Research on the Weld Position Detection Method for Sandwich Structures from Face-Panel Side Based on Backscattered X-ray.

Web-core sandwich panels are a typical lightweight structure utilized in a variety of fields, such as naval, aviation, aerospace, etc. Welding is considered as an effective process to join the face panel to the core panel from the face panel side. However, it is difficult to locate the joint position (i.e., the position of core panel) due to the shielding of the face panel. This paper studies a weld position detection method based on X-ray from the face panel side for aluminum web-core sandwich panels used in aviation and naval structures. First, an experimental system was designed for weld position detection, able to quickly acquire the X-ray intensity signal backscattered by the specimen. An effective signal processing method was developed to accurately extract the characteristic value of X-ray intensity signals representing the center of the joint. Secondly, an analytical model was established to calculate and optimize the detection parameters required for detection of the weld position of a given specimen by analyzing the relationship between the backscattered X-ray intensity signal detected by the detector and the parameters of the detection system and specimen during the detection process. Finally, several experiments were carried out on a 6061 aluminum alloy specimen with a thickness of 3 mm. The experimental results demonstrate that the maximum absolute error of the detection was 0.340 mm, which is sufficiently accurate for locating the position of the joint. This paper aims to provide the technical basis for the automatic tracking of weld joints from the face panel side, required for the high-reliability manufacturing of curved sandwich structures.

A Vision Based Detection Method for Narrow Butt Joints and a Robotic Seam Tracking System.

Automatic joint detection is of vital importance for the teaching of robots before welding and the seam tracking during welding. For narrow butt joints, the traditional structured light method may be ineffective, and many existing detection methods designed for narrow butt joints can only detect their 2D position. However, for butt joints with narrow gaps and 3D trajectories, their 3D position and orientation of the workpiece surface are required. In this paper, a vision based detection method for narrow butt joints is proposed. A crosshair laser is projected onto the workpiece surface and an auxiliary light source is used to illuminate the workpiece surface continuously. Then, images with an appropriate grayscale distribution are grabbed with the auto exposure function of the camera. The 3D position of the joint and the normal vector of the workpiece surface are calculated by the combination of the 2D and 3D information in the images. In addition, the detection method is applied in a robotic seam tracking system for GTAW (gas tungsten arc welding). Different filtering methods are used to smooth the detection results, and compared with the moving average method, the Kalman filter can reduce the dithering of the robot and improve the tracking accuracy significantly.

In-Process Monitoring of Lack of Fusion in Ultra-Thin Sheets Edge Welding Using Machine Vision.

Lack of fusion can often occur during ultra-thin sheets edge welding process, severely destroying joint quality and leading to seal failure. This paper presents a vision-based weld pool monitoring method for detecting a lack of fusion during micro plasma arc welding (MPAW) of ultra-thin sheets edge welds. A passive micro-vision sensor is developed to acquire clear images of the mesoscale weld pool under MPAW conditions, continuously and stably. Then, an image processing algorithm has been proposed to extract the characteristics of weld pool geometry from the acquired images in real time. The relations between the presence of a lack of fusion in edge weld and dynamic changes in weld pool characteristic parameters are investigated. The experimental results indicate that the abrupt changes of extracted weld pool centroid position along the weld length are highly correlated with the occurrences of lack of fusion. By using such weld pool characteristic information, the lack of fusion in MPAW of ultra-thin sheets edge welds can be detected in real time. The proposed in-process monitoring method makes the early warning possible. It also can provide feedback for real-time control and can serve as a basis for intelligent defect identification.

A Weld Position Recognition Method Based on Directional and Structured Light Information Fusion in Multi-Layer/Multi-Pass Welding.

Multi-layer/multi-pass welding (MLMPW) technology is widely used in the energy industry to join thick components. During automatic welding using robots or other actuators, it is very important to recognize the actual weld pass position using visual methods, which can then be used not only to perform reasonable path planning for actuators, but also to correct any deviations between the welding torch and the weld pass position in real time. However, due to the small geometrical differences between adjacent weld passes, existing weld position recognition technologies such as structured light methods are not suitable for weld position detection in MLMPW. This paper proposes a novel method for weld position detection, which fuses various kinds of information in MLMPW. First, a synchronous acquisition method is developed to obtain various kinds of visual information when directional light and structured light sources are on, respectively. Then, interferences are eliminated by fusing adjacent images. Finally, the information from directional and structured light images is fused to obtain the 3D positions of the weld passes. Experiment results show that each process can be done in 30 ms and the deviation is less than 0.6 mm. The proposed method can be used for automatic path planning and seam tracking in the robotic MLMPW process as well as electron beam freeform fabrication process.

A Vision-Aided 3D Path Teaching Method before Narrow Butt Joint Welding.

