Nut former is a specialized machine to produce nuts. The key mechanism of a nut former is its cutting-and-feeding mechanism, which essentially is a translating cam driven by a slider-crank mechanism. In this mechanism, return springs are conventionally used to keep the follower in contact with the cam. It thus requires large space to accommodate the return springs, and the spring force, added to the output load, will increase stresses at the contact points.
In order to eliminate the drawbacks mentioned above, this work proposes an alternative conjugate cam mechanism to replace the original mechanism. The follower motion requirements of the original mechanism are firstly analyzed. Then, a novel conjugate cam mechanism that is capable of meeting the same follower motion requirements is presented, and related parameters that may affect the performance of the mechanism are studied. By employing the concept of velocity instant center, the conjugate cam profiles, the paths of cutter, the pressure angle, and the radius of curvature of the translating cams are derived and expressed parametrically. After a force analysis of the cam mechanism has been undertaken, the Hertz contact stress theory is applied to determine the caused contact stresses. Examples are provided to illustrate the nature and capability of reducing contact stress of the proposed conjugate cam mechanism; the results are compared with those of the original cam mechanisms.
The induced contact stresses are found to be sensitive to the follower mass as well as the running speed. For the proposed conjugate translating cam mechanism, by selecting suitable values of the design parameters, the extreme values of the induced contact stresses may have a reduction of 38%.

Keywords：Nut former, varying-velocity translating cam, conjugate cam mechanism.

螺帽成型機是製造螺帽的專用機器；它的進料切斷裝置是此機器的關鍵機構，而此機構基本上即是滑件曲柄機構所帶動的變速平移凸輪機構。習用的變速平移凸輪機構均是利用回位彈簧來使從動件與凸輪面保持接觸；但回位彈簧會對從動件產生額外的負載，而使從動件滾子與凸輪之間的接觸應力增加，並且也常會因為彈簧體積過大，而產生空間配置的問題。
本文提出以共軛式變速平移凸輪機構替換習用的變速平移凸輪機構以改善上述的缺失，並同時保持從動件原有的運動效果。首先分析原始平移凸輪機構之從動件的運動需求條件。接著提出一替代之新型共軛式變速平移凸輪機構，並分析此機構可加以調整的設計參數項目。對於此選定的新型共軛式凸輪機構，給定適當之從動件運動曲線函數以及機構的設計參數，利用瞬心向量法即可推導出共軛凸輪兩側的輪廓、壓力角、凸輪輪廓曲率半徑的向量參數方程式以及加工凸輪之刀具的中心點相對於凸輪的運動路徑曲線的向量參數方程式。分析凸輪機構受力情形後，可用赫茲接觸應力理論計算出凸輪與從動件的接觸應力。本文以範例的分析並和習用的變速平移凸輪機構比較，以說明本文所提出之共軛式變速平移凸輪機構的特性與優點；此外也探討如何適當調整共軛凸輪機構的設計參數值，以儘量降低從動件滾子與凸輪之間的接觸應力。
根據範例的分析比較結果顯示，從動件的質量以及機構的速度是對從動件滾子與凸輪之間的接觸應力是最具影響力的因素。相對於習用的變速平移凸輪機構，本文所提出之共軛式變速平移凸輪機構若選擇適當設計參數值，可使從動件滾子與凸輪之間的接觸應力降低約38%。

關鍵詞：螺帽成型機、變速平移凸輪機構、共軛式凸輪機構。
 

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