CN1963384A - Method for measuring minute angle based on self-commix interference of laser and apparatus thereof - Google Patents

Abstract

This invention relates to one micro angle measurement method and device based on laser self mixture and intervene, which comprises the following steps: sending the laser beam output by laser into reflection lens of object surface and the incidence line goes off object angle rotation center and the laser output power uses one photoelectricity detector and when the object changes by micro angle, the detector detects laser output power; the angle change leads feedback light process each length and the output laser power changes one ripe circuit and through pre-set angle and output power relationship to realize object rotation angle.

Description

Minute angle measuring method and device based on laser self-mixing interference

Technical field

The present invention relates to the laser measuring technique field, particularly based on the minute angle measuring method and the device of laser self-mixing interference.

Background technology

Measurement of angle is the important component part of measuring science, and the measurement of minute angle all is extremely important in many fields such as Aero-Space, military affairs, MEMS (micro electro mechanical system), Precision Machining, high Precision Detection and acts on.Minute angle measuring method commonly used at present mainly contains: optical autocollimating method, laser interferance method etc.Various devices have characteristics and application limitation separately.Autocollimation method is exactly that object and picture are laid respectively on the conjugate planes, and when object rotated, object imaging point on image planes also was moved thereupon, just can obtain the angle that object rotates by the amount of movement of measuring picture point.The conventional laser interferometric method is to utilize the interference of measuring beam and reference beam, the variation that is about to angle converts the optical path difference variation of two-beam to, thereby cause moving interference fringes,, realize high-acruracy survey angle by measuring the amount of movement of interference fringe.The autocollimation method principle is simple, and is easy to operate, but measuring accuracy is lower; Conventional laser interferometric method device complexity, but measuring accuracy height.

Laser self-mixing interference be meant that laser instrument output light is reflected by exterior object or scattering after, part light feeds back in the laser instrument, after light in the laser cavity mixes mutually, causes the phenomenon that laser output power changes, also can be described as the light feedback, i.e. in the resonator cavity of the light feedback of laser instrument output self.The variable power output signal that the light feedback causes and traditional two-beam interference class signal seemingly, when the external reflection thing whenever moved the displacement of half optical maser wavelength, laser output power changed a fringe period.Only there is an optical channel in the laser self-mixing interference system, and can accomplish " definitely " measurement, traditional relatively laser interference system, have advantages such as simple in structure, compact, easy collimation, can replace the conventional interference instrument in many occasions, be mainly used in the measurement of displacement and distance, speed and vibration etc. at present.Utilize the laser self-mixing interference phenomenon very few to the research of measurement of angle, only there is the scholar to report, because external cavity mirror departs from different angles, make the feedback amount difference of laser through external cavity mirror reflected back inner chamber, thereby the amplitude that causes the laser self-mixing interference striped is also different, can be by measuring the changes in amplitude of self-mixed interference striped, realize measurement to deviation angle, but this measuring method is higher to the stability requirement of laser instrument, be difficult to improve measuring accuracy, and when angle changes continuously, measure difficulty.

Summary of the invention

The object of the present invention is to provide a kind of minute angle measuring method, solve the low and conventional laser interferometric method device complicated problems of autocollimation method measuring accuracy effectively based on laser self-mixing interference.

The present invention also aims to provide a kind of measurement mechanism of realizing said method.

A kind of minute angle measuring method of the present invention based on laser self-mixing interference, see Fig. 1, be one catoptron 3 to be set on testee 4 surfaces, the laser beam of laser instrument 1 output impinges perpendicularly on the catoptron 3 by diaphragm 2, incident ray departs from the angle rotation center of testee 4, laser beam is in catoptron 3 reflected back laser instruments 1, cause laser self-mixing interference, the output power of laser instrument 1 is monitored with a photodetector 5, when the minute angle rotation takes place in testee 4, the output power of the laser instrument 1 that photodetector 5 monitors will change along with the variation of angle, half optical maser wavelength of the every variation of light path of the feedback light that the variation of angle causes, the output power of laser instrument 1 changes a fringe period, by calibrating good angle and the corresponding relation between output power in advance, realize measurement to the testee 4 small anglecs of rotation.

Preferred version: find interference fringe amplitude maximum by curve fitting, with the angle of interference fringe amplitude maximum zero reference angle as measurement of angle.

