JPH07129211A - Automatic correction system for varying load - Google Patents

Abstract

PURPOSE:To provide the automatic varying load correction system which detects an actual cutting load by automatically correcting the varying load on the motor of a numerically controlled machine tool. CONSTITUTION:The automatic varying load correction system for correcting the varying load in the load on the motor 1 of the numerically controlled machine is composed of a cutting load estimating means 2 which detects the load on the motor 1, a storage means 3 which stores the load on the motor before the cutting operation of the numerically controlled machine tool that is obtained through the detection of the cutting load estimating means 2, and an actual cutting load arithmetic means 4 which finds the difference between the load on the motor 1 in the cutting operation of the numerically controlled machine tool that is obtained through the detection of the same cutting load estimating means 2 and the load on the motor 1 before the cutting operation that is stored in the storage means 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cutting load detection of a motor of a numerically controlled machine tool, and more particularly, a variable load automatic correction for automatically correcting a fluctuating load of a motor of a numerically controlled machine tool to detect an actual cutting load. It relates to a method and can be used to prevent wear and damage of tools during cutting.

[0002]

2. Description of the Related Art In a numerically controlled machine tool, a tool may be worn or damaged due to an abnormal load generated during cutting. Therefore, various measures are taken to prevent such wear and damage. . In these measures, the cutting load is mainly detected and it is determined whether the cutting load is an abnormal load. Conventionally, as a method of detecting the cutting load, a method of installing an external sensor such as a torque sensor on a torque tool holder or a table is known, and an abnormal load at the time of cutting is detected by a load value detected by the external sensor. is doing.

[0003]

However, in the method using an external sensor such as the above-mentioned conventional torque sensor, it is necessary to install a detection sensor outside.
In addition to the numerical controller, a sensor signal processing controller is required, which requires complicated adjustment for each cutting condition and has a problem that the structure is complicated and expensive. As a method of solving the problem of load detection by the external sensor, a method of detecting the current value of the motor is known.
Similar to the method using the external sensor, this method also has a problem that good detection accuracy cannot be obtained because the detected load includes the rotation load and acceleration / deceleration load of the motor itself.

FIG. 7 shows detected values of fluctuations in the motor load. Normally, in cutting with a numerically controlled machine tool, as shown by the solid line in the figure, only the motor and drive unit are driven and the process before cutting is not performed, and the cutting load is generated by actually cutting the workpiece. The process and the process are often repeated, and the value of the motor load detected according to this process changes. The entire motor load also fluctuates due to changes in temperature, rotation speed, and the like. In the figure, a load variation due to a temperature change, a rotation speed, or the like is usually a variation that does not depend on the cutting process as shown by a broken line.

The load value detected by the conventional load detection method is detected as a value of the sum of this load fluctuation amount and the load due to cutting, and even if the actual cutting load is in the normal range, May be determined as abnormal (point P in FIG. 7).

Conventionally, a "secondary resistance correction method for induction motors" and the like have been known as a method for correcting a load fluctuation due to a temperature change. This method is a method for correcting the temperature of the motor itself. It did not correct the load fluctuation due to the temperature change of the entire numerical control device including the mechanical system. Also, to correct the load fluctuation due to the number of rotations,
It was difficult due to uncertain factors such as bearing resistance and unbalance of the mechanical system such as unbalance of the rotating body.

Therefore, the present invention solves the above-mentioned problems of the conventional variable load correction system, and provides a variable load automatic correction system for automatically correcting the variable load component of the motor of a numerically controlled machine tool to detect the actual cutting load. The purpose is to provide.

[0008]

According to the present invention, there is provided load detecting means for detecting the load of a motor, and storage means for storing the load of the motor before cutting of a numerically controlled machine tool detected by the load detecting means. By the actual cutting load calculation means for obtaining the difference between the load of the motor during cutting of the numerically controlled machine tool detected by the load detection means and the load of the motor before cutting stored in the storage means, By configuring the variable load automatic correction method that corrects the variable load during the load of the numerically controlled machine tool motor,
To achieve the above objectives.

