JP3838224B2 - screen - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a screen having a projection surface that projects a light beam emitted from an optical device such as a projector to form a projection image.
[0002]
[Background]
2. Description of the Related Art Conventionally, in presentations and the like, an optical device such as a projector that includes a light modulation device that modulates a light beam emitted from a light source in accordance with image information and projects the light beam modulated by the light modulation device has been widely used. Yes.
The luminous flux emitted from these optical devices is projected onto the projection surface of the screen to form a projection image. Thus, by enlarging and projecting onto the projection surface, a large number of presentations can be efficiently performed. Can do.
[0003]
In a state where the light beam emitted from such an optical device is projected on the projection surface of the screen, if the optical device and the screen do not face each other, a trapezoidal distortion occurs in the projected image formed on the projection surface. Sometimes. For example, if the projection surface is inclined in the vertical direction with respect to an optical device such as a projector, a trapezoidal distortion in which either the top side or the bottom side is longer is originally a rectangular projection image. Further, when the projection surface is inclined in the left-right direction with respect to the optical device, a trapezoidal distortion in which either the left side or the right side becomes longer occurs.
[0004]
In such a case, it is sufficient to adjust the position of the screen, but the screen that can be displayed on a large screen is large, and it is difficult to adjust the position with human power. Difficult to do.
For this reason, in recent years, when such trapezoidal distortion occurs, it is known that software for converting the image signal input to the light modulation device and correcting the keystone distortion is installed in the control unit of the projector. .
With such a projector, even when trapezoidal distortion occurs on the projection surface, the projector's trapezoidal correction software is used to slightly deform the contour of the light beam emitted from the projector so that the projection surface Above, a proper rectangular projection image can be formed.
[0005]
[Problems to be solved by the invention]
However, such a correction on the projector side forms a trapezoidal image without using a part of the rectangular image forming area of the light modulation device, and projects this onto the projection surface, thereby correcting the rectangular shape. Since the projected image is formed, it cannot be said that the entire image forming area is efficiently used.
Further, since it is necessary to install such software in an optical device such as a projector, there is a problem that the price of the projector is likely to increase.
[0006]
An object of the present invention is to provide a screen capable of automatically correcting a trapezoidal distortion even when a trapezoidal distortion occurs in a projected image.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the screen of the present invention is a screen having a projection surface that projects a light beam emitted from an optical device such as a projector to form a projection image, and is provided on the projection surface. A light amount detection unit that detects a light amount of an emitted light beam from the optical device, and a posture control unit that controls the posture of the projection surface based on the light amount detected by the light amount detection unit. To do.
[0008]
According to the present invention, since the light amount detection unit and the posture control unit are provided, the light amount of the projection image from the optical device can be detected and the posture of the projection surface can be controlled. The device can be directly opposed to the device, and the trapezoidal distortion or the like of the projected image can be automatically corrected. Therefore, it is not necessary to install software or the like for correcting trapezoidal distortion in an optical device such as a projector, and the price of the optical device does not increase.
[0009]
In the above, the horizontal axis driving mechanism in which the screen rotates about the axis extending the projection plane along the horizontal direction, and the vertical axis rotation about rotating the projection plane about the axis extending along the vertical direction. In the case where a drive mechanism is provided, the posture control means preferably controls the horizontal axis drive mechanism and the vertical axis drive mechanism.
Here, it is preferable that each drive mechanism uses a stepping motor as a drive source.
According to the present invention as described above, since the attitude of the projection surface can be controlled in any direction with only two simple drive mechanisms, the structure of the screen can be simplified.
[0010]
Further, the light amount detecting means described above includes four photoelectric conversion elements, and among the four photoelectric conversion elements, the pair of photoelectric conversion elements are arranged along the vertical direction of the projection plane, and the other pair of photoelectric conversion elements. The photoelectric conversion element is preferably arranged along the horizontal direction of the projection plane.
Here, various photoelectric conversion elements can be employed, and a CCD imaging element can be employed in addition to the photodiode and the phototransistor.
According to the present invention, the pair of photoelectric conversion elements arranged along the vertical direction can be used for light amount detection when the projection plane is rotated around the horizontal axis, and the horizontal direction The other pair of photoelectric conversion elements arranged along the line can be used for detecting the amount of light when the projection plane is rotated around the vertical axis, and the posture adjustment can be simplified.
