Automate for Flexibility
Robotics permits this automotive supplier to deal with batch runs of different frame configurations
By Ian Orr
Toploader Program Manager and Senior Engineer
Fanuc Robotics America Inc.
Rochester Hills, MI
In today's competitive climate, companies demand that suppliers be able to meet their needs quickly and without adding cost. Flexibility is the key to achieving these goals.
Each year UPF (Flint, MI), a leading supplier of truck and bus frames to the automotive industry, supplies thousands of truck and bus frames to its automotive customers. A key to UPF's success is its ability to deliver small, medium, and large batch runs of many different frame configurations. Although it provides a competitive advantage, the company's complicated production process prompted UPF to design a facility that incorporates a wide range of automation solutions to deal with challenges such as these:
- Customers provided as little as eight hours notice of a batch-run order for frame rails.
- Frame and stiffener rails have cutouts (round, square, or rectangular holes) located in one, two, or all-three sides. The cutouts are used either to attach other assemblies, including cross-frames, or to route utilities for the vehicle, such as fuel hoses, electrical cables, and hydraulic lines.
- Truck and bus frame and stiffener rails vary in length from eight to more than 40' (2.5 - 12 m), and weigh 200 - 900 lb (91 - 409 kg). A successful automation solution is necessary to handle this wide range of lengths and weights, especially when little or no time is allowed for changeover.
Working with two of its integrators, Citation Tool Inc. (Fraser, MI) and Custom Machines Inc. (Adrian, MI), UPF designed and built a robotic automation system that incorporated two robotic laser-cutting cells and two heavy-payload material-handling articulated gantries. The laser-cutting robots use a patented, shape-generation software package. Both articulated gantries employ a patent-pending approach where a single robot controller drives two independent robot arms to function as a giant reconfigurable gripper.
Two parallel lines make up the automation system, converging into a single manual frame-assembly line. The parallel automation lines provide UPF with the flexibility to manufacture completely different frame rails on each line, or to increase throughput by building the same type of rail on both lines.
Both automation lines begin with large CNC punch presses fed by servodriven pullers. Indexing-slide punch and button holders on the presses are preloaded with the multiple hole sizes to be punched in the frame rail. A blank frame rail or stiffener rail is attached to the servo-puller, which positions the rail lengthwise within the press.
After leaving the press, the servopuller delivers the rail to a Fanuc ARC Mate 120iB laser-cutting robot. Our company's ShapeGen software is used to program the ARC Mate 120iB to cut pre-determined holes or shapes through the vertical sides of the rail using a CO2 laser. The servopuller accurately positions the rail in the X axis in the laser cell, and the robot positions the laser head in the Z and Y axes for hole-location accuracy.
The rail is then conveyed into an automated material-handling area where one of three things may happen:
- The rail may pass through to the frame assembly area. This movement occurs if no further processing is required, and/or there are currently no rails downstream.
- The rail may be buffered (stored temporarily) on a storage rack. When a partially assembled frame rail is still present in the downstream frame assembly area, there's no room to receive rails from the laser-cutting cell. If the rail were to remain on the conveyor, it would act as a roadblock to all upstream laser cutting, and eventually to the punch press. To prevent this roadblock, a Fanuc dual-arm Toploader (articulated gantry) robot, consisting of two R-2000iA/200T robot arms mounted to the same overhead linear track, will remove the rail from the conveyor and automatically place it on a storage rack. This buffering process allows the laser and punch-press operations to continue without interruption. When the frame assembly area can accept a new rail, the dual-arm robot takes a rail from the storage rack, using FIFO (first-in, first-out) logic, and places it onto a conveyor to assembly.
- The frame rail may be combined with a stiffener rail. Many of the assembled truck and bus frames require that a stiffener rail be added to the main frame rail. These stiffener rails are matched to a particular frame rail (they receive the same punch-press and laser-cutting process). An additional complication is that the frame and stiffener rails come in left and right-handed variations (an assembled truck or bus frame has one left-hand and one right-hand frame rail connected by smaller cross-frames).
