Automatic bearing pressing equipment and tray for speed reducer

Abstract

The application belongs to the field of gear reducer assembly equipment manufacturing, and particularly relates to a gear reducer automatic bearing pressing equipment and a tray, which comprises a frame body, a conveying device, a limiting device, a clamping hand, a servo pressing head and a sensor are arranged on the frame body, the limiting device is located between the start end and the terminal end of the conveying device, the clamping hand is arranged above one side of the conveying device, the servo pressing head is located directly above the limiting device, the servo pressing head is located above the conveying device, the limiting device and the servo pressing head are both within the stroke range of the clamping hand, the sensor signal is connected with the limiting device, the clamping hand and the servo pressing head, the sensing surface of the sensor faces between the conveying device and the servo pressing head, and a preset distance is arranged between the sensor and the conveying surface of the conveying device. The application solves the problem that the current gear reducer automatic bearing pressing equipment can be combined with a flow line and does not need manual participation to start the machine and place the bearing.

Description

Technical Field

[0001] This application belongs to the field of gearbox assembly equipment manufacturing, specifically a gearbox automatic bearing pressing device and tray. Background Technology

[0002] In the current manufacturing process of speed reducers, the bearings that need to be installed on the speed reducer are manually moved to a pressing table by a designated work station. The bearings are then placed in their mounting positions on the speed reducer, and the pressing machine is started to press the bearings into their mounting positions. This method is a semi-automatic assembly, requiring manual operation of the pressing machine, manual placement of the bearings, and manual or robotic lifting of the speed reducer onto the pressing table. This excessive manual intervention leads to low production efficiency. Therefore, it is necessary to design a bearing pressing device that can be integrated into an assembly line and eliminates the need for manual intervention in starting the machine and placing the bearings. Summary of the Invention

[0003] The purpose of this application is to address the shortcomings of existing technologies by designing an automatic bearing press for speed reducers and a tray that works in conjunction with the device, which incorporates a conveying device, a limiting device, a clamping hand, a servo pressure head, and a sensor. This device can automatically assemble bearings into speed reducers on an assembly line, and after the assembly is completed and the conveying restriction on the speed reducer is lifted, the assembled speed reducer can continue to flow to the next workstation under the action of the assembly line. This solves the problem of current automatic bearing press devices for speed reducers that can be integrated with an assembly line without requiring manual intervention to start the machine and place the bearings.

[0004] To achieve the above objectives, this application provides the following technical solution:

[0005] An automatic bearing pressing device for a speed reducer includes a frame. The frame is equipped with a conveying device, a limiting device, a gripper, a servo pressing head, and a sensor. The limiting device is located between the beginning and end of the conveying device. The gripper is positioned above one side of the conveying device. The servo pressing head is directly above the limiting device and located above the conveying device. Both the limiting device and the servo pressing head are within the stroke range of the gripper. The sensor is connected to the limiting device, the gripper, and the servo pressing head. The sensing surface of the sensor faces the area between the conveying device and the servo pressing head. A preset distance exists between the sensor and the conveying surface of the conveying device.

[0006] Preferably, the conveying device includes two parallel conveyor belts, and the limiting device is located directly below the two conveyor belts.

[0007] Preferably, the limiting device includes a lifting cylinder and a support platform. The lifting cylinder is vertically mounted on the frame, with its lower end fixedly connected to the frame and its free end fixedly connected to the support platform.

[0008] Preferably, the limiting device further includes a support block and a transverse cylinder. The transverse cylinder is mounted on the frame and is parallel to the conveying direction of the conveying device. The output end of the transverse cylinder is fixedly connected to the support block. When the transverse cylinder retracts, there is a preset distance between the projection of the transverse cylinder onto the upper surface of the frame and the projection of the support platform onto the upper surface of the frame. The projection of the support platform onto the upper surface of the frame is within the stroke range of the transverse cylinder. The lower surface of the support block is in sliding contact with the frame.

