JP2003334729A - Main spindle device of work machine, load detector used for the device, measuring method, and preload adjusting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure an axial force F acting on a bearing pressing cover with high accuracy by improving the bearing pressing cover, and adopting a 4-gauge method as a strain measuring method. <P>SOLUTION: A projection processing part 41 is formed to a bearing pressing cover type load detector 4 on the central perimeter line of a stationary bolt hole 49 on a pressuring receiving face side, and two (or four) stress concentration holes 42 are formed at an inner edge on a non-pressure receiving face side. At least two (or four) strain gauges 43 for detecting an axial load are attached in a stress concentration hole perimeter direction and a radial direction at the inner edge of the bearing pressing cover type load detector 4. A 4-gauge method, wherein perimeter direction strain outputs and radial direction strain outputs are alternately combined to form a strain gauge circuit, is adopted as a method for measuring outputs from the strain gauges. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spindle device for a machine tool such as a machining center, a preload adjusting method for the device, an axial load measuring method, and an invention applied as an axial load detector.

[0002]

2. Description of the Related Art Conventionally, in order to maintain good support rigidity of a spindle over a wide range of rotational speeds, the preload adjustment of an angular bearing that rotatably supports the spindle is adjusted according to the spindle operating conditions such as the spindle rotational speed. Various spindle devices to be used have already been proposed. FIG. 15 shows a schematic structure of a spindle device of a machine tool for a vertical machining center having such a configuration.

In FIG. 1, reference numeral 1 denotes a casing 10 which is rotatable.
In the main shaft housed in 1, a first angular bearing portion 2A that rotatably supports the main shaft is arranged on the upper side of the inner circumference of the casing 101, and a second angular bearing portion 2B is on the lower side of the inner circumference of the casing 101. It is arranged.

Then, the first angular bearing portion 2A
Is between the angular bearing main body 20A, the ring-shaped inner spacer 106 arranged on the inner ring side of the angular bearing main body 20A and fitted on the outer peripheral surface of the main shaft, and the inner peripheral surface of the casing 101 arranged between the outer ring of the angular bearing main body 20A. The ring-shaped outer spacer 107 to be fitted and the inner spacer 10
An engaging portion 108 having a rectangular ring cross section is provided between the outer spacer 6 and the outer spacer 107, and a ring-shaped preload oil chamber 5 communicating with the hydraulic passage 110 is formed below the engaging portion 108.

In the second angular bearing portion 2B, the angular bearing main body 20B and the angular bearing main body 20B are fitted on the inner peripheral side, and the outer peripheral surface of the main shaft 1 is fitted on the inner peripheral side.
On the other hand, the outer peripheral side is provided with a ring-shaped spacer 109 fitted to the inner peripheral surface of the casing 101, and the upper surface of the spacer 109 supports the spacer lower surface of the first angular bearing portion 2A. On the lower surface of the casing 101 and the lower surface of the spacer 109 of the second angular bearing portion 2B, a ring plate-shaped bearing pressing cover 3'is fixedly arranged integrally with the casing 101 by bolts 112, and the cover 3'is fixed to the main shaft 1. The axial force is configured to be loaded and supported.

By adjusting the hydraulic pressure supplied to the ring-shaped preloading oil chamber (hereinafter referred to as preloading area 5), the preloading conditions of the first and second angular bearing portions 2A, 2B are set to the rotation speed of the main shaft 1 or the like. It is configured so that it can be finely controlled.

More specifically, the spindle 1 of the machine tool 1
In order to improve productivity and surface roughness, the higher the rotation speed, the more advantageous. The key technology for speeding up is control of the bearing loads P ₁ and P ₂ including the preload setting amount between the pair of upper and lower angular bearings 2A and 2B. If this is excessive, seizure will occur due to an increase in the PV value of the spindle. If it is too small, the bearing rigidity will be insufficient and it will run around.
The bearing loads P ₁ and P ₂ of the angular bearing portions 2A and 2B are given by applying a preload p to the preload loading area 5.
Here, when the preload p is applied, the axial load P (= p × A,
(A: total cross-sectional area subjected to preload) is generated, and this load P is distributed to the bearing loads P ₁ and P ₂ and the bearing retainer cover load F,
These relationships are P ₁ = P ₂ = (P−F) / 2.

When the spindle 1 is not rotating, the bearing loads P ₁ and P ₂ can be confirmed by a method such as hammering the spindle 1, so that an appropriate load can be set. However, when the main shaft 1 rotates, the bearing loads P ₁ and P ₂ of the angular bearing portions 2A and 2B are caused by centrifugal force and thermal expansion difference (it is assumed that the temperature of the main shaft also rises to about 60 ° C as the rotational speed increases). Therefore, it is necessary to adjust the preload p in the preload area 5 to control the bearing loads P ₁ and P ₂ in an appropriate state, but at present, the bearing loads P ₁ and P ₂ during the spindle rotation are grasped. Due to lack of technology, it is the actual situation that the operation (spindle rotation) is performed by preload adjustment by hydraulic control to the preload area 5 based on experience, which is a problem in achieving higher speed of the spindle 1.

On the other hand, the bearing retainer cover is provided while the main shaft 1 is rotating.
Axial load (hereinafter referred to as axial force) F acting on 3 '
If it can be obtained by some method, bearing load P₁,
P₂Is P ₁, P₂= (P−F) / 2
(Here, the axial load P due to preload is the preload
p is a pressure gauge that detects the hydraulic pressure applied to the preload area
It can be easily measured via
A method for obtaining the axial force F acting on the cover 3'has been studied.
Came.

