Nestor Perez-Arancibia - Academia.edu (original) (raw)

Papers by Nestor Perez-Arancibia

We present the design, fabrication and feedback control of an earthworm-inspired multi-material m... more We present the design, fabrication and feedback control of an earthworm-inspired multi-material multi-actuator soft robot capable of locomoting inside pipes. The bodies of natural earthworms are composed of repeated deformable structural units, called metameres, that generate the peristaltic body motions required for limbless underground burrowing and above-ground crawling. In an earthworm, each individual metamere is actuated by circular and longitudinal muscles that are activated synchronously by the animal's nervous system. Here, adopting the basic functional principles of metameric worms, we propose a new pneumatically-driven soft robotic system that mimics the motions and replicates the functionality of a single burrowing earthworm's segment. The suitability of the proposed approach is demonstrated experimentally through three basic locomotion tests: horizontal motion, vertical motion and oblique motion inside a varying-slope transparent pipe.

IEEE robotics and automation letters, Oct 1, 2021

We present the shape-memory alloy (SMA) robotic traveling insect (SMARTI), a 60-mg crawling micro... more We present the shape-memory alloy (SMA) robotic traveling insect (SMARTI), a 60-mg crawling microrobot that is driven by two 6-mg high-frequency SMA bending actuators and whose two-module configuration enables controlled differential steering and path following. During operation, the two modules are coordinately excited to generate locomotion patterns based on anisotropic friction. This functionality is enabled by the high compliance of the robotic structure, which comprises very few parts, is easily fabricated, achieves both high precision and performance, and is sufficiently predictable to be controlled in open and closed loop. To demonstrate the locomotive and steering capabilities of the SMARTI, we present a series of experimental tests, including open-loop crawling, closed-loop path following, and high-speed controlled turning. These experiments were performed using a motion capture system for sensing and an off-board digital signal processor for control. In closed loop, the SMARTI reaches a maximum sustained speed of 46 mm/s, equivalent to 3.54 body-lengths per second (BL/s), and a turning rate of 107 degrees per second (D/s) with root-mean-square (RMS) tracking errors as low as 1.7 mm. This combination of speed and maneuverability is currently unparalleled, making the SMARTI the lightest, smallest, and fastest (in BL/s) steerable and controllable crawling robot developed to date.

We present an experimental method for the modeling and system identification of wire actuators ma... more We present an experimental method for the modeling and system identification of wire actuators made from shape memory alloys (SMAs). The proposed approach employs minimum-variance adaptive tuning and control to find parameters for a modified Preisach model that can represent the hysteresis of SMA-based actuators. Thermally-and mechanicallyinduced phase transformations, known as the shape memory effect (SME) and superelasticity (or pseudoelasticity), respectively, allow the recovery of plastic deformation and enable SMA wires to behave as actuators. Both types of phase transformation display hysteretic nonlinearities in the backward and forward directions. Here, we classify the SME phase transformation hysteresis and modify the classical Preisach model to account for experimentally observed superelasticity. The proposed actuator model is validated with experiments in which an SMA wire is statically and dynamically loaded.

Bioinspiration & Biomimetics, Feb 15, 2019

We present the design, fabrication, modeling and feedback control of an earthworm-inspired soft r... more We present the design, fabrication, modeling and feedback control of an earthworm-inspired soft robot capable of bidirectional locomotion on both horizontal and inclined flat platforms. In this approach, the locomotion patterns are controlled by actively varying the coefficients of friction between the contacting surfaces of the robot and the supporting platform, thus emulating the limbless locomotion of earthworms at a conceptual level. Earthworms are characterized by segmented body structures, known as metameres, composed of longitudinal and circular muscles which during locomotion are contracted and relaxed periodically in order to generate a peristaltic wave that propagates backwards with respect to the worm's traveling direction; simultaneously, microscopic bristle-like structures (setae) on each metamere coordinately protrude or retract to provide varying traction with the ground, thus enabling the worm to burrow or crawl. The proposed soft robot replicates the muscle functionalities and setae mechanisms of earthworms employing pneumatically-driven actuators and 3D-printed casings. Using the notion of controllable subspace, we show that friction plays an indispensable role in the generation and control of locomotion in robots of this type. Based on this analysis, we introduce a simulation-based method for synthesizing and implementing feedback control schemes that enable the robot to generate forward and backward locomotion. From the set of feasible control strategies studied in simulation, we adopt a friction-modulation-based feedback control algorithm which is implementable in real time and compatible with the hardware limitations of the robotic system. Through experiments, the robot is demonstrated to be capable of bidirectional crawling on surfaces with different textures and inclinations.

