Torque-insensitive load cell
First Claim
1. A torque-insensitive load cell, comprising:
- first and second spaced-apart force-receiving members;
a cantilever beam extending between said first and second force-receiving members, one end of said beam being connected to said first member in cantilever fashion so that the angle between said first member and said beam at the area of attachment therebetween is substantially constant, the other end of the said beam being connected to said second member through a relatively thin flexure hinge which is capable of transmitting forces to said beam while allowing said beam to freely pivot with respect to said second member;
a second beam extending between said first and second force-receiving members and having at least one of its ends connected to a respective force-receiving member by a flexure hinge which is capable of transmitting forces to said beam while allowing said beam to freely pivot with respect to said first and second members, said second beam having an effective length which is equal to the length of said first beam from its virtual pivot point to the flexure hinge connecting the end of said beam to said second member, said first and second force-receiving members being spaced apart solely by said cantilever beam and said spacer beam so that the longitudinal stress on said cantilever beam is unaffected by variations in the relative lengths of said cantilever beam and said spacer beam;
strain-sensing means mounted on said cantilever beam for providing an electrical indication of the flexing of said beam; and
means for applying a force between said first and second force-receiving members having a component which is perpendicular to said beams, thereby flexing said cantilever beam and causing said strain-sensing means to generate an electrical indication of the force applied between said force-receiving members.
8 Assignments
0 Petitions
Accused Products
Abstract
A load cell having a parallelogram configuration formed by a pair of spaced-apart, generally parallel force-receiving members interconnected by a cantilever beam and a parallel spacer beam. The cantilever beam projects perpendicularly from one of the force-receiving members, and its end is secured to the other beam by a flexure hinge. The ends of the spacer beam are secured to the force-receiving members by respective flexure hinges. In order to maintain the parallelogram configuration of the load cell, the length of the spacer beam is equal to the length of the cantilever beam from the beam'"'"'s virtual pivot point to its end. Rotational moments imparted to the force-receiving members apply forces to the beams along their longitudinal axes without deflecting the cantilever beam, thus making the load cell insensitive to such moments. A reduced thickness portion instrumented with semiconductor strain gauges is formed in the cantilever beam near its point of attachment with the force-receiving member. The reduced thickness portion accurately positions the virtual pivot point of the beam and it concentrates the stress at the strain gauges. The load cell may be used in a scale by securing one of the load-receiving members on a base and mounting a load-receiving tray on the other load-receiving member.
50 Citations
12 Claims
-
1. A torque-insensitive load cell, comprising:
-
first and second spaced-apart force-receiving members; a cantilever beam extending between said first and second force-receiving members, one end of said beam being connected to said first member in cantilever fashion so that the angle between said first member and said beam at the area of attachment therebetween is substantially constant, the other end of the said beam being connected to said second member through a relatively thin flexure hinge which is capable of transmitting forces to said beam while allowing said beam to freely pivot with respect to said second member; a second beam extending between said first and second force-receiving members and having at least one of its ends connected to a respective force-receiving member by a flexure hinge which is capable of transmitting forces to said beam while allowing said beam to freely pivot with respect to said first and second members, said second beam having an effective length which is equal to the length of said first beam from its virtual pivot point to the flexure hinge connecting the end of said beam to said second member, said first and second force-receiving members being spaced apart solely by said cantilever beam and said spacer beam so that the longitudinal stress on said cantilever beam is unaffected by variations in the relative lengths of said cantilever beam and said spacer beam; strain-sensing means mounted on said cantilever beam for providing an electrical indication of the flexing of said beam; and means for applying a force between said first and second force-receiving members having a component which is perpendicular to said beams, thereby flexing said cantilever beam and causing said strain-sensing means to generate an electrical indication of the force applied between said force-receiving members. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
-
-
10. A method of fabricating a load cell, comprising:
-
providing first and second spaced-apart force-receiving members; providing a cantilever beam extending between said first and second force-receiving members, one end of said beam being connected to said first member in cantilever fashion so that the angle between said first member and said beam at the area of attachment therebetween is substantially constant, the other end of said beam being connected to said second member through a relatively thin flexure hinge which is capable of transmitting forces to said beam while allowing said beam to freely pivot with respect to said second member; providing a spacer beam extending between said first and second force-receiving members and having at least one of its ends connected thereto by a flexure hinge which is capable of transmitting forces to said beam while allowing said beam to freely pivot with respect to said first and second members, said second beam having an effective length which is equal to the length of said cantilever beam from its virtual pivot point to the flexure hinge connecting the end of said beam to said second member, said first and second force-receiving members being spaced apart solely by said cantilever beam and said second beam so that the longitudinal stress on said cantilever beam is unaffected by variations in the relative lengths of said cantilever beam and said second beam; providing strain-sensing means mounted on said beam for generating an electrical indication of the flexing of said cantilever beam; and removing material from said cantilever beam to modify the virtual pivot point of said beam so that said load cell is insensitive to rotational moments applied between said first and second members. - View Dependent Claims (11, 12)
-
Specification