How big is your LRA?

This is a guest post written by Matt Burns, who’s on the technical marketing team at Avnet Electronics. It’s the first in a new multi-author Haptics series we’ll be running here on Analog Wire.   

Haptic Feedback: How big is your LRA?

Have you ever had a friend or acquaintance ask, “How big is your LRA?”  Maybe you thought, “What is an LRA?” or “How big should it be?”  If you are work with haptics, these are good questions to ask.

LRAs, or linear resonant actuators, are used in smart phones, tablets and other devices to provide tactile feedback when the user touches the device.  We can understand LRA operation by considering a typical LRA assembly as shown in Figure 1.

A vibration occurs when a weight (Figure 1, Item 2) and magnet (Figure 1, Item 4) assembly moves when acted upon by a magnetic field generated by an electrified voice coil (Figure 1, Item 5). The mechanics of the weight/magnet assembly determines the resonant vibration frequency, which typically ranges between 175 – 235 Hz.  This movement provides faster response times and higher efficiency when compared to other haptic motor types.

Figure 1:  Typical LRA assembly

Many engineers don’t think about the size of their LRA, but there are several good questions that can be asked on this topic.  These include:

  • What size options are there?
  • Are there advantages or disadvantages to using a particular size device?
  • Where can I obtain an LRA?

Size options

Most LRAs are round in nature and are defined by their physical size. For example, “1030” refers to an LRA with a 10mm diameter and a 3.0mm height, “0934” measures 9mm x 3.4mm, and so on.  For more industry standard options, check out Samsung Electro-Mechanical’s LRA portfolio offered by Avnet.

Advantages and disadvantages

In general, the bigger the LRA, the larger the vibration force it will produce. However, the resonant frequency also has an effect. Like any decision, the tradeoffs between LRA size, vibration frequency and vibration strength need to be considered by application. 

In mobile devices and wearable electronics, component size is of the essence. An engineer may choose a smaller LRA with smaller vibration strength because a smaller tactile force may be acceptable for the application. If the LRA has a higher vibration frequency, it allows for small weight/magnet assembly.  This lowers LRA weight, lessens LRA energy consumption and increases LRA reliability and lifetime.

A concern with larger devices, like a touchscreen on an ATM, is how to generate enough vibration strength for the user to “feel” the feedback. An engineer may pick a larger LRA or an array of LRAs to achieve the vibration force needed to achieve the desired effect.

Where can I obtain an LRA?

Traditionally, LRAs and other haptics actuators have been targeted for high-volume, consumer device applications.  Mass-market OEMs have had few options to purchase this technology. However, Avnet has made it possible to gain access to this technology. Check out Samsung Electro-Mechanical’s LRA portfolio offered by Avnet.

Avnet also offers LRA modifications to custom-fit LRAs for any application. These modifications include:

  • Custom-length lead wire attachment
  • Lead wire connector attachment
  • Double-sided tape attachment
  • Prototyping and/or production volumes

Avnet also offers TI’s DRV2605EVM-CT as a complete evaluation and development platform for the DRV2605 LRA and ERM haptic driver. The platform provides touch-sensing and haptic drive with the Samsung LRA in an easy-to-use kit. Armed with this kit, Avnet’s field application engineers (FAEs) can demonstrate a complete haptics solution for any end application. Our FAE team has been trained to answer detailed information about Samsung’s LRAs and TI’s entire portfolio of haptic drivers.

For more information on this topic, check out my video “Enabling Haptics in Industrial Applications.”

Additional Haptics resources: