JPH0658563B2 - Recording device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical recording type recording apparatus using a liquid crystal optical shutter.

[Prior Art] A liquid crystal optical shutter is composed of a large number of micro-shutters arranged in the main scanning direction of a photoconductor, and opens and closes each micro-shutter according to a recording signal on the photoconductor that is uniformly charged in advance. To transmit or block light.
Then, an electrostatic latent image is formed by binarizing a place exposed to light to a low potential and a place not exposed to light to a high potential. The formed electrostatic latent image is developed, transferred and fixed by a well-known electrophotographic process and put into practical use as a so-called hard copy.
Let V _{L be} the photoconductor potential of the portion exposed to light by opening the micro shutter, and let V _D be the photoconductor potential of the portion not exposed to light because the micro shutter is closed. V _L and V _D are liquid crystal optical shutters. It changes as shown in FIG. The temperature of the liquid crystal optical shutter rises due to heat dissipation of the light source or self-heating due to high frequency driving. Note that FIG. 4 is a characteristic diagram when the guest-host type liquid crystal optical shutter is driven by the dual frequency driving method.

On the other hand, there are two types of development processes in the electrophotographic process, a normal development process and a reversal development process. In the case of the regular development process, a voltage having the same polarity as the photoconductor potential and slightly higher than the above-mentioned V _L is applied to the developing sleeve, and toner is not attached to the region corresponding to V _L and the potential opposite to the photoconductor potential is applied to the region corresponding to V _D. This is to attach polar toner.
Further, in the case of the reversal development process, a voltage having the same polarity as the photoconductor potential and slightly lower than V _D is applied to the developing sleeve, and V _D
The toner is not attached to the corresponding portion, and the toner having the same polarity as the photoconductor potential is attached to the _VL corresponding portion.

When an electrostatic latent image is formed on a photoconductor using a liquid crystal optical shutter, even if the same 1-dot line is written due to the effect of flare of light, the 1-dot line exposed to light is It becomes thicker than the 1-dot line that did not hit. Therefore, when the normal development is performed, the 1-dot line as a visible image becomes thin. On the other hand, when reversal development is performed, the part exposed to light is reproduced as a visible image, and the one-dot line becomes thick. Therefore, in order to increase the dot density and raise the printing quality level, it is more advantageous to use the reversal development process with good one-dot reproducibility.

[Problems of conventional technology]

However, as is apparent from FIG. 4, when the normal development is performed with the bias voltage kept constant, _VL is constant regardless of the temperature rise of the liquid crystal optical shutter.
Even if _D is lowered, if a developing method capable of developing with a relatively low potential difference is used, changes in print density and white base stains do not occur. However, when reversal development is performed, V _D decreases as the temperature of the liquid crystal optical shutter rises. Therefore, if the developing bias voltage is constant, white background base stains gradually occur. In order to prevent such a situation, when the bias voltage is set low, V _D rises as the temperature of the liquid crystal optical shutter decreases, and the difference between V _D and the bias voltage increases, so that the case where a two-component developer is used. The carrier adheres to the toner, and when a one-component developer is used, the toner adheres regardless of the polarity.

It is also possible to install a cooling device that does not raise the temperature of the liquid crystal optical shutter, but this requires cooling the liquid crystal optical shutter installed in a sealed and narrow space, and requires a considerably large cooling device. However, the size of the entire device is increased. In addition, there is also a balance with a fan for cooling the light source,
There is a drawback that the liquid crystal optical shutter is cooled too much and the light source is also cooled too much.

[Object of the Invention]

In view of the above-mentioned drawbacks, an object of the present invention is to provide a recording apparatus capable of maintaining high print quality by preventing the occurrence of stains on the base of a white background and the pulling of the carrier even if the temperature rises.

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention is directed to a photoconductor and optical writing in which light from a light source is modulated by a liquid crystal optical shutter and applied to the photoconductor to form an electrostatic latent image. In the recording apparatus, the recording device is provided with: a developing unit for developing the latent image, which has a carrier for carrying a developer, and a voltage applying unit for applying a bias voltage to the carrier for the developer. A temperature detecting means for detecting the temperature of the shutter and a control means for varying the bias voltage of the voltage applying means based on the output of the detecting means are provided.

