WEIGHT SENSING CELL

• US 3,712,395 A
• Filed: 11/16/1970
• Issued: 01/23/1973
• Est. Priority Date: 11/16/1970
• Status: Expired due to Term

• Current Assignee: August L. Streater, John A. Whitney
• Original Assignee: August L. Streater, John A. Whitney
• Inventors: Streater, August L., Whitney, John A.
• Primary Examiner(s): Ward, Jr., Robert S.
• Application Number:
  US05/089,736
• Time in Patent Office: 799 Days
• Field of Search: 84/455,199,297R,297S,402-405,454,458 181/33R,33D 177/1,210,211,255 73/DIG.1,67R,67.2
• US Class Current: 177/210.00R
• CPC Class Codes: G01G 3/16 measuring variations of frequency of oscillations of the body
• CPC Class Codes: Y10S 73/01 Vibration

Abstract

This disclosure deals with a weight sensing cell for a scale, including two differentially loaded vibrating members. The two members are pretensioned, and they are arranged and connected to a weighting platform of the scale such that, by the differential loading, a weight on the platform increases the tension on one member and decreases the tension on the other member, the amount of tension on each member determining its frequency of vibration. Means is provided to generate two signals which are respectively representative of the frequencies of vibration of the two members, and the frequency of one of these members or a combination of the frequencies of the two members is taken as an indication of the amount of weight on the platform. Means is also provided to adjust the amount of pretension on the members and to compensate for any non-linear characteristic, and thereby achieve an essentially linear relationship between frequency and weight.

Claims

1. A weight sensing cell for a scale, comprising a weight receiving member, a pair of differentially loaded vibrating members held under tension, one end of each of said members being connected to said weight receiving member, means for adjusting the tension in said vibrating members, means responsive to vibrations of said vibrating members for generating signals having frequencies which are respectively functions of the frequencies of vibration of said vibrating members, means for generating a fixed frequency, means for combining said fixed frequency with the frequency of one of said signals to produce a difference frequency signal, means for comparing the frequency of said difference signal with the frequency of the other of said signals to produce an error signal, said adjustable means being responsive to said error signal and adjusting the tension in said vibrating members to hold said error signal at a constant value.

2. A weight sensing cell as in claim 1, wherein said vibrating members are in aligned end-to-end relation.

3. A weight sensing cell as in claim 1, wherein said vibrating members make an angle of less than 180* with each other.

4. A weight sensing cell comprising first and second vibrating members, means for connecting one end of one of said members to one end of the other of said members, means for connecting the other ends of said members to a support, means for pretensioning said first and second members, means for applying a weight representative force to said first mentioned means in such a direction to increase the tension in one of said members and to decrease the tension in the other of said members, means for vibrating said members and for sensing the frequencies of vibration of said members, and means responsive to the frequencies of vibration of said members for adjusting the tensions in said members to maintain a predetermined frequency relation therebetween.

5. A cell as in claim 4, and further including guide means for maintaining the movement of said first mentioned means substantially in said direction, and said force applying means making substantially point contact with said first mentioned means and applying said force in said direction.

7. A weight sensing cell for a weighing scale comprising a member adapted to receive a weight to be measured, a pair of differentially loaded vibrating members held under tension, each of said pair of members having one end connected to said weight receiving member, means for vibrating said pair of members and for sensing the frequencies of vibration of said pair of members, and means responsive to said frequencies of vibration of said pair of members for adjusting said tension to maintain a substantially linear function between said weighT and the difference between said frequencies.

8. A cell as in claim 7, wherein said function has a linearity error, and compensating means for introducing a compensating linearity function to thereby produce an essentially linear function.

9. A cell as in claim 8, wherein said compensating means comprises a spring gradient connected to one of said weight receiving and weight applying members.

10. A cell as in claim 9, wherein said spring gradient is adjustable.

11. A cell as in claim 8, wherein said compensating means comprises a characteristic of at least one of said vibrating members to effect different vibrations of said one vibrating member as compared with the other of said vibrating members.

12. A cell as in claim 9, wherein said spring gradient may be determined by the equation k a To/0.0645 l0eo where a the slope of said linearity error, To the tension in said vibrating members with no weight applied, lo the length of said members with no weight applied, and eo the elongation of said members with no weight applied.

13. A cell as in claim 12, wherein A is within the range of approximately 0.0015 to 0.0003.

14. A cell as in claim 7, wherein said tension adjusting means increases said tensions in both of said members simultaneously or decreases said tensions in both of said members simultaneously.

