JP2011141240A - Apparatus for measuring physical quantity for rotating shaft - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an apparatus capable of highly accurately measuring a physical quantity such as a load applied on a rotating shaft rotated at a high speed while receiving loads like main shafts of various machine tools or a displacement amount of the rotating shaft at a low cost while securing sufficient reliability. <P>SOLUTION: The apparatus for measuring the physical quantity for the rotating shaft forms a plurality of detected characteristic change combination parts 17, 17 comprising a pair by a pair of recess grooves 18a, 18b different in inclination directions from each as shown in (A) on a detected face of an encoder 4a circumferentially at a regular interval. Output signals of sensors facing the detected face are changed as shown in (B) and (C). A computing unit obtains the physical quantity concerning the main shaft or the like on the basis of a timing ratio which is a ratio of a cycle in which the output signal is changed once to a cycle in which the output signal is changed twice. The size of the timing ratio regulates a dimension of each part so that it is always reversed between the adjacent timing ratios regardless of the displacement of the encoder 4a. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  This invention is an apparatus capable of accurately measuring a physical quantity such as a load applied to a rotating shaft rotating at high speed while receiving a load, or a displacement amount of the rotating shaft, such as a main shaft of various machine tools such as a milling machine and a machining center. It was invented to be realized at low cost.

  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. In the invention apparatus described in Patent Document 1, a plurality of quartz piezoelectric load sensors are arranged in series with respect to the direction of the load, and the cutting tool is supported and fixed based on the measurement signal of the load sensor. The load (cutting resistance) applied to the rotating 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. . 10 to 12 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 opposed to the detection surface. Of these, the encoder 4 is made of a magnetic metal plate. In the front half of the outer peripheral surface of the encoder 4 (the inner half in the axial direction), which is the detection surface, the through holes 7 and 7 and the column portions 8 and 8 are alternately arranged at equal intervals in the circumferential direction. It is arranged. 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 the rolling bearing unit with a load 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 two sensors The phase at which the output signals 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 detection 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 in FIG. 12A, 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. 12A, the detecting portions of both the sensors 6a and 6b are connected to the chain line H 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.

  If the structure of the rolling bearing unit with a load measuring device like the conventional structure shown in FIGS. 10 to 12 described above is incorporated between a rotating shaft such as a spindle of a machine tool and a non-rotating portion such as a housing, a cutting tool By measuring the load applied to the rotating shaft that supports and fixes the tool, the optimum machining conditions can be found, leading to energy saving and longer tool life, and the cause of tool breakage can be identified. However, in the case of the conventional structure, a plurality of sensors 6a and 6b are required, which is disadvantageous in terms of cost and size. As disclosed in Japanese Patent Application Nos. 2009-37075, 2009-37076, and 2009-225792, it is possible to assemble a pair of sensor elements in one holder, but this is not sufficient in terms of cost reduction. In addition to this, the diameter of the sensor unit is increased, which is insufficient in terms of miniaturization.

  In view of such circumstances, as described in FIGS. 8 to 10 and 15 of Patent Document 2 and the explanation part of each figure in the specification, a plurality of characteristics to be detected are detected on the detection surface of the encoder. It is conceivable that the change combination portions are formed at equal intervals in the circumferential direction in the width direction of the surface to be detected, which coincides with the direction of the load to be measured. This point will be described with reference to FIGS. 1 to 9 including the embodiment of the present invention.

  First, FIGS. 1 and 2 show a structure relating to a physical quantity measuring device for a rotating shaft described in FIGS. 8 to 10 of the Patent Document 2 and an explanation of each drawing in the specification, on a spindle 11 of a machine tool. The structure (prior invention structure) previously considered to be applied to measure the applied axial load is shown. The spindle 11 is rotatably supported by an inner diameter side of a machine tool housing (spindle head) 12 by a multi-row rolling bearing unit 13, and the spindle 11 is rotatably driven by an electric motor 14. Among the plurality of rolling bearings 15a to 15d constituting the multi-row rolling bearing unit 13, two rolling bearings 15a and 15b arranged near the distal end and two rolling bearings 15c and 15d arranged near the proximal end. In addition to applying contact angles opposite to each other, a preload is applied to each of the rolling bearings 15a to 15d. The main shaft 11 is supported rotatably with respect to the housing 12 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 spindle 11 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 11 as a reaction of pressing the tool against the workpiece. In the prior invention structure shown in FIG. 1, the axial load corresponding to the axial direction of the main shaft 11 can be obtained.

