JPH11207501A - Galling detecting method and device for guide bush for machine tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the burnout of a bush by detecting the generation of galling due to the overload of a fixed guide bush, when both sides, of a compared result of a current change rate with a critical value and that of the variation gradient of the current change rate with the critical value, show over-criticality. SOLUTION: A critical value is used as a standard value to be compared with the measured value of a drive current in an actual work piece working process, the change rate of the drive current, and the variation gradient of the change rate of the drive current. When respective critical values show over-criticality, an output signal showing over-criticality is outputted to an alarm sounding part 38 via an interface part 36 to sound a warning signal. In this case, the alarm sounding part 38 sounds the warning signal when the output signal showing over-criticality is sent from e.g. both a current change rate operation part 44 and a current change rate gradient operation part 46.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for detecting galling of a guide bush of a machine tool, and more particularly to a method of fixing a rotating workpiece, which is gripped by a main shaft of a machine tool, in a non-rotating state immediately near a machining position. The workpiece is machined with a tool such as a tool attached to the tool post while being stably supported by the fixed guide bush, and the machining data such as the workpiece feed by the spindle and the cutting amount of the machining tool is controlled by the NC program. The motor is used to monitor the current value of the spindle drive motor for the occurrence of galling of the fixed guide bush that occurs when an overload is applied to the fixed guide bush during machining of workpieces. This is an effective process to detect accurately and prevent the fixed guide bush from burning out beforehand and surely. An apparatus and galling detection method of the machine of the guide bush.

[0002]

2. Description of the Related Art A machine tool, in particular, a workpiece is gripped by a rotating spindle of the machine and fed to a machining position in front of the rotating spindle, and a guide bush is provided immediately near the machining position. It has a configuration to stably support the immediate vicinity of the work part of the work, and to machine the work part of the work with a machining tool such as a cutting tool at the processing position with high precision. Automatic machines that control machining data, such as the amount of cutting of a machining tool by movement and indexing of a machining tool attached to a tool post to a machining position, by a well-known NC program, have already been frequently used.

In this type of automatic lathe, a rotary guide bush is provided as the above-described guide bush so as to be rotatable in the immediate vicinity of the processing position of the work, and supports the work while rotating in synchronization with the rotation of the main shaft and the work. And a fixed type guide bush, which is fixedly held in the non-rotation state in the immediate vicinity of the processing position and slides and supports a rotating work, are known. The fixed type guide bush supports the work rotating with the spindle in the immediate vicinity of the processing position, receives the load applied during processing, and supports the work without swinging, and requires high precision in order to enable high precision processing. In particular, it is frequently used for machining precision parts.

However, in the case of an automatic lathe using a fixed type guide bush, if machining is progressed under conditions of high rotation and high load, friction occurs between the rotating work and the fixed type guide bush. Since galling occurs and the fixed guide bush may be burned out, there is a problem that processing is restricted by the processing conditions. In order to avoid such a problem, in particular, for a fixed guide bush in an automatic lathe having a spindle mechanism for directly rotating a spindle by a motor such as a spindle built in a motor (built-in spindle) or the like, The drive current supplied to the motor for driving the spindle is monitored, an appropriate threshold value is set in advance from the drive current value that increases when galling occurs by an experimental method or the like, and the motor drive current is monitored for this threshold value. An automatic lathe configured to generate an alarm when the threshold value is exceeded is already provided, but the drive current of the spindle motor is simply compared with a threshold value determined by considering the drive current value that increases when galling occurs. When the alarm is issued, the fixed guide bush is seized due to galling at the time when the alarm is issued, and it takes a lot of time to recover the automatic lathe. If a problem such as that occurs there is a problem that frequently. In this case, if the threshold value is set to a low level in order to avoid such burning of the fixed type guide bush, the drive current increases at the time when a load is applied at the time of starting the work of the workpiece and the material condition of the work to be processed ( The problem that the threshold value cannot be easily set to a low level due to the occurrence of new troubles such as the drive current exceeding the set threshold value depending on the size of the work diameter or the difficulty of cutting the work). There is.

[0005]

SUMMARY OF THE INVENTION Accordingly, a main object of the present invention is to eliminate the above-mentioned problems associated with a machine tool, particularly an automatic lathe having a structure for supporting a workpiece using a fixed guide bush. . Another object of the present invention is to provide a machine tool that can detect the occurrence of galling of the fixed guide bush in a machine tool using the fixed guide bush at an early stage and prevent the guide bush from burning. It is an object of the present invention to provide a method and an apparatus for detecting galling of a guide bush.

