JP2008116393A - Load cell unit, weight checker, and balance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a load cell unit capable of satisfactorily weighing the weight of a measuring object, even when the ambient temperature varies, and to provide a weight checker and a balance that utilize the load cell unit. <P>SOLUTION: A strain element has a plurality of strain element parts. Each strain gauge 41 is arranged in the corresponding strain part. A bridge circuit 40 is formed of the strain gauges 41. Each of the strain gauges 41 is a temperature-sensitive compensating type gauge, and roughly corrects the output sensitivity of the bridge circuit 40. A zero-point compensating element 42 roughly corrects the zero point of the bridge circuit 40. A temperature-sensitive resistance 45 is a temperature sensor for detecting the temperature of the strain element. The zero-point compensating element 42 and the temperature-sensitive resistance 45 are disposed in a thick wall portion, sandwiched by the adjacent strain element parts. A signal processing part 50 further compensates the zero point and the output sensitivity of the bridge circuit 40, by conducting fine correction with a secondary or more higher degree of approximation as to the roughly-corrected bridge output. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a load cell unit that measures the weight of an object to be weighed based on a load signal, and a weight sorter and a scale using the load cell unit, and more particularly to output compensation of a bridge circuit using a strain gauge. .

  Conventionally, the output of the bridge circuit is roughly compensated by the temperature-sensitive resistor connected in series to the bridge circuit, and the output sensitivity of the bridge circuit is compensated by finely compensating the coarsely compensated load voltage by a temperature compensation function or the like. A technique is known (for example, Patent Document 1). A technique for compensating for the zero point and output sensitivity based on the temperature detected by a temperature detection sensor has also been known (for example, Patent Document 2). Furthermore, a technique using a temperature-sensitive resistor as a temperature sensor in order to electrically compensate the output sensitivity of the bridge circuit has been conventionally known (for example, Patent Document 3).

  Here, the “zero point” means a no-load output. When a voltage from a power source is applied to a load cell unit in a no-load state, a voltage (load signal) output from the bridge circuit of the load cell unit is Say. “Output sensitivity” refers to the amount of fluctuation in output from the bridge circuit when a certain load is applied to the load cell unit, and is obtained by subtracting the zero point from the output of the bridge circuit.

Japanese Patent Laid-Open No. 11-064123 JP-A-11-125555 Japanese Patent Publication No. 07-069232

  However, when temperature compensation of output sensitivity is performed, if the amount of change of the zero point due to temperature fluctuation is large, the output from the bridge circuit varies greatly due to the influence of this zero point fluctuation. As a result, the technique of Patent Document 1 has a problem that the weight of the object to be weighed cannot be detected stably. Further, in Patent Documents 2 and 3, depending on the arrangement of the temperature sensor and the temperature sensitive resistor, there is a problem that the measurement value is not stable due to the influence of the fluctuation of the ambient temperature.

  Therefore, the present invention provides a load cell unit that can accurately weigh the object to be weighed even when the ambient temperature changes, and a weight sorter and a scale using the load cell unit. Objective.

  In order to solve the above-mentioned problems, the invention of claim 1 is a load cell unit for weighing the weight of an object to be weighed based on a load signal, and is a metal block provided with a through hole. A strain generating body having a plurality of thin strain generating portions sandwiched between a wall surface and an outer peripheral surface of the metal block, and a corresponding strain generating portion among the plurality of strain generating portions, and is caused by a temperature change. By compensating for the amount of change in the longitudinal elastic modulus of the strain body and roughly correcting the bridge output of the bridge circuit, a temperature sensitivity compensation type strain gauge for compensating the output sensitivity of the bridge circuit, and the strain gauge A bridge circuit formed and a strain gauge disposed on one side of the bridge circuit are connected in series, and the zero point of the bridge circuit that fluctuates due to a temperature change is compensated according to the temperature of the strain generating body. By doing so, the zero point compensation element for roughly correcting the output of the bridge circuit, the temperature sensor for detecting the temperature of the strain generating body, the zero point of the bridge circuit is compensated by the zero point compensation element, and the strain gauge A signal that further compensates for the zero point and output sensitivity of the bridge circuit by finely correcting the bridge output that has been coarsely corrected by compensating the output sensitivity of the bridge circuit based on the detection result by the temperature sensor. A strainer, wherein the strain body constitutes a Roverval mechanism via the plurality of strain portions provided between a free end to which a load is applied and a fixed end, and the zero compensation element and the The temperature sensor is provided in a portion sandwiched between adjacent strain generating portions.

  According to a second aspect of the present invention, in the load cell unit according to the first aspect, the temperature sensor is a temperature sensitive resistor.

  The invention of claim 3 is a load cell unit that measures the weight of an object to be weighed based on a load signal, and is a metal block provided with a through hole, and the inner wall surface of the through hole and the metal block A strain generating body having a plurality of thin strain generating portions sandwiched between the outer peripheral surfaces, and a heat generating portion of the strain generating body that is disposed in a corresponding strain generating section among the plurality of strain generating sections and is caused by temperature change. A self-temperature-compensating strain gauge capable of compensating for expansion, a bridge circuit formed by the strain gauge, and a bridge connected in series with a strain gauge disposed on one side of the bridge circuit and fluctuating according to temperature changes Compensating the zero point of the circuit according to the temperature of the strain-generating body, it is connected in series with the zero point compensating element for coarsely correcting the output of the bridge circuit and the input side of the bridge circuit, and the temperature change. By compensating for the amount of change in the longitudinal elastic modulus of the strain body caused by the above and roughly correcting the bridge output of the bridge circuit, a temperature-sensitive resistor that compensates the output sensitivity of the bridge circuit and the zero compensation element Fine correction is performed based on the detection result of the temperature sensor for the bridge output which is compensated for by compensating the zero point of the bridge circuit and by compensating the output sensitivity of the bridge circuit by a pre-temperature sensing resistor. A signal processing unit that further compensates for the zero point and output sensitivity of the bridge circuit, and the strain generating body includes a plurality of the strain generating portions provided between a free end to which a load is applied and a fixed end. The temperature sensitive resistor that can be used as a zero compensation element and a temperature sensor is provided in a portion sandwiched between adjacent strain generating portions. And said that you are.

  According to a fourth aspect of the present invention, in the load cell unit according to the third aspect, the first temperature sensing resistor among the temperature sensing resistors is the first input terminal of the bridge circuit and the second temperature sensing resistor is: It is connected to the input side second terminal of the bridge circuit, respectively.

  According to a fifth aspect of the present invention, in the load cell unit according to the third aspect, the temperature sensitive resistor is connected to one of the terminals on the input side of the bridge circuit. To do.

  The invention of claim 6 is a load cell unit for weighing the weight of an object to be weighed based on a load signal, and is a metal block provided with a through hole, and the inner wall surface of the through hole and the metal block A strain generating body having a plurality of thin strain generating portions sandwiched between the outer peripheral surfaces, and a heat generating portion of the strain generating body that is disposed in a corresponding strain generating section among the plurality of strain generating sections and is caused by temperature change. A self-temperature-compensating strain gauge capable of compensating for expansion, a bridge circuit formed by the strain gauge, and a bridge connected in series with a strain gauge disposed on one side of the bridge circuit and fluctuating according to temperature changes By compensating the zero point of the circuit according to the temperature of the strain generating body, a zero point compensating element for roughly correcting the bridge output of the bridge circuit, a temperature sensitive resistor usable as a temperature sensor, and an input signal A variable gain amplifying unit that is connected to the temperature sensitive resistor and whose amplification degree is controlled based on a resistance value of the temperature sensitive resistor according to a temperature change, and the variable gain amplification A signal processing unit having a compensation calculation unit capable of executing a compensation calculation based on an output signal from the unit, and a switching unit capable of switching between the bridge output and the reference output and inputting to the variable gain amplification unit The strain generating body constitutes a Roverval mechanism via a plurality of strain generating portions provided between a free end to which a load is applied and a fixed end, and the zero compensation element and the temperature sensitive resistor are: Provided in a portion sandwiched between adjacent strain generating sections, the switching section is switched to the bridge output side, and when the bridge output is input to the variable gain amplification section as the input signal, Variable gain amplifier Compensating the output sensitivity of the bridge circuit by compensating for the amount of change in the longitudinal elastic modulus of the strain body due to temperature change and roughly correcting the bridge output, and the compensation calculation unit Based on the detection result of the temperature sensor, the bridge output that has been coarsely corrected by compensating the zero point of the bridge circuit by an element and compensating the output sensitivity of the bridge circuit by the variable gain amplifier. By correcting, the zero point and output sensitivity of the bridge circuit are further compensated, and when the switching unit is switched to the reference output side and the reference output is input to the variable gain amplification unit as the input signal The variable gain amplifying unit outputs an output signal corresponding to a resistance value of the temperature sensitive resistor, and the compensation calculating unit is configured to output the output signal based on the output signal. The temperature of the strain generating body is calculated.

  The invention according to claim 7 is the load cell unit according to any one of claims 1 to 6, wherein the adjacent first and second strain generating portions of the strain generating portions are the outer peripheral surfaces, It is substantially perpendicular to the load direction received from the object to be weighed, and is provided on the first surface side that handles the load from the object to be weighed. The adjacent third and fourth strain generating portions are arranged in the load direction. And is provided on the second surface side opposite to the first surface across the through hole, and the strain gauges are disposed in the first to fourth strain generating portions, respectively. It is characterized by that.

  According to an eighth aspect of the present invention, in the load cell unit according to the first or second aspect, the bridge circuit is formed of first and second strain gauges and first and second fixed resistors. The first strain gauge is between the first input terminal and the first output terminal, and the second strain gauge is between the second input terminal and the first output terminal. Are connected between the first input terminal and the second output terminal, and the second fixed resistor is connected between the second input terminal and the second output terminal, respectively. And

  According to a ninth aspect of the present invention, in the load cell unit according to the eighth aspect, the adjacent first and second strain generating portions of the strain generating portions are received from the measured object side of the outer peripheral surface. It is substantially perpendicular to the load direction, provided on the first surface side that handles the load from the weighing object side, and the adjacent third and fourth strain generating portions are substantially perpendicular to the load direction, It is provided on the second surface side opposite to the first surface across the through hole, and the first and second strain gauges are either one of the first surface and the second surface, It arrange | positions at each of the strain generation part provided in this one surface, It is characterized by the above-mentioned.

  The invention according to claim 10 is the load cell unit according to any one of claims 1 to 9, wherein the signal processing unit finely corrects the coarsely corrected bridge output by a second-order or higher order approximation. By doing so, the zero point of the bridge circuit is further compensated.

  The invention according to claim 11 is the load cell unit according to any one of claims 1 to 9, wherein the signal processing unit finely corrects the coarsely corrected bridge output by a second-order or higher order approximation. Thus, the output sensitivity of the bridge circuit is further compensated.

  According to a twelfth aspect of the present invention, in the load cell unit according to any one of the first to ninth aspects, the signal processing unit accurately performs the second or higher order approximation on the coarsely corrected bridge output. The zero point of the bridge circuit is compensated by correction, and the output sensitivity of the bridge circuit is compensated by finely correcting by a second-order or higher order approximation.

  The invention according to claim 13 is a weight sorter, which is a weighing device for weighing the weight of the sorting object to be conveyed, and each sorting object is determined based on the weighing result of the sorting object by the weighing device. The distribution device includes a distribution device, and the weighing device includes: a load cell unit according to any one of claims 1 to 12; and a weighing conveyor that is supported by the load cell unit and conveys each sorting object. It is characterized by having.

  The invention of claim 14 is characterized by comprising the load cell unit according to any one of claims 1 to 12 and an upper plate part supported by the load cell and for loading an object to be measured. To do.

  In the inventions according to claim 1, claim 2, and claim 7 to claim 12, the zero point of the bridge circuit is compensated by the zero compensation element, and the output sensitivity of the bridge circuit is compensated by the strain gauge, The output of the bridge circuit (bridge output) is roughly corrected. The signal processing unit finely corrects the coarsely corrected bridge output based on the detection result of the temperature sensor, and further compensates for the zero point and output sensitivity of the bridge circuit. That is, the bridge circuit is subjected to two types of zero compensation and two types of temperature sensitivity compensation.

  In the inventions according to claims 1, 2, and 7 to 12, the thin-walled strain generating portion has a larger thermal resistance than the other portions of the strain generating body, and the adjacent strain generating portions. The portion sandwiched between the strained portions is not easily affected by the surrounding heat.

  That is, the zero compensation element provided in the portion sandwiched between the adjacent strain generating portions can compensate the zero of the bridge circuit while accurately reflecting the temperature of the strain generating body. Moreover, the temperature sensor provided in the part pinched | interposed into the adjacent strain generating part can detect the temperature of a strain generating body correctly and stably.

