Cantilevered force sensing assembly utilizing one or two resonating force sensing devices

• US 5,036,715 A
• Filed: 06/30/1989
• Issued: 08/06/1991
• Est. Priority Date: 06/30/1989
• Status: Expired due to Term

• Current Assignee: New SD, Inc.
• Original Assignee: New SD, Inc.
• Inventors: Hanson, Richard
• Primary Examiner(s): Ruehl, Charles A.
• Application Number:
  US07/375,186
• Time in Patent Office: 767 Days
• Field of Search: 73/862.59, 73/517 AV, 73/704, 73/778, 73/DIG. 1, 73/DIG. 10
• US Class Current: 73/862.59
• CPC Class Codes: G01L 1/162 using piezoelectric resonators
• CPC Class Codes: G01L 9/0022 of a piezoelectric element
• CPC Class Codes: Y10S 73/10 instrument mechanisms with acceleration compensation

Abstract

A force sensing assembly and particularly one which is especially suitable for use as a pressure transducer is disclosed herein. This assembly includes at least one and preferably a stacked pair of resonating type force sensing devices supported from one end in a cantilvered fashion.

Claims

1. A force sensing assembly, for use in a coordinate system having x, y and z axes, comprising:

(a) a force sensing device including

(i) elongated vibratable tine means,

(ii) means for vibrating said tine means back and forth in a direction normal to its axis of elongation,

(iii) means supporting said tine means such that its frequency of vibration is a function of the magnitude of an external force which is applied to said supporting means along a sensing axis, and

(iv) mans for sensing the vibrating frequency of said tine means, whereby to determine therefrom the magnitude of said external force;

(b) means for mounting said force sensing device in a cantilevered fashion in the x-y plane of the coordinate system, with one end of the device being affixed along the y-axis, the elongation axis of the tine means extending in a direction parallel to the y-axis, the sensing axis extending in a direction parallel to the z-axis, and the end of the device opposite the one end being free to bend to a limited extent about the y-axis;

(c) means for applying said external force to the device adjacent to the free end thereof and along said sensing axis; and

(d) weighted means connected with and acting on the free end of said force sensing device for causing acceleration forces acting on said force sensing device in the same direction as said external force to have substantially no effect on the vibrating frequency of said tine means.

2. An assembly according to claim 1 wherein said means for applying said external force includes bellows means.

3. An assembly according to claim 2 wherein said bellows means includes first and second bellows acting along said sensing axis in opposite directions.

4. An assembly according to claim 3 wherein said first and second bellows are coaxial to one another.

5. An assembly according to claim 4 wherein said bellows are of different diameters.

6. An assembly according to claim 3 wherein said bellows have the same diameter.

7. An assembly according to claim 3 wherein said bellows are offset one to another.

10. An assembly according to claim 1 including reinforcing means supported by said supporting means in said cantilevered fashion directly below and aligned with said force sensing device.

12. An assembly according to claim 1 wherein said force applying means includes first and second bellows acting on the free ends of said devices in opposite directions.

8. A force sensing assembly, for use in an x, y, z coordinate system, comprising:

(a) a force sensing device including

(i) elongated vibratable tine means,

(ii) means for vibrating said tine means back and forth in a direction normal to its axis of elongation,

(iii) support means including a number of structure links and means interconnecting the links to one another to form a closed loop structure and to opposite ends of said tine means such that the elongation axis of said tine means extends between opposite sides of the structure, said support means also including mounting means located along said structure for connecting the support means to an external member capable of applying an external force to the support means along a sensing axis which is neither parallel nor normal to any of the links of said structure such that the support means applies to said tine means its own internal force in response to and varying with said external force and causes the tine means to vibrate at a frequency that varies with the magnitude of said internal force and therefore said external force, and

(iv) means for sensing the vibrating frequency of said tine means, whereby to determine therefrom the magnitude of said external force;

(b) means for supporting said force sensing device in an cantilevered fashion adjacent one end thereof such that the opposite end of the device is free to bend to a limited extent about said one end;

(c) means for applying said external force to the force sensing device along said sensing axis; and

(d) weighted means connected with and acting on the free end of said force sensing device for causing acceleration forces acting on said force sensing device in the same direction as said external force to have substantially no effect on the vibrating frequency of said tine means.

