JPH074946B2 - Temperature control device - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a temperature control device for a liquid crystal optical shutter used in a liquid crystal printer.

[Conventional technology]

Generally, the liquid crystal optical shutter is driven by a dual frequency driving method in order to speed up the response. The dual-frequency driving method utilizes the property that the dielectric anisotropy of liquid crystal is inverted by the frequency change of the electric field, and the opening / closing control of each micro shutter that constitutes the liquid crystal optical shutter is performed by two frequencies f _L and f _H. To do. That is, the liquid crystal in which the crossover frequency and f _C, f _C
When a lower frequency f _L is applied, the dielectric anisotropy becomes positive,
It has the property that the dielectric anisotropy is inverted negatively when a frequency f _H higher than f _C is applied. Therefore, when the frequency f _L is applied to the liquid crystal, the liquid crystal molecules are aligned parallel to the electric field, and when used as an optical shutter, the shutter is opened. Further, when the frequency f _H is applied, the liquid crystal molecules are aligned perpendicular to the electric field and the shutter is closed. By controlling this opening / closing function, the liquid crystal molecules can be suitably used as an optical writing means to the photoconductor.

By the way, since the operation characteristics of the liquid crystal optical shutter change depending on the temperature, it is required to be used at a constant temperature, and various temperature control devices are used. For example, by attaching a heater along the longitudinal direction of the liquid crystal optical shutter and controlling the energization of the heater based on the detection value of the thermistor that detects the temperature of the heater, the temperature can be kept constant. There is something I did. Then, in general, the liquid crystal optical shutter is controlled to a temperature of about 45 ° C. at which it can be used at the highest speed.

[Problems of conventional technology]

However, when the liquid crystal optical shutter is driven by the dual frequency drive method, the liquid crystal is equivalently a capacitor, and since a drive signal of about 300 KHz is used as the frequency f _H , a high frequency current flows through the liquid crystal and the liquid crystal self-exists. It produces a fever. Also, since a drive signal of 15 KHz is used as f _L , although it does not generate self-heating as much as when f _{H is} applied, it also generates some self-heating. Further, in the state where neither f _H nor f _{L is} applied, no self-heating is generated. Therefore, due to the characteristic of the liquid crystal optical shutter, even if the temperature control device described above controls the temperature, the temperature rises due to the temperature rise due to self-heating of the liquid crystal optical shutter, and the characteristics of the liquid crystal optical shutter, such as the response speed and the contrast. However, there is a problem that the aperture ratio becomes unstable and the print quality is deteriorated. In particular, when using PWM (pulse width modulation) as a temperature control method, it becomes a big problem.

[Object of the Invention]

In view of the above problems, the present invention uniformly controls the temperature of the liquid crystal light shutter without being associated with self-heating, thereby stabilizing the operating characteristics of the liquid crystal light shutter, and thus capable of performing high-quality printing. An object is to provide a temperature control device.

[Main points of the invention]

In order to achieve the above object, the present invention provides a plurality of micro frequency filters by applying a frequency f _H higher than a specific frequency f _{C at} which the dielectric anisotropy of the liquid crystal composition becomes zero and a frequency f _L lower than the specific frequency. A liquid crystal optical shutter that performs optical writing on the photoconductor by selectively opening and closing the shutter and selectively transmitting light from the light source, a heating element provided in the liquid crystal optical shutter, and temperature detection for detecting the temperature of the liquid crystal optical shutter. An element and a temperature control means for controlling energization of the heating element based on the output of the temperature detection element, wherein the temperature control device controls the temperature of the liquid crystal optical shutter by energization control of the heating element. Counting means for counting the number of print dots printed at the frequency f _H applied to the optical shutter,
And a duty ratio changing means for changing the duty ratio to the heating element based on the output of the counting means, and the duty ratio changing means controls the duty ratio to be lower as the count value of the counting means increases. And

Example of Invention

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 2 shows a schematic configuration diagram of a liquid crystal printer according to the present invention.

In FIG. 2, reference numeral 1 is a photosensitive drum having a photoconductive thin film formed on its peripheral surface, around which a charger 2 and a print head 3 are arranged. The print head 3 has a fluorescent lamp 4 as a light source, and a liquid crystal optical shutter 5 including a plurality of micro shutters (not shown) arranged along the main scanning direction of the photosensitive drum 1, and the liquid crystal optical shutter 5. It has an image forming lens 6 for forming an image of the transmitted light. Photosensitive drum 1
The surface of is charged by the charger 2, and then the individual micro-shutters of the liquid crystal optical shutter 5 of the print head 3 are selectively opened and closed according to the print data to perform optical writing on the photosensitive drum 1 and electrostatic latent image. Form an image. The electrostatic latent image is visualized by the developing device 7 using toner, and a toner image is formed on the photosensitive drum 1. This toner image is in the cassette 8
It is transferred to the transfer paper 9 fed from. That is, the transfer paper 9
Is loaded in the cassette 8 and the uppermost transfer sheet 9 is sent out by the sheet feeding roller 10 arranged on the upper surface thereof. The transferred transfer paper 9 is transported by the transport roll 11 until the leading end of the transfer paper 9 contacts the nip portion of the standby roll 12. The standby roll 12 sends out the transfer paper 9 again at the timing when the front end of the transfer paper 9 coincides with the front end of the toner image on the photosensitive drum 1, and the transfer device 13 transfers the toner image onto the transfer paper 9. After the transfer, the transfer paper 9 is separated from the photosensitive drum 1 by the separation roll 14 and further conveyed to the fixing device 15. And
The transfer paper 9 on which the toner image is formed is fixed by the fixing device 15 and then discharged by the paper discharge roll 16 to the outside of the machine.

