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編號(hào)
無(wú)錫太湖學(xué)院
畢業(yè)設(shè)計(jì)（論文）
相關(guān)資料
題目： 四自由度棒料搬運(yùn)機(jī)械手設(shè)計(jì)
信機(jī) 系 機(jī)械工程及其自動(dòng)化 專業(yè)
學(xué) 號(hào)： 0923076
學(xué)生姓名： 陳 華
指導(dǎo)教師： 馮 鮮（職稱：講 師 ）
（職稱： ）
2013年5月25日
目 錄
一、畢業(yè)設(shè)計(jì)（論文）開(kāi)題報(bào)告
二、畢業(yè)設(shè)計(jì)（論文）外文資料翻譯及原文
三、學(xué)生“畢業(yè)論文（論文）計(jì)劃、進(jìn)度、檢查及落實(shí)表”
四、實(shí)習(xí)鑒定表
無(wú)錫太湖學(xué)院
畢業(yè)設(shè)計(jì)（論文）
開(kāi)題報(bào)告
題目： 四自由度棒料搬運(yùn)機(jī)械手設(shè)計(jì)
機(jī)電系 機(jī)械工程及其自動(dòng)化 專業(yè)
學(xué) 號(hào)： 0923076
學(xué)生姓名： 陳 華
指導(dǎo)教師： 馮 鮮 （職稱：講 師 ）
（職稱： ）
2012年11月26日
課題來(lái)源
隨著世界經(jīng)濟(jì)的快速發(fā)展和現(xiàn)代科學(xué)技術(shù)的進(jìn)步,物流產(chǎn)業(yè)作為國(guó)民經(jīng)濟(jì)中一個(gè)新興的服務(wù)部門,正在全球范圍內(nèi)迅速發(fā)展.在國(guó)際上,物流產(chǎn)業(yè)被認(rèn)為是國(guó)民經(jīng)濟(jì)發(fā)展的動(dòng)脈和基礎(chǔ)產(chǎn)業(yè),其發(fā)展程度成為衡量一國(guó)現(xiàn)代化程度和綜合國(guó)力的重要標(biāo)志之一,被喻為促進(jìn)經(jīng)濟(jì)發(fā)展的“加速器”.物流產(chǎn)業(yè)是指鐵路、公路、水路、航空等基礎(chǔ)設(shè)施,以及工業(yè)生產(chǎn)、商業(yè)批發(fā)零售和第三方倉(cāng)儲(chǔ)運(yùn)輸及綜合物流企業(yè)為實(shí)現(xiàn)商品的實(shí)體位移所形成的產(chǎn)業(yè).國(guó)民經(jīng)濟(jì)各個(gè)領(lǐng)域的物流經(jīng)濟(jì)實(shí)體從橫向構(gòu)成了物流產(chǎn)業(yè).這個(gè)產(chǎn)業(yè)由鐵道、公路、水運(yùn)、空運(yùn)、倉(cāng)儲(chǔ)、托運(yùn)等行業(yè)為主體組成,同時(shí)還包含了商業(yè)、物資業(yè)、供銷、糧食、外貿(mào)等行業(yè)中的一半領(lǐng)域,還涉及到機(jī)械、電器業(yè)中的物流裝備生產(chǎn)行業(yè)和國(guó)民經(jīng)濟(jì)所有行業(yè)的供應(yīng)、生產(chǎn)、銷售中的物流活動(dòng)。
近年來(lái)工業(yè)自動(dòng)化的發(fā)展機(jī)械器件逐漸成為一門新興的學(xué)科,并得到了較快的發(fā)展。工業(yè)現(xiàn)場(chǎng)的很多重體力勞動(dòng)必將由機(jī)器代替,這一方面可以減輕工人的勞動(dòng)強(qiáng)度,另一方面可以大大提高勞動(dòng)生產(chǎn)率。例如,目前在我國(guó)的許多中小型生產(chǎn)行業(yè)中,往往沖壓成形這一工序還需人工上下料,既費(fèi)時(shí)費(fèi)力,又影響效率。為此我們研制了一套上下料機(jī)械手模擬裝置，以此為基礎(chǔ),為進(jìn)一步實(shí)用化做好充分準(zhǔn)備。機(jī)械手是工業(yè)自動(dòng)控制領(lǐng)域中經(jīng)常遇到的一種控制對(duì)象. 