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Mikrotron in Action

High Speed Imaging ApplicationsEoSens_3CL

Showcased are two applications where Mikrotron’s high performance EoSens® cameras are successfully utilized.

EoSens ® CL Features

  • Maximum photo sensitivity: 2,500 ASA monochrome, 2,000 ASA RGB
  • Up to 120,000 fps at reduced resolution
  • Base or Full Camera Link® Interface with 700/ 160 MB/second
  • Monochrome or color with BAYER-filter
  • Extended Dynamic Range up to 90 dB
  • Small and compact design

 

Wheels Put to the TestAdaptive Optics

Wheels Put to the Test

Why the WheelWatch system is equipped with high-speed cameras from Mikrotron

Germany and the car share a long history. It was here, in 1886, that Carl Benz registered the patent for a petrol-powered vehicle with a four-stroke engine, the “Benz Patent-Motorcar Number 1”. Today, brands such as VW, Porsche, Mercedes and BMW are famous the world over and represent the very best in quality and innovation. The automotive industry is the driving force of the German economy as well as the catalyst for many other business sectors.

Measuring technology is one such sector, where AICON 3D Systems GmbH is an established expert. The company was founded in 1990 in Braunschweig, and develops, manufactures and markets optical camera-based 3D measurement systems. The company extended its product range to include high-precision 3D scanners following the takeover of Breuckmann GmbH in 2012.

Testing Wheel Behaviour

Analysis of Wheel Motion
A BMW test vehicle executing the fishhook manoeuvre.

AICON 3D System GmbH has set a new standard in vehicle development thanks to WheelWatch, the optical measurement system. Before a car gets anywhere close to serial production, prototypes have already covered millions of kilometres during testing. As part of this process, careful testing examines exactly how wheels behave in the event of extreme manoeuvres. Just how do they handle bumps and wet roads? Do they remain stable when it comes to evasive manoeuvres or when travelling at high speed? Do the wheel wells still provide enough room even when tackling sharp bends? Here, parameters such as track, camber, suspension, steering angle and clearance are crucial.

Detecting Wheel Movement at 250 km/h

detecting wheel movement

The EoSens® camera is accommodated in rugged housing. Here, it is mounted on a test bench.

A high-speed camera from Mikrotron is the key component of WheelWatch. With a maximum speed of almost 500 frames per second, the EoSens® camera, equipped with a CMOS sensor, provides a resolution of 1280 x 1024 pixels. As a result, it takes sharp and detailed images, even at driving speeds of up to 250 km/h. The integrated high-performance flash also takes care of the extremely short exposure times required, which are in the microsecond range.

Tackling Tough Operating Conditions

The camera is exposed to extreme forces and has to be able to withstand accelerations, steering manoeuvres and abrupt braking. Furthermore, the camera must also function reliably during lengthy tests lasting several hours. Therefore, the engineers at AICON 3D Systems demand the very best in terms of sturdiness and long-term stability. “The camera operates reliably, despite sometimes facing tough operating conditions,” confirms Robert Godding, Managing Director of AICON 3D Systems GmbH. “The camera coped very well with various challenging applications – not only in the field of wheel motion – and always delivers high-quality image data.”

Mounting the Measurement System on the Vehicle

Mounting the measurement system on the vehicle.One camera is attached for each wheel, so that the wheel and mudguard are fully captured.

One camera is attached per wheel, to enable it to fully capture the wheel and mudguard. Specially coded measurement targets are placed on the mudguard to identify the vehicle coordinate system. An adapter is mounted on the wheel, featuring a unique pattern of dots. The camera captures the wheel and simultaneously aligns itself with the surrounding mudguard. This means the camera does not have to be kept stable. Likewise, vibrations and bumps do not have any effect on the data measured. The system recalculates its position continuously to achieve the measuring data, thereby achieving maximum positional accuracy of approx. ± 0.1 mm and angular accuracy of approx. ± 0.015°.

Four cameras can be synchronised with each other, as well as with other measuring sensors. By way of example, movements in the engine block can also be detected using the EngineWatch system. Consequently, the system benefits from the compact size of the EoSens® camera. Measuring just 63 x 63 x 47 mm meant that it was possible for AICON 3D GmbH to develop a housing that fits into even the tightest of spaces.

