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  • Open access
  • 30 Reads
The influence of the layer thickness change on the accuracy of the zygomatic bone geometry manufactured using the FDM technology

Designing and manufacturing a model of the anatomical structure while performing a surgical procedure is not a simple task. It is especially true of the craniofacial area, which consists of bone tissues with very complex geometry. Appropriate knowledge and skills in medicine and technical sciences are needed, which will allow the full use of currently available tools in the processes related to the reconstruction of the craniofacial areas. It is especially true of the central craniofacial region, which is most frequently damaged. Due to the unique geometry of the models of anatomical structures, manufacturing them using subtractive methods is very difficult or often impossible. This situation makes the additive methods an ideal alternative for manufacturing this model type. Many factors during 3D printing affect the accuracy of the model geometry. The most important are the type of technology used and the finishing treatment, the material used, the print layer's selected thickness, and the object's orientation in the 3D printer space. The manuscript determined the impact of changing the layer thickness on the zygomatic bone geometry accuracy. The reference model was obtained from the DICOM data obtained from the measurement carried out on a multi-detector tomograph. The printing process was carried out on a Fortus 360 - mc printer. Physical models of the zygomatic bone were made of ABS-M30 material using four-layer thicknesses: 0.127 mm, 0.178 mm, 0.254 mm, and 0.330 mm. To assess the accuracy of the model geometry printout, the MCA-II measuring arm with an MMDx100 laser head system was used. The adjustment of the nominal model obtained at the RE / CAD design stage and the reference model created at the measurement stage using the optical system was carried out using the best fit method with an accuracy of 0.001 mm. The accuracy analysis was presented by presenting statistical parameters and histograms. Based on the obtained results, a gradual deterioration in the accuracy of the model geometry representation with the increase of the print layer thickness was observed. However, all the models manufactured are within the accuracy of +/- 0.25 mm geometry, acceptable to surgeons.

  • Open access
  • 52 Reads
On-Line Diagnostics of Inter-Turn Short-Circuit Faults in Synchronous Reluctance Machines, Based on Voltage Symmetrical Components

Fault diagnosis in electrical drives can be very difficult, especially when the input data comes from an operating electrical machine. The occurrence of Inter-Turns Short-Circuit (ITSC) fault is one of the most dangerous electrical machine failures, and if these are not detected at an early stage of development, they can result in serious consequences, both in terms of repair cost and safety. In this context, an effective on-line approach for diagnosisng ITSC fault is proposed, which is based on the computation and monitoring of a specific severity factor, defined as the ratio of positive and zero symmetrical components. This approach is implemented in a LabVIEW environment and employs the Short Time Least Square Prony's (STLSP) method. This does not require the determination of motor parameters and just involves the use of voltage sensors. Several tests were performed on a Synchronous Reluctance Machine (SynRM), for various operating conditions (healthy and faulty). The obtained results confirm the effectiveness of the proposed technique for diagnosing ITSC faults, with high reliability, rapidity, and accuracy.

  • Open access
  • 32 Reads
Accuracy and repeatability of thread measurements using replication technique

One of the important problems in verifying the dimensional and geometrical accuracy of products is the measurement in hard-to-reach places. One of the non-destructive measurement methods is the indirect measurement, using the replication technique. When evaluating each measurement method in the context of its legitimacy, one should consider its accuracy and repeatability.

This study aimed to determine whether the error values of measurements with the use of replicates are dependent on the thread parameter being checked. Two types of replica materials were used in the study - one in initial liquid consistency, and the other in paste form. Both materials are used on a semi-flexible impression to measure the cross-section on a profile projector or optical microscope. After the replicas were made, they were cut with a double blade cutter to obtain 1 mm slices. The profiles were measured on an iNEXIV VMA-2520 metrology system. As the measurement of the replicas did not provide information on the position of the thread axis, it was not possible to determine the diameter parameters. The thread parameters measured were: thread angle, thread height, pitch and root radius. To assess the accuracy of the replica measurements, the results obtained were compared with the values from the direct measurement of the thread.

The repeatability of the replicas in the context of measuring a given parameter was examined using the analysis of the means method. Irrespective of the replica material used, the largest errors in comparison with direct measurement were recorded for the thread angle. Measurements of this parameter were also characterized by the lowest repeatability. For the other analyzed parameters, the relative error was usually less than 1%.

