JPH0210520Y2 - - Google Patents

Description

[Detailed description of the invention] This invention is an automatic focusing system that automatically measures the distance from the head to the screen and automatically adjusts the focus of the projected image using a distance measuring mechanism consisting of a light emitter and a light receiver. The present invention relates to an improvement of an overhead projector equipped with the device.

With this kind of conventional overhead projector, if the automatic focus adjustment device is always operated in the full light state (projection state), the projector who is in the optical path when explaining the projected image in front of the screen, There is a problem that the automatic focus adjustment circuit may malfunction due to sensing the fingertip, pointer stick, etc., or the light receiving element receiving the projection light reflected by the screen. Ta.

In view of the above-mentioned problems, the present invention includes a dimming circuit that can be switched to either a dimming side that puts a light source in a dimming state or a full-lighting side that puts the light source in a full-bright state, an external switch, and a relay that is switched to either a non-operating state or an operating state, and when the relay is in the non-operating state, the automatic focus adjustment device is turned on at the same time as the dimming circuit is set to the dimming side;
To provide an overhead projector in which the automatic focus adjustment device is prevented from malfunctioning in the full light state by setting the dimming circuit to the full light side and simultaneously turning off the automatic focus adjustment device when the relay is in the operating state. This will be explained based on an embodiment illustrated below. 1 has a light source 2 and a Fresnel lens 3 inside, and a mounting table 4 for materials (film, etc.) on the top surface. 5 is a cradle fixed to the projector body 1 via a support 6; 7 is rotatably supported by the cradle 5 so as to be positioned above the mounting table 4, and has an opening in the center; It is a rotary plate provided with 7a. 8 is fixed on the rotary plate 7 and has a stopper 8a on the upper part and a rack 8 on the side.
9 is a head mounted on the guide column 8 so as to be slidable up and down, with a projection lens 10 and a reflector 11 fixed in the center; 12 is a head of the head 9; a motor 13 fixed to an inner wall and having a pinion 12a fixed to a rotating shaft;
is pivotally supported by a bearing 14 in the head 9, the small gear 13a meshes with the pinion 12a, and the large gear 1
Reference numeral 3b is an intermediate gear meshing with the rack 8b, and these gears are adapted to move the head 9 up and down by the rotation of the motor 12 to adjust the focus. Reference numeral 15 includes a lens 15a and a light emitting element 15b such as an infrared diode, and is fixed to one side of the head 9 (the right side in FIG. 2). Reference numeral 16 includes a lens 16a and a light receiving element 16b. A light projecting unit 16 is located on the other side of the head 9 (left side in Figure 2).
A light receiving part 17 is attached to the inner bottom surface of the head 9 so as to be able to slide from side to side, and has a predetermined distance (baseline length) between the light receiving part 17 and the part directly below the lens 16a. The lever 18 is parallel to the guide column 8 and is fixed on the rotary plate 7 so as to pass through the head 9, and has a cam on the front. Rangefinder cam with groove 18a (see Figure 5), 19 is the other end (right end) of lever 17
These are sliding pins that are fixed to the cam groove 18a and have their tips slidably fitted into the cam grooves 18a.
This constitutes a well-known distance measuring mechanism in which the angle formed by the optical axis of the lens is changed. 20 is a screen.
The light-receiving element 16b is configured to be able to separately sense the amount of light received at portions A and B on the left and right with respect to the center. 21 and 22 are AC amplifiers that amplify the outputs from these parts A and B, respectively; 23 is a differential amplifier that compares the outputs from both AC amplifiers 21 and 22, amplifies the output difference, and inputs it to the motor 12; Reference numeral 24 denotes an oscillator that causes the light emitting element 15b to emit light, and together with the above-mentioned head vertical movement mechanism and distance measuring mechanism, constitutes an automatic focus adjustment device 25. That is,
In this device 25, as shown _{in FIG} .
~3m), the oscillator 24 during on operation
As a result of the operation, the infrared rays emitted from the light projecting section 15 are projected onto the screen 20 within an area that is imaged by the size of the effective light receiving surface of the light receiving element 16b, and are reflected. is screen 2
0 position R ₂ (about 2m) as a standard point, front and rear R ₁ , R ₃
The distance _{difference is} calculated as the deviation of _the received light image on the light receiving surface
It is now possible to detect this and correct it. The amount of light received by the left and right parts A and B of the light receiving element 16b
When a difference occurs between I _A and I _B , the motor 12 is operated by the output from the differential amplifier 23. If I _A > I _B , the motor 12 is operated clockwise, and if I _A < I _B , the motor 12 is operated counterclockwise.
are rotated to move the head 9 up and down (3rd
The light receiving unit 16 is rotated in conjunction with this, and when I _A = I _B , the rotation of the motor 12 is stopped, thereby performing automatic focus adjustment. . In addition, the above distance meter cam 1
8, the cam groove 18a is formed linearly or curved to be inclined at an angle θ with respect to the vertical line, as shown in FIG. This is set based on the relationship between (the amount of upward movement of the head 9) Y and the relative amount of movement X of the light-receiving image on the light-receiving element 16b.

