JP3548247B2 - Laser projection device - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a laser projector that forms a distance measurement, an angle measurement, or a reference plane by using a laser beam emitted from the projector.
[0002]
[Prior art and its problems]
In the field of civil engineering and construction, a surveying object is used by using a laser surveying device (a so-called laser planar) that scans a laser beam from a rotating light projecting portion toward a surveying object around the device body and forms a reference plane by the laser beam. Reference measurement and height measurement are performed by measuring the height of the spot of the laser light that has reached the upper side.
[0003]
Such a laser surveying device includes a light source that emits laser light, an automatic optical axis correction unit that automatically corrects the tilt of the optical axis of the laser light, a collimator lens that converts the laser light emitted from the light source into a parallel light flux, A rotary projection unit for horizontally or vertically rotating and projecting laser light is provided. In recent years, a laser surveying instrument using a semiconductor laser instead of a helium neon laser as a light source has been developed in order to reduce the size of the apparatus and reduce current consumption.
[0004]
This type of conventional laser surveying device is used for reference setting and height measurement in a wide range from a short distance of 0.5 to 1.5 m to a long distance of 100 to 200 m, for example. In such a use, aiming can be easily performed, the detection sensitivity does not fluctuate depending on the measurement distance when the beam height position is detected by the detector, and it can be used sufficiently in the field and so on. It is desired to improve the detection accuracy of the detector and the visibility in visual observation. That is, firstly, aiming can be easily performed, secondly, there is no variation in detection sensitivity when a beam irradiation position is detected by a detector, and thirdly, it is not affected by a temperature change or the like and can be used outdoors. Fourth, it is desired that the detector can be used, and fourthly, the detection accuracy by the detector and the visibility by visual inspection are good. To satisfy these, the following conditions are required.
[0005]
(1) The projection beam diameter must be as small as possible at a given projection distance.
(2) The size of the projection beam diameter is constant regardless of the projection distance
(3) The projected beam diameter does not change due to disturbance such as wavelength change and temperature change.
(4) The beam waist position can be set to any distance (from short distance to long distance) as necessary.
The above conditions (1) and (2) refer to the initial performance of the laser projector, a design technique for determining an optimum emission beam diameter and a beam waist position for a required projection distance, and processing of optical components. It can be overcome by manufacturing techniques such as precision or assembly precision.
[0006]
Condition (3) relates to the stability of the laser projection device, and is very important for a laser surveying device that is frequently used outdoors such as in civil engineering works. In particular, a laser surveying device is required to guarantee performance in a temperature range of −20 ° C. to 50 ° C., which is much wider than that of other precision instruments. Normally, the waist position and waist diameter of the projection laser beam change due to expansion and contraction of the lens support frame, changes in the refractive index of the lens itself, changes in the wavelength of the light source, and the like, as the temperature changes.
[0007]
FIGS. 8 and 9 show examples in which beam diameters at different projection distances are measured using the temperature change as a parameter, and the state of the change is graphed. Although these figures are not described in detail, a lens system for producing a parallel beam of an appropriate size is set in the laser projection device, and an exit diameter (that is, an exit beam diameter) at the exit end of the projection device is determined. The beam size at each distance when the beam waist position (distance from the emission end of the projection device to the position forming the beam waist) x is plotted, that is, the beam diameter at each distance. FIG. 8 and FIG. 9 show the emission beam diameter W = φ8 (mm) and W = φ12.5 (mm), respectively.
[0008]
FIG. 8 shows an initial setting of the projection apparatus when the beam diameter is 8 mm at a temperature of 20 ° C. and the beam waist position x = 39.578 m, that is, the distance from the exit of the projection apparatus to the point where the beam waist is generated. Is x = 39.578 (m), and the temperature is changed to 50 ° C. and −20 ° C., respectively, for the projection apparatus in which the radius of curvature R of the exit wavefront at this time is R = 78 (m). Is shown.
FIG. 9 also shows the initial settings of the exit beam diameter W = φ12.5 (mm), the beam waist position x = 96.605 (m), the radius of curvature R of the exit beam wavefront R = 190 (m), and the temperature of 20 ° C. Shows the beam diameter for each distance when a temperature change is given from this initial setting.
[0009]
As can be seen from these figures, even if the appropriate exit beam diameter, beam waist diameter, and beam waist position are initially set, the beam waist distance x changes due to temperature changes, and the beam diameter at each distance x changes. You can see that Due to such a change in the beam diameter, there has been a problem that the above conditions (3) and the like required for the laser projection device are not satisfied. When the condition (3) is not satisfied, the conditions (1) and (2) initially set are also destroyed.
