Two-stage solenoid design

Solenoid use and design is limited by the fact that as the gap increases, the force greatly decreases. However, by using a solenoid that contains three cores instead of one, it is possible to greatly increase this force. In such a designs, the 3 cores interact as follows: Core 1 is rigidly attached to core 3. At the beginning of the motion, core 3 is in a hole in core 2. Core 2 remains stationary until core 1 reaches it. When this occurs, all cores move until core 3 reaches the shell. To prove this design creates better results, models are created and compared against an equivalent regular solenoid. Models are created in MATLAB using an equivalent resistor circuit to model the solenoid. In this model all flux paths are assumed to be perpendicular to the surfaces they enter and exit. This method shows an improvement of 29 % in the best case scenario. Models are also created in Maxwell 2D Field Solver by Ansoft, a finite elements program. Both models calculate the force that the solenoid can produce as it moves from the open to closed position. Data is collected when various parts of the geometry are varied. It is found that the diameter of core 3, the geometry of core 3,and the length of the connector rod connecting core 1 and core 3 have the greatest impact on the force output through the entire motion. Also it is found that the area with the greatest increase in force can be moved, by changing the initial gap between core 2 and the shell. The best results from the finite element code were found for a solenoid with a 10 mm gap. The results showed an average improvement of 48%. A smaller total stroke yields better results. This is because most of the improvement is localized to area only one area of the stroke path.