Detailed Description
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(first embodiment)
Fig. 1 is a side sectional view of a weft insertion device of an air jet loom showing an embodiment of the present invention, fig. 2 is a schematic front view thereof, and fig. 3 is a perspective view of a main part thereof.
As shown in fig. 1 to 3, the weft insertion device of the air jet loom includes a modified reed 1. The modified reed 1 is attached to a sley 2. The modified reed 1 includes a pair of upper and lower reinforcing members 3 and 4 and a plurality of dents 5 held by the reinforcing members 3 and 4. The modified reed 1 is a long member having a weaving width direction as a longitudinal direction. The plurality of dents 5 are arranged at predetermined intervals in the longitudinal direction X of the modified reed 1. Gaps for passing the warp yarns T are provided between the dents 5 adjacent to each other in the longitudinal direction X of the modified reed 1. Of the pair of reinforcing members 3, 4, the upper reinforcing member 3 sandwiches the upper edge portions of the plurality of dents 5, and the lower reinforcing member 4 sandwiches the lower edge portions of the plurality of dents 5. The lower reinforcing member 4 is fixed to the slay 2 by a fixing member 6.
A main nozzle 7 is disposed upstream of the modified reed 1 in the weft insertion direction X1. In the case of inserting the weft yarn Y by the air injected from the main nozzle 7, the weft insertion direction X1 is the direction in which the weft yarn Y advances. The main nozzle 7 is a nozzle for inserting the weft yarn Y at the opening portion of the warp yarn T divided into upper and lower portions. On the other hand, a plurality of sub-nozzles 8 are arranged in the longitudinal direction X of the modified reed 1. When the weft yarn Y flies by the ejection of air from the main nozzle 7, these sub-nozzles 8 eject air in a relay manner in order to assist the flying of the weft yarn Y. Each sub-nozzle 8 is attached to the slay 2 via a nozzle support member 9. The nozzle support member 9 is fixed to the slay 2 using bolts 11 and nuts 12.
Recesses 15 are formed in the front surfaces of the plurality of dents 5, respectively. The recess 15 is formed by an upper wall surface 16, a lower wall surface 17 and a back wall surface 18. The recess 15 is open on the side facing the back wall surface 18. The back wall surface 18 is a surface including at least a wall surface located on the innermost side when the recess 15 of the dent 5 is viewed from the opening side (front surface side). In the modified reed 1, a weft insertion path S is formed by a recess 15 formed in each dent 5. The weft insertion path S is a path formed by the rows of the recesses 15 of the respective dents 5 by arranging the plurality of dents 5 in the weft insertion direction X1. An axis J passing through the center of the weft insertion path S is an axis parallel to the longitudinal direction X of the modified reed 1. On the other hand, As shown in fig. 3, each sub-nozzle 8 ejects the air As obliquely to the axis J of the weft insertion path S.
The modified reed 1 is provided so as to be capable of swinging operation by a swinging mechanism not shown. The swing motion of the modified reed 1 is a motion performed for beating up. The modified reed 1 performs a swing operation so as to alternately repeat forward movement in the beating-up direction F and backward movement in the reverse beating-up direction R. Then, beating-up by the modified reed 1 is performed while the modified reed 1 is moving forward.
Fig. 4 is a view of the modified reed according to the first embodiment of the present invention, taken at a position D-D in fig. 1.
As shown in fig. 4, the plurality of dents 5 are divided into two dent rows 21 and 22 in the longitudinal direction X of the modified reed 1. The dent row 21 corresponds to a first dent row, and the dent row 22 corresponds to a second dent row. The dent row 21 is composed of a plurality of dents 5a arranged in the longitudinal direction X of the modified reed 1, and the dent row 22 is composed of a plurality of dents 5b arranged in the longitudinal direction X of the modified reed 1. The dent row 22 is disposed downstream of the dent row 21 in the weft insertion direction X1. In addition, the dent 5a disposed on the most downstream side in the dent row 21 and the dent 5b disposed on the most upstream side in the dent row 22 are disposed adjacent to each other in the weft insertion direction X1.
