Control Dependent Drift (CDD)
This classification describes the drift of the resonance
frequencies measured in the unloaded state of different
input voltages and in the loaded state, respectively.
Load Dependent Drift
Load Dependent Drift (LDD)
This classification describes the bandwidth of the resonance frequencies measured between the unloaded and
loaded state of the same input voltage.
Mechanical Power Classes
Mechanical Power
Class (MPC)
This classification describes the dominant frequency
range of the maximal mechanical power output of
LRAs in relation to its mechanical peak output. For
ERMs, the input voltage of the rising edge in the mechanical power curve is described with this classification.
Power Density
Power Density
(PD)
This classification describes the relation between the
component’s installation size in volume and its maximum power output.
Power Linearity
Power Linearity
(PL)
This classification describes the proportionality of the
distribution of the maximal mechanical power output
in relation to the input voltage of LRAs and its deviation from linearity.
Resonance Bandwidth
Resonance Bandwidth (RB)
This classification describes the bandwidth of frequencies at the half-power point for a single input voltage
in both the unloaded and loaded states, respectively.
Signal to Noise Ratio
Signal-to-Noise
Ratio (SNR)
This classification quantifies the distortion in the relationship between the input signal and the cleanliness
of its reproduction, reflecting the fidelity of the output
signal to the original input.
The paper explores the critical role of vibrotactile actuators in haptic feedback systems proposing a novel physics-based test methodology resulting in seven comparable key-performance indicators to cover all relevant dynamic effects to create a decisive fingerprint of the devices. The method employs simple idle and blocked measurements easy to be implemented and reproduced. It was verified with 26 actuators, including linear resonant actuators (LRA) and eccentric rotating mass motors (ERM). The study highlights several hidden and not frequently discussed effects. For example the load dependency of actuators, where changes in load significantly affect resonance frequency and output force amplitude. Additional findings include the inadequacy of acceleration alone as a performance metric, advocating for mechanical power output as a more reliable measure. Three clusters according to dominant frequencies were found in the data ($<$100 Hz, 100–200 Hz, $>$200 Hz). Furthermore power densities are discussed, with smaller actuators, such as ERMs demonstrating higher power density relative to their volume while at the same time elaborating on their low signal-to-noise ratio. This study is conceived as a practical demonstration aiming at addressing the challenges posed by the lack of standardized characterization methods and incomplete datasheet information for vibrotactile actuators, which hinder the comparability of results. The results can furthermore be used for improved physical modeling and performance evaluation of vibrotactile actuators in a design-context of system analysis.
