JP7685779B2 - Weighing device and method using a three-axis acceleration sensor - Google Patents

Description

The present invention relates to a weighing device and a weighing method that utilize a three-axis acceleration sensor.

A balance, which is a weighing device, measures the load component Wv perpendicular to the weighing pan using a weight sensor, and uses the gravitational acceleration g at the location where the balance is installed to calculate the mass m of the object placed on the weighing pan from equation (1).

As shown in Figure 10(A), when the direction in which the gravitational acceleration g acts coincides with the direction perpendicular to the weighing pan, the mass measured by the balance, i.e., the weighing value m, can be said to be a true value. On the other hand, as shown in Figure 10(B), when the direction in which the gravitational acceleration g acts does not coincide with the direction perpendicular to the weighing pan, a component Wh that cannot be detected by the balance occurs, and the weighing value m measured by the balance is lighter than the true value.

Based on the balance situation described above, if the following two conditions occur, the weight value can be said to contain an error.
(i) When the balance is tilted, the load component Wv perpendicular to the weighing pan decreases (ii) When the balance is placed in a different location, causing a change in the gravitational acceleration g In response to the above (i), a typical balance is equipped with a level (air bubble) to detect the inclination of the balance. For example, Patent Document 1 discloses a technology that detects the air bubble in the level with an optical sensor to more accurately manage the level of the balance.

JP 2016-038377 A

Regarding (i) above, there is technology such as that described in Patent Document 1, but this requires mounting multiple optical sensors around the bubble, making the configuration complicated.

Regarding (ii) above, we ask users to adjust the sensitivity using weights if they change the location of the balance, but this is up to the user, and there are cases where this is not done.

To address these issues, the inventors thought that by detecting the acceleration in the three axial directions of the balance, the balance itself would be able to detect and solve the above problems (i) and (ii).

The present invention has been made based on the above-mentioned problems in the conventional technology and the inventors' findings, and aims to provide a weighing device and a weighing method that utilizes a three-axis acceleration sensor to automatically detect acceleration changes in three-axis directions and automatically solve problems caused by the changes.

In order to solve the above problems, a weighing device according to one embodiment of the present invention comprises a weighing pan, a weight sensor connected to the weighing pan, a triaxial acceleration sensor that detects acceleration changes in the three axes of x, y, and z by setting x and y on a plane parallel to the horizontal of the weight sensor and z in a direction perpendicular to the horizontal of the weight sensor, a memory unit that stores reference outputs of the three axes of the triaxial acceleration sensor when the weight sensor is horizontal, and an arithmetic processing unit, wherein the arithmetic processing unit compares the current outputs of the three axes of the triaxial acceleration sensor with the reference outputs, and detects that there is a tilt if the output of x and/or y has changed, and detects that there is a change in the installation location if the output of z has changed, and notifies the user.

In the above aspect, it is also preferable that the calculation processing unit uses equation (14) to correct the weighing value m detected by the weight sensor to a corrected weighing value m' if the x and/or y output of the three-axis acceleration sensor has changed.

In the above aspect, when only the z output of the triaxial acceleration sensor has changed, it is preferable that the calculation processing unit changes the value of gravitational acceleration used to calculate the weighing value m detected by the weight sensor to the local gravitational acceleration value glocal obtained using the z-axis output of the triaxial acceleration sensor, and sets this as the corrected weighing value m'.

In the above aspect, if the z, x and/or y outputs of the triaxial acceleration sensor have changed, it is preferable that the calculation processing unit changes the value of gravitational acceleration used in equation (14) to the local gravitational acceleration glocal calculated using the three-axis outputs of the triaxial acceleration sensor, and corrects the weighing value m detected by the weight sensor to a corrected weighing value m'.

In the above aspect, it is also preferable that the calculation processing unit issues a warning to the user that the correction cannot completely remove the error if the corrected weighing value m' of the weighing object exceeds the allowable threshold range for the reference mass of the weighing object.

In addition, in order to solve the above problem, a weighing method according to one aspect of the present invention uses a weighing device equipped with a weighing pan, a weight sensor connected to the weighing pan, and a triaxial acceleration sensor that detects acceleration changes in the three axes of x, y, and z by setting x and y on a plane parallel to the horizontal of the weight sensor and z in a direction perpendicular to the horizontal of the weight sensor, and is characterized by having the following steps: (A) acquiring the current outputs of the three axes of the triaxial acceleration sensor; (B) comparing the current outputs with reference outputs of the three axes when the weight sensor is horizontal; (C) notifying the user that there is a tilt if the output of x and/or y has changed in step (B); and (D) notifying the user that there has been a change in the installation location if the output of z has changed in step (B).

