JP7020136B2 - Load measuring device - Google Patents

Description

The present invention relates to a load measuring device.

As a prior document disclosing the configuration of a load cell used in a load measuring device, there is Japanese Patent Application Laid-Open No. 8-271357 (Patent Document 1). The load cell described in Patent Document 1 includes a strain-causing body fixed in a cantilever shape and a strain gauge attached to the strain-causing body.

Japanese Unexamined Patent Publication No. 8-271357

In a load measuring device using a load cell, the detection characteristics of the load cell change due to deterioration of at least one of the strain-causing body and the strain gauge of the load cell with time. Therefore, it is necessary to calibrate the load cell in order to confirm whether the detection result of the load cell is correct.

Generally, the calibration of the load cell is to adjust the span and offset so that there is no difference between the detection result of the load cell and the known weight when a weight of known weight is attached to the strain source of the load cell. Is done by.

When the weight is artificially attached to the strain-causing body of the load cell, the calibration work becomes complicated. When the weight is mechanically attached to the strain-causing body of the load cell, the mechanical configuration of the load measuring device becomes complicated.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a load measuring device capable of easily performing calibration while having a simple mechanical configuration.

The load measuring device based on the present invention includes a load cell, an electromagnet, and a control unit. The load cell includes a strain-causing body to which the load of the object to be measured is loaded, and a strain gauge attached to the strain-causing body. The electromagnets are arranged at intervals on the strain-causing body, and are provided so that an electromagnetic force can act on the strain-causing body. The control unit calculates the above load based on the output of the strain gauge. The control unit calibrates the load cell based on the correlation between the output of the strain gauge due to the electromagnetic force and the output of the strain gauge due to the load.

In one embodiment of the present invention, the load measuring device further includes a support portion that supports the strain-causing body in a cantilever shape. The electromagnet is arranged below the end on the side opposite to the support side of the strain-causing body.

In one embodiment of the invention, the strain-causing body includes a magnetic body portion attached at a position facing the electromagnet.

In one embodiment of the present invention, the distance between the straining body and the electromagnet is substantially the same as the maximum allowable displacement of the straining body in a state where the electromagnet does not apply an electromagnetic force to the straining body.

According to the present invention, a load measuring device capable of easily performing calibration can be realized with a simple mechanical configuration.

It is a figure which shows the structure of the load measuring apparatus which concerns on one Embodiment of this invention. It is a partial side view which shows the state before deformation of the strain-causing body provided in the load measuring apparatus which concerns on one Embodiment of this invention. It is a partial side view which shows the state which the strain-causing body provided in the load measuring apparatus which concerns on one Embodiment of this invention bends to the maximum permissible displacement at the time of overload.

Hereinafter, the load measuring device according to the embodiment of the present invention will be described with reference to the drawings. In the following description of the embodiment, the same or corresponding parts in the drawings are designated by the same reference numerals, and the description thereof will not be repeated.

FIG. 1 is a diagram showing a configuration of a load measuring device according to an embodiment of the present invention. FIG. 2 is a partial side view showing a state before the strain-causing body provided in the load measuring device according to the embodiment of the present invention is deformed. FIG. 3 is a partial side view showing a state in which the strain-causing body provided in the load measuring device according to the embodiment of the present invention is bent to the maximum allowable displacement at the time of overload. In FIG. 3, the strain-causing body in the state before bending is shown by a dotted line.

As shown in FIGS. 1 to 3, the load measuring device 100 according to the embodiment of the present invention includes a load cell 110, an electromagnet 130, and a control unit 150. The load measuring device 100 further includes a support portion 120 that supports the strain-causing body 111 in a cantilever shape.

The load cell 110 includes a strain-causing body 111 to which the load of the object to be measured is loaded, and a strain gauge 112 attached to the strain-causing body 111. In the present embodiment, the strain-causing body 111 has a columnar outer shape. The outer shape of the strain-causing body 111 is not limited to a columnar shape, but may be a prismatic shape or the like.

One strain gauge 112 is attached to each of the upper part and the lower part of the tip portion on the side opposite to the support portion side of the strain-causing body 111. Further, one strain gauge 112 is attached to each of the upper portion and the lower portion of the root portion on the support portion side of the strain-causing body 111. That is, four strain gauges 112 are attached to the strain-causing body 111. Each of the four strain gauges 112 contains a resistor film.

