傳統真空機械手臂採用的是永磁式磁力耦合器，但永磁式磁力耦合器有諸多缺點，例如：轉速與輸出扭矩的不可控性、因大量使用永久磁鐵導致成本居高不下、高溫應用領域的退磁問題等等。本論文旨在設計一可調扭矩式磁力耦合器，並成功推導其數學模型，以深入了解該元件。此外，本論文亦發展一全數位式扭矩感測器，並提出最佳化設計流程與設計一專屬之感測電路。最後設計一簡單的控制器，藉由扭矩回授並對磁力耦合器進行閉迴路即時控制。
本論文提出之可調扭矩式磁力耦合器在設計上採用套筒式的結構。其機械結構分為兩部分，分別為永磁外轉子與鼠籠式內轉子。原理上主要參考感應馬達的運作原理，藉由永磁外轉子的轉動，模擬感應馬達定子線圈產生的旋轉磁場，以帶動鼠籠式內轉子。其中，永磁外轉子上嵌入的永久磁鐵，採用Halbach cylinder的排列方式，能夠建立一均勻且同方向的磁場。傳統的磁力耦合器的扭矩控制機制為氣隙調整機構，藉由氣隙的調整達到控制傳遞扭矩的目的。因為氣隙一般都非常微小，卻對傳遞扭矩的影響又非常巨大，所以造成扭矩控制上的困難。本論文捨棄傳統以氣隙調整，控制扭矩的方式，而採用以永磁外轉子軸向的線性移動，改變內外轉子包覆程度的方式達到扭矩控制的目的。
此外本論文提出一全數位式扭矩感測器。扭矩感測器內部裝有一撓性體，當施加扭矩於該撓性體上時，該撓性體將產生形變。藉由偵測此一形變，換算施加之扭矩，達到扭矩感測之目的。為了能夠適用於機械手臂，在幾何結構的設計上朝向薄型化的方向進行。其中薄型化的關鍵在於撓性體之設計。本論文設計一雙柳丁截面形撓性體，滿足薄型化之需求，在3 N-m的施加扭矩下有約 的形變量，並且提出一最佳化設計流程，以加速產品開發。除此之外，本論文亦提出一全數位式偵測撓性體形變的方法。其機械結構上於撓性體兩端各安裝一組光感應器與碼盤，當傳動軸轉動時，光感應器被碼盤接連的觸發，產生脈衝序列。若此時有一外加扭矩施加於撓性體上，使撓性體產生形變，兩組脈衝序列將有一時間差。藉由偵測兩脈衝序列的時間差，推算撓性體的形變量，以達成扭矩感測的目的。最後針對此方法，設計一專屬之數位電路，採用計數IC計算其時間差與週期，以實現即時扭矩感測的功能。
本論文最後成功地製作與整合一套可調扭矩式磁力耦合器與全數位式扭矩感測器，並且針對兩者設計一閉迴路控制實驗平台與規劃一連串實驗，以驗證其功能性以及與理論的契合度。磁力耦合器方面，以手持式高斯計量測永磁外轉子建立之磁場，發現其磁場為一均勻的強力磁場，其磁通密度約為0.35T。之後針對其內外轉子不同的包覆程度與轉速差，量測其傳遞扭矩，觀察其傳遞扭矩之消長大致上與理論契合，且傳遞扭矩可達2.3 N-m。扭矩感測器方面，因為本論文提出之扭矩感測器的輸出為數位資料，不同於傳統類比式感測器，在靈敏度與解析度的定義會稍有不同，因此要先定義其靈敏度與解析度。最後針對量測出的，施加扭矩對感測器輸出之特性曲線圖，作詳細討論並求得其靈敏度為0.103 ，非線線性度百分比約為1.11%，解析度可達183.105 μN-m。在閉迴路控制方面，本論文設計一簡單的控制器，結合提出之磁力耦合器與扭矩感測器，驗證即時扭矩回授控制之功能。
總結而言，本論文完成一具即時扭矩控制功能之磁動力傳輸模組。該模組除了能夠控制其傳遞扭矩外，還能夠非接觸地透過真空腔壁傳遞真空機械手臂所需之扭矩，希望其對於真空機械手臂之發展能有一定程度之貢獻。

SUMMARY

The major target of this research is to develop a contact-less magnetic clutch with adjustable torque output, in addition to its mathematical model derived accordingly. Secondly, a contactless thin-layered torque sensor with fully-digital signal processing circuit is designed and realized to cooperate the control loop and the magnetic clutch. Lastly, an experimental setup is established to verify the efficacy of the torque control system based on the real-time feedback by the proposed digital torque sensor.

