Long-distance moving air floatation guide rail system

Abstract

The utility model relates to the technical field of industrial production equipment, in particular to a long-distance moving air floatation guide rail system. The long-distance moving air floating guide rail system comprises a sliding block installed on a guide rail, the guide rail is provided with a plurality of air channels and air paths connected with an air supply pipeline, a set of air outlet holes are formed in the portion, corresponding to each air path, between the guide rail and the sliding block and connected with the air paths, and air flows out of the air outlet holes to form an air film; the top end of the air throttle is fixed to the side wall of the guide rail, the inner wall of the sliding block makes contact with the top end of the air throttle and presses downwards to open the air throttle, and the air throttle automatically rebounds and is closed after the sliding block leaves. According to the long-distance moving air floating guide rail system, the normally-closed air throttle is used for controlling opening and closing of the air channel, the air throttle is extruded to be opened through movement of the sliding block, the air throttle can be opened and closed at any time according to movement of the sliding block, the air consumption is reduced, meanwhile, the influence of delay of an induction equipment control system is avoided, extra wiring work is not needed, and cost is reduced. The structure is simple and the installation workload is small.

Description

Technical Field

[0001] The utility model relates to the technical field of industrial production equipment, in particular to a long-distance mobile air-floating guide rail system. Background Art

[0002] In industrial production and processing, air-floating guide rail systems have the advantages of high precision, low friction, and long life, and are widely used. During operation, the air-floating guide rail needs to ensure the air-floating stiffness and air film thickness, which results in excessive air output from the air-floating guide rail during operation. How to reduce gas leakage and pressure loss while maintaining stable air path pressure is an important technical issue for existing air-floating rail equipment technology. In the existing technology, sensing devices such as photoelectric switches, magnetic switches, and solenoid valves are often used to control the opening and closing of each air channel in the air-floating guide rail. However, the response speed of the sensing device has a certain delay relative to the movement of the slider, and the reliability is insufficient. At the same time, additional line layout and wiring work are required when installing the sensing device. The device structure is complex and the installation workload is large. Therefore, in response to the above shortcomings, a long-distance movable air-floating guide rail system is proposed. Summary of the Invention

[0003] (1) Technical issues to be resolved

[0004] In response to the shortcomings of the existing technology, the utility model provides a long-distance mobile air flotation guide rail system, which solves the problems of slow response speed, insufficient reliability, complex structure and large installation workload of existing air flotation guide rail equipment in reducing gas leakage and pressure loss.

[0005] (2) Technical solution

[0006] In order to solve the above problems, the utility model provides a long-distance mobile air-floating guide rail system, comprising:

[0007] The slider and guide rail, the bottom surface of the slider is provided with a guide rail groove that cooperates with the guide rail and is buckled downward onto the guide rail and moves back and forth along the guide rail; a number of vertical air channels are evenly arranged inside the guide rail along the front and back directions, each air channel is provided with an air path horizontally arranged along the left and right directions of the guide rail, an air supply pipe is provided under the guide rail, and the bottom end of the air channel is connected to the air supply pipe; on the longitudinal section corresponding to each air channel on the guide rail surface, the part in contact with the slider is evenly provided with a plurality of air outlet holes, the air outlet holes are connected to the air path, and the gas in the air supply line flows out from the air outlet holes to form an air film between the guide rail and the slider; a horizontal and normally closed throttle valve is provided below the air path on each of the air channels, and the top of the throttle valve is fixed on the side wall of the guide rail, and the slider moves along the guide rail to squeeze the top of the throttle valve to open the throttle valve, and the top of the throttle valve automatically rebounds and closes after the slider leaves.

[0008] Preferably, an upper air plug is provided at the top of each airway, and a side air plug is provided at the end of each airway.

[0009] Preferably, the throttle valve includes a sleeve, and a radially penetrating outer air hole corresponding to the position of the air supply branch is provided on the side wall of the sleeve; a valve core and a cylindrical cam are provided in the sleeve, the lower end of the cylindrical cam is inserted into the valve core, and the top end is fixed on the side wall of the guide rail; the side wall of the valve core is provided with a radially penetrating inner air hole, and the slider moves back and forth along the guide rail to press down the top end of the cylindrical cam and rotate the valve core so that the inner air hole and the outer air hole coincide with each other.

