Final Report Summary - MAGDRIVE (Magnetic-Superconductor Cryogenic Non-contact Harmonic Drive)
Executive Summary:
The objective of this project is to design, build and test a magnetic-superconductor cryogenic non-contact harmonic drive (MAGDRIVE). This harmonic drive is a mechanism provided with an input axle and an output hub with a great reduction ratio and it will be able to function at cryogenic temperatures. This harmonic drive is based on “non-contact magnetic teeth” instead of fitting teeth on a flexural wave as conventional harmonic drives are based on. Non-contact magnetic teeth are activated by a magnetic wave (similar to an electrical engine). This solves the problems of contact wearing and mechanical fatigue.
Long life and protection against overloads, vibrations and shocks are additional features.
In a fully non-contact version superconductors are used for non-contact bearings. The new developed design of superconducting bearings demonstrated performances a 60% better than any other previous design.
Two prototypes have been manufactured and tested at room temperature and at cryogenic temperature (below 63K).
Additionally non-contact feedthrough mechanisms, launch lock and release mechanisms and non contact sensors for 6D displacements and rotations (an vibrations up to 30 kHz) of an axle have been developed and patented.
Project Context and Objectives:
Spacecrafts, satellites and exploration rovers need increasingly demanding mechanisms able to work in vacuum and along a large range of temperature. Particularly critical are gears which are needed for deployment of antennas or other elements, releasing instruments, displacement of interferometers or simply propelling wheels. Up to now Harmonic drives are commonly used because of their high specific torque density and high reduction ratio (the higher the ratio the smaller the motor). Drawbacks of harmonic drives are that they need lubrication and their working life is not very long due to fatigue and wear.
The objective of the MAGDRIVE project is to demonstrate a new technology of magnetic non-contact gear that aims to be able to work in cryogenic environment (and vacuum), without contact or wear, with no need for lubrication. Additionally it will provide intrinsic protection against overloads, vibrations and shocks.
Conventional bearings present a longer life than harmonic drives themselves. Therefore the MAGDRIVE technology for the gear itself combined with conventional bearings is a good option to increase the life of the overall device itself. For the demonstration of this technology a Room Temperature Prototype (RTP) has been designed and tested successfully.
Cryogenic conditions are much more difficult than room temperature conditions. Lubrication is always a problem for conventional mechanisms working at cyogenic conditions. For demonstration of the MAGDRIVE technology in cryogenic conditions an ambitiuos design (CTP) was proposed including non-contact superconducting bearings combined with the non-contact magnetic gears. The test bench included thermal cryostat and non-contact magnetic feed-through for transmitting power to the input axle and braking the output axle whose development has been a colateral objective.
In this cryogenic prototype it is neccesary to measure 6 degrees of freedom (displacements and rotations) of the floating axles. For that a specific (also magnetic) sensor was developed and tested succesfully.
Project Results:
Main S&T results
Two test benches have been designed and built to test the performances of the Room Temperature and Cryogenic MAGDRIVE prototypes.
RTP
The room temperature test bench is mainly composed of a driving unit with an electric motor, encoder&torque sensor connected to the input axle of the MAGDRIVE prototype and a “load” set composed of an EMAG brake, encoder & torque sensor connected to the output axle. Rotated angle and torque can be measured both at input and output axles.
The MAGDRIVE RT prototype was designed for a GR=1:21. This must be understood as a nominal ratio, as the behavior of a magnetic gear is somehow different from conventional gears. Magnetic gear teeth do not touch each other, but interact at distance. This makes it necessary to draw the input axle a shift angle to reach a definite torque. Therefore, an objective for the testing was to check the predicted GR at different loads and to measure the shift angle as a function of the load or output torque.
The shift angle in a static condition is nonlinear. The main characteristic is that there is a maximum torque that can be transmitted. If a torque greater than that is applied to the output axle, then the input axle just slips. This is an intrinsic antijamming characteristic that opens many opportunities for this type of devices. The maximum transmitted torque can be customized in the design of the MAGDRIVE.
The angle for which the maximum occurs can also be customized, dividing the circumference into a number of intervals, including a stable and an unstable part each. The prototype tested has two intervals of 180º each. That is, when the output axle is blocked, the maximum torque is reached twice a turn of the input axle.
The input angle adapts to any variation of the output torque. These variations of the output torque in the case of constant speed produce short deviations from the nominal reduction ratio.
Vibrations were also measured on bearings and the box of the MAGDRIVE prototype itself. The level of Vibration measured in all the cases was under the sensitivity of the sensor. Even in the case of jamming of the output axle and slippery of the input axle the level of vibrations has demonstrated to be completely negligible.
As a conclusion we can state that the nominal gear ratio of 1:21 has been experimentally checked, with minor deviations lower than the precision of the measurement or due to sudden changes of the output torque. The input shift is also clearly non-linear with a maximum torque that can be transmitted. Applications for which an intrinsic clutch effect or a torque limiter are required can benefit from this kind of friction-less device. Other interesting properties can be through-wall capability and the possibility of large clearances for dirty environments.
CTP
The Cryogenic MAGDRIVE prototype and test bench to test in vacuum at 60K required a number of additional technologies that were developed: improved superconducting bearings and a test bench to test them, a launch lock reliable mechanism to release the axles below the critical temperature, a cryogenic shell for the test bench, magnetic non contact feedthrough mechanisms and a 6D non contact position and angle sensor.
The cryogenic MAGDRIVE was designed for a -1:20 ratio to make even more evident that the theory for the reduction ration was right (selecting a negative ratio). The success of this demonstration has contundently proved this theory developed in the project to be right.
