JP2014000662A - Tool tip position correction device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tool tip position correction device capable of correcting a tip position of a tool fitted to a main shaft with high precision.SOLUTION: A displacement measurement part 21 measures displacement δa based upon elongation of a main shaft 12 due to heat generation accompanying rotation of the main shaft 12 from a main shaft reference position Ps to a tool reference position Pt by receiving a detection signal from a sensor 142 of a displacement measurement device 14. A displacement calculation part 23 calculates displacement δb based upon elongation and centrifugal expansion of a tool holder H due to heat generation from the rotational frequency of the main shaft 12, the length and diameter of the tool holder H and a relational expression stored in a storage part 22. A correction quantity calculation part 24 calculates the sum δa+δb of the displacement δa, measured by the displacement measurement part 21, based upon the elongation of a main shaft 12 due to the heat generation accompanying the rotation of the main shaft 12 and the displacement δb, calculated by the displacement calculation part 23, based upon the elongation and centrifugal expansion of the tool holder H due to the heat generation as the correction quantity of a tip position of a rotary tool with respect to the main shaft reference position Ps.

Description

  The present invention relates to an apparatus for correcting the tip position of a tool held by a tool holder attached to a main shaft.

  For example, Patent Document 1 describes a method of correcting the tip position of a tool that is generated when a tapered portion of a main shaft to which a tool holder is attached is expanded by centrifugal force accompanying rotation of the main shaft and the tool holder is pulled. . In this correction method, first, a correspondence relationship between the temperature rise value of the tapered portion of the spindle and the amount of the tool holder retracted is obtained in advance. Next, the temperature rise value of the taper portion of the spindle is calculated, and the amount of the tool holder retracted is calculated from the above correspondence. Then, the position command value of the tool tip is corrected by the calculated tool holder pull-in amount.

  Patent Document 2 describes a method for correcting the tip position of a tool attached to a main shaft. In this correction method, first, the change with time of the displacement of the tool tip when the main shaft is rotated and stopped at the maximum number of rotations is actually measured. Next, based on this measured value, the displacement of the tool tip at the time of starting and stopping the rotation of the spindle is expressed by a function that represents the displacement based on the extension due to heat generation of the spindle and the like, and a function that represents the displacement based on the drawing of the tool holder. Represent. In actual machining, the position command value of the tool tip is corrected by multiplying each function by the correction coefficient with respect to the rotation speed of the spindle.

JP 2010-172981 A JP 2007-7752 A

  In the tool tip position correction method described in Patent Document 1, only the displacement based on the pull-in of the tool holder is corrected, and the displacement based on the extension due to heat generation of the spindle or the like is not corrected, so the tip position of the tool attached to the spindle is not corrected. There is a risk that an error will occur in the correction. On the other hand, in the tool tip position correction method described in Patent Document 2, the displacement based on the extension due to heat generation of the spindle and the like and the displacement based on the pull-in of the tool holder are corrected. However, the accuracy of correction is improved. However, in general, the tool holder extends in the radial direction and contracts in the axial direction due to centrifugal expansion accompanying the rotation of the main shaft, but since the displacement based on the centrifugal expansion is not considered, the tip position of the tool attached to the main shaft is not considered. There is a risk that an error will occur in the correction.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a tool tip position correcting device that can highly accurately correct the tip position of a tool attached to a spindle.

  (Claim 1) A tool tip position correcting device according to the present invention measures a spindle driven to rotate by holding a rotary tool via a tool holder, and a displacement of a reference position of the tool holder with respect to a reference position of the spindle. Based on the displacement measuring means, the storage means for storing the relational expression representing the displacement of the tool holder accompanying the rotation of the spindle, the rotational speed of the spindle and the relational expression read from the storage means, Based on the displacement measured by the displacement measuring means, the displacement measured by the displacement measuring means, and the displacement calculated by the displacement calculating means, a correction amount calculation for calculating the correction amount of the tip position of the tool relative to the reference position of the spindle Means.

  (Claim 2) The tool holder may be a two-sided restraint type.

  (Claim 3) The storage means may store the relational expression for each type of the tool holder.

  (Claim 1) Thereby, the displacement based on the extension due to the heat generation of the spindle is corrected by actual measurement, and the displacement based on the extension and the centrifugal expansion due to the heat generation of the tool holder is corrected and expressed as a function. Can be corrected with high accuracy, and the processing accuracy can be improved.

  (Claim 2) Thereby, the tool holder is not pulled in, and the displacement factor of the tool holder is only the elastic element, so that the position command value of the tool tip can be corrected with higher accuracy.

  (Claim 3) Since the tool holder has various shapes depending on the tool, the machining accuracy of the workpiece can be improved in machining using a plurality of tools.

