【菜鳥成長(zhǎng)記】20歲后，我在機(jī)械的每一天

鄒112

一來看各路高手前輩的帖子云里霧里，自覺入門也未同感同感

黑森林的鹿

【20160317】Mobility

An important property in mechanism analysis is the number of degrees of freedom of the linkage. The degree offreedom is the number of independent inputs required to precisely position

all links of the mechanismwith respect to the ground. It can

also be defined as the number of actuators needed to operate

the mechanism. A mechanism actuator could be manually

moving one link to another position, connecting a motor to the

shaft of one link, or pushing a piston of a hydraulic cylinder.

自由度就是完全確定機(jī)構(gòu)位置的獨(dú)立參數(shù)個(gè)數(shù)，也是動(dòng)力源個(gè)數(shù)。

The number of degrees of freedom of a mechanism is

also called the mobility, and it is given thesymbol M. When

the configuration of a mechanism is completely defined by

positioning one link, that system has one degree of freedom.

Most commercially produced mechanisms have one degree

of freedom. In constrast, robotic arms can have three, or

more, degrees of freedom.
自由度記作M。工程上大多是單自由度機(jī)構(gòu)。機(jī)械臂多為多自由度機(jī)構(gòu)。
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9 q9 L0 m2 |0 P; V% ~' N6 _Gruebler'sEquation
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Degrees of freedom for planar linkages joined with common

joints can be calculated through Gruebler'sequation :

(寒假自學(xué)的一堆公式歸結(jié)為一個(gè)常用公式了：3×總機(jī)構(gòu)數(shù)-2×低副數(shù)-高副數(shù)，即為自由度)
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  C, C6 E$ \4 k7 M! W9 ?As mentioned, most linkages used in machines have one

degree of freedom.

Linkages with zero, or negative, degrees of freedom are

termed locked mechanisms.These mechanisms are unable

to move and form a structure. A truss is a structure composed

of simple links and connected with pin joints and

zero degrees of freedom.

Linkages with multiple degrees of freedom need more

than one driver to precisely operate them. Common

multi-degree-of-freedom mechanisms are open-loop

kinematic chains used for reaching and positioning, such

as robotic arms and backhoes. In general,multi-degree-of-freedom linkages offer greater ability to precisely position

a link. These mechanisms are shown in Figure 1.13.
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! J$ M) `9 E/ x7 k( M* x" i這帖居然被專輯收錄了受寵若驚……論壇各位真是太提攜后輩了……感覺更不能簡(jiǎn)簡(jiǎn)單單更課本了呢，聽從各位前輩教導(dǎo)，自己多多在課外、在實(shí)際中學(xué)習(xí)才是！
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黑森林的鹿

牧羊少年 發(fā)表于 2016-3-16 22:47
學(xué)妹的英語(yǔ)底子很好，考了兩次都520（170+240+110）左右，除了偶爾看看新聞、美劇沒啥英文學(xué)習(xí)，學(xué)妹有啥 ...

( M3 S: h% g* a" \2 I0 \根據(jù)一般情況說一下咯，學(xué)長(zhǎng)看看有木有參考~

最有效的方法還是……考前做原題。這里的考前是考前一周左右。
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7 h: _- K- F6 K" q6 T& p# n不過在考前的前，我覺得用好扇貝家的英語(yǔ)系列比較可行（并不是打廣告。。。），他家一共5個(gè)應(yīng)用，除了讀書，其他的：?jiǎn)卧~、聽力、閱讀、煉句都是極好的。雖說我不是專門用扇貝備考的，但是那段時(shí)間確實(shí)是每天這樣學(xué)一會(huì)英語(yǔ)的，而且推薦軟件用法也比推薦題集可行一點(diǎn)不是么~積累階段，技巧沒那么重要，就是靠堅(jiān)持。
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我的用法：早晨起來收拾完到食堂是6:20多，30開飯，正好做完煉句。煉句是練很多固定短語(yǔ)、地道表達(dá)，對(duì)作文有幫助。煉句要選對(duì)應(yīng)課程買的，要很多貝殼，可以充值可以靠打卡賺。看學(xué)長(zhǎng)好像寫作和翻譯分相對(duì)不高，煉句應(yīng)該是比較有用的。
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6 M' F+ S! C" S2 u然后買飯，開背單詞軟件（還不是扇貝單詞）。只扇貝單詞一個(gè)肯定不行的，我當(dāng)時(shí)用過各種，什么百詞斬啊有道啊拓詞啊樂詞啊……現(xiàn)在還在用的叫背單詞Online，按遺忘曲線安排的，感覺比扇貝還科學(xué)，不過用戶體驗(yàn)差了點(diǎn)。有余力可以考慮用。（不過如果感覺背單詞很痛苦的話還是專心一個(gè)就好。）吃飯的時(shí)候看一眼單詞嚼一口，吃完也差不多背完了。
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3 V+ O2 I; h$ a' ]" B然后去晨讀室，聽扇貝聽力。挖空比設(shè)成90，跟聽寫差不多了就，這個(gè)耗時(shí)比較長(zhǎng)，熟練點(diǎn)的話一篇10分鐘能聽完。聽寫的好處就不多說了，選六級(jí)真題，堅(jiān)持聽懂整句話，大概復(fù)述下來再默寫似的填空，盡量減少重聽。過程非常痛苦，非常痛苦，痛苦！但收獲很大，很大，大！不光聽力，常用詞拼寫也從此不是問題~而且練專注力、反應(yīng)力、記憶力，以及語(yǔ)言容量（還是叫什么的忘了，意思就是，咱們母語(yǔ)漢語(yǔ)，可以聽一句好長(zhǎng)的話并記住，整句話說完也不會(huì)忘了開頭，但外語(yǔ)長(zhǎng)句就不容易記住，這就是語(yǔ)言容量不同。多練多記，容量上來了，六級(jí)聽力的難度，一篇文章不記筆記用腦子也能幾個(gè)大概的）

