Permanent maglev rotator in a rotary machine could be stabilized according to the author’s experiences, by use of a non-PM (permanent magnetic) force acting together with the PM force, and a non-PM bearing functioning together with the PM bearing, or a so-called gyro-effect which can stabilize all rotators including permanent maglev rotator. This paper presents both axially and radially driven permanent maglev centrifugal heart pumps, as well as a permanent maglev turbine machine and an industrially used permanent maglev centrifugal pump. In all this devices permanent maglev rotators achieve stable equilibrium by different approaches described in details. Finally, the principle exhibition of gyro-effect and the route chart to stabilization of permanent maglev rotator are presented.
Keywords permanent maglev rotator, stabilizing approaches, gyro-effect, route chart of stabilization.
Department of Biomedical Engineering (BME), Jiangsu University, China.
RecievedMay 18 2014 AcceptedAug 16 2014 PublishedAug 27 2014
CitationQian KX (2014) How to stabilize a permanent maglev rotator in heart pumps and other rotary machines? Science Postprint 1(1): e00029. doi: 10.14340/spp.2014.08R0003
Copyright©2014 The Authors. Science Postprint is published by General Healthcare Inc. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs 2.1 Japan (CC BY-NC-ND 2.1 JP) License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.
FundingNo funding for this project, but the author has had other projects supported by cooperating partners.
Competing interestNo relevant competing interests were disclosed.
Donation messagePermanent maglev has been acknowledged to be unstable in past hundreds of years, I have proved,on the contrary, this is not true! If I could continue my work, I would make permanent maglev rotary machines commercializing and industrializing. Hereby your support is very important and decisive!
PatentsQian KX, Ming Z, inventor. Magnetic suspension bearing. Patent CN2288305 Y, 1998. Aug. 19. Available from: http://www.google.com/patents/CN2288305Y?cl=en.
Rolling bearing, applied most profoundly at present in the world, has advantages of simplicity, reliability and low costs, but can not meet with the special technical requirements in modern science and engineering, for example, in a high speed, continuous and durable performance. The author had met with bearing problems in heart pump research, the available mechanical bearings can not avoid mechanical wear and heat generation which leads to thrombus formation.
The other investigators applied EM (electromagnetic) or hydrodynamic bearings 1-9 to mitigate the drawbacks of pumps with mechanical bearing systems, but resulting in new problems of complicated rotor position detection and control, additional energy consumption, etc.
PM bearing can solve the problems of both mechanical and EM bearings, but nobody believes PM bearing can reach stable equilibrium, because in 1939 an English scientist proved theoretically that permanent maglev can not achieve stable equilibrium in static state 10. The author believed that a permanent maglev rotator in performance is in a state different from standstill, what will happen with a permanent maglev rotator in dynamic state, no answer has been given until now. In past 30 years, efforts have been directed toward whether a permanent maglev object could be stable in dynamic state, a lot of experimental models and prototypes of permanent maglev rotary machines have been designed and manufactured in the author’s institute and laboratory, the experimental results demonstrated that they could be stable by use of different methods.
Figure 1 is a prototype and schematic drawing of an axially magnetically coupling driven centrifugal heart pump with PM bearings.
1.brush-less DC motor coil with iron core; 2. motor magnets disc; 3. PM bearing; 4. outlet; 5. inlet; 6. impeller; 7. one contact-point.
As the electric current is introduced into the motor coil (1), the motor magnets disc (2) will be driven to rotate together with the impeller (6), thus the fluid (blood, water, or others) will enter the pump from inlet (5), and rotate with the rotating impeller. Finally, the fluid will get out of the pump from outlet (4) due to centrifugal forces. The rotor is supported radially by PM bearing (3), and has one contact-point (7) with the stator because of the attraction between the motor iron core (1) and the motor magnets disc (2). At the same time of fluid delivery by rotary impeller, the fluid has acted an axial force on the impeller, tending to pull the impeller to inlet. Thus the rotor will be disconnected from one connect-point if the rotating speed and fluid flow is large enough. In this way the rotator becomes fully suspended from the stator. The PM bearing (3) has an axial reactive force on the rotor when the rotor moves toward inlet direction, the PM bearing design should consider thereafter either the rotor could disconnect from one-connect point or it could not escape from the attraction of motor coil iron core. The maximal axial displacement of the rotor is about 1.0 mm, its corresponding value to 100 mmHg head and 10 L/min flow rate of the pump is 0.80 mm. This is enough for left ventricular assist pump.
