Sliding mode control with third-order contour error estimation for free-form contour following

To reduce the contour error in contour-following tasks, the most common method is to design a contour controller based on the contour error model. Therefore, how to estimate the contour error in real-time and with high accuracy plays an important role in contour-following control. It is difficult to guarantee real-time performance, high estimation accuracy and strong robustness against arbitrary trajectories at the same time. In this paper, a contour error estimation method based on the third-order osculating helix is proposed. The osculating helix can fully consider the geometric characteristics of the interpolation trajectory and is closer to the desired interpolation trajectory. On this basis, PD-type tracking error sliding mode surface and PD-type contour error sliding mode surface are redesigned to fully take into account the regulating effect of the velocity tracking error and velocity contour error. Experimental results demonstrate the effectiveness of the proposed contour control approach.     

A novel curvature circle iterative algorithm for contour error control of multi-axis CNC machine tools

High-precision real-time estimation of contouring errors is a prerequisite for contouring errors control of multi-axis CNC machine tools. This paper focuses on developing a nearest point projection curvature circle iterative (NPP–CCI) algorithm to achieve real-time estimation of multi-axis contouring errors. It is found that the traditional curvature circle iterative (CCI) method has two major shortcomings. The first is that the iterative process may terminate incorrectly at the local contour position, and the other is that the actual tool position and local curvature circle are not necessarily coplanar in three-dimensional space, which would lead to inaccurate calculation of the delay time parameter and eventually affect the estimation accuracy. In order to address the problem of false termination, an index method is used to find the closest reference position with respect to the actual position. At the same time, the projection technology is proposed to overcome the problem met in extending the planar curvature circle iterative method to the spatial applications. The proposed NPP-CCI algorithm is more suitable for spatial contouring errors estimation in tracking complex trajectories and has higher estimation accuracy than the traditional CCI algorithm. Various experiments with different tool paths are conducted on an in-house developed multi-axis experimental platform to verify the effectiveness of the proposed algorithm. The experimental results show that the NPP-CCI algorithm can estimate the contouring errors with higher accuracy than the traditional CCI algorithm, and with the help of real-time computation and compensation, the contouring errors are reduced by more than 44% in terms of the MAX and RMS values.     

Self-adjustment computing method for time-partition interpolation in motion trajectory control of CNC machine tools

For time-partition interpolation in computer numerical control of the motion trajectory of a machine tool, the trajectory in a sampling cycle is approximated by a line segment from the current position of the tool to another on the expected trajectory; and locating the terminal of the line is the goal of the interpolation. In this paper, a self-adjustment computing method applicable to any explicit curve type is proposed. With the method, the terminal of the linear moving path in a cycle is first estimated by the motion information in the previous cycle, then adjusted according to the ratio of the desired moving distance to the computed linear path length. The result of the computation is fairly accurate, and it can be further enhanced with more adjustments performed in a sampling cycle, which is demonstrated in the simulation results. Furthermore, an adaptive feedrate adjustment algorithm is also introduced to enable the proposed method to control the trajectory contour errors.     

Definition and estimation of joint-space contour error based on generalized curve for five-axis contour following control

Five-axis contour following is one of the main tasks for five-axis CNC machine tools. The contour following accuracy directly determines the final machining precision. Therefore, control of the five-axis contour error is significant. Currently, most existing definitions of five-axis contour error are in the Cartesian task space, and this inevitably requires direct and inverse Jacobian transformations between the task-space contour-error computation and the joint-space contour-error control. Different from them, this paper defines the five-axis contour error in the ℝ⁵ joint space through adjusting uniform units of five joints, and accordingly proposes a third-order estimation algorithm for the defined joint-space contour error, with the help of the concept of generalized curve. Based on the joint-space contour-error definition and estimation, a joint-space five-axis cross-coupling control scheme is finally provided. Simulation and experimental results demonstrate that the presented third-order joint-space contour-error estimation algorithm has a satisfactory estimation accuracy, and the presented joint-space five-axis contour control method can decrease both of the joint-space and the task-space five-axis contour errors by more than 49%. It is also analyzed and verified that comparing with routine task-space five-axis contour control method, the presented joint-space method not only needs not the direct and inverse Jacobian transformations during error estimation, which saves the computational burden, but also generates minimum axial contour-control commands, which enhances the control stability, thus resulting in better contour-following performances.     