[0006]

SUMMARY OF THE INVENTION In view of the above-mentioned object, the present invention measures a drive current of a spindle drive motor during a machining process of a workpiece by a machine tool using a fixed guide bush, and measures the measured drive current. Based on the drive current measured together with the drive current value obtained, the change rate of the drive current with respect to time and the change gradient of the drive current with respect to time are also obtained and monitored, and these drive current values and drive currents are monitored. The rate of change of the drive current and the rate of change of the rate of change of the drive current are provided with a configuration that can be compared with the respective critical values experimentally obtained for the fixed guide bush in advance, and the workpiece is gripped by the spindle and rotates. Is fixed by a fixed guide bush, and when the fixed type guide bush is galled during a machining process of machining the work with a machining tool, the above-mentioned three members are used. Machine tool that detects galling at an early stage based on the values and the respective critical values, and can quickly achieve alarm processing to prevent seizures such as spindle rotation stop or withdrawal of the machining tool from the machining position. And a method and apparatus for detecting galling of the guide bush.

That is, according to the present invention, a work held by a main shaft of a machine tool is supported by a fixed guide bush fixed and held in the immediate vicinity of a processing position so that the work is machined. In the method of detecting galling due to overload, a drive current to the drive motor of the main shaft is measured, and a rate of change of current with respect to time is obtained from the measured current value. The change rate of the current change rate with respect to time is obtained from the obtained change rate of the current by comparing with the critical value of the current change rate set in advance, and is set in advance in response to the occurrence of galling of the fixed guide bush. Comparing the current change rate with the critical value, and comparing the current change rate with the critical value and the current change rate. When the comparison result of the two together critical over the value, than is galling detection method of a machine tool guide bush, characterized is provided to detect the galling due to an overload of the fixed guide bush.

The measured value of the drive current of the spindle drive motor is compared with a critical value of the drive current value which is set in advance in response to the occurrence of galling of the fixed guide bush. When both the comparison result with the critical value of the current change rate and the comparison result with the critical value of the variation gradient of the current change rate are over the criticality, the galling due to the overload of the fixed guide bush is detected. A method for detecting galling of a guide bush of a machine tool may be used.

Further, according to the present invention, a work gripped by a spindle of a machine tool is supported by a fixed guide bush fixed and held in the immediate vicinity of a machining position so that the guide bush when machining the work is provided. In the method of detecting galling due to overload, current measuring means for measuring a driving current of the spindle drive motor, and a drive current of the spindle drive motor for causing galling due to overload on the fixed guide bush. A critical value, a critical value of the rate of change of the drive current, a storage unit that stores in advance a critical value in a variation gradient of the rate of change of the drive current as comparison data of a galling condition, and the current when the workpiece is machined by the machine tool. A current calculation unit for comparing whether the current value measured by the measuring means is over the critical value with respect to the critical value of the driving current, and computing the current value; A current change rate calculator for calculating a change rate of current with respect to time from a current value measured by the current measuring means during machining of a workpiece by the machine tool, and comparing and calculating the current change rate with a critical value of the current change rate; A current change rate variation gradient calculator for calculating a change gradient of the current change rate with respect to time from the current change rate and comparing and calculating the change gradient with the critical value of the current change rate; and a critical value of the current change rate Comparison with the calculation result and the critical value of the variation gradient of the current change rate, when at least both of the calculation results are over critical, a signal indicating that galling due to overload of the fixed guide bush is detected. A galling detection device for a guide bush of a machine tool, comprising:

[0010]

According to the above-described method and apparatus for detecting the galling of the guide bush of the machine tool, the cause of the fluctuation in the drive current of the motor for driving the spindle of the machine tool is, for example, due to acceleration at the start of rotation of the spindle. Accurate detection of galling generated in the fixed guide bush by discriminating it from the increase in drive current caused by fluctuations in the load applied to the fixed guide bush at the start of machining with the machining tool using a machining tool for the workpiece However, it is possible to perform burnout prevention processing of the guide bush, such as stopping the spindle rotation and retreating the processing tool, and at the same time, perform an alarm for occurrence of galling to appropriately perform processing for improving work processing conditions. .

