一种实时前瞻的NURBS曲线加减速控制方法

结合NURBS曲线加减速机制,依据插补精度与进给速度的关系,提出了一种实时前瞻的NURBS曲线加减速控制方法。在保证给定弓高误差的基础上,通过对速度尖点的划分,将NURBS曲线划分为若干段,并对各个分段进行相应的速度规划处理。在速度规划过程中,选择相应的加减速曲线,重新计算并修正加减速时间段,得到相应的速度和加加速度,从而得到平滑的速度过渡曲线。通过仿真比较,验证了所提出的实时前瞻的五段S曲线加减速控制算法的正确性、有效性和实时性。     

基于de Boor算法的NURBS曲线插补和自适应速度控制研究

以NURBS曲线deBoor递推插补算法为基础，针对NURBS曲线速度处理的特殊性，建立了一种NURBS曲线自适应速度控制模型，该模型分为速度自适应控制和插补前加减速处理两部分。以deBoor算法为基础对整个插补周期的弓高误差以及切向和法向加速度进行实时监控，分析了误差产生的原因并进行了相应的速度控制；以插补前直线加减速为例引入NURBS反向插补的概念，解决了NURBS曲线减速区长度计算问题。实验结果表明，该模型满足实际的NURBS曲线插补的需要。     

基于曲线长度自调整速度方程的非均匀有理B样条插补算法

针对非均匀有理B样条(NURBS)曲线加工过程中速度规划复杂、效率低以及机床震颤剧烈的问题,提出一种高效规划进给速度的NURBS插补算法。预处理过程计算出待加工NURBS曲线插补参数及误差速度,根据误差速度曲线分析加工路径的加减速情况,并基于加/减速区间长度自动调整三次多项式速度方程,实现平滑的速度与加速度曲线;实时插补过程采用基于Adams-Moulton方法计算初始参数,然后采用二分法对参数进行寻优,将插补过程中速度波动控制到加工要求精度范围内,从而降低机床的振动。通过MATLAB仿真,验证了所提算法加减速规划的高效性和参数计算的精确性,表明该算法在复杂曲线曲面加工领域可以提高机床加工效率与精度。     

全程S曲线加减速控制的自适应分段NURBS曲线插补算法

为满足现代数控加工的高速度、高精度要求,提出基于7段式S曲线加减速全程规划的NURBS曲线自适应分段插补算法。该算法根据NURBS曲线几何形状将其自适应分段,并计算曲线段各项参数值、对应S曲线加减速规划(速度规划为17种类型)中加减速类型和自适应调整速度曲线加减速时间。在固定插补周期下,与单独自适应算法、5段式S曲线加减速控制方法的仿真结果相比,在满足加速度与加加速度限制条件,且最大弦高误差不超过0.5μm时,该算法插补精度高于单独自适应算法,与5段式S曲线加减速控制方法近似,且其全程平均进给速度比5段式S曲线加减速控制方法平均进给速度提高21.7%,达到594mm/s。     

NURBS曲线插补过程中运动平滑处理

由于不能通过积分方法在短时间内精确计算NURBS曲线的长度,使得在数控加工过程中实时计算减速距离、判断最终减速段开始点变得非常困难。基于插补的实际情况,给出一种实时计算减速距离的方法,在此基础上,实现了基于梯形速度曲线的速度平滑处理以及基于S形速度曲线的加速度平滑处理。模拟结果表明,该方法在NURBS曲线实时插补过程中,在保证误差的基础上,满足了插补周期和加减速的要求,且实现了速度以及加速度的平滑过渡。     