As one of them, as shown in FIG.
The strain gauge 121 is attached to the inner surface of the lower surface of the bearing retainer cover 3'of the current structure in close proximity to the temperature sensor 120 to measure strain during operation, and the value is obtained in advance in a laboratory or the like. There is a method (a method in which the bearing retainer cover is used as a load detector) by applying it to the force F and strain calibration diagram ".

Such a procedure is shown in FIG. This figure is a flowchart of axial force estimation based on measured values of strain and temperature. First, a diagram showing the relationship between temperature T and temperature drift εo from uniform temperature load tester data from laboratory tests and a diagram showing the relationship between strain ε and axial force F from axial force load test data were created and made into a map. Capture it. (S ₁ ) Next, based on the actual data of the actual machine, the actual temperature measurement value T and the actual strain measurement value εm are taken in by the temperature sensor and the strain gauge, and the temperature T based on the map and the temperature drift based on the diagram showing the relationship of the temperature εo Removal of drift εo (εm-ε
o) (S ₂ ) Next, F = 1 / α1 (εm−εo) ± β is obtained from the diagram showing the relationship between the strain ε and the axial force F from the map, and is set as the estimated axial force. (S ₃ )

[0012]

However, the output strain due to the estimated axial force F shown in FIG. 16 is shown in FIG. 17 (C).
As is apparent from the graph showing the relationship between the axial force and the measured strain shown in (1), (measured strain εm / axial force F) = 20 μs /
It is as small as 300 kgf, and the output strain εmo (temperature drift strain) due to the change in temperature T changes in the main axis while changing in a curve as shown in the graph showing the relationship between temperature T and strain εmo in FIG. When the temperature rise is from 5 ° C to 65 ° C, there is about εmo / T = 80μs / 60 ° C, and the variation range of the strain measurement value during temperature increase / decrease is ± 5μs at maximum.
As a result, the axial force measurement error (considering only ± 5 μs of the maximum width of the strain measurement value during temperature increase / decrease) considering the reproducibility of strain due to temperature change estimated from these is shown in FIGS. 17 and 18. As shown in the axial force load test results and the axial force calibration diagram obtained by the temperature load test, at least ± 68
kgf (= (300kgf / 20) × 5)) is expected,
It was thought that the measurement error was too large to be established as an axial force measurement method. It was also mentioned that one of the causes of the axial force measurement error is that the temperature drift strain changes in a curve with respect to the temperature change, which makes it difficult to correct the temperature.

17A and 18A show the axial force urging direction of the bearing pressing cover and the position of the strain gauge. (B) shows an example of the voltage / output flow direction and strain output of the 1-gauge method, and one strain gauge and three fixed resistors form a bridge circuit.

In view of the problems of the prior art, an object of the present invention is to improve the bearing retainer cover and adopt the 4-gauge method for strain measurement to accurately measure the axial force F acting on the bearing retainer cover. The invention is to provide.

[0015]

According to the present invention, there is provided a plate-shaped bearing retainer having a main shaft, a bearing portion rotatably supporting the main shaft, and a casing accommodating the bearing portion, the bearing portion being fixed to the casing side. It is also applied as a spindle device of a machine tool supported by a cover, and as a plate-shaped axial load detector that detects an axial load acting on a bearing portion that rotatably supports a spindle of a machine tool. , For example, in the latter case, a plurality of stress concentration holes are provided at circumferentially symmetrical positions of a portion of the non-pressure receiving surface side opposite to the bearing portion pressure receiving surface where an axial load of the bearing portion acts, and the axial load of the bearing portion is provided. Strain gauges for detecting are arranged in the circumferential direction and the radial direction of the stress concentration hole. In this case, in the axial load detector in which the stress concentration holes are a multiple (even number) of 2 and the strain gauges arranged in the circumferential direction and the radial direction of the stress concentration holes are a multiple of 4, Strain gauge bridge circuits are often constructed by alternately combining circumferential strain outputs and radial strain outputs of multiple strain gauges.
Further, the load detector is fixed to a casing located on the outer peripheral side of the bearing portion, and a plurality of convex portions are formed on a circumferential line along the casing fixing means on the pressure receiving surface side of the bearing portion. Furthermore, it is a requirement that a temperature sensor is attached to at least one of the stress concentration holes near the strain measuring portion.

Further, according to the present invention, an axial load (hereinafter referred to as an axial force) of a bearing portion that rotatably supports a main shaft of a machine tool.
In the axial force measuring method for estimating from the strain measurement value, a plurality of stress concentrating portions are provided at circumferentially symmetrical positions of the surface opposite to the pressure receiving surface of the plate-shaped pressure receiving body that receives the axial force of the bearing portion, and the stress Strain gauges of multiples of 4 are arranged in each of the concentrated portions at least two points in the circumferential direction and the radial direction with respect to the main axis, and the strain gauges of multiples of 4 are output by adopting the 4-gauge method of the bridge circuit. At least one temperature sensor is attached in the vicinity of the strain measuring section, the temperature of the pressure receiving body is measured at the same time as the strain, and temperature correction is performed on the strain measurement value. It is characterized in that the axial force is measured while being fixedly supported on the outer peripheral side of the stress concentrating portion and the pressure receiving surface side of the fixed supporting portion is provided with a convex portion.

