Getting Started Tutorials - MechDesigner > Tutorial 12: Spatial Mechanisms

Add Ball-Joint to constrain a Point (in one Part) to be coincident with a Point (in a different Part).

GST-ConnectingPart

Use the Ball-Joint to construct a two dyads:

•SSR (Spherical-Spherical-Revolute) - equivalent to Ball-Joint — Ball-Joint — Pin-Joint

•SSP (Spherical-Spherical-Prismatic) - equivalent to Ball-Joint — Ball-Joint — Slide-Joint

One of the two Parts in the SSR and SSP dyad has two(2) Ball-Joints -.

The term we use for the Part with two Ball-Joints is the Connecting-Part.

The image is a Connecting-Part with a Ball-Joint at its ends.

Before we add a Connecting-Part and the two Ball-Joints we must prepare a kinematic-chain in two different Mechanism-Editors.

GST-12-201

STEP 1: Add a Mechanism and then Geometry to the Base-Part

1.Model-Editor: Model menu > Add Mechanism-Editor to the front Plane.

2.Mechanism-Editor: Rename Mechanism to MECHANISM A

3.Mechanism-Editor A: Edit the Base-Part

4.Part-Editor: Add a Line

5.Part Editor: Add Constraints , Add Dimension to the Line - see image

6.Part-Editor: Close the Part-Editor

GST-12-202

STEP 2: Add a Rocker with a Motion

1.Mechanism-Editor: Kinematics toolbar : Add a Part

2.Mechanism-Editor: Kinematics toolbar > Add Pin-Joint

3.Mechanism-Editor: Click a start-Point of the Part and the start-Point of the Line in the Base-Part.

4.Mechanism-Editor: Kinematics FB toolbar > Add a Motion-Dimension FB : Click the Pin-Joint, the Line in the Base-Part and the CAD-Line in the Part - it is now a Rocker

5.Mechanism-Editor: Edit Motion-Dimension>Base-Value = -15º

6.Mechanism-Editor: Kinematic FB toolbar> Add Motion FB AND Add Linear-Motion FB

7. Mechanism-Editor: Connect the FBs in the usual way.

GST-12-203

STEP 3: Edit the Length of the Part

1.Edit the new Part

2.Part-Editor: Edit the length of the CAD-Line = 190mm

3.Close the Part-Editor

STEP 4: Edit the Motion to have a range of 20º

GA-AddPlanetoRightPlane

We need a new Mechanism-Editor (MECHANISM B). We will add it to a new Plane. The new Plane is offset from the Right Plane in the Model-Editor.

STEP 1: Add the new Plane

1.Mechanism-Editor: Click the Model name-tab

2.Model-Editor: Model elements toolbar > Add Plane

The Add Plane dialog opens.

3.Add Plane-dialog: Click the Right Plane in the Assembly-Tree or graphics-area.

4.Add Plane dialog: Plane Definition = Offset from Plane

5.Add Plane dialog: Distance to New Plane = 200mm

6.Add Plane dialog: Click to exit the Add Plane dialog

Dialog-AddPlanetoRightPlane

GST-12-206

STEP 2: Add the new Mechanism-Editor

1.Use the keyboard arrow keys to spin the model so that you can see the new Plane.

2.Model-Editor: Model toolbar > Add Mechanism

3.Model-Editor: Click Plane4 (See above) - the new Plane.

4.Model-Editor: Click in the Command-Manager.

You jump immediately to the new Mechanism-Editor - MECHANISM B

'Show other kinematic and sketch-elements'

5.Mechanism-Editor B: Click Visibility toolbar > Show other Kinematic and Sketch-Elements

6.AND Right-Click each Mechanism name-tabs, and select Show with other Kinematic and Sketch-Elements

Showbackground

7.Mechanism-Editor-B: Use the keyboard arrow keys to spin the view.

MECHANISM A is Pink - the color of the other Kinematic and sketch-elements

GST-12-208

STEP 3: In Mechanism-B - edit the Base-Part to locate a Pivot-Point.

1.Mechanism-Editor B: Press F3 on your keyboard to show the Front-View.

2.Mechanism-Editor B: Double-click the Base-Part to open the Part-Editor

3.Part-Editor: Add a short horizontal Line

4.Part-Editor : Add Dimensions to locate its start-Point at 100,100

5.Close the Part-Editor

GST-12-209

STEP 4: Add a Part and Define its Length.

1.Mechanism-Editor-B: Add Part - drag to add the new Part

2.Mechanism-Editor-B: Add Pin-Joint - join the Start-Point of the Part to the Point at 100,100.

3.Mechanism-Editor-B: Edit the Part

4.Part-Editor: Edit the length of the Part = 100mm.

This Part is not kinematically-defined. It is a Free-Part.

GST-12-210

View MECHANISM A from MECHANISM B.

Mechanism A

The a Rocker is joined to the Base-Part with a Pin-Joint .

Mechanism B

The Free Part is joined to the Base-Part with a Pin-Joint .

In MECHANISM B: Add a Part. It is Completely Free Part

When we join it to other Parts with Ball-Joints, it has the derived-name of Connecting-Part.

GST-12-211

STEP 1: In Mechanism B add a Completely-Free Part

1.Mechanism-Editor B: Click Visibility toolbar > Show/Hide other Kinematic and Sketch-Elements to show the Rocker in MECHANISM A.

To help you to add the new Part in approximately the correct place:

2.Mechanism-Editor B : Click View toolbar > Spin model or Use the keyboard arrow keys to spin the view.

GST-12-212

3.Mechanism-Editor B : Click Kinematics-toolbar > Add Part (or use the INSERT key) - Drag in the graphics-area.

