JPH09319424A - Feed rate control method and device in numerical control - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the velocity fluctuation and to enable a stable feeding operation by operating an allowable maximum feeding velocity over the NC data of plural blocks and setting that maximum feeding velocity as the feeding velocity of the block to the executed next. SOLUTION: As NC data, a working program 1 is read and interpreted by a program reading and interpreting part 3 and these data are temporarily stored into a buffer memory part 5 for the unit of a block. Then, a velocity arithmetic part 7 operates maximum allowable feeding velocity Va by reading the stored data of plural blocks. At such a time, minimum allowable moving time ta, velocity control coefficient K and velocity setting step Vs, etc., per block in a parameter storage part 9 are utilized for arithmetic. The maximum allowable feeding velocity Va operated for each bloc, by this velocity arithmetic part 7 is sent out to a velocity control part 11. At the velocity control part 11, the velocity of feeding to be next executed is determined while referring to commanded velocity F of the working program or maximum allowable feeding velocity Vao operated the last time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a feed speed control method and device for a feed axis in numerical control of NC machine tools, industrial robots and the like.

[0002]

2. Description of the Related Art In machines such as NC machine tools and industrial robots, a feed axis is controlled by a numerical control device (NC device). In numerical control, when NC data such as a machining program or operation program is input, the NC data is interpreted, the trajectory of the feed axis and the feed speed are determined based on the interpreted data, and operation is performed for each block that is a processing unit. Is done. Taking the case of machining a work with an NC machine tool as an example, there are various machining shapes of the work, and the time required for the operation of one block is long and short. On the other hand, interpretation of NC data requires an interpretation time depending on the operation processing speed of the NC device. Therefore, before starting the processing operation of one block, the data interpretation of the one processing block must be completed. Therefore, conventionally, a buffer memory is prepared, interpretation data for a plurality of blocks is stored in the buffer memory, and the processing operation is performed based on the data read from the buffer memory so that there is no time delay. However, the capacity of the buffer memory is not infinite, and it is usually suppressed to the minimum capacity in consideration of simplification of the configuration, cost, and the like. When the amount of NC data stored in the buffer memory is small and the processing time of the block is shorter than the interpretation time, that is, when the length of the processing portion is short, the necessary interpretation data before the processing operation is started. There is a risk that will not be entered.

FIG. 3 shows a locus (program command path) of a machining tool in the case of performing linear machining at a constant program command speed F for each block N1 to N10. The arrow of each block indicates the direction, and the length indicates the processing movement distance. When processing according to the program,
As shown in FIG. 5, when the program operation time of each block becomes shorter than the permissible minimum movement time ta per block, the movement command pulse output is not in time and the feed speed changes stepwise. As a result, the feed operation of the machine becomes discontinuous, and a mechanical shock is applied to the processing tool, resulting in a problem that the processing accuracy is reduced. Here, the permissible minimum movement time ta per block is the minimum movement time that the feed shaft can move without stopping when the feed shaft moves by the movement distance commanded in one block. This is the minimum time required to read and interpret the NC data of a block, perform interpolation calculation, and send it to the feed axis motor.

This problem has been solved by Japanese Patent Laid-Open No. 7-191.
A feed rate control method and device in numerical control disclosed in Japanese Patent No. 728. That is, the permissible minimum movement time ta per block, which is determined by the data interpretation time, the interpolated sampling time, etc., and the permissible maximum feed speed Fd in the block, which is determined by the movement distance 1 of one block, are obtained in real time during operation, F is the maximum allowable feed rate
If it exceeds Fd, the actual feed rate of the block is set to the allowable maximum feed rate Fd. With this configuration, as shown in FIG. 6, the feed rate is set to a feed rate at which the actual feed does not stop for each block.
Mechanical shock and processing accuracy are improved.

[0005]

However, in the technique disclosed in Japanese Unexamined Patent Publication No. 7-191728, the feed rate is determined for each block, so the feed rate changes for each block, and a short block suddenly appears after a long block. In some cases, since it is necessary to significantly reduce the speed, there is a drawback that the entire processing time is extended, and further improvement is desired. The present invention eliminates such a problem, and the feed rate control in the numerical control capable of performing the stable feed operation by reducing the speed variation as much as possible regardless of the length of movement of a continuous series of blocks and the appearance pattern thereof. It is an object to provide a method and a device.

