Laser head control method

Abstract

The invention aims to provide a laser head control method which can keep a gap between a laser head and a workpiece with high precision and improve the cutting speed. In order to solve the problem, the present invention provides a laser head control method which is applied to a laser processing apparatus for cutting a workpiece using laser light irradiated by a laser head, the laser head control method detects a gap between the laser head and the workpiece and performs feed-forward control, the feed-forward control adjusts the gap on the basis of a predicted value of the gap based on a variation history of the gap. In addition to the feed-forward control, feedback control for adjusting the slot while comparing the slot with a target value of the slot is executed.

Description

Technical Field

[0001] The present invention relates to a method for controlling a laser head, and more particularly to a method for controlling a laser head of a laser processing apparatus that uses a laser irradiated by the laser head to cut a workpiece. Background Art

[0002] Conventionally, as a technique for converging a controlled variable such as temperature, flow rate, and pressure that can be measured by a sensor to a target value, the following controls are known: feedback control, which drives an adjustment means while comparing a sensor measurement value with a target value; and feedforward control, which drives an adjustment means while detecting an external disturbance and predicting in advance the influence of the external disturbance on the controlled variable.

[0003] Patent Document 1 discloses a rolling mill control method in which the post-processing plate thickness of a plate processed by a rolling mill is used as a controlled variable, feedback control is performed on the roll speed and pressing pressure of the rolling mill, and feedforward control is performed on the roll speed and pressing pressure of the rolling mill based on the change history of the pre-processing plate thickness.

[0004] In addition, Patent Document 2 discloses a continuous casting machine control method in which the molten metal surface height of a gate provided in a mold of a continuous casting machine is used as a controlled variable, feedback control is performed on the opening degree of a valve that adjusts the flow rate of molten steel supplied to the gate, and feedforward control is performed on the opening degree of the valve based on the change history of the molten metal surface height.

[0005] [Prior Art Documents]

[0006] (Patent Documents)

[0007] Patent Document 1: Japanese Patent Laid-Open No. 7-16625

[0008] Patent Document 2: Japanese Patent Laid-Open No. 2022-77954 Summary of the Invention

[0009] [Problems to be Solved by the Invention]

[0010] Here, in a laser processing apparatus that cuts a workpiece composed of a thin plate member of aluminum or steel with a laser irradiated by a laser head, in order to continuously perform high-speed cutting or further increase the cutting speed, it is necessary to accurately maintain the gap (clearance) between the laser head and the workpiece. In this regard, in Patent Documents 1 and 2, the gap between the laser head and the workpiece is not studied as a controlled variable.

[0011] An object of the present invention is to solve the above problems of the prior art and provide a laser head control method that can accurately maintain the gap between the laser head and the workpiece and improve the cutting speed.

[0012] [Means for Solving the Problems]

[0013] To achieve the foregoing object, the first feature of the present invention lies in the following aspects: A laser head control method is applied to a laser processing apparatus that uses a laser irradiated by a laser head to cut a workpiece. The laser head control method detects a gap between the laser head and the workpiece and performs feedforward control. The feedforward control adjusts the gap according to a predicted value of the gap based on the change history of the gap.

[0014] In addition, the second feature lies in the following aspects: In addition to the foregoing feedforward control, feedback control is also performed. The feedback control adjusts the gap while comparing the gap with a target value of the gap.

[0015] In addition, the third feature lies in the following aspects: At the start and end of the cutting of the workpiece, the foregoing feedforward control is not performed.

[0016] In addition, the fourth feature lies in the following aspects: The foregoing gap is sampled at a specified interval, and interpolation of the specified interval is performed according to a running speed magnification input by an operator.

[0017] In addition, the fifth feature lies in the following aspects: A finite impulse response (FIR) filter is applied to the sampled data that has undergone the foregoing interpolation.

[0018] In addition, the sixth feature lies in the following aspects: The foregoing FIR filter adjusts the gain of the foregoing feedforward control and filters out frequency components that may become external disturbances.

