MACHINING TOOL WITH HIGH PRECISION MACHINING CAPABILITY

Abstract

The invention relates to a machining tool for machining a workpiece, including a main spindle with a driven shank, a tool holder which can be clamped in the shank, a cutting tool which is arranged on the tool holder, a distance sensor for determining a distance of the shank of the main spindle in relation to a reference point, and a control unit which is configured to perform compensation of the tool path during machining of the workpiece based on an elongation and displacement of the shank and an elongation of the tool holder holding the cutting tool, wherein the elongation and displacement of the shank is determined based on the distance determined using the distance sensor, and wherein the elongation of the tool holder holding the cutting tool is determined based on a rotational speed of the shank.

Claims

1. A machining tool for machining a workpiece, comprising: a main spindle with a driven shank, a tool holder which can be clamped into the shank, a cutting tool which is arranged on the tool holder, a distance sensor for determining a distance of the shank of the main spindle to a reference point, and a control unit which is arranged to perform compensation of the tool path when machining the workpiece based on an elongation and displacement of the shank and an elongation of the tool holder with cutting tool, wherein the elongation and displacement of the shank is determined based on the distance determined with the distance sensor, and wherein the elongation of the tool holder by the cutting tool is determined based on a rotational speed of the shank.

2. The machining tool according to claim 1, further comprising a measuring device, in particular a measuring laser, which determines a length of the tool holder using the cutting tool before start of machining, wherein the control unit is configured to determine the elongation and displacement of the shank and the elongation of the tool holder holding the cutting tool based on the value measured using the measuring device.

3. The machining tool according to claim 1, wherein the control unit is configured to determine a temperature of the shank at a clamping point of the tool holder in the main spindle based on distance values of the distance sensor and on the rotational speed of the shank and therefrom to determine the elongation of the tool holder holding the cutting tool and/or wherein the control unit is configured to determine a temperature of the shank based on a speed curve of the shank over time and/or the curve of the distance values of the distance sensor over time and therefrom to determine the elongation of the tool holder using the cutting tool.

4. The machining tool according to claim 1, wherein the control unit is arranged to determine the elongation of the tool holder using the cutting tool based on a first temperature of the tool holder holding the cutting tool prior to the start of machining.

5. The machining tool according to claim 4, wherein the control unit is configured to determine the first temperature of the tool holder with cutting tool prior to start of machining from a holding time of the tool holder with cutting tool in the tool changer ever since the last clamping on the shank main spindle.

6. The machining tool according to claim 4, further comprising a first temperature sensor (11A, 11C) which determines a first temperature of the tool holder with cutting tool prior to start of machining, wherein the control unit is arranged to determine the elongation of the tool holder holding the cutting tool based on the first temperature before start of machining.

7. The machining tool according to claim 6, wherein the first temperature sensor is arranged below the main spindle adjacent to the clamping point of the tool holder in the shank and/or wherein the first temperature sensor is movable below the main spindle near the clamping point of the tool holder in the main spindle for measuring the first temperature of the tool holder clamped on the shank using a travel unit and/or wherein the first temperature sensor is arranged in the tool changer of the machining tool to measure the first temperature of the tool holder using the cutting tool prior to clamping the tool holder onto the shank.

8. The machining tool according to claim 1, further comprising a second temperature sensor, which determines a second temperature of the shank, wherein the control unit is arranged to determine the elongation of the tool holder holding the cutting tool based on the second temperature detected and/or on a course of the second temperature detected over time.

9. The machining tool according to claim 1, further comprising a third temperature sensor which is arranged on a bearing of the shank and which determines a third temperature of the bearing, wherein the control unit is configured to determine a temperature of the shank based on the third temperature of the bearing and/or a course of the third temperature of the bearing over time and therefrom to determine the elongation of the tool holder holding the cutting tool

10. The machining tool according to claim 1, further comprising a fourth temperature sensor, which detects a fourth temperature of a working space of the machining tool, wherein the control unit is configured to determine elongation of the tool holder holding the cutting tool based on the fourth temperature of the working space and/or a course of the fourth temperature of the working space over time.

11. The machining tool according to claim 1, wherein the control unit is configured to determine the elongation of the tool holder holding the cutting tool based on a geometry of the tool holder, and/or wherein the control unit is configured to determine the elongation of the tool holder holding the cutting tool, based on a geometry of the cutting tool.

