Lens driving mechanism

Abstract

The utility model discloses a lens driving mechanism, which comprises a base and a prism carrier, the base comprises a bottom plate, a side plate and at least one polar plate, and the bottom plate extends along a first direction. The side plate is connected to the side portion, in the second direction, of the bottom plate, the side plate and the bottom plate form a containing space, and the second direction is perpendicular to the first direction. And the polar plate is positioned in the bottom plate. The prism carrier is located in the containing space and arranged to rotate around the axis extending in the first direction and the axis extending in the second direction, the prism carrier comprises a support and a metal frame, and an inclined supporting face is arranged at the front end of the support and used for supporting a prism. The metal frame comprises at least one pole piece, and the pole piece and the pole plate are oppositely arranged to form a capacitor structure. And the capacitance sensing element is electrically connected with the capacitance structure.

Description

Technical Field

[0001] This utility model relates to the field of optical element driving technology, and in particular to a lens driving mechanism. Background Technology

[0002] With the development of technology, many electronic devices today (such as smartphones or digital cameras) have the function of taking pictures or recording videos. The use of these electronic devices is becoming more and more common, and they are developing towards convenient and thinner designs to provide users with more choices.

[0003] Some electronic devices with photographic or video recording functions are equipped with a lens drive mechanism to drive the optical components of the lens to move, thereby achieving the function of autofocus.

[0004] Currently, the lens drive mechanism uses sensors to detect the position of the prism carrier, which usually requires wiring to be laid on the prism carrier. These wirings can affect the operation of the prism carrier. Utility Model Content

[0005] The purpose of this invention is to provide a lens driving mechanism to solve the problems of the prior art.

[0006] To solve the above-mentioned technical problems, the present invention provides a lens driving mechanism, the lens driving mechanism comprising:

[0007] The base includes;

[0008] A base plate, the base plate extending along a first direction;

[0009] A side plate, which is connected to the side of the base plate along a second direction and forms a receiving space with the base plate, wherein the second direction is perpendicular to the first direction;

[0010] At least one electrode plate, said electrode plate being located within the base plate;

[0011] A prism carrier, located within the receiving space and configured to rotate about an axis extending in a first direction and an axis extending in a second direction, the prism carrier comprising:

[0012] A bracket, the front end of which is provided with an inclined support surface for supporting the prism;

[0013] A metal frame, the metal frame including at least one electrode, the electrode being disposed opposite to the electrode plate to form a capacitor structure;

[0014] A capacitive sensing element, which is electrically connected to the capacitor structure.

[0015] In one embodiment, two electrode plates are located within the base plate and are spaced apart along the first direction;

[0016] The other two electrode plates are located inside the side plate and are spaced apart along the first direction;

[0017] The two electrodes are located on the bottom surface of the prism carrier and form a first capacitor structure with the two electrodes;

[0018] The other two electrodes are located on the side of the prism carrier and together with the other two electrodes form a second capacitor structure.

[0019] In one embodiment, the base further includes built-in wiring located within the base plate and the side plate and connected to the first capacitor structure, the second capacitor structure, and the capacitive sensing element.

[0020] In one embodiment, the lens driving mechanism further includes a reed located on the top surface of the bracket and the side plate and connected to the bracket and the side plate.

[0021] In one embodiment, the reed is electrically connected to the metal frame and the built-in wiring.

[0022] In one embodiment, the top surface of the side plate is provided with a recessed clearance notch;

[0023] The top surface of the bracket is provided with an installation notch;

[0024] The reed is located within the clearance notch and the mounting notch.

[0025] In one embodiment, the base further includes a rear end plate connected to the rear side of the base plate;

[0026] The lens driving mechanism also includes multiple coil groups and multiple magnet groups, with some coil groups installed in the rear end plate and other coil groups located in the base plate;

[0027] A portion of the magnet group is located on the rear side of the bracket and is arranged opposite to a portion of the coil group;

[0028] Another portion of the magnet assembly is located at the bottom of the bracket and is positioned opposite to the other portion of the coil assembly.

[0029] In one embodiment, the top surface of the base plate is provided with a support protrusion, and the top surface of the support protrusion is provided with a first ball groove;

[0030] The bottom of the bracket is provided with a groove to accommodate the support protrusion, and the top wall of the groove is provided with a second ball groove;

[0031] The lens drive mechanism further includes ball bearings located in the first ball bearing groove and the second ball bearing groove to support the bracket to rotate about an axis extending in the first direction and about an axis extending in the second direction.