In the above aspect, it is also preferable to have the steps of: (E) if the output of x and/or y has changed in step (B), correcting the weighing value m detected by the weight sensor to a corrected weighing value m' using equation (14); (F) if only the output of z has changed in step (B), changing the value of gravitational acceleration used in calculating the weighing value m detected by the weight sensor to the local gravitational acceleration value glocal obtained using the output of the z axis of the triaxial acceleration sensor to obtain the corrected weighing value m'; and (G) if the outputs of z, x, and/or y have changed in step (B), changing the value of gravitational acceleration used in equation (14) to the local gravitational acceleration glocal obtained using the output of the three axes of the triaxial acceleration sensor to obtain the corrected weighing value m'.

In the above aspect, it is also preferable to have a step (H) of weighing the object to be weighed, and if the corrected weighing value m' of the object to be weighed exceeds the range of the allowable threshold for the reference mass of the object to be weighed, issuing a warning to the user that the error cannot be completely removed by the correction.

The present invention provides a weighing device and a weighing method that automatically detects acceleration changes in three axes and automatically solves problems caused by the changes.

FIG. 2 is a diagram showing the relationship between the components of a three-axis acceleration sensor; FIG. 13 is a diagram showing the result of correction using a three-axis acceleration sensor. 1 is a configuration block diagram of a weighing device according to a first embodiment of the present invention. FIG. 2 is a schematic perspective view of the measuring device. FIG. 4 is a flow diagram of a weighing method using the weighing device. FIG. 11 is a configuration block diagram of a weighing device according to a second embodiment of the present invention. FIG. 4 is a flow diagram of a weighing method using the weighing device. 1A to 1C are diagrams showing a preferred mounting form of an acceleration sensor in the embodiments; 1A to 1C are diagrams showing a preferred mounting form of an acceleration sensor in the embodiments; FIG. 1 is a diagram showing a consideration regarding the weighing value of a balance.

First, the inventor's considerations that led to the creation of a preferred embodiment of the present invention will be explained with reference to the drawings.

1. Observations by the inventor 1-1. Problems with balances As described above with reference to FIG. 10, a balance generally includes a weighing pan and a weight sensor connected to the weighing pan, measures the load component Wv perpendicular to the weighing pan, and determines the mass m of the object to be weighed (measured value) from equation (1) using the gravitational acceleration g at the location where the balance is installed.

For this reason, if the following two conditions occur, the weight value m measured by the balance will contain an error.
(i) When the balance is tilted, the load component Wv perpendicular to the weighing pan decreases. (ii) When the balance is placed in a different location, the gravitational acceleration g changes.

1-2. Considerations for solving the problem In response to this problem, the inventors considered that by equipping the balance with a triaxial acceleration sensor, the inclination of the balance and the acceleration of gravity can be detected, so that firstly, the balance can automatically detect both (i) and (ii) above. Secondly, the inventors considered that by using the values from the triaxial acceleration sensor, the balance can identify and automatically correct the changes in the weight value resulting from the decrease in the load component Wv perpendicular to the weighing pan and the change in the acceleration of gravity g.

Figure 1 shows the relationship between the tilt angle and each component of gravitational acceleration when a triaxial acceleration sensor is mounted on a certain imaginary plane vp. This triaxial acceleration sensor (hereafter referred to as the acceleration sensor) detects acceleration in three orthogonal axial directions of the imaginary plane vp. The x and y of the acceleration sensor are on the imaginary plane vp, and the z is in a direction perpendicular to the imaginary plane vp. The components of gravitational acceleration g with respect to this triaxial acceleration sensor are denoted as "gx, gy, gz". The gx and gy components are on the imaginary plane vp, and the gz component is in a direction perpendicular to the imaginary plane vp. The tilt angle θ is the angle between the direction of gravitational acceleration g and the direction of the gz component.

Let the components output by the acceleration sensor at tilt angle θ be "Xout(θ), Yout(θ), Zout(θ)". When the gravitational acceleration g detected by the acceleration sensor is g = {gx(θ), gy(θ), gz(θ)}, gx(θ), gy(θ), gz(θ) can be expressed by equations (2), (3), and (4) using the outputs "Xout(0), Yout(0), Zout(0)" when tilt angle θ = 0. However, Ax, Ay, and Az are proportionality coefficients, and g = |g|.

The relationship between the tilt angle θ of the acceleration sensor and the gravitational acceleration g is as follows, with reference to FIG.

It becomes.

1-3. Correction for inclination of the balance Let us consider the correction of the weighing value for the inclination of the balance, i.e. the decrease in the load component Wv perpendicular to the weighing pan. The inclination of the balance can be detected by monitoring the x, y output of the acceleration sensor. Let m(0) be the mass of the object when the inclination angle of the balance θ=0, and m(θ) be the mass of the object when the inclination angle is θ. Let W be the load on the weighing pan of the balance, and Wv be the load component perpendicular to the weighing pan. If the aforementioned imaginary plane vp is set parallel to the horizontal of the weight sensor, then when the inclination angle θ=0, W=m(0) and the gravitational acceleration g=Wv, and the relationship in formula (7) is established.

