Machine tool control device and machine tool

Abstract

A machine tool control device capable of preventing a workpiece from flying out according to one embodiment of the present disclosure includes: a total turning inertia estimation unit that estimates a total turning inertia based on feedback from a turning shaft by rotating the turning shaft, the total turning inertia being an inertia of a total of the turning shaft and an object rotating together with the turning shaft around the turning shaft; a workpiece turning inertia estimation unit that estimates a workpiece turning inertia, which is an inertia of the workpiece around the turning shaft, based on the total turning inertia when the workpiece is not held by a holding unit and the total turning inertia when the workpiece is held by the holding unit; a maximum rotational speed calculation unit that calculates a maximum rotational speed of the turning shaft at which a maximum energy when the workpiece is separated from the holding unit is equal to an upper limit value set in advance, based on the workpiece turning inertia; and a rotational speed limitation unit that limits a rotational speed of the turning shaft so that the rotational speed of the turning shaft does not exceed the maximum rotational speed.

Description

Technical Field

[0001] This invention relates to a machine tool control device and a machine tool. Background Technology

[0002] A machine tool is known to perform turning operations by rotating a turning axis, which is equipped with a holding part such as a chuck for holding the workpiece. The kinetic energy generated by the rotation of the rotating body, including the turning axis and the workpiece, during turning is significantly higher than the kinetic energy of the rotating body in operations such as milling. When the moment of inertia (moment of inertia) about the turning axis of the workpiece is large, it may exceed the capacity of a brake used to stop the turning axis in an emergency. Therefore, a technique has been proposed (see, for example, Patent Document 1): estimating the moment of inertia of the rotating body, notifying of a danger when the estimated moment of inertia is large, or limiting the rotational speed based on the moment of inertia.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent No. 6839783 Summary of the Invention

[0006] The problem the invention aims to solve

[0007] In turning, the workpiece rotates at relatively high speeds, raising concerns that it might fly out if it detaches from the holder. This risk is particularly high when the workpiece is held eccentrically. While machine tools sometimes have covers to prevent chip scattering, these may not prevent large workpieces from flying out. Therefore, a technology is needed to prevent workpieces from flying out if they detach during turning.

[0008] Solution for solving the problem

[0009] One aspect of this disclosure relates to a machine tool control device that controls a machine tool to rotate a turning axis for turning. The turning axis is provided with a holding part for holding a workpiece. The machine tool control device includes: an overall turning inertia estimation unit that estimates the overall turning inertia based on feedback from the turning axis by rotating the turning axis; the overall turning inertia being the inertia of the turning axis and an object rotating together with the turning axis about the turning axis; a workpiece turning inertia estimation unit that estimates the workpiece's inertia about the turning axis, i.e., the workpiece turning inertia, 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 speed calculation unit that calculates, based on the workpiece turning inertia, a maximum speed of the turning axis where the maximum energy required to disengage the workpiece from the holding part is equal to a preset upper limit value; and a speed limiting unit that limits the speed of the turning axis to prevent the speed of the turning axis from exceeding the maximum speed.

[0010] The effects of the invention

[0011] According to this disclosure, it is possible to prevent the workpiece from flying out. Attached Figure Description

[0012] Figure 1 This is a schematic diagram illustrating the structure of the machine tool according to the first embodiment of this disclosure. Detailed Implementation

[0013] The embodiments of this disclosure will now be described with reference to the accompanying drawings. Figure 1 This is a schematic diagram showing the structure of the machine tool 1 according to the first embodiment of this disclosure.

[0014] Machine tool 1 includes: a rotary table mechanism 10 for positioning workpiece W; a tool positioning mechanism 20 for driving the tool T used to machine workpiece W; and a machine tool control device 30 for controlling the movements of the rotary table mechanism 10 and the tool positioning mechanism 20, i.e., the movements of machine tool 1. The machine tool 1 in this embodiment is a machining center capable of turning. Machine tool 1 may also include a tool changer (not shown), etc.

