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Use of Voice Recognition for Control of a Robotic Welding Workcell
ABSTRACT: This paper describes work underway to evaluate the effectiveness of voice recognition systems as an element in the control of a robotic welding workcell. Factors being considered for control include program editor access security,Preoperation checklist requirements, welding process variable control,and robot manipulator motion overrides. In the latter two categories, manual vocal control is being compared against manual tactile control and fully automatic control in terms of speed of response, accuracy, stability, reliability. And safety.
Introduction
Voice recognition technology is now recognized as a potential means for easing the
workload of operators of complex systems. Numerous applications have already been implemented, are in various stages of development, or are under consideration. These include data entry,control of aircraft systems, and voice identification and verification for security purposes.
Voice control has also been proposed for use aboard the space station. One prime area for application would be control of some functions of robots used for intraand extravehicular inspection, assembly, repair,satellite retrieval, and satellite maintenance when a crewmember is serving in a supervisory capacity or the system is operating in a teleoperation mode. Voice control of sensors and process variables would free the crewmember’s hands for other tasks, such as direct control or override of the manipulator motion. Similarly, the workload associated with control of many onboard experiments could be eased through the use of this technology.
This paper describes the application of voice recognition for control of a robotic welding workcell. This is a complex system involving inputs from multiple sensors and control of a wide variety of robot manipulator motions and process variables. While many functions are automated, a human operator serves in a supervisory capacity, ready to override functions when necessary. In the present investigation, a commercially available voice recognition system is being integrated with a robotic welding workcell at NASA Marshall Space Flight Center, which is used as a test bed for evaluation and development of advanced technologies for use in fabrication of the Space Shuttle Main Engine. In the system under development, some functions do not yet have automatic closedloop control, thus requiring continuous monitoring and real-time adjustment by the human operator. Presently, these ovemdes are input to the system through tactile commands (;.e.. pushing buttons. turning knobs for potentiometers, or adjusting mechanical devices). Since the operator monitors the process primarily visually, he must either look away from the process to find the proper button or knob or rely on“muscular memory”much as a touch-typist does. In the first case, the time of response to a deviant condition may be excessive. In the second case, there is an increased probability of a secondary error being introduced by the operator.
A voice recognition system could reduce the response time required from the operator.The probability of pushing the wrong button should similarly be reduced. Also, operator fatigue should be minimized.
Since the operator can continuously monitor the process during override input, the effect of the change can be observed more quickly. Thus, if the desired value is exceeded and reverse correction is required, it should be accomplished more quickly, allowing less overshoot. This reduction in oscillation about the desired value makes the system more stable.
Another factor that can be improved is operator safety. In a safety-critical situation,the robot’s operation can be halted immediately by use of the “emergency stop,’’ or E-stop, mode, which is initiated, conventionally, by depressing a large button. If an operator inadvertently finds himself in a hazardous situation, it may be necessary for him to initiate the E-stop sequence. Should the operator not be within reach of the button,however, he may be unable to take the necessary action, and, as a result, could suffer serious injury. Having the capability of stopping the robot by issuing a voice command could significantly improve the operator’s safety by enabling him to stop the robot even when not within reach of the E-stop button.
Manual corrections are occasionally required to adjust the location at which the weld filler wire enters the weld pool. Proper entry location is absolutely critical to sound weld quality. Adjustments are made either by manually adjusting mechanisms that hold the wirefeed guide tube or by issuing tactile commands to a servomechanism. Use of a voice recognition system could eliminate the need for the operator to place his hand within the working envelope of the robot end effector or, if servomechanisms are employed,could improve speed of response and stability.
Another aspect of robot operation in an industrial environment that is very important is the security of a program editing capability of the system. Under no circumstances should any unauthorized person be able to enter this programming mode and alter the robot’s program. A voice recognition system can provide the necessary security by allowing access only for individuals who are authorized and whose voices can be identified by the system.
Background
Robotic welding is under development by NASA and Rocketdyne for the automation of welds on the Space Shuttle Main Engine that are presently made manually. The programmability of a robot can reduce the percentage of welding defects through a combination of consistency and repeatability unattainable by its human counterparts. To do this, the robot is programmed to a nominal weld path and level of weld process parameters (i.e., current, travel speed. voltage,wire addition rate). Some adjustment of these values is often necessary due to conditions changing during the weld. A human making a manual weld accomplishes this adjustment readily, while a robot must rely on the limited talents of sensors and the ability of the operator to override functions when necessary.