In order to solve such a problem, a collimator for compensating for a temperature change in a lens system for forming a parallel beam has been proposed (US Pat. No. 5,225,928). Therefore, it is difficult to completely correct the temperature while correcting other aberrations. Particularly, when a semiconductor laser or the like having a large light emission angle is used as a light source, a collimator lens having a large NA (numerical aperture) is required, so that it has been even more difficult to completely perform temperature compensation.
[0011]
Further, even if the temperature can be compensated by design, it is difficult to completely compensate for the effect of the temperature change. This is because a temperature distribution occurs in each member constituting the laser projection device. For example, a laser projection device has a light source such as a semiconductor laser, and the light source itself acts as a heat source to generate a temperature difference between the temperature and the outside world, thereby generating a temperature distribution. In addition, heat generated by a motor or the like for rotating and irradiating a laser beam cannot be neglected. Therefore, in a conventional laser projector, when a temperature change actually occurs despite a temperature compensation, a desired distance is obtained at a predetermined distance. The beam diameter was not obtained.
[0012]
Next, condition (4) is that, when detecting the height and position of the beam projected at a predetermined distance, when detecting with a detector at a predetermined distance, the size and sensitivity of the detector are determined in accordance with the specifications such as the detector. The objective is to obtain the optimum beam diameter manually or automatically for the conditions such as visibility when viewing it visually.
[0013]
FIGS. 10 and 11 show the projection distance and beam of the laser beam with an emission beam diameter W = φ8 (mm), and FIG. 11 shows the emission beam diameter W = φ12.5 (mm) at the same constant temperature. It is a figure showing the relation with a diameter. In each case, the wavelength of the laser beam is the same, and the symbol “x” in each drawing indicates the beam waist distance.
[0014]
Here, in both figures, if the beam waist position x is changed, it is understood that the beam diameter changes at each distance. For example, in FIG. 11, when the projection apparatus is used in a relatively short range (about 10 to 70 m), it can be seen that the beam waist distance x should be set to 50.879 m. Also, when using from a short distance to a long distance (about 100 to 200 m), it can be seen that the beam waist distance x should be set to 97.505 (m).
It is very useful to be able to set an arbitrary beam waist distance x with one laser projection device.
In view of the above, a laser projector capable of changing the beam waist position and enabling remote control has been disclosed in Japanese Patent Application Laid-Open No. Hei 5-322564.
[0015]
However, in this conventional example, there is no means for confirming the beam waist position (distance) of the projection beam or the beam diameter (waist diameter) at that position. Therefore, in order to satisfy the condition (4), it is necessary to confirm the beam diameter at a distant position actually separated by a predetermined distance (for example, a position separated by several hundred meters), and there is a problem that the operation becomes complicated. Was. In a bright outdoor place, it was difficult to visually recognize the laser beam, and it was difficult to actually detect the beam diameter. In particular, there is a problem that a laser projector using an invisible light source such as a semiconductor laser of near-infrared cannot be visually observed, and it is more difficult to detect a beam diameter. For this reason, the above-mentioned conventional laser projection apparatus capable of changing the beam waist position can be used only with a visible laser light source that is short in distance and bright. Even if the beam waist position and beam waist diameter are once determined, the above condition (3) is not satisfied, and no consideration is given to the fact that the beam diameter of the projection beam changes due to disturbance such as temperature change. Had not been.
[0016]
[Object of the invention]
The present invention has been made based on the problems in the above-described conventional laser surveying apparatus, and at a required distance, it is possible to automatically set an optimal or desired beam waist position and beam waist diameter, Another object of the present invention is to provide a laser projection apparatus that stably maintains a beam waist position and a beam diameter that are set even with disturbances such as temperature and wavelength changes. Still another object of the present invention is to provide a detection system capable of detecting a projection laser beam waist position, and a laser projection device capable of freely setting a beam waist position based on a signal of the detection system.
[0017]
Summary of the Invention
The present invention that achieves the above object is a laser projection device that projects a light beam from a laser light source as a substantially parallel laser beam,A beam waist distance changing optical system for changing a beam waist distance of the laser beam emitted from the laser light source, a branch optical system for branching a part of the laser beam emitted from the beam waist distance changing optical system, and the branch Focus error detecting means for receiving the laser beam branched by the optical system and detecting an amount corresponding to the radius of curvature R of the wavefront of the laser beam by an astigmatism method, and an amount corresponding to the radius of curvature R of the wavefront; Calculating means for calculating the beam waist distance of the projection beam from the laser beam diameter W at a predetermined position, and control means for driving and controlling the beam waist distance changing optical system based on the beam waist distance of the projection beam WhenIt is characterized by having provided.