[0009] Preferably, the gripper includes a gripper, an X-axis driver, and a Z-axis driver. The X-axis driver is fixedly mounted on the frame, the Z-axis driver is fixedly mounted on the output end of the X-axis driver, and the gripper is fixedly mounted on the output end of the Z-axis driver.

[0010] Preferably, the servo pressure head includes a support frame, a reducer pressure head, and a bearing pressure head. The support frame is fixedly mounted on the frame body and is located on one side of the conveying device. The reducer pressure head and the bearing pressure head are respectively mounted on the support frame via a first lifter and a second lifter. The reducer pressure head has a through hole in its center with its axis perpendicular to the conveying surface of the conveying device. The bearing pressure head is coaxial with the through hole, and the projection of the bearing pressure head on the conveying surface of the conveying device is located within the projection of the through hole on the conveying surface of the conveying device.

[0011] Preferably, the first lifting device includes a pneumatic telescopic rod, the reducer pressure head is a horizontal plate parallel to the conveying surface of the conveying device, the horizontal plate is fixedly connected to one end of the pneumatic telescopic rod, and the other end of the pneumatic telescopic rod is fixedly connected to the support frame.

[0012] Preferably, the second lifting device includes a telescopic pressure rod, the bearing pressure head includes a pressure head body, the telescopic pressure rod is fixedly mounted on the support frame, the telescopic pressure rod is perpendicular to the conveying surface of the conveying device, the output end of the telescopic pressure rod is fixedly connected to the top end of the pressure head body, the projection of the telescopic pressure rod on the conveying surface of the conveying device is located within the projection of the through hole on the conveying surface of the conveying device, and the projection of the pressure head body on the conveying surface of the conveying device is located within the projection of the through hole on the conveying surface of the conveying device.

[0013] Preferably, the lower surface of the pressure head body is coaxially provided with a pressure tongue, the projection of the pressure tongue on the conveying surface of the conveying device is within the projection of the pressure head body on the conveying surface of the conveying device, and a plurality of radial inner supports are provided on the outer side wall of the pressure tongue.

[0014] Preferably, the radial inner support includes an inner support shell with an opening at one end. The shape and size of the opening are smaller than the shape and size of the inner cross-section of the middle section of the inner support shell. A spring and a ball are disposed inside the inner support shell. One side of the ball contacts the spring, and the other side contacts the opening. The axis of the spring is parallel to the axis of the inner support shell. The opening end of the inner support shell faces away from the central axis of the pressure head body, and the shape and size of the opening are smaller than the diameter of the ball.

[0015] A tray for use with the aforementioned automatic bearing press for a speed reducer, wherein the tray has a speed reducer placement area and a bearing placement area, wherein there is a preset distance between the speed reducer placement area and the bearing placement area, and the lower surface of the tray has a limiting part that cooperates with the aforementioned limiting device.

[0016] Preferably, the reducer placement area includes four columns, which are respectively located at the four corners of a virtual rectangle on the upper surface of the tray, and the bearing placement area is located outside the virtual rectangle.

[0017] Preferably, the bearing placement area includes a positioning post disposed on the surface of the tray, the positioning post being located outside the virtual rectangle and perpendicular to the upper surface of the tray.

[0018] Preferably, the limiting portion is a recessed portion that mates with the top end of the limiting device, and the recessed portion is located on the lower surface of the tray.

[0019] Compared with the prior art, the beneficial effects of this application are:

[0020] 1. This application designs an automatic bearing pressing device for speed reducers and a tray that works with the device by setting up a conveying device, a limiting device, a clamping hand, a servo pressure head, and a sensor. It can automatically assemble bearings for speed reducers on the production line. After the assembly is completed and the conveying restriction on the speed reducer on the production line is lifted, the assembled speed reducer can continue to flow to the next station under the action of the production line. This solves the problem of current automatic bearing pressing devices for speed reducers that can be integrated with the production line without the need for manual intervention to start the machine and place the bearings.

