JP2516486B2 - Projector - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection device such as an overhead projector, a material presentation table or a real projector, and more particularly to a projection device for adjusting the focus of a projected optical image.

[0002]

2. Description of the Related Art Conventionally, this type of projection apparatus projects spot light in the infrared region toward a screen and couples the reflected light to a light receiving element such as a one-dimensional semiconductor position detecting element (hereinafter referred to as PSD). It is known that an image is formed and the distance to the screen, which is the image forming surface, is measured based on the deviation of the image forming position of the spot light. The projection device adjusts its optical system such as the position of the projection lens according to the distance thus measured, and normally focuses the optical image on the screen.

In such a configuration for optically measuring the distance, the incidence of external light (for example, infrared light from sunlight or an incandescent lamp) on the light receiving element may cause a measurement error, but the light receiving element It cannot completely block the incidence of external light on the. Therefore, it is also possible to remove the influence of external light by pulse-driving the spot light emitting means and using the output signal of the light receiving element (a signal corresponding to external light) when the spot light is not incident. ing. From the viewpoint of measuring the distance to the image plane and adjusting the optical system, such a configuration is the same as an autofocus mechanism such as a camera.

[0004]

However, it is known that when the distance to the screen is actually measured, the measurement result has some variation. Such a variation is not a problem when the depth of focus of the optical system is relatively deep like a camera, but is recognized as a blur of an optical image when the depth of focus is shallow like a projection device. , Cannot be tolerated.

It has been found that such variation in distance measurement depends on variation in the intensity of external light at the timing of distance measurement, although it depends on the method of distance measurement. For example, when a structure is adopted in which the intensity of the external light is measured and the influence of the external light is removed by subtracting the intensity, the timing of measuring the intensity of the external light (the spot light is turned off) and the timing of actually measuring the distance ( The spot light is lit) and the time is off. Therefore, when external light is driven by, for example, commercial alternating current, its intensity fluctuates periodically, and depending on the sampling timing, the intensity of external light may be too large or too small as the intensity of the external light to be subtracted at the time of distance measurement. It does. As a result, the distance measurement varies.

The projection apparatus of the present invention is aimed at accurately measuring the distance to the image plane and properly adjusting the optical system, and has the following constitution to achieve such an object.

[0007]

As shown in the block diagram of FIG. 1, a projection apparatus of the present invention forms an optical image on an image forming plane SR.
A projection device having an optical system OS for projecting light onto the image forming surface SR, and a light projecting means LL for projecting light onto the image formation surface SR, and the light projecting means L.
Light receiving means RL for receiving the reflected light of the light projected by L
And a distance measuring means D for measuring the distance to the image plane based on the reflected light received by the light receiving means RL.
M and an instruction to instruct execution of automatic focus adjustment of the optical system
Means SW and automatic focusing of the optical system OS by the instruction means SW
When a point adjustment instruction is received, the intensity changes periodically.
Detecting a part light phase, said distance measuring means DM, driving means DU for operating with a constant phase of the external light, in accordance with distances the measurement, the focus of the optical image by adjusting the projection optical system OS The gist is that it is provided with a focus adjustment means FA for adjusting

[0008] It is to be noted that the drive means, from the phase of the commercial AC
A configuration is provided in which an operation timing determining unit that detects the phase of the intensity fluctuation of the external light and determines the operation timing of the distance measuring unit DM is provided, and determines the operation timing from the commercial AC used as the power supply inside the projection apparatus. Can also be considered.

[0009]

The projection apparatus of the present invention configured as described above is
The reflected light of the light projected from the light projecting means LL onto the image forming surface SR is received by the light receiving means RL, and the distance measuring means DM determines the distance to the image forming surface SR based on, for example, the position and intensity of the reflected light. To measure. At this time, the driving unit DU is the instructing unit.
When SW instructs execution of automatic focus adjustment of the optical system OS,
Operating the distance measuring means DM at a constant phase of the external light. Therefore, the intensity of the external light at the timing of measuring the distance is always constant, and the measurement result does not vary due to the change in the intensity of the external light. According to the distance thus measured,
The focus adjustment means FA adjusts the optical system OS to adjust the focus of the optical image.

