US 5,442,146 A · Counting scale and load cell assembly therefor

A load cell assembly comprising:

(a) a load cell capable of being subjected to an applied force;
(b) first and second transducers operatively mounted on the load cell, each transducer having a resonant frequency that varies with the applied force;
(c) means for driving the first and second transducers at their resonant frequencies, respectively, for providing first and second frequency signals;
and
(d) means for providing a force value indicative of the applied force on the load cell comprising:
(i) converting means, operatively connected to receive the first and second frequency signals, for converting the first and second frequency signals to first and second values, respectively, wherein the converting means comprises a time base frequency counter and first and second input capture latches operatively connected to receive an output of the counter, wherein the first and second latches have gate inputs operatively connected to receive gating signals from the first and second frequency signals, respectively;
whereby the first and second values provided by the converting means are representative of one or more periods of the first and second frequency signals, respectively:
(ii) means operatively connected to receive the first and second values for linearizing and rejecting common-mode effects therefrom to provide a linearized difference value;
and
(iii) means operatively connected to receive the linearized difference value for rejecting temperature effects therefrom to provide the force value.

7 more elements

A load cell assembly comprising:

(a) a load cell capable of being subjected to an applied force;
(b) first and second transducers operatively mounted on the load cell, each transducer having a resonant frequency that varies with the applied force;
(c) means for driving the first and second transducers at their resonant frequencies, respectively, for providing first and second frequency signals;
and
(d) means for providing a force value indicative of the applied force on the load cell comprising:
(i) converting means operatively connected to receive the first and second frequency signals for converting the first and second frequency signals to first and second values, respectively;
(ii) means operatively connected to receive the first and second values for linearizing and rejecting common-mode effects therefrom to provide a linearized difference value, wherein the means for linearizing and rejecting common-mode effects comprises:
(1) means for providing a first frequency change value representative of the difference between the first value and a first dead load value, the first dead load value being representative of the resonant frequency of the first transducer when no force is applied to the load cell;
(2) means for providing a second frequency change value representative of the difference between the second value and a second dead load value, the second dead load value being representative of the resonant frequency of the second transducer when no force is applied to the load cell;
(3) means for generating an unscaled difference value representative of the difference between the first frequency change value and a scaled second frequency change value, the scaled second frequency change value being representative of the second frequency change value scaled by a first scaling factor;
and
(4) means for generating the linearized difference value which is representative of the unscaled difference value scaled by a second scaling factor;
and
(iii) means operatively connected to receive the linearized difference value for rejecting temperature effects therefrom to provide the force value.

11 more elements

A load cell assembly comprising:

(a) a load cell capable of being subjected to an applied force;
(b) first and second transducers operatively mounted on the load cell, each transducer having a resonant frequency that varies with the applied force;
(c) means for driving the first and second transducers at their resonant frequencies, respectively, for providing first and second frequency signals:
and
(d) means for providing a force value indicative of the applied force on the load cell comprising:
(i) converting means operatively connected to receive the first and second frequency signals for converting the first and second frequency signals to first and second values, respectively;
(ii) means operatively connected to receive the first and second values for linearizing and rejecting common-mode effects therefrom to provide a linearized difference value;
and
(iii) means operatively connected to receive the linearized difference value for rejecting temperature effects therefrom to provide the force value, wherein the means for rejecting temperature effects comprises means for correcting for zero shift error and means for correcting for span error.