[0010] Preferably, sealing rings are provided at the upper and lower ends of the valve core respectively; and a pressure cover is provided at the bottom end of the sleeve.

[0011] Preferably, the cross-section of the fitting point between the bottom end of the cylindrical cam and the valve core is polygonal, the top end of the cylindrical cam is in the shape of a cone, and a spring is provided between the bottom end of the cone and the top end of the valve core; a plurality of guide grooves obliquely extending from top to bottom are evenly provided on the outer wall of the cone at the top end of the cylindrical cam along the circumferential direction, and a guide pin is provided at the position of the inner wall of the sleeve corresponding to the position of the guide groove, and the bottom end of the guide pin is inserted into the guide groove.

[0012] Preferably, washers are provided between the upper and lower ends of the spring and the valve core and the cylindrical cam.

[0013] Preferably, a ball retainer is provided at the top of the cylindrical cam, and balls are provided between the cylindrical cam and the ball retainer; the balls extend out of the side wall of the guide rail, and the slider moves back and forth along the guide rail to squeeze the balls and press the cylindrical cam downward.

[0014] Preferably, an end cover is provided above the ball retainer, the end cover and the side wall of the guide rail are in the same plane, and the top end of the ball extends out from the center of the end cover.

[0015] Preferably, a retaining ring is provided around the ball on the end cover, and a protective cover is provided above the retaining ring.

[0016] Preferably, an inward chamfered structure is provided at the position where the inner wall of the slider contacts the ball.

[0017] (3) Beneficial effects

[0018] The long-distance movable air flotation guide rail system provided by the utility model is provided with a normally closed throttle valve on the air channel and the top end of the throttle valve is fixed to the side wall of the guide rail. The throttle valve is squeezed to open by the movement of the slider. When the slider moves on the slide rail, each throttle valve is opened synchronously to form an air film between the slider and the guide rail. The air valve is opened and closed at any time according to the movement of the slider, thereby reducing the gas consumption of the device during operation. At the same time, the throttle valve is used to replace the traditional sensing equipment, which is not affected by the delay of the sensing equipment control system. The device has a fast response speed and does not require additional wiring work. It has a simple structure and a small installation workload. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1This is a schematic structural diagram of the long-distance mobile air-floating guide rail system of the utility model;

[0020] Figure 2 This is a cross-sectional view of the long-distance mobile air-floating guide rail system of the utility model;

[0021] Figure 3 This is a structural diagram of the throttle valve of the long-distance mobile air floating guide system of the utility model;

[0022] Figure 4 This is a disassembled diagram of the throttle valve of the long-distance mobile air floating guide system of the utility model.

[0023] Among them, 1. slider; 2. guide rail; 201. upper air plug; 202. side air plug; 203. air supply line; 3. throttle valve; 301. pressure cover; 302. sealing ring; 303. valve core; 304. sleeve; 305. guide pin; 306. gasket; 307. spring; 308. cylindrical cam; 309. ball; 3010. ball retainer; 3011. end cover; 3012. retaining ring; 3013. protective cover. DETAILED DESCRIPTION

[0024] 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.

[0025] In the description of the present invention, it is necessary to understand that the directions or positional relationships indicated by “upper”, “lower”, “inside”, “outside”, “top”, “bottom”, etc. are all based on the directions or positional relationships shown in the accompanying drawings. The purpose is only to facilitate the description of the present invention and simplify the description. It does not indicate or imply that the referred parts must have a specific direction, be constructed and operated in a specific direction. Therefore, it cannot be understood as a limitation on the present invention.