[0032] In one embodiment, the metal frame further includes a back plate, which is arranged parallel to the rear end plate and located on the rear side of the bracket.

[0033] In one embodiment, the metal frame further includes a support plate located on the top wall of the groove and recessed to form the second ball groove. Attached Figure Description

[0034] Figures 1-4 This is an exploded view of the lens driving mechanism according to one embodiment of the present invention.

[0035] Figure 5 yes Figure 1 Assembly diagram of the lens drive mechanism in the illustrated embodiment.

[0036] Figure 6 yes Figure 5 A cross-sectional view of the lens drive mechanism along line AA in the embodiment shown.

[0037] Figure 7 yes Figure 5 A cross-sectional view of the lens drive mechanism along line BB in the illustrated embodiment.

[0038] Figure 8 yes Figure 1 An exploded view of the lens drive mechanism in the illustrated embodiment.

[0039] Figure 9 yes Figure 1 The illustrated embodiment is a perspective view of the first metal frame, the second metal frame, the spring, the built-in circuitry, and the four pole pieces.

[0040] Figure 10 yes Figure 9 A perspective view of the first metal frame in the illustrated embodiment.

[0041] Reference numerals: 10. Lens driving structure; 1. Base; 11. Base plate; 111. Support protrusion; 12. Side plate; 121. Clearance notch; 122. Baffle; 13. Front end plate; 14. Rear end plate; 15. Built-in circuitry; 16. First electrode plate; 17. Second electrode plate; 18. Transmitting electrode plate; 19. Receiving electrode plate; 2. Prism carrier; 21. Support; 22. First metal frame; 221. First electrode; 222. Second electrode; 223. Support plate; 224. 1. Backplate; 225. Second ball groove; 226. Metal strip; 23. Nodding magnet assembly; 24. Shaking magnet assembly; 25. Groove; 26. Mounting notch; 27. Support surface; 29. ​​Ball; 3. Lens carrier; 31. Mounting slot; 32. Carrier frame; 33. Second metal frame; 34. Metal plate; 35. Zoom magnet assembly; 36. Damping colloid; 4. Spring; 5. Housing; 6. Nodding coil assembly; 7. Shaking coil assembly; 8. Zoom coil assembly; 9. Capacitor element; Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of this utility model clearer, the various embodiments of this utility model will be described in detail below with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details have been provided in the various embodiments of this utility model to facilitate a better understanding of this application. However, the technical solutions claimed in the claims of this application can be implemented even without these technical details and with various variations and modifications based on the following embodiments.

[0043] Unless the context requires otherwise, throughout the specification and claims, the word “comprising” and its variations, such as “including” and “having”, shall be understood to have an open, inclusive meaning, that is, to be interpreted as “including, but not limited to”.

[0044] The embodiments of this utility model will be described in detail below with reference to the accompanying drawings to provide a clearer understanding of the purpose, features, and advantages of this utility model. It should be understood that the embodiments shown in the drawings are not intended to limit the scope of this utility model, but are merely illustrative of the essential spirit of the technical solution of this utility model.

[0045] Throughout this specification, references to "an embodiment" or "an embodiment" indicate that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Therefore, the appearance of "in an embodiment" or "an embodiment" in various places throughout the specification does not necessarily refer to the same embodiment. Furthermore, a particular feature, structure, or characteristic may be combined in any manner in one or more embodiments.

[0046] The singular forms “a” and “the” used in this specification and the appended claims include plural references unless otherwise expressly stated herein. It should be noted that the term “or” is generally used to mean “and / or” unless otherwise expressly stated herein.

[0047] In the following description, in order to clearly demonstrate the structure and working method of this utility model, a number of directional terms will be used. However, terms such as "front", "back", "left", "right", "outside", "inside", "outward", "inward", "up", and "down" should be understood as convenient terms and not as limiting terms.

