JP5552828B2 - Load measuring device for machine tools - Google Patents

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, not only the durability of the tool is impaired, but also the surface property of the workpiece is deteriorated, 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 head is not constant, but varies greatly depending on the type (size) of the tool and the material and shape of the workpiece. 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 rotating shaft to which the tool is fixed due to the 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, an invention apparatus described in Patent Document 1 has been conventionally known 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 such a conventional 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 relating to a rolling bearing unit with a load measuring device, which includes a magnetic encoder and a sensor assembly, which can be procured at a lower cost than a quartz piezoelectric load sensor. ing. 12 to 14 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 arranged on the inner diameter side of the outer ring 1 that does not rotate even when in use, and the hubs 2 that rotate together with the wheels in a state where the wheels are supported and fixed during use are arranged in double rows. The rolling elements 3 and 3 are supported so as to be rotatable. A preload is applied to each of the rolling elements 3 and 3 together with a contact angle that is 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. Further, a pair of sensor assemblies 6a and 6b 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 sensor assemblies 6a and 6b are provided as described above. The encoder 4 is placed in close proximity to the outer peripheral surface, which is the detected surface. 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 sensor assemblies 6a and 6b includes a permanent magnet and a magnetic detection element constituting a detection unit. These two sensor assemblies 6a and 6b are supported and fixed inside the cover 5, and the detection part of one sensor assembly 6a is used as the first characteristic changing part 9 and the detection of the other sensor assembly 6b. The part is made to face and oppose the second characteristic changing part 10. The positions where the detection parts of both the sensor assemblies 6a and 6b face both the characteristic change parts 9 and 10 are the same with respect to 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 where the inclination direction changes) is just at the center position between the detection parts of the two sensor assemblies 6a, 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 sensor assemblies 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 sensor assemblies 6a and 6b are shown by solid lines A and B in FIG. That is, it faces a portion that is shifted from the most protruding portion by the same amount in the axial direction. Therefore, the phases of the output signals of the two sensor assemblies 6a and 6b coincide with each other 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. 14A, the detecting portions of the sensor assemblies 6a and 6b are shown in FIG. A) is opposed to the broken lines B and B, that is, the portions that are different from each other in the axial direction from the most protruding portion. In this state, the phases of the output signals of the two sensor assemblies 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. 14A, the detecting portions of the sensor assemblies 6a and 6b are shown in FIG. A shift in the axial direction from the chain line C, C, that is, from the most projecting portion is opposed to different portions in the opposite direction. In this state, the phases of the output signals of the sensor assemblies 6a and 6b are shifted as shown in FIG.

  As described above, in the case of a structure conventionally known as described in Patent Documents 2 to 4, the phases of the output signals of the two sensor assemblies 6a and 6b are the same as that of the outer ring 1 and the hub 2. The direction of the axial load applied between the outer ring 1 and the hub 2 deviates in the direction corresponding to the axial direction of the relative displacement in the axial direction. Further, the degree to which the phase of the output signals of the sensor assemblies 6a and 6b is shifted due to the axial load (relative displacement) increases as the axial load (relative displacement) increases. Therefore, the direction of relative displacement in the axial direction between the outer ring 1 and the hub 2 based on the presence and absence of the phase shift of the output signals of the sensor assemblies 6a and 6b and the direction and magnitude of the shift, if any. And the magnitude, and the direction and magnitude of the axial load acting between the outer ring 1 and the hub 2 are obtained. The processing for calculating the relative displacement and the load in the axial direction based on the phase difference between the output signals of the two sensor assemblies 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.

  Patent Document 2 also describes a structure in which a pair of concave grooves having different inclination directions with respect to the axial direction of the encoder are arranged as a pair (in a “C” shape) adjacent to each other in the rotational direction of the encoder. When the detection unit of the sensor is opposed to the detection surface of such an encoder, the relative displacement (other than the rotation direction) between the detection surface and the detection unit based on the load acting on the rotating shaft to which the encoder is fixed is caused. Based on this, the timing at which the output signal of the sensor changes is shifted within one cycle. Therefore, the load acting on the rotating shaft can be obtained by using only a single sensor based on the ratio of the timing to one cycle of the output signal.

