JPH05275070A - Discharge tube for exposure - Google Patents

Abstract

PURPOSE:To hold an optimum temperature of a tube wall homogeneously through the entire length of a discharge tube by varying the heating value per unit in the longitudinal direction of a heater so that the temperature of the tube wall becomes homogeneous at the time of turning the heater ON. CONSTITUTION:A heater which is a characterized part of a discharge tube is formed as follows. In a heater unit 40, a nichrome heater 42 is embedded in a wavy form into an insulator 41 of arc-shaped cross section, by which the outer periphery of a fluorescent lamp 3 is surrounded except for an emission part. A thermistor 43 put almost in the center of the length of the heater between the both ends is connected to a connector 44 connected to a main print circuit board, and a temperature fuse 45 is provided in the middle of a lead connecting the connector to the end part of the heater in the reverse side. The density of the waveform of the nichrome heater 42 is changed according to the distribution of the heating value. The optimal temperature of a tube wall can be held through the entire length of a discharge tube, and unevenness in the image density can thus be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a discharge tube for exposing an original of an electrophotographic copying machine, in which a heater is provided along the outer peripheral surface of the discharge tube.

[0002]

2. Description of the Related Art In an electrophotographic copying machine, for example, as shown in FIG. 7, a document 2 placed on a contact glass 1 is exposed by moving a fluorescent lamp extending in a direction orthogonal to the scanning direction in the scanning direction. The photoconductor 5 is exposed by the scanning and moving optical system 4, or, as shown in FIG. 8, the moving document 6 is illuminated by the fixed fluorescent lamp 3 and the reflected light is reflected by the rod lens array. And the like is projected onto the photoconductor 5 via the fixed optical system 7 to expose the document, an electrostatic latent image corresponding to the document image is formed on the photoconductor 5, and a toner image is developed and transferred to a transfer sheet. Then, fix it and make a copy.

By the way, the fluorescent lamp is a mixed gas discharge tube of mercury and argon, which excites the phosphor coated on the inner wall of the glass tube mainly by 253.7 and 185.0 nm lines in the transition spectrum of mercury atoms due to discharge. It emits light, but the 253.7 and 185.0 nm rays have a relatively low vapor pressure of mercury and a strong radiant intensity. Therefore, the luminous efficiency of a fluorescent lamp is affected by the mercury vapor pressure, in other words, the ambient temperature, and is therefore optimal. Luminous efficiency is lowered at a temperature lower or higher than the ambient temperature of 40 ° C.

Therefore, for example, the actual exploitation 60-166954
As disclosed in Japanese Laid-Open Patent Publication No. 2003-242242, there is known an electrophotographic copying machine in which a heater is mounted along the outer peripheral surface of an exposing fluorescent lamp.

FIG. 9 is a view showing an example of a light control section of a fluorescent lamp equipped with a heater. A heater 31 is attached along the outer peripheral surface of the fluorescent lamp 3, and a thermistor 32 for detecting the temperature of the tube wall is provided at the center of the length of the fluorescent lamp. A dimming sensor 33 for detecting the amount of light emitted from the fluorescent lamp 3 is provided at the center of the length of the fluorescent lamp. The fluorescent lamp 3 is connected to the fluorescent lamp regulator 34, and the heater 3
1, the thermistor 32, the dimming sensor 33, and the fluorescent lamp regulator are connected to a main printed circuit board (main PCB).

According to the lighting timing of the fluorescent lamp, the main P
A dimming signal (LOW active PWM signal) is sent from the CB to the fluorescent lamp regulator. The fluorescent lamp is turned on, and a part of the light emitted from the fluorescent lamp is input to the dimming sensor 33. The output of the light control sensor 33 is the CPU in the main PCB.
Input to (A / D port). The output of the dimming sensor after A / D conversion is compared with a target value (determined by the density notch of the operation unit 36 or the like), and if it is less than the target value, the duty becomes small. The duty of the dimming signal is 20 to 100%. The operation of determining the duty of the dimming signal based on the difference between the target value and the control amount (here, the value after A / D conversion of the output of the dimming sensor 33) is performed by the CPU, R in the main PCB.
This is performed by a microprocessor system including OM and RAM, and the output is output via the I / O element.

