X-ray-based machine vision system for distal locking of intramedullary nails

In surgical procedures for femoral shaft fracture treatment, current techniques for locking the distal end of intramedullary nails, using two screws, rely heavily on the use of two-dimensional X-ray images to guide three-dimensional bone drilling processes. Therefore, a large number of X-ray images are required, as the surgeon uses his/her skills and experience to locate the distal hole axes on the intramedullary nail. The long-term effects of X-ray radiation and their relation to different types of cancer still remain uncertain. Therefore, there is a need to develop a surgical technique that can limit the use of X-rays during the distal locking procedure. A robotic-assisted orthopaedic surgery system has been developed at Loughborough University to assist orthopaedic surgeons by reducing the irradiation involved in such operations. The system simplifies the current approach as it uses only two near-orthogonal X-ray images to determine the drilling trajectory of the distal locking holes, thereby considerably reducing irradiation to both the surgeon and patient. Furthermore, the system uses robust machine vision features to reduce the surgeon's interaction with the system, thus reducing the overall operating time. Laboratory test results have shown that the proposed system is very robust in the presence of variable noise and contrast in the X-ray images.     

五轴电火花机床加工空间斜孔的电极定位参数研究

空间斜孔的加工实质上是电火花机床电极沿孔的轴线的运动。对于由3个坐标轴旋转变换得到的空间斜孔,可通过五轴电火花机床沿3个坐标轴方向上的平移运动和绕两个坐标轴方向的旋转运动,使机床电极轴线与空间斜孔轴线重合,为此需要求解加工空间斜孔的电极定位参数。分析了通过坐标系旋转平移变换得到空间斜孔轴线的过程。根据空间斜孔的空间角度和几何参数求解空间斜孔轴线矢量的坐标变换矩阵,以建立空间斜孔轴线的矢量模型。得到了五轴数控电火花机床加工空间斜孔的电极摆角和电极定位坐标,使电极轴线与空间斜孔轴线重合。并制作了根据空间斜孔几何参数自动求解数控电火花机床的电极摆角和电极坐标的计算软件。     

Design and biomechanical testing of pedicle screw for osteoporotic incidents

In this study, geometrical features of pedicle screws have been modified and their performances are compared. Performance analysis has been made in terms of pull-out strength and torsional strength. The parameters investigated are core diameter, holes drilled normal to screw axis, angle between sequential holes and distance between holes. Three different core diameter have been studied, which are 4 mm (normal core diameter), 5 mm (medium core diameter) and 5.5 mm (high core diameter). Distance between sequential holes has been arranged such that there is either one hole per pitch or one hole per two pitches. Angle between sequential holes is either 90 degrees or 120 degrees. According to the test results, the screw, with medium core diameter (5 mm) containing one hole per two pitches with 90 degrees angle between sequential holes, has exhibited the optimum performance considering torsional strength and pull-out strength requirements. Its torsional strength is slightly higher than and, when Grade 40 polyurethane foam was used as bone simulating material, its pull-out strength is as good as, an undrilled normal core diameter screw, which is already being used in surgical operations. The fatigue performance of this best performed screw has also been found satisfactory according to the related standard. Its pull-out strength is also tested on a calf vertebra and a promising result has been obtained.     

Electro-elastic fields of piezoelectric materials with an elliptic hole under uniform internal shearing forces

