第五章 速度、转速和加速度的测量

1、Contents7.1 Overview7.2 Measurement of Velocity7.3 Measurement of Acceleration7.4 Vibration testMeasurement of velocity and acceleration for vehicle, train, ship, plane, etc，and that of their moving attitudeRotational velocity for output shaft speed of engine and generatorVelocity of rolled plate, s

2、trip, bar, tubing materialMeasurement of vibration for large devices and engineeringApplications in inertial navigationVelocity：a vector which shows the direction and rate of motion. 物体直线运动时单位时间内的位移量，m/sAcceleration：a vector which shows the direction and magnitude of changes in velocity.物体运动时单位时间内的速

3、度增量，m/s2 Rotational Velocity：物体运动时单位时间内的转数，r/minAngular Velocity：物体单位时间内转过的角度，rad/sContents7.1 Overview7.2 Measurement of Velocity7.3 Measurement of Acceleration7.4 Vibration testFrom motion form： measurement of linear velocity(线速度) and angular velocity(角速度)From reference: measurement of absolute ve

4、locity(绝对速度) and relative velocity(相对速度)From numerical feature: measurement of average velocity(平均速度) and instantaneous velocity(瞬时速度) The average velocity of an object is the total displacement during some extended period of time, divided by that period of time. Instantaneous velocity, on the other

5、 hand, describes the motion of a body at one particular moment in time.From accessible means: measurement of direct velocity(直接速度)and indirect one(间接速度)Average velocity methodDefinition of velocity：v=L/tAccelerationintegrationmethod/Differential of the displacement在振动测量中，通过测量振动体的加速度，积分得到振动速度、振幅等Velo

6、city measurement using physical parametersMathematical model of speed and physical quantity，such as E=BLv conductor velocityBernoullis equation in hydromechanicsDoppler velocity measurement光束切断法(短距离平均速度法)Correlation velocity measurement)()(0ttxty000011( )lim( ) ()lim() ()()TTyxxTTRy t x tdtx tt x td

7、tRtTTCorrelation velocity measurementStrong anti-interference ability and make the measurement under complex interference conditions .Application: measurement of plane, ship, and rolling mill strip, etc.In principle, two sensors is set in the direction of velocity of a moving object, and the velocit

8、y can be measured using cross-correlation principle.Spatial filter velocity measurement(空间滤波器测速法)利用可选择一定空间频率的空间滤波器件与被测物体同步运动，然后在单位空间内测得相应的时间频率f，求得运动体的运动速度。/0fNfNtLvLvNL fNt0 Bernoullis equation of ideal incompressible fluid 理想不可压缩流体在重力场中作定常流动时，具有三种形式的能量：位势能、压力势能和动能，在流线上任何一处三者能量之和保持恒定。v2,p2z1z2v1,p12

9、12pgzvConstantMeasuring principle2/2vpppstv/ )(2stppv误差来源：误差来源：皮托管的方向与流体方向不对准；皮托管直径不为零，静压孔实际静压力降低；流体受皮托管的滞止，使滞止点上游的静压力增大。 全静压管静压孔距前端不小于8倍管径，可减小头部激波对静压的影响；静压孔上部4个，下部6个，两侧没有，可在大仰角飞行时减小静压误差；装有加温装置，防止在高空飞行时结冰飞机空速表开口膜盒（指示空速）真空膜盒（真空速）标实真实TTvv当外界气温T实与该气层标准气温T标不等时，应按下式进行修正：皮托管测速装置利用了流体速度和流体动压力之间的关系；在测量时直接测量

10、的是压力，然后再计算出速度，属于间接测量；测量了运动物体和流体的相对速度。皮托管装置的结构坚固耐用，稳定可靠。Doppler effectDoppler velocity measurementicf/0iPvcf1cos2cossPcvf2121(cos)(cos)(coscos)siicvcvfccvisdvfff)cos(cos120多普勒测速的优点：用光的波长作基准，精度高；光电探测器输出频率信号，抗干扰能力强。 Backscattering Doppler velocity measurement00sin/sin/dfvf vc )sin/(0fcfvd光源与光电探测器放置于运动物

11、体的一侧，仪器设计时结构紧凑Backscattering difference Doppler velocity measurementDifference Doppler velocity measurementFor the beam O10131(coscos)dOf vfcFor the beam O20232(coscos)dOf vfc21012(coscos)sin22ddOdOffff vcv)2/sin(2/0dfv Frequency difference is not concerned with the position of photo-electric detect