[0006]

In order to solve the above-mentioned problems, the present invention relates to a feed rate control method in numerical control having a multi-buffer for pre-reading and temporarily storing a plurality of blocks of NC data. A numerical value in which the maximum allowable feed rate is calculated over the NC data of a plurality of predetermined blocks among the NC data stored in, and the calculated maximum allowable feed rate is the feed rate of the block to be executed next. A feed rate control method in control is provided. Further, in a feed rate control method in a numerical control having a multi-buffer for pre-reading and temporarily storing NC data of a plurality of blocks, a total movement amount L of all blocks stored in the multi-buffer is calculated and set in advance. Allowable minimum travel time per block ta
And the number of blocks n stored in the multi-buffer
And the total allowable minimum moving time T is calculated, and the maximum allowable feed speed Va is obtained by dividing the L by the T.
A feed rate control method in numerical control for determining an actual feed rate based on the obtained allowable maximum feed rate Va is provided. Also, in a feed rate control device in numerical control having a multi-buffer for pre-reading and temporarily storing a plurality of blocks of NC data, NC data of a plurality of predetermined blocks among NC data stored in the multi-buffer In a numerical control including a speed calculation unit for calculating the maximum allowable feed speed over the above, and a speed control unit for setting the maximum allowable feed speed calculated by the speed calculation unit as the feed speed of the block to be executed next. A feed rate controller is provided.

[0007]

The maximum allowable feed rate is calculated for each block process across the NC data of a plurality of predetermined blocks stored in the multi-buffer or the NC data of all blocks stored in the multi-buffer, and the calculation is performed. Based on the result, the feed rate of the block to be executed next is determined.
For example, when the calculation result of the allowable maximum feed rate is smaller than the command feed rate input as NC data, the feed rate of the block to be executed next is determined as the allowable maximum feed rate. Since it is the maximum allowable feed speed calculated over the NC data of a plurality of blocks, the feed speed is averaged, the speed difference between blocks is relatively small, and the NC data amount stored in the multi-buffer is small. There is no phenomenon that the feed operation stops because it disappears.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings. In the present embodiment, a case will be described in which the feed speed in numerical control is applied to speed control of the feed axis of an NC machine tool. FIG. 1 is a block configuration diagram of a numerically controlled machine tool including a speed control device of the present invention, FIG. 2 is a flowchart showing a procedure of feed speed control in the numerical control of the present invention, and FIG. 3 is a machining tool in numerically controlled machining. 4 is a diagram showing an example of the movement locus of FIG. 3, FIG. 4 is a feed speed diagram when the feed speed control method in the numerical control of the present invention is applied to the movement locus of FIG. 3, and FIGS. FIG. 10 is a feed rate diagram when a conventional feed rate control method is applied to a movement trajectory.

First, the structure of the present invention applied to the speed control of the feed shaft of an NC machine tool will be described with reference to FIG. The machining program 1 which is NC data is read and interpreted by the program reading and interpreting unit 3. The interpreted data is temporarily stored in the buffer memory unit 5 in block units. The buffer memory unit 5 is a multi-buffer capable of simultaneously storing a plurality of blocks of data,
For example, 30 blocks of data can be stored. The speed calculation unit 7 reads the data of a plurality of blocks stored in the buffer memory unit 5 and calculates the maximum permissible feed speed Va in the procedure described later. At this time, the numerical values such as the permissible minimum moving time ta per block, the speed control coefficient K, the speed setting step Vs, etc., which are input in advance in the parameter storage unit 9, are appropriately read and used for the calculation. The allowable maximum feed speed Va calculated by the speed calculation unit 7 for each block processing is sent to the speed control unit 11 via the buffer memory unit 5. The speed control unit 11 refers to the command speed F of the machining program, the maximum allowable feed speed Vao calculated last time (at the stage before one block), and the like to determine the feed speed to be executed next. The NC data for which the feed speed has been determined is interpolated by the interpolating unit 13 and sent to each feed shaft motor 17 via the servo unit 15, and the movement of each feed shaft of the machine tool 19 is controlled.

Next, the control procedure in the speed calculator 7 and the speed controller 11 will be described with reference to FIG. First, every time the NC data for each block is read, the total movement amount L of all blocks stored in the buffer memory unit 5 is calculated, and the total number n of blocks is counted (step S1). 1 stored in advance in the parameter storage unit 9
The permissible minimum movement time ta per block, the speed control coefficient K, and the speed setting step Vs are read (step 2). Then, the latest (latest) allowable maximum feed speed Va is calculated by the equation Va = (L / (ta · n)) · K (step S3). Here, as the speed control coefficient K, 1 or a numerical value smaller than 1 which is close to 1 is usually selected and acts as a safety coefficient. The speed setting step Vs depends on the processing conditions so that the feed speed is changed when the difference between the maximum allowable feed speed Vao calculated last time (one block before) and the maximum allowable feed speed Va calculated this time is Vs or more. Is a numerical value set in advance. If Vs is set too small, the feed rate is changed rapidly every block processing, and smoothness is lost.

