Need speed? Is there a delta robot in your future?

You've seen them at shows. You've marveled at their speed and agility. Perhaps you've even thought one might be useful in your application. They are delta robots, and one just might be in your future because the patents on the original design are about to run out. That will open the field for more vendors to add them to their product lines and for developers to come up with more design variations.

01/01/2007


You've seen them at shows. You've marveled at their speed and agility. Perhaps you've even thought one might be useful in your application. They are delta robots, and one just might be in your future because the patents on the original design are about to run out. That will open the field for more vendors to add them to their product lines and for developers to come up with more design variations.

A delta robot looks like a three-legged spider holding a flex plate. Each spider leg extends downward from a baseplate mounted to an overhead support. Independently acting servos move each leg's short upper segment a few degrees up or down from horizontal. Each leg's lower segment then hangs from a joint at the upper segment's distal end. The three lower segments come together again at the bottom to hold a flex plate to which whatever grippers or end effectors the application requires.

Each leg's lower segment consists of two rods that connect at either side of the leg's 'knee' by gimbal joints. They similarly connect to two gimbals at the flex plate. These rods form the sides of a parallelogram that helps constrain the flex plate to remain horizontal independent of its motion.

A fourth moving element extends from a servomotor affixed to the baseplate between the three leg servos to a universal joint at the flex plate. This fourth element makes it possible to rotate the gripper around the vertical axis extending through the flex plate's center. Such an arrangement is capable of moving up, down, left and right within a three-dimensional workspace.

Motion-system component manufacturer Rexroth demonstrated a delta robot shown at its Pack Expo 2006 booth (Oct. 29-Nov. 2 in Chicago, IL), showing ability to run the Delta-style robot kinematic profile within their IndraMotion for Packaging control platform, along with kinematics for another 90 robot types.

Dan Throne, food and packaging industry manager at Rexroth pointed out: 'The delta style robot is currently a patented design, but the patent ran out in Europe in 2006 and runs out in the United States [at the] end of 2007.'

The system being demonstrated at the show consisted of seven motion axes: the four for the delta robot and three others to control conveyor belts carrying containers of mints that the robot was to arrange. The robot's task was to arrange the containers in a pattern on one of the conveyors with the logos all in the right direction. A bar set at an angle slid the tins from the 'output' conveyor to the 'input' conveyor while randomizing their positions and orientations.

A Cognex InSight machine-vision system monitored the tins' positions and orientations on the 'input' conveyor. 'The vision system notes [each tin's] position on the belt and the orientation of its logo,' Throne says, 'and the robot then picks them off the in-feed belt and places them on to the out-feed belt in an array with all the logos in a proper direction.

'We wanted to show that we could run the Delta style kinematic and the control but also do dynamic belt tracking or dynamic product tracking on the in-feed and out-feed belts as well as vision system integration. It's important to note that incorporating delta robot kinematics into the programmable automation controller software made it possible to write the robotic program in standard IEC 61131 ladder logic language, rather than a proprietary language.'

Throne lists the delta robot's advantages versus other robot styles as light weight, speed, and flexibility. For applications where the loads are small and need to be moved relatively short distances at high speed, the delta robot shines.

These advantages make it ideal for pick-and-place applications in the packaging and electronic assembly industries. www.boschrexroth.com





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