Search

This paper introduces the structural design of a novel spherical motion generator. The electromagnetic drive mode of a spherical motor is applied to the three-degree-of-freedom (3-DOF) spherical parallel manipulator, in order to solve the problem of motion error caused by the transmission device and motor following in the traditional spherical parallel manipulator. A brief explanation of the electromagnetic drive working principle is mentioned. And the modeling of magnetic field and the optimization of magnetic field distribution are also discussed. In the future work, we will also optimize the magnetic field distribution of the platform and study the high-precision control strategy.

A permanent magnet spherical actuator is an electromagnetic device characterized by achieving multi-degree-of-freedom rotations in one driving unit. Analytical magnetic field modeling of the rotor array is needed for the design, performance analysis and optimization of the spherical actuator. This paper presents an analytical method to formulate the complex magnetic field distribution of rotor array with cylindrical permanent magnets in 3D spherical space. This method combines the current model by toroidal functions and transformation method, thus the magnetic field can be calculated efficiently with reasonable accuracy in order for further design optimization and real-time control. The analytical magnetic model of the permanent magnet rotor array is validated with the numerical finite element method by Ansoft Maxwell and experimental measurement. A permanent magnet spherical actuator is an electromagnetic device characterized by achieving multi-degree-of-freedom rotations in one driving unit. Analytical magnetic field modeling of the rotor array is needed for the design, performance analysis and optimization of the spherical actuator. This paper presents an analytical method to formulate the complex magnetic field distribution of rotor array with cylindrical permanent magnets in 3D spherical space. This method combines the current model by toroidal functions and transformation method, thus the magnetic field can be calculated efficiently with reasonable accuracy in order for further design optimization and real-time control. The analytical magnetic model of the permanent magnet rotor array is validated with the numerical finite element method by Ansoft Maxwell and experimental measurement.

This paper presents modeling of an integrated design of an electromagnetic driven spherical motion generator with multi-layer structure. An analytical method to calculate the complex magnetic field distribution of the rotor array by combining the equivalent charge model and transformation method is developed, upon which torque model is further established analytically by using the moment principle. Both the analytical magnetic model and torque model are validated with the numerical finite element method by Ansoft Maxwell and experimental measurements. With the model, two different designs of the electromagnetic driven SMGs are analyzed to illustrate the application of the developed model. This paper presents modeling of an integrated design of an electromagnetic driven spherical motion generator with multi-layer structure. An analytical method to calculate the complex magnetic field distribution of the rotor array by combining the equivalent charge model and transformation method is developed, upon which torque model is further established analytically by using the moment principle. Both the analytical magnetic model and torque model are validated with the numerical finite element method by Ansoft Maxwell and experimental measurements. With the model, two different designs of the electromagnetic driven SMGs are analyzed to illustrate the application of the developed model.

Short-term traffic forecast is one of the essential issues in intelligent transportation system. Accurate forecast result enables commuters make appropriate travel modes, travel routes, and departure time, which is meaningful in traffic management. To promote the forecast accuracy, a feasible way is to develop a more effective approach for traffic data analysis. The availability of abundant traffic data and computation power emerge in recent years, which motivates us to improve the accuracy of short-term traffic forecast via deep learning approaches. A novel traffic forecast model based on long short-term memory (LSTM) network is proposed. Different from conventional forecast models, the proposed LSTM network considers temporal-spatial correlation in traffic system via a two-dimensional network which is composed of many memory units. A comparison with other representative forecast models validates that the proposed LSTM network can achieve a better performance.

