Modernisation of Brake Testing With CompactRIO

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"The modular nature of the CompactRIO helped us quickly and easily design and configure a test system that exceeded the system requirements."

- Matthew Turner, TBG-Solutions

The Challenge:
Creating an expandable, universal test system for heavy vehicle brakes, which can be used repeatedly for extended periods of time.

The Solution:
Designing and developing a fully integrated system using the NI CompactRIO platform and NI LabVIEW graphical system design software to provide lossless data recording and fully configurable control parameters.

Author(s):
Matthew Turner - TBG-Solutions

TBG Solutions is an engineering solutions provider and NI Alliance Partner. Based across two sites, we provide hardware and software solutions ranging from simple system design to complete bespoke packages. Our systems engineers are fully certified by NI. We employ multiple engineers who are Certified LabVIEW Architects, the highest level of certification, along with several other engineers who are Certified LabVIEW Developers.

Heavy trucks remain the most versatile method of goods transport and continue to increase in number and size. This has fueled a huge market for heavy parts and a continuing need to improve safety-critical components through extensive testing and verification. Unlike smaller vehicles, which rely on hydraulic systems, heavy trucks rely on a pneumatic system of brake application. These brake assemblies require comprehensive testing under very specific conditions. 

Test systems were outdated and did not provide the precise control required for producing and testing safety-critical systems. They required manual control of every variable, along with constant monitoring and adjustment by a trained technician. The data recording capabilities were limited and unable to provide the resolution required for such a safety-critical test system. TBG Solutions was involved from the beginning of this project to design and build a modern test system based on constant rotation of the brake under test.

The new test system uses an integrated CompactRIO chassis with the NI LabVIEW Real-Time Module and the NI LabVIEW FPGA Module, so we can perform tests autonomously without any external connections to the testbed once the system has been configured and the test started. Data logging uses high-resolution C Series modules to meet the accuracy requirement.

Air Brakes

Air brakes are the pneumatic systems used in heavy goods vehicles. They operate by applying compressed air to a piston, which in turn applies pressure to the brake pads, slowing the vehicle down. The main advantage of air brakes over hydraulic brakes is that they can still operate with significant leaks in the system, which adds an extra element of safety and increased reliability to the system.

Our system not only applies specific pneumatic pressure to the attached brake at a specific ramp rate, but also controls the pneumatic system to the point at which we can create a specific torque for any number of applications and timing conditions. Safety is a critical component, and we required multiple safety systems to prevent the test system from becoming unsafe.

Test System Components

We controlled the brake rotation using a 13 kW three phase motor. Our customer also needed to control rotation direction, along with the pneumatic and timing variables.

We needed the test system to be autonomous, not requiring a control PC after setup, but also compact and reliable. We selected the CompactRIO platform as it exceeded our requirements for a control unit. The CompactRIO system featured safety and control calculations that could be performed on FPGA, reconfigurable hardware offering specialised functionality, and faster I/O response times. This eliminated any timing concerns and provided a very fast response to safety issues. The real-time element of the CompactRIO controller helped us develop an autonomous system that we could easily connect to the control PC when required and run independently when not.

With the CompactRIO modular platform, we only needed to add the required inputs and outputs to the test system using specialised C Series modules. We could customize the hardware to contain only the required functionality because of the plug-and-play nature of these modules. We combined thermocouple inputs, full bridge inputs, digital inputs, digital outputs, and analogue outputs in a single unit, incorporating the exact measurement and control channels our system required. This saved costs on other hardware that would provide too much functionality in certain areas and too little in others (Figure 1).

 

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Figure 1. The Test System Control Box With CompactRIO Chassis and Modules

Test System Software

We used LabVIEW to develop the control software used for the Constant Rotation Rig (CRR). Our software architecture was readily expandable and provided seamless integration with CompactRIO using prebuilt function blocks, which reduced development time considerably.

The CRR software contained three main elements, all constructed using the LabVIEW development environment:

  • The FPGA code on the CompactRIO acts as the lowest level of the control system. This contains time-critical functions to read the safety status channels along with the input data channels. The FPGA code also calculates the control output to the pneumatic controller, through use of NI PID algorithms, and controls and monitors the output motor.
  • The real-time code, also deployed onto the CompactRIO, contains the majority of control code and functions. The RT system controls the test station (test motor direction, pneumatic pressure applied, and which channels to record), records data to its internal buffer, communicates with the control PC, and stores all test parameters set from the control PC to allow autonomous test. The test station must also keep track of its position within the test sequence to resume when restarted or on power loss.
  • The control PC controls and monitors up to 10 test stations simultaneously. We used LabVIEW software to create a powerful but intuitive user interface, scalable to the number of systems connected to the PC.

Results

The brake test system proved to meet, and in many cases exceed, the initial specification. This new type of brake test system provided a quick and customizable test method that is now accepted by multiple brake manufacturers.

The system was so well received that multiple duplicate systems were ordered to further increase efficiency. There are currently five in the original location with another three systems installed in other countries to different manufacturers, and two systems planned for additional countries (Figure 2).

 

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Figure 2. Built Test System for Use in Sweden

Conclusion

The modular nature of the CompactRIO helped us quickly and easily design and configure a test system that exceeded the system requirements. CompactRIO and LabVIEW offered an easily expandable framework that we can easily modify with additional measurements or controls if needed. 

The system’s expandable nature empowers us to duplicate and easily modify both hardware and software to control an entirely different type of brake test equipment, such as using hydraulic rams instead of a motor to rotate the brake, which can help us meet even more customer specifications.

Using CompactRIO compared to other test platforms, we saved a lot of money because we could choose the exact modules and functionality we needed. We were able to design and build a bespoke system using off-the-shelf modules, saving not only money, but time as well.

Author Information:
Matthew Turner
TBG-Solutions
3A Midland Court
Barlborough S43 4UL
Tel: 01246 813 666
matt.turner@tbg-solutions.com

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