JP2017040613A - Weighing machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce power consumption of a weighing machine while keeping measurement accuracy of a load.SOLUTION: A weighing machine 1 comprises a detection section 10 for detecting, from current flowing in a load sensor, a load applied to the load sensor and a current control device for switching from a power source VDDB to a power source VDDA when the detection section 10 detects change in the load. The weighing machine 1 is a weighing machine (current control device) which increases current flowing in the load sensor to enable highly accurate measurement of the load.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a weighing scale.

  2. Description of the Related Art Conventionally, as a weight scale such as a weight scale or a weight scale with a body composition scale, a so-called step-on type weight scale that can measure body weight without operating a power switch is known for convenience. As an example of a step-on type weighing scale, in addition to a load sensor that measures body weight, it has a mechanical switch mechanism that detects when a person is placed under the measuring table, and detects that the switch is turned on. It does not have a weight scale that starts measuring body weight with a load sensor or a mechanical switch mechanism, and detects that a person has been placed on the measuring table based on signals taken out from the load sensor at predetermined time intervals. Thus, there is a weight scale that starts measuring the body weight (for example, disclosed in Patent Document 1).

JP 2009-156754 A

When a mechanical switch is attached to the foot part of the scale, the scale is slightly inclined due to the stroke when the switch is turned on. Therefore, when the weighing scale detects step-on by a mechanical switch mechanism, there is a problem that high-precision measurement cannot be performed by the weighing scale.
In addition, a load sensor constituted by a strain gauge needs to apply a voltage of a certain level or more in order to obtain an output level sufficient to obtain an accuracy necessary for accurate weight measurement. The load sensor constituted by the strain gauge is a component having the highest power consumption among the weight gauges. Therefore, when the weigh scale applies a voltage of a certain level or more to the load sensor at regular intervals and detects step-on based on the signal of the load sensor, it is difficult to significantly reduce power consumption.
An object of this invention is to reduce the power consumption of a weight scale, maintaining the measurement accuracy of a load.

  According to the first aspect of the present invention, the weight scale includes a detection unit that detects a load applied to the load sensor from a current flowing through the load sensor, and the load sensor when the detection unit detects a change in the load. And a current control unit that increases the current flowing to the current value higher than a current value sufficient to obtain a desired accuracy.

  According to the second aspect of the present invention, in the weigh scale according to the first aspect, the current control unit determines the current flowing through the load sensor to a desired accuracy when the detection unit detects a change in load. The current value is increased from less than the current value sufficient to obtain the desired accuracy to the current value sufficient to obtain the desired accuracy.

  According to a third aspect of the present invention, in the weighing scale according to the first or second aspect, the current control unit is configured such that when the detection unit does not detect a change in load, the load sensor has a constant interval. Increase the current value and update the zero point data.

  According to a fourth aspect of the present invention, in the weighing scale according to any one of the first to third aspects, the current control unit is connected to the load sensor when the detection unit detects a change in load. A power source that supplies current is a power source that supplies power larger than the first power source from a first power source that is connected to the load sensor, and the current flowing through the load sensor has a desired accuracy. Is switched to the second power source, which is a power source having a current value sufficient to obtain

  According to a fifth aspect of the present invention, in the weighing scale according to any one of the first to third aspects, the current control unit is connected to the load sensor when the detection unit detects a change in load. The resistance between the power supply for supplying the current and the load sensor is reduced so that the current flowing through the load sensor becomes equal to or greater than a current value sufficient to obtain a desired accuracy.

  According to a sixth aspect of the present invention, in the weigh scale according to the fifth aspect, the current control unit is arranged between the power source and the load sensor when the detection unit detects a change in load. A path to be connected is switched from a path having resistance to a path having no resistance.

  According to a seventh aspect of the present invention, in the weighing scale according to any one of the first to third aspects, the current control unit is connected to the load sensor when the detection unit detects a change in load. A constant current power source for supplying a current from a first constant current power source, which is a constant current power source connected to the load sensor, for supplying a current larger than the first constant current power source; The switching from the first constant current power source to the second constant current power source in which the current flowing through the load sensor is equal to or greater than a current value sufficient to obtain a desired accuracy.

  According to at least one of the above aspects, the weight scale can switch the value of the current flowing through the load sensor that detects a change in the load. For this reason, the weight scale can reduce the current flowing through the load sensor when the load is not applied while maintaining the measurement accuracy of the load, so that the power consumption can be greatly reduced.

It is a block diagram of a 1st embodiment. It is a flowchart which shows operation | movement of the weight scale which concerns on at least 1 embodiment. It is a block diagram of a 2nd embodiment. It is a block diagram of a 3rd embodiment.