[0026] like Figure 1-4As shown, the utility model provides a long-distance mobile air-floating guide rail system, specifically comprising: a slider 1 and a guide rail 2. The bottom surface of the slider 1 is provided with a guide rail groove that cooperates with the guide rail 2 and is buckled downward onto the guide rail 2 and moves forward and backward along the guide rail 2. The position of the guide rail 2 is fixed and unchanged. During operation, the slider 1 moves back and forth along the front-to-back direction of the guide rail 2 according to work requirements. The inside of the guide rail 2 is evenly provided with a number of vertical air channels along the front-to-back direction. Each air channel is provided with an air path horizontally arranged along the left-to-right direction of the guide rail 2. An air supply line 203 is provided below the guide rail 2, and the bottom end of the air channel is connected to the air supply line 203. On the longitudinal section corresponding to each air channel on the surface of the guide rail 2, the part in contact with the slider 1 is evenly provided with a plurality of air outlets. The air outlets are connected to the air path. The gas in the air supply line 203 flows out from the air outlets to form an air film between the guide rail 2 and the slider 1. During operation, after connecting the input end of the air supply line 203 to the pressure air source, the pressure air source is turned on to continuously deliver the working air to the air supply line 203. The working air flows into the air channel and the air path along the air supply line 203 and then flows out from the air outlet, flowing to between the slider 1 and the guide rail 2, forming a layer of air film between the slider 1 and the guide rail 2, separating the slider 1 and the guide rail 2. When the slider 1 moves on the surface of the guide rail 2, the air film slightly lifts the slider 1 upward, thereby reducing the friction between the slider 1 and the guide rail 2. While ensuring that the slider 1 can move back and forth along the guide rail 2, the wear between the slider 1 and the guide rail 2 is reduced, thereby extending the service life of the device.

[0027] The strength and thickness of the air film are determined by the air output and pressure of the air outlet. During operation, the greater the air output and pressure, the stronger the air film. Generally, as the weight of the object that the slider 1 needs to bear and carry increases, the strength of the air film also needs to increase. At this time, the air outlet pressure can be increased by controlling the output pressure of the pressure gas source. When the outlet pressure remains unchanged, increasing the diameter of the air outlet can increase the air output of the air outlet. During operation, the outlet well and the output pressure of the pressure gas source are adjusted according to actual work needs.

[0028] It should be noted that in order to reduce the processing difficulty and workload of the device, when making the guide rail 2, the air duct is usually formed by a processing drill bit penetrating the guide rail 2 from top to bottom, and the air duct is formed by a processing drill tool extending from the side wall of the guide rail 2 into the guide rail 2 to the designated position. In order to prevent the gas from overflowing from the air path and the processing position of the air path during operation, resulting in an increase in the gas consumption of the device, an upper air plug 201 is usually provided at the top of each air path and a side air plug 202 is provided at the end of each air path. The air duct and the air path are sealed by the upper air plug 201 and the side air plug 202, thereby improving the sealing of the device and avoiding excessive gas consumption caused by air leakage during operation of the device.

[0029] like Figure 2-4As shown, each airway in the present invention is equipped with a horizontal, normally closed throttle valve 3 below the airway. The throttle valve 3 controls the opening and closing of the airway. When the throttle valve 3 is open, the airway is open, and the working air flows normally from the airway to the outlet, forming an air film between the guide rail 2 and the slider 1. When the throttle valve 3 is closed, the airway is blocked, and the air film disappears.

[0030] In which, the throttle valve 3 includes a sleeve 304, and a radially penetrating external air hole corresponding to the position of the air supply branch is provided on the side wall of the sleeve 304; a valve core 303 and a cylindrical cam 308 are provided in the sleeve 304, and the lower end of the cylindrical cam 308 is inserted into the valve core 303, and the top end is fixed on the side wall of the guide rail 2; the side wall of the valve core 303 is provided with a radially penetrating internal air hole, and the slider 1 moves back and forth along the guide rail 2 to press down the top end of the cylindrical cam 308 and rotate the valve core 303 so that the internal air hole and the external air hole coincide with each other. The sleeve 304 serves as the main body of the throttle valve 3 and is installed in the guide rail 2. The throttle valve 3 controls the switch of the throttle valve 3 through the inner and outer air holes on the valve core 303 and the sleeve 304. When the positions of the inner air hole and the outer air hole coincide with each other, the air passage is opened, and the working air flows upward into the air passage along the inner and outer air holes through the throttle valve, forming an air film between the guide rail 2 and the slider 1; conversely, when the valve core 303 rotates to separate the inner and outer air holes, the throttle valve 3 is closed, and the air film of the corresponding part disappears. The cylindrical cam 308 serves as the switch and transmission device for the throttle valve 3. After the top of the cylindrical cam 308 is fixed to the side wall of the guide rail 2, the slider 1 will contact the top of the guide rail 2 as it moves along the guide rail 2. As the slider 1 continues to move, the inner wall of the slider 1 will squeeze the top of the cylindrical cam 308 into the guide rail 2. As the cylindrical cam 308 moves inward, it converts the pressure of the slider 1 into a torsional force that drives the valve core 303 to rotate, thereby controlling the opening of each throttle valve 3 while the slider 1 moves. By controlling the opening and closing of the airway and the formation of the air film through the throttle valve 3, there is no need to use sensors or other sensing instruments to control the formation of the air film. Relying solely on the mechanical structure, it can respond immediately when the slider 1 passes by. The response speed is fast and no additional wiring work is required when installing the sensing instrument, which reduces the workload of assembling the device and simplifies the device structure.

