PKTRONICS industrial screens and PCs allow exchanges between people and production. Within our company, our engineers and design offices use LCD screens to carry out various tasks, including computer-aided production management. Our industrial displays are designed to blend in with various environments and different business departments. Our integrable industrial displays and industrial monitors are designed to meet specific requirements and can be used in any environment after being upgraded. Whether they are industrial, naval or military, they can meet and be considered according to your needs. Industrial monitors can have different touch technologies.
A touch screen is a computer device that combines the display functions of a screen and a pointing device (such as a mouse, touchpad or optical pen). This can reduce the number of peripherals on some systems and produce ergonomic software that is very suitable for certain functions. Touchscreens are used in a variety of applications such as PDAs, GPS, MP3 players, smartphones, tablets, portable game consoles, etc. The latest generation of touch screens can be sensitive to more than two pressure levels (graphic tablet / pen) with higher resolution, and to more than one position (multi-touch / finger) at the same time.
Surface Wave Technology
Surface wave technology uses ultrasonic waves circulating on the surface of the screen. These waves produce an interference pattern that changes when you touch the screen. Once this change in the interference pattern is detected, it is processed by the controller to determine the coordinates (x, y) of the pressure position. The main disadvantage of this technology is that the smallest scratches (even dust or stains) on the surface will change the basic interference pattern and affect the accuracy of detection on the screen.
Analog resistive technology
The resistor system consists of a glass plate whose surface becomes conductive due to the coating of indium tin oxide. It is covered with a plastic film, and the surface of the plastic film is made with the same technique. The two layers are separated by a thin insulating layer composed of tiny spacer pins. An additional layer has been added to the screen surface to prevent scratches, such as those caused by the stylus tip.
When the user presses the screen with the tip of a stylus or finger, the pressure applied breaks the upper diaphragm over the lower diaphragm in time and creates contact between the two loaded surfaces. The change in resistivity between the two conductive surfaces and the position of the contact point are detected by the touch screen controller, which alternately subjects the screen conductor to very low voltages. In use, the electrical conductivity of these two surfaces degrades due to the micro-sparks caused by the discharge at the moment of contact, and in use, the detection accuracy decreases. This technology requires users to recalibrate the touchpad. This recalibration includes masking the wear of the touchpad by distributing the most commonly used haptic zone errors over the entire surface of the touchpad.
In the capacitive touch system, a charge accumulation layer based on indium (an increasingly rare metal) is placed on the glass plate of the display. When the user touches the tablet with his finger, part of the charge will be transferred to him. The charge leaving the capacitor plate can cause quantifiable defects. There is a sensor at each corner of the board, which can measure and determine the coordinates of the contact point at any time. The processing of this information is the same as the processing of the resistor circuit.
Compared to the resistive touch system, the main advantage of the capacitive touch system is that it can transmit light with higher efficiency. Indeed, up to 90% of the light will pass through the capacitive surface, while the resistive touch system has a maximum of 75%, which provides higher image clarity for the capacitive touch system.
These systems are not easily expandable to screens larger than 20 inches (50 cm). On the other hand, they are very competitive in small size, so they can be found in many mid-range smartphones and tablets and are rare in the low-end market.
The current passes through these wires and the power is measured for each wire. In the process of contacting the conductive materials, the current will be changed over several wires. Based on the data recorded over the entire grid and by understanding the characteristics of the tablet, the location of the touch can be found. Since there are hundreds of points to measure the location of the touch (compared to the original capacitive technology, there are not four points), it is possible to measure the touch at several points.
A display with induction technology is only sensitive to the action of a special stylus. Very close to capacitive technology, Wacom originally developed this technology for graphics tablets. In addition to capacitive technology, it is also used in high-end touchpads and tablets. It uses the windings present in the tablet and the pen. The alternating current flowing through the tablet coil generates a magnetic field. As the pen approaches, the magnetic field induces an excitation of the coil in the pen and generates current inside, which interferes with the magnetic field of the display.