arXiv (Cornell University), May 6, 2019

We introduce Bee + , a 95-mg four-winged microrobot with improved controllability and open-loop-r... more We introduce Bee + , a 95-mg four-winged microrobot with improved controllability and open-loop-response characteristics with respect to those exhibited by state-of-the-art twowinged microrobots with the same size and similar weight (i.e., the 75-mg Harvard RoboBee). The key innovation that made possible the development of Bee + is the introduction of an extremely light (28-mg) pair of twinned unimorph actuators, which enabled the design of a new microrobotic mechanism that flaps four wings independently. A first main advantage of the proposed design, compared to those of two-winged flyers, is that by increasing the number of actuators from two to four, the number of direct control inputs increases from three to four when simple sinusoidal excitations are employed. A second advantage of Bee + is that its four-wing configuration and flapping mode naturally damp the rotational disturbances that commonly affect the yaw degree of freedom of two-winged microrobots. In addition, the proposed design greatly reduces the complexity of the associated fabrication process compared to those of other microrobots, as the unimorph actuators are fairly easy to build. Lastly, we hypothesize that given the relatively low wing-loading affecting their flapping mechanisms, the life expectancy of Bee + s must be considerably higher than those of the two-winged counterparts. The functionality and basic capabilities of the robot are demonstrated through a set of simple control experiments. Index Terms-Micro/nano robots, automation at micro-nano scales, aerial systems: mechanics and control. I. INTRODUCTION I NSECT-SIZED aerial robots have the potential to be employed in a great number of tasks such as infrastructure inspection, search and rescue after disasters, artificial pollination, reconnaissance, surveillance, et cetera, which has motivated the interest of many research groups. Consistently, as an emerging field, research on cm-scale flapping-wing robots driven by piezoelectric actuators has produced numerous design innovations over the course of more than two decades [1]-[4]. However, state-of-the-art flying microrobots, such as those reported in [5] and [6], do not adequately replicate the astounding capabilities exhibited by flying insects. An obstacle that has limited progress is the fact that unlike insects which simultaneously use multiple distributed muscles for flapping and control [7], flapping-wing flying robots are driven by a small number of discrete actuators due to stringent constraints in size and weight as well as fabrication challenges.

IEEE Transactions on Robotics, Apr 1, 2023

We present a new experimental method for the generation and real-time implementation of high-spee... more We present a new experimental method for the generation and real-time implementation of high-speed aerobatic maneuvers, including multiple flips, on a 19-gram autonomous quadrotor. A key element in the proposed approach is the design and experimental tuning of a gain scheduling control strategy in which two linear time-invariant (LTI) controllers are alternatingly activated and deactivated to switch between a normal flight mode and an aerobatic mode, enabling the flyer to perform consecutive multiple flips in a robustly stable manner. The implementation of the controllers is done using on-board power, sensors and computing capabilities, so that the quadrotor remains fully autonomous during flight. Notably, the attainment of autonomy, using real-time control, is made possible by the development of a new method for speed planning based on cubic functions, the geometric generalization of the notion of multi-flip and the empirical identification of the flyer's dynamics, required for trajectory generation and controller synthesis. Compelling experimental results demonstrate the suitability of the proposed approach. In particular, we present maneuvers that include consecutive single, double, and triple flips about the flyer's roll principal axis and a non-principal axis. To the best of our knowledge, to this date, the flyer used in this research is the smallest controlled quadrotor to have autonomously accomplished three consecutive flips while remaining stable.

IEEE Transactions on Control Systems and Technology, Nov 1, 2020

We present a method for synthesizing high-performance controllers for the autonomous execution of... more We present a method for synthesizing high-performance controllers for the autonomous execution of aerobatic quadrotor maneuvers that are defined by rapid variations of the flyer’s angular velocity, such as multi-flips or the Pugachev’s cobra. In the proposed approach, we employ Lyapunov theory to find the sets of control parameters that make the unique fixed point of the closed-loop angular-velocity error dynamics exponentially stable during an aerobatic maneuver, provided that the angular-velocity reference satisfies a set of conditions. Then, we show that the resulting closed-loop attitude error dynamics remain bounded. The proposed controller synthesis method allows for the minimization of a parameterized performance figure of merit (PFM), which is employed to measure the angular-velocity control error accumulated during a maneuver. The approach adopted here is to show that a primal optimization problem can be reformulated as a series of quasiconvex sub-problems; then, we introduce a technique to find a solution and prove that this optimum is global. By design, the resulting controllers have a simple linear time-invariant (LTI) structure that depends on a small number of coefficients, which makes the experimental implementation of the control schemes extremely efficient and the associated real-time computational cost very low. The effectiveness of the introduced methods for controller design and performance optimization is compellingly demonstrated through theoretical analysis, simulations, and experiments in which high-speed multi-flip aerobatic maneuvers are executed.

We present a method for the synthesis and stability analysis of automatic controllers capable of ... more We present a method for the synthesis and stability analysis of automatic controllers capable of autonomously flying a 19-gram quadrotor during the execution of high-speed multi-flip maneuvers. The discussed approach for design and analysis is based on Lyapunov's direct method, numerical results and experimental data. Here, the resulting real-time closed-loop scheme employs a linear time-invariant (LTI) controller that stabilizes the nonlinear unstable dynamics of the open-loop system while enabling high performance during aggressive flight. In this approach, we define a parameterized quadratic proto-Lyapunov function associated with the nonautonomous closed-loop flyer's dynamics that, for a set of feasible parameters, becomes Lyapunov. This parameterization allows for the synthesis and selection of stabilizing controllers which are tested through numerical simulation, employing an open-loop plant model obtained from first principles and simple system identification experiments. The suitability of the proposed method is empirically demonstrated through several aggressive autonomous flight experiments that include single, double and triple flips about two different axes of the flyer.

