Alejandro Ramirez-Serrano | University of Calgary (original) (raw)

Papers by Alejandro Ramirez-Serrano

Robotics

To deploy Unmanned Aerial Vehicles (UAVs) inside heterogeneous GPS-denied confined (potentially u... more To deploy Unmanned Aerial Vehicles (UAVs) inside heterogeneous GPS-denied confined (potentially unknown) spaces, such as those encountered in mining and Urban Search and Rescue (USAR), requires the enhancement of numerous technologies. Of special interest is for UAVs to identify collision-freeSafe Flight Corridors (SFC+) within highly cluttered convex- and non-convex-shaped environments, which requires UAVs to perform advanced flight maneuvers while exploiting their flying capabilities. Within this paper, a novel auxiliary occupancy checking process that augments traditional 3D flight corridor generation is proposed. The 3D flight corridor is established as a topological structure based on a hand-crafted path either derived from a computer-generated environment or provided by the human operator, which captures humans’ preferences and desired flight intentions for the given space. This corridor is formulated as a series of interconnected overlapping convex polyhedra bounded by the pe...

The use of robotics in Urban Search and Rescue (USAR) is growing steadily from their initial ince... more The use of robotics in Urban Search and Rescue (USAR) is growing steadily from their initial inception during the 2001 World Trade Centre incident. Despite years of progress, the core design of robots currently in use for USAR purposes has deviated little, favoring software/control development and optimization of the basic robot template to improve performance instead. Presented here is a novel design description of the Cricket, an advanced robot with a broader range of physical capabilities than traditional USAR robots. By incorporating the tracked structure of earlier robots, appreciated for energy efficiency and robustness, into a multi-limbed walking design, the Cricket enables the use of advanced locomotion techniques. The ability to climb over obstacles many times the height of the robot, ascend vertical shafts without the assistance of a tether, and traverse rough and near vertical terrain improves the Cricket’s capability to successfully locate victims in confined spaces.

Human-Robot Interaction - Perspectives and Applications [Working Title]

This paper presents a practical solution to the problem of multi-legged robot stability moving on... more This paper presents a practical solution to the problem of multi-legged robot stability moving on unstructured 3D terrains using a multi-contact approach. The solution is based on a modified version of the contact wrench set method, which has been reformulated to utilize three arbitrary contact points representing the physics of contact between the robot and the environment. The new formulations are then used to test the stability of a life-size humanoid robot. The proposed method extends available formulations making the CWS tool suitable for a variety of terrains having various physical and geometrical characteristics including heterogenous coplanar (e.g., stairs and sloped terrain) and noncoplanar surfaces (e.g., gravel, sand, compliant terrains, etc.). The results provided by the new formulations are visualized using a graphical visualization tool, showing the adaptability of the proposed formulation in multi-contact locomotion. The results show that the proposed approach effect...

In tilt-rotor UAVs, both the fuselage and tilting rotors contribute to the vehicle's rotation... more In tilt-rotor UAVs, both the fuselage and tilting rotors contribute to the vehicle's rotational motion. Consequently, the system's dynamics rise to a highly-nonlinear system, making it challenging to find feasible and desired control solutions. The common control practices devise a logic-based controller to switch between different flight modes or map the control inputs to the conventional helicopter-type control inputs. However, they fail to provide energy-efficient fast trajectory tracking, especially in the presence of external disturbances. This paper proposes a general-model dynamic formulation and a two-layered constrained Model Predictive Control (MPC) strategy to tackle the trajectory tracking problem for tilt-rotor UAVs. After splitting the vehicle's dynamics into translational and rotational parts, a constrained Linear MPC (LMPC) is designed for the translational dynamic to follow a reference trajectory. We formulate the LMPC as a Quadratically-Constrained Quad...