9. An assembly according to claim 8 wherein the closed loop structure includes four links interconnected to form a parallelogram.

11. A force sensing assembly for use in an x, y, z coordinate system, comprising:

(a) first and second resonating types of force sensing devices positioned in spaced apart stacked alignment with one another, each of said devices including elongated vibrative tine means;

(b) means for supporting said force sensing devices within the x, y plane of said coordinate system in a cantilevered fashion adjacent a common end of each device such that the opposite ends of the devices are free to bend to a limited extent about said common ends and such that the elongated direction of said tine means is normal to the cantilevered direction of said devices;

(c) means for applying an external force to the free ends of said devices in the z direction of said coordinate system, whereby said devices serve to measure said force.

13. An assembly according to claim 11 including weighted means connected with and acting on the free ends of said force sensing devices for causing acceleration forces acting on said force sensing devices in the same direction as said external force to have substantially no effect on the device'"'"'s ability to accurately measure said external force.

14. A force sensing assembly for use in an x, y, z coordinate system, comprising:

(a) resonating type of force sensing means comprising a pair of spaced apart, aligned force sensing devices, each of which includes;

(i) elongated vibratable tine means;

(ii) means for vibrating said tine means back and forth in a direction normal to the elongation axis of the tine means;

(iii) supporting means including a number of structure links and means interconnecting the links to one another to form a closed loop structure and to opposite ends of said tine means such that the elongation axis of said tine means extends between a first pair of opposing corners of the structure, said supporting means also including mounting means located along said structure for connecting the supporting means to an external member capable of applying an external force to the supporting means along a sensing axis which is neither parallel with nor normal to any of the links of said structure such that the supporting means applies to said tine means its own internal force in response to and varying with said external force and causes the tine means to vibrate at a frequency that varies with the magnitude of said internal force and therefore said external force; and

(iv) means for sensing the frequency of said tine means and for determining therefrom the magnitude of said external force;

(b) means for supporting said force sensing means within the x, y plane of said coordinate system in a cantilevered fashion adjacent one end of the force sensing means such that the opposite end is free to bend to a limited extent about said one end;

(c) means for applying said external force to the free end of said force sensing means in the z direction of said coordinate system, whereby said force sensing means serves to sense said force; and

(d) weighted means connected with and acting on said force sensing means for causing acceleration forces acting on said force sensing means in the same direction as said external force to have substantially no effect on the ability of the devices to accurately sense said external force.

15. A force sensing assembly for use in an x, y, z coordinate system, comprising:

(a) a force sensing device, including;

(i) elongated vibratable tine means;

(ii) means for vibrating said tine means back and forth in a direction normal to the elongation axis of the tine means;

(iii) supporting means including a number of structure links and means interconnecting the links to one another to form a closed loop structure and to opposite ends of said tine means such that the elongation axis of said tine means extends between a first pair of opposing corners of the structure, said supporting means also including mounting means located along said structure for connecting the supporting means to an external member capable of applying said external force to the supporting means along a sensing axis which is neither parallel with nor normal to any of the links of said structure such that the supporting means applies to said tine means its own internal force in response to and varying with said external force and causes the tine means to vibrate at a frequency that varies with the magnitude of said internal force and therefor said external force, means for sensing the frequency of said tine means and for determining therefrom the magnitude of said external force;

(b) means for supporting said device within the x, y plane of said coordinate system in a cantilevered fashion adjacent one end of the device such that the opposite end is free to bend to a limited extent about said one end; and

(c) means for applying an external force to the free end of said device in the z direction of said coordinate system, whereby said device serves to sense said force.

16. An assembly according to claim 15 including weighted means connected with and acting on the free end of said force sensing device for causing acceleration forces acting on said force sensing device in the same direction as said external force to have substantially no effect on the vibrating frequency of said tine means.

17. An assembly according to claim 15 including a second force sensing device substantially identical to said first mentioned device and wherein said supporting means supports both of said devices in said cantilevered fashion with said second device directly under and aligned with said first mentioned device such that said external force is applied to the free ends of both of said devices simultaneously.

