JP3187485B2 - Numerically controlled machine tools - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for a machine tool, and more particularly, to a method for determining the inertial load of a tool, and judging from the result whether or not high-speed rotation is possible using the tool. To a numerically controlled machine tool.

[0002]

2. Description of the Related Art A conventional numerically controlled machine tool found in a machining center or the like has an automatic tool changer (ATC). If you have an automatic tool changer and use an ultra-high-speed rotating spindle, it is possible that a heavy tool exceeding the capability of the spindle will be mistakenly mounted, and measures such as interlocking can be considered. Not. At present, as a safety measure, a method of firmly designing a cover is considered at best.

[0003]

When a tool is changed by an automatic tool changer in accordance with a command of a numerical control program, automatic operation is performed. It is not known whether a tool is mounted or a small-diameter end mill is mounted. The tool to be mounted on the main shaft and the rotation speed command to the main shaft are programmed by a human, but the error of the designation of the tool number and the rotation speed cannot be made zero at all. Also,
It is also conceivable that a human may change a tool to be put in a tool magazine attached to an automatic tool changer. As a result, as shown in FIG. 4, the resonance frequency of the main shaft may be extremely lowered, and the main shaft may be rotated at a critical speed, so that an extremely dangerous situation is expected.

Accordingly, an object of the present invention is to provide a numerically controlled machine tool capable of preventing a tool from rotating near or above a critical speed when a tool having an arbitrary mass is mounted. It is in.

[0005]

SUMMARY OF THE INVENTION The object of the present invention is as follows.
Rotation according to the rotation speed command rotational speed of the spindle of a machine tool
Servo drive means for feedback controlling the speed ;
In numerically controlled machine and a numerical control unit for outputting the rotational speed command to the server port drive means, pre
The allowable rotation speed of the spindle for the moment of inertia of
In a state where the feedback control is turned off after the tool is exchanged and before the rotation speed command is output,
Then, the drive shaft motor is connected to the drive shaft by the drive shaft.
A constant power that rotates at a rotation speed sufficiently lower than the steep speed
Power, and from the point in time when the
Find the rise time until the shaft rotation speed rises to the set value.
The tool in the mounted state based on the determined rise time.
Find the moment of inertia of the shaft and
Comparing the rotation speed with the permissible rotation speed, and
It is characterized in that it is determined whether or not the rotation speed is acceptable .

[0006]

[Function] It is assumed that the main shaft is rotated at a predetermined low rotation speed before outputting the actual rotation speed command from the numerical controller.
Rise time until the rotation speed rises to the set value
Alternatively, the time constant is determined by the inertia mode of the spindle with the tool mounted.
Correlates with the statement. In other words, the servo mode that rotates the spindle
From the relationship between the characteristic parameters of the
The moment can be determined.

Next, from the relationship between the value of the moment of inertia of the mounted tool or a value proportional to the moment of inertia and the previously determined inertial moment of the additional tool and the critical speed of the spindle, a program command for numerical control is obtained. It is determined whether or not the main shaft can be rotated at a high speed. As a result, if there is an abnormality, it is desirable to perform consistent operations such as temporarily stopping the rotation of the spindle, outputting an alarm, and correcting the rotation speed command program.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 7 shows a machine tool utilizing the present invention. In FIG. 7, a column 24 is provided on a bed 23, and a spindle head 25 is mounted on the column 24. The drive of the spindle 27 on which the tool 28 is mounted can be directly driven by a servomotor 26 mounted on the spindle. In this case, the transmission means such as a gear or a belt is not used, and the spindle servomotor 26 and the spindle 27 are directly driven. Therefore, loss such as friction is small, and the moment of inertia of the tool can be measured accurately. is there. Although it looks the same as a conventional numerically controlled machine tool, it is possible to automatically determine whether the tool mounted on the spindle is appropriate and whether the rotational speed is appropriate. An example is shown below.

FIG. 1 shows a control circuit for detecting an inertial load of a tool according to the present invention. A portion surrounded by a broken line shown in FIG. 1 shows a servo drive circuit of the main spindle. Usually, when a speed command is issued from the numerical control device 1, the servo motor 3 is driven via the servo amplifier 2 and the tool is driven. The mounted spindle mechanism 4 rotates at a high speed. Then, the speed is detected by the speed detecting means 5, and the switch 9 of the speed feedback signal is detected.
Is closed and the speed is fed back.

