Nikolaos Tsagarakis - Academia.edu (original) (raw)

Papers by Nikolaos Tsagarakis

2017 IEEE-RAS 17th International Conference on Humanoid Robotics (Humanoids)

This is a repository copy of Vision-based foothold contact reasoning using curved surface patches.

First Joint Eurohaptics Conference and Symposium on Haptic Interfaces for Virtual Environment and Teleoperator Systems, 2000

In this paper we present our work towards the realization of a portablewearable tactile display i... more In this paper we present our work towards the realization of a portablewearable tactile display in the form of a 4×4 pin array actuated by miniature remotely (forearm) located motors. The display introduced has a capacity for force generation at up to 3N per tactor and pin displacements of 2.5mm. The bandwidth at this 2.5mm displacement is greater than 15Hz

2016 IEEE-RAS 16th International Conference on Humanoid Robots (Humanoids), 2016

In this work we present the concept of a pilot interface to control a humanoid robot on an abstra... more In this work we present the concept of a pilot interface to control a humanoid robot on an abstract level in unknown environments. The environment is perceived with a stereo camera system and then simplified into a set of environmental primitives. Based on these primitives the interface proposes affordances to the pilot. Affordances are represented as certainty functions over the space of end-effector poses. The pilot operates the robot by selecting among proposed affordances and related action primitives, i.e. Object-Action Complexes (OACs). Before initiating execution, the pilot can review and revise the parameterization of the scheduled action primitive in a 3D reconstruction of the environment. The pilot interface proposed in this work has been implemented and evaluated on the humanoid robot WALK-MAN. With this work we also demonstrate the transferability of the perceptual concept, as our previous experiments have been performed using the humanoid robot ARMAR-III.

2016 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), 2016

This paper describes a new task-oriented grasping method to reorient a rigid object to its nomina... more This paper describes a new task-oriented grasping method to reorient a rigid object to its nominal pose, which is defined as the configuration that it needs to be grasped from, in order to successfully execute a particular manipulation task. Our method combines two key insights: (1) a visual 6 Degree-of-Freedom (DoF) pose estimation technique based on 2D-3D point correspondences is used to estimate the object pose in real-time and (2) the rigid transformation from the current to the nominal pose is computed online and the object is reoriented over a sequence of steps. The outcome of this work is a novel method that can be effectively used in the preparatory phase of a manipulation task, to permit a robot to start from arbitrary object placements and configure the manipulated objects to the nominal pose, as required for the execution of a subsequent task. We experimentally demonstrate the effectiveness of our approach on a full-size humanoid robot (WALK-MAN) using different objects with various pose settings under real-time constraints.

2016 IEEE International Conference on Robotics and Automation (ICRA), 2016

The First IEEE/RAS-EMBS International Conference on Biomedical Robotics and Biomechatronics, 2006. BioRob 2006., 2000

Stroke forms one of the leading causes of death amongst adults in industrialized countries, and a... more Stroke forms one of the leading causes of death amongst adults in industrialized countries, and although survival rates are comparatively high in up to 1/3 of patients there is functional impairments (particularly in the upper limbs) that can persist even after rehabilitation training. Tasked based rehabilitation therapy (shaping) is a new approach that seems to offer good success compared to traditional methods, however, the technique requires very intensive and prolonged treatment. Robot mediated physiotherapy is the recent answer to the shortage of staff and the cost associated with this. In this paper a robotic approach to task based therapy is shown. The work focuses on how a robotic exoskeleton operating in a 3D volume can be used in conjunction with a Virtual Environment rehabilitation suite for training patients in relearning daily motor tasks. Salford Rehabilitation Exoskeleton (SRE) is used as an assistive device which helps individuals retrain in performing motor tasks by assisting them to complete therapy regimes. EMG recordings are used to show the capacity of the system to mediate the level of assistance provided from full assistance to zero aid.

