Machine tool unit with a tool sensor for sensing the loading of a tool

Abstract

The invention proposes a machine tool unit which is driven by motor with a stator unit (2) and a rotor unit (3) which has at least one rotor shaft (105) and is rotatable about a rotational axis (D), wherein the rotor unit (3) comprises at least one tool holder unit with a tool clamping device for fixing and bracing a releasably fixable tool shank of a tool (50), wherein at least one tool sensor (5) for sensing the loading of the tool (50) is provided, wherein at least one electromagnetic drive system is provided, which machine tool unit has improved accuracy and / or by way of which machine tool unit the precision of the machining using the corresponding machine tool can be improved. According to the invention, this is achieved by virtue of the fact that at least one weakening structure (30) is provided between the tool sensor (5) and the rotational axis (D), in order to increase a mechanical deflection in the case of loading of the tool (50) and / or in the case of a changed load situation of the rotor unit (3) or parts thereof.

Description

[0001] "Machine tool unit with a tool sensor for detecting the load on a tool"

[0002] The invention relates to a motor-driven machine tool unit, such as a multi-axis rotary head or a motor spindle, according to the preamble of claim 1.

[0003] State of the art

[0004] Machine tools have various interchangeable devices or tools that are connected to the machine tool via standardized interfaces. These are primarily tools that are connected to the machine tool spindle or motor spindle via a detachable conical connection, and in which so-called collets are opened and closed by an axial movement so that the axial force required to securely fasten the tool can be transferred to the tool or later released again.

[0005] EP 1 889 685 B1 discloses a machine tool in which the surface contour of the peripheral surface of the spindle head is examined using a dial gauge to determine whether any deformation is present. Such deformation is then attributed to, among other things, a foreign body, such as a chip, becoming trapped in the area between the outer surface of the tool and the inner surface of the tool holder. However, this is no longer sufficient given the ever-increasing demands on accuracy and reliability in machine tools.

[0006] Object and advantages of the invention

[0007] The object of the invention is to propose a motor-driven machine tool unit which has improved accuracy and / or with which the precision of machining by the corresponding machine tool can be improved.

[0008] This object is achieved by the features of claim 1, starting from a machine tool unit of the type mentioned in the introduction. Advantageous embodiments and developments of the invention are possible through the measures mentioned in the subclaims. Accordingly, a machine tool unit according to the invention is characterized in that at least one weakening structure is provided between the tool sensor and the axis of rotation in order to increase and / or dampen less a mechanical deflection when the tool is loaded and / or when the load situation of the rotor unit or parts thereof changes.

[0009] With the help of this attenuation structure it is achieved that the sensitivity of the sensor is improved and thus better results and a higher accuracy is achieved. This has a positive effect on the precision of the machine tool. In this case, the term "sensor" refers to the sensor and the sensor element to be sensed or detected. Due to the advantageous stronger deformation of the sensor element or changes in the sensor surface to be sensed and / or the distance of the sensor element to be detected.

[0010] The sensor technology is therefore significantly improved, even though the "actual" sensor is (usually) not changed / improved.

[0011] Advantageously, the weakening structure is designed as a projection of the tool sensor and / or a sensor element of the tool sensor. This advantageously weakens a sensor element of the tool sensor, whereby the deflection or deformation of the sensor element or the projection is less damped and correspondingly increased under corresponding loading or a changed load situation. This advantageously increases the sensitivity of the sensor system.

[0012] In an advantageous variant of the invention, the weakened structure is designed as a recess in the rotor unit and / or the rotor shaft and / or as a recess in the tool holder unit. This recess weakens the stability of the corresponding component, so that greater deformation or greater accuracy of the sensor system is achieved. Advantageously, the recess is formed on a radially outwardly oriented surface of the rotor unit and / or rotor shaft and / or tool holder unit and / or the recess is formed on a radially inwardly oriented surface of the rotor unit and / or rotor shaft and / or tool holder unit. In this way, the recess can be advantageously produced, so that the manufacturing effort and / or cost expenditure is reduced.For example, viewed in the radial direction, the weakening structure and / or the recess are arranged between the tool sensor and the tool holder unit and / or, viewed in the radial direction, the weakening structure and / or the recess are arranged between the tool sensor and the rotation axis. Initial tests have shown that the weakening in this area has a very positive effect on the measurable deformation and, as a result, increased sensor accuracy.

[0013] Advantageously, viewed in the axial direction, the weakened structure and / or the recess are arranged between the tool sensor and the first rolling bearing and / or, viewed in the axial direction, the weakened structure and / or the recess are arranged between the tool holder unit and the first rolling bearing. Here, too, the weakening has a positive effect on the achievable accuracy.