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail based on embodiments shown in the accompanying drawings. Now, FIG.
Equipped with a fixed type guide bush, the work is driven to rotate by holding the work by the main shaft, and at the same time, feed is given toward the processing position, and the processing of the cutting tool etc. attached to the tool post at the processing position It is a schematic sectional drawing which shows the example of the automatic lathe which has the structure which processes a workpiece | work with a tool.

Referring to FIG. 1, the automatic lathe includes a main shaft 10 for gripping a work W. The main shaft 10 has a hollow interior as a feed path for the work W, and has a chuck portion for gripping the work W at its tip. In response to a driving action of a spindle drive motor (not shown), the machine frame 12 of the automatic lathe is driven to rotate around a rotation axis as indicated by an arrow. The spindle 10 is held by a spindle stock 13 and is provided so as to be able to advance and retreat in the longitudinal axis direction as shown by an arrow X, and therefore is advanced together with the spindle stock 13 in advance toward a fixed type guide bush described later. Thus, the workpiece W can be positioned at a position suitable for processing. The spindle 10 positioned
Is configured to be capable of applying a feeding operation to the work W along the longitudinal axis direction.

At one end of the machine frame 12, a tool rest 16 is provided. The tool rest 16 is provided in two axial directions perpendicular to the rotation axis of the main shaft 10, that is, perpendicular to the plane shown in FIG. The tool post 16 is provided with one or a plurality of machining tools 18 such as cutting tools, and is movable with respect to the workpiece W. It is possible to make a predetermined amount of cut in the work tool 18 to the work W by the feed action of the feed mechanism (not shown) in the Z-axis direction at the same time as being able to be positioned toward the processing position where mechanical processing such as cutting is performed. Configuration.

The automatic lathe is further provided with a fixed die disposed coaxially with the axis of the main spindle 10 at a position close to a machining position where the workpiece W is processed by the machining tool 18 in front of the front end of the main spindle 10. The guide bush device 20 is provided. The fixed type guide bush device 20 includes a housing 21 fixed to the machine frame 12 and a non-rotatable guide bush element 22 fixedly arranged at the center of the front end of the housing 21. The latter guide bush element 22 is disposed so as to more stably support the workpiece W gripped by the main shaft 10 at a position immediately close to the processing position. That is, the workpiece W has a configuration in which the workpiece W is supported by the non-rotatable guide bush element 22 of the guide bush device 20 while rotating together with the main shaft 10 during processing. Accordingly, the guide bush element 22 of the fixed type guide bush device 20 slides and supports the work W in a sliding bearing manner during the processing and also supports the work W without play, so that the work W can be processed with high precision. It has.

However, as described above, the machining tool 18
When the workpiece W is machined by the above, a load accompanying the machining action is applied to the contact and support portion between the workpiece W and the support receiving surface of the non-rotating guide bush element 22, and when this load becomes excessive, the fixed guide bush Galling occurs in the guide bush element 22 of the device 20, and if the main shaft 10 and the work W continue to rotate while maintaining this galling state, the guide bush element 22 will burn out due to high frictional heat in the contact support portion. .

The present invention is intended to detect the galling of the non-rotatable guide bush 22 of the fixed type guide bush device 20 at an early stage so as to prevent burnout. In general, the rotation of the spindle 10 shown in FIG. 1, the work feeding operation in the X-axis direction, the Y-axis
The feed operation in the axial direction and the like are controlled by a numerical control (NC) method, and therefore, a configuration is provided in which the machining process of the work W is automatically performed according to the NC program.

FIG. 2 shows a specific embodiment for detecting the galling of the guide bush according to the present invention.
In particular, an embodiment in the case of performing galling detection using a well-known arithmetic element such as a CPU or MPU and a memory element provided in the NC device is illustrated. In the embodiment shown in FIG. 2, the spindle drive motor, that is, the spindle 10 based on the NC program of the NC device described above.
The drive current supplied from the motor control unit 32 that drives and controls the rotation of FIG. 1 to the spindle motor 30 is always measured by the current measurement unit 34, and the measurement result is used as a scoring detection control unit provided in the NC control device. It has a configuration to be sent to the PC 40 via an appropriate interface unit 36.

At this time, in the galling detection control section 40, the drive current as the measurement result is input to the current calculation section 42. The current change rate calculator 44 connected to the current calculator 42 calculates the change rate of the measured drive current of the spindle motor 30 over time. Further, in the current change rate gradient calculation section 46 connected to the current change rate calculation section 44, the change rate of the drive current measured based on the change rate calculated in the current change rate calculation section 44 is further changed with time. A fluctuation gradient is calculated. The current calculation unit 42, the current change rate calculation unit 44, and the current change rate gradient calculation unit 46 can achieve a desired calculation function by using the above-described calculation elements included in the NC device.