A dimming sensor 33 is attached to the center of the length of the fluorescent lamp, and negative feedback is applied so that the light quantity at the center of the fluorescent lamp matches the target value.

As described above, since the heater is on / off controlled by the thermistor for detecting the temperature of the fluorescent lamp tube wall temperature, the tube wall temperature is kept almost constant at the set temperature at the thermistor installation position. Since the density is traditionally uniform, at other positions, it is affected by the ambient temperature and heat generated by the preheater of the fluorescent lamp itself, causing temperature unevenness especially in the longitudinal direction, and as a result, negative feedback is applied. However, the amount of light varies depending on the temperature distribution, which causes unevenness in the density of the copy image, thus degrading the image quality.

[0009]

SUMMARY OF THE INVENTION In view of the above problems of the conventional document exposure discharge tube having a heater provided along the outer peripheral surface thereof, the present invention maintains the optimum tube wall temperature over the entire length of the discharge tube. Therefore, it is an object of the present invention to provide an exposure discharge tube that does not cause unevenness in image density.

[0010]

In order to solve the above-mentioned problems, the exposure discharge tube of the present invention provides a discharge amount when the heater is not provided with the heat generation amount of the heater per unit length in the longitudinal direction of the heater. It is characterized in that the tube wall temperature when the heater is turned on is changed so as to be a uniform temperature in accordance with the tube wall temperature of the tube.

[0011]

With the above structure, by turning on the heater of the discharge tube, the temperature of the tube wall becomes uniform over the entire length in the longitudinal direction, and the luminous efficiency of the discharge tube becomes the same everywhere in the longitudinal direction. Is eliminated, and a high-quality copy without image density unevenness can be obtained. If the tube wall temperature is set to a temperature at which the luminous efficiency is maximized, the luminous efficiency of the discharge tube is maximized over the entire length.

[0012]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a diagram showing an example of a tube wall temperature distribution in the longitudinal direction of a fluorescent lamp under various conditions. In the figure, the solid line is the temperature distribution without a heater, the broken line is the temperature distribution when a heater having a constant amount of heat generation per unit length is turned on, and the dashed-dotted line is the entire length of the fluorescent lamp aimed at by the present invention. Shows a temperature distribution in which the temperature is around 40 ° C. at which the maximum luminous efficiency is obtained.

FIG. 2 shows a light amount distribution (relative value) in the longitudinal direction of the fluorescent lamp corresponding to the temperature distributions shown by the solid line, the broken line and the one-dot chain line shown in FIG. The light quantity of the fluorescent lamp changes depending on the ambient temperature (≒ tube wall temperature) as described above, but when used as an exposure lamp of a copying machine, the lighting time is often less than 1 minute, so the self-heating effect is small and the light quantity depends on the tube wall temperature Changes. In FIG. 2, the three distribution curves match at the center of the length of the fluorescent lamp because the dimming sensor is mounted at the center of the fluorescent lamp as described above and the negative feedback is set so as to match the target value. It is because it is hung.

In the present invention, as shown in FIG. 3, the tube wall temperature distribution shown by the one-dot chain line in FIG. 1, which gives a substantially uniform light amount distribution over the entire length shown by the one-dot chain line in FIG. As shown in, the distribution of the heat generation amount per unit length of the heater is made to correspond to the pipe wall temperature when there is no heater, and the pipe wall temperature distribution curve is rotated around a horizontal line and turned upside down. ..

