You are presented with multiple paper abstracts, alongside the associated literature review and chapter titles. Given the provided information, you are going to do a literature review. Please generate a coherent literature review that synthesizes the content, draws connections between different works, highlights major findings, and identifies any gaps in the existing research.

Literature Review Title: Linear Machines for Long Stroke Applications—A Review 
Chapter Title:  E. NORMAL FORCE 
1. Abstract of Cited Paper (BIB001):  Traditionally, straggering the primaries of the double-sided permanent magnet linear synchronous motor (DS-PMLSM) is beneficial in helping to reduce the detent force caused by the longitudinal end effect, but leading to a reduction of the average thrust. To overcome this disadvantage, this paper provides a novel DS-PMLSM, which adopts the structure of staggering two primaries and rearranging windings. First, the characteristics of the voltage and detent force are analyzed theoretically and verified by finite element (FEM) simulations. The inductance, thrust, and normal forces are then compared with the traditional DS-PMLSM. Furthermore, the geometrical parameters are optimized to improve the thrust. Finally, one DS-PMLSM prototype is tested. The detent force and back electromotive force tested results verify the effectiveness of the topology proposed in this research.

Literature Review:
The high normal force is one of the main disadvantages of single-sided LMs BIB001 . Double-sided configurations can compensate the unbalanced normal force BIB002 , BIB001 . However, if a series magnetic circuit is employed BIB001 the normal force fluctuates, so it still has to be taken into consideration when sizing the linear bearings. The other main solution for balancing the normal force is the adoption of a tubular topology  . However, as stated in  , tubular machines shall be employed only in short-strokes, so that deformation of the long part is avoided.