The optimisation of the grinding of silicon carbide with diamond wheels using genetic algorithms

Modelling and optimisation are necessary for the control of any process to achieve improved product quality, high productivity and low cost. The grinding of silicon carbide is difficult because of its low fracture toughness, making it very sensitive to cracking. The efficient grinding of high performance ceramics involves the selection of operating parameters to maximise the MRR while maintaining the required surface finish and limiting surface damage. In the present work, experimental studies have been carried out to obtain optimum conditions for silicon carbide grinding. The effect of wheel grit size and grinding parameters such as wheel depth of cut and work feed rate on the surface roughness and damage are investigated. The significance of these parameters, on the surface roughness and the number of flaws, has been established using the analysis of variance. Mathematical models have also been developed for estimating the surface roughness and the number of flaws on the basis of experimental results. The optimisation of silicon carbide grinding has been carried out using genetic algorithms to obtain a maximum MRR with reference to surface finish and damage.Nomenclature C constant in mathematical model - C₁ constant in surface roughness model - C₂ constant in the number of flaws model - d depth of cut, m - dof degrees of freedom - f table feed rate, mm/min - M grit size (mesh) - MRR material removal rate, mm³/mm width-min - N_c number of flaws measured - R_a surface roughness measured, m - Y machining response - depth of cut exponent in mathematical model - ₁ depth of cut exponent in surface roughness model - ₂ depth of cut exponent in number of flaws model - feed rate exponent in mathematical model - ₁ feed rate exponent in surface roughness model - ₂ feed rate exponent in number of flaws model - grit size exponent in mathematical model - ₁ grit size exponent in surface roughness model - ₂ grit size exponent in number of flaws model     

一种基于遗传算法的装配序列优化方法

基于遗传算法建立了装配序列生成模型,对装配序列进行优化生成。为提高优化效率,该算法将装配方向作为已知数据给出,并引入子装配体进行分层规划。最后,以蜗轮减速器装拆序列规划为实例验证该方法的有效性。     

基于步距规的数控机床误差测量和补偿技术

提出一种在工业现场进行单轴高精度位置误差的测量系统.使用步距规,可以用来代替激光干涉仪进行轴线位置的高精度标定;安装简单,操作容易.对轴线位置误差的补偿结果表明,通过该方法,可以使机床实现"软"升级.     

Developing a genetic optimisation approach to balance an apparel assembly line

In apparel manufacturing, it is difficult to achieve line balance because the production rate of each workstation is different. This difficulty is particularly prominent in the labour-intensive assembly process. The development of a line balancing technique using genetic algorithms is thus proposed for optimising the assignment of operators in an assembly line. The impact of a different level of skill inventory SI_n on the assembly makespan is also investigated in order to find out the optimal number of task skills an operator should possess in the apparel assembly process. Experimental results will be discussed to demonstrate the performance of the proposed genetic optimisation approach.     

数控机床空间几何误差测量研究进展

数控机床是衡量国家制造装配业水平的重要标志,数控机床的加工精度是反映其性能和水平的一个关键指标。误差补偿是提高数控机床加工精度的一个主要途径和发展趋势,数控机床空间误差快速、精确测量是进行误差补偿、提高数控机床精度的前提与关键。如何快速准确测量数控机床各种误差成为国内外测量域的一个研究热点和重点,出现了很多不同类型的测量方法和仪器。按测量仪方法及仪器与测量策略这两条主线,对现有数控机床空间几何误差测量方法进行较全面介绍,分析了各种方法的优缺点,讨论了其发展趋势。     

