KRD  Cinemàtica i Disseny de Robots
http://hdl.handle.net/2117/99672
20200127T00:32:50Z

A Convolutional Neural Network for the automatic diagnosis of collagen VIrelated muscular dystrophies
http://hdl.handle.net/2117/175193
A Convolutional Neural Network for the automatic diagnosis of collagen VIrelated muscular dystrophies
Rodríguez Bazaga, Adrián; Roldán Molina, Mónica; Badosa Gallego, Maria del Carmen; Jiménez Mallebrera, Cecilia; Porta Pleite, Josep Maria
The development of machine learning systems for the diagnosis of rare diseases is challenging, mainly due to the lack of data to study them. This paper surmounts this obstacle and presents the first ComputerAided Diagnosis (CAD) system for lowprevalence collagen VIrelated congenital muscular dystrophies. The proposed CAD system works on images of fibroblast cultures obtained with a confocal microscope and relies on a Convolutional Neural Network (CNN) to classify patches of such images in two classes: samples from healthy persons and samples from persons affected by a collagen VIrelated muscular distrophy. This finegrained classification is then used to generate an overall diagnosis on the query image using a majority voting scheme. The proposed system is advantageous, as it overcomes the lack of training data, points to the possibly problematic areas in the query images, and provides a global quantitative evaluation of the condition of the patients, which is fundamental to monitor the effectiveness of potential therapies. The system achieves a high classification performance, with 95% of accuracy and 92% of precision on randomly selected independent test images, outperforming alternative approaches by a significant margin.
20200117T13:28:07Z
Rodríguez Bazaga, Adrián
Roldán Molina, Mónica
Badosa Gallego, Maria del Carmen
Jiménez Mallebrera, Cecilia
Porta Pleite, Josep Maria
The development of machine learning systems for the diagnosis of rare diseases is challenging, mainly due to the lack of data to study them. This paper surmounts this obstacle and presents the first ComputerAided Diagnosis (CAD) system for lowprevalence collagen VIrelated congenital muscular dystrophies. The proposed CAD system works on images of fibroblast cultures obtained with a confocal microscope and relies on a Convolutional Neural Network (CNN) to classify patches of such images in two classes: samples from healthy persons and samples from persons affected by a collagen VIrelated muscular distrophy. This finegrained classification is then used to generate an overall diagnosis on the query image using a majority voting scheme. The proposed system is advantageous, as it overcomes the lack of training data, points to the possibly problematic areas in the query images, and provides a global quantitative evaluation of the condition of the patients, which is fundamental to monitor the effectiveness of potential therapies. The system achieves a high classification performance, with 95% of accuracy and 92% of precision on randomly selected independent test images, outperforming alternative approaches by a significant margin.

Forward kinematics of the general triplearm robot using a distancebased formulation
http://hdl.handle.net/2117/132085
Forward kinematics of the general triplearm robot using a distancebased formulation
Rojas, Nicolas; Thomas, Federico
Distancebased formulations have successfully been used to obtain closure polynomialsfor planar mechanisms without relying, in most cases, on variable eliminations. The methods resulting from previous attempts to generalize these techniques to spatial mechanisms exhibit somelimitations such as the impossibility of incorporating orientation constraints. For the first time, thispaper presents a complete satisfactory generalization. As an example, it is applied to obtain a closure polynomial for the the general triplearm parallel robot (that is, the 3RPS 3DOF robot). Thispolynomial, not linked to any particular reference frame, is obtained without variable eliminationsor tangenthalfangle substitutions
The final publication is available at link.springer.com
20190426T07:21:05Z
Rojas, Nicolas
Thomas, Federico
Distancebased formulations have successfully been used to obtain closure polynomialsfor planar mechanisms without relying, in most cases, on variable eliminations. The methods resulting from previous attempts to generalize these techniques to spatial mechanisms exhibit somelimitations such as the impossibility of incorporating orientation constraints. For the first time, thispaper presents a complete satisfactory generalization. As an example, it is applied to obtain a closure polynomial for the the general triplearm parallel robot (that is, the 3RPS 3DOF robot). Thispolynomial, not linked to any particular reference frame, is obtained without variable eliminationsor tangenthalfangle substitutions

