Combination weighing device

Abstract

Ensuring the weighing accuracy of combination weighing devices. [Solution] The combined weighing device comprises a first stepping motor 51 having a heating surface HS and a load cell 90. The load cell 90 has a strain generating body 90a and an electrical circuit including a first temperature sensing resistor R1. The strain generating body 90a has a first thin-walled portion TH1 to which a first strain gauge 1G1 is attached and a second thin-walled portion TH2 to which a second strain gauge 2G1 is attached, and a first intermediate portion C1 positioned between them. The first intermediate portion C1 has a first surface C1A facing the heating surface HS of the first stepping motor 51 and a second surface C1B not facing the heating surface HS. The first temperature sensing resistor R1 is fixed to the second surface C1B.

Description

Technical Field

[0001] The present invention relates to a combination weighing device provided with a load cell.

Background Art

[0002] Conventionally, since the Young's modulus of a strain body changes depending on temperature, there is a load cell that performs temperature correction using resistance. For example, Patent Document 1 (Japanese Patent Application Laid-Open No. 11-125555) discloses a load cell in which a temperature-sensitive resistor for temperature correction is incorporated into an electric circuit.

Summary of the Invention

Problems to be Solved by the Invention

[0003] However, when using a load cell in a combination weighing device, depending on other components surrounding the load cell and the surrounding environment, temperature correction may not be appropriately performed, which may reduce the weighing accuracy of the combination weighing device.

[0004] An object of the present invention is to ensure the weighing accuracy of a combination weighing device.

Means for Solving the Problems

[0005] The combined weighing device according to the first aspect comprises a plurality of hoppers, a first drive unit, and a load cell. The plurality of hoppers include a first hopper for discharging the held articles. Each of the plurality of hoppers has a discharge section. The first drive unit has a first heating section. The first drive unit drives the discharge section. The load cell is fixed to the first hopper. The load cell is used to weigh the articles held by the first hopper. The load cell has a strain-generating body, a first strain gauge, a second strain gauge, and an electrical circuit. The strain-generating body has a first end fixed to the first hopper, a second end opposite to the first end, a first thin-walled section and a second thin-walled section, and a first intermediate section. The first thin-walled section and the second thin-walled section are located between the first end and the second end. The first intermediate section is located between the first thin-walled section and the second thin-walled section. The first strain gauge is attached to the first thin-walled section. The second strain gauge is attached to the second thin-walled section. The electrical circuit includes a first temperature-sensing resistor. The electrical circuit converts the resistance changes of the first and second strain gauges into voltage. The first intermediate section has a first surface facing the first heating element of the first drive unit and a second surface that does not face the first heating element of the first drive unit. The first temperature-sensing resistor is fixed to the second surface of the first intermediate section.

[0006] In this combined weighing device, the first temperature-sensing resistor of the load cell is not fixed to the first surface facing the first heat-generating part of the first drive unit, but rather to the second surface that does not face the first heat-generating part of the first drive unit. Therefore, in the combined weighing device according to the first viewpoint, the influence of the radiant heat of the first heat-generating part on the first temperature-sensing resistor is suppressed, resulting in good weighing results from the load cell and ensuring the weighing accuracy of the combined weighing device.

[0007] The combination weighing device relating to the second viewpoint is the combination weighing device relating to the first viewpoint, wherein the second surface of the first intermediate part is the surface opposite to the first surface of the first intermediate part and is parallel to the first surface of the first intermediate part.

[0008] Here, since the first temperature-sensing resistor is fixed to the second surface opposite to the first surface facing the first heat-generating part of the first drive unit, the first temperature-sensing resistor is not affected by the radiant heat of the first heat-generating part at all or almost.

[0009] The combination weighing device relating to the third viewpoint is the combination weighing device relating to the first viewpoint, wherein the second surface of the first intermediate part is the surface opposite to the first surface of the first intermediate part and is not parallel to the first surface of the first intermediate part.

[0010] Here, since the first temperature-sensing resistor is fixed to the second surface opposite to the first surface facing the first heat-generating part of the first drive unit, the first temperature-sensing resistor is not affected by the radiant heat of the first heat-generating part at all or almost.

[0011] The combination weighing device relating to the fourth aspect is the combination weighing device relating to the first aspect, wherein the second surface of the first intermediate part is the inner surface of a hole formed in the first intermediate part, or one surface of a notch formed in the first intermediate part.

[0012] Here, a hole or notch is formed in the first intermediate portion to create a second surface that does not face the first heat-generating portion of the first drive unit, and the first temperature-sensing resistor is fixed to this second surface. Therefore, by devising the arrangement and size of the hole or notch, the influence of radiant heat from the first heat-generating portion on the first temperature-sensing resistor can be further reduced.