The four strain gauges 112 constitute a bridge circuit and are electrically connected to the connection cable 180. However, the mounting position and the number of mountings of the strain gauge 112 with respect to the strain generating body 111 are not limited to the above, and at least one strain gauge 112 may be mounted on the strain generating body 111.

In the present embodiment, the strain-causing body 111 includes a magnetic body portion 113 attached at a position facing the electromagnet 130 of the main body of the strain-causing body 111. Specifically, the magnetic material portion 113 is attached to the lower portion of the tip portion of the main body of the strain-causing body 111. The magnetic material portion 113 is made of a material such as soft iron having a small residual magnetization. When the main body of the strain-causing body 111 is made of a magnetic material, the magnetic material portion 113 does not necessarily have to be provided.

The electromagnets 130 are arranged at intervals on the strain-causing body 111, and are provided so that an electromagnetic force can act on the strain-causing body 111. The electromagnet 130 is arranged below the tip portion on the side opposite to the support portion 120 side of the strain generating body 111. The electromagnet 130 has a columnar outer shape and is fixed on the base 140. The electromagnet 130 includes a core and a coil wound around the core. The outer shape of the electromagnet 130 is not limited to a columnar shape, but may be a prismatic shape or the like. The core of the electromagnet 130 is made of a magnetic material such as iron.

As shown in FIG. 1, the distance between the lower end of the strain generating body 111 and the upper end of the electromagnet 130 is L. Specifically, the distance between the lower end of the magnetic material portion 113 and the upper end of the core portion of the electromagnet 130 is L.

As shown in FIG. 3, the maximum permissible displacement of the strain-causing body 111 when the overload F2 is loaded is L. That is, as shown in FIGS. 1 and 3, in a state where the electromagnet 130 does not exert an electromagnetic force on the straining body 111, the distance between the straining body 111 and the electromagnet 130 is the maximum allowable displacement of the straining body 111. Is almost the same as. The maximum allowable displacement of the strain-causing body 111 when the overload F2 is loaded may be set to the amount of deflection due to the elastic deformation of the strain-causing body 111 immediately before the strain-causing body 111 is plastically deformed, or the load may be set. The amount of deflection of the strain-causing body 111 when a predetermined maximum measurement load is applied to the measuring device 100 may be set.

The electromagnet 130 is connected to a constant current source 170 that supplies a constant direct current to the electromagnet 130. Specifically, the constant current source 170 is connected to the coil of the electromagnet 130.

The two wires included in the connection cable 180 are connected to the constant voltage source 160. As a result, a constant DC voltage is applied to the bridge circuit composed of the four strain gauges 112.

The strain gauge 112 changes the electric resistance value in proportion to the strain of the strain-causing body 111 when the strain-causing body 111 is elastically deformed by the load of the load F1 of the object to be measured. The strain gauge 112 outputs a change in electric resistance value as a change in voltage. F1 <F2.

The other two wires included in the connection cable 180 are connected to the signal amplification unit 161. As a result, the two midpoints of the bridge circuit composed of the four strain gauges 112 are electrically connected to the signal amplification unit 161. The output voltage between the two midpoints of the bridge circuit is differentially amplified by the signal amplification unit 161.

The signal amplification unit 161 is connected to the noise reduction unit 162. The noise removing unit 162 removes unnecessary signal components from the output signal.

The noise removing unit 162 is connected to the A / D conversion unit 163. The output signal is converted from an analog signal to a digital signal by the A / D conversion unit 163.

The A / D conversion unit 163 is connected to the control unit 150. The control unit 150 includes a calculation unit 151 and a storage unit 152. The calculation unit 151 sets the load F1 of the object to be measured based on the output signal input from the A / D conversion unit 163 and the span adjustment value and the offset adjustment value stored in the storage unit 152 as described later. calculate. That is, the control unit 150 calculates the load F1 of the object to be measured based on the output of the strain gauge 112.

The control unit 150 is electrically connected to the constant current source 170. The control unit 150 controls the start and stop of power supply to the electromagnet 130 by the constant current source 170.

The control unit 150 calibrates the load cell 110 based on the correlation between the output of the strain gauge 112 due to the electromagnetic force acting on the strain generator 111 and the output of the strain gauge 112 due to the load F1 of the measurement object.

Hereinafter, a method of calibrating the load cell 110 in the load measuring device 100 according to the present embodiment will be described.

