Surface Matching Research Articles

Open-source navigation system for tracking dissociated parts with multi-registration.

During reconstructive surgery, knee and hip replacements, and orthognathic surgery, small misalignments in the pose of prosthesis and bones can lead to severe complications. Hence, the translational and angular accuracies are critical. However, traditional image-based surgical navigation lacks orientation data between structures, and imageless systems are unsuitable for cases of deformed anatomy. We introduce an open-source navigation system using a multiple registration approach that can track instruments, implants, and bones to precisely guide the surgeon in emulating a preoperative plan. We derived the analytical error of our method and designed a set of phantom experiments to measure its precision and accuracy. Additionally, we trained two classification models to predict the system reliability from fiducial points and surface matching registration data. Finally, to demonstrate the procedure feasibility, we conducted a complete workflow for a real clinical case of a patient with fibrous dysplasia and anatomical misalignment of the right femur using plastic bones. The system is able to track the dissociated fragments of the clinical case and average alignment errors in the anatomical phantoms of [Formula: see text] mm and [Formula: see text]. While the fiducial-points registration showed satisfactory results given enough points and covered volume, we acknowledge that the surface refinement step is mandatory when attempting surface matching registrations. We believe that our device could bring significant advantages for the personalized treatment of complex surgical cases and that its multi-registration attribute is convenient for intraoperative registration loosening cases.

Surface-GCN: Learning interaction experience for organ segmentation in 3D medical images.

Accurate segmentation of organs has a great significance for clinical diagnosis, but it is still hard work due to the obscure imaging boundaries caused by tissue adhesion on medical images. Based on the image continuity in medical image volumes, segmentation on these slices could be inferred from adjacent slices with a clear organ boundary. Radiologists can delineate a clear organ boundary by observing adjacent slices. Inspired by the radiologists' delineating procedure, we design an organ segmentation model based on boundary information of adjacent slices and a human-machine interactive learning strategy to introduce clinicalexperience. We propose an interactive organ segmentation method for medical image volume based on Graph Convolution Network (GCN) called Surface-GCN. First, we propose a Surface Feature Extraction Network (SFE-Net) to capture surface features of a target organ, and supervise it by a Mini-batch Adaptive Surface Matching (MBASM) module. Then, to predict organ boundaries precisely, we design an automatic segmentation module based on a Surface Convolution Unit (SCU), which propagates information on organ surfaces to refine the generated boundaries. In addition, an interactive segmentation module is proposed to learn radiologists' experience of interactive corrections on organ surfaces to reduce interactionclicks. We evaluate the proposed method on one prostate MR image dataset and two abdominal multi-organ CT datasets. The experimental results show that our method outperforms other state-of-the-artmethods. For prostate segmentation, the proposed method conducts a DSC score of 94.49% on PROMISE12 test dataset. For abdominal multi-organ segmentation, the proposed method achieves DSC scores of 95, 91, 95, and 88% for the left kidney, gallbladder, spleen, and esophagus, respectively. For interactive segmentation, the proposed method reduces 5-10 interaction clicks to reach the same accuracy. To overcome the medical organ segmentation challenge, we propose a Graph Convolutional Network called Surface-GCN by imitating radiologist interactions and learning clinical experience. On single and multiple organ segmentation tasks, the proposed method could obtain more accurate segmentation boundaries compared with other state-of-the-artmethods.

Trueness of full-arch dental models obtained by digital and conventional impression techniques: an in vivo study