Realize the minute angle measurement mechanism based on laser self-mixing interference of described method, as shown in Figure 1, comprise a laser instrument 1, a diaphragm 2, a catoptron 3 that is arranged at testee 4 surfaces, a photodetector 5, a signal acquisition process module 10, the laser beam of laser instrument 1 departs from the angle rotation center of testee 4, and just in time pass the aperture of diaphragm 2, catoptron 3 is placed on the opposite side of diaphragm 2, and laser beam incides on the catoptron after passing diaphragm, the opposite side of catoptron 3 is placed with photodetector 5, and signal acquisition process module 10 links to each other with photodetector 5.

Catoptron 3 preferred antiradar reflectivity mirrors.The preferred wedge catoptron of described antiradar reflectivity mirror.

In the measuring method of the present invention, the angle that feedback light departs from incident ray is more little, the amount that light feeds back in the laser cavity is just big more, the amplitude of self-mixed interference striped is also big more, by curve fitting, can find interference fringe amplitude maximum, herein, therefore the angle of feedback light and incident ray is approximately zero degree, can be with the angle of the interference fringe amplitude maximum zero reference angle as measurement of angle.Find interference fringe amplitude maximum by curve fitting, with the angle of interference fringe amplitude maximum zero reference angle as measurement of angle.

When the anglec of rotation increases, feedback light may depart from laser cavity, this moment, the amplitude of interference fringe was approaching zero, therefore when the amplitude of interference fringe pairing angle when zero, be the maximum angle of institute's energy measurement, laser instrument is near more from the feedback light reflection mirror, and the maximum angle of measuring system institute energy measurement is just big more.

The present invention is the change in optical path length that the angle variation of testee is converted into feedback light, and make the incident ray that incides testee surface (catoptron) depart from the angle rotation center of testee, pressing approximately linear with the light path that guarantees feedback light with the angle of testee changes, and incident ray deviation angle rotation center is far away more, the light path of feedback light just changes more greatly with angle, and the self-mixed interference striped is also just close more.Utilize the stripe subdividing technology to improve measuring accuracy,, adopt weak feedback mode, make that laser instrument self-mixed interference striped is nearly cosine wave (CW) shape for the ease of stripe subdividing.

The present invention compared with prior art has the following advantages and beneficial effect: relative conventional laser interferometric method angle measuring system, and simple in structure, compact, and can carry out the self calibration at zero reference angle; The autocollimation method measuring accuracy is higher relatively.

Description of drawings

Fig. 1 is the structural representation of the device of the inventive method employing, among the figure, and the 1-laser instrument; The 2-diaphragm; The 3-plane mirror; The 4-testee, the 5-photodetector; 10-signal acquisition process module.

Fig. 2 is that light path in the inventive method is with angle variation relation synoptic diagram.

Fig. 3 is the structural representation of a kind of measurement mechanism of the inventive method when being used to measure by the stepper motor driven small anglec of rotation; Among the figure, the 6-signal conditioning circuit; The 7-computing machine; The 8-data collecting card; The 9-stepper motor.

Fig. 4 is the luminous power of surveying according to Fig. 3 measurement mechanism change curve with angle.

Fig. 5 is the structural representation of a kind of measurement mechanism of the inventive method when being used to measure by the stepper motor driven small anglec of rotation.

Fig. 6 is the luminous power of surveying according to Fig. 5 measurement mechanism change curve with angle.

Embodiment

As shown in Figure 1, the laser beam that laser instrument 1 is launched impinges perpendicularly on plane mirror 3 through diaphragm 2, and plane mirror 3 is fixed on the testee 4 and rotates with testee 4, and incident ray departs from the rotation center of testee 4, and the dotted line intersection point is a rotation center; Bias is by the density degree decision of self-mixed interference striped.In order to adopt weak feedback mode, reflectivity can be had only the transparent glass sheet about 4% to be used as plane mirror 3.The output power of laser instrument 1 is by photodetector 5 monitorings, and the laser power signal that photodetector 5 collects is through signal acquisition process module 10 analyzing and processing.

As shown in Figure 2, the distance of establishing between plane mirror and the angle rotation center is d, and the angle that the light beam incidence point departs from rotation center is α, and when testee anglec of rotation θ, the change in optical path length Δ L of feedback light is:

$\mathrm{\ΔL}=2d(\mathrm{tg\α}-\mathrm{tg}\frac{\mathrm{\θ}}{2})\mathrm{tg\θ}---\left(1\right)$

If θ is minute angle (less than 0.1 degree), the change in optical path length Δ L of the feedback light of being represented by (1) formula can be written as:

$\mathrm{\ΔL}\≅\left(2\mathrm{dtg\α}\right)\mathrm{\θ}=2\mathrm{h\θ}---\left(2\right)$

In Fig. 2,, promptly when d=0 and α=pi/2, have equally if the reflecting surface of catoptron is placed on the plane of over-angle rotation center:

ΔL＝2hθ (3)

Obviously, in the above two kinds of cases, when testee anglec of rotation θ was minute angle, the light path of feedback light was pressed approximately linear with the angle of testee and is changed.

