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1、切削力传感器电阻应变传感器测量系统在数控车床切削力测量中的应用为了便于测量和研究数控车床切削力,适应 生产中设计和使用数控机床和刀具的需要,一般都把总切削力Fr分解成三个互相垂直方向的 力Fz、Fy、Fx三个分力来测量分析.该系统 切削力的检测装置,我们采用电阻应变片传感 器设计组成的八角环测力仪,作为测定X、 Y、Z三个方向切削力的传感器.其中的八角 环是弹性元件,在环的内外壁相应的应变节点上 分别粘贴四片电阻应变片,以克服测试过程中 的交叉干扰,把四片电阻应变片按全桥方式联结 分别构成三个测量电桥,以提升测试灵敏度.在数控车床车削时,切削力经工件转动传递于 车刀上,再由车刀刀杆传递到八角环
2、,八角环的 变形使紧贴在其上的电阻应变片也随之变形,电阻值R就会随之发生变化R ? $R .当应变 片受拉伸时,电阻丝直径变细,电阻值增大 R+$R,应变片受压缩变形时,电阻丝直径变 粗,电阻值变小R-$R,电桥会输出与切削力 成正比例电信号.由于电阻应变片的电阻变化 很小,为了适合单片机限制系统进行相应的数 据处理,必须将信号放大到 0 5V后才能输入单片机.电阻应变片组成的测量电桥电路如图2所示.F ig ur e. 2 T he measuring electr ic br idge co mpo sed of the r esistance strain g aug es这是由四个电阻
3、应变片作为电桥桥臂所组成的全桥测量电路,R1、R2、R3、R4分别为四个桥臂 的电阻.当 A、C端加以一定的电压 U时,那么B、R 1 R3-R 2R4$( R + 4U R2 ) ( R3=+) U电压$U = 0,即电桥处于平衡状态.在进行切削力测量前,还须对电桥进行调节,使其处于 平衡缺点：不宜在外界环境变化比拟大的地方使用,对于大应变有较大的非线性、输出信号较弱.优点：精度高,测量范围广寿命长,结构简单, 频响特性好,能在恶劣条件下工作,易于实现 小型化、整体化和品种多样化.轮辐式切削力传感器轮辐式传感是利用轮辐受载后的变形检取应 变,通过敏感元件如电阻应变片来实现力一 电信号的转换.
4、这种传载器根据轮辐的横截面形 式分为变辐式和等辐式两种,本文仅论述便于加 工的等辐式传感器.如图1示,该传感器的形状 恰似一车轮,轮毅和轮缘由对称的四根辐条连接 组成以轮缘为固定支座的交叉梁.b)图i轮圾式切削力但感器示意三向切削力可由轮毅传至轮辐.这种传感器是基 于剪辐式压力传感器的设想提出的川.为保证传 感器的性能可靠,其中轮毅和轮缘的刚度应适当 取大c轮辐的截面为矩形,既保持梁的特性,又 不致使传感器横向尺寸过大.为分析方便,首先 讨论传感器在径向切削力F :单独作用下的情 况.根据对称结构,取传感器在同一直线上由两 轮辐及轮毅、轮缘组成的一跨,可简化成图Za) 示超静定梁,载荷及剪力图
5、.如不计中间轮毅高 度影响,得到Zb )的原形梁,并作出相应的弯 矩由超静定协调条件得到：S2搏感器简化力学矍通过改变在轮辐上贴片的位置,可分别以弹性 辐体的弯曲、剪切或拉压应变作为传感器的输入 信号.而这几类轮辐传感器的工作原理是不同 的.一般的轮辐传感器主要用于单向重载荷的压 力检测,为撼高其刚度多利用纯剪状态下轮辐 截面应力分布规律,在与传感器轴线45方向 布片图2a,即所谓的剪辐式荷重传感器川, 这种形式传感器的特点是传感器的灵敏度只与 筋板抗剪截面积吞X孔有关,因此可缩短轮辐 体长度,进而减小传感器的体积,同时也大大 提升了传感器的刚度.显然,这种设计方案对单 向的重载检测是适用的.
