JP2011075346A - Load measuring device for rotary shaft - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small and inexpensive device measuring a load applied on a rotary shaft, such as main shafts of various machine tools, rotating at a high speed while being applied with the load. <P>SOLUTION: Recessed grooves 19, 19 inclined to the axial direction are formed at an outer periphery of an encoder 4a. Sensors 6a, 6b, equipped with individual permanent magnets, a pair of hole elements 22a, 22b, and ICs 23 outputting a digital signals generated by calculating a difference of magnetic flux densities detected by the both hole elements 22a, 22b and comparing two types of thresholds different each other from the signal indicating the difference, are oppositely disposed at two positions separated in the axial direction of the outer periphery of the encoder 4a. Phase of the output signal of the both sensors 6a, 6b is obtained among the digital signals at the portion changing based on edges of the recessed grooves 19, 19 existing at back side of rotary direction of the rotary shaft. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention was invented to realize a device capable of accurately measuring a load applied to a rotating shaft that rotates at high speed while receiving a load, such as a spindle of various machine tools such as a milling machine and a machining center.

  The spindle of the machine tool rotates at a high speed with a tool such as a blade fixed at the tip, and performs processing such as cutting on the workpiece fixed on the processing table. The head that rotatably supports the main shaft moves by a predetermined amount in a predetermined direction as the workpiece is processed, and processes the workpiece into a predetermined size and shape. In such a machining operation, it is necessary to make the moving speed of the head appropriate in order to ensure the durability of the tool and the quality of the workpiece while ensuring the machining efficiency. If the moving speed is too high, an excessive force is applied to the tool, and not only the durability of the tool is remarkably deteriorated, but also the surface property of the workpiece is deteriorated or, in the case of remarkable, the workpiece. Damage such as cracks occurs. On the contrary, when the moving speed is too slow, the processing efficiency of the workpiece is easily deteriorated.

  The appropriate value of the moving speed of the header is not constant, but varies greatly depending on the type (size) of the tool and the material and shape of the work piece. Therefore, the moving speed is kept constant while keeping the moving speed constant. It is difficult to do. For this reason, it is conventionally known to adjust the moving speed to an appropriate value by measuring the load applied to the rotating shaft to which the tool is fixed. That is, when a work such as cutting is performed on a workpiece with a tool, a load is applied to the tool and a rotating shaft to which the tool is fixed due to processing resistance. The machining resistance, and hence the load applied to the rotating shaft, increases as the moving speed increases, and conversely decreases as the moving speed decreases. Therefore, if the moving speed is adjusted so that the load falls within a predetermined range, the moving speed can be kept within an appropriate range.

  In addition, when other conditions such as the moving speed are the same, the load increases as the cutting property (sharpness) of the tool deteriorates. Therefore, by observing the magnitude of the load in relation to the moving speed, it is possible to know that the tool has reached the end of its life, and deterioration in yield due to continuing processing with a defective tool that has reached the end of its life. Can be prevented. In addition, by continuously observing the load in association with other machining conditions such as the moving speed, it is possible to find the optimum machining conditions and lead to energy saving and long tool life. Furthermore, by continuous observation, the cause of an accident such as tool breakage can be identified.

  For such a purpose, the invention apparatus described in Patent Document 1 is described as an apparatus for measuring a load applied to a rotating shaft such as a main shaft of a machine tool. The invention apparatus described in Patent Document 1 is a rotation in which a plurality of quartz piezoelectric load sensors are arranged in series with respect to the direction of load action, and a cutting tool is supported and fixed based on a measurement signal of the load sensor. The load (cutting resistance) applied to the shaft (spindle) is measured. In the case of the inventive device described in Patent Document 1, since an expensive quartz piezoelectric load sensor is used, it is inevitable that the cost of the entire load measuring device increases.

  On the other hand, Patent Documents 2 to 4 describe inventions related to a rolling bearing unit with a load measuring device, which includes a magnetic encoder and a sensor, which can be procured at a lower cost than a quartz piezoelectric load sensor. . FIGS. 17 to 19 show an example of a conventionally known rolling bearing unit with a load measuring device as described in Patent Documents 2 to 4 and the like. This conventionally known rolling bearing unit with a load measuring device is provided with a plurality of rolling hubs 2 on the inner diameter side of an outer ring 1 that does not rotate even when used. It is rotatably supported via the moving bodies 3 and 3. A preload is applied to each of the rolling elements 3 and 3 together with contact angles that are opposite to each other (in the illustrated case, a rear combination type).

  A cylindrical encoder 4 is supported and fixed concentrically with the hub 2 at the inner end portion of the hub 2. A pair of sensors 6 a and 6 b are supported inside a bottomed cylindrical cover 5 that closes the inner end opening of the outer ring 1, and the detection portions of both the sensors 6 a and 6 b are connected to the encoder 4. The outer peripheral surface, which is the detection surface, is placed close to and facing. Of these, the encoder 4 is made of a magnetic metal plate. In the first half (axially inner half) of the outer peripheral surface of the encoder 4, which is a detected surface, through holes 7 and 7 (first characteristic part) and column parts 8 and 8 (second characteristic part) Are arranged alternately and at equal intervals in the circumferential direction. The boundaries between the through holes 7 and 7 and the pillars 8 and 8 are inclined at the same angle with respect to the axial direction of the encoder 4, and the inclined direction with respect to the axial direction is set to the intermediate portion in the axial direction of the encoder 4 The directions are opposite to each other. Accordingly, each of the through holes 7 and 7 and each of the column portions 8 and 8 has a "<" shape with the axially intermediate portion protruding most in the circumferential direction. And among the axially outer half part and the axially inner half part of the detected surface, the inclination directions of the boundaries are different from each other, the axially outer half part is defined as the first characteristic changing part 9, and the axially inner half part is formed. This portion is the second characteristic changing portion 10.

  Each of the pair of sensors 6a and 6b includes a permanent magnet and a magnetic sensing element constituting a detection unit. The two sensors 6a and 6b are supported and fixed inside the cover 5, with the detection part of one sensor 6a serving as the first characteristic changing part 9 and the detection part of the other sensor 6b serving as the second sensor. The characteristic changing portions 10 are respectively close to and opposed to each other. The positions where the detection parts of both the sensors 6 a and 6 b face both the characteristic change parts 9 and 10 are the same position in the circumferential direction of the encoder 4. Further, in the state where an axial load does not act between the outer ring 1 and the hub 2, the portion that protrudes most in the circumferential direction in the axial direction intermediate portion of each of the through holes 7 and 7 and the column portions 8 and 8 (boundary boundary). The position where each member is installed is regulated so that the portion in which the inclination direction changes) is just at the center position between the detection parts of the sensors 6a and 6b.

