JPH0247690B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is in the field of measurement technology, and more particularly relates to force and pressure measuring devices.

For example, a typical prior art force measuring device in the form of a scale includes a platform, or weighing pan, for receiving the weight to be measured. The weighing pan is connected to a support member or frame by a force transducer. In various types of prior art sensing devices, a transducer and a weighing pan are connected by a linkage adapted to permit relatively accurate weight sensing of objects in the weighing pan. coupled to the support member. For example, force sensors are used in strain gauges or in feedback arrangements a moving coil is placed in a fixed magnetic field.

Although prior art weighing devices provide relatively accurate measurements of objects placed on weighing pans, they have a number of drawbacks. For example, many weighing devices are particularly sensitive to eccentric loading of the object to be measured in the weighing pan. Such eccentric loads can cause errors due to frictional losses in the device. To compensate for such losses, prior art weighing devices often use various types of mechanical linkages to reduce the errors. For example, U.S. Pat.
No. 4,026,416 discloses a flexure arrangement that limits movement of the weighing pan along a single sensing axis. However, such metering devices have a relatively narrow range of motion and therefore a narrow measurable range.

Another drawback of many prior art devices is the temperature effects of the sensing transducer and associated circuitry, as well as temperature variations, such as due to temperature variations in various mechanical assemblies.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a highly accurate metering device that compensates for variations due to temperature.

Another object is to provide a pressure measuring device that is compensated for variations due to temperature.

Briefly described, the present invention is a temperature compensated measurement device. In one form adapted for weighing an object on a force input member, the device includes a storage device for constants K _ij used to evaluate the temperature compensated force function W(F,T). , where W(F,T)= _n 〓 ⁱ⁼¹ a _i (T)F ^i-1 (1) F is a function of the uncompensated force input (i.e., the weight of the object) and T represents the temperature of the device, and a _i (T)= _n 〓 ^j=1 k _ij T ^j-1 (i=1, 2...m) (2) where K _ij is a constant. This device also
It includes a sensor signal generator for generating a sensor signal F _W representative of the force input at the temperature of the device and a temperature signal generator for generating a temperature signal F _T representative of the temperature of the device. In one form of the invention,
These two generators include oscillators whose frequency varies with applied force and temperature, respectively. In this format, signals F _W and F _T represent the respective frequencies of these oscillators.

A force signal generator is responsive to the F _W and F _T signals and a stored constant K _ij to generate a temperature compensated force evaluated at a force input F corresponding to F _W and at a temperature T equal to F _T. A signal representing the function W(F,T) is generated.

According to this configuration, the device provides an output signal representative of the force input, ie the weight of the object on the weighing pan, ie a temperature compensated force signal.

According to another aspect of the invention, the apparatus includes a device for calibrating the temperature compensated force function W(F,T). This calibration generator responds to the application of a series of m predetermined weights of the weighing pan each time the device is at each of n different temperatures T ₁ , T ₂ , ...Tn. a sensor signal generating device for generating a sensor signal. The calibration generator further calculates the function W(F,T) for a _i (T)
and for each temperature of n a _i (T)
and an apparatus for generating a coefficient signal representing the coefficient.
Function (1) is solved for the values of i=1, 2, . . . m. In this case, F corresponds to each of the sensor signals generated at the relevant temperature, and W
(F,T) are equal to the respective weights associated with the sensor signals.

The calibration generator further solves equation (2) for K _ij ,
and includes apparatus for generating a signal representing K _ij for each value of i. The function a _i (T) is j=1,
2,...solved for n. In this case, a _i
(T) is equal to each of the coefficient signals associated with temperatures T ₁ , T ₂ , . . . _To , and T is equal to each temperature associated with these coefficient signals.

In one form of the invention, the device for solving W(F,T) and a _i (T) is a programmed digital computer. In one preferred form, m is equal to 4 and n is equal to 3.

In one form of the invention adapted for pressure measurements, the sensor signal generator is adapted to generate a signal F _W representative of the input pressure. The temperature compensated force function (1) is the same function of F and T, but F is a function of input pressure.

