"Using SimMechanics, we are running simulations approximately five times faster than we were before."
Dr. Andrew Plummer, Instron
To ensure a race car's optimal performance on the track, design engineers must thoroughly test every element of their design--including suspension dynamics, steering behavior, and aerodynamic loading--under strict laboratory conditions.
Instron Structural Testing recently designed a sophisticated new multiaxis test fixture that applies dynamic loads to a race car. The mechanical design team, based in Germany, worked closely with the company's control system specialists in the UK. The fixture can be used in the lab to test the vehicle's response to different steering, braking, and accelerating scenarios, providing data that would be difficult to acquire on a test track.
Instron used Simulink to develop the controller and SimMechanics to develop the mechanical part of the test fixture. "Being able to model and simulate the entire system with a representative race car was critical to the success of the project," says Dr. Andrew Plummer, manager of control and analysis at Instron.
Instron set out to develop a test fixture that applied forces on the race car in multiple axes. Their customer could then measure and evaluate the performance of the car’s suspension and entire handling dynamics.
Instron therefore needed to simulate a highly complex test environment comprising the controller, the test fixture, and the mechanics of the car, which itself had fifteen moving parts for each wheel. The test fixture integrated control systems and sophisticated mechanical components. These included 18 hydraulic actuators, each of which was connected to the car using mechanical linkages with rotating joints. Specialized parts needed to be designed and incorporated into the mechanical design to minimize friction in the joints.
Although Instron has produced many full vehicle test fixtures for passenger cars and race cars, this project required a higher system performance and greater control accuracy than ever before.
In previous projects, Instron had used Simulink to model control systems and a mechanical modeling package to model mechanical parts. Using separate environments slowed down the design process, says Plummer, because it “required information to be passed back and forth between the two solvers at every time step.”
To improve efficiency, Instron used one integrated environment to model every component. They chose MATLAB, Simulink, and SimMechanics to simulate the controller and the test fixture concurrently. They could then use simulation results from the controller and the test fixture to improve the design of each.
The Instron engineers developed the new controller in MATLAB and Simulink and used Simulink and SimMechanics to model the test fixture. Previously, they had developed a Simulink model of hydraulic components that simulated pressure differences across the pistons. They integrated this model into the SimMechanics actuator block, which enables a signal to be taken from Simulink and applied as a force to a SimMechanics body.
They incorporated the MATLAB and Simulink model of the controller into the SimMechanics model of the test fixture. They could then refine the SimMechanics model to enable them to test the performance of any test fixture or controller design.
To accelerate development, the engineers used Simulink Coder™ to generate C code from the Simulink part of the control system. This code runs on a high-speed processing platform that is linked to Instron’s standard digital controllers.
To design a test fixture and controller to test the design of a race car
Use SimMechanics and Simulink to design a specialized digital controller together with the mechanics of the test fixture