JPH01116665A - Light quantity control device such as printer using led head - Google Patents

Abstract

PURPOSE:To eliminate an influence given to a picture quality while a light quantity is controlled by detecting the ambient temperature of a semiconductor light source and making variable the duty of a semiconductor light source in accordance with the vibration of temperature. CONSTITUTION:When the back temperature of a semiconductor light source 1 is detected by a temperature detecting device 2, the change of the environmental temperature and the temperature due to the self-heating of the light source itself is present, and then, a control circuit 4 and a duty control circuit 5 make variable the duty of the semiconductor light source 1 and controls the light quantity in accordance with the variation of the temperature change. Thus, even when the light quantity fluctuation occurs accompanying the temperature change, the light quantity of the semiconductor light source can always be kept constant by making variable the duty.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a light amount control device for a printer or the like using an LED head, and in particular detects the temperature of a semiconductor light source such as an LED array, and detects changes in temperature. An LE in which the duty of the semiconductor light source is varied according to the amount of light to control the amount of light.
The present invention relates to a light amount control device for a printer using a D head.

[Conventional technology]

Conventionally, semiconductor light sources such as LEDs have been used in electrophotographic devices, such as printers using LED heads.

It has been known that such semiconductor light sources change their destination volume when their temperature fluctuates.

For this reason, a temperature sensor is installed around the semiconductor light source, and the heater is heated in accordance with the temperature change detected by the temperature sensor to maintain the semiconductor light source at a constant temperature, thereby keeping the volume at each destination constant. It was known that (
For example, see Japanese Patent Application Laid-Open No. 61-3764).

[Problem that the invention seeks to solve]

Such conventional devices have the following drawbacks.

(1) The semiconductor light source is controlled at a temperature higher than the environmental temperature (temperature inside the machine) (because it is easier to control the temperature at a constant temperature at a high temperature than at a low temperature), the luminous efficiency of the light source is If you try to obtain the same amount of light as at room temperature,
This requires a large amount of current to flow, requires a large-capacity power source, and is uneconomical.

(2) Since a semiconductor light source (for example, an LED) is kept at a high temperature, its lifespan is shortened.

(3) The internal temperature inside the aircraft increases.

(4) Power must be supplied to the heat-retaining Q heater, which is uneconomical.

(5) In conventional laser printers, a photodiode is placed on the back side of the laser diode's optical path and feedbank control is performed by detecting the amount of laser light.
When the D head is used as a light source, it is difficult to arrange a photodiode at such a position.

Furthermore, when positive development, which can be performed using conventional electrophotographic development technology, is performed using an LED head, the amount of light varies due to temperature changes due to self-heating, which affects image quality.

The present invention has been made to solve these conventional drawbacks, and detects the ambient temperature of the semiconductor light source and changes the duty of the semiconductor light source according to the amount of change in temperature, thereby reducing the amount of light. The purpose is to control and eliminate the influence on image quality.

[Means and effects for solving the problems] In order to achieve the above object, the present invention provides an electrophotographic apparatus equipped with a semiconductor light source as a light source for exposure. temperature detection means for detecting the temperature of the light source; receiving and processing a temperature information signal from the temperature detection means;
This device includes a control circuit that outputs a lighting control signal, and a light amount control circuit that receives the lighting control signal from the control circuit and outputs a lighting signal to the semiconductor light source.

In this way, the light intensity can be controlled by varying the lighting time duty, applied voltage, or applied current of the semiconductor light source in accordance with the amount of change in temperature detected by the temperature detection means.

As a result, the amount of light from the semiconductor light source, which until now has been dependent on temperature, can be kept constant, and the effect on image quality can be eliminated.

〔Example〕

Hereinafter, one embodiment of the present invention will be described based on the drawings. FIG. 1 is a schematic diagram of a light amount control device for a printer or the like using an LED head, which is an embodiment of the present invention.

In the figure, 1 is a semiconductor light source such as an LED array, 2 is a temperature detection signal such as a thermistor attached to the semiconductor light source 1, and 3 is an A/D that converts the temperature detection signal output from the temperature detection device 2 into a digital signal. a conversion (analog-to-digital conversion) circuit; 4 is a control circuit (CPU) that receives and processes the temperature information signal output from the A/D conversion circuit 3 and outputs a lighting control signal; 5 is a control circuit (CPU) that receives and processes the temperature information signal output from the A/D conversion circuit 3; This is a duty control circuit that receives a lighting control signal and outputs a lighting signal to the semiconductor light source 1.

The device configured in this way always uses the semiconductor light source 1.
The back surface temperature of the sensor is detected by the temperature detection bag W2. and,
When there is a temperature change due to the environmental temperature (temperature inside the machine) or the self-heating of the light source itself, the duty of the semiconductor light source 1 is varied by the control circuit 4 and the duty control circuit 5 according to the amount of the temperature change. to control the amount of light.

