Detection device for press-fitting angle of motor rotor commutator

Abstract

The utility model discloses a device for detecting the press-fitting angle of a commutator of a motor rotor. The device comprises a workbench and a positioner used for observing the starting point position and the ending point position of a first groove or a second groove in the rotor. The rotating mechanism is matched with the workbench; the angle sensing assembly is connected with the rotating mechanism; the supporting part is used for supporting the rotor and is matched with the rotating mechanism; the driving mechanism is used for driving the positioner to move, and the positioner is connected with the driving mechanism; when the first groove or the second groove in the rotor is detected, the rotor is matched with the supporting component, the driving mechanism drives the positioner to move, and after the positioning part on the positioner coincides with the starting point of the first groove or the second groove, the rotating mechanism is rotated to enable the terminal point of the first groove or the second groove to coincide with the positioning part on the positioner. The device can rapidly detect the press-fitting angle of the motor rotor commutator beside a production line.

Description

Technical Field

[0001] This utility model relates to the field of motor rotors, and specifically to a device for detecting the pressing angle of a motor rotor commutator. Background Technology

[0002] A starting electronic rotor typically consists of a rotor core, windings, a shaft, and a commutator. The windings are fixed to the rotor core, the shaft passes through the rotor core and is connected to it, and the commutator is connected to one end of the shaft. The circumferential surface of the rotor core has multiple first grooves parallel to the axial direction of the rotor core. These grooves are arranged at intervals along the circumference of the commutator. The circumferential surface of the commutator typically has multiple second grooves parallel to the axial direction of the commutator. These second grooves are arranged at intervals along the circumference of the commutator.

[0003] Commutators and shafts are usually assembled by press fitting. Typically, the first and second grooves are required to be 0±1° on the design drawings. After press fitting, it is necessary to determine whether the positions of the first groove on the rotor core and the second groove on the commutator meet the requirements of the design drawings.

[0004] Existing angle measurement devices typically use a universal microscope for testing. This requires transporting the rotor from the production line to a laboratory, placing it under a microscope, marking the corresponding points on the product, and then calculating the angle to be measured. This method has the following drawbacks:

[0005] 1. Difficulty in sending products for testing and cumbersome procedures. Products need to be sent to the laboratory for testing and cannot be tested immediately at the production line.

[0006] 2. The testing process is cumbersome and time-consuming. After the product is sent to the laboratory, the operator uses a multi-functional display to inspect it. Each test takes more than 10 minutes. In addition, the time required for delivery makes the testing efficiency low.

[0007] In summary, the above-mentioned methods are not suitable for small-batch sampling inspections during the mass production process. Summary of the Invention

[0008] This invention provides a device for detecting the pressing angle of a motor rotor commutator. This invention is a device that can quickly detect the pressing angle of a motor rotor commutator next to the production line.

[0009] A device for detecting the pressing angle of a motor rotor commutator, comprising a worktable, a locator for observing the start and end positions of the first or second groove on the rotor, and further comprising:

[0010] A rotating mechanism that works in conjunction with a worktable;

[0011] Angle sensing component, which is connected to the rotation mechanism;

[0012] Support components are used to support the rotor, and the support components cooperate with the rotating mechanism;

[0013] A drive mechanism is used to move the positioner, and the positioner is connected to the drive mechanism.

[0014] When inspecting the first or second groove on the rotor, the rotor is fitted with the support component, and the positioner is moved by the drive mechanism so that the positioning part on the positioner coincides with the starting point of the first or second groove. Then, the rotating mechanism is rotated so that the ending point of the first or second groove coincides with the positioning part on the positioner.

[0015] Furthermore, the rotating mechanism includes a sleeve, a movable seat, and a connecting rod. A first through hole is provided on the worktable. The sleeve is fixed to the worktable and mates with the first through hole. One end of the movable seat is provided with a fitting groove. The other end of the movable seat is fixed to one end of the connecting rod. The other end of the connecting rod passes through the sleeve and is connected to the angle sensing component.

[0016] Furthermore, the rotating mechanism also includes a first positioning pin, a second through hole on the movable seat, and a first insertion hole on the worktable. After the first positioning pin cooperates with the second through hole and the first insertion hole, the angle of the rotating mechanism is limited to the position of the initial angle.

