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Linear encoders for future-proof position measurement in hydraulic cylinders

Mar 12, 2018

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 came to be 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 on the basis of sensor information. This will make it possible, for example, to provide support for assistance systems, avoid sudden machines failures, optimize 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. 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.

 

The MAX linear encoder, which has been developed specially for mobile automation applications, can take complete, integrated, and non-contact absolute position measurements in hydraulic cylinders. It is primarily used in the extreme environmental and operating conditions that are typical for mobile machines.1) The MAX linear encoder, which has been developed specially for mobile automation applications, can take complete, integrated, and non-contact absolute position measurements in hydraulic cylinders. It is primarily used in the extreme environmental and operating conditions that are typical for mobile machines.  

When digging, the option to control the depth of excavator shovels using position measurement avoids damage being caused to cables, pipes, and foundations.2) When digging, the option to control the depth of excavator shovels using position measurement avoids damage being caused to cables, pipes, and foundations.

 

Innovation with magnetostriction

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.

Inside these linear encoders, you will find a number of different technologies and innovations compared to the market standard. On the basis of 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, the optimization of the power density by minimizing measurement dead zones, and the integration of diagnosis and prognosis functionalities that can be used to avoid machine downtimes and improve operational plans and maintenance routines for entire fleets.

Magnetostriction technology offers a number of 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 level of operational safety of the MAX linear encoder as a device within vehicles that requires approval is certified by the E1 approval mark issued by the German Federal Motor Transport Authority.

 

The MAX linear encoders make it possible to automate and monitor work processes performed by mobile machines.3) The MAX linear encoders make it possible to automate and monitor work processes performed by mobile machines.


Excavators can be fully automated and operated with extreme precision when removing highway embankments.4) Excavators can be fully automated and operated with extreme precision when removing highway embankments.

 

Added value with MAX technology

With the MAX product family, SICK STEGMANN is breaking new ground in a number of ways. In terms of product technology, the measured value resolution of 0.1 millimeters 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 minimization of the dead zone that results from the null and cushion zones having been reduced down to 30 millimeters. The measuring ranges are much larger than other position sensors available on the market, which allows for better utilization of the piston stroke in the tight installation space of the cylinder. Last but not least, the MAX sensors are designed for a wider fluid temperature range of between -30 °C and +95 °C.

 

Linear encoders detect linear movements as absolute position values without making contact.

 

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. 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-optimized operation, and potential external disturbance variables.

Some manufacturers have already realized that the MAX is offering them a unique way of improving their mobile machines and making them stand out against 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 the 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 center.

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.

 

Heiko Krebs

Vice President Product Management Motion Control Sensors

Heiko Krebs has been responsible for the Product Management within the Motion Control Sensors business unit at SICK since 2018. A versatile task, because motor feedback systems, inclination sensors or encoders are always used when precise position determination, speed measurement or speed monitoring are required in industrial automation. Previously, he had already worked for ten years as Head of Product Management Encoders.

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