RU2108900C1 - Controller for number program controlled machine tools - Google Patents

Abstract

FIELD: optimization of working process by means of number program control machine tools. SUBSTANCE: controller for optimization of metal working by means of number program control machine tools includes unit 14 for monitoring torque of main drive mechanism of machine tool and determining real instantaneous value of cutting torque; unit 16 for setting cutting torque value determined at self-teaching process; unit 20 for calculating feed rate necessary for maintaining constant value of cutting torque and for controlling feed mechanism of said machine tool; unit 18 for generating values of feed rate preventing breakage according to displayed values of torque of main drive mechanism. Unit 20 for calculating feed rate receives data from compensator 30 and identifying unit 22. Compensator 30 receives signals from unit 24 comparing set value of torque with its real instantaneous value displayed by unit 14. Unit 22 calculates instantaneous value of cross section area of cutting zone. EFFECT: improved structure of units. 10 cl, 5 dwg

Description

 The invention relates to controllers and methods for optimizing CNC machine tools, in particular CNC milling machines and machining centers.

 Despite the fact that CNC machines have existed for many years, their effectiveness and usefulness are limited by the inability to take into account at the programming stage many factors that affect production efficiency, including the number of machined parts, processing cost, tool change time, tool cost, etc. . In addition, a rigidly determined programming technique for CNC machines makes it impossible to take into account real-time unexpected changes during part processing, such as depth and width of metal cutting, tool wear, heterogeneity of the workpiece, etc.

 Developments in the field of CNC machines have led to the appearance of devices for controlling the machine as a function of the load torque on the cutting tool, if the load torque exceeds or falls below a predetermined upper or lower critical value, respectively. For example, in [1] critical load moments are described, including, inter alia, the limiting moment catastrophic with respect to the design of the machine tool, the limiting moment catastrophic with respect to the tool, and also the minimum limiting moment that must exist when the cutting tool contacts the workpiece.

 One of the objectives of the invention is to overcome the limitations and disadvantages of known CNC machines and the creation of an optimizing controller for machines, in particular for CNC milling machines and machining centers, which calculates optimal cutting conditions based on performance criteria and automatically provides adjustable control of the feed speed and spindle speed depending on the cutting conditions in real time, maintaining a constant and set value of the spindle torque A and / or tool life, guaranteeing optimal operating modes of the machine, prevents tool breakage and displays information about the status of the instrument.

 In accordance with the invention, this goal is achieved by creating a controller for optimizing metal processing on CNC machines containing a main drive transmitting power to the machine spindle and feed drives transmitting power to the machine feed mechanisms, the feed drives being made controlled so as to ensure feed rate, determined both by a predetermined value of the cutting moment occurring on the spindle of the cutting tool, and by means of the said controller, specifying new values of the moment of cutting I, instead of the previously installed in the teaching mode of said controller. The controller includes a first unit for monitoring the torque of the main drive of the machine for determining the actual, instantaneous value of the cutting moment, a second unit for setting the value of the cutting moment found in the said self-learning mode depending on the monitored value of the said moment of the main drive, the third unit for calculating the speed feed required to maintain the value of the mentioned moment at a constant level and to control the feed drive of the machine, the fourth block responding to monitoring the measured values of the moment of the main drive and generating signals for limiting the feed rate for said third unit to protect the tool from breakage, characterized in that the said unit for calculating the feed rate receives information from the compensator unit, which, on the one hand, responds to signals from the comparator unit comparing the set the value of the torque with its actual, instantaneous value, monitored by the first block and, on the other hand, by the signals from the first moment monitoring unit a drive unit and by calculating a feed rate, said compensator unit contributes to the stabilization of said torque with high accuracy.

 The invention additionally provides a method for optimizing metal processing on CNC machines containing a main drive transmitting power to the machine spindle, and feed drives transmitting power to the machine feed mechanisms, the feed drives being made controlled so as to provide a feed speed determined by a predetermined moment value cutting occurring on the cutting tool spindle, or defined by the mentioned controller, setting new values of the cutting moment instead of previously set in the self-mode cheniya said controller.

 The method includes the following operations: monitoring the torque of the main drive of the machine to determine the actual, instantaneous value of the cutting moment, setting the value of the cutting moment found in the self-learning mode depending on the monitored value of the moment of the main drive, calculating using the unit for calculating the feed rate required to save the value the mentioned moment at a constant level and for controlling the feed drive of the machine, the formation of feed rate limiting signals for the third block is calculated a feed rate to protect the tool from breakage; comparing the set torque value in the comparator unit with its actual instantaneous value; calculating in the identification unit the instantaneous value of the cross-sectional area of the cutting zone based on the signals generated by the monitoring unit and the feed rate calculation unit, as a result of which high-precision stabilization of the cutting moment is achieved.

