Liquid crystal display apparatus

Abstract: A liquid crystal display panel (7) for mounting on a reclinable seat back (6), wherein the visual angle of the panel (7) relative to a viewer is detected (VR3) to control a voltage impressed on the liquid crystal electrodes to maintain the quality of the image even if the viewing angle of the panel (7) is changed.

Description: This invention relates to liquid crystal display apparatus particularly, but not exclusively, for mounting on the rear face of a reclinable seat back, for example in a passenger aircraft or train. A display system for use in aircraft has been proposed wherein a flat display is mounted on the rear face of the back of each seat, so that a passenger facing the display can enjoy television images or receive information. A liquid crystal panel has been proposed as a suitable flat display. As is known, a liquid crystal display apparatus has a narrow range of allowable visual (or viewing) angle (directivity), and when it is viewed from an angular position falling outside the range, the image quality is considerably degraded. Since the seat back of a passenger seat is normally reclinable, the visual angle will change with the angle of the seat back in front of the viewer, and a degradation in image quality inevitably occurs. Image quality can be improved to some extent by operating an adjusting control. However, each time the reclining angle of a seat is changed, the adjustment must be performed. However, if a passenger is not accustomed to doing the adjustment, he may not adjust the image quality optimally. Copending European Patent Application EP-A-0221582 (relevant for novelty purposes only under Article 54(3) and (4) EPC) discloses a liquid crystal display for use in a mobile communications device in which the signals driving the display can be varied depending on whether or not the device is on its stand hook so as to take account of differing viewing angles. United States Patent No. US-A-4319237 discloses a liquid crystal display in which the signals driving the display are automatically adjusted in dependence upon ambient temperature. According to the present invention there is provided a liquid crystal display apparatus mounted, in use, on a seat having a reclinable back, the apparatus comprising: a liquid crystal display panel on said back of said seat; a circuit for supplying a display signal to said panel and having at least one control electrode to which control signals can be supplied to control the quality of an image displayed on said panel; characterized by detecting means for detecting the reclining angle of said back; and thus said panel; and at least one adder through which said detecting means adjusts the magnitude of said control signals as functions of the detected reclining angle thereby to control the quality of the displayed image. Thus, an embodiment of the present invention may be a liquid crystal display apparatus mounted on a rear face of a passenger seat back of a line of passenger seats. The liquid crystal display apparatus comprises a detection means for detecting a screen viewing angle by detecting the reclining angle of the seat back. The display apparatus also has a circuit for changing a voltage impressed on a liquid crystal electrode in accordance with the output from thedetection means thereby to change the brightness or contrast level asa function of the reclining angle of the seat back. The invention will now be described by way of example withreference to the accompanying drawings, in which: Figure 1 is a circuit diagram of a liquid crystal display controlcircuit; Figure 2 is a side view of a reclining seat; Figure 3 is a waveform chart of a drive voltage for a liquidcrystal display; and Figure 4 is a graph showing the relationship of the drive voltage-visual angle characteristics of a liquid crystal display panel. Figure 1 shows a liquid crystal display control circuit which is arranged on a rear face of a seat back and to which the present invention is applied. An input colour video signal is processed by a luminance/chrominance processing circuit 1, and is decoded into red, green and blue (R, G and B) signals. The R, G and B signals are then supplied to a liquid crystal display unit 2. The circuit 1 has control terminals T1 and T2 for a brightness control input and a contrast (picture) control input respectively. Outputs from potentiometers VR1 and VR2, which are respectively the brightness and the contrast adjusting controls are supplied to the terminals T1 and T1 through the adders 3 and 4, respectively. Therefore, the brightness and contrast of the picture can be adjusted by operating the corresponding controls. Figure 2 is a side view of a reclinable seat 5. A liquid crystal display panel 7 is mounted on the rear face of a seat back 6. A potentiometer VR3 for detecting the reclining angle is mounted on the pivoting shaft about which the seat back 6 reclines, thereby detecting the reclining angle. The potentiometers VR1, VR2 and VR3 are connected between a bias source (not shown) and earth. Referring to Figure 1, a reclining angle output signal from the potentiometer VR3 is supplied to the terminals T1 and T2 of the circuit 1 through the adders 3 and 4. Then, if the screen visual angle changes due to a change in the reclining angle, the directivity of the display unit 2 is automatically corrected in accordance with the reclining angle, so that image quality is not substantially degraded. The relationships between the brightness and contrast adjusting control signals and the reclining angle detection control signal can be respectively determined by the proper selection of values for resistors R1, R2, R3 and R4 which are connected in series between the respective potentiometers VR1, VR2 and VR3, and the adders 3 and 4. Figure 3 shows an AC drive waveform impressed on the opposing electrodes of the display unit 2. Drive video signals having opposite polarities are alternately impressed on the opposing electrodes at the predetermined intervals. An AC amplitude x, that is the pedestal level of the video signal, can be changed in accordance with a signal supplied to the brightness control terminal T1 of the circuit 1, and hence, the luminance level can be changed. The amplitude y of the image component of the waveform shown in Figure 3 can be changed by a signal supplied to the contrast control terminal T2 of the circuit 1, and hence, the image contrast can be changed. The luminance level and the contrast are both changed in accordance with the output from the potentiometer VR3 to perform automatic adjustment, so that the image quality is not substantially degraded even if the visual angle is changed. Figure 4 is a graph showing the display characteristics of a twisted nematic type liquid crystal display unit 2. A visual angle ϑ1 (an axis perpendicular to a screen surface is 0°) is plotted along the Y axis, an impressed voltage x is plotted along the X axis, and the transmissivity (luminance) of the screen is plotted along the Z axis. As can be seen from this graph, when the visual angle ϑ1 is increased, the region where the transmissivity changes linearly with respect to the impressed voltage becomes narrow, and the gradient of the voltage-transmissivity curve is also changed. For this reason, unless the impressed voltage level and the image amplitude are changed, the image quality is considerably degraded. In the region inside the bold curve C in Figure 4, the image quality is degraded due to the large visual angle, and inversion of the black and white portions of the image occurs. Both the transmissivity and the contrast control factors as a function of the reclining angle can be determined based on Figure 4. For example, when the visual angle is 0°, the pedestal level x of the video signal shown in Figure 3 is set to be 1.5 V, and the white peak level is set to be about 4.5 V (picture amplitude v = 3 V ). When the image visual angle is increased by 20° in a + direction, automatic correction is performed in accordance with the output from the potentiometer VR3 so that the pedestal level x is set to 3.5 V, and the white peak level is set to be 5.5 V (picture amplitude y = 2 V ). Thus, black-white inversion of the image can be prevented. In addition, the linear region of the impressed voltage-transmissivity characteristics is corrected so as to prevent degradation such as white or black flat painting.