Further, according to the present invention, the main shaft is rotatably supported by the upper bearing and the lower bearing, and an axial load (hereinafter referred to as an axial force) generated by applying a preload to a preload area provided between the two bearings. Is measured with a strain gauge provided on the bearing retainer cover to estimate the axial force, and the preload in the preload area is adjusted based on the estimated axial force to adjust the bearing load of both bearings to a proper state. When applied to the method, a plurality of stress concentrating portions are provided at circumferentially symmetrical positions of the pressure-receiving surface of the plate-shaped pressure-receiving body that receives the axial force, and the non-pressure-receiving surface on the side opposite to the pressure-receiving surface. On the other hand, a strain gauge of a multiple of 4 is arranged at least at two points in the circumferential direction and the radial direction, and the strain gauge of a multiple of 4 is output by using the 4-gauge method of the bridge circuit, and the vicinity of the strain measuring section. Has at least one temperature sensor Attached, the temperature of the pressure receiving body is measured at the same time as the strain, and the strain measurement value obtained by performing temperature correction on the strain measurement value is acquired in advance. Axial force calibration diagram (axial force F-strain relationship diagram) To estimate the axial force of the bearing portion, adjust the preload in the preload area based on the estimated value, and control the bearing load of both bearings to an appropriate state.

The present invention will be specifically described below. In order to accurately measure the axial force F acting on the bearing retainer cover 3, the strain output is large with respect to the axial force F, and the width (error) of the strain output is small with respect to the temperature change, and the temperature correction is required. It is important that it can be done easily. In order to achieve the above purpose, (1) To increase the strain output with respect to the axial force F
Improving the shape of the bearing retainer cover 3 "(2) Expanding the strain output and reducing the width (error) of the strain output with respect to temperature changes" The 4 gauge method is adopted as the strain output method. “(3)“ Measure temperature simultaneously with strain measurement ”to enable temperature compensation of the strain gauge.

The axial load detector (bearing pressing cover type load detector) of the machine tool spindle of the present invention preferably has the following specific configuration. (1) The bearing retainer cover type load detector 4 is provided with a convex portion 41 on the flange surface side on the circumferential line of the center of the fixing bolt hole within the range that does not affect the rigidity of the bearing. (2) Two to four stress concentration holes (reference numeral 42) are formed on the inner peripheral edge of the bearing pressing cover 4 on the side opposite to the flange surface. (3) Strain gauge 43a for detecting axial load
The mounting of ~ 43d is carried out in the circumferential direction of the inner surface of the stress concentration hole 42 in the inner peripheral edge of the bearing pressing cover and in the radial direction of the general inner peripheral edge.
Do 2 points each (total 4 points) or 4 points each (total 8 points). (4) The output method from these strain gauges is the circumferential strain output εθ ₁ , εθ ₂ (or εθ ₁ , εθ ₂ , εθ ₃ ,
εθ ₄ ) and radial strain output εr ₁ , εr ₂ (or ε
r ₁ , εr ₂ , εr ₃ , εr ₄ ) are alternately combined and the total strain output is “εθ ₁ −εr ₁ + εθ ₂ −εr ₂ ” (or “{(εθ ₁ + εθ ₃ )-( εr ₁ + εr ₃ ) + (εθ ₂ +
Adopt a 4-gauge method in which a strain gauge bridge circuit is assembled so that εθ ₄ )-(εr ₂ + εr ₄ )} / 2) ”. (5) Near the strain measuring section of the bearing retainer cover type load detector 4 At least one temperature sensor 44, such as a thermocouple, is attached to the bearing, and the temperature of the bearing retainer cover type load detector 4 is measured at the same time as the strain, and the strain measurement value is temperature-corrected. Axial force F acting on the detector
Is obtained by collating the strain value and temperature obtained by actual machine measurement with the axial force calibration diagram (axial force F to strain relationship diagram) obtained in advance.

The procedure will be described more specifically as follows. (1) The bearing retainer cover type load detector 4 is provided with a convex portion 41 on the center line of the fixing bolt hole on the flange surface (pressure receiving surface) side and the inner peripheral edge on the non-flange surface (non-pressure receiving surface) side. Two (or four) stress concentration holes 42 are processed in the portion. (2) Strain gauge 43 for detecting axial load
Is attached at least two points (or four points each) in the circumferential direction and the radial direction of the stress concentration hole 42 in the inner peripheral edge portion of the bearing pressing cover type load detector 4, and as an output measuring method from the strain gauges 43, Circumferential strain output εθ ₁ , ε
θ ₂ (or εθ ₁ , εθ ₂ , εθ ₃ , εθ ₄ ) and radial strain outputs εr ₁ and εr ₂ (or εr ₁ , εr ₂ and ε)
r ₃ and εr ₄ ) are alternately combined so that the total strain output is “εθ ₁ −εr ₁ + εθ ₂ −εr ₂ ” (or “{(εθ ₁ +
εθ ₃ ) − (εr ₁ + εr ₃ ) + (εθ ₂ + εθ ₄ ) − (εr ₂
+ εr ₄ )} / 2) ”is adopted so that a strain gauge bridge circuit is assembled. (3) A temperature sensor 44 such as a thermocouple is provided near the strain measuring section of the improved bearing retainer cover 4. Attach and measure at least one temperature at the same time as strain measurement.

