Planning method of irregular curve numerical control machining speed

Abstract

The invention relates to a method for planning the numerical control machining speed of an irregular curve, which comprises the following steps of: randomly taking two points on the irregular curve, respectively making tangent lines, intersecting the tangent lines to form an included angle, judging the curvature of the irregular curve through the change of the size of the included angle, and establishing a vector model of the curvature of the irregular curve and the angle of the included angle by combining forward planning and reverse planning. And the feeding speed of numerical control machining is corrected in real time, so that the optimal interpolation speed is kept under a certain precision requirement. The method is suitable for any irregular curve or curved surface and is wide in application.

Description

Technical Field

[0001] The present invention relates to feed speed planning in a numerical control machining process, and in particular to a feed speed planning method in numerical control machining of irregular curves. Background Art

[0002] In CNC machining, the servo system needs to monitor the difference between the actual motion trajectory and the programmed curve in real time. Contour error is a key indicator of this difference. Contour error is the shortest distance from the actual position point to the programmed curve and is also a key indicator for judging CNC machining accuracy. On complex surfaces or curves, excessive machining speeds can cause large contour errors. Currently, there are many methods for controlling or compensating contour errors, 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 arcs, curves, and other processing scenarios that require multi-axis collaboration; and geometric error compensation and dynamic error compensation. However, there is still much room for improvement in matching contour compensation with interpolation speed.

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

[0004] In response to the shortcomings of the existing technology, the present invention proposes a planning method for the CNC machining speed of irregular curves, which is mainly aimed at planning the machining speed of irregular curves. It adopts a combination of forward planning and reverse planning, establishes a vector model of curvature and angle, and corrects the tool feed speed of CNC machining in real time, so as to maintain the optimal feed speed under certain precision requirements.

[0005] The following is a technical solution of the present invention, a method for planning the speed of CNC machining of irregular curves. Two points on the irregular curve are randomly selected and tangent lines are drawn. The two tangent lines intersect to form an angle. The curvature of the irregular curve is determined by the change in the angle. A vector model of the curvature-angle of the irregular curve is established. Based on the vector model of curvature-angle, combined with bidirectional planning, the tool feed speed of CNC machining is corrected in real time to maintain the optimal tool feed speed under certain precision requirements. The steps are as follows: Bidirectional planning includes forward planning and reverse planning. Forward planning: select three points ABC on a processing curve in a clockwise direction, and the processing speed direction is clockwise; Reverse planning, select three points on the same processing curve, and select three points in the counterclockwise direction as A 1 B 1 C 1 , the processing speed direction is counterclockwise; S1, real-time data acquisition The CNC system uses a high-precision encoder to collect the coordinates of three consecutive points on the tool path in real time. For example, take three points ABC in forward planning, where point A is set as the leading point, point B is set as the current processing point, and point C is set as the subsequent point. The sampling frequency must reach the maximum instruction cycle of the control system, usually ≥1kHz. S2, tangent vector calculation Take any three points ABC on the machining curve, and the tangent vector of point A , by vector The direction is determined, and the tangent vector of point A can be obtained ; Tangent vector at point C , by the vector direction OK, we can get the tangent vector of point C , we can derive formula (1) and formula (2) , (1) (2) S3, angle analysis model Take any three points ABC on the machining curve, draw tangents at the three points, and the two tangents at adjacent points intersect to get the angle θ, which is obtained by the vector dot product arc cosine. (3) S4, dynamic sampling of bidirectional planning Sequential sampling for forward programming, for theoretical trajectory prediction, take 5 consecutive points along the machining direction: ; Sequence sampling for reverse planning, take 5 points in the reverse direction of the processing direction: ; S5, angle θ modeling According to the tangent vector calculation, the current point P i As the center, the positive vector and reverse vector , according to formulas (1) and (2), the forward tangent vector is obtained and the reverse tangent vector , , (4) (5) and is the string length; From formula (3), formula (4) and formula (5), we can get the angle θ as (6) S6, construct curvature-angle vector model When the angle θ changes, the curvature changes, and the curvature is for (7) in, is the chord length. From formula (7), it can be concluded that when the angle θ becomes larger, the curve becomes more curved; S7, construct the correction coefficient of tool feed speed (8) in, For curvature adjustment, is the angle constraint; It is an adjustable coefficient with a value range of 0.05~0.2; is the safety threshold of the angle; S8, dynamic speed planning When the angle The change of is greater than the safety threshold, and the overcut protection is started, and the dynamic speed planning formula is obtained: (9) is the base feed speed; is the maximum feed speed of the control system; When the angle If the change is less than the safety threshold, the original feed speed is used.

