JP4598617B2 - Position control device for numerical control machine - Google Patents

Description

  The present invention relates to a position control device applied to a numerical control machine.

  FIG. 8 is a model showing one axis of a schematic mechanism of a ball screw drive system in a machine tool which is one of conventional numerical control machines. When the servo motor 100 rotates, the ball screw 101 coupled on the shaft rotates, and the spindle head 103 fixed to the ball screw nut receives the thrust Fr and moves in the y direction on the cross rail 102 that also serves as a guide surface. It has a structure to do. The columns 104a and 104b support and fix these structures, and one side is rigidly installed on the ground. The cross rail 102 is provided with a linear scale (not shown) for detecting the spindle head position y, and the servo motor 100 is provided with a position detector (not shown) for detecting the motor rotation angle θm and the angular velocity vm. Is included.

FIG. 7 is a block diagram of a target plant that does not take into consideration the conventional machine base rigidity, and shows the characteristics of the ball screw drive system as a two-inertia target plant. The motor generated torque τm is a torque converted value of the motor acceleration / deceleration torque and the spindle head thrust Fr. The motor acceleration / deceleration torque generates an acceleration am corresponding to the motor inertia moment Im, and becomes a speed vm and a motor rotation angle θm via two integrators (S is an operator of Laplace transform). The motor rotation angle θm becomes the motor position ym in the linear motion direction according to the lead P of the ball screw 101. On the other hand, upon receiving the thrust Fr, the spindle head 103 generates an acceleration ay corresponding to the spindle head mass Mh, and becomes a speed vy and a spindle head position y via two integrators. Further, the spindle head thrust Fr is obtained by multiplying the deviation between the motor position ym and the spindle head position y by the drive system total rigidity Ks.

FIG. 6 is a block diagram of an example of a conventional position control device for controlling the spindle head position y of the target plant as described above in accordance with the position command value θ ^* generated by a host device (not shown). . In order to control the position of the target plant with high accuracy, it is necessary to control the motor rotation angle θm in consideration of the spindle head position y and the deflection amount θdf generated in the ball screw drive system during acceleration / deceleration. In the figure, the deflection amount θdf is determined by the operation of the block Ca.
[Formula 1] θdf = (Mh / Ks) (d ² θ ^* / dt ² )
Is required. The control position command value θc is created by adding θ ^* and the deflection amount θdf by the adder 51.

In the conventional position control device, a feedforward configuration is adopted in order to speed up the response of the motor. Specifically, the deflection amount θdf is differentiated with respect to time to become a deflection velocity Vdf, and is added to the time differential value of the position command value θ ^{* by} the adder 53 to become a velocity feedforward amount Vff. Further, Vff is differentiated with respect to time and becomes an acceleration feedforward amount Aff. Cb is a conversion block for obtaining the torque feedforward amount τff corresponding to the motor torque that generates the acceleration Aff.

  The feedback configuration of the conventional position control device is as follows. First, the spindle head position y of the target plant 50 shown in FIG. 7 and FIG. 8 detected by the linear scale becomes the spindle head position θi which is multiplied by (2π / P) and converted to the motor rotation axis. The position feedback θf is subtracted from the control position command value θc by the subtractor 52, and the output position deviation is amplified by the position deviation amplifier Gp. The output is added to the speed feedforward amount Vff by the adder 54 to become a speed command value Vc. In the subtractor 55, the motor rotational angular velocity vm is subtracted from the speed command value Vc, and the output speed deviation is normally proportional-integral amplified by the speed deviation amplifier Gv. This output and the torque feedforward amount τff are added by an adder 56 to obtain a torque command value, that is, a motor generated torque τm.

The relationship between the position feedback θf and θm, θdf, θi is shown in FIG.
[Formula 2] θf = θm + G (S) [θi− (θm−θdf)]
It is represented by Here, G (S) is 0 ≦ | G (S) | ≦ 1, and has a transmission characteristic of a delay system that is large for a low frequency input and small for a high frequency input. Therefore, in a steady state, θf = θi + θdf, and θc = θf can be achieved by feedback control, so that θ ^* = θi can be achieved. That is, the spindle head position y can be controlled in accordance with the position command value θ ^* . Such a position control device is disclosed in Patent Document 1.

