JP2001141553A - Weight measuring device using ceramic load cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent damage in a distortive body of a load cell in a weight measuring device using a ceramic load cell. SOLUTION: In the load cell 3 with a distortive body formed of ceramic, a fixed rigid part 11 in the distortive body 10 is held between holding members 21, 21 so as to be clamped by them laterally, while a pair of plate spring members 31, 31 are installed in a movable rigid part 12 so as to be clamped vertically, and a scale pan 4 is supported via the plate spring members 31, 31. In this way, compressive force providing sufficient strength for ceramic works on the fixed rigid part 11 and the movable rigid part 12 as the force for supporting the load cell and installing the scale pan.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a weight measuring device, and more particularly to a weight measuring device using a ceramic load cell.
Belongs to the field of weighing technology.

[0002]

2. Description of the Related Art A load cell used in an apparatus for electrically measuring weight, such as an electronic balance, has a fixed rigid part at one end and a movable rigid part at the other end, and a plurality of vertically extending parallel parts between these rigid parts. Using a flexure element provided with a flexible beam section, strain sensors are respectively formed on a plurality of flexible sections of the beam section in the flexure element, and according to the load applied to the movable rigid body section Although the configuration is such that the generated distortion of the beam portion is electrically detected, in recent years, for example,
As disclosed in JP-A-146838, JP-A-4-95738 and the like, attempts have been made to use a ceramic material as the strain-generating body of the load cell.

[0003]

This ceramic load cell has excellent characteristics as a load cell, such as being hardly affected by temperature and hardly causing plastic deformation. However, on the other hand, a tensile load or an impact load is required. However, there is a disadvantage that it is easily damaged by the above-mentioned factors, and overcoming this point has been a problem for practical use.

[0004] Therefore, an object of the present invention is to solve the above-mentioned problems in a weight measuring device using a ceramic load cell by improving a structure for transmitting a load to the load cell and a structure for supporting the load cell. .

[0005]

That is, the invention according to claim 1 of the present application (hereinafter referred to as the first invention) is a cantilever type parallel beam having a fixed rigid portion at one end and a movable rigid portion at the other end. In a weight measuring device using a type load cell, the strain generating body of the load cell is formed of ceramic, and a fixed rigid body of the strain generating body is fixed to a base member via a holding member, and the fixed rigid body is The holding member is configured to be held by compression by a holding surface.

Further, the invention according to claim 2 (hereinafter referred to as “second
Similar to the first aspect, the invention provides a weight measuring device using a cantilever type parallel beam load cell having a fixed rigid body at one end and a movable rigid body at the other end. Formed of ceramic, the movable rigid body of the strain body is attached to the weighing dish via an attachment member, and the attachment member is attached to the movable rigid body of the strain body by compression by the attachment surface of the attachment member. It is characterized by being constituted so that it can be done.

According to a third aspect of the present invention (hereinafter, referred to as a third aspect of the invention), the mounting member is provided with a leaf spring member for absorbing an impact.

Further, in the invention according to claim 4 (hereinafter referred to as a fourth invention), in the third invention, an engaging portion is provided on a leaf spring member constituting the mounting member, and the engaging portion is provided on the engaging portion. It is characterized in that a stopper member is provided that regulates the vertical displacement of the movable rigid body portion of the strain body by a predetermined amount when engaged.

[0009] With the above arrangement, according to the present invention,
The following effects are obtained.

First, according to the first aspect, the fixed rigid body of the strain body is held by compression by the holding surface of the holding member. Therefore, the force acting on the rigid body to fix the fixed rigid body is It becomes a compression force exclusively. Even when the holding member is made of metal having a large thermal expansion coefficient and the holding member thermally expands, the compression force only increases. Therefore, it is possible to firmly support the ceramic strain body having a large strength against the compressive force without causing the fixed rigid body portion to be damaged.

According to the second aspect of the present invention, since the mounting member is attached to the movable rigid portion of the strain body by the compression of the mounting surface, the measuring plate is attached to the movable rigid portion via the mounting member. The force acting on the rigid portion is exclusively a compressive force. In particular, even when the mounting member is made of metal having a high thermal expansion coefficient and the holding member is thermally expanded, the compressive force only increases. Therefore, similarly to the first invention, it is possible to firmly attach the mounting member or the weighing dish without causing the movable rigid body portion to be damaged by the ceramic strain body having a large strength against the compressive force. Become.

