五轴机床伺服特性动态匹配及联动精度智能控制

Five-axis machine tools are key equipment for machining of sculptured surface parts and the foundations of high-end equipment manufacturing industry, such as aerospace. The contouring error of the five-axis machine tool is determined by the velocity command from the interpolator as well as the closed-loop dynamic behavior of the servo feed drive system. In the high speed/acceleration machining process of the sculptured surface, the velocity command of each axis shows high bandwidth and is intensively time-variant. As the closed-loop dynamic behaviors in the medium and high frequency bands are hard to improved, the only way of improving the contouring accuracy is decreasing the feed rate or acceleration in the programming or interpolation stage so as to narrow the bandwidth of the velocity command, making it difficult to compatibly reach high speed/acceleration and high contouring accuracy. In this project, the representation methods of velocity command with the high bandwidth and time-variant characteristics and the closed-loop dynamic behaviors in the low, medium and high frequency bands are investigated. The match criterion of five axes’ closed-loop dynamic behaviors and the time-variant sequence searching algorithm of five axes’ servo parameters are then developed. On this basis, the intelligent control method of the contouring error of the five-axis machine tool is proposed. Via “self feeling” the velocity command of each axis, “self analyzing” the time-frequency characteristics of the velocity command, “self judging” the dynamic matching between the five axes’ closed-loop dynamic behaviors, so that the machine tools can “self deciding” the specialized time-variant sequences of servo parameters for each axis according to the variation and difference of velocity command. And then by “self adjusting” the closed-loop dynamic behaviors of each axis during machining, the five axes’ closed-loop dynamic behaviors can matched dynamically, and hence the high speed/acceleration and high contouring accuracy can be achieved compatibly.

五轴机床是复杂曲面零件加工的关键装备，是支撑航空/航天等高端装备制造业的基础。五轴联动精度由插补输出速度指令和伺服系统自身伺服特性共同决定。五轴高速/高加速加工复杂曲面时，各轴速度指令频宽大且时变剧烈，而五轴机床中、高频段伺服特性却难以改善，只能靠在编程或插补阶段降低进给速度/加速度，减小速度指令频宽来保证联动精度，造成高速/高加速和高联动精度难以统一。本项目研究大频宽时变速度指令及全频段伺服特性表征方法，研究五轴伺服特性动态匹配判据及五轴伺服参数时变序列搜索算法。在此基础上，构建五轴联动精度智能控制方法，通过“自我感知”各轴速度指令序列，“自我分析”各轴速度指令时频特征，“自我判断”各轴伺服特性匹配性，使机床能够根据各轴速度指令的变化和差异“自我决策”各轴伺服参数时变序列，在加工中“自我调整”各轴伺服特性，使各轴伺服特性在进给过程不同时段动态匹配，实现高速/高加速下的高联动精度。

五轴机床是航空结构件、航天火箭舱体零件、航发叶轮叶盘叶片等复杂曲面零件加工的关键装备，是支撑航空/航天等高端装备制造业的基础。由于上述复杂曲面零件的几何特征复杂，加工轨迹曲率变化大，导致在实际加工中，往往采用较低的速度，以牺牲加工效率的方式保证零件的加工精度，造成高速和高联动精度难以统一。.本项目研究五轴机床伺服特性动态匹配及联动精度智能控制方法，通过自适应各轴指令频率成分的变化，智能决策五轴伺服参数时变序列，使五轴伺服特性在加工过程中自动调整和动态匹配，实现高速下的高联动精度。.提出了伺服控制系统时频联合分析方法，实现了伺服控制系统时频响应及其误差求解。所提出的求解方法可以使分析结果同时呈现在时间和频率两个维度上，实现了时域现象与频域机理的统一。相对于时域响应和频域响应，时频响应从一个新的视角分析伺服控制系统，能够对幅值衰减和相位滞后引起的指令损失或跟随误差进行分离；能够针对某指令和伺服控制系统，确定滤波器等策略的冗余与欠缺。.提出了五轴机床伺服特性动态匹配方法，以零件的轮廓误差最小为目标，构建了各轴伺服参数序列，实现了机床根据零件要求对自身状态进行诊断和动态调整，使机床的自身状态与加工零件匹配，解决了伺服特性固定状态下加工精度和效率不能统一的问题。.提出了基于“自我感知-自我分析-自我判断-自我决策-自我调整”思路的五轴联动精度智能控制方法。在复杂曲面零件的五轴加工中或加工前，智能控制方法“自我感知”数控系统插补生成的指令，“自我分析”各轴的指令频宽，“自我判断”各轴动态特性的匹配性，“自我决策”各轴的伺服参数，实现各轴伺服特性的“自我调整”和动态匹配。在保证加工效率的前提下大幅提高了加工精度。经伺服特性动态匹配，S形试件的最大轮廓误差减小了33.82%。.本项目所提出的方法可构建五轴机床伺服特性动态匹配智能分析软件，将五轴数控机床升级为智能机床，具有重要的理论意义和广阔的应用前景。