Media weight sensor using an acoustic resonator
AssigneeHewlett-Packard Company
InventorPhillip R. Luque
Life of this patent
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Abstract
This invention relates to a media weight sensor of the type that includes a transducer consisting of a metal desk with a piezoelectric element fabricated by one side which form the back of a Helmholtz resonator cavity mounted in a printer so that the media going to the printer moves across the top of the Helmholtz resonator where an opening of the resonator is located. A soft, polymeric roller is used to press for media and is the transducer. The resonant frequency of the Helmholtz is affected by the media. The mass of the media adds to the mass of the resonator, thereby lowering the resonant frequency. Consequently, the heavier than media, the more the resonant frequency is lowered.
Claims14
A media weight sensing apparatus, comprising:
- a Helmholtz resonator means having an opening substantially located in one end of the resonator means and a media weight measuring means operatively connected to the other end of said resonator means, wherein said resonator means is further comprised of;
- a resonator housing, a piezoelectric means operatively connected to said resonator housing, and a disk means operatively connected to said piezoelectric means;
- and
- a media traversing means for traversing the media, whose weight is to be determined, across said opening in said resonator means.
A method for determining the weight of a media, comprising the steps of:
- employing a media weight sensing apparatus, comprising a Helmholtz resonator means having an opening substantially located in one end of said resonator means, a media weight measuring means operatively connected to the other end of said resonator means, and a media traversing means, wherein said media weight sensing apparatus is used to measure a first resonant frequency of said apparatus when no media is located on said apparatus, wherein said step of employing said media weight sensing apparatus to determine a resonant frequency of said apparatus when a media is located on said apparatus is further comprised of the step of;
- determining said first resonant frequency according to the equations:
- V=π(D/2)2H=cavity volume(mm{circumflex over ( )}3)
- L′=T+1.7a=effective throat length(mm)
- S=πa2=area of hole(mm{circumflex over ( )}2)
- s=cavity stiffness=ρoc2S2/V(g/sec{circumflex over ( )}2)
- m=effective mass of air in neck=ρoSL′(g)
- cavity is resonant when:
- ωom=s/ωo
- ω o 2 = s m = ρ o c 2 S 2 V ρ o SL ′ = c 2 S V L ′
- traversing said media across said opening in said media weight sensing apparatus;
- determining a second resonant frequency of said media by said media weight sensing apparatus;
- comparing said second resonant frequency of said media with said first resonant frequency of said apparatus when no media is located on said apparatus to obtain a net resonant frequency;
- and
- determining a weight of said media.
A printer, wherein said printer is capable of sensing a media weight, comprising:
- a printer housing;
- a Helmholtz resonator means located substantially within said printer housing and having an opening substantially located in one end of said resonator means, wherein said resonator means is further comprised of;
- a resonator housing, a piezoelectric means operatively connected to said resonator housing, and a disk means operatively connected to said piezoelectric means;
- a media weight measuring means operatively connected to the other end of said resonator means;
- and
- a media traversing means for traversing a media, whose weight is to be determined, across said opening in said resonator means.
Dependencies are inferred from the claim text.