The aim of this study was to compare the trueness of complete- and partial-arch impressions obtained using conventional impression materials and intraoral scanners in vivo. Full-arch impressions were taken using polyether and polyvinylsiloxane. Gypsum casts were digitized using a laboratory scanner (IM, AF). Casts obtained from polyether impressions were also scanned using an industrial blue light scanner to construct 3D reference models. Intraoral scanning was performed using CEREC Omnicam (CO) and Trios 3 (TR). Surface matching software (Atos Professional) enabled to determine the mean deviations (mean distances) from the reference casts. Statistically significant discrepancies were calculated using the Wilcoxon signed-rank test. The mean distance for trueness ranged from 0.005 mm (TR) to 0.023 mm (IM) for the full arch, from 0.001 mm (CO) to 0.068 mm (IM) for the anterior segment, and from 0.019 mm (AF) to 0.042 mm (IM) for the posterior segment. Comparing the anterior vs. the posterior segment, significantly less deviations were observed for anterior with CO (p < 0.001) and TR (p < 0.001). Full-arch comparisons revealed significant differences between AF vs. IM (p = 0.014), IM vs. CO (p = 0.002), and IM vs. TR (p = 0.001). Full-arch trueness was comparable when using Affinis and the two intraoral scanners CEREC Omnicam and Trios 3. The digital impression devices yielded higher local deviations within the complete arch. Digital impressions of the complete arch are a suitable and reliable alternative to conventional impressions. However, they should be used with caution in the posterior region.Trial registration: Registration number at the German Clinical Trial Register (04.02.2022): DRKS00027988 (https://trialsearch.who.int/).

Iterative Fine Point-Set Matching of a Free-Form Surface Based on the Point-to-Sphere Distance

Three-dimensional point-set matching that aligns the moving point set with the fixed design model is an increasingly popular technique in manufacturing automation, which also increases the demand for matching performance. In this article, an iterative fine matching algorithm based on point-to-sphere distance is proposed to balance convergence accuracy, stability, and speed. By considering the neighborhood of a fixed point as a spherical surface, a point-to-sphere distance from a moving point to the design model is derived to improve the distance calculation accuracy with respect to unknown motion parameters. A point-to-sphere iterative closest point (ICP) matching method is presented, which translates the matching into a nonlinear optimization problem. Using the Newton method, a second-order Taylor expansion is applied to iteratively solve the motion parameters. Theoretical analysis verifies the advantages in convergence performance. It is proven that the proposed method can show faster convergence speed than point-to-point ICP and better convergence stability than point-to-plane ICP in large initial poses. Experiments implementing five models verify the feasibility of the point-to-sphere distance and the corresponding matching method.

The Reuse method of the Part CNC process based on 3D feature matching

Aiming at the problem of efficient reuse of existing parts CNC process, this paper presents a reuse method of the part CNC process based on 3D feature matching. It’s assumed the part which is the most similar to the 3D features of the new part has been found in the CNC history library. To reuse the CNC process of the existing part, the CNC programs and machining parameters of the existing part are imported into the new part as the machining template firstly, then the improved 3D polar radius surface moments are used to extract the 3D shape and position vectors of the machining area of each CNC program of the existed part and each face of the new part, finally the weighted Euclidean distance is used as a metric to find the most similar matching of each machining area in the new part, and the matching result is optimized by the greedy algorithm based fragmented surface matching algorithm and the overall optimization algorithm. Hundreds of sets of 3D feature similar parts were verified in the prototype system based on this method. The results show that this method can effectively reuse the existing CNC parts, and significantly improve the efficiency of CNC programming.

Comparison of retention and denture base adaptation between conventional and 3D-printed complete dentures.

Background. In recent years, complete denture construction has been revolutionized using computer-aided designing and computer-aided manufacturing (CAD-CAM) technology. This clinical study compared the retention and denture base adaptation of 3D-printed complete dentures fabricated using dimethacrylate-based resins with a photoinitiator versus conventional complete dentures. Methods. Ten completely edentulous patients were nominated for this study. Each patient received two complete dentures. One complete denture was conventionally fabricated, while the other was digitally fabricated through 3D printing of dimethacrylate-based resins with a photoinitiator. Denture base adaptation for both dentures was evaluated using surface matching software. Denture retention was also evaluated using a digital force meter at the time of complete denture insertion (T0 ), after three months (T3 ) and six months (T6 ) of denture use. Results. Regarding adaptation (mean misfit values), a statistically insignificant difference was detected between the two differently fabricated complete dentures. In addition, comparable satisfactory retention values were observed for both conventionally fabricated and 3D-printed dentures; however, there was an insignificant increase in retention over time. Conclusion. 3D-printed complete dentures fabricated using dimethacrylate-based resins could be a promising alternative to conventionally fabricated complete dentures with satisfactory denture base adaptation and retention.