12. The machining tool according to claim 1, further comprising a fifth temperature sensor, which detects a fifth temperature of the distance sensor and/or a time course of the fifth temperature of the distance sensor, wherein the control unit is configured to determine a temperature of the shank and therefrom the elongation of the tool holder with cutting tool, based on the fifth temperature of the distance sensor.

13. A method for operating a machining tool which comprises a main spindle with a shank, a tool holder which can be clamped into the main spindle and a cutting tool arranged on the tool holder, as well as a distance sensor for determining a distance of the shank of the main spindle from a reference point, wherein, during operation of the machining tool, the elongation and displacement of the shank and the elongation of the tool holder with cutting tool is incorporated to compensate for the tool path during machining of the workpiece, wherein the elongation and displacement of the shank is determined based on distance values of the distance sensor, and wherein the elongation of the tool holder holding the cutting tool is determined based on a rotational speed of the shank.

14. The method according to claim 13, wherein a first temperature of the tool holder holding the cutting tool prior to the start of machining is determined from a holding time of the tool holder with cutting tool in the tool changer since the last clamping on the shank of the main spindle and/or the first temperature of the tool holder with cutting tool prior to the start of machining is determined using a first temperature sensor, and the elongation of the tool holder holding the cutting tool is determined based on the first temperature of the tool holder with cutting tool prior to the start of machining, and/or wherein a second temperature of the shank is determined using a second temperature sensor and the elongation of the tool holder holding the cutting tool is determined based on the second temperature detected and/or is determined from a progression of the second temperature over time, and/or wherein a third temperature of the bearing supporting the shank is determined over time using a third temperature sensor and a temperature of the shank and hence the elongation of the tool holder with cutting tool is determined based on the third temperature of the bearing and/or a temperature progression of the third temperature of the bearing, and/or wherein, based on the values of the distance sensor and the rotational speed of the shank, a temperature of the shank is determined and based on the temperature of the shank determined therefrom, the elongation of the tool holder with cutting tool is determined, and/or wherein, based on the course of the distance values of the distance sensor over time, the elongation of the tool holder holding the cutting tool is determined and/or wherein the elongation of the tool holder with cutting tool is determined over time based on a rotational speed curve of the shank, and/or wherein the elongation of the tool holder holding the cutting tool is determined based on a fourth temperature of a working chamber of the machining tool and/or based on a course of the fourth temperature of the working chamber over time, and/or wherein, based on a fifth temperature of the distance sensor, a temperature of the shank is determined, wherefrom the elongation of the tool holder holding the cutting tool is determined.

15. The method according to claim 13 or 14, wherein for determining the elongation and displacement of the shank and/or the elongation of the tool holder with cutting tool, data history of previous machining operations, in which history the elongation and displacement of the shank and/or the elongation of the tool holder holding the cutting tool were determined, are incorporated.

Description

[0035] Hereinafter, a preferred example embodiment of the invention will be described in detail while reference will be made to the accompanying drawing, wherein:

[0036] FIG. 1 is a schematic, perspective view of a machining tool according to a preferred example embodiment of the invention,

[0037] FIG. 2 is a schematic, perspective view of a tool changer of the machining tool of FIG. 1 with a temperature sensor in a first position,

[0038] FIG. 3 is a schematic, perspective view of the tool changer of FIG. 2 with the temperature sensor in a second position,

[0039] FIG. 4 is a schematic comparative view of the elongation and displacement of a shank and the elongation of a tool holder with cutting tool of the machining tool of FIG. 1,

[0040] FIG. 5 is a schematic lateral view of the main spindle of the machining tool of FIG. 1 during a measuring operation in a measuring device, and

[0041] FIG. 6 is a schematic view of the main spindle with tool holder of the machining tool of FIG. 1.

[0042] In the following, a preferred example embodiment of the invention will be described in detail, while reference will be made to FIGS. 1 to 6.

[0043] As may be seen from FIG. 1, the machining tool 1 for machining a workpiece comprises a main spindle 2 and a tool holder 3, which is clamped into a driven shank 20 (cf. FIG. 6) of the main spindle 2. The tool holder 3 is used for mounting a cutting tool 4, for example a milling cutter, used to machine a workpiece (not shown) on a machining table.

[0044] The machining tool 1, in a working space 9, further comprises a tool changer 15 in which a plurality of tool holders 3 holding cutting tools 4 are arranged and which can provide various tools in a rotating manner. The tool changer may be seen in detail from FIGS. 2 and 3.

[0045] As may further be seen from FIGS. 5 and 6, the machining tool 1 further comprises a distance sensor 5 for determining a distance L of the shank 20 of the main spindle 2 to a reference point. In this example embodiment, the reference point is located directly on a surface of the distance sensor 5.

[0046] The machining tool 1 further comprises a control unit 10. The control unit 10 is configured to perform compensation of the tool path during machining of the workpiece, based on a first elongation and displacement ΔL1 of the shank 20 and a second elongation ΔL2 of the tool holder 3 with cutting tool 4. Thus, by incorporating both elongations and displacements ΔL1 and ΔL2, high-precision machining of a workpiece may be realized.

[0047] The first elongation and displacement ΔL1 of the shank 20 is based on the distance L determined by the distance sensor 5. The second elongation ΔL2 of the tool holder 3 holding the cutting tool 4 is based on a rotational speed of the shank 20. The rotational speed of the shank 20 can be determined by methods known from prior art, e.g. a rotational speed sensor, or rotational speed is a value already known for the control unit 10. It should be noted that basically, the control unit 10 may be a separate control unit or may also be integrated into a main control unit of the machining tool.

[0048] Thus, thermal-induced and speed-induced elongation and displacement of the shank 20 of the main spindle 2 may contactlessly be measured using the distance sensor 5. As may be seen from FIG. 6, the distance sensor 5 is arranged such that a distance L of the shank 20 from a shank end 21 may be determined. The shank end 21 is perpendicular to a center axis X-X of the shank 20.

[0049] The distance sensor 5 is arranged using a holder 7 below the main spindle 2, adjacent to a clamping point 6 of the tool holder 3 in the shank 20.

[0050] The elongation ΔL2 of the tool holder 3 holding the cutting tool 4 is determined based on the rotational speed of the shank 20. This allows the additional second elongation of the tool holder 3 holding cutting tool 4 to be detected in addition to the first elongation and displacement ΔL1 of the shank 20. The second elongation ΔL2 of the tool holder 3 holding the cutting tool 4 is generated by heat conduction from the shank 20 to the tool holder 3, causing the tool holder 3 and the cutting tool 4 to expand in the axial direction. This results in additional displacement of the end of the cutting tool 4, which cannot be detected by the distance sensor 5, since it only detects the axial elongation and displacement of the shank 20 of the main spindle 2. Elongation ΔL2 of the tool holder 3 holding the cutting tool 4 essentially depend on the rotational speed of the shank 20, the rotation also generating a cooling effect by convection at the tool holder 3 holding the cutting tool 4.

[0051] Based on the distance value L and the rotational speed of the shank 20, the control unit 10 can now determine the first and second elongation and displacement ΔL1 and ΔL2, enabling appropriate compensation of the tool path of the cutting tool 4.

[0052] To increase compensation accuracy of the tool path during machining, the machining tool 1 further comprises a first temperature sensor 11A, which, as may be seen from FIG. 6, is arranged below the main spindle 2 adjacent to the clamping point 6 of the tool holder 3 in the shank 20. The first temperature sensor 11A determines a first temperature T1 of the tool holder 3 before start of machining. The control unit is configured to additionally determine the elongation ΔL2 of the tool holder 3 holding the cutting tool 4, based on the first temperature T1. Of course, the first temperature sensor 11A may also continuously determine the first temperature T1 of the tool holder 3 during machining, and the control unit 10 may use the temperature values measured to appropriately compensate the tool path of the cutting tool 4.

[0053] It should be noted that the first temperature sensor 11A may also be movably arranged under the main spindle 2 in the vicinity of the clamping point 6 of the tool holder 3 in the main spindle 2 for measuring the first temperature T1 on a travel unit that is not shown.

[0054] Alternatively or additionally, the machining tool 1 comprises another first temperature sensor 11C in the tool changer 15 (cf. FIGS. 2 and 3) to measure the first temperature T1 of the tool holder 3 holding the cutting tool 4 prior to clamping the tool holder 3 to the shank 20.