[0013] The combination weighing device relating to the fifth aspect is the combination weighing device relating to the first aspect, further comprising a second drive unit. The second drive unit has a second heating unit. The second drive unit drives a discharge unit different from the discharge unit driven by the first drive unit. The strain generating body further comprises a third thin-walled portion, a fourth thin-walled portion, and a second intermediate portion. The third thin-walled portion and the fourth thin-walled portion are arranged between the first end and the second end. The second intermediate portion is arranged between the third thin-walled portion and the fourth thin-walled portion. The load cell further comprises a third strain gauge attached to the third thin-walled portion and a fourth strain gauge attached to the fourth thin-walled portion. The electrical circuit further includes a second temperature-sensitive resistor. In the electrical circuit, the first strain gauge, the second strain gauge, the third strain gauge, and the fourth strain gauge are arranged in a bridge configuration. The second intermediate section has a third surface facing the second heating element of the second drive unit and a fourth surface that does not face the second heating element of the second drive unit. The second temperature-sensing resistor is fixed to the fourth surface of the second intermediate section.

[0014] In this combined weighing device, the second temperature-sensing resistor of the load cell is fixed to the fourth surface of the second drive unit, which does not face the second heat-generating part, rather than to the third surface facing the second heat-generating part of the second drive unit. Therefore, in the combined weighing device relating to the fifth viewpoint, the influence of radiant heat from the second heat-generating part on the second temperature-sensing resistor is suppressed, resulting in good weighing results from the load cell and ensuring the weighing accuracy of the combined weighing device.

[0015] The combined weighing device according to the sixth aspect is the combined weighing device according to the fifth aspect, wherein the plurality of hoppers include a second hopper. The second hopper is located above or below the first hopper. The first drive unit drives the discharge section of the first hopper. The second drive unit drives the discharge section of the second hopper. The load cell is positioned at a height between the first drive unit and the second drive unit.

[0016] In this combination weighing device, there are first and second hoppers arranged vertically, and load cells are positioned between the first and second drive units that drive them. Therefore, if the first and second temperature-sensing resistors were fixed to the strain-generating body of the load cells as in conventional designs, there would be a high risk that the radiant heat from the first heat-generating part of the first drive unit and the second heat-generating part of the second drive unit would adversely affect the first and second temperature-sensing resistors. However, here, the first temperature-sensing resistor is fixed to the second surface of the first intermediate part, and the second temperature-sensing resistor is fixed to the fourth surface of the second intermediate part, thus suppressing adverse effects on the first and second temperature-sensing resistors.

[0017] The combination weighing device according to the seventh perspective is a combination weighing device according to either the first or sixth perspective, in which the first drive unit and load cell overlap in a top view. The first drive unit, load cell and first hopper form an assembly. In the combination weighing device according to the seventh perspective, multiple assemblies are arranged in the circumferential direction.

[0018] Here, an assembly including a first drive unit, a load cell, and a first hopper is arranged in the circumferential direction. In order to miniaturize the combination weighing device, it is necessary to reduce the size of each assembly and the interval in the circumferential direction. In this combination weighing device, even if the load cell is not separated from the first drive unit of its own assembly, or even if the load cell is not separated from the first drive unit of an adjacent assembly, it is possible to suppress an adverse effect on the first temperature-sensitive resistor or the second temperature-sensitive resistor, making it easier to miniaturize the combination weighing device.

[0019] The combination weighing device according to the eighth aspect is any one of the combination weighing devices from the first aspect to the seventh aspect, and the first intermediate portion of the strain generating body overlaps with the first heat generating portion of the first drive unit in a top view.

[0020] The combination weighing device according to the ninth aspect is any one of the combination weighing devices from the first aspect to the eighth aspect, and the first surface of the first intermediate portion of the strain generating body faces the first heat generating portion of the first drive unit without passing through a shielding object.

Advantages of the Invention

[0021] According to the present invention, it is possible to suppress the first temperature-sensitive resistor from being affected by the radiant heat of the first heat generating portion, and the weighing result by the load cell becomes good, ensuring the weighing accuracy of the combination weighing device.

Brief Description of the Drawings

[0022] [Figure 1] It is a layout diagram of each part in a side view of a combination weighing device according to an embodiment of the present invention. [Figure 2] It is a block diagram of the combination weighing device. [Figure 3] It is a perspective view of the combination weighing device, omitting the illustration of the article supply chute and showing a state where a part of the radiation feeder, the pool hopper, and the weighing hopper is removed. [Figure 4] It is a diagram showing the arrangement of the load cell and the stepping motors above and below it. [Figure 5] It is a diagram showing the electrical circuit of the load cell. [Figure 6]It is a side view showing the arrangement of strain gauges and temperature-sensitive resistors attached to the load cell. [Figure 7] It is a top view showing the arrangement of strain gauges and temperature-sensitive resistors attached to the load cell. [Figure 8] It is a diagram showing the arrangement of temperature-sensitive resistors in the load cell of the combined weighing device according to Modification A. [Figure 9] It is a diagram showing the arrangement of temperature-sensitive resistors in the load cell of the combined weighing device according to Modification B.

Mode for Carrying Out the Invention

[0023] Referring to the drawings, the combined weighing device 10 according to an embodiment of the present invention will be described. Note that the embodiments described below are specific examples of the present invention and do not limit the technical scope of the present invention.

[0024] (1) Overall Configuration of the Combined Weighing Device FIG. 1 is a schematic side view of a combined weighing device 10 according to an embodiment of the present invention. FIG. 2 is a block diagram of the combined weighing device 10. FIG. 3 is a perspective view of the combined weighing device 10. In FIG. 3, the drawing of the article supply chute 102 described later is omitted. Also, in FIG. 3, a state in which a part of the radiation feeder 30, the pool hopper 40, and the weighing hopper 50 described later is removed is drawn.

