------What's the best tactile feedback,refer to last article------

1. http://www.coin-motor.com/mod_article-article_content-article_id-215.html
2. http://www.coin-motor.com/mod_article-article_content-article_id-216.html

New Favorite of High end Electronic Equipment: LRA Tactile Technology

LRA motor

 

From the previous discussion, we have seen that if you need a low-cost solution, vibration motors are a good choice, but they have limited feedback quality and can produce low-end rumbling sounds, which are not clean and clear tactile effects. Therefore, advanced electronic device manufacturers have shifted their attention in recent years to another tactile technology - linear resonant actuators (LRA motor).

 

LRA is currently used in many devices to achieve better tactile feedback than ERM solutions; Compared to ERM, they have higher acceleration, faster response time, and clearer tactile feedback. LRA, like ERM motors, is also based on mass motion. The difference is that the mass hangs on the spring and moves up and down under the action of a magnetic field.

Function	ERM	LRA	piezoelectricity
Acceleration(g)	0.6	1.7	2.5
Power consumption	High	Middle	Lower
Start time（ms）	50	25	0.3
Area size	Big	Big	Micro
Integrated force sensing	No	No	Yes
HD tactile feedback	No	No	Yes

LRA has different external dimensions, some are rectangular, while others are circular; Some manufacturers even develop their own LRA versions to achieve better results (refer to tactile engine), but how do they compare to piezoelectric tactile sensors? Let's take a look!

ERM, LRA, piezoelectric tactile ratio one to one

LRA tactile solutions significantly improve performance compared to ERM motors, as they can achieve higher acceleration; Therefore, LRA can create stronger tactile feedback than ERM solutions (larger acceleration values=stronger tactile feedback). However, although the acceleration of LRA is higher than that of ERM motors, they still have the same problem compared to low-cost alternatives - they require moving mass to generate vibration.

Although LRA motors can reach their optimal frequency peak faster than ERM motors (25ms instead of 50ms), they still require some time to accelerate or decelerate to the optimal frequency peak. The piezoelectric actuator can reach its optimal peak within 2ms, and the almost instantaneous acceleration makes it better in feedback strength and more efficient than LRA. LRA used in mobile devices can achieve an acceleration of 1 to 1.7G, while piezoelectric actuators of similar sizes can achieve an acceleration of 2.5 to 5G. 

LRA consumes more power than piezoelectric actuators combined with CapDrive piezoelectric actuators.

Another advantage of LRA compared to ERM motors is its lower power consumption, which is more suitable for battery powered mobile devices. In fact, LRA has been the most effective tactile solution for many years, and before the release of CapDrive technology, LRA was even more efficient than piezoelectric tactile.

However, compared to piezoelectric actuator ICs that integrate CapDrive piezoelectric drivers, LRA consumes 4 to 10 times more power; It's time to reconsider which tactile technology will be used in battery powered devices.

LRA provides better tactile feedback than ERM motors, but does not have high-definition tactile technology

ERM motors can produce inaccurate rumbling sounds, while LRA can generate 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 the acceleration and displacement in a narrow frequency range where you can obtain the optimal vibration to amplify the mass of the actuator.

Although the feedback generated by LRA is clearer than that of ERM, the resonant frequency range is very narrow. Due to the limited frequency range of LRA, their bandwidth is not large and it is difficult to create different tactile effects. However, although the performance of LRA is superior to that of ERM motors, it cannot achieve the infinite frequency range of piezoelectric actuators, and you are still using a limited LRA. On the other hand, piezoelectric actuators offer infinite possibilities for various tactile effects.

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

The second factor behind LRA providing better tactile performance than ERM motors is its faster response time. Like ERM actuators, LRA requires moving mass to generate tactile feedback. Although they do indeed shorten the response time compared to their low-cost alternative products, LRA still requires 25ms to reach its optimal frequency range, and the deceleration period after tactile effect is also the same.

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

Utilizing Piezoelectric Integrated Pressure Sensing to Save Hardware

Another advantage of the CapDrive piezoelectric tactile driver architecture is the integrated piezoelectric pressure sensing. BOS1901 piezoelectric driver IC can sense pressure from the same piezoelectric actuator and generate tactile 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 occupies more space than piezoelectric actuators

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

Like ERM actuators, LRA sizes are larger than piezoelectric actuators with similar acceleration (feedback strength), and the space saved by piezoelectric actuators will far exceed the space lost by integrating piezoelectric actuators. For example, BOS1901 only requires 7 passive components to operate.

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

 

With better performance technologies such as piezoelectric tactile technology, tactile technology is entering a new era.

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