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May 7, 2002

11 Min Read
Technology Notebook: Six-axis robots find a place next to the machine

Editor's note: In addition to linear-motion robots, whose development and applications are discussed in the Robotics/Automation feature, articulating robotics are becoming more involved in plastics operations. Here's a look at the articulating option by Editor Merle R. Snyder.


An overhead-mounted Fanuc articulating robot extracts a baby carrier from an injection machine and places it on a conveyor for transport to downstream stations for additional handling.


A workcell integrated by Robotic Production Technology that uses a Fanuc robot to deflash a fiberglass hot tub.

The manufacturers of articulating robots, also commonly described as six-axis robots, have begun to aggressively seek a larger niche in plastics processing. The units are increasingly recognized as an option, not only in parts handling for injection molding, but also in secondary operations related to blowmolding, thermoforming, and reinforced plastics processes.

Articulating robots, in contrast to the linear motion on rails provided by linear robots, move their end-of-arm tooling from one position to another through the use of multiple arms with rotating joints. The articulating motion has been described as anthropomorphic, which means the units give the appearance of having human attributes, notably arm-like and wrist-like motions.

In dealing with robots, the challenge to the processor is not necessarily to acquire a unit that can do anything, anytime, but to find the best match between the requirements of the situation and the capabilities of the equipment. The following text details several applications, including the development of end-of-arm tooling for a six-axis robot. Secondly, several six-axis robots that are specifically targeted to plastics processing applications will be identified.

Delphi Puts Six-axis Robots to Work
Delphi Automotive Systems recently added 16 injection molding machines to its interior systems production facility in Vandalia, OH. Along with the machines came 16 robots, all from Fanuc Robotics (Rochester Hills, MI). These systems represent the plant's first experience using articulated robots to unload parts from injection molding machines.

Delphi wanted a fully automated part removal system. The company had received orders for a variety of door panels, inserts, and modules for a wide range of vehicles and needed an automation system that was not only flexible but repeatable as well. Another factor in the decision to go with articulated robots was the need to accommodate low ceiling height clearances in the facility.

The overall system incorporates 11 M-16iT overhead rail-mounted robots working on 1500-ton injection molding machines, and five S-20 pedestal robots working on 3000-ton machines. The M-16iT robots are mounted on top of 1500-ton injection molding machines to unload automotive interior door panels and map pockets.

The M-16iT uses rotary axes, or articulated joints, for loading, unloading, and post-processing motions. It uses a linear axis for repositioning, allowing it to make flexible, human-like moves.

The six axes of freedom allow the robot to perform tasks that were typically reserved for a human operator. Most operations, from part rotation to intricate part placement and assembly, can be handled without expensive options or fixturing. The benefit of the rail-mounted configuration is that end-of-arm tooling is simplified, and in some cases can be shared between part runs. The robot arm is flexible enough to extract parts from the top or side of the machine.

The six-axis, S-420 robot has a payload of up to 175 kg (386 lb). The S-420 has a large work envelope and a 360* wrist rotation, allowing it to maneuver large parts.

For most of the operations, the M-16iTs perform the work of typical gantry extractors. As the injection molding machine opens, the M-16iT enters the mold cavity, extracts the parts, and places them onto a takeaway conveyor. For some operations, the simple extraction is coupled with value-added operations such as part degating or heat treating. When one of the additional tasks is required, the robot positions each part in front of a stationary heat gun or material removal tool. The robot's ability to articulate the part allows consistent positioning for secondary operations.

Since the 3000-ton machines do not allow enough ceiling clearance for a top-mounted robot, Delphi uses the S-420 robots to extract large inner door panels as well as interior and exterior trim pieces. The S-420s, which are installed beside each machine, easily change from one job to another without production interruptions.

RXplastics Robots Target Multiple Operations
The RX articulating robots from Stäubli (Duncan, SC) are already operating in plastics processing settings performing insert loading, high-speed parts removal, sprue picking, inmold decoration, glue laying, powder coating, painting, assembly, inspection, and packaging.

Eimo Americas has four custom injection molding plants in Texas and Michigan. The molding plants, formerly under the ownership of Triple S Plastics, serve a wide range of industries. Yet 60 percent of Eimo's business comes from the manufacture of mobile phone windows, covers, and other components for the wireless telecommunications industry.


Yushin America has signed an agreement with Motoman to integrate Motoman's articulated-arm robots and software with its own line of traversing automation equipment in applications that can benefit from the articulated approach in downstream operations, such as deflashing and assembly functions.

Eimo recently installed a new robot from Stäubli in an automated cell in its Georgetown, TX plant to demold, trim the gate, and package phone windows. Since then the company has ordered more than 10 additional robots of the same kind. The performance of the robots reassured the staff that it had made the right choice in moving towards more automation.

From the beginning, system personnel believed that flexible automation would continue to be the most cost-effective solution for many customer applications. Therefore, they were not looking for a robot to simply fill a specific need at the time as much as they wanted to find a robot that had the flexibility to meet the undefined automation requirements of future jobs. Stäubli's recently introduced RXplastics robot line is available in three models: the RX130plastics with a load capacity up to 25 kg and a maximum reach at the wrist of 2185 mm, and two smaller models, the RX60plastics and RX90plastics. The robot control comes preloaded with SPI (and Euromap 12) interface software to coordinate the movements of the robot with the actions of an injection molding machine, notably the ejector function. The graphical user interface reportedly makes the system easier to use.

