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Seeing the light

22 April 2016

The quality of lighting can make or break a machine vision system. Control Engineering Europe takes a look at a solution which fully integrates lighting control into the other elements of a vision solution.

Lighting is a vital element of an optimised inspection solution using machine vision. Even the best camera is only able to capture what it can see, and the best image processing software relies on good results from the camera. 

The quality of illumination consistency, intensity and resolution, therefore, will have an effect on the final accuracy of an application. Despite this, lighting has, historically, not been an integrated part of a machine vision solution.

A fundamental element of a successful and effective vision system is the visibility of the target object to be inspected, and especially the specific objectives for an inspection  – for example missing parts, colour differentiation, blemishes, character recognition or sizing. The starting point for the quality of these source images is the suitability and effectiveness of the lighting for a machine vision system to perform consistently.  The primary images need to be consistent, making undefinable variations in lighting unacceptable.

An intelligent lighting control solution is available from Gardasoft Vision in the form of Triniti, which offers advanced control of machine vision lighting via integration and networking - from the product level, right through to the application software level.

Triniti gives non-expert users access to expert machine vision lighting techniques, enabling them to create, configure and commission vision systems with integrated LED lighting without the risk of damaging the lights.

Users of imaging software will gain a dedicated application, with a single graphical interface, to set up the camera and lighting, visualise the timing and captured images, and save the settings to the camera and controller. It is an approach that is already integrated into many image processing software systems from providers such as Stemmer Imaging, Cognex, National Instruments and Teledyne Dalsa.
The solution comprises three key components. In addition to an API and GigE Vision interface to control the light, the light and controller talk to each other through Gardasoft’s LED light controller technology and a ‘Triniti chip’.

As part of a collaborative program with a variety of machine vision LED light manufacturers the Triniti chip is being built into the lights (or the light cabling), where it holds specification data, stores usage data and returns both fixed and dynamic data from sensors within the lights.

Safe overdriving
Most machine vision applications are short of light, so overdriving LEDs is a common practice – it allows users to increase intensity from LED lights for a short, defined, period of time (with up to 1000% overdriving capability). However, LED overdriving limits are based on generalised parameters that are considered safe for all LEDs so are usually set lower than is possible in reality for a specific light. A significant advantage of intelligent lighting is ensuring the generation of maximum brightness from a light. This is achieved by having data readily available on the actual light being used, therefore enabling the overdriving of a particular light to its safe optimised limits.

Calibrated lighting brightness allows the lighting intensity to be more repeatable. Thresholds and feature detection can be set to be more sensitive, while maintaining good repeatability and reliability of detection. Overdrive limits are also based on the maximum operating temperature, but most lights run at a lower temperature. So, by measuring the actual temperature of the light, it is possible to allow for more overdrive in systems which run below the maximum temperature. 

Some systems need to capture many images of each product item, in a sequence of varying lighting requirements. With application-level visibility of the timing of the system, and a fully featured lighting controller, such systems are easier to set up, monitor and maintain.

An intelligent lighting solution can offer benefits throughout a machine vision project cycle – for OEMs systems integrators and end users.

End users will see benefits with their final applications, such as long-term stability of brightness, which helps to enhance the reliability of machine vision systems over many years.

The integrated and networked functions of Triniti enable OEMs to have remote access to the lights within their systems, including the provision of real-time operational performance data. This gives an opportunity to deliver more functionality with their product offerings such as increased machine functionality, remote servicing and predictive maintenance.
 
System integrators can also gain benefits in terms of speed, flexibility and consistency of development because the lighting will become part of the same development environment as all the other elements of the machine vision system. The graphical set-up of camera and light synchronisation, via the Triniti API’s GUI, also allows for faster system implementation, and importantly, for efficient on-site commissioning and system validation.

Gardasoft has published a whitepaper that looks in some depth at the advantages of intelligent lighting within machine vision systems. This can be freely downloaded from the downloads section of the company website at www.gardasoft.com


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