WO1990010192A1

WO1990010192A1 - Process for measuring cutting edges

Info

Publication number: WO1990010192A1
Application number: PCT/EP1990/000278
Authority: WO
Inventors: Herbert Schulz; Andreas Mootz
Original assignee: Herbert Schulz; Andreas Mootz
Priority date: 1989-02-25
Filing date: 1990-02-20
Publication date: 1990-09-07
Also published as: DE3905949A1

Abstract

The cutting edges (2) on the periphery of a rotary milling tool (1) are measured without contact. Each cutting edge (2) interrupts, in a measurement plane (12), the beam path of an optical scanning device (7). The milling tool (1) and the optical scanning device (7) are moved relative to each other. The positions of this advance movement are recorded by a position transducer (6). The coherent light beam generated by the light source (8) of the optical scanning device (7) is focused in the measurement plane (12). The positions determined by the position transducer (6) when the cutting edges (2) interrupt the beam paths are recorded by an evaluation device (16).

Description

Process for measuring cutting edges

The invention relates to a method for the contactless measurement of cutting edges on the circumference of a rotating milling tool, the cutting edges in each case in the measuring plane containing the milling tool axis being detected by the beam path of an optical scanning device consisting of a light source and a photodetector, the optical axis of which is perpendicular to the measuring plane and extends tangentially to the flight circle of the cutting edges, a coherent light beam generated by the light source falling on the active surface of the photodetector.

The measurement of the cutting edges of milling tools is used to determine the concentricity error and the flight circle diameter. The runout of the cutting edges on milling tools is an important factor influencing both the manufacturing accuracy and the economy of the milling process. The consequences of an impermissibly high concentricity error include reduced tool life due to vibrations and different cutting edge loads, an increased load on the machine, in particular its main spindle, dimensional deviations and a reduced surface quality of the workpiece. Static runout errors of the cutting edges already occur with the slowly rotating or stationary milling tool and are caused by a cutting edge offset on the tool as a result of setting errors in adjustable tools or by manufacturing tolerances for monolithic tools and tools with soldered cutting edges.

Dynamic runout errors of the cutting edges only occur at higher speeds of the milling tool and are caused by a bending of the tool due to unbalance and the resulting unbalance forces, which are usually dependent on the rotational frequency. Centrifugal forces in the area of tool clamping, for example, can lead to rotational errors that are dependent on the rotational frequency due to the widening of collets.

Other causes of static or dynamic runout errors can be clamping errors due to tolerances of the tool holder and possibly the tool chuck or contamination in these areas. This cause of error is of particular importance because the clamping errors that occur can change after every tool change. This poses a serious problem when finishing on unattended machine tools. Even concentricity errors of the milling spindle can manifest themselves as dynamic concentricity errors r of the milling tool.

The dynamic concentricity errors, which depend on the rotational frequency of the milling spindle, are of particular importance for high-speed milling spindles, especially for high-speed milling, because the centrifugal forces that occur increase with the square of the rotational frequency. For a complete recording of the concentricity errors that are important for the work result, it is therefore necessary to measure the milling tools in the clamped state and at the operating rotational frequency.

Known methods for the contactless measurement of cutting edges on the circumference of a milling tool, which work with a laser scanner, are not suitable for use on rotating milling tools because of their mode of operation. With these methods, the projection of the cutting edge is measured; however, this changes constantly with the rotation. These laser scanner methods can therefore not be used for measurements on rotating milling tools, especially not at high rotational frequencies.

In a known method of the type mentioned at the beginning (DE-A-34 10 149), the silhouette of the milling cutter tooth located in the measuring plane, which is generated on the window of the photodetector, is imaged on the active surface of the photodetector. Depending on the shading of the photodetector, an analog output signal from the silhouette sensor is generated. The course of this output signal is evaluated. Each cutting edge creates a local maximum in the shadowing of the photodetector

Output waveform. The height difference between the local maxima during a milling cutter revolution is a measure for diameter deviations or concentricity errors of the cutting edges. It is an analog measurement method. The deviation of the flight circle diameter from a previously defined reference dimension is measured here; it is therefore a relative measurement. The distance between the cutting edge and the axis of rotation (ie an absolute dimension) is not determined.

