Installation Accuracy Research Articles

A robust smoothing analysis strategy for improving particle accelerator alignment and installation accuracy and efficiency based on HALF design

The fourth-generation synchrotron radiation light source under construction has a higher requirement for alignment measurement than former-generation light sources, including the accuracies and efficiencies. In this paper, a robust smoothing analysis strategy that aims to reduce relative position errors is introduced to smooth the magnetic centers’ orbit. First, we pre-process the original data based on gross error detection. Then, we do a smooth analysis of the data of the magnetic centers’ orbit and iteration by using the curve fitting of the Parzen-window function. Finally, the physical accelerator calculation is utilized to terminate the iteration. Simulation results based on the Hefei Advanced Light Facility show that the comparison between the physical calculation results before and after using this strategy verifies that it can dramatically improve beam quality, which has a slight improvement concerning existing methods. Besides, this strategy requires lower quantities of magnets that need to be adjusted, less than that of other methods. This research can provide a robust technical guarantee for the construction of the fourth-generation light source.

Production Process of KAGRA UHV Chambers

We have manufactured two types of ultra-high vacuum vessels for the gravitational wave observation facility KAGRA. Thirteen containers with an inner diameter of 1500 mm and three containers with an inner diameter of 1200 mm were connected using a bellows unit to achieve an installation accuracy of 2 mm and a gas release rate of 10－8 Pa·m3 s－1 m－2.

Анализ точности установки заготовок на опорные призмы с учетом влияния размерных связей

An impact of different accuracy parameters of supporting prisms used in designs of machine units upon the accuracy of billet installation is considered. As a method for the estimate of installation accuracy a dimension analysis is used. There are shown peculiarities of the technological support of supporting prism accuracy.

Installation of the graphite internals in HTR-PM

Internals are one of key equipment in the nuclear islands of High Temperature gas-cooled Reactor Pebble-bed Module (HTR-PM). Their structural integration is very important to the nuclear safety. Different from the internals in pressurized water reactors, a large number of graphite and carbon components are used in the internals of HTR-PM. These components are connected by dowels and keys with gaps between them to compensate the deformation caused by thermal and irradiation stresses. High installation accuracy of each component is required for the important safety and function related devices installed inside the internals, such as control rod and fuel handling system. Due to the cumulative assembly error of the components and the deformation of the supporting structures, the installation of the graphite and carbon internals is very challenging. Detailed requirements for the examination and installation of the graphite component have been developed and continually optimized for both trial assembly and assembly in the reactor. Research was also carried out for measurement techniques, lifting tools, examination and rapid assessments. The installation of graphite and carbon internals has been successfully completed for both modules. Some major installation results, including the position of the channels and levelness of the graphite components as well as the considerations of their acceptance are introduced in the present paper. The lessons-learned and experience can be applied to the installation of internals in HTRs and other reactors using graphite components, such as molten salt reactor.

Comparing Accuracy of Implant Installation with a Navigation System (NS), a Laboratory Guide (LG), NS with LG, and Freehand Drilling.

The aim of this study was to compare the accuracy of implant placement by using the conventional freehand method, the surgical guide alone, the dental navigation system alone, and the dental navigation system with a surgical guide. The participants were aged 20 years or older and were requiring dental implant surgery according to an assessment made by a dentist between July 2014 and December 2017. A total of 128 dental implants were inserted, 32 dental implants in each group, and participants with similar or identical age (i.e., 20–50 years or 50 years or above) and missing tooth locations were paired for comparison. Accuracy was measured by overlaying the real position in the postoperative Cone Beam Computerized Tomography (CBCT) on the virtual presurgical placement of the implant in a CBCT image. Using the dental navigation system with a surgical guide could help dentists to position implants more accurately. Total, longitudinal, and angular error deviation were significantly different (p < 0.0001). The same level of accuracy could be obtained for the different jaws and tooth positions. The one-way analysis of variance (ANOVA) showed that the total, longitudinal, and angular errors differed significantly (p < 0.0001). A comparison of the four dental implant surgical methods indicated that the combination of a dental implant navigation system and a surgical guide kit achieved the highest accuracy in terms of the different tooth positions and jaws.

