Proceedings of the Multi-Disciplinary Senior Design Conference Page 7 s4

Proceedings of the Multi-Disciplinary Senior Design Conference Page 7

Project Number: P13716

Proceedings of the Multi-Disciplinary Senior Design Conference Page 7

andon system for tps lab

Trevor Andrews
Industrial & Systems Engineering / Holli Monroe
Mechanical Engineering
Emily Piccione
Industrial & Systems Engineering / William Wright
Mechanical Engineering

Proceedings of the Multi-Disciplinary Senior Design Conference Page 7

Abstract

The objective of this project was to introduce jidoka to the four-station assembly line within the Toyota Production Systems Lab at the Rochester Institute of Technology. Jidoka is a term used in the Toyota Production System that refers to diagnosing an abnormality immediately and correcting it accordingly so that defects are not passed along to the next operator. In order to improve quality on this line, two andon systems and a corresponding monitoring system were developed. An andon system is a system that is used to notify management, maintenance and other workers of a quality or process problem. One of the andon systems developed consists of a programmable logic controller (PLC) and simple electronics including push buttons and a light stack. The other andon system developed, which incorporated two variations, is purely mechanical in nature. In order to highlight and record abnormalities, which can later be used to perform root cause analysis and develop preventative countermeasures, a system for tracking and displaying abnormalities was designed alongside the andon systems.

introduction

In the Toyota Production System, lean manufacturing is represented visually by the “Toyota House.” The base of the house is “Stability,” the roof of the house is “Customer,” and the two pillars supporting the roof above the base are “Just-in-Time” and “Jidoka.” Stability refers to an extensive set of tools and concepts, which include Standardized Work, 5S, Kaizen, and Heijunka. The goal of lean is to satisfy the customer, which is why it is the most important part of the house. Just-in-Time pertains to production management. Jidoka relates to quality management.

The Toyota Production Systems lab in the Industrial & Systems Engineering department at RIT consists of two assembly lines. The main assembly line consists of four stations where product moves downstream via carriers with wheels. The other line is a roller conveyer, which was not included in the project scope. The lab enables students to learn almost all components of lean manufacturing, with the exception of jidoka quality management. The design objective of this project was to introduce jidoka to the four-station line via an andon system.

In order to improve quality on this line, two andon systems and a corresponding monitoring system were developed. The more in depth system includes push buttons and a light stack at each station, and a PLC to control the entire system. The purely mechanical systems were intended to be designs that could be implemented within a few hours. In order to perform root cause analyses, a LabVIEW program for tracking and recording abnormalities was created.

process

The design process utilized for the completion of this project was (i) customer need identification, (ii) specification development, (iii) benchmarking, (iv) concept generation, (v) system architecture identification, (vi) feasibility analysis, (vii) concept analysis, (viii) building, and (ix) testing/modification.

The planning stage of this project included (i) customer need identification, and (ii) specification development. The customer first expressed what system parameters were necessary, and helped to establish their relative importance, see Figure 1. From these needs, testable specifications with corresponding marginal and ideal values were developed.

Figure 1: Customer Needs

The systems design stage of this project included (iii) benchmarking, (iv) concept generation, and (v) system architecture identification. In order to gain a better understanding of andon systems in a production environment, benchmarking occurred at The Raymond Corporation in Greene, New York. Concurrently, concepts were generated and compared for the various subsystems of the project. At the same time, the system architecture, including both functional decomposition, see Figure 2, and process flow chart, was identified to ensure that all aspects of the project were to be fully developed.

Figure 2: Functional Decomposition

The detailed design stage of this project comprised of the (vi) feasibility analysis and (vii) concept analysis. This included analyzing the feasibility and viability of system functions, states diagram, PLC wiring, ladder logic, and drawings and schematics for both the digital display and mechanical systems, see Figures 3-5.

Figure 3: Global Display Final Concept

Figure 4: Mechanical System A Final Concept Figure 5: Mechanical System B Final Concept

The execution stage of this project consisted of (viii) building, and (ix) testing/modification. The hardware building portion involved disassembling the previous system, installing the push buttons and wiring them to the current lights, wiring the push buttons and lights to the PLC, and creating the network between the computer, PLC and human-machine interface (HMI). The software building portion included writing the ladder logic onto the PLC, creating the screens for the HMI, designing the LabVIEW program and creating the connection between LabVIEW and the PLC software. The assembly of the mechanical systems also occurred at this time. The testing/modification stage of the project involved testing 82 system states and assessing their behavior for accuracy. Accuracy was determined based on whether or not the global and local displays depicted the proper states, the light tree illuminated appropriately, music played appropriately, yellow andons escalated to red andons appropriately, and if the andon could be reset, see Figure 6.

