JP2004188541A - Feed shaft parameter adjusting system for machine tool - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To adjust parameters of a feed shaft of a machine tool by simulation. <P>SOLUTION: This feed shaft parameter adjusting system 100 is provided with measuring devices for measuring motion of a machine to adjust the parameters of the feed shaft based on result of measurement. Five parameters of acceleration, position loop gain, feed-forward gain, acceleration/deceleration filtering, and corner speed are separately adjusted. Above adjustment is executed by conducting simulation on a mathematical model representing machine vibration instead of using a real machine. Constants for the mathematical model are identified using the above-mentioned measuring devices in starting adjustment. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００２６】
図８は、加減速フィルタの調整方法を示す。各軸に発生する許容できない振動のうち最も低い周波数を求める。
その周波数の逆数を求めてフィルタ時定数とする。
この加減速フィルタは移動平均フィルタであるので、フィルタの入出力関係を表す伝達関数は図のように時定数の逆数とその整数倍で伝達率が０となる。ここに問題となる振動の周波数を一致させることで、加減速データから問題の周波数成分を取り除くことができる。
【００２７】
図９は、コーナ速度の調整方法を示す。
他の４パラメータを調整した後、最後にこの調整をおこなう。
方法としてはコーナ速度を小さい値から少しずつ大きくしていきながら、コーナ部の振動を観測し、振動の振幅が許容値を超えない最大のコーナ速度を求める。
【００２８】
図１０は、適用例を示す。
パラメータ調整前の実機データ（ａ）から機械モデルを同定する（ｂ）。
機械モデルを使って、パラメータを調整する。（ｃ）
調整したパラメータ値を使って、実機で精度を確認する（ｄ）。
【００２９】
【発明の効果】
本発明は次の効果を有する。
機械の動きをシュミレートして調整するので、モータのフィードバックだけを使う調整よりも正確な調整ができる。
パラメータの特徴を分析して、それぞれにふさわしい調整をするので、「精度のために効率が犠牲になる、効率のために精度が犠牲になる」といったジレンマが解消される。
所定のアルゴリズムを使うので、オペレータの資質に関係なく的確な調整を行うことができる。
パラメータ調整は実機を動かすことなく行われるので、調整中に発生しがちな危険性が排除される。また、最適なパラメータを迅速に見つけ出すことができる。
加工プログラムをシミュレーションすることで加工プログラム毎に最適なパラメータを提供できる。
【図面の簡単な説明】
【図１】本発明の加減速パラメータ調整システムの概略を示す図。
【図２】加減速パラメータ調整システムのブロック図。
【図３】機械モデルの説明図。
【図４】加減速形状に関するパラメータの説明図。
【図５】加減速の調整方法を示す説明図。
【図６】位置ループゲインの調整方法を示す説明図。
【図７】フィードフォワードゲインの調整方法を示す説明図。
【図８】加速度フィルタの調整方法を示す説明図。
【図９】コーナ速度の調整方法を示す説明図。
【図１０】適用例を示す説明図。
【符号の説明】
１０ ＣＮＣ装置
２０ 切換スイッチ
３０ サーボコントローラ
４０ モータ
５０ 工作機械
６０ 測定器
１００ パラメータ調整システム[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a system for adjusting a feed axis parameter of a machine tool based on a motion path error.
[0002]
[Prior art]
In order to adjust the feed axis parameters, the feedback signals of the encoders attached to the servo motors of the respective axes are observed, and the adjustment is performed so that the torque limit is not exceeded, there is no vibration, and there is no overshoot. As for the automatic adjustment, a system for automatically adjusting servo parameters based on stability is disclosed (see Patent Document 1), but a system for adjusting a time constant of acceleration / deceleration, an acceleration / deceleration filter, and a feedforward gain is disclosed. Absent.
[0003]
[Patent Document 1]
JP-A-11-102211
[Problems to be solved by the invention]
Since the publications described in the above publications only look at the feedback of the servo motor, errors caused by vibrations generated by the machine, machine distortions generated during acceleration / deceleration, and synchronization errors caused by a difference in rigidity between the two axes are reduced. I have not been able to cope. Further, even if the movement of the machine is observed with a non-contact glass encoder or a laser length measuring device capable of measuring the plane movement, there is no appropriate parameter adjustment method based on the observation. Of course, there is no automatic adjustment system. In manual adjustment, careless setting of parameters may cause damage to machines, measuring instruments, jigs, and the like. The present invention provides a system that solves the above-mentioned problems.
