Dynamic bin picking is similar to static bin picking but the parts being picked are in motion. The dynamics of the parts being picked create a need for the parts to be tracked. In a project being developed at Ohio Northern University (Ada, OH, USA; www.onu.edu), the part being tracked is an air-hockey puck that is moving along the surface of an air-hockey table. In this case the puck will not be tracked and picked, but will be tracked and hit back to a person at the other end of the table. In essence, the developers have created a robotic system to compete against a human in the game of air hockey, using technology that can be applied to dynamic bin picking.
The development team, led by assistant professor of technological studies Adam Stienecker, also serves industry through proof-of-concept research and development in the areas of robotics and machine vision.
The frame that supports the robot was fabricated from steel box tubing, plate steel, and M12 bolts. It consists of four towers that are supported by cross members. The air-hockey table is 1498.6 x 736.6 mm, with side rails made of medium density fiberboard.
The KR3 six-axis robot from Kuka (Clinton Township, MI, USA; www.kuka.com/usa) allows for a great deal of freedom of motion. The size of the KR3 makes in an optimal choice for air hockey and the size limitations of the frame and the air hockey table.
The camera chosen by the team is a Flea2 from Point Grey Research (Vancouver, BC, Canada; www.ptgrey.com)--a FireWire, 1/3-in. CCD, color camera with an operating speed of 30 frame/s. The lens on the camera has a focal length of 3.5 mm.
The robot controller is connected to the computer running a VB.net application based on a Cognex (Natick, MA, USA; www.cognex.com) VisionPro application. Communication is handled through a serial port between the robot and the computer. Near the tool mounting plate of the robot there is an I/O port that will run the striker motor. A special connector was made that allows for the motor to be turned on and off through the robot instead of being controlled by an external programmable logic controller. The computer used to process the camera inputs and solve the algorithms is a Dell Precision 690.
For a robot to be able to play air hockey or perform dynamic bin picking, the object that is being affected by the robot must be mathematically described. The distance, velocity, direction, and, in some cases, acceleration must be observed and calculated in a fraction of a second. In this application the object is a hockey puck that is 63.5 mm in diameter. Since a hockey puck only travels in two dimensions, the equations are only concerned with the x and y directions.
To date, the team has successfully developed the ability to defend the goal from the strike of an opponent given a reasonable velocity. The robot will adjust to the path of the puck and hit it back towards its opponent. Work on phase two--offensive play--will begin shortly. In phase-three, the team plans to develop an artificial intelligence that will learn strategy from other opponents.
Click here for a related video available on the Vision Systems Design home page. Additional video, a PDF of the mathematic equations used in the air hockey project, and technical reports are available on the team's Web site: www.onu.edu/a+s/techno/ROBOTHOCKEY or by contacting Stienecker at email@example.com.
Reprinted with permission from the Vision Systems Design article, "From air hockey to bin picking", featured in the August 2008 issue.