Haptic touch applications represent a change in how people interact with machines. Human interfaces featuring haptics are in development for industrial systems, robotics, automobiles, home appliances, point-of-sale and order entry systems, new forms of training simulation, and remote equipment.
Just about everywhere that people have to touch a screen or operate some other kind of electronic control, haptics has a role to play. Simulated tactile experiences are not only important for our pleasure and ease of use – they can add new functions, provide useful new information, enhance control, improve safety of operation, and enable new forms of product differentiation.
Figure 1: Haptic actuators help achieve vibrations by employing the piezo effect
The underlying semiconductor technology that enables haptics is available, inexpensive and easy to design with. As system designers and manufacturers discover how adding haptic features can benefit their products, they will use integrated circuits (ICs) to create applications with simulated tactile feedback to make our interaction with equipment seem more natural.
Taking back control
As electronic control systems replace older mechanical ones we lose the sensation associated with touching, sliding, turning, pushing, pulling and otherwise manipulating the system and feeling it respond. Haptic features simulate this feedback, so that a completely electronic human interface is experienced as if it were a familiar mechanical or electromechanical control.
For example, a video gamer knows how it feels to turn a car with a steering wheel and mechanical linkage, but a steering wheel on a plastic panel feels nothing like that unless haptics in the system simulate the drag of turning. Similarly, touchscreens don’t feel anything like mechanical keypads unless haptics provides some sort of clicking or bumping sensation for the finger when a key is pressed (with perhaps an audible “click” to reinforce the idea through another sense).
Haptic feedback has been extensively incorporated in simulated training for systems where operation is complex and needs to be executed flawlessly. For example, aircraft pilots train extensively in simulated cockpits before they fly a new type of plane. As important as it is for the pilots to learn the procedures and “see” out of the cockpit windows with video simulation, they also need to learn how the plane feels in response to the controls. Haptics helps to provide these sensations, so that when the time comes to sit in a real cockpit, the pilot knows how to use the controls, but also how the plane and controls feel in operation.
Haptic feedback is also used in training for surgery, where it adds the sense of touch to 3D graphic visualisation. Surgeons get a sense of how the tissue feels, and they learn to operate in tight spaces where the body pushes back against their hands and instruments. For laparascopic surgeries and other forms of endoscopy, simulated training with haptic feedback is crucial for learning how to use the tiny instruments involved. In some experimental cases, expert surgeons are using simulation tools with haptics – aided by live video, monitoring instrumentation and a support staff with the patient – to perform real surgeries at distant sites.
New uses for haptics
Simulated training represents the high end of haptic application, where system cost is less critical than achieving something difficult but indispensable. In contrast, with mass-market items such as smartphones, tablets and video games, doing something innovative matters, but must have minimal effect on the price.
Today, the frontier of haptic application is between these extremes, where some increase in price will afford tactile features that can extend a product’s function, make it easier to use, increase safety or otherwise differentiate it. Such applications are found in robots and other equipment for transport, building automation, home appliances, commercial systems, office equipment, and products where users can benefit from haptic interaction with machines.
Among the most promising applications for innovation is keypad input, where flat electronic keys have been displacing mechanical keys for years. For example, consider a worker on an assembly line who may need to input data into a flat-screen panel while keeping an eye on different gauges, instruments, products moving on the line, and other functions. They have to stop watching everything else to look at the panel and push the right series of buttons, risking missing an event or making mistakes from visual overload. It would help matters if the panel offered some non-visual feedback to help the worker register that the data entry is correct. Adding sounds for buttons may not help in a noisy factory, but bumping sensations can report by touch whether the data is being entered.
Consider how useful it would be in the home to sense tactile feedback from the buttons on the smooth keypad of a microwave oven if you need to use it in the dark, or to confirm through fingertip feedback that you’ve found the right controls on the complicated dashboard of a rental car. Haptic features help to provide these experiences and others, such as:
- Giving a waiter a tactile response when selecting a menu item via a touchpad
- Making a computer touchpad feel more as if it is tracking over a solid surface
- Providing directional movement sensations for pointing devices like a computer mouse or TV remote control
- Giving control sensations in the steering wheel and driver’s seat of a car
- Adding subsonic vibration to headphones to enhance the physical sensation of deep bass sounds.
Seemingly simple haptic sensations can have significant applications: the same kind of physical resistance that a video gamer feels in moving a joystick can also help the remote operator of a machine used in hazardous rescue, exploration, mining, manufacturing and other environments where humans cannot go safely.