The invention is also useful in a force measurement format as an accelerator transducer, ie, where the force input is an inertial force applied to a force input member.

These and other objects, various features, and the invention itself of the invention will be better understood from the following description of a preferred embodiment, taken in conjunction with the accompanying drawings.

FIG. 1 shows a schematic diagram of a weighing device (weighing device) 210 according to the invention. This weighing device 210
includes a force input member in the form of a weighing pan 212 and an associated support post 214 adapted to move along a reference axis 216 . Post 214 is connected to a reference member (or housing) fixed relative to axis 216 via mechanical damper assembly 218.
220. Weigh pan 212 and its support post 214 are connected to parallel motion link assembly 16
0 to the armature member 226. Armature member 226 is coupled to reference member (support member) 220 by parallel motion link assembly 110. Force transducer 10 is coupled between armature member 226 and reference member 220. This force transducer 10 is connected to line 1
0a to the position sensor signal 244. Position sensor 244 provides an output signal on line 244a. This output signal represents the movement of the elements of force transducer 10 due to the displacement of weighing pan 212 due to the weight to be measured.

Processor 250 provides an output signal on line 250a in response to the signal on line 244a. This input signal represents the weight of the object on the weighing pan 212.

For example, the elements of metering device 210 may be of the same type as the correspondingly numbered elements described in U.S. patent application Ser.

FIG. 2 shows processor 250 of metering device 210 in block diagram form. Processor 250 generates a signal on line 244a having a frequency representative of the detected force exerted by the weight on weighing pan 212.
a first (weight) oscillator for providing a first (weight) oscillator; The weight oscillator includes a force transducer 10 and a position sensor 244. The signal on line 244a is coupled to counter 260. This counter 260 provides a digital count signal F _W on line 260a representative of the frequency of the signal on line 244a.

A temperature sensor 264 provides an oscillating signal on line 264a. The frequency of the signal on line 264a represents the temperature of metering device 210. line 264
The a signal is coupled to counter 266. This counter 266 provides a digital count signal F _T on line 266a representative of the frequency of the signal on line 264a. lines 260a and 26
The signal at 6a is provided to microprocessor 270.

Microprocessor 270 includes associated random access memory (RAM) 272 and read only memory (ROM) 274 and an input/output keyboard 276. Microprocessor 270 also provides an output signal on line 250a suitable for driving a conventional display device. Timing circuit 277 provides timing control signals to blocks in processor 250.

In one form of the invention, the microprocessor may be a Mostek type 38P70/02 and the ROM 274 is a Hitachi type HM462532;
RAM 272 is NCR type 2055.

In operation, lines 244a and 264a
The signal is the weight of the object on the weighing pan and the weighing device 2.
It is characterized by frequencies, each representing 10 temperatures. counters 260 and 266
are digital counts (F _W and F _T ) representing the frequency of the signals on lines 244a and 264a.
is controlled by timing circuit 277 to act as a window counter providing .

The RAM 272 stores a temperature-compensated force function W(F,
A constant K _ij representing T) is stored.

The function W(F,T) is defined as follows.

W(F,T)= _n 〓 ⁱ⁼¹ a _i (T)F ^i-1 (1) where F is a function of the uncompensated force exerted by the object and T is the temperature of the metering device 210. represent In the above definition, a _i (T)= _n 〓 ^j=1 k _ij T ^i-1 (i=1, 2...m) (2) where K _ij is a constant. In this example, m=4 and n=3. The values F _W and F _T are evaluated at a force input F corresponding to F _W and at a temperature _T corresponding to F T to provide a temperature compensated value representing the weight of the object on the weighing pan 212. can be used with a signal corresponding to the function W(F,T).

This example also represents the force function (1). It can also be used in a calibration mode to generate data and store it in memory 272. To perform this calibration procedure according to the present example, a series of four known weights are placed on the weighing pan 21 at each of three temperatures.
placed at 2. In other embodiments, different numbers of weights and temperatures can be used.

