Eccentric cam for electrophotocopier developer unit

An improvement in an electrophotocopying machine having a photoconductive surface and a retractable, pivotably mounted developer unit for developing an electrostatic image on the photoconductive surface. The improvement comprises at least one eccentric cam for moving said developer unit into and out of developing engagement with said photoconductive surface, said cam having a curved, cantilevered arm extending therefrom, said arm increasing the effective radius of said cam starting from the junction of the arm with the cam to the end of the arm remote from said junction, and means for reciprocally rotating said cam whereby said cam moves said developer unit into and out of developing engagement with said photoconductive surface.