55 results
(View BibTeX file of all listed publications)
2023
Multi-segmented Adaptive Feet for Versatile Legged Locomotion in Natural Terrain
(Outstanding locomotion paper award)
Chatterjee, A., Mo, A., Kiss, B., Goenen, E. C., Badri-Spröwitz, A.
2023 IEEE International Conference on Robotics and Automation (ICRA 2023), pages: 1162-1169 , IEEE, Piscataway, NJ, IEEE International Conference on Robotics and Automation (ICRA), June 2023 (conference)
Most legged robots are built with leg structures from serially mounted links and actuators and are controlled through complex controllers and sensor feedback. In comparison, animals developed multi-segment legs, mechanical coupling between joints, and multi-segmented feet. They run agile over all terrains, arguably with simpler locomotion control. Here we focus on developing foot mechanisms that resist slipping and sinking also in natural terrain. We present first results of multi-segment feet mounted to a bird-inspired robot leg with multi-joint mechanical tendon coupling. Our one- and two-segment, mechanically adaptive feet show increased viable horizontal forces on multiple soft and hard substrates before starting to slip. We also observe that segmented feet reduce sinking on soft substrates compared to ball-feet and cylinder feet. We report how multi-segmented feet provide a large range of viable centre of pressure points well suited for bipedal robots, but also for quadruped robots on slopes and natural terrain. Our results also offer a functional understanding of segmented feet in animals like ratite birds.
Upside down: affordable high-performance motion platform
Pradhan, N. M. S., Frank, P., Mo, A., Badri-Spröwitz, A.
arXiv, 2023 (conference) Accepted
Parallel robots are capable of high-speed manipulation and have become essential tools in the industry. The proximal placement of their motors and the low weight of their end effectors make them ideal for generating highly dynamic motion. Therefore, parallel robots can be adopted for motion platform designs, as long as end effector loads are low. Traditional motion platforms can be large and powerful to generate multiple g acceleration. However, these designs tend to be expensive and large. Similar but smaller motion platforms feature a small work range with reduced degrees of freedom (DoFs) and a limited payload. Here we seek a medium-sized affordable parallel robot capable of powerful and high-speed 6-DoF motion in a comparably large workspace. This work explores the concept of a quadruped robot flipped upside-down, with the motion platform fixed between its feet. In particular, we exploit the high-power dynamic brushless actuation and the four-leg redundancy when moving the motion platform. We characterize the resulting motion platform by tracking sinusoidal and circular trajectories with varying loads. Dynamic motions in 6 DoFs up to 10 Hz and ± 10 mm amplitude are possible when moving a mass of 300 grams. We demonstrate single-axis end-effector translations up to ± 20 mm at 10 Hz for higher loads of 1.2 kg. The motion platform can be replicated easily by 3D printing and off-the-shelf components. All motion platform-related hardware and the custom-written software required to replicate are open-source.
2022
Mechanical Design, Development and Testing of Bioinspired Legged Robots for Dynamic Locomotion
Eberhard Karls Universität Tübingen, Tübingen , November 2022 (phdthesis)
Diaphragm Ankle Actuation for Efficient Series Elastic Legged Robot Hopping
Bolignari, M., Mo, A., Fontana, M., Badri-Spröwitz, A.
2022 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), IEEE, IROS2022, October 2022 (conference) In press
Robots need lightweight legs for agile locomotion, and intrinsic series elastic compliance has proven to be a major ingredient for energy-efficient locomotion and robust locomotion control. Animals' anatomy and locomotion capabilities emphasize the importance of that lightweight legs and integrated, compact, series elastically actuated for distal leg joints. But unlike robots, animals achieve series elastic actuation by their muscle-tendon units. So far no designs are available that feature all characteristics of a perfect distal legged locomotion actuator; a low-weight and low-inertia design, with high mechanical efficiency, no stick and sliding friction, low mechanical complexity, high-power output while being easy to mount. Ideally, such an actuator can be controlled directly and without mechanical cross-coupling, for example remotely. With this goal in mind, we propose a low-friction, lightweight Series ELastic Diaphragm distal Actuator (SELDA) which meets many, although not all, of the above requirements. We develop, implement, and characterize a bioinspired robot leg that features a SELDA-actuated foot segment. We compare two leg configurations controlled by a central pattern generator that both feature agile forward hopping. By tuning SELDA's activation timing, we effectively adjust the robot's hopping height by 11% and its forward velocity by 14%, even with comparatively low power injection to the distal joint.
Gastrocnemius and Power Amplifier Soleus Spring-Tendons Achieve Fast Human-like Walking in a Bipedal Robot
Kiss, B., Gonen, E. C., Mo, A., Buchmann, A., Renjewski, D., Badri-Spröwitz, A.