IEEE robotics and automation letters, Oct 1, 2020

We present the design, fabrication and experimental testing of SMALLBug, a 30-mg crawling microro... more We present the design, fabrication and experimental testing of SMALLBug, a 30-mg crawling microrobot that is 13 mm in length and can locomote at actuation frequencies of up to 20 Hz. The robot is driven by an electrically-powered 6-mg bending actuator that is composed of a thin <italic>shape-memory alloy</italic> (SMA) wire and a carbon-fiber piece that acts as a loading leaf-spring. This configuration enables the generation of high-speed thermally-induced phase transformations of the SMA material to produce high-frequency periodic actuation. During development, several actuator prototypes with different mechanical stiffnesses were tested and characterized by measuring their bending motions when excited with <italic>pulse-width modulation</italic> (PWM) voltages with a variety of frequencies and <italic>duty cycles</italic> (DCs). In a similar manner, the displacement–force characteristic of the actuator chosen to drive SMALLBug was identified by measuring its bending displacements under a number of different loads ranging from 4.22 to 83.8 mN. The locomotion capabilities of SMALLBug were experimentally tested at three different input actuation frequencies, which were observed to produce three distinct gaits. At the <italic>low</italic> frequency of 2 Hz, the robot locomotes with a <italic>crawling gait</italic> similar to that of inchworms; at the <italic>moderate</italic> frequency of 10 Hz, the robot advances smoothly at an approximately constant speed using a <italic>shuffling gait</italic>; and at the <italic>high</italic> frequency of 20 Hz, the robot generates small and fast jumps in a <italic>galloping gait</italic>, reaching average speeds of up to 17 <inline-formula><tex-math notation="LaTeX">$\boldsymbol{\text {mm}} \cdot \boldsymbol{\text {s}}^{\boldsymbol{\text {--}}\boldsymbol{\text {1}}}$</tex-math></inline-formula>, equivalent to 1.3 <italic>body-lengths per second</italic> (BLPS).

arXiv (Cornell University), Jul 11, 2017

We present the design, fabrication, modeling and feedback control of an earthworm-inspired soft r... more We present the design, fabrication, modeling and feedback control of an earthworm-inspired soft robot that crawls on flat surfaces by actively changing the frictional forces acting on its body. Earthworms are segmented and composed of repeating units called metameres. During crawling, muscles enable these metameres to interact with each other in order to generate peristaltic waves and retractable setae (bristles) produce variable traction. The proposed robot crawls by replicating these two mechanisms, employing pneumatically-powered soft actuators. Using the notion of controllable subspaces, we show that locomotion would be impossible for this robot in the absence of friction. Also, we present a method to generate feasible control inputs to achieve crawling, perform exhaustive numerical simulations of feedforward-controlled locomotion, and describe the synthesis and implementation of suitable real-time friction-based feedback controllers for crawling. The effectiveness of the proposed approach is demonstrated through analysis, simulations and locomotion experiments.

We present a study of the dynamics and control of a 28-gram quadrotor during the execution of aer... more We present a study of the dynamics and control of a 28-gram quadrotor during the execution of aerobatic maneuvers in the presence of propeller-aerodynamic-coefficient and torque-latency time-variations. First, through a momentum-theory-based analysis of the flow field surrounding the robot during aerobatic flight, we develop a dynamic linear time-varying (LTV) description of the torque acting on the flyer in which both considered effects explicitly appear as distinct mathematical terms. Then, an adaptive control scheme, composed of a backstepping controller and a modified recursive least-squares (RLS) estimator, is designed to counteract the negative effects produced by the time-varying dynamics of the torque that drives the flyer. The suitability and efficacy of the proposed methods are demonstrated through real-time flight experiments in which the quadrotor autonomously performs three different types of aerobatic maneuvers: triple flips, Pugachev's Cobras and mixed flips. Furthermore, analyses of the experimental data compellingly show that the proposed control scheme consistently improves the performance of the aerial vehicle during aerobatic flight, compared to those achieved by using a high-performance linear time-invariant (LTI) controller that does not account for time-varying torque generation.

The dynamics of quadrotors are affected by time-varying torque latency, which can greatly alter t... more The dynamics of quadrotors are affected by time-varying torque latency, which can greatly alter the stability robustness and performance of the closed-loop control schemes employed for flight; this issue is especially relevant during the execution of aerobatic maneuvers such as high-speed multi-flips. To address this problem, we propose two controller synthesis methods associated with two different modeling approaches. In the first approach, we describe torque latency with a linear time-invariant (LTI)model, identified through ground experiments, which is then used to design a backstepping-based nonlinear controller. In the second approach, we employ an improved linear time-varying (LTV)model with a priori unknown parameters, which is used to synthesize and implement a novel nonlinear adaptive control scheme updated in real time using the recursive least-squares (RLS)algorithm. Empirical observations suggest that the torque delay affecting the system depends on the time-varying angular speed of the flyer and its derivative. This phenomenon is explained by the fact that the aerodynamic forces produced by, and acting on, the rotating propellers vary with the local velocity of the incident flows. Hence, in the proposed adaptive structure, we define the parameters of the LTV latency model as linear functions of the angular speed reference and its derivative. Experimental results compellingly demonstrate the efficacy of the methods introduced in this paper; compared to the highperformance linear controller in [1]–[3], the backstepping-based control scheme and adaptive controller decrease the average root mean square (RMS)value of the control error by 17.82 % and 38.42 %, respectively.