The system has been demonstrated to work at 60K in vacuum. Therefore the main objective was fully satisfied.
Additionally torque limitation, inversion of movement and zero backlash have been experimentally proved as a consequence of MAGDRIVE project. The tests performed have even proved a relatively long life (although the expected one gently overpasses the duration of the tests in MAGDRIVE project).
SC Bearings
Superconducting magnetic bearings (SMB) are used in applications such as in flywheels [1] or Maglev devices among other devices. The lack of contact, the extremely low friction and energy losses and the absence of wear are some of the outstanding characteristics that make this kind of bearings interesting for the mechanical engineer. There were some models that are useful to describe this interaction and that can be applied in finite elements programs as it is commonly used in mechanical engineering. Although these models could be very useful for static loads calculations, they are still limited when dynamics and transient effects are taken into account. Hence the real experimentation of SMBs is a goal of the MAGDRIVE project.
Among superconducting bearings, journal bearings have been typically considered in order to bear high axial and radial loads. For most configurations in the literature, a superconducting journal bearing is composed by a ring permanent magnet (PM) levitating over a disk superconductor (SC). In the FP7 MAGDRIVE project, superconducting magnetic bearings have been used in order to support a novel magnetic harmonic drive where there is no contact between any of the moving parts. As part of this research, a study of different journal superconducting bearings under field cooling conditions has been carried out. Relevant parameters such as the stiffness, the hysteresis or the force relaxation have been characterized using the specifically designed and built test bench.
In order to characterize the axial and radial stiffness of the SMBs, a dedicated test bench has been designed and built. The bench is mainly composed of a metallic structure made of aluminum which fixes the PM in position. Due to the magnetic properties of the aluminum alloy used, low magnetic interaction with the PM and the SC is assured. In addition, the superconductors are placed and fixed inside a LN2 vessel and the last assembled onto a motorized lab-jack from Thorlabs, model L490MZ. This lab-jack stand is intended to modify the gap (Z axis) between the PM and the SC with extreme accuracy (about 5μm) within a stroke about 55 mm. The lab-jack stand is assembled onto a linear slider from Igus able to modify the radial distance between the centers of the SC and the PM (X axis). This slider is controlled in a close-loop using the position signal from a laser triangulator from Microepsilon model ILD 1402-50. In summary, overall repeatability in the radial and axial position has been estimated to be better than 100 μm.
The radial and axial forces between the PMs and the SCs have been measured by using two load cells from SENEL, model SX-1, C3 precision category. They were installed at either side of the T bar that supports the PMs. Finally, all the electronic systems are connected to a PC and data acquisition is synchronized using Labview.
The superconductors were field cooled using liquid nitrogen (LN2) at ambient pressure (≈ 77 K). The permanent magnets were also immersed in LN2 to assure little variation of the forces arising as a consequence of changes in the magnetization of the permanent magnets due to variations of their temperature (see force relaxation chart). After cooling down the bearing the relative axial and radial position of the permanent magnet with respect to the superconductor is modified.
Hysteresis in SMB is a very relevant parameter that must be taken into account when designing a SMB. It not only affects the levitation but also the radial force. Additionally, note that the levitation force start to decrease when the axial displacement is about half the height of the PM.
The force relaxation is the drop in the levitation or radial force with time after a relative motion between a permanent magnet and a field cooled superconductor happens. It must be carefully considered when designing a SMB. The relaxation of the levitation force for an axial displacement of - 4 mm from the FC position is 4%.
Launch Lock mechanisms
The launch lock mechanism is an actuating system that holds the floating axles in the right position while the CTP is cooling down. Then, once the operational temperature is reached inside the vacuum chamber, the launch lock mechanism opens and so the floating input and output axle are allowed to rotate.
The launch lock mechanism is a Hold down and release mechanism. It is composed of a screw-nut mechanism guided by two linear guides and driven by a stepper motor. In order to define a good alignment of the floating axles relatively and in respect to the static part, the mechanism must be touch the axles in two different heights. It is crucial for the mechanism design to understand correctly the friction behavior between nut-screw and guide-plain bearing in order to dimension correctly the power needed for the stepper driver motor.
The proposed launch-lock device is basically composed of a lead screw, a couple of nuts and a couple of guides on which each nut slides. The lead screw is right handed thread on one side and left handed thread on the other side(obviously, one of the nuts is right handed thread while the other is left handed thread, each of them moves along the corresponding side of the screw). Hence according to the lead screw sense of rotation the nuts separate or approach to each other, and this is how the device launches or locks, respectively. Antifriction bearings are mounted between the nuts and the guides, so the corresponding friction can be neglected.
The main objective of the test was to understand better the behavior of this kind of mechanisms at low temperatures. The main parameters of the LL to be analyzed were the friction coefficient of the screw-nut mechanism and the behavior of the system in the start of the movement. Three tested were done: one with the EM at room temperature and oil lubricated, second with the system at room temperature but without lubrication (oil lubrication is not allowed in vacuum and cryogenic conditions), and a last test in a LN2 bath without lubrication. Friction coeficients were measured.
The launch lock mechanism development was done using a previous engineering model to determine a set of key parameters for final design. The final design was dimensioned according to the experiences results, manufactured and integrated in the CTP. The LL was correctly working at room temperature without lubrication.
