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.

GST-ReverseEngineeringModel

Machine

Cam Measurement

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

To get the best results, use a CMM (Coordinate-Measuring-Machine) to measure the cam profile.

Cam and Follower Mechanical Arrangement

To get the best results, we need to represent the design arrangement of the Cam and the Follower's physical design arrangement. 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:

To get the best results, measure the distance between each fixed center, the position of slides, and the length of each part in the Follower's kinematic-chain.


MechDesigner

1.Model the kinematic-chains of the the Cam and the Follower: 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.

C.N.C.

Machine the Cam.