Patent ID: 8508750

Claim:
A friction-coefficient estimating device comprising: an irradiating unit that includes a first irradiating unit that irradiates a light on a surface of a medium in a form of a sheet at a first incident angle, and a second irradiating unit that irradiates a light on the surface of the medium at a second incident angle different from the first incident angle; a specularly-reflected light receiving unit that includes a first specularly-reflected light receiving unit that receives a first specularly-reflected light component of a reflected light obtained when the light irradiated from the first irradiating unit is reflected at the surface and that detects a first specularly-reflected light intensity that is an intensity of the first specularly-reflected light component, and a second specularly-reflected light receiving unit that receives a second specularly-reflected light component of a reflected light obtained when the light irradiated from the second irradiating unit is reflected at the surface and that detects a second specularly-reflected light intensity that is an intensity of the second specularly-reflected light component; a diffusely-reflected light receiving unit that receives a diffusely-reflected light component of a reflected light obtained when the light irradiated from the irradiating unit is reflected at the surface and that detects a diffusely-reflected light intensity that is an intensity of the diffusely-reflected light component; and a control unit that estimates a friction coefficient of the surface based on a first reflected-light intensity coefficient and a second reflected-light intensity coefficient, wherein the first reflected-light intensity coefficient is a ratio of the diffusely-reflected light intensity and the first specularly-reflected light intensity when the first irradiating unit irradiates the light on the surface, and the second reflected-light intensity coefficient is a ratio of the diffusely-reflected light intensity and the second specularly-reflected light intensity when the second irradiating unit irradiates the light on the surface.