A new system for the in situ recalibration of force platforms

Force platforms (FPs) are complex precision instruments and need an accurate calibration procedure, usually made by the manufacturer before delivery. Usage and age may change the instrument sensitivity leading to a significant lack of precision of the instrument. A new system for the periodical recalibration of 6 components FPs was designed. By the system the (6x6) calibration matrix is estimated and the data accuracy of the FP is optimized. This system differs mainly from a similar work previously presented in its simpler structure and easier and more accurate calibration procedure

Portable systems for the periodical in-situ calibration of force platforms

A system, for the in situ calibration of six-component force platforms, is presented. By the system, the calibration matrix of the force platform is accurately and precisely estimated, using a non-linear, weighted least square algorithm. The algorithm assumes that the calibration inputs are 3D, time-varying, known loads, not constrained in their direction of application, and applied to the force platform in different points, of known coordinates. The data are acquired by means of a device ad hoc designed. The device is simple in its structure, and the procedure is easy to be performed, also by non technical personnel. In the device, a high precision, 3D load cell is used. We show that, by means of the proposed system, the force platform functioning can be optimized, by processing its output signals, with the newly estimated calibration matrix

A portable system for in-situ calibration of force platforms: Theoretical validation

The periodic calibration of measurement devices, such as force platforms (FPs), guarantees and optimizes the quality of the acquired data. In this study, the theoretical validation of a portable system for the in-situ calibration of six-component FPs is presented. A least-squares algorithm, that estimates the FP re-calibration matrix, was designed and tested using a simulation approach. The algorithm is the core of a portable system, described in a separate paper, and represents a refinement of an algorithm previously presented by Cappello et al. [Cappello A, Lenzi D, Chiari L. Periodical in-situ re-calibration of force platforms: a new method for the robust estimation of the calibration matrix. Med Biol Eng Comput 2004;42:350\u20135]. The new algorithm assumes that the calibration inputs are known, 3-D, time-varying loads, applied to the FP at known coordinates, and not constrained in their direction of application. Simulation results confirmed the a priori identifiability of the re-calibration matrix and some of the algorithm features were optimized in the perspective of an actual building of the system.With the aid of simple sinusoidal loads, applied in at least five different points, we proved that the algorithm can ensure errors less than 0.2 N and 0.4 Nm when calculating force and moment components of an applied load

A new system for the in-situ recalibration of force platforms

Force platforms (FPs) are complex precision instruments and need an accurate calibration procedure, usually made by the manufacturer before delivery. Usage and age may change the instrument sensitivity leading to a significant lack of precision of the instrument. A new system for the periodical recalibration of 6 components FPs was designed. By the system the (6x6) calibration matrix is estimated and the data accuracy of the FP is optimized. This system differs mainly from a similar work previously presented in its simpler structure and easier and more accurate calibration procedure

Non-linear re-calibration of force platforms

Force platforms (FPs) are used in human movement analysis to measure the ground reaction force and the center of pressure (COP), and calculate derived kinetic and energetic quantities. We propose a re-calibration method that compensates for the FP non-linearity induced by top plate bending under loading. The method develops a previous solution that was proposed for a linear re-calibration and proved suitable for both local and global error compensation (Cedraro et al., 2008). The new method was experimentally tested on 4 commercial FPs by estimating the non-linear re-calibration matrix in a first training trial and by using it to assess the three force components and the COP in a validation trial, comparing the new method to the previously proposed solution for global, linear re-calibration. The average COP accuracy (mm) in the training trial was (mean\ub1std): 2.3\ub11.4, 2.6\ub11.5, 11.8\ub14.3, 14.0\ub12.5 for the 4 FPs before re-calibration, and 0.7\ub10.4, 0.6\ub10.2, 0.5\ub10.2, 2.3\ub11.3 after non-linear re-calibration. In the validation trial, for one of the 4 tested FPs, mean errors for the three force components (N) and COP (mm) were: 3.6\ub12.3 (F(X)), 3.0\ub10.7 (F(Y)), 5.0\ub12.5 (F(Z)), 1.2\ub10.68 (COP) after linear re-calibration, and 2.5\ub10.7 (F(X)), 2.6\ub10.5 (F(Y)), 3.9\ub11.2 (F(Z)), 0.6\ub10.3 (COP) after non-linear re-calibration. The proposed global, non-linear method performed equally well as the local, linear re-calibration method, proving well-suited to compensate for the mild non-linear behavior of FP with the advantage of estimating a single re-calibration matrix

The role of serum uric acid in severe sepsis among patients admitted to Internal Medicine

Background: High serum uric acid(SUA) levels are associated tocardiovascular diseases and death. We evaluated the role of SUA insepsis.Methods:in 2015 we enrolled all septic patients admitted to our de-partment. Age, sex, hypertension, diabetes,cancer, CHF, COPD, smoking,blood gas analysis, SUA, days of hospitalization, death or UTI transferand SOFA were collected. Relationships were explored with bivariatecorrelation. Continuous variables were compared with t-test, dichoto-mous with chi-squared test. Univariate model was used to control for covariates. Analysis was performed with SPSS 13.0 for Windows.Results: 71 patients (M: 49,3%), mean age 76,8 (\ub115,4) years wereenrolled. Hypertension affected 72,9%, diabetes 28,2%, cancer 25,4%,CHF 43,7%, COPD 12,7% of subjects. Mean SUA was 6,49 (\ub10,41)mg/dL, mean SOFA 4,34 (\ub10,24), admission lasted 11,65 (\ub10,68)days. Death or UTI transfer happened in 32,4%. SUA was associatedto SOFA (p<0,05) and death or UTI transfer (p<0,001) at bivariate test.Patients who died or were transferred to UTI had higher SUA(7,68\ub15,07) than survivors (5,92\ub12,24; p<0,05). SUA and SOFA(r2=0,84; p<0,0001) had an exponential relationship. Univariate modeladopted SOFA as outcome,SUA as predictor, age, sex, hypertension,smoking, diabetes, cancer, CHF and COPD as covariates: SUA 657.0 hadsignificantly (p=0.01) higher SOFA (5,13\ub10,72) than patients with SUAbetween 4.0-6.9 (3,56\ub10,86) and SUA <4.0 (3,40\ub10.86).Conclusions:Increased SUA is associated to complexity and severity in sepsis. Subjects with hyperuricemia had higher mortality and SOFA.Larger studies are required to clarify this observatio