Editor | On 10, Dec 2001

Victor Fey, Eugene Rivin
The TRIZ Group, LLC
fey@trizgroup.com, rivin@trizgroup.com

When solving an engineering problem by the trial-and-error method, the starting point of the engineer’s thinking is usually the given problem. “My problem is because this part does not perform well. How to improve it?”  these are typical reflections when attempting the problem. The engineer tries to solve the given problem, that is to find an answer to the question How? for example, How to increase efficiency of this part? or How to prevent damage to this part? etc.This implies that an object of modification is known. However, it may turn out that the real problem is quite different, and the creative efforts should be concentrated on changing another object.

A technological system is not a goal in itself, we need it only to perform a certain function, i.e., to serve some object, may it be another technological system or a human being. Examples of interactions between technological systems and objects are shown in Fig. 1. Various systems may perform the same function. A system is a “fee” for realization of the required function. Among several systems performing similar function, a better one is such that requires fewer resources to build and maintain. An ideal technological system is one that requires no material to build, consumes no energy, does not need space and time to operate, etc. In other words, an ideal system is an absent system. A notion of ideal system is one of the cornerstones of TRIZ. An ideal technological system does not exist as a physical entity but fully performs the required function.

Fig. 1. A function links a system with an object.

The notion of ideality suggests, before looking for solution to the question how? to clear up the situation and find the object to improve, i.e., to answer the question what? How one can realize the concept of ideality? Since the function has to be performed, some material body ought to be responsible for this performance. This can be realized by the following Design Streamlining Approaches:

1. A system is eliminated, if the object of its function is also eliminated (see Fig. 2,a)

2. A system is eliminated, but the object (or some of its components) itself performs the function (see Fig. 2,b)

3. A system is eliminated, but another system or the environment performs its function (see Fig. 2,c).

Fig. 2. Design Streamlining Approaches.

The following examples illustrate these approaches.

Case Story 1

Initial situation

This case story relates to a robotic test station for computer components. The gripper of the robot (see Fig. 3) performs complex manipulations (clamping, handling, and inserting) with very delicate parts. It is energized by two vacuum lines and four compressed air lines and has several sensors transmitting signals via electrical cables. All vacuum, compressed air, and electrical communications are channeled to the distribution/control box at the robot base by a so-called “umbilical cord”  corrugated plastic hose encasing all the tubes and wires. The purpose of this “umbilical cord” is to contain fine particles generated by rubbing between the tubes and wires. The cord has shown a tendency to rupture in service. The rapture was due to fatigue associated with large amplitude high-speed link motions resulting in excessive twisting of the cord. This allowed the wear particles to escape into environment and led to additional contamination due to rubbing of the ruptured surfaces.

The company was trying to improve the situation by solving a problem Howto prevent breakage of the cord? However, more durable plastics for the cord were also more expensive, while not significantly expanding the cord’s useful life. It was also suggested to evacuate air from the “umbilical cord,” thus creating a negative pressure that would not let the dust particles out. However, this would have increased costs.

Fig. 3. Robotic test station.

TRIZ analysis

There is no need to solve this problem, if we know which part of the test station should be changed. The only part that cannot be broken or damaged and does not need any service is an absent one. An ideal “umbilical cord” should not exist. This is possible if the dust particles are not generated in the first place (see Design Streamlining Approach 1).

Solution

To prevent dust generation, i.e., rubbing between the inner conduits and wires, they were separated by elastic support braces (see Fig. 4).

Fig. 4. Ideal “umbilical cord” is absent.

Case Story 2

Initial situation

Compact cars are usually powered by four-cylinder engines that have intense second order vibrations. The second order frequency at idle regimes is not fully attenuated and, for some vehicles, may resonate with the structural modes causing discomfort.

A compact car was equipped with a driver air bag. The steering column without the air bag had its natural frequency well outside the idle RPM, but adding the heavy (~1.6 kg or 3.5 lbs.) air bag substantially reduced its natural frequency. As a result, the steering wheel started shaking with large amplitudes at the idle regimes. This effect was somewhat alleviated by a (rather expensive) reinforcement of the steering column, but still the shake intensity was unacceptable. The shake was so intense that the car could not be launched before a dynamic vibration absorber – a one-pound (0.5 kg) lead block – was installed inside of the steering wheel and attached to the steering column by rubber connectors (see Fig. 5). The lead absorber reduced the shake marginally. But even with this addition there were numerous customer complaints, since the shake intensity was much higher than in other car models of this size.

Fig. 5.Conventional remedy for suppressing steering column shake.

To abate the shake effectively, the absorber had to be at least 4-5 times heavier, but there was no space available for so large chunk of lead. Another way of reducing vibration by avoiding the resonance was increasing the idle rpm, but this would have led to deterioration of the fuel efficiency, and thus could not be accepted. The situation triggered customers’ complaints and high warranty costs.

TRIZ Analysis

We need to reduce vibration of the steering column without major changes in the system. For this, we need to resolve a conflict: a damper reduces vibration of the steering column but increases its size, weight, and cost. So, an ideal solution involves elimination the lead damper and delegating its function to a resource component elsewhere in the car, preferably in the steering column (see Design Streamlining Approach 2).

Solution

It is known in the theory of vibration that in a complex dynamic system, such as a car, an appropriately tuned damper may change (reduce) vibration intensity of a component not directly connected to the damper, or even remotely located. The important parameters determining performance characteristics of a damper are its tuning and the “mass ratio” between the damper’s mass and the effective mass of the element whose vibration has to be reduced.

It was found in testing that the air bag was the most effective “damper” (see Fig. 5). To a large extent, this was due to the fact that using the air bag as a damper resulted in separating it from the steering column structure by flexible tunable connectors. It reduced the effective mass of the column from 7 lbs. (~3.2 kg) down to 3 – 3.5 lbs. (~1.4-1.6 kg) and resulted in the mass ratio of about 1.0, as compared with the mass ratio of the lead-based damper of 0.14. Consequently, shake amplitudes of the steering wheel were dramatically – six to seven times – reduced (see U.S. Patent No. 6,164,689 granted to Ford Global Industries, Inc.).

Fig. 6. Airbag-damper.

Case Story 3

Initial situation

A space agency was designing an autonomous probe to land on Venus. The probe had to carry various electronic devices to the planet. When the project was close to completion, the agency got a request from a group of scientists, headed by a renowned chemist, to place one more device into the probe. This was impossible to do, for the probe was already so crammed with other devices that one could hardly tuck a matchbox in between them, let alone a 6-kg device. However, the person who signed the request had much clout both in the space industry and government, so turning him down would have been politically imprudent. A creative solution to the problem How to find the extra space for the device? was badly needed.

TRIZ Analysis

As it often happens, a problem that many perceive as a management one may have an elegant engineering solution. The ideality approach calls for delegating several functions to one object. What other device can provide the required function? The only way to “squeeze-in” the extra device without removing another one was to integrate functions of the former with some already existing resource.

Solution

A judicious analysis of the probe design revealed the previously overlooked opportunity. Each planetary probe built earlier had carried to outer space almost 6 kg (what a coincidence!) of a “dead weight” made of cast iron. This “dead weight” controlled position of the probe’s center of gravity during landing. The “dead weight” was replaced with the device of interest (see Design Streamlining Approach 3) that performed both functions  its scientific duty and positioning of the center of gravity.