Cutter Location Research Articles

The Effect of Preoperative Bone Density and Subchondral Cysts on Periprosthetic Fracture Risk in Total Ankle Arthroplasty

Category: Ankle Arthritis Introduction/Purpose: Bone density is a modifiable factor which can be addressed prior to elective surgery if necessary. However, its role pertaining to complications of total ankle arthroplasty (TAA) has not been studied. Hounsfield units (HU) can be measured on standard computed tomography (CT) imaging, and have been shown to correlate with bone mineral density measures from dual-energy X-ray absorptiometry (DEXA). There is a precedent for these measurements in the orthopedic literature: different authors have shown that patients with higher vertebral bone density on CT are at lower risk for pedicle screw loosening. We hypothesized that patients with lower bone density, as measured by HU on preoperative CT, or with large preoperative cysts, would be at greater risk for revision and periprosthetic fractures following TAA. Methods: An existing database at the authors’ institution was used to screen all patients who underwent primary TAA. Inclusion criteria included a CT scan within one year prior to surgery. Exclusion criteria included tibial or talar hardware and nonweightbearing status at the time of the CT scan. The primary outcomes were prosthetic revision and periprosthetic fracture. HU were measured on axial CT cuts at 10 mm above the tibial plafond and at 5 mm below the talar dome to approximate the location of bone cuts. HU measurements for 30 patients were made independently by two reviewers in order to establish interrater reliability. Subchondral cysts at least 5 mm in diameter were counted. Additional patient factors analyzed included age, sex, weight, body mass index (BMI), tobacco use, presence of rheumatoid arthritis, preoperative deformity =15°, and pain visual analog scale scores. Results: 198 patients with a mean 2.4 years of follow-up met the inclusion criteria. The intraclass correlation coefficients for tibial and talar HU measurements were both 0.95. Seven patients (3.5%) underwent revision, four for infection, at a mean 1.2 years postoperatively. There were seven intraoperative and nine postoperative periprosthetic fractures (3.5% and 4.5%, respectively). Neither bone density nor cysts were associated with revision (p>.05). Lower tibial and talar HU, lower weight, and lower BMI were all associated with periprosthetic fracture (Table). After controlling for age, sex, and weight, only tibial HU was significantly associated with periprosthetic fractures (p=0.018). All intraoperative fractures occurred in patients with tibial HU <200. Of patients with tibial HU <200, 10 (22%) sustained an intra- or postoperative periprosthetic fracture. Conclusion: Lower tibial and talar bone density on preoperative CT of the ankle was strongly associated with periprosthetic fracture. The low incidence of revision during the relatively short study period limited our ability to analyze effects on revision rates. In patients who have had a preoperative CT, measuring HU represents a quick, simple method of assessing bone density with excellent inter-rater reliability. In patients with tibial HU <200, surgeons may wish to consider prophylactic internal fixation of the medial malleolus.

Revisiting the hunting-versus-scavenging debate at FLK Zinj: A GIS spatial analysis of bone surface modifications produced by hominins and carnivores in the FLK 22 assemblage, Olduvai Gorge, Tanzania

This study presents a taphonomic examination of the ca. 1.84 million year old (Ma) bovid fauna from FLK Level 22 (FLK Zinj), Bed I, Olduvai Gorge using a new GIS spatial analysis approach. The FLK Zinj site contains some of the best preserved evidence for meat eating by hominins and has been used extensively in reconstructions of early hominin behavior. However, despite numerous interpretations of site function, there is currently no consensus regarding how hominins acquired carcasses at FLK Zinj. Some interpretations argue that Early Stone Age hominins had early access to fleshed carcasses through hunting or active scavenging, while others argue hominins had late access to largely defleshed carcasses through passive scavenging. In this study, GIS was used to record bone preservation in the FLK Zinj assemblage as well as in several modern, experimentally-modified bone assemblages, which are used for comparison. The placement of hominin- and carnivore-produced modifications was documented on bones from these assemblages, and the GIS Spatial Analyst was used to identify patterning in tooth mark clusters as well as patterning in cut mark locations. This analysis suggests hominins had early access to fleshed carcasses at FLK Zinj, particularly of smaller prey, which they may have acquired through hunting. Damage patterns on larger carcasses are more difficult to interpret, but are consistent with early access through hunting or aggressive scavenging. A reanalysis of carnivore tooth mark frequencies on the FLK Zinj bovid fauna also supports an early access scenario.

