Analysis and Design of Hardware Architectures and Control Algorithms for an EPAC

EPACs (Electric Pedal Assisted Cycles) represent a very efficient and fashionable mean of non-polluting transport. They are useful for bringing education, for health service and they guarantee the lowest energy cost per distance traveled. In this paper, a power kit has been designed and implemented on a real electric bicycle. In particular, hardware architectures and control algorithms are developed together, taking in account shared needs. An optimal choice of the components and an innovative overboost strategy characterize the provided system. Experimental results and comparison with a benchmark product available in the market demonstrate the efficiency of the whole system.

Life Extending Minimum-Time Path Planning for a Hexapod Robot

This paper presents a life extending minimum-time path planning algorithm for legged robots, with application for a six-legged walking robot (hexapod). The leg joint fatigue life can be extended by reducing the constraint on the dynamic radial force. The dynamic model of the hexapod is built with the Newton Euler Formula. In the normal condition, the minimum-time path planning algorithm is developed through the bisecting-plane (BP) algorithm with the constraints of maximum joint angular velocity and acceleration. According to the fatigue life model for ball bearing, its fatigue life increases while the dynamic radial force on the bearing decreases. The minimum-time path planning algorithm is thus revised by reinforcing the constraint of maximum radial force based on the expectation of life extension. A symmetric hexapod with 18 degree-of-freedom is used for simulation study. As a simplified treatment, the magnitudes of dynamic radial force on proximal joints at the pair of supporting legs are set identical to achieve similar degradation rates on each joint bearing and obtain the dynamic radial force on each joint. The simulation results validate the effectiveness of the proposed idea. This scheme can extend the operating life of robot (joint bearing fatigue life) by modifying the joint path only without affecting the primary task specifications.

Time Lapse Observation Based Modeling and Identification of Cell Behaviors in Angiogenic Sprout Development

This paper presents a method for deriving dynamic equations for Endothelial Cell (EC) motion and estimating parameters based on time lapse imagery of angiogenic sprout development. Angiogenesis is the process whereby a collection of endothelial cells sprout out from an existing blood vessel, degrade the surrounding scaffold and form a new blood vessel. Sprout formation requires that a collection of ECs all work together and coordinate their movements and behaviors. The process is initiated and guided by a collection of external growth factors. In addition, the individual cells communicate and respond to each other’s movements to behave in a coordinated fashion. The mechanics of cell coordination are extremely complex and include both chemical and mechanical communication between cells and between cells and the matrix. Despite the complexity of the physical system, with many variables that cannot be measured in real time, the ECs behave in a predictable manner based on just a few quantities that can be measured in real time. This work presents a methodology for constructing a set of simple stochastic equations for cell motion dependent only on quantities obtained from time lapse data observed from in vitro experiments. Model parameters are identified from time lapse data using a Maximum Likelihood Estimator.

Reduced-Order Cue-Signal-Response Modeling for Angiogenic Cell Migration Control: A Principal Signal Approach

A cell’s behavior in response to stimuli is governed by a signaling network, called cue-signal-response. Endothelial Cells (ECs), for example, migrate towards the source of chemo-attractants by detecting cues (chemo-attractants and their concentration gradient), feeding them into an intra-cellular signaling network (coded internal state), and producing a response (migration). It is known that the cue-signal-response process is a nonlinear, dynamical system with high dimensionality and stochasticity. This paper presents a system dynamics approach to modeling the cue-signal-response process for the purpose of manipulating and guiding the cell behavior through feedback control. A Hammerstein type model is constructed by representing the entire process in two stages. One is the cue-to-signal process represented as a nonlinear feedforward map, and the other is the signal-to-response process as a stochastic linear dynamical system, which contains feedback loops and auto-regressive dynamics. Analysis of the signaling space based on Singular-Value Decomposition yields a set of reduced order synthetic signals, which are used as inputs to the dynamical system. A prediction-error method is used for identifying the model from experimental data, and an optimal system order is determined based on Akaike’s Information Criterion. The resultant low order model is capable of predicting the expected response to cues, and is directly usable for feedback control. The method is applied to an in vitro angiogenic process using microfluidic devices.

Interpretation of the Directional Properties of Voluntarily Modulated Human Ankle Mechanical Impedance

This article presents the results of two in-vivo studies providing measurements of human static ankle mechanical impedance. Accurate measurements of ankle impedance when muscles were voluntarily activated were obtained using a therapeutic robot, Anklebot, and an electromyographic recording system. Important features of ankle impedance, and their variation with muscle activity, are discussed, including magnitude, symmetry and directions of minimum and maximum impedance. Voluntary muscle activation has a significant impact on ankle impedance, increasing it by up to a factor of three in our experiments. Furthermore, significant asymmetries and deviations from a linear two-spring model are present in many subjects, indicating that ankle impedance has a complex and individually idiosyncratic structure. We propose the use of Fourier series as a general representation, providing both insight and a precise quantitative characterization of human static ankle impedance.

