Andrew Warkentin

Multi-point tool positioning strategy for 5-axis machining of sculptured surfaces

Multi-point machining (MPM) is a tool positioning technique used for finish machining of sculptured surfaces. In this technique the desired surface is generated at more than one point on the tool. The concept and viability of MPM was developed by the current authors in previous works. However, the method used to generate the multi-point tool positions was slow and labor intensive. The objective of this paper is to present efficient algorithms to generate multi-point tool positions. A basic multi-point algorithm is presented based on some assumptions about the curvature characteristics of the surface underneath the tool. This basic algorithm is adequate for simple surfaces but will fail for more complex surfaces typical of industrial applications. Accordingly, tool position adjustment algorithms are developed that combine the basic algorithm with non-linear optimization to achieve multi-point tool positions on these more complex surfaces.

Comparison between multi-point and other 5-axis tool positioning strategies

Abstract A method of generating sculptured surfaces at multiple points of contact between the tool and the workpiece was developed and proven viable by the current authors in previous work. They denoted this finish machining method, “Multi Point Machining”, or simply MPM. This paper compares MPM with two other 5-axis tool positioning strategies; namely: the inclined tool, and the principal axis method. It is also compared with 3-axis ball nose machining. Comparisons are conducted using computer simulations and experimental cutting tests. Results obtained show that MPM produced scallop heights that are much smaller than those produced by the other tool positioning strategies.

Development of an automated system for measuring grinding wheel wear flats

Grinding is a time-varying process affected by factors such as wheel construction, dressing parameters, operating parameters, workpiece material, and cooling. As the grinding wheel wears, flat areas form on the wheel surface. Wear flat measurement provides information on the condition of the wheel and is, therefore, an essential tool to study the grinding process. Measuring wear flat area can be a tedious, time-consuming, or expensive process. In this paper, a new system has been developed to measure wear flat area. This system is mounted on the grinding machine and automates wear flat measurement by using computer control to automatically position the wheel and capture digital images of the wheel between grinding cycles. Image processing software is used to automatically analyze the digital images and measure wear flat area in the images. The proposed measurement system was validated using a scanning electron microscope. Experiments were performed on a Brown & Sharpe Micromaster 824 surface grinder to examine the relationship between wear flat area and normal force. The results agree with the literature.

An algorithm for resolving ‘indeterminate’ test results in the platelet serotonin release assay for investigation of heparin‐induced thrombocytopenia

Heparin-induced thrombocytopenia (HIT) is an adverse reaction to heparin anticoagulation that results in thrombocytopenia and increased risk of thrombosis. It is caused by IgG antibodies that recognize complexes of platelet factor 4 (PF4) bound to heparin or certain other polyanions, and that result in Fcc receptor (FccR)-mediated platelet activation [1–3]. HIT is a clinicopathological syndrome as the diagnosis relies on a compatible clinical picture of otherwise unexplained thrombocytopenia temporally related to heparin (typically, beginning 5– 10 days after exposure), and the detection of PF4/heparinreactive antibodies [1,4]. The 4T s scoring system has been used to predict the pretest probability of HIT using the criteria of thrombocytopenia, timing, thrombosis and the exclusion of other causes [4]; however, the diagnosis is most accurate if platelet-activating antibodies are detected [5–7]. Assays addressing both the function and the target antigen of these HIT antibodies are available [5–9]. The C-serotonin-release assay (SRA) is a functional (platelet activation) assay that has high sensitivity and specificity for detecting the antibodies that cause HIT [4,6–11]. The SRA has similar sensitivity, but superior specificity, compared with the anti-PF4-heparin enzyme-immunoassay (EIA), and is used as our gold standard assay. However, on occasion, SRA results are difficult to interpret because of heparin-independent platelet activation or other non-specific reaction profiles, yielding an indeterminate result [6]. We developed a two-step algorithm for resolving indeterminate SRA profiles. First, the SRA was repeated with another aliquot of patient serum that was newly heat inactivated, using pooled target platelets from two different platelet donors. Second, if the results were still indeterminate, then an in-house anti-PF4-heparin-IgGEIAwas used to determine the diagnosis of HIT [2,7,9]. The purpose of this study was to evaluate prospectively the ability of this algorithm to resolve indeterminate SRA reactions, with the ultimate aim of improving the diagnostic yield of HIT testing. This was a descriptive study of consecutive samples referred to the McMaster University Platelet Immunology Research Laboratory for HIT testing from patients suspected of having HIT between 2005 and 2006 (n = 2091 samples). All procedures were approved by the institutional research ethics board. The SRA was performed as previously described [8,10] using pooled platelets obtained from two pre-screened donors whose platelets were known to react well with HIT antibodies. Test serum was heat inactivated, and tested with buffer, pharmacologic (0.1 and 0.3 U mL) and high (100 U mL) concentrations of UFH (Leo Pharmaceuticals, Ballerup, Denmark), and a pharmacologic concentration (0.1 U mL) of the low molecular weight heparin (LMWH), enoxaparin (Lovenox, Sanofi-Aventis, NJ, USA). Platelets pre-incubated with IV.3 were also added to samples with 0.1 U mL UFH. The SRA result was considered positive if the sample caused ‡ 20% serotonin release with pharmacologic UFH and LMWH concentrations, and < 20% serotonin release (inhibition) with high concentrations (100 U mL) of UFH and with the FccR-blocking monoclonal antibody, IV.3. A negative SRA was defined as < 20% serotonin release at all heparin concentrations [8]. Any serum sample that induced ‡ 20% release in any of the reaction wells (including the buffer control, i.e. with no heparin added), but otherwise did not fit the HIT profile (i.e. inhibition was not observed at 100 U mL heparin or in the presence of FccR-blocking monoclonal antibody) was designated as indeterminate . An in-house PF4-heparin, IgG-specific EIA was performed in parallel with the SRA [6,9]. The EIA was used to assess for the presence (OD405 ‡0.45; EIA positive ) or absence (OD405 <0.45; EIA negative ) of anti-PF4/heparin antibodies in SRA-indeterminate samples. Samples from patients with clinical HIT tend to yield OD405 values > 1.0 [7,12]. Correspondence: Jane Moore, HSC 3H42, McMaster University, 1200 Main St W, Hamilton L8N3Z5, ON, Canada. Tel.: +1 905 5259140 ext. 22414; fax: +1 905 5296359. E-mail: moorej@mcmaster.ca

