Gas rectifying mechanism of laser processing head

Abstract

The embodiment of the utility model discloses a gas rectifying mechanism of a laser processing head, a cavity and a positive pressure chamber are arranged in the gas rectifying mechanism, and the flowing direction of gas in the positive pressure chamber deviates from a protective mirror, so that the protective mirror can be prevented from being polluted by reverse slag splashed into the laser processing head. The problem that a protective mirror in an existing laser machining head is prone to being polluted by reverse slag dirt is solved. Moreover, the gas flow is not in direct contact with the protective glasses, so that on one hand, the influence of smudginess of the gas on the protective glasses can be reduced, and the cleanliness of the protective glasses can be ensured; on the other hand, the temperature of the gas can be prevented from being transmitted to the protective glass, and the optical performance of the protective glass is prevented from being affected; in addition, a negative pressure chamber is defined by the protective glass, the sealing piece and the annular protrusion, gas in the negative pressure chamber can press the sealing piece to be tightly attached to the wall face of the cavity, and therefore the protective glass is sealed by the sealing piece.

Description

Technical Field

[0001] The utility model relates to the technical field of laser processing, in particular to a gas rectification mechanism of a laser processing head. Background Art

[0002] In laser cutting applications, the protective mirror inside the laser processing head is easily contaminated by backslag. When the protective mirror is contaminated, stray light increases, weakening the laser energy, resulting in unstable cutting and the inability to cut through the workpiece. When the contaminants accumulate to a certain level, the protective mirror is prone to burning. Once the protective mirror burns out, the laser processing head will not function properly, requiring timely replacement, increasing operating costs. Even more seriously, if the backslag contaminants are large in diameter, they may break the protective mirror. If the backslag penetrates the protective mirror, the impact can paralyze the entire laser cutting optical system, resulting in high repair costs. Utility Model Content

[0003] The utility model aims to propose a gas rectification mechanism for a laser processing head, aiming to solve the problem that the protective mirror in the existing laser processing head is easily contaminated by anti-slag dirt.

[0004] The utility model provides a gas rectification mechanism for a laser processing head, wherein a cavity and a positive pressure chamber are provided in the gas rectification mechanism, the cavity is connected to the mounting port and the air inlet channel of the gas rectification mechanism, a protective mirror is installed at the mounting port, and the positive pressure chamber is connected to the air inlet channel;

[0005] Wherein, the flow direction of the gas in the positive pressure chamber is away from the protective mirror.

[0006] In one embodiment, an annular protrusion is further provided in the cavity, and the annular protrusion and the wall surface of the positive pressure chamber are combined to form a guide channel. The guide channel is connected to the positive pressure chamber and is used to guide the gas transmitted into the positive pressure chamber to flow in a direction away from the protective mirror.

[0007] In one embodiment, the gas rectification mechanism further includes a sealing member, the protective mirror is mounted at the mounting port via the sealing member, and the protective mirror, the sealing member, the wall of the cavity, and the annular protrusion enclose a negative pressure chamber;

[0008] The gas in the negative pressure chamber can compress the sealing member to fit tightly against the wall of the cavity, so that the sealing member seals the protective mirror.

[0009] In one embodiment, the gas rectification mechanism further includes an annular sleeve, the positive pressure chamber is arranged in the annular sleeve, the annular sleeve is arranged in the cavity, and the outer wall of the annular sleeve and the wall surface of the cavity are combined to form an annular cavity, and the air inlet channel is connected to the annular cavity and the positive pressure chamber in sequence.

[0010] In one embodiment, the gas flow direction in the positive pressure chamber is along the axial direction of the annular sleeve, and the gas flow direction in the annular cavity is along the axial direction of the annular sleeve and is opposite to the gas flow direction in the positive pressure chamber.

[0011] In one embodiment, the annular cavity is distributed in a spiral or bow shape.

[0012] In one embodiment, the annular cavity includes a plurality of channels extending in a direction away from the protective mirror, and the channels are spaced apart from each other.

