JPH0751996A - Surplus load detecting method for cnc - Google Patents

Abstract

PURPOSE:To reliably prevent breakage of a tool, in a surplus load detecting system for a CNC to detect a surplus load exerted on a tool and a machine element during a machining work. CONSTITUTION:Disturbance load torque Yz exerted on a servo motor 63 is estimated by a disturbance load torque estimating means 1 based on a speed signal X1z for a servo motor 63 and a current command value U1z to a servo motor 63. A rate of change alpha the estimated disturbance load torque Yz is computed at intervals of a sampling period by a rate of change computing means 2. When the rate of change alpha of the disturbance load torque Yz exceeds a lowermost reference value alpha1, rotation of the servo motor 63 is decelerated by a given amount M1 by a speed command value control means 3. Further, when the rate of change alpha exceeds a reference value alpha2 higher than the reference value alpha1, rotation of the servo motor 63 is decelerated by a given amount M2 being, for example, two times as large as the given amount M1. Moreover, when the rate of change alpha exceeds a highmost reference value alpha3, the rotation of the servo motor 63 is stopped.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CNC overload detection system, and more particularly to a CNC overload detection system for detecting an overload on a tool or a machine element during a machining operation.

[0002]

2. Description of the Related Art In a machine tool controlled by a CNC, a tool or other mechanical elements may be damaged due to an abnormal load generated during a machining operation. In order to prevent the damage, the load torque applied to the axis control motor has been conventionally detected, and when the load torque exceeds a reference value, the rotation of the motor is decelerated or stopped. .

[0003]

However, in such a technique, at the same reference value, the motor is decelerated uniformly regardless of the amount of change in the load torque. When the value exceeds the value, the rotation of the motor cannot be immediately decelerated, the load torque does not immediately decrease, and the load on the tool or the like cannot be quickly removed.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a CNC overload detection method capable of more reliably performing overload detection processing.

[0005]

In order to solve the above problems, the present invention provides a CNC overload detection system for detecting an overload applied to a tool or a machine element during a machining operation.
Disturbance load torque estimating means for estimating a disturbance load torque acting on the motor for controlling the axis, change rate calculating means for calculating a change rate of the estimated disturbance load torque, and a change rate of the motor according to the calculated change rate. And a speed command value control means for controlling the speed command value.

[0006]

The disturbance load torque acting on the motor for controlling the shaft is estimated by the disturbance load torque estimating means, and the change rate of the estimated disturbance load torque is calculated by the change rate calculating means. The speed command value control means controls the speed command value of the motor according to the calculated change rate.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 2 is a hardware block diagram of a numerical controller (CNC) for implementing the CNC mechanical element life estimation method of the present invention. In the figure, 10 is a numerical controller. The processor (CPU) 11 is a processor that is the center of control of the entire numerical controller 10, and is a bus 2
The system program stored in the ROM 12 is read via 1 and the entire numerical controller 10 is controlled according to the system program. The RAM 13 stores temporary calculation data, display data, and the like. RAM
A DRAM is used for 13. The CMOS 14 stores a processing program and various parameters. Further, the CMOS 14 stores a reference value α1 and the like described later. The CMOS 14 is backed up by a battery (not shown) and serves as a non-volatile memory even when the power supply of the numerical control device 10 is turned off. Therefore, those data are retained as they are.

The interface 15 is an interface for an external device, and is connected to an external device 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 numerical controller (CNC) 10 can be output to the paper tape puncher.

A PMC (Programmable Machine Controller) 16 is built in the CNC 10 and controls the machine with a sequence program created in a ladder format. That is, according to the M function, S function, and T function instructed by the machining program, these are converted into necessary signals on the machine side by the sequence program and output from the 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, a pneumatic valve, an electric actuator or the like. Further, it receives a signal from a limit switch on the machine side, a switch on the machine operation panel, etc., performs necessary processing, and passes it to the processor 11.

The graphic control circuit 18 converts the current position of each axis, alarms, parameters, digital data such as image data into an image signal and outputs it. This image signal is sent to the display device 26 of the CRT / MDI unit 25,
It is displayed on the display device 26. Interface 19 is CR
It receives data from the keyboard 27 in the T / MDI unit 25 and passes it to the processor 11.

The interface 20 is a manual pulse generator 3
2 and receives the pulse from the manual pulse generator 32. The manual pulse generator 32 is mounted on the machine operation panel,
Used to precisely position machine working parts manually.

The axis control circuits 41 to 43 receive the movement command of each axis from the processor 11 and output the command of each axis to the servo amplifiers 51 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 servo motor 63 that controls the Z-axis feed incorporates a pulse coder 631 for position detection, and the position signal is fed back from the pulse coder 631 to the axis control circuit 43 as a pulse train. Although not shown here, the servo motor 61 that controls the X-axis feed and the servo motor 62 that controls the Y-axis feed also
A pulse coder for position detection is built in like the servo motor 63, and a position signal is fed back from the pulse coder as a pulse train. In some cases, a linear scale is used as the position detector. Further, the speed signal X1z can be generated by subjecting this pulse train to F / V (frequency / speed) conversion.

