Haptic Actuators: Design Considerations
There are six design considerations that must be accounted for when selecting a haptic actuation solution:
Mass of the surface to excite: The mass of the surface has a direct relationship to the strength and feel of the haptic effect. The haptic system must be designed with a proper suspension system to not only mechanically support the physical mass it is fastened to it (please not that the haptic actuators are not designed as a load supporting component), but it must also be designed with an understanding of the natural frequency that the end haptic effects will be created around
Heavier masses will tend to have lower natural frequencies while lighter masses will tend to have higher natural frequencies if the suspension system is not correctly designed.
Strength of the effect: The strength of the effect is measured in g’s and should be designed with the operating environment in mind. Higher ambient vibration environments like off high vehicle applications have a very high ambient vibration level while applications such as ATMs located in a bank lobby have low ambient vibration levels. The strength of the effect should be higher than that of its surrounding environment so the end user can differentiate it from the ambient level vibrations surrounding the machine.
Please note that it is not recommended to incorporate more than two actuators into the same system and that a more efficient mechanical system can be achieved by selecting one, correctly sized actuator for the job.
Power budget: The power budget should be commensurate with the mass of the surface and the strength of the effect. High mass surfaces that require a high strength effect will require more power to excite. It is important to note that the on time of the input drive signal for these actuators is measured in milliseconds and that these actuators are not rated for continuous duty. This means the instantaneous power required for haptic effects will be much different than the RMS values actually experienced and drive circuits should be designed accordingly.
Effect Feel: The feeling of the effect relates to the output frequency and crispness of the effect and the Johnson Electric haptic actuators are capable of producing high definition effects. Differentiated haptic effects require an actuator that can output effects over a wide frequency range while crisp haptic effects require an actuator with a fast response time. Designers should consider the type of effects suited for the HMI that will give the end user confidence without an unwelcomed feeling. While it is possible to have several effects available to help the end user differentiate between different buttons or tasks associated with the HMI, the ability to achieve differentiated effects is greatly dependent on the mass of the surface, how strong the effects need to be and the available power to create them. Direction of the vibration should also be considered when designing a haptic system knowing that the same mechanical vibration is perceived differently if it is experienced in an axis 90° to its original orientation.
Packaging envelope limitations: The Johnson Electric haptic actuators are not intended to be used as load bearing devices. These units are typically designed into a floating surface that is already in balance with support from a flexible suspension system. Each actuator has its own footprint and mounting options. Care should be taken to incorporate each actuator according to its design intent. If the packaging constraints to not allow for an actuator to be used, Johnson Electric can design a haptic system that eliminates the need for separate actuators to be utilized.Sound: The sound of the effect is just as important as the feel of the effect. Often times the sound of the effect is overlooked or left to be optimized after the system has been designed. Sound itself is a vibration that is comprised of different amplitudes and frequencies and should be gaged against the operating environment that the HMI will placed in.. When haptic actuators are powered, the energy from the system is employed in the movement and vibration that make up the haptic effect. Any energy that remains as the result of poorly timed effects or inefficient mechanical design will be experienced as an elevated operating sound.