Finding a key detection method with TRIZ Author: Dr.-Ing. Robert Adunka Abstract The old design of the 3SB1 lock used a micro switch to detect if the key is within the lock. To use this micro switch, cables had to be run through the lock and to be connected to a special socket. A special device had to be used to connect to this socket and to transfer the signal to the wires. The task was to make the whole design smaller and reduce the costs of the assembly. After several other solutions were tried and none led to the desired end, a TRIZ workshop was conducted. Within that workshop, a function analysis (modern TRIZ, as in TechOptimizer) with a trimming variant was created. Resources were listed and 40 inventive principles were used. The solution that was found reduced the manufacturing costs dramatically, was much smaller than the original design and had also a new feature that was appreciated a lot by the customer. Initial Situation A new generation of a key lock with key detection should be developed. There was already a new generation - the so called 3SB3 locks - in place. The key lock with key detection was in the old fashion series of locks, which is named 3SB1. So this special 3SB1 lock was the object of the improvement. In this lock a micro switch was used to detect the insertion of a key into the lock. The micro switch was inserted in the cylinder of the lock. It detected the key insertion within the first 4mm of the insertion. This is a requirement for the lock, as it is not allowed to detect the key at the very end of its 20mm long insertion. The micro switch gives his signal over two wires to a special socket (see fig. 1). Figure 1: Cross section through the lock with key detection Lock Cylinder Key Pins Lock Housing Contact Element Socket Ball Micro Switch Internal Wires Actuator Assembly
This socket is comparable to a socket which is used for light bulbs. It has two contact areas that are then contacted by a special contacting assembly that is snapped onto the bottom of the lock. This contacting assembly has two contacting elements that touch the contact areas of the socket and that are connected to screws. These screws are used to attach a wire to the contacting elements. Because of the size of the micro switch, the whole body of the lock is bigger than it should be for the 3SB3 design series. There are also problems associated with the assembly of the lock. In order to avoid malfunction, care had to be taken, that the wires that run from the mcro switch to the socket, were not squeezed too hard. To improve the situation, a new generation of locks should be developed. To do this, the main customer for those locks was asked early in the conceptual design phase. In different scheduled meetings, solutions by Siemens and the manufacturer of the key lock were presented to him. Figure 2: Concept Slider One of the solutions presented by Siemens is shown in figure 2. The key 3 moves a slider 5 that lies within the lock cylinder 4. The slider 5 then presses on a pusher 6 that is under spring loaded by spring 7. The pusher 6 then presses on a standard switching element 2. The switching element 2 has a movable bridge within that connects or disconnects two fixed. Via screws wires can be connected to the fixed. With this solution the requirement for the early detection of the key within the lock could be recognized. The first few millimeters the key is inserted into the lock, the slider moves. The contact is made after the first four millimeters. The rest of the key insertion, the slider is out of the way to allow the key to be inserted to the very end of the lock cylinder. Also another concept is shown in this example: the use of the standard switching element. This switching element is used as a normally closed (NC) or normally open (NO) switching element which is attached to the bottom of push buttons and key locks for the detection of the push button being pressed or the key which is turned. As it is used in other assemblies of the 3SB3 series, it would be a good solution to have this standard switching element also used to do the job of the micro switch.
The concept of the solution was very good from the perspective of the functionality. The only drawback was that the key lock manufacturer announced that he is not able to manufacture a lock with a slider inside. Therefore the manufacturer came up with another solution, which is shown in figure 3. Figure 3: Concept 23mm pusher In the manufacturer s solution, the pusher was located in the center of the cylinder and an additional slider was inserted with a little offset. That way the lock would be easy to manufacture. The problem with this solution was, that the slider and the pusher would move the whole 23mm that the key is inserted. So as the key is inserted 23mm, the pusher will come out 23mm from the bottom of the lock. The standard switching element will just need 4mm displacement to connect or disconnect. With that solution of the lock manufacturer, the standard switching element couldn t be used. Along with other solutions those concepts were presented to the main customer one at a time. None of them were accepted by the customer. Therefore a two day workshop was set up to deal with the problem. Proceeding in the workshop The first thing to do in the workshop was to brain write all ideas down, that the participants already had. This is a very important step in every idea workshop. If the participants don t get the possibility to write down what is already in their heads, they could not be open for new concepts and ideas. After this initial step, a function analysis was performed on the system. The model is shown in figure 4 and has some minor drawbacks in terms of accuracy, which is based on the knowledge level of the team members of the workshop. But for the cause of the workshop, the model was of sufficient accuracy. As the model just showed how the different parts of the lock worked together and as there were no problems stated, a trimming was done on the model. With the trimming step different new scenarios were built to create artificially problems. To do a trimming one or more components of the model have to be trimmed and their useful functions transferred to new components. As those functions are transferred to new components which didn t do those functions before, new tasks arise. Those are tasks that question the engineers how the function can be performed by the other component. Finding answers to those tasks results in new concepts for a new key lock. One of those scenarios is shown in figure 5. This scenario also brings in an X-component that wasn t in the original design and now should do magically the job of all the other trimmed components. For better readability two functions were rearranged in figure 5 (numbered function 1 and 2).