However, when the inclination angle θ ≠ 0, the gravitational acceleration gz(θ) perpendicular to the weighing plate is given by equation (8) from equation (6), so the load component Wv perpendicular to the weighing plate is given by equation (9),

From this, the transformations of equations (10) to (13) hold true.

The balance obtains mass m(θ) as the weighing value. From equations (12) and (13), we can see that when there is a tilt angle θ, the balance underestimates the mass because the weighing value m(0) when the tilt angle θ = 0 is multiplied by a correction term that includes θ. Therefore, when there is a tilt angle θ, to obtain the correct mass (weighing value), it is necessary to divide the mass m(θ) when there is a tilt angle θ by a correction term that includes θ, cosθ or √1-sin2θ.

Theoretically, the correction term will have the same value whether calculated using equation (12) or equation (13). However, in reality, we are assuming the detection of an extremely small tilt (0.1° or less) of θ×0, so the cosine component of equation (12) cannot detect small changes in angle. For this reason, it is preferable to use the sine component of equation (13) as the correction term.

Therefore, when the acceleration sensor detects the inclination angle θ, the balance corrects the weight value m (mass m(θ)) measured by the balance based on equations (13) and (5) using the following equation (14) to calculate the corrected weight value m'.

Figure 2 shows the results of verifying the correction using a three-axis acceleration sensor. In the verification, a balance with a weighing capacity of 10 kg and a minimum display of 0.01 g was used, and the object to be weighed placed on the weighing pan was 10,000 g. Here, the inclination angle from the surface on which the balance is placed (which is horizontal) was changed from 0° to 0.5°, and this inclination angle was set to θ, and the weight value m of the object was corrected using equation (14) to obtain a corrected weight value m'. As shown in Figure 2, a corrected weight value m' of 10,000 g was obtained at each inclination angle.

1-4. Correction for changes in the balance's installation location Let us consider the correction of the weight value for changes in gravitational acceleration g caused by changes in the installation location of the balance due to shipment from the factory or relocation of the facility. Changes in gravitational acceleration g can be detected by monitoring the gravitational acceleration gz(θ) in the direction perpendicular to the horizontal of the weight sensor. As mentioned above, in a balance, the weight value m is calculated by equation (1) using the component Wv of the load perpendicular to the weighing pan. Therefore, if the value of "g" used in equation (1) is changed from the value before the balance is moved to the value after the balance is moved (hereinafter referred to as "local gravitational acceleration "glocal"), the error caused by changes in the installation location of the balance can be eliminated.

Here, the local gravitational acceleration glocal is calculated using the output value of the acceleration sensor. From equation (6), glocal is given by equation (15).

When the acceleration sensor detects a change in the gravitational acceleration g, the balance changes the value of the gravitational acceleration g used to calculate the weighing value m detected by the weight sensor in equation (1) to the value of the local gravitational acceleration g obtained using the output of the acceleration sensor obtained in equation (15) to obtain the weighing value. Here, since this discussion considers a case where the location of the balance has changed, that is, a case where only the z component of the acceleration sensor has changed, in equation (15), the inclination angle θ is zero, and g = gz (θ = 0). In other words, when the acceleration sensor detects a change in the gravitational acceleration g, the balance determines the corrected weighing value m' by dividing the load component Wv perpendicular to the weighing pan measured by the weight sensor by the local gravitational acceleration g (where θ = 0) (equation (16)).

In the prior art, the local gravitational acceleration glocal was found by (1) storing the gravitational acceleration values of representative points in the balance's memory (e.g., Ibaraki 9.79952 [m/s2], Sapporo 9.80478 [m/s2], Osaka 9.79703 [m/s2], etc.) and selecting the point closest to the balance's installation location (local site), or (2) adjusting the value using weights at the balance's installation location (local site). In contrast, the above considerations using an acceleration sensor make it possible to reflect the local gravitational acceleration glocal of the balance using the acceleration sensor's output value, which has the advantage of improving the measurement accuracy compared to the prior art method and eliminating the need for on-site adjustment using weights each time the balance's installation location is changed.

1-5. Correction when both the inclination of the balance and the change in installation location occur Let us consider the correction of the weighing value when both a decrease in the load component Wv perpendicular to the weighing pan and a change in the gravitational acceleration g occur. If both occur, based on the considerations in 1-3 and 1-4 above, if the value of "g" used in equation (14) relating to the inclination is changed to the local gravitational acceleration glocal, both errors can be eliminated. glocal is given by equation (15), which can be further transformed into equation (17).

The sine term in equation (17) can be found from equation (5), which includes gx(θ) and gy(θ) detected by the acceleration sensor. Therefore, the local gravitational acceleration glocal can be found from equation (17) by substituting the x, y, and z output values of the acceleration sensor. In other words, when both the balance tilts and there is a change in the gravitational acceleration, the balance corrects the weight value m (mass m(θ)) measured by the balance using the local gravitational acceleration glocal (θ ≠ 0) according to the following equation (18) to calculate the corrected weight value m'.