  Thereby, the signal processing unit can finely correct the bridge output subjected to the coarse correction related to the zero point and the output sensitivity based on the temperature of the strain generating body detected accurately and stably. That is, a software zero and sensitivity compensation can be further applied to the bridge circuit in which zero compensation and sensitivity compensation are performed in a circuit (hardware) manner. Therefore, the output accuracy of the bridge circuit can be further improved, and as a result, the reproducibility of the measurement result by the load cell unit can be further improved.

  In particular, according to the second aspect of the present invention, the temperature of the strain generating body can be detected based on a change in the resistance value of the temperature sensitive resistor.

  In the inventions according to claims 3 to 7 and 10 to 12, the zero point of the bridge circuit is compensated by the zero compensation element, and the output sensitivity of the bridge circuit is compensated by the temperature sensitive resistor, The output of the bridge circuit (bridge output) is roughly corrected. Further, the signal processing unit finely corrects the coarsely corrected bridge output based on the temperature of the strain generating body detected by the temperature sensitive resistor, and further compensates for the zero point and output sensitivity of the bridge circuit.

  In the inventions according to claims 3 to 7 and claims 10 to 12, the thin-walled strain generating portion has a larger thermal resistance than the other portions of the strain generating body, and the adjacent strain generating portions. The portion sandwiched between the strained portions is not easily affected by the surrounding heat.

  That is, the zero compensation element provided in the portion sandwiched between the adjacent strain generating portions can compensate the zero of the bridge circuit while accurately reflecting the temperature of the strain generating body. In addition, the temperature-sensitive resistor that can be used as a temperature sensor is roughly corrected for the output sensitivity of the bridge circuit while accurately reflecting the temperature of the strain-generating body. The temperature of the strain generating body can be detected accurately and stably.

  Thereby, the signal processing unit can finely correct the bridge output subjected to the coarse correction related to the zero point and the output sensitivity based on the temperature of the strain generating body detected accurately and stably. Therefore, the output accuracy of the bridge circuit can be further improved, and the reproducibility of the measurement result by the load cell unit can be further improved.

  In the inventions according to claims 6 and 10 to 12, the zero point of the bridge circuit is compensated by the zero compensation element, and the output sensitivity of the bridge circuit is compensated by the variable gain amplifying unit. The output (bridge output) is roughly corrected. The compensation calculation unit finely corrects the coarsely corrected bridge output based on the temperature of the strain generating body, and further compensates for the zero point and output sensitivity of the bridge circuit.

  Further, in the inventions according to claims 6 and 10 to 12, the thin-walled strain generating portion has a larger thermal resistance than other portions of the strain generating body, and is sandwiched between adjacent strain generating portions. These parts are not easily affected by the surrounding heat.

  That is, the zero compensation element provided in the portion sandwiched between the adjacent strain generating portions can compensate the zero of the bridge circuit while accurately reflecting the temperature of the strain generating body. In addition, when the switching unit is on the bridge output side, the variable gain amplifying unit determines the temperature of the strain generating body based on the change in the resistance value of the temperature sensitive resistor provided in the portion sandwiched between the adjacent strain generating units. The output sensitivity of the bridge circuit can be roughly corrected while accurately reflecting the above. Further, when the switching unit is set to the reference output side, the compensation calculation unit can accurately and stably detect the temperature of the strain generating body.

  Thus, the compensation calculation unit can finely correct the bridge output subjected to the coarse correction related to the zero point and the output sensitivity based on the temperature of the strain generating body detected accurately and stably. Therefore, the output accuracy of the bridge circuit can be further improved, and the reproducibility of the measurement result by the load cell unit can be further improved.

  In particular, according to the tenth aspect of the invention, it is possible to perform zero point compensation by higher-order approximation of the second or higher order on the bridge output after the coarse correction. Therefore, fine correction can be realized at low cost.

  In particular, according to the invention described in claim 11, output sensitivity compensation can be performed on the bridge output after coarse correction by higher-order approximation of the second or higher order. Therefore, fine correction can be realized at low cost.

  In particular, according to the twelfth aspect of the present invention, the zero point and the output sensitivity compensation can be applied to the bridge output after the coarse correction by the higher-order approximation of the second or higher order. Therefore, fine correction can be realized at low cost.

  According to the invention of claim 13, the bridge circuit of the load cell unit is subjected to circuit-like (hardware) zero and output sensitivity compensation, and software zero and output sensitivity compensation. The weight of each sorting object can be calculated based on the bridge output controlled with high accuracy. Therefore, even when a weighing conveyor that is heavier than the selected object is supported by the load cell unit, such as a weight sorter, the amount of fluctuation in the bridge output due to temperature changes can be reduced. The object can be weighed with good reproducibility.

  According to the invention described in claim 14, the bridge circuit of the load cell unit is subjected to circuit-like (hardware-like) zero and output sensitivity compensation, and software zero and output sensitivity compensation. The weight of each weighing object can be calculated based on the bridge output controlled with high accuracy. Therefore, it is possible to set the minimum scale for the rated capacity of the load cell unit small, and as a result, it is possible to further improve the measurement accuracy (measurement resolution) of the measurement object.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

<1. First Embodiment>
<1.1. Configuration of weight sorter>
FIG. 1 is a front view showing an example of the entire configuration of the weight sorter 1 according to the first embodiment. For example, the weight sorter 1 measures the weight of a product brought in from a previous process such as a bagging process, and distributes the product based on the measurement result. Here, the weight sorter 1 measures the weight of the product under a constant gravitational acceleration, and converts the measured weight into a mass.

  As shown in FIG. 1, the weight sorter 1 mainly includes an intake device 10, a weighing device 20, and a sorting device 60. 1 and the subsequent drawings have an XYZ orthogonal coordinate system in which the Z-axis direction is a vertical direction and the XY plane is a horizontal plane, as necessary, in order to clarify the directional relationship. .

  The take-in device 10 has a take-in conveyor 11 as shown in FIG. The take-in device 10 conveys the sorting object 5 delivered from the upstream device as viewed from the conveying direction AR1 of the sorting object 5 to the weighing device 20.

  The weighing device 20 measures the weight of the sorting object 5 while conveying the sorting object (object to be weighed) 5 delivered from the take-in device 10. As shown in FIG. 1, the weighing device 20 mainly has a weighing conveyor 21 and a load cell unit 30.

  The weighing conveyor 21 is a transport unit that transports each sorting object 5 delivered from the capture device 10 to the sorting device 60. Further, as shown in FIG. 1, the weighing conveyor 21 is supported by the strain body 31 of the load cell unit 30 via the attachment member 25. Therefore, the strain body 31 receives the load of the weighing conveyor 21 and the sorting object 5 conveyed on the weighing conveyor 21.

  The load cell unit 30 is a unit that measures the weight of the sorting object 5 that is an object to be weighed based on a load signal. The detailed configuration of the load cell unit 30 will be described later.

  The sorting device 60 sorts the sorting objects 5 based on the weighing result of the sorting objects 5 by the weighing device 20. As shown in FIG. 1, the sorting device 60 mainly includes a transport conveyor 61 and a lever 62. The transport conveyor 61 is a transport unit that transports the weighing target object 5 passed from the weighing device 20 along the transport direction AR1. The lever 62 is pivotable about a pivot shaft 62a that is substantially perpendicular to the transport direction AR1, and sorts the sorting objects 5 transported by the transport conveyor 61.

  For example, when the measurement result by the weighing device 20 falls within the non-defective range, the lever 62 is rotated so that the length direction thereof is substantially parallel to the transport direction AR1 and is positioned to the side of the transport conveyor 61. . Thereby, the sorting object 5 is delivered to a non-defective product line (not shown) arranged on the extension of the transport direction AR1.

  On the other hand, when the measurement result by the weighing device 20 is out of the non-defective range, the lever 62 is rotated so as to block the conveyance of the selection target object 5. As a result, the sorting object 5 that has reached the lever 62 moves along the lever 62 and is delivered to a defective product line (not shown) provided on the side of the transport conveyor 61.

<1.2. Configuration of load cell unit>
2 and 3 are a front view and a plan view showing an example of the hardware configuration of the load cell unit 30, respectively. FIG. 4 is a surface view showing an example of the configuration of the strain gauge 41. Further, FIG. 5 is a block circuit diagram of the load cell unit 30. As shown in FIGS. 2 to 5, the load cell unit 30 mainly includes a strain generating body 31, a plurality of strain gauges 41 (41a to 41d), a zero compensation element 42, a temperature sensitive resistor 45, and a signal processing unit. 50.

  As shown in FIG. 2, the strain body 31 is a metal block provided with a through hole 32, and is an elastic body formed of a metal such as an aluminum alloy or stainless steel, for example. The strain generating body 31 includes a thin strain generating portion 33 (first to fourth strain generating members) sandwiched between the inner wall surface 32a of the through hole 32 and the outer peripheral surface 35 (including the first and second surfaces 35a and 35b). A plurality of (in this embodiment, four) portions 33a to 33d).

  Here, two adjacent strain generating portions 33a and 33b among the plurality of strain generating portions 33 are substantially perpendicular to the load direction AR2 received from the selection target (object to be weighed) 5, and from the selection target 5 side. It is provided on the first surface (upper surface) 35a side that handles the load. Further, two adjacent strain generating portions 33c and 33d among the plurality of strain generating portions 33 are substantially perpendicular to the load direction AR2, and the second surface (lower surface) opposite to the first surface 35a across the through hole 32. ) 35b.

  Further, a first thick portion 34a thicker than the first and second strain generating portions 33a and 33b is formed at a portion sandwiched between the first and second strain generating portions 33a and 33b. Further, a second thick portion 34b having a thickness greater than those of the third and fourth strain generating portions 33c and 33d is formed in a portion sandwiched between the third and fourth strain generating portions 33c and 33d.

  Thus, when the fixed end 31a of the strain generating body 31 is fixed in the weighing device 20 and a load is applied to the free end 31b side, the first surface (upper surface) 35a side of the first strain generating portion 33a and the first end Compressive stress is applied to the second surface (lower surface) 35b side of the fourth strained portion 33d, and tensile stress is applied to the first surface 35a side of the second strained portion 33b and the second surface 35b side of the third strained portion 33c. Will occur. Therefore, mechanical strain occurs in each of the strain generating portions 33a to 33d.

  In addition, when a load is applied to the free end side 31b, the strain body 31 is deformed into a substantially parallelogram shape and functions as a Roverval mechanism. Therefore, the moment acting on the strain generating body 31 is canceled, and as a result, the weight of the selection object 5 is detected as substantially the same value regardless of the position on the weighing conveyor 21. Thus, the strain body 31 constitutes a Roverval mechanism via the plurality of strain portions 33 provided between the free end 31b to which a load is applied and the fixed end 31a.

  As shown in FIGS. 2 and 3, strain gauges 41 (41 a to 41 d) are arranged on the outer peripheral surface 35 of the corresponding strain generating portion among the plurality of strain generating portions 33. That is, the first and second strain gauges 41a and 41b are provided on the first surface 35a of the first and second strain generating portions 33a and 33b, and the third and fourth strain generating portions 33c and 33d are provided on the third and fourth strain surfaces 33a and 33b. Strain gauges 41c and 41d are bonded to each other.

  As shown in FIG. 4, each strain gauge 41 (41 a to 41 d) has a resistor 40 b such as a photo-etched metal foil in a meandering shape on a base member 40 a made of a thin electric insulator (for example, polyimide resin). Formed. Accordingly, when strain occurs in each strain generating portion 33 (33a to 33d) and the strain is transmitted to the resistor 40b via the base member 40a, a resistance change corresponding to the strain amount occurs in the resistor 40b. .

  Here, in this embodiment, the strain body 31 is thermally expanded as the temperature rises in accordance with its linear expansion coefficient. In addition, the longitudinal elastic modulus (Young's modulus) of the strain body 31 decreases as the temperature increases, and the amount of strain under the same stress increases.

  On the other hand, in the present embodiment, a temperature sensitivity compensation type strain gauge is used as the strain gauge 41. That is, the resistor 40b of the strain gauge 41 of the present embodiment is made of a metal such as a nickel chromium (Ni—Cr) alloy. Further, for the resistor 40b of the strain gauge 41, the mixing ratio of nickel and chromium is set so that the temperature coefficient related to the strain sensitivity becomes a negative value and the longitudinal elastic coefficient increases as the temperature rises. The resistance 40b is adjusted and subjected to a predetermined heat treatment.

  Therefore, even if the strain body 31 expands due to a temperature rise and the strain amount of the strain body 31 with respect to the same load increases due to the temperature rise, the resistance of the strain gauge 41 bonded to the strain body 31 is increased. The values are substantially the same within a predetermined temperature range. As described above, the temperature-sensitive compensation type strain gauge 41 compensates for the thermal expansion of the strain generating body 31 that expands and contracts due to a temperature change, suppresses the zero point change of the bridge circuit 40, and longitudinally results from the temperature change. The output sensitivity of the bridge circuit 40 is compensated by roughly correcting the output of the bridge circuit 40 (hereinafter also referred to as “bridge output”) by compensating for the change amount of the elastic coefficient.

