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The principle of men-machine separation dates back to the time of Ohno. At that time, there was an operator for a machine, each of the machines not being set on the same Takt time.

Introduction

The principle of men-machine separation was developed in the years 1950 by Taiichi Ohno. At that time, there was an operator for a machine, each of the machines not being set on the same Takt time. The consequence was twofold:

  1. Some machine generated overproduction since the downstream machine was over a longer cycle time.
  2. The operators of the “ fast ” machines were still waiting, while the others were still running. Ohno explained that at home one rarely stays in front of the washing machine while it turns1.

The principle

Through the observation of this situation, Ohno decided to develop the principle of the separation of the work cycles of the man from the working cycle of the machine. The idea was to arrange the tasks to allow the same person to take care of 2 to 4 machines.

The implementation of this principle is based on two steps that we detail below.

1-Set up “autonomation”

The first, the machine must be ” autonomous “. In other words, it must operate alone without the 100% monitoring of an operator and therefore be able to detect only faults (principle of Jidoka). To do this, this feature should be provided as soon as the process is designed and include sensors or other systems allowing the machine to detect the defect and to stop immediately. The design team will have to list the defect types and identify reliable detection solutions. The consequences that must be observed are:

  • The same operator must be able to take care of several equipments.
  • An abnormal situation must be easily seen.
  • A machine that stops must alert the staff.

2 – Set up the principle of Chaku-Chaku

The Chaku-Chaku is a Japanese term meaning ” load, Load “. It follows from a Japanese onomatopoeia describing the fact of working in rhythm. The principle is to arrange a succession of equipment in the order of the sequence of work, as close as possible to each other, with loads and unloading of simplified parts.

Each machine, automatic or semi-automatic, performs a different operation, all at the same Takt Time. The operator having to perform only the loading of the parts by following a preset ” circuit “. The work is more fluid and without an undesired stop, the operator having more than to load the next workstation , check the quality of the parts and the general good functioning.

This approach has the advantage of bringing together in the same area equipment of the same value stream and thus reducing the Lead Time, stock, displacement….

This is in contradiction with an old method of grouping the equipment by pole. The idea was to assemble the equipment by type of technology or function. The objective was to facilitate maintenance or to limit staff training. But the downside was just to increase the Muda of displacement, stock…

For loading

For the loading of the Part in the machine, one will most often choose a manual solution. The positioning of the Part often requires special attention to guarantee the quality of the work, it is better to keep them in manual rather than to automate them. Between failures, detunings and adjustments, automatic loads may not provide a reliable and repeatable positioning.

For unloading

For unloading, unless special stress is required, an automatic eject function is preferred. This is called the Hanedashi (自働啟動, ” self-ejection “. The inverse of the Hanedashi is the Chaku Datsu). The unloading operation does not require specific attention except to keep the integrity of the Part, an automatic ejection can be easily foreseen.

The rules of the Chaku-Chaku

The application u principle of the Chaku-Chaku impose to follow design rules. We find2.

For the operator

Hand movement

Both hands are used all the time.

You take with your left hand and you drop with your right hand.

Parallel movements: ” up and down “.

Avoid ” front and rear ” movements.

Eye movement

The look is straight forward, no need to look all around.

Handling Time

Less than 3 seconds for each stage of the process.

Safety and quality

There is no element that hinders movement and movement over the entire cycle.

Movement of feet

Parallel movements: ” up and down “.

Avoid ” front and rear ” movements.

Designed to have the least amount of travel.

For process

Hanedashi

There is no need for complex movements to take the Part.

Starts the machine in motion

There is no difficulty in getting the machine cycle started.

Guide

Insertion is easy.

The positioning of the parts does not require any particular adjustment.

Source

1 – T. L. Besser (1996) – Team Toyota: Transplanting the Toyota culture to the Camry plant in Kentucky

2 – Porsche Consulting (2007) – In Search of Lost Time

A. Petitqueux (2001) – Lean implementation, industrial application

C. Hohmann (2009) – Productivity Techniques: How to earn performance points

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