Japanese Patent No. 3351990

  As described above, in the conventional position control device, the ball screw drive system is regarded as a two-inertia model, and the drive unit (spindle shaft) is configured by configuring the position control system in consideration of the deflection generated due to the overall rigidity of the drive system. (Head position) can be controlled according to the position command value. However, when the machine structure (column) that supports and fixes the structure (cross rail) including the drive system is low in machine configuration or when high acceleration / deceleration operations are required, the rigidity of the machine base Due to the low frequency vibration caused by this, the spindle head position could not be accurately controlled. One of the problems to be solved by the present invention is to construct a position control system that takes into account the amount of displacement due to the rigidity of the machine base, so that even when low frequency vibrations occur in the machine base, Is to provide a position control device capable of controlling the spindle head position according to the position command value.

In order to achieve the above object, a position control device for a numerical control machine according to the present invention drives a drive unit of a mechanism constituted by a ball screw drive system of the numerical control machine by a servo motor, and sets the drive unit position. A position control device that indirectly detects with a linear scale or a motor rotation angle detector and controls the position of the drive unit according to the position command value from the host device. A base vibration monitor for determining a base vibration compensation command value for compensating a displacement amount due to vibration generated in the base based on the mass of the structure including the base and the rigidity of the base supporting the structure; from the time differential value of the vibration compensation command value, the block for computing determine vibration of a machine base compensation speed command value and the machine base vibration compensation torque command value, vibration of a machine base compensation command value to the position command value of least position controller Calculated by, and an adder for calculating a new position instruction value, and controls the drive unit position in accordance with the new position instruction value.

Further, in the position control device for a numerically controlled machine according to the present invention, an addition for calculating a new speed command value by adding the machine vibration compensation speed command value to the speed command value calculated based on the position command value from the host device. vessel, or comprises at least one adder adds vibration of a machine base compensation torque command value to the torque command value calculated based on the position command from the host apparatus to calculate the new torque command value, the new velocity The drive unit position is controlled according to the command value or the new torque command value .

Further, in the position control device for the numerical control machine according to the present invention, a block for calculating the drive unit thrust Fr from the position command value from the host device, and φ (Fr) for deriving the drive unit inclination F from the drive unit thrust Fr. ) Position shift compensation value calculation for calculating a position shift compensation value between the conversion block and the point of application of force of the drive unit from the inclination angle φ and the position control target point of the drive unit that is the target of the position command from the host device A block, and adding a position deviation compensation value to at least the position command value of the position control device to calculate a new command value.

Furthermore, in the position control device of the numerical control machine according to the present invention, the new command value is calculated based on the position command value from the host device by calculating the position error speed compensation value from the time differential value of the position error compensation value. It is calculated by adding a position shift speed compensation value to the speed command value that has been set.

Furthermore, in the position control device for the numerical control machine according to the present invention, a displacement detector for detecting a displacement amount due to vibration of the machine base is attached to the machine base, and the machine vibration monitor is replaced with the above calculation method. The machine vibration compensation command value is calculated from the detection value of the displacement detector.

  In the position control device according to the present invention, in a servo motor drive shaft of a numerical control machine including a ball screw drive system, even if low-frequency vibration is generated due to rigidity of a machine base portion that supports and fixes a structure including the drive system. The present invention relates to a position control device that can realize highly accurate position control of a drive unit. The purpose is to estimate or detect the machine base displacement, eliminate the vibration effect included in the position detection value, determine the exact drive unit position in space, and make this drive unit position match the position command value The problem is solved by adding compensation control to the position control device.

  According to the position control device of the present invention, low-frequency vibration is generated in the servo motor drive shaft of a numerical control machine including a ball screw drive system due to the rigidity of a machine base portion that supports and fixes a structure including the drive system. However, it is possible to compensate for this and achieve highly accurate position control of the spatial position of the drive unit. Furthermore, even when the point of application of thrust to the drive unit does not coincide with the center of mass of the drive unit and the drive unit is inclined, an arbitrary point in the drive unit to be controlled according to the position command value and the point of action of the force It is possible to realize position control that compensates for the positional deviation between the two.

  Hereinafter, embodiments of the present invention (hereinafter referred to as embodiments) will be described with reference to the drawings.

