A type of coil press with object measurement function

Abstract

This invention relates to the field of transformer coil pressing technology, specifically to a downward-pressing coil pressing machine with physical measurement function. It includes a servo cylinder, a fixed crossbeam, a pressing platform, guide columns, a bidirectional moving trolley, and a fixed base. At least four guide columns are provided. The fixed crossbeam is connected to the top of each guide column, and the fixed base is connected to the bottom of each guide column. The bidirectional moving trolley is used to load the coil workpiece and is movably mounted on the fixed base. The servo cylinder is connected to the fixed crossbeam, and its output end is connected to the pressing platform. Multiple guide columns pass through the pressing platform. This invention simplifies the coil pressing process, saves pressing costs, and improves pressing efficiency by applying downward pressure through the pressing platform. A laser rangefinder sensor is used to achieve closed-loop servo control of the pressing accuracy from the pressing equipment to the actual coil, ensuring pressing precision. A spoke-type force sensor is used to achieve real-time and precise control of the coil pressing force. The bidirectional moving trolley allows for one workpiece to be used as a backup, significantly improving the production efficiency of automated production lines.

Description

Technical Field

[0001] This invention relates to the field of transformer coil press technology, specifically to a pressure coil press with physical measurement function. Background Technology

[0002] In existing technology, such as CN103187169A, a bottom-mounted device for pressing transformer coils is described. This device divides the coil pressing and shaping into two moving parts: an upper clamping beam and a hydraulic cylinder. When pressing the same batch of products, the height of the upper clamping beam is adjusted first, and then the hydraulic cylinder presses upwards. The advantages of this invention are that the cylinder stroke can be very short, significantly reducing costs; and the bottom-mounted cylinder and piping design eliminates the possibility of coil failure due to oil leakage.

[0003] A novel CNC coil press, disclosed in publication number CN116373370A, includes a work platform, a servo cylinder, a pressure platform, a movable platform, columns, a mechanical force sensor, a linear encoder, and a reading head. The movable platform is located above the pressure platform and moves along the axial direction of the columns under the drive of the servo cylinder. The movable platform, driven by the mechanical force sensor, synchronously moves the pressure platform to press the transformer coil placed on the work platform. Multiple columns are sequentially distributed around the pressure platform and the movable platform. The linear encoder and the reading head are both mounted on the movable platform, with a preset gap between them. The purpose of this novel CNC coil press is to solve the problem of poor pressing accuracy and stability in existing transformer coil pressing equipment.

[0004] The design method of the fully automatic CNC coil press disclosed in CN101593621B involves a pressure plate (9) moving up and down along four lead screws (7), with an upper length measuring mechanism (12) fixed on it precisely recording the length of movement. A safety limit mechanism (10) ensures that the downward-moving pressure plate (9) stops at a suitable position when pressing coils of different heights. The hydraulic cylinder (4) is a plunger cylinder with high output force and stable low-speed movement. The hydraulic cylinder (4) pushes up the platform carriage (6) on it, while the lower length measuring mechanism (3) fixed on it precisely records the length of the push-up. It can safely and reliably press coils of different heights and pressure requirements with one click, and trim the semi-finished coils to the axial design dimensions. This design method of the fully automatic CNC coil press has a reasonable structure, simple operation, safe and reliable operation, and high efficiency.

[0005] Most existing transformer coil pressing equipment uses ordinary four-column hydraulic presses. The size of the coil workpiece varies greatly, and the stroke of the cylinder is very large, generally more than 2 meters. This results in high manufacturing costs and low efficiency when pressing small workpieces. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a downward-pressing coil press with a physical measurement function. By applying downward pressure through a pressure platform, the coil pressing process is simplified, pressing costs are saved, and pressing efficiency is improved.

