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Energy Conversion and Management 49 (–2775
Contents lists available at ScienceDirect
Energy Conversion and Management
journal homepage: /locate/enconman
A new driver based on dual-mode frequency and phase control for traveling-wave type ultrasonic motor
Tien-Chi Chen a,*, Chih-Hsien Yu a, Mi-Ching Tsai b
Department of Engineering Science, National Cheng Kung University, Tainan, Taiwan Department of Mechanical Engineering, National Cheng Kung University, Tainan, Taiwan
a r t i c l e
a b s t r a c t
A mode conversion rotary traveling-wave ultrasonic motor (TWUSM) has potential applications in miniature robotics. However, its electrical drive circuit presents unique challenges, particularly in producing a high frequency (about 40 kHz), high voltage (400 V peak-to-peak) signal input to a low impedance capacitive motor, while achieving high efficiency. A novel driving circuit is proposed to provide twophase balance voltage for a TWUSM. This paper describes the design of TWUSM drive circuit, intended for simultaneously employs both the driving frequency and phase modulation control scheme. The operating principles and a detailed analysis of the proposed driving circuit, consisting of voltage-controlled oscillator (VCO), voltage-controlled phase-shifter circuit and power amplifier circuit, are introduced. To drive the USM effectively a two-phase power amplifier converter using non-resonant technique was designed to provide a balanced two-phase voltage source, and the two-phase output driving voltages could be maintained at the same peak voltage value at the driving frequency under varying phase-modulation processes. Detailed experimental results are provided to demonstrate the effectiveness of the proposed driving circuit. Crown Copyright ? 2008 Published by Elsevier Ltd. All rights reserved.
Article history: Received 6 August 2007 Accepted 24 March 2008 Available online 12 May 2008 Keywords: Ultrasonic motor Frequency and phase modulation control
1. Introduction The ultrasonic motor (USM) has many excellent performance features, including high-retention torque, high torque at low speed, silence, compactness in size, and no electromagnetic interference. The USM has been used in a number of industrial, medical, space, robotic, and automotive applications. The driving principles of the USM are high-frequency mechanical vibrations and frictional force and its mathematical model is thus difficult to derive. As a result, a lumped motor model of the USM is presently unavailable [1]. Moreover, the control characteristics of the USM are complicated and highly nonlinear, as motor parameters are time-varying, owing to increases in temperature and changes in motor-drive operating conditions, such as driving frequency, source voltage and load. Basically, the speed of the TWUSM can be manipulated by controlling the frequency, phase difference and the voltage amplitude of the two sinusoidal voltage waveforms which input to the TWUSM. Many researchers have opted for the frequency of the sinusoidal voltage waveforms as the control variable [2–5]. It can easily be controlled digitally and spans the entire allowable speed range of the TWUSM. Most TWUSMs contain a two-phase halfbridge series-resonant inverter with an approximated unity
* Corresponding author. E-mail address: tchichen@mail.ncku.edu.tw (T.-C. Chen).
switching frequency (fs) to resonant frequency (fo) ratio. According to the description in the previous paragraph, the quality factors of the two phases are different and time varying. Moreover, when the frequency ratio (fs/fo) of a series-resonant inverter approaches unity, the voltage gain varies severely with the variation of the quality factor [6]. Thus, the two-phase sinusoid output voltages are unbalanced under the same switching frequency. Consequently, good dynamic performance of the USM is difficult to obtain due to the variation in the unbalanced peak values of the two-phase voltages. By contrast, a voltage amplitude control strategy using additional boost choppers was employed in [7]. Each chopper–inverter driving circuit is composed of one boost chopper cascading with one half-bridge series-resonant parasitic load impedance inverter. Since the two phase constructions of the USM are coupled mechanically and the reaction from the electrical to the mechanical part is unbalanced for both phases, the equivalent two-phase loads of the rotor are unbalanced and varied for different rotating directions, rotor speeds, load torque, applied voltages and static pressure force between stator and rotor. In addition, the internal two-phase blocking capacitors of the USM are unbalanced and will vary in value under different rotational directions. As a result, it is difficult maintain the two-phase sinusoid output voltages at the same constant peak value at the same switching frequency. However, a driving circuit proposed by Lin and Kuo [8] operates within working limits where the inverter voltage gain is greatly affected by the variation of the quality
/$ - see front matter Crown Copyright ? 2008 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.enconman.
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