Force: Joint Friction

Command ElementThe Force_JointFriction command can be used to modify the parameters of the model element.

Format

Revolute Joint
<Force_JointFriction
  id                         = "integer"  
  [ mu_static                = "real" ]
  [ mu_dynamic               = "real" ]
  [ max_stiction_deform      = "real" ]  
  [ stiction_trans_vel       = "real"]  
  [ inputs                   = "4-bit integer" ]     
  [ torque_preload           = "real" ]
  [ friction_arm             = "real" ]
  [ bending_reaction_arm     = "real" ]
  [ pin_radius               = "real" ]
/>
Spherical Joint
<Force_JointFriction
  id                         = "integer"
  [ mu_static                = "real" ]
  [ mu_dynamic               = "real" ]
  [ max_stiction_deform      = "real" ]
  [ stiction_trans_vel       = "real"]
  [ inputs                   = "4-bit integer" ] 
  [ torque_preload           = "real" ]
  [ ball_radius              = "real" ]
/>
Translational Joint
<Force_JointFriction
  id                         = "integer"
  [ mu_static                = "real" ]
  [ mu_dynamic               = "real" ]
  [ max_stiction_deform      = "real" ]
  [ stiction_trans_vel       = "real" ]
  [ inputs                   = "4-bit integer " ]  
  [ force_preload            = "real" ]
  [ reaction_arm             = "real" ]
  [ initial_overlap          = "real" ]
/>
Cylindrical Joint
<Force_JointFriction
  id                         = "integer"
  [ mu_static                = "real" ]
  [ mu_dynamic               = "real" ]
  [ max_stiction_deform      = "real" ]
  [ stiction_trans_vel       = "real" ]
  [ inputs                   = "4-bit integer" ]
  [ force_preload            = "real" ]
  [ torque_preload           = "real" ]
  [ pin_radius               = "real" ]
  [ initial_overlap          = "real" ]
/>
Universal Joint
<Force_JointFriction
  id                         = "integer"
  [ mu_static                = "real" ]
  [ mu_dynamic               = "real" ]
  [ max_stiction_deform      = "real"]
  [ stiction_trans_vel       = "real"]
  [ inputs                   = "4-bit integer" ]
  [ torque_preload           = "real" ]
  [ friction_arm             = "real" ]
  [ bending_reaction_arm     = "real" ]
  [ pin_radius               = "real" ]
/>

Attributes

id
Element identification number, (integer > 0). This number is unique among all Force_JointFriction elements.
mu_static
Specifies the static friction coefficient, s), in the joint.
MU_STATIC > 0.
mu_dynamic
Specifies the dynamic friction coefficient, d), in the joint.
MU_DYNAMIC > 0.
max_stiction_deform
Specifies the maximum deformation that can occur in a joint for static friction or stiction regime.
stiction_trans_vel
Real value of the absolute velocity below, which the friction transitions from dynamic friction to static friction.
inputs
A 4-bit integer value that specifies the input forces to the friction model. By default, all the preload and joint reaction forces are included. Valid values are 0 or 1 for each bit.
There are four choices to be made:
  • 1st bit: Preload
  • 2nd bit: Reaction_Force
  • 3rd bit: Bending_Moment
  • 4th bit: Torsional_Moment

Setting a 0 or 1 for each bit of the input's value controls individual inputs.

Thus:
  • 1111 - All four inputs are included
  • 0000 - None of the four inputs are included
  • 1000 - Only include Preload
  • 1101 - Include Preload, Reaction_Force and Torsional_Moment, but not Bending_Moment
  • 1001 - Include Preload and Torsional_Moment, but not Reaction_Force and Bending_Moment
Options available per joint type are as defined below:
  • Translational - Preload, Reaction_Force, Bending_Moment, Torsional_Moment
  • Cylindrical, Revolute, Universal, Hooke - Preload, Reaction_Force, Bending_Moment
  • Spherical - Preload, Reaction_Force
force_preload
Specifies the preload friction force for Translational and Cylindrical joints.
torque_preload
Specifies the preload friction torque for Revolute, Cylindrical, Universal and Spherical joints.
friction_arm
Specifies the moment arm used to compute axial friction torque in revolute, universal joints.
reaction_arm
Specifies the moment arm of the reaction torque about the Translation joint axial axes.
bending_reaction_arm
Specifies the moment arm to compute the bending moment in Revolute, Hooke and Universal joints.
pin_radius
Specifies the radius of the pin for Revolute, Cylindrical, Hooke and Universal joints.
ball_radius
Specifies the radius of the Spherical joint.
initial_overlap
Specifies the initial overlap of the sliding parts in Translation and Cylindrical joints.
overlap_delta
Specifies friction characteristics in the sliding joint.
INCREASE - Overlap increases as the I Marker translates in the positive direction of the z-axis of the J Marker.
DECREASE - Overlap decreases in the positive direction of the J marker.