[0018]
DESCRIPTION OF THE PREFERRED EMBODIMENTS
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described based on illustrated embodiments. Before describing the configuration of the present invention, the basic principle of the present invention will be described to facilitate understanding of the present invention.
According to the present invention, the beam waist position of a projection laser beam (generally a Gaussian beam) is defined as a beam diameter at an arbitrary distance (in the case of the present invention, corresponding to an exit beam diameter for emitting from a projection port of a projection device) and a radius of curvature of a beam wavefront. The focus is on the idea that if R is known, it is uniquely determined. Therefore, if the radius of curvature of the beam wavefront is detected by any method, the beam waist position is automatically determined because the emission beam diameter is determined in advance by initial settings according to the specifications of the projection device. Therefore, the beam waist diameter is automatically determined.
[0019]
Generally, in a Gaussian beam such as a laser beam, the beam diameter at the beam waist position is set to W₀  If the beam diameter at a position x away from the beam waist position is W, the radius of curvature of the wavefront at that position is R, and the wavelength of the laser beam is λ, the beam diameter W and the radius of curvature R of the wavefront are given by the following equations. It is known that it can be represented (for example, "Introduction to Imaging Optics" by Yoshiya Matsui, pages 112-115, published by Keigaku Shuppan).
W = W₀  ｛1+ (4λx / πW₀ ²)²  ｝^1/2                ... 1-1
R = x ｛1+ (πW₀ ²/ 4λx)²  ｝ …… 1-2
These equations can be modified as follows.
W₀  = W ｛1+ (πW²  / 4λR)²  ｝^-1/2              ... 1-3
x = R ｛1+ (4λR / πW²  )²  ｝^-1                  ... 1-4
[0020]
Here, if the target laser projector is specified, the wavelength λ of the laser beam and the beam diameter W of the emission beam at the projection port of the laser projector are specified. Therefore, if the radius of curvature R of the wavefront of the laser beam emitted from the laser projector is measured, the beam waist diameter W at the beam waist position can be obtained.₀  Can be obtained by the above equation 1-3, and the distance x from the laser projector to the beam waist can be obtained by the above equation 1-4. FIG. 12 shows the relationship between the radius of curvature R of the wavefront and the beam waist distance x when the beam diameter W at the emission position is used as a parameter. From this figure, it can be seen that the beam waist distance x is determined by the radius of curvature R of the wavefront.
[0021]
As means for detecting the amount corresponding to the radius of curvature R of the wavefront, (1) means for directly detecting the radius of curvature R of the wavefront, and (2) light beam having a wavefront with the radius of curvature R is condensed by a lens, and There is a means for detecting according to the state of light collection. As the detection means (1), for example, a radial sharing interferometer can be used. As the detection means (2), a focus error detection optical system based on an astigmatism method or the like used in a known optical disk device or the like can be used.
[0022]
In one embodiment of the present invention, the radius of curvature R of the wavefront when the diameter W of the laser beam emitted from the laser projection device is determined is measured, and the beam waist distance x and the beam waist diameter W are measured.₀  There is a feature in seeking. This embodiment will be described with reference to FIGS.
[0023]
FIG. 1 shows, as a first embodiment, a laser projection apparatus for measuring a radius of curvature R of a wavefront of an emitted laser beam by a focus error detecting means based on an astigmatism method which is one of the methods (2). is there. This laser projection device includes a laser projection unit having a means for adjusting a beam waist position of a projection laser beam, a laser light source unit 101, and a rotation axis center coincident with an optical axis of a light beam emitted from the laser light source unit 101. A rotating light projecting unit 111 that rotates about the axis 111c and rotationally projects (emits) a laser beam in a direction substantially orthogonal to the rotating axis 111c is provided. Further, as a means for detecting the radius of curvature R of the wavefront, a focus error used in an optical disk device or the like, which receives a branched laser beam emitted from the laser light source unit 101 and detects the radius of curvature R of the wavefront.Detection system121 and focus errorDetection systemA control unit 131 for adjusting the position (distance x) of the beam waist BW based on the focus error signal detected by the control unit 121.
[0024]
The laser light source unit 101 includes a semiconductor laser 102, a collimator lens 103 that converts the laser light emitted from the semiconductor laser 102 into a substantially parallel light beam, and transmits most of the substantially parallel laser beam, for example, about 90%. The beam splitter 104 reflects the remainder toward the focus error detection system 121. The rotary light projecting unit 111 is driven to rotate about a rotation axis 111c by a driving mechanism (not shown). The optical axis of the collimator lens 103 coincides with the rotation axis 111c. That is, the laser beam emitted from the laser light source unit 101 travels around the rotation axis 111c of the rotary light projecting unit 111, and the first mirror 112 and the second mirror 112, whose angle between the surfaces is set to 45 °. The light is reflected by the mirror 113 in a direction orthogonal to the rotation axis 111 c and emitted from the rotation light projecting unit 111. At this time, the radius of curvature of the wavefront of the laser beam at the time of emission is R, and the emission beam diameter is W.
