JP2014174854A - Numerical control apparatus and friction compensation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a numerical control apparatus and a friction compensation method capable of correcting a quadrant projection by highly accurately estimating friction force or friction torque generated when inverting a moving direction of a moving object.SOLUTION: The numerical control apparatus includes a friction compensator 13. The friction compensator 13 estimates friction force generated after a rotation direction of a motor is inverted and a moving direction of a table is inverted. The friction compensator 13 includes a first friction property estimation part 26, a second friction property estimation part 27, a third friction property estimation part 28, and a Stribeck property estimation part 30. The first to third friction property estimation parts 26 to 28 estimate friction torque caused by Coulomb friction. The Stribeck property estimation part 30 estimates friction torque to be changed in accordance with a feeding speed of the table. Thereby, the friction compensator 13 can estimate variation in the friction force due to a speed change of the table in addition to variation in the friction force caused by the Coulomb friction.

Description

  The present invention relates to a numerical controller and a friction compensation method.

  The numerical control device controls the motor to perform the biaxial circular interpolation motion of the moving body. The moving object cannot be reversed immediately when the direction of rotation of the motor is reversed. The reason is the effect of friction generated in the feed mechanism. When the quadrant changes during arc cutting (when the moving direction of the moving body is reversed), the actual moving track of the moving body goes outside the command track. The phenomenon in which the movement trajectory goes out is a quadrant projection, and the processing accuracy is deteriorated. The quadrant protrusion is generated with a sudden change in frictional force when the moving direction of the feed shaft is reversed. In order to obtain the relationship between the friction torque and the displacement, an experiment was performed using a test apparatus as shown in FIG. 1 under the low speed condition of a feed rate of 5 mm / min and a command radius of 0.2 mm. At low speed, viscous friction and inertia can be ignored. Therefore, the motor torque is equal to the total friction torque including all the friction generated in the mechanism.

  The relationship between the measured table displacement and the motor torque is shown by solid lines in FIGS. FIG. 12 shows the result on the X axis, and FIG. 13 shows the result on the Y axis. In any case, the friction torque exhibits a non-linear spring characteristic immediately after reversing the moving direction, and draws a hysteresis curve. Since this experimental apparatus employs an offset preload type feed mechanism (ball screw shaft and ball nut), a change in friction force appears in two stages. The torque output from the servo motor cannot follow the change in frictional force at the time of reversal, and quadrant protrusions are generated.

  For example, Patent Document 1 discloses a numerical control device and a friction compensation method for correcting a quadrant projection by estimating a friction force. The numerical controller includes a first friction estimation unit and a second friction estimation unit. The first friction estimation unit estimates the frictional force of the first mountain that increases after the moving direction is reversed. The second friction estimation unit estimates a second frictional force that increases after moving a predetermined amount after reversing the moving direction.

In order to estimate the change of the frictional force, which is a cause of the quadrant projection, with higher accuracy than the above technique, the following modeling was performed based on FIGS.
F ₁ = f _c1 (tanh (x / a ₁ ) −1) sgn (x ′)
F ₂ = f _c2 (tanh (x / a ₂ ) −1) sgn (x ′)
F ₃ = f _c3 (tanh ((x−b) / a ₃ ) −1) sgn (x ′)
However, if x <b, f = f _c1 + f _c2 , and if x ≧ b, f = f _c1 + f _c2 + f _c3

In the above equation, f _c1 , f _c2 , and f _c3 are Coulomb friction torques [Nm], x is a table displacement [m] from the reversal position, and a ₁ , a ₂ , and a ₃ are rising friction torques after reversing the moving direction. B is the distance [m] from the moving direction reversal position to the starting point at which the friction force changes to the second stage. Then, representing the change in the frictional force by combining three functions _{f 1, f 2, f 3} . Function f ₁ represents a sudden rise immediately after reversal, f ₂ represents a gentle increase, and f ₃ represents the second peak. Each parameter was identified by fitting a curve to match each measured value in FIGS. Curves of the friction model drawn based on the identified values are shown by dotted lines in FIGS. 12 and 13, it can be seen that the fluctuation of the friction force at the time of reversal, which is a factor of the quadrant projection, can be reproduced.

Using the above friction model, a friction compensator that suppresses quadrant protrusions by canceling the fluctuation of the frictional force was applied. Via the friction model, obtains the frictional force f _c of the feed mechanism, the response delay compensation of the servo system, and outputs the compensation torque by performing conversion into torque signals. The quadrant protrusion is corrected by adding this compensation torque to the torque command of the servo system.

JP 2012-108892 A

  An experiment was conducted on changes in frictional force when the compensator was mounted and circular motion was performed at two feed rates. FIG. 14 shows the results obtained at a feed rate = 0.316 m / min, and FIG. 15 shows the results obtained at a feed rate = 3.16 m / min. Although the quadrant protrusion could be suppressed to some extent at both speeds, a protrusion-like error still remained in FIG. This is presumed to be caused by the frictional force change at the time of reversal other than Coulomb friction. In other words, it was found that the quadrant projections could not be corrected sufficiently by simply canceling out the change due to Coulomb friction that appears during reversal.