The axis control circuit 43 has a processor (not shown) for software processing, and has an observer 410 as a part thereof. Observer 41
0 indicates the servo motor 6 in response to the above speed signal X1z and the like.
The disturbance load torque Yz acting on No. 3 is estimated. The estimated disturbance load torque Yz is sent to the processor 11. The details will be described later.

The spindle control circuit 71 receives a spindle rotation command and a spindle orientation command, and outputs a spindle speed signal to a 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 connected to the spindle motor 73 by a gear or a belt. Alternatively, the position coder 82 may be installed inside the spindle motor 73.
Are combined. Therefore, the position coder 82 rotates in synchronization with the spindle motor 73, outputs a feedback pulse, and the feedback pulse is fed back to the spindle control circuit 71. The speed signal X1s can be generated by performing F / V (frequency / speed) conversion on this pulse train.

Like the axis control circuit 43, the spindle control circuit 71 has a processor (not shown) for software processing, and has an observer 710 as part thereof. The observer 710 receives the speed signal X1s and the like and estimates the disturbance torque Ys acting on the spindle motor 73. The estimated disturbance load torque Ys
Is sent to the processor 11 in the same manner as the estimated disturbance load torque Yz described above.

The processor 11 receives these estimated disturbance load torques Yz and Ys and performs a life management process described later by a predetermined software. FIG. 3 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 load torque, the gravity load torque of the gravity axis, and the friction torque of the mechanism section, and the acceleration / deceleration torque for acceleration / deceleration is calculated from the total torque of the servo motor. Excluded.

The processing shown in this block diagram is executed by the observer 410 of the axis control circuit 43 and the observer 710 of the spindle control circuit 71, as described above. Since the observers 410 and 710 have the same configuration, the observer 410 will be described here, and the description of the observer 710 will be omitted.

In the figure, a current command value U1z is a torque command value that is output to the servo motor 63 in response to the movement command from the processor 11, and is input to the element 401 to drive the servo motor 63. The disturbance load torque X2 is added to the output torque of the servo motor in the calculation element 402. The output of the calculation element 402 is the element 40
3 results in the speed signal X1z. Here, J is the inertia of the servomotor 63.

On the other hand, the current command value U1z is the observer 41
Input to 0. The observer 410 has a current command value U1z.
Then, the disturbance load torque is estimated from the speed X1z of the servo motor 63. The speed control of the servo motor 63 is omitted here, and only the calculation for estimating the disturbance load torque will be described. The current command value U1z is multiplied by (Kt / J) in the element 411 and is output to the calculation element 412. The calculation element 412 adds a feedback signal from a calculation element 414, which will be described later, and the calculation element 413 further calculates a calculation element 415.
Add the feedback signals from. Computing elements 412 and 413
The output unit of is acceleration. The output of the calculation element 413 is input to the integration element 416 and output as the estimated speed XX1 of the servo motor 63.

A difference between the estimated speed XX1 and the actual speed X1z is calculated by a calculation element 417, and calculation elements 414 and 4 are respectively calculated.
Return to 15. Here, the proportional element 414 is the proportional constant K
Has 1. The unit of the proportionality constant K1 is sec ^-1 . The integration element 415 also has an integration constant K2. The unit of the integration constant is sec ^-2 .

Here, the output of the integration element 415 (XX2 /
J) can be calculated from the following formula from the figure. (XX2 / J) = (X1z−XX1) · (K2 / S) = (X2 / J) · [K2 / (S ² + K1 · S + K2)] Therefore, if the constants K1 and K2 are selected so that the poles are stable, The above equation becomes the following equation.

(XX2 / J) .apprxeq. (X2 / J) XX2.apprxeq.X2 That is, the disturbance load torque X2 can be estimated by XX2.
However, the output of the integration element 415 is the estimated disturbance load torque X
It is an estimated acceleration (XX2 / J) obtained by dividing X2 by J, and is converted into a current value by the proportional element 420. However,
In order to display the torque, this current value is displayed as the estimated disturbance load torque Yz. Here, J is J of the previous element 403.
Is the inertia of the servo motor 63, and Kt is the same as the torque constant of the element 401. A is a coefficient,
It is a numerical value of 1 or less and is a coefficient for correcting the estimated acceleration (XX2 / J). In this way, the observer 410
Disturbance load torque Yz (X
2) can be estimated.

