Machine Design

Industrial encoder integrates bearing and sensor functions

Fafnir Encoder Survivors measure speed and position of rotating shafts while providing the functions of a housed bearing. The units are available in pillow-block and flanged designs with two and four-bolt configurations and setscrew shaft retention.

A new family of encoders provides speed sensing and bearing performance for tough industrial applications. Fafnir Encoder Survivors, from The Torrington Co., Torrington, Conn., integrate bearing and sensing functions in a housed unit to simplify system design and reduce maintenance and assembly costs.

The design, based on technology developed for automotive ABS applications, eliminates the need for an extra gear-tooth sensor or rotary-pulse generator. Simple bolt-on installation requires no extra brackets or couplings, and the air gap reportedly can't go out of adjustment. The sensors are built on Fafnir Survivor PT bearing platforms, which resist corrosion in washdown, steam cleaning, and contaminated environments.

The units work on the principle of the Hall effect. Hall sensors are solid-state powered devices that provide an output signal proportional to the strength of a nearby magnetic field. A magnetic pulser ring with alternating north and south poles is placed near the Hall element inside the bearing seal. When the ring spins, the waterproof Hall sensor provides an output signal that determines the speed (and position) of the ring.

A single or dual Hall-effect sensor brings the signal out to a waterproof industrial-grade "green-box" enclosure. A small circuit board inside the box converts the Hall signals from analog to digital form and filters out electrical interference.

Single Hall sensors generate single digital output. Dual sensors provide signals that double the resolution and can detect the direction of rotation. The resultant electrical signal is identical to that supplied by digital gear-tooth sensors, which are widely used in industry to measure shaft position and speed. The generated square wave is then available to an external tachometer or PLC, which can provide a position and speed reading, or perform a control function.

Model EU-1 versions have a single-channel output that can provide from 1 to 32 pulses/rev. EU-2 models have two-channel output similar to 32-line digital-quadrature encoders.

A compact encoder unit is recommended for industrial-sensor applications requiring moderate output resolution, reliable performance, and where concerns include difficult operating conditions, space limitations, maintenance, and cost effectiveness. Application examples include food processing, conveyors, packaging machinery, printing, and converting equipment.

The units solve physical space problems typically associated with add-on gear-tooth sensors and their cumbersome mandatory brackets. Replacing a housed unit bearing with a sensor bearing provides the functions of a gear-tooth sensor within the original bearing footprint.


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