machine tool

Abstract

A machine tool (20) comprising: a rotary shaft device including a rotary shaft (2); a sensor attached to the rotary shaft device and configured to obtain information about a phenomenon occurring on the rotary shaft device periodically and synchronously with rotations of the rotary shaft (2); and a control device (12) configured to control the operation of the rotary shaft device and to obtain information about the sensor, wherein when machining is performed during rotation of the rotary shaft (2), the control device (12) determines whether or not the machining is in a stable state in which no change occurs in a command relevant to the operation control of the rotary shaft device, and when the processing is in a stable state, the control device (12) receives information via the sensor with a predetermined query cycle (S T ), associates the information obtained with a rotation phase of the rotating shaft (2), and calculates the change in the phenomenon in a cycle on the basis of the information obtained for a plurality of rotations of the rotating shaft (2).

Description

[0001] The present invention relates to a machine tool having a rotary shaft device, for example, for performing machining while rotating a tool or a workpiece.

[0002] Conventionally, in a machine tool that performs machining during the rotation of a rotating shaft, in order to perform condition diagnosis or machining diagnosis of the machine tool itself, vibration, driving force, and the like are measured during operation and a diagnosis is made based on the measurement results. For example, in the case of a tool attached to the rotating shaft and a workpiece is being machined, the driving force of the rotating shaft is measured during machining, which can identify the cutting amount and detect the condition of the cutting machine.

[0003] In the invention described in Japanese Patent Application Laid-Open No. JP 2004-126956 A, the driving force occurred during machining is calculated based on a chip volume calculated from shape data of a machining target and a machining path, and the material quality of a workpiece, and the calculated driving force is compared with an actually measured driving force to detect abnormal machining.

[0004] In the invention described in Japanese Patent Application Laid-Open No. JP 2012-254499 A, in the case where machining is repeatedly performed, the driving force of the normal machining performed last time is compared with the driving force measured in the machining this time to detect abnormal machining.

[0005] In addition, in recent years, in addition to the driving force of a rotary shaft, attempts have been made to measure a phenomenon occurring on the machine tool more clearly by attaching a vibration sensor or an AE sensor to each part of the machine tool or by using a displacement sensor.

[0006] However, in conventional methods, in order to detect a change in a desired phenomenon, such as a cycle in which the rotating shaft is driven or cutting is performed, or a vibration cycle inherent in a bearing or guide component, it is necessary to perform the measurement with an extremely short sampling cycle. For example, in the case of machining using a rotary tool with six cutting blades, and the change in the driving force of each blade is to be measured if the rotational speed is 10,000 rpm. -1, one chip cycle is 100 µsec. Therefore, the sampling cycle must be less than 10 µsec to sample ten points for each chip blade. If such high-speed sampling is necessary, there is a problem that the measurement and analysis costs increase.

[0007] Accordingly, an object of the present invention is to provide a machine tool capable of obtaining an accurate measurement result regarding the change of a phenomenon occurring on a rotary shaft device at a low cost without performing polling with an extremely short cycle as in the conventional case.

[0008] According to the invention, the solution to the problem consists in a machine tool according to the invention according to claim 1 or 2. An advantageous embodiment of the invention is contained in the subclaim 3.

[0009] To achieve the above object, a machine tool according to a first aspect of the invention is provided. The machine tool comprises a rotary shaft device including a rotary shaft, a sensor attached to the rotary shaft device and configured to acquire information about a phenomenon that occurs on the rotary shaft device periodically and synchronously with the rotation of the rotary shaft, and a control device configured to control the operation of the rotary shaft device and acquire information via the sensor. When machining is performed during rotation of the rotary shaft, the control device can determine whether or not the machining is in a stable state in which no change occurs in a command relevant to the operation control of the rotary shaft device.When the machining is in a stable state, the control device can obtain information from the sensor with a predefined sampling cycle, associate the obtained information with a rotation phase of the rotary shaft, and calculate the change of the phenomenon in one cycle based on the information obtained for a plurality of rotations of the rotary shaft.