基于细菌觅食算法的自适应NURBS曲线插补

制造业对加工过程中进给速度和加速度的平稳变化有着严格要求,为减小速度突变时对机床及刀具产生的冲击,确保加工精度符合要求,提出一种基于细菌觅食算法优化的非均匀有理B样条(NURBS)曲线S型加减速约束插补方法,该方法利用细菌觅食优化算法对NURBS曲线的控制点变量个数及关键位置信息进行优化,构建出更为平滑的NURBS曲线,减小计算负荷,并依据所构图形对弓高误差的要求,确定出每个插补点的进给速度,寻找确定速度改变点及速度波动位置,进而确定加减速度关键点,进行S型加减速控制,从而保证加工时速度稳定过渡,加工曲线平滑精确。该方法通过仿真及实验得以验证。     

基于Muller法的NURBS曲线插补算法

在分析NURBS曲线插补原理的基础上,提出了一种基于Muller法的NURBS曲线实时插补算法。该算法首先进行速度控制,由最大进给速度约束、最大弓高误差约束和最大法向加速度约束得到希望进给步长,保证了加工精度。然后利用Muller法迭代计算满足进给步长要求的插补参数,避免了传统方法的复杂求导运算。该算法稳定性好,运算量小,能够对速度波动进行有效控制,并且能够满足实时插补的要求。     

基于进给速度敏感点识别的NURBS曲线平滑插补算法研究

提出了一种基于进给速度敏感点识别的NURBS曲线插补算法,该方法对于兼容NURBS形式的高档数控系统至关重要。粗插补计算造成的轮廓误差与插补经过该点时的进给速度大小有关,敏感点则可根据插补微段逼近时的弓高误差来界定。进而,根据相邻敏感点之间的距离,通过增设安全缓冲区等方法,进行速度曲线自适应规划。整体进给速度曲线可以由各部分进给速度曲线连接而成。为评价算法的有效性,采用3次NURBS曲线在三种不同进给速度指令下进行仿真计算。仿真结果证明,该算法很好地将轮廓精度和进给速度的平滑性进行了系统考虑,能在相邻危险点复杂分布的情况下执行柔性的插补控制。     

一种参数预估-校正的NURBS曲线插补算法研究

提出了Milne-Simpson参数预估-校正的NURBS曲线插补算法.详细阐述了参数插补预估及校正机理.采用最大弓高误差、最大进给速度和最大法向加速度约束,以便实时调整插补进给步长,从而满足了NURBS曲线插补的高速和高精度要求.     

NURBS曲线实时插补进给速度控制的研究

数控技术标志着现代制造业的核心,数控插补模块是数控技术中最为重要的模块之一。NURBS曲线是自由曲线的一种,由于其NURBS曲线的诸多优越性,使其能够很好的应用到数控领域中。NURBS曲线插补及加减速控制的精度和速度是CNC系统的重要指标。通过分析NURBS曲线的插补原理,提出了基于Taylor展开公式逼近NURBS样条参数。同时考虑速度波动于曲率的关系,弦误差与插补周期的关系,根据弓高误差调节进给速度,能够将进给速度波动控制在理想水平。     

Development of integrated acceleration/deceleration look-ahead interpolation technique for multi-blocks NURBS curves

Modern motion control adopts acceleration/deceleration before interpolation (ADBI) motion planning to eliminate path command errors. However, the individual velocity profiles might not be continuous at the junction of the blocks. Acceleration/deceleration after interpolation (ADAI) method may provide an alternative for solving the discontinuous problems, but it causes path command errors. In this paper, an integrated acceleration/deceleration interpolation (IAD) scheme which integrates the ADBI and ADAI modules is proposed. The ADBI provides a look-ahead function which plans the feedrate profiles based on chord errors, command errors, curvatures, and acceleration limits. Within the look-ahead function, the command error equation is utilized to determine the feedrate at the junction of adjacent blocks. Then the ADBI performs non-uniform rational B-spline (NURBS) interpolation using the planned feedrate profile and outputs the position points to the ADAI module. The ADAI module processes the points by a digital convolution technique such that the continuity of the block junction velocity is ensured. Finally, the IAD is applied to the multi-block NURBS interpolation to validate its effectiveness. Simulations and experiments are conducted to demonstrate the IAD scheme. It is shown that the IAD scheme can reduce the acceleration significantly at the junctions of the blocks under the given tolerance of the command error. Furthermore, the proposed algorithm can improve tracking and contour accuracies as compared to the hybrid multi-blocks look-ahead approach.     

