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滚筒采煤机截割部的设计

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滚筒 采煤 机截割部 设计
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目录

1 前言1

2 方案选定5

3 滚筒采煤机的总体设计及计算7

3.1  采煤机的滚筒7

3.2  采高和截深7

3.3  设计生产功率7

3.4  装机功率7

3.5  摇臂和电动机8

4 滚筒采煤机截割部设计9

4.1  螺旋滚筒设计9

4.2  截割部减速器传动系统15

5 滚筒采煤机的主要技术参数和配套设备21

6 采煤机的主要特点23

7 技术和经济分析25

8 总结26

致谢28

参考文献29

明细表30


1 引言

煤是重要的能源物质,在我国有着很大的储量。采煤一直以来都被人们看作一项非常危险的事情。在以前国内有很多小型煤窑,由于规模小,技术落后,大部分都是靠人工进行挖煤、运输煤。因此经常出现各种事故,而且大量浪费了资源。大型的采煤机械的出现使这一现象得到了改观。采煤机作为采煤的主要工具是实现煤矿生产机械化和现代化的重要设备之一。机械化采煤可以减轻体力劳动、提高安全性,达到高产量、高效率、低消耗的目的。它对提高煤的采掘效率有着重要的影响。因此国内外采煤机的设计、改进一直都在以较快的速度向前发展。

最早的滚筒采煤机出现在英国,它是把截煤机的减速箱部分改成允许安装一根横轴和截割滚筒。由于其水平轴截割滚筒的设计优于截煤机,因此其改进型比刨煤机更适宜英国开采条件,但在20世纪50年代这种采煤机并非是唯一应用的采煤设备。另外有一种有竞争的采煤机是钻削式采煤机。这种采煤机配有一个按螺钻原理设计的主截割部,其应用范围主要局限与薄煤层。

滚筒采煤机经过多次改进设计而得到不断的发展。最早设计的滚筒采煤机仅能单向采煤,输送机和液压支架在向前推移之前,留在轨道上采出的煤在回空段被装载。后来又研发了双向采煤的滚筒采煤机。然而由于这种采煤机受到调向的限制,加之固定滚筒缺乏自由性,因此摇臂滚筒采煤机应运而生。

20世纪60年代末,久益公司生产出10CM、11CM 系列的连续采煤机,它是现代这种机型的雏形。到70年代末,在11CM型基础上又生产出12CM系列连续采煤机。经过对12CM系列连续采煤机的不断改进、完善和提高,生产出适用于开采中硬煤层的12CM12—10B、12CM18—10D和B型机,以及适用于特别坚硬煤层的12HM31C型和B型机(神东常用12CM12—10B、12CM18—10D)。80年代后期至今连续采煤机在采煤业中得到了广泛的应用,并且得到了长足的发展。我国对这种连续型采煤机的应用始于70年代中期。那时主要靠引进外国的产品,80年代以前主要是引进单机。随着国内采煤机技术的发展到了90年代变成以配套引进为主。目前国内在采煤机研发和设计方面和国外有很大的差距。煤炭科学研究总院太原分院早在1990年就开始进行连续采煤机的研究,曾完成了轻型连续采煤机的设计、引进设备的国产化大修等工作。煤炭科学研究总院上海分院也承担了一些项目。尽管国内各大科研院所、生产厂家、煤矿企业曾开展过规模不等的连续采煤机等技术的国产化研究,但均存在一些问题,仍没有真正在煤矿上见到国产连采机的新产品。

我国引进连续采煤机早期使用效果不好的主要问题是:连续采煤机及其配套设备体积大、吨位高,我国老矿井条件受到限制,设备下井困难;缺乏支护、清道、除尘等配套设备,生产能力受到一定限制;引进的连续采煤机设备电气防爆性能与我国防爆标准不一致;主要部件或零件在国内买不到,备件进口渠道不畅通、价格昂贵;国内没有对连续采煤机开采的成套技术进行系统研究;对回采工艺,支护方式和工艺及煤岩柱控制等相关问题没有得到闭,对通风管理不利;对有自然发火危险的矿井,煤体暴露多,带来了安全隐患。因此我国需要自己对采煤机进行设计、改进使其适合我国的煤矿生产情况。