[0010] To achieve the above object, a machine tool according to a second aspect of the invention is provided. The machine tool comprises a rotary shaft device including a rotary shaft, a sensor attached to the rotary shaft device and configured to acquire information about a phenomenon occurring on the rotary shaft device periodically and synchronously with the rotation of the rotary shaft, and a control device configured to control the operation of the rotary shaft device and acquire information about the sensor. When machining is performed during rotation of the rotary shaft, the control device can determine whether or not the machining is in a stable state in which no change in the machining state occurs.When the machining is in a stable state, the control device can obtain information from the sensor with a predefined sampling cycle, associate the obtained information with a rotation phase of the rotary shaft, and calculate the change of the phenomenon in one cycle based on the information obtained for a plurality of rotations of the rotary shaft.

[0011] According to a third aspect of the invention based on the second aspect, a machine tool is provided in which a tool or a workpiece is fixed to the rotating shaft. A cutting amount of the workpiece can be calculated from information about a predetermined shape of the workpiece, a machining path of the tool relative to the workpiece, and the coordinate of a current command, and it can be determined that machining is in a stable state based on the fact that the cutting amount is constant.

[0012] According to the present invention, when machining is performed during the rotation of a rotary shaft, the control device determines whether or not the machining is in the stable state in which no change occurs in a command relevant to the machining control of the rotary shaft device (first aspect), or the control device determines whether or not the machining is in the stable state in which no change occurs in the machining state (second aspect). When the machining is in the stable state, the control device obtains information via the sensor with a predefined sampling cycle, associates the obtained information with a rotation phase of the rotary shaft, and calculates the change of the phenomenon of one cycle based on the information obtained for a plurality of rotations of the rotary shaft.Therefore, for example, with respect to a high-speed changing phenomenon, such as a change in the drive force of the main spindle, a meaningful measurement result can be obtained even though the measurement is performed with a sampling cycle longer than in the conventional case, and cost reduction can be achieved. Furthermore, it is also possible to measure such a phenomenon whose change cycle is so fast that its measurement was technically difficult in the conventional case. And because the measurement is performed only during the steady state, a measurement result with high reliability can be obtained.

[0013] In the following, a machine tool according to an embodiment of the invention is explained in more detail with reference to figures with reference symbols.

[0014] It shows Fig. 1 is a diagram showing a machine tool; Fig. 2 is a flowchart showing the control for measuring a phenomenon occurring on a main spindle device; Fig. 3 is a diagram showing the corresponding relationship between a polling and periodic change in the driving force of a main spindle; Fig. 4 is a graph showing the change in the driving force of the main spindle in one cycle, obtained by taking measurements every 50 µsec; Fig. 5 is a graph showing the change in the driving force of the main spindle in one cycle, which is obtained by taking measurements every 30 msec final;

[0015] Fig. 1 is a diagram showing a machine tool 20.

[0016] The machine tool 20 is a so-called machining center and includes a main spindle device 11 and a control device 12. A main spindle head 3 of the main spindle device 11 is provided with a main spindle 2 functioning as a rotating shaft, a drive device (not shown) for rotating the main spindle 2, and the like. A tool holder 1 provided with a tool is attached to one end of the main spindle 2. A sensor (for example, a sensor for measuring a desired electric power of the drive device) for measuring the driving force of the main spindle 2, a sensor for measuring vibrations occurring on the main spindle device 11, and the like are attached to main components, for example, the main spindle head 3 of the main spindle device 11.On the other hand, the control device 12 is provided for controlling the operation of the main spindle 2 and for diagnosing the state of the main spindle device 11 and the machining of the main spindle device 11. The control device 12 is connected to the above-mentioned various sensors and includes a measuring section 4 that measures various information about the main spindle device 11, a recording section 5 that records a measured value with a predetermined sampling cycle, and a computing section 6 that performs various computing processes based on the recorded value in the recording section 5.

[0017] The control of the measurement of a phenomenon occurring on the main spindle device 11, which is a main part of the present invention, will be explained with reference to the flowchart in Fig. 2. Here, it is assumed that a change in the driving force of the main spindle 2 is measured when machining is performed using a tool with three chipping blades.