1 is a schematic longitudinal sectional view of a main part of a spindle device provided with a tool tip position correcting device. 1 is a schematic block diagram of a tool tip position correction apparatus. It is a flowchart for demonstrating operation | movement of a tool front-end | tip position correction apparatus. It is a figure which shows the time-dependent change of the displacement of a tool holder accompanying rotation of a main axis | shaft. It is a figure which shows the example of a shape of the tool holder from which a kind differs.

(1. Machine configuration of spindle device)
As an example of a spindle device provided with a tool tip position correcting device according to the present embodiment, a spindle device provided in a machine tool such as a machining center will be described as an example and described with reference to FIG. In FIG. 1, only the front side portion on the rotary tool T side of the spindle reference position Ps (position serving as a reference when measuring the displacement of the spindle 12) in the spindle device 1 is shown. The spindle device 1 includes a substantially cylindrical spindle housing 11 having an accommodation space 111 on an inner periphery, a spindle 12 disposed in the accommodation space 111, and two pairs of second bearings that support the front side portion of the spindle 12. The first and second front rolling bearings 131 and 132, the displacement measuring device 14 for measuring the thermal displacement of the main shaft 12, and the rotational control of the main shaft 12 and the position control of the rotary tool T by correcting the tip position of the rotary tool T described later. And a control device 15 or the like. Note that the rear side portion of the main shaft 12 is supported by a pair of rear rolling bearings (not shown).

  A rod hole 121 extending in the axial direction in which the rod 16 is accommodated is formed at the center of the rotation axis of the main shaft 12. The rod hole 121 penetrates the main shaft 12 in the axial direction, and a tapered portion 122 to which a tool holder H that holds the rotary tool T is attached is formed at the front end. The tool holder H includes a taper sleeve Ha that can be in close contact with the taper portion 122, a pull stud Hb that protrudes in the axial direction from the rear portion of the taper sleeve Ha, a flange Hc that is provided at the front portion of the taper sleeve Ha, and a flange. A tool gripping portion Hd and the like provided at the front portion of Hc are formed. The tool holder H is a so-called two-faced holder. That is, by pulling the pull stud Hb to the rear of the main shaft 12, the taper sleeve Ha is in close contact with the taper portion 122, and the rear end surface portion of the flange Hc is in close contact with the front end surface portion of the main shaft 12 and is restrained on two surfaces.

  The rod 16 is accommodated in the rod hole 121 so as to be movable in the axial direction. A collet 161 is attached to the front end of the rod 16. The collet 161 is provided so as to be able to expand and contract in the radial direction, and is formed so as to be able to grip the pull stud Hb of the tool holder H. The rod 16 is always urged backward with respect to the main shaft 12 by a spring (not shown). A hydraulic cylinder (not shown) is provided behind the main shaft 12. When the piston of the hydraulic cylinder moves rearward and the engagement between the piston and the rod 16 is released, the rod 16 is retracted relative to the main shaft 12 by the biasing force of the spring, and the taper sleeve Ha of the tool holder H is tapered. Since the rear end surface portion of the flange Hc is in close contact with the front end surface portion of the main shaft 12, the tool holder H is fixed to the main shaft 12. When the piston moves forward and the piston and the rod 16 are engaged, the rod 16 moves forward against the main shaft 12 against the biasing force of the spring, the collet 161 expands in diameter, and the pull stud of the tool holder H Release the grip of Hb.

  The first and second front rolling bearings 131 and 132 are angular contact bearings, are arranged in parallel in the axial direction on the front side in the accommodating space 111, and have predetermined front side portions on the rotary tool T side of the main shaft 12. Positioned and fixed at the axial position. The first and second front rolling bearings 131 and 132 support the front side portion of the main shaft 12 in order to receive a processing load in the radial direction and the axial direction by the rotary tool T and to receive a load on the main shaft 12 at the maximum rotation.

  The displacement measuring device 14 includes a bar 141 made of a material having a low thermal expansion coefficient, a sensor 142 attached to the bar 141, and the like. One end of the bar 141 is fixed to the main shaft reference position Ps so that the bar 141 is disposed in parallel with the axis of the main shaft 12 and extends in the front side direction of the main shaft 12. The sensor 142 is, for example, an eddy current sensor, and the sensor portion at the tip of the sensor 142 has a tool reference position Pt (when measuring the displacement of the tool holder H) of the annular groove 123 provided on the outer periphery of the front end of the main shaft 12. The rear end of the sensor 142 is attached to the free end of the bar 141 so as to be close to the end face serving as a reference position.

  A stator of an electric motor (not shown) is attached to the inner peripheral surface of the rear side portion of the spindle housing 11. A rotor of an electric motor formed on the outer peripheral surface of the main shaft 12 is provided facing the inner side in the radial direction of the stator. When electric power is supplied to the electric motor, the main shaft 12 rotates together with the rotor. The rotational speed of the main shaft 12 is detected by a rotational speed detection device 25 (see FIG. 2).