arXiv (Cornell University), Oct 25, 2019

We discuss the problem of designing and implementing controllers for insect-scale flapping-wing m... more We discuss the problem of designing and implementing controllers for insect-scale flapping-wing micro air vehicles (FWMAVs), from a unifying perspective and employing two different experimental platforms; namely, a Harvard RoboBee-like two-winged robot and the four-winged USC Bee +. Through experiments, we demonstrate that a method that employs quaternion coordinates for attitude control, developed to control quadrotors, can be applied to drive both robotic insects considered in this work. The proposed notion that a generic strategy can be used to control several types of artificial insects with some common characteristics was preliminarily tested and validated using a set of experiments, which include position-and attitude-controlled flights. We believe that the presented results are interesting and valuable from both the research and educational perspectives.

Sensors and Actuators A-physical, Jul 1, 2022

Abstract Microrobots at the subcentimeter scale have the potential to perform useful complex task... more Abstract Microrobots at the subcentimeter scale have the potential to perform useful complex tasks if they were to become energy independent and could operate autonomously. The vast majority of current microrobotic systems lack the ability to carry sufficient onboard power to operate and, therefore, remain tethered to stationary sources of energy in laboratory environments. Recent published work demonstrated that chemical fuels can react under feedback control on the surfaces of tensioned shape-memory alloy (SMA) nickel-titanium (NiTi) wires coated with platinum (Pt) catalyst. Combining catalytic combustion of fuels with high energy densities with the high work densities of SMA wires is a promising approach to provide onboard power to microrobots. In this article, we present a novel 7-mg SMA-based miniature catalytic-combustion engine for millimeter-scale robotic actuation that is composed of a looped NiTi-Pt composite wire with a core diameter of 38 μ m and a flat carbon-fiber beam with a length of 13 mm. This beam acts as a leaf spring during operation. The proposed design of the engine has a flat and narrow geometry, functions according to a periodic-unimorph actuation mode, and can operate at frequencies as high as 6 Hz and lift 650 times its own weight while functioning at 1 Hz, thus producing 39.5 μ W of average power in the process. For the purposes of design and analysis, we derived a model of the heat transfer processes involved during actuation, which combined with a Preisach-model-based description of the SMA wire dynamics, enabled us to numerically simulate the response of the miniature system, and thus predict its performance in terms of frequency and actuation output. The suitability for microrobotics and functionality of the proposed approach is demonstrated through experimental results using a custom-built fast-response high-precision system of fuel delivery.

IEEE Transactions on Robotics

We present the design, fabrication and feedback control of an earthworm-inspired soft robot capab... more We present the design, fabrication and feedback control of an earthworm-inspired soft robot capable of locomoting inside pipes. The bodies of natural earthworms are composed of repeated deformable structural units, actuated by axial and longitudinal muscles, employed to generate the body motions required for limbless locomotion, such as burrowing. Following this basic notion, we propose a new pneumatically-driven soft robotic system, built by integrating together two radial actuators with an axial actuator, which mimics the motion and functionality of one body segment of a natural earthworm. The suitability of the proposed approach is demonstrated experimentally through three basic locomotion tests: horizontal motion, vertical motion and oblique motion inside a varying-angle transparent pipe.

We present a new experimental method for the generation and real-time implementation of high-spee... more We present a new experimental method for the generation and real-time implementation of high-speed aerobatic maneuvers, including multiple flips, on a 19-g autonomous quadrotor. The proposed approach is based on a gain-scheduling control strategy, where two linear time-invariant (LTI) controllers are employed to switch between a normal flight mode and a high-speed aerobatic flight mode. All the realtime algorithms involved in flight control are implemented and run using on-board power, sensors and computing capabilities in order to maintain complete autonomy during flight. Fully autonomous high-speed aerobatic behavior is accomplished with the use of a new method for speed planning, the generalization of the notion of multi-flip maneuver and the empirical identification of the flyer’s dynamics, required for trajectory generation and controller synthesis. Compelling experimental results demonstrate the suitability of the proposed approach.

2012 IEEE/RSJ International Conference on Intelligent Robots and Systems, 2012

The Harvard RoboBee is the first insect-scale flapping-wing robot weighing less than 100 mg that ... more The Harvard RoboBee is the first insect-scale flapping-wing robot weighing less than 100 mg that is able to lift its own weight. However, when flown without guide wires, this vehicle quickly tumbles after takeoff because of instability in its dynamics. Here, we show that by adding aerodynamic dampers, we can can alter the vehicle's dynamics to stabilize its upright orientation. We provide an analysis using wind tunnel experiments and a dynamic model. We demonstrate stable vertical takeoff, and using a marker-based external camera tracking system, hovering altitude control in an active feedback loop. These results provide a stable platform for both system dynamics characterization and unconstrained active maneuvers of the vehicle and represent the first known hovering demonstration of an insect-scale flapping-wing robot.

Journal of Intelligent & Robotic Systems, 2014

We present a model-free experimental method to find a control strategy for achieving stable fligh... more We present a model-free experimental method to find a control strategy for achieving stable flight of a dual-actuator biologically inspired flapping wing flying microrobot during hovering. The N. O. Pérez-Arancibia and P.-E. J. Duhamel contributed equally to this work.

