JPS6310368B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a weighing device that eliminates eccentricity errors.

Although various configurations of weighing devices have been proposed, there is one that detects strain or deflection (displacement) due to the bending moment of a beam, converts it into weight, and displays it. FIG. 1 shows the main part of the conventional weighing device, that is, the structure around the strain body.
The strain body 1 constitutes a Roberval mechanism, in which in addition to the horizontal member on which the load of the object to be measured acts, another horizontal member is provided below, and both ends of the upper and lower horizontal members are connected with the other member. and one end is fixed to the inner wall of the device. Further, in the figure, reference numeral 2 denotes a strain gauge, which is attached to each part of the strain body 1 to detect the strain of the strain body 1 due to a load.

Now, the load on the object to be measured acts on the position indicated by the thick arrow in the figure, but it does not necessarily apply only to the downward component, but also on the eccentric position of the object placed on the upper plate (not shown). Therefore, a moment is often generated in the X-axis or Y-axis direction in the figure. However,
For eccentricity in the X-axis direction, the Roberval mechanism is adopted, so it does not affect the measured value, but for eccentricity in the Y-axis direction, the strain body 1 twists and the detection is difficult. This method has the disadvantage that it affects the value of the distortion that is applied, resulting in a so-called eccentricity error.

As a method of reducing the above-mentioned eccentricity error, the strain-generating body 1
By increasing the width w, increasing the rigidity against torsion, and setting the relationship between the strain ε due to the bending moment and the strain ε′ due to the torsional force to be ε′/ε<< the required accuracy, the eccentricity error can be reduced to some extent. It can be resolved, but the effect is not expected to be that great. There is also a device that measures the strain ε′ due to torsional force and has the added function of calculating ε=ε″−ε′ from the combined strain ε″ in order to find the bending moment strain ε to be detected. was extremely complex and lacked precision.

The present invention has been proposed in view of the above points, and includes two sets of detection means for detecting deflection (displacement) on both the left and right sides of the free end of the strain body constituting the Roberval mechanism. It is an object of the present invention to provide a weighing device that completely eliminates eccentricity errors and has high measurement accuracy by averaging the signals obtained from these detection means and using it for weight detection.

Hereinafter, the present invention will be described in detail with reference to the drawings showing examples.

Figures 2 and 3 show the first embodiment of the present invention, with Figure 2 showing the configuration of the flexure body and its surroundings, and Figure 3 showing the configuration of the signal processing section from detection to weight display. FIG.

Referring to FIG. 2, the configuration is explained. Convex portions 1a and 1b are provided on both left and right sides of the free end of the flexure element 1, one end of which is fixed to the inner wall of the device, and the flexure element auxiliary for holding the upper plate 3. The lower end of the material 4 is the convex portion 1a, 1
b, and applies a load to the strain body 3. On the other hand, reflective plates 5a and 5b are attached to the end faces of the convex parts 1a and 1b at an angle θ with respect to the perpendicular line, and light emitting elements 6a and 6 are connected to each other through the reflective plates 5a and 5b.
An optical path is formed between the light receiving elements 7a and 7b. Here, the light emitting elements 6a and 6b emit a light beam having a certain area, and the emitted light beam passes through the reflecting plates 5a and 5b to the light receiving elements 7a and 6b.
This will lead you to 7b. The light-receiving elements 7a and 7b are constructed by linearly arranging, for example, n solar cells, and an output is obtained only from the solar cell that is hit by the light beam, so that its position can be known. That is, the deflection of the strain body 1 is converted into an angular change of the reflecting plates 5a, 5b, which changes the arrival position of the reflected light, and the position change is detected by the light receiving elements 7a, 7b.

Next, the configuration of the signal processing section will be explained based on FIG. Note that since the detection circuits attached to both the left and right sides of the free end of the strain body 1 are the same, only one side is illustrated, and the other components are omitted. Now, one end of the n solar cells in the light receiving element 7a is commonly grounded, and the other end of each is connected to the input end of the multiplexer 8a. The multiplexer 8a connects one of a plurality of inputs to the output side, and a multiplexer control circuit in the microcomputer arithmetic circuit 11 sequentially selects the output signals of the n solar cells. Next, the output terminal of the multiplexer 8a is connected to one input terminal of a comparator 10a via a head amplifier 9a.
The other input terminal of the comparator 10a has a reference voltage.
V _ref is applied, and the output terminal is connected to the microcomputer arithmetic circuit 11
is connected to the input port of

In operation, when an object to be measured is placed on the upper plate 3, a load is transmitted to the strain body 1 via the strain body auxiliary material 4, causing the strain body 1 to deform. At this time,
When the object to be measured is placed at the center of the attachment part of the upper plate 3, only a downward load acts, but
When the strain body 3 is eccentrically positioned in the direction of the axis or the Y axis, a moment due to the eccentric position acts on the strain body 3 via the strain body auxiliary member 4 . Here, since the Roberval mechanism is employed, the eccentricity in the X-axis direction has no effect, but the strain-generating body 1 is twisted due to the eccentricity in the Y-axis direction. Therefore, at the free end of the flexure element 3, deflection and torsional deformation due to the load appear simultaneously, and the reflecting plates 5a and 5b provided on both left and right sides of the free end are vertically displaced around a certain value. , project light beams to solar cells at different positions within the respective light receiving elements 7a, 7b. Assuming that the solar cells hit by the light beam are m-th and m'-th, respectively, the outputs of the first to nth solar cells are sequentially selected by multiplexers 8a and 8b, amplified by head amplifiers 9a and 9b, and then outputted by comparators. m and m' can be detected by comparing the solar cells 10a and 10b with the reference voltage _Vref and determining which solar cell is producing the output voltage. When the microcomputer calculation circuit 11 detects m and m', it calculates the average of m+m'/2 and converts it into a weight value (since the detected value and weight value have a linear relationship, they are multiplied by a constant and then a constant is added. ), and display is performed by the display element 12. As mentioned above, the deformation of the free end of the flexure element is a combination of deflection and twist due to the load, so m and m' are centered around the value corresponding to the load and are equal to the moment due to eccentricity. The value obtained by averaging the two values is not affected by eccentricity at all.