  Here, the output sensitivity compensation of the bridge circuit 40 is compared with the case where the temperature sensitivity compensation type strain gauge 41 is compensated and the case where it is compensated by the temperature sensitive resistance.

  First, when compensating the output sensitivity of a bridge circuit with a temperature sensitive resistor, for example, a self-temperature compensated strain gauge is arranged on each side of the bridge circuit, and a temperature sensitive resistor is connected in series with the input side of the bridge circuit. Connected. In this case, it is necessary that a predetermined time elapses after the voltage is applied to the temperature sensing resistor until the resistance value of the temperature sensing resistor is stabilized when the power is turned on. As a result, the output sensitivity of the bridge circuit 40 cannot be coarsely corrected well until the predetermined time has elapsed.

  On the other hand, in the bridge circuit 40 of the present embodiment, a temperature sensitivity compensation type is used as the strain gauge 41. That is, the output sensitivity of the bridge circuit 40 is roughly corrected not by the temperature-sensitive resistor 45 but by the temperature sensitivity compensation type strain gauge 41. For this reason, the output sensitivity of the bridge circuit 40 is coarsely corrected well even before the above-described predetermined time has elapsed. As a result, when the power is turned on, the output of the bridge circuit 40 is quickly stabilized, and the load cell unit 30 can quickly start the weighing process of the selection target object 5.

  The bridge circuit 40 outputs the weight of the selection target object 5 as a load signal. As shown in FIG. 5, the bridge circuit 40 is mainly formed by first to fourth strain gauges 41a to 41d. That is, (1) the first strain gauge 41a is between the plus input terminal 44a and the plus output terminal 43a, and (2) the second strain gauge 41b is between the plus input terminal 44a and the minus output terminal 43b. (3) A third strain gauge 41c is disposed between the plus output terminal 43a and the minus input terminal 44b, and (4) a fourth strain gauge 41d is disposed between the minus output terminal 43b and the minus input terminal 44b. These strain gauges 41 (41a to 41d) constitute a full bridge. The voltage between the output terminals 43a and 43b is detected as the output of the bridge circuit 40.

  The zero point compensation element 42 (42a to 42d) is formed by winding a resistor (copper wire or nickel wire) having a large temperature coefficient of resistance, and is disposed on any one side of the bridge circuit 40. That is, any one of the zero compensation elements 42a to 42d shown in FIG. 5 is used and connected in series with the corresponding strain gauge 41 (41a, 41c, 41b, 41d). The first zero compensation element 42a is provided on the first thick part 34a on the first surface 35a side (see FIG. 2), and the second zero compensation element 42b is provided on the second thick part 34b on the second surface 35b side (see FIG. 2). 2), the third zero compensation element 42c is provided on the first thick part 34a on the first surface 35a side (not shown), and the fourth zero compensation element 42d is provided on the second thick part 34b on the second surface 35b side (see FIG. It is attached in close contact with either one. The zero compensation element 42 is not limited to a wound resistor, and may be, for example, a chip resistor having the same resistance value and resistance temperature coefficient as the resistor.

  Here, as described above, the strain gauge 41 is a temperature sensitivity compensation type strain gauge. Accordingly, the resistance value of each strain gauge 41 when no load is applied to the strain generating body 31 (no load state) becomes substantially the same value even if the ambient temperature of the strain generating body 31 changes. . Therefore, when the physical properties (for example, resistance value and resistance temperature coefficient) of each strain gauge 41 are substantially the same, the zero point of the bridge circuit 40 is substantially the same even when the ambient temperature changes.

  However, when each strain gauge 41 has an individual difference or when the adhesion state of each strain gauge 41 is different, the zero point of the bridge circuit 40 fluctuates according to a change in the ambient temperature, and as a result, the weighing by the weighing device 20 is performed. The result will be affected by the ambient temperature.

  On the other hand, in the present embodiment, the zero compensation element 42 corresponding to the amount of change of the zero due to the temperature change is disposed on one side of the bridge circuit 40 and is connected in series with the corresponding strain gauge 41. Therefore, the zero point that fluctuates due to the temperature change is compensated according to the temperature of the strain generating body 31, and the output of the bridge circuit 40 is roughly corrected so as to be within a certain range.

  Further, the thin-walled strain-generating portion 33 has a larger thermal resistance than the other portions of the strain-generating body 31, and the portion sandwiched between the adjacent strain-generating portions 33 (thick wall portion 34) is the fixed end 31a side or Less susceptible to thermal influence from the mounting surface on the free end 31b side. Therefore, the zero compensation element 42 provided in the thick portion 34 can compensate the zero of the bridge circuit 40 while accurately reflecting the temperature of the strain generating body 31.

  The arrangement of the zero compensation element 42 is not limited to any one side of the bridge circuit 40. For example, the zero compensation element 42 may be disposed on one side of the bridge circuit 40 and on a diagonal side when viewed from the one side. That is, as the zero compensation element 42, the first and fourth zero compensation elements 42a and 42d may be used, or the second and third zero compensation elements 42b and 42c may be used. That is, the zero compensation element 42 only needs to be arranged on at least one side of the bridge circuit 40.

  Similar to the zero compensation element 42, the temperature sensitive resistor 45 is a resistor having a large resistance temperature coefficient. For example, a nickel (Ni), copper (Cu), or platinum (Pt) material is used for the temperature sensitive resistor 45. As shown in FIG. 2, the temperature-sensitive resistor 45 is attached in close contact with the first thick portion 34a on the first surface 35a side.

  As shown in FIG. 5, one end of the temperature sensitive resistor 45 is electrically connected to the temperature measuring terminal 43c, and the other end is electrically connected to the temperature measuring terminal 43d. The temperature measurement terminal 43c is connected to the positive side of the power supply 46 via a precision resistor 46a provided on the signal processing board 50a, and the temperature measurement terminal 43d is provided via a precision resistor 46b provided on the signal processing board 50a. Are electrically connected to the negative side of the power source 46 respectively.

  Therefore, the load cell unit 30 determines the temperature of the strain generating body 31 based on the voltage across the temperature sensing resistor 45 (voltage between the temperature measuring terminals 43c and 43d) and the resistance value-temperature characteristic of the temperature sensing resistor 45. Can be calculated. Thus, in the present embodiment, the temperature of the strain generating body 31 is detected based on the change in the resistance value of the temperature sensing resistor 45, and the temperature sensing resistor 45 is used as a temperature sensor.

  Further, the temperature-sensitive resistor 45 is in close contact with the thick portion 34 that is not easily affected by the surrounding heat, and the resistance value of the temperature-sensitive resistor 45 varies while accurately reflecting the temperature of the strain-generating body 31. . Therefore, the temperature of the strain generating body 31 is accurately and stably detected based on the change in the resistance value of the temperature sensitive resistor 45.

  Here, in order to improve the S / N ratio of the load signal output from the bridge circuit and improve the weighing accuracy of the selection object, the case where the voltage supplied from the power source to the bridge circuit is increased will be examined. .

  When a self-temperature-compensated strain gauge is placed on each side of the bridge circuit and a temperature-sensitive resistor is connected in series on the positive input side and / or negative input side of the bridge circuit, it is supplied to the bridge circuit. As the voltage increases, the supply voltage to the temperature sensitive resistor increases, and the amount of power consumed by the temperature sensitive resistor increases.

  As a result, the temperature sensitive resistor itself generates heat, and it becomes difficult to accurately measure the temperature of the strain generating body based on the temperature sensitive resistance. In addition, in order to accurately measure the temperature of the strain generating body, a standby time is required until the resistance value of the temperature sensitive resistance is stabilized, and the measurement process cannot be started promptly.

  On the other hand, when a temperature-sensitive compensation type strain gauge is used as in this embodiment, the precision resistors 46a and 46b, the temperature-sensitive resistor 45, and the bridge circuit 40 are connected to the power source 46. Can be connected in parallel. As a result, the supply voltage from the power supply 46 is divided by the precision resistors 46 a and 46 b and the temperature sensitive resistor 45.

  Therefore, by adjusting the resistance values of the precision resistors 46a and 46b and the temperature sensitive resistor 45, it is possible to reduce the heat generation of the temperature sensitive resistor 45 while setting the applied voltage to the bridge circuit 40 higher. As a result, it is possible to improve the weighing accuracy of the selection target object 5 and to quickly start the weighing process.

  The signal processing unit 50 executes signal processing based on a signal (for example, a load signal) from the bridge circuit 40. As shown in FIG. 5, the signal processing unit 50 mainly includes a fixed gain amplification unit 51a, an A / D conversion unit 51b, a memory 53, and a CPU 54. These elements 51a, 51b, 53 and 54 are provided on the signal processing board 50a.

  The fixed gain amplifying unit 51a keeps the output of the bridge circuit 40 detected as an analog signal (voltage between the output terminals 43a and 43b) and the voltage applied to the temperature sensing resistor 45 (voltage between the input terminals 43c and 43d), respectively. Amplification is performed at the amplification degree (including the case where the amplification factor is 1). The A / D converter 51b converts the amplified analog signal output from the fixed gain amplifier 51a into a digital signal. The converted digital signal is input to the CPU 54.

  The memory 53 is a storage unit configured by, for example, a nonvolatile memory, and stores programs, variables, and the like. Further, the CPU 54 executes control according to a program stored in the memory 53. Therefore, according to this program, the CPU 54 can execute conversion processing by the A / D conversion unit 51 b, zero point and output sensitivity compensation calculation processing, weight calculation processing including filtering, and the like at a predetermined timing.

  Here, as shown in FIG. 5, the CPU 54 of the signal processing unit 50 is mainly based on the program stored in the memory 53, and the zero point compensation calculation function and the output sensitivity compensation calculation function (the compensation calculation unit 52 corresponds), A weight calculation processing function (corresponding to the weight calculation unit 55) is realized.

  The compensation calculation unit 52 of the CPU 54 detects the temperature of the bridge output that has been coarsely corrected by compensating the zero point of the bridge circuit 40 by the zero point compensation element 42 and compensating the output sensitivity of the bridge circuit 40 by the strain gauge 41. Fine correction is performed based on the detection result of the resistor 45 (temperature sensor). Thereby, the zero point and output sensitivity of the bridge circuit 40 are further compensated by the compensation calculation unit 52. The fine correction process by the compensation calculation unit 52 will be described later.

  The weight calculation unit 55 of the CPU 54 calculates the weight of the selection object 5 based on the finely corrected bridge output. The sorting device 60 executes the sorting process based on the calculation result of the weight calculation unit 55.

<1.3. Zero compensation by signal processing unit (compensation calculation unit)>
FIG. 6 is a diagram illustrating the relationship between the zero value V of the bridge circuit 40 and the temperature T of the strain generating body 31. The vertical axis in FIG. 6 indicates that when the excitation voltage (supply voltage) from the power supply 46 is set to the voltage value Vs (in this embodiment, Vs = 12 V), the strain generating body 31 is separated from the selection object 5. The zero value V (unit: μV / 12V) when no load is received is shown. Further, the horizontal axis of FIG. 6 indicates the temperature T (unit: ° C.) of the strain body 31. Further, a curve Cz1 in FIG. 6 shows the relationship between the zero value V and the temperature T of the strain generating element 31 when the zero compensation element 42 is not used, and a curve Cz2 shows the zero value V when the zero compensation element 42 is used. The relationship with the temperature T of the strain body 31 is shown respectively.

  Here, it is known that the zero compensation element 42 can effectively compensate for the zero when the variation of the zero value due to the temperature change is linear (primary). However, as shown in FIG. 6, when the temperature characteristic of the zero value V in a predetermined temperature range Ra (for example, −10 ≦ T ≦ 40) has a constant curvature, the zero compensation by the zero compensation element 42 is not performed. The fluctuation range Rz of the zero value is merely improved from Rz1 to Rz2, and cannot be made smaller than Rz2. As a result, it becomes difficult to further improve the reproducibility of the measurement result by the signal processing unit 50 only by using the zero compensation element 42.

  Therefore, in the present embodiment, the signal processing unit 50 finely corrects the zero output and the bridge output whose output sensitivity is roughly corrected by the strain gauge 41 by the second order or higher order approximation. Thus, the amount of change in the zero point of the bridge circuit 40 is further compensated. Specifically, regarding (1) zero compensation, a parameter required for precise correction of the bridge output is calculated, and (2) the zero of the bridge circuit 40 is compensated based on this parameter.

  First, calculation of parameters relating to zero compensation will be described by taking the case of second-order approximation as an example. Prior to attaching the load cell unit 30 to the weighing device 20, the temperature characteristic of the zero point change amount after the coarse correction is obtained. For example, with respect to the bridge circuit 40 using the temperature sensitivity compensation type strain gauge 41 and the zero point compensation element 42, the temperature T of the strain-generating body 31 is set to the temperatures T1, T2, T3 (all within the temperature range Ra) while being in the no-load state. ) To obtain the bridge outputs V1, V2, and V3 at the temperatures T1, T2, and T3.

