The Basics of Automatic Guided Vehicle Systems
System Management: Vehicle Dispatch
Onboard dispatch selector involves a control panel on each vehicle, which is used by an operator to dispatch the vehicle to a single, or series of stop stations. He may also select the function he wishes the vehicle to perform at the stop station. This is the most common form of system management and is usually the most flexible type.
An off-board call system can also be used for vehicle management in AGVS systems. These call systems vary in complexity from simple types which involve only a push button at a call location to stop the passing guided vehicle all the way to call terminals which not only can call a specific vehicle, but can also remotely dispatch that vehicle to other destinations without operator interface. Operators can input new destinations into the call box panel at their station, which will communicate those destinations to the guided vehicle after it leaves their stop location. This is useful in systems where load transfer is automatic.
A remote dispatch terminal can be used in systems to give a degree of centralized dispatching to the control of the guided vehicles in the system. The keyboard remote terminal approach allows an operator in a central location to control the individual guided vehicles form a central location. In order to do this the operator must have some visual status of the vehicles’ location and condition so that they might effectively dispatch vehicles to specific areas in the system where they are needed. This is usually a CRT graphic display or locator panel. Many times this approach is used in systems, which can't justify totally computer-controlled solutions yet, where a high degree of selective movement with automatic transfer is required. For example, if loads are received at a receiving area and taken to selective locations in a storage area with automatic load transfer used by the AGVS vehicles, then a centralized control many be an effective solution. A central operator would use the keyboard to send the vehicles to the receiving area to automatically pickup loads and then dispatch those vehicles to selected storage locations where the loads would be automatically dropped off.
Central computer control for system management is the highest level of control possible. The AGVS vehicles would respond to a central computer’s commands for where they should go and what they should do. This would be automating the previous case and eliminating the central dispatcher completely. Most integrated material handling systems incorporate central computer control for AGVS system management. In smaller dedicated systems such as picking up at production machines (injection molding, stretch wrapping, palletizing, machining, etc.), the AGVs are called to the production machine automatically when a load is ready for pickup. The computer control system can select the closest, available AGV for the task and then dispatch it automatically. Once a load is picked up, the central control system will communicate a destination to the AGV. This level of control permits automatic tracking of every load in the system. Where the volume is high and automatic load transfer occurs, the computer form of system management is very efficient.
It is also possible to mix these various forms of system management together at the same time in the same system. This depends on the type of control offered by particular vendors, but in many cases systems can be operated in several different modes at the same time. This is particularly useful if you have a sophisticated level of operation in your system and wish to have a backup to it in case the main level of operation control fails. For example, if your system is computer controlled and the central computer fails, then resorting to remote terminal control or onboard vehicle control would allow the AGVS system to continue to operate in the automated mode. Not all central computer control systems permit this type of operation but it is very important in certain situations. |