<< First Embodiment >>
Hereinafter, the first embodiment will be described in detail with reference to the drawings.
FIG. 1 is a block diagram illustrating a hardware configuration of the weigh scale according to the first embodiment.
The weight scale 1 includes a load detection unit 10, an operational amplifier 20 that amplifies a signal, an A / D converter 30 that converts the amplified analog signal into a digital signal, a CPU 40, a power supply VDDA and a power supply VDDB of a constant voltage power supply. And a switch 50 for switching the power supply of the detection unit 10. The current control unit includes a switch 50 and a CPU 40 that controls the switch 50. Moreover, as an example of the accuracy desired by the weigh scale 1, there is a precision finer than the value obtained by dividing the minimum display on the weigh scale 1 by the maximum weighing. Specifically, when the minimum display of the weighing scale 1 is 100 g and the maximum weighing is 100 kg, an accuracy of 1/1000 is required at a minimum. In this case, as the accuracy desired by the weight scale 1, an accuracy finer than 1/1000, for example, an accuracy of 1/10000 can be employed in order to maintain stable accuracy. Note that the accuracy desired in other embodiments may be equal to the accuracy obtained by dividing the minimum display by the maximum metric.

  The detection unit 10 is a load sensor including a strain body that is a metal member and a plurality of strain gauges g1 to g4 attached to the strain body. The strain gauge g1, the strain gauge g2, the strain gauge g3, and the strain gauge g4 constitute a bridge circuit 11. The bridge circuit 11 includes an input terminal in1, an input terminal in2, an output terminal out1, and an output terminal out2. The input terminal in1 is a terminal provided between the strain gauge g1 and the strain gauge g4. The input terminal in2 is a terminal provided between the strain gauge g2 and the strain gauge g3. The output terminal out1 is a terminal provided between the strain gauge g1 and the strain gauge g2. The output terminal out2 is a terminal provided between the strain gauge g3 and the strain gauge g4. The input terminal in1 is connected to the switch 50. The input terminal in2 is connected to the ground serving as a reference potential on the circuit. The output terminal out1 is connected to the non-inverting input terminal of the operational amplifier 20. The output terminal out2 is connected to the inverting input terminal of the operational amplifier 20.

  The strain gauge g1 and the strain gauge g3 are attached so as to be compressed when the strain generating body is deformed by applying a load. Therefore, when a load is applied to the weighing scale 1, the resistance values of the strain gauge g1 and the strain gauge g3 are lowered. Further, the strain gauge g2 and the strain gauge g4 are attached so as to extend when the strain generating body is deformed when a load is applied. Therefore, the greater the load applied to the weight scale 1, the higher the resistance values of the strain gauge g2 and the strain gauge g4. When a constant voltage is applied to the input terminal in1 of the bridge circuit 11, there is a positive correlation between the voltage at the output terminal out1 between the strain gauge g1 and the strain gauge g2 and the load. Further, there is a negative correlation between the voltage at the output terminal out2 between the strain gauge g3 and the strain gauge g4 and the load.

  The output terminal out1 is input to the non-inverting input terminal of the operational amplifier 20, and the output terminal out2 is input to the inverting input terminal of the operational amplifier 20. The operational amplifier 20 is a differential amplifier and amplifies a minute output of the bridge circuit 11 and outputs the amplified output to the A / D converter 30. The A / D converter 30 is a converter that converts the signal output from the operational amplifier 20 from analog to digital. When the maximum weighing of the weigh scale 1 is 100 kg and the minimum display is 100 g, a resolution of 1/10000 (10 g / 100 kg), which is an accuracy finer than 1/1000, is required as the desired accuracy. This is because, in order to maintain the stable accuracy of the minimum display 100g, it operates with a finer resolution than the minimum display and finely monitors variations and fluctuation factors. For this reason, the A / D converter 30 is, for example, a highly accurate A / D converter such as an integral double integral method, a pulse feedback integral method, or a ΔΣ method.

  The CPU 40 is an arithmetic device such as a microcomputer that controls each part of the weighing scale 1 by executing a program. The storage unit 70 is a unit that is provided inside or outside the CPU 40 and stores programs executed by the CPU 40 and various data. Further, the CPU 40 includes an output unit 80 that outputs a measurement value of the load of the object. The output unit is connected to an output device such as a display device such as a liquid crystal display, a voice generation device, or a printer. The CPU 40 receives the digital signal converted by the A / D converter 30 and performs processing such as scale scale conversion.

  The switch 50 is a switch that is connected to the input terminal in1 and switches a power supply connected to the detection unit 10 between the power supply VDDA and the power supply VDDB. The power supply VDDB is a voltage lower than the power supply VDDA. The switch 50 is switched by the CPU 40.

