Safety analysis on digital hydraulics

Digital hydraulic actuators (DHA) are an interesting new technology that could replace todays system with inefficient proportional valves. By using an array of on/off valves the hydraulic pressures are discretised. This gives a fixed set of force outputs that can be used to control the actuator. DHA systems have been proven to drastically reduce the energy consumption at the cost of higher system complexity. More components and more advanced controllers are needed to maintain an equal system performance.Previous research has been mentioning the fault tolerance of the DHA system without analysing the actual requirements to achieve it. In this thesis a safety analysis is made. One first approach of making an active fault tolerant system is presented and the effects of using this is analysed. In total, over four million failure modes are analysed and grouped into 2402 system outputs. The thesis is also the first within the research of DHA system to present a chamber wise analysis, where all four chambers are analysed independently.The thesis also presents a method to calculate reliability for the system. The method is a new computational way of creating and reducing fault trees. From the fault trees the probability of system failure can be calculated.The conclusion of this thesis is that DHA is not fault tolerant by default but can be if designed correctly. The thesis also concludes that if the components in the DHA system have the same reliability as the components used in today’s system the reliability is similar.