Dynamic workcell project

In conventional industrial automation, there is a fundamental split between sensing and manipulation, as in the illustrated ``belt conveyor'' example (below, left). In this example, widgets are brought into a robotic workcell via a belt conveyor. The location of each widget is unknown. A camera takes a single picture of each widget as it passes. Automated image analysis is used to determine the exact position and orientation of each widget relative to the conveyor belt. From this point, there is no further sensing to guide the robot. The velocity of the conveyor is assumed constant, so that the robot can calculate future positions of the widget. The actual grasp occurs some time later. In this scenario, the environment must be carefully constrained to ensure that nothing disturbs the widget between the time when its pose was measured and the time when it is grasped. If the part vibrates, slips, or is pushed to a new position, then the grasp will fail. Similarly, the widget is assumed to be rigid and the grasp is assumed to be firm. This means that the widget is not expected to flex, bend, or otherwise move except as when directly manipulated by the robot. In summary, the manipulation is ``blind''.

In the dynamic workcell project, manipulation is tightly integrated with continuous visual sensing. In the ``hanging chain conveyor'' example (illustrated above, right), widgets are brought into a robotic workcell via a hanging chain conveyor. The location of each widget is unknown. Additionally, the position and orientation of each widget can vary as it moves down the conveyor, due to sway. Inside the workcell, a set of cameras takes continuous images. Image analysis techniques locate and track the position and orientation of each widget. As the robot initiates a grasp, it continuously references the data supplied by the sensor system. Effectively, the robot is able to grasp objects that are in continuous unpredictable motion. Once grasped, the widget might still sway or flex relative to the robot. The sensing system will continue to provide tracking information to the robot. This information can be used to adjust the delivery of the manipulation.


During 2000-2001 we constructed a prototype dynamic workcell, pictured below. The system uses all off-the-shelf components to facilitate potential technology transfer. The boundary of the robotic workcell is surrounded by a cube of aluminum framing. Six cameras are attached to the framing using adjustable mounts. The two struts on top of the cube are also adjustable. In this configuration, a camera can be placed anywhere on top of the cube, and at any point on the vertical edges of the cube. This leaves the vertical planes of the workcell open for additional automation equipment, such as conveyors. Sitting on one side of the workcell are the robot controller, power supplies, and computing hardware to process the video feeds.


The South Carolina Commission on Higher Education seed funded this project during 2000-2001. Staubli Corporation partially donated a state-of-the-art RX-130 industrial manipulator. The U.S. Office of Naval Research funded the exploration of this technology to naval warehousing through the Expeditionary Logistics program. We gratefully thank all these organizations.


Papers about this project


An analysis of the reaction speed (lag and latency) of our prototype found it to be 260 ms. To measure this, we mounted a laser in the robot's wrist, and measured the distance between the projection of the laser and an object the robot was chasing around a fixed conveyor (see figures below). For perspective, this speed is comparable to a human athlete responding to a pitched baseball or served tennis ball.

Putting this estimate (and model) to work, we implemented a demo to catch balls moving semi-predictably. An ``air conveyor'' was constructed (see pictures, below) that blows lightweight balls around the robot. Note that the ball trajectory can never be predicted exactly (as would be possible on a fixed conveyor).

Click here to see a movie clip of how fast the system operates. This video displays real time.

Click here to see a movie clip of the system scooping balls off the conveyor. This video displays real time.

Click here to see a movie clip of the robot taking a hanger on and off a hook. This video displays real time.

Click here to see a movie clip of a pneumatic end effector catching and lifting randomly moving balls. This video displays real time.