  For this reason, in the case of the structure of the prior invention, an encoder 4a as shown in FIG. 3 is provided between the rolling bearings 15b, 15c constituting the multi-row rolling bearing unit 13 near the tip of the intermediate portion of the main shaft 11. And a sensor unit 16 as shown in FIGS. 2, 4, and 5 is supported and fixed to the housing 12. Of these, the encoder 4a also serves as an inner ring spacer, is made of a magnetic metal such as steel, and has a cylindrical shape as a whole. Then, the detection unit of the sensor unit 16 is brought close to and opposed to the outer peripheral surface of the encoder 4a, which is the detection surface, and acts on the main shaft 11 based on the information regarding the phase included in the output signal of the sensor unit 16. The axial load to be calculated is determined.

  In the case of the physical quantity measuring device for a rotating shaft that is the subject of the present invention, the timing ratio A / L of the output signal of the single sensor 6c (period / cycle at which the output signal changes once) from the viewpoint of cost reduction and size reduction. The physical quantity (one or both of the displacement amount and the axial load in the axial direction) related to the encoder 4a (the main shaft 11 to which the encoder 4a is fixed) is obtained by the cycle in which the output signal changes twice. The sensor 6c used for this purpose is a sensor that is a magnetic detection element such as a Hall IC, a magnetoresistive element, etc., whose output signal changes in the middle of one cycle based on the property of the detection surface of the encoder 4a. A permanent magnet 19 is disposed on the back surface of 6c (the surface opposite to the detection portion facing the outer peripheral surface of the encoder 4a), and the sensor 6c and the permanent magnet 19 are placed on the tip of a holder 20 made of synthetic resin. It is embedded and held. The permanent magnet 19 is magnetized in the direction in which the sensor 6c faces the surface to be detected of the encoder 4a. Then, the timing of changing between the one cycle (time from the beginning of one cycle to the moment of changing in the middle) is shifted with the relative displacement between the sensor 6c and the encoder 4a.

  For this purpose, a plurality of detected characteristic change combination parts 17 and 17 are arranged on the outer peripheral surface of the encoder 4a at equal intervals in the circumferential direction, respectively in the width direction of the detected surface that coincides with the measurement direction of the physical quantity. It is formed in the axial direction of the encoder 4a. Each of the detected characteristic change combination parts 17 and 17 is a pair of characteristic change parts whose inclination directions with respect to the axial direction are different from each other. Each of the detected characteristic change combination parts 17 and 17 has a linear groove 18a or 18b in the circumferential direction of the encoder 4a. It is provided in a separated state. An output signal of the sensor 6c in which the detection unit is closely opposed to the outer peripheral surface of the encoder 4a in which such concave grooves 18a and 18b are formed is a portion where the detection unit of the sensor 6c is opposed (immediately before the detection unit). Change in accordance with the passage of each of the concave grooves 18a and 18b (the detection portion of the sensor 6c scans the outer peripheral surface of the encoder 4a in which the concave grooves 18a and 18b are formed). Output a signal). The timing of the change (the phase at which the pulse is generated) varies depending on which part of the outer peripheral surface of the encoder 4a scans in the axial direction of the encoder 4a. Based on this change, the axial displacement amount of the encoder 4a (the main shaft 11 with which the encoder 4a is fitted) can be obtained. This point will be described with reference to FIG.

  For example, when an axial load is not applied to the main shaft 11 fitted with the encoder 4a and the encoder 4a exists at the neutral position in the axial direction, the detection unit of the sensor 6c is indicated by a solid line a in FIG. As shown, the axial center portion of the outer peripheral surface of the encoder 4a is scanned substantially. As a result, the output signal of the sensor 6c changes, for example, as shown in FIG.

  On the other hand, an upward axial load acts in FIG. 9A on the encoder 4a (the main shaft 11 on which the outer fitting is fixed), and the encoder 4a moves upward in FIG. 9A. When displaced, the detection part of the sensor 4a is positioned on one axial side {lower side of (A) in FIG. 9} on the outer peripheral surface of the encoder 4a as indicated by a chain line b in FIG. 9 (A). Scan the biased part. As a result, the output signal of the sensor 6c changes, for example, as shown in FIG. When the acting direction of the axial load is reverse, the output signal changes in the reverse direction. In the case of the spindle 11 for a machine tool, the acting direction of the axial load is often constant. Therefore, in a state where an axial load is not applied, the detection portion of the sensor 6c scans one end side in the axial direction of the outer peripheral surface of the encoder 4a, and as the axial load increases, the scanning position of the sensor 6c changes in the axial direction or the like. It may be displaced to the end side.

