Force measuring apparatus of the vibratory string type

• US 3,897,681 A
• Filed: 05/11/1973
• Issued: 08/05/1975
• Est. Priority Date: 06/23/1971
• Status: Expired due to Term

• Current Assignee: Mettler-Toledo AG IM Langacher Greifensee Switzerland
• Original Assignee: Eugen Meier
• Inventors: Meier, Eugen
• Primary Examiner(s): Ruehl, Charles A.
• Application Number:
  US05/359,258
• Time in Patent Office: 816 Days
• Field of Search: 73/141R,141AB,DIG.1,517AV,382 177/210 331/156
• US Class Current: 73/862.59
• CPC Class Codes: G01G 1/246 of the parallelogram type
• CPC Class Codes: G01G 21/244 combined with flexure-plate fulcrums flexure-plate fulcrums G01G21/07
• CPC Class Codes: G01G 3/165 Constructional details
• CPC Class Codes: G01L 1/086 using electrostatic or electromagnetic counterbalancing forces
• CPC Class Codes: G01L 1/106 Constructional details
• CPC Class Codes: Y10S 73/01 Vibration

Abstract

Improved force measuring apparatus of the one- or two-string type, including means for applying to the movable member of the apparatus a corrective force that compensates for non-linearities in the response of the apparatus over the full range of travel of the pan carrier member between the no-load and full-load positions, thereby to produce a linear variation in the resulting oscillation frequency with respect to load. In the one-string embodiment, linearization means are provided for applying to the oscillatory string means a corrective force that varies quadratically with the displacement of the movable member over its full range between the no-load and full-load positions. In the two-string embodiment, decoupling spring means are provided for independently connecting the two strings in opposite senses between the frame and pan carrier members. The aforementioned linearization means and/or temperature compensation means are also provided for improving the operation of the two-string embodiment.

Claims

1. Force measuring apparatus of the type including at least one oscillatory string the frequency of oscillation of which affords an indication of the magnitude of a load to be measured, comprising a. a stationary frame member;

b. a movable pan carrier member connected for vertical movement between normal no-load and full-load positions relative to said frame member;

c. oscillatory string means connected under tension between said frame and pan carrier members, said string means including at least one string member connected at one end with one of said frame and pan carrier members, and a spring member connecting the other end of said string member with the other of said frame and pan carrier members; and

d. compensating means for applying a corrective force on said string to compensate for the non-linearity of said string and spring members throughout the entire range of travel of said pan carrier member between said no-load and full-load positions, said compensating means comprising a second string member, and a decoupling spring member independently connecting said second string member between said pan carrier and said frame members in an opposite sense than said one string member, respectively, whereby the tensions of said string members are correspondingly increased and decreased, respectively, upon the application of the load to said pan carrier member.

2. at least two spring means independently connecting the other ends of said string members with the corresponding frame and pan carrier members, respectively, said string members being connected in the opposite sense relative to said pan carrier member to cause the tensions in said string members to be increased and decreased, respectively, upon the application of load to said pan carrier member.

3. Apparatus as defined in claim 1, wherein said compensating means includes means (46, 47, 48) for applying to said oscillatory string means a correcton force that varies cubically with the displacement of said movable member from said no-load position toward said full-load position.

4. Force measuring apparatus of the type including at least one oscillatory string the frequency of oscillation of which affords an indication of thE magnitude of a load to be measured, comprising a. a stationary frame member;

b. a movable pan carrier member connected for vertical movement between normal no-load and full-load positions relative to said frame member;

c. oscillatory string means connected under tension between said frame and pan carrier members, said string means including at least one string member connected at one end with one of said frame and pan carrier members, and a spring member connecting the other end of said string member with the other of said frame and pan carrier members; and

d. compensating means for applying a corrective force on said string to compensate for the non-linearity of said string and spring members throughout the entire range of travel of said pan carrier member between said no-load and full-load positions, said compensating means including magnet means for applying to said movable member a repelling magnetic force biasing said movable member toward said full-load position, whereby upon displacement of said movable member, under load, toward said full-load position, the magnetic biasing force decreases in inverse proportion to the square of the displacement distance.

5. Force measuring apparatus of the type including at least one oscillatory string the frequency of oscillation of which affords an indication of the magnitude of a load to be measured, comprising a. a stationary frame member;

b. a movable pan carrier member connected for vertical movement between normal no-load and full-load positions relative to said frame member; and

c. oscillatory string means connected under tension between said frame and pan carrier members, said string means including

6. Apparatus as defined in claim 5, and further including temperature compensating means for applying to at least one of said strings a corrective force for compensating for temperature-responsive variations in the properties of said string members and said spring means, respectively.

7. Apparatus as defined in claim 6, wherein said string members and the corresponding spring means are arranged on opposite sides of, and are connected with, a lateral extension (127) of said pan carrier member, and further wherein said temperature compensating means comprises a pair of flat springs (128, 128'"'"''"'"') the intermediate portions of which are connected with the junctions between said string members and the corresponding spring means, respectively, and a pair of temperature-responsive wire elements (129, 129'"'"''"'"') connected between the free ends of said flat springs, respectively.