2022 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), IEEE, IROS2022, October 2022 (conference) In press
Legged locomotion in humans is governed by natural dynamics of the human body and neural control. One mechanism that is assumed to contribute to the high efficiency of human walking is the impulsive ankle push-off, which potentially powers the swing leg catapult. However, the mechanics of the human’s lower leg with its complex muscle-tendon units spanning over single and multiple joints is not yet understood. Legged robots allow testing the interaction between complex leg mechanics, control, and environment in real-world walking gait. We developed a 0.49 m tall, 2.2 kg anthropomorphic bipedal robot with Soleus and Gastrocnemius muscle-tendon units represented by linear springs, acting as mono- and biarticular elastic structures around the robot’s ankle and knee joints. We tested the influence of three Soleus and Gastrocnemius spring-tendon configurations on the ankle power curves, the coordination of the ankle and knee joint movements, the total cost of transport, and walking speed. We controlled the robot with a feed-forward central pattern generator, leading to walking speeds between 0.35 m/s and 0.57 m/s at 1.0 Hz locomotion frequency, at 0.35 m leg length. We found differences between all three configurations; the Soleus spring-tendon modulates the robot’s speed and energy efficiency likely by ankle power amplification, while the Gastrocnemius spring-tendon changes the movement coordination between knee and ankle joints during push-off.
Power to the springs: Passive elements are sufficient to drive push-off in human walking
Buchmann, A., Kiss, B., Badri-Spröwitz, A., Renjewski, D.
In Robotics in Natural Settings , pages: 21-32, Lecture Notes in Networks and Systems, 530, (Editors: Cascalho, José M. and Tokhi, Mohammad Osman and Silva, Manuel F. and Mendes, Armando and Goher, Khaled and Funk, Matthias), Springer, Cham, 25th International Conference on Climbing and Walking Robots and the Support Technologies for Mobile Machine (CLAWAR 2022), August 2022 (inproceedings)
For the impulsive ankle push-off (APO) observed in human
walking two muscle-tendon-units (MTUs) spanning the ankle joint play
an important role: Gastrocnemius (GAS) and Soleus (SOL). GAS and
SOL load the Achilles tendon to store elastic energy during stance followed by a rapid energy release during APO. We use a neuromuscular
simulation (NMS) and a bipedal robot to investigate the role of GAS and
SOL on the APO. We optimize the simulation for a robust gait and then
sequentially replace the MTUs of (1) GAS, (2) SOL and (3) GAS and SOL
by linear springs. To validate the simulation, we implement NMS-3 on
a bipedal robot. Simulation and robot walk steady for all trials showing
an impulsive APO. Our results imply that the elastic MTU properties
shape the impulsive APO. For prosthesis or robot design that is, no
complex ankle actuation is needed to obtain an impulsive APO, if more
mechanical intelligence is incorporated in the design.
Learning Plastic Matching of Robot Dynamics in Closed-Loop Central Pattern Generators: Data
Ruppert, F., Badri-Spröwitz, A.
Edmond, May 2022 (techreport)
Data for BirdBot Achieves Energy-Efficient Gait with Minimal Control Using Avian-Inspired Leg Clutching
Badri-Spröwitz, A., Sarvestani, A. A., Sitti, M., Daley, M. A.
Edmond, March 2022 (techreport)
2021
Control Mechanisms for Postural Stability and Trunk Motion in Bipedal Running. A Numerical Study for Humans, Avians, and Bipedal Robots
Drama, Ö.
Universität Stuttgart, Stuttgart, May 2021 (phdthesis)
A little damping goes a long way
Heim, S., Millard, M., Mouel, C. L., Badri-Spröwitz, A.
In Integrative and Comparative Biology, 61(Supplement 1):E367-E367, Oxford University Press, Society for Integrative and Comparative Biology Annual Meeting (SICB Annual Meeting 2021) , March 2021 (inproceedings)
Effects of tendon-network mechanisms on avian terrestrial locomotion
Contreras, F. B., Daley, M., Badri-Spröwitz, A.
In Integrative and Comparative Biology, 61(Supplement 1):E89-E90, Oxford University Press, Society for Integrative and Comparative Biology Annual Meeting (SICB Annual Meeting 2021), January 2021 (inproceedings)
Developing a mechanical model for intraspinal mechanosensing in avians
Mo, A., Kamska, V., Contreras, F. B., Daley, M., Badri-Spröwitz, A.
