Understanding Curve-to-Curve Constraints in Multibody Dynamics Using MotionView and MotionSolve

Welcome to the Multibody Dynamics for Automotive Applications using MotionView and MotionSolve blog series. In this blog, we will explore curve-to-curve (CVCV) constraints, a crucial aspect of multibody dynamics simulation. These constraints help define the interaction between two curves, reducing computational complexity in automotive simulation tools. 

Overview of the Cam-Follower Mechanism 

In this tutorial, we work with a partially built model of a cam-follower mechanism. This model includes four primary bodies: 

• Ground Body (default)
• Cam (green graphic) 
• Follower Shaft (rectangular piece) 
• Follower Roller (circular component) 

Each of these bodies plays a key role in simulating the cam-follower mechanism, which is widely used in vehicle dynamics simulation. 

Joints and Constraints in the Model 

This model uses three types of mechanical system simulation joints: 

• Revolute Joint: Allows the cam to rotate. 
• Translational Joint: Enables the follower to reciprocate. 
• Ball Joint: Allows the roller to move along the cam surface. 

These joints accurately replicate real-world constraints and motion behavior. 

Defining the Curve-to-Curve Constraint 

The curve-to-curve constraint helps model the interaction between the cam profile and the follower roller profile. Instead of using complex 3D contact modeling, we define these profiles as 2D splines, significantly reducing computational time. 

Steps to Define the Curves 

• Cam Profile Curve: Imported from a CSV file containing X, Y, and Z coordinates. 
• Follower Roller Profile: Defined using mathematical expressions. 
• Closed Curve Setting: Ensures continuous motion along the path. 

Creating Markers and Establishing Constraints 

Markers are essential for specifying reference points on the cam and follower. We create: 

• Cam Marker (attached to the cam) 
• Follower Marker (attached to the follower roller) 

Using these markers, we define the curve-to-curve joint, ensuring the follower roller moves precisely along the cam profile. 

Applying Motion Constraints 

To simulate real-world motion, we apply a rotation constraint on the cam, defined as: 

θ=10×simulation time\theta = 10 \times \text{simulation time}θ=10×simulation time 

Additionally, we apply a gravity constraint in the negative Y direction (-9810 mm/s²) to simulate realistic forces acting on the follower shaft. 

Validating the Model with Output Requests 

We monitor reaction forces on the curve-to-curve joint by adding an output request in MotionView. This helps verify the correctness of the simulation and ensures the cam-follower mechanism operates as expected. 

Running the Simulation and Analyzing Results 

Once the model is built, we: 

• Run the simulation for 6.28 seconds. 
• Plot the follower shaft displacement using HyperGraph. 
• Observe peak displacement of 25 mm. 

Understanding Lift-Off in Cam-Follower Mechanisms 

In real-world automotive engineering simulation, dynamic forces may cause the follower to lose contact with the cam. This phenomenon, known as lift-off, cannot be captured using a curve-to-curve constraint. Instead, 3D contact modeling should be used for more accurate multibody dynamics analysis. 

This concludes our first blog on curve-to-curve constraints in multibody dynamics for automotive applications. Stay tuned for the next part, where we explore 3D contact modeling for enhanced accuracy. 

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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