Method for checking the exact alignment and / or position of a tool in a tool holder of a machine tool spindle

Abstract

Method for checking the exact alignment and / or position of a tool (4) in a tool holder (2) of a machine tool spindle (1), comprising the steps: a) Arrangement of the tool (4) in a tool holder (2) of a machine tool spindle (1) on a face surface, b) Identification of the tool (4), c) Measuring a physical quantity according to the position of a pull rod by means of a sensor associated with the pull rod, wherein the pull rod is configured to close and open the tool holder (2) under axial displacement, d) Determining the difference between the value of the measured physical quantity and a setpoint stored in a storage device that is assigned to the identified tool (4), e) Comparison of the determined difference with a predefined tolerance value, and f) Providing relevant information from the comparison regarding the orientation and / or position of the tool (4) in the tool holder (2).

Description

[0001] The invention relates to a method for checking the exact alignment and / or position of a tool in a tool holder of a machine tool spindle.

[0002] During machining, chips can become trapped between the tool assembly and the spindle head. This can lead to tool breakage and / or defective machining of the workpieces. Various methods exist to prevent this. Runout testing with air, such as gap testing, and the evaluation of stress distribution in the spindle head are among the methods used to detect chips trapped between the tool assembly and the spindle head.

[0003] However, these methods can only be implemented on existing machines through hardware and software modifications. This involves high investment costs. Additional components are required for data analysis, which further increases costs.

[0004] Chips trapped between the tool and the tool holder cause runout errors at the cutting edge and deflection of the tool. Furthermore, increased forces from the chips can lead to tool breakage and quality defects in the machined workpiece.

[0005] Retrofitting with alternative systems requires extensive hardware and software changes as well as additional components and is associated with high costs and effort.

[0006] The publication EP 2 495 059 A1 discloses a tool release device for a machine tool spindle comprising a housing, an adjusting shaft for moving a drawbar of the machine tool spindle (the adjusting shaft being axially movably mounted in the housing), a drive unit in the housing for driving the adjusting shaft axially, and a control unit in or outside the housing for controlling the drive unit. Furthermore, the publication discloses a method for commissioning such a tool release device. The publication also discloses a method for operating such a tool release device.

[0007] The present invention is based on the objective of providing a method for checking the exact alignment and / or position of a tool in a tool holder of a machine tool spindle, which enables the exact positioning of a tool in a tool holder of a machine tool spindle in a precise and cost-effective manner.

[0008] The problem is solved according to the invention by a method for checking the exact alignment and / or position of a tool in a tool holder of a machine tool spindle according to claim 1. Advantageous embodiments of the method are shown in dependent claims 2-9.

[0009] A first aspect of the invention is a method for controlling the exact alignment and / or position of a tool in a tool holder of a machine tool spindle, comprising arranging the tool in a tool holder of a machine tool spindle, identifying the tool, measuring a physical quantity corresponding to a position of a drawbar by means of a sensor associated with the drawbar, wherein the drawbar is arranged to close and open the tool holder under axial displacement.Furthermore, the procedure includes determining the difference between the measured physical quantity and a target value stored in a memory unit, which is assigned to the identified tool; comparing the determined difference with a predefined tolerance value; and providing corresponding information from the comparison regarding the orientation and / or position of the tool in the tool holder. The procedure is carried out, in particular, using a Numerical Control Program (NC program). An NC program is a device for controlling machines that reads control commands stored as code on a data carrier and translates them into work or movement sequences. The NC program is stored in a memory unit and executed by an arithmetic unit, whereby both the memory unit and the arithmetic unit can be located in the machine tool spindle.

[0010] A first step of the method according to the invention is an arrangement of the tool in a tool holder of a machine tool spindle on a face contact, in particular on optimal face contact, so that a part of the surface of the tool located in the tool holder rests uniformly on a corresponding surface of the tool holder of the machine tool spindle.

[0011] A second step in the process is the identification of the tool.

[0012] The tool can be identified by recognizing tool-related variables from a tool management system. This identification can be performed via a machining program, in particular an NC machining program, which executes the chip monitoring NC program as a subprogram.

[0013] A third step in the process involves measuring a physical quantity corresponding to the position of a pull rod using a sensor associated with the pull rod. The sensor can be a distance sensor, for example, a capacitive or inductive sensor, or a sensor based on changes in resistance or variable light flux. The pull rod is configured to open and close a tool holder by axial displacement.

[0014] A fourth step of the procedure is to determine the difference between the value of the measured physical quantity and a setpoint stored in a memory device, which is assigned to the identified tool. The setpoints corresponding to the tool can be stored in the form of lookup tables or as empirical functions containing variables that correspond to the identification of the respective tools.

[0015] A fifth step in the procedure is comparing the measured difference with a predefined tolerance value. The tolerance value can be a tool-specific, predefined value corresponding to the measured physical quantity. It can be either a constant value or a variable value defined by an empirical function. If the measured difference exceeds the specified tolerance value, this indicates that the tool holder was not fully closed and / or the tool is not fully seated in the tool holder. If this is the case, it suggests the presence of another object preventing precise seating or positioning, such as chips in or on the holder.