  An object of the present invention is to provide a numerical control device and a friction compensation method capable of correcting a quadrant protrusion by accurately estimating a friction force or a friction torque generated when the moving direction of a moving body is reversed.

  A numerical control device according to a first aspect of the present invention includes a ball screw shaft and a feed mechanism that moves a moving body fixed to the ball nut, the ball screw shaft having a ball nut fitted on the ball screw shaft, and the ball screw shaft. A motor that rotates the motor, a position detection mechanism that detects the position of the moving body moved by the motor based on the rotation amount of the motor, and a position and a control unit of the moving body that are detected by the position detection mechanism A speed generation unit that generates a speed command so as to match a position command to be performed, a speed detection mechanism that detects the speed of the motor, a speed detected by the speed detection mechanism, and a speed command generated by the speed generation unit A torque generation unit that generates a torque command so as to match, a friction estimation unit that estimates a friction force or a friction torque generated after the rotation direction of the motor is reversed, and a friction or torque estimated by the friction estimation unit. In the numerical controller including a correction unit that corrects the torque command based on the friction torque, the friction estimation unit increases the movement direction of the moving body according to the amount of movement of the moving body after the moving direction is reversed. A first friction estimation unit for estimating a frictional force or a friction torque caused by the feed mechanism, and after the moving body moves a predetermined amount after the moving direction of the moving body is reversed, the moving body increases according to the moving amount of the moving body. A second friction estimation unit that estimates a friction force or a friction torque; and a third friction estimation unit that estimates a friction force or a friction torque depending on a moving speed of the moving body after the moving direction of the moving body is reversed. The friction force or the friction torque estimated by each of the first friction estimation unit, the second friction estimation unit, and the third friction estimation unit is added. When the moving body is reversed, a quadrant projection of frictional force is generated. In addition to the change due to Coulomb friction that appears at the time of reversal, the frictional force is influenced by friction depending on the speed of the moving body. Coulomb friction that appears at the time of reversal changes according to the amount of movement of the moving body. The first friction estimation unit and the second friction estimation unit estimate a frictional force that changes according to the moving amount of the moving body. The third friction estimation unit estimates a friction force or a friction torque depending on a moving speed of the moving body after the moving direction of the moving body is reversed. The friction estimation unit adds the friction force or friction torque estimated by the third friction estimation unit in addition to the friction force or friction torque estimated by the first friction estimation unit and the second friction estimation unit. Therefore, the numerical control device can suppress the fluctuation of the frictional force due to the speed change of the moving body. Therefore, the numerical control device can further suppress the quadrant protrusions as compared with the prior art.

  According to a second aspect of the present invention, in addition to the configuration of the first aspect of the invention, the third friction estimator is configured so that the relationship between the speed of the movable body and the frictional force or the friction torque is a Stribeck curve. The friction force or the friction torque corresponding to the speed detected by the speed detection mechanism is estimated based on the indicated Stribeck information. The relationship between the speed of the moving body and the frictional force or frictional torque can be reflected in the Stribeck curve. By using the Stribeck information which is information on the Stribeck curve, the third friction estimation unit can estimate the friction force or the friction torque according to the speed of the moving body.

  According to a third aspect of the present invention, in addition to the configuration of the invention according to the second aspect, the third friction estimation unit is configured so that the striking unit is used only when the absolute value of the speed detected by the speed detection mechanism increases. The friction force or the friction torque corresponding to the speed detected by the speed detection mechanism is estimated using Beck information. Only when the moving body moves while accelerating, the third friction estimation unit estimates the friction force or the friction torque corresponding to the speed detected by the speed detection mechanism using the Stribeck information. Therefore, the third friction estimation unit can favorably estimate the friction force or the friction torque corresponding to the speed detected by the speed detection mechanism.

  According to a fourth aspect of the present invention, there is provided a friction compensation method, comprising: a ball screw shaft; a ball nut that is externally fitted to the ball screw shaft; a feed mechanism that moves a moving body fixed to the ball nut; and the ball screw shaft. And a position detection mechanism that detects the position of the moving body moved by the motor based on the rotation amount of the motor, and is detected by the position detection mechanism. A speed generation step of generating a speed command so that a position command of the moving body and a position command generated by the control unit match, a speed detection mechanism for detecting the speed of the motor, and a speed detected by the speed detection mechanism; A torque generation step for generating a torque command so that the speed command generated in the speed generation step matches, and a friction estimation for estimating a friction force or a friction torque generated after the rotation direction of the motor is reversed. And a correction step of correcting the torque command based on the friction or friction torque estimated in the friction estimation step, the friction estimation step is performed after the moving direction of the movable body is reversed. A first friction estimation step for estimating a friction force or a friction torque caused by the feed mechanism that increases in accordance with a moving amount of the moving body; and after the moving body moves a predetermined amount after the moving direction of the moving body is reversed. A second friction estimating step for estimating a frictional force or frictional torque that increases according to the amount of movement of the moving body, and a frictional force that depends on the moving speed of the moving body after the moving direction of the moving body is reversed, or A third friction estimating step for estimating a friction torque, and adding the friction force or the friction torque estimated in each of the first friction estimating step, the second friction estimating step, and the third friction estimating step. The features. Therefore, the numerical control apparatus can obtain the effect of the first aspect by performing the method of the present invention.