是一種模仿人手動(dòng)作，并按設(shè)定程序，軌跡和要求代替人手抓（吸）取，搬運(yùn)工件或工具進(jìn)行操作的自動(dòng)化裝置。其可以完成許多工作,如搬物、裝配、切割、噴染等等,應(yīng)用面非常廣泛。工業(yè)生產(chǎn)中常用的進(jìn)行水平/垂直位移的機(jī)械設(shè)備的動(dòng)作由氣缸驅(qū)動(dòng)，氣缸又又相應(yīng)的電磁閥控制，該機(jī)械手除外形尺寸比實(shí)物小些以外,其結(jié)構(gòu)、原理及功能與實(shí)際的機(jī)械手是完全一致的。
科學(xué)依據(jù)
機(jī)器人（又稱機(jī)械手，機(jī)械人，英文名稱：Robot），在人類科技發(fā)展史上其來(lái)有自，早在三國(guó)時(shí)代，諸葛亮發(fā)明的木牛流馬即是古代中國(guó)人的智能結(jié)晶。隨著近代的工業(yè)革命，機(jī)器產(chǎn)業(yè)的不斷發(fā)展成為近代工業(yè)的主要支柱。
機(jī)器人的研究從一開(kāi)始就是擬人化的，所以才有機(jī)械手、機(jī)械臂的開(kāi)發(fā)與制作，也是為了以機(jī)械來(lái)代替人去做人力所無(wú)法完成的勞作或探險(xiǎn)。但近十幾年來(lái)，機(jī)器人的開(kāi)發(fā)不僅越來(lái)越優(yōu)化，而且涵蓋了許多領(lǐng)域，應(yīng)用的范疇十分廣闊。
工業(yè)機(jī)器人是典型的機(jī)電一體化高技術(shù)產(chǎn)品。在許多生產(chǎn)領(lǐng)域，它對(duì)于提高生產(chǎn)自動(dòng)化水平，提高勞動(dòng)生產(chǎn)率、產(chǎn)品質(zhì)量和經(jīng)濟(jì)效益，改善工人勞動(dòng)條件的作用日見(jiàn)顯著。不少勞動(dòng)條件惡劣、生產(chǎn)要求苛刻的場(chǎng)合，工業(yè)機(jī)器人代替人力勞動(dòng)已是必然的趨勢(shì)。
工業(yè)機(jī)器人是一種機(jī)體獨(dú)立，動(dòng)作自由度較多，程序可靈活變更，能任意定位，自動(dòng)化程度高的自動(dòng)操作機(jī)械。主要用于加工自動(dòng)線和柔性制造系統(tǒng)中傳遞和裝卸工件或夾具。工業(yè)機(jī)器人以剛性高的手臂為主體，與人相比，可以有更快的運(yùn)動(dòng)速度，可以搬運(yùn)更重的東西，而且定位精度相當(dāng)高，它可以根據(jù)外部來(lái)的信號(hào)，自動(dòng)進(jìn)行各種操作。
國(guó)內(nèi)現(xiàn)狀及發(fā)展趨勢(shì) 物流這一概念的形成和物流管理學(xué)科的建立只不過(guò)幾十年的歷史,引入我國(guó)也僅十幾年時(shí)間。但是物流這一概念賴以形成的流通行業(yè)卻已歷史久遠(yuǎn),早在人類社會(huì)出現(xiàn)商品交換的時(shí)期就已經(jīng)出現(xiàn)了。隨著時(shí)間的流逝，物流的發(fā)展趨勢(shì)大致可以歸納為以下幾點(diǎn)： ①物流需求彈性逐年增高,經(jīng)濟(jì)增長(zhǎng)越來(lái)越依賴于物流的發(fā)展。 ②第三方物流的比重逐年增加。 ③進(jìn)一步加快國(guó)際化進(jìn)程。④ 物流體系綜合化； ⑤ 三流一體化。
國(guó)外機(jī)械手工業(yè)、鐵路工業(yè)中不僅在單機(jī)、專機(jī)上采用機(jī)械手上下料，減輕工人的勞動(dòng)強(qiáng)度，而且在鐵路工業(yè)中應(yīng)用機(jī)械手以加工鐵路車軸、輪等大、中批零件。并和機(jī)床共同組成一個(gè)綜合的數(shù)控加工系統(tǒng)。采用機(jī)械手進(jìn)行裝配更始目前研究的重點(diǎn)，國(guó)外已研究采用攝象機(jī)和力傳感裝置和微型計(jì)算機(jī)連在一起，能確定零件的方位達(dá)到鑲裝的目的。
國(guó)外機(jī)械手的發(fā)展趨勢(shì)是大力研制具有某種智能的機(jī)械手。使它具有一定的傳感能力，能反饋外界條件的變化，作相應(yīng)的變更。視覺(jué)功能即在機(jī)械手上安裝有電視照相機(jī)和光學(xué)測(cè)距儀（即距離傳感器）以及微型計(jì)算機(jī)。 觸覺(jué)功能即是在機(jī)械手上安裝有觸覺(jué)反饋控制裝置。工作時(shí)機(jī)械手首先伸出手指尋找工作，通過(guò)安裝在手指內(nèi)的壓力敏感元件產(chǎn)生觸覺(jué)作用，然后伸向前方，抓住工件。 總之，隨著傳感技術(shù)的發(fā)展機(jī)械手裝配作業(yè)的能力也將進(jìn)一步提高。更重要的是將機(jī)械手、柔性制造系統(tǒng)和柔性制造單元相結(jié)合，從而根本改變目前機(jī)械制造系統(tǒng)的人工操作狀態(tài)。
研究?jī)?nèi)容
本設(shè)計(jì)中的四自由度棒料搬運(yùn)機(jī)械手，主要是針對(duì)圓形棒料的搬運(yùn)。
本設(shè)計(jì)中的機(jī)械手有四個(gè)自由度，由底座的旋轉(zhuǎn)，手臂的升降，手臂的伸縮，手爪 的旋轉(zhuǎn)組成。本設(shè)計(jì)中的機(jī)械手是一種通用型棒料搬運(yùn)機(jī)械手。
通過(guò)氣爪手指的不同選擇可滿足不同直徑的棒料的搬運(yùn)。通過(guò)示教再現(xiàn)或程序的直接控制可實(shí)現(xiàn)在機(jī)械手工作范圍內(nèi)把棒料從指定點(diǎn)搬運(yùn)到另一指定點(diǎn)，并把棒料翻轉(zhuǎn)過(guò)來(lái)。通過(guò)對(duì)機(jī)械手的相應(yīng)控制還可實(shí)現(xiàn)對(duì)棒料的排列。
擬采取的研究方法、技術(shù)路線、實(shí)驗(yàn)方案及可行性分析
由設(shè)計(jì)要求本設(shè)計(jì)機(jī)械手實(shí)現(xiàn)的作用：自動(dòng)線上有A,B兩條輸送帶，之間距離為0.7米，現(xiàn)設(shè)計(jì)機(jī)械手將一棒料翻轉(zhuǎn)過(guò)來(lái)。
確定為四自由度的機(jī)械手。其中2個(gè)為旋轉(zhuǎn)，兩個(gè)為平移。
在工業(yè)機(jī)器人的諸多功能中，抓取和移動(dòng)是最只要的功能。這兩項(xiàng)功能的實(shí)現(xiàn)的技術(shù)基礎(chǔ)是精巧的機(jī)械結(jié)構(gòu)設(shè)計(jì)和良好的伺服控制驅(qū)動(dòng)。
本次設(shè)計(jì)就是在這一思維下展開(kāi)的。根據(jù)設(shè)計(jì)內(nèi)容和需求確定機(jī)械手，利用步進(jìn)電機(jī)驅(qū)動(dòng)和諧波齒輪傳動(dòng)來(lái)實(shí)現(xiàn)機(jī)器人的旋轉(zhuǎn)運(yùn)動(dòng)；利用另一臺(tái)步進(jìn)電機(jī)驅(qū)動(dòng)滾珠絲杠旋轉(zhuǎn)，從而使與滾珠絲杠螺母副固連在一起的手臂實(shí)現(xiàn)上下運(yùn)動(dòng)；考慮到本設(shè)計(jì)中的機(jī)械手工作范圍不大，故利用氣缸驅(qū)動(dòng)實(shí)現(xiàn)手臂的伸縮運(yùn)動(dòng)；末端夾持器則選用氣爪來(lái)做夾持器，用小型氣缸驅(qū)動(dòng)夾緊。氣爪的旋轉(zhuǎn)則由與氣爪連接的擺動(dòng)氣缸實(shí)現(xiàn)。
研究計(jì)劃及預(yù)期成果
研究計(jì)劃：
2012年11月12日~2012年11月18日：按照任務(wù)書要求查閱論文相關(guān)參考資料，填寫畢業(yè)設(shè)計(jì)開(kāi)題報(bào)告書。
2012年11月19日~2012年11月24日：填寫畢業(yè)實(shí)習(xí)報(bào)告。
