Command Element

Description

The Force_JointFriction command can be used to modify the parameters of the Force_JointFriction 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, , in the joint.

MU_STATIC > 0.

mu_dynamic

Specifies the dynamic friction coefficient, , 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:

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

Thus:

Options available per joint type are as defined below:

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.

Command Element

Description

The FRICTION command can be used to modify the parameters of the FRICTION model element.

Declaration

def FRICTION(id, LABEL="", MU_STATIC=0.0, MU_DYNAMIC=0.0,  STICTION_TRANSITION_VELOCITY=0.0, MAX_STICTION_DEFORMATION=0.0, INPUTS="", FRICTION_FORCE_PRELOAD=0.0, REACTION_ARM=0.0, INITIAL_OVERLAP=0.0, OVERLAP_DELTA="", FRICTION_TORQUE_PRELOAD=0.0, FRICTION_ARM=0.0, PIN_RADIUS=0.0, BENDING_REACTION_ARM=0.0, BALL_RADIUS=0.0):

Attributes

id

Element identification number (integer>0).  This number is unique among all the FRICTION elements.

LABEL

Modifies the string containing the FRICTION element description.

MU_STATIC

Modifies the static friction coefficient in the joint.

MU_STATIC > 0.

Default: NONE

MU_DYNAMIC

Modifies the dynamic friction coefficient in the joint.

MU_DYNAMIC > 0.

Default: NONE

STICTION_TRANSITION_VELOCITY

Modifies the real value of the absolute velocity below, which the friction transitions from dynamic friction to static friction.

Default = 0.1 length/time.

MAX­_STICTION_DEFORMATION

Modifies the maximum deformation that can occur in a joint for static friction.  If specified to be non-zero, a finite static friction force is applied even if the relative velocity is zero.

Default = 0.01 length units

INPUTS

Modifies the 4-bit integer value and specifies the input forces to the friction model.  By default, all of the preload and joint reaction forces are included.  Valid values are 0 or 1 for each bit.

Default: 1111.

There are four choices to be made:

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

Thus:

Options available per joint type are as defined below:

FRICTION_FORCE_PRELOAD

Modifies the preload friction force for Translational and Cylindrical joints.

Default: 0.0 force units

REACTION_ARM

Modifies the moment arm of the reaction torque about the Translation joint axial axes.

Default: 1.0 length units

INITIAL_OVERLAP

Modifies the initial overlap of the sliding parts in Translation and Cylindrical joints.

Default: 1000.0 length units

OVERLAP_DELTA

Modifies the 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.

Default: CONSTANT

FRICTION_TORQUE_PRELOAD

Modifies the preload friction torque for Revolute, Cylindrical, Universal, and Spherical joints.

Default: 0.0 force*length units

FRICTION_ARM

Modifies the moment arm used to compute axial friction torque in revolute, universal joints.

Default: 1.0 length units

PIN_RADIUS

Modifies the radius of the pin for Revolute, Cylindrical, Hooke, and Universal joints.

Default: 1.0 length units

BENDING_REACTION_ARM

Modifies the moment arm to compute the bending moment in Revolute, Hooke, and Universal joints.

Default: 1.0 length units

BALL_RADIUS

Modifies the radius of the Spherical joint.

Default: 1.0 length units

Comments

See Force_JointFriction

Example

The example below shows how a FRICTION element can be modified.

FRICTION(1, MU_STATIC=0.5, MU_DYNAMIC=0.3, INPUTS="1011")

Example

<Force_JointFriction

    id                  = "1"

    mu_static           = "0.5"

    mu_dynamic          = "0.3"

    inputs              = "1011"

/>