Fenglei Ni

Switching-State Phase Shift Method for Three-Phase-Current Reconstruction With a Single DC-Link Current Sensor

Instead of directly sampling the phase currents, a technique that adopts a single current sensor in the dc link to reconstruct three-phase currents has arisen. Through this approach, the cost of servo systems can be reduced and the reliability can be improved. However, the duration of an effective vector may be so short that the phase current cannot be measured reliably by the conventional space-vector pulsewidth modulation (PWM) algorithm. In this paper, a new phase-current reconstruction method, switching-state phase shift (SSPS), is proposed based on the PWM pattern modification. The modification is performed by applying phase shifts to the switching-state waveforms of the inverter. The algorithm can realize high-quality reconstruction to the phase current with less impacts on the output current ripples and switching losses. Moreover, it can maximize the linear-modulation region by saturation handling. Measurements on the permanent-magnet synchronous motor servo drives show that the SSPS can offer an attractive performance during both steady-state and dynamic operations in the phase-current reconstruction and regulation.

A Novel Absolute Magnetic Rotary Sensor

To measure the angular position of motors, robot joints, etc., an absolute magnetic rotary position sensor is developed, which possesses small-size, light, robust, and easy-to-integrate properties. The sensor consists of two inductors, i.e., a code disc and a signal processing part. Both of the two inductors are embedded with a big planar spiral copper coil and four smaller copper coils by employing microelectromechanical system (MEMS) technology, and there are two circles of regular copper sheets listing on the surface of the code disc. In addition, mathematical analyses of the inductor structure as well as the relationships of position and dimension among the coils and the copper sheet are addressed. Finite-element simulation results demonstrate that one group of the optimal sine and cosine signals can be generated by each inductor. Then, the absolute position measurement method is validated by a mathematical method. Finally, experiments are performed on the high-speed and the low-speed testing platforms to assess effectiveness and accuracy of the sensor.

Development of reconfigurable space robot arm

This paper presents a reconfigurable modular space robot arm including reconfigurable modular mechanics, electronics, and control software. This robot was composed of six same modular joints and one gripper. A configuration similar to PUMA robot was adopted, which made it possible to fold the robot a compact shape, and save space and cost for transporting it into the space. A big central hole in the modular joint was designed for the placement of the cables and plugs in the robot arm, which prevented them from damage of high temperature, radiation in the space environment and the motion of the robot. Joint torque sensor, joint position sensor and temperature sensors etc. were integrated into the fully modular multi-sensor joint, which made the joint more intelligent. A zero gravity experimental system was developed to verify the functions of the robot under zero gravity environment

Development of the Chinese Intelligent Space Robotic System

This paper gives an overview of the Chinese intelligent space robotic system. The system consists of a 6 DOF robot arm, a large-error tolerated gripper with two stereo cameras and onboard computer. The robot arm is composed of six identical modular joints, a big central hole in the modular joint was designed for the placement of the cables and plugs in the robot arm, which prevented them from damage of high temperature, radiation in the space environment and the motion of the robot. Joint torque sensor, joint position sensor and temperature sensors etc.., were integrated into the fully modular multi-sensory joint, which made the joint more intelligent. Also, a large-error tolerated gripper with two stereo cameras has been also designed to capture a microtarget satellite (MTS). A fault-tolerant onboard computer (OBC) with dual processing modules has been developed for the robot control. A zero gravity experimental system was developed to verify the functions of the robot arm under zero gravity environment

A high performance FPGA-based joint controller with hardware/software co-design method

This work presents studies on application and implementation on the field programmable gate array (FPGA) technology into a robot joint controller in order to improve the tracking performance. The controller can be divided into two parts and designed with software and hardware separately. The first part is developed in Nios II embedded processor which is used to realize the velocity and torque control in C language. The second part is to implement the current vector control which includes coordinate transformation, PI controller, SVPWM (Space Vector Pulse Width Modulation) and some other function modules in Hardware Description Language (HDL). The two parts are integrated in the System-on-a-Programmable-Chip (SoPC) developing environment. Experiments on a PMSM are done and the results demonstrate the effectiveness and correctness of the proposed FPGA-based controller. Joint friction parameters can be estimated by the proposed controller with velocity and current control. Consequently, the controller is applied on a robotic manipulator together with DSP to verify the high performance.

The application of real-time operating system QNX in the computer modeling and simulation

The objective of this study is to show the applications of the simulation implementation of QNX identified model combining with Matlab/Simulink platform, QNX C/C++ compiler and QNX real-time operating system. The HIT/DLR Hand II dexterous hand QNX real-time simulation model is generated by the Simulink platform and QNX C/C++ compiler link files. Moreover, this model can be implemented in the QNX real-time system. Simulations in the QNX real-time system show that the HIT/DLR Hand II dexterous hand QNX model which based on the methods in this research, was able to offer an attractive performance during both real-time simulation and feedback operations.

A Method for Measurement of Absolute Angular Position and Application in a Novel Electromagnetic Encoder System

For the encoders, especially the sine-cosine magnetic ones, a new method to measure absolute angular position is proposed in the paper. In the method, the code disc of the encoder has only two circle tracks and each one was divided into and () equal code cells. The cell angles, changing from 0° to 360° between any two neighboring code cells, are defined to represent any position on the code disc. The position value of the same point can be represented by different cell angle values of different tracks and the absolute angular position of the point can be obtained by the difference value between the cell angle value of the outer track and the inner one. To validate the correctness of the method theoretically, the derivation process of the method was provided. An electromagnetic encoder system was designed and the experimental platform was established to test the method. The experimental results indicate that the electromagnetic encoder can measure the absolute angular position. Besides, it shows that the method is easy to be realized in algorithm and can reduce computational complexity and decrease dimension of the encoder.

A space-saving end-effector with capture and actuation transmission capabilities

A space-saving end-effector is designed for small scale manipulator in this paper. The end-effector is equipped with capture and actuation transmission capabilities. Two subsystems are highly integrated systems of mechanics, electronics and sensors. A trefoil shaped capture system is developed for closed envelop. The worm shaft and worm wheels are adopted for the self-locking property, and they are used in a unique manner. Straight path generation of linkage is proposed in the transmission system. The multisensory system and hardware architecture provide the foundation for control strategies. The effectiveness of the end-effector is verified by simulation and the capturing tolerance is obtained.

Parameter identification and controller design for flexible joint of Chinese space manipulator

Manipulators with flexible joints are widely used as the space manipulators, whereas the elasticity of flexible joint leads to poor dynamic performance. To solve the influence of elasticity, the paper is to establish the model of flexible joint, identify the parameters, and design the controller. The off-line methods are applied to identify the current coefficient and the parameters of flexible joint model. The controller is designed based on the theory of state feedback and pole assignment. To make the calculation of controller gains easier, more precise and more intuitive, the nominal stiffness is introduced. The simulation results and the experimental results indicate that the proposed controller can improve the dynamic performance and reduce the vibration of the manipulator compared with the traditional PD controller.

Cartesian Space Synchronous Impedance Control of Two 7-DOF robot arm manipulators.

In the paper, a new method named Cartesian Space Synchronous Impedance Control (CSSIC) has been developed. The method combines the synchronous control and the impedance control together which can not only be used in the position control but can also realize the purpose of force control of the system with multi-manipulators. Therefore, if there are multi-manipulators grasping the same object, it can ensure the object will not fall and not be destroyed. The mathematical validation process and the stability proof of the method have been given. Besides, an experiment setup which has two 7-DOF robot arms has been established to testify the method. The testing result shows that the dual arm system, under disturbance, can ensure stable grasping of the object with the CSSIC method.