阅读说明：本技术 称重传感器单元以及计量装置 (Weighing sensor unit and weighing device ) 是由 武市真治 于 2021-03-17 设计创作，主要内容包括：本发明涉及称重传感器单元以及计量装置。称重传感器单元具备称重传感器、第一温度传感器以及第二温度传感器,上述称重传感器具有应变体,上述应变体包括自由端侧块、固定端侧块、将自由端侧块的上端与固定端侧块的上端连接的上侧梁部、以及将自由端侧块的下端与固定端侧块的下端连接的下侧梁部,上述第一温度传感器配置于上侧梁部或下侧梁部,上述第二温度传感器配置于自由端侧块和固定端侧块中的任一方。(The present invention relates to a load cell unit and a weighing apparatus. The load cell unit includes a load cell having a strain body including a free end side block, a fixed end side block, an upper side beam portion connecting an upper end of the free end side block and an upper end of the fixed end side block, and a lower side beam portion connecting a lower end of the free end side block and a lower end of the fixed end side block, a first temperature sensor disposed on the upper side beam portion or the lower side beam portion, and a second temperature sensor disposed on either one of the free end side block and the fixed end side block.)

1. A load cell unit includes a load cell, a first temperature sensor, and a second temperature sensor,

the weighing sensor has a strain body including a free end side block, a fixed end side block, an upper side beam portion connecting an upper end of the free end side block with an upper end of the fixed end side block, and a lower side beam portion connecting a lower end of the free end side block with a lower end of the fixed end side block,

the first temperature sensor is disposed on the upper beam portion or the lower beam portion,

the second temperature sensor is disposed on either one of the free end side block and the fixed end side block.

2. The load cell unit of claim 1,

the first temperature sensor and the second temperature sensor are provided in a concentrated manner on one of an upper surface and a lower surface of the strain body.

3. The load cell unit of claim 1 or 2,

the first temperature sensor and the second temperature sensor are disposed in the center of the strain body in a width direction intersecting a direction from the free end side block toward the fixed end side block and intersecting a vertical direction.

4. The load cell unit of any of claims 1-3,

the load cell unit includes a third temperature sensor disposed on either one of the free end side block and the fixed end side block.

5. The load cell unit of any of claims 1-4,

the load cell has a sensing unit for outputting a measurement value corresponding to a deformation amount of the strain body as an analog value,

the load cell unit includes:

a conversion unit that converts the analog value output by the sensing unit into a digital value; and

and a temperature difference compensation unit that performs temperature compensation of an unbalanced state with respect to the digital value converted by the conversion unit, based on a temperature difference between a first temperature detected by the first temperature sensor and a second temperature detected by the second temperature sensor.

6. The load cell unit of claim 4,

the load cell unit includes:

a sensing unit that outputs a measured value corresponding to a deformation amount of the strain body as an analog value;

a conversion unit that converts the analog value output by the sensing unit into a digital value; and

and a temperature difference compensation unit that performs temperature compensation of an unbalanced state of the digital values converted by the conversion unit, based on a temperature difference between a first temperature detected by the first temperature sensor and a second temperature detected by the second temperature sensor, and a temperature difference between the first temperature and a third temperature detected by the third temperature sensor.

7. The load cell unit of claim 5 or 6,

the load cell unit includes a temperature compensation unit that performs temperature compensation in a steady state on the basis of the first temperature for a digital value that has been converted by the conversion unit and has not yet been compensated by the temperature difference compensation unit.

8. The load cell unit of any of claims 1-7,

the second temperature sensor is disposed on one of the free end side block and the fixed end side block which is close to the heat source.

9. The load cell unit of any of claims 1-7,

the second temperature sensor is disposed at the fixed end side block.

10. A metering device is provided with:

the load cell unit of any one of claims 1 to 8;

a conveying conveyor that conveys an article to be measured while placing the article on a conveying surface;

a drive unit that drives the conveyor;

a first frame portion that supports the conveyor and the drive portion;

a foot portion; and

a second frame portion supported by the leg portion,

the free end side block is connected to the first frame portion and is weighted by the articles conveyed by the conveyor,

the fixed end side block is connected to the second frame portion,

the second temperature sensor is disposed at the free end side block.

11. A metering device is provided with:

the load cell unit of any one of claims 1 to 9;

a hopper part having a gate for temporarily retaining and then discharging an article inputted from the outside;

a support portion that supports the hopper portion;

a drive unit that drives the shutter to open and close; and

a main body accommodating the driving part,

the free end side block is connected to the support portion and is added with the weight of the articles staying in the hopper portion,

the fixed end side block is connected with the main body,

the second temperature sensor is disposed at the fixed end side block.

Technical Field

One aspect of the invention relates to a load cell unit and a metering device.

Background

Conventionally, a load cell unit described in japanese patent application laid-open No. 2010-91325 is known. In the load cell unit described in japanese patent application laid-open No. 2010-91325, in order to suppress fluctuation of the measurement signal due to temperature change of the strain body, a temperature sensor is disposed in the strain body, and the measurement signal is compensated based on the temperature detected by the temperature sensor.

Disclosure of Invention

In the above-described load cell unit, the temperature distribution of the strain body may be in an unbalanced state (unstable state), but the output of the load cell cannot be compensated in consideration of the unbalanced state, and therefore, it is difficult to realize stable and high-precision measurement.

Accordingly, an object of one aspect of the present invention is to provide a load cell unit and a weighing apparatus capable of achieving stable and high-precision weighing.

A load cell unit according to one aspect of the present invention includes a load cell including a strain body including a free end side block, a fixed end side block, an upper side beam portion connecting an upper end of the free end side block and an upper end of the fixed end side block, and a lower side beam portion connecting a lower end of the free end side block and a lower end of the fixed end side block, a first temperature sensor disposed on the upper side beam portion or the lower side beam portion, and a second temperature sensor disposed on either one of the free end side block and the fixed end side block.

In this load cell unit, the representative temperature of the entire load cell can be detected by the first temperature sensor. Thus, the output of the load cell can be temperature-compensated based on the representative temperature of the entire load cell. Further, the temperatures of the two portions of the strain body can be acquired by the first temperature sensor and the second temperature sensor. Thus, the temperature difference (thermal imbalance) generated in the strain body can be acquired (calculated), and temperature compensation, that is, temperature compensation in consideration of the temperature distribution in the state of imbalance, can be performed based on the output of the temperature difference load cell. As a result, stable and high-precision measurement can be achieved in the load cell unit.

In the load cell unit according to one aspect of the present invention, the first temperature sensor and the second temperature sensor may be provided in a concentrated manner on one of an upper surface and a lower surface of the strain body. With this configuration, the wiring from each temperature sensor can be easily and simply configured. In addition, as compared with the case where the temperature sensors are disposed on the side surfaces of the strain body, the wiring is less likely to affect the deformation of the strain body, and adverse effects on the accuracy of the measurement can be minimized. In addition, since the strain body is generally of a symmetrical structure, by collectively providing the first temperature sensor and the second temperature sensor on the same plane, it is possible to obtain a stable temperature change without being affected by noise due to a temperature difference between the upper surface and the lower surface.

