Work machine control and work machine control program

Abstract

The purpose of the present invention is to both crush chips and suppress resonant oscillations in a machine. This control device for a work machine superimposes an oscillation command for controlling the relative oscillation between a workpiece and a cutting tool with a movement command for controlling the relative movement between the workpiece and the cutting tool, thereby generating air cuts in the chips of the workpiece to crush the chips. A position information acquisition unit of the work machine control device acquires position information related to the relative positions of the workpiece and the tool.A condition evaluation unit of the work machine control device evaluates that an instability condition is in effect under the condition that a positional deviation exceeds a threshold value, the positional deviation increasing with an increase in the difference between the actual relative positions based on the position information and the command relative positions based on the movement command and the oscillation command. An oscillation switching unit of the work machine control device performs a switching operation for switching an oscillation condition in the relative oscillation when the instability condition is determined to exist.

Description

Technical FieldThe present invention relates to a machine tool controller that controls a machine tool.Prior ArtIn the machine tool controllers, some devices superimpose an oscillation command instructing relative oscillation between a workpiece and a cutting tool on a movement command instructing relative movement between the workpiece and the cutting tool to generate air cuts when the workpiece is cut with the cutting tool, thereby crushing chips.List of Citer ListsPatent DocumentPatent Document 1: Japanese Unexamined Patent Application, Publication No. 2020-144588Disclosure of the InventionProblems to be Solved by the InventionIn such a machine tool control, the chips are crushed into smaller pieces by the relative oscillation, whereby problems such as the chips being caught in the cutting tool can be avoided. However, the present inventors have focused on the potential for the occurrence of the following problems.That is, depending on the oscillation conditions, there is a risk that the frequency of the relative oscillation coincides with the resonance frequency of the machine tool, thereby causing mechanical resonance. As a result, this risk may lead to errors in the machining of the workpiece, stoppage of the machine tool, or damage to the cutting tool. On the other hand, it is difficult to ensure that mechanical resonance does not occur in advance because it requires comprehensive inspection of individual machining conditions because the oscillation conditions may vary depending on the machining conditions.In view of these circumstances, the present disclosure aims to achieve both chip crushing and mechanical resonance suppression.Means for Solving the ProblemsA machine tool controller of the present disclosure controls a machine tool having a cutting tool for cutting a workpiece and superimposes an oscillation command instructing relative oscillation between the workpiece and the cutting tool on a movement command instructing relative movement between the workpiece and the cutting tool, thereby generating air cuts to crush chips when cutting the workpiece, the machine tool controller including:a position information acquisition unit that acquires position information on a relative position between the workpiece and the cutting tool;a state judging unit that judges an unstable state on the condition that a position deviation exceeds a threshold, the position deviation increasing when a difference between an actual relative position as the relative position based on the position information and a target relative position as the relative position based on the movement command and the oscillation command increases; andan oscillation switching unit that performs switching processing for changing an oscillation condition of the relative oscillation on the condition that the unstable state has been detected.A machine tool control program of the present disclosure causes a computer to function as a machine tool controller that controls a machine tool having a cutting tool for cutting a workpiece and superimposes an oscillation command instructing relative oscillation between the workpiece and the cutting tool on a movement command instructing relative movement between the workpiece and the cutting tool, thereby generating air cuts to crush the chips when cutting the workpiece, the machine tool control program further causing the computer to operate as units including:a position information acquisition unit that acquires position information on a relative position between the workpiece and the cutting tool;a state judging unit that judges an unstable state on the condition that a position deviation exceeds a threshold, the position deviation increasing when a difference between an actual relative position as the relative position based on the position information and a target relative position as the relative position based on the movement command and the oscillation command increases; andan oscillation switching unit that performs switching processing for changing an oscillation condition of the relative oscillation on the condition that the unstable state has been detected.Effects of the InventionBy the present disclosure, both the grinding of chips and the suppression of mechanical resonance can be achieved.Brief Description of the DrawingsFIG. 