Advances in Service and Industrial Robotics

2017 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), 2017

This paper proposes a method of tire force estimation designed for use in navigation decision mak... more This paper proposes a method of tire force estimation designed for use in navigation decision making for Unmanned Ground Vehicles (UGVs) operating on off-road terrains. This method (called the Centroid Method) uses a 3D point cloud representation of the terrain to determine tire-ground interaction, and a linear spring to determine the corresponding tire forces. Simulation results of tire force estimation of the Centroid Method are compared against the experimentally validated MF-Swift model, including on a fractal terrain surface which simulates a rough off-road terrain. The results show that the Centroid Method performs well for longitudinal and vertical tire force estimation especially for lower frequencies up to about 8–21Hz. Although the Centroid Method does not provide the same detail as the advanced tire models such as MF-Swift, it is significantly less complex and simpler to implement for enabling efficient on-board UGV navigation decision making.

ICAR '05. Proceedings., 12th International Conference on Advanced Robotics, 2005.

Abstract—Swarm robotics is a rising paradigm which aims at designing new robot artifacts by extra... more Abstract—Swarm robotics is a rising paradigm which aims at designing new robot artifacts by extracting engineering guidelines from Nature. The work presented here shows the use of a particular swarm of robots called swarm-bot for carrying out distributed missions of ...

Robotics

This paper presents an optimized robust trajectory control system for an autonomous tiltrotor bi-... more This paper presents an optimized robust trajectory control system for an autonomous tiltrotor bi-copter based on an incremental nonlinear dynamic inversion (INDI) strategy combined with a set of PID/PD controllers. The methodology includes a lower level, fast attitude control action using an incremental nonlinear dynamic inversion (INDI) strategy, which is driven by a higher level, slow trajectory control action that uses nonlinear dynamic inversion (NDI). The nonlinear dynamic model of the drone is derived, and the basis of the motion and the design of the attitude and position stabilizing controllers are discussed. To develop and test the suggested controller, a circle-shaped flight profile is simulated. The linear control providing inputs to the NDI and INDI controllers is tuned via a novel multi-objective optimization auto-tuning method using the non-dominated sorting genetic algorithm II (NSGA-II). The tracking and disturbance rejection optimization is achieved via the use of t...

2020 IEEE 92nd Vehicular Technology Conference (VTC2020-Fall), 2020

At present, most of the current Simultaneous Localization and Mapping (SLAM) algorithms are limit... more At present, most of the current Simultaneous Localization and Mapping (SLAM) algorithms are limited to work in static environments. However, the world is not static and dynamic objects are typically present in the environments, leading to the failure of the general SLAM. In this paper, a dynamic object removal method combining semantic detection with depth image segmentation is proposed and applied in the real-time SLAM library for cameras ORB-SLAM2 system to achieve robust RGB-D SLAM for dynamic environments. In the proposed method, the potential dynamic regions are captured via YOLOv4 and K-means image segmentation. Different from the general purposes of processing dynamic regions, the potential dynamic regions are redetected by dynamic outliers rejection, which improves the reliability of dynamic object removal. Experiments using the TUM RGB-D dataset demonstrate that the proposed method performs with increased robustness and accuracy when compared to the original ORB-SLAM2 without dynamic object removal in dynamic environments.

ABSTRACT This work describes a modified Nonlinear Model Predictive Control (NMPC) to address cont... more ABSTRACT This work describes a modified Nonlinear Model Predictive Control (NMPC) to address control performance issues that arise when NMPC is applied on unmanned aerial vehicles. The proposed NMPC typically identifies lower cost control options within a set optimization time frame thus producing more stable and robust control. We also introduce an alternative performance (stability) analysis methodology suitable for assessing the stochastic behavior of the NMPC. This analysis method can be used to generate a flight envelope within which the NMPC and UAV combination will act reliably.

Humanoid robots (humanoids), at least in theory, can assist humans and work with them in cluttere... more Humanoid robots (humanoids), at least in theory, can assist humans and work with them in cluttered and confined environments. However, further developments are needed to fully enable them to work in close proximity (even in physical interactions) with humans while not risking the safety of themselves and the objects and people around them. Current methods have not been fully successful in preparing humanoids for 100% safe physical Human Robot Interaction (HRI) due partially to the unresolved challenges of detecting the characteristics of the surrounding environment. Furthermore, current humanoids employ expensive and fragile equipment making them costly, thus limiting humanity of using them. This paper presents a novel real-time and hardware inexpensive collision detection methodology that employs signals from the robots’ motor joints and data processing capabilities from the computers running the robot. The approach enables the safe close-proximity HRI for position-controlled human...

