Knob

Virtual stiffness and damping

You might say: impedance gains

Virtual stiffness K maps displacement from an equilibrium to a restoring force; damping D adds a velocity-dependent term.

What it does

It sets how compliant the robot feels and how quickly contact force grows with displacement.

Ask

What force will the robot apply if the target is 1 cm inside the surface?

Typical

libfranka documents Cartesian stiffness/compliance and gives an impedance example with 150 N/m translational stiffness and 10 Nm/rad rotational stiffness.

What to look for

1. Displacement from equilibrium
2. Restoring force
3. Contact force growing with displacement
4. Push response at a stiffness setting

Catalogue: Stiffness

• Soft: 200 N/m is a low translational stiffness example; a 1 cm displacement gives about 2 N before other terms.
• Medium: 1000 N/m is a middle-of-range translational stiffness example; a 1 cm displacement gives about 10 N before damping.
• Stiff: 3000 N/m is an upper translational stiffness example; a 1 cm displacement gives about 30 N before damping.

Connections

• Measured by: Force-torque sensor

Sources

1. Franka Robotics, libfranka: cartesian_impedance_control.cpp, Example introductionAfter starting the controller try to push the robot around and try different stiffness levels.
2. Franka Robotics, libfranka: franka::Robot Class Reference, setCartesianImpedance parameter boundsSets the Cartesian stiffness/compliance (for x, y, z, roll, pitch, yaw) in the internal controller.

Use it on your project

teardown-apply: hold "Virtual stiffness and damping" (stiffness) from the teardown at https://teardownatlas.com/robotics/ against my project

Paste it into a coding agent that has the teardown skills.

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