piece set at a measurement site with laser light, and the laser light. Using the measurement optical system that measures the scattered light on the surface of the test piece and the output of the measurement optical system, calculate the elongation of the test piece from the movement amount of the speckle pattern included in the scattered light on the surface of the test piece. In an extensometer equipped with a calculation unit, a detection means for detecting the presence or absence of a test piece or breakage at the measurement site using the output from the measurement optical system, and the laser irradiation optical system when detecting the absence or breakage of the test piece. It is characterized in that it is provided with a laser output control means for lowering the laser light below a predetermined level.

Here, in the present invention, the specific method for detecting the presence or absence or breakage of the test piece by using the measurement result of the scattered light from the test piece is not limited. The speckle pattern included in the scattered light can be used to detect the absence or breakage of the test piece when the scattered light level is monitored from the output of the device and the level is below a certain limit. Based on the fact that the displacement speed of any point of the test piece based on the above became faster than a certain limit, and that the speckle pattern included in the scattered light changed instantaneously beyond a certain limit, etc. You can

According to the present invention, a measuring optical system originally possessed by a laser non-contact extensometer for measuring scattered light from a test piece is used, and the measurement output is used to measure the test piece. By detecting the breakage or absence of the laser beam, the laser non-contact extensometer can reduce the laser output in a self-contained manner when the test piece is broken or when the test piece is absent. .

[0013]

1 is a block diagram showing an embodiment of the present invention mounted on a material testing machine, showing a schematic diagram of an optical system and a block diagram showing an electrical structure thereof. It is a figure.

A tensile load is applied to the test piece W by moving the upper grip Cb upward while the both ends of the test piece W are gripped by the upper and lower grips Ca and Cb of the material testing machine. The laser non-contact extensometer includes a laser light irradiation optical system 1 for irradiating the test piece W with laser light, a measurement optical system 2 for measuring scattered light by the surface of the test piece W, and a scattered light by the measurement optical system 2. The measurement / control circuit 3 that processes the measurement output is configured as a main component.

The laser irradiation optical system 1 is a semiconductor laser 1
1, a beam expander 1 including a collimator lens 12 and two cylindrical lenses 13a and 13c.
3, the laser light output from the semiconductor laser 11 is shaped into a beam that extends linearly along the vertical direction that is the measurement direction of elongation, and then the gripper Ca
The test piece W held between Cb and Cb is irradiated. The drive current of the semiconductor laser 11 is supplied from the laser power supply circuit 10.

The measuring optical system 2 is a one-dimensional image sensor 2
1 and a condenser lens 22 for forming an image of scattered light from the test piece W on the light receiving surface of the image sensor 21.

The output of the image sensor 21 is amplified by the amplifier 4, later digitized by the AD converter 5, temporarily stored in the memory 6, and then taken into the measurement / control circuit 3 every second.

The measurement / control circuit 3 includes an image sensor 2
Of the outputs from one channel, 2 of the test piece W
A setter 7 for setting a data group for each of a plurality of channels corresponding to the gage marks A and B at a location as two observation point data corresponding to each gage mark is connected. With this setting device 7, for example, the image sensor 21 is set to 200
If the number of channels is 0, the output of channels 100 to 200 is the observation point data corresponding to one of the reference points A and the output of channels 700 to 800 is the other before the measurement of elongation is started. Is set as the observation point data corresponding to the reference point B of.

The measurement / control circuit 3 is mainly composed of a high-speed signal processing device, a CPU, etc., but in FIG. 1, it is shown as a block for each function. The output from each channel of the image sensor 21 is stored in the memory 6 at every predetermined minute time. The data from the two groups of channels set as the observation point data by the setting device 7 is shown below. Thus, it is used to calculate the elongation between the two gauge points.