[0025]
The collimator lens 103 is moved forward and backward by the lens driving mechanism 105 in parallel with the optical axis. Due to this reciprocation, the distance d between the semiconductor laser 102 and the collimator lens 103 changes, the radius of curvature R of the wavefront of the laser beam changes, and the beam waist BW moves. From these, the beam waist distance x and the beam waist diameter W₀  Changes.
[0026]
The laser beam emitted from the rotary light projecting unit 111 has a beam diameter W at a position that is a predetermined distance x away from the rotary light projecting unit 111.₀  Is formed. If each optical component of the laser projector is manufactured with high precision, the radius of curvature R of the wavefront of the laser beam emitted from the laser projector and the distance x of the beam waist BW are determined by the semiconductor laser 102 and the collimator lens 103. And is uniquely determined only by the distance d between them.
[0027]
On the other hand, the laser beam reflected and branched by the beam splitter 104 is condensed by a condenser lens 122 and further condensed on a four-divided sensor 124 by a cylinder lens 123. In the drawing, the cylinder lens 123 has no lens power in the plane of the paper, and is arranged so as to have the lens power in a direction perpendicular to the plane of the paper. The four-divided sensor 124 is symmetrically divided into four by an orthogonal cross line, and the direction of the divided line is arranged at 45 ° with respect to the generatrix direction (in the plane of the paper) of the cylinder lens 123. When the radius of curvature R of the wavefront of the laser beam changes, the beam spot shape changes to an ellipse, a circle, and an ellipse whose major axis is orthogonal to the ellipse. Therefore, each sensor output of the four-divided sensor 124 changes.
[0028]
The output of the four-divided sensor 124 is subjected to amplification processing or the like in the processing unit 132 of the control unit 131 and is used by the microcomputer 133 for predetermined arithmetic processing. The microcomputer 133 displays the radius of curvature R of the wavefront, the beam waist distance x, and the like based on the calculation result on the display unit 134. Further, the microcomputer 133 calculates a moving direction and a moving amount of the collimator lens 103 that can change, for example, the beam waist position to a predetermined position based on the above value, and based on the calculation result, the lens through the control unit 135. The driving mechanism 105 is driven to move the collimator lens 103. By this movement, the distance x to the beam waist BW can be kept constant against disturbance such as temperature change and wavelength change, or the beam waist BW can be formed at a predetermined distance.
[0029]
The operator operates the input unit 136 to select whether to keep the distance x constant or to change the distance to a predetermined distance, or to set and select various data such as the predetermined distance. Further, it is also possible to program the usage method in advance. This makes it possible to start measurement in a predetermined mode immediately after the switch is turned on. Further, the above operations can also be executed by the remote operation unit 141 formed separately from the control unit 131. The signal output from the remote operation unit 141 is received by the receiving unit 137, and is input to the microcomputer 133 via the input unit 136 in the same manner as the signal from the input unit 136. A signal from the remote operation unit 141 is transmitted to the receiving unit 137 via a wire, infrared rays, radio waves, or ultrasonic waves.
[0030]
The above is an outline of the present embodiment, but the configuration and operation of the focus error detection system 121 will be described in more detail with reference to FIGS. 2 and 3. FIG. 2 is a diagram for explaining the measurement principle of the focus error detection system 121.
[0031]
The focus error detection system 121 according to the present embodiment includes an optical system equivalent to a focus error detection optical system based on the astigmatism method used in the optical disc device. The four-division sensor 124 has four independent division sensors 1241, 1242, 1243, and 1244 divided by a division line in the cross direction, and the laser reflected by the beam splitter 104 around the intersection O of the division line. The beam is focused by the focusing lens 122 and the cylinder lens 123. Then, a focus error signal (FES) is obtained from the difference between the sum of the outputs of the diagonal split sensors 1241 and 1243 and the sum of the outputs of the other diagonal split sensors 1242 and 1244. The output of each of the divided sensors 1241, 1242, 1243, 1244 is represented by S₁  , S₂  , S₃  , S₄  Then
FES = (S₁  + S₃  )-(S₂  + S₄  )
Is represented by The magnitude of the focus error signal FES changes depending on the radius of curvature R of the wavefront of the light beam incident on the focus error detection system 121. This will be described for a focus error detection circuit in comparison with an optical disk device.
