Analysis and Suppression of Detent Force in Tubular Linear Electromagnetic Launcher for Space Use

With the exploitation of the astrospace, platform is playing more and more important roles. Linear electromagnetic launcher offers a lot of merits such as high speed, precision- acceleration control, wide adjustable range of the initial launch velocity and projectile mass, high energy conversion efficiency, etc. So it will be the best choice of space platform launching in the future. The main problem that appears in all linear electromagnetic launchers is the cogging force. This paper deals with the cogging-force characteristics of short primary, long secondary tubular linear permanent magnet synchronous motors (TL-PMSM) for electromagnetic launcher (EML). Using finite element method (FEM) to analysis the magnet field and detent force of TLEML. The result shows that the end effect is the main reason for thrust ripple and the end effect force vary in periodicity of a pole pitch as the length of the primary armature increase. The periodicity of interior PM TLEML (IPM-TLEML) and surface-mounted PM TLEML (SPM-TLEML) are same but SPM-TLEML lags behind IPM-TLEML. For IPM-TLEML, when the side teeth-width/pole pitch is about 0.33-0.5, the cogging force is minimum. For SPM-TLEML, the minimum point is around 0.5. The detent force has nothing to with the size of external diameter. The configuration can only influence the magnitude of detent force, but not the cycle. Accordingly, optimizing the side teeth-width is very effective to reduce detent force while designing.