JP2021185490A - Machine tool - Google Patents

Abstract

To suppress power consumption by reducing retry times in frequency hopping.SOLUTION: A wireless measurement system transmits measurement data by a probe 9 connected to a probe station 1 being a movable part to a machine station 2 installed in a fixing part with the use of frequency hopping. The system performs: confirming communication at usable frequencies so as to preliminarily perform determination to allow a priority degree of a frequency with a higher communication success rate to be higher; dividing frequencies into a frequency group using the usable frequencies and a preliminary frequency group in accordance with priority degrees; determining a use frequency from the frequency group using the usable frequencies, so as to transmit measurement data; and replacing a use frequency with a preliminary frequency belonging to the preliminary frequency group when the data is not appropriately received in the machine station 2.SELECTED DRAWING: Figure 1

Description

The present invention mainly relates to an automatically controlled machine tool that automatically controls workpieces (machined objects to be machined, objects to be measured) such as NC (numerical control) machine tools and machining centers.

In recent years, customers' demands for product specifications have been diversified, and in order to meet the diversified demands, there are an increasing number of cases where product specifications differ depending on the destination of the product. At the same time, new models have been added to meet the needs of users, and the number of product types is increasing.

Therefore, there is an urgent need to manufacture small-lot, high-mix models (high-mix low-volume production) without lowering the operating rate by modifying conventional equipment that has been used for low-mix, high-volume production. Therefore, various automatic control type processing machines such as a turning center and a tapping center that automatically control the processing of an object to be machined, such as an NC processing machine and a machining center, are used.

NC processing machines and machining centers are devices that automatically select various tools according to the processing process and automatically attach them to the spindle to perform various types of processing. Then, a machining table for mounting and fixing the work, a spindle head for driving the machining tool mounted at the position of the tool spindle passing through the tool spindle for mounting the tool, and a machining tool mounted on the spindle head. It is equipped with an automatic tool changer (ATC) that can be appropriately selected and attached / detached.

Tool change is performed by an automatic tool change (ATC: auto tool holder change) device. The ATC device automatically takes out the tool holder to which the tool is attached from the tool magazine and automatically attaches it to the spindle. The processing tool is attached to a holder portion whose size, shape, etc. are determined by a predetermined standard so that it can be attached and detached by ATC. In addition, it is desired to measure whether or not the shape of the object to be machined has been machined to a predetermined value during the machining of the workpiece or at the end of the machining process, and instead of using a tool, a probe for dimension measurement is used. Mount.

Probes or sensors for dimensional measurement include length measuring instruments (electric micrometer and optical scale), position detection probes, temperature sensors, vibration sensors, barometric pressure sensors, pressure sensors, humidity sensors, and the like. Then, for example, in the finishing process of a cylinder block, it is required to automatically measure the bore diameter and the diameter of the crankshaft hole after processing to shorten the tact time.

On a machine tool, it is difficult to wire the measurement probe directly to the control device, and the probe for dimension measurement such as a machining center needs to be replaceable, so the battery is on the probe side. The measurement result is transmitted to the control device on the machine tool side by wireless communication. Therefore, in order to perform automatic measurement in a part of the processing process, it is necessary to provide not only the measurement state in which the wireless unit and the measurement unit are operating but also the sleep state in which the wireless unit is not operating. That is, it is necessary not to waste the power consumption of the measuring unit in the time from the operation of the wireless unit to the use of the measuring unit by putting it into the sleep state except for the measuring process.

Since the environment in which the machining center is installed is mainly for processing, there are many obstacles to wireless communication, and it is difficult to transmit and receive data correctly. Therefore, spread spectrum wireless communication is used to enhance resistance to noise. Spread spectrum is a technique that takes a narrowband signal and spreads it over a wider part of the radio frequency band.

There are two types of spread spectrum links: frequency hopping and direct spread. In the frequency hopping method, the signal is diffused by hopping the narrow band signal as a time function. In the direct spreading method, the signal is spread by calculating the signal based on a specific code (diffusion code).

In the frequency hopping method, signals are transmitted every extremely short time (often about 0.1 seconds) and the transmission frequency is changed one after another, so even if noise occurs at a specific frequency, communication is performed at another frequency. It can be corrected by the data. Therefore, since it is possible to select and transmit a frequency with less noise, it has high fault tolerance and is desirable in an environment where a machining center is installed.

