By Mary Kay Morel, staff writer/editor, Motoman Inc.

The New Holland Agriculture plant in New Holland, Pa., manufactures a wide variety of agricultural equipment, including round balers.

Until recently, roll weld assemblies that to form the bale were welded on a robotic system that was installed in 2002.

Parts were manually loaded, unloaded and clamped using traditional weld fixturing.

Trunnions we relocated manually inside the tubes and pre-tacked prior to presentation to the robot. Both the trunnion weld assemblies and the tubes were clamped in V-blocks.

With this method of holding the parts, all part and material variations were thrown to one side. That resulted in run-out between the shaft and tube, and misalignment between trunnion discs and tube slots.

In addition, welding the trunnion outside diameters (ODs) to the tube inside diameters (IDs) had to be done out of position using coordinated motion between the robot and the positioner.

Getting a good weld on the smaller diameter rolls was difficult.

Weldments had to be checked 100 percent, percent and straightened to maintain run-out requirements. Misalignment resulted in costly extra operations to grind and repair welds manually.

In 2007, the New Holland plant implemented a fully automated robotic work cell to weld rolls. The new work cell holds enough parts to support as much as two hours of unattended production. The new robot cell significantly improves part run-out tolerances and weld quality while reducing direct labor related to loading/ unloading parts. It also eliminates the need for checking roll run-out 100 percent and straightening rolls.

Misalignment between the tube slots and trunnion discs is rare, so grinding and weld repairs have been nearly eliminated.

One robot loads and unloads a mechanical slide fixture that is mounted on a headstock positioner, and the other robot welds the parts.

“Our primary objective was to eliminate the run-out variances and to consistently produce a quality weldment.

The extra operations required to ensure that a quality part went to the assembly line increased the roll weldment part cost significantly, and we wanted to eliminate or at least significantly reduce this cost,” Bob Burkholder, operations specialist for manufacturing processes and technology for New Holland, said.

Burkholder and Clint Hinkle, a welding/manufacturing engineer for New Holland, had primary responsibility for implementation of the new robot system.

“We looked at many alternatives, including machining the tubes and trunnions and a redesign of the rolls, but these approaches would have increased the part cost,” Burkholder said.

“Working with Motoman, we developed the concept that provides even better part quality and higher savings then we initially thought we could achieve,” he added.

Motoman HP200 with a multi-function gripper transfers trunnions from a rotary table positioner and tubes from an infeed conveyor onto a mechanical slide welding fixture mounted on a heavy-duty headstock positioner. A Motoman HP50 welds the parts, then the HP200 robot unloads welded assemblies onto an outfeed rack.

Parts
Round baler roll weldments consist of tubes with trunnions on each end that are robotically tackwelded in place, plug-welded, then final-welded around the entire circumference of the end seam.

Parts are made of 6.0 mm to 6.6 mm (0.24 in. to 0.26 in.) thick ASTMA500 steel.

The robot system accommodates 18 different assemblies that are batch run.

Welded round baler rolls are 1,318 mm to 1,959 mm (51.89 in. to 77.13 in.) long and weigh 21.8 kg to -37.2 kg (48-82 lbs). Additional part variations are determined by the presence, position and/or lack of holes and slots. Trunnions must be inserted accurately to the proper depth in the tubes.

Run-out tolerance must be within ±1.5 mm (0.060 in.) for tubes and ±0.4 mm (0.016 in.) for trunnions. Trunnions must be aligned precisely in the tubes to allow for proper plug welding, and for final alignment of the rolls in the round baler.

Any misalignment (run-out) can lead to vibration that causes wear and, ultimately, can cause weld failure in the field.

“The use of self-centering jaws on the weld fixture and the robot manipulator to hold the trunnions and the tube significantly reduced the run-out variances.

That assures that the trunnion always will be inserted into the center of the tube, despite material and part variances,” Hinkle said. He is in charge of day-to-day operations of the robot cell.

“The trunnion fixture jaws are mounted on servo motors so we can accurately insert the trunnions inside the tube to the correct depth.

On the average, tube run-out is in the neighborhood of 0.508 mm. to 0.635 mm (0.020 in. to 0.025-in.) and trunnion run-out is approximately 0.0508 mm to 0.1524 mm (0.002 in. to 0.006 in.).

The amount of run-out and consistency of the run-out we are seeing is better than we anticipated,” Hinkle said.

Workcell Equipment
Tubes enter the robot cell via a gravity in-feed device that includes a singulator. Trunnions enter the robot cell via a Motoman MR-300 rotary positioner.

The standard MR-300 positioner has a 300 kg (661.5-lb) capacity per side and a 4 sec. index time.

However, for this project, the positioner was modified for a higher – 400 kg (881.8 lb) capacity and a 5 sec. index time.

Two fixtures – one per side of the positioner – holds as many as 24 trunnions.

A six-axis Motoman HP200 robot with a 200-kg (441 lb) payload, 2,651 mm (104.4 in.) horizontal reach and ±0.2 mm (±0.008 in.) repeatability performs the handling operations within the cell.