[0015] The rotary table mechanism 10 includes: a holding portion 11 for holding a workpiece; a turning shaft 12 with the holding portion 11 disposed at its front end for rotating the holding portion 11; and a tilting shaft 13 for tilting the turning shaft 12. The rotary table mechanism 10 may also include one or more positioning shafts (not shown) for moving these components in, for example, a horizontal or vertical direction.

[0016] The holding part 11 can be a known structure such as a platform or chuck that can fix the workpiece W. The turning axis 12 is a drive axis that can rotate and position the holding part 11 or rotate the holding part 11 continuously. For the machine tool 1, the workpiece W can be turned by rotating the turning axis 12 continuously. The tilting axis 13 is configured to tilt the turning axis 12. In addition, in this specification, "axis" means a drive mechanism that includes one degree of freedom of a drive motor.

[0017] The tool positioning mechanism 20 can be configured with multiple drive shafts 21, 22, 23, and 24, enabling it to hold the tool T and bring it into contact with the workpiece W at a desired position from a desired direction for machining. Alternatively, the tool positioning mechanism 20 may also include a tool drive shaft 25 that rotates the tool T.

[0018] The machine tool control device 30 is itself an embodiment of the machine tool control device involved in this disclosure. The machine tool control device 30 controls the entire machine tool 1 according to the machining program so as to machine the workpiece W by actuating the rotary table mechanism 10 and the tool positioning mechanism 20.

[0019] 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 tilting inertia estimation unit 33, a workpiece tilting inertia estimation unit 34, an auxiliary information acquisition unit 35, a maximum speed calculation unit 36, a speed limiting unit 37, an inertia change confirmation unit 38, and a notification unit 39.

[0020] The machine tool control device 30 can be implemented by executing appropriate control programs through a computer device having, for example, a processor, memory, input / output interfaces, etc. Furthermore, the constituent elements of the machine tool control device 30 described above are constituent elements obtained by classifying the functions of the machine tool control device 30, and may not be constituent elements that can be clearly distinguished in terms of physical structure and program structure.

[0021] The overall turning inertia estimation unit 31 estimates the overall turning inertia Iac [kgm] based on feedback from the turning axis 12 by rotating the turning axis 12. 2 The overall turning inertia is the inertia of the turning shaft 12 and the entire object rotating together with the turning shaft 12 (including the holding part 11, the workpiece W, and the fixtures, fasteners, etc. used to fix the workpiece W) about the turning shaft 12. As a specific example, the overall turning inertia estimation unit 31 can be configured to derive an estimate of the overall turning inertia Iac by dividing a representative value (e.g., an average value) of the torque calculated based on the current value of the motor of the turning shaft 12 by a representative value of the angular acceleration calculated based on the feedback value of the rotational position (representative value of torque / representative value of angular acceleration).

[0022] The workpiece turning inertia estimation unit 32 estimates the workpiece turning inertia Iwc[kgm] around the turning axis 12 based on the overall turning inertia Iac0 when the holding unit 11 is not holding the workpiece W and the overall turning inertia Iac1 when the holding unit 11 is holding the workpiece W. 2 The workpiece turning inertia Iwc can be derived as (Iac1-Iac0) by subtracting the overall turning inertia Iac0 without holding the workpiece W from the overall turning inertia Iac1 when holding the workpiece W.

[0023] The overall tilt inertia estimation unit 33 estimates the overall tilt inertia Iat[kgm] by rotating the tilting axis 13 that tilts the workpiece W. 2 The overall tilting inertia Iat is estimated based on feedback from the tilting axis 13, representing the inertia of the tilting axis 13 and the entire object rotating with it (including the turning axis 12, the retaining part 11, the workpiece W, and the fixtures and fasteners used to hold the workpiece W) about the tilting axis 13. The estimated value of the overall tilting inertia Iat can be calculated in the same way as the estimated value of the overall turning inertia Iac.

[0024] The workpiece tilt inertia estimation unit 34 estimates the inertia of the workpiece W about the tilt axis 13, i.e., the workpiece tilt inertia Iwt [kgm], based on the overall tilt inertia Iat0 when the holding unit 11 is not holding the workpiece W and the overall tilt inertia Iat1 when the holding unit 11 is holding the workpiece W. 2 The workpiece tilting inertia Iwt can be calculated as the difference (Iat1-Iat0) between the overall tilting inertia Iat0 when the holding part 11 is not holding the workpiece W and the overall tilting inertia Iat1 when the holding part 11 is holding the workpiece W. Furthermore, in the case where the holding part 11 is a structure that cannot be changed by the user, Iat0 can also be set to a known value. By setting it to a known value, estimation errors can be reduced.

