Richard Stamp

Automated inspection of textured ceramic tiles

Abstract An innovative object-centred approach for the visual inspection of textured ceramic tiles has been developed for the acquisition of product quality control data. A demonstrator system has been constructed for the analysis of complex surfaces, surfaces which possess detailed three-dimensional topographic features, which are concealed by coincident regular or random chromatic patterns. The technique is able to isolate mixed topographic and chromatic surface features in order to allow for subsequent separate analysis. Surface topography is captured as an array of perturbed surface normals, known as a surface bump map, while the surface reflectance is isolated as a separate albedo image. Synthetically rendered images of the bump map description allow surface topography to be viewed off-line under user defined virtual illumination conditions, and in isolation from the surface albedo. Topographic features defined by the bump map description may be subject to analysis in terms of perturbation thresholding, or integrated to recover their three-dimensional relief. The technique has application for the quality inspection of a wide range of manufactured and processed surfaces, uses a low-cost fixed lighting configuration, requires no initial training, is largely pose invariant, and has been tested on a representative range of real tile samples. Experimental results are presented in the paper.

Forces acting between polishing tool and workpiece surface in magnetorheological finishing

Magnetorheological finishing is a computer-controlled polishing technique that is used mainly in the field of high-quality optical lens production. The process is based on the use of a magnetorheological polishing fluid that is able, in a reversible manner, to change its viscosity from a liquid state to a solid state under the control of a magnetic field. This outstanding characteristic facilitates rapid control (in milliseconds) of the yield stress, and thus the pressure applied to the workpiece surface to be polished. A three-axis dynamometer was used to measure the forces acting between the magnetorheological fluid and the workpiece surface during determination of the material removal characteristic of the polishing tool (influence function). The results of a testing series using a QED Q22-X MRF polishing machine with a 50 mm wheel assembly show that the normal forces range from about 2 to 20 N. Knowledge of the forces is essential, especially when thin workpieces are to be polished and distortion becomes significant. This paper discusses, and gives examples of, the variation in the parameters experienced during a programme of experiments, and provides examples of the value of this work.

Comparison of different magnetorheological polishing fluids

Magnetorheological Finishing (MRF) is commonly used to finish high quality optical surfaces. The process is based on a magnetorheological fluid, which stiffens in a magnetic field and thus may be used as a polishing tool. The fluid removal characteristic depends on several parameters, for example the magnetic field strength or the relative velocity between workpiece and polishing tool. Another parameter is the fluid itself. Different compositions of polishing abrasives result in different removal characteristics. At the University of Applied Sciences Deggendorf, five different magnetorheological polishing fluids have been analysed. The results of the research are scanning electron microscope analyses as well as spectra analyses. The removal characteristic for each fluid has been determined for different glass materials. Finally, the fluid conditions during polishing have been analysed. For this purpose, the fluid flow rate, the fluid pressure and the fluid viscosity have been investigated.

Temporal stability and performance of MR polishing fluid

The lifetime of standard magnetorheological (MR) polishing fluids, used for example in polishing machines for optical applications, is limited. Scanning electron microscope examinations as well as chemical analyses of the fluid had been undertaken in order to investigate reasons for limited lifetime. We found out that the removal rate decreases during the course of time. However, the usable fluid life is most limited by the point of time when the critical minimum amount of fluid, necessary to ensure circulation, is reached. The results in association with a new fluid conditioner show, that a standard MR polishing fluid may be used for longer periods than common periods of about 2 weeks.

Advanced techniques for computer-controlled polishing

Computer-controlled polishing has introduced determinism into the finishing of high-quality surfaces, for example those used as optical interfaces. Computer-controlled polishing may overcome many of the disadvantages of traditional polishing techniques. The polishing procedure is computed in terms of the surface error-profile and the material removal characteristic of the polishing tool, the influence function. Determinism and predictability not only enable more economical manufacture but also facilitate considerably increased processing accuracy. However, there are several disadvantages that serve to limit the capabilities of computer-controlled polishing, many of these are considered to be issues associated with determination of the influence function. Magnetorheological finishing has been investigated and various new techniques and approaches that dramatically enhance the potential as well as the economics of computer-controlled polishing have been developed and verified experimentally. Recent developments and advancements in computer-controlled polishing are discussed. The generic results of this research may be used in a wide variety of alternative applications in which controlled material removal is employed to achieve a desired surface specification, ranging from surface treatment processes in technical disciplines, to manipulation of biological surface textures in medical technologies.