[0014] In a particular development of the invention, the recess is formed as a cavity within the rotor unit and, in particular, is completely surrounded by material and / or components of the rotor unit. For example, the weakening structure and / or the recess comprises at least air. This allows the recess to be advantageously realized, thus reducing the manufacturing effort and / or costs.

[0015] The weakened structure advantageously comprises at least one plastic. Alternatively or in combination with this, it comprises at least one metal. In particular, the weakened structure is not made of steel, but rather of copper, aluminum, corresponding alloys or the like. This can also advantageously increase the sensitivity and is also cost-effective to manufacture. The rotor unit rotating relative to the stator unit usually belongs to a motor spindle drive. The actual cutting tool (milling cutter, drill, etc.) is usually held or clamped in a tool holder, which in turn is arranged in a tool clamping device, which is to be regarded as part of the spindle head of the rotor unit. For this purpose, the tool clamping device has a holder for a tool holder.The tool clamping device is typically subjected to a clamping force and adjusted in the longitudinal direction of the rotational axis. Part of the clamping device can be drawn into a tapered recess, for example, so that the tool holder or the tool can be clamped, among other things, with a radially acting force. By releasing the clamping force, the clamped tool can usually be released again, and it can be removed from the machine tool or replaced.

[0016] The actual sensor is usually housed in a so-called sensor head; the sensor measures its distance from the rotor unit and / or a sensor element, with the sensor, or the majority of the sensor, usually being arranged accordingly in the stator unit. The sensor data are advantageously processed or evaluated using an electronic unit or evaluation electronics, which may be computer-controlled.

[0017] The at least one sensor head is usually arranged on the stator unit at a fixed position in the area of ​​the tool clamping device and can measure / detect both on the front side of the rotating spindle head of the rotor unit and / or laterally, i.e. usually the so-called sensor element. Sensors or sensor heads can also be arranged in a variable position. As a rule, for example, a chip clamped between the tool and the tool clamping device / spindle / rotor unit means that the tool no longer runs exactly centrally / straight around the axis of rotation or that the tool clamping device is slightly (also elastically) deformed and unchanged concentricity, unchanged axial runout of the tool or tool holder or turning without change in angle can no longer be guaranteed. A disturbance in the concentricity usually represents a particular impairment of machining.Such displacements and / or deformations generally occur both laterally and at the front / axial side, and are generally detectable there as well. A distance parallel to the rotational axis is measured at the front, and a distance radial to the rotational axis is measured at the side. All such displacements and / or deformations, including displacements of the rotor unit, can be detected in this way. The attenuation structure can improve the accuracy and sensitivity.

[0018] A measurement can generally be carried out at a 90 ° angle to the surface and / or to the axis of rotation of the rotor unit , but also at a different angle .

[0019] Especially with machine tools, high demands are placed on machining accuracy. The tool and thus the cutting edge(s) must usually be inserted and moved in a precisely defined manner in the tool holder or tool clamping device during machining, so that the workpiece to be machined is machined within the specified tolerance limit. Even if the machine tool and in particular the tool clamping device are manufactured with the necessary precision, additional factors come into play when using the machine, which can usually prevent a defined

[0020] Concentricity / axial runout is still maintained or no angular errors occur. For example, during machine operation, chips generated during machining can stick to the tool or jam, preventing the tool from rotating in its actual target position.

[0021] Example from implementation

[0022] An embodiment of the invention is shown in the drawing and is explained in more detail below with reference to the figures.

[0023] In detail:

[0024] Figure 1 is a schematic representation of a first

[0025] Machine tool unit according to the invention,

[0026] Figure 2 schematic representations of three different

[0027] Spindle designs according to the state of the art,

[0028] Figure 3 is a schematic, sectioned section of a

[0029] Motor spindle with radial sensor according to the state of the art Figure 4 a schematic, sectioned section of another motor spindle with axial sensor according to the

[0030] State of the art,

[0031] Figure 5 is a schematic representation of a first

[0032] Sensor unit with a first recess according to the invention,

[0033] Figure 6 is a schematic representation of a second

[0034] Sensor unit with a second recess according to the invention,

[0035] Figure 7 is a schematic representation of a third

[0036] Sensor unit with a third recess according to the invention and

[0037] Figure 8 is a schematic representation of a fourth

[0038] Sensor unit with a first projection according to the invention.

