JPS6268362A - Light source device using fluorescent tube - Google Patents

Abstract

PURPOSE:To obtain always a stable output independently of using a conditions by detecting the luminous quantity of a fluorescent tube and controlling the anode voltage based on the value to correct illuminance changes by a lighting time. CONSTITUTION:An original reader uses light from a light source device D using the fluorescent tube 1 to irradiate the original 2, the reflected light from the original 2 is led to an image sensor 4 via an SELFOC lens array 3. The light source device D is provided with a photodetection means 5 comprising a photodiode at a position receiving only light from the fluorescent tube 1, the signal detected by the photodetection means 5 is processed by a luminous quantity correction circuit 6 thereby controlling the anode voltage fed to the fluorescent tube 1. Thus, always nearly constant illumination is obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a light source device using a fluorescent tube, and in particular, it is equipped with a light amount correction function to control the anode voltage and keep the illuminance constant.
The present invention relates to a light source device for a document reading device.

[Prior art and its problems]

A contact image sensor using a long reading element having a sensor portion having the same width as the document does not require a reduction optical system, and is therefore expected to be widely used in small document reading devices.

Conventionally, light sources for document reading devices using this contact type image sensor include fluorescent lamps and LEDs (Light Em).
Itting [) iode) array etc. are recommended.

However, although fluorescent lamps can provide a sufficiently large amount of light, they are dark at both ends, so in order to obtain uniform illuminance over the entire width of the document, it is necessary to use a fluorescent lamp that is wider than the width of the document. It was loud.

On the other hand, when an LED array is used as a light source, there are problems such as not only the amount of light cannot be obtained sufficiently, but also the amount of light varies greatly depending on the lot of LEDs, so it is difficult to uniformly irradiate the light.

Therefore, in recent years, the principle of fluorescent display tubes has been developed in which thermionic electrons emitted by heating the filament are attracted to an anode formed on the tube wall, stimulating the phosphor coated on the anode to emit light. Fluorescent tubes applied as light sources have been attracting attention as light sources for document reading devices.

This fluorescent tube has a relatively large amount of light and a narrow half-width, so it is less affected by chromatic aberration and can be applied to high-speed, high-resolution document reading devices.

However, as time passes after the fluorescent tube is turned on, the temperature of the filament rises to about 650'C, which causes the temperature of the phosphor near the filament to rise as well, reducing the amount of light. This was an inconvenience. (Changes over time) Also, after long-term use, the luminous efficiency of the phosphor decreases due to deterioration of the phosphor and contamination by evaporated matter from the negative electrode (cathode), resulting in a decrease in the amount of light. there were. (Changes over time) Therefore, the illuminance changes depending on the conditions of use, and when used in a document reading device, the output voltage of the image sensor is not uniform, which has become a serious problem.

The present invention has been made in view of the above-mentioned circumstances, and provides a light source device using a fluorescent tube that is uniform in the length direction and is capable of emitting light that is stable over time and over time. The purpose is to

[Means for solving problems]

Therefore, in the present invention, a light detection means for detecting the amount of light from the fluorescent tube is provided near the fluorescent tube, and by controlling the anode voltage according to the detected value by this light detection means, the amount of light is always uniform. I'm trying to be able to play iLF.

[For production]

For example, if the output voltage of the photodetection means is set to l(-%(light amount is λ)
1. Compare with the corresponding reference voltage, and if the reference voltage is higher than the reference voltage, increase the anode voltage, and if it is lower, decrease the anode voltage so that the amount of light detected by the receiver is always equal to the reference amount of light. The anode voltage is controlled in this manner, and by such control it is possible to always obtain a uniform amount of light.

〔Example〕

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

1 and 2 are a perspective view and a side view showing the structure of a document reading device using a light source device using a fluorescent tube according to an embodiment of the present invention.

This document reading device illuminates two surfaces of the document with light from a light source device using a fluorescent tube 1, and guides the reflected light from the document 2 to the image sensor 9-4 via the Selfox lens array 3. This is what I did.

The light source device is provided with a light receiving means 5 made of a photodiode at a position where it can receive only the light from the fluorescent tube 1, and the signal detected by the light receiving means is processed by a light amount correction circuit 6, The anode voltage supplied to the electrode is controlled.

