JPS6358322A - Control system for light transmissivity - Google Patents

Abstract

PURPOSE:To stably vary light transmissivity with good reproducibility by determining the time width of a voltage applied to a material which varies in light transmissivity according to the variation of the applied voltage as compared with a reference signal with a specific waveform. CONSTITUTION:A digital signal is D/A-converted 11 into an analog signal 11a. Then a triangular wave generator 12 generates a triangular wave signal 12a. A pulse signal 13a obtained by making a comparison between the signals 11a and 12a is inputted to a liquid crystal driving signal generating circuit 2. Further, an on-off signal is inputted from a liquid crystal on-off signal to the liquid crystal driving signal generating circuit 2, the pulse width of the on-off signal is controlled with the pulse signal 13a from a comparator 13, and the opening and closing of the liquid crystal 4 are controlled through a liquid crystal shutter driver 3. Consequently, the light transmissivity is controlled stably with good reproductivity. This liquid crystal array is combined with an electrophotographic process to improve the reproducibility of half-tones.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application in Industry A] The present invention relates to a method for controlling light transmittance, and particularly to a method for controlling light transmittance of a substance whose light transmittance changes according to changes in applied voltage.

[Prior Art] Conventionally, there are printers using liquid crystal shutters that utilize the light transmittance or light shielding properties of liquid crystals and the like. However, the liquid crystal shutter is simply controlled by two types of signals: a signal that transmits light and a signal that blocks light, and by transmitting or blocking light with the liquid crystal shutter, only two types of image gradation, white and black, can be reproduced. First, the image gradation was poor. Therefore, in the case of originals with many intermediate density tones, such as photographs, the gradation of the image is poor, making it unusable.

[Problems to be Solved by the Invention] The present invention eliminates the drawbacks of the above-mentioned conventional example and at the same time
Provided is a light transmittance control method that stably changes the i-passage rate with good reproducibility.

[Means and effects for solving the problem] As a means for solving this problem, the method of controlling the light transmittance of a substance whose light transmittance changes according to changes in applied voltage according to the present invention is as follows. The time width of the applied voltage is determined based on a comparison between a control signal for controlling the ratio and a reference signal having a predetermined waveform.

[Example] FIG. 1(a) is a block diagram of a light transmittance control device according to an embodiment of the present invention, which implements the light transmittance control method of the present invention, and uses pulse width modulation to convert a digital manual signal into an analog pulse. circuit 1
, a liquid crystal shutter driver 3 that receives the signal and drives the liquid crystal shutter, and a liquid crystal shutter 4 that can change the transmittance.
It consists of three main parts. In the pulse width modulation circuit 1, the 64Vlj tone digital human input signal (0 to 63) is
The analog signal 11a converted by the /A conversion circuit 11 is converted into the signal 12 output from the triangular wave generator 12.
By comparing a with comparator 13, the signal becomes 64
The output pulse 13a is converted into a step pulse and outputted as an output pulse 13a.

FIG. 1(b) shows each waveform of the pulse width modulation circuit 1. In response to this 64-step pulse signal, the liquid crystal turns ON10F.
Based on the signal from the F signal generator 5, the liquid crystal drive signal forming circuit 2 creates a predetermined signal, and the liquid crystal shutter driver 3 amplifies the predetermined signal to the applied voltage level necessary for driving the liquid crystal shutter 4. The liquid crystal shutter 4 is driven according to the ON sequence.

Note that a configuration may also be considered in which a circuit for correcting the nonlinear relationship between the human input signal and the light transmittance of the liquid crystal shutter 4 is sandwiched between the pulse width modulation port 281 and the liquid crystal shutter driver 3.

Next, a diagram illustrating the operation of a general liquid crystal shutter 4 is shown in FIG. By applying a certain voltage to the liquid crystal layer 43 sandwiched between the double force bars 41 and 42, the twist angle θ of the liquid crystal with respect to incident light perpendicular to the liquid crystal surface can be determined. This adjusts the amount of transmitted light.

FIG. 3 shows the concentration versus voltage curve of TN liquid crystal.

