JPH01152317A - Load detector - Google Patents

Abstract

PURPOSE:To achieve a highly accurate detection of a load with a smaller temperature drift of a load cell, by providing a load cell, a load mounting base and a rod with different covers respectively to keep temperature within the covers with an air conditioning device and a controller. CONSTITUTION:A cover 5 is arranged to surround a lower half of a rod 3, a load cell 1 and a mounting base 2 in such a manner as to be inserted into an intermediate point of the rod 3 and the internal space thereof is divided with a partition 11 to cover the lower half of the rod 3, the load cell 1 and the mounting base 2 separately. Temperatures of the load cell 1, the load cell mounting base 2 and the lower half of the rod 3 are detected by output signals of temperature measuring elements 7 to be kept at a fixed constant value by an ON-OFF control with controllers 8, 8a and 8b using heaters 6 as different air conditioning devices. A temperature drift is almost zero thereby enabling highly accurate detection of a load.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a load detection device using a strain gauge type load cell, and particularly relates to a load detection device that reduces errors due to temperature drift.

(Prior Art) When detecting a load using a strain gauge type load cell, if the temperature of the load cell is changed while a constant load is applied, the voltage output from the load cell changes. This is called temperature drift.

A conventionally used temperature drift prevention device will be explained with reference to FIG.

(1) is a strain gauge type load cell, (2) is a load cell mount, (3) is a rod, (4) is a load holder, (5) is a cover, (6) is a heating device, and (7) is a temperature measurement device. The element (8) is a control device.

This device is a device that attempts to prevent temperature drift by keeping the load cell (1) at a constant temperature higher than the temperature caused by external disturbances.

What is the temperature drift of the strain gauge type load cell (1)?

The temperature drift changes roughly as shown in Figure 3(b), and this temperature drift occurs between the load cell (1) and rod (3) shown in Figure 4.
The temperature is controlled by three points: the upper joint (9) between the load cell (1) and the lower joint (10) between the load cell (1) and the mounting base (2).

By keeping the temperatures at these three points constant, temperature drift can be eliminated. However, in the conventional device shown in Fig. 4,
Due to heat conduction through the rod (3), air convection within the cover (5), etc., the upper and lower joints where the temperature measuring element (7) is not attached (
9), (10) changes due to changes in outside temperature and rod (3)
It has the disadvantage that it changes due to heat conduction and heat radiation, creating a temperature draft.

(Problems to be Solved by the Invention) This conventional device attempts to keep the temperature inside the cover (5) constant using a temperature measuring element (7), a heating device (6), a control device (8), etc. There is a problem in that a temperature draft is generated due to changes in outside temperature, heat conduction of the rod, and thermal radiation, which tends to cause errors in load detection.

An object of the present invention is to provide a load detection device that maintains the temperature of a load cell constant and prevents temperature drift without being affected by changes in outside temperature or heat conduction or radiation of a rod.

[Structure of the invention]

(Means for Solving the Problems) In order to solve the above problems, in the present invention, in a load detection device using a strain gauge type load cell that outputs a signal according to the load, the load cell and the load cell are supported. a cover that covers each of the mounting base and the lower half of the rod that transmits a load to the load cell; an air conditioner that adjusts the temperature of the space covered by each cover; the load cell, the mounting base;
It is characterized by comprising a temperature measuring element that measures the temperature of each of the rods, and a control device that controls the air conditioner so that the temperature of each space is constant based on the output signal of each of the temperature measuring elements. A load detection device is provided.

(Function) In the device configured in this way, the load cell and
Separate covers are provided for the load cell mounting base and the rod, and the temperature inside each cover is kept constant by the air conditioner and control device, so the temperature drift of the load cell is reduced and a highly accurate load detection device can be obtained.

(Example) An example of the present invention will be described below with reference to FIG.

