Jingmeng Liu

Optimum Design of a Dual-Range Force Sensor for Achieving High Sensitivity, Broad Bandwidth, and Large Measurement Range

Force control is very crucial in nanoimprint lithography (NIL). It is necessary to develop a high-performance force sensor to provide real-time force feedback for the control process. Due to the unique procedure of NIL, the developed force sensor should include a high sensitivity, broad bandwidth, and large measurable range. However, these characteristics are normally conflicting in nature and cannot be physically avoided by any force transducers so far. To address this problem, this paper presents a novel dual-range force sensor, and uses a heuristic multiobjective optimization method to make a tradeoff among these characteristics. This method is based on the particle swarm optimization algorithm, meanwhile employs the Pareto ranking scheme to find optimal solutions. Through proper optimization, not only the three characteristics are compromised, the lowest stress concentration of the sensor body is maintained as well. To demonstrate the effectiveness of the optimization, numerical simulations with finite-element software COMSOL are conducted. A prototype sensor is then fabricated according to the optimization results. The simulation and prototype test results indicate that the optimized sensor has a resolution down to 800

Design of open-loop controller for permanent magnet spherical motor

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A MEMS based sensor for large scale force measurement

N, a bandwidth up to 150 Hz, and a measurable range up to 180 N. All the results prove that the developed force sensor possesses a good property for high-performance force measurement, and satisfies the needs of NIL as well.

An automatic recognition system for patients with movement disorders based on wearable sensors

This paper presents an open-loop control system design for a permanent magnet spherical motor (PMSM). The proposed spherical motor consists of a ball-shaped rotor with a full circle of 8 permanent magnet (PM) poles and a spherical-shell-like stator with two layers of circumferential 24 air-core coils. Based on the torque model of the PMSM, the relationship between current input and torque output can be demonstrated. We design the open-loop controller by decoupling the spinning motion control, which is based on the torque equilibrium theory, from the inclination motion control. Two types of spinning motion control models are proposed and analyzed. The open-loop controller can make the PMSM have the ability to spin continuously and tilt to certain angle. The experiment of open-loop control system based on a personal computer and current controller is designed to validate the control method at last.

Current optimization of 3-DOF permanent magnet spherical motor

Recent advances on micro-engineering have accelerated the development of MEMS force sensors with large scale and high resolutions. To meet this demand, this paper presents the conceptual design of a new MEMS force sensor with dual-phase characteristics. In the first phase, the sensor possesses an ultra-high resolution that is enough for high precision force measurement. While in the second phase, the resolution is decreased, the measurement range is greatly improved such that the sensor can measure forces within large scale with high resolutions. This function is implemented through a specially designed compliant mechanism with carefully placed hard stoppers. The conceived force sensor features an SOI (Silicon-on-Insulator) body with an integrated capacitive sensor for displacement detecting. The obtained displacement signal is then converted to force information through a calibration procedure. This paper will first present the analytical modeling for both static stiffness and eigenfrequency of the sensor body. Then finite element simulations on both structural and electrical analysis will be demonstrated. Both the analytical and numerical results show that the proposed MEMS force sensor can measure forces ranging from nano-Newton to milli-Newton meanwhile keeps very fine resolutions.

Integrated design, modeling and analysis of a novel spherical motion generator driven by electromagnetic principle

Movement disorder in lower extremity has been a major concern for the elder worldwide. Early diagnosis and effective therapy monitoring is an important prerequisite to treat patients and reduce health care costs. Objective and non-invasive assessment strategies are an urgent need in order to achieve this goal. In this study, we apply a wearable, lightweight and easy applicable sensor based gait analysis system to measure gait cycle. We analyse the features of different kinds of patients with movement disorder. An automatic pattern recognition system by machine learning and statistical approaches is proposed to support the classification of different neuro-degenerative diseases. The results demonstrate that it is feasible to apply computational classification techniques in characterise these three diseases with the features extracted from gait cycles.

Analysis and decoupling control of a permanent magnet spherical actuator

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.

Bounded control of a spherical actuator based on orientation measurement feedback

Abstract Spherical motion generators are increasingly needed for constructing robots, manipulators and pointing devices. This paper presents a novel design of spherical motion generator built on the basis of a spherical parallel manipulator. The new motion generator integrates the electromagnetic actuator with the co-axial 3-RRR spherical parallel manipulator, thus leads to a more compact and light-weight structure with the advantages of no backlash, high stiffness and low inertia. In this paper, the inverse kinematics and dynamics of the spherical parallel manipulator are described. The analytical torque model of this spherical motion generator is developed and compared with the numerical finite element method by Ansoft Maxwell. The models allow for comprehensive design analysis and parameter optimization. It is shown that the proposed SMG has better performance with larger workspace and output torques than the existing permanent magnet spherical motors with comparable dimensions. Upon the developed model, a motion control method is developed for tracking trajectory to demonstrate the application of the analytical model.

A dynamic decoupling control structure for permanent magnet spherical actuators based on active disturbance rejection control

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.

An Impedance-Based Force Control Scheme to a Plate-to-Plate Nanoimprinter

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.