According to such a configuration and procedure, (1) the bolt hole 49 on the flange surface side of the bearing pressing cover 3
By providing the convex processing portion 41 on the central circumferential line to such an extent that the bearing rigidity is not affected, the fixing state by the bolt 112 becomes gradual, and the strain generated in the bearing pressing cover with respect to the axial force F increases. In addition, a hole 42 is formed in the inner peripheral edge portion on the side of the non-flange surface, which is the strain measuring portion, so that a stress concentration portion can be created, and the strain generated with respect to the axial force F can be increased. (2) As the strain output method, the circumferential strain gauges 43a and 43c and the radial strain gauges 43b and 4 of the stress concentration hole 42 at the inner peripheral edge of the bearing pressing cover type load detector 4 are used.
By combining 3d alternately and forming a gauge bridge circuit by the 4-gauge method, since the circumferential strain and the radial strain are positive and negative and have different signs, the output by the 4-gauge method e ₀₄
{E ₀₄ = (E / 4) * (εθ ₁ −εr ₁ + εθ ₂ −εr ₂ )}
Is a 1-gauge method output e ₀₁ {e ₀₁ =
It can be increased about 2.6 times in the experiment as compared with (E / ₄ ) * (εθ ₁ )}. (3) Further, by adopting the 4-gauge method, the temperature drifts of the respective strain gauges cancel each other, so that the temperature drift can be reduced. By performing the temperature measurement of the bearing pressing cover type load detector 4 simultaneously with the strain measurement, the temperature drift of the strain gauge can be corrected and the measurement error due to the temperature can be reduced.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below with reference to the embodiments shown in the drawings. However, unless otherwise specified, the dimensions, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention thereto, but are merely illustrative examples.

An example of estimating the spindle axial force using the bearing pressing cover type load detector according to the embodiment of the present invention will be described with reference to FIGS. 1 to 6. FIG. 1 is a side sectional view of a bearing retainer cover type load detector according to a first embodiment of the present invention, and FIG. 2 shows a flange side of the bearing retainer cover type load detector taken along the line AA in FIG. 1 is a top view, FIG. 3 is a bottom view showing the side opposite to the flange taken along the line BB of FIG. 1, and FIG. 4 is an enlarged three-dimensional view of the inner peripheral edge of the bearing retainer cover type load detector.

In FIGS. 1 to 3, reference numeral 4 denotes a load detector provided on the bearing holding cover 3 in the form of a ring plate.
Six bolt holes 49 are evenly formed in the circumferential direction at the 0 ° position. Further, as shown in FIGS. 1 and 2, on the flange surface (upper surface) side of the bearing pressing cover 3, a trapezoidal shape is provided in units of 30 ° on the virtual circumference connecting the centers of the bolt holes 49 from the outer peripheral end toward the center. And has a shape larger than the bolt hole 49.
Two convex processing parts 41 were provided. In addition, as shown in FIGS. 1 and 3, the inner peripheral edge portion on the side opposite to the flange surface is made to correspond to the position of the two convex processed portions 41 at the 180 ° symmetrical position by 18
Two stress concentration holes 42 having a diameter of 6 mm were formed in the inner peripheral edge portion at a diagonal position of 0 degree.

A strain gauge for detecting the axial force F is, as shown in FIGS. 1, 3 and 4, a circumference of the inner peripheral portion of each of the stress concentration holes 42 of φ6 mm in the inner peripheral edge portion on the side opposite to the flange surface. direction,
In other words, two general-purpose circumferential strain gauges 43a and 43c are attached to the inner circumferential symmetrical positions of the stress concentration holes 42 along the circumferential surface parallel to the spindle axis direction. Also stress concentration holes 4
Two general-purpose radial strain gauges 43b and 43d were attached along the radial direction of the inner peripheral edge portion on the side opposite to the flange surface in the vicinity of 2.

FIG. 5 is a strain gauge bridge circuit diagram of the bearing pressing cover type load detector. Strain measurement is performed by measuring the resistance (Rg1, Rg1,
Rg2, Rg3, Rg4) to the circumferential strain gauge 43
The strain gauge output was obtained by forming a bridge circuit by the 4-gauge method so that a and 43c and radial strain gauges 43b and 43d were alternately inserted. In the figure, E is the bridge voltage and e _o is the output voltage from the bridge circuit.

That is, in the bridge circuit, the circumferential strain gauges 43a and 43c and the radial strain gauges 43b and 43d of the stress concentration hole 42 in the inner peripheral edge portion of the bearing pressing cover 3 are used.
By alternately combining and forming a gauge bridge circuit by the 4-gauge method, as shown in FIG. 6, the circumferential strain and the radial strain have positive and negative signs, so that the output by the 4-gauge method e ₀₄ {e ₀₄ = (E / 4) * (εθ ₁ −εr ₁ + εθ
₂ −εr ₂ )} is the 1 gauge method output e ₀₁ which is a general measurement method.
It can be increased about 2.6 times compared to {e ₀₁ = (E / ₄ ) * (εθ ₁ )}.

By adopting the 4-gauge method, the temperature drifts of the respective strain gauges cancel each other out.
The temperature drift can be reduced, and further, the thermocouples 44a and 44b are attached near the strain gauge in the radial direction with the stress concentration hole 42 interposed therebetween so that the temperature can be measured at the same time. Therefore, the temperature drift of the strain gauge can be corrected. You can
Measurement error due to temperature can be reduced.

FIG. 6 shows a measuring apparatus using the bearing retainer cover type load detector 4, and the left side of the figure shows four strain gauges on the bearing retainer cover 3 side and two temperature sensors (thermocouples). A bridge circuit is composed of four strain gauges. The right side of the figure shows the configuration inside the measuring chamber 57, and the strain measuring instrument 5 for measuring strain by measuring the voltage applied to the bridge circuit and the output from the bridge circuit 5
4. Temperature measuring device 55 for measuring the temperature from the temperature sensor,
The personal computer 56 estimates the axial force based on the strain output and the temperature output.