  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 value of the axial load applied to the wheel-supporting rolling bearing unit does not change regularly due to factors other than the axial load to be measured, such as the structure of the wheel support portion. On the other hand, in the case of a rotating shaft (main shaft) of a machine tool, the load applied to the rotating shaft changes regularly (sinusoidally) depending on the type of processing tool supported and fixed at the tip. For example, in the case of a cutting tool (working tool) such as a drill or an end mill, a plurality of cutting parts (working parts) are provided at equal intervals in the circumferential direction on the outer peripheral surface or the tip surface. If all of these cutting parts continue to process the work surface of the work piece evenly, the load applied to the rotating shaft may fluctuate due to the shape of the cutting tool. No. However, in the actual case, it is rare that all of the respective cutting parts cut the work surface of the work piece evenly, and due to the shape of the cutting tool, it is added to the rotating shaft. The load fluctuates regularly.

  FIG. 15 shows an end mill (similar to a drill) having 10 cutting parts on the outer peripheral surface, coupled and fixed to the tip of a rotating shaft of a machine tool concentrically with the rotating shaft, and rotating the rotating shaft at a constant speed. While the workpiece is advanced at a constant speed toward the workpiece and the workpiece is subjected to cutting, the physical quantity fluctuation state with respect to the rotating shaft is shown. (A) in FIG. 15 represents the fluctuation state of the load applied to the rotating shaft, and (B) represents the displacement state of the rotating shaft. Since the load and the displacement are proportional, (A) and (B) in FIG. 15 are substantially the same except that the values on the vertical axis are different.

  As shown in FIGS. 15A and 15B, when a workpiece is machined with a cutting tool having a plurality of cutting portions, a constant speed rotation should be performed so that the load applied to the rotating shaft should be constant. Even in a constant speed forward state, the load applied to the rotating shaft fluctuates regularly. For this reason, if the timing of the load measurement is not taken into account, the measurement accuracy of the load applied to the rotating shaft is deteriorated based on the fluctuations shown in FIGS. For example, in the structure for measuring a load shown in FIGS. 13 to 14 described above, the number of the through holes 7 and 7 (per one circumference) provided on the outer peripheral surface of the encoder 4 is the number of cutting parts of the cutting tool. 15, for example, the phase difference between the output signals of the sensor assemblies 6 a and 6 b is obtained at the portions (measurement points) indicated by black circles in FIGS. Based on the phase difference, the load applied to the rotating shaft is obtained. The parts indicated by black circles in FIGS. 15A and 15B are the same phase part on the sine wave. For this reason, as described above, when the number of the through holes 7 is set to 10 which is the same as the number of the cutting parts of the cutting tool, it is apparent from the description of FIGS. 15A and 15B. As is apparent, the value δ (DC component offset) is an error component based on the variation.

  As shown in Patent Documents 2 to 4, the number of sets of detected portions such as the through holes 7 and 7 and the column portions 8 and 8 existing on the detected surface of the encoder 4 is determined by the cutting portion of the cutting tool. If the average value is obtained by performing load measurement a plurality of times (several tens as in the case of a rolling bearing unit with a load measuring device for supporting wheels of an automobile), the error component δ Can be eliminated. However, since the rotational speed of the rotating shaft (main shaft) of the machine tool is orders of magnitude faster than the rotational speed of the wheels for automobiles, the processing speed of the arithmetic unit (CPU) that has input the sensor output signal is taken into account. It is difficult to increase the number of sets of detected parts beyond the number of cutting parts. In consideration of measuring the load applied to the rotating shaft of the machine tool without using an expensive CPU having an extremely fast processing speed, the encoder constituting the load measuring device for machine tools uses the number of sets of the detected parts. It is realistic to set the number from 1 digit to at most about 10 sets.