It is therefore the object of the invention to develop a method of the type mentioned at the outset in such a way that it can be used in high-speed milling tools, in particular in the operating rotational frequencies customary in high-speed milling.

This object is achieved in that the light beam is focused in the measuring plane and the light source is imaged on the active surface of the photodetector, that the milling tool and the optical scanning device are moved relative to one another during the measuring process, that this relative movement is detected by a position measuring system, and that the position of the displacement measuring system is detected in an evaluation device if the beam path of the optical scanning device is interrupted.

In contrast to the known method, the cutting edge is not imaged on the active surface of the photodetector; rather, the light beam is focused in the measurement plane, ie the light source is imaged on the active surface of the photodetector. Because of the focusing in the measuring plane, the optical scanning device according to the invention is suitable for forming an optical probe of very small dimensions. This optical button, which is formed by the focused light beam, only serves to determine whether there is a cutting edge at the measuring point or not. As soon as a cutting edge focuses on the measuring plane If the beam path is interrupted, essentially the entire active area of the photodetector is darkened.

In contrast to the known method, in the method according to the invention a largely binary output signal is generated by imaging the light source on the active surface of the photodetector. Since the light beam is focused in the measuring plane in the method according to the invention, the focal point lying in the measuring plane forms a measuring point of very small extent. Since the interruption of the beam path is detected precisely at this focal point, there are only the two states that the light beam is either interrupted or uninterrupted. Therefore, the measuring point forms a switching optical button of very small dimensions.

For this measuring process, it is imperative to carry out a relative movement between the milling tool to be measured and the optical scanning device during the measuring process and to detect this relative movement by means of a position measuring system.

In the known method, the output signal of a reflex sensor is used to determine the local maximum. This reflex sensor is adjusted so that there is a time or angular offset between the output signal of the reflex sensor and that of the silhouette sensor. As a result, there is basically a dependency of the sampling time and - due to the different projections of the cutting edge into the measuring plane - a dependency of the output signal on the rotational frequency of the milling cutter. The use of the known method is therefore for the measurement snow-milling cutter, especially for high-speed milling, not possible.

As a result of the relative feed movement provided according to the invention between the optical scanning device and the milling cutter to be measured, the measuring process is carried out by a position measuring system which detects the positions of this feed movement at specific times. The measuring accuracy is therefore only determined by the accuracy of this position measuring system, which can be chosen to be very high, and does not depend on the rotational frequency of the milling tool.

The dynamic runout errors occurring at the operating rotational frequencies during high-speed milling can thus also be detected.

According to a preferred embodiment of the method according to the invention, it is provided that the rotational frequency of the milling tool is detected by a rotational frequency transmitter and a rotational frequency signal is transmitted to the evaluation device, and that the number of interruptions in the beam path of the optical scanning device per revolution of the milling tool is determined in the evaluation device. This simultaneous determination of the rotational frequency of the milling tool and the link with the number of interruptions in the beam path make it possible not only to measure the cutting edge which projects the most radially in each case, but also the other cutting edges.

In a further development of this inventive idea, it is provided that when the optical scanning device approaches the milling tool, the positions of the position measuring system when a occurs for the first time Interruption of the beam path and at the time when the number of interruptions per revolution of the milling tool is equal to the number of cutting edges of the milling tool, and that the distance between these two positions is determined in the evaluation device as a measure of the concentricity error of the milling tool.

According to another advantageous embodiment of the concept of the invention, it is provided that the optical scanning device and the milling tool are moved relative to one another over its diameter, that the positions of the position measuring system are detected when the beam path is interrupted for the first and last time, and that in the evaluation device the The distance between these two positions is determined as a measure of the flight circle diameter of the milling tool. .

Exemplary embodiments of the invention are explained in more detail below with reference to the drawing. It shows:

Fig. 1 in a highly simplified representation, a device for non-contact measurement of cutting edges on the circumference of a rotating milling tool and

FIG. 2 shows a simplified overview of the signal processing in the device according to FIG. 1.

