Smart Springs

Spring elements are inexpensive components and are often used in products that are many times more expensive, in which flawless functioning over their service life is important.

The spring element often performs an important task and must neither lose force nor fail during operation. This would lead to a loss of quality of the component or even to failure of the product.

A broken valve spring in the engine of an oil tanker in the middle of the Indian Ocean, for example, could lead to the ship no longer being steerable and, in the worst case, to an accident and disaster.

However, springs that are installed in places that are difficult to access, such as disc springs installed in buildings for earthquake protection, also perform important functions. They are permanently subject to a static load and must be able to absorb the shock waves in the event of an earthquake. Due to the installation situation, it is not always possible to clearly determine whether they are still functioning in accordance with the design during operation or whether they have lost unacceptable force over the years.

These examples clearly illustrate the importance that technical springs can have in operation.

Although the manufacturer as part of the outgoing goods inspection tests the proper functioning of technical springs, in operation, the springs are usually difficult to access and their function cannot be tested. In addition, the real environmental conditions in which the spring is used often differ from those theoretically designed.

The innovation team at Federnfabrik Schmid has dealt with this important input and has come up with an idea that can minimize the risk of failure of the component in which the spring is working: the Smart Spring.

The heart of this Smart Spring is the newly developed sensor. This consists of a strain gauge, a temperature sensor, an acceleration sensor, a data memory and a battery. The recorded information can be temporarily stored and wirelessly transmitted to a PC, smartphone or tablet.

When spring elements are loaded, the maximum strains usually occur on their surface. By suitable application of a strain gauge, these can be measured and a sufficiently exact statement about the load is possible. If it is possible to record this actual condition over a longer period, the condition of the spring can be characterized. For this purpose, among other things, the occurring stresses, respectively strains, as well as the number of occurring strain maxima are evaluated in order to obtain a statement about the remaining service life, the loss of force over a certain period of time or information about occurring stress peaks.

Since components are often not designed to be fatigue-proof, but rather service-proof, it is of great importance to know the real conditions precisely. Not only do the types of loading, such as static, dynamic or impact, play a role here, but also the possible notch points, stiffness jumps in the component, the manufacturing influences, such as residual stresses, surfaces or edge layers, the material with its strength, hardness and toughness, as well as influences from the environment (environment), such as temperature or humidity. Usually, the real influences are not sufficiently known and theoretical characteristic values, e.g. from the uniaxial tensile test, are used to represent the three-dimensional actual situation of the mechanical strength as well as possible.

At present, springs are designed against theoretical load stresses. These load stresses should not exceed a certain level, otherwise a loss of strength could occur. The calculation of the load stress is based on theoretical assumptions and is usually not confirmed in component tests, as these are too time-consuming or cost-intensive in most cases. With the Smart Spring it is now possible to measure and evaluate the real load stresses of the spring in the application. Deviations between theory and practice can be detected quickly and necessary adjustments can be initiated. The measurement can also be carried out over a longer period. Due to a well thought-out energy concept, it will be possible to operate the Smart Spring  for up to 10 years.

In addition, wireless data transmission makes it possible to avoid the cabling that is otherwise common with strain gages. Cable breaks or difficult-to-access installation locations are no longer an issue for the Smart Spring.

Due to the continuous data evaluation, real load profiles can be created and harmful irregularities, such as stress peaks, can be detected more easily. In the case of time-fixed springs, a statement about the remaining service life or the probability of failure becomes possible. The Smart Spring  becomes the “brain” of the spring, indicating what its condition is and when it makes sense to replace it before it fails.

An app for evaluation helps the user to get a detailed picture of the condition of his spring. It is thus possible to determine various key figures and define a measure for a critical condition. An alarm defined in this way, which also appears in the app, leads to an indication to inform the operator of the spring.

With this new development, occurring damage events can be detected in time. The component is then replaced as part of planned preventive maintenance before a major defect can occur. The use of the Smart Spring  thus avoids expensive follow-up costs.

By cleverly networking the sensor, the spring can even be monitored from anywhere in the world. Several Smart Springs working in parallel in one application can be monitored centrally from a driver’s cab or in an office. Each Smart Spring can be given an individual name so that in parallel applications the springs can be clearly assigned in the evaluation app. It also has a status LED that provides quick and uncomplicated information about its status without an app, on site.

The idea of the Smart Spring was awarded the 2019 Digital Journey  innovation prize by CSEM SA (Centre Suisse d’Electronique et de Microtechnique). CSEM’s mission is to ensure the competitiveness of Swiss industry, especially microtechnologies. It acts as a bridge and catalyst for the transfer of technology and know-how between science and industry and honours outstanding ideas. 

The prize is endowed with CHF 100,000 and is awarded annually to SMEs that transfer their decades of experience in the field of industrial production into a digital approach.