6、但切削力传感器的情况那么复杂得多,由干切剥力的方向未知,通常要 同时测出其在三个既定方向的切削分力Fx、Fz、Fy.而径向切削力FY 一般小于500kgf , 如仍采用上述剪辐式原理设计,势必使轮辐截 而积过小,以至不能满足其它二向分力和贴片 的要求.因此采用图1 (b )的布片形式,即用 轮辐的拉压变形分别测定Fz、Fy二向切削分力, Fy采用辐板的端面布片,还过轮辐的弯曲变形 来测定.考虑到主切削分力 Fz、Fy,而通常弯 曲形与相同结构的拉压形传感器比拟,前者的 灵敏度较高,所以采用图工(b)的设计方案可使 传感器在Fz、Fy分力作用下的输出差距缩小, 便于二次仪表的选配.同时,这种方案
7、也使传感 器具有较好的抗干扰载荷水平,可通过桥路自 动补偿各向切削分力间的相互干扰及偏心载荷 的影响.用薄壁圆筒式切削力传感器测定传感器中部为空心薄壁圆筒,外外表粘贴有 两组电阻应变片.传感器的两端有法兰盘,以此 用螺钉联接安装在试材夹具与制材跑车搁凳之 间.电阻应变片R和R纵向粘贴在圆筒外表Z 方向的位置上,相互错开180,接成半桥.应变 片R3、R4、R、R 6与轴线交叉倾斜45角, 周向均匀分布,接成全桥.锯切时,带锯条对木 材切削力的切向分量Fx和法向分量Fy分别在 薄壁圆筒上形成弯矩 M和扭矩Mx测Fx的电桥 输出反映弯矩M的大小,与F x成正比.测Fy 的电桥输出反映扭矩 Mk的值
8、,与Fy成正比.为 便于数据处理,切削试验时,保持力臂a不变. 在锯切过程中,切削分力Fx和Fy的作用点是 不断变化的,但弯矩M和扭矩Mk不受力点变化 的影响,所以电桥的输出也不受力点变化的影 响.这是在木材切削力传感器的设计和安装中必 须满足的一个条件.与之相反,薄壁圆筒上Z向 弯矩因受Fx作用位置前后变化的影响,所以不 能用来测Fy力.由于R、R、R、R贴片位置 的对称性,切向分力Fx在测Fy的电桥中理论上 无输出.由于应变片R和R的中央位于通过圆 筒中央线平行于z轴的平面内,所以Fy产生的 z向弯矩在测Fx的电桥中理论上也无输出.各 电桥输出信号的单一性是多分量切削力传感器 又一个必须满
9、足的条件.由于 Z向力在两个测 力电桥中都产生输出,所以锯切时不允许有Z 向力存在.一般地,薄壁圆筒式传感器测切削力两个正交分量时,第三方向的切削力分量必须 为零,否那么将干扰两向分力的测定结果.电桥系统框图如图2a所示.木材切削力的两个 分量Fx二和Fy ,通过薄壁圆筒切削力传感器变 为两组电桥的输出,经动态电阻应变仪放大后, 输人光线示波器,记录在示波纸上.切削力分量 的记录曲线如图2b所示.根据记录曲线的相对 高度hx和hy,算得切削力分量Fx和Fy的数 值.图1薄壁画制式切削力隹出赛Design, development and testing of a four-componentm
10、illing dynamometer for the measurement of cutting forceand torque参考文献：Mechanical Systems And Signal Processing Frank Unsacar ) Haci Saglam ) HakanLsik优点：具有很高的线性度和较低的误差, 它已制 定和提供必要的数据采集系统由硬件和软件.测 功机可以衡量三个垂直切割力和扭矩期间同时 铳削和模拟测量值可以存储在计算机数据采集 系统.这是旨在衡量iWj达5000的最大力量和灵 敏度的系统土 5 NoA three-force component ana
11、logue dynamometer capable of measuring cutting forces during milling was designed, developed and tested. A computer connection for data acquisition was also made and calibrated. The analogue data can be evaluated numerically on a computer and when required can be converted back to analogue. The sche
12、matic representation of the cutting force measurement system is capable of measuring feed force ( F,),thrust force(F) and main cutting force ( F) which occursduring milling operations as seen in Fig. 1 . This dynamometer consists of four elastic octagonal rings on which strain gauges were mounted an
13、d necessary connections were made to form measuring the Wheatstone bridgesOn-line and real-time information of the cutting force data are automatically read and stored by a system during metal cutting. Since the output from Wheatstone bridge circuits is very low due to the high stiffness requirement
14、 of the dynamometer, the analogue signals coming from dynamometer amplified by strain gauge input modules (Advantech ADAM 3016) are then converted to digital signals and captured by PCI-1712 data acquisition card installed in MS-Windows-based PC. The stored data can be retrieved and used for analysi
15、s when required. The data acquisition software is capable ofaveraging and graphical simulation of force signals in process. The lists of the experimentalequipments used are shown in Table 1Table 1. Experimental equipments and theirtechnical propertiesMachine Universal milling: Taksan, FU-315toolV/2
16、附 250Dynamom Strain gauge-basedeterfour-component cutting forcedynamometerStrainHBM: LY 41-10/350; effectivegaugegauge length 10 mm; Gauge factor2.09 N%; gauge resistance350 国.3% Q; transverse sensitivityof - 0.3%Strain ring Octagonal in shape; made of AISI 4140 steel; b=30 mm; r=32 mm; t=8 mmStrain
17、Advantech: ADAM 3016amplifierDataAdvantech: A/D converter; PCIacquisition 1712, 16 single channels (8 carddifferential), 1 10 MHzDataWritten in C; capable of recording,recordingsimulating and data processing.softwareVibrationCommtest Instrument vb3000:analyserrange 1 20.000 Hz, ISO 2372andpackageISO
18、10816 standard.Accelerometer: frequency range 0.5 15 kHz, dynamic range 箔0 gCoupler/po Kistler: 5118B2; bandwidth 0.03, wer supply 0.006 Hz; gain 1.10.100 不 output voltage 40 V; operated by internal battery 4 内.5 V or DC external voltage 6 28 VUniversal LLOYD instrument T50 Ktestingmachine The thick
19、ness t, radius r, and width of the circular strain ring b are the three basic icontrollable parameters that affect the rigidityand sensitivity. Since there is no effect of ringwidth b and modulus of elasticity (E) on the strain per unit deflection, d.can be taken as 30-1 mm to set up the rings secur
