Control Issues in Haptic Robot Navigation and Object/Obstacle Recognition Using a Flexible Sensing Antenna

Haptics is the technology of touch. In recent years, there has been an increasing interest in developing integrated sensory systems relating to various tactile sensors. Multiple applications entail integrated systems, as is the case of machine assemblies for precise positioning, impact protection, navigation, etc. Natural tactile sensors, such as whiskers and antennae, have been explored in recent years. Several attempts have been made to build biomimetic active sensory applications, which are also known as vibrational systems. Mammal- or insect-inspired sensing has orchestrated multiple forms of engineering applications such as whisker-based texture discrimination on a mobile robot. The less frequent use of tactile sensing may be partly attributed to its complex and distributed nature. In the last two decades, a robust and compact sensor device has been proposed that efficiently solves some of these problems, which is called “sensing antenna”. It is an active sensor that consists of a flexible-beam moved by some servo-controlled motors and a load-cell placed between the beam and the motors. This device replicates the touch sensors that some animals possess and performs an active sensing strategy in which the servomotor system moves the beam back and forth until it hits an object. At this instant, information of the motor angles combined with force and torque measurements allows us to calculate the positions of the hit points, which are valuable information about the object surface. A 3D map of the surface of an object, which allows its recognition, can be obtained using this device. Two strategies can be applied to obtain such 3D maps. The first one is to keep moving the beam back and forth in order to hit the object at different points, which allows one to determine their 3D coordinates, and then extract the map of the object surface. This strategy is carried out by some insects that use their antennae for this purpose. The other one is to slide the beam across the object, exerting a controlled force on the surface of the object to do not loose contact, and collect the 3D coordinates of points on the object surface during this movement. This strategy is utilized by some mammals that have whiskers as sensors. These strategies can be implemented using the aforementioned sensing antennae and can be used in mobile robot applications to recognize objects and the environment. In order to allow obstacle detection, the beam of the sensing antenna has to be flexible. It induces vibrations in all the structures that must be removed when the robot moves freely by an efficient control system to improve the beam positioning accuracy. Moreover, these vibrations can be used in the contact stage to estimate the 3D coordinates of the object point contacted by the antenna. In this case, efficient algorithms must be used to determine the impact instant, characterize the produced vibration, and control the force exerted by the antenna on the object. In this chapter, we will describe a prototype that we have developed and detail all the signal processing and control algorithms involved in its functioning.