Wu-Sung Yao

Design of a plug-in type repetitive controller for periodic inputs

This paper presents some practical design criteria for a plug-in type repetitive controller to achieve good tracking performance within a specified frequency range. Upper and lower bounds of the repetitive controller parameters that ensure the stability and the desired performance are derived. It has been found that the decay rate of the tracking error due to periodic inputs is related to the peak value of a defined regeneration spectrum function. The control performance of the present method is evaluated in an experimental software cam system, which needs periodic linear motions, where the real-time control algorithms are implemented using a floating-point digital signal processor (DSP). Both computer simulation and experimental results are presented to illustrate the effectiveness of the proposed repetitive controller design.

Analysis and estimation of tracking errors of plug-in type repetitive control systems

Subject to stability constraints, tracking performance of a plug-in type repetitive control system with periodic inputs is explored in this note. An upper bound for the square integral of the tracking error over one time period of periodic input signals is derived based on Fourier analysis. The magnitude and the decay rate of the tracking error can be estimated using the harmonics of the input signal within the designed bandwidth. Both computer simulations and experimental results are presented to illustrate the effectiveness of the proposed method. It is also shown that the tracking error can decay significantly in the first two time periods in the proposed repetitive control system if the required bandwidth conditions are satisfied.

Design and analysis of a unimorph piezoceramic generator with cantilever structure in a low-frequency environment

Piezoelectric materials have the electromechanical capability of converting mechanical vibration energy into electrical energy and are utilized in sensors, generators, and actuator applications. However, with regard to compact-dimension applications, piezoelectric generators have to overcome some shortcomings, such as high voltage, low current, and relatively low power output. This article presents a design method of which the loading-weight vibration on the piezoelectric material can be transferred into an external force, and, additionally, an equivalent electric circuit method is used to calculate the electrical characteristics of piezoelectric material. Compared to the measurement, in a 4 Hz vibration environment with a 30 g loading mass, which is equivalent to a 0.5 N external force, the piezoelectric plate can generate an electric voltage of 19.8 V. A 2.7 per cent error rate of the output voltage in the equivalent force conversion is achieved. Finally, in order to demonstrate the accuracy of the theoretical analysis, a prototype hand-shaking piezoelectric generator is proposed, which is used to drive a wireless-switch device (5 V driving voltage). Experimental results show that the average electrical power of the hand-shaking piezoelectric generator is approximately 50 μW, and a 7 per cent stored power error rate is achieved when comparing the measurement and theoretical estimation.

Voltage-current-based state and disturbance estimation for power-assisted control applied to an electric wheelchair

The dual-drive electric wheelchair with power assisted control is essential for improving the mobility of disabled people. In this paper, a voltage-current-based observer is proposed to realize the force/torque sensorless control of power-assisted wheelchairs. The feature of the proposed observer is that only the input voltage and armature current response of the driving motor are required for the estimation. The observer which is constructed with the motor dynamic model and two low-pass filters is employed to estimate the velocity, acceleration and external disturbance of the electric wheelchair. Then, a decoupling method is presented to retrieve the actual human input from the external disturbance estimated by the observer such that the power-assisted control can be achieved within the humans intuitive motion space. This paper presents a power-assisted control strategy which is conducted directly in both the translational and rotational motions of the dual drive wheelchair. The voltage-current-based observer designed for the force/torque sensorless power-assisted control is implemented on an electric wheelchair, and its effectiveness is verified with experimental results.