Haptics provide mechanical feedback through the use of vibrations to simulate specific events, surfaces, and effects. It can simulate different surfaces and effects by varying frequency, amplitude, duration, and direction of a vibration.

Figure 1-1 illustrates three types of actuators, Eccentric Rotating Mass (ERM), Linear Resonant Actuator (LRA), and Piezo Actuator.

Figure 1-1 Three Types of Actuators

An LRA is a spring-mass system that vibrates in a linear motion. Inside, there is a coil suspended by springs and when voltage is applied, the coil generates a magnetic field. The coil interacts with the magnet and mass, whereas the magnetic field varies with the applied drive signal, the magnet and mass move up and down creating force. This movement is perceived as a vibration.

Noticeable vibrations only occur at the resonant frequency due to the spring constant. Linear actuators must be driven within a narrow band (±2 Hz) around the resonant frequency; otherwise it results in a drop-off of acceleration (see Figure 1-2). Due to manufacturing tolerance, component aging, temperature and mechanical mounting, the LRA’s exact resonant frequency varies. The DRV260x and DRV262x Drivers with auto-resonance function can detect the resonant frequency, helping increase acceleration performance.

Figure 1-2 LRA Resonant Frequency Drift

The LRA acceleration occurs in one axis because it vibrates in an up and down motion. This benefits an LRA to create more vibration strength and have more energy saving

Advantages:

• Faster response time than ERM
• Larger acceleration
• Higher efficiency

Disadvantages:

• Resonant frequency drift reduces acceleration
• Difficult to drive