How Do We Walk? This is what movement scientists at the Locomotion Lab* in the Friedrich Schiller University of Jena are investigating. As well as analyzing movement patterns in humans and animals, they also construct robots. High-speed cameras with high-quality lenses are essential tools for this work.
Eadweard Muybridge would have enjoyed himself at the Locomotion Lab in Jena. He will always be remembered for a bet in 1872 which established him as a pioneer of movement studies in humans and animals. The British photographer developed a complex continuous photography system with very high shutter speeds and was therefore able to prove conclusively and for the first time that all four hooves of horses at full gallop are airborne for a split second. From then on, he remained focused on this topic until his death in 1904. He took hundreds of photographs of humans and animals in order to capture and better understand movement patterns – in running, walking, hopping, jumping and descending stairs.
On the Running Trail
Over a hundred years later, the human walk remains a source of puzzlement. Although everybody walks around 5 kilometers per day as a matter of course, nobody knows exactly how it happens. Movement patterns are extremely complex. Researchers at the Locomotion Lab in Jena construct special robots to aid in their investigations. Sports scientists, engineers, physicists, biologists and IT specialists in an interdisciplinary research group wish to unlock the fundamental secrets of the human gait and to simulate it step-by-step using walking robots.
"Today, we are already quite advanced in describing the walking process, measuring movement patterns and simulating the underlying dynamics using models," says Dr. Sten Grimmer. "However, when it comes to the dynamic reconstruction of individual patterns on the model in order to check our assumptions, we are only at the very beginning." For example, the research group is using one of its walking robots, named JenaWalker, to investigate how the common "push" by the back leg in a human step can be simulated mechanically. The joints of the biped model are braced using springs. The spring unwinds as it is stretched by the leg movement, providing the ankle with momentum for the "push." Amazingly, even if the robot's gait is not fully stable, the ankle's kick still achieves its effect.
From Simulation to Construction
"Our robots do not need to look like humans or animals. We are purely interested in the functional understanding of movement and of its underlying mechanisms," Grimmer emphasizes. Measurements of humans and animals provide the framework for JenaWalker and many other walking robots. The scientists affix markers to the locations of the joints – similar to the procedure of motion tracking for movies and video games. These markers reflect the ring flashes triggered by special infrared cameras. The cameras capture the reflected flash and transmit the coordinates to a computer program. The researchers then match the coordinates to the individual leg joints, so that a 3D image of the joint movement can be generated. Only computer-based capture and analysis using the motion capture technique can precisely decipher the stages of movement.
Besides infrared cameras, which transmit only the reflected marker points, the scientists use several high-speed camera systems to film movement patterns. The installed software subsequently recognizes the markers' movements on the video images, and converts them into a 3D image.
Using the Makro-Planar T* 2/50 at Every Turn
In the high-speed photography for which the Locomotion Lab uses Vosskühler HCC-1000 cameras (resolution: 1024 x 512, max. frame rate: 923 fps), the researchers tested a ZEISS lens, the Makro-Planar T* 2/50 ZF.2, for the first time.
ZEISS lenses with manual focus like the Makro-Planar T* 2/50 ZF are particularly suitable for shooting with high-speed cameras. Only the unique, precise focusing drive of ZEISS enables perfect focusing. Another feature which plays an important role in working with high-speed cameras is the extremely short exposure time; in the range of micro-seconds. A strong light source or a very high-speed lens is also required for capturing usable images. "Thanks to the Makro-Planar T* 2/50 ZF.2's wide (f/2) aperture, sufficient light was directed onto the camera chip for all our high-speed shots – even though not much light was available to us," was how an impressed Sten Grimmer described the performance of the ZEISS lens.
In order to shoot detailed images of the movement patterns with excellent image quality, the researcher must hold the camera very close to the small walking robots, which are often no taller than 15-20 cm. "For this reason, the Makro-Planar T* 2/50, with its short (0.24 m) close focusing distance as well as its natural perspectives was the perfect option," said Dr. Grimmer. The lens has such low distortion that the researchers can extract the location coordinates from the images.
Knowledge gained from the visual movement analyses is gradually enabling the walking techniques of the different robots to be enhanced.
Welcome to the Robot Zoo
Locomorph is another exciting project being supported by the EU, which involves an investigation into how morphology, i.e. the structure of the locomotor system, determines the gait of humans and other bi and quadrupeds. The participants include biologists, engineers, IT specialists and sports scientists from Switzerland, Denmark, Belgium and Canada, as well as the Jena-based researchers working with Sten Grimmer.
"The aim of our project is to construct robotic systems which can move around in various environments, based on our understanding of the morphology of various creatures," explains Dr. Grimmer. Like apes, for example, which typically walk on all fours, but can switch to walking on two legs in certain situations without any difficulty, walking robots should also be able to adopt the optimal gait, depending on the terrain and requirements.
Injuries which impair walking also represent an important part of the investigation. "For instance, if we wish to understand how the body of a dog with a leg injury adjusts to the changed situation, we need to put the specially-constructed robot who also has only three legs on the running track," says Dr. Grimmer. The track is also equipped with both a camera system and force-measuring plates. The ground reaction forces of the individual steps are shown and the movement in space is documented in order to obtain evidence regarding specific body and joint angles.
We are already looking forward to the final results of this EU project which will continue until 2013, and to many other findings from the Locomotion Lab in the future. The curiosity which once drove Eadweard Muybridge is still palpable in this lab every single day. How do we walk?
*Effective 1 February 2012, the Locomotion Lab is no longer located at the Friedrich Schiller University in Jena. Instead, the lab's research is being carried out at the Technical University of Darmstadt, where the scientists from Jena now hold the new Chair of Sport Biomechanics.