Experiments in Parts Feeding

We have built two robots for positioning and orienting (feeding) parts on a fixed-speed moving conveyor. The first of these, the 1JOC (for 1 joint over conveyor), is a rotating fence which interacts with parts on the conveyor by pushing them. We have shown that the 1JOC is capable of taking any polygonal part from any initial planar configuration upstream of the fence, to a desired goal configuration. It accomplishes this by alternately pushing the part and letting it drift on the conveyor.

The successor to this robot is the 2JOC, which adds a prismatic joint to the 1JOC, allowing the rotating fence to move up and down. This allows the 2JOC to roll or "knock over" parts. This allows the 2JOC to change the face of the part in contact with the conveyor.

We have also constructed a variety of vibratory devices to transport, position, and orient parts on a vibrating plate.

Experiments with the 2JOC
Parts feeding using vibration

Other videos: Dynamic underactuated nonprehensile manipulation

The 2JOC (2 joints over conveyor) uses just two controlled degrees-of-freedom to do full 3D parts orienting of parts on a fixed-speed conveyor. It does this by using pushing to orient parts in the conveyor plane, and toppling (or rolling) to accomplish out-of-plane rotations. The video shows the end of an automatically planned and executed sequence of rolls ("topples") and pushes ("turns"). This video is sped up by 150%. AVI, 3741K

See the more recent project page here, which contains a link to a few videos of the 6-DOF shaker.

The device pictured below is a plate that rotates about an axis below the centerline of the plate, built by Dan Sheehan. It is simply an inexpensive car woofer attached to a lever that rotates the plate. The speaker is driven by a stereo amplifier which receives periodic input (sine wave, square wave, or sawtooth wave) from a function generator, typically at frequencies of 20-60 Hz. Due to friction with parts on the plate, the resulting effect on the plate is a "squeeze" field, so that parts on the plate are squeezed toward the centerline. Parts tend to orient along the centerline. The larger part shown has feet at its four corners, increasing the ratio of torque to forces, making the aligning effect more dramatic.

This is a one-degree-of-freedom version of a six-degree-of-freedom device under construction. This new device will be able to implement a wide variety of virtual force fields depending on the programmable vibratory motion. Some example force fields are illustrated below:

(a) ... (b) ... (c) ... (d) ... (e) ... (f)

Some potential applications for the future device include:

• Multiple parts can be moved simultaneously in different directions, based on vision feedback. This allows sorting of parts in parallel.
• "Sink" force fields can be used to position and orient parts without the use of sensors. Force fields can be designed for different parts by altering the vibratory motion.
• Conveyors can be built which both convey parts linearly and eliminate uncertainty in their orientation as they move.
• Two parts can be mated or aligned, then transported while being "squeezed" together.

This device draws inspiration from the super-cool Universal Planar Manipulator (UPM) of Reznik and Canny at UC Berkeley. That device uses three motion freedoms in a horizontal plane to create a subset of force fields that can be created using six motion freedoms. In particular, that device creates only "divergence-free" force fields (no sinks or sources; none of the force fields shown above are possible).