CN104076740B - Numerical-control device - Google Patents

Abstract

A numerically controlled device that compensates with high precision for misalignment that occurs when the direction of movement of an axis is reversed. The numerical control device includes a compensator. The compensator calculates the amount of compensation for misalignment. Dislocation is caused by the elastic deformation of the table mechanism after the moving direction of the table is reversed. The compensator judges whether the workbench is in the process of moving or in the process of stopping (S1), and when it is judged that it is in the process of moving (S1: No), calculates the compensation amount using the formula (1) (S2). The expression (1) is an expression for calculating the compensation amount by adding a value proportional to the movement amount of the table (3) to the previous compensation amount. When it is judged that the stop is in progress (S1: YES), the compensation amount is calculated using (2) formula (S5). The expression (2) is an expression for calculating the compensation amount based on the torque command. Therefore, the numerical control device can compensate for misalignment with high precision according to whether the table is in the process of moving, reversing or stopping.

Description

CNC device

technical field

The invention relates to a numerical control device.

Background technique

Machine tools experience hysteresis due to elastic deformation of the mechanism when the direction of movement of the drive shaft is reversed. Hysteresis is called misalignment, which is a cause of reduction in machining accuracy. In order to compensate for the misalignment, the numerical control device predicts an amount corresponding to the misalignment when the moving direction is reversed, and adds it to the command position. In Japanese Patent Laid-Open No. 1996-152910, the misalignment is compensated using a function whose input is the distance from the reversed position and whose output is the compensation amount. In Japanese Patent Laid-Open No. 154007 of 1998, similarly, the misalignment is compensated using a function of the distance from the reversal position, but the rise of the misalignment is fitted using an exp function (exponential function). The method described in the above-mentioned gazette can well compensate for misalignment during inversion and movement, but it becomes overcompensated when stopped, and there is a technical problem of lowering machining accuracy.

Contents of the invention

The object of the present invention is to provide a numerical control device capable of accurately compensating for misalignment according to whether it is moving, reversing, or stopped.

The numerical control device of technical solution 1 includes: a feed mechanism, the feed mechanism has a ball screw shaft and a ball nut sleeved on the ball screw shaft, and moves a moving body fixed to the ball nut; a motor, the motor drive the ball screw shaft to rotate; a position detection mechanism that detects the position of the moving body moved by the motor based on the rotation amount of the motor; a speed generation unit that generates a speed command to The position of the moving body detected by the position detection mechanism is consistent with the position command generated by the control unit; the speed detection mechanism detects the speed of the motor; the torque generation unit generates the torque. Torque command, so that the speed detected by the above-mentioned speed detection mechanism is consistent with the speed command generated by the above-mentioned speed generation part; Computing the amount of compensation for the generated misalignment; and an adding unit that adds the compensation amount calculated by the computing unit to the position command to correct the position command, wherein the computing unit includes : judging part, the judging part judges whether the above-mentioned mobile body is in the process of moving or in the process of stopping; the first computing part, when the above-mentioned judging part judges that the above-mentioned mobile body is in the process of moving, the first computing part makes the The value of the movement amount of the mobile body is added to the previous compensation amount to calculate the compensation amount; The aforementioned torque command is used to calculate the aforementioned compensation amount. During the movement of the mobile object, the first calculation unit calculates the compensation amount using a function of the movement amount. During the stop of the moving body, the second calculation unit calculates the compensation amount using a function of the torque command. The computing unit distinguishes the usage function according to whether the moving body is moving or is stopping. Therefore, the numerical control device can perform stable compensation during the movement and reverse rotation of the mobile body, and can prevent overcompensation when it stops. Therefore, the numerical control device can compensate for misalignment with high precision according to whether it is in the process of moving, reversing or stopping.

In addition to the configuration of the invention described in claim 1, the numerical control device of claim 2 is characterized in that a torque value when the moving body is moved in a certain direction at a predetermined speed is used as a reference torque, and the second calculation unit The compensation amount is calculated so as to be proportional to the ratio of the reference torque to the torque command. Therefore, the second computing unit can compensate for the misalignment generated during the stop.

