Method for planning the speed of non-regular curve numerical control machining

Abstract

The present application relates to the non-regular curve numerical control processing speed planning method, in the non-regular curve, any two points are taken, respectively, tangent, tangent intersection forms the angle, through the angle size change, the curvature of the non-regular curve is judged, the forward planning and reverse planning are combined, the curvature of the non-regular curve and the angle of the vector model of the angle are established, the feed speed of numerical control processing is corrected in real time, so that under certain accuracy requirements, the optimal interpolation speed is maintained.The present application is suitable for any non-regular curve or surface, and is widely applied.

Description

TECHNICAL FIELD

[0001] The present application relates to the planning of feed speed in numerical control machining process, in particular to a planning method of feed speed in non-regular curve numerical control machining. BACKGROUND

[0002] In numerical control machining, the servo system needs to monitor the difference between the actual motion trajectory and the programmed curve in real time, and the contour error is an important indicator of such difference. The contour error is the shortest distance from the actual position point to the programmed curve, and is also an important indicator for judging the accuracy of numerical control machining. On a complex curved surface or curve, a too high machining speed will cause a larger contour error. At present, there are many methods for contour error control or compensation, such as feedforward control, which has a fast dynamic response to known trajectories, and is particularly suitable for smooth trajectory segments in contour machining; cross-coupling control, which is suitable for machining scenarios requiring multi-axis cooperation such as circular arcs and curves; or geometric error compensation and dynamic error compensation, etc. However, there is still much room for improvement in matching the contour compensation with the interpolation speed.

[0003] In the existing method, the current conventional one-way planning has obvious defects, which are shown in 1, mechanical hysteresis effect (reverse clearance), when the tool suddenly changes from forward motion to reverse motion, the actual position of the transmission components such as ball screws and guide rails lags behind the theoretical command due to clearance and elastic deformation, and in severe cases, the lag can reach 5-20 μm; 2, vibration accumulation amplification, one-way sampling only predicts the theoretical trajectory, but does not suppress the vibration caused by the coupling of the natural frequency of the machine tool and the cutting force, which is amplified at the curvature mutation. SUMMARY

[0004] In view of the shortcomings of the prior art, the present application proposes a planning method of non-regular curve numerical control machining speed, which mainly plans the machining speed of non-regular curves, combines forward planning and reverse planning, establishes a curvature and angle vector model, and real-time corrects the tool feed speed in numerical control machining, so as to maintain the optimal feed speed under certain accuracy requirements.

[0005] The technical solution of the present application is as follows: the planning method of non-regular curve numerical control machining speed, taking any two points on the non-regular curve and drawing tangent lines respectively, the two tangent lines intersect to form an angle, the curvature of the non-regular curve is judged by the size change of the angle, a curvature-angle vector model of the non-regular curve is established, and based on the curvature-angle vector model, the tool feed speed in numerical control machining is real-time corrected in combination with two-way planning, so as to maintain the optimal tool feed speed under certain accuracy requirements, and the steps are as follows:

[0006] The two-way planning is forward planning and reverse planning,

[0007] Forward planning, on a machining curve, arbitrarily select three points A, B, and C in a clockwise direction, with the machining speed direction being clockwise;

[0008] Reverse programming involves randomly selecting three points on the same machining curve, and then selecting three more points in a counter-clockwise direction as A. 1 B 1 C 1 The processing speed direction is counterclockwise;

[0009] S1, Real-time data acquisition

[0010] The CNC system uses a high-precision encoder to collect the coordinates of three consecutive points on the tool path in real time. Taking three points ABC in the forward programming as an example, point A is set as the leader point, point B is set as the current machining point, and point C is set as the subsequent point. The sampling frequency needs to reach the highest command cycle of the control system, usually ≥1kHz.

[0011] S2, Tangent Vector Calculation

[0012] Take any three points A, B, and C on the machining curve, and the tangent vector at point A is... , by vector With the direction determined, the tangent vector at point A can be obtained. ; Tangent vector at point C , by vector direction Once determined, the tangent vector at point C can be obtained. Formulas (1) and (2) are derived.

[0013] , (1)

[0014] (2)

[0015] S3, Angle Analysis Model

[0016] Take any three points A, B, and C on the processing curve. Draw tangent lines at these three points. The intersection of the two tangent lines at adjacent points gives an angle θ. The angle θ is obtained by using the inverse cosine of the vector dot product.

[0017] (3)

[0018] S4, Dynamic Sampling in Bidirectional Programming

[0019] For forward programming, sequential sampling involves taking five consecutive points along the processing direction for theoretical trajectory prediction.