Example of Invention

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 2 is a schematic configuration diagram of the recording apparatus according to the present invention.

In FIG. 2, reference numeral 1 denotes a photosensitive drum having a photoconductive thin film formed on its peripheral surface, which rotates at a constant speed in the illustrated direction. The photosensitive drum 1 is charged by the charger 2, and thereafter, optical writing is performed by the liquid crystal head 3 using the liquid crystal optical shutter. The liquid crystal head 3 has a light source, a liquid crystal optical shutter including a large number of micro shutters arranged along the main scanning direction of the photosensitive drum 1, and the like, which will be described later in detail. An electrostatic latent image is formed on the photosensitive drum 1 by selectively opening and closing in accordance with. The formed latent image is visualized by the developing device 4 using toner. The developing device 4 has a developing sleeve 5 axially supported at a position close to the photosensitive drum 1. By rotating the developing sleeve 5 carrying a developer, the developer contacts the surface of the photosensitive drum. Thus, a toner image is formed by attaching only the toner to the latent image portion. Further, as will be described later in detail, a bias voltage is applied to the developing sleeve 5 from the bias power source 5 whose voltage changes according to the temperature of the liquid crystal optical shutter.

The toner image formed on the photosensitive drum 1 is transferred by the transfer device 7 onto a transfer paper 8 fed from a cassette (not shown). After the transfer, the transfer paper 8 is separated from the photosensitive drum 1 by a separator (not shown), fixed by a fixing device (not shown), and then ejected to the outside of the machine. On the other hand, although untransferred toner remains on the surface of the photosensitive drum 1, the residual toner is removed by the cleaner 9.

FIG. 3 shows a specific structure of the liquid crystal head 3 described above.

As shown in the figure, the liquid crystal head 3 includes a light source 10, a light source heater 11, a liquid crystal optical shutter 12, a liquid crystal heater 13,
The image forming lens 14 and control substrates 15a and 15b are mainly included. A fluorescent lamp is used as the light source 10, and a thermistor 16 that detects the temperature of the light source heater 11 is attached to one end of the light source heater 11. The light source 1 is controlled by controlling the energization of the light source heater 11 or the operation of a cooling fan (not shown) for cooling based on the detection value of the thermistor 16.
The tube wall temperature of 0 is kept constant.

The liquid crystal optical shutter 12 is a guest-host type,
As described above, each micro shutter opens and closes according to the recording signal, so that optical writing is performed on the photosensitive drum 1. A thermistor 17 that detects the temperature of the liquid crystal optical shutter 12 is attached to one end of the liquid crystal heater 13 that heats the liquid crystal optical shutter 12, and the energization of the liquid crystal heater 13 is controlled based on the detection value of the thermistor 17. To be done. However, when continuous printing is performed in a high temperature environment, the temperature of the liquid crystal optical shutter 12 further rises due to heat dissipation of the light source 10 and self-heating of the liquid crystal optical shutter 12. Further, when a so-called dual frequency driving method is used as a driving method of the liquid crystal, an electric field of a relatively high frequency is applied to the liquid crystal, and since the liquid crystal is equivalent to a capacitor, a flowing current value becomes large and self-heating occurs. There is also a large amount.

Therefore, when the liquid crystal optical shutter reaches a predetermined temperature, the energization to the liquid crystal heater 13 is stopped, but when continuous printing is performed, even if the energization is stopped, the liquid crystal optical shutter 1 is as described above.
The temperature of 2 will rise further.

FIG. 1 is a block diagram of an embodiment of the present invention, which is intended to prevent the above-mentioned white background portion base stain and the like due to the temperature rise of the liquid crystal optical shutter 12. The configuration and operation will be described in detail below.

