Projects Inspection & Verification Of LED Panel Displays

Machine Vision System Provides 100% Verification Of LED Panel Displays

Hanover Displays is using a custom designed machine vision system from Scorpion Vision for 100% inspection and verification of its LED panels. The LED panels are used in displays used in passenger information systems for the public transport industry. The vision system is part of a new automated testing facility to speed up panel production, eliminate faulty product reaching customers and to provide valuable data to improve production processes.


Hanover Displays designs and manufactures passenger information systems for the public transport industry.

Satisfied customers in over 75 countries worldwide use a range of Hanover products, attracted by high levels of quality, reliability and customer service. Two fully equipped production facilities in the United Kingdom and the United States enable Hanover to produce more than 45,000 units annually across the product range. These are shipped to customers in over 75 countries throughout the world on a client list that includes transport authorities, fleet operators, and vehicle manufacturers.

Destination display on bus

Building display panels


LED panels are illuminated using a test system with specific test patterns. Test operators observe the process from beginning to end to identify any LED that has not illuminated on a panel. Each panel could contain an average of 960 LEDs and with over 40 panel variants and some panels containing white LEDs and others with amber LEDs, this requires high levels of concentration. Missing a failed LED could lead to a costly product return. A throughput of around 100 panels per day per test system could be achieved using this method, but as production volumes have increased, this has become a bottleneck to production throughput. In addition, new panels in development contain much higher numbers of LEDs making the inspection process even more demanding.


Hanover Displays worked with Scorpion Vision to develop a machine vision-based process for 100% panel inspection, capable of identifying any LEDs that do not illuminate as well as checking the colour and intensity of illumination of those that do. This was part of a co-ordinated approach to increase levels of automation during the testing phase which now also includes the use of COBOTs (Collaborative Robots) in some areas.

A phased development program for the vision system featured the design and development of a prototype which was evaluated and improved over a period of several months before construction of the final production systems. The vision solution consists of a self-contained inspection station housing a high resolution area scan camera with a matched 2/3" 5mm F1.8 Manual Iris C-Mount Lens for the board inspection, an embedded industrial PC and a specially designed fixture onto which the panels are loaded for inspection. A hand-held bar code scanner and touch screen display are positioned by the side of the inspection station. The high-resolution camera ensures that very small LEDs (2mm and 3mm pitch) on densely populated panels can be imaged. 

The system is also integrated with Hanover’s test system which carries out electrical and thermal tests. The inspection process starts by loading the panel into the fixture and using the hand held scanner to read a QR code located near the edge of the panel. The QR code data include information on the specific panel type, allowing the vision system to automatically load the necessary inspection parameters. These include the number of rows and columns on the panel, LED size and intensity threshold and deviation in the X and Y axes which can be used to detect the exact LED(s) turning on during test. The test then begins automatically, running five illumination sequences, where firstly odd columns are illuminated, then even columns are illuminated, followed by odd rows, even rows and finally all LEDs are illuminated simultaneously.

Inspection system

Results display screen

An image of the panel under test is displayed within the specially designed Graphical User Interface (GUI). An operator scans the PCB barcode and initiates electrical and vision tests via this GUI. The results are displayed on the touch screen, with clear pass (green) and fail (red) indicators for the measured parameters, including the electrical test. A log file for each panel inspected is created and saved with all of the test outcomes.

In the event of a failure, the image of the failed panel is also saved, overlaid with markers to clearly show the location of any failed LEDs. A simple panel training process was also included in the design to allow the system to be quickly trained to produce product profile files for any new products.

Image of failed LED panel


The new vision system has brought a number of key benefits. In particular inspection throughput has increased by well in excess of 100%. The human inspection process allowed inspection of 100 panels/day, but this was increased to 200 inspections/day using the prototype vision system. The production versions of the vision system are planned to be capable of 300 inspections/day. Gaurav Bijlani, Production Test Equipment Manager at Hanover Displays, said: “We’re delighted with the performance of the vision system. Automating the inspection process has not only improved throughput and productivity, but also eliminated human errors. The logging of all inspection data has brought additional benefits for the production processes:

  • Data availability of panel failures allows any production problems to be identified and rectified
  • Data analysis of inspection results allow trends in production to be monitored to facilitate process improvements
  • Saved images and failure log speed up the repair process
  • Data analysis allows the effects of new or modified production processes to be evaluated

Overall, Gaurav Bijlani has been very pleased with the quality of support provided by Scorpion Vision. He said: “They understood the scope of the project right from the beginning and worked closely with me to make sure that the system met my exacting requirements both in terms of measurement capability and the user interface. Their customer service has been exceptional and accommodating.” Three production systems are due for delivery and installation in Q1 2021. One will be used at the UK manufacturing facility and the other two in the US.


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