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Belgian solutions integrator AHP Hydraulics carries the tagline of delivering “smart solutions in hydraulics.” Without question, the company’s small team has a history of delivering big results for clients. However, one client presented AHP with a certified stumper of a challenge.

The client, SIDEM NV, develops and produces automotive suspension and steering units. Ball joints play a critical role in these suspension units and thus require rigorous testing to ensure that production batches can be QA-approved and sent into supply. The client had a ball joint tester, but it wasn’t exact enough to meet the application’s needs, so they turned to AHP Hydraulics.

The ball joint test in question uses two hydraulically controlled axes: a horizontal (y-axis) and a vertical (z-axis), both with linear actuators, and both with electric torque axes. The hydraulic cylinders deliver position and force feedback into a programmable user-machine interface. The problem came down to precision and reliability.

“SIDEM NV commented that their existing system was not accurate enough,” says AHP Hydraulics automation engineer Ewout Reuman. They wanted a force tolerance of ±100 newtons over a total range of 6000 newtons. On the rotation, they specified a total tolerance of 0.5 degrees over a total range of 90 degrees while cycling at 4 Hz. “The rotational motion and the hydraulics had to be very accurate, and there I was on Google and YouTube trying to learn about the subject, quickly realizing how much I needed to pick exactly the right control product.”

That path of inquiry quickly led to Delta Motion and its line of controllers.

Identifying the Unknowns

AHP’s first step was procuring the client’s current ball joint tester and disassembling it into the mechanical parts. This allowed them to examine the electronics and consider how to improve the horizontal axis (y-axis) and vertical axis (z-axis) of hydraulic circuits and components. Ultimately, AHP rebuilt the tester from bottom to top and re-engineered the electronics and software. That included scrapping the conventional PC for motion control in the electrical cabinet and replacing it with a Beckhoff PLC functioning as the master and the Delta Motion controller as a slave for the hydraulics.

AHP’s Ewout Reuman found himself tasked with handling the ball joint tester’s electrical engineering and software programming. Once he understood the accuracy needed in the solution and why prior attempts had fallen short, he reached out to Delta Motion, which in turn led to Delta sending a representative to Brussels to work alongside the AHP team in understanding the system’s challenges and how to solve them.

AHP procured Delta’s RMC75E dual-axis motion controller with Ethernet connectivity for communication with the system’s master PLC. Reuman paired this with Delta’s MA2 magnetostrictive I/O module and the AP2 analog I/O module for measuring force feedback from load cells.

The two linear axes are controlled by a hydraulic servo valve and cylinder. The complete testing machine is controlled by a PLC, with the PLC providing set points and controlling both the rotational axes as well as the Delta Motion controller via an Ethernet IP connection. Within that PLC/Delta loop, in which the Delta serves as a network slave to the PLC master, the Delta RMC controls the hydraulic accuracy, error correction, and other factors.

The nature of the directional forces within the apparatus led to some vexing challenges. Imagine the central ball joint continually rotating back and forth within its housing while being pushed on both from the side and below, all while a boom allowed the ball joint to swing back and forth, and the give within that joint housing allowed the ball to be constantly off-center. With these multiple forces all interacting, there was never a perfect center state; the system was always in a state of deviation and change. Asynchronous force testing was always inaccurate. That alone was something AHP’s client could accept, but the deal breaker was the system’s propensity to show force steadily growing over time. The customer demanded that asynchronous force be stable.

“I tuned my axes to specific frequencies, force amplitudes, and oil temperatures and the specific supply pressure for the pump and accumulators,” says Reuman. “But our setup is highly dynamic—the operator can select any combination from 0 to 6000 Newtons and 0 to 4 Hertz. Environmental factors also play a role. For example, if the power unit is located outdoors, weather conditions ranging from -30°C to +40°C will impact oil viscosity during test runs. To address this, we installed both a heater and a cooler. However, at the extremes of this temperature range, the system may struggle to maintain the setpoint consistently.”

“Going into the project,” he adds, “I wasn’t aware how much influence that would have. I would get immense overshoots and undershoots, so I was constantly retuning the system when test frequencies, amplitudes, or oil temperature changed.”

Understandably, Reuman turned to Delta support for help.

Figuring Out the Fix

The situation called for rethinking the tuning. Delta suggested that adaptive amplitude control could fix AHP’s precision and reliability. AHP could measure every sine wave cycle and compare it to the target. Then the controller adjusts the amplitude and offset for the following sine wave cycle until the target and actual forces coincide.

