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Ensuring structural integrity in commercial vehicles

USA

Introduction

Commercial vehicle manufacturers face the challenge of providing reliable, durable vehicles that can withstand the demands of extensive road use. To meet these requirements, a leading North American truck manufacturer and HBK customer, employs a comprehensive testing approach, examining all aspects of their trucks in the lab, on the test track, and on the road.

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To streamline the process of integrating field test data with lab test data, with the aim of simulating real-world conditions.

Sensors, hardware, and software from Hottinger Brüel & Kjær (HBK), including:

  • HBK nCode Automation for data management and collaboration
  • HBK GlyphWorks software for data analytics
  • HBK sensors, SomatXR and catman software for data acquisition

A 60% reduction in test setup time (from 12 to 5 hours), cost savings through a unified solution for field, lab, and test bench, and the provision of high-quality analog data with a reliable, freely scalable solution.

Further information


The customer’s comprehensive approach to testing posed a specific challenge for the test engineers in their structural durability lab. Their task was to streamline the process of integrating field test data with lab test data, with the aim of simulating real-world conditions. This integration was crucial to ensuring the reliability and longevity of their products.

 

To address this challenge, the test team selected sensors, hardware, and software from  Hottinger Brüel & Kjær (HBK), including:

  • HBK nCode Automation for data management and collaboration – a web-based environment for automated storage, analysis and reporting of engineering data
  • HBK GlyphWorks software for data analytics
  • HBK SomatXR data acquisition with catman software

In 2016, our customer upgraded its lab with the addition of Instron Labtronic 8800ML shaker controllers. The decision to choose Instron was influenced by the controller’s capability to connect data acquisition hardware via EtherCAT (Ethernet Control Automation Technology), a high-bandwidth real-time connection protocol.

 

EtherCAT provides efficient real-time communication between devices (clients), ensuring synchronized data transmission. Unlike traditional Ethernet, EtherCAT uses a ‘distributed clock’ technology, enhancing data transmission with predictable timing and precise synchronization.  Ethernet packets are no longer received, interpreted, processed, and copied on to each device in each connection. The EtherCAT protocol continues to transmit data directly in a standard Ethernet frame, without changing the basic structure.

 

EtherCAT clients take the data intended for them as the frame passes through the device. Similarly, input data is inserted as it passes through with an offset of only a few nanoseconds. Because EtherCAT frames contain data from many devices operating in both transmit and receive modes, the usable data rate increases to over 90%. This allows the full duplex characteristics of 100BASE-TX to be fully exploited, achieving effective data rates of over 100 Mbit/s.

 

Before EtherCAT, the shaker controller received analog inputs from sensors via the Somat eDAQ bridge layer dedicated administrator connection (DAC), or Instron’s signal conditioner modules (SCM). The sensors, such as the strain gauge used in bridge type configurations, were digitalized by an analog-to-digital converter (ADC), normalized to 0 to ±10 V, and wired to the controller in parallel, sensor by sensor. This not only consumed valuable time but also increased the risk of errors in the sensor setup process. The channel count for shaker correlations was also fixed by the number of SCMs installed in the 8800ML Controller, which in turn had a physical limitation of available sockets.

 

Integrating EtherCAT provided the customer with increased flexibility and the ease of use required for large channel count simulations, benefits that were not possible with standard SCM modules.

 

However, the customer still needed a rugged, external signal conditioning and data acquisition solution for field testing, a solution that could support the EtherCAT communication standard to compliment the 8800ML controller for lab testing.

After evaluating all options on the T&M market, the customer’s test team chose HBK’s SomatXR series with HBK’s expertise in structural durability and the customer’s existing positive experience with Somat eDAQ data acquisition systems key in their decision-making. The selected system included the following modules:

  • CX22B-R-W Data Recorder
  • MX840B-R Universal Module
  • MX1615B-R Bridge Module
  • MX1601B-R Standard Module
  • CX27C-R EtherCAT Gateway for real-time integration into Instron

 

This configuration, allowing the acquisition of data from the various sensors used in testing, is ideal for harsh environments such as the test track and is used also durability lab.

In the lab, the data acquisition system connects via EtherCAT to provide data to the Instron controller in real-time with minimum latency, while all sensor setup and manipulation can be handled natively with catman software running on the CX22B data recorder wirelessly via a remote desktop connection. The test installation and sensor setup are identical for both the test track and the test lab. The only additional requirement for use in the lab is the CX27C-R EtherCAT gateway and Ethernet cable. Sensor information is available to the 8800ML via the EtherCAT communication link, eliminating the need for secondary sensor programming and setup, and reducing the likelihood of errors.

 

Initially, as with any new technology, the test team faced challenges. EtherCAT’s strength is its cross-platform communication potential, but with that comes the downside that bugs are bound to emerge. However, HBK’s commitment to supporting both the EtherCAT communication protocol and the SomatXR product line, proved that they were the right partner to execute the pairing of the first 8800ML and SomatXR in North America. HBK is one of the few companies that offer a mobile recorder that can operate just as easily in the lab as it can on the durability track.

