564 research outputs found
Perspective distortion modeling for image measurements
A perspective distortion modelling for monocular view that is based on the fundamentals of perspective projection is presented in this work. Perspective projection is considered to be the most ideal and realistic model among others, which depicts image formation in monocular vision. There are many approaches trying to model and estimate the perspective effects in images. Some approaches try to learn and model the distortion parameters from a set of training data that work only for a predefined structure. None of the existing methods provide deep understanding of the nature of perspective problems. Perspective distortions, in fact, can be described by three different perspective effects. These effects are pose, distance and foreshortening. They are the cause of the aberrant appearance of object shapes in images. Understanding these phenomena have long been an interesting topic for artists, designers and scientists. In many cases, this problem has to be necessarily taken into consideration when dealing with image diagnostics, high and accurate image measurement, as well as accurate pose estimation from images. In this work, a perspective distortion model for every effect is developed while elaborating the nature of perspective effects. A distortion factor for every effect is derived, then followed by proposed methods, which allows extracting the true target pose and distance, and correcting image measurements
Novel design and position control strategy of a soft robot arm
This article presents a novel design of a continuum arm, which has the ability to extend and bend efficiently. Numerous designs and experiments have been done to different dimensions on both types of McKibben pneumatic muscle actuators (PMA) in order to study their performances. The contraction and extension behaviour have been illustrated with single contractor actuators and single extensor actuators, respectively. The tensile force for the contractor actuator and the compressive force for the extensor PMA are thoroughly explained and compared. Furthermore, the bending behaviour has been explained for a single extensor PMA, multi extensor actuators and multi contractor actuators. A two-section continuum arm has been implemented from both types of actuators to achieve multiple operations. Then, a novel construction is proposed to achieve efficient bending behaviour of a single contraction PMA. This novel design of a bending-actuator has been used to modify the presented continuum arm. Two different position control strategies are presented, arising from the results of the modified soft robot arm experiment. A cascaded position control is applied to control the position of the end effector of the soft arm at no load by efficiently controlling the pressure of all the actuators in the continuum arm. A new algorithm is then proposed by distributing the x, y and z-axis to the actuators and applying an effective closed-loop position control to the proposed arm at different load conditions
The design and mathematical model of a novel variable stiffness extensor-contractor pneumatic artificial muscle
This article presents the design of a novel Extensor-Contractor Pneumatic Artificial Muscle (ECPAM). This new actuator has numerous advantages over traditional pneumatic artificial muscles. These include the ability to both contract and extend relative to a nominal initial length, the ability to generate both contraction and extension forces and the ability to vary stiffness at any actuator length. A kinematic analysis of the ECPAM is presented in this article. A new output force mathematical model has been developed for the ECPAM based on its kinematic analysis and the theory of energy conservation. The correlation between experimental results and the new mathematical model has been investigated and show good correlation. Numerous stiffness experiments have been conducted to validate the variable stiffness ability of the actuator at a series of specific fixed lengths. This has proven that actuator stiffness can be adjusted independently of actuator length. Finally a stiffness-position controller has been developed to validate the effectiveness of the novel actuator
Bidding at Sequential First-Price Auctions with(out) Supply Uncertainty: A Laboratory Analysis
