# Performance of Magnetic-Superconductor Non-Contact Harmonic Drive for Cryogenic Space Applications

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## Abstract

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^{−3}Pa was demonstrated for more than 1.5 million input cycles. A maximum torque of 3 N·m and an efficiency of 80% were demonstrated. The maximum tested input speed was 3000 rpm, six times the previous existing record for harmonic drives at cryogenic temperatures.

## 1. Introduction

^{−3}Pa. Mechanical performance, including maximum speed, speed ratio, efficiency, torque, and load capability, was characterized in order to establish the criteria for the usage of these MAGDRIVE mechanisms for Space.

## 2. Design and Analysis of the Device

#### 2.1. Magnetic Harmonic Drive Gear

^{3}. In addition, the direction of rotation could be chosen.

^{3}, and an efficiency of 81% (55 W energy power losses at 1000 rpm speed).

#### 2.2. Superconducting Magnetic Bearings (SMB)

#### 2.3. Mechanical and Thermal Design

#### 2.4. Material Selection

## 3. Prototype Manufacturing and Assembly

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## 4. Experimental Test Rig

#### 4.1. Thermal-Vacuum Chamber

^{−3}Pa. The cooling system is composed of two LN2 tanks fed by a LN2 dewar with a 100 L capacity, and a cryocooler DE-104 from ARS Company with a 48 W cooling capacity at 77 K of the cold finger, able to reach 20 K. The chamber is provided with two endoscopic webcams to record video and picture inside the chamber.

#### 4.2. Sensing System

## 5. Performance Test Results and Discussion

^{−3}Pa. Different tests were done in order to characterize the mechanical and thermal performance. Some results are shown below.

#### 5.1 Speed Tests

#### 5.2. Torque Tests (Max Load Tests)

^{3}. Although the torque and corresponding torque density are low for practical applications, they correspond properly with the Finite Element Method (FEM) model results validating them. Torque capability can be easily improved by reducing air gaps (too conservative), using NdFeB magnets (caring about the spin reorientation transition), and optimizing shapes and sizes of the teeth. In fact, recent designs have shown torque densities close to 100 kNm/m

^{3}, in the same order of magnitude as conventional HD.

#### 5.3. Lifetime

## 6. Conclusions

^{−3}Pa. The performance test results are summarized in Table 1.

^{−3}Pa was demonstrated for more than 1.5 million input cycles. A maximum output torque of 3 Nm and an efficiency of 80% were demonstrated. The maximum tested input speed was 3000 rpm, which is six times the previous existing record for HD at a cryogenic temperature.

Parameter | Value |
---|---|

Reduction ratio | −1:20 |

Maximum input speed | 3000 rpm |

Maximum output torque | 3 Nm |

Torque density (without SMB) | 25 kNm/m^{3} |

Specific torque (without SMB) | 7 Nm/kg |

Weight of magnetic gear | 428 g |

Full prototype weight (SMB + sensors) | 15 kg |

Operational test temperature | 40 K |

Operational vacuum pressure | 3 × 10^{−3} Pa |

Lifetime (input cycles number) | 1.5 million |

## Acknowledgments

## Author Contributions

## Conflicts of Interest

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**MDPI and ACS Style**

Perez-Diaz, J.L.; Diez-Jimenez, E.; Valiente-Blanco, I.; Cristache, C.; Alvarez-Valenzuela, M.-A.; Sanchez-Garcia-Casarrubios, J.; Ferdeghini, C.; Canepa, F.; Hornig, W.; Carbone, G.;
et al. Performance of Magnetic-Superconductor Non-Contact Harmonic Drive for Cryogenic Space Applications. *Machines* **2015**, *3*, 138-156.
https://doi.org/10.3390/machines3030138

**AMA Style**

Perez-Diaz JL, Diez-Jimenez E, Valiente-Blanco I, Cristache C, Alvarez-Valenzuela M-A, Sanchez-Garcia-Casarrubios J, Ferdeghini C, Canepa F, Hornig W, Carbone G,
et al. Performance of Magnetic-Superconductor Non-Contact Harmonic Drive for Cryogenic Space Applications. *Machines*. 2015; 3(3):138-156.
https://doi.org/10.3390/machines3030138

**Chicago/Turabian Style**

Perez-Diaz, Jose Luis, Efren Diez-Jimenez, Ignacio Valiente-Blanco, Cristian Cristache, Marco-Antonio Alvarez-Valenzuela, Juan Sanchez-Garcia-Casarrubios, Carlo Ferdeghini, Fabio Canepa, Wolfgang Hornig, Giuseppe Carbone,
and et al. 2015. "Performance of Magnetic-Superconductor Non-Contact Harmonic Drive for Cryogenic Space Applications" *Machines* 3, no. 3: 138-156.
https://doi.org/10.3390/machines3030138