  Of the periods A, B, and L described in FIGS. 9B and 9C, the entire period L relates to the pair of detected characteristic change combination units 17 and 17 that are adjacent in the circumferential direction. This is the cycle of the output signal of the sensor 4a. Specifically, a predetermined portion (in the illustrated example, a pair of concave grooves 18a constituting the detected characteristic change combination unit 17 on the detected characteristic change combination unit 17 on the front side in the rotation direction (left side in FIG. 9). , 18b, from the rising portion of the output signal at the rotation direction rear end edge of the concave groove 18a on the rotation direction front side to the detected characteristic change combination unit 17 on the rear side in the rotation direction (right side in FIG. 9). This is the time until the rising edge of the output signal in the equivalent part. The first partial period A relates to the groove 18a on the front side in the rotational direction (in the predetermined portion) of the pair of concave grooves 18a and 18b constituting the detected characteristic change combination portion 17 on the front side in the rotational direction. This is the time from the rising edge of the output signal to the rising edge of the output signal related to the concave groove 18b on the rear side in the rotation direction. Further, the second partial period B is a rising portion of the output signal related to the concave groove 18b on the rear side in the rotational direction among the pair of concave grooves 18a and 18b constituting the detected characteristic change combination portion 17 on the front side in the rotational direction. From the pair of concave grooves 18a, 18b constituting the detected characteristic change combination section 17 on the rear side in the rotational direction, the rising portion of the output signal related to the concave groove 18a on the front side in the rotational direction (at the same portion) It is time until.

  The total period L of the periods A, B, and L is the sum of the first partial period A and the second partial period B (L = A + B). The timing ratio is A / L (or B / L). The total period L of the respective periods is a period in which the output signal changes twice (a period corresponding to two pulses), and is constant as long as the rotation speed of the encoder 4a is constant. The first partial period A and the second partial period B are periods in which the output signal changes once (periods for one pulse), and even if the rotational speed of the encoder 4a is constant, the encoder It changes when the axial position of 4a changes.

  As is clear from FIG. 9, the timing ratio A / L (the cycle in which the output signal changes once / the cycle in which the output signal changes twice) changes with the axial position of the encoder 6c. The amount of change in A / L increases as the amount of change in the axial position (axial displacement) increases. The axial displacement amount increases as the axial load applied to the main shaft 11 with the encoder 4a fitted and fixed increases. The axial displacement amount based on the axial load decreases as the rigidity of the rolling bearing that supports the axial load among the rolling bearings 15a to 15d constituting the multi-row rolling bearing unit 13 increases. . Further, the relationship between the axial load and the axial displacement amount may be obtained in advance by calculation taking this rigidity into account, or by an experiment measuring the relationship between the known axial load and axial displacement amount. it can. Therefore, if the structures as shown in FIGS. 1 to 5 and 9 are employed, the axial load applied to the spindle 11 of the machine tool can be obtained with a structure that can be configured at low cost and in a small size.

However, the following problems (1) and (2) need to be solved in order to ensure the reliability of the measurement results with the above-described prior invention structure.
(1) As described above, there are two timing ratios, A / L and B / L. For example, when the axial load applied to the spindle 11 is obtained, any one of these two timing ratios is adopted, and the computing unit selects any one of the adopted timing ratios (A / L and B / L). The axial load is calculated based on only one of them. In this case, it is necessary that the timing ratio incorporated in the computing unit is the timing ratio adopted by the computing unit. Therefore, if the axial load is calculated based on a timing ratio that is not employed, a large error occurs in the calculation result.
(2) When an abnormal pulse is mixed into the output signal of the sensor 6c for some reason such as disturbance noise, it is necessary to provide means for detecting that this output signal is abnormal. In the case of a conventional structure using a pair of sensors 6a and 6b as shown in FIGS. 10 to 12 described above, the output signals of both sensors 6a and 6b are mutually monitored, and the output signals of both sensors are detected. Whether or not an abnormal pulse is mixed can be determined. On the other hand, in the structure of the prior invention, since only a single sensor 6c is used, it is impossible to determine the presence or absence of an abnormal pulse based on mutual monitoring.