  In the case of a rolling bearing unit with a state quantity measuring device configured as described above, when an axial load acts between the outer ring 1 and the hub 2 and the outer ring 1 and the hub 2 are relatively displaced in the axial direction, The phase in which the output signals of the sensors 6a and 6b change is shifted. That is, in the neutral state in which an axial load is not applied between the outer ring 1 and the hub 2, the detecting portions of the sensors 6a and 6b are on the solid lines A and B in FIG. It faces a portion that is shifted by the same amount in the axial direction from the most protruding portion. Therefore, the phases of the output signals of the sensors 6a and 6b coincide as shown in FIG.

  On the other hand, when a downward axial load is applied to the hub 2 to which the encoder 4 is fixed as shown in FIG. 19A, the detecting portions of the sensors 6a and 6b are shown in FIG. , Opposite to the portions where the deviations in the axial direction from the most protruding portion are different from each other. In this state, the phases of the output signals of the sensors 6a and 6b are shifted as shown in FIG. Further, when an upward axial load is applied to the hub 2 to which the encoder 4 is fixed as shown in FIG. 19A, the detecting portions of both the sensors 6a and 6b are connected to the chain line hub shown in FIG. The deviation in the axial direction from the uppermost part, that is, the most protruding part, faces different parts in the opposite direction to the above case. In this state, the phases of the output signals of the sensors 6a and 6b are shifted as shown in FIG.

  As described above, in the case of a structure that is conventionally known as described in Patent Documents 2 to 4, the phase of the output signals of both the sensors 6a and 6b is between the outer ring 1 and the hub 2. Is shifted in a direction corresponding to the direction of action of the axial load applied to the outer ring 1 (the direction of relative displacement between the outer ring 1 and the hub 2 in the axial direction). Further, the degree of the phase shift of the output signals of the sensors 6a and 6b due to the axial load (relative displacement) increases as the axial load (relative displacement) increases. Therefore, the direction and magnitude of the relative displacement in the axial direction between the outer ring 1 and the hub 2 based on the presence or absence of the phase shift of the output signals of the sensors 6a and 6b and the direction and magnitude of the deviation, if any. In addition, the acting direction and magnitude of the axial load acting between the outer ring 1 and the hub 2 can be obtained. Note that the processing for calculating the relative displacement and load in the axial direction based on the phase difference between the output signals of the sensors 6a and 6b is performed by a calculator (not shown). For this reason, the relationship between the phase difference, the relative displacement in the axial direction, and the load, which has been examined in advance by theoretical calculation or experiment, is incorporated in this arithmetic unit by a model such as a calculation formula or a map.

  In the case of the above-described conventional structure, it is considered that the axial load applied to the wheel supporting rolling bearing unit for supporting the wheel of the automobile is measured and control for running stability is performed. In such a case, the absolute value of the axial load applied to the wheel supporting rolling bearing unit is considerably increased. In addition, the measurement accuracy required for ensuring running stability is not particularly severe, and an error of about 10 to several tens of N is allowed. On the other hand, the absolute value of the load applied to the rotating shaft such as the main shaft of various machine tools as intended by the present invention is often smaller than the axial load applied to the wheel support rolling bearing unit. In addition, when taking into account high-precision cutting such as precision parts, the measurement accuracy is higher (for example, several N or more severe) than the control for ensuring the running stability. Required.

In this way, when taking into account the measurement of small loads with high accuracy, it is difficult to cope with general measurement techniques as intended by the conventional techniques described in Patent Documents 2 to 4. This point will be described below. In combination with a magnetic encoder, a general Hall IC for measuring displacement (rotation speed, rotation speed or rotation speed if the permanent magnet is an annular encoder) such as rotation (rotation speed) It is well known in the past, as described in Non-Patent Documents 1 and 2. FIG. 20 shows the principle of displacement (displacement amount) measurement by the Hall IC described in Non-Patent Document 2 among them. As shown in the upper part of FIG. 20, in a state where the Hall IC 11 and the permanent magnet 12 in which the S pole and the N pole are alternately arranged are opposed to each other, the Hall IC 11 and the permanent magnet 12 are arranged in an arrangement of these two poles. When the relative displacement is made in the direction, the magnetic field strength of the Hall IC 11 portion (density of the magnetic flux flowing through the Hall IC 11 portion) changes in a sine wave shape as shown in the middle stage. Based on this change, the contact point of the Hall IC 11 is turned ON / OFF by the operating magnetic flux density B _op and the return magnetic flux density B _rp , whereby a digital signal as shown in the lower stage is obtained as an output signal of the Hall IC 11. . From this output signal, the displacement (displacement speed) of the permanent magnet 12 (the member that supports and fixes it) can be obtained. Further, in Non-Patent Document 2, a pair of Hall ICs are arranged so as to be shifted in the displacement direction of the permanent magnet (the movement direction, or the rotation direction when the permanent magnet is an annular encoder), as shown in FIG. A technique is also described in which the displacement direction of the permanent magnet (the member on which the permanent magnet is supported and fixed) is also obtained by a simple mechanism. However, this prior art does not use a pair of Hall ICs to improve measurement accuracy.

  If the load applied to the wheel-supporting rolling bearing unit as shown in FIGS. 17 to 19 is measured, even if the phase in the rotational direction is detected by the mechanism as shown in FIGS. It is considered that sufficient measurement accuracy can be secured in practical use. However, when measurement of the load applied to the rotating shaft such as the main shaft is taken into consideration, when it is necessary to increase the processing accuracy of the workpiece, it may not always be possible to ensure sufficient measurement accuracy. First, as shown in FIG. 20, when an encoder in which N poles and S poles are alternately arranged on the surface to be measured is used as an encoder, it is difficult to regulate the boundaries between these poles with high accuracy. Since it is difficult to exactly correspond to the encoder displacement and the phase difference between the measurement signals of the pair of sensors, it is difficult to ensure the measurement accuracy. On the other hand, the encoder is made of a magnetic metal such as steel, and the magnetic characteristics of the detected surface of the encoder are formed by forming a thinned portion such as a recess, a notch, or a through hole on the detected surface. By changing in the circumferential direction, the position (phase) of the boundary where the magnetic characteristics change can be regulated with high accuracy.