  However, when the number of detected portions provided on the detected surface of the encoder is from one digit to at most about 10 sets, the number m of cutting portions of the cutting tool and the number n of sets of detected portions are: May coincide (m = n), or the number m of cutting parts of the cutting tool may be an integral multiple of the number n of sets of detected parts (m / n = integer). The influence of the error component δ cannot be excluded not only when the numbers m and n match, but also when the ratio m / n of these numbers is an integer. If the number n of sets of detected parts is larger than the number m of cutting parts of the cutting tool, even if the ratio n / m between these numbers n and m is an integer of 2 or more, a plurality of load measurements are performed. The influence of the error component δ can be eliminated by repeating the operation and taking the average value. However, since it is difficult to increase the number n of the detected parts for the reasons described above, it cannot be said that it is a realistic countermeasure. Further, if the phase between the cutting tool and the sensor detection portion is appropriately regulated with respect to the rotation direction and the measurement point shown in FIG. 15 is set to the center position of the sine wave curve, the occurrence of the error component δ is prevented. Things are not impossible. However, it is troublesome to make the phase coincide each time the tool is changed, even if some positioning mark or positioning engaging portion is provided, and it cannot be said that it is a realistic countermeasure.

  In view of the circumstances as described above, the present invention provides a cutting tool in which a plurality of cutting parts (working parts) are provided at equal intervals in the circumferential direction without using an expensive CPU with extremely high processing speed. The present invention has been invented to realize a machine tool load measuring apparatus capable of accurately measuring a load applied to a rotating shaft (main shaft) of a machine tool using a machining tool.

The load measuring apparatus for machine tools of this invention is provided with a housing, a rotating shaft, a cutting tool (processing tool), an encoder, a sensor unit, and a calculator.
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 cutting tool (processing tool) is supported and fixed at the tip of the rotating shaft concentrically with the rotating shaft, and a plurality of cutting portions (working portions) are provided at equal intervals in the circumferential direction. Yes.
The encoder is supported and fixed to a part of the rotating shaft and has a detected surface concentric with the rotating shaft.
The sensor unit includes at least one sensor assembly, and is supported on the housing directly or via another member in a state where the detection portion faces the detection surface.
Further, the detected surface of the encoder is in a state in which a plurality of sets of detected portions whose characteristics are different from those adjacent to each other in the circumferential direction are inclined with respect to the acting direction of the load to be measured. Are provided at equal intervals in the circumferential direction.
The computing unit processes an output signal of the sensor unit, and obtains an average value of a fluctuating load acting on the rotating shaft based on information on a phase of the output signal of the sensor unit.
Furthermore, in the machine tool load measuring apparatus according to the present invention, in order to remove an error component based on the fluctuation of the load, the number m of cutting parts (working parts) provided in the cutting tool (working tool) is set to the encoder. The number m / n divided by the number n of the detected portions present on the detected surface is a non-integer value, and the computing units are provided in a plurality in the circumferential direction. The average value of the measured values of a plurality of loads obtained continuously using the detected part is obtained .

When implementing the machine tool load measuring apparatus of the present invention configured as described above, the encoder is preferably made of a magnetic material, as in the invention described in claim 2, for example.
And the said to-be-detected part is formed in the width direction of the to-be-detected surface of this encoder, and is a thinning part or a ridge part in which the distance with the detection part of the said sensor assembly which comprises the said sensor unit differs from a remainder. A certain distance changing portion is used, and at least a part of the distance changing portion is inclined with respect to the acting direction of the load to be measured.
Further, the sensor assembly includes a 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. And a magnetic detection element such as a magnetoresistive element, and an IC that outputs a signal representing a change in magnetic flux density detected by the magnetic detection element.
Further, the computing unit obtains a load acting on the rotating shaft based on an output signal of the sensor assembly.

In carrying out the invention described in claim 2 as described above, for example, as in the invention described in claim 3, the sensor unit is provided with a single sensor assembly. In this case, the sensor assembly changes an output signal with the passage of the distance changing portion accompanying the rotation of the encoder, and the relative displacement between the magnetic detection element and the encoder due to the load applied to the rotating shaft. Accordingly, it is assumed that the timing at which the output signal changes during one period shifts. Then, the information regarding the phase used by the computing unit for obtaining the load is the ratio of the timing to one period of the output signal.
When carrying out the invention described in claim 3, for example, as in the invention described in claim 4, it is assumed that the encoder is formed in a cylindrical shape, and the encoder is externally fixed to the rotary shaft. To do. The detected surface is the outer peripheral surface of the encoder. The distance changing portion is a plurality of concave grooves or ridges formed on the outer peripheral surface. Each of these concave grooves or protrusions is a pair of concave grooves or protrusions that are different from each other in the inclination direction with respect to the axial direction of the encoder and are adjacent to each other in the rotational direction of the encoder. A three-dimensional detection unit is opposed to each of the concave grooves or protrusions, and the number of detection target units including one pair of the pair of concave grooves or protrusions is n.

