Machine Head Research Articles

TH‐C‐213CD‐01: Accuracy of Proton Dose Computation Algorithms and Need for Improvements

There has been a tacit assumption that semi‐empirical (SE) dose calculation algorithms used in the current practice of passively scattered proton therapy (PSPT) and intensity modulated proton therapy (IMPT) are sufficiently accurate. However, the sharp distal fall‐off of protons, scattering from apertures and other beam line components, interactions of secondary particles produced from beam line components and the patient present significant challenges for the current algorithms. The resulting inaccuracies and their potential clinical impact on outcomes have not been fully appreciated, especially for complex geometries such as those encountered in lung and head and neck. Some of the factors affecting accuracy for PSPT and IMPT are similar while others are quite different. For example, PSPT accuracy is affected by the angular and energy spread of the incident beam and its interactions with compensators and apertures; whereas, scattering from beam‐line components and the transport of secondary particles are more important for IMPT. Complex heterogeneities are of relevance for both PSPT and IMPT. Furthermore, distal edge of protons, assumed to have a sharp fall‐off, may be degraded significantly after passage through heterogeneities. While IMPT may be able to compensate for such degradation, semi‐empirical models are unable to accurately predict this effect.The Monte Carlo (MC) is the most accurate method for calculating proton dose distributions. A Monte Carlo system must be appropriately commissioned by fine tuning the characteristics of the beam entering the nozzle and calibrated using measured data. Once appropriately experimentally validated, Monte Carlo may be assumed to be the “gold standard” for situations where measurements where are difficult, impossible or highly time consuming, e.g., dose distributions in patients. While efforts are being made to accelerate Monte Carlo systems through parallelization and algorithmic improvements, they are likely to be still too slow for routine clinical use especially for applications such as IMPT, robustness analyses, robust optimization, etc. Intermediate solutions, that are simplified variations of Monte Carlo, are being developed. Examples include Macro Monte Carlo, Virtual Monte Carlo and Track Repeating Algorithm for Particles. For lack of a better term, we will call the family of such solutions “abridged Monte Carlo” (aMC). They offer considerable improvement in speed with nearly the same accuracy as Monte Carlo. Nevertheless, greater speed offered by SE models would continue to be required for many of the applications mentioned. A hybrid combination of a SE model and a MC or aMC method may then be applied for certain demanding applications. For instance, in IMPT optimization, most of the iterations may be carried out using a fast SE model interspersed with a small number of MC or aMC iterations.A short introduction giving background and explaining the current state of the art and differences between PSPT and IMPT algorithms will be followed by four presentations. The first one will discuss semi‐empirical dose calculation models for PSPT, their limitations and dosimetric and potential clinical consequences, factors underlying the accuracy limitations and possible improvements. The second presentation will address similar issues for semi‐empirical algorithms for scanning beams and IMPT. The third presentation will discuss the use of Monte Carlo techniques to model proton treatment machine heads for passive scattering and patients and to model scanned beams. It will also talk about calibration and validation of MC systems, inherent uncertainties in MC methods and the efforts to make MC systems easy to use. The fourth presentation will focus on abridged‐Monte Carlo techniques. It will give an overview of acceleration of dose calculations using such techniques and describe one or more algorithms in detail. It will include such topics as transport of particles, validation and calibration, implementation of aMC into a treatment planning systems and applications for IMPT optimization.Learning Objectives:1. Understanding the physics principles underlying current semi‐empirical proton dose computation models, their assumptions and approximations and their effect on accuracy.2. Appreciating the potential impact of approximations on clinical outcomes.3. Understanding the role of Monte Carlo techniques in identifying the causes of differences between results of semi‐empirical models, measurements and Monte Carlo and in the development of more accurate algorithms.4. Learning about the current status of Monte Carlo and abridged‐Monte Carlo techniques for clinical use.Conflicts of interest: Mohan ‐ Research grant from Philips. Soukup ‐ Elekta employee.