数控机床精度评价和螺距误差补偿技术研究

建立了螺距误差补偿的数学模型，设计了利用光栅尺进行螺距误差补偿的装置。对补偿前后的螺距误差进行了精度评价，结果表明，经过螺距误差的补偿，数控机床位置误差降低，实现了机床精度的软升级。     

A Linear Cross-Coupled Control System for High-Speed Machining

We present a linear cross-coupled controller to improve highspeed contouring accuracy independently of tracking accuracy in a biaxial machine tool feed drive servomechanism. Unlike conventional cross-coupled controllers, the cross-coupled controller presented here is a linear system, so it is very easy to perform the stability and steady-state error analysis, and to optimise the controller parameters. The proposed controller is evaluated experimentally on a CNC LOM machine and compared to an uncoupled controller and a conventional cross-coupled controller. Controller performance is evaluated for a circular contour at a feedrate of 30 m min _1 . The experimental results show that the proposed controller can greatly reduce the contour error at large feedrates. The linear cross-coupled controller is simple to implement and is practical.     

数控机床切削负荷误差补偿装置的设计

以开放式数控系统-华中I型为平台研制了数控机床切削负荷误差补偿装置,介绍了这套基于电流检测和处理技术的负荷误差补偿装置的基本构架和设计方法,这套装置被用于数控铣削粗加工中,被证明是成功、有效的,它显著提高了机床加工效率和加工精度。     

符合阿贝原则的数控机床几何误差建模

为提高现有数控机床空间误差分析方法的准确度,本文基于阿贝原则对齐次转换矩阵(HTM)几何误差补偿模型进行优化。首先,推导出XYFZ型三轴机床适用的HTM几何误差补偿模型并给出模型正确使用的前提条件;然后,基于阿贝原则分析了三轴机床的空间误差传递机理,指出阿贝误差对机床定位精度的影响,给出理论计算公式并在机床运动轴上进行实验验证;最后,基于阿贝原则和布莱恩原则对现有的HTM几何误差补偿模型进行优化,采用该模型拟合体对角线空间误差,并与实测机床体对角线误差进行对比验证。现有HTM几何补偿模型可将机床空间误差由41.15μm补偿至16.37μm,补偿率为60.22%;优化后的补偿模型可将机床空间误差补偿至5.32μm,补偿率为87.07%,提高了26.85%。实验结果表明,优化后的补偿模型更加合理,进一步改善了空间误差的补偿精度。     

PCB assembly planning using genetic algorithms

Printed circuit boards (PCB) are used extensively in industry for the manufacture of electronic and electromechanical products. One of the primary concerns in the manufacture of PCBs is the determination of the optimal assembly plan. This paper presents work that leads to the development of an approach to PCB assembly planning using genetic algorithms (GAs). The approach takes into consideration component insertion priority and sequencing decision rules. A polygamy reproduction mechanism with dual mutation has been proposed and implemented. Details of the approach are described. A PCB model extracted from the literature was used for performance evaluation. Details of the evaluation are presented.     

Control of a manipulator robot by neuro-fuzzy subsets form approach control optimized by the genetic algorithms

In this paper, we describe a new form of neuro-fuzzy-genetic controller design for nonlinear system derived from a manipulator robot. The proposed method combines fuzzy logic and neuronal networks which are of growing interest in robotics, the neuro-fuzzy controller does not require the knowledge of the robot parameters values. Furtheremore, the genetic algorithms (GAs) for complex motion planning of robots require an evaluation function which takes into account multiple factors. An optimizing algorithm based on the genetic algorithms is applied in order to provide the most adequate shape of the fuzzy subsets that are considered as an interpolation functions. The proposed approach provides a well learning of the manipulator robot dynamics whatever the assigned task. Simulation and practical results illustrate the effectiveness of the proposed strategy. The advantages of the proposed method and the possibilities of further improvements are discussed.     