The load detecting means of the present invention detects the load of the motor. For example, the disturbance load torque can be estimated by an observer, or the load torque can be estimated by detecting the load current of the motor. It can be configured to.

The motor of the present invention is a motor for driving a spindle or a feed shaft of a numerically controlled machine tool. As a load corrected by the variable load automatic correction system of the present invention, the motor load of the spindle and the feed shaft It can be the load of the motor or the load of the motor on both the spindle and the feed axis.

In the present invention, the load of the motor detected by the load detection before cutting is the load only by the motor and the drive section.

[0012]

According to the present invention, with the above-mentioned configuration,
The load of the motor before cutting the numerically controlled machine tool is detected by the load detecting means, the detected motor load before cutting is stored in the memory means, and the same load detecting means is used during cutting of the numerically controlled machine tool. Detect the motor load. The actual cutting load calculation means calculates the difference between the motor load before cutting stored in the storage means and the motor load during cutting to obtain the variable load during the detected load of the motor of the numerically controlled machine tool. Is corrected to detect only the actual cutting load excluding the variable load.

[0013]

Embodiments of the present invention will now be described in detail with reference to the drawings, but the present invention is not limited to the embodiments.

(Structure of the variable load automatic correction system of the present invention)
First, a configuration for implementing the variable load automatic correction method of the present invention will be described. FIG. 1 is a block diagram for explaining the outline of the variable load automatic correction method of the present invention. In the figure, a cutting load estimation means 2 estimates the load of the motor 1, and the load of the motor before actual cutting,
Also, the load of the motor during the actual cutting is estimated and detected. The cutting load estimation means 2 is, for example, one that estimates the disturbance load torque that acts on the motor based on the speed signal and torque command of the motor 1, or the disturbance that acts on the motor by the load current in the amplifier that drives the motor 1. There is one that estimates the load torque. The storage unit 3 is a unit that stores the load of the motor before cutting estimated by the cutting load estimation unit 2. Actual cutting load calculation means 4
Is the load value of the motor before cutting stored in the storage means 3 and the load value of the motor during cutting estimated by the cutting load estimation means 2 are input. And the value of the motor load before cutting is calculated to obtain the actual cutting load of the motor. The comparison means 5 is
The actual cutting load calculated by the actual cutting load calculation means 4 is compared with a preset reference value. Drive command means 6
Issues various drive commands to the motor 1 based on the determination result by the comparison means 5. For example, when the comparison means 5 determines that the actual cutting load is larger than the reference value, the drive control command means 6 outputs a command signal for decelerating or stopping the feed of the tool, or a command for changing the tool. Output a signal.

(Structure for implementing the present invention) Next, regarding the structure for implementing the variable load automatic correction system of the present invention, numerical control for implementing the variable load automatic correction system of the present invention of FIG. A hardware block diagram of a device (CNC) will be described.

In the figure, 10 is a numerical control device (hereinafter,
A processor 11 (hereinafter referred to as CPU) in the CNC is a processor that controls the entire CNC 10, reads a system program stored in the ROM 12 via the bus 21, and follows the system program. , Controls the entire CNC 10. The RAM 13 is a storage means for storing temporary calculation data, display data, etc., and SRMA or the like can be used. The CMOS 14 is a storage unit that stores a machining program, various parameters, and the like, and is backed up by an auxiliary power source such as a battery (not shown), and the CNC 10
A non-volatile memory that stores data even when the power source is off is configured.

Interface (hereinafter referred to as INT) 1
An external device interface 5 is connected to an external device (hereinafter referred to as TR) 31 such as a paper tape reader, a paper tape puncher, and a paper tape reader / puncher. The processing program is read from the paper tape reader, and the processing program edited in the CNC 10 can be output to the paper tape puncher.

A programmable machine controller (hereinafter referred to as PMC) 16 is built in the CNC 10 and controls the machine with a sequence program formed in a ladder format. That is, according to the M function, the S function, and the T function instructed by the machining program, the signal is converted into a signal necessary for the machine side and output from the input / output unit (hereinafter referred to as I / O unit) 17 to the machine side. This output signal drives a magnet or the like on the machine side to operate a hydraulic valve, an air valve, an electric actuator or the like. Also,
The limit switch on the machine side, the switch on the machine control panel, and other signals are received, necessary processing is performed, and then passed to the CPU 11.

