JP3505876B2 - Balance - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a balance, and more particularly to a balance of a type in which a load acting on a pan is transmitted to a load responsive part by a lever having an elastic fulcrum. . 2. Description of the Related Art In an electromagnetic balance of an electromagnetic force balance type, generally, a plate is supported on a movable column whose displacement direction is restricted only in the vertical direction by a Roberval mechanism, and the movable column is connected to one end of a lever. And by its lever,
In many cases, a configuration is adopted in which the load acting on the plate is reduced at a rate corresponding to the lever ratio and transmitted to the load sensing unit. [0003] The lever in such a balance is normally swingably supported by an elastic fulcrum with respect to the balance frame, and the movable column and the lever are connected by an elastic connecting member. [0004] The elastic fulcrum is usually constituted by a band-shaped member made of an iron-based constant elastic material, and the elastic connecting member is usually a band formed of an iron-based material. On the other hand, an aluminum-based material is used for the lever, the balance frame, the movable column, and the like. Then, as shown in FIG. 1 as an example of a perspective view near the attachment portion of these different materials, the elastic fulcrum member E (or the elastic connecting member)
The lever L (or the balance frame and the movable column) is fixed by a screw S in a state where the flat surfaces of the two are in contact with each other. [0005] By the way, in a balance having the above-described lever, an elastic fulcrum member made of a material different from the lever, and an elastic connecting member, conventionally, when the environmental temperature changes, In the subsequent measurement of the sample, the zero point sometimes changed stepwise. This step-like change of the zero point is caused by a change in the ambient temperature in a state where the ambient temperature is largely changed.
Appears prominently in the second measurement. An object of the present invention is to eliminate a change in the zero point in a measurement after a change in environmental temperature in a balance provided with such levers and elastic fulcrums of different materials. A configuration for achieving the above object will be described with reference to FIGS. 3 and 4 showing an embodiment of the invention. The balance of the present invention is a balance frame. A lever 5 swingably supported with respect to 2 via elastic fulcrum members 8a and 8b, and a movable column 3 which supports the plate 1 and is vertically displaceable by an elastic connecting member 9. In the balance connected and configured so that the load acting on the plate 1 is transmitted to the load sensing portion 7 by the lever, the linear expansion is applied to the elastic fulcrum members 8a and 8b and the attachment portion of the elastic connecting member 9 to the lever 5 respectively. It is characterized by the interposition of a seat plate 10 made of a material whose coefficient has a substantially middle value between the lever 5 and the mating member (elastic fulcrum members 8a, 8b or elastic connecting member 9). In a balance having a structure in which an elastic fulcrum member or the like made of a different material is screwed to the lever, the reason why the zero point changes stepwise during measurement after a change in environmental temperature is as follows. In the coefficient of linear expansion between the two materials. That is, for example, the material of the lever is aluminum (coefficient of linear expansion 23 × 10 ⁻⁶ / deg), and the material of the elastic fulcrum member is an iron-based alloy (coefficient of linear expansion 11 × 10 ⁻⁶ / de).
g), these two members produce a dimensional difference corresponding to a difference in expansion of 12 × 10 ⁻⁶ due to a change in environmental temperature.
Now, as shown in FIG. 1, if the dimension of the attachment portion between the lever L and the elastic fulcrum member E, that is, the dimension h × w of each side of the portion in contact with each other is 10 × 10 mm, the temperature change 1
12 × 10 ⁻⁶ × 10 =
A dimensional difference occurs by 12 × 10 ⁻⁵ mm, and a temperature change of 10 ° C. causes a dimensional difference of 12 × 10 ⁻⁴ = 1.2 μm on each side. The elastic fulcrum member E is strongly tightened against the lever L by the screw S, and the slip of the dimensional difference as described above does not easily occur at the contact surface between the two members. In the state, as shown schematically in FIG. 2A, expansion (or contraction) in the vicinity of the contact surface is prevented by the fastening force of the screw S, and the force to expand (or contract), that is, the thermal stress is It remains in each material as internal stress. The magnitude of the residual stress depends on the amount of change in the environmental temperature, and when the amount of change exceeds a certain value, when the sample to be measured is put down in that state, the shock or the like causes
As shown in FIG. 2B, a slight slip occurs at the contact surface between the two members, and the internal stress is released. This appears as a step change of the zero point described above. According to the present invention, the lever 5 and the elastic fulcrum member 8a,
8b, and between the lever 5 and the elastic connecting member 9,
By screwing with the seat plates 10 each having a linear expansion coefficient intermediate between the linear expansion coefficients of the members fixed to each other, the difference in thermal expansion between the members that are in contact with each other is reduced by half. It is intended to eliminate or alleviate the zero point change as described above. That is, according to the structure of the present invention, as schematically shown in FIG. 5, the lever 5 and the elastic fulcrum members 8a, 8
b (or the elastic connecting member 9) does not contact each other,
Since each screw is screwed in contact with the seat plate 10, the difference in expansion at the contact surface of each member due to a change in environmental temperature is reduced by half compared to the related art. Therefore, the limit temperature change amount at which the step change of the zero point occurs is twice as large as that of the conventional case, and even if the temperature change amount exceeds the limit, the change amount of the zero point is half that of the conventional case. Become. FIG. 3 is an overall view of a mechanism according to an embodiment in which the present invention is applied to an electromagnetic balance of an electromagnetic force type. FIG. 4 shows only the vicinity of a lever 5 of the electronic balance. It is a perspective view. A plate 1 on which a sample to be measured is placed is supported by a movable column 3 which is movable vertically with respect to the balance frame 2. The movable column 3 is fixed to the other ends of upper and lower beams 3a and 3b parallel to each other and fixed at one end to the balance frame 2, and these are roberval mechanisms (parallel guides).