[0011]
Furthermore, the above-described photoelectric conversion element is preferably a photodiode.
That is, since the photodiode is inexpensive and widely used as a photoelectric conversion element, the price of the screen according to the present invention does not increase.
[0012]
The light quantity detection means described above preferably includes a bridge circuit in which four photoelectric conversion elements are regarded as resistance elements.
By providing the bridge circuit in this way, if the output from the bridge circuit becomes 0, it can be determined that the light amounts detected by the four photoelectric conversion elements are the same, so the light amount detection means has an extremely simple structure. Can be configured.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
[First Embodiment]
FIG. 1 shows a screen 1 according to an embodiment of the present invention.
The screen 1 includes a screen body 2 and a support 3.
The screen body 2 as a projection surface includes a white rectangular image forming surface 21 and a frame member 22 provided along the upper and lower ends of the image forming surface 21.
The image forming surface 21 is obtained by embedding a plurality of fine glass beads on the surface of a white paint, and the frame member 22 is bent by the image forming surface 21 during projection of an optical image from an optical device such as a projector. It is provided to prevent this.
[0014]
In the vicinity of the outer periphery of the image forming surface 21 of the screen body 2, four light quantity sensors 4U, 4D, 4L, and 4R are provided as light quantity detection means.
Among these four light quantity sensors 4U, 4D, 4L, and 4R, the light quantity sensors 4U and 4D are arranged along the vertical direction of the image forming surface 21, and the light quantity sensors 4L and 4R are arranged in the horizontal direction of the image forming surface 21. Arranged along. Each light quantity sensor 4U, 4D, 4L, 4R is arranged at the center of the rectangular side of the image forming surface 21 and at a position inside the image G projected from an optical device such as a projector. .
[0015]
The column 3 is a member for allowing the screen main body 2 to stand on its own, and is connected to the screen main body 2 at the approximate center of the screen main body 2. Although not shown in the figure, a leg portion is provided at the lower part thereof.
The support column 3 includes a support column body 31, rotating units 32 and 33, and an arm unit 34. Although the column main body 31 is made of a metal cylindrical tubular member and is not shown in the drawing, an undercut is formed on the surface of the intermediate portion for attaching the rotating portion 32.
[0016]
The rotating portion 32 is configured by a ring-shaped member that engages with an undercut formed in an intermediate portion of the column main body 31, and is rotatable about the cylindrical center of the column main body 31 with respect to the column main body 31. Is attached. Further, the rotating part 32 is connected to the frame member 22 of the screen body 2 via a fastener 32A, and the fastener 32A is attached to the rotating part 32 so as to be rotatable in the vertical direction.
[0017]
The rotating portion 33 is formed of a cylindrical member that engages with the upper end portion of the column main body 31, and is attached to the column main body 31 so as to be freely rotatable, similarly to the rotating unit 32. Although not shown in FIG. 1, an internal gear that meshes with a drive mechanism 50 around a vertical axis, which will be described later, is provided on the cylindrical inner peripheral surface of the rotating portion 33.
The arm portion 34 is configured as a rod-like member that is slidably attached to the outer peripheral surface of the rotating portion 33. Although not shown in FIG. 1, the arm portion 34 meshes with a horizontal axis driving mechanism 50 described later on its lower surface. A rack is provided.
A fastener 34A is provided at the distal end portion of the arm portion 34 in the sliding direction so as to be pivotable in the vertical direction with respect to the arm portion 34. The upper frame member 22 of the screen body 2 is provided on the fastener 34A. The central part of the is engaged.
[0018]
As shown in FIGS. 2 and 3, a vertical axis driving mechanism 50 and a horizontal axis driving mechanism 60 are provided inside the cylindrical tube of the column 3.
As shown in FIG. 2, the vertical axis drive mechanism 50 includes a stepping motor 51, a first gear 52, and a second gear 53.
The stepping motor 51 is a motor that is fixed inside the column main body 31 and is driven by an input electric pulse signal, and rotates clockwise or counterclockwise depending on the polarity of the electric pulse signal.
[0019]
The first gear 52 is attached to the rotating shaft of the stepping motor 51 and rotates with the driving of the rotating shaft.