2018 International Conference on Unmanned Aircraft Systems (ICUAS), 2018

Rotary-wing-based Unmanned Aerial Manipulators (UAM) are gaining attention for their in-place hov... more Rotary-wing-based Unmanned Aerial Manipulators (UAM) are gaining attention for their in-place hovering capability, holonomy in motion, and safe operation due to their redundancy. Task-oriented optimal control strategies can also further improve the flight time by generating energy-optimal coordinated motions. This paper addresses the dynamic modeling, trajectory tracking and control of an UAM that consists of an under-actuated rotary-wing UAV, with a novel pitch-hover-maneuvering capability, and a 2-DOF robotic arm. A decoupled velocity-based Model Predictive Control (MPC) strategy is proposed for tracking a trajectory in the sagittal plane of the UAM while the UAV base pitch hovers in place. Conventional PD controllers were used to generate set-point velocity screws as the inputs to the MPC. A partitioned (but complete) dynamic model of the UAM was developed and used for implementing the proposed control strategy in a simulated environment. The MPC controller takes the force/torque...

IFAC Proceedings Volumes, 2010

Proceedings of the 7th International Conference of Control, Dynamic Systems, and Robotics (CDSR'20), 2020

Humanoid robot perception is challenging compared to perception in other robotic systems. The sen... more Humanoid robot perception is challenging compared to perception in other robotic systems. The sensors in a humanoid are in constant state of motion and their pose estimation is affected by the constant motion of the tens of DOFs (Degrees of Freedom) which in turn affect the estimation of the sensed environmental objects. This is especially problematic in highly cluttered dynamic spaces such as indoor office environments. One of the challenges is identifying the presence of all independent moving/dynamic entities such as people walking around the robot. If available, such information would assist humanoids to build better maps and better plan their motions in unstructured confined dynamic environments. This paper presents a moving object detection pipeline based on relative motion and a novel confidence tracking approach that detects point clusters corresponding to independent moving entities around the robot. The detection does not depend on prior knowledge about the target entity. ...

2016 13th Conference on Computer and Robot Vision (CRV), 2016

Design of a vision-based target tracking control strategy for a dual-rotor UAV with tilting rotor... more Design of a vision-based target tracking control strategy for a dual-rotor UAV with tilting rotors is presented. In this research, the under-study UAV is equipped with a sliding mass that can slide over a motorized linear track attached to the UAV's fuselage enabling it to perform sophisticated maneuvers by monitoring its five controllable degrees of freedom. The dynamic model of the system is first derived and then a model-based controller using vision based pose estimation, obtained via an onboard down-looking camera, is designed enabling the UAV to: (1) pitch hover in position, (2) servo towards a target position, and (3) track a moving target. Simulations show the premise of the proposed vision-based control strategy.

Proceedings of the 18th IFAC World Congress, 2011

International Conference on Robotics and Automation, 1999

The modeling and control flexible-manufacturing workcells (FMCs) has generally been performed in ... more The modeling and control flexible-manufacturing workcells (FMCs) has generally been performed in a hierarchical structure, where at the highest level they have been modeled as discrete-event systems (DESs). In this paper, a new DES control synthesis technique that combines Moore Automata (MA) and Controlled- Automata theories to synthesize supervisors is presented. The obtained supervisors can monitor multiple pieces of information

Multi-modal locomotion (e.g. terrestrial, aerial, and aquatic) is gaining increasing interest in ... more Multi-modal locomotion (e.g. terrestrial, aerial, and aquatic) is gaining increasing interest in robotics research as it improves the robots environmental adaptability, locomotion versatility, and operational flexibility. Within the terrestrial multiple locomotion robots, the advantage of hybrid robots stems from their multiple (two or more) locomotion modes, among which robots can select from depending on the encountering terrain conditions. However, there are many challenges in improving the autonomy of the locomotion mode transition between their multiple locomotion modes. This work proposed a method to realize an autonomous locomotion mode transition of a track-legged quadruped robot steps negotiation. The autonomy of the decision-making process was realized by the proposed criterion to comparing energy performances of the rolling and walking locomotion modes. Two climbing gaits were proposed to achieve smooth steps negotiation behaviours for energy evaluation purposes. Simulati...

