Load cells have long been used to sense and measure force and torque. When properly designed and used, they are very accurate and reliable sensors. Load cells are applied in several different fields, usually for weighing measurements. Among many other things, food, vehicles, and animals are weighed daily with load cells. The gripper of a robotic arm that picks up an object can be equipped with load cells in order to provide compression force feedback to the control system to prevent the object from being damaged or released too early. Also, load cells can be used to sense the compression forces during a robot's walk to provide data for the equilibrium-controlling system. In industrial machinery, rods, beams, wheels and bars are instrumented in order to check the forces exerted on them. The volume or level of a tank can be measured indirectly by means of a load cell that monitors the total weight. Lift units can also have a load's total weight measured to prevent overload. Because of such a variety of possible applications, load cells are very important. This paper describes some of the theory and practice of load cells, including their basic elements and the electronics necessary for measurement. As an application example, the development of a 3-ring spherical load cell is presented which can be used to measure compression forces on fruit during storage and transportation is presented.

This paper presents the analysis of two air-coupled coils used to transfer energy to charge a battery. This battery is used to power an electronic device designed to monitor variables such as impact strength, range of temperature, and humidity associated with the transport of fruits. The device is inside a sealed enclosure that cannot be opened for recharging the battery. The study shows that the coupled coils need to work with a resonance capacitor, at least on the secondary coil. However, the resonance frequency also depends on the coupling factor $k$. Therefore, this work proposes a monitoring system with a closed loop for fine-tuning the resonance frequency of the secondary coil circuit. Before starting charging the battery, the system scans the resonance frequency on the primary coil and measures the output power on the secondary coil looking for the optimal point. This procedure reduces problems of coupling factor variations with positioning of the coils during the battery charging.

Interactions among local pit sites were investigated using a <mml:math display="inline"><mml:mn>5</mml:mn><mml:mo>×</mml:mo><mml:mn>5</mml:mn></mml:math>5×5 array of 25 electrodes consisting of closely spaced, flush-mounted 316 stainless steel wires. Three types of interactions occurred when actively corroding pits existed while the remaining electrodes were initially passive in 0.05 M NaCl solution. Suppression of pitting on nearby electrodes occurred due to ohmic potential drop near pre-existing pits. Enhancement of pitting at initially passive electrodes was observed and attributed to both temporary alternations in the local solution composition and a more persistent effect attributed to some action of the locally altered solution composition on nearby passive surfaces. The exact origin of the damage on the nearby passive surface is unknown. Each of these effects exhibited different periods of persistency after pit deactivation. A phenomenological model was developed and used to simulate some of the features of the experimental findings. The model included stochastic pit initiation and interactions promoted by surface damage and concentration effects or inhibited by ohmic drop. The model successfully reproduced some of experimental observations and illustrated the formation of nonrandom corrosion damage patterns even on a simulated homogeneous surface. © 2002 The Electrochemical Society. All rights reserved.

Interactions among local pit sites were investigated using an array of 25 electrodes. The array consisted of closely spaced, flush‐mounted 316 stainless steel wires polarized in solution. Two types of interactions occurred when either single or rows of actively corroding pits existed while the remaining electrodes were initially passive. Inhibition of pitting on nearby electrodes occurred due to ohmic potential drop near active pre‐existing pits. Enhancement of pitting was observed due to alterations in the local solution composition near just deactivated pits. The former effect was stronger than the latter, but the concentration effect could persist after pit deactivation. ©2000 The Electrochemical Society

Wireless power transfer is a technique usually based on an inductive link, used for delivering energy to remote devices. The power of different applications ranges from microwatts to hundreds of kilowatts, e.g., in biomedical implants and electric vehicles. The transferred power is highly dependent on the relative position between the inductive link coils. Many studies have been presented considering static or quasi-static conditions, based on a fixed tuned circuit. However, when the coils are not stationary, the inductive link must be dynamically tuned to keep the designed output power. This paper presents a methodology for dynamically tune the inductive link by means of a variable capacitance. A voltage-controlled capacitance using concepts of the negative impedance converter and capacitance multiplier is proposed. The phase angle between the input voltage and current is used as the error signal to control the variable capacitance and keep the output power operating point. The experimental evaluation shows that the proposed methodology can significantly improve the power delivered to the load in comparison to a fixed inductive link.

Road pavements are spread over large areas and convey various possibilities for energy sources such as high thermal gradients due to their materials and colors, wind corridors, large flat areas for solar harvesting, and heavy loading from traffic. The latest advances in road energy generation have been discretely implemented and have mainly focused on photovoltaic surface applications; other studies have explored the use of piezoelectric transducers with high stresses for better energy-production performance but limited life span. This study explores the stresses on pavement surfaces from traffic loading shockwaves that yield to the natural frequency vibration a piezoelectric harvester using a cantilever array. The passing vehicles triggered 16 piezoelectric sensors divided into four embedded steel profiles. The peak electrical power obtained in the experiment was 55.6 µW with a single transducer using a tip mass of 16 g. The proposed harvester demonstrated potential for applications in micro-generation of energy with limited infrastructure modification and high endurance under traffic loading over time. Its generation capacity is around 50 mWh a month with 16 piezoelectric cantilevers installed (for a commercial traffic volume of 1500 vehicles a day), enough to power a 200 m flashing LED raised marker strip to guide drivers for lane alignment during night shifts.