A Low-Cost High-Performance Alternative for Controlling a Servo-Hydraulic System for Triaxial Resilient Modulus Apparatus

A triaxial test apparatus for the characterization of pavement materials was designed and built at the Pavement Research Center (PRC) at the University of California, Berkeley (UCB). The system was designed for high quality testing of unbound, stabilized, and asphaltic materials. The design process included the design of the hardware and the servo-controlling systems. An important step in the design of the system was the design of the controller for the servo-hydraulic system. Alternatives for controllers of servo-hydraulic systems for waveform generation included the use of the data acquisition system along with proportional, integral, and derivative (PID) algorithms for setting the minimum and maximum loads/displacement. Software programming for these solutions was very complex with limited satisfactory consistency. Commercial ready-to-use controllers are expensive and limited to the specifications of the manufacturer. Therefore, a commercially available programmable motion controller PIC card was implemented for controlling the servo-hydraulic system. The motion controller required only one PID controller to generate repeated waveforms or monotonic loading. An available commercial test solution software compatible with the motion controller card was used to program the motion controller and data acquisition system. This capability was preferable to provide flexibility in modifying the system based on research needs. Software programming was simple. In addition, the cost of the new system was reduced by about 80 percent with respect to the ready-to-use motion controllers.

The paper describes the implementation of the motion controller, the philosophy of the software program, and the success obtained with the new system. The system meets all the quality control provision of the LTTP Protocol P-46. Currently the triaxial apparatus is being use to investigate the resilient response and permanent deformation performance of typical California aggregate base and subbases.