A new insight into the coupler curves of the RCCC fourbar linkage
http://hdl.handle.net/2117/131805
A new insight into the coupler curves of the RCCC fourbar linkage
Thomas, Federico; Pérez Gracia, Alba
Based on the condition for four points to lie on the unit sphere, derived using Distance Geometry, a new mathematical formulation for the coupler curves of the RCCC linkage is presented. The relevance of this formulation is not only its simplicity, but the elegant way in which we can obtain the derivative of any variable with respect to any other, and the simple way in which intervals of monotonicity can be detected. All these results are compactly expressed in terms of Gramians and, as a consequence, they have a direct geometric meaning contrarily to what happens with previous approaches based on kinematic loop equations.
The final publication is available at link.springer.com
20190423T08:50:44Z
Thomas, Federico
Pérez Gracia, Alba
Based on the condition for four points to lie on the unit sphere, derived using Distance Geometry, a new mathematical formulation for the coupler curves of the RCCC linkage is presented. The relevance of this formulation is not only its simplicity, but the elegant way in which we can obtain the derivative of any variable with respect to any other, and the simple way in which intervals of monotonicity can be detected. All these results are compactly expressed in terms of Gramians and, as a consequence, they have a direct geometric meaning contrarily to what happens with previous approaches based on kinematic loop equations.

A singularityrobust LQR controller for parallel robots
http://hdl.handle.net/2117/130001
A singularityrobust LQR controller for parallel robots
Bordalba Llaberia, Ricard; Porta Pleite, Josep Maria; Ros Giralt, Lluís
Parallel robots exhibit the socalled forward singularities, which complicate substantially the planning and control of their motions. Often, such complications are circumvented by restricting the motions to singularityfree regions of the workspace. However, this comes at the expense of reducing the motion range of the robot substantially. It is for this reason that, recently, efforts are underway to control singularity crossing trajectories. This paper proposes a reliable controller to stabilize such kind of trajectories. The controller is based on the classical theory of linear quadratic regulators, which we adapt appropriately to the case of parallel robots. As opposed to traditional computedtorque methods, the obtained controller does not rely on expensive inverse dynamics computations. Instead, it uses an optimal control law that is easy to evaluate, and does not generate instabilities at forward singularities. The performance of the controller is exemplified on a fivebar parallel robot accomplishing two tasks that require the traversal of singularities.
© 20xx IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works
20190301T13:35:12Z
Bordalba Llaberia, Ricard
Porta Pleite, Josep Maria
Ros Giralt, Lluís
Parallel robots exhibit the socalled forward singularities, which complicate substantially the planning and control of their motions. Often, such complications are circumvented by restricting the motions to singularityfree regions of the workspace. However, this comes at the expense of reducing the motion range of the robot substantially. It is for this reason that, recently, efforts are underway to control singularity crossing trajectories. This paper proposes a reliable controller to stabilize such kind of trajectories. The controller is based on the classical theory of linear quadratic regulators, which we adapt appropriately to the case of parallel robots. As opposed to traditional computedtorque methods, the obtained controller does not rely on expensive inverse dynamics computations. Instead, it uses an optimal control law that is easy to evaluate, and does not generate instabilities at forward singularities. The performance of the controller is exemplified on a fivebar parallel robot accomplishing two tasks that require the traversal of singularities.

The forward kinematics of doublyplanar GoughStewart platforms and the position analysis of strips of tetrahedra
http://hdl.handle.net/2117/129977
The forward kinematics of doublyplanar GoughStewart platforms and the position analysis of strips of tetrahedra
Porta Pleite, Josep Maria; Thomas, Federico
A strip of tetrahedra is a tetrahedrontetrahedron truss where any tetrahedron has two neighbors except those in the extremes which have only one. The problem of finding all the possible lengths for an edge in the strip compatible with a given distance imposed between the strip endpoints has been revealed of relevance due to the large number of possible applications. In this paper, this is applied to solve the forward kinematics of 66 GoughStewart platforms with planar base and moving platform, a problem which is known to have up to 40 solutions (20 if we do not consider mirror configurations with respect to the base as different solutions).
The final publication is available at link.springer.com
20190301T09:33:45Z
Porta Pleite, Josep Maria
Thomas, Federico
A strip of tetrahedra is a tetrahedrontetrahedron truss where any tetrahedron has two neighbors except those in the extremes which have only one. The problem of finding all the possible lengths for an edge in the strip compatible with a given distance imposed between the strip endpoints has been revealed of relevance due to the large number of possible applications. In this paper, this is applied to solve the forward kinematics of 66 GoughStewart platforms with planar base and moving platform, a problem which is known to have up to 40 solutions (20 if we do not consider mirror configurations with respect to the base as different solutions).

