JPS61250533A - Force measuring cell - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a force measuring cell that includes a measuring mechanism that deflects under load and a mechanism that capacitively detects elastic deformation of the measuring mechanism due to the load.

[Conventional technology]

Force-measuring cells of this type are known, for example, from European patent application no.
It is known from No. 017581. The measuring mechanism in this case consists of two bendingly rigid members connected to each other via two bendingly elastic connecting bars, of which one bendingly rigid member is fixed and the other bendingly rigid member is load-bearing. forming the body. The two bending-elastic connecting bars act as measuring elements and form a parallel guide for the relative movement due to the load of the two bending-rigid elements. The electrode support of the capacitive displacement measuring device is fixed to the bending rigid member,
The electrodes are not subjected to mechanical loading and under ideal conditions are parallel to each other in each measurement phase.

[Problem that the invention seeks to solve]

However, even if this measuring mechanism is fairly stable, this stability is limited by the eccentricity of the force, especially if the flexurally rigid member is made from one piece together with the flexurally elastic connecting bar. This has proven to be unsatisfactory when the line of action of the force to be measured extends outside the center of gravity of the load carrier. Such cases are found, for example, in scales in which a corner-loaded load plate is placed directly on the load support of the force-measuring cell. Loading the corners in this way causes rotational moments to act on the load support, which further deforms the measuring mechanism and, as a result, the measurement accuracy is adversely affected. Experiments have shown that slight deviations in the introduction of force into the center can lead to considerable measurement errors. Under these circumstances, the high measurement precision that can be obtained with the capacitive displacement measurement system itself is not fully utilized.

For example, for capacitive displacement-measuring force-measuring cells, as is shown in DE 29 21 614 A1, a load support that acts as fully as possible can absorb the rotational moments caused by corner loads. It is known to compensate for the adverse effects of corner loads by installing parallel guides on the outside of the measuring arrangement.

However, it is also known that external parallel guides of this type impair the measurement accuracy of the force-measuring cell, for example due to temperature changes. For these reasons and the attendant expense, it has therefore become an aim of technical developments to abandon such external parallel guides.

It is therefore an object of the invention to provide a force measuring cell that is substantially insensitive to rotational moments acting on a load support.

[Means for solving problems]

This purpose is to provide a mechanically coupled capacitive force sensor,
Each force sensor consists of a bending rigid member connected to each other by a bending elastic connecting bar and a capacitive displacement measuring device.One of the bending rigid members is fixedly installed, and the capacitive displacement measuring device has a fixed electrode mechanism. , the other movable bending rigidity member is coupled to a common load support via a coupling member, and includes a movable electrode mechanism of a capacitive displacement measuring device;
This is achieved by the force measuring cell of the present invention, which is characterized in that the sum of the capacitances of both force sensors is used as the measurement value of the force to be measured.

[Effect]

When the force-measuring cell is loaded, the positions of the two force sensors change in the same way. When introducing power mainly, the change in capacitance is also the same. If, on the other hand, the line of action of the force to be measured deviates from the center of the load carrier and additional rotational moments are applied to the load carrier, additional capacitance changes occur.

If this displacement of the line of action occurs in a common plane of action of the two force sensors, the capacitances of both force sensors change in the same way, and the sum of these capacitances remains constant over the entire measurement range. In this way, without additional outward parallel guidance,
Substantial corner load compensation is provided.

In order to absorb rotational moments caused by the line of action of the force to be measured extending outside a common working surface of the two force sensors, the force sensors can be reinforced in a direction perpendicular to their working surface. However, there are two or more better solutions that allow compensation of such rotational moments:
For example, four mechanically coupled force sensors are arranged uniformly distributed in a plane perpendicular to the direction of force application.

A preferred configuration of the invention provides that the bending rigidity members of the two force sensors, the connecting bar, the connecting member and the support and load support of the electrode arrangement together form one structural unit and consist of one piece. Features. Omniscient micromechanical methods are suitable for the production of such embodiments, especially if the above-mentioned component units are made of a corrosive material, for example a semiconductor plate, which has a good quality. From the point of view of elasticity, this applies when single crystal silicon is used. The advantage of such an embodiment is, in particular, that the outlay for the production of two mechanically connected force sensors is comparable to that for the production of a single force sensor.

As regards the arrangement of the force sensor with respect to the direction of action of the force to be measured, basically two embodiments are possible. The force sensor is arranged in a plane parallel to the direction of the force or in a plane perpendicular to the direction.

