Prioritized Independent Contact Regions for Form Closure Grasps Robert Krug, Dimitar Dimitrov, Krzysztof Charusta and Boyko Iliev Center for Applied Autonomous Sensor Systems (AASS) Örebro University, Sweden robert.krug@oru.se Robert Krug IROS 2011 1 / 17
Independent Contact Regions (ICR) Impossible to position the fingers of a grasping device precisely at the desired contact locations Robert Krug IROS 2011 2 / 17
Independent Contact Regions (ICR) Impossible to position the fingers of a grasping device precisely at the desired contact locations Representation of a grasp as a set of regions [Nguyen, 1986] Each region is associated with one finger Robert Krug IROS 2011 2 / 17
Independent Contact Regions (ICR) Impossible to position the fingers of a grasping device precisely at the desired contact locations Representation of a grasp as a set of regions [Nguyen, 1986] Each region is associated with one finger If each finger is placed within its respective region . . . . . . certain grasp properties are preserved Robert Krug IROS 2011 2 / 17
Independent Contact Regions (ICR) Impossible to position the fingers of a grasping device precisely at the desired contact locations Representation of a grasp as a set of regions [Nguyen, 1986] Each region is associated with one finger If each finger is placed within its respective region . . . . . . certain grasp properties are preserved Robert Krug IROS 2011 2 / 17
Independent Contact Regions (ICR) Impossible to position the fingers of a grasping device precisely at the desired contact locations Representation of a grasp as a set of regions [Nguyen, 1986] Each region is associated with one finger If each finger is placed within its respective region . . . . . . certain grasp properties are preserved Robert Krug IROS 2011 2 / 17
Independent Contact Regions (ICR) Impossible to position the fingers of a grasping device precisely at the desired contact locations Representation of a grasp as a set of regions [Nguyen, 1986] Each region is associated with one finger If each finger is placed within its respective region . . . . . . certain grasp properties are preserved Robert Krug IROS 2011 2 / 17
Independent Contact Regions (ICR) Impossible to position the fingers of a grasping device precisely at the desired contact locations Representation of a grasp as a set of regions [Nguyen, 1986] Each region is associated with one finger If each finger is placed within its respective region . . . . . . certain grasp properties are preserved Regions are not unique Robert Krug IROS 2011 2 / 17
Motivation Outline Motivation 1 Concept 2 Wrench Spaces Approximating the EWS Algorithm 3 Numerical Evaluation 4 Summary & Outlook 5 Robert Krug IROS 2011 3 / 17
Motivation Current Methods [Pollard, 2004] [Roa and Suárez, 2009] [Krug et al., 2010] Regions are represented by sets of contact points on a discretized object Robert Krug IROS 2011 4 / 17
Motivation Current Methods [Pollard, 2004] [Roa and Suárez, 2009] [Krug et al., 2010] Regions are represented by sets of contact points on a discretized object A grasp family is synthesized from a prototype force-closure grasp . . . . . . using simple heuristics Robert Krug IROS 2011 4 / 17
Motivation Current Methods [Pollard, 2004] [Roa and Suárez, 2009] [Krug et al., 2010] Regions are represented by sets of contact points on a discretized object A grasp family is synthesized from a prototype force-closure grasp . . . . . . using simple heuristics Expected disturbances are considered Frictionless/frictional & soft finger point contact models are eligible Robert Krug IROS 2011 4 / 17
Motivation Current Methods [Pollard, 2004] [Roa and Suárez, 2009] [Krug et al., 2010] Regions are represented by sets of contact points on a discretized object A grasp family is synthesized from a prototype force-closure grasp . . . . . . using simple heuristics Expected disturbances are considered Frictionless/frictional & soft finger point contact models are eligible Problem: Strong conditioning on the prototype grasp → number & distribution of points forming the regions are often undesirable Robert Krug IROS 2011 4 / 17
Motivation Presented approach General idea: Specify a desired grasp family ⇒ validate it against expected disturbances Robert Krug IROS 2011 5 / 17
Motivation Presented approach General idea: Specify a desired grasp family ⇒ validate it against expected disturbances Or, alternatively: Synthesize a grasp family from a prototype grasp Robert Krug IROS 2011 5 / 17
