Holste Says: |
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| Understanding your system's design parameters is essential to being able to consistently obtain the best performance it can deliver. |
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What Do You Say?
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For instance, many DCs have issues with low daily or hourly picking productivity. Often, the pick rate is being measured based on a 420 minute work period (8 hrs minus lunch and break periods). However, if due to system generated accumulative idle time the pickers are only picking between 240 and 360 minutes per period (the rest of the time spent walking, socializing, etc.) – that would translate into low picking productivity on a spreadsheet, but it is a completely inaccurate statement of picking rate.
One of the most important rules of rate measurement is to measure everything against the actual time used for the specific task being measured. In other words – if you want to measure picking rate of a specific picker, you have to ignore all non-picking time. On the other hand – if you want to measure picker productivity, you would have to include all time spent to complete the task.
Don Savage, who developed and designed picking systems for Diamond Phoenix before the company was acquired by System Logistics Corp. (www.systemlogistics.com), said in an article he wrote, “It is critical that all rates are measured against the time actually worked”. While this makes for a more complex measurement, it provides a much clearer picture of the true capabilities of the system. It is also a good indicator of wasted (or available) time throughout the day.
The following examples, taken in part from Mr. Savage’s article, help to explain how a systems’ performance can change based on how it is measured.
Inconsistent Flow of Work:
Mr. Savage points out that many DC operations are unable to provide employees with a steady flow of work, which can be a serious problem for batch picking systems. The lack of constant work could be the result of IT issues, a lack of orders in process, or even a deficient routing system for passing orders – see “Next Generation Equipment And Technology Breathes New Life Into Pick & Pass Systems”.
Pickers cannot pick at high rates if they don’t have enough orders. This drought in orders creates lost time, which cannot be recovered and daily/hourly pick rates plummet.
According to Savage, the best way to track this is to measure the number of orders present in each zone throughout the day in short time increments (5-minute intervals). Although it sounds tedious, this is an exceptionally important measurement because it directly verifies the effectiveness of the order routing and starting operation. If full batches are not available on a constant basis, pick rates will not reach their maximum. Changes should then be made to move more orders into the zones.
Organization of Operations:
Savage has observed that often tasks are not being organized in a way that fills available time; they are pushed into a linear process instead of a concurrent one. Because a separate measurement against time is necessary for each one, the time required for each operation is usually overstated.
Typically, DC systems operate in sporadic bursts of work with time left over in between. It’s a kind of hurry up and wait situation. This is most common in wave picking operations and is referred to as the bell curve effect. Sometimes this can be corrected by overlapping waves. However, you can’t fill that time appropriately if you don’t know when and how long it is. So the first step is to measure this over a period of multiple days so you can see those busy versus slack time windows.
If wave overlapping is not an option – try filling the gaps with other tasks, which may mean combining different tasks in the same time frame (picking and replenishment, for example). I am currently engaged in the planning of an automated continuous order picking system that will direct pickers to replenish active pick locations during slack time windows.
Not Accounting For Peaks:
In this case, Savage acknowledges that it is not uncommon for an entire day’s work to get compressed into a few hours due to response commitments or shipping requirements. In this situation, he says some managers still measure their efficiency rates over an entire day rather than actual time. In addition, when more workers are assigned to picking zones they are frequently not included in the rate measurements. This leads to over or understating rates for both the day and peak times.
To avoid this error, Savage suggests that if work is condensed into a specific period of the day, then measure the rate for that time period and the number of people working concurrently; this gives you your maximum rate per person. You can then use that rate and the peak window to plan the rest of the operations for the day, which may mean different labor assignments during peak and slack times.
Consider the Performance Audit
An effective way to determine how efficiently your DC systems are running is by doing a Performance Audit. A performance audit can help you zero in on productivity drains, evaluating such areas as picking, conveying, and sorting rates. Whether you utilize internal resources or hire an industry expert, a comprehensive audit will analyze systems from both an operational and functional standpoint, including a final report detailing recommended adjustments. Thus, you will be able to pinpoint and fix inefficiencies, realizing cost savings from improved productivity rates and system performance – see “Are Audits, Assessments, & Evaluations Just an Intellectual Exercise?”
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