As a wireless measurement system for machine tools, a probe is installed on the spindle, which is the moving part of the machine tool, to make it a probe station, and the machine station is installed on a fixed part of the machine tool structure, using spread spectrum links such as frequency hopping. Is known to communicate with. Then, in order to eliminate the interference of transmission from the probe, it is described in Patent Document 1 that when the probe station does not receive the reception confirmation signal in response to the signal, the probe station transmits the signal again.

Further, in a wireless communication device, it is spread spectrum using frequency hopping consisting of a slave unit and a master unit, and some channels used from a plurality of channels are used as channels and the remaining channels are used as spare channels. .. Then, all channels are divided into a plurality of channel groups according to the frequency. It is known that when a defective channel occurs, the spare channel of the channel group to which the generated defective channel does not belong is exchanged with the defective channel among the plurality of channel groups, which is described in Patent Document 2.

Japanese Unexamined Patent Publication No. 2013-101685 Japanese Unexamined Patent Publication No. 2005-311931

In the above-mentioned prior art, in the case described in Patent Document 1, when communication fails at the time of frequency hopping, communication (retry) is performed again using another frequency, so that transmission is performed many times until it succeeds, and communication is performed. It takes time to complete. As the number of transmissions increases by retrying, the power consumption increases and the frequency of battery replacement increases. Therefore, it becomes difficult to shorten the tact time (process work time).

In high-mix low-volume production, a dedicated measuring instrument and its driving device are required for each type of work. Therefore, it is necessary to prepare a large number of dedicated measuring instruments and increase the labor due to the replacement setup every time the product type changes, and the long tact time greatly impairs the characteristics of the machining center that enables high-mix low-volume production. It will be.

Further, when the received data is a position detection signal, the detection position varies. Further, when the received data is measurement data, the amount of change over time cannot be ignored with respect to the variation in communication time, and accurate measurement cannot be performed.

The one described in Patent Document 2 uses a spare channel, and is therefore improved as compared with the one described in Patent Document 1. However, since the channel is simply divided into multiple channel groups according to the frequency level, the selected frequency is good in that the exchanged spare channel does not interfere with other devices, but it is not suitable for the number of retries. It is enough.

An object of the present invention is to solve the above-mentioned problems of the prior art, reduce the number of retries in frequency hopping, and suppress power consumption. Further, even if the measuring probe installed in the movable part of the machine tool moves as the transmitting side, the communication accuracy is kept constant and the time from the start to the completion of the communication is shortened. Further, this makes it possible to automatically perform high-precision measurement of the work during the machining of the work or at the time when the machining process is completed.

In order to achieve the above object, the present invention is a machine tool that transmits measurement data by a probe to a machine station installed in a fixed portion by using frequency hopping by wireless communication, and confirms communication at a frequency that can be used at startup. Is performed to determine that the priority of the frequency whose communication success rate is equal to or higher than the predetermined value is high, and according to the priority, the usable frequency is divided into a frequency group using the usable frequency and a spare frequency group, and the frequency used is described. The group is selected in the order of appearance when there is a frequency in which the success rate of communication exceeds the predetermined value for each area divided by frequency band in the communication confirmation, and the success rate exceeds the predetermined value. If the number of frequencies does not meet the predetermined number, the frequency having the higher success rate is selected from each of the areas, the predetermined number is selected, and the specified number of frequencies is used in total. In the communication confirmation, the priority of the frequency having a high success rate is set high to be a preliminary frequency, and when transmitting the measurement data, the frequency to be used is sequentially determined from the frequency group to be used and the frequency hopping is performed. The used frequency that was not properly received by the machine station is moved to the spare frequency group, and the spare frequency having a high priority is replaced with the used frequency that has not been received. It is a machine tool characterized in that a fixed delay time related to the number of retries is set from the request to the output of received data.
The success rate of communication may be, for example, 90% or more, that is, a success rate of 90% to 100%.

Further, in the above machine tool, it is desirable that the probe is equipped with a battery and transmitted to the machine station by the wireless communication.

Further, in the above machine tool, it is desirable to put it into a sleep state except for the measurement process using the probe.

Further, in the machine tool, when the frequency to be used is determined from the frequency group to be used and the measurement data is transmitted, it is desirable that the probe notifies the machine station of the number of retries transmitted due to the transmission failure. ..

