JPH04240039A - Acceleration/deceleration control method for machine tool and device thereof - Google Patents

Abstract

PURPOSE:To provide an acceleration/deceleration control unit with less deformation of a moving body at the acceleration/deceleration time of the moving body. CONSTITUTION:It is a machine tool 1 having a servomotor, a feed screw connected to the output shaft of the servomotor, moving bodies 4, 6 connected to the feed screw and moving on a bed, a tool T for machining provided on the moving bodies 4, 6, and an adjusting speed circuit for driving the servomotor with its control, and is the adjusting speed control method of the machine tool 1 that the displacement at the work point of the tool is reduced with the vibration of the moving bodies 4, 6 being restrained, by having the acceleration/ deceleration according to the time related to the proper vibration cycle upto the steady speed of the moving bodies 4, 6 or from the steady speed.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for controlling acceleration and deceleration of a machine tool. More specifically, the present invention relates to a machine tool acceleration/deceleration control method and apparatus for moving movable bodies such as machine tool tables and columns smoothly and at high speed.

0002

2. Description of the Related Art When movable bodies such as tables, columns, and turrets of machine tools are driven at high speed, they are shocked by acceleration at the start and stop of movement. In order to alleviate this shock, for example, an acceleration/deceleration method has been proposed in which the vehicle gradually accelerates at first, increases the acceleration at an intermediate position, and then decreases the acceleration to reach a constant speed state.

Particularly when the acceleration is large, the deformation of the aircraft body due to the acceleration cannot be ignored. For example, in high-speed feed machining using a column moving type machining center, cutter marks are generated when the feed is switched from the Y-axis direction to the X-axis direction. This is because the column falls forward due to Y-axis acceleration/deceleration (which varies depending on the direction of movement). However, as long as the column falls backwards, no cutter marks will remain, so this will not cause any trouble.

[0004] The depth of the cutter mark varies depending on the feed speed, size and model of the machine, but in some column-moving machines it can be 20 to 50 μm, which cannot be ignored in terms of processing accuracy. The higher the feed rate, the deeper the cutter mark, and the larger the machine, the deeper the cutter mark. In the case of peripheral machining, cutter marks can be avoided by devising a program to let the cutter escape from the workpiece along the feed direction, but in the case of pocket machining, there is no way to let the cutter escape. .

Particularly in the case of machine tools whose purpose is high-speed feeding, the presence of cutter marks due to the above-mentioned causes cannot be ignored.

[0006]

SUMMARY OF THE INVENTION The present invention was invented against the above-mentioned technical background, and achieves the following objects.

An object of the present invention is to provide a method and apparatus for controlling acceleration/deceleration of a machine tool in which the moving body is less deformed during acceleration/deceleration of the moving body.

Another object of the present invention is to provide acceleration/deceleration control for a machine tool that can adjust the vibrational displacement during acceleration/deceleration of a moving body to be equal to the static displacement caused by a steady acceleration force and the vibration speed to be zero. The object of the present invention is to provide a method and an apparatus therefor.

[0009]

[Means and effects for solving the above problems] a. a servo motor; b. a feed screw connected to the output shaft of the servo motor; c. a moving body connected to the feed screw and moving on the bed; d. a machining tool provided on the movable body; e.
A machine tool comprising an acceleration/deceleration circuit for controlling and driving the servo motor, f. A machine tool that suppresses the vibration of the moving body and reduces the displacement of the tool at the machining point by making the acceleration/deceleration of the moving body change in accordance with the time associated with the natural vibration period until steady acceleration. This is an acceleration/deceleration control method.

This acceleration/deceleration control method has a profile table for storing switching times and coefficients at each step during the acceleration/deceleration, and controls the acceleration/deceleration of each of the servo motors according to the contents of this profile table. It is controlled by the machine tool's acceleration/deceleration control device.

[0011]

[Embodiment] The principle of the present invention will be first explained below. In order to make the principle of the present invention easier to understand, a concrete explanation will be given using a column moving type machining center 1 as an example. FIG. 1 shows a column-moving machining center 1. As shown in FIG.