[0048] This utility model relates to a lens driving mechanism, which includes a base 1, a prism carrier 2, a lens carrier 3, a spring 4, and a housing 5. The base 1 has a receiving space for accommodating the prism carrier 2 and the lens carrier 3. The prism carrier 2 is used to mount a prism, which can deflect light. The prism carrier 2 can move to change the direction of light illumination. The lens carrier 3 is used to mount a lens, and its movement enables zooming. The spring 4 drives the prism carrier 2 to return to its original position. The housing 5 covers the top of the receiving space and is connected to the bottom of the base 1.

[0049] In a specific embodiment, such as Figure 1-4 As shown, the base 1 includes a base plate 11, two side plates 12, a front plate 13, and a rear plate 14. The base plate 11 is a plate extending along a first direction, which is the optical axis direction of the lens. The two side plates 12 are respectively connected to both sides of the base plate 11 along a second direction, which is perpendicular to the first direction. Both the first and second directions are perpendicular to the optical axis direction of the lens. Figure 1 The vertical direction is perpendicular. The front plate 13 and the rear plate 14 are respectively connected to the front and rear ends of the base plate 11 along the first direction. The front plate 13 is located at the end near the lens carrier 3 and is provided with a light-shielding hole, while the rear plate 14 is located at the end near the prism carrier 2. The front plate 13, the rear plate 14, the two side plates 12 and the base plate 11 enclose and form an accommodating space.

[0050] The base 1 also includes two sets of four electrode plates and an internal circuit 15. All four electrode plates are conductive and integrally formed with the internal circuit 15. When the internal circuit 15 is energized, it energizes the four electrode plates. Two of the electrode plates are first electrode plates 16, and the other two are second electrode plates 17. The two first electrode plates 16 extend along a second direction and are arranged side-by-side along a first direction within the base plate 11. The two second electrode plates 17 are arranged side-by-side along the first direction within one of the side plates 12. Both the two first electrode plates 16 and the two second electrode plates 17 are located near the rear end of the base 1.

[0051] The prism carrier 2 is located at the rear end of the receiving space, and the top surface of the prism carrier 2 is provided with a recessed support surface 27. The support surface 27 is an inclined surface, which can turn the light coming from the top by 90° and project it to the lens located at the front end of the receiving space.

[0052] Specifically, the prism carrier 2 includes a support 21 and a first metal frame 22 located inside the support 21. The top surface of the support 21 is provided with a support surface 27 for mounting the prism.

[0053] The first metal frame 22 includes four electrode plates, a back plate 224, a support plate 223, and a metal strip 226 that connects the four electrode plates, the back plate 224, and the support plate 223 to each other. The entire first metal frame 22 is integrally formed and is conductive.

[0054] Of the four electrodes, two are located at the bottom of the support 21, forming the first electrode 221. The other two electrodes are located on the side of the support 21 along the second direction, forming the second electrode 222.

[0055] Two first electrode plates 221 and two first electrode plates 16 are aligned vertically, forming a first capacitor structure when energized. Two second electrode plates 222 and two second electrode plates 17 are aligned along a second direction, forming a second capacitor structure when energized. Furthermore, a capacitance sensing element is provided within the base 1, which is electrically connected to the built-in circuit 15 and can sense changes in the capacitance of the first and second capacitor structures.

[0056] The lens drive mechanism also includes three coil groups and three magnet groups. One coil group is the nodding coil group 6, another is the yaw coil group 7, and the last is the zoom coil group 8. The three magnet groups are correspondingly the nodding magnet group 23, the yaw magnet group 24, and the zoom magnet group 35.

[0057] The oscillating coil assembly 7 is installed at the rear end of the base plate 11 and electrically connected to the built-in circuit 15 of the base 1. The oscillating magnet assembly 24 is installed at the bottom of the bracket 21 and aligned vertically with the oscillating coil assembly 7. When the built-in circuit 15 is energized, the oscillating coil assembly 7 and the oscillating magnet assembly 24 work together to drive the bracket 21 to rotate around an axis extending in a second direction. When the bracket 21 rotates, the distance between the two second pole pieces 222 and the two second pole plates 17 changes. When the upper ends of the two first pole pieces 221 are close to the second pole plates 17, the lower ends are away from the second pole plates 17. The projected areas of the two second pole pieces 222 and the two second pole plates 17 change, thereby changing the capacitance of the second capacitor structure. The amplitude of the bracket 21's rotation around the axis extending in the first direction is determined by this change in capacitance. In other words, the amplitude of the bracket 21's oscillation can be determined by the change in the capacitance of the second capacitor structure.