User Figure 4: Function analysis of the 3SB1 lock removes inserts Key displaces Ball actuates Micro Switch Internal Wires turns Pins adjusts locks takes in Lock Cylinder locates Lock Housing Actuator Assembly emits Contact Element Socket Signal Figure 5: Trimming scenario User turns Pins removes adjusts inserts locks displaces 1 Key takes in displaces 1 locates X-Component Lock Cylinder Ball emits 2 Signal Assembly Micro Switch actuates Lock Housing Micro Switch Internal Wires Actuator Assembly Contact Element Socket emits 2 Signal
In the scenario described in figure 5 all components of the micro switch and those associated with the micro switch are trimmed. Those are all the elements that make a detection of the key possible first hand. The key now does something (not necessarily displaces) to the X-Component, which responds on this action with the emission of the wanted signal. That means that the action 1 (displaces) now points to the X-component instead of the ball. The action 2 (emits) that was formerly done by the socket will now be done by the X-component. A task derived from this scenario is: How can the X- component emit a signal when it is displaced? The solution of this problem would remove the need for a micro switch. Besides going for the trimming scenario the group also dealt with the different detection methods that could be used on the key. To tackle the problem of detection, different features of the key were listed, that could be detected: Conducts electricity Reflects light Cuts light beam Changes impedance of a coil Codes with profile Could be magnetic Cohesion Temperature Mass Stability Stiff, static part Robustness With a feature transfer the existing concept was compared to the concept slider (figure 2) and another inferior concept (concept latch ). With the comparison of the three different concepts the team members tried to transfer features of one lesser rated concept to a better rated concept which had a weak shot in the feature under consideration. Although feature transfer normally generates very good solutions, it didn t work to well in the task at hand. Table 1: Feature transfer Simplicity Number of Protection class Micro switch 0 0 0 0 0 0 0 Concept Slider - + + + - + + Concept Latch - + + + - + + Ease of assembly Manufacturability Switching capacity Diameter
Beside those more analytic tools the 40 innovative principles were also used to generate more ideas. The contradiction matrix and analysis of technical contradictions was used in this context but was turned down by the participants. The physical contradiction analysis was not used in that context. A presentation with 40 slides, each depicting one principle and examples for it, was given as a handout. Conclusion There were only four participants in the workshop, but those four generated 39 additional solutions to the given task. Those solutions were then discussed with the lock manufacturer. The solution that was favored by the lock manufacturer was then presented to the customer as a mock up only two weeks after the ideas were discussed with the lock manufacturer. The concept of the solution as it was drawn in the workshop is shown in figure 6. The concept is based on the principle of the 23mm pusher (see figure 3). The pusher is substituted by a telescopic bar clearly a principle 7 (Nesting, Matrioshka ) at work. The telescopic bar is spring loaded. The spring that lies within the telescopic bar pushes the ends away from each other. In the detailed solution, a second spring on the outside of the telescopic bar was added to hold it in place. Also the inner and the outer spring had to be coordinated in that fashion that they correspond to the spring in the standard switching element in the bottom of the key lock. Figure 6: Concept Telescopic Bar A summary of some of the advantages of the new solution in comparison to the old solution is shown in figure 7. What made it also very attractive to the customer is the fact that we were able to add a new feature into the design. The key is now automatically ejected in the 0 -position of the lock. This is good, because with that feature the user now cannot forget his key in this safety relevant key lock.
3SB1 Figure 7: Summary of the parameters 3SB3 Former design 30 V / 0,5 A NC special switching element Vulnerable to dirt Extra size No accessory useable Key is in lock when at 0 position Parameter Switch. capacity Tapping Form and size Key ejection 400 V / 10 A New design NC/NO standard switching element Protected in switch cabinet Standard size Standard accessory usable Key is ejected in 0 position Biography Dr. Robert Adunka was born in 1971 in Sulzbach-Rosenberg, Germany. After his study of production engineering at the Friedrich-Alexander-University Erlangen he worked as a scientific assistant and lecturer at the Institute for engineering design, University Erlangen-Nurnberg. In this timeframe he also had a sideline job as Application Engineer for Invention Machine Germany GmbH (Innovation coach and facilitator of workshops in over 30 companies in Germany, Austria, Switzerland and Liechtenstein). In 2002 he fortified his Ph.D. thesis "Computer-aided Evaluation Process in the Field of Methodic Product Development". After his Ph.D. he went to the Siemens AG, Automation and Drives. After working as an engineer for electro-mechanical switching devices, he took on a job as an internal consultant on innovation methods within the same division. In this position facilitated over 30 Workshops and is now heading the Innovation Tool Academy an internal training program, mainly based on TRIZ. Since 10/2001 he is recognized as "Innovation Master" and since 03/2006 he a MATRIZ Level 3 Certificate. His name is mentioned on 25 invention disclosures, which led up to now to 17 granted patents.