JP5601091B2 - Spindle device for machine tool - Google Patents

Description

  The present invention relates to a machine tool spindle device capable of measuring an axial load acting on a spindle of a machine tool.

  In a machine tool, measuring an axial load acting on a main shaft has a great merit. That is, the axial load acting on the spindle of the machine tool is an important parameter that has a great influence on machining accuracy, machining efficiency, tool life, and the like. Accordingly, knowing the axial load makes it possible to select an appropriate machining condition. For example, machining conditions are generally determined by the rotation speed and feed rate of the tool, but are also affected by factors that are difficult to control, such as friction and heat generated by machining. Even if set to a constant value, the same machining accuracy is not always obtained. Considering the cutting load (that is, the axial load of the spindle) corresponding to the change of the machining surface as a new parameter, it becomes possible to select a more strict machining condition and to improve the machining accuracy.

  Specifically, if the chip discharge amount is the same, the machining condition with a small cutting load is an efficient machining condition, which is advantageous for saving energy and extending the tool life. Further, from the increase in the cutting load, it is possible to estimate the deterioration of the cutting property (sharpness) of the tool and the occurrence of cutting edge wear and the like, and it becomes possible to know the tool life and the tool replacement time. Furthermore, by managing the history of changes in cutting load, it is possible to estimate bearing damage factors such as unreasonable cutting conditions and collisions (impact load) between the tool and workpiece, and from the grasped tool life characteristics The tool can be improved and improved.

  As described above, it is important to know the cutting load in a machine tool. However, in a machine tool of a type in which the tool rotates, it is difficult to detect a load acting on the tool and the spindle as compared with a machine tool of a type in which the tool does not rotate.

  As a conventional apparatus capable of detecting a load applied to a spindle of a machine tool, an apparatus described in Patent Document 1 is conventionally known.

  The apparatus described in Patent Document 1 includes a plurality of quartz piezoelectric load sensors arranged in series with respect to the direction of load application, and a spindle that supports and fixes a cutting tool based on a measurement signal of the load sensor. The load (cutting resistance) applied to the (spindle) is measured. In the case of such an apparatus, since an expensive quartz piezoelectric load sensor is used, it is inevitable that the cost of the entire load measuring apparatus increases.

  On the other hand, Patent Document 2 describes an invention relating to a rolling bearing unit with a load measuring device that uses a magnetic encoder and sensor that are less expensive than a quartz piezoelectric load sensor. In this unit, a load applied between the outer ring and the hub is obtained by an encoder disposed in the hub and a sensor in close proximity to the detection surface of the encoder.

10 to 12 show an example of a conventional rolling bearing unit with a load measuring device described in Patent Document 2. FIG.
In this rolling bearing unit with a load measuring device, a hub 302 that rotates together with a wheel while supporting and fixing the wheel in use is fixed to a radially inner side of an outer ring 301 that does not rotate even when used via rolling elements 303 arranged in double rows. And is supported rotatably. Each of the rolling elements 303 is provided with a preload, and rolls with contact angles opposite to each other (in the illustrated case, a combination of the back surfaces) between the two rows.

  A cylindrical encoder 304 is supported and fixed concentrically with the hub 302 at the inner end of the hub 302. A pair of sensors 306 a and 306 b are supported inside a bottomed cylindrical cover 305 that closes the inner end opening of the outer ring 301, and the detection portions of both the sensors 306 a and 306 b are used as the detected surface of the encoder 304. It is made to face and oppose to the outer peripheral surface. The encoder 304 is made of a magnetic metal plate, and a through hole 307 (first characteristic portion) and a column portion 308 (second portion) are formed in the first half portion (the inner half portion in the axial direction) of the outer peripheral surface of the encoder 304 that is a detection surface. Characteristic portions) are alternately arranged at equal intervals in the circumferential direction. The boundaries between the through holes 307 and the pillars 308 are inclined by the same angle with respect to the axial direction of the encoder 304, and the inclined directions with respect to the axial direction are opposite to each other with the intermediate portion in the axial direction of the encoder 304 as a boundary. It is said. Therefore, each through-hole 307 and each column part 308 has a “<” shape with the axially intermediate portion protruding most in the circumferential direction. Of the outer half and the inner half of the detected surface, the inclination directions of the boundaries are different from each other, the outer half in the axial direction is the first characteristic changing portion 309, and the inner half in the axial direction is the first half. 2 characteristic changing section 310.

  Each of the pair of sensors 306a and 306b includes a permanent magnet and a magnetic detection element that constitutes a detection unit. These two sensors 306a and 306b are supported and fixed inside the cover 305, the detection part of one sensor 306a is the first characteristic change part 309, and the detection part of the other sensor 306b is the second characteristic change part. 310 are closely opposed to each other. The positions where the detection units of both the sensors 306a and 306b face the first and second characteristic change units 309 and 310 are the same in the circumferential direction of the encoder 304. Further, in the state where an axial load is not applied between the outer ring 301 and the hub 302, a portion that protrudes most in the circumferential direction in the axial middle portion of each through hole 307 and the column portion 308 (a portion in which the tilt direction of the boundary changes) ) Regulates the installation position of each member so that it exists just in the center position between the detection parts of both sensors 306a and 306b.

  In the case of the rolling bearing unit with a load measuring device configured as described above, when an axial load is applied between the outer ring 301 and the hub 302 and the outer ring 301 and the hub 302 are relatively displaced in the axial direction, the two sensors 306a and 306b. The phase at which the output signal changes is shifted.

  In other words, in a neutral state where no axial load is applied between the outer ring 301 and the hub 302, the detection portions of both sensors 306a and 306b are on the solid lines a and b in FIG. It faces a portion that is shifted in the axial direction by the same amount. Therefore, the phases of the output signals of both sensors 306a and 306b coincide as shown in FIG.

  On the other hand, when a downward axial load is applied to the hub 302 to which the encoder 304 is fixed in FIG. 12A, the detection units of both sensors 306a and 306b are shown by broken lines in FIG. B, opposite to the upper part, that is, the part different from each other in the axial direction from the most protruding part. In this state, the phases of the output signals of both sensors 306a and 306b are shifted as shown in FIG.

  Furthermore, when the upward axial load in FIG. 12A is applied to the hub 302 to which the encoder 304 is fixed, the detecting portions of both sensors 306a and 306b are shown by chain lines C and C in FIG. The deviation in the axial direction from the uppermost part, that is, the most protruding part, is opposed to different parts in the opposite direction to the case described above. In this state, the phases of the output signals of both sensors 306a and 306b are shifted as shown in FIG.

  As described above, the phases of the output signals of the sensors 306a and 306b are in the direction of the action of the axial load applied between the outer ring 301 and the hub 302 (the direction of relative displacement between the outer ring 301 and the hub 302 in the axial direction). The direction is shifted. Further, the degree to which the phases of the output signals of the sensors 306a and 306b are shifted by this axial load (relative displacement) increases as the axial load (relative displacement) increases.

  Therefore, if there is a phase shift between the output signals of the sensors 306a and 306b, the direction and magnitude of the relative displacement in the axial direction between the outer ring 301 and the hub 302 based on the direction and magnitude, and consequently the outer ring 301. It is possible to determine the acting direction and magnitude of the axial load acting between the hub 302 and the hub 302.

  The processing for calculating the relative displacement and the load in the axial direction based on the phase difference between the output signals of both sensors 306a and 306b is performed by a calculator (not shown). For this reason, in this computing unit, the relationship between the phase difference, which has been examined in advance by theoretical calculation or experiment, and the relative displacement and load in the axial direction is incorporated in a form such as a calculation formula or a map.

  In addition to the above example, Patent Document 2 also includes a structure in which a pair of concave grooves having different inclination directions with respect to the axial direction of the encoder are arranged in a pair of “C” adjacent to each other in the rotational direction of the encoder. Have been described.

  FIG. 13A shows the configuration of the encoder, and FIG. 13B shows the configuration of a sheet metal with a long hole for making the encoder. A plurality of detected portions 324 are arranged at equal intervals in the circumferential direction on the outer peripheral surface of the cylindrical encoder 320 that is the detected surface. Each of these detected portions 324 includes a pair of individualized portions 325 having different characteristics from the other portions. In this example, slit-like long holes are employed as the individualized portions 325. The encoder 320 having such individualized portions 325 is made by rounding a belt-like magnetic metal plate in which each long hole is previously punched and butt-welding the circumferential edges. In addition, as each individualization part 325, it is also possible to employ | adopt a ditch | groove or a convex part.

  The interval in the circumferential direction between the pair of individualized portions 325 constituting each detected portion 324 is continuously changed in the axial direction in all the detected portions 324. That is, the interval in the circumferential direction between the pair of individualized portions 325 constituting each detected portion 324 becomes smaller at one end in the axial direction of the encoder 320, and each detected portion 324 adjacent in the circumferential direction is configured. The intervals in the circumferential direction between the individualized portions 325 to be inclined are inclined so as to become smaller toward the other axial end of the encoder 320.

  The output signal of the sensor in which the detection unit is opposed to the outer peripheral surface, which is the detection surface of the encoder 320, changes at the moment of facing each individualization portion 325. The changing interval (cycle) changes with a change in the axial position of the portion of the sensor facing the detecting portion. That is, the timing at which the output signal of the sensor changes in one cycle based on the axial relative displacement between the detection surface and the detection unit based on the load acting on the main shaft to which the encoder 320 is fixed.

  Therefore, the load acting on the main shaft can be obtained with only a single sensor based on the ratio of the timing to one cycle of the output signal. That is, from the output signal pattern of the sensor, it is possible to determine the degree of displacement of the main shaft in the axial direction with respect to the housing (axial displacement), and from this degree of displacement, the axial acting on the main shaft. The load can be determined.

JP 2002-187048 A JP 2006-317420 A

  By the way, like the rolling bearing unit with a load measuring device described in Patent Document 2, the axial load applied to the wheel supporting rolling bearing unit for supporting the wheel of the automobile is measured to control for running stability. In this case, the value of the axial load 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, when applied to the spindle of a machine tool, the load applied to the spindle may change 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 spindle will not fluctuate due to the shape of the cutting tool. Therefore, it is rare that all of the cutting parts cut the work surface of the work piece evenly, and the load applied to the main shaft fluctuates regularly due to the shape of the cutting tool.

  FIG. 14 shows an end mill (similar to a drill) having 10 cutting portions on the outer peripheral surface, coupled and fixed to the tip of the main spindle of the machine tool concentrically with the main spindle, and rotating the main spindle at a constant speed, This shows the fluctuation state of the physical quantity related to the spindle when the workpiece is cut at a constant speed toward. FIG. 14A shows a fluctuation state of the load applied to the main shaft, and FIG. 14B shows a displacement state of the main shaft. Since the load and the displacement are proportional, (A) and (B) in FIG. 14 are substantially the same except that the values on the vertical axis are different.

