【菜鸟成长记】20岁后，我在机械的每一天

邹112

一来看各路高手前辈的帖子云里雾里，自觉入门也未同感同感

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.

自由度就是完全确定机构位置的独立参数个数，也是动力源个数。

The number of degrees of freedom of a mechanism is

also called the mobility, and it is given thesymbolM. 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.
5 z/ G5 ~# ], I; a: Q; f- |0 s5 ^自由度记作M。工程上大多是单自由度机构。机械臂多为多自由度机构。

5 U. q# c U( @% j4 H2 M% QGruebler'sEquation
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Degrees of freedom for planar linkages joined with common

joints can be calculated through Gruebler'sequation :

(寒假自学的一堆公式归结为一个常用公式了：3×总机构数-2×低副数-高副数，即为自由度)
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! U. H4 n8 `3 `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.

这帖居然被专辑收录了受宠若惊……必威APP精装版下载各位真是太提携后辈了……感觉更不能简简单单更课本了呢，听从各位前辈教导，自己多多在课外、在实际中学习才是！
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黑森林的鹿

牧羊少年 发表于 2016-3-16 22:47
学妹的英语底子很好，考了两次都520（170+240+110）左右，除了偶尔看看新闻、美剧没啥英文学习，学妹有啥 ...

根据一般情况说一下咯，学长看看有木有参考~

' `, }" ?5 ]5 i d5 O5 V/ I. e# M最有效的方法还是……考前做原题。这里的考前是考前一周左右。
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不过在考前的前，我觉得用好扇贝家的英语系列比较可行（并不是打广告。。。），他家一共5个应用，除了读书，其他的：单词、听力、阅读、炼句都是极好的。虽说我不是专门用扇贝备考的，但是那段时间确实是每天这样学一会英语的，而且推荐软件用法也比推荐题集可行一点不是么~积累阶段，技巧没那么重要，就是靠坚持。
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1 r% a1 M1 E+ [我的用法：早晨起来收拾完到食堂是6:20多，30开饭，正好做完炼句。炼句是练很多固定短语、地道表达，对作文有帮助。炼句要选对应课程买的，要很多贝壳，可以充值可以靠打卡赚。看学长好像写作和翻译分相对不高，炼句应该是比较有用的。

! p) Q! V, e4 K2 G* X# C1 w. _9 R+ a然后买饭，开背单词软件（还不是扇贝单词）。只扇贝单词一个肯定不行的，我当时用过各种，什么百词斩啊有道啊拓词啊乐词啊……现在还在用的叫背单词Online，按遗忘曲线安排的，感觉比扇贝还科学，不过用户体验差了点。有余力可以考虑用。（不过如果感觉背单词很痛苦的话还是专心一个就好。）吃饭的时候看一眼单词嚼一口，吃完也差不多背完了。

然后去晨读室，听扇贝听力。挖空比设成90，跟听写差不多了就，这个耗时比较长，熟练点的话一篇10分钟能听完。听写的好处就不多说了，选六级真题，坚持听懂整句话，大概复述下来再默写似的填空，尽量减少重听。过程非常痛苦，非常痛苦，痛苦！但收获很大，很大，大！不光听力，常用词拼写也从此不是问题~而且练专注力、反应力、记忆力，以及语言容量（还是叫什么的忘了，意思就是，咱们母语汉语，可以听一句好长的话并记住，整句话说完也不会忘了开头，但外语长句就不容易记住，这就是语言容量不同。多练多记，容量上来了，六级听力的难度，一篇文章不记笔记用脑子也能几个大概的）

K- k" o Z p然后7点了，扇贝新闻更新了，看新闻。不过这个更适合考完四六级提高用，毕竟都是外文报刊的新闻，不过找里面难度等级高中和四六级的，练阅读速度也很好，它每篇都会给计时，可以比较看自己的速度（别跟评论区里的人比，跟自己比；也不要太在意评论区里各种话，现在扇贝新闻评论区简直了……）
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单词我是中午吃完饭背的（我不午睡），关于背单词的方法见仁见智，我自己是看英英解释，看一眼例句，重点看小伙伴的笔记，里面词根词源、用法例句、记忆法都很多，认真看很有收获。50个单词需1小时左右，没完成就课间用碎片时间背，不过这总没大块时间好，因为没时间看笔记。选单词书方面呢……先去测个单词量，扇贝家测得特别高，比如我在Test your vocabulary上明明才9000多，扇贝说我12000=_= 想鼓励自己可以信，不过一般要减个2、3千才是实际的词量，要是5000以下，还是先背四级单词，不然一下生词太多没兴趣了。至于每天背多少那看你觉得难不难了，要是有一半点了不认识，那还是每天最低50个吧。等每天三分之二都能认识了就加量，注意它算的背完日期，别忘了还有六级的书要刷，也不能太懒散了。学习模式，一定改成拼写，拼写，拼写。

