Synthesis method of new weakly-coupled 5-DOF compliant parallel mechanism

Yajie Zhou,Jing Sun,Fengkui Zhang,Shihua Li 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.8

Compared with the strongly-coupled parallel mechanism, the weakly-coupled mechanism can realize two kinds of mutually independent motions. In this paper, a new method for type synthesis of weakly-coupled compliant parallel mechanisms is proposed. The synthesis conditions, that is, the synthesis conditions of the shared flexure hinges and synthesis condition of the weakly-coupled, are given. The synthesis process is formulated. From the perspective of mechanism innovation, a new synthesis idea of weakly-coupled CPMs is introduced. New weakly-coupled CPMs without intermediate platform are obtained by sharing the flexure hinges of two compliant parallel mechanisms. To obtain five degree of freedom (5-DOFs) weakly-coupled compliant parallel mechanisms, two kinds of sub-sets of compliant mechanism blocks, a two-rotation and one-translation compliant mechanism and a twotranslation compliant mechanism are proposed. With the proposed synthesis method, two blocks are indirectly connected by sharing flexure hinges to obtain an integral mechanism. Then, new 5-DOF weakly-coupled compliant parallel mechanisms are proposed by the synthesis conditions. Additionally, finite element simulation is carried out to verify the correctness of the proposed synthesis method. Thirteen new 5-DOF weakly-coupled compliant parallel mechansims have been synthesized, which enriches the compliant parallel mechanism configurations. And, they have simple structure, compact structure, ease of control and light weight. The synthesized 5-DOF weakly-coupled compliant parallel mechanisms have potential application to pointing, vibration isolation and mirror adjustment platform.

Continuous Sliding Mode Control for Permanent Magnet Synchronous Motor Speed Regulation Systems Under Time-Varying Disturbances

Huiming Wang,Shihua Li,Jun Yang,XingPeng Zhou 전력전자학회 2016 JOURNAL OF POWER ELECTRONICS Vol.16 No.4

This article explores the speed regulation problem of permanent magnet synchronous motor (PMSM) systems subjected to unknown time-varying disturbances. A continuous sliding mode control (CSMC) technique is introduced for the speed loop to enhance the robustness of PMSM systems and eliminate the chattering phenomenon caused by high-frequency switch function in the conventional control law. However, the high control gain of the CSMC law in the presence of strong disturbances leads to large steady-state speed fluctuations for PMSM systems. In many application fields, PMSM systems are affected by time-varying disturbances instead of constant disturbances. For example, electric bicycles are usually affected by changing environmental disturbances, including wind speeds, road conditions, etc. These disturbances may be in the form of constant, ramp, and parabolic disturbances. Hence, a generalized proportional integral (GPI) observer is employed to estimate these types of disturbances. Then, the disturbance estimation method and the aforementioned CSMC method are combined to establish a composite sliding mode control method called the CSMC+GPI method for the speed loop of PMSM systems. Contrary to the conventional sliding mode control technique, the proposed method completely eliminates the chattering phenomenon caused by the switching function in the conventional control law. Moreover, a small control gain for the CSMC+GPI method is chosen by feed-forwarding estimated values to the speed controller. Hence, the steady-state speed fluctuations are small. The effectiveness of the proposed control scheme is verified by simulation and experimental result.

Type synthesis of 3T2R decoupled hybrid mechanisms with large bearing capacity

Sen Wang,Shihua Li,Haoran Li,Yajie Zhou,Yongjie Wang,Xinyu Wang 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.4

This paper proposes a new synthesis method of three translational and two rotational (3T2R) decoupled hybrid mechanism with large bearing capacity, based on the screw theory and the atlas method. According to the degree of freedom and decoupled characteristics of the 3T and 2R mechanisms, the decoupled conditions for the 3T and 2R parallel mechanisms are proposed. The optimal conditions for the motion/force transmission performance of the 3T decoupled parallel mechanisms with redundant actuation is presented. A redundant actuated limb construction method is proposed to improve the load capacity of the hybrid mechanism. Following the design steps of the fully decoupled hybrid mechanism, 3T2R hybrid mechanisms with large load capacity are obtained. Kinematics and statics analysis verify the correctness of the proposed synthesis method. The mechanism synthesized by this method has a good application prospect in large load occasion.

Investigation on the stability of periodic motions of a flexible rotor-bearing system with two unbalanced disks

Chaofeng Li,Shihua Zhou,Shijie Jiang,Hexing Yu,Bang-chun Wen 대한기계학회 2014 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.28 No.7

The stability of periodic motion of a rotor-bearing system with two unbalanced disks is analyzed based on a multi-degree of freedom(M-DOF) finite element model. Nonlinear effects of supporting oil-film and inertia distributions as well as shearing effect are taken intoaccount. Focusing on the more realistic FE method to study the stability of nonlinear rotor-bearing system with the influence of the eccentricityphase, the stability calculation of the M-DOF FE model is done by using the combination of Shooting method and Newmarkmethod. Experiments with a rotor-bearing test rig (two disks on a shaft with two bearings) are then performed and results are presented. Itis found that typical instability characteristic is successfully produced. Through comparisons between calculated results and measurements,it is shown that the combination of Shooting method and Newmark method in studying the M-DOF rotor-bearing system is useful,especially for the complex rotor-bearing system. In addition, altering eccentricity phase of the two disks can significantly influence instabilitytype and speed. When the two disks are out of phase, the occurring of oil whip is restrained effectively. It is suggested that a carefulexamination should be made in modeling more complex non-linear rotor-bearing system.

Continuous Sliding Mode Control for Permanent Magnet Synchronous Motor Speed Regulation Systems Under Time-Varying Disturbances

Wang, Huiming,Li, Shihua,Yang, Jun,Zhou, XingPeng The Korean Institute of Power Electronics 2016 JOURNAL OF POWER ELECTRONICS Vol.16 No.4

This article explores the speed regulation problem of permanent magnet synchronous motor (PMSM) systems subjected to unknown time-varying disturbances. A continuous sliding mode control (CSMC) technique is introduced for the speed loop to enhance the robustness of PMSM systems and eliminate the chattering phenomenon caused by high-frequency switch function in the conventional control law. However, the high control gain of the CSMC law in the presence of strong disturbances leads to large steady-state speed fluctuations for PMSM systems. In many application fields, PMSM systems are affected by time-varying disturbances instead of constant disturbances. For example, electric bicycles are usually affected by changing environmental disturbances, including wind speeds, road conditions, etc. These disturbances may be in the form of constant, ramp, and parabolic disturbances. Hence, a generalized proportional integral (GPI) observer is employed to estimate these types of disturbances. Then, the disturbance estimation method and the aforementioned CSMC method are combined to establish a composite sliding mode control method called the CSMC+GPI method for the speed loop of PMSM systems. Contrary to the conventional sliding mode control technique, the proposed method completely eliminates the chattering phenomenon caused by the switching function in the conventional control law. Moreover, a small control gain for the CSMC+GPI method is chosen by feed-forwarding estimated values to the speed controller. Hence, the steady-state speed fluctuations are small. The effectiveness of the proposed control scheme is verified by simulation and experimental result.