According to the machine tool load measuring apparatus of the present invention configured as described above, a plurality of cutting parts (working parts) are equally spaced in the circumferential direction without using an expensive CPU with extremely high processing speed. The average value of the load applied to the rotating shaft (main shaft) of the machine tool that uses the cutting tool (working tool) provided in can be measured with high accuracy.
That is, when a workpiece is processed in a state where a cutting tool having a plurality of cutting portions is coupled and fixed to the tip portion of the rotating shaft, the load applied to the rotating shaft through the cutting tool varies finely. In order to control the feed speed of the rotating shaft of the machine tool, it is necessary to obtain an average value instead of this finely varying value. When the number m of the cutting parts of the cutting tool is an integral multiple of the number n of the detected parts provided on the detected surface of the encoder, as described above, the error component based on the variation is included in the average value as described above. δ is easy to enter, and when it enters, it cannot be removed.

On the other hand, in the case of the present invention, the number m of cutting parts of the cutting tool is not an integral multiple of the number n of detected parts provided on the detected surface of the encoder (m / n ≠ integer). The average value can be obtained with high accuracy by removing the influence of the error component. That is, even in the case of the present invention, the influence of the load fluctuation as shown by the sine wave curve in FIG. 15 described above is included in the result of one load measurement measured using a certain set of detected parts. There is a high possibility of going out. However, in order to satisfy the requirement “m / n ≠ integer”, the degree and direction of this influence, that is, the magnitude of the error component δ, and whether the error component δ is added to the average value or not. Conversely, whether it occurs in a state where it is subtracted from the average value differs depending on the measurement. Therefore, if an average value of a plurality of measurement values obtained continuously is obtained, the average value can be obtained with high accuracy by eliminating or reducing the influence of the error component δ. The timing for obtaining the average value of the load applied to the rotating shaft is somewhat delayed by obtaining the average value of a plurality of measurement values obtained continuously, but this delay is related to the machine tool load measuring device that is the subject of the present invention. Will not be a problem. The reason is that the rotational speed of the rotating shaft (main shaft) of the machine tool reaches several tens of thousands min ⁻¹ , so even if an average value is calculated during several rotations of the rotating shaft, the time required for it is several milliseconds to Because it is only about several tens of milliseconds. In this way, the time required for obtaining the average value is very short, whereas it is sufficient to control the feed speed of the rotating shaft every several hundreds of milliseconds or several seconds. This is because there is a much longer time for detecting the tool life. For the above reasons, according to the present invention, the average value of the load applied to the rotating shaft can be obtained with high accuracy without causing any particular problems with respect to the timing of measurement.

FIG. 3 is a cross-sectional view of a main part showing a first example of an embodiment of the present invention. 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) before coat | covering a detection part, and the state (B) after coat | covering. The schematic perspective view which takes out and shows a sensor assembly. The schematic diagram for demonstrating the principle of load measurement. The figure similar to FIG. 2 which shows the 2nd example of embodiment of this invention. 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) before coat | covering a detection part, and the state (B) after coat | covering. The schematic perspective view which takes out and shows a sensor assembly. The schematic diagram for demonstrating the principle of load measurement. 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 sensor assembly by the displacement of the encoder based on an axial load. FIG. 5 is a diagram for explaining a situation in which an error occurs in load measurement due to fluctuations in the load applied to the rotary shaft and the displacement of the rotary shaft due to the shape of the cutting tool coupled and fixed to the tip of the rotary shaft.

[First example of embodiment]
FIGS. 1-6 has shown the 1st example of embodiment of this invention corresponding to Claims 1-4. A spindle 12 is rotatably supported by a multi-row rolling bearing unit 13 on the inner diameter side of a machine tool housing (spindle head) 11, and the spindle 12 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 12 is supported rotatably with respect to the housing 11 in a state in which a radial load and a thrust load in both directions are supported. When the machine tool is in operation, a cutting tool 16 such as an end mill or a drill, which is coupled and fixed concentrically to the main shaft 12 via a coupling jig such as a taper cone, is attached to the tip of the main shaft 12 (the left end in FIG. 1). The workpiece is pressed against the workpiece while rotating at a high speed, and the workpiece is subjected to machining such as cutting. When machining is performed in this manner, loads in each direction are applied to the main shaft 12 as a reaction of pressing the cutting tool 16 against the workpiece. In the structure shown in FIG. 1, the axial load corresponding to the axial direction of the main shaft 12 can be obtained.