In Integrative and Comparative Biology , 61(Supplement 1):E618-E619, Oxford University Press, Society for Integrative and Comparative Biology Annual Meeting (SICB Annual Meeting 2021), January 2021 (inproceedings)
Associating functional morphology of the lumbosacral organ and locomotion modalities in avians
Kamska, V., Contreras, F. B., Daley, M., Badri-Spröwitz, A.
In Integrative and Comparative Biology, 61(Supplement 1):E437-E437, Oxford University Press, Society for Integrative and Comparative Biology Annual Meeting (SICB Annual Meeting 2021), January 2021 (inproceedings)
Tackling sensorimotor delays and low control update frequencies during drop impacts with hybrid parallel leg compliance
Ashtiani, M. S., Sarvestani, A. A., Badri-Spröwitz, A.
The 9.5th international symposium on Adaptive Motion of Animals and Machines. Ottawa，Canada (Virtual Platform). 2021-06-22/25. Adaptive Motion of Animals and Machines Organizing Committee., pages: 3, Adaptive Motion of Animals and Machines Organizing Committee, Adaptive Motion of Animals and Machines, 2021 (conference)
2020
Simulating the response of a neuro-musculoskeletal model to assistive forces: implications for the design of wearables compensating for motor control deficits
Stollenmaier, K., Rist, I., Izzi, F., Haeufle, D. F.
In 2020 8th IEEE RAS/EMBS International Conference for Biomedical Robotics and Biomechatronics (BioRob 2020), pages: 779-784, IEEE, Piscataway, NJ, 8th IEEE RAS/EMBS International Conference for Biomedical Robotics and Biomechatronics (BioRob 2020), October 2020 (inproceedings)
Models of the human arm may help to estimate design parameters like peak torque and power of wearable assistive devices by predicting required forces to compensate for motor control impairments. This work focuses on the idea of compensating hypermetria (overshoot)-a motor control deficit that may occur in neurodegenerative diseases-by a simple assistive device. As musculoskeletal dynamics play an important role in the interaction between an assistive device and the neuro-musculoskeletal system, we hypothesized that their consideration in the model might influence the predicted design parameters. To test this, we simulated two-degree-of-freedom point-to-point arm movements. By introducing inconsistent neuronal control parameters, we induced hypermetria. We implemented mechanical and low-level assistive torque strategies in simulation which lead to a reduction of hypermetria. We found that-depending on the type of assistance-the predicted torques and powers can differ by more than a factor of 10 between musculoskeletal and torque-driven arm models. We conclude that the magnitude of torque and power required to reduce hypermetria by simple wearable assistive devices may be significantly underestimated if muscle-tendon characteristics are not considered.
Towards Hybrid Active and Passive Compliant Mechanisms in Legged Robots
Milad Shafiee Ashtiani, A. A. S., Badri-Sproewitz, A.
IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), IEEE, October 2020 (poster) Accepted
FootTile: a Rugged Foot Sensor for Force and Center of Pressure Sensing in Soft Terrain
Ruppert, F., Badri-Spröwitz, A.
In 2020 IEEE International Conference on Robotics and Automation (ICRA 2020), pages: 4810-4816, IEEE, Piscataway, NJ, IEEE International Conference on Robotics and Automation (ICRA 2020) , 2020 (inproceedings)
In this paper, we present FootTile, a foot sensor for reaction force and center of pressure sensing in challenging terrain. We compare our sensor design to standard biomechanical devices, force plates and pressure plates. We show that FootTile can accurately estimate force and pressure distribution during legged locomotion. FootTile weighs 0.9g, has a sampling rate of 330 Hz, a footprint of 10×10 mm and can easily be adapted in sensor range to the required load case. In three experiments, we validate: first, the performance of the individual sensor, second an array of FootTiles for center of pressure sensing and third the ground reaction force estimation during locomotion in granular substrate. We then go on to show the accurate sensing capabilities of the waterproof sensor in liquid mud, as a showcase for real world rough terrain use.
VP above or below? A new perspective on the story of the virtual point
Drama, Ö., Badri-Spröwitz, A.
Dynamic Walking, May 2020 (poster)
The spring inverted pendulum model with an extended trunk (TSLIP) is widely used to investigate the postural stability in bipedal locomotion [1, 2]. The challenge of the model is to define a hip torque that generates feasible gait patterns while stabilizing the floating trunk. The virtual point (VP) method is proposed as a simplified solution, where the hip torque is coupled to the passive compliant leg force via a virtual point. This geometric coupling is based on the assumption that the instantaneous ground reaction forces of the stance phase (GRF) intersect at a single virtual point.
Viscous Damping in Legged Locomotion
Mo, A., Izzi, F., Haeufle, D. F. B., Badri-Spröwitz, A.
