JPH1190758A - Control method for feed screw mechanism - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the moving cycle time of an object by applying a maximum safety rotating speed of each section which is found beforehand according to the position of a nut on a screw which is connected to the moving object, when the moving object is moved, and by rotating the screw within the maximum rotating speed. SOLUTION: When the movement is spread over two sections (speed block) or more, an order value preparation part 6 prepares a moving command for drawing the movement speed pattern according to respective maximum safety rotating speeds permitted in a section where a nut (moving object) belongs at present and a section where the moving object, namely the nut, moves on a ball screw 1 continuously from the aforementioned section, and the traveling distances in respective sections. This prepared moving command controls the rotation of the ball screw 1 and quickly feeds an XY table 2. As a result, the cycle time of the XY table 2 is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control method of a feed screw mechanism for moving an object such as a table in a machine tool or the like.

[0002]

2. Description of the Related Art In machine tools and metal working machines, a feed mechanism using a so-called ball screw is frequently used as a feed mechanism for moving a table or a tool post.

The ball screw converts the rotational motion of the motor into a linear motion of a nut, and integrates the nut with a moving object such as a table so that the moving object is controlled by the rotation accuracy of the motor and the accuracy of the ball screw. Although it is frequently used because it can be controlled with extremely high precision, it also includes various problems.

[0004] For example, when the moving distance of the moving object is long, it is necessary to use a long and large-diameter ball screw. The bending and vibrations caused by the moment limit the rotation speed which is safe and does not cause any problem for the machine, and accordingly the maximum movement speed of the moving object is naturally limited. In addition, long and large-diameter screws are heavy in weight and high in manufacturing cost, which is a bottleneck in machine manufacturing.

For this reason, in the conventional machine, the critical rotation speed of the ball screw used is estimated to be the safest, and the safe rotation maximum speed of the ball screw of the machine is fixed.

However, since the critical rotation speed limit of the ball screw varies depending on the position of the nut, the performance of the ball screw is sufficiently obtained at the critical rotation speed limit fixed and set on the safest side in the past. I could not say that.

For example, in a fast-forward operation of a moving object, the vehicle is accelerated from a start point to a fast-forward speed, that is, the above-mentioned fixed maximum speed. A running pattern in which positioning is performed by decelerating in front is adopted.

At this time, since the object to be moved is moving at a fixed fast-forward speed, the position of the nut changes every moment on the screw, and the change in the position of the nut causes the critical rotation speed limit of the screw. Has also changed. When the position of the nut changes on the screw, even if the section where the screw can be rotated at a rotation speed higher than the fixed critical rotation speed is in the traveling section on the screw, the fixed dangerous rotation is fixed. In this case, there is a problem that the fast-forward efficiency does not have to be high because the motor rotates only at the limit speed. This problem is the same in the case where the moving object is not fast-forwarded.

[0009]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a feed screw mechanism using a ball screw or the like to control the rotational speed of a screw by controlling the screw rotation speed by the position of the nut on the screw. It is to raise the tact.

[0010]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, a control method according to the present invention comprises a feed screw mechanism for moving an object to be moved in a machine tool or the like having a plurality of lengths of screws. Separately, when the nut is located in each section, the maximum safe rotation speed allowed for the screw is determined, and when the moving target is moved, the position of the nut coupled to the moving target on the screw is determined by the position on the screw. In this method, the maximum rotational speed of each section previously determined is applied, and the screw is rotated within the maximum rotational speed.

[0011]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a functional block diagram of a control system for executing the control method of the present invention, FIG. 2 is a flowchart of an example of generating a speed pattern by the control method of the present invention, and FIG. 3 is an example of a target speed pattern generated by the control method of the present invention. FIG. 4 is a speed diagram showing an example of a speed pattern according to the conventional method.

Now, when a screw having an effective feed length of 3000 mm is incorporated in a machine tool as a feed screw to be moved,
The screw is divided into five sections, and the maximum safe rotation speed allowed for the screw in each section is shown in Table 1.

[0013]

[Table-1]

The meaning of Table 1 is that the total length is 3000
mm screw, the section between 0 and 200 mm has a maximum safe rotation speed of 20 m / min, the section between 200 and 500 mm has a maximum speed of 40 m / min, and similarly, the section between 500 and 2500 mm has a range of 60 m / min and 2500
40m / min for 2800mm section, 20m for 2800-3000mm section
/ min.

Therefore, according to the present invention, the 100 m
The nut is moved from the point m to the point 2700 mm, that is, when the moving object, for example, the XY table is fast-forwarded in the section of the screw, the moving speed is applied to each section, and the speed command is applied by applying the speed in Table 1 above. Shape it. The rotation speed pattern of the screw according to this speed command is as shown in FIG. FIG. 4 shows a pattern of the rapid traverse speed according to the conventional method in the feed mechanism using the same screw as described above. In the conventional method, the rotation speed of the screw is set to the maximum speed on the safest side (the critical rotation limit speed). ), The maximum speed is 20m / min.
The time required for rapid traverse of the same 2600 mm will be long.