  For this reason, in the case of the structure of this example, an encoder as shown in FIG. 3 is provided between the rolling bearings 15b and 15c constituting the multi-row rolling bearing unit 13 at a portion near the tip of the intermediate portion of the main shaft 12. The sensor unit 17 as shown in FIGS. 2, 4, and 5 is supported and fixed to the housing 11. 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 17 is brought close to and opposed to the outer peripheral surface of the encoder 4a, which is a detection surface, and acts on the main shaft 12 based on the phase-related information contained in the output signal of the sensor unit 17. The axial load to be calculated is determined.

  In the case of the load measuring device for machine tools of this example, from the viewpoint of cost reduction and miniaturization, the timing ratio α / L of the output signal of the single sensor assembly 6c (period / output at which the output signal changes once) The axial load applied to the encoder 4a (the main shaft 12 to which the encoder 4a is fixed) is obtained according to the cycle in which the signal changes twice. The sensor assembly 6c used for this purpose has an output signal that changes in the middle of one cycle based on the property of the surface to be detected of the encoder 4a. Magnetic sensing elements such as Hall ICs 24a and 24b and magnetoresistive elements A permanent magnet 18 is arranged on the back surface (the surface opposite to the detection portion facing the outer peripheral surface of the encoder 4a) to form the sensor assembly 6c, and this sensor assembly 6c is used as the tip of a holder 19 made of synthetic resin. The sensor unit 17 is configured by being embedded and held in a part. The magnetization direction of the permanent magnet 18 is a direction in which the magnetic detection element constituting the sensor assembly 6c faces the detection surface of the encoder 4a. Then, it is assumed that the timing that changes during the one cycle (the time from the beginning of one cycle to the moment when it changes midway) shifts with the relative displacement between the sensor assembly 6c and the encoder 4a. The pair of Hall elements 24a and 24b function as a differential Hall IC to detect a change in the property of the detection surface of the encoder 4a with high accuracy. For this purpose, the Hall elements 24a and 24b are arranged in the rotation direction of the encoder 4a. If the required accuracy is not high, one Hall element can be substituted.

  For this purpose, a plurality of sets of detected characteristic change combination units 20 and 20, each of which is a detected unit described in the claims and is also a distance changing unit, are arranged on the outer peripheral surface of the encoder 4 a. They are formed at equal intervals in the axial direction of the encoder 4a, which is the width direction of the detected surface that coincides with the measurement direction of the axial load. Each of the detected characteristic change combination parts 20 and 20 is a pair of characteristic change parts whose inclination directions with respect to the axial direction are different from each other. It is provided in a separated state. An output signal of the sensor assembly 6c in which the magnetic detection element as the detection portion is brought close to and opposed to the outer peripheral surface of the encoder 4a in which the concave grooves 21a and 21b are formed is detected by the sensor assembly 6c. The respective concave grooves 21a and 21b pass through a portion (a portion immediately before the detection portion) facing each other (the outer peripheral surface of the encoder 4a in which the detection portion of the sensor assembly 6c has formed the respective concave grooves 21a and 21b). (The pulse signal is output). 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 is scanned in the axial direction of the sensor assembly 6c. Based on this change, the axial displacement amount of the encoder 4a (the main shaft 12 with the outer fitting) 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 12 fitted with the encoder 4a and the encoder 4a is in the neutral position in the axial direction, the detection unit of the sensor assembly 6c is shown by a solid line in FIG. As indicated by a, the central portion in the axial direction is scanned on the outer peripheral surface of the encoder 4a. As a result, the output signal of the sensor assembly 6c changes, for example, as shown in FIG.