Robotics

To deploy Unmanned Aerial Vehicles (UAVs) inside heterogeneous GPS-denied confined (potentially u... more To deploy Unmanned Aerial Vehicles (UAVs) inside heterogeneous GPS-denied confined (potentially unknown) spaces, such as those encountered in mining and Urban Search and Rescue (USAR), requires the enhancement of numerous technologies. Of special interest is for UAVs to identify collision-freeSafe Flight Corridors (SFC+) within highly cluttered convex- and non-convex-shaped environments, which requires UAVs to perform advanced flight maneuvers while exploiting their flying capabilities. Within this paper, a novel auxiliary occupancy checking process that augments traditional 3D flight corridor generation is proposed. The 3D flight corridor is established as a topological structure based on a hand-crafted path either derived from a computer-generated environment or provided by the human operator, which captures humans’ preferences and desired flight intentions for the given space. This corridor is formulated as a series of interconnected overlapping convex polyhedra bounded by the pe...

The use of robotics in Urban Search and Rescue (USAR) is growing steadily from their initial ince... more The use of robotics in Urban Search and Rescue (USAR) is growing steadily from their initial inception during the 2001 World Trade Centre incident. Despite years of progress, the core design of robots currently in use for USAR purposes has deviated little, favoring software/control development and optimization of the basic robot template to improve performance instead. Presented here is a novel design description of the Cricket, an advanced robot with a broader range of physical capabilities than traditional USAR robots. By incorporating the tracked structure of earlier robots, appreciated for energy efficiency and robustness, into a multi-limbed walking design, the Cricket enables the use of advanced locomotion techniques. The ability to climb over obstacles many times the height of the robot, ascend vertical shafts without the assistance of a tether, and traverse rough and near vertical terrain improves the Cricket’s capability to successfully locate victims in confined spaces.

Human-Robot Interaction - Perspectives and Applications [Working Title]

This paper presents a practical solution to the problem of multi-legged robot stability moving on... more This paper presents a practical solution to the problem of multi-legged robot stability moving on unstructured 3D terrains using a multi-contact approach. The solution is based on a modified version of the contact wrench set method, which has been reformulated to utilize three arbitrary contact points representing the physics of contact between the robot and the environment. The new formulations are then used to test the stability of a life-size humanoid robot. The proposed method extends available formulations making the CWS tool suitable for a variety of terrains having various physical and geometrical characteristics including heterogenous coplanar (e.g., stairs and sloped terrain) and noncoplanar surfaces (e.g., gravel, sand, compliant terrains, etc.). The results provided by the new formulations are visualized using a graphical visualization tool, showing the adaptability of the proposed formulation in multi-contact locomotion. The results show that the proposed approach effect...

In tilt-rotor UAVs, both the fuselage and tilting rotors contribute to the vehicle's rotation... more In tilt-rotor UAVs, both the fuselage and tilting rotors contribute to the vehicle's rotational motion. Consequently, the system's dynamics rise to a highly-nonlinear system, making it challenging to find feasible and desired control solutions. The common control practices devise a logic-based controller to switch between different flight modes or map the control inputs to the conventional helicopter-type control inputs. However, they fail to provide energy-efficient fast trajectory tracking, especially in the presence of external disturbances. This paper proposes a general-model dynamic formulation and a two-layered constrained Model Predictive Control (MPC) strategy to tackle the trajectory tracking problem for tilt-rotor UAVs. After splitting the vehicle's dynamics into translational and rotational parts, a constrained Linear MPC (LMPC) is designed for the translational dynamic to follow a reference trajectory. We formulate the LMPC as a Quadratically-Constrained Quad...

Advances in Service and Industrial Robotics

2017 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), 2017

This paper proposes a method of tire force estimation designed for use in navigation decision mak... more This paper proposes a method of tire force estimation designed for use in navigation decision making for Unmanned Ground Vehicles (UGVs) operating on off-road terrains. This method (called the Centroid Method) uses a 3D point cloud representation of the terrain to determine tire-ground interaction, and a linear spring to determine the corresponding tire forces. Simulation results of tire force estimation of the Centroid Method are compared against the experimentally validated MF-Swift model, including on a fractal terrain surface which simulates a rough off-road terrain. The results show that the Centroid Method performs well for longitudinal and vertical tire force estimation especially for lower frequencies up to about 8–21Hz. Although the Centroid Method does not provide the same detail as the advanced tire models such as MF-Swift, it is significantly less complex and simpler to implement for enabling efficient on-board UGV navigation decision making.