The existing investigations on piezoelectric materials containing an elliptic hole mainly focus on remote uniform tensile loads. In order to have a better understanding of the fracture behavior of piezoelectric materials under different loading conditions, theoretical and numerical solutions are presented for an elliptic hole in transversely isotropic piezoelectric materials subjected to uniform internal shearing forces based on the complex potential approach. By solving ten variable linear equations, the analytical solutions inside and outside the hole satisfying the permeable electric boundary conditions are obtained. Taking PZT-4 ceramic into consideration, numerical results of electro-elastic fields along the edge of the hole and axes, and the electric displacements in the hole are presented. Comparison with stresses in transverse isotropic elastic materials shows that the hoop stress at the ends of major axis in two kinds of material equals zero for the various ratios of major to minor axis lengths; If the ratio is greater than 1, the hoop stress in piezoelectric materials is smaller than that in elastic materials, and if the ratio is smaller than 1, the hoop stress in piezoelectric materials is greater than that in elastic materials; When it is a circle hole, the shearing stress in two materials along axes is the same. The distribution of electric displacement components shows that the vertical electric displacement in the hole and along axes in the material is always zero though under the permeable electric boundary condition; The horizontal and vertical electric displacement components along the edge of the hole are symmetrical and antisymmetrical about horizontal axis, respectively. The stress and electric displacement distribution tends to zero at distances far from the elliptical hole, which conforms to the conclusion usually made on the basis of Saint-Venant’s principle. Unlike the existing work, uniform shearing forces acting on the edge of the hole, and the distribution of electro-elastic fields     

缸套孔系镗车复合数控机床的设计研究

根据柴油机机体缸套孔系结构及精度要求,提出了镗车复合加工新工艺,研究设计了双轴进给精镗止口、缸套孔、套筒偏心双层主轴单轴驱动精车止口端面立式数控机床,为稳定高效加工柴油机机体缸套孔系提供了新技术、新装备.     

Arrangement of side holes in a double J stent for high urine flow in a stented ureter

A double J stent (DJS) is widely used as an ureteral stent these days. A DJS is composed of a shaft and proximal and distal coils, and it has multiple side holes along the stent axis. The role of side holes must be a supply of detour. Several studies on side holes have been conducted. Various parameters, such as the number of side holes, the distance between adjacent side holes, and the degree of ureteral stenosis, have been evaluated. Studies have shown that increasing the number of side holes increases the overall flow rate, but it has not presented an important role in the absence of ureteral stenosis. In the absence of ureteral stenosis, only a few proximal and distal side holes show a role of detour, and the flow of urine through a stent is negligible. Here, we examine whether urine flow through a stented ureter is maximized by removing side holes in the midshaft and increasing the number of side holes in the proximal and distal segments of the stent shaft. We establish an undulated curved ureter model and compare a stent with only proximal and distal side holes in the shaft with a stent with side holes along the entire shaft in a point of flow rates in the ureter and flow patterns around side holes. The stent with side holes along the entire shaft (16.5 mL/h) shows a higher total flow rate compared with the stent with only proximal and distal side holes in the shaft (12.7 mL/h).

     

Automated identification of symmetry in CBED patterns: a genetic approach

The genetic algorithm has been applied for automated identification of symmetry in CBED patterns. A normalized inner product between an original and its symmetry operated CBED patterns was found to be a good measure of similarity between them, and this inner product was used as the objective function in the genetic algorithm. A real floating number implementation of this genetic approach has been applied successfully in identifying rotation axes and mirror planes in experimental CBED patterns obtained from a single crystal of silicon. In particular a three-fold rotation axis reflecting the true three-dimensional symmetry of silicon is clearly distinguished from a six-fold rotation axis as expected from a two-dimensional crystal in the experimental <1 1 1> zone axis CBED pattern.     

Optimization of rotations for six-axis machining

Five-axis machines with three translational and two rotation axes are becoming increasingly popular in serving the needs of the mass production industry due to their ability to handle geometrically complex workpieces using the rotational axes. Theoretically, the combination of the five axes offers a minimal number of the degrees of freedom required to transport the tool into a prescribed spatial position and establish a required orientation. However, the rotation axes lead to an inevitable nonlinearity of the tool tip trajectory and the so-called kinematics errors appearing due to the specific kinematics of the machine. Eventually, one arrives at an interesting question. Is it possible to compensate this error by introducing an additional rotation axis? In other words, ??does an additional rotation axis offer any optimization benefits in the sense of the above mentioned error??? In this paper, we answer this question positively by analyzing a hypothetical six-axis milling machine with two rotation axes on the table and one additional rotation axis on the tool. The sixth axis is build on the top of the existing five-axis machine MAHO600E by Deckel Gildemeister. We present an extension of an optimization algorithm developed earlier by the authors for five-axis machining based on an optimal angle sequencing (the shortest path optimization). The extension is a combination of the shortest path strategy and the use of the additional axis. The algorithm leads to an increase in the machining accuracy, in particular, for rough milling. Numerical experiments and cutting by a virtual six-axis machine built in Vericut 5.0 validates the results of the optimization. The proposed optimization procedure is capable of upgrading the existing five-axis G-codes to the case of six-axis machine.     