Figure 2 is a radial driven centrifugal heart pump and its schematic drawing. Different from axial driven pump described above, the rotor magnets (6) is driven to rotate by radial motor coil (5). Two PM bearings (4) and (7) support the rotor radially. As the impeller (3) is driven by this Brushless DC motor to rotate, the fluid will be delivered from inlet (2) to outlet (1). Four hall sensors are located at the end of the device for measuring the rotor position, not for rotor control like an EM bearing, but for demonstration of suspension of the rotor.
1. outlet; 2. inlet; 3. impeller; 4. PM bearing; 5..motor coil with iron core; 6. rotor magnets; 7. PM bearing; 8. 4-hall sensors.
PM bearing (4) and (7) support the rotor mainly in axial direction, because they have larger axial bearing force component and smaller radial one 13. The rotor is supported radially mostly by a fluid membrane bearing which consists of the gap between rotor and stator and the liquid herein. The gap has a dimension 0.15 mm in radius.
Hemo-dynamic bearing can help the permanent maglev rotator to obtain stability, but it’s not the precondition for stabilizing. Figure 3 is a newly developed axially driven centrifugal heart pump. Different from Figure 2, there is no radial hemo-dynamic bearing in Figure 3, the radial support of the rotor is provided by PM attractions between the motor coil iron core (1) and the rotor magnets (3), which opposes the rotor to move eccentrically. In Figure 2, the motor coil iron core (5) attracts the rotor magnets (6), a radial hemo-dynamic bearing is necessary to counterbalance this attractive force and to support the rotor levitating.
1. motor coil with iron core; 2. PM bearing; 3. rotor magnets; 4. impeller; 5. PM bearing.
In order to verify whether the rotator is suspended, the rotor position was detected for radially driven centrifugal heart pumps (Figure 2). Data are shown in Figure 4. The maximal eccentric distance (max. ED) of the rotor is obviously depended on pump rotary speed and the flow rate. At 3,000 rpm, for example, max. ED reaches always 0.15 mm which is the gap between the rotor and the stator in radius, that means the rotor has contact with the stator and is not levitated. If the rotating speed is higher than 3,250 rpm, on the contrary, the max. ED could be smaller than the gap between the rotor and the stator, that is, the rotor has no contact with the stator. Namely, the rotor is levitated. Large speed and large flow rate indicates high fluid pressure in the gap between the rotor and the stator, the liquid membrane bearing force will be larger, the max. ED of the rotor will be smaller. Meanwhile, high rotary speed can generate a so-called gyro-effect which can stabilize all the rotator including the permanent maglev rotator. This gyro-effect is more distinct in permanent maglev turbine machine, because thereby only air exists in the device, no liquid can be formed membrane bearing.
The permanent maglev turbine is shown in Figure 5. In the left the device was in testing, in the middle and the right its experimental model and schematic drawing are exhibited. 1. Rotor axis; 2. Stator magnet; 3. Rotor magnets; 4. Stator magnets.
1.rotor axis; 2.stator magnet; 3.rotor magnets; 4. stator magnets.
The rotor position detection was similar to that in permanent maglev centrifugal heart pump. 4-hall sensors detected the rotor magnets and computerized into the distances to stator. At first the propeller of the experimental model was driven to rotate by a compressor, then the air wind was removed and the rotor’s eccentricity was recorded. Figure 6 is the results of the rotor eccentricity.
In the first 500 ms the rotor has an eccentricity of about 0.13 mm, smaller than the gap between the rotor and the stator, that means the rotor is suspended.
Figure 6 indicates that only in the first 500 ms after the air compressor was removed, the rotor eccentricity (0.09–0.13 mm) is smaller than the gap between the rotor and the stator (0.15mm). It is to say the rotor is suspended only in first 500 ms.
500 ms corresponds to 1,850 rpm of the rotor (Figure 7). It’s clear, when rotor speed is higher than 1,825 rpm, the rotor is suspended, as the rotor speed is reduced gradually to lower the 1,850 rpm, the rotor begins to have contact with the stator.