Grasping unknown objects in clutter by superquadric representation
http://hdl.handle.net/2117/129398
Grasping unknown objects in clutter by superquadric representation
Makhal, Abhijit; Thomas, Federico; Pérez Gracia, Alba
In this paper, a quick and efficient method is presented for grasping unknown objects in clutter. The grasping method relies on realtime superquadric (SQ) representation of partial view objects and incomplete object modelling, well suited for unknown symmetric objects in cluttered scenarios which is followed by optimized antipodal grasping. The incomplete object models are processed through a mirroring algorithm that assumes symmetry to first create an approximate complete model and then fit for SQ representation. The grasping algorithm is designed for maximum force balance and stability, taking advantage of the quick retrieval of dimension and surface curvature information from the SQ parameters. The pose of the SQs with respect to the direction of gravity is calculated and used together with the parameters of the SQs and specification of the gripper, to select the best direction of approach and contact points. The SQ fitting method has been tested on custom datasets containing objects in isolation as well as in clutter. The grasping algorithm is evaluated on a PR2 robot and real time results are presented. Initial results indicate that though the method is based on simplistic shape information, it outperforms other learning based grasping algorithms that also work in clutter in terms of timeefficiency and accuracy.
© 20xx IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.
20190219T14:06:07Z
Makhal, Abhijit
Thomas, Federico
Pérez Gracia, Alba
In this paper, a quick and efficient method is presented for grasping unknown objects in clutter. The grasping method relies on realtime superquadric (SQ) representation of partial view objects and incomplete object modelling, well suited for unknown symmetric objects in cluttered scenarios which is followed by optimized antipodal grasping. The incomplete object models are processed through a mirroring algorithm that assumes symmetry to first create an approximate complete model and then fit for SQ representation. The grasping algorithm is designed for maximum force balance and stability, taking advantage of the quick retrieval of dimension and surface curvature information from the SQ parameters. The pose of the SQs with respect to the direction of gravity is calculated and used together with the parameters of the SQs and specification of the gripper, to select the best direction of approach and contact points. The SQ fitting method has been tested on custom datasets containing objects in isolation as well as in clutter. The grasping algorithm is evaluated on a PR2 robot and real time results are presented. Initial results indicate that though the method is based on simplistic shape information, it outperforms other learning based grasping algorithms that also work in clutter in terms of timeefficiency and accuracy.

Yet another approach to the GoughStewart platform forward kinematics
http://hdl.handle.net/2117/129382
Yet another approach to the GoughStewart platform forward kinematics
Porta Pleite, Josep Maria; Thomas, Federico
The forward kinematics of the GoughStewart platform, and their simplified versions in which some leg endpoints coalesce, has been typically solved using variable elimination methods. In this paper, we cast doubts on whether this is the easiest way to solve the problem. We will see how the indirect approach in which the length of some extra virtual legs is first computed leads to important simplifications. In particular, we provide a procedure to solve 30 out of 34 possible topologies for a GoughStewart platform without variable elimination.
© 20xx IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.
20190219T12:34:15Z
Porta Pleite, Josep Maria
Thomas, Federico
The forward kinematics of the GoughStewart platform, and their simplified versions in which some leg endpoints coalesce, has been typically solved using variable elimination methods. In this paper, we cast doubts on whether this is the easiest way to solve the problem. We will see how the indirect approach in which the length of some extra virtual legs is first computed leads to important simplifications. In particular, we provide a procedure to solve 30 out of 34 possible topologies for a GoughStewart platform without variable elimination.

