Miniature rotary encoder has high accuracy

By: 
May 03, 1999

Amherst, NY --Typically, the smaller the size of the encoder the lower the resolution, as the number of slots is proportional to the diameter of the code disc. Nevertheless, API Harowe's new E9 miniature encoder achieves a resolution of 512 lines per revolution--matching that of much larger encoder offerings.

Design engineers saved space by stacking the connector directly on the device, using a flex circuit that wraps up and around the top. In conventional designs, the connector extends out radially from the device, increasing the size of the footprint. This approach results in what Mike Prentice, product line manager, calls a clumsy-looking geometry. "Motor shafts are cylindrical, and a conventional encoder with the connector hanging off the side is sort of apple-shaped. The two geometries just don't fit well together," he says.

In contrast, the E9's unusually small geometry (21.1 x 22.0 mm diameter) allows it to sit neatly on top of even very small motors. The correspondingly small hub (outsider diameter is 8 mm) of the device translates into an impressively low inertia (0.12 g-cm 2, as compared to the competition's 0.6 g-cm 2). Low inertia is desirable, particularly in applications involving high accelerations such as robotics.

A stacked connector, however, does involve trade-offs. Because the device is taller than competitive designs, the length of the motor shaft must be precise. And, unlike conventional encoders, there is a limitation on shaft length (between 13 and 14 mm).

Also, the encoder's resolution is limited to 512 lines per revolution. The only way to improve upon it without the use of electronics would be by lengthening the optical radius, but that would in turn increase the size of the device.

Some additional advantages of the E9 encoder include:

A proprietary ASIC that performs all electronic functions, including signal detection, conditioning, and output.

  • A standby mode, which reduces current consumption from the usual 10 muA to only 50 muA.

  • A rugged polymer code disc that has good dimensional stability over a temperature range of -40 to 100C.

According to Prentice, the E9 has been specified into a number of applications, including one for a surveillance camera in Europe. Favorable lead times--averaging two days--have also led to better-than-expected sales, says Prentice.

By year's end, API plans to expand the line with both an economical and a high-performance version of the E9. Another goal, says Prentice, is to modify the product to allow its operation at temperatures up to 125C. Such a capability would make the E9 competitive with more robust resolver technology, which typically has higher operating temperatures but costs more.

Additional details...Contact API Motion, Mike Prentice, Hazelwood Dr., Amherst, NY; Tel: (610) 692-2700 x295; FAX: (610) 696-4598; www.apimotion.com.


Typical Applications

  • Small, high-speed motors used in robotics

  • Pick-and-place machines

  • Optical lens grinding

  • Machine tools

  • Robotic end grippers



E9 rotary encoder at-a-glance
Supply voltage 5V plus or minus 10%
Supply current (no load) 10 mA
Standby mode Yes
Differential output Yes
Bandwidth 200 KHz
Operating range -40 to 100C
Resolution 100 to 512 lines per revolution
Size 20.57 x 375.92 x 22.0

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