[0013] In one embodiment, a guide surface is formed on the side of the annular protrusion facing the annular sleeve, and an extension direction of an axial cross section of the guide surface is arranged at an angle of 30° to 40° with the axial direction of the annular sleeve; and / or,

[0014] The air inlet channel includes an air inlet hole and an air inlet cavity. The air inlet cavity is annular and is arranged around the annular cavity. The air inlet hole connects the air inlet cavity and the annular cavity. The flow cross-sectional area of ​​the annular cavity and the flow cross-sectional area of ​​the air inlet cavity are both larger than the flow cross-sectional area of ​​the air inlet hole.

[0015] In one embodiment, the positive pressure chamber is further connected with a gas channel and a tapered channel in sequence along the axial direction of the gas flow, and the radial cross-sectional diameters of the gas channel and the tapered channel gradually decrease along the axial direction of the gas flow.

[0016] In one embodiment, the tapered channel is further connected to a first straight channel and a second straight channel in sequence along the axial direction of the gas flow, and the radial cross-sections of the first straight channel and the second straight channel remain unchanged.

[0017] The present invention employs a gas rectification mechanism for a laser processing head, which includes a positive pressure chamber within an annular sleeve. Because the gas flow within the positive pressure chamber is directed away from the protective mirror, it prevents backslag contamination from splashing into the laser processing head, thereby preventing the protective mirror from being contaminated by backslag contamination. This solves the problem of the protective mirror in existing laser processing heads being easily contaminated by backslag contamination. Furthermore, because the gas flow within the positive pressure chamber is directed away from the protective mirror, the gas flow does not directly contact the protective mirror. This reduces the impact of gas contamination on the protective mirror, ensuring its cleanliness. Furthermore, it prevents the gas temperature from being transferred to the protective mirror, thereby avoiding any impact on its optical performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0019] in:

[0020] Figure 1 FIG. 4 is a cross-sectional view of a laser processing head according to an embodiment.

[0021] Figure 2 for Figure 1 Enlarged schematic diagram of part A in the middle.

[0022] Figure 3 A cross-sectional view of a gas rectification mechanism in a laser processing head according to an embodiment.

[0023] Figure 4 for Figure 3 Enlarged schematic diagram of part B in the middle.

[0024] Figure 5 Schematic diagram of the gas path of a laser processing head in one embodiment.

[0025] Figure 6 The figure is a schematic diagram of the gas path at the gas rectification mechanism in a laser processing head according to an embodiment.

[0026] Figure 7 This is a partial enlarged view of the gas path at the gas rectification mechanism in a laser processing head according to an embodiment.

[0027] Figure 8 Schematic diagram of the gas pressure in a laser processing head according to an embodiment.

[0028] Figure numbers: 10, nozzle; 20, protective mirror; 30, gas rectification mechanism; 40, seal; 50, sealing ring; 60, ceramic ring; 70, locking ring; 100, main body; 110, cavity; 120, air inlet channel; 121, air inlet hole; 122, air inlet cavity; 130, annular protrusion; 131, guide channel; 132, guide surface; 140, cooling channel; 150, gas channel; 160, mounting port 160; 170, negative pressure chamber; 200, annular sleeve; 210, positive pressure chamber; 220, annular cavity; 221, first annular segment; 222, second annular segment; 223, third annular segment; 230, annular boss; 301, tapered channel; 302, first straight channel; 303, second straight channel. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0030] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative position relationship, movement status, etc. between the various components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0031] In addition, the descriptions of "first," "second," etc. in this utility model are for descriptive purposes only and should not be understood as indicating or implying their relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features specified as "first" or "second" may explicitly or implicitly include at least one of the aforementioned features. In addition, the technical solutions between the various embodiments may be combined with each other, but this must be based on the fact that they can be implemented by ordinary technicians in this field. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by this utility model.

[0032] The present invention discloses a gas rectification mechanism for a laser processing head, which can perform laser processing such as laser cutting and laser welding on a workpiece. Figures 1 to 4 A laser processing head of one embodiment includes a laser head, a nozzle 10, a protective mirror 20 and a gas rectifying mechanism 30. The nozzle 10 and the protective mirror 20 are respectively arranged at the axial ends of the gas rectifying mechanism 30. The gas rectifying mechanism 30 can provide protective gas to the bottom of the protective mirror 20, and transport it from the bottom of the protective mirror 20 to the nozzle 10 for ejection. The laser beam generated by the laser head can pass through the protective mirror 20 and finally be ejected from the nozzle 10, thereby performing laser processing on the workpiece by the laser beam.

