Abstract Body

Introduction - In transportation systems employing belts, wheels, or gear conveyors, issues such as friction and wear arise at connecting points. A contactless transporter system has been developed in response to these challenges, particularly suited for specialized environments like clean rooms. This study focuses on a magnetic levitation system incorporating permanent magnets and high-temperature superconductors (HTS). The load stage is equipped with powerful permanent magnets generating levitation force through repulsion, while the stability is maintained by the pinning force of HTS, eliminating the need for a continuous levitation control system [1]-[6]. The transporter smoothly glides above a magnetic rail, and when electric current excites the propulsion coils integrated into it, the transporter is propelled through the generation of a magnetic gradient [7]-[11]. This paper presents an experimental analysis investigating the propulsion force generated by two different sizes of HTSs when the propulsion coils from both the front and rear sides of the transporter are magnetized, and the coil pitch is varied.

The transporter system consists of a magnetic rail composed of neodymium magnets in a Halbach Array, enhancing the magnetic field in the upper of it. The main body of the transporter has containers for the HTSs and a free space in the middle to install the load stage. Here, the main body and the load stage are connected by a vertical linear guideway that allows an independent and free movement of the stage related to the main body. Also, the load stages are composed of neodymium magnets in a way that produces a repulsive force against the magnetic rail. Using four HTSs, the yawing and rolling motion of the transporter is suppressed, and it can move freely along the magnetic rail.

The propulsion method consists of magnetizing the rear propulsion coil and demagnetizing the front one of the transporter. Then, a magnetic gradient is generated, which tilts the HTSs and, consequently, the transporter, creating a forward momentum. This paper considers two types of coil pitch: the coil pitch and excited coil pitch. The coil pitch d is the distance between the central axes of neighboring propulsion coils and for this paper, and the excited coil pitch d_e is the distance between the central axes of the propulsion coils that will be excited, that is, the distance between the rear and front side propulsion coils. Also, two HTSs are used for the experiments, with diameter values of 55 mm and 60 mm.

The present experiment parameters are excitation currents I from 1 to 3 A per coil, coil pitches d = 25, 30 [mm], excited coil pitch d_e = 350, 360 [mm], and levitation gap g = 23 [mm]. Considering the rear side coil’s central axis as the origin position x = 0 mm, the experiment position range x is from 0 to 50 mm with a measuring interval of 5 mm. Load cells installed at the front and rear sides of the transporter measure the propulsion force at each position.

Figure 1 shows the propulsion force for each excited coil pitch and HTSs. For both excited coil pitch values, d_e = 350, 360[mm], the HTS with ⌀ =60mm has a maximum propulsion force that is 4.78% and 0.59% larger, respectively, than the HTS with a diameter of 55 mm. This is likely because, in the magnetic rail length direction, the larger HTS is under the effect of the magnetic field in a larger range than the other HTS. However, the small HTS presents local and global maximum propulsion force while the larger HTS shows only one global maximum force in both results.

Now, analyzing the average propulsion force, there is another discussion. Considering the average calculation range length L = 25[mm] for coil pitch d = 350[mm], the smaller HTS shows an average force of 0.169 N, which is 6.41% larger than the larger HTS. The L = 30[mm] (coil pitch d = 360[mm]), the smaller HTS shows an average force of 0.179 N, which is 8.38% larger than the larger HTS. These results are likely because, although the HTS surface area under the magnetic field influence is smaller for the small HTS, the total area under this influence across the entire experiment range (x = 0-60[mm]) is larger than the larger HTS.

In conclusion, the influence of the relation magnetic field – HTS surface area in the propulsion force was analyzed. From the results, the larger HTS showed a larger maximum propulsion force, but a small average propulsion force. In contrast, the smallest HTS showed a slightly small maximum propulsion force, but it generated a larger average propulsion force. From that, the larger average propulsion force will be considered the optimal result due to the smoothest characteristics, which will impact positively in future research involving velocity control systems.

References

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Figure 1. Propulsion force for d_e = 350[mm] (left) and d_e = 360[mm] (right).

Keywords: High-Temperature Superconductor, Levitation, Permanent Magnet, Pinning, Coils