The robots are approved for cleanroom operation to Class 100. Joint speed ranges to up to 1125* per second. Each robot uses the JCS gearbox, which is said to provide robot travel with zero backlash. Backlash can occur if a robot overaccelerates between positions. When it stops it has to find itself, which can cause it to twitch slightly.

Deflashing, Material Handling Showcased
Robotic Production Technology (Auburn Hills, MI) showcased its six-axis robotic capabilities for plastics deflashing and material handling earlier this year at the Plastec West show in Anaheim. RPT also provides equipment systems for laser trimming and drilling, router trimming, ultrasonic welding, and dispensing. RPT featured a small six-axis robot equipped with a compliance device and knife tool, simulating a deflashing application on a cooler lid. The compliance device compensates for part shrinkage and expansion and allows users to have constant compliance along curved or 90* parting lines on blowmolded or injection molded parts.

The automated deflashing process reportedly improves trim edge quality, as compared to manual operations, and reduces scrap generation. In addition, the automatic process is said to eliminate or reduce employees' risk of suffering carpal tunnel syndrome since manual trimming and cutting is eliminated. RPT has provided the knife trimming systems to several manufacturers.

RPT also featured a material handling cell with a six-axis robot handling a plastic container. Molders can reportedly improve their product by using robotic unloading vs. manual unloading to maintain consistency of mold open and close time.

The robots can also be used to perform secondary operations such as degating, deflashing, trimming, labeling, packing, or palletizing. The robot can unload multiple machines, allowing a flexible plant layout.

EOAT for Six-axis Robots Presents Challenges
End-of-arm tooling represents unique challenges for articulating robots. The flexibility of these five- and six-axis robots enables special applications such as peeling and certain insert molding applications not available to cartesian robot movements. Although only a relatively small segment of automated applications in injection molding use articulating robots, the right combination of robot and EOAT can be instrumental to a cost-effective, high-volume, multishift plastics processing operation, according to SAS Automation (Xenia, OH).


Construction of end-of-arm tooling for six-axis robots can be particularly challenging. This custom-tailored EOAT was produced by SAS Automation on behalf of Milacron for a proprietary automotive application.

In such applications, EOAT designs must allow sufficient room for the robot arm to unfold, as most tools will enter the molding press from the top or side. EOATs will normally be less complex as the robot provides multiple accurate motions within the cell.

Most of these robots do not come with a standard valve package. This must be added to accommodate the EOAT functions. Although programming for injection molding industry applications has been complex, it is improving and will increase the applications available.

Other advantages of the EOAT and articulating robot package, says SAS, include improved ability for gate cutting, deflashing, and interfacing with fixtures.

UP Robots Offer Versatility, Speed
The recently introduced UP20 six-axis robot from Motoman (West Carrollton, OH) is reportedly well suited for applications such as assembly, machine tending, material handling, material removal (such as deflashing), and dispensing. The UP20 robot features a 20-kg (44.1-lb) payload, a 1658-mm (65.3-inch) reach, and a repeatability of +/-.06 mm (.002 inch). The unit requires minimal installation space and can be mounted to the floor, ceiling, or wall. The UP20 robot is good for unloading plastic injection molding machines, particularly when complex motion is required to remove parts from molds.

The UP20 also has the flexibility to feed post-unloading operations and is suitable for deflashing and surface finishing operations—even on uneven surfaces or contoured parts. This feature is enhanced when the robot is equipped with a device that can automatically adjust the tool position to maintain a constant pressure against flat, wavy, or irregular part contours.

The robot can be equipped with a saw or other cutting device and used to remove runners or sprues from injection molded plastic parts.

The recently introduced six-axis UP6R shelf-mounted robot also provides a means for loading and unloading injection machines. Mounting on the fixed platen minimizes floor space requirements.

The six-axis robot can be used for molding applications where inserts need to be placed into the mold before plastic is injected. The UP6R robot also provides complex motion, if necessary, to remove parts from mold cores.

Motoman also offers a UPG floor-mounted unit for side-entry applications from the nonoperator side of the injection machine. The six-axis robots are flexible enough to feed downstream equipment for degating, assembly, printing, hot stamping, bagging, inspection, and material removal.

Both the UP6R and UP6 robots feature a 6-kg (13.2-lb) payload. The UP6R has a 1523-mm (59.96-inch) reach and the UP6 has a 1373-mm (54-inch) reach. Repeatability for both robots is +/-.08 mm (.003 inch).

Motoman, by the way, has recently entered into a relationship with Yushin (Cranston, RI), which will add an outlet for Motoman and allow Yushin to provide articulated robots as well as its line of traversing robots.

The IRB 4400 from ABB Flexible Automation (New Berlin, WI) is a compact robot with medium to heavy handling capacity. It can handle loads up to 60 kg, or up to 45 kg at very high speeds. Applications include material handling, machine tending, grinding, polishing, assembly, spraying, and cutting. The IRB 4400L/10 robot with its long arm and slim wrist is well suited for gluing and sealing.

Contact Information

ABB Flexible Automation
New Berlin, WI
(262) 785-3400

Fanuc Robotics North America
Rochester Hills, MI
(248) 377-7391

West Carrollton, OH
(937) 847-6200

Robotic Production Technology
Auburn Hills, MI
(248) 829-2800

SAS Automation
Xenia, OH
(937) 372-5255

Stäubli Corp., Robotics Div.
Duncan, SC
(864) 433-1980

Yushin America Inc.
Cranston, RI
(401) 463-1800

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