[0007] This invention is achieved through the following technical solution:

[0008] A pressure coil press with physical measurement function includes a servo cylinder, a fixed crossbeam, a pressure platform, guide columns, a bidirectional moving trolley, and a fixed base. At least four guide columns are provided. The fixed crossbeam is connected to the top of each guide column, and the fixed base is connected to the bottom of each guide column. The bidirectional moving trolley is used to load coil workpieces and is movably mounted on the fixed base. The servo cylinder is connected to the fixed crossbeam, and its output end is connected to the pressure platform. Multiple guide columns pass through the pressure platform, which moves up and down along the guide columns. After moving downwards along the guide columns, the pressure platform presses the coil workpieces on the bidirectional moving trolley.

[0009] In a further preferred embodiment, the guide column is equipped with a displacement sensor for controlling the positional accuracy of the pressure platform, and laser range sensors are respectively installed at the four corners of the bottom of the pressure platform for detecting the height of the four corners of the coil workpiece. Both the laser range sensors and the displacement sensors are connected to the hydraulic servo system of the servo cylinder.

[0010] More preferably, the top of the fixed base is circumferentially distributed with multiple spoke-type force sensors for measuring the pressure exerted on the coil workpiece during pressing.

[0011] A further preferred embodiment has a bearing seat on top of the spoke-type force sensor, and the top of the bearing seat is an arc-shaped spherical surface.

[0012] More preferably, a gap-guarantee bolt is provided at the top of the fixed base to adjust the safety gap between the lower plane of the bidirectional moving trolley and the fixed base.

[0013] In a further preferred embodiment, the press also includes guide rails on both sides of multiple guide columns, and a bidirectional moving trolley is slidably connected to the guide rails for the bidirectional moving trolley to move into or out of the fixed base along the guide rails.

[0014] In a further preferred embodiment, the press also includes a wire guiding device, which includes a double-guide wheel wire guiding mechanism and a spring-loaded cable reel mounted on a fixed base. A wire fixing mechanism is provided on a bidirectional moving trolley, and the wire fixing mechanism is connected to the double-guide wheel wire guiding mechanism and the spring-loaded cable reel via cable transmission.

[0015] In a further preferred embodiment, a lifting cylinder is provided inside the fixed base, the output end of the lifting cylinder is connected to the bidirectional moving trolley, and positioning devices are installed on both sides inside the fixed base. The positioning devices include a lifting cylinder, a connecting piece, and a positioning block. The output end of the lifting cylinder is connected to the connecting piece, the connecting piece is connected to the positioning block, and the positioning block abuts against the bidirectional moving trolley.

[0016] In a further preferred embodiment, the pressure platform is provided with an oil baffle ring and an oil discharge port in the circumferential direction.

[0017] The beneficial effects of this invention are:

[0018] 1) This invention simplifies the coil pressing process, saves pressing costs, and improves pressing efficiency by adopting a downward pressing overall approach with the pressing platform positioned above the coil.

[0019] 2) This invention employs a laser rangefinder sensor paired with a high-precision proportional servo valve. This proportional directional valve solution truly achieves closed-loop servo control of the pressing accuracy from the press equipment to the actual coil, ensuring pressing precision.

[0020] 3) This invention uses a spoke-type force sensor to replace the hydraulic system pressure sensor, achieving real-time and precise control of the coil pressing force.

[0021] 4) The bidirectional mobile trolley of the present invention can realize the function of one workpiece for backup and one for use, which greatly improves the production efficiency of automated production lines.

[0022] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings. Attached Figure Description

[0023] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the following detailed description to explain the invention, but do not constitute a limitation thereof. In the drawings:

[0024] Figure 1 This is a schematic diagram of the assembly structure of the downward-pressing coil press with physical measurement function of the present invention;

[0025] Figure 2 This is a side view of the compressive coil press with physical measurement function of the present invention.

