Automated coil handling and in-process inventory system, страница 3

The crane PLCs reside on the CHIPS network through the use of Aironet wireless ethernet bridges. There is one of these spread-spectrum radio devices on each crane and several redundant base station units on the ground, which feed into the level 1 network hub.

The crane PLC software is nearly identical from crane to crane. Once the software was fully commissioned for the first crane, minimal software checkout was required for the remaining cranes.

AGV system

Simulation indicated the need for 14 vehicles and 35 drive-through coil stands. Each coil stand has redundant coil presence sensors and an interlock light. Optomux remote I/O from Opto 22 communicates coil presence and interlock signals to the AGV system Alpha computer. The AGV sys tem computer also communicates to the vehicles via a redundant base station radio.

The AGV system computer receives job commands from the CHIPS computers. The AGV system manages vehicle selection for each job, routing of vehicles from place to place and control of traffic.

The AGV system operator screens (Fig. 4) are accessible from network PCs running Reflection terminal emulation. These screens allow viewing vehicle and job status. There are also screens to enable and disable stands and vehicles. The AGV system keeps track of coil move events, statistics and alarms in logs which may be viewed from the screens.

Guidepath and chargers - AGVs travel along a guide-path, which has passive transponders embedded in the floor roughly every 25 feet. Each transponder tag has a unique identity, which allows the vehicle to verify its location as it passes over. The path was built with AutoCAD and downloaded to each vehicle. Logical points on the path control traffic stops and vehicle functions such as turn signals and speed changes.

The system includes 15 opportunity stations for charging vehicle batteries. Vehicles are routed to these chargers hen there is no work to be done. There is a special charger for performing equalization charging to reset battery memory after every 100 hours of use.

Vehicles — Each AGV (Fig. 5) can carry a 60 ton coil. Empty travel speed is 200 feet per minute along a straight and 120 feet per minute on a curve. Loaded speed is 120 feet per minute along a straight and 80 feet per minute on a curve. Vehicles are equipped with four-wheel drive and four-wheel steering. A hydraulic system handles the steering, lift deck and stabilizer arms. Each vehicle has four sealed lead-acid gel-cell batteries for a total of 2000 amp-hours. These batteries, when fully charged, allow the vehicle to operate continuously loaded for up to four hours before requiring another charge.

Each vehicle has an on-board radio for communication to the AGV system computer. An on-board processor controls the movement and devices on the vehicle. There is a control panel on each vehicle with a status display and keypad for performing diagnostics.

Vehicle guidance is managed by the on-board processor, which handles signals from several devices. A trackwheel encoder measures distance between path points. A solid-state gyro measures inertia as the vehicle turns. A transponder reader sees coded magnetic tags in the floor and converts the code into a guidepath location. Vehicles have in-position optics, which give the vehicle positive indication that it is at a coil delivery location. On either side of the lift deck, there are optics that allow the vehicle to center under the coil it is picking up.

The AGVs have a number of safety devices. On their front and rear are seven object detection sonics, which will bring the vehicle to a controlled stop until the object is removed Compressing the front, rear or side bumpers will cause the vehicle to perform an emergency stop. There is an emergency stop mushroom button on each corner of the vehicle and one on the diagnostic panel. Also on the panel is a button for a controlled stop. Vehicles have flashing lights from and rear, turn signals on each corner and a multitone horn for indicating various stages of movement. There are additional optics on the sides of the vehicle, which also cause an emergency stop to prevent the wheels from rolling over top of an object approaching from the side.

Summary

At the Rockport Works of AK Steel, automated coil movement systems were custom designed for the layout and flow of material. Five automatic cranes typically move about 1200 coils per day and have a capacity of about 2000 moves per day. Fourteen AGVs move about 600 coils per day and have a capacity of about 1000 moves per day. The central computer system that supervises all of these moves also updates the inventory in the level 3 business system. The automation systems for all these coil movements were designed to be flexible and reliable.