- Theory of Constraints
Theory of Constraints (TOC) is an overall
management philosophy. Dr. Eliyahu M. Goldrattintroduced the "Theory of constraints" in his 1984 book titled "The Goal". It is based on the application of scientific principles and logicreasoning to guide human-based organizations. The publicity and leadership behind these ideas has been dominated by Dr. Goldratt through a series of books, seminars and workshops.
TOC is geared to help organizations continually achieve their goals.cite book |author=Goldratt, Eliyahu M. |title=What is this thing called Theory of Constraints an how should it be implemented |publisher=North River Press |location= [Croton-on-Hudson, NY] |year=1990 |pages=161 |isbn=0-88427-166-8 |oclc= |doi=]
TOC is based on a set of basic principles (
axioms)cite video |people=Goldratt, Eliyahu M. (Director, Presenter)|title=TOC - Self Learning Program |publisher=Goldratt Marketing Group |url=http://www.toc-goldratt.com/store/home.php?cat=14&page=1 |medium=Computer CD-ROM |date2=2002 |] , a few simple processes (Strategic Questions, Focusing Steps, Buy-In processes, Effect-Cause-Effect), logic tools (The Thinking Processes or TP) and through the logical derivation of these some applications to specific fields (Operations, Finance, Distribution, Project Management, People Management, Strategy, Sales and Marketing).
According to TOC, every organization has - at any given point in time - at least one constraint which limits the system's performance relative to its goal (see
Liebig's law of the minimum). These constraints can be broadly classified as either an internal constraint or a market constraint. In order to manage the performance of the system, the constraint must be identified and managed correctly (according to the Five Focusing Steps below). Over time the constraint may change (e.g., because the previous constraint was managed successfully, or because of a changing environment) and the analysis starts anew.
Basic principles of TOC
Explicitly articulated in SLP 7 — Managing People and Necessary and Sufficient — Unit 2 The Basic Assumptions of TOCcite video |people=Goldratt, Eliyahu M. (Director, Presenter) |title=Necessary and Sufficient|publisher=Goldratt Marketing Group |url=http://www.toc-goldratt.com/index.php?cont=32 |medium=Computer CD-ROM |date2=2003 |]
The principles are treated as axioms, and therefore have no proof. Even so Goldratt provides, some indication on why he chose these as basic assumptions or principles to base TOC upon.
The first two are a derivation of Newton's words: "natura valde simplex est et sibi consona" (nature is exceedingly simple and conformable to herself), while the third is a bridge on how to deal with human reactions and motivations.
The first principle: Convergence, also called "Inherent Simplicity" states that "The more complex a system is to describe, the simpler it is to manage." Or that the more interconnected a system is the fewer degrees of freedom it has, and consequently the fewer points must be touched (managed) to impact the whole system. A corollary of this principle is that every organization has at least one constraint active in any given point of time (otherwise it would achieve infinite performance relative to its goal). The more complex and interconnected the organization is the lower the number of constraints it will have.
The second principle: Consistency, also called "There are No Conflicts in Nature" states that "If two interpretations of a natural phenomenon are in conflict, one or possibly both must be wrong". That is, when in an organization with a common goal, two parts are in conflict (or in a dilemma) this means that the reasoning that led to the conflict must contain at least one flawed assumption.
The third principle: Respect, also called "People are not Stupid" states that "Even when people do things that seem stupid they have a reason for that behavior". In other words, this principle is stating that people are not inherently irrational.
The five focusing steps
One of the most important processes of the Theory of Constraints is based on the premise that the rate of goal achievement is limited by at least one constraining process. Only by increasing throughput (flow) at the bottleneck process can overall throughput be increased.
The key steps in implementing an effective process of ongoing improvement according to TOC are:
:0. (Step Zero) Articulate the goal of the organization. Frequently, this is something like, "Make money now and in the future.":1. Identify the constraint (the thing that prevents the organization from obtaining more of the goal):2. Decide how to exploit the constraint (make sure the constraint is doing things that the constraint uniquely does, and not doing things that it should not do) :3. Subordinate all other processes to above decision (align all other processes to the decision made above):4. Elevate the constraint (if required, permanently increase capacity of the constraint; "buy more"):5. If, as a result of these steps, the constraint has moved, return to Step 1. Don't let inertia become the constraint.
