Measuring and testing – Dynamometers – Responsive to force
Patent
1994-08-31
1995-04-25
Chilcot, Jr., Richard E.
Measuring and testing
Dynamometers
Responsive to force
177210FP, G01L 100
Patent
active
054088887
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to force or load measuring apparatus and in particular to apparatus which Incorporates a vibratory beam.
BACKGROUND OF THE INVENTION
Apparatus for measuring force or load by the use of vibratory beams are well known. In such apparatus a vibratory beam is excited and vibrates at particular frequencies related to the amount of stress applied to the vibratory beam. Frequency of vibration is also dependent upon the stiffness of the beam. Such apparatus provide substantial advantages in that construction is simple and analogue-to-digital converters are not required because a digital value is directly produced in such apparatus.
In my U.S. Pat. No. 4,734,931 disclose force measuring apparatus wherein mechanical Q is high so that oscillations can be maintained in the vibratory beam whereby smaller sources of external energy are required to excite the beam. In my aforesaid patent the force measuring apparatus comprises a vibratory beam which vibrates back and forth at a measurement frequency and which includes a rotational mass coupled to the beam at an internal nodal point which does not vibrate back and forth at the measurement frequency but wherein the rotational mass rotates at the measurement frequency.
SUMMARY OF THE INVENTION
The present invention aims to provide force or load measurement apparatus which incorporates a vibratory beam and which is at least an alternative to the apparatus disclosed in my above U.S. Patent and which functions efficiently for the measurement of load or force. Other features of the apparatus will become apparent in the following description.
The present invention thus provides apparatus for measuring a load or force comprising a vibratory beam which vibrates back and forth at a measurement frequency said beam having first and second end nodal points and first and second ends adjacent said first and second nodal points, means for coupling said first end of the vibratory beam to said load for applying a stress to said vibratory beam that determines the measurement frequency at which said beam vibrates and a mass coupled to said beam intermediate said first and second ends, said mass reciprocating at said measurement frequency.
Preferably the reciprocatory mass is located at a position along said beam wherein the greatest vibration of said beam back and forth at the measurement frequency occurs. Alternatively, said beam may include one or more intermediate nodal points and a plurality of masses are coupled to said beam intermediate the respective said nodal points so as to reciprocate at the measurement frequency.
In a further aspect, the apparatus comprises a pair of parallel beams which are coupled together at their opposite ends to form a tuning fork, each said beam having a central point which vibrates back and forth at the measurement frequency and wherein respective masses are coupled to the respective said central points so as to reciprocate at said measurement frequency.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate preferred embodiments of the invention and, together with the description, serve to explain the principles of the invention.
FIG. 1 is a schematic view of a force (load) sensor according to the invention comprising a vibratory beam provided with a reciprocatory mass intermediate its ends;
FIGS. 2 and 3 illustrate the operation of the vibratory beam of the invention;
FIG. 4 illustrates schematically a further form of force (load) sensor according to the invention;
FIGS. 5 to 8 illustrate practical embodiments of the invention; and
FIG. 9 is an end view showing details of the masses of the embodiment of FIG. 7.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the drawings and firstly to FIGS. 1 to 3, there is illustrated schematically a force sensor 100 according to the invention which includes a vibratory beam or bar 102. The vibratory beam has a first end 112 and a second end 113. Preferably, the second,
REFERENCES:
patent: 3595329 (1971-07-01), Withwell et al.
patent: 4286459 (1981-09-01), Trimmer et al.
patent: 4544858 (1985-10-01), Nishiguchi et al.
patent: 4669320 (1987-06-01), Simonsen
patent: 4773493 (1988-09-01), Goodier
Biegel R.
Chilcot Jr. Richard E.
SECA GmbH
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