JPH01109053A - Feeding speed control method - Google Patents

Abstract

PURPOSE:To reduce load of programmer by obtaining the radius of a circle passing through motion starting point and ending point of a block and an adjoining block, when a program block to be commanded is linear, then determining a tool feeding speed based on the obtained radius. CONSTITUTION:A maximum allowable feeding speed is provided to a part program 10 while an allowance and a time constant are provided to a parameter setting section 41. When an arch is commanded at N-th block of the program 10, feeding speed calculating section 431 in a program analyzing section 43 employs its radius as it is. When it is commanded by a line, radius of a circle passing through three points of N-1th and Nth motion starting points and Nth motion ending point and following three points is obtained, then a feeding speed for holding reduction of radius within a predetermined error is obtained based on a smaller radius and smaller one of thus obtained feeding speed or a maximum allowable feeding speed is set as a feeding speed. Consequently, programming time can be shortened considerably.

Description

[Detailed Description of the Invention] (Technical Field of the Invention) The present invention relates to a feed rate control method for a numerically controlled machine tool, and is particularly useful in machining complex curved surfaces in mold machining, etc. This invention relates to a feed rate control method that contributes to improving machined surface accuracy by automatically changing the feed rate.

(Conventional technology and problems) FIG. 4 shows a processing block diagram of numerically controlled machining.

In the same figure, the programmer creates (tool movement route,
The part program 1σ (in which the tool feed speed, machining procedure, etc., machining conditions are specified) is subjected to automatic programming processing 20 to create an NC machining program 30. Created NC
The machining program 30 is inputted from the data input/output control section 42'' of the numerical control device 40', analyzed by the program analysis section 42', and converted into data that can be handled by the pulse distribution section 44 for each block. The amount of movement per sampling period for each axis, for example, the x, y, and z axes, is calculated from the servo controller for each axis, and a speed command pulse is given to the servo control unit for each axis, which is output as a speed command of the motor 50. When creating a part program for machining a complex curved surface in a mold, etc., for example, as shown in Figure 5, the programmer should program the feed rate to be low for areas with small curvature of the machined shape, and for areas with large curvature or The feed rate is programmed to be high for long straight shapes.This is because if a part with small curvature is machined at high speed, the machine will not be able to follow the commands from the numerical control device due to mechanical constraints, resulting in a decrease in machining accuracy. In a part program, the feed rate is usually specified using an F code, but it is recommended to select and specify an appropriate F code according to the machining shape of the workpiece when the machining shape is complex. This was an extremely time-consuming task, which placed a heavy burden on programmers.

(Object of the Invention) The present invention has been made to solve the above-mentioned problems, and is made by automatically determining the curvature of the tool path in the program analysis section of the numerical control device and determining the feed rate according to the curvature. The purpose of this invention is to provide a feed rate control method that reduces the burden on the programmer and contributes to improving machined surface accuracy.

(Summary of the Invention) The feed rate control method of the present invention uses commands - If the program block to be processed is a straight line, find the radius of a circle that passes through the three points of the movement start point and movement end point of the block and the block adjacent to the block (if an arc is commanded in the block, The present invention is characterized by comprising a first step in which the radius of the circle is determined as the radius, and a second step in which the feed rate of the tool is determined based on the radius of the determined circle.

(Basis of invention) A block diagram of a normal servo system is shown in FIG.

This block diagram can be simplified and approximated by the following first-order lag system.

here R(S) is input command X(S) is the output T is the time constant of the servo system S is Laplace transform operator It is.

When this servo system is given an arc command human power given by R(t) = R4Wl, the output Δ
R is given by ΔR=R−X(jW).

