Medical Design Briefs: 2021 Technology Leaders - 16

TECHNOLOGY LEADERS Test & Measurement
Six Tips for Ensuring Precise Compact
Distance Measurements
I
n recent years, more and more compact
linear distance measuring systems
are being demanded by designers to
fit into smaller and smaller footprint
medical devices. In addition to fit, of
course, the designed-in system must
deliver to OEM manufacturers - and
their ultimate customers - the high precision,
quality, and repeatability requirements
of the specific medical device.
But, as a designer, how do know
whether the system that you specify is sufficient
for your demanding - and potentially
lifesaving - application? The following
six tips provide a valuable guide.
1. Fit Your Footprint
Look for distance measuring systems
specifically designed for devices like
yours, which feature comparatively
smaller operating parameters plus relatively
clean environments. Obviously,
saving precious space inside the
machine is a key consideration. (This is
opposed to heavier duty measuring systems
intended for use in applications
such as machine tools and industrial
automation, which present larger operating
dimensions, longer stroke lengths,
and more potential exposure to corrosion
and contaminants.)
Pick a slide based on your required
load and stroke length. For these applications,
many users today are finding
that their best options are optical scale
distance measuring systems. These systems
offer a range of compact yet highperformance
solutions.
Make sure the scale is integrated with
the rail to maximize those critical space
savings. A high-precision dimensional
scale is part of a hardened miniature
guideway's surface, in a simplified design
with minimal components. Its sensor
records the optical signals and supplies
them for processing in the interface module,
in either analog or digital format.
Among these compact products, an
advanced ball recirculation model
allows for relatively longer stroke
lengths. A good one can measure
dimensions from a few millimeters to
16
A doctor and medical technician prepare a patient for an MRI scan.
around a meter. If you need a shorter
stroke, even more accuracy, and exceptional
rigidity, look for a ball cage nonrecirculating
model.
Finally, some components have additional
features and options that allow
you to run the cabling away from the carriage,
tucking it in for even greater compactness.
2.
Insist on Integration
Some OEMs take a component ap -
proach, sourcing different parts of their
distance measuring system from different
manufacturers: a linear scale from
one maker, a miniature guideway (rail
and bearings) from another, and carriage
attachments from a third.
But that means you must assemble the
system yourself. You undertake extra
labor and lose precious time. You also
risk ending up with an inaccurate alignment.
Take an integrated approach
instead. Buy an engineered solution
from a high-quality manufacturer: one
integrated assembly - rail, carriage,
and measurement system encoder.
Why? Because integrating measurement
and guidance into one system
helps preserve that precious machine
real estate. It avoids the need for differing
thermal expansions compensation.
And it saves time and effort all along the
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line: from supply chain and purchasing
to receiving, handling within your operation,
and installation.
With a relatively larger ball recirculation
model, you simply lay the rail down, then
put the carriage on. With some smaller
non-recirculating models, you receive a
finished assembly, ready for mounting.
3. Go Directly to Measurement
A number of distance measurement
systems, such as glass scales and rotary
encoders, utilize indirect measurement.
But the most advanced, compact systems
use direct measurement, in a setup
using a sensor, an optical read head, and
LED light sources.
You're not measuring when the ball
screw or the linear motor moves. You're
measuring exactly where the movement
takes place - as the entire assembly with
payload moves - to ensure the smallest
possible error. You avoid loss due to
wind-up in the ball screw, coupling, or
motor, or errors due to ball screw temperature
variations.
Some system makers have only tried
direct measurement fairly recently.
Their designs may not yet be perfected.
And their systems tend to be proprietary,
locking you into one controller type.
Instead, look for a product from a linear
motion specialist manufacturer that
Medical Design Briefs 2021 Technology Leaders
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Medical Design Briefs: 2021 Technology Leaders

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