Dynamic Walking, May 2020 (poster)
Damping likely plays an essential role in legged animal locomotion, but remains an insufficiently understood mechanism. Intrinsic damping muscle forces can potentially add to the joint torque output during unexpected impacts, stabilise movements, convert the system’s energy, and reject unexpected perturbations.
How Quadrupeds Benefit from Lower Leg Passive Elasticity
Ruppert, F., Badri-Spröwitz, A.
Dynamic Walking, May 2020 (poster)
Recently developed and fully actuated, legged robots start showing exciting locomotion capabilities, but rely heavily on high-power actuators, high-frequency sensors, and complex locomotion controllers. The engineering solutions implemented in these legged robots are much different compared to animals. Vertebrate animals share magnitudes slower neurocontrol signal velocities [1] compared to their robot counterparts. Also, animals feature a plethora of cascaded and underactuated passive elastic structures [2].
Viability in State-Action Space. Connecting Morphology, Control, and Learning
Eberhard Karls Universität Tübingen, Tübingen, February 2020 (phdthesis)
Potential for elastic soft tissue deformation and mechanosensory function within the lumbosacral spinal canal of birds
Kamska, V., Daley, M., Badri-Spröwitz, A.
Society for Integrative and Comparative Biology Annual Meeting (SICB Annual Meeting 2020), January 2020 (poster)
2019
Trunk Pitch Oscillations for Joint Load Redistribution in Humans and Humanoid Robots
Drama, Ö., Badri-Spröwitz, A.
Proceedings of 2019 IEEE-RAS 19th International Conference on Humanoid Robots, pages: 531-536, IEEE, Humanoids, October 2019 (conference)
Creating natural-looking running gaits for humanoid robots is a complex task due to the underactuated degree of freedom in the trunk, which makes the motion planning and control difficult. The research on trunk movements in human locomotion is insufficient, and no formalism is known to transfer human motion patterns onto robots. Related work mostly focuses on the lower extremities, and simplifies the problem by stabilizing the trunk at a fixed angle. In contrast, humans display significant trunk motions that follow the natural dynamics of the gait. In this work, we use a spring-loaded inverted pendulum model with a trunk (TSLIP) together with a virtual point (VP) target to create trunk oscillations and investigate the impact of these movements. We analyze how the VP location and forward speed determine the direction and magnitude of the trunk oscillations. We show that positioning the VP below the center of mass (CoM) can explain the forward trunk pitching observed in human running. The VP below the CoM leads to a synergistic work between the hip and leg, reducing the leg loading. However, it comes at the cost of increased peak hip torque. Our results provide insights for leveraging the trunk motion to redistribute joint loads and potentially improve the energy efficiency in humanoid robots.
The positive side of damping
Heim, S., Millard, M., Le Mouel, C., Sproewitz, A.
Proceedings of AMAM, The 9th International Symposium on Adaptive Motion of Animals and Machines, August 2019 (conference)
Quantifying the Robustness of Natural Dynamics: a Viability Approach
Heim, S., Sproewitz, A.
Proceedings of Dynamic Walking , Dynamic Walking , 2019 (conference)
Das Tier als Modell für Roboter, und Roboter als Modell für Tiere
Badri-Spröwitz, A.
In pages: 167-175, Springer, 2019 (incollection)
2018
Learning from Outside the Viability Kernel: Why we Should Build Robots that can Fail with Grace
Heim, S., Sproewitz, A.
Proceedings of SIMPAR 2018, pages: 55-61, IEEE, 2018 IEEE International Conference on Simulation, Modeling, and Programming for Autonomous Robots (SIMPAR), May 2018 (conference)
Shaping in Practice: Training Wheels to Learn Fast Hopping Directly in Hardware
Heim, S., Ruppert, F., Sarvestani, A., Sproewitz, A.
In Proceedings of the IEEE International Conference on Robotics and Automation (ICRA) 2018, pages: 5076-5081, IEEE, International Conference on Robotics and Automation, May 2018 (inproceedings)
Learning instead of designing robot controllers can greatly reduce engineering effort required, while also emphasizing robustness. Despite considerable progress in simulation, applying learning directly in hardware is still challenging, in part due to the necessity to explore potentially unstable parameters. We explore the of concept shaping the reward landscape with training wheels; temporary modifications of the physical hardware that facilitate learning. We demonstrate the concept with a robot leg mounted on a boom learning to hop fast. This proof of concept embodies typical challenges such as instability and contact, while being simple enough to empirically map out and visualize the reward landscape. Based on our results we propose three criteria for designing effective training wheels for learning in robotics.
