ABSTRACT In service robotics, control systems allowing for skillful manipulation and dexterity co... more ABSTRACT In service robotics, control systems allowing for skillful manipulation and dexterity constitute one of the most valuable technologies. Recently, control approaches inspired by humans or animals have attracted widespread attention, due to their merit of allowing various tasks to be performed naturally without precisely calculating their behaviors. This work, thus, focuses on the embodiment of a notable control method for a multi-DOF robotic system considering a human physical activity. In contrast to the traditional approaches, in the proposed control, the linear superposition of four control terms is exploited. These consist of joint spring-damping and virtual spring-damper terms in the joint and Cartesian spaces, respectively. Remarkably, the joint spring term is newly designed for the consideration of the simple passive muscle stiffness effect under gravity to guarantee motion repeatability and avoid the problem of ill-posedness. In the experiment, various abilities with respect to position control and compliant behavior are exposed through a real robot. Additional experiments are performed for the verification of the motion repeatability and energy-efficient motion under DOF redundancy.
2020 17th International Conference on Ubiquitous Robots (UR)
Since the ball-balancing robot has been researched, many kinds of platforms and control methods h... more Since the ball-balancing robot has been researched, many kinds of platforms and control methods have been developed for the ballbot. Even though the behavior of the robot has been achieved by previous studies, there are few studies considering the contact forces between the robot and ball. In this paper, we propose balancing and tracking control of the ballbot, with unilateral constraints. Using an adequate task transformation matrix, the task space dynamics can be divided into the dynamics of the robot and the ball respectively. This decomposition has advantages to obtain the input torque through the ball task dynamics with constraint forces. Through the proposed formalism, the contact force can be computed from the ball task space dynamics with the quadratic programming(QP) with inequality constraints such as unilateral constraints and friction constraints. The obtained contact force is used in the robot task space dynamics to get control input. In addition, the balancing force is computed using CoM reflex as a reference. Hence, using the synthesized controller, the contact force based balancing and tracking control simulation is performed.
IECON 2019 - 45th Annual Conference of the IEEE Industrial Electronics Society, 2019
In this paper, we address the problem of generating a trajectory of the zero-moment point (ZMP) a... more In this paper, we address the problem of generating a trajectory of the zero-moment point (ZMP) and the rate of angular momentum for a bipedal robot in the sagittal plane, with which the balance of the robot is recovered from external push. Unlike most previous works that adjusted a pre-designed ZMP or solved (possibly too heavy) nonlinear optimization problems, our main purpose is to develop a fully reactive step generator in the sense that (a) no pre-calculation of nominal trajectory is required, and (b) the algorithm is simple enough to operate in real time, only by utilizing the current state of the robot. For the design, it is seen by reinterpreting the centroidal dynamics in the hybrid model framework that the balance recovery problem can be recast as the problem of stabilizing a hybrid-type (linear) inverted pendulum model. On the basis of the concept of the divergent component of motion, a simple hybrid control law is then constructed to stabilize the hybrid system, which serves as a step generator that automatically determines where and when to step. This paper briefly sketches a mathematical proof on the performance of the proposed generator from a control-theoretic perspective, which is also supported by simulation results.
2017 IEEE International Conference on Mechatronics and Automation (ICMA), 2017
This paper presents the control strategy for 7-link biped consisting of an underactuated floating... more This paper presents the control strategy for 7-link biped consisting of an underactuated floating trunk, rigid legs, and flat feet. This proposed control enables a biped to perform stable walking without using any pre-designed trajectories. We consider the force direction control in Biped Trunk Spring Loaded Inverted Pendulum (BTSLIP) from our previous study, which shows the stable behavior in walking motion. Then, we aim to inherit the advantage of force direction control related to the BTSLIP. Herein, we add two virtual springs from hip to each foot then map simple virtual model to the real robot joints torque. Furthermore, the control of ankles will adapt with different walking phase by following finite state machine. The dynamical simulation under random initial state validates the stabilizing the floating trunk and maintaining of the robot model equipped with the proposed controller.