[0017] Furthermore, the supporting component includes a connecting sleeve, a mounting plate, and a limiting component for circumferentially limiting the rotor. The mounting plate is fixed to the connecting sleeve and also fixed to the rotating mechanism. There are multiple limiting components, which are fixed to the connecting sleeve.

[0018] Furthermore, the rotating mechanism includes a second positioning pin, and a second insertion hole is provided on the mounting plate. After the second positioning pin engages with the second insertion hole, the second positioning pin positions the supporting component.

[0019] Furthermore, the drive mechanism includes:

[0020] A first drive unit for moving the positioner along the X direction of the worktable, the first drive unit being fixed to the worktable;

[0021] A second drive unit is used to move the positioner along the Z-axis of the worktable, and the second drive unit is fixed to the first drive unit;

[0022] A third drive unit is used to move the positioner along the Y direction of the worktable. The third drive unit is fixed to the second drive unit, and the positioner is fixed to the third drive unit.

[0023] Furthermore, the first drive unit includes a first support, a first sliding seat, and a first rotation drive component for driving the first sliding seat to move along the X direction of the worktable. The first support is fixed to the worktable, the first sliding seat is slidably engaged with the first support, the first rotation drive component is rotatably engaged with the first support, a first gear or a first friction wheel is fixed on the first rotation drive component, and the first sliding seat is provided with a first rack or has a first friction surface. The first gear meshes with the first rack, or the first friction wheel engages with the first friction surface.

[0024] Furthermore, the second drive unit includes a second support, a second sliding seat, and a second rotation drive component for driving the second sliding seat to move along the Z direction of the worktable. The second support is fixed to the first drive unit, the second sliding seat is slidably engaged with the second support, and the second rotation drive component is rotatably engaged with the second support. A second gear or a second friction wheel is fixed on the second rotation drive component. The second sliding seat is provided with a second rack or has a second friction surface. The second gear meshes with the second rack, or the second friction wheel engages with the second friction surface.

[0025] Furthermore, the third drive unit includes a third support, a third sliding seat, and a third rotation drive component for driving the third sliding seat to move along the Y direction of the worktable. The third support is fixed to the second drive unit, the third sliding seat is slidably engaged with the third support, and the third rotation drive component is rotatably engaged with the third support. A third gear or a third friction wheel is fixed on the third rotation drive component. The third sliding seat is provided with a third rack or has a third friction surface. The third gear meshes with the third rack, or the third friction wheel engages with the third friction surface.

[0026] The advantages of this invention are: it allows for rapid inspection at the production line. An optical microscope is used to focus on a specific location on the first or second groove of the rotor, setting this location as the origin. The rotating mechanism drives the rotor to rotate to the next location, where the optical microscope is used again for confirmation. An angle measurement sensor displays the rotation angle in real time, and the final displayed angle is the angle between the two measurement locations on the product. This method is flexible, fast, and can check the angles between different locations on the product. Attached Figure Description

[0027] Figure 1 A perspective view of a device for detecting the pressing angle of a motor rotor commutator.

[0028] Figure 2 This is a cross-sectional view of a device for detecting the pressing angle of a motor rotor commutator.

[0029] Figure 3 This is a 3D view of the drive mechanism.

[0030] Labels in the attached diagram:

[0031] Workbench 1, first through hole 1a, first insertion hole 1b, locator 2, rotating mechanism A, sleeve 3, movable seat 4, insertion slot 4a, second through hole 4b, connecting rod 5, first positioning pin 6, angle sensing component B, support component C, connecting sleeve 7, mounting plate 8, second insertion hole 8a, limiting component 9, second positioning pin 10, drive mechanism D, first support 11, first sliding seat 12, first rotation drive component 13, first friction wheel 14, second support 15, second sliding seat 16, second rotation drive component 17, third support 18, third sliding seat 19, third rotation drive component 20, angle sensor 21, mounting base 22, connecting rod 23, first mounting block 24, first locking bolt 25. Detailed Implementation

[0032] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the drawings used in the description of the embodiments or the prior art are briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other embodiments can be obtained based on the drawings without creative effort, and these embodiments are still within the protection scope of the claims of this utility model.

