WORLD OF INDUSTRIES 02/2018

GMR Tooth Sensor Module
Motor spindle with
air bearings
Levicron GMBH
02 Encoder kit for high speed air-bearing spindle 03 Intelligent legged endoscopic capsule robot
magnetic fields. As mentioned the range of applications for MR
sensors in increasing steadily and each of the following examples
demonstrates how current requirements can be best met with this
type of magnetic sensor
MR-Sensors support lightweight robots
A good example for the “embedding” of sensors within a machine
is given by the latest generation of lightweight robots. The Robotics
and Mechatronics Center of DLR plays a major role in the field of
applied robotics. Numerous generations of lightweight robot arms
have been developed. A further development stage was the design
of an anthropomorphic hand arm system for future service robotics.
This competes with the kinematic, dynamic and force properties
of the human arm. This highly integrated mechatronic system
consists of 52 drives and no less than 112 position sensors, many of
which utilise MR sensor technology. The mobile humanoid robot
“Rollin’ Justin”, shown in Figure 1, is one of the latest creations at
DLR and provides a research platform for autonomous dexterous
mobile manipulation in human environments. The mobile base of
the robot, which allows the long range autonomous operation of
the system also features numerous MR-based encoder kits.
High speed air-bearing spindle
High speed machining is particularly relevant where the requirements
regarding workpiece toleranc-es and surface quality are
particularly high, such as in mould- and tool-making. GMR-based
tooth sensors open up new possibilities for high-speed spindles
with air bearings. As can be seen in Figure 2 a fine
tooth-like structure with a module of 0.3 mm is machined
directly into the surface of the spindle shaft.
This provides the measurement scale for an encoder
module for the commutation of the motor and positioning
of the spindle shaft. There is no need for
an additional encoder disc and the imbalance
of the shaft can be reduced to a minimum. Furthermore
this solution has no additional inertia,
which enables highly dynamic acceleration
and also reduced energy requirements. This
solu-tion allows speeds of up to 90.000 rpm
with an angular resolution of < 0.1°. This
application is for incremental angle
measurement, but absolute measurement
is also possible using two toothed
structures and a vernier principle.
Mars Rover „Curiosity“
MR sensors have been used
successfully in space robotic
applications for more than 10 years. The „Mars Exploration Rover
Mission“ (MER) is a space mission initiated by NASA, which began
in 2003 with two launch vehicles to transport two automatic „rovers“
– called „Spirit“ and „Opportunity“. With this mission the geological
conditions on Mars should be explored to find evidence of water.
Each rover is equipped with 39 magnetoresistive sensors used as
components of the magnetic encoders of special motors supplied
by the Swiss company Maxon Motor AG. In November 2011 another
Mars Mission called „Mars Science Laboratory“ (MSL) started.
The rover named “Curiosi-ty” landed in August 2012 to search for
organic material. The rover shall find out if Mars ever offered the
living conditions for small living organisms. For this purpose the
rover is equipped with a highly complex collection of scientific
instruments. MR sensors are used to control the motors of almost
all the moving mechanisms. The sensors must not only withstand
high mechanical loading during take-off and landing, but also must
withstand temperature swings of 190 °C and also withstand high
levels of radiation.
Miniaturized robotic pill for advanced diagnostics
Sensitec has participated in the EU-funded project Vector with
the objective of developing intelli-gent endoscopic capsules using
innovations in micro- and nanotechnology. The Vector project
aimed at investigating and developing a miniaturized robotic pill
for advanced diagnostics and therapy in the human digestive tract.
The project mission was to make a significant contribution to the
diagno-sis and treatment of digestive cancers and their precursors.
Figure 3 shows the legged endoscopic capsule robot, which is capable
of mesoscale locomotion within the gastrointestinal tract. The
robot has similar dimensions to commercial pill cameras (11 mm
diameter by 25 mm length). Sensitec’s role in the project was therefore
to develop a miniaturized magnetic motor encoder to control
the position of the legs (Figure 3).
Outlook
The innovative MR-solutions for encoder- and motor-feedbacksystems,
as well as for current sensors, are further examples of the
potential of magnetoresistive sensors for opening up new opportunities
for the designers of motors, actuators or machines. Sensitec
is working on the development of sensor modules and kits
with even higher performance and increased functionality. Further
miniaturized dimensions, higher resolution, higher absolute
accuracy or higher intelligence in the form of extended diagnostic
functions are just some of the development themes currently
being explored.
Photographs: 01 DLR, 02 Levicron, 03 Sensitec
www.sensitec.com
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