[0025] As shown in FIG. 1, the combined weighing device 10 mainly includes an article supply chute 102, a dispersion table 20, a plurality of radiation feeders 30, a plurality of pool hoppers 40, a plurality of weighing hoppers 50, stepping motors 41, 51 (see FIG. 2) for driving each hopper 40, 50, a load cell 90 for weighing the articles held in the weighing hopper 50, a collective discharge chute 60, a weighing mechanism frame 80, support legs 81 (see FIG. 3), a main body frame 100 (see FIG. 3), and a control unit 70 (see FIG. 2).

[0026] The combined weighing device 10 functions approximately as follows.

[0027] The combined weighing device 10 receives items to be weighed by a cross feeder 101 (see Figure 1), which is a separate device located upstream. The items transported by the cross feeder 101 are fed into the item supply chute 102. The items fed into the item supply chute 102 are supplied to the distribution table 20. The distribution table 20 transports the items while distributing them and supplies them to a plurality of radial feeders 30 arranged around the distribution table 20. Each radial feeder 30 transports the items supplied from the distribution table 20 to a pool hopper 40 provided in conjunction with each radial feeder 30, and supplies them to the pool hopper 40. The items supplied to each pool hopper 40 are then transferred to a weighing hopper 50 located below the pool hopper 40. The control unit 70 performs a combination weighing calculation based on the weighing values ​​of the load cell 90 (the weighing values ​​of the items in the weighing hopper 50), and selects the combination of items whose result is within a predetermined tolerance range and is closest to the target value. The items in the weighing hopper 50 included in the selected combination are discharged to the collective discharge chute 60. The items discharged to the collective discharge chute 60 are supplied, for example, to a bag-making and packaging machine installed downstream (below) the combination weighing device 10.

[0028] (2) Detailed configuration of the combined weighing device (2-1) Goods supply chute The item supply chute 102 is located below the end of the cross feeder 101, which feeds items into the item supply chute 102. The item supply chute 102 receives the items transported by the cross feeder 101 and supplies the items to the distribution table 20.

[0029] (2-2) Distributed Tables The distribution table 20 is a table-shaped member formed in a cone shape. The distribution table 20 is vibrated by an electromagnet (not shown) to transport the supplied articles radially outward while dispersing them circumferentially. Articles transported to the outer edge of the distribution table 20 are supplied to a plurality of radial feeders 30 located below the outer edge of the distribution table 20.

[0030] (2-3) Radiation feeder The combined weighing device 10 has a plurality of (in this case, 14) radial feeders 30 (see Figure 1). The plurality of radial feeders 30 are arranged in a ring around the distribution table 20. The plurality of radial feeders 30 extend radially from the distribution table 20 as the center. Each radial feeder 30 is vibrated by an electromagnet (not shown) to transport articles supplied from the distribution table 20 radially outward. Articles transported to the outer edge of each radial feeder 30 are supplied to a pool hopper 40 located below the outer edge of each radial feeder 30.

[0031] (2-4) Pool Hoppers The combined weighing device 10 has the same number of pool hoppers 40 as there are radial feeders 30. One pool hopper 40 is positioned below the outer edge of each radial feeder 30. Articles supplied from the radial feeders 30 positioned above are temporarily stored in the pool hopper 40.

[0032] Each pool hopper 40 has a PH gate 40a at its bottom (see Figure 3). When the PH gate 40a is opened, the contents of the pool hopper 40 are supplied to the weighing hopper 50 located below the pool hopper 40. Each PH gate 40a is opened and closed by a link mechanism LC41 which is operated by a stepping motor 41 (see Figures 2 and 4). The rotation of the rotation axis RA41 of the stepping motor 41, i.e., the opening and closing of the PH gate 40a, is controlled by a control unit 70.

[0033] (2-5) Measuring hopper The combined weighing device 10 has the same number of weighing hoppers 50 as there are pool hoppers 40. One weighing hopper 50 is located below each pool hopper 40. The weighing hopper 50 weighs the weight of the items supplied from the pool hoppers 40, i.e., the weight of the items supplied from the radial feeder 30 through the pool hoppers 40.

[0034] Each weighing hopper 50 has a WH gate 50a at its bottom. When the WH gate 50a is opened, the items in the weighing hopper 50 are supplied to the collective discharge chute 60. In other words, the WH gate 50a functions as the discharge section of the weighing hopper. Each WH gate 50a is opened and closed by a link mechanism LC51, which includes a cam and a cam follower, being driven by a stepping motor 51 (see Figure 2). The rotation of the rotation axis RA51 of the stepping motor 51, i.e., the opening and closing of the WH gate 50a, is controlled by the control unit 70.

[0035] Each weighing hopper 50 is paired with a pool hopper 40 located above it. In other words, the weighing hopper 50 is arranged vertically alongside the paired pool hopper 40.

[0036] (2-6) Stepping motor The stepping motor 41 that drives the PH gate 40a and the stepping motor 51 that drives the WH gate 50a are motors with the same structure. Here, we will explain the structure using the stepping motor 51 as an example.