[0058] The nodding coil assembly 6 is installed inside the rear end plate 14 and is also electrically connected to the built-in circuit 15 of the base 1. The nodding magnet assembly 23 is installed at the rear end of the bracket 21 and is used to cooperate with the nodding coil assembly 6 to drive the bracket 21 to rotate around an axis extending in a first direction. During the rotation of the bracket 21, one of the two first pole pieces 221 deflects upward and the other deflects downward. The capacitance of the first capacitor structure formed by the two first pole pieces 221 and the two first plates 16 changes. The amplitude of the bracket 21's rotation around the axis extending in a second direction can be determined by detecting the change in capacitance by the capacitance sensing element 9.

[0059] The amplitude of the bracket 21 can be determined by the change in capacitance of the first capacitor structure.

[0060] The zoom coil assembly 8 is installed at the front end of the side plate 12, and the zoom magnet assembly 35 is installed on the carrier and cooperates with the zoom coil assembly 8 to drive the lens carrier 3 to move in the first direction in order to adjust the focal length of the lens, as will be described in detail below.

[0061] exist Figure 2-5 In the illustrated embodiment, the base 1, rear end plate 14, and side plate 12 are each provided with a receiving groove for mounting coil groups, meaning that multiple coil groups do not occupy the space for mounting. The rear end and bottom of the bracket 21 are also provided with receiving grooves for accommodating the nodding coil group 6 and the swaying coil group 7, and similarly, multiple coil groups do not protrude from the outer side of the bracket 21.

[0062] The bottom of the bracket 21 is also provided with a groove 25, which is located at the center of the bracket 21 along the first and second directions. The top surface of the base plate 11 is also provided with a protruding support protrusion 111, which is located within the groove 25 and has a recessed first ball groove on its top surface. When the bracket makes nodding or shaking movements, it uses the ball as a fulcrum, which can reduce its friction.

[0063] The support plate 223 is located on the top wall of the groove 25 and is recessed towards the top to form a second ball groove 225. The first ball groove and the second ball groove 225 are arranged opposite each other in the vertical direction and accommodate a ball 29. The ball 29 can support the bracket 21 to rotate about an axis extending in the first direction and about an axis extending in the second direction.

[0064] Two springs 4 are located on the top surface of the bracket 21 and the side plate 12 respectively, and on both sides of the bracket 21 along the second direction. The two springs 4 are connected to the bracket 21 and the two side plates 12 respectively, and have a certain elasticity. After the bracket 21 is rotated, it can drive the bracket 21 to reset.

[0065] In addition, the two springs 4 can also be energized and are electrically connected to the built-in circuit 15 and the first metal frame 22 respectively. After the built-in circuit 15 is energized, it can energize the first pole piece 221 and the second pole piece 222.

[0066] Specifically, the top surfaces of the two side plates 12 are each provided with recessed clearance notches 121, which are located near the rear ends of the two side plates 12. The top surface of the bracket 21 is also provided with two mounting notches 26, which are located on both sides of the bracket 21 along the second direction. The two spring pieces 4 are located within the two clearance notches 121 and the two mounting notches 26, respectively.

[0067] In addition, the connection end of the built-in line 15 is located in the clearance notch 121, and the connection end of the first metal frame 22 is also located in the mounting notch 26. The two springs 4 are electrically connected to the connection ends of the built-in line 15 and the first metal frame 22, respectively.

[0068] The back plate 224 is located inside the bracket 21 and close to the rear end of the bracket 21. The back plate 224 is attached to the nodding magnet group 23 to fix the nodding magnet group 23 and can also improve the stability of the bracket 21.

[0069] The base 1 also includes a transmitting electrode 18 and two receiving electrodes 19. The transmitting electrode 18 and the receiving electrode 19 are both metal plates 34 and are integrally formed with the built-in circuit 15. After the built-in circuit 15 is powered on, the transmitting electrode 18 and the two receiving electrodes 19 form two capacitor structures, which are defined as the third capacitor structure.