  As shown in FIGS. 14A and 14B, when a workpiece is machined with a cutting tool having a plurality of cutting portions, a constant-speed rotation and a constant load that should be constant for the load applied to the main shaft should be constant. Even in the fast forward state, the load applied to the main shaft fluctuates regularly.

  For this reason, if the timing of load measurement is not taken into account, the measurement accuracy of the load applied to the main shaft is deteriorated based on the fluctuations shown in FIGS.

  For example, in the structure for measuring a load shown in FIGS. 10 to 12 described above, the number of through holes (per circumference) provided on the outer peripheral surface of the encoder 304 is set to 10 which is the same as the number of cutting parts of the cutting tool. In this case, the phase difference between the output signals of the sensors 306a and 306b is obtained at the portions (measurement points) indicated by black circles in FIGS. 14A and 14B, and the load applied to the spindle based on the phase difference is calculated. Will be asked.

  The portions indicated by black circles in FIGS. 14A and 14B are the same phase portions on the sine wave. For this reason, as described above, when the number of the through holes 307 is ten, which is the same as the number of the cutting parts of the cutting tool, δ is obtained as is apparent from the description of FIGS. The value (DC component offset) is an error component based on the variation.

  As shown in Patent Document 2, the number of sets of detected parts such as the through holes 307 and the pillars 308 existing on the detected surface of the encoder 304 is sufficiently larger than the number of cutting parts of the cutting tool ( The influence of the error component δ can be eliminated by measuring the load several times as in the case of a rolling bearing unit with a load measuring device for supporting a wheel of an automobile and measuring the load a plurality of times. However, since the rotational speed of the spindle of the machine tool is orders of magnitude faster than the rotational speed of the wheels for automobiles, when considering the processing speed of the computing unit (CPU) that has input the sensor output signal, It is difficult to increase the number of sets beyond the number of cutting parts. In consideration of measuring the load applied to the spindle of the machine tool without using an expensive CPU with extremely high processing speed, in the encoder constituting the machine tool load measuring device, the number of sets of detected parts is It is realistic to set the number from one digit to at most about 10 sets.

  However, when the number of detected parts provided on the detected surface of the encoder is changed from one digit to at most about 10 sets, the number m of cutting parts of the cutting tool matches the number n of detected parts ( 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, load measurement is performed a plurality of times even if the ratio n / m of these numbers n and m is an integer of 2 or more. By taking the average value, the influence of the error component δ can be eliminated. However, since it is difficult to increase the number n of sets of detected parts for the reasons described above, it cannot be said that this is a realistic countermeasure. In addition, if the phase between the cutting tool and the detection unit of the sensor is properly regulated with respect to the rotation direction, and the measurement point shown in FIG. It is not impossible. However, it is troublesome to make the above phases 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.

  Further, when the above-described sensor and encoder are incorporated in the spindle device of a machine tool, load detection cannot be performed or detection error becomes excessive if the axial position deviation between the sensor and encoder increases. For this reason, if the range (tolerance) of the axial relative position accuracy of the sensor and encoder is small, general finishing machining of a single component is not satisfactory, and precise finishing is required, and the components are selectively fitted together. A special adjustment process is required during assembly. For this reason, it becomes easy to invite high parts processing cost and assembly adjustment cost, and there is a possibility that parts cannot be easily replaced at the time of repair.

  The present invention has been made in view of the above-described problems, and the object thereof is to provide a plurality of cutting parts at equal intervals in the circumferential direction without using an expensive CPU with extremely high processing speed. The load applied to the spindle of the machine tool that uses the cutting tool can be measured with high accuracy, and the load of the machining and assembly adjustment can be reduced while reducing the relative position accuracy range of the sensor and encoder in the axial direction. It is an object of the present invention to provide a spindle device for a machine tool capable of ensuring the detection accuracy required for detecting the above.

In order to achieve the above object, the present invention is achieved by the following constitution.
(1) a non-rotating housing;
A main shaft rotatably supported on the housing by a rolling bearing provided with a preload in the axial direction;
A cutting tool which is supported and fixed concentrically with the main shaft at the tip of the main shaft, and a plurality of cutting portions are provided at equal intervals in the circumferential direction;
An encoder that rotates integrally with the main shaft and has a detected surface concentric with the main shaft;
A sensor that is supported by the housing in a state in which a detection unit faces the detection surface of the encoder, and outputs a signal according to a change in characteristics of the detection surface;
Arithmetic means for calculating an axial load acting on the spindle based on a pattern in which the output signal of the sensor changes;
In a spindle device of a machine tool equipped with
On the detected surface of the encoder, a plurality of sets of detected portions each formed of a pair of individualized portions having different characteristics from the other portions are formed at equal intervals in the circumferential direction,
Each of the pair of individualized portions is substantially the same in the opposite direction to the axial direction of the encoder so that the interval in the circumferential direction between the pair of individualized portions continuously changes in the axial direction. It is formed in a square shape that is inclined at an angle,
The number m / n obtained by dividing the number m of cutting parts provided in the cutting tool by the number n of detected parts present on the detected surface of the encoder is set to a non-integer, and
A spindle device for a machine tool, wherein an inclination angle at which each individualized portion intersects a line parallel to the circumferential direction is set in a range of 30 ° to 70 °.
(2) The spindle device of the machine tool according to (1), wherein an inner diameter of the rolling bearing is 40 mm to 120 mm.

