On-the-fly laser machining: a case study for in situ balancing of rotative parts

On-the-fly laser machining is defined as a process that aims to generate pockets/patches on target components that are rotated or moved at a constant velocity. Since it is a nonintegrated process (i.e., linear/rotary stage system moving the part is independent of that of the laser), it can be deployed to/into large industrial installations to perform in situ machining, i.e., without the need of disassembly. This allows a high degree of flexibility in its applications (e.g., balancing) and can result in significant cost savings for the user (e.g., no dis(assembly) cost). This paper introduces the concept of on-the-fly laser machining encompassing models for generating user-defined ablated features as well as error budgeting to understand the sources of errors on this highly dynamic process. Additionally, the paper presents laser pulse placement strategies aimed at increasing the surface finish of the targeted component by reducing the area surface roughness that are possible for on-the-fly laser machining. The overall concept was validated by balancing a rotor system through ablation of different pocket shapes by the use of a Yb:YAG pulsed fiber laser. In this respect, first, two different laser pulse placement strategies (square and hexagonal) were introduced in this research and have been validated on Inconel 718 target material; thus, it was concluded that hexagonal pulse placement reduces surface roughness by up to 17% compared to the traditional square laser pulse placement. The concept of on-the-fly laser machining has been validated by ablating two different features (4 × 60 mm and 12 × 4 mm) on a rotative target part at constant speed (100 rpm and 86 rpm) with the scope of being balanced. The mass removal of the ablated features to enable online balancing has been achieved within < 4 mg of the predicted value. Additionally, the error modeling revealed that most of the uncertainties in the dimensions of the feature/pocket originate from the stability of the rotor speed, which led to the conclusion that for the same mass of material to be removed it is advisable to ablate features (pockets) with longer circumferential dimensions, i.e., stretched and shallower pockets rather than compact and deep

On-the-fly laser machining: a case study for in situ balancing of rotative parts

On-the-fly laser machining is defined as a process that aims to generate pockets/patches on target components that are rotated or moved at a constant velocity. Since it is a nonintegrated process (i.e., linear/rotary stage system moving the part is independent of that of the laser), it can be deployed to/into large industrial installations to perform in situ machining, i.e., without the need of disassembly. This allows a high degree of flexibility in its applications (e.g., balancing) and can result in significant cost savings for the user (e.g., no dis(assembly) cost). This paper introduces the concept of on-the-fly laser machining encompassing models for generating user-defined ablated features as well as error budgeting to understand the sources of errors on this highly dynamic process. Additionally, the paper presents laser pulse placement strategies aimed at increasing the surface finish of the targeted component by reducing the area surface roughness that are possible for on-the-fly laser machining. The overall concept was validated by balancing a rotor system through ablation of different pocket shapes by the use of a Yb:YAG pulsed fiber laser. In this respect, first, two different laser pulse placement strategies (square and hexagonal) were introduced in this research and have been validated on Inconel 718 target material; thus, it was concluded that hexagonal pulse placement reduces surface roughness by up to 17% compared to the traditional square laser pulse placement. The concept of on-the-fly laser machining has been validated by ablating two different features (4 × 60 mm and 12 × 4 mm) on a rotative target part at constant speed (100 rpm and 86 rpm) with the scope of being balanced. The mass removal of the ablated features to enable online balancing has been achieved within < 4 mg of the predicted value. Additionally, the error modeling revealed that most of the uncertainties in the dimensions of the feature/pocket originate from the stability of the rotor speed, which led to the conclusion that for the same mass of material to be removed it is advisable to ablate features (pockets) with longer circumferential dimensions, i.e., stretched and shallower pockets rather than compact and deep

Method for in-situ balancing of rotatives by use of an on-the-fly pulsating material removal process

