Optimal filtering and Bayesian detection for friction-based diagnostics in machines.

Non-model-based diagnostic methods typically rely on measured signals that must be empirically related to process behavior or incipient faults. The difficulty in interpreting a signal that is indirectly related to the fundamental process behavior is significant. This paper presents an integrated non-model and model-based approach to detecting when process behavior varies from a proposed model. The method, which is based on nonlinear filtering combined with maximum likelihood hypothesis testing, is applicable to dynamic systems whose constitutive model is well known, and whose process inputs are poorly known. Here, the method is applied to friction estimation and diagnosis during motion control in a rotating machine. A nonlinear observer estimates friction torque in a machine from shaft angular position measurements and the known input voltage to the motor. The resulting friction torque estimate can be analyzed directly for statistical abnormalities, or it can be directly compared to friction torque outputs of an applicable friction process model in order to diagnose faults or model variations. Nonlinear estimation of friction torque provides a variable on which to apply diagnostic methods that is directly related to model variations or faults. The method is evaluated experimentally by its ability to detect normal load variations in a closed-loop controlled motor driven inertia with bearing friction and an artificially-induced external line contact. Results show an ability to detect statistically significant changes in friction characteristics induced by normal load variations over a wide range of underlying friction behaviors.

Stability of somatropin stored in plastic syringes for 28 days.

The stability of somatropin stored in two types of plastic syringes was studied. Reconstituted somatropin at high (3.33-mg/mL) and low (1.0-mg/mL) concentrations was stored in polypropylene and propylene-ethylene copolymer syringes at 2-8 degrees C for 28 days. The contents of all syringes were analyzed immediately and at 7, 14, 21, and 28 days by high-performance liquid chromatography for purity, potency, and preservative (m-cresol) content; pH, physical appearance, clarity, and preservative effectiveness were analyzed at the same times. Glass vials of somatropin reconstituted with diluent served as controls. Somatropin did not show significant losses in purity or potency during the 28-day study. m-Cresol concentrations decreased in both types of plastic syrings, more so in the polypropylene syringes, but remained in excess of the minimum required to pass the USP test of preservative effectiveness. On average, the contents of the propylene-ethylene copolymer syringes had greater turbidity than the contents of the polypropylene syringes and, after 21 days, had an unacceptable level of turbidity. No visible particulates were present except at 28 days in high-concentration samples stored in propylene-ethylene copolymer syringes. Somatropin 3.33 and 1.0 mg/mL was stable in polypropylene syringes for up to 28 days and in propylene-ethylene copolymer syringes for up to 14 days when stored at 2-8 degrees C.