  Subsequently, by substituting (T, V) = (T1, V1), (T2, V2), (T3, V3) into Equation 1 and solving these three simultaneous equations, parameters a1, b1, c1 Is calculated. Then, the obtained parameters a1, b1, and c1 are stored in the memory 53.

    V = a1 · T · T + b1 · T + c1 (Equation 1)

  The parameters a1 to c1 have different values depending on the individual difference of the strain gauge 41 and the adhesion state of the strain gauge 41 even if the load cell units 30 use the same type of strain gauge 41. That is, the parameters a1 to c1 need to be obtained for each load cell unit 30.

  Next, precise correction using parameters will be described. First, prior to weighing the weight of the sorting object 5, the bridge output when the sorting object 5 is not loaded on the weighing conveyor 21 and the temperature of the strain generating body 31 are obtained. Subsequently, the zero point at the obtained temperature is calculated. The calculated zero point is stored in the memory 53.

  Subsequently, when possible, the compensation calculation unit 52 sets the zero point for each measurement when a predetermined time has elapsed from the time when the previous zero was stored, or when a predetermined number of times have been measured since the previous zero was stored. Find the amount of change. In other words, the temperature T of the strain generating body 31 is detected based on the temperature sensitive resistance 45, and the zero value at the present time is obtained by substituting Equation 1 for the detection result. Then, the compensation calculation unit 52 compensates for the zero point of the bridge circuit 40 based on the amount of change of the zero point from the time when the previous zero point was stored, and executes a fine correction process for the zero point.

<1.4. Compensation of output sensitivity by signal processing unit (compensation calculation unit)>
FIG. 7 shows the relationship between the fluctuation rate ΔV (unit: ppm) of the output sensitivity and the temperature T (unit: ° C.) of the strain body 31 when the same load is applied to the strain body 31. This is based on “20”.

  That is, when the zero value at temperature T is Ve (T) and the output sensitivity at temperature T is V0 (T), the variation rate of the output sensitivity at temperature T can be obtained by Equation 2. Therefore, when T = “20”, the value of ΔV is “0”.

ΔV (T) = ((V0 (T) − (Ve (T)) − (V0 (20) −Ve (20)))
/ (V0 (20) -Ve (20)) (Equation 2)

  Here, the vertical axis in FIG. 7 represents the output sensitivity fluctuation rate ΔV, and the horizontal axis represents the temperature T of the strain generating body 31. Further, the curve Cs1 in FIG. 7 shows the variation rate ΔV of output sensitivity and the temperature of the strain generating body 31 when the bridge circuit 40 shown in FIG. 5 is formed by a self-temperature compensation type strain gauge instead of the temperature sensitivity compensation type. The relationship with T is shown. That is, under the measurement environment of the curve Cs1, the variation rate ΔV when the output sensitivity compensation element such as the temperature sensitive resistance is not used is measured.

  Further, a curve Cs2 in FIG. 7 shows the output sensitivity variation rate ΔV and the strain generating body 31 when the bridge circuit 40 is formed by the strain gauge 41 (temperature sensitivity compensation type gauge) that does not require an output sensitivity compensation element. It shows the relationship with the temperature T.

  As shown in FIG. 7, the fluctuation range Rs2 of the curve Cs2 in the temperature range Ra is smaller than the fluctuation range Rs1 of the curve Cs1. Further, the temperature change of the variation rate ΔV in the curve Cs1 is about 600 (ppm / ° C.), while the temperature change of the variation rate ΔV in the curve Cs2 is about 15 (ppm / ° C.).

  In this way, by forming the bridge circuit 40 with the temperature sensitivity compensation type gauge, the fluctuation range Rs of the output sensitivity can be kept within a certain range without using the temperature sensitive resistor, and the fluctuation is caused by the heat treatment of the metal foil. The temperature change of the rate ΔV can be suppressed to about 15 (ppm / ° C.).

  However, it is known that the temperature sensitivity compensation type gauge can effectively compensate the output sensitivity when the change amount of the variation rate ΔV due to the temperature change is linear (primary). Therefore, as shown in FIG. 7, when the temperature characteristic of the variation rate ΔV in the temperature range Ra has a certain curvature, the variation range of ΔV is made smaller than Rs2 only by the sensitivity compensation by the temperature sensitivity compensation type gauge. I can't. As a result, it is difficult to further improve the measurement accuracy by the signal processing unit 50 only by using the temperature sensitivity compensation type gauge.

  Therefore, in the present embodiment, the signal processing unit 50 uses the zero point compensation element 42 and the strain gauge 41 to roughly correct the zero point and the output sensitivity, and outputs the output sensitivity subjected to the zero point compensation by the fine correction process. The output sensitivity of the bridge circuit 40 is further compensated by performing a fine correction by a second-order or higher-order approximation. Thereby, the temperature change of the fluctuation rate ΔV can be further suppressed to about 1 to 5 (ppm / ° C.).

  Specifically, regarding (1) compensation of output sensitivity, a parameter necessary for precise correction of output sensitivity is calculated, and (2) the output sensitivity of the bridge circuit 40 is compensated based on this parameter.

  First, calculation of parameters relating to output sensitivity compensation will be described by taking the case of second-order approximation as an example. In calculating the parameters, the bridge output that has been coarsely corrected by the zero compensation element 42 and the temperature sensitive resistor 45 and finely corrected for the amount of change of the zero before the load cell unit 30 is attached to the weighing device 20 is output. The temperature characteristic of the sensitivity fluctuation rate ΔV is obtained. That is, while applying a load to the strain generating body 31, the temperature of the strain generating body 31 is changed to temperatures T1, T2, and T3 (all within the temperature range Ra), and each temperature T1, T2 (= “20”). , Output sensitivity fluctuation rates ΔV1, ΔV2, and ΔV3 at T3 are obtained.

  Subsequently, (T, ΔV (T)) = (T1, ΔV1), (T2, ΔV2), (T3, ΔV3) are substituted into Equation 3, and the parameters a2, b2 and c2 are calculated. The obtained parameters a2, b2, and c2 are stored in the memory 53.

    ΔV (T) = a2 · T · T + b2 · T + c2 (Equation 3)

  Note that the parameters a2 to c2 in Equation 3 have different values depending on the individual difference of the strain gauge 41 and the adhesion state of the strain gauge 41 even between the load cell units 30 using the same type of strain gauge 41. That is, the parameters a2 to c2 need to be obtained for each load cell unit 30 as in the parameters a1 to c1.

  Next, precise correction using parameters will be described. In the case where the load of the weighing conveyor 21 (see FIG. 1) and the load of the selection target 5 are applied to the strain generating body 31, the compensation calculation unit 52 calculates the amount of change in the zero point of the coarsely corrected bridge output. Compensate and find the bridge output with fine correction for zero. In addition, the compensation calculation unit 52 detects the temperature T of the strain generating body 31 at the time when the coarsely corrected bridge output is obtained based on the temperature-sensitive resistor 45.

  Subsequently, the compensation calculation unit 52 substitutes the detected temperature T and the parameters a2 to c2 stored in the memory 53 into Equation 3 to obtain the variation rate ΔV (T) of the output sensitivity at the temperature T. Ask.

  Subsequently, the compensation calculation unit 52 calculates the load M (T) at the temperature T based on the bridge output subjected to the fine correction related to the zero point compensation at the temperature T. The load M (T) is calculated based on the relationship between the output sensitivity V0 (T) and the load M (T) obtained in advance through experiments or the like.

  Then, the weight calculator 55 calculates the load M (20) at the reference temperature T = “20” by correcting the load M (T) at the temperature T by the variation rate ΔV (T) at the temperature T. That is, the weight calculator 55 obtains the load M (20) based on the temperature T = “20” based on the load M (T) and the variation rate ΔV (T). Specifically, the load M (20) is obtained by substituting the load M (T) and the variation rate ΔV (T) into Equation 4.

    M (20) = M (T) / (1 + ΔV (T)) (Equation 4)

  Here, the weight Mc of the weighing conveyor 21 (see FIG. 1) of the weight sorter 1 is usually larger than the weight Mt of the sorting object 5. Further, the load of the sorting object 5 and the load of the weighing conveyor 21 (tare) are applied to the strain body 31 of the load cell unit 30 used in the weight sorter 1. Further, the amount of change in the bridge output due to the temperature change increases as the load applied to the strain generating body 31 increases. Therefore, the weighing result by the weighing device 20 of the weight sorter 1 is greatly affected by the change in the ambient temperature as compared with the case where only the load to be weighed 5 is applied.

  On the other hand, the load cell unit 30 of the present embodiment can execute two types of zero compensation and two types of temperature sensitivity compensation, and selects each selection target based on the bridge output controlled with high accuracy. The weight of the object 5 can be calculated. Therefore, it is possible to reduce the influence of the bridge output that fluctuates due to a temperature change, and it is possible to measure the selection target 5 with good reproducibility.

  In addition, when the output sensitivity of the bridge circuit 40 is precisely corrected based on the bridge output when the weight Mc of the weighing conveyor 21 (see FIG. 1) is applied to the load cell unit 30, the weighing conveyor 21 is replaced. Every time the weight Mc changes, it is necessary to recalculate the parameters a2 to c2 of Formula 4 by sending the weight sorter 1 back to the factory and performing a temperature test again. As a result, there has been a problem that man-hours required for recalculation further occur.

  On the other hand, in the present embodiment, the fine correction related to the output sensitivity of the bridge circuit 40 is performed on the bridge output that has been compensated for zero by the compensation calculation unit 52. As a result, the weight Mt of the sorting object 5 is obtained by subtracting the weight Mc (20) of the weighing conveyor 21 from the load M (20) calculated by the weight calculator 55. Therefore, even when the weighing conveyor 21 is replaced, it is not necessary to recalculate the parameters a2 to c2 of Formula 4, and the weight Mt of the selection target object 5 can be obtained efficiently.

<1.5. Advantages of Load Cell Unit and Weight Sorter of First Embodiment>
As described above, the bridge circuit 40 according to the first embodiment is compensated for the zero point and the output sensitivity in a circuit (hardware manner) by the zero point compensation element 42 and the temperature sensitivity compensation type strain gauge 41. . Further, the zero compensation of the software and the output sensitivity are further compensated for the bridge output compensated for in circuit.

  Further, the zero compensation element 42 is provided in the thick portion 34 and can roughly correct the zero of the bridge circuit 40 while accurately reflecting the temperature of the strain generating body 31. Further, like the zero compensation element 42, the temperature sensitive resistor 45 is provided in the thick portion 34, and can detect the temperature of the strain generating body 31 accurately and stably.

  As described above, the signal processing unit 50 can finely correct the bridge output subjected to the coarse correction related to the zero point and the output sensitivity based on the temperature of the strain generating body 31 detected accurately and stably. Therefore, the output accuracy of the bridge circuit 40 can be further improved, and as a result, the reproducibility of the measurement result by the load cell unit 30 can be further improved.

  Further, the weight sorter 1 of the first embodiment can execute two types of zero compensation and two types of output sensitivity compensation, and based on the output of the bridge circuit 40 controlled with high accuracy. The weight of each sorting object 5 can be calculated. Therefore, even when the load of the sorting object 5 and the load of the weighing conveyor 21 (tare) are applied to the strain generating body 31 as in the weight sorter 1, the influence of the bridge output that fluctuates due to the temperature change is affected. Therefore, the selection object 5 can be weighed with good reproducibility.

  Further, in the first embodiment, a temperature sensitivity compensation type strain gauge 41 is used as an output sensitivity compensation element instead of a temperature sensitive resistor connected in series to the bridge circuit 40. Thus, unlike the case where the temperature sensitive resistor is used as an output sensitivity compensating element, the load cell unit 30 quickly stabilizes the output when a voltage is applied to the temperature sensitive resistor and does not need to wait for a predetermined time. . Therefore, the load cell unit 30 can start the weighing process of the sorting object 5 promptly.

  Further, in the first embodiment, a temperature sensitivity compensation type strain gauge is used, and the precision resistors 46 a and 46 b, the temperature sensitive resistor 45, and the bridge circuit 40 are parallel to the power supply 46. It is connected to the. Therefore, the heat generation of the temperature sensitive resistor 45 can be suppressed by adjusting the resistance values of the precision resistors 46 a and 46 b and the temperature sensitive resistor 45. As a result, accurate temperature detection becomes possible, and it is possible to shorten the time until the voltage across the temperature sensing resistor 45 (that is, the output from the temperature sensing resistor 45) stabilizes when the power is turned on. The measurement accuracy of the object 5 can be improved.

<2. Second Embodiment>
Next, a second embodiment of the present invention will be described. Here, the weight sorter 100 of the second embodiment is the same as the weight sorter 1 of the first embodiment except that the configuration of the bridge circuit 140 is different. Therefore, in the following, this difference will be mainly described.

  In addition, in the following description, the same code | symbol is attached | subjected about the component similar to the component in the weight sorter 1 of 1st Embodiment. Since the components with the same reference numerals have already been described in the first embodiment, description thereof will be omitted in the present embodiment.