Balancing rotating systems is a challenging task, which requires (dis)assembly of the system to enable mass adjustments; thus the development of a method to balance rotatives in-situ (i.e. without disassembly) using pulsed laser ablation (PLA) is a key technology enabler. PLA for in-situ balancing offers inherent advantages of an adjustable frequency (to match that of the rotating part) and variable pulse energy (to control the mass removal). This thesis presents a novel methodology for balancing components in-situ using PLA in a controlled and automated manner. The method utilises a sensor to measure the acceleration of the rigid rotor-bearing system. After signal conditioning using an adaptive peak filter (i.e. an inverted notch filter), a developed peak detection algorithm determines the maxima of the signal to find the angular imbalance position. If corrective action is necessary, PLA occurs. The method accounts for the time delays in the laser system and electronic circuit. Validation on a rotating part showed a PLA targeting accuracy of < 50μm and a precision of < 30μm; the feasibility of the method was confirmed using a simulation and by balancing a rotor with an arbitrary added imbalance. A concept, which was devised to optimise the PLA strategy for removing imbalances, bases on a novel combination of an analytical and machine learning approach. It determines the optimum process parameters of an ablated feature with a specified shape and volume. Additionally, an error budget for the method has been developed. The concept has been validated and shown to be accurate to < 4mg. The error budget could account for variations. It has been shown long features in the circumferential direction of the part increase the material removal rate with only minor increases in the error magnitude. To conclude, a concept for the integration of the two developed models is presented

Review of ATLAS Software Documentation (February 8-9, 2006)

Review of the ATLAS Offline Documentation: Web pages, WorkBook, TWiki, HyperNews, Doxygen

Pulsed laser ablation as a tool for in-situ balancing of rotating parts

The balancing of complex rotating systems is a challenging task as it may require repetitive (dis)assembly to enable mass adjustments; thus, developing methods for in-situ dynamic balancing of rotatives is regarded as a key technology enabler. In this context laser balancing with its high flexibility in adjusting its firing frequency (to match that of the rotating part) and pulse energy (to vary the material removal) could offer significant advantages from both precision and cost point of view. In this paper, a laser balancing system is developed to continuously remove material from a target part in a controlled and automated manner. The amount of material ablated can be controlled by an influence coefficient, which is related to the change in vibration amplitude for a predefined amount of pulses at a given operational balancing speed, material, and geometry of the rotative part. The proposed system features a three-layered case-driven programmatic approach to optimize single-plane balancing process duration in a fully automated system. This enables the use of prioritization to avoid misfire and therefore, structural damage to the targeted part. Furthermore, the application allows the component to be balanced to all common balancing grades as specified in the ISO 1940/1 standard. Thus, validation trials involved balancing an Inconel 718 rotative to a preliminarily specified balancing grade by extracting the acceleration signals using an IIR peak filter. A computer simulation encompassing the rotor bearing state space system, a model of the laser and the adapted peak detection algorithm, has been developed and used to validate the trials conducted. Henceforth, a maximum deviation from the desired correction position of less than 1 mm has been recorded. Moreover, it has been shown that the detection and correction of imbalances can be reliably achieved by reducing the vibration level of a rotor from G 22.5 to G 19.5

Transcatheter Arterial Embolization of Arterial Esophageal Bleeding with the Use of N-Butyl Cyanoacrylate

Objective: To evaluate the clinical efficacy and safety of a transcatheter arterial embolization (TAE) with N-butyl cyanoacrylate (NBCA) for the treatment of arterial esophageal bleeding. Materials and Methods: Between August 2000 and April 2008, five patients diagnosed with arterial esophageal bleeding by conventional angiography, CT-angiography or endoscopy, underwent a TAE with NBCA. We mixed NBCA with iodized oil at ratios of 1:1 to 1:4 to supply radiopacity and achieve a proper polymerization time. After embolization, we evaluated the angiographic and clinical success, recurrent bleeding, and procedure-related complications. Results: The bleeding esophageal artery directly originated from the aorta in four patients and from the left inferior phrenic artery in one patient. Although four patients had an underlying coagulopathy at the time of the TAE, angiographic and clinical success was achieved in all five patients. In addition, no procedure-related complications such as esophageal infarction were observed during this study. Conclusion: NBCA can be an effective and feasible embolic agent in patients with active arterial esophageal bleeding, even with pre-existing coagulopathy.Burke SJ, 2007, EUR RADIOL, V17, P1714, DOI 10.1007/s00330-006-0477-xVogten JM, 2007, J VASC INTERV RADIOL, V18, P771, DOI 10.1016/j.jvir.2007.02.022Lee CW, 2007, J VASC INTERV RADIOL, V18, P209, DOI 10.1016/j.jvir.2006.12.003Jae HJ, 2007, KOREAN J RADIOL, V8, P48Ripoll C, 2004, J VASC INTERV RADIOL, V15, P447Kuo WT, 2003, J VASC INTERV RADIOL, V14, P1503, DOI 10.1097/01.RV1.0000099780.23569.E6Schenker MP, 2001, J VASC INTERV RADIOL, V12, P1263Aina R, 2001, J VASC INTERV RADIOL, V12, P195Kos X, 1998, CARDIOVASC INTER RAD, V21, P428Toyoda H, 1996, J GASTROEN HEPATOL, V11, P252ENCARNACION CE, 1992, RADIOLOGY, V183, P505STOESSLEIN F, 1982, CARDIOVASC INTER RAD, V5, P264MICHAL JA, 1980, RADIOLOGY, V134, P246CROMWELL LD, 1979, AM J ROENTGENOL, V132, P799CARSEN GM, 1978, RADIOLOGY, V128, P309MICHELS NA, 1955, UNDERLYING BLOOD SUP, P266SWIGART LVL, 1950, SURG GYNECOL OBSTET, V90, P234