The figure which shows a part of structure of the table mechanism. The figure which shows the structure of a part of numerical control apparatus 40 and the table mechanism 20. FIG. The graph which shows the relationship between feed speed and motor torque. The graph at the time of converting feed rate into logarithm about FIG. The block diagram which shows the structure of the friction compensator. The graph which compared the error with the command position at the time of performing circular motion with feed speed = 0.316m / min with and without compensation. The graph which compared the error with the instruction | command position at the time of performing circular motion with feed speed = 3.16m / min with and without compensation. The graph which shows the difference | error with the command position at the time of applying Stribeck compensation at the time of acceleration and deceleration (feed speed = 316 mm / min). The graph which shows the difference | error with the command position at the time of applying Stribeck compensation only at the time of acceleration (feed speed = 316 mm / min). The graph which shows the difference | error with the command position at the time of applying Stribeck compensation at the time of acceleration and deceleration (feed speed = 3162 mm / min). The graph which shows the difference | error with the command position at the time of applying Stribeck compensation only at the time of acceleration (feed speed = 3162 mm / min). The graph which showed the relationship between the table displacement amount of X-axis direction, and friction torque with a prior art. The graph which showed the relationship between the table displacement amount of a Y-axis direction, and friction torque with a prior art. The graph which compared the error with the command position at the time of performing circular motion with feed speed = 0.316m / min with the prior art with and without compensation. The graph which compared the error with the command position at the time of performing circular motion with feed speed = 3.16 m / min by the prior art with and without compensation.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. A numerical control device 40 shown in FIG. 1 is an embodiment of the present invention. The numerical control device 40 cuts the workpiece fixed on the table 3 by controlling the axis movement of the machine tool according to the path designated by the machining program.

  The table mechanism 20 will be described with reference to FIG. The table mechanism 20 is installed in a machine tool (not shown) and supports the table 3 so as to be movable in the X-axis direction and the Y-axis direction. The table mechanism 20 includes a base 1, an intermediate table 50, and a table 3.

  The base 1 has a rectangular parallelepiped shape. The base 1 has a pair of linear guides 6A on the upper surface. The pair of linear guides 6A guide the intermediate table 50 in the Y-axis direction. The ball screw shaft 4A and the ball nut (not shown) are disposed between the pair of linear guides 6A. The lower part of the intermediate table 50 is fixed to a ball nut. The intermediate table 50 has a pair of linear guides 6B at the top. The linear guide 6B guides the table 3 in the X-axis direction orthogonal to the Y-axis direction. The ball screw shaft 4B and the ball nut 5 (see FIG. 2) are disposed between the pair of linear guides 6B.

  As shown in FIG. 2, the table 3 includes a block 51 at the bottom. The block 51 slides on the rail of the linear guide 6B. The pair of shaft support portions 7 support both end portions of the ball screw shaft 4B. The pair of shaft support portions 7 are fixed to the upper surface of the intermediate table 50. The shaft support portion 7 has a bearing 8 inside. The intermediate table 50 includes a block (not shown) at the lower end. The block slides on the rail of the linear guide 6A. A pair of shaft support portions (not shown) supports both ends of the ball screw shaft 4A. The pair of shaft support portions is fixed to the base 1. The shaft support has a bearing (not shown) inside.

  As shown in FIG. 1, the base 1 fixes the motor 2A on the upper surface. The shaft of the motor 2A and the ball screw shaft 4A are connected by a coupling (not shown). The motor 2A has an oil seal (not shown) around the shaft portion. As shown in FIG. 2, the intermediate table 50 fixes the motor 2B on the upper surface. The shaft of the motor 2B and the ball screw shaft 4B are connected by a coupling 9. The motor 2B has an oil seal 52 around the shaft. The table 3 has fixed covers 53 at both ends. The seal member 55 is fixed to the end of the movable cover 54 opposite to the end on the table side. The seal member 55 is made of rubber. The seal member 55 prevents chips and the like from entering between the fixed cover 53 and the movable cover 54.