Machining simulation and system integration combining FE analysis and cutting mechanics modelling

This work presents a method for machining complex three-dimensional surfaces using only one axis of controlled motion for positioning a cutting tool on a specially designed numerically controlled (NC) machine. This single controlled axis lathe is configured like a lathe, but is used to produce complex sculptured surfaces out of wood. This is accomplished by mechanically linking two axes of motion to produce a fixed helical footprint of a tool path with constant step-over distance. As the linked axes are rotated, their location is measured by an encoder and passed directly to a personal computer (PC). Software running on the PC determines the depth of the computer-controlled axis. The depth information is used to control the depth axis. Several test pieces have been machined out of cedar for evaluating the method.     

Biomechanical comparison of three second-generation reconstruction nails in an unstable subtrochanteric femur fracture model

The purpose of this study is to determine if a biomechanical difference exists in dynamic stiffness, fatigue life, and fracture site displacement by comparing three cephalomedullary reconstruction nails. An examination was made of the Biomet Uniflex reconstruction nail, the Biomet Vector nail, and the Stryker Howmedica Long Gamma nail in the fixation of an unstable subtrochanteric femur fracture model, using a synthetic bone model. Mean stiffness for each nail was initially determined in control specimens (i.e. no fracture and no instrumentation). The nail stiffness values were 1764.0 N/mm (controls), 373.61 N/mm (Uniflex), 294.27 N/mm (vector), and 656.36 N/mm (Gamma). The Gamma was statistically stiffer than the Uniflex and Vector (p < 0.002). Mean fatigue life measurements were: Uniflex at 52,891 cycles, failing at the most distal of the proximal two screw holes; Vector at 45,344 cycles, failing in the nail at the level of the fracture site; Gamma at 88,748 cycles failing at the lag screw hole. The p value between the Gamma and Vector was less than 0.01 and between Gamma and Uniflex was less than 0.05. The mean maximal axial displacement at the fracture site was 2.448 mm, 2.305 mm, and 0.790 mm for the Uniflex, Vector and Gamma, respectively. The p value between the Gamma and the other nails was < 0.01. The mean maximal transverse displacement at the fracture site was 1.223 mm, 1.197 mm, and 0.280 mm respectively. The p value between the Long Gamma and the other two nails was < 0.01. In conclusion, the Long Gamma nail demonstrated statistically significant fixation superiority in stiffness, resistance to fatigue, and fracture site displacement compared to the Uniflex and Vector nails. This biomechanical information may aid in choosing implants for fixation of unstable, subtrochanteric femur fractures.     

基于径向基函数的多种类型孔洞修补算法研究

利用径向基函数对散乱数据点进行曲面重建受到越来越多学者的关注,并被应用于解决网格模型中的孔洞修补问题。本文在实现径向基函数对简单孔洞进行修补的基础上,进一步研究了对多种类型孔洞的修补问题,提出了统一的修补算法:首先利用填充算法对孔洞进行填充,然后使用径向基函数建立孔洞区域的隐式曲面,最后将新增加的三角片顶点调整到建立的隐式曲面上,并给出了修补结果的优化处理。实例证明,该算法适用性好,对不同类型孔洞的修补效果理想。     

