JP6380119B2 - Numerical control device and control method - Google Patents

Description

  The present invention relates to a numerical control device and a control method.

  A numerical control device of a machine tool performs machining by moving a tool or a workpiece along a path designated by an NC program. At that time, the numerical control device automatically performs smooth acceleration / deceleration and performs acceleration / deceleration control for suppressing vibration of the machine tool. When acceleration / deceleration control is performed, the cycle time is extended once the block is stopped at the joint between the blocks. Therefore, the numerical controller adopts a control method that starts acceleration of a new block during the deceleration of the previous block, thereby reducing the cycle time. However, this method has a problem that an inward rotation error occurs at the corner of the joint. Therefore, Patent Document 1 predetermines an allowable error that is an allowable inner radius error of a corner, and based on the allowable error, acceleration / deceleration acceleration, and corner angle, the block at the joint of the block is decelerated and a new one is added. We propose a method to obtain the overlap time where the block acceleration overlaps. The numerical controller can start an acceleration of a new block based on the obtained overlap time, thereby making an error occurring in a corner within an allowable error.

JP-A-6-110534

  In a path in which minute blocks are continuous, there are times when the next corner is reached before the inner loop error generated in one corner is resolved. When the overlap time of the next corner is obtained by the method of Patent Document 1 and acceleration of a new block is started based on the overlap time, there is a possibility that an error occurring in the corner exceeds the allowable error.

  An object of the present invention is to provide a numerical control device and a control method capable of suppressing an error generated at a corner within an allowable error even in a path in which minute blocks are continuous.

A numerical control device according to claim 1 of the present invention is a numerical value for executing a workpiece machining by moving a tool or a workpiece along a path obtained by interpolating adjacent command points for a plurality of command points commanded by an NC program. In the control device, the acceleration / deceleration time constant of the motor that moves the tool or workpiece, the allowable error that is allowed for the path, the command speed that commands the moving speed of the tool or workpiece, and the path among the paths When the motor starts the current interpolation command based on the inter-block angle, which is the angle between the first block that is interpolated by the current interpolation command in the NC program and the second block that is interpolated by the previous interpolation command. And a calculation means for causing the motor to execute the current interpolation command based on the timing calculated by the calculation means, the calculation means comprising: An inter-block angle calculating means for calculating the inter-block angle; and a correcting means for correcting the inter-block angle calculated by the inter-block angle calculating means, wherein the correcting means is a block older than the first block. The interpolation command start point of all blocks belonging to the range from the start point of the interpolation command of the past block to the start point of the interpolation command of the first block, and the start point of the interpolation command of the first block and the straight line of multiple binding department mutually, when the smallest angle among angles formed between the first block is smaller than the inter-block angle, and characterized in that to correct the angle between the blocks in the smallest angle To do. The error generated at the corner increases as the angle between the blocks decreases at the same speed. The numerical controller obtains the start points of the interpolation commands for all blocks that belong between the start point of the interpolation command for the past block and the start point of the interpolation command for the first block. Find the smallest angle formed by blocks. When the smallest angle is smaller than the inter-block angle, the numerical controller corrects the inter-block angle to the smallest angle, and calculates the timing for starting the current interpolation command using the corrected inter-block angle. Therefore, the numerical control device can control the error generated in the corner within the allowable error without being affected by the error generated in the past block even in a path in which the minute blocks are continuous.

  According to a second aspect of the present invention, in addition to the configuration of the first aspect of the invention, the past block is a time half the acceleration / deceleration time constant from the start point of the interpolation command of the first block. It is a block including a position traced back to the front. When the next corner is reached before the error generated in one corner is eliminated, the error may remain for half of the acceleration / deceleration time constant. The numerical control apparatus sets a block including a position traced back a half time before the acceleration / deceleration time constant as a past block. Therefore, the numerical control apparatus can suppress an error occurring in a corner in the path within at least an allowable error without being affected by an error occurring in the past.

  According to a third aspect of the present invention, in addition to the configuration of the second aspect of the invention, the acceleration / deceleration time constant is plural. Since there are a plurality of acceleration / deceleration time constants, the movement speed change based on the interpolation command can be made smoother.

According to a fourth aspect of the present invention, there is provided a numerical control apparatus for moving a tool or a workpiece along a path obtained by interpolating adjacent command points with respect to a plurality of command points commanded by an NC program and performing workpiece machining. In the control method, the acceleration / deceleration time constant of the motor that moves the tool or workpiece, the allowable error that is allowed for the path, the command speed that commands the moving speed of the tool or workpiece, and the path, Based on the inter-block angle, which is the angle between the first block to be interpolated with the current interpolation command in the NC program and the second block interpolated with the previous interpolation command, causes the motor to start the current interpolation command. A calculation step for calculating a timing, and an execution step for causing the motor to execute the current interpolation command based on the timing calculated in the calculation step. Comprises an inter-block angle calculation step for calculating the inter-block angle, and a correction step for correcting the inter-block angle calculated in the inter-block angle calculation step. The start point of the interpolation command of each block belonging to the range from the start point of the interpolation command of the past block that is the block to the start point of the interpolation command of the first block and the start of the interpolation command of the first block and the straight line multiple imaging department mutually point, when the smallest angle of the first block and is an angle less than the inter-block angle, to correct the angle between the blocks in the smallest angle Features. Therefore, the numerical control device can obtain the effect of the first aspect by performing the control method.

