| 主权项 |
1. An optical distance sensor including an optical system having a coaxial optical path on which a light emitter for emitting light that is reflected by a detection object, and a light receiver for receiving a reflected light are coaxially placed, together with a front screen placed on the coaxial optical path, the optical distance sensor comprising:
a time counter counting time between emission of the light from the light emitter and reception of the light by the light receiver as counted time; and an foreign matter (FM) detector detecting a deposition of foreign matter on the front screen based on a relationship between the counted time and an amount of the light received by the light receiver, wherein the FM detector detects a first pulse as the light not passing through the front screen and a second pulse as the light reflected back from the detection object,
(A) the FM detector determines that (i) a first light amount L1 of the first pulse is an internal reflection amount Li of the light reflected by an inner surface of the front screen, and (ii) the front screen is in a normal state without foreign matter deposited on the front screen, when a second light amount L2 of the second pulse is greater than the first light amount L1 of the first pulse,(B) the FM detector determines an obstacle cover state that the front screen is covered by an obstacle that is wider than the front cover, when the first light amount L1 of the first pulse is detected to be substantially equal to an excess light amount Lo, without detection of the second pulse, and(C) the FM detector determines a foreign matter deposit state of having foreign matter on an outside of the front screen, when (i) the first light amount L1 of the light of the first pulse is greater than the internal reflection light amount Li and is smaller than the excess light amount Lo, and (ii) the second light amount L2 of the second pulse is smaller than the second light amount L2 detected during the normal state. |
