Improving Image Stabilization With Hexapod Motion Simulators
No one likes blurry, washed-out images, whether they be vacation snapshots taken with a smartphone or video of a bank vault captured by a security camera.
To ensure the highest quality images, camera manufacturers put their products through a battery of tests to check features and attributes, such as resolution, contrast, color, texture, zoom, autofocus, exposure and image stabilization. Thousands of images are taken and evaluated to obtain statistically significant results. For image quality to be comparable, camera components are always tested under the same conditions and using the same methods.
Headquartered in Boulogne, France, DXOMARK manufactures instruments to do just that. The company’s flagship product is Analyzer, a modular system for analyzing, comparing and optimizing image quality. Designed to ensure repeatable, operator-independent results, the system consists of 14 modules, each focusing on a different image-quality attribute. Different modules can be combined, depending on the task at hand. There’s even a module to test the ability of smartphone cameras to take selfies.
Image stabilization is one camera feature that can be checked by the Analyzer. The image stabilization test assesses how well the optical and electronic image stabilization systems built into cameras work. These systems are designed to compensate for slight camera movements and, therefore, avoid blurred images. To guarantee stable image capturing, sensors measure linear and angular motion accelerations—which might be caused by a photographer’s shaky hands or vehicle vibrations—so that the image stabilization system can automatically offset these influences.
For image stabilization tests, it’s important that the simulated shaking or vibrations are reproducible.
“We must ensure that the simulated frequencies and movements—for example, around pitch, yaw, roll—are identical for each test,” emphasizes Nicolas Touchard, vice president of marketing at DXOMARK. “We use hexapods in the latest version of Analyzer because they allow precisely reproducible motions up to frequencies of 30 hertz. We must ensure that the simulated motion remains unchanged for all tests. Hexapods are well-suited to perform this task.”
Test frequencies vary, depending on the product being tested. For example, cameras and smartphones are tested at frequencies up to 12 hertz, while automotive driver assistance systems require much higher frequencies. Thanks to their parallel-kinematic design, hexapods can provide the entire range of test frequencies.
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Compared with serial, or stacked, systems, hexapods have much better path accuracy, repeatability and flatness. In addition, the moved mass is lower, enabling better dynamic performance, which is the same for all motion axes. Also, cable management is no longer an issue, because cables are not moved, and the system has a much more compact design.
The hexapods used in the latest version of Analyzer are from Physik Instrumente (PI). The company’s H-840 hexapod is used in one of DXOMARK’s image stabilization test systems and is certified to the Camera and Imaging Product Association’s standard DC-011-2015. This standard defines rotational axes, test frequencies and vibration amplitudes that are necessary for certification.
A different hexapod, H-860, is used for image stabilization tests requiring higher frequency vibrations. It offers simulation frequencies up to 30 hertz. It can follow predefined trajectories (sinusoids) and freely definable paths with a high degree of trajectory control. Due to the friction-free, voice-coil drives and the lightweight design consisting of stiff carbon fiber parts with low-moving masses, it is possible to achieve fast and smooth motion as well as high acceleration.
The hexapod used for testing is fixed to a base plate. The brackets for the test items are installed on the base plate. They keep the test device safely in place on the hexapod during vibration simulation.
“We favor these hexapods because they have the perfect specifications for vibration simulation and because PI provides support, for example, for the adaptation of the software drivers,” Touchard adds.
PI’s high-performance C-887 digital controller takes care of the control for the hexapods, and the software enables easy programming. Positions are specified in Cartesian coordinates, and transformations for the six individual drives in the hexapod are calculated by the controller. The freely definable rotation or pivot point is an essential feature of the hexapod. This means that the motion of the hexapod platform can be specifically adapted to the position of the image stabilization component in the camera so that, for example, the image sensor is located in the middle of all six degrees of freedom.
Cameras aren’t the only products that are tested with hexapods. Any instrument that incorporates multi-dimensional position sensors can benefit from testing with hexapods. For example, marine gyroscopes are tested with hexapods.
For more information on test equipment, visit https://corp.dxomark.com.
For more information on hexapods and other motion control technology, visit www.pi-usa.us.
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