System Integration
The basic elements of the workcell system are shown diagrammatically in the illustration.The ultimate goal of the system development work in progress is to generate robot manipulator programs and weld process programs off line, download them to the workcell supervisory computer, then use sensor subsystems to make closed-loop corrections to the robot path and process variables. Offline programming is being done with an Intergraph modified VAX 780/785-205 computer system with Interact color graphics workstations. Deviations between the programmed robot path and the actual required path are observed and corrected by a sophisticated vision-based sensor developed for this application by Ohio State University.This sensor system is also designed to permit measurement of the molten weld pool surface dimensions and correct welding current level to maintain the weld pool dimensions within desired limits. Presently, a number of functions are still controlled manually, and manual overrides capability is required for all functions. As stated in the Introduction, use of voice recognition may improve the accuracy and speed of response of these manual overrides. To explore this technology, a Votan VRT 6050 stand-alone voice recognition terminal has been integrated into the workcell. This system provides continuous speech recognition of up to 10 sets of words with 75-150 words per set.
The integration of the voice recognition system is broken into analog and discrete signals for control. The voice recognition system connects to the control computer through a standard RS232-C communications link.
Discrete Control Signals
In this project, most of the control circuitry is based on discrete digital signals.This is due to the on/off state nature of the circuits to be controlled in the robot controller.The circuits of the system to be controlled by the voice recognition control computer (VRCC) by discrete signals are the emergency stop circuit and the positive jog and negative jog circuits for motion control.
Since the safety of the operator is paramount in any automated workcell, the voice recognition system should be incorporated as a safety feature. To accomplish this, the VRCC has been interfaced into the workcell emergency stop circuit. The emergency stop circuit in the robotic workcell will shut down the welding process and the mechanical motion of the manipulators. Through the use of a digital signal from the VRCC, a relay is energized that interrupts the necessary circuits in the weld power supply and robot controller. With the use of the voice recognition system as a safety control for this workcell, we have added a third level of redundancy into the emergency stopping ability of the operator (in addition to the present emergency stop buttons).
Manipulator motions are controlled through an axis select button in conjunction with a positive or negative jog button that is depressed by the operator. Once the operator has selected an axis, he depresses one of the jog buttons for the desired travel distance.This function was selected to be controlled by the VRCC because of its utilization during automatic operation of the manipulator to correct trajectory errors. The circuitry necessary to control this operation draws the signal to ground through the activation of relays for the positive or negative jog motion. Because motion is achieved only as long as these signals are active low. they can be controlled by discrete digital signals from the VRCC.
Analog Control Signals
There are many variables that affect the quality of weld during the welding process. but the welding current has the greatest effect over a small range of values. It was for this reason, that the welding current was chosen to be controlled by the voice recognition system.
The welding power supply controls the current level through a voltage circuit that uses a range of 0-10 V DC. These voltage values are converted to current levels from 0 to 300 A for welding. A digital-to-analog converter is used in conjunction with a multiplying circuit. The converter allows the VRCC to control a voltage level that is used by the weld power supply to achieve the proper welding current. The multiplier circuit is necessary to allow the weld power supply to be controlled by the other subcontroller used in the workcell.
Experimental Investigation
The accuracy and speed of response of corrections to robot manipulator motion and welding process variables made with the VRCC are being compared with those made with the original control system. Step input errors to robot motion and welding current are introduced randomly into the robot program. By graphically recording relevant system output signals,the time required for the operator to detect the change and initiate corrective action may be measured. Response accuracy and stability may also be gaged through similar analysis of the relevant recorded system output signals.
Conclusions
Future work will investigate voice control of welding filler wirefeed speed and location of wire entry into the weld pool. Also to be investigated is voice control of welding arc voltage override. Later, restriction of access to the robot program editor by voice recognition may be implemented.
The use of voice recognition technology for manual supervisory control of industrial robot systems is very promising. This technology has application for aerospace welding due to the need to have constant human supervision over a multitude of process parameters in real time. Future development of this technology will permit rapid expansion of its application to both robotic and nonrobotic processes.
Acknowledgment
Special thanks to Mr. Jeff Hudson of Martin Marietta Corporation for assistance in the preparation of the illustration presented in this article.