1-6. Weighing method using a triaxial acceleration sensor From the above considerations, the inventors first conceived that by equipping the balance with a triaxial acceleration sensor and comparing the reference output "Xout(0), Yout(0), Zout(0)" when the balance is horizontal (tilt angle θ=0) with the current output "Xout(1), Yout(1), Zout(1)", the balance itself would be able to distinguish between (i) the inclination of the balance and (ii) changes resulting from the installation location and detect them. Furthermore, the inventors secondly believed that the weighing value when the balance is inclined can be corrected based on the considerations in 1-3 above, the weighing value when the balance's installation location is changed can be corrected based on the considerations in 1-4 above, and the weighing value when both occur can be corrected based on the considerations in 1-5 above.

Therefore, by equipping the balance with a three-axis acceleration sensor and detecting the following three acceleration change patterns, the balance can automatically detect changes in the inclination and installation location of the balance and automatically correct errors in the weighing values resulting from these changes.
Pattern (1) Only z changes. Pattern (2) x and/or y change (i.e., x and y change, x change, or y change).
Pattern (3) z and x and/or y are changed (i.e., x, y, and z are all changed, x and z are changed, or y and z are changed)

When pattern (1) occurs: The balance detects that the installation location has changed and notifies the user. Then, the weighing value is corrected using equation (16). The local gravitational acceleration g is used as the gravitational acceleration glocal.
When pattern (2) occurs: The balance detects the tilt and notifies the user. Then, the weighing value is corrected using equation (14). The previously used value of the gravitational acceleration g is used as is.
When pattern (3) occurs, the balance detects that both the inclination and the gravitational acceleration have changed and notifies the user. Then, the weighing value is corrected using equation (18). The local gravitational acceleration g is used as the gravitational acceleration glocal.

Based on the above considerations, a preferred embodiment of the present invention will be described with reference to the drawings.

2. First embodiment 2-1. Configuration of the weighing device (balance) Fig. 3 is a configuration block diagram of a weighing device according to a first embodiment of the present invention, and Fig. 4 is a schematic perspective view of the weighing device. The weighing device is an electronic scale (hereinafter referred to as balance 1). Balance 1 has a main body case 10, a weighing pan 11, a weight sensor 12, an arithmetic processing unit 13, a memory unit 14, an operation unit 15, a display unit 16, and a three-axis acceleration sensor 20.

As shown in FIG. 4, the main body case 10 contains a Roberval mechanism 12' that connects the weighing dish 11 and the weight sensor 12. The Roberval mechanism 12' is a structure for transmitting the load received by the weighing dish 11 to the weight sensor 12, and is a well-known structure formed of a rectangular metal block, which includes a floating part that receives the load from the weighing dish 11, a fixed part that is fixed to the main body case 10, upper and lower sub-rods that connect the floating part and the fixed part, and a load transmission part that transmits the load acting on the floating part to the weight sensor 12. The weighing dish 11 is supported by the Roberval mechanism 12' and placed on the main body case 10. The weighing dish 11 has a horizontal surface 11', and the object to be weighed is placed on the horizontal surface 11'. The weight sensor 12 may be an electromagnetic balance type, a strain gauge type, or a capacitance type. The load detected by the weight sensor 12 is A/D converted and input to the calculation processing unit 13, where it is converted into a weighing value.

As mentioned above, a balance generally measures the load component Wv perpendicular to the weighing pan, and uses the gravitational acceleration g at the location where the balance is installed to obtain the weighing value m of the object from equation (1). In order to utilize this principle, the weight sensor 12 is attached to the main body case 10 on a platform that is level when the balance 1 is assembled, using a level or the like, so that the weight sensor 12 remains horizontal (for example, the Roberval mechanism 12' is attached so that the plane of the Roberval mechanism 12' remains horizontal). The weighing pan 11 is supported downward from a direction perpendicular to the horizontal of the weight sensor 12 by a pan boss (not shown) protruding from the Roberval mechanism 12', and is attached so that the horizontal plane 11' of the weighing pan 11 coincides with the horizontal of the weight sensor.

