JPS5817238Y2 - Load cell waterproofing device - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a waterproofing device for a load cell used in a weight measuring device that measures weight by converting a mechanical load into an electrical signal.

The beam is made of steel, beryllium copper, etc. as a means of attaching a metal waterproof cover to the beam to protect the strain gauge attached to the flexible part of the beam from moisture and harmful surrounding atmosphere. If the beam is made of a material that is difficult to solder, such as aluminum alloy, the waterproof cover can be soldered directly to the beam. It is something that

On the other hand, the load transmitted to the pressure-receiving part of the beam acts on the flexible part, and the strain gauge emits a signal corresponding to the strain in the flexible part to measure weight, etc. However, when an external force is applied to the pressure-receiving part of the beam, The distortion of the waterproof cover when it is transmitted also acts on the flexible part.

Therefore, the distortion characteristics of the waterproof cover are also considered in the adjustment.

In other words, the adhesive such as epoxy resin that bonds the beam and the waterproof cover is one of the elements for transmitting force, but this adhesive is weak against temperature and heat shock, and under certain conditions it is difficult to apply force. unable to communicate.

Therefore, the force applied to the pressure-receiving part of the beam should be proportional to the signal emitted by the strain gauge, but in this sense linearity cannot be achieved and hysteresis increases.
It is impossible to make accurate measurements.

□The purpose of this invention is to create a waterproof device for load cells that can solve the above-mentioned drawbacks.

This invention provides a beam to which a strain gauge forming a bridge circuit is attached to each of a plurality of flexible parts, and a bellows that surrounds the strain gauge has a fitting hole fitted into the beam at both end openings. A waterproof cover unit made of a metal material is provided with a flange formed with an attachment portion to the beam watertightly soldered, and this waterproof cover unit is fitted onto the beam, and the attachment portion is attached to the beam with a metal fastening member. After the beam and the flange are fixed together, the fitting portion between the beam and the flange is sealed with a moisture-resistant resin.

In other words, if the beam is made of a material that is difficult to solder, such as aluminum alloy, by fitting a flange soldered to both ends of the bellows into the beam and fixing the attachment part with a metal fastening member such as a screw. In this case, the fitting part between the beam and the waterproof cover unit is sealed with moisture-resistant resin to completely isolate the strain gauge from the outside, and it also allows the installation of a waterproof cover unit. As one of the elements for transmitting force to the beam, a metal fastening member is used that has little change with temperature and is resistant to heat shock, which improves linearity, reduces hysteresis, and enables accurate measurements. It is composed of

An embodiment of this invention will be explained based on the drawings.

Reference numeral 1 denotes a mounting plate fixed to a base (not shown) of a weight measuring device or the like, and a support portion 3 occupying half of the beam 2 is attached to this mounting portion 1 with screws 4.

By forming two elliptical holes 5 in an overlapping manner near the tip of the beam 2, two thin flexible parts 6, 7, 8, and 9 are formed on the upper and lower sides, and bridges are formed between these flexible parts 6 to 9. Strain gauges 12, 13, 14, 1 are connected to the input/output shielded wire 11 via the terminal board 10 while forming a circuit.
5 is installed.

Further, a pressure receiving portion 16 formed by a pivot is formed on the top surface of the tip of the beam 2 .

Next, a waterproof cover unit 20 is provided in which flanges 18 and 19 made of a metal material that can also be soldered are soldered to the openings at both ends of the bellows 17 made of a metal material that can be soldered.

These flanges 18, 19 are formed with a fitting hole 21 that fits into the beam 2 and a piece-shaped attachment part 22.

Then, by fitting the fitting part 21 to the beam 2 and screwing the screw 24, which is a metal fastening member passed through the mounting hole 23 of the mounting part 22, into the screw hole 25 of the beam 2, the waterproof cover unit 20 is attached to beam 2 and strain gauges 12 to 1
It surrounds 5.

The fitting portion between the beam 2 and the waterproof cover unit 20 is sealed with a moisture-resistant resin 26 such as epoxy resin.

In this state, since the width of the fitting hole 21 of one flange 18 is set to a width that allows the connection wires 27 to the strain gauges 12 to 15 to pass through, the coatings of those connection wires 27 may be damaged. There is no.

The terminal board 10 and the like attached to the side surface of the support portion 3 of the beam 2 are protected by a protective cover 28 attached to the support portion 3.

In such a configuration, when an external force is mechanically applied to the pressure receiving part 16, the flexible parts 6 to 9 are distorted, and the strain gauges 12 to 15 emit a signal depending on the degree of this distortion to electrically measure the value of the external force. do.

At this time, the distortion of the waterproof cover unit 20 is also caused by the flexible portion 6~
The force is transmitted by the screws 24 made of a metal material that is not affected much by temperature changes and is resistant to heat shock, so linearity is improved and hysteresis is reduced.

By the way, if we compare the conventional example in which the waterproof cover is fixed only with adhesive and the present invention, the conventional example has a linearity of 0.0175 hiro and a hysteresis of 0.0112, as shown in Figure 5a.
5, whereas the linear hysteresis of the present invention is only 0.0025 as shown in FIG.

Further, unlike the conventional example, the resin 26 in this case only needs to have the function of sealing the fitting portion between the beam 2 and the waterproof cover unit 20, and protects the strain gauges 12 to 15 from moisture and harmful atmosphere.

Therefore, accurate measurements can be made.

In this way, the waterproof cover 20 can be attached to the beam 2 made of a metal material that is difficult to solder without impairing the linear hysteresis characteristic.

. This invention is constructed as described above, and by attaching the flange attachment part of the waterproof cover unit with a metal fastening member that has little change due to temperature and is resistant to heat shock, distortion of the waterproof cover unit is applied to the flexible part. By keeping the action constant, linearity can be improved and hysteresis can be reduced, and the strain gauge can be completely isolated from the outside with the waterproof cover unit and resin, which makes it possible to perform accurate measurements. Moreover, it can also be used for beams made of aluminum alloy, etc., which are difficult to solder.
This has effects such as being able to attach a waterproof cover unit without impeding linear hysteresis characteristics.

[BRIEF DESCRIPTION OF THE DRAWINGS] The drawings show an embodiment of the invention, in which Fig. 1 is an exploded perspective view, Fig. 2 is a partially cutaway perspective view, Fig. 3 is a side view, and Fig. 4 is a partially cutaway perspective view. is a plan view, 5th. The figure is a graph showing a comparison of linearity and hysteresis characteristics between a conventional example and an example according to the present invention. 2...Beam, 6-9...Flexible part, 1
2-15...Strain gauge, 17...Bellows, 18-19...Flange, ...Fitting hole, 20...Waterproof Cover unit, 2122...
... Mounting part, 24 ... Screw (metal fastening member)
, 26...Resin.

Claims (1)

[Scope of utility model registration request] Each of the plurality of flexible parts is provided with a beam to which a strain gauge forming a bridge circuit is attached, and at least a bellows surrounding the strain gauge has a fitting hole fitted into the beam at both end openings, and a fitting hole to be fitted into the beam. After providing a waterproof cover unit made of a metal material with a flange formed with a mounting part and soldered watertightly, and fitting this waterproof cover unit to the beam and fixing the mounting part to the beam with a metal fastening member. A waterproof device for a load cell, characterized in that a fitting portion between the beam and the flange is sealed with a moisture-resistant resin.