Designing and testing an advanced pneumatic braking system for heavy vehicles

Heavy goods vehicles exhibit poor braking performance in emergency situations when compared to other vehicles. Part of the problem is caused by sluggish pneumatic brake actuators, which limit the control bandwidth of their antilock braking systems. In addition, heuristic control algorithms are used that do not achieve the maximum braking force throughout the stop. In this article, a novel braking system is introduced for pneumatically braked heavy goods vehicles. The conventional brake actuators are improved by placing high-bandwidth, binary-actuated valves directly on the brake chambers. A made-for-purpose valve is described. It achieves a switching delay of 3-4 ms in tests, which is an order of magnitude faster than solenoids in conventional anti-lock braking systems. The heuristic braking control algorithms are replaced with a wheel slip regulator based on sliding mode control. The combined actuator and slip controller are shown to reduce stopping distances on smooth and rough, high friction (μ = 0.9) surfaces by 10% and 27% respectively in hardware-in-the-loop tests compared with conventional ABS. On smooth and rough, low friction (μ = 0.2) surfaces, stopping distances are reduced by 23% and 25%, respectively. Moreover, the overall air reservoir size required on a heavy goods vehicle is governed by its air usage during an anti-lock braking stop on a low friction, smooth surface. The 37% reduction in air usage observed in hardware-in-the-loop tests on this surface therefore represents the potential reduction in reservoir size that could be achieved by the new system. © 2012 IMechE.

Flexible pneumatic twisting actuators

Compliant pneumatic actuators have attracted the interests of the robotics community especially for applications where large strokes are needed in delicate environments. This paper introduces a new type of compliant actuator that generates a large twisting deformation upon pressurization. This deformation is similar to torsion in solid mechanics, and can be characterized by a twisting angle along the longitudinal axis of the actuator. To produce prototype actuators, a new fabrication process is developed that uses soft lithography. With this process, prototype actuators with a width of 7mm and a thickness of 0.65mm have been produced that exhibit a twisting rotation of 6.5 degrees per millimeter length at a pressure of 178kPa. Besides design, fabrication and characterization, this paper will go into detail on stroke optimization. © 2013 IEEE.