[0039] Figure 1 shows a schematic representation of a section of a machine tool unit 1 with part of a stator unit 2 and part of a rotor unit 3, wherein in Figure 1 primarily a spindle head can be seen as part of the rotor unit 3. The stator unit 2 has, for example, a ring 4, to which, for example, a sensor head or sensor 5 in the form of an axial sensor is attached. The rotor unit 3 comprises, for example, a measuring ring or sensor element 6 made of a metal, which here is advantageously made of a paramagnetic material. The axial sensor or sensor 5 is arranged such that it measures a distance to an end surface of the rotor unit 3. However, a lateral measurement, radial to the axis of rotation D, is also conceivable. This surface, to which the distance is determined, is located on the measuring ring or sensor element 6. The axial sensor or sensor 5 is, for example,designed as an eddy current sensor in order to obtain the most accurate measurements possible despite possible contamination.

[0040] The sensor head / axial sensor or sensor 5 is connected, for example, to an electronic unit 7; both together form a testing device 8, which in turn is connected to a machine control 9, so that, if excessive axial runout errors occur, the control can be intervened in.

[0041] In a special development, for example, only one sensor head or sensor 5 is provided. It is conceivable to additionally use a trigger sensor, e.g. for detecting an optical reference marking on the measuring ring or sensor element 6, wherein such a trigger sensor can also be attached to the sensor ring 4, for example. The marking can also be designed as a groove or the like. With such a trigger sensor, only the initial point for the measurements is triggered so that the phase relationships of the measured values ​​can be determined more easily during evaluation. A trigger sensor is not absolutely necessary and is not shown in more detail in Figure 1. The stator unit 2 comprises, for example, a cover 10 for the sensor ring 4 and also a bearing cover 11. A tool clamping device 12 is attached to the rotor unit 3 (the conical ring is shown in Figure 1).

[0042] Figure 2 schematically shows three different variants of spindles according to the prior art, wherein an electromagnetic drive system 120 is arranged, on the one hand, between a so-called front spindle bearing 121 and a so-called rear spindle bearing 122 (cf. Figure 2a) ), or behind the so-called rear spindle bearing 122 (cf. Figure 2b) ), or by means of a coupling unit 126, again behind the so-called rear spindle bearing 122 (cf. Figure 2c) ). The spindle bearings 121, 122 are provided for supporting the rotatable rotor unit 3 or rotor shaft 105 or spindle shaft 105 .

[0043] Figures 3 and 4 show two further variants according to the prior art, showing a section through a motor spindle 3 of a machine tool. As is common in machine tool construction, one side of a collet 1 with several clamping segments 2 is shown in the unclamped state (part almost not shown) and in the clamped state of the motor spindle 3 or the collet 101 or the spindle head 1.

[0044] A sensor 104 can be seen in the clamped part of the motor spindle 3 shown in Figures 3 and 4. In Figure 3, this sensor 104 has a radially aligned effective range, and in Figure 4, an effective range aligned along the rotational axis D. Accordingly, a radial sensor 104 is shown in Figure 3, and an axial sensor 104 is shown in Figure 4. However, an optionally usable second or third sensor cannot be seen in Figures 3 and 4, since, if used, these would be / are arranged offset in the circumferential direction, in particular by 90° or 180°, etc., and are therefore not visible in the sectional views.

[0045] Changes in the spindle head 1 or due to a load or force applied to a tool or collet 101 (not shown in more detail) directed axially and / or radially in relation to the axis of rotation D, an area X of a spindle shaft 105 or a counter-holder 106 or stop / ring element 106 of the motor spindle 103, shown schematically in Figure 3, is deformed or widened in the radial direction R. In this case, an element 107 of the spindle shaft 105 transmits a clamping force F or displacement and / or deformation, ie change, to the element 106. As a result, a distance A or

[0046] Air gap 109 between the rotor unit or spindle shaft 105 and a stator unit 100 with the radial sensor 104. The state according to the above-mentioned reference measurement in the area X is the target state and a change due to force / changes in the area of ​​the spindle head 1 of the detected actual displacement and / or deformation or the actual state is accordingly advantageously used to check / control the motor spindle or.

[0047] Rotor unit 3 is used.

[0048] In Figure 4, an axially aligned deformation of a measuring arm 111 with the axial sensor 104 or an axial change A in the distance 109 can be detected and further processed. This axial change A is in turn caused by a force / change F on the tool 50 or on / in the spindle head 1 or axial and / or radial deformation / change on the tool 50 or spindle head 1, which is transferred to the tool holder unit 108 and to the element 106 and thus finally to the measuring arm 111 or its detectable sensor surface / distance 109. Various variants according to the invention are shown (partially in section) in Figures 5 to 8. Various weakening structures 30, 31 are present here. A sensor element 6 or. A detectable sensor surface of the sensor element 6, which is spaced apart from the sensor 5, is arranged on / on the measuring ring 106 or, if appropriate, is formed integrally with the measuring ring 106 which is rotatable about the rotation axis D.The measuring ring 106 is fixed with a threaded ring 125, in particular pressed against the front bearing 121 or its inner ring.

