JPH0690033B2 - Displacement detection device - Google Patents

Description

Detailed Description of the Invention [Industrial applications]

The present invention relates to an improvement of a non-contact apparatus for detecting a displacement of a surface of an object to be measured, which is used for automatic focusing of a reading laser spot such as a laser disk.

[Prior art]

Conventionally, as shown in FIG. 9, a light beam 2 from a light source 1 such as a laser diode passes through a beam splitter 3 and an objective lens 4 and is substantially orthogonal to a surface 5A to be measured of an object 5 to be measured. The reflected light which is projected in the direction and scattered and reflected by the surface 5A to be measured is again reflected by the objective lens 4 and the beam splitter 3.
Then, the light is reflected at a right angle by the reflecting surface 3A of the beam splitter 3, and the light receiving element 8 is passed through the Foucault prism 6.
There is a displacement detection device that is made to be incident on. The light receiving element 8 is an inner element 8A composed of a photodiode or the like.
And an outer element 8B adjacent to the outer side thereof, and outputs of the inner element 8A and the outer element 8B are input to a detector (not shown) via a comparator 9. Here, outputs A and B of the inner element 8A and the outer element 8B
When the distance of the surface 5A to be measured from the light source 1 changes, it increases or decreases correspondingly, and the distance of the surface 5A to be measured from the light source 1, that is, the surface, based on the difference between the outputs of the two. The displacement of can be measured. In other words, when there is a boundary line between the inner element 8A and the outer element 8B at the focus position of the reflected light collected by the Foucault prism 6, the difference ΔS = AB between the outputs of these elements becomes zero.

[Problems to be Solved by the Invention]

By the way, in the displacement detecting apparatus as described above, when the objective lens 4 has an aberration, the image forming point shifts. Therefore, in order to correct this, the light receiving element 8 has to be shifted in the front-back direction and the left-right direction. However, compared with the case where the light receiving element is shifted in the front-back direction, when it is shifted in the left-right direction, the change in the difference in output between the inner element 8A and the outer element 8B is extremely large, which makes adjustment difficult. There is. Further, the difference ΔS = A− between the outputs of the inner element 8A and the outer element 8B.
B becomes as shown in FIG. 10, and it is possible to determine the front pin or the rear pin depending on whether ΔS is positive or negative, but the shift amount cannot be determined. That is, when ΔS = Vr, the position A ₁ close to the point of ΔS = 0
It is unknown whether or not it is the separated position A ₂ . If A _{1 is used} , hunting will occur unless the objective lens is moved at low speed, and if A _{3 is used} , it will take time if the objective lens is not moved at high speed, and measurement efficiency will be reduced. Occurs. The example of FIG. 9 applies the principle of the so-called Foucault method using the Foucault prism, but the same applies to other methods such as the eccentric beam method, the knife edge method, and the autofocus method such as the critical angle method. There is a problem. The present invention has been made in view of the above conventional problems, in which the image forming point is moved without moving the light receiving element, the deviation in the direction orthogonal to the optical axis, that is, the lateral deviation is corrected,
An object of the present invention is to provide a displacement detection device that can quickly measure the aberration of an objective lens. Another invention is to accurately detect the amount of shift of the image formation point,
It is an object of the present invention to provide a displacement detection device capable of efficiently adjusting an image forming point to a focus position.

[Means for solving problems]

The present invention provides a light source that emits a light beam, and an objective lens that is arranged so as to face a surface to be measured of a measured object and has an optical axis on an optical path of the light beam that is substantially orthogonal to the measured surface.
The objective lens is arranged on the opposite side of the object to be measured with respect to the objective lens, and the light beam is formed by passing through the optical path to go straight to the surface to be measured and being reflected by the surface to be measured. A condensing means for condensing the reflected light that has passed through;
At least 4 arranged near the position of the light spot where the reflected light is focused and arranged in an array on the same straight line in the direction orthogonal to the light axis with the light spot as the center.
Individual light receiving elements; array switching means for separating the output signals of these light receiving elements into two groups at arbitrary positions on the straight line;
A detector that detects the amount of displacement of the surface to be measured in the optical axis direction by the change in the difference signal between the sum of the output signals of the one group and the sum of the output signals of the other group; The above object is achieved by constructing a detection device. Another aspect of the present invention is a light source that emits a light beam, and an objective that is disposed so as to face a surface to be measured of the object to be measured and has an optical axis on the optical path of the light beam that is substantially orthogonal to the surface to be measured. A lens disposed on the opposite side of the object to be measured with respect to the objective lens, wherein the light beam travels straight through the optical path to the surface to be measured and is reflected by the surface to be measured; A condensing means for condensing the reflected light passing through the objective lens; in the vicinity of the position of the optical spot where the reflected light is condensed, on the same straight line in the direction orthogonal to the optical axis. At least 2 symmetrically arranged about
A pair of light receiving elements; the amount of displacement of the surface to be measured in the optical axis direction is detected by the change in the difference signal of the sum of the output signals of each group of light receiving elements divided into two groups with the optical spot as a boundary. A detector; a comparator for comparing an output signal of a light receiving element located farther from the optical axis than a pair of light receiving elements adjacent to the optical spot with a reference signal, and outputting a shift signal when the former is larger than the latter The above object is achieved by constructing the displacement detecting device including the following items; Further, the above object is achieved by using a focusing system having a Foucault prism as the light converging means. Further, the above-mentioned object is achieved by using the focusing means as a focusing system based on the eccentric beam method. Further, the above-mentioned object is achieved by using a focusing system by the knife edge method as the focusing means. Further, the above object is achieved by using a focusing system by the critical angle method as the collecting means.