[0018] When measuring the change in the driving force of the main spindle 2, the control device 12 first measures the driving force of the main spindle 2 with a predetermined sampling cycle S T (for example 30 msec) of the main spindle device 11, in which the main spindle 2 is located with a rotation cycle L set for carrying out the machining Ta rotary shaft rotates (S1). The control device 12 then determines whether or not the machining is in a stable zone in which the same machining is performed for a workpiece (whether the machining is in a stable state or not) from a fact that no changes occur in a rotation speed command and a feed rate command from the control device 12 to the main spindle device 11 (no changes occur in commands relevant to the operation control of the rotary shaft device), and a fact that chip amounts of the workpiece are constant in the axial direction and the radial direction (no change occurs in the machining state), wherein the chip amounts are calculated based on information about the shape of the workpiece acquired in advance in the accommodating section 5, a machining path of the tool, and the coordinate of the current command (S2).Only when the machining is in a stable zone, the control device 12 then continues the measurement, and if the machining deviates from the stable zone, the control device 12 stops the measurement immediately.

[0019] When the machining is in the stable zone, the control device 12 calculates a rotation phase of the main spindle 2 at the time of measurement in the N-th sample using the following formula (1), that is, a decimal place of a value obtained by dividing a product of one sample cycle S T and the number N of queries by the rotation cycle L Tof the rotary shaft (S3), and records the calculated rotational phase and the measured value in the recording section 5 to be associated with each other (S4). The control device 12 then continues, at the time of each measurement, the measurement and calculation of the rotational phase of the main spindle 2 for a plurality of rotations of the main spindle 2 to obtain the measured values ​​at different rotational phases, whereby the change in the driving force during one rotation of the main spindle 2 (ie, the change in one cycle) is finally calculated as Fig. 5 shows. [Mathematical 1] Rotation phase at the Nth query measurement = N×STLT−⌊N×STLT⌋(N=1, 2, 3, …) ⌊⌋ stands for a floor function, and ⌊A⌋ represents the largest integer not greater than A.

[0020] In relation to Fig. 3 to 5, the case of performing a measurement every 30 msec as in the present embodiment is compared with a case of performing a measurement every 50 µsec as in a conventional case. In the conventional method in which the measurement is performed every 50 µsec, the change in the driving force of the main spindle 2 can be measured substantially in real time during one rotation of the main spindle 2, and a measurement result such as Fig. 4. On the other hand, in the method in which the measurement is performed every 30 msec as in the present embodiment, the driving force can be measured only at one point or two points during one rotation of the main spindle 2. However, the driving force, as Fig. 3 shows, while the machining is in the stable zone, measured for a plurality of rotations, and further, each measured value is assigned to the rotation phase of the main spindle 2 and the measured values ​​from the plurality of rotations are combined, whereby the change of the driving force in one rotation can be obtained, such as Fig. 5 shows how a comparison between Fig. 4 and Fig. 5 shows, a measurement result close to the measurement result in the case of performing a measurement every 50 µsec can be obtained even in the case of performing a measurement every 30 msec.

[0021] In the machine tool 20 having the above-described configuration, whether or not the machining is in the stable zone in which the same machining is performed for a workpiece is determined from both a fact that no changes occur in the rotational speed command and the feed rate command from the control device 12 to the main spindle device 11 and a fact that chip amounts of the workpiece are constant in the axial direction and the radial direction, the chip amounts being calculated based on information about the shape of the workpiece acquired in advance in the accommodating section 5, a machining path of the tool, and the coordinate of the current command.If machining is in the stable zone, then a rotation phase of the main spindle 2 at the time of measurement in the Nth sample is calculated using formula (1), and the calculated rotation phase and the measured value are recorded in the recording section 5 to be correlated with each other. Further, the measurement and calculation of the rotation phase of the main spindle 2 at the time of each measurement are continued for a plurality of rotations of the main spindle 2 to obtain measured values ​​of different rotation phases. Thereafter, the change in the driving force during one rotation of the main spindle 2 is finally calculated. Therefore, regarding a high-speed changing phenomenon, for example, a change in the driving force of the main spindle 2, even if the measurement thereof is performed with a sample cycle longer than that in the conventional case, a meaningful measurement result can be obtained, and cost reduction can be realized.It is also possible to measure such a phenomenon whose change cycle is so rapid that it is difficult to measure it using conventional technology. Furthermore, a measurement result can be obtained with high reliability because the measurement is only performed during the steady state.

