Skip to content

Station Assignment

Selecting which station serves a task.

Problem

When multiple stations can serve a task, which one should be used?

Task: Deliver item for picking

Available Pick Stations:
  S1: 3 robots queued, 10m away
  S2: 1 robot queued, 25m away
  S3: 5 robots queued, 8m away

Which station?

Assignment Policies

Nearest

Select closest station:

policies:
  station_assignment: nearest

Algorithm:

  1. Find stations that can handle task type
  2. Calculate distance from current position
  3. Select nearest

Example:

Robot at N15

S1: distance = 10m
S2: distance = 25m
S3: distance = 8m   ← Selected

Pros:

  • Minimizes travel
  • Simple

Cons:

  • May create imbalanced loads
  • Longer wait times at popular stations

Shortest Queue

Select station with fewest waiting robots:

policies:
  station_assignment: shortest_queue

Algorithm:

  1. Count robots queued at each station
  2. Select station with shortest queue
  3. Tie-breaker: nearest

Example:

S1: 3 queued
S2: 1 queued   ← Selected
S3: 5 queued

Pros:

  • Balances station utilization
  • Reduces wait times

Cons:

  • May increase travel distance
  • Doesn't consider service speed

Fastest Completion

Select station where task will complete soonest:

policies:
  station_assignment: fastest_completion

Algorithm:

  1. Estimate completion time for each station:
  2. Travel time to station
  3. Wait time in queue
  4. Service time
  5. Select station with earliest completion

Example:

S1: travel=10s, wait=45s, service=15s → 70s
S2: travel=25s, wait=15s, service=15s → 55s   ← Selected
S3: travel=8s, wait=75s, service=15s → 98s

Pros:

  • Optimizes for task completion time
  • Considers all factors

Cons:

  • Requires accurate estimates
  • More computation

Due Time Priority

Select based on task urgency:

policies:
  station_assignment:
    type: due_time_priority
    urgency_factor: 1.5

Algorithm:

  1. For urgent tasks: fastest completion
  2. For non-urgent: shortest queue or nearest

Comparison

Policy Travel Wait Time Balance
Nearest Low Variable Poor
Shortest Queue Medium Medium Good
Fastest Completion Variable Low Good

Station Capacity

Queue Limits

Stations may have queue limits:

stations:
  - id: "S1"
    queue_capacity: 10

Handling Full Queues

Options when queue is full:

  1. Skip: Choose another station
  2. Wait: Wait at distance until queue opens
  3. Overflow: Allow temporary overflow
policies:
  station_assignment:
    type: shortest_queue
    full_queue_behavior: skip

Multi-Station Scenarios

Station Zones

Assign stations by zone:

policies:
  station_assignment:
    type: zone_based
    zones:
      zone_a: [S1, S2]
      zone_b: [S3, S4]

Tasks in zone A use S1 or S2.

Fallback Stations

Primary and backup stations:

policies:
  station_assignment:
    type: nearest
    fallback_enabled: true
    fallback_threshold: 5  # Queue length

Use primary if queue < 5, else fallback.

Dynamic Assignment

Real-Time Adjustment

Reassign if conditions change:

policies:
  station_assignment:
    allow_reassignment: true
    reassignment_threshold_s: 60.0

Conditions for Reassignment

  • Original station queue grows significantly
  • Closer station becomes available
  • Original station goes offline

Station Types

Pick Stations

policies:
  station_assignment:
    pick_stations:
      type: fastest_completion

Charging Stations

policies:
  station_assignment:
    charging_stations:
      type: nearest

Maintenance Stations

policies:
  station_assignment:
    maintenance_stations:
      type: shortest_queue

Performance Metrics

Station-Level

Metric Description
Utilization Time busy / Total time
Avg queue length Mean robots waiting
Throughput Tasks per hour

System-Level

Metric Description
Queue imbalance Stddev of queue lengths
Avg wait time Mean time in queue
Task completion time Total time per task

Configuration Examples

Speed-Focused

policies:
  station_assignment: nearest

Balance-Focused

policies:
  station_assignment:
    type: shortest_queue
    tie_breaker: nearest

Throughput-Focused

policies:
  station_assignment:
    type: fastest_completion
    service_time_estimate: moving_average

Simulation Testing

Compare Policies

waremax compare scenario.yaml \
  --param policies.station_assignment=nearest \
  --param policies.station_assignment=shortest_queue \
  --param policies.station_assignment=fastest_completion

What to Measure

  • Station utilization variance
  • Average queue length
  • Task completion time
  • Travel time