Towards the Design and Evaluation of Robotic Legs of Quadruped Robots

Legged systems have potentials of better mobility than traditional wheeled and tracked vehicles on rough terrain. The reason for the superior mobility of legged systems has been studied for a long period and plenty of robots using legs for locomotion have been developed during recent few decades. However the built legged robots still exhibit insufficiency of expected locomotive ability comparing with their counterparts in nature with similar size. The reason may be complicated and systematic associated with several aspects of the development such as the design, key components, control & planning and/or test and evaluation. The goal of this thesis is to close the gap between legged robots research & development and practical application and deployment. The research presented in this thesis focuses on three aspects including morphological parameters of quadruped robots, optimal design for knee joint mechanism and the development of a novel test bench\u2014 Terrain Simulator Platform. The primary motivation and target for legged robots developing is to overcome the challenging terrain. However few legged robots take the feature of terrain into consideration when determining the morphological parameters, such as limb length and knee orientation for robots. In this thesis, the relationship between morphological parameters of quadruped robots and terrain features are studied by taking a ditch/gap as an example. The influence of diverse types of morphological parameters including limb length, limb mass, the center-of-mass position in limbs and knee configuration on the ditch crossing capability are presented. In order to realize extended motion range and desired torque profile, the knee joint of HyQ2max adopts a six-bar linkage mechanism as transmission. Owing to the complexity of closed-loop kinematic chain, the transmission ratio is difficult to design. In this thesis, I used a static equilibrium based approach to derive the transmission relationship and study the singularity conditions. Further desired torque profile of knee joint are realized by a multi-variable geometric parameters optimization. For the test and performance evaluation of robotic leg, I designed and constructed a novel test bench\u2014 Terrain Simulator Platform (TSP). The main function of the TSP is to provide sufficient test conditions for robotic leg by simulating various terrain features. Thus working status of robotic leg can be known before the construction of the whole robot. The core of the TSP is a 3-PRR planar parallel mechanism. In this thesis, the structure design and implementation, the kinematics including singularity, workspace etc, and dynamics of this 3-PRR mechanism are presented

Overexpression of SIRT1 in Mouse Forebrain Impairs Lipid/Glucose Metabolism and Motor Function

SIRT1 plays crucial roles in glucose and lipid metabolism, and has various functions in different tissues including brain. The brain-specific SIRT1 knockout mice display defects in somatotropic signaling, memory and synaptic plasticity. And the female mice without SIRT1 in POMC neuron are more sensitive to diet-induced obesity. Here we created transgenic mice overexpressing SIRT1 in striatum and hippocampus under the control of CaMKIIα promoter. These mice, especially females, exhibited increased fat accumulation accompanied by significant upregulation of adipogenic genes in white adipose tissue. Glucose tolerance of the mice was also impaired with decreased Glut4 mRNA levels in muscle. Moreover, the SIRT1 overexpressing mice showed decreased energy expenditure, and concomitantly mitochondria-related genes were decreased in muscle. In addition, these mice showed unusual spontaneous physical activity pattern, decreased activity in open field and rotarod performance. Further studies demonstrated that SIRT1 deacetylated IRS-2, and upregulated phosphorylation level of IRS-2 and ERK1/2 in striatum. Meanwhile, the neurotransmitter signaling in striatum and the expression of endocrine hormones in hypothalamus and serum T3, T4 levels were altered. Taken together, our findings demonstrate that SIRT1 in forebrain regulates lipid/glucose metabolism and motor function

Revisiting Event-based Video Frame Interpolation

Dynamic vision sensors or event cameras provide rich complementary information for video frame interpolation. Existing state-of-the-art methods follow the paradigm of combining both synthesis-based and warping networks. However, few of those methods fully respect the intrinsic characteristics of events streams. Given that event cameras only encode intensity changes and polarity rather than color intensities, estimating optical flow from events is arguably more difficult than from RGB information. We therefore propose to incorporate RGB information in an event-guided optical flow refinement strategy. Moreover, in light of the quasi-continuous nature of the time signals provided by event cameras, we propose a divide-and-conquer strategy in which event-based intermediate frame synthesis happens incrementally in multiple simplified stages rather than in a single, long stage. Extensive experiments on both synthetic and real-world datasets show that these modifications lead to more reliable and realistic intermediate frame results than previous video frame interpolation methods. Our findings underline that a careful consideration of event characteristics such as high temporal density and elevated noise benefits interpolation accuracy.Comment: Accepted by IROS2023 Project Site: https://jiabenchen.github.io/revisit_even