Inter-unit variability of multi-leaf collimator parameters for IMRT and VMAT treatment planning: a multi-institutional survey

Modern treatment machines have shown small inter-unit variability regarding beam data. Recently, vendor-provided average beam data, such as the Representative Beam Data (RBD) of the TrueBeam (Varian Medical Systems, Palo Alto, CA, USA), has been used for modeling of the Eclipse (Varian Medical Systems) treatment planning system. However, RBD does not provide multi-leaf collimator (MLC) parameters, such as MLC leaf transmission factor (LTF) and dosimetric leaf gap (DLG). We performed a web-based multi-institutional survey to investigate these parameters as well as the measurement protocols and customization of the parameters for intensity-modulated radiotherapy (IMRT) and/or volumetric modulated radiotherapy (VMAT) commissioning. We collected 69 sets of linear accelerator (linac) data from 58 institutions. In order to measure MLC parameters, most institutions used farmer-type ionization chambers with a sensitive volume of 0.6 cm3, water phantoms, source surface distance of 90 cm with 10 cm depth, and a vendor-provided plan. The LTF showed small inter-unit variabilities, although the DLG showed large variations. For optimization of the parameters for IMRT/VMAT calculations, DLG values were upwardly adjusted at many institutions, whereas the LTF values were modestly changed. We clarified that MLC parameters were measured under the same conditions at more than half of the facilities. Most institutions customized parameters in a similar manner for IMRT/VMAT. The median measured and customized values obtained in our study will be valuable to verify MLC installation accuracy and to shorten the iterative processes of finding the optimal values.

An Enhanced Detection System of Drill Rod Bending Degree Based on Two-Dimensional Laser.

Drill rod straightness has to be strictly controlled and the maximum bending degree detection needs to be used in the straightening process. The mechanical bending degree measurement depends on machinery instruments and workers’ experience, often with low efficiency and precision. While the optical inspection, as a non-contact detection method, with higher precision and lower installation accuracy requirements, is frequently applied in the online detection system. Based on this, an enhanced bending degree detection system for a drill rod is proposed in this paper. Compared to the existing detection system, the main progress is to use a two-dimensional laser to quickly obtain arc profile data and fit with ellipse. Segment inspection idea is also utilized is this system as the camera that could obtain the whole drill rod in one shot needs extremely high resolution and price. A specialized algorithm is designed to fit the cross-section shape and whole centerline displacement based on the least square method. Some laboratory tests are conducted to verify this detection system, findings of which are compared to manual measured results. The maximum bending degree error is 2.14 mm and the maximum position error is 8.21 mm, which are both within the tolerance of error. Those results show the feasibility and precision of this enhanced detection system.

CLAMPING DEVICES WITH SPLIT SLEEVES. ACCURACY OF BLANKS INSTALLATION AND MACHINING

A special place in the known technological system “MDTP” (machine, device, tool, part) is taken by clamping devices since they are intended for positioning of the blank (part) subject to machining in space to prevent its displacement under the action of cutting forces. The devices significantly influence the accuracy of the clamped blank machining. The ratio of inaccuracies caused by the devices may prevail in the total balance of inaccuracies. This may take place during machining of such types of blanks as rings, bushings and cups, especially those with thin walls. The mentioned blanks have a great number of structural configurations, they vary in installation bases, rigidity, accuracy requirements and batch quantity, etc. All this has led to a great number of devices used to install such blanks as rings, bushings and cups. These devices were selected as objects of study. The review thereof has shown two contradictory tendencies: increase in accuracy of machining of blanks clamped in the devices; expansion o the devices’ processing possibilities, in the first instance expansion of the diameter range of blanks which can be installed in a single device. On the basis of the study performed it was determined that mandrels with split sleeves are most promising since they are highly accurate and have a wide range, but there is some room for improvement of these characteristics. The article describes accuracy of blanks’ installation and machining in mandrels with split sleeves and contains recommendations on rational use of such mandrels.

Study protocol: a randomised non-inferiority trial using interactive virtual presence to remotely assist parents with child restraint installations

BackgroundMotor vehicle crashes are the third-leading cause of death to American children aged 1–5 years. When installed correctly, child restraints (car seats) reduce risk of serious injury and death. However,...