Custom end-of-arm tooling is designed to transfer one tube and two trunnions. Two large grippers simultaneously grasp the tube, while two sets of smaller gripper jaws hold individual trunnions.

A laser sensor on the robot gripper, along with a sophisticated software search routine, is used to find holes and slots in the curved tube surface.

Motoman HP50 robot tack-welds, plug-welds, and then make a circumferential weld around the end of the part during the final welding sequence.

The tube then is rotated to locate the holes or slots in the proper position for welding. To eliminate any misalignment errors due to damaged slots or dirt in the slot, the laser sensor also measures the slot length. If the slot is not the proper length, the sensor moves to the next slot.

This laser sensor also verifies the part number and tube length and diameter based on the location and presence or absence of

specific part details. The HP200 transfers two trunnions from a rotary positioner along with individual tubes from an in-feed device to a servocontrolled mechanical slide weld fixture mounted on a heavyduty Motoman MH3000 headstock positioner with a 3,000-kg (6,613-lb) rated load and 4.95-second 180-degree sweep.

Prior to being loaded onto the fixtures, a laser sensor at an inspection station checks each trunnion part to determine the length of the welded trunnion shaft and its position relative to the gripper.

This information is used to determine exactly how far the mechanical slide portion of the fixture will insert each trunnion into the end of each tube.

The servo float function is applied in a unique way for this project.

Servo float is typically used to relax a robot axis to allow an external force to move the manipulator arm slightly, such as when the robot grasps a molded part in a die cast machine before ejector pins push the part out of the mold.

For this project, the servo float function was installed on an external axis (positioner slide) rather than being on the robot. Servo float engages when the trunnion is being inserted into the tube.

If the assembly of the trunnion to the tube should fail, the servo float function detects the mis-assembly and notifies the operator.

The robot controller commands the headstock to reposition the parts during the welding process to facilitate robot access to both sides of the tube for the tack-welding, plug-welding and final-welding operations.

The slide fixture has the same type of Yaskawa servo motors as the robots, and these motors are controlled by the robot controller.

The ends of the slide fixture open and close, as required, to allow the Motoman HP50 robot to tack-weld, plug-weld, and make a circumferential weld around the end of the part during the final welding sequence.

A beefy 50-kg (110.2 lb) payload, general-purpose robot like the HP50 with 2,046 mm (80.6 in.) horizontal reach and ±0.07 mm (±0.003 in.) repeatability is not typically used for arc welding applications.

However, to access the welds, this particular application required a reach that was a few inches longer than that of most of the application-specific welding robots or lower-payload, generalpurpose models commonly used for welding.

The New Holland hay baler.

After the Motoman HP50 robot welds the parts, the HP200 robot unloads them onto a gravity outfeed chute with three-level racks that include rack-full sensors.

Changeover between part runs requires very little manual intervention. Some part sizes require the gripper jaws to be changed out. Generally, changeover between part models and sizes is automatic and simply involves selection of another robot program.

The system includes a purge program that allows the HP200 robot to transfer tubes directly from the in-feed rack to the outfeed rack when changing over the cell to run different tube sizes.

This purge feature improves safety by eliminating the need for manual handling of the heavy tubes.

Controls
Both Motoman robots are controlled by two NX100 DR2C robot controllers, interfaced as a single controller with one programming pendant.

Should New Holland decide to reconfigure and/or redeploy their robot cell in the future, the DR2C controller configuration provides additional layout flexibility that would allow the two robots and controllers to be separated.

One NX100 controller can control as many as 36 axes of motion, or as many as four robots with a single programming pendant. So, the existing cell could have been configured using just one robot controller for the two robots and the external axes, including the headstock positioner and Yaskawa servo motors that are used for positioning the trunnion gripper slide on the weld fixture provided by the plant.

This work cell uses an Allen- Bradley SLC 5/05 Programmable Logic Controller (PLC) with a MotoHMI user interface for overall cell control.

Results
The Motoman system exceeds New Holland’s requirements for quality improvement.

It consistently holds run-out tolerances of less than 0.2 mm (0.008 in.) on trunnions and 0.75 mm (0.030 in.) on tubes. That is twice as good as the original requirement.

The robot cell produces highquality parts and has significantly reduced extra operations and the direct labor costs that are associated with extra operations.

The new system exceeds the plant’s requirement to support one hour of unattended production Its achieved cycle time – (5 min. to 6min. per part, depending on the part number and whether it has slots – meets the facility’s requirements, and is expected to improve as the plant implements additional tooling and part changes.

“The cell was installed in late August 2007, and has been running without significant problems since then. Except for weld gun maintenance, the cell runs the entire shift, through breaks and the lunch period,” Hinkle said.

“At the end of the shift, we fully load the tube in-feed and trunnion positioner.

The cell then runs as long as two hours, depending on which roll we are welding, with the lights out. During the shift, the operator who runs the Drive Roll cell also runs an adjacent robot cell,” he said.

“It was a real team effort between Motoman and New Holland to get us where we are today with this cell,” Hinkle said.