Rehabilitation Robotics, 2007

2014 Ieee Ras International Conference on Humanoid Robots, Nov 1, 2014

This work presents an enriched human-machine interface for performing effective tele-manipulation... more This work presents an enriched human-machine interface for performing effective tele-manipulation using a humanoid robot. To provide the slave with the ability to dexterously interact with the remote environment, we implement an autonomous impedance controller that regulates the slave's joints stiffness and damping according to the manipulation loading conditions. In the proposed strategy, freespace operations are performed with compliant limbs to ensure safe interactions during unforeseen collisions on the wholearm together with a soft behaviour at the initial phase of contact. During the manipulation task, the designed controller accounts for the arm configuration and the direction/amplitude of the external force sensed at the end-effector to stiffen the humanoid arm joints, permitting to handle the task loads. Experiments performed on the compliant humanoid robot COMAN demonstrate the effectiveness of this human-inspired impedance controller during a teleoperated pick-and-place task. The interaction forces during manipulation can destabilize the floating base humanoid robot. To address this concern we also investigate the operators ability to rely on a cutaneous feedback of the slave's balance state to adjust their teleoperation strategy when required so as to complete the task while maintaining the slave's balance. A comparative study shows that the proposed vibrotactile feedback allows for a proper recognition of the slave's drop of stability during interaction tasks and that the tactile guidance leads to enhanced teleoperation performances characterized by a significantly lower number of falls.

2006 Ieee Rsj International Conference on Intelligent Robots and Systems, 2006

The development of successful tactile displays can be assisted by the capacity to assess their pe... more The development of successful tactile displays can be assisted by the capacity to assess their performance in integrated Virtual Reality applications. The design of single tactor or desktop tactile displays has been useful for scientific analysis of the mechanisms of touch. Nevertheless, it does not provide useful information about the quality of immersion in VR environments integrated with tactile feedback where user mobility and comfort are paramount. The present work introduces a new wireless portable tactile display for the finger. This new device demonstrates excellent levels of force output combined with good bandwidth in a configuration of a wearable 4x4 array of vertically moving tactors. The focus of this design is small size, comfort, mobility and ultimately integration into a complete Virtual Reality system for tactile surface texture exploration with 6DOF in the finger's work envelope.

2008 Ieee Rsj International Conference on Intelligent Robots and Systems, 2008

ABSTRACT

IEEE Transactions on Human-Machine Systems, 2013

Computer-assisted therapy is one of the most promising new techniques for those suffering from ph... more Computer-assisted therapy is one of the most promising new techniques for those suffering from physical and neurological dysfunction. Yet, impairments to physical movement arising from a central nervous system dysfunction or from muscle spasms generated through other neurological damage or dysfunction can often make it difficult or impossible for individuals to interact with computer-generated environments using a conventional mouse interface. This paper investigates the use of a 2-D haptic device as an assistive robotic aid to minimize the effects of the pathological absence of motor control in the upper limb in impaired users when using a mouse. The assistive functionality is evaluated in 2-D tracking tasks using a human subject with failure of the gross coordination of the upper limb muscle movements-"Muscle Ataxia." The results demonstrate that with this system the capability of the impaired subject to track predefined trajectories within a computer generated 2D is significantly improved. The average of the means of the error distance for the trajectories performed under the assistive mode was significantly lower (more than 40%) than that of the trajectories without assistance. In addition, when using the assistive device, the impaired subject was able to complete the tracking tasks in less time.

Humanoids 2008 - 8th IEEE-RAS International Conference on Humanoid Robots, 2008

This paper describes the design of a new hand for the robot iCub. Developed as part of the Europe... more This paper describes the design of a new hand for the robot iCub. Developed as part of the European project RobotCub the iCub is a robot baby based on an 18 month to 2.5 year old child. The current iCub hands are under-actuated which means they are not as dexterous as a true child's hand. The hand designed in this work has a total of 22 degrees of freedom of which 18 are independently drivable. In order to minimise weight and cost the hand has been produced from Acrylonitrile Butadiene Styrene (ABS) using 3D printing techniques. This removes the need for extensive machining which would add significantly to the overall cost of the hand. A prototype finger has been produced and tested and a full mechanical design is presented.

