IEEE-ASME Transactions on Mechatronics, Apr 1, 2015
The field of exoskeletons and wearable devices for walking assistance and rehabilitation has adva... more The field of exoskeletons and wearable devices for walking assistance and rehabilitation has advanced considerably over the past few years. Currently, commercial devices contain joints with stiff actuators that cannot adapt to unpredictable environments. These actuators consume more energy and may not be appropriate for human-machine interactions. Thus, adjustable compliant actuators are being cautiously incorporated into new exoskeletons and active orthoses. Some simulation-based studies have evaluated the benefits of incorporating compliant joints into such devices. Another reason that compliant actuators are desirable is that spasticity and spasmodic movements are common among patients with motor deficiencies; compliant actuators could efficiently absorb these perturbations and improve joint control. In this paper, we provide an overview of the requirements that must be fulfilled by these actuators while evaluating the behavior of leg joints in the locomotion cycle. A brief review of existing compliant actuators is conducted, and our proposed variable stiffness actuator prototype is presented and evaluated. The actuator prototype is implemented in an exoskeleton knee joint operated by a state machine that exploits the dynamics of the leg, resulting in a reduction in actuation energy demand and better adaptability to disturbances.
Quiet standing was, for many years, studied as a single inverted pendulum, based on the principle... more Quiet standing was, for many years, studied as a single inverted pendulum, based on the principle that the ankle joint is the most important joint of this movement. However, studies show that hip and knee joints perform, as well, an important role in quiet standing. The aim of this paper is to present a three-segment-inverted pendulum model, using Lagrange’s dynamics, to study human quiet stance in the sagittal plane and, therefore, allow, in future work, its appliance to a lower-limb exoskeleton. As a preliminary study, lower limb kinematic and dynamic data were recorded from 15 healthy subjects while balancing using an optical motion capture system. The center-of-pressure (CoP) was calculated with reference to the ankle joint and the projection of the center-of-mass (CoM) in the sagittal plane was estimated, using the positions given by the mathematical model. The contributions of each joint to the estimated projection of CoM and CoP were also investigated. Finally, a correlation between joints kinematics and kinetics was also made. The first results show a good relationship between estimated CoM and CoP and between joints, supporting the theory that, together, the three joints control the body CoM and, thus, allow postural control.
International Journal of Advanced Robotic Systems, 2012
By analysing the dynamic principles of the human gait, an economic gait-control analysis is perfo... more By analysing the dynamic principles of the human gait, an economic gait-control analysis is performed, and passive elements are included to increase the energy efficiency in the motion control of active orthoses. Traditional orthoses use position patterns from the clinical gait analyses (CGAs) of healthy people, which are then de-normalized and adjusted to each user. These orthoses maintain a very rigid gait, and their energy cost is very high, reducing the autonomy of the user. First, to take advantage of the inherent dynamics of the legs, a state machine pattern with different gains in each state is applied to reduce the actuator energy consumption. Next, different passive elements, such as springs and brakes in the joints, are analysed to further reduce energy consumption. After an off-line parameter optimization and a heuristic improvement with genetic algorithms, a reduction in energy consumption of 16.8% is obtained by applying a state machine control pattern, and a reduction of 18.9% is obtained by using passive elements. Finally, by combining both strategies, a more natural gait is obtained, and energy consumption is reduced by 24.6% compared with a pure CGA pattern.
Humanoid robots are a good option for rescue missions in disaster scenarios when the safety of th... more Humanoid robots are a good option for rescue missions in disaster scenarios when the safety of the rescue team can be compromised. Thus, allowing saving lives without the need of risking the safety of the rescue team. In this study we propose a reactive walking algorithm that provides statically stable locomotion when negotiating difficult terrains (combinations of inclined planes and flat ground) in the case that computer vision is not an option due to occluded terrains. Furthermore, we have tested the algorithm in simulation using the DRCSim software package obtaining good results.
Adjustable compliant actuators are being designed and implemented in robotic devices because of t... more Adjustable compliant actuators are being designed and implemented in robotic devices because of their ability to minimize large forces due to impacts, to safely interact with the user, and to store and release energy in passive elastic elements. Conceived as a new force-controlled compliant actuator, an adjustable rigidity with embedded sensor and locking mechanism actuator (ARES-XL) is presented in this paper. This compliant system is intended to be implemented in a gait exoskeleton for children with neuro muscular diseases (NMDs) to exploit the intrinsic dynamics during locomotion. This paper describes the mechanics and initial evaluation of the ARES-XL, a novel variable impedance actuator (VIA) that allows the implementation of an add-on locking mechanism to this system, and in combination with its zero stiffness capability and large deflection range, provides this novel joint with improved properties when compared to previous prototypes developed by the authors and other state-of-the-art (SoA) devices. The evaluation of the system proves how this design exceeds the main capabilities of a previous prototype as well as providing versatile actuation that could lead to its implementation in multiple joints.
