Natural oscillations of underactuated cable-driven parallel robots

Underactuated Cable-Driven Parallel Robots (CDPR) employ a number of cables smaller than the degrees of freedom (DoFs) of the end-effector (EE) that they control. As a consequence, the EE is underconstrained and preserves some freedoms even when all actuators are locked, which may lead to undesirable oscillations. This paper proposes a methodology for the computation of the EE natural oscillation frequencies, whose knowledge has proven to be convenient for control purposes. This procedure, based on the linearization of the system internal dynamics about equilibrium con_gurations, can be applied to a generic robot suspended by any number of cables comprised between 2 and 5. The kinematics, dynamics, stability and stiffness of the robot free motion are investigated in detail. The validity of the proposed method is demonstrated by experiments on 6-DoF prototypes actuated by 2, 3, and 4 cables. Additionally, in order to highlight the interest in a robotic context, this modelling strategy is applied to the trajectory planning of a 6-DoF 4-cable CDPR by means of a frequency-based method (multi-mode input shaping), and the latter is experimentally compared with traditional non-frequency-based motion planners

Limits on the integration constant of the dark radiation term in Brane Cosmology

We consider the constraints from primordial Helium abundances on the constant of integration of the dark radiation term of the brane-world generalized Friedmann equation derived from the Randall-Sundrum Single brane model. We found that -- using simple, approximate and semianalytical Method -- that the constant of integration is limited to be between -8.9 and 2.2 which limits the possible contribution from dark radiation term to be approximately between -27% to 7% of the background photon energy density.Comment: 8 page

Workspace Computation of Planar Continuum Parallel Robots

Continuum parallel robots (CPRs) comprise several flexible beams connected in parallel to an end-effector. They combine the inherent compliance of continuum robots with the high payload capacity of parallel robots. Workspace characterization is a crucial point in the performance evaluation of CPRs. In this paper, we propose a methodology for the workspace evaluation of planar continuum parallel robots (PCPRs), with focus on the constant-orientation workspace. An explorative algorithm, based on the iterative solution of the inverse geometrico-static problem is proposed for the workspace computation of a generic PCPR. Thanks to an energy-based modelling strategy, and derivative approximation by finite differences, we are able to apply the Kantorovich theorem to certify the existence, uniqueness, and convergence of the solution of the inverse geometrico-static problem at each step of the procedure. Three case studies are shown to demonstrate the effectiveness of the proposed approach

New Five Dimensional Black Holes Classified by Horizon Geometry, and a Bianchi VI Braneworld

We introduce two new families of solutions to the vacuum Einstein equations with negative cosmological constant in 5 dimensions. These solutions are static black holes whose horizons are modelled on the 3-geometries nilgeometry and solvegeometry. Thus the horizons (and the exterior spacetimes) can be foliated by compact 3-manifolds that are neither spherical, toroidal, hyperbolic, nor product manifolds, and therefore are of a topological type not previously encountered in black hole solutions. As an application, we use the solvegeometry solutions to construct Bianchi VI$_{-1}$ braneworld cosmologies.Comment: LaTeX, 20 pages, 2 figures Typographical errors corrected, and references to printed matter added in favour of preprints where possibl

Investigation of transition frequencies of two acoustically coupled bubbles using a direct numerical simulation technique

The theoretical results regarding the ``transition frequencies'' of two acoustically interacting bubbles have been verified numerically. The theory provided by Ida [Phys. Lett. A 297 (2002) 210] predicted the existence of three transition frequencies per bubble, each of which has the phase difference of $\pi /2$ between a bubble's pulsation and the external sound field, while previous theories predicted only two natural frequencies which cause such phase shifts. Namely, two of the three transition frequencies correspond to the natural frequencies, while the remaining does not. In a subsequent paper [M. Ida, Phys. Rev. E 67 (2003) 056617], it was shown theoretically that transition frequencies other than the natural frequencies may cause the sign reversal of the secondary Bjerknes force acting between pulsating bubbles. In the present study, we employ a direct numerical simulation technique that uses the compressible Navier-Stokes equations with a surface-tension term as the governing equations to investigate the transition frequencies of two coupled bubbles by observing their pulsation amplitudes and directions of translational motion, both of which change as the driving frequency changes. The numerical results reproduce the recent theoretical predictions, validating the existence of the transition frequencies not corresponding to the natural frequency.Comment: 18 pages, 8 figures, in pres

Kajian Penerapan Teknologi Biofilter Skala Komunal Untuk Memenuhi Standar Perencanaan Pengolahan Air Limbah Domestik

Ancaman pencemaran air limbah terhadap sumber air baku air minum dapat terus meningkat apabila upaya peningkatan akses sanitasi tidak diiringi dengan teknologi yang ramah lingkungan. Salah satunya dengan teknologi pengolahan air limbah sistem biofilter, yang dapat diterapkan di kawasan perkotaan dengan keterbatasan lahan, muka air tanah tinggi, volume reaktor kecil serta mudah dalam pengoperasian karena lumpur yang dihasilkan lebih sedikit. Namun teridentifikasi kendala kendala dalam penerapan teknologi biofilter skala komunal, diantaranya umur pakai yang pendek, gangguan proses pengolahan dan efluen pengolahan belum dapat mencapai baku mutu yang dipersyaratkan. Pada tulisan ini, diuraikan kajian penerapan sistem biofilter skala komunal di beberapa kota, termasuk faktor faktor yang mempengaruhi keberlanjutan pengelolaan sistem biofilter. Sampling penerapan biofilter komunal dilakukan secara purposif sesuai variasi sistem biofiter, kondisi lokasi dan pengelola, kemudian metoda deskriptif digunakan untuk evaluasi berdasarkan karakteristik tersebut. Desain unit proses biofilter dikaji berdasarkan penyisihan/penguraian bahan organik sebagai BOD, yang didekati dengan reaksi orde pertama kinetika plug flow. Hasil studi menunjukkan faktor faktor yang mempengaruhi keberlanjutan sistem adalah desain unit proses, media biofilter, karakteristik influen, konsumsi pemakaian air, kapasitas pengolahan, media biofilter, proses pembentukan biofilm pada tahap pembibitan dan aklimatisasi, bahan dan konstruksi serta pengelolaan. Beberapa penerapan sistem biofilter yang memenuhi kriteria desain serta pengelolaan yang tepat, dapat menghasilkan air olahan sesuai Keputusan Menteri KLH no 112 tahun 2003 atau Perda terkait, serta berpotensi diolah kembali untuk daur ulang tertentu. Didalam penyusunan standar sistem biofilter perlu mempertimbangkan faktor faktor tersebut, terutama dalam memenuhi standar Pd. T-04-2005-C tentang Tata cara perencanaan dan pemasangan tangki biofilter pengolahan air limbah, Pd. T-02-2004-C, tentang Pengoperasian dan pemeliharaan instalasi pengolah air limbah rumah tangga dengan Tangki Biofilter serta RSNI tentang tata cara perencanaan pengolahan air limbah setempat