  As shown in FIG. 1, the numerical controller 40 is connected to the motors 2A and 2B, respectively. When the motor 2A is driven, the ball screw shaft 4A rotates and the ball nut moves in the Y-axis direction. The intermediate table 50 fixed to the ball nut is guided by the linear guide 6A and moves in the Y-axis direction. When the motor 2B is driven, the ball screw shaft 4B rotates and the ball nut 5 moves in the X-axis direction. The table 3 fixed to the ball nut 5 is guided by the linear guide 6B and moves in the X-axis direction. The ball screw shafts 4A and 4B and the respective ball nuts 5 convert the rotational motions of the motors 2A and 2B into linear motions of the table 3 in the X-axis direction and the Y-axis direction, respectively. Therefore, the table 3 can be moved in the X-axis direction and the Y-axis direction by driving the motors 2A and 2B. The numerical controller 40 controls the position, speed, and acceleration of the table 3 by controlling the motors 2A and 2B. The ball screw shafts 4A and 4B and each ball nut 5 correspond to the feed mechanism of the present invention.

  As shown in FIG. 2, the rotary encoder 60 is attached to each of the motors 2A and 2B. FIG. 2 does not show the motor 2A and the rotary encoder 60 on the motor 2A side. Each rotary encoder 60 detects the positions of the motors 2A and 2B. The numerical control device 40 calculates the position of the table 3 based on the positions of the motors 2A and 2B and the pitch of the ball screw shafts 4A and 4B (interval between screw threads).

  The configuration of the numerical control device 40 will be described with reference to FIG. The numerical control device 40 includes a host controller 10, a position controller 11, a speed controller 12, a friction compensator 13, an adder 14, a current control amplifier 15, and a differentiator 16. The host controller 10 outputs a position command signal to the position controller 11. Each rotary encoder 60 outputs the position detection signals of the motors 2 </ b> A and 2 </ b> B to the position controller 11. The position controller 11 generates a speed command signal so as to match the position command signal and the position detection signal, and applies the speed command signal to the speed controller 12. The differentiator 16 converts the position detection signal into a speed detection signal and applies it to the speed controller 12.

  The speed controller 12 generates a torque command signal so as to match the speed command signal and the speed detection signal, and applies the torque command signal to the adder 14. The friction compensator 13 estimates the frictional force generated after the rotation directions of the motors 2A and 2B are reversed based on the position command signal from the host controller, generates a friction compensation signal, and applies it to the adder 14. The friction compensation signal is a signal for compensating for a frictional force generated when the rotation directions of the motors 2A and 2B are reversed. The adder 14 adds the torque command signal from the speed controller 12 and the friction compensation signal from the friction compensator 13. The adder 14 adds the friction-compensated torque command signal to the current control amplifier 15. The current control amplifier 15 functions as a torque controller. The current control amplifier 15 controls the currents of the motors 2A and 2B so as to generate torque that is as faithful as possible to the friction-compensated torque command signal.

  The position controller 11, the speed controller 12, the adder 14, the current control amplifier 15, and the differentiator 16 have a known configuration. Therefore, the friction compensator 13 directly related to the present invention will be described focusing on the principle and method of friction compensation.

  First, the cause of the friction force generated in the table mechanism 20 will be described. The table mechanism 20 has at least a frictional force caused by each of the first friction source and the second friction source. As the frictional force caused by the first friction source, for example, preload of the block 51 of the linear guides 6A and 6B, preload of the ball nut 5 of the ball screw shafts 4A and 4B, preload of the bearing 8 and the like can be considered. The rigidity of the table mechanism 20 increases as the preload increases, and the frictional force increases. The frictional force caused by the second friction source is, for example, the sliding resistance of the seals of the oil seal 52 and the movable cover 54. The friction force increases as the sealing performance increases.

  As described above, the frictional force changes abruptly when the moving direction of the table 3 is reversed. When the moving direction of the table 3 is reversed, the rotating direction of the motors 2A and 2B is reversed and the rotating direction of the ball screw shafts 4A and 4B is reversed. For example, the numerical controller 40 may perform arc cutting by performing the above-described circular interpolation motion using two orthogonal axes (X axis and Y axis). At this time, since the table mechanism 20 employs an offset preload type feeding mechanism, changes in the frictional force appear in two stages as shown in FIGS. This change in frictional force is due to Coulomb friction. The torque output from the motors 2A and 2B cannot follow the change in the frictional force at the time of reversal, and quadrant protrusions are generated.

Next, modeling of frictional force resulting from Coulomb friction will be described. In the present embodiment, the change in the frictional force caused by Coulomb friction is modeled as the following equation based on the graphs of FIGS.
F ₁ = f _c1 (tanh (x / a ₁ ) −1) sgn (x ′) (1)
F ₂ = f _c2 (tanh (x / a ₂ ) −1) sgn (x ′) (2)
F ₃ = f _c3 (tanh ((x−b) / a ₃ ) −1) sgn (x ′) (3)
However, if x <b, f = f _c1 + f _c2 , and if x ≧ b, f = f _c1 + f _c2 + f _c3

In the above equation, f _c1 , f _c2 , and f _c3 are Coulomb friction torques [Nm], x is a table displacement [m] from the reversal position, and a ₁ , a ₂ , and a ₃ are rising friction torques after reversing the moving direction. B is a distance [m] from the moving direction reversal position to the starting point at which the friction force changes to the second stage. x ′ is a differential value of x. Then, by combining the three functions f ₁ , f ₂ , and f ₃ , it is possible to express a change in the friction force caused by the Coulomb friction force. f ₁ represents a sudden rise immediately after reversal, f ₂ represents a gentle increase, and f ₃ represents the second peak. Each parameter is identified by fitting a curve to match each measured value in FIG.