The back wall surfaces 18 of the dents 5a belonging to the dent row 21 are inclined in the direction of entering the weft insertion path S side in the weft insertion direction X1, and the back wall surfaces 18 of the dents 5b belonging to the dent row 22 are also inclined in the direction of entering the weft insertion path S side in the weft insertion direction X1. Further, the back wall surface 18 of the dent 5a belonging to the dent row 21 is inclined at the first inclination angle θ 1 with respect to the axis J of the weft insertion path S. On the other hand, the back wall surface 18 of the dent 5b belonging to the dent row 22 is inclined at a second inclination angle θ 2 larger than the first inclination angle θ 1 with respect to the axis J of the weft insertion path S. In the dent row 21, the back wall surfaces 18 of the dents 5a are inclined at the same inclination angle θ 1, and in the dent row 22, the back wall surfaces 18 of the dents 5b are inclined at the same inclination angle θ 2.
The boundary position P between the dent row 21 and the dent row 22 is set as follows.
First, when air is injected from each of the main nozzle 7 and the plurality of sub-nozzles 8 at a predetermined timing to fly the weft yarn Y, the weft yarn Y moves in the weft insertion direction X1 in accordance with the flow of the air. At this time, when the position through which the leading end of the weft yarn Y passes at the timing of switching the swing motion of the deformed reed 1 from the backward motion to the forward motion is set as the first position E1, the boundary position P of the dent rows 21 and 22 is set to the first position E1. The first position E1 is a position specified based on the design of the weft insertion device, experimental data when the weft insertion device is operated, simulation results of the weft insertion device, or the like. The setting of the boundary position P of the dent rows 21 and 22 will be described in further detail below.
Fig. 5 is a diagram showing a relationship between an angular velocity of a reed and a machine base angle in a swing operation of a deformed reed.
The angular velocity of the reed may be a negative value or a positive value depending on the moving direction of the deformed reed 1 during the swing motion. The period in which the angular velocity of the reed takes a negative value is a period in which the deformed reed 1 performs backward movement (hereinafter, also referred to as a "backward movement period"). The backward movement period is a period in which the angle of the machine is 0 DEG to 180 deg. On the other hand, a period in which the angular velocity of the reed takes a positive value is a period in which the deformed reed 1 is moved forward (hereinafter, also referred to as "forward movement period"). The forward movement period is a period in which the angle of the machine is 180 DEG to 360 deg. In this case, the timing at which the deformed reed 1 is switched from the backward movement to the forward movement is the timing at which the machine base angle is 180 °. In addition, the timing of switching the back movement to the forward movement of the modified reed 1 may be shifted forward or backward from the timing when the machine base angle is 180 ° due to the design of the weft insertion device.
On the other hand, a period Ta during which weft Y is inserted (hereinafter referred to as "weft insertion period") is a period in which the bed angle is 80 ° to 240 °. Therefore, the intermediate time of the weft insertion period Ta is the time when the bed angle is 160 °, that is, the time when the deformed reed 1 performs the backward movement. Therefore, when the leading end of the weft yarn Y is moved in the longitudinal direction X of the deformed reed 1 during the weft insertion period Ta, if the position at which the leading end of the weft yarn Y passes through at the intermediate time of the weft insertion period Ta is the intermediate position C in fig. 4, the boundary position P between the reed dent row 21 and the reed dent row 22 is set downstream of the intermediate position C in the weft insertion direction X1. The start time and the end time of the weft insertion period Ta may be set to be out of the range of the table angle due to the design of the weft insertion device.
Fig. 6 is a diagram showing a change in the position of the weft yarn leading end in the first embodiment of the present invention. In fig. 6, the vertical axis represents the longitudinal position of the deformed reed, and the horizontal axis represents the machine angle. The position in the longitudinal direction of the deformed reed is 0 at the start end of weft insertion. The leading end of weft insertion refers to the end of the deformed reed on the side where the main nozzle is arranged in the longitudinal direction of the deformed reed.
As shown in fig. 6, the leading end of the weft moves in the longitudinal direction of the deformed reed from the time when the bed angle at the start time of the weft insertion period Ta becomes 80 ° to the time when the bed angle at the end time of the weft insertion period Ta becomes 240 °. Further, the leading end of the weft yarn passes through the first position E1 in the longitudinal direction of the deformed reed at the time when the machine angle is 180 °. A boundary position P between the dent row 21 and the dent row 22 is set to match the first position E1 (see fig. 4).
