Néstor Osvaldo Pérez-Arancibia

Design and control of a bio-inspired soft wearable robotic device for ankle-foot rehabilitation.

We describe the design and control of a wearable robotic device powered by pneumatic artificial muscle actuators for use in ankle-foot rehabilitation. The design is inspired by the biological musculoskeletal system of the human foot and lower leg, mimicking the morphology and the functionality of the biological muscle-tendon-ligament structure. A key feature of the device is its soft structure that provides active assistance without restricting natural degrees of freedom at the ankle joint. Four pneumatic artificial muscles assist dorsiflexion and plantarflexion as well as inversion and eversion. The prototype is also equipped with various embedded sensors for gait pattern analysis. For the subject tested, the prototype is capable of generating an ankle range of motion of 27° (14° dorsiflexion and 13° plantarflexion). The controllability of the system is experimentally demonstrated using a linear time-invariant (LTI) controller. The controller is found using an identified LTI model of the system, resulting from the interaction of the soft orthotic device with a human leg, and model-based classical control design techniques. The suitability of the proposed control strategy is demonstrated with several angle-reference following experiments.

Progress on 'pico' air vehicles

As the characteristic size of a flying robot decreases, the challenges for successful flight revert to basic questions of fabrication, actuation, fluid mechanics, stabilization, and power, whereas such questions have in general been answered for larger aircraft. When developing a flying robot on the scale of a common housefly, all hardware must be developed from scratch as there is nothing ‘off-the-shelf’ which can be used for mechanisms, sensors, or computation that would satisfy the extreme mass and power limitations. This technology void also applies to techniques available for fabrication and assembly of the aeromechanical components: the scale and complexity of the mechanical features requires new ways to design and prototype at scales between macro and microeletromechanical systems, but with rich topologies and material choices one would expect when designing human-scale vehicles. With these challenges in mind, we present progress in the essential technologies for insect-scale robots, or ‘pico’ air vehicles.

First controlled vertical flight of a biologically inspired microrobot

In this paper, we present experimental results on altitude control of a flying microrobot. The problem is approached in two stages. In the first stage, system identification of two relevant subsystems composing the microrobot is performed, using a static flapping experimental setup. In the second stage, the information gathered through the static flapping experiments is employed to design the controller used in vertical flight. The design of the proposed controller relies on the idea of treating an exciting signal as a subsystem of the microrobot. The methods and results presented here are a key step toward achieving total autonomy of bio-inspired flying microrobots.

Biologically Inspired Optical-Flow Sensing for Altitude Control of Flapping-Wing Microrobots

We present the design and fabrication of a 33-mg 1-D optical-flow-based altitude sensor and its integration with a 68-mg flapping-wing flying microrobot. For the first time, an on-board sensor is successfully used to measure altitude for feedback control in a flyer of this size. Both the control strategy and the sensing system are biologically inspired. The control strategy relies on amplitude modulation mediated by optical-flow sensing. The research presented here is a key step toward achieving the goal of complete autonomy for at-scale flying robotic insects, since this demonstrates that strategies for controlling flapping-wing microrobots in vertical flight can rely on optical-flow-based on-board sensors. In order to demonstrate the efficacy of the proposed sensing system and suitability of the combined sensing and control strategies, six experimental cases are presented and discussed here.

Lift Force Control of Flapping-Wing Microrobots Using Adaptive Feedforward Schemes

This paper introduces a methodology for designing real-time controllers capable of enforcing desired trajectories on microrobotic insects in vertical flight and hovering. The main idea considered in this work is that altitude control can be translated into a problem of lift force control. Through analyses and experiments, we describe the proposed control strategy, which is fundamentally adaptive with some elements of model-based control. In order to test and explain the method for controller synthesis and tuning, a static single-wing flapping mechanism is employed in the collection of experimental data. The fundamental issues relating to the stability, performance, and stability robustness of the resulting controlled system are studied using the notion of an input-output linear time-invariant (LTI) equivalent system, which is a method for finding an internal model principle (IMP) based representation of the considered adaptive laws, using basic properties of the z-transform. Empirical results validate the suitability of the approach chosen for designing controllers and for analyzing their fundamental properties.

System identification and linear time-invariant modeling of an insect-sized flapping-wing micro air vehicle

Flapping-wing robots typically include numerous nonlinear elements, such as nonlinear geometric and aerodynamic components. For an insect-sized flapping-wing micro air vehicle (FWMAV), we show that a linearized model is sufficient to predict system behavior with reasonable accuracy over a large operating range, not just locally around the linearization state. The theoretical model is verified against an identified model from a prototype robotic fly and implications for vehicle design are discussed.

Lift force control of a flapping-wing microrobot

This paper introduces a methodology for designing real-time controllers capable of enforcing desired trajectories on microrobotic insects in vertical flight and hovering. The main idea considered in this work is that altitude control can be translated into a problem of lift force control. Through analyses and experiments, we describe the proposed control strategy, which is fundamentally adaptive with some elements of model-based control. In order to test and explain the method for controller synthesis and tuning, a static single-wing flapping mechanism is employed in the collection of experimental data. The empirical results validate the suitability of the chosen approach.

Altitude feedback control of a flapping-wing microrobot using an on-board biologically inspired optical flow sensor

We present experimental results on the controlled vertical flight of a flapping-wing flying microrobot, in which for the first time an on-board sensing system is used for measuring the microrobots altitude for feedback control. Both the control strategy and the sensing system are biologically inspired. The control strategy relies on amplitude modulation mediated by optical flow. The research presented here is a key step toward achieving the goal of complete autonomy for flying microrobots, since this demonstrates that strategies for controlling flapping-wing microrobots in vertical flight can rely on optical flow sensors.

Model-Free Control of a Hovering Flapping-Wing Microrobot

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 main idea proposed in this work is the sequential tuning of parameters for an increasingly more complex strategy in order to sequentially accomplish more complex tasks: upright stable flight, straight vertical flight, and stable hovering with altitude and position control. Each term of the resulting multiple-input–multiple-output (MIMO) controller has a physical intuitive meaning and the control structure is relatively simple such that it could potentially be applied to other kinds of flapping-wing robots.

Pitch-angle feedback control of a Biologically Inspired flapping-wing microrobot

This paper presents the first experimental results on pitch-angle control of a flapping-wing microrobot. First, we describe a control method by which torques can be modulated to change the pitch orientation of the microrobot. The suitability of the proposed method is demonstrated through hardware-in-the-loop experiments, employing a static experimental setup capable of measuring instantaneous torques produced by enforced flapping patterns. Then, using the information learned from the static hardware-in-the-loop experiments, controlled pitch rotation experiments are performed. The pitch-angle is measured using a motion capture system. Compelling results are presented to validate the chosen approach.