Patent ID: 7079245

Claim:
A method for detecting the gap of a liquid-crystal panel, the method comprising the steps of: arranging the liquid-crystal panel so that a polarized incident light is incident almost parallel to the normal to the liquid-crystal panel and the reflected light from the liquid-crystal panel is received by a received light quantity detection device via an analyzer having a transmission axis almost perpendicular to the polarization direction of the incident light; rotating the direction of polarization of the incident light with respect to the liquid-crystal panel and detecting the extinction angle at which the intensity of light detected by the received light quantity detection device reaches minimum; and detecting the gap of the liquid-crystal panel based on the detected extinction angle, wherein gap d of the liquid-crystal panel is detected by the following equations by using the detected extinction angle φ app : tan ⁢ ⁢ 2 ⁢ ⁢ ϕ ⁢ ⁢ app = tan ⁢ ⁢ 2 ⁢ ( ϕ ⁢ ⁢ app + Π 2 ) = ϕ ⁢ ⁢ tan ⁢ ⁢ X X X = ϕ 2 + β 2 ⁢ β = Π ⁢ ⁢ Δ ⁢ ⁢ n ⁢ ⁢ d λ Δ ⁢ ⁢ n = n e · n o n o 2 + ( n e 2 - n o 2 ) ⁢ sin 2 ⁢ θ - n o where λ is the wavelength of the incident light, φ is the twisting angle of the liquid-crystal panel, n o is the refractive index of the liquid crystal material with respect to ordinary light, n e is the refractive index of the liquid crystal material with respect to extraordinary light, Δn is the refractive index anisotropy of the liquid-crystal panel, and θ is the tilt angle of the liquid-crystal panel.