[0032]
Now, suppose the information recording surface 151 of the optical disk is_B  Assuming that the light spot emitted from the objective lens 152 is focused on the information recording surface 151_B  The light beam reflected from the lens and incident on the focus error detection system becomes a parallel light beam as indicated by B, and therefore, the radius of curvature R of the wavefront of the light beam B_B  Becomes ∞. At this time, the light spot on the four-divided sensor 124 has a circular shape like B ', and the focus error signal FES becomes zero.
[0033]
On the other hand, when the information recording surface 151 moves away from the objective lens 152 by Δ, the information recording surface 151_A  The light beam incident on the focus error detection system due to the reflected light from the light source is as shown by A, and the radius of curvature of the wavefront at that time is R_A  It becomes. The light spot on the four-divided sensor 124 has an elliptical shape whose major axis is the diagonal direction of the divided sensors 1241 and 1243, as indicated by A ', and the focus error signal FES ｛(S₁  + S₃  )-(S₂  + S₄  ｝ Is a positive value.
[0034]
When the information recording surface 151 approaches the objective lens 152 by Δ, the information recording surface 151_C  The luminous flux incident on the focus error detection system by the reflected light from the light source becomes C, and the radius of curvature of the wavefront at that time is R_C  It becomes. The light spot on the four-divided sensor 124 has an elliptical shape having a major axis orthogonal to the light spot A ', such as C', and the focus error signal FES ｛(S₁  + S₃  )-(S₂  + S₄  ｝ Is a negative value.
In the optical disk device, the focus error signal FES is always 0, that is, the radius of curvature of the wavefront is R_B  Thus, the objective lens is servo-controlled so that the optical disk is always in focus.
[0035]
As described above, the amount of deviation Δ from the focal point between the optical disc and the objective lens is determined by the focus error detection system.121Wavefront of light beam incident onRadius of curvature R, And further induces a change in the shape of the light spot on the four-divided sensor 124 to generate the focus error signal FES. That is, the focus error detection system 121 calculates the radius of curvature of the wavefront incident thereon.RIs detected.
[0036]
The magnitude of the focus error signal FES changes according to the defocus amount Δ, and an S-curve curve as shown in FIG. 3 is obtained. This S-curve curve is_A  , 151_B  And focal length f₀  3 shows the relationship between the amount of deviation Δ (defocus amount) from the focal point with the objective lens 152 and the magnitude of the focus error signal FES obtained at that time. In FIG. 2, the optical disc 151 is located at the in-focus position._B  The input wavefront is B when there is an optical disc 151 at the out-of-focus position._A  , 151_C  The input wavefronts when there are are A and C, respectively. When the input wavefront is B, the focus error signal FES_B  Point value, and when the input wavefront is A,_A  Points. That is, if the magnitude of the focus error signal FES is known, the shift amount Δ can be easily obtained. At this time, the change of the focus error signal FES with respect to the deviation amount Δ, that is, the range of the linear region in the S-curve,_B  The sensitivity near the point can be freely designed by optimizing the optical system of the focus error detection system. In this embodiment, the focus error signal FES = 0 when the spot is circular and the focus error signal FES = 0 on the four-divided sensor 124 when the wavefront of the light beam B is B. However, when the light beam is A, the FES = It is easy to set it to zero. This is because the radius of curvature of the wavefront is R_A  Is equivalent to setting such that FES = 0 at the time of.
[0037]
On the other hand, the relationship between the shift amount Δ and the radius of curvature R of the wavefront is given by the following equation.
R = f₀ ²/ 2Δ ... 2-1
(However, f₀  >>>)
In other words, the S-curve in the focus error detection system of the optical disk device indicates the relationship between the shift amount Δ and the focus error signal FES, and simultaneously detects the radius of curvature R of the wavefront of the light beam incident on the focus error detection system. It can be said that. That is, the focal length f₀  If the objective lens having the condition (1) and the setting condition (detection sensitivity, etc.) of the focus error detection system corresponding thereto are determined, the focus error signal FES corresponding to the shift amount Δ (corresponding to the change in the radius of curvature R of the wavefront). Is obtained. In an actual laser projection apparatus, there is no objective lens, optical disk, or the like. However, if a light beam having a radius of curvature R of a wavefront to be detected is made incident on a focus error detection system having predetermined setting conditions, the radius of curvature of the wavefront can be obtained. R is obtained by calculation.
In the above method, since the detection signal can be obtained even by an analog signal, high-speed control (real-time control) can be performed.