That is, the respective initial data from the set two channel groups are stored in the specified addresses of the memory 6 as the initial reference data. Then, thereafter, every time data is sampled in the memory 6, the data from the set two channel groups (hereinafter referred to as observation point sampling data) corresponds to each reference point together with the corresponding reference data. It is introduced into the displacement calculation units 31a and 31b provided as above. Displacement calculation unit 31
Each of a and 31b calculates a cross-correlation function between the reference data and the observation point sampling data, and obtains the peak position of the function. The peak position information is obtained from each of the control points A,
The movement information of the speckle pattern included in the scattered light from B, that is, the displacement information of each of the reference points A and B from the time when the reference data was collected to the time when the observation point sampling data was obtained, The information is supplied to the elongation calculation unit 32. In the elongation calculation unit 32, each displacement calculation unit 31a, 3
The elongation between the gauge points A and B is calculated by calculating the difference between the displacement information of the gauge points A and B according to 1b.

In the displacement calculators 31a and 31b, every time the calculated peak position of the cross-correlation function moves by a certain amount, the channel group used as the observation point data source is moved by a certain amount in the direction of the movement. shift.
At the time of this channel shift, the reference data used until then is discarded, and the initial data from the channel group after the shift is used as new reference data, and thereafter,
Using the data from the same channel group as the observation point sampling data, the cross-correlation function is calculated between these data and the peak position is obtained. That is, each displacement calculator 31
In a and 31b, the movement amount of the speckle pattern from the two initially set reference points A and B is calculated, and the channel used as the observation point data source is sequentially changed following the movement. As a result, the amount of movement of the speckle pattern from these points, and thus the amount of displacement of each of the reference points A and B, is obtained while substantially tracking the two reference points A and B initially set on the test piece W. To go.

The channel data from the image sensor 21 stored in the memory 6 is also supplied to the test piece break / presence detection unit 33. Test piece breakage / presence detection unit 3
In 3, the average value of the channel data from the image sensor 21 is calculated, and when the average value level is lower than the preset threshold value, the test piece W is broken or the test piece W is grasped. It is determined that the tool Ca, Cb is not gripped, and a control signal is generated to reduce the drive current supplied from the laser power supply circuit 10 to the semiconductor laser 11 to a value equal to or lower than a preset value.

Further, in this example, the test piece breaking / presence / absence detecting section 33 is supplied with displacement information from the displacement calculating section 31b corresponding to the gauge point B on the moving side gripping tool Cb side,
Even when the gauge point B is displaced at a speed equal to or higher than the set speed, it is determined that the test piece W is broken, and a control signal is also sent in order to reduce the driving current to the semiconductor laser 11 to the set value or less. appear. The reference speed for determining the breakage can be arbitrarily set by the breakage speed setting device 8.

In the above embodiment, first, when the semiconductor laser 11 irradiates the laser beam for measurement with the test piece W not being held between the grippers Ca and Cb,
Since the scattered light from the test piece does not enter the image sensor 21, the average value level of the output of each channel is significantly lower than that in the case where the test piece exists at the same position. A control signal is supplied from the test piece break / presence / absence detection unit 33 to the laser power supply circuit 10 to reduce the drive current of the semiconductor laser 11. As a result, the irradiation laser light immediately drops to a low level.

Further, when the test piece W is broken by the tensile test, if the test piece W is a material having a relatively large elongation, the test piece W is separated into a relatively large upper and lower parts by the breakage, so that the scattering incident on the image sensor 21 is caused. The average level of light is relatively greatly reduced, and in this case as well, the irradiation laser beam is immediately dropped to a low level by the output from the test piece / breakage presence / absence detection circuit 33 as described above.

On the other hand, when the test piece W is made of a material having a relatively low ductility, even if it breaks, it does not largely separate into upper and lower parts as described above, and most of it remains in the laser light irradiation area, and therefore, it does not. The decrease in average level of scattered light is small,
Depending on the monitor, breakage may not be detected in some cases.
However, in such a test piece W, the shock due to breakage is large, so that each part of the test piece W is instantly greatly displaced as compared with the displacement during the tensile test before breakage, and particularly the gripping tool on the moving side of the breakage site. On the side close to Cb, the displacement due to the shock at the time of breaking is large. Therefore, if the reference speed for fracture determination is appropriately set by the fracture speed setting device 8, the fracture of the test piece can be detected by the displacement information of the reference point B supplied from the displacement calculator 31b. It is possible to immediately reduce the irradiation laser light to a low level at the time of breaking.

