JPH0635923B2 - Measuring head structure of speckle length measuring instrument - Google Patents

Description

The present invention relates to a speckle length measuring instrument for measuring an amount of movement of an object using a speckle pattern generated by diffused light from the surface of an object irradiated with laser light. Is related to the structure of.

(Prior Art) Conventionally, a target object is irradiated with a laser beam emitted from a semiconductor laser, a speckle pattern generated by diffused light from the surface of the object is observed, and a speckle pattern associated with movement or deformation of the object is detected. The amount of movement of the object based on the change,
A method of measuring the amount of deformation and the like is known (for example, "Optical Measurement Handbook" published by Asakura Shoten, pages 234 to 245.
page).

By the way, in the technical field of image processing, a CCD exhibiting high resolution has been put into practical use as an image sensor replacing a conventional image pickup tube. By applying this CCD as a speckle pattern detection sensor, highly accurate measurement can be performed. Is possible.

(Problems to be solved) However, conventionally, only the principle of the above-mentioned measurement method and the basic equipment configuration have been clarified, and the detailed arrangement of the equipment and the detailed structure for increasing the measurement accuracy. However, it has not been fully researched and has not yet been put to practical use.

For example, when a speckle length measuring device for measuring the amount of movement of an object is put into practical use, a semiconductor laser, a collimator lens,
Although it is necessary to install components such as an image sensor with high precision, it has been difficult to perform highly accurate positioning because these components have been individually positioned in the past. Further, there is a problem that the temperature changes drastically depending on the place where the semiconductor laser is installed, which causes the mode hop of the semiconductor laser, making it impossible to maintain the same speckle pattern on the same laser irradiation surface. Further, the measurement accuracy may be deteriorated due to the incidence of ambient light other than the laser light on the image sensor.

An object of the present invention is to put a speckle length measuring device into practical use.
It is an object of the present invention to provide a measuring head structure capable of easily and accurately positioning each constituent device and obtaining high measuring accuracy regardless of the measurement atmosphere.

(Means for Solving the Problem) The measuring head structure of the speckle length measuring instrument according to the present invention has a semiconductor laser (21) and a laser beam from the semiconductor laser (21) in a closed casing (10). A collimator lens (25) that emits light to form a laser beam, an electronic cooling device (3) that controls the temperature of the semiconductor laser (21) to be constant, and the temperature of the semiconductor laser (21) is measured for the temperature control. Temperature sensor
The unit (6) and the image sensor (4) for photoelectrically converting the speckle pattern into an image signal were housed and fixed at respective predetermined positions to form a unitized measuring head (1). The casing (10) is provided with a window (14) through which the laser beam from the collimator lens (25) should be emitted, and the image sensor (4) is arranged facing the window (14).

The semiconductor laser (21), the collimator lens (25), and the temperature sensor (6) are arranged in an accommodating chamber (23) provided in an integrated temperature control housing (22), and are provided on the outer surface of the temperature control housing (22). The electronic cooling device (3) is installed in close contact.

The distance between the semiconductor laser (21) and the collimator lens (25) is set so that the laser beam emitted from the collimator lens (25) becomes a parallel beam.

The position of the image sensor (4) is defined so that the scanning area at the time of photoelectric conversion is bilaterally symmetric with respect to the plane including the optical axis of the laser beam.

The window (14) of the casing (10) is formed by an optical filter that passes the frequency component of the laser beam and the frequency components in the vicinity thereof, and slightly with respect to the optical axis of the laser beam emitted from the collimator lens (25). It is deployed at an angle.

Semiconductor laser (21) and temperature sensor (6) have the same substrate
It is attached to (5).

Also, a laser beam aperture (28) is provided in the optical path of the laser beam.
A slit plate (27) having is installed.

(Operation and Effect) During measurement, the measuring head (1) is installed such that the optical axis of the laser beam emitted from the window (14) is perpendicular to the surface of the target object, and An external circuit for processing an image signal obtained from the image sensor (4) is connected to (1). Further, the temperature sensor (6) of the measuring head (1) is connected to a well-known temperature control circuit, and the output end of the control circuit is supplied to the electronic cooling device (3), whereby the temperature of the semiconductor laser (21) is changed. It is controlled to be constant.