  The control device 15 controls the electric motor to rotate the main shaft 12 (rotary tool T), and controls the X-axis, Z-axis, Y-axis, B-axis motors and the like of the unillustrated machine tool, The workpiece is machined by relatively moving the rotary tool T around the X, Z, Y, and B axes. The control device 15 includes a tool tip position correcting device 20 that corrects the tip position of the rotary tool T. However, the tool tip position correcting device 20 is not limited to the one provided inside the control device 15, and can also be applied as an external device.

(2. Explanation of tool tip position correction)
Next, correction of the tool tip position by the tool tip position correction device 20 will be described. As described in the problem, when correcting the tool tip position, the displacement based on the extension due to the heat generation of the spindle 12, the displacement based on the pulling of the tool holder H, and the displacement based on the extension due to the heat generation of the tool holder H and the centrifugal expansion. Need to be considered. Among these displacements, the displacement based on the pull-in of the tool holder H can be ignored because a two-surface constrained holder is used in this embodiment.

  The displacement based on the extension due to the heat generation of the main shaft 12 can be obtained by the displacement measuring device 14. That is, by receiving a detection signal from the sensor 142 fixed to the bar 141 made of a material having a low coefficient of thermal expansion, heat is generated from the spindle 12 accompanying the rotation of the spindle 12 from the spindle reference position Ps to the tool reference position Pt. A displacement δa based on the extension can be obtained. Note that the displacement of the rotary tool T itself can be ignored in this embodiment because the length of the rotary tool T is sufficiently shorter than the length of the tool holder H.

The displacement based on the extension and centrifugal expansion due to heat generation of the tool holder H can be obtained by modeling the relationship with the rotation of the main shaft 12. That is, as shown in the actual measurement data in FIG. 4, the displacement δb based on the expansion and centrifugal expansion due to the heat generation of the tool holder H accompanying the rotation of the main shaft 12 decreases due to the centrifugal expansion immediately after the rotation start time ts of the main shaft 12, Thereafter, the temperature rapidly rises due to heat generation, and changes to a constant value after the time te when the rotation of the main shaft 12 reaches a predetermined rotation speed. The relational expression representing the displacement can be expressed as shown in the following expression (1) when the rotational speed of the main shaft 12 is changed stepwise.
δb = f (N, L, R) (A (1-e ^{−1 / t} ) −C) (1)
Here, f (N, L, R) is a function of N, L, R, where N is the number of rotations of the spindle 12, L is the length of the tool holder H, and R is the diameter of the tool holder H. It is. A is a coefficient related to elongation due to heat generation, and C is a coefficient related to centrifugal expansion.

  From the above, the final displacement δ of the main shaft 12 is the displacement δa based on the extension due to the heat generation of the main shaft 12 accompanying the rotation of the main shaft 12 and the displacement based on the expansion and centrifugal expansion due to the heat generation of the tool holder H accompanying the rotation of the main shaft 12. It can be expressed as the sum of δb. The shape of the tool holder H varies depending on the rotary tool T. For example, as shown in FIG. 5, when the tool holders H1 and H2 are compared, the taper sleeve Ha and the pull stud Hb have the same shape, but the diameters and lengths of the rotary tools T1 and T2 are different (r1>). r2, w1> w2), the diameters (d11> d12, d21> d22) and lengths (w11> w12, w21> w22) of the flanges Hc1, Hc2 and the tool gripping portions Hd1, Hd2 are different shapes. Yes. For this reason, by preparing the relational expression (1) for each type of the tool holder H, the machining accuracy of the workpiece can be improved in machining using the plurality of rotary tools T.

(3. Configuration of tool tip position correction device)
Next, the tool tip position correcting device 20 will be described with reference to FIG. The tool tip position correction device 20 includes a displacement measurement unit 21, a storage unit 22, a displacement calculation unit 23, and a correction amount calculation unit 24. Here, the displacement measuring unit 21, the storage unit 22, the displacement calculating unit 23, and the correction amount calculating unit 24 can be configured by individual hardware, or can be configured by software. You can also.

The displacement measuring unit 21 receives the detection signal from the sensor 142 of the displacement measuring device 14, and thereby the displacement δa based on the extension due to the heat generation of the spindle 12 accompanying the rotation of the spindle 12 from the spindle reference position Ps to the tool reference position Pt. Measure.
The storage unit 22 stores a relational expression (1) representing a displacement based on extension and centrifugal expansion due to heat generation of the tool holder H.