2011 IEEE International Conference on Robotics and Biomimetics, 2011

This work introduces the concept of Tele-Impedance as a method for controlling/teleoperating a ro... more This work introduces the concept of Tele-Impedance as a method for controlling/teleoperating a robotic arm in contact with the environment. Opposite to bilateral force-reflecting teleoperation control approach, which uses a position/velocity command combined with force feedback from the robot side, Tele-Impedance enriches the command sent to the slave robot by combining the position reference with a stiffness (or full impedance) reference. The desired stiffness profile is directly estimated from the arm of the human operating the remote robotic arm. We preliminarily investigate the effectiveness of this method while teleoperating a slave robotic arm to execute simple tasks. The KUKA light weight robotic arm is used as the slave manipulator. The endpoint (wrist) position of the human arm is monitored by an optical tracking system while the stiffness of the human arm is estimated from the electromyography (EMGs) signal measurements of four flexor-extensor muscle pairs, in realtime. The performance of Tele-Impedance control method is assessed by comparing the results obtained while executing a peg-in-hole task, with the slave arm under i) constant low stiffness, ii) constant high stiffness or iii) under Tele-Impedance control. The experimental results demonstrate the effectiveness of the Tele-Impedance control method and highlight its potential use to safely execute tasks with uncertain environment constraints which may result in large deviations from the commanded position trajectories.

2009 IEEE International Conference on Robotics and Automation, 2009

ABSTRACT This paper presents the design, fabrication, and control of a rotational manipulator usi... more ABSTRACT This paper presents the design, fabrication, and control of a rotational manipulator using shape memory alloy (SMA) wire actuated flexures. Monolithic flexure mechanisms have no friction/backlash and are capable of miniaturization. They are well-suited for tasks that required high precision and packed space. To explore flexure shapes beyond traditional notch hinges and leaf springs, we present a general two-step design method to find the optimal flexure shapes for maximal rotation without yield. The advantages gained from shape variations are shown through a simulation example. We further use a SMA wire to drive the flexure. SMA exhibits large stroke with high power density and requires low driving voltage. By using versatile SMA wire, the rotational range of the manipulator can be significantly increased while the overall size can be kept compact. A feedback PID control algorithm with fuzzy-tuned gains is implemented to precisely control the response of the manipulator. We illustrate its performance by tracking and step response experiments. With the merits shown, we expect this type of manipulator can be utilized in meso to micro scale applications.

2011 IEEE World Haptics Conference, 2011

This paper investigates the tactile orientation discrimination of virtual, small-scale, patterned... more This paper investigates the tactile orientation discrimination of virtual, small-scale, patterned surfaces through a tactile display. The tactile display is an array of 4x4 vertically moving pins which can simulate the shape of small scale features. Its small size and low mass allow users to explore virtual surfaces freely and intuitively. The evaluation method consisted of measuring the orientation discrimination threshold for virtual surfaces with sinusoidal profiles. The threshold was compared with the threshold obtained using a non-actuated tactile display of equal spatial resolution and with the threshold obtained using the bare finger to explore real surfaces. This comparison was done to evaluate the quality of the rendered virtual surfaces, the performance of the device as a control system and the efficiency of the tactile rendering algorithm. This study also measured the speed and normal force during the tactile exploration that allowed investigation of the exploration strategies used when touching through normal indentation displays and through the bare finger. Furthermore they are the necessary interaction parameters for assessing the bandwidth and force output of the device.