Nanoimprint lithography (NIL) is a novel technique that utilizes direct deformation of the resist to fabricate micro/nanometer scale patterns. NIL outperforms traditional photolithography technology for its low cost, high productivity, and high repeatability. For a general plate-to-plate NIL, it is of central importance to precisely control the embossing force during the entire embossing process to tune the orientation of the imprint head and also to guarantee the uniformity and fidelity. Existing approaches used in NIL are position-based feedback controls. However, a position signal is believed to be indirect and is more likely to be influenced by the thickness of the photoresist layer. To address this problem, in this paper, we propose a two-stage force control scheme to explicitly control the embossing force based on the impedance control framework. The first stage is to parallelize the template surface with the substrate surface using the small initial contact force before embossing. Then, the second control stage is to regulate the large embossing force to the desired value. With the proposed force control approach, the embossing force can be explicitly controlled during the entire stamp process even without a prior knowledge of the environmental parameters. Experimental tests performed on a 500-nm grating scale further illustrate and verify the effectiveness of the proposed design.

This paper proposes a rotor permanent magnet array applied in the three degree-of-freedom (3-DOF) permanent magnet spherical actuator. To investigate the performance of the permanent magnet array, this paper presents an analytical model for calculating the magnetic field generated by the spherical rotor array using spherical harmonics. Compared with the numerical method 3-D finite element analysis, the spherical harmonics can obtain a closed-form function with the advantages of reasonable accuracy and rapid computational effort. Finally three structural parameters of rotor array are discussed by the analytical model.

This paper presents a novel design of an integrated electro-magnets driven spherical parallel manipulator which produces 3-degree-of-freedom (3-DOF) rotational motion within the workspace. The spherical parallel manipulator is actuated by the interaction between stator coils and the rotor magnetic field. The kinematic and dynamic models are developed. The torque model is formulated analytically based on the magnetic field distribution of the permanent magnet slide unit. Finally, the magnetic field distribution and the torque model are both validated using the finite element analysis.

The problem of missile interception is investigated in this paper. Sliding-mode controllers with finite-time convergence are proposed for the design of guidance laws. In particular, the control design consists of the estimation of the target acceleration by the extended state observer (ESO), and thus, it achieves the decrease of undesired chattering effectively. Also, simulation results are presented to illustrate the effectiveness of the control strategies.

This paper addresses both dynamic modelling and dynamic parameter identification of a permanent magnet spherical actuator, which is capable of performing three-degree-of-freedom (DOF) motion in one single joint. The dynamic model of the spherical actuator is derived from Lagrange’s equations, but the parameters, called dynamic parameters, in the model are usually uncertain. Then the dynamic model is represented in a form that is linear in these parameters. A new identification method based on the output error (OE) method and recursive least square (LS) estimation is proposed to identify the parameters. This method only requires the current measurement of the stator coils in the identification procedure, which greatly simplifies the experimental process and improves the identification accuracy. Lastly, simulation and experimental results illustrate the effectiveness of the proposed method and its robustness to external disturbances. The proposed method can be also applied to other electromagnetic driving spherical actuators.

As an excellent underwater biorobotics, robotic fish has got considerable development in recent decades. However the majority of researches assume that the flow field where the fish swims is a steady one, ignoring the fact that fish in nature has to deal with diverse flow fields. This takes part of responsibility for the low efficiency of robotic fish comparing with live one. In this paper, we present one experimental system which could form steady flow field and utilize the information collected from it on the robot as closed-loop control feedback. With this information we can infer the state of flow so that we can manipulate the robot to adopt corresponding swimming strategy which could increase the swimming efficiency markedly. To get information on the flow field we employ pressure transducer attached on the robotic fish prototype to detect the water surrounding the robot. And this system takes advantage of robot operating system (ROS) ensuring its flexibility and extensibility in future improvement. An experiment conducted on this platform indicates it can distinguish the speed of flow, verifying its feasibility and capability to conduct other experiments on closed-loop control.