The effects of manufacturing technologies on the surface accuracy of CAD-CAM occlusal splints.

To investigate the effects of the manufacturing technologies on the surface (cameo and intaglio) accuracy (trueness and precision) of computer-aided design and computer-aided manufacturing (CAD-CAM) occlusal splints. The digital design of the master occlusal splint was designed in a CAD software program. Six groups (n = 10) were tested in this study, including Group 1- Milling (Wax), Group 2- Heat-polymerizing, Group 3- Milling (M series), Group 4- Milling (DWX-51/52D), Group 5- 3D-printing (Cares P30), and Group 6- 3D-printing (M2). The study samples were placed in a scanning jig fabricated from putty silicone and Type III dental stone. The study samples were then scanned with a laboratory scanner at the intaglio and cameo surfaces, and the scanned files were exported in standard tessellation language (STL) file format. The master occlusal splint STL file, was used as a reference to compare with all scanned samples at the intaglio and cameo surfaces in a surface matching software program. Root mean square (RMS, measured in mm, absolute value) values were calculated by the software for accuracy comparisons. Group means were used as the representation of trueness, and the standard deviation for each group was calculated as a measure of precision. Color maps were recorded to visualize the areas of deviation between study samples and the master occlusal splint file. The data were normalized and transformed to rank scores, and one-way ANOVA was used to test for the differences between the groups. Pairwise comparisons were made between different groups. Fishers least square differences were used to account for the family-wise error rate. A 5% significance level was used for all the tests. The null hypotheses were rejected. The manufacturing technologies significantly affected the trueness of occlusal splints at both intaglio and cameo surfaces (p< 0.001). At the cameo surfaces, Group 1- Milling (Wax) (0.03 ± 0.02mm), Group 3- Milling (M series) (0.04 ± 0.01mm), and Group 4- Milling (DWX-51/52D) (0.04 ± 0.01mm) had the smallest mean RMS values and highest trueness. Group 3 had the smallest standard deviation and highest precision among all groups (p< 0.001, except p = 0.005 when compared with Group 2). Group 5 had the largest standard deviation and lowest precision among all groups (p< 0.001). At the intaglio surfaces, Group 1- Milling (Wax) (0.06 ± 0.01mm) had the smallest RMS values and highest trueness among all groups (p< 0.001), and Group 2- Heat-polymerizing (0.20 ± 0.03mm) and Group 5- 3D-printing (Cares P30) (0.15 ± 0.05mm) had significantly larger mean RMS and standard deviation values than all other groups (p< 0.001), with lowest trueness and precision. In the color maps, Group 2- Heat-polymerizing and Group 5- 3D-printing (Cares P30) showed the most discrepancies with yellow and red (positive discrepancies) in most areas, and Group 1- Milling (Wax) showed the best and most uniform surface matching with the most area in green. The manufacturing technologies significantly affected the trueness and precision of occlusal splints at both intaglio and cameo surfaces. The 5-axis milling units and industrial-level CLIP 3D-printer could be considered to achieve surface accuracy of occlusal splints.

A Novel Pallet Detection Method for Automated Guided Vehicles Based on Point Cloud Data

Automated guided vehicles are widely used in warehousing environments for automated pallet handling, which is one of the fundamental parts to construct intelligent logistics systems. Pallet detection is a critical technology for automated guided vehicles, which directly affects production efficiency. A novel pallet detection method for automated guided vehicles based on point cloud data is proposed, which consists of five modules including point cloud preprocessing, key point extraction, feature description, surface matching and point cloud registration. The proposed method combines the color with the geometric features of the pallet point cloud and constructs a new Adaptive Color Fast Point Feature Histogram (ACFPFH) feature descriptor by selecting the optimal neighborhood adaptively. In addition, a new surface matching method called the Bidirectional Nearest Neighbor Distance Ratio-Approximate Congruent Triangle Neighborhood (BNNDR-ACTN) is proposed. The proposed method overcomes the problems of current methods such as low efficiency, poor robustness, random parameter selection, and being time-consuming. To verify the performance, the proposed method is compared with the traditional and modified Iterative Closest Point (ICP) methods in two real-world cases. The results show that the Root Mean Square Error (RMSE) is reduced to 0.009 and the running time is reduced to 0.989 s, which demonstrates that the proposed method has faster registration speed while maintaining higher registration accuracy.

