JP2945434B2 - LED printer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Table of Contents] Overview Industrial application field Conventional technology (Figs. 8 to 10) Problems to be solved by the invention (Figs. 8 to 10) Means for solving the problems (1) FIG.) Embodiment (FIGS. 2 to 7) Effects of the Invention [Overview] A plurality of recording units are provided, and each recording unit has an LE.
L having an LED array consisting of LED elements arranged with D elements
Regarding ED printers, in an electrophotographic color printer using an LED array, the LED included in the recording unit provided for each color
By making the array temperatures uniform, the LE for each color
A heating means provided in the LED array to heat the LED array, and a temperature sensor provided in the LED array, for the purpose of preventing the displacement of the recording pixels between the colors caused by the difference in length due to the thermal expansion of the D array. Temperature detection means for detecting a temperature based on a signal from a temperature sensor, maximum temperature detection means for detecting a maximum temperature among the temperatures of the respective LED arrays detected by the temperature detection means, and the temperature detection Temperature comparing means for comparing the temperature detected by the means with the maximum temperature detected by the maximum temperature detecting means, and keeping the temperature of the LED array in each recording unit at the maximum temperature detected by the maximum temperature detecting means. Therefore, a heating control means for controlling the amount of heating applied to the heating means provided in the LED array based on the compared temperature difference is provided.

[Industrial applications]

Laser printers and LEDs for electrophotographic printers
Various types of printers and liquid crystal printers have been developed. These printers have features of high speed, high resolution, and high image quality, and are expected to greatly develop in the future.

The present invention relates to an LED printer among the above printers. LED printers are solid-state scanning and do not require mechanical driving parts, can reduce the optical path length and can reduce the size of the device, and can be made smaller due to advances in semiconductor technology, compared to laser printers that have been widely used in the past. It has features such as lower prices. In the future, as the functions of printers become more advanced, needs for color printers will increase. In particular, since the electrophotographic method enables high-speed recording, a high-speed color printer can be realized.

[Conventional technology]

FIG. 8 shows a configuration diagram of a conventional color printer using an LED array. This printer device has four recording units 870 for performing recording of four colors including three primary colors of yellow, magenta, cyan and black. Each recording unit 870 has a photosensitive drum 871 and a charger 87
2, an LED optical system 873, a developing device 874, and a cleaner 875. In each color recording unit 870, electrophotographic recording known to those skilled in the art is performed, and the photosensitive drum 871 is recorded.
A color image with a color toner is formed thereon. The recording paper in the paper cassette 881 is picked up by a pickup roller 882 and conveyed below each recording unit 870 by a recording paper conveyance system 883. When the recording paper is conveyed below each photosensitive drum 871, the color toner image on the photosensitive drum 871 is transferred to the recording paper by the transfer unit 876. The recording paper on which the transfer of the four colors has been performed is fixed on the recording paper by melting the toner by heat in a fixing unit 884, and the stacker 885
Output to In the printer having this configuration, each recording unit
Because the 870 performs the recording operation in parallel in a pipeline manner,
High-speed recording is possible.

FIG. 9 shows the configuration of the LED head of the LED optical system used in the present apparatus. The LED array 840 is composed of a ceramic substrate 848 on which a number of LED array chips 846 and driver ICs 845 are arranged, on which a Selfoc lens (registered trademark) 847 that forms an image of light from the LEDs is maintained at a constant interval. Is held. As shown in Fig. 10, the driver IC845
Has a shift register 844, latch 843, LED driver 842
Is built-in. By serially inputting data, the number of signal lines is reduced and control of the LED array 840 is simplified. Since the ceramic substrate 848 has a high thermal conductivity, an LED array chip 846 including a large number of LED elements 841 is provided.
The generated heat is efficiently transmitted to the entire ceramic substrate 848 to cool the LED array chip 846.

[Problems to be solved by the invention]

By the way, conventionally, since four sets of recording units 870 are arranged, if the exposure dot (pixel) position of the LED array 840 included in each LED optical system 873 is different for each LED optical system 873, There is a problem that an output image is deteriorated due to color shift. For this reason, it is necessary to accurately maintain the position of each dot of the LED array 840. However, if the temperature of the LED array 840 changes due to a change in the temperature of the installation environment of the printer device or a rise in temperature due to heat generated from inside the printer device, a problem occurs in that the length of the LED array 840 changes due to thermal expansion.