Key words: Contact-less Magnetic Clutch, Adjustable Torque Output, Contactless Thin-layered Torque Sensor, Fully-digital Signal Processing Circuit, DSP Controller

INTRODUCTION

Conventionally, the ultrahigh-vacuum robots are often incorporated with permanent magnet couplings for power transfer. However, the type of permanent magnet coupling has many shortcomings such as: poor controllability on rotational speed and output torque of shafts, required numerous permanent magnets leading to high cost, low feasibility of high-temperature applications and so on.

MATERIALS AND METHODS

The proposed contact-less magnetic clutch is of co-axial mechanical structure. Its mechanical structure can be divided into two portions, namely the outer-rotor in which permanent magnets are embedded and the squirrel-cage inner-rotor. The applied operation principle is identical to induction motor. That is, as the outer-rotor, in which permanent magnets are embedded, is rotating, then a rotating magnetic field is induced so that the squirrel-cage inner-rotor is induced to rotate as well. The permanent magnets in outer-rotor are arranged in Halbach array along the outer cylindrical circle and magnetized in particular direction individually so that an uniform magnetic field can be established.

Traditionally, the torque control approach by using magnetic clutch is to apply an air-gap mechanism to adjust the torque output by change of the air gap. Unfortunately, the air gap is, in general, very small or limited so that it is quite difficult to exactly and efficiently control the degree of the air gap. In this research, instead of utilizing air gap, the axial position of outer-rotor axial is controlled to determine the stretch depth by inner-rotor into magnetic clutch. More stretch depth, more torque output.

To achieve feedback control on torque output, a contactless thin-layered torque sensor with fully digital signal processing circuit is proposed and equipped with the magnetic clutch. The applied operation principle of a torque sensor is to quantify the angular deformation of a sandwiched thin disk which is subject to the external torque. The proposed rotary torque transducer is designed to greatly reduce its axial thickness so that it will not prolong the arm length of a robot much once it is equipped together. In this thesis, a pair of orange-slice-alike flexible bodies is designed to meet the needs of reducing the axial thickness and performing the quantity of angular deformation under applied torque 3 N-m. This paper also proposes a method to place a photo detector pair and a code wheel on both ends of the flexible body. As long as the drive shaft starts to rotate, the photo detector and code wheel are triggered and at the same time two pulse sequences are generated by a DSP Chip (dsPIC30F4011) unit.

If the flexible body was deformed by the applied torque, the two pulses sequences would have a certain degree of time delay, due to a twisted angle being induced on the orange-slice-alike thin disc. By conversion of the time delay between the two pulse sequences, the exerted torque can be quantified. A set of digital signal processing circuit, which mainly consists of counter ICs, is incorporated to convert the time delay and time period (or speed of rotation of shaft) into digital data in terms of torque and speed.

RESULTS AND DISCUSSION

Finally, a prototype of contact-less magnetic clutch, whose torque output is adjustable, and the full digital torque sensor is successfully integrated. Besides, a closed-loop controller is included and a series of experiments are designed to verify the efficacy of magnetic clutch and digital torque sensor.

According to the experiments of the magnetic clutch and digital torque sensor, the flux intensity of the magnetic field constructed by the outer-rotor permanent magnets is about 0.35T. The nominal torque which is successfully transmitted in the experiment is about 2.3 N-m. Since the output of the fully digital torque sensor is digital, the corresponding sensitivity and resolution have to be redefined to evaluate the performance of the digital sensor. Namely, its sensitivity is 0.103 , the nonlinearity is about 1.11%, and the resolution is up to 183.105μN-m.

CONCLUSION

To sum up, a closed-loop control system for rotational power transfer, which integrates the controller, the magnetic clutch and the digital torque sensor, is proposed and examined by realistic experiments to verify its capability on the output torque being able to be adjusted automatically by the feedback of the digital torque sensor. The control system is not only able to adjust the degree of torque transferred, but also able to operate under vacuum space without any physical contact. It is, to certain extent, rewarded to authors if this thesis really has a little bit contribution for the evolution of the ultrahigh-vacuum robots, either in academic area or industrial applications, in the future.

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