JPH0725636Y2 - Capacitance type weight sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a weight sensor used for automated equipment that takes in weight information of an article, and more particularly to a capacitance type weight sensor that is smaller than a placing tray.

[Prior Art] The structure of a capacitance type weight sensor using a leaf spring Roberval in a conventional load balancing mechanism is as shown in FIG. 3, in which plate electrodes are attached to each of left and right columns for fixing upper and lower leaf springs. Was fixed, and the amount of displacement of the column was converted into the amount of change in the capacitance of the electrode.

[Problems to be solved by the invention] Since the weight sensor has been incorporated into various household appliances, the shape of the weight sensor, particularly the size, becomes severer, and the weight of the shape corresponding to the size of the object to be weighed. The sensor cannot be applied. In other words, it is not possible to take an ideal configuration as a weighing scale, and countermeasures against eccentric load errors are particularly important issues.

In addition, in repeated use, the base point (zero point) may not be calibrated in some cases, resulting in a perfect base point (zero point) when the load is removed.
Is required to return.

In the conventional configuration shown in FIG. 3, the parallelogram of the Roverval collapses due to the deformation of the leaf spring that also functions as the stay of the Roverval, and the lateral displacement is particularly large in the weight sensor that is smaller and thinner than the placing tray. The tilt of the column portion due to the applied load breaks the parallelism of the two electrodes, and the difference in the rotational moment depending on the load position causes a change in the electrostatic capacitance between the electrodes, making accurate measurement impossible.

This countermeasure is disclosed in Japanese Patent Laid-Open No. 60-165520, but this method has a large shape limitation, and it is difficult to combine it into a thin weight sensor.

On the other hand, since the point where the leaf spring is fixed to the column is the point where the leaf spring has the largest stress, the deformation of the leaf spring material at the fixing point due to the load causes the state before loading even when the load is removed. Immediately it did not completely return, it appeared as a change in the base point (zero point), and it was necessary to reset the zero point for continuous use.

This measure is disclosed in Japanese Utility Model Publication No. 58-69239, Japanese Utility Model Publication No. 62-5236 and Japanese Utility Model Publication No. 64-23629, etc.
Or, there is a problem in manufacturing cost or the like.

Electrostatic discharge that solves these problems of the prior art, has little measurement error due to eccentric load, and returns to the base point (zero point) completely when the load is removed, is small, thin, and is compatible with large dishes. To develop a capacitive weight sensor.

[Means for Solving the Problem] A leaf spring forming a leaf spring Roberval is formed in a two-stage ladder type, and two inflexible portions are formed inside a fixing point of the leaf spring to a column, and one of the inflexible portions is formed. The fixed electrode is rotatably attached to one end of the movable electrode, and the other end of the movable electrode is always in contact with the center of the other inflexible portion formed on the plate spring to which the fixed electrode is fixed.

[Operation] The rotation axes of the fixed electrode and the movable electrode are fixed at the same point of the leaf spring, while the moving end of the movable electrode is caused by the rotation moment.
Since it is in contact with the vicinity of the axis of the Roberval twist, the change in the contact point due to the twist is negligibly small, and the measurement error due to the eccentric load is significantly improved.

Further, since the fixed electrode, the rotating shaft of the movable electrode, and the moving end of the movable electrode are all attached to or in contact with the same leaf spring, a slight change in the coupling point between the leaf spring and the column does not directly affect the electrode. The problem of resetting the base point (zero point) when the load is removed is solved without affecting the interval (without changing the capacitance of the electrode).

Embodiment An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1a is a plan view of an embodiment of a weight sensor according to the present invention,
1b is a sectional view taken along line AA of FIG. 1a, and FIG. 1c is FIG. 1a.
FIG.

The upper and lower leaf springs 1 each have a movable support column 2 and a fixed support column 3, which are connected at the top and bottom to form a rectangular Roverval structure.

The leaf spring 1 which also functions as a stay of the Roberval structure is formed in a two-stage ladder type, and an electrode plate assembly to be described later is fixed to one of the transverse members.

FIG. 2 is an enlarged cross-sectional view of the portion D in FIG. 1b and is an explanatory view of the main part of the electrode assembly.

A fixed electrode plate 5 is attached to the fixed electrode support metal fitting 8 via insulating washers 9, 9 and is fixed to the cross-section of the ladder-type leaf spring 1. Similarly, the movable electrode support fitting 7 to which the movable electrode plate 4 is insulated and attached is rotatably attached to the fixed electrode support fitting 8 by the movable electrode rotation shaft 6.

On the other hand, the free end of the movable electrode plate insulates the tip of the cut-and-raised piece cut and raised at a right angle, and abuts on the center of the other cross-section of the leaf spring. (FIG. 1b) The fixed column 3 is fixed to a base (not shown), and the movable column 2
A mounting table (not shown) is fixed and used.

When a load is applied to the mounting table, the leaf spring 1 bends, the movable support column 2 descends, and the electrode plate assembly attachment portion D moves more than the movable electrode free end contact portion. As a result, the distance between the movable electrode and the fixed electrode is expanded so that the electrostatic capacitance of both electrodes decreases, and the time constant of the oscillator (not shown) is changed,
A change in the transmission frequency proportional to the change in load is obtained.

[Advantages of the Invention] According to the present invention, the rotating shafts of the fixed electrode and the movable electrode are fixed at the same point of the leaf spring, while the moving end of the movable electrode is very close to the axis of torsion of the Roberval due to the rotation moment. Since the change in the contact point due to the twist is negligibly small, the measurement error due to the eccentric load is significantly improved, and the rotation axis of the fixed electrode and the movable electrode and the moving end of the movable electrode are also improved. Since all of them are attached to or in contact with the same leaf spring, a slight change in the connection point between the leaf spring and the support does not directly affect the electrode spacing (changing the electrode capacitance). No.), it becomes a capacitance type weight sensor that completely returns to the base point (zero point) when the load is removed, and it corresponds to a large mounting pan and does not require zero point calibration. It can be manufactured at low cost.

[Brief description of drawings]

Fig. 1a Plan view of an embodiment of the present invention Fig. 1 b AA cross sectional view 1 Fig. C BB cross sectional view Fig. 2 D section cross sectional enlarged view Fig. 3 Explanatory drawing of prior art 1 ...... Leaf spring, 2 ... … Movable columns, 3… Fixed columns, 4…
... Movable electrode plate, 5 ... Fixed electrode plate, 6 ... Movable electrode rotating shaft, 7 ... Movable electrode support fitting, 8 ... Fixed electrode support fitting, 9 ... Insulating washer, 10 ... Insulating material, 11 ... … Leaf spring, 12 …… Movable column, 13 …… Fixed column, 14 …… Movable electrode plate, 15 …… Fixed electrode plate, 20 …… Spring retainer washer

Claims (1)

[Scope of utility model registration request] 1. A capacitance type weight sensor for detecting the weight by balancing the weight of an object to be weighed with a leaf spring Roberval, detecting the amount of displacement of the leaf spring as the amount of change in the capacitance of two electrode plates, and detecting the weight. In, the two inflexible portions are formed inside the fixed point of the leaf spring constituting the Roberval mechanism to the support, and one end of the movable electrode is rotatably attached to one of the inflexible portions to fix the movable electrode. A capacitance type weight sensor, characterized in that the other end of the electrode is always in contact with the central portion of the other inflexible portion formed on a leaf spring to which a fixed electrode is fixed.