機器人設計外文翻譯--- 移動機器人車輛

1、<p><b>　　外文翻譯</b></p><p>　　譯文題目 移動機器人車輛 </p><p>　　原稿題目 Mobile Robot Vehicles </p><p>　　原稿出處 Peter

2、Corke.Robotics,vision and control[M].Australia: Springer Tracts in Advanced Robotics,2011 </p><p><b>　　移動機器人車輛</b></p><p>　　這一章討論如何移動機器人平臺,它帶來一個隨時間變化的函數(shù)來控制。有許多不同的類型，如61頁到63頁所示的機器人平臺。

3、但我們在本章將考慮只有兩種機器人平臺具有重要意義。第一種平臺是一個輪子，像一輛汽車,在二維世界運行。它可以改變輪子的角度使汽車向前或向后移動并控制方向的變化。第二個平臺是一個直升機,在三維運動中，這是一種典型的機器人直升機正變得越來越流行。平臺就像一個機器人，因為他們可以很容易地被模仿和控制。 </p><p><b>　　4.1靈活性</b></p><p>

4、　　我們已經(jīng)談到的多樣性和移動機器人的運動方式，在這個部分中我們將討論有關機器人平臺的靈活性與及它如何在空間移動。</p><p>　　我們先來考慮一下這個簡單的例子：一列火車。從一些資料上顯示，火車在軌道運行，可以通過它的距離來描述它的位置。通過一個標量參數(shù)q，火車可以被完全的描述，叫做廣義。集合所有可能的配置就是配置空間，用q∈C來表示。在這種情況下C?R。我們也說火車上有一個自由度，因為q是一個標量。這趟列

5、車也有一個驅(qū)動器(電機),驅(qū)使它沿軌道向前或向后?；疖囃ㄟ^電機和自由度充分的驅(qū)動,可以到達任意配置空間，就是說可以沿軌道的任何位置。</p><p>　　另一個重要的概念,移動裝置ξ∈T是一套任務空間所有可能的姿勢。這項任務空間取決于應用程序或任務。如果我們的任務是沿軌道運動，那么T?R。如果我們只關心這個火車的位置，那么在一個平面上T?R2。如果我們認為是一個三維世界，那么T ?SE(3)，它的上下移動可以改變

6、高度的變化。不清楚這這種情況下，如果這項任務超出尺寸的空間配置空間，火車就不能達到一個任意的位置，因為火車是不得不沿著固定軌道前進的。既然這樣，我們說火車沿著一個移動空間有一個映射q?ξ。</p><p>　　有趣的是,許多汽車有共同的特性。它們擅長于向前移動,但不擅長于其他方向的移動。汽車、汽墊船、船舶和飛機，它們所有的特點和復雜的操縱都是為了可以向各個方向移動而設計的。這個設計方法是一個非常明智的選擇，因為它

7、針對我們最常見的運動車輛。不常見的運動如停車、兩艘船的對接或更復雜的飛機著陸,這也不是不可能的,人類可以學習這個技巧。這種類型的設計優(yōu)點簡化非常,特別是執(zhí)行機構的要求數(shù)量越少越好。</p><p>　　下一個考慮是氣墊船，它的下面有兩個螺旋槳，但軸平行但不在同一直線上。提供的總向前力產(chǎn)生的扭矩會使氣墊船轉(zhuǎn)向偏移。氣墊船在平面移動及其配置上完全是由三個廣義坐標表示q =(x, y, θ) ∈ C。配置空間有三維空間

8、，因此它有三個自由度。</p><p>　　氣墊船只有兩個執(zhí)行機構，比汽車少一個自由度，因此它是欠驅(qū)動系統(tǒng)。利用這個限制方式可以自由移動。在任何時候我們可以控制前進（平行于推力矢量）、加速和旋轉(zhuǎn)。加速度為零的氣墊船沒有橫向加速度,因為它不產(chǎn)生任何側(cè)向推力。然而一些熟練的操縱，就像汽車能在遵循的路線上把它帶到開始地方的另一側(cè)。欠驅(qū)動系統(tǒng)的優(yōu)點就是可以減少執(zhí)行機構的數(shù)量，缺點就是是汽車無法直接移動到任何一個地方及其配