The bed 2 is a stand that constitutes the main body of the machine tool. The bed 2 is supported on the floor by installation bolts. Two Y-axis linear guides 3 are arranged on the horizontal surface of the bed 2 and fixed with bolts. Y
A moving column 4 is arranged on the shaft linear guide 3 so as to be movable in the Y-axis direction. The movement of the moving column 4 in the Y-axis direction is controlled by a Y-axis servo motor (not shown).

A Z-axis linear guide 5 is arranged on the front vertical surface of the moving column 4 in the Z-axis direction, that is, in the vertical direction. A spindle head 6 is movably provided on the Z-axis linear guide 5. The spindle head 6 is driven and controlled by a Z-axis servo motor (not shown). A tool T is attached to the tip of the spindle head 6.

Deformation Analysis In order to more accurately capture the deformation phenomenon of the moving column 4, more detailed static displacement calculations and transient vibration analysis were performed below.

(1) Static Displacement Displacement can be roughly divided into four types: (1) those caused by changes in the posture of the moving column 4, (2) those caused by changes in the posture of the bed 2, (2) those caused by bending of the bed 2, and (2) others.

Among them, (2) is mainly the Y-axis linear guide 3 and its mounting portion, and (2) the Z-axis linear guide 5 and its mounting portion are the main causes of deformation.

In FIG. 1, the cutting edge of the tool T and the workpiece W
Let δS be the static relative displacement between δS and δS.

[0018]

[Formula 1] However, δY: Displacement due to deformation of the Y-axis linear guide 3 and the mounting portion of the Y-axis linear guide 3 of the moving column 4 δZ: Z
Displacement δB caused by deformation of the mounting portion of the Z-axis linear guide 5 of the shaft linear guide 5 and the spindle head 6: Displacement δE caused by the bending deformation of the bed 2: Displacement caused by other factors.

Further, the force that causes deformation of each part is the acceleration α during acceleration and deceleration. δY is the weight of the moving column 4, Y
It can be calculated using a well-known method using the rigidity value of the mounting portion of the shaft linear guide 3. Similarly to the movable column 4, δZ can be calculated from the weight of the spindle head 6 and the rigidity value of the mounting portion of the Z-axis linear guide 5. δB is the spindle head 6, the moving column 4,
It can be calculated from the weight of the bed 2, the second moment of area of the bed 2, etc.

As a result, in the case of the column moving type machining center shown in FIG. Due to the change in posture and the bending of the bed, a relative displacement in the Z direction of about 8 μm was calculated to occur during processing.

(2) Transient vibration (i) In the case of linear acceleration/deceleration In the case of numerical control devices, it is known that the acceleration/deceleration time constant can be set even in cutting feed. Two to three types of time constants can be selected during acceleration and deceleration. For reasons of accuracy and speed, pre-interpolation linear acceleration/deceleration control, that is, a method in which acceleration or deceleration control is performed before interpolating a programmed line segment, is known. The time constant is, for example, 3
It is set to 300ms when the speed is 0m/min.

In the case of this linear acceleration/deceleration method, the velocity gradient is always constant, so the acceleration during acceleration/deceleration is a certain constant value. If the time during which this acceleration is applied is infinite time, it is equal to a static pressing force, so it is also used for static displacement calculations. However, when the acceleration is applied in a stepwise manner, when dynamically analyzed, the state of the displacement output waveform, that is, the individual response changes. This is greatly influenced by the natural frequency of the moving body.

In the case of the column moving type machining center shown in FIG. ). It was also found that the behavior is determined by the amount of time the acceleration/deceleration takes to occur with respect to the period T.

In the case of the machining center shown in FIG. 1, when the acceleration (0.17G) acts for a long time compared to the natural vibration period of the moving body, the center position of vibration is equal to the static displacement, and the vibration amplitude is equal to the static displacement. It produces vibrations that are twice as strong as the When the time during which acceleration is applied becomes shorter, the state of vibration changes depending on the time. In some cases, there may be no vibrational movement.

However, since an actual machine tool has a damping effect, the vibration amplitude rapidly decreases after the acceleration change disappears. Therefore, the problem is the magnitude of the displacement that is initially caused, and how to reduce this value is an important issue. If we focus on the maximum displacement initially brought about and graph its relationship with the time during which acceleration occurs, we get something like Figure 2. From this figure 2, when the acceleration time is longer than T/2 (half the natural vibration period of the moving body), the maximum displacement is 2 times the static displacement.
It can be seen that the amount is doubled.