[0022] It should be noted that the configuration of the machine tool of the present invention is not limited to the described embodiment. Not only the entire configuration of the machine tool, but also the configurations for controlling the measurement of the phenomenon and the like can be modified as appropriate without departing from the scope of the present invention.

[0023] For example, although the main spindle device is described as a machining center in the above example, the present invention is also suitable for other machine tools and rotary shaft devices for use, for example, a main spindle device and a feed shaft device of a lathe.

[0024] In the above embodiment, the driving force of the main spindle is shown as a periodically changing phenomenon, but it is not limited to this. The phenomenon may be, for example, the driving force of another drive shaft, such as a feed shaft, or the vibration, displacement, temperature, or the like occurring on the rotating shaft device. As a specific example, a vibration sensor (sensor) may be attached to a feed shaft (rotary shaft) to measure the vibration that occurs when the feed shaft is rotated at a certain speed to move a moving body. By obtaining a result of such a measurement, it is possible to analyze the condition of a bearing or a ball screw relevant to the movement of the feed shaft.

[0025] In the above embodiment, whether the machining is in a stable state or not is determined based on both the fact that no changes occur in commands relevant to the operation control of the rotary shaft device and the fact that no changes occur in the machining state. However, whether the machining is in the stable state or not can also be determined based on only one of these facts.

[0026] In the above embodiment, it is determined that no change in the machining state occurs based on the fact that the chip amount of the workpiece is constant. However, it is also possible to use such a configuration to determine that no change in the machining state occurs based on the fact that no change in other conditions occurs, for example, no change in the feed direction or no change in the machine temperature.

[0027] It should be explicitly noted that all features disclosed in the description and / or claims are intended to be disclosed separately for the purpose of original disclosure as well as for the purpose of limiting the claimed invention, regardless of the composition of the features in the embodiments and / or the claims. It should be explicitly noted that all value ranges or indications of the groups of devices disclose every possible intermediate value or unit, for the purpose of original disclosure as well as for the purpose of limiting the claimed invention, in particular as limits of the value ranges.

Claims

[1] A machine tool (20), comprising: a rotary shaft device including a rotary shaft (2); a sensor attached to the rotary shaft device and configured to obtain information about a phenomenon occurring on the rotary shaft device periodically and synchronously with rotations of the rotary shaft (2); and a control device (12) configured to control the operation of the rotary shaft device and to obtain information about the sensor, wherein when machining is performed during rotation of the rotary shaft (2), the control device (12) determines whether or not the machining is in a stable state in which no change occurs in a command relevant to the operation control of the rotary shaft device, and when the processing is in a stable state, the control device (12) receives information via the sensor with a predetermined query cycle (S T ), associates the information obtained with a rotation phase of the rotating shaft (2), and calculates the change in the phenomenon in one cycle on the basis of the information obtained for a plurality of rotations of the rotating shaft (2). [2] A machine tool (20) comprising: a rotary shaft device including a rotary shaft (2); a sensor attached to the rotary shaft device and configured to obtain information about a phenomenon occurring on the rotary shaft device periodically and synchronously with rotations of the rotary shaft (2); and a control device (12) configured to control the operation of the rotary shaft device and to obtain information about the sensor, wherein when machining is performed during rotation of the rotary shaft (2), the control device (12) determines whether or not the machining is in a stable state in which no change in the machining state occurs, and when the processing is in a stable state, the control device (12) receives information via the sensor with a predetermined query cycle (S T ), associates the information obtained with a rotation phase of the rotating shaft (2), and calculates the change in the phenomenon in one cycle on the basis of the information obtained for a plurality of rotations of the rotating shaft (2). [3] The machine tool (20) according to claim 2, wherein a tool or a workpiece is attached to the rotary shaft (2), and a chip amount of the workpiece is calculated from information about a current shape of the workpiece, a machining path of the tool relative to the workpiece, and a coordinate of a current command, and it is determined that the machining is in a stable state based on a fact that the chip amount is constant.

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