Parameters and Driving Force Estimation of Cell Motility via Expectation-Maximization (EM) Approach

Motility is an important property of immune system cells. To describe cell motility, we use a continuous stochastic process and estimate its parameters and driving force based on a maximum likelihood approach. In order to improve the convergence of the maximization procedure, we use expectation-maximization (EM) iterations. The iterations include numerical maximization and the Kalman filter. To illustrate the method, we use cell tracks obtained from the intravital video microscopy of a zebrafish embryo.

A Thrust-Vectored Submersible for Animal Behavior Research: Design and Proof of Concept

In this paper, we present the design and proof of concept of a streamlined, low-cost, and smooth-hulled underwater vehicle (MASUV-1). MASUV-1 utilizes an ad-hoc designed multi-directional thrust-vectoring system for steering and an entirely enclosed propulsion system, allowing for safe operation in the vicinity of marine mammals. Tests of the vehicle in a still water environment show high maneuverability at speeds comparable with similar torpedo-type class underwater vehicles.

Impact of Flow Force to the Constant Flow Characteristic of Load Sensing Pump

Aiming at studying the impact of steady-state flow force to YL-56 load sensing pump and how to reduce the effects of flow force on control valve spool, the factors of steady-state flow force were analyzed using CFD software FLUENT, and virtual prototype of load sensing pump was developed to study its characteristics. Compared with the effect of using position-controlled proportional solenoid to drive the throttle valve in simulation, the use of force-controlled proportional solenoid could suppress the impact of steady-state flow force much better, and the problem that the output flow increased when load pressure rose was solved. The experiment test results indicate that using force-controlled proportional solenoid in throttle valve can decrease the impact of steady-state flow force quite well.

A Monopropellant-Powered Muscle Actuation System

This paper describes the design and control of a new monopropellant-powered muscle actuation system for robotic systems, especially the mobile systems inspired by biological principles. Based on the pneumatic artificial muscle, this system features a high power density, as well as characteristics similar to biological muscles. By introducing the monopropellant as the energy storage media, this system utilizes the high energy density of liquid fuel and provides a high-pressure gas supply with a simple structure in a compact form. This addresses the limitations of pneumatic supplies on mobile devices and thus is expected to facilitate the future application of artificial muscles on bio-robotic systems. In this paper, design of the monopropellant-powered muscle actuation system is presented as well as a robust controller design that provides effective control for this highly nonlinear system. To demonstrate the proposed muscle actuation system, an experimental prototype was constructed on which the proposed control algorithm provides good tracking performance.

Mathematical Modelling of Near-Hover Insect Flight Dynamics

Using a dynamically scaled robotic wing, we studied the aerodynamic torque generation of flapping wings during roll, pitch, and yaw rotations of the stroke plane. The total torque generated by a wing pair with symmetrical motions was previously known as flapping counter-torques (FCTs). For all three types of rotation, stroke-averaged FCTs act opposite to the directions of rotation and are collinear with the rotational axes. Experimental results indicate that the magnitude of FCTs is linearly dependent on both the flapping frequency and the angular velocity. We also compared the results with predictions by a mathematical model based on quasi-steady analyses, where we show that FCTs can be described through consideration of the asymmetries of wing velocity and the effective angle of attack caused by each type of rotation. For roll and yaw rotations, our model provided close estimations of the measured values. However, for pitch rotation the model tends to underestimate the magnitude of FCT, which might result from the effect of the neglected aerodynamics, especially the wake capture. Similar to the FCT, which is induced by body rotation, we further provide a mathematical model for the counter force induced by body translation, which is termed as flapping counter-force (FCF). Based on the FCT and FCF models, we are able to provide analytical estimations of stability derivatives and to study the flight dynamics at hovering. Using fruit fly (Drosophila) morphological data, we calculated the system matrix of the linearized flight dynamics. Similar to previous studies, the longitudinal dynamics consist of two stable subsidence modes with fast and slow time constants, as well as an unstable oscillatory mode. The longitudinal instability is mainly caused by the FCF induced by an initial forward/backward velocity, which imparts a pitch torque to the same direction of initial pitch velocity. Similarly, the lateral dynamics also consist of two stable subsidence modes and an unstable oscillatory mode. The lateral instability is mainly caused by the FCF induced by an initial lateral velocity, which imparts a roll torque to the same direction of initial roll velocity. In summary, our models provide the first analytical approximation of the six-degree-of-freedom flight dynamics, which is important in both studying the control strategies of the flying insects and designing the controller of the future flapping-wing micro air vehicles (MAVs).