Robots Help Assembler Break the Mold
TASUS Corp. (Bloomington, IN) manufactures injection-molded plastic parts for a variety of automotive components. It also provides a range of assembly operations, including ultrasonic welding, vibration welding, leak testing and the attachment of gaskets, brackets and other hardware.
A battery of robots is critical for maintaining a high level of productivity at the plant. In addition to four-axis gantry robots, which remove parts from injection-molding presses, TASUS now has several workcells that use six-axis and SCARA robots from Motoman Inc. to perform tasks such as dispensing, assembly, ultrasonic welding and degating. Vision systems are used extensively in the cells to ensure part quality.
"We installed our first Motoman robot in 2001 and now have 13 of them," says Jim Lanman, director of research and development at TASUS' parent company, Tsuchiya North America. "Robots provide us with tremendous flexibility.
"We run production on some of these robot cells three shifts a day, five or six days a week, and they're very reliable. Robotic automation and vision inspection help us provide the consistent quality demanded by our customers and also meet the part traceability requirements of the automotive industry."
"Our first six-axis robot was put into place to do something we did not want our operators to do," explains Robert Elliott, engineering manager at TASUS. "We needed to apply primer to a plastic part. The primer was not something that you would want on your skin. By putting the primer in an applicator and having the robot apply it, we were able to keep the primer and the operator at opposite ends of the curing conveyor.
"We now design and build our workcells around robots. We use them to do all sorts of things. We love it when people say, ‘No one else does it that way.' We integrate vision system cameras into the workcell and sometimes right onto the robot arm. We verify [the parts] before, during and after each step. If any problems are found, the robot can automatically stop the process and place the bad parts in an isolation area. We try to prevent bad parts, rather than trying to pick out the bad ones from the good ones after the fact."
In the primer cell, a Star four-axis gantry robot removes a pair of automotive headlamp housings made of polypropylene from a 720-ton press and places them in a fixture in front of an SV3J six-axis robot. A PLC is not required to coordinate this activity. Discrete I/O signals between the robots control the cycle.
Equipped with a dispensing head, the six-axis robot applies a narrow bead of liquid primer in a V-shaped pattern onto the outside edge of the housings. The primer contains luminescent dye that glows blue when exposed to black light. This feature makes the primer visible to two DVT vision sensors from Cognex Corp. (Natick, MA), which inspect the parts to ensure that the right amount of primer was dispensed in the right spots.
If the vision system detects insufficient primer on the part, the six-axis robot picks up a new bottle of primer from a nearby slide mechanism using a gripper with angular jaws. The robot can change bottles at any time in the process without shutting down the molding press. The robot verifies that the bottle is full and a wick is present. If the robot detects a problem with the bottle, it takes the bottle to a chute and releases it. The robot then picks up a new bottle from the slide. A tower light and an audible alarm signal the operator that the cell needs a new standby bottle or that the robot has trouble gripping the bottle. The robot then returns to the part and applies primer from the new bottle. The part must pass inspection by the vision system before moving on to the next step in the process.
For the next operation, the same SV3J robot uses an automatic tool changer from ATI Industrial Automation (Apex, NC) to switch from applying primer to placing stickers. A machine from Accuplace (Plantation, FL) presents stickers to the robot. The six-axis robot uses a small vacuum cup to pick up and apply an adhesive strip to the housing. DVT vision cameras check the part for the presence and positional accuracy of the adhesive strip. If the part fails, the gantry robot places it into a reject bin. If the part passes, the gantry robot places it onto a conveyor. Operators then manually pack the parts for shipment.
TASUS' customer for these headlamp housings is a major automotive supplier. "We looked at some of our customer's innovative uses of Motoman robots, and [that led us to consider how we could use robots] at our facility to standardize work and improve efficiencies," Lanman says.
"Seeing the robots in action at our customer's site, we realized the flexibility that [robots could provide]," adds Doug Vaughn, an automation specialist at TASUS. "The application is pretty demanding in terms of range of motion. We needed the six-axis robot...to match all the angles and contours of the part."
TASUS uses SV3X, UP6 and UP20 six-axis robots and an HM four-axis SCARA robot to assemble several different power steering reservoirs for American and Japanese automotive customers.
Operators manually load all of the components for the reservoir onto a pallet that indexes around a loop conveyor. The reservoir consists of four parts: the cover, baffle, filter screen and base. A DVT vision system checks for the presence of all the components prior to the first welding operation.
The first robot, an SV3X, uses a parallel gripper to grasp the reservoir cover, rotate it to the correct orientation, and place it on top of the base. A capacitive proximity switch on the robot arm verifies that the baffle is present inside the reservoir before a vibration welder from Forward Technology (Cokato, MN) welds the cover onto the base.
"Common components are used to construct many different models of reservoirs. After welding, each reservoir is unique because the tube angles differ. This provides flexibility as to where the reservoir will be located under the hood and also allows many configurations for hose connections," Vaughn says.
The line currently produces six different parts, says Vaughn, who likes the flexibility of the robots. "We can program in new robot jobs for new products and use the existing pallet without retooling," he explains. "This eliminates a lot of cost because there are multiple pallets on the line. The flexibility afforded by the robots eliminated the need for specific pallets for each product."
