WORLD OF INDUSTRIES 02/2018

Advantages of MR sensors in
challenging new applications
AUTOMATION
The increasing demand for Magnetoresistive (MR)
sensors is largely the result of increasingly complex
demands on the sensors for high performance electric
drives. The sensors must not only be accurate and
dynamic, but also be robust under difficult operating
conditions and exhibit very high reliability. Recent
market developments are generating additional
demands. This paper describes the principle of
operation and benefits of MR sensors.
There is a growing demand for mechatronic motion systems in
a wide range of industrial fields. Not only in the field of industrial
automation, but also in the automotive and aerospace sectors,
there is a sharp increase in the number of mechatronic actuators
being applied. “Decentralized motion control”, “X-by-wire” or
“more electric aircraft” are just some of the terms used to describe
the results of this trend in different technological areas. Presently
there are number of trends that are changing the technical and
commercial requirements for both actuators and sensors. The high
performance and flexibility of magnetoresistive (MR) technology
is playing an increasingly significant role in helping machine and
actuator designers to deal with these new requwirements. The MR
effect is best known from the read heads of computer hard discs or
from magnetic memory (MRAM) applications, but it is also well
suited to uses in sensor technology.
Trends in Motion Control
The market for motion control technology is characterized by a
number of current trends, which are leading to new requirements
for actuator and sensor technologies: higher accuracy, increased
power density, decentralized motion control, increased use of
closed-loop control, more challenging operating environments and
faster time to market. These trends have continued in the meantime
and inten-sified in the past 5 years. There is, however, a number
of new, additional trends that are playing an increasingly important
role in the selection of sensors for angle, position and speed
measurement:
1) The “embedding” of sensors within motors and actuators is
becoming ubiquitous, leading to stronger demand for compact
sensors.
2) Demand is growing also for sensors with extended functionality
(e.g. for condition monitoring) as well as for sensors that exhibit
functional safety.
3) In new applications e.g. E-boosters for automobiles, motors are
being developed with ever higher speeds and higher dynamic
performance, which is increasing demand for sensors with
extremely high bandwidth and low inertial.
4) The overall trend to higher energy efficiency is increasing the
demand for low-power sensors.
Author: Dr. Rolf Slatter, Managing Director, Sensitec GmbH,
Lahnau, Germany
New requirements for rotary and linear
measurement
These trends have an immediate impact on the sensors used for the
measurement of linear and rotational motion. They result in a complex
set of requirements, most or all of which apply in many new
applications. The actuator or machine designer must search for a
sensor solution that offers the following features. These include high
accuracy for precise positioning or high control quality, high resolution
for accurate control, high bandwidth for dynamic control, compact
dimensions, contactless, wearfree operating principle, high
permissible operating temperature to survive hot environments,
robust against contamination, high reliability, high energy efficiency
and increased integration and functionality (“ready-to-measure”) to
allow a fast “time-to-market”.
This complex combination of requirements is best met by sensor
systems based on MR sensor technology. Magnetic measurement
systems offer a variety of advantages compared to other measurement
principles. For example, the maximum permissible temperature
range of optical encoders is often just 85 °C and seldom as high
as 100 °C. This is significantly lower than MR sensors, which are
qualified for automotive applications at 150 °C. Furthermore, optical
sensors have limited potential for miniaturization due to their
complex construction (LED – glass scale – sensor). Last, but not
least, magnetic sensors are much more robust and less susceptible
to contamination through dirt or fluids. MR sensors exhibit similar
performance benefits in comparison to inductive and capacitive
position sensors as well.
Basics of magnetoresistive sensor technology
Magnetoresistive (MR) sensors are firmly established in numerous
applications in automobiles, mobile telephones, medical
devices, wind turbines, machine tools or industrial robots: be it
for the measurement of path, angle or electrical current, or as
an electronic compass. Originally developed for data storage
applications, the different MR effects open up new measurement
possibilities for sensors, not only in
terrestrial applications, but also in aerospace
applications. MR sensors are
robust, reliable, precise and miniaturized.
This combination of features is
leading to continuous growth in the
application field of MR sensors. The
extremely low power consumption
of MR sensors makes them
ideal for wireless, autonomous
sensor applications. They present
the developers of
many dif-ferent types
of mechanism or instrument
with completely
new possibilities
to measure angle,
path, electrical currents or
01 Special feature of the humanoid
robot “Rollin’ Justin” is the integration of
the complete electronics into the hand
26 WORLD OF INDUSTRIES 2/2018