[0033] like Figures 1 to 3 The present invention relates to a detection device for pressing angle of motor rotor commutator, comprising a worktable 1, a locator 2 for observing the starting and ending positions of the first or second groove on the rotor, wherein the locator 2 preferably adopts an optical microscope, and also includes a rotation mechanism A, an angle sensing component B, a support component C, and a drive mechanism D. The following is a detailed description of each part and the relationship between them.

[0034] Rotating mechanism A cooperates with worktable 1; rotating mechanism A includes sleeve 3, movable seat 4, and connecting rod 5. Worktable 1 is provided with a first through hole 1a. Sleeve 3 is fixed to worktable 1 and cooperates with the first through hole 1a. Sleeve 3 passes through the first through hole 1a and is clearance-fitted with the first through hole 1a. One end of movable seat 4 is provided with insertion groove 4a. The other end of movable seat 4 is fixed to one end of connecting rod 5. Connecting rod 5 is clearance-fitted with sleeve 3. The other end of connecting rod 5 passes through sleeve 3 and is connected to angle sensing component B.

[0035] The rotating mechanism A also includes a first positioning pin 6. The movable seat 4 has a second through hole 4b, and the worktable 1 has a first insertion hole 1b. After the first positioning pin 6 engages with the second through hole 4b and the first insertion hole 1b, it restricts the angle of the rotating mechanism A to the initial angle position. The first positioning pin 6 passes through the second through hole 4b and is in clearance fit with it. When the first positioning pin 6 is inserted into the first insertion hole 1b, it locks the worktable 1 and the movable seat 4 together, preventing the movable seat 4 from rotating relative to the worktable 1. Since the movable seat 4 is connected to the angle sensing component B via the connecting rod 5, the angle sensing component B also cannot rotate at this time. When the angle sensing component B is in this position, its angle returns to the initial angle position. In this embodiment, the initial angle is set to zero degrees. When the first positioning pin 6 separates from the first insertion hole 1b, applying torque to the movable seat 4 allows it to rotate relative to the worktable 1.

[0036] Angle sensing component B is connected to rotation mechanism A. In this embodiment, angle sensing component B includes angle sensor 21, mounting base 22, and connecting rod 23. Angle sensor 21 and mounting base 22 are located below movable seat 4. Angle sensor 21 is connected to connecting rod 5 and mounting base 22. Mounting base 22 is connected to connecting rod 23. After connecting rod 23 is connected to worktable 1, angle sensor 21 is suspended below movable seat 4.

[0037] Support component C supports the rotor and cooperates with rotating mechanism A. Support component C includes a connecting sleeve 7, a mounting plate 8, and limiting components 9 for circumferentially limiting the rotor. The connecting sleeve 7 is used for shaft insertion, with one end inserted into the insertion groove 4a. The mounting plate 8 is fixed to the connecting sleeve 7 and is located on the circumferential surface of the connecting sleeve 7. The mounting plate 8 and connecting sleeve 7 preferably adopt an integral molding structure to ensure structural stability and reliability. The mounting plate 8 is also fixed to rotating mechanism A and is fixed to movable seat 4 by screws. Multiple limiting components 9 are evenly distributed around the inner hole of the connecting sleeve 7. One end of each limiting component 9 is fixed to the connecting sleeve 7, and the other end of each limiting component 9 is a free end for insertion into a groove provided on the axial end face of the rotor core. Thus, through the insertion and cooperation of multiple limiting components with the rotor core, the rotor cannot rotate relative to support component C.

[0038] The rotating mechanism A includes a second positioning pin 10. One end of the second positioning pin 10 is connected to the movable seat 4. The mounting plate 8 is provided with a second insertion hole 8a. After the other end of the second positioning pin 10 engages with the second insertion hole 8a, the second positioning pin 10 positions the supporting component C. After the connecting sleeve 7 is inserted into the insertion groove 4a, the second positioning pin 10 engages with the second insertion hole 8a, thereby restricting the rotation of the connecting sleeve 7 relative to the movable seat 4.

