Existing Vibration Technologies
When product designers develop products that contain vibration, they find that there are no complete solutions available and that they must cobble together a variety of components from a limited number of technologies to create a solution. The results typically do not meet performance or size goals and require the designer to make painful compromises about the size or performance of their product.
Most people are surprised to learn that there are only a few available technologies to generate vibration response including:
ERM - Eccentric Rotary Mass Actuators
ERM motors are rotary motors with attached eccentric mass at a fixed amplitude. As current is supplied to the motor, it spins up and vibration is created as the eccentric mass rotates.
Vibrations are transmitted through the motor, and into the device, which causes the motor to wear out rapidly. Because of the dampening involved with the relatively large mass of the device, these motors tend to have limited frequency response.
These motors have highly variable performance between units, over the life of a battery, and over the life of a device and they tend to wear out quickly.
LRA - Linear Resonant Actuators
Linear Resonating Actuators are small actuators which are run at a single very high frequency with little power and a single-axis of operation. They require an expensive third-party driver chip to remain in resonance. These actuators have high costs and limited performance.
Piezoelectric actuators convert electrical energy to mechanical energy and have great performance properties, but they require high voltage for actuation, effectively limiting their use in battery-powered devices.
Apple® Taptic® Motor
In an effort to provide haptic functionality in Apple’s recent generation of laptops and watches, they developed the Apple Taptic vibration motor. This motor provides high lateral impact to provide haptic feedback. Production issues for the Apple Taptic motor was the cause of a six-week delay in the launch of the Apple Watch.
Alps® Haptic Reactor®
The Alps Haptic Reactor is a large actuator that is designed to provide haptic response for VR, AR and Gaming controllers. Alps claims that it provides two frequencies of response, 160Hz and 320Hz, but the higher 320Hz response is almost beyond human’s ability of perception; making it effectively a single speed actuator.
Motor Driver Technologies
Vibration motors and actuators are only part of a solution. ERM motors are typically brushed motors and require only a simple circuit. LRAs on the other hand, require an AC signal that matches their resonant frequency, so they require a more complex external circuit to be driven successfully.
Open Loop Drivers
The simplest driver for a LRA motor is an open loop driver. These drive send a an AC signal, at a predefined drive frequency, to the motor. They have not ability to determine the motor’s resonant frequency of the motor, which can change as much as +/-3Hz in a handheld device depending on how it is held. These systems are typically used with low-Q motors, like MPlus’s D40 motor, which is used in many Android based handsets.
Closed Loop Drivers
A closed loop driver is designed to determine the resonant frequency of the motor, so that it can send an appropriate drive signal. Most closed loop drivers use reverse-EMF signals to determine the actuator’s resonant frequency. Unfortunately, the reverse-EMF signal is noisy and weak, requiring expensive filtering and algorithms that are error prone. These systems poorly track resonance in small devices with large resonant frequency swings, resulting in a very expensive solution that provides poor haptic performance.
Existing haptic actuators and drivers have very limited performance, so existing haptic APIs are very simple; usually a single API that has a parameter to turn a motor on for a specific time. Software developers have difficulty using these APIs to develop vibration responses that are useful for more than notifying the device’s user that there is an issue; they cannot be used to convey information to the user.
Problems with Existing Vibration Technologies
Existing vibration technologies are the cause of many performance, cost and consumer satisfaction issues with products that contain vibration.
Existing Technologies Performance Issues
Limited Vibration Power
Limited Frequency Response
Slow Start/Stop Speed
Poor Unit-to-Unit Consistency
Existing Technologies Cause Size and Cost Issues
Actuator Size (particularly in the z-axis)
Poor Efficiency = Larger Battery
TI® and DRV® are trademarks of Texas Instruments Incorporated
Alps® and Reactor® are trademarks of Alps Electric Co. LTD.