Each reservoir is tested for leaks with a pressure decay system. A four-axis SCARA robot removes the reservoir from the pallet and places it into a custom fixture. The SCARA was chosen for this task because of its fast and accurate motion capabilities. "Because the leak testing cycle is long, we needed to move the parts from the pallet to leak test and back as quickly as possible," Vaughn says.
At the next station, a six-axis robot installs the cap on the reservoir. "Our customers specify the amount of torque used to twist the cap on, and the Motoman UP6 robot has the capability to limit its torque and also monitor whether or not the twisting motion stalls as it is trying to install the cap," Vaughn explains. "If the motion stops prematurely, it indicates a problem, such as an improperly located O-ring or flash issues on the cap. The robot will fail the part in that situation."
The same robot also presents the finished reservoirs to a DVT vision system, which verifies the presence and orientation of the baffle in the reservoir. A bright LED backlights the part, making the internal components discernable to the vision system. The robot then presents the part to a laser marking system, which marks the part with a unique serial number.
TASUS has now added a third reservoir line. By benchmarking the two previous lines, the company has found ways to lower capital cost and increase accuracy and flexibility. The new line has two UP20 and three UP6 robots. Ultrasonic and vibration welding, leak testing, assembly and laser serialization are all performed with the help of these robots.
Robot Degating Cell
The lenses for some automotive taillamps are molded from acrylic. After molding, the lenses need to be degated. Two robots handle the job.
A Star four-axis gantry robot removes the part from the molding machine and presents it to an SV3X six-axis robot for degating with a carbide cutting wheel. Discrete I/O signals coordinate the activity of the robots and the molding press.
The end-of-arm tooling on the six-axis robot is a Dremel-style tool that first cuts through the gate using the edge of the carbide wheel and then smoothes the surface using the wheel face. The wheel is coated with tungsten carbide grit, so it can push in and sand the gate off flush with the rest of the part. For flexibility, the robot is equipped with an ATI automatic tool changer that will allow a pneumatic nipper or other tools to be used in the future.
After degating, the gantry robot places the lenses onto a conveyor, which transfers them to a manual inspection and packing station.
Filler Neck Assembly
A pair of robots assembles a plastic part called a remote filler neck, which is the part of the engine where the consumer adds coolant to the radiator.
A Star four-axis gantry robot unloads the part from the injection molding machine and places it onto a conveyor. Next, an operator places two compression limiters, a metal radiator cap and a black plastic cover cap onto a custom fixture located in front of an SV3X six-axis robot. An Allen-Bradley Micrologix PLC from Rockwell Automation (Milwaukee), along with several sensors on the fixture, verify that all the components are correctly loaded.
The PLC instructs the robot to move and grasp the molded part. At the same time, pneumatic cylinders press in the compression limiters and screw on the radiator cap. As the cap is rotated, a torque cell from Omega Engineering Inc. (Stamford, CT) monitors the peak torque applied to the part. If the torque exceeds a maximum limit or the compression limiters are not pressed to the correct depth, the robot places the part into an appropriately marked reject bin.
The next phase is pressure decay leak testing. Again, if the part fails, the robot places it into a labeled reject bin. If the part passes the leak test, the robot presses it down onto the black plastic cover cap until it snaps in place.
The robot performs a final inspection to verify that all of the assembly steps have been completed successfully. The robot then moves the assembly in front of a laser sensor that can detect if the cap is loose or if the compression limiters are not seated completely.
Next, the compression limiters are subjected to a push-out test. The robot moves the assembly to a spring-loaded pin and attempts to push out the compression limiters. This is done to ensure a tight fit. The last inspection is accomplished by the robot moving the assembly over an inductive proximity switch. The switch detects the metal of the compression limiter and makes sure the parts did not slip during the push-out test.
Finally, the robot presents the part to an ink-jet printer, which sprays on a unique serial number and a part number designated by the customer.
The robot moves the part in a straight linear path at a constant speed while the ink-jet applies the numbers. Then, the robot places the part on a conveyor, and operators manually pack the parts for shipping.
"We are always looking for ways to push our imagination and creativity to a new level in order to remain competitive. The use of robots and vision systems...will continue to be a big part of our growth," Elliot says.
Supplier Contact Information
For more information about robots, call Motoman at 937-847-3288, visit www.motoman.com, or eInquiry 20.
For more information about machine vision, call Cognex at 877-264-6391, visit www.cognex.com, or eInquiry 21.
For more information about equipment for handling adhesive-backed components, call Accuplace at 954-791-1500, visit www.accuplace.com, or eInquiry 22.
For more information about robotic tool changers, call ATI Industrial Automation at 919-772-0115, visit www.ati-ia.com, or eInquiry 23.
For more information about PLCs, call Rockwell Automation at 414-352-2000, visit www.rockwellautomation.com, or eInquiry 24.
For more information about torque sensors, call Omega Engineering at 800-848-4286, visit www.omega.com, or eInquiry 25.
For more information about vibration welders, call Forward Technology at 320-286-2578, visit www.forwardtech.com, or eInquiry 26.
For more information about injection molded plastic parts, call TASUS at 812-333-6500, visit www.tasus.com, or eInquiry 27.