In the load cell unit according to one aspect of the present invention, the first temperature sensor and the second temperature sensor may be disposed at the center of the strain body in a width direction intersecting a direction from the free end side block toward the fixed end side block and intersecting a vertical direction. According to this configuration, the first temperature sensor and the second temperature sensor can detect the average temperature of the strain body in the width direction.

The load cell unit according to one aspect of the present invention may include a third temperature sensor disposed on either one of the free end side block and the fixed end side block. According to this configuration, in addition to the temperature difference between the two portions of the strain body obtained by the first temperature sensor and the second temperature sensor, the temperature difference between the two portions of the strain body can be further obtained by the first temperature sensor and the third temperature sensor. This enables temperature compensation based on the output of the temperature difference symmetrical load sensor, and more stable and accurate measurement can be achieved.

In a load cell unit according to an aspect of the present invention, a load cell may have a sensing unit that outputs a measurement value corresponding to a deformation amount of a strain body as an analog value, and the load cell unit may include: a conversion unit that converts the analog value output by the sensing unit into a digital value; and a temperature difference compensation unit that performs temperature compensation of an unbalanced state with respect to the digital value converted by the conversion unit, based on a temperature difference between a first temperature detected by the first temperature sensor and a second temperature detected by the second temperature sensor. With this configuration, temperature compensation of the unbalanced state can be performed based on the temperature difference of the strain body.

The load cell unit according to one aspect of the present invention may include: a sensing unit for outputting a measured value corresponding to the amount of deformation of the strain body as an analog value; a conversion unit that converts the analog value output by the sensing unit into a digital value; and a temperature difference compensation unit that performs temperature compensation of an unbalanced state with respect to the digital value converted by the conversion unit, based on a temperature difference between a first temperature detected by the first temperature sensor and a second temperature detected by the second temperature sensor, and a temperature difference between the first temperature and a third temperature detected by the third temperature sensor. With this configuration, temperature compensation of the unbalanced state can be performed based on the temperature difference of the strain body.

The load cell unit according to one aspect of the present invention may include a temperature compensation unit that performs temperature compensation in a steady state on the basis of the first temperature with respect to a digital value before conversion by the conversion unit and compensation by the temperature difference compensation unit. According to this configuration, the temperature compensation unit can perform temperature compensation in a steady state based on the first temperature that is the representative temperature of the entire load cell. Here, the temperature compensation by the temperature compensation unit mainly compensates for the deviation of the output in the thermal equilibrium state, and the temperature compensation by the temperature difference compensation unit mainly compensates for the deviation of the output in the thermal imbalance state. Therefore, according to this configuration, the adjustment of both can be easily divided.

In the load cell unit according to one aspect of the present invention, the second temperature sensor may be disposed on one of the free end side block and the fixed end side block that is close to the heat source. According to this configuration, the heat conduction by the heat source can be detected immediately, and the thermal imbalance generated in the strain body due to the heat source can be compensated for at an early stage.

In the load cell unit according to one aspect of the present invention, the second temperature sensor may be disposed on the fixed-end-side block. Generally, wiring provided to the strain body is concentrated on the fixed end side block side in many cases. Therefore, in the case where the second temperature sensor is disposed on the fixed end side block, it is possible to suppress influence of the wiring from the second temperature sensor on at least the upper side beam portion or the lower side beam portion, as compared with the case where the second temperature sensor is disposed on the free end side block. Specifically, the flexible portion (thin portion) of the wiring crossing the strain body can be reduced, and the influence of the wiring on the measurement accuracy can be eliminated.

A weighing apparatus according to an aspect of the present invention includes: the above-described load cell unit; a conveying conveyor that conveys an article to be measured while placing the article on a conveying surface; a driving unit for driving the conveyor; a first frame portion that supports the conveyor and the drive portion; a foot portion; and a second frame part supported by the legs, wherein the free end side block is connected with the first frame part and is added with the weight of the articles conveyed by the conveyor, the fixed end side block is connected with the second frame part, and the second temperature sensor is arranged on the free end side block.

A weighing device according to one aspect of the present invention includes: the above-described load cell unit; a hopper part having a gate for temporarily retaining and then discharging an article inputted from the outside; a support portion supporting the hopper portion; a driving unit for driving the gate to open and close; and a main body for accommodating the driving part, wherein the free end side block is connected with the supporting part and is added with the weight of the articles accumulated in the hopper part, the fixed end side block is connected with the main body, and the second temperature sensor is arranged on the fixed end side block.

Since these weighing devices include the load cell unit, stable and high-precision weighing can be achieved.

Drawings

Fig. 1 is a configuration diagram showing a weighing apparatus according to a first embodiment.

Fig. 2 is a block diagram showing a measurement signal processing substrate of the load cell unit of fig. 1.

Fig. 3 is a perspective view showing a strain body of the load cell unit of fig. 1.

Fig. 4 is a schematic circuit diagram showing a sensing portion of the load cell unit of fig. 1.

Fig. 5 is a graph showing test results relating to output variation with respect to temperature change of the load cell unit.

Fig. 6 is a structural diagram illustrating a load cell unit according to a second embodiment.

Fig. 7 is a perspective view showing a strain body of the load cell unit of fig. 6.

Fig. 8 is a graph showing test results relating to output variation with respect to temperature change of the load cell unit.

Fig. 9 is a graph showing test results relating to output variation with respect to temperature change of the load cell unit.

Fig. 10 is a structural diagram showing a weighing apparatus according to a third embodiment.

Fig. 11 is a diagram illustrating an example of a relationship between a position in a strain body and a temperature.

Detailed Description

Hereinafter, embodiments will be described in detail with reference to the drawings. In the drawings, the same or corresponding portions are denoted by the same reference numerals, and redundant description thereof is omitted. The terms "upper" and "lower" correspond to the up-down direction of the plumb direction.

[ first embodiment ]

Fig. 1 is a structural diagram showing a weighing apparatus 70. Fig. 2 is a structural view showing the load cell unit 1. Fig. 3 is a schematic circuit diagram showing the strain body 20 of the load cell unit 1. Fig. 4 is a structural diagram showing the sensing unit 30 of the load cell unit 1. The weighing device 70 shown in fig. 1 measures the weight of an article T supplied from the upstream side while conveying the article T to the downstream side.

The weighing device 70 includes: a load cell unit 1; a conveying conveyor 71 that conveys an article T to be measured while being placed on a conveying surface 71 s; a drive unit 72 that drives the conveyor 71; a first frame 73 that supports the conveyor 71 and the drive unit 72; a foot portion 74; and a second frame portion 75 supported by the leg portion 74. The conveyor 71 is not particularly limited, and various conveyors can be used. The driving unit 72 includes, for example, a motor. The load cell unit 1 is housed in a weighing tank 76 of the weighing device 70. The load cell unit 1 includes a load cell 10, a first temperature sensor 41, a second temperature sensor 42, and a measurement signal processing substrate 50.