[0033] In this embodiment, the gas rectification mechanism 30 includes a main body 100 and an annular sleeve 200. The main body 100 is provided with a cavity 110, and an installation port 160 and an air inlet channel 120 connected to the cavity 110. The protective mirror 20 is installed at the installation port 160. A positive pressure chamber 210 is provided in the annular sleeve 200. The annular sleeve 200 is arranged in the cavity 110, and the outer wall of the annular sleeve 200 and the wall surface of the cavity 110 are enclosed to form an annular cavity 220. The air inlet channel 120 is connected with the annular cavity 220 and the positive pressure chamber 210 in sequence; wherein, the gas flow direction in the positive pressure chamber 210 is away from the protective mirror 20.

[0034] It can be understood that since the direction of gas flow in the positive pressure chamber 210 is away from the protective mirror 20, it can prevent the anti-slag dirt from splashing into the laser processing head and contaminating the protective mirror 20, solving the problem that the protective mirror in the existing laser processing head is easily contaminated by anti-slag dirt.

[0035] In addition, since the direction of gas flow in the positive pressure chamber 210 is away from the protective mirror 20, the gas flow does not directly contact the protective mirror 20. On the one hand, it can reduce the impact of the gas's own dirt on the protective mirror 20 and ensure the cleanliness of the protective mirror 20; on the other hand, it can prevent the temperature of the gas from being transmitted to the protective mirror 20, thereby avoiding affecting the optical performance of the protective mirror 20.

[0036] It should be noted that the laser beam tends to be transmitted toward the low temperature direction. If the gas flow directly hits the protective mirror 20, the impurities in the gas will rub against the protective mirror 20 and heat up, which will be detrimental to the laser beam passing through the protective mirror 20, that is, affecting the optical performance of the protective mirror 20.

[0037] In one embodiment, an annular protrusion 130 is further provided in the cavity 110, and the annular protrusion 130 and the wall surface of the positive pressure chamber 210 are enclosed to form a guide channel 131. The guide channel 131 connects the annular cavity 220 and the positive pressure chamber 210, and is used to guide the gas transmitted to the positive pressure chamber 210 to flow in a direction away from the protective mirror 20, so as to prevent the anti-slag dirt from splashing into the laser processing head and contaminating the protective mirror 20, thereby solving the problem that the protective mirror in the existing laser processing head is easily contaminated by anti-slag dirt.

[0038] In one embodiment, the annular cavity 220 includes a first annular segment 221, a second annular segment 222, and a third annular segment 223 that are sequentially connected in a direction from the air inlet channel 120 to the guide channel 131. The flow cross-sectional area of ​​the second annular segment 222 is smaller than the flow cross-sectional area of ​​the first annular segment 221, and smaller than the flow cross-sectional area of ​​the third annular segment 223.

[0039] It can be understood that the gas enters the annular cavity 220 through the air inlet channel 120 and accumulates in the first annular segment 221 for a circle. Since the flow cross-sectional area of ​​the second annular segment 222 is smaller than the flow cross-sectional area of ​​the first annular segment 221, the turbulence of the gas flow can be reduced after the gas passes through the second annular segment 222, so that the gas can be transmitted evenly and stably. The gas then flows smoothly through the third annular segment 223, the guide channel 131 and the positive pressure chamber 210, and finally converges in the nozzle 10 of the laser processing head to blow out the gas flow, thereby achieving smooth blowing of the cutting gas, thereby ensuring sufficient kinetic energy of the cutting gas, and blowing out the anti-slag dirt splashing toward the nozzle 10, solving the problem that the protective mirror 20 in the existing laser processing head is easily contaminated by anti-slag dirt, thereby extending the service life of the protective mirror 20 and reducing the cutting instability caused by stray light, thereby ensuring the stability and reliability of laser cutting and laser welding.

