PVDF ultrasonic sensors for location of small objects

Abstract

Abstract Ultrasonic proximity sensors are, in general, too bulky to be placed directly on robotic end-effectors, such as grippers or anthropomorphic hands, which are also equipped with force-torque or tactile sensors and include part of the electronic unit. For this reason there is a pressing need to reduce the size and weight of any kind of sensory system mounted on robotic end-effectors and many efforts are being directed toward this aim. In the field of ultrasonic sensors, since the strong damping introduced by air imposes work at low frequency (not higher than a few hundred kHz), restricted choices of materials and transducer shape and dimension are necessary. This work presents an ultrasonic sensor for robotic grasping systems and short-range application, based on ferroelectric polymer technology, which is very light, small and cost-effective. The sensor, quite similar in configuration to what has already been considered elsewhere, consists of two unimodal transducers realized by curving a strip of 24 μm thick PVDF in a hemicylindrical configuration. The ultrasonic sensor has a theoretical resonance frequency of about 175 kHz and operates in a short range of 200 mm, although lower-frequency transducers can be used up to 400 mm. Details on the transducer design and characterization will be given and its application for the location of randomly oriented objects a few milimetres in size will be discussed. Finally, the calculation of the tilt of both flat and rough surfaces between 0 and 30° is considered.