  On the other hand, a downward axial load acts on the encoder 4a (the main shaft 12 to which the outer fitting is fixed) in FIG. 6A, and the encoder 4a moves downward in FIG. 6A. When displaced, the detecting portion of the sensor assembly 6c, as indicated by a chain line b in FIG. 6 (A), is axially one side {upper side of FIG. 6 (A)} on the outer peripheral surface of the encoder 4a. The part which is biased to is scanned. As a result, the output signal of the sensor assembly 6c changes as shown in FIG. 6B, for example. When the acting direction of the axial load is reverse, the output signal changes in the reverse direction. In the case of the main spindle 12 for machine tools, 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 assembly 6c scans one axial end side of the outer peripheral surface of the encoder 4a, and as the axial load increases, the scanning position of the sensor 6c becomes an axis. You may decide to displace to the direction other end side.

  Among the periods α, β, and L described in FIGS. 6B and 6C, the entire period L relates to the pair of detected characteristic change combination units 20 and 20 adjacent to each other in the circumferential direction. This is the period of the output signal of the sensor assembly 6c. Specifically, a predetermined portion (in the illustrated example, a pair of concave grooves 21a constituting the detected characteristic change combination unit 20 on the detected characteristic change combination unit 20 on the front side in the rotation direction (left side in FIG. 6). , 21b, the detected characteristic change combination unit 20 on the rear side in the rotational direction (right side in FIG. 6) from the rising portion of the output signal at the rotational direction rear end edge of the concave groove 21a on the front side in the rotational direction. This is the time until the rising edge of the output signal in the equivalent part. The first partial period α is related to the concave groove 21a on the front side in the rotational direction (in the predetermined portion) of the pair of concave grooves 21a and 21b constituting the detected characteristic change combination portion 20 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 21b on the rear side in the rotation direction. Further, the second partial period β is the rising portion of the output signal related to the concave groove 21b on the rear side in the rotational direction among the pair of concave grooves 21a and 21b constituting the detected characteristic change combination unit 20 on the front side in the rotational direction. From the pair of concave grooves 21a and 21b constituting the detected characteristic change combination section 20 on the rear side in the rotational direction, the rising portion of the output signal related to the concave groove 21a on the front side in the rotational direction (at the same portion) It is time until.

  The total period L of the periods α, β, and L is the sum of the first partial period α and the second partial period β (L = α + β). The timing ratio is α / L (or β / L). The total period L of each period 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 α and the second partial period β are periods in which the output signal changes once (period 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 apparent from FIG. 6, the timing ratio α / L or β / L (cycle in which the output signal changes once / cycle in which the output signal changes twice) changes with the axial position of the encoder 6c. The amount of change in the timing ratio α / L or β / L increases as the amount of change in the axial position (the amount of axial displacement) increases. Further, the axial displacement amount increases as the axial load applied to the main shaft 12 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 a structure as shown in FIGS. 1 to 6 is employed, an axial load applied to the spindle 12 of the machine tool can be obtained with a structure that can be configured at a low cost and in a small size.

As is clear from the above description, according to the machine tool load measuring apparatus of this example, if each of the detected characteristic change combination portions 20, 20 is provided at n locations on the outer peripheral surface of the encoder 4a, The axial load applied to the main shaft 12 is obtained n times while the main shaft 12 rotates once. On the other hand, m cutting portions 22, 22 exist on the distal end surface or the outer peripheral surface of the cutting tool 16 coupled and fixed to the distal end portion of the main shaft 12. The load applied to the main shaft 12 fluctuates m times during one rotation of the main shaft 12 as indicated by the broken line in FIG. Based on this variation, in order not to cause an error in the average value of the measured values of the load applied to the main shaft 12, the number m of the cutting portions 22 and 22 provided in the cutting tool 16 is determined by the encoder 4a. A non-integer multiple (m / n ≠ integer) of the number n of sets of the detected characteristic change combination units 20 and 20 provided on the outer peripheral surface.
For this reason, in the case of the present example, for the reasons described above, the cutting in which the plurality of cutting portions 22 and 22 are provided at equal intervals in the circumferential direction without using an expensive CPU with extremely high processing speed. The average value of the axial load applied to the spindle 12 with the tool 16 coupled and fixed to the tip can be accurately measured.

