Modeling Cam-Follower Mechanisms Using Higher Pair Constraints in MotionView

Welcome to the Multibody Dynamics for Automotive Applications using MotionView and MotionSolve blog series! In this chapter, we apply higher pair constraints to a cam-follower mechanism, demonstrating their role in vehicle dynamics simulation. This is an essential part of automotive simulation tools, enabling accurate mechanical system simulation while optimizing solver performance. 

The Importance of Curve-to-Curve Constraints in Cam Mechanisms 

The cam-follower mechanism is a fundamental component in internal combustion engines, valve trains, and robotic actuators. Traditional 3D contact modeling for such systems is computationally expensive and difficult to fine-tune. Instead, multibody dynamics software like MotionView and MotionSolve enables engineers to use curve-to-curve constraints to simplify the simulation. 

How the Curve-to-Curve Joint Works 

• The cam profile is represented as a 2D spline curve. 
• The follower’s trajectory is modeled as another curve. 
• A curve-to-curve constraint ensures the follower follows the cam profile precisely, eliminating the need for contact modeling. 

By using curve-to-curve constraints, we remove three degrees of freedom from the system, allowing the follower to: 

• Slide along the cam profile. 
• Roll along the cam surface. 
• Rotate about the contact point’s common tangent. 

This technique is widely used in automotive engineering simulation, reducing computational time and improving model stability. 

Other Key Higher Pair Constraints in MotionView 

Point-to-Deformable Curve Joint 

• Used when a rigid body moves along a flexible path. 
• Example: A ball constrained to move along a slender beam. 

Point-to-Deformable Surface Joint 

• Models interactions between a point mass and a flexible surface. 
• Example: A ball rolling on a deformable sheet of paper. 
• Useful in multibody dynamics training and certification to replace complex flexible body contact models. 

Quantitative Impact of Higher Pair Constraints on Degrees of Freedom 

In multibody dynamics simulation, higher pair constraints remove specific degrees of freedom. The point-to-curve constraint removes two translational degrees of freedom, while the point-to-surface constraint eliminates two translational and three rotational degrees of freedom, totaling five.

The curve-to-curve constraint restricts two translational and one rotational degree, removing three degrees of freedom. Similarly, curve-to-surface and surface-to-surface constraints each remove two translational and three rotational degrees, eliminating five in total. 

For deformable constraints, point-to-deformable curve removes one translational and three rotational degrees, restricting four degrees of freedom, while point-to-deformable surface removes two translational and three rotational degrees, totaling five. 

These constraints help optimize vehicle dynamics simulation by accurately modeling mechanical system behavior while improving computational efficiency. 

Building a Cam-Follower Mechanism in MotionView 

Step 1: Define the Cam Profile 

• Import a 2D spline curve representing the cam shape. 
• Ensure the motion function is correctly assigned. 

Step 2: Define the Follower Path 

• Create a curve-to-curve joint between the follower and cam profile. 
• Assign initial velocities and constraints. 

Step 3: Validate the Model in MotionSolve 

• Run the multibody dynamics simulation in MotionSolve for automotive engineers. 
• Verify the follower’s trajectory aligns with the cam motion. 
• Check for solver errors due to incorrect constraint definitions. 

Conclusion 

Using higher pair constraints, we successfully model a cam-follower mechanism in MotionView and MotionSolve. By replacing 3D contact modeling with curve-to-curve constraints, we achieve: 

• More efficient simulations. 
• Reduced computational complexity. 
• Better solver convergence. 

In the next chapter, we will explore advanced applications of constraints in automotive dynamics simulation, including flexible body contacts and force-based modeling techniques.

This blog is part of our ongoing Multibody Dynamics blog series. If you missed the previous posts, check them out here.  

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