Measuring the position of a shaft with both linear and rotary motion is a challenging design problem that usually involves two sensors, one for each axes of motion, and two input ports. Three engineers at MTS Sensors just received a patent (U.S. patent 6,600,310) for a sensor technology that does both, potentially saving engineers cost and complexity in their designs. The sensor is an extension of MTS' Temposonics non-contact position sensor technology, which exploits the capability of a magnetostrictive material to deform under the application of a magnetic field. The sensor works by inducing a sonic wave in a magnetostrictive waveguide through the interaction of a magnetic field from a ring-shaped permanent magnet that moves along the sensor tube and a current—or interrogation—pulse. By measuring the elapsed time for the resulting strain pulse to travel along the waveguide to a detector head, the magnet's absolute position can be determined with high accuracy. This sensor takes the concept a step further by employing a second permanent magnet that is helical in shape. In essence, this second magnet provides a reference position so that the amount of rotation of the linear magnet on the shaft can be determined. A first application for the technology is in automatic manual transmissions. Though that may sound like an oxymoron, automakers, in fact, have been looking at ways to take a standard transmission with clutch pedal and manual shift gear selector and automate the two steps. At least two companies are evaluating MTS's two-magnet magnetostrictive position for sensing both linear and rotary motion of the shift shaft as it moves through an H pattern to select the appropriate gear cluster. Engineers say that the sensor resolution can be up to 2 microns, although a version targeted at lower-cost applications has a resolution on the order of 40 microns.
CONTACT:Jesse Russell, MTS Systems Corp., Sensors Div., 300 Sheldon Dr., Cary, NC 27513, Tel (919) 677-2314; Fax (919) 677-2356, Email: firstname.lastname@example.org, www.mtssensors.com/commercial; or enter 509 at www.designnews.com/info