Industrial Robot-an International Journal, Oct 20, 2014
Purpose – The purpose of this study is to present a variable stiffness actuator, one of whose mai... more Purpose – The purpose of this study is to present a variable stiffness actuator, one of whose main features is that the compliant elements simultaneously allow measuring of the torque exerted by the joint. Conceived as a force-controlled actuator, this actuator with Adjustable Rigidity and Embedded Sensor (ARES) is intended to be implemented in the knee of the ATLAS exoskeleton for children to allow the exploitation of the intrinsic dynamic during the locomotion cycle. Design/methodology/approach – A set of simulations were performed to evaluate the behavior of the actuator mechanism and a prototype of the variable impedance actuator was incorporated into the exoskeleton’s knee and evaluations of the torque measurements capabilities along with the rigidity adjustments were made. Findings – Mass and inertia of the actuator are minimized by the compact design and the utilization of the different component for more than one utility. By a proper match of the compliance of the joint and the performed task, good torque measurements can be achieved and no bandwidth saturation is expected. Originality/value – In the actuator, the compliant elements simultaneously allow measuring of the torque exerted by the join. By a proper match of the compliance of the joint and the performed task, good torque measurements can be achieved and no bandwidth saturation is expected.
The movements of sit-to-stand and stand-to-sit are frequently executed on daily life. To develop ... more The movements of sit-to-stand and stand-to-sit are frequently executed on daily life. To develop robotic assistance devices for people with mobility problems, it is important to study how a healthy human performs these tasks. The goal of this study is to present a mathematical model based on acquired kinematic and kinetic data that represents a healthy human body performing these movements. The results revealed that the movements of sit-to-stand and stand-to-sit have symmetric joint angles, torques and ground reaction force. The joint angles and the torques are very similar on each leg. The knee and the hip show more variation of the angle and achieve higher values of torque in comparison to the ankle. Although, ankle has higher torque during standing position. The ground reaction force show that is necessary create a force additional to the standard weight force to achieve a more stable position that is sitting or standing. The acquired data describe as expected the sit-to-stand and stand-to-sit movements and can be used to validate the presented model.
International Journal of Advanced Robotic Systems, 2014
Bioinspired quadruped robots are among the best robot designs for field missions over the complex... more Bioinspired quadruped robots are among the best robot designs for field missions over the complex terrain encountered in extraterrestrial landscapes and disaster scenarios caused by natural and human-made catastrophes, such as those caused by nuclear power plant accidents and radiological emergencies. For such applications, the performance characteristics of the robots should include high mobility, adaptability to the terrain, the ability to handle a large payload and good endurance. Nature can provide inspiration for quadruped designs that are well suited for traversing complex terrain. Horse legs are an example of a structure that has evolved to exhibit good performance characteristics. In this paper, a leg design exhibiting the key features of horse legs is briefly described. This leg is an underactuated mechanism because it has two actively driven degrees of freedom (DOFs) and one passively driven DOF. In this work, two control laws intended to be use in the stan ce phase are described: a control law that considers passive mechanism dynamics and a second law that neglects these dynamics. The performance of the two control laws is experimentally evaluated and compared. The results indicate that the first control law better achieves the control goal; however, the use of the second is not completely unjustified.
Gait cycle has been the target of many studies in the last decades in order to identify the norma... more Gait cycle has been the target of many studies in the last decades in order to identify the normal walking patterns of humans. The usefulness of these studies is of utmost importance to construct mathematical models that are capable to achieve stability during walking. Based on this fact, it seems justified the present effort to construct a model to simulate a complete stride in healthy humans. Thus, in this work, a five-link inverted pendulum model in the sagittal plane with 5 degrees of freedom (DOFs) based on Euler-Lagrange equations is being constructed with the main objective to concern stability during gait cycle. To do that, this study was divided into two parts: the first one is represented by this article and it is regarding to the model construction and data collection; the second part is relative to a future work and it concerns to the model validation and an analysis of the stiffness variation with the power and speed during gait cycle. Regarding to the results of the present study, good correlations were obtained between the data collected and the data presented in literature, which demonstrates a good data acquisition.
The field of exoskeletons and assistive orthotic devices is a multidisciplinary issue in the half... more The field of exoskeletons and assistive orthotic devices is a multidisciplinary issue in the halfway between medicine and robotics. Within the robotic discipline, bipedal robot gaits are generated as a function of parameters such as stride length, foot clearance and body height. These features allow to adapt the gait to different surface characteristics. However, biped robot gaits do not look as natural as human gaits. On the other side, gaits imposed in actual active orthoses are fixed following the Clinical Gait Analysis (CGA) pattern. These CGA patterns ensure a comfortable, natural and safe gait, but do not exhibit flexibility to change some gait features to adapt to the characteristics of the terrain, such as slopes or small obstacles. This paper presents the development of an adaptable gait pattern for a full lower limb active orthosis. Based on an impedance control approach, gait parameters such as step height, body height or step length are modified online, providing a safe and smooth gait pattern. Two shoe insole pressure measurement systems provide ground reaction force and center of pressure to adapt these gait parameters online. To avoid abrupt movements that would affect user comfort, references on position and speed must be smooth, that is, derivable when the characteristics of the gait change. To ensure that position and speed references follow a derivable path, with a very low computational cost, the change from one reference path to another has been modulated with Gaussian windows. Thus, a more adaptable orthosis with soft motion is achieved.
This paper presents the design of a new robotic orthotic solution aimed at improving the rehabili... more This paper presents the design of a new robotic orthotic solution aimed at improving the rehabilitation of a number of neurological disorders (Multiple Sclerosis, Post-Polio and Stroke). These neurological disorders are the most expensive for the European Health Systems, and the personalization of the therapy will contribute to a 47% cost reduction. Most orthotic devices have been evaluated as an aid to inhospital training and rehabilitation in patients with motor disorders of various origins. The advancement of technology opens the possibility of new active orthoses able to improve function in the usual environment of the patient, providing added benefits to state-of-the-art devices in life quality. The active knee orthosis aims to serve as a basis to justify the prescription and adaptation of robotic orthoses in patients with impaired gait resulting from neurological processes.
IEEE-ASME Transactions on Mechatronics, Apr 1, 2015
The field of exoskeletons and wearable devices for walking assistance and rehabilitation has adva... more The field of exoskeletons and wearable devices for walking assistance and rehabilitation has advanced considerably over the past few years. Currently, commercial devices contain joints with stiff actuators that cannot adapt to unpredictable environments. These actuators consume more energy and may not be appropriate for human-machine interactions. Thus, adjustable compliant actuators are being cautiously incorporated into new exoskeletons and active orthoses. Some simulation-based studies have evaluated the benefits of incorporating compliant joints into such devices. Another reason that compliant actuators are desirable is that spasticity and spasmodic movements are common among patients with motor deficiencies; compliant actuators could efficiently absorb these perturbations and improve joint control. In this paper, we provide an overview of the requirements that must be fulfilled by these actuators while evaluating the behavior of leg joints in the locomotion cycle. A brief review of existing compliant actuators is conducted, and our proposed variable stiffness actuator prototype is presented and evaluated. The actuator prototype is implemented in an exoskeleton knee joint operated by a state machine that exploits the dynamics of the leg, resulting in a reduction in actuation energy demand and better adaptability to disturbances.
Quiet standing was, for many years, studied as a single inverted pendulum, based on the principle... more Quiet standing was, for many years, studied as a single inverted pendulum, based on the principle that the ankle joint is the most important joint of this movement. However, studies show that hip and knee joints perform, as well, an important role in quiet standing. The aim of this paper is to present a three-segment-inverted pendulum model, using Lagrange’s dynamics, to study human quiet stance in the sagittal plane and, therefore, allow, in future work, its appliance to a lower-limb exoskeleton. As a preliminary study, lower limb kinematic and dynamic data were recorded from 15 healthy subjects while balancing using an optical motion capture system. The center-of-pressure (CoP) was calculated with reference to the ankle joint and the projection of the center-of-mass (CoM) in the sagittal plane was estimated, using the positions given by the mathematical model. The contributions of each joint to the estimated projection of CoM and CoP were also investigated. Finally, a correlation between joints kinematics and kinetics was also made. The first results show a good relationship between estimated CoM and CoP and between joints, supporting the theory that, together, the three joints control the body CoM and, thus, allow postural control.