Evaluating Images in the Camera

User Interface
User interface of the WheelWatch software

The measurement images are assessed right in the camera sensor using an FPGA image analysis processor and sent to the computer via a GigE interface, in real time. The results are available shortly after. Mr Godding considers the integrated FPGA technology to be one of the camera’s best features. “Being able to use the FPGA built into the camera, for our own image processing purposes, was one of the reasons we opted for a Mikrotron camera. The collaboration required for this has gone really well.”

Versatile Applications

The system is used on the test bench as well as during drives on the test track. However, it is also ideal for other movement analyses:

3D motion and position analysis

  • Door slam testing
  • Examining the opening and closing behaviour of doors, covers, windows
  • Vibration analysis of components
  • Robot rail measurement
  • Machine control

3D deformation analysis

  • Error analysis in the production line (e.g. welding processes)
  • Component behaviour in wind tunnels or climatic chambers
  • Collision analyses
  • Material testing, structural analysis

6D positioning and alignment of individual points and rigid bodies

The Sun’s Surface in Stunning Detail

How High-Speed Helps to Reduce the Effects of Atmospheric Distortion

stockholm university

Located on the Canary Island of La Palma, the Swedish 1-meter Solar Telescope (SST) is the world’s leading facility for high resolution observations of the Sun. It is operated by the Institute for Solar Physics(ISF), which is part of Stockholm University’s department for Astrophysics. Research at the institute primarily aims to gain knowledge about the outer layer of the solar atmosphere, which is dominated by magnetic fields. How do magnetic fields arise? How are they formed and ultimately destroyed or removed from the solar surface? How do they affect the Sun‘s outer atmosphere? How do they give rise to solar storms and the radiant energy that the Sun emits?

The Swedish Solar Telescope (SST)

The Swedish Solar Telescope (SST)

These questions are explored using observational data registered with the Swedish Solar Telescope. The telescope system looks at 60 x 60 arc-seconds of the Sun, which equals 43,320 x 43,320 km on the solar surface. This is an area that is more than three times bigger than the Earth’s surface but represents only 0.03% of the Sun’s surface.

The telescope uses adaptive optics to reduce the effects of atmospheric distortion. Atmospheric distortion is caused by the Earth’s atmosphere, which bends the light in random directions. It is the reason why stars seem to twinkle and why the Sun seems rippled at sunset. Without adaptive optics, the Swedish Solar Telescope would generate blurry images.

The Concept of Adaptive Optics

The adaptive optics system within the Swedish Solar Telescope, which was funded by the Swedish Research Council, consists of a Shack-Hartmann wavefront sensor and a deformable mirror. The Shack-Hartmann wavefront sensor is a glass plate with many lenslets etched on it, which subdivide the pupil of the telescope in 85 segments. Each segment delivers an individual image of the Sun. When the atmosphere disturbs the image, it causes the image to shift, and this shift is different for each segment. The shifts are measured and translated into commands to the deformable mirror, so that it takes a shape that compensates for the distortions.

Adaptive Optics Technology

Adaptive Optics Technology

Schematic showing the principle of Shack-Hartmann wavefront sensors. Left: If there is no atmosphere, incoming light rays remain parallel. The wavefront is plane. Right: Where there is atmospheric distortion, the light rays bent by the atmosphere hit the lenslets at different angles. The wavefront is corrugated. The deformable mirror reacts continuously to compensate for the shifts.

 

Wavefront Sensor Beam

Wavefront Sensor Beam

The wavefront sensor beam. From the bottom left to the top right: first is the Mikrotron camera, right in front of it is the Shack-Hartmann lenslet array, halfway the optical rail is the re-imaging lens, and at the end of the rail is a movable field stop. A little further is a broadband filter to select green light, behind it is a stack of prisms and a beamsplitter which divert part of the light to the wavefront sensor.

The Need for High-Speed Equipment

High-Speed Camera Close-Up
EoSens® CL with Shack-Hartmann Wavefrontsensor

The problem is that the atmosphere changes quickly, so this has to be done very accurately and at a very high frequency. The adaptive optics system at the Swedish Solar Telescope has to correct the deformable mirror at least several hundred and preferably more than 1,000 times per second. This requires high-speed equipment.