[0070] Specifically, the emitting electrode 18 extends along a first direction and is located within one of the side plates 12, while the two receiving electrodes 19 and the emitting electrode 18 are located within the same side plate 12 and at the bottom end of the emitting electrode 18. The two receiving electrodes 19 are arranged side-by-side along the first direction. The built-in circuit 15 can energize the two receiving electrodes 19 and the emitting electrode 18. In addition, the base 1 also has another capacitive sensing element 9, which is located within the same side plate 12 as the two receiving electrodes 19 and is electrically connected to the built-in circuit 15 and the two third capacitor structures, for sensing the capacitance of the two third capacitor structures.

[0071] The lens carrier 3 includes a carrier frame 32 and a second metal frame 33. The carrier frame 32 extends along a first direction and has a recessed mounting groove 31 at its top. The mounting groove 31 extends through the carrier frame 32 along the first direction and is used to mount the lens. The mounting groove 31 is aligned with the light-shielding hole of the front end plate 13 along the first direction, allowing light to escape from the light-shielding hole.

[0072] The front sidewall of the mounting groove 31 is an inclined surface that gradually deviates from the center of the mounting groove 31 along the second direction from back to front. In other words, the front opening of the mounting groove 31 gradually increases from back to front, which facilitates the emission of light.

[0073] The second metal frame 33 is located within the carrier frame 32 and includes two metal plates 34, which are respectively located on both sides of the carrier frame 32 along the second direction. One of the metal plates 34 is arranged opposite to the emitting electrode 18 and the two receiving electrodes 19. The height of the metal plate 34 exceeds the height of the emitting electrode 18, forming a floating capacitor structure with the emitting electrode 18 and the receiving electrode 19. As the carrier frame 32 moves along the first direction, the capacitance of the third capacitor structure between the emitting electrode 18 and one of the receiving electrodes 19 gradually increases, while the capacitance of the third capacitor structure between the emitting electrode 18 and the other receiving electrode 19 gradually decreases. The change in the capacitance of the two third capacitor structures can determine the position of the carrier frame 32, allowing for more precise control of the carrier frame 32 to move to the target position, thereby improving the accuracy of the closed-loop control of the carrier frame 32.

[0074] Another metal plate 34 is located on the other side of the carrier frame 32 and is used to attract the zoom magnet group 35 inside the carrier frame 32. The zoom magnet group 35 is installed inside the carrier frame 32 and is arranged opposite to the zoom coil group 8 of the other side plate 12. The zoom coil group 8 is electrically connected to the built-in circuit 15. After being powered on, it can cooperate with the zoom magnet group 35 to drive the carrier frame 32 to move the carrier along the first direction, which is the optical axis direction of the lens.

[0075] In addition, a metal plate 34 is provided at the bottom of the carrier frame 32. The three metal plates 34 are connected to each other to form a stable second metal frame 33 structure to increase the stability of the carrier frame 32.

[0076] The base plate 11 also has a bottom metal plate 34, which is integrally formed with the built-in circuit and can also electrically connect the built-in circuits 15 in the two side plates 12 to each other.

[0077] As a preferred embodiment, the inner surfaces of the emitting electrode 18 and the receiving electrode 19 are flush with the inner surfaces of their corresponding side plates 12. The emitting electrode 18 and the receiving electrode 19 are respectively embedded within the side plates 12, and their inner surfaces do not protrude beyond the inner surfaces of the side plates 12. Similarly, the outer surface of the metal plate 34 corresponding to the emitting electrode 18 and the receiving electrode 19 is also flush with the side of the carrier frame. In other words, the metal plate 34 does not protrude beyond the outer surface of the carrier frame 32 and is closer to the emitting electrode 18 and the receiving electrode 19.

[0078] The length of the emitting electrode 18 along the first direction is greater than or equal to the total length of the two receiving electrodes 19 arranged side by side along the first direction. The emitting electrode 18 needs to form a capacitor structure with the two receiving electrodes 19 respectively, and its length should be as great as possible greater than the length of the two receiving electrodes 19.

[0079] The front end of the carrier frame 32 is provided with a damping colloid 36, which is arranged on both sides of the carrier frame 32 near the second direction to buffer the force of the carrier frame 32 touching the front end plate 13 when it moves along the first direction.

[0080] The inner sides of the two side plates 12 are also provided with baffles 122. The two baffles 122 are aligned along the second direction and located between the prism carrier 2 and the lens carrier 3, in order to prevent the prism carrier 2 and the lens carrier 3 from interfering with each other when they move.

