A Cutter Orientation Modification Method for the Reduction of Non-linearity Errors in Five-Axis CNC Machining

In the machining of sculptured surfaces, five-axis CNC machine tools provide more flexibility to realize the cutter position as its axis orientation spatially changes. Conventional five-axis machining uses straight line segments to connect consecutive machining data points, and uses linear interpolation to generate command signals for positions between end points. Due to five-axis simultaneous and coupled rotary and linear movements, the actual machining motion trajectory is a non-linear path. The non-linear curve segments deviate from the linearly interpolated straight line segments, resulting in a non-linearity machining error in each machining step. These non-linearity errors, in addition to the linearity error, commonly create obstacles to the assurance of high machining precision. In this paper, a novel methodology for solving the non-linearity errors problem in five-axis CNC machining is presented. The proposed method is based on the machine type-specific kinematics and the machining motion trajectory. Non-linearity errors are reduced by modifying the cutter orientations without inserting additional machining data points. An off-line processing of a set of tool path data for machining a sculptured surface illustrates that the proposed method increases machining precision.     

A local smoothing interpolation method for short line segments to realize continuous motion of tool axis acceleration

In traditional processing, a large number of G01 blocks are adopted to discretize free surface or curve for NC machining. But, the continuity of G01 line segments is only C⁰, which may lead to discontinuity of axis acceleration, resulting in the frequent fluctuation of tool motion at the junctions in high-speed machining, deteriorating the quality of work piece, and reducing processing efficiency. To solve this problem, a local smoothing interpolation method is proposed in this paper. At first, the analytic relationship between the continuity of the trajectory and the continuity of the axes motion is first systematically described by formula. Based on this relationship, a local smoothing algorithm and a feed-rate scheduling method are proposed to generate a C² continuous tool path motion with axis-acceleration continuity. The local smoothing algorithm smoothes the corners of G01 blocks by the cubic B-spline according to the cornering error tolerance specified by the user. After the feed rate at critical points of smoothed tool path was determined by a modified bidirectional scanning algorithm by considering constrains of chord error and kinematic property, an iterative S-shape feed rate scheduling is employed to minimize residual distance caused by round of time while ensuring the continuity of feed rate and acceleration. Then, a look-ahead interpolation strategy combined with smoothing algorithm and feed-rate scheduling as mentioned is proposed for real-time interpolation of short line segments. At last, simulations are conducted to verify the effectiveness of the proposed methods. Compared with the traditional G01 interpolation, it can significantly improve the processing efficiency and shorten the processing time within error tolerance.     

Tool path optimization in postprocessor of five-axis machine tools

Generally, tool path is generated in a computer-aided manufacturing software considering only the geometry of machining parts. It is converted into numerical control (NC) codes in the postprocessor based on the particular machine kinematics. For some special types of five-axis machine tools, e.g., non-orthogonal five-axis machine tools, the generated NC codes may produce unqualified parts because of the existence of the non-linear error. Conventional commercialized postprocessors usually do not have the function of non-linear error checking. Observing that the tool path is a non-smooth trajectory full of corners and a series of connected line segments, cubic spline interpolation is applied to smooth the tool path at regular points in this study. The cutter tip center points are computed by the cubic spine interpolation, while the cutter posture vectors are obtained via linear interpolation. At the splines (for regular points) and the line segments (feature points), more points are chosen to be converted into NC codes to reduce the non-linear error, which is called data densification. Using the cubic spline to smooth the tool path and the data densification to reduce the non-linear error, a novel tool path optimization algorithm in postprocessor is proposed. Experiments were carried out on an inclined rotary spindle axis non-orthogonal five-axis machine tool. It shows that the proposed tool path optimization provides improved accuracy and surface quality.     