As shown in fig. 1, 2, and 3, the load cell 10 is a device that obtains a measurement signal (measurement value) from the weight of the article T. The load cell 10 includes a strain body 20 and a sensing portion 30. The strain body 20 has a rectangular block shape. The straining body 20 has a so-called roberval mechanism. The strain body 20 is formed by forming a through hole in a metal block of aluminum alloy, stainless steel, or the like, and has a symmetrical structure.

The strain body 20 includes: a free end side block 20 a; a fixed-end side block 20 b; an upper beam portion 20c connecting the upper end of the free end side block 20a and the upper end of the fixed end side block 20 b; and a lower beam portion 20d connecting the lower end of the free end side block 20a and the lower end of the fixed end side block 20 b. The strain body 20 has a characteristic of being deformed into a substantially parallelogram shape in accordance with a load applied to the free end side block 20 a. The free end side block 20a is connected to the first frame portion 73, and is added with the weight of the article T conveyed by the conveyor 71. The fixed end side block 20b is connected to the second frame member 75. The free end side block 20a and the fixed end side block 20b are substantially the same size. The first temperature sensor 41 is disposed on the upper beam portion 20 c. The shape of the upper beam portion 20c on which at least the first temperature sensor 41 is disposed is symmetrical with respect to the centers of the four notched portions (symmetrical in the width direction, and symmetrical in the left-right direction which is the extending direction of the upper beam portion 20 c).

The sensing unit 30 includes four strain gauges 31, and outputs a measurement signal corresponding to the amount of deformation of the strain body 20 as an analog value. The strain gauge 31 is attached to the upper surface of the notch portion (thin portion, flexible portion) of two portions of the upper beam portion 20c and the lower surface of the notch portion of two portions of the lower beam portion 20 d. The four strain gauges 31 constitute a bridge circuit 35, and when the strain body 20 is deformed, a measurement signal corresponding to the amount of deformation is output from the bridge circuit 35. In the bridge circuit 35, the compensation of the zero point drift in the bridge balance is performed by inserting the resistance wire 35x having a temperature coefficient into the wheatstone bridge. In the bridge circuit 35, a temperature sensitive resistor 35y for adjusting a voltage applied to the wheatstone bridge is provided in accordance with a change in the young's modulus of the strain body 20, and output sensitivity is compensated.

The first temperature sensor 41 is a temperature sensor disposed on the upper beam portion 20 c. The second temperature sensor 42 is a temperature sensor disposed on the fixed end side block 20 b. The first temperature sensor 41 and the second temperature sensor 42 are provided on the upper surface of the strain body 20 in a concentrated manner. The first temperature sensor 41 and the second temperature sensor 42 are disposed at the center in the width direction of the strain body 20. The width direction is a direction orthogonal to the direction from the free end side block 20a toward the fixed end side block 20b and orthogonal to the vertical direction. The first temperature sensor 41 and the second temperature sensor 42 are, for example, temperature sensitive resistors (temperature measuring elements) whose resistance values change according to temperature.

The compensation by the temperature sensitive resistor has an effect of suppressing a fluctuation range (dynamic range) of an output before a/D conversion described later to a small extent. The fluctuation range cannot be completely compensated by the temperature sensitive resistor alone, but by reducing the fluctuation range in advance, a value (so-called count value) after a/D conversion, which is assigned as the fluctuation range of the output to be compensated in the measurement signal processing substrate 50 at the subsequent stage, can be assigned to a smaller change. Therefore, this configuration can improve the resolution with respect to the fluctuation of the compensated output and improve the compensation accuracy. However, the compensation by the temperature sensitive resistor is not an essential structure. If the required accuracy can be compensated only by measuring the signal processing substrate 50, the arrangement of the temperature sensitive resistor may be omitted.

The measurement signal processing substrate 50 is a substrate that performs processes such as amplification, a/D conversion, and temperature compensation on the measurement signal output from the load cell 10. The measurement signal processing substrate 50 includes a signal amplifier 51x, a signal amplification unit 51y, an a/D converter (conversion unit) 52x, an a/D conversion unit 52y, and an operation unit 53.

The signal amplifier 51x amplifies the measurement signal output from the load cell 10. The signal amplification unit 51y includes: a signal amplifier that amplifies a first temperature signal related to a first temperature detected by the first temperature sensor 41; and a signal amplifier that amplifies a second temperature signal associated with the second temperature detected by the second temperature sensor 42. The signal amplifiers are connected to the first and second temperature sensors 41 and 42, respectively, via wires. The signal amplification units 51y are configured by the same number of signal amplifiers as the number of temperature sensors provided in the strain body 20.

The a/D converter 52x converts the measurement signal, which is an analog value amplified by the signal amplifier 51x, into a weight count x, which is a digital value. The a/D conversion section 52y includes: an a/D converter that converts the first temperature signal as an analog value amplified by the signal amplifying section 51y into a first temperature count t as a digital value; and an a/D converter that converts the second temperature signal, which is an analog value, amplified by the signal amplifying section 51y into a second temperature count t1, which is a digital value. Each a/D converter is connected to each signal amplifier of the signal amplification section 51y via a wiring. The a/D converter 52y is constituted by the same number of a/D converters as the number of temperature sensors provided to the strain body 20.

The calculation unit 53 includes an equilibrium temperature compensation unit (temperature compensation unit) 53a and an imbalance temperature compensation unit (temperature difference compensation unit) 53 b. The arithmetic Unit 53 is constituted by, for example, a CPU (Central Processing Unit), and functions thereof are realized by the CPU operating in accordance with a predetermined program.

The equilibrium temperature compensation unit 53a performs temperature equilibrium and steady-state temperature compensation on the weight count x based on the first temperature count t. In the present embodiment, the temperature states include three states, namely, "temperature equilibrium and stable state", "temperature imbalance and stable state", and "temperature imbalance and unstable state". The "temperature equilibrium and stable state" is a state in which all the strain bodies 20 are at the same temperature. The "temperature imbalance and steady state" is a state in which there is a temperature difference between the free end side block 20a and the fixed end side block 20b, but there is no temporal change in the difference. For example, "a temperature imbalance and a stable state" corresponds to a state in which the temperature distribution does not change even with the passage of time after the output (heat generation amount) of the heat source is stabilized for a long time. The "temperature imbalance and unstable state" is a state in which a temperature difference exists between the free end side block 20a and the fixed end side block 20b, and a temporal change occurs in the difference. For example, the "temperature imbalance and unstable state" corresponds to a state immediately after the power of the heat source is increased (described later).

Specifically, the equilibrium temperature compensation unit 53a performs temperature compensation of the following expression (1) and calculates the compensated weight count y. In the following formula (1), the first half is a temperature zero compensation term, and the second half is a temperature sensitivity compensation term. In the following formula (1), d, e, f, p, q, and r are predetermined coefficients. The coefficient can be calculated by approximating the relationship between the temperature and the output fluctuation at the time of the steady state by a quadratic function by changing the temperature of the load cell 10 the necessary number of times using a thermostatic bath or the like.

y＝(x-dt²+et+f)*(s/(pt²+qt+r))…(1)

The above formula (1) will be explained in detail.

