Special-purpose encoders meet your specific needs

Nov. 29, 2007
Encoders are being designed and engineered to meet increasingly specific needs. Space considerations, environmental factors and applications come into play when determining which encoder is best suited for a given job.

Encoders are being designed and engineered to meet increasingly specific needs. Space considerations, environmental factors and applications come into play when determining which encoder is best suited for a given job. When properly matched, plants can achieve their operational objectives while avoiding unnecessary and costly downtime.

Physical environment: Encoders can be designed to meet particular environmental conditions, including dust, dirt and explosion hazards. For instance, magnetic encoders and digital tachometers by Dynapar are designed to be more rugged than optical rotary encoders and resistant to contaminants such as dust, moisture, shock and vibration. The encoders use magneto-resistive (MR) technology to track machine speed and provide digital feedback on shaft velocity. A magnetic pulse wheel, imprinted with a number of small magnetic poles, works with an integrated MR sensor to produce magnetic fields that effectively penetrate dust, dirt, oil and other contaminants. The wheel rotates with the machine shaft, and the sensor’s resistors respond by changing resistance with the application of the magnetic field.

In harsher environments, where caustic chemicals and corrosive agents threaten equipment reliability, stainless steel encoders offer a rugged alternative to aluminum and plastic housings. Encoder Products’ Model 865T, designed to mount on NEMA C-face motors, has a housing milled from solid piece of 316 stainless steel, making it resistant to rust, oxidation and corrosion. An optional stainless steel cover protects internal bearings and electronics from dust and machine wash-downs.
 Another example is BEI’s H25 and H20 incremental rotary encoders, available with a stainless steel housing option. These can be ordered with a type 304 stainless steel encoder body and bearing housing to resist equipment failure and downtime. Applications are chemical or petrochemical processing, food packaging, medical and similarly harsh industrial environments.

Space constraints: Industrial machinery and equipment is getting smaller, and so are the electronic components. For space-constrained automation applications, an array of compact, ultra-compact and miniaturized encoders is available. One example is the miniature surface-mounted encoder series by Avago Technologies. Measuring 6.5 mm by 4.2 mm by 1.69 mm, the AEDR-8320 is useful in robotic equipment, pick-and-place machines and other applications. The reflective analog optical encoder offers precise, real-time positioning and directional sensing. It can be used with a reflective code wheel to sense rotary position and velocity, or with a linear code strip to sense linear position and velocity. Two-channel analog signal output offers 180 lines per inch (LPI) resolution that can be increased through interpolation. The lead-free package is compliant with the European Union’s Restriction of Hazardous Substances (RoHS) directive.

Targeted applications: Some encoders were designed with specific applications in mind. Dynapar’s Hengstler Acuro AX71 absolute encoder was designed with the help of a major drilling services firm to withstand conditions in oil and gas drilling applications, including severe mechanical shock and vibration, high temperatures and explosive environments. Its stainless steel construction, IP67 sealing and rugged bearings allow the encoder to withstand shock loads to 100 g. An ATEX-certified housing allows the encoder to be used safely in explosive environments without electrical barriers. To mitigate the effects of extreme temperatures and radiant heat, the Acuro AX71’s electronics incorporate heat-stable substrates and diodes that ensure reliable operation to 140°F. In addition, the encoder is self-grounding to prevent shortsing.

Heidenhain’s new LS 688C linear encoder is designed for manually operated machine tools with digital readout (DRO) applications. The encoder’s scanning carriage rides on ball bearings, providing measuring direction rigidity and tight backlash and mounting tolerances. By comparison, in machine tools without linear encoders, the measuring standard is the pitch of the ball screw. Ball screws can deform and expand from thermal changes caused by high speeds and acceleration levels, resulting in inaccurate position values. Linear encoders fully compensate for thermal expansion of the ball screws, thereby allowing the machine tools to remain thermally stable and produce tight manufacturing tolerances throughout machining operations.

Built-in encoders are available for applications such as conveyor belts and door openers that require low-resolution speed and position feedback. Bodine’s custom-made Incodermotors with built-in magnetic encoders are available as permanent magnet DC, brushless DC or gearmotors. The encoder is pre-wired and dropped into the OEM’s design, reducing assembly time and protecting it from the environment.

E-mail Contributing Editor Sheila Kennedy, managing director of Additive Communications, at [email protected].

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