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| | Aerial Grasping and
Manipulation |
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Unmanned Aerial Vehicles (UAVs) avoid interacting with their environments. Aircraft "look, but don't touch", with UAVs avoiding contacting objects and obstacles around them. However, the ability for small robotic aerial vehicles to grasp and manipulate objects around them has numerous applications across a variety of disciplines, including sample retrieval, highspeed courier services, intelligence gathering, and explosives disposal. This task is very challenging due to the need to precisely position the aircraft over the target object to grasp with a rigid gripper, the coupled mechanics of ground forces and the inherent instability of rotorcrafts, and the presence of aerodynamic disturbances. We have developed a robot helicopter integrated with a compliant gripper, able to directly grasp and transport objects while hovering in mid-air outdoors, without need for external motion sensors.
The special tuned elasticity properties of the gripper allow the aircraft to robustly contact objects, using a stock fligh controller without inducing pathological destabilizing effects.
To watch a video of the Yale Aerial Manipulator,
click here.
Sample Publications:
Paul E.I. Pounds, Daniel R. Bersak, and Aaron M. Dollar
Grasping From the Air: Hovering Capture and Load Stability, proceedings of the 2011 IEEE International Conference on Robotics and Automation (ICRA), Shanghai, China, May 9-13, 2011.
Paul E.I. Pounds and Aaron M. Dollar
Hovering Stability of Helicopters with Elastic Constraints, proceedings of the 2010 ASME Dynamics Systems and Control Conference (DSCC 2010).
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| | Robotic Grasping |
One of the greatest challenges of robotics is grasping and
manipulating objects in unstructured, real-life environments, where
object properties are not known a priori and sensing is prone to
error. The resulting uncertainty in the relationship between the
object and gripper makes it difficult to control contact forces and
establish a successful grasp. Robotics researchers have spent 30 years
and millions of dollars in an effort that by almost any measure has
failed: robots today cannot autonomously perform even simple grasping
tasks in a typical home setting.
Much of the reason for the current limitations is that traditional
robot hands, which typically involve complex mechanisms, sensing
suites, and control, are difficult to use, fragile, and
impractical. Alternatively, by carefully designing the mechanical
structure of the hand to appropriately incorporate features such as
compliance and adaptability, the uncertainty inherent in unstructured
grasping tasks can be more easily accommodated. These features can
reduce the need for complicated sensing and control by passively
adapting to the object properties and positioning, making the hand
easier to operate, more robust, and less expensive.
After undertaking design optimization studies to determine the best
means of incorporating these features into a robot hand, we built a
novel, four-fingered robot hand that is both compliant and highly
underactuated (see figure). The hand uses only a single actuator for
the eight joints yet is able to passively adapt to large variations in
object geometry. Experimental work with the prototype hand showed that
even with three positioning degrees of freedom and open loop hand
control, target objects spanning a large range of size, shape, and
mass could be reliably grasped.
To watch a video of the SDM Hand,
click here.
Sample Publications:
Aaron M. Dollar and Robert D. Howe
Simple, Robust Autonomous Grasping in
Unstructured Environments, proceedings of the 2007 IEEE
International Conference on Robotics and Automation (ICRA), Rome,
Italy, April 10-14, 2007.
Aaron M. Dollar and Robert D. Howe
Joint Coupling Design of
Underactuated Grippers, proceedings of the ASME 30th Annual
Mechanisms and Robotics Conference, 2006 International Design
Engineering Technical Conferences (IDETC), Philadelphia, PA,
Sept. 10-13, 2006.
Aaron M. Dollar and Robert D. Howe
Towards Grasping in Unstructured
Environments: Grasper Compliance and Configuration Optimization,
Advanced Robotics, vol. 19(5), pp. 523-543, 2005.
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| | Underactuated Mechanisms |
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Project 1: While much work has been done on how underactuated
mechanisms perform when actuated internally, it is still unclear how
they perform in the presence of external disturbances. Our work
identifies how the response behavior varies as a function of the
coupling mechanism (cable-driven or linkage-driven) and the
actuation mode (backdriveable or non-backdriveable) the hand is
operated in.
Project 2: While prior work in underactuated robotic hands has
defined a mechanism's adaptability as its ability to curl its distal
degrees of freedom inward even after the proximal degrees of freedom
are constrained by contact with the environment, we have explored how
a system's adaptability varies in terms of both motion and
force-application capabilities as a function of the coupling
mechanism.