On the other hand, the galling detection control unit 40 includes an NC
A comparison data storage unit 48 is provided, which is configured using the memory means of the device. The comparison data storage unit 48 includes a main spindle in the case where the guide bush element 22 of the fixed type guide bush device 20 is liable to galling. The drive current of the motor 30 is measured for various types of work samples, and a critical current value set from an increase in the drive current due to galling, and a time lapse calculated from a measured value of the drive current when galling occurs The values of the critical change rate in the current change rate and the critical gradient value in the change gradient of the change rate of the drive current are experimentally obtained and stored.

These critical values are used as reference values to be compared with the measured value of the drive current, the rate of change of the drive current, the variation gradient of the rate of change of the drive current in the actual work processing step, and the like. In the case where the threshold value is over the critical value, an output signal indicating the critical over is output to the alarm generating unit 38 via the interface unit 36 to generate an alarm signal. In this case, the alarm generation unit 38 is configured to generate an alarm signal when an output signal indicating over criticality is sent from both the current change rate calculation unit 44 and the current change rate gradient calculation unit 46, for example. Or an alarm signal is generated when an output signal indicating criticality over is sent from all three of the current calculation unit 42, the current change rate calculation unit 44, and the current change rate gradient calculation unit 46. The external command signal E ₀ for instructing whether to perform the setting is configured to be applied in the form of a command signal according to, for example, an NC program or in a form input from an input unit of the NC device by a manual operation of an operator. .

It should be noted that the comparison with each of the critical values described above is based on the fact that the current measuring section 34
Is calculated by subtracting the drive current value of the spindle motor 30 and the critical current value measured in step (1) to determine whether the criticality is exceeded.
In, an operation for determining whether or not the criticality is exceeded is performed by subtracting the previously calculated drive current change rate and the critical change rate value. Further, the current change rate gradient calculator 46 subtracts the previously calculated change gradient in the current change rate of the drive current from the critical slope value to perform an operation for determining whether or not the criticality is exceeded. Is done. In addition, with respect to the variation gradient of the change rate of the drive current over time, a lower critical value and an upper critical value of the critical variation gradient are provided, and the variation gradient of the change rate calculated based on the measured drive current is calculated. It has been experimentally confirmed that it is appropriate to detect that the fixed type guide bush device 20 is galling when it is within the upper and lower critical value ranges.

Referring now to FIGS. 3 to 5, FIG.
3 is a graph showing the fluctuation value of the drive current of the spindle motor 30 (FIG. 2) measured by the current measuring unit 34 (see FIG. 2) with the horizontal axis as the time axis and the vertical axis as the graph. In the curve indicated by the solid line, the peak value P1 of the drive current on the left end indicates a rising peak of the drive current of the spindle motor 30 in the process of increasing the speed of the spindle 10 of the automatic lathe from a stationary state to a predetermined machining rotation, When the predetermined machining rotational speed is reached, the drive current is reduced, indicating that only the rotational speed is maintained. When machining on the workpiece W is started at time Ta, the drive current for the spindle motor 30 starts machining. At this point, the curve once rises, but indicates that the drive current value is maintained in a stable horizontal linear state while the normal machining process is maintained thereafter. And
When galling occurs in the fixed guide bush device 20 at the time Tb for some reason, the drive current exceeds the above-described critical value Ia. Therefore, at this time, if a brake signal is applied to the spindle motor 30 by, for example, a known electromagnetic braking method at the same time as issuing an alarm signal, the drive current for the spindle motor 30 temporarily decreases until the start of application of the braking current, and then the braking is performed. This indicates that the current rises sharply. This braking current decreases rapidly when the spindle motor 30 stops.