  Of these, the problem (1) will be described in more detail with reference to FIG. When the sensor 6c outputs a pulse signal as shown in FIGS. 9B and 9C, the first partial period A is defined as a numerator as a timing ratio for obtaining an axial load acting on the spindle 11. The case where the timing ratio A / L is adopted and the case where the timing ratio B / L where the second partial period B is a numerator are adopted are considered. Regardless of which of these timing ratios A / L and B / L are not confused (if not confused), the above-mentioned axial load can be obtained by employing a calculation formula, map, etc. according to the employed timing ratio. Is required correctly. However, since these two timing ratios A / L and B / L are opposite to each other in the tendency of change with respect to the axial load, when these two timing ratios A / L and B / L are confused (misunderstood) In the axial load measurement result, an unacceptably large error occurs. When these are considered, it is necessary to consider not to confuse (do not confuse) the two timing ratios A / L and B / L.

  In view of the circumstances as described above, the present invention provides sufficient physical quantities such as a load applied to a rotating shaft that rotates at high speed while receiving a load, such as a main shaft of various machine tools, or a physical amount such as a displacement amount of the rotating shaft. The invention was invented to realize a device capable of measuring with high accuracy while ensuring reliability at a low cost.

The rotating shaft physical quantity measuring device of the present invention includes a housing, a rotating shaft, an encoder, one sensor, and a computing unit.
Of these, the housing does not rotate.
The rotating shaft is rotatably supported inside the housing by a plurality of rolling bearings each provided with a preload.
The encoder has a detection surface concentric with the rotating shaft, and is supported and fixed to a part of the rotating shaft.
The sensor is supported by the housing (directly or via another member) with the detection unit facing the detection surface.
Furthermore, the computing unit processes the output signal of the sensor, and has a function of obtaining a physical quantity related to the rotating shaft based on information related to the phase of the output signal.

The detected surface of the encoder is formed with a plurality of detected characteristic change combination portions at equal intervals in the circumferential direction in the width direction of the detected surface that coincides with the measurement direction of the physical quantity. Each of the detected characteristic change combination portions is provided with a pair of characteristic change portions having different inclination directions with respect to the width direction in a state of being separated in the circumferential direction of the encoder.
Further, the sensor changes the output signal at the moment when each of the characteristic changing parts constituting each of the detected characteristic changing combination parts passes through a portion facing the detecting part.
The computing unit obtains the physical quantity based on a timing ratio that is a ratio of a cycle in which the output signal changes once and a cycle in which the output signal changes twice.

In particular, in the physical quantity measuring device for a rotating shaft according to the present invention, the encoder is independent of the position of the sensor detection unit facing each of the detected characteristic change combination units in the width direction of the detection surface. Of each of the pair of characteristic change parts constituting each detected characteristic change combination part so that the magnitudes of the timing ratios sequentially generated along with the rotation of the counter are always reversed between adjacent timing ratios. The pitch in the circumferential direction and the pitch between the detected characteristic change combination portions adjacent to each other in the circumferential direction are regulated.
Specifically, as in the invention described in claim 2, with respect to the circumferential direction of the encoder, the pitch of the portion where the pair of characteristic change parts constituting each detected characteristic change combination part is farthest is determined. The pitch of the adjacent characteristic change combination for detection is made smaller than the closest pitch.
When implementing the present invention as described above, it is preferable to set a threshold value for the timing ratio as in the third aspect of the present invention. In addition, a comparator that compares a timing ratio sequentially acquired with the rotation of the encoder with the threshold value and a determiner that determines the presence or absence of an abnormality based on the determination result of the comparator are provided. Then, the determination unit determines that there is an abnormality when the timing ratio is continuously less than the threshold value twice or more, and when the timing ratio is continuously more than twice.
Alternatively, as in the invention described in claim 4, the second threshold value is set with respect to the rate at which the cycle in which the output signal changes twice is changed. Further, a comparator and a determination unit are provided for determining a rate at which the period changes and comparing the obtained result with the second threshold value. The determiner determines that there is an abnormality when the rate at which the period changes is greater than the second threshold.
Preferably, when the invention described in claims 3 to 4 is implemented, a signal related to a physical quantity is output from the arithmetic unit when the determiner determines that there is an abnormality as in the invention described in claim 5. Stop the output of.
Alternatively, as in the invention described in claim 6, when the determination unit determines that there is an abnormality, a signal indicating that there is an abnormality is output while continuing to output a signal relating to the physical quantity from the arithmetic unit. .
Alternatively, as in the invention described in claim 7, when the determiner determines that there is an abnormality, the output of the signal related to the physical quantity is stopped from the arithmetic unit and a signal indicating that there is an abnormality is output.