FIG. 6 shows the control circuit of the overhead projector of the present invention, and 26 is a dimming circuit connected in series with the light source ₂ and connected to the power source P via the transformer T1. Fixed resistance for
Connect R ₁ and variable resistor R ₂ for dimming (only a conductor is required when used only for full light) in parallel at one end, and use switching terminals a ₁ and a ₂ at the other ends, respectively.
Furthermore, the switching terminals a ₁ and a ₂ and a movable contact piece b connected to the light source 2 constitute a switching switch SW ₁ . Further, 27 is connected to the automatic focus adjustment device 2 via a switch SW ₂ consisting of terminals c ₁ and c ₂ and a movable contact piece d.
5 and is connected to the power supply P in parallel with the dimmer circuit 26 via the transformer _T2 , and is in an inactive state or in an active state by turning off or on an external switch (not shown). Then, switch the movable contact piece b of the changeover switch SW ₁ to the terminal a ₁ side and the movable contact piece d of the switch SW ₂ to the terminal c ₁ side, or move the movable contact piece b of the changeover switch SW ₁ to the terminal a ₂ side. It has the function of switching the movable contact piece d of the switch SW ₂ to the terminal c ₂ side. Note that SW ₀ is a power switch.

Since the overhead projector according to the present invention is constructed as described above, the power switch is
When SW ₀ is turned on, the external switch of relay 27 is initially off, so the relay 27 does not operate, and as a result, the movable contact b of changeover switch SW ₁ is on the terminal a ₁ side, so the fixed resistance R ₁ brings the light source 2 into a dimmed state, and at the same time, since the movable contact piece d of the switch SW ₂ is on the terminal c ₁ side, the automatic focus adjustment device 25 is turned on, and focus adjustment is performed according to the above principle. When the focus state is reached, the automatic focus adjustment device 25 stops operating. Next, relay 27
When the external switch is turned on and the relay 27 is activated, the movable contact b of the changeover switch _SW1 is connected to the terminal.
Since it is switched to the a ₂ side, the light source 2 becomes fully illuminated by the action of the variable resistor R ₂ , making it possible to observe the projected image. At the same time, the movable contact piece d of the switch SW ₂ is switched to the terminal c ₂ side, so it is automatically activated. The focusing device is turned off. Therefore, there is no possibility that the automatic focus adjustment device will malfunction in full light conditions.

As mentioned above, the overhead projector according to the present invention has an important practical advantage in that there is no possibility that the automatic focusing device will malfunction in full light conditions.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway side view of an embodiment of an overhead projector according to the present invention; FIGS. 2 and 3 are a partially cutaway plan view and a partially cutaway rear view of the head and surroundings of the above embodiment, respectively; FIG. 4 is an explanatory diagram showing the principle of the automatic focus adjustment device of the above embodiment, and FIG.
The figure shows the relationship between the position of the sliding pin of the distance meter cam and the position of the light receiving element in the above embodiment, and FIG. 6 is a diagram showing the control circuit of the above embodiment. 1...Projector main body, 2...Light source, 3...
... Fresnel lens, 4... Mounting stand, 5... Rest, 6... Support, 7... Rotating plate, 8... Guide support, 9... Head, 10... Projection lens, 11...
... Reflector, 12 ... Motor, 13 ... Intermediate gear,
14...Bearing part, 15...Light emitter part, 16...Light receiving part, 17...Lever, 18...Distance meter cam, 19
...Sliding pin, 20...Screen, 21, 22
... AC amplifier, 23 ... Differential amplifier, 24 ...
Oscillator, 25... automatic focus adjustment device, 26... dimming circuit, 27... relay, SW ₁ ... changeover switch, SW ₂ ... switch, SW ₀ ... power switch.

Claims (1)

[Scope of utility model registration request] In an overhead projector equipped with an automatic focus adjustment device that automatically measures the distance from the head to the screen and automatically adjusts the focus of the projected image using a distance measuring mechanism consisting of a light emitter and a light receiver, the light source a dimming circuit that can be switched to either a dimming side that puts the light source in a dimming state or a full-lighting side that puts the light source in a full-light state; a relay that can be switched, when the relay is in an inoperative state, the dimmer circuit is set to the dimming side, and at the same time the automatic focus adjustment device is turned on, and when the relay is in the operative state, the dimmer circuit is set to the full light side. An overhead projector characterized in that the automatic focus adjustment device is turned off at the same time as the projector is turned on.