Delta robots vs SCARA robots

Ever since I wrote my feature article on the Delta robot, more than a decade ago, I’ve been wondering whether the Delta robot — or any similar parallel robot — is really better than a SCARA robot. Of course, the Delta robot, invented by Prof. Reymond Clavel some thirty years ago, has been a huge success. More than 10,000 units of pick-and-place Delta robots have been sold by ABB, SIG, BOSCH and many other companies. (ABB alone claims to have sold more than 1800 units.) Now, that the original patent of the Delta robot has expired, there are dozens of companies manufacturing Delta robots for material handling applications (FANUC, Motoman, KawasakiCodian Robotics, Asyril, etc.). Some of these Deltas are suspiciously low-cost (TOSY Robotics of Vietnam sells their TI P306-01 Deltas for $2,500 each), but in general, a 4-axis Delta robot such as the FlexPicker costs more than $40,000.

Of course, in theory, a Delta robot is supposed to be much faster than a SCARA robot. Both robots were introduced commercially in the early 1980s, but the SCARA robot concept  picked up steam much faster. According to the International Federation of Robotics, there are more than 10,000 SCARA robot installations… per year.

Five years ago, a major user of FlexPickers told me: “We have used SCARA and Delta style robots for high speed pick and place applications across our manufacturing network. The downside of SCARA robots is slower speed, greater footprint, and reduced flexibility. The early Adept robots were designed to handle heavy items, not cookies. Delta style robots, which include the SIG Delta, ABB Flexpicker, and Adept Quattro, offer an automation solution that is designed for high speed pick and place applications, integrated vision systems, and greater flexibility. We have delta style robots running over 120 picks per minute compared to 60-70 on a conventional SCARA. Therefore, the cost difference is minimal when utilizing half the number of robots for the same application.”

We at the ÉTS have ABB’s latest FlexPicker model (here is a video of the previous model). It flies like an arrow, but its accuracy is quite poor. We also built a high-speed five-bar parallel robot, which is highly accurate, but it is hardly as fast and as cheap as a standard SCARA robot. Indeed, you can purchase a good SCARA robot for less than $20,000. Only the motors of our five-bar robot cost $6,000 each…

Last year, Mitsubishi Electric launched a new top-mounted SCARA robot that can handle 188 parts per minute and is said to be up to 40% less expensive than Delta robots. A few months later, Stäubli launched their impressive top-mounted TP80 SCARA robot. The robot’s price starts at about $46,000, but it can handle 200 parts per minute (at a payload of 0.1 kg) and covers almost completely a circular area of 1600 mm in diameter. Adept’s Quattro parallel robot is still marketed as “World’s fastest industrial robot” but it can handle the same number of parts per minute (at 0.1 kg) and covers a slightly smaller working area.

I was recently told off-the-record by a key player that Delta style parallel robots are still sold mainly thanks to good marketing. Logically, parallel robots should be faster than serial robots. And they are surely more attractive and have more intricate designs (think of LIRMM’s Quattro or Laval University’s Tripteron). Search “Delta robot” in YouTube and you will see dozens of home-made Deltas, but you won’t see any do-it-yourself SCARAs. Parallel robots are fascinating, but if I had a cookie factory, I think I might consider purchasing SCARA robots instead.

 

About Ilian Bonev

Professor at the ÉTS
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