Magnetic non contact feed-through or magnetic couplings
The magnetic coupling is a power transmission device intended to transmit torque and speed from outside the cryogenic chamber to the MAGDRIVE and the other way around without contact between moving parts. Then, the vacuum and cryogenic conditions inside the chamber can be kept during operation of MAGDRIVE, placing part of the measurement equipment and actuators outside the vacuum chamber. Therefore is a through-wall solution that will highly simplify the experimental set up and experimental procedure in the test campaign of the MAGDRIVE CTP.
The magnetic couplings used in the MAGDRIVE CTP are a technology developed by partner UC3M using contactless magnetic forces between permanent magnets.
NdFeB permanent magnets (coercitivity: 990 kW/m and remanence: 1.4T) were used in the simulations. Constructive material for the PM housings and the wheels of the MC are made of AISI 1008 steel and the airgap between magnets in opposite wheels is 3 mm.
A total of 9 different configurations for the MCs have been simulated using a FEM tool. A variety of configurations were simulated in 3D to find the optimum model in terms of cost, weight and size.
These MCs will guaranteed a through-wall transmission of torque and speed from the AC motor outside the vacuum chamber to the MAGDRIVE input shaft and from the output shaft of MAGDRIVE to the equipment outside the chamber. A set of bearings, circlips and couplings were designed in a detailed mechanical model.
The PMs in the MCs were attached to a set of wheels made of carbon steel. Flexible shafts were used to connect the MCs to the MAGDRIVE.
Both tests at room temperature and test in cryogenic conditions and final prototype have been successful.
6D Sensor
A completely new non contact sensor for measuring 6D displacement and rotation angles have been developed and tested (and patented).
A precision of 1 micrometer in the displacement of the designated point of an axle with a bandwidth of 30 kHz is an important goal of the MAGDRIVE project.
Potential Impact:
The expected final result is a non-contact gear, able to work in a cryogenic environment and vacuum.
They have no wear, no production of debris, intrinsic antijamming characteristics and are good isolators for vibration. Moreover it has zero backlash and will be a much more precise gear than any other for precise instruments in vacuum and cryogenic environments. Protection of mechanisms and structures from overloads is another advantage of the devices here developed. They can be useful for space, aeronautics, energy generation, underwater turbines, X-ray facilities, etc. Many applications related to spinning axles in hard environments can be affected.
A non contact sensor system able to measure the displacement and all-rotations of a rotating axle has been developed and tested for use in any rotating machine (probably for use in railways, vehicles and others to increase their reliability and safety). Other developements can be also useful for vacuum machinery or for pumps and the like.
Socio economic impact will come in the following ways:
1. Impact of the technology.
1.1. Impact of the technology in Space longer lifer and reliability of mechanisms.
Although long life tests have not yet been performed, it can be estimated that the life for mechanisms can be enlarged in more than 100% of the maximum life. This will have a very positive economic impact. I will reduce the amortization of a satellite per year to about a half.
Launch lock and release mechanisms and shock isolation here developed may also have an impact.
1.2. Impact of this technology in Aeronautics.
The possibility to have intrinsic antijamming function and protection of the structures is currently explored in the FP7 Clean Sky “MAGBOX” project.
The use of these devices will provide a reduction of weight and energy consumption while increasing safety ad reliability for control actuators.
1.3. Impact of technologies for measurement of vibrations in conventional mechanical systems.
The measurement of vibrations in rotating axles without contact will provide a useful tool for diagnostics of axles. This is critical for railway, automobiles and big machinery. The precise development of this is still to be defined.
1.4. Impact of zero backlash, feed-through and great reduction ratio
Zero backlash and feed-through can be great goals for precision machinery, robotics and scientific mechanisms (telescopes, vacuum positioners, clean room actuators, etc.) The impact of it will be clear in the next years.
1.5 Impact of improved superconducting bearings.
Although it is necessary further development it will pave the way to the use of them for energy storage in flywheels of for precision applications.
2. Socio economic impact of the exploitation
The exploitation of the technologies will be based on licensing the patents and know-how to the spin-off company MAGSOAR.
The socio economic benefit of job creation and economy activation will be produced in the European Union, particularly in Spain, Czech Republic and Germany.
The final benefits from the patent exploitation will go to all the partners.
3. Enabling of new technological possibilites.
Finally, a technical consequence of this technology is that it will enable other new technological possibilitities, for example for micromachining or clean pumping.
Dissemination activities
In this project a policy of first protecting IP and afterwards publishing has been followed. Part of the results have not been published, waiting for the corresponding patents to be presented.
The MAGDRIVE project received the 1st award Madri+d to a cooperative international project 2011. As a consequence it attracted attention of mass media in Spain.
Papers in journals:
- Jose-Luis Perez-Diaz, Efren Diez-Jimenez, Ignacio Valiente-Blanco and Javier Herrero de Vicente, “Stable thrust on a finite-sized magnet above a Meissner superconducting torus”, J. Appl. Phys. 113, 063907 (2013); doi: 10.1063/1.4792037
- Jose-Luis Perez-Diaz, Juan Carlos Garcia-Prada, Ignacio Valiente-Blanco and Efren Diez-Jimenez, “Magnetic-Superconductor Cryogenic Non-contact Harmonic Drive: Performance and Dynamical Behavior”, New Trends in Mechanism and Machine Science Mechanisms and Machine Science Volume 7, 2013, pp 357-364.
- Efren Diez-Jimenez, Jose Luis Perez-Diaz, Fabio Canepa and Carlo Ferdeghini, Invariance of The Magnetization Axis under Spin Reorientation Transitions. J. Appl. Phys. 112 (6) Article Number: 063918 DOI: 10.1063/1.4754445 Published: SEP 15 2012
- JL Perez-Diaz and E. Diez-Jimenez,” Magnetic-Superconductor Cryogenic Non-contact Harmonic Drive”, Let's embrace space, vol. 2, European Comission, Brussels, 3/4/2012.
