# Adjustable Stiffness-Based Supination-Pronation Forearm Physical Rehabilitation
## 2 Methodology  
This section illustrates the methodology used to develop the adjustable stiffness rehabilitator and to validate its performance. The steps mentioned below constitute a well-known general method for developing medical devices  
1. **Medical requirements identification:** The characterization of the required motion is established by performing a literature review and by consulting physiotherapists. Range of motion, torques, and physical dimensions are some of the requirements that must be defined.
2. **Mechanical design conceptualization:** In this iterative phase, several concepts of the rehabilitation are generated in order to be evaluated based on medical requirements. Different mechanical elements and materials are considered, as well as manufacturing processes. The best option is selected to be developed. Figure 2 and Figure 3 show a schematic representation of some elements of the rehabilitator.
3. **Dynamic mathematical model synthesis:** A dynamic mathematical representation of the selected option is synthesized, taking into account mechanical interactions defined by physical laws and behaviors of the respective materials. The dynamic mathematical model (DMM) can be obtained in the time domain. If the mathematical model is linear, a frequency domain representation can be obtained too. The DMM representing the adjustable stiffness rehabilitator is provided in Equation (2) in the time domain.
4. **Open loop numerical simulations:** In order to analyze the behavior of the mathematical model under specific excitation signals, numerical simulations are performed. If needed, adjustments can be made to the mathematical model.
5. **Closed-loop control strategy synthesis:** starting from a precise mathematical model of the rehabilitator, the synthesis of a closed-loop control strategy is generated by taking into account the angular position trajectory tracking (supination-pronation) and the cable's tension regulation (resistance to be overcome). This is, in general, an iterative step. Section 5 shows the proposed closed-loop control strategy.
6. **Closed-loop numerical simulations:** Several numerical simulations are performed in order to analyze the closed-loop behavior of the mathematical model (the rehabilitation) based on the established requirements. It is in this phase where the controllers are tuned. This step represents a first validation that allows one to initiate the manufacturing process.  
**Experimental platform manufacturing:** Based on the materials, on the mechanical elements, and on the manufacturing processes considered in the selected proposal, an experimental platform is built (see Figure 2). This platform will allow one to, experimentally, validate the mechanical design, the dynamic mathematical model, and the control strategy.
* **Experimental platform instrumentation:** Actuators, sensors, and other elements are incorporated to the experimental platform that will interact with an embedded system.
* **Embedded system generation:** Generally speaking, in this step a microcontroller is selected, programmed and connected to the manufactured and instrumented platform. At this point, the electronic interface (see Section 4) is ready for performing experiments.
* **Experimental tests:** Before using new medical technology in patients for clinical trials or treatment, it is necessary to validate, experimentally, its performance. The angular trajectory tracking and the stiffness (tension or torque) regulation are the two main aspects of interest to validate the performance of the rehabilitator reported in this paper (see Section 6).