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In the above article [1], the financial support should be updated as follows. This work was supported in part by the Zhejiang Provincial Natural Science Foundation of China under Grants LY18E070006 and LY18E050016, and in part by the National Natural Science Foundation of China under Grants 51307151 and 51677172.

In the above paper [1], the financial support should be update as follows: This work was supported in part by the Zhejiang Provincial Natural Science Foundation of China under Grants LY18E070006 and LY18E050016 and in part by the National Natural Science Foundation of China under Grants 51307151 and 51677172.

A vector control method based on two-phase space vector pulse width modulation is proposed for two- phase hybrid step motor. An especial two-phase inverter bridge based on the up and down bridge complementary conduction and the diagonal bridge conduction at the same time is designed. The modulation method of the two-phase space vector modulation algorithm is derived and given out. Speed and current loop based on integral separated PI regulator and position loop based on P regulator are designed. The simulation and experimental results show that the system with proposed method has good tracking and steady-state performance and its maximum speed is higher than the open-loop system.

In order to improve the speed control performance on the heavy load driving system of servo press, a control strategy based on speed observer with load torque identification and feed-forward compensation was proposed. It can identify and compensate the actual applied load torque by adjusting the machine quadrature axis current in real time. By identifying the problem in the traditional current feedback decoupling control scheme, a current vector control strategy based on voltage feed-forward decoupling control was proposed. Simulation analysis and experimental tests on a heavy load drive system were carried out using the proposed new control strategy. The results show that the control strategy is effective and the system designed by this method not only can identify the operating speed applied load torque, but also has good speed control performance.

The characteristics of longitudinal-torsional hybrid transducer-type ultrasonic motors (HTUSM) are low speed and high torque. The discontinuous-surface-contact mode between the stator and the rotor is different from the many-point-contact mode of traveling wave motors, which is also an essential cause for high torque. Therefore, it is important to analyze its force transfer model between the rotor and the stator. In this paper, issues of using the method of equivalent circuit model are addressed. The relationships between the contact angle, preload, and physical parameters of frictional materials are given, according to the impulse conservation law axially. The equations describing output torque, amplitudes of longitudinal and torsional. vibration, and parameters of the rotor are derived according to the principle that the work done by the load is equal to that by the driving force in one vibrating cycle. All factors that influence the mechanical characteristics are analyzed, and accuracy arid suitability of the force transfer model are verified by comparison with the prototype motor. The formula for transfer efficiency on the stator/rotor interface is given, and the low-efficiency of this type motor is explained. The wide-working frequency range property of this type motor is shown with experimental results. Based on this study, the parameters of the rotor and preload are determined. The maximum torque of the prototype motor is up to 13.2 nm, and no-load speed of this type of motor is 12.5 rpm.