Automatic platform for assembling rotating shafts on two sides by using force control sensor

Abstract

The invention belongs to the technical field of automobile assembling, and particularly relates to an automatic platform for assembling rotating shafts on the two sides through a force control sensor. Comprising a mechanical arm, a connecting assembly, a gripper assembly and a force control sensor, one end of the force control sensor is connected to the gripper assembly, the other end of the force control sensor is connected to a lower cover of the connecting assembly, an upper cover of the connecting assembly is connected to the end of the mechanical arm, and the mechanical arm drives the upper cover to be in sliding connection with the lower cover. The locking mechanism in the upper cover pushes the buckling mechanism in the lower cover to be buckled on the clamping opening of the upper cover, the buckling mechanism comprises a first spring, a push plate and a spring bolt, a sliding hole is formed in the push plate, the spring bolt is sleeved with the sliding hole in a sliding mode, the first spring is connected between the push plate and the inner wall of the lower cover, and the first spring is connected between the push plate and the inner wall of the lower cover. The first spring forwards pushes the push plate to outwards buckle the spring bolt on the bayonet of the upper cover, and the first spring backwards retracts to pull the push plate to inwards retract the spring bolt to be separated from the bayonet; the centering precision of assembly can be improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of automobile assembly, and particularly relates to an automated platform for assembling two-side rotating shafts using a force control sensor. Background Art

[0002] During the mechanical assembly process, the assembly quality of the rotating shaft assembly directly affects the performance and service life of the overall equipment. Although the traditional manual assembly method is flexible, it has problems such as low efficiency, low precision, and dependence on workers' experience. Especially during the assembly of the rotating shaft, it is not easy to control the torque and centering precision.

[0003] With the development of technology, in order to improve the assembly efficiency, robotic arms are used in some high-end manufacturing industries. Various data of the robotic arm are collected through devices such as force control sensors and vision sensors to improve the assembly precision of the robotic arm. However, when the robotic arm clamps different workpieces, different grippers need to be switched, or when the grippers and force control sensors are overhauled and maintained, the grippers and force control sensors need to be separated from the robotic arm, and the disassembly is relatively inconvenient. In order to improve the disassembly efficiency, for example, a connection device for the upper cover of a six-axis force sensor at the end of a robotic arm in Chinese Patent CN214502743U includes a six-axis force sensor and a sensor housing. The sensor housing includes a sensor bottom shell and a sensor top cover. The six-axis force sensor is directly fixed inside the sensor bottom shell through a fixing device. The sensor top cover is arranged at the top of the sensor bottom shell. A plurality of connection inserts are evenly arranged along the edge of the sensor top cover. Connection slots corresponding to the connection inserts one by one are arranged at the top of the sensor bottom shell. The plurality of connection inserts are respectively connected to the connection slots in an embedded manner. A clamping connection device is used to connect between the connection insert and the connection slot. This existing technology does not require screw fixation, has simple operation, does not require professional disassembly and assembly tools, and has high installation efficiency, simple operation, and low technical requirements.

[0004] However, in this existing technology, the connection between the insert and the slot and then the spring is used to push the clamping block to be clamped in the slot. When the spring is used for a long time and becomes loose, it is easy to cause the problem of poor assembly centering precision. Based on this, an automated platform for assembling two-side rotating shafts using a force control sensor is proposed. Summary of the Invention

[0005] To solve the above problems existing in the prior art, the present invention provides an automated platform for assembling two-side rotating shafts using a force control sensor.

[0006] The object of the present invention can be achieved by the following technical solutions:

[0007] An automated platform for assembling two-side rotating shafts using a force control sensor according to the present invention includes a robotic arm, a connection assembly, a gripper assembly, and a force control sensor. One end of the force control sensor is connected to the gripper assembly, and the other end is connected to the lower cover of the connection assembly. The upper cover of the connection assembly is connected to the end of the robotic arm. The robotic arm drives the upper cover to be slidably connected to the lower cover, and the locking mechanism in the upper cover pushes the fastening mechanism in the lower cover to be fastened to the bayonet of the upper cover.

