Machine tool control device and machine tool

Abstract

A machine tool control device according to one aspect of the present disclosure, which can prevent a workpiece from flying out, comprises: a total turning inertia estimation unit that, estimates the total turning inertia on the basis of feedback from a turning shaft by causing the turning shaft to rotate, said total turning inertia being the total inertia, around the turning shaft, of the turning shaft and an object that rotates together with the turning shaft; a workpiece turning inertia estimation unit that estimates the workpiece turning inertia on the basis of the total turning inertia when a retention unit is not retaining a workpiece and the total turning inertia when the retention unit is retaining a workpiece, said workpiece turning inertia being the inertia, around the turning shaft, of the workpiece; a maximum rotational speed calculation unit that, on the basis of the workpiece turning inertia, calculates the maximum rotational speed of the turning shaft, at which the maximum energy when the workpiece separates from the retention unit is equal to a preset upper limit value; and a rotational speed limiting unit that limits the rotational speed of the turning shaft so as not to exceed the maximum rotational speed.

Description

[Technical Field]

[0001] The present invention relates to a machine tool control device and a machine tool. [Background technology]

[0002] Machine tools are known that perform turning by rotating a turning shaft provided with a holding part such as a chuck for holding a workpiece. The kinetic energy generated by the rotation of a rotating body, including the turning shaft and workpiece, during turning is significantly greater than the kinetic energy of a rotating body during, for example, milling. If the inertia (moment of inertia) of the workpiece about the turning shaft is large, it may exceed the capacity of a brake for emergency stopping the turning shaft. For this reason, technologies have been proposed that estimate the inertia of a rotating body and, if the estimated inertia value is large, issue a warning of a danger or limit the rotational speed according to the inertia (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6839783 Summary of the Invention [Problem to be solved by the invention]

[0004] In turning, the workpiece is rotated at a relatively high speed, and if it comes off the holder, there is a risk that the workpiece will fly out. In particular, if the workpiece is held eccentrically, the risk of the workpiece coming off and flying out increases. Machine tools are sometimes equipped with covers to prevent chips from scattering, but this may not be enough to prevent heavy workpieces from flying out. For this reason, there is a need for technology that can prevent the workpiece from flying out if it comes off during turning. [Means for solving the problem]

[0005] A machine tool control device according to one aspect of the present disclosure is a machine tool control device that controls a machine tool that performs turning by rotating a turning shaft provided with a holding part that holds a workpiece, and includes: an overall turning inertia estimation unit that estimates an overall turning inertia, which is the inertia around the turning shaft of the entire body that rotates with the turning shaft, based on feedback from the turning shaft by rotating the turning shaft; a workpiece turning inertia estimation unit that estimates a workpiece turning inertia, which is the inertia of the workpiece around the turning shaft, based on the overall turning inertia when the holding part is not holding the workpiece and the overall turning inertia when the holding part is holding the workpiece; a maximum rotation speed calculation unit that calculates, based on the workpiece turning inertia, the maximum rotation speed of the turning shaft at which the maximum energy when the workpiece is released from the holding part is equal to a predetermined upper limit value; and a rotation speed limiting unit that limits the rotation speed of the turning shaft so as not to exceed the maximum rotation speed. [Effects of the Invention]

[0006] According to the present disclosure, the workpiece can be prevented from popping out. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a schematic diagram showing a configuration of a machine tool according to a first embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0008] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Fig. 1 is a schematic diagram showing the configuration of a machine tool 1 according to a first embodiment of the present disclosure.

[0009] The machine tool 1 includes a rotary table mechanism 10 that positions a workpiece W, a tool positioning mechanism 20 that drives a tool T that machines the workpiece W, and a machine tool control device 30 that controls the operation of the rotary table mechanism 10 and the tool positioning mechanism 20, i.e., the operation of the machine tool 1. The machine tool 1 of this embodiment is a machining center capable of performing turning. The machine tool 1 may further include a tool changer (not shown) and the like.

[0010] The rotary table mechanism 10 has a holder 11 that holds a workpiece, a turning axis 12 that has the holder 11 at its tip and rotates the holder 11, and a tilting axis 13 that tilts the turning axis 12. The rotary table mechanism 10 may further have one or more positioning axes (not shown) that move these components, for example, in the horizontal or vertical direction.

