White Paper Abstract

In order to achieve the rapid acceleration required the use of direct drive motor technology has increased. High-power, rare-earth magnets in direct drive rotary motors and the use of low inertia rotary and linear motors have made top speeds and acceleration rates much higher than were possible even a couple years ago. Increasing the speeds and acceleration rates that the machine is capable of is important to improving productivity but in order to realize this increase - accuracy must be maintained.

The increase in acceleration has introduced additional challenges when trying to maintain part accuracy. One such challenge is the affect of an eccentric load located on the table. It is very common for a part and fixture mounted on the rotary table to be off-center. This results in an eccentric load on the table. When the rotary table with eccentric load is located on top of one of the linear axes there is an interactive force between these axes. When the rotary axis accelerates, there is a centrifugal force and reaction force due to the acceleration applied to the linear axis. The same is true of acceleration of the linear axis; interactive force is applied to the rotary axis during acc/dec of the linear axes. The interaction between axes can be seen as a reduction in accuracy - in the form of a tool mark, step or oscillation at the tool tip. This is especially troublesome during 5-axis, high-speed machining cycles.