A senior design team studying mechatronics at Rensselaer Polytechnic Institute (RPI) set out to develop a two-wheeled robotic locomotion platform inspired by (and with permission from) the Segway Corporation. Many design engineers, including the RPI team, face two main challenges when developing new products – the number of tools needed to model, design, prototype, and deploy embedded systems and the lack of integration between different tools. These challenges can increase the amount of work required to develop a product and extend its design cycle. By using a common software framework, the RPI team was able to reuse much of its work throughout the different phases of the design cycle. While the students conquered many significant design and implementation challenges, perhaps the most significant was the short time frame in which they completed the project. The entire design from conception through modeling and analysis, experimental validation and control design, to construction and implementation was completed in three months. The team attributes this success to the single development platform and tight integration of NI LabVIEW software and NI hardware used to create a streamlined progression from modeling and analysis to prototyping and deployment.
1. Design
The first step in development began with the mathematical model of the physical system. In this project phase, LabVIEW simulation tools played a key role helping the team understand the dynamics of the system and explore different sensor configurations without resorting to a trial-and-error approach. Once the model was designed, the team decided to build a prototype to explore and evaluate different sensor solutions and control algorithms. This prototype, called “LOT-V” (Light Object Transport Vehicle), was a small platform, but it needed many sensors. The team used the LOT-V to test and design space exploration with fewer safety concerns than with a larger-scale model. All sensors were connected to a data acquisition device connected to a PC, where the team used the LabVIEW System Identification Toolkit to validate the mathematical model and find unknown parameters.
2. Prototype
The team quickly discovered that it needed to integrate several different sensors to obtain a single acceptable measurement. Testing sensor combinations was easy because the team implemented the entire system in a single environment. It could first evaluate sensor schemes in simulation and then transition to real-world hardware with no extra effort. LOT-V used LabVIEW and the LabVIEW Control Design and Simulation Module for algorithm development and deployment. LabVIEW was essential to the success of the project because of the ease and speed with which the software could be reconfigured and shared between platforms. The team then researched a full-state feedback controller to control the balancing of the platform. It developed the controller using the linear-quadratic regulator (LQR) technique on a linear model of the system.
3. Deployment
The final system, called “HOT-V” (Human/Object Transport Vehicle), was scaled specifically to transport an adult human or large object. It incorporated the lessons learned from the LOT-V prototype, in both mechanical and electrical design, to be as safe and modular as possible. Much of the code developed in the design and prototyping phases for the final deployment could be reused. The team chose the NI CompactRIO programmable automation controller for final deployment because it provides a rugged, high-performance real-time computation package coupled with high speed, electrically-isolated I/O, and a reconfigurable FPGA, making it an ideal self-contained control system. While the HOT-V is a much larger and more complex platform, it uses everything the team developed and learned from the smaller LOT-V. It is constructed from primarily off-the-shelf components and went from an assortment of parts to a completely integrated and operational platform in just a few days. Once assembled, the team simply ported the software from one LabVIEW target to another. The students were able to take the complete LOT-V control system, compute new controller gains, modify the I/O to work with the CompactRIO platform, and deploy it in a few hours. The algorithms and software architecture used on the LOT-V were effortlessly ported over to the HOT-V for execution on the CompactRIO controller with minimal modification. Because the HOT-V platform is completely self-contained, it is important for the team to be able to monitor and interact with the system during operation. The LAN port on the CompactRIO is interfaced to an 802.11 wireless router inside the system. This increases the functionality of the system by an order of magnitude by creating a wireless communication connection with the system. Therefore, the team can control the HOT-V from multiple platforms such as the Hewlett-Packard iPAQ Pocket PC.
4. Conclusion
In only three months, a team of RPI students modeled, designed, and deployed a complex mechatronic application. By using LabVIEW throughout the process, the team could focus its efforts on the plant and controller implementation rather than on low-level implementation details such as embedded programming. Also, by using the same software platform throughout the process, the team was able to reuse the code developed in the early stages of the design cycle for the final deployment. To learn more, view the Design Complex Control Systems with LabVIEW webcast