- Perez-Diaz, J. L, Diez-Jimenez E., Cristache C., Valiente-Blanco I., Alvarez-Valenzuela M.A. Castro V., Ruiz-Navas E.M. Sanchez-Garcia-Casarrubios J., Ferdeghini C., Canepa F., Hornig W., Carbone G., Plechacek J., Amorim A., Serrano J., Sanz V. (2013) Magnetic non-contact Harmonic Drive Proceedings of ASME International Mechanical Engineering Congress and Exposition 10.1115/IMECE2013-63718
- Diez-Jimenez, E., Valiente-Blanco, I., Cristache C., Alvarez-Valenzuela M.A. & Perez-Diaz, J. L, (2013), Characterization and Improvement of Axial and Radial Stiffness of Contactless Thrust Superconducting Magnetic Bearings, Tribology Letters, 10.1007/s11249-013-0204-0
- Valiente-Blanco, I., Diez-Jimenez, E., Cervantes-Montoro J. A., & Perez-Diaz, J. L, (2013) Characterization of commercial-off-the-shelf electronic components at cryogenic temperatures, Instruments and Experimental Techniques 2013, Vol 56, nº 6, pp 665-671 DOI 10.1134/S0020441214010187
- Diez-Jimenez E., Perez-Diaz J.L. Issue 1, “Losing Contact” (2014) ANSYS Advantage
Conferences
- Pérez-Díaz J.L. Díez-Jiménez E., García-Prada J.C and Ignacio Valiente-Blanco Simplified local model for the mechanical interaction between a finite magnet and a superconductor in the Meissner state Autor; III Internation Workshop on Numerical Modelling High Temperature Superconductors; ICMAB-CSIC, UPC and UAB, Barcelona; 10-13 Abril 2012
- Jose-Luis Perez-Diaz, Juan Carlos Garcia-Prada, Ignacio Valiente-Blanco and Efren Diez-Jimenez, “Magnetic-Superconductor Cryogenic Non-contact Harmonic Drive: Performance and Dynamical Behavior”, 4th European Conference on Mechanism Science EUCOMES Septiembre 2012 (Santander, España)
- Perez-Diaz, Jose-Luis; Diez-Jimenez, E.; Cristache, C.; Valiente-Blanco, I.; Álvarez-Valenzuela, M.; Sánchez-García-Casarrubios, J.; Carbone, G.; Ferdeghini, C.; Canepa, F.; Plechácek, Jan; Hornig, Wolfgang; Sanz, Violeta; Amorim, António J. Rosa, (2013) MAGDRIVE: a Non-Contact Magnetic Superconducting Harmonic Drive, 15th European Space Mechanisms and Tribology Symposium (Noordwijk, Netherland)
- Diez-Jimenez E., Valiente-Blanco I., Sanchez-Garcia-Casarrubio J. Perez-Diaz J.L. (2013) Mechanical characterization of journal superconducting magnetic bearings: stiffness, hysteresis and force relaxation, 11th European Conference on Applied Superconductivity, (Genova, Italy)
- Diez-Jimenez E., Valiente-Blanco I., Sanchez-Garcia-Casarrubio J. Perez-Diaz J.L. (2013 Design rules of magnet-superconductor non-contact mechanisms considering the mechanical interaction in the Meissner state, 11th European Conference on Applied Superconductivity, (Genova, Italy)
- Valiente-Blanco I., Cristache C., Diez-Jimenez, E., Alvarez-Valenzuela M.A. Sanchez-Garcia-Casarrubios J. and Perez-Diaz, J. L (2013) Characterization and improvement of axial and radial stiffness of contactless thrust superconducting magnetic bearings, 5th World Tribology Congress, (Turin, Italy)
- Cristache C., Diez-Jimenez, E., Valiente-Blanco I., Alvarez-Valenzuela M.A Sanchez-Garcia-Casarrubios J. and Perez-Diaz, J. L 2013) Levitation force relaxation and hysteresis in a frictionless superconducting magnetic bearing, VII Iberian Conference on Tribology, (Porto, Portugal)
Media
- Interview in “Onda Aranjuez” radio and weekly journal “Más”, 6 July 2012
- "Magdrive: diseño español para satélites europeos” J.L. Pérez Díaz Época, 15-4-2012, 51.
- Muy Interesante; "Unidos pero sin fricciones" sobre MAGDRIVE; 02/05/2012
- RNE; A hombros de gigantes ; MAGDRIVE; 17/02/2012
- Onda Cero. Partiendo de Cero; MAGDRIVE; 26/02/2012
- Radio Euskadi; La Mecánica del Caracol; MAGDRIVE; 05/03/2012
Exploitation
Two patents have been applied at the moment:
EP13382535 “High-performance radial gap superconducting magnetic bearing”.
ES P201430110 “DISPOSITIVO PARA LA MEDIDA SIN CONTACTO EN EJES ROTATIVOS DE SUS TRES COORDENADAS INDEPENDIENTES DE DESPLAZAMIENTO Y TRES ÁNGULOS DE GIRO INDEPENDIENTES”.
MAG SOAR SL, a spin-off company, has been incorporated as planned in the project. The model for explotation is patent licensing to MAG SOAR SL that will develop the products for commercialization.
