For many, today's SUV -- with its robust construction and large size -- represents the union of tough safety standards for on-road travel with the rugged performance necessary for off-road adventures. It's not surprising that an SUV manufacturing facility would use time-proven assembly line conveyors for the vehicles' construction. But equally striking are the steel frame automated guided carts (AGCs) being used as both traveling assembly stations for the instrument panel (I/P) subassembly process, and as the delivery conveyance getting the subassemblies to the vehicle assembly line.
The AGCs used at the vehicle maker's facility are an engineered hybrid of a system developed by Creform Corp. The carts are driven, routed, and controlled by Creform power units and guidance system while the welded frame, not typically used within the Creform system, provides a sturdy, firm base for the various assembly procedures. Normally, the Creform AGC system carts would be fabricated from the company's strong yet lightweight pipes, metal or plastic joints, and hardware accessories. But as a maintenance supervisor at the facility whose responsibilities include the AGC line reports, the carts were fabricated for durability in what can be at times a severe work environment.
"We built the carts with the heavy gauge steel framing for the rigidity that we thought would be advantageous for the assembly process," the supervisor notes. "It turns out that the flexibility of the system, afforded by the ease of installation and the simplicity to modify and rearrange routes, is one of the biggest benefits we found with the Creform AGC system. And, though a single control unit issues timing directives, the fact that each cart is independently powered and capable of individualized responses to isolated commands offers an additional level of agility that may be required to meet future production layout requirements.
"In the approximate 2 1/2 years that the system has been in use, its route has been altered several times. To change a route, one only needs to place adhesive-backed magnetic tape on the floor surface that a cart-mounted sensor follows. That's the guidance system.
"As a matter of fact, we've recently moved the offloading station of the assembled I/P, where the unit is mounted in the vehicle on the main assembly line," the maintenance chief continues. "The new location is working out well, so the AGC line is being reconfigured with a more permanent installation. That simply involves etching the floor with a 1/8 in. deep x 4 in. wide channel, then placing the tape in the recess and covering it with a protective epoxy coating. Because the instrument panel carts must cross an extremely high-traffic aisle on their way to reach the main vehicle assembly line, the channel/epoxy mounting method offered a greater level of protection for the tape."
Though many of the plant's personnel at first questioned the concept of the AGC moving assembly line, the system's performance has won over even the most skeptical. The line now has 10 carts running during the two shift operations at the plant. The I/P assembly process consists of 7 workstations, 5 of which are where assembly takes place; a quality control station is the 6th; and the 7th is the offload location. In addition, two carts with completed subassemblies are usually queued as a buffer, waiting for offloading while the 10th cart is returned to and prestaged in front of the first assembly station. The entire loop of the I/P assembly circuit is approximately 250 ft long.
At the assembly stations, an operator installs specific components of the I/P in place, which may include electronics and gauges, driver's controls, and HVAC. After crossing the busy aisle, the I/P install operator on the main line uses a lift assist mechanism to offload the panel and place it in position in the vehicle's passenger compartment. Currently, each operator is given approximately 4 1/2 minutes to complete their assigned tasks before the carts provide a warning signal, a safety delay, and finally move on to the next station in line.
At one of the stations along the route, Creform has placed what they call an "opportunity" charger where each cart's battery is automatically given a charge, every time through the loop. When twin photo sensors at the station and on the cart verify the presence of a cart in position, the charger's power leads are actuated, extending out to and making contact with the charging terminals on the cart. When the system calls for the carts to move, the charger's leads retract from the cart and it proceeds to the next assembly station. In addition, a charging station has been incorporated near the line to reenergize cart batteries during overnight downtimes.
The line's traffic controller is quite simple and consists mainly of two timers. One tracks the stop-time at each station and sends warning and start signals, while the second controls the timing for the warning alarm (light and horn) and activation of the queued carts at the aisle. When carts are positioned at the aisle crossing staging area, the alarm starts approximately 90 (adjustable) seconds prior to anticipated cart movement. Timing of the cart crossing can vary in that the cart must receive a signal from the controller that the assembly offload area is clear of the previous cart. This all-clear signal is relayed when the I/P install operator finishes the offloading process and manually pushes the now empty cart's start button, sending it on the return loop back to the start station.
Other commands to each cart -- for example, the stopping position at each station -- are even simpler than setting the control function. Typically all that is needed to send commands to a cart is to place small pieces of magnetic tape perpendicular to the guide path and in various sequences. When read by the cart-mounted magnetic induction sensor, one of these settings may slow down the unit in preparation for stopping or turning, then a second tape command will halt the unit. In other applications, where multiple loops and destinations may be necessary, tape commands, like railway switches, can send carts around alternating corners.
For the SUV manufacturing plant installation, the carts are equipped with Creform's Model FCH-A32 drive unit. This series has forward-only direction, a parking brake, and a load limit of up to 350 kg (770 lb), including cart weight. Dual travel speed ranges are provided with a normal operating rate of 79 fpm and a low speed of 13 fpm. A 24 in. minimum turning radius allows for floor area space-saving layouts.
And for the assembly team at the SUV plant, the Creform system has helped optimize the instrument panel build and the entire vehicle assembly process. "The simplicity of the AGC system has allowed us to try several layouts, to stretch out the line and make adjustments where necessary," the supervisor points out. "This would have been prohibitive with most other automated material handling and delivery systems, whether overhead or with embedded rails. They require time-consuming, expensive, and disruptive installations. With the Creform guidance system, it's as close to 'plug-and-play' as one can get, so there's no constraints to implementing the modifications and improvements."
While numerous applications of the AGC vehicles, like this SUV instrument panel assembly example, utilize custom designed and built carts, still many installations of the Creform AGC concept use the firm's pipe, joints, and hardware accessory components to build the carts. Ease of construction and the potential for numerous cart configurations allow users to produce vehicles to specific application requirements with respect to widths, heights, shelving, etc., then, with the addition of a bolt-on drive unit, convert the carts into an intelligent and economical automated material handling unit. A Creform AGC system can keep investment costs low, make guidance system installation easy, instill flexibility of both cart design and route in the system, and free up floor areas with narrow aisle needs as compared to large, wide-turn radius vehicles.