2012年11月25日~2012年12月2日：按照要求修改畢業(yè)設(shè)計(jì)開(kāi)題報(bào)告。
2013年12月3日~2013年12月17日：學(xué)習(xí)并翻譯一篇與畢業(yè)設(shè)計(jì)相關(guān)的英文材料。
2013年1月11日～2013年1月15日：PLC程序設(shè)計(jì)。
2013年1月21日~2013年2月2日：CAD設(shè)計(jì)。
2013年3月6日~2013年5月25日：畢業(yè)論文撰寫和修改工作。
預(yù)期成果：
通過(guò)氣爪手指的不同選擇可滿足小于直徑60mm的棒料的搬運(yùn)。通過(guò)示教再現(xiàn)或程序的直接控制可實(shí)現(xiàn)在機(jī)械手工作范圍內(nèi)把棒料從指定點(diǎn)搬運(yùn)到另一指定點(diǎn)，并把棒料翻轉(zhuǎn)過(guò)來(lái)。通過(guò)對(duì)機(jī)械手的相應(yīng)控制還可實(shí)現(xiàn)對(duì)棒料的排列。
特色或創(chuàng)新之處
采用多自由度，可一定程度的模擬人手動(dòng)作。
可配合一些簡(jiǎn)單的工具并行使用。
已具備的條件和尚需解決的問(wèn)題
機(jī)械爪通用性不強(qiáng)，有一定的限制。
指導(dǎo)教師意見(jiàn)
指導(dǎo)教師簽名：
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教研室（學(xué)科組、研究所）意見(jiàn)
教研室主任簽名：
年 月 日
系意見(jiàn)
主管領(lǐng)導(dǎo)簽名：
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英文原文
Spin control for cars
Stability control systems are the latest in a string of technologies focusing on improved diriving safety. Such systems detect the initial phases of a skid and restore directional control in 40 milliseconds, seven times faster than the reaction time of the average human. They correct vehicle paths by adjusting engine torque or applying the left- or-right-side brakes, or both, as needed. The technology has already been applied to the Mercedes-Benz S600 coupe.
Automatic stability systems can detect the onset of a skid and bring a fishtailing vehicle back on course even before its driver can react.
Safety glass, seat belts, crumple zones, air bags, antilock brakes, traction control, and now stability control. The continuing progression of safety systems for cars has yielded yet another device designed to keep occupants from injury. Stability control systems help drivers recover from uncontrolled skids in curves, thus avoiding spinouts and accidents.