[Action]

The present invention includes at least four light receiving elements arranged in an array near the position of the light spot and on the same straight line in a direction orthogonal to the optical axis with the light spot as the center. Is divided into two groups according to the aberration of the objective lens by the array switching means, and focusing is performed based on the difference of the total sum of the output signals of each group. Therefore, the light receiving element is arranged in the direction orthogonal to the optical axis. It is possible to correct the deviation of the image forming point due to the aberration of the objective lens without moving the lens and to easily and surely perform the measurement. Further, in another invention, in the case of the similar Foucault method, at least two pairs of light receiving elements are arranged linearly in the vicinity of the position of the optical spot symmetrically with respect to the optical spot, and the optical spot position is used as a boundary. The in-focus point is detected from the difference in the sum of the output signals of each group of light-receiving elements, and when the image formation point is greatly deviated, this is detected based on the output signal of the light-receiving element at a position distant from the optical spot position. Thus, the image formation point can be returned to the in-focus position at high speed.

【Example】

An embodiment of the first invention will be described below with reference to the drawings. In this embodiment, as shown in FIGS. 1 to 3, a light source 12 such as a laser diode for emitting a light beam 10 and a surface 14A to be measured of an object 14 to be measured are arranged so as to face each other. The optical axis 11 is provided on the optical path of the light beam substantially orthogonal to the measurement surface 14A.
Is disposed on the opposite side of the object to be measured 14 with respect to the objective lens 16, and the light beam 10 goes straight to the surface to be measured 14A through the optical path, and The objective lens 1 is formed by being reflected by the measurement surface 14A.
Foucault prism 18 that collects the reflected light that passed through 6,
Eight light-receiving elements 20A arranged in an array in the vicinity of the position of the light spot where the reflected light is focused, and centered on the light spot and on the same straight line in the direction orthogonal to the optical axis 11. , 20B, ... 20H and these light receiving elements 20A, 20
Array switching means 22 for separating the output signals of B, ..., 20H into two groups at an arbitrary position on the straight line, and the sum of the output signals of the one group and the sum of the output signals of the other group. A displacement detecting device is configured to include a detector 28 that detects the amount of displacement of the measured surface 14A in the optical axis 11 direction based on the change in the difference signal. The light source 12 emits its light beam 10 with respect to the optical axis 11.
Are arranged on the sides of the optical axis 11 so that the optical axes of are orthogonal to each other. At the intersection between the light beam 10 emitted from the light source 12 and the optical axis 11, at a position between the objective lens 16 and the Foucault prism 18, a half mirror 30 is used to emit light from the optical axis 11 and the light source 12. It is arranged so as to form an angle of 45 ° with respect to each of the exit optical axes of the beam 10. A focusing lens 32 is arranged on the optical axis 11 between the half mirror 30 and the Foucault prism 18. Further, between the half mirror 30 and the light source 12, the light source 12
A collimator lens 34 is arranged on the emission optical axis of the light beam 10 from. The collimator lens 34 makes the light beam 10 emitted from the light source 12 incident on the half mirror 30 as a parallel light beam orthogonal to the optical axis 11. Further, the objective lens 16 collects the light beam 10, which is a parallel light beam reflected along the optical axis 11 at a right angle by the half mirror 30, on the surface 14A to be measured, and reflects the light beam reflected from the surface 14A to be measured. The parallel rays are made to reach the focusing lens 32 via the half mirror 30. The focusing lens 32 focuses the reflected light, which is a parallel light beam along the optical axis 11, and passes through the Foucault prism 18 to receive the light.
It focuses on 20A to 20H. The light receiving elements 20A to 20H are at the focus positions of the reflected light rays that have passed through the Foucault prism 18, and the boundary lines of the respective light receiving elements are parallel to the two opposite sides of the square end face of the Foucault prism 18. Thus, they are arranged at equal intervals on a straight line orthogonal to the two sides. Further, the light receiving elements 20A to 20H have the same sensitivity, and when the objective lens 16 has no aberration, the reflected light is focused on the boundary line between the fourth light receiving element 20D and the fifth light receiving element 20E. Has been The detector 28 shown in FIG. 3 has outputs A to A of the light receiving elements 20A to 20F.
