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Lean Production6 min read

Man-Machine Chart Analysis: Synchronous Operations Design

This article introduces Man-Machine Chart analysis, a practical approach to addressing high machine idle rates caused by asynchronous interactions between operators and equipment, often leading to "man waiting for machine, and machine waiting for man." It explains how to identify and eliminate time gaps to transform waste into efficient production, optimizing workflows and reducing operational costs.

That Day, Machine Idle Rate Skyrocketed, and the Boss Was Furious

That afternoon, the production line supervisor suddenly rushed into the office, his face ashen, saying, "The latest machine idle rate report is out, and some machines have a utilization rate of less than 70%! What's going on? A yield Cpk of 1.08 is one thing, but with such a high idle rate, are we just throwing money into the water?" My heart sank; this indicated a serious production capacity problem. After a careful investigation, I discovered the problem stemmed from the "interaction" between our engineers and the machines. We were short-staffed, often having to wait for one operation to complete before executing the next, creating an endless loop of "man waiting for machine, machine waiting for man."

What's the Problem? Simply Put, It's "Asynchronicity"

In essence, this is the problem that "Man-Machine Chart Analysis" aims to solve. Simply put, it's about identifying the "time difference" between you and the machine. Think about it: when you're performing one operation and the machine is running another, can these two actions be performed synchronously? If not, there's definitely idle time.

Take a common example: you load a wafer into the machine (manual operation), and then the machine starts running the process (machine operation). During the time the machine is running, are you just standing there "waiting"? Or do you go do other things, only to have to spend time "waiting" for you to handle it when the machine finishes? This waiting in between is waste. Man-Machine Chart analysis identifies these "waiting times" to see if they can be transformed into "synchronous operations" by adjusting the sequence or allocation of tasks.

So, the key is to break down the work of both man and machine into the smallest steps, and then measure the time for each of these steps, to identify opportunities for synchronization.

How Is It Actually Done? A Chart Is Clearest!

Frankly, Man-Machine Chart analysis isn't difficult, just a bit tedious.

  1. List all actions: Write down all your and the machine's actions from start to finish, the more detailed, the better. For example: picking up a wafer, loading a wafer, closing the machine door, pressing start, checking the screen, opening the machine door, unloading a wafer… these all count.
  2. Measure time: Use a stopwatch to measure the time for each action. Measure multiple times and take the average to ensure data accuracy. For example: loading wafer 3 seconds, machine process 120 seconds, unloading wafer 5 seconds.
  3. Draw the Man-Machine Chart: This chart typically has three columns: "Manual Operation," "Machine Operation," and a middle column for "Synchronous Operation." Draw out a timeline and plot each action. You'll clearly see when it's "man working, machine idle," "machine working, man idle," and when "both man and machine are working" or "both man and machine are waiting."

For example, if your process is like this:

  • Manual: Action A (10 seconds)
  • Machine: Process B (60 seconds)
  • Manual: Action C (15 seconds)

Are you idle during the 60 seconds of Process B? If there's another machine running nearby, and you can use those 60 seconds to handle the loading/unloading of that other machine, that's an excellent synchronization opportunity. Suppose you manage two machines simultaneously, and each machine's process is the same. You could handle Action A on the second machine while the first machine is running Process B. This significantly reduces your idle time. A problem like DPMO 6210 might even be related to the "asynchronicity" of the process steps.

In other words, through the chart, you'll discover which manual operations can be performed synchronously while the machine process is running.

The Most Common Pitfalls: Numerical Fallacy and "Just Get Used to It"

The biggest pitfall I've encountered is the "numerical fallacy." Some engineers, after measuring time, see a long machine process time and think, "Ah, I'm supposed to wait during this period!" and then skip optimization. But we need to challenge this "inherent waiting."

Another common pitfall is "just getting used to it." Many production line personnel are accustomed to a certain workflow, and even if there's obvious idle time, they'll think, "It's always been this way, it doesn't matter." But these accumulated "doesn't matters" were the reason our idle rate was so high that the boss was furious that time. I remember one instance where a machine operation took a very long time, and our engineers were accustomed to scrolling on their phones while the machine was running. Later, a Man-Machine Chart analysis revealed that this time could actually be used to prepare materials for the next batch of wafers or perform some preventive maintenance checks, which would significantly reduce batch changeover time.

Truth be told, Man-Machine Chart analysis isn't about making you a superhero who's never idle for a moment, but rather about making your time usage more efficient and minimizing the time you truly need to "wait."

One Thing You Can Do Today

Choose the machine you operate most frequently daily, and use a stopwatch to measure the time for each of your and the machine's actions.

Want to try it yourself?

Every tool mentioned in this article is available on InsightFab — just upload a CSV to analyze.

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