In this way, when the boundary position P between the dent row 21 and the dent row 22 is set to the first position E1, the measurement result of the wind pressure value (cmAq) in the weft insertion path S is as shown in fig. 7. The measurement of the wind pressure value is performed in a state where the deformed reed 1 is stopped without swinging. As a procedure for measurement, first, a sub-nozzle for measuring a wind pressure is disposed at a position 50mm away from a wind pressure measurement point in the weft insertion path S of the modified reed 1 in the weft insertion direction X1. Next, while a constant amount of air is ejected from the sub-nozzle for measuring wind pressure toward the weft insertion path S, the position of the sub-nozzle for measuring wind pressure is moved in the longitudinal direction X of the modified reed 1, and during the movement, the wind pressure value at the wind pressure measurement point in the weft insertion path S is measured by the sensor. At this time, the position of the wind pressure measurement point moves in accordance with the movement of the sub-nozzle for wind pressure measurement. When the measurement result is observed, the wind pressure value in the weft insertion path S is constant L1 from the start end of weft insertion to the first position E1, but increases Δ L beyond the first position E1 and becomes constant L2 from that point to the end of weft insertion.
The reason why the wind pressure value in the weft insertion path S is changed in this way is as follows.
First, in the longitudinal direction X of the modified reed 1, the dent row 21 is located closer to the weft insertion start side than the first position E1, and the dent row 22 is located closer to the weft insertion end side than the first position E1. Further, the back wall surface 18 of the dents 5a belonging to the dent row 21 is inclined at a first inclination angle θ 1, and the back wall surface 18 of the dents 5b belonging to the dent row 22 is inclined at a second inclination angle θ 2 larger than the first inclination angle θ 1. When air is ejected from the sub-nozzle for measuring wind pressure toward the weft insertion path S, the larger the inclination angle of the back wall surface 18 of the dent 5 is, the larger the value of wind pressure in the weft insertion path S becomes. This is because, when the air is ejected from the sub-nozzle for measuring the wind pressure toward the weft insertion path S, if the inclination angle of the back wall surface 18 is increased, the amount of air reflected toward the weft insertion path S in contact with the back wall surface 18 of the reed dent 5 increases, and the wind pressure value in the weft insertion path S increases due to the increase in the amount of air. Therefore, the value of the wind pressure in the weft insertion path S is larger by Δ L than the first position E1 on the weft insertion terminal side in the longitudinal direction X of the deformed reed 1 as shown in fig. 7.
Next, a technical meaning of a case where the boundary position P between the dent row 21 and the dent row 22 is set at the first position E1 will be described.
First, when the reed 1 is oscillated, air flows between the dents 5 due to the movement of the reed 1 during the oscillating operation. Specifically, as shown in fig. 8, when the modified reed 1 moves in the reverse beating-up direction R, the air a flows between the dents 5 in the direction opposite to the moving direction R. As shown in fig. 9, when the modified reed 1 moves in the beat-up direction F, the air a flows between the dents 5 in the direction opposite to the moving direction F.
On the other hand, when air is ejected from each sub-nozzle 8 toward the weft insertion path S, a part of the air leaks to the rear side of the deformed reed 1 through the gap between the dents 5. At this time, the amount of air leaking through between the dents 5 differs between the case where the modified reed 1 moves in the reverse beating-up direction R and the case where the modified reed 1 moves in the beating-up direction F. The reason for this is as follows.
First, when the modified reed 1 moves in the reverse beating-up direction R, the air a (see fig. 8) flowing between the dents 5 plays a role of suppressing leakage of the air As ejected from the sub-nozzles 8 toward the weft insertion path S. Therefore, the amount of air leaking to the rear side B of the modified reed 1 becomes small. On the other hand, when the modified reed 1 moves in the beating-up direction F, the air a (see fig. 9) flowing between the dents 5 functions to promote leakage of the air As ejected from the sub-nozzles 8 toward the weft insertion path S. Therefore, the amount of air leaking to the rear side B of the modified reed 1 becomes large.
Here, if only the dent row 21 is disposed in the entire longitudinal direction X of the modified reed 1, the leading end of the weft yarn Y is easily drawn between the dents 5 by the action of the air a (see fig. 9) flowing between the dents 5 by the forward movement of the modified reed 1, as shown in fig. 10. When the leading end of the weft yarn Y is inserted between the dents 5, the leading end of the weft yarn Y comes into contact with the dents 5 and the flying state becomes unstable, and a phenomenon occurs in which the leading end side of the weft yarn Y is curled into waves, that is, end curling.