FIG. 3 is a block diagram showing an electrical configuration of the numerical control device 30 and the machine tool 1. The figure which processed the moving speed with the two-stage FIR filter. The flowchart of the main process. The flowchart of an error fixed control process. The flowchart of the angle correction process between blocks. The figure of the path | route comprised by linear interpolation block B1 and circular interpolation block B2. The figure of the path | route comprised by linear interpolation block B1 and circular interpolation block B2. The figure of the path | route comprised by circular interpolation block B1 and linear interpolation block B2. The figure of the path | route comprised by circular interpolation block B1 and circular interpolation block B2. The figure of the path | route comprised by linear interpolation block B1 and B2. The figure which shows the change of the moving speeds 1 and 2 when moving the path | route shown in FIG. A diagram of a continuous path of corners. The figure which shows the relationship between the moving speed and moving time at the time of moving the path | route shown in FIG. The figure which shows the change ( _Td = 0) of the speed 1 and the speed 2. FIG. It shows changes in velocity 1 and speed 2 _{(T d ≧ t 1 -t 2} ). Graph showing changes in speed 1 and speed _{2 (T d = t 1 +} t 2).

  Embodiments of the present invention will be described below with reference to the drawings. In the following description, the top, bottom, left and right, front and back indicated by arrows in the figure are used. The numerical control device 30 controls the machine tool 1 to cut a workpiece (not shown) held on the upper surface of a table (not shown). The left-right direction, the front-rear direction, and the vertical direction of the machine tool 1 are an X-axis direction, a Y-axis direction, and a Z-axis direction, respectively.

  A configuration of the machine tool 1 will be briefly described with reference to FIG. The machine tool 1 includes a spindle mechanism, a spindle movement mechanism, a tool changer, and the like (not shown). The spindle mechanism includes a spindle motor 52, and rotates the spindle on which a tool is mounted. The main shaft moving mechanism includes a Z-axis motor 51, an X-axis motor 53, and a Y-axis motor 54, and moves the main shaft in each of the XYZ axial directions relative to a workpiece supported on the upper surface of a table (not shown). The tool changer includes a magazine motor 55, drives a tool magazine (not shown) that stores a plurality of tools, and exchanges the tool mounted on the spindle with another tool. The machine tool 1 further includes an operation panel 10. The operation panel 10 includes an input unit 24 and a display unit 25. The input unit 24 is a device for performing various inputs, instructions, settings, and the like. The display unit 25 is a device that displays various screens. The operation panel 10 is connected to the input / output unit 35 of the numerical controller 30. The Z-axis motor 51 includes an encoder 51B. The spindle motor 52 includes an encoder 52B. The X-axis motor 53 includes an encoder 53B. The Y-axis motor 54 includes an encoder 54B. The magazine motor 55 includes an encoder 55B. The encoders 51B to 55B are connected to drive circuits 51A to 55A, which will be described later, of the numerical control device 30, respectively.

  The electrical configuration of the numerical control device 30 will be described with reference to FIG. The numerical control device 30 includes a CPU 31, a ROM 32, a RAM 33, a storage device 34, an input / output unit 35, drive circuits 51A to 55A, and the like. The CPU 31 performs overall control of the numerical control device 30. The ROM 32 stores various programs such as a main program. The RAM 33 stores various data during execution of various processes. The storage device 34 is a nonvolatile memory. The input / output unit 35 is connected to the operation panel 10. The drive circuit 51A is connected to the Z-axis motor 51 and the encoder 51B. The drive circuit 52A is connected to the spindle motor 52 and the encoder 52B. The drive circuit 53A is connected to the X-axis motor 53 and the encoder 53B. The drive circuit 54A is connected to the Y-axis motor 54 and the encoder 54B. The drive circuit 55A is connected to the magazine motor 55 and the encoder 55B. The drive circuits 51A to 55A receive drive signals described later from the CPU 31, and output drive currents (pulses) to the corresponding motors 51 to 55, respectively. The drive circuits 51A to 55A receive feedback signals from the encoders 51B to 55B and perform position and speed feedback control. The drive circuits 51A to 55A may be, for example, FPGA circuits.

  The moving average filter and time constant used for post-interpolation acceleration / deceleration will be described with reference to FIG. The numerical controller 30 calculates a target position, a moving distance, a moving speed, a moving time, and the like for each of the X-axis, Y-axis, and Z-axis drive axes based on the interpolation command in the NC program. The interpolation command is a control command used when moving the axis at the moving speed designated by the address, and is, for example, a linear interpolation command, a circular interpolation command, or the like. The numerical control device 30 performs post-interpolation acceleration / deceleration by passing a moving average filter (hereinafter referred to as an FIR filter) at least twice through the calculated movement speed for each drive axis to smooth the speed change. The NC program has a plurality of blocks composed of control commands such as G code and M code.

2, the moving speed of the tool to be moved from x ₁ to x ₂ in the X-axis direction is a chart showing the result of processing twice with FIR filters. The acceleration / deceleration time constant of the FIR filter (hereinafter referred to as the time constant) corresponds to the number of samples that the FIR filter averages. For example, when the sampling time is 1 msec and the time constant of the FIR filter is 10 msec, the FIR filter uses the average of up to 10 commands including the current interpolation command as the current output. The time constant of the first stage of the FIR filter (FIR1) _{t 1,} the time constant of the second stage of the FIR filter (FIR2) and _{t 2.}

As a result of processing the moving speed with the two-stage FIR filter (FIR1, FIR2), the change in the acceleration is less than a certain value, so the tool gradually increases the speed by applying t ₁ + t ₂ and reaches the maximum speed. Apply t ₁ + t ₂ and slow down to stop. Therefore, the numerical control device 30 can absorb a sudden change in the moving speed by processing the moving speed with a plurality of FIR filters, and therefore can suppress the vibration of the machine tool 1 and the maximum torque required for the operation.

