1. Field of the Invention
This invention relates to a touch panel which detects an input position inputted by a nib of a pen or a fingertip by means of optical sensors and an electronic equipment provided with such a touch panel.
2. Description of the Related Art
Conventionally, a touch panel is provided with pressure sensitive type sensors or electrostatic capacity type sensors on an entire panel surface and when the panel surface is touched with the nib or the fingertip, the sensors detect the position of the nib or the fingertip. Such a touch panel, however, requires mounting of sensors on the entire panel surface so that manufacturing of the touch panel is difficult and there also exists a problem in terms of its mechanical strength.
As a touch panel which can solve the above-mentioned problems, an optical type (or a photoconductive type) touch panel which disposes light emitting elements and light receiving elements on the periphery of a panel in an opposed manner is known. FIGS. 8A and 8B show such an optical type touch panel schematically. FIG. 8A is a top view and FIG. 8B is a cross-sectional view taken along a dashed line A-A′ of FIG. 8A.
As shown in FIGS. 8A and 8B, the light emitting elements 12a, 12b, 12c, 12d and 12e are arranged in line on one side of the panel 11 and the light receiving elements 13a, 13b, 13c, 13d and 13e are arranged in line on an opposing side of the panel 11. When the finger touches the panel 11, a light emitted from the light emitting element 12b is interrupted at a touched position and hence, an output signal of the light receiving element 13b opposing to the light emitting element 12b is reduced. That is, the finger touched position is detected as a position of the light receiving element of which the output signal has been reduced.
With respect to such an optical type touch panel shown in FIGS. 8A and 8B, however, the light propagates in air so that the light is liable to receive an outdoor daytime light. Furthermore, there is a drawback that the surfaces of the light emitting members 12a, 12b, 12c, 12d and 12e and the light receiving members 13a, 13b, 13c, 13d and 13e easily get dirty. One of touch panels in which this defect have been improved is disclosed in Japanese Patent Laid-Open No. 7-253853. An entire disclosure of the Japanese Patent Laid-Open No. 7-253853 is incorporated herein by reference.
As shown in FIG. 9, in the Japanese Patent Laid-Open No. 7-253853, light emitting elements 22 are arranged in line on a side face of a deformable panel 21 including anisotropic transparent crystal and light receiving elements 23 are arranged in line on a side face opposing to the above-mentioned side face. Since the light emitting elements 22 and the light receiving elements 23 are mounted in close contact with the side faces of the panel 21, the panel hardly receives the influence of stain.
An emitted light from the light emitting element 22 advances toward the light receiving element 23 along an optical path P. When the panel 21 is pushed by a finger, a pushed portion is distorted and the emitted light from the light emitting element 22 advances along an optical path Q so that the emitted light is not received by the light receiving element 23. In this manner, a position of a portion which the finger touched can be detected. In such a touch panel, since the emitted light from the light emitting element advances in the inside of the panel and hence, it receives no influence of an outdoor daytime light.
With respect to the touch panel described in the Japanese Patent Laid-Open No. 7-253853 shown in FIG. 9, however, since the panel 21 is deformed, when the panel 21 is mounted on the upper surface of a liquid crystal panel, the influence caused by the deformation of the panel 21 is transferred to the liquid crystal panel and affects the maintenance of cell gaps.
Furthermore, although the emitted light from the light emitting element 22 is reflected and guided to the outside of the panel by making use of the deformation of the panel 21, depending on the degree of deformation of the panel 21, that is, depending on the radius of curvature of a deformed portion, there is a case that the light advancing along the optical path P cannot be reflected to the outside of the panel 21 and the light is scattered in the inside of the panel 21. When such scattering of light occurs, a finger touched position cannot be accurately detected.