Patent ID: 8193885
Filing Date: 2012-06-05
Classification: H01F,H02K,H04R

Abstract:
1. A linear actuator comprising: a housing of soft magnetic material, the housing having a first end and a second end; a coil assembly positioned in the housing; a field assembly positioned in the housing for movement relative to the coil assembly and including an axially magnetized permanent magnet, wherein a force is provided between the field assembly and the housing when the coil assembly is not energized; and further including a housing extension of hard magnetic material positioned at the first end of the housing and having an axial length selected so that the field assembly assumes a particular position offset from the coil assembly and nearer to the first end of the housing than to the second end of the housing each time that the coil assembly is not energized, wherein an attraction force between the housing extension and the field assembly provides a predetermined spring characteristic of the actuator such that an amount of attraction force applied to the field assembly by the housing extension changes based at least in part on the proximity of the field assembly to the housing extension, wherein a polarity of an end the housing extension proximate to the field assembly is opposite of a polarity of an end of the axially magnetized permanent magnet of the field assembly proximate to the housing extension to create the attraction force between the housing extension and the field assembly, and wherein the attraction force between the housing extension and the field assembly is opposite in direction to a force provided by the coil assembly when the coil assembly is energized and a current is passing through coils of the coil assembly in a first direction.