What is a Magnetic-Joint?

Add Magnetic-Joint pulls a Profile, that is in one Part, to be in continuous contact with a Profile, that is in a different Part. One Profile is circular and the other Profile is irregular*.

Why use a Magnetic-Joint?

A frequent application of the Magnetic-Joint is to reverse-engineer a cam, and to find the motion of a Cam-Follower from the shape of an existing cam.

Add Magnetic Joint

Add Magnetic-Joint icon

 

[Right-Side of graphic-area] Machine Elements Toolbar : Add Ball-Joint icon

Menu:

Add menu > Mechanism sub-menu > Add Magnetic-Joint

 

Use the Add Magnetic-Joint command to pull two Profiles that are in two different Parts, together so that they become in continuous contact.

One Profile is circular and the other Profile is irregular*.
Add Magnetic-Joint 'pulls' the circular Profile onto the irregular* Profile.
The Part with the irregular Profile rotates or slides.

* The shape of the 'irregular' Profile can be derived from a Point-Cloud or a sketch-loop.

Dialog-box:

Magnetic-Joint dialog-box

GA-AddMagneticJoint-0

PREPARATION:

Two kinematically-defined chains,

At least one Part and one Profile in each kinematic-chain.

With reference to the image above:

KINEMATIC-CHAIN 1; PART 1: [see image to the left]

2s Has an irregular Profile , or a Curve derived from a Point-Cloud

1s-red A Motion-Dimension FB. Its motion is specified with

The Part rotates in this model (it is a Rocker / Crank). It might also be a Slider.

Profile2s does not need to be a child to the Part that has its motion specified by the Motion-Dimension FB1s-red, it must only belong to Kinematic-Chain 1.

KINEMATIC-CHAIN; PART 2: [see image above]

3s A Motion-Dimension FB specifies the position of the Part before you apply the Magnetic-Joint. It is not necessary to connect a wire to its input-connector. If a wire is connected, then the motion-values are ignored.

4s Has a circular Profile as a child to the Part

This Part is pulled by the Magnetic-Joint so that the circular Profile4s becomes in continuous contact with the irregular Profile2s.

Profile4s does not need to be a child to the Part that has the Motion-Dimension FB3s, it must only belong to a Part in Kinematic-Chain 2.

CM-AddMagneticJoint-1

ADD MAGNETIC-JOINT:

1.Click Add Magnetic-Joint in the Machine elements toolbar.
2.Click the Profile [or Point-Cloud]2s that is the irregular shape
3.Click the Motion-Dimension FB3s to 'drive' by the new contact between the circular and irregular Profile.
4.Click the Profile4s with the circular shape.
5.Click OK-tiny-13-17 in the Command-Manager

 

GA-AddMagneticJoint-1

Result:

The Magnetic-Joint 'pulls' the two Profiles2s4s together.
The Magnetic-Joint FB5s shows in the graphic-area
When you cycle the machine, the two Profiles stay in continuous contact.
The Motion-Dimension FB3s becomes 'driven' by the Magnetic-Joint.

TO EDIT MAGNETIC-JOINT:

1.Identify the Magnetic-Joint FB5s in the graphic-area
2.Double-click the Magnetic-Joint FB in the graphic-area

- or -

2.Click the Magnetic-Joint FB in the graphic-area so it shows in the Selection-Window
3.Right-click the Magnetic-Joint FB in the Selection-Window
4.Click 'Edit Element...' in the contextual-menu.

See: Magnetic-Joint dialog-box

Magnetic-JointwithHorseShoe

Model: Unacceptable Irregular Profile.

The image shows a shape that is not acceptable.

The irregular Profile should:

NOT be to one side of the centre of rotation or its Origin
NOT form a 'horse-shoe' shape around the centre of rotation, or its Origin.
NOT have a radius-of-curvature that is less than the circular Profile.

If the irregular Profile is not acceptable, the circular Profile will jump to different contact solutions as you cycle the model.

Video:

 

How to...

Add Magnetic-Joint

More Information:

The Magnetic-Joint does not use 'closed mathematical equations'. The motion of the Magnetic Driven Part is 'solved' using optimization techniques. Thus:

The modeling is slower.
A Magnetic-Joint may fail if the Profiles cannot stay in continuous contact for a complete Machine Cycle.

See Also: Magnetic-Joint dialog-box, Add Profile, Sketch-Loop, Add Motion-Dimension FB; YouTube Video : http://youtu.be/IME9Eb4mpQE

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