[0031] It should be noted that the cross-section of the bottom end of the cylindrical cam 308 where it mates with the valve core 303 is polygonal, while the top end of the cylindrical cam 308 is truncated. Several guide grooves extending diagonally from top to bottom are evenly distributed along the circumference of the outer wall of the truncated cone at the top of the cylindrical cam 308. A guide pin 305 is provided on the inner wall of the sleeve 304 at a position corresponding to the guide groove, with the bottom end of the guide pin 305 inserted into the guide groove. Under the action of the guide pin 305 and the guide groove, when the slider 1 moves into the guide rail 2 and pushes the cylindrical cam 308, due to the fixed position of the guide pin 305, the guide pin 305 contacts the inner wall of the guide groove and, along the shape of the guide groove, pushes the cylindrical cam 308 to rotate. When the cylindrical cam 308 rotates, since the cross-section of its bottom and the valve core 303 is polygonal, when the cylindrical cam 308 rotates, the wall of the bottom end contacts the inner wall of the valve core 303 and transmits the rotational force of the cylindrical cam 308 to the valve core 303, driving the valve core 303 to rotate synchronously, thereby realizing opening the throttle valve 3 when the cylindrical cam 308 is pushed inward.

[0032] In order to save the air output of the device, the throttle valve 3 should automatically close the throttle valve after the slider 1 passes so that the air film on the surface of the guide rail 2 disappears after the slider 1 passes. Therefore, it is necessary to make the top of the cylindrical cam 308 in the throttle valve 3 automatically rebound after the slider 1 passes. To achieve the above effect, a spring 307 is usually provided between the bottom end of the cone and the top end of the valve core 303. When the top end of the cylindrical cam 308 loses the pressure of the slider 1 after the slider 1 passes, the spring 307 pushes the cylindrical cam 308 outward under its own elastic action. During the upward movement of the cylindrical cam 308, the guide pin 305 pushes the cylindrical cam 308 along the guide groove to rotate. The rotation direction of the cylindrical cam 308 is opposite to the rotation direction when the cylindrical cam 308 is squeezed inward. At this time, the bottom end of the rotating cylindrical cam 308 drives the valve core 303 to rotate synchronously, thereby restoring the valve core 303 and the cylindrical cam 308 to their original positions, realizing the automatic closing of the throttle valve 3.

[0033] To improve the sealing performance of the device, sealing rings 302 are provided at the upper and lower ends of the valve core 303 to prevent working air from leaking out of the ends of the valve core 303 when the throttle valve 3 is closed, thereby increasing the device's gas consumption. Furthermore, a gland 301 is provided at the bottom end of the sleeve 304. This gland 301 is primarily used to seal the sleeve 304, sealing the throttle valve 3 and its internal components into a single unit. Washers 306 are provided between the upper and lower ends of the spring 307, the valve core 303, and the cylindrical cam 308. These washers 306 act as a buffer between the upper and lower ends of the spring 307, the valve core 303, and the cylindrical cam 308, preventing the spring 307 from wearing out the valve core 303 and the cylindrical cam 308 during repeated compression and extension, thereby reducing wear on the device during use and extending its service life.