A graphic control circuit (hereinafter referred to as CRTC) 18 has a current position of each axis, an alarm, a parameter,
Digital data such as image data is converted into an image signal and output. This image signal is sent to the display device (hereinafter referred to as CRT) 26 of the CRT / MDI unit 25 and displayed. The INT 19 receives data from a keyboard (hereinafter referred to as KEY) 27 in the CRT / MDI unit 25 and transfers it to the CPU 11.

The INT 20 is connected to the manual pulse generator 32 and receives the pulse from the manual pulse generator 32. The manual pulse generator 32 is mounted on a machine operation panel (not shown) and used for precise positioning of the machine operating part by hand.

The axis control circuits 41 to 43 receive the movement command of each axis from the CPU 11 and send the command of each axis to the servo amplifier 5.
Output to 1 to 53. The servo amplifiers 51 to 53 receive the movement command and drive the servo motors 61 to 63 of the respective axes. The servomotor 63 that controls the Z-axis feed rotates the ball screw 64, and controls the position and feed rate of the spindle head 74 connected to the spindle motor 73 in the Z-axis direction. Further, the servo motor 63 has a built-in pulse coder 631 for position detection.
The position signal from 31 is fed back to the axis control circuit 43 as a pulse train. Further, a servo motor 61 for controlling the X-axis feed and a servo motor 62 for controlling the Y-axis feed.
Also, like the servo motor 63, a pulse coder for position detection is incorporated (not shown), and a position signal is fed back from the pulse coder as a pulse train.
As a position detection means, a linear scale may be used instead of the position detection pulse coder. Also, by converting the pulse train into F / V (frequency / speed),
It is also possible to generate a velocity signal. The axis control circuit 43 is
Software processing is performed by a processor (not shown),
An observer 410 is provided in a part thereof, and the disturbance load torque acting on the servo motor 63 is estimated by receiving the speed signal. The estimated disturbance load torque is sent to the PMC 16.

The spindle control circuit 71 receives a spindle rotation command, a spindle orientation command, and the like, and outputs a spindle speed signal to the spindle amplifier 72. The spindle amplifier 72 receives the spindle speed signal and rotates the spindle motor 73 at the commanded rotation speed. In addition, the spindle is positioned at a predetermined position according to the orientation command.

A position coder 82 is coupled to the spindle motor 73 via a gear or a belt. This position coder 82 is for the spindle motor 7
It rotates in synchronization with 3 and outputs a feedback pulse. This feedback pulse is read by the CPU 11 via the INT 81, moves the other shaft in synchronization with the spindle motor 73, and is used for machining such as drilling.

On the other hand, this feedback pulse is converted into a speed signal by the CPU 11 and sent to the spindle control circuit 71 as the speed of the spindle motor 73. Similar to the axis control circuit 43, the spindle control circuit 71 performs software processing by a CPU (not shown), and has an observer 710 built in a part thereof.
The disturbance load torque excluding the acceleration component is estimated, the processing load is obtained, and the processing load is sent to the PMC 16.

A drill 75 is attached to the spindle head 74 of the spindle motor 73, and the spindle motor 73 controls the rotation of the drill 75. The control of the position and feed rate of the drill 75 in the Z-axis direction is performed by the servo motor 63 via the spindle head 74.

The drill 75 is sent by the servo motor 63 in the Z-axis direction and drills the work 91. This work 91 is fixed to a table 92, and the table 92 is
The movement is controlled by the X-axis servo motor 61 and the Y-axis servo motor 62 in the X-axis direction and the Y-axis direction, respectively.

(Structure of Disturbance Estimating Observer) Next, an observer for estimating the disturbance load torque will be described by taking the observer 410 as an example, and the observer 710 has the same structure, and the description thereof will be omitted. FIG. 6 is a block diagram of an observer for estimating the disturbance load torque. Here, the disturbance load torque includes the disturbance load torque such as the cutting torque and the friction torque of the mechanism portion.