This paper presents a permanent magnet (PM) spherical actuator embedded with a novel three-dimensional (3D) orientation measurement system. The study covers actuator design, torque modeling, and motion control. The spherical actuator consists of a stator with 24 coils and a rotor with 8 PM poles. A high accuracy and resolution, non-blinding 3D measurement mechanism is designed for the rotor orientation detection. The torque output is formulated from finite element (FE) computation and curve fitting method. Due to the nonlinear property of dynamic model, computed torque control law is utilized for the three degree-of-freedom (3-DOF) system motion control. The space geometry method is employed to study the redundancy feature of current inputs, which offers the opportunity for control optimization to improve the power efficiency and the fault tolerance capability of the spherical actuator. Simulations and experiments are then conducted on the developed prototype to validate the design concept, mathematic models and control strategy.

This paper presents a two-level geometric calibration method for the permanent magnet (PM) spherical actuator to improve its motion control accuracy. The proposed actuator is com- posed of a stator with circumferential coils and a rotor with multiple PM poles. Due to the assembly and fabrication errors, the real geometric parameters of the actuator will deviate from their design values. Hence, the identification of such errors is critical for the motion control tasks. A two-level geometric calibration approach is proposed to identify such errors. In the first level, the calibration model is formulated based on the differential form of the kinematic equation, which is to identify the geometric errors in the spherical joint. In the second level, the calibration model is formulated based on the differential form of torque formula, which is to calibrate the geometric parameters of the magnetization axes of PM poles and coils axes. To demonstrate the robustness and availability of the calibration algorithm, simulations are conducted. The results have shown that the proposed two-level calibration method can effectively compensate the geometric parameter errors and improve the positioning accuracy of the spherical actuator. a 2014 Production and hosting by Elsevier Ltd. on behalf of CSAA & BUAA.

For the purpose of developing a comprehensive set of rehabilitation system, this paper presents a novel design of pressure sensing foot for lower limb exoskeleton. The pressure sensing foot measures plantar pressure and acceleration to give instruction of the contact between human foot and ground and reflects behavior of the wearer. Compared with previous works, the pressure sensing foot described in this paper has compact design as well as reliable structural strength. Its bionic design minimizes the exoskeleton's impact on the wearer and improves performance of the pressure sensing system during walking. Further details of the mechanical structure and experiment result are described in the paper.

This paper presents a geometric calibration approach of a permanent magnet (PM) spherical actuator to improve its positioning accuracy. The proposed actuator consists of a ball-shaped rotor with multiple PM poles and a spherical-shell-shaped stator with circumferential air-core coils. Due to manufacturing and assembly restrictions, the actual geometric parameters of the spherical actuator differ from their nominal values. Hence, the identification of such errors is significant for high accuracy motion control. The calibration model is formulated based on the differential form of torque equation. To identify the position vector errors in the magnetization axes of PM poles and coils axes, an iterative least-squares algorithm is employed. The proposed calibration method can also be applied to other PM spherical actuators. To verify the robustness and effectiveness of the proposed calibration algorithm, simulations are conducted on the spherical actuator. The results have shown that the positioning accuracy of the spherical actuator is greatly improved after calibration.

This paper presents a dynamic control algorithm of a permanent magnetic spherical actuator, which is capable of performing 3-degree-of-freedom (DOF) in a single rotor. This algorithm is based on the orientation measurement feedback of the rotor. As the orientation measurement of the spherical actuator has been a challenging problem so far. An orientation measurement system for the rotor is proposed in this paper and its performance is validated in an experimental platform. The dynamic model is also presented in this paper, which is derived by Lagrange's equations. The dynamic control algorithm is based on the computed torque method, which can linearize and decouple the control. Simulation results indicate the feasibility of the dynamic control algorithm.

This paper presents a permanent magnetic spherical actuator, which is capable of performing 3-degree-of-freedom (DOF). The orientation measurement of the spherical actuator has been a challenging problem so far. An interesting orientation measurement system for the rotor is proposed in this paper. Based on the position measurements, the trajectory tracking of the rotor with output feedback is addressed. As the current input is usually limited to certain degree in the applications, which leads to the bounded control torque input, the trajectory tracking controller with bounded torque input is designed. Simulation results indicate feasibility of the proposed controller. At last the experimental system is designed to validate the proposed orientation measurement system.