(ii) Case of exponential acceleration/deceleration after interpolation Next, the behavior when exponential acceleration/deceleration after interpolation is used will be discussed. Since there is a servo delay, its time constant (for example, 33ms)
), the study results can be applied here. When accelerating or decelerating, the speed changes exponentially (
(See Figure 3). If the command speed is Vf and the loop gain is K, then

[0027]

[Formula 2] Acceleration is calculated by differentiating this,

[0028]

It is given by [Formula 3]. It is common to set the loop gain K to 30. Since the time constant is the reciprocal of the loop gain, the time constant t0 = 1/K = 1/30 = 33 ms.

As an example, when calculating the acceleration when the command speed is 5 m/min,

[0030]

[Formula 4] , and then gradually decreases over time.

[0031]

[Formula 5] For other feed speeds, the magnitude of the acceleration is proportional to the feed speed, and exhibits exactly the same behavior in terms of time.

When the case of exponential acceleration/deceleration is dynamically simulated and the maximum displacement is determined, it is approximately 1.65 times the static displacement corresponding to the acceleration at t=0.

From the above analysis, although there is a method of increasing mechanical rigidity to reduce deformation of the aircraft body, the present invention minimizes deformation using the following acceleration/deceleration pattern.

[0034] Method using feed acceleration/deceleration pattern Since fine feed control is possible by adopting the acceleration/deceleration control device described later, the maximum displacement can be suppressed by devising the feed acceleration/deceleration pattern as shown below. It turns out that it is basically possible.

There are several acceleration/deceleration patterns (hereinafter referred to as amplitude suppression patterns) for suppressing the maximum displacement to the same amount as the static displacement. In either case, the basics are linear acceleration/deceleration, but by changing the initial and/or final stages of acceleration/deceleration to suppress the vibrational behavior of the aircraft, that is, transient phenomena, the maximum displacement is made the same amount as the static displacement described above. (In principle, it is impossible to make the displacement smaller than the static displacement.) At this time, the time axis of the acceleration pattern is closely related to the natural vibration period T of the moving body.

Since these behaviors can be analyzed or explained using the phase plane method used to analyze linear vibrations, this method will be explained below. In FIG. 4, the upper right diagram represents temporal changes (horizontal axis) in acceleration and vibration displacement (vertical axis), and the lower left diagram represents temporal changes (vertical axis) in vibration velocity (horizontal axis). The lower right shows the feed rate based on the acceleration in the upper right diagram. The upper left diagram is a phase diagram, with the vertical axis representing vibration displacement and the horizontal axis representing vibration velocity. It is known that if the units of simple harmonic vibration displacement and vibration velocity are set appropriately, they can be expressed as a circle on a phase diagram.

A method that utilizes this fact to analyze the dynamic behavior when acceleration is applied in steps is called the phase plane method. Here, this method is applied by replacing acceleration (that is, force) with its equivalent static displacement.

First Acceleration Method A method for obtaining a pattern for suppressing body displacement using this method will be described below. In the diagram representing vibration displacement (top right), when the first peak comes, its height must match the maximum acceleration (the same amount of displacement as the static displacement), and the acceleration as an external force at that point. is required to be at its maximum, and the vibration velocity at that time must be "0".

The simplest pattern that satisfies these requirements is the pattern shown in FIG. That is, in the first step of acceleration (solid line on the upper right), 1/2 of the maximum acceleration is applied for a time of 1/2 of the natural vibration period. In the second step, the acceleration is increased to the maximum and this state is continued until the required feed rate is reached. In such an acceleration/deceleration pattern,
Although the maximum displacement is certainly suppressed, oscillatory behavior is observed during constant speed feeding after reaching the required feed speed. If this is not desirable, it is sufficient to provide a period of 1/2 period at which the acceleration is 1/2 at the end of acceleration, as shown in FIG. The same pattern applies to deceleration.