In the former case, the bending elastic connecting bar of each force sensor is
It serves as a parallel guide for the relative movement of the two bending rigid members. The latter solution (this can be achieved by making the height of the force measuring cell particularly low).In the case of a measuring cell with two or more force sensors, the direction of action of the force to be measured by this force sensor can be reduced. The two different arrangements at , which take into account the intended component structure, solve various problems.If the force sensor is installed in a plane parallel to the direction of the force, for example two Two identical structural units with two force sensors are combined in a cross shape,
In this case, each component unit can form one half of a common load carrier. In the other case, ie when the force sensors are arranged in a plane perpendicular to the direction of the force, it is also possible to combine all force sensors into a single component and to manufacture them in one piece.

Two embodiments of capacitive displacement measuring instruments are particularly suitable for the unit construction of the force measuring cell described above.

In the first embodiment, two plates are provided as supports for the electrode mechanism, each of which is connected to one of the bending rigid members of the force sensor and installed in parallel planes with a distance between them, at least one of which is movable. The plate attached to the bendingly rigid member extends into a space surrounded by the bendingly rigid member and the bendingly elastic connecting bar. Furthermore, the at least 10,000 plates can be constructed in one piece with attached bending stiffness elements. Electrode arrangements are located on opposite sides of both plates.

In the case of a force-measuring cell with a force sensor installed in a plane parallel to the direction of the force, when the force to be measured is applied, the two plates move relative to each other in the plane with a constant distance from each other. In this case, the electrode surface acting on the capacitance of the electrode mechanism changes.On the other hand, in the case of a force measuring cell with a force sensor installed in a plane perpendicular to the direction of the force, , under the action of the force to be measured, the spacing of the plates or the spacing of the electrodes changes.

A second method of implementing a capacitive displacement measuring device is to use a large number of electrode mechanisms as supports for the electrode mechanism, which are left in one plane, engage each other in a comb (teeth) pattern, and are alternately connected to the bending rigid member of the force sensor. The method comprises providing rods spaced from each other and electrodes on opposite sides of the rods.

In this solution, the relationship with respect to the capacitive variables (spacing of the electrodes, their surface area), which varies as a function of the force to be measured, is completely opposite to that of the first implementation of the displacement measuring device, i.e. the force sensor is When in a plane parallel to the direction of force,
The electrode spacing varies as a function of the force, and when the force sensor is in a plane perpendicular to the direction of the force, the effective electrode surface area varies as a function of the force.

In each embodiment in which a change in the effective electrode surface area with respect to the force to be measured is standard, in order to increase the increased value of the capacitance per unit force, the electrodes are arranged on each plate or six, as is known per se. In the rod, it is desirable to select an electrode arrangement that forms a linear raster extending across the direction of the force.

〔Example〕

The force-measuring cell in FIG. 1 consists of two identical force sensors, both of which are mounted on a common working surface and mechanically connected by a common load support 3. The force-measuring cell of FIG.

Each force sensor has a measuring means which deflects elastically under load and consists of bendingly rigid elements 6.7 connected to one another via bendingly elastic connecting bars 4,5.

One bendingly rigid member 6 is fixedly installed, while the other bendingly rigid member 7 is connected to the load support 3 via connecting members 8 and 9. All bending-elastic connecting bars and connecting members have local bends consisting of waists 10 of the material;
It has a so-called bending joint. When the force F to be measured acts, the measuring means is elastically distorted, the bending-elastic connecting bars 4, 5 acting as parallel guides for the movement of the bending-rigid element 7. In this example, both force sensors 1 and 2 are
They extend parallel to the direction of action of the force and within the action plane of these force sensors.

Each force sensor 1, 2 is further provided with a capacitive displacement measuring device for detecting the elastic deformation (strain) of the measuring means based on the load.As a support for the electrode arrangement of this displacement measuring device, parallel Two plays set up at intervals on the surface) 1
1.12 is provided. One of the plates 11 is fixedly installed outside the working surface of the force sensor and is connected to the fixed bending rigidity member 6, and the other plate 12 is connected to the movable bending rigidity member 7. , extending into a space surrounded by bendingly rigid members 6, 7 and bendingly elastic connecting bars 4, 5. play) 1
1.12 are provided with electrode arrangements 13.14, each electrode forming a linear raster as shown in dotted lines. When the measuring means undergoes elastic deformation under the action of the force F to be measured, the movable plate 12 is displaced relative to the fixed plate 11 with a constant mutual spacing, and at this time the electrode mechanism 13
．． The electrode surface (relationship) that acts on the capacitance of 14 changes. The sum of the capacitances of both force sensors 1, 2 is used as the measured value of the force to be measured)'.

Bending rigid members 6, 7° of both force sensors 1, 2 connecting bars 4, 5. The coupling element 8.9 and the movable plate 12 and the load carrier 3 together form a structural unit and are made of one piece, in particular of corrosive material. The mechanical part of this component can be produced in a single processing step. The electrode arrangement 14 is mounted on the plates 12 of both force sensors in a separate processing step. The fixed plate 11 is manufactured separately and fixed to the side of the fixed bending rigid member 6.

The force measuring cell shown in FIG. 2 has basically the same configuration as that shown in FIG. G is different in that it is in .

Fixed and movable bending stiffness members 23, 24, bending elastic articulation with bending joints 27, 28/NJ 25° 26, support plate 29 of the electrode of the double-edged sensor incorporated in the movable bending stiffness member 24; The common load support 30 is made of one piece. The whole rests on a support plate 31 common to both force sensors 21, 22, which support plate 31 is provided with counter electrodes. In this example, the electrodes not shown are
The supporting plates 29 and 31 are formed by surface plating on opposing sides. When the force sensors 21, 22 are elastically deformed under the action of the force F to be measured, the distance between the support plates 29 and 31 or the distance between the electrodes provided thereon changes, unlike in the embodiment of FIG. However, two force sensors 21
．． The sum of the 22 capacitances is likewise used as the measurement value of the force F to be measured.

In order to form a force-measuring cell with two acting surfaces perpendicular to each other, four mechanically coupled force sensors are provided in the structure of FIG. 2, which are evenly distributed in a plane perpendicular to the direction of force application and can be placed. As an example of this, FIG. 3 shows a mechanical connection of four implied force sensors 41 , 42 , 43 , 44 to a common load support 45 . This connection is provided by a coupling member 46 with a bending joint 47, 48 acting between the load support 45 and the movable bendingly rigid member of the corresponding force sensor. Coils 49.50 on the dual side of this force sensor are shown by dotted lines; coil 49 is attached to force sensor pair 41.43, and coil 50 is attached to force sensor pair 42.44.

All four force sensors are shaped as shown in Figure 3.
It can be manufactured in bulk from a single piece of material.

Only common supports with counter electrodes are excluded from this as well. In this case as well, all four force sensors 41
The sum of the ~44 capacitances is the measure of the force to be measured.

In the same way, three or more force sensors having the means shown in FIG. 3 can be connected to a common load support plate. This increases the number of active surfaces of the force sensor or force sensor pair and thus improves the compensation of side effects caused by corner loading of the force-measuring cell.

The force measuring cell in FIG. 4 has the same construction as in FIG. 1 with respect to the measuring mechanism, and corresponding parts are given the same reference numerals. The difference lies in the configuration of the capacitive displacement measuring device.

The capacitive displacement measuring device provided here consists of a plurality of rods 6 each installed on the working surface of the force sensor as a support for the electrode mechanism.
0. , 61, and these rods are engaged with each other in a comb (teeth) shape at intervals, and are alternately connected to the bending rigidity members 6, 7. Electrodes, not shown, are located on opposite sides of the rods 60, 61. As shown in FIG. 4, the rods 60 and 61 have bending rigidity members 6 and 7.
It can also be formed from one piece and can be fixed to this piece in the form of a separately manufactured comb.

When a load is applied to this force-measuring cell, the spacing between the electrodes of both displacement measuring devices changes depending on the force F to be measured. Due to the parallel connection of a large number of single exposures, the total capacity of the displacement measuring device is considerably higher than for example in the case of the simple displacement measuring device of European Patent Application No. 0017581.

In order to configure a force measurement cell in which four mechanically coupled force sensors shown in FIG. 4 are evenly distributed in a plane perpendicular to the direction of force, the load support of the structural unit shown in FIG. , a slit 62 (shown in dotted lines) extending over half the length of the load support and having a width equal to the thickness of the material measured perpendicular to the drawing of this component.
can be provided. This slight modification allows two identical components, each with two force sensors, to be assembled in a cross-shape. In this case each component unit forms one half of a common load carrier. This results in 2
The production of a force-measuring cell with four force sensors on one working surface becomes very simple.

