gpe - autenticação · critical chain , eliyahu m. goldratt, 1997, north river press leach,...
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Theory of Constraints views systems as chainsThe weakest link is the constraint (bottleneck). It is the constraint that keeps the chain from doing any better at achieving its goal
• The Theory of Constraints is essentially about change– where is the constraint?– work on it– where did it change to?
• In order to be performing well the natural state of the system is changing. If a system doesn’t change it will die
• TOC is a systemic way of thinking– poses questions at the system-level– helps to establish the necessary conditions to reach the goal
CCPM and TOC
Cost versus ThroughputCost World• Optimizes the cost of development• Optimizes each link of the chain• Considers local improvements rewarding
Throughput World• Improving the weakest link improves and strengthens the entire chain• Local improvements are only rewarding on the bottleneck • System optimums is not the sum of local optima
CCPM and TOC
Those who make decisions on efficiency and productivity measurements based primarily on costs/expenses live in the "cost world" as opposed to those who measure by throughput (i.e. value, profitability and utility). Two paradigms (activities/system, machine/holistic, systemic view)
Throughput – is the rate at which a system generates value. For example, the amount of units per day a factory produces to meet customer orders. Units that go into inventory are not counted as part of throughput
Goldratt (1997)definedtheoldaccountingsystemastheCostWorldbecauseitoperatesontheassumptionthatproductcostistheprimarywaytounderstandvalueandmakebusinessdecisions
Laboratthetimewasmostlyappliedtoveryunskilledjobsand,therefore,plentifulandeasytoreplace.Therefore,itwaseasytovarytheworkforcewithdemand
Today,theskilledworkforceismuchlessvariable,andthetraditionalfixedcostsaremuchlessfixed
CCPM and TOC
CriticalChain,EliyahuM.Goldratt,1997,NorthRiverPressLeach,LawrenceP.,2005,CriticalChainProjectManagement,SecondEdition,ARTECHHOUSE,INC
Goldratt’s businessmodelisbasedontwoprinciples
The first principle defines three ways to measure whether or not businesses isachieving the goal of making money. These three measurements areinterrelated and easy enough to apply to any process.
The three measurements are throughput, or “the rate at which the systemgenerates money through sales;” inventory, or “all the money that the systemhas invested in purchasing things that it intends to sell;” and operationexpense, or “all the money the system spends in order to turn inventory intothroughput” (Goldratt & Cox, 1992)
ThesecondprincipleofGoldratt’s modelrelatesdependenteventsandstatisticalfluctuations tothemanufacturingprocess.
Dependent events are processes that must first take place beforeother ones can begin (Goldratt & Cox, 1992).
Statistical fluctuations occur when one is unable to precisely predictevents or quantities (Goldratt & Cox, 1992). Look at this exampleillustrating this principle. Alex and Jonah sit in a restaurant and Jonahpoints out that they are able to precisely predict the capacity of therestaurant by counting the available seats. On the other hand, theyare unable to predict how long the waiter will need to fulfill theirorder (Goldratt & Cox, 1992). This uncertainty is referred to asstatistical fluctuations.
InTheTheoryofConstraints,Goldratt introducesmathematicalformulastohelporganizationsfurtherjudgetheirprocesses.Theseformulasare:
WilliamDettmer (1997)proposesthefollowinglistofprinciplesinhisbook
1 System thinking is preferable to analytical thinking in managing change and solvingproblems
2 An optimal system solution deteriorates after time as the system’s environmentchanges. A process of ongoing improvement is required to maintain, update orimprove the effectiveness of a solution
3 The system optimum is not the sum of the local optima
4 Systems are analogous to chains. Each system has a “weakest link” (constraint) thatultimately limits the success of the entire system
Dettmer,William,1997,EliyahuM.Goldratt’sTheTheoryofConstraints,ASystemsApproachtoContinuousImprovement,ASQQualityPress
CCPM and TOC
….5 Strengthening any link in the chain other than the weakest one does nothing toimprove the strength of the whole chain
6 Knowing what to change requires a thorough understanding of the system’scurrent reality, its goal, and the magnitude and direction of the difference betweenthe two
7 Most of the UDEs (undesired effects) within a system are caused by a few coreproblems