[0039] A drive mechanism D is used to move the positioner 2. The positioner 2 is connected to the drive mechanism D. The drive mechanism D includes a first drive unit, a second drive unit, and a third drive unit. The first drive unit is used to move the positioner 2 along the X-direction (lateral direction) of the worktable 1. The first drive unit is fixed to the worktable 1. In this embodiment, the first drive unit includes a first support 11, a first sliding seat 12, and a first rotation drive component 13 for driving the first sliding seat 12 to move along the X-direction of the worktable 1. The first support 11 is fixed to the worktable 1. The first sliding seat 12 is slidably engaged with the first support 11. The first support 11 is provided with a first sliding groove, which is a dovetail groove. The first sliding seat 12 is provided with a first protrusion, which is dovetail-shaped and slidably engaged with the first sliding groove.

[0040] The first rotation drive component 13 is rotatably engaged with the first support 11. The first rotation drive component 13 consists of a first rod and a first handwheel fixed to the first rod. The first rod is rotatably engaged with the first support 11 via, for example, a bearing. A first receiving cavity is provided on the first support 11, and the first rod extends into the first receiving cavity on the first support 11.

[0041] A first gear or a first friction wheel 14 is fixed on the first rotation drive component 13. The first gear or the first friction wheel 14 is located in the first receiving cavity on the first support 11. The first gear or the first friction wheel 14 is fixed to the first rod in the first rotation drive component 13. The first sliding seat 12 is provided with a first rack or has a first friction surface. The first gear meshes with the first rack, or the first friction wheel 14 cooperates with the first friction surface.

[0042] When torque is applied to the first rotation drive component 13, the first rotation drive component 13 rotates, causing the first gear or the first friction wheel 14 to rotate. The first gear or the first friction wheel 14 transmits power to the first sliding seat 12, thereby causing the first sliding seat 12 to move along the X direction of the worktable 1, and in turn causing the positioner 2, which is connected to the drive mechanism D, to move along the X direction of the worktable 1.

[0043] The second drive unit is used to move the positioner 2 along the Z-axis (longitudinal direction) of the worktable 1. The second drive unit is fixed to the first drive unit. The second drive unit includes a second support 15, a second sliding seat 16, and a second rotation drive component 17 for driving the second sliding seat 16 to move along the Z-axis of the worktable 1. The second support 15 is fixed to the first drive unit and to the first sliding seat 12 in the first drive unit. The second sliding seat 16 is slidably engaged with the second support 15. The second support 15 is provided with a second sliding groove, which is a dovetail groove. The second sliding seat 16 is provided with a second protrusion, which is dovetail-shaped and slidably engaged with the second sliding groove.

[0044] The second rotation drive component 17 is rotatably engaged with the second support 15. The second rotation drive component 17 consists of a second rod and a second handwheel fixed to the second rod. The second rod is rotatably engaged with the second support 15 via, for example, a bearing. A second receiving cavity is provided on the second support 15, and the second rod extends into the second receiving cavity on the second support 15.

[0045] A second gear or a second friction wheel is fixed on the second rotation drive component 17. The second gear or the second friction wheel is located in the second receiving cavity on the second support 15. The second gear or the second friction wheel is fixed to the second rod in the second rotation drive component 17. The second sliding seat 16 is provided with a second rack or has a second friction surface. The second gear meshes with the second rack, or the second friction wheel cooperates with the second friction surface.

[0046] When torque is applied to the second rotation drive component 17, the second rotation drive component 17 rotates, causing the second gear or the second friction wheel 14 to rotate. The second gear or the second friction wheel 14 transmits power to the second sliding seat 16, thereby causing the second sliding seat 16 to move along the Z direction of the worktable 1, and in turn causing the positioner 2, which is connected to the drive mechanism D, to move along the Z direction of the worktable 1.

[0047] The third drive unit is used to move the positioner 2 along the Y-axis (height direction) of the worktable 1. The third drive unit is fixed to the second drive unit, and the positioner 2 is fixed to the third drive unit. The third drive unit includes a third support 18, a third sliding seat 19, and a third rotary drive component 20 for driving the third sliding seat 19 to move along the Y-axis of the worktable 1. The third support 18 is fixed to the second drive unit, and the third support 18 is fixed to the second sliding seat 16 in the second drive unit. The third sliding seat 19 is slidably engaged with the third support 18. The third support 18 is provided with a second sliding groove, which is a dovetail groove. The third sliding seat 19 is provided with a third protrusion, which is dovetail-shaped and slidably engaged with the third sliding groove.