[0034] In the present invention, a ball retainer 3010 is provided at the top of the cylindrical cam 308, with a ball 309 positioned between the cylindrical cam 308 and the ball retainer 3010. The ball extends out from the sidewall of the guide rail 2, and the slider 1 moves back and forth along the guide rail 2, squeezing the ball 309 and pressing the cylindrical cam 308 downward. The ball retainer 3010 secures the ball 309 to the top of the cylindrical cam 308. When the slider 1 passes, the inner wall of the slider 1 contacts the ball 309, gradually pushing the ball 309 and the cylindrical cam 308 inward, thereby opening the throttle valve. When the ball 309 contacts the inner wall of the slider 1, it rotates according to the direction of the pressure applied to it, balancing the tangential pressure applied to it, reducing friction when it releases from the slider 1, and increasing its service life.

[0035] An end cap 3011 is located above the ball retainer 3010. This end cap 3011 is flush with the sidewall of the guide rail 2, and the top of the ball 309 extends from the center of the end cap 3011. This end cap 3011 secures the throttle valve 3 within the guide rail 2, preventing it from moving outward during operation. It also maintains a flat surface around the ball 309, keeping the slider 1 flat during movement and preventing jolting that could affect the device's efficiency.

[0036] It should be noted that the end cap 3011 is provided with a retaining ring 3012 around the ball 309, and a protective cover 3013 is provided above the retaining ring 3012. The retaining rings 3012 and 3013 cooperate to fill the gap around the ball 309 and protect the ball 309, preventing dust, gravel, and other debris from falling into the gap between the ball 309 and the end cap 3011 during operation, causing the ball to jam.

[0037] In addition, an inward chamfered structure is provided at the contact position between the inner wall of the slider 1 and the ball 309. When the slider 1 contacts the ball 309, the ball 309 contacts the chamfered structure. As the slider 1 moves, the ball 309 is gradually pressed down to reduce the friction force on the ball 309. At this time, the ball 309 will roll along the chamfered structure and will not produce rigid contact with the slider 1, further reducing the wear between the slider 1 and the ball 309 when pressing the ball 309.

[0038] The long-distance mobile air-floating guide rail system provided by this utility model can reduce gas leakage and pressure loss while maintaining stable gas line pressure and has strong reliability. The specific operation process of the device is as follows:

[0039] Step 1: Select a guide rail of appropriate length according to work requirements and install the slider on the guide rail.

[0040] Step 2: Start the pressure gas source connected to the gas supply line. At this time, the working gas flows into the airway along the gas supply line, and after the throttle valve is opened, the working gas flows out from the gas outlet along the gasway and gas line.

[0041] Step 3: Move the slider on the guide rail according to work requirements. During this process, when the slider moves in the specified direction, the inner wall of the slider will contact and press the ball bearings protruding from the side wall of the guide rail in the forward direction. The ball bearings press down the cylindrical cam and drive the valve core to rotate, so that the inner air hole on the valve core coincides with the outer air hole on the sleeve. At this time, the throttle valve opens, and the working air flows out from the air channel and the air outlet hole along the inner edge of the air path corresponding to the open throttle valve. At this time, the working air flows into the space between the slider and the guide rail, forming an air film to reduce the friction between the guide rail and the slider.

[0042] Step 4: The slider continues to move. At this point, the slider continues to move forward, opening the throttle valves in front of it one by one along the trajectory as described in step 3, so that there is always an air film between the slider and the guide rail. At the same time, after the end of the slider passes, the ball bearing separated from the slider loses the pressure applied by the slider, and the spring bounces upward and drives the valve core to rotate back to its original position, separating the inner and outer air holes, closing the throttle valve, and eliminating the air film in the area after the slider passes.

[0043] Step 5. Repeat steps 3 and 4. When the slider moves on the guide rail, the throttle valve at the position where it moves opens so that there is always an air film between the slider and the guide rail. When the slider leaves, the throttle valve in the area it passes through automatically closes to eliminate the air film, saving gas consumption of the device.

