JPH03152604A - Feed speed control method for numerical controller - Google Patents

Abstract

PURPOSE:To eliminate the shock to be applied to a mechanical system by using the pre-read/preinterpolation acceleration/deceleration to read the next block during interpolation of a current block. CONSTITUTION:A command speed FN2 of the next block N2 is previously read during interpolation of a block N1. If the speed F2 is higher than a command speed FN1 of the N1, the FN1 is defined as a target feed speed at the end point C of the N1. Then a speed command FN3 of a block N3 is previously read when the N2 is shifted to the N3. The FN3 is defined as a target feed speed at the end point F of the N2 if the FN1 is higher than the FN3. In such a constitution, the acceleration never changes suddenly at the start and end points of acceleration. Thus on shock is given to a mechanical system at the preinterpolation acceleration/deceleration. A CPU produces a control signal for mechanical side with use of a ROM and a RAM and based on a sequence program of a programmable controller.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a feed rate control method for a numerical control device, and in particular, a method in which the acceleration when accelerating and decelerating the feed rate to a target feed rate before interpolation is made variable. The present invention relates to a feed rate control method for a numerical control device.

[Conventional technology]

In a numerical control device (CNC), a workpiece is machined into a desired shape by moving a tool along a path specified by a cutting program at a specified speed.

By the way, in this type of machining, the speed of each axis changes suddenly at the start or end of tool movement, when there is a change in the commanded feed rate, or when there is a sudden change in the direction of tool movement. Therefore, there is a problem that the shock to the machine is large.

Therefore, conventionally, interpolation curve linear acceleration/deceleration is performed to linearly accelerate/decelerate the command speed before interpolation, and if there is a sudden change in the direction of tool movement, the speed is decelerated to an appropriate speed at that point. Alternatively, post-interpolation acceleration/deceleration is performed to accelerate/decelerate the feed rate of each axis after interpolation.

[Problem to be solved by the invention]

However, in the case of acceleration/deceleration after interpolation, acceleration and deceleration are performed for each axis at a predetermined time constant at the start and stop of movement to avoid shock to the mechanical system, so there is a problem that machining errors are large.

On the other hand, in the case of interpolated curve linear acceleration/deceleration, the acceleration changes rapidly between the start and end points of acceleration and deceleration, so there is a problem in that a large shock is applied to the mechanical system. This will be explained below using the drawings.

FIG. 5 is a diagram showing conventional interpolation curved linear acceleration/deceleration in which linear acceleration/deceleration is performed to the command speed before interpolation. three blocks N
l, N2 and N30 command speeds are FNI and FN2 respectively.
and FN3. The vehicle is accelerated in a straight line from the start point of block N1 to the end point B until reaching the specified speed FNI, and after reaching the specified speed FNI, the specified speed FNI is maintained until the starting point C of the next block N2. Next, in block N2, the vehicle is accelerated in a straight line from the starting point C of block N2 to the end point until reaching the designated speed FN2. Specified speed FN2
After reaching the start point F of the next block N3, the speed is maintained, but as the start point F of the next block N3 approaches, the speed is decelerated in a straight line from the point E on the specified speed FN2 to the start point F of the block N3, and after reaching the start point F of the block N3. The designated speed FN3 is maintained. and,
When the end point H of block N3 approaches, the speed is decelerated in a straight line from point G on designated speed FNa to end point H of block N3.

In this way, in the case of interpolated linear acceleration/deceleration, acceleration and deceleration are performed in a straight line, so the acceleration starting points A and C1
There is a problem that the acceleration suddenly changes at the acceleration end point B and D1, the deceleration start point E and G, and the deceleration end point F and ■], and a large shock is given to the mechanical system.

The present invention has been made in view of the above points, and an object of the present invention is to provide a feed control method for a numerical control device that can perform acceleration/deceleration without giving a shock to the mechanical system during interpolative acceleration/deceleration. .

