Computer controlled inspection for operation of plastic molding machine

Abstract

This report involves the overall design of a closed loop computer control plastic injection molding system and detailed design of the inspection portion of the system for a specific part. This project is concentrated on the inspection portion of the system. A part and its print specifications were provided. Design requirements called for 100% inspection of the critical part dimensions which were most subject to change. The main system constraints influencing the design were inspection accuracy and speed. The system also had to be designed using available hardware. A gaging system was designed to be used in conjunction with a Digital Equipment Corporation (DEC) PDP-8/I computer to inspect plastic parts produced by an Allrounder 100 injection molding machine. The design of a gage system that allows fast and automatic checking of the part requires sensitive instruments. Linear transducers were used in order that fast checking would be accomplished and allow the gage to be paced with the plastic molding machine. After the checking fixture design was completed and components ordered, a work station design was made in order to fully utilize the check fixture. Two designs were completed with one under an inspector's control and the other completely mechanized for future hookup with a computer controlled robot. A computer program was written to accept voltage signals from the transducers, convert them to part deviations, compare them to specified tolerances, and make an accept/reject decision on each part. The design is limited to one specific part, but that does not decrease the importance of the project because the parameters worked with are measured in all parts. The checking method may vary somewhat for different parts, but the basic concept will not change. The design phase is complete. It was planned that the building of the system should be completed in two successive phases and a third phase used for a critical evaluation of the system. In phase 1 the system should be completed, the computer software developed and tested, the checking fixture completed and checked out, and the manual work station designed in detail. Phase 2 would involve a balance of the work and decision making between the computer and the operator. The necessary computer hardware and software would be developed and debugged and the work station changed to allow automatic operation, thus saving an inspector's time. The final stage will be an analysis of phases 1 and 2 and possible further extension of the system to other parts so that it is more universal. The analysis will be directed at determining the economic feasibility of the system for industrial applications.