The procedure for measuring the moment of inertia of a tool mounted on the main shaft will be described below. Speed feedback signal switch 9
To make an open loop servo drive circuit. Next, when a relatively low speed signal of about 1000 rpm is output from the numerical controller 1 and a predetermined voltage is applied to the servo circuit input of the main shaft, the main shaft rotates with a first-order lag characteristic as shown in FIG. Since the moment of inertia of the rotating shaft system differs between the case of the main spindle alone and the case of mounting the tool, a difference occurs in the time constant of the rise. Here, the time constant T is defined as the time required to reach approximately 63% of the steady speed V, but is not actually limited to this value, but may be any time required to reach the predetermined speed. It can be arbitrarily determined. Time constant T
In order to determine the rotation speed, a means 5 for detecting the rotation speed is provided on the spindle or the spindle motor of the machine tool, a rotation start command signal and a clock signal for time measurement are output from the numerical controller 1, and a speed comparison circuit 6, a timer counter 7, and a time constant measurement-moment of inertia calculation circuit 8 are added.

The rotation start reset signal is applied to the speed comparison circuit 6 and the timer counter 7 to reset each of them, and at the same time, apply the predetermined voltage to rotate the spindle servomotor 26 as described above. From this time, the timer counter 7 starts accumulating the clock pulses. The speed comparison circuit 6 outputs a gate signal when the speed reaches 63% of the steady speed in the open loop system. This gate signal is input to the timer counter 7 to close the counter circuit 7 so that no clock pulse flows to the counter 7 thereafter. As a result, the time constant T of the spindle drive system can be obtained from the clock pulse period and the number of accumulated pulses.

When the time constant T is determined, the relationship between the time constant T and the moment of inertia J of the main shaft is determined by Equation 1.

[0013]

(Equation 1)

Where Ra is the armature resistance of the servomotor,
Kt is the torque constant of the motor, and Ke is the back electromotive force constant of the motor.

Assuming that the rising time constant including the spindle and the spindle servomotor is Ts, and the time constant when the tool is mounted is Tt, the moment of inertia Jt when the tool is mounted can be obtained by Equation 2.

[0016]

(Equation 2)

Here, C is a constant determined by the characteristics of the servomotor.

Here, the rising time constant Ts including the spindle and the spindle servomotor is determined in advance, and R
Since it can be recorded on the OM or the hard disk, even if an unknown tool is inserted into the main spindle, the time constant Tt when the tool is mounted is measured and obtained, and the tool mounting is determined from the above equation (2). Moment of inertia Jt
Is possible.

The relationship between the moment of inertia Jt when the tool is mounted and the mass of the tool is shown in FIG. 3, which is the result of a study on a face milling cutter and an end mill, which are commonly used. It can be seen that there is a proportional relationship. That is, the moment of inertia J when the tool is mounted
Once t is known, it is possible to estimate the mass of the tool. When a tool having an excessive mass is mounted on the spindle, the natural frequency of the spindle system decreases as shown in FIG. 4, and the resonance frequency of the spindle system including the tool exists within the specification range of the rotation speed of the spindle. It is extremely dangerous. In the conventional apparatus, it is necessary for the user of the machine tool to carefully determine the tool and the number of revolutions. However, there is a risk that the machine may rotate to the critical speed range due to an error on the operator side.

In the present invention, the relationship between the moment of inertia Jt when the tool is mounted and the permissible number of revolutions of the spindle is determined in advance as shown in FIG. 5, and is recorded in a temporary storage device such as a hard disk or ROM. Then, from the result and the measured result of the inertia moment Jt when the tool is mounted, the numerical controller 1 determines whether or not the instructed rotation speed is equal to or less than an allowable value. A closed loop is set up to the normal rotation speed, and cutting is performed. If the commanded rotation speed is outside the allowable range shown in FIG. 5, the rotation is temporarily stopped and an alarm message is output. Based on the result, the operator of the machine mounts a correct tool or corrects the rotation speed.

