6 DOF SHAKER VIDEOS
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. Research into this type of assembly will lead to new strategies for manipulating parts in manufacturing processes; it may also lead to insights in fields far removed from manufacturing such as granular mixing and the emergent flocking and swarming behavior seen in many biological systems.
The specific goal of this research is to control the movements of parts placed on a flat rigid plate using only a small number of sensors and actuators. The plate is capable of undergoing small amplitude periodic motion with up to six degrees-of-freedom. Frictional forces between the plate and the parts induce part motion. The device is novel for its ability to vibrate out of the horizontal plane. This capability allows control to be gained over the effective gravitational force (and therefore the frictional force) that the part experiences as a function of its location on the plate. For a particular vibratory input of the plate, a unique velocity field is created to which point parts will converge. We call this field the asymptotic velocity field.
Vibratory systems using single plates have already been shown effective manipulators. Of particular note is the Universal Planar Manipulator designed, built, and studied by Reznik and Canny. Using a single plate to manipulate parts is advantageous because these types of systems are purely software driven. Indeed, a major disadvantage of most current manipulation devices, such as bowl feeders, is that hardware must be redesigned every time a new part is introduced. Systems utilizing vibratory plates, however, can be purely software driven; the vibrations can be programmed to deal with a wide variety of parts and part manipulation tasks without the need for any mechanical alterations. Most importantly, the motion of the plate can be programmed such that parts move around independently of each other, thereby enabling parallel manipulation and assembly. However, all the systems based on vibratory plates studied previously 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 degree-of-freedom system cannot create fields with sources or sinks. Because our device can be actuated with all six degrees-of-freedom, it can generate a larger class of fields than previous related devices. For a given part, we wish to show that a plate motion motion can be designed to move the part into a unique, stable configuration without the use of sensors or position feedback. There are some non-vibratory parts handling devices are capable of performing this task, but they do so using a pixelated array of numerous actuators. Our device is the first one capable of creating a continuous field on a rigid plate with sources and sinks.
We have been building different types of "shakers" to test our ideas. Shown below are two one-degree-of-freedom shakers. The one on the left is a translational shaker. Asymmetrical in-plane oscillations of the plate cause the penny to slide at a constant and controllable speed. The shaker on the right is a one-degree-of-freedom rotational shaker. Symmetrical linear motion of the speaker is transformed into rotational motion of the plate about an axis 5 cm below the plate's surface. We have shown both experimentally and theoretically that this symmetrical motion profile induces a velocity field with a squeeze line over the rotation axis. This is a simple example of out-of-plane motion yielding a field with non-zero divergence. A video of this shaker can be found here.
Shown belos is our six-degree-of-freedom known as PPOD (Programmable Part-feeding Oscillatory Device). By controlling the input voltages to the six speakers, we are to able to control the motion of the plate surface and thereby generate a large class of interesting velocity fields. A second more powerful version of the PPOD is currently being designed.
We have generated a number of simple primitive fields, such as those shown below, that we first discovered through numerical simulations. Nearly all the fields we have studied so far are genreated from sinusoidal plate motions. We call the field on the left "DivCircle" because parts diverge and then converge as they go around in a circle. It is produced by rotating the plate symmetrically about an axis that pierces the plate at 45 degrees. The field in the center is called a "SqeezeTrans". Movies showing parts moving in these and other fields can be found at: 6 DOF SHAKER VIDEOS.
We have also written a graphical user interface (GUI) in MATLAB that numerically simulates our system (click figure below to enlarge). The GUI allows us to create and animate periodic plate motions, simulate the motion of parts, and generate asymptotic velocity fields. All results are based on the assumption that the part maintains contact with the plate at all times. When parts have planar extent it is assumed that they make contact with the plate at a finite number of "feet", which are modeled as points.
More detailed information can be found in the papers and presentations listed below.
Papers:
T. H. Vose, P. Umbanhowar, and K. M. Lynch. Vibration-Induced Frictional Force Fields on a Rigid Plate. IEEE International Conference on Robotics and Automation, 2007.
T. H. Vose, P. Umbanhowar, and K. M. Lynch. Friction-Induced Lines of Attraction and Repulsion
for Parts Sliding on an Oscillated Plate. Accepted for publication in IEEE Transactions on Automation Science and Engineering. Accompanying VIDEO.
T. H. Vose, P. Umbanhowar, and K. M. Lynch. Friction-Induced Velocity Fields for Point Parts
Sliding on a Rigid Oscillated Plate. Robotics: Science and Systems Conference 2008. Accompanying VIDEO.
Presentations:
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.
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.