As described above, there is neither non-PM force nor non-PM bearing in the permanent maglev turbine, the rotator could be even so stable if the speed is large enough. This is a so-called gyro-effect, its principle will be exhibited in the following.
With the same PM bearing structure, a new industrially used permanent maglev centrifugal pump has been developed (Figure 8). It’s driven by an AC motor via magnetic coupling axially, its impeller has a form like a UFO disc. Radial suspension of the rotor is provided by attractive forces of magnetic coupling, and the axial suspension of the rotor is realized through the PM bearing demonstrated in Figure 5 (right). This new contribution reveals that many different methods for stabilizing permanent maglev rotator can either alone or together function to ensure the stable equilibrium of the permanent maglev rotator.
Gyro-effect can be described as in Figure 9 (left). A gyro stands above a ball, it can be stable if its rotating speed is high. Otherwise, if it does not rotate, or it is rotating but its speed is not high enough, it will fall down off the ball.
Left: A gyro can stand up a ball if its rotating speed is high enough, but will go down if it is in standstill or rotates not fast; Right: The toy Levitron has same property. The small magnetic ring can rotate above the large ring if the small ring has enough speed, but will fall off if its speed decreases to certain value 14, 15.
Levitron (Figure 9, right) has two magnetic rings: small one is above the big one. The small ring is rotating and the big ring is fixed. If the rotating speed is high enough, it can be suspended and rotate above the big ring stably. When the small ring reduced its speed gradually, its stable suspension state will be destroyed and will fall dawn onto the ground. The magnetized direction by Levitron is different from that in the author’s bearing (Figure 2), this is due to achieving less axial occupation but larger bearing force in heart pump.
Gyro-effect can be understood as a function of inertia like some thing following Newton’s first law, as simple as riding a bicycle: with certain high speed the rider can avoid to fall over, though theoretically a two-wheel bicycle cannot achieve stable equilibrium. People may think a bicyclist can use the steering for control, but nobody can maintain a stable equilibrium of a bike in standstill.
The critical speed between unstable to stable equilibrium, named as minimal stable speed 16, may change according to the bearing force and the rotating inertia of the system: by larger bearing force or with larger inertia of the rotor the critical speed will be lower 17.
After theoretical and experimental investigations, a route chart to stabilization of permanent maglev rotator has been clear (Figure 10): 1. In static state, permanent maglev is unstable (Earnshaw's theory); as the rotating speed gradually increases but not up to a critic speed, the permanent maglev rotator is also unstable. 2. In case that the speed equals or is larger than this critic speed, the permanent maglev rotator is suspended stably because of gyro-effect. 3. The critic speed is affected by rotating inertia of the rotor and the bearing force, by larger inertia and larger bearing force, the critic speed will be smaller.
Permanent maglev rotary machines have advantages of simpler structure, lower costs and more reliability compared with other maglev devices 19. The traditional concepts exclude the possibility of passive maglev because of Earnshaw’s theorem. In fact, few of the people who disregard permanent maglev know that Earnshaw’s theorem was deduced in static status. Actually, Earnshaw’s theorem is not valid for dynamic equilibrium of permanent maglev. There should be another principle to answer the question whether a rotating passive magnetic levitator can achieve a stable equilibrium; and why if it can.
This paper presented a route chart to stabilization of permanent maglev rotator. It is attempted to explain whether and why permanent maglev rotator can achieve a stable equilibrium.
"Permanent maglev cannot be stable” has been a hundreds of years misunderstanding. At first, most people believe Earnshaw had proved this concept theoretically but they do not know Earnshaw’s theory has two preconditions: 1. only PM force acts; 2. whole system is in still stand. In fact almost by every case it is hardly possible to exclude other force except PM force in action. Levitron in Figure 9 (right) becomes stable due to the gravity which balances the PM force. If the gravity is not existed, it can not keep rotating meanwhile suspended. Secondly, rotator in machines works for certain purpose, it can not keep standstill for ever. That means Earnshaw theory can not govern a rotator because it is not still. Fortunately the author has developed a lot of permanent maglev devices which could be stable, it will follow many investigators in the future expectedly.