References
[1] C. A . Simpson. hl. E. McCauley. E. F. Rolland. J . C. Ruth. and B. H. Williges. "System Design for Speech Recognition and Generation." Hutnnn Factors. vol. 27. no. 2. pp.115-1-11. 1985.
[2] National Research Council. Committee on Computerized Speech Recognition Technologies.Automatic Speech Rerop1irior1 in severe Environments National Research Council.1984.
[3] E. J. Lerner. "Talking to Your Aircraft." Aerospace America. vol. 24. no. 2. pp. 85-88. 1986.
[4] J. T. Memlield. "Bosing Explores Voice Recognition for Future Transpon Flight Deck." Ariarinn Week and Space Techno/- og!. vol. 124. no. 16. pp. 85-91. 1986.
[5] A. Cohen and J. D. Erickson, ..Future Uses of Machine Intelligence and Robotics for the Space Station and Implications for the U.S. Economy.'' IEEE J. Robotics and Automarion.vol. SMC-16. pp. 1 11-12 I. Jan.iFeb.1986
[6] "Automation and Robotics for the National Space Program," California Space Institute Automation and Robotics Panel. Cal Space Repon CS1185-01, Feb. 25, 1985.
[7] "Advancing Automation and Robotics Technology for the Space Station and for the U.S. Economy." Advanced Technology AdvisoryCommittee. NASA TM 87566. Mar. 1985.
使用語音識別技術(shù)控制的焊接機(jī)器人工作單元
摘要：本文論述了使用聲音識別技術(shù)的焊接機(jī)器人工作單元在工作過程中的效果、程序編輯者接近機(jī)器人的安全﹑試行運轉(zhuǎn)的必要性﹑焊接過程的控制變量﹑機(jī)器人操作者的動作規(guī)范等因素給與考慮。在焊接過程控制和操作動作兩個方面，按照反應(yīng)速度﹑定位精確性﹑焊接穩(wěn)定性﹑焊接可靠性和安全性把人工聲音控制與手工觸覺控制和完全自動化控制進(jìn)行了比較。
緒論
聲音識別技術(shù)已經(jīng)成為可能緩解操作者工作負(fù)擔(dān)的一種有潛力的復(fù)雜系統(tǒng)。許多應(yīng)用已經(jīng)落實,或正陸續(xù)開發(fā),或正在研究之中。這些措施包括數(shù)據(jù)的輸入﹑飛機(jī)的控制﹑和以安全為目的的語音識別。
許多應(yīng)用語音控制技術(shù)還建議用于太空站. 一個主要的應(yīng)用領(lǐng)域?qū)C(jī)器人控制功能用于太空艙內(nèi)檢查、裝配、維修、衛(wèi)星回收、維修衛(wèi)星,是在船上服務(wù)的監(jiān)督能力和系統(tǒng)運作模式的反饋. 聲音感應(yīng)器和過程控制的變數(shù)將使船員影響他手上的其它工作,例如直接控制或推翻的操縱議案。 同樣,利用工作量控制機(jī)載實驗這種技術(shù)可以緩解許多工作負(fù)擔(dān)。