[0008] Further, the fastening mechanism includes a first spring, a push plate, and a locking tongue. A sliding hole is formed in the push plate, and the sliding hole is slidably sleeved on the locking tongue. The first spring is connected between the push plate and the inner wall of the lower cover. The first spring pushes the push plate forward to snap the locking tongue outwardly onto the bayonet of the upper cover, and the first spring retracts backward to pull the push plate to retract the locking tongue inwardly to separate it from the bayonet.

[0009] Further, a second spring is arranged at the bottom of the locking tongue and connected to the side wall of the lower cover. A support plate is arranged at the bottom of the locking tongue and connected to the side wall of the lower cover. The bottom of the locking tongue abuts against the support plate.

[0010] Further, the locking mechanism includes a flat head slider which is slidably arranged in a through groove on the upper cover facing the lower cover, and the flat head slider pushes the push plate to retract.

[0011] Further, the locking mechanism further includes a pointed head slider which is slidably arranged at the other end of the through groove. A third spring is arranged between the flat head slider and the pointed head slider. The robotic arm pushes the pointed head slider to retract into the through groove to push the flat head slider to extend out of the through groove.

[0012] Further, sliding grooves are formed on both side walls outside the through groove of the upper cover. A connecting seat is slidably arranged in the sliding grooves. The top of the connecting seat is used to be connected to the robotic arm. The side of the connecting seat is slidably abutted against the outer side wall of the upper cover. The connecting seat slides downward to push the pointed head slider to retract into the through groove.

[0013] Further, both the upper and lower ends of the pointed head slider are inclined surfaces. A through hole is formed on the side of the connecting seat abutting against the pointed head slider. The through hole is used for the pointed head slider to reset and lock the locking mechanism and the fastening mechanism after the connecting seat slides downward.

[0014] Further, the gripper assembly includes a mounting frame, clamping jaws, and a cylinder. The clamping jaws are rotatably connected in the mounting frame. The cylinder is arranged on the mounting frame and connected to the clamping jaws to drive the clamping jaws to act.

[0015] Further, the jaw includes two clamping plates, and the inner sides of the two clamping plates are semi-circular arcs.

[0016] The beneficial effects of the present invention are as follows:

[0017] (1) By providing a connection component that can be quickly disassembled between the robotic arm and the force control sensor, the connection component is divided into an upper cover and a lower cover. The upper cover is connected to the end of the robotic arm, the lower cover is connected to the force control sensor, and the force control sensor is connected to the gripper assembly, so that the force control sensor and the gripper assembly are connected as a whole. During the connection process, the bottom of the outer rim of the upper cover driven by the robotic arm abuts against the bottom of the inner rim of the lower cover, and then the robotic arm pushes the upper cover towards the lower cover, so that the locking mechanism in the upper cover pushes the fastening mechanism in the lower cover, causing the fastening mechanism to contract and extend into the upper cover. Then the locking mechanism retracts and no longer pushes the fastening mechanism, causing the fastening mechanism to expand again and fasten on the bayonet in the upper cover. This enables the force control sensor to be stably connected to the robotic arm, while improving the connection efficiency between the force control sensor and the robotic arm, reducing manual operation while ensuring the centering accuracy of the robotic arm assembly;

[0018] (2) First, the robotic arm pushes the lower section of the through hole of the connection seat to abut against the pointed slider, causing the pointed slider to retract into the through groove, and the robotic arm pushes the upper cover and the lower cover to be connected. After the upper cover and the lower cover are connected, the robotic arm pushes the connection seat to continue moving downward, causing the pointed slider to protrude from the through hole. Since there is a third spring between the flat slider and the pointed slider, when the pointed slider protrudes from the through hole, the flat slider can no longer push the push plate backward. And because the pointed slider protrudes from the through hole, the connection seat is also locked by the pointed slider. Only when the gripper assembly is fixed on the pedestal can the through hole of the connection seat be pulled out and the pointed slider be pushed into the through groove. In this state, the flat slider can push the push plate backward, and then the upper cover can be taken out from the lower cover, and the robotic arm drives the connection seat to reset, completing the separation of the robotic arm from the gripper assembly and the force control sensor. Description of the Drawings

[0019] For the convenience of those skilled in the art to understand, the present invention will be further described below with reference to the accompanying drawings.

