JPWO1997046896A1 - Optical axis direction variable type photodetector - Google Patents

Abstract

(57) [Abstract] A movable plate (5) and a torsion bar (6) are integrally formed on a silicon substrate (2). A planar coil (7) is provided on the periphery of the movable piece (5), and a photodiode (8) is provided in the center. Permanent magnets (10A, 10B, 11A, 11B) are arranged above and below the periphery of the movable plate (5), and detection coils (12A, 12B) are provided below the movable plate (5) to detect the displacement angle of the movable plate (5). When a current is passed through the planar coil (7), a force is generated in relation to the magnetic field generated by the permanent magnets (10A, 10B, 11A, 11B), causing the movable plate (5) to rotate around the torsion bar (6) as an axis, changing the optical axis direction of the photodiode (8). The displacement angle in the optical axis direction can be detected by a change in mutual inductance between the planar coil (7) and the detection coils (12A, 12B), i.e., a change in the induced voltage of the detection coils (12A, 12B).

Description

[Detailed Description of the Invention] Variable Optical Axis Direction Photodetector Technical Field The present invention relates to a photodetector suitable for monitoring relatively large objects such as roads and airports.

BACKGROUND ART This type of device may involve a motor-driven optical detector, or multiple optical detectors arranged with their optical axes relatively spaced apart.

However, the above-mentioned methods have the drawbacks of being large, not being able to operate at high speed, and being impractical from a cost perspective. Additionally, the above-mentioned methods have the drawback of requiring correction for variations in the characteristics of each element.

The present invention was developed in response to these circumstances, and aims to provide a photodetector that is compact, capable of high-speed scanning, allows for cost reduction through mass production, and does not require correction for variations in the characteristics of each element.

DISCLOSURE OF THE INVENTION (1) To achieve this objective, the optical axis direction-variable photodetector of the present invention comprises a movable plate integrally formed on a semiconductor substrate, a torsion bar supporting the movable plate so that it can swing freely relative to the semiconductor substrate, a drive coil provided on the periphery of the movable plate, a magnetic field generating means for applying a static magnetic field to the drive coil, and a photodetector formed on the movable plate. The movable plate is driven by a force generated by passing a current through the drive coil, thereby varying the optical axis direction of the photodetector.

(2) In order to detect the displacement angle of the optical axis, a detection coil is provided which is electromagnetically coupled to the drive coil of the configuration described in (1) above.

(3) In order to move the photodetector element of the movable plate in one dimension, the movable plate is constructed as a single piece.

(4) The movable plate of (1) has an inner double structure, thereby enabling two-dimensional operation of the photodetector element of the movable plate. The outer movable plate is integrally formed with a semiconductor substrate, and includes an outer movable plate, a first torsion bar pivotally supporting the outer movable plate relative to the semiconductor substrate, an inner movable plate located inside the outer movable body, and a second torsion bar pivotally supporting the inner movable plate relative to the outer movable plate, the axial direction of which is perpendicular to that of the first torsion bar. The optical axis direction of the photodetector element is changed by a force generated by passing a current through the first and second drive coils, which drives the outer and inner movable plates.

(5) To detect the displacement angle of the optical axis, a first detection coil and a second detection coil are provided that are electromagnetically coupled to the first drive coil and the second drive coil, respectively, of the configuration described in (4).

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows the configuration of Example 1, Figure 2 is a cross-sectional view taken along line A-A in Figure 1, Figure 3 is an explanatory diagram of the operation of Example 1, Figure 4 is an explanatory diagram of the detection of the displacement angle of the movable plate in Example 1, Figure 5 is a diagram showing the configuration of Example 2, Figure 6 is a diagram showing the configuration of Example 3, Figure 7 is a cross-sectional view taken along line B-B in Figure 6, Figure 8 is a cross-sectional view taken along line C-C in Figure 6, Figure 9 is a block diagram of an example using a photodiode, Figure 10 is a flowchart showing the operation of the device of Figure 9, Figure 11 is a block diagram of an example using a line sensor, and Figure 12 is a block diagram of an example using an area sensor.

Best Mode for Carrying Out the Invention The present invention will now be described with reference to the following examples.

