Coulomb And Viscous Friction — Control Systems/Discontinuities
Control_Systems/Discontinuities/Coulomb_And_Viscous_Friction · 1 input / 1 output port(s) at insert · exports to Python, MATLAB, Java, Rust, C, C++, VHDL, Verilog, SystemVerilog, PLC Structured Text
Description#
The block's own DESCRIPTION_HTML, rendered verbatim — the same text the config dialog's info panel and the library navigator show. Fix a wrong sentence in the block's .cpp (R-D9), never here.
Coulomb & Viscous Friction
Control Systems / Discontinuities
Models friction as a function of velocity: y = sign(u) · (gain · |u| + offset). The viscous term grows with speed, the Coulomb term is a constant break-away force that flips sign with direction – so the curve jumps by 2 · offset across the origin. Applied entry by entry, so a matrix signal is treated element for element.
Ports
- Input – the velocity u, of any size [m,n].
- Output – the friction force y, of the SAME size [m,n]. The block never reshapes a signal.
Parameters
- Coulomb Friction Value – scalar, the constant break-away magnitude (the offset at zero velocity). Defaults to 1.
- Coefficient of Viscous Friction – scalar, the slope of the speed-proportional term. Defaults to 1.
- Sampling Time (s) – zero or less inherits the solver's rate; a positive value runs the block at that period. This one is ICore-side only – see the bridge note below.
Both parameters are scalars. Simulink's block accepts a VECTOR offset
(its default is [1 3 2 0]), giving one friction curve per signal
element; that form is not implemented here and is reported rather than
broadcast from its first entry.
Code export
All ten targets: Python, MATLAB, Java, Rust, C, C++, VHDL, Verilog, SystemVerilog and PLC Structured Text. Both parameters are baked into the generated code as constants at export time. Every target emits the three-branch form rather than calling a sign/abs pair, so no target needs a library function for it.
Simulink bridge
Import and export, mapped to
simulink/Discontinuities/Coulomb & Viscous Friction.
"Coulomb Friction Value" to offset and "Coefficient of Viscous
Friction" to gain – both lowercase, as the mask defines them.
"Sampling Time (s)" does NOT cross: this Simulink block has no
SampleTime parameter at all, so the rate stays on the ICore side
and an explicitly set one is reported rather than written.
Notes
- Algebraic, with no state.
- At exactly zero velocity the output is zero, not ±offset: sign(0) = 0. That is the same convention Simulink uses.
- Not linear, and so deliberately carries no state space – model reduction reports it as unmergeable rather than absorbing the jump.
Code facts#
| Fact | Value |
|---|---|
| registered type | Control_Systems/Discontinuities/Coulomb_And_Viscous_Friction |
| family | Control_Systems/Discontinuities |
| solver environment class | ICoreBlock_0_Control_Systems_1_Discontinuities_2_Coulomb_And_Viscous_Friction |
| source | src/ICoreSDK/ICoreBlockLibrary/Blocks/Control_Systems/Discontinuities/Coulomb_And_Viscous_Friction/ICoreBlock_0_Control_Systems_1_Discontinuities_2_Coulomb_And_Viscous_Friction.cpp |
| header | src/ICoreSDK/ICoreBlockLibrary/Blocks/Control_Systems/Discontinuities/Coulomb_And_Viscous_Friction/ICoreBlock_0_Control_Systems_1_Discontinuities_2_Coulomb_And_Viscous_Friction.h |
| default size on canvas | 70 × 70 px |
| ports at insert | 1 in, 1 out |
| code generators implemented | Python, MATLAB, Java, Rust, C, C++, VHDL, Verilog, SystemVerilog, PLC Structured Text |
Ports#
| # | Direction | Signal type | Description label |
|---|---|---|---|
| 1 | in | ICoreDouble | — |
| 2 | out | ICoreDouble | — |
Ports the constructor creates. A block whose port list changes with its configuration adds or removes ports at load time; the count above is the one a freshly inserted block has.