Research on precision assembly error statistics and sensitivity based on vertical launcher model

The installation accuracy of the shipborne vertical launcher and the different state parameters of the launcher’s guide rail will have different degrees of impact on the initial accuracy of the test-mounted missile. Therefore, it is of great practical significance to study the assembly error characteristics of the launcher. In this paper, the influence law of equipment installation accuracy and the influence of each component’s correlation error on assembly precision are analysed. The error law of the launching device is analysed based on mathematical statistics. At the same time, the sensitivity of the error is studied by multi-body theory method to improve the accuracy, efficiency and stability of the assembly. Through the established error sensitivity analysis model, the geometric error of the main components that have a great influence on the assembly accuracy during the assembly process of the launching device is effectively identified. The results show that the error data probability distribution of the vertical launcher conforms to the normal distribution, and the key factors of the assembly error are effectively detected, which provides a theoretical basis for the assembly precision control research.

Влияние угловой координаты неподвижного зубчатого колеса на кинематическую погрешность волновой передачи

When designing harmonic drives, it is important to address the issue of reducing the kinematic error of the drive occurring due to the deformation of the flexible gear, radial oscillations of the cam, manufacturing and installation errors of the gears. Conventionally, this problem is solved by increasing the accuracy class of the gears and the parts where manufacturing errors impact the accuracy of cam installation. A mathematical model is proposed that enables researchers to study the dependency of the kinematic error of the harmonic drive on various factors already at the design stage. Calculation techniques are developed that take into account elastic interaction between the main elements of the drive as well as manufacturing and installation errors. The results of theoretical studies of the influence of the angular position of the flexible and rigid gears on the kinematic error of a harmonic drive with a cam wave generator are presented. The possibility of reducing the kinematic error by turning the fixed gear is proven.

ЭКСПЕРИМЕНТАЛЬНОЕ ОПРЕДЕЛЕНИЕ ТОЧНОСТИ БАЗИРОВАНИЯ И ЗАКРЕПЛЕНИЯ ИНСТРУМЕНТА

There are presented results of experimental investigations allowing the definition of factors (parameters) influencing the accuracy of basing and fastening a tool in a machine spindle. &#x0D; The plant design developed allows modeling the work of elements and mechanisms of a spindle unit of a jig-boring machine (JBM) at the moment of tool changing. &#x0D; The series of experiments carried out allowed drawing the following conclusions: &#x0D; - the accuracy of a tool installation in a machine spindle depends upon its angular position in a spindle taper; &#x0D; - angular errors of a tool cone element decrease a rigidity of a “spindle-tool” subsystem by 10…15%; &#x0D; - elastic movements in the area of a contact increase by 2-2.5 times at the presence of ovality in the cross-section of a holder (at ovality 18mkm); &#x0D; - the accuracy of tool location in a spindle increases with the increase of an axial tightening force (recommended tightening force – 3 ≤ Ptight. ≤ 5kN); &#x0D; - the holder operation results in the rigidity decrease of a tool system by 10…15% (operation term – 5 years).

Vision guided geometric regulation of PTC frame structures

PurposeGeometric structure error of parabolic trough concentrator (PTC) frame affects the installation accuracy of mirrors and absorber tubes and thus decreases the solar energy concentrating efficiency. Until now, there is no effective method to instruct the assembly and regulation of PTC frames. This paper aims to propose a vision guided method for fast and accurate regulation of mirror and absorber supports to improve the geometric quality of PTC frames.Design/methodology/approachThe PTC frame support regulating system consists of a general-purpose online photogrammetry system, frame support measurement adaptors and data analyzing software. First, the positions and angles of all the supports are measured in real time by the online photogrammetric system. Then, the measured positions and angles are aligned to the design reference frame through the transformation calculated by an absorber position constrained nonlinear optimization so as to get the geometric errors and regulating amounts. Finally, a graduated pseudo-color-based visualization method is proposed to assist the manual or automated regulation of PTC frame supports in site.FindingsThe proposed method does not need to construct a reference system nor specify the rotation attitude of the PTC frame, and it is capable of conducting efficient and accurate regulation on PTC frame assembly line. The method is applied to manual regulation of a light type PTC frame structure. After regulation, the maximum position and angle errors of supports are reduced to less than 0.15 mm and 0.15° respectively and the intercept factor is increased to 97%, which meets the requirement for a qualified PTC concentrator.Originality/valueTo the authors’ knowledge, this paper is the first to propose a vision guided assembly or regulation method for PTC frame structures. The research uses online photogrammetry system to provide real-time geometric quality information feedback, elaborates the data analysis algorithm and provides the visualization method for accurate and efficient in site regulation. Furthermore, this paper also provides theories, methods and experiences for other applications that use vision guidance for attitude regulation and digital flexible assembly of large equipment.

