Change the Closure of a Dyad.

It may be possible to model the two Parts of a dyad in different positions. We call the different positions: 'Dyad Closures' or, more simply: 'Closures'.

When you add the Parts and Joints to build a dyad, MechDesigner has a first guess of the dyad 'closure'. However, it may not be the closure you want in your design.

Thus, we have a tool to move the Parts from  the different closures. The tool is 'Change-Dyad-Closure'.

Use the tool again and again until the closure is correct for your design.

Objective of this Step.

Use the Change Dyad Closure tool
Review 'Valid' and 'Invalid' Dyad Closures.

Note the 'convenient terms':

A 'Valid Dyad Closure' is a convenient term for the state in which the joints in a Dyad can remain together for a complete machine cycle.

An 'Invalid Dyad Closure' is a convenient term for the state in which the joints in a Dyad cannot remain together for a complete machine cycle.


Background to 'Dyad Closures'

KT-RRRDyad

It is helpful to explore the Kinematic-Tree to identify the 'Dyad'.

In this case, there is an RRR Dyad.

If you click the 'R-R-R Dyad', then the two Parts and three Joints turn Red [the default 'selection' colour].

RRR-Dyad-1

Note: The Dyad does NOT actually have a 'red patch' over the two Parts when you click the Dyad in the Kinematics-Tree.

I have added a 'shape' around the two Parts and three Joints in this Dyad to show you which Parts and Joints are in the RRR Dyad.

tog_minusTo change the Closure of a Dyad

ClickPArt-DyadClosure1

To change the closure of a dyad:

STEP 1: Click the Part-Outline of one of the two Parts in the dyad.

In this image, we have clicked 'Part 2' in an RRR dyad.

[Remember: R is the abbreviation for 'Revolute'. This is the same Joint as a 'Pin-Joint'].

Dyad Closure2

STEP 2: Click Change Dyad Closure in the Mechanism Local Toolbar.

The Part should be in the selection-box in the Command-Manager.

 

STEP 3: Click 'OK' in the Command Manager

The dyad changes to a new closure.

Do 'Change Dyad Closure' again to change to the 'next' closure, or to change the dyad to the original closure.

tog_minusFour(4) Valid Closures of the Offset RRP Dyad

Dyad-Clousre1

STEP 1: Click one of the Parts in the Dyad that you want to change closure.

Here, I have clicked the 'Connecting Rod' in the RRP Dyad.

Dyad Closure2

STEP 2: Click the Change Dyad Closure icon in the Mechanism Local Toolbar.

The image shows the 'Change Dyad Closure' icon.

Dyad Closure 1- RRP

Dyad Closure 1- RRP

Dyad Closure 2 - RRP

Dyad Closure 2 - RRP

Dyad Closure 3 - RRP

Dyad Closure 3 - RRP

Dyad Closure 4 - RRP

Dyad Closure 4 - RRP

Use Change Dyad Closure again and again to move the Dyad to the four closures.

See image to the left which show the four different closures.

tog_minusVideo Showing Valid and Invalid Closures of an Offset Slider

Change a Dyad-Closure.

tog_minusChange Dyad Closure: RRR DYAD

The RRR Dyad has zero or two Closures.

Dyad-Closure0

This Image shows a four-bar mechanism.

Motion-Part - the Fixed Rocker

The input part to the mechanism. Its position will not move when we use the 'Change-Closure' tool.
It is a Motion-Part. Its position is defined by the angle in the Motion-Dimension FB.

Dyad

Part 1
oPart 1 has two Joints: J1 and J3.
oJ1 is fixed by the end of the 'Fixed Rocker'.
Part 2
oPart 2 has two Joints: J2 and J3
oJ2 is defined by its position in the Base-Part, the Frame.

Kinematic or Dyad Closure- four-bar Mechanism

In this image, I have added two circles to the mechanism.

Circle 1

Centre-Point is at J1. Radius: equal to the length of Part 1.
The Circle must pass through J3

Circle 2

Centre-Point is at J2. Radius: equal to the length of Part 2.
The Circle must pass also through J3

In this kinematic-chain, the circles intersect at two positions: one position is at J3, the other at 'J3'.

These are the two possible Closures. Closure 1 [J1–J3–J2] OR Closure 2 [J1–J3–J2].

It is also possible that the circles do not intersect. Theoretically, they can intersect at one point where the two circles become tangent to each other.

Dyad-Closure2

This schematic sketch shows the two possible ways you can assembly the two Parts in the RRR Dyad.

Closure 1 is in Blue

Closure 2 is in Green

tog_minus        VALID and INVALID CLOSURES - 'Offset' RRP DYAD

Closures-RRP

Four Closures

'Offset RRP Dyads' can have four closures.

In the image, the:

Circle gives possible positions for the Joint at the end of the rotating-part - Part 1.
Two Parallel Lines show the two(2) possible positions for the Joint that is offset to the sliding-part - Part 2. (The sliding-part must 'flip over' to give the two parallel lines).

The Circle and the parallel Lines intersect at four Points - C1 to C4 in the image.

Closures-RRP-2

Two Closures

If the rotating-Part is shorter, it is possible that the Circle can only intersect one of the Lines, and not two.

In this case, there are only two Closures - C1 and C4

As you use the Change Dyad Closure, MechDesigner will 'attempt' to make the two closures - C2 and C3 - which are not, in fact, possible.

You must use Change Dyad Closure again to change the closure to C1 or C4.

Dyad-Brocken1

If you are not sure if Dyad is broken, looking the Kinematics-Tree.

If you see the Dyad with a red cross1s-red, then the dyad is 'broken'. MechDesigner is attempting to assemble the Dyad in Closure C2 or C3.

Use Change Dyad Closure to change the Dyad to Closure C1 or C4.

tog_minusTo change the Closure of a Dyad

Dyad Closure2

The order of these two Steps is important.

STEP 1: Click one of the two Parts in the Dyad.
STEP 2: Click the Change Dyad Closure icon in the Mechanism Local Toolbar.

Note: If you click the 'Change Dyad Closure' icon before you click the Part, then deselect the icon, and then follow the two steps.

tog_minusMore than two Closures: Four(4) Valid Closures of the Offset RRP Dyad

Dyad-Clousre1

STEP 1: Click one of the Parts in the Dyad that you want to change closure.

Here, I have clicked the 'Connecting Rod' in the RRP Dyad.

Dyad Closure2

STEP 2: Click the Change Dyad Closure icon in the Mechanism Local Toolbar.
Dyad Closure 1- RRP

Dyad Closure 1- RRP

Dyad Closure 2 - RRP

Dyad Closure 2 - RRP

Dyad Closure 3 - RRP

Dyad Closure 3 - RRP

Dyad Closure 4 - RRP

Dyad Closure 4 - RRP

Use Change Dyad Closure again and again to move the Dyad to the four closures.

See images to the left.

Help Files for MechDesigner and MotionDesigner 11.1 + © Machine, Mechanism, Motion and Cam Design Software by PSMotion Ltd