Kistler enables digital measuring chains for advanced vehicle test stands

Faced with the challenge of modernizing its kinematics and compliance test machine for automotive engineering, AB Dynamics implemented the new digital charge amplifier 5074A from Kistler. It enables a fully digital measuring chain including a set of load cells to measure tire forces and moments in real time, no matter how complex the requirements might be.

Today's cars are high-powered technology hubs, packed with mechatronic components that deliver ever-increasing levels of driver assistance; they can even perform some maneuvers autonomously. However, impressive features and functions such as these need to be supported by comprehensive testing with specialized equipment, backed by specific know-how. One leading provider of these resources is Anthony Best Dynamics Limited, a British company based in the picturesque town of Bradford on Avon in south-western England. It is a member of the international AB Dynamics Group, which offers a portfolio of solutions for measurement and analysis systems, simulation, and proving ground automation.

“We went through a period of rapid growth in recent years, so our new headquarters here in Bradford on Avon has already become too small,” says Joanna Maddams, Marketing Manager at AB Dynamics. “That's why we're currently adding another new building opposite our head office. Our worldwide headcount has increased from about 70 back in 2015 to more than 200 today. We also have a network of offices in Europe, Japan and the USA that handle the distribution of our validation and durability solutions to many automotive OEMs, suppliers and vehicle test centers across the globe.”

Seamless integration into a state-of-the-art machine design

Matthew Dustan, Product Manager for Laboratory Test Systems at AB Dynamics, singles out some current trends in automotive testing: “Progress in testing Advanced Driver Assistance Systems (ADAS) has triggered higher demand for complex track test solutions and is generating some exciting opportunities for proving ground automation. There is also a move towards simulation in vehicle development and modeling ‒ this is particularly apparent with new electric vehicle manufacturers.”

Many vehicle developers throughout the world operate one of AB Dynamics' leading solutions: the Suspension Parameter Measuring Machine (SPMM), a complex test stand that can simulate a car's behavior by applying combined roll, pitch, bounce, and yaw motions on a moving platform. Under each of the four wheel stations, a multicomponent force link set of piezoelectric load cells ensures accurate measurement of all forces and moments: the 9366CC series from Kistler is a customizable kit with four sensing elements that deliver maximum accuracy thanks to their high rigidity and natural frequency. “Load cells from Kistler have always played a key part in the success of this product, and they are highly integrated into the overall system. They deliver zero values at high resolution when the vehicle is mounted on the test stand, and they also provide very precise measurements of all the specific high-load forces applied during kinematics and compliance testing. And by no means least, they help to prevent overloading and potential damage,” Dustan explains.

Faced with the growing complexity of automotive testing, the engineers at AB Dynamics wanted to digitize the entire SPMM system to provide higher bandwidth for advanced testing requirements in the future. “Our goal was to create an updated SPMM with a fully digital measuring chain and a closed-loop force control system,” Dustan continues.

"It took us about two years to complete this development project, and the digital charge amplifier from Kistler was crucial to its success.”

Matthew Dustan, Product Manager Laboratory Test Systems at AB Dynamics

In the new SPMM 5000e, the signals from every wheel station are digitized by two 5074A digital charge amplifiers (each with four channels); they form part of a distributed EtherCAT topology that delivers live force readings at high frequencies.

“We're currently running a 2 kHz cycle on our machine, but the Kistler amplifier is capable of doing even more ‒ the bottleneck is elsewhere,” Dustan explains. “We plan to go to 4 kHz in the near future. We've also reduced the size of the electrical cabinet by about 40 percent; the machine now requires much less cabling and wiring, and far less installation effort. It comes with advantages such as high bandwidth, low latency and resilience to drift even in humid environments ‒ to mention only a few.” AB Dynamics has already delivered its new state-of-the-art solution to several customers in Europe and Asia.

Real-time force and moment measurements: precise, robust and high-resolution

One outstanding advantage of the 5074A digital amplifier from Kistler is its switchable measuring range. This allows precise measurements covering almost five decades of amplitude, providing greater flexibility for many applications. It is also a practical instrument for optimizing the measuring chain: “The measurement range setting can be used to individually adapt the optimal load capability and resolution. Using the 16-bit signals, we can start out by estimating the load and then make adjustments based on the first measurement data,” Dustan explains. This process results in high data quality ‒ a critical factor for AB Dynamics' customers, who use the data to inform their design decisions throughout the entire vehicle development process.

Dustan sums up the collaboration between the two companies: “We couldn't have completed the new machine without the digital charge amplifier from Kistler. It allowed us to run a closed-loop force control at high frequencies and also ‒ thanks to the amplifier's form factor ‒ we were able to package the complete measuring chain locally into sections of the machine. What's more, Kistler customized the load cells to ensure smooth integration into the new setup. In short, they provided exactly what you'd expect from a market leader: innovative products and custom solutions.”

Innovative, customized solutions that push the limits of automotive testing

How will the automotive testing market evolve over the next decade? According to Matthew Dustan: “Vehicles are generally becoming more complex and computerized ‒ and for testing, that presents challenges as well as opportunities. We're seeing a strong push towards simulation and electrification to improve vehicle behavior and ADAS support. Simulation, in particular, is data-driven ‒ so good measuring equipment is more critical than ever before as a factor in generating added-value data sets. After 25 years of working with Kistler solutions, we're now developing a new type of test stand for axle suspension NVH analysis that will also include accelerometers specifically designed by Kistler to accomplish these measurement tasks.”