Further, in the above machine tool, it is desirable that the probe can be attached to and detached from the machine tool by an automatic tool changer.

According to the present invention, in a machine tool that transmits using frequency hopping, the priority of the frequency having a high communication success rate is set in advance, and when the measurement data by the probe is transmitted and is not properly received, the frequency to be used is reserved. Since the frequency is replaced with the frequency of, even if the probe installed in the movable part moves, the number of retries can be reduced and the power consumption can be suppressed. As a result, the communication accuracy can be kept constant, and high-precision measurement of the work can be performed during the machining of the work or at the time when the machining process is completed.

Front view showing a machining center according to an embodiment of the present invention. A side view showing a machining center according to an embodiment of the present invention. Explanatory drawing which shows the state of transmission and reception and frequency hopping before the exchange of a frequency by one Embodiment of this invention. Explanatory drawing which shows frequency hopping after exchange of a state of transmission and reception and frequency by one Embodiment of this invention. Flow chart for exchanging frequencies in one embodiment Time chart showing the relationship between conventional transmission / reception and delay time A time chart showing the relationship between transmission / reception and delay time in one embodiment. A time chart showing measurement data and received measurement results in one embodiment and the prior art.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. For example, in the production of automobiles, it is desired to produce a large number of models in small quantities in order to meet the diversifying needs of consumers for automobiles. Under such multi-model low-volume production, it is possible to handle multiple models rather than assembling products on a dedicated line for each model from the viewpoints of production efficiency, total length of the line, cost related to incidental equipment, and line operation rate. It is preferable to assemble the product on a multi-model mixed line.

For example, an automobile engine manufacturing factory has a cylinder block transport line, and in many cases, a plurality of types of cylinder blocks coexist as workpieces in this transport line. As the cylinder block, a cast iron or an aluminum alloy casting is generally used. In the finishing process of the cylinder block, it is required to automatically measure the bore diameter and the diameter of the crankshaft hole after processing to shorten the tact time.

A machining center is a numerically controlled machine tool that performs various machining such as milling, drilling, boring, and screwing without changing the mounting of the work. A large number of cutting tools are stored in the tool magazine. Then, the tools are automatically replaced and machined according to the command of computer numerical control. Therefore, since the main purpose is processing, the environment in which the machining center is installed includes oil mist and dust which are fine particles, and further, dust and chips are present around the work and the spindle.

FIG. 1 is a front view showing the appearance of a machining center provided with a wireless measurement system according to an embodiment of the present invention, and FIG. 2 is a side view. In FIGS. 1 and 2, the work (which becomes an object to be processed at the time of processing and an object to be measured at the time of measurement) 24 is fixed by the fixture 23 in a state of being placed on the upper surface of the movable table 21 of the machining center 20. A spindle head 26 on which a machining tool (for example, a cutting tool) 25 is mounted is arranged above the work 24.

The spindle head 26 mounts the tool 25 at a predetermined position passing through the tool spindle 29 to which the tool 25 is attached, and is controlled to move in the direction of the tool spindle 29. The spindle head 26 includes a mechanism for feeding the tool 25 in the vertical direction and a mechanism for giving a rotational operation in a horizontal plane, and the tool spindle 29 is a rotary shaft on which the tool 25 rotates.

The tool 25 is individually attached to the holder 11 by the automatic tool changer (ATC) 27, and the holder 11 is automatically attached to and detached from the spindle head 26. Further, the automatic tool changer (ATC) 27 uses the arm 17 under the control of the control device 22 to take out the tool 25 from the tool magazine 28 for storing the tool 25 via the holder 11. Further, it is provided with a mechanism for attaching / detaching to / from the spindle head 26 and storing in the tool magazine 28.

Similar to the tool 25, the probe 9 whose work size can be measured is configured to be automatically attached to and detached from the spindle head 26 by the automatic tool changer (ATC) 27 by the control device 22 executing a program. Has been done. That is, the probe 9 which is a measuring unit can be integrally mounted on the holder 11 having a shape and dimensions conforming to the standard of the tool 25. Further, the probe station 1 which is the transmission side of the measurement data is connected to the probe 9. The machine station 2 on the receiving side is fixed to the machining center 20 and connected to the control device 22.

