J.M. Martín

Design and implementation of an aided fruit‐harvesting robot (Agribot)

This work presents a robot prototype designed and built for a new aided fruit‐harvesting strategy in highly unstructured environments, involving human‐machine task distribution. The operator drives the robotic harvester and performs the detection of fruits by means of a laser range‐finder, the computer performs the precise location of the fruits, computes adequate picking sequences and controls the motion of all the mechanical components (picking arm and gripper‐cutter). Throughout this work, the specific design of every module of the robotized fruit harvester is presented. The harvester has been built and laboratory tests with artificial trees were conducted to check range‐finder’s localization accuracy and dependence on external conditions, harvesting arm’s velocity, positioning accuracy and repeatability; and gripper‐cutter performance. Results show excellent range‐finder and harvesting arm operation, while a bottleneck is detected in gripper‐cutter performance. Some figures showing overall performance are given.

Estimating the 3D-position from time delay data of US- waves: Experimental analysis and a new processing algorithm.

This paper presents an analysis of the main sources of error in a 3D-positioning system using ultrasonic waves, coming to different technical improvements. We suggest a new processing algorithm that will overcome the main sources of error encountered in practice. Comparing with existing processing methods, the proposed technique shows an error reduction by a factor of 20, making the system especially robust against outliers measurements.

Improving the Accuracy of Magnetostrictive Linear Position Sensors

Magnetostrictive (MS) sensors are based on the transmission of ultrasonic signals in a waveguide and constitute an interesting alternative to optical encoders for long-range absolute high-precision measurement of linear position. Despite their inherent conceptual simplicity, many aspects of the sensor design must be considered to achieve an accuracy in the 10-mum range. This paper describes research in a new kind of MS linear position sensor, focusing on the enhancement of the processes of generation, transmission, and reception of the ultrasonic waves, with the aim of obtaining high measurement accuracy. Empirical results obtained with a sensor prototype indicate an improvement of six times over the precision of standard MS sensors.

Nonlinear Performance Index (npi): A Tool for Manipulator Dynamics Improvement

The precise control of manipulators depends nonlinearly on the velocity of the motion as well as on manipulator configuration and commanded acceleration requiring complex control strategies. This paper presents a useful tool for identifying and quantifying nonlinear effects appearing during the motion of any manipulator, the Nonlinear Performance Index (npi). The npi takes into account not only the geometrical parameters defining the manipulator but also its structural dynamics through the use of inertial parameters like mass, inertia, centre of mass... The npi can be used in the design stage for analysing and reducing these undesirable nonlinear effects in any general motion or in the trajectory planning looking for paths along which more precise control is expected. The last part of the paper shows how this design optimisation and path planning has been applied to the Agribot, a fruit picking robot designed at the IAI.

Ultrasonic signal variations caused by thermal disturbances

Abstract This paper presents a study of the influence of temperature (0–60 °C) on the behaviour of different ultrasonic sensors. Measurements have been carried out by means of a sensor head connected to an automatic data-acquisition system using a controlled-temperature chamber. The influences are measured and analysed from the viewpoint of possible applications of ultrasonic sensors in environments with a wide temperature range. Special attention has been given to the study of echo signal amplitude, frequency behaviour, damping time and variations of the speed of sound; where possible a theoretical analysis of the changes is made.

Ultrasonic sensors and arc welding – a noisy mix

Evaluates the applicability of ultrasonic sensors in a welding environment and reports on experimental measurements carried out with a sensory head containing ultrasonic transducers with different frequencies. Analyses the effects on the sensors of factors such as noise, temperature and shielding gas flow and concludes by suggesting appropriate protective measures for the sensors for them to operate effectively in a welding environment.

Adaptive ultrasonic range finder for robotics

The Instituto de Automatica Industrial has carried out researches in the field of sensors since its very beginning. During the last five years, the work on sensors has been, and still is, going on within the general program of the Instituto de Automatica Industrial about Flexible Manufacturing Integrated Systems. In this field of activities the research is focused on two different topics: machining processes cutting condition appraisement and industrial robots perception. On the first one, and related with other works performed on machine-tools at the Instituto, the pursued objectives are the continuous appraisal of the cutting and tool wear down conditions and its breakage prediction. Attainment of these objectives would allow disposing of unmanned machining processes by means of adaptive control of machining parameters, dynamic compensation of machining and replacement of tool at the adequate moment.

Environment recognition in welding processes by ultrasonic sensors

Abstract The welding process is one of the most interesting industrial problems that can be solved by robotic systems. This kind of process presents different sensory aspects as environment and parts recognition, seam location and tracking, and obstacles avoidance. At the present time there is not a simple sensor for all these requirements. Nevertheless some measuring devices can satisfy particular needs. In this way, scanning-laser systems are used for locating the welding seam, vision cameras supply a survey of the general environment, tactile devices can be used to detect close obstacles in the trajectory and electric measurements by means of arc-furnish data for the fine control of the welding activity and tracking movements. This paper describes an original development and application—made in an Esprit project (Hephaestos I)—of an ultrasonic sensor focused on the environment and parts recognition for trajectory definition and real-time obstacle avoidance for welding work in large ship-repairing plants.

Photosensor tracks transients

Outlines research work on the control of flexible single‐link robot arms in which the link is modelled as a beam and the end‐point position is controlled by measuring that position and using that measurement as a basis for applying a torque to the link joint. A position sensor device [PSD] is used as the measuring device. Describes how the measurement is taken and explains the measurement circuit and how the links are analyzed. Concludes that the simplicity of the general configuration of the photosensor system and the nature of the direct data obtained allows it to be used in a wide range of applications.