The Influence of Discharge Mode on Morphology of Al–Ni Nanoparticles Prepared by Underwater Electrical Wire Explosion

We report the results of experiments investigating the influence of discharge mode on morphology of Al–Ni bimetallic nanoparticles prepared by underwater electrical explosion (UEE) of intertwined Al/Ni wire. The experiments were conducted using a pulsed power generator with the stored energy of [Formula: see text][Formula: see text]J (underheat mode) and [Formula: see text][Formula: see text]J (overheat mode), delivering to the intertwined Al/Ni wire a [Formula: see text][Formula: see text]kA current rising during [Formula: see text]s. By analyzing electrical signals, we conclude that there exists a competitive process between Al wire and Ni wire, and the latter always lags behind the former in various stages, duo to the difference of electrical resistivity. Using transmission electron microscope (TEM) and energy dispersive spectroscopy (EDS), the morphology and element composition of nanopowders obtained at underheat mode and overheat mode were studied. The results reveal that core-shell structured Al–Ni nanoparticles can be easily obtained at underheat mode, due to the mismatched specific surface energy and matching lattice type between aluminum and nickel. Besides, the Al–Ni powder prepared by underwater electrical wire explosion (UEWE) has a smaller particle size (less than 100[Formula: see text]nm) and more consistent particle size distribution compared with traditional preparation methods. These results show that UEWE is very attractive for the preparation of Al–Ni nanopowders, which is helpful in improving the specific surface area of Raney–Ni catalyst.

Microstructure evolution and strength-toughness matching mechanism of Fe-Cr-Ni gradient alloy steel prepared by direct laser deposition

A novel 70Cr8Ni2Y alloy steel powder was designed and prepared to meet the requirement for composition design and preparation of gradient alloys with strength-toughness matching the preparation of nuclear power camshafts by direct laser deposition (DLD). A three-layer gradient structure alloy sample with strength-toughness matching was successfully prepared by DLD using 70Cr8Ni2Y, 50Cr6Ni2Y and 12CrNi2Y alloy steel powder. The microstructure evolution and strength-toughness matching mechanism of the gradient sample were studied. The interfaces between the gradient layers were metallurgical bonding and had no defects such as cracks and pores. With the change of the alloy composition of the three gradient layers, the main microstructure of the sample changed from granular bainite to lath bainite, and to martensite in turn. The mechanism of strength-toughness matching was that the changes of the three alloy components made the strength of microstructure increase, and a metallurgical bond formed at the interfaces of the gradient layers. The gradient sample demonstrated strength-toughness matching of high-strength surface and good toughness core through adjusting of the gradient layers and change of microstructure. The high-strength 70Cr8Ni2Y surface layer ensured the high hardness and wear resistance of the gradient sample, and the 50Cr6Ni2Y gradient layer acted as an intermediate layer to support the surface and protect the bottom layer. The 12CrNi2Y gradient layer with good toughness played a role in delaying fracture and hindering crack propagation. The microhardness of the gradient sample showed a gradient distribution of 739-534-321 HV. The average tensile strength was 1076 MPa, the elongation was 1.6%, and the specific wear rate (SWR) of the sample surface was 9.5 × 10−5 mm3/(N·m). This paper can provide a useful reference for the preparation of nuclear power camshaft parts with gradient properties of good toughness of the core and high hardness and wear resistance of the surface by DLD.

The effects of additive manufacturing technologies and finish line designs on the trueness and dimensional stability of 3D-printed dies.

