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

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

Compare a Motion-Part to 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 its 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, whose position is identified by its Motion-Point Dimension, and whose motion is defined by the input to the Motion-Path FB.

The Motion-Path FB and Motion-Dimension FB - compared

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/sketch-path.

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.

Note:

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

GA-RockerandSlider

Add Motion-Dimension FB does three things. It:

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 from 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

GA-BlendCurve

About the 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:

oAngle

oCurvature

oRate-of-Change of Curvature

oVelocity-Scaling a normalisation parameter that controls the overall length and shape of the Blend-Curve.

Question: Why do we need a Blend-Curve?

Answer: To eliminate a curvature-discontinuity.

Question: What is a curvature-discontinuity?

Answer: Even with tangency, at the instant a Motion-Point moves between sketch-elements that have different radii, (e.g. from an Arc to a Line (and vice versa), or from an Arc to a different Arc with a different radii) it experiences a curvature-discontinuity.

Question: What is wrong with a curvature-discontinuity?

Answer: If you join a machine element to the moving Motion-Point, the curvature-discontinuity between different sketch-elements will give rise to vibrations of 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.