A milling tool 1 has a plurality of cutting edges 2 to be measured on its circumference. The milling tool 1 is received on a milling spindle 3, which is mounted in a machine slide 4 and is driven at its operating rotational frequency. The machine slide 4 can be moved in a feed direction indicated by an arrow 5. This feed movement is detected by a position measuring system 6.

An optical scanning device 7, which is constructed in the manner of a light barrier, consists of a light source 8 which emits coherent light. The beam 9 emitted by the light source 8 falls parallel to an optical axis 10 of the scanning device 7 into a focusing lens 11 and is focused by the latter in a measuring plane 12 and produces an image of the light source 8 on the active surface of a photodetector 13.

The feed movement of the milling tool 1 takes place in the measuring plane 12, in which the milling cutter axis 14 of the milling tool 1 also lies. The milling tool 1 is moved in the common normal direction of the milling tool axis 14 and the optical axis 10.

In the exemplary embodiment shown in FIG. 1, the relative movement of the milling tool 1 to the optical scanning device 7 takes place by the displacement of the tool carriage 4 in which the milling tool 1 is mounted. For this, the already existing feed drive of the machine slide 4 and its position measuring system are used.

Instead, it is also possible to move the optical scanning device 7 relative to the milling tool axis 14 by means of a separate feed device and a displacement measuring system. A rotary frequency transmitter 15 connected to the milling spindle 3 supplies a rotary frequency signal to an evaluation device 16, to which the output signals of the photodetector 13 are also fed. The path signals of the path measuring system 16 are also supplied to the evaluation device 16.

Details of the signal processing can be found in FIG. 2.

The output signals of the photodetector 13, which are only schematically shown in FIG. 2, are amplified in a transmitter 17 and converted into a binary signal 18 by means of a comparator circuit. The state of this binary signal 18 (0 or 1) indicates whether the light beam in the optical scanning device 7 in the measuring plane 12 has been interrupted by a cutting edge 2 or not.

The rotary frequency transmitter 19 generates a binary signal 21 at a frequency which is equal to the rotary frequency of the milling tool 1 to be measured via a measuring transducer 20.

A pulse counter 22, to which the binary signal 18 is fed, is a binary counter with a number of digits of 8 bits. The pulse counter 22 is rotating, i.e. after reaching the highest count of 25, the next pulse of signal 21 causes a transition to the value 0.

A holding register 23 is used to scan the counter reading of the pulse counter 22 synchronously with the rotational frequency of the milling tool 1. The counter reading of the pulse counter 22 is for this purpose with the (arbitrarily determined) active edge of the signal 21 in the holding register 23 and held there until the next active edge of the signal 21.

A microcomputer 24, to which the signals 18 and 21 and the output signal of the holding register 23 are supplied, represents a conventional microprocessor system, consisting of a microprocessor, a read-only memory (ROM) for program storage, and a read-write memory Memory (RAM), a programmable parallel interface module (VIA) and some auxiliary circuits such as clock generator, power drivers and the like.

A display unit 25 is connected to an output of the microcomputer 24 and serves to display the state of the signal 18, to output the determined number of cutting edges 2 engaging in the light beam and to signal system states (ready and error messages).

The measurement of the concentricity of the cutting edges 2 of the milling tool 1 takes place as follows. By moving the machine slide 4, the milling tool 1 to be measured, driven at its operating rotational frequency, and the optical scanning device 7 are positioned relative to one another such that the light beam emitted by the light source 8 reaches the photodetector 13 and is not interrupted by a cutting edge 2 of the milling tool 1. This is recognized by the downstream evaluation unit 16 and displayed.

By means of the feed device for the machine slide 4, the milling tool 1 and the optical scanning device 7 are moved towards one another until at least one cutting it 2 penetrates into the light beam and interrupts it periodically (due to the rotation of the milling tool 1). This leads to a periodic change in the output signal 18 of the photodetector 13. In the connected processing device 16, the counter reading of the pulse counter 22 is transmitted to the microcomputer 24 in synchronism with the rotational frequency of the milling tool 1 via the holding register 23. The microcomputer 24 calculates the difference to the previous counter reading and thus the number of interruptions of the light beam per revolution of the tool. The determined value is displayed on the display device 25. The displacement measuring system 6 delivers a first position in the position in which the beam path in the measuring plane 12 is interrupted for the first time by a cutting edge 2 during the feed movement.

