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Linear Resonant Actuator (LRA) Vibration Motors :: Haptic Feedback

Overview

Within our Precision Haptic™ range of vibration motors, we offer several types of Linear Resonant Actuator (LRA) vibration motors, which are also known as linear vibrators. LRA motors are different to Eccentric Rotating Mass (ERM) vibration motors, in the way they work, they way that they are used, and how long they last.

If you have an application that requires a durable vibration, or a high confidence MTBF rating, consider our Linear Resonant Actuator vibration motors as an alternative to long life brushless vibration motors. But, understand that that longer life and control does come at a slightly increased cost of complexity - continue reading to find out more.

General Construction for a Y-axis LRA Linear Vibrator

  • Precision Microdrives Y-axis LRA Linear Vibrator Motor
  • Precision Microdrives Y-axis LRA Linear Vibrator Motor

The illustration above shows the general arrangement of parts within a Y-axis LRA vibration motor. Those readers familiar with audio engineering will note that the voice coil drive is very similar to that loud speaker. However, instead of a cone that generates sound pressure waves, there is a mass that generates vibrations.

Below is another LRA which works in the same way, however the vibrations are directed in only the Z-axis. This offers users a greater choice in design as they can produce vibrations in either horizontal or vertical directions.

  • Precision Microdrives Z-Axis Linear Resonant Actuator

A magnetic field is generated by the voice coil which interacts with the magnet & mass, which are suspended on a spring. As the magnetic field varies with the applied drive signal, the magnet & mass are moved up and down as they interact with the spring.

Resonant Frequency of Operation

  • Linear Vibrator LRA Resonant Frequency Bode Plot
  • Linear Vibrator LRA Resonant Frequency Bode Plot

Again, those readers familiar with vibration, RF, or audio engineering, will quickly spot that attaching a mass to a spring causes a resonance effect. The combination of spring stiffness, mass and magnet / coil size will cause the linear vibrator to have a natural resonant frequency.

This natural resonant frequency is where the LRA is most efficient in its operation, as can be seen by the output amplitude vs frequency on the bode plot above for our C10-100 Linear Resonant Actuator.

Typically for Y-axis vibrators resonant frequencies are around 175 Hz.

Driving Linear Resonant Actuators / Linear Vibrators

LRA linear vibrators needs to be driven with an AC signal, much like a loud speaker. It's preferable that this signal is a sinewave at the resonant frequency as shown below.

  • Linear Vibrator Driving Waveform
  • Linear Vibrator Driving Waveform

The driving waveform can of course be amplitude modulated to generate more advanced haptic feedback effects.

Take a read of our application bulletin about driving LRA vibration motors to learn more.

Extended Lifetime for Linear Vibrators

Unlike most vibration motors which have a mechanical commutation, LRA vibration motors are effectively brushless; commutation being via a voice-coil. This means that there the only moving parts that are prone to failure are the springs. These springs are modelled with finite element analysis (FEA) and are operated within their non-fatigue zone.

With little mechanical wear, failure modes are restricted to aging of internal components which results in much longer MTBF failure modes than traditional brushed eccentric rotating mass (ERM) vibration motors.

We also sell an increasing range of brushless ERM motors which offer long-life vibration in two planes rather the single plane offered by the LRA motors.

C10-100 - 10mm Linear Resonant Actuator - 3.6mm Type C10-100
Precision Haptic
Dia.: 10 mm
Voltage: 2 V
Amplitude: 1.4 G
Min Ordr Qty: 1+
See Specs & Prices

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Quick Vib. Estimator

For calculating theoretical vibration output from ERM parameters.

Motor speed (rpm)
Normalised amplitude (G) *
Target Mass (g)
Vibration Force (N)
Acceleration (G) *
Vib. displacement (mm) *
* peak-peak