[0026] Figure 3 This is a schematic diagram of the pressure platform in the coil press of the present invention;

[0027] Figure 4 This is a schematic diagram of the bidirectional moving trolley and fixed base structure in the coil press of the present invention;

[0028] Figure 5 This is a schematic diagram of the spoke-type force sensor and gap-ensuring bolt between the fixed base and the bidirectional moving trolley in the coil press of the present invention;

[0029] Figure 6 This is a schematic diagram of the mounting structure of the spoke-type force sensor on the fixed base in the coil press of the present invention;

[0030] Figure 7 This is a schematic diagram of the guide rail and bidirectional moving trolley structure in the coil press of the present invention;

[0031] Figure 8 This is a schematic diagram of the positioning device in the coil press of the present invention.

[0032] 1-Servo cylinder, 2-Fixed crossbeam, 3-Pressure platform, 4-Guide column, 5-Bidirectional moving trolley, 6-Fixed base, 7-Displacement sensor, 8-Laser rangefinder sensor, 9-Coil workpiece, 10-Spoke type force sensor, 11-Guide rail, 12-Double guide wheel wire mechanism, 13-Spring type cable reel, 14-Wire fixing mechanism, 15-Lifting cylinder, 16-Connector, 17-Positioning block, 18-Bearing seat, 19-Clearance guarantee bolt, 20-Oil retaining ring. Detailed Implementation

[0033] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0034] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of the stated features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0035] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection, an electrical connection, or a connection that allows for communication; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0036] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0037] The following disclosure provides many different embodiments or examples for implementing various structures of the invention. To simplify the disclosure, specific examples of components and arrangements are described below. These are merely examples and are not intended to limit the invention. Furthermore, reference numerals and / or letters may be repeated in different examples; such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. In addition, examples of various specific processes and materials are provided in this invention, but those skilled in the art will recognize the application of other processes and / or the use of other materials.

[0038] Please refer to Figure 1-8This invention discloses a pressure-type coil press with object measurement function, comprising a servo cylinder 1, a fixed crossbeam 2, a pressure platform 3, guide columns 4, a bidirectional moving trolley 5, a fixed base 6, a displacement sensor 7, a laser rangefinder 8, and a spoke-type force sensor system 10. At least four guide columns 4 are provided, the fixed crossbeam 2 is located at the top of the guide columns 4, and the fixed base 6 is located at the bottom of the guide columns 4. The coil press is composed of a rigid main structure formed by the fixed crossbeam 2, multiple guide columns 4, and fixed base 6, similar to a mature four-column press design, with a mature design and structure. Reliable; the bidirectional moving trolley 5 is used to load the coil workpiece 9 and move it in or out from the fixed base 6 inside the coil press. The servo cylinder 1 is connected to the fixed crossbeam 2. The output end of the servo cylinder 1 is connected to the pressure platform 3. The four corners of the pressure platform 3 are sleeved on the guide column 4. Under the drive of the drive cylinder 1, the pressure platform 3 moves from top to bottom along the guide column 4 and applies pressure to the coil workpiece 9 loaded on the bidirectional moving trolley 5 to maintain the pressure. The coil press can be used in conjunction with existing conventional CNC technology, such as CNC systems and peripheral technologies.

[0039] Traditional coil presses typically contain at least two sets of transmission mechanisms: an upper movable crossbeam transmission mechanism and an upper-mounted pressure platform 3 installed at the bottom. The upper movable crossbeam transmission mechanism usually consists of a motor reducer, commutator, and lead screw transmission assembly. This mechanism is complex and must withstand the full-tonnage pressure from the pressure platform 3 when pressing the coil, resulting in a large load and high cost. Furthermore, this mechanism is usually installed at a height greater than 3m, making maintenance difficult. The lower-mounted pressure platform 3 used in this application combines the movable crossbeam and the pressure platform 3 into one unit, completely eliminating the need for the upper movable crossbeam mechanism in traditional designs. In addition, the pressure platform 3 in this design is driven by a servo cylinder 1, with a specific design similar to a mature four-column hydraulic press, making maintenance convenient and the design and manufacturing mature and reliable.