As described above, in the post-interpolation acceleration / deceleration, due to the influence of the time constants t ₁ and t ₂ , the path on which the tool actually moves causes an error with respect to the path commanded by the NC program. Therefore, the numerical control device 30 delays the movement start timing of the current interpolation command after the movement of the previous interpolation command is completed in order to move the tool within the tolerance set in advance by the user. The numerical control device 30 can easily calculate the command start delay time of the current interpolation command with a small calculation load by executing main processing described later.

  A main process executed by the CPU 31 will be described with reference to FIG. The operator inputs the NC program number of the workpiece shape to be processed with the input unit 24 of the operation panel 10 and presses a processing start key (not shown). When the CPU 31 detects pressing of the machining start key, it reads the main program stored in the ROM 32 and executes this processing.

  First, the CPU 31 reads an NC program corresponding to the number input by the input unit 24 from the storage device 34 (S1). The CPU 31 interprets the read NC program from the first line (S2) and recognizes the control command in one line. The CPU 31 determines whether or not the recognized control command is an end command for instructing the end of the NC program (S3). When the control command is not an end command (S3: NO), the CPU 31 determines whether or not the control command is an interpolation command (S4). When the control command is a command other than the interpolation command (for example, positioning command, tool radius correction command, tool change command, etc.) (S4: NO), the CPU 31 executes an operation corresponding to the control command (S14).

  When the control command is an interpolation command (S4: YES), the CPU 31 generates the coordinate position (command position) of the command point after interpolation (S5). Subsequently, the CPU 31 determines whether or not the constant error control is effective (S6). The constant error control is a control method for controlling the operation of the machine tool 1 so that the path in which the tool actually moves is within a preset allowable error with respect to the path commanded by the NC program in acceleration / deceleration after interpolation. It is. The operator can select in advance whether the constant error control is valid or invalid on the operation panel 10. The CPU 31 stores the validity or invalidity of the constant error control input by the worker in the RAM 33 or the like using a flag or the like, for example.

−Invalid constant error control−
When the constant error control is invalid (S6: NO), the CPU 31 executes the interpolation process without executing the constant error control (S12). In the interpolation process, the current position and the command position are interpolated, and the target position, moving distance, moving speed, moving time, etc. are calculated for each of the X-axis, Y-axis, and Z-axis drive axes. Next, the CPU 31 executes FIR filter processing (S13). In the FIR filter processing, as described above, the moving speed for each drive shaft is processed by the two-stage FIR filters (FIR1, FIR2). Therefore, the speed change of each drive shaft becomes smooth.

  The CPU 31 generates a drive signal and outputs it to the corresponding drive circuits 51A, 53A, 54A (S11). The drive signal is a signal including various information such as a target position, a moving distance, a moving speed, and a moving time on each drive axis. The drive circuits 51A, 53A, and 54A output drive currents (pulses) to the corresponding motors 51, 53, and 54 based on the drive signals received from the CPU 31, respectively. Therefore, the numerical control device 30 can move the tool according to the path commanded by the interpolation command of the NC program.

-Effective error control-
When the constant error control is valid (S6: YES), the CPU 31 executes the constant error control (S7). The constant error control process will be described with reference to FIG. The CPU 31 determines whether or not the interpreted interpolation command is a circular interpolation command (S21). When circular interpolation command (S21: YES), the influence of the constant t ₁ and t ₂ when the FIR filter processing to be executed after the tool is likely to move to the inward turning relative command arc circular interpolation command is a command . Therefore, CPU 31, in order to move within the tolerances of the tool relative to the instruction arc, using the following parameters and Equation 1, to calculate the arc rate _{F c} (S22). [Equation 1] is obtained by arranging the gain of the transfer function of the FIR filter by Taylor expansion approximation.
_Fc : arc speed (mm / min)
・_Rc : Arc radius (mm)
・ Ε: Allowable error (mm)
T ₁ : Time constant 1 (FIR1)
T ₂ : Time constant 2 (FIR2)
_Rc is calculated from a circular interpolation command. When the radius of the start point and the end point of the command arc is different, the CPU 31 may set the smaller one as the arc radius. ε, t ₁ , and t ₂ are input in advance by the operator through the input unit 24 of the operation panel 10 and are stored in the storage device 34, for example.

CPU31 is calculated arc rate _{F c} is less determines whether than the command speed F of the circular interpolation command (S23). Since the calculated arc speed F _c is a numerical value for moving within the allowable error ε, when the arc speed F _c is smaller (S23: YES), the CPU 31 sets the calculated arc speed F _c to the command speed F. Set (S24). On the other hand, when the command speed F is smaller (S23: NO), the CPU 31 does not change the command speed F because it can move within the allowable error ε. When the interpreted interpolation command is a linear interpolation command (S21: NO), the CPU 31 advances the process to S25 because no error is generated for the path.