LED array 840 has many LED elements on ceramic substrate 848
A plurality of LED chips on which 841 are integrated are arranged side by side. Usually, the ceramic substrate 848 has a linear expansion coefficient of 6.8 × 10 ⁻⁶ / deg. For example, if the total length of the LED array 840 is 300 mm and the temperature rise is 30 ° C., the ceramic substrate 848
Is calculated by the following equation.

ΔL = 300 × 30 × 6.8 × 10 ^-6 = 0.0612 (mm) Here, assuming that the resolution of the LED array 840 is 400 dpi, the pitch of one bit is 63.5 μm, and the change of the length of about one dot is Will happen. For example, if the temperature of the LED array 840 of the exposure unit of one of the four colors is higher than that of the other LED arrays 840 by 30 ° C., the recording width is increased by that color. Assuming that the position of the dot on the left end matches all four colors, the position of the dot on the right end is shifted to the right by about 60 μm only in the LED array 840 having a high temperature. If the recording positions of the respective colors are shifted, there arises a problem that a color shift occurs and characters are difficult to read. When the length of the LED array 840 is long, or when the substrate is made of a material having a high expansion coefficient such as a metal, the change in the length becomes large, which poses a further problem.

Therefore, in the present invention, in order to make the temperature of each LED array uniform, a temperature detector (for example, a thermistor or the like) for detecting the temperature of the LED array is provided, and the power applied to the heater is controlled based on the detected temperature of the LED array. In addition, the temperature of the entire LED array is made uniform, thereby preventing the dot displacement of the LED array due to thermal expansion.

[Means for solving the problem]

In order to solve the above technical problems, the present invention relates to an LED printer for obtaining a color image by superimposing images of a plurality of color components, as shown in FIG. Each of the recording units includes an LED array 1 including a light emitting element group in which LED elements arranged independently for each recording unit are provided.
A heating means 3 provided for each array 1 for heating the corresponding LED array 1; a temperature sensor 2 provided for each LED array 1; and a corresponding temperature sensor 2 provided for each temperature sensor 2. Temperature detecting means 4 for detecting the temperature of the LED array 1 based on the signal of the above, and a maximum temperature detecting means for detecting the maximum value of the temperature from the temperatures of the LED arrays 1 detected by the respective temperature detecting means 4. Means 7 and corresponding temperature detecting means 4 provided for each temperature detecting means 4.
Temperature comparing means 5 for comparing the temperature detected by the above with the maximum value of the temperature detected by the maximum temperature detecting means 7
And the amount of heating applied to the corresponding heating means 3 is provided for each temperature comparing means 5 and the temperature of the LED array 1 is set to the maximum based on the temperature difference obtained by comparison by the temperature comparing means 5. Heating control means 6 for controlling the temperature detected by the temperature detecting means 7 to be kept at the maximum value.

[Action]

The operation of the LED printer according to the present invention will be described. As shown in FIG. 1, the temperature of the LED array 1 is detected by a temperature detecting means 4 based on a signal from a temperature sensor 2 provided in the LED array 1. Subsequently, the maximum temperature detecting means 7 detects the maximum temperature from the temperatures of the LED arrays 1 detected as described above. Next, the temperature comparison unit 5 compares the detected maximum temperature with the temperature detected by the temperature detection unit 4. Based on the compared temperature difference, the heating control unit 6 controls the amount of heating supplied to the heating unit 3 provided in the LED array 1. Here, in order to stabilize the control, the temperature of each LED array 1 is kept at a temperature lower by 1 to 2 ° C. than the maximum temperature detected by the maximum temperature detecting means 7,
The length of each LED array 1 accompanying the thermal expansion of the LED array 1 is kept uniform.

〔Example〕

Next, examples according to the present invention will be described. Second
FIG. 1 shows a configuration diagram according to an embodiment in which four recording units (1) to (4) are mounted.