  Next, the speed dependency of the frictional force will be described. In this embodiment, in addition to the Coulomb friction, the factor of the change in the friction force that occurs when the moving direction is reversed is considered to be the speed dependency of the friction force. Therefore, in order to confirm the speed dependency of the frictional force, a constant speed motion experiment of the table 3 was performed, and the relationship between the feed speed and the motor torque was examined. The result is shown in FIG. The diamond mark indicates the X-axis result, and the square mark indicates the Y-axis result. According to FIG. 3, it was confirmed that the relationship is a Stribeck curve for both the X axis and the Y axis. Since quadrant protrusions occur at the reversal position in the moving direction, it can be considered that they are affected by the Stribeck curve. Further, FIG. 4 shows the result of converting the feed rate on the horizontal axis into logarithm for the result of FIG. According to FIG. 4, it was clearly confirmed that the frictional force was greatly changed due to the difference in the feeding speed in both the X axis and the Y axis. Therefore, it has been found that the frictional force fluctuation factor when the moving direction is reversed is influenced by the Stribeck curve in addition to the Coulomb friction.

Next, modeling of the Stribeck curve will be described. In order to model the curve shown in FIG. 4, the compensation amount (Nm) at the feed speed v (mm / min) is set as F _n (v). For example, the measurement results in FIG. When numbering from 1 to N, the maximum speed (mm / min) that satisfies x _n <| v | is x _n , and the motor torque (Nm) at that time is y _n (if there is no n that satisfies the left, n = 1), the Stribeck curve model is as follows. As will be described later, the following formulas (4) and (5) are preferably applied only during acceleration.

[When v ≧ 0]
Fn (v) = {(y _{n + 1} −y _n ) / (x _{n + 1} −x _n )} (v−x _n ) + y _n − {y ₁ −x ₁ (y ₂ −y ₁ ) / (x ₂ −x ₁ )} (4)
[When v <0]
Fn (v) = {(y _{n + 1} −y _n ) / (x _{n + 1} −x _n )} (v + x _n ) −y _n + {y ₁ −x ₁ (y ₂ −y ₁ ) / (x ₂ −x ₁ )} (5)

Here, the (4) (5) is the speed _{v x} n <| v ₁ | a satisfying maximum speed _{x n} and the speed _{x n + 1} as the motor torque _{y n} and _x n _{<x n + 1} at that time at that time From this motor torque yn _{+ 1} , the frictional force resulting from the Stribeck characteristic is calculated by linear interpolation. The Stribeck curve models (4) and (5) and the information on each parameter identified by the experiment are used as the Stribeck information by the Stribeck characteristic estimation unit 30 described later.

  The friction compensator 13 of the present embodiment combines the equations (4) and (5), which are model equations of the Stribeck curve, in addition to the equations (1) to (3) that are the model equations of the frictional force caused by the Coulomb friction. Thus, the change in the frictional force that occurs when the moving direction of the table 3 is reversed is estimated.

  The configuration of the friction compensator 13 that implements the above theory will be described with reference to FIG. The friction compensator 13 includes an actual position estimation unit 21, a differentiator 22, a sign inversion detection unit 23, an integrator 24, a first friction characteristic estimation unit 26, a second friction characteristic estimation unit 27, a third friction characteristic estimation unit 28, a differential Device 29, a Stribeck characteristic estimation unit 30, an adder 31, and a response delay compensation unit 32. The first, second, and third friction characteristic estimation units 26 to 28 and the Stribeck characteristic estimation unit 30 include an absolute value calculation unit and a polarity calculation unit. The absolute value calculator obtains the absolute value of the input signal. The polarity calculator obtains the polarity of the signal obtained by time differentiation of the input signal.

  The host controller 10 (see FIG. 2) inputs a position command signal to the actual position estimation unit 21. The actual position estimation unit 21 uses a model of a servo control system that performs the feed movement of the table 3. The actual position estimation unit 21 estimates the actual position of the table 3 corresponding to the position command signal and generates an actual position signal. The actual position estimation unit 21 may be configured with, for example, a first-order lag element. The differentiator 22 is connected to the actual position estimation unit 21. The differentiator 22 differentiates the actual position signal and outputs it as a speed signal. The sign inversion detection unit 23 and the integrator 24 are connected to the differentiator 22.

