Walking is a complex way of moving, as the nervous system, musculoskeletal system and cardiovascular system must function properly to perform effectively. Any failure of these systems can cause balance and gait disturbances, which in turn lead to injuries related to falls or even death. The main causes of balance and gait disturbances are aging, cardiovascular disease, orthopedic defects and neurological disease. Due to the aging population and increased chances of survival of neurological and cardiovascular diseases, the need for rehabilitation is increasing. As a result, the costs of performing manual walking training and balance therapy are increasing, and at the same time a shortage of staff is happening. Therefore, there is a tendency to develop rehabilitation devices that allow physiotherapists to make walking easier, more repeatable and more effective.
Most rehabilitation devices on the market address the issue of pathological walking in terms of improving the mechanisms of walking, but do not address the issue of reactive balance control to prevent falls. To this end, a new approach to walking rehabilitation is being developed, based on the implementation of controlled perturbations in a safe and controlled environment. For this purpose, the University Institute for Rehabilitation of the Republic of Slovenia - SOČA has developed a parallel robotic balance assessment mechanism (BAR).
In the master's thesis we discussed the problem of reducing the negative impact of the persistence of the parallel mechanism on the dynamics of the user, which is the main weakness of BAR. We developed a cable system that would impose controlled perturbations on users pelvis in one degree of freedom, but could help during movement and promote balance learning. The developed system consists of a custom-made construction that connects two drive parts, each on one side of the platform on which the user stands. An individual drive part pulls a cable that runs along the pulley system from the drive part to the belt with which the user is fastened to the system. Motor control and the calculation of the virtual environment interaction is running on a programmable logic controller. After examining the requirements, we decided to use closed-loop admittance control. The operation of the cable system was divided into the initialization process, which met the required initial conditions of the cable system and free operation, in which we generated various profiles of external forces on the user, allowed free pelvis movement and generated a force field.
The operation of the tendon system was evaluated with the results of the transparency of the system, with the results of the ability to generate a force field in one degree of freedom and with the results of the ability to generate different perturbation profiles. A satisfactory display of empty space was achieved by introducing compensation of cable system dynamics and studying its influence on the ability to generate interactive forces of the virtual environment. We found that our method of compensation impairs the ability to generate the interaction forces of the virtual environment, so we can introduce additional logic into the management of changing the impact of compensation. The tendon system provided the generation of an appropriate force field, which prevents the user from excessive deviation from the desired position and thus provides assistance in walking. Due to the limitations of the power supply system, the string system allowed the generation of 100 ms short pulses of forces only up to the amplitude of 85 N.
As part of this work, we developed a tendon system to guide the human pelvis in one degree of freedom. We supported further development with the results of measurements and the fact that the performance of the system could be improved by using dedicated and higher quality components. The use of pulleys allows a large number of different configurations, and the system can be extended with additional actuators. The mechanical expansion of the system is therefore trivial, and in addition, the use of cable systems makes it possible to reduce the influence of the system's own dynamics on the user's movement. This cannot be argued for making a similar system using a rigid parallel mechanism.
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