2017 14th International Conference on Ubiquitous Robots and Ambient Intelligence (URAI), 2017
In this paper, we present a new control strategy for the Bipedal Trunk Spring Loaded Inverted Pen... more In this paper, we present a new control strategy for the Bipedal Trunk Spring Loaded Inverted Pendulum (BTSLIP) model, consisting of springy legs and rigid trunk. Our walking controller is inspired from the Virtual Pendulum (VP) concept. In this concept, by intersecting the ground reaction forces (GRF) to a virtual pivot point (VPP), the trunk is provided the restoring moment to keep its balance and to behave like a virtual hanging pendulum. The simple hip torque control was presented with the name the VPP method. However, this approach is not reliable in terms of rejecting disturbances. Thus, we propose a new control strategy to achieve the robustness and stabilize the walking gait. Herein, the control is introduced with the combination of two strategies, 1) updating the position of the VPP by using Discrete Linear Quadratic Regulator controller and 2) controlling the stiffness of springy legs by feedback linearization controller to track both reference vertical position and velocity of the Center of Mass (CoM). We present the dynamic simulation of the BTSLIP model under the presence of external disturbances. The performance of the proposed control strategy shows stable, robust walking which is compared with the VPP method.
This study presents a new vibrotactile fingertip interface and a rendering algorithm for 2.5D sur... more This study presents a new vibrotactile fingertip interface and a rendering algorithm for 2.5D surface features on a touch screen. The fingertip device has four piezoelectric actuators surrounding both sides of a user's finger. The proposed algorithm generates a time-varying vibration flow in-between actuators, in which their intensities and durations adaptively changes according to local geometry under touch point. The proposed approach can provide separate effects on individual fingers by using multiple interfaces. The experiments revealed that a user can reliably distinguish height of virtual bump by the levels of 2.5+ out of 4, for both single and multi-touch interactions.
2017 IEEE International Conference on Robotics and Automation (ICRA), 2017
Based on the liner inverted pendulum model (LIPM) for the dynamics of biped humanoid robots, an a... more Based on the liner inverted pendulum model (LIPM) for the dynamics of biped humanoid robots, an analytical method for computing stability regions relevant to standing balance of the biped humanoid robots is introduced in this paper. More precisely, two types of the stability regions are discussed in this paper with the consideration of that the zero moment point (ZMP) should be located in the supporting region to guarantee stable standing of the biped humanoid robots. First, assuming no external disturbances affecting the motion of the biped humanoid robots, the set of the initial values of the center of mass (CoM) position and velocity with which the location of the ZMP is limited to be inside the supporting region can be explicitly obtained by solving a finite number of linear inequalities. Second, two admissible sets of external force disturbances (impulse and finite energy) with which the ZMP does not deviate from the supporting region are characterized by solving finite number of linear inequalities or the discrete-time Lyapunov equation, respectively. The validity and effectiveness of the analytical method proposed in this paper are verified through a simulation result.
2016 IEEE International Conference on Mechatronics and Automation, 2016
A human walking has some general characteristics such as general timing of walking cycle, foot st... more A human walking has some general characteristics such as general timing of walking cycle, foot state at each timing, relationship with the stride per stature and walking speed, joint angle patterns of leg, pelvis movement, foot clearance during swing phase. So we collected and analysed the normal walking characteristics to generating natural walking pattern for general biped rigid-body configuration and we explained how to generate the walking pattern in sagittal plane possessing human normal walking characteristics. Finally, we demonstrated that our walking pattern properly have the normal walking characteristics.
2014 IEEE-RAS International Conference on Humanoid Robots, 2014
This paper presents a novel method for controlling a dual arm robot to pick heavy objects. The mo... more This paper presents a novel method for controlling a dual arm robot to pick heavy objects. The motivation for this study is inspired from the observation of human motion in their daily activities. Two reflex actions are proposed in this work. The first reflex is designed to control the COM of the robot when its stability is endangered by the effect of the object weight. Static stability criterion is used to observe this dangerous effect and a simple minimization technique is used to generate the reflex torque. The second reflex aims to reduce the consumed torque of the motors by simply finding a pose at which the gravity term minimized. A control law is suggested for a dual arm robot to perform picking motion for both two cases with known and unknown objects. The control state space is the operational space and no inverse kinematics are needed. Finally, several dynamic simulations are introduced to validate the efficiency of the proposed controller.
