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Chapter 37 — Contact Modeling and Manipulation

Imin Kao, Kevin M. Lynch and Joel W. Burdick

Robotic manipulators use contact forces to grasp and manipulate objects in their environments. Fixtures rely on contacts to immobilize workpieces. Mobile robots and humanoids use wheels or feet to generate the contact forces that allow them to locomote. Modeling of the contact interface, therefore, is fundamental to analysis, design, planning, and control of many robotic tasks.

This chapter presents an overview of the modeling of contact interfaces, with a particular focus on their use in manipulation tasks, including graspless or nonprehensile manipulation modes such as pushing. Analysis and design of grasps and fixtures also depends on contact modeling, and these are discussed in more detail in Chap. 38. Sections 37.2–37.5 focus on rigid-body models of contact. Section 37.2 describes the kinematic constraints caused by contact, and Sect. 37.3 describes the contact forces that may arise with Coulomb friction. Section 37.4 provides examples of analysis of multicontact manipulation tasks with rigid bodies and Coulomb friction. Section 37.5 extends the analysis to manipulation by pushing. Section 37.6 introduces modeling of contact interfaces, kinematic duality, and pressure distribution and soft contact interface. Section 37.7 describes the concept of the friction limit surface and illustrates it with an example demonstrating the construction of a limit surface for a soft contact. Finally, Sect. 37.8 discusses how these more accurate models can be used in fixture analysis and design.

Pushing, sliding, and toppling

Author  Kevin Lynch

Video ID : 802

This video demonstrates sliding or toppling of a pushed object depending on the support friction coefficient, the object's center of mass location, and the pushing force, as illustrated in Figure 37.8.

Horizontal transport by 2-DOF vibration

Author  Kevin M. Lynch, Paul Umbanhowar

Video ID : 803

This video demonstrates the use of vertical and horizontal vibration of a supporting bar to cause the object on top to slide one way or the other. Upward acceleration of the bar increases the normal force, thereby increasing the tangential friction force during sliding. With periodic vibration, the object achieves a limit-cycle motion. By choosing the phasing of the vertical and horizontal vibration, the net motion during a limit cycle can be to the left or right. Video shown at 1/20 actual speed. This video is related to the example shown in Fig. 37.9 in Chap. 37.4.3 of the Springer Handbook of Robotics, 2nd ed (2016).

Programmable velocity vector fields by 6-DOF vibration

Author  Tom Vose, Matt Turpin, Philip Dames, Paul Umbanhowar, Kevin M. Lynch

Video ID : 804

This video generalizes the idea of transporting parts using horizontal and vertical vibration shown in the previous video and illustrated in Fig. 37.9 in Chap. 37.4.3 of the Springer Handbook of Robotics, 2nd ed (2016). In this video, a rigid supporting plate is vibrated with an arbitrary periodic 6-DOF motion profile. This periodic vibration enables control of the normal forces and horizontal plate velocities as a function of the position on the plate, effectively creating programmable velocity vector fields induced by friction. This video demonstrates five such velocity fields in sequence, each created by a different periodic vibration of the plate.