For better welding quality, accurate path teaching for actuators must be achieved before welding. Due to machining errors, assembly errors, deformations, etc., the actual groove position may be different from the predetermined path. Therefore, it is significant to recognize the actual groove position using machine vision methods and perform an accurate path teaching process. However, during the teaching process of a narrow butt joint, the existing machine vision methods may fail because of poor adaptability, low resolution, and lack of 3D information. This paper proposes a 3D path teaching method for narrow butt joint welding. This method obtains two kinds of visual information nearly at the same time, namely 2D pixel coordinates of the groove in uniform lighting condition and 3D point cloud data of the workpiece surface in cross-line laser lighting condition. The 3D position and pose between the welding torch and groove can be calculated after information fusion. The image resolution can reach 12.5 µm. Experiments are carried out at an actuator speed of 2300 mm/min and groove width of less than 0.1 mm. The results show that this method is suitable for groove recognition before narrow butt joint welding and can be applied in path teaching fields of 3D complex components.

Analysis of Soft Tissue Changes and Influencing Factors of Implant Absorption after Immediate Restoration of Anterior Teeth.

Objective: Using a digital model, evaluate the changes in the soft tissue following rapid restoration of anterior teeth and analyze the factors impacting implant absorption. Methods: A retrospective analysis was performed on 84 patients who received immediate implant restoration for a single anterior tooth in the department of Stomatology of our hospital from April 2020 to August 2021. According to different surgical methods, they were divided into the study group (n = 42) and control group (n = 42). Immediate implant repair was given to the research group, while delayed implant restoration was given to the control group. The influence of the two surgical techniques on the alterations of soft tissues around implants was studied using a 3Shape oral scan and a digital model before and 1, 3, and 5 months after the operation, respectively. Patients in the study group were divided into the excellent group (n = 26) and poor group (n = 16) according to the test results of implant bone absorption, and the risk factors of poor implant absorption after immediate restoration of anterior teeth were analyzed by univariate and multivariate analyses. Results: The levels of 1 mm and 3 mm below the gum mucosa margin in the two groups increased gradually with the time, and the gingival level and soft tissue thickness at the lip of the baseline implant also increased gradually. However, the changes of soft tissue in the study group were better than those in the control group at 3 and 6 months after surgery (P < 0.05). The PES score was significantly improved in both groups after treatment, and the aesthetic score was higher in the study group than in the control group (P < 0.05). Univariate and binary logistic multifactor regression showed that smoking and poor implant health were the related factors affecting implant absorption (P < 0.05). Conclusion: Immediate anterior tooth implantation and pharyngeal implant restoration can better restore the soft tissue and aesthetic degree of patients, but immediate implant restoration can more effectively restore the soft tissue, and controlling smoking and keeping clean around the implant after surgery is conducive to implant absorption.

[Retrospective study on treating thoracolumbar fractures with video-assisted thoracoscopic surgery and traditional anterior approach surgery].

OBJECTIVE: To investigate the feasibility and the efficacy of video-assisted thoracoscopic surgery in treating thoracolumbar fractures. METHODS: From October 2000 to December 2009, the data of 44 patients with thoracolumbar fractures were retrospetively analyzed. All patients were treated with anterior decompression, auto-iliac bone graft and anterior internal fixation system. They were divided into thoracoscopic group (23 cases, treated with video-assisted thoracoscopic surgery) and traditional group (21 cases, treated with traditional anterior approach surgery). In the thoracoscopic group, there were 15 males and 8 females with an average age of 41.4 years (ranged, 19 to 76); and in the traditional group, there were 14 males and 7 females with an average age of 39.3 years (ranged, 20 to 74). All patients were followed up from 6 to 36 months with an average of 18 months. The operative time, volume of the blood loss, the decreased value of the occupation ratio of spinal canal (OR), the corrected and loss degree of Cobb angle, the improved condition of ASIA classification were compared between two groups. RESULTS: In traditional group, operative time, volume of the blood loss, the decreased value of the occupation ratio of spinal canal (OR), the corrected and loss degree of Cobb angle, the improved grade of ASIA classification were (150.0 +/- 19.4) min, (970.0 +/- 72.0) ml, (35.5 +/- 6.4)%, (25.1 +/- 4.8) degrees, (1.0 +/- 0.7) degrees, (1.8 +/- 0.9) grades, respectively; and in thoracoscopic group, the above items were (170.0 +/- 20.8) min, (650.0 +/- 65.4) ml, (33.2 +/- 8.0)%, (23.6 +/- 5.4) degrees, (1.1 +/- 0.8) degrees, (2.0 +/- 1.1) grades, respectively. There was significant difference in volume of the blood loss between two groups (P < 0.05); there was no significant difference in operative time, the decreased value of the occupation ratio of spinal canal (OR), the corrected and loss degree of Cobb angle,the improved grade of ASIA classification between two groups (P > 0.05). The rate of fusion of all patients was 100%. CONCLUSION: Compared with the traditional anterior approach surgery, video-assisted thoracoscopic surgery has advantages of little incision,less blood loss, less trauma, can obtain same clinical outcome and is a safe,effective method in treating thoracolumbar fractures.