According to the physical quantity measuring device for a rotating shaft of the present invention configured as described above, a device that can accurately measure a physical amount such as a load applied to a rotating shaft rotating at a high speed while receiving a load, or a displacement amount of the rotating shaft. Can be realized at low cost.
That is, in the case of the physical quantity measuring device for a rotating shaft according to the present invention, the magnitude of the timing ratio that is sequentially generated as the encoder rotates is always reversed between the adjacent timing ratios. For this reason, there are two types of timing ratios in which the output signal changes twice (long and short) during the cycle (all cycles), and the cycle in which the output signal changes once makes the numerator, for example, always small. The timing ratio can be selected. That is, the physical quantity can always be obtained correctly by employing the timing ratio A / L with the first partial period A as a numerator. Therefore, the timing ratio B / L with the second partial period B as a numerator can be employed to prevent an illegal physical quantity from being obtained {the above-mentioned problem (1) can be solved}.

Further, as in the third aspect of the present invention, if a threshold is set for adjacent timing ratios, and the timing ratio sequentially acquired with the rotation of the encoder is compared with this threshold, the output signal of the sensor is abnormal. When a pulse is mixed, it can be detected that this output signal is abnormal. In other words, it is possible to determine the presence or absence of an abnormal pulse with a structure that uses only a single sensor {can solve the above-mentioned problem (2)}.
Alternatively, as in the invention described in claim 4, it is possible to determine the presence or absence of an abnormal pulse with a structure in which only a single sensor is used even by comparing a cycle in which the output signal changes twice with a second threshold value. Yes {Can solve the problem (2) above}.

Sectional drawing which shows one example of the structure used as the object 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 of a sensor. The schematic diagram for demonstrating the situation where the timing ratio of the output signal of one sensor changes by the displacement of the encoder based on an axial load in the case of using the encoder which belongs to the technical scope of the present invention. The schematic diagram for demonstrating the condition where abnormality similarly by disturbance etc. occurred. FIG. 7 is a schematic diagram similar to FIG. 6, used to explain the reason why an appropriate timing ratio cannot be adopted when using an encoder that is out of the technical scope of the present invention. The schematic diagram similar to FIG. 6 used in order to demonstrate the structure considered prior to this invention. 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.

  An example of an embodiment of the present invention will be described with reference to FIGS. The feature of this example is the pitch in the circumferential direction of the encoder 4a of the plurality of detected characteristic change combination portions 17 and 17 provided on the outer peripheral surface of the encoder 4a. Even if only a single sensor 6c is used by restricting in relation to the pitch in the same direction of the pair of concave grooves 18a, 18b constituting each of these detected characteristic change combination parts 17, 17, A physical quantity such as a load applied to the spindle 11 can be measured in a state where sufficient reliability is ensured. Since the other points are the same as in the case of the above-described prior invention structure, the description of the equivalent parts will be omitted or simplified, and hereinafter, the characteristic parts of this example will be mainly described.

In the case of this example, in order to solve the problems (1) and (2) described above, as shown in FIGS. 6 and 7 (A), as shown in FIG. The interval between the detected characteristic change combination portions 17 and 17 adjacent in the circumferential direction is made sufficiently larger than the interval between the concave grooves 18a and 18b. That is, the pitch P _{18 of} the portion where the pair of characteristic change portions 18a and 18b constituting each of the detected characteristic change combination portions 17 and 17 is the farthest is determined as the adjacent detected characteristic change combination portions 17 and 17. Is smaller than the pitch P ₁₇ of the closest part (P ₁₈ <P ₁₇ ).

Therefore, the one period of the output signal of the sensor 6c that are opposed to the detection section is changed to the outer circumferential surface of the encoder 4a, corresponding to the two characteristic changing portion 18a, the portion of the pitch P ₁₈ of 18b becomes farthest change The period {the maximum value of the first partial period A shown in FIG. 9B} corresponds to the pitch P ₁₇ of the part where the adjacent detected characteristic change combination parts 17 and 17 are closest. It does not become longer than the changing period {minimum value of the second partial period B shown in FIG. 9B). In other words, the first partial period A is always smaller than the second partial period B, and the first partial period A is adopted as the numerator of the timing ratio described above {timing ratio = A / L = A / (A + B) The timing ratio A / L is always less than 0.5 (50%). On the other hand, when the second partial period B is adopted as the numerator of the timing ratio {the timing ratio = B / L = B / (A + B)}, the timing ratio B / L is always 0. The value exceeds 5 (50%).