Study on straightness measurement technology of slender rod based on time-domain three-point method

Straightness is the key geometric accuracy index of the slender rod of key parts of large machinery, which directly affects the manufacturing and installation accuracy, working efficiency and service life of mechanical products. In order to improve the manufacturing precision of the slender rod and overcome the limitations of the existing methods, a method for measuring the straightness of the slender rod based on the time-domain three-point method is proposed. According to the structural characteristics of the slender rod, the measurement principle and the overall scheme of the measurement system are given, and the mathematical model of the straightness measurement is established. Taking the core components of a construction machine as an example, the measurement and comparison of the designed measuring device and the laser tracker are used to prove that the measurement error of the designed measuring device is less than 0.005 mm. The measurement system analysis results show that the R&R of the designed measuring device has less than 10% of the research variation, indicating that its repeatability and reproducibility are good, which further proves that it can be applied to the actual production site.

ANALYSIS OF DEFORMED CONDITION OF SHUTTERS LOCATED ON ROLLER-PROOFERS

When assembling the shells of cylindrical vessels and apparatus, there are increased requirements for deviations of geometrical parameters and for the accuracy of installation of internal devices. The requirements for deviations of the shape and size of the shells of cylindrical vessels and apparatus, the maximum allowable values of the displacement of the edges during welding of shells were considered. The study of deformations will allow to understand their structure, which, in turn, will increase the accuracy in the manufacture of vessel shells and apparatus. Most of the cylindrical shells are assembled in a horizontal position when the shells lie on the roller supports. The article presents an analysis of the deformations arising under the action of gravity in the shells located on the roller supports. A simulation of the deformations occurring in the shells located on the roller bearings due to the action of gravity was carried out using the finite element method. The simulation was carried out in the ANSYS software package, in the Mechanical APDL module. The dependences of the magnitude of the maximum strain as a function of the angle of the rollers were studied. The dependence of the deviation of the conventional axis of the apparatus on the real from the distance between the pairs of rollers was also investigated. Methods for controlling the geometric parameters of the shells, such as a mechanical profilograph and an automatic system for controlling geometric parameters using modern laser technologies, were considered. The results of the study showed that gravity did not significantly affect the deformation of the shells. The studies did not take into account the residual welding stresses, stresses and strains that occur during the assembly of the shells. The obtained value of the optimal angle of location of the rollers is 140o. It is necessary to establish the maximum angle of location of the roller, if they can not be located at an angle of 70o. The deviation of the real axis of the apparatus from the conditional is within 0.5 mm, which does not significantly affect the accuracy of production. The resulting ovality of the end and central sections under the influence of gravity on the body does not exceed 0.1 %, which is within the limits of acceptable values.

Application of passive image-free navigation system for total knee arthroplasty

Total knee arthroplasty(TKA) has been the final clinical treatment of knee osteoarthritis at the final stage, postoperative limb and prosthesis alignment restoration directly affect clinical effect. In recent years, computer-assisted surgery has been used in TKA and obtained satisfied results. There paper has investigated that the use of computer-assisted systems could improve soft tissue balance after TKA, improve accuracy of installation of prosthesis, recover limb alignment and decrease intro-blood loss, postoperative fat embolism. Although computer-assisted navigation is not mainstream, with the continuous improvement of technology and innovation, the computer-assisted surgery could exert a more important role in TKA, and considerably beneficial effect on improvement of postoperative clinical effects.

