RU2465116C2 - Nc lathe cutting stabiliser - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to real-time NC lathe ACS. Proposed stabiliser comprises odd controller to generate control signals in real time mode in response to current temperatures in cutting zone. Current temperatures in cutting zone are compared with calculated temperature values to re-calculate step motor turn angle.

EFFECT: compensated temperature variations.

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Description

The invention relates to the field of machine tools, in particular to systems for active control and accuracy control of machining of parts on precision turning equipment with CNC in real time. Since in the process of turning in the cutting zone the cutting tool and the part are heated, a temperature error appears as a result of this. The control of this value allows you to stabilize the cutting process in real time.

A control device for precision machining of parts on CNC equipment is known [RF Patent No. 2280540, class. B23B 25/06, 2006 (analog)].

The disadvantage of this device is the presence of the ADC used to convert analog to digital signal, which complicates its design.

Closest to the invention in technical essence is a thermal control device for precision machining of parts, containing a thermal imager with a digital code at the output, a computer, a signal amplification unit, actuators of CNC equipment, a cutter, a headstock and a tailstock, a part, and a lubricant cooling fluid [RF Patent No. 2381888, cl. B23Q 15/18, B23B 25/06, 2010 (prototype)].

The disadvantages of this device are the decrease in dynamic accuracy due to the speed of temperature changes in the cutting zone, that is, the device is configured for a certain response threshold, upon reaching which the actuators are switched on and moved by the temperature error, however, in reality, the temperature after reaching a certain threshold in the zone cutting can significantly increase or decrease, and the known device will only move by the value of a certain wound its errors, which reduces the accuracy of the device, another disadvantage is the presence of a feed mechanism in the cutting zone of cutting fluid, which complicates the design of the device.

A known method of controlling the mixing of hot and cold water [Patent No. JP 3110442, class. 7 G05D 23/13, 2000 (analogue)]. The disadvantage of this method is that the fuzzy controller that performs fuzzy logic operations has a long response time, which in some cases makes it impossible to use it to control high-speed processes, which include turning parts on CNC equipment.

Closest to the claimed technical solution is the method used for a fuzzy controller with linguistic feedback for process control [RF Patent No. 23039443, cl. G05B 13/02, G05B 11/01, 2007 (prototype)]. However, in the system of production rules (1) (p. 6, para. 40) in the fifth rule “If P≤P _nom , then B = B ₀ ”, it is indicated that P is less than or equal to P _nom , which means that for the fifth rule of the production system will be true two more expressions: P≤P _lower and P≤R ^d _lower . Therefore, the conclusion "then B = B ₀ " will have two more solutions: B = + 0.5B _max and B = + B _max , and this will undoubtedly cause a failure and / or loop in the algorithm, that is, the result of the fifth rule will produce wrong result.

An object of the invention is the stabilization of temperature errors that occur in the cutting zone when the cutter passes along the workpiece surface.

The problem is solved in that in a method of stabilizing the cutting process on CNC turning equipment, including determining the temperature in the cutting zone according to the formula

Θ = 166.5 · V ^0.4 · t ^0.105 · S ^0.2 ,

where V is the cutting speed; t is the depth of cut; S - feed

and comparing the result with the current value of the temperature in the cutting zone coming from the thermal imager with a digital output, if the current and calculated values of the temperature in the cutting zone do not match, the angle of rotation of the stepper motor is recalculated depending on fuzzy control rules

1. If "t≤t _{o_m} ", then "u≤u is _{strongly left} ";

2. If "t = t _m ", then "u = u _left ";

3. If "t = t _n ", then "u = u _n ";

4. If "t = t _b ", then "u = u _{to the right} ";

5. If “t≥t _{o_b} ”, to “u≥u _{strongly_right} ”

according to the formula

where u _{min ... max} - numerical values of the angle of rotation of the stepper motor in the cutting zone (from minimum to maximum value, that is, from -90 ° to + 90 °); µ '(u _{min ... max} ) - new values of the output value of the angle of rotation of the stepper motor in the form of new terms of membership functions.

