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Friction-Induced Part Manipulation on a Rigid Oscillated Plate

Grad Students: Tom Vose Undergrad Students: Matt Turpin Eric Bell Philip Dames

Professors: Kevin Lynch Paul Umbanhowar Funded by: NSF Grant No. 0700537

• Friction-Induced Lines of Attraction and Repulsion for Parts Sliding on an Oscillated Plate. T. H. Vose, P. Umbanhowar, and K. M. Lynch. IEEE Transactions on Automation Science and Engineering, to be published in late 2009. Video supplement.
  
  
• Friction-Induced Velocity Fields for Point Parts Sliding on a Rigid Oscillated Plate . T. H. Vose, P. Umbanhowar, and K. M. Lynch. International Journal of Robotics Research, 28(8):1020-1039, August 2009. Video supplement 1, video supplement 2.
  
  
• Friction-Induced Velocity Fields for Point Parts Sliding on a Rigid Oscillated Plate. T. H. Vose, P. Umbanhowar, and K. M. Lynch. Robotics: Science and Systems Conference 2008. Best Student Paper Award. Video supplement.
  
  
• Optimal Vibratory Stick-Slip Transport . P. Umbanhowar and K. M. Lynch. IEEE Transactions on Automation Science and Engineering, 5(3) July 2008.
  
  
• Vibration-Induced Frictional Force Fields on a Rigid Plate . T. H. Vose, P. Umbanhowar, and K. M. Lynch. IEEE International Conference on Robotics and Automation, 2007. Best Automation Paper Award

• Video of parts moving on PPOD2 in sequential of fields.
  
  
• Video supplement for Friction-Induced Lines of Attraction and Repulsion for Parts Sliding on an Oscillated Plate (T-ASE2009). This video shows parts moving and self-orienting in LineSink fields.
  
  
• Video supplement 1 for Friction-Induced Velocity Fields for Point Parts Sliding on a Rigid Oscillated Plate (IJRR2009). This video shows parts moving in LineSink and Whirlpool fields, and parts moving and mating in sequential fields. Video supplement 2 for Friction-Induced Velocity Fields for Point Parts Sliding on a Rigid Oscillated Plate (IJRR2009). This video shows an animation of parts converging to an asymptotic velocity.
  
  
• Video supplement for Friction-Induced Velocity Fields for Point Parts Sliding on a Rigid Oscillated Plate (RSS2008). This video shows parts moving in LineSink and Whirlpool fields, parts mating while moving in three sequential fields, and an animation of parts converging to a asymptotic velocity.

PPOD1 (our 1st PPOD)	PPOD2 (our 2nd PPOD)

Project Overview:

In typical robotic assembly, a single robot sequentially performs a number of tasks to assemble complex objects. However, if the number of parts required for assembly is very large, or if the size of the parts is very small, this method becomes cumbersome or even impossible. A solution is to endow the parts themselves with simple sensory and actuating capabilities. An example is the design of magnetized parts that fit together like puzzle pieces when properly oriented. To induce self-assembly or pattern formation, parts can be powered by controllable external energy from the environment in the form of heating, shaking, stirring, etc. This method of assembly is advantageous because it enables massive parallel manipulation of multiple parts.

Our research is focused on controlling the motion of parts placed on a flat rigid plate using only a small number of sensors and actuators. To this end, we have built devices called PPODs (Programmable Part-feeding Oscillatory Devices). A PPOD consists of a rigid plate attached to six linear actuators via six linkages. Each linkage has compliant flexures that serve as joints and allow the plate to move with six degrees-of-freedom (DoF). Thus, a PPOD is similar to a 6-DoF flexure-based Stewart platform. Dual-axis accelerometers are mounted around the perimeter of the plate to provide information about the plate's motion. By controlling the voltages to the six actuators, we are able to make the plate to move with desired small-amplitude periodic motions.

Parts placed on the plate move because of the frictional forces between them and the plate. For any small-amplitude periodic plate motion, we have shown that point parts move as if they are immersed in a position-dependent velocity field. Specifically, there is a mapping from every small-amplitude periodic plate motion to a corresponding velocity field on the plate surface. We call this the asymptotic velocity field. We are actively researching what types of asymptotic velocity fields can be generated with a PPOD and how we can use those fields to perform manipulation tasks such as positioning, orienting, assembling, sorting, etc.

Our PPODs are novel as parts manipulating devices for their ability to vibrate out of the horizontal plane in a controlled manner. This capability allows us to control the effective gravitational force (and therefore the frictional force) that a part experiences as a function of its location on the plate. Previously studied systems based on vibratory plates have been limited in the types of fields they can generate because the plate motion has been restricted in some manner. For example, Reznik and Canny's three-DoF system (the Universal Planar Manipulator) cannot create fields with sinks or sources because it cannot rotate out of the horizontal plane. Because PPODs can move with all six-DoF, they can generate a larger class of fields than previous vibratory devices. In particular, this class includes fields with sink and source characteristics (i.e., fields with nonzero divergence).

Example Fields:



Because PPODs can create fields with sink behavior, they can potentially be used to sensorlessly position and orient parts. There are some non-vibratory parts handling devices that are capable of doing this as well, but they usually do so using pixelated arrays of numerous actuators. PPODs are the first devices capable of creating a continuous field with sources and sinks on a rigid plate. Another advantage of PPODs are their flexibility. Because they are software driven, the plate's motion can be easily reprogrammed to deal with new parts or new manipulation tasks without the need to make any mechanical alterations. Most traditional manipulation devices, such as bowl feeders, require hardware modification every time a new part is introduced.

We have written a graphical user interface (GUI) in MATLAB to study the dynamics of parts on a PPOD. The GUI allows us to create and animate periodic plate motions, simulate the motion of parts, and generate asymptotic velocity fields.

MATLAB GUI Screenshot:

• Characterizing the set of all obtainable asymptotic velocity fields arising from 6-DoF periodic plate motion.
• Determining bounds on the rate of convergence to the asymptotic velocity for arbitrary plate motions.
• Mapping a desired field into a plate motion.
• Using asymptotic velocity fields to describe the motion and equilibruim configurations of planar parts.

• T. H. Vose. Vibration-Induced Frictional Force Fields on a Rigid Plate. Presented at IEEE International Conference on Robotics and Automation. Rome, Italy, 2007.
  
  
• T. H. Vose. Vibration-Induced Velocity Fields for Point Parts Sliding on a Rigid Oscillated Plate. Presented at Robotics: Science and Systems. Zurich, Switzerland, 2008.
  

• Assembly Magazine article on frictional fields created by the PPOD, December 19, 2007.

This material is based upon work supported by the National Science Foundation under Grant No. 0700537. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.