[0006] Further, processing conventional materials is generally desirable is 0.1, for , can meet the precision requirements of CNC machining, unless there are special requirements; each additional The feed speed can be reduced by 15%. The dynamic speed planning formula is: (10).

[0007] The beneficial effects of the present invention are: By determining the curvature of an irregular curve and establishing a vector model of its curvature-angle, the feed speed is adjusted and matched according to the angle and its rate of change, thereby maintaining the optimal feed speed under certain precision requirements. The present invention is applicable to any irregular curve or surface and has a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 Schematic diagram of forward planning and reverse planning in the present invention; DETAILED DESCRIPTION

[0009] To make the technical problems solved, the technical solutions adopted, and the technical effects achieved by the present invention more clearly understood, the technical solutions of the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings. It is obvious that the described embodiments are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative work shall fall within the scope of protection of the present invention.

[0010] Example: The planning method for the CNC machining speed of irregular curves is to randomly select two points on the irregular curve and draw tangents for each point. The two tangents intersect to form an angle. The curvature of the irregular curve is determined by the change in the angle. A vector model of the curvature-angle of the irregular curve is established. Based on the vector model of curvature-angle, combined with bidirectional planning, the tool feed speed of CNC machining is corrected in real time, so that the optimal tool feed speed is maintained under certain precision requirements. Bidirectional planning includes forward planning and reverse planning. like Figure 1 In the forward planning shown, three points ABC are randomly selected in a clockwise direction on a processing curve, and the processing speed direction is clockwise; Reverse planning, select three points on the same processing curve, and select three points in the counterclockwise direction as A 1 B 1 C 1 , the processing speed direction is counterclockwise.

[0011] The planning steps for the CNC machining speed of irregular curves are as follows: S1, real-time data acquisition The CNC system uses a high-precision encoder to collect the coordinates of three consecutive points on the tool path in real time. For example, take three points ABC in forward planning, where point A is set as the leading point, point B is set as the current processing point, and point C is set as the subsequent point. The sampling frequency must reach the maximum instruction cycle of the control system, usually ≥1kHz. S2, tangent vector calculation Take any three points ABC on the machining curve, and the tangent vector of point A , by vector The direction is determined, and the tangent vector of point A can be obtained ; Tangent vector at point C , by the vector direction OK, we can get the tangent vector of point C , we can derive formula (1) and formula (2) , (1) (2) S3, angle analysis model Take any three points ABC on the machining curve, draw tangents at the three points, and the two tangents at adjacent points intersect to get the angle θ, which is obtained by the vector dot product arc cosine. (3) S4, dynamic sampling of bidirectional planning Sequential sampling for forward programming, for theoretical trajectory prediction, take 5 consecutive points along the machining direction: ; Sequence sampling for reverse planning, take 5 points in the reverse direction of the processing direction: ; S5, angle θ modeling According to the tangent vector calculation, the current point P i As the center, the positive vector and reverse vector , according to formulas (1) and (2), the forward tangent vector is obtained and the reverse tangent vector , , (4) (5) and is the string length; From formula (3), formula (4) and formula (5), we can get the angle θ as (6) S6, construct curvature-angle vector model When the angle θ changes, the curvature changes, and the curvature is for (7) in, is the chord length. From formula (7), it can be concluded that when the angle θ becomes larger, the curve becomes more curved; S7, construct the correction coefficient of tool feed speed (8) in, For curvature adjustment, is the angle constraint; It is an adjustable coefficient with a value range of 0.05~0.2; is the safety threshold of the angle; it is adjusted according to the characteristics of the processed material, and is generally is 0.1; for , which has met the precision requirements of conventional CNC machining.