To ensure that the frame and stiffener rails are combined with the correct frame rail, the stiffener rails are manufactured just after the matching frame rails. The dual-arm robot must then match the appropriate rails to one another. When the frame and stiffener rails arrive in the material-handling area, the dual-arm robots match and combine the left and right-hand rails and stiffeners. Simultaneously, the robots align the various holes and shapes in the frame rail with the matching holes and shapes in the stiffener rail.
To reduce expensive work in process (WIP), UPF only stocks blank frame and stiffener rails. After the company receives an order, the appropriate frame rail is manually loaded onto a conveyor in front of one of the two punch presses, and connected to a linear servopuller. The C-shaped frame rails are positioned on the conveyor so that the horizontal back of the "C" is flat against the conveyor, and the L-shaped stiffener rails are positioned as needed. Through-hole shapes are then stamped in the rails by the CNC punch press. The linear servopuller positions the rail lengthwise under the punch press. Positioning of the rail and the action of the press are coordinated by a PLC to guarantee accurate and repeatable hole locations.
The servopuller removes the rail from the punch press, and moves it down to the CO2 laser-cutting cell. At this cell, various shapes are cut through the vertical sides of the frame and stiffener rails. Under control of a PLC, the servopuller positions the rail within the work envelope of the ARC Mate 120iB laser-cutting robot, and the PLC sends a signal to the robot controller to begin the cutting process. The robot controller, running ShapeGen software, makes a two-step laser cut on the rail. Its first cut uses a low-power laser setting to remove the paint along the path of the desired cut, ensuring a clean, efficient final cut. For the second cut, laser power is increased to ensure the desired shape is cut completely through the rail.
The software package gives robot programmers a choice of predetermined shapes (circle, hexagon, rectangle, slot, keyhole, or pommel), or they can configure a custom shape. The software also supports setting a kerf (cutting angle) to optimize the cut. As the rail is removed from the laser-cutting cell, it's pulled through a brush to remove any small metal particles created by the cutting process. Once the laser cutting is complete, the servopuller releases the rail onto a conveyor for delivery to the Toploader dual-arm robots.
If the rail doesn't require any additional processing and the downstream frame-assembly area is clear, the rail is conveyed straight through to the assembly area. If the frame rail has to be buffered to one of the eight adjacent storage areas or combined with a stiffener, then a dual-arm robot is pressed into action. To handle the UPF frame rails, Fanuc provided a dual-arm R-2000iA/200T Toploader robot powered by one robot controller. Each robot can handle a payload of up to 440 lb (200 kg) and is equipped with electromagnetic grippers, providing up to 16,000 lb (7300 kg) of lifting force. Rails less than 15' (4.6-m) long are light enough to be lifted from the conveyor by a single robot. Longer rails are too heavy for one robot and cause excessive wrist loading.
The patent-pending solution uses a single controller to coordinate the motion of both robots, effectively turning them into one 12-axis servogripper. When a long rail enters the robots' work envelope, one or both change position along the linear rail to ensure that they share the load equally. The position of a robot arm, relative to the second robot arm and also to the rail to be picked, varies considerably with each unique rail length. This on-the-fly servo-controlled adjustment allows adding rails of unknown lengths to the system at any time.
Once the two robot arms are positioned correctly along the rail, they move down and pick the rail up using electromagnetic grippers. When the electromagnets turn on and grip the rail, both robot arms are mechanically coupled, in that they must move together to lift, move, and place the rail. Whether the robots are moving under program (automatic) control or jog (manual operation) control, the motion of both arms is synchronized by the controller. Next the rail is either moved to a buffer location or, in a series of pick-place motions, combined with a stiffener rail. When the downstream frame assembly area becomes clear, a rail stored in the buffer location will be removed by the dual-arm robot and placed on the outbound conveyor.
This automated system gives UPF various short and long-term benefits:
- The company can produce and ship complete frame rails with minimal advance notice.
- The system eliminates storage of expensive, partially processed rails.
- The system's flexibility allows it to handle a large number of frame and stiffener rails with little or no changeover.
- New rail designs can be processed via simple reprogramming of the CNC punch press, servopuller, laser-cutting robot, and the dual-arm robots.
This article was first published in the September 2004 edition of Manufacturing Engineering magazine.