RU2465115C2 - Nc lathe cutting speed control device - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to high-tolerance machine tools, particularly, to computer-aided NC lathes operated in real time. Proposed device comprises fuzzy controller to generate control signals in real time mode in response to cutting force change in cutting zone and machined part diameter.

EFFECT: stabilised, cutting force, higher precision.

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Description

The invention relates to the field of high-precision machine tools, and in particular to automated control systems for CNC turning equipment in real time. That is, during the turning of parts on CNC equipment under the influence of various random factors, for example, under the influence of temperature deformations, the cutting tool lengthens, which leads to fluctuations in cutting forces, and as a result of the displacement of the axes of the spindles of the front and rear headstock relative to the axis of the part, barrel, saddle, or taper of the part. Management of these errors will allow in real time to stabilize the process of processing parts on CNC turning equipment.

A control device for high-precision machining of parts on CNC equipment is known [RF Patent No. 2309034, class. B23Q 11/02, 2007 (analog)].

The disadvantage of this device is that with the help of a cutting force sensor, only the point in time is recorded when the effective value of the cutting force exceeds the permissible value. In order to respond to fluctuations in the cutting force (to maintain a constant value of the cutting force), feedback is necessary, which will allow, by recalculating the parameters of the cutting mode, to ensure the constancy of the cutting force and thereby increase the accuracy of the machined parts.

Closest to the invention in technical essence is a control device for precision machining of parts containing a part, a cutter, a tool holder, a force gauge, actuators of CNC equipment [RF Patent No. 2379169, cl. B23Q 15/00, 2010 (prototype)].

The disadvantage of this device is the decrease in the accuracy of surface treatment of parts due to the lack of control of fluctuations in the diameter size along the machined surface of the part, another disadvantage is the complex design of the device.

A known method for determining the optimal cutting speed [RF Patent No. 2374038, class. B23B 1/00, 2009 (analogue)]. The disadvantage of this method is that to determine the optimal cutting speed, preliminary heating of the carbide tool is necessary, in which the endothermic effect is most manifested in its structure, which increases the time it takes for the CNC equipment to process the workpieces.

Closest to the claimed technical solution is the method used for a fuzzy controller with linguistic feedback for process control [RF Patent No. 2309443, cl. G05B 13/02, G05B 11/01, 2007 (prototype)]. However, the disadvantage of this method is that only one parameter, for example, cutting force, can be used as an input quantity. Which reduces the functionality of this method.

An object of the invention is to stabilize the cutting force and / or diameter fluctuations along the workpiece surface as a result of disturbing effects on the workpiece in the cutting zone.

The problem is solved in that in the method of controlling the cutting speed on CNC turning equipment, including determining the value of the cutting force

P = 10C _p · V ⁿ · S ^y · t ^x · K _p ,

where C _p is the overall coefficient, depending on the type of material being processed, on the type of processing, tool material and other general parameters; t, S, V - cutting mode parameters: depth, feed and cutting speed, respectively; x, y, n - exponents with the parameters of the cutting conditions; To _p - correction factor;

and diameter of the workpiece

where n is the speed of rotation of the part;

and comparing the results with the current value of the cutting force coming from the force gauge and the diameter of the workpiece obtained from the optical sensor, if the current and calculated values of the cutting force and the diameter of the workpiece do not match, the cutting force is recalculated depending on fuzzy control rules