[0038]
The process of obtaining the radius of curvature R described above is controlled and executed by the computer 133 as a whole. First, the computer 133 calculates the beam waist diameter W according to the above equations 1-3 and 1-4 based on the radius of curvature R of the exit wavefront and the exit beam diameter W.₀  , The beam waist distance x is calculated. Then, the control unit 135 and the lens are controlled such that the calculated beam waist distance x matches the beam waist distance input via the input unit 136 or the beam waist distance preset (memory) in the computer 133. The collimator lens 103 is moved via the drive mechanism 105.
[0039]
FIG. 4 shows a second embodiment of the present invention using a radial sharing interferometer as means for directly detecting the radius of curvature R of the wavefront of the means (1). It is to be noted that members having the same structure as the first embodiment shown in FIG. 1 and having the same function are denoted by the same reference numerals, and detailed description thereof will be omitted.
[0040]
The configurations of the laser light source unit 101 and the laser projection unit 111 are the same as those of the embodiment shown in FIG. The laser beam emitted from the semiconductor laser 102 is converted into a substantially parallel light beam by the collimator lens 103, reflected by the beam splitter 104, and guided into the interferometer 221.
[0041]
The laser beam guided into the interferometer 221 is split by the first half mirror 222 into a transmitted reference laser beam and a reflected test laser beam. The beam diameter of the reference laser beam transmitted through the first half mirror 222 is expanded by a beam expanding optical system (beam expander) 223, and the center of the wavefront having a small wavefront aberration is reduced to the first mirror 224 and the second half mirror 226. And reaches the CCD camera 228 (the light receiving surface of the CCD image sensor) by the observation lens 227. This means that the reference wavefront is formed from the test wavefront.
[0042]
On the other hand, the test laser beam reflected by the first half mirror 222 maintains the beam diameter, that is, maintains the wavefront shape of the test laser beam itself, and is transmitted to the second half mirror 226 by the second mirror 225. The reflected light is transmitted through the second half mirror 226 and reaches the imaging surface of the CCD camera 228 by the observation lens 227. That is, on the CCD camera 228, the reference wavefront and the test wavefront are superimposed. This superposition causes the reference laser beam and the test laser beam to interfere with each other, and the CCD camera 228 captures an image of the interference state.
[0043]
The interference fringes are imaged by the CCD camera 228, converted into digital image signals in the image memory 232, and stored. Then, the digital image signal is read from the image memory 232 by the computer 233. Then, the computer 233 calculates the radius of curvature R of the wavefront from the amount of bending of the interference fringes, and further calculates the beam waist distance x and the beam waist diameter W according to the expressions 1-3 and 1-4.₀  Is calculated and displayed on the display unit 234. Further, the computer 233 drives the lens driving mechanism 105 via the control unit 235 based on the calculated values of the radius of curvature R of the wavefront and the beam waist distance x, and moves the collimator lens 103 to adjust the distance d. By moving the collimator lens 103, the beam waist distance x can be kept constant against disturbances such as temperature change and wavelength fluctuation, and the beam waist position can be moved to a desired position. The function of the input unit 236 is the same as that of the input unit 136 of the first embodiment, and the second embodiment may have a configuration including the receiving unit 137 and the remote control unit 141.
[0044]
A method for obtaining the radius of curvature R from the interference fringes captured by the CCD camera 228 will be described in detail with reference to FIGS. FIGS. 6A, 6B, and 6C show the states of the interference fringes at the wavefronts A, B, and C in which the radius of curvature R of the incident wavefront changes in FIG.
[0045]
Assuming that the number of bends due to the radius of curvature R of the wavefront of the imaged interference fringes is k, the radius of curvature R of the wavefront is obtained by the following equation. Note that the number k is determined by k = ΔP / P in FIG.
R = W²  / 8λk 3-1
(However, R >> W)
The number k can be easily obtained by an interference fringe analysis method such as a known phase shift method. In addition, actually, not only the curvature radius R of the wavefront, but also the influence of the wavefront aberration, which is a higher-order term, exists. In addition to the radius of curvature, other aberrations can also be obtained. Due to these various aberrations, not only the initial performance, but also information obtained when the initial performance deteriorates due to a disturbance or some reason can be extracted. Therefore, the operation state of the laser projection device can be monitored.
[0046]
If the radius of curvature R of the wavefront is obtained, the beam waist distance x and the beam waist diameter W can be calculated by the above equations 1-3 and 1-4.₀  Can be requested.
[0047]
Further, a third embodiment of the present invention will be described with reference to FIG. In this embodiment, a detection system for detecting a radius of curvature R of an emitted laser beam is a laser projection device that projects a laser beam emitted from a laser light source 101 in three different directions (horizontal, vertically upward, vertically downward). It is applied to. Members having the same configuration and the same function as those of the embodiment shown in FIGS. 1 and 4 are denoted by the same reference numerals, respectively, and detailed description is omitted.
