Servo - February 2009

GEERHEAD

charts were complete, it was a matter of converting them to the robot code, KRL. This language is proprietary for the KUKA robots."

Ice cream sundae construction is split between an ice cream robot and a toppings robot. The programming of the latter enables it to select one of six different toppings based on choices made by customers at the touch panel. The same programming also enables the robot to wait for data from the camera coming through the high speed serial connection to tell it where the spoon is located.

In addition, the robot must know the orientation of the spoon so it does not place it in the cup of ice cream the wrong way. To do this, the robot relies on the VisionPro software to compute a rotation angle for the robot to use to adjust the alignment of the spoon and put it in the ice cream just right.

As for the KUKA robot assigned to the ice cream itself, this bot moves based on inputs from the touch panel, delivered through the PLC. "The code in the ice cream robot is pretty unintelligent, that is, it just moves through several points and waits while ice cream is dispensed and then returns to a position."

The VisionPro software runs on a PC. "The software receives images from the camera, analyzes them, and relays the location of the spoon to the robot by way of an RS-232 serial connection. The vision system was programmed by first giving it a training image of the spoon. That is, an image was taken of the spoon and recorded in the VisionPro software. Then, the software was told that this was what it should be looking for. It was also told at what point on the spoon it should consider its origin and at what angle the training spoon image was. Then, the program was set up to find this spoon, its location,

Robot arm releases selected toppings into cup.

and its angle of rotation, and then relay that information to the robot via the serial port."

The PLC sequencer was programmed in simple Ladder Logic, using the RSLogix500 development tool.

"It is a very simple program with only a few lines of code. It takes the topping selection button push from the touch panel, remembers it, then transmits it out to the robots when the Go button has been pushed on the touch panel."

A side shot of the entire robotic ice cream dispensing apparatus.

Computer Vision

As mentioned earlier, a Flea2 Fire Wire camera fitted with a 9 mm lens was used. Optical calculations derived the ideal location for the camera in relation to the area where the spoon would be placed.

After the VisionPro was trained in spoon identification, in operation it locates a predetermined point on the spoon within that image, down to the pixel.

Next, the computer vision software runs some vision related equations that relate the selected pixel position to the real-world measurement and placement of that part of the spoon in millimeters. The computer forwards that value to the robot via RS-232 serial communications.

"Along with that location is an angle of rotation that when applied,

Customers making selections at interface.

yields a grasped spoon in an ideal orientation for the next task. That is, it has been relocated from a random position to a position that the robot knows." This is the core of part bin picking. The robot accomplishes this maneuver mechanically using a suction cup that attaches to the spoon at the widest point of its handle.