Further, according to the third aspect of the present invention, since the attachment member is provided with the leaf spring member, even when the object to be weighed is placed on the weighing dish in an impact manner, the impact is applied to the leaf spring member. And the load cell is protected from the impact load. Accordingly, the load cell is reliably prevented from being damaged even though the strain body is formed of a ceramic which is weak against an impact load.

According to the fourth invention, a mechanism for protecting the load cell from a large load by regulating the displacement of the movable rigid portion of the load cell by a predetermined amount comprises an engaging portion provided on the leaf spring member; Since the stopper is engaged with the engaging portion, when a large load is applied, the displacement of the movable rigid portion of the load cell is regulated via the leaf spring member. Therefore, damage of the flexure element due to direct contact of the movable rigid portion of the ceramic flexure element with the stopper member when a large load is applied is also prevented.

[0014]

Embodiments of the present invention will be described below.

As shown in FIG. 1, a weight measuring device 1 according to this embodiment includes, as main components, a base member 2 and a load cell 3 having one end fixed to the base member 2 and cantilevered. And a weighing dish 4 attached to the other end of the load cell 3.

The load cell 3 has a fixed rigid portion (fixed rigid portion) 11 and a movable rigid portion (movable rigid portion) 12.
And a pair of beam members 13 and 14 erected in parallel between the rigid members 11 and 12 in a vertical direction. Strain gauges 15... 15 are respectively provided on the surfaces of the thin portions 13 a, 13 b, 14 a, 14 b provided at two locations on each of the portions 13, 14. Then, an electric circuit including these strain gauges 15... 15 is formed, and when the weight of the object to be weighed is loaded on the movable rigid part 12, these strain gauges 15. The weight is electrically detected by detecting the compressive strain or the tensile strain generated in each of 13a, 13b, 14a, and 14b and changing the electric resistance.

Although the structure of the load cell 3 is well known, the strain body 10 of the load cell 3 is formed of ceramic, and the supporting structure of the load cell 3 and the coupling structure of the load cell 3 to the weighing plate 4 are ceramic. It conforms to the characteristics of

That is, first, the support structure of the load cell 3 will be described. As shown in FIGS. 1 to 3, the fixed rigid body portion 11 of the flexure element 10 of the load cell 3 includes a pair of right and left erected on the base member 2. The holding members 21 and 21 are clamped from both left and right sides, and are tightened by bolts 22 penetrating these in the left and right direction and nuts 23 screwed to the bolts 22 and the base member via these holding members 21 and 21. It is fixed to 2.

Here, as shown in FIGS. 2 and 3, the left and right holding members 21, 21 are provided with a stepped surface 21a in contact with the end surface of the flexure element on the side of the fixed rigid body 11, and a step in contact with the upper surface. And a stepped surface 21c which is in contact with the lower surface, and which is fixed by the pair of holding members 21, 21.
At the same time as holding the rigid body 11 from both the end face and the upper and lower faces.

The mounting structure of the load cell 3 and the weighing pan 4 will be described. The upper and lower surfaces of the movable rigid portion 12 of the strain body 10 of the load cell 3 are provided with one end of a pair of upper and lower rectangular plate spring members 31, 31. Are two bolts 32, 32 penetrating the movable rigid part 12 up and down, and these bolts 3
The plate spring members 31, 31 are attached so as to extend in a cantilever manner in the longitudinal direction of the flexure element 10 in a vertically parallel state.

The free ends at the other ends of the leaf spring members 31, 31 are connected by a connecting member 34, and two bolts 35, 35 penetrating therethrough are screwed to these bolts 35, 35. The nuts 36, 36 are joined together.

On the upper surface of the upper leaf spring member 31, one end of a dish receiving member 37 is disposed.
The bolt 35 for connecting the connecting member 34 to the connecting member 34;
35 and nuts 36, 36, this dish receiving member 37
Are fastened together, and the other end of the dish receiving member 37 supports the weighing dish 4.

Further, an extension 31a is provided at a free end of the lower leaf spring member 31, and a stopper member 38 is fixed to the base member 2, and the stopper member 38 The lower contact surface 38 that contacts when the extension 31a of the spring member 31 is displaced downward by a predetermined amount.
a and an upper limit contact surface 38b that comes into contact when the extension portion 31a is displaced upward by a predetermined amount.

As shown in FIGS. 1 and 2, the leaf spring members 31, 31 have holes 3 for adjusting their elastic coefficients.
1b and 31b are provided.

Next, the operation of the weight measuring device 1 according to this embodiment will be described.

When the object to be weighed is placed on the weighing pan 4, its weight is transmitted from the pan receiving member 37 to the free ends of the pair of leaf spring members 31, 31 connected by the connecting member 34. The load is applied to the movable rigid portion 12 of the strain body 10 of the load cell 3 via these leaf spring members 31, 31. When the movable rigid body 12 is displaced downward according to the weight applied, the thin portions 13a, 1a, 1b of the beam portions 13, 14 of the flexure element 10 are formed.
The strains 3b, 14a, and 14b are distorted, and the strain gauges 15... 15 detect the respective strains, so that the weight of the object to be weighed is electrically detected.

In that case, the flexure element 1 of the load cell 3
0 is made of a ceramic which is easily damaged by an impact load. However, even if an object to be weighed is placed on the weighing pan 4 in an impact manner, the impact load causes the leaf spring members 31, 31 to bend. Therefore, the transmission of the impact load to the strain generating element 10 is reduced, and the damage of the strain generating element 10 due to the impact load is prevented.

Further, when an object to be weighed is placed on the weighing dish 4 such that a large amount of strain is generated in the strain body 10 below the limit, the lower portion of the free ends of the pair of leaf spring members 31, 31 is provided. The amount of displacement of the lower leaf spring member 31
The extension portion 31a provided at the free end of the stopper member 3
By contacting the lower contact surface 38a of FIG. 8, excessive displacement of the movable body 12 of the flexure element 10 downward is prevented, and the flexure element 10 due to the occurrence of distortion exceeding the above-described limit is prevented. Will be prevented from being damaged.

In this case, since the excessive displacement of the movable rigid portion 12 is indirectly restricted via the leaf spring member 31, the downward displacement is restricted by the contact with the stopper member 38. Is also absorbed by the leaf spring member 31 in the same manner as when the impact load is applied,
Directly acting on the flexure element 10 of the load cell 3 is prevented. Therefore, this also prevents the ceramic strain body 10 from being damaged.

The stopper member 38 is also provided with an upper limit contact surface 38b for restricting the upward displacement of the extension 31a of the leaf spring member 31 by a predetermined amount. An upward displacement due to an upward load or a recoil at the time of placing an object to be weighed is also regulated by a predetermined amount, and the strain body 10 of the load cell 3 is displaced upward of the movable rigid portion 12. Will also be protected.

On the other hand, the fixed rigid body 11 of the strain body 10
Is fixed to the base member 2 via a pair of holding members 21, 21.
Is fixed by being pinched from the left and right by the pair of holding members 21 and 21 and tightened by bolts 22 and nuts 23. Therefore, as the force for holding the load cell, the compressive force of the ceramic having sufficient strength mainly acts on the fixed rigid body portion 11 of the strain body 10, and the holding member 2
1 and 21 are made of metal having a large coefficient of thermal expansion, and even when the thermal expansion occurs, the fixed rigid body 1 of the flexure element 10
Only the compressive force acting on 1 is increased.

Therefore, it is possible to prevent the strain body 10 from being damaged by the force for holding the strain body 10 in a cantilever state.

In this embodiment, the strain body 1
The fixed rigid body portion 0 is sandwiched from both left and right sides by a pair of holding members 21 and 21 and is also held from both end surfaces and upper and lower surfaces, so that unnecessary force does not act on the flexure element 10. Thus, the strain body 10 is more firmly held.

Further, the movable rigid portion 12 of the strain body 10
One end of a pair of leaf spring members 31, 31 is attached to the upper and lower surfaces by bolts 32, 32 and nuts 33, 33, and the movable rigid portion is sandwiched from above and below by the pair of leaf spring members 31, 31. It is in a state of being left. That is, a structure for attaching the weighing dish 4 to the movable rigid portion 12 of the strain body 10 via the attaching members including the leaf spring members 31, 31, the connecting member 34, the dish receiving member 37, and the like,
The movable rigid portion 12 is compressed by the mounting surfaces of the pair of leaf spring members 31, 31.