[0037] The stepping motor 51 is an electric motor that rotates the rotating shaft RA51 shown in Figure 4, and it has a built-in coil that generates heat. Therefore, the outer shell of the stepping motor 51 is a heat-generating surface HS. Consequently, the lower surface of the stepping motor 51 shown in Figures 4 and 5 is also a heat-generating surface HS. In other words, the stepping motor 51 has a lower surface that is a heat-generating surface HS. As shown in Figure 5, the heat-generating surface HS of the stepping motor 51 and the upper surface of the strain-generating body 90a of the load cell 90 are close to each other and face each other.

[0038] (2-7) Load cell (2-7-1) Overview of load cells Each weighing hopper 50 is provided with a load cell 90 for weighing the items held in the weighing hopper 50 (see Figure 2). The arrangement of the load cells 90 is shown in Figure 4, the electrical circuit EC1 of the load cell 90 is shown in Figure 5, and the detailed configuration of the load cell 90 is shown in Figures 6 and 7.

[0039] The load cell 90 is fixed to the weighing hopper 50 and is used to weigh the items held by the weighing hopper 50. The weighing result from the load cell 90 is transmitted as a weighing signal to the multiplexer 71 of the control unit 70, which will be described later, via an amplifier (not shown) (see Figure 2).

[0040] As shown in Figure 4, the load cell 90 is located below the stepping motor 51 that drives the WH gate 50a of the weighing hopper 50. The load cell 90 is also located above the stepping motor 41 that drives the PH gate 40a of the pool hopper 40. In other words, the load cell 90 is positioned at a height between the stepping motors 41 and 51. Furthermore, as shown in Figure 7, the stepping motors 41 and 51 and the first intermediate section C1 and second intermediate section C2 of the strain-generating body 90a of the load cell 90 overlap in a top view.

[0041] As shown in Figures 6 and 7, the load cell 90 includes a first strain gauge 1G1, a second strain gauge 2G1, a third strain gauge 1G2, a fourth strain gauge 2G2, a first temperature-sensitive resistor R1, a second temperature-sensitive resistor R2, an electrical circuit EC1 (Figure 5) including these, and a strain-generating element 90a.

[0042] The strain-generating body 90a has a first end 90a1 fixed to the weighing hopper 50, a second end 90a2 which is the end opposite to the first end 90a1, a first thin-walled portion TH1 and a second thin-walled portion TH2, a first intermediate portion C1, a third thin-walled portion TH3 and a fourth thin-walled portion TH4, and a second intermediate portion C2. The first thin-walled portion TH1 and the second thin-walled portion TH2 are located in the upper part between the first end 90a1 and the second end 90a2. The first intermediate portion C1 is located between the first thin-walled portion TH1 and the second thin-walled portion TH2. The third thin-walled portion TH3 and the fourth thin-walled portion TH4 are located in the lower part between the first end 90a1 and the second end 90a2. The second intermediate portion C2 is located between the third thin-walled portion TH3 and the fourth thin-walled portion TH4. The first strain gauge 1G1 is attached to the upper surface of the first thin-walled section TH1. The second strain gauge 2G1 is attached to the upper surface of the second thin-walled section TH2. The third strain gauge 1G2 is attached to the lower surface of the third thin-walled section TH3. The fourth strain gauge 2G2 is attached to the lower surface of the fourth thin-walled section TH4.

[0043] The electrical circuit EC1 converts the resistance changes of the first strain gauge 1G1, the second strain gauge 2G1, the third strain gauge 1G2, and the fourth strain gauge 2G2 into voltage. In the electrical circuit EC1, the first strain gauge 1G1, the second strain gauge 2G1, the third strain gauge 1G2, and the fourth strain gauge 2G2 are arranged in a bridge configuration. In addition to these first strain gauges 1G1, 2G1, 3G2, and 4G2, the electrical circuit EC1 also includes a first temperature-sensing resistor R1 and a second temperature-sensing resistor R2, as shown in Figure 5. Furthermore, the electrical circuit EC1 includes resistors R11 and R12 for zero balance adjustment, resistors R21 and R22 for zero-point temperature effect compensation, resistors R31 and R32 for output sensitivity adjustment, and a resistor R40 for input resistance adjustment.

[0044] The first temperature-sensitive resistor R1 and the second temperature-sensitive resistor R2 are temperature-sensitive resistors provided to correspond to the change in output (output OUT in Figure 5) due to the temperature-dependent change in the elastic modulus of the strain-generating body 90a and the temperature-dependent change in the gauge fraction of each strain gauge 1G1, 2G1, 1G2, and 2G2. As shown in Figure 5, the first temperature-sensitive resistor R1 and the second temperature-sensitive resistor R2 are inserted on the input IN side of the electrical circuit EC1 to perform temperature compensation.

[0045] Note that the electrical circuit EC1 shown in Figure 5 is just one example of a known circuit, and it may be a circuit with some resistors removed. Also, since the electrical circuit EC1 is a known circuit, a detailed explanation of its principle and configuration will be omitted.