1. If "p = p ₁ " AND "d = d ₁ " To "v = v ₉ ";

2. If "p = p ₁ " AND "d = d ₂ " To "v = v ₈ ";

3. If “p = p ₁ ” and “d = d ₃ ” then “v = v ₇ ”;

4. If "p = p ₁ " AND "d = d ₄ " Then "v = v ₆ ";

5. If "p = p ₁ " AND "d = d ₅ " Then "v = v ₅ ";

6. If "p = p ₂ " AND "d = d ₁ " To "v = v ₈ ";

7. If "p = p ₂ " AND "d = d ₂ " To "v = v ₇ ";

8. If "p = p ₂ " AND "d = d ₃ " Then "v = v ₆ ";

9. If "p = p ₂ " AND "d = d ₄ " Then "v = v ₅ ";

10. If "p = p ₂ " AND "d = d ₅ " To "v = v ₄ ";

11. If "p = p ₃ " AND "d = d ₁ " To "v = v ₇ ";

12. If "p = p ₃ " AND "d = d ₂ " To "v = v ₆ ";

13. If “p = p ₃ ” AND “d = d ₃ ” To “v = v ₅ ”;

14. If “p = p ₃ ” AND “d = d ₄ ” To “v = v ₄ ”;

15. If "p = p ₃ " AND "d = d ₅ " To "v = v ₃ ";

16. If "p = p ₄ " AND "d = d ₁ " To "v = v ₆ ";

17. If "p = p ₄ " And "d = d ₂ " To "v = v ₅ ";

18. If "p = p ₄ " And "d = d ₃ " Then "v = v ₄ ";

19. If "p = p ₄ " And "d = d ₄ " To "v = v ₃ ";

20. If "p = p ₄ " And "d = d ₅ " To "v = v ₂ ";

21. If "p = p ₅ " AND "d = d ₁ " To "v = v ₅ ";

22. If “p = p ₅ ” and “d = d ₂ ” then “v = v ₄ ”;

23. If “p = p ₅ ” AND “d = d ₃ ” To “v = v ₃ ”;

24. If “p = p ₅ ” AND “d = d ₄ ” To “v = v ₂ ”;

25. If "p = p ₅ " AND "d = d ₅ " To "v = v ₁ ",

according to the formula

where v _{1 ... 9} are the numerical values of the cutting speed (from minimum to maximum value); µ '(v) _{1 ... 9} - new values of the output value of the cutting speed in the form of new terms of membership functions.

A device for controlling the cutting speed on CNC turning equipment contains a part, a cutter, a tool holder, a force gauge, actuators for CNC equipment, characterized in that it is equipped with an optical sensor, front and rear headstock and a fuzzy controller containing an accessory function generation unit, a unit fuzzification, aggregation unit, composition unit, accumulation unit and defuzzification unit, connected in series with each other, allowing real-time control s signals depending on changes in cutting force and the diameter of the workpiece and to interact by means of actuators for changing speed of cutting in order to increase the accuracy of machined surfaces.

Figure 1 shows a diagram of a device for controlling the cutting speed on CNC turning equipment.

The cutting speed control device on CNC turning equipment contains a part 1, a cutter 2, a retaining block 3, a gravity sensor 4, a front headstock 5, a tail head 6, an optical sensor 7, a fuzzy controller 8, including an accessory function generation unit 9, an fuzzification unit 10 , aggregation block 11, composition block 12, accumulation block 13, defazzification block 14; signal amplification unit 15 and actuators 16.

The connections in the cutting speed control device on CNC turning equipment are arranged in the following order: the workpiece 1 is installed in the centers of the front 5 and rear 6 headstock. Cutter 2 and a gravity sensor 4 are installed on the tool holder 3, the output of which is connected to the first input of the fuzzification unit 10, an optical sensor 7 is connected to the second input of the fuzzification unit 10, the third input of the fuzzification unit 10 is connected to the output of the accessory function formation unit 9. The output of the unit fuzzification 10 is connected to the input of the aggregation block 11, the output of which is connected to the input of the composition block 12. The output of the composition block 12 is connected to the input of the accumulation block 13, the output of which is connected to the input of the diffusion block 14. The output signal of the fuzzy controller 8 is the signal from the output of the defuzzification unit 14, which is connected to the input of the signal amplification unit 15. The output of the signal amplification unit 15 is connected to the input of the actuators 16. Using these connections in the device will allow you to control the cutting speed on turning equipment with CNC when processing parts in real time in order to improve the accuracy of the machined surfaces.

The control device cutting speed on a turning equipment with CNC operates as follows. From the moment of turning on the rotation of part 1 in the centers of the front 5 and rear 6 of the headstock of the CNC machine when passing the cutter 2 installed in the tool holder 3, the cutting tool lengthens along its surface under the influence of temperature deformations, which leads to fluctuation of the cutting forces, and as a result displacements of the axles of the spindles of the front and rear headstock relative to the axis of the part may appear barrel-shaped, saddle-shaped or taper of the part. As a result, there is a decrease in the accuracy of the workpiece surface.