[0040] In addition, since the cutting gas blown out of the nozzle 10 has sufficient kinetic energy, the nozzle 10 can be controlled to be farther away from the plate during the laser processing process. On the one hand, the influence of the reflected blue light on the follow-up stability of the laser processing system can be reduced. On the other hand, the probability of the nozzle 10 colliding with the plate can be reduced, thereby ensuring the stability of the laser processing.

[0041] In one embodiment, the laser processing head further includes a seal 40, through which the protective mirror 20 is mounted at the mounting opening 160. The protective mirror 20, the seal 40, the wall of the cavity 110, and the annular protrusion 130 enclose a negative pressure chamber 170. Gas within the negative pressure chamber 170 compresses the seal 40 to form a tight fit with the wall of the cavity 110, allowing the seal 40 to seal the protective mirror 20, thereby ensuring the sealing performance of the seal 40 and preventing dust from entering the surface of the protective mirror 20 facing away from the negative pressure chamber 170. Specifically, the seal 40 can be a flood seal.

[0042] It can be understood that the positive pressure chamber 210 is below the negative pressure chamber 170, and the gas pressure at the positive pressure chamber 210 is greater than the gas pressure at the negative pressure chamber 170, that is, the negative pressure chamber 170 is in a negative pressure state relative to the positive pressure chamber 210, but this negative pressure state is a relative state, that is, the gas pressure in the negative pressure chamber 170 is not necessarily lower than the external atmospheric pressure, and may also be higher than the external atmospheric pressure. Specifically, due to the viscosity of the airflow, when the airflow blows downward in the positive pressure chamber 210 in the direction away from the protective mirror 20, it will drive the airflow here to rotate, thereby forming a negative pressure state in the negative pressure chamber 170.

[0043] Furthermore, in the direction from the plenum chamber 210 to the nozzle 10, the gas pressure in the plenum chamber 210 is the highest. As the gas is transported along the direction from the plenum chamber 210 to the nozzle 10, the gas pressure gradually decreases. The pressure difference drives the gas to be transported along the direction from the plenum chamber 210 to the nozzle 10, resulting in the highest gas pressure in the plenum chamber 210 and lower gas pressure in the upper negative pressure chamber 170 and the direction of the nozzle 10 below. It should be noted that because the upper negative pressure chamber 170 is semi-enclosed and only connected to the lower plenum chamber 210, the airflow does not flow upward from the plenum chamber 210, and the pressure cannot be relieved in the negative pressure chamber 170.

[0044] Furthermore, in this embodiment, the laser processing head further includes a sealing ring 50, which elastically seals between the body 100 and the annular sleeve 200. Specifically, the body 100 further includes a gas passage 150 connected to the plenum chamber 210. The gas passage 150 connects the plenum chamber 210 and the nozzle 10, and the radial cross-sectional area of ​​the plenum chamber 210 gradually decreases along the direction of gas flow.

[0045] In one embodiment, see Figures 1 to 4 The gas flow direction in the plenum chamber 210 is along the axial direction of the annular sleeve 200. The gas flow direction in the annular cavity 220 is along the axial direction of the annular sleeve 200 and opposite to the gas flow direction in the plenum chamber 210. The provision of the flow guide channel 131 can change the gas flow direction so that the gas flow direction in the plenum chamber 210 is parallel to the transmission direction of the laser beam, thereby preventing damage to the protective mirror 20.

[0046] Furthermore, in this embodiment, a guide surface 132 is formed on the side of the annular protrusion 130 facing the annular sleeve 200. The extending direction of the axial cross section of the guide surface 132 is set at an angle of 30° to 40° with the axial direction of the annular sleeve 200, so that the guide channel 131 can guide the gas flow into the positive pressure chamber 210 along the corresponding angle, thereby preventing damage to the protective mirror 20. See the attached Figure 3 In the figure, the angle α is the included angle between the extending direction of the axial cross section of the guide surface 132 and the axial direction of the annular sleeve 200 .