We present the design, fabrication and feedback control of an earthworm-inspired multi-material m... more We present the design, fabrication and feedback control of an earthworm-inspired multi-material multi-actuator soft robot capable of locomoting inside pipes. The bodies of natural earthworms are composed of repeated deformable structural units, called metameres, that generate the peristaltic body motions required for limbless underground burrowing and above-ground crawling. In an earthworm, each individual metamere is actuated by circular and longitudinal muscles that are activated synchronously by the animal's nervous system. Here, adopting the basic functional principles of metameric worms, we propose a new pneumatically-driven soft robotic system that mimics the motions and replicates the functionality of a single burrowing earthworm's segment. The suitability of the proposed approach is demonstrated experimentally through three basic locomotion tests: horizontal motion, vertical motion and oblique motion inside a varying-slope transparent pipe.

IEEE robotics and automation letters, Oct 1, 2021

We present the shape-memory alloy (SMA) robotic traveling insect (SMARTI), a 60-mg crawling micro... more We present the shape-memory alloy (SMA) robotic traveling insect (SMARTI), a 60-mg crawling microrobot that is driven by two 6-mg high-frequency SMA bending actuators and whose two-module configuration enables controlled differential steering and path following. During operation, the two modules are coordinately excited to generate locomotion patterns based on anisotropic friction. This functionality is enabled by the high compliance of the robotic structure, which comprises very few parts, is easily fabricated, achieves both high precision and performance, and is sufficiently predictable to be controlled in open and closed loop. To demonstrate the locomotive and steering capabilities of the SMARTI, we present a series of experimental tests, including open-loop crawling, closed-loop path following, and high-speed controlled turning. These experiments were performed using a motion capture system for sensing and an off-board digital signal processor for control. In closed loop, the SMARTI reaches a maximum sustained speed of 46 mm/s, equivalent to 3.54 body-lengths per second (BL/s), and a turning rate of 107 degrees per second (D/s) with root-mean-square (RMS) tracking errors as low as 1.7 mm. This combination of speed and maneuverability is currently unparalleled, making the SMARTI the lightest, smallest, and fastest (in BL/s) steerable and controllable crawling robot developed to date.

We present an experimental method for the modeling and system identification of wire actuators ma... more We present an experimental method for the modeling and system identification of wire actuators made from shape memory alloys (SMAs). The proposed approach employs minimum-variance adaptive tuning and control to find parameters for a modified Preisach model that can represent the hysteresis of SMA-based actuators. Thermally-and mechanicallyinduced phase transformations, known as the shape memory effect (SME) and superelasticity (or pseudoelasticity), respectively, allow the recovery of plastic deformation and enable SMA wires to behave as actuators. Both types of phase transformation display hysteretic nonlinearities in the backward and forward directions. Here, we classify the SME phase transformation hysteresis and modify the classical Preisach model to account for experimentally observed superelasticity. The proposed actuator model is validated with experiments in which an SMA wire is statically and dynamically loaded.

Bioinspiration & Biomimetics, Feb 15, 2019

We present the design, fabrication, modeling and feedback control of an earthworm-inspired soft r... more We present the design, fabrication, modeling and feedback control of an earthworm-inspired soft robot capable of bidirectional locomotion on both horizontal and inclined flat platforms. In this approach, the locomotion patterns are controlled by actively varying the coefficients of friction between the contacting surfaces of the robot and the supporting platform, thus emulating the limbless locomotion of earthworms at a conceptual level. Earthworms are characterized by segmented body structures, known as metameres, composed of longitudinal and circular muscles which during locomotion are contracted and relaxed periodically in order to generate a peristaltic wave that propagates backwards with respect to the worm's traveling direction; simultaneously, microscopic bristle-like structures (setae) on each metamere coordinately protrude or retract to provide varying traction with the ground, thus enabling the worm to burrow or crawl. The proposed soft robot replicates the muscle functionalities and setae mechanisms of earthworms employing pneumatically-driven actuators and 3D-printed casings. Using the notion of controllable subspace, we show that friction plays an indispensable role in the generation and control of locomotion in robots of this type. Based on this analysis, we introduce a simulation-based method for synthesizing and implementing feedback control schemes that enable the robot to generate forward and backward locomotion. From the set of feasible control strategies studied in simulation, we adopt a friction-modulation-based feedback control algorithm which is implementable in real time and compatible with the hardware limitations of the robotic system. Through experiments, the robot is demonstrated to be capable of bidirectional crawling on surfaces with different textures and inclinations.