Analysis of Nonlinear Error Caused by Motions of Rotation Axes for Five-Axis Machine Tools with Orthogonal Configuration

Since a nonlinear relationship exists between the position coordinates of the rotation axes and components of the tool orientation, the tool will deviate from the required plane, resulting in nonlinear errors and deterioration of machining accuracy. Few attempts have been made to obtain a general formula and common rules for nonlinear error because of the existence of various kinematic structures of machine tools with orthogonal configuration. This paper analyzes the relationship between the deviation of cutter location points and motion of tool orientations. Five-axis CNC machine tools are divided into two groups according to the configuration of the two rotational joints and the home position. Motions of the tool are regarded as a combination of translation and rotation. A model for error calculation is then built. The maximum deviation of the tool with respect to the reference plane generated by the initial and the final orientation is used to quantify the magnitude of the errors. General formulas are derived and common change rules are analyzed. Finally, machining experiment is conducted to validate the theoretical analysis. The research has important implications on the selection of a particular kinematic configuration that may achieve higher accuracy for a specific machining task.

Conversion method study from cutter-location points to nonuniform rational B-spline toolpath NC file for high-speed machining

Parts with complex curved surfaces are widely applied and the demands for the machining quality and the machining efficiency of such complex parts become increasingly higher. In order to realize high-speed and high-quality machining, the nonuniform rational B-spline interpolator is widely researched and demonstrated to be superior to the conventional linear or circular interpolators. However, the nonuniform rational B-spline toolpath NC files cannot be directly generated from the computer-aided design (CAD) models by using commercial computer-aided manufacturing (CAM) software. To deal with this problem, a conversion method from the cutter-location points to the nonuniform rational B-spline toolpath numerical control (NC) file is presented. To avoid the bad curve-fitting effect at sharp corners of the toolpath and to meanwhile reduce the computational burden, the cutter-location pre-processing method, consisting data segmentation and data simplification, is provided first. Then, the least-square method is employed to fit the cutter locations to the nonuniform rational B-spline curves, and an iterative fitting approach is proposed for linear/nonuniform rational B-spline hybrid toolpath generation. Finally, a user interface is designed for displaying the fitting results and outputting the NC file with nonuniform rational B-spline toolpaths. By using this method, nonuniform rational B-spline and linear toolpaths hybrid interpolation NC program can be generated for the high-speed machining of complex curved surface parts with the utilization of the nonuniform rational B-spline interpolator. The experimental results demonstrate the feasibility and the advantages of the presented method.

An Error Compensation Method for Rectangular Window Based on NURBS Reconstruction Theory

Aiming at the error compensation problem for rectangular window, this paper presents a method of compensation for rectangular window based on NURBS (Non-Uniform Rational B-Splines) reconstruction. In the method, the machining surface is digitally obtained by means of on-machine measurement. The measured data are divided into four regions and different error compensation schemes are used for different regions. The adaptive compensation of the machining error calculated based on NURBS reconstruction theory is achieved by modifying the coordinates of the tool point in the cutter location file. The automation of error calculation and compensation is implemented by software development based on Visual Studio 2012. At the end of the paper, a compensating tool path is emulated in VERICUT. The results show our method is feasible.