To evaluate the effects of 5 manufacturing technologies and 2 finish line designs on the trueness and dimensional stability of 3D-printed definitive dies at finish line regions under different storage conditions and time. Preparation of light chamfer and round shoulder finish lines were adopted individually on two mandibular first molar typodont teeth and digitalized as standard tessellation language (STL) files. A total of 240 samples (192 AM definitive dies and 48 definitive conventional stone dies) in 20 groups (n=12) were manufactured based on 2 finishing line designs (chamfer and shoulder), 5 manufacturing technologies (4 additively manufactured technologies and conventional stone die), and 2 storage conditions (light exposure and dark). The 4 additively manufactured (AM) technologies include a DLP 3D-printer, an economic LED 3D-printer, a CLIP 3D-printer, and an SLA 3D-printer. All the study samples were distributed into two storage conditions. Subsequently, samples were digitalized to STL files at 3 different time points (within 36 hours, 1-month, and 3-months). A surface matching software was used to superimpose the sample STL files onto the corresponding original STL files with the best-fit alignment function. The trueness of each printed and stone definitive dies and their dimensional stabilities were measured by the root mean square (RMS, in mm). A linear mixed-effects model was used to test the effects of the finish line design, manufacturing technology, storage condition, and storage time on RMS values (α=0.05). While finish line designs had no significant effects [F(1, 220)=0.85, p<0.358], the manufacturing technologies [F(3, 220)=33.02, p<0.001], storage condition [F(1, 220)=4.11, p=0.044], and storage time F(2, 440)=10.37, p<0.001] affected the trueness and dimensional stability of 3D-printed dies at finish line regions. No significant interactions were found among the 4 factors. For the manufacturing technologies, Type IV stone groups and LCD 3D-printer groups had significantly higher RMS values than the other 3 printers (p<0.001) with no significant differences between Type IV stone and LCD 3D-printer groups (p=0.577). DLP 3D-printer groups had higher RMS values than both SLA 3D-printer groups and CLIP 3D-printer groups (p<0.001). There were no significant differences between SLA 3D-printer groups and CLIP 3D-printer groups, p=0.671. For the effects of storage conditions, RMS values were significantly higher in the groups stored with the direct light exposure than the ones stored in the dark, p=0.044. In terms of the effects of storage time, the RMS values were significantly higher after 1-month storage, p=0.002; and 3-month storage, p<0.001, than the ones at the immediate postmanufacturing stage. However, the RMS values after 1-month and 3-month storage were not significantly different from each other (p=0.169). Manufacturing technologies, storage conditions, and storage time significantly affected the trueness and dimensional stability of 3D-printed dies at finish line regions, while finish line designs had no significant effects. Among the AM technologies tested, all have produced either comparable or truer 3D-printed dies than the Type IV dental stone dies, and the CLIP and SLA 3D-printers produced the best outcomes. 3D-printed dies showed significant distortion after 1-month and 3-months storage, especially under light exposure storage conditions. These findings may negate the clinical need to preserve 3D-printed dies, and digital data should be preserved instead.

The trueness of scans using one intraoral scanner in different partially edentulous conditions.

To investigate the trueness of intraoral scanning in 8 commonly seen partially edentulous conditions. A maxillary dentoform was modified into the 8 commonly seen partially edentulous conditions. Each modification was scanned with a laboratory desktop scanner. Each modification was then scanned 10 times (n = 10) with an intraoral scanner. All scans were exported as STL files and then imported into a surface matching software using the best-fit alignment method. The dimensional differences between the study STL files from the intraoral scanner were compared to the corresponding reference STL files. The measurements were calculated as the root mean square (RMS) and defined as the trueness of the intraoral scans. In addition to the RMS values, qualitative assessments were completed on the color maps. The color maps produced by the surface matching software were used to visualize the areas of deviation between scans from the intraoral scanner and their corresponding reference files. One-way analysis of variance (ANOVA), followed by pair-wise comparisons using Fisher's Protected Least Significant Difference were utilized to compare the differences between the groups in RMS values (α = 0.05). Partially edentulous condition significantly affected the trueness of the intraoral scans. Group 8 (Class IV) had significantly lower RMS (0.1878±0.0455 mm) than all other groups (p < 0.001). Group 2 (Class II) and Group 7 (Class III modification I) are not significantly different from each other (Group 2: 0.5758±0.0300mm; Group 7: 0.5602±0.0231 mm, p = 0.571), while they both had significantly higher RMS than all other groups (p < 0.001). The remaining groups showed the RMS values were within the range of 0.3001±0.0891 mm (Group 6 - Class III with Long Edentulous Span) and 0.4541±0.1039 mm (Group 1 - Class I). Different partially edentulous conditions affected the trueness of the scans generated from the selected intraoral scanner. Class IV edentulous condition had the highest intraoral scan trueness. It is unknown if RMS values are clinically significant, and the validity of using intraoral scans directly for PRDP fabrication will need further studies.

