Using Design of Experiments to Make Processes More Robust to Environmental and Input Variations
To achieve this objective, Taguchi advised that input variables be divided into two categories: control factors, such as the adjustments a technician makes to your office copier, and noise factors, such as the humidity that fluctuates in your office environment.
Ideally, processes will be adjusted by way of the control factors to be insensitive to the noise factors, whose variation presumably cannot be eliminated. For example, the office copy machine should handle paper properly during humid summer months as well as in the winter, when conditions are dry and prone to static electricity. To accomplish these objectives, Taguchi advocated planned experimentation using a layout called "parameter design."1