FIG. 4 is a model showing a schematic mechanism of the ball screw drive system for one axis in consideration of the rigidity of the machine base (column) in the embodiment. Considering the column as a beam, the column displacement amount of the cross rail portion is set to y ₁ , but the other portions are the same as the model of FIG. Here, the model of FIG. 4 is regarded as a target plant, and its equation of motion is derived. In this case, the motor rotation angle θm, the spindle head position y, and the column displacement y ₁ may be taken as a generalized coordinate system, and the following three equations of motion are obtained.
[Expression 3] τm = Im · am + (P / 2π) Ks [(P / 2π) θm− (y + y ₁ )]
[Equation 4] 0 = Mh · ay−Ks [(P / 2π) θm− (y + y ₁ )]
[Equation 5] 0 = Mr · ay ₁ −Ks [(P / 2π) θm− (y + y ₁ )] + Kb · y ₁ + Db · vy ₁
Here, the column displacement velocity vy _1, column displacement acceleration ay _1, a cross rail (spindle Atama含Manai) mass Mr, y-direction stiffness Kb of the column, a viscous damping coefficient Db column.

FIG. 3 is a block diagram showing equations of motion of Formulas 3 to 5 for the target plant in consideration of the machine base rigidity in the embodiment. The machine base vibration block in the figure is a block having the spindle head thrust Fr as an input and the cross rail displacement y ₁ as an output.
[Expression 6] Fr = Mr · ay ₁ + Db · vy ₁ + Kb · y ₁
Can be shown. Further, if the column displacement y ₁ is added to the spindle head position y, the linear scale position detection value y + y ₁ in this target plant is obtained. The other parts are the same as those in FIG.

Here, since the spindle head position to be controlled according to the position command value θ ^* is y, the spindle head thrust Fr to be controlled is determined. However, since the position detection value includes the column displacement y _{1 as} described above, an accurate head position y in the space, which is estimated or detected and removed from the position detection value, is derived. Further, a motor rotation angle θm for giving a driving system deflection amount for generating the spindle head thrust Fr to be controlled is derived in consideration of the column displacement y _1, and a speed feedforward amount for speeding up the motor response. Vff, torque feedforward amount τff and control position command value θc are determined.

FIG. 1 is an example of a block diagram of a position control device according to an embodiment of the present invention. In this block diagram, the same parts as those in FIG. 6 (conventional example) are given the same names and numbers, and the description thereof is omitted. The target plant 10 in the figure corresponds to the block diagram in FIG. Here, in order to control the spindle head position y in accordance with the position command value θ ^* , the spindle head thrust Fr is calculated from FIG.
[Formula 7] Fr = Mh · (P / 2π) (d ² θ ^* / dt ² )
The relationship between Fr and the column displacement y ₁ can be obtained from equation (6). Here, the machine vibration compensation command value θsw is
[Equation 8] θsw = (2π / P) · y ₁
It is determined. The machine vibration monitor performs the above series of operations.

  θsw is added by the adder 1 to the output of the adder 51 in the conventional position control apparatus of FIG. 6 to become the control position command value θc in the embodiment of the present invention. Next, θsw is time-differentiated to become a machine vibration compensation speed command value Vsw, which is added by the adder 2 to the output of the adder 53 in the conventional position control device of FIG. 6 to become the speed feedforward amount Vff. Further, the machine vibration compensation torque command value τsw is calculated by multiplying Asw obtained by time differentiation of Vsw by the motor inertia moment Im. τsw is added to τff in the conventional position control device of FIG. 6 by the adder 3 to constitute the torque feedforward amount τff in the embodiment of the present invention. The above feed-forward configuration is for speeding up the response operation for the servo motor base vibration compensation command value θsw.

In the position control apparatus according to the embodiment of the present invention having the above-described configuration, from Equation 2, it is possible to constantly obtain θf = θi + θdf and θc = θf by feedback control.
[Equation 9] θc = θ ^* + θdf + θsw = θi + θdf
Become
[Expression 10] θ ^* + θsw = θi = (2π / P) (y + y1)
It becomes. Here, from the above-described operation of the machine base vibration monitor, since the relationship of Formula 8 is established, θ ^* = (2π / P) y can be achieved. That is, the spindle head position y can be controlled in accordance with the position command value θ ^* .

