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SINGULARITY in Mobile Symmetric Frameworks

SINGULARITY in Mobile Symmetric Frameworks. Offer Shai. - The main definition of Assur Graphs. - The singularity of Assur Graphs. - Deriving the symmetric frameworks with finite motions through Assur Graph singularity. - The method relies on: - Face forces

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SINGULARITY in Mobile Symmetric Frameworks

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  1. SINGULARITY in Mobile Symmetric Frameworks Offer Shai - The main definition of Assur Graphs. - The singularity of Assur Graphs . - Deriving the symmetric frameworks with finite motions through Assur Graph singularity. - The method relies on: - Face forces - Equimomental lines. Results

  2. The main definition of Assur Graphs: E A B 6 9 10 D G is a bar&joint Assur Graph IFF G is a pinned isostatic graph and it does not contain any proper pinned isostatic graph. 4 5 3 C 1 7 8 2 Not Asssur Graph Asssur Graph

  3. The singularity of Assur Graphs Servatius B., Shai O. and Whiteley W., "Geometric Properties of Assur Graphs", European Journal of Combinatorics, Vol. 31, No. 4, May, pp. 1105-1120, 2010.

  4. Assur Graph Singulariy Theorem (Servatius et al., 2010): E G is an Assur Graph IFF it has a configuration in which there is a unique self-stress on all the edges and all the inner vertices have 1dof andinfinitesimal motion . D This topology does not have such configuration.

  5. In Assur Graphs, it is easy to prove: If there is a unique self-stress on all the edges THEN all the inner vertices have 1dof andinfinitesimal motion. So, the problem is to characterize the configurations where there is a unique self-stress on all the edges.

  6. Deployable/foldable TensegrityAssur robot • The robots works constantly at the singular position. • The control is very easy (controls only one element).

  7. Tensegrity Assur Graph at the Singular Position Changing the singular point in the triad

  8. From singular Assur Graphs into Symmetric Frameworks with finite motions

  9. This is done in three steps: Characterize the singularity of the given Assur Graph– apply a combinatorial method that uses face force (projection of polyhedron). Transform the infinitesimal motion into finite motion using sliders and other methods (not systematic, yet). Replication – resulting with floating overbraced framework.

  10. Face Force – a force appearing in Maxwell’s diagram. It is a force acting in a face, like a mesh current in electricity.

  11. Maxwell Diagram I VI IV V III II O

  12. Face force is the corresponding entity in statics of absolute linear velocity of the dual mechanism. I VI IV V III II O Dual mechanism

  13. The force in the bar is equal to the subtraction between its two adjacent Face Forces I VI IV V III II O

  14. Face Forces define ALL the forces in the bars.

  15. If Face Forces are forces thus where do they act? Where is the line upon which they exert zero moment?

  16. Relation between two forces: For any two forces Fi, Fj in the plane there exists a line upon which they exert the same moment. This line is termed: the relative equimomental line eqm(Fi, Fj).

  17. F2 F1 Finding the eqm(F1,F2)

  18. Absolute eqm(F1) Absolute eqm(F2) Relative eqm (F1, F2) Equimomental line is defined by the subtraction between the two forces. F2 F1 Finding the relative eqm(F1,F2)

  19. Now, bars become the relative eqimomental lines of the two adjacent Face Forces. Face i Face j Relative eqm(FFi, FFj)

  20. If one of the adjacent faces is the zero face (reference face), thus the bar defines the absolute equimomental line of the other face. The reference face (the ground) Face j Absolute eqm(FFj)

  21. Theorem: For any three forces, the corresponding three relative equimomental lines must intersect at the same point.

  22. Now we can answer where the Face Force acts.

  23. Face forces and equimomental lines in projections of polyhedrons

  24. Absolute eqm (1)

  25. Characterization of the singularity of the Tetrad

  26. 1 3 A B 2 The singular position of the Tetrad 8 4 6 D C 7 5 (1  7)  (3  5)  (2  6) = 0 =(0, II) 1 A 2 B 3 (0,II) 4 8 6 C D 5 7 Characterization done by equimomental lines and face force

  27. 2. Transforming the infinitesimal motion of the Tetrad into finite motion A 1 C 5 2 8 6 4 B D 7 3 A 1 C 5 2 8 6 4 B D 7 3

  28. The replication step. L

  29. 0 10 Last example – The double Triad Assur Graph 5 IV I 8 6 4 2 9 V III 1 7 II 3

  30. 0 Connecting vertex 1. Singularity characterization of the Double Triad. 0 5 9 10 0 I V 5 1 IV 10 I 5 8 0 9 6 I V 4 2 2 9 1 9 10 V IV 7 III 4 10 1 II 2 7 5 II 3 IV 6 I 8 IV 7 3 4 6 4 II 2 III V 6 (13)  (79)  ( 45) = 0 = (III,0) III 3 (a) 1 7 II 3 III (13)  (79)  ( 46) = 0 = (III,0) (b) Figure 7. Characterization of the singular configuration of double triad through dual Kennedy circuit in statics. Figure 8. The double triad at the singular configuration having an infinitesimal motion.

  31. 2. Transforming the infinitesimal motion of the Double-triad into a finite motion L Infinitesimal motion Infinitesimal motion Replacing with sliders  finite motion

  32. 3. The replication step

  33. Thank you!!!!

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