20、ely 6.The deformation of circular ring under the effect of thrust force Ft and main cutting force F. separately is shown in Fig. 2(b) and (c), respectively. As long as strain on A and B where the strain gauges are going to be fixed (Fig. 2(a) are within the elastic limits of the ring material, the s
21、train and deflection due to the main cutting force should be considered for the purpose of the ring design for maximisation of sensitivity ( e/F) and stiffness ( F S).a)The strain gauges should be placed where the stress concentration has maximum value. The experiments have shown that good results a
22、re obtained for octagonal rings when the inclined gauges are at points 45 from the vertical instead of 39.6 required by the circular ring theory. The strain per unit deflection can be expressed as 6where 占 is the deflection in a radial directionand is the strain due to thrust forceFt. It isclear tha
23、t for maximum sensitivity andrigidity / 占 should be as large as possible. Thisrequires that r should be as small as possibleand t as large as possible. But small r bringsI some difficulties in mounting the internalI strain gauges accurately. Therefore, for a given size of r and b, t should be large
24、enoughIto be consistent with the desired sensitivity. Ito et al. 7 performed a finite element analysisIfor the elastic behaviour of octagonal rings.IThey expressed that the octagonal ring isI substantially stiffer than the circular ring when t/r less then or equals to 0.05, theIdifference in displac
25、ement of circular ring and octagonal ring is 10% if t/r greater then orIequals 0.25. In order to be consistent with this expression, the ring thickness and ring radius Iwere taken as 8 and 32 mm, respectively. Thus, the rate of t/r (8/32=0.25) providescorresponding sensitivity to stiffness ratio d(
26、Nr) for the octagonal ring.The cross-sensitivity can be expressed asstrain measured on axes that is normal to themain axes. It is desired that dynamometers_imust not be completely insensitive to thecross-strain. It is possible to measure thecutting forces independently and accurately aslong as the c
27、ross-sensitivity is small. The strain I errors will be less if this effect is within anacceptable range. These errors can arisebecause the strain gauges are not fittedsymmetrically to the ring axes and if the strain rings are not mounted in the direction ofmeasured force axes. The average errors for
28、 cross-sensitivity in three axes were calculated in range of 0.6 T.7% as shown in Table 2(b).Table 2. The results of tests performed on the dynamometer(a) The results of linearity testAxLoadOutput- CalibrationErrores(N)(mV)value-(mV)(%)Ff2400128.3130.01.3Fc2400126.8125.01.4F5000134.2135.81.2(b) The
29、results of crosssensitivity testA Loa Output Averag xe d (mV/ Mm)e errors (N)(%)XYZXYZFf24012-01.3-10. 08.86 3Fc 240 - 1 12 -2.2 -11.0.2 6.78Ft 500 1. 1.134.0.062211. 9,2(c) The results of eccentricity testALoae=0e=50(%)xedmmmmOutputs(N)(mV)(mV)errorFf10054.654.70.180Fc10053.853.90.180Ft10025.8625.5
30、30.13% Output errorAccuracy=1000/1014.9=0.985(d) The results of performance testA ( F( F(N)xe m Ns V)X 14. 245 55Y13.21014.9 NError=14.9/1005050=0.0150Z32.9Error=0.15%87 50In this study, strain gauge-based dynamometer has been designed and developed. It has beendevised and connected with necessary d
31、ataacquisition system consisting of hardware andsoftware. Dynamometer can measure three_iperpendicular cutting force components and torque simultaneously during milling and themeasured numerical values can be stored incomputer by data acquisition system. Thisdynamometer was designed to measure up to
32、 5000 N maximum force and the sensitivity ofsystem is i5 N.The orientation of octagonal rings and straingauge locations were determined to obtain maximum output of ring minimum cross-sensitivity underdeformation.Tomeasure the dynamiccutting force,anaccelerometer was attached to the dynamometer in me
33、asurement direction and the dynamic cutting force calculation was also given. For data transfer between the dynamometer and PC, a proper experimental set-up was performed and suitable software was written. In order to determine accuracy, the dynamometer was calibrated statically and dynamically and
34、subjected to the linearity test, cross-sensitivity test, eccentricity test and performance test.The static calibration curves for Ff, F.and F* forces have shown that it has very high linearity (in errors 1.3%, 1.4% and 1.2%) and low cross-sensitivity errors (in range of 0.6 T.7%). In face-milling op