[0020] Figure 1 It is a schematic diagram of the overall structure of the present invention;

[0021] Figure 2 It is a schematic diagram of the main structure of the present invention;

[0022] Figure 3 It is a schematic diagram of the initial state of the connection component of the present invention;

[0023] Figure 4 It is a schematic diagram of the connection process of the connection component of the present invention;

[0024] Figure 5 Schematic diagram of the connection component of the present invention after connection is completed.

[0025] Legend: 1. Robot arm; 2. Gripper assembly; 3. Connection component; 4. Force control sensor; 5. Lower cover; 6. Upper cover; 7. First spring; 8. Support plate; 9. Second spring; 10. Lock tongue; 11. Push plate; 12. Flat head slider; 13. Pointed head slider; 14. Connection seat; 15. Third spring; 16. Mounting bracket; 17. Cylinder; 18. Jaw. Specific embodiments

[0026] To further elaborate on the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following will, in conjunction with the accompanying drawings and preferred embodiments, elaborate in detail on the specific embodiments, structures, features and their effects of the present invention.

[0027] As Figures 1 - 5 shown, an automated platform for assembling two-side rotating shafts using a force control sensor according to the present invention includes a robot arm 1, a connection component 3, a gripper assembly 2 and a force control sensor 4. One end of the force control sensor 4 is connected to the gripper assembly 2, and the other end is connected to the lower cover 5 of the connection component 3. The upper cover 6 of the connection component 3 is connected to the end of the robot arm 1. The robot arm 1 drives the upper cover 6 to be slidably connected to the lower cover 5, and the locking mechanism in the upper cover 6 is used to push the fastening mechanism in the lower cover 5 to be fastened to the bayonet of the upper cover 6;

[0028] Since it is difficult to control the torque and centering accuracy of the robot arm 1 during the process of assembling the rotating shaft by the robot arm 1, generally, a force control sensor 4 and a vision sensor are arranged on the robot arm 1 for combined use to improve the control accuracy of the torque and position of the robot arm 1. When connecting the force control sensor 4, generally, the force control sensor 4 needs to be connected to the robot arm 1 by bolts. After the force control sensor 4 is connected to the robot arm 1, since the jaws 18 at the front end of the robot arm 1 need to be disassembled and replaced according to different types of workpieces to be grasped or during the process of disassembly and repair, generally, manual replacement is required, separating the jaws 18 connecting the robot arm 1 and the force control sensor 4, resulting in low disassembly and assembly efficiency and poor accuracy;

[0029] By providing a connection component 3 that can be quickly disassembled between the robotic arm 1 and the force control sensor 4, the connection component 3 is divided into an upper cover 6 and a lower cover 5. The upper cover 6 is connected to the end of the robotic arm 1, and the lower cover 5 is connected to the force control sensor 4. The force control sensor 4 is connected to the gripper assembly 2, making the force control sensor 4 and the gripper assembly 2 integrated. During the connection process, the bottom of the outer rim of the upper cover 6 driven by the robotic arm 1 abuts against the bottom of the inner rim of the lower cover 5. Then, the robotic arm 1 pushes the upper cover 6 towards the lower cover 5, causing the locking mechanism in the upper cover 6 to push the fastening mechanism in the lower cover 5, making the fastening mechanism contract and extend into the upper cover 6. Then, the locking mechanism retracts and no longer pushes the fastening mechanism, causing the fastening mechanism to expand again and fasten onto the bayonet in the upper cover 6. This enables the force control sensor 4 to be stably connected to the robotic arm 1, while improving the connection efficiency between the force control sensor 4 and the robotic arm 1, reducing manual operation while ensuring the centering accuracy of the robotic arm 1 assembly.

[0030] Specifically, the fastening mechanism includes a first spring 7, a push plate 11, and a locking tongue 10. A number of sliding holes are provided on the push plate 11 in a circular array, and the number of sliding holes respectively slidably sleeved on a number of locking tongues 10. The upper cover 6 and the lower cover 5 are cylindrical. The first spring 7 is located at the axial center position inside the lower cover 5 and is connected between the push plate 11 and the inner wall of the lower cover 5. The first spring 7 pushes the push plate 11 forward to buckle the locking tongue 10 outward onto the bayonet of the upper cover 6, and the first spring 7 retracts backward to pull the push plate 11 to contract the locking tongue 10 inward to separate from the bayonet.