In the first embodiment, the boundary position P between the dent row 21 and the dent row 22 is set to the first position E1. The first position E1 is a position at which the leading end of the weft yarn Y passes when the swing motion of the reed 1 is switched from backward movement to forward movement. Therefore, the leading end of the weft yarn Y passes through the section of the dent row 21 when the deformed reed 1 moves backward and passes through the section of the dent row 22 when the deformed reed 1 moves forward. In the first embodiment, the back wall surface 18 of the dent 5b belonging to the dent row 22 is inclined at the second inclination angle θ 2 larger than the first inclination angle θ 1. Therefore, the amount of air reflected toward the weft insertion path S in contact with the back wall surface 18 of the reed dent 5b in the air discharged from the sub-nozzle 8 increases on the weft insertion terminal side of the boundary position P between the reed dent row 21 and the reed dent row 22. Therefore, when the leading end of the weft yarn Y passes the weft insertion terminal side of the boundary position P, the amount of air reflected from the back wall surface 18 of the dent 5b increases, and the weft yarn Y is less likely to approach the back wall surface 18. As a result, even during the forward movement of the deformed reed 1, the leading end of the weft yarn Y is less likely to be sucked between the dents 5b, and therefore, the occurrence of end crimp can be suppressed. Further, since the amount of air leaking to the rear side of the deformed reed 1 through the gap between the dents 5b is reduced on the weft insertion terminal side with respect to the boundary position P, a drop in flying speed due to air leakage can be suppressed.
When the boundary position P between the dent row 21 and the dent row 22 is set upstream of the first position E1 in the weft insertion direction X1, the leading end of the weft yarn Y reaches the dent row 22 during backward movement of the deformed reed 1. In this case, the momentum of the air reflected from the back wall surface 18 of the dents 5b belonging to the dent row 22 toward the weft insertion path S is increased by the air a (see fig. 8) flowing between the dents 5 by the backward movement of the deformed reed 1. Therefore, a trouble that the leading end of the weft yarn Y flies out from the weft insertion passage S is likely to occur. On the other hand, when the boundary position P between the dent row 21 and the dent row 22 is set to the first position E1, the leading end of the weft yarn Y does not reach the dent row 22 during the backward movement of the modified reed 1, and therefore, the occurrence of a failure in which the leading end of the weft yarn Y flies out from the weft insertion passage S can be suppressed.
(second embodiment)
Next, a second embodiment of the present invention will be explained.
First, the effect obtained by the first embodiment described above can be obtained also when the boundary position P between the dent row 21 and the dent row 22 is set on the downstream side in the weft insertion direction X1 from the first position E1. However, in this case, in consideration of the braking process performed after the leading end of the weft yarn Y passes through the first position E1, it is necessary to set the boundary position P between the dent row 21 and the dent row 22. The following description is made in detail.
First, in a weft insertion device of an air jet loom, when air is injected from each of the main nozzle 7 and the plurality of sub-nozzles 8 at a predetermined timing to fly the weft yarn Y, a brake may be applied to the flying weft yarn Y. The timing of starting the application of the brake to the weft yarn Y is later than the timing of switching the swing motion of the reed 1 from the backward movement to the forward movement. Therefore, if the position at which the leading end of the weft yarn Y passes at the timing when the brake starts to be applied to the flying weft yarn Y is set as the second position E2, the second position E2 is shifted downstream in the weft insertion direction X1 from the first position E1.
When the brake is applied to the flying weft yarn Y, the flying speed of the weft yarn Y is reduced and the linearity of the weft yarn Y is weakened, so that the tip of the weft yarn Y is easily sucked between the dents 5. Therefore, in the present second embodiment, as shown in fig. 11, the boundary position P between the dent row 21 and the dent row 22 is set to the second position E2 so that the leading end of the weft yarn Y is less likely to be sucked between the dents 5 even if the leading end of the weft yarn Y passes through the second position E2. The second position E2 is a position specified based on the design of the weft insertion device, experimental data when the weft insertion device is operated, simulation results of the weft insertion device, or the like.
Fig. 12 is a diagram showing a change in the position of the weft yarn leading end in the second embodiment of the present invention.
