Laser-generated trailer solid model cuts test costs

How can engineers make sure that trailer components such as axles and suspensions can last hundreds of thousands of miles?

One way is to take the trailer to the proving grounds for testing. But this approach is time-consuming and costly.

Another option is to use multibody simulation software, which uses road profile data obtained on the proving ground. That is the approach a trailer supplier recently took to validate the design of a new component.

According to NVision, it would have taken a designer three to four months to build the solid model of the line haul trailer needed for the simulation. Instead, the supplier saved time and money by contracting with NVision's service bureau to model the trailer in only one month. The virtual trailer will generate test track savings each time it is used.

Trailer components are subject to harsh loads throughout the course of operation. In order to accurately predict fatigue life, as in rig testing, the entire load-time history needs to be taken into account. The normal approach is for engineers to develop representative load profiles by running a test vehicle on a proving ground under a variety of different conditions. Time histories are then generated that indicate the loads seen by the individual components under these conditions.

The problem with this approach is that long periods of proving ground driving are required to produce the component-level loads needed as input for either physical testing or fatigue analysis. This process is costly because of the need to outfit trucks with custom hardware and instrumentation and the time required on the part of engineers and technicians to set up and run the tests. The large number of miles that must be run to ensure realistic results clearly increase product development cycles and costs.

Multibody simulation makes it possible to refine the design to a higher level of maturity at an early stage in the development process in order to reduce time-to-market and use fewer physical prototypes. The process begins with the creation of a whole vehicle model, such as the one for a line haul trailer created by the supplier. Detailed joints, nonlinear forces, state and design variables, auxiliary differential equations, and hydraulics are added in the multibody simulation software. The model can be used to quickly predict dynamic loads and kinematic behavior over a time cycle based on road profiles obtained from proving ground testing.

Full trailer model

The supplier's project engineer faced the challenge of developing the full vehicle model required as a first step in the virtual proving ground process. The size and complexity of the trailer meant that it would have taken a designer several months to create the model from hand measurements and existing 2D drawings. Measurement error could affect the accuracy of the simulation and would be impossible to detect.

The engineer sought an alternate approach and considered laser-scanning technologies that he had used in the past on smaller projects. Laser scanning systems work by projecting laser light onto surfaces while cameras continuously triangulate the changing distance and profile of the laser as it sweeps along, enabling the object to be accurately replicated. Laser scanners are able to quickly measure large parts while generating far greater numbers of data points than coordinate measuring machines without the need for templates or fixtures.

The engineer didn't feel that he could justify the cost of a laser scanner for the small number of jobs that the company does every year. Instead he used NVision, Inc a laser scanning service bureau located in Wixom, Michigan.

He had used the company several times in the past and was happy with the results.

“They offered the convenience of doing the job right here at our facility,” he said. “They also offered the capability to use a laser tracker, which is the right tool for making accurate large-scale dimensional measurements, and a mechanical digitizer, which is the fastest way to measure points that are relatively close together. NVision made these measurements in single frame of reference and combined the results into a single solid geometry assembly. They were able to complete the job in less time and at a lower cost to my company.”

Laser scanning saves time

NVision technicians brought their equipment to the supplier's commercial vehicle systems headquarters. They mounted targets all over the trailer and used the tripod-mounted laser tracker to measure the distance to each target. They measured not only features but also fine details such as the location of the thousands of rivets used to fasten the trailer body to the frame.

The supplier will use the data to create a detailed finite element model of the trailer and use it to generate a modal neutral file that would take the flexibility of the trailer into account for the multibody simulation. The technicians used the laser scanner to generate models of the more complex trailer components, such as the suspension system and the landing gear on the front of the trailer. The technicians removed the suspension from the trailer and scanned each of the components.

The technicians moved the NVision laser scanner mounted on a mechanical digitizer freely around the components, capturing the data in a motion similar to spray painting. As the technician moved the sensor over the surface of the object, real time rendering of the data on screen showed the areas that were missed so the technician could fill them in with another pass. By operating a single switch and without removing the scanner head, they were able to switch to digitizer mode to pick up points such as hole locations on brackets. The technicians used the same coordinate system for all types of measurements, so they were easily able to combine the results into a single point cloud in Imageware's Surfacer software. They exported an STL file, which they then converted to a solid model.

“The model provided by NVision accurately and completely depicted the trailer geometry,” the engineer concluded. “It saved us time, money and effort and is more accurate than what we could have achieved by building the model. We plan to generate the modal neutral file needed to model the trailer as a flexible body in a multibody simulation. Then we will be able to change the suspension components and evaluate the performance and durability of the new design as we perform typical proving ground maneuvers such as lane changes and Belgian blocks on the computer. While simulation will never replace proving ground testing, it will greatly reduce the amount that is required by allowing us to evaluate various design concepts on the computer and only test the best design on the proving ground.”

NVision Inc is based in Southlake, Texas.

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