JPH0295189A - Controller for synchronized operation of motor - Google Patents

Abstract

PURPOSE:To enable tapping machine having high precision by using a rigid tapper by estimating and computing the dead time until a positional command or a speed command to a servo-shaft is generated after the rotational position of a main shaft is detected and the variation of the rotational position of the main shaft during the dead time. CONSTITUTION:An estimating arithmetic means 100 estimating and computing the dead time until a positional command or a speed command to a servo-shaft after the rotational position of a main shaft 20 is generated and the variation of the rotational position of the main shaft during the time corresponding to the control dead time in a servo-shaft control section 4 is provided. The servo- shaft control section 4 controls the relative positions or speed of a tool and a work on the basis of an output from a main-shaft position detector 3 and an output from the estimating arithmetic means 100. Accordingly, when tapping machining is executed, the feed rate of the work 22 can be conformed accurately to the product of the rotational speed of a tapper 21 and screw pitches, thus realizing tapping machining with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a synchronous operation control device for electric motors in a control device for a numerically controlled machine tool.

(Prior Art) In machine tools such as machining centers, there are many examples of processing in which a tapper is attached to the spindle to perform tapping processing. In such tapping, the tapper rotates,
The feed speed of the work or tapper must be controlled according to the cutting speed into the work. Then, the rotational speed W (rev/m1n) of the tapper and the screw pitch P (m
m/m1n) and the feed rate F (mm/mi) has the following relationship.

F (mm/m1n) = W (rev/min) x P (
mm/m1n) (1) For this reason, conventionally, control has been performed using a device having a block configuration as shown in FIG. That is, the main shaft motor control section 1 controls the main shaft motor 2 based on the position command PN from the position command generation section 7, and the main shaft is driven by the main shaft motor 2 via a gear or the like. Further, a spindle position detector 3 is directly connected to the spindle, and its output MP is fed back to the subtraction section 16 of the spindle motor control section 1 to control the rotational position of the spindle. Further, the servo motor control section 4 controls a servo motor 5, and this servo motor 5 controls the position and feed speed of the workpiece via a hole screw or the like. The position command generation unit 7 detects the rotational speed of the spindle based on the spindle position signal MP sent from the spindle position detector 3, and uses the detected speed and the thread pitch P to obtain the above-mentioned (1).
A feed rate command that does not satisfy the equation, that is, a position command PT, is commanded to the servo motor control unit 4. A rotational speed detector 6 is connected to the main shaft motor 2, and a speed signal PSM is input to a speed detecting section 14 for speed control.

In such a conventional example, detection of the spindle rotational speed and calculation of the feed rate command based on the above equation (1) are executed by the position command generation section 7 of the numerical control device.

There is a dead time (time delay) between detecting the rotational speed of the spindle, calculating the feed rate command, and actually operating the servo motor 5, and furthermore, there is a dead time (time delay) between when the rotation speed of the spindle is detected and when the feed speed command is calculated, until the servo motor 5 actually operates. Usually, changes in the rotational position of the main shaft are not considered.

Therefore, in a transient state of acceleration/deceleration operation such as stop 2 reversal at the start of rotation or the end of the tapping cut, a situation occurs where equation (1) becomes inaccurate transiently due to a processing delay. This will cause an error in the feed rate. Conventionally, in order to absorb such errors, tapping has been performed using a tool called a floating tapper, which has a structure that can be expanded and contracted in the feeding direction.

However, as is clear from its structure, this floating tapper does not guarantee the end position of the tapping process, that is, the position of the bottom of the tapped hole, and is expensive.
It has drawbacks such as the inability to use small-diameter tappers due to play in the floating part.

On the other hand, as another conventional example, there is a device shown in the block configuration of FIG. In this method, the spindle motor control section 1 and the servo motor control section 4 each independently control the spindle position and feed position, and each control section] and 4 perform acceleration/deceleration processing (11, 41) that determines responsiveness. , position loop key Kv (13, 43), etc. are set to equal constants. According to this method, the rotational speed and feedrate of the main shaft, that is, the tapper, always operate with the same response and the same amount of error, so as a result, the rotational speed and feedrate of the tapper are relatively 1) Satisfy the formula,
Tapping can be done using a floating tapper.