Therefore, the movable rigid portion 1 of the strain body 10
2, a compressive force of ceramic having sufficient strength mainly acts as a force for attaching the weighing pan 4, and when the leaf spring members 31 are thermally expanded so as to become thicker. The movable rigid body 1 of the strain body 10
Only the compressive force acting on 2 is increased. Therefore, like the fixed rigid portion 11 described above, the movable rigid portion 12
Is prevented from being damaged.

In the above structure, a vertical compressive force acts on the movable rigid portion 12 of the strain body 10, but the movable rigid portion 12 and a pair of upper and lower leaf spring members 31, 3
1 and an intermediate member for connecting them is interposed between the movable rigid body 12 and the fixed rigid body 11.
In the same manner as described above, the mounting may be performed so that a compressive force in the left-right direction acts.

[0037]

As described above, according to the first aspect of the present invention, the fixed rigid body of the strain body of the ceramic load cell is fixed by compression by the holding member, so that the fixed rigid body is fixed. For this reason, the force acting on the fixed rigid portion is exclusively a compression force. According to the second invention, since the mounting member for mounting the weighing dish to the movable rigid body portion of the strain body is attached by compression, the mounting member is attached to the movable rigid body via the mounting member. The force acting on the movable rigid part is exclusively a compression force. In any case, even if the holding member or the mounting member thermally expands, only the above-described compressive force increases.

Accordingly, the load cell is firmly supported or the weighing pan is firmly supported by the ceramic strain body having a large strength against the compressive force without causing damage to the fixed rigid portion and the movable rigid portion. It can be attached.

According to the third aspect of the present invention, since the attachment member is provided with the leaf spring member, even when the object to be weighed is placed on the weighing dish in an impact manner, the impact is applied to the leaf spring member. And the load cell is protected from the impact load. Accordingly, the load cell is reliably prevented from being damaged even though the strain body is formed of a ceramic which is weak against an impact load.

According to the fourth invention, a mechanism for protecting the load cell from a large load by regulating the displacement of the movable rigid portion of the load cell by a predetermined amount is provided by an engaging portion provided on the leaf spring member; Since the stopper is engaged with the engaging portion, when a large load is applied, the displacement of the movable rigid portion of the load cell is regulated via the leaf spring member. Therefore, it is possible to prevent the strain body from being damaged due to the movable rigid body portion of the ceramic strain body coming into direct contact with the stopper member when a large load is applied.

[Brief description of the drawings]

FIG. 1 is an internal structural diagram of a weighing device according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view taken along line AA of FIG.

FIG. 3 is a sectional view taken along line BB of FIG. 1;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 weight detection device 3 load cell 4 weighing pan 10 strain body 11 fixed rigid body 12 movable rigid body 21 holding member 31 mounting member (leaf spring member) 31a engaging portion (extended portion) 34 mounting member (connecting member) 37 mounting member (Dish receiving member) 38 Stopper member

Claims (4)

[Claims] 1. A weight measuring apparatus using a cantilever type parallel beam load cell having a fixed rigid body at one end and a movable rigid body at the other end, wherein a strain-generating body of the load cell is formed of ceramic. Along with the fixed rigid body of the strain body is fixed to a base member via a holding member, and
A weight measuring device using a ceramic load cell, wherein the fixed rigid portion is held by compression by a holding surface of the holding member. 2. A weight measuring device using a cantilever type parallel beam load cell having a fixed rigid body at one end and a movable rigid body at the other end, wherein a strain-generating body of the load cell is formed of ceramic. Along with the movable rigid body of the strain body is attached to a weighing dish via an attachment member, and
A weight measuring device using a ceramic load cell, wherein the attachment member is attached to a movable rigid portion of the strain body by compression by an attachment surface of the attachment member. 3. The weight measuring device using a ceramic load cell according to claim 2, wherein the mounting member includes a leaf spring member for absorbing a shock. 4. An engagement portion is provided on a leaf spring member constituting an attachment member, and the vertical displacement of a movable rigid body portion of the strain body is reduced by a predetermined amount by engaging with the engagement portion. 4. The weight measuring device using a ceramic load cell according to claim 3, further comprising a stopper member for regulating the weight.