焊接机器人的摆动焊接轨迹规划策略研究

基于机器人空间直线插补和圆弧插补算法,设计了时间最优的空间直线摆焊轨迹和圆弧摆焊轨迹规划的策略,并于MATLAB软件中完成验证路径算法。最后通过由VS2019搭建的上位机示教软件、基于STM32H7平台设计的运动控制卡和SCARA机器人平台组成的控制系统,验证了算法的可靠性和准确性。实验结果表明,用户可以通过示教焊接机器人的方式获取空间摆焊的参数,并且机器人能够根据获取的参数在限定的轨迹上进行较为高效的空间直线摆焊运动和空间圆弧摆焊运动,具有一定的实际意义和参考价值。     

数控机床高精度轨迹控制的一种新方法

针对数控技术和装备向高速高精度发展的需求,研究开发了一种新的高精度轨迹控制技术。其核心内容是以高频高分辨率采样插补生成刀具运动轨迹,通过新型转角—线位移双位置闭环控制保证希望轨迹的准确实现,并以信息化轨迹校正消除机械误差和干扰对轨迹精度的影响,从而保证所控制的机床可在生产环境中长期高精度运行。由此构成的新型数控系统已在多种国产数控机床上进行了应用,取得了良好效果。     

基于摆线运动规律的悬索并联机器人轨迹规划

六自由度绳索悬挂式并联机器人属于大柔性机械系统，为保证运动的平稳性，要求动平台的运动轨迹光滑连续，为此提出了基于摆线运动规律的笛卡儿空间连续轨迹规划方法，该方法计算简单，实时性好。利用该方法对直线轨迹、圆轨迹和过离散点轨迹进行了规划。运动学和动力学方程的计算结果表明，绳索的速度、加速度和拉力变化连续平缓，而且绳索拉力始终大于0，因此动平台运行过程中动态响应小，绳索张紧可靠。该方法适用于悬索机器人的轨迹规划，同样也适用于对运动平稳性要求较高的其它机器人系统。     

隐曲线的线性和旋转插补

基于数控五轴刀具运动分析,提出了旋转插补的概念,给出了旋转插补的相关定义,在此基础上提出了隐曲线的线性和旋转插补原理和方法,并进一步提出了改进的插补方法。     

基于高阶非均匀有理 B 样条插补的多轴运动控制方法研究

针对传统多轴运动控制系统在作业中存在轨迹转折处不平顺、加速度和加加速度切换不平滑产生变速冲击以及轨迹不能进行局部修改的问题,提出了一种基于高阶非均匀有理 B 样条插补的多轴运动控制算法。首先,构建五次非均匀有理 B 样条插补算法,对样条曲线数据进行预处理,根据非均匀有理 B 样条曲线反算出控制点并生成控制多边形;其次,利用 MATLAB 构建多轴机械臂和高阶非均匀有理 B 样条插补算法模型,通过给定型值点进行轨迹规划仿真。仿真结果表明:基于高阶非均匀有理 B 样条的多轴运动控制插补方法相对于低阶非均匀有理 B 样条曲线轨迹更圆滑,末端更能高效平稳地到达给定目标点;速度、加速度和加加速度的过渡更加平滑减少机械磨损,从而提高了运动的平稳性;并且该方法还能够对运动轨迹进行局部修改,提升了多轴运动控制的作业质量。     

虚拟轴机床刀具运动轨迹的直接控制

本文提出了虚拟轴机床刀具运动轨迹的直接控制方法,该方法可根据可信息和加工工艺信息,直接生成刀具希望轨迹和虚轴运动指令,并通过虚实变换对实轴的联动控制,从而有效保证刀具轨迹与希望轨迹一致,所得结果为开发新型虚拟轴机床控制系统奠定了基础。     

5轴联动数控系统速度控制方法

高速加工过程中,在刀具路径上容易产生过冲,影响加工精度,因此必须提前对加工速度进行优化处理.基于数据采样法,利用当量位移和坐标轴方向系数实现了5轴联动线性插补;利用直线加减速原理进行插补前加减速控制;对速度前瞻控制方法进行了深入探讨,实现了相邻程序段转接处速度优化、连续微小程序段速度计算、减速点提前预测及前瞻程序段数动态选择等.仿真结果表明,速度平滑连续,有效地解决了5轴联动线性插补中的速度控制问题,提高了加工精度和加工效率.     

