Improving legacy automated systems

Recommendations on dealing with legacy automation when implementing lean production

Version 1, 3/19/99

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Abstract

“Legacy” systems are those installed before the company decided to convert to lean production. Management must now decide whether they may stay, and, if so, how to use them in the new environment. The transfer line concept is compatible with lean production. FMS’s with parallel machining centers linked by shuttles and central control systems are not commonly found in lean shop floors, but can be operated in a way that is compatible with lean production if the work force has the requisite skills. Rotary indexing machines have work flowing around the equipment, which means poor visibility, poor serviceability, and inflexibility. Asynchronous systems with stacked conveyor loops or other WIP accumulators are among the strongest candidates for dismantling. AS/RS’s can be used but must not dictate lot sizes, do not need to be kept full, and must provide reliable inventory status information in useful formats to compensate for the lack of visibility of the materials.

That “these machines are down too often,” is the most common complaint about automatic systems, and not much else matters as long as it is true. Limping along with excess WIP and extra operators is not an acceptable option in lean production; the equipment problems must either be solved or the system replaced. Once an acceptable level of equipment availability is achieved, the lean way to operate these systems is centered on operator tasks and the flows of parts and resources. Routine operator tasks include mounting/dismounting parts on fixtures, cleaning, storing/retrieving fixtures, molds, pallets, tools or patterns. This work is done outside the equipment and needs to be designed with the same principles as cell or assembly line jobs. In addition, operators monitor automatic cycles and respond to alarms.

Monitoring is combined with other tasks in order to keep operators alert. Sensor-generated alarms are communicated to operators through audible and visible signals.
Like cells or assembly lines, automated systems should produce one piece at a time at the required takt times for all items. Sequencing work through tranfer lines is simple. Through an FMS, it requires making parts in sets going into the same assemblies, and sequencing items so that sets are finished about the same time, at takt intervals for all sets.