[0031] A second spring 9 is provided at the bottom of the locking tongue 10 and is connected to the side wall of the lower cover 5. A support plate 8 is provided at the bottom of the locking tongue 10 and is connected to the side wall of the lower cover 5. The bottom of the locking tongue 10 abuts against the support plate 8. The second spring 9 and the support plate 8 are oriented towards the axis on the side wall of the lower cover 5. Since the sliding holes on the push plate 11 are arranged in a circular array, the locking tongues 10 are also circularly distributed on the push plate 11. The bottoms of the locking tongues 10 are respectively limited by a plurality of support plates 8 and pushed by the second spring 9. When there is no external force, the locking tongues 10 are in a state of tilting outwards with the bottom away from the side wall of the lower cover 5 and the top close to the side wall of the lower cover 5. Moreover, the first spring 7 at the bottom of the push plate 11 pushes the push plate 11 forward, causing a plurality of locking tongues 10 to be in an open state. In this state, the diameter formed by the plurality of locking tongues 10 is larger than the inner diameter of the upper cover 6, so the upper cover 6 and the lower cover 5 cannot be connected. Only after the locking mechanism of the upper cover 6 pushes the push plate 11 backward, the bottom of the locking tongue 10 retracts towards the inner wall of the lower cover 5, and the top of the locking tongue 10 tilts inwards, reducing the diameter formed by the plurality of locking tongues 10 to facilitate insertion into the upper cover 6. Then, the locking mechanism no longer applies a force to the push plate 11, and the push plate 11 is reset towards the upper cover 6 under the thrust of the first spring 7, causing the plurality of locking tongues 10 to change from contraction to expansion after being inserted into the upper cover 6, facilitating the locking tongues 10 to be buckled on the bayonet of the upper cover 6, completing the rapid connection of the upper cover 6 and the lower cover 5. And since each locking tongue 10 is correspondingly connected to the bayonet, there will be no relative rotation and relative movement between the upper cover 6 and the lower cover 5 after connection, ensuring the stability of the connection and thus improving the centering accuracy of the assembly.

[0032] In order to realize the backward movement of the push plate 11 during the docking of the upper cover 6 and the lower cover 5, in one embodiment, the locking mechanism includes a flat head slider 12. The flat head slider 12 is slidably arranged in the through groove of the upper cover 6 facing the lower cover 5, and the flat head slider 12 pushes the push plate 11 to move backward and retract. When the push plate 11 moves backward, the first spring 7 is in a compressed state. Since in the structure of the above embodiment, only the rapid docking of the upper cover 6 and the lower cover 5 can be achieved, but when the locking mechanism in the upper cover 6 pushes the push plate 11 to move backward, although the push plate 11 can push several locking tongues 10 to contract, however, when the upper cover 6 and the lower cover 5 are separated, as the upper cover 6 separates, the push plate 11 will reset again, resulting in several locking tongues 10 expanding again and buckling on the bayonet, so that the upper cover 6 and the lower cover 5 cannot be separated. Therefore, in the above structure, the upper cover 6 can only be quickly docked but cannot be quickly separated. To avoid this problem, in one embodiment, the locking mechanism further includes a pointed head slider 13. The pointed head slider 13 is slidably arranged at the other end of the through groove. A third spring 15 is arranged between the flat head slider 12 and the pointed head slider 13. The robotic arm 1 pushes the pointed head slider 13 to retract into the through groove for pushing the flat head slider 12 to extend out of the through groove. Sliding grooves are formed on the outer side walls on both sides outside the through groove of the upper cover 6. A connecting seat 14 is slidably arranged in the sliding grooves, and the connecting seat 14 vertically slides on the upper cover 6 through the sliding grooves. The top of the connecting seat 14 is used to connect with the robotic arm 1. The side surface of the connecting seat 14 is in sliding contact with the outer side wall of the upper cover 6. The downward sliding of the connecting seat 14 is used to push the pointed head slider 13 to retract into the through groove;