连续采煤机的特点是截割滚筒长,截割功率大,因此截割能力强,生产效率高,调动灵活,可控性好。尚需研究的主要内容如下。

1 连续采煤机总体参数的研究。机器牵引力及速度的确定,滚筒长度、直径、功率、转速及切割牵引力大小和变化等研究。

2 整机截割稳定性的研究。机器的重心位置、截割臂长度、截割速度、功率等切割参数对机器工作稳定性的影响。

3 截割机构方式的研究。根据电机不同的安装形式,其截割机构方式的确定须进行专项调查研究与分析对比。

4 切割技术的研究。截割滚筒上截齿排列对机器的截割效率、振动及截齿的寿命有着重要的影响,必须利用计算机进行截齿排列优化设计和实验室模拟试验。

5 行走电机变频调速系统的研究。连续采煤机工作时,需要频繁调动;截割时,根据煤的硬度,行走速度在0~4m/rain之间自动调整,以适应截割电

动机的工作特性;调动时,需以20m/rain的行走速度实现快速调动。

6 机器的自动控制、工况检测和故障诊断系统的研究。连续采煤机常在环境恶劣、安全得不到保障的工况下工作,因此必须使机器具有自动化控制功能,装设离机摇控系统。为了提高机器的可靠性,需研制工况检测和故障诊断系统,使连续采煤机具有监控电流、电压、电机功率、油温油位油压等的自动监测、存储、显示、报警及故障提示等功能。

7 机载集尘装置的研究。需进行水喷雾集尘系统的试验研究。

8 对专用电动机、传感器、扭矩轴等特性元部件的研究。

我国在长期煤炭生产实践中,也已陆续研制生产了一系列国产采煤机,并且在借鉴国外先进机型的基础上,迅速发展了大功率电牵引采煤机(总装机功率达1 400KW 以上),但是和国外先进的技术和设备相比较还有很大的差距。因此我们必须抓住机遇,加快采煤机的设计和改进步伐,加快缩短与国外技术和设备的差距。

关于采煤机的设计可以从以下方面着手进行改进设计:

1 横向布置多个电动机。即将截割部、牵引部、泵站和破碎机构设计成横向布置方式。采用这种电动机布置方式,可将摇臂回转传动装置取消,而代之不传动功率的铰接轴,简化了结构,减少了薄弱环节和故障因素;可将传动链中锥齿轮取消,消除了加工、装配、维修锥齿轮的复杂工艺,提高了可靠性;各电动机传动系统功能单一,无过轴、旁轮等多余饥件和交叉重叠环节,部件为自封闭,部件之间无饥械传动, 只有管线等柔性联接,故结构简单、紧凑、机身长度可缩短;便于组装拆卸及在维修更换部件、换摇臂及截割电动机时不需拆卸底托架和对口螺栓。

2 将机身设计成使部件可侧面拉装的整体箱式。即整个机身是个箱形结构的焊接件,根据需要分成若干个间隔室,安放变压器电控部 电牵引部、液压站等部分;而在采空区一侧将其敞开,可以将上述具有自封结构的部件方便地装入固定和拆下拉出,而机身两端铰接的截割部及其电动机也可以从采空区侧拆装。采用这种机身设计方式,可以为井下组装维修创造更方便快捷的条件,同时可实现整个机身无对口螺栓,也无底托架,强度大,刚性好, 免除了螺栓紧固的麻烦可将机身做成两段拼装,并用液压螺栓紧固。

3 破碎机采用单独电动机传动。即将滚筒做成电动滚筒,由单独电动机经行星传动机构驱动破碎滚筒。采用这种破碎机驱动方式,可以利用按钮控制破碎机,操作方便,而且单独电动机还便于控制和保护。

改进挡煤板传动装置。即用中低速摆线马达,通过内齿轮或柱销传动。比如,可在挡煤板回转臂环架圆周安装轴向柱销,利用固装在摇臂上的液压马达带动长牙齿轮驱动柱销翻转挡煤板。采用这种挡煤板传动装置,可使挡煤板结构更可靠,且不怕煤粉堵塞,不易存煤泥,可大幅减少故障。

4 增大截煤深度。截深在750mm 以上方能称为大截深,由于加大了截深,相应的滚筒轴、轴承和摇臂强度也应加大,同时适当增大螺旋叶片的升角(一般大于等于20),以改善装煤效果。采用强力截齿。由于速度加大,截齿的切削厚度增大, 可采用齿伸较长(120mm -l50mm 左右)、大断面齿柄(30*50ram)、硬质合金片厚度达l8ram以上的强力截齿,同时加大齿座尺寸和强度,这样可减少截齿数、降低截齿消耗、增大块煤率和降低煤尘。