[0046] (2-7-2) Arrangement of strain gauges and temperature-sensitive resistors in load cells In the load cell 90, as described above, the first strain gauge 1G1 is attached to the upper surface of the first thin-walled portion TH1 of the strain body 90a, the second strain gauge 2G1 is attached to the upper surface of the second thin-walled portion TH2 of the strain body 90a, the third strain gauge 1G2 is attached to the lower surface of the third thin-walled portion TH3 of the strain body 90a, and the fourth strain gauge 2G2 is attached to the lower surface of the fourth thin-walled portion TH4 of the strain body 90a (see Figure 6). The attachment is usually done with an adhesive such as a thermosetting epoxy adhesive.

[0047] The first temperature-sensing resistor R1 is fixed to the second surface C1B, which is the lower surface of the first intermediate portion C1 of the strain-generating body 90a (see Figure 6). The second surface C1B of the first intermediate portion C1 is the surface opposite to the first surface C1A of the first intermediate portion C1, and is parallel to the first surface C1A of the first intermediate portion C1. The first surface C1A, which is the upper surface of the first intermediate portion C1, faces the lower surface (heat-generating surface HS) of the stepping motor 51. The gap between the first surface C1A of the first intermediate portion C1 and the heat-generating surface HS of the stepping motor 51 is narrow, and there are no obstacles between the first surface C1A of the first intermediate portion C1 and the heat-generating surface HS of the stepping motor 51.

[0048] The second temperature-sensing resistor R2 is fixed to the fourth surface C2B, which is the upper surface of the second intermediate portion C2 of the strain-generating body 90a (see Figure 6). The fourth surface C2B of the second intermediate portion C2 is the surface opposite to the third surface C2A of the second intermediate portion C2, and is parallel to the third surface C2A of the second intermediate portion C2. The third surface C2A, which is the lower surface of the second intermediate portion C2, faces the upper surface (heat-generating surface HS) of the stepping motor 41. The gap between the third surface C2A of the second intermediate portion C2 and the heat-generating surface HS of the stepping motor 41 is narrow, and there is no shielding between the third surface C2A of the second intermediate portion C2 and the heat-generating surface HS of the stepping motor 41.

[0049] (2-7-3) Unit having a pool hopper, weighing hopper, and load cell As shown in Figure 4, the pool hopper 40, the weighing hopper 50, and the load cell 90 fixed to the weighing hopper 50 are unitized to form an assembly. In the combined weighing device 10, there are multiple units, each having a pool hopper 40, a weighing hopper 50, and a load cell 90. These multiple units are then mounted on the weighing mechanism frame 80 so that they are arranged in the circumferential direction.

[0050] (2-8) Collective discharge chute The collective discharge chute 60 is a component for discharging goods. After combined weighing based on the weighing results of the load cell 90, the weighed goods selected for combination are supplied to the collective discharge chute 60 from the weighing hopper 50. The collective discharge chute 60 collects the goods supplied from the weighing hopper 50 and discharges them downward. The goods discharged from the collective discharge chute 60 are then passed to downstream equipment such as a bag-making and packaging machine located below the combined weighing device 10.

[0051] The articles discharged from the combined weighing device 10 are supplied, for example, from the discharge port 60a at the bottom of the collective discharge chute 60 to a bag-making and packaging machine (not shown) installed below the collective discharge chute 60.

[0052] (2-9) Measuring mechanism frame The weighing mechanism frame 80 is a cylindrical frame (see Figure 3).

[0053] The weighing mechanism frame 80 primarily supports the distribution table 20, the radial feeder 30, the pool hopper 40, and the weighing hopper 50 (see Figure 3). The weighing mechanism frame 80 supports the distribution table 20 and the radial feeder 30 from below. The unit containing the pool hopper 40 and the weighing hopper 50 is attached to the side of the weighing mechanism frame 80 (see Figure 3). Note that Figure 3 depicts the combined weighing device 10 with all but one set of radial feeder 30, pool hopper 40, and weighing hopper 50 removed.

[0054] Various devices are housed inside the weighing mechanism frame 80. Specifically, the weighing mechanism frame 80 houses an electromagnet (not shown) for vibrating the distribution table 20, an electromagnet (not shown) for vibrating the radiating feeder 30, a stepping motor 41 for driving the PH gate 40a of the pool hopper 40, a stepping motor 51 for driving the WH gate 50a of the weighing hopper 50, a load cell 90, and the like.

[0055] (2-10) Support legs and main frame The support legs 81 are members that connect the weighing mechanism frame 80 and the main body frame 100 (see Figure 3). A total of four support legs 81 are provided. One support leg 81 extends from each of the four support columns 110 of the main body frame 100 toward the weighing mechanism frame 80.

[0056] The main frame 100 supports the weighing mechanism frame 80 via support legs 81. The support legs 81 also support the collective discharge chute 60. The main frame 100 is placed on a stand (not shown). Below the stand, devices (not shown), such as a bag-making and packaging machine, are placed, and these devices are supplied with articles discharged from the discharge port 60a of the collective discharge chute 60.

[0057] (2-11) Control Unit As shown in Figure 2, the control unit 70 includes a CPU 76 and memory 77 such as ROM or RAM. The control unit 70 also includes a multiplexer 71, an A / D converter 72, and a DSP (digital signal processor) 73.