And the inclination of the movable column 3 and thus the inclination of the plate 1 are suppressed. The load to be measured acting on the movable column 3 via the plate 1 is slidably supported on the balance frame 2,
Further, a lever 5 having one end connected to the movable column 3 and the other end to which the coil 4a of the electromagnetic force generating device 4 is fixed is constituted by a servo mechanism having the electromagnetic force generating device 4, the displacement sensor 6, and the like as constituent elements. The power is transmitted to a known load sensing unit 7. The load responsive part 7 is provided with a lever 5 by the measured load acting on the plate 1.
Is detected by the displacement sensor 6, and the magnitude of the current flowing through the coil 4 a of the electromagnetic force generating device 4 is determined so as to generate an electromagnetic force such that the detected displacement value becomes 0 and balance the lever 5. The magnitude of the load to be measured is determined from the magnitude of the current required to balance the lever 5. The electromagnetic force generating device 4 includes a permanent magnet 4b in addition to the coil 4a.
It is composed of a yoke 4c, a pole piece 4d, and the like. The lever 5 has a substantially cross shape as a whole, on a plane perpendicular to the central axis in the longitudinal direction, and
At two locations equidistant from each other from the center axis thereof, they are swingably supported on the balance frame 2 via elastic fulcrum members 8a and 8b, respectively. The elastic fulcrum members 8a,
Reference numeral 8b denotes an iron-based alloy material having a high elasticity formed in a substantially band shape and a flexible portion provided at a central portion thereof. One end is provided on the lever 5 and the other end is provided on the balance frame 2 with the screw S.
The lever 5 and each elastic fulcrum member 8
a, 8b, and between the elastic fulcrum members 8a, 8b and the balance frame 2, respectively.
0 is inserted. The lever 5 and the movable column 3 are formed of the same iron-based alloy material as the above-mentioned elastic fulcrum members 8a and 8b in a substantially band shape, and are provided with two flexible portions at an intermediate portion. They are interconnected by a member 9. One end of the elastic connecting member 9 is connected to the lever 5 and the other end is
The seat plate 10 is completely inserted between the elastic connecting member 9 and the lever 5 and between the elastic connecting member 9 and the movable column 3. The materials of the lever 5, the movable column 3, and the balance frame 2 are aluminum, respectively, and the elastic fulcrum members 8a, 8 made of these materials and an iron-based alloy material.
b and each seat plate 1 inserted between the elastic connecting member 9
0 is formed of a material having a substantially intermediate value between the linear expansion coefficient of aluminum and the linear expansion coefficient of an iron-based alloy, such as austenitic stainless steel or a copper alloy. According to the above-described embodiment of the present invention, when the environmental temperature changes, the distance between the aluminum member such as the lever 5 and the elastic fulcrum members 8a and 8b and the elastic connecting member 9 made of an iron-based alloy is changed. A difference in dimensional change corresponding to the difference in linear expansion coefficient occurs between the lever 5 and the elastic fulcrum member 8.
a, 8b, and the lever 5 and the elastic connecting member 9 are not in direct contact with each other, and the seat plate 10 having a linear expansion coefficient substantially intermediate between them is interposed therebetween. As schematically shown, the difference in dimensional change between the contact surfaces of the members is approximately １ ／ compared to the case where the seat plate 10 is not inserted. As a result, the thermal stress generated at the contact surfaces of the members is approximately 1 /
It becomes 2. Therefore, when the elastic fulcrum members 8a and 8b or the elastic connecting members 9 are directly screwed to the lever 5 without inserting the seat plate 10, the difference in dimensional change due to the change in environmental temperature is caused. Assuming that the lower limit of the temperature change amount at which the slippage occurs at the contact surface between the two and the step-like zero point change is 10 ° C., in the embodiment of the present invention in which the seat plate 10 is Only when there is a temperature change of 20 ° C., the contact surface slips and the zero point changes.
