Haptics and Force Feedback

When you teleoperate a robot, you cannot feel what it touches unless the system sends the forces back. Force feedback, or haptics, lets the operator feel contact, so they push gently instead of crushing things. But sending forces both ways over a delayed link creates a feedback loop that can oscillate, so delayed haptic systems need extra damping or passivity control.

Send contact force back to the operator Network delay (each way) Extra damping (passivity)

Bilateral teleoperation

The operator's device position $x_m$ is sent to the remote robot, which tracks it. When the robot touches the wall, the contact force $F_e$ is sent back and the device pushes on the operator's hand:

$$x_s(t) \to x_m(t - T) \qquad F_m(t) = -k_f\,F_e(t - T) - b\,\dot x_m$$

With round-trip delay $2T$, the force arrives after the hand has already moved, which can pump energy into the loop. Damping $b$ and passivity-based controllers remove that extra energy.

What to notice

Without feedback, the operator keeps pushing because they feel nothing, and the contact force climbs high. With feedback and low delay, the operator feels the wall and the force settles at a gentle level. Raise the delay, and the force bounces, contact and release, contact and release. Adding damping calms it, at the cost of a more sluggish feel. Haptic teleoperation is used for surgery, bomb disposal, and space robotics, where delay is the main challenge.