基于轨迹控制的AGV运动控制器设计研究

对基于计算机视觉的AGV路径跟踪技术进行了研究,提出了基于轨迹控制的AGV运动控制器设计新方法,重点解决AGV路径跟踪效果与高速运动稳定性问题。首先对AGV工作环境与计算机视觉的特点进行分析,设计了适合AGV路径跟踪的图像处理流程。然后在深入分析两轮差速驱动运动平台的基础上,提出了基于轨迹控制的AGV运动控制器设计新方法。该控制器以AGV相对路径所处的状态量为输入,输出AGV控制指令——两轮的速度差和运动时间,从而控制AGV按指定轨迹运动,实现轨迹控制即AGV路径跟踪的目标。试验结果表明,AGV路径跟踪技术对直线和弧线具有较好的跟踪效果且AGV运动平稳。     

基于曲线物理模型的轨迹运动规律研究

为了把轨迹的位置控制转变为运动规律控制,取消插补运算,建立数控机床运动控制的物理模型。根据运动学原理和几何学原理研究轨迹的几何参数、运动参数、规划参数之间的关系,写出了轨迹运动微分方程组。根据轨迹函数、规划参数可以计算出各坐标轴的瞬态运动参数。运动规律的代表是一组运动参数,用运动参数控制运动等于同时控制运动规律和几何规律。一条轨迹的位置点有无穷多个,但规律只有一个,按运动规律控制的方法是最简捷、最全面的。经过试验和仿真,证明运动参数控制轨迹的方法是能够同时控制位置和运动的好方法。     

TRAJECTORY GENERATION AND CONTROL FOR NON-CIRCULAR CNC TURNING

A trajectory generation method which is based on NURBS interpolation is studied to improve the fitting accuracy and smoothness of non-circular cross section and obtain higher accuracy of the final non-circular profile control. After using the NURBS, the most optimized and smooth trajectory for the linear actuator can be obtained. For the purpose of machining the non-circular cross section by CNC turning, the fast response linear actuator has been used. The control algorithm which is compound control of proportional-integral-differential （PID） and iterative learning control has been developed for non-circular profile generation. By using the NURBS interpolation and the compound control of PID and iterative learning control, the final motion accuracy of linear actuator has been improved, therefore, the machining accuracy of the non-circular turning can be improved.     

面向铣削加工的STEP-NC文件到G代码转换技术

为使STEP-NC能在传统的数控系统中得到应用,研究了面向铣削加工的STEP-NC数控文件到传统G代码程序的转换技术,提出了一种面向制造特征的刀具轨迹规划方法。首先对制造特征进行分类,然后为每类制造特征设计走刀轨迹模型,在进行G代码转换时,通过前置处理将制造特征的走刀轨迹模型转换成对应数控系统的宏程序,不但提高了G代码的转换效率,而且缩短了G代码程序的长度。论述了STEP-NC文件信息提取和信息处理技术,以及G代码程序自动转换过程。最后,以一个铣削类零件为例,对上述技术进行了测试和验证。     

五轴联动数控加工的刀具路径优化方法研究

为解决五轴联动加工复杂曲面过程中的刀具路径不连续问题,提出了五轴数控的刀具路径优化方法。通过五轴NC代码的坐标变换还原有效切削路径,对切削路径进行误差约束下的非均匀有理B样条(NURBS)曲线拟合。对旋转轴路径采用五次样条曲线进行插值,建立切削路径和旋转轴路径的参数映射关系,通过机床逆运动变换求解C2连续的平动轴路径。实验表明,经过该方法优化后,切削路径和各驱动轴运动路径具有良好的平滑性,显著提高了五轴加工曲面精度和表面质量。     

基于DMC的机器人轨迹规划研究与实现

在分析6自由度机器人运动控制系统架构的基础上,提出基于DMC(digital motion controller)的开放式运动控制系统的6自由度机器人轨迹插补算法.主要研究在笛卡尔空间规划中直线的插补算法.同时介绍了插补算法在DMC上的具体实现方式.实验证明了控制器能可靠精确地实现机器人轨迹运动.     