Surface form error prediction in five-axis flank milling of thin-walled parts

Abstract The dimensional tolerance of flexible, thin-walled aerospace parts can be violated by the excessive static deflections during milling. This paper proposes a method to predict the dimensional surface form errors caused by deflections of both flexible workpiece and slender end-mill in five-axis flank milling of thin-walled parts. The end-mill is modeled as a cantilevered beam. The stiffness of the thin-walled part varies as the metal is removed and the tool-part contact location changes. The time varying stiffness of the thin-walled part is predicted by an efficient structural stiffness modification method that only needs the FE model of the initial workpiece and avoids re-meshing the part at each cutter location. The cutting forces are distributed over both the cutting tool and the part in the engagement zone, and the effect of deflections on the immersion is calculated. The effect of radial runout of the tool is considered in chip thickness, hence in the cutting force prediction. Finally, the cutter and the workpiece deflections are considered to predict the surface errors left on the finished part. The proposed method has been proven in five-axis blade milling experiments.

A solid-analytical-based model for extracting cutter-workpiece engagement in 5-axis flank machining

5-axis flank milling is applied extensively in aerospace, die-molds, and automotive industries because of high efficient material removal rate. Commercial CAM software can only simulate the tool path and collision at present, but cannot handle with cutting force during cutting process due to the variable geometrical cutter workpiece engagement (CWE) region of 5-axis milling. This paper presents a novel solid analytical model for extracting the CWE maps. The CWE is obtained analytically by performing Boolean operations between the cutter and in-process-workpiece (IPW) at any given cutter location (CL) point, instead of using the cutter and the removal volume. The proposed process simulation method could identify the CWE efficiently and precisely for general cutting tools. Finally, the CWE boundaries are mapped from a 3D space into a 2D plane defined by the immersion angle and the axial depth of a given cutter. The proposed solution can be easily integrated into the CAM software for predicting milling force and optimizing parameters in 5-axis milling.

High order analysis of the limit cycle of the van der Pol oscillator

We have applied the Lindstedt-Poincaré method to study the limit cycle of the van der Pol oscillator, obtaining the numerical coefficients of the series for the period and for the amplitude to order 859. Hermite-Padé approximants have been used to extract the location of the branch cut of the series with unprecedented accuracy (100 digits). Both series have then been resummed using an approach based on Padé approximants, where the exact asymptotic behaviors of the period and the amplitude are taken into account. Our results improve drastically all previous results obtained on this subject.

CutFEM Method for Stefan--Signorini Problems with Application in Pulsed Laser Ablation

In this article, we develop a cut finite element method for one-phase Stefan problems with applications in laser manufacturing. The geometry of the workpiece is represented implicitly via a level set function. Material above the melting/vaporization temperature is represented by a fictitious gas phase. The moving interface between the workpiece and the fictitious gas phase may cut arbitrarily through the elements of the finite element mesh, which remains fixed throughout the simulation, thereby circumventing the need for cumbersome remeshing operations. The primal/dual formulation of the linear one-phase Stefan problem is recast into a primal nonlinear formulation using a Nitsche-type approach, which avoids the difficulty of constructing inf-sup stable primal/dual pairs. Through the careful derivation of stabilization terms, we show that the proposed Stefan--Signorini--Nitsche CutFEM method remains stable independently of the cut location. In addition, we obtain optimal convergence with respect to space and time refinement. Several 2D and 3D examples are proposed, highlighting the robustness and flexibility of the algorithm, together with its relevance to the field of micromanufacturing.

