Mechanical interfaces

In this subsection the mechanical interfaces are introduced. We classified those technologies into this group, which require mechanical impact from the driver, which could be the following:

• Press by hand, finger or foot

• Pull, slide or rotate by hand

• Touch by hand or finger

3.1.1. Pedal, lever

Beside the steering wheel the pedals are the basic primary inputs in an automobile. As mentioned in the earlier sections electronic throttle control solutions are commonly used in today‘s road vehicles.. The driver feeling of the ―traditional‖ accelerator pedal can be substituted with a simple spring, because it requires only a constant pressure force. Furthermore the electronic pedal gives the possibility to use haptic feedback, such as vibration or variable pedal force to support the economic driving.

In conventional passenger cars the brake pedal is connected to the brake system via a rod in the hydraulic cylinder. Brake-by-wire systems are increasingly being integrated into or replacing conventional hydraulic or pneumatic brake systems. Such electrical brake systems are preferable because they reduce the mass of the system and provide greater ability to integrate the system into the vehicle's other electronic circuits and controls.

In hybrid cars it is essential because of the electronic braking by the driving motor. During depression of the brake pedal in a conventional hydraulic braking system, the hydraulic fluid will exert a force back on the brake pedal due to the hydraulic pressure in the brake lines. Since an electronic brake system may not have such hydraulic pressure at the brake pedal, the vehicle operator will not detect any countering force, which in turn can disorient the operator. Accordingly, a typical electrical brake system will include a brake pedal feel simulator to provide a simulation force on the brake pedal. The simulation force provided by the simulator acts opposite the brake pedal force generated by the vehicle driver. It has to be noted that the brake pedal simulator has to suit to the different driving situations especially during emergency. The system has to adjust automatically its operation to reduce or eliminate the simulation force during emergency or failure conditions. (Source: [52])

The clutch pedal is usually hydraulic also, and exists only in vehicles with manual gearbox. It doesn‘t require such developments as mentioned above, because with the use of automatic, automated or semi-automatic gearboxes the clutch pedal itself is eliminated.

Traditionally one mechanical lever exists in vehicles, i.e. the parking brake lever. In European vehicle designs it is operated by hand (hand-brake) but in the US the parking brake is generally operated by the left foot. In modern vehicle the parking brake lever is often substituted by a push button or a fully automatic parking brake.

3.1.2. Steering wheel

The steer-by-wire system (mentioned in Section ―Intelligent actuators‖) is also an enabler of good haptic HMI systems as it provides as much design freedom as possible, because the characteristics of the steering wheel are dynamically independent from the front axle steering. For example, a vibration induced in the steering wheel for warning purposes in a mechanically decoupled steer-by-wire systems can be designed with no effect on the actual steering behaviour at the front wheels.

3.1.3. Button, switch, stalk, slider

With the help of these components the driver can activate/deactivate or set the vehicle‘s primary and secondary functions. These switching components could be single buttons or switches for each function, a stalk or a slider.

Figure 4.6. Indicator stalk with cruise control and light switches (Source:

http://www.carthrottle.com/)

3.1.4. Integrated controller knob

The integrated controller knobs are such input devices which integrate more input functions into one device to support the much easier and more intuitive handling of the vehicle. These input functions could be rotation, push/pull and 4-way joystick.

A typical example is the BMW iDrive as mentioned in Section Input channels4.2.2.1, but a lot of simpler utilizations exist, such HVAC and radio control knobs.

Figure 4.7. Integrated radio and HVAC control panel with integrated knobs (Source:

TRW)

3.1.5. Touchscreen

Infotainment displays often have touchscreen features enabling the driver to select functions via touching the display. Touchscreen technology is the direct manipulation type gesture based technology. A touchscreen is an electronic visual display capable of detecting and locating a touch over its display area. It is sensitive to the touch of a human finger, hand, pointed finger nail and passive objects like stylus. Users can simply move things on the screen, scroll them, zoom them and many more.

There are four main touchscreen technologies:

• Resistive

• Capacitive

• Surface Acoustic Wave

• Infrared

The most wide-spread ones are the resistive and the capacitive touchscreens, thus these types will be detailed in the following paragraphs.

Resistive LCD touchscreen monitors rely on a touch overlay, which is composed of a flexible top layer and a rigid bottom layer separated by insulating dots, attached to a touchscreen controller. The inside surface of each of the two layers is coated with a transparent metal oxide coating (ITO) that facilitates a gradient across each layer when voltage is applied. Pressing the flexible top sheet creates electrical contact between the resistive layers, producing a switch closing in the circuit. The control electronics alternate voltage between the layers and pass the resulting X and Y touch coordinates to the touchscreen controller. The touchscreen controller data is then passed on to the computer operating system for processing.

Figure 4.8. Resistive touchscreen (Source: http://www.tci.de)

Because of its versatility and cost-effectiveness, resistive touchscreen technology is the touch technology of choice for many markets and applications. Resistive touchscreens are used in food service, retail point-of-sale (POS), medical monitoring devices, industrial process control and instrumentation, portable and handheld products. Resistive touchscreen technology possesses many advantages over other alternative touchscreen technologies (acoustic wave, capacitive, infrared). Highly durable, resistive touchscreens are less susceptible to contaminants that easily infect acoustic wave touchscreens. In addition, resistive touchscreens are less sensitive to the effects of severe scratches that would incapacitate capacitive touchscreens. Drawback can be the too soft feeling when pressing it, since there is a mechanical deformation required to connect the two resistive layers to each-other. (Source: [53])

One can use anything on a resistive touchscreen to make the touch interface work; a gloved finger, a fingernail, a stylus device – anything that creates enough pressure on the point of impact will activate the mechanism and the touch will be registered. For this reason, resistive touchscreen require slight pressure in order to register the touch, and are not always as quick to respond as capacitive touchscreens. In addition, the resistive touchscreen‘s multiple layers cause the display to be less sharp, with lower contrast than we might see on capacitive screens.

While most resistive screens don‘t allow for multi-touch gestures such as pinch to zoom, they can register a touch by one finger when another finger is already touching a different location on the screen. (Source: [54]) The capacitive touchscreen technology is the most popular and durable touchscreen technology used all over the world. It consists of a glass panel coated with a capacitive (conductive) material Indium Tin Oxide (ITO). The capacitive systems transmit almost 90% of light from the monitor. In case of surface-capacitive screens, only one side of the insulator is coated with a conducting layer. While the screen is operational, a uniform electrostatic field is formed over the conductive layer. Whenever, a human finger touches the screen, conduction of electric charges occurs over the uncoated layer which results in the formation of a dynamic capacitor. The controller then detects the position of touch by measuring the change in capacitance at the four corners of the screen. In the projected-capacitive touchscreen technology, the conductive ITO layer is etched to form a grid of multiple horizontal and vertical electrodes. It involves sensing along both the X and Y axis using clearly etched ITO pattern. The projective screen contains a sensor at every intersection of the row and column, thereby increasing the accuracy of the system. (Source: [55])

Figure 4.9. Projected capacitive touchscreen (Source: http://www.embedded.de)

Since capacitive screens are made of one main layer, which is constantly getting thinner as technology advances, these screens are not only more sensitive and accurate, the display itself can be much sharper.

Capacitive touchscreens can also make use of multi-touch gestures, but only by using several fingers at the same time. If one finger is touching one part of the screen, it won‘t be able to sense another touch accurately. (Source:

[54])