JPH04199126A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To facilitate the easy adjustment of brightness by freely turnably providing a polarizing plate for light control in parallel with a front polarizing plate so that a liquid crystal is visible with the high brightness in the daytime and is viewed in the non-dazzling state with the lowered brightness at the nighttime or in a dark place. CONSTITUTION:This device has a liquid crystal display plate 11, the front polarizing plate 12 and rear polarizing plate 13 disposed in parallel by holding the liquid crystal display plate 11 in-between and an illuminating device 14 which irradiates these plates from behind. The light control plate 15 for regulating the light quantity is freely turnably provided in parallel with the front polarizing plate 12. The light control plate 15 is turned from 0 deg. to an arbitrary angle up to 90 deg. with respect to the axis of polarization of the front polarizing plate 12 by means of a turning means 16. The brightness of the liquid crystal display device is adjusted according to use environment in such a manner; for example, the liquid crystal is visible with the high brightness in the daytime and is viewed in the non-dazzling state with the lowered brightness at the nighttime or in the dark place.

Description

[Detailed description of the invention] [Industrial application field]

The present invention mainly relates to a TPT color liquid crystal display device, and in particular is used in in-vehicle displays such as navigation meters, which require controlling the brightness of the display screen according to the surrounding brightness. It is.

[Conventional technology]

Conventionally, in order to dim the liquid crystal display, a method has been used to control the brightness of a lighting device (backlight) placed behind the liquid crystal. That is, this method controls the brightness of the fluorescent tube by controlling the electrical characteristics of the fluorescent tube used as a light source for the backlight, thereby controlling the brightness of the backlight. These methods include a method in which the output voltage of the transformer is varied by varying the voltage applied to the input of the inverter for driving the fluorescent tube, thereby limiting the tube current and dimming (voltage dimming method); is input as a pulse, and by varying this pulse width, the transformer output current is controlled and dimmed (Pulse Width Modular).
(hereinafter referred to as PWM) dimming method).
In either case, the brightness of the fluorescent tube is controlled by adjusting the current of the fluorescent tube. An example of such prior art is shown in FIG. Here, in the figure, 1 is a cold cathode fluorescent tube of the backlight, 2 is an inverter circuit that drives the fluorescent tube 1, and 3 is an input voltage variable circuit that varies the voltage applied to the input of the inverter circuit 2, or the pulse width of the input signal. PWM variable circuits that vary the PWM are shown respectively.

[Problem to be solved by the invention]

When controlling the electrical characteristics of fluorescent tubes as shown in the conventional example, the variable range of dimming is usually very narrow, 50% to 100%, and the dimming range required for in-vehicle displays (1 to 10%) is very narrow.
0%) is difficult to achieve. In addition, with conventional voltage dimming methods, lamp lighting tends to become unstable during low-temperature dimming, and when multiple lamps are being driven, there are problems such as imbalance in brightness.Furthermore, The PWM dimming method has problems such as the generation of noise depending on the pulse frequency.Furthermore, when dimming a hot cathode fluorescent tube, there are problems such as shortening the life of the fluorescent tube. In view of the above problems, it is an object of the present invention to provide a liquid crystal display device that easily realizes a very wide dimming range while maintaining a stable lighting state.

[Means for Solving the Problem] The means for solving the problem according to claim 1 of the present invention is as shown in FIGS. Polarizing plate 12 and rear polarizing plate 1
3, in which a light control polarizing plate 15 for adjusting the amount of light is rotatably provided parallel to the polarizing plate 12. The problem solving means according to claim 2 of the present invention is that the polarizing axis of the light control polarizing plate 15 according to claim 1 can be rotated at any angle from 0 degrees to 90 degrees with respect to the polarizing axis of the front polarizing plate 12. A rotating means 16 for rotating the light control polarizing plate 15 is provided. [Function] In the above problem solving means according to claims 1 and 2, the light from the illumination device 14 is linearly polarized by the rear polarizing plate 13, a part of it is changed to elliptically polarized light by the liquid crystal display plate 11, and the light from the illumination device 14 is linearly polarized by the rear polarizing plate 13. The light is linearly polarized again by the polarizing plate 12 to form an image. At this time, since the light control polarizing plate 15 is rotatably provided parallel to the front polarizing plate 12, the light control polarizing plate 15 can be rotated from 0 degrees with respect to the polarization axis of the light transmitted through the front polarizing plate 12. It can be rotated to any desired angle up to 90 degrees. Therefore, the brightness of the liquid crystal display device is adjusted according to the environment in which it is used, such as displaying the liquid crystal at high brightness during the day and lowering the brightness in dark places at night to avoid glare. This adjustment can be easily performed by using a linear motor, gear motor, etc., since it can be rotated continuously.