2012 IEEE International Conference on Robotics and Automation, 2012

ABSTRACT This work presents the novel concept of Tele-Impedance as a method for controlling/teleo... more ABSTRACT This work presents the novel concept of Tele-Impedance as a method for controlling/teleoperating a robotic arm while performing tasks which require significant dynamics variation. As an alternative method to bilateral force-reflecting teleoperation control approach, which uses a position/velocity command combined with force feedback from the robot side, Tele-Impedance enriches the command sent to the slave robot by combining the position reference with a stiffness (or full impedance) reference estimated from the arm of the human operator. We propose a new method to estimate the stiffness of the human arm based on the agonist-antagonist muscular co activations. The concept of the Tele-Impedance is demonstrated using the KUKA light weight robotic arm as the slave manipulator in a ball reception experiment. The performance of Tele-Impedance control method is assessed by comparing the results obtained while receiving the ball, with the slave arm under i) constant low stiffness, ii) constant high stiffness or iii) under Tele-Impedance control. Performance indexes are defined and used for the comparative study of the ball reception performances under the different endpoint elastic profiles. The experimental results demonstrate the effectiveness of the task-related Tele-Impedance control method and highlight its potential use to execute tasks which require significant dynamics variation.

2009 IEEE/RSJ International Conference on Intelligent Robots and Systems, 2009

Recent investigations show that compliant systems can be more safe and energy-efficient than conv... more Recent investigations show that compliant systems can be more safe and energy-efficient than conventional stiff actuated systems. As a result, researchers are increasingly implementing compliance within actuation systems using a variety of mechanisms. In general, these actuators can be grouped in 2 main categories. The first category includes all the actuation systems with a compliant element connected in series (SEA), while the second group contains all those systems that employ two actuators placed antagonistically. In both designs the ability to regulate the stiffness is essential in order to meet safety and/or performance demands. Energy consumption is a very important aspect to be considered, especially in autonomous robots. This paper presents a theoretical study on the energy consumption of variable stiffness actuators, comparing the amount of energy required in order to perform a certain task.

2009 IEEE International Conference on Robotics and Automation, 2009

This paper presents the development of a new compact soft actuation unit intended to be used in m... more This paper presents the development of a new compact soft actuation unit intended to be used in multi degree of freedom and small scale robotic systems such as the child humanoid robot "iCub" [1]. Compared to the other existing series elastic linear or rotary implementations the proposed design shows high integration density and wider passive deflection. The miniaturization of the newly developed high performance unit was achieved with a use of a new rotary spring module based on a novel arrangement of linear springs. The model and the control scheme of the actuator are analysed. The proposed control scheme is a velocity based controller that generates command signals based on the desired simulated stiffness using the spring deflection state. The overall system is evaluated with experimental trials performed using a prototype unit. Preliminary results are presented to show that the unit and the proposed control scheme are capable of replicating virtual impedances within a wide range and with good fidelity.

2009 IEEE/RSJ International Conference on Intelligent Robots and Systems, 2009

This paper presents an energy-based control strategy to be used in robotic systems working closel... more This paper presents an energy-based control strategy to be used in robotic systems working closely or cooperating with humans. The presented method bounds the dangerous behavior of the robot during the first instants of the impact by limiting the energy stored into the system to a maximum imposed value.Two critical physical human robot interaction (pHRI) cases are studied, these are the collision either against a free or a clamped head. Safe energy values that can be used as reference were retrieved by analysing experimental data of energy absorption to failure of cranium bones and cervical spinal cords.The energy regulation control is implemented in a series elastic actuator prototype joint. The model and the control scheme of the system are analysed. The proposed control scheme is a position-based controller that adjusts the position trajectory reference in function of the maximum energy value imposed by the user. Preliminary results are presented to show that the actuator unit and this control scheme are capable of limiting the energy to a maximum imposed value.

2010 IEEE International Conference on Robotics and Automation, 2010

This paper introduces the development of a semi-active friction based variable physical damping a... more This paper introduces the development of a semi-active friction based variable physical damping actuator (VPDA) unit. The realization of this unit aims to facilitate the control of compliant robotic joints by providing physical variable damping on demand assisting on the regulation of the oscillations induced by the introduction of compliance. The mechatronics details and the dynamic model of the damper are introduced. The proposed variable damper mechanism is evaluated on a simple 1-DOF compliant joint linked to the ground through a torsion spring. This flexible connection emulates a compliant joint, generating oscillations when the link is perturbed. Preliminary results are presented to show that the unit and the proposed control scheme are capable of replicating simulated relative damping values with good fidelity.

