JPH0411062B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an image projection device, and more particularly to an image projection device suitable for a non-impact printer.

Prior Art In recent years, information processing devices such as computers, facsimile machines, and word processors have become rapidly popular.
For printers, which are one of the output devices, there are increasing demands for high speed, high image quality, low cost, and small size. Recording methods in printers are roughly divided into impact methods and non-impact methods.In the past, data was processed in alphanumeric characters, but as Japanese information processing progressed, the proportion of kanji output increased. There is a transition from impact methods to non-impact methods.

Among non-impact printers, there is an electrophotographic recording method as a high-quality printer. The image projection device used in this method requires a large laser oscillator, a polygonal rotating mirror for scanning, and a modulator, and the method of scanning the laser beam with a mirror is well known, but these optical systems The disadvantages include that the entire machine becomes large because it occupies a large space, and that each member and device are expensive.

As an alternative to such large image projection devices,
Recently, small image projection devices using light emitting diodes (LEDs), optical fiber tubes (OFT), semiconductor lasers, etc. have been proposed, and some of them use liquid crystal cells arranged in an array as optical switching elements. There are shutters that project images when opened and closed in response to electrical signals.

An image projection device using such a shutter array is shown in FIG. In this figure, an image projection device 1 consists of a shutter array 11 using a large number of liquid crystal cells and a lamp 12.
It has aperture rows as shown in Figures a and b, and these apertures are selectively opened and closed by signals from a signal generator 13 that generates electrical signals representing images. On the other hand, since the lamp 12 is always on, the image projection device 1
From there, a light image corresponding to the image signal is formed on the photoreceptor 2.
projected on. The photoreceptor 2 is charged by a charging device 3, and a latent image is formed on the surface by the light image,
The image is developed by the developing device 4, transferred to the paper 7 with the aid of the transfer discharge device 5, and fixed by the fixing roller 8. On the other hand, the photoreceptor 2 is cleaned by a cleaner 6.

Regarding the liquid crystal shutter array 11, Japanese Patent Application Laid-Open No. 1986-
This is disclosed in Japanese Patent No. 93568, in which a fluorescent lamp is used as a light source for exposing a photoreceptor through a liquid crystal shutter array. Although it is sometimes easy to select the emitted color of fluorescent lamps by changing the type of phosphor, the most suitable light source has a brightness distribution that uniformly illuminates the LCD shutter array in the longitudinal direction. This is because.

However, the luminance distribution in the longitudinal direction of the fluorescent lamp is well uniform near the center of the lamp, but the luminance gradually decreases as it approaches the ends. Therefore, the total length of a fluorescent lamp that can actually be used must be approximately 200 mm or more longer than the effective length of the liquid crystal shutter array. Therefore, although a device using a liquid crystal shutter array including a lamp should be more compact than the above-mentioned large-sized image projector, it has the disadvantage that the length of the lamp is unnecessarily longer than the effective recording length.

The detailed construction of an image projection device having a light shutter array is shown in FIGS. 3a and 3b, and the above drawbacks will be explained in more detail. In FIGS. 3a and 3b, the light emitted from the lamp 12 is transmitted to the optical shutter array 11.
The light is selectively modulated into an optical image signal, and this optical image signal is imaged onto the photoreceptor 2 by the imaging lens 15. In order to illuminate the minute shutter opening, the lamp 12 must first have high brightness.
It is used by converging the light beam onto the shutter opening using a cylindrical lens 14 or the like. This cylindrical lens 14 has a fourth
As shown in the figure, cylindrical, semi-cylindrical,
There are two vertical semi-cylindrical types and various other types.

Second, the brightness distribution in the longitudinal direction of the array must be uniform. This uniformity of brightness distribution means that uniform light reaches each shutter aperture, and small variations in the size of the aperture, that is, within a small range of several tens of microns to 1 mm, become a problem. This means that there should not even be dark or bright spots of such size.

Conventionally, fluorescent lamps have been widely used as a light source that satisfies this kind of brightness distribution, but as mentioned earlier, the brightness distribution of fluorescent lamps has a severe drop at both ends, and only the central part is used as an effective part. This is the current situation, and uneven brightness occurs due to uneven coating of the fluorescent substance on the inner wall of the glass tube.

Figure 5 shows that the total length of the glass tube excluding the cap is 400 mm.
This is an example of the brightness distribution of a fluorescent lamp (green) for a copying machine, which has a length of 100 mm at each end.The brightness drops sharply at each end of the lamp, about 100 mm long, and this tendency becomes stronger as the lamp is used. Therefore, when a fluorescent lamp is used as a light source for an image projection device, the length of the lamp must be at least 200 mm longer than the effective length of the optical shutter array, which poses the problem of making the entire image projection device larger. Ta. For example, an optical signal output device for A4 paper (width 210 mm) had to be approximately twice as large as the effective output width.