2017
Scalable Pneumatic and Tendon Driven Robotic Joint Inspired by Jumping Spiders
Sproewitz, A., Göttler, C., Sinha, A., Caer, C., Öztekin, M. U., Petersen, K., Sitti, M.
In Proceedings 2017 IEEE International Conference on Robotics and Automation (ICRA), pages: 64-70, IEEE, Piscataway, NJ, USA, IEEE International Conference on Robotics and Automation (ICRA), May 2017 (inproceedings)
Linking Mechanics and Learning
Heim, S., Grimminger, F., Drama, Ö., Spröwitz, A.
In Proceedings of Dynamic Walking 2017, 2017 (inproceedings)
Is Growing Good for Learning?
Heim, S., Spröwitz, A.
Proceedings of the 8th International Symposium on Adaptive Motion of Animals and Machines AMAM2017, 2017 (conference)
2016
On designing an active tail for body-pitch control in legged robots via decoupling of control objectives
Heim, S. W., Ajallooeian, M., Eckert, P., Vespignani, M., Ijspeert, A.
In ASSISTIVE ROBOTICS: Proceedings of the 18th International Conference on CLAWAR 2015, pages: 256-264, 2016 (inproceedings)
2015
Comparing the effect of different spine and leg designs for a small bounding quadruped robot
Eckert, P., Spröwitz, A., Witte, H., Ijspeert, A. J.
In Proceedings of ICRA, pages: 3128-3133, Seattle, Washington, USA, 2015 (inproceedings)
We present Lynx-robot, a quadruped, modular, compliant machine. It alternately features a directly actuated, single-joint spine design, or an actively supported, passive compliant, multi-joint spine configuration. Both spine con- figurations bend in the sagittal plane. This study aims at characterizing these two, largely different spine concepts, for a bounding gait of a robot with a three segmented, pantograph leg design. An earlier, similar-sized, bounding, quadruped robot named Bobcat with a two-segment leg design and a directly actuated, single-joint spine design serves as a comparison robot, to study and compare the effect of the leg design on speed, while keeping the spine design fixed. Both proposed spine designs (single rotatory and active and multi-joint compliant) reach moderate, self-stable speeds.
2014
Automatic Generation of Reduced CPG Control Networks for Locomotion of Arbitrary Modular Robot Structures
Bonardi, S., Vespignani, M., Möckel, R., Van den Kieboom, J., Pouya, S., Spröwitz, A., Ijspeert, A.
In Proceedings of Robotics: Science and Systems, University of California, Barkeley, 2014 (inproceedings)
The design of efficient locomotion controllers for arbitrary structures of reconfigurable modular robots is challenging because the morphology of the structure can change dynamically during the completion of a task. In this paper, we propose a new method to automatically generate reduced Central Pattern Generator (CPG) networks for locomotion control based on the detection of bio-inspired sub-structures, like body and limbs, and articulation joints inside the robotic structure. We demonstrate how that information, coupled with the potential symmetries in the structure, can be used to speed up the optimization of the gaits and investigate its impact on the solution quality (i.e. the velocity of the robotic structure and the potential internal collisions between robotic modules). We tested our approach on three simulated structures and observed that the reduced network topologies in the first iterations of the optimization process performed significantly better than the fully open ones.
2013
Benefits of an active spine supported bounding locomotion with a small compliant quadruped robot
Khoramshahi, M., Spröwitz, A., Tuleu, A., Ahmadabadi, M. N., Ijspeert, A. J.
In Robotics and Automation (ICRA), 2013 IEEE International Conference on, pages: 3329-3334, May 2013 (inproceedings)
We studied the effect of the control of an active spine versus a fixed spine, on a quadruped robot running in bound gait. Active spine supported actuation led to faster locomotion, with less foot sliding on the ground, and a higher stability to go straight forward. However, we did no observe an improvement of cost of transport of the spine-actuated, faster robot system compared to the rigid spine.
Central pattern generators augmented with virtual model control for quadruped rough terrain locomotion
Ajallooeian, M., Pouya, S., Spröwitz, A., Ijspeert, A. J.
In Proceedings of the 2013 IEEE International Conference on Robotics and Automation (ICRA), pages: 3321-3328, IEEE, Karlsruhe, 2013 (inproceedings)
We present a modular controller for quadruped locomotion over unperceived rough terrain. Our approach is based on a computational Central Pattern Generator (CPG) model implemented as coupled nonlinear oscillators. Stumbling correction reflex is implemented as a sensory feedback mechanism affecting the CPG. We augment the outputs of the CPG with virtual model control torques responsible for posture control. The control strategy is validated on a 3D forward dynamics simulated quadruped robot platform of about the size and weight of a cat. To demonstrate the capabilities of the proposed approach, we perform locomotion over unperceived uneven terrain and slopes, as well as situations facing external pushes.
