Patent ID: 7019321

Claim:
A sensing device in which a light emitted from a light-emitting member is introduced to a transparent plate, reflected by a sensing surface of the transparent plate and then received by a photo-detector, thereby detecting a condition of an object that has impacted on the sensing surface, the sensing device comprising: a sampling part for sampling signals from the photo-detector; a fluctuation sensing part for sensing a fluctuation of the signals from the photo-detector; and a judging part for estimating a size of a liquid drop as the object on the sensing surface based on a changing pattern of the signal fluctuation sensed by the fluctuation sensing part; wherein the fluctuation sensing part comprises a part for compressing signals in a sequence of the sampled signals when they continue within a single segment, where a plurality of the segments defined by a plurality of predetermined values are set with respect to an input signal, and a part for calculating a compressibility from the number of the sampled signals to be compressed by the part for compressing the signals and the number of the sampled signals that have been compressed thereby, and senses a period of the signal fluctuation from a time the signal fluctuation is sensed to a time an attenuation of a degree of the signal fluctuation to a predetermined degree is sensed based on the compressibility, the fluctuation sensing part further comprises a part for calculating the number of times that signals in the sequence of the sampled signals change from one segment to another within a predetermined period and a part for calculating a direction of increase or decrease of the change and a change amount thereof, and senses a degree of the signal fluctuation based on the direction of increase or decrease of the change and the change amount, the changing pattern of the signal fluctuation used in the judging next is a changing pattern of the period of the signal fluctuation sensed in the fluctuation sensing part, and the changing pattern of the signal fluctuation used in the judging part is a changing pattern of the degree of the signal fluctuation sensed in the fluctuations sensing part.