In addition to fluorescent lamps, it is also possible to use incandescent lamps, and there are some known incandescent lamps that are elongated like the above-mentioned fluorescent lamps. For example, a halogen lamp used for illuminating a document in a copying machine is one example. This is shown in FIG. As shown in the figure, in this incandescent lamp, the filament 16 is in the form of a coil, and anchor members 18 that support each coil and prevent vibration are provided at various locations, so these are imaged on the projection plane, resulting in uneven illuminance. However, since the bright spots are dispersed, bright spot unevenness occurs, and the requirement for uniformity of the brightness distribution cannot be met.

OBJECTS OF THE INVENTION It is an object of the present invention to solve these problems and to significantly downsize an image projection apparatus having an optical shutter array as an optical switching means.
Still another object of the present invention is to miniaturize an electrophotographic printer using an image projection device and expand its range of use.

Structure of the Invention In order to achieve the above object, according to the present invention,
An image projection device comprising at least an illumination means and an optical switching element array that opens and closes according to an electric signal, and projects an image when the optical switching elements of the optical switching element array open and close according to an image signal. The illumination means comprises an elongated glass tube, a straight single wire filament disposed inside the glass tube, and a means for applying tension to the filament, and the length of the straight single wire filament is set to the length of the optical switching element array. An image projection device is provided, characterized in that it is an incandescent lamp whose length is longer than its effective length.

Embodiment The image projection device of the present invention has the same configuration as the image projection device 1 in FIG. 1 or the image projection device 1 in FIG. 3, except that the fluorescent lamp 12 is replaced with another illumination means, and Specifically, as shown in Figure 1,
It consists of an illumination means and a light switching means, and if necessary, a light focusing means such as a cylindrical lens 14 may be provided as shown in FIG. Various types of lenses can be used. In addition, a typical example of an optical shutter array as a light switching means is a liquid crystal cell, but other light switching means may also be used.In short, it turns on and off the transmission or reflection of light according to electrical signals. It is fine as long as it is something.

The illumination means of the image projection apparatus according to the present invention will be described below with reference to the drawings. FIG. 7 shows an example of illumination means that will be helpful in understanding the present invention.
This lamp 20 has an elongated glass tube 21 and a straight single wire filament 22 disposed inside the tube.
3 and 23 are connected, and caps 24 and 24 are provided at both ends of the glass tube 21. Generally, the material for the straight single wire filament 22 is preferably tungsten, but other materials may be used as long as they emit light when energized. Further, in order to prevent filament arrangement, etc., it is preferable to fill the inside of the tube 21 with an inert gas such as argon gas, and it is also preferable to fill it with halogen gas.

FIG. 8 shows an embodiment of the present invention, in which a spring 25 is provided at the end of the filament 22 in the lamp 20 as the illumination means shown in FIG. This spring applies tension to the filament 22, thereby causing the filament 2
2 can be held without slack. In particular, even if the filament 22 is stretched due to heat during lighting, the tension is applied by the spring 25, so that the filament is maintained in a tensioned state without sagging. If there is no spring 25 as a tension applying means, the position of the filament 22 will be slightly shifted due to the heat during lighting, and this positional shift will change the illuminance on the shutter array. That is, the spring 25 prevents a position error of the filament 22 during lighting, prevents a change in illuminance on the shutter array, and prevents unevenness in the amount of light. This spring 25 may also serve as a part of the lead, and has a length of about 5 to 25 mm, for example.

In an incandescent lamp, the light emitting part is a minute filament, and the luminance of the light emitting part itself is generally higher than that of a fluorescent lamp in which the entire inner surface of the tube wall emits light. On the other hand, when the size of the light source is minute, it is necessary to accurately set the position of the light source in the optical system. For single wire filament lamps, the diameter of the filament depends on the desired brightness, but for tungsten filaments it is approximately 20 for A4 size (210mm width) in the range of 10 to 100W.
~200 μm. Because the diameter of the filament is thus small, care must be taken to obtain uniformity of the illuminance distribution in the width direction of the shutter array when irradiating the shutter opening with light.
Particularly when trying to efficiently utilize the luminous flux by concentrating the lamp light onto the shutter opening using a cylindrical lens, etc.
A minute error in the position of the filament causes a large change in the illuminance on the shutter array, which also affects the illuminance distribution in the array direction.

This problem can be solved by the spring 25 as a means for applying tension to the filament 22 during lamp operation, as described above. and,
Frosting the surface of the glass tube of the lamp is an additional solution. The frosting of the glass tube surface can be achieved, for example, by treating the tube surface with a hydrogen fluoride solution to make the tube surface micro-rough with a roughness of several microns to several hundred microns. The frosted surface of the lamp tube receives light from the filament and functions as a secondary light source, giving the appearance the same effect as widening the light emitting part. As a result, the optimal setting position for the cylindrical lens becomes wider,
Positioning becomes easy, and even if the positioning is rough, the illuminance distribution on the shutter opening can be made uniform in both the longitudinal and width directions of the array.