  For this reason, the first partial period A and the second partial period B are used as the numerator of the timing ratio for obtaining the axial displacement amount of the encoder 4a, and hence the axial load applied to the main shaft 11 on which the encoder is fitted and fixed. In any case, the axial load can be correctly obtained by employing a calculation formula, a map, or the like corresponding to the employed timing ratio. That is, when the first partial period A is employed, the timing ratio is less than 0.5, and when the second partial period B is employed, the timing ratio is greater than 0.5. If the axial load is calculated, these two types of timing ratios (A / L, B / L) will not be confused (misunderstood), and the axial load can be obtained without causing a large error.

  On the other hand, when the first partial period A is not always smaller than the second partial period B (when the relationship between the two partial periods A and B may be reversed), the two types of timings are used. It is difficult to prevent confusion (mixture) of the ratios (A / L, B / L). That is, a pulse based on one characteristic changing unit 18a of the pair of characteristic changing units 18a, 18b constituting each of the detected characteristic change combining units 17, 17 and a pulse based on the other characteristic changing unit 18b Cannot be distinguished depending on the timing ratio. Accordingly, the two kinds of timing ratios (A / L) are not used unless the pulse based on one characteristic changing unit 18a and the pulse based on the other characteristic changing unit 18b are distinguished from each other by some means different from the present invention. , B / L) cannot be prevented. This point will be described below with reference to FIG.

For example, as shown in FIG. 8A, two types of characteristic changing portions 18a and 18b whose inclination directions are opposite to each other are arranged at equal intervals in the circumferential direction {each detected characteristic change combining portion 17, The pitch p _{18 of} the portion where the pair of characteristic changing portions 18a and 18b constituting the portion 17 are closest to each other, and the pitch p _{17 of} the portion where the adjacent detected characteristic change combining portions 17 and 17 are closest to each other are When equal (p ₁₈ = p ₁₇ )}, as shown in FIG. 8B, the first partial period A is smaller than the second partial period B, as shown in FIG. In some cases, the first partial period A is larger than the second partial period B. In this way, when there is a possibility that the magnitude relationship between the first and second partial periods A and B may be reversed, as described above, unless one means different from the present invention is adopted, one characteristic is obtained. The pulse based on the change part 18a cannot be distinguished from the pulse based on the other characteristic change part 18b. For example, the width dimensions of the two types of characteristic changing portions 18a and 18b in the circumferential direction are different from each other, and the pulse width based on one of the characteristic changing portions 18a and 18a and the pulse width based on the other characteristic changing portions 18b and 18b. Are different from each other, it is possible to distinguish the pulses based on both of these characteristic changing portions 18a and 18b. However, when such a configuration is adopted, it is necessary to obtain not only the pulse generation timing but also the pulse width, and the processing of the arithmetic unit becomes complicated, so this arithmetic unit can be processed at a particularly high speed. It becomes necessary to use a new one, which causes an increase in cost.

On the other hand, in the case of the present invention, it is only necessary to compare the magnitude relationship between the timing ratio and a preset threshold value (for example, 0.5), which is originally necessary for obtaining the axial load. The processing of the calculator is not complicated, and it is not necessary to use a calculator capable of high-speed processing as this arithmetic unit, thereby reducing the cost.
It should be noted that the threshold value employed in order not to calculate the axial load in a partial period other than the employed partial period need not be limited to 0.5 as described above. For example, when the axial load is obtained at the timing ratio A / L with the first partial period A as a numerator, the threshold value can be set to a value smaller than 0.5, such as 0.4, 0.3, or the like. Further, when the axial load is obtained with the timing ratio B / L with the second partial period B as the numerator, the threshold value is set to a value larger than 0.5, for example, 0.6, 0.7, etc. You can also. In this case, the detected characteristic change combination parts 17 and 17 that constitute the respective detected characteristic change combination parts 17 and 17 are adjacent to the detected characteristic change combination that is adjacent to the pitch P _{18 at} the farthest part. The pitch P _{17 of} the portion where the portions 17 and 17 are closest is made sufficiently large (P ₁₈ << P ₁₇ ). In order to prevent erroneous determination due to calculation error of the calculator, it is desirable to provide a dead band at the set threshold value. For example, when a value of 0.5 is set as the threshold value, the dead zone is 0.45 to 0.55, and the timing ratio A / L of the two types of timing ratios A / L and B / L described above is set. 0.45 or less (the maximum value of this timing ratio A / L is 0.45), and the timing ratio B / L is 0.55 or more (the minimum value of this timing ratio B / L is 0.55) ).