The three-axis acceleration sensor 20 (hereinafter referred to as the acceleration sensor 20) is an IC module equipped with a sensor in which a spring and a weight are integrated, and an element that captures the displacement when acceleration is applied to the sensor. The acceleration sensor 20 is placed on an imaginary plane vp parallel to the horizontal of the weight sensor 12, with the x and y of the acceleration sensor 20 being placed on the imaginary plane vp, and the z being placed in a direction perpendicular to the imaginary plane vp. As a result, the acceleration sensor 20 is set with x and y parallel to the horizontal of the weight sensor 12, and z being perpendicular to the horizontal of the weight sensor 12, and detects acceleration in the orthogonal three-axis directions (x, y, z) of the imaginary plane vp. In other words, the acceleration sensor 20 is attached so that the horizontal of the acceleration sensor 20 and the horizontal of the weight sensor 12 coincide. In this embodiment, the purpose is to detect and correct the change due to the inclination of the load received by the weight sensor 12, so by attaching the acceleration sensor 20 so that the horizontal of the weight sensor 12 coincides with the horizontal of the weight sensor 12, the origins of the inclination angles of both coincide, and the error can be reduced. The virtual plane vp on which the acceleration sensor 20 is disposed may be set at any position within the main body case 10 as long as it does not interfere with the weight sensor 12. A suitable setting for the virtual plane vp on which the acceleration sensor 20 is mounted, i.e., the mounting position of the acceleration sensor 20, will be described later. Note that the settings of the x-axis and y-axis in FIG. 4 may be reversed.

After the acceleration sensor 20 is attached to the balance 1, and before the balance 1 is shipped from the factory, the reference outputs "Xout(0), Yout(0), Zout(0)" of each component are measured on a table that is kept horizontal, i.e., with the weight sensor 12 horizontal, and are stored in the memory unit 14 described later.

The operation unit 15 and the display unit 16 are provided on the front side of the main body case 10 of the balance 1. The operation unit 15 allows the user to perform weighing operations, which will be described later. The display unit 16 displays a screen associated with weighing, which will be described later.

The calculation processing unit 13 is, for example, a microcontroller in which a CPU, ROM, RAM, etc. are implemented in an integrated circuit. The calculation processing unit 13 has an acceleration change detection unit 131 and a change notification unit 132 to detect acceleration changes using the acceleration sensor 20. The calculation processing unit 13 also has an inclination correction unit 133 and a gravity correction unit 134 to perform corrections associated with acceleration changes. The functions of the functional units 131, 132, 133, and 134 are realized, for example, by the CPU reading and executing a program stored in the memory unit 14. Details of the functions of each functional unit will be explained in "2-2. Weighing method" below.

The memory unit 14 is a semiconductor memory element such as a RAM or a flash memory, or a storage medium such as a memory card. The memory unit 14 stores various programs for the calculations of the calculation processing unit 13. Furthermore, the memory unit 14 stores the reference outputs "Xout(0), Yout(0), Zout(0)" of the acceleration sensor 20 for detecting changes using the acceleration sensor 20.

The above is the configuration of the balance 1 using the acceleration sensor 20 according to the first embodiment. Next, the weighing method using the balance 1 will be explained.

5 is a flow diagram of a weighing method using the weighing device according to the first embodiment. This flow starts automatically before the balance 1 switches to the weighing mode, for example, when the balance 1 is turned on or when the balance 1 has not been used for a certain period of time.

When the flow starts, first, in step S101, the acceleration change detection unit 131 functions to obtain the current output "Xout(1), Yout(1), Zout(1)" of the acceleration sensor 20.

Next, proceeding to step S102, the acceleration change detection unit 131 reads out the reference outputs "Xout(0), Yout(0), Zout(0)" and compares them with the current outputs "Xout(1), Yout(1), Zout(1)".

Next, the process proceeds to step S103, where acceleration change detection section 131 determines which of the following patterns the change corresponds to.
Pattern (1): Only z changes. Pattern (2): x and/or y changes. Pattern (3): z and x and/or y change.

If there is no change in any of patterns (1) to (3), the process proceeds to step S104, where the change notification unit 132 functions to notify the user that there is no change in acceleration. The change notification unit 132 displays a message on the display unit 16, for example, to the effect that there is no change in acceleration, or, more specifically, that there is no abnormality in the inclination of the balance or the gravitational acceleration. When the notification by the change notification unit 132 has finished, the balance 1 transitions to weighing mode.

On the other hand, if pattern (1) is detected in step S103, the flow proceeds to step S105 and step S106. In step S106, change notification unit 132 notifies the user that there has been a change in pattern (1). Change notification unit 132 displays, for example, on display unit 16, a message indicating that there has been a change in the acceleration in the z direction, or, more specifically, that a change in the installation location has affected the measurement value.

Next, the flow proceeds to step S107, where the gravity correction unit 134 begins to function. The gravity correction unit 134 applies the current outputs "Xout(1), Yout(1), Zout(1)" of the acceleration sensor 20 to equation (15) to obtain the local gravitational acceleration glocal, and sets it to obtain the weighing value using equation (16). When the gravity correction unit 134 has completed setting the correction, the scale 1 transitions to weighing mode. At this time, it is also preferable for the gravity correction unit 134 to notify the user that a correction corresponding to a change in the installation location (change in acceleration in the z direction) has been set. Then, in subsequent weighings, the scale 1 takes the corrected weighing value m' obtained by equation (16) as the true value, displays the corrected weighing value m' on the display unit 16, and records it in the memory unit 14 or a designated memory device.

