We describe a new control method for vibrations-based planar manipulation. We've developed a device-the Universal Planar Manipulator (UPM)-based on a single, horizontally-vibrating plate. Though minimalist in construction (one moving part), the UPM can manipulate several parts on its surface in parallel, simply using friction. The authors previously showed (1998) that a sequence of rigid plate rotations can be computed which produces pre-specified part displacements. Here we present a new method based on a special motion primitive-the "jet"-which displaces a chosen part in a desired direction while keeping all others still. Parallel manipulation then reduces to a round-robin application of jets. This technique is both faster and more robust than the old rotations-based method. Experiments on parallel trajectory following and part sorting are presented. With jets, the UPM becomes a practical technology for applications such as part singulation, feeding, sorting, food handling, product displays, and interactive devices such as active desks and toys.

This is a continuation of our research on the Universal Planar Manipulator (UPM), a device capable of manipulating multiple generic objects with a single horizontally-vibrating, rigid plate (3 DOFs). Objects are propelled by sliding frictional forces developed against the vibrating plate. A special plate vibration creates an average force field called the "jet" which is local, i.e., it is only non-zero near its center. By applying jets at different objects' locations in succession, objects can be made to displace a small amount individually, enabling full parallel manipulation. In particular, a single object can leave on a plane jet, if the jet's center is made to track and its direction made aligned with that object's motion. We provide visualization of the jet with respect to changes in its center, orientation, and focus parameters. Described also are two experiments showing the UPM as a tangible-user interface (docking a beer can to the user's hand) and as a chess player (executing moves of an endgame).

Part feeders, which separate and orient parts prior to packing and insertion, are critical components of an assembly line. Existing feeders utilize off-plane vibrations of a rigid structure to convey parts along a track. Repeated part hopping/landing phases are concerns if parts are delicate and/or high positioning accuracy is required. Here we consider a simpler feeder design in which parts are in permanent contact with a horizontally-vibrating flat plate. Each vibration is a "pump-like" motion along a single degree of freedom: the plate spends more time moving forward than backward. Parts are propelled forward since dynamic friction is fixed and independent of the relative velocity at the interface. In designing plate vibration profiles we consider issues of waveform simplicity, bandwidth, and feed rate performance. Both bang-bang and sinusoidal control waveforms are analyzed. Expressions are derived for equilibrium feed rates for both waveforms; dynamic simulation is used to verify the analysis. A prototype of the proposed feeder has been implemented with cheap mechanical parts. A simple experiment with the device is presented.

We consider the problem of parallel part manipulation, i.e., the simultaneous position and orientation control of one or more parts in a bounded region of the plane. We propose a novel, minimalist device, based on a single horizontally-vibrating flat plate. We show that a closed rigid motion of the plate, involving its 3 DOF, can be computed which produces desired average forces at a finite number of points, e.g., parts locations. This implies that one or more parts can follow independent trajectories simultaneously, as they interact with a single vibrating plate. This is in sharp contrast with more complex designs such as massively-parallel actuator arrays and/or prehensile manipulation. Dynamic simulation is used to test the current method in two parallel part manipulation examples. A prototype of the device has been built with inexpensive parts; physical implementation of the proposed method is currently underway.

We use dynamic simulation to optimize the design of an existing micro-electromechanical (MEM) device, called the manipulation chip (M-Chip). This device contains an excess of 10000 moving actuators, called resonators, which oscillate torsionally at a few kHz. Parts dropped on the chip's surface are conveyed towards a unique direction. Given the enormous number of moving parts, it is impractical to attempt to measure the device's (or part's) dynamic state during a manipulation task. Yet, knowing this information is crucial for redesign and optimization. We make use of a powerful dynamic simulation tool, called "Impulse", to generate synthetic measurements over a range of experiments. From these results, we suggest redesign options which debug existing problems and improve the feed rate. The array is found to behave similar to a viscous spring-loaded conveyor belt; most of its energy is spent on driving the part vertically, calling for a more efficient design.

We analyze the dynamics of part motion for a novel type of planar parts feeder consisting of a longitudinally vibrating flat plate and a part placed on its surface. For each vibration cycle, the plate's velocity is held positive (forward motion) for a longer time than it is held negative (backward motion). This type of asymmetric vibration combined with the nonlinear nature of Coulomb friction causes the part to accelerate along a straight line to a terminal velocity called the "feed rate". The average force exerted by the plate on the part is shown to be proportional to the latter's deviation from the feed rate. In other words, the part behaves as if it were immersed in a forward moving viscous fluid. Expressions for the feed rate and viscosity constants are derived with respect to various physical and control parameters. Rigid-body dynamic simulation results are shown to be in good agreement with the analysis.

An efficient computational model for the dynamics of a deformable robot fingertip is presented. The dynamic model is based on a discretization of the fingertip's volume into a lattice of masses locally interconnected by damped springs. The lattice's parameters are adjusted in correspondence with bulk properties of the fingertip's deformable material (rubber). In the task studied, the fingertip moves toward a rigid flat surface, contacts it, and presses against it. This motion is commanded by an external feedback controller which communicates with the dynamic model through a virtual control interface: The controller applies forces and torques to the dynamic model and the dynamic model responds in real-time with position/velocity/force feedback information. In this fashion, the controller interacts with the fingertip's model in the same way it would interact with the actual physical system. This type of paradigm is envisioned as a prototyping/testing tool in the design of control systems for deformable objects as well as for applications involving the haptic (i.e., sensorially realistic) interaction between a human and a virtual (deformable) object. Graphical snapshots of a real time simulation of the task under study are presented which reveal the physical and computational plausibility of the model.

Considers the problem of planning the grasp operation for a multi-finger hand. The hand is expected to be able to handle three-dimensional objects of arbitrary unknown shapes as long as they are of "reasonable" size so as to make the grasping operation meaningful. The object geometry is not known beforehand. To provide input information for the interaction necessary, a whole-sensitive hand is assumed-every point of its surfaces possesses tactile sensing. The important property of the problem formulation is that in the grasp produced the hand and the fingers are expected to "hug" the object in a manner a human hand holds an apple-with the maximum contact with its surface for a firm, comfortable grasp. A novel, powerful strategy for real-time grasping is suggested which makes use of techniques for highly redundant sensor-based planar motion planning. An example is given that illustrates the performance of the approach.>

A strategy is described for on-line motion ]planning with incomplete information for a special type of highly redundant planar robot kinematics, called a snake. The snake consists of many simple serially connected links and has on-line sensing which provides information about its immediate surroundings. The task is to move the snake head point from its starting position to a known target position while generating collision-free motion for the rest of the snake body, in an environment filled with unknown obstacles of arbitrary shape. Computationally, the procedure is linear in the number of the snake Links; it is highly efficient and can be easily realized in real time. The procedure makes use of a unit motion far a single link based on the tractriz curve. This choice results in automatically achieving a “natural” motion distributed continulously and asymmetrically along the snake body - the joint displacements tend to ‘“die out” in the direction from the head to the tail. The generated path possessies an optimality property - the instantaneous total displacement of all the links/joints is minimum.