8 Core problems are almost never apparent. They manifest themselves through anumber of UDEs linked by a network of effect→ cause→ effect
9 Resolving individual UDEs gives a false sense of security while ignoring theunderlying core problem. Solutions based on local problems are likely to be short-lived
Dettmer,Willim,1997,EliyahuM.Goldratt’sTheTheoryofConstraints,ASystemsApproachtoContinuousImprovement,ASQQualityPress
CCPM and TOC
10 Core problems are usually perpetuated by a hidden or underlying conflict.Solution of core problems requires challenging the assumptions underlying theconflict
11 System constraints can be either physical, process dependent, or policy-based. Physical constraints are relatively easy to identify and simple to eliminate.Policy-based constraints are usually more difficult to identify and eliminate, butthey normally result in a larger degree of system improvement than theelimination of a physical constraint
12 Inertia is the worst enemy of a process of ongoing improvement. Resistance tochange is normally very strong
13 Ideas are not solutions
CCPM and TOC
Dettmer,Willim,1997,EliyahuM.Goldratt’sTheTheoryofConstraints,ASystemsApproachtoContinuousImprovement,ASQQualityPress
All systems have a (1) constraint that limits output (therefore, non-constraints haveexcess capacity…)
Goal = System Throughput
System optimum is not the sum of the local optima
Adopted measurement systems should– induce what is good for the whole (system optima = Goal)– direct managers to areas needing specific attention
CCPM and TOC Constraint, throughput, measurements
CCPM and TOC TOC – Theory of Constrains and optimal
Local optima and global optima don’t relate
• project throughput needs to be protected, but not with a local optima police
• we need to concentrate resources on the bottleneck (not to the the benefit of every task in the project)
TOC – Theory of Constrains five steps
1. Identify the constraint (IDENTIFY)
2. Decide how to exploit the constraint (EXPLOIT)
3. Subordinate and synchronize (align) everything else to the above decisions (SUBORDINATE)
To improve the performance of that same value-chain, continue
4. Elevate the performance of the constraint (ELEVATE)
5. If in any of the above steps the constraint has shifted, go back to Step 1 (PREVENT ENERTIA)
CCPM and TOC
Tirar partido
Aumentar desempenho
1. Identify the System's constraintsThe system/process is analyzed so that a task or activity that limits the productivity of the entire systemcan be identified. A system constraint can be identified by a long queue of work or long processing times. Itcan be a resource (plant, team, …)
2. Decide how to exploit the system's constraintsIn this step, decisions must be made on how to modify or redesign the task or activity so that work can beperformed more effectively and efficiently. Explore installed capacity
3. Subordinate everything else to the above decisionNow, management directs all its efforts to improving the performance of the constraining task or activity andany other task or activity that directly affects the constraining task or activity. Focus on the problem
4. Elevate the system's constraintIn this step, we need additional capacity to increase (elevate) the overall output of the constraining task oractivity. This differs from step 2 in that the added output comes from additional purchased capacity, such asbuying a second machine tool or implementing a new information technology. In step 2 existing capacity isexploited
5. Go back to step one. In the previous step a constraint has been broken, and most likely the problemwas transferred to another resource (another constrain)
CCPM and TOC
Constraints usually relate to
• MARKET• CAPACITY• RESOURCES (people)• PROCESS DESIGN• SUPPLIERS• FINANCE• KNOWLEDGE OR COMPETENCE• POLICIES
CCPM and TOC
In a project the Critical Chain is THE constraint
Goldratt argues that most of the time system constraints
trace back to a flawed policy
rather than to a physical constraint
CCPM and TOC
Leach,LawrenceP.,2005,CriticalChainProjectManagement,SecondEdition,ARTECHHOUSE,INC
Murphy – AreferencetoMurphy’sLaw
“ifanythingbadcanhappen,itWILLhappen."
Inprojectmanagement,manyunexpectedproblemstendtooccur
Don’taskmeifitwilloccur,askmewhen!
Goldratt saysthatMurphyexists!- Always!!!
CCPM syndromes
Key point …… remove excess time
Everyone estimates ....“Student Syndrome”, “Parkinson’s Law”, …Functional managers protect their resourcesSenior management (& client) wants everything early (yesterday)!
