2021/02/12
Selecting a touch panel for use in industrial settings requires consideration for how usable and reliable the device will be in the usage environment.
There are many types of touch panels available, but analog resistive devices have been the go-to in the industrial field for many years. In addition to being highly reliable with few unintentional operations, analog resistive devices can be operated while wearing gloves.
Projected capacitive (PCAP) touch screens such as those commonly used in smartphones and tablets are also expected to be adopted in a wide variety of fields due to their high operability with multi-touch capabilities. However, such technology has yet to be introduced in industrial fields due to susceptibility to noise and difficulty of use when wearing gloves.
The following blog introduces the mechanisms and features of touch panel systems and provides useful information for selecting a touch panel to use in an industrial setting. The blog also speculates on upcoming advancements in industrial-use touch panels being made possible by significant technological innovations in electrostatic capacitance.
Analog resistive touch screens—sometimes referred to as pressure-sensitive touch panels—are the most commonly used devices in the industrial field.
The structure of these devices is simple: two transparent electrode films are placed facing each other with a small gap in the middle. Pressing on the panel causes the electrode films to come into contact, resulting in current flowing at different values depending on the key area. That current is measured to determine which key is being pressed.
Digital (matrix) resistive touch panels that include two X and Y coordinate pattern layers for identifying the key area coordinates are also available.
Whereas electrostatic capacitance methods use capacitive coupling between the electrodes, resistive film methods use non-conductive materials for touch responses. This means touch operations do not need to be done with a finger. Compared to infrared (IR), surface acoustic wave (SAW), and other wavelength-based methods, the touch sensor surface is also the most resistant to foreign particles such as dust and water droplets.
However, multi-touch operations are not possible, optical transparency is low, the surface is prone to scratching, frequently used parts easily wear out, and large screen sizes are difficult to produce.
A wide variety of LCDs and all-in-one PCs have been introduced since Windows began supporting multi-touch operations.
Optical imaging systems consist of infrared LEDs and optical sensors in the upper left and right sides of the screen. Retroreflective sheets are also used along the left, right, and bottom of the screen. The optical sensors detect the shadow of a finger or other object used to touch the screen, and the shadow’s coordinates are calculated through triangulation.
These devices offer high transmittance and durability as well as touch operations with gloves on and multi-touch support. The structure is also simple, making it easy to increase screen sizes.
However, the bezels must be wide enough to fit the light emitters and detectors along the outside of the screen display area, and devices are susceptible to false detections caused by outside lights and shadows.
Projected capacitive (PCAP) devices are one type of electrostatic capacitance devices first introduced to the general market in the early 2000s.
With improved functionality from conventional surface capacitive devices, this method is widely used in consumer devices such as smartphones and tablets. As a result, PCAP quickly became the standard for touch panels. (SCAP ; Surface Capacitive)
In most applications, PCAP devices enable dual-touch rotating, zooming, and flipping, as well as up to 10-point multi-touch operations, setting them apart from other devices.
In these devices, the electrode film—also called the ITO (indium tin oxide) layer—features an electric field generated by a constant capacitive coupling. As a finger or other conductive material nears this layer, capacitive coupling is generated between the conductor and the electrode, causing the capacitive coupling value between the electrodes to change. The coordinates in the key area are then detected according to this capacitive coupling change.
Because PCAP screens are highly durable and scratch-resistant, they are commonly used in applications where heavy use is expected, such as ATMs, retail locations, and kiosks. Use in industrial settings is also increasing. The high transmittance of these screens allow for bright, high-visibility, making PCAP screens popular choices in the medical field.
Each touch panel type offers its own advantages and disadvantages. Selecting the best device means taking into account the product application and usage environment.
Analog resistive touch panels have long been the standard in the industrial field. Surface capacitive (SCAP) devices were once considered for use in industrial applications thanks to their high reliability, including a lower susceptibility to noise and a reduced likelihood of unintentional operations with operation only being possible with fingers (bare hands) or a dedicated stylus. However, industrial use proved impossible as operability while wearing gloves is a must.
Meanwhile, projected capacitive (PCAP) screens are highly sensitive to noise, but dramatic advances in touch panel control technology and noise suppression have made this less of a problem. The size of the electric field (projection area) can also be adjusted so that touch operation with gloves is possible, opening the door to major touch panel advancements in the industrial field.
The principle behind PCAP devices makes them susceptible to noise and increases the likelihood of unintentional operations. Frequency hopping, where touch events are detected in multiple frequency bands, can help ensure only correct touch events are detected, thereby eliminating unintentional operations.
Contec uses frequency hopping and various noise countermeasures to tune industrial equipment for enhanced quality.
Water can be another source of unintentional touch panel operations due to its ability to cause changes in capacitance. Techniques such as frequency hopping can be used to disable key areas if capacitance changes specific to water are detected.
In addition to drip-proof and waterproof performance, CONTEC is utilizing such tuning methods for research and development of capacitive touch panel computer products for use in areas exposed to water.
With PCAP devices, the electric field (projection area) can be adjusted for specific applications. For example, touch operations are possible while wearing work or safety gloves by controlling the detection distance (electric field magnitude) for touch events according to the glove material and thickness.
Contec offers a variety of project-specific touch panel tuning options. Don’t hesitate to contact us for more information.
See one more blog about PCAP vs. Resistive Touch on the Factory Floor :Why Advancements in PCAP Technology Are Replacing Resistive as the Go-To for Industrial Applications. Click here for get more details.
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