外文翻译--数控开环系统

附 录 1 开环系统的优点是系统简单、成本低，但缺点是精度不高。反向间隙、丝杠螺距误差、起停误差等都会影响定位精度。下面几种改进措施可以使定位精度明显改善。 1 反向间隙误差补偿 数控机床加工刀具与工件的相对运动是依靠驱动装置带动齿轮、丝杠转动，从而推动工作台面等移动部件产生位移来实现的。作为传统元件的齿轮、丝杠尽管制造精度很高，但总免不了存在间隙。由于这种间隙存在，当运动的方向改变时，开始段时间必然会引起驱动元件的空走，出现指令脉冲推不动执行元件的局面。这就影响了机床的加工精度，即指令脉冲与实际进 给步数不相符合，产生加工误差 因此，开环数控系统一般都设置有反向间隙误差补偿功能，用以补足空走的步数反向间隙差补偿就是首先实测反向进给的误差，把它折算成脉冲当量数，作为间隙补偿子程序的输出量，当计算机判断出现的指令为反向运动时，随即调用间隙补偿子程序，通过输出补偿脉冲消除反向间隙后再进行正常的插补运行 。 2 常值系统性定位误差补偿 类库以供设计者调用。这样在零件的设计阶段，设计者只需输入特征的参数，系统直接生成特征的实例模型：在数据库中我们必须存储相关的特征类的结构信息，数据库表集就是用于存储这一部 分的相关信息。根据特征类型定义的需要，我们定义了特征类编码表、特征类版本信息表表示特征类型；定义了特征类构造表表达特征类的结构；并通过零件特征配置表与零件的特征层信息联系起来。特征层数据表集是本零件模型数据库设计的核心，记录了特征实例模型的设计、工艺等信息。特征构造表记录了特征的几何结构；特征尺寸表、特征形位公差表、特征表面粗糙度表记录了特征的工程语义引用；尺寸表、形位公差表、表面粗糙度表存储了所有零件特征的数据信息。在特征层，利用特征 ID、几何要素 ID、尺寸 ID、公差 ID、粗糙度 ID 等主键进行数据检索。我 们将该零件信息模型的数据库应用于工厂环境下某型组件的 CAD AM 集成系统中，较好地实现了 CAD 与CAPP 的特征信息共享。在该系统中主要使用现成的 CAD CAM 软件 (Unigraphics 1I)进行产品设计和 NC 编程，并通过对该软件进行二次开发获取零件的尺寸信息；同时利用自行开发的对话窗体，让设计人员交互输入其它特征信息，实现该软件与系统的共享数据库的连接。在辅助工艺设计时，工艺设计人员通过程序的查询功能，从共享数据库中查询所需的零件信息，进行交互工艺设计。从而方便了 CAPP 的零件信息获取，提高了工艺设 计的效率。在利用 UG 进行 NC 编程时，可以从共享数据库中获取所需的工艺及制造信息，进行各工序的刀轨设计与加工仿真在数控机床上建立一个绝对零点，实测出各坐标轴相对点的全部定位误差，做出曲线以便确定补偿点。图 l 所示是一个实测的定位误差曲线，把这个曲线的纵坐标 (误差 )以脉冲当量为单位进行分割，作出横线，每个横线与曲线的交点即为目标补偿点。图 1 中的 1 到 6 点处的定位误差为正，需要作减脉冲补偿；而 6至 9 处需要进行加脉冲补偿图中阴影部分为补偿区。把这些补偿点列成误差 .修正表存入计算机，当工作台由零点位置移动时，安装在绝对原 点处的微动开关发出绝对原点定位信号，以后计算机将随时发出目标补偿点的补偿信号，对机床进行定位误差补偿。 3 反馈补偿开环控制 该系统由开环控制和感应同步器直接位置测量两个部分组成。这里的位置检测不用作位置的反馈，而是作为位置误差的补偿反馈。其基本的原理是：由机床数控装置 CNC 发出的指令脉冲，一方面供给开环系统，控制步进电机按指令运转，并直接驱动机床工作台移动，构成开环控制；另一方面该指令脉冲又供给感应同步器的测量系统 (即数字式正、余弦发生器 )，作为位置给定信号。工作在鉴幅方式的感应同步器此时既是位置 检测器，又是比较器，它把由正、余弦发生器给定的滑尺激磁信号传送给步进电机。 4 结 论 CIMS 环境下基于特征的零件信息建模还是一门不断发展的技术，怎样提高特征设计所能完成的零件复杂度；如何使特征设计适应特征识别、特征语义转换的要求等问题还有待人们去解决。本文介绍了特征技术在零件信息建模中的应用，重点描述该零件数据模型的数据库实现；所建立的零件信息数据库系统可以较好地满足 CIMS 系统对性 附录 2 The open system merit of Computer Numerical Control The open system merit is the system simple, the cost low, but the shortcoming is the precision is low. The reverse gap, the guide screw pitch error, stop inferiorly can affect the pointing accuracy by mistake. Following several kind of improvements measure may cause the pointing accuracy distinct improvement. 1. reverse gap error compensates The numerical control engine bed processing cutting tool and the work piece relative motion is depends upon the drive impetus gear,the guide screw rotation, thus the impetus work floor and so on moves the part to produce moves realizes. As traditional part gear, guide screw although the manufacture precision is very high, but always unavoidably has the gap. As a result of this kind of gap existence, when movement direction change, starts the section time to be able to cause inevitably actuates the part wasting time, appears the instruction pulse to push the motionless functional element the aspect. This has affected the engine bed processing precision, namely the instruction pulse and actual enters for the step does not tally,has the processing error therefore, the split-ring numerical control system all establishes generally has the reverse gap error compensatory function, with by makes up which wastes time the step reverse gap difference compensates is first actual reverse enters for the error, converts the pulse equivalent number it, compensates the subroutine as the gap the output, when the computer judgment appears when instruction for counter motion, transfers the gap to compensate the subroutine immediately, compensates the pulse after the output to eliminate the reverse gap to carry on again normally inserts makes up the movement. 2. often the value systematic characteristic position error compensates A kind of storehouse by transfers for the designer. Like this in the components design stage, the designer only must input the characteristic the parameter, the system direct production characteristic example model: We must save the related characteristic class in the database the structure information, the database table collection are use in saving this part of related information. According to the characteristic type definition need, we defined the characteristic class code table, the characteristic class edition information have outstanding shown the characteristic type； Defined the characteristic class structure outstanding to reach the characteristic class the structure； And relates through the components characteristic disposition table and the components characteristic level information. The characteristic level data sheet collection