Here, the fluctuation of the periodic intensity of external light is
Normal, or arising from in accordance with the frequency of the commercial AC, commercial AC
By detecting the phase of the intensity fluctuation of the external light from the phase of
If the operation timing of the distance measuring means DM is determined based on the phase of the commercial AC, the accuracy of distance measurement is improved with a simple configuration.

[0011]

Preferred embodiments of the present invention will be described below in order to further clarify the structure and operation of the present invention described above. 2 is an external view of an overhead projector as an embodiment, and FIG. 3 is an enlarged perspective view of the projection head.

As shown in FIG. 2, the overhead projector 3 includes a main body 5 for accommodating a metal halide lamp as a light source and a control device therefor, a stage glass 7 for mounting a transparent sheet on which an original is drawn, a projection lens. Projection head 11 and projection head 1 incorporating 9 and a reflector 10
It is composed of an arm portion 12 supporting 1 and the like.
A power switch 15 for turning the power on and off is provided on the front side of the main body 5.

The projection head 11 is provided with a distance measuring control device 20 and a focus adjusting mechanism 25 on a support 28, as shown in FIG. 3, in addition to the projection lens 9 and the reflecting mirror 10. The distance measurement control device 20 measures the distance to the screen and controls the position of the projection lens based on the measured distance, and the projector 31 and the light receiver 31 fixed to the support 28 with an elevation angle of several degrees. 33 and an electronic control unit 35 that controls these and the focus adjustment mechanism 25. In addition,
Details of the configuration of the distance measurement control device 20 will be described later.

On the other hand, the focus adjustment mechanism 25 is a mechanism for moving up and down the projection lens 9 having a cylindrical frame body, and is for adjusting the focus position of the optical image projected on the screen. The focus adjustment mechanism 25 includes a rotary cylinder 36 in which the projection lens 9 is inserted together with its frame, a stepping motor 37 as a drive source, a gear assembly 40 that transmits the rotation of the stepping motor 37 to the rotary cylinder 36, and a gear assembly 40. It is composed of an adjusting knob 41 and the like for driving manually.

A tooth row 43 that meshes with the gears of the gear assembly 40 is formed on the outer periphery of the rotary cylinder 36, and when the stepping motor 37 (or the adjusting knob 41) rotates, the rotary cylinder 36 becomes the same as the stepping motor 37. Rotate in the direction (opposite to the adjustment knob 41). A spiral groove (not shown) is formed on the inner circumference of the rotary cylinder 36, and a projection (not shown) provided on the outer circumference of the frame of the projection lens 9 is slidably fitted in the groove. In addition, the projection lens 9
Is restricted from moving in the rotation direction by a fixing mechanism (not shown).

Therefore, when the rotary cylinder 36 rotates, the projection lens 9 moves vertically along the spiral groove on the inner peripheral surface of the rotary cylinder. When the rotary cylinder 36 rotates in the direction of the arrow CW in the drawing, the projection lens 9 rises and the focus position of the optical image projected on the screen SR approaches the overhead projector 3, and when it rotates in the direction of the arrow CCW, the projection lens 9 descends. The position of the focal point moves away. In this way, by rotating the stepping motor 37 and the adjusting knob 41, the focal length of the optical system that projects the image on the stage glass 7 onto the screen is adjusted.

A convex portion 45 is formed on the outer circumference of the rotary cylinder 36, and a stopper 47 is provided upright from the support 28 in the vicinity of the rotary cylinder 36. Further, a reset switch 49 is provided on the opposite side of the stopper 47 with the rotary cylinder 36 interposed therebetween.
Is provided. Since the convex portion 45 rotates together with the rotary cylinder 36, when the rotary cylinder 36 rotates in the arrow CW direction, the convex portion 45 eventually comes into contact with the stopper 47 and the rotation of the rotary cylinder 36 is blocked. Also, when the rotary cylinder 36 rotates in the direction of the arrow CCW, the convex portion 45 eventually reaches the position of the reset switch 49 and operates it.