18. An assembly according to claim 15 including reinforcing means supported by said supporting means in said cantilevered fashion directly below and aligned with said force sensing device.

19. A force sensing assembly for use in an x, y, z coordinate system, comprising:

(a) a force sensing device including;

(i) elongated vibratable tine means;

(ii) means for vibrating said tine means back and forth in a direction normal to the elongation axis of the tine means.

(iii) supporting means including a number of structure links and means interconnecting the links to one another to form a closed loop structure and to opposite ends of said tine means such that the elongation axis of said tine means extends between a first pair of opposing corners of the structure, said supporting means also including mounting means located along said structure for connecting the supporting means to an external member capable of applying said external force to the supporting means along a sensing axis which is neither parallel with nor normal to any of the links of said structure such that the supporting means applies to said tine means its own internal force in response to and varying with said external force and causes the tine means to vibrate at a frequency that varies with the magnitude of said internal force and therefor said external force; and

(iv) means for sensing the frequency of said tine means and for determining therefrom the magnitude of said external force; and

(b) means for supporting said force sensing device adjacent one end thereof in a cantilevered fashion along a cantilever axis extending in the x, y plane of said coordinate system such that the opposite end of said device is free to bend to a limited extent about said one end and such that the axis of elongation of said tine means also extends in the said x, y plane but normal to said cantilever axis.

20. An assembly according to claim 19 including a second force sensing device substantially identical to said first mentioned device and supported by said supporting means in said cantilevered fashion directly below and aligned with said first mentioned device such that said external force is applied to both devices simultaneously and in the same way and weighted means connected to said devices such that said weighted means acts on both devices in the same way.

21. An assembly according to claim 19 including reinforcing means supported by said supporting means in said cantilevered fashion directly below and aligned with said force sensing device.

22. A force sensing assembly, for use in an x, y, z coordinate system, comprising:

(a) a force sensing device including

(i) elongated vibratable tine means,

(ii) means for vibrating said tine means back and forth in a direction normal to its axis of elongation,

(iii) means supporting said tine means such that its frequency of vibration is a function of the degree to which the tine means is placed in tension or compression along its elongation axis which, in turn, is a function of the magnitude of an external force which is applied to said supporting means along a sensing axis, and

(iv) means for sensing the vibrating frequency of said tine means, whereby to determine therefrom the magnitude of said external force;

(b) means for mounting said force sensing device in a cantilevered fashion in the x-y plane of the coordinate system, with the sensing axis extending the z-direction, and the end of the device opposite the one end being free to bend to a limited extent about said one end;

(c) means for applying said external force to the device adjacent to the free end thereof and along said sensing axis; and

(d) weighted means connected with and acting on the free end of said force sensing device for causing acceleration forces acting on said force sensing device in the same direction as said external force to have substantially no effect on the vibrating frequency of said tine means, said weighted means being configured such that said acceleration forces acting on said force sensing device in said z-direction place said tine means in shear along its length and not in tension or compression along its length.

23. A force sensing assembly, for use in an x, y, z coordinate system, comprising:

(a) a force sensing device including

(i) elongated vibratable tine means,

(ii) means for vibrating said tine means back and forth in a direction normal to its axis of elongation,

(iii) means supporting said tine means such that its frequency of vibration is a function of the magnitude of an external force which is applied to said supporting means and along a given sensing axis, and

(iv) means for sensing the vibrating frequency of said tine means, whereby to determine therefrom the magnitude of said external force;

(b) means for supporting said force sensing device in an cantilevered fashion adjacent one end thereof such that the opposite end of the device is free to bend to a limited extent about said one end;

(c) means for applying said external force to said supporting means along said given sensing axis;

(d) weighted means connected with and acting on the free end of said force sensing device for causing acceleration forces acting on said force sensing device in the same direction as said external force to have substantially no effect on the vibrating frequency of said tine means; and

(e) a second force sensing device substantially identical to said first mentioned device and supported by said supporting means in said cantilevered fashion directly below and aligned with said first mentioned device such that said external force is applied to both devices simultaneously and in the same way and such that said weighted means acts on both devices in the same way.