We report on a series of experiments that test the effects of an uncertain supply on the formation of bids and prices in sequential first-price auctions with private-independent values and unit-demands. Supply is assumed uncertain when buyers do not know the exact number of units to be sold (i.e., the length of the sequence). Although we observe a non-monotone behavior when supply is certain and an important overbidding, the data qualitatively support our price trend predictions and the risk neutral Nash equilibrium model of bidding for the last stage of a sequence, whether supply is certain or not. Our study shows that behavior in these markets changes significantly with the presence of an uncertain supply, and that it can be explained by assuming that bidders formulate pessimistic beliefs about the occurrence of another stage.Financial support from the University of Valencia (project GV98_08/2960) and from a EU-TMR ENDEAR Network Grant (FMRX-CT98-0238) is gratefully acknowledged
Π‘ΠΈΡΡΠ΅ΠΌΠ½ΡΠΉ ΠΏΠΎΠ΄Ρ ΠΎΠ΄ ΠΊ ΡΠΏΡΠ°Π²Π»Π΅Π½ΠΈΡ ΡΠΊΠΎΠ½ΠΎΠΌΠΈΠΊΠΎΠΉ Π·Π½Π°Π½ΠΈΠΉ
ΠΠΏΠΈΡΡΠ²Π°ΡΡΡΡ ΠΎΡΠΎΠ±Π΅Π½Π½ΠΎΡΡΠΈ ΠΈ ΡΡΠΎΠ²Π½ΠΈ ΡΠΏΡΠ°Π²Π»Π΅Π½ΠΈΡ ΡΠΊΠΎΠ½ΠΎΠΌΠΈΠΊΠΎΠΉ Π·Π½Π°Π½ΠΈΠΉ. Π§Π΅ΡΠ΅Π· ΡΠΈΡΡΠ΅ΠΌΠ½ΡΠΉ ΠΏΠΎΠ΄Ρ
ΠΎΠ΄ Π² ΡΠΎΠ²ΡΠ΅ΠΌΠ΅Π½Π½ΠΎΠΌ ΠΌΠ΅Π½Π΅Π΄ΠΆΠΌΠ΅Π½ΡΠ΅ ΡΠ°ΡΡΠΌΠ°ΡΡΠΈΠ²Π°Π΅ΡΡΡ ΠΎΡΠ³Π°Π½ΠΈΠ·Π°ΡΠΈΠΎΠ½Π½ΠΎΠ΅ ΠΈ ΡΠ΅ΡΡΡΡΠ½ΠΎΠ΅ ΡΠΏΡΠ°Π²Π»Π΅Π½ΠΈΠ΅ ΡΠΊΠΎΠ½ΠΎΠΌΠΈΠΊΠΎΠΉ Π·Π½Π°Π½ΠΈΠΉ. ΠΠ±ΠΎΡΠ½ΠΎΠ²ΡΠ²Π°Π΅ΡΡΡ Π²Π·Π°ΠΈΠΌΠΎΠΎΠ±ΡΡΠ»ΠΎΠ²Π»Π΅Π½Π½ΠΎΡΡΡ ΡΠ°Π·Π²ΠΈΡΠΈΡ ΡΠΎΠ²ΡΠ΅ΠΌΠ΅Π½Π½ΠΎΠ³ΠΎ ΠΌΠ΅Π½Π΅Π΄ΠΆΠΌΠ΅Π½ΡΠ° ΠΈ ΡΠΊΠΎΠ½ΠΎΠΌΠΈΠΊΠΈ Π·Π½Π°Π½ΠΈΠΉ. ΠΠ΅Π½Π΅Π΄ΠΆΠΌΠ΅Π½Ρ ΠΏΠΎΡΡΠΌΠΎΠ΄Π΅ΡΠ½Π° ΡΠ²Π»ΡΠ΅ΡΡΡ Π΄ΡΠ°ΠΉΠ²Π΅ΡΠΎΠΌ Π΄Π»Ρ ΡΠΎΠ²Π΅ΡΡΠ΅Π½ΡΡΠ²ΠΎΠ²Π°Π½ΠΈΡ ΡΡΡΠ°ΡΠ΅Π³ΠΈΡΠ΅ΡΠΊΠΎΠΉ ΠΊΠΎΠ½ΡΠ΅ΠΏΡΠΈΠΈ ΡΠΊΠΎΠ½ΠΎΠΌΠΈΠΊΠΈ Π·Π½Π°Π½ΠΈΠΉ, ΠΈ ΠΏΠΎΡΠ»Π΅Π΄Π½ΡΡ, Π² ΡΠ²ΠΎΡ ΠΎΡΠ΅ΡΠ΅Π΄Ρ, Π²Π½ΠΎΡΠΈΡ ΠΊΠΎΡΡΠ΅ΠΊΡΠΈΠ²Ρ Π² ΡΡΠ°Π΅ΠΊΡΠΎΡΠΈΡ Π΄ΠΈΠ½Π°ΠΌΠΈΠΊΠΈ ΠΌΠ΅ΡΠΎΠ΄ΠΎΠ»ΠΎΠ³ΠΈΠΈ ΡΠΎΠ²ΡΠ΅ΠΌΠ΅Π½Π½ΠΎΠ³ΠΎ ΠΌΠ΅Π½Π΅Π΄ΠΆΠΌΠ΅Π½ΡΠ°
Bioreactor analyses of tissue ingrowth, ongrowth and remodelling around implants: an alternative to live animal testing
Introduction: Preclinical assessment of bone remodelling onto, into or around novel implant technologies is underpinned by a large live animal testing burden. The aim of this study was to explore whether a lab-based bioreactor model could provide similar insight. Method: Twelve ex vivo trabecular bone cylinders were extracted from porcine femora and were implanted with additively manufactured stochastic porous titanium implants. Half were cultured dynamically, in a bioreactor with continuous fluid flow and daily cyclic loading, and half in static well plates. Tissue ongrowth, ingrowth and remodelling around the implants were evaluated with imaging and mechanical testing. Results: For both culture conditions, scanning electron microscopy (SEM) revealed bone ongrowth; widefield, backscatter SEM, micro computed tomography scanning, and histology revealed mineralisation inside the implant pores; and histology revealed woven bone formation and bone resorption around the implant. The imaging evidence of this tissue ongrowth, ingrowth and remodelling around the implant was greater for the dynamically cultured samples, and the mechanical testing revealed that the dynamically cultured samples had approximately three times greater push-through fixation strength (p < 0.05). Discussion: Ex vivo bone models enable the analysis of tissue remodelling onto, into and around porous implants in the lab. While static culture conditions exhibited some characteristics of bony adaptation to implantation, simulating physiological conditions with a bioreactor led to an accelerated response
PA-Tree: A Parametric Indexing Scheme for Spatio-temporal Trajectories
Abstract. Many new applications involving moving objects require the collec-tion and querying of trajectory data, so efficient indexing methods are needed to support complex spatio-temporal queries on such data. Current work in this domain has used MBRs to approximate trajectories, which fail to capture some basic properties of trajectories, including smoothness and lack of internal area. This mismatch leads to poor pruning when such indices are used. In this work, we revisit the issue of using parametric space indexing for historical trajectory data. We approximate a sequence of movement functions with single continuous polynomial. Since trajectories tend to be smooth, our approximations work well and yield much finer approximation quality than MBRs. We present the PA-tree, a parametric index that uses this new approximation method. Experiments show that PA-tree construction costs are orders of magnitude lower than that of com-peting methods. Further, for spatio-temporal range queries, MBR-based methods require 20%β60 % more I/O than PA-trees with clustered indicies, and 300%β 400 % more I/O than PA-trees with non-clustered indicies.
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