# Personalization of the 3D-Printed Upper Limb Exoskeleton Design--Mechanical and IT Aspects
## 5 Discussion
### Mechanical Design Aspects  
Support strength and range of movement are key values for a hand exoskeleton. A study by [PERSON] et al. [74] of the Tenoexo hand exoskeleton showed that a prototype of a lightweight rehabilitation hand exoskeleton combining rigid parts with a soft mechanism could produce a contact force of up to 8 N and overcome a range of motion of 91.5\({}^{\circ}\) in 3 s [74]. Other important parameters arehigh power-to-weight ratio and fast start-up time. They are difficult to achieve with traditional solutions; hence, there is a search for new categories of actuators made of highly twisted nylon fibers with a high pitch per cycle with reversible contraction. At the moment, twisted and coiled polymer (TCP) actuators with different nylon fibers require further research but are a promising technology [74].  
HandMATE (Hand Movement Support Exoskeleton) showed minimal errors in assisting grip strength (<1%) comparable to the performance of a healthy hand without an exoskeleton. The exoskeleton communicates wirelessly with a tablet (Android operating system) and dedicated software, offering guided exercises, therapeutic games and feedback on the effects of the exoskeleton [75]. Force myography (FMG) control of the hand exoskeleton uses two strands of sensors with a force-sensing resistor (FSR). Sensor arm bands measure forces produced by muscle contraction/relaxation, and hand movements are identified by classifying threshold values [76]. An alternative is to measure the intention of motion by compressing the elastic elements in the actuator. This allows the use of a virtual dynamic system combining user support with maintenanceof motion stability. However, the performance was tested using the integrated one-finger exoskeleton gauntlet mechanism using two types of input motion, making this hand exoskeleton testing system more difficult to use than our proposed one [77].  
Monitoring of the patient's home use of the exoskeleton is facilitated by the recording of sessions and the ability to reproduce the use of the exoskeleton on a virtual twin. It also allows for the assessment of changes in the patient's health and their functional capabilities, allowing modifications of the rehabilitation plan and the settings/construction of the exoskeleton. Thus, the need for cyclical visits to the clinic is reduced, and the importance of telerehabilitation is increasing (in study [78] with spinal muscular atrophy), reducing the burden on the health care system [78].  
The integration of the dexterity of the hand movement in the exoskeleton when performing everyday tasks gives rise to various concepts. In RELAbtenoexo [79], there is a generation using a remote activation system of the four most frequently used grips (individually created for each user). This provides the range of motion and fingertip strength required for 80% of all finger gripping activities. The key factors for acceptance by users were low weight, small size, high comfort of use and attractive appearance [79]. Development (modifications to the family of exoskeletons or modernization with newer elements) remains an important element of the life cycle of the hand exoskeleton [80; 81]. In bilateral therapy, the exoskeleton of the deficient hand follows and repeats the movement of the other unaffected hand during bi-handed activity, but this solution has significant limitations due to the fact that both hands are involved in therapy and has a poor translation into everyday life activities [82].