Considering Multisensor Data Fusion and Data-Driven Special Effects Animation Simulation

The data-driven simulation algorithm uses the method of surface matching to establish the corresponding relationship between the surfaces of the two dynamic models at the same time. It also calculates the appropriate deformation field to align the animated character surface and then uses the interpolation operation to further expand the new animated character motion. With the promotion of industrial application requirements such as games, film and television, and education and entertainment, computer animation special effects simulation technology has a wide range of application prospects. Based on a multisensor and data-driven approach, this paper conducts a targeted study on the realistic simulation of typical special effects animations. Aiming at the high time complexity and time-consuming problems of simulation algorithms, data-driven simulation methods are studied and scenes or objects that simulate the real environment can be created. They are given different properties and parameters, and the desired results are obtained through computer calculation and rendering. Finally, it can be output into a smooth animation. Based on the animation simulation data and multisensor data fusion method proposed in this paper, the on-site calculation process can be accelerated and efficient animation simulation driven by data can be realized. In 3ds Max 2013, there is also a small function that can sort the bone list in ascending or descending order in alphabetical and numerical order. This helps manage bones attached to the skin modifier more efficiently. This saves a lot of time when picking bones. About 44.3% of the people during the study were proficient in the use of software. After 1200 frames, the number of foam particles increases sharply, and the two-way coupling algorithm takes time. As the number of foam particles decreases, the time required for bidirectional coupling decreases. The article gives a brief description of the data-driven fusion model. The fluid simulation algorithm generates two different sequences by utilizing two different sets of setup parameters. It is then transformed into a spatiotemporal surface as input data for the fusion model. This research contributes to the development of special effects animation simulations.

Global optimization point-set registration based on translation/rotation decoupling for image-guided surgery applications.

In image-guided surgery systems, image-to-patient spatial registration is to get the spatial transformation between the image space and the actual operating space. Although the image-to-patient spatial registration methods using paired point or surface matching are used in some image-guided neurosurgery systems, the key problem is that the global optimization registration result cannot be achieved. Therefore, this paper proposes a new rotation invariant feature for decoupling rotation and translation space, based on which global optimization point set registration method is proposed. The new rotation invariant features, constructed based on the edges and the angles, are the rotation invariant, which has high feature resolution. Some of them are not only the rotation invariant, but also the translation invariant. To obtain the global optimal solution, branch and bound search strategy is used to search the parameter space of the translation and the computational cost is reduced simultaneously. The registration accuracy of the spatial registration method is analyzed by comparing the difference between the estimated transform and the standard transform to calculate the registration error. To validate the performance of the spatial registration method proposed, the registration performance was analyzed by comparing the experimental results with the results of the two mainstream registration methods (the iterative closest point [ICP] registration method and the coherent point drift method). In the experiments, the comparison was based on the registration accuracy and the execution time. We show our registration method can obtain higher accuracy in a shorter time in most cases. At the same time, when using ICP to further refine our results, the ICP method can converge in a very short time, which also shows that our method provides a good initial pose for the ICP method and can help the ICP converge to the global optimal solution faster. Our method can achieve an average rotation error of 0.124 degrees and an average translation error of 0.38 mm on 10 clinical data. The results reveal that the surface registration method based on translation rotation decoupling can achieve superior performance regarding both the registration accuracy and the time efficiency in the image-to-patient spatial registration.