Figure 6: Test Summary Excerpt

Results and discussion

The team leader of the assembly line begins the process by inputting the product’s takt time on the HMI touch screen and presses the start button, see electrical system diagram in Figure 7. The operators at each station must complete their assembly within the allotted takt time. Once the operator finishes their assembly, they are instructed to push the green button which will illuminate the green light on the light stack and display, indicating their assembly is complete. Once all four stations have green lights, the operators pass their assembly to the next station and the cycle resets. If they anticipate not completing their assembly or if there is an issue (defect, missing part or tool), they are instructed to push the yellow “andon” button. If the button is pressed during the first X% (default value of X% is 80%) of the takt time, the yellow light on the light stack and the LabVIEW display turns on, alerting the team leader of an issue(s) on the line. If the button is pressed during the last X% of the takt time, the red light on the light stack and LabVIEW display turns on. Once the issue is solved, the operator/team leader pushes the yellow button to turn the light off. If the issue is not solved within the first X% of the takt time, the yellow light will turn off while the red light turns on. If the red light is on at a station when takt time finishes, the red lights at all stations will illuminate and overtime will be recorded.

Figure 7: Electrical System Diagram

The functions of each of the push buttons and lights are controlled via ladder logic programmed onto the PLC. The PLC keeps track of the takt time that is inputted on the HMI screen in order to determine if the yellow or red light is illuminated. The HMI home screen has an input for the takt time and an input for percent andon escalation. The operation screen displays the elapsed takt time of that cycle, total downtime for the system and the amount of downtime each station has contributed. There is also start button on the home screen and stop buttons on both screens of the HMI, as well as a button to toggle between the home screen and the operation screen. The stop button is used to stop the system once assembly is complete so that it is no longer collecting data.

The LabVIEW program serves as a global display on the TV in the corner of the assembly line between stations one and two. From anywhere in the lab, the operators and team leaders will be able to see which stations are complete with their assemblies and which stations have pressed the andon button. The LabVIEW program will also collect and output data to track information regarding the number of times the andon is signaled and how much downtime is recorded.

The idea of the two mechanical systems is that they would be designed in a facility looking to implement andon into their assembly line within a day’s time. Both mechanical systems have individual visual and audio cues, see Figures 8 and 9. The first mechanical system is simply a stand that holds a yellow cone and a red cone. When the operator wants to signal the yellow or red andon, they move the cone from its original position to the top of the stand so it becomes visible to the team leader. The operator will shout to alert the team leader of the issue. The second mechanical system is also a stand with a magnetic white board and two magnetic circles that are red and yellow. Similarly to the other systems, when the operator wants to signal a yellow or red andon, they move the appropriate magnetic circle to the top of the white board so it can be seen by the team leader. For this mechanical system, a bell is attached for the operator to sound the bell in order to alert the team leader of the issue.

Figure 8: Mechanical System A Final Product Figure 9: Mechanical System B Final Product

Upon completion of the project, the vast majority of specifications were satisfied, see Figure 10. Due to LabVIEW VI difficulties, the auditory alert associated with an andon push was never successfully brought online. Multiple attempts to code the auditory loop of the VI were attempted, and, while successful in trial attempts, never passed the test of repeatability. Due to time constraints, the global display was never mirrored to local displays at each of the stations. If time permitted, the local displays theoretically would have been connected to the global display via online meeting functionality.

Figure 10: Specifications Check List

Conclusions and recommendations

The objective of this project was to introduce jidoka to the four-station assembly line within the Toyota Production Systems Lab at the Rochester Institute of Technology. In order to improve quality on this line, two andon systems and a corresponding monitoring system were developed. One of the andon systems developed consists of a PLC and simple electronics including push buttons and a light stack. The other andon system developed, which incorporated two variations, is purely mechanical in nature. In order to highlight and record abnormalities, which can later be used to perform root cause analysis and develop preventative countermeasures, a system for tracking and displaying abnormalities was designed alongside the andon systems.

The core objectives of this project were fulfilled. Three different andon systems were designed and implemented. These systems are easy to use, expandable, inexpensive, and have the ability to be incorporated into a paced line. Despite meeting or exceeding most specifications, the electrical andon system came up short with regards to the incorporation of an audible alert and use of local displays.

In order to improve upon the project, the electrical andon system may have benefitted from the use of a uniform set of hardware and software. As constructed, the electrical andon system incorporates a Siemens PLC, National Instruments OPC server, and National Instruments LabVIEW VI. Throughout the course of building, there were substantial connectivity issues between Siemens and National Instruments components. These issues baffled the project team, perplexed technical support representatives, and resulted in substantial time delays. If either all Siemens equipment or all National Instruments equipment had been used, it is conceivable that these connectivity issues would not have occurred.

Acknowledgments

The project team would like to acknowledge and express appreciation to RIT faculty member Scott Bellinger for all of his help and assistance in executing this project. Without Scott Bellinger’s continuous help and guidance, this project would not have come to fruition.