Motor Control Adaptation to Changes in Robot Body Dynamics for a Compliant Quadruped Robot
Pouya, S., Eckert, P., Spröwitz, A., Moc̈kel, R., Ijspeert, A. J.
In Biomimetic and Biohybrid Systems, 8064, pages: 434-437, Lecture Notes in Computer Science, Springer, Heidelberg, 2013 (incollection)
One of the major deficiencies of current robots in comparison to living beings is the ability to adapt to new conditions either resulting from environmental changes or their own dynamics. In this work we focus on situations where the robot experiences involuntary changes in its body particularly in its limbs’ inertia. Inspired from its biological counterparts we are interested in enabling the robot to adapt its motor control to the new system dynamics. To reach this goal, we propose two different control strategies and compare their performance when handling these modifications. Our results show substantial improvements in adaptivity to body changes when the robot is aware of its new dynamics and can exploit this knowledge in synthesising new motor control.
Gait Optimization for Roombots Modular Robots - Matching Simulation and Reality
Möckel, R., Yura, N. P., The Nguyen, A., Vespignani, M., Bonardi, S., Pouya, S., Spröwitz, A., van den Kieboom, J., Wilhelm, F., Ijspeert, A. J.
In Proceedings of the 2013 IEEE/RSJ International Conference on Intelligent Robots and Systems, pages: 3265-3272, IEEE, Tokyo, 2013 (inproceedings)
The design of efficient locomotion gaits for robots with many degrees of freedom is challenging and time consuming even if optimization techniques are applied. Control parameters can be found through optimization in two ways: (i) through online optimization where the performance of a robot is measured while trying different control parameters on the actual hardware and (ii) through offline optimization by simulating the robot’s behavior with the help of models of the robot and its environment.
In this paper, we present a hybrid optimization method that combines the best properties of online and offline optimization to efficiently find locomotion gaits for arbitrary structures. In comparison to pure online optimization, both the number of experiments using robotic hardware as well as the total time required for finding efficient locomotion gaits get highly reduced by running the major part of the optimization process in simulation using a cluster of processors. The presented example shows that even for robots with a low number of degrees of freedom the time required for optimization can be reduced by a factor of 2.5 to 30, at least, depending on how extensive the search for optimized control parameters should be. Time for hardware experiments becomes minimal. More importantly, gaits that can possibly damage the robotic hardware can be filtered before being tried in hardware. Yet in contrast to pure offline optimization, we reach well matched behavior that allows a direct transfer of locomotion gaits from simulation to hardware. This is because through a meta-optimization we adapt not only the locomotion parameters but also the parameters for simulation models of the robot and environment allowing for a good matching of the robot behavior in simulation and hardware.
We validate the proposed hybrid optimization method on a structure composed of two Roombots modules with a total number of six degrees of freedom. Roombots are self-reconfigurable modular robots that can form arbitrary structures with many degrees of freedom through an integrated active connection mechanism.
Modular Control of Limit Cycle Locomotion over Unperceived Rough Terrain
Ajallooeian, M., Gay, S., Tuleu, A., Spröwitz, A., Ijspeert, A. J.
In Proceedings of the IEEE/RSJ International Conference on Intelligent Robots and Systems, 2013, pages: 3390-3397, Tokyo, 2013 (inproceedings)
We present a general approach to design modular controllers for limit cycle locomotion over unperceived rough terrain. The control strategy uses a Central Pattern Generator (CPG) model implemented as coupled nonlinear oscillators as basis. Stumbling correction and leg extension reflexes are implemented as feedbacks for fast corrections, and model-based posture control mechanisms define feedbacks for continuous corrections. The control strategy is validated on a detailed physics-based simulated model of a compliant quadruped robot, the Oncilla robot. We demonstrate dynamic locomotion with a speed of more than 1.5 BodyLength/s over unperceived uneven terrains, steps, and slopes.
2012
Development of a Minimalistic Pneumatic Quadruped Robot for Fast Locomotion
Narioka, K., Rosendo, A., Spröwitz, A., Hosoda, K.
In Proceedings of the 2012 IEEE International Conference on Robotics and Biomimetics (ROBIO), 2012, pages: 307-311, IEEE, Guangzhou, 2012 (inproceedings)
In this paper, we describe the development of the quadruped robot ”Ken” with the minimalistic and lightweight body design for achieving fast locomotion. We use McKibben pneumatic artificial muscles as actuators, providing high frequency and wide stride motion of limbs, also avoiding problems with overheating. We conducted a preliminary experiment, finding out that the robot can swing its limb over 7.5 Hz without amplitude reduction, nor heat problems. Moreover, the robot realized a several steps of bouncing gait by using simple CPG-based open loop controller, indicating that the robot can generate enough torque to kick the ground and limb contraction to avoid stumbling.