[0019] Furthermore, the seventh feature lies in the following aspects: A laser processing apparatus uses a laser irradiated by a laser head to cut a workpiece. The laser processing apparatus includes: a gap detection means for detecting a gap between the laser head and the workpiece; and a feedforward control means for performing feedforward control. The feedforward control adjusts the gap according to a predicted value of the gap based on the change history of the gap.

[0020] (Effects of the Invention)

[0021] According to the first feature, a laser head control method is applied to a laser processing apparatus that uses a laser irradiated by a laser head to cut a workpiece, and the laser head control method detects a gap between the laser head and the workpiece and performs feedforward control. The feedforward control adjusts the gap according to a predicted value of the gap based on the change history of the gap. Therefore, by keeping the gap between the laser head and the workpiece at a constant value, the cutting speed is increased, and the production volume of the laser processing apparatus can be increased.

[0022] According to the second feature, in addition to the foregoing feedforward control, feedback control is also performed. The feedback control adjusts the foregoing gap while comparing the foregoing gap with the target value of the gap, so that more stable gap control can be performed.

[0023] According to the third feature, at the start and end of the cutting of the foregoing workpiece, the foregoing feedforward control is not performed. Therefore, although at the start or end of the cutting of the workpiece, the workpiece may vibrate and become a state unsuitable for feedforward control, the stabilization of gap control can be achieved by performing only feedback control in this area.

[0024] According to the fourth feature, the foregoing gap is sampled at a specified interval, and interpolation of the foregoing specified interval is performed according to the operation speed magnification input by the operator, so that sampling can be performed by a simple method.

[0025] According to the fifth feature, the FIR filter is applied to the sampled data after the foregoing interpolation, so that more stable gap control can be performed.

[0026] According to the sixth feature, the foregoing FIR filter adjusts the gain of the foregoing feedforward control and filters out the frequency components that may become external disturbances, so that more stable gap control can be performed.

[0027] According to the seventh feature, a laser processing apparatus cuts a workpiece using the laser irradiated by a laser head. And the laser processing apparatus includes: a gap detection means for detecting the gap between the foregoing laser head and the foregoing workpiece; and a feedforward control means for performing feedforward control, which adjusts the foregoing gap according to the predicted value of the foregoing gap based on the change history of the foregoing gap. Therefore, the cutting speed can be increased by keeping the gap at a constant value, and the production volume of the laser processing apparatus can be increased. Description of the Drawings

[0028] Figure 1 is a left side view showing the overall structure of the laser processing system.

[0029] Figure 2 is a perspective view of the laser processing apparatus.

[0030] Figure 3 is a partially enlarged plan view of the laser processing apparatus.

[0031] Figure 4 is Figure 3 a sectional view taken along line IV-IV of

[0032] Figure 5 is a conceptual diagram showing the method of deriving the gap.

[0033] Figure 6 is a block diagram showing the structure of the gap control device.

[0034] Figure 7 It is a control block diagram showing the process of gap control. Detailed implementation manners

[0035] Hereinafter, the preferred implementation manners of the present invention will be described in detail with reference to the drawings. Figure 1 It is a left side view showing the overall structure of a laser processing system 1 according to an implementation manner of the present invention. The laser processing system 1 includes: a leveling machine device 2 that levels a workpiece W fed out from a roll-shaped material R formed by winding a thin plate member of aluminum or steel; and a laser processing device 10 that cuts the workpiece W leveled by the leveling machine device 2 with a laser. In the direction arrows in the figure, "front" corresponds to the upstream side in the feeding direction of the workpiece W, and "rear" corresponds to the downstream side in the feeding direction of the workpiece W.

[0036] The leveling machine device 2 has three upper rollers 3 that contact the upper surface of the workpiece W and four lower rollers 4 that contact the lower surface of the workpiece W. The upper rollers 3 and the lower rollers 4 having parallel rotation axes are arranged in a staggered manner in the front-rear direction. The workpiece W clamped between the upper rollers 3 and the lower rollers 4 and leveled is fed out to the laser processing device 10. The number, arrangement, diameter, etc. of the upper rollers and the lower rollers can be variously deformed.