基于粒子群算法的机械平台自动升降轨迹控制方法

机械平台升降轨迹受到多个关节、连杆运动参量的影响,很难对其进行精准控制,因此提出基于粒子群算法的机械平台自动升降轨迹控制方法。分析机械平台结构与基本参数,构建机械平台升降轨迹模型,采用多项式插值方法插值处理机械平台升降轨迹,获得轨迹插值方程,确立升降轨迹控制函数。采用粒子群算法求解升降轨迹控制函数,算法输出结果即为升降轨迹最佳控制量,从而实现机械平台自动升降轨迹控制。实验结果表明,该方法获取最佳控制量迭代次数较少,升降轨迹控制效果较好,应用性能较佳。     

五轴联动数控加工中的刀具轨迹控制算法

已有的五轴联动数控加工系统往往忽略刀轴矢量插补问题,只是简单地通过对线性轴进行插补、对旋转轴进行跟随的方式来实现刀具轨迹的控制,导致产生非线性误差和刀具碰撞与干涉等问题。为此,提出一种基于刀轴矢量插补的刀具轨迹控制算法。该算法采用大圆弧插补法对加工过程中的刀轴矢量进行控制,同时采用NURBS曲线拟合方法对控制过程中产生的中间点进行处理,并通过对拟合而成的NURBS曲线进行插补来实时计算各运动轴的位置。该算法不仅能够有效地提高五轴联动数控加工的精度,而且可以有效减小数据存储量。仿真和实际加工验证了算法的有效性和实用性,证明算法具有轨迹过渡平稳、非线性误差小的特点。     

数控机床高精度轨迹控制方法探讨

针对数控技术和装备向高速高精度发展的需求,研究开发了一种新的高精度轨迹控制技术。其核心内容是以高频高分辨率采样插补生成刀具运动轨迹,通过新型转角—线位移双位置闭环控制保证希望轨迹的准确实现,并以信息化轨迹校正消除机械误差和干扰对轨迹精度的影响,从而保证所控制的机床可在生产环境中长期高精度运行。由此构成的新型数控系统已在多种国产数控机床上进行了应用,取得了良好效果。     

Capturing the tacit knowledge of the skilled operator to program tool paths and tool orientations for robot belt grinding

This paper describes a novel methodology for generating grinding tool paths, orientations and grinding parameters based on the captured trajectories of a surface finishing tool operated by the skilled operator. First, a variable frame size moving window principal component analysis is performed on the trajectories. Next, features such as the amplitude, speed of the tool centre point, direction of travel, average position, contact force and orientation of the grinder are calculated. Kernel k-means clustering is applied to the trajectory’s feature vectors for segmentation into the tool path primitives. The robotic tool path primitives would be ordered similar to the manual tool path primitives in the grinding strategy. The robotic tool path primitives are then generated based on the boundaries of the manual tool path primitive in a computer-aided manufacturing software. Anchor points are selected from the corners and at intermediate sections along the robotic tool path to inherit the orientations of the manual tool path. Using the inherited skilled operator tool orientations, spherical linear interpolation and spherical spline quaternion interpolation are used to interpolate the orientations for the robotic tool path points along the cross curves, followed by the flow curves, respectively. A finite element model of the belt grinding process is also introduced to quantify the effect of the contact wheel serrations on the material removal rate. This is to account for the difference in contact wheel design between the handheld and robotic grinding tool. The programmed robotic tool paths generated from the trajectories captured from a skilled operator were proven to be able to grind the workpiece to the desired profile within the desired tolerance in a pre-production environment.