Locomotion through Reconfiguration based on Motor Primitives for Roombots Self-Reconfigurable Modular Robots
Bonardi, S., Moeckel, R., Spröwitz, A., Vespignani, M., Ijspeert, A. J.
In Robotics; Proceedings of ROBOTIK 2012; 7th German Conference on, pages: 1-6, 2012 (inproceedings)
We present the hardware and reconfiguration experiments for an autonomous self-reconfigurable modular robot called Roombots (RB). RB were designed to form the basis for self-reconfigurable furniture. Each RB module contains three degrees of freedom that have been carefully selected to allow a single module to reach any position on a 2-dimensional grid and to overcome concave corners in a 3-dimensional grid. For the first time we demonstrate locomotion capabilities of single RB modules through reconfiguration with real hardware. The locomotion through reconfiguration is controlled by a planner combining the well-known D* algorithm and composed motor primitives. The novelty of our approach is the use of an online running hierarchical planner closely linked to the real hardware.
2011
Oncilla Robot—A Light-weight Bio-inspired Quadruped Robot for Fast Locomotion in Rough Terrain
Spröwitz, A., Kuechler, L., Tuleu, A., Ajallooeian, M., D’Haene, M., Moeckel, R., Ijspeert, A. J.
Symposium on adaptive motion of animals and machines (AMAM 2011), January 2011 (conference)
On the hardware level, we are proposing and testing a bio-inspired quadruped robot design (Oncilla robot), based on light-weight, compliant, and three-segmented legs. Our choice of placing the compliance such that it is spanning two joints enforces a non-linear spring stiffness. Based on the SLIP-model assumption, we compare progressive and de- gressive stiffness profiles against a linear-leg stiffness. To facilitate fast and throughout testing also of control approaches we have created a robot model of Oncilla robot in simulation (in Webots [1], a physics-based simulation environment). Here we are presenting new simulation results based on open-loop-central pattern generator (CPG) control and PSO- optimization of the CPG parameters. Our quadruped robot is equipped with passive compliant elements in its legs, and we apply two different strategies to make use of the legs’ compliance during stance phase. This enables us to find stable trot gait patterns propelling the robot up to 1 m/s (more than four times the robot’s leg length), depending on the applied stance phase leg-strategy. Different trot gait patterns emerge, and resulting trot gaits are variable in stability (tested as robustness against external perturbations) and speed.
2010
Graph signature for self-reconfiguration planning of modules with symmetry
Asadpour, M., Ashtiani, M. H. Z., Spröwitz, A., Ijspeert, A. J.
In Proceedings of the 2009 IEEE/RSJ International Conference on Intelligent Robots and Systems, pages: 5295-5300, IEEE, St. Louis, MO, 2010 (inproceedings)
In our previous works we had developed a framework for self-reconfiguration planning based on graph signature and graph edit-distance. The graph signature is a fast isomorphism test between different configurations and the graph edit-distance is a similarity metric. But the algorithm is not suitable for modules with symmetry. In this paper we improve the algorithm in order to deal with symmetric modules. Also, we present a new heuristic function to guide the search strategy by penalizing the solutions with more number of actions. The simulation results show the new algorithm not only deals with symmetric modules successfully but also finds better solutions in a shorter time.
Roombots - Towards decentralized reconfiguration with self-reconfiguring modular robotic metamodules
Spröwitz, A., Laprade, P., Bonardi, S., Mayer, M., Moeckel, R., Mudry, P., Ijspeert, A. J.
In Proceedings of the 2010 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), pages: 1126-1132, IEEE, Taipeh, 2010 (inproceedings)
This paper presents our work towards a decentralized reconfiguration strategy for self-reconfiguring modular robots, assembling furniture-like structures from Roombots (RB) metamodules. We explore how reconfiguration by loco- motion from a configuration A to a configuration B can be controlled in a distributed fashion. This is done using Roombots metamodules—two Roombots modules connected serially—that use broadcast signals, lookup tables of their movement space, assumptions about their neighborhood, and connections to a structured surface to collectively build desired structures without the need of a centralized planner.
Distributed Online Learning of Central Pattern Generators in Modular Robots
Christensen, D. J., Spröwitz, A., Ijspeert, A. J.