  According to the present invention, the axial load applied to the spindle of a machine tool using a cutting tool in which a plurality of cutting portions are provided at equal intervals in the circumferential direction without using an expensive CPU with extremely high processing speed. The average value 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 parts is coupled and fixed to the tip of the main shaft, the load applied to the main shaft through the cutting tool varies finely. In order to control the feed speed or the like of the spindle of the machine tool, it is necessary to obtain an average value instead of this finely varying value. When the number m of cutting parts of the cutting tool is an integer multiple of the number n of detected parts provided on the detected surface of the encoder, as described above, the error component δ based on the fluctuation is included in the average value. 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 accurately obtained by removing the influence of the error component. That is, even in the case of the present invention, the influence of load fluctuations as shown by the sine wave curve in FIG. 14 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 that “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, Conversely, whether it occurs in a state where it is subtracted from the average value differs for each 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. By obtaining an average value of a plurality of measurement values obtained continuously, the timing for obtaining the average value of the load applied to the spindle is somewhat delayed, but this delay is related to the load measuring device for machine tools that is the subject of the present invention. There is no problem. The reason for this is that the rotational speed of the spindle of the machine tool reaches several tens of thousands of times / minute, so even if an average value is obtained during several revolutions of the spindle, the time required for it is about several milliseconds to several tens of milliseconds. By not too much. In this way, the time required for obtaining the average value is very short, but it is sufficient to control the feed speed of the spindle every several hundreds of milliseconds or several seconds. This is because there is a much longer time margin than this for the life detection. For the above reasons, according to the present invention, the average value of the load applied to the main shaft can be obtained with high accuracy without causing any particular problems with respect to the timing of measurement.

  Further, according to the present invention, the inclination angle at which the pair of individualized portions constituting the detected portion provided on the detected surface of the encoder intersects the line parallel to the circumferential direction is in the range of 30 ° to 70 °. As a result, the detection accuracy required to detect the load is ensured while reducing the load of parts processing and assembly adjustment without reducing the range of the relative position accuracy in the axial direction of the sensor and encoder. Can do.

  In other words, by limiting the tilt angle to 30 ° or more, it becomes possible to widen the range of the relative positional accuracy of the sensor and encoder in the axial direction, and no special sorting and fitting adjustments such as component matching are required. The range can be satisfied by stacking parts with general processing tolerances. In addition, by limiting the tilt angle to 70 ° or less, the machine tool can be used to set the optimum machining conditions (cutting feed and machining rotation speed), change the cutting edge sharpness, and determine the load during machining that is a criterion for detecting tool life. The detection accuracy required for detection can be ensured.

It is sectional drawing of the spindle apparatus of the machine tool incorporating the bearing apparatus of embodiment of this invention. It is a principal part expanded sectional view of FIG. It is a perspective view of the encoder shown in FIG. FIG. 4 is a development view of the encoder of FIG. 3. It is a perspective view which takes out the sensor shown in FIG. 1, and shows the state (A) before coat | covering a detection part, and the state (B) after coat | covering. It is a perspective view which shows the structure of the principal part of the sensor. It is a schematic diagram for demonstrating the principle of load measurement. FIG. 6 is a characteristic diagram showing a relationship between a C-shaped angle (inclination angle of a ditch) of a pair of C-shaped concave grooves (individualized portions) formed in the encoder and an axial relative position range of the sensor and the encoder. is there. It is a characteristic view which shows the relationship between the C-shaped angle (inclination angle of a ditch | groove), and detection accuracy of a pair of ditch | groove (individualization part) of C-shape formed in the said encoder. It is sectional drawing of the conventional rolling bearing unit with a load measuring apparatus. It is the figure which looked at a part of the to-be-detected surface of the encoder used for the unit from radial direction. It is a mimetic diagram for explaining the situation where a phase difference arises in the output signal of a pair of sensors due to the displacement of the encoder in the axial direction. (A) is a perspective view which shows the other example of the conventional encoder, (B) is a perspective view which expands and shows it. (A) and (B) are due to the shape of the cutting tool coupled and fixed to the tip of the main shaft, and explain the situation in which the load applied to the main shaft and the displacement of the main shaft fluctuate, resulting in an error in load measurement. FIG.

  Hereinafter, a spindle device of a machine tool incorporating a bearing device according to an embodiment of the present invention will be described in detail with reference to the drawings.

  As shown in FIGS. 1 and 2, the spindle device 10 of the machine tool according to the embodiment is of a motor built-in type, and a main shaft 11 is provided at the center thereof. A cutting tool 3 such as an end mill or a drill is attached to one end portion of the main shaft 11 in the axial direction (left end portion in FIG. 1) via a tool holder 2.

  The main shaft 11 is rotatably supported by a housing 50, which is a stationary member that does not rotate, by a front bearing group 20 that supports the tool side and a rear bearing 40 that supports the counter tool side.

  A rotor 61 is fitted on the outer peripheral surface of the main shaft 11 between the front bearing group 20 and the rear bearing 40. The stator 62 disposed around the rotor 61 is fixed to the housing 50. By supplying electric power to the stator 62, a rotational force is generated in the rotor 61 to rotate the main shaft 11. ing. The housing 50 is configured by sequentially connecting a plurality of divided housings 51 to 53, an outer ring retainer 54, covers 55 and 56, and the like.