On the other hand, a part of the untransferred toner remains on the photosensitive drum 1 after the transfer, but the residual toner is removed by the cleaner 17. Reference numeral 18 in the drawing denotes a main motor which is a drive source for the photosensitive drum 1, the paper feed roller 10 for feeding the transfer paper 9, the transport roll 11, and the like.

FIG. 3 shows a specific structure of the liquid crystal optical shutter 5 provided inside the print head 3 described above.

The liquid crystal optical shutter 5 encloses the liquid crystal mixture between the glass substrates 19 and 20, and has a large number of signal electrodes (not shown) on the glass substrate 19 and a large number of common electrodes (not shown) on the glass substrate 20. This is the configuration provided. A large number of micro shutters 21 are formed at the intersections of the signal electrodes and the common electrodes, and the airtightness of the micro shutters 21 is 240 dots / inch (9.45 dots / mm) in this embodiment. The micro shutter 21 is driven by the dual frequency driving method utilizing the dielectric anisotropy of liquid crystal as described above. Therefore, the frequency f _L lower than the crossover frequency f _C
When is applied, the shutter is opened, the light from the fluorescent lamp 4 is transmitted to erase the potential on the photosensitive drum 1, and when a frequency f _H higher than f _C is applied, the light of the fluorescent lamp 4 is blocked. The potential on the photosensitive drum 1 is not erased. In this way, by opening and closing the individual micro shutters 21 using the two frequencies f _L and f _H , an electrostatic latent image having a dot structure is formed on the photosensitive drum 1.

A thin plate-shaped heater 22 for heating the liquid crystal optical shutter 5 is attached to the surface of the glass substrate 20 on both sides of the micro shutter 21. A thermistor 23 is attached near the heater 22, and temperature control is performed based on the detection value of the thermistor 23, as will be described later.

FIG. 1 shows an embodiment of the temperature control device of the present invention. In this embodiment, the control temperature is set to 45 ° C. which is the optimum temperature condition of the liquid crystal optical shutter 5.

In FIG. 1, reference numeral 24 is an AND circuit to which the recording data signal S ₁ and the clock signal S ₂ are input. As shown in FIG. 4B, the recording data signal S ₁ includes, as serial data, black-and-white information for opening and closing the micro shutter according to the white portion and the black portion of the image to be printed. That is, the high-level part corresponds to the black part of the image,
The low-level part corresponds to the white part. The clock signal S _2, as shown in 4 (a), consists of a pulse of a constant period synchronized with the timing of the actual opening and closing of the micro-shutter, black or white printing one dot at that one pulse It is carried out. Therefore, the AND circuit 24 outputs one pulse each time printing is performed with black dots, and the black dots are formed by applying the frequency f _H.

The output of the AND circuit 24 is output to the 1/2 ⁸ frequency divider 25, where it is 1/2 ^8-divided. That is, the output of the 1/2 ⁸ divider circuit 25 each time a pulse from the AND circuit 24 is output 2 ⁸ is a binary counter constituted by flip-flop Q ₁ to Q ₁₀ of the 10-digit counter circuit 26 Entered in. The output signal of the 1/2 ⁸ divider circuit 25 is inputted to the clock terminal of the first flip-flop Q _1, its output is input to the clock terminal of the succeeding flip-flop Q _2. Similarly, the output of the flip-flop Qn (n = 1, 2, ..., 9) is input to the clock terminal of the next-stage flip-flop Qn _{+ 1} . Furthermore,
A constant voltage (V _D ) is applied from the power supply to the J terminal and the K terminal of each of the flip-flops Q _{1 to} Q ₁₀ . In such a counter circuit 26, the 1/2 ⁸ divider circuit 25
Pulse output from is counted up at the time of fall of the H L, and the output of the 2 ^10th flip-flops 9 stage at the falling edge of the pulse Q ₉ (not shown) falls. Due to this fall, the final flip-flop Q
The output of ₁₀ switches to H level.

