隨著半導體產業的蓬勃發展，真空幫浦的性能也越來越強大，但是為了得到超高真空度的環境情況下，精抽幫浦和粗抽幫浦必須得同時使用。在目前對於耗能產品都講求節能的大環境下，必須要個別使用兩個輸入源的真空幫浦，這是屬於耗能的行為，因此為了達到節能的目的，將來希望能夠將兩種幫浦結合在一起，並且只用一個輸入源。為此，本研究選用可調速式磁耦合器作為他們的動力傳動元件。這種耦合器不但是屬於非摩擦的能量傳遞，並且因為沒有摩擦而造成的損耗，因此這種耦合器更為耐用且保養間隔長。目前，可調速式磁耦合器已經被廣泛地應用，根據美國 Magnomatics公司提供的應用範圍可以包含風機、船、汽車、幫浦和飛輪等等，可見其應用的廣泛性。從這些應用領域中可以發現，以上都是大功率輸入且目的為減速。此外，目前文獻對於較低功率輸入和增速情況下的應用範圍涉及甚少，為此，本研究著手於這方面的研究，設計可調速式磁耦合器應用於較低功率輸入且目的為增速的場合用。
本論文所提出的可調速式磁耦合器是一個三明治結構的裝置，主要分為內轉子、中轉子和外轉子，其中，內轉子和外轉子都搭配有永久磁鐵，而中轉子則是導磁材料，負責將內轉子永久磁鐵的磁力傳導至外轉子，反之亦然。此外，根據內轉子和外轉子的磁極對與中轉子導磁段材（或稱鐵條）個數的組合可以形成相應的齒數比。本研究設計了4-23-19（內轉子磁極對-中轉子鐵條數目-外轉子磁極對）的組合，這樣的組合能夠讓可調速式磁耦合器擁有10.5的最大齒數比。4-23-19代表的意思是指內轉子磁極對為4對，而中轉子的導磁材料為23個，最後的外轉子磁極對為19對。正如前面所說，本研究會對可調速式磁耦合器探討其在增速的情況，因此可調速式磁耦合器的外轉子與中轉子為輸入端，而輸出端為內轉子。理論上，當外轉子和中轉子的轉速相同並且旋轉方向互為相反方向的時候，內轉子的輸出轉速會得到對於輸入轉速的10.5倍。這個齒數比10.5具有重大的應用意義，因為這個齒數比能夠讓輸入端的轉速，也就是粗抽幫浦的轉速(3,000rpm)經由可調速式磁耦合器提升至31,500rpm並由內轉子輸出給精抽幫浦，使得精抽幫浦能夠達到其最大運轉速度，而且也能達到精抽幫浦的最大壓縮比。
本研究利用Ansoft Maxwell模擬得到在4-23-19的組合下，各個轉子的最大磁矩慣量，而內轉子、中轉子和外轉子的最大磁矩慣量分別是5.7Nm、32.33Nm和26.6Nm，此結果是在內轉子永久磁鐵與外轉子永久磁鐵的重疊深度(Overlapped Depth)為60mm的情況之下。本研究所設計的重疊深度是可以調整的。因此接下來在文中都會以埋入深度作為重疊深度的代名詞。經由將外轉子的磁矩慣量轉換後，要克服26.6Nm的扭矩慣量需要馬力至少為7.5HP的四極三相感應馬達，這種功率的四極三相感應馬達比目前商用型粗抽幫浦的輸出功率還大。為了能夠有效地將可調速式磁耦合器應用於結合粗抽幫浦和精抽幫浦，本研究對三明治結構的可調速式磁耦合器做了兩種改良的方式，以便能夠降低輸入端的輸入扭矩（此輸入扭矩為克服磁矩慣量）。此兩種改良的的方式分別是在中轉子的內側加入一個厚度為1mm的薄環，另外本研究將原本內轉子的埋入深度由60mm改為20mm，這讓外轉子的最大扭矩由原本26.6Nm降低至1.74Nm，這時候的扭矩慣量相當於0.5HP的四極三相感應馬達就可以轉動。這樣的結果（磁矩慣量在改良後的數值）非常符合地應用於結合粗抽幫浦和精抽幫浦的場合上。
除了進行模擬分析以得出較佳的設計之外，本研究也對可調速式磁耦合器進行齒數比的理論推導，務求能夠以更有系統的方式推導齒數比方程式。本研究利用氣隙內的磁通密度推得氣隙內的磁矩慣量，並根據磁矩慣量列出各個轉子的動態方程式，接著利用急跳度(Jerk)的概念推得齒數比方程式。
經過模擬與理論推導以後，本研究設計並製作出一顆可調速式磁耦合器，並對其作理論與模擬的驗證。在實驗結果裡，不管是齒數比還是增速曲線都與理論的推導結果相符，由此可見可調速式磁耦合器是具備本研究在預期上的性能與功能性。另一方面，可調速式磁耦合器在實驗進行期間，當中轉子固定在輸入頻率（由變頻器輸入到感應馬達）為7Hz，並且外轉子由0Hz增加至某一個輸入頻率（由變頻器輸入到感應馬達）之後，可調速式磁耦合器的輸出轉速發生失步的情況。這樣的情況發生可以解釋為，內轉子埋入深度影響內外轉子間磁吸力的強度，內轉子的埋入深度越深，則交互磁吸力越強。加上當輸出轉速逐漸提升，輸出扭矩就會跟著下降，而當輸出扭矩降低至連內轉子的慣性都無法帶動的情況下，則失步的現象便會發生。最直覺的解決方法就是將內轉子的埋入深度增加，可是這會導致輸入端的輸入功率也必須增加以克服磁矩慣量。
由此可見內轉子的埋入深度是一把雙面刃，也是所謂的有得必有失。這是因為內轉子的埋入深度會影響內轉子和外轉子永久磁鐵間的重疊面積，當重疊面積越小則由磁矩公式可以得知磁矩也跟著越小。這裡的磁矩在本研究中也可稱之為磁矩慣量。因此當埋入深度越深則磁矩慣量越強，使得輸入扭矩（輸入功率）也必須一起上升；反之若埋入深度越淺則磁矩慣量越低，此時則容易因為負載扭矩較大而發生失步（內轉子轉速跟不上理論的轉速）的情況。