Calculation of MRF influence functions

Magnetorheological finishing (MRF) is a commonly used computer-controlled polishing (CCP) technique for high precision optical surfaces. The process is based on a magnetorheological abrasive fluid, which stiffens in a magnetic field and may be employed as a sub-aperture polishing tool. Dependent upon the surface error-profile of the workpiece and the polishing tool characteristic (influence function) an individual polishing procedure is calculated prior to processing. However, determination of the influence function remains a time consuming and laborious task. A user friendly and easy to use software tool has been developed, which enables rapid computation of MRF influence functions dependent on the MRF specific parameters, such as, magnetic field strength or fluid viscosity. The software supersedes the current cumbersome and time consuming determination procedure and thus results in considerably improved and more economical manufacture. In comparison with the conventional time period of typically 20 minutes to ascertain an influence function, it may now be calculated in a few seconds. An average quality improvement of 57% relating to the peak-valley (PV) value, and approximately 66% relating to the root-mean-square (RMS) of the surface error-profiles was observed during employment of the artificial computed influence functions for polishing.

Coherences between influence function size, polishing quality, and process time in magnetorheological finishing

Magnetorheological finishing (MRF) is a computer controlled polishing process (CCP), which is commonly used in the field of high quality optical lens production. The process uses the material removal characteristic of the polishing tool (influence function) and the surface error-profile to calculate individual, surface error-profile dependent polishing sequences. At the University of Applied Sciences Deggendorf a testing series with a magnetorheological finishing machine has been performed, and effects of the influence function size and its removal capacity on the polishing quality and the process time have been investigated. The result of the research shows that the influence function size has a major effect on the process time, whereas the polishing quality is nearly independent of the influence function size. During the testing series the process time was significantly reduced using an appropriate influence function size. The process time decreased about 9% relating to the original influence function.

New viscosity measurement for magnetorheological polishing fluid

In Magnetorheological Finishing (MRF) a magnetic field is applied to a stream of abrasive magnetorheological fluid, in order that the fluid behaves as the polishing tool. The process may be used to finish the surface of high quality optical lenses. The fluid viscosity is one important parameter the polishing tool characteristic depends on. At the University of Applied Sciences Deggendorf a new viscosity measurement, which uses the inductance of the fluid had been tested. The result of the research is a close relationship between viscosity and inductance. The new viscosity measurement is not an absolute, but a comparative system, based on inductance of the flowing fluid and the fluid age.

A cell based voronoi roadmap for motion planning of articulated robots using movement primitives

The manufacturing industry today is still focused on the maximization of production. A possible development able to support the global achievement of this goal is the implementation of a new support system for trajectory-planning, specific for industrial robots. This paper describes the trajectory-planning algorithm, able to generate trajectories manageable by human operators, consisting of linear and circular movement primitives. First, the world model and a topology preserving roadmap are stored in a probabilistic occupancy octree by applying a cell extension based algorithm. Successively, the roadmap is constructed within the free reachable joint space maximizing the clearance to the obstacles. A search algorithm is applied on robot configuration positions within the roadmap to identify a path avoiding static obstacles. Finally, the resulting path is converted through an elastic net algorithm into a robot trajectory, which consists of canonical ordered linear and circular movement primitives. The algorithm is demonstrated in a real industrial manipulator context.

A robot manipulator communications and control framework

The use of industrial scale experimental machinery robot systems such as the Mitsubishi RV-2AJ manipulator in research to experimentally prove new theories is a great opportunity. The robot manipulator communications and control framework written in Java simplifies the use of Mitsubishi robot manipulators and provides communication between a personal computer and the robot. Connecting a personal computer leads to different communication modes each with specific properties, explained in detail. Integration of the framework for scientific use is shown in conjunction with a graphical user-interface and within Simulink as a Simulink block. An example application for assisted robot program generation is described.