[0020] ;

[0021] The sequence sampling for backward programming involves taking 5 points in the reverse direction of the processing direction: ;

[0022] S5, modeling of the angle θ

[0023] According to the tangent vector calculation, the current point P i is taken as the center, the forward vector and the reverse vector are divided According to formulas (1) and (2), the forward tangent vector and the reverse tangent vector ,

[0024] , (4)

[0025] (5)

[0026] and is the chord length;

[0027] The angle θ is obtained from formula (3), formula (4) and formula (5)

[0028] (6)

[0029] S6, construct curvature-angle vector model

[0030] When the angle θ changes, the curvature changes, then the curvature is

[0031] (7)

[0032] where, is the chord length, from formula (7), when the angle θ increases, that is, the curve is more curved;

[0033] S7, construct the correction coefficient of tool feed speed

[0034] (8)

[0035] where, is the curvature adjustment, is the angle constraint; is the adjustable coefficient, the value range is 0.05~0.2; is the safety threshold of the angle;

[0036] S8, dynamic speed planning

[0037] When the change of the angle is greater than the safety threshold, the overcut protection is started, and the dynamic speed planning formula is obtained:

[0038] (9)

[0039] is the reference feed rate; is the maximum feed rate of the control system;

[0040] When the included angle changes less than the safety threshold, the original feed rate is maintained.

[0041] Further, for machining conventional materials, it is generally desirable that 0.1, 0.1, that is, the precision requirement of NC machining can be met, unless there is a special requirement; when the feed rate is increased by 15%,

[0042] The dynamic speed planning formula is

[0043] (10).

[0044] The beneficial effects of the present application are:

[0045] By judging the curvature of the irregular curve, a curvature-included angle vector model of the irregular curve is established, and the feed rate is adjusted and matched according to the angle of the included angle and its change rate, so that the optimal feed rate is maintained under certain precision requirements. The present application is applicable to any irregular curve or surface and has wide application. BRIEF DESCRIPTION OF DRAWINGS

[0046] Figure 1 are schematic diagrams of forward planning and reverse planning in the present application; DETAILED DESCRIPTION

[0047] To make the technical problems solved by the present application, the technical solutions adopted and the technical effects achieved more clear, the technical solutions of the embodiments of the present application will be further described in detail below with reference to the drawings. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0048] EMBODIMENT:

[0049] The planning method of the irregular curve NC machining speed selects two points on the irregular curve, respectively makes tangent lines, forms an included angle by the intersection of the two tangent lines, judges the curvature of the irregular curve through the size change of the included angle, establishes a curvature-included angle vector model of the irregular curve, combines the curvature-included angle vector model with bidirectional planning, and real-time corrects the tool feed rate of NC machining, so that the optimal tool feed rate is maintained under certain precision requirements,

[0050] Bidirectional planning is forward planning and reverse planning,

[0051] As shown in the forward planning, three points A, B and C are taken in sequence in the clockwise direction on a machining curve, and the machining speed direction is clockwise. Figure 1

[0052] Reverse planning, take three points on the same machining curve, take three points in sequence in the counterclockwise direction as A 1 B 1 C 1 , and the machining speed direction is counterclockwise.

[0053] The steps of the planning of the machining speed of the irregular curve are as follows:

[0054] S1, real-time data acquisition

[0055] The numerical control system acquires the coordinates of three consecutive points on the tool path through a high-precision encoder in real time. Taking three points A, B and C in the forward planning as an example, A is the leading point, B is the current machining point, and C is the subsequent point. The sampling frequency needs to reach the highest instruction period of the control system, usually ≥1kHz.

[0056] S2, tangent vector calculation

[0057] Taking three points A, B and C on the machining curve, the tangent vector of point A is determined by the direction of vector , and the tangent vector of point A is obtained. ; The tangent vector of point C is determined by the direction of vector , and the tangent vector of point C is obtained. , and formulas (1) and (2) are derived

[0058] , (1)

[0059] (2)

[0060] S3, angle analysis model

[0061] Taking three points A, B and C on the machining curve, draw tangent lines on the three points, and the intersection of the two tangent lines on adjacent points gives the included angle θ. The included angle θ is obtained by vector dot product and inverse cosine.