  The sign inversion detection unit 23 detects that the sign of the speed signal is inverted. The sign inversion detection unit 23 outputs a reset signal. The integrator 24 restores the actual position signal by integrating the speed signal. The integrator 24 resets the integral value to zero for each reset signal output from the sign inversion detection unit 23. The integrator 24 generates a displacement signal from a position where the table 3 reverses the moving direction.

The first friction characteristic estimation unit 26, the second friction characteristic estimation unit 27, and the third friction characteristic estimation unit 28 are connected to the integrator 24. The Stribeck characteristic estimation unit 30 is connected to the integrator 24 via the differentiator 29. The first friction characteristic estimation unit 26 obtains the friction torque f ₁ [N · m] using the equation (1). The friction torque f ₁ increases rapidly after the moving direction of the table 3 is reversed. The second friction characteristic estimating unit 27 obtains the friction torque f ₂ [N · m] using the equation (2). Friction torque f ₂ is gradually increased after the inversion of the table 3. The third friction characteristic estimation unit 28 obtains the friction torque f ₃ [N · m] using the equation (3). After the movement direction reversal of the friction torque f ₃ is table 3, increasing after moving a predetermined amount b _3. Stribeck characteristic estimating section 30 with reference to (4) (5), friction torque _{f 4} Request [N · m]. The friction torque f ₄ increases or decreases after the table 3 is reversed depending on the feed speed of the table 3. f ₄ inputs the _F n (v) or _F t (v) depending on the acceleration or deceleration of the speed. The adder 31 is connected to the first friction characteristic estimation unit 26, the second friction characteristic estimation unit 27, the third friction characteristic estimation unit 28, and the Stribeck characteristic estimation unit 30, respectively.

The adder 31 adds the _{f 1} and _{f 2} and _{f 3} and _{f 4.} The response delay compensation unit 32 is connected to the output terminal of the adder 31. The response delay compensation unit 32 is configured by an inverse function of the transfer function. The transfer function models the characteristics from the torque command signal to the torque actually output by the motors 2A and 2B. The torque command signal is input to the current control amplifier 15 (see FIG. 2). The response delay compensation unit 32 multiplies the estimated friction torque to generate a friction compensation signal.

  Next, the friction compensator 13 described above was mounted on the numerical controller 40 and a circular motion experiment was performed. 6 and 7 show the experimental results. FIG. 6 shows the results obtained at a feed rate = 0.316 m / min, and FIG. 7 shows the results obtained at a feed rate = 3.16 m / min. According to FIG. 6 and FIG. 7, it was confirmed that cuts and protrusions were generated before reversal in both cases. This is a phenomenon that was not seen before the introduction of the Stribeck characteristic estimation unit 30 (see FIGS. 14 and 15). Although the Stribeck characteristic estimation unit 30 outputs the same compensation value without distinguishing between acceleration and deceleration, the table mechanism 20 is caused by the fact that the speed dependency of the frictional force shows different changes between acceleration and deceleration. it is conceivable that. In the present embodiment, the time of acceleration refers to a phenomenon in which the absolute value of speed increases, and the time of deceleration refers to a phenomenon in which the absolute value of speed decreases.

  In addition, the first peak of the quadrant protrusion is a quadrant protrusion when the friction compensator 13 in consideration of the Stribeck characteristic is applied than when only the first to third friction compensators 26 to 28 are applied. It was confirmed that it was suppressed. However, the second peak of the quadrant protrusion was hardly suppressed even by the friction compensator 13 considering the Stribeck characteristic. This is considered to be due to the fact that the speed dependence of the frictional force obtained by the constant speed motion is different from the speed dependence of the frictional force during acceleration and deceleration.

Therefore, the friction compensator 13 was tested for the effect of suppressing quadrant protrusions by properly using the compensation by the Stribeck characteristic estimation unit 30 during acceleration and deceleration. In the experiment, the following cases 1 to 4 were set, and the error from the command position when the table 3 performed a circular motion was examined. The experimental conditions of cases 1 to 4 are as follows. In the following description, the compensation performed by the Stribeck characteristic estimation unit 30 using Equations (4) and (5) is referred to as Stribeck compensation.
[Case 1]
・ Stribeck compensation is applied during acceleration and deceleration.
・ Feeding speed = 316mm / min
・ Command radius = 10mm
[Case 2]
・ Stribeck compensation is applied only during acceleration.
・ Feeding speed = 316mm / min
・ Command radius = 10mm
[Case 3]
・ Stribeck compensation is applied during acceleration and deceleration.
-Feed rate = 3162 mm / min
・ Command radius = 10mm
[Case 4]
・ Stribeck compensation is applied only during acceleration.
-Feed rate = 3162 mm / min
・ Command radius = 10mm

  In cases 1 to 4, in addition to the case where the Stribeck compensation is applied, as a comparison object, the error from the command position is also obtained even when the compensation is not performed at all or the friction compensation is performed without applying the Stribeck compensation. I examined each one. The experimental results are shown in FIGS. Graph A is not compensated, Graph B is applied only to the first to third friction characteristic estimation units 26 to 28, and Graph C is further applied to the Stribeck compensation in addition to the first to third friction characteristic estimation units 26 to 28. Results are shown.

