A magnetostrictive sensor has been conventionally used for detecting a torque acting on a component of equipment or detecting a load acting on the component. A known configuration example of the magnetostrictive sensor includes: a columnar substrate having an outer peripheral surface on which a magnetostrictive portion is provided; and a detection coil that generates a magnetic flux passing through the magnetostrictive portion. In the case of using the magnetostrictive sensor having such a configuration as a torque sensor, when a force in a rotation direction is applied to the substrate, a tensile stress or a compressive stress occurs in the magnetostrictive portion. Accordingly, the magnetic permeability of the magnetostrictive portion changes. The torque sensor detects a change in the magnetic permeability of the magnetostrictive portion using the detection coil to thereby detect a force acting on the substrate.
For example, an amorphous thin strap or a plating film can be used as the magnetostrictive portions. In the case of using an amorphous thin strap as the magnetostrictive portion, the sensitivity of the magnetostrictive sensor can be increased. In the case of using the amorphous thin strap as the magnetostrictive portion, the amorphous thin strap needs to be bonded to the outer peripheral surface of the substrate with an adhesive. To accurately bond the amorphous thin strap to the outer peripheral surface of the substrate, the adhesive needs to be uniformly applied onto the outer peripheral surface of the substrate. It is, however, difficult to uniformly apply the adhesive onto the outer peripheral surface of the substrate. In addition, if an inappropriate amount of the adhesive is used, for example, the adhesive is likely to extend off between the amorphous thin strap and the substrate in bonding the amorphous thin strap to the substrate. In this case, a process for removing the excess adhesive is needed. In addition, since the amorphous thin strap is thin, it is difficult to use the amorphous thin strap with an industrial robot. In view of these circumstances, in the case of using the amorphous thin strap as the magnetostrictive portion, it is difficult to enhance productivity.
From the viewpoint of productivity, the use of a plating film as the magnetostrictive portion is conceivable. In the case of forming a plating film by electroplating, as disclosed in Patent Document 1, for example, the substrate is immersed in a plating solution with a predetermined portion of the substrate masked with a masking member. Thereafter, a current is caused to flow in the plating solution so that a plating film is formed in an unmasked portion of the substrate.