Automated Guided Vehicle System

The AGV system described below was originally developed by a company called Flexible Manufacturing Systems (FMS) in California for an international pharmaceutical company. However FMS was unable to make the system work, mainly due to software problems, and eventually went out of business.

The pharmaceutical company then called Helix Systems, Inc. to see if the project could be salvaged. After a virtual rewrite of the entire software over a period of several years (and some minor hardware changes), the system was made to work reliably and as intended.

The system consists of two AGVs designed to move trays of vaccine vials in a sterile production facility. The main purpose is to reduce human handling of the material and thus the risk of biological contamination.

The veichles are electrically powered carts that can move over preset paths. The paths are not permanently laid down on the floor like conventional AGV systems, but reside in a data base, and are, thus, readily changeable. The vehicles guide themselves via inertial navigation, with periodic fixes based on laser scanning of special mirrors mounted in fixed locations.

The system is controlled by an external computer, which talks to the vehicles over infrared data links. This system also controls various plant equipment; opening and closing doors, starting and stopping conveyor belts, etc.

The system software consists of many modules written in several different languages running on varied types of hardware. Summary of the modules:

• System controller - a VAX system controlling the entire operation. Software is in C using the VMS operating system. It consists of several modules interconnected via messaging and a local (RAM) data base. These modules include:
  
  
  • System manager - The overall control program for the system. Controls the jobs to be performed, individual tasks assigned each vehicle, etc.
    
    
  • Vehicle manager - communicates with and sequences the vehicles; maintains vehicle status.
    
    
  • Component manager - communicates with and controls the factory machinery interfacing with the vehicles (doors, conveyor belts, etc).
    
    
  • Terminal manager - interfaces to the operator terminals (PCs) via TCP/IP.
    
    
  • Infrared manager - interfaces to the vehicles via infrared data links.
    
    
  • Database manager - acts as a buffer between other processes and the relational data base, so processes are not slowed by lengthy accesses.
    
    
  • Server - a relational database server. Controls all actual data base accesses. Connected internally to the database manager and externally via TCP/IP to the operator terminals.
  
  
• The vehicles each contain four different linked computers. These are:
  
  
  • Main vehicle computer (MVC) - the overall controlling computer for the vehicle. A 68000 running a multitasking operating system called USX. Programs are written primarily in C with some assembly language subruoutines. This computer contains a number of software modules which communicate with the system control computer over the IR link, sequence the material handling hardware on the vehicle, and communicate with the subordinate computers listed below.
    
    
  • Drive computer - controls the movement of the vehicle. A Z80 programmed in C plus extensive assembly language. This computer interfaces with the front wheel drive motor, a steering motor, an odometer and a rate gyroscope. It moves the vehicle an exact distance at a precise direction (relative to the current heading of the vehicle) when told to by the MVC.
    
    
  • Docking computer - A Motorola 6303 computer programmed in assembly language. When directed by the MVC, scans using a rotating laser for specially formulated mirrors that return a reflection when the laser is pointed at each end and when the laser is perpendicular to the mirror. Returns the three angles found, from which the MVC is able to calculate the position of the vehicle, using the known position and orientation of the mirror.
    
    
  • Sonar computer - A Motorola 6303 computer programmed in assembly language. Uses a number of sonar transducers to sense for obstacles in the path of the vehicle. If an obstacle is found, alerts the MVC.
  
  
• Operator terminals - PC compatible terminals used for operator interface. Programmed in C and assembly language under DOS. Allows the operators to control the entire operation. Also produces various reports, using data extracted from the relational data base in the VAX. A graphic display is provided, which shows the exact loaction of each vehicle at all times, plus the status of each factory component interfaced to the system.
  
  
• PLC - An Analog Devices MicroMac-6000 device programmed in BASIC. Acts as the digital I/O interface for the VAX when communicating with factory devices.

One of the most challenging technical aspects of this system was the design of the routing and traffic handling software for the system. The requirements were for two vehicles to be operating simultaneously in a rather restricted area (approximately 30 ft. by 180 ft.) carrying product at random between 6 different pickup points and 10 discharge points.

The routing problem was to get a vehicle from source to destination in the least possible time considering the paths available and the predicted path of the other vehicle.

The traffic control problem was to assure that two vehicles never occupied the same spot at the same time or were on the same line segment at the same time. Vehicles were not always where they were predicted to be when routes were assigned (for example a vehicle could unexpectedly stop for a while if an obstacle was detected in its path).

Of course deadlocks (when both vehicles were trying to get to the same point at the same time) had to be avoided whenever possible, and if they occured there had to be a deadlock breaking mechanism.

All of these problems (and many others not mentioned) were solved and the customer was extremely pleased with the result after implementation.