(Problem to be Solved by the Invention) However, in the system shown in FIG. In 1, the required response could not be obtained due to the following reasons,
The expected behavior is not obtained. The causes are mainly nonlinear elements such as backlash in the transmission mechanism that exists between the spindle motor 2 and the spindle, and cutting resistance that changes significantly.
In particular, since the main shaft generally has a complicated speed change mechanism with a wide speed change range, it is almost impossible to obtain the same good responsiveness as the feed shaft. In addition, the above method exhibits its performance under limited conditions such as a direct connection structure between the spindle motor 2 and the main shaft 11jb, but -
In a machine having a numerical speed change mechanism, the responsiveness of the servo motor control section 4 is lowered to a lower performance in accordance with the main shaft side, and sufficient performance cannot be achieved.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to accurately synchronize the rotational speed and feed rate of the tap during synchronous operation of the electric motor for tapping processing in a machine tool such as a machining center. It is an object of the present invention to provide a synchronous operation control device for an electric motor of a machine tool, which can perform tapping with high accuracy without using a floating tapper or the like. That is, an object of the present invention is to realize a control device that can perform highly precise tapping using a rigid tapper without using a floating tapper.

(Means for Solving the Problems) The present invention includes a spindle to which a tool is attached, a spindle position detector that detects the rotational position of the spindle, and a servo that controls the relative position or speed of the tool and the workpiece. The present invention relates to a synchronized operation control device for a main spindle and a servo axis, which is used in a machine tool equipped with an axis control section. Estimating calculation means is provided for estimating and calculating an amount of change in the spindle rotational position within a time corresponding to dead time until generating a position command or a speed command and a control dead time in the servo axis control unit, and the servo axis control unit This is achieved by controlling the relative position or speed of the tool and workpiece based on the output of the spindle position detector and the output of the estimation calculation means.

(Function) In the present invention, the output of the spindle position detector attached to the spindle is provided in the servo motor control section of the feed shaft, and the servo motor control section detects the rotation speed W (rev/m1n) of the spindle.
is detected, and this rotational speed W and neck bit P (mm/
m1n) to 2-axis feed rate F (mm/m1n) -
W×1) and drive. Furthermore, an error component caused by a delay time in detecting the rotational speed of the spindle is corrected by performing predictive calculation based on the rotational acceleration of the spindle or the torque command value received from the spindle motor control section.

According to the present invention, since the servo motor control section directly detects the rotational position of the main shaft, the main shaft position can be detected at high speed. In addition, changes in the spindle rotational position that occur during the detection and processing delay time are predicted and deduced from spindle motor torque commands, spindle rotational speed commands, one-rotation position commands, etc., so spindle rotation The feed rate can be accurately synchronized without any lag in position,
The above formula (1) is always accurately satisfied. It is possible to realize a new level of control.

(Example) FIG. 1 shows an embodiment of the present invention, corresponding to FIG.

In the present invention, the spindle position signal MP from the spindle position detector 3
An estimation calculating section 100 is provided which inputs the bit bit P from the 100 command generation section 7, and the use foot calculating section 100 is made up of a correction circuit 101 and a multiplier +02. Further, an example of the structure driven by the main shaft motor 2 and the servo motor 5 is shown in FIG. The main shaft motor 2 drives the main shaft 20 via a transmission mechanism using a gear train.
A tapper 21 is attached to the. The workpiece 22 to be machined is driven along with the table 23 in the Z@force direction by the servo motor 5 via the pole screw 24, and the main shaft 20 is rotated in accordance with the rotational speed of the tapper 21, that is, the cutting speed. The axial feed rate is controlled.

Next, its operation will be explained.

The main shaft motor control section 1 receives a rotational position command PN for the main shaft 20 from a positioning command generation section 7 of the numerical control device, and rotates the main shaft 20. At this time, the servo motor control section 4 receives a starting point position command for tapping from the position command generating section 7, and moves the workpiece 22 to the starting point position in advance. The estimation calculation unit 100 estimates the spindle 20 based on the output MP of the spindle position detector 3.
The position and rotational speed W are detected. Further, the position command generating section 7 gives the thread pitch P to the estimation calculation section 100, and the feed rate F of the workpiece 22 is calculated from the thread pitch P and the spindle rotation speed W based on the above equation (1). However, the servo motor control section 4 controls the servo motor 5 using this feed rate F as a command value. Here, the control cycle of the servo motor control section 4 is set to be sufficiently fast to achieve highly precise control.

