Friction-coefficient estimating device and friction-coefficient estimating method

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.