A reactive GRASP and Path Relinking for balancing reconfigurable transfer lines

A line balancing problem for reconfigurable transfer lines with sequence-dependent setup times and parallel machines was studied. These lines are paced and serial, i.e. a part to be machined passes through a sequence of stations. Stations are composed of CNC (Computer Numerical Control) machines. At least one CNC machine is installed at each station. These CNC machines are mono-spindle head machines, hence setup times between operations have to be taken into account. The origins of setup times are various, for example, the necessity to rotate the part, change and displace the tool, etc. Because of setup times, the station workload depends on the sequence in which the operations are assigned to the station. In addition, accessibility constraints have to be considered. The objective consists of assigning a given set of operations as well as machines to a sequence of workstations in order to minimise the total cost of the line. Keeping in mind the industrial importance of this problem and the lack of available methods in the literature tackling it efficiently, we propose a new heuristic based on GRASP combined with Path Relinking. A MIP approach is used to select the sequences of operations on workstations. Numerical experiments are presented and show that the proposed heuristic can provide good solutions even for large-sized instances while requiring a computational time that is fully compatible with a practical application. An industrial case study is also described.

A mathematical model for a reconfiguration problem of transfer machining lines

In this paper, we introduce a new optimization problem that aims to minimize the reconfiguration cost of a transfer line. A line has to be reconfigured if a new product has to be produced by an existing line or any changes in product characteristics occur. In such cases, new operations have to be integrated on existing equipment while some previously assigned operations are deleted. Since transfer lines consist of a sequence of unit head machines, their reconfiguration is not an easy issue because of numerous constraints on compatibility of operations to be taken into account. In this paper, a Mixed Integer Program is proposed for solving this problem with objective to minimize the cost of the final line configuration. An illustrative example is presented.

Scalability planning for reconfigurable manufacturing systems

Scalability is a key characteristic of reconfigurable manufacturing systems, which allows system throughput capacity to be rapidly and cost-effectively adjusted to abrupt changes in market demand. This paper presents a scalability planning methodology for reconfigurable manufacturing systems that can incrementally scale the system capacity by reconfiguring an existing system. An optimization algorithm based on Genetic Algorithm is developed to determine the most economical way to reconfigure an existing system. Adding or removing machines to match the new throughput requirements and concurrently rebalancing the system for each configuration, accomplishes the system reconfiguration. The proposed approach is validated through a case study of a CNC-based automotive cylinder head machining system.

The physical and compressive load properties of sunflower (Helianthus annuus L.) fruit

SUMMARY The physical properties and compressive loading of six domestic sunflower hybrids were studied. The mean values of length, width, thickness, geometric diameter, surface area, porosity, single kernel mass, sphericity, bulk and true density, 1000-kernel weight and coefficient of friction were measured at a single level of moisture content. The results for the sunflower seeds showed that the length, width, thickness and geometric diameter dimensions ranged from 9.31-11.52 mm, 4.71-5.92 mm, 2.95-4.87 mm and 5.12-6.31 mm, respectively. The mean sphericity, porosity, static coefficient of friction, bulk and true density ranged from 0.313-0.550, 0.313-0.363, 0.211-0.237, 330.10-449.86 and 502.74-701.21 kg m -3 , respectively. The objective of this study was to evaluate and compare the behavior of six domestic sunflower hybrids (Perun, Bačvanin, Krajišnik, NS-H-111, Pobednik and Šumadinac hybrids) during compressive loading considering the seed moisture content. The seeds of NS-H-111, Šumadinac, Pobednik and Krajišnik demonstrated low values of bio yield force ranging from 29.3 N to 45.2 N when seeds had a low moisture content (between 3.7 and 5.9% w.b.). The opposite occurred for the Bačvanin and Perun hybrids (60.6 N and 76.2 N, respectively) within the same seed moisture content. For all the hybrids, the machine head displacement (deformation) increased as the seed moisture content increased. The linear model shows a decreasing trend of bio yield modulus for all hybrids as the moisture content of seeds increased.