If the feed speed (circumferential speed) is tF, it is given by F = RW, so in order to keep the radius reduction amount ΔR within a certain error, it is necessary to control the free-form surface in the part program. It is approximated by a straight line or a series of circular arcs.Since the radius R is given for the part approximated by a circular arc, it is easy to calculate F using the formula.As shown in Figure 6, the curve is approximated by a straight line. In this case, in order to determine the feed rate using the formula 0, it is necessary to calculate the circular arc R from the data of the straight block. Using FIG. 7, three points p1 on the two-dimensional x-y plane. P2. p,
A method of calculating the radius R of an arc passing through is shown.

In the same figure If we set p, p, = t, it follows from the law of sine.

From now on, α=αl-α2 Substituting equations ■ and ■ into equation ■, linear command value (ΔX1+Δ)'
l), (Δx2+Δyzl), it is possible to calculate the approximate curvature 1< of the curve.

(Embodiment of the Invention) An embodiment of the present invention will be described below. FIG. 1 shows a processing block diagram of numerically controlled machining in which the feed rate control method of the present invention is implemented. In the figure, the same reference numerals are given to the parts in which the same processing as in the conventional processing block is performed.

In the part program 10, the allowable maximum feed rate FM is specified only once as feed rate data input.11 In the parameter setting section 41 of the numerical control machining 40, the allowable error ε and the time constant T are input using an input device such as a keyboard (not shown). be done. The program analysis section 43 includes a feed rate calculation section 4.
31 to calculate the feed rate corresponding to each program block. Fig. 2 shows the feed rate calculation section 43 in Fig. 1.
The details of the process in step 1 are shown in a flowchart. In ST10 in the same figure, it is determined whether a straight line or a circular arc is commanded in the Nth block, and if a circular arc is commanded, the radius corresponding to the Nth block is set as the radius R of the commanded circle. 5T21° When a straight line is commanded in the Nth block, the movement start point pN-1,F of the N-1st block is shown in Figure 3 for the Nth block.
and the movement start point PNP()'N-1 of the Nth block.
A) and the movement end point PNA(PN+l) of the Nth block
, Pl, the movement start point PNy (PN-5^) of the Nth block, the movement end point PNA (PN+1.F) of the Nth block, N + the movement end of the 1st block. There is a circular RNA that passes through three points.

In 5T21 and 5T22, the radius R is calculated using formulas ■, ■, and ■.
, and find the RNA. Compare the size of RNF and RNA with 5T3Q and find the smaller one as the radius 5T41 to 5T4
3゜For 5T5Q, calculate FC by the formula, and for 5T60, determine the size of FC and maximum feed rate)M, and when pc is smaller than FM, set the feed speed p @ pc for the Nth block, and 5T71゜FC is greater than FM. When the feed rate Fl is large, the allowable maximum feed rate ppa is 8T70. −.

(Effects of the Invention) As described above, according to the feed rate control method of the present invention, the feed rate automatically changes according to the curvature of the machined shape, so the programmer takes the feed rate into consideration when creating a part program. Since this is not necessary, it is possible to significantly shorten the program creation time.

Furthermore, since minute speed adjustments can be made according to the curvature, highly accurate machined surface accuracy can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a process diagram of numerical control machining in which the feed rate control method of the present invention is implemented. FIG. 2 is a detailed flowchart of the feed rate calculation process. FIG. 3 is a diagram for explaining the relationship between the command block and the radius of curvature. FIG. 4 is a conventional processing block diagram. Figure 6 is a block diagram of the servo system. FIG. 7 is a diagram showing an example of approximating a curved line with a straight line. FIG. S is a diagram for explaining a calculation formula for determining the radius of curvature.

Claims (1)

[Claims] When moving a machining tool based on an NC machining program created to approximate a curved surface with a straight line and a circular arc and process a workpiece into a predetermined shape, if the commanded program block is a straight line, the above block and the above block A first step in which the radius of a circle passing through the three points of the movement start point and movement end point of the block adjacent to is found (if an arc is commanded in the block, the radius of the commanded circle is the radius to be found); A feed rate control method comprising a second step of determining the feed rate of the tool based on the radius of the circle determined above.