What Is Admittance Control? How Robots Respond to External Forces.

What Is Admittance Control?

Admittance control is a robotics control method that adjusts a robot's movement in response to an external force.

Instead of requiring a robot to follow a rigid trajectory regardless of contact, admittance control allows it to move according to how strongly and in what direction it is pushed.

For example, a worker guiding a robotic arm by hand may be able to push it gently toward a desired position. The robot senses the applied force and commands movement in that direction.

This makes admittance control useful for physical human-robot interaction and tasks where machines need to respond to contact.

Key Takeaways

• Admittance control converts measured external forces into commanded movement.
• It is often implemented on robots that already have accurate position or velocity controllers.
• The robot's response can be adjusted to behave as though it has different levels of mass, damping, or stiffness.

How Does Admittance Control Work?

An admittance controller measures an external force, often using a force-torque sensor.

The controller then calculates how the robot should move in response.

Its calculations typically use a virtual mechanical model representing properties such as mass, damping, and stiffness.

Imagine pushing a heavy shopping cart.

A heavier cart requires more force to accelerate, while friction and other resistance affect how easily it moves.

Admittance control can create similar behavior in a robot through software.

Engineers can adjust the virtual properties so the robot responds more freely to gentle forces or resists movement more strongly.

The resulting motion command is sent to the robot's lower-level controller.

Admittance Control vs. Impedance Control

These two approaches are closely related but work in opposite directions.

Admittance control measures force and calculates the movement that should result.

Impedance control defines how a robot should generate or respond with force when its motion differs from a desired mechanical behavior.

Both approaches can make robots behave more compliantly during contact.

The distinction is particularly relevant to the robot's control architecture. Admittance control is often attractive for systems with established position-control loops.

Where Is Admittance Control Used?

Applications include hand-guided robot teaching, rehabilitation devices, collaborative manipulation, and certain assembly operations.

For example, a worker may guide a robot through a task by applying force to its arm. The control system interprets that force and moves the robot accordingly.

The responsiveness must be carefully configured. Poorly selected controller settings, sensor noise, or unexpected contact can produce unstable movement.

Frequently Asked Questions

Does admittance control require a force sensor?

It requires information about external forces, but this may come from a dedicated sensor or from appropriate force-estimation methods.

Does admittance control make a robot safe to touch?

Not automatically. Safe human-robot interaction also depends on the robot's hardware, operating limits, protective measures, and application-specific risk assessment.

The Bottom Line

Admittance control allows robots to translate physical forces into controlled movement. It is particularly valuable when machines need to interact with people or objects rather than simply follow fixed paths.