Patent ID: 6868743
Filing Date: 2005-03-22
Classification: G01L

Abstract:
1. A torque sensor comprising: a first shaft; a second shaft; an elastic member coupling said first shaft to said second shafts in alignment with each other, upon input of torque, said elastic member undergoing torsion; a hard magnetic member joined to said first shaft, said hard magnetic member having magnetic poles arrayed on a periphery thereof to produce a magnetic field therearound; an assembly of a first and a second soft magnetic member which is joined to said second shaft and placed around said hard magnetic member within the magnetic filed produced by said hard magnetic member to form a magnetic circuit so that upon a change in position of the first and second magnetic members relative to said hard magnetic member arising from the torsion of said elastic member, density of magnetic flux developed within the magnetic circuit changes; and a magnetic sensor placed in non-contact with said first and second soft magnetic members, working to measure the density of magnetic flux within the magnetic circuit, wherein said first and second soft magnetic members are opposed to each other through a given gap in a direction of the alignment of said first and second shafts, said first and second soft magnetic members having as many claws as the poles of said hard magnetic member which are arrayed at regular intervals on peripheries of said first and second soft magnetic members, respectively, each of the claws of said first soft magnetic member being interposed between adjacent two of the claws of said second soft magnetic member, each of the claws having a base portion and a head portion to have substantially a trapezoidal shape, the base portion having a width A extending in a circumferential direction of said first and second soft magnetic members, the head portion having a width B extending in the circumferential direction which is smaller than the width A, the widths A and B being selected to meet relations below where F is a distance between said first and second soft magnetic members in the direction of the alignment of said first and second shafts, L is a length of each of the claws from the base portion to the head portion, and P is a distance between one of outer edges of each of the claws of the first soft magnetic member and one of outer edges of an adjacent one of the claws of the second magnetic member which lies on the same side as the first soft magnetic member in the circumferential direction of the first and second soft magnetic members.