ICAR '05. Proceedings., 12th International Conference on Advanced Robotics, 2005.

Abstract—Swarm robotics is a rising paradigm which aims at designing new robot artifacts by extra... more Abstract—Swarm robotics is a rising paradigm which aims at designing new robot artifacts by extracting engineering guidelines from Nature. The work presented here shows the use of a particular swarm of robots called swarm-bot for carrying out distributed missions of ...

Robotics

This paper presents an optimized robust trajectory control system for an autonomous tiltrotor bi-... more This paper presents an optimized robust trajectory control system for an autonomous tiltrotor bi-copter based on an incremental nonlinear dynamic inversion (INDI) strategy combined with a set of PID/PD controllers. The methodology includes a lower level, fast attitude control action using an incremental nonlinear dynamic inversion (INDI) strategy, which is driven by a higher level, slow trajectory control action that uses nonlinear dynamic inversion (NDI). The nonlinear dynamic model of the drone is derived, and the basis of the motion and the design of the attitude and position stabilizing controllers are discussed. To develop and test the suggested controller, a circle-shaped flight profile is simulated. The linear control providing inputs to the NDI and INDI controllers is tuned via a novel multi-objective optimization auto-tuning method using the non-dominated sorting genetic algorithm II (NSGA-II). The tracking and disturbance rejection optimization is achieved via the use of t...

2020 IEEE 92nd Vehicular Technology Conference (VTC2020-Fall), 2020

At present, most of the current Simultaneous Localization and Mapping (SLAM) algorithms are limit... more At present, most of the current Simultaneous Localization and Mapping (SLAM) algorithms are limited to work in static environments. However, the world is not static and dynamic objects are typically present in the environments, leading to the failure of the general SLAM. In this paper, a dynamic object removal method combining semantic detection with depth image segmentation is proposed and applied in the real-time SLAM library for cameras ORB-SLAM2 system to achieve robust RGB-D SLAM for dynamic environments. In the proposed method, the potential dynamic regions are captured via YOLOv4 and K-means image segmentation. Different from the general purposes of processing dynamic regions, the potential dynamic regions are redetected by dynamic outliers rejection, which improves the reliability of dynamic object removal. Experiments using the TUM RGB-D dataset demonstrate that the proposed method performs with increased robustness and accuracy when compared to the original ORB-SLAM2 without dynamic object removal in dynamic environments.

ABSTRACT This work describes a modified Nonlinear Model Predictive Control (NMPC) to address cont... more ABSTRACT This work describes a modified Nonlinear Model Predictive Control (NMPC) to address control performance issues that arise when NMPC is applied on unmanned aerial vehicles. The proposed NMPC typically identifies lower cost control options within a set optimization time frame thus producing more stable and robust control. We also introduce an alternative performance (stability) analysis methodology suitable for assessing the stochastic behavior of the NMPC. This analysis method can be used to generate a flight envelope within which the NMPC and UAV combination will act reliably.

Humanoid robots (humanoids), at least in theory, can assist humans and work with them in cluttere... more Humanoid robots (humanoids), at least in theory, can assist humans and work with them in cluttered and confined environments. However, further developments are needed to fully enable them to work in close proximity (even in physical interactions) with humans while not risking the safety of themselves and the objects and people around them. Current methods have not been fully successful in preparing humanoids for 100% safe physical Human Robot Interaction (HRI) due partially to the unresolved challenges of detecting the characteristics of the surrounding environment. Furthermore, current humanoids employ expensive and fragile equipment making them costly, thus limiting humanity of using them. This paper presents a novel real-time and hardware inexpensive collision detection methodology that employs signals from the robots’ motor joints and data processing capabilities from the computers running the robot. The approach enables the safe close-proximity HRI for position-controlled human...

