Magnetic actuators now provide an ever-increasing range of applications – thanks to technical improvements such as increased durability and improved tolerance of high temperatures. A mechatronic approach when designing magnetic actuators, as detailed in guideline VDI 2206 by the Association of German Engineers, ensures that optimal methods for closed-loop and open-loop control of the actuator factor into the design stage. However, this means magnetic properties need to be more stable than ever. Financial pressures and high material prices mean that magnetic actuators often use ferromagnetic materials, the magnetic properties of which have not been guaranteed by the manufacturer. In response to this, the team of experts at the Steinbeis Transfer Center for Mechatronics has developed a cost-effective measuring and testing method to characterize the magnetic properties of materials and actuators.
Devices for measuring magnetic flux – commonly known as fluxmeters – employ integrators which are complex and expensive. Now, the Steinbeis team in Ilmenau has successfully developed an alternative solution. MagHyst® is a modular measuring and testing system for determining magnetic properties, which is based on an innovative measuring method using a constant rate of flux change. This allows the voltage, which has a highly unpredictable amplitude and frequency range, to be integrated by calculating the sum of a constant voltage per time segment. As a result, this procedure can be carried out at low cost using a microcontroller.
The team in Ilmenau designed all software and hardware to be fully modular. Modular hardware makes it easy to vary the power, voltage and measuring speed – plus it allows the use of additional sensors to measure further physical variables in parallel. When it came to designing the software, the team created an interface which would allow us- ers to operate a range of programs by programming a DLL module. This allows users to tailor the system to different applications – whether it is used as a full laboratory tool, or merely to monitor production by indicating whether materials are “good” or “bad”.
MagHyst® offers a wide range of measuring applications. To name a few: analyzing the properties of raw materials, inspecting incoming goods, monitoring production, assessing the durability of used actuators, and condition monitoring. MagHyst® also measures the B(H) curves of materials in bar or ring form – using an adaptor in the case of bars. To measure rings directly, they must first be fitted with two measurement coils. These curves can then serve as material parameters in simulation programs, or alternatively, the material can simply be classified as “good“ or “bad“ by comparing the curve against a reference curve.
Using a reference magnetic circuit fitted with a coil or specially modified adapter, it is possible to easily integrate individual components such as armatures or conduits into the circuit, localize them in a fixed position, and record their characteristic Ψ(i) curves for that position. By comparing these curves against a reference curve, the component can then easily be classified as “good” or “bad” without first having to integrate it into the magnetic system. This method has potential industrial applications for quality control of supplier parts. Another possible application is in production, to test components upon completion of critical process steps.
Monitoring polarized systems during production – a common practice in engine production, make-to-stock production and magnet production – remains a highly complex procedure. This new system developed by the Steinbeis Transfer Center in Ilmenau allows professionals to check whether a) magnetic components have been mounted in the correct position, b) they are sufficiently magnetized, and c) permanent magnets have been mounted with the poles correctly orientated. This method also makes it possible to check for short circuits or tears in a coil. Measurements can be conducted using either the system’s own coils or special measuring circuits, although the two-coil method is best for measuring multi-phase systems. Using the new system, firms can slash costs by identifying and removing faulty components before or during production, instead of rejecting finished products during quality control.
The single-coil measuring technique of MagHyst® allows professionals to measure and test the switching behavior of electromagnetic components and actuators without destroying them. Mechanical effects can cause major changes to the switching behavior of electromagnetic actuators throughout a magnet’s working life. Measuring Ψ(i) curves and comparing them to a reference curve is an ideal way to appraise the switching behavior and overall quality of a magnetic system. This method makes it possible to estimate the component’s working life.
The new system also allows professionals to non-destructively measure the quality of fully mounted systems – such as proportional magnets – based on their switching behavior. By analysing the Ψ(i) curves, engineers can inspect these systems for mechanical and magnetic faults. A variety of factors can negatively affect the mechanical integrity of fully mounted systems, such as spring rigidity, friction, contamination, and incorrect mounting. Factors which may impair the magnetic quality include changes to materials, insufficient modulation and faulty permanent magnets.
MagHyst® is an innovative measuring system which offers a wide range of applications in quality monitoring and quality control. It allows professionals to measure the magnetic properties of materials, semifinished products and actuators, while slashing the time and resources needed to prepare samples for measurement. One major benefit of MagHyst® is its ability to measure magnetic actuators using only the field coil, without the need for an additional measuring coil – resulting in a higher standard of production monitoring. Simplified measurement of magnetic properties (i.e., non-linear Ψ(i,δ)-curves) also allows improved openloop control of magnetic actuators.