The EoSens® CL high-speed camera by Mikrotron was installed in 2011 and is used to record the image formed by the Shack-Hartmann wavefront sensor. The image to the right shows a close-up of the Mikrotron camera with the Shack-Hartmann sensor in front. On the CMOS sensor itself you see a reflection of the image that the camera sees; a honeycomb pattern that is created by the Shack-Hartmann sensor.This image is composed of many small images of the Sun, each produced by one segment of the pupil. As the image is being sent to the computer, it is already being processed. By the time the last lines of the camera image are being received, the computer has already calculated the phase variation of the whole pupil. It then only has to calculate how to shape the mirror to produce an inverse phase variation. Within one second, 2,000 images are extracted, pre-processed and measured.

Adaptive Optics Software

 

Image formed by the Shack-Hartmann wavefront sensor recorded by a Mikrotron EoSens® CL high-speed camera. You can see how its lenslets subdivide the pupil of the telescope in 85 segments. Each video is made of 1,000 images. The camera was running at 2,000 frames per second (2 kHz). The telescope was pointed slightly to the side of a small sunspot, which is the black spot in the sub-images.

Watch the video.

 

 

 

Adaptive Optics Software

The image shows the interface observers at the Swedish Solar Telescope see. The green boxes indicate the sub-images of the lenslet array. The small red crosses show the shifts in these sub-images as calculated by the software. The shifts are then translated into commands to the deformable mirror.

Watch the video.

Fast Data Transfer

To ensure the highest bandwidth possible, the researchers at the Institute for Solar Physics use the following features of the EoSens® CL:

  • The images are transferred using Full CameraLink®.This robust and powerful interface is widely used and makes integration into the existing setup easy. It enables high-speed data transfer in three configurations. The fastest variant, „Full,“ is set.
  • The EoSens® CL is equipped with 8 taps. A tap is a data path transferring the image data.
  • The pixel clock frequency is set at 80 MHz. With every pixel clock, the digital value of one pixel is transferred. CameraLink®supports a pixel clock range of 20 to 85 MHz.
  • A region of interest consisting of 432 x400 pixels is selected. This means more than 2,400 images per second can be read out before the CameraLink®bus is saturated.
  • In practice though, the frame rate is set to 2,000 frames per second. If the camera is run at the limit, any glitch or delay in processing will immediately cause a frame to be missed. Reducing the speed ensures the system runs flawlessly 24 hours a day.
  • The in-frame counter is activated to detect missed frames and to check whether the frame grabber is correctly synched with the incoming frames.

The EoSens® CL offers a 10-bit per pixel output. “Although this is a nice feature to have, we are doing image processing in real time,” says Guus Sliepen, Research Engineer at the Institute for Solar Physics. “8-bit per pixel allows certain optimizations which are necessary for us not to exceed the available CPU power.”

Provision of Raw Data

Sun Spots
Sunspots are the most visible effects of magnetic activity. They appear dark because they are cooler than the surrounding photosphere.

Magnetic field lines are most visible in H-alpha images.
Magnetic field lines are most visible in H-alpha images.

While some features of the EoSens® CL are put to good use, others are not. All image enhancement tools within the EoSens® CL can be disabled. At the Swedish Solar Telescope, both the digital gain and the fixed-pattern noise (FPN) correction are switched off to ensure the EoSens® CL delivers raw data. “The reason we do not want the camera to do any corrections is because our optical system itself is not perfect, and also introduces variations in gain and offset for each pixel,” explains Guus Sliepen. “So we measure the dark field and flat field for the whole optical system, and apply the correction using our software.” One exception is the black level offset. It is raised accordingly to ensure that, even in total darkness, the pixel values are always above 0.

Easy Handling

When asked about the camera’s best features, Guus Sliepen mentions its uncompromising speed and excellent performance. He, however, also highlights on its easy handling. “It does not require firmware updates and proprietary tools,” he says. “The serial interface ASCII is also easy to use.” He further compliments the camera’s well thought out design. “It is very solid and compact and its screw holes are very well placed, making it easy to mount.” He sums it up by saying: “The EoSens® CL camera is the easiest CameraLink®camera I have worked with.”

Quiet Sun

The Sun is unusually quiet, meaning that its activity is at a moderate level. This can be evidenced by the low number of sunspots. The granules, caused by convection, are blobs of rising and falling gas. The bright spots formed in the canyons between the granules are solar faculae. The video shows the image quality obtained with the Swedish Solar Telescope. With smaller telescopes, bright spots cannot be resolved. And thanks to adaptive optics and the excellent location of La Palma, a sharp image is acquired during the whole movie.

Watch the video. 

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