Second Acceleration Method The first acceleration method described above (the same applies to deceleration) has the disadvantage that the time required for acceleration and deceleration is longer than the conventional method of suddenly providing maximum acceleration from the beginning. There is. In order to compensate for this shortcoming to some extent, a slightly more complex pattern than the first acceleration method can be considered. An example is shown in FIG. In the pattern of FIG. 6, the first step is to give the maximum acceleration during 1/6 of the vibration period, and the second step is to set the acceleration to 0 during the next 1/6 period. Do not add.

In the third step, the acceleration is returned to the maximum and continued until the required feed rate is reached. In some cases, a similar pattern may be added at the end of acceleration (not shown). The second acceleration method, compared to the first acceleration method,
The required feed rate can be reached in a shorter period of time. However, frequent changes in acceleration may have an adverse effect on the mechanical system.

Third Acceleration Method A number of patterns exist between the first acceleration method and the second acceleration method. We will introduce two representative patterns among them. In the acceleration method shown in FIG. 7, as a first step, the maximum acceleration is 0.6
Give 75 times the acceleration, the second step is the next 5/24
During the cycle, the acceleration is 0.325 times the maximum acceleration, and in the third step, the maximum acceleration is continued until the required feed rate is reached.

In this type, the acceleration and time are set so that the maximum displacement becomes 1/2 at the end of the first step, and the second step takes the same time as the first step to achieve the remaining 1/2. This causes a displacement of . And the second
At the end of the step, the vibration velocity must be zero. A combination of a1, a2, t1, and t2 that satisfies this is determined as follows. However, the first acceleration/deceleration a during acceleration or deceleration in the first step
1, the first acceleration/deceleration time t1, the second acceleration/deceleration rate a2 during acceleration or deceleration of the second step, and the second acceleration/deceleration time t2. Let the maximum acceleration be a and the vibration period T. Now, if a1 is defined as the following formula,

[0044]

[Equation 6] The first acceleration pattern shown above is equivalent to setting K1 in the above equation to K1 = 0.5, and the second acceleration pattern can also be obtained by setting K1 = 1.

Fourth acceleration method If the acceleration pattern in Figure 8 is the fourth acceleration method,

[
0046

[Formula 7] Also in the above equation, if t1 = 0, the first
If we set t1 = T/6, we get an acceleration pattern of
This is the second acceleration pattern and is essentially the same.

[0047] The idea common to each of the patterns shown above is that by making the acceleration pattern in the initial stage up to steady acceleration change according to time associated with the natural vibration period of the moving body, vibrational The objective is to suppress this behavior and minimize the displacement at the machining point. More specifically, the magnitude of the acceleration is adjusted so that the vibration displacement is equal to the static displacement caused by the steady acceleration force and the vibration velocity becomes 0 after the initial stage of acceleration ends and before transitioning to steady acceleration. , consists in adjusting the time.

Basic Functions Required of the Acceleration/Deceleration Device To realize the acceleration/deceleration pattern described above, the following setting functions are required for the linear acceleration/deceleration of the acceleration/deceleration device.

(1) Amplitude suppression pattern on/off (see FIG. 9) 0: off 1: Executed only at the beginning of acceleration and deceleration 2: Executed only at the end of acceleration and deceleration 3: Executed at the beginning and end of acceleration and deceleration (2) Time and acceleration ratio of each step ST1: First step time (0.1 ms unit) SR1:
Ratio of acceleration to steady acceleration in the first step (3 digits or more, e.g. 0.333) ST2: Second step time SR2: Ratio of acceleration to steady acceleration in the second step. Slow down. For the end of acceleration/deceleration, perform in reverse order. Steps whose time is 0 do not need to be executed. The steady acceleration here refers to the acceleration determined by the time constant of linear acceleration/deceleration when this function is not used.

When the command speed is low and the moving distance is short, the handling is as follows. As the commanded speed becomes lower, the time required for acceleration becomes shorter, making it impossible to execute all steps. In that case, steady acceleration → second
The period is shortened or steps are omitted in the order of step→first step. The same concept applies when the travel distance is short.

(3) Details of Operation Among CNC machines using digital servo, one having arbitrary acceleration/deceleration function is known. This function is usually provided as firmware, and the acceleration/deceleration pattern is written in a profile table provided in the memory, and this is read out to control the servo motor, thereby driving the motor in the desired acceleration/deceleration pattern.