[0058] The multiplexer 71, following instructions from the DSP 73, selects a metering signal of 1 from the metering signals of the load cell 90 and transmits it to the A / D converter 72. The A / D converter 72 converts the metering signal (analog signal) received from the multiplexer 71 into a digital signal according to the timing signal transmitted from the DSP 73 and transmits it to the DSP 73. The DSP 73 performs filtering on the digital signal transmitted from the A / D converter 72.

[0059] The control unit 70 is connected to various parts of the combination weighing device 10, including the distribution table 20, the radiating feeder 30, the stepping motor 41, the stepping motor 51, and the touch panel 75. In the control unit 70, the CPU 76 controls each part of the combination weighing device 10 by executing a program stored in the memory 77.

[0060] Specifically, the control unit 70 performs the following control, for example:

[0061] The control unit 70 performs a combination weighing calculation based on the weighing values ​​in the weighing hoppers 50. Specifically, the control unit 70 uses the signal filtered by the DSP 73 to calculate the weight of the items held in each weighing hopper 50, and performs a combination weighing calculation so that the sum of the weights is within a predetermined target weight range and as close to the target value as possible. Then, based on the results of the combination weighing calculation, the control unit 70 determines the combination of weighing hoppers 50 and controls the operation of the stepping motor 51 so that the WH gate 50a of the determined weighing hopper 50 opens. In addition, if any of the weighing hoppers 50 is empty, the control unit 70 operates the stepping motor 41 to open the PH gate 40a of the pool hopper 40 located above that weighing hopper 50.

[0062] (3) Features (3-1) As described in Patent Document 1 (Japanese Patent Publication No. 11-125555), load cells incorporating a temperature-sensitive resistor for temperature compensation into the electrical circuit are known. The elastic modulus of the strain-generating body of the load cell changes with temperature, and the gauge factor of the strain gauge also changes with temperature, so the output of the load cell also changes with temperature. To address this change, it is known to perform temperature compensation using a temperature-sensitive resistor.

[0063] However, load cells incorporated into combination weighing devices are strongly affected not only by the temperature of the surrounding atmosphere but also by the radiant heat from heat-generating objects placed nearby. The influence of this radiant heat from heat-generating objects has not been considered in the design of conventional combination weighing devices. Furthermore, the inventors of this invention have found that the temperature influence of the surrounding atmosphere of the load cell and the influence of the radiant heat from heat-generating objects are not necessarily proportional, and that a significant difference occurs between the two when the combination weighing device transitions from a stopped state to an operating state (or from an operating state to a stopped state).

[0064] Specifically, the inventors of this invention repeatedly measured the surface temperature of each part of the load cell before and after state transitions, the temperature of the temperature-sensing resistor, and the ambient temperature around the load cell, and verified the error in the load cell's output (measured value). As a result, they came to recognize that the factors that most significantly affect the change in the measured value are the temperature difference between the temperature-sensing resistor and the strain-generating element, and that the temperature-sensing resistor is greatly affected by the heat generated by a nearby motor (heat-generating element).

[0065] In the combination weighing device 10 according to this embodiment, invented based on such experiments and verifications, the first temperature-sensing resistor R1 of the load cell 90 is fixed to a second surface C1B that does not face the heat-generating surface HS of the stepping motor 51, rather than to a first surface C1A that faces the lower surface (heat-generating surface HS) of the stepping motor 51. Therefore, in the combination weighing device 10, the influence of radiant heat from the heat-generating surface HS of the stepping motor 51 on the first temperature-sensing resistor R1 is suppressed. Specifically, the discrepancy between the temperature of the first temperature-sensing resistor R1 and the temperature of the first intermediate part C1 of the strain-generating body 90a is suppressed. As a result, the weighing results by the load cell 90 are improved, and the weighing accuracy of the combination weighing device 10 is ensured.

[0066] Furthermore, the effects of the above-described combination weighing device 10 are particularly effective when a dustproof and waterproof structure is adopted to protect motors and printed circuit boards from seasoning of goods. In such cases, because the structure is sealed, the load cell 90 is susceptible to the effects of heat from the heat-generating surface of the motor, which increases the risk of weighing errors. When the above-described combination weighing device 10 was subjected to demonstration tests, it was found that it could suppress changes in weighing values ​​compared to a combination weighing device using a conventional load cell. When comparing the change in weighing values ​​after 1 hour of normal operation and then 30 minutes of stopping the device, the change in weighing values ​​was 0.3g to 0.5g with the conventional device, while the change in weighing values ​​was reduced to 0.1g with the above-described combination weighing device 10. As a result, even when the device is used in a manner that involves repeated operation and stopping, it is possible to suppress the decrease in production line yield due to weighing errors.

[0067] (3-2) In the combination weighing device 10 according to this embodiment, the first temperature-sensing resistor R1 is fixed to the second surface C1B, which is the surface opposite to the first surface C1A that faces the heat-generating surface HS of the stepping motor 51 and is parallel to the first surface C1A. Therefore, the first temperature-sensing resistor R1 is hardly affected by the radiant heat from the heat-generating surface HS of the stepping motor 51.