5 增大块煤率,减少煤尘生成。即采用双行星传动截割头,适当降低滚筒转速,使其转速在22—24r/rain左右,以增大块煤率,减少二次破碎;或减少截齿数,增大截距(60ram左右)以使块煤率增加;滚筒结构上还可采用碟形端盘开窗口,轮毂采用锥形或指数曲线形,以使截落的煤快速排出,从而减少二次破碎;此外还可在螺旋叶片上采用盘形滚刀以及采用抽风和吸尘滚筒。加设高压水射流喷雾装置。即在采煤机上加装增压水泵(60—70kW ),使喷雾水压达到l8MPa以上,流量达到140L/min以上,这样可有效降低煤尘和防止截割时产生火花。

另外减少喷雾喷嘴的直径(0.5—0.8ram),可形成高压射流,起到辅助切割作用,以减少截齿受力,降低能耗。同时还可加设流量压力自动控制型水泵,使采煤机滚筒只在割煤时喷雾洒水,以节约水能源。

改进滚筒材质和结构。即采用国际最新耐磨合金钢板制造滚筒,以提高其刚度、强度和耐磨性,同时加大轮毂板厚度和叶片板厚度。在有条件的情况下,我国煤机厂可适当引进国外成型高强度滚筒。

由上述分析,我们确定了我国新型采煤机的设计的大方向以及在设计中应该注意的方面。下面我就对本次采煤机设计作一个总体的介绍。

本次采煤机设计采用电牵引,多电机横向布置。该机具有电机横摆、结构先进、运行可靠、可实现电液互换、大功率能力强等特点。截割电机、牵引电机的启动、停止等操作采用旋转开关控制外,其余控制如牵引速度调整、方向设定、左右摇臂的升降,急停等操作均由设在机身两端操作站的按钮进行控制,操作简单、方便。 所有电机横向布置。机械传动都是直齿传动。电机、行走箱驱动轮组件等均可从老塘侧抽出。故传动效率 高,容易安装和维护。采用强力耐磨滚筒,提高割煤效果和滚筒寿命,降低截齿消耗量和用户成本。可通过更换电控部或液压传动部而成为交流变频调速电牵引或液压牵引采煤机以实现电液互换,而其它 部件通用。两动力输入部位可安装液压马达,也可安装40Kw牵引电机。两种形式联接尺寸相同。


2 方案选定

1 滚筒的数量和位置:

滚筒采煤机有单滚筒和双滚筒之分。由于滚筒直径不宜过大,当煤层较厚

单滚筒采煤机往返截割两个行程才能推进一个截深;双滚筒采煤机每截割一个行程就可以推进一个截深,对煤层变化和顶板、底板的起伏,适应性也好。在滚筒采煤机的设计中虽然也曾出现过三滚筒或四滚筒,但因出煤碎、粉尘多、结构复杂,却对提高采煤机性能无益,故不予考虑。综上述本次设计采用双滚筒。

对于双滚筒可有两种位置布置,一是对称布置于两端,另一种就是两滚筒都布置于一端即采用不对称布置。不对称布置虽然设计相对简单,但是其工作稳定性不好。所谓工作稳定性就是采煤机在工作过程中保持不翻转、倾斜和不脱离导向物的能力。工作稳定性好将有利于正常工作。而对称布置的滚筒采煤机受到的外力基本是平衡的,因而工作稳定性较好。因此采用双滚筒对称布置。

2 调高方式:

本机采用摇臂调高,这种调高方式不仅调高范围大,并且随时可以调高。

3 摇臂:

采用大角度弯摇臂。这样可以加大过煤空间,提高装煤效果,卧底量大。

4 轴承:

轴承主要有滑动轴承和滚动轴承。滑动轴承的润滑和密封条件一般都比较差,轴承的磨损可能引起摇臂较大的径向窜动。截割部主减速箱最后一级传动不宜用圆锥齿轮,以免摇臂的径向窜动严重影响齿轮的啮合质量。滚动轴承的密封和润滑问题比较好解决,轴承的磨损也比较轻微。本机采用滚动轴承。

5 牵引方式:

滚筒采煤机有各种不同的牵引方式。牵引部和截割部联结成一个整体,在工作面上来回移动,称为内牵引。工作面上只有截割部,却把牵引部设在工作面短头上下顺槽里,牵引部不跟截割部一起移动,只随工作面向前推移,则为外牵引。外牵引只能为有链牵引,而内牵引可以为有链条牵引和无链牵引。有链牵引有断链和跳链的危险,链条的弹性振动和链传动造成的速度脉动,使采煤机受到较大的动负荷,链条对于滚筒的装载、运输机和液压支架的推移也有一定的妨碍,所以有链牵引有很多不足之处。而无链牵引和有链牵引相比具有很多优点:

(1)采煤机移动比较平稳,保证了采煤机的载荷比较稳定;

(2) 提高了设备的可靠性和生产的安全;

(3)采煤机移动所消耗的能量较少;

(4)采煤机的运转噪音较低,有利于改善工作面的劳动条件;

(5)提高了采煤机的爬坡能力;

(6)在一个工作面上可能采用多台采煤机同时作业,以提高工作面量。通过以上比较本机采用无链牵引中的液压传动。

6 驱动方式:

采煤机驱动的方式有萨那种:

1)单驱动方式——用一台电动机驱动采煤机的各个部分,包括牵引部、全部截割部及其他辅助装置等‘

2)分别驱动方式——各截割部由单独的电动机驱动,牵引部和其他辅助装置可以由截割部电动机驱动,或另设电动机驱动;

3)联合驱动方式——把两台电动机结合成整体,共同驱动采煤机的各部分。

分别驱动时,各电动机的功率一般相同。双滚筒采煤机每台截割部电动机的功率只有单机驱动和联合驱动时的一半,截割部可以设计的较小,且结构简单,可以取消易引起发热等问题的横贯牵引部的过轴。本次设计采用分别驱动方式,用两个250KW的电机分别驱动两个截割部,用两个40KW的电动机驱动牵引部,也可用液压马达驱动牵引部。

7 采煤机的附属设备:

灭尘方式:采煤机在工作中会产生很多的粉尘,需要采取多方面的处理措施。主要有喷雾灭尘、泡沫灭尘和吸尘器捕尘。喷雾灭尘就是用喷嘴把具有一定压力的水高度扩散,使其雾化,形成把粉尘源与外界隔离的水幕。泡沫灭尘虽然具有一定的优点但是泡沫灭尘需要较复杂的设备,目前还不能大量生产高效、无毒和廉价的泡沫剂,因此在采煤机上未能得到推广。吸尘器从粉尘源吸取尘空气,排入捕尘器,利用扩散、碰撞或离心力等,使粉尘与空气分离,沉积在捕尘器的壳体内壁,然后用水冲洗排入运输机,净化空气直接排出。通过吸尘器的粉尘约95%-98%,灭尘效率相当高。但是,吸风管口要靠近粉尘源,吸入的含尘空气要多,否则含尘空气在旁边流走,就达不到净化空气的目的了。本机采用喷雾灭尘方式。喷雾灭尘有可分为内喷雾灭尘和外喷雾灭尘,在这里我们选择内外喷雾结合灭尘。


3 滚筒采煤机的总体设计及计算

3.1 本采煤机采用双滚筒对称布置,采用液压缸调高,调高范围:1.3~3.0(米)。由经验和理论基础取滚筒水平中心距为10810mm、两摇臂铰接中心距为6700mm、两牵引轮中心距为5591mm, 机身宽为1210mm。

3.2 采高为:1.6~3.2(米)。截深为 0.62m  0.66m。滚筒直径分别为:1400m   1600m。牵引速度为0~8(米/分)

3.3 设计生产功率:[1]

          Q = 60•J•H•Vq•γ                     (3-1)

   式中    J——滚筒的有效截深(米)J = 0.63;

           H——采煤机的平均采高(米)H = 2.4;

           Vq——采煤机的最大工作牵引速度(米/分)Vq =8;

           γ = 1.35——煤的重率(吨/ )。

          Q = 60×0.63×2.4×8×1.35

            = 979.7(吨/时)

            = 979.7/60(吨/分)

3.4 装机功率:[1]

                       (3-2)