Embodiment 1

As Fig. 3, it is that 250 millimeters, output power are the helium-neon laser of 3 milliwatts that laser instrument 1 adopts chamber length; One transparent wedge catoptron 3 is fixed on the universal stage 4, adopt wedge can avoid the reflected light on two surfaces of plane mirror to feed back in the laser cavity simultaneously as catoptron, have only the reflected light on a surface can feed back in the laser cavity like this, transparent wedge reflectance of reflector is the weak feedback modes of about 4% formation; Laser beam depart from testee 4 angle rotation centers apart from d=0.75mm, the distance h=1.5cm of wedge catoptron 3 elongation degree rotation centers.Survey the beam energy that sees through wedge with a silicon photocell 5, silicon photocell 5 is gathered for data collecting card 8 after signal conditioning circuit 6 amplifies after light signal is converted into electric signal again, computing machine 7 is mainly finished the data acquisition of measuring-signal and the functions such as control of stepper motor driver 9, and native system adopts the PCI-6025E type data collecting card of America NI (National Instruments) company.

Fig. 4 is the curve that the luminous power of surveying changes with angle.Among the figure, dotted line is the curve fitting line, can find interference fringe amplitude maximum by the curve fitting line, with the zero reference angle of corresponding herein angle as measurement of angle.By good pairing angle value of fringe period of every variation and the stripe subdividing technology of calibration in advance, utilize Fig. 4 can realize measurement to the small anglec of rotation of testee.

Embodiment 2

Among Fig. 5, difference from Example 1 is, it is the semiconductor laser of 5 milliwatts that laser instrument 1 adopts output power, and laser beam departs from the distance h=3mm of testee 4 angle rotation centers, and the plane at the reflecting surface place of wedge catoptron 3 is by the angle rotation center.

Fig. 6 is the curve that the luminous power of surveying changes with angle.Among the figure, dotted line is the curve fitting line, can find interference fringe amplitude maximum by the curve fitting line, with the zero reference angle of corresponding herein angle as measurement of angle.By good pairing angle value of fringe period of every variation and the stripe subdividing technology of calibration in advance, utilize Fig. 6 can realize measurement to the small anglec of rotation of testee.

Claims (5)

1, a kind of minute angle measuring method based on laser self-mixing interference, it is characterized in that one catoptron (3) being set on testee (4) surface, the laser beam of laser instrument (1) output impinges perpendicularly on the catoptron (3) by diaphragm (2), incident ray departs from the angle rotation center of testee (4), laser beam is in catoptron (3) reflected back laser instrument (1), cause laser self-mixing interference, the output power of laser instrument (1) is monitored with a photodetector (5), when the minute angle rotation takes place in testee (4), the output power of the laser instrument (1) that photodetector (5) monitors will change along with the variation of angle, half optical maser wavelength of the every variation of light path of the feedback light that the variation of angle causes, the output power of laser instrument (1) changes a fringe period, by calibrating good angle and the corresponding relation between output power in advance, realize measurement to the small anglec of rotation of testee (4).

2, minute angle measuring method according to claim 1 is characterized in that: find interference fringe amplitude maximum by curve fitting, with the angle of the interference fringe amplitude maximum zero reference angle as measurement of angle.

3, realize the minute angle measurement mechanism based on laser self-mixing interference of claim 1 or 2 described methods, it is characterized in that: described minute angle measurement mechanism comprises a laser instrument (1), a diaphragm (2), a catoptron (3) that is arranged at testee (4) surface, a photodetector (5), a signal acquisition process module (10), the laser beam of laser instrument (1) departs from the angle rotation center of testee (4), and just in time pass the aperture of diaphragm (2), catoptron (3) is placed on the opposite side of diaphragm (2), laser beam incides on the catoptron after passing diaphragm, the opposite side of catoptron (3) is placed with photodetector (5), and signal acquisition process module (10) links to each other with photodetector (5).

4, device according to claim 3 is characterized in that: catoptron (3) is the antiradar reflectivity mirror.

5, according to claim 3 or 4 described minute angle measurement mechanisms, it is characterized in that: described antiradar reflectivity mirror (3) is the wedge catoptron.

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