Overdriving consists of applying a voltage that is higher than the steady state voltage for a short period of time to reduce the time that an actuator takes to transition from the rest state to the desired steady state (start-time) and from the steady state to the rest state (braking).
Overdriving can be achieved by careful manual tuning, but this process faces the same limitations as manual tuning for braking, and therefore is not the optimal solution. A closed-loop system can automatically overdrive and dynamically adjust to the actuator's changes to optimize the overdrive performance.
An alert effect with an LRA in a closed-loop with automatic overdrive and braking is show in Figure 3-4. The reduced start-time and brake-time when compared with performances such as the one shown in Figure 3-2, translate into a crisper and sharper haptic feel.