(a) Coefficient setting method In order to carry out this invention, acceleration/deceleration is performed before interpolation, and a profile table (described later) for arbitrary acceleration/deceleration after interpolation includes the differential value (jump) of the acceleration to be output. = J),
The total number is 1 (it is set as 1 for simplicity, any other number is fine.) For example, the profile table is α0
Assuming that 64 coefficients can be set from α63,
The coefficient αn corresponds to the passage of time nms from the beginning.

An example is shown below.

In the case of the first acceleration method: Let A be the linear acceleration/deceleration value before interpolation. Since half of the original acceleration/deceleration is given at 0ms and 20ms, J0 = J20 = 0.5A.

[0055]

[Formula 8] For the second acceleration method: J = A (0 ms), J = -A (6
．． 6...ms), J=A(13.3...ms), so round the time to the ms unit,

[0056]

[Formula 9] In the case of the third acceleration method and the fourth acceleration method: Using the same idea, set n1=ST1, n2=ST1+ST2,

[0057]

[Equation 10] (b) Description of operation The command pulses that enter this system are, for example, 100 pulses every 1 ms over a period of 100 ms. The total number of pulses is 10,000 pulses, and the distance traveled in μm per pulse is 10 mm. Further, the command speed is F=10×60/0.1=6 m/min.

By the linear acceleration/deceleration before interpolation, this pulse train is transformed into a form in which the front and back are linearly accelerated/decelerated, and is input to the interpolator. Now, if the time constant here is 50 ms, the pulse train input to the interpolator starts from 0 and linearly increases to 100 during 50 ms. The moving distance during this period corresponds to 2.5 mm. During the next 50ms, 100
The rate is pulses/ms and decreases linearly from 100 to 0 over the next 50 ms.

In the interpolator, the programmed direction of movement,
Although the pulse train is distributed to each axis according to the shape, it is not directly related to the current discussion, so for the sake of simplicity, it is assumed that the pulse train does not change before and after the interpolator. It is assumed that, for example, a pattern of the first acceleration method is set in the post-interpolation acceleration/deceleration profile table by the method described above.

In the post-interpolation acceleration/deceleration block, the input pulse is multiplied by each coefficient of the profile table, time-expanded, and the results are sequentially accumulated. The cumulative value is output as a pulse train every 1 ms.

[0061] Since it has such a function, now,
Coefficient α0 for the pattern of the first acceleration method = 0.5
, α1 ~ α19 = 0, α20 = 0.5, α21 ~ α6
Assuming that 3=0 is set in the profile table, the output of the post-interpolation acceleration/deceleration block for the input subjected to the pre-interpolation linear acceleration/deceleration processing will have the intended shape as shown in the figure.

Similarly, it is possible to obtain the intended output for the other patterns described above.

Functional block diagram of acceleration/deceleration control device FIG. 1
1 is a functional block diagram showing an outline of an acceleration/deceleration control device 10 for realizing the acceleration/deceleration pattern described above. C.P.
U12 is a central processing unit for controlling the entire control device. An input/output device 14 such as a CRT and a keyboard is connected to the CPU 12 via a bus 13. The input/output device 14 is a well-known device for displaying data and inputting/outputting data. The machining program memory 15 is a memory for storing a machining program for machining a workpiece.

In the profile table 16, the above-mentioned coefficient αn and switching point, ie, time, are set and stored for each acceleration/deceleration step. The speed pulse output circuit 17 outputs a combined pulse train for each axis according to the machining program read from the machining program memory 5. The pulse train output from the speed pulse output circuit 17 enters the pre-interpolation acceleration/deceleration circuit 18.

In this pre-interpolation acceleration/deceleration circuit 18, primary waveform processing is performed in order to apply acceleration/deceleration to the feed speed command. This is a trapezoidal constant acceleration command in this example. Thereafter, the interpolator 19 distributes the pulse train to each axis in order to approximate it with a group of points along a given function curve such as a straight line, circular arc, or paraboloid. The pulse train output from the interpolator 19 is shaped for acceleration/deceleration by the post-interpolation acceleration/deceleration circuits 20a, 20b according to the principle described above. The shape of this shaping is performed by data stored in the profile table 16.