[0021] 2. The two conveyor belts provided in this application can ensure that the pallet on the conveyor belt is stable and can move stably under the drive of the conveyor belt; while the limiting device is located directly below the two conveyor belts, so that when the limiting device is not limiting, it does not affect the conveyor belt from conveying the pallet, and when the limiting device is limiting, it can prevent the pallet on the conveyor belt from moving, thus avoiding the situation where the setting of the limiting device affects the conveyor belt.

[0022] 3. The transverse cylinder in this application allows the support block to be driven directly below the pallet after the lifting cylinder lifts the pallet, thus supporting the pallet. This prevents the force applied by the servo pressure head during the process of pressing the bearing against the reducer from acting on the lifting cylinder, thereby protecting the lifting cylinder.

[0023] 4. This application allows for direct use by setting a tray that works with the automatic bearing pressing equipment of the reducer, eliminating the need for users to collect (purchase) additional trays. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the structure of this application.

[0025] Figure 2 This is a schematic diagram of the tray structure;

[0026] Figure 3 for Figure 2 A schematic diagram of the bottom structure;

[0027] Figure 4 for Figure 1 A partial schematic diagram of bearing assembly;

[0028] Figure 5 for Figure 4 A structural diagram showing the structure after removing a side plate from the support frame on the right side;

[0029] Figure 6 This is a schematic diagram of the structure after the gripper, servo pressure head, and sensor have been removed from this application.

[0030] Figure 7 This is a schematic diagram of the bearing indenter structure;

[0031] Figure 8 This is a schematic diagram of the external structure of the radial inner support;

[0032] Figure 9 for Figure 8 This is a cross-sectional view.

[0033] The components are as follows: 1. Frame; 2. Clamping hand; 2-1. Gripper; 2-2. X-axis driver; 2-3. Z-axis driver; 3. Sensor; 4. Conveyor belt; 5. Lifting cylinder; 6. Support platform; 7. Support block; 8. Horizontal cylinder; 9. Support frame; 10. Through hole; 11. Pneumatic telescopic rod; 12. Horizontal plate; 13. Telescopic pressure rod; 14. Pressure head body; 15. Inner support shell; 16. Spring; 17. Ball bearing; 18. Tray; 19. Recess; 20. Virtual rectangle; 21. Column; 22. Positioning column. Detailed Implementation

[0034] See Figure 1-9 An automatic bearing pressing device for a speed reducer includes a frame 1. The frame 1 is equipped with a conveying device, a limiting device, a gripper 2, a servo pressing head, and a sensor 3. The limiting device is located between the beginning and end of the conveying device. The gripper 2 is positioned above one side of the conveying device. The servo pressing head is located directly above the limiting device and above the conveying device. Both the limiting device and the servo pressing head are within the stroke range of the gripper 2. The sensor 3 is signal-connected to the limiting device, the gripper, and the servo pressing head. The sensing surface of the sensor 3 faces the area between the conveying device and the servo pressing head. A preset distance exists between the sensor 3 and the conveying surface of the conveying device.

[0035] In this embodiment, during use, the conveyor is connected to the assembly line, and the trays on the assembly line automatically flow onto the frame 1 as the assembly line moves. Since the sensing surface of sensor 3 is set to face between the conveyor and the servo pressure head, and there is a preset distance between sensor 3 and the conveying surface of the conveyor, in actual application, the distance between sensor 3 and the conveying surface of the conveyor is adjusted to be greater than or equal to the distance between the upper surface of tray 18 and the conveying surface of the conveyor. Therefore, when the conveyor only conveys tray 18, sensor 3 will not receive a signal and will not trigger the limit device to stop tray 18. However, when tray 18 contains a speed reducer and is conveyed... When the bearing is moved onto the frame 1 under the drive of the device, the sensor 3 senses the reducer and triggers the limit device to pull the tray 18. Since both the limit device and the servo pressure head are within the stroke range of the gripper, the tray 18 restricted by the limit device is also within the stroke range of the gripper 2. At this time, the gripper 2 picks up the bearing on the tray 18 and places it on the reducer. Then, the servo pressure head starts and squeezes the bearing onto the reducer, completing the action of assembling the bearing onto the reducer. After the assembly is completed, the limit device releases the limit, and the tray 18 flows out of the frame 1 under the action of the conveyor, so that the reducers that have not been assembled on the production line flow into the conveyor to continue the assembly action.