However, as is clear from the curve in FIG. 3, when the rotation of the spindle 10 is started, the drive current of the spindle motor 30 sharply increases and exceeds the critical value Ia. In the illustrated example, the rise of the drive current due to the load at the start time Ta does not exceed the critical value Ia, but, for example, the start time of cutting of the large-diameter work W by the cutting tool or the start time of machining of the difficult-to-cut work W, etc. In this case, the driving current curve Ib shown by a dotted line in FIG. 3 may exceed the critical value Ia. Accordingly, the present invention improves the method of detecting the occurrence of galling of the fixed type guide bush device 20 by simply comparing the drive current with the critical value Ia as in the prior art, and further improves the rate of change of the drive current of the spindle motor 30. Further, the change gradient of the drive current change rate is focused on. That is, referring to FIG. 3 again, even when the fixed guide bush device 20 is galled, if the spindle motor 30 is left without braking, the drive current is compared with a drive current curve Ic indicated by a dotted line. It has been experimentally confirmed that a gradually increasing curve is obtained. The rate of change of this curve is clearly different from the rate of change of the drive current increase at the start of the no-load rotation of the spindle 10 or at the start of machining of the workpiece W. Attention is paid to, as described above, the critical value relating to the rate of change or the gradient of the drive current is obtained, and the galling detection of the fixed type guide bush device 20 is performed by comparing with the critical value. .

FIG. 4 is a graph showing the relationship between the change rate and the critical change rate of the drive current over time, which is performed by the current change rate calculator 44 (FIG. 2) based on the measurement result of the drive current of the spindle motor 30 shown in FIG. In the illustrated graph, the no-load drive current at the start of rotation of the main shaft 10 is still the critical value I.
p, but in the rotation acceleration process at the time of starting the rotation of the main shaft 10, the fixed guide bush device 20
Naturally, no galling occurs. Further, it can be seen that the rate of change of the drive current with respect to time at the processing start time Ta of the workpiece W does not exceed the critical rate of change Ip.

On the other hand, at the time point Tb when the occurrence of galling in the fixed type guide bush device 20 is confirmed, the change rate definitely exceeds the critical change rate Ip. However, in FIG. 3, when the drive current sharply increases at the start of machining, it is expected that the rate of change will exceed the critical rate of change Ip. For this purpose, in the present invention, the variation gradient of the rate of change with respect to time is compared with the critical gradient value.

That is, referring to FIG. 5, the graph of FIG. 5 shows the variation gradient of the drive current at the time of starting the rotation of the main shaft 10, the variation gradient at the start of machining of the workpiece W Ta,
The result of calculating the variation gradient at the time of the galling occurrence Tb of the fixed type guide bush device 20 by the current variation rate gradient calculator 46 (see FIG. 2) and the critical variation gradient value (in this case, the lower limit variation gradient value Iq and the upper limit value) The variation gradient value Ir) is illustrated, and when galling occurs in the fixed type guide bush device 20, the variation gradient intervenes between the lower limit variation gradient value Iq and the upper limit variation gradient value Ir. You can see that there is.

Therefore, according to the present invention, the fluctuations of the drive current, the change rate of the drive current with time, and the change rate of the change of the drive current with time shown in FIGS. , Iq, Ir, etc.
Rate of change of the drive current of the spindle motor 30 over time,
When the variation gradient of the rate of change of the drive current over time exceeds the respective critical values Ip and enters the critical range Iq to Ir, it is detected that the fixed type guide bush device 20 has galled. Thus, it is possible to reliably detect the occurrence of galling.

By measuring the drive current of the spindle motor 30, three parameters are calculated: the drive current variation, the rate of change of the drive current over time, and the variation gradient of the rate of change of the drive current over time. Therefore, by comparing the critical values Ia and Ip and the critical ranges Iq to Ir for these three parameters, an alarm signal is generated when all three parameters detect the occurrence of galling of the fixed guide bush device 20. Needless to say, it may occur.

FIGS. 6 and 7 are block diagrams showing another embodiment of the present invention. In this embodiment, a hardware element is used instead of an operation method using an operation element such as a CPU. 1 shows a configured embodiment. Also in the present embodiment, the configuration in which the drive current of the spindle motor 30 driven and controlled by the motor control unit 32 is measured by the current measuring unit 34 is the same as in the previous embodiment.

Here, first, referring to FIG. 6, the device for detecting galling of the fixed type guide bush according to the present embodiment is as follows.
It is provided with a drive current monitoring unit 50, a drive current change rate monitoring unit 60, and a drive current change rate fluctuation gradient monitoring unit 80. The driving current value measured by the current measuring unit 34 is stored in the storage 52 of the driving current monitoring unit 50, the first storage 62 in the driving current change rate monitoring unit 60, and the change gradient monitoring of the driving current change rate. First storage unit 8 in unit 80
2 has been entered.