arXiv (Cornell University), May 6, 2019

We introduce Bee + , a 95-mg four-winged microrobot with improved controllability and open-loop-r... more We introduce Bee + , a 95-mg four-winged microrobot with improved controllability and open-loop-response characteristics with respect to those exhibited by state-of-the-art twowinged microrobots with the same size and similar weight (i.e., the 75-mg Harvard RoboBee). The key innovation that made possible the development of Bee + is the introduction of an extremely light (28-mg) pair of twinned unimorph actuators, which enabled the design of a new microrobotic mechanism that flaps four wings independently. A first main advantage of the proposed design, compared to those of two-winged flyers, is that by increasing the number of actuators from two to four, the number of direct control inputs increases from three to four when simple sinusoidal excitations are employed. A second advantage of Bee + is that its four-wing configuration and flapping mode naturally damp the rotational disturbances that commonly affect the yaw degree of freedom of two-winged microrobots. In addition, the proposed design greatly reduces the complexity of the associated fabrication process compared to those of other microrobots, as the unimorph actuators are fairly easy to build. Lastly, we hypothesize that given the relatively low wing-loading affecting their flapping mechanisms, the life expectancy of Bee + s must be considerably higher than those of the two-winged counterparts. The functionality and basic capabilities of the robot are demonstrated through a set of simple control experiments. Index Terms-Micro/nano robots, automation at micro-nano scales, aerial systems: mechanics and control. I. INTRODUCTION I NSECT-SIZED aerial robots have the potential to be employed in a great number of tasks such as infrastructure inspection, search and rescue after disasters, artificial pollination, reconnaissance, surveillance, et cetera, which has motivated the interest of many research groups. Consistently, as an emerging field, research on cm-scale flapping-wing robots driven by piezoelectric actuators has produced numerous design innovations over the course of more than two decades [1]-[4]. However, state-of-the-art flying microrobots, such as those reported in [5] and [6], do not adequately replicate the astounding capabilities exhibited by flying insects. An obstacle that has limited progress is the fact that unlike insects which simultaneously use multiple distributed muscles for flapping and control [7], flapping-wing flying robots are driven by a small number of discrete actuators due to stringent constraints in size and weight as well as fabrication challenges.

IEEE Transactions on Robotics, Apr 1, 2023

We present a new experimental method for the generation and real-time implementation of high-spee... more We present a new experimental method for the generation and real-time implementation of high-speed aerobatic maneuvers, including multiple flips, on a 19-gram autonomous quadrotor. A key element in the proposed approach is the design and experimental tuning of a gain scheduling control strategy in which two linear time-invariant (LTI) controllers are alternatingly activated and deactivated to switch between a normal flight mode and an aerobatic mode, enabling the flyer to perform consecutive multiple flips in a robustly stable manner. The implementation of the controllers is done using on-board power, sensors and computing capabilities, so that the quadrotor remains fully autonomous during flight. Notably, the attainment of autonomy, using real-time control, is made possible by the development of a new method for speed planning based on cubic functions, the geometric generalization of the notion of multi-flip and the empirical identification of the flyer's dynamics, required for trajectory generation and controller synthesis. Compelling experimental results demonstrate the suitability of the proposed approach. In particular, we present maneuvers that include consecutive single, double, and triple flips about the flyer's roll principal axis and a non-principal axis. To the best of our knowledge, to this date, the flyer used in this research is the smallest controlled quadrotor to have autonomously accomplished three consecutive flips while remaining stable.

IEEE Transactions on Control Systems and Technology, Nov 1, 2020

We present a method for synthesizing high-performance controllers for the autonomous execution of... more We present a method for synthesizing high-performance controllers for the autonomous execution of aerobatic quadrotor maneuvers that are defined by rapid variations of the flyer’s angular velocity, such as multi-flips or the Pugachev’s cobra. In the proposed approach, we employ Lyapunov theory to find the sets of control parameters that make the unique fixed point of the closed-loop angular-velocity error dynamics exponentially stable during an aerobatic maneuver, provided that the angular-velocity reference satisfies a set of conditions. Then, we show that the resulting closed-loop attitude error dynamics remain bounded. The proposed controller synthesis method allows for the minimization of a parameterized performance figure of merit (PFM), which is employed to measure the angular-velocity control error accumulated during a maneuver. The approach adopted here is to show that a primal optimization problem can be reformulated as a series of quasiconvex sub-problems; then, we introduce a technique to find a solution and prove that this optimum is global. By design, the resulting controllers have a simple linear time-invariant (LTI) structure that depends on a small number of coefficients, which makes the experimental implementation of the control schemes extremely efficient and the associated real-time computational cost very low. The effectiveness of the introduced methods for controller design and performance optimization is compellingly demonstrated through theoretical analysis, simulations, and experiments in which high-speed multi-flip aerobatic maneuvers are executed.

We present a method for the synthesis and stability analysis of automatic controllers capable of ... more We present a method for the synthesis and stability analysis of automatic controllers capable of autonomously flying a 19-gram quadrotor during the execution of high-speed multi-flip maneuvers. The discussed approach for design and analysis is based on Lyapunov's direct method, numerical results and experimental data. Here, the resulting real-time closed-loop scheme employs a linear time-invariant (LTI) controller that stabilizes the nonlinear unstable dynamics of the open-loop system while enabling high performance during aggressive flight. In this approach, we define a parameterized quadratic proto-Lyapunov function associated with the nonautonomous closed-loop flyer's dynamics that, for a set of feasible parameters, becomes Lyapunov. This parameterization allows for the synthesis and selection of stabilizing controllers which are tested through numerical simulation, employing an open-loop plant model obtained from first principles and simple system identification experiments. The suitability of the proposed method is empirically demonstrated through several aggressive autonomous flight experiments that include single, double and triple flips about two different axes of the flyer.