The LED array unit 31 as the LED array 1 includes an LED array in which a plurality of LED chips on which a large number of light emitting elements are integrated and a ceramic substrate on which the LED array is mounted. A thermistor 32 as the sensor 2 is mounted on a ceramic substrate. In the temperature detection circuit 34 as the temperature detection means 4, the temperature is detected by utilizing that the resistance value of the thermistor 32 changes according to the temperature. In other words, if a voltage is applied from the stabilized power supply (+ 5V) to the thermistor 32, the resistance value changes in accordance with the temperature. Therefore, the voltage dividing ratio between the detection resistor 34a that detects the voltage corresponding to the temperature and the thermistor 32 changes. Detection resistor 3
Since the voltage applied to 4a changes, the output of the differential amplifier 34b changes according to the change in the voltage, and a voltage corresponding to the changed temperature is obtained from the amplifier circuit 34c. In the temperature comparison circuit 35 as the temperature comparison means 5, the voltage applied to the detection resistor 34a is amplified by the amplification circuit 34c and compared with the voltage from the reference voltage generator 50 that generates the reference voltage corresponding to the reference temperature. Thus, it is determined how much the temperature of the ceramic substrate is lower than the reference temperature.

In the PWM (Pulse Width Modulation) circuit 36a, the duty of the current applied to the heater is changed based on the difference from the reference voltage compared by the temperature comparison circuit 35, and a signal having a pulse width corresponding to the voltage difference is obtained (FIG. 4). reference). That is, the width of the pulse output from the square wave oscillator 51 is changed by the output of the temperature comparison circuit 35. The signal of the pulse width corresponding to the voltage corresponds to the power applied to the heater 33 as the heating means 3. Next, in the heater drive circuit 36b, electric power corresponding to the pulse width signal of the PWM circuit 36a is supplied to the heater 33. Here, the PWM circuit 36a and the heater drive circuit 36b
Corresponds to the heating control means 6.

Now, if the temperature of the ceramic substrate is close to the reference temperature, control is performed to reduce the power applied to the heater 33 attached to the ceramic substrate. If the temperature of the ceramic substrate is much lower than the reference temperature, control is performed to increase the electric power applied to the heater 33. By performing this control, the temperature of the ceramic substrate is set to the reference temperature. By setting the reference temperature slightly higher than the temperature during normal use of the LED array section 31, each LED array section 31 can be maintained at the reference temperature.

As a result, according to the present embodiment, each recording unit (1)
The temperatures of the LED array units 31 to (4) are kept uniform, and the lengths of the LED array units 31 of the recording units accompanying the thermal expansion are the same. Therefore, each of the recording units (1) to
(4) There is no relative displacement of the recording dots between the recording dots, and recording without color displacement can be performed.

Further, according to the present embodiment, the dot position accuracy of the output image can be increased, and it can be used for applications requiring high accuracy such as the output of CAD drawings.

Next, a second embodiment will be described. By the way, in the case of the color printer of the present configuration, it is not always necessary to set each LED array section 31 to a certain temperature. 4
If the set of LED array units 31 have the same length, no color shift occurs in one image. For that purpose, it is sufficient that the temperatures of the four sets of LED array units 31 are the same. Further, it is preferable that the heat generation of the LED array portion is small, so that the power consumption is small, and that the heat generation of the entire device is small. Therefore, a method of making the temperature of the four LED array units 31 uniform at the lowest possible temperature, that is, by setting the temperature of the other LED array unit 31 to the LED array unit 31 having the highest temperature among the four LED array units 31 A method of matching was realized.

FIG. 4 is a configuration diagram according to an embodiment in which four recording units (1) to (4) are mounted.

In this configuration, the LED array unit 31 and the thermistor 32
, A heater 33, a temperature detection circuit 34, and a temperature comparison circuit 35
, The PWM circuit 36a and the heater driver circuit 36b are the same as those in the first embodiment, and a description thereof will be omitted. Here, a maximum temperature detection circuit 37 for selecting the maximum temperature from the temperatures detected by each temperature detection circuit 34 is further provided.

Next, the operation will be described. First, the temperature detection circuit 34 detects the temperature of the LED array unit 31 based on the resistance value of the thermistor 32. Subsequently, the maximum temperature detecting circuit 37 as the maximum temperature detecting means 7 compares the temperature detection results detected by each temperature detecting circuit 34 and selects the maximum temperature among them. Next, in order to match the temperatures of the other three sets of LED arrays 31 to the maximum temperature, a difference between the maximum temperature and the temperature detected by the temperature detection circuit 34 is obtained in the temperature comparison circuit 35. Subsequently, based on the temperature difference, the PWM circuit 3 described above is used.
The power applied to the heaters 33 of the other three sets of LED arrays 31 is controlled by the heater drive circuit 36b and the heater drive circuit 36b. In order to stabilize the control, the temperatures of the other LED array units 31 are controlled so as to keep the temperature lower by 1 to 2 ° C. than the LED array unit 31 indicating the maximum temperature. If the temperature is 1 to 2 ° C., the difference in length between the LED array units 31 is very small and can be ignored.

