For this design to be valid, we have to control the axial movement of the stator. Thus, the cam mechanism of a retractable pen is applied for the linear flux area variant design. In a retractable pen, the axial movement is transferred to horizontal movement by the cam. However, the horizontal movement is changed to circular motion as the cam body is formed as a cam ring. This movement mechanism is applied to the motor design but reversed. By giving a rotational input to the cam ring, axial movement of the cam body is established.

The axial distance of the stator (yellow) can be controlled by the rotational movement of the cam ring (orange). Therefore, an external actuator (e.g. stepper motor) is added to the end of the BLDC motor for control of the cam ring. We can observe that the stator can be fully inserted into the rotor (green) as the cam ring rotates 90 degrees. The rotation angle (𝜃) and the axial distance (𝑑) is related as 𝜃 ∝ 𝑑 , which shows a linear relation, and the incrementation of the axial distance by the rotation angle can be controlled by changing the inclination of the cam.

Design Analysis

The stator position is controlled by three components, stepper motor – cam ring – cam body, which can be used to enable mechanical field weakening for the BLDC motor. However, due to the internal rotor design in the conceptual design, high speed rotation of the rotor may cause internal damage in events where the components are not aligned precisely. Thus, an elaborate manufacture process may be required for the operation of the BLDC motor. Therefore, a design improvement is necessary where the shaft is fixed to secure the concentricity within an allowed range or relocation of the rotor component is recommended.