Tech Briefs Magazine - August 2022 - MD-4

Encoder Technologies
Resolution
Size
Optical
Ease of Use
Cost
Magnetic
Durability
Absolute
Environmental
Immunity
Resolver
Inductive
020406080100
Relative Strength
Figure 1: At-a-glance comparison of each encoder technology's strengths and weaknesses. (Image: Motion)
nected controller to interpret where a
system exists within a range of motion. A
system that relies on an incremental encoder
must have some method of homing
or calibration, where the system will
advance to a known location before it can
" zero " its position data and proceed with
normal operation. This routine can be
unacceptably long for systems with a
large range of movement coupled with
slow motion (e.g., a large satellite dish
that can take hours to home). Absolute
encoders will output a unique signal anywhere
within a system's range of motion.
This signal will still need to be referenced
from a mechanical location; however, this
is usually done only once during system
construction, or later if some mechanisms
are replaced and a new calibration
is necessary.
Availability and Interchangeability:
Incremental encoders are the most common
style of encoder found in the industrial
marketplace, with many brands to
choose from and a huge breadth of
shapes, sizes, and mounting styles. If a
specific make or model becomes unavailable,
they are usually easily interchangeable
with another. Incremental encoders
with special environmental ratings are
also easier to find than similarly rated
absolute encoders. Absolute encoders
tend to be highly specialized and engineered
for specific applications. Many
combinations of signal types, communication
protocols, single-turn and multiturn
resolutions can be selected. Vendors
often have limited pairings to select from,
making finding interchanges impossible
without significant re-engineering by the
system integrator.
Cost: Incremental encoders are typiMagnetic
encoders work via a sensor or sensors, such as the hall-effect type that passes over a series of
magnets placed along a disc. (Image: Fouad A. Saad/Shutterstock.com)
4
cally less expensive to use on simple applications;
however, it is important to
consider the total cost to implement
when deciding on a technology. If a homing
routine is necessary, the time it takes
to design and implement these routines
can be costly. There are also the costs of
limit sensors, which may be expensive.
Another often overlooked cost is the time
needed to perform the homing routine if
it takes time away from revenue-generating
production. Absolute encoders tend
to be more expensive as they typically
have more complex components and
embedded circuitry to handle the higher
resolution, position data storing, and signaling
protocol processing. It is important
to note that the increased component
cost can be offset by the benefits previously
discussed.
Motion Design, August 2022
Technologies

Tech Briefs Magazine - August 2022

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