One learning I had from a recent MBA was to rank the relevance of different sources of evidence. In a lot of cases, we place a major emphasis on ‘my professional experience’ but this is just one source of ‘evidence’.. and a pretty flimsy one at that. What robust proof is there behind the experience as being correct? The best source of evidence comes from peer reviewed studies like this one. In peer reviewed studies, there is a robust and blind testing of the veracity of the findings, there must be real data & supporting theory to support findings. For this reason, building your opinions on the back of findings from such studies as this are the most robust foundation you can make.
In this example, the question is which of 3 picking method’s is best? No opinions, just facts!
Vitaly Brazhkin from the University of West Florida and William J. Rose from Iowa State University have explored the optimization of order-picking routes in wide-aisle mechanized warehouses. Their study, published in the Transportation Journal, compares three popular routing policies for lift-truck order picking: return, traversal, and Z-pick, with a focus on how these policies perform under different pick densities.
Understanding the Policies
- Traversal Policy:
- The picker moves in an S-shaped pattern, crossing the aisle as needed to reach the nearest pick location.
- Best suited for low pick densities.
- Return Policy:
- The picker collects items from one side of the aisle before turning around to pick from the other side.
- Most efficient at high pick densities.
- Z-Pick Policy:
- A hybrid approach where the picker crosses the aisle after a set number of picks on one side.
- Provides a balance between traversal and return policies and performs consistently across different pick densities.
Key Findings
The study utilized a simulation model to test these policies at various pick densities (from 7% to 50%). The results showed:
- Traversal Policy: Outperforms others at low pick densities (below 10%).
- Return Policy: Becomes the most efficient as pick density increases, particularly above 15%.
- Z-Pick Policy: Offers a viable middle ground, performing nearly as well as the best policy at any given density.
Practical Implications
For warehouse managers, these findings offer clear guidance on selecting the right routing policy:
- Low Density: Use the traversal policy to minimize travel time.
- High Density: Shift to the return policy for better efficiency.
- Universal Solution: Consider the Z-pick policy for consistent performance across various conditions.
Additionally, the study suggests that the traditional Z-pick policy can be improved by adjusting the string length based on lift-truck movement parameters, making it more adaptable and efficient.
Conclusion
Brazhkin and Rose’s research highlights the importance of choosing the right order-picking policy to enhance warehouse efficiency. By understanding and applying the most suitable routing policy, warehouse managers can significantly reduce picking times and improve overall productivity.
For more detailed insights and to explore the simulation models used, you can access the full study in the Transportation Journal.