【Example】

Hereinafter, one embodiment of the present invention will be described based on the drawings. FIG. 1 is a sectional view of a liquid crystal display device showing an embodiment of the present invention, FIG. 2 is a perspective view of the same, FIG. 3 is a plan view thereof, and FIG. As shown in the figure, the liquid crystal display device of this embodiment has a liquid crystal display panel 1.
1, a front polarizing plate 12 and a rear polarizing plate 13 arranged in parallel with the liquid crystal display plate 11 in between, and an illumination device 14 for illuminating these from the rear, and for adjusting the amount of light. A rotating means 1 in which a plate 15 is rotatably provided parallel to the front polarizing plate 12 and rotates the dimming polarizing plate 15.
6 is provided. The liquid crystal display panel 11 includes a thin film transistor (T
PT) is used, and as shown in FIG. 2, it is formed into a rectangular shape in plan view. The front polarizing plate 12 and the rear polarizing plate 13 are, for example,
Iodine is adsorbed onto a thin film of a polymer such as polyvinyl alcohol, of which the front polarizing plate 12 is placed on the front of the liquid crystal display plate 11, and the rear polarizing plate 13 is placed on the back of the liquid crystal display plate 11. The illumination device 14 is of a backlight type, as shown in FIG. It consists of an arcuate reflecting plate 22 that reflects the light toward the liquid crystal display panel 11 side. As shown in FIGS. 2 and 3, the light control polarizing plate 15 is formed into a circular shape using the same material as the front polarizing plate 12 and the rear polarizing plate 13, and the edge 23 is attached to the lower surface. It is formed into an annular shape via the ring 23a. This is a linear motor consisting of a movable element 31 and a magnetic field forming member 32 provided on the support frame 24 so as to face the movable element 31. The movable member 31 is a short arc-shaped permanent magnet, and is fixed to two opposing sides of the light control polarizing plate 15. The magnetic field forming member 32 is a large number of coiled electromagnets arranged in parallel along the support frame 24, and by switching the surface of the magnetic field forming member 32 facing the movable element 31 to an N pole or an S pole. The movable element 31 is guided by attraction or repulsion. The magnetic field forming member 32 is connected to the support frame 24
An insertion groove 24b into which the ring 23 of the polarizing plate 15 is inserted is formed by being spaced apart from the detachment prevention ring 24a of the support frame 24. Then, each electromagnet of the magnetic field forming member 32 is controlled by an external linear motor control circuit so that the polarization axis of the dimming polarizing plate 15 is set at any angle from 0 degrees to 90 degrees with respect to the polarization axis of the front polarizing plate 12. N/S switching control is performed so that it can be rotated at different angles. In the above configuration, the light from the illumination device 14 is first linearly polarized by the rear polarizing plate 13, then a part of it is changed to elliptically polarized light by the liquid crystal display plate 11, and this is further changed to elliptically polarized light by the front polarizing plate 12. By being linearly polarized, the liquid crystal display plate 11
Only a portion of the light that has passed through passes through the front polarizer 12, thereby forming an image on the front polarizer 12. Here, when adjusting the amount of light according to the usage environment, an external control circuit (not shown) is adjusted, and the control circuit controls the magnetic field forming member 32 of the rotating means 16. , the light control polarizing plate 15 is rotated to a desired angle from 0 degrees to 90 degrees with respect to the polarization axis of the light transmitted through the front polarizing plate 12. FIG. 4 shows data on the dimming range obtained through experiments on light amount adjustment. As can be seen from this experimental data, the light control polarizing plate 15
the polarization axis of the front polarizing plate 12 from 0 degrees to 9 degrees.
By changing to 0 degrees, the dimming range is 100 +
