OPMT 303 1st Edition Lecture 11 Previous Chapter Outline 1 Production activity control 2 Common scheduling criteria 3 SPT EDD and CR characteristics 4 Johnson s priority rule Chapter Outline 1 Quality Control 2 SPC Errors 3 Tools for Controlling Process 4 Management of Waiting Lines 5 System Performance Basic Measures I II Quality control a Two causes of process variation i Random cause 1 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 for ii assignable cause 1 Malfunctions or specific faults in the system Breakdown of equipment absenteeism lack of training Corrective actions should bring the process back to statistical control iii The essence of statistical process control is to assure that the output of a process is random so that future output will be random SPC Errors a Type I error 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 III IV V b Type II error i Concluding a process is in control when it is not c Where to inspect i Raw materials and purchased parts ii Finished products iii Before a costly operation iv Before an irreversible operation v Before a covering process Tools for Controlling Process a Control charts for variables i X bar ii R Charts iii Central limit theorem 1 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 and variance 2 n b Control charts for attributes i P charts ii Process capability 1 Inherent variability of process output relative to the variation allowed by the design specifications iii Process capability ratio 1 If the process is centered use process capability ratio Cp Management of Waiting Lines a Waiting lines tend to form even when a system is not fully loaded because of variability in arrival of customers and service times of customers i Notation A B C 1 A arrival rates 2 B service rates 3 C number of servers channels b Cost of Waiting Lines i Loss of business customers refusing to wait ii Cost of waiting space iii Loss of goodwill decrease in customer satisfaction iv Delay in work process inventory holding cost v Impact on other operations in the same process disruption cuased by congestion at the bottleneck c Queue discipline i Priority rules used to determine the order of customers 1 FCFS first come first serve 2 EDD earliest due date 3 SPT shortest process time System Performance Basic Measures a Capacity measures i Capacity utilization ii Average number of customers waiting iii Average number of customers in system 1 Waiting being served b Customer measures i Average time customers wait ii Average service time iii Average time in system c Decision variables i Arrival rates through marketing ii Facility capacity to increase
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