[0047] Specifically, the extending direction of the axial cross-section of the guide surface 132 is set at an angle of 30°, 32°, 34°, 36°, 38°, or 40° to the axial direction of the annular sleeve 200. Of course, in other embodiments, the extending direction of the axial cross-section of the guide surface 132 can also be set at an angle of 25°, 28°, 43°, 45°, or other angles to the axial direction of the annular sleeve 200.

[0048] In one embodiment, the first annular segment 221 is a through annular gas storage cavity or a plurality of interconnected fan-shaped gas storage cavities, which is mainly used for gas storage.

[0049] In one embodiment, the flow cross-sectional area of ​​the first annular segment 221 is greater than the flow cross-sectional area of ​​the third annular segment 223 .

[0050] In this embodiment, the second annular segment 222 can have various implementations. The inner wall of the second annular segment 222 is an arc surface or a conical surface.

[0051] In one embodiment, see Figures 1 to 4 An annular boss 230 is formed on the outer wall of the annular sleeve 200, and the annular boss 230 and the wall surface of the cavity 110 are enclosed to form a second annular segment 222. Through such an arrangement, the flow cross-sectional area of ​​the second annular segment 222 can be made smaller than the flow cross-sectional area of ​​the first annular segment 221. Therefore, after the gas passes through the second annular segment 222, the turbulence of the gas flow can be reduced, thereby enabling the gas to be transmitted evenly and stably.

[0052] In another embodiment, an annular boss 230 is formed on the wall surface of the cavity 110, and the annular boss 230 and the outer wall of the annular sleeve 200 are enclosed to form a second annular segment 222. Through such an arrangement, the flow cross-sectional area of ​​the second annular segment 222 can be made smaller than the flow cross-sectional area of ​​the first annular segment 221. Therefore, after the gas passes through the second annular segment 222, the turbulence of the gas flow can be reduced, thereby allowing the gas to be transmitted evenly and stably.

[0053] In another embodiment, a first boss is formed on the outer wall of the annular sleeve 200, and a second boss is formed on the wall of the cavity 110. The first boss and the second boss are combined to form a second annular segment 222. Through such an arrangement, the flow cross-sectional area of ​​the second annular segment 222 can be made smaller than the flow cross-sectional area of ​​the first annular segment 221. Therefore, the turbulence of the gas flow can be reduced after the gas passes through the second annular segment 222, so that the gas can be transmitted evenly and stably.

[0054] In one embodiment, see Figures 1 to 4 In the first annular segment 221, the distance between the outer wall of the annular sleeve 200 and the wall of the cavity 110 is a first spacing dimension. In the second annular segment 222, the distance between the outer wall of the annular sleeve 200 and the wall of the cavity 110 is a second spacing dimension. In the third annular segment 223, the distance between the outer wall of the annular sleeve 200 and the wall of the cavity 110 is a third spacing dimension. The second spacing dimension is smaller than the third spacing dimension, and the third spacing dimension is smaller than the first spacing dimension. This arrangement allows the flow cross-sectional area of ​​the second annular segment 222 to be smaller than that of the first annular segment 221. Therefore, the turbulence of the gas flow can be reduced after passing through the second annular segment 222, thereby ensuring uniform and stable gas transmission.

[0055] In another embodiment, the annular cavity 220 is distributed in a spiral or bow shape; alternatively, the annular cavity 220 includes a plurality of channels extending in a direction away from the protective mirror 20, and the channels are spaced apart from each other.

[0056] In one embodiment, please refer to Figures 5 to 7 , the intake channel 120 includes an intake hole 121 and an intake cavity 122. The intake cavity 122 is annular and is disposed around the first annular segment 221. The intake hole 121 connects the intake cavity 122 and the first annular segment 221; the flow cross-sectional area of the first annular segment 221 and the flow cross-sectional area of the intake cavity 122 are both larger than the flow cross-sectional area of the intake hole 121.

[0057] By setting it in this way, the gas flow accumulates in the intake cavity 122 for one circle, enters the first annular segment 221 through the intake hole 121, and the turbulence of the gas flow can be reduced after passing through the second annular segment 222, so that the gas can be transmitted evenly and stably, thereby ensuring sufficient kinetic energy of the cutting gas and blowing out the slag and dirt splashing towards the nozzle 10, solving the problem that the protective mirror 20 in the existing laser processing head is easily contaminated by the slag and dirt.