First, the electromagnet 130 is fixed on the base 140 so as to be positioned at intervals with respect to the strain-causing body 111 supported by the support portion 120 to form the load measuring device 100, and then a weight whose weight is known. Is attached to the strain generating body 111 of the load cell 110, and the output of the strain gauge 112 at this time is used as a reference output. The load on the strain-causing body 111 by the above weight is used as the reference load.

Next, the weight is removed from the strain-causing body 111, and an electromagnetic force is applied to the strain-causing body 111 by an electromagnet 130 to determine a reference current supply amount of a constant current source 170 whose output of the strain gauge 112 is a reference output. The correlation between the output of the strain gauge 112 due to the electromagnetic force and the output of the strain gauge 112 due to the load of the weight determined in this way is stored in the storage unit 152 of the control unit 150.

It should be noted that the weight is attached to and detached from the strain-causing body 111 of the load cell 110 as described above only when the reference output of the strain gauge 112 and the reference current supply amount of the constant current source 170 are determined.

The magnitude of the electromagnetic force acting on the strain-causing body 111 by the electromagnet 130 is determined by the coil characteristics, the electrical characteristics, the mechanical characteristics, and the environmental characteristics. Coil characteristics are determined by the electrical resistance, number of turns and winding density of the coil. The electrical characteristics are determined by the amount of current supplied to the coil. The mechanical properties are determined by the material of each of the strain generating body 111 including the magnetic material portion 113 and the core portion of the electromagnet 130, and the size of each of the core portions of the magnetic material portion 113 and the electromagnet 130. The environmental characteristics are determined by the ambient temperature and the distance between the magnetic material portion 113 and the core portion of the electromagnet 130. If the coil characteristics, electrical characteristics, mechanical characteristics, and environmental characteristics are substantially constant, the magnitude of the electromagnetic force acting on the strain-causing body 111 by the electromagnet 130 is substantially constant.

The electric resistance value of the coil changes due to the self-heating of the coil when a current flows through the coil. Therefore, the constant current source 170 maintains the current supply amount to the coil so as to be substantially constant with the reference current supply amount. The size of each of the core portion of the magnetic material portion 113 and the electromagnet 130 changes slightly due to the change in the ambient temperature, but the amount of this change is within the range in which the load measurement result is not affected.

Among the factors affecting the coil characteristics, electrical characteristics, mechanical characteristics, and environmental characteristics described above, factors other than the electrical resistance value of the coil and the ambient temperature hardly change with time. Therefore, when the constant current source 170 supplies the current of the reference current supply amount to the electromagnet 130, the electromagnet 130 exerts a substantially constant electromagnetic force on the strain generating body 111 so that the output of the strain gauge 112 becomes the reference output. Is possible.

The control unit 150 calibrates the load cell 110 based on the correlation between the output of the strain gauge 112 due to the electromagnetic force and the output of the strain gauge 112 due to the load of the weight stored in the storage unit 152.

Here, an example of a calculation method performed by the calculation unit 151 of the control unit 150 when calibrating the load cell 110 will be described. The calculation method performed by the calculation unit 151 is not limited to the following method, and various statistical methods can be used.

First, the calculation unit 151 acquires a digital signal of the output of the strain gauge 112 in a state where the electromagnetic force by the electromagnet 130 is not generated. The magnitude of the digital signal at this time is X1. The load on the strain-causing body 111 at this time is 0, and is set to Y1.

Next, the digital signal of the output of the strain gauge 112 in the state where the electromagnetic force is generated is acquired by supplying the current of the reference current supply amount from the constant current source 170 to the electromagnet 130. The magnitude of the digital signal at this time is X2. The load on the strain-causing body 111 at this time is the above-mentioned reference load, and is set to Y2.

The load on the strain generator 111 has linearity with respect to the magnitude of the digital signal. Therefore, the following relationship is established.

Y1 = A × X1 + B ・ ・ ・ (1)
Y2 = A × X2 + B ・ ・ ・ (2)
A is a span adjustment value, and B is an offset adjustment value.

From the above mathematical formulas (1) and (2), the following mathematical formulas (3) and (4) are established.
A = (Y1-Y2) / (X1-X2) ... (3)
B = (X1 x Y2-X2 x Y1) / (X1-X2) ... (4)
The span adjustment value can be obtained from the above formula (3). The offset adjustment value can be obtained from the above formula (4).