  The power supply VDDA supplies power to the CPU 40, peripheral circuits, and detection unit 10, and supplies the detection unit 10 with a current value equal to or higher than a current value sufficient to obtain the accuracy desired by the weigh scale 1, for example, a resolution of 1/10000. . The current value supplied to the detection unit 10 is proportional to the output voltage output from the detection unit 10 to which a load is applied. That is, the output voltage output from the detection unit 10 by the power supply VDDA satisfies the input voltage for obtaining a predetermined resolution of the A / D converter 30 and satisfies the accuracy desired by the weight scale 1. The power supply VDDB is a voltage lower than the power supply VDDA and outputs a voltage that can output a voltage larger than the quantization width of the A / D converter 30 from the detection unit 10 when a person gets on the weighing scale 1. To do. Preferably, the power supply VDDB is such that a voltage corresponding to the quantization width of the A / D converter 30 is output from the detection unit 10 when the lightest weight (for example, 30 kg) assumed for the weight scale 1 is applied. Is output. That is, the output voltage output from the detection unit 10 by the power supply VDDB is less than the input voltage for obtaining the resolution of the A / D converter 30, the resolution of the A / D converter 30 is insufficient, and the weight The total desired accuracy cannot be satisfied. On the other hand, the output voltage output from the detection unit 10 when a person gets on the weighing scale 1 with the power supply VDDB is larger than the quantization width of the A / D converter 30, It is possible to determine whether or not a person is on board. Here, an example in which the output voltage of the power supply VDDA is 3V and the output voltage of the power supply VDDB is 0.15V will be described. When the resistance of the strain gauge of the bridge circuit 11 is 350Ω, when the power supply VDDA is supplied to the detection unit 10, the current flowing to the detection unit 10 is about 8.6 mA (1/10000 accuracy). On the other hand, when the power supply VDDB is supplied to the detection unit 10, the current flowing to the detection unit 10 is about 0.43 mA (1/500 accuracy). As described above, the CPU 40 can reduce the accuracy (resolution) of the detection unit 10 and reduce the current flowing to the detection unit 10 by switching the power supplied to the detection unit 10 from the power supply VDDA to the power supply VDDB. . In this embodiment, the power supply VDDB outputs a voltage lower than the power supply VDDA. However, even if the power supply VDDB outputs a voltage higher than the power supply VDDA, the A / D converter 30 determines whether or not a person is on board. A discriminable signal is output. On the other hand, when the power supply VDDB outputs a voltage higher than the power supply VDDA, it is not possible to expect a reduction in power consumption.

Here, the operation state of the weighing scale 1 will be described. The weigh scale 1 has three types of operation states: a standby state, a zero point update state, and a measurement state. When the CPU 40 determines that the operation state of the weighing scale 1 is the standby state, the CPU 40 determines whether or not there is a load in a state where the current flowing to the detection unit 10 is reduced and the resolution of the detection unit 10 is reduced. Next, when determining that the operation state of the weighing scale 1 is the zero point update state, the CPU 40 increases the current flowing to the detection unit 10 for a certain period. Then, the CPU 40 obtains zero point data (hereinafter, referred to as zero point data hs ₀ ) with the resolution of the detection unit 10 increased, and updates the zero point data hs ₀ . Then, after updating the zero point data hs ₀ , the CPU 40 obtains load detection reference data (hereinafter referred to as reference data Ls ₀ ) in a state where the current flowing to the detection unit 10 is reduced and the resolution is lowered. Data Ls ₀ is updated. Next, when determining that the operation state of the weighing scale 1 is the measurement state, the CPU 40 increases the current flowing to the detection unit 10 and increases the resolution of the detection unit 10 to measure the body weight. Further, after measuring the body weight, the CPU 40 changes the operation state of the scale 1 from the measurement state to the standby state.

Further, the zero point data hs ₀ is load data (hereinafter referred to as load data hs) acquired by the CPU 40 by increasing the resolution of the detection unit 10, and nothing is placed on the measuring table of the weighing scale 1. Is the load data hs acquired. The load data hs of when a person resting on the measuring table, the change of the zero point data hs ₀ caused by impact applied from the outside, or zero point data hs ₀ caused by the influence of the weight meter 1 Temperature Changes are included. Therefore CPU40 includes a load data hs of when a person resting on the measuring table, by obtaining the difference between the latest zero-point data hs _0, it is possible to accurately measure the load.

The load detection reference data Ls ₀ is load data (hereinafter referred to as load data Ls) acquired by the CPU 40 with the resolution of the detection unit 10 lowered, and is placed on the measurement table of the weighing scale 1. It is the load data Ls acquired when not. The CPU 40 uses the load detection reference data Ls ₀ to determine whether or not any load is applied to the measuring table of the weighing scale 1. Further, the CPU 40 obtains and updates the load detection reference data Ls ₀ every time the zero point data hs ₀ is updated.

The CPU 40 starts the update process of the zero point data hs ₀ at certain intervals (for example, once every few seconds). The execution time of the zero point data update process by the CPU 40 is several tens of milliseconds.

  The operation of the CPU 40 will be described. FIG. 2 is a flowchart showing the operation of the CPU 40 according to at least one embodiment. The CPU 40 shifts to the standby state and operates the switch 50 to switch the power supply of the detection unit 10 from the power supply VDDA to the power supply VDDB, thereby reducing the current flowing to the detection unit 10 (step S1). The weigh scale 1 operates in a state where power consumption is low according to the state of step S1. That is, the power supply VDDB is a power supply connected to the detection unit 10 before a change in load is detected.

The CPU 40 determines whether or not the current time is the timing for starting the zero point update process (step S2). When the current time is the timing for starting the zero point update process in step S2 (step S2: Yes), the CPU 40 shifts from the standby state to the zero point update state for executing the zero point update process (steps S3 to S3). Step S6). When the zero point update process is started, the CPU 40 operates the switch 50 to switch the power supply of the detection unit 10 from the power supply VDDB to the power supply VDDA. Thereby, the electric current which flows into the detection part 10 increases (step S3), and the resolution of the detection part 10 goes up. Next, CPU 40 acquires the zero point data hs _0, this zero point data hs _0, updates the zero point data hs ₀ stored in the storage unit 70 (step S4). Next, the CPU 40 operates the switch 50 to switch the power supply of the detection unit 10 from the power supply VDDA to the power supply VDDB. Thereby, the electric current which flows into the detection part 10 reduces (step S5), and the resolution of the detection part 10 falls. Subsequently, CPU 40 obtains the reference data Ls ₀ of the load detection, this reference data Ls _0, and updates the reference data Ls ₀ which is stored in the recording unit 70 (step S6). The reference data Ls ₀ is load data Ls in a state where the resolution of the detection unit 10 is low, which is acquired when nothing is placed on the measuring table of the weighing scale 1. In addition, when the current time is not the timing for starting the update process of the zero point in Step S2 (Step S2: No), or the CPU 40 completes the zero point update process of Steps S3 to S6 and shifts to the standby state. The process proceeds to the next step S7.

The CPU 40 determines whether or not there is load detection (step S7). Specifically, the CPU determines whether or not there is load detection according to the following procedure. First, the CPU 40 acquires the load data Ls with the detection unit 10 having a low resolution. Next, the CPU 40 compares the load data Ls with a threshold value, and determines whether or not the load data Ls is equal to or greater than the threshold value. The threshold is a value obtained by adding an arbitrary load count in the reference data Ls ₀ acquired in a state where the resolution of the detection unit 10 is low. For example, when it is desired to detect a load of 5 kg or more, the CPU 40 calculates a value obtained by adding a load count for 5 kg to the reference data Ls ₀ and sets it as a threshold value. In another embodiment, the CPU 40 may determine that there is load detection when the output load data L _s and the reference data Ls ₀ indicate different values.
When the load data Ls is equal to or greater than the threshold value (step S7: Yes), the CPU 40 shifts from the standby state to the measurement state, operates the switch 50, and switches the power supply of the detection unit 10 from the power supply VDDB to the power supply VDDA. Thereby, the electric current which flows into the detection part 10 increases (step S8), and the resolution of the detection part 10 goes up. Then, the CPU 40 proceeds to the next step S9. On the other hand, when the load data is less than the threshold value (step S7: No), the CPU 40 returns to step S2 for determining whether or not it is time to start the zero point update process.

  The CPU 40 acquires the load data hs indicating the load applied to the measurement table, and performs a load (weight) measurement process based on the load data hs (step S9). The CPU 40 proceeds to the next step S10.

The CPU 40 determines whether or not the load is confirmed by the measurement process (step S10). As a method for determining whether or not the body weight has been determined, for example, a state in which the difference between the load data hs acquired this time and the previous load data hs stored in the storage unit 70 is equal to or less than a predetermined value continues for a predetermined number of times. In this case, it can be determined that the load has been confirmed. When the CPU 40 determines that the load is confirmed in step S10 (step S10: Yes), the average value of the load data hs is converted into a multiple of the minimum unit (0.05 kg, etc.), and the data is output from the output unit 80. To do. Then, the CPU 40 shifts from the measurement state to the standby state, operates the switch 50, switches the power source of the detection unit 10 from the power source VDDA to the power source VDDB, and returns to step S1. Thereby, the electric current which flows into the detection part 10 reduces, and the resolution of the detection part 10 falls.
When CPU 40 determines that the load is not fixed in step S10 (step S10: No), CPU 40 continues the load measurement process in step S9.

As described above, the weighing scale 1 of the first embodiment reduces the current flowing to the detection unit 10 and reduces the resolution of the detection unit 10 by switching the power supply of the detection unit 10 from the power supply VDDA to the power supply VDDB. Then, take the standby action. For this reason, the weight meter 1 can reduce power consumption. Note that the detection unit 10 consumes the largest amount of power among the components constituting the weight scale 1, and therefore the current flowing to the detection unit 10 can be reduced. High contribution to low power consumption. Since the weigh scale 1 detects the load by the detection unit 10, it does not require a mechanical switch for detecting the load, and therefore the inclination due to the stroke for turning on the mechanical switch does not occur. High-precision measurement is possible. Further, the scale 1 of the first embodiment increases the current flowing to the detection unit 10 by switching the power supply of the detection unit 10 from the power supply VDDB to the power supply VDDA when the detection unit 10 detects a change in load. Let Thereby, the resolution | decomposability of the detection part 10 goes up and the weight scale 1 can measure a load correctly.
In this embodiment, the detection unit 10 as a load sensor using a strain gauge has been described. However, the present invention can be applied to other load sensors.

<< Second Embodiment >>
Next, a second embodiment will be described. The weigh scale 1 according to the first embodiment switches the power supply VDDA and the power supply VDDB to switch the current flowing to the detection unit 10. On the other hand, the weighing scale 1 according to the second embodiment switches the value of the current flowing to the detection unit 10 by switching the resistance. FIG. 3 is a block diagram showing a hardware configuration of the weigh scale 1 according to the second embodiment. (In the following embodiments, elements having the same functions and functions as those in the first embodiment are the same as above. A description will be omitted as appropriate with reference numerals.
The weigh scale 1 connects a load detection unit 10, an operational amplifier 20 that amplifies a signal, an A / D converter 30 that converts the amplified analog signal into a digital signal, a CPU 40, a power supply VDDA, and the detection unit 10. And a switch 51 that switches a power supply path to be switched between a path that does not pass through the resistor 60 and a path that passes through the resistor 60.

  The switch 51 connects the power supply VDDA connected to the input terminal in1 of the bridge circuit 11 of the detection unit 10 and the detection unit 10 between a path not passing through the resistor 60 and a path passing through the resistor 60. Switch to switch. The resistance 60 has a resistance value equal to or higher than the resistance value of the strain gauge. Here, “equivalent” is not necessarily limited to the same, and may have values before and after. The switch 51 is switched by the CPU 40. The current control unit includes a switch 51 and a CPU 40 that controls the switch 50.

  Assuming that the resistance value of the resistor 60 is the same as, for example, the strain gauge resistance value of 350Ω, when the CPU 40 selects the path from the power supply VDDA via the resistor 60, the power supply VDDA / (gauge resistance + resistance 60) The current Bi2 obtained by the above flows through the detection unit 10. In addition, when the CPU 40 selects a path that does not pass through the resistor 60 from the power supply VDDA, the current Bi <b> 3 flows to the detection unit 10. The current Bi3 is a current sufficient to obtain the necessary accuracy of the weight scale 1. Further, the current Bi3 is a current double the current Bi2, and the resolution of the detection unit 10 in the current Bi3 is double the resolution of the current Bi2. Here, a case where the output voltage of the power supply VDDA is 3 V and the resistance 60 is 6650Ω will be described. The power supply VDDA supplies the detection unit 10 with a current that is equal to or greater than a current value sufficient to obtain the necessary accuracy of the weighing scale 1. At this time, the current flowing to the detection unit 10 is 3V / 350Ω = about 8.6 mA (1/10000 accuracy). On the other hand, when the CPU 40 selects a path of the switch 51 from the power supply VDDA via the resistor 60, the current flowing to the detection unit 10 is 3V / (350Ω + 6650Ω) = about 0.43 mA (1/500 accuracy). Therefore, the CPU 40 can reduce the accuracy (resolution) of the detection unit 10 and reduce the current flowing to the detection unit 10 by switching the switch 51 of FIG.

  The operation of the CPU 40 will be described. FIG. 2 is a flowchart showing the operation of the CPU 40 according to the second embodiment. The CPU 40 shifts to the standby state and operates the switch 51 to switch the power source of the detection unit 10 from the power supply VDDA to the path via the resistor 60 to reduce the current flowing to the detection unit 10 (step S1). The weigh scale 1 operates in a state where power consumption is low according to the state of step S1.

The CPU 40 determines whether or not the current time is the timing for starting the zero point update process (step S2). When the current time is the timing for starting the zero point update process in step S2 (step S2: Yes), the CPU 40 shifts from the standby state to the zero point update state for executing the zero point update process (steps S3 to S3). Step S6). When the zero point update process is started, the CPU 40 operates the switch 51 to switch the power supply of the detection unit 10 from the path from the power supply VDDA through the resistor 60 to the path not through the resistor 60 to the detection unit 10. The flowing current is increased (step S3). CPU40 acquires the zero point data hs _0, this zero point data hs _0, updates the zero point data hs ₀ which is stored in the storage unit 70 (step S4). Next, the CPU 40 operates the switch 51 to switch the power source of the detection unit 10 from the path passing through the resistor 60 from the power source VDDA to the path not passing through the resistor 60 to reduce the current flowing to the detection unit 10 ( Step S5). The resolution of the detection unit 10 is lowered. Subsequently, CPU 40 updates the reference data Ls ₀ of the load detected (step S6). In addition, when the current time is not the timing for starting the zero point update process in Step 2 (Step S2: No), or when the CPU 40 completes the zero point update process of Steps S3 to S6 and shifts to the standby state. The process proceeds to the next step S7.

  Next, the CPU 40 determines whether or not there is load detection (step S7). When the load is detected (step S7: Yes), the CPU 40 shifts from the standby state to the measurement state, operates the switch 51, and switches the power supply of the detection unit 10 from the path from the power supply VDDA via the resistor 60 to the resistance. By switching to a route that does not pass through 60, the current flowing to the detection unit 10 is increased (step S8), and the resolution of the detection unit 10 is increased. Then, the CPU 40 proceeds to the next step S9. If the load data is less than the threshold value (step S7: No), the process returns to step S2 where it is determined whether it is time to start the zero point update process.

  CPU40 acquires the load data hs which shows the load applied to a measurement stand, and performs the measurement process of a load (step S9). The CPU 40 proceeds to the next step S10.

  The CPU 40 determines whether or not the load is confirmed in the measurement process (step S10). If the CPU 40 determines that the load is confirmed in step S10 (step S10: Yes), the average value of the load data hs is converted into a multiple of the minimum unit (0.05 kg, etc.), and the data is output from the output unit 80. To do. Then, the CPU 40 shifts from the measurement state to the standby state, operates the switch 51, switches the power source of the detection unit 10 from the path not passing through the resistor 60 from the power supply VDDA to the path passing through the resistor 60, and proceeds to step S1. Return. Thereby, the electric current which flows into the detection part 10 reduces, and the resolution of the detection part 10 falls. When CPU 40 determines that the load is not fixed in step S10 (step S10: No), CPU 40 continues the load measurement process in step S9.

As described above, the weighing scale 1 according to the second embodiment switches the path connecting the detection unit 10 and the power supply VDDA from the path not passing through the resistor 60 to the path passing through the resistor 60, thereby detecting the detection unit. The current flowing to 10 can be reduced, and the same effect as in the first embodiment can be obtained. Therefore, the weight scale 1 can realize reduction of power consumption in the standby state. In the first embodiment, two types of power sources, the power source VDDA and the power source VDDB, are used. In the second embodiment, the power source VDDB is reduced and replaced with the resistor 60. Thereby, the weighing scale 1 of the second embodiment can reduce the number of parts and the cost around the power supply VDDB as compared with the first embodiment.
In addition, when the detection unit 10 detects a change in load, the weigh scale 1 of the second embodiment changes the path connecting the detection unit 10 and the power supply VDDA from the path via the resistance 60 to the resistance 60. By switching to a route that does not pass, the current flowing to the detection unit 10 is increased. Thereby, the resolution | decomposability of the detection part 10 goes up and the weight scale 1 can measure a load correctly.

  Note that the number of resistors 60 in the weighing scale 1 of the second embodiment is not limited to one. For example, if the power supply to the detection unit 10 is set in three stages of the power supply VDDA, the resistor 60, and a resistance larger than the resistor 60, the CPU 40 sets the current flowing to the detection unit 10 in three ways, and the resolution of the detection unit 10 is 3 Can be staged. Further, the combination of the resistor 60 and the switch 51 may be replaced with a variable resistor to cope with it.

<< Third Embodiment >>
Next, a third embodiment will be described. The weigh scale 1 according to the first embodiment switches the power supply VDDA and the power supply VDDB to switch the current flowing to the detection unit 10, and the weigh scale 1 according to the second embodiment switches the resistance to detect the detection unit 10. The value of the current that flows to is switched. On the other hand, the weigh scale 1 according to the third embodiment switches the current source IA and the current source IB to switch the current value flowing to the detection unit 10. The current source IA and the current source IB are constant current sources that allow a constant current to flow. FIG. 4 is a block diagram showing a hardware configuration of the weigh scale 1 according to the third embodiment. (In the following embodiments, the same functions and functions as those of the first embodiment are described above. The same reference numerals are given and the description thereof is omitted as appropriate). The weigh scale 1 includes a load detection unit 10, an operational amplifier 20 that amplifies a signal, an A / D converter 30 that converts the amplified analog signal into a digital signal, a CPU 40, and a current that supplies current to the detection unit 10. A source IA and a current source IB, and a switch 52 for switching between the current source IA and the current source IB are provided.
The current control unit includes a switch 50 and a CPU 40 that controls the switch 50.

  The switch 52 is a switch that switches a current source connected to the input terminal in1 of the bridge circuit 11 of the detection unit 10 between the current source IA and the current source IB. This switch 52 is operated by the CPU 40. The current source IA is a current source that supplies the detection unit 10 with a current that is sufficient to obtain the accuracy desired by the scale 1, for example, 1/10000 accuracy. The current source IB is a current source that supplies a current corresponding to an accuracy less than the accuracy desired by the weighing scale 1, for example, 1/500 accuracy, to the detection unit 10. For example, if the current source IA is a constant current source of 8.6 mA and the current source IB is a constant current source of 0.43 mA, the CPU 40 detects by switching the switch 52 from the current source IA to the current source IB. The current flowing to the unit 10 can be reduced from about 8.6 mA (1/10000 accuracy) to about 0.43 mA (1/500 accuracy), and the accuracy (resolution) of the detection unit 10 can be lowered.

  The operation of the CPU 40 will be described. FIG. 2 is a flowchart showing the operation of the CPU 40 according to the third embodiment. The CPU 40 shifts to the standby state, operates the switch 52, switches the current source supplied to the detection unit 10 from the current source IA to the current source IB, and reduces the current flowing to the detection unit 10 (step S1). The weigh scale 1 operates in a state where power consumption is low according to the state of step S1.

The CPU 40 determines whether or not the current time is the timing for starting the zero point update process (step S2). When the current time is the timing for starting the zero point update process in step S2 (step S2: Yes), the CPU 40 shifts from the standby state to the zero point update state for executing the zero point update process (steps S3 to S3). Step S6). When the zero point update process is started, the CPU 40 operates the switch 52 to switch the current source supplied to the detection unit 10 from the current source IB to the current source IA. As a result, the current flowing to the detection unit 10 increases (step S3), and the resolution of the detection unit 10 increases. CPU40 acquires the zero point data hs _0, this zero point data hs _0, updates the zero point data hs ₀ stored in the storage unit 70 (step S4). Next, the CPU 40 operates the switch 52 to switch the current source supplied to the detection unit 10 from the current source IA to the current source IB. Thereby, the electric current which flows into the detection part 10 reduces (step S5), and the resolution of the detection part 10 falls. Subsequently, the CPU 40 updates the reference data Ls for load detection (step S6). In addition, when the current time is not the timing for starting the zero point update process in Step 2 (Step S2: No), or when the CPU 40 completes the zero point update process of Steps S3 to S6 and shifts to the standby state. The process proceeds to the next step S7.

  The CPU 40 determines whether or not there is load detection (step S7). When the load is detected (step S7: Yes), the CPU 40 shifts from the standby state to the measurement state, operates the switch 52, and switches the current source supplied to the detection unit 10 from the current source IB to the current source IA. As a result, the current flowing to the detection unit 10 increases (step S8), and the resolution of the detection unit 10 increases. Then, the CPU 40 proceeds to the next step S9. On the other hand, when the load data is less than the threshold value (step S7: No), the CPU 40 returns to step S2 for determining whether or not it is time to start the zero point update process.

  CPU40 acquires the load data hs which shows the load applied to a measurement stand, and performs the measurement process of a load (step S9). The CPU 40 proceeds to the next step S10.

  The CPU 40 determines whether or not the load is confirmed in the measurement process (step S10). If the CPU 40 determines that the load is confirmed in step S10 (step S10: Yes), the average value of the load data hs is converted into a multiple of the minimum unit (0.05 kg, etc.), and the data is output from the output unit 80. To do. Then, the CPU 40 shifts from the measurement state to the standby state, operates the switch 52, switches the current source supplied to the detection unit 10 from the current source IA to the current source IB, and returns to step S1. Thereby, the electric current which flows into the detection part 10 reduces, and the resolution of the detection part 10 falls. When CPU 40 determines that the load is not fixed in step S10 (step S10: No), CPU 40 continues the load measurement process in step S9.

As described above, the weighing scale 1 of the third embodiment is equivalent to the first embodiment and the second embodiment by switching the current source supplied to the detection unit 10 from the current source IA to the current source IB. The effect of can be obtained. Further, the scale 1 of the first embodiment and the second embodiment can improve the output voltage of the power supply VDDA, for example, by increasing the output voltage of the battery. For example, when the output voltage of the power source VDDA is 4.2 V when the output voltage of the battery is 3 V, the current flowing to the detection unit 10 is changed from about 8.6 mA to about 6 mA by replacing the battery with a 6 V output battery. 12.0 mA. Thus, in order to increase the current flowing to the detection unit 10 and further increase the resolution, it is necessary to increase the output voltage of the power supply VDDA. On the other hand, in the third embodiment, the current value of the constant current source supplied to the detection unit 10 can be increased without changing the output voltage of the power supply VDDA. This is because the current value in the constant current source can be set regardless of the voltage value of the power source. Therefore, the weigh scale 1 of the third embodiment increases the current flowing to the detection unit 10 and reduces the resolution even if the supply voltage of the circuit other than the detection unit 10 is lowered and the power consumption of the weigh scale 1 is further reduced. Higher operation is possible. In addition, the weight scale 1 of the present embodiment needs to use two types of current sources, that is, the current source IA and the current source IB. However, a resistor that uses one type of current source and sets a constant current value. It is also possible to switch.
Further, the weighing scale 1 of the third embodiment is configured such that when the detection unit 10 detects a change in load, the current source supplied to the detection unit 10 is switched from the current source IB to the current source IA. Increase the current flowing to Thereby, the resolution | decomposability of the detection part 10 goes up and the weight scale 1 can measure a load correctly.