By detecting the spindle rotation speed W in the estimation calculating section +00 at the control cycle of this servo motor control section 4, the spindle rotation speed W can be detected accurately, and as a result, the command value of the feed speed of the workpiece 22 is 17. can be made to exactly match the above equation (1). Then, the servo motor control unit 4 receives this feed speed command value F as a position command for the workpiece 22, and as shown in FIG.
The servo motor 5 is controlled based on the deviation from ss, and the position command value F is differentiated by the differentiation circuit 42.
The calculation unit 47 uses this result as a speed command for the servo motor 5.
The Fitterer 1-word control is performed by inputting the . By this foot-word control, the servo motor control unit 4 can control the position of the workpiece 22 accurately and with almost no delay in response to the input position command F, and as a result, the position of the workpiece 22 can be controlled accurately with respect to the input position command The speed of 22 also exactly matches the above equation (1). In addition, in the present invention, the delay time that occurs when detecting the position of the main lIb 20 can be extremely reduced, realizing high-precision tapping processing. I can do this. However, there is a certain delay time between the arithmetic processing of equation (1) in the servo motor control unit 4 and the actual operation of the servo motor 5, and during this delay time, the actual spindle rotational speed W or rotational position This is a cause of errors due to changes in the Therefore, if high accuracy is required for the -layer, it is necessary to divide the error due to this delay time by 141.

Therefore, in the present invention, the following methods (1) to (4) are used to realize control that can suppress the occurrence of this error.

First, we will explain a control method that does not require any changes to the hardware.

The servo motor control unit 4 is activated at a certain point in time j, 1. ) is the spindle position detected at P,. , and the spindle position detected in the control cycle one time before time Llnl is P3. , - Mouth, at this point again. -1, time L+n-11~l'
, (The average spindle rotational speed W(1,) up to nl is expressed as. Also, the average spindle rotational acceleration dw, , , /
dt. Then, assuming that there is a delay time of ΔT before the servo motor control unit 4 calculates the command value of the feed rate F and the servo motor 5 actually operates, then at time t+
At the time of 1+l+ΔT, the spindle position P fn+ is approximated as follows. Here, the delay time ΔT is known in advance, and this spindle position 1). , is the predicted value of the spindle rotational position, and this spindle position P°,. , the position command P□ of the workpiece 22. , is calculated using the following equation (5).

P z +nl -P (nl・P ・・・・・・・・・(5) This equation (5) means exactly the same phenomenon as the above equation (1), and in the east, (1) This is the result of integrating the equation and converting it into position information.

Through the above-mentioned calculations, the error caused by the delay time of the spindle position detection and arithmetic processing as described above is corrected, and the feed speed, that is, the position, of the workpiece 22 is synchronized with the rotation speed of the main shaft 4i+l+20 without delay. can. The block configuration of this control system is as shown in FIG. 1, and a correction circuit 101 in the figure performs predictive calculation of the spindle position based on the above equation (4).

(2) Next, the second method will be explained.

As in the case of the first method described above, let Znl be the spindle position detected by the two-point motor control unit 4 at time L+nl, and let W be the average spindle rotation speed from time tal+-11 to t+nl. Then, if the time from when the servo motor control unit 4 calculates the feed speed command value F to when the servo motor 5 actually operates is ΔT, the change in the spindle rotational speed that occurs during the time period ΔW is the main shaft motor 2 and the main! 1iIh2
It is approximated by the following equation (7) from the equation of motion of 0.

JM Spindle motor inertia Js Spindle and tool inertia TM Spindle motor output torque T1.・Cutting load torque Here, the spindle motor inertia JM and the inertia J5 of the spindle and tool are known, and the cutting load torque TL can also be estimated in advance based on the cutting conditions, so if the spindle motor output torque Ti+ is known, the speed can be calculated. It is possible to calculate the amount of change ΔW. Here, the spindle motor output torque T
M almost accurately responds to the output torque command value calculated within the spindle motor control section 1, and can be approximated by this torque command value.

As described above, in the apparatus shown in the block configuration of FIG. 3, the torque command TQ of the spindle motor 2 is input from the spindle motor control section 1 to the servo motor control section 4, and the arithmetic circuit 103 calculates the speed change ΔW. When the servo motor actually operates 1. The predicted value W' +n+ of the spindle rotation speed at nl''ΔT is calculated as follows.

Pfnl-P(.)+W,. ,・ There are 2 guns,
This predicted value P゛,. The position command Pz(.) is calculated using the above formula (5), and the feed speed of the workpiece 22 is controlled. As a result, it becomes possible to accurately synchronize the feed rate, that is, the position, of the workpiece 22 with the rotational speed of the main shaft 20 without delay. In FIG. 3, the arithmetic processing based on equation (9) is performed by the arithmetic circuit 103 in the figure.

