L. Calderón

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.

A robotic vehicle for disabled children

One of the most frequent effects of physical disability is reduced or impaired mobility. There are a number of technical aids for all the cases of physical impairment but none of the systems described in the literature address the particular problems of children affected by neuromotor disorders accompanied by mental retardation. The following addresses the development of the PALMA [(plataforma de apoyo ludico a la movilidad alternative) (assistive platform for alternative mobility)] system as a tool to assist the mobility of children affected by cerebral palsy. PALMA is specifically adapted to a personalized and early cognitive development of children affected by severe neuromotor problems. The rehabilitation process based on PALMA has an impact on the interaction between children and environment, on their motor dexterity, and on decision-making ability.

Measuring the 3D-position of a walking vehicle using ultrasonic and electromagnetic waves

The knowledge of the true position of a walking machine (rover) in an inertial reference frame is a problem of paramount importance for realistic application of mobile robots. The points of the robot follow three-dimensional trajectories even on even terrain. When no position feedback is possible, a good knowledge of the dynamical behaviour of the rover is needed to get an estimation of the position and orientation of the robot. There already exist some sophisticated optical systems which track the path followed by specific (lighted) points of the robot. Although these systems can provide very precise measurements, they cannot cover larger areas with the same precision. This paper presents a laboratory prototype capable of measuring the position of a four-legged walking robot using a combination of electromagnetic (EM) and ultrasonic (US) waves produced by a spark-generator, avoiding any physical link between the robot and the environment.The 3D position is obtained from range data that can be estimated from the travel time of the acoustical wave from the sparking point to three static receivers. The EM wave is used for synchronization. The system provides real time data to operate in a wider space than the optical systems. After the processing and filtering of the signal, a final precision better than 1 mm is reached in a work range of about 5 m. The track-data obtained by the position meter is used to know the dynamic behaviour of the robot and to study the improvement introduced by the use of inclinometers.

Novel modeling technique for the stator of traveling wave ultrasonic motors

Traveling wave ultrasonic motors (TWUM) are a promising type of piezoelectric transducers, which are based on the friction transmission of mechanical propagating waves. These waves are excited on the stator by using high Q piezoelectric ceramics. This article presents a modeling strategy, which allows for a quick and precise modal and forced analysis of the stator of TWUM. First-order shear deformation laminated plate theory is applied to annular subdomains (super-elements) of the stator. In addition to shear deformations, the model takes into account the effect of rotary inertia, the stiffness contribution of the teeth, and the linear varying thickness of the stator. Moreover, the formulation considers a more realistic function for the electric field inside the piezoelectric ceramic, i.e., a linear function, instead of the generally assumed constant electric field. The Ritz method is used to find an approximated solution for the dynamic equations. Finally, the modal response is obtained and compared against the results from classical simplified models and the finite element method. Thus, the high accuracy and short computation times of the novel strategy were demonstrated.

Ultrasonic echoes from complex surfaces: An application to object recognition

Abstract This paper analyses the theoretical and practical possibilities of ultrasound sensors for object discrimination. The study is restricted to simple mono-element transducers working as transmitter and receiver. A method is described for comparison of the ultrasonic signals which can be used as a means of identifying an object from a previously studied set. The results of this method are described and discussed.

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.

Shaping the detection lobe of ultrasonic ranging devices

The detection lobe or radiation area of an ultrasonic ranging device is of primary importance in almost any application of such measuring systems, but in some cases the form of the lobe makes its use in real systems difficult or even impossible. The use of focusing arrays of sensors is difficult because of the large size of the transducers in air, the complexity of the processing devices and the slowness of the measuring process. In this paper we present a new way of conforming the operation field of an ultrasonic sensor that allows almost any arbitrary form to be fixed within the range of the sensor. The application of the system is studied in a sensor for blind people and in an obstacle detection sensor for mobile robots.

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.