In addition to the structure of the invention described in claim 2, the numerical control device of claim 3 is characterized in that the maximum compensation amount when the moving body is moved in the predetermined direction at the predetermined speed is used as the maximum compensation amount, and the second The calculation unit calculates the compensation amount by multiplying the maximum compensation amount by the ratio. Therefore, the second computing unit can compensate for the misalignment generated during the stop.

In addition to the structure of the invention described in any one of claims 1 to 3, the numerical control device of claim 4 is characterized in that, when the moving body starts to move from the stop process, the above-mentioned first calculation unit will The above-mentioned compensation amount is used as the above-mentioned previous compensation amount. Therefore, the numerical control device can satisfactorily compensate for a change in misalignment at the time of shifting from a stop to a movement.

Description of drawings

FIG. 1 is a perspective view of the table mechanism 20 .

FIG. 2 is a diagram showing an electrical configuration of the numerical control device 1 .

Fig. 3 is a diagram showing compensation amounts during movement.

Fig. 4 is a diagram showing compensation amounts during a stop.

Fig. 5 is a diagram showing a compensation start position when shifting from a stop to a movement.

Fig. 6 is a diagram showing compensation amounts when shifting from moving to stopping.

FIG. 7 is a flowchart of compensation processing.

FIG. 8 is a block diagram of the table mechanism 40 .

FIG. 9 is a diagram showing the result of calculating the compensation amount by the first method.

FIG. 10 is a diagram showing the result of calculating the compensation amount by the second method.

FIG. 11 is a diagram showing the result of calculating the compensation amount by the third method.

detailed description

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following description, up and down, left and right, and front and rear indicated by arrows in the drawing are used. The left-right direction, front-rear direction, and up-down direction of the table mechanism 20 are the X-axis direction, the Y-axis direction, and the Z-axis direction, respectively. The table mechanism 20 shown in FIG. 1 is provided in a machine tool (not shown). The table mechanism 20 supports the table 3 so as to be movable in the X-axis direction and the Y-axis direction. The spindle (not shown) of the machine tool can be raised and lowered in the Z-axis direction. The numerical control device 1 controls the movement of the spindle and the table mechanism 20 according to a path specified by an NC (numerical control) program, and performs cutting on a workpiece (not shown) fixed on the table 3 by a jig.

The configuration of the table mechanism 20 will be described with reference to FIG. 1 . The workbench mechanism 20 includes a base 2 , an intermediate workbench 50 , and a workbench 3 . The base 2 supports the intermediate table 50 on its upper surface so as to be movable in the Y-axis direction. The intermediate table 50 supports the table 3 so as to be movable in the X-axis direction on its upper surface. Therefore, the table 3 can move in the X-axis direction and the Y-axis direction with the base 2 as a reference. The base 2 has a pair of linear guides 6A, a ball screw shaft 4A, a motor 2A, and the like on its upper surface. The linear guide 6A extends in the Y-axis direction. The linear guide 6A guides the intermediate table 50 in the Y-axis direction. The ball screw shaft 4A is provided between the pair of linear guides 6A in parallel to the Y-axis direction. Ball nuts (not shown) are fixed to the lower surface of the intermediate table 50 . The ball screw shaft 4A is inserted into the ball nut. The motor 2A rotates the ball screw shaft 4A. When the ball screw shaft 4A is rotated, the intermediate table 50 moves in the Y-axis direction via the ball nut. The intermediate table 50 has a long plate shape in the X-axis direction, and a pair of linear guides 6B, a ball screw shaft 4B, a motor 2B, and the like are provided on the upper surface thereof. The linear guide 6B extends in the X-axis direction. The linear guide 6B guides the table 3 in the X-axis direction. The ball screw shaft 4B is provided between the pair of linear guides 6B in parallel to the X-axis direction. A ball nut 5 is fixed to the lower surface of the table 3 (see FIG. 8 ). The ball screw shaft 4B is inserted into the ball nut 5 . The motor 2B rotates the ball screw shaft 4B. When the ball screw shaft 4B is rotated, the table 3 moves in the X-axis direction via the ball nut 5 . Therefore, the table mechanism 20 can move the table 3 in the X-axis direction and the Y-axis direction.