[0081] In this invention, both the transmitting and receiving electrodes are located within the side plate and are electrically connected to the built-in wiring, eliminating the need for any wiring on the lens carrier. Furthermore, the first metal frame within the prism carrier can be electrically connected to the built-in wiring via a spring, also eliminating the need for additional wiring. The entire lens drive mechanism requires no internal wiring, ensuring uninterrupted operation of both the prism and lens carriers.

[0082] The preferred embodiments of the present invention have been described in detail above, but it should be understood that, if necessary, aspects of the embodiments can be modified to utilize aspects, features, and concepts from various patents, applications, and publications to provide other embodiments.

[0083] In light of the detailed description above, these and other changes can be made to the embodiments. Generally, the terminology used in the claims should not be considered limited to the specific embodiments disclosed in the specification and claims, but should be understood to include all possible embodiments together with the full scope of equivalents enjoyed by these claims.

[0084] Those skilled in the art will understand that the above embodiments are specific examples of implementing the present invention, and in practical applications, various changes can be made to them in form and detail without departing from the spirit and scope of the present invention.

Claims

1. A lens driving mechanism, characterized in that, The lens driving mechanism includes: The base includes; A base plate, the base plate extending along a first direction; A side plate, which is connected to the side of the base plate along a second direction and forms a receiving space with the base plate, wherein the second direction is perpendicular to the first direction; At least one electrode plate, said electrode plate being located within the base plate; A prism carrier, located within the receiving space and configured to rotate about an axis extending in a first direction and an axis extending in a second direction, the prism carrier comprising: A bracket, the front end of which is provided with an inclined support surface for supporting the prism; A metal frame, the metal frame including at least one electrode, the electrode being disposed opposite to the electrode plate to form a capacitor structure; A capacitive sensing element, which is electrically connected to the capacitor structure.

2. The lens driving mechanism according to claim 1, characterized in that, Two electrode plates are located inside the base plate and are spaced apart along the first direction; The other two electrode plates are located inside the side plate and are spaced apart along the first direction; The two electrodes are located on the bottom surface of the prism carrier and form a first capacitor structure with the two electrodes; The other two electrodes are located on the side of the prism carrier and together with the other two electrodes form a second capacitor structure.

3. The lens driving mechanism according to claim 2, characterized in that, The base also includes built-in wiring, which is located within the base plate and the side plate and connected to the first capacitor structure, the second capacitor structure and the capacitive sensing element.

4. The lens driving mechanism according to claim 3, characterized in that, The lens driving mechanism also includes a spring, which is located on the top surface of the bracket and the side plate and is connected to the bracket and the side plate.

5. The lens driving mechanism according to claim 4, characterized in that, The reed is electrically connected to the metal frame and the built-in wiring.

6. The lens driving mechanism according to claim 5, characterized in that, The top surface of the side plate is provided with a recessed clearance notch; The top surface of the bracket is provided with an installation notch; The reed is located within the clearance notch and the mounting notch.

7. The lens driving mechanism according to claim 4, characterized in that, The base also includes a rear end plate, which is connected to the rear side of the base plate; The lens driving mechanism also includes multiple coil groups and multiple magnet groups, with some coil groups installed in the rear end plate and other coil groups located in the base plate; A portion of the magnet group is located on the rear side of the bracket and is arranged opposite to a portion of the coil group; Another portion of the magnet assembly is located at the bottom of the bracket and is positioned opposite to the other portion of the coil assembly.

8. The lens driving mechanism according to claim 4, characterized in that, The top surface of the base plate is provided with a support protrusion, and the top surface of the support protrusion is provided with a first ball groove. The bottom of the bracket is provided with a groove to accommodate the support protrusion, and the top wall of the groove is provided with a second ball groove; The lens drive mechanism further includes ball bearings located in the first ball bearing groove and the second ball bearing groove to support the bracket to rotate about an axis extending in the first direction and about an axis extending in the second direction.

9. The lens driving mechanism according to claim 7, characterized in that, The metal frame also includes a back plate, which is arranged parallel to the rear end plate and located on the rear side of the bracket.

10. The lens driving mechanism according to claim 8, characterized in that, The metal frame also includes a support plate located on the top wall of the groove and recessed to form the second ball groove.

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