9、置的空間，因為它必須遵循一定的路徑。如果我們增加了第三個螺旋槳，那么氣墊船就可以實現(xiàn)全向移動。氣墊船的任務空間就是T ? SE(2)，對于配置空間是等效的。</p><p>　　一架直升飛機有四個執(zhí)行機構。其大小主要是由轉(zhuǎn)軸產(chǎn)生推力矢量控制的橫向、縱向循環(huán)。第四個驅(qū)動器后面的轉(zhuǎn)子提供了一個橫擺力矩。直升機的配置可以描述為六個廣義坐標q =(x, y, z, θr, θp, θy) ∈ C，那是其位置與方向在三維空

10、間的取向角。配置空間C?R3×S3有六個維度,因此車輛有六個自由度。直升機是欠驅(qū)動系統(tǒng),它沒有旋轉(zhuǎn)加速，因為直升機保持自由是不需要操作的，機尾的朝向保持穩(wěn)定的均衡力，因此可以做俯仰運動。重力就像一個額外的驅(qū)動器,它提供一個向下的力，這使得直升機加速側(cè)推力矢量水平分量的垂直分量推力由重力抵消，如果沒有重力直升飛機是飛不起來的。直升機的工作空間就是T?SE(3)。</p><p>　　一個固定翼飛機前進,也

11、有4個極其有效地執(zhí)行機構：前進、副翼、升降、方向。對飛機來說飛機的推力加速度在不同時刻都會對方向和控制產(chǎn)生不同的影響：方向舵（偏航力矩）、副翼（軋輥扭矩）、升降（旋轉(zhuǎn)扭矩）。飛機的配置空間是相同的,有6個尺寸。欠驅(qū)動系統(tǒng)的飛機沒有側(cè)向方向的加速。直升機的工作空間就是T?SE(3)。</p><p>　　在62頁的深井熱量探測器顯示的水下機器人也有一個配置空間C ?R3× S3 ，是六個維度的，但是相比之

12、下是完全啟動的。車輛的執(zhí)行機構可以運用六個方面對任意一個力及力矩平衡，它可以使任意方向軸的加速。它的工作空間是T?SE(3)</p><p>　　最后,我們來到了輪子———人類偉大的成就。輪子是在公元前3000年左右發(fā)明的,兩個輪子的車是在公元前2000年左右發(fā)明的。今天四個輪子的交通工具是無處不在的,擁有的人數(shù)接近十億。汽車的有效性和我們對它的熟悉讓它們可以在平臺上自由移動。</p><p&

13、gt;　　一輛滾滑駕駛的車輛,比如一輛坦克，可以在危險中移向一邊并立即停下來。這是一個機動時變控制策略的特點,是一種不完整的系統(tǒng)。坦克有兩個執(zhí)行機構，就像在每條賽道上,一輛車就是一個欠驅(qū)動系統(tǒng)。</p><p>　　機動車輛參數(shù)表,我們討論的是在表4.1。第二欄是大量的自由度的車輛或其設置的空間維度，第三欄是大量的執(zhí)行機構，第四欄的是是否完全驅(qū)動的車輛。</p><p>　　Mobile

14、Robot Vehicles</p><p>　　This chapter discusses how a robot platform moves, that is, how its pose changes with time as a function of its control inputs. There are many different types of robot platform as sho

15、wn on pages 61–63 but in this chapter we will consider only two which are important exemplars. The first is a wheeled vehicle like a car which operates in a 2-dimensional world. It can be propelled forwards or backwards

16、and its heading direction controlled by changing the angle of its steered wheels. The second plat</p><p>　　However before we start to discuss these two robot platforms it will be helpful to consider some gen

17、eral, but important, concepts regarding mobility.</p><p>　　4.1 lMobility</p><p>　　We have already touched on the diversity of mobile robots and their modes of locomotion.In this section we will

18、discuss mobility which is concerned with how a vehicle moves in space.</p><p>　　We first consider the simple example of a train. The train moves along rails and its position</p><p>　　is describe

19、d by its distance along the rail from some datum. The configuration of the train can be completely described by a scalar parameter q which is called its generalized coordinate. The set of all possible configurations is t

20、he configuration space, or C-space, denoted by C and q∈C. In this case C?R. We also say that the train has one degree of freedom since q is a scalar. The train also has one actuator (motor) that propels it forwards or ba