$ e% W4 T' G: T# V7 }7 b$ K然后7點(diǎn)了，扇貝新聞更新了，看新聞。不過這個(gè)更適合考完四六級(jí)提高用，畢竟都是外文報(bào)刊的新聞，不過找里面難度等級(jí)高中和四六級(jí)的，練閱讀速度也很好，它每篇都會(huì)給計(jì)時(shí)，可以比較看自己的速度（別跟評(píng)論區(qū)里的人比，跟自己比；也不要太在意評(píng)論區(qū)里各種話，現(xiàn)在扇貝新聞評(píng)論區(qū)簡(jiǎn)直了……）

/ K3 o1 ?( f( E4 P9 o4 s7 A單詞我是中午吃完飯背的（我不午睡），關(guān)于背單詞的方法見仁見智，我自己是看英英解釋，看一眼例句，重點(diǎn)看小伙伴的筆記，里面詞根詞源、用法例句、記憶法都很多，認(rèn)真看很有收獲。50個(gè)單詞需1小時(shí)左右，沒完成就課間用碎片時(shí)間背，不過這總沒大塊時(shí)間好，因?yàn)闆]時(shí)間看筆記。選單詞書方面呢……先去測(cè)個(gè)單詞量，扇貝家測(cè)得特別高，比如我在Test your vocabulary上明明才9000多，扇貝說我12000=_=  想鼓勵(lì)自己可以信，不過一般要減個(gè)2、3千才是實(shí)際的詞量，要是5000以下，還是先背四級(jí)單詞，不然一下生詞太多沒興趣了。至于每天背多少那看你覺得難不難了，要是有一半點(diǎn)了不認(rèn)識(shí)，那還是每天最低50個(gè)吧。等每天三分之二都能認(rèn)識(shí)了就加量，注意它算的背完日期，別忘了還有六級(jí)的書要刷，也不能太懶散了。學(xué)習(xí)模式，一定改成拼寫，拼寫，拼寫。

最后，考前至少留兩套真題，按考試的樣子做一遍，包括計(jì)時(shí)！作文可以不寫，因?yàn)闆]人給改。尤其聽力，一定要模擬考試，模擬考試，模擬考試，對(duì)聽力提高太特么有幫助了。這也可能是我唯一做準(zhǔn)備的地方了。
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剩下的就是自己的投入了。

' A( Z& i  s. z7 O/ N首先想混打卡是很容易的，單詞全點(diǎn)我認(rèn)識(shí)，新聞點(diǎn)開等3分鐘，聽力設(shè)成0%，煉句全點(diǎn)流利復(fù)述，5分鐘就能打卡。但是，有用么？英語(yǔ)這玩意就是吃功夫，就是靠時(shí)間耗出來的，不像理科，腦子不開竅想多久都得考60多……（我慘痛的上學(xué)期！！！） 我小學(xué)學(xué)新概念，高二背雅思單詞，考四級(jí)前刷完六級(jí)單詞，開始用扇貝以后每天平均1小時(shí)，現(xiàn)在打卡370多天了。周末或者出去坐地鐵通勤時(shí)間長(zhǎng)還會(huì)背700單詞，4個(gè)多小時(shí)……所以我總共花了多少時(shí)間？不是顯擺，只是想說，學(xué)個(gè)語(yǔ)言還是蠻辛苦的，得真花時(shí)間，花心思，so做好心理準(zhǔn)備，每天把這當(dāng)個(gè)事放在心上。