2017 IEEE-RAS 17th International Conference on Humanoid Robotics (Humanoids)

This is a repository copy of Vision-based foothold contact reasoning using curved surface patches.

First Joint Eurohaptics Conference and Symposium on Haptic Interfaces for Virtual Environment and Teleoperator Systems, 2000

In this paper we present our work towards the realization of a portablewearable tactile display i... more In this paper we present our work towards the realization of a portablewearable tactile display in the form of a 4×4 pin array actuated by miniature remotely (forearm) located motors. The display introduced has a capacity for force generation at up to 3N per tactor and pin displacements of 2.5mm. The bandwidth at this 2.5mm displacement is greater than 15Hz

2016 IEEE-RAS 16th International Conference on Humanoid Robots (Humanoids), 2016

In this work we present the concept of a pilot interface to control a humanoid robot on an abstra... more In this work we present the concept of a pilot interface to control a humanoid robot on an abstract level in unknown environments. The environment is perceived with a stereo camera system and then simplified into a set of environmental primitives. Based on these primitives the interface proposes affordances to the pilot. Affordances are represented as certainty functions over the space of end-effector poses. The pilot operates the robot by selecting among proposed affordances and related action primitives, i.e. Object-Action Complexes (OACs). Before initiating execution, the pilot can review and revise the parameterization of the scheduled action primitive in a 3D reconstruction of the environment. The pilot interface proposed in this work has been implemented and evaluated on the humanoid robot WALK-MAN. With this work we also demonstrate the transferability of the perceptual concept, as our previous experiments have been performed using the humanoid robot ARMAR-III.

2016 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), 2016

This paper describes a new task-oriented grasping method to reorient a rigid object to its nomina... more This paper describes a new task-oriented grasping method to reorient a rigid object to its nominal pose, which is defined as the configuration that it needs to be grasped from, in order to successfully execute a particular manipulation task. Our method combines two key insights: (1) a visual 6 Degree-of-Freedom (DoF) pose estimation technique based on 2D-3D point correspondences is used to estimate the object pose in real-time and (2) the rigid transformation from the current to the nominal pose is computed online and the object is reoriented over a sequence of steps. The outcome of this work is a novel method that can be effectively used in the preparatory phase of a manipulation task, to permit a robot to start from arbitrary object placements and configure the manipulated objects to the nominal pose, as required for the execution of a subsequent task. We experimentally demonstrate the effectiveness of our approach on a full-size humanoid robot (WALK-MAN) using different objects with various pose settings under real-time constraints.

2016 IEEE International Conference on Robotics and Automation (ICRA), 2016

The First IEEE/RAS-EMBS International Conference on Biomedical Robotics and Biomechatronics, 2006. BioRob 2006., 2000

Stroke forms one of the leading causes of death amongst adults in industrialized countries, and a... more Stroke forms one of the leading causes of death amongst adults in industrialized countries, and although survival rates are comparatively high in up to 1/3 of patients there is functional impairments (particularly in the upper limbs) that can persist even after rehabilitation training. Tasked based rehabilitation therapy (shaping) is a new approach that seems to offer good success compared to traditional methods, however, the technique requires very intensive and prolonged treatment. Robot mediated physiotherapy is the recent answer to the shortage of staff and the cost associated with this. In this paper a robotic approach to task based therapy is shown. The work focuses on how a robotic exoskeleton operating in a 3D volume can be used in conjunction with a Virtual Environment rehabilitation suite for training patients in relearning daily motor tasks. Salford Rehabilitation Exoskeleton (SRE) is used as an assistive device which helps individuals retrain in performing motor tasks by assisting them to complete therapy regimes. EMG recordings are used to show the capacity of the system to mediate the level of assistance provided from full assistance to zero aid.

