Haptic Sensor Basics: Types and Comparison

This page introduces the fundamentals of haptic sensors and compares different types. It covers:

• Linear Resonant Actuators (LRAs)
• Eccentric Rotating Mass (ERM) Vibration Motors
• Piezo Haptic Actuators

“Haptic” refers to the sense of touch. This technology provides feedback to electronic devices like smartphones and tablets, typically using vibration. The most common actuators used for haptic feedback are linear resonant actuators and eccentric rotating mass vibration motors.

Therefore, we can broadly categorize haptic sensors based on these actuator types.

Haptic Sensor Types

Let’s explore the principles behind these different sensor types.

Linear Resonant Actuators (LRAs)

These sensors operate based on the movement of a mass, causing repeated displacement in a single direction (linear movement). The principle is similar to how a loudspeaker works.

A loudspeaker produces audio waves proportional to displacement. However, unlike a loudspeaker designed for a broad range of frequencies, an LRA is tuned to operate at a specific resonant frequency.

LRA haptic sensors use magnetic fields and electrical currents to generate force. Unlike loudspeakers, the voice coil remains stationary while the magnetic mass moves.

In the sensor’s design, the mass is attached to a spring that helps it return to the center position. Driving the magnetic mass up and down causes displacement, creating the vibration force in the LRA haptic sensor.

Eccentric Rotating Mass Vibration Motors (ERMs)

These sensors generate vibrations in two perpendicular directions relative to the rotation axis. An ERM sensor has an off-center load. The rotation of this load creates a centripetal force that causes the motor to move, producing vibrations.

Rotation is achieved by applying current to the armature windings attached to the motor shaft. This creates a force that makes the shaft rotate.

To ensure continuous rotation in the same direction, the current in the windings is reversed using static metal brushes that connect to a commutator. The commutator rotates along with the shaft and windings.

Comparison Between Haptic Sensors | How Haptic Sensor Technology Works

Image showing how haptic technology works