A device for stabilizing the cutting process on CNC turning equipment includes a thermal imager with a digital output, a signal amplification unit, a tool holder, a front and rear headstock, a part characterized in that it is equipped with a stepping motor, a gear wheel, a link, a tailstock of the tailstock and rear guides headstock, which is a mechanism for converting rotational motion into translational, as well as a fuzzy controller containing a block for forming membership functions, a fuzzification block, a composition block II, the accumulation unit and the defuzzification unit, connected in series with each other, which allows real-time generation of control signals depending on the temperature change in the cutting zone and interact through the mechanism of converting rotational motion into translational motion on the tailstock tailstock to change it and the spatial arrangement details .

Figure 1 shows a diagram of a device for stabilizing the cutting process on CNC turning equipment.

The stabilization device of the cutting process on CNC turning equipment contains a thermal imager with digital output 1, a fuzzy controller 2, including an accessory function generation unit 3, a fuzzification unit 4, a composition unit 5, an accumulation unit 6, a defuzzification unit 7, a signal amplification unit 8, a stepper motor 9, a gear wheel 10, a link 11, a tailstock of a tailstock 12, guiding pins of a tailstock 13, a part 14, a headstock 15 and a tool holder 16.

The connections in the stabilization device of the cutting process on CNC turning equipment are arranged in the following order: the digital output of the thermal imager 1 is connected to the input of the fuzzification unit 4, to which the output of the accessory function formation unit 3 is also connected, which are included in the structure of the fuzzy controller 2. The output of the fuzzification unit 4 is connected with the input of the composition unit 5, the output of which is connected to the input of the accumulation unit 6. The output of the accumulation unit 6 is connected to the input of the dephasification unit 7. The output signal of the fuzzy controller 2 is the signal from the output of the defuzzification unit 7, which is connected to the input of the signal amplification unit 8. The output of the signal amplification unit 8 is connected to the input of the stepper motor 9, on the spindle of which the gear wheel 10 is fixed, the gear wheel 10 interacts with the input of the backstage 11, and the output of the backstage 11 acts on the tailstock tailstock 12, while the tailstock 12 moves along the guides of the tailstock 13. In this case, the part 14 is installed in the centers of the headstock 15 and the tailstock of the tailstock 12, and with the workpiece surface 14 odeystvuet reztsederzhatelny block 16. Using these connections the device to stabilize the cutting process on a lathe with CNC equipment in real time in order to increase the accuracy of machined surfaces detail.

Figure 2 shows the conversion of the rotational movement of the stepper motor 9 into the translational movement of the tailstock of the tailstock 12. In the case of rotation of the gear wheel 10 by -90 ° (position 1) with respect to the ordinate axis y ₁ , the tailstock of the tailstock 12 moves along the guides 13 by the value of w ₁ relative to its ordinate axis y ₂ . In the case of rotation of the gear wheel 10 by + 90 ° by a step electric motor 9 (position 2, indicated by a dotted line) relative to the ordinate axis y ₁ , the tailstock 12 pins move along the guides 13 by the amount of w ₂ relative to its ordinate axis y ₂ . The maximum movement along the x-axis x ₂ pintles of the tailstock 12 relative to the guides 13 is w = w ₁ + w ₂ . In this case, the displacement along the x-axis x ₂ must not exceed the runout value, so for CNC lathes with the largest workpiece diameter 400 mm, the runout should not exceed 0.02 mm, i.e. the displacement value is w = 0.02 mm, aw ₁ = w ₂ = 0.01 mm.

The stabilization process of cutting on turning equipment with CNC operates as follows. From the moment of turning on the rotation of the part 14 in the centers of the front 15 and the back of the rear 12 of the headstock of the CNC machine when the cutter of the tool holder 16 passes over its surface, the temperature in the cutting zone changes, causing inconsistent cutting forces and / or the axis and spindles of the front and rear headstock relative to the axis of the part. As a result, there is a decrease in the accuracy of the surface being machined, and barrel-like, saddle-like, or tapering of the part may appear.

