Dimensions and Body Constraints

Dimensions and Body Constraints

Dimensions and Body Constraints are used to constrain the faces and edges of the model in certain ways while still allowing free-form Direct Manipulation of the model in other ways.

Dimensions and Body Constraints are used to constrain the faces and edges of the model in certain ways while still allowing free-form Direct Manipulation of the model in other ways. Dimensions can be used to drive the model, or can be used as pure annotations (non-driving).

For more information about dimensions as annotations, see Dimensions. Body constraints are used to constrain faces and edges within a single component. For information on how to constrain or assemble components relative to each other, see Position and Constrain Components on page 200.


Inventor Fusion will respect the design intent of the constraints while using the Move and Press/Pull commands and when changing dimension values. If you are moving a face that is constrained to another face, then the other face is also moved in order to respect the constraint.

Constraints are propagated through patterns. If you are moving a face that is part of a pattern, then all corresponding faces in that pattern move in the same way. If any of those faces are constrained to any other faces, they are also moved as appropriate. The face or faces that you are explicitly moving are always moved exactly as you specify. The other faces are moved to respect constraints.

If Inventor Fusion cannot find a suitable solution, then the preview stops and the Error Glyph appears. Note that you don’t always need to use body constraints to merely move a face in a constrained way. You can use the move triad, possibly aligning it to an edge, and by selecting the appropriate element of the triad, you can force the face to only move in certain limited directions.

Body constraints

Body constraints include the following types:

■ Coplanar: Two planar faces are made to lie in the same plane

■ Center: Two cylindrical faces are made to lie along the same axis

■ Parallel: Two planar faces are made to be parallel

■ Perpendicular: Two planar faces are made to be perpendicular

All of these body constraint types are accessible from the Constrain command. Note: In addition to body constraints, the Constrain command offers the ability to create inter-component (assembly) constraints. Component constraints are discussed here: Position and Constrain Components on page 200 Body constraints are used to constrain faces and edges within a single component.

You can constrain faces or edges between different bodies within the same component, but you cannot use body constraints between faces or edges of different components. Body constraints cause the body to change shape to meet the constraints. In contrast, Component (assembly) constraints treat each component rigidly. Inventor Fusion solves body constraints first, and then component constraints. When you use the Constrain command to create body constraints:

■ Only the appropriate type of faces are available to be selected (cylindrical faces for Center constraints, planar faces for the other types).

■ The first face that you select is marked as grounded, using the Anchor glyph. This means that when the constraint is first applied, the grounded face will remain where it is, and the other face will move (as well as any other faces that may need to move).

■ You can switch the grounded face with the Tab key, before applying the constraint.

■ The groundedness is temporary; after the constraint is created, either or both faces may move to satisfy the entire set of constraints. There is no way (nor no need) to make a face permanently grounded. Unconstrained faces are never moved by the solver. (In contrast, assembly components can be grounded.)

Locked Dimensions

In addition to explicit body constraints, you can lock a dimension to force the model to maintain that dimension at the current value regardless of other changes. The following video shows the basic operation: Locked dimensions are shown in bold.

You can lock a dimension in one of two ways:

■ Double-click the dimension and change its value (pressing Enter when done, or Escape to cancel)

■ Use the context-menu Lock command (check box) to lock the dimension at its current value

You can uncheck the Lock check box to make a dimension unlocked again.

Only certain dimensions can be locked. If double-clicking does nothing, and the Lock check box is not available on the context menu, then the dimension cannot be locked.

Dimensions and explicit body constraints are solved together. No precedence is given to one or the other. Locked dimensions constrain edges. The adjacent faces are moved to make the edges be the correct size and in the correct position.

When editing the value of a dimension:

■ Inventor Fusion shows you a preview of the new value. There is a built-in delay to minimize unnecessary previews of intermediate values as you are typing.

■ Most dimensions show an anchor glyph. This indicates which side is grounded, and the other side will move in response to the new value of the dimension. Move the mouse to the other side to swap the anchor.


Inventor Fusion sometimes includes invisible provisional constraints to maintain obvious perpendicularity and parallelism.If this is not appropriate, you can move the faces slightly, before applying the constraint or locking the dimension.

If a Move or Press/Pull operation causes an edge or face to be split, and the edge/face has a dimension or constraint attached to it, then Inventor Fusion will automatically apply the dimension/constraint to one of the resulting entities.The other edge/face will not inherit any constraining behavior from the original. It is not possible to predict or specify which edge/face will acquirethe constraint.

It is possible to create situations where a dimension becomes invalid. In this situation, the dimension changes color during the preview. If you finish the command with dimensions in this state (sick), then the sick dimensions are deleted.

It is possible to create a set of constraints that cannot be solved. In such a case, the error glyph will appear. You will have to Undo or delete constraints to get back to a properly solved model.

Dimensions and body constraints are saved when using the DWG format. They are not saved in any other format.


Current limitations:

■ Constraints are not respected when using the Draft command.

■ Under some circumstances, invisible intermediate states may fail for no visible reason.

Some of these situations may be worked around by moving the elements through a different route. Other situations may be worked around by moving a little bit at a time, and accepting each move.

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