Quantitative analysis of facial symmetry by using three-dimensional technology

BackgroundFacial symmetry is becoming increasingly important in today's orthodontic treatment. But the asymmetrical boundary is not clearly demarcated. Stereophotogrammetry has a clear advantage in measuring facial asymmetry. The aim of this study was to quantify the facial asymmetry by three-dimensional (3D) technology as well as to study whether the evaluation by non-experts about facial asymmetry was consistent with the analysis by 3D technology.MethodsThe facial symmetry of 330 patients was evaluated by 10 non-experts. 3D facial images were taken using 3dMD stereophotogrammetry equipment. The original face and its mirror shell were divided into 7 regions and the surface matching was measured in the whole face and all regional areas. The degree of symmetry was calculated by the software 3-matic STL 9.0. The difference between the two groups was analyzed by Independent-Samples T Test and the diagnostic efficiency of symmetry degree was analyzed by ROC curve analysis. The consistency between the symmetric degree and the result of evaluation was analyzed by Pearson correlation analysis.ResultsThe ROC analysis revealed significant diagnostic values in the determination of the facial asymmetry of lip, chin, cheek and lateral mandible areas. The cut-off values of symmetry degree were between 60 and 80%. The evaluation was middle correlation with the symmetric degree of the whole face.ConclusionsThe chin and lateral mandible contribute most significantly to the facial symmetry. The objective measurement of facial symmetry, 3D technology, is reliable.

Matching Measurement Strategy and Form Error Compensation for Freeform Surface Machining Based on STS Turning

The freeform surface quality is limited by the measurement, and form error cannot be convergent via compensation machining. This paper proposed a surface matching measurement strategy based on the least squares principle and iterative precision adjustment to precisely obtain surface form error after manufacturing by single point diamond turning. Through the coordinate transformation of translation and rotation, the measured surface was aligned with theoretical surface at the same coordinate system. The corresponding simulation was carried out to verify the performance of the proposed method, and the simulation results indicated that this method can achieve accurate alignment in a sub-nanometer range. Finally, with XY polynomial freeform surface as the ideal surface, compensation experiments were undertaken. The form error of freeform converged continuously after compensation machining for three times, during which the form accuracy of PV and RMS were down to 335 nm and 34 nm respectively from 1.4 um and 173 nm. The results showed that capability of the proposed compensation method was verified and the form accuracy could be improved effectively.

The Effect of Patellar Surface Morphology on Subchondral Bone Alignment When Matching Patellar Osteochondral Allografts to the Central Ridge of the Patella

Background: Cartilage transplants in the patellofemoral joint have demonstrated lower success rates than in the femoral condyles. This is likely related to the more complex morphology and biomechanics of the joint. While previous studies have evaluated cartilage surface matching and congruence, little work has been done to study the associated subchondral bone congruency in these grafts. Purpose: To determine if differences in patellar morphology play a role in the alignment of the donor patellar osteochondral allograft subchondral bone with the native patellar subchondral bone. Study Design: Controlled laboratory study. Methods: A total of 20 (10 Wiberg I and 10 Wiberg II/III) fresh-frozen human patellae were designated as recipients and size-matched to both a Wiberg I and a Wiberg II/III patellar donor. A 16-mm osteochondral allograft transplant to the central ridge of the patella was performed in random order with each matched donor. Transplanted patellae underwent a nano—computed tomography (nano-CT) scan, were digitally reconstructed, and were superimposed on the initial nano-CT scan of the native recipient patella. MATLAB was used to determine the surface height deviation between the native and donor subchondral bone surfaces. DragonFly 3-dimensional imaging software was used to measure subchondral bone step-off heights at the native-donor interface. Differences between matched and unmatched grafts were compared using a 2-way analysis of variance and the Sidak post hoc test. Results: Subchondral bone surface deviation did not differ between Wiberg matched and unmatched allografts. The step-off height was significantly greater in unmatched (1.38 ± 0.49 mm) compared with matched (1.14 ± 0.52 mm) plugs (P = .015). The lateral quadrant step-off differed between matched (0.89 ± 0.43 mm) and unmatched (1.60 ± 0.78 mm) grafts (P = .007). Conclusion: While unmatched Wiberg patellar osteochondral allograft implantation did not result in significantly different subchondral bone surface height deviations, there was a significant difference in the circumferential subchondral bone step-off height in the lateral quadrant. Further investigation using finite element analysis modeling will help determine the role of subchondral bone surface on shear and compression force distributions in these areas. Clinical Relevance: Given that subchondral bone stiffness and morphology play a role in cartilage health, subchondral bone congruency may play a role in graft survival. Understanding how this congruency plays a role in cartilage force distribution will help surgeons improve the long-term success of osteochondral allograft transplants.