  The front bearing group 20 includes four rows of angular ball bearings 21 to 24 having the same size arranged in order from the tool 3 side (front side). The front two angular ball bearings 21 and 22 and the rear two angular ball bearings 23 and 24 are arranged in a rear combination, and each of the angular ball bearings 21 to 24 includes an outer ring 26, an inner ring 27, and an outer ring 26. And a plurality of balls 28 as rolling elements disposed with a contact angle between the outer ring raceway groove and the inner ring raceway groove of the inner ring 27.

  The outer ring 26 of each of the angular ball bearings 21 to 24 of the front bearing group 20 is fitted into the housing 50 by an outer ring presser 54 that is fitted inside the housing 50 and bolted to the housing 50 via the outer ring spacers 70, 81, and 82. It is fixed. A sensor mounting hole 70 a is formed in the outer ring spacer 70 disposed between the outer rings 26 of the second angular ball bearing 22 and the third angular ball bearing 23 from the front side.

  Further, the inner ring 27 of each angular ball bearing 21 to 24 of the front bearing group 20 is externally fitted to the main shaft 11 and is attached to the main shaft 11 via inner ring spacers 71, 83, 84 by a nut 85 fastened to the main shaft 11. It is fixed. An inner ring spacer 71 arranged between the inner ring 27 of the second angular ball bearing 22 and the third angular ball bearing 23 from the front side so as to face the outer ring spacer 70 also serves as an encoder 72 described later. .

  In addition, the angular ball bearings 21 to 24 of the front bearing group 20 are loaded with a fixed position preload by the nut 85, whereby the main shaft 11 supports a radial load and a thrust load in both directions with respect to the housing 50. And it is supported so that it can rotate freely.

  Further, the rear bearing 40 is a cylindrical roller bearing and is not denoted by a reference numeral in the drawing, but has an outer ring, an inner ring, and a plurality of cylindrical rollers as rolling elements. The outer ring of the rear bearing 40 is fitted in the housing 50 and is fixed to the housing 50 by an outer ring presser or a spacer bolted to the housing 50. The inner ring of the rear bearing 40 is also fixed to the main shaft 11 by other nuts or spacers fastened to the main shaft 11.

  Further, in this machine tool, during operation, the cutting tool 3 such as an end mill or a drill is pressed against the work piece while rotating at a high speed to cut the work piece, so that the axial load as a reaction force is applied to the spindle 11. Act. Therefore, a cylindrical encoder 72 as shown in FIG. 3 is interposed between the second angular ball bearing 22 and the third angular ball bearing 23 from the front side of the front bearing group 20 so that this axial load can be measured. The inner ring spacer 71 is externally fitted, and a sensor 100 as shown in FIGS. 5 and 6 is supported and fixed on the housing 50 side at the position of the outer ring spacer 70.

  The encoder 72 rotates integrally with the main shaft 11, and as shown in FIG. 3, a plurality of sets of detected portions 75 are equally spaced in the circumferential direction on the outer peripheral surface of an inner ring spacer 71 made of a magnetic metal material. It has a configuration arranged in. Each of these detected portions 75 is configured by a pair of individualized portions 75a and 75b each having a characteristic different from that of the other portions. In this embodiment, each of the individualized portions 75a and 75b has a concave groove. It is formed by machining.

  Instead of the concave groove, a long hole or a protruding line penetrating the encoder 72 can be adopted, and other elements can be adopted depending on the type of the sensor 100. For example, in the case of an optical sensor, it is possible to provide a portion having a light reflectance different from that of the surrounding area and to make the portion a personalized portion.

  When the individualized portions 75a and 75b are constituted by concave grooves or ridges, the concave grooves and ridges correspond to distance changing portions that are different in distance from the detection portion of the sensor 100 from the remaining portions.

  As shown in FIG. 4, the pair of individualized portions 75 a and 75 b constituting each detected portion 75 extend in a slanted manner at substantially the same angle in opposite directions with respect to the axial direction of the encoder 72. As a result, the distance between the pair of individualized portions 75a and 75b in the circumferential direction continuously changes in the axial direction.

  The encoder 72 constitutes a sensor unit together with the sensor 100, and the sensor 100 is supported by the housing 50 in a state where the detection unit faces the detection surface of the encoder 72. The sensor 100 outputs a pulse signal according to the rotation of the encoder 72 by alternately changing the characteristics of the detection surface of the encoder 72 in the circumferential direction. That is, the sensor 100 outputs a signal that changes as the detector 72 faces the individualized portions 75a and 75b as the encoder 72 rotates. The interval (cycle) at which the signal changes varies with the change in the axial position of the portion of the sensor 100 where the detection unit faces. A signal from the sensor 100 is input to a calculator (not shown), and the calculator calculates an axial load acting on the main shaft 11 based on a pattern in which the output signal from the sensor 100 changes.

  As shown in FIG. 5, the sensor 100 has a structure in which the Hall IC 105 is disposed and embedded at the tip of the resin holder 101. As shown in FIG. 6, the rear surface of the Hall IC 105 (the side opposite to the encoder 72). ) Is provided with a permanent magnet 107. The magnetization direction of the permanent magnet 107 is a direction in which the Hall IC 105 constituting the sensor 100 faces the detected surface of the encoder 72. Then, with the relative displacement between the sensor 100 and the encoder 72, the pulse interval changes.

