Adaptive Structures Technology for Improved Performance of Form Measuring Machines

Vibration suppression in form measuring machines constitutes a very promising application of smart structures techniques. A form measuring machine is used in order to check the shape of workpieces and that the prescribed form tolerances are not exceeded. The shape evaluation relies on displacement measurements whose precision ranges from some tens of nanometers to some microns depending on the size and kind of machine. The environment in which the machine operates (typically near the production line) is particularly rich in vibration sources. A relative motion between the probe (the element of the measuring machine which hosts the displacement sensor) and the measured object due to vibrations in the machine results in measurement errors which can easily prejudice the result. In this paper, a smart solution to this problem is presented in which the machines vibrations are counteracted actively. For this purpose, the machine has to be equipped with a sensing system, an active interface and special controller. This new concept has been successfully tested on a real form measuring machine. In the sensing system, accelerometers were used, while the active interface was realized with piezoelectric elements. The controller was implemented on a fast digital signal processor using modern adaptive filtering techniques. The experimental results are encouraging. The proposed concept represents a decisive step forward in the development of a completely new generation of more efficient, lighter and cheaper form measuring machines