Specifications

4 Designing Controllers Using the Command Line

4-22

When the desired position changes step-wise to 5, the two masses separate briefly (with

appropriate switching to MPC1) but for the most part move together and settle rapidly at

the desired position. The transition back to –5 is equally well behaved.

Now suppose we force MPC2 to operate under all conditions. The figure below shows the

result. When the masses are separated, as at the start, MPC2 applies excessive force

and then over-compensates, resulting in oscillatory behavior. Once the masses join, the

movement smooths out, as would be expected.

The oscillations are especially severe in the last transition. The masses collide frequently

and M

never reaches the desired position.