  • Open access
  • 46 Reads
A Critical View on the Partial Discharge Models for Various Electrical Machines’ Insulation Materials

Synchronous Generators (SGs) play a vital role in energy production as well as for the Industry. The insulation system of them, of which epoxy resin and mica are the most used insulation materials, plays the most significant role in proper operation and in extending its lifetime. Epoxy resin and mica have characteristics, which make them very good materials for a reliable SG insulation. Partial Discharges (PDs) are one of the most serious problems, because they can cause problems on the SG insulation. PDs are both a symptom of insulation degradation and a means to identify possible insulation faults. So, it is very important to detect PDs with offline or/and online PD Tests. A comparison of different MATLAB/Simulink PD models are presented in this paper. Epoxy resin, mica and a combination of these two insulation materials are used for simulations in order to investigate factors, such as the applied voltage, the geometry of the void inside the insulation, and how these affect the condition of the materials, and how these are related to PDs and flashover voltages, which may appear also in electrical machines’ insulation. The aforementioned factors can be used in order to check which of the materials is affected the most and which one is the most proper for SGs’ insulation system.

  • Open access
  • 70 Reads
Effect of printing speed and layer height on geometrical accuracy of FDM-printed resolution holes of PETG artifacts

Poly Ethylene Terephthalate Glycol (PETG) is a thermoplastic polyester with excellent formability, durability and chemical resistivity. Thus, it is an ideal choice for a wide range of applications, such as food and drink containers (cooking oil containers, bottles, FDA-compliant food storage containers), cosmetics packaging and medical and pharmaceutical applications (implants, packaging of pharmaceutical and medical devices). Furthermore, PETG-filament prints easily and gives excellent layer adhesion, thus it is widely used in Fused Deposition Modeling (FDM). However, in order to achieve high levels of process repeatability, it is essential to correlate process parameters with the mechanical properties and the geometrical accuracy of the final PETG product. In literature, there is a wide variety of studies that examine the mechanical properties of 3D-printed parts. On the other hand, studies of geometrical accuracy of FDM-processed parts are limited, according to authors’ best knowledge. In the current study, 5-hole PETG features are created by a low-budget FDM printer, according to the ISO ASTM 52902-2021 standard. The holes are of diameters of 4mm, 3mm, 2mm, 1mm and 0.5mm. The artifacts are built with three different printing speeds (20mm/s, 50mm/s and 80mm/s) and with three different layer heights (0.1mm, 0.2mm, 0.3mm). The measurements on these artifacts are the diameters of the holes, which are obtained with a microscope. The results are then analyzed statistically and commented.

  • Open access
  • 26 Reads
Reliability Analysis of Hydraulic System of Tunnel Erecting Machine Based on Dynamic Fault Tree and Bayesian Network

Prefabricated utility tunnel plays an important role in the modern urban infrastructure construction. However, the weight of prefabricated utility tunnel segment is heavy and the hoisting conditions are complicated, which puts forward higher requirements on the reliability of the main equipments for the erection and paving of the utility tunnel, especially the hydraulic system of the tunnel erecting machine. Therefore, the reliability analysis of the hydraulic system of the tunnel erecting machine is carried out in this paper. Firstly, the working principle of the tunnel erecting machine and hydraulic system is analyzed, and the T-S dynamic fault tree model is constructed by using the T-S dynamic fault tree analysis method, and it is transformed into a Bayesian network model. Secondly, according to the failure probability of the root node, combined with the Bayesian network conditional probability table, the failure probability of the leaf nodes of the hydraulic system of the tunnel erecting machine in each time period and task time is forwardly inferred. Then, through the quantitative analysis of the probability importance, key importance and sensitivity parameters in the Bayesian network analysis method, the importance of the components in the system can be reflected. Finally, the posterior probability of the root node of hydraulic system fails is calculated through the reverse reasoning of the Bayesian network analysis method, and the sensitive components of the system are found. The results show that the proposed method can find out the main reasons that affect the hydraulic system of the tunnel erecting machine, and provide reference for the safe operation of the equipment and system maintenance.

  • Open access
  • 21 Reads
Innovative Design of Hydraulic Press Mobile Station Based on TRIZ Theory

As one of the most widely used equipment in the forging industry, the hydraulic press can complete various free forging processes. As the main working part of the hydraulic press, the mobile station plays the role of installing, fixing and moving the workpiece in the system. Due to the rigid connection between the mobile station and the support structure at present, it is easy to cause damage to the support structure. Therefore, in order to reduce the impact wear of the workpiece machining on the support structure of the hydraulic press mobile station, an innovative design scheme of the hydraulic press mobile station based on the Theory of Inventive Problem Solving (TRIZ) is proposed. Firstly, the hydraulic press process model is established, and the overall process of the hydraulic press is transformed into a system function analysis model composed of multiple components, so as to determine the root cause of the problem of the hydraulic press under different working conditions, and then define the innovative design goals that need to be improved. Then, the established functional model is trimmed and improved, and several alternative technical solutions are obtained by using the Technical Contradiction Matrix, the Substance-Field Model and the Ideal Final Result. Finally, combined with the actual technical requirements of the hydraulic press mobile station system, the obtained scheme is analyzed to determine the final innovative design scheme of the mobile station. The results show that the proposed scheme can not only meet the working requirements of the hydraulic press, but also improve the stress condition of the support structure. The research results can provide a new idea for the structural design of the hydraulic press mobile station.