First, a coefficient for compensation is determined with respect to an output in a state where no load is applied to the load cell 10 (a state where no deformation due to an external force is generated). In this case, the right part of the multiplication sign of expression (1) is set to 1 (ignored). In the no-load state, an output at three points of temperature (low temperature, normal temperature, high temperature, however, the value substituted into the equation is an absolute temperature) is obtained. The temperature at this time needs to be measured by placing the load cell 10 in a constant temperature bath for a long time at a stable temperature. In general, although there is a variation in apparent output, the coefficients d, e, and f are determined so as to be constant values by correcting the variation. The positive and negative coefficients d, e and f are different from each other in the current stage. This enables temperature compensation in a stable state with temperature balance at the zero point. The temperature need not be three points, but may be two or four points. In the case of n points, the term on the left side of the multiplication symbol (#) is vertical as an n-1-th-order expression of the temperature t (in this case, the coefficient of the constant to be determined is n).

For example, the normal temperature is approximately the temperature of the environment in which the apparatus is used (outside air temperature). However, it is not always exactly the same as the actual place of use. For example, the high temperature and the low temperature may also be temperatures (higher or lower) to the same extent as or outside the durable temperature of the load cell 10. Since the accuracy of the obtained value is improved between high temperature and normal temperature and between low temperature and normal temperature, the difference can be made as large as possible. The difference between the high temperature and the normal temperature and the difference between the low temperature and the normal temperature are preferably the same. As an example, the normal temperature may be an average value of the high temperature and the low temperature.

Next, a coefficient for compensation is determined with respect to an output of a state in which the load is applied to the weighing sensor 10 (a state in which deformation due to an external force is generated). Here, the constant s is the magnitude (weight) of the applied load, and is not a tentative multiplier. When a load is applied, an output value that varies from the zero point (the difference from the output of the zero point is a span value) is obtained. Even in the case where the same load is applied, since the output value varies depending on the temperature, compensation is required. Similarly, stable output at three-point temperatures (low temperature, normal temperature, high temperature, and also absolute temperature) was obtained. Then, coefficients p, q, r are obtained. This can also be used to determine the degree of the mathematical expression from ground by the number of outputs (number of temperatures measured) taken. Thus, the acquired temperature may be two points or four points. In the case of n points, the term on the right side of the multiplication symbol (#) is expressed as (the reciprocal of) the expression of degree n-1 of the temperature t (in this case, the coefficient of the constant to be determined is n).

As described above, based on (1) above, the compensated weight count y (true value) can be obtained from the weight count x (apparent value). The compensated weight value y compensates for the output variation caused by the temperature of the load cell 10 with high accuracy under the condition that the temperature of the load cell 10 is in the equilibrium state. However, it is found that, when the temperature of the load cell 10 is not uniform, further output fluctuation occurs due to the occurrence of a temperature gradient, and the output deviates from the true value. Therefore, in order to compensate for the deviation of the output due to such temperature imbalance, an imbalance temperature compensation portion 53b is further provided.

The unbalance temperature compensation unit 53b performs temperature compensation of the unbalanced state with respect to the compensated weight count y after the temperature compensation by the equilibrium temperature compensation unit 53a based on the temperature difference between the first temperature count t and the second temperature count t 1. The unbalanced state is a state in which a temperature gradient is generated, and is not limited to a stable state or an unstable state. The unbalanced state is a state in which the temperature of the strain body 20 varies depending on the location, and an uneven temperature distribution occurs. The unbalanced state includes, for example, a state in which the temperature distribution is dynamic and changes with time. As an example, the unbalanced state includes a state in which the temperature of the device is gradually increased by starting the device, mainly receiving heat conduction from the heat source (motor), and generating heat inflow from the heat source side. In this case, the temperature of the heat source side is also transmitted to the opposite side. The temperature gradient is a temperature gradient in which the heat source side is at a relatively high temperature and the opposite side is at a relatively low temperature. In addition, the unbalanced state includes a state in which the temperature distribution is static and does not change with time. As an example, the apparatus is heated up and the commodity throughput is stabilized after ten minutes from the start of the apparatus. At this time, the motor side of the strain body 20 has a higher temperature than the opposite side, and a temperature gradient is generated, but the inflow and outflow of heat are balanced, and a temperature change is not generated. In the present embodiment, the unbalanced state includes the above-described "temperature unbalanced and stable state" and "temperature unbalanced and unstable state" (the same applies to the "unbalanced state" below).

Specifically, the unbalance temperature compensation unit 53b performs temperature compensation of the following expression (2) and calculates the unbalance temperature compensated weight count y'. In the following formula (2), j is a predetermined coefficient. The coefficients can be calculated by causing the load cell 10 to produce an intentional temperature difference. The generation of the temperature difference can be caused by heat generated by operating the motor. Further, by intentionally applying heat using a heater or the like, the time can be shortened. When the compensation formula is a linear function as in the following formula (2), a certain temperature difference and a set of outputs at the temperature difference need to be small, and a compensation coefficient as a solution can be obtained from a simultaneous linear equation. In addition, the higher the function of the compensation formula, the higher the compensation accuracy, but the number of points of the temperature difference data required may increase.

y’＝y-j*(t1-t)…(2)

The above formula (2) will be explained in detail.

First, a relational expression between the compensated weight count y and the unbalanced temperature compensated weight count y' is obtained. If the temperature distribution is generated, there is a deviation in output, which is assumed to depend on a difference between the temperature of the central portion and the temperature of the end portion of the strain body 20. In addition, it is assumed that the strain body 20 can generate a thermal gradient from one side toward the other side (therefore, it is assumed that the measurement of the end portion can be at least one). Here, one end portion is heated to artificially generate a thermal gradient, a temperature difference (t-t1) between the center and one end portion at that time is generated, and a coefficient j corresponding to how much the temperature difference varies the output is obtained. Here, when t1 is 0, the constant term is 0 (f included in the calculation of y), and therefore the unknown constant is only one of j. Although a quadratic term can be created and set to- { j1(t-t1) + j2(t-t1) ^2} or the like, in this case, in order to determine a undetermined multiplier, two temperature differences and a set of outputs at the temperature differences (the positive and negative of j1 and j2 are different for each unit) are required. However, manual setting of the unstable state is more time-consuming and labor-consuming than a thermostat capable of automatically setting the apparatus according to the determination. Therefore, the number of acquired temperature differences is set to a point of minimum limit in consideration of time and effort required for the production. In this way, the stable state and the unstable state can be adjusted in a divided manner, and the accuracy (the number of times to obtain) can be freely set.

In the load cell unit 1 configured as described above, first, the output of the load cell 10 is roughly compensated by the above-described analog compensation (compensation of zero drift by the resistance wire 35x and compensation of output sensitivity by the temperature sensitive resistor 35 y). Next, based on the first temperature (representative temperature of the entire load cell 10) detected by the first temperature sensor 41, the output of the weighing cell 10 is subjected to steady-state temperature compensation. Then, the temperature compensation is further performed on the output subjected to the temperature compensation in an unbalanced state. The representative temperature is a temperature that accurately represents the temperature of the two strain gauges 31 on the upper surface of the strain body 20. How to obtain the proper representative temperature and whether the verification is proper will be described in detail later.

