Cascade Control System Using Feedback From Real-time Digital Image Point Tracking

Real-time digital image point tracking feedback was used to control a servo-hydraulic load train during the loading of a Glass Fiber Reinforced Plastic (GFRP) cantilever beam. The loading pattern was defined in terms of two translational and one rotational in-plane degrees-of-freedom at a single control point on the beam. Tests were performed with both single-and multi degree-of-freedom controls, using independent and simultaneous control of the actuators, respectively. A reference control system was set up to transfer the displacements of three hydraulic actuators into a theoretical displacement of the control point using an assumption of rigidity. The discrepancies between this theoretical displacement and the actual displacement were addressed through three control configurations that used a linear transfer function, a feedback signal from the digital image point tracking using Proportional and Integral control, and a combination of these two. Performance was evaluated at frequencies ranging from 0.01 – 1 Hz. The combined implementation of the linear transfer function and digital image point tracking feedback showed the greatest improvement over the reference configuration, reducing the error between the desired and measured signal by 51–93%.