Using computers and an array of sensors, a stability control system detects the onset of a skid and restores directional control more quickly than a human driver can. Every microsecond, the system takes a "snapshot," calculating whether a car is going exactly in the direction it is being steered. If there is the slightest difference between where the driver is steering and where the vehicle is going, the system corrects its path in a split-second by adjusting engine torque and/or applying the cat's left- or right-side brakes as needed. Typical reaction time is 40 milliseconds - seven times faster than that of the average human.
A stability control system senses the driver's desired motion from the steering angle, the accelerator pedal position, and the brake pressure while determining the vehicle's actual motion from the yaw rate (vehicle rotation about its vertical axis) and lateral acceleration, explained Anton van Zanten, project leader of the Robert Bosch engineering team. Van Zanten's group and a team of engineers from Mercedes-Benz, led by project manager Armin Muller, developed the first fully effective stability control system, which regulates engine torque and wheel brake pressures using traction control components to minimize the difference between the desired and actual motion.
Automotive safety experts believe that stability control systems will reduce the number of accidents, or at least the severity of damage. Safety statistics say that most of the deadly accidents in which a single car spins out (accounting for four percent of all deadly collisions) could be avoided using the new technology. The additional cost of the new systems are on the order of the increasingly popular antilock brake/traction control units now available for cars.
The debut of stability control technology took place in Europe on the Mercedes-Benz S600 coupe this spring. Developed jointly during the past few years by Robert Bosch GmbH and Mercedes-Benz AG, both of Stuttgart, Germany, Vehicle Dynamics Control (VDC). in Bosch terminology, or the Electronic Stability Program (ESP), as Mercedes calls it, maintains vehicle stability in most driving situations. Bosch developed the system, and Mercedes-Benz integrated it into the vehicle. Mercedes engineers used the state-of-the-art Daimler-Benz virtual-reality driving simulator in Berlin to evaluate the system under extreme conditions, such as strong crosswinds. They then put the system through its paces on the slick ice of Lake Hornavan near Arjeplog, Sweden. Work is currently under way to adapt the technology to buses and large trucks, to avoid jack-knifing, for example.
Stability control systems will first appear in mid-1995 on some European S-Class models and will reach the U.S. market during the 1996 model year (November 1995 introduction). It will be available as a $750 option on Mercedes models with V8 engines, and the following year it will be a $2400 option on six-cylinder $1650 of the latter price is for the traction control system, a prerequisite for stability control.
Bosch is not alone in developing such a safety system. ITT Automotive of Auburn Hills, Mich., introduced its Automotive Stability Management System (ASMS) in January at the 1995 North American International Auto Show in Detroit. "ASMS is a quantum leap in the evolution of antilock brake systems, combining the best attributes of ABS and traction control into a total vehicle dynamics management system," said Timothy D. Leuliette, ITT Automotive's president and chief executive officer.
"ASMS monitors what the vehicle controls indicate should be happening, compares that to what is actually happening, then works to compensate for the difference," said Johannes Graber, ASMS program manager at ITT Automotive Europe. ITT's system should begin appearing on vehicles worldwide near the end of the decade, according to Tom Mathues, director of engineering of Brake & Chassis Systems at ITT Automotive North America. Company engineers are now adapting the system to specific car models from six original equipment manufacturers.
A less-sophisticated and less-effective Bosch stability control system already appears on the 1995 750iL and 850Ci V-12 models from Munich-based BMW AG. The BMW Dynamic Stability Control (DSC) system uses the same wheel-speed sensors as traction control and standard anti-lock brake (ABS) systems to recognize conditions that can destabilize a vehicle in curves and corners. To detect such potentially dangerous cornering situations, DSC measures differences in rotational speed between the two front wheels. The DSC system also adds a sensor for steering angle, Utilizes an existing one for vehicle velocity, and introduces its own software control elements in the over allantilock-brake/traction-control/stability-control system.
