Development of an electromagnetic actuator with magnetic-shape-memory active core for stroke enlargement and noise reduction

As a high-efficiency electro-mechanical drive element for limited rotational and linear movements in many areas of technology, an electromagnet first converts the electrical energy introduced into magnetic energy before it is converted into kinetic energy. Depending on the area of application, electromagnets can be divided into actuating and holding solenoids among other distinctions. On the one hand, an actuating solenoid is characterized by the coverage of a larger setting range up to a few millimeters with an adjustable force-displacement characteristic. Design adjustments to the soft magnetic components, i. e. the cone of the solenoid body, allow the force-displacement curve to be configured via magnetic flux density. The main tasks of a holding magnet, on the other hand, are the attraction and fixation of magnetizable workpieces or objects. Due to the generated magnetic holding force, ferromagnetic material is magnetized and held with high force by the generated magnetic field. However, the force effect is limited to a very short air gap of only a few tenths of a millimeter and is characterized by a strongly nonlinear increasing force-displacement characteristic with decreasing air gap up to the rear end position. In this paper, a hybrid holding-and-actuating solenoid is represented which combines the best of both worlds as accurately as possible. If established electromagnets are combined with novel materials, innovative actuator concepts can be developed, which are reinventing a well-known component. In this paper, these novel materials are magnetic-shape-memory alloys (MSM) made of nickel, manganese and gallium. Exposed to an external magnetic field, they are capable of up to 6 % strain in the vertical direction perpendicular to the magnetic field orientation. This intrinsic motion of the MSM-sticks can be harnessed for novel drive concepts like the hybrid holding-actuating solenoid presented in this paper.