35、erations, appropriate results were obtained in cutting force measurements. As a result, recorded cutting force data were presented for evaluation. Also the natural frequency of dynamometer in X-, Y- and Z-directions satisfies the necessary rigidity and dynamic range.The results obtained from the mac
36、hining tests performed at different cutting parameters showed that the dynamometer could be used reliably to measure cutting forces not only in milling but also in other machining processes as turning, grinding and shaping.The signal recording and processing unit can be used, for example, to monitor
37、 or control processes. This type of measuring chain has proved successful for measuring force and torque.An overview of data acquisition system for cutting force measuring and optimization in milling参考文献： Journal of Materials Processing Technology F.Cus, J.Balic优点：特别适合运用在刀具磨损检测的领域,并 且能够在运作过程中监测刀具的磨损
38、情况.One of the most significant developments inthe manufacturing environment is the increasing use of tool and process monitoring systems. Many different sensor types, coupled with signal processing technologies are now available, and many sophisticated signal and information processing techniques ha
39、ve been invented and presented in research papers. However, only a few have found their way to industrial application. The aim of this paper is to present the cutting force measurement system for the ball-end milling. The system is based on LabVIEW software, the data acquisition system and the measu
40、ring devices (sensors) for the cutting force measuring. The system collects the variables of the cutting process by means of sensors and makes transformation of those data into numerical values. Generally used measuring devices for cutting force measuring are piezoelectric dynamometer. Delivered sig
41、nals are distorted due to their self-dynamic behaviour. Their dynamic characteristics are identified under normal machining operation. The proposed method is based on the interrupted cutting of aspecially designed workpiece that provides a strong broadband excitation. The three components of the exc
42、iting force and the accelerationof the gravity centre of thedynamometer cover plate are measured simultaneously. The measured values are delivered to the computer program through the data acquisition system.The data obtained from the acquisition system, are a basis for the optimization of the machin
43、ing process cutting parameters.Application of AE and cutting force signals in tool condition monitoring in micro-milling参考文献：CIRP Journal of Manufacturing Science and Technology P.J.Arrazola优点：灵敏度很高.Cutting forces and acoustic emission signals provide very useful information for tool condition monit
44、oring in micro-milling. An acoustic emission signal is free from mechanical disturbances like resonance vibrations, which is very important in micromachining applications, where spindle speeds have to be very high due to the small tool diameter. Despite the small material removal rate in micromachin
45、ing, the obtainedAE signal was strong, easy to register, and showed a very short reaction time to the tool workpiece contact, which makes it a very good means of detecting this contact and monitoring the integrity of the cutting process.The cutting force signals acquired in this study were severely
46、disturbed by resonance vibrations in the dynamometer. In spite of this, the measurements still appeared to be very useful in tool wear monitoring.Signal feature integration in tool condition monitoring minimizes the diagnosis uncertainty, reducing the randomness in one SF and providing a more reliab
47、le tool condition estimation. The number of SFs should be as big as possible, preferably originating from different sensors. Very good results can be achieved using cutting forces and acoustic emission. TCM based on AE only, as an AE sensor is much less expensive and easier to install, is worse than
48、 that based on four signals, yet still provides acceptable results.Tool condition monitoring strategies should be tested on tool lives that are different from the tool life used to train the system. A good practice is to repeat the test for every available tool life to avoid selecting the best results,w