[0011] The holding unit 11 may be a well-known structure such as a table or chuck capable of fixing the workpiece W. The turning axis 12 is a drive axis capable of rotationally positioning or continuously rotating the holding unit 11. In the machine tool 1, the turning of the workpiece W can be performed by continuously rotating the turning axis 12. The tilting axis 13 is configured to tilt the turning axis 12. In this specification, the term "axis" refers to a drive mechanism with one degree of freedom including a drive motor.

[0012] The tool positioning mechanism 20 may be configured to have a plurality of drive shafts 21, 22, 23, and 24 so that it can hold the tool T and bring the tool T into contact with a desired position on the workpiece W from a desired direction to perform machining. The tool positioning mechanism 20 may also have a tool drive shaft 25 that rotates the tool T.

[0013] The machine tool control device 30 is itself an embodiment of the machine tool control device according to the present disclosure. The machine tool control device 30 controls the entire machine tool 1 to machine the workpiece W by operating the rotary table mechanism 10 and the tool positioning mechanism 20 in accordance with a machining program.

[0014] The machine tool control device 30 according to this embodiment includes an overall turning inertia estimation unit 31, a workpiece turning inertia estimation unit 32, an overall tilt inertia estimation unit 33, a workpiece tilt inertia estimation unit 34, an auxiliary information acquisition unit 35, a maximum rotation speed calculation unit 36, a rotation speed limiting unit 37, an inertia change confirmation unit 38, and an alarm unit 39.

[0015] The machine tool control device 30 can be realized by causing a computer device having, for example, a processor, a memory, an input / output interface, etc. to execute an appropriate control program. Note that the components of the machine tool control device 30 described above are merely classifications of the functions of the machine tool control device 30, and do not necessarily have to be clearly distinguishable in terms of physical configuration and program configuration.

[0016] The overall turning inertia estimation unit 31 rotates the turning shaft 12, and calculates the overall turning inertia Iac [kgm], which is the inertia around the turning shaft 12 of the entire object (including the holding unit 11, the workpiece W, the jig for fixing the workpiece W, the fasteners, etc.) that rotates together with the turning shaft 12, based on feedback from the turning shaft 12. 2 As a specific example, the overall turning inertia estimating unit 31 may be configured to derive an estimated value of the overall turning inertia Iac by dividing a representative value of torque (for example, an average value) calculated from the current value of the motor of the turning shaft 12 by a representative value of angular acceleration calculated from the feedback value of the rotation position (representative value of torque / representative value of angular acceleration).

[0017] The workpiece turning inertia estimation unit 32 calculates the workpiece turning inertia Iwc [kgm 2 The workpiece turning inertia Iwc can be derived as the value (Iac1-Iac0) obtained by subtracting the overall turning inertia Iac0 when the workpiece W is not being held from the overall turning inertia Iac1 when the workpiece W is being held.

[0018] The overall tilt inertia estimation unit 33 estimates the overall tilt inertia Iat [kgm 2 The overall tilt inertia Iat is the inertia around the tilt axis 13 of the tilt axis 13 and the entire object that rotates together with the tilt axis 13 (including the turning axis 12, the holding part 11, the workpiece W, the jig for fixing the workpiece W, fasteners, etc.) based on feedback from the tilt axis 13. The estimated value of the overall tilt inertia Iat can be calculated in the same way as the estimated value of the overall turning inertia Iac.

[0019] The workpiece tilt inertia estimation unit 34 calculates the workpiece tilt inertia Iwt [kgm 2 The workpiece tilt inertia Iwt can be calculated as the difference (Iat1-Iat0) between the overall tilt inertia Iat0 when the holder 11 is not holding the workpiece W and the overall tilt inertia Iat1 when the holder 11 is holding the workpiece W. Note that if the holder 11 is configured so that it cannot be changed by the user, Iat0 may be a known value, and by using a known value, estimation errors can be reduced.

[0020] The auxiliary information acquisition unit 35 acquires auxiliary information including the density of the workpiece W. The auxiliary information acquisition unit 35 may be configured to interpret the auxiliary information described in the machining program, or may be configured to provide a user interface that prompts the user to input the auxiliary information. The density of the workpiece W may be acquired by referring to a reference table that stores the correspondence between material and density based on the material of the workpiece W specified by the machining program or user input.

