Getting Started Tutorials - MechDesigner > Tutorial 16: Motion-Path FB and Blend-Curves > 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 similar elements:

•Motion-Part: a joint constrains a Part, a Motion Dimension FB controls the motion of the Part.

•Motion-Point: a sketch-path constrains a Point, a Motion-Path FB controls the motion of the Point along the sketch-path.

Motion-Path FB & Motion-Point

Motion-Path FB and Motion-Point

Kinematic-FB toolbar > Add Motion-Path FB:

1.Click Add Motion-Path FB

2.Click a sketch-path*

3.Click in the Command-Manager.

The Motion-Point is at the start-Point of the sketch-element that you select.

The Motion-Point is constrained to move along the sketch-path*

* sketch-path is one or more sketch-elements joined end-to-end, with Merged-Points, arranged as an open or closed path.

Motion-Path> Point-List & Data Display

To see the dimension next to the Motion-Point you must:

1.Open and edit the Motion-Path FB > Point Parameters >

2.Expand Point List and Data Display :

3.Select:

Nothing: do not show Displacement or Phase

Displacement: the absolute linear position of the Motion-Point along the sketch-path.

Phase: the normalized position of the Motion-Point along the sketch-path. The total length of the sketch-path is normalized to 360.

Motion-Dimension FB & Motion-Parts

Motion-Dimension Rocker and Slider

Kinematic FB toolbar > Add Motion-Dimension FB

When we add a Motion-Dimension FB, we:

•Control the position of a sketch-element in a Part relative to a sketch-element in a different Part - we reference sketch-elements (Lines or Points) in the Parts.

•Add a Motion-Dimension FB to the graphics-area.

•Add a Motion Dimension - it shows the dimension between the sketch-elements in the two Parts

When we control the Angular Displacement of a Part we call it a Rocker.

When we control the Linear Displacement of a Part we call it a Slider.

Why use a Blend-Curve?

A Blend-Curve is a sketch-element.

Use the Blend-Curve dialog to control at its start-Point and at its end-Point these parameters:

•Angle

•Curvature

•Rate-of-Change of Curvature

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

The advantages of a Blend-Curve over Lines and Arcs, are its smoothness and how it blends with other sketch-elements at its start-point and end-Point.

Questions:

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. when you join an Arc 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 moves along a sketch-path with curvature-discontinuity will vibrate. 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.