If the main charger fails the transfer charger can be engaged to charge the drum in addition to its primary function to transfer toner. For this to work it is necessary not only to have the sensor data, but perhaps more importantly to have a model of what the machine is supposed to do, and how parameter changes affect machine functions. So a key ingredient is the development of a system model. I don't see any way other than having this produced by or with assistance of experts. This involves conceptual design, basic design, and control sequence design.
Functional redundancy is designed in during the first step, or conceptual design.
The modeler represents design objects based on the diagram. It allows the representation of functions in an object oriented manner. A key part of representation is the decomposition of functions, allowing the designer to build up a functional hierarchy. Ultimately behavior simulation can be performed, with a reasoning system providing a variety of information. This works on top of the FBS Modeler.