[0005]
[Means for Solving the Problems]
The feed axis parameter adjusting system for a machine tool according to the present invention includes, as basic means, a device for measuring a relative motion between a main shaft of a machine tool and a table, and a means for adjusting a feed shaft parameter based on measurement data of a measuring device. Prepare. Then, five parameters of acceleration, position loop gain, feedforward gain, acceleration filter, and corner speed are adjusted.
[0006]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 schematically shows an acceleration / deceleration parameter adjustment system according to the present invention.
A predetermined machining program is executed on the actual machine to measure the relative motion between the spindle and the table (initial test step S1).
From the measured data, a coefficient of a mathematical model (hereinafter, mechanical model) is identified so that the generated vibration can be expressed (step S2). The acceleration / deceleration parameters are adjusted so that the accuracy is within an allowable value while performing a simulation using this machine model (step S3). The acceleration / deceleration parameters are acceleration, position loop gain, feed forward gain, acceleration / deceleration filter, and corner speed. After the adjustment by the simulation on the machine model, the accuracy is confirmed on the actual machine using the parameters (step S4).
[0007]
FIG. 2 shows an acceleration / deceleration parameter adjustment system.
The figure shows a conventional machine tool feed drive system comprising a CNC device 10, a servo controller 30, a motor 40 and a machine tool 50, a measuring device 60 for measuring the relative movement of the spindle and the table, and a parameter adjustment system 100 (hereinafter referred to as "parameter adjustment system 100"). Adjustment system). In the figure, of the parameters to be adjusted, only the feed forward gain and the position loop gain are shown. The other three parameters are used for processing inside the CNC 10.
[0008]
The adjustment system 100 receives a servo command from the CNC and measurement data from the measuring device as input signals, and outputs a parameter change and operation start of the CNC as output signals. The interior of the adjustment system has feedforward processing means 110, a position control device 120, and a machine model 130 for simulating the machine. In this example, it is assumed that the speed control and the current control have sufficient control responsiveness, and a case where the transfer function is set to 1 and modeling is not performed is shown. However, there is no problem even if these control processes are incorporated in the model.
[0009]
A changeover switch 20 is provided at the subsequent stage of the CNC 10, and switches between providing a servo command to the servo controller 30 and providing the servo command to the adjustment system 100 with this switch.
[0010]
In this description, the feedforward processing means is provided in the servo controller, but may be provided in the CNC. In addition, the processing of the CNC may be simulated in the adjustment system. In this case, the input to the adjustment system is not a servo command but an NC program.
[0011]
FIG. 3 shows a machine model. The machine model only needs to be able to reproduce the vibration of the machine to some extent. The model a given as an example is a mathematical model having two frequencies. The coefficients ω _a and ω _b represent frequencies, and ζ _a and _{ｂ b} represent extinction coefficients for the respective frequencies. The magnitude of vibration at each frequency is determined by coefficients a and b.
The mechanical model may be a higher-order linear model such as a model b, or may be a discrete model such as a model c.
[0012]
The parameter to be adjusted can be divided into a parameter related to the servo control and a parameter related to the acceleration / deceleration shape. The parameters related to the servo control are the feedforward gain and the position loop gain described in FIG.
[0013]
FIG. 4 shows parameters related to the acceleration / deceleration shape, and the parameters are an acceleration, an acceleration / deceleration filter, and a corner speed.
According to the procedure for creating an acceleration / deceleration shape, parameters used for the procedure will be described. First, the movement distance of the interpolation command block indicated in the machining program is time-divided based on the speed command. If it is left as it is, the acceleration will be infinite and an extremely large impact will be given to the machine. Therefore, the linear acceleration / deceleration processing is performed so that the acceleration indicated by the parameter is obtained.
[0014]
Next, an acceleration / deceleration filter process is performed to make the acceleration change continuous. This filter is a moving average filter, and the time constant of this filter is set by a parameter.
[0015]
Next, the corner speed will be described. If the adjacent interpolation command blocks are applied to the acceleration / deceleration filters and continue without overlapping in time series, the processing time of the machining program becomes longer. In order to prevent this, blocks are superimposed and the overlapping part is redistributed to the preceding and succeeding blocks. This minimum value is called a corner speed and is set by a parameter. As an actual physical phenomenon, it is impossible for an object to turn a 90-degree corner at a certain speed, but it is possible because a servo command is a matter in numerical processing. However, if this value is set too large in order to shorten the machining program, the machine will vibrate.
[0016]
The adjustment procedure will be described. First, the changeover switch is set to the contact a, a predetermined program is executed, and the machine is operated. The operating parameters are set to values that make the machine easy to vibrate within the safe range. The motion trajectory of the machine at that time is measured by a measuring device and input to the adjustment system. The adjustment system analyzes the measured data and identifies the parameters of the machine model.