In the figure, reference numeral 14 is a transfer function of the torque constant kt, I is a torque command as an input, v is speed, and TL is disturbance torque. In the block diagram of FIG. 6, the speed v and the disturbance torque T are calculated by a general method of forming an observer.
When an observer for estimating L is assembled, it becomes an observer indicated by reference numeral 410 in the figure.

The terms 414, 4 of the disturbance estimation observer 410
The k1 and k2 of 15 are parameters of the disturbance estimation observer, the α of the term 411 is the value of the parameter that is multiplied by the current value I that is the torque command actually output to the servo motor, and the estimated value of the torque constant of the motor. the kt ^* expressed as divided by the inertia estimate ^{Jm * (α = kt * /} Jm *). 416 is an integral term, and terms 411, 414, 4
This is a term for calculating an estimated speed va of the motor by integrating a value obtained by adding all the outputs of 15. Further, the term 420 is the term 41
Estimated disturbance torque Td by multiplying the output from 5 by (1 / α)
This is the term for which 2 is obtained.

In the block diagram shown in FIG. 6, α =
kt ^* / Jm ^* , the motor torque constant kt is made equal to its estimated value kt ^* (kt = kt ^* ), and the motor inertia Jm is set to its estimated value Jm ^* (Jm = J
m ^* ), (Ikt + TL) (1 / JmS) = v (1) is obtained by the calculation of the term 402, and considering the output va of the term 416, {I (kt / Jm) + (v-va) k1 + (v-va) (k2 / S)}. (1 / S) = va (2) is obtained. When the equation (1) is modified, the following equation is obtained: I = (v · Jm · S−TL) / kt (3) When this equation (3) is substituted into the equation (2) and rearranged, (v * Jm * S-TL) / Jm + (v-va) k1 + (v-va) (k2 / S) = va * S ... (4) S (v-va) + (v-va) * k1 + (v -Va) (k2 / S) = TL / Jm (5) Also, from the expression (5), Verr (= v-va)
Then, Verr = v-va = (TL / Jm) [1 / {S + k1 + (k2 / S)}] (6) and the output Td1 of the term 415 from the above equation (6) is It is expressed by the equation 7).

Td1 = Verr · (k2 / S) = (TL / Jm) {k2 / (S ² + k1 · S + k2)} (7) In the equation (7), the poles of the parameters k1 and k2 are stabilized. If selected, Td1 = TL / Jm can be approximated, and this relational expression shows that the total disturbance torque Td1 can be estimated.

Then, in item 420, the total disturbance torque Td1 is multiplied by 1 / α (= Jm ^* / kt ^* ) to obtain the estimated disturbance torque Td2. In this way, the disturbance load torque of the motor can be estimated using the observer.

This disturbance estimation observer constitutes the cutting load estimation means 2 in FIG. 1, and the estimated disturbance load torque of the motor is sent to the PMC 16. PM
C16 stores the cutting load value obtained from the cutting load estimation means 2 in the storage means 3 as described above, and the storage means 3
The cutting load value stored in the cutting load value is read out, the cutting load value read from the cutting load estimating means 2 is subtracted from the cutting load value to calculate the actual cutting load, and the actual cutting load is calculated based on the calculation result. If an abnormal load is determined, a command for deceleration, stop, or tool change is sent to the servo motor. The processing in the PMC 16 will be described below with reference to FIGS.

(Operation of Embodiment of the Present Invention) FIG. 3 is a diagram showing changes in the motor load, in which the vertical axis can be the motor load and the horizontal axis can be time, temperature, or rotation speed. Figure 3
(A) is the load of the motor that can be obtained by the cutting load estimation means 2, and the load value of this motor includes the load component caused by cutting and the load component due to the rotation load and acceleration / deceleration load of the motor itself. Is included, and the obtained load fluctuates due to the load fluctuation due to the cutting process and the load fluctuation due to the temperature and the rotational speed of the rotation load and acceleration / deceleration load of the motor itself. The broken line in (b) of FIG. 3 shows the load fluctuation due to the temperature and rotational speed of the rotational load and acceleration / deceleration load of the motor itself, and the solid line of (c) of FIG. 3 shows the actual cutting load.