FIG. 6 is an overall flowchart showing the operation according to the present invention. When the process is started, first, NC program data is input 10 and automatic tool change 11 is performed. Then, it is determined 12 whether or not to measure the moment of inertia of the tool. If so, the servo circuit of the spindle drive system is set to an open loop, and a spindle rotation 13 for measuring the tool inertia is commanded. The time constant Tt of the spindle rotation and the moment of inertia Jt are measured 14 and calculated. When the moment of inertia Jt is determined, it is determined 15 whether or not high-speed rotation is possible with the mounting tool. The rotation is started up, the positioning is performed, and the cutting is started 17. When the cutting is performed and the cutting by the tool is completed 18, it is determined 19 whether or not the processing is completed. If the processing is completed, the processing ends. If not completed, the NC program data input 1 is performed again.
Return to 0. Further, when it is determined whether or not high-speed rotation is possible with the mounted tool, if it is determined that the high-speed rotation is impossible, an alarm display 20 and a tool inertia moment are displayed, and a temporary stop 21 of the spindle rotation is performed. After the rotation number command is corrected or the mounting tool is optimized 22, the process proceeds to the start 16 of spindle rotation. In this embodiment, the moment of inertia Jt at the time of mounting the tool is determined, and it is determined whether or not the commanded rotational speed is equal to or less than the allowable value from the relationship between the previously determined allowable rotational speed of the spindle. Not only the moment of inertia Jt but also a value proportional to this moment of inertia may be used.

In the above embodiment, the servo circuit of the spindle drive system is opened to form an open loop circuit, but this is to increase the difference in the time constant due to the difference in the moment of inertia.
Even if a closed loop circuit with a speed feedback circuit is configured, the moment of inertia can be measured by utilizing the fact that a slight difference occurs in the time constant due to the moment of inertia. In addition, the time required to reach 63% of the steady speed is used as the time constant. However, using a plurality of data (speed and time) relating to the rise of the spindle speed, the time constant and the moment of inertia are calculated using the least square method or the like. , It is also possible to estimate more accurately. The time required for measuring the moment of inertia of the tool can be about 5 to 10 seconds, and there is little hindrance to workability due to the measurement.

[0023]

As described above, according to the present invention, by measuring the time constant and the moment of inertia of the mounted tool, it is determined whether the rotational speed specified by the program is appropriate or not. If there is a problem, take measures such as suspending operation and outputting an alarm message, optimizing the number of revolutions, or optimizing the tool, and then start up to the normal number of revolutions. Heavy tools that exceed the capability of the machine are no longer accidentally installed.

[Brief description of the drawings]

FIG. 1 is a block diagram for measuring a servo drive system of a spindle and a moment of inertia of a tool.

FIG. 2 is a diagram showing a rise of a rotation speed of a spindle.

FIG. 3 is a diagram showing a relationship between a tool mass and a moment of inertia.

FIG. 4 is a diagram showing a relationship between a resonance curve of a spindle system and addition of a tool. .

FIG. 5 is a diagram showing a relationship between an allowable rotation speed of a spindle and a moment of inertia of a tool.

FIG. 6 is an overall flowchart showing the operation of the present invention.

FIG. 7 is a diagram showing a numerically controlled machine tool to which the present invention is applied.

[Explanation of symbols]

 Reference Signs List 1 Numerical controller 2 Spindle drive system servo amplifier 3 Servo motor block diagram 4 Spindle mechanism block diagram 5 Speed detection gain 6 Speed comparison circuit 7 Timer counter 8 Time constant-moment of inertia calculation circuit 9 Speed feedback system switch 23 Bed 24 Column 25 Spindle head 26 Spindle servomotor 27 Spindle 28 Tool

Claims (1)

(57) [Claims] 1. A numerical control comprising: servo drive means for feedback-controlling the rotational speed of a main shaft of a machine tool according to a rotational speed command; and a numerical control device for outputting the rotational speed command to the servo drive means. In a machine tool, the spindle
Allowable rotation speed is determined, and after the tool is exchanged and before the rotation speed command is output, feedback control is performed.
In the off state, the drive motor of the spindle is
At a rotation speed sufficiently lower than the critical speed of the spindle
Supply a certain amount of power to start the supply of the power
From the point in time until the spindle speed rises to the set value
Determine the rise time and set the tooling based on the determined rise time.
Determine the moment of inertia of the spindle in the mounted state
By comparing the rotation speed specified in the above and the allowable rotation speed,
A numerically controlled machine tool for determining whether or not the specified rotation speed is possible.