[0048] The third rotation drive component 20 is rotatably engaged with the third support 18. The third rotation drive component 20 consists of a third rod and a third handwheel fixed to the third rod. The third rod is rotatably engaged with the third support 18 via, for example, a bearing. A third receiving cavity is provided on the third support 18, and the third rod extends into the third receiving cavity on the third support 18.

[0049] A third gear or a third friction wheel is fixed on the third rotation drive component 20. The third gear or the third friction wheel is located in the third receiving cavity on the third support 18. The third gear or the third friction wheel is fixed to the third rod in the third rotation drive component 20. The third sliding seat 20 is provided with a third rack or has a third friction surface. The third gear meshes with the third rack, or the third friction wheel cooperates with the third friction surface.

[0050] When torque is applied to the third rotation drive component 20, the third rotation drive component 20 rotates, causing the third gear or the third friction wheel 14 to rotate. The third gear or the third friction wheel 14 transmits power to the third sliding seat 19, thereby causing the third sliding seat 19 to move along the Y direction of the worktable 1, and in turn causing the positioner 2 located in connection with the drive mechanism D to move along the Y direction of the worktable 1.

[0051] The first drive unit also includes a first locking mechanism, which includes a first mounting block 24 and a first locking bolt 25. The first mounting block 24 is fixed to the first support 11. The first mounting block 24 is provided with a strip hole, and the first sliding seat 12 is provided with a threaded hole. The first locking bolt 25 passes through the strip hole and is threadedly connected to the threaded hole on the first sliding seat 12. When the first locking bolt 25 is pressed on the first mounting block 24, the first sliding seat 12 cannot slide relative to the first support 11. When the first locking bolt 25 is separated from the first mounting block 24, the first sliding seat 12 can slide relative to the first support 11.

[0052] The second drive unit is provided with the same structure as the first locking mechanism for locking the second sliding seat 16 when it is not necessary to slide the second sliding seat 16. The third drive unit is provided with the same structure as the first locking mechanism for locking the third sliding seat 19 when it is not necessary to slide the third sliding seat 19.

[0053] When inspecting the first or second groove on the rotor, the rotor is engaged with the support component C, that is, the rotor is inserted into the connecting sleeve 7. The limiting component 9 engages with the groove on the rotor. By rotating the first rotation drive component 13 and / or the second rotation drive component 17 and / or the third rotation drive component 20, the drive mechanism D moves the positioner 2 to the position required by the operator. Since the positioner 2 in this embodiment is an optical microscope, the lens of the optical microscope has a cross-shaped positioning part. The first positioning pin 6 is pulled out, so that the first positioning pin 6 is separated from the first insertion hole 1b. The operator applies torque to the movable seat 4 manually to rotate the movable seat 4. The connecting sleeve 7, rotor, connecting rod 5, and angle sensing component B all rotate with the movable seat 4. When the positioning part on the positioner 2 coincides with the starting point of the first or second groove on the rotor, this point is taken as the angle origin of the first or second groove. Then, rotating mechanism A, connecting sleeve 7, rotor, connecting rod 5, and angle sensing component B all rotate again with movable seat 4, so that the end point of the first groove or the second groove coincides with the positioning part on the positioner 2. At this time, the corresponding angle is displayed by the digital display connected to angle sensing component B. When detecting the first groove, for example, it is the angle between the end point of the first groove and the initial angle position of angle sensing component B. When detecting the second groove, for example, it is the angle between the end point of the second groove and the initial angle position of angle sensing component B. The angle between the first end point and the angle between the second end point are compared to determine whether the angle difference between the end points of the first groove and the second groove after pressing is within the allowable range (0±1°).

Claims

1. A device for detecting the pressing angle of a motor rotor commutator, comprising a worktable (1) and a locator (2) for observing the starting and ending positions of a first or second groove on the rotor, characterized in that, Also includes: Rotating mechanism (A), which cooperates with worktable (1); Angle sensing component (B) is connected to the rotation mechanism (A); A support component (C) is used to support the rotor, and the support component (C) cooperates with the rotating mechanism (A); A drive mechanism (D) for moving the positioner (2), the positioner (2) is connected to the drive mechanism (D); When testing the first or second groove on the rotor, the rotor is engaged with the support component (C), and the positioner (2) is moved by the drive mechanism (D) so that the positioning part on the positioner (2) coincides with the starting point of the first or second groove. Then, the rotating mechanism (A) is rotated so that the ending point of the first or second groove coincides with the positioning part on the positioner (2).