The thermal imager with digital output 1 constantly monitors the temperature in the cutting zone. In this case, a digital signal of the current temperature value t from the imager 1 is fed to the input of the fuzzification unit 4, which is part of the structure of the fuzzy controller 2. In the fuzzy controller, depending on the current temperature value, according to the method described below, the control signal is recalculated - the angle of rotation of the stepper motor 9 , which is transmitted to the stepper motor 9 through the signal amplification unit 8. In this case, the pintles of the tailstock of the CNC machine move along the abscissa. A rotation of the stepper motor 9 by -90 ° moves the tailstock of the tailstock 12 to the left by 0.01 mm, and a rotation of the stepping motor 9 by + 90 ° moves the tailstock of the tailstock 12 to the right by 0.01 mm. For example, if the stepper motor 9 rotates the gear wheel 10 by -45 °, then the tailstock headstock will move to the left relative to the y-axis y ₂ by 0.005 mm. If the current temperature t is lower than the calculated one, the tailstock 12 should move to the left and shift the axis of the part 14 closer to the tool holder 16. If the current temperature t is higher than the calculated one, the tailstock 12 should move to the right and move the part 14 axis further from the tool holder 16. Therefore, in real time the stabilization of thermal processes in the cutting zone. Thus, automated stabilization of the cutting process is carried out during turning of parts on CNC equipment.

A method of stabilizing the cutting process on CNC turning equipment is as follows.

Before turning on CNC equipment for steel parts, as is known [p. 76, Handbook of a machine-building technologist. In 2 T.T.1. / Ed. A.G. Kosilova and R.K. Meshcheryakova. - 4th ed., Revised. and add. - M.: Engineering, 1986. 656 S.] is determined by the temperature in the cutting zone:

where V is the cutting speed; t is the depth of cut; S - feed.

In the block of forming the functions of accessories 3, which is part of the fuzzy controller 2, the functions of the accessories of the terms input (temperature - T) and output (rotation angle of the stepper motor - U) are formed:

where t _{min ... max} - numerical values of temperature in the cutting zone (from minimum to maximum value); µ (t _{min ... max} ) → [0, 1] - values of the membership function corresponding to the temperature values (from the interval from 0 to 1); u _{min ... max} - numerical values of the angle of rotation of the stepper motor in the cutting zone (from minimum to maximum value, that is, from -90 ° to + 90 °); µ (u _{min ... max} ) → [0, 1] - the values of the membership function corresponding to the angle of rotation (from the interval from 0 to 1).

The membership function of the input T and output U quantities consists of five terms. For the temperature T = (t _{o_m} , t _m , t _n , t _b , t _{o_ b} ), for the angle of rotation U = (u is _{strongly left} , u _left , u is _normal , u _right , u is _{strongly right} ). There are no fundamental restrictions on the number of terms of the input and output variables; in order to reduce the amount of computation, we restrict ourselves to five terms.

The fuzzification unit 4 from the accessory function generation unit 3 transfers the values of the membership functions and depending on the current temperature t received from the thermal imager 1, a fuzzified vector of values is generated for each term of the membership function t ', where the current temperature t is the argument µ (t _{min ... max} ), allowing us to find a quantitative value from the interval [0, 1] for t '= µ (t). The fuzzification stage is considered completed when the values of t 'are found for five terms of the membership function of the input quantity T:

In composition block 5, a system of fuzzy control rules is introduced, consisting of five rules and having the following form:

1. If "t≤t _{0_m} ", then "u≤u is _{strongly left} ";

2. If "t = t _m ", then "u = u to the _left ";

3. If "t = t _n ", then "u = u _n "; (four)

4. If "t = t _b ", then "u≤u _right ";

5. If "t≥t _{0_b} ", then "u≥u is _{strongly_right} ."

Moreover, the system of fuzzy control rules is constructed in such a way that at any moment the conditional part is true in only one fuzzy control rule and false in all other rules of this system. As a result of this, in each scan cycle of the system of fuzzy control rules, not the entire system is processed, but only that part of it that has in the formula (3) the values of the weight coefficients (t ' _{o_m} , t' _m , t ' _n , t' _b , t ' _{o_b} ) other than zero.

