This work presents a 2D human model and its use in a novel gait analysis framework, which only requires a stereo camera to produce impressive results for the inverse kinematics, inverse dynamics, as well as ground reaction forces during gait. The model is designed to resemble the human body in the sagittal plane, with anatomical landmarks used as keypoints in the inverse kinematics calculations that yield accurate estimates of the joints' motion during gait. The gait dynamics are formulated in compact form, allowing the simultaneous estimation of internal joint torques, as well as ground reaction forces via the solution of a fully-defined system of linear algebraic equations. The proposed framework offers an affordable alternative to costly gait analysis systems, and can have various applications in robotics and in biomechanics.

This paper introduces a virtual gravity controller for underactuated biped robots. A bio-inspired model of passive bipedal walking is used as the basis for the controller's design. An analytical expression of the controller is obtained, allowing on-line implementations of the developed control scheme. Following a design modification tailored to the controller, the robot is able to reproduce its passive gait even on level-ground. The results are verified via independent high-fidelity physics simulations of the real robot's digital twin. The active robot demonstrates significant dynamic convergence to the passive model's dynamics, with only minor motorization efforts. The developed control scheme showcases robustness and energetic efficiency, and leads the way to a design-oriented approach in active biped locomotion.

This paper studies a passive biped walker with knees and biomimetic feet and its behavior, as a function of key parameters. The model includes a continuous dynamic representation of the knee joint's interaction with a viscoelastic kneecap, as well as a complete kinematic description of feet that are designed to mimic the human rollover shape. First, the analytical model is derived and studied numerically for its passive walking capabilities. Then, the model is verified through independent simulations in a different platform. Finally, to increase the efficiency of its passive gaits and to map out its walking capabilities, the model is investigated parametrically. The methods used as well as the results obtained can offer significant assistance in the field of designing passivity-based biomimetic walking robots and prosthetic devices.

This paper studies the effects of replacing pin-joint knees in passive dynamic bipedal walkers with biomimetic four-bar knees. The kinetic model of the four-bar knees is presented in detail, and an analytical model of the passive walking dynamics is derived. The resulting four-bar kneed biped is compared with a pin-joint kneed walker, for their passive walking performance. The geometry of the four-bar knees used in the study is based on human anatomical data. It is found that the biomimetic four-bar knee configuration works to the advantage of the biped, especially around the extended-knee singular position. The four-bar knees are found to overperform the pin-joint ones, resulting in significant reduction of peak impact loads and energetic expenditure.

A methodology for implementing arbitrary foot shapes in the passive walking dynamics of biped robots is developed. The dynamic model of a walking robot is defined in a way that allows shape-dependent foot kinetics to contribute to the robot's dynamics, for all convex foot shapes regardless of the exact foot geometry: for the developed method, only the set of points describing the foot profile curve is needed. The method is mathematically derived and then showcased with an application. The open-source pose estimation system OpenPose is used to determine the foot profile that enables the rigid-foot passive robot to reproduce the ankle trajectory of the actively powered, multi-DOF human foot complex. The passive gait of the biped robot walking on the specified foot shape is simulated and analyzed, and a stable walking cycle is found and evaluated. The proposed model enables the study of the effects of foot shape on the walking dynamics of biped robots, eliminating the necessity of solely using simple, and analytically defined geometric shapes as the walking robots' feet. The method can be used for foot shape optimization towards achieving any desired walking pattern in walking robots.

This paper studies the effects of varying rollover curvature on the passive dynamic gait of a biped walker. The dynamic model of a compliant biped robot is extended with the implementation of semielliptical feet, to mimic human rolling-radius progression during a step. The process of modeling the semielliptical foot shape and integrating its kinematics to the biped's dynamics is presented in detail. The passive dynamic behavior of the biped for elliptic feet of various dimensions is investigated through numerical simulations to provide results about gait stability, walking speed, energetic efficiency, and impact force levels. The concept of energetic efficiency in passive walking is discussed thoroughly, and an efficiency comparison methodology is proposed. Finally, it is shown that the biomimetically-inspired semielliptical foot profile can lead to higher gait efficiency. The results of this study can be used to optimize energetic efficiency in biped walking machines and/or gait assisting prosthetic equipment by means of foot shape optimization.

This paper presents an efficient method of stabilizing the gait of an underactuated biped with compliant legs and semicircular feet. First, the model is defined, incorporating elements that are often present in experimental biped robots. The biped's passive behavior is studied through numerical simulations that provide insight into the gravity's contribution as an energy input to the system. Based on this study, it is shown that an augmented biped -with the addition of a counterweight joint at the hip- is able to perform stable gaits with minimal input. This design is implemented easily as it does not require ankle torques; instead, both motors are mounted at the biped's hip. The control law used for the stabilization is the combination of virtual-gravity components with non-linear PD terms. The stable gaits performed by the augmented biped on level floor strongly resemble the passive gaits of the original biped walking on a slope, resulting in an efficient, natural-like motion of low transport cost.