2. The detection device for the pressing angle of the motor rotor commutator according to claim 1, characterized in that, The rotating mechanism (A) includes a sleeve (3), a movable seat (4), and a connecting rod (5). The worktable (1) is provided with a first through hole (1a). The sleeve (3) is fixed to the worktable (1) and cooperates with the first through hole (1a). One end of the movable seat (4) is provided with a fitting groove (4a). The other end of the movable seat (4) is fixed to one end of the connecting rod (5). The other end of the connecting rod (5) passes through the sleeve (3) and is connected to the angle sensing component (B).

3. The detection device for the pressing angle of the motor rotor commutator according to claim 2, characterized in that, The rotating mechanism (A) also includes a first positioning pin (6), a second through hole (4b) on the movable seat (4), and a first insertion hole (1b) on the worktable (1). After the first positioning pin (6) cooperates with the second through hole (4b) and the first insertion hole (1b), the angle of the rotating mechanism (A) is limited to the position of the initial angle.

4. The detection device for the pressing angle of the motor rotor commutator according to claim 1, characterized in that, The support component (C) includes a connecting sleeve (7), a mounting plate (8), and a limiting component (9) for circumferentially limiting the rotor. The mounting plate (8) is fixed to the connecting sleeve (7) and is also fixed to the rotating mechanism (A). There are multiple limiting components (9) and they are fixed to the connecting sleeve (7).

5. The detection device for the pressing angle of the motor rotor commutator according to claim 4, characterized in that, The rotating mechanism (A) includes a second positioning pin (10), and a second insertion hole (8a) is provided on the mounting plate (8). After the second positioning pin (10) cooperates with the second insertion hole (8a), the second positioning pin (10) positions the support component (C).

6. The detection device for the pressing angle of the motor rotor commutator according to claim 1, characterized in that, The drive mechanism (D) includes: A first drive unit for moving the positioner (2) along the X direction of the worktable (1) is fixed to the worktable (1); A second drive unit is used to move the positioner (2) along the Z direction of the worktable (1), and the second drive unit is fixed to the first drive unit; A third drive unit is used to move the positioner (2) along the Y direction of the worktable (1). The third drive unit is fixed to the second drive unit, and the positioner (2) is fixed to the third drive unit.

7. The detection device for the pressing angle of the motor rotor commutator according to claim 6, characterized in that, The first drive unit includes a first support (11), a first sliding seat (12), and a first rotation drive component (13) for driving the first sliding seat (12) to move along the X direction of the worktable (1). The first support (11) is fixed to the worktable (1), the first sliding seat (12) is slidably engaged with the first support (11), and the first rotation drive component (13) is rotatably engaged with the first support (11). A first gear or a first friction wheel (14) is fixed on the first rotation drive component (13). The first sliding seat (12) is provided with a first rack or has a first friction surface. The first gear meshes with the first rack, or the first friction wheel (14) engages with the first friction surface.

8. The detection device for the pressing angle of the motor rotor commutator according to claim 6, characterized in that, The second drive unit includes a second support (15), a second sliding seat (16), and a second rotation drive component (17) for driving the second sliding seat (16) to move along the Z direction of the worktable (1). The second support (15) is fixed to the first drive unit, the second sliding seat (16) is slidably engaged with the second support (15), and the second rotation drive component (17) is rotatably engaged with the second support (15). A second gear or a second friction wheel is fixed on the second rotation drive component (17), and a second rack or a second friction surface is provided on the second sliding seat (16). The second gear meshes with the second rack, or the second friction wheel engages with the second friction surface.

9. The detection device for the pressing angle of the motor rotor commutator according to claim 6, characterized in that, The third drive unit includes a third support (18), a third sliding seat (19), and a third rotation drive component (20) for driving the third sliding seat (19) to move along the Y direction of the worktable (1). The third support (18) is fixed to the second drive unit, the third sliding seat (19) is slidably engaged with the third support (18), and the third rotation drive component (20) is rotatably engaged with the third support (18). A third gear or a third friction wheel is fixed on the third rotation drive component (20), and a third rack or a third friction surface is provided on the third sliding seat (19). The third gear meshes with the third rack, or the third friction wheel engages with the third friction surface.

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