Laser light from the semiconductor laser (21) is received by the collimator lens (2
The laser beam passes through 5) and is emitted from the window (14) of the casing (10) toward the moving object.

The diffused light reflected from the surface of the moving object is the window of the casing (10).
The light passes through (14) and enters the image sensor (4), which converts the speckle pattern into an image signal.
The image signal is sent to the external circuit and subjected to arithmetic processing for calculating the moving distance of the moving object.

According to the above measuring head structure, if the casing (10) of the measuring head (1) is installed with high accuracy, at the same time the casing (10)
Each component inside will be positioned with high precision,
Highly accurate length measurement is possible. Moreover, since the inside of the casing (10) is maintained at an appropriate temperature by the operation of the temperature sensor (6) and the electronic cooling device (3), high measurement accuracy can be obtained regardless of the measurement atmosphere.

If the semiconductor laser (21), the collimator lens (25) and the temperature sensor (6) are housed in the temperature control housing (22) and the electronic cooling device (3) is installed in close contact with the housing (22), the semiconductor Not only the laser (21) but also the collimator lens (25) is accurately maintained at a constant temperature, and even when the plastic collimator lens (25) is used, the optical characteristics such as the focal length do not change. In addition, even if the temperature of the measurement atmosphere drops, the temperature inside the casing (10) is maintained at an appropriate height, and the collimator lens due to dew condensation
Fogging of (25) is prevented.

Common substrate for semiconductor laser (21) and temperature sensor (6)
When attached to (5), heat is conducted through the substrate (5), so that the temperature detection accuracy of the semiconductor laser (21) by the temperature sensor (6) can be increased.

When the distance between the semiconductor laser (21) and the collimator lens (25) is adjusted so that the laser beam emitted from the collimator lens (25) becomes a parallel beam, the measurement head (1) and the target object are Regardless of the distance, the measurement sensitivity can be kept constant, which is convenient for the signal processing necessary for calculating the object movement amount.

In addition, as described above, by installing the image sensor (4) in a position symmetrical to the plane including the optical axis of the laser beam, the light intensity of the speckle pattern imaged on the image sensor (4). Distribution, ie image sensor
The level of the image signal obtained from (4) is made uniform,
For example, it is convenient in signal processing such as sampling of an image signal.

Furthermore, with this arrangement, the amount of object movement and the image sensor
(4) It is possible to simplify the relationship with the movement amount of the speckle pattern above.

By forming the window (14) of the casing (10) with an optical filter, the disturbance light that enters the window (14) from outside is blocked, and the measurement accuracy due to the disturbance light entering the image sensor (4) Is prevented.

When the window (14) is arranged with a slight inclination with respect to the optical axis of the laser beam, even if the laser beam from the collimator lens (25) is reflected by the window (14), the optical path of the reflected light is Since the laser beam is deviated from the semiconductor laser (21) due to the inclination, mode hopping due to the reflected light entering the semiconductor laser is prevented.

Also, install a slit plate (27) in the optical path of the laser beam,
By narrowing the laser beam from the collimator lens (25) to a predetermined diameter, a specx diameter that is almost the same as the pixel pitch of the image sensor (4) is formed, and the contrast of the speckle pattern on the image sensor (4) is thereby formed. At the same time, the feature of the speckle pattern can be efficiently detected.

Therefore, according to the above-mentioned measuring head structure, not only the measuring head (1) is easy to handle because it is unitized,
High accuracy of measurement can be obtained by the constitution of each part as described above, and it can be sufficiently put into practical use.

(Example) Hereinafter, a specific configuration of the measuring head structure according to the present invention will be described with reference to the drawings. It should be noted that the examples are for explaining the present invention and should not be understood as limiting the invention described in the claims or reducing the scope.

