  Industrial robots are commonly used in various industries due to their
flexibility. However, their adoption for machining tasks is minimal because of
the low dynamic stiffness characteristic of serial kinematic chains. To
overcome this problem, we propose coupling two industrial robots at the flanges
to form a parallel kinematic machining system. Although parallel kinematic
chains are inherently stiffer, one possible disadvantage of the proposed system
is that it is heavily overactuated. We perform a modal analysis to show that
this may be an advantage, as the redundant degrees of freedom can be used to
shift the natural frequencies by applying tension to the coupling module. To
demonstrate the validity of our approach, we perform a milling experiment using
our coupled system. An external measurement system is used to show that
tensioning the coupling module causes a deformation of the system. We further
show that this deformation is static over the tool path and can be compensated
for.
