Integrating liquid lens control into machine vision applications

mean that they can accommodate high throughput. Liquid lenses can be easily fitted to any conventional lens and are mounted either between the lens and camera for macro imaging, or on the front of the lens for longer working distances.


iquid lens technology is a highly significant new technology for

machine vision and is creating a huge amount of interest around the world. The shape of a liquid lens can be changed in milliseconds through the application of a current to change the focal length. This approach can improve the performance of machine vision systems by allowing a range of techniques which were not possible before. Where multiple cameras were used to inspect features at different heights on a product, now a single camera equipped with a liquid lens can be used to take images at different focus distances. Objects of different height can be brought into focus instantly, by using a distance sensor to measure the height and then changing the focus. Gardasoft’s GigE Vision compliant TR-CL180 lens controller allows integration of liquid lenses into machine vision systems using any compatible GigE Vision client image processing software.

LIQUID LENS TECHNOLOGY Liquid lenses are based on a combination of optical fluids and a movable polymer membrane. To tune the lens to different focal lengths, fluid is pressed into the centre of the lens by applying a control current to move the diaphragm and change the shape of the lens. They offer a number of benefits in machine vision applications since they allow a much faster change of the focus than would be possible by moving conventional lenses using mechanical actuators and avoid the cost of these motorised lenses. In addition, since no translational mechanics are involved these systems are extremely robust and have a MTBF of billions of cycles. Machine vision users therefore benefit from smaller, cheaper and faster optical systems. Fast lens response times


Gardasoft TR-CL180 lens controller and Optotune focus tunable lens

LENS CONTROL The new TR-CL180 lens controller brings additional integration capabilities for machine vision users. It is GigE Vision compliant, so any compatible GigE Vision client image processing software such as Cognex VisionPro, Teledyne Dalsa Sherlock, National Instruments LABVIEW and Stemmer Imaging CVB etc can be used to view and change controller settings. This also means that it can be fully integrated into the triniti machine vision platform to allow control of system cameras, lighting and lenses in a single machine vision environment. The controller is designed to work with the EL-10-30 and EL-16-40 focus-tunable lenses from Optotune. The EL-10-30 lens has a clear aperture of 10mm, and operates as a plano-convex lens. The EL- 16-40 is one of the world’s largest electrically focus tunable lenses with a clear aperture of 16mm and can operate as either a plano-convex or a plano- concave lens for added versatility. When a lens is connected the controller will read the properties and calibration for the lens from the memory in the lens. The controller will then allow the lens to be set to any optical power from its minimum to maximum. This could be at a single configurable value or at two different optical powers using a digital input. In addition it is possible to set the optical power and program a timed sequence of optical power settings using an analogue signal. The controller has waveform input options including square, triangle, saw tooth, sine and user defined. These bring extra advantages such as increased depth of field for life science and medical technology applications. The

User interface showing camera and lighting timing diagrams and acquired image

controller will automatically compensate for temperature changes within the lens.

THE TRINITI PRINCIPLE Machine vision systems consist of a number of different components including cameras, lighting and image processing software. Triniti was originally introduced to take lighting control to a new level by the networking of LED lighting, camera and imaging software to provide an integrated application with a single graphical interface for set up and control. Control of machine vision lighting can be provided through commercially available image processing software, enabling users to set up both the camera and lighting, visualise the timing and captured images, and save the settings to the camera and controller. Now set-up and control of a focus- tunable lens can be done in the same way. An additional major benefit of triniti technology is that the data feedback from triniti-enabled LEDs allows the system to provide a long-term stability of brightness that helps to enhance the reliability of machine vision systems.

PRACTICAL APPLICATIONS FOR LIQUID LENSES The extremely rapid focusing time of focus-tunable lenses make them particularly useful in a diverse range of applications where objects of different height need to be imaged. This could include reading of barcodes or labels on packages of different heights in logistics or postal sorting applications. Using a laser displacement sensor to monitor the heights in real time and send an analogue signal to the lens controller to drive the lens to the correct optical power setting allows macro changes in lens settings to be completed in less than 10ms. The lens controller also allows improved depth of field. With a conventional lens, depth of field is improved by stopping down the iris, but this reduces the light reaching the camera. With the lens controller is it possible to open the aperture and take images at different focal lengths without reducing light throughput. Microscopy, life sciences and medical devices are other key market sectors for tunable lens control.

Gardasoft Vision /AUTOMATION T: 01763 262621

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