The inevitable fact is that touch interactions within the user interface (UI) have rapidly spread over the
past decade, replacing many different forms of mechanically based UI. Interacting in this way is considered more intuitive and less likely to cause user frustration. The role of haptic technology is to bring touch control to a whole new level-allowing users to receive feedback about operations performed by mechanical vibration or other resistance. From this you can determine if the expected operation has been successfully completed.
There are many examples of daily use of haptics. For example, when operating in a racing game, the vibration on the game machine, and in "shooting up", it can mimic the shock wave generated by the explosion or the firearm recoil is fired, making these games more lifelike. Alternatively, it could be the vibration of a smartphone handset to indicate the receipt of a text message or an incoming call, or the vibration of a handheld device provided to a customer while waiting to sit in a restaurant to let them know that employees are ready to pick them up. To their table. Tactile sensors are now even incorporated into child care products, such as teethers.
As a result, tactile sensation provides a degree of sensory stimulation for individuals operating the UI-but how does this actually happen? The basic steps are as follows. When the user places his finger on a button displayed on the touch screen, the touch controller passes the corresponding touch point data to the system processor for processing. At the same time, the processor activates haptics. This in turn starts the motor, which then generates vibrations. The motor that generates the vibration needs to be driven by a suitable driver IC.
Classification of Haptic Motors
Currently, several different types of haptic motor actuator systems are used in UI design.
Eccentric Rotating Mass (ERM) Type-Rotates an unbalanced mass. The mass produces an asymmetrical centripetal force, which causes the motor to shift.
Cylindrical-similar to ERM, but larger, so slower response to vibration requirements. Neither the ERM type nor the cylindrical type is particularly durable.
Linear Resonant Actuator (LRA) Type-Relying on a spring to attach a magnet to the housing. The magnetic field from the coil induces vibrations (similar to how vibrational motion occurs in audio speakers, which can produce sound). Vibration is at a single frequency.
Compared with other cylindrical or ERM haptic solutions, LRA technology-based haptic technology has several key advantages-including more compact packaging, faster response time, and higher operational stability. Because of these features, LRA is particularly well-suited for modern portable applications-covering everything from smartphones and tablets to wearable electronics. The LRA method requires much less peripheral circuitry.
Figure 1. Basic structure of a linear resonant actuator (LRA).
Haptic driver solutions
In the past, haptic drivers were often implemented by implementing discrete solutions. These usually consist of a clock generator with two buffer amplifiers or a sine wave generator with an audio amplifier.
Figure 2. Discrete haptic driver based on a clock generator.
Figure 3. Discrete haptic driver based on a sine wave generator.
For clock generator haptic drivers, the buffer amplifier works with the clock generator to increase the amplitude of the output. They also help smooth the sharp edges of the applied voltage curve from the square wave output of the clock generator. This type of driver also has relatively high current consumption and requires a specific number of other external components. These factors hinder the applicability of the solution for space- and power-constrained applications such as handheld electronics.
With a sine wave generator haptic driver, the sharp edges of the clock generator driver are no longer an issue. This method provides a smoother response. The moving masses vibrate without hitting the sides. However, the number of external components involved again means that valuable board space must be allocated.
Despite the drawbacks of traditional haptic driver solutions, in the recent past, specialized, highly integrated haptic motor driver ICs have begun to be introduced. These ICs have certain key characteristics, such as their ability to change the frequency of the driver (which we will see as very advantageous), so they can surpass the performance of discrete sine wave generator and clock generator solutions.
Driving the LRA at a frequency that matches the resonant frequency (FR) of the motor will maximize the response of the haptic element of the UI. It must be noted that FR may actually vary as much as 1.0 Hz, depending on its orientation, ambient temperature or the material on which the LRA is lying. For example, the FR will be different if the product containing the LRA is held in the user's hand, resting on a hard surface, hanging from a belt, or in the user's pocket.
If the condition is insufficient actuated vibration, the vibration force can be increased by increasing the driving force or by adjusting the driving frequency to match the new resonance frequency. Obviously, it is more efficient if the FR can be tracked and the drive frequency adjusted accordingly to match the FR. Conversely, if the motor driver fails to coordinate it with the motor's FR, the resulting vibration intensity will decrease and additional power will need to be spent to make up for this deficiency.
Figure 4. Based on ON Semiconductor's LC89830x high-efficiency haptic driver, ON Semiconductor
realized that frequency modulation capability is of great value in haptic design. Therefore, ON Semiconductor has developed a high-efficiency LRA driver family. Energy pin. Due to the auto-tuning function, the LC898300, LC898301 and LC898302 can automatically adjust the driving frequency to reflect changes in the motor driving frequency. This can increase the perceived vibration force by more than 20%, making it far more effective than traditional haptic drive solutions.
These devices can generate the same level of vibration force as the sine wave drive method, but consume 20% less current. They do this by halving the on / off time of the drive current. By rounding the corners on the output, you can eliminate audible noise. In addition, the braking function allows the vibration to be switched off more quickly. This means it can be used to provide a wider range of haptic effects, opening up new possibilities for UI designers. In addition, they only require a separate external bypass, which reduces board space usage and reduces overall bill of materials costs-both are important in space-constrained, cost-sensitive consumer electronics designs. These drivers were originally configured using the I2C interface,
Figure 5. Comparison between square wave and LC89830x drive profile
Haptics effectively makes touch interaction two ways. They provide feedback to those operating electronic devices to ensure that the system has received the required input and prevent potential errors. Alternatively, they can be used to mimic certain actions to enable a significantly better user experience. By combining them, and with the support of optimized drive technology, you can create more advanced touch-based UI solutions that provide greater engagement and stand out from standard touch-enabled UIs.