Claims: A liquid crystal display apparatus mounted, in use, on a passenger seat (5) having a reclinable back (6), the apparatus comprising: a liquid crystal display panel (7) on said back (6) of said seat (5); a circuit (1) for supplying a display signal to said panel (7) and having at least one control electrode (T1, T2) to which control signals can be supplied to control the quality of an image displayed on said panel (7); characterized by detecting means (VR3) for detecting the reclining angle of said back (6); and thus said panel (7); and at least one adder (3, 4) through which said detecting means (VR3) adjusts the magnitude of said control signals as functions of the detected reclining angle thereby to control the quality of the displayed image. A liquid crystal display apparatus as claimed in claim 1, wherein said control electrode (T1) controls the brightness of said image and said detecting means (VR3) includes a potentiometer (VR3) mechanically coupled between a base of said seat (5) and said back (6) such that, when said back (6) is reclined from a first position to a second position, said potentiometer (VR3) supplies a control voltage to said control electrode (T1), said control voltage varying in accordance with said reclining angle thereby automatically to adjust the brightness of the displayed image on said panel (7). A liquid crystal display apparatus as claimed in claim 1, wherein said control electrode (T2) controls the contrast of said image and said detecting means (VR3) includes a potentiometer (VR3) mechanically coupled between a base of said seat (5) and said back (6) such that, when said back (6) is reclined from a first position to a second position, said potentiometer (VR3) supplies a control voltage to said control electrode (T2), said control voltage varying in accordance with said reclining angle thereby automatically to adjust the contrast of the displayed image on said panel (7). A liquid crystal display apparatus as claimed in claim 1, wherein the contrast and brightness of said panel (7) are controllable in response to external control voltages from external control means (VR1, VR2) through respective inputs of said adders, said detecting means (VR3) including a potentiometer (VR3) which supplies other control voltages to said circuit (1) through other inputs of said adders. A liquid crystal display apparatus as claimed in any one of claims 2 and 4, wherein said display signal is a colour video signal having a pedestal level and said detecting means (VR3) controls said pedestal level. A liquid crystal display apparatus as claimed in any one of claims 3 and 4, wherein said display signal is a colour video signal and said variable means (VR3) controls the amplitude of said colour video signal.

Inventors: TOMITA HIDEO C O PATENT DIVISI, TOMITA, HIDEO C/O PATENT DIVISION
Applicants: SONY CORP, SONY CORPORATION
Application year: 1987
Main classification: G09G3
IPC codes: G09G3, G02F1, G09F9, B64D11