Adder 36 for adding F and output C of light receiving elements 20C to 20H
Adder 38 for adding H, output signal of adder 36 and adder
Subtractor 40 for calculating the difference between the output signals of 38 and adders 36, 38
It is configured to include an adder 42 that adds the outputs of the above, and a divider 43 that calculates the quotient using the output signals of the subtractor 40 and the adder 42 as the numerator and denominator, respectively. The array switching means 22 includes switching devices 44C to 44F provided between the light receiving elements 20C to 20F and the adder 36, and the light receiving device.
Switching device 46C provided between 20C to 20F and the adder 38
.About.46F and a switching controller 48 for switching these switching devices 44C to 44F and 46C to 46F. The switching controller 48 divides the light receiving elements 20A to 20H into two groups based on the array switching data shown in FIG. 3, and outputs one output signal to the adder 36 and the other output signal. Switchers 44C to 44F, 46 to distribute to adders 38, respectively.
It is designed to control C to 46F. That is, the light receiving elements 20B and 20C are divided into two groups with the boundary as the boundary, and the output signals of the light receiving elements 20A and 20B are assigned to the adder 36 and the output signals of the other light receiving elements 20C to 20H are assigned to the adder 38. 1
Mode, a second mode in which the light receiving elements 20C and 20D are used as boundaries, a third mode in which the light receiving elements 20D and 20E are used as boundaries, and a third mode in which the light receiving elements 20E and 20F are used as boundaries The switchers 44C to 44F and 46C to 46F can be controlled so as to selectively switch between the four modes and the fifth mode in which the light receiving elements 20F and 20G are distributed as boundaries. Next, the operation of the apparatus of the above embodiment will be described. The light beam 10 is emitted from the light source 12, reflected by the half mirror 30 along the optical axis 11, and is reflected via the objective lens 16.
The surface 14A to be measured of the object 14 to be measured is irradiated. Surface to be measured 14A
The reflected light from passes through the objective lens 16 again, further passes through the half mirror 30, the focusing lens 32, and the Foucault prism 18, and is focused on the light receiving elements 20A to 20H. When there is no shift of the image forming position based on the aberration of the objective lens 16, the output signal ΔS ₃ of the subtractor 40 becomes zero at the in-focus position in the third mode, and is minus on the rear pin side and on the front pin side. It becomes a plus sine curve. Accordingly, the objective lens 16 is moved along the optical axis 11, and the difference ΔS ₃ = (A +) between the outputs of the light receiving elements 20A to 20D and 20E to 20H.
If B + C + D)-(E + F + G + H) = 0, the in-focus point can be detected. That is, the output signal of the subtractor 40 in the detector 28 may be set to zero. Here, in the divider 43, the output signal Δ of the subtractor 40
The reason why S ₃ is divided by the output signal (A + ... + H) of the adder 42 is that when ΔS ₃ is divided by the total amount of light received by the light-receiving elements 20 and 22, the reflectance of the surface 14A to be measured is measured. This is because the influence of the difference can be reduced and a stable resolution can be obtained. When the light source 12 or the objective lens 16 is changed, the image forming position due to the aberration shifts toward the light receiving elements 20A to 20H. This deviation is known in advance depending on the type of the light source 12 or the type of the objective lens 16. Accordingly, in response to this, the switching controller 48 causes the switching device 44 to
Switches C to 44F and 46C to 46F. For example, when the image formation point is offset between the light receiving elements 20C and 20D due to aberration, the second mode is selected by the switching controller 48, and the light receiving elements 20A to 20C are received by the adder 36 and the light receiving elements 20A to 20C. The switches 44C to 44F and 46C to 46F are switched so that the elements 20D to 20H can output the signals to the adder 38, respectively. In this second mode, the focus signal ΔS ₂ is ΔS ₂ = (A +
B + C)-(D + E + F + G + H) = 0,
The objective lens 16 can be driven to detect the focal point. In this embodiment, the shift of the image forming point due to the aberration can be corrected by the array switching means 22 without moving the light receiving element, and the in-focus point can be detected quickly and surely. Next, an embodiment of the second invention shown in FIG. 5 will be described. This embodiment is the same as in the first embodiment of the present invention, and in the displacement detecting device provided with the light source 12, the objective lens 16 and the Foucault prism 18, the reflected light reflected by the surface of the object to be measured is collected. 2 is symmetrically arranged in the vicinity of the position of the light spot 11A to be illuminated, centered on the spot and on the same straight line in the direction orthogonal to the optical axis of the objective lens.