  The pair of magnetic detection elements 105a and 105b function as differential elements, and detect the change in the properties of the detection surface of the encoder 72 with high accuracy. For this purpose, both elements 105 a and 105 b are arranged in the rotation direction of the encoder 72. When the encoder 72 is a multi-pole magnet encoder, a Hall IC having one Hall element can be used.

  The structure of the sensor 100 is not particularly limited as long as it incorporates a permanent magnet. In other words, even a so-called passive type in which a coil is wound around a pole piece that guides the flow of magnetic flux from a permanent magnet, a so-called active element incorporating a magnetic detection element that changes its characteristics according to the density of the magnetic flux. Even mold types can be used. The sensor 100 according to the present embodiment may be any sensor that can detect the edges of the individualized portions 75a and 75b that are long grooves, and an optical sensor or the like can also be used.

  The relative position between the sensor 100 and the detection surface of the encoder 72 is set so that the magnetic detection elements 105a and 105b are located in the intermediate portion in the axial direction of the detection surface. Specifically, the positions of the magnetic detection elements 105a and 105b are the positions of the encoder 72 which is the intermediate position in the axial direction of the inner ring spacer 71 disposed between the angular bearings 22 and 23 of the front bearing group to which the fixed position preload is applied. It is set so as to coincide with the intermediate portion in the axial direction.

  The output signal of the sensor 100 changes as the individualized portions 75a and 75b of the encoder 72 pass through the detection portion (the portion where the magnetic detection elements 105a and 105b are disposed) of the sensor 100 (outputs a pulse signal). ). The timing of the change (the phase at which the pulse is generated) varies depending on which part of the detection surface of the encoder 72 scans the detected surface of the encoder 72 with respect to the axial direction. Based on this change, the axial displacement amount of the encoder 72 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 72 and the encoder 72 is in the neutral position in the axial direction, the detection unit of the sensor 100, as shown by a solid line a in FIG. Of the outer peripheral surface of the encoder 72, the central portion in the axial direction is scanned. As a result, the output signal of the sensor 100 changes, for example, as shown in FIG.

  In contrast, when a downward axial load is applied to the encoder 72 (main shaft 11) in FIG. 7A and the encoder 72 is displaced downward in FIG. Scans a portion of the detected surface of the encoder 72 that is biased toward one side in the axial direction {upper side in Fig. 7A), as indicated by a chain line b in Fig. 7A.

  As a result, the output signal of the sensor 100 changes as shown in FIG. When the acting direction of the axial load is reverse, the output signal changes in the reverse direction. Among the periods α, β, and L described in FIGS. 7B and 7C, the total period L is the period of the output signal of the sensor 100 related to the pair of detected parts 75 adjacent in the circumferential direction. It is.

  Specifically, a predetermined portion related to the detected portion 75 on the front side in the rotational direction (left side in FIG. 7) (in the illustrated example, of the pair of individualized portions 75a and 75b constituting the detected portion 75, the front side in the rotational direction. Is the time from the rising portion of the output signal at the rear end edge in the rotation direction of the individualized portion 75a to the rising portion of the output signal at the equivalent portion of the detected portion 75 on the rear side in the rotation direction (right side in FIG. 7) . Further, the first partial period α is the output related to the individualization portion 75a on the front side in the rotation direction (in the predetermined portion) among the pair of individualization portions 75a and 75b constituting the detected portion 75 on the front side in the rotation direction. This is the time from the rising edge of the signal to the rising edge of the output signal related to the individualized portion 75b on the rear side in the rotation direction. Further, the second partial period β is the rotation direction from the rising portion of the output signal related to the individualization portion 75b on the rear side in the rotation direction among the pair of individualization portions 75a and 75b constituting the detected portion 75 on the front side in the rotation direction. Of the pair of individualized portions 75a and 75b constituting the rear-side detected portion 75, this is the time to the rising portion of the output signal (in the equivalent portion) related to the individualized portion 75a on the front side in the rotational direction.

  The total period L of the periods α, β, 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 72 is constant. The first partial cycle α and the second partial cycle β are cycles in which the output signal changes once (cycle for one pulse). Even if the rotation speed of the encoder 72 is constant, the axial direction of the encoder 72 It changes when the position changes.

  As is clear from FIG. 7, 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 72. The amount of change in the timing ratio α / L or β / 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 72 fitted and fixed increases. Further, the amount of axial displacement based on the axial load decreases as the rigidity of the rolling bearing that supports the axial load among the angular ball bearings 21 to 24 constituting the front bearing group 20 increases. In addition, the relationship between the axial load and the axial displacement amount can be obtained in advance by a calculation that takes this rigidity into account, or by an experiment that measures the relationship between the known axial load and the axial displacement amount. .

  Therefore, according to the present embodiment, 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.

  As is clear from the above description, according to the spindle device of the machine tool of this example, if each detected portion 75 is provided at n locations on the outer peripheral surface of the encoder 72, the axial load applied to the spindle 11 is It is obtained n times while the main shaft 11 rotates once. On the other hand, there are m cutting portions 3 a on the tip surface or the outer peripheral surface of the cutting tool 3 that is coupled and fixed to the tip portion of the main shaft 11. Then, based on these m cut portions 3a, the load applied to the main shaft 11 fluctuates m times while the main shaft 11 makes one rotation as shown by the broken line in FIG. Based on this variation, the number m of the cutting portions 3 a provided in the cutting tool 3 is provided on the outer peripheral surface of the encoder 72 so as not to cause an error in the average value of the measured values of the load applied to the spindle 11. A non-integer multiple (m / n ≠ integer) of the number n of sets of each detected portion 75 is used.

