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TOC Trees Help TRIZ

TOC Trees Help TRIZ

| On 20, Sep 1999

Eduardo C. Moura, Qualiplus / ASI Brasil
Campinas, SP – Brazil

Keywords: TRIZ, TOC, ARIZ, Current Reality Tree (CRT), Conflict Resolution Diagram (CRD), Ideal Final Result, Physical Contradiction, problem formulation.


This article shows how some of the Theory of Constraints (TOC) logical trees, namely the Current Reality Tree (CRT) and the Conflict Resolution Diagram (CRD) can be useful for graphically describing the inventive situation and identifying / selecting the core problem to be tackled via ARIZ or other TRIZ methods, as well as to more easily identify the contradictions involved in the problem.


By this article I humbly request entrance to the TRIZ authors community. That’s because I don’t consider myself a TRIZ wiseman, given my experience of just three years with such a powerful and complex methodology. Incidentally, before going into the main subject of discussion, I’d like to share with the readers some frustration I had during my first steps on the TRIZ road. By attending to TRIZ symposia in the USA and listening to some long-time travelers along that road (famous consultants), I always left with the somewhat exaggerated perception that one should not dare to use TRIZ without a 20-year experienced black belt by his side (preferably the one who was giving the lecture). But soon I was glad to read in a book from the TRIZ Master of Masters: “I want to emphasize that anyone can become a professional – you just have to learn the subject matter. That’s it. … Talent is 99% hardwork. … First, you have to become a professional. Anyone can accomplish that. Then, we will see…. This book is enough for you to start” [1] . So after a relatively short period of TRIZ study and “incubation” (this actually never ends…) I started to use it and had the rewarding surprise that much can be accomplished in the creativity arena with just a little TRIZ basics. That is not to say that TRIZ is trivial (much on the contrary) nor that there is no benefit in hiring a consultant (which I am too, by the way). The point is that TRIZ is so powerful that once you study and add a pinch of it to your technical knowledge and engineering common sense, you’re on the way to becoming a more creative professional. And, along the road, you will probably want to call that consultant for help, so we’ll all be happy. But that should not preclude you from self-studying and self-learning TRIZ.


Working with teams in the application of ARIZ for problem solving and concept generation, I usually had no difficulty in finding a problem to attack, or even finding a contradiction. There are plenty of them out there. But an uncomfortable feeling was always there in the background, as this question pounded my mind: “How do you know this is the problem? How do you know this is the right contradiction to solve?”. That was when I started to consider tools that could shed light onto the task of describing the inventive situation, so that the core inventive problem and corresponding contradiction(s) are selected. In this sense, I found very useful to borrow some tools from the Theory of Constraints (TOC), namely the Current Reality Tree (CRT) and Conflict Resolution Diagram (CRD).

The above mentioned difficulty of correct problem identification is acknowledged in the article by Zlotin and Zusman, ARIZ on the Move [2] : “The most serious problem took place, however, when students were trying to solve real life (and thus poorly formulated) problems, due to the absence of ‘problem clarification and formulation’ steps in ARIZ-85C. This section existed in previous modifications of ARIZ (ARIZ-71, 77) but was excluded in later versions due to the lack of improvement it had undergone compared to other, more rigorous and quickly evolving sections of ARIZ”. Later in this same paper, the authors state that a poorly formulated problem contributes to make the solution process extremely difficult and that the transition from the initial problem statement to a correctly defined mini-problem is a challenge, even for experienced TRIZ specialists. Therefore, tools that can help identify the core problem and corresponding conflicts are very welcome to TRIZ. These are exactly the first steps in the Goldratt’s TOC Thinking Process (for more on the subject of TOC, I recommend reference [3] ).

Earlier in 1997, Rizzo [4] briefly comments about the synergy between TRIZ and TOC tools, with more emphasis on the use of the CRD to identify contradictions, but no examples are given. Later, Domb and Kowalick [5] quickly stated ‘en passant’ that TOC could help TRIZ in the problem identification steps. More recently, Domb and Dettmer [6] suggested that TRIZ can help TOC and vice-versa, but again more emphasis is given to the use of the CRD. The following sections add evidence to those observations, by giving examples on how the use of CRT and CRD could help the application of TRIZ to some real life problems in the automotive industry. However, no explanations are given here about how to build a CRT or a CRD. For that purpose, the refer is again referred to Dettmer’s book [3] . In the following examples the author apologizes for eventual problems in the translation of technical terms from Portuguese into English. Please also note that emphasis is given only to the usefulness of the TOC trees, instead of going into details about the complete case studies nor about the final solutions (both for the sake of conciseness and for protection of patentable ideas).

How to read the logical trees

Before we jump into the examples, a short explanation about how to read a CRT and a CRD. A CRT is made up of two types of elements: “entities” and logical symbols, connected by arrows. Entities are single-idea, clear statements about the current reality, enclosed in a text box. Consider a plastic encapsulated microcircuit with 300 external leads (external conductors) separated by a fraction of a millimeter. The following are examples of entities: “there is voltage between leads”; “ambient air is moist”; “parasitic current flows between leads”; “ionic contaminant is left on device surface”. The ellipse is one of the logical symbols, and works like an AND logical gate. By joining those elements following certain logical rules one may get a better understanding of the current reality, as shown in the right branch of beside figure , which is read like this: IF “there is voltage between leads” AND “ambient air is moist” AND “ionic contaminant is left in device surface” THEN “parasitic current flows between leads” (effect). If a single cause (or an additional set of causes going through another ellipse) can give the same effect, there will be another arrow path going to the effect entity . In this case, we link the logical statements with the OR clause. Thus, the complete reading of that figure would be: IF “there is voltage between leads” AND “ambient air is moist” AND “ionic contaminant is left in device surface” OR IF “metallic micro-particles are left on device surface” AND “there is voltage between leads” THEN “parasitic current flows between leads”.