Tool path generation for the five-axis CNC multi-stage incremental forming

Because the intermediate-stage forming surface and the intermediate-stage forming tool path of the complex shape model are difficult to generate, the existing multi-stage CNC incremental forming takes the regular rotary body model or the square model as the research objects, and all adopt the three-axis CNC incremental forming mode. In this paper, a method for generating the intermediate-stage surface by using a longitude line that can reflect the personality of the surface and the five-axis CNC multi-stage incremental forming tool path was proposed. Firstly, the vertexes of the triangular facets of the STL model are used to generate the longitude lines which can reflect the characteristic of the surface, then the longitude lines are offset according to the multi-stage forming strategy and the characteristics of each surface associated with the longitude lines so that the intermediate-stage longitude lines could be generated, and then the intermediate-stage surfaces are built using the intermediate-stage longitude lines. Finally, the cutter location points of each intermediate stage are obtained by cutting the intermediate-stage surfaces, and the postures of the five-axis CNC pressing tool are determined according to the normal vector of the cutter location points. The case studies show that the proposed method can well generate the five-axis CNC multi-stage incremental forming path for the complex shape sheet metal part. The results of the numerical simulation analysis and forming experiments show that the proposed method is applicable.

Development of post-processor approach for an industrial robot FANUC R2000iC

In this paper, a post-processor for the industrial robot FANUC R2000iC is introduced. Without going through the conventional teaching process, the post-processor regularly generates a rigorous robotic program from cutter location source data called CLS data. The CLS data are easily made through the main process of CAD/CAM, so that a promising data interface is realized between the industrial robot and CAD/CAM. The effectiveness is evaluated through simulations of trajectory following and also through an actual machining experiment of foamed polystyrene with a complex shape.

Machining robot with vibrational motion and 3D printer-like data interface

In this paper, a vibration motion control is proposed and implemented on a foamed polystyrene machining robot to suppress the generation of undesirable cusp marks, and the basic performance of the controller is verified through machining experiments of foamed polystyrene. Then, a 3 dimensional (3D) printer-like data interface is proposed for the machining robot. The 3D data interface enables to control the machining robot directly using stereolithography (STL) data without conducting any computer-aided manufacturing (CAM) process. This is done by developing a robotic preprocessor that helps to remove the need for the conventional CAM process by directly converting the STL data into cutter location source data called cutter location (CL) or cutter location source (CLS) data. The STL is a file format proposed by 3D systems, and recently is supported by many computer aided design (CAD)/CAM softwares. The STL is widely used for rapid prototyping with a 3D printer which is a typical additive manufacturing system. The STL deals with a triangular representation of a curved surface geometry. The developed 3D printer-like data interface allows to directly control the machining robot through a zigzag path, rectangular spiral path and circular spiral path generated according to the information included in STL data. The effectiveness and usefulness of the developed system are demonstrated through actual machining experiments.

Tool-path planning with constraint of cutting force fluctuation for curved surface machining

Curved surface parts are widely used in the industrial applications and the three-axis NC machining with ball-end cutter is the commonly adopted method for certain curved surface parts machining due to its high stiffness and simple operation. With the usage of this approach, the cutting area for different machining positions of the curved surface is changing all the time which results in a severe cutting force fluctuation among the machining process and the cutting force fluctuation is one of the vital factors that affect the machining quality of curved surface parts and the tool life. For the tool-path becomes the main factor that influences the cutting force fluctuation under the condition that the processing condition is determined, an appropriate tool-path planning method with the constraint of cutting force fluctuation for the curved surface machining is crucial for not only guaranteeing machining quality but also prolonging tool life. Based on the cutter location points obtained by the constant scallop-height method, cutting path interval and cutting step length are optimized and the cutter location mesh units are divided firstly, so as to meet the geometry accuracy for the curved surface machining. Taking the nodes of the cutter location mesh units as the cutter location points, the tool-path planning with the constraint of small cutting force fluctuation for the curved surface machining is carried out to improve the surface quality. Taking a saddle surface workpiece as an example, the experimental results show that the novel tool-path planning method proposed in this study has the smallest cutting force fluctuation compared with the other three traditional tool-path planning methods and can truly improve the machining quality of the curved surface parts. This research puts forward an novel tool-path planning approach on account of both the geometric feature of curved surface and the cutting force fluctuation in machining process of the curved surface parts, which provides a guidance for superior quality and high efficiency machining.