The span adjustment value and the offset adjustment value obtained by the calculation by the calculation unit 151 are stored in the storage unit 152. When measuring the load of the object to be measured, the calculation unit 151 applies the span adjustment value and the offset adjustment value stored in the storage unit 152 to the digital signal of the output of the strain gauge 112 to be measured. Calculate the load of an object.

In the load measuring device 100 according to the present embodiment, the load cell 110 is calibrated as described above. When both the magnitudes X1 and X2 of the digital signal are 0, the control unit 150 determines that the strain gauge 112 or the electric system connected to the strain gauge 112 is out of order.

As described above, the weight is attached to and detached from the strain-causing body 111 of the load cell 110 only when the reference output of the strain gauge 112 and the reference current supply amount of the constant current source 170 are determined. After determining the reference output of the strain gauge 112 and the reference current supply amount of the constant current source 170, an electromagnetic force is applied to the straining body 111 by the electromagnet 130 without attaching or detaching a weight to the straining body 111 of the load cell 110. This makes it possible to calibrate the load cell 110.

Therefore, after determining the reference output of the strain gauge 112 and the reference current supply amount of the constant current source 170, it is necessary to artificially attach the weight to the strain-causing body 111 of the load cell 110 every time calibration is performed. do not have. Further, it is not necessary to mechanically attach the weight to the strain-causing body 111 of the load cell 110. As a result, the load measuring device 100 according to the present embodiment can be easily calibrated while having a simple mechanical configuration.

In the load measuring device 100 according to the present embodiment, the strain-causing body 111 is supported in a cantilever shape, the electromagnet 130 is arranged below the tip of the strain-causing body 111, and the electromagnet 130 is the strain-causing body 111. The distance between the strain-causing body 111 and the electromagnet 130 is substantially the same as the maximum allowable displacement of the strain-causing body 111 in a state where no electromagnetic force is applied to the strain-generating body 111. As a result, as shown in FIG. 3, when the overload F2 is loaded, the tip portion of the strain generating body 111 can be supported by the core portion of the electromagnet 130, so that the strain generating body 111 bends by the maximum allowable displacement or more. It can be suppressed. That is, the electromagnet 130 functions as a stopper that prevents the strain-causing body 111 from bending more than an allowable limit when an overload acts on the load cell 110.

In the load measuring device 100 according to the present embodiment, the strain-causing body 111 is supported in a cantilever shape, and the electromagnet 130 is arranged below the tip of the strain-causing body 111. The present invention is not limited to the above, and for example, the magnetic material portion 113 may be arranged in the central portion of the strain generating body 111, and the electromagnet 130 may be arranged below the magnetic material portion 113.

It should be noted that the above-described embodiment disclosed this time is an example in all respects and does not serve as a basis for a limited interpretation. Therefore, the technical scope of the present invention is not construed solely by the embodiments described above, but is defined based on the description of the scope of claims. It also includes all changes within the meaning and scope of the claims.

100 load measuring device, 110 load cell, 111 strain generator, 112 strain gauge, 113 magnetic material part, 120 support part, 130 electromagnet, 140 base, 150 control unit, 151 arithmetic unit, 152 storage unit, 160 constant voltage source, 161 Signal amplification unit, 162 noise removal unit, 163 converter unit, 170 constant current source, 180 connection cable.

Claims (4)

A strain-generating body to which the load of the object to be measured is loaded, and a load cell containing a strain gauge attached to the strain-causing body,
An electromagnet arranged at intervals on the strain-causing body and capable of applying an electromagnetic force to the strain-causing body,
A control unit that calculates the load based on the output of the strain gauge is provided.
The control unit is a load measuring device that calibrates the load cell based on the correlation between the load and the electromagnetic force at which the outputs of the strain gauges are the same . A support portion that supports the strain-causing body in a cantilever shape is further provided.
The load measuring device according to claim 1, wherein the electromagnet is arranged below an end portion on the side opposite to the support portion side of the strain-causing body. The load measuring device according to claim 1 or 2, wherein the strain-causing body includes a magnetic body portion attached at a position facing the electromagnet. Claims 1 to claim that the distance between the straining body and the electromagnet is substantially the same as the maximum allowable displacement of the straining body in a state where the electromagnet does not apply an electromagnetic force to the straining body. The load measuring device according to any one of 3.

Images