Sample publications:
Ravi Balasubramanian and Aaron M. Dollar
A Comparison of Workspace and Force Capabilities between Classes of
Underactuated Mechanisms, proceedings of the 2011 IEEE International Conference on Robotics and Automation (ICRA), Shanghai, China, May 9-13, 2011.
Ravi Balasubramanian and Aaron M. Dollar
Variation in Compliance In Two Classes of Two-Link
Underactuated Mechanisms, proceedings of the 2011 IEEE International Conference on Robotics and Automation (ICRA), Shanghai, China, May 9-13, 2011.
Ravi Balasubramanian, Joseph T. Belter, and Aaron M. Dollar
External Disturbances and Coupling Mechanisms in Underactuated Hands, proceedings of the 2010 ASME International Design Engineering Technical Conferences, Mechanisms and Robotics Conference (IDETC 2010).
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| Dexterous Manipulation |
Underactuated robot hands are effective at grasping objects of uncertain size, shape, or location, because they are free to passively adapt to the shape of objects they contact. This reduces the need for precise sensing and control at each joint. Hands having a small number of actuators are simpler to manufacture and ruggedize. At present, underactuated hands are used for immobilizing objects in fixed grasps, rather than dexterous within-hand manipulation. The barriers to developing simpler dexterous hands are partially practical issues of machine design, as it is clearly difficult to perform complex manipulation tasks with a limited set of actuators. However, the lack of complete mathematical tools for predicting underactuated hand behavior also hampers progress in this area. Specifically, better methods are needed for modeling the instantaneous kinematics of underactuated hands. Theoretical definitions of dexterity and assumptions about the nature of contact constraints can dominate the design requirements for dexterous hands. Relaxing these assumptions to account for underactuated mechanisms will result in creative hand designs that use fewer actuators to perform dexterous tasks.
Sample Publications:
Lael U. Odhner and Aaron M. Dollar
Dexterous Manipulation with Underactuated Elastic Hands, proceedings of the 2011 IEEE International Conference on Robotics and Automation (ICRA), Shanghai, China, May 9-13, 2011.
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| Human Manipulation |
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Human manipulation skill is unparalleled in the animal kingdom and is believed to have coevolved with our superior cognitive abilities, with each playing a complimentary role in the development of the other. However, as with many aspects of studying the hand, its familiarity frequently causes us to overlook its complexity. Each of our hands has as many controllable degrees of freedom (twenty one) as both arms, both wrists, and one leg combined. The combination of motions that can be produced by the fingers on a manipulated object is therefore large. Understanding how humans utilize their hands is important not only in robotics but also fields such as biomechanics, hand surgery, and rehabilitation.
Sample Publications:
Ian M. Bullock and Aaron M. Dollar
Classifying Human Manipulation Behavior, proceedings of the 2011 IEEE International Conference on Rehabilitation Robotics (ICORR), Zurich, Switzerland, June 29-July 1, 2011.
Joshua Z. Zheng, Sara De La Rosa, and Aaron M. Dollar
An Investigation of Grasp Type and Frequency in Daily Household and Machine Shop Tasks, proceedings of the 2011 IEEE International Conference on Robotics and Automation (ICRA), Shanghai, China, May 9-13, 2011.
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| Prosthetic Hands |
Over 10,000 major amputations of the upper extremities occur every
year in America. However, while technology has improved drastically,
very few advances in prosthetic devices have been adopted by the
amputee community in the last century. During their every day lives,
most patients still choose hooks or other simple mechanisms as
terminal devices for functionality, switching to a less functional,
more cosmetic terminal device for social activities. We would like to
address this dichotomy by working towards the development of a hand
prosthesis that is both multi-functional and realistic. Size and
weight constraints as well as limitations inherent with both
myoelectric and body-powered methods of control and actuation limit
the number of degrees of actuation that can reasonably be incorporated
into a prosthesis. The strategy we have taken with hand design fits
well with this problem: careful choice of compliance, smart design of
joint coupling, and an emphasis on
durability.