[0017]
Next, the changeover switch is set to the contact b, and a servo command is given to the adjustment system. Perform a simulation in the adjustment system. If the same servo command is used when the machine model is identified, the same motion trajectory should be obtained.
[0018]
Based on this data, parameters are adjusted using a predetermined algorithm. For example, there is a method in which the feedforward gain is changed to a certain value, the simulation is performed again, and the simulation result before the change is changed to a more appropriate value. When changing the parameters used in the CNC, the parameters of the CNC are changed before the simulation, and then a servo command is received from the CNC to perform the simulation.
[0019]
Normally, it takes a very long time to adjust the parameters while checking the accuracy on an actual machine.
In addition, if such adjustment is automatically performed using a so-called optimization method, an unexpected combination of parameters may be created in order to find an extreme value of the evaluation value, which is dangerous.
Therefore, by performing the adjustment based on the simulation based on the mathematical model on a computer, it is possible to safely and quickly perform the parameter adjustment.
[0020]
Once the machine model is identified, it is saved, and then, for various machining programs used on site, the motion accuracy is simulated using the saved machine model so that the motion accuracy falls within the specified tolerance. Next, adjust the acceleration / deceleration parameters.
This makes it possible to provide optimal acceleration / deceleration parameters according to each machining program.
[0021]
Hereinafter, an adjustment method for each parameter will be described.
FIG. 5 shows a method of adjusting the acceleration.
First, the mechanical error of each axis during acceleration / deceleration is measured. Subtracting the feedback position of the servomotor or the output value of the simulated position control loop from the measured machine position or the machine position obtained by simulation can determine the machine distortion caused by acceleration.
[0022]
Since this may appear as an overshoot at a corner, the acceleration is determined so that this value becomes equal to or less than an allowable value. Considering that the relationship between the maximum strain generated in the machine and the acceleration is proportional to the rigidity of the machine as a spring constant, a value close to the target value can be obtained by calculation from a single trial result. Further, this adjustment may be performed by trial and error, or may be adjusted using an optimization unit.
When performing the interpolation processing, the acceleration takes the same value for all feed axes for which simultaneous interpolation is to be performed, so that the acceleration is eventually adjusted to the axis having the smallest rigidity.
[0023]
Next, the deviation (relative error) of the previously obtained mechanical error is calculated for two axes that can be combined from all the axes for which simultaneous interpolation is performed. In the case of simultaneous two-axis interpolation, this relative error appears as an error on the trajectory. The acceleration is determined so that the relative error or the trajectory error becomes equal to or less than an allowable value.
[0024]
FIG. 6 shows a method of adjusting the position loop gain.
The lowest frequency ωi among the unacceptable vibrations occurring on the i-th axis is measured. At the frequency ωi, the upper limit value Kplim of the position loop gain is determined so that the transfer function from the command value of the position loop control system to the motion locus of the machine is 0 dB or less. The position loop gain Kp0 determined by the conventional method of adjusting using the feedback signal is compared so as not to impair the stability of the axis control, and the smaller one is determined as the position loop gain Kpi of the axis.
When performing the interpolation processing, it is necessary to set the same value for all feed axes that perform simultaneous interpolation, so the smallest value of Kpi is set as a common position loop gain Kpc.
[0025]
FIG. 7 shows a method of adjusting the feed forward gain.
First, two different feedforward gains are prepared.
An arc is performed for each set value of the feedforward gain, and the radius at that time is measured.
r ₁ : radius at the gain K ₁ r ₂ : radius at the gain K ₂ The optimum feedforward gain K is obtained by Equation 2 according to the formula presented from each combination of the radius gain and the radius.
(Equation 2)

[0026]
FIG. 8 shows a method of adjusting the acceleration / deceleration filter. Find the lowest frequency among unacceptable vibrations that occur in each axis.
The reciprocal of the frequency is obtained and used as a filter time constant.
Since the acceleration / deceleration filter is a moving average filter, the transfer function representing the input / output relationship of the filter has a reciprocal of a time constant and an integral multiple thereof as shown in FIG. By matching the frequency of the vibration in question here, the frequency component in question can be removed from the acceleration / deceleration data.
[0027]
FIG. 9 shows a method of adjusting the corner speed.
After adjusting the other four parameters, this adjustment is finally performed.
As a method, while gradually increasing the corner speed from a small value, the vibration of the corner portion is observed, and the maximum corner speed at which the amplitude of the vibration does not exceed the allowable value is obtained.
