An automated storage and retrieval system for use in a flexible manufacturing cell

Abstract

The requirement of the project was to design an automatic storage and retrieval system (AS/RS) to be incorporated into a flexible manufacturing cell (FMC) at the University of the Witwatersrand. This flexible manufacturing cell currently being developed in the Industrial engineering department consists of a CNC milling machine and a CNC turning centre supported by an automated materials handling system, and an integrated computer control system. The automated materials handling system consists of a loop conveyor, parts transfer device, tool changing robot and the AS/RS. All the devices of the materials handling system have been constructed from low cost items readily available or alternatively have been manufactured at the University. The research philosophy adopted was to produce a low cost FMC, using local technology and expertise, to produce a system that is both economically feasible and relatively simple to implement. The AS/IRS is computer controlled consisting of three axis, driven by direct current motors. The AS/RS has a storage matrix of sixteen pallets (four by four) and is able to operate autonomously. The controlling software was written in turbo Pascal and designed to allow interface with the other material handling devices. The software allows for future incorporation of scheduling rules such as first in first out, shortest operating time or a schedule desired by the user. The AS/RS also allows the system to generate managerial reports on the status of the system as well as feedback to the FMC supervisory computer. The design was carried out with the same philosophy used In the FMC i.e, to use low cost items to provide an economically feasible design that is both flexible yet simple to incorporate within a FMC. In conclusion the AS/RS performs the required pick and place function with sufficient accuracy to ensure that parts are correctly positioned. The controlling program of the AS/RS functions correctly in terms of controlling the AS/RS. The AS/RS is fully autonomous in all operations. The AS/RS has the following specifications : Value Units Accuracy 3.67 mm Repeatability 7.2 mm Resolution 0.00977 mm Average pick & place time 41.6 s X Axis travel 1000 mm Y Axis travel 640 mm Z Axis travel 420 mm Lifting capacity 20 N Gripping force 10 N Degrees of freedom 3

The design can be further improved by using stepper motors instead of direct current motors to provide a finer control in terms of velocity and position accuracy. A!though the stepper motors need to have the same price for performance characteristics.