<2.1. Configuration of load cell unit>
2 and 3 are a front view and a plan view showing an example of the hardware configuration of the load cell unit 130, respectively. FIG. 4 is a surface view showing an example of the configuration of the strain gauge 141. Further, FIG. 8 is a block circuit diagram of the load cell unit 130. As shown in FIG. 2 to FIG. 4 and FIG. 8, the load cell unit 130 mainly includes a strain generating body 31, a plurality of strain gauges 141 (141a to 141d), a zero compensation element 42, and a temperature sensitive resistor 145 ( 145a, 145b) and a signal processing unit 50.

  As shown in FIGS. 2 and 3, strain gauges 141 (141 a to 141 d) are arranged on the outer peripheral surface 35 of the corresponding strain generating portion among the plurality of strain generating portions 33. That is, the first and second strain gauges 141a and 141b are provided on the first surface 35a of the first and second strain generating portions 33a and 33b, and the third and fourth strain generating portions 33c and 33d are provided on the third and fourth strain surfaces. Strain gauges 141c and 141d are bonded to each other.

  As shown in FIG. 4, each strain gauge 141 (141 a to 141 d) has a resistor 140 b such as a photo-etched metal foil serpentine on a thin electric insulator (for example, polyimide resin) base member 140 a. Formed. Accordingly, when strain is generated in each strain generating portion 33 (33a to 33d) and the strain is transmitted to the resistor 140b via the base member 140a, a resistance change corresponding to the strain amount occurs in the resistor 140b. .

  In the present embodiment, a self-temperature compensated strain gauge is used as the strain gauge 141. That is, the resistor 140b of the strain gauge 141 is made of a metal such as a copper nickel (Cu—Ni) alloy, for example. In addition, the resistor 140b of the strain gauge 141 is heat-treated so that its resistance temperature coefficient becomes a predetermined negative value corresponding to the linear expansion coefficient of the strain generating body 31.

  Therefore, when the temperature of the strain generating body 31 rises, the strain generating body 31 expands, the gauge length of the strain gauge 41 bonded to the strain generating body 31 is extended, and the resistance temperature coefficient of the resistor 40b is decreased. Therefore, the resistance value of the strain gauge 141 adhered to the strain generating body 31 is substantially the same within a predetermined temperature range. Thus, the self-temperature compensation type strain gauge 141 can compensate for the thermal expansion of the strain generating body 31 that expands and contracts due to a temperature change, and can suppress the zero point change of the bridge circuit 140.

  The bridge circuit 140 outputs the weight of the selection target object 5 as a load signal. As shown in FIG. 8, the bridge circuit 140 is mainly formed by first to fourth strain gauges 141a to 141d. That is, (1) the first strain gauge 141a is between the plus input terminal 144a and the plus output terminal 143a, and (2) the second strain gauge 141b is between the plus input terminal 144a and the minus output terminal 143b. (3) A third strain gauge 141c is disposed between the plus output terminal 143a and the minus input terminal 144b, and (4) a fourth strain gauge 141d is disposed between the minus output terminal 143b and the minus input terminal 144b. These strain gauges 141 (141a to 141d) constitute a full bridge. Then, the voltage between the output terminals 143a and 143b is detected as the output of the bridge circuit 140.

  The zero point compensation element 42 (42a to 42d) is formed by winding a resistor (copper wire or nickel wire) having a large resistance temperature coefficient, and is disposed on any one side of the bridge circuit 140. That is, any one of the zero compensation elements 42a to 42d shown in FIG. 8 is used and connected in series with the corresponding strain gauge 141 (141a, 141c, 141b, 141d). The first zero compensation element 42a is provided on the first thick part 34a on the first surface 35a side (see FIG. 2), and the second zero compensation element 42b is provided on the second thick part 34b on the second surface 35b side (see FIG. 2). 2), the third zero compensation element 42c is provided on the first thick part 34a on the first surface 35a side (not shown), and the fourth zero compensation element 42d is provided on the second thick part 34b on the second surface 35b side (see FIG. It is attached in close contact with either one. The zero compensation element 42 is not limited to a wound resistor, and may be, for example, a chip resistor having the same resistance value and resistance temperature coefficient as the resistor.

  Here, as described above, a self-temperature compensated strain gauge is used for the strain gauge 141. As a result, the resistance value of each strain gauge 141 when no load is applied to the strain generating body 31 (the unloaded state) becomes substantially the same value even if the ambient temperature of the strain generating body 31 changes. . Therefore, when the physical properties (for example, the resistance value and resistance temperature coefficient of the resistor 140b) of each strain gauge 141 are substantially the same, the zero point of the bridge circuit 140 is substantially the same even when the ambient temperature changes.

  However, when each strain gauge 141 has an individual difference, or when the adhesion state of each strain gauge 141 is different, the zero point of the bridge circuit 140 fluctuates according to a change in the ambient temperature. The result will be affected by the ambient temperature.

  On the other hand, in the present embodiment, the zero point compensation element 42 corresponding to the amount of change of the zero point due to the temperature change is disposed on one side of the bridge circuit 140 and is connected in series with the corresponding strain gauge 141. Therefore, the zero point that fluctuates due to a temperature change is compensated according to the temperature of the strain generating body 31, and the output of the bridge circuit 140 is roughly corrected so as to be within a certain range.

  Further, the thin-walled strain-generating portion 33 has a larger thermal resistance than the other portions of the strain-generating body 31, and the portion sandwiched between the adjacent strain-generating portions 33 (thick wall portion 34) is the fixed end 31a side or Less susceptible to thermal influence from the mounting surface on the free end 31b side. Therefore, the zero compensation element 42 provided in the thick portion 34 can compensate the zero of the bridge circuit 140 while accurately reflecting the temperature of the strain generating body 31.

  The arrangement of the zero compensation element 42 is not limited to any one side of the bridge circuit 140. For example, the zero compensation element 42 may be arranged on one side of the bridge circuit 140 and on a diagonal side when viewed from the one side. That is, as the zero compensation element 42, the first and fourth zero compensation elements 42a and 42d may be used, or the second and third zero compensation elements 42b and 42c may be used. That is, the zero compensation element 42 may be disposed on at least one side of the bridge circuit 140.

  Similar to the zero compensation element 42, the temperature sensitive resistor 145 (145a, 145b) is a resistor having a large resistance temperature coefficient. For example, a nickel (Ni) based material is used for the first temperature sensitive resistor 145a, and a copper (Cu) based material is used for the second temperature sensitive resistor 145b.

  As shown in FIG. 2, the first temperature sensing resistor 145a is on the first thick part 34a on the first surface 35a side, and the second temperature sensing resistor 145b is on the second thick part 34b on the second surface 35b side, respectively. It is attached closely. Further, as shown in FIG. 8, the first temperature sensing resistor 145a is a terminal 144a on the plus input side 147 of the bridge circuit 140, and the second temperature sensing resistor 145b is a terminal 144b on the minus input side 148 of the bridge circuit 140, respectively. Electrically connected.

  Here, when the stress acting on the strain generating body 31 is σ and the longitudinal elastic modulus of the strain generating body 31 is E, the strain amount ε 1 generated in the strain generating section 33 can be obtained by Equation 5.

    ε1 = σ / E (Equation 5)

  Further, when the strain amount of the strain gauge 141 due to stress is ε2, the resistance value of the strain gauge 141 is R, and the change amount of the resistance value of the strain gauge 141 due to stress is ΔR, the gauge factor of the strain gauge 141 is Can be expressed as:

    K = ΔR / (R · ε2) (Equation 6)

  Then, the strain gauge 141 is bonded to the outer peripheral surface 35 (35a, 35b) of the strain generating portion 33, and if the strain amount 33 of the strain generating portion 33 and the strain amount ε2 of the strain gauge 141 are substantially the same, the gauge 141 is provided. The change amount ΔR of the resistance value can be expressed as shown in Equation 7.

    ΔR = R · σ · K / E (Expression 7)

  The longitudinal elastic modulus E usually decreases as the ambient temperature increases. That is, even if the load applied to the strain generating body 31 is the same, the strain generated in each strain generating portion 33 increases as the temperature rises.

  Therefore, when the longitudinal elastic modulus E decreases as the ambient temperature of the strain generating body 31 increases, the change amount ΔR of the resistance value of the gauge 141 increases as can be seen from Equation 7.

  On the other hand, the resistance value of the temperature-sensitive resistor 145 increases as the ambient temperature increases, and the voltage applied to the bridge circuit 140 (voltage between the input terminals 144a and 144b) decreases.

  As described above, when the temperature-sensitive resistor 145 is connected to the plus and minus input sides 147 and 148 of the bridge circuit 140, the applied voltage of the bridge circuit 140 is adjusted according to the ambient temperature of the strain generating body 31. Therefore, the output change of the bridge circuit 140 due to the temperature change is suppressed, and the output sensitivity of the bridge circuit 40 is electrically corrected.

  That is, when the temperature sensitive resistor 145 is connected to the positive and negative input sides 147 and 148 of the bridge circuit 140, the fluctuation range Rs2 of the output sensitivity fluctuation rate ΔV is connected to the temperature sensitive resistor 145 as shown in FIG. It becomes smaller than the fluctuation range Rs1 when not. Further, the temperature change of the variation rate ΔV in the curve Cs1 is about 600 (ppm / ° C.), while the temperature change of the variation rate ΔV in the curve Cs2 is about 15 (ppm / ° C.).

  In this way, by connecting the temperature sensitive resistor 145 to the plus and minus input sides 147 and 148 of the bridge circuit 140, the fluctuation range Rs of the output sensitivity can be kept within a certain range, and the temperature change of the fluctuation rate ΔV. Can be suppressed to about 15 (ppm / ° C.).

  Further, the temperature coefficient of resistance of the temperature sensitive resistor 145 used in the present embodiment is larger than that of each strain gauge 141. Thereby, when compared with the temperature sensitive resistor 145, each strain gauge 141 can be regarded as a precision resistor. Therefore, based on the voltage applied to the bridge circuit 140 (voltage between the input terminals 144a and 144b), the excitation voltage of the power supply 46, and the resistance value-temperature characteristic of the temperature sensitive resistor 145, the temperature of the strain generating body 31 is Calculated. That is, in the present embodiment, the temperature of the strain generating body 31 is detected based on the change in the resistance value of the temperature sensitive resistor 145.

  As described above, the temperature-sensitive resistor 145 is used not only as a sensitivity correction unit that compensates for the output sensitivity of the bridge circuit 140 due to a temperature change, but also as a temperature sensor of the strain generating body 31. Therefore, the number of parts of the load cell unit 130 can be reduced, and the manufacturing cost of the load cell unit 130 can be reduced.

  Furthermore, the temperature-sensitive resistor 145 is in close contact with the thick portion 34 that is not easily affected by heat from the mounting surface on the fixed end 31a side or the free end 31b side. Thereby, the resistance value of the temperature-sensitive resistor 145 varies while accurately reflecting the temperature of the strain generating body 31. Therefore, the temperature of the strain generating body 31 is accurately and stably detected based on the change in the resistance value of the temperature sensitive resistor 145.

  The signal processing unit 50 performs signal processing based on a signal (for example, a load signal) from the bridge circuit 140. As shown in FIG. 8, the signal processing unit 50 mainly includes a fixed gain amplification unit 51a, an A / D conversion unit 51b, a memory 53, and a CPU 54. These elements 51a, 51b, 53 and 54 are provided on the signal processing board 50a.

  The fixed gain amplifying unit 51a sets the output voltage (voltage between the output terminals 143a and 143b) detected as an analog signal and the voltage applied to the bridge circuit 140 (voltage between the input terminals 144a and 144b) to be constant. Amplification is performed at the amplification degree (including the case where the amplification factor is 1). The A / D converter 51b converts the amplified analog signal output from the fixed gain amplifier 51a into a digital signal. The converted digital signal is input to the CPU 54.

  The memory 53 is a storage unit configured by, for example, a nonvolatile memory, and stores programs, variables, and the like. Further, the CPU 54 executes control according to a program stored in the memory 53. Therefore, the CPU 54 can execute the conversion process by the A / D conversion unit 51b, the zero point and output sensitivity compensation calculation process, the weight calculation process, and the like at a predetermined timing according to this program.

  Here, as shown in FIG. 8, the CPU 54 of the signal processing unit 50 mainly has a zero point compensation calculation function and an output sensitivity compensation calculation function (compensation calculation unit 52 corresponds) based on the program stored in the memory 53. A weight calculation processing function (corresponding to the weight calculation unit 55) is realized.