[Means to solve the problem]

In order to solve the above problems, the present invention accelerates the feed speed at the starting point of the first block to the target command speed within the first block, and changes the feed speed within the first block to the target command speed within the first block.
In a feed rate control method for a numerical control device in which acceleration/deceleration to decelerate to a target command speed at a block end point is performed before interpolation, when accelerating from the feed speed at the first block start point to the target command speed within the first block. gradually increases the positive acceleration until it reaches a predetermined positive acceleration, and when it approaches the target command speed in the first block, gradually decreases the positive acceleration, and 1
When decelerating from the feed speed within the block to the target command speed at the end point of the first block, gradually increase the negative acceleration until it reaches a predetermined negative acceleration,
There is provided a feed rate control method for a numerical control device, characterized in that the magnitude of the negative acceleration is gradually reduced when the target commanded velocity at the end point of the first block is approached.

[Effect]

In the case of acceleration, the positive acceleration gradually increases until it reaches a predetermined positive acceleration, and when it approaches the target command speed, the positive acceleration starts from the point where the positive acceleration becomes zero at the target command speed. gradually decreases. Similarly, in the case of deceleration, the negative acceleration gradually increases until it reaches a predetermined negative acceleration, and when it approaches the target command speed, the negative acceleration decreases from the point where the negative acceleration becomes zero exactly at that target command speed. acceleration gradually decreases. This prevents shock from being applied to the mechanical system during interpolative acceleration/deceleration.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a diagram showing the hardware configuration of a numerical control device (CNC) for implementing the feed rate control method of the present invention. As shown in the figure, a processor 11 controls the entire numerical control device, executes a feed rate control process to be described later, and variably controls acceleration during acceleration and deceleration.

The ROM 12 is composed of an EPROM or an EEPROM, and stores control programs and the like. RAM13
is composed of DRAM and stores various data. Non-volatile memory 14 is CMO3 with battery backup
etc., stores the parameters of the computer program 14a1, etc., and retains the contents even after the numerical control device is powered off.

PC (programmable controller) 15 has M function,
Upon receiving commands such as S function and 1 function, the sequence program 15a decodes and processes the commands and outputs signals for machine tool control. In addition, the PCl5 receives a limit switch signal from the machine side or a switch signal from the machine operation panel, and processes it with the sequence program 15a.
Outputs signals for machine side control. Signals required by the numerical control device are transferred via bus 25 to RAM 13 and read by processor 11.

The graphic control circuit 16 converts data such as the current position and movement amount of each axis stored in the RAM 13 into display signals.
It is output to the display device 16a. The display device 16a is a CRT,
A graphic control circuit 16 consisting of a liquid crystal display device, etc.
Display the display signal from. The keyboard 17 is used to enter various data manually.

The axis control circuit 18 controls the servo motor 20, and sends a command speed according to the rotation program to the processor II.
After receiving from
A speed command signal for controlling the servo motor 20 is output to the servo amplifier 19. The servo amplifier 19 amplifies this speed command signal and drives the servo motor 20. A pulse coder 21 that outputs a position feedback signal is coupled to the servo motor 20. The pulse coder 21 feeds back position feedback pulses to the axis control circuit 18. In addition to the pulse coder 21, a position detector such as a linear scale may be used. These elements are required for the number of axes, but since the configuration of each element is the same, only one axis is shown here.

The input/output circuit 22 sends and receives human output signals to and from the machine side.
That is, it receives limit switch signals from the machine, switch signals from the machine operation panel, etc. The received signal is PCl5
read by. In addition, the input/output circuit 22 is
It receives an output signal from 5 for controlling the pneumatic actuator etc. on the machine side and outputs it to the machine side.

The manual pulse generator 23 outputs a pulse train for precisely moving each axis according to the rotation angle, and is used to precisely position the machine. Manual pulse generator 23 is usually mounted on a machine operation panel.

In the figure, the spindle control circuit, spindle amplifier, spindle motor, etc. for controlling the spindle are omitted.

Further, although there is one processor here, a multi-processor system using a plurality of processors can be used depending on the system.

In this embodiment, the acceleration at the start of acceleration/deceleration at the start and end points of a block is gradually increased, and the acceleration at the end of acceleration/deceleration is gradually decreased.

FIG. 1 is a diagram showing a feed rate control method of accelerating or decelerating a commanded rate before interpolation according to the present invention. This figure shows a case where the same command speed as in FIG. 5 is commanded. That is, three blocks N
The command speeds of 1, N2 and N3 are FNI and FN2, respectively.
and FN3.

