What Is Velocity Control? How Robots Regulate Speed.

What Is Velocity Control?

Velocity control is a control method that regulates how quickly a motor, joint, wheel, or other moving component travels.

Instead of commanding only a target position, a velocity controller attempts to maintain a specified rotational or linear speed.

For example, a mobile robot may use velocity control to regulate its wheel speeds while following a planned route.

Velocity control is common in motor drives, conveyors, autonomous mobile robots, and industrial equipment.

Key Takeaways

• Velocity control regulates movement speed, usually using feedback or another suitable control method.
• It is different from position control, which regulates location, and torque control, which regulates turning effort.
• Velocity-control performance depends on motor capabilities, load, feedback, and controller tuning.

How Does Velocity Control Work?

Imagine a mobile robot traveling along a warehouse aisle.

Its navigation software commands a forward speed.

The robot's motion system converts that command into suitable wheel-speed targets.

Encoders measure how quickly the wheels are rotating.

A velocity controller compares the measured speed with the target.

If one wheel rotates more slowly than intended, the controller can adjust its motor command to reduce the difference.

The process repeats as the robot moves.

This helps the robot respond to changes in load and other disturbances.

How Is Velocity Measured?

Linear velocity describes displacement per unit of time.

It is commonly measured in meters per second.

Angular velocity describes the rate of rotation.

It is commonly measured in radians per second or revolutions per minute.

For example, a wheel rotating at 60 RPM completes one revolution per second.

Its angular velocity is approximately:

6.28 radians per second

If the wheel radius is 0.1 meters and there is no slipping, the wheel's linear rolling speed is approximately:

6.28 × 0.1 = 0.628 meters per second

In actual mobile robots, wheel slip can cause ground speed to differ from the value calculated from wheel rotation.

Velocity Control vs. Position Control

Position control: Regulates where a mechanism moves.

Velocity control: Regulates how quickly it moves.

For example, a robotic arm may use position control to reach a specific joint angle.

A conveyor may use velocity control to maintain a target belt speed.

The methods can also operate together.

A position controller may generate velocity commands that a lower-level controller follows.

Velocity Control vs. Torque Control

Velocity control regulates speed.

Torque control regulates rotational effort.

Imagine a robot wheel climbing a gentle slope.

A velocity controller attempts to maintain the commanded wheel speed.

It may increase the required motor effort to compensate for the added load.

A torque controller, by contrast, attempts to maintain a specified torque.

The resulting speed may change with the load.

The distinction matters when selecting control methods for different applications.

What Is a Velocity Control Loop?

A velocity control loop repeatedly compares desired and measured speed.

For example:

Velocity Error = Target Velocity − Measured Velocity

Suppose a motor's target speed is 100 RPM.

Its measured speed is 90 RPM.

The error is:

100 − 90 = 10 RPM

A controller uses the error to calculate a suitable corrective command.

Depending on the architecture, the output may be a torque, current, or other motor-control request.

Why Does Velocity Control Matter for AMRs?

Autonomous mobile robots need to coordinate several moving components.

For example, a differential-drive robot changes direction by adjusting the relative speeds of its left and right wheels.

If both wheels move at the same speed, the robot can travel approximately straight under suitable conditions.

If the wheel speeds differ, the robot turns.

Velocity control helps execute the desired motion.

However, the complete navigation system must also account for localization, obstacles, and mechanical limits.

What Are the Limitations?

Velocity feedback can be noisy, particularly at low speeds or when encoder resolution is limited.

Sudden speed changes can also require excessive acceleration or torque.

Controllers therefore need suitable limits and tuning.

For example, commanding an immediate increase from zero to maximum wheel speed may exceed the motor's available torque or produce undesirable wheel slip.

Higher-level software can limit acceleration to create more manageable movements.

Frequently Asked Questions

Does velocity control require an encoder?

Closed-loop velocity control needs a suitable speed measurement or estimate, which may come from encoders or other methods.

Can a robot control speed and position at the same time?

Yes. Nested control systems often use position commands together with lower-level velocity or current control.

The Bottom Line

Velocity control regulates how quickly robot components move. It is a fundamental capability for wheels, joints, conveyors, and other mechanisms that must maintain predictable speed despite changing operating conditions.