這份文件描述應(yīng)用語音識別控制的焊接機(jī)器人工作單元。 這是一個復(fù)雜的系統(tǒng),涉及多個傳感器及控制投入各種機(jī)械操作件和變化多樣的工藝參數(shù)。雖然許多功能是自動化，且為人類監(jiān)督管理能力所控制,但在必要時隨時準(zhǔn)備超越這些功能。 在當(dāng)前的調(diào)查中， 在美國航天局的馬歇爾空間飛行中心可供商業(yè)使用語音識別系統(tǒng)結(jié)合了焊接機(jī)器人工作單元的技術(shù)，這一技術(shù)作為試點的評價和開發(fā)先進(jìn)技術(shù)并用于制造航天飛機(jī)主發(fā)動機(jī)。在系統(tǒng)開發(fā)中，有些功能尚不具備自動跟蹤控制,因此需要不斷地人力監(jiān)測和實時調(diào)整操作。目前,該系統(tǒng)投入方案是通過觸覺指令(即： 推動按鈕. 旋轉(zhuǎn)電位計、或者調(diào)整機(jī)械裝置)。由于操作過程中,主要監(jiān)測者必須考慮在遠(yuǎn)離的過程中尋找適當(dāng)?shù)陌粹o或把手或靠像打字員一樣那種打字時的肌肉記憶。第二種情況，可能由于操作者的的二次反應(yīng)而增加了錯誤發(fā)生的可能性。
一個語音識別系統(tǒng)可減少操作者的反應(yīng)時間。操作者按錯按鈕的可能性了同樣的也會減少。并且,操作者勞累也會大大減小。
由于在方案運行的過程中操作者不斷監(jiān)測，可以更快地觀察到運行狀況改變所帶來的影響。 因此,如果超過了預(yù)期值,應(yīng)該更快糾正,，但不能太過度。 這對減少振蕩,使系統(tǒng)更加穩(wěn)定的實現(xiàn)了預(yù)期的價值。
另一個因素是可以改善操作者的安全.。在一個安全的緊急情況下，機(jī)器人的操作者可以采取緊急停止來停止其運行，這種緊急停止模式一般來說是設(shè)置一個大按鈕，按慣例是一種經(jīng)常用的方式。如果操作者無意中發(fā)現(xiàn)自己在危險的情況下，這時也許他有必要采取緊急停止這種模式。如果操作者不能夠按到的按鈕，可他也沒有能力采取必要的行動時，這樣下去，他可能會受重傷。如果操作者者能通過發(fā)出聲音指令來停止機(jī)器人的運行那將會大大的改善操作者的安全，即使操作者在不能按到緊急停止按鈕無法停止機(jī)器的情況下也將很安全。
手工調(diào)整有時候需要適應(yīng)焊絲填充到焊接溶池中的位置。填充到正確合適的位置是焊接質(zhì)量的關(guān)鍵。既可通過手工調(diào)節(jié)機(jī)制來控制送絲導(dǎo)管也可給自動控制裝置發(fā)出移動指令來進(jìn)行調(diào)整。使用語音識別系統(tǒng)可以讓操作者者不必再把機(jī)器人控制效應(yīng)得指令文件拿在手中，如自動控制裝置被使用，可以改善操作的反應(yīng)速度和運行穩(wěn)定性。
另一方面，編輯系統(tǒng)程序權(quán)限的安全是工業(yè)機(jī)器人在作業(yè)環(huán)境中很重要的一個安全。在任何情況下，任何未經(jīng)授權(quán)的人能進(jìn)入程序編輯模式，并且可以改變機(jī)器人的控制程序。 一個語音識別系統(tǒng)，可提供必要的安全，使他們那些久久是獲得授權(quán)的人的聲音，才能被機(jī)器人系統(tǒng)識別。
背景
美國航天局正在開發(fā)焊接機(jī)器人并且焊接自動化設(shè)備來代替目前正在用手工焊接的航天飛機(jī)的主發(fā)動機(jī)。使用該機(jī)器人的程序，可以通過用手工來難以做到的焊接一致性和重復(fù)操作來達(dá)到減少焊接缺陷的比例。為此，焊接機(jī)可以編成控制額定的焊接通路和所需要的焊接過程參數(shù)，(即焊接電流、焊接速度、焊接電壓、送絲速度等)。當(dāng)焊接條件改變的時候做一些有價值調(diào)整是很有必要的。一個人用手工來操作焊接時作出調(diào)整是很容易的，但是機(jī)器人的調(diào)節(jié)靠傳感器的智能和必要的人工操作者的方案調(diào)節(jié)。
系統(tǒng)綜述