As shown in FIG. 3, the light intensity correction circuit is configured by an illuminance detection circuit 7 that converts the light intensity of the fluorescent tube 1 detected by the light receiving means 5 into a voltage Vin, and a reference illuminance setting means 8.
A comparison control circuit 9 that compares a reference voltage Vref corresponding to the IB illuminance with a voltage Vin and controls the anode voltage 11iII so that the light amount of the fluorescent tube 1 becomes equal to the reference illuminance, and the output of the comparison control circuit The fluorescent lamp drive circuit 10 applies an anode voltage to the fluorescent lamp to drive the fluorescent lamp.

Here, the relationship between the anode voltage of the fluorescent tube and the illuminance is as shown in FIG. For the base r% illuminance, select the illuminance when a voltage smaller than the rated value is applied to the anode voltage, and when the illuminance decreases due to aging or change, the corrected anode voltage exceeds the rated value (Vc). set to no value. In reality, if the illuminance decreases by 30% due to aging or aging, then the reference illuminance is 70% or less of the illuminance when the rated voltage VC is applied to the anode voltage, and the voltage at that time is v
Let it be rer.

Next, the operation of this light source device will be explained.

First, the amount of light from the fluorescent tube detected by the light receiving means 5 is
It is converted into a voltage value vin in the illuminance detection circuit 7 and output to the comparison control circuit.

On the other hand, the reference illuminance setting means 8 sets a reference voltage vrer corresponding to the reference illuminance determined in the manner described above for the comparison control circuit 9.

Then, in the comparison control circuit 9, the voltage value Vin is compared with base<%j voltage vre[, and if the reference voltage Vref is larger, the anode voltage of the fluorescent tube is increased, and if it is smaller, it is decreased. , the anode voltage is controlled so that the amount of light detected by the light receiving means 5 is always equal to the value.

Further, based on the value of the anode voltage determined by the comparison control circuit 9, the fluorescent tube drive circuit 10 drives the fluorescent tube.

Curve N showing the relationship between lighting time and illuminance between the light source device according to the embodiment of the present invention that performs light amount correction in this manner and the conventional light source device that does not perform light amount correction.

O is shown in FIGS. 5 and 6. Here, the horizontal axis is lighting time (min>1.1) and the axis is illuminance (IX). Figure 5 shows the change over time (min), and Figure 6 shows the change over time (x10
3h). As is clear from these figures, it is possible to maintain almost constant illuminance at all times.

Note that this light source device is a contact type image sensor called SenCC.
It can also be applied to document reading devices, copying machines, etc. using D.

Furthermore, although the present invention can compensate for changes in illuminance over time or over time, when combined with an image sensor and Selfox lens, variations in illuminance in the longitudinal direction of fluorescent tubes, and changes in the image sensor and Selfox lens Variations may cause variations in the output of the image sensor. Therefore, it is even more effective to combine various shading corrections, and highly accurate output correction becomes possible.

〔effect〕

As explained above, according to the light source device of the present invention,
Since the amount of light from the fluorescent tube is detected and the anode voltage is controlled based on this value, changes in illuminance due to lighting time are compensated for.
It is possible to always obtain a stable output without using the condition t31.

[Brief explanation of drawings]

1 and 2 are diagrams showing the structure of a document reading device according to an embodiment of the present invention, FIG. 3 is a block diagram of a light amount correction circuit of the same device, and FIG. 4 is a diagram of a fluorescent tube of the same device. Figures 5 and 6, which show the relationship between illuminance and reference voltage, are comparative diagrams showing the relationship between lighting time and illuminance between the light source device of the same device and the conventional light source device. DESCRIPTION OF SYMBOLS 1... Fluorescent tube, 2... Document, 3... Selfox lens array, 4... Image sensor, 5... Light receiving means, D... Light source device, D... Light amount correction circuit ,7
... Illuminance detection circuit, 8... Reference illuminance setting means, 9.
... Comparison control circuit, 10... Fluorescent tube drive circuit, N...
- Curve showing the light source device of the embodiment of the present invention, 0...Curve showing the light source device of the conventional example. Figure 1 Figure 2 Figure 3 (■ Orchid) (ve) Figure 4 Figure 6 x*O' (h)

Claims (1)

[Claims] The anode comprises an anode disposed on a part or the entire inner wall of the vacuum container, and a phosphor layer coated on top of the anode, and emits thermoelectrons emitted by heating the filament. A light source device using a fluorescent tube that causes the phosphor layer to emit light by colliding with the anode, comprising: a light amount detecting means for detecting the light amount of the fluorescent tube; and a light amount detecting means for detecting the light amount of the fluorescent tube; 1. A light source device using a fluorescent tube, comprising: a light amount correction circuit including an anode voltage control means for controlling a voltage applied to the anode so that the voltage always exhibits a reference value.