IEEE robotics and automation letters, Oct 1, 2020

We present the design, fabrication and experimental testing of SMALLBug, a 30-mg crawling microro... more We present the design, fabrication and experimental testing of SMALLBug, a 30-mg crawling microrobot that is 13 mm in length and can locomote at actuation frequencies of up to 20 Hz. The robot is driven by an electrically-powered 6-mg bending actuator that is composed of a thin <italic>shape-memory alloy</italic> (SMA) wire and a carbon-fiber piece that acts as a loading leaf-spring. This configuration enables the generation of high-speed thermally-induced phase transformations of the SMA material to produce high-frequency periodic actuation. During development, several actuator prototypes with different mechanical stiffnesses were tested and characterized by measuring their bending motions when excited with <italic>pulse-width modulation</italic> (PWM) voltages with a variety of frequencies and <italic>duty cycles</italic> (DCs). In a similar manner, the displacement–force characteristic of the actuator chosen to drive SMALLBug was identified by measuring its bending displacements under a number of different loads ranging from 4.22 to 83.8 mN. The locomotion capabilities of SMALLBug were experimentally tested at three different input actuation frequencies, which were observed to produce three distinct gaits. At the <italic>low</italic> frequency of 2 Hz, the robot locomotes with a <italic>crawling gait</italic> similar to that of inchworms; at the <italic>moderate</italic> frequency of 10 Hz, the robot advances smoothly at an approximately constant speed using a <italic>shuffling gait</italic>; and at the <italic>high</italic> frequency of 20 Hz, the robot generates small and fast jumps in a <italic>galloping gait</italic>, reaching average speeds of up to 17 <inline-formula><tex-math notation="LaTeX">$\boldsymbol{\text {mm}} \cdot \boldsymbol{\text {s}}^{\boldsymbol{\text {--}}\boldsymbol{\text {1}}}$</tex-math></inline-formula>, equivalent to 1.3 <italic>body-lengths per second</italic> (BLPS).

arXiv (Cornell University), Jul 11, 2017

We present the design, fabrication, modeling and feedback control of an earthworm-inspired soft r... more We present the design, fabrication, modeling and feedback control of an earthworm-inspired soft robot that crawls on flat surfaces by actively changing the frictional forces acting on its body. Earthworms are segmented and composed of repeating units called metameres. During crawling, muscles enable these metameres to interact with each other in order to generate peristaltic waves and retractable setae (bristles) produce variable traction. The proposed robot crawls by replicating these two mechanisms, employing pneumatically-powered soft actuators. Using the notion of controllable subspaces, we show that locomotion would be impossible for this robot in the absence of friction. Also, we present a method to generate feasible control inputs to achieve crawling, perform exhaustive numerical simulations of feedforward-controlled locomotion, and describe the synthesis and implementation of suitable real-time friction-based feedback controllers for crawling. The effectiveness of the proposed approach is demonstrated through analysis, simulations and locomotion experiments.

We present a study of the dynamics and control of a 28-gram quadrotor during the execution of aer... more We present a study of the dynamics and control of a 28-gram quadrotor during the execution of aerobatic maneuvers in the presence of propeller-aerodynamic-coefficient and torque-latency time-variations. First, through a momentum-theory-based analysis of the flow field surrounding the robot during aerobatic flight, we develop a dynamic linear time-varying (LTV) description of the torque acting on the flyer in which both considered effects explicitly appear as distinct mathematical terms. Then, an adaptive control scheme, composed of a backstepping controller and a modified recursive least-squares (RLS) estimator, is designed to counteract the negative effects produced by the time-varying dynamics of the torque that drives the flyer. The suitability and efficacy of the proposed methods are demonstrated through real-time flight experiments in which the quadrotor autonomously performs three different types of aerobatic maneuvers: triple flips, Pugachev's Cobras and mixed flips. Furthermore, analyses of the experimental data compellingly show that the proposed control scheme consistently improves the performance of the aerial vehicle during aerobatic flight, compared to those achieved by using a high-performance linear time-invariant (LTI) controller that does not account for time-varying torque generation.

The dynamics of quadrotors are affected by time-varying torque latency, which can greatly alter t... more The dynamics of quadrotors are affected by time-varying torque latency, which can greatly alter the stability robustness and performance of the closed-loop control schemes employed for flight; this issue is especially relevant during the execution of aerobatic maneuvers such as high-speed multi-flips. To address this problem, we propose two controller synthesis methods associated with two different modeling approaches. In the first approach, we describe torque latency with a linear time-invariant (LTI)model, identified through ground experiments, which is then used to design a backstepping-based nonlinear controller. In the second approach, we employ an improved linear time-varying (LTV)model with a priori unknown parameters, which is used to synthesize and implement a novel nonlinear adaptive control scheme updated in real time using the recursive least-squares (RLS)algorithm. Empirical observations suggest that the torque delay affecting the system depends on the time-varying angular speed of the flyer and its derivative. This phenomenon is explained by the fact that the aerodynamic forces produced by, and acting on, the rotating propellers vary with the local velocity of the incident flows. Hence, in the proposed adaptive structure, we define the parameters of the LTV latency model as linear functions of the angular speed reference and its derivative. Experimental results compellingly demonstrate the efficacy of the methods introduced in this paper; compared to the highperformance linear controller in [1]–[3], the backstepping-based control scheme and adaptive controller decrease the average root mean square (RMS)value of the control error by 17.82 % and 38.42 %, respectively.

