Performance characterization Don Clausing Don Clausing 1998 16 881 Fig 1 Failure modes Noises lead to failure modes FM One set of noise values leads to FM1 Opposite set of noise values leads to FM2 Simple problem solving chases the problem from FM1 to FM2 and back again but does not avoid both FMs with the same set of design values endless cycles of build test fix B T F Don Clausing 1998 16 881 Fig 2 Failure modes occurrence Failure modes occur when the essential performance characteristic deviates excessively from its ideal value Some failure modes are simply values that deviate so far that output is not useful e g voltage from power supply is too low Some failure modes are catastrophic e g paper that arrives too soon jams in copier Don Clausing 1998 16 881 Fig 3 Performance characteristic What is good performance characteristic to use when reducing the occurrence of failure modes Don t merely count occurrence of failure modes Can t distinguish between following two cases Don Clausing 1998 16 881 Fig 4 Case 1 easy to fix Occurrence of failure mode FM1 FM2 Don Clausing 1998 16 881 Fig 5 Case 2 difficult to fix Occurrence of failure mode FM1 FM2 Don Clausing 1998 16 881 Fig 6 Case 1 and Case 2 Both cases have same failure rate But situations are very different Counting failure rate is very weak approach to the reduction of failure rate Concentrate on ideal function What is the system supposed to do Then make system do it all of the time Don Clausing 1998 16 881 Fig 7 The engineered system Noise Signal System Response Control factors Don Clausing 1998 16 881 Fig 8 Ideal function RESPONSE Ideal function response SIGNAL M 16 881 Fig 9 Don Clausing 1998 Actual response RESPONSE Ideal response Effect of noises M1 16 881 SIGNAL Fig 10 M2 Don Clausing 1998 Keep performance close to ideal Identify ideal performance function response Then make actual performance stay as close as possible to ideal Linear response is called dynamic desired value for response depends on input value of signal Don Clausing 1998 16 881 Fig 11 Examples of dynamic response Car turning radius Car stopping distance Copy quality Casting Electrical resistance What are the signals Don Clausing 1998 16 881 Fig 12 Case study hitch Used to connect implements to tractor Transmits power from tractor to implement We can all see its function But what is a good engineering statement of its function Don Clausing 1998 16 881 Fig 13 Functions of hitch Provide mechanical interface with implement Provide proper vehicle performance Meet ISO dimensional requirements Protect people from moving parts Don Clausing 1998 16 881 Fig 14 More detail on first function Provide adequate performance in working range Proper attitude through working range Provide adequate depth Provide adequate lift capacity at breakout Provide Draft Control Provide adequate performance in transport mode Provide adequate height Provide proper kick angle Provide adequate lift capacity at transport Provide easy hookup and disconnect Provide easy linkage adjustments Don Clausing 1998 16 881 Fig 15 Yes but what is ideal function Meet ISO dimensional requirements Protect people from moving parts are important generic requirements but are not elements of the ideal function Don Clausing 1998 16 881 Fig 16 Functions of hitch Provide mechanical interface with implement Provide proper vehicle performance are related to ideal function Candidate for ideal function Transmit load Don Clausing 1998 16 881 Fig 17 Forces on system H I T C H H IMPLEMENT TRACTOR W FT FF FD FR FS Don Clausing 1998 16 881 Fig 18 Noises in the field HARD ROWS Change in earth impedance causes forces to change Which changes do we wish to minimize Don Clausing 1998 16 881 Fig 19 Keep what constant Constant force Constant depth of engagement into the soil Constant power Don Clausing 1998 16 881 Fig 20 Candidate ideal function Ideal function response Actual depth SIGNAL depth set by farmer Don Clausing 1998 16 881 Fig 21 Determination of ideal function Identify the performance variations that we would like to go to zero The performance that remains when the undesirable variations are zero is the ideal performance In the hitch case further analysis tests and discussions with customers are needed to identify verify ideal function Don Clausing 1998 16 881 Fig 22 Ideal function Want Ideal Response to Signal usually straight line function Definition is often not trivial In the absence of explicit definition the objective of improvement activities is unclear success unlikely Don Clausing 1998 16 881 Fig 23 Signal noise ratio Measure of deviation from ideal performance Based on ratio of deviation from straight line divided by slope of straight line Many different types depends on type of performance characteristic Larger values of SN ratio represent more robust performance Don Clausing 1998 16 881 Fig 24 Summary Knowing ideal function is crucial for success we have to know where we are trying to get to or it is unlikely that we will get there in a reasonable time Requires detailed engineering analysis of conditions for customer satisfaction Don Clausing 1998 16 881 Fig 25 End