[0058] Furthermore, in this embodiment, a plurality of intake holes 121 are provided and are circumferentially spaced apart on the first annular segment 221. The diameter dimension of the intake hole 121 is D, and the axial dimension at the junction of the third annular segment 223 and the diversion channel 131 is L, where 0.5D < L <​​​​​​​​The above disclosure is only a preferred embodiment of the present invention, and certainly cannot be used to limit the scope of rights of the present invention. Therefore, equivalent changes made according to the claims of the present invention are still within the scope covered by the present invention.

Claims

1. A gas rectification mechanism for a laser processing head, the laser processing head including a protective mirror, characterized in that: The gas rectification mechanism is provided with a cavity and a positive pressure chamber, and the gas rectification mechanism has a mounting port and an air inlet channel, the mounting port, the cavity and the air inlet channel are connected, the protective mirror is installed at the mounting port, and the air inlet channel is connected to the positive pressure chamber; Wherein, the flow direction of the gas in the positive pressure chamber is away from the protective mirror.

2. The gas rectification mechanism according to claim 1, characterized in that: An annular protrusion is also provided in the cavity, and the annular protrusion and the wall surface of the positive pressure chamber are enclosed to form a guide channel. The guide channel is connected to the positive pressure chamber and is used to guide the gas transmitted into the positive pressure chamber to flow in a direction away from the protective mirror.

3. The gas rectification mechanism according to claim 2, characterized in that: The gas rectification mechanism further includes a sealing member, the protective mirror is mounted at the mounting port via the sealing member, and the protective mirror, the sealing member, the wall surface of the cavity and the annular protrusion enclose a negative pressure chamber; The gas in the negative pressure chamber can compress the sealing member to fit tightly against the wall of the cavity, so that the sealing member seals the protective mirror.

4. The gas rectification mechanism according to claim 2, characterized in that: The gas rectification mechanism also includes an annular sleeve, the positive pressure chamber is arranged in the annular sleeve, the annular sleeve is arranged in the cavity, and the outer wall of the annular sleeve and the wall surface of the cavity are combined to form an annular cavity, and the air inlet channel is connected to the annular cavity and the positive pressure chamber in sequence.

5. The gas rectification mechanism according to claim 4, characterized in that: The gas flow direction in the positive pressure chamber is along the axial direction of the annular sleeve, and the gas flow direction in the annular cavity is along the axial direction of the annular sleeve and is opposite to the gas flow direction in the positive pressure chamber.

6. The gas rectification mechanism according to claim 4, characterized in that: The annular cavity is distributed in a spiral or bow shape.

7. The gas rectification mechanism according to claim 4, characterized in that: The annular cavity includes a plurality of channels extending in a direction away from the protective mirror, and the channels are spaced apart from each other.

8. The gas rectification mechanism according to claim 4, characterized in that: The annular protrusion is formed with a guide surface on one side facing the annular sleeve, and the extending direction of the axial cross section of the guide surface is arranged at an angle of 30° to 40° with the axial direction of the annular sleeve; and / or, The air inlet passage includes an air inlet hole and an air inlet cavity, the air inlet cavity is annular and arranged around the annular cavity, and the air inlet hole communicates with the air inlet cavity and the annular cavity; The flow cross-sectional area of ​​the annular cavity and the flow cross-sectional area of ​​the air inlet cavity are both larger than the flow cross-sectional area of ​​the air inlet hole.

9. The gas rectification mechanism according to claim 1, characterized in that: The positive pressure chamber is also connected to a gas channel and a tapered channel in sequence along the axial direction of the gas flow, and the radial cross-sectional diameters of the gas channel and the tapered channel gradually decrease along the axial direction of the gas flow.

10. The gas rectification mechanism according to claim 9, characterized in that: The tapered channel is further connected with a first straight channel and a second straight channel in sequence along the axial direction of the gas flow, and radial cross-sections of the first straight channel and the second straight channel remain unchanged.

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