Device for weighing flat objects in motion

1. Device for weighing flat objects in motion comprising a conveyor ( 12 ) comprising drive rollers ( 22 A, 22 B) having a first horizontal axis for conveying along a horizontal transport path ( 14 ) the flat objects laying on the conveyor by one of their flat surface, a weighing plate ( 16 ) above the conveyor and facing said horizontal transport path and comprising a set of free rollers ( 160 ) having a second horizontal axis for receiving the flat surface of the flat objects oriented horizontally, a bias mechanism coupled to bias said conveyor relatively toward said weighing plate to apply a reference load to said weighing sensor even in absence of the flat objects, and a weighing sensor ( 18 ) attached to the weighing plate for measuring the weight of the flat objects during their passage of the flat objects along the horizontal transport path between the conveyor and the weighing plate, the weighing sensor senses a load applied to at least the weighing sensor,

wherein the weighing sensor is arranged above the conveyor and the horizontal transport path and the conveyor is configured to move vertically and thereby press, in a vertical direction, the flat objects in motion against the weighing plate such that the sensed load is inversely proportional to the weight of the flat objects is subtracted from the load as sensed by the weighing sensor.

2. Device according to claim 1 , wherein the conveyor is adapted to further apply a load which is constant regardless of the thickness of the flat object.

3. Device according to claim 2 , wherein the load applied by the conveyor is obtained by a balance system comprising at least one lever arm ( 28 A, 28 B) attached at its upper end to the conveyor by a first pivot connection ( 27 A, 27 B) and attached at its lower end to a counterweight ( 30 A, 30 B), said at least one lever arm being adapted to rotate around at least a second pivot connection ( 32 A, 32 B) attached to a chassis ( 26 ) of the device and attached to the at least one lever arm between its upper and lower ends.

4. Device according to claim 1 , wherein the conveyor is adapted to further apply a load which is sensibly constant regardless of the thickness of the flat object.

5. Device according to claim 1 , wherein the conveyor comprises at least one conveyor belt ( 20 ) driven by said drive rollers.

6. Device according to claim 1 , wherein the load applied by the conveyor is obtained by a spring system comprising at least one lever arm ( 28 A, 28 B) attached at its lower end to a chassis ( 26 ) of the device by a second pivot connection ( 32 A, 32 B) and attached at the upper end to the conveyor by a first pivot connection ( 27 A, 27 B), and at least one spring ( 44 A, 44 B) attached to the chassis of the device and pushing the conveyor vertically in the upper direction.

7. Device according to claim 6 , wherein said at least one spring has a tensile elongation at least equal to the length of the horizontal projection of said at least one lever arm.

8. Device according to claim 6 , wherein said at least one spring has a stiffness coefficient of at least 0.5 N/mm and typically 1 N/mm.

9. Device according to claim 6 , wherein the at least one spring is a tension spring ( 44 A 44 B) attached at its lower end to the chassis of the device and at its upper end to one end of at least a one traction cable ( 40 A, 40 B) running around at least one pulley ( 42 A, 42 B) and the other end of said at least one traction cable is connected to the upper end of said at least one lever arm.

10. Device according to claim 6 , wherein the at least one spring is a spiral spring ( 46 A, 46 B) attached at its central end to the chassis ( 26 ) of the device, the other end of said at least one spiral spring being attached to the upper end of said at least one lever arm.

11. Device according to claim 1 , wherein a dashpot ( 38 ) is placed under the conveyor and perpendicular thereto in order to reduce shocks and vibrations due to the passage of flat objects on the transport path.

12. Device according to claim 1 , wherein the flat objects are envelopes.

13. Mailing machine comprising a device for weighing envelopes in motion Device according to claim 12 wherein the device is a part of a mailing machine.

14. Device according to claim 1 wherein said weighing sensor senses the reference load minus the weight of said flat objects when said flat objects are present on said conveyor.

15. Device according to claim 14 wherein said bias mechanism comprises a lever arm and a counterweight, said lever arm coupled proximate one end thereof to said conveyor, coupled proximate another end thereof to said counterweight, and pivotally coupled to pivot about a pivot point to apply a constant applied force to said weighing plate.

16. Device according to claim 14 wherein said bias mechanism comprises a lever arm and a tension spring, at least one cable, and a pulley, the at least one cable coupled between said tension spring and said conveyor, and passing over said pulley.

17. Device according to claim 14 wherein the bias mechanism comprises a spiral spring coupled to said conveyor.

18. Device according to claim 14, further comprising: a dashpot coupled to said conveyor to dampen vertical vibration thereof.

19. Device according to claim 14 wherein the applied force applied via the bias mechanism is at least equal to a nominal weight of a heaviest one of the flat objects for which the apparatus is rated.