Browsing by Author "Askari, Mohammad"
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Item Open Access Control and study of bio-inspired quadrupedal gaits on an underactuated miniature robot(Institute of Physics, 2023-01-25) Askari, Mohammad; Uğur, Mustafa; Mahkam, Nima; Yeldan, Alper; Özcan, OnurThis paper presents a linear quadratic Gaussian (LQG) controller for controlling the gait of a miniature, foldable quadruped robot with individually actuated and controlled legs (MinIAQ-III). The controller is implemented on a palm-size robot made by folding an acetate sheet. MinIAQ-III has four DC motors for actuation and four rotary sensors for feedback. It is one of the few untethered robots on a miniature scale capable of working with different gaits with the help of its individually-actuated legs and the developed controller. The presented LQG controller controls each leg’s positions and rotational speeds by measuring the positions and estimating the rotational speeds, respectively. With the precise gait control on the robot, we demonstrate different gaits inspired by quadrupeds in nature and compare the simulation and experiment results for some of the gaits. An extensive simulation environment developed for robot dynamics helps us to predict the locomotion behavior of the robot in various environments. The match between the simulation and the experiment results shows that the proposed LQG controller can successfully control the miniature robot’s gaits. We also conduct a case study that shows the potential to use the simulation to achieve different robot behavior. In a case study, we present our robot performing a prancing similar to horses. We use the simulation environment to find the required motor configuration phases and physical parameters, which can make our robot prance. After finding the parameters in simulation, we replicate the configuration in our robot and observe the robot making the same moves as the simulation. © 2023 IOP Publishing Ltd.Item Open Access Design and operation of MinIAQ: an untethered foldable miniature quadruped with individually actuated legs(IEEE, 2017) Karakadıoğlu, Cem; Askari, Mohammad; Özcan, OnurThis paper presents the design, development, and basic operation of MinIAQ, an origami-inspired, foldable, untethered, miniature quadruped robot. Instead of employing multilayer composite structures similar to most microrobotic fabrication techniques, MinIAQ is fabricated from a single sheet of thin A4-sized PET film. Its legs are designed based on a simple four-bar locomotion mechanism that is embedded within its planar design. Each leg is actuated and controlled individually by separate DC motors enabling gait modification and higher degree of freedom on controlling the motion. The origami-inspired fabrication technique is a fast and inexpensive method to make complex 3D robotic structures through successive-folding of laser-machined sheets. However, there is still a need for improvement in modulating and extending the design standards of origami robots. In an effort to addressing this need, the primitive foldable design patterns of MinIAQ for higher structural integrity and rigidity are presented in detail. The current robot takes less than two hours to be cut and assembled and weighs about 23 grams where 3.5 grams is the weight of its body, 7.5 grams is its motors and encoders, 5 grams is its battery, and about 7 grams is its current on-board electronics and sensors. The robot is capable of running about 30 minutes on a single fully charged 150mAh single cell LiPo battery. Using the feedback signals from the custom encoders, MinIAQ can perform a trot gait with a speed of approximately 0.65 Bodylengths/sec, or equivalently 7.5 cm/s.Item Open Access Design, control, modeling, and gait analysis in miniature foldable robotics(2018-09) Askari, MohammadMiniature or micro robotic platforms are perfect candidates for accomplishing tasks such as inspection, surveillance, and hazardous environment exploration where conventional macro robots fail to serve. Such applications require these robots to potentially traverse uneven terrain, implying legged locomotion to be suitable for their design. However, despite the recent advances in the nascent eld of miniature robotics, the design and capabilities of these robots are very limited as roboticists favor legged morphologies with low degrees of freedom. This limits small robots to work with a single gait set during the design phase, as opposed to legged creatures which bene t from e cient gait modi cation during locomotion. MinIAQ, a 23 g origami-inspired miniature foldable quadruped with individually actuated legs, is designed to address such limitations. The design of the robot is unique in which a high structural integrity is achieved by transforming a single exible thin sheet into a rigid mechanical system through folding. MinIAQ's design novelties help modulate and extend the design standards of origami robots. The actuation independency of MinIAQ enables gait modi cation and exhibits maneuvering capabilities which is another novel quality for a robot at this scale. The design of the compliant four-bar legs is optimized for better foot trajectory in a newer version of the robot, MinIAQ{II, through dimensional synthesis of mechanisms. The resulting robot demonstrates signi cant improvements over its predecessor. For characterization and synchronization of the motors, custom encoders are designed to estimate speed and phase of each leg. Accordingly, a closed-loop feedback control algorithm is applied to follow an envisioned gait pattern. Towards understanding these gaits in robots with passive closed-chain legs, a comprehensive mathematical model is developed to describe the 6-DOF rigid body dynamics of MinIAQ. The proposed dynamics employs a nonlinear viscoelastic spring-damper model to estimate the feet-ground interactions. An interactive GUI is developed based on the model in MATLAB to simultaneously visualize the e ects of design parameters on performance. 