1 is a configuration diagram showing the machine tool controller and the machine tool of the first embodiment; FIG. 2 is a configuration diagram illustrating the machine tool controller; FIG. 3 is a diagram showing the transition between the actual relative position and the positional deviation; FIG. 4 is a configuration diagram showing the machine tool controller of the second embodiment; FIG. 5 is a diagram illustrating the transition of the positional deviation; and FIG. 6 is a configuration diagram showing the machine tool controller of the third embodiment.Preferred Modes for Carrying Out the InventionHereinafter, embodiments of the present disclosure will be described with reference to the drawings. However, the present disclosure is not limited to the following embodiments and can be implemented with appropriate changes without departing from the spirit of the present disclosure.[First Embodiment]As illustrated in FIG. 1, the machine tool 80 includes a workpiece holding unit 85 that holds the workpiece 86 and a tool holding unit 87 that holds the cutting tool 88. The workpiece holding unit 85 is driven by, for example, a first motor 81 aas a spindle motor, while the tool holding unit 87 is driven by a second motor 81 band a third motor 81 c. Hereinafter, the first motor 81 a, the second motor 81 b, and the third motor 81 care collectively referred to as "motor 81".The relative movement between the workpiece holding unit 85 and the tool holding unit 87 results in a relative movement between the workpiece 86 and the cutting tool 88. The relative oscillation between the cutting tool 88 and the workpiece 86 in a direction intersecting the direction of the relative movement is simply referred to as "relative oscillation".Each motor 81 includes an encoder 82 that detects the rotation angle of the motor 81. Hereinafter, the relative position based on the rotation angle detected by the encoders 82 is referred to as "actual relative position Pa".The machine tool controller 50 controls the machine tool 80 as described above. The machine tool controller 50 is mainly composed of, for example, a numerical controller and a servo controller that operates the motor 81 and the like on the basis of commands from the numerical controller. From another viewpoint, the machine tool controller 50 is configured mainly by a computer Cp and a machine tool control program Pg that causes the computer Cp to function as the machine tool controller 50. Here, the computer Cp includes a numerical controller, a servo controller, and the like, and includes a computing unit, a display, an operation unit, etc. The computing unit of the computer Cp includes, for example, a CPU, RAM, ROM, etc.The machine tool controller 50 presses the cutting tool 88 against the workpiece 86 by a relative movement controlled by the machine tool 80 and cuts the workpiece 86 with the cutting tool 88 by another relative movement. Further, by the machine tool controller 50 superimposing the relative movement in cutting the workpiece 86 with the relative oscillation, the cutting tool 88 intermittently generates air cuts in which the cutting tool does not cut the workpiece 86, thereby crushing the chips.As illustrated in FIG. 2, the machine tool controller 50 includes a machining command unit 11, a movement command unit 18, an oscillation command unit 28, an adder 21, a subtractor 22, a position / speed control unit 35, and a current control unit 36.The machining command unit 11 is configured to allow a machining program to be input by the user who operates, for example, the operation unit while checking the display of a numerical control device or the like.The movement command unit 18 calculates a "movement command C 1" as a relative movement command value on the basis of the machining command Cx derived from the machining program. The oscillation command unit 28 calculates an "oscillation command C 2" as a command value for relative oscillation on the basis of the machining conditions X derived from the machining program. Specifically, the oscillation command unit 28 calculates a repetitive sinusoidal command as the oscillation command C 2.The adder 21 acquires the motion command C 1 from the motion command unit 18 and the oscillation command C 2 from the oscillation command unit 28. the adder 21 then calculates a superposition command C 3 by adding the oscillation command C 2 to the motion command C 1. Hereinafter, the relative position when the relative movement is accurately performed in accordance with the superimposition command C 3 is referred to as a "target relative position Pc".The subtracter 22 acquires the target relative position Pc from the adder 21 and the actual relative position Pa from the encoder 82, and then the subtracter 22 calculates the position deviation ΔP by subtracting the actual relative position Pa from the target relative position Pc.The position / velocity