As described above, in the load cell unit 1, the representative temperature of the entire load cell 10 can be detected by the first temperature sensor 41. This enables temperature compensation based on the representative temperature of the entire load cell 10 to be performed with respect to the output of the load cell 10. Further, the temperatures of two portions of the strain body 20 can be acquired by the first temperature sensor 41 and the second temperature sensor 42. This makes it possible to acquire (calculate) the temperature difference (thermal imbalance) generated in the strain gauge 20, and perform temperature compensation, that is, temperature compensation taking into account the temperature distribution in the state of imbalance, on the output of the load cell 10 based on the temperature difference.

As a result, the load cell unit 1 can achieve stable and high-precision measurement. For example, in a general weighing machine, since each electrical component generates heat and the measured value fluctuates immediately after the power supply is turned on, a certain measurement prohibition time needs to be set before the weighing machine is stabilized, whereas in the weighing device 70 in which the load cell unit 1 is mounted, the time required for stabilization can be shortened and usability can be improved by performing temperature compensation in an unbalanced state.

In the load cell unit 1, the second temperature sensor 42 is disposed at the fixed-end side block 20 b. The wiring H provided in the strain body 20 extends toward the fixed end side block 20b and is concentrated (see fig. 1). Therefore, when the second temperature sensor 42 is disposed on the fixed end side block 20b, the influence of the wiring H from the second temperature sensor 42 on at least the upper side beam portion 20c or the lower side beam portion 20d can be suppressed as compared with the case where the second temperature sensor 42 is disposed on the free end side block 20 a. Specifically, the wiring H can be reduced from crossing the notch portion (flexible portion, thin portion) of the strain body 20, and the influence of the wiring H on the measurement accuracy can be eliminated. The reason why the wirings H provided on the straining body 20 are concentrated on the fixed end side block 20b side is that the measurement signal processing substrate 50 is provided on the fixed end side block 20b side. This is because if the measurement signal processing substrate 50 is provided on the free end side block 20a side, the weight is tare, and the wiring H extending from the measurement signal processing substrate 50 to the sensitive part 30 affects the deformation of the strain body 20.

In the load cell unit 1, the first temperature sensor 41 and the second temperature sensor 42 are collectively provided on the upper surface of the strain body 20. With this configuration, the wiring H from the first temperature sensor 41 and the second temperature sensor 42 can be easily and simply configured. In addition, compared to the case where the first temperature sensor 41 and the second temperature sensor 42 are disposed on the side surface of the strain body 20, the wiring H is less likely to affect the deformation of the strain body 20, and adverse effects on the accuracy of measurement can be minimized. Further, since the strain body 20 has a symmetrical structure, by collectively providing the first temperature sensor 41 and the second temperature sensor 42 on the same plane, it is possible to obtain a stable temperature change without being affected by noise due to a temperature difference between the upper surface and the lower surface. The first temperature sensor 41 and the second temperature sensor 42 may be provided on the lower surface of the strain body 20 instead of the upper surface of the strain body 20.

In general, the load cell 10 (strain body 20) is used by physically connecting the free end side block 20a and the fixed end side block 20b to the outside (a frame of the device, etc.). Therefore, the inflow and outflow of heat are mainly generated by heat conduction through the connection portions of the free end side block 20a and the fixed end side block 20 b. Therefore, a thermal gradient (difference in temperature) is easily generated mainly in the direction from the free end side block 20a toward the fixed end side block 20 b. However, depending on whether the heat source is located above or below the free end side block 20a or the fixed end side block 20b, a temperature gradient is also generated in the up-down direction. Therefore, in order to compensate for the temperature gradient generated by the heat source more accurately, the first temperature sensor 41 and the second temperature sensor 42 are preferably disposed at the same position when viewed from the vertical direction. Here, the first temperature sensor 41 needs to be provided on the upper beam portion 20c or the lower beam portion 20d, but is difficult to dispose because the side surface of the upper beam portion 20c or the lower beam portion 20d has a small area. Therefore, in order to dispose the first temperature sensor 41 and the second temperature sensor 42 at the same position when viewed from the vertical direction, it is preferable to dispose them at the same time on the upper surface or at the same time on the lower surface. Comparing the upper surface and the lower surface, it is more preferable to provide the upper surface because it is more accessible to the operator at the time of production and maintenance.

In the load cell unit 1, the first temperature sensor 41 and the second temperature sensor 42 are disposed at the center of the strain body 20 in the width direction. With this configuration, the first temperature sensor 41 and the second temperature sensor 42 can detect the average temperature of the strain body 20 in the width direction.

In the load cell unit 1, the load cell 10 includes a sensing unit 30 that outputs a measurement signal corresponding to a deformation amount of the strain body 20 as an analog value. The load cell unit 1 includes an a/D converter 52x and an unbalance temperature compensation unit 53 b. The a/D converter 52x converts the analog measurement signal output from the sensor unit 30 into a digital weight count x. The unbalance temperature compensation unit 53b performs temperature compensation of the unbalanced state with respect to the digital value converted by the a/D converter 52x and the compensated weight count y after the temperature compensation performed by the balance temperature compensation unit 53 a. With this configuration, temperature compensation of the unbalanced state can be performed based on the temperature difference of the strain body 20.

The load cell unit 1 includes an equilibrium temperature compensation unit 53 a. The equilibrium temperature compensation unit 53a performs temperature compensation in a steady state on the digital value converted by the a/D converter 52x and the weight count x before the temperature compensation by the imbalance temperature compensation unit 53b based on the first temperature count t. According to this configuration, the equilibrium temperature compensation unit 53a can perform temperature compensation in a steady state based on the first temperature that is the representative temperature of the entire load cell 10. Here, the temperature compensation by the equilibrium temperature compensation portion 53a mainly compensates for the deviation of the output in the thermally balanced state, while the temperature compensation by the unbalance temperature compensation portion 53b mainly compensates for the deviation of the output in the thermally unbalanced state. Therefore, according to this configuration, the adjustment of both can be easily divided.

In addition, for example, the following division may be made: the compensation in the steady state (compensation with respect to the average temperature of the strain body 20 approximately) is compensated by a higher-order equation with respect to the temperature (quadratic equation, compensation in which the temperature and the output at three points need to be measured), and the compensation in the unbalanced state (compensation in which the temperature distribution of the strain body 20 is also considered) is compensated by a lower-order equation with respect to the temperature (primary equation, compensation in which the temperature difference and the output at one point need to be measured). The mathematical expression for performing compensation is generally higher in the degree and higher in the compensation accuracy, but accordingly, the number of coefficients to be determined is larger. That is, the higher the high-order compensation is performed, the more the process of changing the temperature of the strain body 20 and acquiring the output of the sensitive part 30 (the relationship between the temperature to be acquired and the output) is performed in order to adjust the compensation formula. In general, it is relatively easy to obtain the output of the sensitive part 30 in a steady state by changing the temperature of the strain body 20 (the strain body may be left in the constant temperature bath for a predetermined time). However, it is difficult to obtain the output of the sensitive unit 30 in an unbalanced state by changing the temperature of the strain body 20 (in this case, to be precise, the temperature difference between the first temperature sensor 41 and the second temperature sensor 42). Therefore, if the compensation in the steady state and the compensation in the unbalanced state are divided as in the present embodiment, it is easy to appropriately adjust each compensation by comparing the accuracy obtained from the consideration and the difficulty of adjustment.

