Clifford Allan Hobson

Phase-measuring methods for measurement of three-dimensional shapes in automated inspection of manufactured electronic assemblies

This paper describes research into a noncontact system for the measurement of components and solder on printed circuit boards (PCBs). The objective of the system is the inspection of the PCB to identify faults in the manufacturing process. A fringe pattern is generated on the PCB, using either interferometric methods or projection of a grating, and the image of the fringe pattern is captured and stored on a frame store. The pattern is then processed to reconstruct the 3D shape of the PCB surface from which parameters which relate to PCB integrity can be determined. Results demonstrate the feasibility of the method.

Non-Contact Ranging Using Dynamic Fringe Projection

Major advances in imaging technology have seen the advent of 3-dimensional imaging systems, and the ensuing advantages that they have over 2-dimensional systems in many situations. Both passive and active systems for 3-dimensional image production have been widely used for robot control, and for high accuracy measurements in engineering metrology. This paper will concentrate on a discussion of the development of a new instrument employing dynamic fringe projection techniques, capable of simultaneously measuring the range at each point in the field of view of, say, a CCD camera in real time. The instrument, called the Dynamic Automated Range Transducer, (DART), uses a method of fringe projection based upon the principle of triangulation. The current investigations aimed at automating the ranging process will be described, and an error analysis and theoretical maximum resolution of the system will be included.

Diffraction pattern analysis for automatic defect classification in manufactured electronic assemblies

A technique for the quality assessment of fine-pitch electronic components is described. A system for the capture of Fraunhofer diffraction patterns reflected from the component is presented. The processing of the image to enable classification by a neural network is discussed. Simulation results are presented, showing the feasibility of the technique.

Data compression for digital video cameras in online machine vision systems

The work has set out to investigate the application of data compression on real-time images used in shape measurement and machine vision applications. The quality of monochromatic images produced from compression based on the lossless schemes and DCT transform were analyzed for their degradation level. The lossy based DCT method appeared to provide the higher compression ratio of 6:1 required. Special concern was focused into the fringe pattern analysis area, whereby how the degraded compressed fringe images could possibly effect the accuracy of its application output. The real-time image compression mechanism is anticipated for a seamless transmission to a personal computer, through a standard interface channel.

Optical measurement of solder bonds on printed circuit boards

This paper describes research into a non-contact system for the measurement of components and solder on printed circuit boards (PCBs). The objective of the system is the inspection of the PCB to identify faults in the manufacturing process. Two approaches are described: diffraction pattern analysis and fringe pattern analysis. For the diffraction pattern analysis, a diffraction pattern is formed by the lead array on a component. For fringe pattern analysis, a fringe pattern is generated on the PCB using either interferometric methods or projection of a grating. For both methods, an image of the pattern is captured and stored on a frame store. The pattern is then processed to provide data from which parameters which relate to solder joint integrity can be determined. Results demonstrate the feasibility of the methods.

Automated measurement of human body shape and curvature using computer vision

A system to measure the surface shape of the human body has been constructed. The system uses a fringe pattern generated by projection of multi-stripe structured light. The optical methodology used is fully described and the algorithms used to process acquired digital images are outlined. The system has been applied to the measurement of the shape of the human back in scoliosis.

Detection and measurement of surface defects by automatic fringe analysis

Abstract A novel measurement and inspection system for the detection and measurement of surface defects, such as chips and cracks, has been developed and applied to engineering components such as cylindrical rollers. The position, depth and volume of such a defect can be determined automatically. Measurement of such defects requires that three-dimensional information be made available for computer analysis. This is achieved by using a grating projection technique to provide contour fringes on the object, i.e. to give depth information. The contoured object is viewed by a charge coupled device (CCD) camera, the output of which is digitised and stored in a frame buffer from which it is available to a computer system for digital image processing, analysis and comparison. Calibration tests on defects of known size have confirmed that the system is fast and accurate.

Digital filters for surface shape recovery from phase-modulated structured light

A rarely used fringe demodulation method which uses similar technique to phase demodulation in satellite communications is demonstrated in this paper. The processing is done in the space domain utilizing zero phase digital filters. In this paper, a recursive pole-zero placement digital filter design method has been employed, and the filters have been applied to both 1-D simulated signals and real 2-D images. The results are explained and suggestions to further improve either the quality or speed of the method are also presented. Two methods of producing zero-phase digital filters are explained which is important in preserving the integrity of an image. Theoretical derivation and detailed analysis of the demodulation method and filter design are presented. Images are included as to give a better understanding of the approach. Finally, comments, improvements and comparisons of the method are included.

Digital monochrome CCD camera for robust pixel correspondant, data compression, and preprocessing in an integrated PC-based image-processing environment

This paper describes the development of a compact digital CCD camera which contains image digitization and processing which interfaces to a personal computer (PC) via a standard enhanced parallel port. Digitizing of precise pixel samples coupled with the provision of putting a single chip FPGA for data processing, became the main digital components of the camera prior to sending the data to the PC. A form of compression scheme is applied so that the digital images may be transferred within the existing parallel port bandwidth. The data is decompressed in the PC environment for a real- time display of the video images using purely native processor resources. Frame capture is built into the camera so that a full uncompressed digital image could be sent for special processing.

Parallel digital signal processing architectures for image processing

This paper describes research into a high speed image processing system using parallel digital signal processors for the processing of electro-optic images. The objective of the system is to reduce the processing time of non-contact type inspection problems including industrial and medical applications. A single processor can not deliver sufficient processing power required for the use of applications hence, a MIMD system is designed and constructed to enable fast processing of electro-optic images. The Texas Instruments TMS320C40 digital signal processor is used due to its high speed floating point CPU and the support for the parallel processing environment. A custom designed VISION bus is provided to transfer images between processors. The system is being applied for solder joint inspection of high technology printed circuit boards.