Transcatheter Arterial Embolization of Nonvariceal Upper Gastrointestinal Bleeding with N-Butyl Cyanoacrylate

OBJECTIVE: To evaluate the clinical efficacy and safety of transcatheter arterial embolization (TAE) with N-Butyl Cyanoacrylate (NBCA) for nonvariceal upper gastrointestinal bleeding. MATERIALS AND METHODS: Between March 1999 and December 2002, TAE for nonvariceal upper gastrointestinal bleeding was performed in 93 patients. The endoscopic approach had failed or was discarded as an approach for control of bleeding in all study patients. Among the 93 patients NBCA was used as the primary embolic material for TAE in 32 patients (28 men, four women; mean age, 59.1 years). The indications for choosing NBCA as the embolic material were: inability to advance the microcatheter to the bleeding site and effective wedging of the microcatheter into the bleeding artery. TAE was performed using 1:1-1:3 mixtures of NBCA and iodized oil. The angiographic and clinical success rate, recurrent bleeding rate, procedure related complications and clinical outcomes were evaluated. RESULTS: The angiographic and clinical success rates were 100% and 91% (29/32), respectively. There were no serious ischemic complications. Recurrent bleeding occurred in three patients (9%) and they were managed with emergency surgery (n = 1) and with a successful second TAE (n = 2). Eighteen patients (56%) had a coagulopathy at the time of TAE and the clinical success rate in this group of patients was 83% (15/18). CONCLUSION: TAE with NBCA is a highly effective and safe treatment modality for nonvariceal upper gastrointestinal bleeding, especially when it is not possible to advance the microcatheter to the bleeding site and when the patient has a coagulopathy

Beam-Induced Nuclear Depolarisation in a Gaseous Polarised Hydrogen Target

Spin-polarised atomic hydrogen is used as a gaseous polarised proton target in high energy and nuclear physics experiments operating with internal beams in storage rings. When such beams are intense and bunched, this type of target can be depolarised by a resonant interaction with the transient magnetic field generated by the beam bunches. This effect has been studied with the HERA positron beam in the HERMES experiment at DESY. Resonances have been observed and a simple analytic model has been used to explain their shape and position. Operating conditions for the experiment have been found where there is no significant target depolarisation due to this effect.Comment: REVTEX, 6 pages, 5 figure

Observation of a Coherence Length Effect in Exclusive Rho^0 Electroproduction

Exclusive incoherent electroproduction of the rho^0(770) meson from 1H, 2H, 3He, and 14N targets has been studied by the HERMES experiment at squared four-momentum transfer Q**2>0.4 GeV**2 and positron energy loss nu from 9 to 20 GeV. The ratio of the 14N to 1H cross sections per nucleon, known as the nuclear transparency, was found to decrease with increasing coherence length of quark-antiquark fluctuations of the virtual photon. The data provide clear evidence of the interaction of the quark- antiquark fluctuations with the nuclear medium.Comment: RevTeX, 5 pages, 3 figure

The Flavor Asymmetry of the Light Quark Sea from Semi-inclusive Deep-inelastic Scattering

The flavor asymmetry of the light quark sea of the nucleon is determined in the kinematic range 0.02<x<0.3 and 1 GeV^2<Q^2<10 GeV^2, for the first time from semi-inclusive deep-inelastic scattering. The quantity (dbar(x)-ubar(x))/(u(x)-d(x)) is derived from a relationship between the yields of positive and negative pions from unpolarized hydrogen and deuterium targets. The flavor asymmetry dbar-ubar is found to be non-zero and x dependent, showing an excess of dbar over ubar quarks in the proton.Comment: 7 Pages, 2 figures, RevTeX format; slight revision in text, small change in extraction of dbar-ubar and comparison with a high q2 parameterizatio