Next, the distance measurement control device 20 will be described with reference to FIG. 4, which is a block diagram mainly showing the configuration of the electronic control device 35. The electronic control device 35 of the distance measurement control device 20 is connected to a projector 31 that projects infrared light and a photoreceiver 33 that includes a filter that selectively transmits infrared light. A distance measurement calculation circuit 50 for measuring the distance to the screen SR using the devices 31 and 33 is provided.
The distance measurement calculation circuit 50 is a well-known circuit used for auto-focusing of a camera, etc., and is based on the shift of the image forming position in the light receiver 33 of the spot light projected on the screen SR by the light projector 31. , The distance to the screen SR is measured. In this embodiment, an IC for autofocus, H2152 (manufactured by Hamamatsu Photonics KK) is used.

The principle of distance measurement is shown in FIG.
An infrared LED 51 for light projection incorporated in 1 forms spot light on the screen SR by a light projection lens 52. The reflected light of this spot light is reflected by the PSD in the light receiver 33.
An image is formed on 53 by the light receiving lens 54. Since the distance L to the screen SR and the deviation d of the center position of the spot light on the PSD 53 are inversely proportional, the deviation d on the PSD 53 decreases as the distance L increases.

The PSD 53 shifts the position of the spot light d.
Output current ΔI from the electrodes provided at both ends of
It has a characteristic that the ratio between 1 and ΔI2 changes. That is, the baseline length that is the distance between the projector 31 and the light receiver 33 is S, the distance between the light receiving lens 54 and the PSD 53 is f, and the PSD 53 is
Assuming that the total length of the output current is 2 · C, the ratio of the output currents ΔI1 and ΔI2 is expressed by the following equation (1).

ΔI1 / ΔI2 = (C · L + f · S) / (C · L−f · S) (1)

Since the values C, f, and S are fixed values for the device, the current ratio ΔI1 / ΔI2 depends on the distance L in principle and does not depend on the intensity of the spot light. become. However, since external light including light in the infrared region is incident on the PSD 53 and the incident light is not always uniform, the external light is used even though the infrared LED 51 is used as a light source for spot light. It is necessary to remove the effect of output current due to. Therefore, the distance measurement calculation circuit 50 stores the output current of the PSD 53 immediately before the infrared LED 51 is turned on, and subtracts it from the output current after the infrared LED 51 is turned on to measure the distance. The distance measurement calculation circuit 50 performs such calculation and outputs a voltage (hereinafter, also referred to as a linear signal) according to the distance to the screen SR. An example of the output characteristic of the distance measurement calculation circuit 50 is shown as a solid line J in FIG.

Each part of the electronic control unit 35 will be described. The electronic control unit 35 is provided with a power supply circuit 61 that generates a stabilized DC power supply from commercial AC. The secondary side line of the step-down transformer (not shown) in the power supply circuit 61 is connected to the zero-cross detection circuit 63,
Here, the zero cross of commercial AC is detected. That is, the zero-cross detection circuit outputs a rectangular signal (hereinafter, referred to as a synchronization signal, see FIG. 7) that is inverted at the zero-cross point of the commercial AC.

The synchronization signal from the zero-cross detection circuit 63 is input to the trigger terminal of the first monostable multivibrator 65. On the other hand, to the enable terminal of the monostable multivibrator 65, the signal line from the switch SW1 for automatic focus adjustment provided on the front surface of the housing of the electronic control unit 35 is connected. The switch SW1 is a normally open type, and one end thereof is connected to the power supply line. The other end of the switch SW1 has a resistor R0.
Is connected to the ground line via the capacitor C0, and is also connected to the enable terminal to the monostable multivibrator 65 via the capacitor C0. The enable terminal is connected to the ground line by the pull-down resistor R1.