   式中    ——功率利用系数,以为该机的驱动方式为分别驱动所以 =0.8。

           ——功率水平系数,由表3—1查得 =0.9。

           ——后滚筒的工作条件系数, =0.8。

           ——采煤机的比能耗,由表3—2查得 =0.44(KW.h/T)。

           =

          ≈ =300N/mm。

           。



       取 N = 591KW。


内容简介:
IMPROVING ACCURACY OF CNC MACHINETOOLS THROUGH COMPENSATIONFOR THERMAL ERRORSAbstract: A method for improving accuracy of CNC machine tools through compensation for the thermal errors is studied. The thermal errors are obtained by 1-D ball array and characterized by an auto regressive model based on spindle rotation speed. By revising the workpiece NC machining program , the thermal errors can be compensated before machining. The experiments on a vertical machining center show that the effectiveness of compensation is good.Key words : CNC machine tool Thermal error Compensation0 INTRODUCTIONImprovement of machine tool accuracy is essential to quality cont rol in manufacturing processes. Thermally induced errors have been recognized as the largest cont ributor to overall machine inaccuracy and are probably the most formidable obstacle to obtaining higher level of machine accuracy. Thermal errors of machine tools can be reduced by the st ructural improvement of the machine tool it self through design and manufacturing technology. However , there are many physical limitations to accuracy which can not be overcome solely by production and design techniques. So error compensation technology is necessary. In the past several years , significant effort s have been devoted to the study. Because thermal errors vary with time during machining ,most previous works have concent rated on real-time compensation. The typical approach is to measure the thermal errors and temperature of several representative point s on the machine tools simultaneously in many experiment s , then build an empirical model which correlates thermal errors to the temperature statues by multi-variant regression analysis or artificial neural network.During machining , the errors are predicted on-line according to the pre-established model and corrected by the CNC cont roller in real-time by giving additional signals to the feed-drive servo loop.However , very few practical cases of real-time compensation have been reported to be applied to commercial machine tools today. Some difficulties hinder it s widespread application. First , it is tedious to measure thermal errors and temperature of many point s on the machine tools. Second ,the wires of temperature sensors influence the operating of the machine more or less. Third , thereal-time error compensation capability is not available on most machine tools.In order to improve the accuracy of production-class CNC machine tools , a novel method is proposed. Although a number of heat sources cont ribute to the thermal errors , the f riction of spindle bearings is regarded as the main heat source. The thermal errors are measureed by 1-D ball array and a spindle-mounted probe. An auto regressive model based on spindle rotation speed is then developed to describe the time-variant thermal error. Using this model , thermal errors can be predicted as soon as the workpiece NC machining program is made. By modifying the program , the thermal errors are compensated before machining. The effort and cost of compensation are greatly reduced. This research is carried on a JCS2018 vertical machining center.1 EXPERIMENTAL WORKFor compensation purpose , the principal interest is not the deformation of each machine component , but the displacement of the tool with respect to the workpiece. In the vertical machining center under investigation , the thermal errors are the combination of the expansion of spindle , the distortion of the spindle housing , the expansion of three axes and the distortion of the column.Due to the dimensional elongation of leadscrew and bending of the column , the thermal errors are not only time-variant in the time span but also spatial-variant over the entire machine working space.In order to measure the thermal errors quickly , a simple protable gauge , i. e. , 1-D ball array , is utilized. 1-D ball array is a rigid bar with a series of balls fixed on it with equal space. The balls have the same diameter and small sphericity errors. The ball array is used as a reference for thermal error measurement . A lot of pre-experiment s show that the thermal errors in z-axis are far larger than those in x-axis and y-axis , therefore major attention is drawn on the thermal errors in z-axis. Thermal errors in the other two axes can be obtained in the same way.The measuring process is shown in Fig.1. A probe is mounted on the spindle housing and 1-D ball array is mounted on the working table. Initially , the coordinates of the balls are measured under cold condition. Then the spindle is run at a testing condition over a period of time to change the machine thermal status. The coordinates of the balls are measured periodically. The thermal drift s of the tool are obtained by subt racting the ball coordinates under the new thermal status f rom the reference coordinates under initial condition. Because it takes only about 1 min to finish one measurement , the thermal drifts of the machine under different z coordinates can be evaluated quickly and easily. According to the rate of change , the thermal errors and the rotation speed are sampled by every 10 min. Since only the drift s of coordinates deviated from the cold condition but not the absolute dimensions of the gauge are concerned , accuracy and precise inst rument such as a laser interferometer is not required. There are only four measurement point s z 1 ,z 2 , z 3 , z 4 to cover the z-axis working range whose coordinates are - 50 , - 150 , - 250 , - 350 respectively. Thermal errors at other coordinates can be obtained by an interpolating