Physical and Mechanical Characteristics of Soft Rock Tunnel and the Effect of Excavation on Supporting Structure

The problem of large deformation is very prominent in deep-buried tunnel excavation in soft rock, which brings serious potential safety hazards and economic losses to projects. The knowledge of deformation law and support measures is the key to ensure the rational design and safe construction in a large deformation tunnel of soft rock. This paper describes rock physical and mechanical tests and field monitoring is employed to investigate the cause and development process of large deformation in Dongsong hydropower station in Sichuan Province, China. The results show that the free expansion rate of the rock sample is 20.0%, the average expansion stress of the rock sample is 11.0 kPa, and the expansibility of the rock is low. Large deformation of surrounding rock mainly comes from the dilatancy effect with high geostress and relaxation deformation with weak support. Shotcrete sealing exposed surrounding rock, and early strength support avoiding water immersion are useful to deal with the three main factors (weathering, water and confining pressure) that affect the strength of surrounding rocks. The second lining applied in time can effectively limit the further development of stress and deformation of initial support, and prevent the cracking and large deformation of concrete. Clearance convergence is suggested to be the main monitoring work in construction, because of its advantages of intuitive results, easy quality assurance of instrument installation and high accuracy.

Remote handling tools for hydraulic connections of divertor cassettes in JT-60SA

Two types of alignment tools has been developed for hydraulic connection between cooling pipes in divertor cassette and vacuum vessel in JT-60SA. These tools were designed to be used by a remote handling system that are planned for the maintenance and repair of the divertor cassette in the latter research phase of JT-60SA. Plasma facing components on the divertor cassette will be actively cooled because they are exposed to high heat flux. Before connecting two cooling pipes by a laser welding tool, an alignment of the groove is required. Here, the outer diameter, thickness and material of the cooling pipe are 59.8 mm, 2.8 mm and SUS316 L, respectively. The axial misalignment at the groove position is predicted to be 3 mm as the maximum owing to the installation accuracy of the pipes in the vacuum vessel. The axial misalignments were successfully aligned less than the welding range of <0.5 mm by these alignment tools. These alignments were achieved by a simple z-motion by bolting that were to be applicable to a remote handling tool.

Experimental Validation for Globally Optimized Tractor-Trailer Base Flaps

Using wind-tunnel testing, this study validates a design that was globally optimized under uncertainty and used computational fluid dynamics. The computational study determined a design for a 3-D tractor-trailer base (back-end) drag-reduction device that reduces the wind-averaged drag coefficient by 41% at 57 mph (92 km/h). The wind-tunnel testing applies the same method of including some uncertainties, such that the design is relatively insensitive to variation in wind speed and direction, elevation, and installation accuracy. The validation testing shows a 20.1% reduction in wind-averaged drag coefficient, or 1.3% better than a non-optimized commercial design, and is conducted on a 1/24-scale model of the simplified tractor trailer at a trailer-width-based Reynolds number (<i>Re_W</i>) of 4.9x10⁵. Test data include both force and pressure measurements on the simplified tractor trailer, as well as pressure measurements on the tunnel wall. Measurements are taken at static side-slip angles to enable wind-averaged calculations. Since the original computations are conducted for a full-scale tractor-trailer at <i>Re_W</i> = 4.4x10⁶, this study does not fully validate the computational design due to the wind tunnel limitations and resulting inability to match the <i>Re_W</i>; however, the results show qualitative and quantitative improvement over the non-optimized design.

ПРОЧНОСТЬ И ДЕФОРМАТИВНОСТЬ СБОРНО-МОНОЛИТНЫХ ПЛАТФОРМЕННЫХ СТЫКОВ ПАНЕЛЬНЫХ ЗДАНИЙ

Given a new constructive solution of precast-monolithic platform butt joint panel stand-frame and the disk overlap panel buildings, Otley significant feature of which is the presence of a special centering device to improve the accuracy of installation of the panels-frames. Given the estimated model of the design of the junction and the analysis of the stress-deformirovannogo status of this design at various levels of loading with nonlinear deformarea-tion and cracking. A special method of jointing of plane-stressed finite elements along the boundaries of these elements was used to model cracks. The analysis of deformation, crack formation and destruction of the considered structure of the platform joint is carried out. It is shown that the proposed version of the computational model with the task of explicit cracks-cracks jointing allows to predict the scheme of the platform joint development.