The load cell sensor 4 constantly monitors the value of the cutting force in the cutting zone. In this case, the signal of the current value of the cutting force p from the load cell sensor 4 is fed to the first input of the fuzzification unit 10 included in the structure of the fuzzy controller 8. The optical sensor 7 constantly monitors the diameter value of the workpiece in the cutting zone. In this case, the signal of the current value of the diameter d from the optical sensor 7 is fed to the second input of the fuzzification unit 10.

In the fuzzy controller 8, depending on the current value of the cutting force and the diameter of the workpiece, according to the method described below, the control signal is re-calculated - the cutting speed, which is transmitted through the signal amplification block 15 to the actuators 16 in order to change the cutting speed of the cutting tool 2. When this is the movement of the tool holder 3 along the machined surface of the part 1. If the current values of the cutting force p and the diameter of the machined surface d of the part are less than the calculated, 2 of the cutter must be moved with high speed cutting, otherwise the cutter 2 will move with a lower cut rate. Therefore, in real time, the cutting speed is controlled. Thus, automated control of the cutting speed is carried out during turning of parts on CNC equipment.

The method of controlling the cutting speed on CNC turning equipment is as follows.

Before turning on CNC equipment for parts, as you know [p. 271, Handbook of a machine-building engineer. In 2 vols. T.2 / Ed. A.G. Kosilova and R.K. Meshcheryakova. - 4th ed., Revised. and add. - M.: Engineering, 1985, 496 p.], The cutting force will be determined:

where C _p is the overall coefficient, depending on the type of material being processed, on the type of processing, tool material and other general parameters; t, S, V - cutting mode parameters: depth, feed and cutting speed, respectively; x, y, n - exponents with the parameters of the cutting conditions; To _p - correction factor.

And also, as you know [p. 280, Handbook of a technologist-machine builder. In 2 vols. T.2 / Ed. A.G. Kosilova and R.K. Meshcheryakova. - 4th ed., Revised. and additional.- M.: Mechanical Engineering, 1985, 496 p.], the diameter of the workpiece

where n is the speed of rotation of the part.

In the block of forming the functions of accessories 9, which is part of the fuzzy controller 8, the functions of accessories of the terms of the input variables are formed: cutting force - P; diameter - D, as well as the output variable: cutting speed - U:

where p is the numerical value of the cutting force; µ (p) → [0, 1] - values of the membership function corresponding to the values of the cutting force (from the interval from 0 to 1); d - numerical values of the diameter of the workpiece; µ (d) → [0, 1] - values of the membership function corresponding to the values of the diameter of the workpiece (from the interval from 0 to 1); v - numerical values of the cutting speed; µ (v) → [0, 1] - values of the membership function corresponding to the cutting speed (from the interval from 0 to 1).

The membership functions of the input variables P and D consist of five terms. For the cutting force P = (p ₁ , p ₂ , p ₃ , p ₄ , p ₅ ), for the diameter D = (d ₁ , d ₂ , d ₃ , d ₄ , d ₅ ). The membership function for the output variable V consists of nine terms - the cutting speed V = (v ₁ , v ₂ , v ₃ , v ₄ , v ₅ , v ₆ , v ₇ , v ₈ , v ₉ ).

The fuzzification unit 10 from the accessory function generation unit 9 transfers the values of the accessories functions and depending on the current value of the cutting force p received from the load cell sensor 4 and the diameter of the workpiece d received from the optical sensor 7, a fuzzified vector of values is generated for each function term belonging p 'and d', where the current value of the cutting force p is the argument µ (p), and the current value of the diameter of the workpiece d is the argument µ (d), allowing you to find value from the interval [0, 1] for p '= µ (p) and d' = µ (d). The fuzzification stage is considered completed when the values of p 'and d' are found for five terms of membership functions of the input quantities P and B:

Data from the fuzzification unit 10 is transferred to the aggregation unit 11 in which, using the fuzzy logic operation "AND", the minimum value is selected from the terms of the input variables:

Where

In the composition block 12, a system of fuzzy control rules is introduced, consisting of 25 fuzzy control rules and having the following form:

1. If "p = p ₁ " and "d = d ₁ " then "v = v ₉ ";

2. If "p = p ₁ " AND "d = d ₂ " To "v = v ₈ ";

3. If “p = p ₁ ” and “d = d ₃ ” then “v = v ₇ ”;

4. If "p = p ₁ " And "d = d ₄ " To "v = v ₆ ";

5. If "p = p ₁ " AND "d = d ₅ " To "v = v ₅ ";

6. If "p = p ₂ " AND "d = d ₁ " To "v = v ₈ ";

7. If "p = p ₂ " AND "d = d ₂ " To "v = v ₇ ";

8. If "p = p ₂ " AND "d = d ₃ " To "v = v ₆ ";

9. If "p = p ₂ " AND "d = d ₄ " To "v = v ₅ ";

10. If "p = p ₂ " AND "d = d ₅ " To "v = v ₄ ";

11. If "p = p ₃ " AND "d = d ₁ " To "v = v ₇ ";

12. If "p = p ₃ " AND "d = d ₂ " To "v = v ₆ ";

13. If “p = p ₃ ” AND “d = d ₃ ” To “v = v ₅ ”; (6)

14. If “p = p ₃ ” AND “d = d ₄ ” To “v = v ₄ ”;

15. If "p = p ₃ " AND "d = d ₅ " To "v = v ₃ ";

16. If "p = p ₄ " AND "d = d ₁ " To "v = v ₆ ";

17. If "p = p ₄ " And "d = d ₂ " To "v = v ₅ ";

18. If "p = p ₄ " AND "d = d ₃ " To "v = v ₄ ";

19. If "p = p ₄ " And "d = d ₄ " To "v = v ₃ ";

20. If "p = p ₄ " And "d = d ₅ " To "v = v ₂ ";

21. If "p = p ₅ " AND "d = d ₁ " To "v = v ₅ ";

22. If “p = p ₅ ” AND “d = d ₂ ” To “v = v ₄ ”;

23. If “p = p ₅ ” AND “d = d ₃ ” To “v = v ₃ ”;

24. If “p = p ₅ ” AND “d = d ₄ ” To “v = v ₂ ”;

25. If "p = p ₅ " AND "d = d ₅ " To "v = v ₁ ".

отличные от нуля.Moreover, the system of fuzzy control rules is constructed in such a way that at any time the conditional part is true only in 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 the values of the weighting coefficients in formula (5)

nonzero.

Also, in composition block 12, each rule is assigned weighting factors: F = (f ₁ , f ₂ , ..., f _n ), where n is the number of fuzzy control rules (n = 25). 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 ₂₅ = 1.

Next, in the block of compositions 12, an algebraic product of the values of the fuzzified vector of values for each term of the membership function A 'is made by the values of the corresponding weight coefficients F:

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

µ '(v) ₁ = min {max (b ₂₅ ); µ (v) ₁ },

μ '(v) ₂ = min {max (b ₂₀ , b ₂₄ ); µ (v) ₂ },

μ '(v) ₃ = min {max (b ₁₅ , b ₁₉ , b ₂₃ ); µ (v) ₃ },

μ '(v) ₄ = min {max (b ₁₀ , b ₁₄ , b ₁₈ , b ₂₂ ); µ (v) ₄ },

μ '(v) ₅ = min {max (b ₅ , b ₉ , b ₁₃ , b ₁₇ , b ₂₁ ); µ (v) ₅ }, (8)

μ '(v) ₆ = min {max (b ₄ , b ₈ , b ₁₂ , b ₁₆ ); µ (v) ₆ },

µ '(v) ₇ = min {max (b ₃ , b ₇ , b ₁₁ ); µ (v) ₇ },

μ '(v) ₈ = min {max (b ₂ , b ₆ ); µ (v) ₈ },

µ '(v) ₉ = min {max (b ₁ ); µ (v) ₉ },

new values of the output value of the cutting speed are calculated in the form of new terms of membership functions.

In the accumulation block 13, a logical union of new terms of the membership function obtained by (8) is made by the formula, and a fuzzy vector of membership functions V 'is formed:

In the defazzification block 14, the fuzzy vector of the accessory functions V 'is converted to a single clear value by the method of center of gravity:

Thus, the choice of a new value for the output parameter of the cutting speed for its control during turning on CNC equipment is made according to the formulas (1 ÷ 10).

