- 學位論文
凸輪連桿自定心中心架的設計
The Design of Cam-linkage Self-centering Steady Rests
摘要
中心架的作用為保持圓柱工件的中心位置，為車床切削細長軸工件時加裝的配備，而自定心中心架為利用機構作動以有效達成自定心夾持工件的目的。凸輪連桿型中心架是現今使用最普遍的類型，但至今尚無系統化的研究。本文的目的即對凸輪連桿型自定心中心架作基礎研究，以求瞭解其相關特性。 本文提出以平移凸輪以及以平移滾子驅動兩種類型的凸輪連桿自定心中心架的設計方法，文中首先選定適當之機構設計參數後，找出三夾持滾子之間的位移關係，使之達成自定心夾持功能。接著利用瞬心向量法推導出凸輪輪廓、壓力角、夾持角度等相關參數式。再者，藉由各機件幾何關係，推導若干個幾何上的尺寸參數限制，包含凸輪輪廓過切限制、各桿件干涉情形等。隨後再分析機構靜力平衡，得到三夾持力相互關係，並利用赫茲接觸應力理論算出夾頭與工件間的接觸壓應力。最後，以等效連桿的概念推導出此兩種凸輪連桿自定心中心架的誤差分析方程式，並以工件中心與工件半徑偏差作為輸出誤差，藉此可作為制定自定心中心架各機件的公差依據。
並列摘要
The steady rest is a gripping device to support a long cylindrical workpiece and is often used when a slender shaft is machined on the lathe. Furthermore, the self—centering steady rest can help the cutting cylindrical workpiece to additionally keep a stationary center. The cam-linkage type self-centering steady rest is the most popular one, but how to design such a device has not been illustrated. The purpose of this thesis is to present a method for designing the cam-linkage self-centering steady rest. The cam-linkage self-centering steady rest can be either the active translating cam type or the active translating roller link type, and both of them have three grippers. In order to keep the cutting workpiece having a stationary center, the relative positions and the instant centers of three grippers must be a function of the workpiece radius. Either the contact points between the cam and the followers or the contact points between the active roller links and the inverse cam can then be determined according to the locations of instant centers. Consequently, the cam profiles, their radii of curvature, and the pressure angles can be expressed in the form of parametric equations. In addition, for their proper operation, some geometric constraints of each link of the self-centering steady rest must be observed and can be calculated. After a force analysis of the steady rest has been undertaken, the forces applied on each gripper can be determines, and the contact stress among the workpiece and three gripping rollers can be calculated. By applying the equivalent linkage method, finally, the radius varaion as well as the eccentric amount of the cutting workpiece caused by each link length deviation can be estimated. The designer may accordingly assign proper tolerances on each member of the steady rest to restrict the output within a specified maximum value.