[Treatment of odontoid process fracture with pedicle screws by location through inferior and inner wall of atlas and superior and inner wall of axis].

OBJECTIVE: To evaluate the therapeutic effects of atlantoaxial pedicle screw in treating odontoid process fracture by location through inferior and inner wall of atlas and superior and inner wall of axis. METHODS: From June 2006 to September 2010, 12 patients with odontoid process fracture were treated with the atlantoaxial pedicle screw fixation by location through inferior and inner wall of atlas and superior and inner wall of axis. There were 8 males and 4 females, ranging in age from 18 to 62 years, with an average of 37.9 years. According to classification of Anderson, type II was in 10 cases and type III was in 2 cases. Fresh fracture was in 9 cases and old fracture was in 3 cases. All patients had symptoms such as cervical pain, stiffness and limitation of activity and 9 cases with symptoms were found physical signs of cervical spinal injury. According to grade of ASIA, grade C was in 4 cases and grade D was in 5 cases. RESULTS: There were no severe complications such as injuries of vertebral artery, nerve root and spinal cord during operation. The mean time of follow-up was 14 months (6 to 24 months). The X-ray film and CT scanning showed that all patients had steady bony union and all screws were in the proper position, no screws loosening or breaking were found. Clinical symptoms of all patients improved significantly. Nine patients with spinal injury before operation, of which nerve function obtained improvement, grade C was in 1 case, grade D was in 2 cases and grade E was in 6 cases according to grade of ASIA. CONCLUSION: Location through inferior and inner wall of atlas and superior and inner wall of axis is an effective method for the atlantoaxial pedicle screw implantation; atlantoaxial pedicle screw could be accurately and safely implanted thought this way.

[Clinical analysis of vertebral laminae reconstruction after laminectomy and pedicle screw fixation in treating lumbar spinal stenosis].

OBJECTIVE: To observe the curative effects of vertebral laminae reconstruction after laminectomy and pedicle screw fixation for the treatment of lumbar spinal stenosis in early (at the 3rd months after operation) and metaphase (at the more than 1 year after operation). METHODS: Twenty-two patients with lumbar spinal stenosis were treated by vertebral laminae reconstruction after laminectomy and pedicle screw fixation, there were 12 males and 10 females, the age was from 55 to 76 years with an average of 65.8 years, including single segment (6 cases), double segments (13 cases) and three segments (3 cases) of L3-S1. The follow-up period was for 1-3 years, preoperative and postoperative (at the 3rd months after operation and last follow-up) to assess the subjective symptoms, physical signs, the limit of daily activities and bladder function according to JOA scoring; and observe saggital diameter measurement and radiological changes through X-ray and CT. RESULTS: All the patients were followed up, the JOA scoring were respectively 5.3 +/- 1.6, 23.2 +/- 2.0, 22.9 +/- 2.4 before operation and after operation (at the 3rd after operation and last follow-up); at the 3rd months after operation, 18 cases obtain excellent results, 3 good, fair 1, and at the last follow-up, 17 cases obtain excellent results, 3 good, fair 2, there was no significant difference between two postoperative periods (u = 0.413, P < 0.05). The mean sagittal diameter of narrow segment was respectively (6.8 +/- 0.9), (17.6 +/- 2.5), (16.9 +/- 1.8) mm before operation, at the 3rd months after operation and the last follow-up. Through statistics processing, there was significant different comparing JOA scoring at 3 months after operation, last follow-up with preoperative (P < 0.05). There was significant difference of vertebral canal sagittal diameter between at the 3rd months after operation and before operation (t = 35.116, P < 0.01); there was no significant difference between at the 3rd months after operation and last follow-up (t = 1.814, P > 0.05). The CT examination of last follow-up showed the vertebral canal have no stenosis, the dural sac and nerve roots have no compression, the rebuilt vertebral laminae have fused well, the graft bone are no absorbed and the fixation have no failure. CONCLUSION: Treatment of lumbar spinal stenosis with vertebral lamina reconstruction after vertebral laminectomy and pedicle screw fixation can obtain satisfactory results in early and metaphase. The method had advantages of decompression thoroughly and fixation solidly, and could prevent vertebral canal restenosis causing by nerve oppression of the postoperative scar and nerve adhesion.

[Efficacy of posterior microendoscopic foraminotomy for cervical radiculopathy].