On the Time Validity of John Philip's Two-Term Rainfall Infiltration Model

Rainfall infiltration, the process wherein water enters the soil surface and replenishes moisture in the vadose zone, is an important component of the water balance and hydrologic cycle. Infiltration guarantees a continued availability of moisture to sustain root water uptake, plant growth, groundwater recharge and soil structure. There are several ways to estimate rainfall infiltration rates and volumes. The most rigorous approach would use a partial differential equation (Richards' equation), coupled, if necessary, with a surface water routine and groundwater model (Darcy's law), to describe infiltration into variably-saturated soils. Analytic solutions of Richards' equation and/or Darcy's law and empirical infiltration functions may work well under certain conditions (deep-drained soils with uniform initial moisture content) and/or single rainfall events. Among all research conducted, the Philip's two-term infiltration model, $I = S\sqrt{t} + c K_\text{s}t$, where $I$ [\,\si{L}\,] is the cumulative infiltration, $S$ [\,L\cdot \text{T}$^{-1/2}$\,] signifies the sorptivity, $K_\text{s}$ [\,L\cdot \text{T}$^{-1}$\,] denotes the saturated soil hydraulic conductivity, $c$ is a unitless curve fitting coefficient and $t$ denotes time in units of length, has found widespread use and applicability. This model is particularly easy to use as (1) it only has three unknown parameters, (2) the least squares parameter values are easily determined from experimental data using linear regression, and (3) two of the estimated parameters, $S$ [\,L\cdot \text{T}$^{-1/2}$\,] and $K_\text{s}$ [\,L\cdot \text{T} $^{-1}$\,], have a clear physical significance. In favor of this simplicity, Philip's two-term infiltration model eliminates higher-order terms of a polynomial series of time that account for the effect of gravity on infiltration. This effect becomes more important at later times as a larger proportion of the soil reaches saturation and the soil water pressure head gradient becomes negligible. As a result, Philip's two-term infiltration model, $I = S\sqrt{t} + c K_\text{s}t$, has a limited time validity, $t_{\text{valid}}$ [\,\si{T}\,]. In his work, Philip provides theoretical guidance on the time validity of his two-term infiltration model. This time validity is of great importance as it determines the time span of experimental infiltration data to use for parameter estimation. In this research, we explore the time validity of Philip's two-term infiltration model using Bayesian inference and the , Soil Water Infiltration Global (SWIG) database. This database consists of a large ensemble of measured cumulative infiltration curves of a wide variety of soils worldwide. Essentially, we test, benchmark and evaluate the approach of Jaswal et al. (2020) on measured data rather than synthetic infiltration data simulated with HYDRUS-1D. The methodology consists of two parts. First, we determine the values of the parameters $S$ [\,L\cdot \text{T}$^{-1/2}$\,] and $K_\text{s}$ [\,L\cdot \text{T} $^{-1}$\,] via Bayesian inference of the Haverkamp infiltration equation using the \textbf{D}iffe\textbf{R}ential \textbf{E}volution \textbf{A}daptive \textbf{M}etropolis (DREAM) algorithm. As semi-implicit solution of Richards' equation, the Haverkamp model is valid for the entire duration of the infiltration experiment. Then, the posterior distribution of the sorptivity and saturated soil hydraulic conductivity of each measured infiltration curve are used in Philip's two-term infiltration model to determine the optimal value of the coefficient $c$ via linear regression. We implement the Bayesian information criterion (BIC) to return, as byproduct of our analysis, the optimal time validity of Philip's two-term infiltration model. The uncertainty of the time validity, $t_\text{valid}$ [\,T\,], can be estimated by evaluating the different posterior samples of $S$ [\,L\cdot \text{T}$^{-1/2}$\,] and $K_\text{s}$ [\,L\cdot \text{T} $^{-1}$\,]. We particularly focus on the ``best'' samples of each soil type in the SWIG database as results confirm that the temporal resolution of the infiltration data plays a critical role. Results demonstrate that coarse textured soils (e.g. sand, loamy sand, sandy loam) have a rather small value of $t_\text{valid}$ [\,T\,] ranging between 0.10 hour to 1.00 hour. Medium textured soils (sandy clay loam, loam, clay loam) exhibit somewhat larger values of the time validity ranging between 1.00 hour to 4.76 hours. Unfortunately, the measured infiltration curves in the SWIG database did not allow us to determine adequate values of the time validity for fine textured soils. The time validity, $t_\text{valid}$ [\,T\,] of clay loam, silty clay loam, silty clay, and clay soils was simply equal to the time of the last infiltration measurement. In other words, the experiments did not last long enough to determine accurately their respective time validity. All results were compared to those of Jaswal et al. (2020) using synthetic infiltration data. This analysis made evident that (1) the measurement errors of the infiltration data increase the uncertainty of $t_\text{valid}$ [\,T\,]; (2) The much poorer measurement (time) resolution of the infiltration data in the SWIG database makes it difficult to accurately determine the time validity of Philip's two-term infiltration model; (3) For fine textured soils, the infiltration experiments were of insufficient length to reliably estimate the value of $t_\text{valid}$ [\,T\,]. Altogether, we conclude that it is not particularly easy to estimate the time validity of Philip's two-term infiltration model from measured cumulative infiltration data. A large cohort of the infiltration experiments in the SWIG database lack the temporal resolution and necessary length of the experiment to warrant an accurate determination of the time validity. Thus, we recommend using synthetic infiltration data simulated derived from numerical solution of Richards' equation to determine an approximate time validity for each soil type. The resulting estimates of $t_\text{valid}$ [\,T\,] can then serve as guidelines for analysis of real-world infiltration experiments