The paper proposes 'Network-based Humanoid', that is, a humanoid endowed with its perception capa... more The paper proposes 'Network-based Humanoid', that is, a humanoid endowed with its perception capability and intelligence by an external computer system connected with wireless network. The network-based humanoid is composed of a humanoid test-bed, an internal control system and an external computer system. The internal distributed control system is composed of two parts. One is responsible for motion control of the humanoid following commands from the external computer system while the motion control is done by a CAN-based distributed motor controller. The other is for real-time data transmission of image data, voice data, and sensor data for motion control by wireless network to the external computer system. The external computer system, a network-based distributed control system, processes the transmitted data, decides the final action command for the humanoid, and transmits the action command to the internal control system. A network-based humanoid, whose name is 'MAHRU', is developed successfully. The humanoid can walk using two legs with the maximum speed of 0.9 Km/h. It is noted that the humanoid can recognize faces, gestures of human beings in real-time, three-dimensional objects, and 100 voice words with the help of the external computer system connected through wireless network. And, the humanoid interacts with human beings via a stereo camera, a microphone, and force/torque sensors.
This work presents a walking pattern generator based on the control of the center of mass (COM) s... more This work presents a walking pattern generator based on the control of the center of mass (COM) states and its experimental validations on the compliant humanoid robot COMAN powered by intrinsically compliant joints. To cope with the inaccuracies of the joint position tracking resulted by the physical compliance, the proposed pattern generator uses the feedback states of the COM and on-line computes the updated COM references. The position and velocity of the COM are the state variables, and the constrained ground reaction force (GRF) limited by the support polygon is the control effort to drive the real COM states to track the desired references. The frequency analysis of the COM demonstrates its low frequency spectrum that indicates the demand of a low control bandwidth which is suitable for a robot system with compliant joints. The effectiveness of the proposed gait generation method was demonstrated by the experiments performed on the COMAN robot. The experimental data such as the COM position and velocity tracking, the GRF applied on feet, the measured step length and the walking velocity are analyzed. The effect of the passive compliance is also discussed.
In this paper, a robust torque control method is proposed for a robot arm which is equipped with ... more In this paper, a robust torque control method is proposed for a robot arm which is equipped with joint torque sensor. The proposed controller is used to control the joint torque and make it to be equal with the torque controller reference input torque. A flexible joint robot model will be introduced to model the robot arm system. The disturbance observer scheme is used to reduce the disturbance effects on the system. The PI torque controller is implemented using the characteristics of disturbance observer. The performance of the proposed controller is demonstrated through experiments with a one degree of freedom robot arm.
Wearable glove type haptic interfaces are often required to be light weight, which constrains the... more Wearable glove type haptic interfaces are often required to be light weight, which constrains the actuator to exert low torques. This causes a virtual object to feel compliant, reducing the range of presented surface properties. To overcome the limitation, we propose to compensate the hardness of a virtual object with cutaneous feedback. A cutaneous haptic interface is designed to present the hardness to a user's fingertip along with a force-feedback interface and the corresponding rendering strategy is proposed. Two experiments were conducted to evaluate the proposed approach for one-finger touch and two-finger grip for stiffness values under 0.3 N/mm. Experimental results indicate that the addition of cutaneous feedback led the virtual surface to feel significantly harder than the nominal stiffness felt by force-feedback alone. In addition, the perceived hardness was significantly affected by the rate of hardness rendered with cutaneous interface when the nominal stiffness was increased.
In this paper, a torque control method in task-space for redundant manipulators with friction is ... more In this paper, a torque control method in task-space for redundant manipulators with friction is proposed. A previous simple control approach based on virtual spring damper hypothesis is used to generate human-like motions. The method is efficient in the system which is difficult to identify the exact dynamics, however, the controller has steady state errors. To eliminate the steady state error, the gravity and friction, which is the part of the system dynamics, are compensated. Although the gravity and friction are compensated, the error of the modelling remains in the system. Hence, to reduce the nonlinearity, unknown effects, and modelling errors of the system, a torque controller based on Time-Delay Control (TDC) that eliminates the friction and unknown effects, is used. The performance of the control method, in Cartesian space control, is experimented with the torque sensor based 3-joints robot manipulator. Keywords–Task-Space; Virtual spring damper hypothesis; TimeDelay Contro...