[0040] Guide rails 11 are provided on both sides of the main structure for the bidirectional moving trolley 5 to move in or out of the main structure along the guide rails 11. Traditional coil presses use unidirectional moving trolleys when loading materials. When the current workpiece is being pressed, the trolley is occupied and the preparation work for the next workpiece cannot be carried out. The design of this application adopts a bidirectional moving trolley 5, that is, the bidirectional moving trolley 5 can move in and out from both the front and rear of the main structure of the press. This design can ensure that when the coil workpiece 9 is being pressed in the press, coil stacking and other work can be carried out on another bidirectional moving trolley 5. Since the pressing and holding time of the coil press is long and the coil stacking time is long, the bidirectional moving trolley 5 designed in this application can greatly improve the production efficiency. The bidirectional movement of the trolley 5 is complicated by the fact that the moving directions are intersecting and the travel distance is long, making it impossible to use ordinary moving cable chains for the drive motor. In addition, the coil press has high requirements for the workshop environment, high degree of automation, and no exposed wire troughs or cables on the ground, which increases the difficulty of designing the bidirectional moving trolley 5 for cable routing. This application adopts a bidirectional moving trolley 5 cable routing device, which includes a double guide wheel cable routing mechanism 12 and a spring-type cable reel 13 fixed on the fixed base 6, and a cable fixing mechanism 14 fixed on the bidirectional moving trolley 5. The double guide wheel structure design changes the routing direction to achieve bidirectional cable routing, and the spring-type cable reel 13 enables cable extension and retraction, thereby meeting the requirement of no exposed wires during operation.

[0041] A lifting cylinder is installed inside the fixed base 6. The output end of the lifting cylinder is connected to the bidirectional moving trolley 5. The lifting cylinder inside the fixed base 6 raises and lowers the moving trolley. When the bidirectional moving trolley 5 is raised, its wheels are suspended in the air under pressure. When the bidirectional moving trolley 5 is lowered, it contacts the guide rail 11. At the same time, the bidirectional moving trolley 5 is equipped with a positioning device with a lifting cylinder 15 to ensure accurate positioning of the bidirectional moving trolley 5 after it enters the press. Positioning devices are installed on both sides inside the fixed base 6. The positioning device includes a lifting cylinder 15, a connecting piece 16, and a positioning block 17. The output end of the lifting cylinder 15 is connected to the connecting piece 16, the connecting piece 16 is connected to the positioning block 17, and the positioning block 17 abuts against the bidirectional moving trolley 5. The positioning device driven by the lifting cylinder 15 ensures the positional accuracy of the bidirectional moving trolley 5 when it moves into the press.

[0042] A displacement sensor 7 is provided on the guide column 4 for position accuracy control of the pressure platform 3. Four laser range sensors 8 are provided at the four corners of the bottom of the pressure platform 3 for height detection of the four corners of the coil workpiece 9. Both the laser range sensors 8 and the displacement sensors 7 are connected to the hydraulic servo system of the servo cylinder 1. The coil object measurement function of this application is used to ensure the pressing accuracy of the coil after pressing. Specifically, the laser range sensors 8 need to be installed below the pressure platform 3. They need to be supported by a mounting bracket that can be processed to ensure verticality. After installation, zeroing and debugging are performed to avoid the influence of errors in the measurement data of each group. Taking the four groups of four corners evenly distributed as an example, the measurement data H1 to H4 of each group need to be controlled simultaneously by the press electronic control system. The error between each value of H1 to H4 and the standard set H value meets the setting requirements. At the same time, it is necessary to ensure that the difference between each value of H1-H2 and H2-H4 is within the tolerance range.

