Blend-Curve dialog-box

Notes:

Use the Blend-Curve dialog-box to edit the Blend-Curve sketch-element exactly.

Use the Blend-Curve drag-handles to edit the Blend-Curve sketch-element approximately.


About the Geometric Properties of the Blend-Curve

We control the geometric-properties of the Blend-Curve at its start-Point and end-Point, not their actual positions.

If you want to edit their positions, then use the normal sketch-editor to add dimensions or other constraints.

Its geometric properties at its start-Point and end-Point include its:

Angle
Curvature
Curvature Rate

These three parameters can be set to 'blend' with its adjacent sketch-element, or set to an other value.

'Velocity-Scale' parameter for the start-Point and end-Point.

The Velocity-Scaling parameter increases or decreases the length of the Blend-Curve [imagine inflating a balloon].


See: Add Blend-Curve dialog-box


Note: The Blend-Curve is a sketch-element developed by PSMotion Ltd. It is particularly useful to guide a Point with a smooth Path - specifically a Motion-Point. It is not a Bezier Curve.

tog_minus        To open the Blend-Curve dialog box:

There must be a Blend-Curve in the model.

1.Double-click a Blend-Curve in the:
Part-Editor

- or -

Mechanism-Editor

tog_minus        Edit Blend-Curve Exactly : Blend-Curve dialog box

Each Blend-Curve sketch-element has a 'start-Point' and an 'end-Point'.

Thus, the two separators in the Blend-Curve dialog-box are:

Start-Point parameters 
End-Point parameters 

The parameters in each separator apply to geometric properties of the Blend-Curve.

Dialog-BlendCurve-StEdPT

Start Point or End Point

Angle [Units: º]:

Default Value = 0 ; Maximum =360º ; Minimum = –360º

'Blend' check-box:

Make the angle of the Blend-Curve at the start-Point (or end-Point) equal the angle of the sketch-element with which you merge the Blend-Curve.
Enter a different angle for the Blend-Curve at the start-Point (or end-Point).

Curvature k [Units:1 ∕ m]:

Default Value = 0, Curvature = 1Radius-of-Curvature.

Curvature is the reciprocal of the radius of the Osculating Circle you can make with the Blend-Curve at the start-Point (or end-Point).

'Blend' check-box:

Make the curvature of the Blend-Curve at the start-Point (or end-Point) equal the curvature of the sketch-element with which you merge the Blend-Curve.
Enter a different curvature for the Blend-Point at the start-Point (or end-Point).

Note: Curvature of a Line is Zero, Curvature of an Circle is 1 ∕ Radius.


Curvature-Rate dk ∕ ds [Units: 1 ∕ m^2]:

Default Value = 0

Curvature-Rate is the rate-of-change of curvature with respect to the distance along the Blend-Curve.

'Blend' check-box:

Make the curvature-rate of the Blend-Curve at the start-Point (or end-Point) equal the curvature-rate of the sketch-element with which you merge the Blend-Curve.
Enter a different curvature-rate for the Blend-Point at the start-Point (or end-Point).

Note: Only a different Blend-Curve can have a Curvature-Rate value that is not zero. The Curvature-Rate of a Line and Arc are zero.

Velocity Scaling

Increase Velocity-Scaling, to 'inflate' the Blend-Curve.

Decrease Velocity-Scaling, to 'deflate' the Blend-Curve.

Velocity Scaling parameter does not have units.

Default Value = 1 ; Maximum Value = 10 ; Minimum 0.01

'Smoothness' of sketch-elements

You frequently need a sketch to be smooth when it acts as the Path for a Motion-Point.

To join Blend-Curves to other sketch-elements, and other Blend-Curves, and to keep the sketch-path smooth:

Imagine that one Blend-Curve is 'later' or 'after' another:

1.Edit the Blend-Curve that comes later
2.Select the start-Point separator in the Blend Curve dialog
3.Click all of the 'Blend' check boxes
4.Edit the Blend-Curve that comes earlier
5.Select the end-Point separator in the Blend-Curve dialog
6.Clear the 'Blend' check boxes

Now edit the values of the end-Point.

7.Edit the values of the end-Point of the 'earlier' Blend-Curve

As you edit the values, the start-Point of the Blend-Curve that is 'later' will update to the new values you enter in the 'earlier' Blend-Curve.

tog_minus        Edit Blend-Curve Approximately: Drag-Handles

Like other sketch-elements, it is possible to edit the position of the start-Point and the end-Point in the Part-Editor. You can do this with a dimension, a constraint, or you can drag the Points with your mouse.

Blend-Curve-Drag-Handle1

To edit the properties of the Blend-Curve with the Drag-Handles:

1.Click the Blend-Curve one time to show Drag-Handles (one click)

Four Green drag-handles show - two at the start-Point and two at the end-Point - but they are not active.

At each end of the Blend-Curve, there is a drag-handle with an:

Arrow1s-red: this drag-handle can control the Velocity-Scaling and the Angle
Small Circle2s : this drag-handle can control the Curvature.

You must use the Blend-Curve dialog to control the Curvature-Rate.

Blend-Curve-Drag-Handle2

To make a drag-handle active, so that you can 'drag' it.

2.Double-click a drag-handle to make it active

You must double-click each drag-handle to make each one active.

The colour of the drag-handle will change to Blue to indicate the drag-handle is 'active'.

Blend-Curve-Drag-Handle3

To change the shape of the Blend-Curve at the start-Point or end-Point or both:

1.Drag the drag-handle.

If you drag the Arrow1s-red then:

Move the arrowhead further away from the Point to increase the Velocity-Scaling factor
Rotate the arrowhead around the Point to control its Angle.
If you do rotate the Arrowhead around the Point,  the Angle continuity with the adjoining sketch-element will be broken.

Blend-Curve-Drag-Handle4

If you move the Small-Circle2s between 90º and ±180º

The Curvature increases from 0 Curvature (a straight-line) to +ve 'Large Value'

If you move the Small-Circle2s between 90º and ±180º

The Curvature increases from 0 (a straight-line) to –ve 'Large Value'

Note: the angle is always relative to the +Y-axis of the Mechanism Plane, Not the Angle of the Blend-Curve.

Thus 0º is Vertical Upwards - always- and will tend to make the Blend-Curve 'straight' at the Point.

Tutorial and Reference Help Files for MechDesigner and MotionDesigner 13.2 + © Machine, Mechanism, Motion and Cam Design Software by PSMotion Ltd