In the vicinity of the starting point of block N1, the acceleration gradually increases until it reaches a predetermined acceleration, and the feed rate gradually increases, and when it approaches the designated speed FNI, that is, in the vicinity of point B, the feed rate The magnitude of the acceleration gradually decreases until it reaches the designated speed FNI. Specified speed FN
After reaching point I, the designated speed FNI is maintained until the starting point C of the next block N2. Then, the same acceleration control as in block N1 is performed near the starting point C and the dot of block N2 until the feed speed reaches the designated speed FN2.

Therefore, near the starting point A of block N1 and the starting point C of block N2, acceleration starts with a small acceleration at first, and then the acceleration gradually increases until it reaches a predetermined acceleration. Further, near the point B of block N1 and the dot of block N2, the predetermined acceleration gradually decreases until the designated speeds FNI and FN2 are reached.

Next, when the starting point F of the next block N3 approaches on block N2 maintaining the specified speed FN2, the specified speed FN2
Deceleration is performed between the upper point E and the starting point F of block N3. This deceleration is performed in the same way as acceleration.

That is, in the vicinity of point E of block N2, the absolute value of the negative acceleration gradually increases until it reaches a predetermined magnitude of negative acceleration, and the feed rate gradually decreases until it approaches the designated speed FN3. That is, the starting point F of block N3
In the vicinity of , until the feed speed reaches the specified speed FN3,
The absolute value of negative acceleration gradually decreases. After reaching the designated speed FN3, the designated speed FN3 is maintained until point G on block N3. Then, point G on block N3
And even at the end point H of block N3, the feed speed is the command speed FO.
The same deceleration control as in block N2 is performed until reaching the block N2.

Therefore, at point E on block N2 and point GF on block N3, deceleration starts with a small negative acceleration, and then the negative acceleration gradually increases until it reaches a predetermined negative acceleration. That is, the absolute value of acceleration increases.

Also, the starting point F of block N3 and the ending point 1 of block N3
In the vicinity of 1, the absolute value of the predetermined negative acceleration gradually decreases until the command speeds FN3 and FO are reached.

According to this embodiment, unlike the acceleration/deceleration control shown in FIG. 5, the acceleration does not suddenly change at the start and end points of acceleration/deceleration, so there is no shock to the mechanical system during interpolative acceleration/deceleration. .

The operation of this embodiment will be explained using the drawings. FIG. 3 is a diagram showing a flowchart of the feed rate control method of this embodiment. FIG. 4 is a diagram showing details of the feed rate during acceleration in FIG. 1, and shows the case of accelerating from commanded speed FO to commanded speed FNI.

This embodiment employs look-ahead interpolation acceleration/deceleration in which the next block is read while the current block is being interpolated. As shown in Fig. 1, when interpolating block N1 and moving from the block (current block) Nl being interpolated to the next block N2, the commanded speed FN2 of the next block N2 is read in advance, and the commanded speed FN2 is set to the commanded speed FN2. If the speed is greater than the speed FNI, the commanded speed FNI of the current block N1 is set as the target feed speed at the end point C of the block N1. In addition, when moving from the current block N2 to the next block N3, the command speed FN3 of the next block N3 is read in advance, and the command speed FN3 is changed to the command speed FN3.
If it is smaller than NI, the command speed FN of the current block N3
3 is the target feed rate at the end point F of block N2.

That is, if the command speed of the next block is read in advance and the command speed of the next block is smaller than the command speed of the current block, the target feed speed at the end point of the current block is set as the command speed of the next block, and vice versa. If the commanded speed of the next block is greater than the commanded speed of the current block, the target feed speed at the end point of the current block is directly used as the commanded speed of the current block.

On the premise of the above-mentioned pre-read interpolation acceleration/deceleration, the operation of this embodiment will be explained according to the flowchart of FIG. 3. In the figure, the number following S indicates the step number.

[S1] For each distribution cycle, the distance required to reach the target command speed FNI at the end point C of the current block N1 even if deceleration starts immediately is defined as the deceleration distance Dk, and the remaining distance of the current block N1 being executed is Let the distance be Dr. Then, the remaining distance Dr is compared with the deceleration distance Dk, and if the remaining distance Dr is larger than the deceleration distance Dk, the process proceeds to S2, and if it is smaller, the process proceeds to S2.
Proceed to step 7.

