Static Tactile Sensing for a Robotic Electronic Skin via an Electromechanical Impedance-Based Approach

Abstract

Tactile sensing is paramount for robots operating in human-centered environments to help in understanding interaction with objects. To enable robots to have sophisticated tactile sensing capability, researchers have developed different kinds of electronic skins for robotic hands and arms in order to realize the ‘sense of touch’. Recently, Stanford Structures and Composites Laboratory developed a robotic electronic skin based on a network of multi-modal micro-sensors. This skin was able to identify temperature profiles and detect arm strikes through embedded sensors. However, sensing for the static pressure load is yet to be investigated. In this work, an electromechanical impedance-based method is proposed to investigate the response of piezoelectric sensors under static normal pressure loads. The smart skin sample was firstly fabricated by embedding a piezoelectric sensor into the soft silicone. Then, a series of static pressure tests to the skin were conducted. Test results showed that the first peak of the real part impedance signal was sensitive to static pressure load, and by using the proposed diagnostic method, this test setup could detect a resolution of 0.5 N force. Numerical simulation methods were then performed to validate the experimental results. The results of the numerical simulation prove the validity of the experiments, as well as the robustness of the proposed method in detecting static pressure loads using the smart skin.

Static Force Measurement Using Piezoelectric Sensors

“…Since this type of sensor is not affected by leakage current, it can be effectively used for both dynamic and static measurements without the signal drift. Static force can be measured by using the change in the resonance frequency of the piezoelectric sensor [25][26][27][31][32][33]. The resonance frequency is determined by the effective stiffness (or spring constant) and mass of the sensor structure.…”

“…Liu et al have developed a static force sensing technique using an electromechanical impedance measurement with the piezoelectric resonator for smart skin applications [33]. A prototyped sensor was made of a PZT plate with a resonance frequency of 900 kHz and embedded in the skin-like soft silicon rubber material as shown in Figure 2(c).…”

“…Numerous designs of piezoelectric sensors have been suggested for static force sensing using various measurement parameters including the resonance frequency, decay time constant, and capacitance [25][26][27][28][29][30]. Recent studies also demonstrated that the electrical impedance or admittance amplitude at resonance (or antiresonance) varies by applied force-induced acoustic load variation with feasible sensitivity and linearity which can be effectively used for static force sensing [31][32][33]. Despite increasing attention for taking full advantage of piezoelectricity in static force sensing, a collective resource that provides a comprehensive review of each measurement mechanism is hardly available to date.…”

Tactile Sensors for Parallel Grippers: Design and Characterization

“…The latter are more frequently used to measure contact force intensity or magnitude. Both sensor principles may be supported by different transduction technologies, e.g., resistive [ 1 , 2 , 3 ], capacitive [ 4 , 5 ] and magnetic [ 6 , 7 , 8 ], which can be selected depending on the costs, weight, integration level, dimensions and specific task to perform. The number of papers on this subject is very large and here are reported only some among the most recent.…”

“…The bubbles, in contact with the object surface, allow for the detection of the object texture through sliding and slipping operations during manipulation tasks. Differently from the previous solution, Klimaszewski et al [ 2 ] and Liu et al [ 3 ] developed a distributed tactile sensor, i.e., a robotic skin, for contact pressure detection that uses a matrix of resistive or piezoelectric sensing elements integrated into a flexible and soft material. Suen et al [ 4 ] presented a new concept of capacitive tactile sensor to detect three axial force via five independent concentric-shape sensing electrodes, aimed to decouple the normal and shear forces and to measure torsion around the sensor axes.…”