[0033] The pointed slider 13 and the flat-headed slider 12 are both limited within the through groove to prevent them from sliding out of the sliding groove. During the installation process, the robotic arm 1 is connected to the connecting seat 14 on the upper cover 6. Then, the robotic arm 1 moves the upper cover 6 to be coaxial with the lower cover 5. The length of the lower cover 5 at the lower edge is relatively long, so that the upper cover 6 can abut against the lower edge of the lower cover 5 before being sleeved with the lower cover 5, providing a fulcrum for the upper cover 6 on the lower cover 5. When the upper cover 6 is at the fulcrum of the lower edge of the lower cover 5, the robotic arm 1 presses down on the connecting seat 14 until the connecting seat 14 moves downward. The downward movement of the connecting seat 14 will push the pointed slider 13 to retract into the through groove. By the pointed slider 13, the flat-headed slider 12 is pushed to move towards the lower cover 5 and remain stationary. Then, the robotic arm 1 continues to push the upper cover 6 towards the lower cover 5, causing the flat-headed slider 12 inside the upper cover 6 to push the push plate 11 to move backward. The backward movement of the push plate 11 can cause several locking tongues 10 to contract. After the upper cover 6 and the lower cover 5 move to the position where the locking tongues 10 are in place, the robotic arm 1 drives the connecting seat 14 to separate from the pointed slider 13, causing the pointed slider 13 to reset. The flat-headed slider 12 is pushed by the push plate 11 to retract into the through groove. The reset of the push plate 11 causes several locking tongues 10 to lock onto the bayonet. Under the action of the first spring 7 pushing the push plate 11, the flat-headed slider 12 loses the driving force. Therefore, regardless of the subsequent working state of the robotic arm 1, the robotic arm 1 and the gripper assembly 2 of the force control sensor 4 cannot be separated. When disassembly is required, the robotic arm 1 is used to push the connecting seat 14 to move again. The movement of the connecting seat 14 will push the pointed slider 13 to retract into the through groove. The retraction of the pointed slider 13 will push the flat-headed slider 12 to move towards the lower cover 5, causing the push plate 11 to be in a backward movement state. At this time, the robotic arm 1 is used to drive the upper cover 6 to separate from the lower cover 5 to complete the quick disassembly. In order to provide a fulcrum when applying a force to the connecting seat 14 by the robotic arm 1, the gripper assembly 2 needs to be firmly grasped on the pedestal of the gripper assembly 2 during connection. Therefore, it is necessary to achieve electrical connection between the control device on the robotic arm 1 and the gripper assembly 2. Each time of connection or separation, the gripper assembly 2 needs to be firmly grasped on the pedestal.

[0034] Further, both the upper and lower ends of the pointed slider 13 are inclined surfaces. A through hole is provided on the side of the connecting seat 14 that abuts against the pointed slider 13. The through hole is used for the pointed slider 13 to reset and lock the locking mechanism and the fastening mechanism after the connecting seat 14 slides downward;

[0035] Since there are through holes on the side surface of the connecting seat 14, when the upper cover 6 and the lower cover 5 are installed, the robotic arm 1 first pushes the lower section of the through hole of the connecting seat 14 to abut against the pointed slider 13, causing the pointed slider 13 to retract into the through groove, and then the robotic arm 1 pushes the upper cover 6 to connect with the lower cover 5. After the connection between the upper cover 6 and the lower cover 5 is completed, the robotic arm 1 pushes the connecting seat 14 to move downward continuously, causing the pointed slider 13 to extend out of the through hole. Since there is a third spring 15 between the flat-headed slider 12 and the pointed slider 13, when the pointed slider 13 extends out of the through hole, the flat-headed slider 12 can no longer push the push plate 11 to move backward. And because the pointed slider 13 extends out of the through hole, the connecting seat 14 is also locked through the pointed slider 13. Only when the gripper assembly 2 is fixed on the pedestal can the through hole of the connecting seat 14 be pulled out and the pointed slider 13 be pushed into the through groove. In this state, the flat-headed slider 12 can push the push plate 11 to move backward, and then the upper cover 6 can be taken out from the lower cover 5, and the robotic arm 1 drives the connecting seat 14 to reset, completing the separation of the robotic arm 1 from the gripper assembly 2 and the force control sensor 4.

