# Design Methodology for Soft Wearable Devices--The MOSAR Case
## 2 Design Methodology
### Phase 2: Modeling  
After compiling the information regarding the physical condition of the patient and defining the SWD objective, the modeling phase can initiate. This second phase represents the starting point for EPM conceptual design with the definition of the SWD design criteria (Step 9) based on SEG criteria which are established in References [15; 24]. Thus, SWD design is integrated by mobility, usability and control criteria as it is portrayed in Figure 3. All these criteria interact between them in order to allow researchers to build functional SWD systems for different applications. The following usability criteria are oriented to emphasize the medical attributes of the system to incorporate current technology and expertise of therapists and neurologists. 1. Selection of the impaired portion of the body
2. Definition of the application (pathology)
3. Identification of the function (rehabilitation or assistance)  
Figure 3: Design criteria for soft wearable devices. Establishment of the associated tasks (movements)
* Selection of the assistance mode (passive or active)
* Maintenance
* Customization
* Configuration (open or closed) design
* Modularity
* Portability (home rehabilitation)
* Mode of intervention (unilateral or bilateral)  
The mobility criteria, incorporated in the proposed methodology, are related to enhancing flexibility, compactness, ergonomics, wearability, payload capacity and lifespan of the system. Moreover, these criteria seek to guarantee SWD functionality in such a way that the patient can feel confident with the system and are provided below. 1. Definition of joints ROM based on impaired limbs
* Definition of the number of DOF per joint
* Definition of the power supply (pneumatic, hydraulic or electric)
* Establishment of the type of actuation
* Selection of the type of transmissions (if necessary)
* Definition of the maximum weight
* Selection of materials
* Definition of the manufacturing processes
* Operation tests
* Costs analysis
* Synthesis of a control strategy
* Performing of assessment tests
* Evaluation of the case study  
Control criteria must provide safe interactions between SWD and patients even under unexpected disturbances. To do so, closed-loop control strategies are employed to minimize errors and guarantee stability [34]. These criteria are:  
1. Human-SWD interface to control actuators
* Detection of patient's effort (EMG)
* Presence of a safety button for emergency stops  
Depending on the mathematical model and on the desired performance of the SWD, the closed-loop control strategy will be developed. Reported values of pressure [10], torque [35] or payload capacity [36] can be considered as reference for the associated control strategy. This methodology proposes to measure the functional ROM values at each joint of the patient (Step 10) and compare them to normal healthy ROM to determine the operational ranges of the SWD depending on the joints' impairment. A manual or electrical goniometer can be used along with therapist's assistance to measure the patient's joints ROM. The design concept is developed through reverse engineering, firstly by a casting model from the impaired limb (Step 11) to gather the patient's anatomical information and then, to obtain a silicon model (dummy limb) for practical and safe handling which will serve as a morphological reference for future assessments. The reverse engineering tool will consider natural morphology to know how the joints are affected and obtain a skeleton reference frame for a customized SWD design concept. Additionally, the reverse engineering approach could diminish the design time between development and innovation for future SWD products. Development continues with a 3D digitalization of the dummy limb (Step 12) using a 3D scanner. This computational model is the parameterized reference for SWD design. The 3D scanner handling requires a straightforward training depending on the scanner type, the associated software, the number of cameras and their calibration procedure.