As shown in FIG. 1, the measuring head (1) is a closed casing.
Inside the (10), the semiconductor laser unit (2) and the electronic cooling device
(3), image sensor with CCD arrayed in one dimension
(4) etc. are deployed and unitized.

The casing (10) constitutes a hermetically sealed container by fixing a rubber packing (11) and a cover (12) for closing the opening to a main body of a rectangular parallelepiped body having one side surface opened as shown in the figure.
A window for emitting a laser beam is provided on the front wall of the casing (10).
(14) is provided.

As shown in FIG. 2, the semiconductor laser unit (2) has a laser beam generating part including a semiconductor laser (21), a collimator lens (25), etc., integrated in a temperature control housing (22). Is. The semiconductor laser (21) is mounted on the first substrate (5) together with the temperature sensor (6), and the substrate is screwed and fixed to the back surface of the temperature control housing (22) to fix the semiconductor laser (21) and the temperature. sensor
(6) is the storage chamber (23) in the temperature control housing (22)
It is housed in. In addition, the temperature control housing (2
A screw hole (24) communicating with the storage chamber (23) is formed in 2).

The collimator lens (25) is fixed to the end of a beam adjusting screw cylinder (26) having an external thread, and the screw cylinder (26) is screwed into the screw hole (24) of the temperature control housing (22). By collapsing the collimator lens (25), the collimator lens (25)
Alternatively, it is housed in the screw hole (24).

As a result, the storage chamber (2
3) is sealed by a substrate (5) and a collimator lens (25), and a semiconductor laser (21) and a temperature sensor are provided in the sealed space.
(6) will be placed. Therefore, the temperature sensor
(6) and the semiconductor laser (21) are always maintained at the same temperature,
The temperature control of the semiconductor laser (21) is accurately performed without error.

Attach the beam adjustment screw tube (26) to the temperature control housing.
By screwing it in (22) and rotating it forward and backward,
The distance L between the semiconductor laser (21) and the collimator lens (25) can be adjusted, and here the laser beam (8) emitted from the collimator lens (25) is a parallel beam as shown in FIG. The interval L is set.

As a result, the curvature radius Ls of the laser beam on the target object (7) in FIG. 9 becomes infinite, and the measurement sensitivity can be kept constant regardless of the distance between the measuring head and the target object. The following formula is established in FIG.

X = {(L ₀ · cos ² θs / Ls · cos θ ₀ ) + cos θ ₀ }
X, where X is the amount of movement of the speckle pattern on the image sensor, L _{0 is} the distance between the target object and the image sensor, x is the amount of movement of the target object, and the collimator lens (25) of the beam adjusting screw tube (26) A slit plate (27) having a laser beam aperture (28) is fixed to the opposite end. The inner diameter D of the laser beam aperture hole (28) becomes substantially equal to or slightly larger than the arrangement pitch (for example, 13 μm) of the CCDs forming the one-dimensional image sensor (4) when the average speckle diameter α of the speckle pattern is large. Is prescribed.

It is known that the average speckle diameter α is represented by α = 1.22λZ / L _{0 according} to the wavelength λ of the laser light and the distance L ₀ between the one-dimensional image sensor (4) and the target object. When the wavelength λ of the laser light is 780 nm and the distance L ₀ between the one-dimensional image sensor (4) and the target object is approximately 25 to 75 mm, the inner diameter D of the laser beam aperture hole (28) is set to approximately 2 mm.

As shown in Fig. 1, the base (1
A plate-shaped electronic cooling device (3) is installed on the upper surface of the device (3), and the semiconductor laser unit (2) is fixed in close contact with the upper surface of the electronic cooling device (3).

As shown in FIG. 6, the electronic cooling device (3) has a large number of P-type semiconductors (33) and N-type semiconductors (34) alternately arranged between a pair of ceramic plates (31) and (32). Has a well-known structure in which the electrode plates (35) are connected in a row and the lead wires (36) are connected to the electrode plates (35) at both ends.