Disturbance load torque Y of the spindle motor 73
Similarly, s can be estimated using the observer 710. In this case, the observer 710 determines that the current command value U1s
Then, the disturbance load torque Ys is estimated from the speed signal X1s of the spindle motor 73. The current command value U1s is a torque command value output to the spindle motor 73 in response to the spindle rotation command from the processor 11.

These estimated disturbance load torques Yz and Ys
Of course, these estimated disturbance load torques Yz and Ys, which are estimated values, will be described below as disturbance load torques. FIG. 1 is a conceptual diagram of an overload detection method by the CNC 10 having such a configuration. Here, the boring process will be described as an example. The servo motor 63 rotates the ball screw 64 to control the position in the Z-axis direction and the feed rate of the spindle head 74 connected to the spindle motor 73. The speed signal X1z of the servo motor 63 is input to the disturbance load torque estimation means (observer 410) 1 of the axis control circuit 43.

A drill 75 is attached to the spindle head 74 of the spindle motor 73. The drill 75 processes the work 91 by the rotation of the spindle motor 73. The speed signal X1s of the spindle motor 73 is used as the disturbance torque estimating means (observer 710) of the axis control circuit 71.
4 is input.

The disturbance load torque estimating means 1 estimates the disturbance load torque Yz acting on the servo motor 63 based on the speed signal X1z of the servo motor 63 and the current command value U1z to the servo motor 63. The change rate calculation means 2 calculates the estimated change rate α of the disturbance load torque Yz for each sampling cycle. The speed command value control means 3 controls the speed command value of the motor according to the calculated change rate α. The speed command value control means 3 stores and holds reference values α1, α2, α3 for determining whether the disturbance load torque Yz is excessive with respect to the drill 75, the ball screw 64, or the like.

The speed command value control means 3 constantly compares the change rate α of the disturbance load torque Yz with the reference values α1, α2, α3. When the change rate α exceeds the lowest reference value α1, the rotation of the servo motor 63 is decelerated by the predetermined amount M1. When the change rate α exceeds the reference value α2 which is larger than the reference value α1, the rotation of the servo motor 63 is decelerated by the predetermined amount M2 which is twice as large as the predetermined amount M1. Further, when the change rate α exceeds the highest reference value α3, the rotation of the servo motor 63 is stopped. Further, the rotations of the other servo motors 61 and 62 and the spindle motor 73 are also stopped depending on the case.

While controlling the speed command value in this way, the speed command value control means 3 informs the operator by displaying the state of the change rate α of the disturbance load torque Yz on the display device 26 or the like.

On the other hand, the disturbance load torque estimating means 4 estimates the disturbance load torque Ys acting on the spindle motor 73 based on the speed signal X1s of the spindle motor 73 and the current command value U1s to the spindle motor 73. The change rate calculation means 5 calculates the estimated change rate β of the disturbance load torque Ys for each sampling cycle. Speed command value control means 6
Controls the motor speed command value in accordance with the calculated change rate β. The speed command value control means 6 determines the disturbance load torque Y
Reference values β1, β2 for determining whether s is excessive with respect to the drill 75, internal bearings, etc.
It holds β3 in memory.

The speed command value control means 6 constantly compares the rate of change β of the disturbance load torque Ys with the reference values β1, β2, β3. Then, when the change rate β exceeds the lowest reference value β1, the rotation of the servo motor or the spindle motor 73 is decelerated by the predetermined amount N1. When the change rate β exceeds the reference value β2 which is larger than the reference value β1, the rotation of the servo motor or the spindle motor 73 is decelerated by the predetermined amount N2 which is, for example, twice as large as the predetermined amount N1.
Further, when the change rate β exceeds the highest reference value β3, the rotation of the spindle motor 73 is stopped. Also,
Depending on the case, the rotations of the other servomotors 61 to 63 are also stopped.

While controlling the speed command value as described above, the speed command value control means 6 displays the state of the rate of change β of the disturbance load torque Ys on the display device 26 or the like, as in the speed command value control means 3. And inform the operator.

FIG. 4 is a diagram showing the time variation of the disturbance load torque. FIG. 4A is a diagram showing the time variation of the disturbance load torque Yz in a normal machining state, and FIG. 4B is an abnormal machining state. FIG. 6 is a diagram showing a change over time of the disturbance load torque Yz.
The disturbance load torque Yz is estimated every sampling period T, and when the disturbance load torque Yz is newly estimated, the change rate α thereof is calculated. For example, in the figure (A), time t1
Assuming that the disturbance load torque Yz value at 1 is d1 and the disturbance load torque Yz value at time t2 is d2, the change rate αa at this time is αa = (d2-d1) / (t2-t1) = D1 / It becomes T. Since FIG. (A) shows the characteristics in the normal processing state, αa = D1 / T is always the reference value α1 or less.