Utilizing an In-Process Automatic Tool Change for Drilling and Reaming Large Diameter Holes

A drill/ream cycle is necessary to produce high quality, large diameter holes in carbon-titanium stacks. Manual tool changes and traditional automatic tool changers limit hole-tohole cycle times and hole quality. An in-process tool changer, mounted directly on the machine head, replaces a cutting tool with a reaming tool while clamp-up is maintained on the aircraft panel. By reducing or eliminating operator intervention, machine-axis moves, and optical resynchronization, an in-process automatic tool changer shortens cycle time, improves hole quality, and increases positional accuracy of holes. Automating this process also reduces risk of harm to the operator and aircraft structure.

Sequential monitoring of surface spatial variation in automotive machining processes based on high definition metrology

The ability to monitor machining processes within micron level is critical to high precision manufacturing. New non-contact measurement technology, such as holography based high definition metrology (HDM), makes this feasible through monitoring of both the part shape and its surface texture. However, conventional statistical process monitoring and diagnostic schemes based on low definition measurement technology have limitations in addressing the HDM data since such data are in high-dimensional form and may show strong spatial correlation. Based on a previously published sequential strategy for global and localized monitoring of shape variations in HDM data, this paper improves the method by refining the localized monitoring scheme, and applies the method to HDM data collected from an automotive engine head machining process. The results show that the proposed HDM monitoring scheme can effectively localize the defective regions on the out-of-control parts.

Compensability of errors in product quality in multistage manufacturing processes

Recent advances in model-based feedforward control of quality in multistage manufacturing processes (MMPs) are used to introduce the concept of compensability of errors in product quality. It is defined as the system-level ability to automatically eliminate quality errors accumulated in the product, given the allocation of measurements and controllable tooling. Significant similarities are observed with the control theory concepts of controllability and observability. In addition, just like in control theory, it is shown that relatively simple matrix rank tests can be used to determine the compensability of a MMP and are related with the previously introduced notion of diagnosability. The theory introduced in this paper enables rapid quantitative analysis of one's ability to actively control the quality in a manufacturing system, which is crucial for optimal allocation of measurements and controllable tooling in an MMP. Compensability studies based on the newly introduced methods are conducted using models of the flow of errors in product quality in two automotive cylinder head machining lines and a multi-layer semiconductor lithography process.

SU‐E‐T‐204: Real‐Time Monitoring of Age‐Related Macular Degeneration Radiosurgery Using Plastic Scintillation Dosimetry

Purpose: Age‐related macular degeneration (AMD) is the leading cause of vision loss and blindness among those over age 65. In its wet form, blood vessels grow from the choroid, causing macular tension and sometimes retinal displacement. As an alternative to monthly direct‐injection methods, Oraya Therapeutics has developed the IRayTM stereotactic radiosurgery device. This table‐top system has been validated in Monte Carlo simulations, human cadaver eye studies, pre‐clinical animal studies, and a phase 1 clinical trial. A plastic scintillation dosimetry (PSD) system was developed to monitor dose delivery in real‐time and provide measurement of total dose delivered. Methods: The IRayTM uses 100 keV x‐rays to deliver 24 Gy of macular dose, divided into three positions along the inferior pars plana. The PSDˈs small volume (0.5 mm diameter and 2 mm height), allows placement within the machine head. The PSD is fiber‐optically coupled to a photomultiplier tube via a plastic waveguide. Before direct characterization of the IRayTM, the preliminary PSD performance was tested using a portable x‐ray unit, mobile c‐arm fluoroscopy unit, and an ion chamber. Results: In order to avoid buffering issues, real‐time measurements used 250 ms bins, but can be adjustable to 10 ms. A calibration factor (CF) from PSD percent‐depth‐dose to ion chamber percent‐depth‐dose was 1.06 at a depth of 1.5 cm in solid water, the typical macular target depth. Counts‐to‐exposure CF varied less than 1% from 0.862 to 15.26R. Counts‐to‐exposure CF remained linear with R2 of 0.999 up to 16R even with varying dose rate (.002 R/s to 1.0 R/s). Conclusions: The PSD demonstrated linear dose measurements even at high dose and high dose rates. This study demonstrates the feasibility, accuracy, and precision of a PSD for clinical implantation in the IRayTM, a device for treatment of AMD.This research was supported by a grant from Oraya Therapeutics, Inc.