  The results of cases 1 and 2 will be described with reference to FIGS. In Case 1, Stribeck compensation was applied both during acceleration and deceleration. As shown in FIG. 8, in graph A, quadrant protrusions are generated after inversion. In the graph B, the quadrant protrusion is smaller than that in the graph A, but still remains. In the graph C, the quadrant protrusion is smaller than that in the graph B, but it was confirmed that the protrusion was generated before the inversion. On the other hand, in case 2, as shown in FIG. 9, it was confirmed that the protrusion generated in the graph C of case 1 disappeared. Furthermore, in the graph C, it was confirmed that the quadrant protrusion of the graph A was smaller than that of the graph B.

  The results of cases 3 and 4 will be described with reference to FIGS. In cases 3 and 4, the feed rate is higher than that in cases 1 and 2. In Case 3, Stribeck compensation was applied both during acceleration and deceleration. As shown in FIG. 10, in the graph A, a large quadrant protrusion is generated after inversion. In the graph B, the quadrant protrusion is smaller than that in the graph A, but still remains. In the graph C, the quadrant protrusion is further smaller than that in the graph B, but as in the case 1, it was confirmed that the protrusion was generated before the inversion. On the other hand, in case 4, as shown in FIG. 11, it was confirmed that the protrusions generated in the graph C of case 3 disappeared, as in case 2. Furthermore, in the graph C, it was confirmed that the quadrant protrusion of the graph A was smaller than that of the graph B.

From the above results, the friction compensator 13 applies the Stribeck compensation only at the time of acceleration and not at the time of deceleration, so that the friction force or the friction torque generated when the moving direction of the table 3 is reversed is estimated with high accuracy. It has been demonstrated that protrusions can be corrected effectively. Based on the above results, it is desirable that the above-described Stribeck characteristic estimation unit 30 uses the above equations (4) and (5) during acceleration and uses the following equations (6) and (7) during deceleration. t is a sampling period.
(During deceleration)
[When v ≧ 0]
F _t (v) = (F _t−1 / v _t−1 ) v _t
[When v <0]
F _t (v) = − (F _t−1 / v _t−1 ) v _t

  In the above description, the table 3 corresponds to the moving body of the present invention, the rotary encoder 60 corresponds to the position detection mechanism of the present invention, the host controller 10 corresponds to the control unit of the present invention, and the position controller 11 The differentiator 16 corresponds to the speed detection mechanism of the present invention, the speed controller 12 corresponds to the torque generation unit of the present invention, and the friction compensator 13 corresponds to the friction estimation unit of the present invention. The adder 14 corresponds to the correction unit of the present invention. The first friction characteristic estimation unit 26 and the second friction characteristic estimation unit 27 correspond to the first friction estimation unit of the present invention, and the third friction characteristic estimation unit 28 corresponds to the second friction characteristic estimation unit of the present invention. The Beck characteristic estimation unit 30 corresponds to the third friction characteristic estimation unit of the present invention.

  As described above, the numerical controller 40 of the present embodiment includes the friction compensator 13. The friction compensator 13 estimates the frictional force generated after the rotation directions of the motors 2A and 2B are reversed and the moving direction of the table 3 is reversed. The friction compensator 13 includes a first friction characteristic estimation unit 26, a second friction characteristic estimation unit 27, a third friction characteristic estimation unit 28, and a Stribeck characteristic estimation unit 30. The first to third friction characteristic estimators 26 to 28 estimate friction torque caused by Coulomb friction. The Stribeck characteristic estimation unit 30 estimates a friction torque that changes according to the feed speed of the table 3. Therefore, the numerical controller 40 can suppress the fluctuation of the frictional force due to the speed change of the table 3 in addition to the fluctuation of the frictional force caused by the Coulomb friction. Therefore, the numerical control device 40 can further suppress the quadrant protrusion as compared with the conventional case.

  Moreover, in the said embodiment, the Stribeck characteristic estimation part 30 estimates the friction torque corresponding to the speed detected with the rotary encoder 60 and the differentiator 16 based on the Stribeck information. The Stribeck information is information indicating the relationship between the feed speed of the table 3 and the friction torque with a Stribeck curve. Therefore, the numerical controller 40 can also suppress the fluctuation of the frictional force due to the speed change of the table 3.

  In the above embodiment, the Stribeck characteristic estimation unit 30 estimates the friction force or the friction torque corresponding to the feed speed using the Stribeck information only when the absolute value of the feed speed in the table 3 increases. Therefore, the numerical controller 40 can satisfactorily suppress the fluctuation of the frictional force due to the speed change of the table 3.

