Mini movers

Zoom lens cameras on mobile phones and vibrating alerts on a range of hand-held devices are becoming standard, but as the demand for smaller models increases, engineers have had to design smaller motors that will drive these features in the same effective way.

US ceramic motor manufacturer New Scale Technologies claims to have developed the world's smallest linear motor — the Squiggle — for use in 3x optical zoom lens modules for phone cameras.

The company worked with photographic lens specialist Tamron to demonstrate the capabilities of the Squiggle, which measures only 10.8 x 18.2 x 16.3mm.

New Scale has also demonstrated a smaller version —measuring 3.4 x 3.4 x 10 mm — for tiny devices such as portable sensors.

While there are many applications for miniature motors, the company is putting a great deal of focus on the mobile phone industry. As it said, the world market for mobile phone cameras is forecast to be nearly one billion by 2009.

Mobile phone companies are moving to produce models with image quality that rivals stand-alone digital cameras by incorporating high-end 3 and 5 megapixel image sensors.

However, achieving that quality also requires high-end precision optics, auto focus and optical zoom capabilities to project sharp and clear images on to the sensors.

'Until now, no-one has delivered a combination automatic focus 3x zoom lens in a module this small,' said New Scale's president and chief technology officer David Henderson.

'The Squiggle has enabled Tamron to deliver high-quality optics in the tiny form that mobile handset designers demand.'

Its motor design consists of piezo- electric ceramics bonded to a threaded nut with a mating screw inside. When electrical signals are applied to the ceramics, it creates ultrasonic vibrations in the nut, causing the screw to rotate and translate with precise linear movement in a very small space.

New Scale claims that while Squiggles are much smaller than conventional electromagnetic motors they are more precise, less expensive and more efficient.

Other companies are also getting in on the miniature motor market.

Precision Microdrives, a UK supplier of precision motion control components and miniature DC motor assemblies, for example, has been rapidly increasing its supply of small vibration motors for mobiles and medical technology applications.

According to the company, it is shrinking the size of its motors to under 10mm in diameter with the use of coreless technology, which allows motors to be designed with rotors without any iron cores.

'We are looking to treble our supply of miniature motors,' said operations director Tsuyoshi Kihara.

Precision has been supplying electric motors for years, he said, but there is a recent trend from customers wanting hand-held devices with vibration functionality.

Most phones have had vibration capabilities for years, but other applications in areas such as the medical field are still up and coming. Kihara gave an example of the increasing demand for haptics in digitised operations. With the use of tiny vibration motors, medical students can get vibration, instead of audio or visual, feedback on their surgical movements.

Tiny vibration motors could also have security applications. Kihara gave an example of how Precision is working with one company to incorporate them into electronic ankle tags. With current models, the tags will beep if offenders are somewhere they shouldn't be.

'The vibration motor would be handy if, for example, the offender was out somewhere noisy,' he said. 'They would still have a sensory feedback to tell them they had to return to where they needed to be.'

While the trend is to develop smaller motors, Kihara said decreasing size sometimes decreases functionality. 'We found that the smaller the motor, the less power, or vibration intensity generated,' he said. 'Currrently the smallest size we have is 4mm diameter and 8mm long — slightly bigger than a rice grain.'

For certain applications, the intensity of the vibration is more important than the size of the motor. Precision is now working with a metal detecting company to develop underwater metal detectors that provide vibration feedback.

'Users detect metal by putting a headphone on and listening for the beeps as it goes over the ground,' he said. 'The company wanted a device that emitted a signal that could be picked up by holding it, rather than using headphones, so it asked us for a miniature vibration motor.' For this particular application, Kihara said the company is more concentrated on maximum feedback than motor size.

Still, in the growing micro electro-mechanical system (MEMS) industry, size remains important. It's here that New Scale's Squiggle remains at the forefront. According to the company, it operates continuously from room temperature to cryogenic temperatures of 77 Kelvin (-196°C) and below.

In cryogenic sensor applications, such as hyperspectral imaging, cooled optics greatly improves image quality. Until now, the alignment of cooled optics has been a lengthy process requiring the operator to align the optics at room temperature, cool the sensor, test the alignment, note corrections, bring the sensor to room temperature, make adjustments and repeat. The Squiggle eliminates this process by allowing precise, active alignment of the optics at any temperature.

'The Squiggle is a unique solution for cryogenic nanopositioning,' said New Scale's Henderson. 'Conventional electromagnetic motors do not work at all at cryogenic temperatures. Other piezoelectric motors lack the Squiggle's high push force and sub-micron position resolution.'

The company claimed the tiny cryogenic motor provides up to 30 mm of travel and holds its position with the power off. Its tiny size and low-power draw minimises heat load in the cryostat.