(Example 1) Figures 1 and 2 show the configuration of Example 1, a "variable optical axis direction photodetector." This example, like Examples 2 and 3 described below, operates on the same principle as a galvanometer. Note that the dimensions in Figures 1 and 2 are exaggerated for clarity. The same applies to Figures 3, 5, 6, 7, and 8 described below.

1 and 2, variable optical axis direction photodetector 1 has a three-layer structure in which flat upper and lower glass substrates 3 and 4, which serve as upper and lower insulating substrates made of, for example, borosilicate glass, are bonded to the top and bottom surfaces of silicon substrate 2, which is a semiconductor substrate. Upper glass substrate 3 is laminated on the left and right ends (in FIG. 1) of silicon substrate 2 so as to leave the area above movable plate 5, which will be described later, open.

A planar movable plate 5 and a torsion bar 6, which supports the movable plate 5 at its center so that it can swing vertically relative to the silicon substrate 2, are integrally formed on the silicon substrate 2 by anisotropic etching during the semiconductor manufacturing process. Therefore, the movable plate 5 and the torsion bar 6 are made of the same material as the silicon substrate 2. A planar coil 7 made of thin copper film is provided around the periphery of the upper surface of the movable plate 5 and is covered with an insulating film. This coil carries a drive current for driving the movable plate 5 and a detection current for detecting the displacement angle that is superimposed on the drive current. The detection current detects the displacement of the movable plate 5 based on the mutual inductance with detection coils 12A and 12B, which are provided on the lower glass substrate 4 as described below.

Here, the coil suffers from Joule heat loss due to its resistance, and if highly resistive thin-film coils are densely packed as the planar coil 7, the heat generated will limit the driving force. Therefore, in this embodiment, the planar coil 7 is formed using the well-known electroplating coil method using electrolytic plating. The electroplating coil method forms a thin nickel layer on a substrate by sputtering, then forms a copper layer on top of this nickel layer by copper electroplating, and then removes the copper and nickel layers except for the portion corresponding to the coil, thereby forming a thin-film planar coil consisting of the copper and nickel layers. This method is characterized by its ability to pack thin-film coils with low resistance and high density, making it effective for miniaturizing and thinning micromagnetic devices.

Additionally, a pn photodiode 8, which serves as a photodetector, is formed by a known method in the center of the top surface of the movable plate 5, surrounded by the planar coil 7. Furthermore, a pair of electrode terminals 9, 9 are provided on the upper surface of the silicon substrate 2, on the sides of the torsion bar 6, electrically connecting the planar coil 7 to the torsion bar 6 via the torsion bar 6. These electrode terminals 9, 9 are formed on the silicon substrate 2 at the same time as the planar coil 7 by electroforming.

Pairs of circular permanent magnets 10A, 10B and 11A, 11B are provided on the left and right sides (in FIG. 1) of the upper and lower glass substrates 3, 4. These magnets apply a magnetic field to the planar coil 7 on opposite sides of the movable plate 5 that are parallel to the axial direction of the torsion bar 6. The upper and lower pairs of three permanent magnets 10A, 10B are arranged so that the upper and lower polarities are the same, e.g., as shown in FIG. 2, the lower side has a north pole and the upper side has a south pole. The other pairs of three permanent magnets 11A, 11B are also arranged so that the upper and lower polarities are the same, e.g., as shown in FIG. 2, the lower side has a south pole and the upper side has a north pole. The permanent magnets 10A and 11A on the upper glass substrate 3 and the permanent magnets 10B and 11B on the lower glass substrate 4 are arranged so that the upper and lower polarities are opposite to each other, as can be seen in FIG. 2.

As mentioned above, a pair of coils 12A, 12B are patterned on the underside of the lower glass substrate 4, arranged to be electromagnetically coupled to the planar coil 7. Each end of the coils is electrically connected to a pair of electrode terminals 13, 14 (note that while shown schematically by a single dashed line in FIG. 1 , they actually have multiple windings). The detection coils 12A, 12B are arranged symmetrically with respect to the torsion bar 6 to detect the displacement angle of the movable plate 5. The mutual inductance between the planar coil 7 and the detection coils 12A, 12B, which is based on a detection current superimposed on the drive current flowing through the planar coil 7, changes with the angular displacement of the movable plate 5, increasing one coil as it approaches and decreasing the other coil as it moves away from the other coil. Therefore, the displacement angle of the movable plate 5 can be detected, for example, by differentially detecting the change in the voltage signal output based on the mutual inductance.