As an example, let us examine the control of the cutting speed during the finishing pass during the turning of part 1, depending on the current value of the cutting force p received from the load cell sensor 4 and the diameter of the workpiece surface d received from the optical sensor 7.

Step 1. According to the formulas (1 ÷ 2), it is necessary to calculate the value of the cutting force and the diameter of the workpiece’s surface to be processed and transfer it to the accessory function formation unit 9. For example, during the calculation, it was obtained that the cutting force is P = 100 N and the diameter D = 20 mm.

Step 2. In the block for forming accessory functions 9, we construct, according to formula 3, the terms of the accessory functions for input and output quantities. Graphs of the functions of the accessories are shown in figure 2. Figure 2, a presents a graph for the input quantity - cutting force. Moreover, the extreme points on the graph are equal: P ₁ = P-20 = 100-20 = 80, N; P ₂ = P + 20 = 100 + 20 = 120, NA middle graph corresponds to the calculated value of the cutting force by the formula 1, i.e. 100, N. Terme p ₁ and p _{is 5} presented as a trapezoid and are: p ₁ = 80 [ , 80, 82, 95], p ₅ = [105, 118, 120, 120]. The terms p ₂ , p ₃ and p _{4 are} represented in the form of triangles and are equal to: p ₂ = [80, 90, 100], p ₃ = [90, 100, 110] and p ₄ = [100, 110, 120]. Data shown in Newtons.

Figure 2, b presents a graph for the input value - the diameter of the workpiece. Moreover, the extreme points on the graph are equal: D ₁ = D-0,1 = 20-0,02 = 19.98, mm; D ₂ = D + 0.02 = 20 + 0.02 = 20.02, mm. The middle of the graph corresponds to the calculated diameter value according to the formula 2, that is, 20, mm. The terms d ₁ and d _{5 are} presented in the form of a trapezoid and are equal: d ₁ = [19.98, 19.98, 19.982, 19.995], d ₅ = [20.005, 20.018, 20.02, 20.02]. The terms d ₂ , d ₃ and d _{4 are} represented in the form of triangles and are equal: d ₂ = [19.98, 19.99, 20], d ₃ = [19.99, 20, 20.01] and d ₄ = [20, 20.01, 20.02]. Data shown in millimeters.

Figure 2, in a graph for the output value is the cutting speed. Moreover, the extreme points on the graph are equal: V ₁ = V-20 = 150-20 = 130, m / min; V ₂ = V + 20 = 150 + 20 = 170, m / min. The middle of the graph corresponds to the set value of the cutting speed, i.e. 150, m / min. The terms v ₁ and v _{9 are} presented in the form of a trapezoid and are equal: v ₁ = [130, 130, 131, 135], v ₉ = [165, 169, 170, 170]. The terms v ₂ , v ₃ , v ₄ , v ₅ , v ₆ , v ₇ and v _{8 are} represented in the form of triangles and are equal: v ₂ = [130, 136, 142], v ₃ = [136, 142, 148], v ₄ = [142, 148, 154], v ₅ = [144, 150, 156], v ₆ = [146, 152, 158], v ₇ = [152, 158, 164] and v ₈ = [158, 164, 170]. Data are in meters / minute.

Step 3. The values of the accessories functions from block 9 are sent to the fuzzification unit 10. Also, the real value of the cutting force and from the optical sensor 7 the current value of the diameter of the workpiece are transmitted in real time from the force sensor 4. Let the load-bearing sensor 4 determine that the cutting force is 88 N, this value is not equal to the calculated one, that is 88 ≠ 100 N. Let the optical sensor determine the diameter of the workpiece - 19,994 mm, this value is not equal to the calculated one, that is 19,994 ≠ 20 mm . Therefore, recalculation is necessary.

In the fuzzification unit 10, there is a fuzzified vector of values for each term of the input membership function p 'and d' (Fig. 3, a and 3, b):

For the input parameter, the cutting force - the third, fourth and fifth terms have a zero result, and for the input parameter the diameter of the workpiece - the fourth and fifth terms have a zero result, so these terms will not be used in further calculations. The received data is transmitted to the aggregation unit 11.

