MBD Modelling of CAM-Follower mechanism using Curve to Curve Joint in Altair HyperWorks MotionView MotionSolve

Introduction:

Cam Mechanism

The transformation of one of the simple motions, such as rotation, into any other motions, is often conveniently accomplished by means of a cam mechanism. A cam mechanism usually consists of two moving elements, the cam and the follower, mounted on a fixed frame. Cam devices are versatile, and almost any arbitrarily-specified motion can be obtained. In some instances, they offer the simplest and most compact way to transform motions.

A cam may be defined as a machine element having a curved outline or a curved groove, which, by its oscillation or rotation motion, gives a predetermined specified motion to another element called the follower. The cam has a very important function in the operation of many classes of machines, especially those of the automatic type, such as printing presses, shoe machinery, textile machinery, gear-cutting machines, automobiles and screw machines. In any class of machinery in which automatic control and accurate timing are paramount, the cam is an indispensable part of a mechanism.

 Disc Cam: In the Disc cams, the working surface of the cam is designed such that follower moves in a plane perpendicular to the axis of the cam performing a reciprocating or oscillating motion.

Roller follower: The contact end of the follower is roller and the rolling motion exists between the cam and follower. Compared to knife-edge followers, the rate of wear and tear is less due to less friction.

CAM Follower Mechanism With CVCV Joint

 CVCV or curve to curve joint fall under the category of higher pair constraints. In this only one point or line is responsible to form a joint between two links. A CVCV joint is useful for modelling cams where the point of contact between two parts changes during the motion of the system.

The curve to curve constraint removes 3 Degrees Of Freedom from each of the systems. When the body of the first curve is in space and the other curve is allowed to moves in three ways

• It can slide along the first curve
• It can roll along the first curve
• Rotate about the common tangent.

 Step 1) Created 3 joints namely Revolute joint (between Cam and Ground body), Translational joint (between follower shaft and Ground body) and Ball joint (between follower roller and follower shaft). 

2) A .csv file for the CAM profile is added under the 'Curves' toolbar. The .csv file has 3 columns which contain data about the movement of CAM in x,y and z directions. Since a 2-D CAM is being modelled, the 3rd column for z-axis has zero values.

3) The follower profile is created as a mathematical expression (function) in X, Y and Z directions. The function for X is {5*sin(2*PI*(0:1:0.01))}, similarly                                                                  function function for Y is {5*cos(2*PI*(0:1:0.01))}. 

4) Two new markers were created for CAM and Follower, one at the CAM pivot and the other at the Follower roller. The direction of gravity is changed from -Z to -Y because the follower is aligned along the y-axis. Motion is defined at the CAM pivot joint with an expression '10*Time'. 

5) In the final step, a CVCV joint is added from the Advanced Joint toolbar. Curve 1 is assigned to the CAM profile and curve 2 to follower roller profile. Their respective markers were also assigned. A CVCV output is also created as an expression to measure the force between follower and roller. In real-world applications, there is a higher probability for the follower to lose contact with the cam. This phenomenon is called lift-off 

It can be seen that the maximum displacement of the follower shaft was 25.

Since there are no negative forces have been seen in the above plot then the current model does not have any lift-off from the follower means the CAM and Follower will stay in contact. In order to study the lift-off phenomena of CAM and Follower mechanism, it is advisable to use 3D contact modelling instead of CVCV joints. As CVCV joints are computationally easy to simulate compared to 3D modelling. 

Session files and Model files can be found here:

https://drive.google.com/open?id=1eGIiZq0m7-n524kKG6hkiWNCF59wmnYl