In the variable load automatic correction method of the present invention, the load change amount due to the temperature and the rotation speed of the rotation load and acceleration / deceleration load of the motor itself shown in FIG. The motor load stored in the storage unit 3 is obtained from the estimation unit and stored in the storage unit 3, and is stored in the storage unit 3 from the motor load value shown in FIG. 3A obtained by the same cutting load estimation unit. Is subtracted to obtain the actual cutting load shown in FIG.

The operation procedure of the variable load automatic correction system of the present invention will be described with reference to the flowchart of the embodiment of the variable load automatic correction system of the present invention shown in FIG. 2 and the diagram showing the time change of the motor load shown in FIG. . In the following description of the flow chart, the reference numeral of step S is used, and in FIG. 4, the step corresponding to the step S is given the reference numeral of S. Also,
One step from step S1 to step S9 in FIG.
It corresponds to each processing 1 and processing 2 in FIG.

Step S1: First, the rotation of the motor is started.

Step S2: After starting the rotation of the motor and before performing the cutting process, the cutting load estimation means 2 obtains the load component (To) due to the rotation load and the acceleration / deceleration load of the motor itself,
This motor load To is stored in the storage means 3. The motor load T ₀ stored in the storage means 3 does not include the load component caused by cutting, but is the load component due to the rotation load and the acceleration / deceleration load of the motor itself, and varies depending on the temperature and the rotation speed. It is a variable load. FIG. 4B shows the motor load To before cutting in the process 1.

The estimation of the load before the cutting load by the cutting load estimating means 2 is performed at every sampling interval of a predetermined cycle,
As the value of the cutting load stored in the storage means 3, any value can be selected from this sampling value. For example,
It is possible to store the sampled value after a fixed time has passed from the start of the steady rotation, the rotation of the motor or the end of cutting, or the average value of the sampled values. In the case of storing the sampling value after a fixed time, for example, the number of times of sampling for setting the sampling value to be stored can be set by a timer (not shown), and the processing means when the average value of the sampling values is used. Is, for example, a configuration in which an average value is obtained by a processing unit (not shown) and then stored in the storage unit 3, or a sampling value is stored in the storage unit 3 and the stored sampling value is provided on the actual cutting load calculation unit 4 side. Means (not shown) may be used to perform the averaging process. For example, the RAM 13 can be used as the storage unit 3.

Step S3: The start of the actual cutting is judged, and if the actual cutting is started, the motor load during cutting is obtained in the next step S4. The determination of the start of actual cutting can be made after the variation rate of the motor load obtained by the cutting load estimation means 2 or after an arbitrary fixed time from steady rotation. The determination of the start of actual cutting based on the variation rate of the motor load usually uses that the variation rate of the motor load due to the start of actual cutting is greater than the variation rate of the load variation due to temperature and rotation speed. The fluctuation rate can be obtained by calculating the difference between two adjacent sampling values by a processing unit (not shown).

Step S4: Next, the same cutting load estimating means 2 used in step S2 is used to sample the motor load (Ta) during cutting. The motor load Ta includes a load caused by cutting and a load caused by the rotation load and the acceleration / deceleration load of the motor itself.

Step S5: The motor load Ta during cutting, which is obtained by sampling in step S4, and the motor load To before cutting stored in the storage means 3 in step S2 are stored in the actual cutting load calculation means 4. Input and perform a calculation to subtract the motor load To from the motor load Ta,
The actual cutting load T is calculated.

T = Ta-To By this calculation, the actual cutting load T in which the fluctuation load due to the temperature and the rotation speed of the rotation load or acceleration / deceleration load of the motor itself is corrected is obtained. The actual cutting load T is shown in FIG.

Steps S6, 7: Based on the actual cutting load T obtained in step S5, the comparison means 5 makes various determinations, and the drive control means 6 controls the motor 1.

