Reactivos y equipos

The system output depends on its constraints and therefore, other activities

must be coordinated, in order to optimise the constraints output ― and

actions that contradict the subordination rationale should be avoided. This means non-constraint activities must be paced to the constraints ‘drum’ and any excess capacity is used as protective capacity to protect the system from any fluctuation, in order for the constraint to operate at its maximum effectiveness. This idea is similar to the Kanban concept of Lean, which is used to limit the supply of material into the production process to a rate of

capacity constraint resources can handle. The ‘drumbeat’ (rate of the

constraint) is similar to the Takt time of Lean.

The average speed of non-constraints is paced to the rate of the constraints, in order to ensure that constraint resources always have the correct amount to be processed. Therefore, when jobs enter into the system, the non- constraints must work as soon as possible and pass on their completed work for the constraints to work on, as soon as they are received: this is known asa rely-running works ethic. This reduces cycle time and improves on time delivery (AGI-Goldratt Institute, 2010) The idea of balancing capacity with

workload, based on Takt time, may increase the efficiency, but it can

deteriorate the system when ‘Murphy’ strikes, if protective capacity has been

eliminated. Just a small changed in demand can cause a negative impact that often takes a costly task to recover (Rhodes, Warren, & Carter, 2006). Moreover, according to Dr. Deming (Cox & Schieler,2010) , there will always be variations in systems, but these can be absorbed by time buffers and protective capacity, which are adopted by DBR (Institute TOC-Lean, 2008). Therefore, only an unbalanced line (in terms of capacity) can work well, in order to protect throughput.

Although an unbalanced capacity line technique is seen as not being totally

‘efficient’ from a cost world point of view, the ability of unbalanced capacity to

provide backup capacity, in order to protect a system from any disruption and enable a system to produce more throughputs, compares well to the balanced-line of the Lean technique. Therefore, it is important to understand that, in this step, Lean can be used to define, measure and analyse the waste and variation that exists, but it does not balance resources in the non- constraint (Sproull, 2009). This is to avoid the non-constraint becoming a constraint.

As Figure 2.14 of TOC-DBR shows, material is only released into the system when there is a pull signal from a customer order and it does not exceed what the constraints can produce. Therefore, inventory is not needed at every work centre (Wright, 2011). The amount of work-in-progress is based on processing time on the constraint resources. Variations in the system will be absorbed by buffers, in order to protect constraints and to meet job order due dates. In addition, the unbalanced line of DBR provides additional protective capacity at non-constraint resources, when there is a disruption in supply. This means non-constraints have the capacity to re-produce more at faster rates than constraint operations and thus, this allows non-constraints to be quick enough to resupply before the buffers runs out of inventory. Those extra resources can also be used to handle greater product diversity and volume, without acquiring a new resource (Noreen et al., 1995).

Furthermore, the inventory-based system (Kanban) will not work effectively in volatile environments, because variability and uncertainty, in combination with dependency, can lead to instability of Takt time. In such environments Takt time must be adjusted frequently, which is often a costly task (Jacob et al., 2009)b . Furthermore, if the system fails to work at a pace with the adjusted Takt time, then the Kanban system cannot work, especially if the line is prone to breakdowns, which can cause a bottleneck and disrupt the flow and therefore it results in a negative impact on throughput (Cox & Schieler 2010) .

Previous discussion on the unbalanced line has showed that a time-based system will work well under variation and uncertainty, as it is protected by time buffers, which result in a small amount of inventory (equal to an amount of constraint processing time adequate to cover most forms of fluctuation) at the constraint and shipping points, which protect throughput. This indicates that a time-based system provides early system stability and it works best in all environments, compared to the Kanban system (inventory-based signal). DBR unbalanced and time-based signals also adopt the pull concept and they work well with high variation and uncertainty, compared to the Lean Kanban system and therefore, DBR of TOC is the best option to be adopted in these steps. After implementation of this step, the overall system is evaluated, in order to determine if the constraint has moved to another location. If the constraint has been eliminated, then go back to Step One: if not, then continue to Step Four.