If pattern (2) is detected in step S103, the flow proceeds to step S108 and step S109. In step S109, change notification unit 132 notifies the user that a change in pattern (2) has occurred. Change notification unit 132 displays, for example, on display unit 16, a message indicating that there has been a change in acceleration in the x and y directions, or in other words, that the tilt of the balance has affected the weighing value.

Next, the flow proceeds to step S110, where the tilt correction unit 133 functions. The tilt correction unit 133 is set to correct the weighing value using equation (14). When the setting of the correction by the tilt correction unit 133 is complete, the scale 1 transitions to weighing mode. At this time, it is also preferable for the tilt correction unit 133 to notify the user that a correction corresponding to the inclination of the scale (change in acceleration in the x and y directions) has been set. Then, in subsequent weighings, the scale 1 takes the corrected weighing value m' corrected using equation (14) as the true value, displays the corrected weighing value m' on the display unit 16, and records it in the memory unit 14 or a specified external memory device.

If pattern (3) is detected in step S103, the flow proceeds to step S111 and step S112. In step S112, change notification unit 132 notifies the user that a change in pattern (3) has occurred. Change notification unit 132 displays, for example, on display unit 16, a message indicating that there have been changes in acceleration in the x, y, and z directions, or in other words, that the weighing value has been affected by changes in the inclination of the balance and the installation location.

Next, the flow moves to step S113, where both the gravity correction unit 134 and the tilt correction unit 133 function. First, the gravity correction unit 134 functions to calculate the local gravitational acceleration glocal from the current outputs "Xout(1), Yout(1), Zout(1)" of the acceleration sensor 20 using equation (17). Next, the tilt correction unit 133 functions to set the weighing value to be calculated using equation (18), which is the local gravitational acceleration glocal applied to equation (14). Once this setting is complete, the balance 1 transitions to the weighing mode. At this time, it is also preferable that the tilt correction unit 133 and the gravity correction unit 134 notify the user that corrections have been set to correspond to both the tilt of the balance and changes in the installation location (changes in acceleration in the x, y, and z directions). Then, in subsequent weighings, the balance 1 uses equation (18) to calculate the corrected weighing value m', displays it on the display unit 16, and records it in the memory unit 14 or a specified external memory device.

2-3. Effects As described above, by mounting the three-axis acceleration sensor 20 on the balance 1 of this embodiment,
Balance 1 can detect both of the following problems: (i) when the balance is tilted and the load component Wv perpendicular to the weighing pan decreases; and (ii) when the location where the balance is installed changes and the gravitational acceleration g changes.

In particular, by simultaneously monitoring changes in the x, y, and z outputs using the three-axis acceleration sensor 20, it is possible to identify whether the problem is due to problem (i) or problem (ii) above, and the measurement values can be appropriately corrected to address each problem.

In addition, for (i) above, it is only necessary to attach the triaxial acceleration sensor 20, so the configuration is not complicated. For (ii) above, whereas responses resulting from changes in the installation location were left to the user, it is now possible for the balance itself to detect and automatically correct the changes.

3. Second embodiment In the second embodiment, the measurement method in the first embodiment is combined with daily inspection. The elements described in the first embodiment are denoted by the same reference numerals and the description thereof will be omitted.

6 is a block diagram of the weighing device according to the second embodiment of the present invention. The balance 1 has a main body case 10, a weighing pan 11, a weight sensor 12, an arithmetic processing unit 13, a memory unit 14, an operation unit 15, a display unit 16, a three-axis acceleration sensor 20, a built-in weight 17, a weight adding/removing unit 18, and a level 19.

The built-in weight 17 and the weight adding/removing unit 18 are well known in balances with an automatic calibration function. Before the balance 1 is shipped from the factory, the built-in weight 17 is placed on a table that is level, and the reference mass "mw0" is stored. The motor and cam of the weight adding/removing unit 18 are controlled by the calculation processing unit 13, and the built-in weight 17 is placed on and removed from the weight receiving part 17' multiple times. The weight receiving part 17' is linked to the beam described above, and the load of the built-in weight 17 is transmitted to the weight sensor 12. A pump type may be used for the weight adding/removing unit 18.

The level 19 is a well-known device that allows the user to visually check whether the air bubble is located in the center of the reference line. The level 19 is provided on the front side of the main body case 10.

The calculation processing unit 13 has a daily inspection unit 135 that executes a daily inspection application. The memory unit 14 stores a program for executing the daily inspection application, the reference mass "mw0" of the built-in weight 17, and an allowable threshold value for the reference mass "mw0".

