Haptic Feedback and Vibration Alerting

Overview

Many products have to communicate with their owners, users and operators to function. For the last 100 years the main communication methods available have been audible or visual.

There are examples of this in almost every type of electrical equipment; computers beep when switched on, remote controls use LEDs to show a button has been pressed, and telephones ring. In many cases these notification methods are very effective, but there are many others where product functionality can be improved by augmenting our sense of hearing and sight with our sense of touch.

For example Electronic torque wrenches may be used in a noisy environment making the audible indicator ineffective, or in orientations where a visual indicator isn’t visible. In this example scenario, neither a buzzer nor an LED can be relied on to alert the operator of an event - e.g. the correct torque having been reached. Harnessing the operator’s sense of touch as a 3rd alerting method with controlled vibration is a practical and valuable solution.

Meanwhile, many every-day products are now being built with capacitive touch displays and interfaces. They’re cheaper to construct than control panels with discrete switches, and designers love the freedom to produce UI’s with unique shapes. But a big drawback is that capacitive interfaces offer no feedback that a ‘button’ has been pressed... there’s no longer a mechanical click or touch feeling of a switch being pushed. Haptics technology can simulate the feeling of pressing tactile switches.

Both vibration alerting and haptic feedback methods use eccentric rotating mass (ERM) vibration motors or linear resonant actuators (LRAs) to generate the touch sensations, but they are used in different ways.

Explaining the Difference Between Haptic Feedback and Vibration Alerting

Before looking at haptic feedback, also referred to as haptics, and vibration alerting methods in detail, we will first explain the difference between them.

Vibration alerting is based on using vibrating signals to inform the user of an event. Examples of this are common in mobile phones, or pagers, where the device vibrates when a message is received. This vibration ‘alerts’ the user to the event taking place. In many vibration alerting applications, vibration is used alongside (or as a discrete alternative to) audible or visual alerts.

Haptic feedback is more sophisticated than a simple event notification. It provides a user with tactile information through varying vibration strengths, frequency, and patterns. A good example of this is found in popular game consoles and capacitive touch panels. The controllers or panels will vibrate depending on the circumstances in the game, providing the user with additional information through touch.

Haptic Feedback Overview

The benefits of haptics can be enormous, and as a result,  it is a fast growing field of electronics. It can be applied to a wide range of products to improve user experience, increase productivity, increase safety, or provide other benefits depending on its implementation. For product manufacturers it is great way of differentiating from the competition, and for customers the extra dimension of tactile feedback can be essential.

The choices made in the design stage will greatly influence the user’s experience, as the vibrations may be required to accurately convey a wide range of information to the operator. With a combination of haptic feedback control processing, motor drivers, and vibration actuators all influencing the output, there are many areas to consider.

From the actuator's point of view, the enhancement of haptic experiences generally revolves around improving response times. Decreasing the actuator ‘rise and lag’ times give the user a ‘crisp’ feedback sensation. This can also enable designers to create more complicated patterns of vibration, and therefore communicate more information to the user. Depending on the type of vibration actuator, this is achieved in several ways.

For ERM vibration motors, simple H-bridge circuitry can quickly change the polarity of the voltage applied to the motor. As the polarity at the motor terminals controls the direction of the eccentric mass’ rotation, the technique of reversing the voltage to drive the motor in the opposite direction to its current rotation is called ‘active-braking’. This improves the lag time of the ERM motor. To improve rise times, DC motor circuitry sometimes use ‘overdrive’ techniques to apply a large initial voltage to quickly start the motor. Pulse Width Modulated (PWM) signals are often employed to generate the necessary drive signals from haptic processors.

Some processors use a PWM signal and H-bridge in conjuction where at 50% duty cycle puts the motor in a stationary state. Altering the duty cycle above or below 50% controls the motor’s speed and direction. This technique enables a single PWM signal to completely control the vibration actuator.

LRAs require a sinusoidal input with a frequency that matches their resonant frequency. This means their vibration amplitude can be easily controlled by changing the amplitude of the sinusoid driver signal. They typically have short rise times, and there are several drivers available that can drive both ERMs and LRAs.

Haptic feedback is being used in more and more applications; some typical markets include:

• Mobile phone and tablet PC touchscreens,
• Medical equipment, e.g. using robotics for surgery,
• Industrial and instrument equipment, e.g. electronic torque wrenches,
• Games consoles and their controllers,
• White goods,
• Car / Automobile dashboards.

Vibration Alerting Technology

Most notably, vibration is a standard feature in mobile phones as it takes advantage of the users sense of touch to relay information. Now in more and more products, designers are implementing similar vibrating communications to interact with the operator.

Vibration alerting is simpler and cheaper to implement than haptics as the system does not need to provide a great level of detail to the user, it simply needs to convey that an event has occurred.

Therefore the main considerations for design are the vibration amplitude and the power consumption. Vibration actuator ‘rise and lag’ times are not as important as with haptic feedback systems. We stock the widest range of vibrating motors available anywhere in the world, and many of our products are suitable for a range of vibration alerting applications, with a variety of vibration strengths and drive voltages.

Digital lines from application host processors can be used, or PWM signal control can also be used to altering the strength of vibration which may be desirable. Circuit-wise many vibration alerting methods can be implemented with a simple vibration motor drive circuit.

Vibration alerting became common place in mobile phones in the 1990s, and now can be found in a wide range of ubiquitous applications. Here are some examples:

• Pagers,
• Silent watches,
• Healthy living bracelets,
• Restaurants / cafes, hand held devices are given to customers which vibrate when their food is ready for collection,
• Handheld medical instruments and industrial equipment user interfaces.

Summary

Haptic feedback and vibration alerting functions offer different levels of information they provide to the user at different costs. Vibration alerting indicates an event has occurred, while haptics uses more advanced techniques to convey more information or better simulates tactcile swithes, through tactile feedback.

They are becoming popular in many new markets, with several haptics devices evolving from simpler vibration alerting models. The addition of haptic feedback or vibration alerting is a popular method for product differentiation and can help with a product’s competitive advantage.

Both technologies use similar actuators to mechanically produce the sense of touch, and Precision Microdrives offers the widest selection of both ERM and LRA vibration motors. Vibration feedback is easy to implement, whereas haptic feedback is more complex.

Precision Microdrives will be releasing a complete range of haptic feedback solutions in Q1 2012, which are aimed at making real haptic feedback as simple as possible to implement.