Step 4. In the aggregation block according to the formula (5) there is a vector value A ':

A '= (0.007, 0.54, 0.4, 0, 0, 0.007, 0.6, 0.4, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0),

Where

The resulting vector is transmitted to the composition block 12.

Step 5. In the composition block 12, fuzzy control rules that have an intersection are selected. These are fuzzy rules with numbers 1, 2, 3, 6, 7, and 8:

1. If "p = p ₁ " AND "d = d ₁ " To "v = v ₉ ";

2. If "p = p ₁ " AND "d = d ₂ " To "v = v ₈ ";

3. If “p = p ₁ ” and “d = d ₃ ” then “v = v ₇ ”;

6. If "p = p ₂ " AND "d = d ₁ " Then "v = v ₈ ";

7. If "p = p ₂ " AND "d = d ₂ " Then "v = v ₇ ";

8. If "p = p ₂ " AND "d = d ₃ " To "v = v ₆ ".

Further, according to the formula (7), an algebraic product of the values of the vector of values of A 'is made by the values of the corresponding weighting factors F:

B = (<0.007 · 1> ₁ , <0.54 · 1> ₂ , <0.4 · 1> ₃ , <0.007 · 1> ₆ , <0.6 · 1> ₇ , <0.4 · 1> ₈ ) = (<0.007> ₁ , <0.54> ₂ , <0.4> ₃ , <0.007> ₆ , <0.6> ₇ , <0.4> ₈ )

Then, according to the formula (8), the fuzzy composition is determined

μ '(v) ₁ = 0, μ' (v) ₂ = 0, μ '(v) ₃ = 0, μ' (v) ₄ = 0, μ '(v) ₅ = 0,

µ '(v) ₆ = min {max (0; 0.4; 0; 0); µ (v) ₆ } = min {0.4; µ (v) ₆ },

µ '(v) ₇ = min {max (0.4; 0.6; 0); µ (v) ₇ } = min {0.6; µ (v) ₇ },

µ '(v) ₈ = min {max (0.54; 0.007); µ (v) ₈ } = min {0.54; µ (v) ₈ },

µ '(v) ₉ = min {max (0.007); µ (v) ₉ } = min {0.007; µ (v) ₉ }.

The result of the fuzzy composition is shown in Fig.4. Further, the data enters the accumulation unit 13.

Step 6. In the accumulation block 13 according to the formula (9), a logical union of all new terms is made and a fuzzy vector of membership functions V 'is formed. The result of the operation is graphically shown in FIG.

Step 7. In the defazzification block 14 according to formula (10), the vector of accessory functions V 'is converted to a single clear value (Fig.6), in order to simplify the computational procedure for calculation, we restrict ourselves to seven points, for a more accurate calculation, the number of points must be increased:

Using the proposed method, a new value of the cutting speed is calculated and the accuracy of turning is controlled on CNC equipment.

Thus, the proposed method and the device implementing it will allow real-time control of the cutting speed during turning of the part on CNC equipment in real time, by recalculating the cutting speed in order to change it in case of inequality of the set value of the cutting force and the diameter of the workpiece obtained with the help of gravity and optical sensors.

Claims (1)

A device for controlling the cutting speed on CNC turning equipment, comprising a tool holder with a cutter, a force gauge and actuators for CNC equipment, characterized in that it is equipped with an optical sensor, front and rear headstock and a fuzzy controller containing an accessory function formation unit, a unit fuzzification, aggregation unit, composition unit, accumulation unit and defuzzification unit, connected in series with each other, while a force meter is installed on the reserving unit an optical sensor whose output is connected to the first input of the fuzzification unit, an optical sensor is connected to the second input of the fuzzification unit, the third input of the fuzzification unit is connected to the output of the accessory function formation unit, the output of the fuzzification unit is connected to the input of the aggregation unit, the output of which is connected to the input of the composition unit, and the output of the composition unit is connected to the input of the accumulation unit, the output of which is connected to the input of the dephasification unit, and the output signal of the fuzzy controller is the output signal a defuzzification unit, which is connected to the input of a signal amplification unit and its output connected to the input actuators.

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