arXiv (Cornell University), Oct 25, 2019

We discuss the problem of designing and implementing controllers for insect-scale flapping-wing m... more We discuss the problem of designing and implementing controllers for insect-scale flapping-wing micro air vehicles (FWMAVs), from a unifying perspective and employing two different experimental platforms; namely, a Harvard RoboBee-like two-winged robot and the four-winged USC Bee +. Through experiments, we demonstrate that a method that employs quaternion coordinates for attitude control, developed to control quadrotors, can be applied to drive both robotic insects considered in this work. The proposed notion that a generic strategy can be used to control several types of artificial insects with some common characteristics was preliminarily tested and validated using a set of experiments, which include position-and attitude-controlled flights. We believe that the presented results are interesting and valuable from both the research and educational perspectives.

Sensors and Actuators A-physical, Jul 1, 2022

Abstract Microrobots at the subcentimeter scale have the potential to perform useful complex task... more Abstract Microrobots at the subcentimeter scale have the potential to perform useful complex tasks if they were to become energy independent and could operate autonomously. The vast majority of current microrobotic systems lack the ability to carry sufficient onboard power to operate and, therefore, remain tethered to stationary sources of energy in laboratory environments. Recent published work demonstrated that chemical fuels can react under feedback control on the surfaces of tensioned shape-memory alloy (SMA) nickel-titanium (NiTi) wires coated with platinum (Pt) catalyst. Combining catalytic combustion of fuels with high energy densities with the high work densities of SMA wires is a promising approach to provide onboard power to microrobots. In this article, we present a novel 7-mg SMA-based miniature catalytic-combustion engine for millimeter-scale robotic actuation that is composed of a looped NiTi-Pt composite wire with a core diameter of 38 μ m and a flat carbon-fiber beam with a length of 13 mm. This beam acts as a leaf spring during operation. The proposed design of the engine has a flat and narrow geometry, functions according to a periodic-unimorph actuation mode, and can operate at frequencies as high as 6 Hz and lift 650 times its own weight while functioning at 1 Hz, thus producing 39.5 μ W of average power in the process. For the purposes of design and analysis, we derived a model of the heat transfer processes involved during actuation, which combined with a Preisach-model-based description of the SMA wire dynamics, enabled us to numerically simulate the response of the miniature system, and thus predict its performance in terms of frequency and actuation output. The suitability for microrobotics and functionality of the proposed approach is demonstrated through experimental results using a custom-built fast-response high-precision system of fuel delivery.

IEEE Transactions on Robotics

We present the design, fabrication and feedback control of an earthworm-inspired soft robot capab... more We present the design, fabrication and feedback control of an earthworm-inspired soft robot capable of locomoting inside pipes. The bodies of natural earthworms are composed of repeated deformable structural units, actuated by axial and longitudinal muscles, employed to generate the body motions required for limbless locomotion, such as burrowing. Following this basic notion, we propose a new pneumatically-driven soft robotic system, built by integrating together two radial actuators with an axial actuator, which mimics the motion and functionality of one body segment of a natural earthworm. The suitability of the proposed approach is demonstrated experimentally through three basic locomotion tests: horizontal motion, vertical motion and oblique motion inside a varying-angle transparent pipe.

We present a new experimental method for the generation and real-time implementation of high-spee... more We present a new experimental method for the generation and real-time implementation of high-speed aerobatic maneuvers, including multiple flips, on a 19-g autonomous quadrotor. The proposed approach is based on a gain-scheduling control strategy, where two linear time-invariant (LTI) controllers are employed to switch between a normal flight mode and a high-speed aerobatic flight mode. All the realtime algorithms involved in flight control are implemented and run using on-board power, sensors and computing capabilities in order to maintain complete autonomy during flight. Fully autonomous high-speed aerobatic behavior is accomplished with the use of a new method for speed planning, the generalization of the notion of multi-flip maneuver and the empirical identification of the flyer’s dynamics, required for trajectory generation and controller synthesis. Compelling experimental results demonstrate the suitability of the proposed approach.

2012 IEEE/RSJ International Conference on Intelligent Robots and Systems, 2012

The Harvard RoboBee is the first insect-scale flapping-wing robot weighing less than 100 mg that ... more The Harvard RoboBee is the first insect-scale flapping-wing robot weighing less than 100 mg that is able to lift its own weight. However, when flown without guide wires, this vehicle quickly tumbles after takeoff because of instability in its dynamics. Here, we show that by adding aerodynamic dampers, we can can alter the vehicle's dynamics to stabilize its upright orientation. We provide an analysis using wind tunnel experiments and a dynamic model. We demonstrate stable vertical takeoff, and using a marker-based external camera tracking system, hovering altitude control in an active feedback loop. These results provide a stable platform for both system dynamics characterization and unconstrained active maneuvers of the vehicle and represent the first known hovering demonstration of an insect-scale flapping-wing robot.

Journal of Intelligent & Robotic Systems, 2014

We present a model-free experimental method to find a control strategy for achieving stable fligh... more We present a model-free experimental method to find a control strategy for achieving stable flight of a dual-actuator biologically inspired flapping wing flying microrobot during hovering. The N. O. Pérez-Arancibia and P.-E. J. Duhamel contributed equally to this work.