This paper shows a simplified mathematical model for a torque-motor used in servovalves. The torque-motor treated in this paper is a commonly used prototype, in which an armature and flapper assembly is supported by a flexure tube. Combining mathematical expressions for mechanical and electromagnetic elements, transfer functions between variables are given. To represent the mechanical structure, a one-degree-of-freedom vibration system is assumed. This assumption simplifies the model, although restricts the frequency range in which the model can be applied. The analysis includes the influence of eddy currents in the yokes and armature. A first-order delay relating coil current to armature torque is used to represent the influence. Experiments verified that the presented mathematical model is valid up to the fundamental natural frequency of the vibration system.

Keywords: torque-motor, servovalve, one-degree-of-freedom model, magnetic circuit, eddy current, frequency characteristic