  In addition, it is advantageous from the viewpoint of improving accuracy to use a differential Hall IC conventionally known as described in Patent Document 5, for example, as the pair of sensors. This differential Hall IC is composed of a combination of one permanent magnet and a pair of Hall elements, and outputs a signal corresponding to the difference between the measured values of these Hall elements. Since such a differential Hall IC has a pair of Hall elements arranged close to each other, if for some reason noise based on disturbance enters the outputs of these Hall elements, the outputs of these Hall elements will be the same at the same time. Changes by the same amount in the direction. In such a case, if the difference between the outputs of these Hall elements is taken, the noise is canceled (cancelled) and does not appear in the output of the differential Hall IC as a sensor. For this reason, it is difficult to be affected by noise and can perform highly reliable measurement. Also, by obtaining the difference between the measured values of a pair of Hall elements, the output signal of the sensor is obtained with the DC component (DC component) contained in the signal representing the measured values of both Hall elements being canceled. The gain (change amount per unit time) of the output signal is increased, which is advantageous in ensuring measurement accuracy.

  For the above reasons, in order to realize a highly accurate load measuring device for a rotating shaft as the object of the present invention, a magnetic material with a thinned portion formed on the detection surface is used as an encoder. At the same time, it is conceivable to use a differential Hall IC as a sensor. However, it has been found by the inventor's research that the measurement accuracy cannot always be sufficiently improved if the load measuring device for a rotating shaft is configured in such a combination. The first reason why the measurement accuracy cannot be improved is the non-uniform magnetic flux density due to the structure of the differential Hall IC, and the second is the shape of the thinned portion formed on the detection surface of the encoder. It is an error.

  The first of these is due to the fact that only one permanent magnet is used for flowing magnetic flux through a pair of Hall elements. The differential Hall IC employs a structure in which a magnetic flux is passed through a pair of Hall elements by a single permanent magnet in order to reduce the size. Therefore, at least one (generally both) Hall elements cannot be provided in the central portion of the end face in the magnetization direction of the permanent magnet. As a result, the state in which the magnetic flux density flows through the Hall element becomes non-uniform, and overshoot or undershoot occurs in the output signal of the Hall element, and further in the output signal of the differential Hall IC.

  The second reason is that when forming the thinned portion, a minute convex portion such as a burr is formed at the boundary (edge) of the thinned portion, or a minute concave portion such as sagging is formed. This is because it is easily formed. Due to the presence of such a small convex portion or concave portion, the detection of the boundary of the thinned portion becomes inaccurate, and an overshoot or an output signal is output to the output signals of both Hall elements, and further to the differential Hall IC. Undershoot occurs.

  If any cause causes overshoot or undershoot in the output signal of the differential Hall IC, the differential Hall IC cannot accurately determine the phase in the rotational direction of the detection surface of the encoder. As a result, by using the differential Hall IC as a sensor, it is difficult to ensure the measurement accuracy of the load when measuring the load applied to the rotating shaft. Regarding the first reason, if a permanent magnet is provided for each pair of Hall elements constituting the differential Hall IC, accuracy can be improved, but a small differential type while ensuring the amount of magnetic flux emitted from the permanent magnet. Since it becomes very difficult to realize a Hall IC, it is not realistic. Further, regarding the second reason, it is possible to improve the measurement accuracy by processing the thinned portion with high accuracy, but it is inevitable that the cost will increase significantly.

  In view of the circumstances as described above, the present invention is a compact device capable of accurately measuring a load applied to a rotating shaft that rotates at high speed while receiving a load, such as a spindle of various machine tools such as a machining center, and the like. It was invented to be realized at low cost.

The load measuring device for a rotating shaft according to the present invention includes a housing, a rotating shaft, an encoder, and at least one sensor.
Of these, the housing corresponds to, for example, a casing of a machine tool, and does not rotate during use.
The rotating shaft is rotatably supported inside the housing by a plurality of rolling bearings each provided with a preload.
The encoder is made of a magnetic material such as steel and is supported and fixed to a part of the rotating shaft, and has a detected surface concentric with the rotating shaft.
The sensor is supported by the housing directly or via another member in a state where the respective detection portions are opposed to the detection surface.
And the load which acts on the said rotating shaft is calculated | required based on the information regarding the phase of the output signal of the said sensor.

In particular, in the case of the load measuring device for a rotating shaft according to the present invention, the detected surface of the encoder is partly removed in the circumferential direction, and the distance between the sensor and the detecting part is larger than the remaining part. Are formed in the width direction of the detected surface. And this thinning part has a shape in which at least one part inclined with respect to the acting direction of the load which should be measured.
The sensor includes one permanent magnet, a pair of Hall elements, and an IC.
Among these, the permanent magnet is magnetized in a direction in which the detected surface and the detection unit face each other (a direction orthogonal to the detected surface).
The two Hall elements are arranged on the end face of the permanent magnet in the magnetizing direction opposite to the surface to be detected, separated in the rotation direction of the rotary shaft. In other words, the permanent magnet is provided in a state of being stretched over the two Hall elements.
The IC obtains a difference in magnetic flux density detected by the Hall elements and outputs a digital signal generated by comparing a signal representing this difference with two different threshold values.
Further, in the case of the rotary shaft load measuring device of the present invention, information relating to the phase of the output signal of the sensor is obtained from the digital signal in the rotational direction rear side of the rotary shaft (exit side with respect to the sensor scanning direction). It is calculated | required in the part which changes based on the edge of the said thinning part which exists in.

When implementing the load measuring apparatus for rotating shafts of the present invention as described above, a pair of sensors are provided as in the invention described in claim 2, for example. And the information regarding the said phase used in order to obtain | require a load is made into the phase difference which exists between the output signals of these both sensors.
When implementing such a load measuring device for a rotating shaft according to claim 2, for example, as in the invention according to claim 3, the encoder is formed in a cylindrical shape by a magnetic material such as a steel material and the rotation is performed. Fit on the shaft. The detected surface is the outer peripheral surface of the encoder.
Moreover, let the said thinning part be a ditch | groove formed in this outer peripheral surface. The concave groove is formed in a “<” shape with the axially opposite side portions inclined opposite to each other with respect to the axial direction of the encoder, with the axially intermediate portion of the encoder as a boundary.
Then, the detection part of one of the two sensors is opposed to the concave groove at a portion closer to one side of the encoder in the axial direction, and the detection part of the other sensor is also set to the concave groove, and the axial direction of the encoder. Make them face each other.

