JPH0477863B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for measuring thrust acting on a rotating shaft without being affected by the centrifugal force of the rotating shaft.

Generally, various forces and moments act on a rotating shaft. However, in the following, to simplify the explanation, we will consider the case where thrust is measured using a strain gauge when two components of thrust and torque are acting on the rotating shaft.

In the past, various problems occurred when attempting to accurately measure thrust under such conditions.
For example, if the torque is large compared to the thrust,
The rotating shaft becomes thicker and therefore has a larger cross-sectional area. In this way, as the cross-sectional area increases, the output of the strain gauge against thrust decreases, so
To increase the power output, a hollow pipe rotating shaft is generally used. The axis of rotation of such a hollow pipe is
For example, it is assumed that it is formed from a thin steel pipe with an outer diameter D ₀ =252 mm and an inner diameter D ₁ =250 mm, and the measurement is performed under the following conditions.

Assume that this rotating shaft is subjected to two components of force: 2 tons of thrust and 1000 kg-m of torque at a rotational speed of 2100 rpm (35 rps). In this case, the thrust F is
It can be measured using strain gauges attached to required locations. For example, examples of the relationship in which strain gauges are attached are shown in FIGS. 1-1 and 1-2. 1-1
The figure is a three-dimensional view, and Figures 1-2 are developed views. In the figure, reference numeral 1 designates the axis of rotation, and reference numeral 2
~9 is axially spaced at 45 degree intervals on the rotation axis, and
There are eight strain gauges, four each attached in a 90-degree direction, that is, in the circumferential direction.

FIG. 2 shows an example in which the aforementioned strain gauge is assembled into a bridge. In addition, Figures 1-1 and 1-
In FIGS. 2 and 2, 8 strain gauges are combined, but it goes without saying that a combination of 4, 16, etc. is also possible.

In such a configuration, when a thrust of F=2 tons is applied, the strain gauges indicated by even reference numbers in FIGS. 1-1 and 1-2, that is, each strain gauge 2 attached in the axial direction, The strain ε occurring at 4, 6, and 8 is expressed by the following equation.

ε=1/E F/π/4 (D ₀ ² −D ₁ ² ) (1) where E is the Young's modulus of the rotating shaft material. Here, if E≒21000Kg/mm ² , the strain ε is as follows.

ε=120×10 ^-6 Also, the strain ε′ generated in each of the strain gauges 3, 5, 7, and 9 attached in the circumferential direction, indicated by odd reference numbers in FIGS. 1-1 and 1-2, is , considering Poisson's ratio, it becomes as follows.

ε′≒0.3ε Therefore, the bridge output ε _T in this case is as follows.

ε _T = 2 (ε + ε′) ≒ 2.6 ε = 312 × 10 ^-6 When this rotating shaft is rotating at N rps,
The strain ε _R generated in each strain gauge 3, 5, 7, and 9 due to centrifugal force is as follows.

ε _R = 1/E ρ(D ₀ /2) ² /g(2πN) ² …(2) Here, g is the acceleration of gravity, 9.8m/s ² ρ is the density of the shaft material, 7.80× 10 ^-6
Kg/mm ³ N is the rotation speed, which is assumed to be 35rps.

ε _R under this condition is as follows.

ε _R =29.1×10 ^-6 Also, strain ε _R ′ occurring in strain gauges 2, 4, 6, and 8
is expressed by the following formula.

ε _R ′=0.3ε _R In this case, the bridge's total output ε _RT is as follows.

ε _RT = 2.6 ε _R = 75.7×10 ^-6 This output ε _RT is generated even though no thrust is actually acting when the shaft is rotating, which naturally results in a measurement error. . This error is as follows.

ε _RT /ε _T = 24% This value is too large as a measurement error, so
It is not practical as it is. As a countermeasure for this, the strain gauge 3 shown in Figures 1-1 and 1-2,
Dummy gauges pasted at different positions may be used for 5, 7, and 9, but the measurement error is only 1/2.5 of the above calculated value, so
This cannot be said to be an essential improvement measure.

