## 1 Introduction  
The physiological functions and internal organs of a human being are adapted to the standing upright position and biped locomotion. Accidents and diseases such as cerebral palsy, embolism, spinal cord injury (SCI), muscular dystrophy, and post-polio syndrome generate adverse conditions such as muscular stiffness, tendon deformations, bone density loss, urinary infections, and intestinal constipation [1]. SCIs present different grades of affectations in the body (partial and total paralysis in human limbs) and are classified with respect to the level of location according to the American Spinal Injury Association (ASIA) using the International Standards for Neurological and Functional Classification of Spinal Cord Injury [2]. The mobility options for people affected by SCI are limited [1] and in the case of motor disability the option of mobility that is widely used is the wheelchair of manual impulse [3]. However, the wheelchair produces secondary problems generated by long periods of time when the users remain seated, producing physical and social problems called secondaries such as blisters, osteoporosis, gastric problems, urinary tract infections, tendon deformation, muscle atrophy, mental stress and low self-esteem. The low self-esteem is presented by the condition of looking from a low position, but can be decreased if the patient stands up, remains standing and moves in a standing upright position. Exoskeletons are an option for substituting wheelchairs, and those high-technology devices allow them to accomplish Activities of Daily Living (ADL) such as those listed in Table 1. It is worth mentioning that both devices have their own problems with working effectively in an urban environment designed for healthy people. The trend in exoskeletons is to add everyday high technology sensors, actuators, and electronic control devices [4] that, in short, are genuine contributions to science and technological development but, due to their level of complexity, are susceptible to failure and, therefore, have low reliability and high costs that do not allow their massive application. Exoskeletons have the following drawback: biological joints do not have a fixed rotation center; therefore, a slight misalignment with the user's kinematics will produce forces and torques against the movement, increasing the required effort [5; 6; 7]. The reduction of degrees of freedom (DOF) reduces the complexity of Exoskeletons resulting in the reduction of the system weight, robustness, and reliability of the systems and, therefore, a lower cost for end-users [8]. A heavy exoskeleton requires high electromechanical power, therefore demanding a higher battery capability and weight. Today, the control algorithms that rule robots have not reached a behavior to be compared with the methods of strength, control of force, and natural sensors developed in the human body [5; 9]. From seated to standing is the first step of the transition to help SCI users move to their wheelchairs and progress towards their mobility. The structure of exoskeletons equipment is very complex and uncomfortable, turning into fixing and maintenance issues. The new Soft-EXO rehabilitation devices greatly simplify the structure and weight, but the applied force is reduced. The most important achievement of the exoskeletons is to enable patients with total paraplegia to stand up and walk [10]. On the other hand, passive exoskeletons have features such as a lower level of complexity, structural simplicity, and operational ease. Moreover, their designs avoid energy problems, actuation systems, and control [11]. Objects and the urban architecture are designed for healthy people capable of walking and remaining in a biped posture [10]. Although there is a great effort to adapt urban architecture for people in wheelchairs, it is common to find different problems such as curbs, ramps, obstacles, and slopes on the streets, generating a complex environment in which to drive a wheelchair.