International Journal of Advanced Robotic Systems, 2012
By analysing the dynamic principles of the human gait, an economic gait-control analysis is perfo... more By analysing the dynamic principles of the human gait, an economic gait-control analysis is performed, and passive elements are included to increase the energy efficiency in the motion control of active orthoses. Traditional orthoses use position patterns from the clinical gait analyses (CGAs) of healthy people, which are then de-normalized and adjusted to each user. These orthoses maintain a very rigid gait, and their energy cost is very high, reducing the autonomy of the user. First, to take advantage of the inherent dynamics of the legs, a state machine pattern with different gains in each state is applied to reduce the actuator energy consumption. Next, different passive elements, such as springs and brakes in the joints, are analysed to further reduce energy consumption. After an off-line parameter optimization and a heuristic improvement with genetic algorithms, a reduction in energy consumption of 16.8% is obtained by applying a state machine control pattern, and a reduction of 18.9% is obtained by using passive elements. Finally, by combining both strategies, a more natural gait is obtained, and energy consumption is reduced by 24.6% compared with a pure CGA pattern.
Humanoid robots are a good option for rescue missions in disaster scenarios when the safety of th... more Humanoid robots are a good option for rescue missions in disaster scenarios when the safety of the rescue team can be compromised. Thus, allowing saving lives without the need of risking the safety of the rescue team. In this study we propose a reactive walking algorithm that provides statically stable locomotion when negotiating difficult terrains (combinations of inclined planes and flat ground) in the case that computer vision is not an option due to occluded terrains. Furthermore, we have tested the algorithm in simulation using the DRCSim software package obtaining good results.
Adjustable compliant actuators are being designed and implemented in robotic devices because of t... more Adjustable compliant actuators are being designed and implemented in robotic devices because of their ability to minimize large forces due to impacts, to safely interact with the user, and to store and release energy in passive elastic elements. Conceived as a new force-controlled compliant actuator, an adjustable rigidity with embedded sensor and locking mechanism actuator (ARES-XL) is presented in this paper. This compliant system is intended to be implemented in a gait exoskeleton for children with neuro muscular diseases (NMDs) to exploit the intrinsic dynamics during locomotion. This paper describes the mechanics and initial evaluation of the ARES-XL, a novel variable impedance actuator (VIA) that allows the implementation of an add-on locking mechanism to this system, and in combination with its zero stiffness capability and large deflection range, provides this novel joint with improved properties when compared to previous prototypes developed by the authors and other state-of-the-art (SoA) devices. The evaluation of the system proves how this design exceeds the main capabilities of a previous prototype as well as providing versatile actuation that could lead to its implementation in multiple joints.
Industrial Robot-an International Journal, Oct 20, 2014
Purpose – The purpose of this study is to present a variable stiffness actuator, one of whose mai... more Purpose – The purpose of this study is to present a variable stiffness actuator, one of whose main features is that the compliant elements simultaneously allow measuring of the torque exerted by the joint. Conceived as a force-controlled actuator, this actuator with Adjustable Rigidity and Embedded Sensor (ARES) is intended to be implemented in the knee of the ATLAS exoskeleton for children to allow the exploitation of the intrinsic dynamic during the locomotion cycle. Design/methodology/approach – A set of simulations were performed to evaluate the behavior of the actuator mechanism and a prototype of the variable impedance actuator was incorporated into the exoskeleton’s knee and evaluations of the torque measurements capabilities along with the rigidity adjustments were made. Findings – Mass and inertia of the actuator are minimized by the compact design and the utilization of the different component for more than one utility. By a proper match of the compliance of the joint and the performed task, good torque measurements can be achieved and no bandwidth saturation is expected. Originality/value – In the actuator, the compliant elements simultaneously allow measuring of the torque exerted by the join. By a proper match of the compliance of the joint and the performed task, good torque measurements can be achieved and no bandwidth saturation is expected.
The movements of sit-to-stand and stand-to-sit are frequently executed on daily life. To develop ... more The movements of sit-to-stand and stand-to-sit are frequently executed on daily life. To develop robotic assistance devices for people with mobility problems, it is important to study how a healthy human performs these tasks. The goal of this study is to present a mathematical model based on acquired kinematic and kinetic data that represents a healthy human body performing these movements. The results revealed that the movements of sit-to-stand and stand-to-sit have symmetric joint angles, torques and ground reaction force. The joint angles and the torques are very similar on each leg. The knee and the hip show more variation of the angle and achieve higher values of torque in comparison to the ankle. Although, ankle has higher torque during standing position. The ground reaction force show that is necessary create a force additional to the standard weight force to achieve a more stable position that is sitting or standing. The acquired data describe as expected the sit-to-stand and stand-to-sit movements and can be used to validate the presented model.