The operation of this embodiment will be described step by step. The bearing retainer cover type load detector 4 of the present embodiment described above.
Is incorporated in place of the bearing retainer cover 3'of the main spindle device of the machine tool shown in FIG. 15, the axial force F is measured using this load detector 4 during operation, and the bearing loads P ₁ , P ₂ and preload By utilizing the fact that the relationship between the axial force P due to and the axial force F acting on the bearing retainer cover is “P ₁ = P ₂ = (P−F) / 2”, finally an appropriate bearing load P Used to adjust the preload (p) so that ₁ and P ₂ can be obtained.

In order to confirm the effect of the bearing retainer cover type load detector of the present invention, an actual machine large model was manufactured and subjected to an axial load test and a temperature load test. FIG. 7 is an axial load test procedure diagram of the bearing retainer cover type load detector applied to the embodiment of the present invention, and (A) is an overall view. In FIG. 7 (A), reference numerals 51, 52 and 53 are all axial load force jigs.
A cylindrical casing-shaped jig 52 having a lower flange is installed on a load receiving base 51 of a ring-shaped base. On the inner circumference of the casing-shaped jig 52, a cylindrical jig 53 corresponding to a main shaft or a spacer is provided as a pair of upper and lower angular bearing portions 2.
It is arranged rotatably up and down through A and 2B,
A load of F = 0 to 500 kgf is applied from the upper surface of the cylindrical jig by a precision universal testing machine so that an axial force is applied. FIG. 7B shows the dimensions of the bearing retainer cover type load detector 4 and the positions of the four strain gauges 43a to 43d.

In such a device, the bearing retainer cover type load detector 4 is attached to the lower surface of the casing jig 52 by the bolt 11.
It is fixed by 2 (49 is a bolt hole), and the cylindrical jig 53 corresponding to the main shaft or the spacer is supported from the lower surface side. Then, an axial load of up to 500 kgf was applied from the upper surface of the cylindrical jig 53 with a precision universal tester, and the strain at that time was measured. The result is shown in FIG.

FIG. 8 is a first example of an axial load test result of the bearing retainer cover type load detector tested based on FIG. 7, and (A) shows the axial direction of the load detector and the strain gauge. The arrangement position is shown, and since it is similar to FIG. 3, its detailed description is omitted. FIG. 5B shows an example of voltage / output flow direction and strain output in the 4-gauge method, which is configured by the bridge circuit shown in FIG. (C) is a graph showing the relationship between axial force and measured strain. Strain output ε _m4 due to axial load of 300 kgf
Is 108 μs, which is the value measured by the conventional method (εθm0
= 20 μs / 300 kgf) about 5.5 times (≈ε
_m4 / εθ _m0 = 108 μs / 20 μs) A high value was obtained.

Furthermore, in order to confirm the details of this increase in strain output, the circumferential strain ε of the inner surface of the φ6 mm stress concentration hole 42 of the bearing pressing cover type load detector 4 is confirmed.
theta _{m 1,} and the circumferential strain Ipushironshita _m01 and radial strain .epsilon.r _m1 of the general portion of the inner peripheral edge portion try to measure individually 1 gauge method. The results are shown in FIG.

FIG. 9 is a second example of the axial load test results of the bearing retainer cover type load detector tested based on FIG. 7, (A) shows the axial direction of the load detector and the stress concentration. Hole 42
And the arrangement positions of the strain gauges in the circumferential direction and the radial direction are shown. Since they are the same as in FIG.
Incidentally, 43 ₀ is the circumferential direction strain gauge general portion provided in a location other than the stress concentration hole 42. Further, the radial strain gauge of the general portion is provided at the position shown in FIG. Figure 9
17B shows an example of the voltage / output flow direction and strain output in the 1-gauge method, which is configured by a bridge circuit in combination with the fixed resistor 124 shown in FIG. 17B. Figure 9
(C) is a graph showing the relationship between the axial force and the measured strain, and shows the circumferential strain portion of the stress concentration hole 42 and the strain in the circumferential portion and the radial portion of the general portion, respectively. The circumferential strain εθ _m1 of the inner surface of the stress concentrating hole 42 of φ6 mm is 48 μs / 30.
0 kgf, circumferential strain Ipushironshita _m01 of the general portion of the inner peripheral edge portion 3
0 μs / 300 kgf, and radial strain εr _m1 of the general portion of the inner peripheral edge portion is −9 μs / 300 kgf. From these facts, the strain increasing effect according to the present invention is obtained by forming a convex portion on the flange surface side of the bearing retainer cover. 1.5 times (= ε
_{θ m01 / εθ m0 = 30μs /} 20μs), 1.6 times by processing the stress concentration hole 42 of φ6mm the inner peripheral edge portion (=
_{εθ m 1 / εθ m01 = 48μs} / 30μs), and FIG. 7
As shown in Fig. 3, the stress concentration hole 42 is machined and the 4-gauge method is further adopted to obtain 2.3 times (= ε _m4 / ε
θ _m1 = 108 μs / 48 μs).

Next, FIG. 10 shows a temperature load test procedure of the bearing retainer cover type load detector 4 of the present invention. FIG. 10 is a temperature load test procedure diagram of the bearing retainer cover type load detector applied to the embodiment of the present invention. FIG. 10A shows the arrangement position of the strain gauge of the load detector and the accommodation state in the heating furnace. (B) shows an example of voltage / output flow direction and strain output based on the 4-gauge method of the strain gauge housed in the heating furnace.
In (A), the single body of the bearing pressing cover type load detector 4 was put in the heating furnace 50, and the temperature was raised and lowered between 10 ° C. and 65 ° C., and the strain (temperature drift) at that time was measured. The result is shown in FIG.

