Leonel Paredes-Madrid

Fleets of robots for precision agriculture: a simulation environment

Purpose – The purpose of this paper is to propose going one step further in the simulation tools related to agriculture by integrating fleets of mobile robots for the execution of precision agriculture techniques. The proposed new simulation environment allows the user to define different mobiles robots and agricultural implements.Design/methodology/approach – With this computational tool, the crop field, the fleet of robots and the different sensors and actuators that are incorporated into each robot can be configured by means of two interfaces: a configuration interface and a graphical interface, which interact with each other.Findings – The system presented in this article unifies two very different areas – robotics and agriculture – to study and evaluate the implementation of precision agriculture techniques in a 3D virtual world. The simulation environment allows the users to represent realistic characteristics from a defined location and to model different variabilities that may affect the task perf...

Detailed Study of Amplitude Nonlinearity in Piezoresistive Force Sensors

This article upgrades the RC linear model presented for piezoresistive force sensors. Amplitude nonlinearity is found in sensor conductance, and a characteristic equation is formulated for modeling its response under DC-driving voltages below 1 V. The feasibility of such equation is tested on four FlexiForce model A201-100 piezoresistive sensors by varying the sourcing voltage and the applied forces. Since the characteristic equation proves to be valid, a method is presented for obtaining a specific sensitivity in sensor response by calculating the appropriate sourcing voltage and feedback resistor in the driving circuit; this provides plug-and-play capabilities to the device and reduces the start-up time of new applications where piezoresistive devices are to be used. Finally, a method for bypassing the amplitude nonlinearity is presented with the aim of reading sensor capacitance.

Dataglove-based interface for impedance control of manipulators in cooperative human–robot environments

A dataglove-based interface is presented for tracking the forces applied by the hand during contact tasks with a 6-degree-of-freedom (DOF) manipulator. The interface uses 11 force sensors carefully placed on the palm-side fabric of a 16 DOF dataglove. The force sensors use piezoresistive technology to measure the individual force components from the hand. Based on the dataglove measurements, these components are transformed and summed to assemble the resultant force vector. Finally, this force vector is translated into the manipulator frame using orientation measurements from an inertial measurement unit placed on the dorsal side of the dataglove. Static tests show that the dataglove-based interface can effectively measure the applied hand force, but there are inaccuracies in orientation and magnitude when compared to the load cell measurements used as the reference for error calculation. Promising results were achieved when controlling the 6 DOF manipulator based on the force readings acquired from the dataglove interface; the decoupled dynamics of the dataglove interface with respect to the robot structure yielded smooth force readings of the human intention that could be effectively used in the impedance control of the manipulator.

Accurate modeling of low-cost piezoresistive force sensors for haptic interfaces

In this paper we present a new method for measuring forces using piezoresistive sensors. This method dramatically increases the accuracy and repeatability of the readings compared with traditional methods. These improvements will allow the common use of piezoresistive sensors in robotic applications, where only expensive and sophisticated force sensors such as load cells are currently used. We also present a sketch of a haptic interface under development, consisting of a data glove in which these force sensors are integrated. This interface is intended to control an Intelligent Assist Device by measuring operator-applied forces to the load. The new method proposed for measuring forces in piezoresistive sensors consists of reading conductance and capacitance by applying DC and sinusoidal waveforms to the sensors, thereby allow us to determine a multivariable estimation of force, instead of using the traditional, purely resistive model that has been used up to now.

Underlying Physics of Conductive Polymer Composites and Force Sensing Resistors (FSRs). A Study on Creep Response and Dynamic Loading

Force Sensing Resistors (FSRs) are manufactured by sandwiching a Conductive Polymer Composite (CPC) between metal electrodes. The piezoresistive property of FSRs has been exploited to perform stress and strain measurements, but the rheological property of polymers has undermined the repeatability of measurements causing creep in the electrical resistance of FSRs. With the aim of understanding the creep phenomenon, the drift response of thirty two specimens of FSRs was studied using a statistical approach. Similarly, a theoretical model for the creep response was developed by combining the Burger’s rheological model with the equations for the quantum tunneling conduction through thin insulating films. The proposed model and the experimental observations showed that the sourcing voltage has a strong influence on the creep response; this observation—and the corresponding model—is an important contribution that has not been previously accounted. The phenomenon of sensitivity degradation was also studied. It was found that sensitivity degradation is a voltage-related phenomenon that can be avoided by choosing an appropriate sourcing voltage in the driving circuit. The models and experimental observations from this study are key aspects to enhance the repeatability of measurements and the accuracy of FSRs.

Improving the performance of piezoresistive force sensors by modeling sensor capacitance

Piezoresistive force sensors exhibit considerable lower accuracy compared with load cells and force measuring systems based in strain gauges, however a new method for measuring forces using piezoresistive sensors is described in this paper, leading to a considerable increase in the repeatability of force readings. The new method consists of reading sensors conductance and capacitance by applying DC and sinusoidal waveforms, thereby allow us to determine a multivariable estimation of force, instead of using the traditional, purely resistive model that has been used up to now. A study of sensor nonlinearities is also described which will allow us to determine the optimal setup to perform capacitance readings under sinusoidal excitation.