OBJECTIVE: To evaluate the clinical results of posterior microendoscopic foraminotomy in the treatment of cervical radiculopathy and cervical intervertebral disc protrusion. METHODS: From February 2004 to June 2007, 24 cases of cervical radiculopathy received posterior microendoscopic foraminotomy. There were 16 males and 8 females, aging 42-68 years (59 years on average), including 16 cases of cervical radiculopathy and 8 cases of cervical intervertebral disc protrusion. The course of disease was 6-15 months. The affected intervertebral discs were C4, 5 in 8 cases, C5, 6 in 12 cases, and C6, 7 in 4 cases. The radiological examinations showed that 8 protrusions included 6 soft tissue protrusions and 2 rigid tissue protrusions, and that cervical radiculopathy were caused by yellow ligament hypertrophy, Luschka's joint hyperplasia, and abnormal position of facet joint. According to Japanese Orthopedic Association (JOA), the score before operation was (12.60 +/- 1.52) points. RESULTS: The operation time was 90 to 120 minutes (100 minutes on average), the bleeding during operation was 100 to 150 mL (120 mL on average). Nerve root pain were relieved completely in 19 cases and were relieved partly in 4 cases. One case of calcified nucleus pulposus had neurological traction injury and recovered completely after 3 months. All cases were followed up 24-36 months (28 months on average). The radiological examinations after operation showed the intervertebral disc site was decompressed completely and the height of intervertebral disc and the cervical segmental alignment were normal. At 24 months postoperatively, the JOA score was (16.10 +/- 0.29) points, showing significant difference when compared with that of preoperation (P < 0.01). CONCLUSION: The posterior microendoscopic foraminotomy can get to the operation site with mini-incision, decrease tissue damage during operation, and avoid narrow intervertebral space, so it has satisfactory clinical results.

[Flavectomy of cervical vertebrae in treating cervical spinal canal stenosis].

OBJECTIVE: To investigate the operational method of cervical vertebral flavectomy and its clinical application in the management of cervical canal stenosis. METHODS: From June 1997 to June 2007, 25 patients suffering from cervical spinal canal stenosis caused by obvious flaval ligament hypertrophy were given flavectomy. There were 22 males and 3 females, with an age range of 32 to 68 years (average 54 years). The course of disease was from 3 weeks to 7 years, with an average of 3 years and 7 months. All patients had degenerative cervical canal stenosis; of them, 5 cases had a history of cervical injury 2 to 3 weeks before operation (3 cases of falling injury and 2 cases of traffic accident injury). The X-ray film, CT, and MRI examinations showed that the compression locations were C4-7 in 12 cases, C3-7 in 9 cases, C5-7 in 3 cases, and C6,7 in 1 case. Spinous process and vertebral lamella were exposed by central posterior approach. The insertions of flaval ligaments were cut off at the superior vertebral lamella border, then the starting points of which were cut down from the anterior side of the upper vertebral lamella at their inferior border after lifting up the flaval ligaments. The residual flaval ligaments in front of the vertebral lamella were scraped off by slope rongeur, the dura mater then could be seen to inflate from the intervertebral lamella space, showing the compression having been relieved. Twenty-five cases were all given posterior flavectomy. At 1 week to 3 months after operation, 12 patients received anterior cervical discectomy or vertebral gaining decompression with fusion by bone graft. RESULTS: The time for flavectomy was from 60 to 180 minutes, with an average of 95 minutes. The blood loss during operation was from 90 to 360 mL, with an average of 210 mL. The dura matters were lacerated by knife tips during operation with the cervical vertebrae in hyperflexion in 2 cases. Immediate suture and repair were performed and there were no postoperative cerebrospinal fluid leakage. All the incisions healed by first intension after operation. All of the 25 cases were followed up from 2 to 10 years, with an average of 3 years and 9 months. All patients had no complication of axial symptoms, and no restenosis at their operation site of cervical canal stenosis. The section area ratios of functional spinal canal to spinal cord were 1.12 +/- 0.07 before operation and 2.11 +/- 0.19 at 24 months after operation, showing significant difference (P < 0.05). The range of motion of cervical vertebrae was (39.4 +/- 3.2) degrees before operation and (42.1 +/- 2.9) degrees at 24 months after operation in 13 cases without anterior cervical discectomy fusion, showing no significant difference (P > 0.05); was (34.3 +/- 3.4) degrees before operation and (29.2 +/- 3.6) degrees at 24 months after operation in 12 cases with anterior cervical discectomy fusion, showing significant difference (P < 0.05). The bone graft achieved bony union 3-5 months after operation (average 3.8 months). The Japanese Orthopaedic Association (JOA) scores were 7.9 +/- 2.2 before operation and 15.6 +/- 1.4 at 24 months after operation, showing significant difference (P < 0.05), with an average improvement rate of 86.3%. CONCLUSION: Cervical flavectomy could relieve compression to spinal cord and nerves caused by the flaval ligament hypertrophy without damaging the normal integrality of bony canal, thus avoiding the complication of axial symptoms and so on which are encountered in open-door expansile cervical laminoplasty.