[0048]
The laser beam emitted from the semiconductor laser 102 passes through the collimator lens 103 and becomes a substantially parallel light beam. The parallel laser beam enters the beam splitter 311 and is mostly directed toward the rotary light projecting unit 111 (in the second target direction O).₂  ) Reflected and partially transmitted. In addition, this laser projection device has a second object direction O₂  And the rotation axis 111c are parallel. Usually, they are installed so as to coincide with the vertical upward direction, and function as a vertical upward reference beam.
[0049]
A part of the laser beam transmitted through the beam splitter 311 passes through the third reflecting plate 312, and the rest is reflected and travels backward in the optical path.₃  To reflect. The laser beam transmitted through the third reflection plate 312 enters the first focus error detection / processing system 321. The first focus error detection / processing system 321 has the same configuration as the focus error detection system 121 and the control unit 131 described above. Note that the third target direction O₃  And the second target direction O₂  Is only opposite to each other, and is usually arranged so as to coincide with the vertically downward direction, and functions as a vertically downward reference beam.
[0050]
The laser beam reflected by the beam splitter 311 in the direction of the rotary light projecting unit 111 is expanded to a predetermined beam diameter by the beam expander 313. The beam expander 313 is a Galileo type having a concave lens 314 and a convex lens 315, and the concave lens 314 is provided so as to be movable toward and away from the convex lens 315 in the optical axis direction.
[0051]
Most of the expanded laser beam passes through the first reflecting mirror 316 and is incident on the rotary light projecting unit 111, and part of the laser beam is reflected by the first reflecting mirror 316. The laser beam reflected by the first reflecting mirror 316 enters a second focus error detection / processing system 331 similar to the focus error detection system 121 and the control unit 131 shown in the first embodiment.
[0052]
As in the first embodiment, a part of the laser beam transmitted through the first reflecting mirror 316 and incident on the rotary light projecting unit 111 is transmitted through the half mirror 112 and travels in the second target direction O.₂  And the other is reflected by the half mirror 112, further reflected by the mirror 113, and in the first target direction O orthogonal to the rotation axis 111c.₁  Injected into. Usually, the first target direction O₁  Emitted in the second target direction O₂  A plane is formed by rotating about the axis, and functions as a horizontal reference plane.
[0053]
The first focus error detection / processing system 321 mainly performs the third target direction O₃  Laser beam L emitted to₃  Is monitored, and the radius of curvature R of the laser beam wavefront when emitted from the collimator lens 103 is measured. In addition, the first focus error detection / processing system 321 detects the radius of curvature R of the wavefront at the time of emission from the collimator lens 103, so that the laser beam L in the first and second target directions can be detected.₁  , L₂  The effect of most of the radius of curvature is also monitored.
[0054]
Here, the first focus error detection / processing system 321 moves the collimator lens 103 by the lens driving mechanism 105 based on the detection result, and adjusts the radius of curvature R of the wavefront. With this adjustment, the first, second, and third target directions O₁  , O₂  , O₃  Laser beam L emitted to₁  , L₂  , L₃  Changes the radius of curvature R of the wavefront, and the beam waist position can be moved.
[0055]
The second focus error detection / processing system 331 outputs the third target direction O₃  Laser beam L to₃  Irrespective of the first and second target directions O₁  , O₂  Laser beam L₁  , L₂  Is measured and monitored. Then, based on the measurement result, the lens driving mechanism 333 is driven to move the concave lens 314 toward and away from the convex lens 314, and the laser beam L₁  , L₂  Is adjusted, and the beam waist position is moved.
[0056]
In the third embodiment, the laser beam L in the first and second target directions having a long projection distance is easily affected by disturbance.₁  , L₂  And the third target direction O₃  Laser beam L to₃  Has little effect. Therefore, if the second focus error detection / processing system 331, the lens driving mechanism 105 and the lens driving mechanism 333 exist, the laser beam L₁  , L₂  Beam waist position can be adjusted.
[0057]
However, actually, the laser beam L₁  , L₂  Among the factors that change the radius of curvature R of the wavefront on the side, the largest one is due to the change in the distance between the collimator lens 103 and the semiconductor laser 102. Therefore, if the wavefront of the laser beam after the emission of the collimator lens 103 that changes due to the disturbance is to be monitored, the laser beam L that is easily affected by the disturbance can be used only with the first focus error detection / processing system 321.₁  , L₂  Can be adjusted.