機(jī)器人工作系統(tǒng)的基本情況如圖表所示，最終的系統(tǒng)開發(fā)工作是編輯操作的程序和焊接過程生產(chǎn)線的控制程序，下載這些程序到控制工作單元的電腦，然后使用子系統(tǒng)傳感器修正機(jī)器人的運行路徑和過程，使其可變。利用VAX 780/785-205電腦連接到彩色圖形處理工作站來進(jìn)行圖表處理實現(xiàn)脫機(jī)設(shè)計。機(jī)器人由于程序編輯和實際需要之間的偏差是通過俄亥俄州大學(xué)研究的精密的視覺傳感器來發(fā)現(xiàn)和糾正的。這種傳感系統(tǒng)也設(shè)計成允許測量焊接溶池表面尺寸和改變電流大小來調(diào)節(jié)焊接溶池保持理想的形狀。目前，仍有許多功能人工控制，而且各個方面的功能都需要人工的操作。如前緒論中所述，引進(jìn)聲音識別技術(shù)可以改進(jìn)人工操作的準(zhǔn)確性和反應(yīng)速度。為研究這項技術(shù)，Votan VRT 6050聲音識別單機(jī)終端被引入到機(jī)器人的工作單元中。這個連續(xù)的語音識別系統(tǒng)可以提供多達(dá)10套，每套有75—150句話。
把語音識別系統(tǒng)的模擬和離散信號輸入控制。語音識別系統(tǒng)通過RS232-C的通信連接到控制主機(jī)。
圖1焊接機(jī)器人系統(tǒng)設(shè)計
離散控制信號
在這個項目中，大多數(shù)控制電路是基于不同的數(shù)字信號。這主要是用在一些國產(chǎn)性質(zhì)的機(jī)器人控制器上的。通過語音識別技術(shù)控制的計算機(jī)來控制的電路系統(tǒng)是通過一種離散信號來控制，這種信號有緊急停止電路和積極響應(yīng)和消極響應(yīng)電路的功能。
因為任何自動化工作單元中操作者的安全是必須保障的,所以應(yīng)把語音識別系統(tǒng)的安全也考慮在內(nèi)。 為達(dá)到這一目標(biāo)，貞技術(shù)已引入緊急停止電路的工作單元。機(jī)器人工作單元中的緊急停止電路將會停止焊接過程的終止操作者的操作。通過使用數(shù)字貞信號，需要中斷焊接動力供電線路和機(jī)器人控制器的繼電器被廣泛使用。由于在這一工作單元中使用的語音識別技術(shù)這一安全系統(tǒng)，我們又增加了第三種供選擇的緊急停車的方案（除了現(xiàn)在已經(jīng)有的緊急停車按鈕）。
方案是通過操作者在軸配合正按鈕或負(fù)按鈕之間選擇來實現(xiàn)控制的。一旦操作者選擇了軸，它可以在理想的距離之內(nèi)控制負(fù)按鈕。這種功能的選用是通過控貞信號來控制的，因為貞信號的使用在自動操作中可以糾正運行的錯誤。在這一操作中有必要通過繼電器的正負(fù)極的地面信號來達(dá)到目的。只因為這些信號很微弱才能達(dá)到目的。他們可以通過貞信號遠(yuǎn)距離控制。
模擬控制信號
有很多因素影響焊接過程的質(zhì)量，但是焊接電流對焊接質(zhì)量的影響絕不是一個小的因素。正因為如此，所以焊接電流被選擇為聲音識別系統(tǒng)控制的對象。
使用0—10V直流電壓來控制焊接電源從而控制電流大小，這種電壓可以使電流在焊接過程中從0—300A之間變化。數(shù)子—模擬轉(zhuǎn)化器配合的電路在廣泛的使用。這種轉(zhuǎn)換器允許貞信號控制電壓的大小從而使電源能提供合適的焊接電流。這種電路必須允許焊接電源通過工作單元中的其它輔助設(shè)備來控制。
實驗研究
在準(zhǔn)確性和反應(yīng)速度方面通過貞信號控制的各種焊接過程與原始的控制系統(tǒng)進(jìn)行了比較。目前焊接機(jī)器人操作的的輸入誤差提和焊接電流已經(jīng)被引入到機(jī)器人程序中。 通過圖表記錄了系統(tǒng)相關(guān)的信號，可以通過操作者發(fā)覺錯誤和糾正這一錯誤所需要的時間來衡量。反應(yīng)的準(zhǔn)確性和穩(wěn)定性也可以通過類似的記錄儀器來分析系統(tǒng)信號的輸入。
結(jié)論
今后的工作將會把語音控制技術(shù)應(yīng)用到焊絲填充速度焊絲填入溶池位置的控制，也會將該技術(shù)用在弧焊電壓控制上。以后，那些現(xiàn)在在機(jī)器人編程受到限制的的方案在采用語音識別技術(shù)之后有可能實現(xiàn)。
利用語音識別技術(shù)控制工業(yè)機(jī)器人系統(tǒng)非常有前景的。由于航空焊接需要大量人力監(jiān)管過程實時參數(shù)控制所以這項技術(shù)已申請用于航空焊接。 這一技術(shù)的未來發(fā)展將可迅速擴(kuò)展為機(jī)器人的應(yīng)用和非機(jī)器人的處理過程。
致謝
在此特別感謝Martin Marietta 公司的Mr. Jeff Hudson協(xié)助編作本篇論文。
參考文獻(xiàn)
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