  The present invention is not limited to the above embodiment, and various modifications can be made. In the above embodiment, the table 3 is a moving body. The moving body may be a mechanism that supports the main shaft holding the tool. Keep the table fixed. The mechanism may be composed of a spindle head and a column. The spindle head supports the spindle rotatably. The column supports the spindle head so as to be movable up and down or back and forth.

  Although the said embodiment estimates the change of the frictional force resulting from Coulomb friction by said Formula (1)-(3), you may estimate using another type | formula. The friction compensator 13 uses three friction estimation units 26 to 27 to estimate a change in frictional force due to Coulomb friction, but may use three or more friction estimation units.

  In the above embodiment, an offset preload type feed mechanism is used. The present invention can obtain the same effect even in a feed mechanism of a double nut preload system. The double nut preload type feed mechanism has the same friction characteristics as the offset preload type. The feed mechanism of the double nut preload system comprises a single nut composed of a pair of nuts and a spacer. Further, the same effect can be obtained when the Stribeck compensator 30 is placed in a feeding mechanism using another pressurization method (oversize ball pressurization or the like).

2A, 2B Motor 3 Table 4A, 4B Ball screw shaft 4B Ball screw shaft 5 Ball nut 10 Host controller 11 Position controller 12 Speed controller 13 Friction compensator 14 Adder 26 First friction characteristic estimation unit 27 Second friction characteristic estimation Unit 28 third friction characteristic estimation unit 30 stribeck characteristic estimation unit 40 numerical control device 60 rotary encoder

Claims (4)

A feed mechanism having a ball screw shaft and a ball nut externally fitted to the ball screw shaft, for moving a moving body fixed to the ball nut, a motor for rotationally driving the ball screw shaft, and the motor moved by the motor Generates a speed command so that the position detection mechanism that detects the position of the moving body based on the amount of rotation of the motor matches the position of the moving body detected by the position detection mechanism and the position command generated by the control unit. A speed generation unit that detects the speed of the motor, and a torque generation unit that generates a torque command so that the speed detected by the speed detection mechanism matches the speed command generated by the speed generation unit A friction estimation unit that estimates a friction force or a friction torque generated after the rotation direction of the motor is reversed, and the torque command based on the friction or the friction torque estimated by the friction estimation unit. A numerical controller having a positive correcting unit,
The friction estimation unit is
A first friction estimation unit that estimates a friction force or a friction torque caused by the feed mechanism that increases in accordance with a moving amount of the moving body after the moving direction of the moving body is reversed;
A second friction estimation unit that estimates a friction force or a friction torque that increases in accordance with a movement amount of the moving body after the moving body has moved a predetermined amount after the moving direction of the moving body is reversed;
A third friction estimation unit that estimates a frictional force or a friction torque depending on a moving speed of the moving body after the moving direction of the moving body is reversed,
A numerical controller that adds the friction force or the friction torque estimated by each of the first friction estimation unit, the second friction estimation unit, and the third friction estimation unit. The third friction estimation unit is
Estimating the friction force or the friction torque corresponding to the speed detected by the speed detection mechanism based on the Stribeck information indicating the relationship between the speed of the moving body and the friction force or the friction torque by a Stribeck curve. The numerical control apparatus according to claim 1, wherein The third friction estimation unit is
The friction force or the friction torque corresponding to the speed detected by the speed detection mechanism is estimated using the Stribeck information only when the absolute value of the speed detected by the speed detection mechanism increases. The numerical control device according to claim 2. A feed mechanism having a ball screw shaft and a ball nut externally fitted to the ball screw shaft, for moving a moving body fixed to the ball nut, a motor for rotationally driving the ball screw shaft, and the motor moved by the motor A numerical control device including a position detection mechanism that detects the position of the moving body based on the rotation amount of the motor, and the position command generated by the control unit and the position of the moving body detected by the position detection mechanism The speed generation process for generating the speed command so that the speeds match, the speed detection mechanism for detecting the speed of the motor, the speed detected by the speed detection mechanism, and the speed command generated in the speed generation process match. A torque generation step for generating a torque command, a friction estimation step for estimating a friction force or a friction torque generated after the rotation direction of the motor is reversed, and a friction estimated in the friction estimation step. Or in friction compensation method and a correction step of correcting the torque command based on the friction torque,
The friction estimation step includes
A first friction estimation step for estimating a frictional force or a friction torque caused by the feed mechanism that increases in accordance with a moving amount of the moving body after the moving direction of the moving body is reversed;
A second friction estimating step for estimating a frictional force or a friction torque that increases in accordance with the moving amount of the moving body after the moving body has moved a predetermined amount after the moving direction of the moving body is reversed;
A third friction estimating step of estimating a frictional force or a friction torque depending on a moving speed of the moving body after the moving direction of the moving body is reversed,
A friction compensation method characterized by adding the friction force or the friction torque estimated in each of the first friction estimation step, the second friction estimation step, and the third friction estimation step.