6 more elements

A load cell controller for use in a load cell assembly having a load cell capable of being subjected to an applied force, the load cell having first and second transducers operatively mounted thereon, each transducer having a resonant frequency that varies with the applied force, the controller comprising:

(a) means capable of driving first and second transducers at their resonant frequencies, respectively, for providing first and second frequency signals;
and
(b) means capable of providing a force value indicative of an applied force on a load cell comprising:
(i) converting means operatively connected to receive the first and second frequency signals for converting the first and second frequency signals to first and second values, respectively;
(ii) means operatively connected to receive the first and second values for linearizing and rejecting common-mode effects therefrom to provide a linearized difference value, wherein the means for linearizing and rejecting common-mode effects comprises:
(1) means for scaling the first and second values to obtain first and second scaled values, respectively, such that changes in sensitivity of the first and second transducers are substantially similar;
and
(2) means for taking the difference of the first and second scaled values to obtain the linearized difference value;
whereby the linearized difference value is linearized and common-mode errors have been rejected therefrom;
and
(iii) means operatively connected to receive the linearized difference value for rejecting temperature effects therefrom to provide the force value.

8 more elements

A method for providing a force value indicative of an applied force on a load cell of the type having first and second transducers operatively mounted thereon, each transducer having a resonant frequency that varies with the applied force, and means for driving the first and second transducers at their resonant frequencies and providing first and second frequency signals therefrom, respectively, the method comprising the steps of:

(a) converting the first and second frequency signals to first and second values, respectively, wherein the converting step comprises the steps of:
(i) providing a time base frequency counter and first and second input capture latches operatively connected to receive an output of the counter, wherein the first and second latches have gate inputs operatively connected to receive gating signals from the first and second frequency signals, respectively;
and
(ii) generating the first and second values, wherein the first and second values are representative of one or more periods of the first and second frequency signals, respectively;
(b) rejecting common-mode and non-linearity effects from the first and second values and providing a linearized difference value therefrom;
and
(c) rejecting temperature effects from the linearized difference value and providing the force value therefrom.

4 more elements

A method for providing a force value indicative of an applied force on a load cell of the type having first and second transducers operatively mounted thereon, each transducer having a resonant frequency that varies with the applied force, and means for driving the first and second transducers at their resonant frequencies and providing first and second frequency signals therefrom, respectively, the method comprising the steps of:

(a) converting the first and second frequency signals to first and second values, respectively;
(b) rejecting common-mode and non-linearity effects from the first and second values and providing a linearized difference value therefrom, wherein the step of rejecting common-mode and non-linearity effects comprises the steps of:
(i) providing a first frequency change value representative of the difference between the first value and a first dead load value, the first dead load value being representative of the resonant frequency of the first transducer when no force is applied to the load cell;
(ii) providing a second frequency change value representative of the difference between the second value and a second dead load value, the second dead load value being representative of the resonant frequency of the second transducer when no force is applied to the load cell;
(iii) generating an unscaled difference value representative of the difference between the first frequency change value and a scaled second frequency change value, the scaled second frequency change value being representative of the second frequency change value scaled by a first scaling factor;
and
(iv) generating the linearized difference value which is representative of the unscaled difference value scaled by a second scaling factor;
and
(c) rejecting temperature effects from the linearized difference value and providing the force value therefrom.

6 more elements

A method for providing a force value indicative of an applied force on a load cell of the type having first and second transducers operatively mounted thereon, each transducer having a resonant frequency that varies with the applied force, and means for driving the first and second transducers at their resonant frequencies and providing first and second frequency signals therefrom, respectively, the method comprising the steps of:

(a) converting the first and second frequency signals to first and second values, respectively;
(b) rejecting common-mode and non-linearity effects from the first and second values and providing a linearized difference value therefrom;
and
(c) rejecting temperature effects from the linearized difference value and providing the force value therefrom, wherein the step of rejecting temperature effects comprises the steps of:
(i) providing a temperature indicator representative of the error in the first and second values due to temperature effects;
(ii) generating a zero shift error from the temperature indicator;
(iii) generating a span error from the temperature indicator;
(iv) subtracting the zero shift error from the linearized difference value to provide a shifted difference value;
and
(v) scaling the shifted difference value by the span error to generate the force value.

7 more elements

Counting scale and load cell assembly therefor

Life of this patent

Counting scale and load cell assembly therefor

Life of this patent

Abstract

Claims35