2017 IEEE International Conference on Advanced Intelligent Mechatronics (AIM), 2017
In this paper, we propose an energy-efficient robotic leg design using a redundantly actuated par... more In this paper, we propose an energy-efficient robotic leg design using a redundantly actuated parallel mechanism (RAPM). By adding an actuator parallel to the serially-actuated leg, we show that the legged machine can reduce mechanical energy loss. We begin with reviewing kinematic model of parallel mechanisms and then present an optimal torque distribution algorithm among redundant actuators which minimizes antagonistic power, a measure for mechanical energy loss due to power conflict in actuators. As an example study, given end-effector (foot) force and motion profile generated by the spring-loaded-inverted-pendulum (SLIP) running, we demonstrate how much the antagonistic power can be reduced by applying the proposed leg design and optimization algorithm in simulation. Also, it is presented that the choice of actuated joints in parallel mechanism affects the performance (energy efficiency). Finally, we demonstrate that the proposed design is also effective in walking, which validates the hypothesis that the proposed RAPM leg design can be effective in a range of locomotion tasks.
We investigate the effect of adding cutaneous cues to kinesthetic feedback on the perception of a... more We investigate the effect of adding cutaneous cues to kinesthetic feedback on the perception of a virtual object's hardness. A cutaneous haptic interface is designed to deliver hardness information to a user's fingertip along with a force-feedback interface, and the corresponding rendering strategy is implemented. Two sets of experiments are conducted to evaluate the proposed approach for hardness perception using one-finger touch and two-finger grasp. Experimental results indicate that the addition of cutaneous feedback can make the virtual surface feel significantly harder than the nominal stiffness delivered by force-feedback alone. In addition, the perceived hardness is significantly affected by the rate of hardness rendered with a cutaneous interface for the nominal stiffness K ¼ 0:3 and 0.5 N/mm. For two-finger grip, the effect of a virtual object's thickness has a significant effect on the perceived hardness measured in stiffness. When the perceived hardness is converted to Young's modulus, the effect of thickness is insignificant.
2012 IEEE/RSJ International Conference on Intelligent Robots and Systems, 2012
This paper discusses a balance control method with kinodynamic constraints for leg-wheel hybrid s... more This paper discusses a balance control method with kinodynamic constraints for leg-wheel hybrid structures in an effort to improve the mobility of locomotion over hard, flat surfaces. Preliminarily, we defined a prioritized Jacobian and a prioritized inverse of Jacobian to formulate the dynamically decoupled model in the task space for the constrained multi-contact multi-rigid-body system with a floating base. Our strategy has two tracks to accommodate the uncertainty and the complexity of the system dynamics. 1) The time-delay estimation and control are combined with the nonlinear programming. 2) Whole kinodynamic constraints are derived as functions of the control input. The proposed balance control algorithm allows the system to traverse desired trajectories satisfying the kinodynamic constraints and improves the mobility of locomotion. The effectiveness of the algorithm is tested with the dynamic simulations.
Proceedings. 1998 IEEE International Conference on Robotics and Automation (Cat. No.98CH36146)
An approach to resolve the kinematic redundancy and to control the motion/force of redundant mani... more An approach to resolve the kinematic redundancy and to control the motion/force of redundant manipulators is presented. By defining a proper metric in joint space, minimal parametrization of motion and force controlled subspaces as well as the null motion component is realized. With this formulation, control of both motion~orce and internal motion of redundant manipulator can be achieved via a new hybrid impedance control method with inertial decoupling of each space. Some numerical examples are given to demonstrate the pet-jormance of the proposed cotztrol method. space, the dynamics of remaining degrees of freedom does not appear in this formulation[3]. Thus, in order to take a full advantage of the redundancy, dealing with the hidden internal dynamics is essential for achieving higher performance of both position and compliant motions because the hidden dynamics affects the task space motions of redundant manipulators. The motivation of this paper is to provide a method to express the behavior of redundant manipulators with task and null space dynamics with decoupled manner using appropriate decomposition method.
