Definition
The full-work system (フルワーク・システム, furu wāku shisutemu) is the mechanism that stops a machine or process when the standard in-process stock ahead of that machine or process is full. Each process is allowed to hold only its standard in-process stock. When that quantity is reached the feeding process stops, and the feeding process restarts when a piece is taken away. The processes run interlocked, so no process can run ahead of the next.
Toyota's definition, as recorded in Taiichi Ohno's 1978 book, reads as follows. The system that runs each process in an interlocked state so that the standard in-process quantity within each process is always held, in other words the system that prevents the waste of overproduction, is called the full-work system. The full-work device is standard equipment on Toyota's automated lines.
In physical form the full-work system is a switch on a chute, a holding stand, or a conveyor that detects the full condition and cuts the start signal to the preceding machine. The full-work system is one of the jidoka devices. Toyota fits almost every machine with automatic stop devices, and the full-work system belongs to that group with the fixed-position stop and poka-yoke.
Japanese Origin
The term is an English loanword written in katakana. "Full work" is the state in which the holding position after a machine is full. Toyota writes the hardware as フルワーク装置 (furu wāku sōchi, full-work device), and lists フルワーク (full work) with ワークなし (wāku nashi, no work) and 通過確認 (tsūka kakunin, pass confirmation) as the switch conditions an automated line must have. Poka-yoke and the full-work system are Toyota's standard examples of the additions that give a purchased automatic machine the human element of jidoka.
Some sources render the idea as 満杯システム (manpai shisutemu, "full-to-capacity system"). The Toyota documents cited here use the katakana term.
How the Full-Work System Works
The condition the full-work switch detects. A holding position downstream of a machine has a fixed capacity equal to the standard in-process stock. When a piece arrives and the position is full, the machine that would feed the position is stopped. The mirror condition is "no work": the machine has no piece to process because the position upstream of that machine is empty. On an automated machining line both states are wired to the andon, and the andon board shows each operation stopped in either the full-work or the no-work state, so supervisors see at once which machine is holding the line up.
Why the full-work system stops the machine rather than the operator. An automatic machine keeps cycling as long as the machine is fed. Without an interlock, a fast machine or an operator running ahead fills the space after the machine, and the waiting that should have appeared is converted into stock. The full-work stop makes the machine wait instead. The waiting is then visible, which is the precondition for rebalancing the work.
Safety. An early Toyota case of a finger amputation involved an automated line whose no-work, pass-confirmation, and full-work switches had not been maintained, so the machine did not stop when an abnormality occurred. The full-work switch is part of the equipment's safety as well as its production control.
Why the Full-Work System Matters
The first step of man-hour reduction at Toyota is to remove overproduction. The way to do this is to set up the line with rules and with equipment constraints, such as full-work devices, that make overproduction impossible. Only then does the flow return to its proper form. What is needed gets made one piece at a time when it is needed, and the surplus shows up as waiting. From that state the sequence of removing waste, redistributing work, and reducing headcount becomes workable.
Overproduction is the most fundamental waste because it hides the others, and grasping waste only roughly is useless. The full-work system is the hardware that enforces the standard in-process quantity minutely, machine by machine, rather than leaving the quantity to discipline.
Common Mistakes
Treating the full-work switch as a buffer sensor. A full-work switch set at a large quantity is a buffer, not a full-work system. The stop must trip at the standard in-process stock, which is the minimum needed for the work sequence to hold.
Removing the switch to raise machine utilization. Letting the machine run into a full position raises apparent output and creates stock the next process has not asked for. Ohno called this apparent efficiency. The machine waiting at the full-work stop is the correct condition, not a loss.
Confusing the full-work system with the fixed-position stop. The fixed-position stop halts a moving line at a set point when an abnormality is signaled. The full-work system halts a process because the next position is full. Both are jidoka stops. They answer different conditions.