; w8 ~ P7 K1 O ?( z最后，考前至少留两套真题，按考试的样子做一遍，包括计时！作文可以不写，因为没人给改。尤其听力，一定要模拟考试，模拟考试，模拟考试，对听力提高太特么有帮助了。这也可能是我唯一做准备的地方了。
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剩下的就是自己的投入了。
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0 t. X$ S8 X, n首先想混打卡是很容易的，单词全点我认识，新闻点开等3分钟，听力设成0%，炼句全点流利复述，5分钟就能打卡。但是，有用么？英语这玩意就是吃功夫，就是靠时间耗出来的，不像理科，脑子不开窍想多久都得考60多……（我惨痛的上学期！！！） 我小学学新概念，高二背雅思单词，考四级前刷完六级单词，开始用扇贝以后每天平均1小时，现在打卡370多天了。周末或者出去坐地铁通勤时间长还会背700单词，4个多小时……所以我总共花了多少时间？不是显摆，只是想说，学个语言还是蛮辛苦的，得真花时间，花心思，so做好心理准备，每天把这当个事放在心上。
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还有，并不推荐看美剧和新闻。个人看法，美剧是用来养节奏的，和老外说话的节奏，包括语音语速俚语俗语，对应试帮助甚少。如果看完一集美剧，脑子里没有洗脑地回放某几句很好的台词（好指的是有个连读啦，夸张的语调啦，地道的转音啦，俏皮的比喻啦之类的）直到自己脱口而出，就像小孩子学大人的舌一样，我认为这集美剧看的就没有价值，或者说，只有娱乐的价值。新闻倒是可以，只要找感兴趣的、能边听边联想自己的，也就是产生积极互动的就好，否则只为“磨耳朵”，泡着，不去沉浸，也是不可取的。

当然目标每个人不同，肯定有自己的取舍，这个不多说。方法也因人而异，我说这么多也只是参考，具体合不合适还得自己尝试。加油！祝早日取得好成绩！O(∩_∩)O~
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long_wzq

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牧羊少年

黑森林的鹿 发表于 2016-3-17 18:08
! {# ?! |1 M8 q& T根据一般情况说一下咯，学长看看有木有参考~

r9 L# f0 e% a# g* w& s3 ^' h最有效的方法还是……考前做原题。这里的考前是考前一周左 ...

谢谢！很有参考，扇贝听力深有体会，炼句倒没用过，准备试试。学妹的功夫下的很大，态度更值得参考！
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however1241

不论多寡，只求有得

黑森林的鹿

【20160318】Actuators and Drivers
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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:
每个自由度需要独立的驱动力来完全确定机构位置。常用驱动源如下：
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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.
交流电动机：最廉价；转速受限。
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) P) Q u! h! Q& L8 [5 Y. FElectric 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.
直流电动机：高速、多种速度需求，用于交通工具等。
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L- d$ j& W8 p: ?0 `, F$ ]4 oEnginesalso 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.
发动机：动力足。户外器械。

5 n' [2 q5 l+ |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.
伺服电机：精确运动控制，如机器人。

1 T% h% ~8 n. h. y* uAir 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.
+ V! s ?3 M8 |2 G6 P& C" w9 d$ A气压/液压机：如飞机等可提供大量流体处。

) F: D# e- ~" p- B4 H+ BHydraulic 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.
气压/液压缸：冲程有限处。


- c- }$ }# q$ R" q, { yThe 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.
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# ~4 ?& ` c& CScrew 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.
$ Q5 J1 F" s9 h' {螺旋致动器：类似气压/液压缸，精确控制、有限冲程。
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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.
人力驱动……

haneast

大学六级刚过500，现在看到学妹一贴下来的英语各种666，表示十分惭愧，现在也天天看扇贝，看到学妹的水平才知道自己其实还水得很

however1241

haneast 发表于 2016-3-18 17:05
大学六级刚过500，现在看到学妹一贴下来的英语各种666，表示十分惭愧，现在也天天看扇贝，看到学妹的水平才 ...

5 E3 a) E3 z0 N3 u不求多寡，只求有得

黑森林的鹿

【20160319】Commonly Used Links and Joints

/ \$ n6 ^8 E2 C. w9 T% x* OEccentric Crank
* ^! n y. L* z- ^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.
4 ~2 M3 b4 y% n v偏心曲柄，由于尺寸过小而不能保证铰合处销钉尺寸合适。
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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.
因此将该销钉放大，以至于包裹整个曲柄。这个大销钉中心与曲柄转轴中心间的距离即为有效的曲柄长度。这样配置的好处在于移动销钉的巨大的接触面积，这减少了磨损。
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6 I2 e7 |" v/ l4 ]+ j# @5 ePin-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.
注意滑槽是高副，包含一个滑动副和一个转动副。
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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.
" u. L, d# n. Q- [螺纹连接只有一个自由度，因为轴向运动和转动是相关的。
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5 ]. J1 L5 B2 g9 PA 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.
可以简化为平面铰接，但必须注意还有空间旋转，虽然在研究时不考虑。
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