Skip to content

Storage & Inventory

Racks, bins, and inventory management.

Storage Hierarchy

Warehouse
└── Racks
    └── Levels
        └── Bins
            └── SKUs (with quantities)

Racks

Definition

Physical storage structures containing multiple levels of bins.

Properties

Property Description
id Unique rack identifier
node Map node location
levels Number of vertical levels
bins_per_level Bins per level

Example

racks:
  - id: "R1"
    node: "N10"
    levels: 5
    bins_per_level: 20
    # Total: 100 bin locations

Bins

Definition

Individual storage locations within a rack.

Addressing

Bins are addressed by:

(rack_id, level, bin_number)

Example: (R1, 3, 15) = Rack R1, Level 3, Bin 15

Capacity

Each bin can hold one SKU type (simplified model).

SKUs

Definition

Stock Keeping Units - unique product identifiers.

Properties

  • SKU ID (e.g., "SKU001")
  • Quantity at each location

Placement

placements:
  - rack: "R1"
    level: 2
    bin: 5
    sku: "SKU001"
    quantity: 100

Inventory Flow

Pick Operations

  1. Order specifies SKU
  2. System locates SKU in storage
  3. Robot travels to rack
  4. Item picked, quantity decremented

Putaway Operations

  1. Inbound items arrive
  2. System assigns bin location
  3. Robot travels to rack
  4. Item stored, quantity incremented

Replenishment

When bin quantity drops below threshold:

  1. Replenishment task created
  2. Robot retrieves from reserve
  3. Bin replenished

SKU Popularity

Zipf Distribution

Models realistic popularity:

  • Few SKUs are very popular
  • Many SKUs are rarely picked
orders:
  sku_popularity:
    type: zipf
    alpha: 1.0

Alpha Effect

Alpha Distribution
0.5 More even
1.0 Standard Zipf (80/20 rule)
1.5 More concentrated

Storage Strategy

Slotting

Place fast-movers near stations:

  • Reduces travel time
  • Improves throughput

Zoning

Group related SKUs:

  • Zone A: Fast movers
  • Zone B: Medium movers
  • Zone C: Slow movers

Level Assignment

Ergonomic considerations:

  • Levels 2-3: Fast movers (easy access)
  • Levels 1, 4+: Slow movers

Capacity Planning

Total Capacity

Capacity = Σ(levels × bins_per_level) for all racks

SKU Coverage

Ensure sufficient locations for:

  • Active SKUs
  • Safety stock
  • Seasonal inventory

Example Configuration

racks:
  # Zone A - Fast movers
  - id: "ZoneA_R1"
    node: "N10"
    levels: 4
    bins_per_level: 15

  - id: "ZoneA_R2"
    node: "N11"
    levels: 4
    bins_per_level: 15

  # Zone B - Medium movers
  - id: "ZoneB_R1"
    node: "N20"
    levels: 5
    bins_per_level: 20

placements:
  # Fast movers in Zone A, ergonomic levels
  - rack: "ZoneA_R1"
    level: 2
    bin: 1
    sku: "SKU001"
    quantity: 500

  - rack: "ZoneA_R1"
    level: 3
    bin: 1
    sku: "SKU002"
    quantity: 400