In this study, a newly designed electro-magnetic proportional actuator composed of an armature and a stator with a cylindrical two-step pole to control oil hydraulic valves was constructed and examined. In the actuator, two traction forces generated by the magnetic flux flow in the radial air gap and the axial air gap between the armature and the stator are added and become thrust force on the actuator. Furthermore, these air gaps are arranged at two places in the magnetic circuit of the actuator so the total of the traction forces in their air gaps becomes a large thrust force on the actuator. The dimensions of this actuator are 60 mm diameter, by 83 mm length. As a result of measurements of the characteristics of this actuator, it became clear that its thrust force was constant within 2mm of the armature stroke, producing about 290N at an electronic power consumption of 15W. The thrust of this actuator is nearly 2.5 times larger than that of conventional proportional solenoids and linear motors of the same size and power consumption.
The principle of producing thrust force in the newly designed actuator is based on the above mentioned addition of the traction forces in the air gaps. Therefore, the actuators for producing the traction forces in the axial and radial air gaps separately were designed and made. Then, the two traction force curves were measured and a thrust force curve was made up by adding these traction force curves. This thrust force curve agrees well with the experimental curve of this actuator. As a result, a simple design method of this actuator can be shown in this study.

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