It is possible to control more than one. Also, the deviation angle of the polarization axis is 0 degrees, 45 degrees, and 60 degrees. By changing the brightness in steps of 70 degrees and 85 degrees, the brightness of the screen can be changed to 100%, 50%, 25%, 10%, and 1%. Therefore, for example, in the daytime, the polarization axis of the light control polarizing plate 15 is set to be 0 degrees with respect to the polarization axis of the front polarizing plate 12, and the screen of the liquid crystal display device is made to have high brightness. In addition, in dark places at night, set the polarization axis of the light control polarizing plate 15 at a phase angle of about 70 to 85 degrees with respect to the polarization axis of the front polarizing plate 12 to lower the brightness and view without dazzling. becomes possible. Furthermore, in a relatively dark place during the day or a relatively bright place at night, the angles of both polarization axes may be set to be in phase with each other by about 45 degrees. In this way, since the light control polarizing plate 15 is rotatably provided parallel to the front polarizing plate 12, the liquid crystal can be seen with high brightness during the day, and the brightness can be lowered in dark places at night to prevent glare. The brightness of the liquid crystal display device can be adjusted according to the usage environment, such as when viewing a display, making it possible to adjust the brightness over a wider range and more precisely than by changing the brightness of conventional fluorescent tubes. Therefore, a very wide dimming range can be easily achieved while maintaining a stable lighting state. The effect is particularly great when the liquid crystal display device is used inside a vehicle such as an automobile, where dimming is most necessary regardless of day or night. Moreover, since the polarization axis of the dimming polarizing plate 15 can be rotated to any angle from 0 degrees to 90 degrees with respect to the polarization axis of the front polarizing plate 12, the brightness of the liquid crystal display device can be adjusted over a wide range. be able to. Moreover, if a large number of magnetic field forming members 32 of the rotating means 16 are used, the polarizing plate 15 can be rotated little by little, thereby allowing fine dimming. Note that the present invention is not limited to the above embodiments (
Of course, many modifications and changes can be made to the embodiments described above without departing from the scope of the invention. For example, in the above embodiment, it is assumed that a circular polarizing plate is provided as the dimming polarizing plate 15, but if the angle variable range is limited, a rectangular polarizing plate as shown in FIG. It is possible. Moreover, instead of a magnet, the rotating means 16 is, for example, as shown in FIG. 6, toothed shapes 33 are formed on the lower surface of the light control polarizing plate 15, and the rotating means 16 is driven using a gear 34 and a motor 35. It may be. Alternatively, a manually operable dial plate may be used instead of the motor. [Effects of the Invention] As is clear from the above description, according to claim 1.2 of the present invention, since the polarizing plate for dimming is rotatably provided parallel to the front polarizing plate, the brightness is high during the daytime. The brightness of the liquid crystal display device can be easily adjusted according to the usage environment, such as by lowering the brightness in dark places at night and viewing without glare.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of a liquid crystal display device showing one embodiment of the present invention. FIG. 2 is the same (a perspective view thereof. FIG. 3 is a plan view thereof. FIG. 4 is an explanatory diagram showing the optical characteristics of this embodiment. FIG. FIG. 6 is a plan view of a liquid crystal display device showing an embodiment. FIG. 6 is a side view showing another embodiment of the rotating means of the liquid crystal display device of the present invention. FIG. 7 is a circuit diagram of a conventional liquid crystal display device. It is a diagram showing the configuration. 11: Liquid crystal display board, 12: Front polarizing plate, 13, Back polarizing plate, 14: Illumination device, 15: Polarizing plate for dimming, 16 Two rotation means. Applicant Sharp Corporation

Claims (1)

[Claims] 1. A dimming device for adjusting the amount of light in a liquid crystal display device comprising a liquid crystal display plate, and a front polarizing plate and a rear polarizing plate arranged in parallel with the liquid crystal display plate in between. A liquid crystal display device, characterized in that a polarizing plate is rotatably provided parallel to the polarizing plate. 2. The liquid crystal display device according to claim 1, further comprising a rotating means for rotating the polarizing plate for light control, and the polarizing axis of the polarizing plate for light control is rotated by the rotating means with respect to the polarizing axis of the front polarizing plate. A liquid crystal display device characterized in that it can be rotated to any angle from 0 degrees to 90 degrees.