Circuit Troubleshooting Based on Applying Lean Six Sigma Techniques

This paper presents Lean Six Sigma techniques and methods that Electrical Engineering Technology (EET) students have found useful in their in-class circuit troubleshooting activities. When students are first learning circuit analysis and fabrication, they often lack the skills to troubleshoot failed circuits based on a specification. In addition to presenting the tools used in the instruction of the test student group this paper also describes how the Lean Six Sigma method were used to arrive at the optimal course content. For this paper, two student groups, in an EET laboratory experience, are compared based on the primary metric number of failed attempts to meet circuit board test specifications. The student test body was divided into two groups. A control course section group, where no troubleshooting instruction was given and designated the “As Is” state. The second section group, “Improved State” was given an extensive troubleshooting methodology as part of their initial training. The primary metric, number of failed attempts to meet specification, was chosen as it is easy to measure by student Teaching Assistants (TA) and was also used to assess the Sigma process capability for each group. The Sigma capability of each group provided a further measure of the overall success of the intervention. The authors quickly realized that students in the control group were making two classic types of errors. Many students were making a rule or knowledge-based error, where students were not following the instructions for the specific circuit fabrication and test. This type of error was addressed by improving instructional material and adding root-cause analysis checklists to the course content. The second type of observed error, where a student is incorrectly applying a base skill to the construction protocol, is classified as event-based and is more difficult to resolve. Theoretically, there can be many possible solutions to an event based error. Perhaps there may even be no optimal solution to the error, or “right answer,” just a work around that students must find. To address this type of error students were instructed how to apply Lean Six Sigma tools such as root-cause analysis and Failure Modes and Effects (FMEA) matrices in their problem-solving sessions. Also, Sneak Analysis was included to address typical design flaws. Introduction The course targeted for this project is ECET 10700 Introduction to Circuit Analysis. This course teaches dc circuit analysis and laboratory skills to freshman electrical, computer and healthcare management engineering technology students. The students have already demonstrated competency in college algebra, and during the last part of the course are able to apply trigonometric functions in the context of reactance calculations. They have had previous instruction in problem identification, computer applications for calculations and graphing, and laboratory report writing. For some of the students, the lab assignment targeted in this project is the first time they have measured resistance, current or voltage in the laboratory. During the lecture, they have learned about the concepts of resistance, current, and voltage. They have been introduced to Ohm’s Law, and have been instructed that an ammeter should be in line with the current to be measured. However, it is during this lab period that they will test their understanding of these concepts in a practical way. The instructions for this lab assignment begin by having the students locate three resistor values and verifying their values and tolerance. Then the students are instructed to build the circuit in Figure 1. This circuit is simply a resistor mounted in series with a dc voltage supply and dc ammeter. The dc voltage measured across the resistor should be the same as the voltage supply. The objective of the assignment is to verify Ohm’s law by graphing the current-voltage relationship for three different resistors. Over several semesters, instructors and teaching assistants have noticed a variety of mistakes students make during this assignment. When students struggle with equipment and circuit connections, they grow frustrated and cannot meet the objectives of the lab assignment. We were looking for a way to improve student performance during the circuit building and measurement components of laboratory assignments. The Rapid Lean Six Sigma, Kaizen, process management method was utilized to provide a framework for the entire project management process. Kaizen is a Japanese word that describes the concept of continuous process improvement that involves all branches of a facility or company and is typically associated with the rapid or intense activity and workflow. The Kaizen method of managing events is now part of every Lean Six-Sigma facilitators toolkit. Kaizen is most effective if the specific issue or project solution is known, easy to find, or can practically be described as a “quick hit.” Typically a Kaizen event will last for 3-5 days where most of the time is spent in preparation for the trial solution event that may only last a matter of hours. Figure 2 illustrates the process steps and requirements for a Kaizen event that was followed throughout this project. Figure 1 Circuit for Laboratory Assignment Figure 2 The Kaizen process overview One of the project goals is to provide mistake proofing and prevention tools that our students can use not only within the confines of this laboratory experience but also be part of their troubleshooting arsenal that can be applied to future courses and jobs. To address this requirement another Lean Six Sigma tool referred to as Poka-Yoke (error prevention) was inserted into the Kaizen event. The Kaizen event, Figure 2, can be viewed as the high-level process and the Poka-Yoke tool is the structured problem-solving technique applied to the problem. Poka-yoke (poh-ka –yoh-kay) was developed by Shigeo Shingo as part of the Toyota Production System, or ZQC, Shingo’s Zero Quality Control System. The idea of this system is to have sufficient detection mechanism such that mistakes are prevented from occurring and propagating through the manufacturing process. The Poka-Yoke technique requires that both mistake prevention, the ability to stop mistakes from occurring, and mistake proofing, making it impossible for a mistake to occur, must be addressed simultaneously. There is no universally accepted procedure for Poka-Yoke; however, the eight steps that follow are generally accepted as fulfilling the basic requirements of this technique. Step 1: Describe the Problem • Create a clear, complete problem statement. Describe how it impacts the customer. Step 2: Use a Team Approach to ID the process and process step causing the error • Construct a process flow diagram and identify the point of deviation. Step 3: Contain the problem • Always stabilize the current situation. Step 4: Find the Root Causes . • Techniques to search for the root cause can include: • The Five-Whys • FMEA • Data Collection plus Analysis • Design of Experiments (DOE) Step 5: Develop Mistake-Proofing Solutions • Use the Brainstorming technique to find possible solutions. • Always think outside of the box. • Do your solutions work in practice? Step 6: Implement the Solution • Apply a simple action plan. Step 7: Prevent Errors From Occurring Again • Test the solution; make sure the solutions work. • Is the solution is robust or does it need to be simplified? Step 8: Congratulate the Team We held a Kaizen event, including the students and teaching assistants, aimed at improving student performance when building circuits and collecting voltage and current data. Experimental procedure Although the faculty have been aware that students struggle in lab, no data had been collected that would identify and quantify the types of student mistakes associated with this assignment. Therefore, an experienced lab instructor listed typical student errors for each part of the assignment. This list of common errors was transferred to a tally sheet for data collection. (See Figure 3 for an excerpt.) Table 4 OBSERVATION ERROR Number The DMM (ammeter) reads 0 mA Ammeter incorrectly located Ammeter lead incorrectly ported Ammeter fuse blown Power supply issues The voltage indicated at the power supply is less than that expected, and the current reading on the power supply is 1.0 A Circuit built incorrectly There is a short across the resistor Ammeter is installed across resistor Voltage indicated is different from that calculated Resistor value is incorrect Resistance calculated is off by more than the 10% expected. Indicated voltage error Calculation error Figure 3 Excerpt from tally sheet Two laboratory sections were used in this experiment: the control group met on Wednesday, and the intervention group on the following Monday. The tally sheets were used by the instructor and teaching assistants during the Wednesday lab period to quantify the students’ issues. After the lab period, the data was evaluated, and the prevalent types of mistakes were identified. Two days later, during the Friday recitation period, the authors led all the students in a process mapping activity (see below). On the following Monday, the intervention laboratory section was observed and student issues were tallied. Intervention Between the lab periods of the control group (Wednesday) and the experimental group (Monday), the class in-total meets for a recitation period (Friday). These meetings are led by undergraduate teaching assistants who also support students in the laboratory. The recitation topics are selected by the course instructor and TAs in conference and vary based on the week’s objectives: organizing parts kits, practice problems, test review, and general concept questions. At beginning of the recitation session, the class met together for approximately ten minutes for an introduction to Structured Mistake Proofing and Prevention, process mapping and instructi