  Next, FIG. 7 shows the reason why the above problem (2) can be solved, that is, when an abnormal pulse is mixed in the output signal of the sensor 6c, it can be detected that the output signal is abnormal. This will be described with reference to FIG. As described above, in the case of this example, since the magnitude relationship between the two types of timing ratios A / L and B / L does not reverse, any timing ratio A can be used as the timing ratio for obtaining the axial load. Even when / L (B / L) is adopted, as long as the output signal is normal, the magnitude relationship between the timing ratio A / L (B / L) and the threshold is normal in FIG. It reverses alternately as shown. That is, at the normal time, the timing ratio always repeats “more than threshold value → less than threshold value → more than threshold value → less than threshold value →...”. On the other hand, when an abnormal pulse is generated due to a disturbance such as noise as shown in the middle left part of FIG. 7B, the timing ratio is changed as shown in FIG. However, “threshold value or more → less than threshold value → less than threshold value → threshold value or more → less than threshold value →. In this way, when the magnitude relationship with respect to the threshold does not reverse (when the threshold is greater than or equal to twice or less than the threshold is continued twice or more), it can be determined that the output signal of the sensor 6c is abnormal. Invention).

  However, regarding the threshold, in order to prevent misjudgment, a dead zone is provided in the threshold set to solve the problem (1), or when this threshold is a value other than 0.5, When an abnormal pulse other than a normal pulse that occurs as each of the concave grooves 18a and 18b passes through the detection unit of the sensor 6c occurs at a timing close to the normal pulse, regardless of the presence of the abnormal pulse, There is a possibility that the magnitude relationship between the timing ratio and the threshold value, which is a criterion for determining whether or not there is an abnormality, may remain the same as in the normal case (threshold value or higher, lower than threshold value, higher than threshold value, lower than threshold value,. In such a case, the presence of the abnormal pulse cannot be detected by the invention according to claim 3.

  Therefore, in order to detect an abnormality in such a state, not only the magnitude relationship between the timing ratio and the threshold value is compared, but also the denominator (total period L in a normal state) when calculating the timing ratio and The change of the cycle in which the output signal changes twice (cycle of two pulses) is watched. The period of the two pulses changes according to the rotation speed of the main shaft 11, but the change based on the change in the rotation speed does not become abrupt. On the other hand, the change in the period of the two pulses accompanying the appearance of the abnormal pulse occurs as an abrupt change. Therefore, when the second threshold is provided for the rate at which the period (L) for two adjacent pulses changes, and the change in the period for the two pulses that has been watched exceeds this second threshold, If it is determined that there is an abnormality, the presence or absence of an abnormal pulse, which cannot be determined by the invention according to claim 3 described above, can be determined to further improve the reliability of the axial load measurement (invention according to claim 4). ).

  The invention according to claim 4 described above may be implemented together with the invention according to claim 3 described above, but even if implemented alone (the invention according to claim 3 is omitted), the presence or absence of an abnormal pulse is detected. Judgment can be made. In any case, when the determiner determines that there is an abnormality, the output of the signal related to the physical quantity from the calculator is stopped (in the case of the invention according to claim 5), or the output of the signal related to the physical quantity is continued from the calculator. However, the signal indicating that there is an abnormality is output (invention according to claim 6), or the output of the signal relating to the physical quantity from the computing unit is stopped and the signal indicating that there is an abnormality is output (claim 7). Invention). As the second threshold value, in the state where an axial load may be applied to the main shaft 11 (a workpiece is being processed), when the rotational speed of the main shaft 11 changes most greatly, The value is set slightly larger than the rate at which the period of two pulses changes. When measuring the axial load applied to the main spindle 11 of a general machine tool, for example, when the ratio is 1.05 or more or 0.95 or less, it can be determined that there is an abnormal pulse. If this value (1.05, 0.95) is set as the second threshold, the measurement error of the axial load based on the presence of the abnormal pulse can be suppressed to about 5% or less, for example. . Such an error does not cause any particular problem in the operation of the machine tool.