「英文延伸摘要」Summary

SUMMARY

An innovative design of magnetic coupler for shaft speed amplification is presented in this thesis. The structure of proposed magnetic coupler for speed change is similar to an infinite-stage gearbox. In addition, the mathematical model of flux density is derived to obtain the equation of adjustable gear ratio and effect of speed amplification. At last, the setup of experiments applied on thin-film deposition process is built up to examine the capability of the proposed variable gear-ratio magnetic coupler.

Keywords: Magnetic Coupler, Speed Amplification, Gear Ratio

INTRODUCTION

Nowadays the magnetic coupler for shaft speed change is highly used for high power input condition, such as automotive, truck, marine, aerospace, and so on. Although some are used in pumping systems, yet most of them are for speed reduction. On the other hand, the research for low power input and speed amplification problems are not addressed much. Instead, this thesis is to investigate the problem in which the innovative magnetic coupler is employed for low-speed input but high-speed output.

MATERIALS AND METHODS

The variable gear-ratio magnetic coupler is designed to be of co-axial mechanical structure. It is divided into three portions: namely they are outer rotor, core rotor and inner rotor. Rare-earth permanent magnets are attached on both outer rotor and inner rotor, while core rotor is inlaid by ferrite sticks. In this thesis, sintered NdFeB permanent magnet is employed and the corresponding grade is N35. As to the matter of speed amplification, the outer rotor and core rotor are treated as the low-speed inputs, while the inner rotor as the high-speed output.

As to applications of magnetic coupler, there are two typical types: fixed gear-ratio case and variable gear-ratio case. For the fixed gear-ratio case, the rotation speed is altered from either the core rotor or the outer rotor to the inner rotor while the other low-speed rotor is held stationary. More generally, the two low-speed rotors are involved in the speed amplification mechanism with different speeds for the variable gear-ratio case. The maximum gear ratio is obtained as the two low-speed rotors rotate at same speeds but in opposite direction.

