CHARACTERISTICS OF THE VARIABLE LEAD SCREW MECHANISM WITH 3-DEGREES CONIC FRUSTUM MESHING ELEMENTS

This paper outlines the theoretical and experimental analyses of the k inematic and kinetostatic characteristics of a variable lead screw mec hanism (VLSM) used in high-speed shuttleless weaving looms. The mechan ism consists of a slider-crank submechanism equipped with four conic f rustum meshing elements with a 3 degrees conical angle to drive the va riable lead screw in an oscillating manner. The screw and meshing elem ents act as a spatial cam pair. The conjugate surface theory and coord inate transformation are applied to develop the theoretical models use d to analyze the mechanism. The kinematic curve is synthesized using o ptimization techniques that minimize the dissipated power due to the f riction between the screw and meshing elements. The power equation is applied to analyze the input power of the VLSM, and the generalized La nchester balancer technique is used in the design of the counterweight to reduce the shaking force. Experimental instruments are used for me asuring the characteristics of the mechanism, including the angular ve locity of the crank, the motion (including angular displacement, veloc ity and acceleration) of the screw, the input power, and the shaking f orces before and after adding the counterweight. Using a specified con stant speed or the measured state of motion of the crank, the VLSM is analyzed theoretically, and results are compared with the measured res ults. It is shown that the input power of the prototype proposed is ab out one-quarter less than that of a commercial product, and the shakin g force of the mechanism can be reduced by 46% once the proposed count erweight is added.