Next, the operation will be described.

For example, suppose one electrode terminal 9 is set as a positive pole and the other electrode terminal 9 as a positive pole and current is passed through planar coil 7. On both sides of movable plate 5, permanent magnets 10A and 10B and permanent magnets 11A and 11B generate a magnetic field in a direction that crosses planar coil 7 along the plane of movable plate 5, as indicated by arrow B in Figure 3. When current flows through planar coil 7 in this magnetic field, a force F acts on planar coil 7 (or, in other words, on both ends of movable plate 5) in a direction (indicated by arrow F in Figure 3) according to the current density and magnetic flux density in planar coil 7, according to Fleming's left-hand rule of current, magnetic flux density, and force. This force can be calculated from the Lorentz force.

This force F can be calculated by the following equation (1), where i is the current density flowing through the planar coil 7 and B is the magnetic flux density due to the upper and lower permanent magnets.

F = i × B (1) In practice, this depends on the number of turns n of the planar coil 7 and the coil length w (shown in Figure 3) on which the force F acts, and is expressed as equation (2) below.

F = nw(i × B) ... (2) Meanwhile, as the movable plate 5 rotates, the torsion bar 6 is twisted. The relationship between the resulting spring reaction force F' of the torsion bar 6 and the displacement angle φ of the movable plate 5 is expressed as follows: Equation (3)

φ=(Mx/GIp)=F'(L/8.5×10⁹r⁴) x l₁ ……(3) Here, Mx is the torsional moment, G is the modulus of transverse elasticity, and Ip is the polar moment of inertia. Also, L and l₁, r are the distance from the central axis of the torsion bar to the point of force, the length of the torsion bar, and the radius of the torsion bar, respectively, as shown in FIG. 3.

The movable plate 5 then rotates to a position where the force F and the spring reaction force F' are balanced. Therefore, by substituting F in equation (2) for F' in equation (3), it is found that the displacement angle φ of the movable plate 5 is proportional to the current i flowing through the planar coil 7.

Therefore, by controlling the current flowing through the planar coil 7, the displacement angle φ of the movable plate 5 can be controlled. For example, the optical axis direction of the photodetector element 8 can be freely controlled within a plane perpendicular to the axis of the torsion bar 6. Continuously changing the displacement angle allows for one-dimensional scanning of the monitored object.

When controlling the displacement angle φ of the optical axis of the photodetector element 8, a detection current for detecting the displacement angle is superimposed on the drive current and flows through the planar coil 7 at a frequency at least 100 times greater than the drive current frequency. This detection current generates induced voltages in the detection coils 12A and 12B due to the mutual inductance between the planar coil 7 and the detection coils 12A and 12B provided on the lower glass substrate 5. When the movable plate 5, i.e., the photodetector element 8, is in a horizontal position, the distances between the detection coils 12A and 12B and the corresponding planar coil 7 are equal, and the difference between the induced voltages is zero. When the movable plate 5 rotates around the torsion bar 6 due to the driving force described above, the induced voltage increases in one of the detection coils 12A (or 12B) due to increased mutual inductance, while the induced voltage decreases in the other detection coil 12B (or 12A) due to decreased mutual inductance. Therefore, the induced voltage generated in the detection coils 12A and 12B changes in response to the displacement of the photodetector element 8, and by detecting this induced voltage, the optical axis displacement angle ψ of the photodetector element 8 can be detected.

For example, as shown in FIG. 4, a power supply is connected to a bridge circuit configured with two resistors in addition to the detection coils 12A and 12B, and a differential amplifier is provided to which the voltage between the midpoint between the detection coils 12A and 12B and the midpoint between the two resistors is input. The output of the differential amplifier, which corresponds to the voltage difference between the two midpoints, is fed back to the drive system of the movable plate 5 to control the drive current, thereby enabling precise control of the optical axis displacement angle φ of the photodetector element 8.

