3DCS contains several types of mechanical Constraints and joints to give users the ability to model a large range of assembly processes. This section divides move routines groups based on frequency of use and briefly defines the routines.
For a given attachment between parts, the user may be able to choose between multiple moves or multiple sets of moves. For example, a hinge could be modeled with a Revolute joint or with a Cylinder joint followed by a Planar joint.
Joints and constraints can act similar and have two main differences. The first difference is that a constraint will locate parts differently based on the types of features selected in a move. For example, a coincidence move with a hole and pin selected will locate them like a cylinder joint. A coincidence move with two planes selected will locate them like a planar joint. Joints are coded for just one type of feature. For example, a Planar joint with a hole and pin selected (not recommended) will attempt to locate them as though they were planes. The other main difference is that joints have Drop DOF set to No by default while most constraints have Drop DOF set to Yes by default.
The Drop DOF setting controls the method of trying to solve over-constrained systems. All the moves are used to generate a set of equations for the system. If Drop DOF is active for a move or set of moves, 3DCS searches through a set of cases (e.g. Plane,Plane, Plane; Plane, Axis, Axis; etc.) and finds the case that best represents the moves. It then uses the equations for that case to solve the model. Moves with drop DOF active are recommended for fully or over constrained parts because the locators should fit one of the cases. The over-constraining locators will be projected into planes so that the moves will always be solved. 3DCS has about 120 cases representing the most typical sets of locators. The move summary will tell you what case was chosen for debugging purposes. No list of the cases is available. If it is deemed no case represents the situation, a solver error will occur.
If Drop DOF is inactive for a move or set of moves, 3DCS generates equations based on the features and moves chosen. If the system is over-constrained 3DCS will keep dropping equations until it can be solved. If all the equations have to be dropped then a solver error will occur.