These related to machining such as cutting, measurement of workpiece shape and machining error, such as movement control of the movable table 21 in the X-axis and Y-axis directions, movement control of the spindle head 26 in the Z-axis direction, replacement control of the tool 25, etc. A series of control of the above is performed by executing the machining and measurement programs stored in the control device 22.

The measurement data is transmitted between the probe station 1 and the machine station 2 by a spread spectrum link that sends individual packages of serial binary data, in this example wireless communication using frequency hopping. Since the probe station 1 for measuring moves inside the machining center 20, the positional relationship between the transmitting side and the receiving side changes. Therefore, the communication environment differs depending on the positional relationship such as a place where the number of retries is small or a place where the number of retries is large.

In wireless communication, communication may fail due to multipath or radio wave interference, so the frequency is switched to a frequency of a predetermined pattern on each of the transmitting side and the receiving side, and frequency hopping is performed until a frequency that does not cause communication failure is used. Therefore, transmission may be performed many times until it succeeds, and it may take time to complete the communication.

By selecting the frequency used for frequency hopping, the number of retries is reduced and power consumption is suppressed. Further, even if the transmitting side performing the measurement moves inside the machine tool, the number of retries is kept small, the time from the start to the completion of communication is shortened, and the variation is kept constant.

Communication is confirmed at all frequencies that can be used at the first startup, and the frequency priority is determined so that the frequency with the highest communication success rate has the highest priority. A high communication success rate means that the number of successful communications is better than the number of trials. Specifically, a high communication success rate means a success rate of 90% or more, that is, 90% to 100%. Further, it may be determined so that the frequency having a high received electric field strength at the selected frequency has a high priority.

When actually communicating, a frequency group that uses a frequency with a high priority and a frequency with a lower priority are classified as a spare frequency group. FIG. 3 is an explanatory diagram showing a state of transmission / reception and frequency hopping performed between the probe station 1 and the machine station 2, and is a state before the frequency is exchanged. The frequency group used for communication indicates f1 to fn (example: n = 20), and the spare frequency group indicates fn + 1 to fn + m (example: m = 60). Frequencies are sequentially selected according to the determined priority so that communication failures are reduced when actually exchanging data.

In addition, the frequencies actually used for communication are selected from the frequencies with the highest communication success rate in the area divided by frequency band in the communication confirmation at the first startup. As a result, the frequency group used means that the frequency bands of the individual frequencies are dispersed, and the same frequency band is used to prevent all frequencies of the frequency group used from communication failure due to radio wave interference. Can be done. For example, assuming that all frequencies are 80 types, 20 types of frequencies are used, and 5 bands are divided by frequency band, communication confirmation is performed at all usable frequencies. Then, the frequency actually used for communication is selected from the higher frequencies having a high communication success rate for each area divided by frequency band. Four frequencies with the highest success rate are selected from each area so that the total number of frequencies used is 20, which is the specified number. Here, if there is a frequency having a success rate of more than 90%, it is selected in the order of appearance. As a result, even if the frequency having the success rate exceeding 90% does not satisfy the specified number, the frequency having the higher success rate is selected from within each area, and the specified number of frequencies are selected.

Frequency hopping is performed by sequentially determining the frequency to be used from the frequency group to be used. In FIG. 3, when f1, f2, and f3 are used frequencies when communication is performed, the communication fails because the communication is not properly received, so that a retry is performed and the communication is successful at the used frequency f4.

FIG. 4 is an explanatory diagram showing a state of transmission / reception and frequency hopping performed between the probe station 1 and the machine station 2, and is a state after the frequencies are exchanged. Since communication failed in f1, f2, and f3 in FIG. 3, in FIG. 4, f1 to f3 are moved to the spare frequency group, and the spare frequencies fn + 1 to fn + 3 belonging to the spare frequency group are replaced with the frequencies used to move to the frequency group to be used. It means that you have moved.

Here, the frequency other than the frequency used for communication is set as a spare frequency, and the priority of the spare frequency having a high communication success rate is set high in the communication confirmation at the first startup. When switching frequencies, switch from the preliminary frequency with the highest priority. As a result, the frequency having a high communication success rate is preferentially used, so that the number of retries can be reduced.

