Three mainstream haptic feedback technologies: What is the difference between ERM, LRA, and piezoelectric?

ERM, LRA, piezoelectric tactile comparison

LRA haptic solutions have significantly improved performance than ERM motors, and they can achieve higher acceleration; therefore LRA can create stronger haptic feedback than ERM solutions (larger acceleration values = stronger haptic feedback). However, although LRA has higher acceleration than ERM motors, it still has the same problem compared to lower-cost alternatives-they require moving masses to generate vibration.

Although LRA can reach its optimal frequency peak faster than ERM motors (here we are talking about 25ms instead of 50ms), they still need some time to accelerate or decelerate to the optimal frequency peak. Piezoelectric actuators can reach the best peak within 2ms, and the almost instantaneous acceleration makes it better and more efficient than LRA in terms of feedback strength. The LRA used in mobile devices can reach accelerations of 1 to 1.7G, and piezoelectric actuators of similar size can reach accelerations of 2.5 to 5G.

LRA consumes more power than piezoelectric actuators plus CapDrive piezoelectric actuators.

Compared with ERM motors, another advantage of LRA is lower power consumption, which is more suitable for battery-powered mobile devices. In fact, LRA has been the most effective haptic solution for many years. Before the release of CapDrive technology, LRA was even more efficient than piezoelectric haptics.

However, compared with piezoelectric actuator ICs that integrate CapDrive piezoelectric drivers, LRA consumes 4 to 10 times higher power; now it’s time to reconsider which haptic technology will be used in battery-powered devices.

LRA provides better haptic feedback than ERM motors, but does not have HD haptic technology

ERM motors can produce inaccurate rumbles, while LRA can produce clearer tactile feedback; this is mainly because the latter has better acceleration.

LRA produces clearer tactile feedback than ERM, mainly due to their resonant frequency; resonant frequency refers to a narrow frequency range in which you can obtain the best vibration to amplify the acceleration and displacement of the mass of the actuator.

Although the feedback generated by LRA is clearer than ERM, the resonance frequency range is very narrow. Since the LRA frequency range is quite limited, their bandwidth is not large and it is difficult to create different tactile effects. However, although the performance of the LRA is better than the ERM motor, it cannot achieve the unlimited frequency range of the piezoelectric actuator, and you are still using the limited LRA. On the other hand, piezoelectric actuators offer unlimited possibilities for various tactile effects.

LRA response time is faster than ERM motors, but slower than piezoelectric actuators

LRA provides better tactile performance than ERM motors. The second factor behind it is its faster response time. Just like ERM actuators, LRA requires moving mass to generate haptic feedback. Although they do have shorter response times than their low-cost alternatives, it still takes 25ms for the LRA to reach its optimal frequency range, as does the deceleration period after the haptic effect.

Piezoelectric actuators can begin to exert their tactile effects within 2ms, providing the possibility of creating clearer and precise tactile feedback.

Use piezoelectric integrated pressure sensing to save hardware

Another advantage of the CapDrive piezoelectric haptic driver architecture is the integrated piezoelectric pressure sensing. The BOS1901 piezoelectric driver IC can sense pressure from the same piezoelectric actuator and generate haptic feedback; this means that when your application requires pressure sensing (such as button replacement), you can remove the previously used pressure sensing hardware from the design .

LRA takes up more space than piezoelectric actuators

LRAs are smaller in size than piezoelectric actuators, and they are generally considered to be more suitable for small devices, but when the size of the actuator is considered, it is completely different.

Like ERM actuators, LRAs are larger in size than piezoelectric actuators with similar acceleration (feedback strength). The space saved by piezoelectric actuators will far exceed the space lost by integrating piezoelectric actuators. For example, BOS1901 only needs 7 passive components to operate.

CapDrive piezoelectric IC vs. LRA (*The mass is 100 grams. The acceleration is related to the feedback strength. Higher numbers = stronger feedback)

If you want to know more, our website has product specifications for ERM, LRA, and piezoelectric, you can go to ALLICDATA ELECTRONICS LIMITED to get more information