The drive current monitor 50 is provided with the storage 52,
A fixed-interval time generator 54 composed of a timing pulse generating circuit, and a critical current value Ia of the drive current of the spindle motor 30 corresponding to the occurrence of galling of the fixed guide bush (see FIG. 3).
Is output as a set value, and a comparator 58 is provided. The drive current change rate monitoring unit 60 includes a first storage unit 62, a second storage unit 64, and a fixed interval time generator 66 including a timing pulse generation circuit similar to the fixed interval time generator 54; An operation setting device 68 for outputting a critical change rate value Ip (see FIG. 3) in a change rate of the drive current of the spindle motor 30 corresponding to the occurrence of galling of the fixed type guide bush as a set value, and a comparator 74 are provided. ing.

Further, the variation gradient monitor 80 for the change rate of the drive current has second to fourth storage units 84, 86 and 88 together with the first storage unit 82. It includes a fixed interval time generator 94 similar to the generators 54 and 66, first to third subtractors 96, 98, 102, and a comparator 104. In the drive current monitoring unit 50, the spindle motor drive current value of the measurement result input from the current measurement device 34 to the storage device 52 is output from the constant time generator 54.
From the storage device 52 in accordance with the time signal at which
Sent to At this time, the comparator 58 operates the operation setting device 5
6 and the drive current value sent from the storage device 52 are compared with the timing of the timing signal output from the fixed time generator 54, and the critical current value set by the operation setting device 56 is compared. When the drive current value sent from the storage device 52 exceeds Ia, the comparator 58 outputs an output signal C.

In the drive current change rate monitoring unit 60, the spindle motor drive current value of the measurement result input from the current measuring unit 34 to the first storage unit 62 is further output from the constant interval time generator 66. The second signal according to the timing signal
Is input to the storage unit 62 of. At this time, the second storage device 6
Numeral 2 stores the same drive current value as the current value stored in the first storage device 62. The first and second storage devices 62, 6
4 is input to a subtractor 72 in accordance with a timing signal output from a fixed interval time generator 66, and subtraction is performed to obtain a difference between the drive currents from both storage devices. In this case, the subtracter 72 outputs the subtraction result to the comparator 74. In the comparator 74, the operation setting unit 68
The critical change rate Ip set and output is set, and the output value of the difference between the drive currents output from the subtractor 72 in accordance with the timing signal output from the fixed time generator 66, the critical change rate Ip, and Compare. Then, the operation setting device 66
If the difference between the drive current output from the subtractor 72 and the change rate of the drive current with respect to the elapse of time with respect to the critical change rate Ip from, the output signal A is output from the comparator 74.

Further, in the variation gradient monitoring section 80 of the change rate of the drive current, when the measured value of the drive current of the spindle motor 30 is input to the first storage device 82, the first storage device 82 The data is sent to the second memory 84 and the first subtractor 96. Then, these first and second storage units 82, 8
4. The subtractor 96 is configured to receive the timing signal of the fixed interval time generator 94 and control the operation timing.

The second storage unit 84 stores the same drive current value as the measured drive current value stored in the first storage unit 82 at a shifted timing. Then, the measured value of the drive current stored in the second storage device 84 is further converted to a third value in accordance with the timing signal output from the constant interval time generator 94.
Is output to the storage unit 86 and to the first subtractor 96. The measured values of the drive current from the first and second storage units 82 and 84 sent to the first subtractor 96 in this way are
The difference is obtained by executing the subtraction in the subtractor 96 of the third embodiment.
02 is output.

On the other hand, the third storage unit 86 further stores the measured value of the drive current stored in the second storage unit 84 in accordance with the timing signal output from the fixed interval time generator 94, and is stored here. The measured drive current is output to the fourth storage unit 88 in accordance with the timing signal output from the fixed-interval time generator 94, and further output to the second subtractor 98.

