Automation Supplement

Battling Robots

By Mark Stephen, associate editor

Photos In This Story

Wittmann's W7x5 robots, with SCARA kinematics, are suited to pick and place applications of lightweight parts with fast molding cycles, e.g. cell phone, thin wall packaging parts, consumer electronic parts, etc. Typical removal times are in the range of 0.4 seconds for 400mm of in/out stroke motions.

The new Axess Twin beam robot from Sepro America, which comes with two vertical-axis arms for use with three-plate molds.

Ask any boxing fan and they’ll tell you: the key to a good contest lies in the matchup. When it comes to robotic automation, the champions have long been beam, or linear, robots, which are the first choice in North America owing to their speed, affordability and easy programming. The contenders in recent years have been the six-axis articulated-arm robots, which provide the same flexibility as the human arm, and are highly adaptable for performing secondary processing on injection molded parts. For the injection molder looking to make the right purchase, understanding the strengths and weakness of each is crucial.


In comparing the two technologies, some manufacturers begin by suggesting that beam robots are inherently better suited for injection molding operations, period. “Beam robots developed along with the injection molding machine, while the articulated-arm robots are really general-purpose systems,” said Jim Healy, vice president, sales and marketing, for Sepro America. “For suppliers of general-purpose articulated arm units, plastics are just another market.” Manufacturers and suppliers of articulated-arm robots argue that that actually works in their machines’ advantage, beginning -- in some instances -- with price. Although beam robots are often less expensive, the increasing use of articulated-arm robots in the automotive and other manufacturing industries has driven production volumes up, allowing for lower, often competitive prices for plastics production. “The return on investment (ROI) on a six-axis unit is still not as attractive as on a top-entry servo beam robot for smaller tonnage presses, but as you move to 500 tons and larger, costs equal out and the ROI on articulated-arm robots is similar,” said Doc Breger, automation sales manager for ACS Group, a channel partner integrator for ABB Inc. A related benefit, some suggest, is reliability. “Leading manufacturers of six-axis robots make between 12,000 and 15,000 units world-wide every year,” said Doug Niebrugge, plastics segment manager, North America, for ABB. “The sheer volume allows for greater reliability in six-axis robots.” Less need for maintenance is a third advantage, they continue. “In general, six-axis models require less maintenance than beam models,” said Larry Pascucchi, general manager for Negri Bossi Inc., a supplier for Kuka Robotics Corporation. “During the first 20,000 hours of operation of a Kuka six-axis robot, for example, there is virtually no maintenance required beyond periodic checks of fuel levels; this is not true for beam units.”


Manufacturers of articulated-arm units concede, however, that beam robots are still faster. “Even the fastest articulated–arm robots can’t match the speed of a servo beam robot for getting into a mold and picking out a part,” said Martin Pemberton, president of Sierra Automation Inc. But this gap is narrowing, they suggest, as articulated-arm models get faster, particularly for larger tonnage machines. “Above 500 tons, and especially into the 1,000 ton or more range, the speed advantage of the beam robot is decreasing,” said ABB’s Niebruegge.


Another longstanding advantage of beam robots is easy programming, and this has not been seriously challenged by articulating-arm units, according to some. “The six-axis robots often need a dedicated person trained to operate them,” said Troy Smale, automation manager for En-Plas Inc., which represents Yushin Precision Equipment. “They are not user friendly because they are designed to be a general-purpose robot rather than for injection molding.” The opposite is true for beam robots, according to Sepro’s Jim Healy. “The control systems of today’s beam robots were developed specifically for injection molding and they include a lot of built-in programming that facilitate their use in injection molding,” he said. “Programming can often be performed by a relatively low-skill operator with little or no formal training.” Others counter that the articulated-arm units of today are much simpler to set up and operate than just a few years ago, thanks to software that does the programming and simplified graphic interfaces that guide a technician through set-up. “ABB’s RobotWare Plastics programming environment offers an icon-driven touch-screen set-up that makes it easy for someone who is a top-entry robot user to transition to the controls of an ABB six-axis robot because it presents in the same fashion,” ACS Group’s Breger said. Nonetheless, the perception of more complicated programs on a six-axis robot remains a barrier to wider acceptance, ABB’s Niebrugge said. “There is a big fear in the marketplace that articulated-arm robots are very complex,” he noted. “And although the industry is addressing this with easy to use operator interface, it’s true that the programming is still more complicated.” This more difficult learning curve has, potentially, other disadvantages that purchasers should consider, some suggest. “Many employers don’t want to risk paying to send their employees on a three-week training course for an articulating arm robot only to have them leave and possibly join competitors a short time later,” said Michael Wittmann, general manager of Vienna, Austria-based Wittmann GmbH “There can also be problems integrating the articulating arm robots into a production line,” said Christian Weiss, technical sales, robots and automation, for Wittmann Canada. “There are many companies that know how to integrate a beam robot, whereas with articulated arm there are a very limited number of integrators, other than the actual supplier of the robot.” In response, manufacturers of the articulated-arm units point out that they are developing new relationships with systems integrators to ease a customer’s transition into the new technology.