The output of the thermistor that detects the temperature of the liquid crystal optical shutter 12 is output to the temperature control circuit 18, and the temperature control circuit 18 controls the energization of the liquid crystal heater 13 based on the detection value of the thermistor 17 to generate the liquid crystal light. The temperature of the shutter 12 is controlled so as to be maintained at the set temperature (however, the temperature is not kept constant at all for the above reason). The output of the thermistor 17 is output to the comparison calculation circuit 19, and the comparison calculation circuit 19 calculates the voltage applied to the developing sleeve 5 according to the temperature of the liquid crystal optical shutter 12 from the detection value of the thermistor 17. That is, since the liquid crystal optical shutter 12 has the temperature characteristic as described above, the voltage applied to the developing sleep 5 is changed according to the temperature of the liquid crystal optical shutter 12. More specifically, since the light transmittance depends on the temperature when the micro shutters of the liquid crystal optical shutter 12 are closed, as shown by the broken line in FIG. Thus, the voltage applied to the developing sleeve 5 is changed. Therefore, the calculation result of the comparison calculation circuit 19 is output to the developing bias voltage control circuit 20, and the control circuit 20 outputs a variable voltage signal to the bias power source 6 based on the above calculation result. As a result, the bias power source 6 generates a voltage according to the temperature characteristic of the liquid crystal optical shutter 12 as described above, and applies this voltage to the developing sleeve 5. Therefore, since the voltage applied to the developing sleeve 5 changes according to the temperature of the liquid crystal optical shutter 12, when the reversal phenomenon is performed, the white background base stain occurs even if the photoconductor potential changes when the shutter is closed. There is no such thing. In this case,
Since the voltage of the bias power supply is changed based on the output of the thermistor 17 for temperature control, a photoelectric conversion element for detecting the light transmittance when the shutter is closed, a detection element for detecting the potential of the photoconductor, etc. are required. There is no such thing.

As a result of experiments conducted by the inventor of the present application, the set temperature of the liquid crystal optical shutter 12 is set to 44 ° C., the ambient temperature is set to 35 ° C., and the bias voltage is varied according to the temperature characteristics of the liquid crystal optical shutter as shown by the broken line in FIG. Then, when 1000 sheets were continuously printed, the liquid crystal optical shutter rose to 48 ° C and the developing bias voltage was 380 V at this time, but the white background base stain did not occur at all and printing started. We were able to obtain the same high printing quality as at the time.

In the example, the guest-host type liquid crystal optical shutter is used, but when a TN (orthogonal Nicol) liquid crystal optical shutter is used, opening and closing of the shutter are opposite to those of the guest-host type. Since the light transmittance at the time of opening has a temperature characteristic, the bias voltage may be changed when the developing method is normal development.

〔The invention's effect〕

As described above, according to the present invention, the bias voltage to the carrier that conveys the developer to the photoconductor is changed based on the output of the temperature detection unit that detects the temperature of the liquid crystal optical shutter, so that the temperature rises. As a result, even if the light transmittance of the shutter changes, it is possible to prevent the occurrence of dirt on the white background base and the occurrence of carrier pulling. Therefore, even if the liquid crystal optical shutter is continuously printed at a high temperature, good printing quality can be maintained. Further, since it is unnecessary to use a large-sized cooling device, the entire recording device does not become large.

[Brief description of drawings]

 FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a schematic configuration diagram of a recording apparatus according to the present invention, FIG. 3 is a sectional view of a liquid crystal head, and FIG. 4 is a temperature characteristic diagram of a liquid crystal optical shutter. Is. 1 ... Photosensitive drum, 3 ... Liquid crystal head, 4 ... Developing device, 5 ... Developing sleeve, 6 ... Bias power source, 10 ... Light source, 11 ... Light source heater, 12 ... Liquid crystal optical shutter, 13 …… Liquid crystal heater, 16, 17 …… Thermistor, 18 …… Temperature control circuit, 19 …… Comparison arithmetic circuit, 20 …… Development bias voltage control circuit.

Claims (1)

[Claims] 1. A photoconductor, an optical writing unit for forming an electrostatic latent image by modulating light from a light source by a liquid crystal optical shutter and irradiating the photoconductor, and a carrier carrying a developer. In a recording apparatus including a developing unit having the latent image and developing the latent image, and a voltage applying unit applying a bias voltage to the carrier of the developer, a temperature detecting unit detecting the temperature of the liquid crystal optical shutter, A recording apparatus, comprising: a control unit that varies a bias voltage of the voltage applying unit based on an output of the detecting unit.