Calnetix Technologies specializes in high-speed rotating machinery supported by patented active magnetic bearings (AMBs), which help optimize system efficiency and enhance reliability and sustainability.
We have developed numerous magnetic bearing systems used in a wide variety of commercial systems, including high-efficiency blowers, high-speed compressors, Organic Rankine Cycle (ORC) systems and many more. We have been able to reduce the costs associated with magnetic bearing integration by improving the manufacturing processes of our magnetic bearing components and further optimizing our controllers, which are a substantial percentage of the overall system cost.
We offer Powerflux™ Magnetic Bearings in radial and side by side combination configuration and Xcelflux™ Magnetic Bearings with a unique coil architecture. The unique advantages of Calnetix’s active magnetic bearings include the following:
Powerflux™ AMBs utilize homopolar permanent-magnet-bias magnetic fields in conjunction with an electromagnetic field, whereas Xcellflux™ AMBs use heteropolar electromagnetic bias fields in conjunction with electromagnetic control fields. Both products are low-cost and easy to assemble, as shown and described below.
Magnetic bearings do not function on their own; they require multiple components working together as a unique system. Calnetix has designed and developed all of the components that make up the active magnetic bearing system, and these components are shown and described below.
The actuator in an active magnetic bearing is the electromagnet that applies a controlled force to the shaft of a machine to control its position. A radial actuator consists of a lamination stack with control coils and poles arranged to give two orthogonal axes of control. An arrangement of permanent magnets is also used in Calnetix actuators to produce a linearizing bias flux. Other AMB manufacturers produce the linearizing flux with a DC current in the control coil. Two other common actuator configurations are a combination radial/axial actuator and a stand-alone axial actuator.
An AMB actuator must be connected to a Magnetic Bearing Controller (MBC) that supplies the control current to the coils based on a position sensor feedback signal and a control algorithm.
To learn about the operational principle of homopolar, permanent magnet-biased active magnetic bearing, please click here.
Position sensors are critical components of any active magnetic bearing. Their role is to continuously provide the controller with accurate up-to-date information about the rotor position unaffected by the external factors, such as speed, temperature, dust, working fluids, external magnetic and electrical fields, etc. Even though significant progress has been made in developing self-sensing AMBs, wherein the functions of the position measurement and the force generation are combined in one physical component, their fundamental performance limitations will likely limit their use to low-cost, low-speed machines. A conventional bearing arrangement utilizing dedicated radial and axial sensors will remain dominant.
Different types of position sensors have different combinations of properties, making some of them more suitable for a given application than the others. However, in the industrial environment, it is typically preferable to have one technology that would cover as many applications as possible. From a wide variety of the available technologies, including optical, capacitive and electromagnetic position sensors, the latter appears to be the most universal solution. Calnetix utilizes four types of sensors, depending on the application specifics:
All sensors include the sensitive element (sensor head) located in the machine, where the displacement needs to be measured, and sensor electronics, typically located in the Magnetic Bearing Controller (MBC).
A speed sensor provides the active magnetic bearing with information about the rotational speed and the angular position of the rotor needed for adjusting the control parameters as speed changes and enabling the rotor unbalance cancellation. Calnetix uses two types of dedicated speed sensors. Both sensors utilize a source of a DC magnetic field, a Hall-effect element measuring that field and a feature on the rotor, such as a notch modulating the magnetic field.
Backup bearings provide support for the rotating assembly when the magnetic bearing system is deactivated, and provide rotor support in the event of an overload of the magnetic bearings or a failure of some component of the magnetic bearings. In normal operation, the backup bearings are not active as they will have a small radial and axial clearance to the rotating assembly. This clearance is at most one-half of the magnetic bearing air gap and typically considerably smaller.
The most common backup bearing configuration used by Calnetix is two duplex pairs of angular contact ball bearings preloaded face-to-face (DF). This mounting requires the bearing outer races to be clamped – either hard or through a spring – on the outer race. Hybrid bearings with conventional SAE 52100 steel races and SiN3 balls are standard. Backup bearings for high-speed applications are usually cageless and use either a grease film, dry film lubricant or a light grease fill.
Calnetix Technologies has developed and deployed advanced Magnetic Bearing Controllers (MBCs) that contain all of the elements necessary to operate magnetic bearing systems. The company currently produces two different MBC platforms in the Insight™ series and one in Concurrence™ series.
For more information, see the Magnetic Bearing Controllers product page.
The Calnetix Service Graphical User Interface (GUI) is used for system setup, monitoring, diagnostics and system identification. The upper half of the front panel, shown below, displays orbit plots from the two radial bearing sensors and a time history plot from the axial bearing sensor. Other operating variables shown include spin speed, static current, and synchronous displacement and current. Status variables, such as levitation and fault status, are indicated as well. A system Information window on the right gives version information for the GUI, firmware, parameter file and machine serial number specifier.
More detailed information or functionality can be accessed through the action buttons: Digital Signal Processors (DSP) Actions, View Logs, Fault Summary, View/Set Parameters and Measurements. The additional functionality includes:
Active Magnetic Bearings (AMBs) have been in commercial rotating machinery for over 30 years, offering increased performance and extended machine lifespan due to frictionless operation and the lack of wearable parts. There has been an industry-wide increase in the production of magnetic bearing systems, which has led to overall cost reduction and more rapid market adoption. Some of the advantages of switching to magnetic bearings, include:
To see more information about AMB advantages, click here.
How Magnetic Bearings Work
How A Magnetic Bearing Controller Works
Advantages of Magnetic Bearings
Transient Simulation of Magnetic Bearing and Backup Bearing Interaction in a High Speed Rotary Atomizer Subjected to Impulsive Loads
Design and Shop Testing of a 165kW Cryogenic Expander/Generator on Magnetic Bearings
Comparative Study of Axial/Radial Magnetic Bearing Arrangements for Turbocompressor Applications