Fig. 5 is a graph showing test results relating to output variation with respect to temperature change of the load cell unit. In the figure, the waveform D1 is the result of the load cell unit 1 according to the present embodiment, the waveform D2 is the result of the load cell unit according to comparative example 1, and the waveform D3 is the result of the load cell unit according to comparative example 2. Comparative example 1 has the same configuration as the load cell unit 1, except that the second temperature sensor 42 and the unbalance temperature compensation portion 53b are not provided. Comparative example 2 has the same configuration as the load cell unit 1, except that the first temperature sensor 41, the second temperature sensor 42, the equilibrium temperature compensation portion 53a, and the unbalance temperature compensation portion 53b are not provided. In this test, various load cell units were disposed in a thermostatic bath so that the in-bath temperature N1 changed substantially stepwise in the order of normal temperature → high temperature → low temperature → normal temperature. As shown in fig. 4, in the waveform D2 and the waveform D3 (comparative example 1 and comparative example 2), when the in-tank temperature N1 abruptly changes, the output temporarily fluctuates. In contrast, the variation of the output value (waveform D1) in the present embodiment is smaller than the waveforms D2 and D3. In the load cell unit 1, it was confirmed that the fluctuation can be greatly suppressed and a high fluctuation improvement effect can be obtained.

In the load cell unit 1, the second temperature sensor 42 may be disposed on the free end side block 20 a. In this case, since the driving unit 72 as a heat source is disposed on the free end side block 20a side, the free end side block 20a is close to the heat source. That is, the second temperature sensor 42 may be disposed on the free end side block 20a, and the free end side block 20a may receive heat conduction from the driving unit 72 serving as a heat source more than the fixed end side block 20 b. The "side close to the heat source" is a relative concept. When heat sources are present on both the free end side block 20a side and the fixed end side block 20b side, the side where the heat source having a higher temperature is present is the "side closer to the heat source". According to this configuration, the heat conduction by the heat source can be detected immediately, and the thermal imbalance generated in the strain body 20 by the heat source can be compensated at an early stage.

In addition, when the weighing device 70 meters the relatively cold article T, the temperature of the free end side block 20a may be abruptly decreased by the temperature of the relatively cold article T. In this case, if the second temperature sensor 42 is disposed on the free end side block 20a, the heat conduction by the relatively cold article T can be immediately detected, and the thermal imbalance in the strain body 20 due to the relatively cold article T can be compensated for at an early stage.

In the present embodiment, the following particular effects are exhibited from the viewpoint of accuracy and the viewpoint of adjustment, respectively.

< viewpoint of precision >

By acquiring a representative temperature (representative temperature) of the load cell 10 as a whole by one first temperature sensor 41 located in the middle of the free end side block 20a and the fixed end side block 20b, it is possible to compensate for a deviation in the output of the load cell 10 as a whole due to an average (representative, and substantially middle value) temperature of the load cell 10 as a whole. The second temperature sensor 42 positioned on one of the free end side block 20a and the fixed end side block 20b can compensate for the output variation associated with the unbalanced state.

In the second embodiment, three temperature sensors 41 to 43 are arranged. Since the second temperature sensor 42 and the third temperature sensor 43 are symmetrically positioned, the inventors studied the possibility of setting the average temperature obtained by averaging the respective temperatures detected by the second temperature sensor 42 and the third temperature sensor 43 as a representative temperature. However, as a result of the study, it was found that, in fact, when only the temperature detected by the first temperature sensor 41 is used, the actual representative temperature of the entire load cell 10 (strain body 20) can be represented, as compared with the average temperature using the second temperature sensor 42 and the third temperature sensor 43. The following description will be specifically made.

Fig. 11 is a diagram illustrating an example of a relationship between a position in the strain body 20 and a temperature. In the figure, the solid line is the actual temperature of the strain body 20. Three "x" on the solid line correspond to the temperature detected by the second temperature sensor 42, the temperature (temperature a) detected by the first temperature sensor 41, and the temperature detected by the third temperature sensor 43, respectively, from the left side in the figure. The broken line is a straight line connecting the leftmost "x" and the rightmost "x" on the solid line. The one-dot chain line is an actual temperature of the strain body 20 immediately after the power of the heat source disposed on the free end side block 20a side is increased (for example, immediately after the rotation speed (heat generation amount) of the motor is increased). Of the two "x" on the one-dot chain line, the left "x" corresponds to the temperature detected by the second temperature sensor 42 immediately thereafter. The "x" on the right side corresponds to the temperature detected by the third temperature sensor 43 immediately thereafter. The two-dot chain line is a straight line connecting the left side "x" and the right side "x" on the one-dot chain line. Of the three "x" on the two-dot chain line, the "x" in the center of the left and right corresponds to an average temperature (temperature B) of the temperature detected by the second temperature sensor 42 and the temperature detected by the third temperature sensor 43 immediately after that.

The difference between the case where the temperature compensation of the load cell 10 is performed by the temperature a of the beam portion (the upper beam portion 20c or the lower beam portion 20d) of the strain body 20 and the case where the temperature compensation of the load cell 10 is performed by the average temperature B of the temperatures of two portions of the free end (the free end side block 20a) and the fixed end (the fixed end side block 20B) is as follows. That is, as shown in fig. 11, the temperature gradient of the strain body 20 is generated by inflow and outflow of heat at the free end and the fixed end. It is assumed that the temperature of the free end is higher than that of the fixed end when heat flows in from the free end side and flows out from the fixed end side. Heat is conducted from the higher temperature side to the lower side in the same manner as in the case of resistance, and a temperature drop occurs due to the influence of the cross-sectional area and distance of the conduction path. Therefore, in the case of the strain body 20, the portion where a particularly large temperature drop occurs is the notch portion (thin portion), and the cross-sectional area of the beam portion connecting between the notch portions, i.e., the free end and the blocks 20a and 20b at the fixed end, which are the other portions, is extremely large as compared with the notch portion, and therefore the temperature drop is negligible. This is because the larger the sectional area is, the larger the amount of movement of heat per unit time is, and therefore the temperature is diffused in a short time, and the temperature becomes almost the same (equalized at an early stage). As a result, since the amount of heat movement per unit time is small in the notch portion, even if a temperature difference occurs across the notch portion, the temperature is not immediately transmitted between the two (in the present embodiment, between the free end side block 20a and the upper side beam portion, and between the lower side beam portion and the fixed end side block 20a), and the state where the temperature difference exists is not immediately eliminated. On the other hand, in the inside of each of the free end, fixed end blocks 20a, 20b, and the beam portion (the upper beam portion 20c or the lower beam portion 20d) connecting the notch portions, since the amount of heat movement per unit time is relatively large, even if a temperature difference occurs, the heat is eliminated in a short time (temperature equalization in each portion). Here, the strain gauge 31 is attached to the notch portion, and the temperature drop becomes large particularly at the position where the strain gauge 31 is disposed, for the reason described above.