As shown in fig. 12, the leading end of the weft moves in the longitudinal direction of the deformed reed from the time when the bed angle at the start time of the weft insertion period becomes 80 ° to the time when the bed angle at the end time of the weft insertion period becomes 240 °. The leading end of the weft yarn passes through the first position E1 in the longitudinal direction of the modified reed at the time when the machine angle is 180 °, and passes through the second position E2 in the longitudinal direction of the modified reed at the time when the machine angle is 205 °. After the leading end of the weft yarn passes through the second position E2, the ratio of the position change of the leading end of the weft yarn is reduced. This is because the braking of the weft yarn is started at the timing when the leading end of the weft yarn passes through the second position E2, and the flying speed of the weft yarn is thereby reduced. The boundary position P between the dent row 21 and the dent row 22 is set to match the second position E2.
In this way, when the boundary position P between the dent row 21 and the dent row 22 is set to the second position E2, as shown in fig. 13, the measurement result of the wind pressure value (cmAq) in the weft insertion path S is a constant value L1 from the start end of weft insertion to the second position E2, and Δ L is increased beyond the second position E2 to a constant value L2 from there to the end of weft insertion. The measurement result indicates that the amount of air reflected by contacting the back wall surface 18 of the dent 5b of the dent row 22 at the weft insertion terminal side from the second position E2 is larger than the amount of air reflected by contacting the back wall surface 18 of the dent 5a of the dent row 21 at the weft insertion starting side from the second position E2.
Next, a technical meaning of a case where the boundary position P between the dent row 21 and the dent row 22 is set to the second position E2 will be described.
First, when the reed 1 is oscillated, as shown in fig. 8 and 9, the air a flows between the dents 5 in accordance with the moving direction of the reed 1. At this time, the air a (see fig. 9) flowing between the dents 5 due to the movement of the deformed reed 1 in the beating-up direction F acts to promote the leakage of the air ejected from each sub-nozzle 8 toward the weft insertion path S. However, at the timing when the swing operation of the modified reed 1 is switched from the backward movement to the forward movement, the moving speed of the modified reed 1 is substantially zero, and the modified reed 1 starts the forward movement from this state. Therefore, the influence of the forward movement of the modified reed 1 on the flying state of the weft yarn Y is small during the period from the start of the forward movement of the modified reed 1 to the sufficient increase of the moving speed of the modified reed 1. Therefore, even if the boundary position P between the dent row 21 and the dent row 22 is set to be shifted from the first position E1 toward the weft insertion terminal side, a large difference is not generated in the effect of suppressing the occurrence of end crimp. However, when the leading end of the weft yarn Y passes through the second position E2, the brake is applied to the weft yarn Y, and the flying speed of the weft yarn Y is reduced, so that the leading end of the weft yarn Y is easily sucked between the dents 5. On the other hand, when the boundary position P between the dent row 21 and the dent row 22 is set to the second position E2, the amount of air that comes into contact with the back wall surface 18 of the dent 5b and is reflected toward the weft insertion path S increases on the weft insertion terminal side of the second position E2. Therefore, even if the leading end of the weft yarn Y passes through the second position E2, the leading end of the weft yarn Y is less likely to be sucked between the dents 5 b. Therefore, the occurrence of end curl can be suppressed.
(third embodiment)
Next, a third embodiment of the present invention will be explained.
In the third embodiment of the present invention, as shown in fig. 14, the point different from the first embodiment is that the plurality of dents 5 are divided into three dent rows 20, 21, 22 in the longitudinal direction X of the modified reed 1. The dent row 21 corresponds to a first dent row, the dent row 22 corresponds to a second dent row, and the dent row 20 corresponds to a third dent row. The dent row 20 is composed of a plurality of dents 5c arranged in the longitudinal direction X of the modified reed 1. The dent row 20 is disposed upstream of the dent row 21 in the weft insertion direction X1. The boundary position P0 between the dent row 20 and the dent row 21 is set closer to the main nozzle 7 than the boundary position P between the dent row 21 and the dent row 22.