A further feed movement then takes place until the indicated number of interruptions of the light beam per revolution of the milling tool is equal to the number of cutting edges 2 of the milling tool 1. This second position is also detected by the measuring system 6. The path difference between these two positions of the path measuring system 6 is calculated in the scanning device 16; this path difference corresponds to the difference between the largest and the smallest distance between the cutting edges 2 and the milling cutter axis 14 and thus represents the concentricity error of the milling tool 1.

To measure the flight circle diameter of the milling tool 1, the position in which the beam path of the optical path is interrupted for the first time is first determined in the manner already described in the path measuring system 6 Scanning device 7 is carried out by a cutting edge 2. The machine carriage 4 is then moved in the feed direction 5 until the beam path of the optical scanning device 7 is no longer interrupted. The position of the path measuring system 6 when the beam path occurs for the last time is detected. The path difference of these two positions is calculated in the evaluation device 16; it corresponds to the flight circle diameter of the milling tool 1.

The determination of the rotational frequency of the milling tool 1 by the separate rotational frequency transmitter 15 can be omitted if the rotational frequency of the milling tool 1 is exactly detected by the control of the machine tool during the measurement and / or a signal corresponding to the signal 21 is available at another point in the control, that can be used accordingly.

In the description of the exemplary embodiment shown, it was assumed that the optical axis 10 of the optical scanning device 7, the milling cutter axis 3 and the measuring axis connecting them, in which the feed movement 5 takes place, are perpendicular to one another. Deviations from this vertical arrangement create a systematic measurement error; however, this can be corrected by calculation so that such deviations can also be permitted. It is important, however, that the optical axis 10 of the optical scanning device 7 intersects the measuring plane 12 spanned by the cutter axis of rotation 3 and the adjusting axis determined by the feed movement 5 at the focal point of the beam path.

Claims

Process for measuring cutting edges

1. A method for non-contact measurement of cutting edges on the circumference of a rotating milling tool, the cutting edges in each case in the measuring plane containing the milling tool axis being detected by the beam path of an optical scanning device consisting of a light source and a photodetector, the optical axis of which is perpendicular to the measuring plane and tangential to Flight circle of the cutting edges runs, a coherent light beam generated by the light source falling on the active surface of the photodetector, characterized in that the light beam focuses in the measuring plane (12) and the light source (8) is imaged on the active surface of the photodetector (13) that the milling tool (1) and the optical scanning device (7) are moved relative to one another during the measuring process, that this relative movement is detected by a displacement measuring system (6), and that the position of the displacement measuring system (6 ) with an interruption echo of the beam path of the optical scanner (7) is detected.

2. The method according to claim 1, characterized in that the relative movement of the milling tool (1) and the optical scanning device (7) in the common normal direction of the milling tool axis (14) and the optical axis (10).

3. The method according to claim 1, characterized in that the rotational frequency of the milling tool (1) is detected by a rotational frequency transmitter (15) and a rotational frequency signal is transmitted to the evaluation device (16), and that in the evaluation device (16) the number of interrupts the beam path of the optical scanning device per revolution of the milling tool (1) is determined.

4. The method according to claims 1 and 3, characterized gekenn¬ characterized in that when approaching the optical Abtasteinrich¬ device (7) to the milling tool (1), the positions of the measuring system (6) detected when an interruption of the beam path occurs for the first time and at the time if the number of interruptions per revolution of the milling tool (1) is equal to the number of cutting edges of the milling tool, and that the distance between these two positions is determined in the evaluation device (16) as a measure of the concentricity error of the milling tool (1).

5. The method according to claim 1, characterized in that the optical scanning device (7) and the milling tool (1) are moved relative to each other over the diameter thereof, that the positions of the displacement measuring system (6) when the beam path is interrupted for the first and last time are detected, and that in the evaluation device (16) the distance between these two positions is determined as a measure of the flight circle diameter of the milling tool (1).