See the attached file "Summary of technological developments MAGDRIVE3.pdf" for more details on the capabilities of the technology. For more info also consult www.magdrive.eu and www.magsoar.com
List of Websites:
www.magdrive.eu
www.magsoar.com
info@magsoar.com
The objective of this project is to design, build and test a magnetic-superconductor cryogenic non-contact harmonic drive (MAGDRIVE). This harmonic drive is a mechanism provided with an input axle and an output hub with a great reduction ratio and it will be able to function at cryogenic temperatures. This harmonic drive is based on “non-contact magnetic teeth” instead of fitting teeth on a flexural wave as conventional harmonic drives are based on. Non-contact magnetic teeth are activated by a magnetic wave (similar to an electrical engine). This solves the problems of contact wearing and mechanical fatigue.
Long life and protection against overloads, vibrations and shocks are additional features.
In a fully non-contact version superconductors are used for non-contact bearings. The new developed design of superconducting bearings demonstrated performances a 60% better than any other previous design.
Two prototypes have been manufactured and tested at room temperature and at cryogenic temperature (below 63K).
Additionally non-contact feedthrough mechanisms, launch lock and release mechanisms and non contact sensors for 6D displacements and rotations (an vibrations up to 30 kHz) of an axle have been developed and patented.
Project Context and Objectives:
Spacecrafts, satellites and exploration rovers need increasingly demanding mechanisms able to work in vacuum and along a large range of temperature. Particularly critical are gears which are needed for deployment of antennas or other elements, releasing instruments, displacement of interferometers or simply propelling wheels. Up to now Harmonic drives are commonly used because of their high specific torque density and high reduction ratio (the higher the ratio the smaller the motor). Drawbacks of harmonic drives are that they need lubrication and their working life is not very long due to fatigue and wear.
The objective of the MAGDRIVE project is to demonstrate a new technology of magnetic non-contact gear that aims to be able to work in cryogenic environment (and vacuum), without contact or wear, with no need for lubrication. Additionally it will provide intrinsic protection against overloads, vibrations and shocks.
Conventional bearings present a longer life than harmonic drives themselves. Therefore the MAGDRIVE technology for the gear itself combined with conventional bearings is a good option to increase the life of the overall device itself. For the demonstration of this technology a Room Temperature Prototype (RTP) has been designed and tested successfully.
Cryogenic conditions are much more difficult than room temperature conditions. Lubrication is always a problem for conventional mechanisms working at cyogenic conditions. For demonstration of the MAGDRIVE technology in cryogenic conditions an ambitiuos design (CTP) was proposed including non-contact superconducting bearings combined with the non-contact magnetic gears. The test bench included thermal cryostat and non-contact magnetic feed-through for transmitting power to the input axle and braking the output axle whose development has been a colateral objective.
In this cryogenic prototype it is neccesary to measure 6 degrees of freedom (displacements and rotations) of the floating axles. For that a specific (also magnetic) sensor was developed and tested succesfully.
Project Results:
Main S&T results
Two test benches have been designed and built to test the performances of the Room Temperature and Cryogenic MAGDRIVE prototypes.
RTP
The room temperature test bench is mainly composed of a driving unit with an electric motor, encoder&torque sensor connected to the input axle of the MAGDRIVE prototype and a “load” set composed of an EMAG brake, encoder & torque sensor connected to the output axle. Rotated angle and torque can be measured both at input and output axles.
The MAGDRIVE RT prototype was designed for a GR=1:21. This must be understood as a nominal ratio, as the behavior of a magnetic gear is somehow different from conventional gears. Magnetic gear teeth do not touch each other, but interact at distance. This makes it necessary to draw the input axle a shift angle to reach a definite torque. Therefore, an objective for the testing was to check the predicted GR at different loads and to measure the shift angle as a function of the load or output torque.
The shift angle in a static condition is nonlinear. The main characteristic is that there is a maximum torque that can be transmitted. If a torque greater than that is applied to the output axle, then the input axle just slips. This is an intrinsic antijamming characteristic that opens many opportunities for this type of devices. The maximum transmitted torque can be customized in the design of the MAGDRIVE.
The angle for which the maximum occurs can also be customized, dividing the circumference into a number of intervals, including a stable and an unstable part each. The prototype tested has two intervals of 180º each. That is, when the output axle is blocked, the maximum torque is reached twice a turn of the input axle.
The input angle adapts to any variation of the output torque. These variations of the output torque in the case of constant speed produce short deviations from the nominal reduction ratio.
Vibrations were also measured on bearings and the box of the MAGDRIVE prototype itself. The level of Vibration measured in all the cases was under the sensitivity of the sensor. Even in the case of jamming of the output axle and slippery of the input axle the level of vibrations has demonstrated to be completely negligible.
As a conclusion we can state that the nominal gear ratio of 1:21 has been experimentally checked, with minor deviations lower than the precision of the measurement or due to sudden changes of the output torque. The input shift is also clearly non-linear with a maximum torque that can be transmitted. Applications for which an intrinsic clutch effect or a torque limiter are required can benefit from this kind of friction-less device. Other interesting properties can be through-wall capability and the possibility of large clearances for dirty environments.
CTP
The Cryogenic MAGDRIVE prototype and test bench to test in vacuum at 60K required a number of additional technologies that were developed: improved superconducting bearings and a test bench to test them, a launch lock reliable mechanism to release the axles below the critical temperature, a cryogenic shell for the test bench, magnetic non contact feedthrough mechanisms and a 6D non contact position and angle sensor.
The cryogenic MAGDRIVE was designed for a -1:20 ratio to make even more evident that the theory for the reduction ration was right (selecting a negative ratio). The success of this demonstration has contundently proved this theory developed in the project to be right.