As described above, in this embodiment, the movable portion including the photodetector element can be made small and lightweight, allowing the optical axis direction of the photodetector element to be adjusted at high speed, enabling high-speed scanning of the monitored object. Furthermore, the key components, such as the movable plate, torsion bar, and photodiode, can be formed on the same semiconductor substrate using semiconductor device manufacturing processes, which can lead to cost reductions through mass production. Furthermore, because the monitored object is scanned with a single photodiode, there is no need to compensate for variations in the characteristics of each element.

(Example 2) Figure 5 shows the configuration of an "optical axis direction variable photodetector" according to Example 2.

While the first embodiment described above oscillates one-dimensionally along the optical axis, this embodiment is an example of a two-axis photodetector in which two torsion bars are provided perpendicular to each other so that the optical axis can oscillate two-dimensionally. Note that elements that are the same as those in the first embodiment are designated by the same reference numerals and will not be described again.

In Figure 5, the variable optical axis direction photodetector 21 of this embodiment has a three-layer structure in which upper and lower glass substrates 3 and 4, each made of borosilicate glass or the like, are stacked and bonded to the top and bottom surfaces of a semiconductor silicon substrate 2, as indicated by the arrows. As shown in the figure, the upper and lower glass substrates 3 and 4 each have a rectangular recess 3A or 4A formed in their center, for example, by ultrasonic machining. When bonded to the silicon substrate 2, the upper glass substrate 3 is bonded with the recess 3A facing downward and positioned toward the silicon substrate 2, while the lower glass substrate 4 is bonded with the recess 4A facing upward and positioned toward the silicon substrate 2. This configuration ensures and seals the oscillation space of the movable plate 5 on which the photodetector element 8, described below, is mounted.

The silicon substrate 2 is provided with a flat movable plate 5 consisting of a frame-shaped outer movable plate 5A and an inner movable plate 5B pivotally supported inside the outer movable plate 5A. The outer movable plate 5A is pivotally supported on the silicon substrate 2 by first torsion bars 6A, 6A, and the inner movable plate 5B is pivotally supported inside the outer movable plate 5A by second torsion bars 6B, 6B whose axial direction is perpendicular to that of the first torsion bars 6A, 6A. The movable plates 5A, 5B and the first and second torsion bars 6A, 6B are integrally formed on the silicon substrate 2 by anisotropic etching and are made of the same material as the silicon substrate 2.

Additionally, on the upper surface of the outer movable plate 5A, a planar coil 7A (schematically shown by a single line in the figure, but having multiple turns on the movable plate 5A) is provided, coated with an insulating layer. Both ends of the planar coil 7A are electrically connected to a pair of outer electrode terminals 9A, 9A formed on the upper surface of the silicon substrate 2 via one of the first torsion bars 6A. On the upper surface of the inner movable plate 5B, a planar coil 7B (schematically shown by a single line in the figure, but having multiple turns on the inner movable plate 5B, similar to the outer movable plate 5A) is provided, coated with an insulating layer. The planar coil 7B is electrically connected to a pair of inner electrode terminals 9B, 9B formed on the silicon substrate 2 via one of the second torsion bars 6B, passing through the outer movable plate 5A, and the other side of the first torsion bar 6A. As in Example 1, these planar coils 7A, 7B are formed by the electroforming coil method using electrolytic plating, as described above. The outer and inner electrode terminals 9A, 9B are formed on the silicon substrate 2 simultaneously with the planar coils 7A, 7B by electroforming. A photodiode 8, which is a light-detecting element, is formed in the center of the inner movable plate 5B, surrounded by the planar coil 7B, by a known method.