 In FIG. 1 is a block diagram of a first embodiment of a controller according to the invention; in FIG. 2 is a graph illustrating an effect in a compensation unit for feed rate and torque values; in FIG. 3 is a block diagram of a second embodiment of a controller; in FIG. 4 and 5 depict respectively the third and fourth embodiments of the controller.

 The main input parameters in the first and second versions of the controller according to the invention are one or more parameters of the main drive proportional to the cutting moment M. The main output parameter is a signal that determines the feedrate F as a function of M, and the problem solved by the invention is to maintain the value of this torque at a constant level, determined depending on the properties of the specific milling cutters used. The required values can be found in the respective tables.

резания путем обработки одной или нескольких идентичных деталей. Режим самообучения является особенно эффективным для обработки больших партий идентичных деталей.Another concept embodied in the invention is the presence of a controller self-learning mode, in which, instead of the maximum set value of the cutting moment M ₀ , the maximum moment value is determined

cutting by machining one or more identical parts. Self-learning mode is especially effective for processing large batches of identical parts.

Another important parameter used by the controller and designated as ρ [mm ² ] is the cross-sectional area of the cutting zone (cutting zone), which is a product of the width b and the cutting depth h.

The controller (Fig. 1) comprises a housing 2 configured to be mounted on a CNC machine and with the possibility of arranging various controller units in this housing, and a panel 4 arranged for operator access to it. On panel 4 there is a switch 6 for selecting the operating mode: "Self-learning mode (TM)"("withTM");"Start" for working with the value M ₀ found in the self-learning mode and for working with the preset value M ₀ ("Without TM"). In the latter mode, the value of M _{0 is} set using the selector 8. Other elements on the panel 4 contain a start button 10 and an indicator 12 of the status of the tool, providing light or sound signaling if the wear of the cutting tool exceeds the set limit.

 In FIG. 1 shows a block 14 of a monitor displaying the current value of the cutting moment (applied to the cutter).

The signal M from the block 14 of the monitor is transmitted to the following blocks of the controller:
a) block 16 for setting the approximate value of the cutting moment M ₀ for operation in self-learning mode;
b) a cutting tool protection unit 18 transmitting a value limiting signal to a feed rate calculator 20;
c) block 22 for identifying the current value of ρ, a signal is also transmitted to it from the feed rate calculator 20, and
d) a comparator unit 24 comparing the set value of the cutting moment M ₀ with the actual instantaneous value M.

According to the position of the mode switch 6, the logic element 26 transmits the value M ₀ to the comparator 24, also determined by the block 16 or the manual setting selector 8.

 The controller also includes a self-diagnosis unit 28 located between the start button 10 on the panel 4, and a feed rate calculator 20. When the button 10 is pressed, block 28 performs testing of the system as a whole and, if the controller is ready for operation based on the test results, an enable signal is sent to calculator 20.

 The central part of the controller is formed by the compensator unit 30 in conjunction with the aforementioned unit 22 of the parameter identifier ρ.

 The following is a description of the principle of compensation.

и фактическим значением M.The feed rate is determined based on the difference ΔM between the set value m ₀ or

and the actual value of M.

The metal cutting process (as a static process) can be represented by the following expression:
M = A • F ^Y • ρ ^γ,,
Where
ρ is the aforementioned value of the area of the cutting zone;
F is the feed rate;
A, Y, γ - coefficients depending on the type of tool and cutting conditions of the metal.

,
где
K_с - коэффициент усиления ЧПУ (статический);
K₁ текущее значение коэффициента усиления монитора.Considering ΔM as a stabilization error of the cutting moment, it can be defined as

,
Where
K _with - CNC gain (static);
K ₁ current monitor gain.

However, in real work, ρ ≪ 1 / K ₁ K _with A ₀ , as a result of which ΔM ≈ M ₀ , or M ≈ 0, which makes it impossible to achieve stabilization of the cutting moment at medium and small values of ρ.

,
где
B - константа.To ensure the independence of the value of M from changes in ρ, it is necessary to enter the gain K _K

,
Where
B is a constant.

Thus, to calculate K _K, it is necessary to determine ρ at each moment of the cutting process, which is performed by block 22 based on the assumption that the quantity ρ is proportional to the expression ΔM / F ^α , where α is the value determined for each type of processed material.

The action of the compensator unit is shown in FIG. 2, where the solid curves 32 and 34 display the values of F and M / M ₀ as functions of ρ (specifically, as a function of the cutting height h) with compensation, and the dashed curves 36 and 38 display the same values of F and M / M ₀ without compensation.

 Obviously, the feed rate of the machine is controlled by the output value F of the feed rate calculator 20.