Post-processor development for a turning and milling composite machine tool

The accomplishment of a turning and five-axis milling in only one setup is extremely useful and is possible on a turning and milling composite machine tool. In this work, we present a control algorithm and develop a post-processor for this machine, which has six linear and three rotary axes. To calculate a generalized kinematics model, coordinate systems are established by analyzing the basic kinematic chain relation of the turning and milling composite machine tool. The two vectors, which control the motions of the cutter contact workpiece, are simultaneously transformed to provide the algorithms of the rotary angles and motion coordinate. A special post-processor written in JAVA language is developed according to the proposed algorithm. To evaluate the effectiveness and accuracy of the developed post-processor, a specimen (blade) is used in the cutting simulation and real machining experiment. Experimental results showed the effectiveness and accuracy of the proposed algorithm. Furthermore, Compatibility is improved by adding new functions such as change of target machine, cutter location data change, workpiece origin offset, and cutting feed rate control.

Elliptical curve machining with variable feed rate for shape accuracy

Abstract Generally, tool path deviates from curved geometry as tool path interpolates linearly between two successive cutter location points. Deviation of the tool is directly proportionate with a curvature of the geometry. Any approach improving the shape accuracy is laborious and time consuming. The main objective of the present study is to reduce the problem of shape accuracy. This required generating a curved profile from a set of control points such that the tool moves smooth from one point to another point. Various methods are studied for the interpolation of elliptical curve by deciding a number of control points as per curvature. The control points can be decided by two ways: a) Minimizing difference between arc length and chord length between two cutter location points. b) Minimizing chordal height between two successive cutter location points on the curve. The novel approach, finding shape error by the intersection of lines, is suggested to determine the number of control points to improve shape accuracy. Variable feed rate is proposed as per the number of control points considering the curvature effect of the tool path. The shape accuracy of elliptical curve of the present approach is compared with the earlier studies and reported.

Inverse kinematics for a novel hybrid parallel–serial five-axis machine tool

A unique successful postprocessor for a hybrid parallel-serial machine tool is developed.Smart machining must be accomplished without forcing the tool to make sharp turns when HSM controls detect a turn approaching.NC codes are recalculated to form a new path for the pivot that can avoid the discretization near the singularity points in this study.The novelty of the paper is successfully to propose a new hybrid parallel-serial five-axis machining model.The manufacturers that are interested in integrating the inverse kinematics into the design process of their hybrid product. Instead of obsessively emphasizing to interpolate more points from the linearization algorithm, the NC codes are recalculated to form a new path for the pivot that can avoid the discretization near the singularity points in this study. In previous studies, orientable-spindle machines were directly used to generate smooth tool paths traversing singular positions through inverse kinematics. In many characteristics and practices, PKMs (parallel kinematic machines) and serial machines are the opposites of each other. Fully PKMs have relatively very limited working-space, especially in terms of orientation characteristics. Fully serial machines have a problem of error accumulation. This paper presents a modular method to construct a postprocessor system for a novel hybrid parallel-serial five-axis machine tool. A hybrid parallel-serial mathematical model is introduced to analyze a structural configuration. The configuration decomposition of machine tools is used to create the kernel of the postprocessor. The proposed modified DenavitHartenberg notation is used in the coordinate conversion procedure, and then an algorithm is used for developing the inverse kinematics of five-axis machines. The feasibility of solutions depends on the surface normal along the tool path satisfying certain orientation constraints. The proposed algorithm can be easily adapted to convert between cutter contact path and cutter location code and implemented on computer-aided design and computer-aided manufacturing systems. Examples with end-milling and side-milling tools are demonstrated and real cutting parts are implemented for verifying the algorithm.

Using Procedure Based on Item Response Theory to Evaluate Classification Consistency Indices in the Practice of Large-Scale Assessment.