[0068] (3-3) In the combined weighing device 10 according to this embodiment, the second temperature-sensing resistor R2 of the load cell 90 is fixed to the fourth surface C2B of the second intermediate portion C2, which does not face the heat-generating surface HS of the stepping motor 41, rather than to the third surface C2A of the second intermediate portion C2, which faces the heat-generating surface HS of the stepping motor 41. As a result, the influence of radiant heat from the heat-generating surface H of the stepping motor 41 on the second temperature-sensing resistor R2 is suppressed, resulting in good weighing results from the load cell 90 and ensuring the weighing accuracy of the combined weighing device 10.

[0069] (3-4) In the combined weighing device 10 according to this embodiment, there are pool hoppers 40 and weighing hoppers 50 arranged vertically, and the load cell 90 is positioned between stepping motors 41 and stepping motors 51 that drive them (see Figure 4). Therefore, if the first temperature-sensing resistor R1 and the second temperature-sensing resistor R2 were fixed to the strain-generating body 90a of the load cell 90 according to the conventional arrangement, the radiant heat from the heat-generating surface HS of the motor would adversely affect the first temperature-sensing resistor R1 and the second temperature-sensing resistor R2.

[0070] However, as described above, in the combined weighing device 10, the first temperature-sensing resistor R1 is fixed to the second surface C1B of the first intermediate section C1, which does not face the heat-generating surface HS, and the second temperature-sensing resistor R2 is fixed to the fourth surface C2B of the second intermediate section C2, which does not face the heat-generating surface HS of the second intermediate section C2. Therefore, it is possible to suppress the radiant heat from the heat-generating surface HS of the motor from affecting the first temperature-sensing resistor R1 and the second temperature-sensing resistor R2.

[0071] (3-5) In the combined weighing device 10 according to this embodiment, the pool hopper 40, weighing hopper 50, and load cell 90 fixed to the weighing hopper 50 are arranged vertically and unitized to form an assembly. In the combined weighing device 10, multiple units are arranged in a circular direction. In order to miniaturize the combined weighing device 10, the size of the units and the spacing between units in the circular direction have been reduced.

[0072] Therefore, in the combined weighing device 10, the stepping motors 41 and 51 had to be placed near the load cell 90, and as shown in Figure 7 in the top view, the stepping motors 41 and 51 and the load cell 90 overlap. Furthermore, there are no shields to block radiant heat between the stepping motor 41 and the load cell 90, or between the stepping motor 51 and the load cell 90.

[0073] Thus, in the combined weighing device 10, the radiant heat from the heat-generating surfaces HS of the stepping motors 41 and 51 is likely to affect the load cell 90. However, by devising the arrangement of the first temperature-sensing resistor R1 and the second temperature-sensing resistor R2 as described above, excessive heating of the temperature-sensing resistors R1 and R2 by the radiant heat from the heat-generating surfaces HS is suppressed.

[0074] (4) Variations The following are modifications of the above embodiment. These modifications may be combined with other modifications to the extent that they do not contradict each other.

[0075] (4-1) Variation A In the combination weighing device 10 according to the above embodiment, the first temperature-sensing resistor R1 is fixed to the second surface C1B, which is the surface opposite to the first surface C1A that faces the heat-generating surface HS of the stepping motor 51 and is parallel to the first surface C1A. However, the first temperature-sensing resistor R1 may also be fixed to the curved surface C1Y shown in Figure 8. The curved surface C1Y is the inner surface of the first intermediate portion C1 of the strain-generating body 90a and is the surface opposite to the first surface C1A that faces the heat-generating surface HS of the stepping motor 51. The curved surface C1Y is not parallel to the first surface C1A. Even when the first temperature-sensing resistor R1 is fixed to this curved surface C1Y, the radiant heat from the heat-generating surface HS of the stepping motor 51 will hardly heat the first temperature-sensing resistor R1 from the outside, and the weighing accuracy of the combination weighing device 10 can be ensured.

[0076] (4-2) Modification B In the combination weighing device 10 according to the above embodiment, the first temperature-sensing resistor R1 is fixed to the second surface C1B, which is the surface opposite to the first surface C1A that faces the heat-generating surface HS of the stepping motor 51. However, the first temperature-sensing resistor R1 may also be fixed to the inner surface C1ZS of the hole C1Z shown in Figure 9. In Figure 9, the hole C1Z is a hole that extends from the front to the back of the paper and penetrates the first intermediate part C1 of the strain-generating body 90a. Within this hole C1Z, no matter where the first temperature-sensing resistor R1 is fixed, almost no radiant heat from the heat-generating surface HS of the stepping motor 51 reaches it. The inner surface C1ZS of the hole C1Z may be the surface opposite to the first surface C1A that faces the heat-generating surface HS of the stepping motor 51, or it may be the bottom surface of the hole C1Z. Furthermore, the hole C1Z may be a hole that does not penetrate the strain-generating body 90a, a small hole just large enough to insert the first temperature-sensing resistor R1, or a hole or groove formed by cutting out a part of the strain-generating body 90a.

[0077] (4-3) Modification C In the combined weighing device 10 according to the above embodiment, a pool hopper 40 is provided above the weighing hopper 50, but the pool hopper 40 can be omitted. In this case, the stepping motor 51 that drives the weighing hopper 50 and the strain-generating body 90a of the load cell 90 are arranged side by side in the vertical direction.