Numerical control device 1 is connected to motors 2A and 2B, respectively. The numerical control device 1 drives the motors 2A and 2B to move the table 3 in the X-axis direction and the Y-axis direction. The ball screw shafts 4A, 4B and the ball nuts and ball nuts 5 mounted on the ball screw shafts 4A convert the rotational motion of the motors 2A, 2B into motions of the table 3 in the two-axis directions (X-axis direction and Y-axis direction). straight into motion. The numerical control device 1 controls the motors 2A, 2B to control the position, speed and acceleration of the table 3 . Rotary encoders 60 (hereinafter referred to as encoders 60 ) are attached to the motors 2A, 2B, respectively. Each encoder 60 detects each position (rotation angle) of the motors 2A, 2B. The numerical control device 1 calculates the position of the table 3 based on the respective positions of the motors 2A, 2B and the pitch of the ball screw shafts 4A, 4B (interval between screw threads).

Referring to FIG. 2 , the configuration of the numerical control device 1 will be described. The numerical control device 1 includes a host control unit 10 , a position controller 11 , a speed controller 12 , a compensator 13 , a current control amplifier 15 , a differentiator 16 , an adder 17 and the like. The host control unit 10 outputs a position command signal to the position controller 11 based on the NC program. Each encoder 60 outputs a position detection signal of the motors 2A, 2B to the position controller 11 . The position controller 11 generates a speed command signal so that the position command signal coincides with the position detection signal, and outputs it to the speed controller 12 . The differentiator 16 converts the position detection signal into a speed detection signal, and outputs it to the speed controller 12 . The speed controller 12 generates a torque command signal so that the speed command signal matches the speed detection signal, and outputs the torque command signal to the current control amplifier 15 and the compensator 13, respectively.

The compensator 13 calculates the misalignment compensation amount (hereinafter referred to as compensation amount) based on the position command signal from the host control unit 10 or the torque command signal from the speed controller 12 according to the state of the table 3, and generates a misalignment The compensation signal is then output to adder 17. The adder 17 adds the misalignment compensation signal to the position command signal output from the host control unit 10 to the position controller 11 . Therefore, the position controller 11 generates a torque command signal so that the position command signal compensated for the misalignment coincides with the position detection signal. The speed controller 12 generates a torque command signal that compensates for the misalignment. The current control amplifier 15 controls the current of the motors 2A, 2B so as to generate a torque as faithful as possible to the torque command signal.

Referring to FIGS. 3 to 6 , a method for compensating for a misalignment performed by the compensator 13 will be described. The characteristics of the misalignment differ depending on the state of the table 3 . The state of the table 3 includes at least a moving state and a stopped state. The machine tool repeatedly moves and stops the table 3 alternately in order to process the workpiece. Therefore, the numerical control device 1 needs to change the calculation method of the compensation amount for the moving state and the stopped state, respectively. In addition, the numerical control device 1 needs to set the compensation amount when shifting from the moving state to the stopped state, and when shifting from the stopped state to the moving state. Therefore, in this embodiment, the compensation amount is calculated as follows according to the state of the table 3 . The compensator 13 calculates the compensation amount of the movement state using the following formula (1). Lc _n is the output of the compensator, Lc _n-1 is the output of the previous compensator, Pc is the maximum compensation amount, Ap is the slope coefficient, and Δx is the increment of the position command. Pls is pulse.

