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Coulomb and Viscous Friction - Model discontinuity at zero, with linear gain elsewhere

Library

Discontinuities

Description

The Coulomb and Viscous Friction block models Coulomb (static) and viscous (dynamic) friction. The block models a discontinuity at zero and a linear gain otherwise. The block implementation is

y = sign(u) * (Gain * abs(u) + Offset)

where y is the output, u is the input, and Gain and Offset are block parameters.

The Offset corresponds to Coulomb friction. By default, the Offset is a vector with four elements: [1 3 2 0]. This default vector tests the same input value against four different offset values. You can specify a vector with a different number of elements, such as one.

The Gain corresponds to the signal gain for nonzero input values. By default, the Gain is 1.

The block accepts one input and generates one output. The input can be a scalar, vector, or matrix. For a vector or matrix input, the Offset and Gain must have the same dimensions as the input or be scalars. For a scalar input, the output will be a scalar, vector, or matrix based on the dimensions of the Offset and Gain. For example, passing a scalar input to the block when using the default Offset produces an output vector with four elements.

Data Type Support

The Coulomb and Viscous Friction block accepts and outputs real signals of the following data types:

• Floating-point

• Built-in integer

• Fixed-point

Parameters and Dialog Box

Coulomb friction value

The offset, applied to all input values. The default is [1 3 2 0].

Coefficient of viscous friction

The signal gain for nonzero input values. The default is 1.

Characteristics

Direct Feedthrough	Yes
Sample Time	Inherited from driving block
Scalar Expansion	Yes
Dimensionalized	Yes
Zero Crossing	Yes, at the point where Coulomb (static) friction is overcome

Constant

Counter Free-Running

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