As shown in FIG. 1, the base (13) has a second substrate (51) having a through hole (53) through which the laser beam from the semiconductor laser unit (2) passes at the end on the window (14) side. Standing, the substrate (51)
The one-dimensional image sensor (4) is fixed to.

As shown in FIGS. 4 and 5, the one-dimensional image sensor (4) has an optical axis L of the laser beam emitted from the semiconductor laser unit (2) and a detection unit (of the one-dimensional image sensor (4) ( 41) CCD arrangement direction, that is, scanning direction S
Are positioned so that they are orthogonal to each other, and the central position (point O) of the scanning region of the detection section (41) is located on a plane P that includes the optical axis L of the laser beam and is orthogonal to the scanning direction S. To be done.

Therefore, the diffused laser light reflected by the target object and incident on the one-dimensional image sensor (4) is substantially symmetrical and symmetrical about the center position (point O) of the signal scanning area as shown in FIG. The intensity distribution will be different. In such a distribution, all the signals to be sampled at the time of binarizing the image signal exceed the minimum level capable of signal processing, and accurate length measurement becomes possible.

Further, in FIG. 9, cos θs = cos θ ₀ = 1 can be set, and the movement amount of the target object (7) and the image signal can be handled with a simple relationship.

The window (14) of the casing (10) shown in FIG. 1 is formed by a glass plate that allows only infrared rays to pass through, and ambient light other than laser light is blocked by the window (14). The glass plate is the fourth
As shown in the figure, it is attached in a posture inclined by a slight angle θ (approximately 2 degrees) with respect to a plane orthogonal to the optical axis L of the laser beam. Therefore, even when the laser beam from the semiconductor laser unit (2) is reflected on the inner surface of the window (14), the reflected light travels along an optical path deviating from the semiconductor laser and directly enters the semiconductor laser (21). There is no fear. Therefore, the semiconductor laser (21) does not cause a mode hop due to the reflected light.

As shown in FIG. 1, a third substrate (52) is further fixed in the casing (10) above the semiconductor laser unit (2).

A semiconductor laser is provided on the first to third substrates (5) (51) (52).
Besides the circuit for driving (21), the first stage amplifier that should be directly connected to the one-dimensional image sensor (4) as shown in FIG.
(9) and the buffer amplifier (90) are formed.

FIG. 7 shows an example of the configuration of an external circuit for connecting to the measuring head (1), calculating the amount of movement of the object based on the image signal from the one-dimensional image sensor (4), and displaying it. ing.

As is well known, the one-dimensional image sensor (4) repeats scanning in the CCD array direction at regular intervals by a reset signal, a start signal and a shift signal sent from the buffer amplifier (90). The output signal of the sensor (4) is the first stage amplifier.
It is connected to the sample hold circuit (91) via (9), and the noise peculiar to CCD is removed by this.

The output signal of the sample hold circuit (91) is sent to the binarization circuit (93) via the gain control amplifier (92), and the image signal as shown in FIG. 8 is binarized and further binarized. The signal is sent to the correlator (94), the cross-correlation between the speckle pattern at the reference position of the target object and the speckle pattern after movement is sequentially calculated while shifting the reference position, and the calculation result is micro Computer (96)
Sent to. The microcomputer (96) calculates the moving distance of the object from the peak position of the cross-correlation function and digitally displays the result on the display (97).

Further, the buffer amplifier (90) and the sample hold circuit (9
1) Binarization circuit (93) and correlator (94) are timing generators
The operations are controlled by the timing signals supplied from (95).

At the time of measurement, the measuring head (1) shown in FIG. 1 is such that the surface of the target object (7) is irradiated with the laser beam (8) vertically, and the scanning direction of the one-dimensional image sensor (4) is the target object.
It is installed so that it is parallel to the moving direction of (7). In this state, the circuit of FIG. 7 is operated to measure the moving distance of the target object.