21、ckwards along the rail. With one motor and one de</p><p>　　Another important concept is task space which is the set of all possible poses ξ of the vehicle and ξ ∈ T. The task space depends on the application

22、 or task. If our task was motion along the rail then T ?R. If we cared only about the position of the train in a plane then T ?R2. If we considered a 3-dimensional world then T ? SE(3), and its height changes as it moves

23、 up and down hills and its orientation changes as it moves around curves. Clearly for these last two cases the dimensions of the tas</p><p>　　pose since it is constrained to move along fixed rails. In these

24、cases we say that the train moves along a manifold in the task space and there is a mapping from qξ.</p><p>　　Interestingly many vehicles share certain characteristics with trains – they are good at moving f

25、orward but not so good at moving sideways. Cars, hovercrafts, ships and aircraft all exhibit this characteristic and require complex manoeuvring in order to move sideways. Nevertheless this is a very sensible design appr

26、oach since it caters to the motion we most commonly require of the vehicle. The less common motions such as parking a car, docking a ship or landing an aircraft are more complex, but </p><p>　　Next consider

27、a hovercraft which has two propellors whose axes are parallel but not collinear. The sum of their thrusts provide a forward force and the difference in thrusts generates a yawing torque for steering. The hovercraft moves

28、 over a planar surface and its configuration is entirely described by three generalized coordinates q =(x, y, θ) ∈ C and in this case C ? R2× S. The configuration space has 3 dimensions and the vehicle therefore has

29、 three degrees of freedom.</p><p>　　The hovercraft has only two actuators, one fewer than it has degrees of freedom,and it is therefore an under-actuated system. This imposes limitations on the way in which

30、it can move. At any point in time we can control the forward (parallel to the thrust vectors) acceleration and the rotational acceleration of the the hovercraft but there is zero sideways (or lateral) acceleration since

31、it does not generate any lateral thrust. Nevertheless with some clever manoeuvring, like with a car, the hove</p><p>　　forward, sideways and rotational acceleration. The task space of the hovercraft is T ? S

32、E(2) which is equivalent, in this case, to the configuration space.</p><p>　　A helicopter has four actuators. The main rotor generates a thrust vector whose magnitude is controlled by the collective pitch, a

33、nd the thrust vector’s direction is controlled by the lateral and longitudinal cyclic pitch. The fourth actuator, the tail rotor, provides a yawing moment. The helicopter’s configuration can be described by six generaliz

34、ed coordinates q =(x, y, z, θr, θp, θy) ∈ C which is its position and orientation in 3-dimensional space, with orientation expressed in roll-pitch-yaw</p><p>　　A fixed-wing aircraft moves forward very effici

35、ently and also has four actuators(forward thrust, ailerons, elevator and rudder). The aircraft’s thrust provides acceleration in the forward direction and the control surfaces exert various moments on the aircraft: rudde

36、r (yaw torque), ailerons (roll torque), elevator (pitch torque). The aircraft’s configuration space is the same as the helicopter and has six dimensions. The aircraft is under-actuated and it has no way to accelerate in

37、the lateral d</p><p>　　The DEPTHX underwater robot shown on page 62 also has a configuration space C ?R3× S3 of six dimensions, but by contrast is fully actuated. Its six actuators can exert an arbitrar

38、y force and torque on the vehicle, allowing it to accelerate in any direction or about any axis. Its task space is T ?SE(3).</p><p>　　Finally we come to the wheel – one of humanity’s greatest achievements. T

39、he wheel was invented around 3000 bce and the two wheeled cart was invented around 2000 bce.Today four wheeled vehicles are ubiquitous and the total automobile population of the planet is approaching one billion. The eff

40、ectiveness of cars, and our familiarity with them, makes them a natural choice for robot platforms that move across the ground.</p><p>　　A skid-steered vehicle, such as a tank, can turn on the spot but to mo

41、ve sideways it would have to stop, turn, proceed, stop then turn – this is a manoeuvre or time-varying control strategy which is the hallmark of a non-holonomic system. The tank has two actuators, one for each track, and

42、 just like a car is under-actuated.</p><p>　　Mobility parameters for the vehicles that we have discussed are tabulated in Table 4.1.The second column is the number of degrees of freedom of the vehicle or the