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【20160324】Slider-Crank Mechanism

/ c+ `4 K0 q* x- m! EAnother mechanism that is commonly encountered is a slider-crank. This mechanism also consists of a combination offour links, with one being designated as the frame. This mechanism, however, isconnected by three pin joints and one sliding joint. A mechanism that drives a manual water pump is shown in Figure 1.37a. The corresponding kinematic diagram is givenin Figure 1.37b.
曲柄滑块机构也很常见。事实上它也是由4个构件组成，只是其中之一被指定为机架。另外，此机构是以3个转动副、一个滑动副连接的。图示为手摇泵及其运动图示。
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Because the slider-crank mechanism has one degree of freedom, it is constrained or fully operated with one driver. The pump in Figure 1.37 is activated manually by pushing on the handle (link 3). In general, the pivoted link connected to the frameis called the crank. This link is not always capable of completing a full revolution. The link that translates is calledthe slider. This link is the piston/rod of the pump in Figure1.37. The coupler or connecting rod “couples” the motion of the crank to the slider.
因为机构只有一个自由度，因此只需要一个主动力。一般来说曲柄无法完成整周运动。作滑移运动的构件称滑块，连接滑块和曲柄的称连杆。

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黑森林的鹿

风雪关怀 发表于 2016-3-24 13:13
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黑森林的鹿

【20160325】Position and Displacement Analysis

8 {- P: {4 J5 R2 k! uObjectives：
1. Determine the position of all links in a mechanism as the driver links are displaced.
2. Determine the limiting positions of a mechanism.
# R# T  T- H3 ^目标：
6 k5 i, M4 n4 l( i4 F' d1.在主动件位置已知的情况下确定其余构件的位置；
2.确定机构的极限位置。

" t! ]0 E- ~3 Z( _+ s( e- {0 }, iTwo types of methods

• GraphicalAnalysis
• AnalyticalAnalysis
  

两种方法：图示法、解析法

* P& n( D6 e# o& B) R8 TPosition and displacement analysis：
locating the position of all links (configuration) in amechanism as the driver link(s) is displaced.
# m6 P4 `( U* }: {$ V  n' M( H定义：在主动件位置已知的情况下确定其余构件的位置。
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Graphical Analysis
图解法分析步骤
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1.Point B moves to B’
2.Point C must always lay on its constrained path
! `* b- k& j9 `, O3.The length between B and C must stay constant
5 G8 D8 {( w' U$ U2 `画主动件→画定轴转动轨迹→连杆长度不变→交点

1 B' d5 g" W, l! c+ b# pAnalytical Analysis
( A4 M9 J$ v8 q1 q# U. ~" E解析法
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% q* t6 b3 x# n4 F+ T# ALimiting position
- [" o  K" e8 B1 z# mThe configuration of a mechanism that places one of the follower links in an extreme location is called a limiting position.
从动件之一处于其极限位置的机构位置称极限位置。

* e5 g4 G3 s7 DThe crank and coupler become collinear.
Imbalance angle - the angle between the coupler configuration at the two limiting positions.
8 k7 k  P+ B0 r/ Z' G7 j曲柄和连杆共线时达到极限位置；
' i; H% b! Q3 \+ j# W; M0 l1 g* e极位夹角：连杆在两极限位置之间时所形成的角。
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Transmission Angle
The mechanical advantage ( output force/ input force) is proportional to the sine of the transmission angle.
传动角：机械增益（输出力比输入力）与传动角的正弦成正比。
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黑森林的鹿

【20160326】Mechanism design
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- `2 i! f! ?4 z( HThe task of mechanism design: given a desired motion, a mechanism form and dimensions must be determined.
结构设计：根据运动确定构型。

Synthesis: describe the process of designing a mechanism that produces a desired output motion for a given input motion.
" ^( \% i* T. i8 E; J构型综合：描述给定输入运动实现输出运动的机构设计过程。

! N+ Y0 m0 f' Q# u分类：
Type synthesis: selecting a mechanism type
Dimensional synthesis: determining the link lengths

0 a3 Z3 D7 H! t" pTime Ratio

Kinematically balanced mechanisms：the motion characteristics of the outward stroke are identical to those of the inward stroke.
7 ]) @/ ]( f$ W, ?6 b2 C: P; P$ }运动对称机构：内外冲程等时。
! E4 g$ _5 M9 t4 GQuick-return mechanisms：difference in the speed of the forward and return strokes.
( x9 [8 K0 K' o+ N# ?' L: l1 ~  p9 Q急回机构：冲程不等时。

Working stroke: smoothing the surfaces of metal. ( slower) 工作冲程
' W0 ^+ j3 c7 R' {" Y0 _* t1 }& |Return stroke:nothing to do. ( quicker) 急回冲程

Time ratio: a measure of the quick return action of a mechanism
: `8 t" I" P. p# _4 e时间比：用于度量急回机构

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黑森林的鹿

【20160327】Design of Slider-Crank Mechanisms
曲柄滑块机构设计
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In-line slider-crank mechanism: has the crank pivot coincident with the axis of the sliding motion of piston pin.
# W- Z! I, O3 F  {0 c曲柄轴心与滑块运动轨迹共线。

In-line slider-crank mechanism produces balanced motion.
3 g! i, D: x6 ~: q该机构产生平衡运动。

Offset slider-crank mechanism: has the crank pivot not coincident with the axis of the sliding motion of pin.
曲柄轴心与滑块运动轨迹不共线。
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Determining an appropriate offset distance, L1, and the two links lengths, L2 and L3, to achieve the desired stroke, |ΔR4|max, and imbalance angle.
0 z. X2 D! Q* l: g+ N, j& a确定补偿距离及构件杆长以获得需要的冲程、极位夹角。
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Questions
9 P8 Q2 A* d6 K  p/ M' a6 IThe stroke, |ΔR4|max, and imbalance angle are given, determining an appropriate offset distance, L1, and the two links lengths, L2and L3.
; W# V0 u" W7 [+ \9 O3 x常见题型，给定冲程、极位夹角，确定补偿距离及构件杆长。

" @; `5 k, o+ o7 n4 {解题公式：

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