Conversely, even if the zero point changes due to a slip on the contact surface of the dissimilar member due to the change in the environmental temperature in the embodiment of the present invention, the change amount of the zero point is the same at the same temperature change. The slip amount in the conventional configuration in FIG.
, Which is approximately の of the conventional value. Here, in the above-described embodiment, the seat plate 10 is also provided at a portion where the elastic fulcrum members 8a and 8b and the balance frame 2 and the elastic connecting member 9 and the movable column 3 are attached.
, But these are not necessary. That is, the lever 5 and the elastic fulcrum members 8a,
This is the difference in expansion between the elastic connection member 8b and the elastic connecting member 9, and the seat plate 10 may be inserted into at least these mounting portions. However, as in the above embodiment, the elastic fulcrum member 8
By inserting the seat plate 10 into all of the a, 8b and the elastic connecting member 9 attached to different materials, the effect of suppressing the zero point change is further improved. The screw S for fixing the elastic fulcrum members 8a and 8b and the elastic connecting member 9 to the lever 5, the balance frame 2 and the like also changes its dimensions due to a change in environmental temperature. The fastening force of the screw S, that is, the lever 5 is determined in accordance with the difference in linear expansion coefficient between the lever 5 to which the screw S is fixed and the elastic fulcrum members 8a and 8b.
The tightening pressure between the seat plate 10 and the elastic fulcrum members 8a, 8b changes. This change in the tightening pressure causes a change in the magnitude of the critical internal stress at which slippage occurs between the members. Therefore, if the linear expansion coefficient of the screw S is also set to a value approximately in the middle between the linear expansion coefficient of the lever 5 and the linear expansion coefficient of the elastic fulcrum members 8a and 8b or the elastic connecting member 9 which is the member to which the lever 5 is attached, The change in the tightening pressure due to the temperature change is reduced, and the effect of suppressing the change in the zero point is further improved. The present invention is applicable not only to the electronic balance of the electromagnetic force balanced type as in the above-described example, but also to a balance of a type in which the load acting on the plate is transmitted to the load sensitive portion by the lever.
Of course, it is equally applicable to any balance. According to the present invention, the linear expansion coefficients of both materials are fixed between the elastic fulcrum member and the elastic connecting member which are screwed to the lever and made of a different material from the lever. The thermal stress generated on the contact surface at the mounting portion of each member due to the difference in the dimensional change of each member due to the change in environmental temperature is approximately 1 / 2, the step-like change of the zero point at the first measurement after the environmental temperature change can be greatly reduced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing an example of a structure of a mounting portion between different members such as a conventional lever and an elastic fulcrum member. FIG. 2 is a first measurement after a change in environmental temperature in the structure of FIG. FIG. 3 is an overall view of a balance mechanism according to an embodiment of the present invention. FIG. 4 is a perspective view showing only the vicinity of a lever 5 of the balance mechanism. FIG. Description of operation of the embodiment [Description of reference numerals] 1 plate 2 balance frame 3 movable columns 3a, 3b beams 5 levers 7 load sensitive parts 8a, 8b elastic fulcrum members 9 elastic connecting members 10 seat plate S screws

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-2-82120 (JP, A) JP-A-1-165921 (JP, A) JP-A-6-25733 (JP, U) Field (Int.Cl. ⁷ , DB name) G01G 21/14 G01G 23/48 G01G 21/24 G01G 3/14 G01G 3/18 G01G 21/28 G01G 21 / G01G 23 / G01L 1/22

Claims (1)

(57) [Claim 1] A lever pivotally supported by a balance frame via an elastic fulcrum member and a movable column which supports a plate and is vertically displaceable. A balance connected to each other by an elastic connecting member and configured so that a load acting on the plate is transmitted to the load sensitive portion by a lever, wherein the elastic supporting member and the attaching portion of the elastic connecting member with respect to the lever are respectively provided. A balance, wherein a seat plate made of a material having a linear expansion coefficient having a substantially intermediate value between a lever and a mating member is inserted.