ABSTRACT In service robotics, control systems allowing for skillful manipulation and dexterity co... more ABSTRACT In service robotics, control systems allowing for skillful manipulation and dexterity constitute one of the most valuable technologies. Recently, control approaches inspired by humans or animals have attracted widespread attention, due to their merit of allowing various tasks to be performed naturally without precisely calculating their behaviors. This work, thus, focuses on the embodiment of a notable control method for a multi-DOF robotic system considering a human physical activity. In contrast to the traditional approaches, in the proposed control, the linear superposition of four control terms is exploited. These consist of joint spring-damping and virtual spring-damper terms in the joint and Cartesian spaces, respectively. Remarkably, the joint spring term is newly designed for the consideration of the simple passive muscle stiffness effect under gravity to guarantee motion repeatability and avoid the problem of ill-posedness. In the experiment, various abilities with respect to position control and compliant behavior are exposed through a real robot. Additional experiments are performed for the verification of the motion repeatability and energy-efficient motion under DOF redundancy.
2020 17th International Conference on Ubiquitous Robots (UR)
Since the ball-balancing robot has been researched, many kinds of platforms and control methods h... more Since the ball-balancing robot has been researched, many kinds of platforms and control methods have been developed for the ballbot. Even though the behavior of the robot has been achieved by previous studies, there are few studies considering the contact forces between the robot and ball. In this paper, we propose balancing and tracking control of the ballbot, with unilateral constraints. Using an adequate task transformation matrix, the task space dynamics can be divided into the dynamics of the robot and the ball respectively. This decomposition has advantages to obtain the input torque through the ball task dynamics with constraint forces. Through the proposed formalism, the contact force can be computed from the ball task space dynamics with the quadratic programming(QP) with inequality constraints such as unilateral constraints and friction constraints. The obtained contact force is used in the robot task space dynamics to get control input. In addition, the balancing force is computed using CoM reflex as a reference. Hence, using the synthesized controller, the contact force based balancing and tracking control simulation is performed.
IECON 2019 - 45th Annual Conference of the IEEE Industrial Electronics Society, 2019
In this paper, we address the problem of generating a trajectory of the zero-moment point (ZMP) a... more In this paper, we address the problem of generating a trajectory of the zero-moment point (ZMP) and the rate of angular momentum for a bipedal robot in the sagittal plane, with which the balance of the robot is recovered from external push. Unlike most previous works that adjusted a pre-designed ZMP or solved (possibly too heavy) nonlinear optimization problems, our main purpose is to develop a fully reactive step generator in the sense that (a) no pre-calculation of nominal trajectory is required, and (b) the algorithm is simple enough to operate in real time, only by utilizing the current state of the robot. For the design, it is seen by reinterpreting the centroidal dynamics in the hybrid model framework that the balance recovery problem can be recast as the problem of stabilizing a hybrid-type (linear) inverted pendulum model. On the basis of the concept of the divergent component of motion, a simple hybrid control law is then constructed to stabilize the hybrid system, which serves as a step generator that automatically determines where and when to step. This paper briefly sketches a mathematical proof on the performance of the proposed generator from a control-theoretic perspective, which is also supported by simulation results.
2017 IEEE International Conference on Mechatronics and Automation (ICMA), 2017
This paper presents the control strategy for 7-link biped consisting of an underactuated floating... more This paper presents the control strategy for 7-link biped consisting of an underactuated floating trunk, rigid legs, and flat feet. This proposed control enables a biped to perform stable walking without using any pre-designed trajectories. We consider the force direction control in Biped Trunk Spring Loaded Inverted Pendulum (BTSLIP) from our previous study, which shows the stable behavior in walking motion. Then, we aim to inherit the advantage of force direction control related to the BTSLIP. Herein, we add two virtual springs from hip to each foot then map simple virtual model to the real robot joints torque. Furthermore, the control of ankles will adapt with different walking phase by following finite state machine. The dynamical simulation under random initial state validates the stabilizing the floating trunk and maintaining of the robot model equipped with the proposed controller.