Therefore, the target command speed at the end point C of block N1 is FN
I, the deceleration distance Dk becomes zero, and the process proceeds to S2. On the other hand, in the case of block N2, the target command speed at the end point F is FN3, so the acceleration or deceleration operation is performed depending on the relationship between the value of the deceleration distance Dk and the remaining distance Dr.

[52) When Dr>Dk in Sl, the acceleration obtained by increasing the acceleration Ak-1 of the previous distribution cycle by the acceleration change amount ΔA is set as the acceleration Ak in that distribution cycle. At the same time, the feed rate is also increased by the acceleration Ak to the feed rate Fk-1 of the previous distribution cycle, and is set as the feed rate Fk in that distribution cycle. That is, in the distribution cycle TI of FIG. 4, the acceleration Ak-1 of the distribution cycle immediately before the starting point A of the block N1 is zero and the feed rate is FO, so the acceleration A1 is ΔA and the feed rate is F1 is FO+ΔA. Therefore, the processing of S2 is performed from distribution period T1 to T6, and the processing of 83 and S
In the case of judgment 5, proceed in the direction of “NO” and exit as is (E
ND)L, acceleration Ak is acceleration Δ1, A2, A3, A4
, A5 increases by the acceleration change amount ΔA.

From distribution period T6 to T7, the next step 83 and S4
is processed.

[:S3] Compare whether the acceleration Ak in S2 is larger than a predetermined acceleration Aa set as a parameter. If the acceleration Ak is greater than the acceleration Aa, the process proceeds to S4, and if it is smaller, the process proceeds to S5. Therefore, in the distribution period T6, S2
The acceleration Ak becomes 6×ΔA. However, since the predetermined acceleration Aa in this embodiment is 5XΔA, the process advances to S4.

[54) If it is determined in S3 that the acceleration Ak is greater than the acceleration Aa, the acceleration Ak is set to the acceleration Ak-1 of the previous distribution cycle, and the feed rate Fk is also set to the feed rate Fk- of the previous distribution cycle. 1 and increased by the acceleration Ak. Therefore, in the distribution period T6, the acceleration Ak has the same value (5×ΔA) as the acceleration A5 in the previous distribution period T5,
The feed rate Fk also becomes a value obtained by increasing the feed rate Fk-1 of the previous distribution cycle by the acceleration Ak (5xΔA).

Thereafter, the distribution cycles T6 and T7 are processed in S2, S3, and S4, and in the judgment in S5, the process proceeds in the direction of rNOJ, and the process ends (END) L. The acceleration Ak is a constant acceleration A.
a (5XΔA).

From the distribution period T8 to Tll, the next steps S5 and S
6 is processed.

[S5] Absolute value 1Fa-Fk of the value obtained by subtracting the feed speed Fk of the currently executed distribution cycle from the command speed Fa of the current block
1 is compared with a value n (=Aa/ΔΣi) obtained by subtracting 1 from the value obtained by dividing the predetermined acceleration Aa by the acceleration change amount ΔA.

mn Here the sum is 10×ΔA. The comparison result is “YES”
”, the process proceeds to S6, and if rNOJ (7), the process ends. Therefore, in distribution period T8, S2, S3 and S4
As a result of the processing, the acceleration Ak is 5XΔA, but S5
In the determination of the absolute value |Fa−Fk1 value, that is, the value of IFNI−
Since the value of F81 is 5XΔA, the process advances to S6.

[S6] The value obtained by decreasing the acceleration change amount ΔA from the acceleration Ak-1 of the previous distribution cycle is set as the acceleration A in that distribution cycle.
Let it be k. At the same time, the feed rate is also increased by the acceleration Ak to the feed rate Fk-1 of the previous distribution cycle, and is set as the feed rate Fk in that distribution cycle. Therefore, in the distribution cycle T8, as a result of the processing in steps S2, S3, S4, and S5,
Since the acceleration Ak is 5xΔA, the acceleration A is
k becomes 4×ΔA, and the feed rate becomes FT+4×ΔA. From now on, the process of S6 is performed from the distribution period T8 to Tll, and the acceleration Ak is changed to 8, A9, Al0.
The acceleration change amount ΔA decreases in the order of 1All, and reaches the target command speed FNI at the end point C of block N1.