This paper presents a novel two level current optimization algorithm for the control of the spherical motor. The proposed spherical motor consists of a rotor with 8 cylindrical permanent magnet (PM) poles and a stator with 24 air-core coils. An analytical expression of the torque model is obtained based on finite-element method. Based on this expression, the relationship between the motor torque and the coil current input is acquired. In order to make better use of the redundant coils, the space geometry method is exploited to study the redundant feature of the spherical motor. The current optimization algorithm is designed in two levels, which can not only minimize the energy consumption of the spherical motor, but also improve the stability and reliability of the spherical motor greatly.

In this paper, the block diagram of the principles and the structure of the PMSM ac servo vector controlling system are described. The distinct features of the system are to replace electric current hysteresis controller with SVPWM. Besides, the paper introduces the principle of space voltage vector PWM (SVPWM) and the algorithm of SVPWM and also introduces the function of every module. Moreover, it introduces how to apply SVPWM algorithm into the computer to increase the efficiency of calculating ,and gives the Simulink simulation diagram of current and speed double closed loop. And it analyses the structure and realization method of inside modules of SVPWM system and offers the simulation waveforms of permanent-magnetic synchronous motor servo system

The rapid development of the network technology, especially that of the fieldbus, is changing the traditional control system. In order to solve the problem of the linkage synchronization and the network data transmission of the Multi-Ac Servo system, we recently designed a CAN bus protocol named CANServo. It is a high-level protocol of CAN bus , it is used to replace traditional parallel data transmission between NC and servos. In this study, we described the method to solve the synchronization problem, the setting up of the communications, the strategy of dynamic reorganization of priorities, the structure of the buffer track and the operation of the track. In the end, we illustrated the results of the experiment which the correctness of our design can be proved by.

The paper concerns with the speed stability of permanent magnet synchronous servo system. Used in numerical control machines, the servo system is required to output steady rotor speed. Based on vector control theory, a servo system is designed with PID module as the regulators of the speed and current loops. The effect of important factors including speed regulator, current regulator, the speed and current feedback are analyzed. Then the methods to enhance the rotor speed stability are discussed, including optimizing the regulators and filtering the current signals. The feedback speed gotten from positional sensor whose precision is decided by the sensor adapts to this servo system. The result of both simulation and screw thread process experiments on NC lathe validated their effectiveness.

This paper presents the analysis and decoupling control of a spherical actuator, which is capable of performing three degree-of-freedom motion in one joint. The proposed actuator consists of a rotor with multiple PM (Permanent Magnet) poles in a circle and a stator with circumferential coils in three layers. Based on this actuator design, a decoupling control approach is developed. Unlike existing control methods that each coil is responsible for both the spinning and tilting motion, the proposed control strategy specifies the function of each coil. Specifically, the spinning motion is governed by the middle layer coils with a step control approach; while the tilting motion is regulated by upper and lower coils with a computed torque control method. Experiments have been conducted on the prototype to verify the validity of the design procedure, and the experimental results demonstrate the effectiveness of the analysis and control strategy.

High performance force sensors often encounter the problem of vibrations during the process of calibration and measurement. To address this problem, this paper presents a novel passive eddy current damper (ECD) for vibration suppression. The conceived ECD utilizes eight tubular permanent magnets, arranged in Halbach array, and a conductive copper rod to generate damping. The ECD does not require an external power supply or any other electronic devices. In this paper, an accurate, analytical model for calculating the magnetic field distribution and damping coefficient is developed. The dynamics of the system is obtained by applying an energy method and an equivalent pseudo-rigid-body model. Moreover, finite element simulations are conducted to optimize the design. Experiments are carried out to validate the effectiveness of the design. The results indicate that the proposed ECD has a damping coefficient of 4.3 N s m−1, which can provide a sufficient damping force to quickly suppress the sensor's vibration within 0.1 s.