OPMT 303 1st Edition Lecture 11Previous Chapter Outline1. Production activity control2. Common scheduling criteria3. SPT, EDD, and CR characteristics4. Johnson’s priority ruleChapter Outline1. Quality Control2. SPC Errors3. Tools for Controlling Process4. Management of Waiting Lines5. System Performance: Basic MeasuresI. Quality controla. Two causes of process variationi. Random cause1. Random factors that are inherent in the process and beyond control. Inability of the process to execute perfection, exact duplication, on each successive output unit. Residual variations after all other behaviors are accounted forii. assignable cause 1. Malfunctions or specific faults in the system. Breakdown of equipment, absenteeism, lack of training. Corrective actions shouldbring the process back to statistical controliii. The essence of statistical process control is to assure that the output of a process is random so that future output will be randomII. SPC Errorsa. Type I error (α)i. Concluding a process is not in control when it actually is (false alarm)These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.b. Type II error (β)i. Concluding a process is in control when it is notc. Where to inspecti. Raw materials and purchased partsii. Finished productsiii. Before a costly operationiv. Before an irreversible operationv. Before a covering processIII. Tools for Controlling Processa. Control charts for variablesi. X-bar ii. R Chartsiii. Central limit theorem1. As the sample size increases, the distribution of sample averages approaches a normal distribution regardless of the shape of the sampled population with a mean µ and variance σ2/nb. Control charts for attributesi. P chartsii. Process capability1. Inherent variability of process output relative to the variation allowed by the design specificationsiii. Process capability ratio1. If the process is centered use process capability ratio CpIV. Management of Waiting Linesa. Waiting lines tend to form even when a system is not fully loaded because of variability in arrival of customers and service times of customersi. Notation: A/B/C1. A- arrival rates2. B- service rates3. C- number of servers (channels)b. Cost of Waiting Linesi. Loss of business: customers refusing to waitii. Cost of waiting spaceiii. Loss of goodwill: decrease in customer satisfactioniv. Delay in work process: inventory holding costv. Impact on other operations in the same process: disruption cuased by congestion at the bottleneckc. Queue disciplinei. Priority rules used to determine the order of customers1. FCFS: first come first serve2. EDD: earliest due date3. SPT: shortest process timeV. System Performance: Basic Measuresa. Capacity measuresi. Capacity utilizationii. Average number of customers waitingiii. Average number of customers in system1. Waiting + being servedb. Customer measuresi. Average time customers waitii. Average service timeiii. Average time in systemc. Decision variablesi. Arrival rates λ through marketingii. Facility capacity to increase
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