Future-proof position measurement in hydraulic cylinders

The new linear
encoders in the MAX product family from SICK STEGMANN boast a compact design
and compatibility, precision and performance, reliability and raised levels of
availability thanks to status monitoring. The absolute path measurement systems
for non-contact and fully integrated position measurement in hydraulic
cylinders within mobile machines have been
redesigned from scratch. They operate in line with the robust operating
principle of magnetostriction, provide extensive diagnosis functions as the
first sensors of their kind, and thereby also offer added value for mobile
machines that will continue to be relevant as we head into the future.

There
is an increase in the demand for linear sensors for mobile automation in
general and even more so for hydraulically driven machines. But the
quantitative aspect is just one side of the story. More and more vehicle
manufacturers, integrators, and operations managers are setting their sights on
top-quality innovations. Everyone wants the added value that became standard
within industrial automation long ago: the encoder needs to gather status and
process information. In future, precise, high-performance position measurement
is set to come with the added option of performing detailed analyses based on sensor information. This will make it possible, for example, to
provide support for assistance systems, avoid sudden machines failures, optimise maintenance routines, and improve
machine availability on the whole. Within the field of hydraulic measurement
technology for mobile automation, the linear encoders in the MAX product family
are currently the only devices of their kind to offer this added value.

A compatible yet innovative new
development

One
key feature of the new SICK linear encoders is their full mechanical
compatibility with existing cylinder constructions that are already prepared for integration into a path measurement
system. Integration into hydraulic cylinders is therefore guaranteed to be a
quick and easy process. The product family also offers the most compact linear
encoder for hydraulic cylinders around at the moment in the form of the MAX30.
The reduction of the diameter of the sensor head to 30 millimetres does not impact negatively on the
housing volume, allowing for space-saving integration into hydraulic cylinders
that are in turn smaller too.

Inside
these linear encoders, you will find a number of
different technologies and innovations compared to the market standard. Based on more than 25 years of experience
in linear path measurement technology for mobile machines, SICK STEGMANN
started off by studying the market requirements and then went on to develop a
radical new sensor concept from there. The main features include the use of
magnetostriction, optimisation of the
power density by minimising measurement
dead zones, and integration of diagnosis and prognosis functionalities that can
be used to avoid machine downtimes and improve operational plans and
maintenance routines for entire fleets.

Non-contact, interference-free, and
maintenance-free magnetostriction with micrometre
accuracy

Magnetostriction is a
time-of-flight measurement method. The distance between two points is measured
using the travel time of a short current pulse and its partial reflection within
a waveguide. The components of the MAX linear encoder are a basic module with a
sender module and signal transducer, a
waveguide as the sensor element, and a movable permanent magnet. The emitted
current pulse generates a circular magnetic
field around the waveguide. The permanent magnet on the cylinder rod acts as the
position encoder – its magnet field lines run at a right angle to the
pulse-induced magnet field of the waveguide. At the point where the two magnetic fields overlap, magnetostriction
brings about elastic deformation in the micrometre
range. This creates a mechanical wave
that partly continues to travel along the
waveguide and is partly ‘reflected’ back to the MAX basic module. When the
magnetostrictive wave arrives, the signal transducer uses it to produce an
electrical signal. By the known propagation speed of the wave in the
waveguide, the time between the current
pulse being sent, and the returned
magnetostrictive wave being detected, the
distance of the permanent magnet is calculated,
as is the position of the hydraulic piston in turn, with a resolution in the µm
range.

Magnetostriction technology
offers multiple benefits when linear encoders
are used in hydraulic machines. Position
measurement is absolute – the precise piston position is detected as soon as on-board
voltage is supplied when the machine is
started up. There is no need for a reference run as is the case with
incremental sensors. During operation, magnetostriction is exceptionally
reliable, wear-free, and even robust, proving particularly resistant to
mechanical stress and extreme electrical influences, such as those caused by
radiated or coupled faults in the on-board
power supply of a vehicle. The high operational safety level of the MAX linear
encoder within vehicles that require approval
is certified by the E1 approval mark,
issued by the German Federal Motor Transport Authority.

Added value with MAX technology

With the MAX product family,
SICK STEGMANN is breaking new ground in a number
of ways. Regarding product
technology, the measured value resolution of 0.1 millimetres given measuring ranges of up to 2.5 meters with
the MAX48 and 1.5 meters with the MAX30 is certainly notable. Another
special feature of the linear encoder is the significant minimisation of the dead zone that results from
the null and cushion zones being reduced down to 30 millimetres. The measuring ranges are much
larger than other position sensors available on the market, allowing for better
utilisation of the piston stroke in the tight
installation space of the cylinder. Last but not least, MAX sensors are designed for a wider fluid temperature
range between -30¡C and +95¡C.

Real market innovation: the integrated diagnosis functions of the MAX
linear encoders for hydraulic cylinders

What wear are steering cylinders
and spring systems subjected to; when exactly should lifting and pressing
mechanisms in garbage trucks be serviced; what causes a hydraulic cylinder for
load torque restriction on mobile cranes to fail; how many operating hours have
stroke, swivel, and tilt cylinders on
telescopic cranes completed? The MAX linear encoders are the first sensors of
their kind in a position to provide valid answers to all of these questions.
This issue of status monitoring is nothing new to SICK STEGMANN as a
manufacturer – it has not just been among the standard requirements for sensors
and sensor systems within industrial applications since Industry 4.0 became a
hot topic. Monitoring and counting piston strokes, recording operating hours
and peak loads, and checking maximum permitted oil temperatures, are all ways
of deriving information about the current status of a machine, its cost-optimised
operation, and potential external disturbance variables.

Some manufacturers have already realised that the MAX is offering them a unique
way of improving their mobile machines, making them stand out from the competition. Their business partners –
those responsible for procurement and operations on behalf of their customers –
value the opportunity to reduce operating costs for vehicles fitted with this
equipment, while improving their capacity and availability at the same time.
Plus, the MAX linear encoders make it possible to automate and monitor work
processes performed by mobile machines. When digging, the option to control depth of excavator shovels using position
measurement avoids damage being caused to cables, pipes, and foundations. Excavators
can also be fully automated and operated with extreme precision when removing
highway embankments. Measuring the piston position for the presses in refuse
vehicles reveals the current load. Arrangements can be changed so that a vehicle that is still half-empty is sent to
empty garbage cans at further collection points, thereby avoiding half-empty
vehicles making inefficient journeys back to the recycling centre.

The list of advantages up for
grabs extends to almost all applications within mobile automation. But that is
not all! The application possibilities for intelligent, future-proof linear
encoders working with magnetostriction are also seemingly endless within
industrial settings – the wood industry, rubber and plastics processing, wind
energy, packaging technology, and mechanical engineering are just a few
examples. These product families are ready to show the world what they can do!

Written by Alexander Hirt, Linear Encoders Manager, SICK STEGMANN
GmbH, Donaueschingen

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