A pair of light receiving elements 52A, 52B and 54A, 54B and the optical spots.
The light receiving elements 52A and 54 divided into two groups with 11A as a boundary.
A and 52B, a detector 56 for detecting the amount of displacement in the optical axis direction of the surface to be measured by a change in the difference signal of the sum of the output signals of each, and a light receiving element 54A on the side remote from the optical spot 11A, The comparators 58A, 5 which compare the output signal of 54B with the reference signal Vref and output a shift signal when the former is larger than the latter
8B is provided. The computing unit 56, as shown in FIG.
An adder 60A that calculates the sum of the output signals of A and 54A, an adder 60B that adds the output signals of the light receiving elements 52B and 54B, and an adder 6
Adder 62 that calculates the sum of the output signals of 0A and 60B, and adder 6
The subtractor 64 that calculates the difference between the output signal of the 0A and the output signal of the adder 60B and the subtractor 64 that uses the output signal of the adder 62 as the denominator
And a divider 66 that performs division using the output signal of 1 as the numerator. The output signals of the comparators 58A and 58B are the deviation indicators 68A and 68B.
Is output to display that the image forming point is deviated. The output signal of the divider 66 is also output to the focus indicator 70 to display the focus state. Since the process of detecting the in-focus point based on the in-focus signal ΔS which is the output signal of the divider 66 is the same as the above, the description thereof will be omitted. When the image forming point is largely deviated, for example, when it is deviated to the right side in FIG. 5, the output signal of the light receiving element 54B becomes very large as compared with the normal case. Therefore, the output signal from the light receiving element 54B and the reference signal Vre
f is compared in the comparator 58B, and when the output signal from the light receiving element 54B exceeds the reference signal, this is displayed on the shift indicator 68B, and the image formation point is greatly shifted to the right side in the figure. indicate. Therefore, in this case, the objective lens can be moved at high speed to quickly obtain the focal point. When the image forming point is displaced to the light receiving element 54A side, the displacement is displayed on the displacement indicator 68A by the output signal from the comparator 58A. In this case as well, the objective lens is quickly moved to the in-focus point. Can be made. When there is little deviation of the image formation point, as described above, the objective lens is finely adjusted and adjusted so that the focus signal ΔS = 0.
Focus can be obtained. Therefore, when no deviation is displayed on the deviation indicators 68A and 68B, the objective lens can always be finely moved to obtain the in-focus point without causing hunting. In the above embodiment, the number of light receiving elements is two, but the present invention is not limited to this, and there may be a plurality of three or more pairs. In this case, a comparator for outputting the shift signal is required corresponding to the light receiving element, and a shift indicator is also required corresponding to the comparator. The first and second embodiments of the present invention both relate to a system using the Foucault method, but the present invention is not limited to this. For example, a third embodiment shown in FIG. Such as the one using the eccentric beam method, the one using the knife edge method like the fourth embodiment shown in FIG. 7, or the fifth embodiment shown in FIG.
It is applied to any of those utilizing the critical angle method. Regarding the third embodiment, in FIG. 6, reference numeral 72 is an objective mirror and 74 is a diaphragm. With respect to other configurations, the same or corresponding portions as those of the embodiment shown in FIG. 1 are designated by the same reference numerals as those in FIG. 1 and their explanations are omitted. Also in the case of the displacement detector using this eccentric beam method, the light receiving element
21A to 21F, the switching means therefor, and the detector are the same as those shown in FIG. 3 and / or FIG. In the fourth embodiment, in FIG. 7, reference numeral 76 is a quarter-wave plate arranged between the objective lens 16 and the half mirror 30, and 78 is between the light receiving element 20 and the converging lens 32. , Knife edges arranged at the focal position of the converging lens 32, respectively. Also in this embodiment, the arrangement of the light receiving elements 21A to 21F and the structure of the detector may be the same as the structure shown in FIG. 3 or FIG. In the case of the fifth embodiment utilizing the critical angle method shown in FIG. 8, a prism 80 is arranged in place of the converging lens 32 and the knife edge 78 in the embodiment of FIG. The prism 80, for the reflected light from the half mirror 30,
It is arranged so that the refraction angle becomes a critical angle. Also in this embodiment, the light receiving elements 21A to 21F, or the switching means and the detector have the same configurations as those shown in FIG. 3 or FIG.