An innovative method to perform maskless plain waterjet milling for pocket generation: a case study in Ti-based superalloys

This paper presents an innovative methodology/jet path on which plain waterjet (PWJ) can generate pockets of good dimensional/geometrical definition (minimised under/over-erosion) while the proposed method leads to the avoidance of grit embedment on the target workpiece and the elimination of extra cost and time related to the use of mask. The novelty of the paper relies on the proposal of jet-path strategy that minimises the variations in jet dwell time by providing “continuous” relative movement during the jet-part interaction (through minimisation of accelerations/decelerations of the machine head) and by removing a controlled amount of material in a series of layers using special techniques. The proposed method is powerful in its approach from which it ensures (quasi)equal exposure time for each zone of material over which the jet passes, so that the jet path is “totally contained” within the form to be generated; hence, no masking is necessary to define the contour/shape. This approach has been employed for generating pockets on two Ti-based superalloys commonly used in aerospace industries, followed by dimensional, geometrical and surface quality analysis. The results proved that this approach can produce milled surfaces of straightness of the pocket bottom (<200 μm), tolerance on depth of cut per layer (<20 μm), tolerance on the radii at the bottom of the pockets (<100 μm), surface roughness ( Ra=4–14 μm) and waviness ( Wa=10–13 μm) characteristics in conditions of high surface integrity (no cracks, contaminations, etc.).

Comparison of Calculated and Experimentally Determined Punch Displacement on a Rotary Tablet Press Using both Manesty and IPT Punches

An indirect method of calculating punch displacement on a rotary tablet press from measurements of the change in punch force with the turret position was in good agreement with direct measurements of punch displacement made using a linear variable displacement transducer (LVDT)-slip ring system. The direct measurements were made during the compaction of three direct compression agents using Manesty punches. However, the agreement between calculated and experimentally determined punch displacements was unsatisfactory when IPT punches were used. The IPT punches have a much flatter punch head profile than the Manesty punches. Due to this difference, the analytic equation does not accurately describe the dynamics of the press under normal operating conditions. Terms in the analytic equation, determined originally under static conditions, were re-evaluated under dynamic conditions for both sets of tooling using the LVDT-slip ring system. Excellent agreement for both IPT and Manesty punches was found between punch displacement calculated using the revised analytic equation and direct experimental measurements. Punch displacements determined from punch head profile and machine geometry only, without taking machine deformations into account, were shown to differ widely from the calculated and experimental values.

Design and Optimization of Ultrasonic Vibration Mechanism using PZT for Precision Laser Machining

As the aged population grows around the world, many medical instruments and devices have been developed recently. Among the devices, a drug delivery stent is a medical device which requires precision machining. Conventional drug delivery stent has problems of residual polymer and decoating because the drug is coated on the surface of stent with the polymer. If the drug is impregnated in the micro sized holes on the surface, the problems can be overcome because there is no need to use the polymer anymore. Micro sized holes are generally fabricated by laser machining; however, the fabricated holes do not have a high aspect ratio or a good surface finish. To overcome these problems, we propose a vibration-assisted machining mechanism with PZT (Piezoelectric Transducers) for the fabrication of micro sized holes. If the mechanism vibrates the eyepiece of the laser machining head, the laser spot on the workpiece will vibrate vertically because objective lens in the eyepiece shakes by the mechanism's vibration. According to the former researches, the vibrating frequency over 20kHz and amplitude over 500nm are preferable. The vibration mechanism has cylindrical guide, hollowed PZT and supports. In the cylinder, the eyepiece is mounted. The cylindrical guide has upper and low plates and side wall. The shape of plates and side wall are designed to have high resonating frequency and large amplitude of motion. The PZT is also selected to have high actuating force and high speed of motion. The support has symmetrical and rigid configuration. The mechanism secures linear motion of the eyepiece. This research includes sensitivity analysis and design of ultrasonic vibration mechanism. As a result of design, the requirements of high frequency and large amplitude are achieved.

