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Allocating Reliability

Allocating Reliability. Planning for the Worst!. Effect. Overall System Reliability goes down as you add more components to the system. Typically the number of components is high That means you have to have more reliability in each component.

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Allocating Reliability

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  1. Allocating Reliability Planning for the Worst!

  2. Effect • Overall System Reliability goes down as you add more components to the system. • Typically the number of components is high • That means you have to have more reliability in each component. • If you add another component for redundancy in parallel you increase reliability but reduce your rate of return. • Don’t bank all your efforts on redundancy to improve reliability.

  3. How to allocate reliability • Overall reliability specified by customer. • Partition system into subsystems. • Assign known reliabilities. • Assign weights to unknown components based on complexity. • Allocate Reliability to unknowns • Use Parallel and serial models to check overall system reliability • Iterate • Margins

  4. Assigning known reliabilities in your robot • Ask the manufacturer the reliability of their part. • Direct field testing. • Engineering Estimates

  5. Assign weights to unknown components based on complexity

  6. Redundancy • Improves Reliability • Adds weight, space, $, power • Types • Operating redundancy (all systems in parallel fully operational all the time) • Standby Redundancy

  7. Standby Redundancy A B

  8. Standby Redundancy • Operating Period = 200 hours • Lamda = .002 failures per hour • Switch reliability = 1 (can’t fail) • Operational Reliability = Rop • Rop = 1 – (1 - e^(-lamda * t))(1 – e^(lamda * t)) = .8913

  9. Availability (inherent) • MCT = Mean Corrective Time MTBF A(i) = MTBF + MCT

  10. Availability (Achieved) • MCT = Mean Corrective Time • MTBM = Mean Time Between Maintenance • MPT = Mean Preventative Time MTBM A(a) = MTBM + MCT + MPT

  11. Availability (Operational) • MCT = Mean Corrective Time • MTBM = Mean Time Between Maintenance • MPT = Mean Preventative Time • AD = Administrative Delays • LD = Logistic Delays MTBM A(o) = MTBM + MCT + MPT +AD + LD

  12. Maintainability • concerns of ease, accuracy, safety, and economy in the performance of maintenance functions. • Design parameters • Maintenance : series of actions required to retain or restore a system to an effective operating state.

  13. Types of maintenance • Preventative: scheduled actions • Corrective: unscheduled

  14. Measures • Deals with time • Deals with labor hours

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