28 research outputs found
Sensor Observability Index: Evaluating Sensor Alignment for Task-Space Observability in Robotic Manipulators
In this paper, we propose a preliminary definition and analysis of the novel
concept of sensor observability index. The goal is to analyse and evaluate the
performance of distributed directional or axial-based sensors to observe
specific axes in task space as a function of joint configuration in serial
robot manipulators. For example, joint torque sensors are often used in serial
robot manipulators and assumed to be perfectly capable of estimating end
effector forces, but certain joint configurations may cause one or more
task-space axes to be unobservable as a result of how the joint torque sensors
are aligned. The proposed sensor observability provides a method to analyse the
quality of the current robot configuration to observe the task space. Parallels
are drawn between sensor observability and the traditional kinematic Jacobian
for the particular case of joint torque sensors in serial robot manipulators.
Although similar information can be retrieved from kinematic analysis of the
Jacobian transpose in serial manipulators, sensor observability is shown to be
more generalizable in terms of analysing non-joint-mounted sensors and other
sensor types. In addition, null-space analysis of the Jacobian transpose is
susceptible to false observability singularities. Simulations and experiments
using the robot Baxter demonstrate the importance of maintaining proper sensor
observability in physical interactions.Comment: 7 pages, 5 figures, conference pape
Softness Effects on Manipulability and Grasp Stability
This paper presents a novel analysis for the effects of softness at the fingertip on the manipulability and stability of grasping. The stability for grasping can be regarded that how much magnitude of external wrench we can balance. We formulate manipulability and the set of generable object wrenches for grasping system, taking deformation of the fingertips into consideration, and show that the increase of the softness decreases the manipulability while it increases generable object wrench. The validity of our analysis is shown by numerical examples. © 2011 IEEE
Positioning two redundant arms for cooperative manipulation of objects
Bimanual manipulation of objects is receiving a lot of attention nowadays, but there is few literature addressing the design of the arms configuration. In this paper, we propose a way to analyze the relative positioning of two redundant arms, both equipped with spherical wrists, in order to obtain the best common workspace for grasping purposes. Considering the geometry of a robot with a spherical wrist, the Cartesian workspace can be discretized, with an easy representation of the feasible end-effector orientations at each point using bounding cones. After having characterized the workspace for one robot arm, we can evaluate how good each of the discretized poses relate with an identical arm in another position with a quality function that considers orientations. In the end, we obtain a quality value for each relative position of two arms, and we perform an optimization using genetic algorithms to obtain the best workspace for a cooperative task.Peer ReviewedPostprint (author’s final draft
Coordination control of robot manipulators using flat outputs
Published ArticleThis paper focuses on the synchronizing control of multiple interconnected flexible robotic manipulators
using differential flatness theory. The flatness theory has the advantage of simplifying trajectory tracking
tasks of complex mechanical systems. Using this theory, we propose a new synchronization scheme
whereby a formation of flatness based systems can be stabilized using their respective flat outputs.
Using the flat outputs, we eliminate the need for cross coupling laws and communication protocols
associated with such formations. The problem of robot coordination is reduced to synchronizing the
flat outputs between the respective robot manipulators. Furthermore, the selection of the flat output
used for the synchronizing control is not restricted as any system variable can be used. The problem of
unmeasured states used in the control is also solved by reconstructing the missing states using flatness
based interpolation. The proposed control law is less computationally intensive when compared to earlier
reported work as integration of the differential equations is not required. Simulations using a formation
of single link flexible joint robots are used to validate the proposed synchronizing control
Coordination control of robot manipulators using flat outputs
Published ArticleThis paper focuses on the synchronizing control of multiple interconnected flexible robotic manipulators
using differential flatness theory. The flatness theory has the advantage of simplifying trajectory tracking
tasks of complex mechanical systems. Using this theory, we propose a new synchronization scheme
whereby a formation of flatness based systems can be stabilized using their respective flat outputs.
