Touchscreens are rapidly gaining popularity as user input devices. As seen in certain applications (such as Apple's iPhone), a superior user interface can provide a significant competitive advantage. However, for other applications, challenges remain, such as security, entertainment distraction, and other usability issues. Users across all market sectors, including industrial, commercial, and consumer, are constantly seeking better human-machine interfaces. Currently, the latest technology in touch-activated interfaces is haptic feedback, which provides users with immediate and accurate confirmation. This feature is used to improve user performance and satisfaction. Furthermore, product designers can minimize functional complexity by providing intuitive haptic cues. This article will discuss how to add haptic feedback (haptic technology) to the touch-activated interface of a product. Current Status Touch interface systems capable of providing haptic feedback rely on actuators to generate tactile sensation. Advances in actuator and control technologies have enabled current actuators to support touch feedback on a wide range of touch panels and touchscreens, from very small to very large, covering products ranging from mobile phones to widescreen touch monitors. Additionally, the processor load required to support haptic systems is relatively small, touch input technology is already widespread, and electromechanical solutions are readily available. How It Works The common explanation for haptic technology used for touch-activated control is that the entire action of a button or switch must be perfectly replicated for it to be most effective. However, the sensory sensitivity of the human finger is not actually that low. Numerous studies have found that, when combined with appropriate acceleration, neurons in the human finger can detect very small movements. At accelerations above 1.5g, a movement as small as 0.1mm can be perceived as a confirmation response by humans. However, this minimum level of acceleration of 1.5g is insufficient to produce optimal haptic feedback. A more effective haptic feedback can be achieved by generating an acceleration and a displacement with a stronger stimulus. These accelerations and displacements can be seen in the "phase portraits" shown in this article. Phase portraits are generated after successfully integrating haptic technology into a haptic interface device electromechanically. Solution The architecture of a haptic feedback system typically includes: (1) an actuator, which can be a DC electromagnetic type or a large, custom-made device that must be correctly installed in the touchscreen; (2) haptic control software, which can be installed on a control board or embedded in the product's main processor; (3) a haptic effects library; and (4) a programmable interface that calls haptic effects from the main program. An incorrect implementation of any of these components can lead to the failure of the entire design. Execution Mechanism The best approach is to use actuators specifically designed to produce haptic effects, as repurposing a general-purpose motor and solenoid is extremely challenging. An actuator designed for haptic applications converts haptic signals from the controller into mechanical motion described by a specific phase diagram. Clearly, in addition to providing a good dynamic response, the selected actuator needs to meet stringent power, efficiency, and reliability specifications. Two actuators commonly used in mobile phones are also well-suited for small touchscreen products (diagonal length less than 7 inches). These are the eccentric rotary block motor (ERM) (shown in the photo) and the linear resonant actuator (LRA), in which a block vibrates between two magnetic poles. Products with larger screens, such as those ranging from 7 inches to 36 inches with touch interfaces, require larger actuators. The Immersion A100 and A300 are two such products. Figure 1: Displacement vs. Time for the A300 Actuator; Figure 2: Acceleration vs. Time for the A300 Actuator; Figure 3: Acceleration vs. Displacement in the A300 (Phase Diagram); Figure 4: The ERM motor uses an eccentric block to provide haptic feedback for small devices. The photo shows a miniature DC motor from Sanyo; Figure 5: A100 haptic actuator; Figure 6: A300 haptic actuator; Figure 7: Proper positioning and installation of the actuators will ensure that motion is effectively transmitted to the user's fingertips. All actuators should be optimized to generate significant force with minimal displacement, and these actuators should be carefully selected to meet performance and lifespan requirements. The type and number of actuators required by the design depend on the size, weight, and implementation scheme of the touchscreen or panel. Misusing simple solenoids and motors to produce haptic feedback often leads to poor implementation. Common problems in haptic systems include delayed or slow actuator acceleration, excessive displacement, or a lack of precise displacement control, often caused by the use of inappropriate actuator performance. Poor actuator installation is also a common issue. If poorly implemented, not only the touch interface itself but the entire system can resonate. While this might not be a major problem in handheld devices, it is a different story in fixed systems. Excessive resonance can have an effect akin to an earthquake, rather than a friendly confirmation indication. Other extreme consequences can occur if the installation configuration compresses the interface to the point where its acceleration and displacement are suppressed outside the detection point. Proper actuator installation effectively transfers displacement to the user's fingertips. The touchscreen display is mounted on a base and then flexibly sealed. The haptic actuator provides the main auxiliary device between the display and the base, allowing the touch surface to "float," thus transferring maximum energy to the fingertips. Control System Proper control of the actuator is achieved through software and circuitry, which primarily process touch input and provide the actuator with the correct instructions. Control instructions should be optimized for the relevant actuator technology and an ideal phase diagram that correctly confirms the user's input without distracting the user. Providing such a response requires selecting a processor with suitable drive output capability and 0.25 MIPS redundant processing capacity, as well as a suitable amplifier for the target actuator. The latency of the entire communication path (from user input to haptic response initiation) should be less than 30 ms. Haptic Effects Library The haptic effects library should include a variety of effects, allowing users to clearly distinguish the feel of various touchscreen controls and separate numerous functions. Ideally, the haptic development system should provide user interface designers with a convenient way to experience effects so they can select the best effects from the library. Programming Interface Calling haptic effects from the main program via a simplified API facilitates software integration. Software development tools are also useful. Immersion provides such tools, offering designers several programming options, including Windows ActiveX controls, cross-platform APIs in source code form, and communication support for custom interfaces. Sample code and a complete description of how to add haptic feedback to the main program are also included. Today's new haptic interfaces provide users with a more familiar, engaging, and satisfying user experience in touch-activated controls. Fortunately, haptic systems are now technologically mature, and electromechanical integration is widely adopted. Key elements of this emerging technology include actuator integration, installation, haptic control, and programming. When designing according to the guidelines outlined in this paper, we find that haptic systems offer significant advantages in terms of touch-activated control sensations, as well as intuitiveness, satisfaction, and natural user interaction.