2017 14th International Conference on Ubiquitous Robots and Ambient Intelligence (URAI), 2017
In this paper, we present a new control strategy for the Bipedal Trunk Spring Loaded Inverted Pen... more In this paper, we present a new control strategy for the Bipedal Trunk Spring Loaded Inverted Pendulum (BTSLIP) model, consisting of springy legs and rigid trunk. Our walking controller is inspired from the Virtual Pendulum (VP) concept. In this concept, by intersecting the ground reaction forces (GRF) to a virtual pivot point (VPP), the trunk is provided the restoring moment to keep its balance and to behave like a virtual hanging pendulum. The simple hip torque control was presented with the name the VPP method. However, this approach is not reliable in terms of rejecting disturbances. Thus, we propose a new control strategy to achieve the robustness and stabilize the walking gait. Herein, the control is introduced with the combination of two strategies, 1) updating the position of the VPP by using Discrete Linear Quadratic Regulator controller and 2) controlling the stiffness of springy legs by feedback linearization controller to track both reference vertical position and velocity of the Center of Mass (CoM). We present the dynamic simulation of the BTSLIP model under the presence of external disturbances. The performance of the proposed control strategy shows stable, robust walking which is compared with the VPP method.
This study presents a new vibrotactile fingertip interface and a rendering algorithm for 2.5D sur... more This study presents a new vibrotactile fingertip interface and a rendering algorithm for 2.5D surface features on a touch screen. The fingertip device has four piezoelectric actuators surrounding both sides of a user's finger. The proposed algorithm generates a time-varying vibration flow in-between actuators, in which their intensities and durations adaptively changes according to local geometry under touch point. The proposed approach can provide separate effects on individual fingers by using multiple interfaces. The experiments revealed that a user can reliably distinguish height of virtual bump by the levels of 2.5+ out of 4, for both single and multi-touch interactions.
2017 IEEE International Conference on Robotics and Automation (ICRA), 2017
Based on the liner inverted pendulum model (LIPM) for the dynamics of biped humanoid robots, an a... more Based on the liner inverted pendulum model (LIPM) for the dynamics of biped humanoid robots, an analytical method for computing stability regions relevant to standing balance of the biped humanoid robots is introduced in this paper. More precisely, two types of the stability regions are discussed in this paper with the consideration of that the zero moment point (ZMP) should be located in the supporting region to guarantee stable standing of the biped humanoid robots. First, assuming no external disturbances affecting the motion of the biped humanoid robots, the set of the initial values of the center of mass (CoM) position and velocity with which the location of the ZMP is limited to be inside the supporting region can be explicitly obtained by solving a finite number of linear inequalities. Second, two admissible sets of external force disturbances (impulse and finite energy) with which the ZMP does not deviate from the supporting region are characterized by solving finite number of linear inequalities or the discrete-time Lyapunov equation, respectively. The validity and effectiveness of the analytical method proposed in this paper are verified through a simulation result.
2016 IEEE International Conference on Mechatronics and Automation, 2016
A human walking has some general characteristics such as general timing of walking cycle, foot st... more A human walking has some general characteristics such as general timing of walking cycle, foot state at each timing, relationship with the stride per stature and walking speed, joint angle patterns of leg, pelvis movement, foot clearance during swing phase. So we collected and analysed the normal walking characteristics to generating natural walking pattern for general biped rigid-body configuration and we explained how to generate the walking pattern in sagittal plane possessing human normal walking characteristics. Finally, we demonstrated that our walking pattern properly have the normal walking characteristics.
2014 IEEE-RAS International Conference on Humanoid Robots, 2014
This paper presents a novel method for controlling a dual arm robot to pick heavy objects. The mo... more This paper presents a novel method for controlling a dual arm robot to pick heavy objects. The motivation for this study is inspired from the observation of human motion in their daily activities. Two reflex actions are proposed in this work. The first reflex is designed to control the COM of the robot when its stability is endangered by the effect of the object weight. Static stability criterion is used to observe this dangerous effect and a simple minimization technique is used to generate the reflex torque. The second reflex aims to reduce the consumed torque of the motors by simply finding a pose at which the gravity term minimized. A control law is suggested for a dual arm robot to perform picking motion for both two cases with known and unknown objects. The control state space is the operational space and no inverse kinematics are needed. Finally, several dynamic simulations are introduced to validate the efficiency of the proposed controller.
