A Reactive and Efficient Walking Pattern Generator for Robust Bipedal Locomotion

Available possibilities to prevent a biped robot from falling down in the presence of severe disturbances are mainly Center of Pressure (CoP) modulation, step location and timing adjustment, and angular momentum regulation. In this paper, we aim at designing a walking pattern generator which employs an optimal combination of these tools to generate robust gaits. In this approach, first, the next step location and timing are decided consistent with the commanded walking velocity and based on the Divergent Component of Motion (DCM) measurement. This stage which is done by a very small-size Quadratic Program (QP) uses the Linear Inverted Pendulum Model (LIPM) dynamics to adapt the switching contact location and time. Then, consistent with the first stage, the LIPM with flywheel dynamics is used to regenerate the DCM and angular momentum trajectories at each control cycle. This is done by modulating the CoP and Centroidal Momentum Pivot (CMP) to realize a desired DCM at the end of current step. Simulation results show the merit of this reactive approach in generating robust and dynamically consistent walking patterns

How Does Voxel Size of Cone-beam Computed Tomography Effect Accurate Detection of Root Strip Perforations

Introduction: Our study aimed to assess the diagnostic accuracy of different voxel sizes for cone-beam computed tomography (CBCT) when detecting strip perforations of variable sizes. We used 0.2 and 0.3 mm3 voxel for detecting root strip perforations. Methods and Materials: This was an in vitro study conducted on 155 extracted humans' mandibular first molars. The teeth were randomly divided into five groups (n=31). Perforation were not induced in the control group. In the remaining four groups, strip perforations of 0.5, 1, 1.5, and 2 mm diameters were created in the mesiolingual canal using #3 Gates Glidden drills. The CBCT scans were taken first with a 12×9 cm field of view (FOV), 90 kVp, 4 mA, and 0.2 mm3 voxel size for 24 sec and then with a 12×9 cm FOV, 90 kVp, 2 mA, and 0.3 mm3 voxel size for another 24 sec. Two observers evaluated the images and reported the largest diameter of perforations. The results were compared with the gold standard values (determined by an electronic digital caliper) using statistical methods, including the kappa coefficient and generalized estimating equation (P<0.05). Results: Based on the findings of our study, the inter-observer agreement ranged from 58-100%, while the intra-observer agreement was reported to be around 100%. The difference in accuracy between 0.2 and 0.3 mm3 voxel sizes was not statistically significant (P>0.05). In addition, the accuracy of detecting different perforation sizes in the CBCT did not follow a specific pattern.  Conclusion: This in vitro study showed that CBCT is a reliable diagnostic tool, and even in lower dosages of 0.3 mm3 voxel size, image resolution and diagnostic accuracy was not affected. Moreover, smaller root perforations could be detected as accurately as larger ones with CBCT