From this predicted value W° (.), the predicted value P Znl of the spindle rotational position at time Fnl + ΔT is ■Next, as a third method, the change in spindle rotational speed that occurs during the two delay times is controlled by the spindle motor. The calculation is based on the spindle rotational position command PN input to the spindle motor control section 1 and a transfer function between this position command PN and the actual spindle rotational position, or the rotational speed command calculated in the spindle motor control section 1 and the actual rotational speed command are calculated. It is also possible to calculate based on the transfer function between the rotational speed of the main shaft and the rotational speed of the main shaft. That is, these transfer functions are known in advance, and the spindle rotational speed or rotational speed can be predictively calculated from the rotational position command or rotational speed command.

By the way, the above explanation describes the case where the feed direction of the workpiece 22 is driven by the two-point motor 5 having only one axis.
A case is shown in which the rotational speed of the main shaft 20 and the feed speed of only one shaft are synchronized. However, the main 1Till1
In some cases, such as when attaching a special accommodation to the tip of the 20 or performing diagonal tapping, it is necessary to synchronize the multiple feed shaft servo motors with the main 1 inch + rotational speed. Such a case can be realized by distributing the output signal -qMp of the spindle position detector 3 to a plurality of servo motor control sections. Furthermore, in the actual implementation technology, the spindle motor control section 1 and the servo motor control section 4 shown in FIG. 1 are each constituted by a digital circuit, and perform sampling control for each control period.

Here, if the control period of the spindle motor control section 1 and the servo motor control section 4, that is, the timing at which the control is executed, is the same, an error will occur due to the difference in timing. For this reason, we synchronize each control cycle to ensure that control is executed at the same timing.

(Effect of the invention) The uninvented synchronous operation 11i on the above line (according to the J control device, when performing tapping, the feed speed of the workpiece is accurately matched to the product of the rotational speed of the tapper and the screw bit). Therefore, there is no need for a floating tapper, etc., which was conventionally used to absorb errors in the feeding direction, and tapping processing can be achieved with high precision.
By detecting the spindle rotation speed at high speed using the servo motor control section, the Z-axis feed rate can be accurately synchronized with the spindle rotation speed under any operating conditions.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG.
Figure 3 shows the configuration of a machine tool that is subject to uninvention.
The figure is a block diagram showing another embodiment of the present invention, and FIGS. 4 and 5 are block diagrams showing conventional devices, respectively. 1... Main shaft motor control section, 2... Main II+11 motor, 3... Main shaft position detector, 4... Servo motor control section, 5... No.-bo motor, 7... Position command generation Part, 20... Main i1i+b, 21... Tappa, 22.
...Work, 23...Table, 24...Pole connection, +00...Estimation calculation unit, 101...Correction circuit,
102... Multiplier, +03... Arithmetic circuit, 104...
...Adder.

Claims (1)

[Claims] 1. A main shaft to which a tool is attached, a main shaft position detector that detects the rotational position of the main shaft, and a servo shaft control section that controls the relative position or speed of the tool and the workpiece. In the synchronous operation control device for a main spindle and a servo axis in a machine tool, the dead time from detecting the rotational position of the main spindle until generating a position command or speed command to the servo axis and the servo axis control section Estimating calculation means is provided for estimating and calculating the amount of change in spindle rotational position within a time corresponding to the control dead time in , and the servo axis control section is configured to: A synchronous operation control device for an electric motor, characterized in that the relative position or speed of the tool and the workpiece is controlled. 2. The estimation calculation means calculates the amount of change in the spindle rotational position based on a torque command value of the spindle motor input from a spindle motor control unit that controls the rotational position or speed of the spindle. A synchronous operation control device for an electric motor according to claim 1. 3. The servo axis control unit adjusts the position of the speed command based on the deviation between the command value of the relative position of the tool and the workpiece and the detected value of the actual relative position of the tool and the workpiece. The relative speed command value of the tool and workpiece is determined by calculating the deviation and adding the position deviation and the change in the position command value. The synchronous operation control device for an electric motor according to claim 1, wherein the device is configured to control the relative speed of a workpiece. 4. The period of detecting the rotational position of the main shaft from the output of the main shaft position detector and the period of estimating and calculating the amount of change in the rotational position of the main shaft by the estimation calculation means are equal to the control period of the servo axis control section. The synchronous operation control device for an electric motor according to claim 1, wherein the synchronous operation control device for an electric motor is configured to perform processing in cycles.