【菜鳥成長記】20歲后，我在機械的每一天

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

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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構(gòu)位置的獨立參數(shù)個數(shù)，也是動力源個數(shù)。

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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構(gòu)。機械臂多為多自由度機構(gòu)。
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Gruebler'sEquation
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Degrees of freedom for planar linkages joined with common

joints can be calculated through Gruebler'sequation :

(寒假自學的一堆公式歸結(jié)為一個常用公式了：3×總機構(gòu)數(shù)-2×低副數(shù)-高副數(shù)，即為自由度)

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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% W* e! b, j; V# l+ n" q; z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……感覺更不能簡簡單單更課本了呢，聽從各位前輩教導，自己多多在課外、在實際中學習才是！

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黑森林的鹿

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

9 O( e% g/ x1 m  j5 d根據(jù)一般情況說一下咯，學長看看有木有參考~

0 L2 @6 a  b8 f( \1 a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。

不過在考前的前，我覺得用好扇貝家的英語系列比較可行（并不是打廣告。。。），他家一共5個應用，除了讀書，其他的：單詞、聽力、閱讀、煉句都是極好的。雖說我不是專門用扇貝備考的，但是那段時間確實是每天這樣學一會英語的，而且推薦軟件用法也比推薦題集可行一點不是么~積累階段，技巧沒那么重要，就是靠堅持。
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# H. Q3 U* C* F! o8 g+ |6 b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、地道表達，對作文有幫助。煉句要選對應課程買的，要很多貝殼，可以充值可以靠打卡賺。看學長好像寫作和翻譯分相對不高，煉句應該是比較有用的。

然后買飯，開背單詞軟件（還不是扇貝單詞）。只扇貝單詞一個肯定不行的，我當時用過各種，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，不過用戶體驗差了點。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就好。）吃飯的時候看一眼單詞嚼一口，吃完也差不多背完了。
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7 R2 z' L6 `( ]7 r8 ~然后去晨讀室，聽扇貝聽力。挖空比設成90，跟聽寫差不多了就，這個耗時比較長，熟練點的話一篇10分鐘能聽完。聽寫的好處就不多說了，選六級真題，堅持聽懂整句話，大概復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、反應力、記憶力，以及語言容量（還是叫什么的忘了，意思就是，咱們母語漢語，可以聽一句好長的話并記住，整句話說完也不會忘了開頭，但外語長句就不容易記住，這就是語言容量不同。多練多記，容量上來了，六級聽力的難度，一篇文章不記筆記用腦子也能幾個大概的）

然后7點了，扇貝新聞更新了，看新聞。不過這個更適合考完四六級提高用，畢竟都是外文報刊的新聞，不過找里面難度等級高中和四六級的，練閱讀速度也很好，它每篇都會給計時，可以比較看自己的速度（別跟評論區(qū)里的人比，跟自己比；也不要太在意評論區(qū)里各種話，現(xiàn)在扇貝新聞評論區(qū)簡直了……）

0 L. H% T5 K+ c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，重點看小伙伴的筆記，里面詞根詞源、用法例句、記憶法都很多，認真看很有收獲。50個單詞需1小時左右，沒完成就課間用碎片時間背，不過這總沒大塊時間好，因為沒時間看筆記。選單詞書方面呢……先去測個單詞量，扇貝家測得特別高，比如我在Test your vocabulary上明明才9000多，扇貝說我12000=_=  想鼓勵自己可以信，不過一般要減個2、3千才是實際的詞量，要是5000以下，還是先背四級單詞，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，要是有一半點了不認識，那還是每天最低50個吧。等每天三分之二都能認識了就加量，注意它算的背完日期，別忘了還有六級的書要刷，也不能太懶散了。學習模式，一定改成拼寫，拼寫，拼寫。

