Transducer with conductive polymer bridge

• US 4,974,596 A
• Filed: 07/28/1989
• Issued: 12/04/1990
• Est. Priority Date: 12/14/1987
• Status: Expired due to Fees

• Current Assignee: Medex Incorporated (Smiths Group International Holdings Ltd.)
• Original Assignee: Medex Incorporated (Smiths Group International Holdings Ltd.)
• Inventors: Frank, Thomas P.
• Primary Examiner(s): Hindenburg, Max
• Assistant Examiner(s): Lacyk, J. P.
• Application Number:
  US07/386,211
• Time in Patent Office: 494 Days
• Field of Search: 128/672-673, 128/675, 128/748, 338/3-4, 338/36, 338/42, 73/725-727
• US Class Current: 600/485
• CPC Class Codes: G01L 1/20 by measuring variations in ohmic resistance of solid materials or of electrically-conductive fluids of piezo-resistive materials G01L1/18; by making use of electrokinetic cells, i.e. liquid-containing cells wherein an electrical potential is produced or varied upon the application of stress
• CPC Class Codes: G01L 1/2231 the supports being disc- or ring-shaped, adapted for measuring a force along a single direction
• CPC Class Codes: G01L 1/2287 constructional details of the strain gauges adjustable resistors H01C10/00
• CPC Class Codes: G01L 9/0055 bonded on a diaphragm
• CPC Class Codes: G01P 15/12 by alteration of electrical resistance G01P15/0897, G01P15/105 take precedence

Abstract

A transducer has a thick perimeter and an integral diaphragm extending across said perimeter, all formed of a thermoplastic resin. A thick mass is molded at the center of the diaphragm. Resistive elements formed of a conductive polymer are printed and baked on the diaphragm to form a Wheatstone bridge. The transducer is used as an accelerometer or load cell.

Claims

1. Apparatus comprising a body whose acceleration in a first direction is to be monitored,

a primary transducer consisting of an integrally molded thermoplastic having a thick border, thin, flexible central diaphragm within said border and thick central boss forming a mass movable with respect to said border to flex said diaphragm,

said mass being movable in said first direction when said body accelerates,

a secondary transducer consisting of at least one conductive polymer resistor printed and baked on said diaphragm,

and conductors connected to said secondary transducer.

2. A force sensor comprising:

a molded high temperature, thermoplastic substrate having a thin, flexible section, a thick mass molded on said thin, flexible section, the thick mass and thin section forming a primary transducer,

at least one conductive polymer resistor printed on said flexible section,

said resistor changing its resistance when said substrate is flexed and forming a secondary transducer.

3. A force sensor comprising:

a thick thermoplastic perimeter,

a thin, flexible thermoplastic section molded integrally with and within said thick perimeter, a thick mass integrally molded on said thin section, the flexible section and the mass forming a primary transducer,

at least one conductive polymer resistor printed and baked on said thin section between said mass and said perimeter, said resistor changing its resistance when said substrate is flexed and forming a secondary transducer.

4. A sensor as in claim 3 in which:

said flexible section is in the form of a band fixed at one end to said perimeter and having said mass on the other end.

5. A sensor as in claim 3 in which:

said perimeter is circular in cross section, and in which said flexible section is a strap extending across said perimeter and having said mass mounted in the center of said strap.

6. A force sensor as in claim 3 in which:

said perimeter is circular in cross section and said thin, flexible section is a circular diaphragm extending across said perimeter, said mass being mounted at the center of said diaphragm.