control unit 35 acquires the position deviation ΔP from the subtracter 22. In other words, the position / velocity control unit 35 performs feedback control in cooperation with the subtracter 22.The current control unit 36 calculates a current value based on the torque command received from the position / speed control unit 35, and operates the motor 81 based on the calculated current value. In this way, the cutting tool 88 can cut the workpiece 86 while making air cuts to crush the chips.Next, with reference to FIG. 3, the problem to be solved by the present embodiment will be described. The upper curve in FIG. 3 shows an example of the transition of the actual relative position Pa. In other words, the upper curve is drawn black because it is close to each other in the lateral direction, but indicates a wave shape including relative oscillation. The broken line superimposed on the curve having the actual relative position Pa indicates the target relative position Pc. The amplitude of the target relative position Pc is smaller than the amplitude of the actual relative position Pa in most periods of time t 1 and t 2 described later. The lower curve shows the transition of the position deviation ΔP. The positional deviation ΔP is also colored in black because they are close to each other in the lateral direction, but exhibits a wavy shape with a cycle almost equal to that of the actual relative position Pa. In FIG. 3, the positional deviation ΔP is illustrated with an enlarged vertical axis. Therefore, the length of "ΔP" on the vertical axis in FIG. 3 is longer than the length of the difference between "Pc" and "Pa" on the vertical axis.Hereinafter, the period in which the relative movement and the relative oscillation are performed in a predetermined manner is referred to as "first period t 1" and the period in which the relative movement and the relative oscillation are performed in another manner is referred to as "second period t 2". During the first period t 1, no appreciable mechanical resonance occurs, so that the position deviation ΔP remains relatively small. In contrast, during the second period t 2, the mechanical resonance occurs more strongly, so that the positional deviation ΔP is larger than that in the first period t 1. This may result in errors in the machining of the workpiece 86, stoppage of the machine tool 80, or damage to the cutting tool 88.To solve these problems, as illustrated in FIG. 2, the machine tool controller 50 further includes a threshold setting unit 24, a state judgment unit 25, and an oscillation switching unit 26.The threshold setting unit 24 acquires the oscillation command C 2 from the oscillation command unit 28, calculates the "command amplitude" as the amplitude of the target relative position Pc, and sets a value larger than this command amplitude as the threshold ΔPth for the positional deviation ΔP. Specifically, the threshold setting unit 24 sets the threshold ΔPth to a larger value as the command amplitude increases. More specifically, the threshold setting unit 24 sets the threshold ΔPth to, for example, a value obtained by multiplying the command amplitude by a predetermined value or by further adding or subtracting a predetermined value to / from the obtained value. Alternatively, the threshold ΔPth may be increased stepwise as the command amplitude increases. In other words, the threshold value ΔPth may be calculated not only by multiplying the command amplitude by a fixed value, but also may vary the predetermined value to be multiplied depending on the magnitude of the command amplitude. The threshold setting unit 24 transmits the set threshold ΔPth to the state judging unit 25.The state judging unit 25 acquires the positional deviation ΔP from the subtracter 22 and acquires the threshold value ΔPth from the threshold value setting unit 24. when the positional deviation ΔP is less than or equal to the threshold value ΔPth, the state judging unit 25 determines a stable state and determines an unstable state when the positional deviation ΔP exceeds the threshold value ΔPth. In other words, the state judgment unit 25 judges an unstable state when the positional deviation ΔP exceeds the threshold value ΔPth. The state judging unit 25 transmits the judgment result J to the oscillation switching unit 26.The oscillation switching unit 26, upon receiving the judgment result J indicating an unstable state, transmits a switching command Cs to the oscillation command unit 28.Hereinafter, the vibration frequency of the target relative position Pc is referred to as "command frequency". The oscillation switching unit 26 transmits at least one command for changing the command frequency or a command for decreasing the command amplitude as a switching command Cs to the oscillation command unit 28.When the stable state is not reached even after the switching, the state judgment unit 25 again determines an unstable state, and the oscillation switching unit 26 outputs another switching command Cs for switching the oscillation conditions again. This switching of the oscillation conditions is repeated until the stable state is reached, i.e., until the amplitude of the positional deviation ΔP falls below the threshold value ΔPth. Finally, a stable state is achieved.The configuration and the effects of the present embodiment will be summarized below.The adder 21 generates a superposition command C 3 by superposing the oscillation command C 2 on the movement command C 1. Based on this overlay command C 3, the position / velocity control unit 35 and the current control unit 36 control the motor 81 to perform cutting of the workpiece 86 and generate air cuts. This enables cutting of the workpiece 86 while crushing the generated chips, thereby preventing problems such as chip catching in the cutting tool 88.The subtracter 22 detects the target relative position Pc from the adder 21 and the actual relative position Pa from the encoder 82, and calculates the position deviation ΔP. The state judgment unit 25 determines an unstable state when the position deviation ΔP exceeds the threshold value ΔPth. The oscillation switching unit 26 switches the oscillation conditions of the relative oscillation when an unstable state is detected. By avoiding the unstable state, the mechanical resonance can be suppressed.As described above, the present embodiment can achieve both the grinding of chips and the suppression of mechanical resonance. In particular, the following effects can be obtained:When the oscillation switching unit 26 detects an unstable state, it performs either the change of the command frequency or the decrease of the command amplitude as the switching operation. When the command frequency is changed, the frequency of the relative oscillation is shifted away from the resonance frequency of the machine tool 80, whereby mechanical resonance can be avoided. As the command amplitude is decreased, the amplitude of the relative oscillation is suppressed, whereby mechanical resonance can be decreased. Therefore, the mechanical resonance can be suppressed by these methods.The threshold setting unit 24 calculates the threshold ΔPth based on the magnitude of the command amplitude. Specifically, the threshold setting unit 24 may set an appropriate threshold ΔPth by setting the threshold ΔPth to a value larger than the command amplitude calculated by the oscillation commanding unit 28 each time.[Second Embodiment]Next, the second embodiment will be described with reference to FIGS. 4 and 5. The present embodiment will be described with a focus on the differences from the first embodiment, and the aspects that are the same or similar to the first embodiment will be omitted as appropriate.As illustrated in FIG. 4, the machine tool controller 50 of the present embodiment further includes a deviation storage unit 23. the deviation storage unit 23 acquires and stores the positional deviation ΔP from the subtractor 22. This will be described in detail as follows.As illustrated in FIG. 5, the oscillation cycle of the position deviation ΔP is referred to as "deviation oscillation cycle ωΔ", and the oscillation cycle of the target relative position Pc is referred to as "command oscillation cycle ωc". As described above, the adder 21 superimposes the motion command C 1 on a repetitive sinusoidal command as the oscillation command C 2. Therefore, the positional deviation ΔP includes noises such as cut noises and also many frequency components that match the aforementioned sinusoidal command. In other words, the command oscillation cycle ωc and the deviation oscillation cycle ωΔ are substantially the same. Hereinafter, the command oscillation cycle ωc and the deviation oscillation cycle ωΔ are collectively referred to as "oscillation cycle ω". Further, the interval divided based on the oscillation cycle ω is referred to as a "divided portion Sc", and the maximum value of the positional deviation ΔP within the divided portion Sc is referred to as a "maximum portion deviation ΔPmax". However, instead of the maximum value of the position deviation ΔP, the maximum absolute value of the position deviation ΔP may be referred to as "maximum section deviation ΔPmax".The threshold setting unit 24 calculates the maximum section deviation ΔPmax for each divided section Sc. In the present embodiment, the length of each divided portion Sc is an integer multiple of half the length of the oscillation cycle ω. Therefore, the maximum value of the positional deviation ΔP in each divided section Sc becomes the maximum section deviation ΔPmax in this divided section Sc. The state in which the maximum section deviation ΔPmax reaches the minimum value ΔPmax_min can be regarded as a stable state of the position deviation ΔP, i.e., a stable state.The threshold setting unit 24 sets the threshold ΔPth to a value obtained by multiplying the minimum value ΔPmax_min of the maximum section deviation by a predetermined multiplication factor larger than 1. Alternatively, the threshold value ΔPth may be set to a value obtained by multiplying the average value of the maximum section deviation ΔPmax within a plurality of predetermined divided sections Sc by a predetermined multiplication factor greater than 1.The threshold setting unit 24 transmits the set threshold ΔPth to the state judging unit 25 as illustrated in FIG. 4. The subsequent steps are the same as in the first embodiment. Therefore, the state judging unit 25 performs state judgment based on the received threshold value ΔPth.The following is a summary of the configuration