CONFIGURING THE 'POWER SOURCE'

A simple cam-mechanism typically has two kinematic-chains, each with a Motion-Dimension FB.

a kinematic-chain that moves the cam
a kinematic-chain that moves the cam-follower

In the default case, the Power Source of each kinematic-chain is assigned to the joint with the Motion-Dimension FB. However, the Power-Source for the cam-follower is nearly always as a result of the contact between the cam to the cam-follower.

The power flows from the main drive motor, to the cam-shaft and cam, to the cam-follower, and finally to the tool or payload.

Thus, nearly always, the default arrangement of the Power Source is NOT correct.

We must move the Power-Source for the kinematic-chain that includes the cam-follower to the make the cam its Power Source.

The action: 'move the Power-Source from one element to a different element' is to 'Configure the Power Source'.


Special Cases of 'Configure the Power Source'

In MechDesigner, it is possible that a kinematic-chain has more Parts and Joints than are necessary for the real-world application. In the real-world application, some Parts would be removed from the kinematic-chain that you have modelled.

An example of this is where we use a set of Piggyback Sliders to define the path of a Point. Usually, we connect Dyads from the Piggyback Sliders to the Machine-Frame. The Dyads belong to the real-world kinematic-chain and the Piggyback Sliders define the motion requirements.

When this is the case, you MUST model the mechanism again, but without the Piggyback Sliders. You must then define the motions again for the Parts that will actually be driven, and then give the Power Source directly to these Parts and Joints.  There are some very useful MechDesigner 'tricks' that you can use to create the motions of the new mechanism. Please email for details.


General Case of 'Configure Power Source' to correctly model the Payload for Cam Analysis

Step 1: Set the machine speed

Use Edit menu (or toolbar) > Edit Machine Settings

Step 2: Add the correct masses and inertia to each Part.

See CAD-Line dialog-box | Mass-Properties tab

See CAD-Line dialog-box | SOLIDWORKS tab

See Extrusion dialog-box

Step 3: Power Source

Make sure the kinematic-chain receives its 'power' from the cam.

See Configure the Power Source

Step 4: Extrusion Depths

Make sure the Extrusion Depth of the Cam-Follower Profile is the same as the Cam-Follower you will use in your machine.

Note: MD14.1: See 2D-Cam Properties and Display display dialog-box > Display tab > Contact Force/Contact Stress : Select the Correct Cam-Follower from the drop down list.

Step 5: Direction of Force: towards or away from the cam?

As a cam rotates, the Contact-Force and Contact-Stress values change continuously. It is important to review their values with a Graph FB to find when, and if, in the machine cycle their values become less than 0.0N and 0.0N/mm2 respectively.

If the values do become less than zero, then if the cam is a:

Form or Body Closed Cam

Conjugate Cam: You must decide on which cam the contact-force is active.

Groove Cam: You must decide on which cam-flank the contact-force is active.

If necessary, use the Cam Display and Properties dialog-box to change the cam from Cam 1 to Cam 2.

Force Closed Cam

Make sure the Contact-Force does not become less than 0.0N

MechDesigner does not show the cam-follower literally lift off the cam.

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