刘焱

摘  要：考虑凸轮机构的正、负偏置涉及内容繁杂、教材及其它教学资源对此少有述及，学生无法灵活应对该知识点等问题，文章对此进行深入研究。首先，以偏置直动从动件盘形凸轮机构为研究对象，分析推程及回程压力角的特点并给出凸轮机构压力角的两种表达式;其次，从减小推程压力角以提高传力性能的角度，分析凸轮机构的合理偏置方式;最后，定义凸轮机构的正、负偏置。上述提供了凸轮机构合理偏置的清晰思路，对正、负偏置的全面理解及应用给予了切实的理论依据。

关键词：凸轮机构;正偏置;负偏置;推程压力角;回程压力角

中图分类号：G642 文献标志码：A         文章编号：2096-000X（2020）35-0120-04

Abstract： As positive & negative offset of cam mechanism is related to complicated contents， the explanations of it seldom appear in textbooks and other available teaching materials， college students usually have difficulties in understanding and flexibly applying of it， this paper carries out an intensive research on offset of cam mechanism and its related problems. Firstly， taking the plate cam mechanism with offset translating follower as research objects， the pressure angle for actuating and return travelis respectively analyzed， meanwhile， two formulas expressing pressure angle are derived. Then， reasonable offset style of cam mechanism is obtained according to reducing pressure angle for actuating travelso as to improve the force-transmission characteristics. Finally， the positive & negative offset of cam mechanism frequently confused by most learners is defined. The above provides clarity of thought about reasonable offset style of cam mechanism and concrete theoretical basis for comprehensive understanding and application of positive & negative offset of cam mechanism.

Keywords： cammechanism; positive offset; negative offset; pressure angle for actuating travel; pressure angle for return travel

引言

凸輪机构的正、负偏置在各类《机械设计基础》《机械原理》及相关教材中少有提及，偶见教材中出现“什么是正、负偏置”及“正偏置可减小压力角”等的结论性文字，但其中的原委未见说明[1-3]。教材以外的其它教学资源（如教学参考书及网络资源）对于凸轮机构偏置也只见只言片语的表述，未见全面透彻分析正、负偏置的由来等。

关于凸轮机构的偏置，教师在课上往往一带而过甚至不会述及，然而凸轮机构一章的习题以及研究生入学考试的专业课试题中，经常会出现与此相关的题目，学生往往不知如何作答，加之参考资料少之又少，以至于学生只能机械记忆“什么是正偏置”“什么是负偏置”，至于“为什么”，不得而知，从而造成该知识点的缺失以及无法灵活处理相关问题的现象。……