Touchscreens using infrared technology have two very different forms:
- The first uses heat-resistant surfaces. This method is often criticized as being slow and requiring the hands to warm up (therefore the pen response is not valid).
- The second form is the form of infrared radiation sensor arrays, both horizontal and vertical. When one of these modulated infrared beams is interrupted (i.e. to avoid interference between the detectors), contact detection is complete.
Infrared touchscreens have the highest resistance and are therefore commonly used in military applications.
Optical technology for interactive displays
This is a relatively new technology in which two (or more) cameras are placed around the edge of the screen (mainly in the corners). Each camera is equipped with an infrared diode, and the periphery of the screen is surrounded by an edge (a few millimeters) covered with a retro-reflector. The light emitted by the diode is reflected by the mirror and the finger (or pointer) appears as a shadow on each camera. A simple triangulation allows to find the position and size of the pointer. The technology is very cheap and very suitable for large screens (maximum 120″-3 m), so it is becoming more and more popular.
Total reflection is the foundation of FTIR (Frustrated Total Internal Reflection) technology. The incident angle of the infrared rays must be less than the critical angle at which refraction occurs. If it is greater than the critical angle, no refracted light will be observed and all light will be reflected. This is a phenomenon of total reflection.
This total reflection occurs over the entire tactile surface. The diode placed on the edge of the Plexiglas plate emits continuous infrared radiation. The Plexiglas plate acts as a waveguide and the infrared rays are emitted at an angle slightly greater than the critical angle. This angle completely reflects the light along the board.
When a finger is placed on the board, it diffuses the radiation in all directions. As a result, some of the rays deflected by the finger will reach the underside of the board at an angle less than the critical angle, and can therefore be emitted from there. These rays form an infrared spot on the underside of the board. This can be seen through a dedicated camera located underneath the device.
The FTIR touch screen contains the following elements :
- A Plexiglas plate;
- Infrared LEDs, responsible for emitting the radiation ;
- Resistors to power the LEDs;
- A projection screen, which collects the image from the projector;
- A projector;
- Silicone, which acts as a bridge between the plate and the finger;
- An infrared camera, specifically designed to capture the rays;
- A visible light filter, specifically designed to let only a certain wavelength through;
- A computer, which processes the image sent by the camera.
NFI technology (Near Field Imaging)
NFI capacitor technology is resistant and adapted to strict technical specifications: it can detect contact with gloves or dirty surfaces (grease, paint, etc.).
The principle is to insert a conductive layer between the two glass plates (the principle is the same as the capacitance and resistance principle). Then, a low intensity electrostatic field will be permanently generated on the outer surface of the glass plate in contact with the user.
The originality of this technique is that the Z coordinate can also be calculated. This type of implementation makes it possible to obtain a high luminosity screen. They are very resistant in hostile environments (intentional destruction, industrial environments).
The iTouch application of Electrotouch System allows this principle to be used on regular screens (no need to add glass plates).
Strain gauge technology
Four strain gauges are installed at the four corners of the screen to determine the deformation caused by finger or stylus pressure on the screen. This technique can also determine the (usually small) displacement caused by pressure on the screen. The use of deformation counters in particular allows haptic applications on ticket reservation terminals, which are extremely vulnerable to damage.
Risks and Disadvantages
Despite its name, the touch screen has no touch marks. Therefore, if they do not bring a sound generating device (such as a smartphone), this will pose the main problem of accessibility for the blind. However, for some obstacles, mechanical equipment cannot be used. Compared to mechanical systems, tactile control may require a longer waiting time and make the operation more complicated, and in some cases there is also a risk of accident. This is why in August 2019, because in 2017, several touchscreens caused a collision between an American destroyer (John McCain) and a container ship (Alnwick MC) off the coast of Singapore, the US Navy. Killing 10 sailors and injuring 48 others, the US Navy announced within two years that it would abandon all destroyers to regain control.