還有，并不推薦看美劇和新聞。個(gè)人看法，美劇是用來養(yǎng)節(jié)奏的，和老外說話的節(jié)奏，包括語(yǔ)音語(yǔ)速俚語(yǔ)俗語(yǔ)，對(duì)應(yīng)試幫助甚少。如果看完一集美劇，腦子里沒有洗腦地回放某幾句很好的臺(tái)詞（好指的是有個(gè)連讀啦，夸張的語(yǔ)調(diào)啦，地道的轉(zhuǎn)音啦，俏皮的比喻啦之類的）直到自己脫口而出，就像小孩子學(xué)大人的舌一樣，我認(rèn)為這集美劇看的就沒有價(jià)值，或者說，只有娛樂的價(jià)值。新聞倒是可以，只要找感興趣的、能邊聽邊聯(lián)想自己的，也就是產(chǎn)生積極互動(dòng)的就好，否則只為“磨耳朵”，泡著，不去沉浸，也是不可取的。

當(dāng)然目標(biāo)每個(gè)人不同，肯定有自己的取舍，這個(gè)不多說。方法也因人而異，我說這么多也只是參考，具體合不合適還得自己嘗試。加油！祝早日取得好成績(jī)！O(∩_∩)O~

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long_wzq

給個(gè)贊

牧羊少年

黑森林的鹿 發(fā)表于 2016-3-17 18:08
根據(jù)一般情況說一下咯，學(xué)長(zhǎng)看看有木有參考~

最有效的方法還是……考前做原題。這里的考前是考前一周左 ...

謝謝！很有參考，扇貝聽力深有體會(huì)，煉句倒沒用過，準(zhǔn)備試試。學(xué)妹的功夫下的很大，態(tài)度更值得參考！

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however1241

不論多寡，只求有得

黑森林的鹿

【20160318】Actuators and Drivers

In order to operate a mechanism, an actuator, or driver device, is required to provide the input motion and energy. To precisely operate a mechanism, one driver is required for each degree of freedom exhibited. Many different actuators are used in industrial and commercial machines and mechanisms. Some of the more common ones are given below:
; D1 ^6 N9 f# o" e& y% d每個(gè)自由度需要獨(dú)立的驅(qū)動(dòng)力來完全確定機(jī)構(gòu)位置。常用驅(qū)動(dòng)源如下：

- v- v7 p8 ^& M- O  s/ C9 zElectric motors (AC) provide the least expensive way to generate continuous rotary motion. However, they are limited to a few standard speeds that are a function of the electric line frequency. In North America the line frequency is 60 Hz, whichcorresponds to achievable speeds of 3600, 1800, 900, 720, and 600 rpm. Single-phase motors are used inresidential applications and are available from 1/50 to 2 hp. Three-phase motors are more efficient, but mostly limited to industrial applications because they require three-phase power service. They are available from 1/4 to 500 hp.
1 I# X" W5 r" |+ |交流電動(dòng)機(jī)：最廉價(jià)；轉(zhuǎn)速受限。

0 S: [- z1 Z  ~9 Q* @5 q! C( QElectric motors (DC) also produce continuous rotary motion. The speed and direction of the motion can be readily altered, but they require power from agenerator or a battery. DC motors can achieve extremely high speeds––up to 30,000 rpm. These motors are most often used in vehicles, cordless devices, or in applications where multiple speeds and directional control are required, such as a sewing machine.
: J; x6 h  A& X# S/ ~: j直流電動(dòng)機(jī)：高速、多種速度需求，用于交通工具等。
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6 _3 {9 U1 ?; Z: c, HEnginesalso generate continuous rotary motion. The speed of an engine can be throttled within a range of approximately 1000 to 8000 rpm. They are a popular and highly portable driver for high-power applications. Because they rely on the combustion of fuel, engines are used to drive machines that operate outdoors.
. {* {  M# f7 G' p; q發(fā)動(dòng)機(jī)：動(dòng)力足。戶外器械。

Servomotorsare motors that are coupled with a controller to produce a programmed motion or hold a fixed position. The controller requires sensors onthe link being moved to provide feedback information on its position, velocity, and acceleration. Thesemotors have lower power capacity than nonservomotors and are significantly more expensive, but they can beused for machines demanding precisely guided motion, such as robots.
% b1 j6 n+ Y  v3 E# b+ `" D伺服電機(jī)：精確運(yùn)動(dòng)控制，如機(jī)器人。

Air or hydraulic motors also produce continuous rotary motion and are similar to electric motors, but have more limited applications. This is due to the need for compressed air or a hydraulic source. These drive devices are mostly used within machines, such as construction equipment and aircraft, wherehighpressure hydraulic fluid is available.
氣壓/液壓機(jī)：如飛機(jī)等可提供大量流體處。
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Hydraulic or pneumatic cylinders are common components used to drive a mechanism with a limited linear stroke. Figure 1.20a illustrates a hydraulic cylinder. Figure 1.20b shows the common kinematic representation for the cylinder unit.
. T0 _4 S9 E! W: s- T2 t2 S: w( @" U$ d氣壓/液壓缸：沖程有限處。


The cylinder unit contains a rod and piston assembly that slides relative to a cylinder. For kinematicpurposes, these are two links (piston/rod and cylinder), connected with a sliding joint. In addition, the cylinder and rod end usually have provisions for pin joints.

