Zhang Ce

A study on dynamics of roller gear cam system considering clearances

In this paper, dynamics of a roller gear cam system is studied, with the clearance taken into account. It is found in an experimental study that clearances have little influence on angular acceleration response of output element, the rotary table. In this paper, numerical solutions of theoretical dynamic model have verified this phenomenon and pointed out that clearances may cause much more severe impacts for turret of the mechanism.

Direct power control for three-level PWM rectifier based on hysteresis strategy

This paper presents a mathematical model of three-level voltage PWM rectifier, and derives a power control model from the theory of instantaneous power. In the vector-space, the influences on instantaneous power exercised by all the switching vectors are studied and illustrated separately, then a direct power control (DPC) scheme for three-level PWM rectifier which uses multistage band hysteresis comparator is proposed, and a novel switching table is designed. Meanwhile, the neutral-point voltage unbalance is inhibited by selecting the redundancy switching states of small voltage vectors. Simulation and experimental results show that the proposed strategy can not only stabilize the DC bus voltage but also realize the unity power factor operation and the balance of neutral-point voltage. Moreover, the proposed method can improve the performance of the three-level rectifier.

Rank of loop, constraint degree of path, coupling degree of graph and their application

Some new concepts (rank of a loop, degree of freedom of a graph, path unit and ordered path arrangement, constraint degree of path, coupling degree of a graph, basic graph, etc.), formulas, and algorithms, are proposed in this paper. Based on these concepts, a new systematic theory and practical method for the design of topological structure, kinematics and dynamics of mechanical systems is established. Some conjectures and problems needed to be researched are also put forward. The concepts, formulae and algorithms presented in this paper will find wide potential applications. Supported by the National Natural Science Foundation of China (Grant Nos. 59375203, 59875084, and 50275070)

Inverse dynamic simulation of the limited-DOF parallel mechanism

Due to the advantages of simple mechanical structure, low manufacturing cost, simple control algorithm, the limited-DOF mechanism has caught most attention from researchers. Out of the number of its DOF is less than six, the limbs must transmit actuation and constraint force at the same time. So both the required actuation and constraint force analysis are necessary in the dynamic control and optimization design of mechanism. In this paper, inverse dynamics equations of 2UPS-2RPS, as an example, are modeled by using the Newton-Euler formulation, through solving which the required actuation and constraint forces can be obtained when the motion of moving platform and working load are given. A computational example is provided.

Principle and curve of planetary indexing cam mechanisms

A new type of planetary indexing cam mechanism called type IV is presented. The transmission principle of type IV is discussed. Based on the principle of formation of conjugate tooth contour, the equations of the cam’s pitch curve are derived. The continuity and symmetry of the cam’s pitch curve are also analyzed. It can be concluded that: 1) This type has no output institution so the output precision can be improved; 2) The asymmetrical two-ring structure is used to overcome dead point and its phase angle is equal to (π − 2π/n); 3) The continuous condition of the cam’s pitch curve is that the average transmission ratio is −n in an intermittent motion period.