[0025] 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 auxiliary information described in the machining program, or it may be configured to provide a user interface that prompts the user to input auxiliary information. Alternatively, the density of the workpiece W may be acquired based on the material of the workpiece W determined by the machining program or user input, by referring to a reference table storing the correspondence between material and density.

[0026] The maximum rotational speed calculation unit 36 ​​calculates, at least based on the workpiece turning inertia Iwc, the maximum rotational speed of the turning shaft 12 such that the maximum energy Jw[J] that causes the workpiece W to detach from the holding part 11 is equal to a preset upper limit value Ju[J]. Alternatively, the maximum rotational speed calculation unit 36 ​​may be configured to calculate the maximum energy Jw by converting all the rotational energy of the workpiece W into the kinetic energy of the workpiece W when it detaches from the holding part 11.

[0027] In this case, when the rotational speed of workpiece W is set to n [rpm], the maximum energy Jw [J] of workpiece W when it is separated from holding part 11 can be calculated by the following equation (1).

[0028] Jw = 1 / 2·Iwc·(2πn / 60) 2 …(1)

[0029] On the other hand, the upper limit of the maximum energy Jw is set as the value obtained by multiplying the energy that can destroy the safety cover of machine tool 1 by the safety factor (destruction energy × safety factor). The energy that can destroy the safety cover can be determined by the impact resistance test of the safety cover.

[0030] The maximum speed calculation unit 36 ​​can also further consider auxiliary information to calculate the maximum speed. For example, if the density, diameter, and length (shape) of the workpiece W are considered, by limiting the maximum speed to satisfy both the maximum speed calculated based on the theoretically calculable workpiece turning inertia Iwc and the maximum speed calculated based on the workpiece turning inertia Iwc estimated by the workpiece turning estimation unit 32, machining can be performed at a safer speed that reduces the possibility of errors in the estimated inertia and auxiliary information.

[0031] The maximum rotational speed calculation unit 36 ​​can also further consider the workpiece tilting inertia Iwt to calculate the maximum rotational speed. By considering the workpiece turning inertia Iwc and the workpiece tilting inertia Iwt, the shape of the workpiece W can be estimated. As a result, the maximum energy Jw released by the workpiece W in the event of workpiece W detachment can be estimated more accurately.

[0032] Let the distance from the rotation center of the tilting axis 13 to the mounting surface of the workpiece W be r [m], assuming the workpiece W is cylindrical, the height of the workpiece W be h [m], the diameter of the workpiece W be d [m], and the density of the workpiece W be ρ [kg / m³]. 3 When the workpiece turning inertia Iwc is ], it can be expressed by the following formula (2).

[0033] Iwt=1 / 32·ρπd 4 h…(2)

[0034] In addition, the workpiece tilting inertia Iwt can be expressed by the following equation (3).

[0035] Iwt=1 / 16·ρπd 2 h{(d 2 / 4+h 2 / 3)+4(r+h / 2) 2}…(3)

[0036] Therefore, if the distance r from the rotation center of the tilting 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 tilting inertia Iwt into the above two formulas. The distance r from the rotation center of the tilting axis 13 to the mounting surface of the workpiece W is pre-input when the mounting and holding unit 11 is mechanically activated. The density ρ of the workpiece W can be obtained by the auxiliary information acquisition unit 35. If it cannot be obtained by the auxiliary information acquisition unit 35, the density of steel or stainless steel (7.9 g / cm³), which is a common material for the workpiece W, can be used. 3 To calculate.