[0021] The maximum rotation speed calculation unit 36 ​​calculates the maximum rotation speed of the turning shaft 12 at which the maximum energy Jw [J] when the workpiece W is released from the holder 11 becomes equal to a preset upper limit value Ju [J], based on at least the workpiece turning inertia Iwc. The maximum rotation speed calculation unit 36 ​​may calculate the maximum energy Jw on the assumption that all of the rotational energy of the workpiece W is converted into kinetic energy of the workpiece W when the workpiece W is released from the holder 11.

[0022] In this case, the maximum energy Jw [J] when the workpiece W is released from the holder 11 can be calculated by the following formula (1), where n [rpm] is the rotation speed of the workpiece W. Jw=1 / 2·Iwc·(2πn / 60) 2 …(1)

[0023] On the other hand, the upper limit of this maximum energy Jw is set as a value (breaking energy × safety factor) obtained by multiplying the energy that can destroy the safety cover of the machine tool 1 by a safety factor. The energy that can destroy the safety cover can be determined by an impact resistance test of the safety cover.

[0024] The maximum rotation speed calculation unit 36 ​​may further take auxiliary information into consideration when calculating the maximum rotation speed. For example, by taking into consideration the density, diameter, and length (shape) of the workpiece W, it is possible to limit the maximum rotation speed to one that satisfies both the theoretically calculable workpiece turning inertia Iwc and the maximum rotation speed calculated from the workpiece turning inertia Iwc estimated by the workpiece turning inertia estimation unit 32, thereby reducing the possibility of errors in the estimated inertia or auxiliary information and enabling processing at a safer rotation speed.

[0025] The maximum rotation speed calculation unit 36 ​​may further calculate the maximum rotation speed taking into account the workpiece tilt inertia Iwt. By taking into account the workpiece turning inertia Iwc and the workpiece tilt inertia Iwt, it is possible to estimate the shape of the workpiece W. This makes it possible to more accurately estimate the maximum energy Jw of the workpiece W that is released when the workpiece W is detached.

[0026] The distance from the rotation center of the tilt axis 13 to the mounting surface of the workpiece W is r [m]. Assuming that the workpiece W is cylindrical, the height of the workpiece W is h [m], the diameter of the workpiece W is d [m], and the density of the workpiece W is ρ [kg / m 3 ], the workpiece turning inertia Iwc can be expressed by the following equation (2). Iwt=1 / 32·ρπd 4 h …(2)

[0027] Moreover, the workpiece tilt inertia Iwt can be expressed by the following equation (3). Iwt=1 / 16·ρπd 2 h{(d 2 / 4+h 2 / 3)+4(r+h / 2) 2}…(3)

[0028] Therefore, if the distance r from the rotation center of the tilt axis 13 to the mounting surface of the workpiece W and the density ρ of the workpiece W are known, the height h and diameter d of the workpiece W can be derived by substituting the estimated values ​​of the workpiece turning inertia Iwc and the workpiece tilt inertia Iwt into the two equations above. The value of the distance r from the rotation center of the tilt axis 13 to the mounting surface of the workpiece W is input in advance when starting up the machine to which the holding unit 11 is attached. The density ρ of the workpiece W may be acquired by the auxiliary information acquisition unit 35, or if it cannot be acquired by the auxiliary information acquisition unit 35, the density ρ of 7.9 g / cm 3 , which is the density of steel or stainless steel, which is a material that is generally used for the workpiece W, is used. 3 It may be calculated using the following formula:

[0029] When the columnar workpiece W estimated in this way rotates in an inclined state with respect to the rotation center line in the case of a vertically long shape with d < h, the energy may become larger than the energy obtained by the formula (1). When one end face is positioned on the rotation center line of the turning shaft 12 by the holding portion 11 and the center line of the workpiece W is held so as to be inclined by an angle θ [°] with respect to the rotation center line of the turning shaft 12, the maximum energy Jw at the time of detachment of the workpiece W can be expressed by the following formula (4). The angle θ may be set to a value obtained experimentally. For example, a uniform value such as θ = 30° may be set, or the value may be changed according to the ratio of d to h. Jw = 1 / 8·ρπd 2 h·{πh(n / 60)sinθ} 2 +1 / 16·ρπd 2 h·(d 2 / 4 + h 2 / 3)·{π(n / 60)sinθ} …(4)

