Contention Management for Mobile Drive Units
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Solution Overview
Problem
Current inventory management systems in storage facilities, particularly those using robotic mobile drive units (MDUs), face inefficiencies due to a lack of effective contention resolution methods when MDUs compete for space, leading to performance delays and reduced system performance.
Innovation Solution
A contention management system that includes a facility management module and one or more contention management modules to plan and manage MDU paths, identify contentions, and generate schedules to resolve conflicts by scoring different execution scenarios based on cost factors such as dynamics, task priority, and deadlock reduction, ensuring efficient space allocation and path execution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If MDUs select random time periods to wait before submitting new requests for space, then contentions are resolved, but MDUs become stationary during wait periods leading to performance inefficiencies
Solution Approach 1:
The system performs preliminary scheduling of MDU paths to identify and resolve potential contentions before execution. The contention management module analyzes planned paths in advance, determines time windows of conflict, and establishes execution schedules that prevent contentions from occurring, allowing MDUs to maintain continuous motion without random waiting periods.
Solution Approach 2:
The system implements feedback mechanisms where the contention management module continuously monitors MDU positions and path executions, dynamically adjusting schedules when contentions are detected. This real-time feedback allows the system to resolve contentions efficiently while minimizing disruptions to MDU productivity.
2Reliability
If new paths are computed to avoid contentions, then space conflicts are resolved, but the reduced travelable area leads to further delays and additional contentions
Solution Approach 1:
The system computes and reserves paths in advance before MDUs begin execution, identifying non-conflicting routes through temporal and spatial analysis. By performing path planning preliminarily and securing reservations, the system eliminates the need for real-time path recomputation, reducing delays while maintaining effective use of travelable area.
Solution Approach 2:
The system resolves path conflicts by introducing the time dimension to path planning. Instead of merely finding alternative spatial routes, the contention management module schedules MDUs to traverse the same physical paths at different time windows, effectively adding temporal dimensionality to resolve contentions without reducing travelable area or increasing computation delays.
3Reliability
If MDUs make simultaneous requests to reserve the same space, then the common management system must deny both requests, but this leads to increased contention and reduced system throughput
Solution Approach 1:
The contention management module performs preliminary analysis of MDU requests to identify potential conflicts before they reach the common management system. By pre-determining which requests can be granted without conflict and scheduling them accordingly, the system minimizes denials and maintains high throughput while ensuring correct space allocation.
Solution Approach 2:
The contention management module acts as an intermediary between MDUs and the common management system. It receives path requests, performs contention analysis, and only forwards non-conflicting requests to the common management system for reservation. This intermediary function filters out conflicting requests before they reach the central system, reducing denials and improving overall system throughput.
Data Source
AI summary
Systems and methods are provided herein for mitigating contentions between mobile drive units (MDUs) within a workspace. Contentions between planned traversal paths of a set of MDUs may be identified by a contention management module. A schedule for interleaving execution of the planned traversal paths may be determined. The contention management module may submit space allocation requests to a facility management module on behalf of one or more MDUs in accordance with the schedule. The facility management module may decide to grant or deny usage of space within the workspace based on the space allocation requests. The decision may be communicated to the MDU (e.g., via the contention management module), and the MDU may act accordingly. In this manner, the contention management module may affect the timing of execution of steps within the planned traversal paths to reduce wait times of the MDUs and improve the throughput of the system.