This paper presents a method to measure gripping force of a bipedal wall-climbing robot (WCR) with spiny toe pads. The spiny toe pad is designed based on inspiration of an insect’s tarsal system. Each foot of the robot consists of a pair of opposed linear spiny arrays. The foot employs a pulley system to actuate the arrays via four pairs of tension and compression springs. Two Hall effect sensors are embedded into the robot feet to sense the gripping force by detecting the linear deformation of the springs. The two Hall effect sensors are calibrated and the relationship between the voltage signal output of the sensors and displacement is established before measuring gripping force. Then the consistency and accuracy of Hall effect sensor measurement method are verified by comparing with a commercial force sensor. A horizontal crawling test of the WCR is carried out and the gripping force verse time when the WCR moves. The experimental results show that the measured force history is in accordance with the actual movement states.

This paper describes a proof-of-concept non-contact strain sensor, using a magnetostrictive Fe-Ga alloy (Galfenol). Magnetostrictive materials demonstrate dimensional changes in response to a magnetic field. In contrast with typical piezoceramic materials, Galfenol is the most ductile of the current transduction materials and appears to have an excellent ability to withstand mechanical shock and tension. Galfenol also exhibits the inverse (Villari) effect: both the magnetization and permeability change in response to an applied stress. Galfenol has low hysteresis loses, less than ∼10% of its transduction potential over a range of −20 to +80 °C. The magnetization’s response to stress depends strongly on both magnetic field bias and alloy composition. Galfenol’s Villari effect can be used in various sensor configurations together with either a giant magnetoresistance (GMR) sensor, Hall Effect sensor or pickup coil to sense the magnetization / permeability changes in Galfenol when stressed. The sensor described in this paper utilizes the permeability change, which is not time dependent and can measure static loads. The design reported here targets low force, low frequency applications, such as inclination measurements and stress monitoring. The sensor was able to measure both static and dynamic stress. The static sensitivity was +3.64 Oe/kN for the Hall sensor close to the bias magnet and −1.49 Oe/kN for the Hall sensor at the other end of the Galfenol strip. We conclude that a Galfenol strain sensor is a viable candidate for bolt stress monitoring in critical applications.

Alfenol (Fe x Al 100−x ) is an alloy similar to Galfenol (Fe-Ga alloys) in crystal lattice structure and magnetostriction trend (peaking at ∼20% composition). Although single-crystal Fe 80 Al 20 exhibits lower magnetostriction (∼184 ppm, about half of Fe 80 Ga 20 ), its magneto-elastic coupling coefficient is on par with that of Fe-Ga. In addition, characteristics such as machinability and rollability are superior to that of Galfenol, making it possible to achieve textured sheets (thickness∼200 μm) which, while having a high elastic modulus, are very flexible. Furthermore, Aluminum is non toxic, cheap (∼1% the cost of Ga) and is available in abundance. These attributes make Alfenol an ideal candidate for a bio-inspired whisker-like tactile sensor (mimicking mystacial vibrissae of cats, sea lions, etc.). This work deals with the design and development of an accurate, cost efficient, real-time, and non-invasive sensor prototype that tracks displacements, vibrations and scour on bridge piers with minimal signal conditioning. Making such a sensor is possible thanks to Alfenol’s linear response to strain in the presence of appropriate bias magnets. The change in its magnetic state due to inverse magnetostriction from applied bending stresses will be observed using Hall Effect sensors to derive deflection information. A protocol to manufacture rolled and textured Alfenol whisker samples will be presented in this research. The effect of bias conditions on sensor performance will be studied empirically and by using multi-physics simulations. Optimization of the sensor by varying the dimensions of the whisker, and its correlation to flux leakage will also be examined followed by an effort to understand the micro-magnetic response of Alfenol to mechanical stimulation. Finally, results from using this biomimetic sensor to measure displacements and vibrations, and its viability to be used as a flow sensor will be discussed. The robustness of this sensor has been exploited to develop a novel real-life application to provide an early warning system for bridge pier scour due to soil transportation during a weather event. The effectiveness of these sensors for scour detection in riverbeds will subsequently be simulated in a water flume and analyzed.

This work deals with the development of a non-contact torque sensor system prototype made from rolled and textured Galfenol, a magnetostrictive alloy of Iron and Gallium. It is already known that this smart material exhibits a linear response to strain in the presence of appropriate biasing magnets. The response of a sensor system built from it follows commercially available strain gages. In this research, the magnetic change in Galfenol due to shear strain experienced by the shaft in torque will be monitored using Hall effect sensors to derive the torque information. Factors affecting the performance of this Wireless Magneto-Elastic Torque Sensor System (WIMETs) such as annealing, rolling process and strain transfer of adhesives shall be explored. The ability to provide real-time measurements with minimal signal conditioning requirements make a well-designed torque system attractive for applications such as condition based maintenance. Factors such as being non-contact and passive to the shaft, compact and easy to install, accurate, sensitive and cost effective are highly desired for any torque measurement system. A rate-of-change torque sensor that demonstrates both a sensitivity and time resolution high enough to not only recognize failing machinery, but to specifically identify the failing part is also a critical feature. These characteristics have been incorporated in the current design of WIMETs. A mathematical model for the magneto-elastic coupling along with simulations from COMSOL shall be presented. Results from static tests for various torques and dynamic tests for various torques at different RPMs will be discussed. It will be shown that the WiMET sensor system setup in a clamshell is reliable and exhibits sensitivity of up to 10mV/in-lb. over a wide range of torque (0–150 lb.-in). Its performance will be compared with a commercial torque sensor and results for detection of eccentric loads on the shaft will also be furnished.