[0043] Existing coil pressing technology cannot detect the height of the coil after pressing. This design can directly detect the height around the coil after pressing by using a distributed laser rangefinder 8 to directly measure the surrounding area of ​​the coil and thus measure accurate data. At the same time, this application combines a hydraulic servo system design for fine-tuning, truly realizing a fully closed-loop coil fitting high-precision position control with interconnection between the physical object and the equipment. Note: Even if traditional designs include a grating ruler and reading head with a lead screw mechanism for closed-loop precision control, this improvement method only adjusts the precision at the equipment end and cannot guarantee the precision control of the workpiece after forming when the grating ruler application system fails. Moreover, even when the grating system is effective, under special conditions such as the tilt of the pressing platform 3 or the precision deviation caused by long-term use of the press, the compaction precision of the coil after pressing cannot be measured. This is an unacceptable defect in medium and large-sized transformer coil products with high precision requirements and poses a safety hazard.

[0044] Traditional coil press pressure control uses a pressure sensor to measure the hydraulic system pressure and calculates the pressing force through a program. This method has large measurement errors, is easily affected by the hydraulic system, and has poor timeliness. This design uses a spoke-type force sensor 10 instead of a pressure sensor, which can directly measure the pressure applied during coil pressing. The measurement results are not affected by the hydraulic system and can be measured and displayed in real time. The spoke-type force sensor 10 system in this design monitors the coil pressing force. Because transformer coils usually have a large projected area, the spoke-type force sensor 10 is positioned within the fixed base 6 along approximately 2 / 3 of the effective table surface circumference. The coils are evenly distributed to ensure compatibility with coils of different sizes. To ensure the structural reliability of the spoke-type force sensor 10 during measurement, a spherical transition is used between the support base 18 and the load-bearing base (i.e., the head of the fixed support base 18 connected to the spoke-type force sensor 10 is spherically connected). At the same time, to ensure measurement reliability, a safety gap is designed to be maintained between the lower plane of the bidirectional moving trolley 5 and the fixed base 6 during pressing. A gap guarantee bolt 19 is set at the top of the fixed base 6 to adjust the safety gap between the lower plane of the bidirectional moving trolley 5 and the fixed base 6. The safety gap distance is preferably at least 3mm.

[0045] Working principle: After the coil workpiece 9 enters the press, the pressure platform 3, driven by the servo cylinder 1, moves from top to bottom and applies pressure during the pressing process. During the movement, the displacement sensor 7 controls the position accuracy. After pressing, the laser rangefinder 8, which is distributed under the pressure platform 3, detects the height of the four corners of the coil workpiece 9. The press program automatically reads and compares the height values ​​of each group, controls the values ​​and tolerances of each value, and thus fine-tunes the position of the pressure platform 3 or completes the pressing process for subsequent actions. During the pressing process, the spoke-type force sensor system 10, which is evenly distributed in the fixed base 6, monitors and displays the pressing force acting on the coil workpiece 9 in real time to ensure that the coil is not overpressed or the pressing force is insufficient. After pressing is completed, the bidirectional moving trolley 5 moves the coil workpiece 9 out of the press, and at the same time, it can accept the coil workpiece 9 of the next bidirectional moving trolley 5 to enter the press for the next round of operation.

[0046] Traditional coil pressing machines have a complex workflow, requiring at least six steps. This design, with the addition of a physical measurement function (capable of detecting the actual height of the coil), simplifies the workflow to five steps, improving equipment efficiency. Traditional designs are top-down, meaning the pressure platform 3 presses from bottom to top, requiring the upper moving beam to move downwards before the lower pressure platform 3 moves upwards to apply pressure. This design uses a bottom-up servo action for the pressure platform 3, allowing for simultaneous position adjustment and pressure application / holding, thus simplifying the process. Note: Traditional bottom-up pressing designs are designed to prevent oil leakage from affecting the coil. This design addresses this through: A) A dedicated anti-scraping structure for the cylinder, with a slag-retaining ring at the cylinder port to prevent particles from entering the cylinder sleeve, extending the lifespan of the seals and cylinder; B) An oil-retaining ring 20 and an oil discharge port on the upper surface of the pressure platform 3, preventing oil leakage from directly contacting the coil; C) The hydraulic system can be designed to use transformer oil, such as Great Wall I-10℃ transformer oil, ensuring that even if leakage occurs, coil contamination is avoided.