function.Previous experiment s show that the thermally induced displacement between the spindle housing and the working table is the same with that between the spindle and table. So the thermal errorsz measured reflect those in real cutting condition with negligible error.In order to obtain a thorough impression of the thermal behavior of the machine tool andidentify the error model accurately , a measurement strategy is developed. Various loads of the spindle speed are applied. They are divided into three categories as the following : (1) The constant speed ; (2) The speed spect rum ; (3) The speed simulating real cutting condition. The effect of the heat generated by the cutting process is not taken into account here. However , the influence of the cutting process on the thermal behaviour of the total machine structure is regarded to be negligible in finishing process.In this machine , the most significant heat sources are located in the z-axis. Thermal errors in z direction on different x and y coordinates are approximately the same. It implies that the positions of x-carriage and y-carriage have no strong influence on the z-axis thermal errors.Fig.1(L) Thermal error measurement 1.Spindle mounted probe 2.1-D ball array Fig.2 (R)Thermal errors at different z coordinates 1. z = - 50 2. z = - 150 3. z = - 250 4. z = - 350Fig.2 plot s the time-history of thermal drift z at different z coordinates under a test . Itshows that the resultant thermal drift s are obvious position-dependent . The thermal drift s at z 1 ,z 2 , z 3 , z 4 are coincident initially but separate gradually as time passes and temperature increases.The reason is that , initially most of thermal drift s result f rom the position-independent thermal growth of the spindle housing which would rise fast and go to thermal-equilibrium quickly compared to other machine component s with longer thermal-time-constant s. However , as time passes , those position-dependent thermal errors such as the lead screw and the column cont ribute to the resultant thermal drift s of the tool more and more. As a result , the thermal drifts at different z coordinates have different magnitude and thermal characteristics. However , the thermal errors at different coodinates vary with z coordinate continuously.2 AR MODEL FOR THERMAL ERRORPrecise prediction of thermal errors is an important step for accurate error compensation.Since the knowledge of the machine structure , the heat source and the boundary condition are insufficient , a precise quantitative prediction based on theoretical heat transfer analysis is quite difficult . On the other hand , empirical-based error models using regression analysis and neural networks have been demonst rated to predict thermal errors with satisfactory accuracy in much application.Thermal errors are caused by various heat sources. Only the influence of the heat caused by the fiction of spindle which is the most significant heat source is considered. The influence of external heat source on machining accuracy can be diminished by environment temperature control.From the obtained data , it is found that thermal errors vary continuously with time. Thevalue of error at one moment is influenced by that of the previous moment and the rotation speed of spindle. So a model representing the behavior of the thermal errors as written is the formwhere z ( t) Thermal error at time tk , m Order of the modelai , bi Coefficient of the modeln ( t - i) Spindle rotation speed at time t - iThe order k and m are determined by the final prediction-error criterion. The coefficients aiand bi are estimated by artificial neural network technique. A neural network is a multiple nonlinear regression equation in which the coefficient s are called weight s and are t rained with an iterative technique called back propagation. It is less sensitive than other modeling technique to individual input failure due to thresholding of the signals by the sigmoid functions at each node. The neural network for this problem is shown in Fig.3. ( k = 1 , m = 0) . The number of hidded nodes is determined by a trial-and error procedure.Using the data obtained (thermal errors and correspondence speed) , four models for the errors at z 1 , z 2 , z 3 and z 4 are established. Thermal errors at positions other than z 1 , z 2 , z 3 , z 4 are calculated by an interpolating function. So the errors at any z coordinates can be obtained.In order to verify the prediction accuracy of the model , a number of new operation conditions are used. Fig14 shows an example of predicted result on a new condition. It shows that the auto regressive model based on speed can descibe thermal errors well in a relative stable environment .Fig.3 A neural network for thermal errorsFig.4 Thermal error predicting 1.Measuring results 2Predicting results3 PRE-COMPENSATION FOR THERMAL ERRORSThe principle of pre-compensation for thermal errors is shown in Fig.5. The spindle rotation speed and the z coordinates are known as soon as the workpiece NC machining program is made.By , for example , every 10 min , the thermal errors z are calculated by the model. Then the program is corrected by adding the calculated z to the original z . So the thermal errors are compensated before machining.The effectiveness of the error compensation is verified by many cutting test s. Several surfaces are milled under cold start and after 1 h run with varying speeds. As shown in Fig.6 , the depth difference of the milled surface is used to evaluate the compensation result of the thermal errors in z direction. It shows that the difference is reduced from 7m to 2m.Fig.5 Compensation for thermal errors by revising machining programFig.6 The effectiveness of compensation4 CONCLUSIONSA novel method
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