FIG. 5 is an operation explanatory diagram according to the embodiment. The fifth
The figure shows a case where two sets of LED array units 31 are used for ease of explanation.

The temperature of the LED array unit 31 varies depending on the ambient temperature, self-heating, etc., but among the four LED array units 31, the other LED array units 31 according to the temperature of the LED array unit 31 indicating the maximum temperature.
Temperature also changes. Compared to the method of maintaining a certain reference temperature, the method of maintaining the maximum temperature in each LED array unit 31 is 4
In one set of the LED array units 31, the power applied to the heater is zero, and since the temperature difference from the other three sets is relatively small, the power applied to the heater is small.

According to the present embodiment, even if the ambient temperature changes, the lengths of the LED array units 31 included in the respective recording units are all kept uniform, so that recording can be performed without relative displacement of the recording dots. Further, power consumption for keeping the length of each LED array uniform can be reduced.

 Hereinafter, another embodiment of the second embodiment will be described.

FIG. 7 is a block diagram showing another embodiment of the second embodiment,
FIG. 7 is a flowchart showing a control sequence of the LED array. As the configuration of FIG.
, RAM 63, A / D converter 64, D / A converter 65, and four sets of L
It has an ED array 31 (LED1, LED2, LED3, and LED4, respectively).

 The operation will be described below with reference to FIG.

First, the temperature of each LED array 31 is converted into a voltage by each thermistor 32. This voltage is input to the A / D converter 64. The processing unit 61 has a CPU and operates according to a control program stored in the RAM 63. First, the temperature value (T _{1 to} T ₄ ) of each LED array 31 converted into a digital signal by the A / D converter
Is read (step ~). Next, the processing unit 61 compares them to determine the maximum temperature value (T _M ) (step). Next, the processing unit 61 sets the LED array 3 indicating the maximum temperature.
The power applied to the heater 33 is reduced or set to zero so that the temperature does not increase any more. The remaining 3 sets of LED array 3
For 1, the LE of the LED array 31 indicates the maximum temperature.
Data is supplied to the D / A converter 65 according to the difference between the temperature value of each LED array 31 and the temperature of the LED array 31 indicating the maximum temperature so that the temperature falls within 1 ° C. to 2 ° C. of the temperature of the D array 31. .

That is, the processing unit 61 determines the temperature values T _{1 to} T ₄ of each LED array 31.
And the difference between the maximum value T _M and the maximum value T _M (step ~). Then, the processing unit 61 is the temperature difference is stored in the ROM62 based on the temperature difference data for each LED array 31 - with reference to the heater power table, obtains a power value supplied to the LED array 31 (P ₁ ~P ₄₎ (Step). Subsequently, the processing unit 61 passes the obtained power values (P _{1 to} P ₄ ) through the D / A converter 65, respectively, to a heater driver circuit (not shown) (for example, corresponds to the PWM circuit 36a and the heater driver circuit 36b in FIG. 2). (Step).

In the D / A converter 65, the given data is converted into an analog voltage and applied to the heater driver circuit. As described in the above embodiment, in the heater driver circuit, the current applied to the heater is subjected to pulse width modulation depending on the applied voltage. As a result, the calorific value of the heater changes,
The temperature of the LED array 31 approaches the target temperature.

Note that the LED array 31 indicating the maximum temperature value gradually cools down because the temperature rise due to the heat generated by the heater is eliminated. The temperature of the other LED arrays 31 also changes according to this temperature. However, when the state of light emission changes significantly, the LED array 31 showing the maximum temperature value is switched. In this case, according to the control sequence described above, each of the new temperature values will be
The heater of the LED array 31 is controlled.

If the processing capacity of the processing unit 61 has a margin, the D / A
The functions of the converter 65 and the PWM circuit can be processed inside the processing unit 61. In this case, the D / A converter 65 and the PWM circuit become unnecessary, and the circuit is simplified.