物体三维数字化中消除遮挡孔洞的视点规划方法研究

针对视点规划研究中的遮挡与孔洞问题,提出了通过建立点云孔洞边界点最小包容盒来有效消除遮挡孔洞的新方法。把视点规划分为侧面信息激光扫描视点规划和遮挡孔洞表面扫描视点规划,以孔洞边界点最小二乘平面的平行面为视觉系统扫描遮挡孔洞表面的运动平面,视觉系统的平移运动范围大于最小包容盒的四周平面范围,对孔洞轮廓表面进行点云数据采集。最后通过实例验证了所提方法的有效性。     

Residual stress field of ballised holes

Ballising, involving pushing a slightly over-sized ball made of hard material through a hole, is a kind of cold working process. Applying ballising process to fastener holes produces compressive residual stress on the edge of the holes, and therefore increases the fatigue life of the components or structures. Quantification of the residual stress field is critical to define and precede the ballising process. In this article, the ballised holes are modeled as cold-expanded holes. Elastic-perfectly plastic theory is employed to analyze the holes with cold expansion process. For theoretical simplification, an axially symmetrical thin plate with a cold expanded hole is assumed. The elasticplastic boundaries and residual stress distribution surrounding the cold expanded hole are derived. With the analysis, the residual stress field can be obtained together with actual cold expansion process in which only the diameters of hole before and after cold expansion need to be measured. As it is a non-destructive method, it provides a convenient way to estimate the elastic-plastic boundaries and residual stresses of cold worked holes. The approach is later extended to the case involving two cold-worked holes. A ballised hole is looked upon as a cold expanded hole and therefore is investigated by the approach. Specimens ballised with different interference levels are investigated. The effects of interference levels and specimen size on residual stresses are studied. The overall residual stresses of plates with two ballised holes are obtained by superposing the residual stresses induced on a single ballised hole. The effects of distance between the centers of the two holes with different interference levels on the residual stress field are revealed.     

Finite element analysis of intramedullary devices: the effect of the gap between the implant and the bone

This paper examines the interaction interface between the implant and the bone for an intramedullary femoral nailing system using a finite element (FE) model and specifically considers the hypothesis that the local geometry at the interface is significant to the resulting localized contact stress between the medial and lateral aspect of nail and endosteum. Contact mechanics algorithms are used in the FE modelling technique that can be developed to deal with any form of intramedullary device for which contact at the bone-implant interface is important. Global stiffness data from the FE model are compared with available data from an experiment carried out on a construct of the bone and the device that uses intramedullary femoral nails. Acceptable agreement is obtained. The results demonstrate that the mechanical interface between the implant and the bone is significantly affected by the gap geometry and magnitude. In particular, larger gaps lead to greater concentrations of stress on the medial side, while the distribution of stress is more uniform at the lateral contacts. Furthermore, the results show that the gap can have a marked effect on the stresses that occur on the fracture plane.     

基于2D激光扫描的基准检测技术研究

在机器人自动制孔系统中,基准孔检测的准确性会直接影响整个机器人制孔过程的位置精度。为获取基准孔孔位准确信息,采用激光扫描的方式对基准孔进行检测。设计了2D线激光扫描在基准平面内点云的三维转化方法,通过分析基准孔在扫描仪坐标系下点云的分布特点,提出了一种基于坐标差值的基准孔边界提取算法。通过设定相邻点云在线激光扫描仪坐标系下z轴的坐标差值获取边界点,实验验证该算法能有效地去除点云中的噪声点,获取准确的基准孔边缘特征信息,进而得到准确的基准孔孔位信息。     

Development of a practical high-performance laser-guided deep-hole boring tool: Improvement in guiding strategy

In this study, a practical laser-guided deep-hole boring tool with a diameter of 110 mm is fabricated with a view to preventing hole deviation. Thus far, it has not been possible to control and guide the boring tool at all times during the boring process because current tool guiding approaches are not sufficiently reliable. This paper describes improvements in the following three main aspects of boring tool operation: (1) the method of impressing voltage to piezoelectric actuators used for controlling the tool position and inclination; (2) speed of actuator response; and (3) guiding strategy. After the improvements are incorporated, boring experiments are carried out using duralumin workpieces to examine the performance of the new boring tool. The experimental results show that the tool can be controlled and guided at all times. Further, the guiding accuracy of the boring tool is within a range of ±20 μm for two lines on both sides along the guiding axis, and the holes are bored along the guiding axis within a straightness range of ±25 μm, even when prebored hole having a thin part on one side of the hole wall is used.     