15. Apparatus comprising a string, means for supporting one end of said string, and tension adjusting means for supporting the other end of said string, said adjusting means comprising a movable armature, spring means for guiding the movement of said armature along a path which is parallel to the axis of said string and for applying a force on said armature, said force being directed along said path and pretensioning said string, and adjustable means for applying an additional force on said armature and thereby further tensioning said string, said spring means comprising at least one Belleville spring.

16. A weight sensing cell for a scale comprising first and second vibrating members, one end of said first member being connected to one end of said second member, means anchoring the other end of said first member, adjustable servo means for supporting the other end of said second member and holding said members under tension, means responsive to the weight of an article to be measured and connected to apply a force on said connection between said first and second members for increasing the tension in one of said members and for decreasing the tension in the other of said members by amounts which are functions of the weight of the article, means responsive to vibrations of said first and second members for generating first and second signals having frequencies which are functions of the frequencies of said first and second members respectively, and circuit means responsive to said first and second signals and connected to actuate said servo means to adjust the tension in said first and second members to maintain a predetermined relation between the frequencies of vibration of said first and second members.

17. Apparatus as in claim 16, wherein said circuit means comprises means for generating a fixed frequency, means for combining said fixed frequency with the frequency of one of said first and second signals to produce a difference signal, means for combining the frequency of said difference signal with the frequency of the other of said first and second signals to produce an error signal, and means for applying said error signal to said servo means such as to adjust the tension in said first and second members to eliminate said error signal.

18. Apparatus as in claim 16, wherein one of said first and second signals serves as an output signal having a frequency which is representative of the weight of said article.

19. Apparatus as in claim 16, wherein saId first and second members comprise elongated strings arranged in aligned end-to-end relation, said servo means applying said tension in the line of said strings, and said force on said connection being applied in said line.

20. A weight sensing cell for a weighing scale comprising a member adapted to receive a weight to be measured, a pair of differentially loaded vibrating members, adjustable means connected to said members for pretensioning said members, each of said pair of vibrating members having one end connected to said weight receiving member, drive means for vibrating said pair of members and for sensing the frequencies of vibration of said pair of members, means responsive to said frequencies of vibration of said vibrating members and connected to actuate said adjustable means to adjust said pretension to maintain a predetermined frequency relation between said frequencies of vibration of said vibrating members, said drive including means for controlling the amplitude of vibration of said members.

21. A cell as in claim 20, wherein said amplitude controlling means maintains the amplitude of vibration of said vibrating members at a substantially constant value.

22. A cell as in claim 20, wherein said amplitude controlling means maintains the amplitude of vibration of said vibrating members at below a predetermined maximum value.

23. A weight sensing cell for a weighing scale comprising a member adapted to receive a weight to be measured, a pair of differentially loaded vibrating members, adjustable means connected to and pretensioning said members, each of said vibrating members having one end connected to said weight receiving member, drive means for vibrating said pair of members, means responsive to the frequencies of vibration of said members and connected to actuate said adjustable means to pretension said vibrating members to maintain a predetermined frequency relation between the frequencies of vibration of said members, the frequency of vibration of at least one of said members being a substantially linear function of weight when said predetermined frequency relation is maintained, and means for introducing a compensating linearity error to compensate for any nonlinearity in said function.

24. Apparatus as in claim 23, wherein said means for introducing a compensating linearity error comprises the spring gradient of a spring connected to said weight receiving member.

25. Apparatus as in claim 23, wherein said means for introducing a compensating linearity error comprises having said one of said members with a greater length than the other of said members.

26. Apparatus as in claim 23, wherein said means for introducing a compensating linearity error comprises having one of said members with a greater mass per unit length than the other of said members.

27. A weight sensing cell for a weighing scale comprising a member adapted to receive a weight to be measured, a pair of differentially loaded vibrating members, adjustable means connected to and pretensioning said members, each of said vibrating members having one end connected to said weight receiving member, drive means for vibrating said pair of members, said drive means including means for controlling the amplitude of vibration of said members, means responsive to the frequencies of vibration of said members and connected to actuate said adjustable means to pretension said vibrating members to maintain a predetermined frequency relation between the frequencies of vibration of said members, the frequency of vibration of at least one of said members being a substantially linear function of weight when said predetermined frequency relation is maintained, and means for introducing a compensating linearity error to compensate for any nonlinearity in said function.