# A Robust Controller for Upper Limb Rehabilitation Exoskeleton
## 2 Development  
Figure 2a shows the exoskeleton for rehabilitation of the right upper extremity, indicating its main components. The exoskeleton is designed to place the motors in the base that is placed on the back of the user. The movement of the links of the arm and forearm will be made through cables connected to the motors. However, in this analysis, it is considered that the torques act directly on the shoulder and elbow joints in order to estimate the torque required in the engines when using cables. The three degrees of freedom to provide the movements of flexion-extension and abduction-adduction of the arm and flexion-extension of the forearm are shown in Figure 2b. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \begin{tabular}{c} F–E = flexion/extension; C = circumduction = C; P-S = pronation/supination; AB–AD = abduction/adduction; R–U = radial/ulnar; n/a = not available. \\ \end{tabular}  &
\begin{tabular}{c} S’-E = flexion/extension; C = circumduction = C; P-S = pronation/supination; AB–AD = abduction/adduction; R–U = radial/ulnar; n/a = not available. To achieve the objective of the controller that tracks the trajectory of the exoskeleton links, a proportional-integral robust controller (GPI) based on integral reconstructs for time-dependent first-order disturbances was designed. The procedure for the controller design is the same for each of the three actuators, so the development of the controller is shown in a general way. The mechanical part of the exoskeleton arm has a weight of 2.51 kg, and the base where the motors are placed with all the components for their operation is 6 kg, which makes the exoskeleton light. The materials used were aluminum and Nylamid; some parts were machined in steel. The approximate weight of the exoskeleton is 8.5 kg. Although adding weight to a person who has suffered an injury may generate another injury of lower intensity, it should be understood that sometimes such sacrifices are necessary. In relation to Table 1, most designs have 5 DOF, and the movements are almost coincidental. In the same way, the application is mostly focused on rehabilitation, with most of the authors focusing on stroke rehabilitation. Our design has a substantial relationship to the rehabilitation of stroke. We decided on 3 DOF because rehabilitation experts indicate that to regenerate the neuronal bonds of the damaged brain, it is appropriate to use the basic DOF, since saturating the brain with information can, depending on the damage caused, cause more posttraumatic stress. Robot-mediated therapy has been found to produce improvements in the recovery of motor capacity; however, so far, the use of robots has not shown qualitative benefit over classical therapist-led training sessions performed on the same quantity of movements. Multi-degree-of-freedom robots, like the modern upper-limb exoskeletons, enable distributed interactions across the whole assisted limb, and can exploit a large amount of sensory feedback data, potentially providing new capabilities within standard rehabilitation sessions. Surprisingly, most publications in the field of exoskeletons have focused only on mechatronic device designs, while little focus has been given to the control aspects. On the contrary, a primordial aspect for the potentiality of robots resides in the control part [3]. Portable exoskeleton designs address the problem of the weight thereof, and this situation involves placing motors (ASME-03B High Power High Voltage Servo Motor 12 V \(\sim\) 24 V 380 kg/m 0.5 s/60\({}^{\circ}\)) in the middle of the back. Transmission pairs are with Bowden cables, and pulley arrangement is used to minimize torque. The arrangement of pulleys and motors does not need to be aligned. [PERSON], 2018 used several controllers: PD, PID, PD + g Adapt, and the adaptive sliding mode (Slide), and these were simulated in the dynamic model. Regulation tests were performed to compare the different controllers that were proposed, and graphs only giving position results with respect to time were shown.