FIG. 11 is a schematic view of a heating furnace in accordance with FIG.
The example of the temperature drift of the temperature load test result of the bearing retainer cover type load detector which temperature-rising test was carried out between ℃ -65 ℃ is shown. It can be understood that the strain output shows a linear relationship having a width of about ± 2.5 μs as the temperature rises and falls when the temperature changes.
Therefore, it was found that temperature correction is easy because the temperature drift strain shows a linear relationship with the temperature change, and the strain measurement error with respect to the temperature change should be observed at about ± 2.5 μs.

Further, based on these test results, an axial force calibration diagram of the bearing retainer cover type load detector of the present invention was prepared and the measurement accuracy was estimated. The results are shown in FIG. FIG. 12 is a graph showing an example of axial force load force estimation from measured strain in the axial force load test results of FIG. 9 and FIG. 10 and the axial force calibration diagram obtained by the temperature load test. From this graph, the measurement error of the bearing retainer cover type load detector is ± 11.
It has been confirmed that kgf is considered, and the measurement accuracy is significantly improved compared to the conventional method (about ± 68 kgf).

In addition to the above-mentioned four strain gauges, the bearing retainer cover type load detector also has stress concentration holes 42 formed at four locations on the inner peripheral edge as shown in FIG. A method in which eight gauges are attached in the circumferential direction and in the radial direction of the inner peripheral edge general portion is also conceivable. The strain gauge bridge circuit at that time is as shown in FIG.

That is, as shown in FIG. 13, the second embodiment of the present invention is a side sectional view and a plan view showing the structure of a bearing retainer cover type load detector when eight strain gauges are used. The ring-plate-shaped bearing retainer cover type load detector has six bolt holes 49 evenly formed in the circumferential direction at 60 ° positions on the outer peripheral side. Further, similar to FIG. 2, on the flange surface (upper surface) side of the bearing pressing cover 3, trapezoidal bolt holes are formed in units of 30 ° on the virtual circumference connecting the centers of the bolt holes 49 toward the center from the outer peripheral end. Twelve convex processing portions 41 having a larger shape of 49 were provided. The lower part of FIG. 13 corresponds to FIG. 3, and four stress concentration holes 42 of φ6 mm are formed in the inner peripheral edge portion on the side opposite to the flange surface at diagonal positions of 90 degrees.

A strain gauge for detecting the axial force F is, as shown in the lower part of FIG. 13, circumferentially on the circumferential direction 1 side of the inner peripheral portion of each of the φ6 mm stress concentration holes 42 at the inner peripheral edge portion on the opposite flange surface side. Directional strain gauges 43aA, 43aB, 43cA, 43
Four pieces of cB are attached to the center side peripheral surface position in the stress concentration hole 42. Four general-purpose radial strain gauges 43bA, 43bB, 43dA, 43dB were attached along the radial direction of the inner peripheral edge portion on the side opposite to the flange surface near the stress concentration hole 42.

FIG. 14 is a strain gauge bridge circuit diagram of the bearing retainer cover type load detector. Strain measurement is performed by measuring the resistance (Rg1) of these four circumferential / radial strain gauges.
~ Rg8) circumferential strain gauge (43aA, 43a
B) (43cA, 43cB) and radial strain gauges (43bA, 43bB), (43dA, 43dB) are connected in series to each side so that a bridge circuit is assembled by the 8 gauge method to obtain strain output. I chose Incidentally, E in the figure
Is the bridge voltage and e _o is the output voltage from the bridge circuit.

Returning to FIG. 13, further, at the 180 ° symmetrical position.
A strain gage in the radial direction across a stress concentration hole 42
Attach thermocouples 44a and 44b in the vicinity to measure temperature.
I am able to do it from time to time. Anti flan of bearing retainer cover 4
Two or four stress concentration holes 42 are formed in the inner peripheral edge of the surface
Process 4-2. Also in this embodiment, the axial load
Of strain gauges 43a to 43d for detecting
Is the inner surface of the stress concentration hole 42 at the inner peripheral edge of the bearing retainer cover.
Four points each in the circumferential direction and the radial direction of the inner peripheral edge general part (total 8
Do) The output method from those strain gauges is
Directional strain output εθ₁, Εθ₂, Εθ ₃, Εθ_FourAnd radial
Total output εr₁, Εr₂, Εr₃, Εr_FourAlternate combinations
And the total strain output is e_o= (E / 4) * εo εo ＝ {(Εθ₁+ εθ₃)-(Εr₁+ εr₃) + (Εθ₂+ ε
θ_Four)-(Εr₂+ εr_Four)} / 2) 4 gauge with strain gauge bridge circuit
Adopt the law.

At least one thermocouple 44 is attached near the strain measuring portion of the bearing retainer cover type load detector 4,
The temperature of the bearing retainer cover type load detector 4 is measured at the same time as the strain, the temperature is corrected for the strain measurement value, and the axial force F acting on the bearing retainer cover type load detector is equal to the strain value obtained by actual machine measurement. Obtaining the temperature by collating it with the axial force calibration diagram (axial force F-strain relationship diagram) acquired in advance is the same as in the above embodiment.