8. Apparatus as defined in claim 7, wherein said string members and the corresponding spring means are arranged on opposite sides of, and are connected with, a lateral extension (127) of said pan carrier member, and further wherein said temperature compensating means comprises a pair of rigid beams the intermediate portions of which are connected with the junctions between said string members and the corresponding spring means, respectively, and a pair of springs connected between the free ends of said beams, respectively.

9. Apparatus as defined in claim 6, wherein said string members and the corresponding spring means are arranged on opposite sides of a lateral extension (127) of said pan carrier member, and further wherein said temperature compensating means comprises temperature-responsive bimetallic means (137) connecting one end of at least one of said string meMbers with said lateral extension.

10. Apparatus as defined in claim 6, wherein said temperature compensation means comprises a sinusoidally prestressed flat spring (138) the end portions of which are connected with said frame member and the central portion of which is connected with said pan carrier member, said sinusoidal spring having a negative spring constant.

11. Apparatus as defined in claim 5, and further including means for adjusting the spring constant of at least one of said spring means.

12. Apparatus as defined in claim 5, wherein at least one of said spring means comprises a pair of partial springs (F21, F22).

13. Apparatus as defined in claim 12, wherein the partial springs have different dimensions.

14. Apparatus as defined in claim 13, wherein said partial springs comprise a first partial spring, and a coiled second partial spring arranged concentrically about said partial spring.

15. Apparatus as defined in claim 12, wherein said partial springs are each connected at one end with said pan carrier member, a lever (116) connecting the other ends of said partial springs with the corresponding string (S2), and further including means pivotally connecting said lever with said frame member.

16. Apparatus as defined in claim 15, and further including means (14a) for adjusting the tension of one of said partial springs.

17. Apparatus as defined in claim 15, wherein said partial springs have different degrees of resiliency.

18. Apparatus as defined in claim 15, wherein one of said partial springs comprises a coil spring arranged concentrically about the other of said partial springs.

19. Apparatus as defined in claim 18, and further including temperature compensation means for compensating for the differences of temperature on said string members and said string means, said temperature compensating means being connected between said pan carrier member and said one end of said partial springs and comprising a. a flat spring (122) connected at one end with said pan carrier;

b. a lever (121) pivotally connected intermediate its ends with the other end of said flat spring, said lever being connected at one end with said partial spring means;

c. a first temperature-responsive wire (123) connected at one end with the other end of said lever, said first wire extending parallel with the direction of movement of, and being connected at its other end with a first lateral extension (113) on, said pan carrier member; and

d. a second temperature-responsive wire (124) connected at one end with an intermediate portion of said flat spring, said second wire extending parallel with the direction of movement of, and being connected at its other end with a second lateral extension (125) of, said pan carrier member.

20. Apparatus as defined in claim 5, and further including additional spring means (131) connected between one of said spring means and said pan carrier member.

21. Apparatus as defined in claim 5, and further including magnetic means (135, 135'"'"''"'"') for applying to said pan carrier member a correction force that varies with the displacement of said movable member from said no-load position toward said full-load position, thereby to modify the dependency of the frequency change of the string on the load force and to produce a linear variation in the oscillating frequency with respect to load.

22. Apparatus as defined in claim 5, wherein at least one of said spring means has a non-linear spring characteristic.

23. Apparatus as defined in claim 5 and further including taring spring means (115) for adjusting the tension of at least one of said spring means.

24. Apparatus as defined in claim 5, and further including first parallel lever means (112, 112'"'"''"'"') connected with said frame member for guiding said pan carrier member for vertical movement, an auxiliary mass (M) having a weight that corresponds with the weight of the pan and pan carrier assembly, second parallel lever meaNs connected with said frame member for guiding said auxiliary mass for vertical movement, said first string member and the corresponding spring means being so connected between said frame and pan carrier members that the tension of the first string is increased upon the application of load to said pan carrier, said second string member and the corresponding spring means being so connected between said frame and said auxiliary mass for tensioning by the normal force of gravity on said auxiliary mass, a lever (133) pivotally connected intermediate its ends with said frame for pivotal movement about a horizontal pivot axis, means (133a, 134a) pivotally connecting one end of said lever with the junction between said second string member and the corresponding spring means (131) for connecting the other end of said lever with said pan carrier member.

25. Apparatus as defined in claim 5, and further including first parallel lever means (112, 112'"'"''"'"') connected with said frame member for guiding said pan carrier member for vertical movement, an auxiliary mass (M) having a weight that corresponds with the weight of the pan and pan carrier assembly, second parallel level means connected with said frame member for guiding said auxiliary mass for vertical movement, a first one of said string members and the spring means associated therewith being connected between said frame and said pan carrier members and the other of said string members and the spring means associated therewith being connected between said frame member and said auxiliary mass on the same side of said pan carrier member as said first string member, and magnetic means (135, 135'"'"''"'"') for applying between said string members a repelling force which causes the tensions of said strings to be varied inversely during movement of said pan carrier between said no-load and full-load positions.