[0016] A sixth step in the process is to provide relevant information from the comparison regarding the orientation and / or position of the tool in the tool holder. This makes it possible to detect whether a foreign object, such as a chip, is present that could cause problems.

[0017] The method according to the invention has the advantage that no additional investments are necessary, since it is a purely NC-programmable solution. Existing machines can be retrofitted with minimal effort, and the implementation of the method is user-friendly.

[0018] The method according to the invention avoids rejects and reduces tooling costs by preventing breakage and reducing tool wear. Additional investment costs can be avoided by retrofitting existing machines. Furthermore, additional investment costs for the purchase of new machines can also be avoided. The method according to the invention leads to increased process reliability, as additional quality assurance measures in the machining process, such as 100% inspections and production downtime, can be avoided. Furthermore, field failures due to faulty component machining can be prevented.

[0019] According to one embodiment of the method, the physical quantity can be measured when the machine tool spindle is stationary. In other words, the measurement is performed when the machine tool spindle is stationary to avoid the interference of "drilling". The measurement can be carried out, in particular, directly after a tool change, and a comparison of the stored target value with the current value can be made before each use of the tool.

[0020] According to another embodiment of the method, the setpoint can be updated depending on the information. For example, if the current value is lower than the setpoint, the current value can be set as the corresponding new setpoint. This allows the monitoring range to be optimally adjusted.

[0021] According to a further embodiment of the method, the identification of the arranged tool can be achieved by querying the system variables of a machine tool and / or the tool management system. The query can be performed indirectly via the currently executed NC machining program, which can execute the NC program used for chip monitoring as a subprogram.

[0022] According to a further embodiment of the method, an offset value can be determined empirically, depending on the temperature of the tool holder, for calculation with the value of the measured physical quantity. The tool temperature can be determined in the following three steps. A first step involves setting a variable in the current tool details as a function of time, namely the time of tool use and the date of the first use of the tool, i.e., when the tool is used for the first time. A second step involves storing information about the last tool use in the tool management system of a machine tool. A third step involves calculating a temperature value associated with a tool usage time that was used in the machine tool spindle prior to the current tool, based on the second step.Based on the three steps mentioned above, the temperature of the current tool is determined. Once the temperature of the currently used tool has been determined, the offset value corresponding to the measured physical quantity can be empirically determined. Determining the offset value corresponding to the physical quantity can be based on previous observations from earlier machining operations and experiments, so that the offset values ​​corresponding to a specific temperature of a specific tool are stored, for example, in the form of a lookup table or a polynomial function. The calculation of the offset value can be performed via the currently executed NC machining program.

[0023] According to another embodiment of the method, the physical quantity measured by the sensor can be an electrical voltage. The sensor can be an inductive sensor designed to measure an induced electrical voltage in mV. This measured induced electrical voltage allows the position of the pull rod to be determined accurately and efficiently.

[0024] According to a further embodiment of the method, the information can include a message if the determined difference is greater than the sum of a threshold value of 80 mV and the offset value determined as a voltage value. In other words, according to the sixth step of the method according to the invention, the information can include a message, for example, in the form of a text file. If the actual value of the physical quantity, which is an electrical voltage value, deviates from a learned value, referred to as the target value in the fourth step of the method according to the invention, by more than the sum of 80 mV and the offset value, the information is generated in the form of an error message, and the machine is stopped before the actual machining process. At the same time, the value, along with the tool name and time stamp, is saved in an "Error" file.

[0025] According to a further embodiment, a new setpoint is automatically acquired for the tool in the tool holder after a tool change due to wear. The tool change corresponds to the initial use of the machining tool. This ensures that a new setpoint is always automatically learned and stored. This is intended to eliminate various disruptive factors, particularly wear of the tool holder / taper and the clamping system. Similarly, a new setpoint can be acquired for the tool in the tool holder after a repair-related replacement of the machine tool spindle. A new setpoint acquisition is performed particularly when the machine tool spindle is stationary to advantageously avoid disturbances caused by the "drill" process.

[0026] The invention is explained below with reference to the embodiment of the invention shown in the accompanying drawing.

[0027] It shows Fig. Figure 1 shows a side sectional view of a machine tool spindle 1 in a tool holder 2 with a positional displacement of a tool (4). The tool holder 2 is designed to accommodate different tools 4; in particular, the tool holder 2 has a recess 3 into which the tool 4 is inserted. The tool 4 comprises an insert section 5, a middle section 6, and a machining section 7, wherein the middle section 6 is arranged along an axis 14 between the insert section 5 and the machining section 7.

[0028] The insert section 5 has a conical structure that is designed to complement the shape of the recess 3 of the tool holder 2, so that the insert section 5 fits optimally into the tool holder 2. In other words, the surface 13 of the insert section 5, which is located in the recess 3 of the tool holder 2, rests evenly against a corresponding surface 16 of the recess 2 of the tool holder 3. In such a case, the tool 4 is positioned in an optimal position 8, which is suitable for efficient machining. The optimal position 8 is shown by the dashed lines.

[0029] The central section 6 has a projection area 10 which is suitable for uniformly and in planar contact a front surface 11 of the projection area 10 against an axial outer surface 12 of the tool holder 2.