12、or, and it measures in any direction.可使用大口径的接收透镜，使粒子散射的光能量极大地被利用，提高信噪比。Optical fibre Doppler velocity measurement of blood 探头体积小，便于调整测量位置，可以深入到难以测量的角落；抗干扰能力强，可在高电压、强电磁感应等环境中使用。密封型的光纤探头可直接放入液体中使用。 Satellite tracking system Satellite tracking system电磁波多普勒效应Structure of gyroscope2-DOF gyroSingle-DOF gy

13、roSupport mode of gyroscope液浮陀螺仪气动陀螺仪静电陀螺仪挠性陀螺仪Basic characteristics of gyroscopeGyroscopic inertia(定轴性)：当陀螺仪的转子高速旋转时，如果不受任何外加力矩的作用，其主轴将稳定地保持在惯性空间初始方向上，这种特性称为陀螺仪定轴性或者稳定性。角动量H越大，摩擦力矩越小，则主轴方向越稳定。HJ Basic characteristics of gyroscopeGyro-precession(进动性)：当转子高速旋转时，如果外加力矩M作用在陀螺仪的某一框架旋转轴上，迫使主轴绕另一框架的轴旋转，主轴以

14、最短的途径向外力矩的方向靠拢。在实际使用中如果内框架和外框架重合，陀螺仪将会失去了一个自由度，这种情况被称为“环架自锁”。陀螺的进动是没有惯性滞后微分陀螺仪角速度测量ykHFibre-optic gyroscopeInvented with Sagnac effect光纤陀螺对角速度的敏感轴是单轴，常使用三个或四个光纤陀螺构成惯性测量组合Measuring methodExpressed by revolution per minute. That is r/min By measuring principle:模拟法计数法同步法 By transforming mode：机械式电气式光电式频

15、闪式22rcFmrkksFk x离心式转速表具有测量结果显示直观、成本低、运行可靠、坚固耐用等优点，故在生产、维修现场使用较多。但是离心式转速表的测量原理简单，测量精度相对较低。接触式接触式非接触式非接触式ztNn60zfn60随着转速下降输出感应电动势的幅值也随之减小，当转速低到一定程度时，电压幅值将会无法检测出来。这种传感器不适合于低转速测量。Stroboscopic effect(Stroboscopic effect(频闪效应)物体在人的视野中消失后，人眼视网膜上能在一段时间内保持视觉印象，即视后暂留现象。其维持时间，在物体平均亮度条件下，约为(1/51/20)s的范围。Measuri

16、ng principle用一个频率连续可调的闪光灯照射被测旋转轴上的某一固定标记(如齿轮的齿，圆盘的辐条或在旋转轴上涂以黑白点)，并调节闪光频率f，直到旋转轴上出现一个单定像为止，即达到n=f的条件，这时便可以从电子计数器或圆刻度盘上读出被测的转速值。Measuring method被测转速n与闪光频率n0相同，或者n为n0的整数倍时，都会出现单定像若已知被测转速的范围是nn，则首先将闪光频率调到大于n，然后从高频逐渐下降，第一次出现单定像的闪光频率等于被测转速若被测转速的频率范围无法估计，则调整闪光频率，记录下连续出现两次单定像的闪光频率n1和n2，设n1n2，则1212n nnnnCont

17、ents7.1 Overview7.2 Measurement of Velocity7.3 Measurement of Acceleration7.4 Vibration testMeasure the load of mechanical system by testing its acceleration. 防止损坏或提供控制指标Vehicle ：防撞气囊、警报器Accelerometer-based mouseMobile phoneSomaticgame(体感游戏Measure motion state of an object by testing its acceleratio

18、n, such as inertial navigationsystemMeasurement of acceleration is made by detecting the displacement between the mass block and the base.Acceleration can be got by measuring inertial force. 质量块通过连接的阻尼器和弹簧感受到加速度的变化，质量块会受到与加速度成比例的惯性力的作用，通过检测惯性力可以实现加速度的测量Piezoelectric accelerometerMagnetoelectric induction accelerometerCapacitiveaccelerometerMEMS电容加速度计Servo accelerometer Working principle：closed-loop test system based force-ba