−Calculation of inter-block angle β−
The CPU 31 determines whether at least one of the first block and the second block is a circular interpolation block (S25). The first block is a block that is interpolated by the current interpolation command, and the second block is a block that is interpolated by the previous interpolation command connected to the start point of the first block. The circular interpolation block means a block to be interpolated with an arc locus, and the linear interpolation block means a block to be interpolated with a linear locus. When at least one of the first block and the second block is a circular interpolation block (S25: YES), the CPU 31 calculates an inter-block angle β considering circular interpolation (S26). On the other hand, when both the first block and the second block are linear interpolation blocks (S25: NO), the CPU 31 calculates the inter-block angle β between the two linear interpolations (S27). The inter-block angle β means an angle at a command point connecting the first block and the second block. The CPU 31 obtains the direction vectors of the two linear interpolation blocks, and obtains the angle between these vectors as the inter-block angle β.

  On the other hand, when at least one of the first block and the second block is a circular interpolation block, as described above, the tool moves inward with respect to the command arc of the circular interpolation command. Therefore, the CPU 31 determines the direction vector of the circular interpolation block in consideration of the actual circular arc including the inward error in the command circular arc in addition to the command circular arc, and determines the inter-block angle β with the direction vector of the other block. It is necessary to calculate.

A scene in which at least one of the first block and the second block is a circular interpolation block has the following three patterns in the order of interpolation (the order of the second block and the first block).
(1) Linear interpolation block-Circular interpolation block (2) Circular interpolation block-Linear interpolation block (3) Circular interpolation block-Circular interpolation block

(1) Linear Interpolation Block-Circular Interpolation Block FIG. 6 shows a path in which the circular interpolation block B2 is connected at the command point P after the linear interpolation block B1. The CPU 31 obtains the previous linear interpolation vector a, the current command arc tangent vector b, and the current actual arc tangent vector c. The vector a is a vector of the command straight line of the block B1. The vector b is a tangent vector drawn from the command point P of the command arc of the block B2. The vector c is a tangent vector drawn from the command point P of the real arc K. The actual arc K is a trajectory including an inward error in the command arc of the block B2. The inward error can be replaced with an allowable error ε. The actual arc K is obtained from the command speed F of the command arc of the block B2 and the radius of the actual arc K. The radius of the actual arc K is the length obtained by subtracting the allowable error ε from the arc radius R _c of the instruction arc block B2. The CPU 31 obtains an angle formed by the vector a and the vector b and an angle formed by the vector a and the vector c. The inward rotation error at the corner increases as the angle decreases at the same speed. In the example shown in FIG. 6, the angle formed by the vector a and the vector b is smaller than the angle formed by the vector a and the vector c. Therefore, the CPU 31 determines the angle between the vector a and the vector b as the inter-block angle β.

  FIG. 7 shows a path in which the command arc of the arc interpolation block B2 is counterclockwise. Similarly to FIG. 6, the CPU 31 obtains the previous linear interpolation vector a, the current command arc tangent vector b, and the current actual arc tangent vector c, and the angle formed by the vector a and the vector b, and the vector a and the vector c are formed. Find the angle. In the example shown in FIG. 7, the angle formed by the vector a and the vector c is smaller than the angle formed by the vector a and the vector b. Therefore, the CPU 31 determines the angle between the vector a and the vector c as the inter-block angle β.

(2) Circular Interpolation Block-Linear Interpolation Block FIG. 8 shows a path where the linear interpolation block B2 is connected at the command point P next to the circular interpolation block B1, contrary to FIG. The CPU 31 obtains the previous command arc tangent vector a, the previous actual arc tangent vector b, and the current linear interpolation vector c. The vector a is a tangent vector drawn from the command point P of the command arc of the block B1. The vector b is a tangent vector drawn from the command point P of the real arc K. The actual arc K is a trajectory including an inward error in the command arc of the block B1. The inward error can be replaced with an allowable error ε. The actual arc K is obtained from the command speed F of the command arc of the block B1 and the radius of the actual arc K. The radius of the actual arc K is the length obtained by subtracting the allowable error ε from the arc radius R _c of the instruction arc block B1. The vector c is a vector of the command straight line of the block B2. The CPU 31 obtains an angle formed by the vector a and the vector c and an angle formed by the vector b and the vector c. In the example shown in FIG. 8, the angle formed by the vector a and the vector c is smaller than the angle formed by the vector b and the vector c. Therefore, the CPU 31 determines the angle between the vector a and the vector c as the inter-block angle β.

(3) Circular Interpolation Block-Circular Interpolation Block FIG. 9 shows a path in which the circular interpolation block B2 is connected at the command point P after the circular interpolation block B1. In this scene, since both the first block and the second block are circular interpolation blocks, the CPU 31 determines the previous command arc tangent vector a, the previous actual arc tangent vector b, the current command arc tangent vector c, and the current command arc tangent vector c. The real arc tangent vector d is obtained. The vector a is a tangent vector drawn from the command point P of the command arc of the block B1. The vector b is a tangent vector drawn from the command point P of the real arc K1. The actual arc K1 is a locus including an inward error in the command arc of the block B1. The inward error can be replaced with an allowable error ε. The actual arc K1 is obtained from the command speed F of the command arc of the block B1 and the radius of the actual arc K. The radius of the actual arc K1 is the length obtained by subtracting the allowable error ε from the arc radius R _c of the instruction arc block B1.

On the other hand, the vector c is a tangent vector drawn from the command point P of the command arc of the block B2. The vector d is a tangent vector drawn from the command point P of the real arc K2. The actual arc K2 is a trajectory including an inward error in the command arc of the block B2. The inward error can be replaced with an allowable error ε. The actual arc K2 is obtained from the command speed F of the command arc of the block B2 and the radius of the actual arc K2. The radius of the actual arc K2 is the length obtained by subtracting the allowable error ε from the arc radius R _c of the instruction arc block B2.