[0047] In summary, although the present invention has been disclosed above with reference to preferred embodiments, the above preferred embodiments are not intended to limit the present invention. Those skilled in the art can make various modifications and refinements without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be determined by the scope defined in the claims.

Claims

1. A type of coil press with object measurement function, characterized in that: The device includes a servo cylinder (1), a fixed crossbeam (2), a pressure platform (3), guide pillars (4), a bidirectional moving trolley (5), and a fixed base (6). At least four guide pillars (4) are provided. The fixed crossbeam (2) is connected to the top of the guide pillars (4), and the fixed base (6) is connected to the bottom of the guide pillars (4). The bidirectional moving trolley (5) is used to load coil workpieces (9). The bidirectional moving trolley (5) is movably mounted on the fixed base (6). The servo cylinder (1) is connected to the fixed crossbeam (2). The output end of the servo cylinder (1) is connected to the pressure platform (3). Multiple guide pillars (4) pass through the pressure platform (3). The pressure platform (3) moves up and down along the guide pillars (4). After the pressure platform (3) moves down along the guide pillars (4), it presses the coil workpieces (9) on the bidirectional moving trolley (5). The press also includes guide rails (11) on both sides of the plurality of guide columns (4), and the bidirectional moving trolley (5) is slidably connected to the guide rails (11) for the bidirectional moving trolley (5) to move into or out of the fixed base (6) along the guide rails (11). The press also includes a wire guide device, which includes a double guide wheel wire guide mechanism (12) and a spring-type cable reel (13) mounted on the fixed base (6). A wire fixing mechanism (14) is provided on the bidirectional moving trolley (5). The wire fixing mechanism (14) is connected to the double guide wheel wire guide mechanism (12) and the spring-type cable reel (13) via cable transmission.

2. The pressure coil press with object measurement function according to claim 1, characterized in that: The guide post (4) is equipped with a displacement sensor (7) for position accuracy control of the pressure platform (3). Laser range sensors (8) are respectively provided at the four corners of the bottom of the pressure platform (3) for height detection of the four corners of the coil workpiece (9). Both the laser range sensor (8) and the displacement sensor (7) are connected to the hydraulic servo system of the servo cylinder (1).

3. The pressure coil press with object measurement function according to claim 1, characterized in that: The fixed base (6) has multiple spoke-type force sensors (10) evenly distributed around its top circumference, which are used to measure the pressure on the coil workpiece (9) when it is pressed.

4. A pressure coil press with object measurement function according to claim 3, characterized in that: The spoke-type force sensor (10) has a support seat (18) on top, and the top of the support seat (18) is an arc-shaped spherical surface.

5. A pressure coil press with object measurement function according to claim 1, characterized in that: The top of the fixed base (6) is provided with a gap guarantee bolt (19) for adjusting the safety gap between the lower plane of the bidirectional moving trolley (5) and the fixed base (6).

6. A pressure coil press with object measurement function according to claim 1, characterized in that: A lifting cylinder is installed inside the fixed base (6). The output end of the lifting cylinder is connected to the bidirectional moving trolley (5). Positioning devices are installed on both sides inside the fixed base (6). The positioning devices include a lifting cylinder (15), a connector (16), and a positioning block (17). The output end of the lifting cylinder (15) is connected to the connector (16). The connector (16) is connected to the positioning block (17). The positioning block (17) abuts against the bidirectional moving trolley (5).

7. A pressure coil press with object measurement function according to claim 1, characterized in that: The pressure platform (3) is provided with an oil baffle ring (20) and an oil discharge port in the circumferential direction.

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