2 L! Q/ b3 s# F最后，考前至少留兩套真題，按考試的樣子做一遍，包括計時！作文可以不寫，因為沒人給改。尤其聽力，一定要模擬考試，模擬考試，模擬考試，對聽力提高太特么有幫助了。這也可能是我唯一做準備的地方了。
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3 s. n% b- K# o+ ?- x& y  W, a首先想混打卡是很容易的，單詞全點我認識，新聞點開等3分鐘，聽力設成0%，煉句全點流利復述，5分鐘就能打卡。但是，有用么？英語這玩意就是吃功夫，就是靠時間耗出來的，不像理科，腦子不開竅想多久都得考60多……（我慘痛的上學期！！！） 我小學學新概念，高二背雅思單詞，考四級前刷完六級單詞，開始用扇貝以后每天平均1小時，現(xiàn)在打卡370多天了。周末或者出去坐地鐵通勤時間長還會背700單詞，4個多小時……所以我總共花了多少時間？不是顯擺，只是想說，學個語言還是蠻辛苦的，得真花時間，花心思，so做好心理準備，每天把這當個事放在心上。
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還有，并不推薦看美劇和新聞。個人看法，美劇是用來養(yǎng)節(jié)奏的，和老外說話的節(jié)奏，包括語音語速俚語俗語，對應試幫助甚少。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詞（好指的是有個連讀啦，夸張的語調(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，就像小孩子學大人的舌一樣，我認為這集美劇看的就沒有價值，或者說，只有娛樂的價值。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)生積極互動的就好，否則只為“磨耳朵”，泡著，不去沉浸，也是不可取的。
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, p" @: F& \# F4 M當然目標每個人不同，肯定有自己的取舍，這個不多說。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！O(∩_∩)O~
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long_wzq

給個贊

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，學長看看有木有參考~

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，煉句倒沒用過，準備試試。學妹的功夫下的很大，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

+ v# k: k- }2 P/ q* Q" g* p! BIn 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:
) r1 |" T% n0 E' j/ N" C每個自由度需要獨立的驅(qū)動力來完全確定機構(gòu)位置。常用驅(qū)動源如下：

Electric 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.
交流電動機：最廉價；轉(zhuǎn)速受限。
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Electric 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.
直流電動機：高速、多種速度需求，用于交通工具等。

2 V. ~) _' G0 xEnginesalso 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.
發(fā)動機：動力足。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.
+ u& b$ H8 m8 V- ?  M5 [( C- ^2 h伺服電機：精確運動控制，如機器人。

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.
9 L4 d/ h$ p7 @/ |3 e6 s氣壓/液壓機：如飛機等可提供大量流體處。

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.
氣壓/液壓缸：沖程有限處。

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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.

5 c. S: m" v( r1 TScrew 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.
螺旋致動器：類似氣壓/液壓缸，精確控制、有限沖程。

/ K% X: B3 t  u- d8 m, K3 z- Q! {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.
4 T5 `( V% U; j5 }6 `, z/ D( G人力驅(qū)動……
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haneast

大學六級剛過500，現(xiàn)在看到學妹一貼下來的英語各種666，表示十分慚愧，現(xiàn)在也天天看扇貝，看到學妹的水平才知道自己其實還水得很

however1241

haneast 發(fā)表于 2016-3-18 17:05
& p0 R$ _0 r& m大學六級剛過500，現(xiàn)在看到學妹一貼下來的英語各種666，表示十分慚愧，現(xiàn)在也天天看扇貝，看到學妹的水平才 ...

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
On 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.
5 [7 m# h! i# F6 U偏心曲柄，由于尺寸過小而不能保證鉸合處銷釘尺寸合適。
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6 ]* e4 ?: R' x" @; J7 l# x! qThe 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，以至于包裹整個曲柄。這個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度。這樣配置的好處在于移動銷釘?shù)木薮蟮慕佑|面積，這減少了磨損。

Pin-in-a-Slot Joint
7 p! U5 j9 o1 u9 Q5 A- s! J- fA 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.
: t1 N! [* C. |' }. t1 ]+ O% B注意滑槽是高副，包含一個滑動副和一個轉(zhuǎn)動副。
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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.
5 c7 `- h2 O# a" L6 F! D螺紋連接只有一個自由度，因為軸向運動和轉(zhuǎn)動是相關(guān)的。

$ X! n8 I7 c) P/ jA 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.
可以簡化為平面鉸接，但必須注意還有空間旋轉(zhuǎn)，雖然在研究時不考慮。
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