In FIG. 3 shows another embodiment of the controller. This option differs from the previous one in that the controller is not accessible to the operator, and only works from the program. In this embodiment, the following elements are added - the program interface 40 for communication between the controller and the program and the storage unit 42 for the set moment value M ₀ for a number of different tools N (as indicated by MN ₃ - MN ₂₅ ) for use in cutting operations, with MN ₀ and MN ₁ , indicating the choice of self-learning mode, and MN ₂ - without a self-learning mode. The remaining blocks are identical to the blocks of the previous embodiment and work in a similar way.

The embodiment depicted in the block diagram of FIG. 4, is designed to optimize the operation of the machine based on any one of two criteria:
1) the maximum removal of metal per unit time (mm ² / min);
2) the minimum cost of removal of a unit volume of metal ($ / min).

 It is possible to compromise between these criteria.

 The embodiment of FIG. 4 contains all the blocks described in connection with the description of FIG. 1 and 3 (except for panel 4 and its elements), as well as some additional blocks, which will be described below.

,
где
A₃ - коэффициент, зависящий от конкретного применяемого инструмента;
α₃, α₄, α₅- - коэффициенты, зависящие от обрабатываемого материала;
ρ - площадь зоны резания, величина передается от блока 22 идентификатора;
F - скорость подачи;
T₀ - время межсервисной работы инструмента, требуемое для выбранных критериев оптимизации.While the first criterion is affected by the circuit "F" contained in blocks 20, 22, 24, and 30 (Figs. 1 and 3), and it is due to the equality M = M ₀ , the second criterion requires the input of an additional block 44, forming the working part of the contour "S" of the speed control (S) of the machine spindle. This block consists of a calculator 44 that implements the expression

,
Where
A ₃ - coefficient depending on the specific tool used;
α ₃ , α ₄ , α ₅ - - coefficients depending on the processed material;
ρ is the area of the cutting zone, the value is transmitted from the block 22 of the identifier;
F is the feed rate;
T ₀ - tool service time required for the selected optimization criteria.

Второй критерий обусловлен соотношением

,
где
m - коэффициент, зависящий от типа применяемого инструмента и обрабатываемого материала;
τ - вспомогательное время или время простоя, мин;
D - стоимость инструмента ($);
B - стоимость одной минуты обработки на станке ($/мин).The first criterion is due to the following relation

The second criterion is due to the relation

,
Where
m is a coefficient depending on the type of tool used and the material being processed;
τ - auxiliary time or downtime, min;
D - instrument value ($);
B - the cost of one minute of processing on the machine ($ / min).

Calculator 44 has five input parameters:
a) coefficients A ₃ for tool types N3-N25 (from memory block 46, addressed from input MN ₃ to MN ₂₅ );
b) coefficients α ₃ , α ₄ , α ₅ from four different groups of materials (from block 48 of the memory, addressed from input MN ₂₆ - MN ₂₈ );
c) signal F (from block 20 of the calculator);
d) cutting area ρ (from identifier block 22);
e) the estimated service life of the tool T ₀ (from the calculation unit T ₀ ).

Input MN ₀ initiates self-learning mode, and input MN ₁ performs self-learning mode for all tool diameters.

 The controller output parameters in this embodiment are the same as in the previous embodiment (tool status and feedrate control signal F), with the addition of a speed control signal S.

 The embodiment of FIG. 5 has all the functional blocks described in the previous three versions, with the addition of two additional blocks, namely, the vibration reduction and rattling contour of the machine, and the finish processing circuit for high-precision machining of thin-walled sections of workpieces.

 The first block contains a vibration analyzer 50, which receives a signal from the transducer 51 of any suitable type, which responds to vibration and rattle of the machine. The output signal of the converter 51 is analyzed by a block 50, which generates a signal supplied to the calculator 20, which in turn changes the feed rate F to the level required to suppress vibration, while restoring the original value of the feed rate after vibration suppression.

 The problem of thin-walled sections is their elastic deformation from the impact of the cutter pressure during processing. So, milling an aluminum wall with a thickness of, for example, 2.5 mm and a length of 200 mm, with a cutting depth of 0.5 mm at a feed speed of 500 mm / min, with a cutter speed of 1000 rpm and its diameter of 12 mm will give an error in 0.04 mm, while milling a section with a thickness of 10 mm with the same values of cutting depth, feed speed, rotational speed and mill diameter will give an error of only 0.005 mm. This difference, of course, is due to elastic deformation with subsequent "springing back" of the thin wall and leads to the need to reduce the feed rate when the cutter reaches such thin-walled sections.

 This not only complicates the machine control program, but also makes it difficult to determine the point after the thick-walled section at which the section with thin walls actually begins. In addition, a worn cutter will cause large deforming forces, while a new cutter will cause much lower values.

