Why is takt time so easy on the one hand and yet so difficult on the other. Everyone understands the simple concepts of the seven deadly wastes. Everyone understands the simple idea of working to the “beat” of the market. Few people have difficulty drawing a current state value stream map. But ask people to understand FIFO lande, supermarkets, and heijunka? What has your experience been?
I believe that the difficulty lies in the failure to teach the idea that a lean organization is cybernetic, that is, self-controlling or self-regulating. Truly, lean enterprise means the elimination of schedules as we know them.
In constructing a lean future state map, there are two major questions:
Will the organization be entirely scheduled by customer demand? (I call this “no hands” scheduling.”)
Will the organization have its own internal schedule or pacemaker?
If the organization is designed to respond entirely to customer demand, then the market is the pacemaker. We may pull information or material from the receiving dock to the shipping dock using one-piece-flow and supermarkets. If the organization is designed to have an internal pacemaker, then we may pull material from the shipping dock to the pacemaker, and flow material from the pacemaker to the shipping dock and from there to the customer.
Sounds easy, right? The trick is to help people see the progressive auto-mation or de-scheduling of decisions about the sequence and timing of information and material movement. Clearly, on the shipping dock, in a just-in-time system every movement should be dictated by customer demand. That is, the customer signals its requirements to us, and we ship. The question in lean scheduling is: To what extent may we link the rest of the supply chain to customer demand without interposing moderating buffers of inventories in FIFO lanes and supermarkets.
FIFO lanes give us the least amount of insulation from customer demand, because once an item of information or material enters a FIFO land we cannot change its sequence and we can only change its timing to a limited extent. There is no queue-jumping in a FIFO lane. Everything else in the system had better be moving in the same sequence and at the same pace, because there will be no more signals from the internal pacemaker, only the customer. If anything is out of sequence or moving at the wrong speed, there will be mismatches when subprocess intersect.
Supermarkets give us the most insulation from customer demand, because once an item enters a supermarket, we can still change either its sequence or its timing. Queue-jumping is allowed when the pacemaker says so. And, depending upon the circumstances, I could sit on the shelf for a relatively long time before the pacemaker asked me to move on.
In sum, we may want to think of the pacemaker as a traffic cop whose job it is to interpret the customer’s demand signals, which are insufficiently clear to achieve information or material flow. Material in supermarkets is like cars in a major parking lot next to the highway of flow. The pacemaker receives a certain amount of information from the customer in real time that permits him to choose who should go first and should go second up the ramp to the highway. It doesn’t matter where or when you parked. Even if you were the last car driven on the lot and farthest from the exit, you may be asked to exit now.
Once you’re on the highway, however, the rules change. On the highway of flow, there is only one lane, and no speeding, tailgating, or passing.
April 1, 2009