(1) formula

Fig. 3 is a diagram showing the compensation amount of the movement state calculated by the expression (1). The compensation amount increases or decreases in proportion to the movement amount of the table 3 . Among them, -Pc/2≤Lc _n ≤Pc/2, outside this range, the compensation amount will not increase but remain constant. The slope which increases in proportion to the movement amount and the maximum compensation amount are parameters determined by actual measurement. When the moving direction is reversed after the compensation amount is constant, the compensation amount will decrease immediately. Therefore, the amount of compensation traces the trajectory of the hysteresis characteristic. The trajectory of the hysteresis characteristic is a trajectory that does not return to the original position.

The compensator 13 calculates the compensation amount for the stopped state using the following equation (2). Lc is the output of the compensator, Pc is the maximum compensation amount, Tl is the reference torque, and Tc is the torque command. Wherein, -Pc/2≤Lc≤Pc/2.

(2) formula

Fig. 4 is a diagram showing a compensation amount in a stopped state calculated by the expression (2). The compensation amount increases in proportion to the value of the torque command. When the compensation amount reaches a certain value, the compensation amount will no longer increase. The slope of the compensation amount proportional to the torque command is obtained by actual measurement. The maximum compensation amount Pc is the same as the maximum compensation amount during the movement. The reference torque is a torque value when the table 3 is moved in a certain direction at a predetermined speed. When the torque command is reversed halfway, the compensation amount returns to the original position differently from the moving state.

As shown in FIG. 5 , when shifting from a stopped state to a moving state, the compensator 13 performs compensation from a position corresponding to the compensation amount at the time of stopping.

As shown in FIG. 6 , when shifting from the moving state to the stopped state, the compensator 13 determines the compensation amount based on the torque command at the time of the stop.

Compensation processing performed by the compensator 13 will be described with reference to FIG. 7 . When the machine tool starts to operate, the compensator 13 executes this process based on the position command signal from the host control unit 10 or the torque command signal from the speed controller 12 . The compensator 13 judges whether Δx is 0 (S1). When Δx is not 0 (S1: No), the table 3 is in a moving state. Therefore, the compensator 13 calculates the compensation amount using the formula (1) (S2). The previous stop state was a transition from the stop state to the moving state. Therefore, as shown in FIG. 5 , the compensator 13 performs compensation from a position corresponding to the compensation amount at the time of stop. The compensator 13 generates a misalignment compensation signal based on the calculated compensation amount, and outputs it to the adder 17 (S3).

When Δx=0 (S1: Yes), the table 3 is in a stopped state. Therefore, the compensator 13 calculates the compensation amount using the formula (2) (S5). As shown in FIG. 6 , when shifting from the moving state to the stopped state, the compensator 13 calculates the compensation amount based on the torque command at the time of the stop. The compensator 13 generates a misalignment compensation signal based on the calculated compensation amount, and outputs it to the adder 17 (S3). The compensator 13 judges whether or not the operation of the machine tool has ended (S4). When the action continues (S4: NO), the compensator 13 returns to S1 and repeats the process. When the action has ended (S4: YES), the compensator 13 ends the processing.

Various tests performed to confirm the effects of the present embodiment will be described below. The table mechanism 40 used in the test will be described with reference to FIG. 8 . The table mechanism 40 is comprised from the part which guides the table 3 in the X-axis direction in the table mechanism 20 shown in FIG. Table mechanism 40 includes table 3 , ball nut 5 , ball screw shaft 4B, X-axis feed guide (not shown), motor 2B, encoder 60 , and linear scale 30 . The linear scale 30 is a detector that acquires position information from a scale (scale), and detects the position of the table 3 . The feedback position (hereinafter referred to as FB position) output by the encoder 60 is the position of the table 3 indicated by the position detection signal of the motor 2B. Misalignment can be considered as the difference between the FB position and the linear scale position at the same moment.

