Nimrod Gileadi
aed4254d65
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48 lines
1.8 KiB
Markdown
48 lines
1.8 KiB
Markdown
# Actuator plugins
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## PID
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The `mujoco.pid` actuator plugin implements a configurable [PID controller](https://en.wikipedia.org/wiki/Proportional%E2%80%93integral%E2%80%93derivative_controller):
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$$f(t) = K_\text{p} e(t) + K_\text{i} \int_0^t e(\tau) \,\mathrm{d}\tau + K_\text{d} \frac{\mathrm{d}e(t)}{\mathrm{d}t},$$
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where $e(t) = u(t) - \ell(t)$ is the difference between the control $u$ and the actuator length $\ell$.
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You can use it like:
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```xml
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<mujoco>
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<extension>
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<plugin plugin="mujoco.pid">
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<instance name="pid">
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<config key="kp" value="40.0"/>
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<config key="ki" value="40"/>
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<config key="kd" value="4"/>
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<config key="slewmax" value="3" />
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<config key="imax" value="1"/>
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</instance>
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</plugin>
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</extension>
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<worldbody>
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<body>
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<joint name="j" type="slide" axis="0 0 1" />
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<geom size="0.01" mass="1"/>
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</body>
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</worldbody>
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<actuator>
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<plugin joint="j" plugin="mujoco.pid" instance="pid" />
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</actuator>
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</mujoco>
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```
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The available options are:
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|Attribute | Default | Meaning |
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|----------|---------|---------|
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|`kp` | 0 | **P** gain for the controller. |
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|`ki` | 0 | **I** gain for the controller.<p/>If nonzero, one activation variable will be added to `mjData.act`, containing the current I term (in units of force). |
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|`kd` | 0 | **D** gain for the controller. |
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|`imax` | Optional | If specified, the force produced by the I term will be clipped to the range `[-imax, -imax]`. |
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|`slewmax` | Optional | The maximum rate at which the setpoint for the PID controller can change.<p/>If a bigger change is requested between two timesteps, it will be clipped to the range `[ctrl - slewmax * dt, ctrl + slewmax * dt]`<p/>If specified, one activation variable will be added to `mjData.act` containing the previous value of `ctrl`. |
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