Performance Verification of a Flexible Vibration Monitoring System

The performance of measurement or manufacturing systems in high-precision applications is dependent upon the dynamics of the system, as vibration can be a significant contributor to the measurement uncertainty and process variability. Technologies making use of accelerometers and laser vibrometers are available to rapidly measure and process structural dynamic data but the software infrastructure is yet to be available in an open source or standardised format to allow rapid inter-platform use. In this paper, we present a novel condition monitoring system, which uses commercially available accelerometers in combination with a control-monitoring infrastructure to allow for the appraisal of the performance of a measurement or manufacturing system. A field-programmable gate array (FPGA)-based control system is implemented for high-speed data acquisition and signal processing of six triaxial accelerometers, with a frequency range of 1 Hz to 6000 Hz, a sensitivity of 102.5 mV/ms−2 and a maximum sample rate of 12,800 samples per second per channel. The system includes two methods of operation: real-time performance monitoring and detailed measurement/manufacturing verification. A lathe condition monitoring investigation is undertaken to demonstrate the utility of this system and acquire typical machining performance parameters in order to monitor the “health” of the system

The effects of vibration on fringe projection systems

Mechanical vibration noise is a significant source of error in precision measuring instruments. Errors due to vibration can be detected in measurement signals, and so methods to control mechanical vibration must be considered throughout the design process. Fringe projection (FP) is a fast, non-contact and non-destructive measurement technology, that allows for the rapid form measurement of engineering components. There is an increasing demand in industry for low-intervention, factory-friendly FP systems. Vibration is reported to be a significant source of mechanical error in FP measurements, and so in order to design an effective metrology solution, it is vital to first understand the FP systems’ sensitivity to vibrational noise. In this research, a methodology for assessing the effects of vibration on the measurement accuracy and repeatability of a low-cost FP system is presented. The research includes a theoretical investigation of the effects of vibration on FP measurements using a computational simulation technique, as well as an experimental study, which is compared with the simulated results. The methodology presented here allows for the rapid benchmarking of a given FP system operating in any configuration, and can be used to define the required vibrational performance parameters of the system

Rapid tracking of extrinsic projector parameters in fringe projection using machine learning

In this work, we propose to enable the angular re-orientation of a projector within a fringe projection system in real-time without the need for re-calibrating the system. The estimation of the extrinsic orientation parameters of the projector is performed using a convolutional neural network and images acquired from the camera in the setup. The convolutional neural network was trained to classify the azimuth and elevation angles of the projector approximated by a point source through shadow images of the measured object. The images used to train the neural network were generated through the use of CAD rendering, by simulating the illumination of the object model from different directions and then rendering an image of its shadow. The accuracy to which the azimuth and elevation angles are estimated is within 1 classification bin, where 1 bin is designated as a ±10° patch of the illumination dome. To evaluate use of the proposed system in fringe projection, a pyramidal additively manufactured object was measured. The point clouds generated using the proposed method were compared to those obtained by an established fringe projection calibration method. The maximum dimensional error in the point cloud generated when using the convolutional network as compared to the established calibration method for the object measured was found to be 1.05 mm on average

Characterisation of a multi-view fringe projection system based on the stereo matching of rectified phase maps

Multi-view fringe projection systems can be effective solutions to address the limitations imposed by the limited field of view, line-of-sight issues and occlusions when measuring the geometry ofcomplex objects, associated with single camera-projector systems. However, characterisation of a multi-view system is challenging since it requires the cameras and projectors to be in a common global coordinate system. We present a method for characterising a multi-view fringe projection system which does not require the characterisation of the projector. The novelty of the methodlies in determining the correspondences in the phase domain using the rectified unwrapped phase maps and triangulating the matched phase values to reconstruct the three-dimensional shape of theobject. A benefit of the method is that it does not require registration of the point clouds acquired from multiple perspectives. The proposed method is validated by experiment and comparison with a conventional system and a contact coordinate measuring machine

The effects of vibration on fringe projection systems

Mechanical vibration noise is a significant source of error in precision measuring instruments. Errors due to vibration can be detected in measurement signals, and so methods to control mechanical vibration must be considered throughout the design process. Fringe projection (FP) is a fast, non-contact and non-destructive measurement technology, that allows for the rapid form measurement of engineering components. There is an increasing demand in industry for low-intervention, factory-friendly FP systems. Vibration is reported to be a significant source of mechanical error in FP measurements, and so in order to design an effective metrology solution, it is vital to first understand the FP systems’ sensitivity to vibrational noise. In this research, a methodology for assessing the effects of vibration on the measurement accuracy and repeatability of a low-cost FP system is presented. The research includes a theoretical investigation of the effects of vibration on FP measurements using a computational simulation technique, as well as an experimental study, which is compared with the simulated results. The methodology presented here allows for the rapid benchmarking of a given FP system operating in any configuration, and can be used to define the required vibrational performance parameters of the system