Fork lift scale

• US 4,421,186 A
• Filed: 12/28/1982
• Issued: 12/20/1983
• Est. Priority Date: 08/25/1980
• Status: Expired due to Term

• Current Assignee: Avery Weigh-Tronix LLC (Illinois Tool Works Inc.)
• Original Assignee: Weigh-Tronix, Inc. (Illinois Tool Works Inc.)
• Inventors: Bradley, Richard S.
• Primary Examiner(s): Hartary, Joseph W.
• Application Number:
  US06/453,996
• Time in Patent Office: 357 Days
• Field of Search: 177/139, 177/136, 177/147, 177/152, 177/211, 177/229, 73/862.66, 414/21
• US Class Current: 177/139
• CPC Class Codes: G01G 19/083 lift truck scale
• CPC Class Codes: G01G 3/1404 combined with means to connect the strain gauges on electrical bridges

Abstract

The weight of items carried by a fork lift truck may be measured by this fork lift scale. This fork lift scale consists of horizontally disposed load sensors connecting a crossbar frame to the crossbars of the fork lift truck. Forks are supported by the crossbar frame. Strain gages are mounted on the load sensors to sense the weight of items carried on the forks. The strain gages are mounted to sense vertical shear or bending in the load sensors. The strain gages are positioned on the load sensors and are electrically interconnected so that types of loading, other than vertical loading due to the weight of items placed on the forks, are rejected and not measured by this fork lift scale.

Claims

1. A fork lift scale for weighing items placed on a fork of a fork lift truck, said fork lift scale comprising:

a deformable member for use in attaching a fork to the fork lift truck, said deformable member having a material axis and comprising a single beam being disposed in substantially horizontal relation and extending in a fore and aft direction, said deformable member having opposed substantially vertically disposed planar surfaces intermediate the ends thereof, a plurality of electrical strain gages mounted on said planar surfaces of said deformable member and positioned on the neutral axis of the latter to sense the deformation of said deformable member caused by the weight of an item placed on the fork, the load exerted on the deformable member by the fork of the fork lift truck being spaced longitudinally of said strain gages,

and, a Wheatstone bridge circuit including said strain gages operable to produce an output signal caused by deformation of said deformable member, said strain gages being connected in said bridge circuit to electrically sense vertical load only and being insensitive to and rejecting all other loads, and means for converting the output signal into a perceptive weight readout.

2. A fork lift scale for weighing items placed on the fork of a fork lift truck, said fork lift scale comprising:

a plurality of deformable members for use in attaching a fork to the fork lift truck, each deformable member having a neutral axis and comprising a single elongate beam being disposed in substantially horizontal relation and extending in a fore and aft direction, each of said deformable members having opposed substantially vertically disposed planar surfaces intermediate the ends thereof,

a plurality of electrical resistant strain gages mounted on said planar surfaces of each of said deformable members, said strain gages for each deformable member being positioned symmetrically on the neutral axis of the latter to sense the deformation of the latter caused by the weight of an item placed on the fork, the load exerted on each deformable member by the fork of the fork lift truck being spaced longitudinally of said strain gages on each deformable member,

a plurality of electrically connected Wheatstone bridge circuits, each circuit including the strain gages of each deformable member, each bridge circuit producing an output signal caused by deformation of the associated deformable member, said strain gages being connected to the associated bridge circuit to electrically sense vertical load only and rejecting all other loads, and means summing the output signals from each bridge circuit and for converting the summed output signals into perceptive weight readout.

3. The fork lift scale as defined in claim 2 wherein the neutral axis of said deformable members are disposed in parallel relation with respect to each other and extend generally in the direction of travel of the fork lift truck, the load exerted on each deformable member by the fork of the fork lift truck being spaced forwardly of the strain gages on each deformable member.

4. In combination with a fork lift truck having ground engaging propulsion wheels, a lifting guide mounted on the front end of the lift truck, a lifting fork assembly projecting forwardly of the truck for use in lifting items, a scale for use in measuring the weight of items placed on the fork assembly, comprising:

a plurality of horizontally disposed members for use in connecting the fork assembly to the lifting guide and extending in a fore and aft direction, each deformable member having a neutral axis and having opposed substantially vertical planar surfaces,

a plurality of electrical resistant strain gages mounted on said planar surfaces of each of said deformable members and being symmetrically disposed on the neutral axis of each deformable member to sense the deformation of the latter caused by the weight of an item placed on the fork assembly, the load exerted on each of said deformable members by the lifting fork assembly of the fork lift truck being spaced longitudinally forwardly of said strain gages on each deformable member,

and a plurality of Wheatstone bridge circuits, each circuit including the strain gages of each deformable member, each bridge circuit producing an output signal caused by deformation of the associated deformable members, said strain gages being electrically connected in the associated bridge circuit to electrically sense vertical loads only and to electrically reject all other loads, and means for converting the output signals into a perceptive weight readout.

5. The fork lift truck as defined in claim 4 wherein each of said deformable members has a pair of strain gages mounted on each planar surface thereof, and wherein the load exerted on each deformable member by the lifting fork is spaced longitudinally forwardly of the strain gages for each deformable member.

6. The fork lift truck as defined in claim 4 and wherein each of said deformable members is provided with an annular stop element intermediate the ends thereof, said lifting guide engaging the annular stop element on each deformable member to space the lifting guide rearwardly of said strain gages on each deformable member.

7. The fork lift truck as defined in claim 4 and means on the forward end portion of each deformable member connected with the lifting frame assembly whereby the load exerted on each deformable member by the weight of an object on the lifting fork assembly is spaced longitudinally of the strain gages on each deformable member.

8. A fork lift scale for weighing items placed on the fork of a fork lift truck, said fork lift scale comprising:

a plurality of deformable members for use in attaching a fork to the fork lift truck, each deformable member having a neutral axis and each comprising a single elongate beam,

a plurality of electrical resistant strain gages mounted on each of said deformable members and being disposed on the neutral axis of the associated deformable member to sense the deformation of the latter caused by the weight of an item placed on the fork, the load exerted by the weight of an item positioned on the fork of the fork lift truck being spaced longitudinally of the strain gages of each deformable member,

and a plurality of bridge circuits including said strain gages producing output signals caused by deformation of said deformable members, said strain gages being connected in the associated bridge circuit to electrically sense vertical loads only and reject all other loads, and means for converting said output signal into a perceptive weight readout.

9. The fork lift scale as defined in claim 8 wherein each of said deformable members comprises a single, elongate, horizontally disposed beam having threads thereon to define a bolt for use in connecting the fork with the fork lift truck, each deformable member extending in a fore and aft direction, the load exerted by the weight of an object on the fork of the fork lift truck on each deformable member being spaced longitudinally forwardly of the strain gage on each deformable member.