4.Edit the new Part

5.Part-Editor : Edit its length to 100mm

...

STEP 2: Add Ball-Joint #1

1.Mechanism-Editor-B: Click Kinematic-elements toolbar >Add Ball-Joint

The pointer changes to the Add Ball-Joint pointer.

Add Ball-Joint - you must select two Points : the two Points are in Mechanism-Editor-B

2.Mechanism-Editor-B : Click a Point at the end of the: Completely-Free Part

3.Mechanism-Editor-B : Click a Point at the end Free-Part

In the image, Point has been selected – it is red - and we are about to click Point.

GST-12-213

When you click Point to add Ball-Joint #1:

•The two Points do NOT snap together

•The end of the Part that will be the Connecting-Part has a Ball-Joint symbol.

You must add Ball-Joint #2.

One of the Points in Ball-Joint #2 is from the Mechanism-Editor-A.

STEP 3: Add Ball-Joint #2

1.Mechanism-Editor-B: If necessary, click Kinematic-elements toolbar >Add Ball-Joint

The pointer changes to the Add Ball-Joint pointer.

Add Ball-Joint - you must select two Points : one Point in Mechanism-B, and other Point in Mechanism-A

2.Mechanism-Editor-B : Click a Point at the end of the Completely-Free Part

3.Mechanism-Editor-B : Click a Point at the end Rocker in Mechanism-A

Note: Point is near to the origin of the Base-Part It is at the end of the PINK Part.

GST-12-214

GST-12-215

GST-12-216

Now, in the graphics-area:

The Completely-Free Part is now the Connecting-Part

•The Connecting-Part has a symbolic rod and two Ball-Joints.

•The symbol of the Connecting-Part and the Ball-Joints are Green

Green indicates it is kinematically-defined.

KT-Rocker-SSR

Kinematics-Tree

Kinematics-Chain now includes an R-S-S dyad.

Each S is a Spherical-Joint. They are the Ball-Joints.

Note

Mechanism B began with a Free-Part and a Completely-Free Part.

After we add the two Ball-Joints they become the two Parts in the S-S-R dyad.

It is easy to edit a Connecting-Part.

It is easier to enable Show other Kinematic and sketch-elements to show the sketches of other Parts, even in the Part-Editor.

GST-12-217

STEP 1: Edit the Length of the Connecting-Part.

1.Mechanism-Editor-B: Hover above the Symbol for the Connecting-Part

2.Mechanism-Editor-B: Double-Click

The Connecting-Part in the open in the Part-Editor.

When the Part is open in the Part-Editor, it returns to the position it had before we added the Ball-Joints.

GST-12-218

3.Part-Editor: Double-Click the dimension that controls the length of the Connecting-Part.

Remember, to edit a dimension, double-click the extension lines or arrowheads, but NOT the dimension number itself.

The Dimension dialog is now open.

To edit the dimension:

•use your keyboard to enter a new value,

4.Dimension dialog: Enter 100+5

5.Press the Enter key on your keyboard

The dimension is now 105mm

6.Close the Part-Editor

GST-12-219

GST-12-220

The Connecting-Part is now 105mm long.

You cannot import Solids or add Profiles/Extrusions to Connecting-Parts.

You can add a Symbolic Rod as a MD-Solid between the Ball-Joints.

GST-12-217

The dimension of the first sketch-element we add to a Connecting-Part controls its Radius.

STEP 1: Edit the Radius of the Connecting-Part

1.Mechanism-Editor B: Double-click the the Connecting-Part

The Connecting-Part in open in the Part-Editor.

GST-12-221

While the Connection-Part is open in the Part-Editor, it returns to the position it was at before we added the Ball-Joints.

2.Part-Editor: Add a Circle to the Part

3.Part-Editor: Add a dimension to the Circle - 12mm in this example.

4.Close the Part-Editor

GA-Edit-ConnectingPartME

To see the Symbolic-Radius for the Connecting-Part:

5.Click : Visibility toolbar > Show Solids in Mechanism

The Connecting-Part is still not attractive!

Use the Ball-Joint dialog to edit parameters that change the:

•Appearance

•Kinematic motion-values

•Kinetostatic force values

GST-12-222

STEP 1: Hide Solids

1.Click Visibility toolbar > Disable Show Solids in Mechanism

STEP 2: Open the Ball-Joint dialog

the Ball-Joint dialog.

1.Click the Ball-Joint in the graphics-area so that it is in the Selection-Window

2.Double-click the Ball-Joint in the Selection-Window

or

2.Right-click the Ball-Joint in the Selection-Window

3.Click Edit element... in the shortcut-menu

The Ball-Joint dialog is now open.

SW-EditBallJoints

GST-12-223

Ball Joint dialog

Ball Diameter (mm)

The diameter of the Symbol for the Ball-Joint.

You must use Visibility toolbar > Show Solids in Mechanisms to see the Ball-Joint symbol.

Ball Offset from Plane (mm).

Ball-Joints frequently do not lie on the Mechanism-Plane. When the Ball-Joints are not on the Mechanism-Plane, the kinematic analysis changes. See Also: Ball-Joint configurations

Ball Equivalent Mass (kg)

0.03 (30 grammes)

MechDesigner calculates Planar Forces.

Enter the mass of the Ball-Joint. This mass is 'referred to' the Ball-Joint from the kinematic-chain in the other Mechanism.

GST-12-224

STEP 1: Show Solids

1.Click Visibility toolbar > Enable Show Solids in Mechanism

Tutorial 12: Design a Spatial Mechanism

Tutorial 12: Design a Spatial Mechanism

Design of a Spatial Mechanism that is common in Packaging Machines

Design a Spatial Mechanism

Video:

Add the Connecting-Part and two Ball-Joints.