The second gear 53 partly meshes with the first gear 52 and the other part meshes with an internal gear 331 provided inside the rotation part 33, thereby rotating the first gear 52 to rotate the rotation part. Conducted to 33.
In such a vertical axis driving mechanism 50, when an electric pulse signal having a predetermined number of steps is input to the stepping motor 51, the rotation shaft of the stepping motor 51 is driven by the number of steps, and the first gear 52 and the second gear 52 are driven. The rotation unit 33 is rotated via the gear 53.
When the rotating unit 33 rotates, the screen body 2 shown in FIG. 1 rotates about the vertical axis, and the attitude about the vertical axis with respect to the optical device such as a projector is adjusted.
[0020]
As shown in FIG. 3, the horizontal axis driving mechanism 60 includes a stepping motor 61 provided inside the rotation unit 33 and a gear 62 provided at the tip of the rotation shaft of the stepping motor 61. It is disposed outside the moving portion 33 and meshes with a rack 341 provided on the lower surface of the arm portion 34.
When the stepping motor 61 rotates, the gear 62 rotates, and the arm portion 34 slides in the direction perpendicular to the plane of FIG. 3 by the rack 341 engaged therewith.
When the arm 34 slides, the screen body 2 shown in FIG. 1 has its upper edge moved forward and backward in the normal direction of the screen surface, and rotated with the lower edge of the screen body 2, that is, the lower frame member 22 as the horizontal axis. By driving, the attitude around the horizontal axis with respect to the optical apparatus such as a projector is adjusted.
[0021]
As shown in FIG. 4, the drive mechanisms 50 and 60 are driven and controlled by a control unit 70 provided in the column main body 31.
The control unit 70 as an attitude control unit is configured as an ASIC (Application Specific Integrated Circuit), and includes a current detection unit 71, an arithmetic processing unit 72, a memory 73, a vertical axis drive control unit 74, and a horizontal axis drive control unit 75. It is configured with.
[0022]
The current detection unit 71 is a part that detects electrical signals from the light quantity sensors 4U, 4D, 4L, and 4R described above.
More specifically, the light quantity sensors 4U, 4D, 4L, and 4R are configured as a closed circuit including a photodiode 41 as a photoelectric conversion element and a power source 42.
The power source 42 is a portion that applies a bias voltage in the reverse direction to the photodiode 41. In a state where such a bias voltage is applied, the PN junction portion of the photodiode 41 serves as a barrier and is in a closed circuit. No current flows.
[0023]
However, when the photodiode 41 is irradiated with light, holes and electrons are separated at the PN junction surface of the photodiode 41 and move to the − side and the + side, respectively, so that a current flows.
The current detection unit 71 described above detects the current flowing in the closed circuit of the light quantity sensors 4U, 4D, 4L, and 4R, converts the current value into a digital signal, and outputs the digital signal to the arithmetic processing unit 72. The light intensity sensors 4U, 4D, 4L, and 4R are connected in parallel to the current detector 71, and the current detector 71 calculates the current values of the light intensity sensors 4U, 4D, 4L, and 4R. 72.
[0024]
The arithmetic processing unit 72 is a part for determining the posture of the screen body 2 with respect to the optical device based on the detected current value, and by comparing the current values of the four light quantity sensors 4U, 4D, 4L, and 4R, The posture of the screen body 2 is determined.
The calculation processing unit 72 also has a function of performing correction calculation according to image characteristics of the optical device.
[0025]
For example, when an optical image is formed on the screen main body 2 with a tilt projection type projector, the brightest area in the projected image is the central part of the lower edge of the image forming surface, and the other parts are darker than that. The arithmetic processing unit 72 corrects and compares the current values of the light quantity sensors 4U, 4D, 4L, and 4R.
The correction data is recorded and stored in the memory 73, and when tilt projection is selected in the connected setting switch 76, the arithmetic processing unit 72 calls the correction data from the memory 73 and compares the current values. Do.
[0026]
The horizontal axis drive control unit 74 and the vertical axis drive control unit 75 are parts that generate and output control signals for the horizontal axis drive mechanism 60 and the vertical axis drive mechanism 50 based on the determination result by the arithmetic processing unit 72. is there.
The control signal around the horizontal axis is generated based on the comparison of the current values of the light quantity sensors 4U and 4D, and is generated based on the control signal around the vertical axis.