Inward Leakage in Tight-Fitting PAPRs

A combination of local flow measurement techniques and fog flow visualization was used to determine the inward leakage for two tight-fitting powered air-purifying respirators (PAPRs), the 3M Breathe-Easy PAPR and the SE 400 breathing demand PAPR. The PAPRs were mounted on a breathing machine head form, and flows were measured from the blower and into the breathing machine. Both respirators leaked a little at the beginning of inhalation, probably through their exhalation valves. In both cases, the leakage was not enough for fog to appear at the mouth of the head form.

Numerical Simulation of Oil Mist Process in Cold Heading Machine

Based on control equations in fluid dynamics, the main thought of oil mist process for cold heading machine is proposed according to the idea of green manufacturing. The computation fluid dynamics (CFD) software is applied to simulate the multi-phase oil mist flow in control box. The simulation results give some figures including distribution and stream line path of multi-phase flow of oil mist in the control box. The results show that the inlet position of oil mist effects on its process and three types of control box are compared, from which the best type is obtained.

Tool path smoothing of a redundant machine: Application to Automated Fiber Placement

Automated Tape Laying and Fiber Placement of composite materials are the two principal automated processes used for fabrication of large composite structures in aeronautical industry. The aluminum parts produced by High Speed Machining tend to be replaced by carbon fiber composite parts realized with these processes. However, structural parts present reinforcement zones which disturb the tool path follow-up and generate an increase of the manufacturing time. Thus, this paper deals with the optimization of tool paths of a 7-axis machine tool of Fiber Placement with the objective of reducing the manufacturing time while ensuring the requested quality of the final part. In this paper, two complementary methods are detailed. The first method takes advantage of the degree of redundancy of the machine tool to decrease the kinematic loads of the control joints. The second method aims to smooth the orientation of the machine head along the tool path while ensuring quality constraints. These two methods are then applied on a test tool path and bring to a significant decrease of the manufacturing time (32.9%).

DEVELOPMENT AND EVALUATION OF A LOCAL OIL SEEDEXPLIER TO IMPROVE THE EXTRACTION EFFICIENCY

In small-scale industries for dyeing and in medicines as anti-inflammatory substance. Seeds have been used as insecticide and oil extraction for fuel, soap and varnish production. Seed cake has been used as fertilizer, as solid fuel, or in biogas production. Non toxic varieties detoxified seed cake has been used as feed for animal. An local oil extraction machine used to extract different varieties of oil seeds developed and evaluated to increase the extraction efficiency , and find the solution for the most problem of all oil press extraction machines that the high percentage of oil in cotton seed cake by use the press screw pitch of double flight , number of blades of 18 blades , development the machine head to control the clearance between machine head and press screw of 1, 1.5 . 2 and 2.5mm, and studying the effect of press screw speed of 30, 60, 90 and 120 rpm on machine efficiency and final product quality .The optimum parameters and condition of machine were 32.43kg/ h machine productivity , 88.10 kW .h/ton energy requirement , 63.905 extraction efficiency , 11.08% oil extracted percentage, 6.51% oil percentage in cake, by using double flight press screw , clearance of 1.5mm, screw speed of 90 rpm and 18blades number .the obtained results were very important for oil extraction industries that use the oil press method for oil extraction .

Influence from bends on a pressure-time measurement

One of the criteria for using the pressure-time method is that there is a straight pipe between the measurement cross sections. If the physical influences from a bend were known the method could be expanded for use over bends and hence on more power plants. At the Norwegian University of Science and Technology (NTNU) a test rig suited for experiments on the pressure-time method has been built. In addition to earlier experiments performed on straight pipe and double 90 degree bend, experiments on double 45 degree bend has been performed. This is done in order to try to find out if there is a clear relationship between bend geometry and its influence on the pressure time curve. To further develop the knowledge a full scale test in the field has been conducted on a 5 MW 58 meter head machine with a vertical penstock and a 90 degree bend. In the laboratory a double 90 degree bend caused an underestimation of the flow of about 1 % compared to a straight pipe, while for a double 45 degree bend a conclusion can not be found as the spread around the mean and uncertainty bands is within the range for the straight pipe. The field measurements with a 90 degree bend showed that the underestimation became 8.5%. When measuring pressure difference over bends the resulting calculation will give an underestimation of the flow. This should imply that the measured transient pressure is damped. (Regardless if this is the correct term it is here chosen to call this damping.) The question is if the damping is caused by friction or kinetic effects. The rapid deceleration of the water masses will give transient friction. How transient friction behaves is a topic of interest in hydraulic research. Bends will also cause skewed velocity and pressure profile on inlet and outlet of the bend as well as secondary flows. How this affects the transient pressure is also an interesting parameter.