At this time, the fourth storage 88 outputs the stored measured value of the driving current to the second subtractor 98 in accordance with the timing signal of the fixed time generator 94. Accordingly, the second subtractor 98 obtains the difference between the measured values at the two timings shifted by the minute timing of the driving current stored in the third and fourth storages 86 and 88 by subtraction, and calculates the driving current. Find the rate of change of current. Then, the difference obtained by the second subtractor 98 is output to the third subtractor 102, and the difference from the difference indicating the change rate previously output from the first subtractor 96 is obtained. The change gradient of the change rate of the drive current is finally obtained. The difference indicating the obtained fluctuation gradient is output to the comparator 104, and the critical value I of the fluctuation gradient output from the operation setting unit 92 is output.
It is compared with q and Ir to determine whether or not it is within the critical range. Then, when it is determined from the result of this determination that the output from the third subtractor 102 has entered the critical range (Iq to Ir), the comparator 104 outputs the output signal B. The signals C, A, and B output from the drive current monitoring unit 50, the drive current change rate monitoring unit 60, and the drive current change rate change gradient monitoring unit 80 are sent to the galling control unit 120 shown in FIG. Sent out. The galling control unit 120 includes first to fifth AND circuits 121 to 125
The high-potential signal is input to one input terminal of the first AND circuit 121 when the selection switch 131 of the selection circuit 130 is closed, and the output signal C (spindle) is input to the other input terminal. A signal indicating that the drive current of the motor has exceeded the critical value Ia) is input.

On the other hand, when the selection switch 132 of the selection circuit 130 is closed, a high potential signal is input to one input terminal of the second AND circuit 122, and the output signal A ( A signal indicating that the rate of change of the drive current of the spindle motor exceeds the critical value Ip) is input. Further, when the selection switch 132 of the selection circuit 130 is closed, a high potential signal is input to one input terminal of the third AND circuit 123, and the output signal B (for the spindle motor) is input to the other input terminal. A signal indicating that the variation gradient in the change rate of the drive current enters the critical range Iq to Ir) is input.

The selection circuit 130 is a circuit for selecting the opening and closing of the switches 131 and 132 as necessary. The selection circuit 130 operates only the first AND circuit 121 and simultaneously operates only the second and third AND circuits. And the first to third
Are provided as circuit means which can be selectively operated when all of the AND circuits 121 to 123 are operated.

Then, the second and third AND circuits 122,
When only 123 is selected, the same circuits 122, 12
When there are outputs at both output terminals of No. 3, the rate of change of the drive current of the spindle motor exceeds the critical value Ip, and the variation gradient in the rate of change of the drive current of the spindle motor enters the critical range Iq to Ir. Therefore, the second and third AND circuits 1
A detection signal D1 indicating the occurrence of galling is sent from a fourth AND circuit 124, whose outputs are output to the input terminals, to an appropriate alarm circuit for notifying an alarm state by, for example, an alarm sound or flashing of an alarm light. . On the other hand, when all of the first, second, and third AND circuits 121 to 123 are selected, and the output is generated at all the output terminals of these AND circuits, the drive current of the spindle motor has the critical value Ia. The rate of change of the drive current of the spindle motor exceeds the critical value Ip,
Further, since it is shown that the variation gradient in the change rate of the drive current of the spindle motor enters the critical region Iq to Ir,
Output terminal of fourth AND circuit 124 and first AND circuit 1
A galling detection signal D2 indicating that galling has occurred in the fixed type guide bush is output from the output terminal of the fifth AND circuit 125 in which both input terminals are connected to the output terminal of 21.
It can be sent to an appropriate alarm circuit as described above.

According to the present embodiment, a device for detecting the galling of a guide bush (fixed type guide bush) of a machine tool can be obtained from a commercially available product at a relatively low cost. By using hardware means such as a comparator, it is possible to make the configuration relatively inexpensive, and therefore, it is possible to implement accurate and reliable galling detection by mounting it on an existing automatic lathe.

[0042]

As described above, the present invention has been described based on two typical embodiments. In short, the present invention relates to a method for driving a spindle during machining of a workpiece by a machine tool using a fixed guide bush. The drive current of the motor is measured, and the rate of change of the drive current with respect to time and the rate of change of the drive current with respect to time are further determined based on the measured drive current together with the measured drive current. And a configuration that can be compared with the respective critical values experimentally determined in advance for the fixed guide bush with respect to these three values of the drive current value, the change rate of the drive current, and the change gradient of the change rate of the drive current. A fixed guide bush is used to support a workpiece that is gripped and rotated by the main spindle, and is fixed to the fixed guide bush during a machining process of machining the workpiece with a machining tool. If galling occurs, galling is detected early from the above three values and their respective critical values to prevent seizures such as stopping rotation of the spindle or withdrawing the machining tool from the machining position. Since the method and the device for detecting the galling of the guide bush of the machine tool capable of quickly achieving the alarm process are configured, the occurrence of the galling of the fixed type guide bush is accurately and quickly detected, and the It is possible to reliably prevent burnout.