The system has been demonstrated to work at 60K in vacuum. Therefore the main objective was fully satisfied.
Additionally torque limitation, inversion of movement and zero backlash have been experimentally proved as a consequence of MAGDRIVE project. The tests performed have even proved a relatively long life (although the expected one gently overpasses the duration of the tests in MAGDRIVE project).
SC Bearings
Superconducting magnetic bearings (SMB) are used in applications such as in flywheels [1] or Maglev devices among other devices. The lack of contact, the extremely low friction and energy losses and the absence of wear are some of the outstanding characteristics that make this kind of bearings interesting for the mechanical engineer. There were some models that are useful to describe this interaction and that can be applied in finite elements programs as it is commonly used in mechanical engineering. Although these models could be very useful for static loads calculations, they are still limited when dynamics and transient effects are taken into account. Hence the real experimentation of SMBs is a goal of the MAGDRIVE project.
Among superconducting bearings, journal bearings have been typically considered in order to bear high axial and radial loads. For most configurations in the literature, a superconducting journal bearing is composed by a ring permanent magnet (PM) levitating over a disk superconductor (SC). In the FP7 MAGDRIVE project, superconducting magnetic bearings have been used in order to support a novel magnetic harmonic drive where there is no contact between any of the moving parts. As part of this research, a study of different journal superconducting bearings under field cooling conditions has been carried out. Relevant parameters such as the stiffness, the hysteresis or the force relaxation have been characterized using the specifically designed and built test bench.
In order to characterize the axial and radial stiffness of the SMBs, a dedicated test bench has been designed and built. The bench is mainly composed of a metallic structure made of aluminum which fixes the PM in position. Due to the magnetic properties of the aluminum alloy used, low magnetic interaction with the PM and the SC is assured. In addition, the superconductors are placed and fixed inside a LN2 vessel and the last assembled onto a motorized lab-jack from Thorlabs, model L490MZ. This lab-jack stand is intended to modify the gap (Z axis) between the PM and the SC with extreme accuracy (about 5μm) within a stroke about 55 mm. The lab-jack stand is assembled onto a linear slider from Igus able to modify the radial distance between the centers of the SC and the PM (X axis). This slider is controlled in a close-loop using the position signal from a laser triangulator from Microepsilon model ILD 1402-50. In summary, overall repeatability in the radial and axial position has been estimated to be better than 100 μm.
The radial and axial forces between the PMs and the SCs have been measured by using two load cells from SENEL, model SX-1, C3 precision category. They were installed at either side of the T bar that supports the PMs. Finally, all the electronic systems are connected to a PC and data acquisition is synchronized using Labview.
The superconductors were field cooled using liquid nitrogen (LN2) at ambient pressure (≈ 77 K). The permanent magnets were also immersed in LN2 to assure little variation of the forces arising as a consequence of changes in the magnetization of the permanent magnets due to variations of their temperature (see force relaxation chart). After cooling down the bearing the relative axial and radial position of the permanent magnet with respect to the superconductor is modified.
Hysteresis in SMB is a very relevant parameter that must be taken into account when designing a SMB. It not only affects the levitation but also the radial force. Additionally, note that the levitation force start to decrease when the axial displacement is about half the height of the PM.
The force relaxation is the drop in the levitation or radial force with time after a relative motion between a permanent magnet and a field cooled superconductor happens. It must be carefully considered when designing a SMB. The relaxation of the levitation force for an axial displacement of - 4 mm from the FC position is 4%.
Launch Lock mechanisms
The launch lock mechanism is an actuating system that holds the floating axles in the right position while the CTP is cooling down. Then, once the operational temperature is reached inside the vacuum chamber, the launch lock mechanism opens and so the floating input and output axle are allowed to rotate.
The launch lock mechanism is a Hold down and release mechanism. It is composed of a screw-nut mechanism guided by two linear guides and driven by a stepper motor. In order to define a good alignment of the floating axles relatively and in respect to the static part, the mechanism must be touch the axles in two different heights. It is crucial for the mechanism design to understand correctly the friction behavior between nut-screw and guide-plain bearing in order to dimension correctly the power needed for the stepper driver motor.
The proposed launch-lock device is basically composed of a lead screw, a couple of nuts and a couple of guides on which each nut slides. The lead screw is right handed thread on one side and left handed thread on the other side(obviously, one of the nuts is right handed thread while the other is left handed thread, each of them moves along the corresponding side of the screw). Hence according to the lead screw sense of rotation the nuts separate or approach to each other, and this is how the device launches or locks, respectively. Antifriction bearings are mounted between the nuts and the guides, so the corresponding friction can be neglected.
The main objective of the test was to understand better the behavior of this kind of mechanisms at low temperatures. The main parameters of the LL to be analyzed were the friction coefficient of the screw-nut mechanism and the behavior of the system in the start of the movement. Three tested were done: one with the EM at room temperature and oil lubricated, second with the system at room temperature but without lubrication (oil lubrication is not allowed in vacuum and cryogenic conditions), and a last test in a LN2 bath without lubrication. Friction coeficients were measured.
The launch lock mechanism development was done using a previous engineering model to determine a set of key parameters for final design. The final design was dimensioned according to the experiences results, manufactured and integrated in the CTP. The LL was correctly working at room temperature without lubrication.
Magnetic non contact feed-through or magnetic couplings
The magnetic coupling is a power transmission device intended to transmit torque and speed from outside the cryogenic chamber to the MAGDRIVE and the other way around without contact between moving parts. Then, the vacuum and cryogenic conditions inside the chamber can be kept during operation of MAGDRIVE, placing part of the measurement equipment and actuators outside the vacuum chamber. Therefore is a through-wall solution that will highly simplify the experimental set up and experimental procedure in the test campaign of the MAGDRIVE CTP.
