Analysis of cross-talk effects in a parallel kinematic machine for rehabilitation therapies

The increasing interest in balance and cognitive rehabilitation leads to the use of cutting-edge technologies to improve individual well-being. Traditional rehabilitation therapies, such as balance boards, have paved the way for platform-based therapies assisted by robotic platforms. This paper presents the analysis of a four-legged platform with three degrees of freedom, which is already widespread in the gaming and motorsport markets for driving simulations and not yet in rehabilitation applications. A kinematic analysis is performed, pointing out the presence of movements along the not controlled degrees of freedom (i.e. cross talk) of the device. As a second step, dynamic analysis shows how, in the machine under analysis, the actual values of cross-talk also depends on the dynamic response of the platform, governed by friction at the contact between the actuators’ ends and the ground.Finally, the paper explores a design solution, based on spring constraint system, aimed at reducing the dominance of the role played by friction in determining the dynamic response of the system, thus improving the predictability and the deterministic evaluation of cross-talk values.Results indicate promising prospects for the proposed platform in rehabilitation applications, in which the exploitation of cross-talks could turn into an added value to modulate the difficulty levels of the therapy with a compact machine.