As described above, according to the present invention, the bearing pressing cover is improved and the 4 gauge method is adopted as the strain measuring method, so that the axial force F acting on the bearing pressing cover 3 can be accurately measured. . Specifically, by providing the convex processing portion 41 on the center circumferential line of the bolt hole 49 on the flange surface side of the bearing pressing cover 3 to the extent that bearing rigidity is not affected, the fixing state by the bolt 112 becomes gentle, and The strain generated in the bearing pressing cover 3 with respect to the force F increases. Further, according to the present invention, the stress concentration portion (stress concentration hole 4
2) can be created, and the strain generated with respect to the axial force F can be expanded. Further, as a strain output method, the stress concentration hole 42 in the inner peripheral edge portion of the bearing pressing cover 3 is used.
By alternately combining circumferential strain gauges and radial strain gauges to form a gauge bridge circuit using the 4-gauge method, since the circumferential strain and the radial strain have different positive and negative signs, the output of the 4-gauge method is Compared with the 1 gauge method output which is a general measurement method, it can be greatly increased,
By adopting the 4-gauge method, the temperature drifts of the respective strain gauges cancel each other out, so that the temperature drift can be reduced. Further, by measuring the temperature of the bearing pressing cover 3 simultaneously with the strain measurement, the temperature drift of the strain gauge can be corrected and the measurement error due to the temperature can be reduced.

[Brief description of drawings]

FIG. 1 is a side sectional view of a bearing retainer cover type load detector according to a first embodiment of the present invention.

FIG. 2 is a top view of the bearing retainer cover type load detector according to the first embodiment, showing a flange side of arrow AA in FIG.

FIG. 3 is a bottom view of the bearing retainer cover type load detector according to the first embodiment, showing the side opposite to the flange taken along the line BB in FIG. 1.

FIG. 4 is an enlarged three-dimensional view of an inner peripheral edge portion of the bearing retainer cover type load detector according to the first embodiment.

FIG. 5 is a strain gauge bridge circuit diagram of the bearing retainer cover type load detector according to the first embodiment.

FIG. 6 is a diagram showing an axial load measuring system using a bearing retainer cover type load detector according to an embodiment of the present invention.

7A and 7B are axial force load test procedure diagrams of a bearing retainer cover type load detector applied to an embodiment of the present invention, where FIG. 7A is an overall view, and FIG. 7B is a dimension of the bearing retainer cover type load detector. The position of the strain gauge is shown.

8 (A) is a first example of the axial load test result of the bearing retainer cover type load detector tested based on FIG. 7, and (A) shows the axial direction of the load detector and the position of the strain gauge. ,
(B) shows an example of the voltage / output flow direction and strain output of the 4-gauge method, and (C) is a graph showing the relationship between axial force and measured strain.

FIG. 9 (A) in Part 2 of the example of the axial load test of the bearing retainer cover type load detector tested based on FIG. 7 shows the axial direction of the load detector, the stress concentration hole and the circumference. Positions of strain gauges in the radial and radial directions, (B) shows an example of voltage / output flow direction and strain output of the 1 gauge method,
(C) is a graph showing the relationship between the axial force and the measured strain, and shows the strain in the circumferential direction strained portion of the stress concentration hole and the strain in the circumferential direction and the radial direction of the general portion.

FIG. 10 is a temperature load test procedure diagram of a bearing retainer cover type load detector applied to an embodiment of the present invention, in which (A) shows the arrangement position of the strain gauge of the load detector and the accommodation state in the heating furnace; (B) shows an example of voltage / output flow direction and strain output based on the 4-gauge method of the strain gauge housed in the heating furnace.

FIG. 11 shows an example of temperature drift as an example of a temperature load test result of the bearing retainer cover type load detector tested based on FIG.

FIG. 12 is a graph showing an example of axial force load force estimation based on measured strain in the axial force load test diagrams of FIGS. 9 and 10 and the axial force calibration diagram obtained by the temperature load test.

13A and 13B are a side sectional view and a plan view showing a configuration of a bearing retainer cover type load detector when eight strain gauges according to a second embodiment of the present invention are used.

14 is a gauge bridge circuit diagram of the bearing retainer cover type load detector according to the second embodiment of FIG. 13. FIG.

FIG. 15 is a sectional view showing a main structure of a spindle device of a vertical machining center of a machine tool to which the present invention is applied.

FIG. 16 is a flowchart showing the measurement of the main shaft axial force according to the conventional technique, and FIG. 16 (A) shows the axial force urging direction of the bearing retainer cover and the strain and temperature measurement positions. (B) is a flowchart of axial force estimation based on measured values of strain and temperature.

FIG. 17 is an example of strain output when an axial force is applied according to the prior art. (A) shows the axial force biasing direction of the bearing retainer cover and the position of the strain gauge, and (B) shows the voltage of 1 gauge method /
An example of the output flow direction and strain output is shown, and (C) is a graph showing the relationship between axial force and measured strain.

FIG. 18 is an example of strain output at the time of temperature load based on the prior art, (A) shows the axial force urging direction of the bearing retainer cover and the position of the strain gauge, and (B) shows the voltage of 1 gauge method /
An example of the output flow direction and strain output is shown, and (C) is a graph showing the relationship between temperature and total strain.

FIG. 19 is a graph showing an example of estimating the axial load force from the measured strain in the axial load test result and the axial force calibration diagram obtained by the temperature load test of FIGS. 17 and 18 based on the conventional technique.