International Journal of Advanced Robotic Systems, 2014
Bioinspired quadruped robots are among the best robot designs for field missions over the complex... more Bioinspired quadruped robots are among the best robot designs for field missions over the complex terrain encountered in extraterrestrial landscapes and disaster scenarios caused by natural and human-made catastrophes, such as those caused by nuclear power plant accidents and radiological emergencies. For such applications, the performance characteristics of the robots should include high mobility, adaptability to the terrain, the ability to handle a large payload and good endurance. Nature can provide inspiration for quadruped designs that are well suited for traversing complex terrain. Horse legs are an example of a structure that has evolved to exhibit good performance characteristics. In this paper, a leg design exhibiting the key features of horse legs is briefly described. This leg is an underactuated mechanism because it has two actively driven degrees of freedom (DOFs) and one passively driven DOF. In this work, two control laws intended to be use in the stan ce phase are described: a control law that considers passive mechanism dynamics and a second law that neglects these dynamics. The performance of the two control laws is experimentally evaluated and compared. The results indicate that the first control law better achieves the control goal; however, the use of the second is not completely unjustified.
Gait cycle has been the target of many studies in the last decades in order to identify the norma... more Gait cycle has been the target of many studies in the last decades in order to identify the normal walking patterns of humans. The usefulness of these studies is of utmost importance to construct mathematical models that are capable to achieve stability during walking. Based on this fact, it seems justified the present effort to construct a model to simulate a complete stride in healthy humans. Thus, in this work, a five-link inverted pendulum model in the sagittal plane with 5 degrees of freedom (DOFs) based on Euler-Lagrange equations is being constructed with the main objective to concern stability during gait cycle. To do that, this study was divided into two parts: the first one is represented by this article and it is regarding to the model construction and data collection; the second part is relative to a future work and it concerns to the model validation and an analysis of the stiffness variation with the power and speed during gait cycle. Regarding to the results of the present study, good correlations were obtained between the data collected and the data presented in literature, which demonstrates a good data acquisition.
The field of exoskeletons and assistive orthotic devices is a multidisciplinary issue in the half... more The field of exoskeletons and assistive orthotic devices is a multidisciplinary issue in the halfway between medicine and robotics. Within the robotic discipline, bipedal robot gaits are generated as a function of parameters such as stride length, foot clearance and body height. These features allow to adapt the gait to different surface characteristics. However, biped robot gaits do not look as natural as human gaits. On the other side, gaits imposed in actual active orthoses are fixed following the Clinical Gait Analysis (CGA) pattern. These CGA patterns ensure a comfortable, natural and safe gait, but do not exhibit flexibility to change some gait features to adapt to the characteristics of the terrain, such as slopes or small obstacles. This paper presents the development of an adaptable gait pattern for a full lower limb active orthosis. Based on an impedance control approach, gait parameters such as step height, body height or step length are modified online, providing a safe and smooth gait pattern. Two shoe insole pressure measurement systems provide ground reaction force and center of pressure to adapt these gait parameters online. To avoid abrupt movements that would affect user comfort, references on position and speed must be smooth, that is, derivable when the characteristics of the gait change. To ensure that position and speed references follow a derivable path, with a very low computational cost, the change from one reference path to another has been modulated with Gaussian windows. Thus, a more adaptable orthosis with soft motion is achieved.
This paper presents the design of a new robotic orthotic solution aimed at improving the rehabili... more This paper presents the design of a new robotic orthotic solution aimed at improving the rehabilitation of a number of neurological disorders (Multiple Sclerosis, Post-Polio and Stroke). These neurological disorders are the most expensive for the European Health Systems, and the personalization of the therapy will contribute to a 47% cost reduction. Most orthotic devices have been evaluated as an aid to inhospital training and rehabilitation in patients with motor disorders of various origins. The advancement of technology opens the possibility of new active orthoses able to improve function in the usual environment of the patient, providing added benefits to state-of-the-art devices in life quality. The active knee orthosis aims to serve as a basis to justify the prescription and adaptation of robotic orthoses in patients with impaired gait resulting from neurological processes.
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Papers by Daniel Sanz-Merodio