Using the flat outputs, we eliminate the need for cross coupling laws and communication protocols
associated with such formations. The problem of robot coordination is reduced to synchronizing the
flat outputs between the respective robot manipulators. Furthermore, the selection of the flat output
used for the synchronizing control is not restricted as any system variable can be used. The problem of
unmeasured states used in the control is also solved by reconstructing the missing states using flatness
based interpolation. The proposed control law is less computationally intensive when compared to earlier
reported work as integration of the differential equations is not required. Simulations using a formation
of single link flexible joint robots are used to validate the proposed synchronizing control
Optimal Contact Force Distribution for Compliant Humanoid Robots in Whole-Body Loco-Manipulation Tasks
The stiffness ellipsoid, i.e. the locus of task-space forces obtained corresponding to a deformation of unit norm in different directions, has been extensively used as a powerful representation of robot interaction capabilities. The size and shape of the stiffness ellipsoid at a given end-effector posture are influenced by both joint control parameters and - for redundant manipulators - by the chosen redundancy resolution configuration. As is well known, impedance control techniques ideally provide control parameters which realize any desired shape of the Cartesian stiffness ellipsoid at the end-effector in an arbitrary non-singular configuration, so that arm geometry selection could appear secondary. This definitely contrasts with observations on how humans control their arm stiffness, who in fact appear to predominantly use arm configurations to shape the stiffness ellipsoid. To understand this discrepancy, we provide a more complete analysis of the task-space force/deformation behavior of redundant arms, which explains why arm geometry also plays a fundamental role in interaction capabilities of a torque controlled robot. We show that stiffness control of realistic robot models with bounds on joint torques can't indeed achieve arbitrary stiffness ellipsoids at any given arm configuration. We first introduce the notion of maximum allowable Cartesian force/displacement (“stiffness feasibility”) regions for a compliant robot. We show that different robot configurations modify such regions, and explore the role of different configurations in defining the performance limits of Cartesian stiffness controllers. On these bases, we design a stiffness control method that suitably exploits both joint control parameters and redundancy resolution to achieve desired task-space interaction behavior
Manipulability Measures taking Necessary Joint Torques for Grasping into consideration
This paper presents new manipulability measures to evaluate how much easily the robot manipulates the grasped object, simultaneously taking how much magnitude of joint torque we need to keep grasping into consideration. For the purpose, we use operation range. The operation range is for actuator attached to every joint of robot and provides generable joint torque and velocity and their relation (between generating torque/velocity and addable velocity/torque). While we introduced a manipulability measure using the operation range in our previous paper, it was for a limited class due to large computational effort and we could not evaluate whole space of object velocity and could not consider whole space of external wrench. This paper proposes new manipulability measures which can evaluate whole space of object velocity, taking the effect of external wrench in whole space into consideration. ©2010 IEEE
Joint Torque-velocity Pair Based Manipulability for Grasping System
This paper provides a new approach of manipulability for general grasping system. While conventional manipulability is analysis in velocity domain and can not include force effect such as gravitational force, the proposing approach can include the force effect to keep grasping. For the purpose, an operation range is introduced. The operation range is for actuator attached with every joint of robot and provides generable joint torque and velocity and their relation (between generating torque/velocity and addable velocity/torque). Using the operation range, we derive manipulability set and measure in velocity domain, including force effect. The proposing method can evaluate not only the performance in velocity domain but also effects of friction, contact state, and external forces, which were not obtained in conventional studies. ©2008 IEEE
Towards Whole Arm Manipulation by Contact State Transition
This paper discusses the whole arm manipulation allowing the contact state transition. For manipulation of an object under fully constrained, the contact state transition becomes necessary. In order to realize the object manipulation, we first derive the feasible direction of the object manipulation by analyzing the active/passive closure properties for every combination of contact states. Second, we derive the set of joint torque to move the object in the feasible direction. These analyses also provide the joint torque to realize the manipulation at the planned contact states. Effectiveness of the proposed method is confirmed by some simulation results. © 2006 IEEE