# Improvement of the Sensor Capability of the NAO Robot by the Integration of a Laser Rangefinder
## 2 Materials and Methods  
### NAO6--Aldebaran, Part of United Robotics Group  
The NAO is a commercially available anthropomorphic robot designed to imitate human movement, while performing user-friendly interactions (Figure 1). It is a small robot, 58 cm in height, about 5.5 kg in weight, and one of the most widely used robotic platforms with similar features in the research field. In particular, several applications of innovative social and creative robotics algorithms are currently available. The NAO robot is compatible with the ROS (Robot Operating System) standards [33], which makes it remarkably versatile and relatively easy to use in various applications. Moreover, it can be considered one of the most advanced humanoid robots that is commercially available today and is capable of expressing itself in several languages. Due to these features, the NAO robot represents a good example of an SAR that demonstrates excellent interaction capabilities when employed with autistic children, the elderly, or persons with disabilities, as reported by numerous studies available in the literature [34; 35; 36; 37; 38; 39; 40; 41]. Figure 1: Robot NAO. In this study, the model H25 (version 6) has been used. It is equipped with two 5-megapixel cameras with a resolution of 2592 \(\times\) 1944 that are located in the forehead and are capable of a frame rate of up to 30 images/s in the high-definition mode. Moreover, to allow interaction with the user using voice commands, the robot is provided with four directional microphones positioned on the head, a speech synthesizer, and two high-fidelity speakers at ear height. An Intel quad-core Atom E3845 processor at 1.91 GHz that is able to process up to 8 GB of memory and a software system based on the Linux Built-in OS are the core of the onboard processing unit devoted to engine control, communications, and ancillary services (e.g., voice recognition, etc.). The data transmission with peripherals outside of the robots or with the user themselves is assured by a network card provided with an Ethernet cable (the port is positioned on the back of the head), a Wi-Fi wireless transmitter, and two infrared transceivers placed on the robot's head at eye height. From a mechanical point of view, NAO is a robot with 25 DoF (degrees of freedom) that uses four typologies of electric motors to move its joints, each presenting a different torque value. The robot has also been provided with sensors to control the joints' positions (i.e., encoders) and to measure each motor's electrical absorption for complete control of its movements. A lithium polymer battery (LiPo; 21.6V/2.9 Ah) provides the robot with an operating time that varies from 45 to 120 min, depending on the performed activities. Regarding the availability of on-board sensors for its localization and obstacle avoidance, NAO is provided with different families of sensors. An inertial measurement unit (IMU) with six degrees of freedom is located in the middle of the trunk. With this device, the robot can measure its kinematic parameters and, in this way, also evaluate its postural position. Furthermore, it is equipped with contact sensors positioned on its surface to act as additional touch input and for collision detection. The former are three capacitive touch sensors that have been installed on the head and each of the hands, respectively. The latter are two bumper sensors that have been placed on the front of each foot and four FSR (force sensitive resistor)-type pressure sensors in their lower part for the measure of the applied pressure. The robot performs the obstacle detection operations by using, in addition to the two cameras, an ultrasonic (US) system composed of several transmitters and receivers working at 40 kHz that allow the scan of the scene in front of it.