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. 7 to 9 of Patent Document 2 described above, the side surface in the axial direction of the annular encoder is used as a detected surface, and a thinned portion is formed on the detected surface. At the same time, the detection unit of the sensor is opposed to the detection surface in the axial direction.
Further, each characteristic changing portion constituting each detected characteristic changing combination portion provided on the detection surface of the encoder is not limited to the concave groove as in the illustrated example, but is a bank-like (however, the edge portion is sharp). It can also be an article.

DESCRIPTION OF SYMBOLS 1 Outer ring 2 Hub 3 Rolling body 4, 4a Encoder 5 Cover 6a, 6b, 6c Sensor 7 Through-hole 8 Column 9 First characteristic change part 10 Second characteristic change part 11 Main shaft 12 Housing 13 Multi-row rolling bearing unit 14 Electric motors 15a to 15d Rolling bearings 16 Sensor unit 17 Characteristic change combination for detection 18a, 18b Groove 19 Permanent magnet 20 Holder

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

Claims (7)

A non-rotating housing and a plurality of rolling bearings, each of which is preloaded, and a rotating shaft that is rotatably supported inside the housing, and a concentric with the rotating shaft that is supported and fixed to a part of the rotating shaft An encoder having a surface to be detected, one sensor supported by the housing in a state where the detection portion faces the surface to be detected, and an arithmetic unit for processing an output signal of the sensor. The device has a function of obtaining a physical quantity relating to the rotation axis based on information relating to the phase of the output signal,
The detected surface of the encoder is formed with a plurality of detected characteristic change combination portions at equal intervals in the circumferential direction, respectively in the width direction of the detected surface that matches the measurement direction of the physical quantity, The detected characteristic change combination unit is provided with a pair of characteristic change units having different inclination directions with respect to the width direction in a state of being separated in the circumferential direction of the encoder,
The sensor is configured to change an output signal at a moment when each of the characteristic changing units constituting the detected characteristic changing combination unit passes a portion where the detecting unit faces.
In the rotation axis physical quantity measuring apparatus, the computing unit obtains the physical quantity based on a timing ratio which is a ratio of a cycle in which the output signal changes once and a cycle in which the output signal changes twice.
Regardless of the position of the detection part of the sensor facing each detected characteristic change combination part in the width direction of the detected surface, the magnitude of the timing ratio that is sequentially generated as the encoder rotates is adjacent to each other. The pitches in the circumferential direction of the pair of characteristic change parts constituting each detected characteristic change combination part and the respective detection target adjacent to each other in the circumferential direction so as to always reverse between the matching timing ratios. A physical quantity measuring device for a rotating shaft, characterized by regulating the pitch between the characteristic change combination parts.   With respect to the circumferential direction of the encoder, the pitch of the part where the pair of characteristic change parts constituting each detected characteristic change combination part is farthest is greater than the pitch of the part where the adjacent characteristic change combination part for detection is closest The physical quantity measuring device for a rotating shaft according to claim 1, which is also small.   A threshold is set for the timing ratio, and a comparator for comparing the timing ratio acquired sequentially with the rotation of the encoder with the threshold and a determination unit for determining the presence or absence of abnormality based on the determination result of the comparator are provided. 3. The determination device according to claim 1, wherein the determination unit determines that there is an abnormality when the timing ratio is continuously less than the threshold value twice or more, and when the timing ratio is equal to or more than two times continuously. The physical quantity measuring device for rotating shafts described in 1.   The threshold is set with respect to the rate at which the cycle in which the output signal changes twice, and the comparator includes a comparator and a determiner for determining the rate at which the cycle is changed and comparing the obtained result with the threshold. The physical quantity measuring device for a rotating shaft according to any one of claims 1 to 3, wherein when the ratio exceeds the threshold value and is large, it is determined that there is an abnormality.   The rotation-axis physical quantity measuring device according to any one of claims 3 to 4, wherein when the judging device judges that there is an abnormality, the output of a signal relating to the physical quantity from the computing device is stopped.   5. The method according to claim 3, wherein when the determiner determines that there is an abnormality, the signal indicating that there is an abnormality is output while continuing to output the signal relating to the physical quantity from the arithmetic unit. Physical quantity measuring device for rotating shaft.   5. The method according to claim 3, wherein when the determiner determines that there is an abnormality, the output of the signal relating to the physical quantity from the arithmetic unit is stopped and a signal indicating that there is an abnormality is output. Physical quantity measuring device for rotating shaft.

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