In this way, even if the light intensity fluctuates due to temperature changes, the light intensity of the semiconductor light source can always be kept constant by varying the duty.

FIG. 2 shows a specific example of the embodiment shown in FIG. 1, and the same reference numerals as in FIG. 1 indicate the same parts. This embodiment is an example in which an LED (light emitting diode) head is applied to electrophotography to realize positive development.

In FIG. 2, 1' is an LED array that is a semiconductor light source, 2' is a thermistor that detects the back temperature of the LED array 1' and outputs a temperature detection signal, 6 is a head block, and 7
8 is a photosensitive drum, 8 is a charging section, 9 is a developing section, 10 is a transfer section, and 11 is a cleaning section.

In such a configuration, the conventional technology and hardware can be used as is for the parts other than the exposure system including the photosensitive drum 7, and only the exposure system is newly equipped with an LED head.

The LED head consists of an LED array 1', a head block 6 to which it is attached, and a heat sink (cooling fins, blower, etc., which is attached to the head block 6 and dissipates heat from the LED array, but these are not shown). It consists of a thermistor 2' attached to the head block 6.

The thermistor 2' is embedded in the head block (Aj2 or other material with good thermal conductivity is used) 6 by suitable means such as screwing in order to reduce the influence of outside air.

The photosensitive drum 7 repeats the steps of charging, exposure, development, transfer, and cleaning according to a conventional electrophotographic process.

At this time, the LED array 1' generates self-heat by emitting light, so the amount of light decreases, but this is corrected by the A/D conversion (analog, digital conversion) circuit 3, the control circuit 4, and the duty control. This is circuit 5.

Next, the outline of the operation will be explained with reference to FIGS. 3 and 4. FIG. 3 shows a schematic operation flowchart, and FIG. 4 shows a characteristic diagram of the LED array.

As shown in FIG. 4, a semiconductor light source such as an LED array has a characteristic that the amount of light emitted decreases as the temperature rises. Therefore, by correcting the variation in the amount of light due to temperature changes by varying the duty, it is possible to always obtain a constant amount of exposure.

In FIG. 3, after turning on the power, the control circuit (CPU) 4 checks for disconnection in the thermistor 2'.

If this is not done, even if the temperature of the LED head is high, the thermistor will be disconnected, so it will be mistakenly determined to be low temperature, the ON duty will be minimized, and the printed sample will be affected by a black color.

When a disconnection is detected by the thermistor disconnection detection, the control circuit 4
sets the backside temperature of the LED head to 20°C and displays a message indicating that the thermistor is disconnected.

This is to prevent the printer from stopping its function even if the thermistor is disconnected.

Next, when thermistor disconnection is detected and the thermistor is normal, the control circuit 4 converts the back surface temperature of the LED head into a digital signal using the A/D conversion circuit 3, and calculates the light emission duty value based on the value. .

The result is set in the duty control circuit 5, and then
It will be printed.

By repeating this, the printing operation is performed.

However, in this type of control, the duty is not changed in the middle of the page, but at the beginning of the page.

In other words, the image quality does not change within one page. Also, one duty change is one step (for example, 0.
4%), and if more changes are required, the condition is set that the next change, that is, one step change between pages, is set to prevent the duty from changing suddenly. This is also to prevent large changes in image quality between the previous and subsequent print samples.

In addition, in the above embodiment, as the temperature detection means,
Although the case where a thermistor is used has been described, the present invention is not limited to such a device, and for example, a thermocouple, other temperature detecting element, or temperature detecting means may be used.

Details of the operation of the present invention will be explained based on FIGS. 5 to 8.

Figure 5 is a flowchart explaining the details of the operation of the present invention, Figure 6 is a diagram explaining the variation range, Figure 7 is a diagram explaining each timing and control relationship, and Figure 8 is the calculated value D1 of the light emission duty and the actual setting. FIG.

As shown in Figure 5 (Part 1), when the power is turned on,
The control circuit 4 has a reference duty D based on initial settings (for example, dial settings by the user). Set. The setting of this reference duty Do can be changed depending on changes in the sight of the LED head due to aging or the like. In the present invention, by detecting the back temperature of the LED head and controlling the duty, the upper side of the reference duty D0 is up to a positive change width DO (for example, +13% of Do), and the lower side is a negative change width D: (for example, It is controlled within 7% of Do. The control circuit 4 calculates the positive change width Di and the negative change width D based on the reference duty D0.

At this time, in order to prevent the duty from rising too much and causing temperature runaway in the LED head, it is limited to not exceed 80%, so as shown in Figure 6 CASE 1, the positive change width D'o is 80%. If larger, change this to 8
0%. Similarly, when the negative change width D; is larger than 80%, it is set to 80%. Of course, the CASE in Figure 6
In the case of 2, it is less than 80%, so the calculated Do, D,
Let be the positive change width and the negative change width.