Taking inspiration from Delta’s sample projects, Reuman identified a repeating wave pattern in the force curve. While the sample project provided the foundation for implementing adaptive amplitude control, Reuman added the wave pattern solution he developed. If all axes were synchronous, then the peaks would be flat. Based on the input frequencies, Reuman used Delta’s RMCTools software to identify the wave pattern in the wave crests and troughs and arrive at a method of offset and amplitude gains to compensate for it. For example, if the highest peaks occurred with every fourth wave, then the instance of one peak wave could inform how to compensate for the next fourth peak. (In reality, Reuman ultimately compensated for every sixteenth peak.) This dynamic approach proved far better than AHP’s previous approach of applying one set of offset and amplitude gain values for every wave. With wave peaks brought back within acceptance tolerances, AHP could successfully use PID control to control force between the peaks and thus rectify that runaway force growth.

This combination of adaptive control and PID tuning was the missing key that allowed AHP to succeed with its ball joint tester.

With some fine-tuning, Reuman easily mapped the changes he worked out in RMCTools to his own application. No additional sensors or other equipment were needed to successfully implement adaptive control. It simply dropped into place via software.

“One of the things that convinced me to use Delta Motion was their support,” says Reuman. “Starting with the training – by the end of a two-day training session, I had a really good understanding of how the software worked and what I could do with it, which saved me a lot of time at the beginning of the project.”

The training enhanced what was already a streamlined, highly functional experience with Delta’s RMCTools software. Reuman found it easy to connect with the controller and get feedback from it. Similarly, connecting to the PLC and other third-party equipment proved surprisingly simple. There were a few occasions where Reuman and his team needed “a little support,” but email requests to Delta were answered on the same day and sometimes even within the hour.

Between the help and the excellent product experience, Reuman says he had his sine wave, complete with initial tuning, running “literally in a couple of hours — it’s that easy.” Normally, such tuning could have consumed several days. Instead, he was running his first complete axis within a day. By saving time on setup and initial tuning, Reuman could focus more on identifying the wave pattern and fine-tuning the gain settings for the adaptive amplitude control to flatten out the waves effectively.

“One really helpful feature with Delta Motion is that it can autotune,” says Reuman. “During autotuning, it measures the system behavior and creates a system response. Based on the Actual Position, Target Position, and Control Output, the Auto Tuning algorithm calculates a system response model. That’s very important when controlling hydraulics because there are so many unknown factors in the system.”

Specifically, Reuman points to oil temperatures and the temperature fluctuations that impact system behavior. The variation in oil temperature caused large fluctuations in system response. Implementing a Gain Schedule enabled the controller to dynamically adjust control response based on the system (or in this case, environmental) conditions. The RMC Motion Controller has the ability to dynamically adjust parameters to maintain the required performance levels.

The Precise Results Needed

All told Reuman says it took AHP roughly one week to configure the hydraulics fully and another one to two weeks to fully tune and integrate the Delta RMC with the entire ball joint testing system. In comparing the Delta implementation with similar past projects, Reuman estimates that Delta cut the deployment time in half. However, time savings are only part of the value because no prior controller solution has come close to Delta’s level of hydraulic accuracy.

Like many solution integrators, AHP isn’t privy to whatever ROI metrics the client used for its ball joint tester project. However, in a sense, the ROI boils down to a 0 or 1 proposition. The automotive manufacturer can do something it simply couldn’t before. Alternatively, ROI might be estimated using hypothetical failure rates.

Reuman says, “You have to imagine that when a batch is coming off the production line, and they are distributing those parts all around the world, a batch with production failures — because it wasn’t well tested — is going to cause very high expenses. That’s why we picked the best components and partners for this job. There are so many factors in hydraulics that aren’t the same for electric-driven axes. Without Delta, I think this project could not have succeeded.”

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Sidem is a family-owned company founded in 1933, the leading specialist in engineering and manufacturing of steering and suspension parts for Original Equipment Manufacturers (OEM) and the Independent Aftermarket (IAM). The company offers the most comprehensive range in the industry with over 10,000 references for private and light commercial vehicles. Sidem has its own in-house engineering team, an IATF certified manufacturing facility and a central warehouse, all based in Europe.

AHP Hydraulics, established in 1999, is a Belgium-based company specializing in custom made hydraulic solutions for industrial applications and agricultural machinery. Our multidisciplinary team delivers a full spectrum of services, encompassing engineering, automation and full system integration, with seamless support from design to commissioning. Our hydraulic test benches enable precise diagnostics and reliable system revisions, ensuring the highest standards in maintenance and repair services.