2018 International Conference on Unmanned Aircraft Systems (ICUAS), 2018

Rotary-wing-based Unmanned Aerial Manipulators (UAM) are gaining attention for their in-place hov... more Rotary-wing-based Unmanned Aerial Manipulators (UAM) are gaining attention for their in-place hovering capability, holonomy in motion, and safe operation due to their redundancy. Task-oriented optimal control strategies can also further improve the flight time by generating energy-optimal coordinated motions. This paper addresses the dynamic modeling, trajectory tracking and control of an UAM that consists of an under-actuated rotary-wing UAV, with a novel pitch-hover-maneuvering capability, and a 2-DOF robotic arm. A decoupled velocity-based Model Predictive Control (MPC) strategy is proposed for tracking a trajectory in the sagittal plane of the UAM while the UAV base pitch hovers in place. Conventional PD controllers were used to generate set-point velocity screws as the inputs to the MPC. A partitioned (but complete) dynamic model of the UAM was developed and used for implementing the proposed control strategy in a simulated environment. The MPC controller takes the force/torque...

IFAC Proceedings Volumes, 2010

Proceedings of the 7th International Conference of Control, Dynamic Systems, and Robotics (CDSR'20), 2020

Humanoid robot perception is challenging compared to perception in other robotic systems. The sen... more Humanoid robot perception is challenging compared to perception in other robotic systems. The sensors in a humanoid are in constant state of motion and their pose estimation is affected by the constant motion of the tens of DOFs (Degrees of Freedom) which in turn affect the estimation of the sensed environmental objects. This is especially problematic in highly cluttered dynamic spaces such as indoor office environments. One of the challenges is identifying the presence of all independent moving/dynamic entities such as people walking around the robot. If available, such information would assist humanoids to build better maps and better plan their motions in unstructured confined dynamic environments. This paper presents a moving object detection pipeline based on relative motion and a novel confidence tracking approach that detects point clusters corresponding to independent moving entities around the robot. The detection does not depend on prior knowledge about the target entity. ...

2016 13th Conference on Computer and Robot Vision (CRV), 2016

Design of a vision-based target tracking control strategy for a dual-rotor UAV with tilting rotor... more Design of a vision-based target tracking control strategy for a dual-rotor UAV with tilting rotors is presented. In this research, the under-study UAV is equipped with a sliding mass that can slide over a motorized linear track attached to the UAV's fuselage enabling it to perform sophisticated maneuvers by monitoring its five controllable degrees of freedom. The dynamic model of the system is first derived and then a model-based controller using vision based pose estimation, obtained via an onboard down-looking camera, is designed enabling the UAV to: (1) pitch hover in position, (2) servo towards a target position, and (3) track a moving target. Simulations show the premise of the proposed vision-based control strategy.

Proceedings of the 18th IFAC World Congress, 2011

International Conference on Robotics and Automation, 1999

The modeling and control flexible-manufacturing workcells (FMCs) has generally been performed in ... more The modeling and control flexible-manufacturing workcells (FMCs) has generally been performed in a hierarchical structure, where at the highest level they have been modeled as discrete-event systems (DESs). In this paper, a new DES control synthesis technique that combines Moore Automata (MA) and Controlled- Automata theories to synthesize supervisors is presented. The obtained supervisors can monitor multiple pieces of information

Multi-modal locomotion (e.g. terrestrial, aerial, and aquatic) is gaining increasing interest in ... more Multi-modal locomotion (e.g. terrestrial, aerial, and aquatic) is gaining increasing interest in robotics research as it improves the robots environmental adaptability, locomotion versatility, and operational flexibility. Within the terrestrial multiple locomotion robots, the advantage of hybrid robots stems from their multiple (two or more) locomotion modes, among which robots can select from depending on the encountering terrain conditions. However, there are many challenges in improving the autonomy of the locomotion mode transition between their multiple locomotion modes. This work proposed a method to realize an autonomous locomotion mode transition of a track-legged quadruped robot steps negotiation. The autonomy of the decision-making process was realized by the proposed criterion to comparing energy performances of the rolling and walking locomotion modes. Two climbing gaits were proposed to achieve smooth steps negotiation behaviours for energy evaluation purposes. Simulati...