JPS6420890A - Cloth thickness detector of sewing machine - Google Patents

Abstract

PURPOSE: To collect the correct cloth thickness of a place where seams are actually formed, to correctly calculate a required thread quantity corresponding to the cloth thickness and to form the excellent seams by detecting a work cloth by means of the contact resistance of the work cloth, which is worked on a needle. CONSTITUTION: A work cloth detecting means 14 detects the work cloth based on the contact resistance of the work cloth, which is worked on the needle, by the downward movement of the needle which is vertically moved through the work cloth on a work cloth support surface. A cloth thickness arithmetic means 42 calculates the thickness of the work cloth by a timing for detecting the cloth work by the means 14 and a timing when the needle comes to a prescribed position in the vertical movement locus of the needle, that is, the timing when it arrives at an upper dead center. Therefore, correct cloth thickness data of a needle fall point position, that is, the places where the seams are actually formed are collected regardless of a cloth feeding direction. Then, a correct upper thread quantity corresponding to the cloth thickness is calculated and fed so that the excellent seams are formed.