Piezoresistive force sensor

A method for manufacturing a force sensor comprising the following steps:

• providing electrically conductive first staple fibers and electrically non-conductive second staple fibers,
• mixing the first staple fibers and the second staple fibers to a mixture in which the first staple fibers and the second staple fibers are distributed,
• forming from the mixture, an elastically deformable resistance layer comprising a first outer surface and a second outer surface that is opposite to the first outer surface, wherein a portion of the first staple fibers of a total amount of the first staple fibers and the second staple fibers is set to obtain a desired conductivity of the resistance layer in force measuring direction orthogonal to the outer surfaces, whereby the larger the portion of the first staple fibers of the total amount of the first staple fibers and the second staple fibers, the higher the conductivity of the resistance layer in the force measuring direction orthogonal to the outer surfaces,
• attaching an electrically conductive first electrode on the first outer surface or on the second outer surface and attaching an electrically conductive second electrode on the first outer surface or the second outer surface, such that an electrically conductive path is created from the first electrode via the resistance layer to the second electrode, wherein a resistance value of a total resistance of the electrically conductive path depends on an external force applied between the first outer surface and the second outer surface;
• wherein the resistance layer comprises a volume resistance depending from the external force that is created by individual contact resistances connected in parallel and/or in series to one another that are established at each contact site between two first staple fibers being in contact to one another;
• and
• wherein the total resistance of the electrically conductive path is created by a series connection of a first contact resistance between the first electrode and the resistance layer, a volume resistance of the electrically conductive path within the resistance layer and a second contact resistance between the resistance layer and the second electrode.

A piezo-resistive force sensor, comprising:

• an elastically deformable resistance layer that comprises a first outer surface and a second outer surface opposite the first outer surface and that comprises a mixture of distributed electrically conductive first staple fibers and electrically non-conductive second staple fibers,
• an electrically conductive first electrode and an electrically conductive second electrode, wherein the first electrode and the second electrode are either arranged on the first outer surface or the second outer surface such that an electrically conductive path is created from the first electrode via the resistance layer to the second electrode, wherein a resistance value of a resistance of the electrically conductive path depends on an amount of an external force that is effective between the first outer surface and the second outer surface,
• wherein a portion of the first staple fibers of a total amount of the first staple fibers and the second staple fibers is set to obtain a desired conductivity of the resistance layer in force measuring direction orthogonal to the outer surfaces, whereby the larger the portion of the first staple fibers of the total amount of the first staple fibers and the second staple fibers, the higher the conductivity of the resistance layer in the force measuring direction orthogonal to the outer surfaces,
• wherein the resistance layer comprises a volume resistance depending from the external force that is created by individual contact resistances connected in parallel and/or in series to one another that are established at each contact site between two first staple fibers being in contact to one another,
• wherein a total resistance of the electrically conductive path is created by a series connection of a first contact resistance between the first electrode and the resistance layer, a volume resistance of the electrically conductive path within the resistance layer and a second contact resistance between the resistance layer and the second electrode, and
• wherein the resistance value of a total resistance of the electrically conductive path amounts to maximum 1000 MΩ, if no external force is applied on the force sensor.