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Tutorial 21: Reverse Engineer Cams

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Tutorial 21: Reverse Engineer Cams

Reverse-Engineer Cams

What does Reverse-Engineer a Cam mean?

The simplest definition of Reverse-Engineer a Cam is to copy the original cam.

You can copy-mill a cam. Or, you can measure it with a CMM, and then output that data to a CNC.

However, you will not improve the performance of a machine if you try to make a direct copy of a cam. In fact, you will most likely make the machine's performance worse.

OEMs (Original Equipment Manufacturers) will usually want to improve the performance of their machines.

Reverse-Engineering a Cam in MechDesigner.

The steps below are one way to reverse engineer a cam with MechDesigner. To also improve the performance of the machine.

Machine

Cam Measurement

If you do not have a drawing of the original cam, you must measure its shape.

Cam and Follower Mechanical Arrangement

We need to represent the design arrangement of the Cam's and Follower's kinematic-chains. We should be able to model them in MechDesigner.

If the Follower-Part oscillates, and the Follower-Profile is a Roller bearing, you need:

the distance between the cam's rotational center and the center of the Follower-Part

the distance between the center of the Roller bearing and the rotational center of the Follower-Part

the diameter of the Roller, or get its part-number

the minimum and maximum radius of the cam

If the Follower-Part reciprocates, you need:

the offset distance between the the sliding-axis of the Follower-Part sliding axis cam's rotational center

the offset between the Roller bearing and the sliding-axis of the Follower-Part

the diameter of the Roller bearing, or get its part-number

the minimum and maximum radius of the cam

Other parts in the kinematic-chains:

Measure the distance between each fixed axis, the position of slide axes, and the length of each part in the Follower's kinematic-chain.

MechDesigner

1.Model the kinematic-chains of the Cam and the Follower kinematic-chains: Represent the mechanism(s) you have measured on the machine.

2.Represent the Cam-Profile

To do this:

a.Import a Point-Cloud : Add a Point-Cloud FB to the rotating Cam-Part; edit the Point-Cloud dialog to import data you have measured for the cam-profile. Use the Point-Cloud dialog to fit a Curve to the Point-Cloud data.

or

a.Import a DXF-Drawing of the Cam; edit a CAD-Line to show the DXF-Drawing of the cam. Convert DXF Entities to MD sketch-elements. Make a sketch-loop to represent the cam. Add a Profile element to the sketch-loop that represents the cam.

or

a.Use Import SolidWorks Sketch FB; edit a Part to import a SOLIDWORKS sketch of the cam. Make sure the imported sketch is a sketch-loop. Use Merge-Point, if needed. Add a Profile element to the sketch-loop that represents the cam-profile.

3.Add a Magnetic-Joint FB to pull the Follower-Profile onto the Curve (derived from the Point-Cloud) or the Profile element (derived from the DXF or SOLIDWORKS sketch), and to drive a Motion-Dimension FB.

4.Connect wires from the Motion-Dimension FB that is driven by the Magnetic-Joint to a Graph FB to plot the Follower's motion - its displacement, velocity and acceleration.

MotionDesigner

1.Use the Data Transfer Table to import the plot / data from the Graph FB

2.Put the Data in the table to a Z-Raw-Data or Position-List motion-law (List segment type) (this is to make sure you do not lose the data if you close MechDesigner).

3.If necessary, 'Get the motion' from the Z-Raw-Data (if the Data Transfer table is empty after closing MechDesigner).

4.Add a new Motion and Motion tab and 'Put the data' as an 'Overlay Trace'.

5.Edit the new motion so that it becomes almost the same as the 'Overlay Trace'.

MotionDesigner - MechDesigner Interaction

1.Build a new model with new kinematic-chains to represent the Cam and Follower again.

2.Put the Joints and Parts in the same positions as those in the original kinematic-chain.

3.Add the new motion, which is similar to the Overlay-Trace.

Now there are two motions to compare - one driven by the Magnetic-Joint and the other by the new motion.

Improve the New Motion

1.Make sure the acceleration of the new motion is continuous

2.Reduce the number-of-segments

3.Balance the new motion to reduce peak accelerations and velocities

4.Change motion-laws to suit the application

5.Check the Pressure-Angle and Radius-of-Curvature to make sure they are acceptable.

Export the Cam to SOLIDWORKS

Use a Cam-Data FB and Cam-Coordinates dialog to export the Cam to SOLIDWORKS.

SOLIDWORKS

If necessary, in SolidWorks, move the cam to put it in the correct orientation for machining.

Add various details - bore, boss, key-way, , dowel holes. ... to make a full cam model

From the model, add a drawing with tolerances

Export to C.A.M.

C.A.M.

Generate the G-Code that is needed for C.N.C. Machine.

If necessary, reverse the cam surface data to cut the cam with 'climb' or 'conventional' milling.

Machine the Cam.