  The compensation calculation unit 52 of the CPU 54 calculates the temperature of the strain generating body 31 based on the detection result by the temperature sensitive resistor 145. In addition, the compensation calculation unit 52 compensates for the bridge output that has been coarsely corrected by compensating the zero point of the bridge circuit 140 by the zero point compensation element 42 and compensating the output sensitivity of the bridge circuit 140 by the temperature sensing resistor 145. Fine correction is performed based on the temperature of the strain body 31 detected by the temperature resistor 145. As a result, the zero point and output sensitivity of the bridge circuit 140 are further compensated by the compensation calculation unit 52 (see Equations 1 and 3), and the temperature change of the variation rate ΔV is further suppressed to about 1 to 5 (ppm / ° C.). Is done.

  The weight calculation unit 55 of the CPU 54 calculates the weight of the selection target object 5 based on the output of the bridge circuit 140 that has been finely corrected. The sorting device 60 executes the sorting process based on the calculation result of the weight calculation unit 55.

<2.2. Advantages of Load Cell Unit and Weight Sorter of Second Embodiment>
As described above, in the second embodiment, circuit (hardware) zero compensation and sensitivity compensation are performed by the temperature compensation resistor 145 connected in series to the zero compensation element 42 and the bridge circuit 140. Further, the zero compensation of the software and the output sensitivity are further compensated for the bridge output compensated for in circuit.

  The zero compensation element 42 is provided in the thick portion 34 and can compensate the zero of the bridge circuit 140 while accurately reflecting the temperature of the strain generating body 31. Further, the temperature-sensitive resistor 145 is provided in the thick portion 34, similarly to the zero compensation element 42. Accordingly, the output sensitivity of the bridge circuit 140 can be compensated while accurately reflecting the temperature of the strain generating body 31, and the temperature of the strain generating body 31 can be detected accurately and stably. Therefore, the output accuracy of the bridge circuit 140 can be further improved, and as a result, the reproducibility of the measurement result by the load cell unit 30 can be further improved.

  The weight sorter 100 according to the second embodiment can execute two types of zero compensation and two types of temperature sensitivity compensation based on the output of the bridge circuit 140 controlled with high accuracy. The weight of each sorting object 5 can be calculated. Therefore, even when the load of the sorting object 5 and the load of the weighing conveyor 21 (tare) are applied to the strain generating body 31 as in the weight sorter 100, the influence of the bridge output that fluctuates due to the temperature change is affected. Therefore, the selection object 5 can be weighed with good reproducibility.

  Furthermore, in the second embodiment, the temperature sensitive resistor 145 (145a, 145b) is connected in series to the plus and minus input sides 147, 148 of the bridge circuit 140. Accordingly, the temperature-sensitive resistor 145 not only serves as a sensitivity compensation unit that compensates for the change in the longitudinal elastic modulus of the strain generating body due to temperature fluctuations and corrects the output of the bridge circuit 140, but also as a temperature sensor for the strain generating body 31 Can be used. Therefore, the number of parts of the load cell unit 130 can be reduced, and the manufacturing cost of the load cell unit can be reduced.

<3. Third Embodiment>
Next, a third embodiment of the present invention will be described. Here, the weight sorter 200 of the third embodiment is the same as the weight sorter 1 of the first embodiment except that the configuration of the bridge circuit 240 is different. Therefore, in the following, this difference will be mainly described.

  In addition, in the following description, the same code | symbol is attached | subjected about the component similar to the component in the weight sorter 1 of 1st Embodiment. Since the components with the same reference numerals have already been described in the first embodiment, description thereof will be omitted in the present embodiment.

<3.1. Configuration of load cell unit>
2 and 3 are a front view and a plan view showing an example of the hardware configuration of the load cell unit 230, respectively. FIG. 4 is a surface view showing an example of the configuration of the strain gauge 241. Further, FIG. 9 is a block circuit diagram of the load cell unit 230. As shown in FIGS. 2 to 4 and 9, the load cell unit 230 mainly includes a strain generating body 31, a plurality of strain gauges 241 (241 a and 241 b), a zero compensation element 242, a temperature sensitive resistor 45, and the like. And a signal processing unit 50.

  As shown in FIGS. 2 and 3, strain gauges 241 (241 a and 241 b) are arranged on the outer peripheral surface 35 of the corresponding strain-generating part among the plurality of strain-generating parts 33. That is, the first and second strain gauges 241a and 241b are bonded to the first surfaces 35a of the first and second strain generating portions 33a and 33b.

  Note that the arrangement of the strain gauges 241 is not limited to this. For example, the second and first strain gauges 241b and 241a may be bonded to the second surface 35b of the third and fourth strain generating portions 33c and 33d. That is, each of the first and second strain gauges 241a and 241b has a strain generating portion provided on one of the first surface 35a (upper surface) and the second surface 35b (lower surface). It suffices if they are arranged.

  Here, as each strain gauge 241 (241a, 241b), a temperature sensitivity compensation type similar to that of the strain gauge 41 of the first embodiment is used. Therefore, the strain gauge 241 compensates for the thermal expansion of the strain generating body 31 that expands and contracts due to a temperature change, suppresses the zero point change of the bridge circuit 240, and compensates the amount of change in the longitudinal elastic modulus due to the temperature change. Thus, the output change of the bridge circuit 240 can be suppressed.

  The bridge circuit 240 outputs the weight of the selection target object 5 as a load signal. As shown in FIG. 9, the bridge circuit 240 is mainly formed by first and second strain gauges 241a and 241b and first and second fixed resistors 246c and 246d. That is, (1) the first strain gauge 241a is provided between the plus input terminal 44a (first input terminal) and the plus output terminal 243a (first output terminal), and (2) the plus output terminal 243a and the minus input terminal 44b. A second strain gauge 241b is provided between the second input terminal and (3) a first fixed resistor 246c is provided between the positive input terminal 44a and the negative output terminal 243b (second output terminal). ) A second fixed resistor 246d is arranged between the minus output terminal 243b and the minus input terminal 44b, and these strain gauges 241 (241a, 241b) constitute a half bridge. The voltage between the output terminals 243a and 243b is detected as the output of the bridge circuit 240.

  The zero compensation element 242 (242a, 242b) is formed by winding a resistor (copper wire or nickel wire) having a large resistance temperature coefficient, like the zero compensation device 42 of the first embodiment. As shown in FIG. 2, one of the first and second zero compensation resistors 242a is attached in close contact with the first thick portion 34a on the first surface 35a side. Also, as shown in FIG. 9, the zero compensation element 242 (242a, 242b) is connected in series with one of the strain gauges 241 (241a, 241b) arranged on one side of the bridge circuit 240. The zero compensation element 242 is not limited to a wound resistor, and may be, for example, a chip resistor having the same resistance value and resistance temperature coefficient as the resistor.

  Here, as described above, the strain gauge 241 is a temperature sensitivity compensation type strain gauge. However, when each strain gauge 241 has an individual difference, or when the adhesion state of each strain gauge 241 is different, the zero point of the bridge circuit 240 fluctuates according to a change in the ambient temperature. The result will be affected by the ambient temperature.

  On the other hand, in the present embodiment, the zero compensation element 242 corresponding to the amount of change of the zero due to the temperature change is arranged on one side of the bridge circuit 240 and is connected in series with the corresponding strain gauge 241. Therefore, the zero compensation element 242 roughly corrects the zero that fluctuates due to the temperature change according to the temperature of the strain generating body 31.

  Further, the thin-walled strain-generating portion 33 has a larger thermal resistance than the other portions of the strain-generating body 31, and the portion sandwiched between the adjacent strain-generating portions 33 (thick wall portion 34) is the fixed end 31a side or Less susceptible to thermal influence from the mounting surface on the free end 31b side. Therefore, the zero compensation element 242 provided in the thick portion 34 can compensate the zero of the bridge circuit 240 while accurately reflecting the temperature of the strain generating body 31.

  The temperature sensitive resistor 45 is a resistor having a large resistance temperature coefficient, like the zero compensation element 242. As shown in FIG. 2, the temperature-sensitive resistor 45 is attached in close contact with the first thick portion 34a on the first surface 35a side. The resistance temperature coefficient of the temperature sensitive resistor 45 is larger than that of the precision resistors 46a and 46b (see FIG. 9) provided on the signal processing board 50a.

  Therefore, the temperature of the strain-generating body 31 can be calculated based on the voltage across the temperature-sensitive resistor 45 (the voltage between the temperature measuring terminals 43c and 43d) and the resistance value-temperature characteristic of the temperature-sensitive resistor 45. . Thus, in the present embodiment, the temperature of the strain generating body 31 is detected based on the change in the resistance value of the temperature sensing resistor 45, and the temperature sensing resistor 45 is used as a temperature sensor.

  Further, the temperature-sensitive resistor 45 is in close contact with the thick portion 34 that is not easily influenced by heat from the mounting surface on the fixed end 31a side or the free end 31b side. It fluctuates while accurately reflecting the temperature of the body 31. Therefore, the temperature of the strain generating body 31 is accurately and stably detected based on the change in the resistance value of the temperature sensitive resistor 45.

  Here, the bridge circuit 240 of the present embodiment and the bridge circuit formed by the strain gauge 141 used in the second embodiment instead of the strain gauge 241 will be considered. As described above, the strain gauge 141 is a self-compensating strain gauge, and it is necessary to connect the temperature-sensitive resistor 145 (145a, 145b) for sensitivity correction to the input side of the bridge circuit (FIG. 8). reference).

  However, the resistance temperature characteristic of the strain gauge 141 is about 3 (ppm / ° C.), the resistance temperature coefficient of the fixed resistors 246c and 246d is 25 (ppm / ° C.), and the relative resistance temperature coefficient is about 5 (ppm / ° C.). It is. Therefore, the voltage applied to the bridge circuit (that is, the voltage between the input terminals) is affected not only by the resistance value fluctuation of the temperature sensitive resistor 145 due to the temperature change but also by the resistance value fluctuation of the fixed resistors 246c and 246d. It will be.

  Therefore, in the half-bridge type bridge circuit formed by the two self-temperature compensation type strain gauges 141 and the fixed resistors 246c and 246d, the output sensitivity is improved even if the temperature-sensitive resistor 145 connected in series is used. It may not be possible to correct.

  On the other hand, in the present embodiment, a temperature sensitivity compensation type strain gauge 241 is used as a strain gauge, and it is not necessary to provide a temperature-sensitive resistor for sensitivity correction on the input sides 47 and 48 of the bridge circuit 240. . Therefore, even when the half-bridge type bridge circuit 240 is formed, the output sensitivity can be corrected favorably.

  In the present embodiment, the precision resistors 46 a and 46 b, the temperature sensitive resistor 45, and the bridge circuit 240 are connected in parallel to the power supply 46. As a result, the supply voltage from the power source 46 is divided by the precision resistors 46 a and 46 b and the temperature sensitive resistor 45. Therefore, the heat generation of the temperature sensitive resistor 45 can be suppressed by adjusting the resistance values of the precision resistors 46 a and 46 b and the temperature sensitive resistor 45. As a result, accurate temperature detection becomes possible, and it is possible to shorten the time until the voltage across the temperature sensing resistor 45 (that is, the output from the temperature sensing resistor 45) stabilizes when the power is turned on. The measurement accuracy of the object 5 can be improved.

  The signal processing unit 50 executes signal processing based on a signal (for example, a load signal) from the bridge circuit 240. As shown in FIG. 9, the signal processing unit 50 mainly includes a fixed gain amplification unit 51a, an A / D conversion unit 51b, a memory 53, and a CPU 54. These elements 51a, 51b, 53 and 54 are provided on the signal processing board 50a.

  The memory 53 is a storage unit configured by, for example, a nonvolatile memory, and stores programs, variables, and the like. Further, the CPU 54 executes control according to a program stored in the memory 53. Therefore, the CPU 54 can execute the conversion process by the A / D conversion unit 51b, the zero point and output sensitivity compensation calculation process, the weight calculation process, and the like at a predetermined timing according to this program.

  Here, as shown in FIG. 9, the CPU 54 of the signal processing unit 50 is mainly based on the program stored in the memory 53, the zero point compensation calculation function and the sensitivity compensation calculation function (the compensation calculation unit 52 corresponds), the weight An arithmetic processing function (corresponding to the weight calculation unit 55) is realized.

  The fixed gain amplifying unit 51a outputs the output voltage of the bridge circuit 240 detected as an analog signal (the voltage between the output terminals 243a and 243b) and the voltage across the temperature sensing resistor 45 (that is, the output from the temperature sensing resistor 45). Amplification is performed at a constant amplification factor (including the case where the amplification factor is 1). The A / D converter 51b converts the amplified analog signal output from the fixed gain amplifier 51a into a digital signal. The converted digital signal is input to the CPU 54.

  The compensation calculation unit 52 of the CPU 54 detects the temperature of the bridge output that has been coarsely corrected by compensating the zero point of the bridge circuit 240 by the zero point compensation element 42 and compensating the output sensitivity of the bridge circuit 240 by the strain gauge 241. Fine correction is performed based on the detection result of the resistor 45 (temperature sensor). Thereby, the zero point and output sensitivity of the bridge circuit 240 are further compensated by the compensation calculation unit 52 (see Equations 1 and 3).