Joint allocation of measurement points and controllable tooling machines in multistage manufacturing processes

Stream of variations (SoV) modeling of multistage manufacturing process has been studied for the past 15 years and has been used for identification of root causes of manufacturing errors, characterization and optimal allocation of measurements, process-oriented tolerance allocation, fixture design, and operation sequence optimization. Most recently, it was used for optimal in-process adjustments of programmable, controllable tooling (controllable fixtures, CNC machines) in order to enable autonomous minimization of errors in dimensional product quality. However, due to the time and resources needed to take the measurements and the high cost of controllable tooling, it is plausible to strategically position such measurements and controllable devices across a manufacturing system in a way that the ability to mitigate quality problems is maximized. In this article, a distributed stochastic feed-forward control method is devised to optimally (in the least square sense) reduce the variations in dimensional workpiece quality with a limited number of controllable tooling components and measurements distributed across a multistage manufacturing process. Based on this, a reactive tabu search algorithm is proposed to enable joint optimal allocation of measurement points a controllable tooling devices. Theoretical results are evaluated and demonstrate using the SoV model of an actual industrial process for automotive cylinder head machining.

On Comparing the Quality of Head and Neck Imrt Plans Delivered with Two Different Linear Accelerator Manufacturers

The purpose of this work was to determine whether 2 different types of linear accelerators manufacturers with similar MLC leaf widths deliver equivalent IMRT distributions for head and neck radiotherapy patients. In this study, plans delivered with Siemens linacs were re-optimized with an Elekta linac and vice versa. To test for significance, paired t-tests were computed to examine differences in target and normal tissue doses and monitor units. Dose distributions, dose-volume histograms, and dose to targets and normal tissues were found to be equivalent irrespective of the linac type. However, approximately 15% more monitor units were delivered when planned on the Elekta machine ( p < 0.002). Both linear accelerators provide plans of comparable dosimetric quality; however, Elekta machines deliver slightly more monitor units than Siemens machines. This increase is likely due differences in geometric properties of the machine head designs, as modeled in the treatment planning system.

What is a Cameragraph?

The picture above is of an early film projector (pictures only) called the Powers Cameragraph No. 6. Manufactured by The Nicholas Powers Company of New York, it used 35 millimeter film, instead of the slides common to Magic Lanterns, to deliver images to a wall or screen. The AECT Archives’ Cameragraph (1910-1916) is not whole; it is essentially the machine head, that part of the film projector which holds the film and has the film-moving mechanism. An intact Cameragraph had a lamp house made of metal, to protect the projectionist from possible blindness created by stray sparks flying out of the lamp house. It also had carbon rods, used to light the lamp. These were changed every thirty minutes during viewing. One of the technological flaws when employing these film projectors was the ingredient used to create the actual film. This ingredient, nitrate, is chemically identical to smokeless gunpowder. Linked together with the sparks often flying out of the lamp, there was always a potential for fire. The Nicholas Powers Company was issued three patents for the Cameragraph. One was filed by inventor John Pross, who, at one time, was an employee of Thomas Edison. Pross introduced a new shutter design, which gave the projector less flicker or jump when moving. Called the Maltese Cross movement, the Cameragraph used a four-pin gear that ran through an “X” shaped slot, increasing the speed of movement between frames and giving the receiver a brighter image and less jumping with the film. (The Maltese movement is still used in cameras and film projectors today.)