The magnetic couplings used in the MAGDRIVE CTP are a technology developed by partner UC3M using contactless magnetic forces between permanent magnets.
NdFeB permanent magnets (coercitivity: 990 kW/m and remanence: 1.4T) were used in the simulations. Constructive material for the PM housings and the wheels of the MC are made of AISI 1008 steel and the airgap between magnets in opposite wheels is 3 mm.
A total of 9 different configurations for the MCs have been simulated using a FEM tool. A variety of configurations were simulated in 3D to find the optimum model in terms of cost, weight and size.
These MCs will guaranteed a through-wall transmission of torque and speed from the AC motor outside the vacuum chamber to the MAGDRIVE input shaft and from the output shaft of MAGDRIVE to the equipment outside the chamber. A set of bearings, circlips and couplings were designed in a detailed mechanical model.
The PMs in the MCs were attached to a set of wheels made of carbon steel. Flexible shafts were used to connect the MCs to the MAGDRIVE.
Both tests at room temperature and test in cryogenic conditions and final prototype have been successful.
6D Sensor
A completely new non contact sensor for measuring 6D displacement and rotation angles have been developed and tested (and patented).
A precision of 1 micrometer in the displacement of the designated point of an axle with a bandwidth of 30 kHz is an important goal of the MAGDRIVE project.
Potential Impact:
The expected final result is a non-contact gear, able to work in a cryogenic environment and vacuum.
They have no wear, no production of debris, intrinsic antijamming characteristics and are good isolators for vibration. Moreover it has zero backlash and will be a much more precise gear than any other for precise instruments in vacuum and cryogenic environments. Protection of mechanisms and structures from overloads is another advantage of the devices here developed. They can be useful for space, aeronautics, energy generation, underwater turbines, X-ray facilities, etc. Many applications related to spinning axles in hard environments can be affected.
A non contact sensor system able to measure the displacement and all-rotations of a rotating axle has been developed and tested for use in any rotating machine (probably for use in railways, vehicles and others to increase their reliability and safety). Other developements can be also useful for vacuum machinery or for pumps and the like.
Socio economic impact will come in the following ways:
1. Impact of the technology.
1.1. Impact of the technology in Space longer lifer and reliability of mechanisms.
Although long life tests have not yet been performed, it can be estimated that the life for mechanisms can be enlarged in more than 100% of the maximum life. This will have a very positive economic impact. I will reduce the amortization of a satellite per year to about a half.
Launch lock and release mechanisms and shock isolation here developed may also have an impact.
1.2. Impact of this technology in Aeronautics.
The possibility to have intrinsic antijamming function and protection of the structures is currently explored in the FP7 Clean Sky “MAGBOX” project.
The use of these devices will provide a reduction of weight and energy consumption while increasing safety ad reliability for control actuators.
1.3. Impact of technologies for measurement of vibrations in conventional mechanical systems.
The measurement of vibrations in rotating axles without contact will provide a useful tool for diagnostics of axles. This is critical for railway, automobiles and big machinery. The precise development of this is still to be defined.
1.4. Impact of zero backlash, feed-through and great reduction ratio
Zero backlash and feed-through can be great goals for precision machinery, robotics and scientific mechanisms (telescopes, vacuum positioners, clean room actuators, etc.) The impact of it will be clear in the next years.
1.5 Impact of improved superconducting bearings.
Although it is necessary further development it will pave the way to the use of them for energy storage in flywheels of for precision applications.
2. Socio economic impact of the exploitation
The exploitation of the technologies will be based on licensing the patents and know-how to the spin-off company MAGSOAR.
The socio economic benefit of job creation and economy activation will be produced in the European Union, particularly in Spain, Czech Republic and Germany.
The final benefits from the patent exploitation will go to all the partners.
3. Enabling of new technological possibilites.
Finally, a technical consequence of this technology is that it will enable other new technological possibilitities, for example for micromachining or clean pumping.
Dissemination activities
In this project a policy of first protecting IP and afterwards publishing has been followed. Part of the results have not been published, waiting for the corresponding patents to be presented.
The MAGDRIVE project received the 1st award Madri+d to a cooperative international project 2011. As a consequence it attracted attention of mass media in Spain.
Papers in journals:
- Jose-Luis Perez-Diaz, Efren Diez-Jimenez, Ignacio Valiente-Blanco and Javier Herrero de Vicente, “Stable thrust on a finite-sized magnet above a Meissner superconducting torus”, J. Appl. Phys. 113, 063907 (2013); doi: 10.1063/1.4792037
- Jose-Luis Perez-Diaz, Juan Carlos Garcia-Prada, Ignacio Valiente-Blanco and Efren Diez-Jimenez, “Magnetic-Superconductor Cryogenic Non-contact Harmonic Drive: Performance and Dynamical Behavior”, New Trends in Mechanism and Machine Science Mechanisms and Machine Science Volume 7, 2013, pp 357-364.
- Efren Diez-Jimenez, Jose Luis Perez-Diaz, Fabio Canepa and Carlo Ferdeghini, Invariance of The Magnetization Axis under Spin Reorientation Transitions. J. Appl. Phys. 112 (6) Article Number: 063918 DOI: 10.1063/1.4754445 Published: SEP 15 2012
- JL Perez-Diaz and E. Diez-Jimenez,” Magnetic-Superconductor Cryogenic Non-contact Harmonic Drive”, Let's embrace space, vol. 2, European Comission, Brussels, 3/4/2012.
