Friction Block

Friction parameters for the LuGre model are defined in the Friction block as shown in the following table:

Parameter Name	Dimension
Mu_Static	Specifies the static friction coefficient $(μ_{s})$ in the connector. `MU_STATIC > 0`. This is a mandatory parameter and it must be specified. Recommended Value: `0.5`
Mu_Dynamic	Specifies the dynamic friction coefficient $(μ_{d})$ in the connector. `0 ≤ MU_DYNAMIC ≤ MU_STATIC.` This is a mandatory parameter and it must be specified. Recommended Value: `0.3`
Analysis_Modes	Specifies the analysis modes for which the frictional effect is on. The choices are the strings: `‘STATICS_AND_DYNAMICS’` `‘DYNAMICS_ONLY’` This is an optional parameter that defaults to `‘DYNAMICS_ONLY’`. Both static and dynamic frictions are considered. Recommended Value: `‘STATICS_AND_DYNAMICS’`.
Effect	Specifies the types of friction models to support. Available options are: `‘STICTION’` `‘SLIDING’` This is a mandatory parameter and it must be specified. Recommended Value: `‘SLIDING’`.
Transition_Velocity	The absolute velocity at which the friction transitions from dynamic friction to static friction. `TRANSITION_VELOCITY > 0`. This is a mandatory parameter and it must be specified. Recommended Value: `0.1` mm/second.
Bristle_Stiffness	Specifies the bristle stiffness in the LuGre model. Usually represented as $σ_{0}$ . `BRISTLE_STIFFNESS > 0`. This is a mandatory parameter and it must be specified. Recommended Value: `100.0`/mm.
Bristle_Damping	Defines the damping coefficient for the pre-displacement (or stiction) regime. Its main role is to damp out bristle vibrations in the pre-displacement regime. Usually represented as $σ_{1}$ . `BRISTLE_DAMPING ≥0.` This is a mandatory parameter and it must be specified. Recommended Value: `0.316` second/mm.
Slip_Damping	Specifies the coefficient for the viscous damping force that occurs when relative sliding actually begins. Usually represented as $σ_{2}$ . `SLIP_DAMPING ≥ 0`. This is a mandatory parameter and it must be specified. Recommended Value: `0.0004` second/mm.
Torque_From_Preload	Specifies the preload friction torque in the Spherical Connectors. `TORQUE_FROM_PRELOAD ≥0`. This is a mandatory parameter and it must be specified. Recommended Value: Not available.
Ball_Radius	Specifies the radius of the spherical connector. `BALL_RADIUS > 0`. This is a mandatory parameter and it must be specified. Recommended Value: Not available.

The following table describes the type and dimension for the various input parameters. Abbreviations are: [F] = force, [L] = length, [T] = time.

Parameter Name	Type	Dimension
Mu_Static	real	No-Units
Mu_Dynamic	real	No-Units
Analysis_Modes	real	-
Effect	real	-
Transition_Velocity	real	[L][T^-1]
Bristle_Stiffness	real	[L^-1]
Bristle_Damping	real	[T][L^-1]
Slip_Damping	real	[T][L^-1]
Torque_From_Preload	real	[F][L]
Ball_Radius	real	[L]

The example below shows the specification of a LuGre Friction block in the .gbs file:

$---------------------------------------------------------------
[LUGRE_FRICTION]
MU_STATIC           = 0.0
MU_DYNAMIC          = 0.0
ANALYSIS_MODES      = 'STATICS_AND_DYNAMICS'
EFFECT              = 'SLIDING'
USE_FORCE           = 'YES'
TRANSITION_VELOCITY = 0.1000
BRISTLE_STIFFNESS   = 0.0100
BRISTLE_DAMPING     = 0.31625
SLIP_DAMPING        = 0.0008
TORQUE_FROM_PRELOAD = 526.882
BALL_RADIUS         = 10.0