Or when implementing the load measuring apparatus for rotating shafts of this invention as mentioned above, a single sensor is provided like the invention described in Claim 4, for example. In this sensor, the output signal changes in the middle of one cycle based on the property of the detection surface of the encoder. Furthermore, it is assumed that the timing of changing during this one cycle (time from the beginning of one cycle to the moment of changing in the middle) shifts with the relative displacement between the sensor and the encoder. And the information regarding the phase used in order to obtain | require a load is made into the timing ratio which is the ratio of the said timing with respect to 1 period of the output signal of the said sensor.
When implementing the load measuring device for a rotating shaft as described in claim 4, for example, as in the invention described in claim 5, the encoder is formed in a cylindrical shape by a magnetic material and is attached to the rotating shaft. Fit and fix. The detected surface is the outer peripheral surface of the encoder.
Moreover, let the said thinning part be the some recessed groove formed in this outer peripheral surface. Each of these concave grooves has a pair of concave grooves whose inclination directions with respect to the axial direction of the encoder are different from each other and are paired adjacent to each other in the rotation direction of the encoder. To face.

According to the present invention configured as described above, there is provided a rotary shaft load measuring device that can accurately measure a load applied to a rotary shaft that rotates at high speed while receiving a load, such as a spindle of various machine tools such as a machining center. It can be realized at a cost.
That is, according to the present invention, a differential Hall IC that can be configured in a small size by incorporating a single permanent magnet is used, and the boundary of a portion where the magnetic characteristics change as an encoder can be accurately regulated at low cost. In addition, the structure using a thinned portion of a magnetic material can prevent measurement accuracy from deteriorating due to overshoot or undershoot existing in the output signal.
For this reason, not only can it be configured in a small size, but it is possible to accurately measure even a large load as well as a small load, even without using parts that are particularly expensive.

Sectional drawing which shows the 1st example of embodiment of this invention. The X section enlarged view of FIG. The perspective view which takes out and shows an encoder. The perspective view which takes out a sensor unit and shows with the state (A) which is not covering the sensor mounting part of the front-end | tip, and the state (B) which covered. The schematic diagram which shows the arrangement | sequence state of a pair of sensor. The schematic diagram which shows the relationship between the sensor and encoder in driving | operation. The diagram which shows the output signal generation process of the sensor at the time of a driving | operation. The schematic diagram for demonstrating the principle which a phase difference produces between the output signals of a pair of sensors based on the load added to a rotating shaft. Based on the offset of the permanent magnet with respect to a pair of Hall elements and the minute convexities and concaves present on the edge of the concave groove, the state in which the measured values of the magnetic flux density detected by these Hall elements are disturbed Diagram. The diagram which shows the result of the experiment conducted in order to confirm the effect of calculating | requiring a displacement with the rotation direction rear-end edge of a ditch | groove. The figure similar to FIG. 5 which shows the 2nd example of embodiment of this invention. The same figure as FIG. The perspective view of an encoder which shows the 3rd example of embodiment of this invention. Similarly, a schematic diagram of a sensor. The schematic diagram for demonstrating the principle from which the timing ratio of the output signal of a sensor changes based on the load added to a rotating shaft. The diagram which shows the result of the experiment conducted in order to confirm the effect of calculating | requiring a displacement with the rotation direction rear-end edge of a ditch | groove. Sectional drawing which shows one example of the conventional structure considered in order to measure the axial load added to the rolling bearing unit for wheel support. The figure which looked at a part of the to-be-detected surface of an encoder from radial direction. The schematic diagram for demonstrating the condition where a phase difference arises between the output signals of a pair of sensors by the displacement of the encoder based on an axial load. The schematic diagram for demonstrating the condition which produces | generates the output signal of Hall IC. The schematic diagram for demonstrating the condition which calculates | requires a rotation direction using a pair of Hall IC.

[First example of embodiment]
The structure of the first example of the embodiment corresponding to claims 1 to 3 and the reason why the displacement amount of the rotating shaft can be accurately obtained by the structure will be described with reference to FIGS.
This example shows a case where the rotary shaft load measuring device of the present invention is configured to measure the axial load applied to the main shaft 13 of the machine tool. The spindle 13 is rotatably supported by a multi-row rolling bearing unit 15 on the inner diameter side of a housing (spindle head) 14 of a machine tool, and the spindle 13 is rotatably driven by an electric motor 17. Of the plurality of rolling bearings 16a to 16d constituting the multi-row rolling bearing unit 15, the two rolling bearings 16a and 16b arranged near the distal end and the two rolling bearings 16c arranged near the proximal end. , 16d are given contact angles opposite to each other, and a preload is given to these bearings 16a to 16d. Therefore, the main shaft 13 is supported rotatably with respect to the housing 14 in a state in which a radial load and a thrust load in both directions are supported. During operation of the machine tool, a tool (not shown) fixed to the tip end portion (left end portion in FIG. 1) of the main spindle 13 is pressed against the workpiece while rotating at high speed, and the workpiece is subjected to cutting or the like. Apply processing. When machining is performed in this manner, a load in each direction is applied to the main shaft 13 as a reaction of pressing the tool against the workpiece. In the case of this example, among these, the axial load corresponding to the axial direction of the main shaft 13 is obtained.

  Therefore, in the case of this example, an encoder 4a as shown in FIG. 3 is provided between the rolling bearings 16b and 16c constituting the multi-row rolling bearing unit 15 at a portion near the tip of the intermediate portion of the main shaft 13. The sensor unit 18 is supported and fixed to the housing 14 while being externally fixed. Of these, the encoder 4a is entirely made of a magnetic metal such as steel and has a cylindrical shape. The detection portion of the sensor unit 18 is opposed to the outer peripheral surface of the encoder 4a, which is a detection surface, in the radial direction. ing. And it is comprised so that the axial load which acts on the said spindle 13 may be calculated | required based on the information regarding the phase contained in the output signal of this sensor unit 18. FIG.