With regard to a series of operations in which the table 3 alternately repeats moving and stopping, experiments were performed in which compensation amounts were calculated and compared using three methods. A series of actions are as follows. Move in the positive direction (500mm/min) for a specified time, stop for a specified time, move in a negative direction (-500mm/min) for a specified time, and then stop for a specified time. The positive direction and the negative direction are opposite to each other in the X-axis direction.

The three approaches are described below. The first method is a method of compensating only by the formula (1), the second method is a method of compensating only by the formula (2), and the third method is the method of the present invention. The technique of the present invention is a method of performing compensation by separately using (1) and (2) formulas when moving and when stopping. In each test, the displacement was actually measured, and the actual measurement value was compared with the compensation amount obtained by each method and evaluated.

The result obtained by calculating the compensation amount by the first method will be described with reference to FIG. 9 . As shown in FIG. 9 , the measured value of misalignment slightly fluctuates up and down during the movement of the worktable 3 , decreases steadily after the worktable 3 stops, and then maintains a certain value. The cause of the floating is likely to be a frictional force fluctuation due to accuracy deviation of the X-axis feed guide, ball screw shaft 4B, and the like. The compensation amount calculated by the first method can represent a value close to the actual measurement value during the movement. During a stop, the compensation amount does not change from the previous movement, so it cannot approach the actual measurement value. The reason is that the formula (1) used in the first method is a calculation formula applicable only to the moving state of the table 3 and is not applicable to the stationary state at all.

The result obtained by calculating the compensation amount by the second method will be described with reference to FIG. 10 . The actual measured value of misalignment is the same as that in Fig. 9 . The compensation amount calculated by the second method can show a value close to the actual measurement value during the stop. During the movement, the compensation amount calculated by the second method fluctuates more than the measured value, and deviates from the measured value. The reason is that the equation (2) used in the second method calculates the influence of the above-mentioned fluctuation of the frictional force during the movement of the table 3 to be larger than the actual measured value of the misalignment. (2) formula does not apply to the moving state at all.

The result obtained by calculating the compensation amount by the third method will be described with reference to FIG. 11 . The actual measured value of misalignment is the same as that in Fig. 9 . The compensation amount calculated by the third method can show a value close to the actual measurement value both during the movement and during the stop. Therefore, in the third method, the compensation amount corresponding to the state of the table 3 can be calculated by using the formula (1) during the movement and using the formula (2) during the stop, and using them separately.

In the above description, the table 3 corresponds to the moving body of the present invention, the table mechanism 20 corresponds to the feed mechanism of the present invention, the encoder 60 corresponds to the position detection mechanism of the present invention, and the host control unit 10 corresponds to the moving body of the present invention. In the control section, the position controller 11 corresponds to the speed generation section of the present invention, the differentiator 16 corresponds to the speed detection mechanism of the present invention, the speed controller 12 corresponds to the torque generation section of the present invention, and the compensator 13 corresponds to the torque generation section of the present invention. The calculating unit, the adder 17 corresponds to the adding unit of the present invention. The compensator 13 that executes the S1 process shown in FIG. 7 corresponds to the judging unit of the present invention, the compensator 13 that executes the S2 process corresponds to the first calculation unit of the present invention, and the compensator 13 that executes the S5 process corresponds to the first calculation unit of the present invention. Second computing department.

As described above, the numerical control device 1 of this embodiment includes the compensator 13 . The compensator 13 calculates the amount of compensation for the misalignment. The dislocation is caused by the elastic deformation of the table mechanism 20 after the moving direction of the table 3 is reversed. The compensator 13 judges whether the table 3 is in the process of moving or in the process of stopping, and when it is judged that it is in the process of moving, it calculates by adding a value proportional to the amount of movement of the table 3 to the previous compensation amount out the amount of compensation. As an example of the calculation formula, Lc _n =Lc _n-1 +(Pc/Ap)Δx. Lc _n is the output of the compensator, Lc _n-1 is the output of the previous compensator, Pc is the maximum compensation amount, Ap is the slope coefficient, and Δx is the increment of the position command. Wherein, -Pc/ _2≤Lc n≤Pc/2. The compensator 13 calculates the compensation amount based on the torque command when it is determined that the stop is in progress. As an example of the calculation formula, Lc=(Pc/2)(Tc/Tl). Lc is the output of the compensator, Pc is the maximum compensation amount, Tl is the reference torque, and Tc is the torque command. Wherein, -Pc/2≤Lc≤Pc/2. The compensator 13 uses mathematical formulas differently according to whether the workbench 3 is in the process of moving or in the process of stopping. Therefore, the compensator 13 can perform stable compensation during the movement and inversion of the table 3, and can prevent overcompensation when the table 3 stops. Therefore, the numerical control device 1 can compensate for the misalignment with high precision according to whether the table 3 is moving, reversed or stopped.