Randomized planning of dynamic motions avoiding forward singularities
http://hdl.handle.net/2117/125332
Randomized planning of dynamic motions avoiding forward singularities
Bordalba Llaberia, Ricard; Ros Giralt, Lluís; Porta Pleite, Josep Maria
Forward singularities, also known as direct, or actuator singularities, cause many problems to the planning and control of robot motions. They yield position errors and rigidity losses of the robot, and generate unbounded actions in typical control laws. To circumvent these issues, this paper proposes a randomized kinodynamic planner for computing trajectories avoiding such singularities. Given initial and final states for the robot, the planner attempts to connect them by means of a dynamicallyfeasible, singularityfree trajectory that also respects the force limits of the actuators. The performance of the strategy is illustrated in simulation by means of a parallel robot performing a highly dynamic task.
The final publication is available at link.springer.com
20181203T14:08:36Z
Bordalba Llaberia, Ricard
Ros Giralt, Lluís
Porta Pleite, Josep Maria
Forward singularities, also known as direct, or actuator singularities, cause many problems to the planning and control of robot motions. They yield position errors and rigidity losses of the robot, and generate unbounded actions in typical control laws. To circumvent these issues, this paper proposes a randomized kinodynamic planner for computing trajectories avoiding such singularities. Given initial and final states for the robot, the planner attempts to connect them by means of a dynamicallyfeasible, singularityfree trajectory that also respects the force limits of the actuators. The performance of the strategy is illustrated in simulation by means of a parallel robot performing a highly dynamic task.

Randomized kinodynamic planning for constrained systems
http://hdl.handle.net/2117/125331
Randomized kinodynamic planning for constrained systems
Bordalba Llaberia, Ricard; Ros Giralt, Lluís; Porta Pleite, Josep Maria
Kinodynamic RRT planners are considered to be general tools for effectively finding feasible trajectories for highdimensional dynamical systems. However, they struggle when holonomic constraints are present in the system, such as those arising in parallel manipulators, in robots that cooperate to fulfill a given task, or in situations involving contacts with the environment. In such cases, the state space becomes an implicitlydefined manifold, which makes the diffusion heuristic inefficient and leads to inaccurate dynamical simulations. To address these issues, this paper presents an extension of the kinodynamic RRT planner that constructs an atlas of the statespace manifold incrementally, and uses this atlas both to generate random states and to dynamically steer the system towards such states. To the best of our knowledge, this is the first randomized kinodynamic planner that explicitly takes holonomic constraints into account. We validate the approach in significantlycomplex systems.
© 20xx IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.
20181203T14:05:03Z
Bordalba Llaberia, Ricard
Ros Giralt, Lluís
Porta Pleite, Josep Maria
Kinodynamic RRT planners are considered to be general tools for effectively finding feasible trajectories for highdimensional dynamical systems. However, they struggle when holonomic constraints are present in the system, such as those arising in parallel manipulators, in robots that cooperate to fulfill a given task, or in situations involving contacts with the environment. In such cases, the state space becomes an implicitlydefined manifold, which makes the diffusion heuristic inefficient and leads to inaccurate dynamical simulations. To address these issues, this paper presents an extension of the kinodynamic RRT planner that constructs an atlas of the statespace manifold incrementally, and uses this atlas both to generate random states and to dynamically steer the system towards such states. To the best of our knowledge, this is the first randomized kinodynamic planner that explicitly takes holonomic constraints into account. We validate the approach in significantlycomplex systems.

Accurate computation of quaternions from rotation matrices
http://hdl.handle.net/2117/124384
Accurate computation of quaternions from rotation matrices
Sarabandi, Soheil; Thomas, Federico
The main nonsingular alternative to 3×3 proper orthogonal matrices, for representing rotations in R3, is quaternions. Thus, it is important to have reliable methods to pass from one representation to the other. While passing from a quaternion to the corresponding rotation matrix is given by EulerRodrigues formula, the other way round can be performed in many different ways. Although all of them are algebraically equivalent, their numerical behavior can be quite different. In 1978, Shepperd proposed a method for computing the quaternion corresponding to a rotation matrix which is considered the most reliable method to date. Shepperd’s method, thanks to a voting scheme between four possible solutions, always works far from formulation singularities. In this paper, we propose a new method which outperforms Shepperd’s method without increasing the computational cost.
The final publication is available at link.springer.com
20181115T13:50:44Z
Sarabandi, Soheil
Thomas, Federico
The main nonsingular alternative to 3×3 proper orthogonal matrices, for representing rotations in R3, is quaternions. Thus, it is important to have reliable methods to pass from one representation to the other. While passing from a quaternion to the corresponding rotation matrix is given by EulerRodrigues formula, the other way round can be performed in many different ways. Although all of them are algebraically equivalent, their numerical behavior can be quite different. In 1978, Shepperd proposed a method for computing the quaternion corresponding to a rotation matrix which is considered the most reliable method to date. Shepperd’s method, thanks to a voting scheme between four possible solutions, always works far from formulation singularities. In this paper, we propose a new method which outperforms Shepperd’s method without increasing the computational cost.