基于传动系统动力学的NURBS曲线插补算法

对机床传动系统、伺服驱动系统和数控插补模块进行动力学建模和求解。提出一种新的NURBS插补算法,按照进给率自适应轨迹规划算法进行当前插补周期的速度设定,并且根据曲线当前位置的曲率特性,进行基于曲率的最大速度限定,通过求解动力学模型,获得按照这一速度进行插补时系统需要的最大驱动力,若该驱动力超过系统能够提供的最大驱动力,则再次按照用户设定的加速度进行减速,获得的速度作为指令速度,按照一阶泰勒展开近似进行插补点的计算。该算法不仅在NURBS曲率较大的区域自动降低进给速度,保证要求的弦误差,而且使输出的插补速度指令区域平滑,保证不会出现插补输出的位置值系统无法进行位置控制造成更大的加工误差。     

Real-time NURBS curve interpolator based on section

Parameter interpolation is more capable of modern computer numerical control (CNC) than traditional linear/circular interpolation with higher speed and higher precision. Most of non-uniform rational B-spline (NURBS) interpolation algorithms were developed based on the chord error and machines capability, where interpolation points are calculated beforehand to overcome acceleration/deceleration (acc/dec) and jerk problem, which needs large memory. In this paper, a NURBS interpolator based on feedrate section is proposed. Instead of a single interpolation point, this interpolator aims to feedrate section, which makes it possible to run on a digital signal processor or field programmable gate array (FPGA) whose memory is limited. Experiment on FPGA showed the performance of interpolation. A mould experiment verifies the feasibility of application.     

Development of a real-time look-ahead interpolation methodology with spline-fitting technique for high-speed machining

Methodologies for converting short line segments into parametric curves were proposed in the past. However, most of the algorithms only consider the position continuity at the junctions of parametric curves. The discontinuity of the slope and curvature at the junctions of the parametric curve might cause feedrate fluctuation and velocity discontinuous. This paper proposes a look-ahead interpolation scheme for short line segments. The proposed interpolation method consists of two modules: spline-fitting and acceleration/deceleration (acc/dec) feedrate-planning modules. The spline-fitting module first looks ahead several short line segments and converts them into parametric curves. The continuities of the slope and curvature at each junctions of the spline curve are ensured. Then the acc/dec feedrate-planning module proposes a new algorithm to determine the feedrate at the junction of the fitting curve and unfitted short segments, and the corner feedrate within the fitting curve. The chord error and acceleration of the trajectory are bounded with the proposed algorithm. Simulations are performed to validate the tracking and contour accuracies of the proposed method. The computational efforts between the proposed algorithm and the non-uniform rational B-spline (NURBS)-fitting technique are compared to demonstrate the efficiency of the proposed method. Finally, experiments on a PC-based control system are conducted to demonstrate that the proposed interpolation method can achieve better accuracy and reduce machining time as compared to the approximation optimal feedrate interpolation algorithm.     

NURBS曲线S形加减速双向寻优插补算法研究

由于非均匀有理B样条(Non-uniform rational B-splines,NURBS)曲线的弧长与参数之间无精确解析关系,并且进给速度总是受到非线性变化的曲线曲率的约束,因此基于S形加减速进行NURBS曲线插补时,减速点难以准确预测。传统算法通常是沿曲线单方向插补,不仅未考虑曲率对进给速度的持续限制,而且加减速分类与计算公式复杂。为此,提出运动路程未知情况下不依赖于弧长精确计算的正向和反向同步加速的插补新算法,实时动态地求解曲线段内最大进给速度和正反向插补会合点,从而实现处处满足全部速度约束条件的最优插补。该算法无需求解高次方程与繁琐的加减速模式分类,并可保证以确定的速度通过曲率极值点和曲线终点。通过两个插补实例证明算法简明高效,适应性好,能够满足高速高精度数控要求。     