The paper proposes 'Network-based Humanoid', that is, a humanoid endowed with its perception capa... more The paper proposes 'Network-based Humanoid', that is, a humanoid endowed with its perception capability and intelligence by an external computer system connected with wireless network. The network-based humanoid is composed of a humanoid test-bed, an internal control system and an external computer system. The internal distributed control system is composed of two parts. One is responsible for motion control of the humanoid following commands from the external computer system while the motion control is done by a CAN-based distributed motor controller. The other is for real-time data transmission of image data, voice data, and sensor data for motion control by wireless network to the external computer system. The external computer system, a network-based distributed control system, processes the transmitted data, decides the final action command for the humanoid, and transmits the action command to the internal control system. A network-based humanoid, whose name is 'MAHRU', is developed successfully. The humanoid can walk using two legs with the maximum speed of 0.9 Km/h. It is noted that the humanoid can recognize faces, gestures of human beings in real-time, three-dimensional objects, and 100 voice words with the help of the external computer system connected through wireless network. And, the humanoid interacts with human beings via a stereo camera, a microphone, and force/torque sensors.
This work presents a walking pattern generator based on the control of the center of mass (COM) s... more This work presents a walking pattern generator based on the control of the center of mass (COM) states and its experimental validations on the compliant humanoid robot COMAN powered by intrinsically compliant joints. To cope with the inaccuracies of the joint position tracking resulted by the physical compliance, the proposed pattern generator uses the feedback states of the COM and on-line computes the updated COM references. The position and velocity of the COM are the state variables, and the constrained ground reaction force (GRF) limited by the support polygon is the control effort to drive the real COM states to track the desired references. The frequency analysis of the COM demonstrates its low frequency spectrum that indicates the demand of a low control bandwidth which is suitable for a robot system with compliant joints. The effectiveness of the proposed gait generation method was demonstrated by the experiments performed on the COMAN robot. The experimental data such as the COM position and velocity tracking, the GRF applied on feet, the measured step length and the walking velocity are analyzed. The effect of the passive compliance is also discussed.
In this paper, a robust torque control method is proposed for a robot arm which is equipped with ... more In this paper, a robust torque control method is proposed for a robot arm which is equipped with joint torque sensor. The proposed controller is used to control the joint torque and make it to be equal with the torque controller reference input torque. A flexible joint robot model will be introduced to model the robot arm system. The disturbance observer scheme is used to reduce the disturbance effects on the system. The PI torque controller is implemented using the characteristics of disturbance observer. The performance of the proposed controller is demonstrated through experiments with a one degree of freedom robot arm.
Wearable glove type haptic interfaces are often required to be light weight, which constrains the... more Wearable glove type haptic interfaces are often required to be light weight, which constrains the actuator to exert low torques. This causes a virtual object to feel compliant, reducing the range of presented surface properties. To overcome the limitation, we propose to compensate the hardness of a virtual object with cutaneous feedback. A cutaneous haptic interface is designed to present the hardness to a user's fingertip along with a force-feedback interface and the corresponding rendering strategy is proposed. Two experiments were conducted to evaluate the proposed approach for one-finger touch and two-finger grip for stiffness values under 0.3 N/mm. Experimental results indicate that the addition of cutaneous feedback led the virtual surface to feel significantly harder than the nominal stiffness felt by force-feedback alone. In addition, the perceived hardness was significantly affected by the rate of hardness rendered with cutaneous interface when the nominal stiffness was increased.
In this paper, a torque control method in task-space for redundant manipulators with friction is ... more In this paper, a torque control method in task-space for redundant manipulators with friction is proposed. A previous simple control approach based on virtual spring damper hypothesis is used to generate human-like motions. The method is efficient in the system which is difficult to identify the exact dynamics, however, the controller has steady state errors. To eliminate the steady state error, the gravity and friction, which is the part of the system dynamics, are compensated. Although the gravity and friction are compensated, the error of the modelling remains in the system. Hence, to reduce the nonlinearity, unknown effects, and modelling errors of the system, a torque controller based on Time-Delay Control (TDC) that eliminates the friction and unknown effects, is used. The performance of the control method, in Cartesian space control, is experimented with the torque sensor based 3-joints robot manipulator. Keywords–Task-Space; Virtual spring damper hypothesis; TimeDelay Contro...