Sample Publications:
Joseph T. Belter and Aaron M. Dollar
Performance Characteristics of Anthropomorphic Prosthetic Hands, proceedings of the 2011 IEEE International Conference on Rehabilitation Robotics (ICORR), Zurich, Switzerland, June 29-July 1, 2011. (in press)
Aaron M. Dollar and Robert
D. Howe
The SDM Hand as a
Prosthetic Terminal Device: A Feasibility Study, Winner of the
Best Student Paper Award, proceedings of the 2007 IEEE
International Conference on Rehabilitation Robotics (ICORR),
Noordwijk, Netherlands, June 12-15,
2007.
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| Active Orthoses and Exoskeletons for the
Lower Limbs |
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Nearly 7 million people in the US suffer some form of leg
weakness and would benefit from the use of an orthosis. However, with
few exceptions, options for orthotic devices for this population are
limited to passive brace technologies that cannot provide the
augmentation necessary to replicate the function of an unaffected
limb. Accordingly, there is great potential for the development of
electromechanical devices to drastically increase the quality of life
of this population. We would like to develop mechanically simple powered
orthotic devices that harness the passive dynamics of locomotion to
reduce energetic
requirements.
Sample Publications:
Aaron M. Dollar and Hugh Herr
Design
of a Quasi-Passive Knee Exoskeleton to Assist Running, proceedings
of the 2008 IEEE/RSJ International Conference on Intelligent Robots
and Systems (IROS 2008).
Aaron M. Dollar and Hugh Herr
Lower
Extremity Exoskeletons and Active Orthoses: Challenges and State of
the Art, IEEE Transactions on Robotics, special issue on
Biorobotics, vol. 24(1), February 2008.
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| Modeling of Flexural Joints |
We have been working towards new and comprehensive methods
of modeling robots having highly flexible members such as
flexure joints. An accurate model of large deformation bending is
important for precisely describing the configuration of the
flexible member. Additionally, the accuracy of the Jacobian and
Hessian of the forward kinematics are critically important at
large angles for predicting the deformation and the stiffness of
the joint under load. We have introduced a model based on the
assumption that the curvature of a beam in bending is smooth,
and thus can be approximated by low-order, orthogonal
polynomials. This produces a parameterized description of
flexure motion that can be used as a joint model when expressed
in Denavit-Hartenberg form, as a transformation from one rigid
link to the next in a serial manipulator. We show that with
only three parameters, this model faithfully reproduces the
elastic deformation of a flexure hinge predicted by the continuum
model, even for large angles, without requiring numerical
integration or many finite elements. It can also be used to
compute the compressive buckling load of the flexure as
predicted by the continuum model.
Sample Publications:
Lael U. Odhner and Aaron M. Dollar
Fast, Accurate Models for Predicting the Compliance of Elastic
Flexure-Jointed Robots, proceedings of the 2010 ASME International Design Engineering Technical Conferences, Mechanisms and Robotics Conference (IDETC 2010).
Lael U. Odhner and Aaron M. Dollar
The Smooth Curvature Flexure Model: An Accurate,
Low-Dimensional Approach for Robot Analysis, proceedings of the 2010 Robotics: Science and Systems Conference (RSS 2010).
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| Robust Robotic Mechanisms and Sensors
via Shape Deposition Manufacturing |
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One of the greatest successes of biologically-inspired design has
been the development of mechanically robust robots. One promising
biomimetic facbrication technique is Shape Deposition Manufacturing
(SDM), which alternates material deposition and machining to produce
robot structures with compliant joints and embedded sensing and
actuation elements. This process, while currently being implemented in
only a handful of research laboratories worldwide, is quickly gaining
popularity in the robotics and mechatronics community. We have utilized
Shape Deposition Manufacturing in much of the robot hand research we
have undertaken. Throughout these design and fabrication exercises, we
have sought to add to the tools available to robot designers by
developing a range of sensing modalities compatible with the process.
These include Hall-effect sensors for joint angle sensing, embedded
strain gauges for 3 axis force measurements, optical reflectance
sensors for tactile sensing, and piezoelectric polymers for contact
detection. In addition to a simple construction process, the resulting
parts are extremely robust, fully functional after high impact loads
and other forces due to unintended contact.
Sample Publication:
Aaron M. Dollar, Christopher R. Wagner, and
Robert D. Howe
Embedded Sensors for
Biomimetic Robotics via Shape Deposition Manufacturing,
proceedings of the first IEEE / RAS-EMBS International Conference on
Biomedical Robotics and Biomechatronics (BioRob), selected for a
single-track podium presentation, Pisa, Italy, Feb. 20-22,
2006. |
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