The new Bosch and ITT Automotive stability control systems benefit from advanced technology developed for the aerospace industry. Just as in a supersonic fighter, the automotive stability control units use a sensor-based computer system to mediate between the human controller and the environment - in this case, the interface between tire and road. In addition, the system is built around a gyroscopelike sensor design used for missile guidance.
Beyond abs and traction control
Stability control is the logical extension of ABS and traction control, according to a Society of Automotive Engineers paper written by van Zanten and Bosch colleagues Rainer Erhardt and Georg Pfaff. Whereas ABS intervenes when wheel lock is imminent during braking, and traction control prevents wheel slippage when accelerating, stability control operates independently of the driver's actions even when the car is free-rolling. Depending on the particular driving situation, the system may activate an individual wheel brake or any combination of the four and adjust engine torque, stabilizing the car and severely reducing the danger of an uncontrolled skid. The new systems control the motion not only during full braking but also during partial braking, coasting, acceleration, and engine drag on the driven wheels, circumstances well beyond what ABS and traction control can handle.
The idea behind the three active safety systems is the same: One wheel locking or slipping significantly decreases directional stability or makes steering a vehicle more difficult. If a car must brake on a low-friction surface, locking its wheels should be avoided to maintain stability and steerability.
Whereas ABS and traction control prevent undesired longitudinal slip, stability control reduces loss of lateral stability. If the lateral forces of a moving vehicle are no longer adequate at one or more wheels, the vehicle may lose stability, particularly in curves. What the drive "fishtailing" is primarily a turning or spinning around the vehicle's axis. A separate sensor must recognize this spinning, because unlike ABS and traction control, a car's lateral movement cannot be calculated from its wheel speeds.
Spin handlers
The new systems measure any tendency toward understeer (when a car responds slowly to steering changes), or over-steer (when the rear wheels try to swing around). If a car understeers and swerves off course when driven in a curve, the stability control system will correct the error by braking the inner (with respect to the curve) rear wheel. This enables the driver, as in the case of ABS, to approach the locking limit of the road-tire interface without losing control of the vehicle. The stability control system may reduce the vehicle's drive momentum by throttling back the engine and/or by braking on individual wheels. Conversely, if the hteral stabilizing force on the rear axle is insufficient, the danger of oversteering may result in rear-end breakaway or spin-out. Here, the system acts as a stabilizer by applying the outer-front wheel brake.
The influence of side slip angle on maneuverability, the Bosch researchers explained, shows that the sensitivity of the yaw moment on the vehicle, with respect to changes in the steering angle, decreases rapidly as the slip angle of the vehicle increases. Once the slip angle grows beyond a certain limit, the driver has a much harder time recovering by steering. On dry surfaces, maneuverability is lost at slip-angle values larger than approximately 10 degrees, and on packed snow at approximately 4 degrees.
Most drivers have little experience recovering from skids. They aren't aware of the coefficient of friction between the tires and the road and have no idea of their vehicle's lateral stability margin. When the limit of adhesion is reached, the driver is usually caught by surprise and very often reacts in the wrong way, steering too much. Oversteering, ITT's Graber explained, causes the car to fishtail, throwing the vehicle even further out of control. ASMS sensors, he said, can quickly detect the beginning of a skid and momentarily activate the brakes at individual wheels to help return the vehicle to a stable line.
It is important that stability control systems be user-friendly at the limit of adhesion - that is, to act predictably in a way similar to normal driving.
The biggest advantage of stability control is its speed - it can respond immediately not only to skids but also to shifting vehicle conditions (such as changes in weight or tire wear) and road quality. Thus, the systems achieve optimum driving stability by changing the lateral stabilizing forces.
For a stability control system to recognize the difference between what the driver wants (desired course) and the actual movement of the vehicle (actual course), current cars require an efficient set of sensors and a greater computer capacity for processing information.
