Modified Tooth Design of a Trochoidal Sprocket for a Roller Chain Drive to Improve Positioning Accuracy

Two types of modified sprocket tooth profiles based on trochoidal sprockets are proposed to improve the positioning accuracy of roller chain drive mechanisms. The proposed sprocket tooth profiles consider reductions in polygonal action and polygonal action + undercut. To reduce polygonal action, a method to shave off the excess feed displacement of the chain roller from the trochoidal sprocket tooth profile is applied. To reduce undercut, a method to smooth the convex part is applied, in which the radius of curvature of the tooth profile is less than the radius of the chain roller by cubic spline interpolation. The prototype sprockets with the proposed tooth profiles are produced, and the positioning performance test is evaluated using relative values based on a commercially available JIS sprocket. The average positioning errors for the two modified sprockets show performance improvements of 4.5% and 9.0%, respectively. In addition, the average positioning error at a medium load torque can be improved better than those at other load torques. From these results, the two proposed modified sprockets are found to be useful for positioning performance.