Capturing a convex object with three discs

Jeff Erickson, Shripad Thite, Fred Rothganger, Jean Ponce

Research output: Contribution to journalArticlepeer-review


This paper addresses the problem of capturing an arbitrary convex object P in the plane with three congruent disc-shaped robots. Given two stationary robots in contact with P, we characterize the set of positions of a third robot, the so-called capture region, that prevent P from escaping to infinity via continuous rigid motion. We show that the computation of the capture region reduces to a visibility problem. We present two algorithms for solving this problem, and for computing the capture region when P is a polygon and the robots are points (zero-radius discs). The first algorithm is exact and has polynomial time complexity. The second one uses simple hidden surface removal techniques from computer graphics to output an arbitrarily accurate approximation of the capture region; it has been implemented, and examples are presented.

Original languageEnglish (US)
Pages (from-to)1133-1140
Number of pages8
JournalIEEE Transactions on Robotics
Issue number6
StatePublished - Dec 2007


  • Caging
  • Capture region
  • Capturing
  • Industrial manipulators
  • Manipulators
  • Motion control
  • Motion-planning
  • Multiple manipulators
  • Robots

ASJC Scopus subject areas

  • Control and Systems Engineering
  • Computer Science Applications
  • Electrical and Electronic Engineering


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