Shaft Speed Determination via Vibration Signal Analysis
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Solution Overview
Problem
Existing methods for determining the rotational speed of shafts in rotating machinery powered by reciprocating engines require dedicated hardware like encoders or tachometers, which can be costly and impractical to install, especially in situations where stopping the machine is not feasible.
Innovation Solution
The method uses standard vibration sensors mounted on distant machinery components to record and process vibrations related to the engine's firing sequence, calculating the rotational speed without additional instrumentation, by deriving an instantaneous frequency signal and creating a shaft speed vector based on the combustion process's torsional oscillations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If dedicated hardware like tachometers or encoders is installed on the shaft to determine rotational speed, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The system uses the vibration sensor already installed on the machinery for its primary purpose (condition monitoring) to also provide rotational speed information. The same sensor and data acquisition system serve dual functions: monitoring vibration for bearing health and extracting speed information from the vibration signal's frequency content, eliminating the need for separate tachometer or encoder hardware
Solution Approach 2:
The vibration sensor and data processing system are designed to perform multiple functions simultaneously: condition monitoring of rotating machinery and determination of rotational speed. By analyzing the frequency spectrum of the vibration signal, the system extracts speed information without requiring dedicated speed measurement instrumentation
2Measurement precision
If dedicated hardware like tachometers or encoders is installed on the shaft to determine rotational speed, then measurement precision is improved, but installation difficulty increases due to limited accessibility
Solution Approach 1:
The system uses the vibration sensor already installed on the machinery for its primary purpose (condition monitoring) to also provide rotational speed information. The same sensor and data acquisition system serve dual functions: monitoring vibration for bearing health and extracting speed information from the vibration signal's frequency content, eliminating the need for separate tachometer or encoder hardware
Solution Approach 2:
The vibration signal acts as an intermediary that carries information about both the mechanical condition of the bearing and the rotational speed of the shaft. By analyzing this intermediate signal, the system derives speed information without needing direct access to the shaft for installing additional sensors
3Measurement precision
If the machine is stopped to install dedicated speed measurement hardware, then installation precision is improved, but productivity is reduced due to downtime
Solution Approach 1:
The system enables rotational speed measurement without stopping the machine by utilizing the vibration signal continuously generated during normal operation. The data acquisition system processes the vibration signal in real-time to extract speed information, allowing the machinery to remain operational and eliminating installation downtime
Solution Approach 2:
The system uses the vibration sensor already installed on the machinery for its primary purpose (condition monitoring) to also provide rotational speed information. The same sensor and data acquisition system serve dual functions: monitoring vibration for bearing health and extracting speed information from the vibration signal's frequency content, eliminating the need for separate tachometer or encoder hardware
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for a robust determination of shaft rotational speed without additional hardware, reducing complexity and cost, and can be used in condition monitoring systems to assess the mechanical condition of rotating machinery.
Implementation Method 1
The vibration generated by the rotating machine is recorded by means of dedicated sensors, for example accelerometers
Implementation Method 2
Hilbert Transform and Analytical Signal, Transform Applications in Mechanical Vibration
Data Source
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AI summary
A method of automatic determination of a rotational speed of a shaft in a system powered by a reciprocating engine, comprises a data acquisition and measurement processes, performed in a computer device for acquiring and processing the data, wherein the step of measuring data comprises the measurement of a vibration signal x[n], where n is the length of the acquired signal, of the rotational shaft, further comprises the steps of: obtaining an instantaneous angle signal xiA[n] of the measured vibration signals x[n] given to a standard preprocessing actions for receiving a filtered vibration signal samples xF[n] and receiving an analytic signal xA[n]; calculating an instantaneous frequency signal xiF[n] as the sample derivative of the instantaneous angle signal xiA[n] of the analytic signal xA[n]; creating an impulses samples vector M[m] from the time domain plot of the instantaneous frequency signal xiF[n], which vector represents the torsional oscillations of the shaft caused by abrupt combustion process of the reciprocating engine and determination of the shaft speed vector S[m].