3-2. Weighing method Figure 7 is a flow diagram of a weighing method using the weighing device according to the second embodiment. Here, the daily inspection of the balance includes (1) checking the horizontal state, (2) checking for dirt and foreign matter, (3) checking for zero point return, (4) checking reproducibility, and (5) checking for eccentricity error. The balance 1 has a "daily inspection" button on the operation unit 15, and a screen that guides the user to check items (1) to (5) related to the daily inspection is displayed on the display unit 16 by a daily inspection application. Daily inspection applications are publicly known, so details are omitted. The weighing method of this embodiment combines the weighing method of the first embodiment with part of this daily inspection.

When the flow starts, the daily inspection unit 135 functions and displays a screen instructing the user to check whether the air bubble in the level 19 is within the reference line in step S200 (item (1): checking the horizontal state). The user adjusts the adjuster (not shown) connected to the main body case 10 to adjust the position of the air bubble. However, because this is a manual operation, there is a possibility that an extremely slight tilt (0.1° or less) may remain.

After the manual horizontal adjustment in step S200 is completed, the flow proceeds to step S201. In step S201, similar to step S101, the acceleration change detection unit 131 acquires the current output "Xout(1), Yout(1), Zout(1)" of the acceleration sensor 20.

The subsequent steps S202 to S213 are the same as steps S102 to S113 in the first embodiment. When the correction settings are completed in each of steps S207, S210, and S213, the flow proceeds to step S214.

In step S214, the daily inspection unit 135 weighs the internal weight 17 as item (4): confirmation of reproducibility. At this time, the internal weight 17 is measured with the corrected weighing value m' according to the settings in steps S207, S210, and S213.

Next, the flow proceeds to step S215, where the daily inspection unit 135 compares the weight value m' of the internal weight 17 with the reference mass mw0 to determine whether there is a problem. If the error between the weight value m' and the reference mass mw0 is within the allowable threshold range, the daily inspection unit 135 determines that there is no problem (YES), and the balance 1 determines that items (1) and (4) have been cleared. After checking the remaining items, the daily inspection unit 135 proceeds to the weighing mode.

On the other hand, if the error between the weight value m' and the reference mass mw0 exceeds the allowable threshold range in step S215, the daily inspection unit 135 determines that there is a problem (NO) and proceeds to step S216. In step S216, the daily inspection unit 135 determines that the error cannot be completely removed by software correction given the resolution of the balance 1, and issues a warning to the user. The daily inspection unit 135 displays a warning message on the display unit 16, for example, to advise the user to redo the sensitivity adjustment using an external weight.

As described above, according to this embodiment, in addition to the effects of the first embodiment, by combining a weighing method using the triaxial acceleration sensor 20 with daily inspection of the balance, it is possible to effectively correct minute tilts that cannot be completely removed by human operation.

In this embodiment, (4) the internal weight 17 is used as the object to be measured in order to confirm reproducibility. However, this embodiment can be implemented even in a balance that does not have an internal weight 17, since it is sufficient to carry out item (4) using an external weight with a known reference mass.

4. Mounting Position of Acceleration Sensor It is important to mount the acceleration sensor 20 so that its horizontality coincides with that of the weight sensor 12. The imaginary plane vp on which the acceleration sensor 20 is disposed may be set at any position within the main body case 10 as long as it does not interfere with the weight sensor 12 (Roberval mechanism 12'), but it is preferable to mount the acceleration sensor 20 in the following configuration, for example.

Figure 8 shows a preferred mounting form of the acceleration sensor 20 in the first and second embodiments, and is an example in which the acceleration sensor 20 is mounted to the "lower case." Figure 8 is a vertical end view of the balance 1.

The main body case 10 is divided into an upper case 10u and a lower case 10d, which are fitted together with a sealant such as silicone rubber. The acceleration sensor 20 is placed on a sensor mounting plate 21, and is fixed to the inner surface of the lower case 10d, for example by screws, preferably via three or more mounting bosses 22, to prevent the sensor from wobbling. The sensor mounting plate 21 has a flush flat surface, and the sensor mounting plate 21 becomes the virtual surface vp. The IC board of the acceleration sensor 20 may be used as the sensor mounting plate 21.

When assembling the balance 1, the acceleration sensor 20 is fixed to the lower case 10d on a table that is kept level, using a spirit level or the like to ensure that the sensor mounting plate 21 remains level.

As described above, the weight sensor 12 (Roberval mechanism 12') is fixed to the main body case 10 via the support member 10c, for example by using a level on a platform where the level is ensured, and the weight sensor 12 is fixed to the main body case 10. Therefore, if the acceleration sensor 20 is also attached horizontally to the main body case 10, the acceleration sensor 20 and the weight sensor 12 can be attached so that their horizontality coincides.

Figure 9 is a diagram showing a preferred mounting form of the acceleration sensor 20 in the first and second embodiments, and is an example in which the acceleration sensor 20 is mounted to the "upper case". Similarly, the acceleration sensor 20 is placed on the sensor mounting plate 21 and screwed to the inner surface of the upper case 10u via three or more mounting bosses 22. Similarly, when assembling the balance 1, the acceleration sensor 20 is mounted on a table that is kept horizontal, for example using a spirit level, and then fixed to the main case 10, so that the horizontality of the acceleration sensor 20 and the horizontality of the weight sensor 12 match.