- Perez-Diaz, J. L, Diez-Jimenez E., Cristache C., Valiente-Blanco I., Alvarez-Valenzuela M.A. Castro V., Ruiz-Navas E.M. Sanchez-Garcia-Casarrubios J., Ferdeghini C., Canepa F., Hornig W., Carbone G., Plechacek J., Amorim A., Serrano J., Sanz V. (2013) Magnetic non-contact Harmonic Drive Proceedings of ASME International Mechanical Engineering Congress and Exposition 10.1115/IMECE2013-63718
- Diez-Jimenez, E., Valiente-Blanco, I., Cristache C., Alvarez-Valenzuela M.A. & Perez-Diaz, J. L, (2013), Characterization and Improvement of Axial and Radial Stiffness of Contactless Thrust Superconducting Magnetic Bearings, Tribology Letters, 10.1007/s11249-013-0204-0
- Valiente-Blanco, I., Diez-Jimenez, E., Cervantes-Montoro J. A., & Perez-Diaz, J. L, (2013) Characterization of commercial-off-the-shelf electronic components at cryogenic temperatures, Instruments and Experimental Techniques 2013, Vol 56, nº 6, pp 665-671 DOI 10.1134/S0020441214010187
- Diez-Jimenez E., Perez-Diaz J.L. Issue 1, “Losing Contact” (2014) ANSYS Advantage
Conferences
- Pérez-Díaz J.L. Díez-Jiménez E., García-Prada J.C and Ignacio Valiente-Blanco Simplified local model for the mechanical interaction between a finite magnet and a superconductor in the Meissner state Autor; III Internation Workshop on Numerical Modelling High Temperature Superconductors; ICMAB-CSIC, UPC and UAB, Barcelona; 10-13 Abril 2012
- Jose-Luis Perez-Diaz, Juan Carlos Garcia-Prada, Ignacio Valiente-Blanco and Efren Diez-Jimenez, “Magnetic-Superconductor Cryogenic Non-contact Harmonic Drive: Performance and Dynamical Behavior”, 4th European Conference on Mechanism Science EUCOMES Septiembre 2012 (Santander, España)
- Perez-Diaz, Jose-Luis; Diez-Jimenez, E.; Cristache, C.; Valiente-Blanco, I.; Álvarez-Valenzuela, M.; Sánchez-García-Casarrubios, J.; Carbone, G.; Ferdeghini, C.; Canepa, F.; Plechácek, Jan; Hornig, Wolfgang; Sanz, Violeta; Amorim, António J. Rosa, (2013) MAGDRIVE: a Non-Contact Magnetic Superconducting Harmonic Drive, 15th European Space Mechanisms and Tribology Symposium (Noordwijk, Netherland)
- Diez-Jimenez E., Valiente-Blanco I., Sanchez-Garcia-Casarrubio J. Perez-Diaz J.L. (2013) Mechanical characterization of journal superconducting magnetic bearings: stiffness, hysteresis and force relaxation, 11th European Conference on Applied Superconductivity, (Genova, Italy)
- Diez-Jimenez E., Valiente-Blanco I., Sanchez-Garcia-Casarrubio J. Perez-Diaz J.L. (2013 Design rules of magnet-superconductor non-contact mechanisms considering the mechanical interaction in the Meissner state, 11th European Conference on Applied Superconductivity, (Genova, Italy)
- Valiente-Blanco I., Cristache C., Diez-Jimenez, E., Alvarez-Valenzuela M.A. Sanchez-Garcia-Casarrubios J. and Perez-Diaz, J. L (2013) Characterization and improvement of axial and radial stiffness of contactless thrust superconducting magnetic bearings, 5th World Tribology Congress, (Turin, Italy)
- Cristache C., Diez-Jimenez, E., Valiente-Blanco I., Alvarez-Valenzuela M.A Sanchez-Garcia-Casarrubios J. and Perez-Diaz, J. L 2013) Levitation force relaxation and hysteresis in a frictionless superconducting magnetic bearing, VII Iberian Conference on Tribology, (Porto, Portugal)
Media
- Interview in “Onda Aranjuez” radio and weekly journal “Más”, 6 July 2012
- "Magdrive: diseño español para satélites europeos” J.L. Pérez Díaz Época, 15-4-2012, 51.
- Muy Interesante; "Unidos pero sin fricciones" sobre MAGDRIVE; 02/05/2012
- RNE; A hombros de gigantes ; MAGDRIVE; 17/02/2012
- Onda Cero. Partiendo de Cero; MAGDRIVE; 26/02/2012
- Radio Euskadi; La Mecánica del Caracol; MAGDRIVE; 05/03/2012
Exploitation
Two patents have been applied at the moment:
EP13382535 “High-performance radial gap superconducting magnetic bearing”.
ES P201430110 “DISPOSITIVO PARA LA MEDIDA SIN CONTACTO EN EJES ROTATIVOS DE SUS TRES COORDENADAS INDEPENDIENTES DE DESPLAZAMIENTO Y TRES ÁNGULOS DE GIRO INDEPENDIENTES”.
MAG SOAR SL, a spin-off company, has been incorporated as planned in the project. The model for explotation is patent licensing to MAG SOAR SL that will develop the products for commercialization.
See the attached file "Summary of technological developments MAGDRIVE3.pdf" for more details on the capabilities of the technology. For more info also consult www.magdrive.eu and www.magsoar.com
List of Websites:
www.magdrive.eu
www.magsoar.com
info@magsoar.com
