【20160404】Follower Motion Schemes+ T% }) D/ b `2 `5 C6 M
从动件运动模式
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Q& M( x& l+ U4 s2 D2 PIn designing a cam, the objective is to identify a suitable shape for the cam. The primary interest is to ensure that the follower will achieve the desired displacements. The shape of the cam is merely a means to obtain this motion.
. C" y) B$ b( E- S4 H6 B. d7 y设计凸轮时,我们的目标是找出合适的凸轮外形。但最初的目的是确保从动件将按照预期进行运动。凸轮外形仅仅是获得此种运动的方式。1 s3 Z- L# a/ r' F
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Constant Velocity:Uniform velocity, and zero acceleration
* d# k. f- _$ u5 F常速运动:匀速,加速度为零1 F+ A& v+ ?* B p" ^
Problems:The instantaneous jump from one constant value of velocity to another constant value of velocity results in an infinite acceleration.+ [7 n2 t1 q) N1 N3 Y9 |
问题:从一种匀速状态到另一状态,所需加速度无限大。
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constant velocity
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Constant Acceleration:Constant positive and negative accelerations
$ b1 n" t4 Z* q. o2 X0 h匀加速运动:加速度连续同向( b: }8 T9 l% {1 X# k' I" v; M" ~
Problems:The abrupt changes of acceleration at the end of the motion result in abrupt changes in inertial forces.
* T& _0 Z B- k+ {+ y4 }1 x; B问题:加速度突然转变,所需内力无限大。5 e% s O$ H1 z* J6 M& |/ D: `8 [
constant acceleration
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Harmonic Motion:Harmonic motion is derived from trigonometric functions, thus exhibiting very smooth motion curves.+ A9 z, r6 H# x. @
简谐运动:三角函数推导而来,因此具有平滑的运动曲线。0 ^/ b2 h; r" V4 B
Problems:It has a sudden change of acceleration at the ends of the motion, which can be objectionable at higher speeds.# W# Z5 w3 U1 L% @' E; g8 B- x5 y7 o
问题:在运动末尾加速度会突变,这在高速下十分不便。
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harmonic motion
+ N6 s0 S" f, f% y2 e; u, I+ T; |Cycloidal Motion:Cycloidal motion is another motion scheme derived from trigonometric functions.6 v7 E4 w- Z# p L# W
摆线运动:另一种由三角函数导出的运动类型。
* J' M( z# ?, R6 ]! e2 eThis scheme does not have the sudden change in acceleration at the ends of the motion, which makes it popular for high-speed applications.
! b8 G" M0 \3 D* e4 v加速度不突变,在高速运动中广为应用。# H$ w( Y- U5 E
cycloidal motion
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1 W7 r& D4 S: T* }5 o) ]The time derivative of the acceleration is referred to as jerk.. F; D" E% e$ i6 o
加速度对时间的导数称为急动度。
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! \% o. C! L+ g1 y5 vA summary of the peak velocity, peak acceleration, and peak jerk for the different motion schemes, as a function of the rise H and period of the interval T, is shown in Table 9.5.1 B/ F/ T5 i3 `
如表所示是各种运动模式的速度峰值、加速度峰值及急动度峰值的对比。# p/ Z5 o( C) t' w _
Table 9.5
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