The prioritized spare frequencies are ranked as frequency patterns in descending order of priority in the spare frequency group. That is, the frequency pattern is information indicating the priority in the spare frequency group. Since the frequency pattern information needs to be frequency hopping using the same frequency on the transmitting side and the receiving side, it is stored in the probe station 1 and the machine station 2 so that the transmitting side and the receiving side can share the information.

FIG. 5 is a flowchart in which the frequencies shown in FIG. 4 are exchanged. In FIG. 5, the frequency that failed in one communication is confirmed and replaced with the spare frequency. If communication is performed multiple times before confirming the replacement, the redundancy will increase, but it can be made more reliable. First, communication is started and transmitted from the probe station 1 at a frequency f1. If the communication is successful in f1, this communication is terminated and frequency hopping is continued.

If communication fails at f1, the same data is transmitted at frequency f2. If the communication is successful in f2, the communication is unsuccessful in f1, so f1 is set as a spare frequency. Then, fn + 1, which is classified as a spare frequency at the first startup or in the previous communication, is taken out from the spare frequency group and replaced with f1.

If communication fails even at f2, the same data is transmitted at frequency f3. If the communication is successful in f3, the communication has failed in f1 and f2, so f1 and f2 are set as spare frequencies. Then, fn + 1 and fn + 2, which are classified as spare frequencies at the first startup or in the previous communication, are taken out from the spare frequency group and replaced with f1 and f2, respectively.

If communication fails even at f3, the same data is transmitted at frequency f4. If the communication is successful in f4, the communication has failed in f1, f2, and f3, so f1, f2, and f3 are set as spare frequencies. Then, fn + 1, fn + 2, and fn + 3, which are classified as spare frequencies at the first startup or in the previous communication, are taken out from the spare frequency group and replaced with f1, f2, and f3, respectively. FIG. 4 shows this state. Hereinafter, frequency hopping is continued in the same manner.

Further, the probe station 1 on the transmitting side notifies the machine station 2 on the receiving side of the number of transmissions due to retries. As a result, the receiving side can also grasp the frequency with a large number of retries or the frequency with which communication has failed. Therefore, conversely, when transmitting measurement instruction data or the like from the machine station 2 to the probe station 1, the frequency with which communication has failed should not be used. Can be.

Therefore, the used frequency and the backup frequency are exchanged on both the transmitting side and the receiving side. Then, since frequency hopping is performed using the same frequency on the transmitting side and the receiving side, the same frequency is exchanged. As a result, the number of retries can be reduced in transmission from either the probe station 1 or the machine station 2.

When the probe station 1 moves to a position different from that at the start of measurement and performs communication, the communication environment changes. However, since the frequency is repeatedly exchanged and the frequency used for frequency hopping is dynamically selected, communication can be established with a small number of retries. In addition, the frequency at which communication fails is unlikely to succeed in communication in that environment, but it is highly likely that communication will succeed if the environment changes, so it is saved as a spare frequency.

FIG. 6 is a time chart showing the relationship between transmission / reception and delay time in conventional communication in which frequencies are not exchanged. The upper figure shows the case where the number of retries is 3 and the lower figure shows the case where the number of retries is 6. The time from the transmission request (input on the leftmost side in the figure) to the output of the received data (output on the right side in the figure) is the delay time, and it is necessary to keep it constant in order to perform high-precision measurement. For that purpose, it is necessary to set the delay time in consideration of the time required for the expected maximum number of retries.

It is assumed that f1 to f8 are frequencies used in frequency hopping and that communication is successful between the frequency hopping. In the conventional communication, even if the communication fails at f1 and f2 and succeeds at f3 as shown in the above figure, f1 and f2 are used as they are in the second and subsequent communications. Therefore, as shown in the figure below, the number of retries may increase. Therefore, the delay time t1 must be set to a time corresponding to eight retries.

FIG. 7 is a time chart showing the relationship between transmission / reception and delay time in communication according to one embodiment. The upper figure shows the case where the number of retries is three, and the lower figure shows the case where the number of retries is two. The delay time is the time from the transmission request (input on the leftmost side in the figure) to the output of the received data (output on the right side in the figure). For example, the number of retries can be reduced by not using the frequency in which communication has failed in the upper figure in the lower figure, and the delay time t2 can be set as the delay time for four retries, which is shorter than t1 in FIG.