The strain gauge type load cell (1) is attached to the mount (2) via the lower joint (10). A rod (3) is attached to the upper side of the load cell (1) via an upper joint (9), and a load holder (4) is attached to the upper part of the rod (3). A cover (5) is provided to surround the lower half of the rod (3), the load cell (1), and the mounting base (2) so that the middle of the rod (3) is inserted through it, and the internal space is separated by a partition plate (11). Divide the lower half of the rod (3), the load cell (1), and the mounting base (2) so that they are each covered separately. Each divided space is provided with a heating device (6), which is an air conditioner. A temperature measuring element (7) is attached to the lower half of the rod (3), the load cell (1), and the mounting base (2), respectively. a control device (8) that controls the air conditioner on and off so that the temperature of each space is constant according to the output signal of each temperature measurement element (7);
(8a) and (8b) are provided.

In the device configured in this way, the load cell (1
), the load cell mounting base (2), and the lower half of the rod (3) are detected by the output signal of each temperature measuring element (7),
Control device (8) with heater (6) each being a separate air conditioner
, (8a) and (8b), the temperature can be maintained at a constant constant temperature. The heater (6) is used because it makes it easy to maintain a constant temperature higher than the maximum temperature caused by disturbances.

Next, the temperature drift of the above embodiment and the temperature drift of the conventional example will be explained using test examples shown in FIGS. 2 and 3.

Figures 2(a) and (b) show this example, and Figure 3(a)
.

(b) is a conventional example. Here, Ta is the temperature of the upper joint (9) between the rod (3) and the load cell (1) Tb is the temperature of the load cell mounting base (2) and the lower joint (10) To is the ambient temperature ■ is the load cell output T1 is the time when the device reaches a steady state (measurable)
Let ta be the ambient temperature change time. Looking at these figures, it can be seen that the conventional example shown in Fig. 3 (a
), To is about 20deg from time t2 to t3.
As the temperature rises, the temperature rise of the upper joint (9) becomes significantly large, and as shown in Figure 3 (b), the load cell output V becomes significantly large, that is, the temperature drift is large and the error in load detection is large. become. In contrast, FIG. 2(a) of this embodiment
So even if TO becomes large, Ta, Tb.

It can be seen that there is no change in Tc, and as shown in FIG. 2(b), the load cell output V is constant, that is, the temperature drift is almost zero, and the accuracy of load detection is high.

In the embodiment shown in FIG. 1, the air conditioner (6) is used as a heating device and is kept at a constant temperature higher than the maximum temperature caused by disturbance by on/off control, but as a modified example,
The air conditioner (6) may be a cooling device to maintain a constant temperature lower than the lowest temperature caused by external disturbances, or a cooling device and a heating device may be used to maintain a desired constant temperature.

〔Effect of the invention〕

As explained above, according to the present invention, the temperature of the load cell is kept constant by the air conditioner without being affected by changes in outside temperature, heat conduction or heat radiation of the rod, and temperature drift is prevented. We were able to provide a load detection device with high performance.

[Brief explanation of the drawing]

Figure 1 is a partial elevational view of a cover showing an embodiment of the load detection device of the present invention, Figures 2 (a) and (b) are curve diagrams showing the characteristics of the device in Figure 1, and Figure 3. (a) and (b) are curve diagrams showing the characteristics of the conventional example, and FIG. 4 is a partial elevational view of the cover showing the conventional example. 1...Load cell, 2...Mounting base, 3
...Rod, 4...Load receiver, 5
...Cover, 6.Heating device which is an air conditioner, 7.Temperature measuring element, 8.8
a, 8b...control device. 9... Upper joint part, 10... Lower joint part, 11... Partition plate.

Claims (1)

[Claims] In a load detection device using a strain gauge type load cell that outputs a signal according to a load, the load cell includes a cover that covers each of the load cell, a mounting base that supports the load cell, and a lower half of the rod that transmits the load to the load cell; The temperature of each space is kept constant by an air conditioner that adjusts the temperature of the space covered by the cover, a temperature measurement element that measures the temperature of each of the load cells, mounting bases, and rods, and output signals from each of the temperature measurement elements. A load detection device comprising: a control device that controls the air conditioner so that the following is achieved.