  For this reason, in the case of this example, the radial shape of the part of the outer peripheral surface of the encoder 4a (for example, 4 to 5 positions at equal intervals in the circumferential direction) Each of the grooves 19 and 19 is a thinned portion described in the claims. Each of these concave grooves 19, 19 is provided in the width direction of the outer peripheral surface of the encoder 4a (the axial direction of the encoder 4a) as a whole, but each portion is inclined with respect to the width direction. Further, the inclination direction is opposite to each other in the width direction half and the other half (however, the absolute value of the inclination angle is equal between the two halves). In such a portion where the concave grooves 19, 19 are formed, the distance from the detection portion of the sensor unit 18 is larger than the remaining portion, and the magnetic force between the detection portion of the sensor unit 18 and the encoder 4a is increased. Resistance increases. In the case of this example, the width dimension of each of the concave grooves 19, 19 is suppressed to be as small as the outer diameter of a processing tool such as an end mill, and the concave grooves 19, 19 can be easily (1 It can be formed only by moving it once.

  The reason why the number of the concave grooves 19, 19 formed on the outer peripheral surface of the encoder 4a is significantly smaller than the number of the through holes 7, 7 in the structure shown in FIGS. This is to secure time for calculating the axial load. That is, the rotational speed of the main shaft 13 is significantly faster than the rotational speed of the wheels. Therefore, in the case of this example, by suppressing the number of the concave grooves 19 and 19 to be small, it is not necessary to use an expensive calculator with a particularly high processing speed as a calculator for calculating the axial load. This axial load is required. In consideration of only calculating the axial load applied to the main spindle 13 of the machine tool at time intervals that do not cause any practical problems, it is sufficient to provide the concave grooves 19 only at one place in the circumferential direction. However, in the case where the whirling motion, the shape error, etc. of the encoder 4a are removed by the filtering process, the range of the processing of the computing unit is in time when considering the removal of not only the rotation primary component but also the rotation n-order component. Therefore, it is preferable to increase the number of the concave grooves 19 and 19 (n). Furthermore, in the case of this example, the encoder 4a has a function as an inner ring spacer. In other words, the concave grooves 19 and 19 are formed on the outer peripheral surface of the inner ring spacer, thereby providing a function as the encoder 4a.

On the other hand, the sensor unit 18 is formed by supporting and fixing a pair of sensors 6a and 6b to the front end of a holder 20 made of synthetic resin.
Each of these sensors 6a and 6b includes a permanent magnet 21, a pair of hall elements 22a and 22b, and an IC 23, as shown in FIGS.
Of these, the permanent magnet 21 is magnetized in the radial direction of the encoder 4a, which is the direction in which the outer peripheral surface of the encoder 4a and the detection unit of the sensor unit 18 face each other. In the case of this example, as shown in FIG. 5, the magnetization directions of the permanent magnets 21 and 21 incorporated in both the sensors 6a and 6b are the same (the N pole on the inner side and the S pole on the outer side in the radial direction of the encoder 4a). Pole).

  The hall elements 22a and 22b are arranged in the direction of rotation of the main shaft 13 on the end face on the N-pole side facing the outer peripheral surface of the encoder 4a among the both end faces in the magnetization direction of the permanent magnet 21 (see FIG. 5, 6, 8 in the left-right direction). The diameter of the permanent magnet 21 is sufficiently large so that the hall elements 22a and 22b can be disposed on the end face of the permanent magnet 21. And this permanent magnet 21 is provided in the state hung over both said Hall elements 22a and 22b. Therefore, both of these Hall elements 22a and 22b are arranged in a portion deviated from the center of the end surface of the permanent magnet 21 in the magnetization direction. The Hall elements 22a and 22b have the same characteristics (use the same type).

The IC 23 obtains a difference in magnetic flux density detected by the Hall elements 22a and 22b (actually, a voltage signal that changes in accordance with the difference in magnetic flux density), and further differs from a signal representing this difference. A digital signal generated by comparing two kinds of threshold values (operation magnetic flux density B _op and return magnetic flux density B _rp , threshold level) is output as an output signal of the sensor 6a (6b). This point will be described with reference to FIGS.

  As shown in FIG. 6, when a concave groove 19 formed on the outer peripheral surface of the encoder 4a passes in the vicinity of a pair of Hall elements 22a and 22b that are spaced apart in the rotational direction of the encoder 4a, both the holes The density of the magnetic flux passing through the elements 22a and 22b is temporarily reduced, and the characteristics of both Hall elements 22a and 22b change accordingly. In addition, since both the Hall elements 22a and 22b are arranged with a predetermined distance apart in the rotation direction of the encoder 4a, the phase in which the characteristics of the Hall elements 22a and 22b change is equal to the predetermined distance. It shifts by the amount that matches. That is, the magnetic flux density of the Hall element 22a portion arranged on the front side with respect to the rotation direction of the encoder 4a changes as shown by the solid line a in the upper stage of FIG. 7, whereas the Hall element 22b portion arranged on the rear side changes. The magnetic flux density changes prior to the magnetic flux density of the front Hall element 22a, as shown by the broken line b.

The IC 23 is inputted with a pair of signals indicated by a solid line a and a broken line b in the upper part of FIG. 7, each of which changes according to the density of magnetic flux passing through both the Hall elements 22a and 22b. First, a difference between these two signals is obtained to obtain a voltage signal indicated by a one-dot chain line c in the middle stage of FIG. Further, the IC 23 compares this voltage signal with a pair of threshold values indicated by two-dot chain lines d and e in the middle stage of FIG. 7 to obtain a digital signal shown in the lower stage of FIG. That is, by turning ON / OFF the contact of the IC 23 with the operating magnetic flux density B _op and the return magnetic flux density B _rp based on the voltage signal that changes like the one-dot chain line c, a digital signal as shown in the lower stage is obtained. And output as an output signal of the IC 23.

  As described above, the generation of the digital signal based on the characteristic change of the pair of Hall elements 22a and 22b is performed for each of the pair of sensors 6a and 6b. A pair of digital signals that change as shown in the lower part of FIG. 7 are output to an arithmetic unit (not shown) for obtaining an axial load applied to the main shaft 13. This arithmetic unit uses both the digital signals in the same manner as in the case of the conventional structure described with reference to FIGS. 17 to 19, and these digital signals are shown in FIGS. 19 (B) to (D). By using instead of a pair of digital signals}, the axial load is obtained.

  In particular, in the case of this example, in order to obtain this axial load, the phase difference existing between the output signals of the two sensors 6a and 6b is converted into the output signals of the two sensors as the grooves 19 and 19 pass. Among the portions where the change occurs (rising and falling), the portion that changes corresponding to the exit side in the scanning direction of the sensors 6a and 6b is obtained. This point will be described with reference to FIG.