The steps from S2 to 86 described above are processes for acceleration operations, while the steps from S7 to 312, which will be described later, are processes for deceleration operations.

[S7] In this step, in Sl, the remaining distance Dr
This process is performed when the remaining distance Dr is determined to be smaller than the deceleration distance Dk. That is,
From the starting point C of block N2 to the point, the judgment of Sl is rY
Since EsJ, the acceleration operation from S2 to 86 is executed, and from the point of block N2 to point E, the command speed is FN.
2, and approaches point E, and from point E to end point F when the remaining distance Dr becomes smaller than the deceleration distance Dk.
This is the process that will be executed until

In this step, contrary to S2, the acceleration A of the previous distribution cycle is
The acceleration decreased by the acceleration change amount ΔA from k-1 is defined as the acceleration Ak in that distribution cycle, and at the same time, the feed rate is also calculated by adding the acceleration Ak to the feed rate Fk-1 of the previous distribution cycle. Let the feed rate in the period be Fk.

[S8] Determine whether the acceleration Ak obtained in S7 is a positive (plus) acceleration or a negative (minus) acceleration. If it is a positive acceleration, the process ends; if it is a negative acceleration, proceed to S9. . That is, when moving from block N2 to block N3 in FIG. 1, the feed rate is decelerated from commanded speed FN2 to commanded speed FN3, so acceleration A
k is always a negative acceleration. However, if the interval between blocks N2 is short and the end point of the block approaches while accelerating from the starting point C toward the point, the positive acceleration during acceleration is gradually reduced to zero,
From there, it is necessary to gradually decelerate with negative acceleration. This step assumes a case where the vehicle decelerates during such acceleration. Therefore, if the acceleration Ak determined in S7 is positive, the process ends and the process of S7, that is, the operation of decreasing the acceleration Ak by the acceleration change amount ΔA, is repeated until the positive acceleration becomes zero.

If the acceleration Ak obtained in S7 is a negative acceleration, S
Processes from 9 to 312 are performed.

[S9] Compare whether the absolute value of the negative acceleration Ak obtained in step 37 is larger than a predetermined acceleration Aa set as a parameter. If the absolute value of the negative acceleration Ak is greater than the acceleration Aa, proceed to S10; if it is smaller, proceed to S10.
Proceed to ll.

[S10] If it is determined in S9 that the absolute value of the negative acceleration Ak is greater than the acceleration Aa, the negative acceleration Ak is set to the negative acceleration Ak-1 of the previous distribution cycle.
The feed rate Fk is also the feed rate Fk of the previous distribution cycle.
-1 plus a negative acceleration, that is, a value that is reduced from the feed rate Fk-1 by the absolute value of the negative acceleration Ak.

[S11] Absolute value of the command speed Fa of the current block minus the feed speed Fk of the currently executed distribution cycle | Fa-F
kl and the sum Σi obtained by subtracting 1 from the value obtained by dividing the predetermined acceleration Aa by the acceleration change amount ΔA (=Aa/ΔA-1), multiplied by ΔA (ΔAL+here, the sum is IOXΔA). The comparison result is rYEs
In the case of J, the process proceeds to S6, and in the case of ``NO'', the process ends.

[312] Negative acceleration Ak- of the previous distribution cycle
The value increased by the acceleration change amount ΔA from 1 is defined as the negative acceleration Ak in that distribution cycle.

At the same time, the feed rate is also changed to the feed rate Fk- of the previous distribution cycle.
A value obtained by adding a negative acceleration to 1, that is, a value obtained by decreasing the feed rate Fk-1 by the absolute value of the negative acceleration Ak, is set as the feed rate Fk in that distribution cycle.

Through the above series of processes, it becomes possible to perform acceleration/deceleration without giving a shock to the mechanical system during pre-interpolation acceleration/deceleration.

In the above explanation, the number of blocks to be read ahead is one, but the number of blocks to be read ahead is 10 to 10.
The number may be increased to about 15 blocks. In that case, if the commanded speed of the prefetched block is smaller than the commanded speed of the current block, the commanded speed of the prefetched block is set as the target feed rate at the end point of the block mentioned above, and the total distance to the prefetched block is calculated as described above. Current block N1 being executed
Sl is determined as the remaining distance Dr. This allows deceleration processing to be performed across multiple blocks.

