Small Encoders Don’t Skimp on Performance

November 8, 2007

4 Min Read
Small Encoders Don’t Skimp on Performance

Encoders with a reduced package size can be a big help when space on and around the motor shaft gets tight. And suppliers have recognized that fact and developed new models that squeeze high resolution encoders into a smaller package size. Some of the impetus comes from mobile platforms. “Reduced size and weight matter a great deal in systems that move over the land, sea or air,” says Scott Orlosky, marketing manager for BEI Industrial Encoders. Yet, the need for more space-efficient encoders isn’t limited to mobile applications. Real estate can be at a premium on all sorts of high-end industrial machines and robots, too. “We’re seeing increased calls for high-performance encoders in a smaller package size,” says Scott Hewitt, president of Sick Stegmann. Martin Gordinier, vice president of Gurley Precision Instruments agrees. “Smaller, higher resolution and less expensive is what’s happening in encoder design, he says. Here’s a look at three examples of high-performance encoders that fit in tighter spaces.

SMALL ENCODER FOR ASYNCHRONOUS APPLICATIONS

Sick Stegmann has come out with a high-resolution incremental hollow shaft encoder that primarily targets ac induction motor applications that need better precision than available with vectorless control. Called the VFS60, this encoder measures just 60 mm or a bit less than 2.4 inches across. At the same time, the VFS60 doesn’t short users on resolution. It offers nine user-selectable line counts, ranging from 1,000 to 10,000. Those line counts include those most commonly used for ac induction motor — namely 1,024 and 2,048. Normally, encoders with up to 10,000 lines of resolution would have a bigger package size, according to Scott Hewitt, president of Sick Stegmann. “In the past you would be looking at 3.5-inch encoder for that kind of performance,” he says. Aside from size, the VFS60 has been optimized for mechanical robustness, as well. Its design puts the metal code disc and optic between two bearings, rather than the more common arrangement in which the disc and optics sit on a shaft outside the bearings. Hewitt believes the VFS60’s bearing arrangement can extend encoder life significantly, by helping it hold up to mechanical vibrations and motor shaft runout. “These encoders haven’t been out long enough for us to know how long they’ll last, but our endurance testing suggests they would reach 24 months,” he says. “With traditional designs you’d feel lucky to get 12 or 18 months.”

MODULAR ENCODER LINE EXPANDED

Gurley Precision Instruments has expanded its line of 7700 Series Virtual Absolute encoders to support the growing demand for smaller, higher-resolution encoders. These modular rotary and linear encoders cover a resolution range from 12 to 19 bits with temperature options from –40 to 100C. Each of these modular system includes a read head, a disc-hub or linear scale and compact external decoding electronics. Standard disc diameters are 33 and 44.5 mm, with bore sizes to 14 mm. Disc and scale materials include glass, metal and plastic. Initialization angles of 1.92 or 3.52 degrees for rotary motion, or a few millimeters for linear motion, need to be read before achieving absolute position. Optional three-phase motor commutation is available at 2, 4, 6 or 8 pole pairs. For straightforward interfacing, standard outputs include SSI, multiplexed parallel and Universal Serial Bus (USB). According to Gurley Vice President Martin Gordinier, the 7700 Series has been integrated into a variety of sophisticated motion systems, including gimbals, gyroscopes, machine tool spindles, tracking pedestals for telescopes and antennas, robotics, laboratory instruments and photonics equipment.

SMALL ENCODER, BIG COUNTS

BEI Industrial Encoders’ latest high-performance encoder measures just 1.5 inches in diameter. Yet, it still offers up to 40,640 cycles per turn — or up to 162,560 counts using the quadrature detection now found on PLCs, counters and controllers. “It’s ideal for space-limited applications requiring high accuracy,” says BEI marketing manager Scott Orlosky. Among these applications are semiconductor equipment and robotics. The L15 encoder features a size 15 servo mount package and a 0.25-inch-diameter stainless-steel shaft. It accommodates radial and axial loads up to 5 lb. The L15 encoder package also has ASIC electronics, sealed dual bearings and code disk in an all-metal housing to ensure ruggedness and reliability.

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