The Bosch VDC/ESP electronic control unit contains a conventional circuit board with two partly redundant microcontrollers using 48 kilobytes of ROM each. The 48-kB memory capacity is representative of the large amount of "intelligence" required to perform the design task, van Zanten said. ABS alone, he wrote in the SAE paper, would require one-quarter of this capacity, while ABS and traction control together require only one half of this software capacity.
In addition to ABS and traction control systems and related sensors, VDC/ESP uses sensors for yaw rate, lateral acceleration, steering angle, and braking pressure as well as information on whether the car is accelerating, freely rolling, or braking. It obtains the necessary information on the current load condition of the engine from the engine controller. The steering-wheel angle sensor is based on a set of LED and photodiodes mounted in the steering wheel. A silicon-micromachine pressure sensor indicates the master cylinder's braking pressure by measuring the brake fluid pressure in the brake circuit of the front wheels (and, therefore, the brake pressure induced by the driver).
Determining the actual course of the vehicle is a more complicated task. Wheel speed signals, which are provided for antilock brakes/traction control by inductive wheel speed sensors, are required to derive longitudinal slip. For an exact analysis of possible movement, however, variables describing lateral motion are needed, so the system must be expanded with two additional sensors - yaw rate sensors and lateral acceleration sensors.
A lateral accelerometer monitors the forces occurring in curves. This analog sensor operates according to a damped spring-mass mechanism, by which a linear Hall generator transforms the spring displacement into an electrical signal. The sensor must be very sensitive, with an operating range of plus or minus 1.4 g.
Yaw rate gyro
At the heart of the latest stability control system type is the yaw rate sensor, which is similar in function to a gyroscope. The sensor measures the speed at which the car rotates about its vertical axis. This measuring principle originated in the aviation industry and was further developed by Bosch for large-scale vehicle production. The existing gyro market offers two widely different categories of devices: $6000 units for aerospace and navigation systems (supplied by firms such as GEC Marconi Avionics Ltd., of Rochester, Kent, U.K.) and $160 units for videocameras. Bosch chose a vibrating cylinder design that provides the highest performance at the lowest cost, according to the SAE paper. A large investment was necessary to develop this sensor so that it could withstand the extreme environmental conditions of automotive use. At the same time, the cost for the yaw rate sensor had to be reduced so that it would be sufficiently affordable for vehicle use.
The yaw rate sensor has a complex internal structure centered around a small hollow steel cylinder that serves as the measuring element. The thin wall of the cylinder is excited with piezoelectric elements that vibrate at a frequency of 15 kilohertz. Four pairs of these piezo elements are arranged on the circumference of the cylinder, with paired elements positioned opposite each other. One of these pairs brings the open cylinder into resonance vibration by applying a sinusoidal voltage at its natural frequency to the transducers; another pair, which is displaced by 90 degrees, stabilizes the vibration. At both element pairs in between, so-called vibration nodes shift slightly depending on the rotation of the car about its vertical axis. If there is no yaw input, the vibration forms a standing wave. With a rate input, the positions of the nodes and antinodes move around the cylinder wall in the opposite direction to the direction of rotation (Coriolis acceleration). This slight shift serves as a measure for the yaw rate (angular velocity) of the car.
Several drivers who have had hands-on experience with the new systems in slippery cornering conditions speak of their cars being suddenly nudged back onto the right track just before it seems that their back ends might break away.
Some observers warn that stability controls might lure some drivers into overconfidence in low-friction driving situations, though they are in the minority. It may, however, be necessary to instruct drivers as to how to use the new capability properly. Recall that drivers had to learn not to "pump" antilock brake systems.
Although little detail has been reported regarding next-generation active safety systems for future cars (beyond various types of costly radar proximity scanners and other similar systems), it is clear that accident-avoidance is the theme for automotive safety engineers. "The most survivable accident is the one that never happens," said ITT's Graber. "Stability control technology dovetails nicely with the tremendous strides that have been made to the physical structure and overall capabilities of the automobile." The next such safety system is expected to do the same.
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