Theory of Friction in Cam-Follower
The Friction subnode (described under Friction (Cam-Follower)) is used to add frictional forces and losses to a Cam-Follower.
The friction force is modeled using a continuous friction law, capable of modeling sliding-sticking phenomena. A strict application of Coulomb’s law involves a discrete transition from sticking to sliding, and vice versa, as dictated by a vanishing relative velocity. A discrete transition can cause numerical difficulties. To avoid it, the friction force is approximated by a continuous friction law. The magnitude of the friction force is calculated as
Here, F is the contact force, Ff,r is the additional sliding resistance, Ff,max is the maximum friction force, vslip is the slip velocity vector and v0 is the characteristic slip velocity. The term:
is called the regularization factor. The regularization factor smooths the friction force discontinuity.
The characteristic slip velocity should be small compared to the characteristic relative velocities encountered during the simulation. The continuous friction law describes both sliding and sticking behavior, and it replaces Coulomb’s law. Sticking is replaced by creeping between the contacting bodies with a small relative velocity below the characteristic slip velocity.
The normal force at the contact point can be taken as the computed connection force.
The friction force vector is defined as
where Ff is the magnitude of the friction force.
Energy Dissipation Rate
The energy dissipation rate due to friction at the contact point is defined as