【The invention's effect】

Since the first aspect of the present invention is configured as described above, even if the image forming point is deviated due to the aberration caused by the change of the objective lens or the light source, the deviation of the image forming point is corrected without moving the light receiving element. Thus, there is an excellent effect that the in-focus point can be detected quickly and surely. The second aspect of the present invention reliably discriminates and detects the magnitude of the deviation of the image formation point, switches the moving speed of the objective lens according to the deviation amount, causes hunting, or does not take extra time. It has an excellent effect that the focused point can be detected quickly.

[Brief description of drawings]

FIG. 1 is a sectional view showing a displacement detecting device to which the present invention is applied, FIG. 2 is a plan view showing a relationship between a light receiving spot and a light receiving element in an embodiment of the first invention, and FIG. 3 is a detection of the same embodiment. FIG. 4 is a circuit diagram showing the detector and array switching means, FIG. 4 is a diagram showing the state of the output signal of the detector in the same embodiment, and FIG. 5 is a circuit diagram showing the essential parts of the second embodiment of the present invention. 6 to 8 are sectional views showing third to fifth embodiments in which the first and second inventions are applied to other detection methods, and FIG. 9 is a sectional view showing a conventional displacement detecting device, The figure is a diagram showing a focusing signal in the conventional displacement detecting apparatus. 10 ... Light beam, 11 ... Optical axis, 12 ... Light source, 14 ... Object to be measured, 16 ... Objective lens, 18 ... Foucault prism, 20A-20H ... Light receiving element, 22 ... Array switching means , 28 …… Detector, 52A, 52B, 54A, 54B …… Light receiving element, 56, 84 …… Detector, 58A, 58B …… Comparator, 68A, 68B …… Displacement indicator, 78 …… Knife edge, 80 ……prism.

Claims (6)

[Claims] 1. A light source which emits a light beam, and an objective lens which is arranged so as to face a surface to be measured of an object to be measured and has an optical axis on an optical path of the light beam which is substantially orthogonal to the surface to be measured. ;
The objective lens is arranged on the opposite side of the object to be measured with respect to the objective lens, and the light beam is formed by passing through the optical path to go straight to the surface to be measured and being reflected by the surface to be measured. A condensing means for condensing the reflected light that has passed through;
At least 4 arranged near the position of the light spot where the reflected light is focused and arranged in an array on the same straight line in the direction orthogonal to the light axis with the light spot as the center.
Individual light receiving elements; array switching means for separating the output signals of these light receiving elements into two groups at arbitrary positions on the straight line;
A detector for detecting a displacement amount of the surface to be measured in the optical axis direction, based on a change in a difference signal between a sum total of output signals of the one group and a sum total of output signals of the other group; Displacement detection device. 2. A light source which emits a light beam, and an objective lens which is arranged so as to face a surface to be measured of the object to be measured and has an optical axis on an optical path of the light beam which is substantially orthogonal to the surface to be measured. ;
The objective lens is arranged on the opposite side of the object to be measured with respect to the objective lens, and the light beam is formed by passing through the optical path to go straight to the surface to be measured and being reflected by the surface to be measured. A condensing means for condensing the reflected light that has passed through;
At least two pairs of light-receiving elements which are arranged in the vicinity of the position of the light spot where the reflected light is focused and which are symmetrically arranged about the light spot on the same straight line in the direction orthogonal to the optical axis; A detector for detecting the displacement amount of the surface to be measured in the optical axis direction by the change of the difference signal of the sum of the output signals of the respective groups of the light receiving elements divided into two groups with the optical spot as a boundary; A comparator that compares the output signal of the light receiving element located farther from the optical axis than the pair of light receiving elements adjacent to the reference signal with the reference signal and outputs a shift signal when the former is larger than the latter. Displacement detection device. 3. The displacement detecting device according to claim 1, wherein the light converging means is a focusing system including a Foucault prism. 4. A displacement detecting device according to claim 1 or 2, wherein said light converging means is a focusing system based on an eccentric beam method. 5. The displacement detecting device according to claim 1, wherein the light converging means is a focusing system based on a knife edge method. 6. The displacement detecting device according to claim 1 or 2, wherein the collecting means is a focusing system based on a critical angle method.