[0037] Figure 2 It is a perspective view of the laser processing device 10. The laser processing device 10 includes: an upstream transfer device 25a and a downstream transfer device 25b for transferring the workpiece W; a laser head H that irradiates the workpiece W with a laser from above; a laser head drive mechanism 11 that moves the laser head H in the front-rear, left-right directions; and a dust collection device 20 that collects spatter generated by solidification of molten metal blown away by an assist gas when cutting the workpiece W.

[0038] The upstream transfer device 25a and the downstream transfer device 25b, which are so-called belt conveyors, include: an upstream conveyor belt 19a wound around a first conveyor belt roller 15 and a second conveyor belt roller 16; a downstream conveyor belt 19b wound around a third conveyor belt roller 17 and a fourth conveyor belt roller 18; and a conveyor belt roller drive device (not shown).

[0039] Between the upstream transfer device 25a and the downstream transfer device 25b, more specifically, between the second conveyor belt roller 16 and the third conveyor belt roller 17, a dust collection box 21 for collecting spatter is provided. The second conveyor belt roller 16 and the third conveyor belt roller 17 are configured to be movable upstream or downstream in synchronization with the dust collection box 21 by a drive mechanism (not shown).

[0040] The laser head driving mechanism 11 has an X-axis rail 12 extending in the left-right direction (the width direction of the workpiece W) above the dust collection box 21, and a pair of left and right Y-axis rails 14 extending in the front-rear direction on the side of the workpiece W. The X-axis rail 12 supports the laser head H so as to be slidable in the left-right direction, and the Y-axis rail 14 supports the X-axis rail 12 so as to be slidable in the front-rear direction. Thus, the laser head H is configured to be movable in the front, rear, left, and right directions.

[0041] The box-shaped dust collection box 21 extending in the left-right direction is configured to be movable in the front-rear direction by a driving mechanism (not shown). At the upper part of the dust collection box 21, an opening 13 having a rectangular shape elongated in the left-right direction is formed when viewed from above. The driving mechanism of the dust collection box 21 moves the dust collection box 21 in the front-rear direction such that the opening 13 is always located directly below the laser head H. The spatter generated when cutting the workpiece W is recovered from the opening 13 into the dust collection box 21, and the recovered spatter is appropriately discharged from a discharge port 22 provided on the side portion of the dust collection box 21.

[0042] Figure 3 It is a partially enlarged plan view of the laser processing apparatus 10. In addition, Figure 4 is Figure 3 a sectional view taken along line IV-IV. The two edges in the front-rear direction of the opening 13 of the dust collection box 21 are respectively formed by the edges of a substantially square upstream side cover 30 and a downstream side cover 31. The upstream side cover 30 and the downstream side cover 31 are each composed of a thin plate member provided with seven circular windows and six square windows. In a plan view, the seven circular windows respectively face the disk-shaped support pads 7, and in addition, the six square windows respectively face the roller pair 50 composed of an inner roller 51 and an outer roller 52.

[0043] Referring to Figure 4 , the inner roller 51 and the outer roller 52 are arranged such that there is a slight gap between them in the front-rear direction, and their upper end portions are located above the square window. Thus, the lower surface of the workpiece W abuts against the inner roller 51 and the outer roller 52 at a position above the dust collection box 21. On the other hand, counter rollers 60 for power transmission are respectively abutted against the outer rollers 52 on the upstream side and the downstream side. Moreover, the upstream counter roller 60 abuts against the upstream conveyor belt 19a, and the downstream counter roller 60 abuts against the downstream conveyor belt 19b. Therefore, the outer roller 52 rotates in synchronization with the conveying operation of the workpiece W.

[0044] Thus, when moving the dust collection box 21 in the front-rear direction, the outer roller 52 supports the workpiece W while rolling. Therefore, the lower surface of the workpiece W is protected, and even when the moving direction of the dust collection box 21 is reversed, the positional deviation of the workpiece W can be prevented.

[0045] Here, in order to cut the workpiece W using the laser irradiated by the laser head H, it is necessary to melt the workpiece W with a certain amount of energy. In order to impart a certain amount of energy, it is necessary to maintain the gap (clearance) G between the laser head H and the workpiece W with high precision. Regarding this problem, the laser head control method of the present invention is characterized in the following aspects: By performing feedforward control on the gap G to be controlled based on the change history of the gap G, the energy of the laser can be stabilized, and the cutting speed can be further increased.