[0037] When the cylindrical workpiece W is estimated to have a longitudinal shape of d < h, the energy generated when the workpiece W rotates at an angle relative to the rotation centerline is greater than the energy calculated by equation (1). When the workpiece W is held by the holding part 11 with one end face located on the rotation centerline of the turning axis 12, and the centerline of the workpiece W is inclined at an angle θ [°] relative to the rotation centerline of the turning axis 12, the maximum energy Jw when the workpiece W is released can be expressed by the following equation (4). Furthermore, the angle θ can also be set to a value obtained experimentally. For example, it can be set to a uniform value such as θ = 30°, or the value can be changed according to the ratio of d to h, etc.

[0038] 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)

[0039] Here, when d <h、d 2 <<h 2 When, the above equation (4) can be simplified to the following equation (5).

[0040] Jw=1 / 6·ρπ 3 d 2 h 3 ·(n / / 60) 2 sin 2 θ…(5)

[0041] By using this formula, the maximum energy Jw when the workpiece W is released can be estimated more accurately. Thus, even if the workpiece W has a longitudinal shape with d < h, it is possible to set a safe maximum speed, that is, a speed n at which the maximum energy Jw is equal to the upper limit value Ju, for processing.

[0042] The maximum speed calculation unit 36 ​​can also be configured to accept the user's approval or modification of the maximum speed calculated as described above. Furthermore, regarding the modification of the maximum speed, it can also be configured to set the value that reduces the safety factor to a predetermined limit as an upper limit.

[0043] The speed limiting unit 37 limits the speed of the turning shaft 12 to ensure that the speed does not exceed the maximum speed. The upper limit of the speed of the turning shaft 12 can be set to the maximum speed calculated by the maximum speed calculation unit 36, or a maximum value that can be set within the range not exceeding the maximum speed. The method for limiting the speed of the turning shaft 12, that is, limiting the speed of the workpiece W during turning, can be a known method.

[0044] The inertia change confirmation unit 38 causes the overall turning inertia estimation unit 31 to estimate the overall turning inertia Iac at a predetermined time to confirm the change in the overall turning inertia Iac, and further confirm the change in the workpiece turning inertia Iwc. The timing for confirming the change in the workpiece turning inertia Iwc can be appropriately selected, such as when the workpiece W is changed, when the machining program starts executing, at a certain time after each action, or at a fixed time. Furthermore, the inertia change confirmation unit 38 can also be configured to confirm the change in the workpiece turning inertia Iwc based on user instructions.

[0045] The inertia change confirmation unit 38 can also be configured to confirm the change in workpiece turning inertia Iwc midway through the machining program. During machining, the workpiece turning inertia Iwc will be smaller than at the start of machining, thus the maximum speed calculated by the maximum speed calculation unit 36 ​​will decrease. Therefore, the speed limit unit 37's restriction on the speed of the turning axis 12 is relaxed, allowing the machining speed to be increased in conjunction with the decrease in workpiece turning inertia Iwc. The timing for inertia estimation can be appropriately selected from the timing indicated in the program, any timing when the workpiece W's rotation stops, etc. Alternatively, the overall turning inertia Iac can be estimated using acceleration and deceleration during workpiece W machining.

[0046] If the maximum rotational speed calculated by the maximum rotational speed calculation unit 36 ​​is less than the set value or the turning requirement value derived from the machining program, the notification unit 39 considers the rotational speed to be limited and issues a notification. As a notification method, visual signals, auditory signals, or external devices can be used to delegate the notification by sending a signal to an external device.

[0047] When the maximum rotational speed is too low, it is highly likely that the workpiece W will be held at an angle relative to the turning axis 12, and the workpiece W is also likely to detach from the holding part 11. Therefore, when the maximum rotational speed is less than the set value, by notifying the user of the danger, the detachment of the workpiece W can be prevented by adjusting the holding state of the workpiece W. In addition, when the maximum rotational speed is less than the required turning value, by notifying the user that the desired machining conditions cannot be obtained and the machining time may increase, the user can be encouraged to consider whether to adjust the holding state of the workpiece W.

[0048] The machine tool 1 equipped with the machine tool control device 30 described above can set the maximum rotational speed of the turning axis 12 to an optimal value based on the workpiece W and the fixture used to fix the workpiece W to the holding device. Therefore, it can prevent excessive reduction in rotational speed or conversely, machining at dangerous speeds, thus enabling efficient and safe machining of the workpiece W. Furthermore, for the machine tool 1, the machine tool control device 30 estimates the workpiece turning inertia Iwc to set the maximum rotational speed of the turning axis 12, so the user does not need to calculate the inertia. Therefore, the machine tool 1 can shorten the setup time required for machining the workpiece W.

