Online Structural Health Monitoring and Parameter Estimation for Vibrating Active Cantilever Beams Using Low-Priced Microcontrollers

Abstract

This paper presents a structural health monitoring and parameter estimation system for vibrating active cantilever beams using low-cost embedded computing hardware. The actuator input and the measured position are used in an augmented nonlinear model to observe the dynamic states and parameters of the beam by the continuous-discrete extended Kalman filter (EKF). The presence of undesirable structural change is detected by variations of the first resonance estimate computed from the observed equivalent mass, stiffness, damping, and voltage-force conversion coefficients. A fault signal is generated upon its departure from a predetermined nominal tolerance band. The algorithm is implemented using automatically generated and deployed machine code on an electronics prototyping platform, featuring an economically feasible 8-bit microcontroller unit (MCU). The validation experiments demonstrate the viability of the proposed system to detect sudden or gradual mechanical changes in real-time, while the functionality on low-cost miniaturized hardware suggests a strong potential for mass-production and structural integration. The modest computing power of the microcontroller and automated code generation designates the proposed system only for very flexible structures, with a first dominant resonant frequency under 4 Hz; however, a code-optimized version certainly allows much stiffer structures or more complicated models on the same hardware.

An Actively Controlled Journal Bearing With Increased Resistance to Instability

“…Additionally, it should be emphasized that research was focused at rigid rotors and the journal bushing of the cylindrical bore, where the journal motion is measured at the location closest to the bearing bushing. The research work resulted in putting into operation of the active vibration control system, which became the first functional bearing prototype known up to now [Tuma 2013]. The mechanical arrangement of the actively controlled bearing is shown on the right of Fig.…”

“…Application besides communication with CompactRIO system communicates with frequency converter using OPC communication and a switching unit that controls individual switching relays via serial communication. The performance of the supervising PC allows deploying routine rotor diagnostics [Takacs 2015].…”

“…It is known that a conventional journal bearing has a limit angular rotation speed, which can be designated as CRIT  . Analysis of the effect of the proportional feedback with P K gain on stability margin shows that the limit of the rotational speed is increased as follows [Tuma 2013] . 1…”

“…The effect of the linear proportional controller on the operational range is positive, but there are some residual deviations of the journal position. Parametric damping means that at least one parameter of the system varies periodically in time according to a sinusoidal function as was suggested by Tondl [Tondl 1991]. The gain of the proportional controller was selected as this varying parameter.…”

“…The excitation frequency was selected 30 Hz, which is approximately equal to the frequency of vibration at the low rpm. According to the theory proposed by Tondl [Tondl 1991], the frequency of 30 Hz is considered to be the basic Parametric Resonance of the controlled system. Rotor speed increases according to a ramp function as is shown in the first left panel of Fig.…”