is this components model database design core, has recorded characteristic example information and so on model design, craft. The characteristic structure table has recorded the characteristic geometry structure； The characteristic size table, the characteristic shape position table of limits, the characteristic surface roughness table has recorded the characteristic project semantics quotation； The size table, the shape position table of limits, the surface roughness table saved all components characteristic data message. In the characteristic level, using characteristic ID, geometry principal linkage and so on essential factor ID, size ID, common difference ID, roughness ID carries on the data retrieval. We apply this components information model database under the factory environment some module CAD in the AM integrative system, has realized CAD and the CAPP characteristic information sharing well. Main use ready-made CAD/the CAM software (Unigra phics 1I) carries on the product design and the NC programming in this system, and through carries on two times of developments gains components to this software the size information； At the same time uses the dialogue window which develops voluntarily, lets design the personnel to input other characteristic information alternately, realizes this software and the system sharing database connection. When assistance technological design, the technological design personnel through the procedure inquiry function, inquires the components information from the sharing database which needs, carries on the interactive technological design. Thus has facilitated the CAPP components information acquisition, enhanced the technological design efficiency. When carries on the NC programming using UG, may from the sharing database gain the craft and the manufacture information which needs, carries on various working procedures the knife axle design and the processing simulation establishes an absolute zero spot on the numerical control engine bed, the actual various coordinate axes syzygy completely position error, makes the curve in order to determined compensates the spot. Attempts l to show is an actual position error curve, (error) carries on this curve y-coordinate take the pulse equivalent as the unit the division, makes the horizontal line, each horizontal line and the curve point of intersection namely compensates the spot for the goal. Chart 1 the center 1 to 6 oclock place position errors for, needs to do reduces the pulse to compensate； But needs to carry on 6 to 9 adds the pulse to compensate in the chart the shadow partially for to compensate the area. Compensates the range of points these to become the error The calibration corrections stores the computer, when work table by zero displacement in position, installs sends out the absolute zero point localization signal in the absolute zero point micros witch, later computer as necessary will send out the goal to compensate to compensate the signal, will carry on the position error to the engine bed to compensate. The cosine generator assigns slide guage initiation signal a electricity and by step of transmission. 3. feedbacks compensates the open-loop control Chart 2 has produced this kind of system schematic diagram. This system surveys two parts by the open-loop control and the induction synchromesh direct position to be composed. Here position examination does not serve as the position the feedback, but is compensates the feedback as the position error. Its cardinal principle is: Installs the instruction pulse by the engine bed numerical control which CNC sends out, on the one hand the supplies open system, the control step-by-steps the electrical machinery according to the instruction revolution, and the direct drive platen moves, constitutes the open-loop control； On the other hand this instruction pulse supplies the induction synchromesh the measurement system (namely digitally, cosine generator), as position demand signal a by. The work in the warning way induction synchromesh this time not only is the position sensor, also is the comparator, it by, The cosine generator assigns slide guage initiation signal a electricity and by step of transmission. 4. conclusions Under the CIMS environment the technology which develops unceasingly based on characteristic components information modeling, how enhances the components order of complexity which the characteristic design can complete； How cau