SolutionReduce all activity estimate durations by 50% and place aggregated time buffers to protect project schedule and resource constraints
CCPM on the way
Key point …… manage to the constraint
Resources can be scarce because of other concurrent projects
Scarce resources comprise the “Critical Chain” (abrange, estão incluídas)
Critical Chain: The longest set of dependent activities, with explicit consideration of resource availability, to achieve a project goal
The Critical Chain does not equal the Critical Path. Critical Chain is the longest pass ofdependent activities, being the dependence an effect of either sequence or use of thesame resources. If there is no resource restriction Critical Chain is the Critical Path
CCPM on the way
Key point …… multi-tasking is inefficient
Spreads resources over several tasks at once
Loses focus
Restarts (set up times) = loses efficiency
Solution = “Roadrunner” Performance Focus 100% of resource’s time on one task until it is complete
CCPM on the way
Whenever I put down one task and pick up another, I lose productive time
How much time is loose switching depends on how deep the task in hand is
Putting a stop to multi-tasking effectively creates extra capacity
CCPM on the way Key point …… multi-tasking is inefficient
Jan, Shu-Hui & Ho, 2006, ISARC, CONSTRUCTION PROJECT BUFFER MANAGEMENT IN SCHEDULING PLANNING AND CONTROL
CCPM on the way Buffers
Resourcesmustfocusononetaskatatimeandpassontheresultsassoonasthetaskiscompleteimmediatelycontinuingwiththenext
CCPM on the way
Using CCPM we normally agree that the bottleneck is the critical chain. To protect it and increase its effectiveness (reduce waist of time) we use a Project Buffer (PB) at the end of CC (we use an overall safety to the project and not to the single activities)(remember we reduced the safety at the activity level using the 50% rule and remember what we said about local and system optima. PB should have a duration of 50% of about the duration of the CC)
We use the Feeding Buffer (FB) at the end of each non-critical path, when joining with the critical chain, to prevent repercussion of delays in this non critical branch. Even when delays are exceeded and are superior to the buffer (feeding) capacity, project buffer can still absorb delays. FB should have a duration of about 50% of the non-critical chain duration before it.
PF and FB are time buffers
With CCPM due date is a limit (we don’t think in terms of finishing dates as we are in throughput world). Like that we eliminate the students syndrome
Besides it is necessary to guaranty the redness of resources to activities in the critical chain. The Resource Buffer is a warning flag to prepare the resource
CCPM on the way Buffers
Broken Critical Chain, Oak Logic Consulting, Communications in Business
CCPM on the way Aggressive time estimates and Buffers
Broken Critical Chain, Oak Logic Consulting, Communications in Business
CCPM on the way Multitasking
1. Identifythecriticalchain
- Thetasksmustestimatethemeantime-durationconversion(50–50time)andprimaryresourcerequirements.(Fortaskswithmultipleresources,identifytheprimaryresourceyoubelievewillbeaconstraint.Ifthereareseveralconstraintresources,breakthetaskupforeachprimaryresource)
- Ifyoudonothaveresourcecontentioninyourproject,gotothelaststep- Identifythecontentionyouwillresolvefirst.Thisshouldbethecontentionnearestto
projectcompletionortheonethatshowsthemostconflict.Ifseveralshowaboutthesameamountofpotentialconflict,choosethefirstoneyoucometoworkingbackwardsfromtheendoftheschedule
- Removeresourcecontentionbysequencingtasksearlierintime.(Donotworryaboutcreatingnewconflictswiththisstep;youwillresolvethoseinsequence)
- Returntotheendofthescheduleandfollowstep1.4forthenextresource.Asyouresolveconflictsforthenextresource,youmustmaintainthelackoftheconflictfortheresourcesyouresolvedearlier.Repeatuntilallidentifiedresourcetypesareresolved
- Identifythecriticalchainasthelongestchainofdependentevents
CCPM on the way
Leach,LawrenceP.,2005,CriticalChainProjectManagement,SecondEdition,ARTECHHOUSE,INC
2 Exploitthecriticalchain-Reviewyourplantodetermineifsequencingcanshortentheoverallprojectduration.Ifso,doit.Donottrial-and-errorvarioussolutions-Addtheprojectbuffertotheendofthecriticalchain
3 Subordinate theothertasks,paths,andresourcestothecriticalchain-Protectthecriticalchainbyaddingfeedingbufferstoallchainsthatfeedthecriticalchain.Sizethesebuffersusingthelongestprecedingpath.(Note:Allnoncriticalchainsfeedthecriticalchaintocompletetheproject.Ifchainsgodirectlytotheprojectbuffer,theyalsoneedfeedingbuffers)-Resolveanyresourcecontentionscreatedbyaddingfeedingbuffersthroughsequencingtasksearlierintime-Movetoanearliertimeanydependenttasksprecedingthosemoved
4 Elevate (shorten)thelead-timeoftheprojectbyusingaddedproducingartifactsforcertainwindowsoftimetobreakcontention
5 Gobacktostepone.Donotallowinertiatobecometheconstraint
CCPM on the way
Leach,LawrenceP.,2005,CriticalChainProjectManagement,SecondEdition,ARTECHHOUSE,INC
• A resource buffer isn’t a time buffer at all; it’s a flag to warn that a
particular resource will be needed soon
– So it’s an alarm clock!