With the above configuration, when the switch SW1 is operated, the enable terminal of the monostable multivibrator 65 becomes active high for a predetermined time determined by the capacitance of the capacitor C0, and the first monostable multivibrator 65 is activated. A signal that is triggered when the input signal to the trigger terminal is inverted to a high level and is at a high level for a predetermined time (hereinafter referred to as a trigger signal; see FIG. 7) is normally output only once. This trigger signal is input to the operation timing instruction circuit 70.

The operation timing instructing circuit 70 starts its operation in response to the trigger signal from the first monostable multivibrator 65, and the distance measuring arithmetic circuit 50 and the motor initial position returning circuit 72 immediately receive the oscillator 71, The motor drive circuit 75 outputs a start signal after a predetermined time. Upon receiving this start signal, the distance measurement calculation circuit 50 starts the above-described distance measurement processing.
That is, as shown in FIG. 7, after a predetermined time (31.27 [msec] in this embodiment) from the input of the first trigger signal,
PSD5 by external light prior to the emission of the infrared LED 51
Infrared LED 5 for light emission
Make 1 emit light. Further, the predetermined time (0.
55 [msec]), before turning off the infrared LED 51,
The distance to the screen SR is measured based on the output current of the PSD 53, and a voltage (linear output) corresponding to the distance is output. The linear output is obtained by the distance measurement calculation circuit 50.
It is maintained for a predetermined time by a hold circuit (not shown) inside.

After a lapse of a predetermined time after the linear distance output is established by the distance calculation circuit 50 and the linear output is established, the oscillator 71 starts oscillating according to the instruction of the operation timing instruction circuit 70, and the motor 71 The drive circuit 75 inverts the output and activates the motor 37. Further, the motor initial position return circuit 72 inverts its output to a high level until the reset switch 49 is activated. This signal is transmitted to the motor drive circuit 75 and the second monostable multivibrator 7
6 is output.

Upon receiving the start signal from the operation timing instruction circuit 70, the motor drive circuit 75 rotates the stepping motor 37 in the direction determined by the level of the signal from the motor initial position return circuit 72. While the output of the motor initial position return circuit 72 is at a high level, the motor drive circuit 75 keeps the stepping motor 37 at a high level as shown in FIG.
Rotate in the reverse direction. As a result, the rotary cylinder 36 is indicated by the arrow C.
It rotates in the CW direction and reaches the position where the convex portion 45 contacts the reset switch 49. The convex portion 45 is the reset switch 49.
When it comes into contact with, the motor initial position return circuit 72 inverts its output to a low level, and the motor drive circuit 75 switches the rotation direction of the stepping motor 37 to the forward rotation direction. As a result, the rotary cylinder 36 starts to rotate in the arrow CW direction.

The second monostable multivibrator 76 is
The stepping motor 37 is activated by an inversion signal of the motor initial position return circuit 72 for switching the rotation direction from reverse rotation to forward rotation, and its output signal is, after a time determined by the semi-fixed resistor RT for determining the time constant and the capacitor CT, Invert to low level. This output signal is input to the gate 78. The time of the output signal of the second monostable multivibrator 76 can be varied by adjusting the semi-fixed resistor RT, and the rotary cylinder 36 moves in the direction of arrow CW from the position where the convex portion 45 contacts the reset switch 49. Rotate
Adjust the machine difference in the amount of rotation until the focus automatically adjusts. When the time for adjusting the machine difference, that is, the time when the output of the second monostable multivibrator 76 is inverted, the gate 78 is opened and the clock from the oscillator 71 is output to the counter 80.

As a result, the counter 80 counts up with the clock from the oscillator 71. Counter 80
The 5-bit output of is a digital-to-analog converter (DA
C) 82, and the output of the DAC 82 is connected to the comparison circuit 85. Therefore, when the gate 78 is opened, the output of the DAC 82 is gradually increased as shown in FIG.