[Second Example of Embodiment]
FIGS. 7-11 has shown the 2nd example of embodiment of this invention corresponding to Claim 1,2. In the case of this example as well, as in the case of the first example of the above-described embodiment, a load in the axial direction that matches the axial direction of the main shaft 12 is obtained. For this reason, in the case of this example, the rolling bearings 15b, 15c constituting the multi-row rolling bearing unit 13 (refer to FIG. In the meantime, an encoder 4 b as shown in FIG. 8 is externally fitted and fixed, and a sensor unit 17 a is supported and fixed to the housing 11. Of these, the encoder 4b is entirely cylindrical with a magnetic metal such as steel, and the detection portion of the sensor unit 17a is made to face the outer peripheral surface of the encoder 4b, which is the 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 17a.

  For this reason, in the case of this example, a part of the outer peripheral surface of the encoder 4b has a “<” shape when viewed in the radial direction, and each is a detected portion described in the claims. Concave grooves 23 and 23, which are also distance changing portions, are formed. Each of the concave grooves 23 and 23 is provided in the width direction of the outer peripheral surface of the encoder 4b as a whole (the axial direction of the encoder 4b), but each portion is inclined with respect to the width direction. Also, 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). Also in this example, the encoder 4b is provided with a function as an inner ring spacer.

On the other hand, the sensor unit 17a is formed by supporting and fixing a pair of sensor assemblies 6a and 6b to the tip of a holder 19a made of synthetic resin.
Each of these sensor assemblies 6a and 6b includes a permanent magnet 18a, a pair of Hall elements 24a and 24b, and an IC 25, as shown in FIGS.
Of these, the permanent magnet 18a is magnetized in the radial direction of the encoder 4b, which is the direction in which the outer peripheral surface of the encoder 4b and the detection unit of the sensor unit 17a face each other. In the case of this example, as shown in FIG. 10, the magnetizing directions of the permanent magnets 18a and 18a incorporated in the two sensor assemblies 6a and 6b are the same (the inner side is the N pole and the outer side in the radial direction of the encoder 4b). Is S pole).

  Further, the hall elements 24a and 24b are arranged in the direction of rotation of the main shaft 12 on the end face on the N pole side facing the outer peripheral surface of the encoder 4b among the both end faces in the magnetization direction of the permanent magnet 18a (see FIG. 10 and 11 in the left-right direction). The diameter of the permanent magnet 18a is sufficiently large so that the Hall elements 24a and 24b can be disposed on the end face of the permanent magnet 18a. And this permanent magnet 18a is provided in the state hung over both said Hall elements 24a and 24b. The Hall elements 24a and 24b have the same characteristics (use the same type).

  The IC 25 obtains a difference in magnetic flux density detected by the Hall elements 24a and 24b (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 the two kinds of threshold values is output as an output signal of the sensor assembly 6a (6b). That is, this sensor assembly 6a (6b) has been widely known as a magnetic detection element from Patent Document 5, Non-Patent Documents 1 and 2, etc., as in the case of the first example of the embodiment described above. By utilizing the principle of the differential Hall IC, the positions of the circumferential edges of the concave grooves 23 and 23 can be obtained with high accuracy. Then, as shown in FIGS. 11A and 11B, the output signal of the sensor assembly 6a that scans one half of each of the grooves 23 and 23, and the sensor assembly 6b that scans the other half as well. The axial load applied to the main shaft 12 to which the encoder 4b is externally fitted and fixed can be measured based on the phase difference from the output signal. The principle of obtaining this axial load based on the phase difference is the same as that of the conventional structure shown in FIGS.

In the case of the structure of this example as well, if each of the concave grooves 23 and 23 is provided at n locations on the outer peripheral surface of the encoder 4b, the main shaft 12 makes one rotation of the axial load applied to the main shaft 12. N times in between. If m cutting portions 22 and 22 (see FIG. 1) are present on the front end surface and the outer peripheral surface of the cutting tool 16 coupled and fixed to the front end portion of the main shaft 12, a load applied to the main shaft 12 is applied to the main shaft 12. It is the same as in the case of the first example of the above-described embodiment that it fluctuates m times during one rotation. Therefore, also in this example, the number m of the cutting parts 22 and 22 provided in the cutting tool 16 is a non-integer multiple of the number n of sets of the concave grooves 23 and 23 provided on the outer peripheral surface of the encoder 4b. As (m / n ≠ integer), an error is not caused in the average value of the load applied to the main shaft 12 based on the variation.
Therefore, in the case of this example as well, as in the first example of the above-described embodiment, the average value of the load applied to the spindle 12 can be obtained without using an expensive CPU with extremely high processing speed. Can measure well.