[0046] Figure 5 It is a conceptual diagram showing a method for deriving the gap G. The gap G formed between the front end of the laser head H and the upper surface of the workpiece W is directly measured by a measuring device such as a capacitance sensor. On the other hand, a non-contact linear encoder or the like is used as a measuring device to measure the distance from the origin O to the front end position of the laser head as an encoder value. In the present embodiment, the distance from the origin O to the front end position of the laser head is a negative value, and the workpiece position of the negative value is calculated by subtracting the absolute value of the gap G from the front end position of the laser head.

[0047] Figure 6 It is a block diagram showing the overall configuration of the gap control device 70. The gap control device 70 applied to the laser processing system 1 includes: a gap detection means 71 including a measuring device such as a capacitance sensor; a gap adjustment means 73 for moving the laser head H in the vertical direction using an actuator or the like; a feedforward control means 74 for performing gap adjustment based on a predicted value of the influence of an external disturbance on the workpiece position; a feedback control means 75 for performing gap adjustment based on a comparison between the current value and the target value of the gap G; and a control unit 72 composed of a microcomputer or the like.

[0048] The control unit 72 drives the gap adjustment means 73 in such a way as to maintain the gap G as a target value based on the information of the gap G detected by the gap detection means 71, the information from the feedforward control means 74, and the information from the feedback control means 75.

[0049] Figure 7 It is a control block diagram showing the flow of gap control. In the present embodiment, both feedforward control and feedback control are configured to be executable in order to maintain the gap G as a target value. Specifically, feedback control is performed based on the gap G, and feedforward control is performed in such a way that the gap G becomes the optimum value according to the future workpiece position (estimated workpiece position) estimated from the past history of the workpiece position. On the other hand, depending on the situation, only feedforward control or only feedback control may be performed.

[0050] Here, since the variation waveform of the slit G as the control object always changes, it is desirable to generate the variation waveform in real time. For this purpose, in the present embodiment, the accumulation of the variation waveform using a real-time operating system (OS) and the filtering of the fixed-frequency components based on a FIR (Finite Impulse Response) filter are performed. Further, a resampling technique used in audio data or the like is applied so that a feedforward control capable of coping with a rapid speed change can be executed.

[0051] The current slit G and the target value of the slit G are input to the first subtractor 80. On the other hand, the current slit G and the encoder value from the origin O to the front end position of the laser head are input to the second subtractor 81, and a series of feedforward controls are performed on the workpiece position obtained by subtracting the slit G from the encoder value.

[0052] In step S2, the variation waveform formed based on the encoder values sampled at a predetermined interval is converted into an OVR100% waveform. The workpiece position is sampled at a predetermined interval and interpolation of the predetermined interval is performed according to the operation speed magnification input by the operator. Sampling of the workpiece position can be performed, for example, every 500 / μs.

[0053] In step S3, the sampling data of the workpiece position for the past 10 times is saved as a history, and in step S4, the weighted moving average of the saved sampling data is obtained.

[0054] In step S5, conversion to an OVR50% waveform that is to be executed is performed. In step S6, for the interpolated sampling data, a FIR filter is applied. The FIR filter performs fine adjustment of the gain for the feedforward command and filtering processing of the frequency components that may become external disturbances. The FIR filter has the following characteristics: after a finite time of adjusting the gain of the feedforward control and filtering the frequency components that may become external disturbances, the impulse response decays to 0.

[0055] In step S7, a laser head position control value is calculated based on the predicted value of the next workpiece position based on the corrected variation waveform. Then, in step S8, masking processing corresponding to the output of the masking MAP from step S9 is executed. The masking MAP in step S9 determines whether it is the start or end of the cutting of the workpiece W by inputting the horizontal position of the laser head. When a negative determination is made and "1" is output, the FF (feedforward) control commands in steps S2, S3, S4, S5, S6, S7, and S8 are input to the adder 82.