and the effects of the present embodiment.The deviation storage unit 23 stores the position deviation ΔP. The threshold value setting unit 24 calculates the threshold value ΔPth on the basis of the history ΔPd of the positional deviation ΔP stored in the deviation storage unit 23. Therefore, instead of simply setting the threshold value ΔPth based on the command amplitude, the threshold value ΔPth may be set based on the history of the positional deviation ΔP. Therefore, more appropriate setting of the threshold value ΔPth is expected.The threshold setting unit 24 calculates the maximum section deviation ΔPmax for each divided section Sc. The maximum section deviation ΔPmax is calculated sequentially, the calculated maximum section deviation ΔPmax is then compared with the stored maximum section deviation ΔPmax, and the smaller of the two values is continuously updated as the minimum value ΔPmax_min. This minimum value ΔPmax_min can be regarded as a stable state of the position deviation ΔP, i.e., a stable state. Since the threshold value ΔPth is determined based on this minimum value ΔPmax_min, more appropriate settings of the threshold value ΔPth are expected.The adder 21 superimposes a repetitive sinusoidal command on the motion command C 1 as the oscillation command C 2. As a result, the positional deviation ΔP also contains many frequency components that match those of this sinusoidal command. In consideration of this property, the cycle of the divided portion Sc is set to an integer multiple of half the cycle of the command oscillation cycle ωc. By setting the threshold value ΔPth by setting the maximum deviation in this divided section Sc as the maximum deviation ΔPmax, more appropriate settings for the threshold value ΔPth can be achieved.The threshold setting unit 24 sets the threshold ΔPth to a value obtained by multiplying the minimum value ΔPmax_min of the maximum section deviation or the average value of the maximum section deviation ΔPmax within a plurality of divided sections Sc by a predetermined multiplication factor greater than 1. This provides a margin between the minimum value ΔPmax_min and the threshold value ΔPth or between the average value and the threshold value ΔPth. This can prevent an unstable state from being detected each time the positional deviation ΔP exceeds the threshold value ΔPth due to noise or the like.[Third Embodiment]Next, the third embodiment will be described with reference to FIG. 6. The present embodiment will be described with emphasis on the differences from the second embodiment, and the aspects that are the same or similar to the second embodiment will be omitted as appropriate.The machine tool controller 50 further includes a learning unit 33 and a second adder 21 b. The learning unit 33 calculates a correction amount α based on the position deviation ΔP, and decreases the position deviation ΔP by adding the calculated correction amount α to the position deviation ΔP using the second adder 21 b. The learning unit 33 includes a memory, and stores the oscillation phase and the positional deviation ΔP in association with each other in the memory within one or more oscillation cycles. The learning unit 33 outputs the correction amount α calculated based on the positional deviation ΔP stored in the memory to the second adder 21 bat a timing that can compensate the phase delay of the oscillation operation in accordance with the response characteristics of the motor 81. In general, the higher the oscillation frequency, the larger the position deviation ΔP with respect to the command amplitude. By correcting with this learning unit 33, it is possible to improve the tracking performance of the actual relative oscillation to the cyclic oscillation command C 2. This also improves the tracking performance of the actual relative position Pa to the target relative position Pc, thereby decreasing the positional deviation ΔP. Consequently, the machining accuracy can be improved.As described above, the learning unit 33 calculates the correction amount α based on the position deviation ΔP, and corrects the position deviation ΔP by adding the calculated correction amount α to the position deviation ΔP. Thereby, the positional deviation ΔP is decreased. The oscillation conditions are changed on condition that the positional deviation ΔP exceeds the threshold value ΔPth. Therefore, it is expected that the frequency of the changes in the oscillation conditions is suppressed and that the mechanical resonance is further suppressed.[Other Embodiments]The above-described embodiments may be modified as follows, for example. As the switching operation, the oscillation switching unit 26 may perform an operation of notifying the user of that the oscillation conditions need to be changed by at least one of a display and a sound instead of changing the oscillation conditions. In particular, for example, the display can provide the display as a switching operation. Alternatively, the oscillation switching unit 26 may include a speaker, and the speaker may output the sound as a switching operation. 22 Subtractor (position information acquisition unit) 23 Deviation storage unit 24 Threshold setting unit 25 State judgment unit 26 Oscillation switching unit 33 Learning unit 50 Machine tool controller 80 Machine tool 86 Workpiece 88 Cutting tool C 1 Movement command C 2 Oscillation command C 3 Superimposition command Cp Computer Pa Actual relative position Pc Target relative position Pg Machine tool control program ΔP Position deviation ΔPthThreshold value ΔPmax Maximum section deviation ΔPmax_min Minimum value of maximum section deviation ω Oscillation cycleReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedJP 2020-144588

