&lt;title&gt;Class of algorithms for real-time subpixel registration&lt;/title&gt;

Frischholz, Robert; Spinnler, Klaus

doi:10.1117/12.164889

Cited by 21 publications

(14 citation statements)

References 5 publications

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“…Due to about 20-fold subpixel resolution according to our marker-camera setup and the tracking algorithm [3,17] implemented in "WINanalyze" ("mikromak", Berlin, Deutschland), we reached a spatial resolution of 0.01 mm for the marker positions. The spatial resolution of whole body centre of mass (COM) position and centre of pressure (COP) data was 0.1 mm.…”

Section: Processing Of Kinematic and Kinetic Datamentioning

confidence: 99%

Watching quiet human stance to shake off its straitjacket

2010

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The single-inverted pendulum (SIP) model is still the paradigm describing dynamics and control of quiet human stance in the sagittal plane. We used two methods to verify this paradigm. First, in an experimental approach we acquired kinematic data of both legs of ten subjects at high spatial resolution while quietly standing on two force platforms. We calculated all leg joint angles, the belonging joint torques using inverse dynamics and estimates of joint stiffnesses. Some linear correlations and regressions of both local (joint) and global (COM, COP: centre of mass respectively pressure) variables predicted by the SIP model were investigated. All three verification criteria applied to mean values extracted from experimental data revealed that the SIP is not a valid model for quiet human stance. As a second method, we used computer synthesis to demonstrate that a double-inverted pendulum (DIP) model enters a stable attractor when just the "hip" joint torque is regulated, whereas no torque is applied to the "ankle" joint. Here, angle and torque fluctuations are necessary because such a DIP strategy is of inevitable dynamic character. The two predicted eigenfrequencies of this regulated DIP model approximate the upper and lower limits of the main part of measured power spectra of quiet human stance. We suggest this dynamic necessity to be representative of the biological constraints under which a mechanically unstable inverted multi-segment chain must be stabilised.

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Section: Processing Of Kinematic and Kinetic Datamentioning

confidence: 99%

Watching quiet human stance to shake off its straitjacket

2010

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“…The resolution of the camera was 1024ϫ512pixels, so minimum tracking accuracy was approximately 0.25mm. An accuracy of at least half that value can be assumed because the digitisation software (WINAnalyze ® , Micromak Service, Berlin, Germany) that we used is able to compute subpixel resolutions via interpolating algorithms (Frischholz and Spinnler, 1993). For the experiments, we used four adult female specimens of the large South American araneomorph species Ancylometes concolor (Perty 1833) (mean ± s.d.…”

Section: Methodsmentioning

confidence: 99%

Hydraulic leg extension is not necessarily the main drive in large spiders

Weihmann

Günther

Blickhan

2012

Journal of Experimental Biology

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SUMMARYUnlike most other arthropods, spiders have no extensor muscles in major leg joints. Therefore, hydraulic pressure generated in the prosoma provides leg extension. For decades, this mechanism was held responsible for the generation of the majority of the ground reaction forces, particularly in the hind legs. During propulsion, the front leg pairs must shorten whereas the hind legs have to be extended. Assuming that hind legs are essentially driven by hydraulics, their force vectors must pass the leg joints ventrally. However, at least in accelerated escape manoeuvres, we show here for the large cursorial spider species Ancylometes concolor that these force vectors, when projected into the leg plane, pass all leg joints dorsally. This indicates a reduced impact of the hydraulic mechanism on the generation of ground reaction forces. Although hydraulic leg extension still modulates their direction, the observed steep force vectors at the hind legs indicate a strong activity of flexors in the proximal joint complex that push the legs against the substrate. Consequently, the muscular mechanisms are dominant at least in the hind legs of large spiders.

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“…Camera resolution was 768×512 pixels, so minimum tracking accuracy was below 0.1 mm. An accuracy of at least 0.05 mm can be assumed as WINanalyze, is able to compute sub-pixel resolutions via interpolating algorithms (Frischholz and Spinnler, 1993). We used the graph paper on the tread to calibrate the video sequences.…”

Section: Digitisationmentioning

confidence: 99%

Level locomotion in wood ants: evidence for grounded running

Reinhardt

Blickhan

2014

Journal of Experimental Biology

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In order to better understand the strategies of locomotion in small insects, we have studied continuous level locomotion of the wood ant species Formica polyctena. We determined the three-dimensional centre of mass kinematics during the gait cycle and recorded the ground reaction forces of single legs utilising a self-developed test site. Our findings show that the animals used the same gait dynamics across a wide speed range without dissolving the tripodal stride pattern. To achieve higher velocities, the ants proportionally increased stride length and stepping frequency. The centre of mass energetics indicated a bouncing gait, in which horizontal kinetic and gravitational potential energy fluctuated in close phase. We determined a high degree of compliance especially in the front legs, as the effective leg length was nearly halved during the contact phase. This leads to only small vertical oscillations of the body, which are important in maintaining ground contact. Bouncing gaits without aerial phases seem to be a common strategy in small runners and can be sufficiently described by the bipedal spring-loaded inverted pendulum model. Thus, with our results, we provide evidence that wood ants perform 'grounded running'.

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<title>Class of algorithms for real-time subpixel registration</title>

Cited by 21 publications

References 5 publications

Watching quiet human stance to shake off its straitjacket

Watching quiet human stance to shake off its straitjacket

Hydraulic leg extension is not necessarily the main drive in large spiders

Level locomotion in wood ants: evidence for grounded running

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