Applying haptics in new areas will create demand for more sophisticated forms of tactile experience. Online shoppers may be able to feel the difference between fabrics through the touchpad. This technology is not in place yet, but new areas of application for haptics are creating a market environment that will favour its development.
Technology for haptics
While the psychology of tactile simulation and its interpretation can be complex, creating haptic effects is relatively straightforward. Controls like joysticks convey haptic information through shaking and bumping, as well as through resistance that can increase, decrease or stop movement altogether.
On flat surfaces such as touchscreens, effects can be created through whole-body vibration, where the entire surface shakes, as with an alarm or ring vibration on a smartphone. By contrast, local vibrations slightly, briefly deform the surface where it is touched, creating an apparent bump or dip under the fingertip. Some systems are appearing that can move the deformation along to lead or follow the fingertip. The brain interprets the resulting sensation in a way that corresponds to feeling a button pressed, a knob sliding or a different surface texture.
Figure 2: How haptic effects are created
Size and vibrating requirements determine the type of actuator that the system uses to create its haptic effects: whole-body effects can be created by an electric rotating mass (ERM), which is a small rotating motor with an off-centre mass that spins at various speeds to create vibrating effects. Button or key effects in fixed positions use an array of linear resonant actuators (LRAs), which are spring-mass systems that vibrate up and down in response to changes in a magnetic field.
More complicated local vibrations can be achieved with actuators that employ the piezo effect (Figure 1) – the tendency for certain materials to change shape when a voltage is applied. Piezo actuators enable precision control of high-definition haptics and are being increasingly used for novel effects in touchscreens, including the sensation of friction or texture recreation. Since the piezo effect is two-way, with deformation creating a voltage as well as voltages deforming the materials, piezo devices are capable of serving for sensing as well as actuating, so that the same device handles both pressure input and tactile output. The devices are very thin compared with other actuators, giving them an advantage in low-profile systems such as keyboards.
Haptic system components
The elements of a haptic system (Figure 2) include a sensor-switch, such as a key on a touchpad, which accepts the external input stimulus and sends a signal to the system microcontroller (MCU). In addition to its other processing functions, the MCU generates an output waveform, which a driver amplifies to the appropriate voltage and sends to an actuator. In the actuator an appropriate mechanical vibration for the bump, click, swipe or other movement is created. The only devices added for haptic effects are the driver and actuator. Other devices are already part of the system, which also requires software for the MCU to generate the waveform as a constant voltage, sine-wave or pulse-width modulate or (PWM) driven waveform, depending on the actuator type and properties.
Haptic devices themselves must feature a high level of integration and a small footprint, since a human interface is limited in scale, however large the system it is meant to control. In handheld, battery-operated applications, extremely low-power consumption is essential – a feature that is beneficial in wired systems as well, though less significant.
Since haptic technology is a new area of design for almost everyone, the IC hardware has to be easy to design into new systems and to add to existing ones, and the software must be straightforward to operate using standard MCU interfaces. Because technology applications are growing, system developers need haptic solutions from IC providers who will continue to offer more advanced options.
TI haptic solutions
Figure 3: Haptic actuators help achieve vibrations by employing the piezo effect
As a leading provider of analogue technology, including sensors and drivers for system interfaces, TI has developed an extensive portfolio of solutions to help system developers introduce differentiated haptic features in their products quickly and economically. TI haptic drivers support ERMs, LRAs and piezo actuators that can be used for applications ranging from hand-held consumer electronics to industrial robots, from intelligent building management to the latest cars.
Unlike traditional motor drivers, these devices are designed specifically for driving haptic actuators, simplifying the design process by eliminating unnecessary functions and their software controls. All parts needed for haptic driving are already integrated, including the high voltages required for piezo actuators (Figure 3). Any type of touch input can be used, so the drivers can adapt to new applications.
Essential features for haptic effects are designed into the drivers to improve performance and simplify design. These include automatic closed-loop feedback to improve response from ERMs and every actuator; and auto-resonance detection to sense the resonant frequency of LRAs. Ready-made waveform effects such as clicks, buzzes and ramps come with the drivers, and the developer can create custom waveforms to make software prototyping easy.
Integrated diagnostics simplify design speed up testing for manufacture. TI’s manufacturing process technologies keep power requirements for its haptic drivers to the minimum needed for full functionality.
TI has reference designs for applications including personal, domestic and industrial products, and collaborates with third parties on additional system design and integration support. The company believes that its research effort will keep it well positioned to support new developments such as polymer-based actuators and haptic effects based on electrical stimulus.
Brian Burk is applications manager at the haptics business unit of Texas Instruments
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