[0058]
Although the present invention has been described based on the embodiment applied to the laser projection apparatus, the present invention is not limited to the illustrated embodiment. For example, the focus error detection system may be a knife edge method or a spot size method. In the case of the interferometry, a lateral sharing interferometer may be used. In short, the present invention is not limited to the configuration of the optical system as long as it has means for detecting the radius of curvature R of the wavefront when the laser beam is emitted.
[0059]
In the present invention, the equations 1-1 to 1-4 have been discussed assuming that the laser beam to be projected is a Gaussian beam. Alternatively, actually, an influence such as aberration of the optical system also occurs.
However, even in such a case, data such as the beam waist position and the beam waist diameter are added while adding some correction term to the equations 1-1 to 1-4 or actually changing the curvature radius R of the wavefront only once. May be obtained, and processing such as performing correction based on the data may be performed. In short, the present invention has an essential feature in that the radius of curvature of the wavefront can be measured on the spot by the laser projector itself.
[0060]
【The invention's effect】
As is apparent from the above description, the present invention detects the amount corresponding to the radius of curvature R of the wavefront of the laser beam at the time of emission.And the diameter of the laser beam at the time of injection set in advance.And the beam waist distance of the laser beam is detected fromSince the beam waist distance is controlled to be a predetermined value, the beam waist distance can be kept constant, and the beam waist position can be easily adjusted to a desired distance without observing the irradiated laser beam. Can be adjusted.
[Brief description of the drawings]
FIG. 1 is a diagram showing a main configuration of a first embodiment of a laser projection apparatus to which the present invention is applied.
FIG. 2 is a diagram illustrating an outline of a focus error detection system applied to the first embodiment.
FIG. 3 is a graph showing a focus error signal of the first embodiment in a graph.
FIG. 4 is a diagram showing a main configuration of a second embodiment in which the present invention is applied to a laser projection device.
FIG. 5 is a diagram illustrating an outline of a radial sharing interferometer applied to a second embodiment.
FIG. 6 is a diagram illustrating the relationship between interference fringes observed by the radial sharing interferometer and the radius of curvature of the wavefront of the laser beam.
FIG. 7 is a diagram illustrating an outline of a third embodiment in which the present invention is applied to a laser projection device.
FIG. 8 is a graph showing a relationship between a beam projection beam diameter of a laser beam and a temperature.
FIG. 9 is a graph showing a relationship between a beam waist distance of a laser beam and a temperature.
FIG. 10 is a graph showing a relationship between a beam waist position and a beam diameter.
FIG. 11 is a graph showing a relationship between a change in a beam waist position and a beam diameter.
FIG. 12 is a graph showing the relationship between the radius of curvature of the wavefront at the time of emission and the beam waist distance.
[Explanation of symbols]
101 Laser light source section
102 Semiconductor laser
103 Collimator lens
105 Lens drive mechanism
111 Rotating light emitter
112 Half mirror (first mirror)
113 mirror (second mirror)
121 Focus error detection system
131 Operation and control unit
221 interferometer
321 First focus error detection / processing system
331 Second focus error detection / processing system

Claims (5)

In a laser projection device that projects a light beam from a laser light source as a substantially parallel light beam,
A beam waist distance changing optical system that changes a beam waist distance of the laser beam emitted from the laser light source,
A branch optical system that branches a part of the laser beam emitted from the beam waist distance changing optical system,
Focus error detecting means for receiving the laser beam split by the splitting optical system and detecting an amount corresponding to the radius of curvature R of the wavefront of the laser beam by an astigmatism method;
Calculating means for calculating a beam waist distance of the projection beam from an amount corresponding to the radius of curvature R of the wavefront and a laser beam diameter W at a predetermined position set in advance;
Control means for controlling the drive of the beam waist distance changing optical system based on the beam waist distance of the projection beam . 2. The laser projection device according to claim 1, wherein the calculation unit calculates a beam waist distance x from an emission end of the laser projection device to a beam waist position,
x = R ｛1+ (4λR / πW ² ) ² ｝ ⁻¹
Calculated by the following formula: 3. The laser projection apparatus according to claim 2, wherein said control means drives said beam waist distance changing optical system to keep said laser beam waist distance x constant. Laser projector according to claim 3, comprising an optical member for the parallel beam of the laser beam emitted from the laser light source, the beam waist distance changing optical system includes a lens for moving the optical member in the optical axis direction A laser projection device comprising a driving unit. Oite the laser projection device according to claim 4, optical members into a parallel beam of the laser beam, a beam expander comprising at least two groups of lens system, one lens group parallel to the optical axis moving A laser driving device for driving the laser.

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