In the present invention, when the absence or breakage of the test piece is detected, the level of the irradiation laser beam is reduced and the current supplied to the semiconductor laser 11 is set to 0, that is, the power supply circuit is turned off. You may

Normally, in a device using a laser as a light source, it is not possible to turn ON / OFF the power supply or change the output level indiscriminately in order to stabilize the output, but like the present invention. When the displacement information is obtained by using the speckle pattern contained in the scattered light from the test piece, the requirement for the stability of the irradiation laser light is low, and even if the output level is changed frequently, the measurement accuracy is not affected. It has no effect. Therefore, according to the above embodiment, even if the output level of the semiconductor laser is automatically lowered or the power is cut off when the test piece is broken, the measurement result is not particularly affected next time.

In the present invention, the method for detecting the breakage of the test piece is not limited to the above-mentioned example, but in the case where only the test piece having a relatively large elongation is measured, the scattered light level monitor is used. The presence / absence of breakage of the test piece may be detected only by itself, and the position of the test piece used for monitoring the displacement speed for judging the breakage is not limited to the reference point B as described above, but may be any position. And moreover,
Instead of monitoring the displacement speed as described above, the breakage point of the test piece is basically limited to between the two reference points. Therefore, for example, the large and small patterns of the output of all channels of the image sensor 21 are monitored and tested. Any method can be adopted, such as detecting the breakage by utilizing the fact that the pattern at any one of the breaks greatly changes when the piece breaks.

Further, in the present invention, the laser non-contact extensometer itself detects the breakage of the test piece, but it does not prevent the use together with the breakage detection signal utilizing the load detection output by the material testing machine. .

[0031]

As described above, according to the present invention, the non-contact type extensometer for measuring the elongation of the test piece by utilizing the speckle pattern included in the scattered light of the laser light from the surface of the test piece. In the above, using scattered light from the test piece, the presence or absence or breakage of the test piece at the measurement site is automatically detected, and the output level of the irradiation laser light is lowered to a predetermined level or lower based on the detection result. Irradiation when the test piece is broken or when it is absent, without the need for a test piece break detection signal from other equipment such as a material testing machine, and without the provision of a screen for blocking. It is possible to reliably prevent the laser light from causing a danger to the human body. At the same time, reducing the laser output when not needed is
It can also contribute to reduction of power consumption and improvement of laser life.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention mounted on a material testing machine, in which a schematic diagram of an optical system and a block diagram showing an electrical configuration are shown together.

[Explanation of symbols]

 1 Laser Light Irradiation Optical System 10 Laser Power Supply Circuit 11 Semiconductor Laser 12 Collimator Lens 13 Beam Expander 2 Measurement Optical System 21 Image Sensor 22 Condenser Lens 3 Measurement / Control Circuits 31a, 31b Displacement Calculator 32 Elongation Calculator 33 Specimen Break・ Presence detection unit 5 A-D converter 6 Memory 7 Setting device 8 Breaking speed setting device Ca, Cb Grasping tool W Test piece

Claims (1)

[Claims] 1. A laser irradiation optical system for irradiating a test piece set at a measurement site with laser light, a measurement optical system for measuring scattered light of the laser light on the surface of the test piece, and an output of the measurement optical system. Using an extensometer with a calculation unit that calculates the elongation of the test piece from the amount of movement of the speckle pattern contained in the scattered light on the surface of the test piece, at the measurement site using the output from the measurement optical system. Detecting means for detecting the presence or absence of a test piece or breakage, and laser output control means for lowering the laser light from the laser irradiation optical system to a predetermined level or less when detecting the absence or breakage of the test piece A laser non-contact extensometer characterized in that