  When practicing the present invention, the detected surface of an encoder externally fitted and fixed to a rotating shaft such as a main shaft is defined as an axial side surface, and the detection portion of the sensor is opposed to the detected surface in the axial direction. If it does, the radial load added to the said rotating shaft will be calculated | required.

DESCRIPTION OF SYMBOLS 1 Outer ring 2 Hub 3 Rolling element 4, 4a, 4b Encoder 5 Cover 6a, 6b, 6c Sensor assembly 7 Through-hole 8 Column part 9 First characteristic change part 10 Second characteristic change part 11 Housing 12 Main shaft 13 Multi-row rolling bearing Unit 14 Electric motor 15a, 15b, 15c, 15d Rolling bearing 16 Cutting tool 17, 17a Sensor unit 18, 18a Permanent magnet 19, 19a Holder 20 Characteristic change combination part for detection 21a, 21b Groove 22 Cutting part 23 Groove 24a 24b Hall element 25 IC

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 (4)

A non-rotating housing,
A rotating shaft rotatably supported inside the housing by a plurality of rolling bearings each preloaded.
A cutting tool that is supported and fixed concentrically with the rotating shaft at the tip of the rotating shaft, and provided with a plurality of cutting portions at equal intervals in the circumferential direction;
An encoder having a detected surface concentric with the rotary shaft, supported and fixed to a part of the rotary shaft;
At least one sensor assembly supported by the housing directly or via another member in a state where the detection portion is opposed to the detection surface;
An arithmetic unit for processing the output signal of the sensor assembly,
The detected surface of the encoder has a plurality of sets of detected portions different from portions adjacent to each other in the circumferential direction in a part of the circumferential direction, in a state where the detected surface is inclined with respect to the acting direction of the load to be measured. It is provided at equal intervals in the circumferential direction,
The calculator based on the phase information on the output signal of the sensor assembly, a machine tool load measuring device for determining the average value of the load varying acting on the rotary shaft,
In order to remove the influence of the error component based on the fluctuation of the load, the number m obtained by dividing the number m of the cutting parts provided in the cutting tool by the number n of the detected parts existing on the detection surface of the encoder. / N is a non-integer value, and the arithmetic unit is a plurality of load measurement values obtained continuously using a plurality of detected portions provided continuously in the circumferential direction. A load measuring device for machine tools, characterized by obtaining an average value of . The encoder is made of a magnetic material, and the detected portion is formed in the width direction of the detected surface of the encoder, and the distance between the detected portion and the detecting portion of the sensor assembly is a thinned portion or a protruding portion that is different from the remaining portion. The distance changing portion is a changing portion, and at least a part thereof has a shape inclined with respect to the acting direction of the load to be measured,
The sensor assembly is disposed on a permanent magnet that is magnetized in a direction in which the detection surface and the detection unit face each other, and an end surface that faces the detection surface among both end surfaces in the magnetization direction of the permanent magnet. And an IC for outputting a signal representing a change in magnetic flux density detected by the magnetic detection element,
The machine tool load measuring device according to claim 1, wherein the computing unit obtains a load acting on the rotating shaft based on an output signal of the sensor assembly.   The sensor assembly includes a single sensor assembly, and the sensor assembly changes an output signal according to the passage of the distance changing portion accompanying the rotation of the encoder, and the sensor assembly according to the load applied to the rotating shaft. As the relative displacement between the encoder and the encoder, the timing at which the output signal changes during one period shifts, and information regarding the phase used to determine the load is the timing for one period of the output signal. The load measuring apparatus for machine tools according to claim 2, wherein   The encoder is formed in a cylindrical shape and is externally fixed to the rotating shaft, the detected surface is the outer peripheral surface of the encoder, and the distance changing portion is a plurality of concave grooves formed on the outer peripheral surface. Alternatively, each of the grooves or ridges is a pair of grooves or ridges having different inclination directions with respect to the axial direction of the encoder and adjacent to each other in the rotational direction of the encoder. The detection part of the single sensor assembly is opposed to each of the concave grooves or the ridges, and the number of detected parts including the pair of concave grooves or ridges as one set is n. The load measuring device for machine tools according to claim 3.

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