Processor 250 effectively processes the function W(F,T)
Generate a set of 12 simultaneous equations based on .
The processor 250 solves these 12 simultaneous equations, and calculates a ₁ obtained at temperatures T ₁ , T ₂ and T ₃ , and
A signal representing a ₂ determined at T ₁ , T ₂ and T ₃ , a ₃ determined at temperatures T ₁ , T ₂ and T ₃ , and a ₄ determined at temperatures T ₁ , T ₂ and T ₃ I will provide a.

Processor 250 then _processes these 12
A set of 12 simultaneous equations based on equation (2) is solved for the 12 values of K _ij using the obtained values. In general, three values for a ₁ at temperatures T ₁ , T ₂ and T ₃ and a ₂ at these three temperatures
three values for and at these three temperatures
The three values for a ₃ and the three values for a ₄ at these three temperatures are K _ij (i=1, 2,...
4, j=1, 2,).

Following the determination of these values for K _ij , the function W
(F,T) is fully specified. Data representing these values is stored in RAM 272.

In general calibration mode, processor 250
determines the “calibration plane” for metering device 210. Here, the weight value (W) is a function of the oscillator frequency (F) of sensor 244 and the temperature (T) of metering device 210 relative to the applied weight. This functional relationship W(F,T) describes the calibration plane for metering device 210. A series of reference weights are placed on weighing pan 212 at each of a number of temperatures. In response to placing a weight on the weighing pan 212, the force acting on the weighing pan due to the weight is transmitted to the force transducer 10 and link assembly 1
60 and 110 minimize the effects of moments applied about axis 216 (such as can be caused by eccentric loads of weight). A force applied to transducer 10 causes relative movement of the conductive surfaces of the transducer, resulting in a change in capacitance. This change in capacitance causes a corresponding change in the oscillator output frequency on line 244a. The processor then uses these values in the manner described above to completely define W(F,T) and stores data representing this function in RAM 27.
Store in 2.

In the weigh mode, in response to placing the weight to be measured on weighing pan 212, processor 250 outputs these signals (on line 244a) as well as the signal from temperature oscillator 264 (on line 264a). is used to identify the value of the function W(F,T) at corresponding values for F and T. This value of W(F,T) is converted into a signal representing the weight on weighing pan 212 at the current temperature of weighing device 210.

Figure 3 shows the pressure sensor 280 and processor 2.
A pressure measuring device 278 is shown in block diagram form, including a pressure measuring device 50. In this preferred form, pressure sensor 280 includes a capacitive pressure transducer (such as model 270 with a deformable diaphragm manufactured by Setra Systems, Inc.) as the sensing element. In general, the apparatus 278 operates in substantially the same manner as that of FIG. 1, except that the sensor 280 provides an oscillating signal characterized by a frequency that is a function of input pressure.

The invention may be embodied in other specific forms without departing from its spirit or essential characteristics. Therefore, the present embodiments can be considered to be illustrative in all respects and not limiting, and the scope of the present invention is indicated by the claims rather than by the above description. Therefore, all modifications and changes that come within the meaning and range of equivalency of the claims are intended to be embraced by the present invention.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an example of a measuring device implementing the present invention, FIG. 2 is a block diagram showing a processor of the device in FIG. 1, and FIG. 3 is an example of a pressure measuring device implementing the present invention. It is a block diagram. 10: Force transducer, 110, 160:
Parallel motion link assembly, 210: Metering device, 21
2: Measuring pan, 220: Reference member, 226: Armature member, 244: Position sensor, 250: Processor, 260: Counter, 264: Temperature sensor,
266: Counter, 270: Microprocessor, 272: RAM (Random Access Memory), 274: ROM (Read Only Memory), 276: Input/Output Keyboard, 277:
Timing circuit, 278: Pressure measuring device, 28
0: Pressure sensor.