[0028]
FIG. 10 shows an application example.
A machine model is identified from actual machine data (a) before parameter adjustment (b).
Adjust the parameters using the machine model. (C)
Using the adjusted parameter values, confirm the accuracy with the actual machine (d).
[0029]
【The invention's effect】
The present invention has the following effects.
Because the movement of the machine is simulated and adjusted, a more accurate adjustment can be made than an adjustment using only motor feedback.
Since the characteristics of the parameters are analyzed and adjusted accordingly, the dilemma of "efficiency is sacrificed for accuracy and accuracy is sacrificed for efficiency" is eliminated.
Since a predetermined algorithm is used, accurate adjustment can be performed regardless of the qualities of the operator.
Since the parameter adjustment is performed without moving the actual machine, the danger that often occurs during the adjustment is eliminated. In addition, the optimum parameters can be quickly found.
By simulating the machining program, optimal parameters can be provided for each machining program.
[Brief description of the drawings]
FIG. 1 is a diagram schematically showing an acceleration / deceleration parameter adjustment system according to the present invention.
FIG. 2 is a block diagram of an acceleration / deceleration parameter adjustment system.
FIG. 3 is an explanatory diagram of a machine model.
FIG. 4 is an explanatory diagram of parameters relating to an acceleration / deceleration shape.
FIG. 5 is an explanatory diagram showing a method of adjusting acceleration / deceleration.
FIG. 6 is an explanatory diagram showing a method for adjusting a position loop gain.
FIG. 7 is an explanatory diagram showing a method of adjusting a feed forward gain.
FIG. 8 is an explanatory diagram showing a method of adjusting an acceleration filter.
FIG. 9 is an explanatory diagram showing a method of adjusting a corner speed.
FIG. 10 is an explanatory diagram showing an application example.
[Explanation of symbols]
Reference Signs List 10 CNC device 20 Changeover switch 30 Servo controller 40 Motor 50 Machine tool 60 Measuring instrument 100 Parameter adjustment system

Claims (8)

In a machine tool equipped with a numerical controller,
A device for measuring the relative movement between the main shaft of the machine tool and the table, and a means for adjusting the parameters of the feed axis based on the measurement data of the measuring device, acceleration, position loop gain, feed forward gain, acceleration / deceleration filter, corner speed A machine tool feed axis parameter adjustment system for adjusting the five parameters. How to adjust the acceleration parameters
Measuring the mechanical error of each axis during acceleration / deceleration;
Adjusting the acceleration so that the mechanical error of each axis is equal to or less than a certain allowable value;
Calculating a relative error between the errors of the first axis and the second axis;
The feed axis parameter adjusting system for a machine tool according to claim 1, further comprising a step of adjusting the acceleration so that the relative error is equal to or less than a predetermined allowable value. How to adjust the position loop gain parameter
Measuring the lowest frequency of unacceptable vibrations occurring in each axis;
Determining an upper limit value of the position loop gain so that a transfer function from the command value of the position loop control system to the motion locus of the machine at that frequency is 0 dB or less;
Compare the position loop gain determined by the conventional method to adjust using the feedback signal so as not to impair the stability of axis control, and the upper limit determined in the previous process, and use the smaller value as the position loop gain. The step of determining;
2. The feed axis parameter adjustment system for a machine tool according to claim 1, further comprising: determining an upper limit value of the smallest position loop gain as a common upper limit value among the axes for which simultaneous interpolation is performed. How to adjust the feed forward gain parameter
Measuring the radius error of the arc for two different feedforward gains;
The process of finding the optimal feed forward gain by Equation 1

The feed axis parameter adjusting system for a machine tool according to claim 1, further comprising: To adjust the parameters of the acceleration filter,
Measuring the lowest frequency of unacceptable vibrations occurring in each axis;
2. The feed axis parameter adjusting system for a machine tool according to claim 1, further comprising a step of setting a reciprocal of the frequency as a filter time constant. How to adjust the corner speed parameter
2. The machine tool feeder according to claim 1, further comprising a step of observing the vibration of the corner portion while gradually increasing the corner speed from a small value, and obtaining a maximum parameter value such that the magnitude of the vibration does not exceed an allowable value. Axis parameter adjustment system. 2. The feed shaft parameter adjusting system for a machine tool according to claim 1, wherein the means for adjusting the feed shaft parameter includes a machine model simulation means, and adjusts the feed shaft parameter without operating the target machine tool. 8. The machine tool feed axis parameter adjustment system according to claim 7, further comprising means for simulating a machine model for various machining programs to find an optimal acceleration / deceleration parameter for each machining program.

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