Constraints

Constraints at the system level lead to constraints at the assembly and component level. Therefore, it is important to define the envelope of operation, which is the range of conditions and parameters that the system must operate within, to reduce the design space to feasible solutions. Several important constraints are power, spatial, and sequence of operations.

Power constraints refer to the amount and type of energy that the system requires to function properly. For example, a laptop computer has a power constraint at the system level, which is the battery capacity and voltage. This constraint affects the assembly level, such as the motherboard and the processor, which have to consume less power and generate less heat. The component level, such as the transistors and resistors, also have to meet the power constraint by having low resistance and high efficiency.

Force, strength, or stress constraints refer to the capacity of the material to resist deformation or mechanical failure under load. For many mechanical systems these are derived from the power constraints. The weight capacity for a product is an example of a system level constraint that will affect the geometry and material choices for the components within that system.

Spatial constraints refer to the physical dimensions and shape of the system and its parts. For example, a bicycle has a spatial constraint at the system level, which is the overall size and location of assemblies. These constraints affect the assembly and component level, such as the frame, wheels, and gearing.

Sequence of operations constraints refer to the order and timing of events that occur within the system. For example, a coffee machine has a sequence of operations constraint at the system level, which is the process of brewing coffee. This constraint affects the assembly level, such as the water tank and the filter, which have to work in sync. The component level, such as the valves and the sensors, also have to meet the sequence of operations constraint by having accurate control and feedback.