This work presents a framework for the simultaneous optimization of motors, transmissions, and mechanisms of different joints of robotic legs with the goal of achieving an energy efficient, precisely controllable and stable locomotion in dynamic environments. This unified framework allowed us to introduce and formulate new performance metrics for the separate evaluation of the system's stabilizing ability during stance and swing. Moreover, through a case study, this design optimization framework was applied to an anthropomorphic robot leg model and the optimal actuation configurations for the leg were obtained. This case study also helped us investigate the relationships among our three objectives (energy efficiency, and stance and swing control). It was shown that while in some cases a clear trade-off exists, it is not always valid and as such, careful consideration of all three objectives is necessary.

We present the design of a powered knee-ankle prosthetic leg, which implements high-torque actuators with low-reduction transmissions. The transmission coupled with a high-torque and low-speed motor creates an actuator with low mechanical impedance and high backdrivability. This style of actuation presents several possible benefits over modern actuation styles in emerging robotic prosthetic legs, which include free-swinging knee motion, compliance with the ground, negligible unmodeled actuator dynamics, less acoustic noise, and power regeneration. Benchtop tests establish that both joints can be backdriven by small torques (~1-3 Nm) and confirm the small reflected inertia. Impedance control tests prove that the intrinsic impedance and unmodeled dynamics of the actuator are sufficiently small to control joint impedance without torque feedback or lengthy tuning trials. Walking experiments validate performance under the designed loading conditions with minimal tuning. Lastly, the regenerative abilities, low friction, and small reflected inertia of the presented actuators reduced power consumption and acoustic noise compared to state-of-art powered legs.

This paper describes the design of a powered knee- and-ankle transfemoral prosthetic leg, which implements high torque density actuators with low-reduction transmissions. The low reduction of the transmission coupled with a high-torque and low-speed motor creates an actuator with low mechanical impedance and high backdrivability. This style of actuation presents several possible benefits over modern actuation styles implemented in emerging robotic prosthetic legs. Such benefits include free-swinging knee motion, compliance with the ground, negligible unmodeled actuator dynamics, and greater potential for power regeneration. Benchtop validation experiments were conducted to verify some of these benefits. Backdrive and free-swinging knee tests confirm that both joints can be backdriven by small torques (~3 Nm). Bandwidth tests reveal that the actuator is capable of achieving frequencies required for walking and running. Lastly, open-loop impedance control tests prove that the intrinsic impedance and unmodeled dynamics of the actuator are sufficiently small to control joint impedance without torque feedback.

Although there has been recent progress in control of multi-joint prosthetic legs for periodic tasks such as walking, volitional control of these systems for non-periodic maneuvers is still an open problem. In this paper, we develop a new controller that is capable of both periodic walking and common volitional leg motions based on a piecewise holonomic phase variable through a finite state machine. The phase variable is constructed by measuring the thigh angle, and the transitions in the finite state machine are formulated through sensing foot contact together with attributes of a nominal reference gait trajectory. The controller was implemented on a powered knee-ankle prosthesis and tested with a transfemoral amputee subject, who successfully performed a wide range of periodic and non-periodic tasks, including low- and high-speed walking, quick start and stop, backward walking, walking over obstacles, and kicking a soccer ball. The proposed approach is expected to provide better understanding of volitional motions and lead to more reliable control of multi-joint prostheses for a wider range of tasks.

Many control policies developed for legged robots are based on control of an underlying, simplified version of the dynamics of the robot. A good example is the Linear Inverted Pendulum Model (LIPM) which has become the standard control template for ZMP-based rigid robots. For compliant robots, this reduced order model is naturally the Spring-Loaded Inverted Pendulum (SLIP), which has proven to have many interesting traits that are potentially useful for control of full order robots. The methods proposed so far for this purpose are mainly focused on either matching the dynamics of the robot to those of SLIP, or following a SLIP-produced trajectory. These methods can be problematic, especially for underactuated systems. In the present work, we explore an opposite approach, by starting from SLIP and step-by-step constructing toward the full order robot. The goal is to detect and capture the essential stabilizing variables in the reduced order model that can potentially maintain their stabilizing effect in the full order robot, as well. Our initial investigations show that the proposed method provides excellent potentials for synthesizing stable gaits for underactuated compliant robots by use of a much simpler and more robust approach compared to the ones previously presented in the literature.

With regard to the important role of motors and transmissions in the performance of electromechanical and robotic systems, this paper intends to provide a solution for the problem of selection of these components for a general load case. Appropriate objectives are formulated, and by the use of them, a procedure is suggested to compare the performance of different motors for a specified task. Moreover, considering different limitations, the range for feasible transmission ratios is analytically obtained and suggestions for choosing a transmission ratio from this range, and if available, motor torque constant, are provided. As a case study, the methods are applied to the problem of actuator design for a legged robot.

This paper proposes a multi-objective structure for the optimization of an engine control unit mapping. In this way, first an integrated engine-vehicle model is developed. The objective functions for the optimization problem can be defined from this model. After describing the structure of the optimization problem, two different multi-objective genetic algorithms, namely distance-based Pareto genetic algorithm and non-dominated sorting genetic algorithm (together with entropy-based multi-objective genetic algorithm), are proposed and implemented. The results demonstrate the superiority of this computerized structure to the manual mapping methods and also more generality of the multi-objective methods compared to single-objective ones.