After all, by connecting the 1/2 ⁸ divider circuit 25 and the counter circuit 26 in series, the pulse output from the AND circuit 24 can be accumulated, and 2 ¹⁸ (≈1
870,000) pulses can be counted. On the other hand, the clock (CLK) of the printer control circuit 27 is output to the arithmetic circuit 28 and the correction circuit 29 every 0.2 seconds as shown in FIG. 5 (b), and this 0.2 seconds is converted into a process distance of 10 mm. Is.
Here, the total number of dots with a length of 10 mm is 182 × 9.45 for B5.
× 10 × 9.45 ≈ 162,000 dots, A4 210 × 9.45 × 10 ×
9.45 = 187,000 dots. Further, as shown in FIG. 5A, the printer control circuit 27 outputs a clear signal to each reset terminal of each flip-flop of the counter circuit 26 every 0.2 seconds in synchronization with the above-mentioned clock signal. As a result, the counter circuit 26 is reset every 0.2 seconds, that is, every 10 mm of process distance. Thus 1/2 ⁸ frequency divider 25
And since the counter circuit 26 with 2 ¹⁸ (≒ 26 50,000) can dot count can be counted a 187,000 dots even when the 10mm printed A4 is sufficient total number of dots.

The number of black dots counted by the counter circuit 26 is output from the bus line A to the arithmetic circuit 28. Since the black dots correspond to the frequency f _H for closing the micro shutter described above, the self-heating amount is indirectly detected by counting the number of black dots. The arithmetic circuit 28 calculates a correction value for the energization rate to the heater 22 according to the number of black dots. The calculation result is sent to the correction circuit 29, and the correction circuit 29 outputs a correction signal based on the correction result to the PWM temperature control circuit 30.

The PWM temperature control circuit 30 is a temperature control circuit of a PWM (pulse width modulation) control method, and is synchronized with a clock signal output from the printer control circuit 27, and a heater via an inverter 31 based on a detection value of the thermistor 23. The power supply to 22 is controlled (see FIG. 5 (c)). In this case, the PWM temperature control circuit 30
When no drive signal is applied to the liquid crystal optical shutter, f _{L is} continuously applied, and f _{H is} continuously applied, the duty as shown in FIG. 6 is determined.

That is, when no drive signal is applied to the liquid crystal optical shutter, the heat generation amount and the heat dissipation amount are balanced at 45 ° C. by setting the duty to 60%. When f _{L is} continuously applied, some self-heating occurs, so the duty is set to 50
When set to%, it stabilizes at 45 ° C as above,
Since f _H the continuous application is self-heating is further larger than the time f _L continuous application, thermal equilibrium is maintained by 40% lowering the duty, stabilized at 45 ° C.. Furthermore, when printing is performed by applying f _H and f _L (data in which closed and open are mixed in the main scanning direction), the arithmetic circuit 28 calculates a correction value according to the number of black dots described above, Based on this calculation result, the duty is 40% ~
It is changed between 50% to correct self-heating, thereby stabilizing the temperature at 45 ° C.

〔The invention's effect〕

As described above, according to the present invention, since the duty ratio to the heating element is changed by the waveform applied to the liquid crystal optical shutter, the temperature accuracy can be stabilized regardless of the driving state, and the liquid crystal optical shutter It can be controlled uniformly without being involved in self-heating. Therefore, the response speed, aperture ratio, contrast and the like of the liquid crystal optical shutter are stable, and thus there is an effect that high quality printing can be performed.

[Brief description of drawings]

1 is a block diagram of an embodiment of the present invention, FIG. 2 is a schematic configuration diagram of a liquid crystal optical printer according to the present invention, FIG. 3 is a perspective view of a liquid crystal optical shutter, and FIGS. 4 (a) and 4 (b). ) Is a waveform diagram of the input signal for counting the number of black dots printed, FIG. 5 is a time chart showing the operation of the above-mentioned embodiment, and FIG. 6 shows the relationship between temperature and duty of the temperature control device of the present invention. It is a characteristic diagram. 5 …… Liquid crystal light shutter, 21 …… Micro shutter, 22 …… Heater, 23 …… Thermistor, 24 …… AND circuit, 25 …… 1/2 ⁸ divider circuit, 26 …… Counter circuit, 27 …… Printer Control circuit, 28 ... arithmetic circuit, 29 ... correction circuit, 30 ... PWM temperature control circuit.

Claims (1)

[Claims] 1. A plurality of micro shutters are selectively opened and closed by applying a frequency f _H higher than a specific frequency f _{C at} which the dielectric anisotropy of the liquid crystal composition is zero and a frequency f _L lower than the specific frequency, A liquid crystal optical shutter that optically writes light to a photoconductor by selectively transmitting light from a light source, a heating element provided in the liquid crystal optical shutter, a temperature detection element that detects the temperature of the liquid crystal optical shutter, and the temperature detection A temperature control device that controls energization of the heating element based on the output of an element, and a temperature control device that controls the temperature of the liquid crystal optical shutter by controlling the energization of the heating element is applied to the liquid crystal optical shutter. counting means for counting the number of print dots to be printed by the frequency f _H, and the duty factor changing means for changing the duty ratio to the heating element based on the output of the regimen number means provided, vent collector Change means temperature controller and controls lower the duty ratio larger the count value by the counting means.