JP3713888B2 - Electronic balance - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electronic balance of an electromagnetic force balance type, and to an electronic balance provided with a built-in weight for sensitivity calibration and a mechanism for loading / unloading the built-in weight with respect to a load sensitive part.
[0002]
[Prior art]
In electromagnetic balance electronic balances, in general, the displacement of the balance beam engaged with the load-sensitive part is detected, and the balance beam is always balanced against the load acting on the load-sensitive part via the pan. It has a servo mechanism that generates force. And the magnitude | size of the load on a plate is calculated | required from the magnitude | size of the electromagnetic force required to balance the beam.
[0003]
In the electromagnetic balance type electronic balance as described above, in order to increase the weight / resolution value to a certain level or more, the magnitude of the electromagnetic force for balancing the beams is determined based on the detection result of the beam displacement. Must be determined by digital value. That is, for example, a configuration is adopted in which the beam displacement detection result is digitally converted, and the duty of the pulse current flowing through the coil of the electromagnetic force generator is determined by digital calculation based on the digital displacement data.
[0004]
In addition, some electronic balances of this type include a so-called weight addition / removal mechanism that incorporates a weight with a known mass for sensitivity calibration, and loads / releases the built-in weight with respect to a load-sensitive portion. In an electronic balance equipped with such a built-in weight and weight adjustment mechanism, a built-in weight is automatically loaded to the load sensitive part when a sensitivity calibration command is generated, and the balance is generated. The magnitude P1 of the electromagnetic force, and the magnitude P0 of each electromagnetic force before the load of the built-in weight and in the state where the balance of the beam is obtained after the load of the built-in weight is released, that is, in the no-load state before and after the load The sensitivity coefficient is calculated and updated from the difference {P1- (P0 + P2) / 2} from the average value of P1 and the known mass value of the built-in weight.
[0005]
[Problems to be solved by the invention]
By the way, in a conventional electromagnetic force balance type electronic balance with a built-in weight and its addition / deletion mechanism, the balance beam can be applied to the load sensitive part of the built-in weight in the same way as when the load to be measured is loaded on the pan. The digital value which determines the electromagnetic force which should balance a beam was calculated | required by the calculation based on displacement detection data. In addition, when releasing the load from the load-sensitive part of the built-in weight, the electromagnetic force to balance the beam by calculation based on the displacement detection data of the balance beam in the same way as when removing the measured load from the pan. Wanted to determine the digital value.
[0006]
Here, based on the momentary displacement detection data of the beam, it is dependent on the response of the system to actually balance the beam while calculating the digital value that determines the electromagnetic force to balance the beam every moment. It takes a considerable amount of time. For this reason, the electromagnetic force balance type balance provided with the conventional built-in weight and its adding / subtracting mechanism has a problem that it takes a long time until the sensitivity coefficient is actually updated after the sensitivity calibration command is generated.
[0007]
The present invention has been made in view of such a situation, and in an electromagnetic force balance type electronic balance equipped with a built-in weight and its addition / deletion mechanism, it is necessary from the generation of the sensitivity calibration command to the actual update of the sensitivity coefficient. The purpose is to provide an electronic balance that can shorten the time.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the electronic balance of the present invention detects the displacement of the balance beam 3 that engages with the load sensitive portion 21 that supports the pan 1, as shown in FIG. Based on the detection result, a servo mechanism is provided for determining an electromagnetic force that balances the balance beam 3 against the load acting on the pan 1 by a digital value, and the magnitude of the electromagnetic force required to balance the balance beam 3 In the electronic balance provided with the built-in weight 11 for calibrating the sensitivity and the mechanism 12 for loading / unloading the weight 11 with respect to the load-sensitive part 21, the weighing display value is obtained from the built-in weight 11. A memory 8 in which a digital value corresponding to a change in electromagnetic force necessary for balancing the beam 3 at the time of loading is provided, and a load sensitivity of the built-in weight 11 at the time of sensitivity calibration. When the load / unloading for 21, the digital value for determining the electromagnetic force, characterized by being configured to forcibly add / subtract by the value amount written in the memory 8.
[0009]
The present invention utilizes the fact that the mass of the built-in weight 11 is known, and at the time of loading / releasing the load to the load sensing portion 21 of the known mass, the digital value for determining the electromagnetic force to be generated is By forcibly adding / subtracting the value corresponding to the known mass, the time until the balance beam 3 reaches a completely balanced state is to be shortened.
[0010]
That is, a digital value corresponding to the mass of the internal weight 11 is stored in the memory 8 in advance, and the digital value for determining the electromagnetic force is forced by the stored value when the internal weight 11 is loaded / unloaded. When the addition / subtraction is performed, the balance beam 3 is substantially in an equilibrium state from the beginning except for a slight unbalance amount corresponding to the sensitivity change of the balance. Therefore, at the time of loading / unloading the built-in weight 11, the servo mechanism only needs to eliminate the remaining unbalance, and the balance beam 3 is balanced as compared with the case where the balancing operation is performed from the beginning. The time required for this can be greatly reduced.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a configuration diagram of an embodiment of the present invention, and is a diagram illustrating a schematic diagram showing a mechanical configuration and a block diagram showing an electrical configuration.
[0012]
The pan 1 for placing the load to be measured is supported by a movable column 21 of the Roverval mechanism 2, and this movable column 21 is connected to one end of the balance beam 3 to substantially constitute a load sensitive portion. Yes.
[0013]
The balance beam 3 is supported so as to be rotatable and displaceable about a fulcrum 31, and a movable coil 41 of the electromagnetic force generator 4 is fixed to the other end. Further, the rotational displacement of the balance beam 3 is detected by a displacement sensor 5 arranged close to the other end.
[0014]
The electromagnetic force generation unit 4 includes a movable coil 41 arranged in a static magnetic field created by a magnetic circuit 42 having a permanent magnet 42a as a main component, and generates an electromagnetic force corresponding to the magnitude of a current flowing through the movable coil 41. The electromagnetic force acts on the balance beam 3 via the movable coil 41 and functions to eliminate the balance of the balance beam 3 by a servo mechanism described later. In this example, the movable coil 41 is supplied with a pulse current whose peak value is constant and whose duty changes.
[0015]
The displacement detection signal of the balance beam 3 by the displacement sensor 5 is amplified by the amplifier 51, digitized by the AD converter 6, and taken into the pulse duty conversion unit 71. The pulse duty conversion unit 71 performs a predetermined calculation process such as a digital PID calculation process on the displacement data to generate a digital value signal having a magnitude corresponding to the displacement amount of the balance beam 3. The digital value signal is supplied to the pulse duty signal generator 72. The pulse duty signal generation unit 72 generates a rectangular wave signal in which H level and L level appear alternately within a certain period, and the time ratio between the H level and L level is from the pulse duty conversion unit 71. It is configured to change according to a digital value signal.
[0016]
The rectangular wave signal from the pulse duty signal generator 72 is supplied to the pulse current generator 73. The pulse current generation unit 73 includes a constant current generation circuit and a switching element that chops the output current. The switching element is turned on / off by a rectangular wave signal from the pulse duty signal generation unit 72. A pulse current having a duty corresponding to the digital value from the pulse duty converter 71 is generated. The pulse current is passed through the movable coil 41.
[0017]
The servo for balancing the balance beam 3 against the action of the load to be measured by the displacement sensor 5, the pulse duty conversion unit 71, the pulse duty signal generation unit 72, the pulse current generation unit 73, and the electromagnetic force generation unit 4. The mechanism is configured.
[0018]
The digital value signal from the pulse duty conversion unit 71 described above is also supplied to the measured value calculation unit 74. The measurement value calculation unit 74 calculates a measurement value using the digital value signal and the sensitivity coefficient stored in the nonvolatile memory 8 and displays the measurement value on the display unit 9. The pulse duty conversion unit 71, the measurement value calculation unit 74, and the sensitivity calibration calculation unit 75, which will be described later, are actually constituted by a microcomputer and its peripheral devices, and the pulse duty signal generation unit 72 includes, for example, It is composed of a logic circuit under the control of a microcomputer.
[0019]
The movable column 21 is provided with a weight receiver 21a. The weight receiver 21a can be loaded with a built-in weight 11 of known mass for sensitivity calibration. The built-in weight 11 is automatically loaded / unloaded to / from the weight receiver 21a by the weight adding / subtracting mechanism 12. The weight addition / removal mechanism 12 includes, for example, a motor, an eccentric cam, and a lever, and operates according to a sensitivity calibration command generated by operating a sensitivity calibration key 13, for example.
[0020]
The built-in weight 11 is in a non-contact state with respect to the weight receiver 21a during normal measurement, and when a sensitivity calibration command is generated, a digital value signal at the balance point of the balance beam 3 in that state is a sensitivity coefficient calculation unit. After being read by 75, the weight receiving mechanism 21 loads the weight receiver 21a. Then, after the digital value signal at the time when the balance beam 3 is balanced in the loaded state is read by the sensitivity coefficient calculation unit 75, it is removed from the weight receiver 21a by the weight adding and removing mechanism 12 and is brought into a non-contact state again. In this state, the digital value signal at the time when the balance beam 3 is in an equilibrium state again is read by the sensitivity coefficient calculation unit 75.
[0021]
In the sensitivity coefficient calculation unit 75, when the sensitivity calibration command is generated, the digital value signal P0 from the pulse duty conversion unit 71 in the equilibrium state of the balance beam 3 before the load of the internal weight 11 and the load state of the internal weight 11 are obtained. In addition, the digital value signal P1 from the pulse duty converter 71 in the balanced state of the balance beam 3 and the pulse duty when the built-in weight 11 is removed after loading and when the balance beam 3 becomes balanced again. Using the digital value signal P2 from the conversion unit 71, the change in the digital value due to the load of the internal weight 11 is calculated as P1- (P0 + P2) / 2, and the sensitivity coefficient is calculated from the value and the known mass of the internal weight 11. The sensitivity coefficient in the nonvolatile memory 8 is updated by calculation.
[0022]
In the nonvolatile memory 8, a digital value corresponding to the mass of the built-in weight 11 is also written. This digital value is obtained when, for example, the balance beam 3 is balanced again when only the built-in weight 11 is loaded in a state where the balance beam 3 is balanced in a no-load state at a specified temperature. A value corresponding to the change in the digital value signal from the pulse duty converter 71, that is, a digital value corresponding to the mass of the built-in weight 11, and this value is written in the non-volatile memory 8 when the balance is shipped, for example.
[0023]
The digital value written in the nonvolatile memory 8 is loaded into the pulse duty conversion unit 71 at the same time when the built-in weight 11 is loaded on the weight receiver 21a by the weight addition / subtraction mechanism 12 by the generation of the sensitivity calibration command. It is added to the digital value signal from the duty converter 71 so far. Further, the added digital value is subtracted at the same time when the built-in weight 11 is removed from the weight receiver 21a.
[0024]
According to the above-described embodiment of the present invention, when the sensitivity calibration command is generated, the internal weight 11 is loaded on the weight receiver 21a, and at the same time, the digital value corresponding to the mass of the internal weight 11 is stored in the pulse duty conversion unit 71. Since it is added to the output signal, the current required to generate an electromagnetic force for substantially balancing the balance beam 3 against the load of the built-in weight 11 is immediately applied to the movable coil 41 at the same time. Washed away. Due to the generation of such electromagnetic force, the balance beam 3 is substantially in an equilibrium state except for a slight unbalance amount corresponding to the sensitivity change of the balance due to the environmental temperature or the like. It is necessary to operate only to balance the balance, and the time required for the balance beam 3 to be in an equilibrium state after loading the built-in weight 11 is simply the balance operation by the servo mechanism after loading the built-in weight 11. Compared to the time required to equilibrate the beam 3, this is greatly reduced. In addition, since the added digital value is subtracted simultaneously with the removal of the internal weight 11 from the weight receiver 21a, even in this case, a current substantially equal to the current before the load of the internal weight 11 is immediately applied to the movable coil 41. The time required for the balance beam 3 to be in an equilibrium state after the internal weight 11 is removed is also greatly reduced.
[0025]
Therefore, according to the above embodiment, the sensitivity coefficient calculation unit 75 reads the digital value P1 from the pulse duty conversion unit 71 after the sensitivity calibration command is generated and the internal weight 11 is loaded on the weight receiver 21a. The time required is shortened, and after the built-in weight 11 is removed from the weight receiver 21 after the reading, the time required for the balance beam 3 to be in an equilibrium state again and read the digital value P2 from the pulse duty conversion unit 71. As a result, the time required for the sensitivity coefficient to be updated after the sensitivity calibration command is generated is significantly shortened as compared with the conventional case.
[0026]
In the above embodiment, after the displacement detection result of the balance beam 3 by the displacement sensor 5 is digitized by the AD converter 6, the digital value obtained by the PID calculation or the like in the pulse duty conversion unit 71 is used. Although the example in which the duty of the pulse current flowing through the movable coil 41 is determined is shown, the displacement detection result of the balance beam 3 by the displacement sensor 5 is replaced with one corresponding to, for example, the displacement 0 or a minute range in the vicinity thereof. Or, it is compared with two reference values of upper and lower limits, and based on the comparison result, the digital value from the pulse duty converter is added or subtracted by one count so that the displacement data is within 0 or a minute range near it. The present invention is also applied to a method for obtaining the digital value for determining the duty of the pulse current by going every step. It is possible to apply.
[0027]
In the above example, the current flowing through the movable coil 41 of the electromagnetic force generating unit 4 is set as a pulse current, and the duty of the pulse current is changed according to the magnitude of the load. The present invention is not limited to electronic balances of various types, and can be widely applied to electronic balances of a type in which the electromagnetic force for balancing the balance beam 3 is determined by some digital value.
[0028]
FIG. 2 shows an example in which the present invention is applied to an electronic balance of a system in which a direct current is supplied to the movable coil 41. In FIG. 2, members having the same functions as those in the previous example are denoted by the same reference numerals as those in FIG. 1, and detailed description thereof is omitted.
[0029]
In the embodiment of FIG. 2, the output of the A / D converter 6 that digitizes the output of the displacement sensor 5 is read by the digital setting unit 271. In this digital setting unit 271, a digital value for determining the magnitude of the direct current to be passed through the movable coil 41 is obtained by performing a PID calculation process or the like on the displacement data taken in via the AD converter 6. . The digital value is converted into an analog voltage signal by the DA converter 272, converted into a current signal by the power amplifier 273, and passed through the movable coil 41.
[0030]
When the present invention is applied to the electronic balance of such a system, when the built-in weight 11 is loaded / released when the impression calibration command is generated, it is written in advance in the nonvolatile memory 8 in the same manner as in the previous embodiment. The digital value corresponding to the mass of the built-in weight 11 may be forcibly added / subtracted to the digital value from the digital setting unit 271 and supplied to the DA converter 272.
[0031]
Further, in each of the above embodiments, the case where the load / unload of the internal weight 11 and the update operation of the sensitivity coefficient are performed by operating the sensitivity calibration key 13 has been described. It goes without saying that the present invention can be equally applied to a case where the sensitivity calibration command is automatically generated when the value exceeds the set time or when the set time has elapsed since the previous sensitivity calibration.
[0032]
【The invention's effect】
As described above, according to the present invention, the digital value for generating the electromagnetic force required to eliminate the balance imbalance of the balance beam caused by loading the built-in weight on the load sensitive part is stored in the memory in advance. Since the built-in weight is loaded / unloaded, its digital value is forcibly added / subtracted to / from the digital value for determining the electromagnetic force generated by the servo mechanism. As a result of shortening the time required for the balance beam to equilibrate at the time of loading and unloading, the time required for sensitivity calibration using the built-in weight can be greatly reduced.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an embodiment of the present invention, and is a diagram showing a schematic diagram showing a mechanical configuration and a block diagram showing an electrical configuration. FIG. 2 is a diagram of another embodiment of the present invention. A block diagram showing a mechanical configuration and a block diagram showing an electrical configuration in the configuration diagram.
DESCRIPTION OF SYMBOLS 1 Plate | plate 2 Robarval mechanism 21 Movable column 3 Balance beam 31 Support point 4 Electromagnetic force generation part 41 Movable coil 5 Displacement sensor 51 Amplifier 6 AD converter 71 Pulse duty conversion part 72 Pulse duty signal generation part 73 Pulse current generation part 74 Weighing Value calculation unit 75 Sensitivity coefficient calculation unit 8 Non-volatile memory 9 Display 11 Built-in weight 12 Weight adjustment mechanism 13 Sensitivity calibration key

Claims (1)

Servo mechanism that detects the displacement of the balance beam that engages the load sensitive part that supports the pan, and based on the detection result, determines the electromagnetic force that balances the balance beam against the load acting on the pan by digital values This is an electronic device that has a built-in weight for sensitivity calibration and a mechanism for loading / unloading the weight to the load-sensitive part as well as obtaining the weighing display value from the magnitude of the electromagnetic force required to balance the balance beam. The balance is equipped with a memory in which a digital value corresponding to the change in electromagnetic force necessary to maintain the balance of the beam is loaded when the built-in weight is applied to the load-sensitive part. Forcibly add / subtract the digital value for generating electromagnetic force by the value written in the memory when loading / unloading the load sensitive part Electronic balance, characterized by being configured to.

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