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Interaction Force Control
A comparison of two fundamental approaches to force control in robotics: Impedance Control and Admittance Control.
Impedance vs Admittance Control
| Aspect | Impedance Control | Admittance Control |
|---|---|---|
| What you command | Force/torque | Motion (position/velocity) |
| What you measure | Motion (q, ẋ) | Force/torque |
| Core idea | Robot behaves like a virtual spring–damper–mass | Robot moves according to a virtual mechanical system driven by force |
| Typical equation | τ = K(x − x_d) + D(ẋ − ẋ_d) |
Mẍ + Dẋ + Kx = F_ext |
| Needs force sensor? | Not required | Usually required |
| Best for | Torque-controlled robots | Position-controlled robots |
Intuition
Impedance control: "I push back with a force proportional to how much you deform me."
Admittance control: "If you push me with a force, I will move accordingly."
Key Takeaways
- Impedance control outputs force based on measured motion - ideal for torque-controlled robots
- Admittance control outputs motion based on measured force - ideal for position-controlled robots
- Both achieve compliant robot behavior but through opposite input/output relationships