Also, in the composition block, each rule is assigned weighting factors: F = (f ₁ , f ₂ , f ₃ , f ₄ , f ₅ ). The numerical values of the weights are assigned by the expert. If they are not specified, then by default these coefficients are equal to unity, that is, f ₁ = f ₂ = f ₃ = f ₄ = f ₅ = 1.

Next, in the composition block 5, an algebraic product of the values of the fuzzified value vector is made for each term of the membership function t 'by the values of the corresponding weight coefficients F:

After that, the method of fuzzy composition according to the formula:

µ '(u _{min ... max} ) _{1 ... 5 =} min {a _{1 ... 5} , µ (u _{min ... max} )} (6)

new values of the output value of the angle of rotation of the stepper motor are calculated in the form of new terms of membership functions.

In accumulation block 6, a logical union of new terms of the membership function obtained by formula (6) is performed, and a fuzzy vector of membership functions U 'is formed:

In the defuzzification unit 7, the fuzzy vector of the accessory functions U 'is converted to a single clear value by the method of center of gravity:

where n is the number of fuzzy control rules.

Thus, the choice of a new value for the output parameter of the angle of rotation of the stepper motor to stabilize the cutting process during turning on CNC equipment is made according to formulas (1) - (8).

As an example, we will analyze the stabilization of the cutting process during the finishing pass during turning part 14 depending on the current temperature in the cutting zone t obtained from the thermal imager 1. Data for calculation: cutting speed V = 130 m / min; cutting depth t _p = 0.5 mm; feed 0.18 mm / rev.

Step 1. According to the formula (1), it is necessary to calculate the temperature in the cutting zone and transfer it to the accessory function formation block 3:

Θ = 166.5 · 130 ^0.4 · 0.5 ^0.105 · 0.18 ^0.2 = 768 ° С.

Step 2. In the block for forming accessory functions 3, we construct, according to formula (2), the terms of the accessory functions for input and output quantities. Graphs of accessory functions are shown in FIG. 3. Figure 3, a presents a graph for the input value - temperature. Moreover, the extreme points on the graph are equal: Θ ₁ = Θ-100 = 768-100 = 668, ° С; Θ ₂ = Θ + 100 = 768 + 100 = 868, ° С. The middle of the graph corresponds to the calculated temperature value according to the formula (1), i.e. 768 ° С. The terms t _{o_m} and t _{o_b are} presented in the form of a trapezoid and are equal to: t _{o_m} = [668, 668, 678, 728], t _{o_b} = [808, 858, 868, 868]. The terms t _m , t _n and t _{b are} presented in the form of triangles and are equal: t _m = [668, 718, 768], t _n = [718, 768, 818] and t _b = [768, 818, 868]. Data are in degrees Celsius.

Figure 3, b shows a graph for the output value - the angle of rotation of the stepper motor 9. In this case, the extreme points on the graph are equal to u ₁ = -90 °, u ₂ = + 90 °, that is, when the gear 10 rotates by these angles, the tailstock pintles will be: when the gear 10 rotates to the left by -90 °, the tailstock pins 12 will move along the guides 13 to the left by 10 microns; when the gear wheel 10 rotates to the right by + 90 °, the tailstock tailstock 12 will move along the guides 13 to the right by 10 μm. The middle of the graph corresponds to zero, that is, the spindle of the stepper motor 9 does not rotate clockwise or counterclockwise. The terms u are _{strongly left} and u are _{strongly right} represented in the form of a trapezoid and are equal to: u _{strongly_ left} = [- 90, -90, -85, -40], u _{strongly_right} = [40, 85, 90, 90]. The terms u _left , u _normal and u _{right are} represented as triangles and are respectively equal: u _left = [- 90, -45, 0], u _normal = [- 45, 0, 45] and u _right = [0, 45, 90]. Data shown in corners.