  When an axial load is applied to the main shaft 13 through a tool fixed to the tip end portion of the main shaft 13, as shown in FIG. 8A, of the concave grooves 19, 19 formed on the outer peripheral surface of the encoder 4a Therefore, the phase in the circumferential direction of the portion scanned by one sensor 6a is shifted from the phase of the portion scanned by the other sensor 6b. Then, the phases of the output signals of both the sensors 6a and 6b obtained as shown in FIG. 7 are shifted as shown in FIG. 8B. In the case of this example, the characteristics of the output signals of both the sensors 6a and 6b are different from each other for reasons of installation of the sensors 6a and 6b at the tip of the holder 20, as will be described later. It is reversed. That is, the output signal of the one sensor 6a falls at a portion where the detection portion enters the concave groove 19, and rises at a portion where the detection portion similarly exits the concave groove 19. On the other hand, the output signal of the other sensor 6b rises when the detection part enters the concave groove 19 and also falls when the detection part exits the concave groove 19.

  In the case of this example, in order to obtain the axial load, the phase difference δ existing between the output signals of the two sensors 6a and 6b is set to the rising portion of the output signal of the one sensor 6a and the other signal. It is obtained as a time difference from the falling part of the output signal of the sensor 6b. Then, the axial load is calculated based on the phase difference δ obtained in this way. Specifically, an empirical formula obtained in advance based on a phase difference ratio (= phase difference δ / cycle L) which is a ratio between the phase difference δ and the cycle L of the output signals of the sensors 6a and 6b. From the above, the axial load is calculated.

  In the case of this example, in order to reduce the size of the sensor unit 18 (the diameter of the tip portion), the installation positions of the sensors 6a and 6b are set to the rotation of the encoder 4a as shown in FIG. It is shifted in the direction. The terminals 24 and 24 of the ICs 23 and 23 constituting the sensors 6a and 6b are arranged on the sides facing each other. More specifically, the terminals 24 and 24 of one IC 23 and the main body of the other IC 23 are overlapped with respect to the rotation direction of the encoder 4a. The amount by which the sensors 6a and 6b are displaced in the rotational direction is determined by design (as long as the processing of the output signals of the sensors 6a and 6b is not troublesome). Therefore, when the difference existing between the output signals of both the sensors 6a and 6b, which will be described later, is obtained, the shift amount in the rotational direction is calculated from the difference actually existing between these two output signals. Decrease the corresponding amount. 4A shows a state where both the sensors 6a and 6b are assembled to the front end surface of the holder 20, and FIG. 4B shows a state where the sensor 20 is covered with the synthetic resin constituting the holder 20. , Respectively. In the completed state of the sensor unit 18, both the sensors 6a and 6b are prevented from being contaminated with lubricating oil or the like as in (B).

  In the case of this example, the magnetizing directions of the permanent magnets 21 and 21 incorporated in both the sensors 6a and 6b are the same, and the installation directions of the ICs 23 and 23 are also different by 180 degrees for the reasons described above. Yes. For this reason, in a state where the detection parts of both the sensors 6a and 6b are opposed to the same kind of part of the outer peripheral surface of the encoder 4a (the edge part of any one of the concave grooves 19 and 19), The direction of change of the output signal of 6b is opposite to each other (when one rises, the other falls). Therefore, in the case of the present example, as described above, the phase difference existing between the output signals of the two sensors 6a and 6b is determined by using the rising portion of the output signal of the one sensor 6a and the other sensor. The time difference from the falling portion of the output signal 6b is obtained.

According to the present invention configured as described above, a rotary shaft load measuring device that rotates at high speed while receiving a load and can accurately measure the load applied to the main shaft 13 can be realized at low cost. The reason for this will be described with reference to FIGS.
In the case of this example, the point for obtaining the phase difference is the point where the output signals of the sensors 6a and 6b change with the passage of the concave grooves 19 and 19, of both the sensors 6a and 6b. A portion that changes in correspondence with the exit side in the scanning direction, that is, an intersection α of the voltage signal indicated by the alternate long and short dash line c and the threshold indicated by the alternate long and two short dashes line d shown in the middle stage of FIG. As a starting point for obtaining the phase difference, there is an intersection point β between the voltage signal indicated by the solid line c and the threshold value indicated by the chain line e in addition to the intersection point α. As indicated by the solid line a and the broken line b in the upper part of FIG. 7, the density of the magnetic flux detected by the Hall elements 22 a and 22 b corresponds to the unevenness of the concave groove 19 as the concave groove 19 passes. If the voltage signal indicated by the alternate long and short dash line c in the middle of FIG. 7 is obtained as a difference between the detection values of the Hall elements 22a and 22b, the load measurement is performed. As a point used for obtaining the phase difference, either of the intersections α and β may be used.

  However, the position of the intersection β corresponding to the entrance side of the groove 19 out of the intersections α and β is the burr or sag present at the opening edge of the groove 19 or the center of the permanent magnet 21. And the non-uniformity of the magnetic flux distribution in each of the Hall elements 22a and 22b based on the deviation from the center of the Hall elements 22a and 22b. This point will be described by taking the case of the sensor 6a shown in the upper part of FIGS. 8A and 8B as an example. In the case of the sensor 6b, the change direction of the digital signal accompanying the passage of the concave groove 19 is reversed, and basically the same. The density of the magnetic flux detected by each of the Hall elements 22a and 22b due to the above-described causes is as shown in the upper solid line a 'and broken line b' in FIG. In addition to changing in accordance with the unevenness of the portion, so-called overshoot or undershoot that changes excessively at the inlet and outlet portions of the groove 19 may occur. The causes of these overshoots and undershoots are the burrs, sagging, uneven magnetic flux distribution, and the like. In addition, overshoot and undershoot may occur in the voltage signal obtained as the difference between the Hall elements 22a and 22b as shown by the one-dot chain line c 'in the lower stage of FIG. In addition, such overshoot and undershoot often appear irregularly.

  The voltage signal and the two-dot chain line d representing the difference between the overshoot or undershoot generation site indicated by the one-dot chain line c 'in the lower part of FIG. 9 and the magnetic flux density indicated by the one-dot chain line c in the middle part of FIG. As is clear from the comparison of the positions of the intersections α and β with the thresholds indicated by e, the intersection β corresponding to the entrance portion of the concave groove 19 is close to the overshoot or undershoot occurrence site. . For this reason, the position of the intersection β may be shifted irregularly, though slightly, under the influence of these overshoots or undershoots. On the other hand, the intersection α corresponding to the exit portion of the concave groove 19 is far from the location where the overshoot or undershoot occurs, and is not easily affected by the overshoot or undershoot. In other words, the intersection α corresponding to the exit portion of the concave groove 19 indicates that the density of the magnetic flux detected by the Hall elements 22a and 22b shown by the solid line a ′ and the broken line b ′ in the upper stage of FIG. It is obtained corresponding to a portion that changes stably without being affected by overshoot or undershoot.

