Antropomotoryka nr 57 [2012]. - Akademia Wychowania Fizycznego ...

The movement of a human being in the medical exoskeleton – the anthropomotoric aspectswrist joint – used mostly to support the movementof the disabled people,• the advanced exoskeletons equipped with the supportof a palm, including 16 joints – four for eachfinger – used in the reeducation of the everydayactivities, also after surgeries.In steering the exoskeletons, particularly the prototypeones [15], the steering devices equipped withneuro-fuzzy controllers can be helpful since their easyadaptation to the EMG signals of the user [14, 15].Optimizing the power [16] is still a matter of interestsince the values obtained from experimental research,however useful, require additional modeling. A very precisereflection of the natural power is not necessary herebut its optimization in the given application is important.It concerns all the muscles and functions, walking included.To calculate the optimal powers in the real time, oneneeds to follow quite complicated operational mathematicalprocedures, often solving the problem of numerouscontradictions and inter-relations with the simultaneousmovement of other muscles. One of the methods allowingthe assessment of the muscle power on the basis ofthe EMG signal analysis, the Bogey’s and co-workers’method [17] is often used in different variants.The presupposition of involuntary reduction in humanstrength in the human-machine interface [18] isreflected in the hypothesis formulated by Lewis andFerris that users cooperating in the human-machineinterface involuntarily lower the power of muscles andthe moments in joints, which influences the resultantmoments of the user-exoskeleton interface. In effect,these values may differ from the natural ones achievedby the same human being. As for today, the research inthis field is being conducted and the initial results do notconfirm the above hypothesis, however, the effectiveimplementation of commercial exoskeletons requiresfull explanation of that problem.The improvement of the exoskeletons’ inertia [19] asone of the means aimed at providing the exoskeletonmovements with the agility natural for a human being,particularly in the area of the upper limbs movements,has caught the researchers’ attention. It is believedthat the exoskeleton numbness disturbs naturalness(also lowering the natural frequency) of the exoskeletonmovements of the human-user. Particular role may beplayed here by great accelerations given to some elementsof the exoskeleton, among others, in the substitutesof the hip and knee joints which can sometimescause the so called jerky movements of the exoskeletonwhile attempting a quick acceleration of a walk by theuser. Hence, the attempts to create the compensationalgorithms in that area are in interest [19].Proportional myoelectric control [20] intensifies theprocess of the user’s adaptation, both the one withdeficits, and the healthy one to steer the exoskeletonalso in case of the necessity to reduce and to diminishthe energy consumption. It is what makes the abovemethod the leading one in the market. In this method,the value of powers of the particular muscles is proportionalto the amplitudes of the equivalent EMG signals.It should be noted that EMG signals have to beprocessed here in the real time. It is suspected thatthe precision of movements in this method may not bean effect of a certain specific action of the descendingstimuli but may rather depend on the long-lasting exercises,proprioceptive feedback or mechanics of joints(e.g. the movement in the elbow may be less precisesince the associated movement in the wrist will expandit) [20, 21, 22].The control of an individual muscle [23] is realizedmainly by the “individual muscle-force control” supportedby the exoskeleton which allows obtaining muchbroader spectrum of data than with the help of suchconventional methods as gripping or pushing the handles.In the controlling of groups of muscles, there mayarise problems with coordination of the movementsof the synergistic muscles both in case of the healthypeople and the people with movement deficits in thatsphere. Although in exoskeletons the issue of the artificial“muscles” construction as such is of a secondaryimportance, the choice of the appropriate pneumatic orhydraulic elements as well as electric actuator may significantlyinfluence the algorithms of steering itself andthe construction of the steering system, e.g. in the fieldof the energetic optimization or using the numbness ofthe limbs movement.In accordance with all above-mentioned, two crucialproblems should be taken under consideration:1. Education and coordination of the user-exoskeletoninteraction in the situation of a temporary using ofthe exoskeleton (e.g. for the time of convalescencein case of weakening of the user, and also while usingthe exoskeleton as the support of the weakenedmuscles with its gradual reduction) as well as theestimation of the influence of the exoskeleton’s periodof exploitation upon the possibility of returningto the natural (self-reliant) patterns of movement.2. Not sufficiently examined effects of a long-time stayin the exoskeleton in case of using it as an alterna­– 119 –