  The CPU 31 obtains an angle formed by the vector a and the vector c, an angle formed by the vector a and the vector d, an angle formed by the vector b and the vector c, and an angle formed by the vector b and the vector d. The inward rotation error at the corner increases as the angle decreases at the same speed. In the example shown in FIG. 9, the angle formed by the vector a and the vector c is the smallest compared to the other angles. Therefore, the CPU 31 determines the angle between the vector a and the vector c as the inter-block angle β.

-Correction of inter-block angle β-
Returning to FIG. 4, as described above, after calculating the inter-block angle β (S26, S27), the CPU 31 executes an inter-block angle correction process for the calculated inter-block angle β (S28).

  The reason for correcting the inter-block angle β will be described with reference to FIGS. A path L1 shown in FIG. 10 is formed by two linear interpolation commands. The linear interpolation block B2 is connected by the command point P next to the linear interpolation block B1. Block B1 is linear interpolation in the X-axis direction, and block B2 is linear interpolation in the Y-axis direction. The inter-block angle β is 90 °. FIG. 11 is a diagram in which the moving speed (speed 1) of the block B1 and the moving speed (speed 2) of the block B2 when moving along the path L1 in FIG. 10 are respectively processed by the two-stage FIR filters (FIR1, 2). It is.

When speed 1 begins to descend from maximum speed, speed 2 begins to rise. In the part where the speed 1 and the speed 2 overlap, the tool moves inward along the corner of the path L1. When speed 1 starts to drop from maximum speed, the tool is located at A1. When speed 1 and speed 2 overlap at the same speed, the tool is located at A2. When speed 1 drops from maximum speed to zero, the tool is located at A3. A2 is a position where the error is maximum with respect to the path L1. A3 is a position where the error is eliminated. Time to A1~A3 until the error is eliminated occurs when corresponds to the sum of the constants _{t 1} and _{t 2.} That is, the error generated at the corner of the path L1 is not eliminated unless it passes through A3. For example, when there is a corner of the next block immediately after A2, the error may remain for half the time constant. Therefore, this embodiment corrects the inter-block angle β calculated in S26 and S27 in consideration of the influence of errors that have occurred in the past in the corner.

The inter-block angle correction process will be described with reference to FIGS. 5, 12, and 13. This embodiment will be described assuming a route L2 shown in FIG. The path L2 is a path in which a plurality of corners are continuous and curved as a whole. P _N is the starting point of the current interpolation command. P _{N + 1} is the movement command position of the current interpolation command. _PN-1 is the start point of the previous (previous) interpolation command. P _N−2 is the start point of the previous interpolation command. P _N-3 is the start point of the previous three interpolation commands. _PN-4 is the start point of the previous four interpolation commands. FIG. 13 is a chart before the FIR filter processing is performed on the change in the moving speed when moving along the route L2 shown in FIG.

As shown in FIG. 5, first, CPU 31 is going back seek time _{T B} by the following equation (2) (S40). Going back time _{T B} is half the sum of the time constant _t 1, _{t 2.}
(Equation 2)
T _B = (t ₁ + t ₂ ) / 2
・ T _B : Retroactive time (msec)
T ₁ : Time constant of FIR1 (msec)
T ₂ : Time constant of FIR2 (msec)

Then, CPU 31 is, _{T B} is determines whether _{T N-1} or less (S41). As shown in FIG. 13, T _N−1 is the sum of the command start delay time T _{d of the} previous interpolation command and the movement time. The command start delay time _Td is a time for delaying the timing for starting the movement based on the current interpolation command after the movement based on the previous interpolation command is completed. As will be described later, the _Td of the current interpolation command is calculated after the inter-block angle correction process (see S29 in FIG. 4), but the _Td of the past interpolation command has already been calculated. When T _B is equal to or less than T _N−1 (S41: YES), the past path error has already been eliminated. Therefore, the CPU 31 ends this process without doing anything, and proceeds to S29 in FIG.

・Ｔ_Ｎ−Ｍ：Ｍ個前の補間指令の指令開始遅延時間と移動時間の合計時間（ｍｓｅｃ）
・β_Ｎ−Ｍ：直線Ｐ_Ｎ−ＭＰ_Ｎと直線Ｐ_ＮＰ_Ｎ＋１の内角（ｄｅｇ）
・β´：補正後のブロック間角度（ｄｅｇ） On the other hand, when T _B is larger than T _N−1 (S41: NO), the past error remains, so the CPU 31 substitutes 2 for M (S42), and T _B is the following [Equation 3] It is determined whether or not the condition is satisfied (S43). M is an integer parameter.

・ T _N-M : Total time (msec) of command start delay time and movement time of M previous interpolation commands
.Beta.N _-M : Interior angle (deg) of straight line P _N-M P _N and straight line P _N P _{N + 1}
Β ′: Angle between blocks after correction (deg)

・Ｔｄ_Ｎ−Ｍ：Ｍ個前の補間指令の指令開始遅延時間（ｍｓｅｃ）
・Ｌ_Ｎ−Ｍ：Ｍ個前の補間指令のブロック長（ｍｍ）
・Ｆ_Ｎ−Ｍ：Ｍ個前の補間指令の指令速度（ｍｍ／ｍｉｎ） However, _TN-M is obtained by the following [Equation 4].