Next, as shown in FIG. 5 (part 2), the control circuit 4 refers to a disconnection flag (not shown) in order to see if it has already been detected that the thermistor is disconnected. If the thermistor remains disconnected in the past, control is performed by assuming that the back temperature of the LED head is 20°C.

If there has been no disconnection in the past, temperature is detected when the photosensitive drum motor starts up or when the gate sensor output signal starts up. Here, the gate sensor is a paper detection sensor at the gate that has a claw for aligning the paper supplied from the paper feed tray to a certain position, and the paper is temporarily stopped on the claw to align the paper.

To detect a disconnection of a thermistor, for example, its resistance value is checked, and if it is a very large value such as infinity a certain number of times, for example, three times in a row, it is determined that the thermistor is disconnected.

Therefore, if a disconnection is not detected, the disconnection detection counter is reset, the back surface temperature of the LED head is measured, and control is performed accordingly. However, when a disconnection state is detected, a disconnection detection counter (not shown) is incremented.

When the disconnection detection counter counts "3", it is determined that the disconnection has occurred completely, and the back temperature of the LED head is assumed to be 20° C. and controlled, and a disconnection flag is set.

In this way, by selectively detecting the temperature at the time of the rise of the photosensitive drum motor and the time of the rise of the gate sensor output signal, it is possible to prevent the duty from being changed in the middle of a page.

That is, in the case of the first image in FIG. 7, temperature information is detected when the drum motor is on, but at this time, the information when the gate sensor is on is controlled not to be read.

The reason for this is that calculations are first performed using the data when the drum motor is on, so if calculations are then performed using the data when the gate sensor is on, the end of the calculation when the gate sensor is on is delayed and the page is interrupted. This is to prevent the duty from being changed in the middle of the page.

Then, as shown in FIG. 5 (part 3), the light emission duty D is calculated based on the temperature information detected (or assumed) in this way. -Then, it is determined whether the temperature information is the first temperature information detected after power-on, and if it is the first temperature information, that is, the temperature information detected when the photosensitive drum motor starts up,
The duty is changed by the number of steps proportional to the temperature. However, when the range of change exceeds the positive change range or negative change range D; as shown in Figure 8 (A),
Make it D'g or D-. If the temperature information is from the second or subsequent time after the power is turned on, a one-step control flow is entered. Here, processing is performed so that the duty does not change suddenly. Now, the memory capacity is 28=25
6 bits, when all 1, duty change 1
If it is 00%, the change for each bit will be approximately 0.4% (
'/zs-).

As shown in FIG. 5 (part 4), the light emission duty value thus determined is set in the duty control circuit 5, and a print cycle is started.

As a result of such control, L, which has changed due to temperature changes,
The amount of light from the ED head can be made constant, and good image quality can always be maintained.

〔Effect of the invention〕

As explained above, the present invention has the following effects.

(1) The back temperature of the semiconductor light source can be detected by a temperature detection means such as a thermistor, and the duty of the semiconductor light source can be varied to control the amount of light according to the environmental temperature or the amount of change in temperature due to self-heating of the light source itself.

As a result, the light intensity of the semiconductor light source, which has hitherto been dependent on temperature, can be kept constant, and the influence on image quality can be eliminated, and the lifespan of the light source will not be shortened.

(2) There is no need for a power source for heat insulation, and the internal temperature of the device will not rise and cause problems in other parts.

(3) A printer that uses an LED array as a semiconductor light source and performs positive development using electrophotography.
ine) is particularly effective in improving reproducibility (because the amount of light can be accurately controlled).

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a light amount control device for a printer or the like using an LED head, which is an embodiment of the present invention, and FIG.
3 is a schematic operation flowchart, FIG. 4 is a characteristic diagram of the semiconductor light source, FIG. 5 is a flowchart explaining the details of the operation of the present invention, and FIG. 6 is a diagram explaining the variation range. , FIG. 7 is an explanatory diagram of the relationship between each timing and control, and FIG. 8 is an explanatory diagram of the relationship between the calculated value of the light emission duty and the actually set value. 1-Semiconductor light source 2-Temperature detection device 3-・-A/
D conversion circuit 4 - Control circuit (CPU) 5 - Duty control circuit 1' - LED array 2' - Thermistor 6 - Head block 7 - Photosensitive drum 8 - Charging section
9-Developing section 10・-Transfer section 11・-Cleaning section Patent applicant Fuji Xerox Co., Ltd. Representative Patent Attorney
Akira Yamatani Figure 1 Figure 4 (From Part 3) Figure 5 C Part 4) Bui-hui time Figure 6

Claims (1)

[Claims] In an electrophotographic apparatus equipped with a semiconductor light source as a light source for exposure, a temperature detection means attached to the semiconductor light source detects the temperature of the semiconductor light source, and a temperature information signal received from the temperature detection means and processed. An electrophotographic apparatus comprising: a control circuit that outputs a lighting control signal; and a light amount control circuit that receives the lighting control signal from the control circuit and outputs a lighting signal to the semiconductor light source.