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Walking motor marches into linear motion market

01 December, 2002

`Walking` motor marches into linear motion market

A Swedish company has developed an ant-sized motor that "walks" on four piezoelectric "legs". The company, PiezoMotor Uppsala, is convinced that the simple, rugged machine, which can lift 1,000 times its own weight, could replace conventional motors in many applications, especially where space is limited.

The PiezoLegs motor (above) consists of a single, solid body with four movable legs, each formed from a sandwich of 100 or more layers of piezoceramic materials, interleaved with conductors. By applying a sequenced voltage to each pair of legs, they can be raised, made to bend forwards or backwards, and lowered, to deliver a propulsive force. As one pair of legs moves, the other stays in contact with the surface.

Although each step is typically just 3.5µm, the motor can take more than 10,000 steps per second to reach speeds of several cm/s. The motor produces a pulling force of up to 8N. By partly bending the legs instead of taking a full step, it can operate to a resolution of 10nm.

The 21.9mm-long motor is 10.7mm wide and 15.5mm high, and weighs just 20g. It operates from a DC supply of 4-48V. Its stroke length is typically 35mm, although longer strokes are possible by using longer drive rods.

PiezoMotor claims that its machine has many advantages over conventional motion technologies. For example, as well as being much smaller than a comparable standard motor, the PiezoLegs machine does not need gears, drive screws, bearings or other mechanical components which can reduce efficiency, introduce backlash, and are subject to wear. The walking motor is said to be backlash-free and the only parts that can wear are the "soles" of the legs, which are fitted with wear-resistant materials.

The electronics used to control the motor are said to be no more complex than those used for conventional brushless or stepping motors. The motor works best in a closed-loop system, with feedback coming from a position sensor or from signals at a higher level in an application.

PiezoMotor says that because of the motor`s simple design, it is easy to manufacture in large quantities to a high degree of precision. In volume production, the motor is expected to cost less than conventional machines.

"We believe that this is a breakthrough in piezoelectric motors as the motor combines power, resolution and speed in a very small package," says Peo Sollerud, PiezoMotor`s marketing manager. "The motor`s simple design not only makes it very robust, but also possible to produce in volume and therefore also cost-effective compared to conventional electromagnetic linear motion systems".

As well as replacing conventional motors in many applications, PiezoMotor expects the new design`s unique characteristics to open up new applications. Potential areas of use include keyhole surgery, the automotive industry, and aviation, where the light weight of the motors will save on fuel bills.

PiezoMotor Uppsala was founded in 1997 by two Swedes, Stefan Johansson and Mats Bexell, originally to develop an award-winning rotating piezoelectric motor. The company subsequently started work on the linear motor and has already supplied selected customers with the machines. It now hopes to broaden the market. PiezoMotor says that to make the best use of its motors, they should be optimised for each application. Demonstration kits, including a motor and a controller, are available.




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