二十辊轧机机架镗床镗削头结构设计

二十辊轧机的整体机架孔系复杂、加工深度长,要求精度高,需要采用专用的加工设备来完成孔系的加工。为此,针对整体机架孔系的特点,设计了一款二十辊轧机机架镗床镗削头,成功解决了非整圆深孔孔系加工中容易出现的孔径大小超差、孔系直线度及平行度超差、内孔粗糙度低及孔系整体加工精度不稳定等问题。     

Surface accuracy optimization of mechanical parts with multiple circular holes for additive manufacturing based on triangular fuzzy number

Surface accuracy directly affects the surface quality and performance of mechanical parts. Circular hole, especially spatial non-planar hole set is the typical feature and working surface of mechanical parts. Compared with traditional machining methods, additive manufacturing (AM) technology can decrease the surface accuracy errors of circular holes during fabrication. However, an accuracy error may still exist on the surface of circular holes fabricated by AM due to the influence of staircase effect. This study proposes a surface accuracy optimization approach for mechanical parts with multiple circular holes for AM based on triangular fuzzy number (TFN). First, the feature lines on the manifold mesh are extracted using the dihedral angle method and normal tensor voting to detect the circular holes. Second, the optimal AM part build orientation is determined using the genetic algorithm to optimize the surface accuracy of the circular holes by minimizing the weighted volumetric error of the part. Third, the corresponding weights of the circular holes are calculated with the TFN analytic hierarchy process in accordance with the surface accuracy requirements. Lastly, an improved adaptive slicing algorithm is utilized to reduce the entire build time while maintaining the forming surface accuracy of the circular holes using digital twins via virtual printing. The effectiveness of the proposed approach is experimentally validated using two mechanical models.     

AXIS-BASED LOOK-AHEAD INTERPOLATOR FOR MACHINING OF SURFACES REPRESENTED BY NURBS CURVES

The dynamics influence on each axis doing high speed machining is significant but always ignored in most of the interpolators. The proposed Axis-based Look-ahead NURBS Interpolator (ALANI) strictly confines the component acceleration and jerk on each axis according to the servo system and cutting status, so that the acceleration and jerk on axes are kept under the limit in order to avoid immoderate vibrations and shocks. Chord error is also confined during interpolating. ALANI may trace back and recalculate previous data while encountering dangerous points. The recalculation algorithm is composed of acceleration decreasing algorithm (ADA) and synchronously decreasing algorithm (SDA), which are able to choose secure feed rate as well as to attain high efficiency. The simulation and experiment are presented in this paper.     

三维封闭三角网格模型的缺失实体孔洞修复算法

提出一种针对三维封闭三角网格模型的缺失实体孔洞修复算法,由初始导引点出发,根据几何特征搜索孔洞边界,并以水平集方法扩展边界,获取目标问题区域。基于边界采样和投影方法建立代理曲面,实现了内环三角化细分和三维网格表面的自由变形。通过合并环间区域和引入边缘约束的平滑过程,得到缺失实体孔洞的上缝合面。在此基础上向内扩展,获取孔洞下表面边界轮廓,搜索出上下边界环之间的三角网格区域,并利用同样的方法构建缺失实体孔洞的下缝合面。最终,连接上下缝合面以及两个边界轮廓环之间的三角网格区域得到修复实体。试验制作的样件表明,算法能简化人工交互设计的步骤,生成高质量的修补结果。