· _{Td N-M:} M pieces before the interpolation command instruction start delay time of (msec)
・ L _N-M : Block length of mm previous interpolation command (mm)
・ F _N-M : Command speed of mm previous interpolation command (mm / min)

When satisfying the Equation 3 with M = 2 (S43: YES) , since the past errors are eliminated, CPU 31 obtains the angle β~β _N-M (S45). On the other hand, when M = 2 and [Equation 3] is not satisfied (S43: NO), the CPU 31 adds 1 to M (S44) and returns to S43 to determine again whether or not [Equation 3] is satisfied. . When filled with Equation 3] (S43: YES), CPU31 is a value of M which satisfies the equation (3), determining the angle β~β _N-M (S45). For example, FIG. 12, as shown in FIG. 13, suppose the position _{P B} going back to going back time _{T B} min past from the starting point _{P N} of this interpolation command (see Figure 12). When P _N is between P _N−2 and P _N−3 , the CPU 31 goes back to the start point P _N−3 of the interpolation command of the previous three blocks (corresponding to “past block” of the present invention) Angles β _N-2 and β _N-3 are obtained. CPU31 determines the corrected interblock angle β'the minimum angle among the angles β~β _N-M obtained in S45 (S46). In the example shown in FIG. 12, βN _-3 is determined to be β ′. CPU31 complete | finishes this process and advances a process to S29 of FIG.

- calculation of the command start delay time T _d -
Returning to the constant error control process of FIG. 4, the CPU 31 calculates _Td (S29). This will be described with reference to the path L1 shown in FIG. FIG. 14 shows the changes in the speeds 1 and 2 to which the FIR filter processing is performed when _Td is 0, as in FIG. The part where the speeds 1 and 2 overlap is the part where the tool goes around the corner. The length of the portion where the speeds 1 and 2 overlap corresponds to the time constant t ₁ + t ₂ . In a portion where rate 1 and 2 overlap, curved section of the speed 1 and 2 corresponds to the width t ₂ of the FIR2 the second stage. A2 where the speeds 1 and 2 overlap most is the maximum error point. In the present embodiment, T _d is obtained from the error. In order to obtain the error of the maximum error point, it is necessary to calculate both the curve portion where the speed changes with a curve and the straight line portion where the speed changes with a straight line after the speeds 1 and 2 start to overlap.

On the other hand, as shown in FIG. 15, when the overlapping time of the speeds 1 and 2 is shorter than 2 × t ₂ , the speed change in the part where the speeds 1 and 2 overlap is a curve. Therefore, the formula for obtaining _Td from the error is different from that in FIG. As shown in FIG. 16, when T _d is t ₁ + t ₂ , the speeds 1 and 2 do not overlap and the error at the corner is zero. At this time, _Td is the maximum value.

Based on the above, the following relationship holds for _Td . ε _max is the maximum value of error.
If T _d = 0, error = ε _max
If T _d = t ₁ + t ₂ then error = 0

As shown in FIG. 14, when T _d <t ₁ -t ₂ , the change in the portion where the speeds 1 and 2 overlap includes both the straight line portion and the curved portion. On the other hand, as shown in FIG. 15, when T _d ≧ t ₁ −t ₂ , the change of the portion where the speeds 1 and 2 overlap is only the curved portion. That is, the equation for calculating the error differs depending on the length of _Td . Therefore, in this embodiment, in order to obtain T _d from the allowable error ε, if the error ε _t1−t2 when T _d = t ₁ −t ₂ is obtained in advance, It can be easily determined which formula should be used to determine _Td . Therefore, the CPU 31 replaces (ε _{t1 -t 2} / ε _max ) = K, and calculates T _d when ε / ε _max is less than or greater than K as shown in the following [Equation 5] and [Equation 6]. Determine which expression to use. The formula for calculating _Td shown in [Equation 5] and [Equation 6] was obtained from the relationship between the position obtained by integrating the velocity waveform shown in FIG. 15 and _Td .

Note that the larger the command speed F, the larger the error, so that _Td increases. Therefore, it is desirable to use a larger command speed F of the block B1 and the command speed of the block B2 when calculating _Td .

As shown in FIG. 4, the CPU 31 calculates _Td using one of the equations according to the value of K, and stores the calculated _Td in the storage device 34 (S30). Therefore, the CPU 31 can easily calculate _Td according to the overlapping degree of the speeds 1 and 2 based on the time constants t1 and t2, the allowable error ε, the command speed F, and the inter-block angle β. The CPU 31 finishes the constant error control process, and advances the process to S8 of the main process in FIG.

Next, based on the current interpolation command, the CPU 31 executes an interpolation process from the command point (current position) of the previous interpolation command to the command position (S8). Next, the CPU 31 executes a two-stage FIR filter process on the moving speed for each drive axis (S9), and generates a drive signal for each drive axis. Next, the CPU 31 determines whether or not _Td stored in the storage device 34 has elapsed since the last movement of the interpolation command was completed (S10). When _Td has not elapsed (S10: NO), the CPU 31 stands by. When _Td has elapsed (S10: YES), the CPU 31 outputs a drive signal to the drive circuits 51A, 53A, 54A of the motors 51, 53, 54 corresponding to the interpolation command (S11). The motors 51, 53, 54 corresponding to the drive circuits 51A, 53A, 54A that have received the drive signal are driven. After _{Td has} elapsed since the last movement of the interpolation command has been completed, the movement of the tool based on the current interpolation command is started.