3D simulation results closely match with the experiments and e ectively predict locomotion trends on at terrain. Since there is no control on foot placement in such underactuated robots, the model has given an insight into analyzing how close the actual locomotion is to the envisioned gait. This suggests that a comprehensive locomotion study with the model can lead to optimizing the gait and improve performance of miniature legged robots.Item Open Access Dynamic modeling and gait analysis for miniature robots in the absence of foot placement control(Institute of Electrical and Electronics Engineers Inc., 2019) Askari, Mohammad; Özcan, OnurThe study of animals and insects have led to realization that animals select their gaits, patterns of leg movement, according to speed. For proper gait planning, the legs must be controlled for proper foot placement with respect to the body motion and ground interactions. However, in small scale robotic platforms gait planning through foot placement control is neither cost effective nor easily attainable due to a lack of available sensors. Thus, even though a desired gait is envisioned at the design phase, it is not known whether the gait is optimum. In this work, we present the comprehensive dynamic model of the miniature foldable robot, MinIAQ-II, which has four independently actuated legs. Dynamic model is used to perform gait analysis, to investigate the difference between the intended gait and the achieved gait in the absence of foot placement control. The model is verified through slow speed walking experiments on flat terrain. The work presented can be modified for different miniature robots with passive legs to predict their locomotion under no foot placement control.Item Open Access The effect of large deflections of joints on foldable miniature robot dynamics(Springer, 2020) Karakadıoğlu, Cem; Askari, Mohammad; Özcan, OnurIn miniature robotics applications, compliant mechanisms are widely used because of their scalability. In addition, compliant mechanism architecture is compatible with the manufacturing methods used to fabricate small scale robots, such as “foldable robotics”, where the size and the materials used allow much larger deflections. In this paper, the kinematics of compliant mechanisms used in miniature foldable robots are investigated with the assumption of nonlinear large deflections that occur at the flexure joints. The solution of the large beam deflection is acquired using elliptic integrals and is verified with finite element analysis and experiments on a simple small foldable leg linkage. The large deflection model takes joint strain energies into account and yields accurate estimations for load capacity of the mechanism as well as the necessary input torque for actuation of the leg. Therefore, the model presented can be used to estimate the load capacity of a miniature robot, as well as to select appropriate actuators. The work is also extended to estimate the compliant leg kinematics and rigid body dynamics of a foldable robot. The robot’s large deflection simulation results are compared with experiments and a simplified rigid-link pin-joint kinematic model. Our results demonstrate the modeling accuracy of the two approaches and can be used by foldable robotics community when deciding on the strategy to choose for modeling their robots.Item Open Access MinIAQ-II: a miniature foldable quadruped with an improved leg mechanism(IEEE, 2018) Askari, Mohammad; Karakadıoǧlu, Cem; Ayhan, Furkan; Özcan, OnurOrigami has long been renowned as a simple yet creative form of art and its folding techniques have recently inspired advances in design and fabrication of miniature robots. In this work, we present the design and fabrication novelties, enhancements, and performance improvements on MinIAQ (Miniature Independently Actuated-legged Quadruped), an origami-inspired, foldable, miniature quadruped robot with individually actuated legs. The resulting robot, MinIAQ-II, has a trajectory-optimized leg actuation mechanism with longer stride, improved traction, less flexure joint bending, and smaller leg lift resulting in faster and smoother walking, better maneuverability, and higher durability and joint life. In order to maximize the joint fatigue life while keeping the leg design simple, the initial four-bar mechanism is optimized by manipulating the joint locations and changing the leg link into a non-straight knee shape with a fixed-angle lock. Despite having a 1 cm longer frame to embed its new actuation mechanism, the overall weight and dimensions are similar to its first version as its legs are no longer extended beyond its frame. As a result, MinIAQ-II is 12-cm-long, 6-cm-wide, 4.5-cm-high and weighs 23 grams. The test results demonstrate the improvement in speed over its predecessor from 0.65 to more than 0.8 bodylengths/s at 3 Hz, and an approximate decrease in body's roll ±21° to ±9° and pitch from 0°-11° to 0°-7°. The independent actuation and control over each leg enables such a robot to be used for gait studies in miniature scale, as is the next direction in our research.