  In short, among the digital signals shown in the lower part of FIG. 7 and the upper part of FIG. 8B, the position of the falling part obtained corresponding to the entrance part of the concave groove 19 is the overshoot or undershoot. Although easily affected, the position of the rising portion required corresponding to the exit portion of the concave groove 19 is not easily affected by the overshoot or undershoot. Therefore, the phase in the rotation direction of the encoder 4a can be obtained with high accuracy without being affected by the presence or absence of overshoot or undershoot, and the axial load applied to the spindle 13 can be accurately determined. Often required. In the case of this example, as shown in FIG. 8 (B), both of these between the rising part of the output signal (digital signal) of the sensor 6a and the falling part of the output signal of the sensor 6b. A phase difference δ between the output signals of the sensors 6a and 6b is obtained. Then, based on the ratio (δ / L) between the phase difference δ and the period L of the output signals of both the sensors 6a and 6b, the amount of axial displacement of the main shaft 13 is added to the main shaft 13. Find the axial load. For this reason, the measurement accuracy of this axial load can be improved.

  Next, an experiment conducted by the present inventor in order to confirm the effect of this example will be described. In this experiment, the axial load applied to the main shaft 13 was increased stepwise, and the main shaft 13 was moved in the axial direction little by little (about 0.01 mm) (displaced in the axial direction). Then, the axial displacement amount of the main shaft 13 was measured. Among the digital signals shown in the lower part of FIG. 7 that are used to measure the amount of displacement, the rising part corresponding to the outlet part is the same as the case where the falling part corresponding to the inlet part of the concave groove 19 is used. The effect on the measured value was observed when the sensor is used (in the case of the sensor 6a, in the case of the sensor 6b, the rise and fall are reversed). The result is shown in FIG. The solid line in FIG. 10 indicates the case where the axial displacement amount is obtained using the rising part or the falling part corresponding to the outlet part. Similarly, the broken line indicates the falling part or the rising part corresponding to the inlet part. The case where the amount of axial displacement was calculated using the part is shown. As is apparent from the description of FIG. 10, the axial displacement amount can be obtained with high accuracy by using the portion where the signal voltage changes corresponding to the exit portion of the concave groove 19. The axial load applied to the main shaft 13 is determined based on the axial displacement amount in consideration of the axial rigidity of the multi-row rolling bearing unit 15, so that the axial load amount can be determined by accurately determining the axial displacement amount. Measurement accuracy can be improved.

[Second Example of Embodiment]
FIGS. 11-12 shows the 2nd example of embodiment of this invention corresponding to Claims 1-3. In the case of this example, one sensor 6a having the same configuration as that of the first example of the embodiment described above is used. On the other hand, as the other sensor 6c, the one in which the magnetization direction of the permanent magnet 21a is opposite to that of the one sensor 6a is used. These two sensors 6a and 6c are combined in a state where the terminals 24 and 24 are opposed to each other and shifted by a predetermined distance in the circumferential direction, as in the case of the first example of the embodiment. . In the case of this example, by reversing the magnetization directions of the permanent magnets 21 and 21a incorporated in the sensors 6a and 6c in this way, regardless of the difference in the assembling direction of the sensors 6a and 6c. In the state where the detection parts of both the sensors 6a and 6c face the same kind of the outer peripheral surface of the encoder 4a, the direction of change of the output signals of both the sensors 6a and 6c is made the same.

  In the case of this example, the phase difference between the output signals of both the sensors 6a and 6c is accurately determined by making the direction of change of the output signals of the pair of sensors 6a and 6c the same. It is often requested. That is, the digital signals that are the output signals of the sensors 6a, 6b, and 6c are rectangular waves, but do not change completely at a right angle. Specifically, the deviation from the right angle of the angle formed by the rising portion with respect to the time lapse axis is larger than that when the falling portion is nearly perpendicular to the time lapse axis. Therefore, as in the first example of the above-described embodiment, if the phase difference between both output signals is calculated between the rising portion of one output signal and the falling portion of the other output signal, the accuracy is not necessarily obtained. There is a possibility that a good value cannot be obtained. On the other hand, in the case of this example, since the phase difference between a pair of output signals to be compared is obtained between portions where both signals change in the same direction, this phase difference can be obtained with high accuracy. . Since the configuration and operation of other parts are the same as those of the first example of the above-described embodiment, illustration and description regarding the equivalent parts are omitted.

[Third example of embodiment]
FIGS. 13 to 16 show a third example of the embodiment of the invention corresponding to claims 1, 4 and 5. This example shows a case where the present invention is applied to the structure described in FIG. Both the first example of the embodiment described above and the second example of the embodiment described above are provided with a pair of sensors, and the axial direction of the main shaft 13 based on the phase difference between the output signals of these two sensors. It was configured to obtain the amount of displacement. On the other hand, in the case of this example, information on the phase used for obtaining the load is obtained from the timing ratio of the output signal of the single sensor 6d. For this reason, the sensor 6d is assumed that the output signal changes in the middle of one cycle based on the property of the detected surface of the encoder 4b. Further, it is assumed that the timing (the time from the beginning of one cycle to the moment when it changes midway) is shifted with the relative displacement between the sensor 6d and the encoder 4b.

  The encoder 4b used in this example also serves as an inner ring spacer, is made of a magnetic material in a cylindrical shape, and is externally fitted and fixed to an intermediate portion of the main shaft 13 (see FIGS. 1 and 2). A plurality of linear concave grooves 19a and 19b, each of which is a thinned portion, are formed on the outer peripheral surface of the encoder 4b, which is the detection surface. Each of the concave grooves 19a and 19b is a pair of concave grooves 19a and 19b having different inclination directions with respect to the axial direction of the encoder 4b and adjacent to each other in the rotational direction of the encoder 4b. A plurality of sets (for example, 4 to 5 sets) are provided at equal intervals. And the detection part of the said single sensor 6d is made to oppose the part which provided each said ditch | groove 19a, 19b in the outer peripheral surface of the said encoder 4b.