The description so far has been made on the assumption that a linear scale for detecting the spindle head position y is installed on the cross rail. However, when the linear scale is not installed, the following control is performed. . First, by setting the transfer characteristic G (S) in FIG. 1 to G (S) ≡0, θf = θm. When θm is in the relationship of FIG. 4, from FIG.
[Formula 11] θm = (2π / P) [(Fr / Ks) + (y + y ₁ )]
However, since Fr and θsw are controlled by equations 7 and 8,
[Equation 12] θm = (Mh / Ks) (d ² θ ^* / dt ² ) + (2π / P) y + θsw
It becomes. Since feedback control can make θc = θf = θm,
[Expression 13] θc = θ ^* + θdf + θsw = (Mh / Ks) (d ² θ ^* / dt ² ) + (2π / P) y + θsw
Here, since the relationship of Formula 1 is established, θ ^* = (2π / P) y can be achieved. That is, even when a linear scale is not installed, position control that eliminates the influence of machine vibration can be achieved.

Next, consider a case where the spindle head generates an inclination in the y direction. FIG. 5 is a diagram in which only the relative relationship between the spindle head 103 and the ball screw 101 in FIG. 4 is extracted. In the figure, a point O at which thrust Fr is applied from the ball screw nut to the spindle head, a mass center G of the spindle head, a distance 1 from the lower end point Q of the spindle head to the ball screw, and a distance H from the ball screw to the upper end point of the spindle head. If the point O and the point G do not coincide with each other, the spindle head tilts in the y-axis direction with an angle φ as shown in the figure due to the moment by the thrust Fr. Here, in a machine tool or the like, it is necessary to control the spatial position in the y direction of the lower end point Q, which is the end of the cutting tool, in accordance with the position command value θ ^*. Is displaced by 1φ.

FIG. 2 shows an example of a position control device according to the present invention that can cope with this problem and the above-described problem caused by machine vibration. Note that in this block diagram, the same parts as those in FIG. 1 (Embodiment 1) are assigned the same names and numbers, and the description thereof is omitted. The block Cc calculates the spindle head thrust Fr from the position command value θ ^* according to the equation (7). Fr is converted into an inclination angle φ of the spindle head by a φ (Fr) conversion block (hereinafter referred to as Fr → φ conversion block). This conversion is performed using, for example, a distance between the point O and the point G: (l−H) / 2 and a constant k having a positive correlation.
[Equation 14] φ = k · Fr
And so on. The multiplier 6 multiplies the inclination angle φ and (2π / P) l to thereby provide a positional deviation compensation value θsl that is a motor shaft conversion value of the positional deviation lφ between the point O and the point Q.
[Formula 15] θsl = (2π / P) l · φ
Is output.

  The position deviation compensation value θsl is added to the machine base vibration compensation command value θsw by the adder 4 and added to the control position command value θc. Next, θsl is differentiated with respect to time to become a displacement speed compensation value Vsl, which is added to the machine vibration compensation speed command value Vsw by the adder 5 and added to the speed feedforward amount Vff. The above feed-forward configuration is for speeding up the response operation corresponding to the position deviation compensation value θsl of the servo motor.

In the position control apparatus according to the embodiment of the present invention having the above-described configuration, from Equation 2, it is possible to constantly obtain θf = θi + θdf and θc = θf by feedback control.
[Equation 16] θc = θ ^* + θdf + θsw + θsl = θi + θdf = (2π / P) (y + y1) + θdf
Since the relationship of Equation 8 is established,
[Equation 17] θ ^* + θsl = (2π / P) y
It becomes. Furthermore, since the relationship of Formula 15 is established,
[Equation 18] θ ^* = (2π / P) (y−1 · φ)
Get. In other words, the spindle head lower end point position (y · φ) can be controlled in accordance with the position command value θ ^* .

When no linear scale is installed, θf = θm is obtained by setting the transfer characteristic G (S) to G (S) ≡0 as in the first embodiment. When θm is in the relationship of FIG. 4, it can be expressed by Equation 11 or Equation 12 as in Example 1, regardless of the inclination of the spindle head shown in FIG. 5. Here, θc = θf = θm can be obtained by feedback control.
[Equation 19] θc = θ ^* + θdf + θsw + θsl = (Mh / Ks) (d ² θ ^* / dt ² ) + (2π / P) y + θsw
It becomes. Furthermore, since the relationship of Formula 1 is established with respect to this formula, this formula can be transformed into Formula 17, and Formula 18 is obtained similarly to the case where a linear scale is installed. In other words, the spindle head lower end point position (y · φ) can be controlled in accordance with the position command value θ ^* .