[Explanation of symbols]

1 spindle 2 Angular bearing 3 Bearing retainer cover 4 Bearing retainer cover type load detector 5 Preload area 41 Convex part 42 stress concentration holes 43 strain gauges (43a-4d)

─────────────────────────────────────────────────── ─── Continued Front Page (51) Int.Cl. ⁷ Identification Code FI Theme Coat (Reference) F16C 19/52 F16C 41/00 41/00 G01L 5/12 G01L 5/12 B23Q 1/08 Z (72) Inventor Ryu Kawabata 4-6-22 Kannon Shinmachi, Nishi-ku, Hiroshima City Mitsubishi Heavy Industries Ltd. Hiroshima Research Institute (72) Inventor Keiji Mizuta 4-22 Kannon Shinmachi, Nishi-ku Hiroshima City Mitsubishi Heavy Industries Ltd. (Reference) 2F051 AA11 AB09 AC04 BA01 3C029 CC01 EE02 3C048 EE02 EE07 3J101 AA01 AA54 AA62 BA77 FA22 FA25 FA26 FA41 GA31

Claims (11)

[Claims] 1. A machine tool comprising a main shaft, a bearing portion for rotatably supporting the main shaft, and a casing accommodating the same, the bearing portion being supported by a plate-shaped bearing pressing cover fixed to the casing side. In the main spindle device, a plurality of stress concentration holes are provided at positions symmetrical to the bearing force receiving surface of the bearing pressing cover on the non-pressure receiving surface side on the bearing axial force acting peripheral line, and the axial load of the bearing portion is provided. A spindle device for a machine tool, wherein strain gauges for detection are arranged in a circumferential direction and a radial direction of the stress concentration hole. 2. The machine tool according to claim 1, wherein the stress concentration holes are multiples (even numbers) of 2, and the strain gauges arranged in the circumferential direction and the radial direction of the stress concentration holes are multiples of 4. A spindle device for machine tools, characterized in that a strain gauge bridge circuit is configured by alternately combining circumferential strain output and radial strain output. 3. The spindle device for a machine tool according to claim 1, wherein a plurality of convex portions are formed on a circumferential line along the casing fixing means on the bearing portion pressure receiving surface side of the bearing retainer cover. 4. The spindle device for a machine tool according to claim 1, wherein at least one temperature sensor is mounted in the vicinity of the strain measuring portion of the stress concentration hole of the bearing pressing cover. 5. A plate-shaped axial load detector for detecting an axial load acting on a bearing portion that rotatably supports a main shaft of a machine tool, wherein a non-pressure receiving surface side opposite to the bearing portion pressure receiving surface is provided. A plurality of stress concentration holes are provided at symmetrical positions in the circumferential direction of the acting portion where the axial load of the bearing portion acts, and strain gauges for detecting the axial load of the bearing portion are provided in the circumferential direction and the radial direction of the stress concentration hole. An axial load detector characterized by being provided. 6. The axial load according to claim 5, wherein the stress concentration holes are multiples (even numbers) of 2, and the strain gauges arranged in the circumferential direction and the radial direction of the stress concentration holes are multiples of 4. In the detector, an axial load detector characterized in that a strain gauge bridge circuit is configured by alternately combining circumferential strain outputs and radial strain outputs of the strain gauges in multiples of four. 7. The load detector is fixed to a casing located on the outer peripheral side of the bearing portion, and a plurality of convex portions are formed on a circumferential line along the casing fixing means on the bearing portion pressure receiving surface side. The axial load detector according to claim 5, which is characterized in that. 8. The axial load detector according to claim 5, wherein a temperature sensor is attached to at least one of the stress concentration holes near a strain measuring portion. 9. An axial force measuring method for estimating an axial load (hereinafter referred to as an axial force) of a bearing portion that rotatably supports a main shaft of a machine tool from a strain measurement value, wherein the axial force of the bearing portion is received. A plurality of stress concentrating portions are provided at symmetrical positions in the circumferential direction on the surface opposite to the pressure receiving surface of the plate-shaped pressure receiving body, and each stress concentrating portion has a multiple of 4 at least two points in the circumferential direction and the radial direction with respect to the main axis. Strain gauge of
A strain gauge of a multiple of is output by adopting the 4-gauge method of the bridge circuit, and in the vicinity of the strain measuring section,
At least one temperature sensor is attached, the temperature of the pressure receiving body is measured at the same time as the strain, and temperature correction is performed on the strain measurement value. 10. The axial force measurement is performed while the pressure receiving body is fixed and supported on the outer peripheral side of the stress concentration portion, and the pressure receiving surface side of the fixed support portion is provided with a convex portion. 1. A method for measuring the axial force of a bearing portion according to 1. 11. An axial load (hereinafter referred to as axial force) generated by rotatably supporting a main shaft with an upper bearing and a lower bearing and applying a preload to a preload area provided between the bearings. In the preload adjusting method for controlling the bearing load of both bearings by adjusting the preload of the preload load area based on the estimated axial force by measuring the axial force by measuring with the strain gauge provided in the cover, A plurality of stress concentrating portions are provided at circumferentially symmetrical positions of the non-pressure receiving surface opposite to the pressure receiving surface of the plate-shaped pressure receiving body that receives the axial force, and each of the stress concentrating portions has a circumferential direction and a radial direction with respect to the spindle. At least two strain gauges each having a multiple of 4 are provided, and the strain gauges having a multiple of 4 are output by adopting the 4-gauge method of the bridge circuit, and at least one strain gauge is provided near the strain measuring unit. Attach a temperature sensor, The temperature of the pressure body is measured at the same time as the strain, and the strain measurement value obtained by correcting the temperature of the strain measurement value is compared with the axial force calibration diagram (axial force-strain relationship diagram) that was acquired in advance. A preload adjusting method characterized by estimating the axial force of a part and adjusting the preload in the preload area based on the estimated value to control the bearing load of both bearings to an appropriate state.