[0044] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or make equivalent replacements for some of the technical features therein. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A long distance mobile air float guide rail system, characterized in that: include: A slider (1) and a guide rail (2), wherein the bottom surface of the slider (1) is provided with a guide rail groove that matches the guide rail (2) and is buckled downwardly onto the guide rail (2) and moves forward and backward along the guide rail (2); a plurality of vertical air channels are evenly arranged inside the guide rail (2) along the front-back direction, each air channel is provided with an air channel horizontally arranged along the left-right direction of the guide rail (2), an air supply pipe (203) is provided below the guide rail (2), and the bottom end of the air channel is connected to the air supply pipe (203); on the longitudinal section corresponding to each air channel on the surface of the guide rail (2), the part in contact with the slider (1) A plurality of air outlet holes are evenly arranged, and the air outlet holes are connected to the air path. The gas in the air supply pipeline (203) flows out from the air outlet holes to form an air film between the guide rail (2) and the slider (1); a horizontal and normally closed throttle valve (3) is provided below the air path on each of the air paths, and the throttle valve (3) controls the opening and closing state of the air path; the top end of the throttle valve (3) is fixed on the side wall of the guide rail (2), and the slider (1) moves along the guide rail (2) to squeeze the top end of the throttle valve (3) to open the throttle valve (3), and after the slider (1) leaves, the top end of the throttle valve (3) automatically rebounds and closes.

2. The long-distance mobile air-floating guide rail system according to claim 1, characterized in that: An upper air plug (201) is provided at the top of each airway, and a side air plug (202) is provided at the end of each airway.

3. The long-distance mobile air-floating guide rail system according to claim 2, characterized in that: The throttle valve (3) comprises a sleeve (304), and a radially penetrating outer air hole corresponding to the position of the air supply branch is provided on the side wall of the sleeve (304); a valve core (303) and a cylindrical cam (308) are provided in the sleeve (304), and the lower end of the cylindrical cam (308) is inserted into the valve core (303), and the top end is fixed on the side wall of the guide rail (2); the side wall of the valve core (303) is provided with a radially penetrating inner air hole, and the slider (1) moves forward and backward along the guide rail (2) to press down the top end of the cylindrical cam (308) and rotate the valve core (303) so that the inner air hole and the outer air hole overlap.

4. The long-distance mobile air-floating guide rail system according to claim 3, characterized in that: The upper and lower ends of the valve core (303) are respectively provided with sealing rings (302); the bottom end of the sleeve (304) is provided with a pressure cover (301).

5. The long-distance mobile air-floating guide rail system according to claim 3, characterized in that: The cross section of the fitting portion between the bottom end of the cylindrical cam (308) and the valve core (303) is polygonal, the top end of the cylindrical cam (308) is truncated, and a spring (307) is provided between the bottom end of the truncated cone and the top end of the valve core (303); a plurality of guide grooves extending obliquely from top to bottom are uniformly provided on the outer wall of the truncated cone at the top end of the cylindrical cam (308) along the circumferential direction, and a guide pin (305) is provided on the inner wall of the sleeve (304) at a position corresponding to the guide groove, and the bottom end of the guide pin (305) is inserted into the guide groove.

6. The long-distance mobile air-floating guide rail system according to claim 5, characterized in that: Washers (306) are provided between the upper and lower ends of the spring (307) and the valve core (303) and the cylindrical cam (308).

7. The long-distance mobile air-floating guide rail system according to claim 5, characterized in that: A ball retainer (3010) is provided at the top of the cylindrical cam (308), and a ball (309) is provided between the cylindrical cam (308) and the ball retainer (3010); the ball extends out of the side wall of the guide rail (2), and the slider (1) moves forward and backward along the guide rail (2) to squeeze the ball (309) and press the cylindrical cam (308) downward.

8. The long-distance mobile air-floating guide rail system according to claim 7, characterized in that: An end cover (3011) is provided above the ball retainer (3010), the end cover (3011) and the side wall of the guide rail (2) are in the same plane, and the top end of the ball (309) extends from the center of the end cover (3011).

9. The long-distance mobile air-floating guide rail system according to claim 8, characterized in that: A retaining ring (3012) is provided on the end cover (3011) around the ball (309), and a protective cover (3013) is provided above the retaining ring (3012).

10. The long-distance mobile air-floating guide rail system according to claim 9, characterized in that: An inward chamfered structure is provided at the contact position between the inner wall of the slider (1) and the ball (309).

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