FIG. 9 is a diagram showing an example of the brightness distribution of the linear single-wire filament lamp 20 according to the present invention.
These are the measurement results when the length of the glass tube 21 excluding 24 is 250 mm. As is clear from the figure, in the case of a linear single-wire filament lamp, the brightness falls sharply at both ends, and the length of the falling part is shorter than that of a fluorescent lamp (Fig. 5), which is 10 to 15 mm at both ends. In the end, the length required for a single wire filament lamp is 24mm.
Including this, the length is only about 50 to 60 mm longer than the length at which uniform brightness can be obtained, that is, the effective length of the optical shutter array. Furthermore, the tube diameter of a single-wire filament lamp can be reduced to one-third or less of that of a fluorescent lamp, and the entire image projection device can be made much more compact than conventional ones.

Next, a specific prototype of the image projection device of the present invention will be described. In this prototype, the lamp 20 in FIG. 7 or 8 was replaced with the lamp 12 in FIG. 3a. The liquid crystal shutter array 11 has apertures with a pitch of 10 per 1 mm formed by sealing a liquid crystal material made of nematic liquid crystal with an optically active substance added between transparent electrodes.
is an acrylic resin rod lens with a diameter of 13 mm.
A linear single-wire filament lamp 20 was installed so that the filament 22 was located 40 mm from the liquid crystal shutter array 11. The linear single-wire filament lamp 20 was an incandescent lamp made by enclosing a tungsten filament with a diameter of 60 μm and a length of 225 mm in a glass tube with an outer diameter of 8 mm, and when a voltage of 40 volts at 50 Hz was applied, a current of 1 A flowed.
At this time, the light emitted from the liquid crystal shutter array 11 is guided by a self-ox lens (registered trademark: condensing light transmitter) onto a Se-Te photoreceptor that is charged to a surface temperature of 1000 volts and that moves at a linear velocity of 50 mm/sec. The surface potential of the photoreceptor during opening and closing operations of the liquid crystal shutter 11 was measured and found to be 350 volts and 750 volts, respectively. The electrostatic latent image thus created was developed using a single-component developing device to which a developing bias of 700 volts was applied, and the image was transferred and fixed onto plain paper. When the density of the obtained image was measured, a value of 1.3 was obtained.

Effects of the Invention As described above, according to the image projection device of the present invention, since a straight single wire filament is disposed inside the incandescent lamp as the illumination means, the effective illumination range can be extremely long. The length of the entire lamp can be made close to the effective length of the optical switching element array, and the length of the straight single wire filament is longer than the effective length of the optical switching element array, and this filament is given tension. , ensuring that the required illumination range is covered,
It is a small light source and can prevent minute positional deviations due to elongation due to heating of the thin filament during lighting, eliminating unevenness in light intensity, making it possible to obtain uniform illuminance over the entire area of the optical switch element array, improving image density. A uniform image projection device that is significantly smaller than conventional ones can be realized. As a result, a printer device using the image projection device of the present invention can also be made compact. In addition, since such printers can use a common electrophotographic image recording system except for the exposure optical system of the electrophotographic copying device, the image projection device that replaces the original exposure optical system can be made more compact. Therefore, conversion from a copying device to a printer device can be easily performed from both a design and manufacturing standpoint. Furthermore, since the image projection device of the present invention has been significantly miniaturized, it is easy to add and incorporate it into a part of an electrophotographic image recording system while leaving the exposure optical system in the copying machine, and it can be used as both a copying machine and a printer. To easily create an image recording device having multiple functions.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of a non-impact printer, FIGS. 2 a and b are plan views showing the arrangement of shutter arrays, FIGS. 3 a and b are side views and perspective views of a conventional image projection device, and FIG. 4 5 is a perspective view showing various cylindrical lenses, FIG. 5 is a graph showing luminance versus tube length of a fluorescent lamp, FIG. 6 is a front view of a conventional incandescent lamp, and FIG. 7 is a reference example for understanding the present invention. FIG. 8 is a front view of an incandescent lamp according to an embodiment of the present invention, and FIG. 9 is a graph showing luminance versus tube length of an incandescent lamp according to the present invention. DESCRIPTION OF SYMBOLS 1... Image projection device, 2... Photoreceptor, 4... Developing device, 11... Light shutter array (light switching means), 12... Fluorescent lamp, 14... Cylindrical lens, 20... Incandescent lamp according to the present invention , 21...
Glass tube, 22... Straight single wire filament, 2
4...cap, 25...spring.

Claims (1)

[Scope of Claims] 1. A device comprising at least an illumination means and an optical switching element array that opens and closes in response to an electric signal, and projects an image by opening and closing the optical switching elements of the optical switching element array in accordance with an image signal. In the image projection apparatus, the illumination means includes an elongated glass tube, a straight single wire filament disposed inside the tube, and means for applying tension to the filament, and the length of the straight single wire filament is set to the length of the straight single wire filament. An image projection device characterized in that it is an incandescent lamp whose length is longer than the effective length of an optical switching element array. 2. The image projection device according to claim 1, wherein the glass tube surface of the illumination means is frosted.