As described above, the temperature a is considered to be substantially uniform at the beam portion, and the strain gauges 31 attached to the notch portions at both ends have a value close to the temperature of the beam portion (described later). On the other hand, with respect to the temperature B, even if the amount of heat flowing into and out of the strain body 20 is constant, there is a difference in temperature between the free end and the fixed end, and when the difference is in a stable state without variation, the temperature B becomes equal to the temperature a, and characteristics equivalent to the temperature a can be obtained. This is because the strain body 20 has a high shape of a symmetrical shape as viewed from the center portion (center of deformation) of the four notch portions, and if the temperature distribution reaches a steady state, the amount of temperature drop at each notch portion is equal as viewed from the extending direction of the beam portion. However, when there is a fluctuation in the inflow and outflow of heat, that is, in the unstable state, the temperature B ≠ temperature a, and a difference occurs between the temperature B and the actual temperature of the strain gauge 31. Therefore, the temperature of the beam portion is set to the representative temperature of the load cell 10, and the compensation accuracy can be improved while adapting to all temperature conditions. The strain gauge 31 is generally smaller than the width of the notch portion. The strain gauge 31 is affected by the temperature of the beam portion in half and by the temperature of the free end side block 20a or the fixed end side block 20b in half. When the contribution rate of the influence is taken into consideration, the temperature of the beam portion becomes a representative temperature of the whole (a value close to a value obtained by averaging the temperature distribution of the whole of the load cell 10 and conforming to the actual condition). For the above reasons, the second embodiment can improve the accuracy as compared with the case where two temperature sensors are disposed in total in the free end side block 20a and the fixed end side block 20b, respectively.

< viewpoint of adjustment >

Temperature compensation in a state of temperature equilibrium ("temperature compensation in a temperature equilibrium and stable state") can be performed based on the first temperature of the one first temperature sensor 41 between the free end side block 20a and the fixed end side block 20b, and the accuracy can be improved by increasing the number of temperature acquisition points according to the obtained accuracy. The temperature compensation in the state of the temperature imbalance ("temperature imbalance and steady state" and "temperature imbalance and unsteady state" temperature compensation) can be performed based on the temperature difference between the first temperature sensor 41 and the second temperature sensor 42, and the number of acquisition points of the temperature difference is increased according to the obtained accuracy, thereby improving the accuracy.

The deviation of the output based on the temperature change of the entire strain body 20, which occupies most of the deviation of the output, can be compensated simply and highly accurately using one first temperature sensor 41. The temperature can be easily maintained constant by using a thermostatic bath, and automation can be achieved. In automation using a thermostatic bath, first, the load cell 10 is disposed in the thermostatic bath. The temperature of the thermostatic bath is changed, and the output of the load cell 10 at each temperature is obtained. For example, the output of the load cell 10 at each temperature is obtained by changing the temperature of the thermostatic bath in the order of normal temperature → high temperature → low temperature → normal temperature. The output of the load cell 10 is acquired after changing the temperature of the thermostatic bath until the temperature of the strain body 20 is equalized, preferably after waiting a sufficient time (e.g., 5 hours). At this time, in the load cell 10, the fixed end side block 10b is supported (fixed), and the load (specifically, the placement of the weight) can be applied to or released from (turned on/off) the free end side block 10a by the robot arm. Therefore, by turning the load of the robot arm on and off, the output of the load cell 10 when a load is applied at each temperature and the output of the load cell 10 when the load is removed can be automatically obtained at the same time.

The compensation of the additional adjustability according to the temperature difference (at the start of operation, at the time of change of the setting of operation, etc.) can be performed by obtaining the temperatures of the first temperature sensor 41 and the second temperature sensor 42 to obtain the temperature difference. Temperature adjustment of unbalanced states (unbalanced and stable states and unbalanced and unstable states) which are difficult to adjust can be performed in a divided manner. The state in which the temperature difference occurs can be artificially generated by, for example, bringing the heater into contact with one of the free end side block 10a and the fixed end side block 10 b. However, it is difficult to automate the acquisition of the output of the load cell 10 in the thermostatic bath as described above. Therefore, by dividing the temperature adjustment, the number of points of the group of the value of the temperature difference and the value of the output, which are required to be obtained for the compensation performed in the case of the temperature imbalance (the unbalanced and stable state and the unbalanced and unstable state), can be reduced as compared with the number of points of the group of the value of the temperature and the value of the output, which are required to be obtained for the compensation performed in the case of the temperature imbalance (the temperature equilibrium and stable state). In this regard, the temperature difference of the necessary number of points can be acquired with a desired accuracy.

[ second embodiment ]

Next, a second embodiment will be explained. In the description of the present embodiment, only the points different from the first embodiment will be described, and redundant description will be omitted.

Fig. 6 is a structural view showing the load cell unit 100. Fig. 7 is a perspective view showing the strain body 20 of the load cell unit 100. As shown in fig. 6 and 7, the load cell unit 100 is different from the load cell unit 1 (see fig. 1) in that it further includes a third temperature sensor 43.

The third temperature sensor 43 is a temperature sensor disposed on the free end side block 20 a. The third temperature sensor 43 is provided on the upper surface of the strain body 20. The third temperature sensor 43 is disposed at the center in the width direction of the strain body 20. The third temperature sensor 43 is constituted by, for example, a temperature sensing resistor (temperature measuring element) whose resistance value changes according to the temperature. The second temperature sensor 42 and the third temperature sensor 43 are disposed at symmetrical positions.

The second temperature sensor 42 and the third temperature sensor 43 are disposed at positions equidistant from the centers of the four notched portions in the strain body 20 in the direction from the free end side block 20a toward the fixed end side block 20 b. This is to compensate for the output deviation caused by the expansion and contraction of the strain gauge 31 due to temperature. The second temperature sensor 42 and the third temperature sensor 43 are disposed at the center of the strain body 20 in the width direction. This is because the temperature close to the center, and further the temperature close to the entire temperature of the strain body 20 can be detected by the second temperature sensor 42 and the third temperature sensor 43.

In the present embodiment, the signal amplification unit 51y amplifies the third temperature signal relating to the third temperature detected by the third temperature sensor 43. The a/D conversion section 52y converts the third temperature signal, which is an analog value amplified by the signal amplification section 51y, into a third temperature count t2, which is a digital value.

The unbalance temperature compensation unit 53b performs temperature compensation of the unbalanced state with respect to the compensated weight count y after the temperature compensation by the equilibrium temperature compensation unit 53a based on the temperature difference between the first temperature count t and the second temperature count t1 and the temperature difference between the first temperature count t and the third temperature count t 2. For example, the unbalance temperature compensation unit 53b performs temperature compensation of the following expression (3) and calculates the unbalance temperature compensated weight count y'.

y’＝y-j*(t1-t)-k*(t2-t)…(3)

In addition, in the formula (3), in order to compensate with higher accuracy, the acquired temperature difference may be added to n points (n is an integer of 3 or more) and added to the term of degree n-1 of t1-t and the term of degree n-1 of t-2. In this case, it is necessary to obtain a large number of relationships between the temperature differences and the outputs in accordance with the number of times each temperature difference has occurred.