The Z-axis of this embodiment is affected by gravity during the stop process. In order to eliminate the influence of gravity on the Z-axis, an example of the calculation formula during the above stop is Lc=(Pc/2)[(Tc-To)/(Tl-To)]. Lc is the output of the compensator, Pc is the maximum compensation amount, Tl is the reference torque, Tc is the torque command, and To is the torque generated by gravity. Wherein, -Pc/2≤Lc≤Pc/2.

The present invention is not limited to the above-described embodiments, and various modifications are possible. For example, in the above-mentioned embodiment, the expressions (1) and (2) used by the compensator 13 are examples, and other mathematical expressions may be used. For example, formula (1) can use exponential function and tanh function in addition to linear approximation formula. In addition, one tanh function may be used, but two or more may be used.

In this embodiment, a machine tool that supports the table 3 so as to be movable in the X-axis direction and the Y-axis direction and supports the spindle so that it can move in the Z-axis direction relative to the table 3 has been described as an example. However, it may also be a machine tool in which the table 3 is fixed and the spindle moves relative to the table 3 in the X-axis direction and the Y-axis direction. The machine tool only needs to be able to move the tool attached to the spindle relative to the table.

Claims (4)

1. A numerical control device, comprising: a feed mechanism, the feed mechanism has a ball screw shaft and a ball nut sleeved on the ball screw shaft, and moves a moving body fixed to the ball nut; a motor, the a motor drives the ball screw shaft to rotate; a position detection mechanism that detects the position of the moving body moved by the motor based on the amount of rotation of the motor; a speed generating unit that generating a speed command so that the position of the moving body detected by the position detection means coincides with the position command generated by the control part; a speed detection means for detecting the speed of the motor; a torque generating part , the torque generation unit generates a torque command so that the speed detected by the speed detection mechanism is consistent with the speed command generated by the speed generation unit; the calculation unit reverses the moving direction of the moving body Afterwards, calculating the compensation amount of misalignment due to the elastic deformation of the feed mechanism; and an adding unit that adds the compensation amount calculated by the calculation unit to the position command to Correcting the position command is characterized in that, The computing unit includes: a judging unit that judges whether the moving body is moving or stopping; The first computing unit is configured to add a value based on the amount of movement of the moving body to the previous compensation amount when the judging unit determines that the moving body is moving to calculate the amount of said compensation; and A second calculation unit that calculates the compensation amount based on the torque command when the determination unit determines that the moving body is in the process of stopping. 2. Numerical control device as claimed in claim 1, is characterized in that, Taking the torque value when the mobile body is moved in a certain direction at a predetermined speed as the reference torque, The second calculation unit calculates the compensation amount so as to be proportional to a ratio of the reference torque to the torque command. 3. Numerical control device as claimed in claim 2, is characterized in that, taking the maximum compensation amount when the moving body is moved in the predetermined direction at the predetermined speed as the maximum compensation amount, The second calculation unit calculates the compensation amount by multiplying the maximum compensation amount by the ratio. 4. The numerical control device according to any one of claims 1 to 3, characterized in that, The first computing unit may use the compensation amount during the stop as the previous compensation amount when the moving body starts to move from the stop.