  The weight calculation unit 55 of the CPU 54 calculates the weight of the selection target object 5 based on the output of the bridge circuit 240 that has been precisely corrected. The sorting device 60 executes the sorting process based on the calculation result of the weight calculation unit 55.

<3.2. Advantages of Load Cell Unit of Third Embodiment>
As described above, the bridge circuit 240 according to the third embodiment is circuit-like (hardware-like) by the zero-point compensation element 42 and the temperature sensitivity compensation type strain gauge 241 as in the first embodiment. Zero compensation and sensitivity compensation are performed. Further, the zero compensation of the software and the output sensitivity are further compensated for the bridge output compensated for in circuit.

  The zero compensation element 42 is provided in the thick portion 34 and can roughly correct the zero of the bridge circuit 240 while accurately reflecting the temperature of the strain generating body 31. Further, the temperature-sensitive resistor 45 is provided in the thick portion 34 similarly to the zero compensation element 42, and can detect the temperature of the strain generating body 31 accurately and stably.

  Therefore, in the third embodiment, the output accuracy of the bridge circuit 240 can be further improved, and as a result, the reproducibility of the measurement result by the load cell unit 230 can be further improved.

  In addition, the load cell unit 230 of the third embodiment can execute two types of zero compensation and two types of temperature sensitivity compensation, as in the first embodiment, and is controlled with high accuracy. The weight of each selection object 5 can be calculated based on the output of the bridge circuit 240. Therefore, even when the load of the sorting object 5 and the load of the weighing conveyor 21 (tare) are applied to the strain generating body 31 as in the weight sorter 200, the influence of the bridge output that fluctuates due to the temperature change is affected. Therefore, the selection object 5 can be weighed with good reproducibility.

  Furthermore, in this embodiment, a temperature sensitivity compensation type strain gauge is used, and the precision resistors 46a and 46b, the temperature sensitive resistor 45 and the bridge circuit 240 are connected in parallel to the power supply 46. ing. Therefore, the heat generation of the temperature sensitive resistor 45 can be suppressed by adjusting the resistance values of the precision resistors 46 a and 46 b and the temperature sensitive resistor 45. As a result, accurate temperature detection becomes possible, and it is possible to shorten the time until the voltage across the temperature sensing resistor 45 (that is, the output from the temperature sensing resistor 45) stabilizes when the power is turned on. The measurement accuracy of the object 5 can be improved.

<4. Fourth Embodiment>
Next, a fourth embodiment of the present invention will be described. Here, the weight sorter 400 according to the fourth embodiment is different from the second method except that the signal acquisition method from the bridge circuit 140 is different from the signal processing unit. This is the same as the weight sorter 100 of the embodiment. Therefore, in the following, this difference will be mainly described.

  In addition, in the following description, the same code | symbol is attached | subjected about the component similar to the component in the weight sorter 100 of 2nd Embodiment. Since the components with the same reference numerals have already been described in the second embodiment, description thereof will be omitted in this embodiment.

<4.1. Configuration of load cell unit>
2 and 3 are a front view and a plan view showing an example of the hardware configuration of the load cell unit 430, respectively. FIG. 4 is a surface view showing an example of the configuration of the strain gauge 141. Further, FIG. 10 is a block circuit diagram of the load cell unit 430. As shown in FIGS. 2 to 4 and 10, the load cell unit 430 mainly includes a strain generating body 31, a plurality of strain gauges 141 (141 a to 141 d), a zero compensation element 42, and a temperature sensitive resistor 445. , A plurality (four in this embodiment) of precision resistors 446 (446a to 446d) and a signal processing unit 450 are provided. Here, as described in the second embodiment, a self-temperature compensation type strain gauge is used as the strain gauge 141.

  The temperature sensitive resistor 445 is a resistor having a large resistance temperature coefficient, similarly to the temperature sensitive resistor 145 of the second embodiment. For example, a nickel (Ni) -based, copper (Cu) -based, or platinum (Pt) -based material is used for the temperature sensitive resistor 445. As shown in FIG. 2, the temperature-sensitive resistor 445 is attached in close contact with the first thick portion 34a on the first surface 35a side.

  Each of the precision resistors 446a to 446d is a resistor having a small resistance variation due to a temperature change. As shown in FIG. 10, the precision resistors 446a to 446c are provided on the signal processing board 50a, and are electrically connected in this order from the top. The precision resistor 446a is electrically connected to the plus side of the power source 46, and the precision resistor 446c is electrically connected to the minus side of the power source 46. Furthermore, as shown in FIG. 10, the precision resistor 446d is electrically connected to the temperature sensitive resistor 445.

  The switching unit 448 (448a, 448b) is a so-called selector switch. As shown in FIG. 10, the switching unit 448a is switched to the plus output terminal 143a side and the switching unit 448b is switched to the minus output terminal 143b side (that is, each switching unit 448 is switched to the lower side: The bridge output of the bridge circuit 140 is input to the variable gain amplifying unit 451a.

  On the other hand, when the switching unit 448a is switched to the reference voltage terminal 443c side and the switching unit 448b is switched to the reference voltage terminal 443d side (that is, each switching unit 448 is switched to the upper side), variable gain amplification is performed. The voltage across the precision resistor 446b (that is, the output from the precision resistor 446b) is input to the part 451a. Here, as will be described later, the voltage across the precision resistor 446 b is used as a reference output having a substantially constant value in the temperature detection of the strain generating body 31.

  As described above, each switching unit 448 can switch between the bridge output and the reference output and input the variable output to the variable gain amplifying unit 451a.

  The signal processing unit 450 performs predetermined signal processing on the input signal. As shown in FIG. 10, the signal processing unit 450 mainly includes a variable gain amplification unit 451a, an A / D conversion unit 51b, a memory 53, and a CPU 54. These elements 451a, 51b, 53 and 54 are provided on the signal processing board 50a.

  The variable gain amplifying unit 451a is configured by an instrumentation amplifier, for example, and is connected to a temperature sensitive resistor 445 and a precision resistor 446d as shown in FIG. Thereby, the amplification degree of the variable gain amplifier 451a is controlled based on the resistance value of the temperature sensitive resistor 445 corresponding to the temperature change of the strain generating body 31. The variable gain amplifying unit 451a amplifies the input signal based on the amplification degree.

  The A / D converter 51b converts the amplified analog signal output from the variable gain amplifier 451a into a digital signal. The converted digital signal is input to the CPU 54.

  Here, the longitudinal elastic modulus (Young's modulus) of the strain generating body 31 decreases as the temperature rises, and the amount of strain under the same stress increases. Therefore, when the temperature rises, the output sensitivity of the bridge circuit 140 increases. On the other hand, in the present embodiment, the amplification degree of the variable gain amplifying unit 451a is set so as to decrease as the temperature of the strain generating body 31 increases (the resistance value of the temperature sensitive resistor 445 increases accordingly). ing.

  Accordingly, an appropriate temperature-sensitive resistor 445 is selected in advance, and each switching unit 448 is switched to the bridge output side (lower side), and the bridge output of the bridge circuit 140 is input to the variable gain amplification unit 451a as an input signal. In this case, the variable gain amplifying unit 451a can roughly correct the bridge output by compensating for the amount of change in the longitudinal elastic coefficient of the strain generating body 31 due to the temperature change. As a result, the output sensitivity of the bridge circuit 140 is compensated.

  That is, when the variable gain amplifying unit 451a electrically connected to the temperature sensitive resistor 445 is used, as shown in FIG. 7, the fluctuation range Rs2 of the output sensitivity fluctuation rate ΔV is equal to the temperature sensitive resistor 445 and the variable gain. This is smaller than the fluctuation range Rs1 when the amplifying unit 451a is not used. Further, the temperature change of the variation rate ΔV in the curve Cs1 is about 600 (ppm / ° C.), while the temperature change of the variation rate ΔV in the curve Cs2 is about 15 (ppm / ° C.).

  Thus, by using the temperature-sensitive resistor 445 and the variable gain amplifying unit 451a, the fluctuation range Rs of the output sensitivity can be kept within a certain range, and the temperature change of the fluctuation rate ΔV is 15 (ppm / ° C. ) To a certain extent.

  On the other hand, when each switching unit 448 is switched to the reference output side (upper side) and the reference output is input to the variable gain amplifying unit 451a as the input signal, the variable gain amplifying unit 451a An output signal corresponding to the resistance value of 445 is output.

  Here, the timing for switching each switching unit 448 between the reference output side (temperature detection mode) and the bridge output side (bridge output detection mode) will be described. 11 and 12 are diagrams for explaining the switching timing between the bridge output detection mode and the temperature detection mode.

  For example, as shown in FIG. 11, the operation of each switching unit 448 may be controlled so that the detection mode is switched to the temperature detection mode at regular intervals, and the temperature of the strain body 31 is measured at regular intervals. . In addition, as shown in FIG. 12, the operation of each switching unit 448 is controlled so that the temperature detection mode is switched at regular intervals during the non-measurement period and the bridge output detection mode is set when the measurement process is executed. May be.

  In the present embodiment, digital filter processing is performed on the output signal of the A / D converter 51b. Therefore, the delay time associated with the filter processing does not occur, and both modes can be switched at a predetermined interval as shown in FIGS.

  The compensation computation unit 52 of the CPU 54 executes compensation computation processing based on the output signal from the variable gain amplification unit 451a. For example, when the switching unit 448 is switched to the reference output side (upper side) and a reference output is input as an input signal of the variable gain amplification unit 451a, the compensation calculation unit 52 is output from the variable gain amplification unit 451a. Based on the digitized signal digitally converted by the A / D converter 51b, the temperature of the strain generating body 31 is calculated.

  When the switching unit 448 is switched to the bridge output side and a bridge output is input as an input signal of the variable gain amplifying unit 451a, the compensation calculation unit 52 finely corrects the coarsely corrected bridge output.

  That is, the zero point is compensated by the zero point compensation element 42, and the output sensitivity is compensated by the variable gain amplifying unit 451a, whereby the bridge output is roughly corrected. The coarsely corrected bridge output is finely corrected based on the detection result of the temperature sensitive resistor 445 used as the temperature sensor. That is, the zero point and output sensitivity of the bridge circuit 140 are further compensated (see Equations 1 and 3), and the temperature change of the variation rate ΔV is further suppressed to about 1 to 5 (ppm / ° C.).

  The weight calculation unit 55 of the CPU 54 calculates the weight of the selection target object 5 based on the output of the bridge circuit 140 that has been finely corrected. The sorting device 60 executes the sorting process based on the calculation result of the weight calculation unit 55.

<4.2. Advantages of Load Cell Unit and Weight Sorter of Fourth Embodiment>
As described above, in the fourth embodiment, circuit-like (hardware-like) zero compensation and sensitivity compensation are performed by the zero compensation element 42 and the variable gain amplification unit 451a to which the temperature sensitive resistor 445 is connected. Is done. Further, the zero compensation of the software and the output sensitivity are further compensated for the bridge output compensated for in circuit.

  The zero compensation element 42 is provided in the thick portion 34 and can compensate the zero of the bridge circuit 40 while accurately reflecting the temperature of the strain generating body 31. Further, the temperature-sensitive resistor 445 is provided in the thick portion 34, similarly to the zero compensation element 42. Thereby, the variable gain amplifying unit 451a can compensate the output sensitivity of the bridge circuit 140 while accurately reflecting the temperature of the strain generating body 31. Further, the compensation calculation unit 52 can accurately and stably detect the temperature of the strain-generating body 31. Therefore, the output accuracy of the bridge circuit 140 can be further improved, and as a result, the reproducibility of the measurement result by the load cell unit 430 can be further improved.

  The weight sorter 400 according to the fourth embodiment can execute two types of zero compensation and two types of temperature sensitivity compensation based on the output of the bridge circuit 140 controlled with high accuracy. The weight of each sorting object 5 can be calculated. Therefore, even when the load of the sorting object 5 and the load of the weighing conveyor 21 (tare) are applied to the strain generating body 31 as in the weight sorter 400, the influence of the bridge output that fluctuates due to the temperature change is affected. Therefore, the selection object 5 can be weighed with good reproducibility.

  Furthermore, in the fourth embodiment, the temperature-sensitive resistor 445 and the variable gain amplifying unit 451a serve as a sensitivity compensation unit that compensates for the change in the longitudinal elastic coefficient of the strain generating body due to temperature fluctuations and corrects the output of the bridge circuit 140. In addition, it can be used as a temperature sensor for the strain body 31. Therefore, the number of parts of the load cell unit 430 can be reduced, and the manufacturing cost of the load cell unit can be reduced.

<5. Modification>
Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications can be made.

  (1) In the second embodiment, the temperature-sensitive resistor 145 (145a, 145b) has been described as being connected in series to both the positive and negative input sides 147, 148 of the bridge circuit 140. It is not limited to.