〔Effect of the invention〕

As explained above, according to the present invention, the machining speed can be determined without giving a shock to the mechanical system during pre-interpolation acceleration/deceleration.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the feed rate control method of the present invention that accelerates or decelerates the commanded speed before interpolation, and Fig. 2 is a diagram showing the hardware of a numerical controller' (CNC) for implementing the feed rate control method of the present invention. Figure 3 is a flowchart of the feed rate control method of this embodiment. Figure 4 is a diagram showing details of the feed rate during acceleration in Figure 1. Figure 5 is before interpolation. FIG. 3 is a diagram showing conventional linear acceleration/deceleration before interpolation in which linear acceleration/deceleration is performed to a command speed. 1-2 13-・4 4a 5 Processor OM AM Non-volatile memory Niprogram PMC (programmable machine controller) Sequence program display device Keyboard axis t control circuit Servo amplifier Servo motor 5a 6a 7 8 9 0 1 22 3 5 ・- -Valse coder/input/output circuit -Manual pulse generator-Nox

Claims (5)

[Claims] (1) Acceleration/deceleration to accelerate from the feed speed at the start point of the first block to the target command speed within the first block and decelerate from the feed speed within the first block to the target command speed at the end point of the first block. In a method for controlling the feed rate of a numerical control device performed before interpolation, when accelerating from the feed rate at the start point of the first block to the target command speed within the first block, the speed is increased until a positive acceleration of a predetermined magnitude is reached. Gradually increase the positive acceleration, and when it approaches the target command speed within the first block, gradually decrease the magnitude of the positive acceleration, and from the feed speed within the first block to the end point of the first block. When decelerating to the target command speed of A feed rate control method for a numerical control device that is characterized by gradually decreasing the speed. (2) The feed rate at the kth distribution is F_k, and the acceleration is A
_k, and when the amount of change in acceleration for each distribution period is ΔA, for each distribution period, the above A_k is A in the case of acceleration.
_k=A_k_-_1+ΔA, and in case of deceleration, A_k
=A_k_-_1-ΔA, and the above F_k is F_k=
F_k_−_1+A_k, and when the absolute value of A_k becomes larger than the parameter-set acceleration A_a,
The above A_k and F_k are A_k=A_k_-_1, F_
k=F_k_-_1+A_k, the target command speed in the first block and the target command speed at the end point of the first block are Fa, and the absolute value of the value obtained by subtracting the feed speed Fk of the distribution cycle currently being executed from Fa. The value |Fa-Fk| is the sum of the value n (=Aa/ΔA-1) obtained by subtracting 1 from the value obtained by dividing the predetermined acceleration Aa by the acceleration change amount ΔA ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ ▼ If the value is smaller than the multiplied value (ΔA×▲mathematical formula, chemical formula, table, etc.▼),
The A_k is A_k=A_k_-_1-ΔA in the case of acceleration, A_k=A_k_-_1+ΔA in the case of deceleration, and the feed rate F_k is F_k=F_k_-_1+A_k. A feed rate control method for a numerical control device according to item 1. (3) Read in advance the commanded speed of the second block following the first block, and if the commanded speed of the second block is smaller than the commanded speed of the first block,
The target command speed at the end point of the block is the command speed of the second block, and conversely, if the command speed of the second block is greater than the command speed of the first block, the target command speed at the end point of the first block. 2. The method of controlling the feed speed of a numerical control device according to claim 1, wherein the command speed of the first block is directly used as the command speed of the first block. (4) For each distribution cycle, the distance required to reach the target command speed at the end point of the first block even if deceleration starts immediately is defined as the deceleration distance, and the remaining distance of the first block being executed. , and if the remaining distance is larger than the deceleration distance, the acceleration is performed, and if the remaining distance is smaller than the deceleration distance, the deceleration is performed. A feed control method for a numerical control device according to item 1. (5) If the commanded speed of the prefetched block is smaller than the commanded speed of the first block, the commanded speed of the prefetched block is set as the target commanded speed at the end point of the first block, and the distance to the prefetched block is Feed rate control of the numerical control device according to claim 3, characterized in that the remaining distance and the deceleration distance are determined by taking the total as the remaining distance of the first block being executed. Method.