The frequency dividing circuit 23 divides the frequency of the pulse train oscillated by the oscillator 24. The frequency-divided pulse train is
It is input to the speed pulse output circuit 17, and the servo motor 22a
, 22b. The frequency division speed of the frequency dividing circuit 23 is switched by the frequency division ratio switching command circuit 25 according to a program. Post-interpolation acceleration/deceleration circuits 20a, 20b
controls each pattern described above using the coefficient αn and time stored in the profile table 16.

[0067]

[Other Embodiments] The above embodiments have been explained using a column moving type machining center. However, the deformation of the driven body during acceleration and deceleration is not limited to this type, and other machine tools have similar problems, and the present invention can be applied to other types of machine tools. In addition, the pre-interpolation acceleration/deceleration circuit 18
The pulse waveform is shaped in the above manner, and after further interpolation, the pulse waveform is shaped into the above pattern. However, it will be clear to those skilled in the art that this shaping may be performed in one stage.

[0068]

As described in detail above, according to the acceleration/deceleration control method of the present invention, the deformation of the machine body can be suppressed to less than the static deformation and high-speed feeding can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a column moving type machining center.

FIG. 2 is a diagram showing the relationship between acceleration/deceleration time and maximum displacement.

FIG. 3 is a diagram showing the relationship between acceleration time, acceleration, and velocity.

FIG. 4 is a diagram showing a first acceleration method.

FIG. 5 is a diagram showing a second acceleration method.

FIG. 6 is a diagram showing a third acceleration method.

FIG. 7 is a diagram showing another acceleration method.

FIG. 8 is a diagram showing still another acceleration method.

FIG. 9 is a diagram showing an example of an acceleration/deceleration pattern of the present invention.

FIG. 10 is a diagram showing an example of an acceleration/deceleration pattern.

FIG. 11 is a diagram showing an embodiment of an acceleration/deceleration control device.

[Explanation of symbols]

1 Column moving machining center 2 bet 3 Y-axis linear guide 4. Moving column 5 Z-axis linear guide 6 Spindle head 10 Acceleration/deceleration control device 12 CPU 16 Profile table 17 Speed pulse output circuit 18 Pre-interpolation acceleration/deceleration circuit 20a, 20b Post-interpolation acceleration/deceleration circuit

Claims (5)

[Claims] [Claim 1] a. a servo motor; b. a feed screw connected to the output shaft of the servo motor; c. a moving body connected to the feed screw and moving on the bed; d. a machining tool provided on the movable body; e.
and an acceleration/deceleration circuit for controlling and driving the servo motor, f. The vibration of the moving body is suppressed and the displacement of the tool at the machining point is reduced by making acceleration/deceleration of the moving body up to or from a steady speed change according to time in relation to a natural vibration period. Acceleration/deceleration control method for machine tools. [Claim 2] a. a servo motor; b. a feed screw connected to the output shaft of the servo motor; c. a moving body connected to the feed screw and moving on the bed; d. a machining tool provided on the movable body; e.
A machine tool comprising acceleration/deceleration control means for controlling and driving the servo motor, f. A method for controlling acceleration/deceleration of a machine tool, wherein the moving body is accelerated or decelerated so that the vibration displacement of the moving body is equal to the static displacement caused by a steady acceleration force and the vibration speed is reduced. 3. In claim 2, a first acceleration/deceleration rate a1 during acceleration or deceleration in the first step, a first acceleration/deceleration time t1, and a second acceleration/deceleration rate during acceleration or deceleration in the second step. a2, second acceleration/deceleration time t2
A method for controlling acceleration/deceleration of a machine tool, characterized in that is calculated from the maximum feed acceleration a and the vibration period T of the moving body using the following formula. 4. In claim 2, a first acceleration/deceleration rate a1 during acceleration or deceleration in the first step, a first acceleration/deceleration time t1, and a second acceleration/deceleration rate during acceleration or deceleration in the second step. a2, second acceleration/deceleration time t2
A method for controlling acceleration/deceleration of a machine tool, characterized in that is calculated from the maximum feed acceleration a and the vibration period T of the moving body using the following formula: 5. The servo motor according to claim 2, further comprising a profile table for storing switching times and coefficients at each step during the acceleration/deceleration, and controlling the acceleration/deceleration of each of the servo motors according to the contents of the profile table. Acceleration/deceleration control device for machine tools.