HapticWalker---a novel haptic foot device

Abstract

This paper presents a new haptic locomotion interface, which comprises two programmable foot platforms with permanent foot machine contact. It is designed as a scalable and modular system with unit-by-unit extensibility offering up to six plus one degrees of freedom (DOF) per foot. The basic setup comprises three DOF per foot in the sagittal plane.The machine is based on a rigid hybrid parallel-serial robot kinematics structure. It is equipped with electrical direct drive motors, enabling highly dynamic footplate motions. For contact force measurement, six DOF force/torque sensors are mounted under each foot platform. The system was developed for major application in gait rehabilitation, hence great importance was attached to the incorporation of maximum passive and active security measures for machine users and medical operating personnel.The simulator is able to perform walking trajectories with speeds of up to 5 km/h and 120 steps/min. The system is able to simulate not only slow and “smooth” trajectories like walking on an even floor, up/down staircases, but also foot motions like walking on rough ground or even stumbling or sliding, which require high system dynamics.The machine is controlled by a self-developed full-featured robot control whose soft and hardware is based on up-to-date industrial standards and interfaces. The robot control software is based on RTLinux and runs on an industrial PC. The real-time motion generator includes a newly developed Fourier-based algorithm for the interpolation of natural cyclic walking trajectories. For the implementation of asynchronous events (e.g., sliding, stumbling), the controller comprises especially developed algorithms for automatic motion override adaptation. Different modes of haptic behavior needed for gait rehabilitation, ranging from full foot support during swing phase to completely passive behavior, are currently under development.Intuitive and safe machine operation by nontechnical personnel such as clinicians and physiotherapists is achieved via a separate Windows-based graphical user interface software comprising different window areas for machine programming and operation, real-time off-line simulation and online data visualization in two and three dimensions has been developed as well.A working prototype of the system has been built and tested successfully, including all soft and hardware components. Although the machine has been designed and built for major application in gait rehabilitation, its range of applicability is not limited to this area. It could be integrated into any setup requiring a highly dynamic haptic foot interface and permanent foot machine contact if needed.