# Behavior-Based Control Architecture for Legged-and-Climber Robots
## 1 Introduction  
Due to the increased size and complexity of civil construction, using climbing robots in infrastructure inspection is becoming increasingly relevant. Regular maintenance and surveillance of large complexes are extremely important to guarantee their life-cycle. The European consortium SPARC (euRobotics) carried out an analysis, revealing in the \"European Robotics & AI workshop Applied to Inspection and Maintenance\" report [1] that in the coming years the task of inspection will be increasingly important, and robots will play the main role in maintenance, inspection and dismantling. Inspection is a particularly structured repetitive task, that requires permanent attention during the operation, and in many cases, it involves placing the human operator in risk situations. That is why robotics is revealed as a technology of direct application. The number of service robots, mainly driven by drones, has increased by 25% in recent years, and the number of autonomous vehicles in a non-manufacturing environment, has increased by 51% in one year [2]. Many solutions are based on remote visual inspection, but this is not valid for many industrial structures. We may not have direct visual access to the areas to be inspected, and in other cases it is not possible to carry a flying drone because of the narrowness or typology of the environment. In addition, an inspection usually requires much more than seeing. Non-destructive techniques require contact or proximity to the surface that is not possible to achieve while flying. Climbing robots have become increasingly attractive for effective infrastructure inspection due to their ability to overcome these limitations. A crucial part of these robots is their control. Typically, robots are controlled based on control architectures. The lack of existing control architectures for legged-and-climber robots drives a need to design a new architecture. The state-of-the-art of control architectures for this kind of robot reveal that much work remains, because although plenty of legged-and-climber robots are structurally defined, they lack a defined architecture. Only afew control architectures are found for climber robots. [PERSON] et al. [3] proposed a climber robot for oil tank inspection, whose control architecture only covers the kinematic control of the robot. Several control architectures for legged robots can be found easily, such as [4] or [5], which describe the motion controller of two-legged robots. However, these kinds of legged robots are unable to climb due to their bipedal disposal. Robots with more than two legs, like [6], for example, have a control system that only covers legs management and exclude the high-level control. A control architecture specifies the organization guidelines of a robot's behavior, establishes the action and movements that the robot must carry out to achieve a goal or a set of goals, according to the robot state. It has the main purpose of establishing a way to organize the system to maintain defined roles, modularize the system components and make the system as fault-tolerant as possible, always trying to keep the system under control over as many situations as possible. The main characteristics of the control architectures are the capacity to (a) face multiple goals simultaneously, (b) integrate data from different sensors, (c) be robust against component failures, (d) be adaptive to new environments, (e) extend and modify its content easily, (f) make its own decisions according to the robot state, and (g) modify the surroundings properly.