Rehabilitation Robotics, 2007

2014 Ieee Ras International Conference on Humanoid Robots, Nov 1, 2014

This work presents an enriched human-machine interface for performing effective tele-manipulation... more This work presents an enriched human-machine interface for performing effective tele-manipulation using a humanoid robot. To provide the slave with the ability to dexterously interact with the remote environment, we implement an autonomous impedance controller that regulates the slave's joints stiffness and damping according to the manipulation loading conditions. In the proposed strategy, freespace operations are performed with compliant limbs to ensure safe interactions during unforeseen collisions on the wholearm together with a soft behaviour at the initial phase of contact. During the manipulation task, the designed controller accounts for the arm configuration and the direction/amplitude of the external force sensed at the end-effector to stiffen the humanoid arm joints, permitting to handle the task loads. Experiments performed on the compliant humanoid robot COMAN demonstrate the effectiveness of this human-inspired impedance controller during a teleoperated pick-and-place task. The interaction forces during manipulation can destabilize the floating base humanoid robot. To address this concern we also investigate the operators ability to rely on a cutaneous feedback of the slave's balance state to adjust their teleoperation strategy when required so as to complete the task while maintaining the slave's balance. A comparative study shows that the proposed vibrotactile feedback allows for a proper recognition of the slave's drop of stability during interaction tasks and that the tactile guidance leads to enhanced teleoperation performances characterized by a significantly lower number of falls.

2006 Ieee Rsj International Conference on Intelligent Robots and Systems, 2006

The development of successful tactile displays can be assisted by the capacity to assess their pe... more The development of successful tactile displays can be assisted by the capacity to assess their performance in integrated Virtual Reality applications. The design of single tactor or desktop tactile displays has been useful for scientific analysis of the mechanisms of touch. Nevertheless, it does not provide useful information about the quality of immersion in VR environments integrated with tactile feedback where user mobility and comfort are paramount. The present work introduces a new wireless portable tactile display for the finger. This new device demonstrates excellent levels of force output combined with good bandwidth in a configuration of a wearable 4x4 array of vertically moving tactors. The focus of this design is small size, comfort, mobility and ultimately integration into a complete Virtual Reality system for tactile surface texture exploration with 6DOF in the finger's work envelope.

2008 Ieee Rsj International Conference on Intelligent Robots and Systems, 2008

ABSTRACT

IEEE Transactions on Human-Machine Systems, 2013

Computer-assisted therapy is one of the most promising new techniques for those suffering from ph... more Computer-assisted therapy is one of the most promising new techniques for those suffering from physical and neurological dysfunction. Yet, impairments to physical movement arising from a central nervous system dysfunction or from muscle spasms generated through other neurological damage or dysfunction can often make it difficult or impossible for individuals to interact with computer-generated environments using a conventional mouse interface. This paper investigates the use of a 2-D haptic device as an assistive robotic aid to minimize the effects of the pathological absence of motor control in the upper limb in impaired users when using a mouse. The assistive functionality is evaluated in 2-D tracking tasks using a human subject with failure of the gross coordination of the upper limb muscle movements-"Muscle Ataxia." The results demonstrate that with this system the capability of the impaired subject to track predefined trajectories within a computer generated 2D is significantly improved. The average of the means of the error distance for the trajectories performed under the assistive mode was significantly lower (more than 40%) than that of the trajectories without assistance. In addition, when using the assistive device, the impaired subject was able to complete the tracking tasks in less time.

Humanoids 2008 - 8th IEEE-RAS International Conference on Humanoid Robots, 2008

This paper describes the design of a new hand for the robot iCub. Developed as part of the Europe... more This paper describes the design of a new hand for the robot iCub. Developed as part of the European project RobotCub the iCub is a robot baby based on an 18 month to 2.5 year old child. The current iCub hands are under-actuated which means they are not as dexterous as a true child's hand. The hand designed in this work has a total of 22 degrees of freedom of which 18 are independently drivable. In order to minimise weight and cost the hand has been produced from Acrylonitrile Butadiene Styrene (ABS) using 3D printing techniques. This removes the need for extensive machining which would add significantly to the overall cost of the hand. A prototype finger has been produced and tested and a full mechanical design is presented.