The focusing steps, or this "Process of Ongoing Improvement" has been applied to
Manufacturing, Project Management, Supply Chain / Distribution generated specific solutions. Other tools (mainly the TP) also led to TOC applications in the fields of Marketingand Sales, and Finance. The solution as applied to each of these areas are listed below.
Within manufacturing operations and
operations management, the solution seeks to pull materials through the system, rather than push them into the system. The primary methodology use is Drum-Buffer-Rope (DBR),cite book |author=Cox, Jeff; Goldratt, Eliyahu M. |title=The goal: a process of ongoing improvement |publisher=North River Press |location= [Croton-on-Hudson, NY] |year=1986 |pages= |isbn=0-88427-061-0 |oclc= |doi=] and a variation called Simplified Drum-Buffer-Rope (S-DBR).cite paper | author = Eli Schragenheim and H. William Dettmer | title = Simplified Drum-Buffer-Rope: A Whole System Approach to High Velocity Manufacturing | date= 2000 | url = http://www.goalsys.com/books/documents/S-DBRPaper.pdf | format =
Drum-Buffer-Rope is a manufacturing execution methodology, named for its three components. The "drum" is the physical constraint of the plant: the work center or machine or operation that limits the ability of the entire system to produce more. The rest of the plant follows the beat of the drum. They make sure the drum has work and that anything the drum has processed does not get wasted.
The "buffer" protects the drum, so that it always has work flowing to it. Buffers in DBR have time as their unit of measure, rather than quantity of material. This makes the priority system operate strictly based on the time an order is expected to be at the buffered operation. Traditional DBR usually calls for buffers at several points in the system: the constraint, synchronization points and at shipping. S-DBR requires only a single buffer at shipping.
The "rope" is the work release mechanism for the plant. Only at "buffer time" before an order is due does it get released into the plant. Pulling work into the system earlier than a buffer time guarantees high work-in-process and slows down the entire system.
There are four primary types of plants in the TOC lexicon. Draw the flow of material from the bottom of a page to the top, and you get the four types. They specify the general flow of materials through a system, and they provide some hints about where to look for typical problems. The four types can be combined in many ways in larger facilities.
* I-Plant: Material flows in a sequence, such as in an assembly line. The primary work is done in a straight sequence of events (one-to-one). The constraint is the slowest operation.
* A-Plant: The general flow of material is many-to-one, such as in a plant where many sub-assemblies converge for a final assembly. The primary problem in A-plants is in synchronizing the converging lines so that each supplies the final assembly point at the right time.
* V-Plant: The general flow of material is one-to-many, such as a plant that takes one raw material and can make many final products. Classic examples are meat rendering plants or a steel manufacturer. The primary problem in V-plants is "robbing" where one operation (A) immediately after a diverging point "steals" materials meant for the other operation (B). Once the material has been processed by A, it cannot come back and be run through B without significant rework.
* T-Plant: The general flow is that of an I-Plant (or has multiple lines), which then splits into many assemblies (many-to-many). Most manufactured parts are used in multiple assemblies and nearly all assemblies use multiple parts. Customized devices, such as computers, are good examples. T-plants suffer from both synchronization problems of A-plants (parts aren't all available for an assembly) and the robbing problems of V-plants (one assembly steals parts that could have been used in another).
upply chain / logistics
The solution for supply chain is to move to a replenishment to consumption model, rather than a forecast model.
* TOC-VMI (vendor managed inventory)
Finance and accounting
The solution for finance and accounting is to apply
holisticthinking to the finance application. This has been termed throughput accounting. Throughput accounting suggests that one examine the impact of investments and operational changes in terms of the impact on the throughput of the business. It is an alternative to cost accounting.