[0003] JP

Claims

A machine tool controller that controls a machine tool having a cutting tool for cutting a workpiece and superimposes an oscillation command instructing relative oscillation between the workpiece and the cutting tool on a movement command instructing relative movement between the workpiece and the cutting tool, thereby generating air cuts for crushing chips when cutting the workpiece, the machine tool controller comprising: a position information acquisition unit that acquires position information on a relative position between the workpiece and the cutting tool; a state judging unit that determines an unstable state on the condition that a position deviation exceeds a threshold, the position deviation increasing when a difference between an actual relative position as the relative position increases based on the position information and a command relative position as the relative position based on the movement command and the oscillation command; and an oscillation switching unit that executes switching processing for changing an oscillation state of the relative oscillation on the condition that the unstable state has been detected.The machine tool control device according to claim 1, wherein the oscillation switching unit performs, as the switching operation, at least one of a relative oscillation frequency changing processing and a relative oscillation amplitude reducing operation based on the oscillation command.The machine tool controller according to claim 1, wherein the oscillation switching unit performs an operation for notifying a user that the oscillation condition needs to be changed through at least one of a display and a sound as the switching operation.The machine tool controller according to any one of claims 1 to 3, further comprising a threshold setting unit that sets the threshold to a value larger than the amplitude of the relative oscillation based on the oscillation command.The machine tool controller according to any one of claims 1 to 3, further comprising: a deviation storage unit that stores the positional deviation; and a threshold setting unit that sets the threshold on the basis of the history of the positional deviation stored in the deviation storage unit.The machine tool controller according to claim 5, wherein the threshold setting unit calculates a maximum section deviation as a maximum value of the position deviation or a maximum absolute value of the position deviation for each divided section divided based on an oscillation cycle as a cycle of the relative oscillation, and determines the threshold based on the maximum section deviation.The machine tool controller according to claim 6, wherein a length of each divided portion is an integer multiple of a half length of the oscillation cycle.The machine tool controller according to claim 6 or 7, wherein the threshold setting unit sets the threshold to a value obtained by multiplying the maximum section deviation of the divided section in which the maximum section deviation s becomes minimum or an average value of the maximum section deviation for a plurality of the divided sections by a predetermined multiplication factor greater than 1.The machine tool controller according to any one of claims 1 to 8, further comprising a learning unit that calculates a correction amount of the positional deviation based on the positional deviation and corrects the positional deviation by adding the calculated correction amount to the positional deviation.A machine tool control program that causes a computer to function as a machine tool controller that controls a machine tool having a cutting tool for cutting a workpiece and superimposes an oscillation command that instructs relative oscillation between the workpiece and the cutting tool on a movement command that instructs relative movement between the workpiece and the cutting tool, thereby generating air cuts for crushing chips when cutting the workpiece, wherein the machine tool control program causes the computer to operate as units including: a position information acquisition unit that acquires position information on a relative position between the workpiece and the cutting tool; a state judging unit that determines an unstable state on the condition that a position deviation exceeds a threshold, the position deviation increasing when a difference between an actual relative position as the relative position based on the position information and a target relative position as the relative position based on the movement command and the oscillation command increases; and an oscillation switching unit that executes switching processing for changing an oscillation state of the relative oscillation on the condition that the unstable state has been detected.

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