[0036] Further, the gripper assembly 2 includes a mounting bracket 16, clamping jaws 18 and a cylinder 17. The clamping jaws 18 are rotatably connected inside the mounting bracket 16. The cylinder 17 is arranged on the mounting bracket 16 and is connected to the clamping jaws 18 and drives the clamping jaws 18 to act. Since driving the clamping jaws 18 to grip the workpiece by the cylinder 17 is a prior art, it will not be described in detail in this embodiment.

[0037] Further, the clamping jaws 18 include two clamping plates, and the inner sides of the two clamping plates are semi-circular. Through the semi-circular shapes of the inner sides of the two clamping plates, it can be used to grip the rotating shaft of an automobile, and can also be fixed on the pedestal of the gripper assembly 2 by the clamping jaws 18 for the quick disassembly and assembly of the gripper assembly 2.

[0038] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to the above-disclosed technical content to make equivalent embodiments with equivalent changes, but as long as it does not depart from the technical content of the present invention, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. An automated platform for assembling rotating shafts on both sides using a force control sensor, characterized in that: It includes a mechanical arm, a connecting component, a gripper component and a force control sensor, wherein one end of the force control sensor is connected to the gripper component, and the other end is connected to the lower cover of the connecting component. The upper cover of the connecting component is connected to the end of the mechanical arm. The mechanical arm drives the upper cover to be slidably connected with the lower cover, and pushes the buckling mechanism in the lower cover to buckle on the bayonet of the upper cover through the locking mechanism in the upper cover.

2. The automated platform for assembling rotating shafts on both sides using a force control sensor according to claim 1, characterized in that: The snap-fitting mechanism includes a first spring, a push plate and a lock tongue. A sliding hole is provided on the push plate, and the sliding hole is slidably sleeved on the lock tongue. The first spring is connected between the push plate and the inner wall of the lower cover. The first spring pushes the push plate forward to snap the lock tongue outward onto the bayonet of the upper cover. The first spring retracts and pulls the push plate backward to shrink the lock tongue inward and separate it from the bayonet.

3. The automated platform for assembling rotating shafts on both sides using a force control sensor according to claim 2, characterized in that: A second spring is arranged at the bottom of the lock tongue and connected to the side wall of the lower cover. A supporting plate is arranged at the bottom of the lock tongue and connected to the side wall of the lower cover. The bottom of the lock tongue abuts against the supporting plate.

4. The automated platform for assembling rotating shafts on both sides using a force control sensor according to claim 2, characterized in that: The locking mechanism comprises a flat-head slider, which is slidably arranged in a through slot on the upper cover facing the lower cover, and the flat-head slider pushes the push plate to retract.

5. The automated platform for assembling rotating shafts on both sides using a force control sensor according to claim 4, characterized in that: The locking mechanism also includes a pointed slider, which is slidably arranged at the other end of the through slot, and a third spring is arranged between the flat slider and the pointed slider. The mechanical arm pushes the pointed slider to retract into the through slot to push the flat slider to extend out of the through slot.

6. The automated platform for assembling rotating shafts on both sides using a force control sensor according to claim 5, characterized in that: Slide grooves are provided on the side walls on both sides outside the through slot of the upper cover, and a connecting seat is slidably arranged in the slide groove. The top of the connecting seat is used to connect with the robotic arm, and the side surface of the connecting seat is slidably abutted against the outer wall of the upper cover. The connecting seat slides downward to push the pointed slider to retract into the through slot.

7. The automated platform for assembling rotating shafts on both sides using a force control sensor according to claim 6, characterized in that: The upper and lower ends of the pointed slider are inclined surfaces, and a through hole is provided on one side where the connecting seat abuts against the pointed slider. The through hole is used to reset the pointed slider and lock the locking mechanism and the snapping mechanism after the connecting seat slides downward.

8. The automated platform for assembling rotating shafts on both sides using a force control sensor according to claim 1, characterized in that: The gripper assembly comprises a mounting frame, a clamping jaw and a cylinder. The clamping jaw is rotatably connected in the mounting frame. The cylinder is arranged on the mounting frame and connected to the clamping jaw to drive the clamping jaw to move.

9. The automated platform for assembling rotating shafts on both sides using a force control sensor according to claim 8, characterized in that: The clamping jaw comprises two clamping plates, and the inner side surfaces of the two clamping plates are semi-arc-shaped.

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