A CRD has a fixed structure and is formed by one common objective, two requirements and two conflicting prerequisites, as shown in the figure to the left, which is read: On one hand, in order to reach “common objective” we must have “requisite 1”. In order to reach “requisite 1” we must have “prerequisite 1”. On the other hand, to reach “common objective” we must have “requisite 2”. In order to reach “requisite 2” we must have the conflicting “prerequisite 2”. And those conflicting prerequisites usually are the hidden reason why the common objective is not attained.

Air conditioning odor

Under certain climatic conditions, fungi and bacteria grow inside the dark and moist environment in the evaporator comb of an automotive air conditioning system. That gives rise to a most annoying odor when starting up system’s ventilation, after a shut down period. A team decided to apply TRIZ in order to generate conceptual solutions to the problem. They first built a functional tree, shown in Figure 1.

That diagram was very useful to highlight the involved functions and harmful effects, but it does not show the dynamics of the problem, that is, the sequential combination of events which culminate in the final effect of bad start up odor. Thus, the team decided to build the CRT of Figure 2 (following page). The tree clearly showed the root causes behind the odor effect:

  • Filter lets microorganisms and particles (pollen, etc.) get into the system.
  • Current design allows water retention inside the evaporator.

Then the initial problem “we want to eliminate bad start up odor” could be more precisely restated as the following mini-problems, which pinpointed two main directions for solution, either of which could eliminate the odor effect:

  • “We want to eliminate water retention in the evaporator” (e.g.: dry evaporator after use, change design etc.).
  • “We want to eliminate intrusion of particles and / or microorganisms into the system” (e.g.: improve filter efficiency, kill microorganisms before they get inside etc.).

Rear spring noise

The blades of a truck’s rear spring set are separated by a plastic disc intended to eliminate the squeak noise due to friction between the blades. However, the plastic disc quickly wears out and noise begins. Again, the CRT in Figure 3 was useful to complement the understanding provided by a previously built functional diagram. The CRT pinpointed the basic problems that were giving rise to the final noise effect (which was not apparent in the functional diagram).

Out of the nine final concept solutions generated in this case after applying ARIZ, two good ones immediately popped up just by looking at the root cause “plastic disc is fixed to the secondary blade”, disclosed by the CRT. The solutions offered were:

  • “Rubber sandwich” (elimination of surface friction by use of a thick, flexible rubber disc fixed to both blades).
  • “Split disc” (change from heterogeneous metal-plastic friction to homogeneous plastic-plastic friction by splitting disc in two halves and fixing both of them to the blades).

Air exhaust valve

In order to avoid discomfort or safety problems to the passengers, a car must have an air exhaust valve that relieves the internal air pressure generated when the ventilation system is on or, in a more critical situation, when an air bag is inflated. A certain car’s exhaust valve was properly and safely accomplishing its “relieve air pressure” function, but another harmful effect was present: “dust gets into the car”. The valve consists of a box fixed to a opening in the car body. Inside the box are six little plastic molded doors, inclined with respect to the vertical plane, which close by their own weight and open under a certain air pressure level built inside the car. In this case, the functional diagram of Figure 4 clearly showed that the core problem was the harmful function: “mechanical oscillations from car displacement shake and open valve doors, which then make rattle noise and let dust get in”, so it was not necessary to build a CRT.

Figure 4

Figure 5

From that clear problem statement we decided to use a CRD in order to identify a technical conflict or, preferably, a physical contradiction behind the situation. Starting from the ideal final result “valve relieves any excess internal air pressure and does not let any dust get inside” as the CRD’s objective (Figure 5), we worked down to two conflicting prerequisites, thus highlighting the physical contradictions (“door must be easyto open and door must be hardto open”; “door must be lightandheavy”) which opened a nice path to an extremely simple, cheap and very effective solution. Incidentally, the author believes that this case was the very first industrial application of TRIZ in Brazil.

Damaged fuel level meter

An automotive fuel level meter was being damaged during installation and maintenance operations due to mechanical stresses imparted to the relatively thin and long metal lever that transmits movement from the buoy to the electric cursor inside the meter. Two CRDs disclosed the contradictions shown in Figure 6, which then quickly led to an amazingly simple and cost effective idea that significantly increased the mechanical strength and solved the problem.


Real life examples were given which show that the stand-alone or combined use of two logical trees from the Theory of Constraints’ Thinking Process, namely the CRT (Current Reality Tree) and the CRD (Conflict Resolution Diagram) can be very helpful to, respectively, correctly formulate the mini-problem and reveal the basic technical / physical contradictions.


  1. Altshuller, G., And Suddenly the Inventor Appeared – TRIZ the Theory of Inventive Problem Solving, Technical Innovation Center, Worcester Massachusets, 1996, p. 122.
  2. Zlotin, B. and Zusman, A., ARIZ on the Move, Ideation International Inc., 1998 – in TRIZ Journal, March 1999.
  3. Dettmer, H. W., Goldratt’s Theory of Constraints – A systems approach to continuous improvement, ASQ Quality Press, 1997.
  4. Rizzo, A., Tools from the Theory of Constraints, TRIZ Journal, May 1997.
  5. Domb, E. and Kowalick, J., How to Bring TRIZ into Your Organization, TRIZ Journal, October 1997.
  6. Domb, E. and Dettmer, W., Breakthrough Innovation in Conflict Resolution – Marrying TRIZ and the Thinking Process, TRIZ Journal, March 1999.