Specifically, when the arithmetic processing unit 72 determines that the current value of the light amount sensor 4D is smaller than the current value of the light amount sensor 4U, the upper end of the screen body 2 is approaching the optical device. Therefore, the horizontal axis drive control unit 74 generates a control pulse signal that moves the arm unit 34 in the direction in which the arm unit 34 approaches the column main body 31, and outputs the control pulse signal to the horizontal axis drive mechanism 60.
[0027]
Next, the operation of the screen 1 will be described based on the flowchart shown in FIG.
(1) As shown in FIG. 6, when the power of the drive mechanisms 50 and 60 of the screen 1 and the control unit 70 is turned on in a state where the projection image of the projector 100 is formed on the image forming surface 21 of the screen body 2, The arithmetic processing unit 72 confirms the state of the setting switch 76, and acquires a correction value corresponding to the setting from the memory 73 (processing S1).
[0028]
(2) The current detection unit 71 detects the current flowing through the closed circuit including the photodiode 41 constituting the light quantity sensor 4U, converts it into a digital signal, and outputs it to the arithmetic processing unit 72 (processing S2). Subsequently, the current detection unit 71 detects a current flowing in the closed circuit including the photodiode 41 constituting the light amount sensor 4D, converts it into a digital signal, and outputs it to the arithmetic processing unit 72 (processing S3).
[0029]
(3) The arithmetic processing unit 72 corrects the output current values of the received light quantity sensor 4U and the light quantity sensor 4D (process S4), and then compares the output current values with each other (process S5). The correction of the output current value is performed by weighting each output current value based on the design illuminance in the upper projection area of the projector 100 and the design illuminance in the lower projection area.
[0030]
(4) If the deviation between the corrected output current value of the light quantity sensor 4U and the output current value of the light quantity sensor 4D does not become zero, the arithmetic processing unit 72 outputs the deviation amount to the horizontal axis drive control unit 74.
(5) The horizontal axis drive control unit 74 generates a control pulse signal composed of the rotation direction and the number of steps based on the obtained deviation amount, and outputs the control pulse signal to the horizontal axis drive mechanism 60 (processing S6). . The horizontal axis driving mechanism 60 advances and retracts the arm portion 34 with respect to the column main body 31 based on the control pulse signal (processing S7). The arithmetic processing unit 72 and the horizontal axis drive control unit 74 repeat the comparison of the output current value and the generation of the control pulse signal until the deviation of the output current value becomes 0, thereby adjusting the vertical inclination of the screen body 2.
[0031]
(6) When the vertical posture adjustment of the screen body 2 is completed, the current detector 71 detects the output current value of the left light amount sensor 4L (processing S8), and detects the output current value of the right light amount sensor 4R. (Processing S9), each converted into a digital signal and output to the arithmetic processing unit 72.
(7) The arithmetic processing unit 72 performs comparison determination of each output current value (processing S10). At this time, in this example, the arithmetic processing unit 72 calculates the deviation by directly comparing both output current values without performing the correction process as in the vertical adjustment. This is because it is unlikely that deviations in the design illuminance will occur in the left-right direction with an optical device such as the projector 100.
[0032]
(8) If it is determined as a result of the comparison determination that there is a deviation in the output current value, the vertical axis drive control unit 75 generates a control pulse signal corresponding to this deviation (processing S11), and the vertical axis Output to the rotation drive mechanism 50. The vertical axis drive mechanism 50 rotates the rotation unit 33 based on the control pulse signal (processing S12), and ends the processing when the deviation of the output current values of the light quantity sensors 4L and 4R becomes zero. Maintain that state.
[0033]
According to this embodiment as described above, the following effects are obtained.
The screen 1 includes light amount sensors 4U, 4D, 4L, and 4R, a horizontal axis drive control unit 74, a vertical axis drive control unit 75, a vertical axis drive mechanism 50, and a horizontal axis drive mechanism 60. Since the posture of the image forming surface 21 can be controlled by detecting the amount of light of the projected image from the projector 100, the image forming surface 21 of the screen 1 can be directly opposed to the projector 100, and trapezoidal distortion or the like of the projected image is automatically performed. Can be corrected. Therefore, it is not necessary to separately install software or the like for correcting the keystone distortion in the projector 100, and the price of the optical device does not rise.