The primary measures for a TOC view of finance and accounting are: Throughput (T), Operating Expense (OE) and Investment (I). Throughput is calculated from Sales (S) - Totally Variable Cost (TVC). Totally Variable Cost usually considers the cost of raw materials that go into creating the item sold.
Critical Chain Project Managementis utilized in this area. Based on the realization that all projects look like A-plants: all operations must converge to a final deliverable. As such, synchronization of activities is a common problem that CCPM seeks to address.
Marketing and sales
While originally focused on manufacturing and logistics, TOC has expanded lately into sales management and marketing. For effective sales management one can apply Drum Buffer Rope to the sales process similar to the way it is applied to operations (see Reengineering the Sales Process book reference below). This technique is appropriate when your constraint is in the sales process itself or you just want an effective sales management technique and includes the topics of
funnel managementand conversion rates.Fact|date=December 2007
The TOC thinking processes
The Thinking Processes are a set of tools to help managers walk through the steps of initiating and implementing a project. When used in a logical flow, the Thinking Processes help walk through a buy-in process:
# Gain agreement on the problem
# Gain agreement on the direction for a solution
# Gain agreement that the solution solves the problem
# Agree to overcome any potential negative ramifications
# Agree to overcome any obstacles to implementation
TOC practitioners sometimes refer to these in the negative as working through "layers of resistance" to a change.
Development and practice
TOC was initiated by Dr.
Eliyahu M. Goldratt, being still the main driving force behind the development and practice of TOC. There is a network of individuals and small companies loosely coupled as practitioners around the world. TOC is sometimes referred to as "Constraint Management" but this understates enormously what TOC is. TOC is a large body of knowledge with a strong guiding philosophy of growth.
Some academics in the
Operations Researchand Management Sciencecommunities claim Who|date=December 2007 that the TOC founder, Eliyahu M. Goldratt, and some of his followers display a strong guru-like and sales pitch attitude that it is not compatible with the spirit of true scientific investigation.Fact|date=December 2007
In particular, people claimFact|date=November 2007 Goldratt's books fail to acknowledge that TOC borrows from more than 40 years of previous Management Science research and practice, particularly from PERT/CPM and JIT. A rebuttal to these crticisms is offered in Goldratt's "What is the Theory of Constraints and How Should it be Implemented?", and in his audio program, "Beyond The Goal". In these, Goldratt discusses the history of disciplinary sciences, compares the strengths and weaknesses of the various disciplines, and acknowledges the sources of information and inspiration for the Thinking Processes and Critical Chain methodologies.
D. Trietsch from University of Auckland argues that DBR methodology is inferior to competing methodologies. [http://iospress.metapress.com/openurl.asp?genre=article&issn=0167-2533&volume=24&issue=1&spage=105 D. Trietsch, From Management by Constraints (MBC) to Management By Criticalities (MBC II), Human Systems Management (24) 105-115, 2005] [http://ac.aua.am/trietsch/web/WorkingPaper281.pdf D. Trietsch, From the Flawed “Theory of Constraints” to Hierarchically Balancing Criticalities (HBC), Department of Information Systems and Operations Management, University of Auckland, Working Paper No. 281, May 2004.]
It is not clear that this criticism acknowledges that the earlier approaches did not explain the Theory nor did they lead to the level of results that are routinely achieved through TOC. Goldratt's position is that the methodologies should not compete; they should work together to create better results and generate and disseminate more knowledge. Moreover, it is arguable that earlier approaches were often centered around: continuous mass production rather than discrete batch production, assumptions of infinite capacity rather than finite capacity, and many localised but ineffective safety buffers rather than one or a few critical global safety buffers. Perhaps most importantly TOC is argued to be "portable" over a wide range of logistical problems that were previously intractable.
Liebig's law of the minimum
List of Theory of Constraints topics
Systems thinking— Joint decision traps
Twelve leverage pointsby Donella Meadows
Quantum Improvement Method
* John Tripp TOC Executive Challenge A Goal Game. ISBN 0-88427-186-2
* [http://www.dbrmfg.co.nz/ A Guide to Implementing the Theory of Constraints]
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