Step 16.1: About the Blend-Curve & Motion-Path FB

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Step 16.1: About the Blend-Curve & Motion-Path FB

A Motion-Part and a Motion-Point

A Motion-Part and a Motion-Point are very similar elements:

Motion-Part: a Part, whose motion is constrained by a joint, whose position is identified by a Motion Dimension, and whose motion is defined by the input to the Motion-Dimension FB.

Motion-Point: a Point, whose motion is constrained by a sketch-path, whose position is identified by its Motion-Point Dimension, and whose motion is defined by the input to the Motion-Path FB.

Motion-Path FB & Motion-Point

GA-Motion-Path FB3Dialog-MotionPathFB-PointPosition

Add Motion-Path FB:

1.Adds a Motion-PointRed-14-1b to a sketch-element/sketch-path AND specifies its position relative to the start-Point of the sketch-element.

2.Adds a Motion-Path FBRed-14-2 to the graphic-area

3.Adds a dimension to the Motion-PointRed-14-3 to indicate how far the Motion-Point is from the start-Point of the sketch-element in 1.


To see the Motion-Point DimensionRed-14-3 you must:

1.Edit the Motion-Path FB

In the Motion-Path dialog-box > Point List and Data Display  separator:

2.Click the Displacement / Phase radio-button

Displacement: the linear distance along the sketch-path.

Phase: the distance along the sketch-path normalized between 0 and 360. 360 is the complete length of the sketch-path.

Motion-Dimension FB & Motion-Part


Add Motion-Dimension FB

1.Specifies the position of a sketch-elementRed-14-1b (Line or Point) in a Motion-Part relative to a different sketch-element (Line or Point) in another Part.

2.Adds a Motion-Dimension FBRed-14-2 to the graphic-area.

3.Adds a Motion DimensionRed-14-3 to indicate the dimension between the sketch-elements in the two Parts.

Motion-Part: a Part constrained by a joint. Its position, relative to a sketch-element in a different Part, is the total of values given by:

Motion-values at the input-connector of the Motion-Dimension FB.

Base-Value as entered in the Motion-Dimension dialog-box.

Why use a Blend-Curve


A Blend-Curve is a sketch-element.

Use the Blend-Curve dialog-box to specify, at its start-PointRed-14-1b and its end-PointRed-14-2, these parameters:



Rate-of-Change of Curvature

Velocity-Scaling a normalization parameter that controls the overall length and shape of the Blend-Curve.

Its advantage is its smoothness and how it blends with other sketch-elements at its start-point and end-Point.

Question: Why do we need a Blend-Curve?

Answer: To eliminate a curvature-discontinuity.

Question: What is a curvature-discontinuity?

Answer: A Curvature Discontinuity is a step change in Radius-of-Curvature. E.g. an Arc that is joined to a Line (and vice versa), or even an Arc to a an Arc with a different radii.

Question: What is wrong with a curvature-discontinuity?

Answer: A machine element that you join to a Motion-Point that moves along a sketch-path with the curvature-discontinuity will vibrate the machine-element. To reduce mechanical vibrations, you must eliminate the curvature-discontinuity.

The purpose of the Blend-Curve element is to eliminate curvature-discontinuities as the Motion-Point moves along the sketch-path and between sketch-elements.