In spite of the growing interest in the methods of evaluating the classification consistency (CC) indices, only few researches are available in the field of applying these methods in the practice of large-scale educational assessment. In addition, only few studies considered the influence of practical factors, for example, the examinee ability distribution, the cut score location and the score scale, on the performance of CC indices. Using the newly developed Lee's procedure based on the item response theory (IRT), the main purpose of this study is to investigate the performance of CC indices when practical factors are taken into consideration. A simulation study and an empirical study were conducted under comprehensive conditions. Results suggested that with negatively skewed distribution, the CC indices were larger than with other distributions. Interactions occurred among ability distribution, cut score location, and score scale. Consequently, Lee's IRT procedure is reliable to be used in the field of large-scale educational assessment, and when reporting the indices, it should be treated with caution as testing conditions may vary a lot.

Optimization of machining strip width using effective cutting shape of flat-end cutter for five-axis free-form surface machining

Tool postures of the flat-end cutter can make a huge difference to both machining strip width and machining efficiency in five-axis end milling. Most of current methods evaluate the machining strip width and implement a tool orientation optimization by finding two intersection points between the effective cutting profile of a flat-end cutter and the offset surface profile which represents machined surface. However, real machining strip width and real residual height should be formed between two adjacent cutter contours. As the results, two problems of current methods cannot be avoided: (1) Machining strip width computed on a single cutter location cannot accurately represent the distance between two adjacent tool paths and (2) excessive overlap or larger span length between two adjacent cutter contours leads to unsteady residual height, which causes surface quality differences. In order to solve the above problems, a more suitable method for computing machining strip width is presented and proved in this paper. A flat-end cutter is adopted and the analytical model of effective cutting shape for this kind of tool is constructed firstly. Later, a geometric foundation to achieve optimization is established by investigating the impact of different flat-end cutter postures on the machining strip width. Furthermore, the reasonable strip width is obtained and optimized by implementing an iterative and optimization approach under the given scallop height. A three-dimensional centrifugal compressor blade is used as a numerical example to verify the approach presented in this paper. To prove the superiority of the involved method, the research gives a comparison with UG method with the same cutting parameters. Numerical experiment suggests that machining efficiency of the paper’s method improves by 37.85%. Finally, a machining simulation is performed in the VERICUT software to testify that a uniform error distribution is created.

An efficient algorithm for calculating the cutter location point based on projection method

Aiming at improving the efficiency of calculating the cutter location point with toroid cutter based on the projection method in NC machining for surface, a new algorithm is proposed to calculate the cutter location point directly by torus surface approximating the surface to be machined. According to the geometric information of the points on the surface, the geometrical conditions of the two tangential tori are figured out, and then the contact point is obtained by solving multivariate non-linear equations. Parameters of the tangent point on the surface to be machined are calculated in the next step. Finally, the cutter location point is calculated by a small adjustment. The proposed algorithm is applied to calculate the cutter location point with toroid cutter in surface machining and compared with the existing algorithm. The results show that the computing time of the proposed algorithm in this paper saved about 63–78%.

An optimization method of tool-path parameters for curved surface by construction of cutter location mesh units

Curved surface parts are widely used in industrial applications and its machining is still a major problem because of the continuously geometric feature variation. When the processing condition is determined, the machining quality and efficiency of curved surface are affected directly by the generation of tool-path, especially by the selection of tool-path parameters including cutting step length and cutting path interval. However, the common selection method for cutting step length and cutting path interval is usually conservative in the tool-path planning process for curved surface parts, so as to affect the machining efficiency. In this way, an optimization method of tool-path parameters for curved surface by the construction of cutter location mesh units is proposed. Based on the cutter location points obtained by constant scallop-height method, the cutter location mesh units are constructed by optimizing cutting step length and cutting path interval, and then the nodes of the cutter location mesh units are taken as the final cutter location points. Take a saddle surface workpiece as an example, the results of simulation and experiment show that the tool-path with the optimized cutting step length and cutting path interval can not only maintain the machining quality but also improve the machining efficiency obviously. These research achievements are of vital importance in tool-path planning for realizing high-quality and high-efficient machining for the curved surface parts.