Among the three dent rows 20, 21, and 22, the back wall surface 18 of the dents 5a belonging to the dent row 21 is inclined at the first inclination angle θ 1, and the back wall surface 18 of the dents 5b belonging to the dent row 22 is inclined at the second inclination angle θ 2, which is the same as the first embodiment. On the other hand, the back wall surface 18 of the dent 5c belonging to the dent row 20 is set to a third inclination angle smaller than the first inclination angle θ 1 with respect to the axis J of the weft insertion path S, specifically, an inclination angle of substantially 0 °.
In this way, when the reed dent row 20 is disposed in the vicinity of the main nozzle 7 and the inclination angle of the back wall surface 18 of the reed dent 5c belonging to the reed dent row 20 is set to be small, the measurement result of the wind pressure value (cmAq) in the weft insertion path S is as shown in fig. 15. That is, the wind pressure value in the weft insertion path S is a constant value L0 from the start end of weft insertion to the E0 position, increases by Δ L1 when exceeding the E0 position, and is a constant value L1 from that position to the first position E1. When the wind pressure exceeds the first position E1, the wind pressure value in the weft insertion path S increases by Δ L, and from there to the end of weft insertion, the wind pressure value becomes a constant value L2. The measurement result indicates that the amount of air reflected by contacting the back wall surface 18 of the dent 5c of the dent row 20 at the weft insertion start side from the position E0 is smaller than the amount of air reflected by contacting the back wall surface 18 of the dent 5a of the dent row 21 at the weft insertion end side from the position E0. The measurement result described above means that the amount of air reflected by the contact with the back wall surface 18 of the dent 5b of the dent row 22 on the weft insertion terminal side from the first position E1 is larger than the amount of air reflected by the contact with the back wall surface 18 of the dent 5a of the dent row 21 on the weft insertion starting side from the first position E1.
When the dent row 20 is arranged in the vicinity of the main nozzle 7, the air injected from the main nozzle 7 greatly affects the flying state of the weft yarn Y when the leading end of the weft yarn Y passes through the section of the dent row 20. Therefore, if the inclination angle of the back wall surface 18 of the dent 5c belonging to the dent row 20 is set to be large, the amount of air that comes into contact with the back wall surface 18 of the dent 5c and is reflected toward the weft insertion path S side, among the air injected from the main nozzle 7, increases. In this way, a failure in which the leading end of the weft yarn Y flies out from the weft insertion passage S is likely to occur.
Therefore, in the third embodiment, the inclination angle of the back wall surface 18 of the dent 5c belonging to the dent row 20 is set to be small. Therefore, when the leading end of the weft yarn Y passes through the section of the dent row 20, the amount of air reflected toward the weft insertion path S in contact with the back wall surface 18 of the dent 5c is reduced by the ejection of air from the main nozzle 7. Therefore, the occurrence of a failure in which the leading end of the weft yarn Y flies out from the weft insertion passage S due to the air reflected from the back wall surface 18 of the reed dent 5c can be suppressed. On the other hand, since the boundary position P between the dent row 21 and the dent row 22 is set to the first position E1, the occurrence of end curl can be suppressed as in the first embodiment.
The technical scope of the present invention is not limited to the above-described embodiments, and various modifications and improvements may be made within the scope of deriving the specific effects obtained by combining the constituent elements of the invention.
For example, in the first and third embodiments, the boundary position P between the dent row 21 and the dent row 22 is set to the first position E1, and in the second embodiment, the boundary position P between the dent row 21 and the dent row 22 is set to the second position E2, but the present invention is not limited thereto. That is, the boundary position P between the dent row 21 and the dent row 22 may be set downstream of the first position E1 in the weft insertion direction X1, or may be set upstream of the second position E2 in the weft insertion direction X1. That is, any position can be set as long as the boundary position P of the dent row 21 and the dent row 22 is between the first position E1 and the second position E2.
In the third embodiment, the inclination angle of the back wall surface 18 of the dents 5c belonging to the dent row 20 is set to substantially 0 °, but the present invention is not limited thereto. That is, the inclination angle of the back wall surface 18 of the reed dent 5c may be set to an angle larger than 0 ° as long as the condition that the inclination angle is smaller than the first inclination angle θ 1 is satisfied.
In the first, second, and third embodiments, the back wall surface 18 is inclined in the upper wall surface 16, the lower wall surface 17, and the back wall surface 18 forming the recess 15 of the reed dent 5, but one or both of the upper wall surface 16 and the lower wall surface 17 may be inclined similarly to the back wall surface 18.