An object of the present invention is to provide a method for measuring the thrust of a rotating shaft for accurately measuring the thrust acting on the shaft without being affected by the rotational speed of the rotating shaft.

This object is achieved by a method for measuring the thrust of a rotating shaft having the structure described in the claims.

According to the method for measuring thrust according to the present invention, with a relatively simple configuration and without any particular difficulty in operation, it is possible to almost eliminate the influence of the shaft rotation speed and to measure thrust extremely accurately. It becomes possible.

The present invention will be described in detail below with reference to FIG. 3, which is a block diagram showing the configuration of an embodiment.

In Fig. 3, for example, Fig. 1-1 and Fig. 1-
As shown in FIG. 2, the output of a bridge 11 formed by eight strain gauges arranged on the surface of the rotating shaft is applied to a strain amplifier 12.

The rotation speed of the rotating shaft is detected by a rotation speed detector 13, and then squared by a rotation speed square calculator 14. An output representing the result of this calculation is supplied to one input of an adder 16 via a sensitivity adjuster 15.

On the other hand, the output of the distortion amplifier 12 described above is also
is supplied to the other input of the sensitivity adjuster 15, and is added to the output of the sensitivity adjuster 15. The result of this addition is taken out from the output terminal 17.

In this configuration, a series of processing results input to the adder 16 via the rotation speed detector 13, rotation speed square calculator 14, and sensitivity adjuster 15 are expressed by the above-mentioned formula.
It is clear that this corresponds to the strain ε _R expressed by (2).

Here, it is clear that in order to accurately measure the thrust acting on the rotating shaft, it is sufficient to subtract the error from the output of the distortion amplifier 12. Such processing can be implemented as follows.

To actually subtract the error, read the output value of the output terminal 17 in Fig. 3 when the rotation speed N=0 with no thrust applied.

(b) Increase the rotation speed to the maximum rotation speed of the relevant rotating shaft. In this case, no thrust load is applied.

C. Adjust the sensitivity adjuster 15 so that the output value of the terminal 17 in state B becomes the value in state A (N=0).

This can be achieved by performing each operation.

Through such processing, the thrust acting on the rotating shaft can be accurately measured regardless of the rotational speed of the rotating shaft. This error is about 0.3% or less, achieving significantly higher accuracy than conventional measurement methods.

In order to carry out the present invention, well-known elements such as strain gauges and other circuit elements mentioned in this specification can be used. Furthermore, although this explanation discloses analog processing and manual adjustment of the strain gauge output, rotational speed N, etc., each signal is appropriately converted to digital and digital control is used to add and adjust the signals. It will be obvious to those skilled in the art that the techniques can be applied.

[Brief explanation of the drawing]

FIGS. 1-1 and 1-2 are a perspective view and a developed view showing how the strain gauge is mounted on the rotating shaft to be measured. FIG. 2 is a connection diagram of a bridge circuit composed of each strain gauge. FIG. 3 is a block diagram showing the configuration of an apparatus for carrying out the present invention. In the figure, the correspondence of main reference numerals is as follows. DESCRIPTION OF SYMBOLS 1... Rotating shaft, 2, 4, 6, 8... Strain gauge mounted in the axial direction, 3, 5, 7, 9... Strain gauge mounted in the circumferential direction, 11... Bridge circuit, 12... Strain amplifier, 13... ...Rotation speed detector, 14...Squaring calculator, 15...Sensitivity adjuster, 16...Adder, 17
...Output terminal.

Claims (1)

[Claims] 1. A method for measuring thrust acting on a rotating shaft without being affected by the rotational speed, comprising a required number of strain gauges affixed on the rotating shaft in the axial direction and the circumferential direction. Take the output signal obtained by adding the output of the bridge and the output proportional to the square of the rotation speed of the rotating shaft and whose sensitivity can be adjusted to obtain the output signal when the rotation speed is zero with no thrust applied, and then In this state, the sensitivity of the output proportional to the square of the rotation speed is adjusted so that the added output signal when the rotating shaft is rotated at the maximum rotation speed is equal to the output signal when the rotation speed is zero. A method to measure the thrust of a rotating shaft without being affected by the rotation speed.