As a result, when machining a workpiece with a machine tool, particularly an automatic machine, there is no need to worry about burning of the fixed type guide bush. Therefore, the machining conditions of the workpiece can be freely set, and the machining accuracy of the workpiece can be improved. It is also possible to obtain an improvement in processing efficiency and the like.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of a main part of a general machine tool in a case where a work having a fixed guide bush and performing a work while supporting a work gripped by a main spindle with the fixed guide bush is used. is there.

FIG. 2 is a block diagram showing an embodiment realized by utilizing an arithmetic element or the like of an NC device as an embodiment of a method and an apparatus for detecting galling of a guide bush of a machine tool according to the present invention.

FIG. 3 shows the variation of the drive current of the spindle motor until the occurrence of galling on the fixed type guide bush during machining of the workpiece gripped by the spindle, and the time axis is shown on the horizontal axis. FIG.

FIG. 4 is a graph showing the current change rate in the variation of the drive current shown in FIG. 3 on the vertical axis, and the time lapse on the horizontal axis.

5 is a graph showing the variation gradient of the current change rate of the drive current with respect to time shown in FIG. 4 on the vertical axis, and the time progress on the horizontal axis.

FIG. 6 is a block diagram showing another embodiment of a method and a device for detecting galling of a guide bush of a machine tool according to the present invention, which are realized by using hardware elements.

FIG. 7 is a block diagram illustrating a configuration example of a galling control unit for generating an alarm signal in the embodiment illustrated in FIG. 6;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Spindle 12 ... Machine frame 16 ... Turret 18 ... Machining tool 20 ... Fixed type guide bush 30 ... Spindle motor 34 ... Current measurement part 38 ... Alarm generation part 40 ... Galling detection control part 42 ... Current calculation part 44 ... Current change Rate calculation unit 46: current change rate gradient calculation unit 50: drive current monitoring unit 60: drive current change rate monitoring unit 80: drive current change rate change gradient monitoring unit 120: galling control unit

Claims (3)

[Claims] 1. A work gripped by a spindle of a machine tool is supported by a fixed guide bush fixed and held in the immediate vicinity of a processing position, thereby preventing galling due to overload of the guide bush when machining the work. In the detecting method, a drive current to the drive motor of the spindle is measured, and a rate of change of the current with respect to time is obtained from the measured current value, and a current change set in advance in response to occurrence of galling of the fixed guide bush. The change rate of the current change rate with respect to time is calculated from the obtained change rate of the current, and the change rate of the current change rate is set in advance in response to the occurrence of galling of the fixed guide bush. Both the comparison result with the critical value of the current change rate and the comparison result with the critical value of the variation gradient of the current change rate are compared with the critical value of A method for detecting galling of a guide bush of a machine tool, comprising detecting the occurrence of galling due to overload of the fixed guide bush when both are over critical. 2. A measured value of a drive current of the spindle drive motor is compared with a critical value of a drive current value set in advance in response to occurrence of galling of the fixed guide bush. The method according to claim 1, wherein when both the comparison result with the critical value of the current change rate and the comparison result with the critical value of the fluctuation gradient of the current change rate are over the criticality, the galling due to the overload of the fixed guide bush is detected. The method for detecting galling of a guide bush of a machine tool as described above. 3. A work gripped by a main shaft of a machine tool is supported by a fixed guide bush fixed and held in the vicinity of a processing position, thereby preventing galling due to overload of the guide bush when machining the work. In the detecting method, a current measuring means for measuring a drive current of the spindle drive motor; a critical value of the drive current of the spindle drive motor for causing galling due to overload on the fixed guide bush; A storage unit for storing in advance the critical value of the change rate of the change rate and the critical value of the change gradient of the change rate of the drive current as comparison data of the galling condition; and a current measured by the current measuring means during machining of the workpiece by the machine tool. A current calculator for comparing and calculating whether the value is over the critical value with respect to the critical value of the drive current, A current change rate calculator for calculating a change rate of current with respect to time from a current value measured by the current measuring means during machining of a workpiece, and comparing and calculating the current change rate with a critical value of the current change rate; A rate of change of the rate of change of the current with respect to time from the rate and comparing and calculating the rate of change of the rate of change of current with the critical value; and comparing the rate of change of the rate of change of current with the critical value of the rate of change of current. Comparison between the calculation result and the critical value of the variation gradient of the current change rate, and when at least both of the calculation results are above the criticality, a signal indicating that galling due to overload of the fixed guide bush is detected is output. A signal generating unit; and a device for detecting galling of a guide bush of a machine tool.