FIG. 4 and FIG. 5 are a side view and a sectional view showing an example of a heater unit that can obtain such a calorific value distribution. The heater unit 40 has a nichrome wire heater 42 embedded in a wavy shape in an insulator 41 having an arc-shaped cross section surrounding the outer peripheral portion of the fluorescent lamp 3 excluding the light emitting portion, and is provided at both ends and about the center of the length. The thermistor is connected to the connector 44 connected to the main PCB. A thermal fuse 45 is provided in the middle of the conductor connecting the connector 44 and the end of the heater on the opposite side. The nichrome wire heater 42 changes the waveform density according to the distribution of the amount of heat generation. That is, the density is increased in a portion requiring a large amount of heat generation, and the wavy density is decreased in a place where a small amount of heat generation may be required.

Therefore, the calorific value per unit length changes according to the density of the nichrome wire heater 42, and the required calorific value distribution can be obtained.

When it is difficult to flatten the temperature of the fluorescent lamp tube wall with one heater due to the complicated temperature distribution of the tube wall without the heater, a short heater unit 50 is formed as shown in FIG. Similar to the heater unit shown in FIGS. 4 and 5, the unit is configured such that a nichrome wire heater 52 is embedded in an insulator 51, a thermistor 53 and a temperature fuse 55 are provided in the central portion, and are connected to a main PCB via a connector 54.
By dividing the fluorescent lamp into a plurality of parts in the longitudinal direction and arranging the short heater units 50 at the respective parts and independently controlling the temperature, the complicated tube wall temperature can be obtained without the heater. Even a fluorescent lamp having a distribution can have a flat temperature distribution, and as a result, the light amount distribution in the longitudinal direction of the fluorescent lamp can be flat.

[0019]

As described above, according to the present invention, since the light quantity distribution of the discharge tube for exposing the original of the electrophotographic copying machine can be made flat, the unevenness of the image density of the copy can be eliminated and the image quality can be improved. The effect is obtained.

[Brief description of drawings]

FIG. 1 is a curve diagram showing an example of a tube wall temperature distribution of a fluorescent lamp under various conditions.

FIG. 2 is a curve diagram showing a light amount distribution with respect to each tube wall temperature distribution shown in FIG.

FIG. 3 is a curve diagram showing an example of a heat generation amount distribution of a heater provided in a discharge tube according to the present invention.

FIG. 4 is a side view showing a configuration of an embodiment of a heater provided in the discharge tube of the present invention.

FIG. 5 is a sectional view thereof.

FIG. 6 is a side view showing the configuration of another embodiment of the heater provided in the discharge tube of the present invention.

FIG. 7 is a sectional view showing an example of an exposure apparatus of an electrophotographic copying machine.

FIG. 8 is a cross-sectional view showing another example of the exposure device of the electrophotographic copying machine.

FIG. 9 is a block diagram showing an example of a light control unit of a fluorescent lamp equipped with a heater.

[Explanation of symbols]

 3 Fluorescent lamp (discharge tube) 40, 50 Heater unit 41, 51 Insulator 42, 52 Nichrome wire heater (heat generating element) 43, 53 Thermistor 44, 54 Connector

Claims (3)

[Claims] 1. In a discharge tube for exposing an original of an electrophotographic copying machine, wherein a heater is provided along the outer peripheral surface of the discharge tube, the heater is provided with a heating value distribution of the heater per unit length in the longitudinal direction of the heater. A discharge tube characterized in that the tube wall temperature when the heater is turned on is made uniform so as to correspond to the tube wall temperature of the discharge tube when the heater is not turned on. 2. A plurality of heaters corresponding to each portion obtained by dividing one discharge tube into a plurality of portions in the longitudinal direction and a temperature detector corresponding to each heater as a means for changing the heat generation amount of the heater in the longitudinal direction. 2. The discharge tube according to claim 1, further comprising: and each heater being independently controllable. 3. The discharge tube according to claim 1, wherein the density per unit length of the heating element of the heater is changed in the longitudinal direction as a means for changing the amount of heat generated by the heater in the longitudinal direction. ..