The output of the DAC 82 is compared with the linear output of the distance measurement calculation circuit 50 by the comparison circuit 85. The output of the comparison circuit 85 is connected to the operation timing instruction circuit 70, and when the output voltage of the gradually increasing DAC 82 becomes equal to and exceeds the linear output, the output of the comparison circuit 85 is inverted, and the operation timing instruction circuit 70. Operate. As a result, the operation timing instruction circuit 70 stops the oscillator 71 and instructs the motor drive circuit 75 to stop the stepping motor 37. Upon receiving this instruction, the stepping motor 37 stops its rotation. The characteristics of each circuit are adjusted so that the output of the comparison circuit 85 is inverted when the distance to the screen SR is equal to the distance obtained by adjusting the focus of the projection lens 9 by the stepping motor 37. When stopped, the image on the stage glass 7 is correctly focused on the screen SR.

The linear output from the distance measurement calculation circuit 50 is output to the window comparator 88 as well as the comparison circuit 85. The window comparator 88 is the distance measurement calculation circuit 5
This is a circuit for determining whether or not the linear output of 0 is within the predetermined voltage range. When the linear output is not within the predetermined voltage range, the light emitting diode 89 provided on the front surface of the electronic control unit 35 is operated. Light. Since the linear output of the distance measuring calculation circuit 50 is inversely proportional to the distance to the screen SR, the voltage range is discriminated by the window comparator 88 so that the distance to the screen SR falls within the focus adjustable range. It is decided whether or not there is. As shown as the range H in FIG. 6, in this embodiment, the range in which the distance to the screen is 1.5 meters to 3 meters is the focus adjustable range.

The output of the window comparator 88 is also input to the operation timing instruction circuit 70,
If the distance to the screen SR is not within the focus adjustable range, the operation timing instruction circuit 70 is activated to interrupt the subsequent control and prohibit the activation of the stepping motor 37. This state is shown as a broken line b1 in FIG.

According to the overhead projector of this embodiment having the above configuration, the switch S for automatic focus adjustment is used.
When W1 is pressed, a trigger signal is output after waiting for the phase of the commercial AC to become zero next, and after a certain time from this, external light is taken in and the distance to the screen SR is measured. Therefore, as shown in FIG. 7, with respect to the flicker of the fluorescent lamp that is turned on by the commercial alternating current, the timing of taking in the external light and the timing of the distance measurement are always performed in the same phase. The accuracy is greatly improved.

For example, when the variation of the output voltage (linear output) of the distance measurement calculation circuit 50 is measured, when the distance measurement is performed without being synchronized with the phase of the commercial AC, the broken line B in FIG.
As shown by the above, the distance was measured in synchronization with the phase of the commercial AC while the output voltage fluctuated by about 0.1 [V] with respect to the maximum value of the output voltage within the adjustment range H. In this case, the variation is about 0.02 volt at the maximum, and is within about 3% with respect to the maximum value of the output voltage. Such an effect is obtained regardless of whether the frequency of the commercial AC is 60 [Hz] or 50 [Hz], as shown in FIG. 7, since the external light taking-in timing and the distance measuring timing have a constant relationship. It is realized regardless of the AC frequency.

Further, in the overhead projector of the present embodiment, the focus is automatically adjusted when the switch SW1 is pressed. Therefore, for example, when a person crosses between the overhead projector and the screen SR, the focus is adjusted one by one. It does not make any adjustments.
Further, since the distance is measured by the optical system incorporated in the projection head 11, the measured distance is in good agreement with the distance of the light passing through the projection lens 9 to the screen SR, and the accuracy of focus adjustment is improved. Further improvements are being made. Further, infrared light is used for distance measurement to reduce the influence of external light, which contributes to improvement in distance measurement accuracy.

In this embodiment, the focus can be automatically adjusted and manually adjusted by the adjusting knob 41. Therefore, even if the focus is out of the automatic adjustment range, the focus is adjusted to obtain a clear optical image on the screen SR. You can get on.