  The CPU 31 returns to S2 and interprets the next block. When the next block is not an end command (S3: NO), the CPU 31 repeats the process for the next block. When the next block is an end command (S3: YES), the CPU 31 ends this process. Therefore, the numerical controller 30 can move the tool within the allowable error ε with respect to the path commanded by the NC program by executing this process.

As described above, the numerical control device 30 according to the present embodiment moves a tool along a path instructed by the NC program and executes workpiece machining. The route is obtained by interpolating adjacent command points for a plurality of command points. The CPU 31 of the numerical controller 30 includes acceleration / deceleration time constants t ₁ and t _{2 of} the motor that moves the tool, an allowable error ε that is allowed for the path, a command speed F that commands the moving speed of the tool, Based on the inter-block angle β between the first block and the second block, the command start delay time T _d from the end of the movement of the previous interpolation command to the motors 51, 53, 54 until the start of the current interpolation command is obtained. Calculate. The first block is a block that is interpolated by the current interpolation command, and the second block is a block that is interpolated by the previous interpolation command. Based on the calculated _Td , the CPU 31 outputs to the drive circuits 51A, 53A, and 54A a drive signal for executing the movement of the current interpolation command to the corresponding motors 51, 53, and 54. Therefore, the numerical controller 30 can always control the path error within the allowable error ε with a small calculation load for the path commanded by the NC program.

In particular, in the above embodiment, after calculating the inter-block angle β between the first block and the second block, the calculated inter-block angle β is corrected in consideration of an error occurring in the corner of the past block. The CPU 31 performs interpolation for all the blocks belonging to the range from the start point of the interpolation command of the past block, which is a block before the first block corresponding to the current interpolation command, to the start point of the interpolation command of the first block. department forming a starting point of the interpolation command of the start point and the first block of instructions mutually determine the straight line multiple. CPU31 is the angle between the multiple lines and first blocks obtained respectively determined. When the smallest angle among the obtained angles is smaller than the inter-block angle β, the CPU 31 corrects the inter-block angle β to the smallest angle β ′. Therefore, the numerical control device 30 suppresses the error generated in the corner in the path to at least the allowable error ε without being affected by the error generated in the past block even in the path where the minute blocks are continuous. Can do.

In the above embodiment, the interpolation command is changed from the start point of the interpolation command of the block including the position that goes back half the sum of the time constants t ₁ and t ₂ from the start point of the interpolation command of the first block. The start point of the interpolation command of all the blocks belonging to the corresponding start point of the interpolation command of the first block is obtained, and the smallest angle between the start point of the interpolation command of all the blocks and the first block is obtained. When the smallest angle is smaller than the inter-block angle β, the CPU 31 corrects the inter-block angle β to the smallest angle β ′ and uses the corrected inter-block angle β ′ to start the current interpolation command. Calculate. Therefore, the numerical controller 30 can control the error generated in the corner within the allowable error ε without being affected by the error generated in the past block, even if the path is a continuous path of minute blocks.

  Since there are two time constants in the above embodiment, the change in the moving speed based on the interpolation command can be made smooth. Therefore, the numerical control device 30 can reduce the load on the machine tool 1.

  In the above description, the CPU 31 that executes the process of S7 corresponds to the calculation means of the present invention, the CPU 31 that executes the processes of S10 and S11 corresponds to the execution means of the present invention, and the CPU 31 that executes the processes of S26 and S27. Corresponds to the inter-block angle calculation means of the present invention, and the CPU 31 that executes the processing of S28 corresponds to the correction means of the present invention.

The present invention is not limited to the above embodiment, and various modifications can be made. For example, in the above embodiment, the moving speed is processed by a two-stage FIR filter (FIR1, FIR2), but may be processed by a three-stage or more FIR filter. For example, when the time constant when processing with a three-stage FIR filter is set to t ₁ , t ₂ , and t _{3 in} order from the largest, the command start delay time T _d is calculated as follows: What is necessary is just to calculate like [Formula 11]. Hereinafter, the description will be divided into [when t ₁ ≦ t ₂ + t ₃ ] and [when t ₁ > t ₂ + t ₃ ].

・Ｋ_１＜ε／ε_ｍａｘ≦Ｋ_２の時

・Ｋ_２＜ε／ε_ｍａｘ≦Ｋ_３の時

なお、［数９］の解の候補（１）〜（４）のうち、次の二つの条件［１］、［２］を共に満たす解をＴ_ｄとする。
［１］ルート内の計算結果が０以上である。
［２］Ｔ_ｄが「−ｔ_１＋ｔ_２＋ｔ_３≦Ｔ_ｄ≦ｔ_１−ｔ_２＋ｔ_３」を満たす。
・Ｋ_３＜ε／ε_ｍａｘ≦１の時

なお、［数１０］の解の候補（１）〜（４）のうち、次の二つの条件［１］、［２］を共に満たす解をＴ_ｄとする。
［１］ルート内の計算結果が０以上である。
［２］Ｔ_ｄが「０≦Ｔ_ｄ≦−ｔ_１＋ｔ_２＋ｔ_３」を満たす。
但し、

[When t ₁ ≦ t ₂ + t ₃ ]
・ When 0 ≦ ε / ε _max ≦ K ₁

・ When K ₁ <ε / ε _max ≦ K ₂

・ When K ₂ <ε / ε _max ≦ K ₃

Of the solution candidates (1) to (4) in [Equation 9], _let T _d be a solution that satisfies both of the following two conditions [1] and [2].
[1] The calculation result in the route is 0 or more.
[2] T _d satisfies “−t ₁ + t ₂ + t ₃ ≦ T _d ≦ t ₁ −t ₂ + t ₃ ”.
・ When K ₃ <ε / ε _max ≦ 1