[0034]
In addition, since the attitude control means includes the vertical axis driving mechanism 50 and the horizontal axis driving mechanism 60, the attitude of the image forming surface 21 of the screen main body 2 in all directions with only two rotating mechanisms. Can be controlled, and the structure of the screen 1 can be simplified.
Further, the light quantity sensors 4U and 4D are arranged along the vertical direction, and the light quantity sensors 4L and 4R are arranged along the horizontal direction, whereby the posture adjustment of the image forming surface 21 by the horizontal axis driving mechanism 60 and the vertical direction are performed. The posture adjustment of the image forming surface 21 by the shaft driving mechanism 50 can be performed independently, and the posture adjustment can be simplified.
[0035]
Since the light quantity sensors 4U, 4D, 4L, and 4R are configured to include the photodiode 41, the light quantity detection configuration can be provided on the screen 1 at a low cost, and the price of the screen 1 does not increase.
In addition, since the arithmetic processing unit 72 is configured to correct the output current value detected by the current detection unit 71 according to the model of the projector 100, even if the projector 100 is a tilt projection type, the screen The image forming surface 21 of the main body 2 can be adjusted to an appropriate posture.
[0036]
[Second Embodiment]
Next, a second embodiment of the present invention will be described. In the following description, the same members and the like as those already described are denoted by the same reference numerals, and description thereof is omitted or simplified.
In the first embodiment described above, the light quantity sensors 4U, 4D, 4L, and 4R are connected in parallel to the current detection unit 71.
[0037]
On the other hand, the light quantity sensors 5U, 5D, 5L, and 5R according to the second embodiment are configured as a bridge circuit in which the photodiode 41 of each sensor is regarded as a resistance element, as shown in FIG. Is different. The arrangement of the light quantity sensors 5U, 5D, 5L, and 5R on the screen is the same as in the first embodiment. The light quantity sensor 5U is on the upper side of the screen, the light quantity sensor 5D is on the lower side of the screen, and the light quantity sensor 5L is on the left side of the screen. The sensor 5R is on the right side of the screen.
[0038]
In this bridge circuit, the photodiodes 41 constituting each light quantity sensor 5U, 5D, 5L, 5R are arranged in such a direction that the applied voltage Vcc applied to the bridge circuit is applied in the reverse direction. Further, the light quantity sensors 5U and 5D are connected in parallel so as to be voltage application portions, and the light quantity sensors 5L and 5R are connected in parallel at the subsequent stage.
In such a bridge circuit, the resistance value of each photodiode 41 is set to Ru (light quantity sensor 5U), Rd (light quantity sensor 5D), Rl (light quantity sensor 5L), Rr (light quantity sensor 5R), and the current flowing through the light quantity sensor 5L. Assuming that I ₁ and the current flowing through the light quantity sensor 5R are I ₂ , when the output current Io becomes 0 and the current I ₁ becomes equal to the current I ₂ , the projection surface of the screen can face the optical device. Although not shown in FIG. 7, the current detector 81 detects the current I ₁ and the current I ₂ .
Further, when the output current Io becomes 0, an equilibrium state expressed by the following equation (1) is established.
[0039]
[Expression 1]
Ru × Rr = Rd × Rl (1)
[0040]
In the screen having such a configuration, first, the arithmetic processing unit 82 of the control unit 80 monitors the output current Io, the current I ₁ , and the current I ₂ detected by the current detection unit 81, while driving the horizontal axis drive control unit 83. The vertical axis drive control unit 84 performs drive control of the horizontal axis drive mechanism 60 and the vertical axis drive mechanism 50.
Then, when the output current Io detected by the current detection unit 81 becomes 0, the arithmetic processing unit 82 establishes the equilibrium state of the above equation (1) and the current I ₁ becomes equal to the current I _2. The light amounts detected by the photodiodes 41 are determined to be equal, and the drive control by the horizontal axis drive control unit 83 and the vertical axis drive control unit 84 is terminated.
[0041]
Such a second embodiment has the following effects in addition to the effects described in the first embodiment.
Since the arithmetic processing unit 82 determines that the light amounts detected by the light amount sensors 5U, 5D, 5L, and 5R are equal based on the equilibrium state of the bridge circuit, the three output currents Io and I ₁ from the bridge circuit are determined. , I ₂ can be determined only by detecting the current detection unit 81, and the structure of the light quantity detection means can be simplified.