FIG. 8 is a time chart showing measurement results received by communication with measurement data when there is a request for acquisition of measurement data from the outside at regular intervals. A comparison is made with and without the delay time setting. The horizontal axis is time, and the vertical dashed line indicates the time interval. The above figure shows that the actual measured values 1, 2, 3, and 4 of the measurement target were obtained at each time interval. The middle figure shows the received data when the delay time is provided.

Since a fixed delay time is set from the transmission request to the output of the received data, the measurement data can be received during that time, that is, by the data acquisition request. Therefore, the received data is an accurate measurement result at that time.

The figure below shows the received data when the time from the transmission request to the output of the received data is not constant, that is, when the delay time is not set. In the case of the actual measured value 1, the reception is successful and the correct value is obtained. However, in the case of the actual measured value 2, the communication fails and the reception of the measured data is not completed by the time of the data acquisition request. Therefore, the output measurement data is the same as the previous time, that is, the received data of the measurement value 1, and an accurate measurement result at that time cannot be obtained.

Hereinafter, similarly, the reception of the actual measured value 2 is finally completed at the timing of the actual measured value 3. The reception of the actual measured value 2 is longer than the delay time from the transmission request for the actual measured value 1 to the output of the received data by the increase in the number of retries. Further, when the reception of the measured value 2 is started, the time of the next actual measured value 4 has already arrived, so that the actual measured value 3 cannot be received. As described above, when the amount of change over time in the actual measured value of the measurement target becomes so large that it cannot be ignored with respect to the variation in communication time, accurate measurement cannot be performed. Therefore, it is necessary to set the delay time in order to perform accurate measurement, and the delay time can be shortened in the present invention.

In the above description, a machining center is exemplified as a machine tool, but the present invention is applied to any measuring device in which a probe or sensor for dimension measurement moves and transmits measurement data to a fixed portion. Suitable for. Further, the probe or sensor for dimension measurement is the same as that of one embodiment, such as a length measuring device (electric micrometer and optical scale), a position detection probe, a temperature sensor, a vibration sensor, a barometric pressure sensor, a pressure sensor, a humidity sensor, and the like. Is. In particular, the present invention is particularly suitable for automatically measuring the bore diameter and the diameter of the crankshaft hole after machining, for example, in the finishing machining process of a cylinder block.
Further, the wireless measurement system of the present invention requires less battery consumption because the number of retries is reduced, and is suitable for use with a battery.

1 Probe station 2 Machine station 9 Probe 11 Holder 17 Arm 20 Machining center 21 Movable table 22 Control device 23 Fixture 24 Work 25 Tool 26 Spindle head 29 Tool spindle 27 Automatic tool changer (ATC)
28 Tool Magazine

Claims (5)

A machine tool that transmits measurement data from a probe to a machine station installed in a fixed unit using frequency hopping by wireless communication.
Communication is confirmed at the frequency that can be used at startup, and it is determined that the priority of the frequency whose communication success rate is equal to or higher than the predetermined value is high. Sort into groups,
The frequency group to be used is selected in the order of appearance when there is a frequency in which the success rate of communication exceeds the predetermined value for each area divided by frequency band in the communication confirmation, and the success rate is the predetermined value. If the frequency exceeding the value does not satisfy the predetermined number, the frequency having the higher success rate is selected from each of the areas, the predetermined number is selected, and the total number of frequencies used is specified.
The spare frequency group is set as a spare frequency by setting the priority of the frequency having a high success rate in the communication confirmation to be high.
When transmitting the measurement data, the used frequency is sequentially determined from the used frequency group, the frequency hopping is performed, and the used frequency that is not properly received by the mechanical station is moved to the spare frequency group. , The spare frequency having the higher priority is replaced with the used frequency that has not been received.
A machine tool characterized in that a fixed delay time related to the number of retries is set from the transmission request to the output of received data. The machine tool according to claim 1, wherein a battery is attached to the probe and the probe is transmitted to the machine station by wireless communication. The machine tool according to claim 1 or 2, wherein the machine tool is put into a sleep state except for the measurement step using the probe. Claims 1 to 3, wherein when the frequency to be used is determined from the frequency group to be used and the measurement data is transmitted, the probe notifies the machine station of the number of times of retry transmission due to a transmission failure. The machine tool according to any one of the items. The machine tool according to any one of claims 1 to 4, wherein the probe is attached to and detached from the machine tool by an automatic tool changer.

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