The formation of the speed command according to the above-described method of the present invention is formed in the control system of FIG. 1 in accordance with the flow of the flowchart of FIG. 2. This will be described below. When a rapid traverse command is issued, the current position of the moving object, the rapid traverse movement amount, and the allowable maximum safe rotation speed of each section are captured in step S1, and the nut is preset to the entire length of the screw by the commanded movement. It is determined in step S2 whether or not two or more sections (speed blocks) exist.
If the movement does not extend over two or more sections, the current trapezoidal speed pattern is used at step S3 at the current position to be moved, that is, the maximum speed allowed for the section to which the current position on the nut screw belongs. (Movement trajectory) is executed in step S5.

On the other hand, if the movement spans two or more sections (speed blocks), in step S4, the section to which the current position of the nut (object to be moved) belongs and the object to be moved following this section, that is, the nut Based on the maximum safe rotation speed allowed for each of the sections where the robot moves on the screw and the traveling distance in each section, a movement command that draws a movement speed pattern as illustrated in FIG. 3 is formed. In the next step S5, Then, fast-forwarding based on the formed movement command is executed.

FIG. 1 illustrates a control system for performing drive control based on a movement command created by the above-described flow.
Is a ball screw, and 2 is an XY coupled with the nut of the screw.
Table 3, reference numeral 3 denotes a servo motor for driving the ball screw, reference numeral 4 denotes a servo amplifier of the motor 3, reference numeral 5 denotes a servo compensator for supplying a control signal to the amplifier, and reference numeral 6 denotes a command value forming section including generation of the above-mentioned movement command. is there.

In the control system shown in FIG. 1, reference numeral 7 denotes a motor position detector which is sufficient if it is disposed on at least one of the ball screw 1, the XY table 2, the motor 3, and the servo amplifier 4. Feedback
The position of the XY table 2 to be moved or the position of the nut (not shown) of the ball screw 1 to be replaced at that position, or the rotation speed of the motor 3 or the rotation speed of the screw, or the input signal of the servo amplifier 4 or The table 2 formed in the servo compensator 5 based on the detection signal of the output signal
Alternatively, the driving of the motor 3 is controlled by comparing the current value indicating the current position of the nut and the current speed converted into the rotation speed of the screw with the above-described command value. Although the above example describes fast-forwarding of a moving object, it is a matter of course that the method of the present invention can be applied in a forwarding mode other than fast-forwarding.

[0020]

The present invention is as described above. In the conventional feed screw mechanism, for example, in speed control in rapid traverse, the speed within the safest rotation critical speed of the screw used is controlled as the maximum speed. Although the efficiency of the rapid traverse tact could not be increased any more, the length of the screw of the feed screw mechanism for moving the moving object in the machine tool etc. was divided into a plurality of sections, and nuts were added to each section. The maximum safe rotation speed allowed for the screw is determined when is located, and when moving the moving object, each section previously determined by the position of the nut coupled to the moving object on the screw. Since the rotation safe maximum speed is applied and the screw is controlled to rotate within the maximum rotation speed, the driving efficiency of the feed screw can be significantly increased as compared with the conventional method. This effect can be obtained even in a feed mode other than the fast-forward mode.

Further, by adopting the above control method, the selection range of the ball screw used for the feed screw mechanism is expanded, which is advantageous in designing and manufacturing the feed screw mechanism.

[Brief description of the drawings]

FIG. 1 is a functional block diagram of a control system that executes a control method of the present invention.

FIG. 2 is a flowchart of an example of creating a speed pattern by the control method of the present invention.

FIG. 3 is a velocity diagram showing an example of a target velocity pattern created by the control method of the present invention.

FIG. 4 is a velocity diagram showing an example of a velocity pattern according to a conventional method.

[Explanation of symbols]

 Reference Signs List 1 ball screw 2 XY table 3 servo motor 4 servo amplifier 5 servo compensator 6 command value forming unit 7 motor position detector

Claims (2)

[Claims] A length of a screw of a feed screw mechanism for moving an object to be moved in a machine tool or the like is divided into a plurality of sections, and when a nut is located in each section, a maximum safe rotation speed allowed for the screw is determined. In advance, when the moving object is moved, the rotationally safe maximum speed of each section previously determined is applied according to the position on the screw of the nut coupled to the moving object, and the maximum rotational speed is determined within the maximum rotational speed. A method for controlling a feed screw mechanism, comprising rotating a screw. 2. The control method of a feed screw mechanism according to claim 1, wherein the position of the nut on the screw is detected by replacing it with one of a signal of a servo amplifier, the number of rotations of a motor, and a position to be moved such as an XY table. .