Next, FIGS. 4 and 5 show a second embodiment of the present invention, which utilizes changes in the tension of the string as a means for detecting the displacement of the free end of the flexure element. . FIG. 4 shows the structure around the flexure body. The convex portions 1a and 1b provided on both left and right sides of the free end of the flexure body 1 are connected to a vibrator (e.g. Ultrasonic transducer) 14a, 14
It is connected to the vibrating piece b, and the string tension is changed by the displacement of the free end of the flexure element, and the vibration amplitude is changed.

FIG. 5 shows the configuration of the signal processing section, showing only one of the left and right detection means. To explain the configuration in FIG. 5, the signal input terminal P of the vibrator 14a is connected to the oscillation output of the reference oscillation circuit 15 as a signal source, and the terminal Q that outputs a voltage proportional to the vibration is connected to a high impedance amplifier. 16a to one input terminal of a comparator 17a, and the other input terminal of the comparator 17a is connected so that the output of a staircase oscillator 18 that outputs a step-like waveform is added, and the output terminal of the comparator 17a is connected to a microcomputer operation terminal. It is connected to the input port of circuit 11. Here, the comparator 17a and the staircase oscillator 18 constitute a so-called successive approximation type A/D converter, and by counting the number of steps until the input signal matches the input signal in the microcomputer calculation circuit 11, the analog signal is converted into a digital signal. It is something that becomes.

In operation, when the string tension of the vibrating strings 13a, 13b changes due to the displacement of the free end of the strain body 1, the vibration amplitude of the vibrators 14a, 14b changes,
This amplitude change is digitized by amplifiers 16a, 16b, comparators 17a, 17b, etc., and sent to the microcomputer calculation circuit 11 as a detection signal. The microcomputer arithmetic circuit 11 averages the signals obtained from the left and right detection means, converts it into a weight value, and displays it, as in the first embodiment described above. Note that the A/D converter is not limited to one using a staircase oscillator, but may also be an A/D converter using other methods.
It goes without saying that a similar configuration can be achieved using a converter.

Figure 6 shows the external appearance of the scale body shown for reference. The explanation will be omitted.

As described above, in the present invention, in a weighing device that measures and displays the weight of an object by deflection of a beam, there is provided a strain-generating body constituting a roberval mechanism, and the free end portions of the left and right ends of the strain-generating body. two sets of detection means for detecting displacement on both sides; a flexure element auxiliary member installed over the free end of the flexure element and connecting the flexure element to the upper plate on which the object to be measured is placed; and a signal. A processing section is provided, and the signals obtained from the two sets of detection means are averaged, converted into a weight value, and displayed.
It is possible to provide a highly accurate weighing device that does not cause errors due to any eccentric position of the object to be measured.

[Brief explanation of the drawing]

Figure 1 is a drawing showing the main parts of a conventional weighing device, Figure 2
Figures 3 and 3 are block diagrams showing the first embodiment of the present invention, Figures 4 and 5 are block diagrams showing the second embodiment, and Figure 6 is a reference diagram showing the external appearance of the scale. It is. DESCRIPTION OF SYMBOLS 1... Strain body, 1a, 1b... Convex part, 3... Upper plate, 4... Strain body auxiliary material, 5a, 5b... Reflection plate, 6a, 6b... Light emitting element, 7a, 7b... ...Photodetector, 8a, 8b...Multiplexer, 9a,
9b...Head amplifier, 10a, 10b, 17
a, 17b... Comparator, 11... Microcomputer arithmetic circuit, 12... Display element, 13a, 13b...
... Vibrating strings, 14a, 14b... Vibrator, 15...
Reference oscillation circuit, 16a, 16b...Amplifier, 18
...Staircase oscillator.

Claims (1)

[Claims] 1. A weighing device that measures and displays the weight of an object by deflection of a beam, which includes a strain-generating body constituting a roberval mechanism and a displacement on both left and right sides of the free end of this strain-generating body. two sets of detection means for detecting; a flexure body auxiliary member that is disposed astride the free end of the flexure body and connects the flexure body with the upper plate on which the object to be measured is placed; and a signal processing section. A weighing device characterized in that the signals obtained from the two sets of detection means are averaged, converted into a weight value, and displayed. 2. Claim 1, wherein the detection means is constituted by a reflecting plate disposed on both left and right sides of the free end of the strain-generating body, and a light emitting element and a light receiving element having an optical path set through the reflecting plate. Weighing device as described. 3. The detection means is configured by connecting a portion of the left and right sides of the free end of the strain-generating body to a vibrator via a vibrating string, and detects a change in string tension caused by deflection of the strain-generating body as a vibration amplitude of the vibrator. A weighing device according to claim 1 taken out as a variation of.