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Commercial Applications of Ultrasonic Motors in China
XinwenLV

1. Introduction
1.1Background:
Traditional motors based on the electromagnetic principle have been invented and developed for more than one hundred years. As actuators and power sources, the motors have been widely used in many fields across the world and have made great contributions to our society. However, with the development of hi-tech products such as satellites, precision instruments, many new requirements for motors have been raised, which is difficult to meet for traditional motors due to its limitations on principle and structures. Many developed countries like Japan, America and Former Soviet Union, began to strive to explore new and special motors such as ultrasonic motors.

1.2The Mechanism of Ultrasonic Motors (USMs)
The concepts of USMs have been put forward since 1940s. It utilizes the vibration of the elastic body in the ultrasonic frequency band and the reverse piezoelectric effect of piezoelectric materials. The mechanical movement and torque are obtained by means of the frictional contact force between the stator and rotor or slider. USMs can meet the new requirements for small and special motors because of its advantages which would be explained in detail in following chapter.

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1.3The features of USMs (Compared to traditional motors)
Advantages: (1) Compact structure, design flexibility, large torque density: As piezoelectric component can excite different types of vibration, their torque density can be 3-5 times of traditional motors. (2) High torque at low speed, and could drive loads without gear directly which can enhance the positioning accuracy and responses speed as this advantage reduces additional volumes and weight caused by gear box, noise and position error caused by transmission. (3) No electromagnetic interference: USMs do not produce magnetic fields and will not be suffered from electromagnetic interference in the process of running, which is totally different from traditional motors. (4) Fast responses (microsecond level), Self-locking, Low noise(beyond the scope of human being) (5) Operating in extreme environmental conditions (Vacuum or High/low temperature) Disadvantages: (1) Small power output, low efficiency. Clearly, this limits the applied fields of USMs. (2) A short operational life and unsuitability of continuous operating (3) Special requirement for drive signal

1.4The history and application of USMs
In 1965, Scientists from Soviet Union designed a kind of ultrasonic motor, which used the vibration of piezoelectric plate to drive the rotor. In 1973, Barth in IBM proposed a structural design scheme with the principle of modern ultrasonic motor. In 1983, a scientist named Sashida designed and manufactured a traveling wave ultrasonic motor, which paved the way to practical applications of ultrasonic motors. Applications: Due to its unique advantages, USMs can be used in many fields such as precision positioning system (Camera), auto-mobile. Seeing the potential market in the future, many Japanese scientists have dedicated to commercialize the prototype motor developed by Americans and Soviet. One common application of ultrasonic motors is in camera lenses where they are used to move lens elements as part of the

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auto-focus system. Ultrasonic motors replace the noisier and often slower micro-motor in this application. That’s why Japan has a dominate place in camera industry.

2. USM in China
2.1Research in China
In China, research on ultrasonic motor started in 1990s, and Tsinghua University, Zhejiang University, Jilin University and Nanjing University of Aeronautics and Astronautics and Harbin Institute of Technology, began with the research on ultrasonic motor in turn and got some achievement. Chunsheng Zhao (from NUAA) developed a disk-type travelling wave USM. Later with the lead of Academician Zhao, the Precision Driving Laboratory has developed more than 30 kinds of USMs, which consolidated its leading position in China.

2.1Manufacturing and Applications in China
As emerging high-tech products, the manufacturing of ultrasonic motors just started. Based on the research institution mentioned in the last paragraph, There are only few companies that can produce USMs :Jiangsu Chunsheng ultrasonic motor CO., LTD, GUODIAN NANJING AUTOMATION CO.,LTD and Xian Chuanglian ultrasonic motor CO., LTD. Overall, the manufacturing of USMs still remains small scale. The applied fields are limited in some particular fields such as aerospace and military fields. It’s a shame that the manufacturing companies are struggling to live due to its limitation. Therefore there is a long way to go for the commercial applications of ultrasonic motors in China.

TRUM-30-P-A

TRUM-45-P-A

TRUM-60-P-A

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TRUM-60-R-A

TRUM-60-P-N

TRUM-100-P-A

2.3Limiations
(1) High manufacturing cost: Due to its small production scale, the average cost of each USM ranges from 300RMB to 1000RMB, which is much more expensive than other micro motor. In other words, there is a lack of big buyer in this supply chain. And also, the manufacturers which need motor component have to cooperate with USM manufacturer so that they can make a perfect integration. Otherwise, the USMs may not meet the requirement of particular condition. However, every cloud has a sliver line. As long as the production scale is enlarged, the cost will be reduced dramatically, which is even much lower that foreign manufacturers. Provided that this requirement is meted, many fields that once could not adopt USMs due to economic considerations can accept USMs. (2) The technological limitations of USMs: Compared to one hundred years development of traditional motors, the history of USMs is just around 30 years from the first invention. Some functions are not mature (A short operational life and unsuitability of continuous operating, for example) compared to traditional motors which hinders its promotions.

2.4The future trend of USMs’ application in China 2.4.1The prospect of USMs
Despite with some disadvantages in its functions, USMs have a vibrant future since its unique characteristics conform to the requirement of tendencies of human being’s development: Energy-saving, Environment-friendly, Smaller and Lighter, and Intelligent. First of all, USMs will save more energy for example if used in cars to replace Diesel drives or traditional motors drives. What’s more, as USMs are compact, the precision products would become even smaller and lighter with the application of USMs. Last

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but vital, USMs is helpful to make the world intelligent, particularly USMs used in intelligent robots. Overall, USMs will replace traditional motors in many fields if price is reasonable.

2.4.2 From military filed to civilian field
USMs can work well in extreme condition, which fits the requirement of Aeronautic and Astronautic field when used as controller. Similarly, due to its no electromagnetic interference and fast response, ultrasonic motor is increasingly used in military field as controller and drive. However, the military filed do not care, in some ways, the price compared to civilian field. It is necessary to convert it into civilian field in order to develop USMs in long term. For a telling example, USMs are widely used in camera and now Japanese brands, such as Cannon, Nikon, play dominate role in the world. This reminds us that USMs can be used in optical instruments and diagnostic instruments to improve positioning system in medical industry whose products have high-added value. Similarly, USMs have much potential in machine tool industry.

2.4.3 From High-tech field to public field
In perspective of development path, due its high-tech value and cost, it makes sense to use USMs in precision instruments such as Cameras, microscopes, precision machine tools and intelligent robots. Later the product line could be expanded to luxury products; high-end luxury car is a good example. It is said that a high-end luxury car is equipped with more than 80 micro-motors. If replaced by ultrasonic motors, it will reduce the noise and offer precise control. As the most successful country in the commercialization of ultrasonic motors, Japanese Companies like Toyota have begun to use ultrasonic motors in its luxury cars. Finally, it can be used in public field particularly home appliance industry such as High-end washing machines, bridges and electric curtains (It has been put forward to use in some five star hotels by Chusheng Company).

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3. Ways to commercialization
3.1. Sell component VS Sell terminal products
Unquestionably, for high-tech product, it is impossible for manufacturers of USMs to extend the product line. There seems to have no choice but to sell it directly to downstream enterprises. However, for public products like electric curtains, it may be a practical to found a joint company cooperated with a curtain producer to sell terminal products.

3.2 Who is Best Strategic Partner?
The best way for manufacturers of USMs to commercialize is seeking for Giant enterprise as partner. The bottom line is that the partner need motors as its core component, otherwise the counterpart may not have the will to invest in USMs.

Conclusion:
USMs have vibrant future due to its unique advantage, while it is still a long way for USMs to be widely used in many fields especially civilian field.