[0062] (3)

[0063] S4, dynamic sampling of bidirectional planning

[0064] Forward planning sequence sampling, for theoretical trajectory prediction, take five consecutive points along the machining direction:

[0065] ;​​​

[0066] Reverse planning sequence sampling, reverse direction of processing direction 5 points: ;

[0067] S5, angle θ modeling

[0068] According to the tangent vector calculation, the current point P i Center, positive vector And negative vector , according to formula (1) and (2), the positive tangent vector And the negative tangent vector ,

[0069] , (4)

[0070] (5)

[0071] And Chord length;

[0072] From formula (3), formula (4) and formula (5), the angle θ is

[0073] (6)

[0074] S6, construct curvature-angle vector model

[0075] When the angle θ changes, the curvature changes, then the curvature Is

[0076] (7)

[0077] Where, Chord length, from formula (7), when the angle θ increases, that is, the curve is more curved;

[0078] S7, construct the correction coefficient of tool feed speed

[0079] (8)

[0080] Where, Curvature adjustment, Angle constraint; Adjustable coefficient, the value range is 0.05~0.2; Safety threshold of angle; according to the characteristics of processing materials to adjust, generally can take 0.1; , Has met the accuracy requirements in conventional numerical control machining.

[0081] S8, dynamic speed planning

[0082] When the included angle changes more than , the overcut protection is started, in practice, the feed speed can be planned in real time at irregular curvature according to the machining precision requirement, when there is no special requirement for the machining speed, such as increasing , the feed speed can be reduced by 15%.

[0083] The dynamic speed planning formula is obtained:

[0084] (10).

[0085] is the reference feed speed; is the maximum feed speed of the control system;

[0086] When the included angle changes less than , the original feed speed is followed.

Claims

1. A method for planning the speed of a non-regular curve NC machining, characterized in that, Two points are taken on the irregular curve, and tangent lines are drawn at the two points. The two tangent lines intersect to form an angle. The curvature of the irregular curve is determined by the angle. A curvature-angle vector model of the irregular curve is established. Based on the curvature-angle vector model, two-way planning is combined to correct the tool feed speed in real time, so that the optimal tool feed speed is maintained under certain accuracy requirements. The two-way planning is forward planning and reverse planning, The forward planning is that three points ABC are taken in turn on a machining curve in a clockwise direction, and the machining speed direction is the clockwise direction. Reverse planning, take three points on the same processing curve, in anticlockwise direction, take three points as A 1 B 1 C 1 , the processing speed direction is anticlockwise direction; The planning steps of the tool feed speed are as follows: S1, real-time data acquisition The numerical control system acquires the coordinates of three consecutive points on the tool machining trajectory in real time through a high-precision encoder, wherein the A point is set as a leading point, the B point is set as a current machining point, and the C point is set as a subsequent point. The sampling frequency needs to reach the highest instruction period of the control system, and the sampling frequency is greater than or equal to 1 kHz. S2, tangent vector calculation Take three points ABC on the machining curve, the tangent vector of A is determined by the vector direction , the tangent vector of C is determined by the vector direction , and the formulas (1) and (2) are derived （1） （2） is the chord length of AB, is the chord length of BC; S3, angle analysis model Three points ABC are taken on the machining curve, the tangent lines of the A point and the C point intersect to form an angle θ, and the angle θ is obtained through vector dot product and inverse cosine, （3） S4, dynamic sampling of two-way planning The sequence sampling of the forward planning is that, for theoretical trajectory prediction, five consecutive points are taken along the machining direction: ； Reverse planning sequence sampling, 5 points in reverse direction of processing: ​ S5, angle θ modeling According to the tangent vector calculation, the current point P i is the center, the forward vector and the reverse vector , according to formulas (1) and (2), the forward tangent vector and the reverse tangent vector , （4） （5） is the chord length of is the chord length of is the chord length of​ The angle θ is obtained from formulas (3), (4) and (5) （6） S6, construction of curvature-angle vector model When the included angle θ changes, the curvature changes, and the curvature is obtained （7） wherein is the chord length, and from equation (7) it follows that the curve is more curved as the included angle θ becomes larger; S7, constructing a correction coefficient of the tool feed speed （8） wherein, is curvature adjustment, is angle constraint; is adjustable coefficient, value range 0.05~0.2; is angle safety threshold; S8, dynamic speed planning When the included angle changes less than the safety threshold, the tool is processed at the original feed speed; When the included angle changes greater than a safety threshold, an overcut protection is initiated, obtaining a dynamic speed Planning formula: （9） is the reference feed speed; is the control system maximum feed speed.

2. The method of claim 1, wherein, Safety threshold for included angle in S7 for Each increase The feed rate can be reduced by 15%, and the dynamic speed planning formula is as follows: （10）。

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