Most current multi-shaker, Multiple Input Multiple Output (MIMO), tests are performed on the basis of a "square" arrangement, in which the number of control accelerometers equals the number of controlled exciters. However, in some cases more control accelerometers than exciters may be desirable. This arrangement is referred to as "rectangular" control. Recent advances in digital control of multi-shaker and multi-axes systems have made rectangular control an achievable, if not a simple, reality.
This paper examines the theory behind this approach and also gives some practical results. Some unexpected benefits resulting from this new control approach are included.