In From Animals to Animats 11, 6226, pages: 402-412, Lecture Notes in Computer Science, Springer, Berlin, 2010, author: Doncieux, Stéphan (incollection)
In this paper we study distributed online learning of locomotion gaits for modular robots. The learning is based on a stochastic ap- proximation method, SPSA, which optimizes the parameters of coupled oscillators used to generate periodic actuation patterns. The strategy is implemented in a distributed fashion, based on a globally shared reward signal, but otherwise utilizing local communication only. In a physics-based simulation of modular Roombots robots we experiment with online learn- ing of gaits and study the effects of: module failures, different robot morphologies, and rough terrains. The experiments demonstrate fast online learning, typically 5-30 min. for convergence to high performing gaits (≈ 30 cm/sec), despite high numbers of open parameters (45-54). We conclude that the proposed approach is efficient, effective and a promising candidate for online learning on many other robotic platforms.
Automatic Gait Generation in Modular Robots: to Oscillate or to Rotate? that is the question
Pouya, S., van den Kieboom, J., Spröwitz, A., Ijspeert, A. J.
In Proceedings of the 2010 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), pages: 514-520, IEEE, Taipei, 2010 (inproceedings)
Modular robots offer the possibility to design robots with a high diversity of shapes and functionalities. This nice feature also brings an important challenge: namely how to design efficient locomotion gaits for arbitrary robot structures with many degrees of freedom.
In this paper, we present a framework that allows one to explore and identify highly different gaits for a given arbitrary- shaped modular robot. We use simulated robots made of several Roombots modules that have three rotational joints each. These modules have the interesting feature that they can produce both oscillatory movements (i.e. periodic movements around a rest position) and rotational movements (i.e. with continuously increasing angle), leading to very rich locomotion patterns. Here we ask ourselves which types of movements —purely oscillatory, purely rotational, or a combination of both— lead to the fastest gaits. To address this question we designed a control architecture based on a distributed system of coupled phase oscillators that can produce synchronized rotations and oscillations in many degrees of freedom. We also designed a specific optimization algorithm that can automatically design hybrid controllers, i.e. controllers that use oscillations in some joints and rotations in others, for fast gaits. The proposed framework is verified by multiple simulations for several robot morphologies. The results show that (i) the question whether it is better to oscillate or to rotate depends on the morphology of the robot, and that in general it is best to do both, (ii) the optimization framework can successfully generate hybrid controllers that outperform purely oscillatory and purely rotational ones, and (iii) the resulting gaits are fast, innovative, and would have been hard to design by hand.
Roombots: Design and Implementation of a Modular Robot for Reconfiguration and Locomotion
Spröwitz, A.
EPFL, Lausanne, Lausanne, 2010 (phdthesis)
2009
Roombots-mechanical design of self-reconfiguring modular robots for adaptive furniture
Spröwitz, A., Billard, A., Dillenbourg, P., Ijspeert, A. J.
In Proceedings of the 2009 IEEE International Conference on Robotics and Automation (ICRA), pages: 4259-4264, IEEE, Kobe, 2009 (inproceedings)
We aim at merging technologies from information technology, roomware, and robotics in order to design adaptive and intelligent furniture. This paper presents design principles for our modular robots, called Roombots, as future building blocks for furniture that moves and self-reconfigures. The reconfiguration is done using dynamic connection and disconnection of modules and rotations of the degrees of freedom. We are furthermore interested in applying Roombots towards adaptive behaviour, such as online learning of locomotion patterns. To create coordinated and efficient gait patterns, we use a Central Pattern Generator (CPG) approach, which can easily be optimized by any gradient-free optimization algorithm. To provide a hardware framework we present the mechanical design of the Roombots modules and an active connection mechanism based on physical latches. Further we discuss the application of our Roombots modules as pieces of a homogenic or heterogenic mix of building blocks for static structures.
2008
Passive compliant quadruped robot using central pattern generators for locomotion control
Rutishauser, S., Spröwitz, A., Righetti, L., Ijspeert, A. J.
In Proceedings of the 2008 2nd Biennial IEEE/RAS-EMBS International Conference on Biomedical Robotics and Biomechatronics, pages: 710-715, IEEE, Scottsdale, AZ, 2008 (inproceedings)
We present a new quadruped robot, “Cheetah”, featuring three-segment pantographic legs with passive compliant knee joints. Each leg has two degrees of freedom - knee and hip joint can be actuated using proximal mounted RC servo motors, force transmission to the knee is achieved by means of a Bowden cable mechanism. Simple electronics to command the actuators from a desktop computer have been designed in order to test the robot. A Central Pattern Generator (CPG) network has been implemented to generate different gaits. A parameter space search was performed and tested on the robot to optimize forward velocity.