Second, maintainability design suffers bad influences by improper testability design. First, testability design requires much labor and knowledge preparation, and wastes the sensor recording information. Among all PHM designs, testability design and maintainability design face critical difficulties. Resulting from the short production cycle and rapid design technology development, traditional prognostic and health management (PHM) approaches become impractical and fail to match the requirement of systems with structural and functional complexity. The industrial relevance of this method is illustrated on a case study related to a manufacturing testing phase of a lithographic machine. The benefits of hierarchically modeling a problem are less computational effort and less modeling effort, because not all relations are needed. This paper describes a hierarchical test sequencing model and proposes two algorithms to compute an optimal test sequence.

The tests at the system level correspond to the solutions of low-level problems. Such a hierarchical test sequencing problem consists of a high-level model that describes a test sequencing problem at the system level, and one or more low-level models that describe the test sequencing problems at the subsystem or module level. Because complex systems are composed of several subsystems, which are again composed of several modules, there exists a need to hierarchically model test sequencing problems. In a previous work, a test sequencing method to calculate time-optimal test sequences has been developed. Testing complex systems, such as the ASML TWINSCAN lithographic machine, is expensive and time consuming.

Hierarchical sequential testing