Abstract: A method of planning tasks to be performed in a machine derives a precedence graph by linking subsidiary tasks to a sequence of key tasks to create a scheduling problem that can be solved by an automated scheduler. In the event of a trigger, such as an order for new work or a machine exception, work can be retimed, rescheduled or replanned.

Abstract: A method of generating a schedule for operation of a machine forming at least a part of a lithographic apparatus or a lithographic processing cell is disclosed. In the method, a plurality of weight factors are received for respective ones of a plurality of qualities affecting the outcome of a lithographic process. An optimum schedule of tasks to be performed to complete said lithographic process is generated, the optimum schedule being one whose outcome has a maximum value of total quality, where total quality is the sum of the products of the values of each of said qualities and the respective weight factors.

Abstract: Scheduling of tasks in a lithographic apparatus, track unit or lithocell is performed by maintaining a register of the state of the machine and a database of tasks performable by the machine, generating possible sequences of tasks based on pre- and post-conditions on the system state (rather than a precedence relation) and selecting a sequence from the generated sequences that meets a given beginning state of the machine and a desired end state. Embodiments of the invention also allow for automated recovery from exceptions.