Configuration variables#
| Config variable | Default | Simulink parameter |
|---|---|---|
Coulomb Friction Value | 1 | offset |
Coefficient of Viscous Friction | 1 | gain |
Every block also carries Sampling Time (s) from ICoreBlockSolverEnvironment: zero or less inherits the solver's rate, a positive value runs the block at that period.
Simulink bridge#
| support | Support::Both |
| Simulink path | simulink/Discontinuities/Coulomb & Viscous Friction |
| port-count rule | PortsParam::None |
SampleTime parameter | no — the counterpart defines none; the rate stays on the ICore side |
| ICore config | Simulink parameter | Value translation |
|---|---|---|
Coulomb Friction Value | offset | passes through |
Coefficient of Viscous Friction | gain | passes through |
Caveat (shown to the user): the block runs at the surrounding Simulink rate; "Sampling Time (s)" does not cross
Catalog contract: src/ICoreSDK/ICoreCoder/ICoreCommandSystem/SimulinkBridge/ICoreSimulinkBlockCatalog.h
Description vs code#
The lists agree. check_block_descriptions.py finds no disagreement between the description's Ports, Parameters, Code export and Simulink bridge lists and the code's.
The verdict above is
tools/docs/check_block_descriptions.py(P7.1), which compares LISTS. It cannot read a sentence: "stateless" on a block with a state, an initial-value semantic the recursion does not implement, a "not synthesizable" caveat the HDL banner contradicts. That is the agent audit (P7.3) on BLOCK_DESCRIPTION_AUDIT.md, and this tool's green is not a substitute for one.
File banner (developer view)#
The top comment of the block's .cpp — the maths, the realization and the export strategy, addressed to whoever changes it. It must not contradict the description above (P7.5).
Coulomb & Viscous Friction block — per-entry friction curve y = sign(u) * (gain * |u| + offset), which expands branch-free of abs/sign to u > 0 : gain*u + offset u < 0 : gain*u - offset u = 0 : 0 The 2*offset jump across the origin is the discontinuity. Algebraic and stateless, and deliberately carries no state space (see the header).
Simulink's mask parameters are lowercase
offsetandgain, and the block has NO SampleTime parameter -- verified against the R2026a block dialog, hence hasSampleTimeParam = false on the catalog entry.
Sample results#
| t | in ICoreDouble-Out-0 | out ICoreDouble-Out-0 |
|---|---|---|
| 0 | -2 | -3 |
| 0.4 | 0.5 | 1.5 |
| 0.8 | -2 | -3 |
| 1.2 | 0.5 | 1.5 |
| 1.6 | -2 | -3 |
| 2 | 0.5 | 1.5 |
| 2.4 | -2 | -3 |
| 2.8 | 0.5 | 1.5 |
| 3.2 | -2 | -3 |
| 3.6 | 0.5 | 1.5 |
| 4 | -2 | -3 |
| 4.4 | 0.5 | 1.5 |
| 4.8 | -2 | -3 |
| 5.2 | 0.5 | 1.5 |
Every 4th of 60 samples, from the table stimulus.
The same rig also ran:
| Stimulus | What it is | Output range |
|---|---|---|
impulse | Impulse: one sample of 1 at k = 5, 0 elsewhere (Repeating Sequence Stair) | 0 … 2 |
ramp | Ramp: slope 1 from t = 0 | 0 … 6.8 |
sine | Sine Wave: amplitude 1, 2 rad/s, no phase, no bias | -2 … 2 |
step | Step: 0 -> 1 at t = 1 s | 0 … 2 |
Plotted: table — Repeating Sequence Stair: [-2 -1 -0.5 0 0.5 1 2 3], one entry per sample
Category static · sample time 0.1 · 60 steps · commit ccf005c8 · produced by docsSample --out <folder> --steps 60 · data docs/generated/samples/Control_Systems__Discontinuities__Coulomb_And_Viscous_Friction.json · the SVG is generated from those numbers by tools/docs/plot_svg.py, so it is a run and not a drawing (R-D10).