Yongjun Bai

Kinematic and dynamic analyses of the multi-actuated mechanical press with parallel topology

This article proposes a new type of multi-actuated mechanical press with parallel topology to develop high stamping capacity. Four active limbs actuated by servomotor deliver forces and motions to moving platform, and the passive limbs are driven by moving platform to push or pull the ram. This four-input-single-output system realizes multiple actuations without causing being over-constrained. Due to infinite number of solutions for the inverse kinematics, selection of actuation schemes for given ram trajectories is more crucial. Further, the principle of virtual work is used in the inverse dynamic problem. By choosing the pose variables of moving platform as generalized coordinates to describe the manipulator system, the linear form of dynamic models is derived. A typical deep-drawing process with nominal 25,000 kN capacity and 1200 mm stroke is simulated, and the required driving torques are computed. These performance analyses provide a basis to the design of the control law or the estimation of servomotor parameters for the mechanical press.

Dynamic Modeling and Experiment of a New Type of Parallel Servo Press Considering Gravity Counterbalance

The large capacity servo press is traditionally realized by means of redundant actuation, however there exist the over-constraint problem and interference among actuators, which increases the control difficulty and the product cost. A new type of press mechanism with parallel topology is presented to develop the mechanical servo press with high stamping capacity. The dynamic model considering gravity counterbalance is proposed based on the virtual work principle, and then the effect of counterbalance cylinder on the dynamic performance of the servo press is studied. It is found that the motor torque required to operate the press is a lot less than the others when the ratio of the counterbalance force to the gravity of ram is in the vicinity of 1.0. The stamping force of the real press prototype can reach up to 25 MN on the position of 13 mm away from the bottom dead center. The typical deep-drawing process with 1 200 mm stroke at 8 strokes per minute is proposed by means of five order polynomial. On this process condition, the driving torques are calculated based on the above dynamic model and the torque measuring test is also carried out on the prototype. It is shown that the curve trend of calculation torque is consistent to the measured result and that the average error is less than 15%. The parallel mechanism is introduced into the development of large capacity servo press to avoid the over-constraint and interference of traditional redundant actuation, and its dynamic characteristics with gravity counterbalance are presented.