Experimental and numerical investigation into workpiece surface topology in point grinding

Point grinding is a cylindrical grinding process where the grinding wheel axis can be tilted relative to the workpiece axis by a swivel angle to yield a point contact. This feature enables complex parts to be ground in a single set-up on a point grinding machine. In this article, the effect of the swivel angle on the workpiece surface finish was investigated experimentally and numerically for different workpiece materials. There was good agreement between the measured and predicted workpiece surface roughness values Ra with an average difference of 6.3% for the three cutting speeds tested. It was also observed that, for the grinding conditions investigated, the swivel angle does not significantly influence the resulting workpiece surface roughness.

An investigation into the effect of nozzle shape and jet pressure in profile creepfeed grinding

An experimental comparison of cutting fluid delivery nozzles was carried out with application to profile creepfeed grinding. A novel method of nozzle design and development involving rapid-prototyping enabled an exhaustive experimental approach. Circular, rectangular, and elliptical orifice nozzles were compared in terms of workpiece profile error, workpiece surface roughness, and grinding power over a variety of workpiece feedrates and cutting fluid jet pressures. For the grinding conditions used in this research, it was observed that, although the circular nozzle performed best, higher nozzle inlet pressures yielded smoother workpiece surface finishes.

Modelling a Single-Wheel Testbed for Planetary Rover Applications

This paper presents a dynamic model for a smooth wheel travelling through loose sandy soil. Many models that are used for such wheel-soil interactions are typically static or quasi-static models. The new model builds upon these widely-used models by adding the dynamic effect of the soil deformation. The new model is validated using experiments that were carried on a new single wheel testbed which was constructed at Dalhousie University. During experiments with a smooth wheel it was noticed that the track of the wheel had repeatable ridges. Moreover, it was noticed that the corresponding torque and force data also had oscillations in it with the periods of the harmonic coinciding with the ridges in the sand left by the track of the wheel.Copyright

Dynamic Wheel-Soil Model for Lightweight Mobile Robots with Smooth Wheels

This paper extends traditional wheel–soil modeling for lightweight mobile robots operating with smooth wheels on dry sandy soil to capture the transient oscillations that have been observed in drawbar pull measurements. To model these drawbar pull fluctuations, a new dynamic pressure–sinkage relationship was extrapolated from the literature and experimental observations of smooth rigid wheels operating in sandy soil. The resulting two-dimensional high-fidelity analytical model was validated with a unique single-wheel testbed designed from a Blohm Planomat 408 computer-numerically-controlled creep-feed grinding machine. For the experimental conditions used in this research, the resulting model is able to predict the fluctuating values of the drawbar pull for a variety of slip ratios and normal loads tested with a smooth rigid wheel in sandy soil. The new model was tuned at a single normal load over a variety of slip ratios and was then able to predict the amplitude and frequency of the oscillations about the mean drawbar pull at different normal loads and slip ratios.

Development of a new cutting fluid delivery system for creepfeed grinding

This paper develops and validates a new cutting fluid application technique for creepfeed grinding with aluminium oxide grinding wheels. The new fluid delivery system incorporates several concepts found in the literature including high-speed fluid application, coherent jets, air scrapers and concentration effects associated with synthetic cutting fluids. Experiments were carried out on a Blohm Planomat 408 creepfeed grinding machine in Dalhousie Universitys Grinding Laboratory. These experiments show that the new coolant delivery system can achieve an 83% increase in material removal rate over a state-of-the-art coherent jet and provide the capability of keeping the liquid cutting streams separate during creepfeed grinding. As a result, this new system has the potential to significantly increase production rates.

Application of a dynamic pressure-sinkage relationship for lightweight mobile robots

This paper investigates a dynamic pressure-sinkage relationship which can be used in a wheel-soil model to better capture periodic variations observed in sinkage, drawbar pull and normal force as a rigid wheel interacts with loose sandy soil. The dynamic wheel-soil model can be used for wheels with or without grousers. Several case studies are presented to demonstrate the usefulness and applicability of this dynamic pressure-sinkage relationship. Hill climbing experiments were carried out using a smooth-wheel micro rover with a fixed suspension to confirm operational regions of the dynamic pressure-sinkage relationship. Single wheel testbed experiments were carried out to determine how well the model can predict changes in the number and length of the grousers on the wheel. It was concluded that dynamic pressure-sinkage relationship can predict the observed oscillations in the sinkage, drawbar pull and normal force with a single tuning case as the slip ratio and the configuration of the wheel changes.