Of the solution candidates (1) to (4) in [Equation 10], _let T _d be a solution that satisfies both of the following two conditions [1] and [2].
[1] The calculation result in the route is 0 or more.
[2] T _d satisfies “0 ≦ T _d ≦ −t ₁ + t ₂ + t ₃ ”.
However,

・Ｋ_１≦ε／ε_ｍａｘ≦Ｋ_２の時

・Ｋ_２≦ε／ε_ｍａｘ≦Ｋ_３の時

なお、［数１４］の解の候補（１）〜（４）のうち、次の二つの条件［１］、［２］を共に満たす解をＴ_ｄとする。
［１］ルート内の計算結果が０以上である。
［２］Ｔ_ｄが「ｔ_１−ｔ_２−ｔ_３≦Ｔ_ｄ≦ｔ_１−ｔ_２＋ｔ_３」を満たす。
・Ｋ_３≦ε／ε_ｍａｘ≦１の時

但し、

[When t ₁ > t ₂ + t ₃ ]
・ When 0 ≦ ε / ε _max ≦ K ₁

・ When K ₁ ≦ ε / ε _max ≦ K ₂

・ When K ₂ ≦ ε / ε _max ≦ K ₃

Of the solution candidates (1) to (4) in [Equation 14], _let T _d be a solution that satisfies both of the following two conditions [1] and [2].
[1] The calculation result in the route is 0 or more.
[2] T _d satisfies “t ₁ −t ₂ −t ₃ ≦ T _d ≦ t ₁ −t ₂ + t ₃ ”.
・ When K ₃ ≦ ε / ε _max ≦ 1

However,

  Further, various modifications can be made to the above embodiment. In the above embodiment, the inter-block angle correction process (S28) in the constant error control process shown in FIG. 4 may be omitted.

  Moreover, although the said embodiment moves a tool along the path | route which an NC program commands, you may move a workpiece | work along a path | route.

  Moreover, although the said embodiment demonstrated the vertical type machine tool 1 in which the axis line of a main axis | shaft extended to an up-down direction as an example, it is applicable also to the horizontal type machine tool in which the axis line of a main axis | shaft extends in a horizontal direction.

Moreover, although the said embodiment used the time constant of the FIR filter which performs a moving average as an acceleration / deceleration time constant of a motor, it is applicable also to the other filter with a time constant. For example, acceleration / deceleration may be performed using a primary low-pass filter as shown in [Equation 17] instead of the FIR filter. T is a time constant.

1 Machine tool 30 Numerical control device 31 CPU
51 Z-axis motor 52 X-axis motor 53 Y-axis motor

Claims (4)

In a numerical control apparatus for moving a tool or a workpiece along a path obtained by interpolating adjacent command points for a plurality of command points commanded by an NC program,
The acceleration / deceleration time constant of the motor that moves the tool or workpiece, the allowable error that is allowed for the path, the command speed that commands the moving speed of the tool or workpiece, and the path in the NC program Calculation that calculates the timing for the motor to start the current interpolation command based on the angle between the first block that is interpolated by the current interpolation command and the second block that is interpolated by the previous interpolation command. Means,
An execution means for causing the motor to execute the current interpolation command based on the timing calculated by the calculation means;
The computing means is
An inter-block angle calculating means for calculating the inter-block angle;
Correction means for correcting the inter-block angle calculated by the inter-block angle calculation means,
The correction means includes
The interpolation command start point of each block belonging to the range from the start point of the interpolation command of the past block, which is a block past the first block, to the start point of the interpolation command of the first block, and the first block when the start point of the interpolation command of the block and mutually sintering department number multiple of straight, the smallest angle of the first block and is an angle less than the inter-block angle, the most the interblock angle A numerical control device characterized by correcting to a small angle. The numerical control device according to claim 1,
The past block is
The numerical control apparatus according to claim 1, wherein the numerical control apparatus is a block including a position retroactive to a half time before the acceleration / deceleration time constant from the start point of the interpolation command of the first block. The numerical control device according to claim 2,
The numerical control apparatus according to claim 1, wherein the acceleration / deceleration time constant is plural. In a control method of a numerical controller that moves a tool or a workpiece along a path obtained by interpolating adjacent command points for a plurality of command points commanded by an NC program,
The acceleration / deceleration time constant of the motor that moves the tool or workpiece, the allowable error that is allowed for the path, the command speed that commands the moving speed of the tool or workpiece, and the path in the NC program Calculation that calculates the timing for the motor to start the current interpolation command based on the angle between the first block that is interpolated by the current interpolation command and the second block that is interpolated by the previous interpolation command. Process,
An execution step of causing the motor to execute the current interpolation command based on the timing calculated in the calculation step;
The calculation step includes
An inter-block angle calculating step for calculating the inter-block angle;
A correction step of correcting the inter-block angle calculated in the inter-block angle calculation step,
In the correction step,
The interpolation command start point of each block belonging to the range from the start point of the interpolation command of the past block, which is a block past the first block, to the start point of the interpolation command of the first block, and the first block when the start point of the interpolation command of the block and mutually sintering department number multiple of straight, the smallest angle of the first block and is an angle less than the inter-block angle, the most the interblock angle A control method characterized by correcting to a small angle.

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