ระบบการจัดเก็บในคลังสินค้า

1. ระบบการจัดเก็บในคลังสินค้าระบบการจัดเก็บในคลังสินค้า

2. Storage Systems • Dedicated Storage Location Policy • Randomized Storage Location Policy • Class-based Dedicated Storage Location Policy • Shared Storage Location Policy • Continuous Warehouse Layout

3. Determination of Space Requirement

4. Dedicated Storage Location Policy • Also call “fixed slot storage” • Specific storage location is assigned to each product • Storage system • Part number sequence • Throughput-based dedicated storage Throughput: Number of storages or retrievals per time period เช่น 320 storages ต่อ 8 ชั่วโมงการทำงาน เป็นต้น

5. Space Requirement • One and only one product is assigned to a specific location • Number of storage locations assigned must be capable of satisfying the maximum storage requirement of product. • Determination method • Maximum storage location • Service level • Cost based

6. Space Requirement • Maximum storage requirement • The number of storage slots provided  max. storage requirement • See example (workshop)

7. Space Requirement • Service Level • Can be determined based on a probability of having sufficient storage slots to satisfy storage demand • Service level = Demand Satisfied/Total Demand • Let’s • Qj = Number of slots provided for product j

8. Space Requirement • Probability of having sufficient slots for product j is: P[Sj Qj] Sj represent the slot demand for product j The CDF of the function is: Fj(Qj) = P[Sj  Qj]

9. Space Requirement • Probability of 1 or more slot shortage P[1 or more shortage] = 1 – P[no shortage] • Hence, probability of no shortage for all product j = 1, 2, …, n P[no shortage] = (P[no shortage of product j]) P[1 or more shortage] =1-(P[no shortage of product j])

10. Space Requirement • Service Level • จากทฤษฎีความน่าจะเป็น เมื่อกำหนดให้ • Z แทนค่ามาตรฐานของตัวแปรสุ่มที่แจกแจงแบบปกติมาตรฐาน มีค่าเฉลี่ย และค่าเบี่ยงเบนมาตรฐาน เท่ากับ 0 และ 1 ตามลำดับ •  แทนระดับบริการ (service level) ที่ต้องการ

11. Space Requirement จะได้ จำนวน Slots ที่รับประกันระดับบริการ  คือ Qj = Mj + ZSDj เมื่อ Qj = จำนวน slots ที่ต้องการเพื่อรับประกันระดับบริการ  Mj = จำนวน Slots เฉลี่ยที่ต้องการต่อวัน SDj = ค่าเบี่ยงเบนมาตรฐานของ Slots ที่ต้องการต่อวัน • See example (workshop)

12. Optimized Qj Minimize Qj ST: (Fj(Qj))  P Qj  0 P = minimum probability of no shortage of storage slot

13. Space Requirement Maximize (Fj(Qj)) ST: Qj  S Qj  0 S = Total slots available

14. Space Requirement • Cost-based • Mathematical model is needed, (example) • Conditions: • There are fixed cost Co for “owned” storage Qj • The operating cost for owned storage is C1,t per space period • If owned storage is less than demand, the excess requirement can be leased at an operating cost of C2,t per space period

15. Example math. Model (cont.) Definition of parameters - Qj : ‘owned’ storage capacity for product j - T : length of the planning horizon in time period - dt,j: storage space required for product j during period t - TC(Q1,…,Qn) : Total cost function over the planning horizon as a function of the set of storage capacities - Co : discount present worth cost per unit storage capacity owned during planning horizon of T time period - C1, t: discount present worth cost per unit stored in owned space during planning time t - C2,t: discount present worth cost per unit stored in leased space during planning time t

16. Example math. Model (cont.) • Therefore, the Total Cost function is: • Fixed cost + Operating cost

17. Example math. Model (cont.) • min(dt,j,Qj) = dt,j if dt,j < Qj =Qjif dt,j ≥ Qj • max(dj,t-Qj,0) = 0 if dt,j-Qj < Qj = dt,j-Qj if dt,j-Qj ≥ Qj

18. Example math. Model (cont.) • Solution technique (one of them) • Let’s C’ = C0/(C2-C1) Then, • Sequence in decreasing order the demand for space • Sum the demand frequencies over the sequence • When partial sum is first equal to or greater than C’, stop; the optimum capacity equals that demand level

19. Example math. Model (cont.) • Take a hand on example and see if we can…

20. Assigning ProductsStorage/Retrieval Locations • Given That • s = number of storage slots or location • n = number of product to be stored • m = number of inputs/outs (I/O) points • Sj = storage requirement for product j, expressed in number of storage slots • Tj = throughput requirement or activities level for product j, expressed by the number of storage/retrievals (S/R) performed per unit time

21. Assigning ProductsStorage/Retrieval Locations • pi,j =percent of S/R tripe for product j that are from/to I/O point i • Ti,k = time required to travel betweenI/Opoint i and S/R location k • Xj,k = 1 if product i is assigned to S/R location k or 0 otherwise • f(x) = expect time required to satisfies the throughput requirement for the system • See workshop

22. Assigning ProductsStorage/Retrieval Locations • Mathematical model as shown can be used (also discuss via workshop)

23. Assigning ProductsStorage/Retrieval Locations

24. Randomized Storage Location Policy • Also known as “Floating Slot Storage” • Each open storage slot has equal chance of being assigned when a load arrive • In practice, when the load arrive, it is placed in the “closest” open feasible location • Retrieval occurs on a FIFO basis

25. Space Requirement • Storage space requirement equal the maximum of the aggregate storage requirements for products. • See example (workshop)

26. Dedicated (D) VS Randomized (R) Storage Location Policy • R requires less space than D • It is more difficult to determine the exact location of R than that of D • D requires less travel time (on average) in storages and retrievals of products

27. Class-based Dedicated Storage Location Policy • A compromise between dedicated and randomized storage location policies • Products are classified into classes according to their S/R ratios • Dedicated policy applies between classes while Randomized policy applies within each class. • See example (workshop)

28. Shared Storage Location Policy • Shared storage recognizes and takes advantage of the inherent differences in lengths of timethat individual pallet loads remain in storage