* G' G# U8 C4 S$ x9 s  t1 L: l6 GScrew actuators also produce a limited linear stroke. These actuators consist of a motor, rotating ascrew. A mating nut provides the linear motion. Screwactuators can be accurately controlled and can directly replace cylinders. However, they are considerably more expensive than cylinders if air or hydraulic sources are available. Similar to cylinders, screwactuators also have provisions for pin joints at the two ends. Therefore, the kinematic diagram is identicalto Figure 1.20b.
+ d. |. u- L; u9 j* }螺旋致動(dòng)器：類似氣壓/液壓缸，精確控制、有限沖程。

Manual, or hand-operated, mechanisms comprise a large number of machines, or hand tools. The motions expected from human “actuators” can be quite complex. However, if the expected motions are repetitive, caution should be taken against possible fatigue and stain injuries.
人力驅(qū)動(dòng)……

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haneast

大學(xué)六級(jí)剛過500，現(xiàn)在看到學(xué)妹一貼下來的英語(yǔ)各種666，表示十分慚愧，現(xiàn)在也天天看扇貝，看到學(xué)妹的水平才知道自己其實(shí)還水得很

however1241

haneast 發(fā)表于 2016-3-18 17:05
大學(xué)六級(jí)剛過500，現(xiàn)在看到學(xué)妹一貼下來的英語(yǔ)各種666，表示十分慚愧，現(xiàn)在也天天看扇貝，看到學(xué)妹的水平才 ...

不求多寡，只求有得

黑森林的鹿

【20160319】Commonly Used Links and Joints
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Eccentric Crank
2 N  j0 t7 y7 w  @# iOn many mechanisms, the required length of a crank is so short that it is not feasible to fitsuitably sized bearings at the two pin joints. A commonsolution is to design the link as an eccentric crankshaft, as shown in Figure 1.23a. This is the design used in most engines and compressors.
/ ]' X% t2 b' R9 \% i偏心曲柄，由于尺寸過小而不能保證鉸合處銷釘尺寸合適。

The pin, on the moving end of the link, is enlarged such that it contains the entire link. The outside circumference of the circular lobe on the crankshaft becomes the moving pin joint, as shown in Figure 1.23b. The location of the fixed bearing, or bearings, is offset from the eccentric lobe. This eccentricity of the crankshaft, e , is the effective length of the crank. Figure 1.23c illustrates a kinematic model of the eccentric crank. The advantage of theeccentric crank is the largesurface area of the moving pin, which reduces wear.
因此將該銷釘放大，以至于包裹整個(gè)曲柄。這個(gè)大銷釘中心與曲柄轉(zhuǎn)軸中心間的距離即為有效的曲柄長(zhǎng)度。這樣配置的好處在于移動(dòng)銷釘?shù)木薮蟮慕佑|面積，這減少了磨損。
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Pin-in-a-Slot Joint
A common connection between links is a pin-in-a-slot joint, as shown in Figure 1.24a. This is a higher-order joint because it permits the two links to rotate and sliderelative to each other. To simplify the kinematic analysis, primary joints can be used to model this higher-order joint. The pin-in-a-slot joint becomes a combination of a pin joint and a sliding joint, asin Figure 1.24b. Note that this involves adding an extra link to the mechanism. In both cases, the relative motion between the links is the same. However, using a kinematic model with primary joints facilitates the analysis.
! Z$ w% g- |4 T" q2 b注意滑槽是高副，包含一個(gè)滑動(dòng)副和一個(gè)轉(zhuǎn)動(dòng)副。

Screw Joint
A screw joint, as shown in Figure 1.25a, is another common connection between links. Screw mechanisms are discussed in detail in Chapter 12. To start with, a screw joint permits two relative, but dependent, motions between the links being joined. A specific rotation of one link will cause an associated relative translation between the two links. For example, turning the screw one revolution may move the nut along the screw threads a distance of 0.1 in. Thus, only one independent motion is introduced.
螺紋連接只有一個(gè)自由度，因?yàn)檩S向運(yùn)動(dòng)和轉(zhuǎn)動(dòng)是相關(guān)的。
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A screw joint is typically modeled with a sliding joint, as shown in Figure 1.25b. It must be understood that out-of plane rotation occurs.However, only the relative translation between the screw and nut is considered in planar kinematic analysis.
# l' m% Q+ q3 D* y* X! B8 s可以簡(jiǎn)化為平面鉸接，但必須注意還有空間旋轉(zhuǎn)，雖然在研究時(shí)不考慮。

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