 The objective of the invention is to automatically reduce the feed rate at the moment when a thin-walled section is detected.

 It was found that certain harmonics of the feed drive current decrease during milling of thin walls due to changes in the frequency characteristics of the electromechanical circuit, of which a thin-walled section is a part. So, based on the variance analysis of the feed drive current signals, special signals can be generated that inform about the actual beginning and end of the thin-walled section. These signals are used to reduce the feed rate during processing of such a thin-walled section, thereby increasing the accuracy of processing.

 The additional circuit available in the embodiment of FIG. 5, contains a corresponding sensor 52, which responds to the feed drive current and transmits a signal to the analyzer 54 for analyzing the harmonics of the feed drive current, the analyzer transmits a signal to the converter 56, which creates a signal that, when transmitted to the feed rate calculator 20, changes its output signal , reducing the feed rate at the moment when the sensor 52 and the analyzer 54 signal the actual beginning of the thin-walled section, and restores the previous value of the feed speed when the sensor 52 and the analyzer 54 signal about konchaniya this portion.

 The embodiment of FIG. 3 is particularly well suited for CNC machining centers using a pre-programmed sequence of various tools and is more efficient than the previous version, especially due to availability, as shown in FIG. 3, a storage unit 42 eliminating the need for a controller reboot each time a tool is changed.

 The invention is not limited to the details of the above options and can be performed in other forms than those described without departing from its essence. The presented embodiments in this way should be considered in all cases as illustrative and not as restrictive, while the scope of the invention is indicated by the attached claims and not by the above description, and all changes that are made within the meaning and range of equivalence of the claims are thus covered the claims.

Claims (10)

1. The method of adaptive control of the feed rate F of the cutter relative to the workpiece in a machine having a main drive, including the operation of monitoring the actual cutting torque M on the main drive, calculating the difference in moments ΔM by the formula
ΔM = M ₀ -M,
where M ₀ - a predetermined reference moment of cutting on the main drive, installed for the cutter and the workpiece material,
determining and establishing the feed rate as a function of the difference in moments ΔM, characterized in that the operation of determining the feed rate F as a function of ΔM includes calculating the instantaneous value of the cross-sectional area of the cutting zone and determining the feed rate F as a function of ρ to stabilize the moment M so that ΔM tends to zero. 2. The method according to claim 1, characterized in that the calculation of the instantaneous value of the area ρ of the cross section of the cutting zone is made from the ratio
M = A • F ^y • ρ ^γ ,
where A, y, γ are coefficients depending on the cutter and the workpiece material. 3. The method according to claim 1 or 2, characterized in that it additionally carry out the operation of adaptive control of the rotational speed of the cutter to achieve the desired specified period T ₀ tool service.  4. The method according to any one of claims 1 to 3, characterized in that it additionally carries out the operations of measuring the vibrations of the cutter, comparing the indicated vibrations with a predetermined value, changing the feed rate to suppress said vibrations to values below a predetermined one and restoring the feed rate to the original value after vibration reduction below the set value.  5. The method according to any one of claims 1 to 4, characterized in that it additionally performs operations of measuring the feed drive current of the cutter, analyzing the feed drive current for the presence of harmonics indicating the beginning of processing of a thin-walled section, and when these harmonics are detected, reduce the feed rate for a significant suppression of the specified harmonics. 6. Device adaptive control of the feed speed F of the cutter relative to the workpiece in a machine with a main drive, including a monitor for displaying the actual cutting moment M on the main drive, a torque comparator for calculating the moment difference by the formula
ΔM = M ₀ -M,
where M ₀ - a predetermined reference moment of cutting on the main drive, installed for the cutter and the workpiece material,
as well as a feed rate regulator F as a function of the difference of moments ΔM, characterized in that the speed controller is designed to calculate the instantaneous value of the cross-sectional area ρ of the cutting zone and determine the feed rate F as a function of ρ to stabilize the moment M so that the difference of moments ΔΜ tends to zero. 7. The device according to claim 6, characterized in that said speed controller calculates the indicated instantaneous value of the cross-sectional area ρ of the cutting zone from the ratio
M = A • F ^y • ρ ^γ ,
where Α, y, γ are coefficients depending on the cutter and the workpiece material. 8. The device according to claim 6 or 7, characterized in that it comprises a spindle rotation speed regulator designed to adaptively control the rotational speed of the cutter to achieve the required predetermined tool life T ₀ .  9. The device according to any one of paragraphs.6 to 8, characterized in that it contains a vibration suppression unit, designed to minimize the vibration of the cutter below a predetermined level.  10. The device according to any one of paragraphs.6 to 9, characterized in that it comprises a feed drive current analyzer to reduce the feed rate during processing of a thin-walled part of the workpiece.

Images