  In the case of this example, when the encoder 4b is displaced in the axial direction together with the main shaft 13, the phase at which the output signal changes as the detection portion of the sensor 6d passes through the pair of concave grooves 19a and 19b. The magnitude (timing) of the deviation changes. Therefore, from the ratio (δ / L, timing ratio) of the magnitude δ of the deviation to the period L in which the output signal changes due to the sets adjacent in the circumferential direction, the axial displacement amount of the main shaft 13, An axial load applied to the main shaft 13 is obtained.

  In the case of this example as well, if the magnitude δ and the period L of the deviation are obtained at the portion of the output signal of the sensor 6d that changes corresponding to the exit portions of the concave grooves 19a and 19b, The magnitude δ and the period L of these deviations can be obtained with high accuracy. The axial displacement of the main shaft 13 and the axial load applied to the main shaft 13 can be obtained with high accuracy. FIG. 16 shows the axial displacement of the main shaft 13 using the portion where the output signal of the sensor 6d changes corresponding to the exit portions of the concave grooves 19a and 19b in the case of the structure of this example. The result of the experiment conducted to confirm the effect of the thing is shown. The meanings of the solid line and the broken line in FIG. 16 are the same as those in FIG. FIG. 16 shows that the axial load is calculated based on the timing ratio, and the axial displacement amount is obtained by using the portion where the signal voltage changes corresponding to the exit portions of the concave grooves 19a and 19b. It can be seen that it is required with high accuracy.

  The above description has been made when the present invention is applied to a structure for measuring an axial load. However, the present invention is not limited to an axial load, but can be applied to a structure for measuring a radial load. When measuring the radial load, for example, as shown in FIGS. 6 to 9 of Patent Document 2 described above, the side surface in the axial direction of the annular encoder is used as a detection surface, and a thinned portion is formed on this detection surface. At the same time, the detection unit of the sensor is opposed to the detection surface in the axial direction. Furthermore, the present invention can be implemented with a structure in which an encoder provided with a trapezoidal thinning portion and one sensor are combined as shown in FIGS.

DESCRIPTION OF SYMBOLS 1 Outer ring 2 Hub 3 Rolling element 4, 4a, 4b Encoder 5 Cover 6a, 6b, 6c, 6d Sensor 7 Through-hole 8 Pillar part 9 First characteristic change part 10 Second characteristic change part 11 Hall IC
DESCRIPTION OF SYMBOLS 12 Permanent magnet 13 Main shaft 14 Housing 15 Multi-row rolling bearing unit 16a-16d Rolling bearing 17 Electric motor 18 Sensor unit 19, 19a, 19b Groove 20 Holder 21, 21a Permanent magnet 22a, 22b Hall element 23 IC
24 terminals

JP 2002-187048 A JP 2006-317420 A JP 2008-39155 A JP 2008-64731 A JP-A-8-220200

Asahi Kasei Corporation website, “Hall IC operating principle: Hall IC: Product introduction: Asahi Kasei magnetic sensor”, [online], [August 13, 2009 search], Internet <URL: http: // www. asahi-kasei.co.jp/ake/jp/product/ic/outline.html> ROHM Co., Ltd. homepage, “Alternating magnetic field detection Hall IC”, [online], [Search August 13, 2009], Internet <URL: http://www.rohm.co.jp/products/databook/sensor /pdf/bu52040hfv-j.pdf>

Claims (5)

A non-rotating housing and a plurality of rolling bearings each provided with preload, a rotating shaft that is rotatably supported inside the housing, and a magnetic material that is supported and fixed to a part of the rotating shaft. An encoder having a detection surface concentric with the rotating shaft, and at least one sensor supported on the housing directly or via another member in a state where the detection portions are opposed to the detection surface. A rotation axis load measuring device for obtaining a load acting on the rotation axis based on information on the phase of the output signal of the sensor,
The detected surface of the encoder is formed by forming a thinned portion in the width direction of the detected surface at a part in the circumferential direction, the distance from the detecting portion of the sensor being larger than the remaining portion. The thinned portion has at least a portion that is inclined with respect to the acting direction of the load to be measured,
The sensor has one permanent magnet that is magnetized in a direction in which the detected surface and the detection unit face each other, and an end surface that faces the detected surface among both end surfaces of the permanent magnet in the magnetization direction. , A pair of Hall elements arranged apart from each other in the rotation direction of the rotating shaft, a difference in magnetic flux density detected by both Hall elements, and two different thresholds different from a signal representing this difference. And an IC that outputs a digital signal generated by comparison,
Rotating shaft characterized in that information on phase of output signal of said sensor is obtained in a portion of said digital signal that changes based on an edge of said thinning portion existing on the rear side of said rotating shaft in the rotation direction. Load measuring device.   The rotary shaft load measuring device according to claim 1, comprising a pair of sensors, wherein the information regarding the phase used for obtaining the load is a phase difference existing between the output signals of both sensors.   The encoder is made of a magnetic material in a cylindrical shape, and is fitted and fixed to the rotary shaft. The detected surface is the outer peripheral surface of the encoder, and the thinned portion is a concave formed on the outer peripheral surface. The groove is a "<" shape with both sides in the axial direction inclined opposite to each other with respect to the axial direction of the encoder, with a middle portion in the axial direction of the encoder as a boundary. The detection portion of one of the sensors faces the concave groove at a portion closer to one axial direction of the encoder, and the detection portion of the other sensor similarly faces the concave groove at a portion closer to the other axial direction of the encoder. The load measuring device for a rotating shaft according to claim 2, which is opposed to the rotating shaft.   A single sensor is provided, and this sensor has an output signal that changes in the middle of one cycle based on the property of the detected surface of the encoder, and with the relative displacement between the sensor and the encoder, The rotation according to claim 1, wherein the timing that changes during the one cycle is shifted, and the information related to the phase used for obtaining the load is a ratio of the timing to one cycle of the output signal of the sensor. Shaft load measuring device.   The encoder is made of a magnetic material in a cylindrical shape and is externally fixed to the rotary shaft. The detected surface is the outer peripheral surface of the encoder, and a plurality of thinning portions are formed on the outer peripheral surface. Each of these concave grooves is a pair of concave grooves whose inclination directions with respect to the axial direction of the encoder are different from each other, adjacent to each other in the rotational direction of the encoder. The load measuring device for a rotating shaft according to claim 4, wherein the detection unit faces each of the concave grooves.

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