## FrictionBristle:

Path: SC/Actuator

```% Friction model. This model uses a bristle state.

F    = sigma0*z + sigma1*zDot + sigma2*v

zDot = v - |v|*z/g(v)

g(v) = (fC + (fS - fC)*exp(-(v/vS)^2))/sigma0;

The maximum damping coefficient |v|/g(v) is an input. This prevents
numerical instabilities. When the damping coefficient is set to the
maximum value and

zDot = max(|v|/g(v))*(zSS - z)

so it damps to the equilibrium value which is

zSS = sign(v)*g(v)/sigma0

The maximum damping constant should be set to a number that is
consistent with the time step. For example: 1/dT.

--------------------------------------------------------------------------
Form:
[zDot, f, cDamp] = FrictionBristle( z, t, d )
--------------------------------------------------------------------------

------
Inputs
------
z			  (:)     State
t       (1,1)   Time (not used)
d			  (:)     Data structure
.v         - velocity
.fStatic   - Static friction
.fCoulomb  - Coulomb friction maximum
.vStribeck - Stribeck velocity
.sigma0    - Bristle stiffness
.sigma1    - Bristle damping
.sigma2    - Viscous friction coefficient
.maxC      - Maximum damping constant

-------
Outputs
-------
zDot          (:)    Bristle state derivative
f             (:)    Friction
cDamp         (:)    The damping coefficient

--------------------------------------------------------------------------
```

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