[0056] On the other hand, when an affirmative determination is made in step S9, that is, when it is determined that it is the start or end of the cutting of the workpiece W, "0" is output from the shielding MAP, and a series of feedforward controls are not executed. This is to ensure that even at the start and end of the cutting of the workpiece W, where the workpiece W may vibrate and become unsuitable for feedforward control, only feedback control is employed in this region to stabilize the gap control.

[0057] For the feedforward control in steps S2, S3, S4, S5, S6, S7, and S8, in step S1 that constitutes the feedback control, a laser head position control value using the difference from the target value is calculated. Then, the above-mentioned FF (feedforward) control instruction and the FB (feedback) control instruction in step S1 are input to the adder 82. Figure 6 The shown feedforward control means 74 is constituted by the above-mentioned steps S2, S3, S4, S5, S6, S7, and S8. Additionally, Figure 6 The shown feedback control means 75 is constituted by the above-mentioned step S1.

[0058] As described above, according to the laser head control method of the present embodiment, the gap G between the laser head H and the workpiece W is detected, and feedforward control is executed. The feedforward control adjusts the gap G according to the predicted value of the gap G based on the change history of the gap G. Therefore, the cutting speed can be increased by keeping the gap G at a constant value, and the production volume of the laser processing apparatus 10 can be increased. In addition to the feedforward control, feedback control is also executed. The feedback control adjusts the gap G while comparing the gap G with the target value of the gap G. Therefore, more stable gap control can be achieved.

[0059] Furthermore, the laser processing apparatus 10 applying the laser head control method of the present embodiment includes: a gap detection means 71 that detects the gap G between the laser head H and the workpiece W; and a feedforward control means 74 that executes feedforward control. The feedforward control adjusts the gap G according to the predicted value of the gap G based on the change history of the gap G. Therefore, the cutting speed can be increased by keeping the gap G at a constant value, and the production volume of the laser processing apparatus 10 can be increased.

[0060] The structure or configuration of the laser processing system or laser processing apparatus, the shape or structure of the laser head, the structure or configuration of measuring devices such as linear encoders, the method of detecting the gap, the method of setting the workpiece position, the target value of the gap, the sampling interval of the workpiece position, the number of samples saved as history, the structure of the feedforward control, etc. are not limited to the above-mentioned embodiments and can be variously changed. The laser head control method of the present invention can be applied to laser processing systems of various sizes or structures.

[0061] Reference Numerals

[0062] 1: Laser processing system

[0063] 10: Laser processing device

[0064] 70: Gap control device

[0065] 71: Gap detection means

[0066] 72: Control unit

[0067] 73: Gap adjustment means

[0068] 74: Feedforward control means

[0069] 75: Feedback control means

[0070] H: Laser head

[0071] W: Workpiece

[0072] G: Gap

Claims

1. A laser head control method is applied to a laser processing apparatus that uses the laser irradiated by a laser head to cut a workpiece. The laser head control method detects the gap between the laser head and the workpiece, and performs feedforward control, where the feedforward control adjusts the gap according to the predicted value of the gap based on the change history of the gap.

2. The laser head control method according to claim 1, wherein, in addition to the feedforward control, feedback control is also performed, and the feedback control adjusts the gap while comparing the gap with the target value of the gap.

3. The laser head control method according to claim 2, wherein, at the start and end of the cutting of the workpiece, the feedforward control is not performed.

4. The laser head control method according to claim 1, wherein, the gap is sampled at a specified interval, and interpolation of the specified interval is performed according to the operation speed magnification input by the operator.

5. The laser head control method according to claim 4, wherein, a finite impulse response filter is applied to the sampled data after the interpolation.

6. The laser head control method according to claim 5, wherein, the finite impulse response filter adjusts the gain of the feedforward control and filters out the frequency components that may become external disturbances.

7. A laser processing apparatus uses the laser irradiated by a laser head to cut a workpiece. The laser processing apparatus includes: a gap detection means for detecting the gap between the laser head and the workpiece; and, a feedforward control means for performing feedforward control, where the feedforward control adjusts the gap according to the predicted value of the gap based on the change history of the gap.

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