Motivation Presented approach General idea: Specify a desired grasp family ⇒ validate it against expected disturbances Or, alternatively: Synthesize a grasp family from a prototype grasp Resulting regions are less dependent on the prototype grasp Robert Krug IROS 2011 5 / 17
Motivation Presented approach General idea: Specify a desired grasp family ⇒ validate it against expected disturbances Or, alternatively: Synthesize a grasp family from a prototype grasp Resulting regions are less dependent on the prototype grasp Formal definition of resistible disturbances w.r.t. grasp families . . . . . . and an efficient way to approximate them Robert Krug IROS 2011 5 / 17
Motivation Presented approach General idea: Specify a desired grasp family ⇒ validate it against expected disturbances Or, alternatively: Synthesize a grasp family from a prototype grasp Resulting regions are less dependent on the prototype grasp Formal definition of resistible disturbances w.r.t. grasp families . . . . . . and an efficient way to approximate them The frictionless point contact model is used Robert Krug IROS 2011 5 / 17
Concept Outline Motivation 1 Concept 2 Wrench Spaces Approximating the EWS Algorithm 3 Numerical Evaluation 4 Summary & Outlook 5 Robert Krug IROS 2011 6 / 17
Concept Wrench Spaces The Grasp Wrench Space (GWS) Which disturbance wrenches can a single grasp resist? Robert Krug IROS 2011 7 / 17
Concept Wrench Spaces The Grasp Wrench Space (GWS) Assuming the frictionless point contact model . . . Robert Krug IROS 2011 7 / 17
Concept Wrench Spaces The Grasp Wrench Space (GWS) Assuming the frictionless point contact model . . . � f s � τ s = ( p s × f s ) , w s = τ s Robert Krug IROS 2011 7 / 17
Concept Wrench Spaces The Grasp Wrench Space (GWS) Assuming the frictionless point contact model . . . Robert Krug IROS 2011 7 / 17
Concept Wrench Spaces The Grasp Wrench Space (GWS) Grasp Wrench Space (GWS) → Wrenches exertable by a single grasp Robert Krug IROS 2011 7 / 17
Concept Wrench Spaces The Grasp Wrench Space (GWS) GWS → mirror image of resistible disturbance wrenches Robert Krug IROS 2011 7 / 17
Concept Wrench Spaces The Exertable Wrench space (EWS) Which disturbance wrenches can a grasp family resist? Robert Krug IROS 2011 8 / 17
Concept Wrench Spaces The Exertable Wrench space (EWS) Consider adding points to ICR / grasp members to the grasp family Robert Krug IROS 2011 8 / 17
Concept Wrench Spaces The Exertable Wrench space (EWS) Consider adding points to ICR / grasp members to the grasp family Robert Krug IROS 2011 8 / 17
Concept Wrench Spaces The Exertable Wrench space (EWS) The Exertable Wrench Space → analogue to the GWS for single grasps Robert Krug IROS 2011 8 / 17
Concept Wrench Spaces The Exertable Wrench space (EWS) Mirror image of the disturbances resistible by every member of a grasp family Robert Krug IROS 2011 8 / 17
Concept Wrench Spaces The Exertable Wrench space (EWS) Intersection of the GWS corresponding to members of the grasp family � EWS { GWS 1 ,..., GWS V } = # of grasp family members = V Robert Krug IROS 2011 8 / 17
Concept Wrench Spaces The Task Wrench Space (TWS) How to take expected disturbances into account? Robert Krug IROS 2011 9 / 17
Concept Wrench Spaces The Task Wrench Space (TWS) How to take expected disturbances into account? TWS → wrenches necessary to counter expected disturbances Robert Krug IROS 2011 9 / 17
Concept Wrench Spaces The Task Wrench Space (TWS) How to take expected disturbances into account? TWS → wrenches necessary to counter expected disturbances EWS of a specified desired grasp family has to contain the TWS Robert Krug IROS 2011 9 / 17
Concept Approximating the EWS Approximating the EWS Computing the EWS is costly (computing & intersecting V convex hulls ) Robert Krug IROS 2011 10 / 17
Concept Approximating the EWS Approximating the EWS Computing the EWS is costly (computing & intersecting V convex hulls ) Approximate confining hyperplanes . . . Robert Krug IROS 2011 10 / 17
Concept Approximating the EWS Approximating the EWS Computing the EWS is costly (computing & intersecting V convex hulls ) Approximate confining hyperplanes . . . . . . by solving Quadratic Programs (QP’s) Robert Krug IROS 2011 10 / 17
Concept Approximating the EWS Approximating the EWS Computing the EWS is costly (computing & intersecting V convex hulls ) Approximate confining hyperplanes . . . . . . by solving Quadratic Programs (QP’s) Current Methods → Approximation based on the prototype grasp’s GWS Robert Krug IROS 2011 10 / 17
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