Getting Started Tutorials - MechDesigner > Tutorial 16: Motion-Path FB and Blend-Curves > Step 16.1: About the Blend-Curve & Motion-Path FB

Difference between a Motion-Part and a Motion-Point

A Motion-Part and a Motion-Point are similar elements.

Motion-Path FB & Motion-Point

Motion-Path FB and Motion-Point

Function-Block menu > Motion-Path FB:

1.Click Function-Block menu > Motion-Path FB

2.Click a sketch-element in a sketch-path*

3.Click in the Command-Manager.

After you add a Motion-Path FB, the Motion-Point is at the start-Point of the sketch-element that you select on the sketch-path.

The sketch-path constrains the path of the Motion-Point.

Motion-values at the input-connector to the Motion-Path FB control the motion of the Motion-Point along the sketch-path.

Motion-Path> Point-List & Data Display

To see the dimension near to the Motion-Point:

1.Edit the Motion-Path FB to open the Motion-Path dialog

2.Expand the Point Parameters > Point List and Data Display

3.In “Display Motion-Point #1 as:” **

Nothing: do not show Displacement or Phase

Displacement: the absolute linear position of the Motion-Point along the sketch-path from the start-Point of sketch-path - see dimension (above)

Phase: the phase of the Motion-Point along the sketch-path. The total “phase-angle” length of the sketch-path is normalized to 360.

** You can use the Motion-Path dialog to add more Motion-Points, but we show the Displacement or Phase of the first Motion-Point.

Motion-Dimension FB & Motion-Part

Motion-Dimension Rocker and Slider

Function-Blocks menu > Add Motion-Dimension FB

1.Click the Motion-Dimension FB command icon to add a Motion-Path FB

2.Click a joint and two sketch-elements*

3.Click in the Command-Manager.

A Motion-Dimension FB controls the angular position or linear position of the Motion-Part relative to a different Part.

* The sketch-elements are Lines when you select a Pin-Joint - to give a Rocker.

* The sketch-elements are Points when you select a Slide-Joint - to give 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 1: Why do we need a Blend-Curve?

Answer 1: To eliminate a curvature-discontinuity.

Question 2: What is a curvature-discontinuity?

Answer 2: A curvature-discontinuity is a step in Radius-of-Curvature.

E.g. when you join an Arc to a Line (and vice versa), or join two Arcs with a different radii. Even if the sketch-elements are tangent with each other, there is a step in the Radius-of-Curvature.

Question 3: What is wrong with a curvature-discontinuity?

Answer 3: A machine element that moves along path with a 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.