Application of a Magnetic Bearing Spindle to Non-Circular Fine Boring

A magnetic bearing spindle is used in non-circular fine boring. The displacement of the rotor is controlled to follow a non-circular profile by the magnetic bearing. The reference trajectory of the rotor displacement is determined by choosing the axis trajectory having a lower frequency component and minimizing control current on the magnetic coils. The periodic learning control with inverse transfer function compensation is applied to get the desired non-circular profile. This control technique, which is a type of feedforward control, can make periodic output errors converge to zero by repeatedly compensating the input data. Several cutting tests are carried out for a non-circular piston pin bore by using the developed boring machine, which consists of a magnetic bearing spindle and a hybrid controller. The difference between the reference profile and the cutting profile was within 2 [mu m] at a rotational speed of 25[rps] (l,500[rpm]).