[0055] Accuracy of the determination of the second elongation ΔL2 of the tool holder 3 holding the cutting tool 4 can be further improved by detecting additional temperatures. As may be seen from FIG. 6, a second temperature sensor 12 is provided which determines a second temperature T2 of the shank 20, wherein the control unit 10 is configured to additionally or alternatively determine the second elongation ΔL2 of the tool holder 3 with cutting tool 4 based on the detected second temperature T2. Thus, the elongation ΔL2 of the tool holder 3 with cutting tool 4 can be determined more precisely based on the rotational speed and the second temperature T2.

[0056] As may be seen from FIG. 6, a third temperature sensor 13 is arranged on a bearing 22 for supporting the shank 20. The third temperature sensor 13 detects a third temperature T3 of the bearing 22, wherein the control unit 10 is configured to additionally or alternatively determine a temperature of the shank 20 and therefrom an elongation ΔL2 of the tool holder 3 with cutting tool 4 based on the third temperature T3. Thus, the accuracy of the elongation of the tool holder 3 with cutting tool 4 may even further be improved.

[0057] As can be seen from FIG. 1, a fourth temperature sensor 14 is provided, which detects a fourth temperature T4 of the working space 9 of the machining tool 1. The control unit 10 is configured to additionally or alternatively determine the second elongation ΔL2 of the tool holder 3 with cutting tool 4 based on the fourth temperature T4 of the working space 9. This may further improve accuracy in compensating the tool path.

[0058] A fifth temperature sensor 15 is integrated into the distance sensor 5. The fifth temperature sensor 15 detects a fifth temperature T5 of the distance sensor 5, wherein the control unit 10 is configured to determine the elongation ΔL2 of the tool holder 3 holding the cutting tool 4 additionally or alternatively on the fifth temperature T5.

[0059] With respect to the first to fifth temperatures detected, it should be noted that the control unit 10 is configured to determine both the absolute values of the detected temperatures and additionally or alternatively, the temperature curves over time for determining the second elongation ΔL2 of the tool holder 3 with cutting tool 4.

[0060] Furthermore, the control unit 10 is arranged for processing data history input variables and to determine the first and second elongation and displacement of the shank 20 and the tool holder 3 with cutting tool 4.

[0061] Thus, the first elongation and displacement ΔL1 of the shank 20 can be determined based on distance values L of the distance sensor 5 and the second elongation ΔL2 of the tool holder 3 with cutting tool 4 can be determined based on a rotational speed of the shank 20 and, in this embodiment example, additionally or alternatively based on the first to fifth temperatures T1, T2, T3, T4 and T5. In this way, in particular the second elongation ΔL2 of the tool holder 3 with cutting tool 4 can be determined with high precision and incorporated into the machining process.

[0062] FIG. 4 schematically shows the first and second elongation and displacement ΔL1 and ΔL2 of the shank 20 and the tool holder 3 with cutting tool 4. The left-hand illustration shows the main spindle 2 holding the tool holder 3 and the cutting tool 4, for which no elongation and displacement due to thermal and speed effects has yet occurred. The right-hand illustration schematically shows a first elongation and displacement ΔL1 of the shank 20 and a second elongation ΔL2 of the tool holder 3 with cutting tool 4. The total of the first and second elongations and displacements ΔL1 plus ΔL2 results in total elongation and displacement of the shank 20 and the tool holder 3 with cutting tool 4 in the axial direction X-X.

LIST OF REFERENCE NUMBERS

[0063] 1 Machining tool
2 Main spindle
3 Tool holder
4 Cutting tool
5 Distance sensor
6 Clamping point of the tool holder in the main spindle
7 Tool holder
8 Measuring device
9 Working area
10 Control unit
11 First temperature sensor
11A First temperature sensor below main spindle
11C First temperature sensor in tool changer
12 Second temperature sensor
13 Third temperature sensor
14 Fourth temperature sensor
15 Fifth temperature sensor
16 Tool changer

20 Shank

21 Shank end

22 Bearing

[0064] L Distance shank-reference measuring point
ΔL1 Elongation and displacement of the shank
ΔL2 Elongation of tool holder with cutting tool
T1 through T5 First through fifth temperature
X-X Rotational axis
Z Vertical direction