# A Numerical Study of the Vibration Characteristics of a Haptic Actuator for a Dial Gear Shifter
###### Abstract  
Human-machine interaction (HMI) is becoming increasingly important, especially in the automotive industry, where advancements in automated driving and driver assistance systems are key to enhancing driver safety and convenience. Among the many HMI interfaces, tactile sensing has been widely used in automotive applications as it enables instant and direct interactions with drivers. An area that remains underexplored among the tactile HMI interfaces is the application of haptic feedback to gear shifter modules. Therefore, this study investigates the design optimization of a dial gear shifter by analyzing the vibrations transmitted to the knob surface from an integrated haptic actuator. Specifically, we first tuned the mechanical properties of the haptic actuator (in terms of the resonance frequency and vibration level) in a simulation model by referring to experimental results. Next, a numerical model of a dial gear shifter was constructed, integrated with a haptic actuator, and tuned with the experimental results. The model was further optimized based on the design of the experiment and sensitivity analyses. The optimized design yielded a 24.5% improvement in the vibration level compared with the reference design, exceeding the minimum threshold (\(\sim\)-2.5 m/s\({}^{2}\) at 200 Hz) required for tactile sensing. The vibration enhancement (\(\gtrsim\)22.x%) was also confirmed under the simulated hand-grabbing condition. This study is technically significant as it demonstrates that the haptic vibration in a dial gear shifter can be efficiently optimized through numerical analyses. This research will be used for the actual prototyping of a dial gear shifter to provide a safe driving experience for drivers. haptic actuator; finite element analysis; design optimization; dial gear shifter; transducer design; human-machine interaction +
Footnote †: journal: Applied  
Accepted: 8 October 2024  
and pressure [10, 11]. For example, haptic actuators are embedded in most mobile phones and can produce tactile feedback through which users recognize incoming calls or the arrival of important messages. In the automotive industry, the role of haptics has become increasingly important in various application fields because it can alter traditional feedback methods such as audio or vision. Audio feedback can be missed owing to the atmospheric noise that occurs while driving, and visual feedback can be missed while the driver concentrates on the outer driving environment. In contrast, haptic feedback can provide more effective attention to drivers under emergency conditions, such as impending collisions, unrecognized penetration into another driving lane, and unexpected jaywalkers [12, 13]. A crucial technical advantage of haptics is that it can directly interact with human tactile sensations as long as the user touches a part of the machine. When driving a car, the driver must grip the steering wheel, place their feet on the pedals, and fasten the seatbelt while sitting on the car seat, all of which can play a role in the pass-through of haptic feedback [14, 15, 16]. Hence, haptics in cars can immediately and efficiently convey important information to drivers by using the vibration sensations of humans, which are less affected by the external environment. For decades, several haptic assistance systems have been introduced in the automobile industry to ensure safe driving. Vibration stimulation on the dashboard can significantly reduce eyes-off-road time and decrease the potential for an accident while driving [17, 18]. A steering wheel with haptic actuators can provide reference information to drivers for efficient steering movements while parking or while driving [19, 20]. Haptics can aid in augmenting car safety by providing warnings during emergencies. For example, drivers can be made aware of potential collisions through tactile sensations [21]. Moreover, warning signals for sudden lane departures or violations of speed limits can be communicated via haptics [22].