Multi-axis Force Sensing with Pre-stressed Resonant Composite Plates : An Alternative to Strain Gauge Force Sensors

International audienceIndustrial robots embedding multi-axis force sensors at the robot/environment interface presents numerous advantages in terms of safety, dexterity and collaborative perspectives. The key-point of these developments remains the availability of cheap but sufficiently precise multi-axis force sensors. This paper proposes a model-based approach to design a new alternative to commonly used strain gauge sensors. The principle of the device relies on pre-stress resonant composite plates where feedback control and measurement are achieved with piezoelectric transducers. The main originality of this work is that the force to be measured may present multi-axis components. Based on pre-stress and piezoelectric theories, a complete electromechanical model is proposed. This one is used during the design of a resonating composite Mindlin plate, embedding piezoelectric patches. It is shown that the effects of in-plane and out-of-plane external forces can be considered as pre-stress components. These ones, at the root of buckling phenomena, alter the stiffness of the structure and shift the plate resonance frequencies. Then, by solving the eigenvalue problem of the pre-stress vibrating structure, we can find the relationship between the natural frequencies of the structure and the externally applied multi-axis force. The proof of concept of this sensor is achieved on a case study. Finally, numerical results from both, home-made and commercial, finite element software demonstrates the interest of our approach to design integrated and inexpensive multi-axis force sensors solutions

Conception d'un capteur de force / couple résonnant multi-axes pour la robotique

Les capteurs de force / couple au poignet utilisés dans les applications robotiques augmentent les performances et la flexibilité des tâches automatisées. Ils offrent également de nouvelles possibilités dans le processus de fabrication, où un contact physique entre la pièce et l'environnement est requis. La large diffusion de ces capteurs est pour le moment limitée par leurs caractéristiques. En guise d'alternative aux capteurs de force existants dans le jeu de contraintes, notre travail présente une structure composite résonante, sensible aux multiples composantes de la force prises en compte via l'effet de précontrainte. Des patchs piézoélectriques liés structurellement sont utilisés pour amener la structure à sa résonance, qui est décalée en fonction des forces appliquées. La relation entre la force et le décalage de fréquence est modélisée en tenant compte de la multi-physique de cette structure intelligente. Un prototype a été testé et validé.Wrist force/torque sensors used in robotic applications increase the performances and flexibility of the automated tasks. They also offer new possibilities in the manufacturing process, where physical contact between the work-piece and environment is required. The wide spreading of these sensors is for now restricted by their features. As an alternative to the existing strain­gauges force sensors, our work presents a resonant composite structure, which is sensitive to multiple components of force that are considered via the pre-stress effect. Structurally bonded piezoelectric patches are used to bring the structure to its resonance, which is shifted according to applied forces. The relationship between force and frequency shift is modelled considering the multi-physics of this smart structure. A prototype was tested and validated

Resonant sensors for multi-axis force and torque estimation in collaborative robotics

International audienc

Design and Validation of a Resonant Multi-Axis Force Sensor for Collaborative Robotics

International audienc