According to the speckle length measuring instrument, by accurately installing the casing (10) of the measuring head (1), at the same time, the semiconductor laser (21) and the collimator lens in the casing (10) are installed.
Since the (25) and the one-dimensional image sensor (4) are respectively positioned with high accuracy, it is possible to measure with high accuracy without being affected by the measurement atmosphere and the like due to the above-mentioned components.

The above description of the embodiments is for explaining the present invention, and should not be construed as limiting the invention described in the claims or limiting the scope. The configuration of each part of the present invention is not limited to the above-mentioned embodiment, and it goes without saying that various modifications can be made within the technical scope described in the claims.

For example, the external circuit to be connected to the measuring head (1) is not limited to that shown in FIG. 7, and various known circuits for calculating the moving distance based on the speckle pattern can be adopted.

[Brief description of drawings]

FIG. 1 is a partially broken exploded perspective view of a measuring head according to the present invention, FIG. 2 is an exploded perspective view of a semiconductor laser unit, and FIG.
FIG. 4 is a side view illustrating the positional relationship between the semiconductor laser and the collimator lens, FIG. 4 is a side view illustrating the tilted state of the window,
FIG. 5 is a front view for explaining the position of the one-dimensional image sensor, FIG. 6 is a sectional view of the electronic cooling device, FIG. 7 is a block diagram of an external circuit, and FIG. 8 is a light intensity distribution on the one-dimensional image sensor. FIG. 9 is a graph for explaining the relationship between the movement amount of the target object and the movement amount of the speckle pattern on the image sensor. (1) …… Measuring head, (10) …… Casing (14) …… Window, (21) …… Semiconductor laser (25) …… Collimator lens, (3) …… Electronic cooling device (4) …… Image Sensor, (6) …… Temperature sensor

Claims (8)

[Claims] 1. A surface of a moving object to be measured is irradiated with a laser beam, and a speckle pattern appearing on an observation surface facing the laser irradiation surface of the object is photoelectrically converted into an image signal, which accompanies movement of the object. In a Specks length measuring instrument that measures the amount of movement of an object based on a change in the image signal, a semiconductor laser is provided at a predetermined position in a closed casing (10).
(21), a collimator lens (25) for condensing laser light from the semiconductor laser (21) to form a laser beam, and an electronic cooling device (3) for controlling the temperature of the semiconductor laser (21) to be constant.
A measuring head (1) containing a temperature sensor (6) for measuring the temperature of the semiconductor laser (21) for controlling the temperature and an image sensor (4) for converting the speckle pattern into an image signal. The casing (10) has a window (1) through which the laser beam from the collimator lens (25) is to be emitted.
4), and the image sensor (4) is arranged facing the window (14), the measuring head structure of the speckle length measuring instrument. 2. A semiconductor laser (21) and a collimator lens (25)
The temperature sensor (6) and the temperature sensor (6) are provided in the housing chamber (23) provided in the integrated temperature control housing (22), and the electronic cooling device (3) is installed in close contact with the outer surface of the temperature control housing (22). A measuring head structure according to claim 1. 3. A semiconductor laser (21) and a collimator lens (25)
The measuring head structure according to claim 1, wherein the interval is set so that the laser beam emitted from the collimator lens (25) becomes a parallel beam. 4. The image sensor (4) according to claim 1, wherein the scanning region at the time of photoelectric conversion is positioned so as to be bilaterally symmetrical with respect to a plane including the optical axis of the laser beam. Measuring head structure. 5. The measuring head structure according to claim 1, wherein the window (14) is provided so as to be inclined with respect to the optical axis of the laser beam. 6. The measuring head structure according to claim 1, wherein the window (14) is formed by an optical filter which allows a frequency component of the laser beam and a frequency component in the vicinity thereof to pass therethrough. 7. The measuring head structure according to claim 1, wherein the semiconductor laser (21) and the temperature sensor (6) are mounted close to each other on a common substrate (5). 8. A slit plate (27) having a diaphragm hole (28) for narrowing the laser beam to a predetermined diameter in the optical path of the laser beam.
The measuring head structure according to claim 1, wherein the measuring head structure is installed.