[0012] S8, dynamic speed planning When the angle The change is greater than , start overcut protection, in practice, according to the processing accuracy requirements, at irregular curvatures, the feed speed can be planned in real time. When there is no special requirement for the processing speed, such as every increase The feed speed can be reduced by 15%.

[0013] Get the dynamic speed planning formula: (10).

[0014] is the base feed speed; is the maximum feed speed of the control system; When the angle The change is less than , according to the original feed speed.

Claims

1. A speed planning method for CNC machining of irregular curves is characterized by taking two arbitrary points on the irregular curve and drawing tangent lines. The two tangent lines intersect to form an angle. The curvature of the irregular curve is determined by the change in the angle. A vector model of the curvature-angle of the irregular curve is established. Based on this vector model of curvature-angle, combined with bidirectional planning, the tool feed rate of CNC machining is corrected in real time to maintain the optimal tool feed rate under certain precision requirements. The steps are as follows: The two-way planning mentioned above is forward planning and reverse planning. The forward planning is to select three points ABC in sequence on a processing curve in a clockwise direction, and the processing speed direction is clockwise; Reverse planning, select three points on the same processing curve, and select three points in the counterclockwise direction as A 1 B 1 C 1 , the processing speed direction is counterclockwise.

2. The method for planning the speed of irregular curve numerical control machining according to claim 1, characterized in that The planning steps for tool feed rate are as follows: S1, real-time data acquisition The CNC system uses a high-precision encoder to collect the coordinates of three consecutive points on the tool processing trajectory in real time. Take three points ABC in forward planning as an example, where point A is set as the leading point, point B is set as the current processing point, and point C is set as the subsequent point. The sampling frequency must reach the maximum instruction cycle of the control system, usually ≥1kHz. S2, tangent vector calculation Take any three points ABC on the machining curve, and the tangent vector of point A By vector The direction is determined, and the tangent vector of point A can be obtained ; Tangent vector at point C By vector direction OK, we can get the tangent vector of point C , we can derive formula (1) and formula (2) ， （1） （2） is the length of the chord AB, is the chord length of BC; S3, angle analysis model Take any three points ABC on the machining curve, draw tangents at the three points, and the two tangents at adjacent points intersect to get the angle θ, which is obtained by the vector dot product arc cosine. （3） S4, dynamic sampling of bidirectional planning Sequential sampling for forward programming, for theoretical trajectory prediction, take 5 consecutive points along the machining direction: ； Sequence sampling for reverse planning, take 5 points in the reverse direction of the processing direction: ; S5, angle θ modeling According to the tangent vector calculation, the current point P i As the center, the positive vector and reverse vector , according to formulas (1) and (2), the forward tangent vector is obtained and the reverse tangent vector , ， （4） （5） yes chord length; It's P i+1 P i chord length; The angle θ is obtained from formula (3), formula (4) and formula (5): （6） S6, construct curvature-angle vector model When the angle θ changes, the curvature changes, and the curvature is （7） in, is the chord length. From formula (7), it can be concluded that when the angle θ becomes larger, the curve becomes more curved; S7, construct the correction coefficient of tool feed speed （8） in, For curvature adjustment, is the angle constraint; It is an adjustable coefficient with a value range of 0.05~0.2; is the safety threshold of the angle; S8, dynamic speed planning When the angle The change is less than the safety threshold, and the tool processes at the original feed speed; When the angle The change is greater than the safety threshold, the overcut protection is started, and the dynamic speed is obtained. Planning formula: （9） is the base feed speed; It is the maximum feed speed of the control system.

3. The method for planning the speed of irregular curve NC machining according to claim 2, characterized in that Angle safety threshold in S7 for ; Each additional The feed speed can be reduced by 15%, and the dynamic speed planning formula is: （10）。 4. The method for planning the speed of irregular curve NC machining according to claim 2, characterized in that In S7, the material characteristics are adjusted according to the processing material. is 0.1.

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