Eight disk-shaped permanent magnets 10A-13A and 10B-13B are arranged in pairs on the upper and lower glass substrates 3 and 4, respectively, as shown in the figure. The opposing permanent magnets 10A and 11A on the upper glass substrate 3, together with the permanent magnets 10B and 11B on the lower glass substrate 4, apply a magnetic field to the planar coil 7A of the outer movable plate 5A, thereby rotating the outer movable plate 5A through interaction with the drive current flowing through the planar coil 7A. The opposing permanent magnets 12A and 13A on the upper glass substrate 3, together with the permanent magnets 12B and 13B on the lower glass substrate 4, apply a magnetic field to the planar coil 7B of the inner movable plate 5B, thereby rotating the inner movable plate 5B through interaction with the drive current flowing through the planar coil 7B. The opposing permanent magnets 10A and 11A are arranged so that their upper and lower polarities are opposite to each other. For example, when the upper surface of permanent magnet 10A is a south pole, the upper surface of permanent magnet 11A is a north pole. Furthermore, they are arranged so that their magnetic flux crosses parallel to the planar coil portion of the movable plate 5. The same is true for the other opposing permanent magnets 12A and 13A, permanent magnets 10B and 11B, and permanent magnets 12B and 13B. Furthermore, the upper and lower polarities of the corresponding permanent magnets 10A and 10B are the same. For example, when the upper surface of permanent magnet 10A is a south pole, the upper surface of permanent magnet 10B is also a south pole. The same is true for the other opposing permanent magnets 11A and 11B, permanent magnets 12A and 12B, and permanent magnets 13A and 13B. As a result, forces act in opposite directions at both ends of the movable plate 5.

The lower surface of the lower glass substrate 4 is patterned with detection coils 15A, 15B and 16A, 16B, which are arranged to be electromagnetically coupled to the aforementioned planar coils 7A, 7B, respectively. The detection coils 15A, 15B are arranged symmetrically with respect to the first torsion bar 6A, and the detection coils 16A, 16B are arranged symmetrically with respect to the second torsion bar 6B, forming a pair. The pair of detection coils 15A, 15B detects the displacement angle of the outer movable plate 5A. The mutual inductance between the planar coil 7A and the detection coils 15A, 15B, which is based on a detection current superimposed on the drive current flowing through the planar coil 7A, changes with the angular displacement of the outer movable plate 5A, and outputs an electrical signal corresponding to this change. This electrical signal allows the displacement angle of the outer movable plate 5A to be detected. A pair of detection coils 16A and 16B similarly detect the displacement angle of the inner movable plate 5B.

Next, the operation will be described.

When a drive current is applied to the planar coil 7A of the outer movable plate 5A, the outer movable plate 5A rotates in accordance with the direction of the current, with the first torsion bars 6A, 6A serving as a fulcrum. At this time, the inner movable plate 5B also rotates integrally with the outer movable plate 5A. In this case, the photodiode 8 moves in the same manner as in Example 1. On the other hand, when a drive current is applied to the planar coil 7B of the inner movable plate 5B, the inner movable plate 5B rotates relative to the outer movable plate 5A, with the second torsion bars 6B, 6B serving as a fulcrum, in a direction perpendicular to the rotation direction of the outer movable plate 5A.

Therefore, for example, by controlling the drive current of planar coil 7A to rotate outer movable plate 5A once, and then controlling the drive current of planar coil 7B to displace inner movable plate 5B by a fixed angle, and by repeating this operation periodically, the optical axis of photodiode 8 can be swung two-dimensionally, thereby enabling two-dimensional scanning of the monitored object.

In addition, if there is glass above the photodiode 8 as in this embodiment, it is advisable to coat this glass surface with an anti-reflection film or the like.

On the other hand, if a detection current is superimposed on the drive currents passed through the planar coils 7A and 7B, the displacement of the outer movable plate 5A can be detected by the differential output of the detection coils 15A and 15B via a circuit similar to that shown in FIG. 4, for example, based on the mutual inductance between the detection coils 15A and 15B and the planar coil 7A, and between the detection coils 16A and 16B and the planar coil 7B, using the same principle as in Example 1. The displacement of the inner movable plate 5B can be detected by the differential output of the detection coils 16A and 16B. If this differential output is fed back to the drive systems of the outer movable plate 5A and the inner movable plate 5B, the displacement of the outer movable plate 5A and the inner movable plate 5B can be accurately controlled.

Needless to say, in the case of the two-axis photodetector of this embodiment, two circuits similar to that shown in FIG. 4 are provided, one for detecting the displacement of the outer movable plate and one for detecting the displacement of the inner movable plate.