These manufacturers also stress that even the addition of wrist motions on beam robots cannot alter the articulated-arm system’s advantage of a more flexible work envelope. “A six-axis robot has a spherical work envelope; it can reach above, below and all around itself, which adds versatility for performing actions outside the press,” said David Arceneaux, business development, marketing, for Staubli Corporation. In addition, they note, articulated-arm robots can be mounted in wider variety of positions than most customers realize, such as on top of the fixed platen, on the machine frame, or even upside down on the ceiling of the machine. “The average processor thinks articulated-arm robots are still mounted on the floor,” said John Nelson, plastics sales manager for Kuka. “The message that we’re trying to put out is that these units actually can do much more.” Others deny that six-axis robots have an advantage in this regard. “There are many configurations available for beam robots,” En-Plas’ Troy Smale said. “For example, Yushin’s three-axis robots have single arm or double arm for stack and three-plate molds, as well as a T-style traverse frame so you can discharge products on both operator and non-operator sides.” Manufacturers also point to developments with optional servo-wrist motions that have brought five- or six-axis capability to the beam models. Payload and required reach are other factors to keep in mind when shopping for a robot, manufacturers say; but here, too, opinion is divided. “A beam robot has the same payload across virtually the entire length of its stroke, whereas the articulating-arm unit may have lower payload capability at its maximum extension,” Michael Wittmann said. Manufacturers or articulating-arm robots counter that recent refinements have virtually eliminated this deficiency. According to ABB’s Niebrugge, for example, the company’s new IRB 6650s six-axis unit, which has a 3.9-m reach and a 90-kg payload, can manipulate parts as large as bumper fascias.


Manufacturers and suppliers of articulated-arm robots claim an increasing interest in the machines. “There’s definitely a growing demand for them in North America,” said Harold Luttmann, general manager, robotics, for Engel Canada. But despite a concerted push from manufacturers, and the growing buzz surrounding them, articulated-arm robots actually account for only a small portion of overall robot sales. “World-wide, articulated-arm models have only a four to five per cent share of the robot market,” said Michael Wittmann. “Linear robots remain the workhorses of the industry, and with recent developments in flexibility there’s very little they can’t do.” Wittmann also noted that, contrary to popular perception, linear beam robots are actually gaining market share in some segments of the plastics industry. “The cell phone industry was dominated in the past by suppliers who used articulated-arm robots exclusively,” he said. “Recently, however, more of them have been moving towards beam robots because of the quick part removal.” The debate among manufactures and suppliers over strengths and weaknesses of beam and articulated-arm robots will likely continue, but everyone agrees that both have a proper place, and that a customer’s selection should be based on this understanding. ”If the cycle time on an injection molding machine is short, and a pick-and-place movement is all that’s needed, then beam robots are the right choice,” said Negri Bossi’s Pascucchi. “However, if a molder wants to add value to a part or perform multiple tasks such as inspection, deburring and assembly during longer cycle times, articulated-arm units are an option they should consider.”

Resource List

ABB Inc. -- Business Unit: Robot Automation (Brampton, Ont.); 800-293-4503

ACS Group (Schaumburg, Ill.); 847-273-7700

Engel Canada Inc. (Guelph, Ont.); 519-836-0220

En-Plas Inc. (Toronto); 416-286-3030

Kuka Robotics Corporation (Clinton Township, Mich.); 866 873 5852

Negri Bossi Inc. (Mississauga, Ont.); 905-625-7257

Sepro America (Pittsburgh, Pa.); 412-459-0450

Sierra Automation Inc. (Cambridge, Ont.); 519-653-2919

Staubli Corporation, Robotics Division (Duncan, S.C.); 864-433-1980

Wittmann Canada Inc. (Richmond Hill, Ont.); 888-466-8266