In the first and second embodiments of the present invention described above, the column displacement y ₁ is obtained from the machine vibration monitor consisting of the equations (6), (7) and (8), but the displacement detector can directly detect the column displacement y ₁ . And using this output as y ₁ , the machine base vibration compensation command value θsw can be determined using only Equation 8, and the structure of the machine base vibration monitor can be simplified.

It is a block diagram which shows an example of the position control apparatus which concerns on embodiment of this invention. It is a block diagram which shows another example of the position control apparatus which concerns on embodiment. It is a block diagram of the object plant in consideration of machine stand part rigidity in an embodiment. It is a schematic mechanism model of a ball screw drive system in consideration of machine stand rigidity in an embodiment. It is a general | schematic mechanism model explaining the inclination of the spindle head in embodiment. It is a block diagram which shows an example of the conventional position control apparatus. It is a block diagram of the object plant which does not consider the conventional machine stand part rigidity. This is a schematic mechanism model of a ball screw drive system that does not take into account the conventional machine base rigidity.

Explanation of symbols

  1, 2, 3, 4, 5 adder, 6 multiplier, 10 target plant considering machine base rigidity, 50 target plant not considering machine base rigidity, 51, 53, 54, 56, 58 adder, 52, 55, 57, 59 Subtractor, 100 servo motor, 101 ball screw, 102 cross rail, 103 spindle head, 104a, 104b column.

Claims (5)

The drive unit of the mechanism composed of the ball screw drive system of the numerical control machine is driven by a servo motor, the drive unit position is indirectly detected by a linear scale or a motor rotation angle detector, and driven according to the position command value from the host device. A position control device for controlling the position of a part,
Based on the position command value from the host device, based on the mass of the structure including the drive system and the rigidity of the machine base that supports the structure, the machine base vibration to compensate for the displacement caused by the vibration generated in the machine base A machine vibration monitor that determines the compensation command value;
A block for calculating and determining a machine vibration compensation speed command value and a machine vibration compensation torque command value from the time differential value of the machine vibration compensation command value;
An adder that adds a machine vibration compensation command value to at least the position command value of the position control device and calculates a new position command value;
With
A position control device for a numerically controlled machine, wherein the position of a drive unit is controlled in accordance with the new position command value. The position control device for a numerically controlled machine according to claim 1,
An adder that calculates the new speed command value by adding the machine vibration compensation speed command value to the speed command value calculated based on the position command value from the host device, or calculated based on the position command from the host device. Comprising at least one adder for adding a machine vibration compensation torque command value to the torque command value and calculating a new torque command value;
A position control device for a numerically controlled machine, wherein the position of a drive unit is controlled according to the new speed command value or the new torque command value. In the numerical control machine position control device according to claim 1 or 2,
A block for calculating the drive unit thrust Fr from the position command value from the host device;
A φ (Fr) conversion block for deriving the tilt angle φ of the drive unit from the drive unit thrust Fr;
A displacement compensation value calculation block that calculates a displacement compensation value between the point of action of the force of the drive unit from the inclination angle φ and the position control target point of the drive unit that is the target of the position command from the host device;
With
A position control device for a numerical control machine, wherein a new command value is calculated by adding a position deviation compensation value to at least the position command value of the position control device. In the position control device of the numerical control machine according to claim 3,
Furthermore, the new command value is
A position shift speed compensation value is calculated from a time differential value of the position shift compensation value, and is calculated by adding the position shift speed compensation value to the speed command value calculated based on the position command value from the host device. Position control device for numerical control machine. The position control device for a numerically controlled machine according to any one of claims 1 to 4,
A displacement detector that detects the amount of displacement due to vibration of the machine base is attached to the machine base.
A position control device for a numerically controlled machine, wherein the machine vibration monitor calculates a machine vibration compensation command value from a detection value of a displacement detector instead of the calculation method of claim 1 .

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