All Keyed Up: Quality Inspection for Keyboards & Backlit Characters

Mon, April 6, 2020
Anne Corning  | 

Today’s electronics customers expect flawless device quality right out of the box, and that holds just as true for keyboards as it does for smartphones or televisions. Device quality is paramount—just ask this Reddit user, who posted a complaint about tiny cosmetic defects on a keyboard. 

This photo from a Reddit post demonstrates that consumers notice every tiny defect. This customer returned the (otherwise perfectly functional) keyboard unit for a full refund due to these small cosmetic defects. (Image Source)

Manufacturers of laptops and keyboards need to perform precision visual inspection of these devices during the assembly process to ensure that defective products don’t end up in customer hands. Once a product has shipped, the costs associated with an undetected defect can be severe. Cosmetic flaws, reduced product performance, and latent failures can result in rapidly escalating direct and indirect costs, including:

  • Returns, repairs, or warranty claims
  • Customer dissatisfaction and loss of customer loyalty
  • Damage to brand reputation and perception of quality

Manufacturers need a solution that can catch tiny and often random defects—at production-line speeds. For both backlit and non-lit keyboard components, Radiant offers high-resolution, high-speed inspection solutions that fit the bill.

Automated Inspection

At every stage of assembly—from the component level to the point at which components are full assembled and devices are sealed—inspection verifies the inside-out integrity of the final product. Employing automated visual inspection at each stage confirms that unintended damage, misalignment, or mislabeling has not occurred during assembly and manufacturing operations.

Defects on flat products like keyboards and keyboard frames can be hard for human inspectors to spot reliably, due the complex visual patterns and random occurrence of defects. Human inspectors become visually fatigued by scrutinizing parts with a high degree of detail and a variety of contrasts and colors within a small area. However, catching minute defects in complex arrays (like keyboards, or keyboard components as shown below) is critical for preventing defects in subsequent assemblies.

Small assembly defects such as broken tabs in a keyboard frame may allow critical components to become loose or detach during shipment or operation.

Radiant’s automated visual inspection (AVI) solutions can capture extremely detailed images of complex parts due to the high resolution and dynamic range of our ProMetric® Imaging Photometers and Colorimeters. Using single- or multi-camera integrations, manufacturers can capture and analyze several inspection images—each up to as much as 43 megapixels (8040 x 5360 CCD pixels)—to find minute defects precisely and quickly.

Automated visual inspection also prevents any further damage to product assemblies that may be caused during handling by human inspectors before products ship. Visual inspection systems may be used to check the placement of device back plates, bezels, buttons, glass, and other exterior surfaces; the alignment of camera lenses, ports, and connectors relative to apertures in device housing; the position and placement of keys on a keypad; the presence or position of labels and printed or etched information on a product surface; and much more. Radiant provides inspection capability through its line of Advanced Vision systems (such as the INSPECT.assembly™ Visual Inspection Station) which include tools to address a variety of non-lit keyboard assembly and quality verification tasks.

Inspection images of the back of a laptop unit (left image) reveal that feet, connectors, and battery cover are present, but the center component is missing. On the keyboard (right image), the inspection system verifies the alignment and configuration of the keys and keyboard elements.

Keyboard Assembly Inspection

There are multiple types of defects that can occur in the process of keyboard manufacture due to the large number of parts and visual elements that must all come together perfectly. For example, issues with character quality, print quality, positioning and orientation, the placement of keys, or the spacing between keys can impact the appearance and performance of a keyboard.

Radiant automated visual inspection solutions can assess character quality (left) such as thickness of letter strokes, print location (center), and check key placement (right)—identifying that the letters A and Q are in the reverse placement they should be for a correct “QWERTY” keyboard layout.

For example, if key gap width (spacing between keys) is not consistent, then keys might make contact with other component surfaces during use, causing sticking or wear. Radiant’s photometry-based visual inspection systems can measure minute inspection areas for very precise tolerances–spotting keys that are off by as little as 0.1 µm (about the width of a human hair) to ensure proper placement.

Radiant’s Advanced Vision solutions check the gap widths in assemblies. Improper gaps are flagged as a failure, as they can result in damage and latent failures during operation.