As described above, the present embodiment also achieves the above-described operational effects such as enabling stable and highly accurate measurement.

The load cell unit 100 is provided with a third temperature sensor 43. According to this configuration, in addition to the temperature difference between the two portions of the straining body 20 obtained by the first temperature sensor 41 and the second temperature sensor 42, the temperature difference between the two portions of the straining body 20 can be further obtained by the first temperature sensor 41 and the third temperature sensor 43. This enables temperature compensation based on the temperature difference to be performed with respect to the output of the load cell 10. Output fluctuations due to temperature changes can be further suppressed, and more stable and highly accurate measurement can be realized.

In the load cell unit 100, the unbalance temperature compensation unit 53b performs temperature compensation of the state in which the compensated weight count y is unbalanced, based on a temperature difference between the first temperature detected by the first temperature sensor 41 and the second temperature detected by the second temperature sensor 42 and a temperature difference between the first temperature detected by the first temperature sensor 41 and the third temperature detected by the third temperature sensor 43. This enables temperature compensation of the unbalanced state based on the temperature difference between the first temperature and the third temperature. In the case of temperature compensation in the unbalanced state, it is possible to obtain information in a curved shape of the temperature distribution of the strain body 20, which cannot be grasped only by the first temperature sensor 41 and the second temperature sensor 42, with high accuracy.

Fig. 8 is a graph showing test results relating to output variation with respect to temperature change of the load cell unit. In the figure, a waveform D4 is a result of the load cell unit 100 according to the present embodiment, and a waveform D5 is a result of the load cell unit according to comparative example 3. Comparative example 3 has the same configuration as the load cell unit 100, except that the temperature sensors 41 to 43, the equilibrium temperature compensation section 53a, and the unbalance temperature compensation section 53b are not provided. In this test, the fixed end block of the heater correspondence type was heated, and the temperature difference N2 between the free end block and the fixed end block was changed as shown in the drawing. As shown in fig. 8, in comparative example 3, the output varied with the occurrence of the temperature difference N2. In contrast, in the load cell unit 100, it was confirmed that the fluctuation can be largely suppressed.

Fig. 9 is a graph showing test results relating to output variation with respect to temperature change of the load cell unit. In the figure, the waveform D6 is the result of the load cell unit 100 according to the present embodiment, the waveform D7 is the result of the load cell unit according to comparative example 4, and the waveform D8 is the result of the load cell unit according to comparative example 5. Comparative example 4 has the same configuration as the load cell unit 100, except that the second temperature sensor 42, the third temperature sensor 43, and the unbalance temperature compensation portion 53b are not provided. Comparative example 5 has the same configuration as the load cell unit 100, except that the temperature sensors 41 to 43, the equilibrium temperature compensation section 53a, and the unbalance temperature compensation section 53b are not provided. In this test, various load cell units were disposed in a thermostatic bath so that the in-bath temperature N3 changed substantially stepwise in the order of normal temperature → high temperature → low temperature → normal temperature. As shown in fig. 9, in the waveform D7 and the waveform D8 (comparative example 4 and comparative example 5), when the in-tank temperature N3 abruptly changes, the output temporarily fluctuates. In contrast, the variation of the output value (waveform D6) in the present embodiment is smaller than the waveforms D7 and D8. In the load cell unit 100, it was confirmed that the fluctuation can be greatly suppressed and a high fluctuation improvement effect can be obtained. The output value of the present embodiment has a smaller fluctuation range of the output than the output value (waveform D1) of the first embodiment (see fig. 5). In fig. 5 and 9, the scale of the vertical axis (output) is the same.

[ third embodiment ]

Next, a third embodiment will be explained. In the description of the present embodiment, only the points different from the first embodiment will be described, and redundant description will be omitted.

Fig. 10 is a configuration diagram showing a weighing apparatus 170 according to a third embodiment. The weighing device 170 shown in fig. 10 is, for example, a device used in a combination weighing machine. The weighing device 170 is different from the weighing device 70 (see fig. 1) in that a hopper portion 171, a support portion 172, a drive portion 173, and a main body 174 are provided instead of the conveyor 71, the drive portion 72, the first frame portion 73, the leg portions 74, and the second frame portion 75 (see fig. 1).

The hopper 171 has a gate G, and discharges the articles T once accumulated therein. The support portion 172 supports the hopper 171. The driving unit 173 drives the shutter G to open and close via the link 173 x. When the gate G is closed, the driving portion 173 and the gate G are separated from each other so that the metering is not affected. The driving unit 173 includes, for example, a motor. The main body 174 accommodates the driving portion 173. In the present embodiment, the free end side block 20a is connected to the support portion 172, and adds the weight of the article T retained in the hopper 171. The fixed end side block 20b is connected to a main body 174 accommodating the driving portion 173 via a frame 175.

As described above, the present embodiment also achieves the above-described operational effects such as enabling stable and highly accurate measurement.

In the present embodiment, the second temperature sensor 42 is disposed on the fixed end side block 20 b. Since the driving unit 173 as a heat source is disposed on the fixed end block 20b side, the fixed end block 20b is close to the heat source. That is, the second temperature sensor 42 is disposed on the fixed end side block 20b that receives more heat conduction from the driving unit 173, which is a heat source, than the free end side block 20 a. According to this configuration, the heat conduction by the heat source can be detected immediately, and the thermal imbalance generated in the strain body 20 by the heat source can be compensated at an early stage. In the present embodiment, as in the second embodiment, three temperature sensors 41 to 43 may be provided.

The embodiments have been described above, but one aspect of the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention.

In the above embodiment, the first temperature sensor 41 may be disposed on the lower beam portion 20 d. In the above embodiment, at least one of the first temperature sensor 41, the second temperature sensor 42, and the third temperature sensor 43 may be disposed on the lower surface of the strain body 20, or may be disposed on the side surface of the strain body 20. In the above embodiment, at least one of the first temperature sensor 41, the second temperature sensor 42, and the third temperature sensor 43 may be disposed at a position other than the center of the strain body 20 in the width direction.

In the above embodiment, the compensation accuracy may be further improved by making at least one of the above formula (2) and the above formula (3) higher. In the above-described embodiments, the load cell units 1 and 100 are applied to the weighing devices 70 and 170, but the present invention is not limited thereto. The load cell unit according to one embodiment of the present invention can be applied to various known weighing devices.

The configurations in the above-described embodiment and modification are not limited to the materials and shapes described above, and various materials and shapes can be applied. Each configuration in the above embodiment or modification can be arbitrarily applied to each configuration in other embodiments or modifications. A part of each structure in the above embodiment or modification can be omitted as appropriate within a range not departing from the gist of an embodiment of the present invention.

According to an aspect of the present invention, a load cell unit and a weighing apparatus capable of achieving stable and high-precision weighing can be provided.