According to the configuration of Example 2, in addition to the same effects as Example 1, scanning of the monitored object can be performed two-dimensionally, thereby increasing the scanning area compared to the uniaxial scanning of Example 1. Furthermore, the oscillation space of movable plate 5 is sealed by upper and lower glass substrates 3 and 4 and the surrounding silicon substrate 2, and by creating a vacuum in this sealed space, air resistance to the rotational movement of movable plate 5 is eliminated, thereby improving the responsiveness of movable plates 5A and 5B.

Furthermore, when increasing the drive current flowing through the planar coils 7A and 7B to increase the displacement of the movable plates 5A and 5B, it is preferable to fill the sealed movable plate oscillation space with an inert gas such as helium or argon rather than creating a vacuum. Helium, which has particularly good thermal conductivity, is preferred. This is because increasing the current flowing through the planar coil 7 increases the amount of heat generated by the planar coil 7, and a vacuum around the movable plates 5A and 5B reduces heat dissipation from the movable plates. Therefore, by filling the space with an inert gas, heat dissipation from the movable plates 5A and 5B can be improved compared to a vacuum state, thereby reducing thermal effects. However, filling the space with an inert gas will result in a slight decrease in the responsiveness of the movable plates 5A and 5B compared to a vacuum state.

It goes without saying that the upper and lower glass substrates of the first embodiment may be provided with a recess similar to that of the second embodiment, thereby sealing the movable plate portion.

(Example 3) Figures 6, 7, and 8 show the configuration of Example 3, a "variable optical axis direction photodetector."

This embodiment is a two-axis example similar to the second embodiment. Elements identical to those in the second embodiment are designated by the same reference numerals and will not be described further.

The two-axis variable optical axis direction photodetector 31 of this embodiment has a configuration similar to that of the second embodiment. However, as shown in FIGS. 6-8, the upper and lower glass substrates 3, 4 are flat, without recesses 3A, 4A, unlike those of the second embodiment. The upper glass substrate 3 has an angular opening 3a formed above the movable plate 5 in accordance with the shape of the movable plate 5, leaving the portion above the photodiode 8 open so that detection light can directly enter the photodiode 8. Because the upper and lower glass substrates 3, 4 are flat, the intermediate silicon substrate 2 is formed with two silicon substrates stacked above and below it to form a three-layer structure, and the movable plate 5 is formed in the middle layer to provide space for the movable plate 5 to rotate.

As shown by the dashed lines in FIG. 6 , detection coils 15A and 15B for detecting the displacement of the outer movable plate 5A and detection coils 16A and 16B for detecting the displacement of the inner movable plate 5B are patterned and provided on the lower surface of the lower glass substrate 4 at positions that allow electromagnetic coupling with the corresponding planar coils 7A and 7B.

The operation and effects of this embodiment having such a configuration are similar to those of the second embodiment, and therefore a description thereof will be omitted.

(Variations) In the above embodiments, photodiodes are used as the light-detecting elements, but the present invention is not limited to this. Line sensors or area sensors made up of multiple photodiodes can also be used. Phototransistors, photoconductors, CCDs, etc. can also be used as light-detecting elements. If necessary, microlenses can be provided in front of these light-detecting elements to focus incident light.

Although linear scanning is performed in Example 2, scanning can be performed concentrically or spirally depending on the object.

Furthermore, in each embodiment, the center of the movable plate is pivotally supported by a torsion bar, but this is not limiting and the movable plate may be pivotally supported at its end, such as the right side of movable plate 5 in FIG. 1. In this case, a single detection coil would be provided on the left side to detect the displacement angle.

In each embodiment, a drive current and a detection current are passed through the planar coil provided on the movable plate. However, when the frequency of the drive current is as high as several kilohertz, the drive current can also be used as the detection current, and the detection current can be implemented without being superimposed.

In each embodiment, the displacement angle is detected by the difference in the outputs of two detection coils, but it is also possible to provide a single detection coil and detect the displacement angle by its output.

(Example of Use) Examples of use of the variable optical axis direction photodetector described above are explained with reference to Figures 9 through 12.

Figure 9 is a block diagram of an example of two-axis drive using photodiodes PD as light detection elements. This example uses the devices described in Examples 2 and 3. An example using the device described in Example 1 corresponds to the absence of one axis, such as the Y-axis, in this example.

