Low-cost torque sensor `overcomes drawbacks`

A German-based start-up company has developed a non-contact torque sensing technology that, it claims, overcomes the limitations of existing technologies, such as dynamometers and strain gauges, at a fraction of their costs. The company, Fast Technology, estimates that there is a potential market for 200 million of its sensors a year in applications ranging from machine controls to power steering systems on vehicles.

Fast`s technique - on which there are 20 patents pending - is to magnetise the shaft and to sense the changes in the magnetic field that occur when torque is applied. These changes are detected by a sensing head typically placed about 1mm from the shaft, and are then converted into an electrical signal by conditioning electronics.

Fast says that the technique is unaffected by the presence of dirt and fluids, or by the speed of the shaft, which can be stationary or spinning at up to 100,000 rpm. The sensing range is 0.5-100mm and typical accuracy is claimed to be 0.5% of full scale.

Potential industrial applications include:

• controlling the forces applied in machine tools;
• regulating web tensions in paper and textile production; and
• monitoring torque levels in electrical and pneumatic wrenches.

According to the company, the only limitations on the technology are that the shaft must be made of a ferromagnetic material, must not reach its Curie point (the temperature at which it loses magnetism), and must not be exposed to strong magnetic fields without protection.

Marc Rosenbaum, Fast`s vice-president for marketing and business development, says that the typical price for a standalone torque sensing system will be about $500, compared to $2,000-5,000 for existing technologies. For volume applications, such as sensors integrated into vehicle systems, the price will be much lower, he adds.

Fast will either supply ready-magnetised shafts, or it will magnetise shafts for its customers. In some cases, it may supply large-volume customers with the magnetising equipment.

Fast was formed in Newbury in March 1999 by the inventor Lutz May, who had been working for Analog Devices. Last year it moved its headquarters to a site near Munich where a 30-strong multinational team is putting its sensors into production.

More than $10m has been invested in the company so far, mainly in the form of venture capital. Fast plans to build up a global engineering, production and distribution structure over the coming five years.

The company is working on further developments of its technology to measure variables such as angular position, rotational speed, and the bending of mechanical components. It says that these developments will allow users to measure the true instantaneous power output of a rotating machines with a single, low-cost sensing system. Fast is also working on other non-contact techniques to perform measurements such as torque values on discs and surface pressures.