Technical notes of the Pull system
In my last post, I collected some episodes from pull system implementations.
Episodes of "Pull System" implementations (hmoperationsmanagement.com)
Based on the above implementations, I made a technical note using my points – lines – areas – body framework. As a comparison, I compared the pull system against chaos and push system.
A trigger point is where permission to take action is issued. The activity can be to produce or to transport.
In chaos, every process has a trigger point. Each process can judge what to do, which causes chaotic conditions inside operations. "Each process" includes a warehouse, material handlers, quality, maintenance, etc.
In the push system, the trigger point should belong to the bottleneck process. The bottleneck triggers actions to maximize the efficiency of its process. In many cases, since there are many processes inside an operation, it does look the same as chaos.
In the pull system, the trigger point belongs to the customer. "The customer" means the virtual Levelized customer, not the panicking sales department who is changing the orders every day. Because the trigger point can be virtual, the trigger point must be visual.
The drop point is the other end of the trigger point. It is where the information is received, and the responsibility of action belongs.
In the chaos, the drop point is unclear. The responsibility is unclear.
In the push system, the drop point is also unclear. The responsibility is also inexact. The duty is to protect the bottleneck by keeping the inventory in front and after the bottleneck.
In the pull system, the drop point belongs to one process. Based on the dropped information, the responsible process makes judgments and takes action.
The connection between the trigger point and the drop point is the information flow.
In the chaos, this information flow is unclear. Or too much. The arrow of information is back and forth, left and right. Due to the information technology developments, it is possible to have an information system that handles all these transactions. Yet, just because it is possible to run, it doesn't mean that it is efficient for the entire operation. Problems usually cause excess transactions.
In the push system, information comes from the bottleneck. Based on the efficiency of the bottleneck, the information is released. To some degree, the subsequent processes should produce without information and produce whatever the bottleneck made.
In the pull system, the information flow is one-to-one, direct, and unambiguous. It is stated as rule 2 of "Decoding Toyota DNA" by Dr. Bowen and Dr. Spear. The word "direct" is critical. Very often, we like to add additional lead time inside the information flow for safety reasons. But that hides problems. As TPS states, it is creating a condition where "the thread is stretched."
Then there is the material flow.
In the chaos, it is chaos—nothing to add.
The push system is about how quickly we deliver and take away the material from the bottleneck. The worst thing that could happen is stopping the bottleneck.
The push system requires to follow rule No. 3 of "Decoding Toyota DNA." "The pathway for every product and service must be simple and direct." The pathway should connect from the drop point to the trigger point.
In the chaos, since the responsibilities are not clear, there is no way to define the area.
In a push system, the bottleneck must be the center of the design of the area. In front and back of the bottleneck, the area must have sufficient space to hold inventory. The cycle time of the bottleneck will pace the operators' standardized work. The material handler should immediately "push" the finish goods to the subsequent processes so that the area will not overflow.
In a pull system, takt time will become the center of the design of the area. All operators and material handlers must have standardized work. The standardized work is an absolute necessary pre-condition of the pull system. Somewhere inside the standardized work, the responsible person should judge what to produce or transport. The pull system is the connection of such standardized works.
In the chaos, the organization design does not matter.
In the push system, the factory will most likely choose the job shop organization since the job shop will most likely optimize the bottleneck. The staff will form the functional organization. Here, the relationship between the line and staff becomes unclear. In many cases, the staff pushes their services to the line, as well. They think they are already doing a good job, while the shop floor suffers. Most likely, each function has its own KPIs. While each functional is showing excellent results, the overall performance can suffer.
In the pull system, the factory will likely re-organize itself into a flow-based organization. Flow-based organization requires multi-skilled operators and multi-functional managers. In such an organization, the line becomes the staff's customer, where the staff provides services to the line. It is the staff's responsibility to support problem-solving when problems happen. However, the more critical task is to prevent the problem from happening. It is also important to note that we should allow the line to stop if there is a problem in this system so that the entire organization is aware of the problem.
If you have time, please read my previous post so that this technical note becomes more vivid.