 

QuantumX, the non-ruggedized brother of SomatXR, introduced real-time EtherCAT integration in 2008. Like QuantumX, SomatXR offers two signal paths. All inputs create two digital signal paths, overcoming the bandwidth limitations of EtherCAT and allowing users to keep working with catman software for data acquisition and analysis of the structural durability of the test specimen in parallel with test control:

  • First signal, real-time low latency output oriented with 1 ms loop time,
  • Second signal, high-speed, time-stamped, PC-based data acquisition and analysis of the test specimen with up to 100 kS/s per signal depending on module type.

To perform realistic durability tests in the lab, our customer relies on data gathered from the physical tests on the track. The track surface is a complex topography, realistically reproducing the vehicle responses that drivers experience through a lifetime of hard highway miles, or long stretches of unimproved roads. The test vehicle, equipped with various sensors, captures data from accelerometers, bridge/strain gauges, wheel force transducers, displacement sensors, and voltage measurements.

 

Although the number of channels varies depending on the type of vehicle, the minimum number of channels required to drive a shaker test is equal to the number of actuators used to drive the test. In the case of our customer’s cab shaker, a minimum of seven channels are required to produce a road signal through iteration to replay in the lab. The cab shaker has four vertical inputs, two horizontal or lateral inputs, and one fore-aft input. This allows for six degrees of freedom (DOF) on the cab shaker excluding torsion. However, seven channels do not always provide enough information to accurately describe the response of the vehicle on the test bench compared to the track.

 

The test team typically gather data from approximately 50 different sensors shared between the test track and the shaker lab. The more accurate the data, the better the simulation result when iterations are complete in the shaker lab. The SomatXR data acquisition equipment gathers data from these channels while a test driver pilots the vehicle on the test track. This phase takes about two weeks to complete.

 

Once the test data has been collected, it is then analyzed using HBK’s GlyphWorks data processing system, which contains a comprehensive set of standard and specialized tools for durability analysis. Designed to handle huge amounts of data, GlyphWorks allows the engineers to visualize, analyze, and manipulate the test data, helping identify the most significant parts of the road test data. This selective data is then used to refine the drive file for lab testing.

 

Once the track data is trimmed, it is placed in the shaker controller and loaded into Instron’s road signal software, TWR. TWR handles all road signal iterations and specimen response characteristics such as white/pink noise models.

 

To refine the drive file, the engineers instrument an assembly, such as a truck cab, with sensors installed in the same positions as those for the test track vehicle. They then feed the drive file to the Instron controller, run it, and measure the response data at each sensor location.

 

Using TWR and GlyphWorks processes, the test engineers can determine the iteration quality. Typically, pseudo damage calculations are performed in GlyphWorks to ensure that the vehicle or test specimen is receiving the appropriate damage targets in the test lab just as it would at the proving ground. When damage values and RMS error converge to a constant, the final iteration is analyzed for conformity across the vehicle to the test track. To get to this point typically takes between 12 to16 iteration steps.

 

Reasonable value is based on a judgment call from the durability test engineers based on understanding the differences between the full vehicle and chassis. The Instron TWR software blends RMS error and pseudo damage calculations on the transducers with a fixed intercept and slope. The test engineers also use level crossing comparisons to judge if the right number of zero crossings occurred during the test, and at what amplitude levels are captured. This varies based on the test intent – a simple hood test and a test on the chassis frame are treated differently.

 

At this point, the team is ready to start durability testing using the final drive file. Once a test has been run, they use GlyphWorks to analyze the test data. And, when the data is ready to be archived, they use nCode Automation that not only eases test data storage and retrieval, but also makes it easier to share test data with design engineers.

The integration of EtherCAT in the SomatXR system has greatly benefitted our customer, providing:

  • Cost savings: one solution for field, lab, and test bench,
  • High-quality analog data and a reliable, freely scalable solution,
  • A simplified setup: going fully digital has reduced complexity and setup time by offering, plug-and-play integration into Instron without intermediate file generation.

 

Much of the success has been attributed to the decision to ‘go digital’ by choosing EtherCAT to connect their data acquisition systems to the test stands in the lab and to their IT infrastructure in parallel. The SomatXR data acquisition system also works very well with the Instron test stands. “It’s basically plug and play,” says one of the test engineers.

 

With the new equipment, the test team has reduced test setup time by 60% – from 12 to 5 hours. Instead of running long, analog sensor cables from the test piece to the controller, the sensors are connected to an on-board SomatXR data acquisition system, which then connects to the controller via EtherCAT. This not only reduces cabling time, but eliminates time spent troubleshooting analog noise problems and finding and eliminating ground loops in the analog cabling. The digital signal is noise-immune, moving through a built-in analog filter that digitises the data immediately in the amplifier.

 

The team also credit SomatXR’s catman software for saving setup time and improving data quality. “HBK’s catman software guides us through the setup in a user-friendly way. We love that it checks channels for sensor or cable failure, and the raw data acquisition, data analysis and preparation help us to get from idea to result quicker.”

 

Finally, all agree that the measurement data is of a far higher quality than previously obtained data. As one of the team says, “Improved data gives Design Engineering, our internal customer, better insights into how to improve and optimise their designs.”

Despite some early challenges, the decision to go digital and integrate EtherCAT as a 2nd digital interface to test control in lab has proved successful, leading to more reliable trucks, lower test costs, and a shorter time-to-market for our customer.

Technology used

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