  For example, the temperature-sensitive resistor 145 may be connected only to the plus input side 147 of the bridge circuit 140 (see FIG. 13), or may be connected only to the minus input side 148 of the bridge circuit 140. Thereby, the number of parts can be reduced and the manufacturing cost of the load cell unit 30 can be reduced. As described above, the temperature-sensitive resistor 145 only needs to be connected in series to at least one of the plus and minus input sides 147 and 148 of the bridge circuit 140. As a material for the temperature sensitive resistor 145, a material such as nickel (Ni), copper (Cu), or platinum (Pt) is selected according to the output sensitivity of the bridge circuit 140.

  (2) In the first to third embodiments, the signal processing unit 50 is illustrated as being configured separately from the strain body 31 (see FIG. 1). However, the strain generating body 31 and the signal processing unit 50 may be configured integrally.

  (3) In the first to third embodiments, the load cell units 30, 130, 230, and 430 have been described as being used for the weighing process in the weight sorters 1, 100, 200, and 400. The application target of the load cell unit 130 is not limited to this.

  FIG. 14 is a front view showing another example of a device (balance 300) to which the load cell unit 30 (130, 230) is applied. The scale 300 is an industrial scale that requires high-precision weighing results, and is a device that measures the weight of the weighing object 305 in a stationary state. As shown in FIG. 14, the scale 300 mainly includes a load cell unit 30 (130, 230) and an upper plate part 310. In the following, the case where the load cell unit 30 of the first embodiment is used will be mainly described. Note that the scale 300 acquires the mass of the measurement object by converting the measured weight in the same manner as the weight sorters 1, 100, 200, and 400 of the first to third embodiments.

  The upper plate part 310 is used as a loading part for loading the weighing object 305. As shown in FIG. 14, the upper plate 310 is supported on the free end 31 b side of the strain body 31 via an attachment member 325. Further, the fixed end 31 a of the strain body 31 is attached to a fixed portion 321 in the main body 320. Therefore, the strain body 31 is responsible for the load in the load direction AR3 (substantially Z-axis direction). Then, the signal processing unit 50 calculates the weight of the weighing object 305 based on the load signal output from the bridge circuit 40 (see FIG. 5).

  As described above, the bridge circuit 40 (140, 240) of the scale 300 is provided with circuit-like (hardware-like) zero point and output sensitivity compensation and software zero point and output sensitivity compensation. The weight of each measurement object 305 can be calculated on the basis of the bridge output controlled to the above. Therefore, it is possible to set the minimum scale for the maximum capacity of the load cell unit 30 (130, 230) small, and as a result, the measurement accuracy (measurement resolution) of the measurement object can be further improved. For example, even when a small amount of additive is added to the raw material, the weight of the additive can be accurately measured.

It is a front view which shows an example of the weight sorter in the 1st thru | or 3rd embodiment of this invention. It is a front view which shows an example of the hardware constitutions of the load cell unit in the 1st thru | or 3rd Embodiment of this invention. It is a top view which shows an example of the hardware constitutions of the load cell unit in 1st thru | or 3rd Embodiment. It is a top view which shows an example of a structure of the strain gauge in 1st thru | or 3rd Embodiment. It is a block circuit diagram of the load cell unit in a 1st embodiment. It is a figure which shows the relationship between the zero of a bridge circuit, and the temperature of a strain body. It is a figure which shows the relationship between the output sensitivity of a bridge circuit, and the temperature of a strain body. It is a block circuit diagram of the load cell unit in 2nd Embodiment. It is a block circuit diagram of the load cell unit in 3rd Embodiment. It is a block circuit diagram of the load cell unit in 4th Embodiment. It is a figure for demonstrating the switching timing of the bridge | bridging output detection mode in 4th Embodiment, and temperature detection mode. It is a figure for demonstrating the switching timing of the bridge | bridging output detection mode in 4th Embodiment, and temperature detection mode. It is a block circuit diagram of the load cell unit in a modification. It is a front view which shows the other example of the apparatus to which the load cell unit in embodiment of this invention is applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,100,200,400 Weight sorter 5 Sorting object 10 Take-in device 20 Weighing device 21 Weighing conveyor 30, 130, 230 Load cell unit 31 Strain body 31a Fixed end 31b Free end 32 Through hole 32a Inner wall surface 33 Strain Part 34 Thick part 35 Outer peripheral surface 35a First surface 35b Second surface 40, 140, 240 Bridge circuit 40a Base member 40b Resistor 41, 141, 241 Strain gauge 42, 242 Zero compensation element 45, 145, 445 Temperature sensitive resistance 50, 450 Signal processing unit 50a Signal processing board 60 Sorting device 300 Scale 310 Upper plate part AR2 Load direction

Claims (14)

A load cell unit that measures the weight of an object to be weighed based on a load signal,
(a) a metal block provided with a through hole, a strain generating body having a plurality of thin strain generating portions sandwiched between an inner wall surface of the through hole and an outer peripheral surface of the metal block;
(b) Arranged in the corresponding strain generating portion among a plurality of strain generating portions, and compensates for the amount of change in the longitudinal elastic modulus of the strain generating body due to temperature change, and roughly corrects the bridge output of the bridge circuit. A temperature sensitivity compensation type strain gauge that compensates for the output sensitivity of the bridge circuit, and
(c) a bridge circuit formed by the strain gauge;
(d) It is connected in series with a strain gauge arranged on one side of the bridge circuit, and compensates for the zero point of the bridge circuit that fluctuates due to a temperature change according to the temperature of the strain generating body. A zero compensation element for coarse correction of the output;
(e) a temperature sensor that detects the temperature of the strain body;
(f) The detection result of the temperature sensor for the bridge output that has been compensated by the zero compensation of the bridge circuit by the zero compensation element and the coarse correction by compensating the output sensitivity of the bridge circuit by the strain gauge. A signal processing unit that further compensates for the zero point and output sensitivity of the bridge circuit by performing fine correction based on
With
The strain body constitutes a Roverval mechanism via a plurality of the strain portions provided between a free end to which a load is applied and a fixed end,
The load cell unit, wherein the zero compensation element and the temperature sensor are provided in a portion sandwiched between adjacent strain generating portions. In the load cell unit according to claim 1,
The load cell unit, wherein the temperature sensor is a temperature sensitive resistor. A load cell unit that measures the weight of an object to be weighed based on a load signal,
(a) a metal block provided with a through hole, a strain generating body having a plurality of thin strain generating portions sandwiched between an inner wall surface of the through hole and an outer peripheral surface of the metal block;
(b) a self-temperature-compensated strain gauge that is arranged in a corresponding strain-generating portion among a plurality of strain-generating portions and can compensate for thermal expansion of the strain-generating body caused by temperature change;
(c) a bridge circuit formed by the strain gauge;
(d) It is connected in series with a strain gauge arranged on one side of the bridge circuit, and compensates for the zero point of the bridge circuit that fluctuates due to a temperature change according to the temperature of the strain generating body. A zero compensation element for coarse correction of the output;
(e) It is connected in series to the input side of the bridge circuit, and compensates for the amount of change in the longitudinal elastic coefficient of the strain body due to temperature change, thereby roughly correcting the bridge output of the bridge circuit, A temperature-sensitive resistor that compensates for the output sensitivity of the bridge circuit,
(f) Detection by the temperature sensor of the bridge output that has been coarsely corrected by the zero point of the bridge circuit being compensated by the zero compensation element and the output sensitivity of the bridge circuit being compensated by a pre-temperature sensing resistor. A signal processor that further compensates for the zero and output sensitivity of the bridge circuit by finely correcting based on the results;
With
The strain body constitutes a Roverval mechanism via a plurality of the strain portions provided between a free end to which a load is applied and a fixed end,
The temperature sensing resistor that can be used as the zero compensation element and the temperature sensor is provided in a portion sandwiched between adjacent strain generating portions. In the load cell unit according to claim 3,
Of the temperature-sensitive resistors, the first temperature-sensitive resistor is connected to the input-side first terminal of the bridge circuit, and the second temperature-sensitive resistor is connected to the input-side second terminal of the bridge circuit. Load cell unit. In the load cell unit according to claim 3,
The load cell unit, wherein the temperature-sensitive resistor is connected to one of terminals on the input side of the bridge circuit. A load cell unit that measures the weight of an object to be weighed based on a load signal,
(a) a metal block provided with a through hole, a strain generating body having a plurality of thin strain generating portions sandwiched between an inner wall surface of the through hole and an outer peripheral surface of the metal block;
(b) a self-temperature-compensated strain gauge that is arranged in a corresponding strain-generating portion among a plurality of strain-generating portions and can compensate for thermal expansion of the strain-generating body caused by temperature change;
(c) a bridge circuit formed by the strain gauge;
(d) It is connected in series with a strain gauge arranged on one side of the bridge circuit, and compensates for the zero point of the bridge circuit that fluctuates due to a temperature change according to the temperature of the strain generating body. A zero compensation element for coarse correction of the bridge output;
(e) a temperature sensitive resistor that can be used as a temperature sensor;
(f) Perform signal processing on the input signal,
(f-1) a variable gain amplification unit that is connected to the temperature sensing resistor and whose amplification degree is controlled based on a resistance value of the temperature sensing resistor according to a temperature change;
(f-2) a compensation calculation unit capable of executing a compensation calculation based on an output signal from the variable gain amplification unit;
A signal processing unit having
(g) a switching unit capable of switching between the bridge output and the reference output and input to the variable gain amplifying unit;
With
The strain body constitutes a Roverval mechanism via a plurality of the strain portions provided between a free end to which a load is applied and a fixed end,
The zero compensation element and the temperature sensitive resistor are provided in a portion sandwiched between adjacent strain generating portions,
When the switching unit is switched to the bridge output side and the bridge output is input to the variable gain amplification unit as the input signal,
i) The variable gain amplifying unit compensates for the output sensitivity of the bridge circuit by compensating for the amount of change in the longitudinal elastic coefficient of the strain generating body due to a temperature change and roughly correcting the bridge output,
ii) The compensation calculation unit compensates for the bridge output that has been coarsely corrected by compensating the zero of the bridge circuit by the zero compensation element and compensating the output sensitivity of the bridge circuit by the variable gain amplifier. , Further compensating for the zero point and output sensitivity of the bridge circuit by finely correcting based on the detection result of the temperature sensor,
When the switching unit is switched to the reference output side and the reference output is input to the variable gain amplification unit as the input signal,
iii) The variable gain amplifier outputs an output signal corresponding to the resistance value of the temperature sensitive resistor,
iv) The load cell unit, wherein the compensation calculation unit calculates the temperature of the strain generating body based on the output signal. The load cell unit according to any one of claims 1 to 6,
The first and second strain generating portions adjacent to each other among the strain generating portions are substantially perpendicular to the load direction received from the object to be weighed in the outer peripheral surface, and are responsible for the load from the object to be weighed. It is provided on one side,
Adjacent third and fourth strain generating portions are substantially perpendicular to the load direction, and are provided on the second surface side opposite to the first surface across the through hole,
The load cell unit, wherein the strain gauge is disposed in each of the first to fourth strain generating portions. In the load cell unit according to claim 1 or 2,
The bridge circuit is formed by first and second strain gauges and first and second fixed resistors,
The first strain gauge is between the first input terminal and the first output terminal,
The second strain gauge is between a second input terminal and the first output terminal,
The first fixed resistor is between the first input terminal and the second output terminal,
The second fixed resistor is between the second input terminal and the second output terminal,
Each load cell unit is connected to each other. The load cell unit according to claim 8,
The first and second strain generating portions adjacent to each other among the strain generating portions are substantially perpendicular to the load direction received from the object to be weighed in the outer peripheral surface, and are responsible for the load from the object to be weighed. It is provided on one side,
Adjacent third and fourth strain generating portions are substantially perpendicular to the load direction, and are provided on the second surface side opposite to the first surface across the through hole,
The first and second strain gauges are arranged on either one of the first surface and the second surface in each of the strain-generating portions provided on the one surface. Load cell unit. The load cell unit according to any one of claims 1 to 9,
The signal processing unit further compensates for a zero point of the bridge circuit by finely correcting the coarsely corrected bridge output by a second-order or higher order approximation. The load cell unit according to any one of claims 1 to 9,
The signal processing unit further compensates the output sensitivity of the bridge circuit by finely correcting the coarsely corrected bridge output by a second-order or higher order approximation. The load cell unit according to any one of claims 1 to 9,
The signal processing unit compensates the zero point of the bridge circuit by finely correcting the coarsely corrected bridge output by a second-order or higher-order approximation and finely correcting by the second-order or higher-order approximation. Thus, the load cell unit compensates the output sensitivity of the bridge circuit. A weight sorter,
A weighing device for weighing the object to be sorted,
A sorting device that sorts each sorting object based on the weighing result of the sorting object by the weighing device;
With
The weighing device is
The load cell unit according to any one of claims 1 to 12,
Supported by the load cell unit, a weighing conveyor for conveying each sorting object,
A weight sorter characterized by comprising: The load cell unit according to any one of claims 1 to 12,
Supported by the load cell, and an upper platen portion on which a weighing object is loaded;
A balance characterized by comprising.

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