| The main objective of this research is the development of a prototype of a digital flow control electro-hydraulic DAC valve which has low cost and good dynamic performance, and then to apply this new valve to control the position of a mass load.;First, the idea of a weighted-resistor DAC circuit is converted to the concept of a digital, flow-control, electro-hydraulic DAC valve. Secondly, based on the design data, a prototype of the DAC valve is built. An A/D converter circuit is also made to interconnect the input command (from MTS control system) and the DAC valve since the input command is an analog signal and the DAC valve is driven by six digital signals. Linear transformer LVDT and LVT are used to measure the displacement and velocity of the load and send the feedback signals to MTS control system to form a closed-loop control. Next, bond graph technique is used to develop the model of the DAC valve. The bond graph is a relatively new technique in modeling arbitrary systems, particularly hydraulic, electric and thermal systems. This methodology has the strength to extend the graphic model from a subsystem to a complete system.;Using the bond graph technique, a model of a subsystem is first created from an imaginary prototype. This subsystem contains a pair of opposing electrical coils, an armature and three orifices. The numerical simulation of the subsystem, developed by bond graph techniques agrees with the results based on fluid flow equations. A second subsystem consisting of a pair of directional valves (solenoids) is added to the previous subsystem. The final system which is extended from the second subsystem, includes six solenoids of which four are used to control different amounts of flow rate and the other two are used to work as directional valves. On the basis of the fluid flow equations, a software package has been developed to size the orifices and simulate the performance of the DAC valve.;From the experimental results, it is shown that the DAC valve has rise time... |