  For this reason, in the case of this example, for the reasons described above, the cutting tool 3 in which a plurality of cutting portions 3a 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 main shaft 11 coupled and fixed to the tip can be measured with high accuracy.

  Further, as described above, the output signal of the sensor 100 changes in accordance with the direction of the axial load acting on the main shaft 11 and in proportion to the magnitude of the axial load. Therefore, if the relationship between the magnitude of the axial load and the displacement amount of the main shaft 11 is obtained by measuring or calculating in advance the rigidity (spring constant) of the front bearing group 20 loaded with the fixed position preload, the sensor 100 can obtain the relationship. Based on the output signal pattern, the direction and magnitude of the axial load acting on the main shaft 11 are obtained by the calculation means.

  Further, since the inner ring spacer 71 constituting the encoder 72 is arranged between the pair of angular ball bearings 22 and 23 arranged in the rear combination, the intermediate position in the axial direction of the inner ring spacer 71 is caused by the heat of the main shaft 11. Since it becomes the center in the axial direction when expanding and contracting, the influence of expansion and contraction of the main shaft 11 is suppressed, and accurate load measurement becomes possible.

  Further, in the present embodiment, the surface to be detected of the encoder 72 is configured by a single row in the axial direction where the pitch of the characteristic that changes in the circumferential direction continuously changes in the axial direction. It can be configured by only one Hall IC. As a result, the cost of the sensor unit can be reduced, and the axial width of the inner ring spacer 71 constituting the sensor 100 and the encoder 72 can be reduced. Thereby, the axial direction length of the spindle apparatus 10 can also be shortened. In particular, in the case of a method in which the main spindle turns with a 5-axis machine or the like (for example, turns around ± 120 °), if the main spindle length is shortened, the turning radius can be reduced, and space saving of the entire machine tool can be achieved. There is a merit that the machining space can be secured, the operation of the spindle device 10 becomes easy, for example, when three-dimensional machining is performed, and the ease of machining program creation and machinability can be improved.

  Further, in the case of a spindle device for a general machine tool, particularly a spindle device for a cutting type machine tool such as a lathe or a machining center, angular ball bearings 21 to 24 having an inner diameter of φ40 mm to φ120 mm are mainly used. In addition, the encoder 72 incorporated between the angular ball bearings 22 and 23 preferably has a radial thickness of 5 mm or more, that is, an outer diameter of φ50 mm or more from the viewpoint of maintaining strength and ensuring processing dimensional accuracy. Furthermore, considering the arrangement space of the sensor facing the outer diameter part of the encoder and interference between the encoder and the outer ring spacer, the radial thickness of the encoder 72 is preferably 10 mm or less, and the inner diameters of the angular ball bearings 21 to 24 Is φ40 mm, the outer diameter is preferably φ60 mm or less.

  In addition, if the number of detected portions 75 provided on the detected surface of the encoder 72 (= number of pair pulses) is increased, the displacement detection accuracy is improved, but the groove machining cost is increased and the bearing inner diameter is set to 120 mm or less. In consideration of the circumferential space of the encoder 72 in this case, it is desirable that the number of detected portions 75 is 13 sets or less. Furthermore, in order to avoid interference with the number m of blades of the cutting part 3a of the cutting tool 3 described above, the detected part 75 preferably exceeds the number of 3 sets, and more preferably the number of sets of 5 or more.

  Here, when the encoder 72 having an outer diameter of φ50 mm or more is used, the inclination angle θ at which the individualized portions 75a and 75b arranged in a pair of C-shapes intersect the line S1 parallel to the circumferential direction. Is set in the range of 30 ° to 70 ° in consideration of both the range of the relative positional accuracy of the sensor 100 and the encoder 72 in the axial direction and the detection accuracy required for detecting the load.

  FIG. 8 shows the relationship between the range of the relative position in the axial direction of the sensor 100 and the encoder 72 and the inclination angle θ of the pair of individualized portions 75a and 75b constituting each detected portion 75 of the encoder 72. Further, in FIG. 8 and FIG. 9 described later, one pair pulse indicates one set of detected portions 75 corresponding to one pair of individualized portions 75a and 75b, and five pair pulses indicate five sets of detected portions 75. Is expressed.

  When the tolerances of general processed parts including bearing inner and outer ring width dimensional accuracy, housing depth accuracy, inner and outer ring spacer width dimensional accuracy, sensor mounting hole position accuracy, etc. are stacked, the relative axial position of sensor 100 and encoder 72 The accuracy range is limited to ± 0.5 mm. Therefore, as shown in FIG. 8, when the outer diameter of the encoder 72 having five sets of detected portions 75 is 50 mm or more, if the inclination angle θ of the individualized portions 75a and 75b is 30 ° or more, the sensor And the range of the axial relative position accuracy of the encoder can be set to ± 0.5 mm or more. Therefore, the accuracy range can be ensured only by processing and assembling each component constituting the spindle device at a general processing accuracy level, that is, by stacking tolerances of components having a general processing accuracy. Therefore, it is possible to easily assemble without reducing the processing cost and performing the current joining between the parts.

