A new miniaturethree-channel reflective encoder from Avago Technologies features built-ininterpolation for high-resolution measurement that is ideal for use inclosed-loop stepper motors, miniature motors, printers, copiers, card readers,insulin pumps and other types of industrial, consumer and medical equipment.

"The integrated third-channel,compact size and high-resolution encoding performance of the Avago AEDR-850xmodules is truly revolutionary, enabling smaller motor encoding systems thanever before possible," says Hassan Hussain, general manager of the MotionControl Products Division at Avago. "These modules cut design costs and savePCB board space for our customers, and expand the reach of our reflectiveencoder offerings into the industrial automation and medical segments."

A standard reflective encoder moduleuses two digital output channels for direction sensing, and another module forindexing purposes. For motion feedback applications requiring high-resolutionmeasurement, an external interpolation device has previously been necessary.The new reflective encoders integrate an LED light source, photo detection andinterpolator circuitry, and the three channels in a single package have a 3.95 mmby 3.40 mm footprint. With high resolution encoding of 304 lines per inch (12lines per mm), the compact, highly-integrated modules enable a new level ofminiaturization for applications where size and space are primary concerns.

"There are two major areas ofuniqueness with this encoder," says Swee-Hing Young, technical marketing engineerfor Avago. "It is the world's first LED-based miniature reflective encoder, andthe design actually accommodates A, B and index using a single track for thethree channels."

"In a conventional optical encoder,typically there are separate tracks for the A and B channels, and a separateoptical track for the index. With this new encoder, it allows us to add ourexisting two-channel reflective disk into an area that is less than fourmillimeters square," Young says. "The single track helps make the deviceachieve both miniature and low cost design objectives, along with the use ofLED technology."

By comparison, laser-basedthree-channel encoders on the market are more expensive and require much higherpower consumption than LED encoders. Those solutions are also much larger, asmuch as seven times larger than the reflective encoder.

The third index channel which is typicallyused for homing is also useful. Since the devices are incremental encoders,using the index (I) channel provides the homing position (or zero reference).With only one index signal in one mechanical revolution, the system knows itsposition from the index point onwards.

The device also offers powerconsumption savings, primarily because of its LED light source. Because thedesign uses TTL signals, even the interpolator that provides the TTL orfrequency multiplication is logic-based and customers that are already using TTLcan interface the encoder in a straightforward way.

The AEDR-850x encoders offerinterpolation of up to 4X and enable various resolution designs by changing thecode wheel size. The optical-based modules are significantly less susceptibleto EMI compared with Hall Effect devices. With an absolute operatingtemperature range of -20 to 85C, the rugged encoders are suitable forcommercial and industrial operation environments. The encoders are priced at$6.75 each in 100 piece quantities.