2011 IEEE International Conference on Robotics and Biomimetics, 2011

This work introduces the concept of Tele-Impedance as a method for controlling/teleoperating a ro... more This work introduces the concept of Tele-Impedance as a method for controlling/teleoperating a robotic arm in contact with the environment. Opposite to bilateral force-reflecting teleoperation control approach, which uses a position/velocity command combined with force feedback from the robot side, Tele-Impedance enriches the command sent to the slave robot by combining the position reference with a stiffness (or full impedance) reference. The desired stiffness profile is directly estimated from the arm of the human operating the remote robotic arm. We preliminarily investigate the effectiveness of this method while teleoperating a slave robotic arm to execute simple tasks. The KUKA light weight robotic arm is used as the slave manipulator. The endpoint (wrist) position of the human arm is monitored by an optical tracking system while the stiffness of the human arm is estimated from the electromyography (EMGs) signal measurements of four flexor-extensor muscle pairs, in realtime. The performance of Tele-Impedance control method is assessed by comparing the results obtained while executing a peg-in-hole task, with the slave arm under i) constant low stiffness, ii) constant high stiffness or iii) under Tele-Impedance control. The experimental results demonstrate the effectiveness of the Tele-Impedance control method and highlight its potential use to safely execute tasks with uncertain environment constraints which may result in large deviations from the commanded position trajectories.

2009 IEEE International Conference on Robotics and Automation, 2009

ABSTRACT This paper presents the design, fabrication, and control of a rotational manipulator usi... more ABSTRACT This paper presents the design, fabrication, and control of a rotational manipulator using shape memory alloy (SMA) wire actuated flexures. Monolithic flexure mechanisms have no friction/backlash and are capable of miniaturization. They are well-suited for tasks that required high precision and packed space. To explore flexure shapes beyond traditional notch hinges and leaf springs, we present a general two-step design method to find the optimal flexure shapes for maximal rotation without yield. The advantages gained from shape variations are shown through a simulation example. We further use a SMA wire to drive the flexure. SMA exhibits large stroke with high power density and requires low driving voltage. By using versatile SMA wire, the rotational range of the manipulator can be significantly increased while the overall size can be kept compact. A feedback PID control algorithm with fuzzy-tuned gains is implemented to precisely control the response of the manipulator. We illustrate its performance by tracking and step response experiments. With the merits shown, we expect this type of manipulator can be utilized in meso to micro scale applications.

2011 IEEE World Haptics Conference, 2011

This paper investigates the tactile orientation discrimination of virtual, small-scale, patterned... more This paper investigates the tactile orientation discrimination of virtual, small-scale, patterned surfaces through a tactile display. The tactile display is an array of 4x4 vertically moving pins which can simulate the shape of small scale features. Its small size and low mass allow users to explore virtual surfaces freely and intuitively. The evaluation method consisted of measuring the orientation discrimination threshold for virtual surfaces with sinusoidal profiles. The threshold was compared with the threshold obtained using a non-actuated tactile display of equal spatial resolution and with the threshold obtained using the bare finger to explore real surfaces. This comparison was done to evaluate the quality of the rendered virtual surfaces, the performance of the device as a control system and the efficiency of the tactile rendering algorithm. This study also measured the speed and normal force during the tactile exploration that allowed investigation of the exploration strategies used when touching through normal indentation displays and through the bare finger. Furthermore they are the necessary interaction parameters for assessing the bandwidth and force output of the device.