8 and 9, the weight sensor 12 is fixed to the upper case 10u, but this is not limited thereto, and the weight sensor 12 may be fixed to the lower case 10d. It is preferable that the fixing position of the acceleration sensor 20 coincides with the case on the side to which the weight sensor 12 is fixed.

The above describes preferred embodiments of the present invention, but the above embodiments are merely examples of the present invention, and these can be combined based on the knowledge of those skilled in the art, and such forms are also included in the scope of the present invention.

Reference Signs List 1: Balance 11: Weighing pan 11': Horizontal surface of weighing pan 12: Weight sensor 13: Calculation processing unit 14: Memory unit 17: Built-in weight 20: Three-axis acceleration sensor

Claims (8)

A weighing pan;
A weight sensor connected to the weighing pan;
a three-axis acceleration sensor that detects acceleration changes in three axes, x, y, and z, by setting x and y on a plane parallel to the horizontal of the weight sensor and z in a direction perpendicular to the horizontal of the weight sensor;
a storage unit that stores the three-axis reference outputs of the three-axis acceleration sensor when the weight sensor is horizontal;
A calculation processing unit,
The calculation processing unit compares the current outputs of the three axes of the three-axis acceleration sensor with the reference outputs, and detects that there is a tilt if the x and/or y output has changed, and detects that there is a change in the installation location if the z output has changed, and notifies the user. The weighing device according to claim 1, characterized in that, when the x and/or y output of the three-axis acceleration sensor has changed, the calculation processing unit corrects the weighing value m detected by the weight sensor to a corrected weighing value m' using equation (14).

however,
g: value of gravitational acceleration θ: angle between the direction of gravitational acceleration and the z-axis detected by the triaxial acceleration sensor gx(θ): value of x output detected by the triaxial acceleration sensor gy(θ): value of y output detected by the triaxial acceleration sensor The weighing device according to claim 1, characterized in that, when only the z output of the three-axis acceleration sensor has changed, the calculation processing unit changes the value of gravitational acceleration used to calculate the weighing value m detected by the weight sensor to a local gravitational acceleration value glocal calculated using the z-axis output of the three-axis acceleration sensor, and sets this as a corrected weighing value m'. The weighing device according to claim 2, characterized in that, when the z, x and/or y outputs of the three-axis acceleration sensor have changed, the calculation processing unit changes the value of gravitational acceleration used in equation (14) to a local gravitational acceleration g local calculated using the three-axis outputs of the three-axis acceleration sensor, and corrects the weighing value m detected by the weight sensor to a corrected weighing value m'. The weighing device according to any one of claims 2 to 4, characterized in that, if the corrected weighing value m' of the weighing object exceeds a tolerance threshold range for the reference mass of the weighing object, the calculation processing unit issues a warning to a user that the error cannot be completely removed by the correction. A weighing device including a weighing pan, a weight sensor connected to the weighing pan, and a three-axis acceleration sensor that detects acceleration changes in the three axial directions of x, y, and z, with x and y set on a plane parallel to the horizontal of the weight sensor and z set in a direction perpendicular to the horizontal of the weight sensor,
(A) obtaining current outputs of the three axes of the three-axis acceleration sensor;
(B) comparing the current outputs with reference outputs of the three axes when the weight sensor is horizontal;
(C) if the x and/or y output has changed in the step (B), notifying the user that there is a tilt;
(D) if the output of z has changed in the step (B), notifying the user that the installation location has changed;
A weighing method comprising the steps of: (E) if the output of x and/or y has changed in the step (B), correcting the weight value m detected by the weight sensor to a corrected weight value m' using equation (14);
(F) if only the z output has changed in step (B), changing the value of gravitational acceleration used in calculating the weight value m detected by the weight sensor to a local gravitational acceleration value g determined using the z-axis output of the three-axis acceleration sensor, and setting the value as a corrected weight value m';
(G) if the outputs of z, x and/or y have changed in step (B), the value of the gravitational acceleration used in the equation (14) is changed to the local gravitational acceleration g determined using the outputs of the three axes of the three-axis acceleration sensor, and the weight value m detected by the weight sensor is corrected to a corrected weight value m';
7. The method according to claim 6, further comprising:

however,
g: value of gravitational acceleration
θ: Angle between the direction of gravitational acceleration and the z-axis detected by the three-axis acceleration sensor
gx(θ): x output value detected by the three-axis acceleration sensor
gy(θ): y output value detected by the three-axis acceleration sensor
(H) weighing an object to be weighed, and if the corrected weight value m′ of the object to be weighed is outside a tolerance threshold range for the reference mass of the object to be weighed, issuing a warning to a user that the error cannot be completely removed by the correction;
The weighing method according to claim 7, further comprising: