JPH1019652A - Electronic balance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To regularly perform a precise span and linearity calibration even when a displacement error is caused by setting the load position to a movable column of upper and lower built-in weights onto the vertical axis of the center of a tray, and adding and subtracting the loads of the weights. SOLUTION: A tray 1 is supported by a movable column 21 through a tray receiving shaft 1a bent in crank form. Two built-in weights 41, 42 are loaded on the movable column 21 on the vertical axis Cv passing the center of the tray 1. Namely, weight receivers 211, 212 protruded on the side surface of the movable column 21 are inserted into the frame body 51 of a weight adding and subtracting mechanism 5, and an end surface cam 54 is rotated by a motor 55 to vertically move first and second weight lifting shafts 52, 53. Then, each weight 41, 42 is laid into either one of the state placed on the weight receiver 211, 212 on the vertical axis Cv, and the state lifted by each lifting shaft 52, 53. Thus, even in the load state of both the weights 41, 42 or one of the weights 41, 42, the load acts on the central axis of the tray 1, and is never influenced by the displacement error.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic balance,
More specifically, the present invention relates to an electronic balance having a roberval mechanism, a built-in weight, and a mechanism for adding and removing the weight.

[0002]

2. Description of the Related Art In an electronic balance, generally, a plate is supported by a mechanism called a roberval mechanism or a parallel guide to restrict the direction of its displacement in a vertical direction, and to correct an error caused by an eccentric load on the plate.
That is, consideration is given to eliminating the eccentric errors (four corner errors). The Roberval mechanism is a mechanism in which a movable column is supported on fixed columns fixed to a balance base or the like via upper and lower beams parallel to each other, and a plate is supported on the movable column,
The movable column is connected to the load sensitive part.

[0003] Some of such electronic balances have a built-in weight of a known mass for calibration and a mechanism for adding and removing the weight. Two built-in calibration weights are necessary to enable both span calibration and linearity calibration. Usually, each of the weights has a known mass, has a mass approximately equal to each other, and the total mass is the balance. A weight with a mass near the weighing capacity is built-in. At the time of span calibration, two weights are simultaneously applied to the movable column, and the span coefficient is calculated from the load data in that state and the total mass thereof. At the time of linearity calibration, the load of one weight under the loaded state is A linearity correction coefficient is calculated from the data, the mass value of the weight, and the load data of the two weights in the loaded state and the total mass value.

In such an electronic balance having two built-in weights, conventionally, each weight is loaded on the movable column at a position horizontally separated from each other by a predetermined distance, for example, on the left and right sides of the movable column. Is configured.

[0005]

By the way, the roberval mechanism is capable of eliminating an eccentric error when the upper and lower beams are horizontal, and the adjustment is carried out in a process of manufacturing the balance by placing the beam on a plate. Strictly performed while changing the load position of the load.

However, even after such an eccentricity error is strictly adjusted, a slight eccentricity error may occur due to, for example, a temperature distribution inside the balance mechanism. When such an eccentricity error occurs, a conventional electronic balance having two built-in weights has a problem that accurate calibration cannot be performed.

That is, in a conventional electronic balance having two built-in weights and a mechanism for adding and removing the same, as described above, the two built-in weights are horizontally separated from the movable column by a predetermined distance from each other. Since the weights are loaded, the loading positions of the two weights are equidistant from each other horizontally across the center axis of the pan, and the weights of the two weights are equal to each other. In the load state, the center of gravity of the total mass is located on the center axis of the plate, so it is not affected by the eccentricity error.However, even if such conditions are satisfied, the load state of only one weight at the time of linearity calibration Then, it is always affected by the deviation error. Also, the weights of the two weights may differ, or
If the distances between the load positions of the two weights from the center axis of the pan are different from each other, the eccentricity error is also affected even when both weights are loaded. If linearity calibration and span calibration are performed based on the load data affected by such an eccentric error, it is naturally impossible to perform correct calibration, and all the measurement results after calibration will have errors. Is included.

The present invention has been made in view of such circumstances, and in an electronic balance having two built-in weights and an addition / removal mechanism, an eccentricity error occurs due to a temperature distribution inside the balance mechanism. Another object of the present invention is to provide an electronic balance capable of always performing accurate span calibration and linearity calibration.

[0009]

A structure for achieving the above object will be described with reference to FIGS. 1 and 2 showing an embodiment. In the electronic balance of the present invention, a plate 1 is provided with a roberval mechanism 2. And the movable column 21 of the roberval mechanism 2 is connected to the load sensitive part 3 and has two built-in weights 41 and 4 for linearity and span calibration.
2 and a weight adding / removing mechanism 5 for loading / unloading one or both of these built-in weights 41 and 42 on the movable column 21.
In an electronic balance equipped with two internal weights 41, 4
The position of the load on the second movable column 21 is characterized by being on a vertical axis Cv passing through the center of the dish 1.

[0010] The two built-in weights 41 and 42 are respectively loaded on the movable column 21 on the center line of the plate 1 in a vertical relationship with each other. In either state where both or one of them is loaded, the load always acts on the center line of the dish 1. Therefore, even if the electronic balance has an eccentric error for some reason, the eccentric error does not affect the load data when the internal weight is loaded during the span calibration and the linearity calibration.

[0011]

FIG. 1 is a schematic overall configuration diagram of an embodiment of the present invention, in which a weight adding / removing mechanism 5 has been removed in order to clarify the load positions of built-in weights 41 and 42 on a movable column 21. It is a figure shown in a state.

A plate 1 on which a sample is to be placed has a plate receiving shaft 11
Through the movable column 21 of the roberval mechanism 2. The roberval mechanism 2 has a structure in which a movable column 21 and a fixed column 24 are connected to each other by upper and lower beams 22 and 23 having flexible portions e at both ends thereof, which are parallel to each other.
The movable column 21 is connected to one end of the lever 31 via a connecting member 31a.

The lever 31 is rotatably supported by an elastic fulcrum 31b.
2 detected. The force coil 33a of the electromagnetic force generator 33 is fixed to the lever 31.
The electromagnetic force generating device 33 includes a magnetic circuit 33b mainly composed of a permanent magnet and a force coil 33a which is displaceable in a static magnetic field generated by the magnetic circuit 33b. And
The lever 31, the displacement sensor 32, and the electromagnetic force generator 33 constitute the load sensing unit 3. That is, the load acting on the plate 1 is transmitted to the lever 31 via the movable column 21, but the displacement of the lever 31 is detected by the displacement sensor 32, and the electromagnetic force is generated so that the displacement detection result is always zero. The current flowing through the force coil 33a of the device 33 is controlled, and the magnitude of the load on the plate 1 is detected from the magnitude of the current.

In this example, the plate receiving shaft 11 is bent in a crank shape, and the plate 1 supported on its upper end is located outside the movable column 21, that is, on the side opposite to the fixed column 24. It has been taken out. Thereby, the vertical axis Cv passing through the center of the plate 1 passes outside the movable column 21, and the two built-in weights 41 and 42 are loaded on the movable column 21 on the vertical axis Cv. That is, two upper and lower weight receivers 211 and 2 are provided on the side surface of the movable column 21.
12 is formed so as to protrude across the vertical axis Cv,
Built-in weights 41 and 42 are loaded on the weight receivers 211 and 212, respectively.

Each of the built-in weights 41 and 42 is individually loaded or unloaded by the weight adding / removing mechanism 5 to each of the weight receivers 211 and 212, so that the two built-in weights 41 and 42 are not loaded. It is possible to take three states: a state where only the internal weight 42 is loaded and a state where both the internal weights 41 and 42 are loaded.

FIG. 2 is an explanatory view of a detailed structure of the weight adding / removing mechanism 5, and FIG. 1 is a cross-sectional view cut along a plane indicated by AA in FIG. FIG. 2 shows a load state of only one internal weight 42.

As shown in FIG. 2, the weight adding / removing mechanism 5
Is a frame 51 and a guide portion 5 formed on the frame 51.
A first weight lifting shaft 52 guided vertically displaceably by 1a and 51b, and a second weight lifting shaft 53 guided vertically vertically by a guide portion 51c also formed on the frame 51. An end cam 54 for moving the weight lifting shafts 52 and 53 up and down, and a motor 55 for rotating the end cam 54 are provided.

As shown in a plan view in FIG. 3, the end face cam 54 has three projections 54b, 54c and 54d formed on the upper surface of a disk 54a along a pitch circle P concentric with the center of rotation thereof. And the first and the second on the pitch circle P.
The lower ends of the weight lifting shafts 52 and 53 are in contact with each other. Accordingly, both weight lifting shafts 52 and 53 move upward in the rotation position of FIG. 3A according to the rotation position of the end face cam 54, and lift one of the weights in the position of FIG. Only the shaft 52 moves upward, and at the position shown in FIG. 4C, each of the weight lifting shafts 52 and 53 is located below.

Each of the weight receivers 211 and 212 protruding from the side surface of the movable column 21 is inserted into the frame 51, and each of the built-in weights 41 and 42 is connected to an end face cam 54 driven by a motor 55. The first and second weight lifting shafts 52 and 53 move up and down with the rotation of the weight, so that the weights are placed on the weight receivers 211 and 212 on the vertical axis Cv or lifted by the respective weight lifting shafts 52 and 53. State.

That is, lifting members 52a and 53a for lifting the built-in weights 41 and 42 are mounted on the weight lifting shafts 52 and 53, respectively.
The 212 is formed with through holes 211a and 212b through which the lifting members 52a and 53a can pass. When the weight lifting shafts 52 and 53 are moved upward, the internal weights 41 and 42 are sandwiched between the lifting members 52a and 53a and the weights 51d and 51e provided on the frame 51, respectively. In the state, each built-in weight 41,
The weight 42 and the weight lifting shafts 52 and 53 are not in contact with the weight receivers 211 and 212. on the other hand,
In the state where the weight lifting shafts 52 and 53 are located below,
The built-in weights 41 and 42 are placed on the weight receivers 211 and 212 on the vertical axis Cv by their own weights. In this state, the weight lifting shafts 52 and 53 are also connected to the weight receiver 2.
A non-contact state is maintained at 11 and 212.

In the above embodiment of the present invention, each of the built-in weights 41 and 42 is loaded on the movable column 21 via the weight receivers 211 and 212 on the vertical axis Cv passing through the center of the plate 1. Even if the weights of the internal weights 41 and 42 do not match, in both the loaded state of the two internal weights 41 and 42 and the loaded state of the one internal weight 42, the load is the center of the plate 1. Acts on the shaft and is not affected by eccentric errors. Therefore, in this embodiment, even if an eccentric error occurs for some reason,
Accurate span calibration and linearity calibration can be performed without being affected.

In the above embodiment, the dish receiving shaft 1a is bent in a crank shape so that the built-in weights 41 and 42 are loaded on the movable column 21 on the vertical line Cv passing through the center of the dish 1. However, the present invention is not limited to this. For example, the plate 1 is supported on the central axis of the movable column 21, the central portion of the movable column 21 is hollow, and each built-in weight 41 is provided in the hollow portion. , 42 makes it possible to load each built-in weight on the vertical axis Cv passing through the center of the dish 1 without bending the dish receiving shaft.

The mechanism for adding and removing each internal weight is not limited to the above example, and any other known mechanism may be used as long as it can load each internal weight on a vertical axis passing through the pan. It goes without saying that it can be done.

[0024]

As described above, according to the present invention, since the two built-in weights for span and linearity calibration are respectively loaded on the movable column on the vertical axis passing through the center of the plate, the temperature of the balance mechanism is reduced. Even if the calibration operation is performed while an eccentricity error is occurring due to some reason such as distribution, the load of each built-in weight acts independently on the center axis of the dish, so it may be affected by the eccentricity error And accurate calibration can always be performed.

[Brief description of the drawings]

FIG. 1 is a schematic overall configuration diagram of an embodiment of the present invention.
FIG. 3 shows the internal weights 41 and 42 with the weight removing mechanism 5 removed to clarify the load position on the movable column 21.

FIG. 2 is an explanatory diagram of a detailed structure of a weight adding / removing mechanism 5 shown in a cross-sectional view cut along a plane indicated by AA in FIG. 1;

FIG. 3 is an explanatory view of an operation of an end cam shown in a plan view.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 plate 1a plate receiving shaft 2 roberval mechanism 21 movable column 211, 212 weight receiver 3 load sensitive part 31 lever 32 displacement sensor 33 electromagnetic force generator 41, 42 built-in weight 5 weight adding and removing mechanism 51 frame 52 first weight lifting shaft 53 Second Weight Lifting Shaft 54 End Face Cams 54a, 54b, 54c Projection 55 Motor

Claims (1)

[Claims] 1. A dish is supported by a Roberval mechanism, and
The movable column of the roberval mechanism is connected to the load sensitive part, and two internal weights for linearity and span calibration, and a weight addition / removal for loading / unloading one or both of these internal weights to / from the movable column. An electronic balance provided with a mechanism, wherein a load position of the two built-in weights on the movable column is on a vertical axis passing through a center of the plate.