[0078] Furthermore, in the combined weighing device 10 according to the above embodiment, the stepping motor 41 that drives the pool hopper 40 is located below the load cell 90, and the stepping motor 51 that drives the weighing hopper 50 is located above the load cell 90. However, the arrangement of the stepping motors 41 and 51 can be reversed by changing the configuration of the link mechanism and cam mechanism.

[0079] (4-4) Modification D In the combined weighing device 10 according to the above embodiment, there is no hopper below the weighing hopper 50, but a known booster hopper may be provided below the weighing hopper 50. In this case as well, it is preferable to apply the present invention in such a way that the radiant heat from the heat-generating surface of the motor driving the booster hopper does not have a significant effect on the temperature-sensing resistance of the load cell 90. [Explanation of Symbols]

[0080] 10. Combination weighing device 40 Pool Hoppers (Hopper No. 2) 40a PH gate (discharge section) 41 Stepping motor (second drive unit) 50 Measuring hopper (1st hopper) 50a WH gate (discharge section) 51 Stepping motor (first drive unit) 90 load cells 90a Strain body 90a1 1st end 90a2 2nd end TH1 1st thin section TH2 2nd thin section C1 1st intermediate section C1A First Intermediate Section, First Face C1B Second surface of the first intermediate section TH3 3rd thin section TH4 4th thin-walled section C2 2nd middle part C2A Second Intermediate Section, Third Side C2B Second Intermediate Section, 4th Face 1G1 First Strain Gauge 2G1 Second strain gauge 1G2 Third Strain Gauge 2G2 4th strain gauge R1 First temperature-sensitive resistor R2 2nd temperature sensitive resistor EC1 Electrical Circuit HS heating surface (first heating element, second heating element) Hole formed in the first intermediate part of C1Z [Prior art documents] [Patent Documents]

[0081] [License 1] Special Announcement No. 11-125555

Claims

1. A plurality of hoppers, each having a discharge section, including a first hopper for discharging the held items, A first drive unit having a first heat-generating section and driving the discharge section, A load cell fixed to the first hopper and used for weighing the articles held by the first hopper, Equipped with, The aforementioned load cell is A strain-generating body having a first end fixed to a first hopper, a second end which is the end opposite to the first end, a first thin-walled portion and a second thin-walled portion disposed between the first end and the second end, and a first intermediate portion disposed between the first thin-walled portion and the second thin-walled portion, A first strain gauge is attached to the first thin-walled portion, A second strain gauge is attached to the second thin-walled portion, An electrical circuit including a first temperature-sensing resistor that converts the resistance change of the first strain gauge and the second strain gauge into a voltage, It has, The first intermediate portion has a first surface facing the first heating element of the first drive unit and a second surface that does not face the first heating element of the first drive unit. The first temperature-sensitive resistor is fixed to the second surface of the first intermediate portion. Combination weighing device.

2. The second surface of the first intermediate portion is the surface opposite to the first surface of the first intermediate portion and is parallel to the first surface of the first intermediate portion. The combination weighing apparatus according to claim 1.

3. The second surface of the first intermediate portion is the surface opposite to the first surface of the first intermediate portion and is not parallel to the first surface of the first intermediate portion. The combination weighing apparatus according to claim 1.

4. The second surface of the first intermediate portion is the inner surface of a hole formed in the first intermediate portion, or one surface of a notch formed in the first intermediate portion. The combination weighing apparatus according to claim 1.

5. A second drive unit having a second heating element, which drives a discharge unit different from the discharge unit driven by the first drive unit, Furthermore, The strain generating body further comprises a third thin-walled portion and a fourth thin-walled portion disposed between the first end and the second end, and a second intermediate portion disposed between the third thin-walled portion and the fourth thin-walled portion. The load cell further comprises a third strain gauge attached to the third thin-walled portion and a fourth strain gauge attached to the fourth thin-walled portion. The aforementioned electrical circuit further includes a second temperature-sensitive resistor, and the first strain gauge, the second strain gauge, the third strain gauge, and the fourth strain gauge are arranged in a bridge configuration. The second intermediate portion has a third surface facing the second heating element of the second drive unit and a fourth surface that does not face the second heating element of the second drive unit. The second temperature-sensitive resistor is fixed to the fourth surface of the second intermediate portion. The combination weighing apparatus according to claim 1.

6. The plurality of hoppers further include a second hopper located above or below the first hopper. The first drive unit drives the discharge unit of the first hopper, The second drive unit drives the discharge unit of the second hopper, The load cell is positioned at a height between the first drive unit and the second drive unit. The combination weighing apparatus according to claim 5.

7. The first drive unit and the load cell overlap in a top view. The first drive unit, the load cell, and the first hopper form an assembly, Multiple such aggregates are arranged in the circumferential direction. A combination weighing device according to any one of claims 1 to 6.

8. The first intermediate portion of the strain generating body overlaps with the first heating portion of the first drive unit in a top view. A combination weighing device according to any one of claims 1 to 6.

9. The first surface of the first intermediate portion of the strain generating body faces the first heating portion of the first drive unit without an intervening shield. A combination weighing device according to any one of claims 1 to 6.

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