  • Open access
  • 6 Reads
Research on Assembly Sequence Planning of Construction Machinery Drive Axle Based on Semantic Knowledge

The assembly process is one of the most important spots in the process of product production. the assembly workload accounts for 20% to 60% of the manufacturing workload for mechanical products. A suitable assembly sequence can not only reduce the assembly workload, but also reduce the manufacturing cost of products. Therefore, this paper proposes a product assembly sequence planning method based on semantic process knowledge. Firstly, a research framework of product assembly sequence planning based on semantic process knowledge was constructed by analyzing the requirement of product assembly sequence planning for assembly process semantic knowledge. Secondly, an assembly semantic process knowledge information model was proposed, which included hierarchical structure information, attribute information and semantic information of sub-assembly. Based on this, assembly sequence planning ontology and SWRL (Semantic Web Rule Language) assembly semantic rules were constructed in Protege software. Thirdly, based on the analysis of product model structure and assembly sequence planning process in a drive axle of construction machinery, sequence traversal algorithm was established for traversing sub-assembly structure. Aiming at the structure of atypical sub-assembly group, an iterative modification method for inferring the sequence of atypical sub-assembly group was designed. Finally, Taking the assembly sequence planning process of drive axle of construction machinery as an example, the construction method of assembly semantic process knowledge information model and the assembly sequence planning decision technology in this thesis were applied to verify the reliability of the information model.

  • Open access
  • 47 Reads
A Stator Faults Diagnostic Approach Immune to Unbalanced Supply Voltage, Based on the Analysis of the Midpoint Electrical Potential of the Stator Star

The inter-turn short circuit fault (ITSCF) diagnostics in induction motors under unbalanced supply voltage conditions has been a challenging over the last few years. The asymmetries caused by both conditions are similar, and the detection of an ITSCF becomes compromised. An ITSCF diagnostic approach based on the analysis of the electrical potential of the midpoint of the stator star, in a symmetrical six-phase induction machine (S6PIM) supplied by unbalanced voltages, is addressed in this paper. Firstly, the measurement of the midpoint electrical potential and the six supply voltages are performed. Then, the obtained midpoint electrical potential of the stator star value is subtracted from the one that results from the sum of the measured six supply voltages, divided by six. This operation allows the isolation of the contribution of the unbalanced supply voltage presented in the midpoint of the stator star, which means that a zero value is obtained whenever the motor is operating healthfully, supplied by balanced or unbalanced voltages. However, in the event of the occurrence of a short-circuit, a fault-related component will result from the mentioned subtraction, and its amplitude increases as the fault severity increases. Secondly, to classify the fault severity, a fast Fourier transform analysis is applied to the obtained fault-related component at a frequency of the supply voltage, and its amplitude value is analyzed. Finally, simulation and experimental results, covering different load torques, unbalanced supply voltage levels and fault severities, are presented in order to prove the effectiveness of the proposed technique.

  • Open access
  • 69 Reads

Defining the Technical Availability of a Production System with Respect to its Complexity

Production systems are becoming increasingly complex, for example due to digitalization, new technical possibilities and smaller batch sizes. This means that the main task of industrial maintenance, ensuring technical availability of a production system, is also becoming increasingly difficult. The previous focus of maintenance efforts on individual machines and plants must give way to a holistic view encompassing the whole production system in order to meet the requirements of interlinked production. Against this background, the technical availability of a production system must be redefined. Different definition approaches range from focusing on the respective availability of individual machines and adding them to an overall key figure without attention to their context in the production system to only focusing on the output quantity of the production system. The incompatibility of these definitional approaches can be well illustrated by contrasting extreme types of production systems such as a full concatenation without intermediate buffers or systems with very large buffers between two consecutive machines. The aim of this publication is to present definition approaches of the technical availability of production systems and to demonstrate the effects of random machine failures on the key figure. The demonstration is based on discrete event simulations of production systems with different levels of complexity to show how each definition approach reacts to different complexity levels. Based on the simulation results, a recommendation is developed as to which definition approach of technical availability of production systems should be employed depending on the individual focus and complexity.

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