Of course, the mechanical configuration of the displacement measuring device of FIG. 4 and the multiple division of capacities can also be applied to the case of the force measuring cell of FIG. 2. In this application, the comb-shaped electrode supports (rods) move relative to each other in a direction perpendicular to the bridge surface, so the electrode spacing remains the same (as in Figure 4) and the effective electrode surface area increases. change.

In the case of such a displacement measuring device, it is preferable that the six rod electrodes form a straight line raster extending across the direction of force.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention, and FIG. 1 shows two force sensors installed in a plane parallel to the direction of force application;
Figure 2 shows a force-measuring cell with parallel plates as supports for the electrode arrangement; FIG. Figure 3 showing a force-measuring cell with a plate of
The figure is a detailed view of the mechanical connection means of the four force sensors of the force measurement cell configured as shown in FIG. 2, and FIG. 1 shows a force-measuring cell with rows of rods engaging each other in a comb-like manner as a support for the electrode arrangement; FIG. 1.2, 21.22... force sensor, 3, 30.45.
...Load support, 4,5,25.26...Connection bar,
6.7, 23.24... Bending rigidity member, 8, 9, 32
．． 46...Connecting member, 1' 3, 14... Electrode mechanism.

Claims (10)

[Claims] (1) At least two capacitive force sensors 1 mechanically connected in a force measuring cell equipped with a measuring mechanism that elastically deflects due to a load and a mechanism for capacitively detecting the elastic deformation of the measuring mechanism due to the load; 2:21, 22, and each force sensor consists of bending rigid members 6, 7; 23, 24 connected to each other by bending elastic connecting bars 4, 5; 25, 26, and a capacitive displacement measuring device. One bending rigid member 6
23 is installed in a fixed state and is provided with the fixed electrode mechanism 13 of the capacitive displacement measuring device, and the other movable bending rigidity member 7; is connected to the load support 3; 30; Features a force measurement cell. (2) Four mechanically connected force sensors 41 to 44 are provided, and these force sensors are uniformly distributed in a plane perpendicular to the direction of the force. Force measuring cell according to item 1. (3) Bending rigid members 6, 7; 23, 24 of two sensors 1, 2; 21, 22, bending elastic connecting bars 4, 5; 25
, 26, connecting members 8, 9; 32; 46 and electrode mechanism 1
3, 14 supports 11, 12; 29, 31; 60, 61
and the load support 3; 30; 45 together form a structural unit and consist at least in part of one piece. measurement cell. (4) The third aspect of the present invention is characterized in that the structural unit is formed of a member made of a corrosive material such as a semiconductor board.
Force measuring cell as described in section. (5) The force sensors 1 and 2 are installed in a plane parallel to the direction of the force, so that the bending elastic connecting bars 4 and 5 of each force sensor are controlled by the relative movement of both bending rigid members 6 and 7. Claim 1, characterized in that it serves as a parallel guide for
The force measurement cell according to any one of items 1 to 4. (6) The force measurement cell according to any one of claims 1 to 5, wherein the force sensors 21 and 22 are installed in a plane perpendicular to the direction of force. (7) A patent characterized in that two identical structural units, each having two force sensors 1, 2, are assembled in a cross-shape, and each structural unit forms one half of a common load support 3. A force measuring cell according to any one of claims 2, 3, or 5. (8) As supports for the electrode mechanism, two plates 11 and 12 are provided, which are installed on parallel surfaces with a space between each other and are connected to the bending rigid members 6 and 7 of the force sensors 1 and 2, respectively, and at least one of these plates is movable. Claim 1, characterized in that the plate 12 attached to the bendingly rigid member 7 extends into the space surrounded by the bendingly rigid member 6, 7 and the bendingly elastic connecting bar 4, 5. The force measurement cell according to any one of items 7 to 7. (9) As supports for the electrode mechanism, a plurality of rods 60 and 61 are installed in one plane, engage each other in a comb-like manner, and are alternately connected to both the bending rigid members 6 and 7 of the force sensors 1 and 2;
9. The force measuring cell according to claim 1, further comprising electrodes arranged at intervals from each other and on opposite sides of the rod. (10) Claim 5, characterized in that the electrodes of both electrode mechanisms of each force sensor form a straight line raster extending across the direction of force in each plate 11, 12 or each rod, The force measurement cell according to any one of paragraphs 8, 6, or 9.