[0030] In other words, in the optimal position 8, the surface 13 of the insert section 5 lies uniformly against the surface 16 of the recess 3 of the tool holder 2, while the end face surface 11 of the projection area 10 rests uniformly against an outer surface 12 of the tool holder 2.

[0031] During the machining process, the tool 4 rotates about the axis 14 to perform a machining operation on a workpiece, which is not shown in the figure. During this process, machining chips and / or swarf 9, 15 can be generated by friction between surfaces 11, 13 of the tool 4 that are in contact with the surfaces 12, 16 of the parts of the tool holder 2. A first chip 9 can be located between the surface 13 of the insert section 5 and the surface 16 of the tool holder 3, while a second chip 15 can form between the end face 11 of the projection 10 of the middle section 6 and the outer surface 12 of the tool holder 2. The first chip 9 and / or the second chip 15 can cause the tool 4 to deflect into an inclined position 17, which is Fig. Figure 1 illustrates this. In this case, the axis 14 of the tool 4 is tilted, so that the axis 14 is no longer parallel to the axis of rotation of the tool holder. This leads to uneven rotation of the tool 4, which in turn can lead to breakage of the tool 4. Furthermore, quality defects and workpiece scrap are to be expected.

[0032] Fig.Figure 1 shows that the tool 4 is not positioned in the tool holder 2 with a face contact. The positioned tool 4 is identified by querying the system variables of a machine tool (not shown in the figure) and / or tool management. The physical quantity corresponding to the position of a drawbar is measured by means of a sensor assigned to the drawbar, which is configured to open and close the tool holder 2 under axial displacement. A difference between the value of the measured physical quantity and a target value stored in a memory device, which is assigned to the identified tool 4, is determined. The determined difference is then compared with a predefined tolerance value. The corresponding information regarding the orientation and / or position of the tool 4 in the tool holder 2 is then provided based on this comparison.

[0033] This information enables a machine operator or operating logic to decide whether the tool 4 needs to be removed from the tool holder 2 and cleaned, or not. Reference symbol list 1 machine tool spindle 2 Tool holder 3 recesses 4 tools 5 Operational Section 6 Middle section 7. Processing section 8 Optimal Position 9 First Span 10 Lead area 11 Surface of the protrusion area 12 Outer surface of the tool holder 13 Surface of the operational section 14 axle 15 Second Span 16 Surface of the recess 17 Inclined position

Claims

[1] Method for checking the exact alignment and / or position of a tool (4) in a tool holder (2) of a machine tool spindle (1), comprising the steps: a) Arrangement of the tool (4) in a tool holder (2) of a machine tool spindle (1) on a face surface, b) Identification of the tool (4), c) Measuring a physical quantity according to the position of a pull rod by means of a sensor associated with the pull rod, wherein the pull rod is configured to close and open the tool holder (2) under axial displacement, d) Determining the difference between the value of the measured physical quantity and a setpoint stored in a storage device that is assigned to the identified tool (4), e) Comparison of the determined difference with a predefined tolerance value, and f) Providing relevant information from the comparison regarding the orientation and / or position of the tool (4) in the tool holder (2). [2] Method for checking the exact alignment and / or position of a tool (4) in a tool holder (2) of a machine tool spindle (1) according to claim 1, characterized by , that the physical quantity is measured when the machine tool spindle (1) is at rest. [3] Method for checking the exact alignment and / or position of a tool (4) in a tool holder (4) of a machine tool spindle (1) according to claim 1 or 2, characterized by , that the target value is updated depending on the information. [4] Method for checking the exact alignment and / or position of a tool (4) in a tool holder (3) of a machine tool spindle (1) according to one of the preceding claims, characterized by, that the identification of the ordered tool (2) is carried out by querying the system variables of a machine tool and / or the tool management system. [5] Method for checking the exact alignment and / or position of a tool (4) in a tool holder (2) of a machine tool spindle (1) according to one of the preceding claims, characterized by , that an offset value is empirically determined as a function of the temperature of the tool holder (2), for calculation with the value of the measured physical quantity. [6] Method for checking the exact alignment and / or position of a tool (4) in a tool holder (2) of a machine tool spindle (1) according to one of the preceding claims, characterized by that the physical quantity measured by the sensor is an electrical voltage. [7] Method for checking the exact alignment and / or position of a tool (4) in a tool holder (2) of a machine tool spindle (1) according to claims 5 and 6, characterized by , that the information includes a message if the determined difference is greater than the sum of a threshold value of 80 mV and the offset value determined as a voltage value. [8] Method for checking the exact alignment and / or position of a tool (4) in a tool holder (2) of a machine tool spindle (1) according to one of the preceding claims, characterized by , that after a tool change due to wear, a new target value measurement of the tool (4) arranged in the tool holder (2) takes place. [9] Method for checking the exact alignment and / or position of a tool (4) in a tool holder (3) of a machine tool spindle (1) according to one of the preceding claims, characterized by, that after a repair-related change of the machine tool spindle (1) a new setpoint measurement of the tool (4) arranged in the tool holder (2) takes place.

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