[0042]
[Modification of Embodiment]
In addition, this invention is not limited to the above-mentioned embodiment, It includes the deformation | transformation as shown below.
In the second embodiment, the bridge circuit is configured with the four photodiodes 41 constituting the four light quantity sensors 5U, 5D, 5L, and 5R as resistance elements. However, the present invention is not limited to this. .
[0043]
That is, as shown in FIG. 8, a photodiode circuit 41 constituting the light quantity sensors 6U, 6D, 6L, 6R, a known fixed resistance R1, R2, and a variable resistance R3 constitute a bridge circuit, and a predetermined light quantity The resistance value of the photodiode 41 in the state where the light is received may be obtained from the adjustment value of the variable resistor R3.
In this case, the control unit 90 is provided with a resistance adjustment unit 95 in addition to the current detection unit 91, the arithmetic processing unit 92, the horizontal axis drive control unit 93, and the vertical axis drive control unit 94, and the current detection unit The resistance value of the photodiode 41 may be obtained by adjusting the value of the variable resistor 63 with the resistance adjusting unit 95 so that the output current Io of the bridge circuit detected at 91 becomes zero.
[0044]
In the first embodiment, the photodiode 41 is used as the photoelectric conversion element of the light quantity sensors 4U, 4D, 4L, and 4R. However, the present invention is not limited to this, and for example, a photoelectric conversion element such as a phototransistor is used. It may be used.
Further, in the above-described embodiment, the present invention is applied to the front projection type screen. However, the present invention is not limited to this, and the present invention may be applied to the rear projection type screen.
In addition, the actual structure and shape of the present invention may be other structures and the like as long as the object of the present invention can be achieved.
[0045]
【The invention's effect】
According to the present invention as described above, since the light amount detecting means and the posture control means are provided, the light amount of the projected image from the optical device can be detected and the posture of the projection surface can be controlled. There is an effect that the optical device can be directly faced and trapezoidal distortion or the like of the projected image can be automatically corrected.
[Brief description of the drawings]
FIG. 1 is a front view, a plan view, and a side view showing a structure of a screen according to an embodiment of the present invention.
FIG. 2 is a schematic diagram showing a configuration of a vertical axis driving mechanism in the embodiment.
FIG. 3 is a schematic diagram showing a configuration of a horizontal axis driving mechanism in the embodiment.
FIG. 4 is a block diagram showing the structure of posture control means in the embodiment.
FIG. 5 is a flowchart showing the operation of the screen in the embodiment.
FIG. 6 is a schematic diagram showing a state of screen posture adjustment in the embodiment.
FIG. 7 is a block diagram showing the structure of screen attitude control means according to a second embodiment of the present invention.
FIG. 8 is a block diagram showing a structure of a screen attitude control unit according to a modification of the embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Screen, 4U, 4D, 4L, 4R, 5U, 5D, 5L, 5R ... Light quantity sensor (light quantity detection means), 41 ... Photodiode (photoelectric conversion element), 70, 80, 90 ... Control part (Attitude control means) ), 100 ... Optical equipment

Claims (5)

A screen having a projection surface that projects a light beam emitted from an optical device such as a projector to form a projected image,
A light amount detecting means provided on the projection surface for detecting a light amount of an emitted light beam from the optical device;
A screen comprising: an attitude control means for controlling the attitude of the projection plane based on the light quantity detected by the light quantity detection means. The screen of claim 1,
A horizontal axis driving mechanism for rotating the projection plane about an axis extending along the horizontal direction, and a vertical axis driving mechanism for rotating the projection plane about an axis extending along the vertical direction,
The attitude control means controls the horizontal axis driving mechanism and the vertical axis driving mechanism. The screen according to claim 2.
The light amount detecting means includes four photoelectric conversion elements,
Of the four photoelectric conversion elements, the pair of photoelectric conversion elements are arranged along the vertical direction of the projection plane, and the other pair of photoelectric conversion elements are arranged along the horizontal direction of the projection plane. A screen characterized by. The screen according to claim 3,
The screen, wherein the photoelectric conversion element is a photodiode. The screen according to claim 3 or 4,
The light quantity detecting means includes a bridge circuit in which the four photoelectric conversion elements are regarded as resistance elements.

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