TABLE OF CONTENTS We like to let the parts fall into place by themselves. The Europeans want to overpower the parts and force them into shape. So we always have to redesign their tooling.
In Chapter 3 we discussed how to represent assemblies as chains of coordinate frames so that we could capture mathematically the fact that parts connect to each other. Some frames are at the nominal center of parts while others tell the location of assembly features on the parts relative to the part center frame. We noted that each feature frame could be joined to a feature frame on an adjacent part and that there was some mathematical constraint between the adjacent frames. But we did not say how the features mechanically operated to secure the location and orientation of one part relative to its neighbor. In this chapter we deal with mechanical constraint between parts and how assembly features impose that constraint.
First, we deal with the basic idea of constraint, that is, how to describe the motions that a part can undergo after some of its degrees of freedom have been constrained. A degree of freedom (dof) is said to be constrained when it can have only one value. This is not the same as being stable, which means that the dof is held at that value and cannot slip away. [1]
Second, we will define the degree of constraint between two parts and distinguish proper (also known as kinematic or exact) constraint,...