• A resource buffer is established some time interval before the resource
is needed (1 week, a month, etc.)
Buffers
CCPM on the way
Q
If in a project, during execution, you achieved 60% of project buffer, what does this mean (it is ok, or not)?
BUFFER
OK WATCH& PLAN ACT
RemainingProject Buffer:
20 15 14 8 7 0
RemainingFeeding Buffer:
8 7 6 4 3 0
Buffers Provide Focus and Early Warning
Buffers to Monitor Project Status
%CBR/%CCR >=1
%CBR/%CCR 1>2/3
%CBR/%CCR 2/3>
CCR - Critical Chain RemainingCBR – Completion Buffer Remaining
Corrective Action
We compare the percentage of the Completion Buffer Remaining(%CBR) with the percentage of the Critical Chain Remaining(%CCR)
We set trigger points for corrective action, for example:
•When the ratio %CBR / %CCR is 1 or more, Project status isGREEN - Watch•When %CBR / %CCR is between 1 and 2/3, Project status isAMBER - Prepare a recovery plan•When %CBR / %CCR is less than 2/3, Project status is RED -Implement recovery plan
CRITICAL PATH / CRITICAL CHAIN
• Places high value on the completion of tasks on time
• Employs techniques to minimise slack or float
• Uses the amount of slack or float to set priorities
• Places low value on tasks being completed on time
• Inserts buffers even on paths that are not critical
• Manages buffers to minimise unplanned expediting, overtime and other costly deviations from schedule.
CCPM differences
• Resources are given due dates• No buffer, later tasks are forced to make up any slide• Local optimization is not systemic• Management attention on all tasks• Resources not de-conflicted• Judge resources on whether they completed by due date and quality of work
CRITICAL PATH / CRITICAL CHAIN
CCPM differences
• Cultural change in how to manage projects and evaluate team members
• Avoid multi-tasking • Protect against uncertainty by aggregating
all safety time at the end of the project• Concentrate on the constraint of the project:
the longest chain of dependent tasks or resources
“Goodenough” isanimportantideaindevelopingcritical-chainprojectplans.Formathematicalreasons,itisimpossibletobuildapreciseoptimizingalgorithmforresourceleveling.Theproceduretodevelopthecritical-chainplanensuresthattheplanyoubuildwillbe“goodenough.”Thismeansthattheoveralllengthoftheschedulewillbe,withinasmallpartofthelengthoftheprojectbuffer,nearlytheshortestoroptimumschedulepath.Sincerealitywillchangemanyassumptions,andwecannotexplicitlypredicttheresultsofstatisticalfluctuations,thisisgoodenough
CCPM differences
Leach,LawrenceP.,2005,CriticalChainProjectManagement,SecondEdition,ARTECHHOUSE,INCSTOP HERE
Scarcity of Resources
Task C – 10 d
Task B – 10 d
Task A – 10 d
Project Time required - 20 d
Task C depends on both A and BEach task uses a different resource
Scarcity of Resources
Task C – 10 d
Task B – 10 d
Task A – 10 d
Task C depends on both A and B, Both A and B need exclusive use of the same resource
Project Time required - 30 d
Resource conflict
Don't overreact to buffer erosion
• We expect our buffer to be used up over the course of the Project
• Our date is not threatened if the buffer is used up in proportion to progress– If we have 2/3 of the completion buffer left and only 1/3 of the Project to
do we are doing fine
• Our date is threatened if the buffer is used up disproportionately– If we have 2/3 of the Project still to do but have only 1/3 of the
completion buffer left we have a problem
Buffer Management Meeting
Attendees: Project Manager, Project Sponsor / Owner, Task Managers, Resource Managers
Agenda:1. Reminder of what tasks are on the Critical Chain.2. Review Project status ( % Critical Chain outstanding).3. Review Completion buffer status (Red, Amber, Green).
If necessary, initiate corrective actions.4. Review Feeding buffers status (Red, Amber, Green). If
necessary, initiate corrective actions.5. Review tasks in progress to ensure earliest completion in full.6. Review tasks not started to ensure earliest start where
appropriate.
Using Buffer Management to drive ongoing improvement
• Buffer Management measures are fact-based and objective
• Buffer Management meetings highlight buffer erosion / Project delays
• Preventing the causes of delay will speed up your Projects
• Your process of ongoing improvement is simply to eliminate the causes of delay by following up on the issues highlighted in Buffer Management meetings
• As your Projects run faster and more reliably, continue to eliminate more and more causes of delay
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