Claims (1)

[Claims] 1. In a temperature-compensated force sensing device for sensing a force on a force input member, a constant K _ij used to evaluate a temperature-compensated force function W (F, T) is stored. W(F,T)= _n 〓 ⁱ⁼¹ a _i (T)F ^i-1 (1) where F is a function of the force input and T is the function of the force sensed It represents the temperature of the device, and a _i (T)= _n 〓 ^j=1 k _ij T ^j-1 (i=1, 2...m) (2) where K _ij is the above constant, and the sensor signal F means for generating _W , where F _W represents the force input at the temperature of the force sensing device; means for generating a temperature signal F _T ;
F _T represents the temperature of the force sensing device, means for generating a temperature compensated force signal from said signals F _W and F _T and said stored constant K _ij , W(F, T ), wherein said temperature-compensated force signal is said to have been evaluated at a force input F corresponding to F _W and at a temperature T corresponding to F _T . A force sensing device characterized in that it represents a temperature compensated force function W(F,T). 2. Calibration means for calibrating the temperature-compensated force function W(F, T), the calibration means comprising: a force sensing device at each of n temperatures T ₁ , T ₂ ,...T _o ; means for generating a series of m sensor signals _FW and n sensor signals _FT in response to applying a series of m predetermined forces to the input member; Generate a set of m×n simultaneous equations based on (1), solve them for a _i (T), and calculate a _i ( means for generating coefficient signals representative of T), with the respective sensor signals F _W and F _T generated at associated forces and temperatures;
For each, W(F, T) is evaluated at a force input corresponding to F _W and at a temperature T corresponding to F _T , and a set of m × n simultaneous equations based on function (2) and Generate the m×n values of a _i (T) and n associated temperature values and convert them to
Solve for K _ij and value of each i (i=1, 2,...m)
and K _ij for each value of j (j=1, 2,...n)
2. A force sensing device as claimed in claim 1, comprising: means for generating a signal representative of . 3. The force sensing device according to claim 1 or 2, wherein m=4 and n=3. 4. The sensor signal generating means includes a first oscillator, F _W represents the frequency of the first oscillator, the temperature signal generating means includes a second oscillator, F _T
3. A force sensing device according to claim 1, wherein represents the frequency of the second oscillator. 5. In a temperature-compensated pressure measuring device for measuring input pressure, means for storing constants K _ij used to evaluate the temperature-compensated pressure function W(F,T), with W(F , T)= _n 〓 ⁱ⁼¹ a _i (T)F ^i-1 (1) where F is a function of the input pressure, T represents the temperature of the pressure measuring device, and a _i (T )= _n 〓 ^j=1 k _ij T ^j-1 (i=1, 2...m) (2) Here, K _ij is the above constant, and the means for generating the sensor signal _FW , provided that F _W are means for generating a temperature signal F _T representative of the input pressure at the temperature of the pressure measuring device;
F _T represents the temperature of the pressure measuring device; means for generating a temperature-compensated pressure signal from said signals F _W and F _T and said stored constant K _ij ; pressure signal generating means comprising means for evaluating, provided that the temperature compensated pressure signal is the temperature compensated pressure signal evaluated at an input pressure F corresponding to F _W and at a temperature T corresponding to F _T ; A pressure measuring device characterized in that it represents a pressure function W (F, T). 6 Calibration means for calibrating the temperature-compensated pressure function W(F, T), the calibration means comprising: a pressure measuring device at each of n temperatures T ₁ , T ₂ ,...T _o ; means for generating a series of m sensor signals _FW and n sensor signals _FT in response to applying a series of m predetermined pressures to the input member; Generate a set of m×n simultaneous equations based on (1), solve them for a _i (T), and then calculate a _i (T), with respective sensor signals F _W and generated at associated pressures and temperatures;
For each F _T , W(F, T) is evaluated at an input pressure corresponding to F _W and at a temperature T corresponding to F _T , forming a set of m×n systems based on function (2). Generate the equation and the m×n values of a _i (T) and n associated temperature values and convert this to
Solve for K _ij and value of each i (i=1, 2,...m)
and K _ij for each value of j (j=1, 2,...n)
6. A pressure measuring device as claimed in claim 5, comprising: means for generating a signal representative of . 7. The pressure measuring device according to claim 5 or 6, wherein m=4 and n=3. 8. The sensor signal generation means includes a first oscillator, F _W represents the frequency of the first oscillator, the temperature signal generation means includes a second oscillator, and F _T
7. A pressure measuring device according to claim 5, wherein represents the frequency of the second oscillator.