As described above, the embodiment has been described in detail with reference to the drawings. However, the specific configuration is not limited to that described above, and various design changes and the like can be made.
For example, when the current flowing to the detection unit 10 is reduced and the resolution of the detection unit 10 is reduced, in another embodiment, the CPU 40 can set the amplification factor (gain) of the operational amplifier 20 high in order to increase the sensitivity of load detection. It may be. In the above-described embodiment, the detection unit 10 as the load sensor in the bridge circuit 11 using the strain gauge has been described. However, the present invention is not limited to this. For example, in another embodiment, a pressure sensor using a piezo element as a load sensor, or a sensor using a semiconductor gauge or the like may be applied. In addition, the weighing scale 1 according to another embodiment further reduces power consumption by causing a current to flow through the detection unit 10 only during a predetermined period in a standby state in which the current flowing through the detection unit 10 is reduced. It is also possible.
Further, the number of power supplies may be increased to other than VDDA and VDDB, and, for example, in a stepwise manner according to a period during which no load is detected, for example, the standby state 2 may be shifted to the standby state 2 where power consumption is reduced. Good.

  The operation of the CPU 40 is defined by a program. The operation of each processing unit described above is stored in the storage unit 70 in the form of a program. The CPU 40 executes the above process according to the program stored in the storage unit 70.

  In at least one embodiment, the storage unit 70 is an example of a tangible medium that is not temporary. Other examples of the tangible medium that is not temporary include a magnetic disk, a magneto-optical disk, a CD-ROM, a DVD-ROM, and a semiconductor memory connected via an interface. When this program is distributed to a computer via a communication line, the CPU 40 of the computer that has received the distribution may develop the program in the storage unit 70 and execute the above processing.

  The program may be for realizing a part of the functions described above. Further, the program may be a so-called difference file (difference program) that realizes the above-described function in combination with another program already stored in the auxiliary storage device.

  DESCRIPTION OF SYMBOLS 1 ... Weigh scale 10 ... Detection part 11 ... Bridge circuit 20 ... Operational amplifier 30 ... A / D converter CPU ... 40 50, 51, 52 ... Switch 60 ... Resistance 70 ... Memory | storage part 80 ... Output part

Claims (7)

A detection unit for detecting a load applied to the load sensor from a current flowing through the load sensor;
A weight scale comprising: a current control unit configured to increase a current flowing through the load sensor to a current value sufficient to obtain a desired accuracy when the detection unit detects a change in load. When the detection unit detects a change in load, the current control unit increases the current flowing through the load sensor from less than a current value sufficient to obtain a desired accuracy to a value greater than a current value sufficient to obtain a desired accuracy. The weight scale according to claim 1. 3. The weight scale according to claim 1, wherein when the detection unit does not detect a change in load, the current control unit updates the zero point data by increasing the current value of the load sensor at a certain interval. 4. When the detection unit detects a change in load, the current control unit supplies a power source that supplies a current to the load sensor from a first power source that is a power source connected to the load sensor. 4. The power source for supplying power larger than the power source of the first power source is switched to a second power source that is a power source in which a current flowing through the load sensor is equal to or higher than a current value sufficient to obtain a desired accuracy. 5. The weighing scale according to claim 1. When the detection unit detects a change in load, the current control unit has a resistance between a power source that supplies current to the load sensor and the load sensor, and the current flowing through the load sensor has a desired accuracy. The weight scale according to any one of claims 1 to 3, wherein the weight is decreased so as to be equal to or more than a current value sufficient to obtain. The said current control part switches the path | route which connects between the said power supply and the said load sensor from the path | route which has resistance to the path | route which does not have resistance, when the said detection part detects the change of a load. The scale described. The current control unit includes a constant current power source that supplies a current to the load sensor when the detection unit detects a change in load, and a first constant current that is a constant current power source connected to the load sensor. A constant current power source that supplies a current larger than the first constant current power source from the power source is switched to a second constant current power source in which the current flowing through the load sensor is greater than or equal to a current value sufficient to obtain a desired accuracy. The weight scale according to any one of claims 1 to 3.

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