The effective voltage on the horizontal axis is determined by using the values in Figure 4, which will be described later.
(Effective voltage) = 1 ・ It can be written as. The change in density is large with respect to a change in the load voltage (2), and fine adjustment of the voltage V is required to determine the density with good gradation.

Figure 4 shows the ON wave and OFF wave of the liquid crystal.

The ON and OFF waves of the liquid crystal have the general shapes shown in the figure, but the reproduction of intermediate tones depends on the division and shape of the tip of the first pulse of the ON wave. Drive potential V02 is 1/3 bias or higher, bias a is 9 to 11, I/T (d
(utility ratio) shall be 64 to 128. In other words, O
By controlling the leading edge pulse width of the N wave by the pulse width modulation circuit 1, it is possible to faithfully control the light transmittance of the liquid crystal shutter 4.

Note that by changing the configuration from the comparator to the liquid crystal drive by simplifying the configuration, it is possible to take the input signal and reflect it faithfully on the light transmittance of the liquid crystal.

Furthermore, although the present invention has been shown as an example of driving only one liquid crystal, it can be applied to improve halftone reproduction in displays, etc. by using a plurality of liquid crystals or a large number of liquid crystals.

An example of application to a liquid crystal display is shown in FIG.

A digital video human input signal 51 is passed through a pulse width modulation circuit 2@52 to drive the liquid crystal of a display consisting of a liquid crystal having nxm pixels. Therefore, it is possible to display an image with good halftone reproduction on the liquid crystal display 53.

Furthermore, by combining this liquid crystal array with an electrophotographic process, a digital liquid crystal printer 60 with very good halftone reproducibility can be obtained. An example of application to a digital liquid crystal printer is shown in FIG. The digital human input signal 61 is pulse width modulated by a pulse width modulation circuit and a drive generator 62, and the drive generator drives the liquid crystal shutter array 63. The amount of exposure at that time is adjusted by the density of the liquid crystal shutter, and the intermediate tones can also be changed with good reproducibility.

With the configuration of the embodiment described above, it is possible to convert signal pulses relatively easily by performing signal conversion called pulse width modulation for processing human input signals. By controlling the light transmittance of the liquid crystal shutter using this signal pulse, it is possible to control the light transmittance more faithfully than the original input signal.

In this embodiment, control of light transmittance using liquid crystal has been explained, but the technical idea of the present invention can also be applied to other substances whose light transmittance is changed by applied pressure.

[Effects of the Invention] The present invention can provide a light transmittance control method that stably changes the light transmittance with good reproducibility.

[Brief explanation of the drawing]

Fig. 1(a) is a configuration diagram of the light transmittance control neck device of this embodiment, Fig. 1(b) is a waveform diagram of the pulse width modulation circuit of this embodiment, and Fig. 2 is an explanatory diagram of the operation of the liquid crystal shutter. , Figure 3 shows the concentration vs. voltage curve of TN liquid crystal, Figure 4 shows the ON wave and OFF wave of liquid crystal, Figure 5 shows an example of application to liquid crystal display, and Figure 6 shows digital liquid crystal. It is a diagram showing an example of application to a printer. In the figure, 1... pulse width modulation circuit, 2... liquid crystal drive signal forming circuit, 3... liquid crystal shutter driver, 4...
Liquid crystal shutter, 5... Liquid crystal ON10FF signal generator, 11... D/A conversion circuit, 12... Triangular wave generator, 13... Comparator. Patent applicant: Canon Co., Ltd. Figure 1 (0) Figure 1 (b)

Claims (3)

[Claims] (1) In a method of controlling the light transmittance of a substance in which the light transmittance changes according to a change in applied voltage, the applied voltage is A light transmittance control method characterized by determining the time width of the light transmittance. (2) The light transmittance control method according to claim 1, wherein the reference signal has a waveform such as a triangular wave that repeatedly rises and falls. (3) The light transmittance control method according to claim 2, wherein a predetermined applied voltage is applied while the control signal is greater than the reference signal.