The determination in this step can be made by comparing the actual cutting load T with a preset reference value. For example, if T1 is the tool breakage detection level and T2 is the tool wear detection level, the actual cutting load T
Is greater than the tool damage detection level T1, processing 1 such as machine stop is performed, and if the actual cutting load T is less than the tool damage detection level T1 and greater than the tool wear detection level T2, feed deceleration or Process 2 for tool exchange is performed.

Step S8: When the actual cutting load T is smaller than the tool breakage detection level T1 and the tool wear detection level T2 in the judgments at the steps S6 and S7, the steps S4 to S7 are repeated until the cutting is completed. If the cutting is completed, the process proceeds to the next step S9.
The determination as to whether or not the cutting is completed can be performed by reversing the feed direction of the cutting feed, detecting the rotation stop of the main shaft, the Z-axis rising, or the like.

Step S9: When the cutting is completed, the motor load To obtained in step S2 and stored in the storage means 3 is cleared to prepare for the next processing.

After clearing To, the motor load To before cutting is again obtained in step S2 in the next process, stored in the storage means 3, and the processes of steps S3 to S9 are repeated.

FIG. 4B shows the motor load To2 before cutting in the process 2.

(Effects of the Embodiment) Since the load before the cutting force is applied is subtracted from the load detected during cutting to obtain the actual cutting load, the load of rotating the motor and the driving portion itself is removed, and Load fluctuations due to the number of revolutions and temperature differences are also corrected, and it is possible to detect the actual cutting torque with high accuracy and to detect tool wear and damage in the processing state where the cutting load is small.

(Modification of Embodiment) The motor load in the above embodiment may be a load on the main shaft or the feed shaft, or a load on the main shaft and a single shaft or a plurality of shafts among a plurality of feed shafts. When the motor load is applied to the main shaft and a single shaft or multiple shafts of a plurality of feed shafts, it can be performed by combining the respective motor loads obtained by the cutting load estimation means provided in the servo motor and the spindle motor. it can.

Further, in the above embodiment, the observer for estimating the disturbance load torque is used as the cutting load estimating means, but the load current of the motor of the main shaft or the feed shaft can be used in place of the observer. .

The estimation of the disturbance load torque of the servo motor can be applied to each of the X axis, Y axis, and Z axis.

In the above embodiment, the estimated disturbance load torque and the reference torque are compared and the drive control is performed by the PMC, but it may be performed by a processor that controls the entire numerical control device.

[0055]

As described above, according to the present invention,
The actual cutting load can be detected by automatically correcting the variable load of the motor of the numerically controlled machine tool.

[Brief description of drawings]

FIG. 1 is a block diagram illustrating an outline of a variable load automatic correction method of the present invention.

FIG. 2 is a flowchart of an embodiment of the variable load automatic correction method of the present invention.

FIG. 3 is a diagram showing a change in motor load.

FIG. 4 is a diagram showing a time change of a motor load of the present invention.

FIG. 5 is a block diagram of hardware of a numerical controller for implementing the variable load automatic correction method of the present invention.

FIG. 6 is a block diagram of an observer for estimating a disturbance load torque.

FIG. 7 shows detected values of fluctuations in the load of the motor.

[Explanation of symbols]

 1 Motor 2 Cutting Load Estimating Means 3 Storage Means 4 Actual Cutting Load Computing Means 5 Comparing Means 6 Drive Control Command Means

Claims (4)

[Claims] 1. In a variable load automatic correction method for correcting a variable load component in a detected load of a motor of a numerically controlled machine tool, load detecting means for detecting the load of the motor, and the load detecting means for detecting the load of the motor, Storage means for storing the load of the motor before cutting of the numerically controlled machine tool, load of the motor during cutting of the numerically controlled machine tool detected by the load detection means, and cutting stored in the storage means A variable load automatic correction method comprising: an actual cutting load calculation means for obtaining a difference from a load of a front motor. 2. The variable load automatic correction method according to claim 1, wherein the load detection means is an observer for estimating a disturbance load torque of the motor. 3. The variable load automatic correction method according to claim 1, wherein the load detection means detects a load current of the motor. 4. The variable load automatic correction method according to claim 1, 2, or 3, wherein the motor is a main shaft or a feed shaft of the numerically controlled machine tool.