临界曲率值分割曲线尖角的NURBS曲线插补

为兼顾插补含尖角NURBS曲线的精度与速度,提出尖角分割且速度修正插补算法。由插补弦高误差限、法向加速度及其导数约束,得满足插补精度及机床动力学性能的临界曲率;用大于临界曲率的局部极大曲率及临界曲率分割NURBS曲线为是否包含尖角的若干子段;用S曲线加减速算法规划各子段进给速度,并用段间速度及位移协调关系修正各段加速度及其导数,使各段加减速时间为整数倍插补周期。在相同约束条件下,分别用曲率单调无速度修正、尖角分割无速度修正及尖角分割有速度修正算法,规划一条含大曲率尖角NURBS曲线插补速度,并用一阶泰勒级数展开算法插补该曲线。对比结果表明尖角分割且有速度修正算法可稳定得到较高插补精度,因此该算法可用于含大曲率尖角NURBS曲线高速度高精度加工。     

Adaptive parametric interpolation scheme with limited acceleration and jerk values for NC machining

Parametric interpolation has many advantages over the traditional linear or circular interpolation in computer numerical control (CNC) machining. The existing work in this regard is reported to have achieved constant feedrate, confined chord error and limited acceleration/deceleration in one interpolator. However, the excessive jerk still exists due to abrupt change in acceleration profile, which will cause shock to the machine as well as deteriorate the surface accuracy. In this paper, an adaptive interpolation scheme incorporating machine’s dynamics capability consideration is proposed and illustrated in details. In the proposed algorithm, the commanded feedrate is maintained at most of the time and adaptively reduced in large curvature areas to meet the demand of the machining accuracy requirement, while at the same time, the acceleration and jerk values are limited within the machine’s capabilities during the whole interpolation process. It ensures a high machining accuracy, eliminates the phenomenon of overshoot/undershoot and reduces mechanical shock to the machine tools. The real-time performance of this interpolator is also measured to demonstrate its practical application. Two non-uniform rational B-spline (NURBS) curve interpolation experiments are provided to verify the feasibility and advantages of the proposed scheme.     

Real-time NURBS interpolator: application to short linear segments

This study proposes the use of a real-time non-uniform rational B-spline (NURBS) interpolator with a look-ahead function to handle numerous short linear segments. The short linear segments conforming to the continuous short block (CSB) criterion can be fitted into NURBS curves in real time. A modified maximum feedrate equation based on the geometric characteristics of the fitting curves and the dynamics of the servo control system has been derived in this paper. Taking advantage of the multi-thread design and the look-ahead function, the real-time NURBS interpolator can process enough G01 block information and complete feedrate planning before interpolation. In addition, the S-shaped jerk-limited acceleration method is adopted for smoother feedrate profiles. Two part shapes, which possess more than 1,000 short linear segments, are tested on our PC-based real-time control system. Both simulation and experimental results verify the feasibility and precision of the proposed interpolation algorithm.     

Precision NURBS interpolator based on recursive characteristics of NURBS

In NURBS interpolation, real-time parameter update is an indispensable step which affects not only feedrate fluctuation but also contour error. Using Taylor approximation interpolation method to find the next interpolation point causes a large feedrate fluctuation due to the accumulation and truncation errors. This paper presents a new, simple, and precise NURBS interpolator for CNC systems. The proposed interpolation algorithm does not use Taylor’s expansion, but the recursive equation of the NURBS formula. A simulation study is conducted to demonstrate the advantages of this proposed interpolator compared with those using Taylor’s equation. It is readily seen that this interpolator using the new concept of interpolation for modern CNC systems is simple and precise. The proposed method can be used for interpolating a continuous NURBS curve.