  In addition, when the number of sets of the detected parts 75 increases, the range of the axial relative position accuracy of the sensor and the encoder decreases. For this reason, although not shown, for example, in an encoder having an outer diameter of φ50 mm or more having 13 sets or less of the detected parts 75, the range of the axial relative position accuracy between the sensor and the encoder is ± 0.5 mm or more. The inclination angle θ of the individualized portions 75a and 75b is preferably 35 ° or more.

  In addition, when the sensor 100 is used for setting optimum machining conditions (cutting feed and machining rotation speed), detecting tool sharpness deterioration, detecting tool life, etc., it is necessary to detect at least an axial load of about 500 N, The displacement detection accuracy (detection sensitivity) needs to be 4 μm or less in terms of the rigidity of the incorporated bearing (the axial spring constant is approximately 100 to 200 N / μm).

  FIG. 9 is a graph showing the relationship between the detection accuracy of the sensor 100 and the inclination angle θ of the pair of individualized portions 75a and 75b constituting each detected portion 75. As can be seen from FIG. 9, the greater the inclination angle of the individualized portions 75a and 75b, the wider (deteriorates) the displacement detection accuracy. In other words, if the inclination angle of the individualized portions 75a and 75b is small (the cross-section is open), a large sensor signal change can be produced even if the axial displacement is small, so that the possible detection accuracy of the displacement is increased. On the other hand, if the individualized portions 75a and 75b have a large inclination angle (the cross-section is closed), even if the axial displacement is large, only a small change in the sensor signal can be generated. Become.

  Here, the encoder 72 having an outer diameter of φ80 mm having the 5 to 13 sets of the detected portions 75 described above has individualized portions 75a and 75b as shown in FIG. 9 in order to make the displacement detection accuracy 4 μm or less. It is necessary that the inclination angle θ be 70 ° or less. In order to make the displacement detection accuracy more preferably 3 μm or less, the inclination angle θ of the individualized portions 75a and 75b needs to be 65 ° or less.

  Note that as the outer diameter of the encoder 72 increases, the displacement detection accuracy increases. For this reason, although not shown, for example, in an encoder having 5 to 13 sets of detected portions 75 and having an outer diameter of φ130 mm or less, in order to set the displacement detection accuracy to 4 μm or less, the individualized portions 75a and 75b are inclined. The angle θ is preferably 60 ° or less.

  For example, in the spindle apparatus as an embodiment, the inner diameter of the angular bearings 21 to 24 is φ70 mm, the outer diameter of the encoder 72 between the angular ball bearings 22 and 23 is φ80 mm (diameter thickness 5 mm), The number of sets is 5, and the inclination angle θ of each individualized portion 75a, 75b is 45 °. Further, an error in the axial relative position between the center position of the encoder 72 in the width direction and the center position of the sensor 100 obtained by stacking parts by general finishing is ± 2 mm with respect to the reference set position.

  In such a spindle apparatus, the detection accuracy (detection sensitivity) is 1.5 μm from FIG. 9, and the actual axial relative position error ± 2 mm is the axial relative position range ± 3 given from FIG. 8. Since it is .6 mm or less, the function as a detection device can be satisfied.

  The present invention is not limited to the above-described embodiments, and modifications, improvements, and the like can be made as appropriate. In addition, the material, shape, dimensions, number, arrangement location, and the like of each component in the above-described embodiment are arbitrary and are not limited as long as the present invention can be achieved.

DESCRIPTION OF SYMBOLS 3 Cutting tool 3a Cutting part 10 Spindle apparatus 11 Spindle 72 Encoder 50 Housing 75 Detected part 75a, 75b Individualization part (distance changing part)
100 sensor 105 Hall IC (detector)
105a, 105b Magnetic detection element 107 Permanent magnet

Claims (2)

A non-rotating housing,
A main shaft rotatably supported on the housing by a rolling bearing provided with a preload in the axial direction;
A cutting tool which is supported and fixed concentrically with the main shaft at the tip of the main shaft, and a plurality of cutting portions are provided at equal intervals in the circumferential direction;
An encoder that rotates integrally with the main shaft and has a detected surface concentric with the main shaft;
A sensor that is supported by the housing in a state in which a detection unit faces the detection surface of the encoder, and outputs a signal according to a change in characteristics of the detection surface;
Arithmetic means for calculating an axial load acting on the spindle based on a pattern in which the output signal of the sensor changes;
In a spindle device of a machine tool equipped with
On the detected surface of the encoder, a plurality of sets of detected portions each formed of a pair of individualized portions having different characteristics from the other portions are formed at equal intervals in the circumferential direction,
Each of the pair of individualized portions is substantially the same in the opposite direction to the axial direction of the encoder so that the interval in the circumferential direction between the pair of individualized portions continuously changes in the axial direction. It is formed in a square shape that is inclined at an angle,
The number m / n obtained by dividing the number m of cutting parts provided in the cutting tool by the number n of detected parts present on the detected surface of the encoder is set to a non-integer, and
A spindle device for a machine tool, wherein an inclination angle at which each individualized portion intersects a line parallel to the circumferential direction is set in a range of 30 ° to 70 °.   2. The spindle device for a machine tool according to claim 1, wherein an inner diameter of the rolling bearing is 40 mm to 120 mm.

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