The operation will be described with reference to FIG. 10. In step S1, the output of the X-axis displacement angle detector 25, which includes an X-axis detection coil, is converted to digital data by the A-D converter 26 and input to the microcomputer 23. In step S2, the X table is searched based on the digital data, and in step S3, the X-axis position is calculated based on the search results. In step S4, the output of the Y-axis displacement angle detector 27, which includes a Y-axis detection coil, is converted to digital data by the A-D converter 26 and input to the microcomputer 23. In step S2, the Y-axis table is searched based on the Y-axis digital data, and in step S6, the Y-axis position is calculated based on the search results. In step S7, an image frame address is calculated based on the results of calculations in steps S3 and S6. In step S8, the output of the photodiode 20 is amplified and converted to digital data by the A-D converter 22 and input to the microcomputer 23. In step S9, the digital data from the photodiode is transferred to the image frame address in memory 24 and stored therein. This operation is repeated for all image frame addresses to obtain the required monitoring data for the monitoring target.

11 shows an example in which a CCD line sensor is used as the light detecting element and driven in one axis. In this case, the optical axis of the line sensor 28 is swung to scan the monitored object in the Y-axis direction, and the signals from each pixel of the line sensor 28 are sequentially extracted to scan the monitored object in the X-axis direction.

FIG. 12 shows an example in which a CCD area sensor is used as the light detection element and is driven in two axes.

In this case, the optical axis of the area sensor 29 is swung to scan the monitored object in both the X-axis and Y-axis directions, and signals from each pixel of the area sensor 29 are sequentially extracted to scan the monitored object in more detail.

As described above, according to the present invention, it is possible to provide a photodetector that is small, capable of high-speed scanning, and capable of reducing costs through mass production.

Furthermore, according to the invention described in claim 3, two-dimensional scanning is possible, and according to the inventions described in claims 2 and 4, the displacement angle of the optical axis can be detected and the displacement angle of the optical axis can be controlled with high precision by utilizing feedback.

INDUSTRIAL APPLICABILITY As described above, the present invention can be used as a sensor for various devices, such as barcode scanners, CD-ROM drives, and automatic ticket gates, and can be controlled with extremely high precision.

───────────────────────────────────────────────────── (Note) This publication is based on the publication published internationally by the International Bureau of Patents (WIPO). The effect of the international publication of the Japanese patent application (Japanese utility model registration application) related to this publication arises pursuant to Article 184-10, Paragraph 1 of the Patent Act (Article 48-13, Paragraph 2 of the Utility Model Act) and is unrelated to this publication.

Claims (1)

[Claims] 1. A variable optical axis direction photodetector comprising: a movable plate integrally formed on a semiconductor substrate; a torsion bar supporting the movable plate relative to the semiconductor substrate so that the movable plate can swing freely; a drive coil provided on the periphery of the movable plate; magnetic field generating means for applying a static magnetic field to the drive coil; and a photodetector formed on the movable plate, wherein the movable plate is driven by a force generated by passing a current through the drive coil, thereby varying the optical axis direction of the photodetector. 2. The variable optical axis direction photodetector of claim 1, further comprising a detection coil electromagnetically coupled to the drive coil. 3. The variable optical axis direction photodetector of claim 1, further comprising a single movable plate. 4. A variable optical axis direction photodetector comprising an outer movable plate integrally formed on a semiconductor substrate, a first torsion bar pivotally supporting the outer movable plate relative to the semiconductor substrate, an inner movable plate inside the outer movable body, and a second torsion bar pivotally supporting the inner movable plate relative to the outer movable plate, the second torsion bar having an axial direction perpendicular to that of the first torsion bar, a first drive coil provided on the periphery of the outer movable plate, a second drive coil provided on the periphery of the inner movable plate, a first magnetic field generating means for applying a static magnetic field to the first drive coil, a second magnetic field generating means for applying a static magnetic field to the second drive coil, and a photodetector formed on the inner movable plate, wherein the optical axis direction of the photodetector is varied by driving the outer movable plate and inner movable plate with a force generated by passing a current through the first drive coil and second drive coil. 5. The optical axis direction variable type photodetector according to claim 4, further comprising a first detection coil and a second detection coil electromagnetically coupled to the first drive coil and the second drive coil, respectively.