JP3783428B2 - electronic balance - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electronic balance incorporating a calibration weight.
[0002]
[Prior art]
Conventionally, an electronic balance has a known load detection mechanism including a load detector of an electromagnetic force balance system or the like in its housing, and this load detection mechanism is a load that acts on a sensitive member via a sample pan. It is comprised so that it can detect.
Usually, such an electronic balance is provided with a calibration weight (that is, a built-in calibration weight) in the load detection mechanism so as to ensure a certain accuracy over a long period of time. There is no need to prepare, and daily calibration can be done easily using this built-in calibration weight, ensuring the accuracy required for mass measurement.
[0003]
In this case, an eccentric cam, a slide cam, or the like is used as a calibration weight adding and removing mechanism constituting the load detecting mechanism. For example, FIG. 1 discloses a lever-type weight adding and removing method using an eccentric cam. In the case of this eccentric cam, the weight is moved up and down by applying a lever principle. Further, in the case of a slide cam, it is a vertically moving rod type weight addition and removal method in which the weight is directly moved up and down by a single vertically moving up and down moving rod, which is widely known as a known technique.
[0004]
A power source such as an electric motor is connected to the cam, which plays a central role in such an addition and removal mechanism, and the electric motor acts as an external force that applies a rotational force and a longitudinal motion to the cam. By using the locus of the cam peripheral part generated by the above, a method is adopted in which the calibration weight is moved up and down to load and release the load on the load detector.
A DC motor (hereinafter referred to as a motor in the present text) is often used as a drive source for such an addition / subtraction mechanism.
[0005]
On the other hand, in the adding and removing mechanism, the state of adding or removing the calibration weight to the load detector can be known by a position detection sensor for the weight position provided in the peripheral portion of the cam, and the calibration weight is obtained from the signal. Can be determined whether the load is loaded on the load detector or the load is released, and the ON / OFF (start / stop of rotation) of the supply voltage to the motor is performed according to the determination result. The calibration weight can be added to or removed from the load detector.
[0006]
By the way, a series-winding motor is often used as a drive source in the calibration weight adding and removing mechanism. An example of the circuit of this series-wound motor and an example of motor characteristics relating to the torque and the rotational speed are as shown in FIGS. That is, FIG. 2 is an example showing a supply circuit of the applied voltage (V) to the series-wound motor, and the diode (D) in the figure also serves as protection for the motor (M) and noise countermeasures for the external circuit. In what is called a spark killer. FIG. 3 shows the correlation between the current (Ia) flowing through the motor (M) and the rotational speed (N) of the motor (M), and the generated current (T) of the current (Ia) and the motor (M). The correlation with each is shown.
[0007]
In the case of rotating a motor having such characteristics at a constant speed, the conventional technique obtains in advance the maximum torque of torque required for adding and removing the calibration weight and uses a characteristic table as shown in FIG. Then, a method of determining the applied voltage of the motor necessary for generating the torque and obtaining a desired rotational speed of the motor is taken, and the applied voltage to the motor thus determined is determined from the position of the addition / deduction weight. In response to this signal, the applied voltage is turned ON / OFF, and the calibration weight is added or removed.
[0008]
[Problems to be solved by the invention]
As described above, the torque required to add / remove the calibration weight, which is determined in advance, is the same as that used when the calibration weight is actually lifted in the lever weight addition / desorption system using the eccentric cam, and the vertical movement rod type weight addition / removal using the slide cam. In the method, the torque is the largest of the necessary torques associated with the addition and removal of the calibration weight, such as the torque when the calibration weight is actually pushed up and pressed against the weight holder.
That is, these mean that the torque associated with the load release of the calibration weight to the load detector is much larger than the torque at the time of loading.
[0009]
However, as described above, it is clear that obtaining a large torque required for releasing the load on the motor when adding or removing the calibration weight is unnecessary especially when the calibration weight is loaded, and It was also uneconomical.
Furthermore, when the torque required for rotation is required only a little, such as when a calibration weight is applied to the load detector, the applied voltage to the motor must be set to a voltage that satisfies the maximum torque condition beforehand. Therefore, there is a problem that the rotational speed is increased due to the characteristics of the motor, and the noise and vibration of the motor are increased accordingly.
The present invention eliminates unnecessary power as much as possible in the function as a driving source such as rotational force and forward / backward movement of the motor cam as described above, and various problems of noise and vibration due to unnecessary increase in rotational speed. An electronic balance that eliminates the problem is provided.
[0010]
[Means for Solving the Problems]
In order to solve the above problems, an electronic balance of the present invention includes a weight position sensor for detecting a weight position that is linked to a load and a load release of a calibration weight, and a motor control circuit for controlling the rotational speed of the motor, By controlling the input voltage to the motor control circuit according to the signal from the weight position sensor, the rotational speed of the motor, that is, the load on the load detector of the calibration weight and the operation speed of the load release are controlled, and the calibration weight The torque and rotational speed necessary for loading and unloading can be supplied from the motor when necessary.
[0011]
Embodiment
The configuration of the present invention will be described below based on the embodiment shown in FIGS.
An electronic balance is usually roughly divided into two groups, a mechanical element system and an electrical element system. FIG. 1 is a system diagram in which the main components are specifically shown in a block diagram. It also means a block diagram of the main components of the electronic balance according to the invention.
[0012]
That is, the mechanical element system includes an addition / removal mechanism 4 that adds and removes the calibration weight 3 by using the lever principle 4b and the lever 4a, and a driving motor 9 that performs a predetermined motion necessary for the addition and removal of the calibration weight 3. And a cam 8 directly connected to the motor 9, and a weight receiver 6, a tray support column 5, a tray receiver 2, a sample tray 1 and the like suspended from a load detector 10 (also referred to as a load sensor).
On the other hand, the electric element system detects the position of a load detector 10 using an electromagnetic force balance method, an A / D converter 11 that converts an analog signal from the load detector 10 into a digital signal, and a calibration weight 3. The weight position sensor 7 for driving, the driver circuit 12 for driving the motor 9, the interface circuit 13 for optimizing various input / output signals, and the microcomputer 14 (CPU, RAM, ROM, etc.) for processing various input / output signals. Etc.). However, the display etc. which display the digital conversion data from the load detector 10, various calculation results, etc. are omitted.
[0013]
In the above configuration, the specific operation will be described with reference to FIG.
When an external load placed on the sample pan 1 or a calibration weight 3 is loaded, the load detector 10 generates and outputs an electrical signal corresponding to the load. The output signal is taken into the interface circuit 13 via the A / D converter 11 and input to the microcomputer 14.
The microcomputer 14 is a CPU for controlling various operations and programs and controlling each peripheral device via the interface circuit 13, a ROM in which a program is written, digital conversion data from the load transducer 10, various calculation results, and the like. It is composed of a non-volatile RAM having an area for storing.
[0014]
The adjusting mechanism 4 for the calibration weight 3 includes a cam 8 rotated by a motor 9, a lever 4a displaced about a fulcrum 4b by the rotation of the cam 8.
The calibration weight 3 is loaded or released from the weight receiver 6, that is, the load detector 10 by driving the motor 9 via the driver circuit 12 based on the command of the CPU.
At this time, the weight position sensor 7 disposed in the vicinity of the cam 8 indicates the position of the calibration weight 3 interlocked with the rotation of the cam 8, that is, the load state of the calibration weight 3 on the load detector 10 as an electric signal. To the microcomputer 14 via the interface circuit 13. The microcomputer 14 is configured to judge the state of this position from a signal and supply the optimum applied voltage prepared in advance according to the position to the motor 9 to control the motor 9.
[0015]
In addition, although the example of a circuit of the series winding direct current motor used for addition and removal of the calibration weight of an electronic balance and the example of the characteristic of the same motor are shown in Drawing 2 and Drawing 3, these are the above-mentioned and detailed. Description is omitted.
[0016]
The motor control circuit of the present invention is as shown in FIG. 4 and employs a pulse width modulation (PWM) system. Using a PWM pulse signal output from the CPU of the microcomputer 14 based on a signal from the weight position sensor 7 corresponding to the position of the calibration weight, the motor applied voltage reference value (Vs) is determined using a regulator (Re). It is configured to perform ON / OFF control, adjust the applied voltage (V) to the motor 9 in the range of 0 to the voltage reference value (Vs), and perform optimal control in the motor drive according to the position state.
Therefore, when the motor 9 is rotated to release the load of the calibration weight 3 from the load detector 10, that is, when the torque required for the motor 9 is maximum, the signal from the weight position sensor 7 is known. Therefore, by changing the PWM according to the timing, the motor applied voltage (V) is raised to the maximum to cope with it, and when the calibration weight 3 is loaded, the signal of the weight position sensor 7 is also used. The PWM is changed again to lower the motor applied voltage (V), and the motor 9 is controlled to rotate slowly and slowly.
Note that the resistor R and the capacitor C in FIG. 4 are elements that form a smoothing circuit for the voltage (V) applied to the motor 9. In FIG. 4, the exciting coil (Rc) and the diode (D) are omitted.
[0017]
Although the present invention has been described in detail above, the present invention is not limited to the above-described and illustrated embodiments, and includes other modified embodiments utilizing the gist of the present invention.
For example, in the present invention, a configuration example in which the voltage control of the motor applied voltage (V) is performed by the PWM method is disclosed. Are selected according to the signal of the weight position sensor 7, that is, the position of the cam 8, and optimal control is performed for each cam 8 position of the motor 9 to exhibit the same effect as the present invention. Can do. In FIG. 1, a method using a contact type micro switch is disclosed as the weight position sensor 7, but of course, a non-contact detection method such as an optical sensor is also included in the present invention. The content.
[0018]
【The invention's effect】
As described in detail above, the electronic balance provided by the present invention uses the output signal from the sensor at the weight position to generate a torque that is suitable for both loading and unloading, It is configured to be able to perform addition and removal operations, and there is a margin in the selection conditions of the motor as the drive source, and the selection conditions of the motor itself from an economical viewpoint can be given a wider range. It has become possible. In addition, as described above, when only a small amount of torque is required for the rotation of the motor (when the calibration weight is applied to the load detector), it is possible to prevent the noise and vibration phenomenon of the motor accompanying the increase in the rotational speed. It has together.
[Brief description of the drawings]
FIG. 1 is a block diagram of the main components of an electronic balance according to the present invention.
FIG. 2 shows a circuit example of a series-winding DC motor for adding and removing weights used in an electronic balance according to the present invention.
FIG. 3 shows an example of characteristics of a series-wound DC motor for adding and removing weights used in an electronic balance according to the present invention.
FIG. 4 is a block diagram of a motor control circuit used in the electronic balance according to the present invention.
[Explanation of symbols]
1 ......... Sample pan V ......... Motor applied voltage 2 ......... Plate receiver Ia ... Current 3 ......... Calibration weight M ......... Motor 4 ......... Addition / removal mechanism D ......... Diode 4a ... Lever Rc …… Excitation coil 4b …… Supporting point N ……… Number of revolutions 5 ……… Tray rest support T ……… Torque 6 ……… Weight receiver R ……… Resistance 7 ……… Weight position sensor C ………… Capacitor 8 ......... Cam Re ... Regulator 9 ...... Motor Vs ... Motor applied voltage reference value 10 ... Load detector 11 ... A / D converter 12 ... Driver circuit 13 ... Interface circuit 14 ... Micro Computer

Claims (1)

In an electronic balance that uses an electric motor as a power source for loading and releasing the calibration weight to the load detector, the weight position sensor for detecting the weight position that is linked to the loading and releasing of the calibration weight and the rotational speed of the motor A control motor control circuit, and by controlling the input voltage to the motor control circuit by a signal from the weight position sensor, the load on the load detector of the calibration weight and the operation speed of the load release are controlled. An electronic balance characterized by being made possible.

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