[0049] The embodiments of this disclosure have been described above, but the present invention is not limited to the embodiments described above. Furthermore, the effects described in the above embodiments are merely examples of preferred effects produced by the present invention, and the effects of the present invention are not limited to the effects described in the above embodiments.

[0050] In the machine tool control device disclosed herein, 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 arbitrary structures and can be omitted.

[0051] In the machine tools disclosed herein, the structures of the rotary table mechanism and the tool positioning mechanism are not limited to the embodiments described above. As a specific example, the machine tool disclosed herein may also be an NC lathe, and the rotary table mechanism may not have a tilting axis.

[0052] Explanation of reference numerals in the attached figures

[0053] 1: Machine tool; 10: Rotary table mechanism; 20: Tool positioning mechanism; 30: Machine tool control device; 11: Holding unit; 12: Turning axis; 13: Tilt axis; 21, 22, 23, 24: Drive axis; 25: Tool drive axis; 31: Overall turning inertia estimation unit; 32: Workpiece turning inertia estimation unit; 33: Overall tilt inertia estimation unit; 34: Workpiece tilt inertia estimation unit; 35: Auxiliary information acquisition unit; 36: Maximum speed calculation unit; 37: Speed ​​limiting unit; 38: Inertia change confirmation unit; 39: Notification unit; W: Workpiece; T: Tool.

Claims

1. A machine tool control device for controlling a machine tool that rotates a turning axis to perform turning, wherein the turning axis is provided with a holding part for holding a workpiece, the machine tool control device comprising: The overall turning inertia estimation unit estimates the overall turning inertia based on feedback from the turning axis by rotating the turning axis. The overall turning inertia is the overall inertia of the turning axis and the object rotating together with the turning axis about the turning axis. The workpiece turning inertia estimation unit estimates the workpiece's inertia about the turning axis, i.e., the workpiece turning inertia, based on the overall turning inertia when the holding part does not hold the workpiece and the overall turning inertia when the holding part holds the workpiece. The maximum rotational speed calculation unit calculates, based on the workpiece's turning inertia, the maximum rotational speed of the turning axis that equals the maximum energy required to disengage the workpiece from the holding part and a preset upper limit value; and A speed limiting unit limits the speed of the turning shaft so that the speed of the turning shaft does not exceed the maximum speed.

2. The machine tool control device according to claim 1, wherein, It also includes an auxiliary information acquisition unit, which acquires auxiliary information including the density of the workpiece. The maximum speed calculation unit calculates the maximum speed by taking into account the auxiliary information.

3. The machine tool control device according to claim 1 or 2, further comprising: An overall tilt inertia estimation unit estimates the overall tilt inertia based on feedback from the tilt axis by rotating the tilt axis used to tilt the workpiece. The overall tilt inertia is the inertia of the tilt axis and the object rotating with it about the tilt axis as a whole. The workpiece tilt inertia estimation unit estimates the workpiece tilt inertia about the tilt axis based on the overall tilt inertia when the holding part is not holding the workpiece and the overall tilt inertia when the holding part is holding the workpiece. The maximum rotational speed calculation unit calculates the maximum rotational speed by taking into account the workpiece's tilting inertia.

4. The machine tool control device according to claim 1 or 2, wherein, It also includes an inertia change confirmation unit, which causes the overall turning inertia estimation unit to perform the estimation of the overall turning inertia at a predetermined time interval to confirm the change of the overall turning inertia.

5. The machine tool control device according to claim 4, wherein, The inertia change confirmation unit relaxes the restrictions imposed by the speed limit unit in coordination with the reduction of the workpiece turning inertia by having the overall turning inertia estimation unit estimate the overall turning inertia midway through the machining process.

6. The machine tool control device according to claim 1 or 2, wherein, It also includes a notification unit that notifies the user when the maximum rotational speed is less than a set value or the required value for turning.

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

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