Backlit Keyboard Inspection

Radiant also offers solutions for testing illuminated keyboards and backlit signage in high-volume manufacturing environments. Illuminated keyboards and keypads can exhibit variations in brightness (luminance) and color (chromaticity) from key to key, and even within a single key, that are noticeable to the end-user.

These flaws detract from the user experience and, in some cases, strongly impact product usability. Automated visual inspection of illuminated keyboards and keypads focuses on measuring luminance and chromaticity of individual characters, and of the keyboard as a whole, for uniformity.

Our PM-KB™ Illuminated Keyboard Testing Software system also performs optical character recognition (OCR), allowing the software to determine if keycaps are installed correctly and if each key is in its proper location and position (e.g., not inverted or sideways).

Keyboard analysis shown in PM-KB Software. Output data includes individual character luminance, individual key luminance, local luminance versus proximal keys for individual keys, and full keyboard uniformity. All values can be evaluated against programmed thresholds for minimum and maximum luminance.

Radiant Imaging Systems

Combining extremely high-resolution imaging optimized for low image noise, Radiant’s ProMetric® Imaging Photometers and Colorimeters can capture superior levels of detail and evaluate contrast ratios within images beyond traditional machine vision systems to ensure the most precise and accurate assembly inspection. Systems are also quantifiable and consistent, capturing and grading defects on complex assemblies beyond the capabilities of human inspectors. While the position and presence of text, logos, and labels are easily verifiable, our systems can further analyze the quality of text and symbols using OCR and OCV to ensure print quality, legibility, and consistency.

All Radiant inspection systems are calibrated based on NIST-traceable samples and internal performance tolerances, ensuring that all cameras on the line—or from one line to the next—are able to image and evaluate products to the same tolerances of visual quality. This consistency enables manufacturers to trace product assembly data across lines and ensure that all inspection systems produce identical data across inspection conditions. Calibration also guarantees that all products installed on various lines adhere to the manufacturer’s precise standards of brand quality, preventing unacceptable products from escaping into the marketplace.

Radiant ProMetric® I-Series Imaging Colorimeter (left) and Y-Series Imaging Photometer (right).

PM-KB™ Illuminated Keyboard Testing Software

Illuminated keyboards and keypads can exhibit variations in brightness and color from key to key, and even within keys, that are noticeable to the end-user. This inconsistency can detract from the user experience and, in extreme cases, these variations may strongly impact product usability.

Part of the Radiant family of inspection software, PM-KB is used with a ProMetric® Imaging Colorimeter or Photometer to perform rapid, automated visual inspection of backlit keyboards and keypads for character luminance and chromaticity, and assess overall keyboard luminance and color uniformity. PM-KB can be used to test that key caps are installed correctly and that each key is in its proper location. The system tests all keys and characters simultaneously, capturing and processing data much faster and more consistently than a human inspector or a spot measurement device.

PM-KB, used with a ProMetric Imaging Photometer or Colorimeter, is designed for high-volume production inspection of backlit keyboards.

On the production line, PM-KB presents a simple, easy-to-use interface with straightforward test initiation commands and pass/fail indicators. PM-KB can record device barcodes (or accept input from a production control system) as part of the testing process. Test reports can also be generated to preserve data for later examination.

To allow sequential testing of multiple keyboard or keypad models, PM-KB maintains a database of keyboard configurations, testing parameters, and keyboard-specific pass/fail criteria. These can be quickly changed in production, making it simple to update models or pass/fail requirements. Unlike with human operators, no retraining is required.

To ensure line-to-line and location-to-location consistency, Radiant provides a special-purpose calibration light source for use with the PM-KB system, which ensures that common calibrations between PM-KB and additional ProMetric products are incorporated into the system.

Watch PM-KB in Action: Pattern Matching on Backlit Keyboards

The video below gives a demonstration of the PM-KB Software, walking through inspections of keyboards with various defects, and demonstrating how PM-KB can be used to catch defects using pattern matching. (Pattern matching is a comparison between a stored reference measurement (representing the ideal pattern) and a received pattern (such as a keyboard on a production line).) PM-KB can identify defects in shape, pattern, luminance, and color of each symbol on the keyboard, regardless of the language of characters on the keys. To learn more, watch the video: “Pattern Matching in the PM-KB™ System.”