Wang J., Lai Y.

The conventional mechanical presses generally are driven by a fly-wheel with a constant angular velocity. There are many shortcomings of a mechanical press with a constant angular velocity, especially for cold forging and deep drawing application. Recently, mechanical presses driven directly by servo motors with variable speed have got high interest by many researchers and industry. The dynamic behaviors of a mechanical press with a variable speed are more complicate than that of a press with a constant speed. The unavoidable bearing clearance between linkages may not be a problem for the conventional press, but could be a serious problem for the mechanical press with a variable speed. In this work, the effect of the bearing clearance on the dynamic behaviors of a mechanical press with variable angular velocity was investigated. The results show that the bearing clearance may induce serious impact problem for most applications without a careful design of the velocity profile. To overcome this problem, an optimization procedure was developed in this work to design a proper velocity profile of the input in order to minimize the impact force. Instead of the traditional Bezier function, a periodic function was used in this work to design the velocity function of the input by specifying the values of the ram speed at some control points. The results show that the impact force can be effectively reduced by the proposed method with the constraint of the specified ram speed at the working region. The results also demonstrate that the stroke velocity characteristics of a mechanical press with complex linkage drive (for instance, drag-link, double knuckle drive) can be realized by a simple four-bar linkage with a proper design of the input velocity by the proposed method. Keywords: Mechanical Press, Variable Speed, Vibration.