[0030] Here, when d < h, d 2 << h 2 assuming this, the formula (4) can be simplified as the following formula (5). Jw = 1 / 6·ρπ 3 d 2 h 3 ·(n / 60) 2 sin 2 θ …(5)

[0031] By using this formula to more accurately estimate the maximum energy Jw at the time of detachment of the workpiece W, even when the workpiece W has a vertically long shape with d < h, a safe maximum rotational speed, that is, a rotational speed n at which the maximum energy Jw becomes equal to the upper limit value Ju can be set, and machining can be performed.

[0032] The maximum rotational speed calculation unit 36 may be configured to accept approval or correction by the user for the maximum rotational speed calculated as described above. Further, the correction of the maximum rotational speed may be configured such that the upper limit is a value obtained by reducing the safety factor to a predetermined limit value.

[0033] The rotation speed limiting unit 37 limits the rotation speed of the turning spindle 12 so that it does not exceed the maximum rotation speed. The upper limit value of the rotation speed of the turning spindle 12 can be set to the maximum rotation speed calculated by the maximum rotation speed calculating unit 36 ​​or a maximum value that can be set within a range that does not exceed the maximum rotation speed. Known methods can be used to limit the rotation speed of the turning spindle 12, that is, the method for limiting the rotation speed of the workpiece W during turning.

[0034] The inertia change confirmation unit 38 causes the overall turning inertia estimation unit 31 to estimate the overall turning inertia Iac at a predetermined timing, and confirms changes in the overall turning inertia Iac and, ultimately, the workpiece turning inertia Iwc. The timing for checking changes in the workpiece turning inertia Iwc can be appropriately selected, such as when the workpiece W is replaced, when the machining program starts to be executed, every certain period of operation, or at regular intervals. The inertia change confirmation unit 38 may also be configured to be able to check changes in the workpiece turning inertia Iwc in response to a user instruction.

[0035] The inertia change confirmation unit 38 may be configured to confirm changes in the workpiece turning inertia Iwc during the machining program. Since the workpiece turning inertia Iwc is smaller during machining than at the start of machining, the maximum rotation speed calculated by the maximum rotation speed calculation unit 36 ​​decreases. This relaxes the restriction on the rotation speed of the turning spindle 12 by the rotation speed limiting unit 37, allowing the machining speed to increase in accordance with the decrease in the workpiece turning inertia Iwc. The timing for executing inertia estimation can be selected appropriately, such as the timing commanded during the program or any timing when the rotation of the workpiece W stops. Furthermore, the overall turning inertia Iac may be estimated using the acceleration / deceleration during machining of the workpiece W.

[0036] When the maximum rotation speed calculated by the maximum rotation speed calculation unit 36 ​​is smaller than the set value or the required value for turning derived from the machining program, the notification unit 39 notifies that the rotation speed is limited. The notification method may be a visual signal, an auditory signal, or the like, or an external device may be used to notify by transmitting a signal to the outside.

[0037] If the maximum rotation speed is excessively small, it is highly likely that the workpiece W is being held at an angle to the turning axis 12, and it is also highly likely that the workpiece W will come off the holder 11. For this reason, if the maximum rotation speed is smaller than the set value, the user is notified of the danger, and the workpiece W can be prevented from coming off by adjusting the holding state of the workpiece W, etc. Furthermore, if the maximum rotation speed is smaller than the required value for turning, the user is notified that the desired machining conditions cannot be obtained or that the machining time may be long, which can prompt the user to consider whether or not to adjust the holding state of the workpiece W.

[0038] The machine tool 1 equipped with the machine tool control device 30 described above can set the maximum rotation speed of the turning spindle 12 to an optimal value depending on the workpiece W and the jig for fixing the workpiece W to the holder. This makes it possible to prevent the rotation speed from being reduced more than necessary, or conversely, to prevent machining at a dangerous rotation speed, thereby enabling the workpiece W to be machined efficiently and safely. Furthermore, in the machine tool 1, the machine tool control device 30 estimates the workpiece turning inertia Iwc and sets the maximum rotation speed of the turning spindle 12, eliminating the need for the user to calculate the inertia. This makes it possible to shorten the time required for setting up for machining the workpiece W in the machine tool 1.