Once the input rotors (outer rotor and core rotor) and the output rotor (inner rotor) are well defined, the most significant factor determining how the speed of output rotor is adjusted is the gear ratio. The interplay between the number of outer rotor’s permanent magnet pole pairs, the number of inner rotor’s permanent magnet pole pairs and the number of ferrite stick together determines the gear ratio. The different combinations will result in the different gear ratio. Moreover, the cogging torque can be eliminated by selecting appropriate combinations.

In this thesis, the rotational speed of inner rotor is altered even though the speed of outer rotor is constant if the core rotor acts as a control rotor, which controls the output speed and direction. After analysis and computer simulations, the combination of pole pairs for the proposed magnetic coupler is designed as 4 pole pairs on the inner rotor, 23 ferrite sticks on the core rotor and 19 pole pairs on the outer rotor.

In summary, three types of gear ratio can be acquired under certain conditions:
(i) Gear ratio between the outer and inner rotors, as core rotor is held stationary, is 4.75.
(ii) Gear ratio between the core and inner rotors, as outer rotor is held stationary, is 5.75.
(iii) The maximum gear ratio between either the core rotor or the outer rotor and inner rotor is 10.5, as the core rotor and the outer rotor rotate at the same speed but in opposite direction.

Under specific operation mode of three types above, the torque inertia of the each rotor can be analyzed by using Ansoft Maxwell. From the simulation analysis, it can be seen that the torque inertia of inner rotor is 5.7Nm, the outer-rotor’s torque inertia is 26.6Nm and the core-rotor’s torque inertia is 32.33Nm. Since the torque inertia of outer rotor is up to 26.6Nm, it implies a three-phase induction motor with at least 7.5kW is required to counter-balance the torque inertia of outer rotor to rotate. However, the commercial coarse pump is about 3HP for its maximum output power. Therefore, the modification on magnetic coupler to reduce the torque inertia at outer rotor is necessary.

In order to reduce the torque inertia of outer rotor, a bush is inserted to the inner side of the core rotor to reduce the flux density. On the other hand, the overlapped area of permanent magnets, which are attached on the inner rotor and outer rotor, is to be modified. The smaller the overlapped area, the weaker is the magnetic attractive force. As long as these two modifications are validated, the torque inertia of outer rotor can be significantly reduced. As a result, the torque inertia at outer rotor is reduced from 26.6Nm to 1.5Nm such that the required power for the equipped induction motor to rotate the outer rotor is greatly reduced as well.

RESULTS AND DISCUSSION

Finally, a proposed magnetic coupler, applied for low power input and speed amplification, is verified by experiments. It is shown that the speed profile for amplification is matched with the theoretical analysis though the stall phenomenon occasionally appears. It is noticed that the smaller the overlapped area of permanent magnets between low-speed rotor (the positions of the outer rotor and the core rotor are held stationary) and high-speed rotor (the overlapped depth depends on the position of the inner rotor), the weaker the magnetic attractive force between low-speed rotor and the high-speed rotor. In other words, the stall phenomenon certainly occurs.

Conclusion

To sum up, a variable-gear ratio magnetic coupler for shaft speed amplification is proposed and examined by intensive experiments to verify its capability of expected gear ratio and output speed amplification. From the experiments, the proposed magnetic coupler shows its desired gear ratio matched with the theory analysis. Besides, the rotational speed of the output rotor is well amplified. These two points verify that the proposed magnetic coupler is satisfied for the function of speed amplification. However, insufficient the overlapped depth between the high-speed rotor and low-speed rotor results in the stall phenomenon, which is caused by the magnetic attractive force between the high-speed rotor and the low-speed rotor being weaker than the start-up torque inertia. In other words, the reduced overlapped depth can reduce the torque inertia of outer rotor but stall phenomenon may occur accordingly.

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