偏心滾子用於平移式從動件之共軛平移凸輪機構的設計

The Design of Conjugate Translating Cam Mechanisms with Translating Follower Having an Eccentric Roller

林煜晟(Lin, Yu Cheng)

指導教授 ： 吳隆庸

國立清華大學/工學院/動力機械工程學系/碩士(2016年)

摘要

盤型凸輪機構通常需使用回動彈簧以使得凸輪與從動件保持接觸，但回動彈簧會增加機構的空間，且彈簧的作用力將增大凸輪的接觸應力。為改善這種情形，設計時可採用共軛凸輪。共軛凸輪與滾子間的間隙可藉由精確控制凸輪輪廓的精度以及在接觸面建立油膜而消除，但此舉將使成本提高。若使用偏心滾子用以消除間隙則可有效控制成本。但當凸輪運轉時，所產生的接觸應力也會造成間隙。因此，本文即針對在理想狀況下，如何裝配偏心滾子用以消除接觸應力造成的間隙進行探討。
首先，本研究利用瞬心的觀念，以解析法合成出一組初始的凸輪輪廓。然後調整偏心滾子與凸輪裝配的形式，並計算一組配合調整滾子偏心量所對應的凸輪輪廓。將新舊凸輪的輪廓差異量當作裝配偏心滾子時所需要的預壓量。接著，本研究進行凸輪機構的力量分析與接觸應力分析，藉此找出偏心滾子合適的調整範圍與凸輪裝配的形式。根據本研究結果發現，採用共軛凸輪並裝配一個偏心滾子即可有效消除滾子與凸輪間的間隙，當偏心滾子的偏心量為0.25 mm時，偏心滾子的安裝角度應該介於 之間。同時，本研究發現設計時應儘量讓共軛凸輪之兩個凸輪輪廓的面積相近，以避免因其質量分佈不均所造成的額外振動。本文歸納出最合適的準則，可用以設計製造省工且容易裝配的共軛凸輪機構。

關鍵字

偏心滾子 ； 共軛平移凸輪機構 ； 赫茲接觸應力

並列摘要

Generally the disk cam mechanism needs to equip with a return spring to maintain the contact between the cam and the follower. However, a larger space is required to accommodate the return spring, and the force exerted by the spring may result in a larger contact stress. To avoid the aforementioned disadvantages, the conjugate cam mechanism can be employed instead. The clearance between the conjugate cam and its roller follower can be controlled by means of accurately machined cam profiles and an adequate lubrication at the contact surface. Nevertheless, the accurate cam profile is costly to fabricate. Alternatively, by the application of the adjustable eccentric roller, the clearance can be eliminated efficiently and economically. But when cam works, the contact stress will also create the clearance .Hence, it is the aim of this research to show in ideal situation how to adjust the eccentricity of the eccentric roller to eliminate the clearance caused by contact stress.
Firstly, the ideal profiles of the conjugate cams were analytically synthesized by employing the concept of velocity instant centers. Then, the accompanying cam profiles were calculated with considering the adjusted design dimensions caused by the eccentricity of the eccentric roller. The profile differences between the ideal cam and the accompanying cam were regarded as the expected amount of preloading. Next, the force analysis and the contact stress analysis of the conjugate cam mechanism were performed for allocating the suggested range of adjustment of eccentric roller and the conjugate cam arrangement. The obtained results indicated that the conjugate cam mechanism with an adjustable eccentric roller was effective in eliminating the clearance.When the eccentric roller had 0.25 mm eccentricity , the center orientation of the adjustable eccentric roller was suggested to be between 5 and 15 degrees. Meanwhile, the areas of two conjugate cams should be nearly the same so as to avoid undesired vibrations due to non-uniform mass distribution. The arrangement and the roller adjustment of the conjugate cam mechanism presented in this research may be helpful to achieve its expected purpose easily and directly.

並列關鍵字

eccentric roller ； conjugate translating cam mechanisms ； Hertz contact stress

參考文獻

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