Augmented reality for oral and maxillofacial surgery: The feasibility of a marker-free registration method.

Recognition of markers in the augmented reality system can reduce the additional cost of a guide plate required for the removal of benign tumours in oral and maxillofacial surgery, but the use of markers often has complex problems. In order to avoid the complex problem of using markers, an augmented reality system based on a marker-free registration method was proposed to track the contour of the mandible edge. Use the computer to perform preoperative planning on the jaw model, select and mark the path of maxillofacial lesion resection. This method has an error of the surface matching was mm, and an error of the surgical resection was mm. We demonstrate that the system can accurately enhance the display of the surgical path and provide guidance for the tradition of maxillofacial surgery.

Fibular registration using surface matching in navigation-guided osteotomies: a proof of concept study on 3D-printed models.

Fibula free flap is currently used in mandibular reconstruction. The main difficulties involved in this surgery concern mandible shaping and therefore, osteotomy positioning on the fibula. The use of navigation could help in osteotomy positioning, but accurate registration is required. We assess a surface-matching method for fibula registration that relies on an iterative closest point (ICP) algorithm. Since the fibula shape is landmark free, a robust registration initialization approach is used to avoid non-optimal local minimums in the ICP. Bone surface-matching registration was evaluated on a 3D printed fibula and compared to its virtual reference model. The registration initialization relied on 3 initialization points placed on the surgically exposed area, geometrically remote from the fibular distal extremity. The bone surface was digitized, and the obtained point clouds were registered to the virtual reference model. The position of 3 assessment points engraved on the 3D printed fibula was then compared to that of the equivalent points on the virtual model. The registration procedure was performed 24 times by an expert surgeon. Seventy-two target registration errors (TRE) were computed, corresponding to the distance between the paired assessment points. Most TRE (86.1%) were less than 1mm, with a maximum of 1.552mm. The overall mean value was 0.759 ± 0.302mm. This study illustrates a surface-matching approach for fibula registration, with an initialization method based on points remote from the fibula distal extremity. This registration technique gave promising results and should be considered as a valid registration method for straight bones like the fibula. These findings indicate that navigation can be used for fibula flap shaping for mandibular reconstruction, with a noninvasive and accurate registration method.

Multi-physics field coupling and microstructure numerical simulation of laser cladding for engine crankshaft based on CA-FE method and experimental study

During engine operation, the crankshaft journals are prone to wear, resulting in a decrease in surface matching accuracy and abnormal vibration and noise. Therefore, it is important to strengthen the surface and improve the wear resistance. Laser cladding, which involves multiple disciplines, such as automation control, optics, fluid mechanics, heat transfer, etc., is an effective method. In this paper, based on the finite element method, a numerical model of the laser cladding for the crankshaft journal was established. A disk laser was used to laser clad Fe45 powder on the ASTM1045 substrate. The multi-physics field coupling evolution mechanism of the laser cladding process was quantitatively revealed. The cladding temperature, liquid metal flow rate, and stress are positively correlated with the laser power. Combined with the cellular automata method, the microstructure evolution model during the solidification was established, and the morphology and size distribution of the grains in the cladding layer was obtained. In the middle area of the cladding layer, the grains are mostly columnar and equiaxed crystals. At the same time, the change of material physical parameters with temperature was taken into account in the model, which makes the numerical simulation results more accurate. The numerical simulation results were compared with the experimental results through the microscopic characterization experiment, and the accuracy of the numerical model was verified. Finally, through a friction-wear test, the wear resistance between the cladding layer and the substrate is compared. The average wear amount of the substrate is 1.86mm3 and the average wear amount of the cladding layer is 0.64mm3. The experiment shows that the wear resistance of the cladding layer is higher than that of the substrate, and the wear rate is reduced by 65.59%.