A new class of position sensing devices is manufactured with proven technologies such as pc-board assembly and injection molding techniques. Called the Sine/Cosine Rotary Electric Encoderô, from Netzer Precision Motion Sensors Ltd., the design relies on the physics of electricity instead of using the magnetic or optic principles applied in most encoders.
Inherently insensitive to magnetic fields and internally shielded against electrostatic fields, the Rotary Electric Encoder is available in a two-plate version for cost-sensitive applications.
The new technology provides non-contacting, full-rotation, absolute output at an economical price, according to Yitsay Netzer, inventor and engineer. "Practically every performance parameter is improved, compared with existing technologies, while cost is reduced and design flexibility is enhanced."
In fact, Design News
recognized the encoder for its ingenuity and innovation as winner of the Best Products of 2001 in the Power Transmission & Motion Control category (See 12/03/2001 Design News pg. 76). Contest judge Hagen Schempf, Director of the Hazardous Environments Robotics Laboratory at Carnegie Mellon, notes the design for its use of basic physical principles, and simple and elegant implementation of innovative materials.
Electric position sensing differs from optic and magnetic sensors in that it uses a dielectric rotor attached to a rotating shaft. As the rotor moves with respect to a stationary, time modulated, space patterned, field transmitter and stationary field receiver, angular displacement influences a patterned electric field that is continuously measured to provide position feedback. The output is a continuously varying voltage proportional to the sine and cosine of the measured angle.
Instead of using a local read head, as in optical encoders, the electric encoder averages the interaction between the field and the rotor over the whole area of the rotor. Consequently, the speed/resolution trade-off is virtually eliminated up to 30,000 rpm, according to Netzer. Moreover, the design is less sensitive to mechanical mounting inaccuracies, vibration (15g @ 0 to 2,000 Hz), temperature (-55 to +125C), and humidity (to 100%, condensing).
The electric encoder technology is available in two-plate rotary (shown), three-plate rotary with separate field receiver and transmitter disks, and a linear version. Currently only SIN/COS analog outputs that can be digitized and processed by commercial multipliers are available. However, Netzer is developing a programmable ASIC that will support A Quad B and serial communications protocols.
"Easy to customize pc-board technology," says Netzer, "means that engineers working with encoders can tailor the sensor to suit the machine, rather than tailor the machine to suit the sensor."
For more information about rotary electric encoders from Netzer Precision Motion Sensors Ltd.: Enter 536