2017 IEEE International Conference on Advanced Intelligent Mechatronics (AIM), 2017
In this paper, we propose an energy-efficient robotic leg design using a redundantly actuated par... more In this paper, we propose an energy-efficient robotic leg design using a redundantly actuated parallel mechanism (RAPM). By adding an actuator parallel to the serially-actuated leg, we show that the legged machine can reduce mechanical energy loss. We begin with reviewing kinematic model of parallel mechanisms and then present an optimal torque distribution algorithm among redundant actuators which minimizes antagonistic power, a measure for mechanical energy loss due to power conflict in actuators. As an example study, given end-effector (foot) force and motion profile generated by the spring-loaded-inverted-pendulum (SLIP) running, we demonstrate how much the antagonistic power can be reduced by applying the proposed leg design and optimization algorithm in simulation. Also, it is presented that the choice of actuated joints in parallel mechanism affects the performance (energy efficiency). Finally, we demonstrate that the proposed design is also effective in walking, which validates the hypothesis that the proposed RAPM leg design can be effective in a range of locomotion tasks.
We investigate the effect of adding cutaneous cues to kinesthetic feedback on the perception of a... more We investigate the effect of adding cutaneous cues to kinesthetic feedback on the perception of a virtual object's hardness. A cutaneous haptic interface is designed to deliver hardness information to a user's fingertip along with a force-feedback interface, and the corresponding rendering strategy is implemented. Two sets of experiments are conducted to evaluate the proposed approach for hardness perception using one-finger touch and two-finger grasp. Experimental results indicate that the addition of cutaneous feedback can make the virtual surface feel significantly harder than the nominal stiffness delivered by force-feedback alone. In addition, the perceived hardness is significantly affected by the rate of hardness rendered with a cutaneous interface for the nominal stiffness K ¼ 0:3 and 0.5 N/mm. For two-finger grip, the effect of a virtual object's thickness has a significant effect on the perceived hardness measured in stiffness. When the perceived hardness is converted to Young's modulus, the effect of thickness is insignificant.
2012 IEEE/RSJ International Conference on Intelligent Robots and Systems, 2012
This paper discusses a balance control method with kinodynamic constraints for leg-wheel hybrid s... more This paper discusses a balance control method with kinodynamic constraints for leg-wheel hybrid structures in an effort to improve the mobility of locomotion over hard, flat surfaces. Preliminarily, we defined a prioritized Jacobian and a prioritized inverse of Jacobian to formulate the dynamically decoupled model in the task space for the constrained multi-contact multi-rigid-body system with a floating base. Our strategy has two tracks to accommodate the uncertainty and the complexity of the system dynamics. 1) The time-delay estimation and control are combined with the nonlinear programming. 2) Whole kinodynamic constraints are derived as functions of the control input. The proposed balance control algorithm allows the system to traverse desired trajectories satisfying the kinodynamic constraints and improves the mobility of locomotion. The effectiveness of the algorithm is tested with the dynamic simulations.
Proceedings. 1998 IEEE International Conference on Robotics and Automation (Cat. No.98CH36146)
An approach to resolve the kinematic redundancy and to control the motion/force of redundant mani... more An approach to resolve the kinematic redundancy and to control the motion/force of redundant manipulators is presented. By defining a proper metric in joint space, minimal parametrization of motion and force controlled subspaces as well as the null motion component is realized. With this formulation, control of both motion~orce and internal motion of redundant manipulator can be achieved via a new hybrid impedance control method with inertial decoupling of each space. Some numerical examples are given to demonstrate the pet-jormance of the proposed cotztrol method. space, the dynamics of remaining degrees of freedom does not appear in this formulation[3]. Thus, in order to take a full advantage of the redundancy, dealing with the hidden internal dynamics is essential for achieving higher performance of both position and compliant motions because the hidden dynamics affects the task space motions of redundant manipulators. The motivation of this paper is to provide a method to express the behavior of redundant manipulators with task and null space dynamics with decoupled manner using appropriate decomposition method.
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Papers by Yonghwan Oh