• • • AUTOMOTIVE • • •
Exploring haptic feedback So, how does haptic feedback work? A basic haptic feedback system typically comprises three components: sensor, control system, and actuator. Sensors detect the stimulus, such as a finger on a touchscreen. This input signal is digitised by an analogue-to-digital converter (ADC) and sent to a microcontroller.
The microcontroller determines the frequency and amplitude required to generate the desired vibration effect and uses this information to control the actuators.
The actuators themselves generate the vibrations, with three actuator types to choose from. Eccentric rotating mass or ERM actuators were the traditional motor of choice. These motors spin an unbalanced mass to create an uneven centripetal force, which results in forward and backward movement as well as vibrations. Where cost is the major factor and resolution is not of huge importance, ERMs are still used in simple circuits.
More common nowadays is the linear resonant actuator, or LRA. These actuators use electrical currents and magnetic fields to move a mass up and down along a single axis, generating a vibration. Because these actuators don’t rely on inertia, LRAs have a much quicker response time than ERMs, making them ideal for automotive
applications when reactions must be as fast as possible.
Applications that require a low profile or a more compact actuator system might opt for piezoelectric effect actuators. These can operate at a wider range of frequencies and amplitudes compared to ERM and LRA actuators, allowing for a more precise vibration, ideal for touchscreens. They tend to have a higher power consumption, but can offer response times as quick as 1ms, compared to 40ms for ERMs and 20ms for LRAs.
Keeping control
When it comes to the control chip, the nature of these applications means that haptic devices must retain a tiny footprint. And while low power consumption isn’t essential in mains powered systems, for anything battery-operated, the system must be optimised for the lowest power usage possible.
Initial prototypes of haptic devices may be achieved using a variety of off-the-shelf ICs, but for a complete solution, opting for a tailored design offers the best possible user experience. This can be achieved with an Application Specific Integrated Circuit, or ASIC. ASICs are designed exactly to fit a customer’s specific requirements, resulting in a fully optimised chip. By removing unnecessary features and investing
in areas relevant to the chip’s application, ASICs can offer a much lower power consumption while maintaining high performance. This also results in a lower manufacturing cost per board, with a lower bill of materials and a smaller silicon area.
Custom ASIC design also means that companies can retain their IP. ASICs are extremely difficult to reverse engineer or re-use in other designs, making them valuable in setting your product and company apart from the competition. Non-obsolescence is another advantage that comes with the use of ASICs over standard ICs. ASIC suppliers will have non-obsolescence plans ready to ensure a continuous supply of chips for the lifetime of the product.
When it comes to automotive applications, the chip must be reliable if it is to improve the driving experience and safety. Design teams will integrate as much of the circuitry as possible into an ASIC, reducing the overall component count and therefore potential points of failure. As our cars become increasingly connected, making more use of current and emerging technologies, haptic feedback implementation is only going to grow. As we seek to optimise every aspect of the driving experience, it’s only right to take that approach right down to the component level if we want to build cars for the future.
38 ELECTRICAL ENGINEERING • FEBRUARY 2024
electricalengineeringmagazine.co.uk
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