Although one embodiment of the present invention has been described above, the present invention is not limited to such an embodiment. For example, the output of the distance measurement calculation circuit 50 is AD-converted at a high speed and taken into a microcomputer to measure the distance. A configuration for making a determination, a configuration incorporated in an actual projector or a material presentation table, a configuration for actually detecting flicker of a fluorescent lamp and using this to determine the operation timing of the distance measurement calculation circuit 50, an optical image on the screen Various configurations are possible within the scope not departing from the gist of the present invention, such as a configuration in which an image is shifted from a focused position by a predetermined amount and a CCD or other optical element is used instead of PSD for measuring the distance. Of course, it can be implemented in.

[0039]

As described above in detail with reference to the embodiments, according to the projection apparatus of the present invention, the intensity is periodically changed like the light from the fluorescent lamp which is turned on by the commercial alternating current or the like. Even if light is present, the distance to the image plane is operated with a constant phase of the external light, so that the distance measurement accuracy is significantly improved. Therefore, even with a projection device having a shallow depth of focus, a proper optical image can be obtained on the image plane. Since the fluctuation of the external light is usually synchronized with the cycle of the commercial alternating current, if the operation timing is determined from the commercial alternating current used by the projection device itself for the power supply, the entire configuration is simplified. can do.

[Brief description of drawings]

FIG. 1 is a block diagram illustrating a basic configuration of the present invention.

FIG. 2 is an external view of an overhead projector as one embodiment of the present invention.

FIG. 3 is a perspective view showing a main part of a projection head 11 of the overhead projector of the embodiment.

FIG. 4 is a block diagram showing a configuration of an electronic control unit 35 that performs automatic focus adjustment.

FIG. 5 is an explanatory diagram showing the principle of measuring the distance to the screen SR.

FIG. 6 is a graph showing the relationship between the measured distance and the output voltage of the distance measurement calculation circuit 50.

7 is a timing chart showing the power supply frequency and distance measurement timing in the distance measurement calculation circuit 50. FIG.

FIG. 8 is a timing chart showing the operation timing of each unit in the electronic control unit 35.

9 is a graph showing the relationship between the measured distance and the variation in the output voltage of the distance measurement calculation circuit 50. FIG.

[Explanation of symbols]

 3 Overhead Projector 9 Projection Lens 10 Reflector 11 Projection Head 20 Distance Measurement Control Device 25 Focus Adjustment Mechanism 31 Projector 33 Light Receiver 35 Electronic Control Device 37 Stepping Motor 50 Distance Measuring Arithmetic Circuit 61 Power Supply Circuit 63 Zero Cross Detection Circuit 65 1st Monostable multivibrator 70 operation timing instruction circuit 72 motor initial position return circuit 75 motor drive circuit 76 second monostable multivibrator 80 counter 82 DAC 85 comparison circuit DM distance measurement means DU drive means FA focus adjustment means OS optical system RL Light receiving means SR screen

Claims (2)

(57) [Claims] 1. A projection apparatus having an optical system for projecting an optical image on an image forming surface, the light projecting means for projecting light on the image forming surface, and the reflected light of the light projected by the light projecting means. A light receiving means for receiving the light, a distance measuring means for measuring a distance to the image plane based on the reflected light received by the light receiving means, and an instruction means for instructing execution of automatic focus adjustment of the optical system.
And received an instruction for automatic focus adjustment of the optical system by the instruction means.
At this time, the phase of external light whose intensity changes periodically is detected,
It said distance measuring means, and driving means for operating at a fixed phase of the external light, in accordance with distances the measurement, and a focus adjustment means for adjusting the focus of the optical image by adjusting the projection optical system projected apparatus. 2. The projection device according to claim 1, wherein the driving means changes the intensity of the external light from the phase of commercial AC.
A projection apparatus having an operation timing determining means for detecting the phase of the distance and determining the operation timing of the distance measuring means.