基于LS-SVM与遗传算法的数控机床热误差辨识温度传感器优化策略

提出一种在数控机床热误差辨识建模过程中,利用最小二乘支持向量机结合遗传算法对温度传感器进行筛选与优化的新方法。对布置在一台数控车床上的温度传感器进行了优化,首先根据热模态理论,对传感器进行分组,利用最小二乘支持向量机方法构建数控机床热误差辨识模型,再根据遗传算法对其进行传感器优化布置。结果表明,遗传算法与最小二乘支持向量机方法的结合,不但很好地避免温度测点的相互影响,保证模型精度,而且节约了硬件成本,提高了辨识建模速度。     

基于G代码修改的数控机床几何误差补偿方法

为减小数控机床的空间运动定位误差,研究了一种基于G代码修改的几何误差补偿方法。以多体系统理论为基础,构建起多轴数控机床的通用误差模型,并据此建立了三轴数控机床空间误差模型。提出三维空间内任意直线轨迹的直线插补补偿算法和可提高圆心位置精度的平面内圆弧插补补偿算法,且这2种补偿算法都可分别设定不同的插补精度。采用修改G代码方式实现补偿方法的通用性,在XZOY型三轴数控机床上开展了误差补偿实验,验证了其有效性。     

Stochastic U-line balancing using genetic algorithms

The advantages of U-type lines are very well known in industry. They offer improved productivity and quality, and are considered as one of the better techniques in implementing just-in-time (JIT) systems. There is a growing interest in the literature to organize traditional assembly lines as U-lines for improved performance. U-type assembly line balancing is an extension of the traditional line balancing problem, in which tasks can be assigned from both sides of the precedence diagram. Although there are many studies in the literature for the design of traditional straight assembly lines, the work on U-type lines is limited. Moreover, in most of the previous studies, task times are assumed to be deterministic. In this paper, a new multiple-rule-based genetic algorithm (GA) is proposed for balancing U-type assembly lines with stochastic task times.     

数控机床热误差补偿最佳转速选择

为提高数控机床热误差补偿模型在实际工程应用中的补偿精度和稳健性,研究了热误差补偿建模时机床最佳转速状态的选择方法。首先,以Leaderway V-450数控加工中心主轴Z向为研究对象,控制机床主轴在空转状态下,以图谱和恒定转速两种方式进行了多批次实验。然后,采用模糊聚类结合灰色关联度选择温度敏感点并建立多元线性回归模型。最后,分析不同转速类型下模型的预测效果并对同种转速类型下模型预测效果进行相对评价,从而给出热误差补偿建模时机床最佳转速状态的选择方法。实验结果表明,根据国际标准中不同主轴转速类型建立的热误差补偿模型,对于机床热误差预测效果存在较大差异。根据实际工程应用选择的最佳转速状态建立的补偿模型有较好的预测效果。     

A geometrical approach to computer-aided process planning for computer-controlled machine tools

This paper documents part of a research program which has been under way at the CIM Centre at Swinburne University of Technology since 1989. The purpose of the research program was to develop an open-architecture machine tool control system and then to see how that system could be used to change the distribution of traditional manufacturing design, planning and control functions. This paper examines one part of that research program and focuses on a methodology which could prove to be useful in the machine tool selection, cutter selection and cutter path generation phases of process planning for cutting operations on workpieces in computer-controlled machine tools.It is suggested that a configuration space transform be used for each cutter/machine tool combination to find the volume that the combination could remove from the uncut workpiece without removing any of the material that will form the final workpiece. A method of comparing these volumes from different combinations is then outlined. The output of this method is a reasonable sequence of machine tools and cutters. Path planning can then be carried out for each of the chosen combinations using a method similar to the one used to find the possible volume to be removed.Possible implementation techniques, and their limitations on existing computer hardware, are discussed and the most promising of these are identified, based upon some properties of configuration space transforms.