On the other hand, in the figure (B), the change rate αb of the disturbance load torque Yz between the time t3 and the time t4 is αb = (d4-d3) / (t4-t3) = D2 / T. As shown in the figure, D2 = d4-d3 is D = d2
Clearly larger than -d1. Therefore, the change rate αb
Is naturally larger than the rate of change αa. If the rate of change αa is larger than any of the reference values α1, α2, α3, the deceleration or stop process as described above is performed.

Similar processing is performed on the disturbance load torque Ys. FIG. 5 is a flowchart showing a processing procedure on the processor side for performing such an overload detection method. An example of control of the servo motor 63 is shown here. [S1] The disturbance load torque Yz estimated by the observer 410 is read. [S2] The change rate α of the disturbance load torque Yz is calculated. [S3] It is determined whether the rate of change α is less than or equal to the minimum reference value α1.

[S4] It is determined whether or not the change rate α is larger than the maximum reference value α3. If it is larger, the process proceeds to step S5, and if not, the process proceeds to step S6. [S5] At least the operation of the servo motor 63 is stopped. [S6] It is determined whether or not the rate of change α is larger than the reference value α2 of the intermediate value. If it is larger, the process proceeds to step S7, and if not, the process proceeds to step S8. [S7] The rotation of the servo motor 63 is greatly reduced. [S8] The rotation of the servo motor 63 is slightly reduced. [S9] The change state of the disturbance load torque Yz is displayed.

The basic procedure of the spindle motor 73 is almost the same. As described above, in this embodiment, the change rate α of the disturbance load torque Yz or the like is calculated,
The rate of change α is compared with the reference values α1, α2, α3 so that the speed command value of the servo motor 63 for axis control is controlled to be decelerated, so that the change can be made before the disturbance load torque reaches an abnormal value. It can be perceived and the response of the motor deceleration control can be improved. Therefore, it is possible to more reliably prevent damage to tools and the like.

In this embodiment, the reference value is set to 3 for the servo motor 63 and the spindle motor 73, respectively.
Although they are provided one by one, the number can be changed each time according to the design.

Further, in the present embodiment, an example in which the processor 11 performs the life estimation calculation based on the disturbance load torque Yz and the like estimated by the observer 410 and the like has been shown. It may be performed by an external device.

In this embodiment, the life of each mechanical element connected to the servo motor 63 and the spindle motor 73 is estimated, but the life of the other servo motors 61 and 62 is estimated by the same procedure. It can be performed.

[0041]

As described above, according to the present invention, the disturbance load torque acting on the motor for axis control is estimated, the change rate of the disturbance load torque is calculated, and the speed command value of the motor is calculated according to the change rate. Since the disturbance load torque reaches the abnormal value, the change can be detected and the response of the motor deceleration control can be improved.
Therefore, it is possible to more reliably prevent damage to tools and the like.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of an overload detection method by CNC.

FIG. 2 is a block diagram of hardware of a numerical controller (CNC) for implementing the tool damage prevention system of the present invention.

FIG. 3 is a block diagram of an observer according to the present invention.

FIG. 4 is a diagram showing a time change of a disturbance load torque,
(A) is a diagram showing a time variation of a disturbance load torque in a normal machining state, and (B) is a diagram showing a time variation of a disturbance load torque in an abnormal machining state.

FIG. 5 is a flowchart showing a processing procedure on the processor side for performing overload detection.

[Explanation of symbols]

 1,4 External load torque estimation means 2,5 Change rate calculation means 3,6 Speed command value control means 10 Numerical control device (CNC) 11 Processor (CPU) 14 CMOS 16 PMC 43 Axis control circuit 53 Servo amplifier 63 Z axis servo Motor 64 Ball screw 71 Spindle control circuit 72 Spindle amplifier 73 Spindle motor 74 Spindle head 74 82 Position coder 91 Work 410,710 Observer 631 Pulse coder

Claims (4)

[Claims] 1. A disturbance load torque estimating means for estimating a disturbance load torque acting on a motor for axis control in a CNC overload detection method for detecting an excessive load applied to a tool or a machine element during a machining operation, and the estimation. A change rate calculating means for calculating a change rate of the disturbance load torque, and a speed command value control means for controlling a speed command value of the motor according to the calculated change rate. Overload detection method. 2. The speed command value control means has a plurality of predetermined values of different sizes, and when the rate of change exceeds any of the predetermined values, the speed command value control means responds to the magnitude of the exceeded predetermined value. 2. The overload detection method for a CNC according to claim 1, wherein the output of the motor is reduced. 3. The CNC according to claim 2, wherein the speed command value control means is configured to stop the motor when the change rate exceeds a maximum predetermined value. Overload detection method. 4. The speed command value control means is configured to issue a command to externally display a state of an excessive load applied to the tool or machine element according to the change rate. Item 3. The CNC overload detection method according to Item 1.