[0049] In the variant according to Figure 5, a recess 30 is provided which is designed as a groove of the rotor shaft 105 or spindle shaft 105 and is covered by the measuring ring 106.

[0050] In the variant according to Figure 6, a recess 30 is provided which is designed as a groove of the measuring ring 106 and is realized as an open groove.

[0051] In the variant according to Figure 7, a recess 30 is provided which is designed as a groove of the measuring ring 106 and is covered by the rotor shaft 105 or spindle shaft 105.

[0052] In the variant according to Figure 8, a recess of the measuring ring 106 is provided as a projection 31, on which the sensor element 6 or the detectable sensor surface of the sensor element 6, which is spaced apart from the sensor 5, is arranged.

Claims

Claims 1. A motor-driven machine tool unit, such as a multi-axis rotary head or a motor spindle, with a stator unit (2) and a rotor unit (3) having at least one rotor shaft (105) and rotatable about a rotational axis (D), wherein the rotor unit (3) comprises at least one tool holding unit (101) with a tool clamping device (102), which is adjustable in particular in the longitudinal direction of the rotational axis (D) and can be subjected to a clamping force, for fixing and clamping a releasably fixable tool shank of a tool (50), wherein at least one tool sensor (5) is provided for detecting the load on the tool (50), wherein a distance (109) is provided between the tool sensor (5) and the rotational axis (D), wherein at least one first spindle bearing (121), in particular a front roller bearing, and a second spindle bearing (122), in particular a rear roller bearing, are provided between the rotor unit (3) and the stator unit (2),are provided and wherein, viewed in the axial direction, the tool sensor (5) is arranged between the first spindle bearing (121) and the tool clamping device (101) and / or the tool shank, wherein at least one electromagnetic drive system (120) is provided and, in particular viewed in the axial direction, is arranged between the first spindle bearing (121) and the second spindle bearing (122), characterized in that at least one weakening structure (30, 31) is provided between the tool sensor and the axis of rotation in order to increase a mechanical deflection when the tool (50) is loaded and / or when the load situation of the rotor unit (3) or parts thereof changes.

2. Machine tool unit according to claim 1, characterized in that the weakening structure (30, 31) is designed as Projection (31) of the tool sensor (5) and / or a Sensor element (6) of the tool sensor (5).

3. Machine tool unit according to one of the preceding claims, characterized in that the weakening structure (30, 31) is designed as a recess (30) of the rotor unit (3) and / or the rotor shaft (105).

4. Machine tool unit according to one of the preceding claims, characterized in that the weakening structure (30, 31) is designed as a recess (30) of the tool holding unit (101).

5. Machine tool unit according to one of the preceding claims, characterized in that the recess (30) is formed on a radially outwardly oriented surface of the rotor unit (3) and / or rotor shaft (105) and / or tool holder unit (101).

6. Machine tool unit according to one of the preceding claims, characterized in that the recess (30) is formed on a radially inwardly directed surface of the rotor unit (3) and / or rotor shaft (105) and / or tool holder unit (101).

7. Machine tool unit according to one of the preceding claims, characterized in that, viewed in the radial direction, the weakening structure (30, 31) and / or the recess (30) is arranged between the tool sensor (5) and the tool holding unit (101).

8. Machine tool unit according to one of the preceding claims, characterized in that, viewed in the radial direction, the weakening structure (30, 31) and / or the recess (30) is arranged between the tool sensor (5) and the axis of rotation (D).

9. Machine tool unit according to one of the preceding claims, characterized in that, viewed in the axial direction, the weakening structure (30, 31) and / or the recess (30) is arranged between the tool sensor (5) and the first rolling bearing (121).

10. Machine tool unit according to one of the preceding claims, characterized in that, viewed in the axial direction, the weakening structure (30, 31) and / or the recess (30) is arranged between the tool holding unit (101) and the first rolling bearing (121).

11. Machine tool unit according to one of the preceding claims, characterized in that the recess (30) is designed as a cavity (30) within the rotor unit (3) and in particular is completely surrounded by material and / or components of the rotor unit (3).

12. Machine tool unit according to one of the preceding claims, characterized in that the weakening structure (30, 31) and / or the recess (30) comprises at least air.

13. Machine tool unit according to one of the preceding claims, characterized in that the weakening structure (30, 31) comprises at least one plastic.

14. Machine tool unit according to one of the above Claims, characterized in that the weakening structure (30, 31) comprises at least one metal and / or does not consist of steel.

15. Machine tool with a tool (50) and a Machine tool unit according to one of the preceding claims.

Images