[0039] Although the embodiments of the present disclosure have been described above, the present invention is not limited to the above-described embodiments. Furthermore, the effects described in the above-described embodiments are merely a list of preferred effects resulting from the present invention, and the effects of the present invention are not limited to those described in the above-described embodiments.

[0040] In the machine tool control device according to the present disclosure, the overall tilt inertia estimation unit, the workpiece tilt inertia estimation unit, the auxiliary information acquisition unit, the inertia change confirmation unit, and the notification unit are optional configurations and can be omitted.

[0041] In the machine tool according to the present disclosure, the configurations of the rotary table mechanism and the tool positioning mechanism are not limited to those in the above-described embodiment. As a specific example, the machine tool according to the present disclosure may be an NC lathe, and the rotary table mechanism may not have a tilt axis. [Explanation of symbols]

[0042] 1 Machinery 10 Rotating table mechanism 20 Tool positioning mechanism 30 Machine tool control device 11 Holding part 12 Turning shaft 13 Tilt axis 21, 22, 23, 24 Drive shaft 25 Tool drive shaft 31 Overall turning inertia estimation section 32 Workpiece turning inertia estimation section 33 Overall slope inertia estimator 34 Work tilt inertia estimation section 35 Auxiliary information acquisition section 36 Maximum rotation speed calculation unit 37 Rotation speed limiter 38 Inertia change confirmation section 39 Information Department double work T-tool

Claims

1. A machine tool control device that controls a machine tool that performs turning by rotating a turning shaft provided with a holding part that holds a workpiece, an overall turning inertia estimating unit that estimates an overall turning inertia, which is an inertia around the turning axis of the entire turning axis and an object rotating together with the turning axis, based on feedback from the turning axis by rotating the turning axis; a workpiece turning inertia estimation unit that estimates a workpiece turning inertia, which is the inertia of the workpiece around the turning axis, based on the overall turning inertia when the holding unit does not hold the workpiece and the overall turning inertia when the holding unit holds the workpiece; a maximum rotation speed calculation unit that calculates, based on the workpiece turning inertia, a maximum rotation speed of the turning shaft at which a maximum energy when the workpiece is released from the holding unit becomes equal to a preset upper limit value; a rotation speed limiting unit that limits the rotation speed of the turning shaft so that it does not exceed the maximum rotation speed; A machine tool control device comprising:

2. Further, an auxiliary information acquisition unit that acquires auxiliary information including the density of the workpiece is provided, The machine tool control device according to claim 1 , wherein the maximum rotation speed calculation unit calculates the maximum rotation speed taking into account the auxiliary information.

3. an overall tilt inertia estimating unit that estimates an overall tilt inertia, which is the inertia of the entire tilt axis and the object rotating together with the tilt axis, around the tilt axis based on feedback from the tilt axis by rotating the tilt axis that tilts the workpiece; a workpiece tilt inertia estimation unit that estimates a workpiece tilt inertia, which is the inertia of the workpiece about the tilt axis, based on the overall tilt inertia when the holding unit is not holding the workpiece and the overall tilt inertia when the holding unit is holding the workpiece; Furthermore, The machine tool control device according to claim 1 or 2, wherein the maximum rotation speed calculation unit calculates the maximum rotation speed taking into account the workpiece tilt inertia.

4. 4. The machine tool control device according to claim 1, further comprising an inertia change confirmation unit that causes the overall turning inertia estimation unit to estimate the overall turning inertia at a predetermined timing and confirms a change in the overall turning inertia.

5. 5. The machine tool control device according to claim 4, wherein the inertia change confirmation unit causes the overall turning inertia estimation unit to estimate the overall turning inertia during the machining program, thereby relaxing the restriction imposed by the rotation speed limiting unit in accordance with a decrease in the workpiece turning inertia.

6. The machine tool control device according to claim 1 , further comprising a notification unit that issues a notification when the maximum rotational speed is smaller than a set value or a required value for turning.

7. A machine tool comprising the machine tool control device according to any one of claims 1 to 6.

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