The equations of profile curve of the eccentric cam from the self-locking conditions satisfied at any point of the cam profile are deduced in the present paper.The shape of the curve is classified into two kinds: the accurate shape of the cam and the logarithmic spiral as the first approximation. An analysis of forces exerting on the cam is obtained according to the two kinds of curves and the magnitude of clamping forces calculated. In dealing with the self-locking conditions and the analysis of forces exerting on the cam, the friction on the axle is considered and the concept of the circle of friction is introduced.