In this way, of all the four LED arrays 31, all LEDs are set to a temperature according to the temperature of the LED array 31 showing the maximum temperature.
The temperature of the ED array 31 is controlled. Compared to the method of maintaining a certain reference temperature, one of the four sets of LED arrays 31 requires 0 or very little electric power to be applied to the heater, and the other three sets have the temperatures shown in the above embodiment. Since it may be lower, less power needs to be applied to the heater.

〔The invention's effect〕

As described above, in the present invention, in order to maintain the dot position accuracy of the recording pixels between the colors of the color LED printer,
Temperature detecting means for detecting the temperature of the LED array of each recording unit, maximum temperature detecting means for detecting the detected maximum temperature, and temperature comparing means for comparing these detected temperatures with the maximum temperature And heating control means for controlling the amount of heating applied to the heating means attached to each LED array based on the detected temperature, based on the temperature difference between the maximum temperature of each LED array and the temperature of each LED array. The amount of heating supplied to the heating means is controlled by the heating control means,
By keeping the temperature of the LED array at the maximum temperature detected by the maximum temperature detecting means, the temperature of each LED array is made uniform and the fluctuation of the dot position due to thermal expansion is prevented. At least one set of LEs
The D array requires 0 or very little power to be applied to the heating means, and the average temperature of other LED arrays is half that of the power from low to high power even if the temperature is wide. Therefore, the required temperature can be maintained with a small amount of power supply, and the power applied to the heating means as a whole can be reduced as compared with the conventional one.

For this reason, even when the ambient temperature changes, the length of the LED array for each recording unit is kept uniform, and the relative positional deviation of the recording dots of each color is eliminated, so that good color recording without color deviation can be performed.

[Brief description of the drawings]

FIG. 1 is a block diagram of the principle of the present invention, FIG. 2 is a block diagram according to the first embodiment, FIG. 3 is an explanatory diagram (1) of the operation according to the embodiment, and FIG. FIG. 5 is an explanatory diagram (2) of the operation according to the second embodiment, FIG. 6 is a configuration diagram according to another embodiment of the second embodiment, FIG. 7 is a temperature control sequence of the LED array, FIG. 8 is a block diagram according to a conventional example, and FIG.
The figure shows the configuration of an LED head, and FIG. 10 shows the configuration of an LED array chip and its driver IC. 1, (31) ... LED array (LED array section) 2, (32) ... temperature sensor (thermistor) 3, (33) ... heating means (heater) 4, (34) ... temperature detection means (temperature Detection circuit) 5, (35): Temperature comparison means (Temperature comparison circuit) 6, (36a, 36b): Heating control means (PWM circuit, heater drive circuit) 7, (37): Maximum temperature detection means ( Maximum temperature detection circuit)

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-218864 (JP, A) JP-A-59-202878 (JP, A) JP-A-62-299360 (JP, A) (58) Investigation Field (Int.Cl. ⁶ , DB name) B41J 2/447 B41J 2/45-2/46 G03G 15/01

Claims (1)

(57) [Claims] 1. An LED printer for obtaining a color image by superimposing images of a plurality of color components, wherein a plurality of recording units (A to N) corresponding to the respective color components are provided.
Each of the recording units corresponds to an LED array (1) comprising a light emitting element group in which LED elements provided independently for each recording unit are arranged, and is provided for each of the LED arrays (1). Heating means (3) for heating the LED array (1) to be heated; temperature sensors (2) provided for each of the LED arrays (1); and corresponding temperature sensors provided for each of the temperature sensors (2) Temperature detecting means (4) for detecting the temperature of the LED array (1) based on the signal from (2), and the LEDs detected by the temperature detecting means (4)
Maximum temperature detecting means (7) for detecting the maximum temperature from among the temperatures of the array (1), and the temperature detected by the corresponding temperature detecting means (4) provided for each temperature detecting means (4) Temperature comparing means (5) for comparing the temperature with the maximum temperature detected by the maximum temperature detecting means (7); provided for each temperature comparing means (5), and added to the corresponding heating means (3). Based on the temperature difference obtained by comparing the heating amount by the temperature comparing means (5), the temperature of the LED array (1) is maintained at the maximum temperature detected by the maximum temperature detecting means (7). An LED printer comprising: a heating control means (6) for controlling the temperature of the LED printer.