2012 IEEE International Conference on Robotics and Automation, 2012

ABSTRACT This work presents the novel concept of Tele-Impedance as a method for controlling/teleo... more ABSTRACT This work presents the novel concept of Tele-Impedance as a method for controlling/teleoperating a robotic arm while performing tasks which require significant dynamics variation. As an alternative method to bilateral force-reflecting teleoperation control approach, which uses a position/velocity command combined with force feedback from the robot side, Tele-Impedance enriches the command sent to the slave robot by combining the position reference with a stiffness (or full impedance) reference estimated from the arm of the human operator. We propose a new method to estimate the stiffness of the human arm based on the agonist-antagonist muscular co activations. The concept of the Tele-Impedance is demonstrated using the KUKA light weight robotic arm as the slave manipulator in a ball reception experiment. The performance of Tele-Impedance control method is assessed by comparing the results obtained while receiving the ball, with the slave arm under i) constant low stiffness, ii) constant high stiffness or iii) under Tele-Impedance control. Performance indexes are defined and used for the comparative study of the ball reception performances under the different endpoint elastic profiles. The experimental results demonstrate the effectiveness of the task-related Tele-Impedance control method and highlight its potential use to execute tasks which require significant dynamics variation.

2009 IEEE/RSJ International Conference on Intelligent Robots and Systems, 2009

Recent investigations show that compliant systems can be more safe and energy-efficient than conv... more Recent investigations show that compliant systems can be more safe and energy-efficient than conventional stiff actuated systems. As a result, researchers are increasingly implementing compliance within actuation systems using a variety of mechanisms. In general, these actuators can be grouped in 2 main categories. The first category includes all the actuation systems with a compliant element connected in series (SEA), while the second group contains all those systems that employ two actuators placed antagonistically. In both designs the ability to regulate the stiffness is essential in order to meet safety and/or performance demands. Energy consumption is a very important aspect to be considered, especially in autonomous robots. This paper presents a theoretical study on the energy consumption of variable stiffness actuators, comparing the amount of energy required in order to perform a certain task.

2009 IEEE International Conference on Robotics and Automation, 2009

This paper presents the development of a new compact soft actuation unit intended to be used in m... more This paper presents the development of a new compact soft actuation unit intended to be used in multi degree of freedom and small scale robotic systems such as the child humanoid robot "iCub" [1]. Compared to the other existing series elastic linear or rotary implementations the proposed design shows high integration density and wider passive deflection. The miniaturization of the newly developed high performance unit was achieved with a use of a new rotary spring module based on a novel arrangement of linear springs. The model and the control scheme of the actuator are analysed. The proposed control scheme is a velocity based controller that generates command signals based on the desired simulated stiffness using the spring deflection state. The overall system is evaluated with experimental trials performed using a prototype unit. Preliminary results are presented to show that the unit and the proposed control scheme are capable of replicating virtual impedances within a wide range and with good fidelity.

2009 IEEE/RSJ International Conference on Intelligent Robots and Systems, 2009

This paper presents an energy-based control strategy to be used in robotic systems working closel... more This paper presents an energy-based control strategy to be used in robotic systems working closely or cooperating with humans. The presented method bounds the dangerous behavior of the robot during the first instants of the impact by limiting the energy stored into the system to a maximum imposed value.Two critical physical human robot interaction (pHRI) cases are studied, these are the collision either against a free or a clamped head. Safe energy values that can be used as reference were retrieved by analysing experimental data of energy absorption to failure of cranium bones and cervical spinal cords.The energy regulation control is implemented in a series elastic actuator prototype joint. The model and the control scheme of the system are analysed. The proposed control scheme is a position-based controller that adjusts the position trajectory reference in function of the maximum energy value imposed by the user. Preliminary results are presented to show that the actuator unit and this control scheme are capable of limiting the energy to a maximum imposed value.

2010 IEEE International Conference on Robotics and Automation, 2010

This paper introduces the development of a semi-active friction based variable physical damping a... more This paper introduces the development of a semi-active friction based variable physical damping actuator (VPDA) unit. The realization of this unit aims to facilitate the control of compliant robotic joints by providing physical variable damping on demand assisting on the regulation of the oscillations induced by the introduction of compliance. The mechatronics details and the dynamic model of the damper are introduced. The proposed variable damper mechanism is evaluated on a simple 1-DOF compliant joint linked to the ground through a torsion spring. This flexible connection emulates a compliant joint, generating oscillations when the link is perturbed. Preliminary results are presented to show that the unit and the proposed control scheme are capable of replicating simulated relative damping values with good fidelity.