The displacement calculating unit 23 is based on the rotational speed of the main shaft 12, the length and diameter of the tool holder H, and the relational expression stored in the storage unit 22. Is calculated.
The correction amount calculation unit 24 applies the displacement δa based on the extension due to the heat generation of the main shaft 12 due to the rotation of the main shaft 12 measured by the displacement measurement unit 21 and the extension and centrifugal expansion due to the heat generation of the tool holder H calculated by the displacement calculation unit 23. The sum δa + δb of the displacement δb based is calculated as a correction amount for the tip position of the rotary tool T with respect to the spindle reference position Ps.

(4. Processing by tool tip position correction device (control device))
Next, processing by the tool tip position correcting device 20 (control device 15) will be described with reference to FIG. It is assumed that the relational expression (1) representing the displacement of the tool holder H accompanying the rotation of the spindle 12 is obtained in advance and stored in the storage unit 22 of the tool tip position correcting device 20. As shown in FIG. 3, the main shaft 12 is rotated (step S1), and the displacement of the main shaft 12 accompanying the rotation of the main shaft 12 is measured (step S2). Specifically, the control device 15 controls the electric motor to rotate the main shaft 12. Then, the displacement measuring unit 21 of the tool tip position correcting device 20 receives the detection signal from the sensor 142 of the displacement measuring device 14, and calculates the displacement δa of the tool reference position Pt with respect to the spindle reference position Ps based on the extension due to heat generation of the spindle 12. taking measurement.

  Based on the relational expression (1), the displacement of the tool holder H accompanying the rotation of the main shaft 12 is calculated (step S3). Specifically, the displacement calculation unit 23 of the tool tip position correcting device 20 is based on the rotational speed of the spindle 12, the length and diameter of the tool holder H, and the relational expression (1) stored in the storage unit 22. Then, the displacement δb based on the extension and centrifugal expansion due to heat generation of the tool holder H is calculated.

  Then, the correction amount of the tip position of the rotary tool T is calculated based on the displacement of the main shaft 12 and the displacement of the tool holder H accompanying the rotation of the main shaft 12 (step S4). Specifically, the displacement correction amount calculation unit 24 of the tool tip position correction device 20 reads the displacement δa based on the extension due to the heat generation of the main shaft 12 accompanying the rotation of the main shaft 12 from the displacement measurement unit 21, and from the displacement calculation unit 23. A displacement δb based on extension and centrifugal expansion due to heat generation of the tool holder H is read out, and the displacements δa and δb are added and calculated as a correction amount of the tip position of the rotary tool T with respect to the spindle reference position Ps.

  Then, based on the calculated correction amount of the tip position of the rotary tool T, the command value of the tip position of the rotary tool T is corrected (step S5), and the process ends. Specifically, the control device 15 corrects the command value of the tip position of the rotary tool T based on the added displacement δa + δb, and controls the X-axis, Z-axis, Y-axis, B-axis motor, etc. of the machine tool. The workpiece is processed by relatively moving the workpiece and the rotary tool T around the X axis, Z axis, Y axis direction, and B axis.

(5. Effect of tool tip position correction)
As described above, the displacement δa based on the extension due to the heat generation of the main shaft 12 is corrected by actual measurement, and the displacement δb based on the extension due to the heat generation of the tool holder H and the centrifugal expansion is corrected as a function. The position command value can be corrected with high accuracy, and machining accuracy can be improved. In addition, since the two-surface constrained type tool holder H is used, the tool holder H is not pulled in, the displacement factor of the tool holder H is only an elastic element, and the position command value of the tip of the rotary tool T is made more accurate. It can be corrected.

  DESCRIPTION OF SYMBOLS 1 ... Main axis | shaft apparatus, 12 ... Main axis | shaft, 14 ... Displacement measuring apparatus, 15 ... Control apparatus, 20 ... Tool tip position correction apparatus, 21 ... Displacement measurement part, 22 ... Memory | storage part, 23 ... Displacement calculation part, 24 ... Correction amount calculation Part, 25 ... rotational speed detection device, H ... tool holder, T ... rotary tool.

Claims (3)

A spindle driven to rotate by holding a rotary tool via a tool holder;
A displacement measuring means for measuring a displacement of a reference position of the tool holder with respect to a reference position of the spindle;
Storage means for storing a relational expression representing displacement of the tool holder accompanying rotation of the spindle;
Displacement calculating means for calculating the displacement of the tool holder based on the rotational speed of the spindle and the relational expression read from the storage means;
A correction amount calculating means for calculating a correction amount of the tip position of the tool with respect to a reference position of the spindle based on the displacement measured by the displacement measuring means and the displacement calculated by the displacement calculating means;
A tool tip position correcting device.   The tool tip position correcting device according to claim 1, wherein the tool holder is of a two-surface constraining type.   The tool tip position correcting apparatus according to claim 1 or 2, wherein the storage means stores the relational expression for each type of the tool holder.

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