Step 3. The values of the accessories functions from block 3 are sent to the fuzzification unit 4. Also, the current temperature value in the cutting zone is transmitted in real time from the imager 1 to the fuzzification unit. Let thermal imager 1 determine that the temperature in the cutting zone is 708 ° С, this value is not equal to the calculated one, that is, 708 ≠ 768 ° С. Next, in the fuzzification unit 4, there is a fuzzified vector of values for each term of the membership function t '(Fig. 4):

,

,

,

,

)=(0,4;0,8;0;0;0).t '= (

,

,

,

,

) = (0.4; 0.8; 0; 0; 0).

The third, fourth and fifth terms have a zero result, therefore, they will not be used in further calculations. The resulting vector is transmitted to composition block 5.

Step 4. In the composition block 5, it is determined that the values of the first t ' _{о_м} and the second t' _m term of the vector t 'are nonzero, therefore, for the further fuzzy-logical conclusion, only the first and second fuzzy control rules defined by formula (4) will be considered :

1. If "t≤t _{o_m} ", then "u≤u is _{strongly left} ";

2. If "t = t _m ", then "u = u to the _left ."

Further, in the composition block 5, according to formula (5), an algebraic product of the values of the fuzzified value vector for each term of the membership function t 'is produced by the values of the corresponding weight coefficients F. Let all the weight coefficients be 1, then:

A = (a ₁ , a ₂ ) = (0.4 · 1; 0.8 · 1) = (0.4; 0.8).

Then, using the formula (6), using the fuzzy composition method, new values of the output value of the angle of rotation of the stepper motor 9 are calculated in the form of new terms of membership functions. Figure 5, a shows the new term µ '(u _{min ... max} ) ₁ , corresponding to the term u _{strongly_left} . Figure 5, b shows the new term µ '(u _{min ... max} ) ₂ , corresponding to the term u to the _left .

Step 5. In the accumulation block 6 according to the formula (7), two new terms of the membership function obtained by the formula (6) are logically combined and a fuzzy vector of membership functions U 'is formed. The result of the operation is graphically shown in Fig.6.

Step 6. In the defuzzification block 7 according to formula (8), the vector of accessory functions U 'is converted to a single clear value (Fig. 7), in order to simplify the computational procedure for calculation, we restrict ourselves to four points, for a more accurate calculation, the number of points must be increased:

.

.

The rotation of the gear wheel 10 by a step electric motor 9 by -57 ° will cause the quill of the tailstock 12 to move to the left along the guides 13 relative to the zero line y ₂ (figure 2) by 0.0063 mm.

Thus, using the proposed method, the rotation angle of the stepper motor is calculated in order to stabilize the cutting process and transfer it to the actuators of the CNC equipment.

Thus, the proposed method and the device implemented on it allow real-time stabilization of the cutting process when turning the part on CNC equipment in real time by calculating the angle of rotation by which the gear wheel must be rotated with the help of a stepper motor in order to offset the pins tailstock of the CNC machine.

Claims (1)

A device for stabilizing the cutting process on CNC turning equipment containing a thermal imager with a digital output, a signal amplification unit and a tool holder, characterized in that it is equipped with a stepper motor, a gear wheel, a link, a tailstock quill and tailstock guides, which are a transformation mechanism rotational motion in translational, as well as a fuzzy controller containing a block for forming membership functions, a fuzzification block, a composition block, an accumulation block, and a block for fuzzification connected in series with each other, while the digital output of the thermal imager is connected to the input of the fuzzification unit, to which the output of the unit for forming the functions of accessories belonging to the fuzzy controller is also connected, the output of the fuzzification unit is connected to the input of the composition block, the output of which is connected to the input of the accumulation unit, and its output is connected to the input of the defazzification unit, while the output signal of the fuzzy controller is the signal from the output of the defuzzification unit, which is connected to the input at the signal amplification unit, its output is connected to the input of a stepper motor, on the spindle of which the gear wheel is rigidly fixed, with the possibility of interaction with the input of the scenes, and its output is made with the possibility of influencing the tailstock tailstock.

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