Next, the speed control unit 11 compares the command feed speed F with the latest allowable maximum feed speed Va (step S
4) If F> Va, proceed to step 5. If not F> Va, set the feed speed to the command feed speed F. Step 5
Then, the latest allowable maximum feed speed Va is compared with the previous allowable maximum feed speed Vao, and if | Va−Vao | ≧ Vs, the feed speed is calculated and the latest allowable maximum feed speed Va is set (step S7). . If | Va−Vao | ≧ Vs is not established, the feed speed is set to the previous allowable maximum feed speed Vao (step S8).

The feed rate of the feed axis when the tool is fed along the movement trajectory as shown in FIG. 3 by using such a feed rate control method is as shown in FIG. For example, when the buffer memory unit 5 stores 6 blocks of data from N1 to N6, the allowable maximum feed speed Va is calculated over the data of 6 blocks, and the block N
Then, the actual maximum feed speed Va is calculated over the data of 6 blocks from N2 to N7, and the actual feed speed of the block N2 is changed to the latest Va. The actual feed speed of the block N5 is the same speed because the difference between Va calculated for machining the N4 portion and the N5 portion is less than Vs. As described above, the feed rate according to the present invention is determined based on the average maximum feed rate, which is the maximum allowable feed rate calculated over a plurality of blocks, so that the feed rate becomes 0 as shown in FIG. This is not the case, and the feed rate does not fluctuate for each block as shown in FIG. 6 and changes smoothly.

In the present embodiment, the allowable maximum feed speed is calculated over the NC data of all blocks stored in the buffer memory. For example, the capacity of the buffer memory is 100 blocks, and NC of 60 blocks is NC. The maximum allowable feed rate may be calculated over the data, that is, the number of blocks that cross the maximum allowable feed rate may be set in advance. Note that the feed rate diagrams of FIGS. 4, 5 and 6 are shown assuming that the acceleration / deceleration time constant is 0 for the sake of simplicity.
Although the NC machine tool has been described in the present embodiment, the same configuration can be applied to the operation control of another numerical control machine such as an industrial robot, and the same operation and effect can be obtained.

[0014]

As described above, the method and apparatus for controlling the feed rate in the numerical control according to the present invention calculates the allowable maximum feed rate over the NC data of a plurality of blocks stored in the multi-buffer, The calculated allowable maximum feed rate is used as the feed rate for the next block to be executed. Therefore, regardless of the length of the block movement distance and its appearance pattern, the speed fluctuation is minimized to ensure a smooth and stable feed operation. Can be done. Yet, the operating time does not extend beyond the prior art. Also, the amount of storage in the buffer memory does not change, either increasing or decreasing,
There is also an effect that it is always maintained at a predetermined target amount.

[Brief description of drawings]

FIG. 1 is a block configuration diagram of a numerically controlled machine tool including a speed control device of the present invention.

FIG. 2 is a flowchart showing a procedure of feed rate control in the numerical control of the present invention.

FIG. 3 is a diagram showing an example of a movement trajectory of a machining tool in numerical control machining.

FIG. 4 is a feed rate diagram when the feed rate control method in the numerical control of the present invention is applied to the movement trajectory of FIG.

5 is a feed rate diagram when a conventional feed rate control method is applied to the movement trajectory of FIG.

FIG. 6 is a feed rate diagram when the conventional improved feed rate control method is applied to the movement trajectory of FIG.

[Explanation of symbols]

 1 ... Machining program 3 ... Program reading interpretation unit 5 ... Buffer memory unit 7 ... Speed calculation unit 9 ... Parameter storage unit 11 ... Speed control unit 13 ... Interpolation unit 15 ... Servo unit 17 ... Feed axis motor

Claims (3)

[Claims] 1. A feed rate control method in numerical control having a multi-buffer for pre-reading and temporarily storing a plurality of blocks of NC data, wherein a plurality of predetermined blocks among NC data stored in said multi-buffer are provided. The feed rate control method in numerical control is characterized in that the maximum permissible feed rate is calculated over the NC data, and the calculated maximum feed rate is the feed rate of the block to be executed next. 2. A feed rate control method in numerical control having a multi-buffer for pre-reading and temporarily storing NC data of a plurality of blocks, wherein a total movement amount L of all blocks stored in the multi-buffer is calculated, A product of a predetermined permissible minimum movement time per block ta and the number n of blocks stored in the multi-buffer, that is, a total permissible minimum movement time T is calculated, and the value L is divided by the value T to allow. Maximum feed rate V
A feed rate control method in numerical control, characterized in that a is determined and an actual feed rate is determined based on the determined maximum allowable feed rate Va. 3. A feed rate control device in numerical control having a multi-buffer for pre-reading and temporarily storing a plurality of blocks of NC data, wherein a plurality of predetermined blocks among NC data stored in said multi-buffer are provided. And a speed controller for setting the maximum allowable feed speed calculated by the speed calculator as the feed speed of the block to be executed next. A feed rate control device in numerical control characterized by the above.