[0036] As a preferred embodiment, the conveying device includes two parallel conveyor belts 4 (the power source of the conveyor belts is not shown in this application because the power source of the conveyor belts is prior art, such as a motor driving rollers), and the limiting device is located directly below the two conveyor belts 4. This arrangement ensures that the two conveyor belts 4 are stable and can move steadily under the drive of the conveyor belts 4; while the limiting device, located directly below the two conveyor belts 4, does not affect the conveyor belts 4 from conveying the tray 18 when it is not limiting, and prevents the tray 18 from moving when it is limiting, thus avoiding any interference from the limiting device on the conveyor belts 4.

[0037] In a preferred embodiment, the limiting device includes a lifting cylinder 5 and a support platform 6. The lifting cylinder 5 is vertically mounted on the frame 1, with its lower end fixedly connected to the frame 1 and its free end fixedly connected to the support platform 6. With this configuration, during limiting, the lifting cylinder 5 extends, causing the support platform on the lifting cylinder 5 to lift the tray 18 away from the conveyor surface of the conveyor belt 4.

[0038] As a preferred embodiment, the limiting device further includes a support block 7 and a transverse cylinder 8. The transverse cylinder 8 is mounted on the frame 1 and is parallel to the conveying direction of the conveying device. The output end of the transverse cylinder 8 is fixedly connected to the support block 7. When the transverse cylinder 8 retracts, there is a preset distance between its projection on the upper surface of the frame 1 and the projection of the support platform 6 on the upper surface of the frame 1. The projection of the support platform 6 on the upper surface of the frame 1 is within the stroke range of the transverse cylinder 8. The lower surface of the support block 7 slides in contact with the frame 1. The transverse cylinder 8 is mainly designed to drive the support block 7 directly below the pallet 18 after the lifting cylinder 5 lifts the pallet 18, supporting the pallet 18. This prevents the force applied by the servo pressure head during the process of pressing the bearing against the reducer from acting on the lifting cylinder 5, thus protecting the lifting cylinder 5.

[0039] In a preferred embodiment, the gripper 2 includes a gripper 2-1, an X-axis driver 2-2, and a Z-axis driver 2-3. The X-axis driver 2-2 is fixedly mounted on the frame 1, the Z-axis driver 2-3 is fixedly mounted on the output end of the X-axis driver 2-2, and the gripper 2-1 is fixedly mounted on the output end of the Z-axis driver 2-3. After this setup, once the tray 18 is stopped by the limiting device, the X-axis driver 2-2 drives the gripper 2-1 to move towards the conveying device. When the gripper 2-1 moves directly above the conveying device, the Z-axis driver 2-3 descends, causing the gripper 2-1 to clamp the bearing placed on the tray 18. Then, the Z-axis driver 2-3 rises, making the position of the gripper 2-1 holding the bearing higher than the position of the reducer on the tray 18. Then, the X-axis driver 2-2 drives the gripper 2-1 holding the bearing to move directly above the bearing mounting point on the reducer on the tray 18. Then, the Z-axis driver 2-3 descends again, causing the gripper 2-1 to place the bearing on the reducer on the tray 18 for bearing mounting. Finally, the X-axis driver 2-2 drives the gripper 2-1 away from the conveying device to prevent the gripper 2-1 from blocking the servo pressure head. The X-axis driver 2-2 and Z-axis driver 2-3 can be rodless cylinders. Of course, other driving methods are also possible, such as directly using cylinders as the X-axis driver 2-2 and Z-axis driver 2-3.

[0040] In a preferred embodiment, the servo pressure head includes a support frame 9, a reducer pressure head, and a bearing pressure head. The support frame 9 is fixedly mounted on the frame 1 and is located on one side of the conveying device. The reducer pressure head and the bearing pressure head are respectively mounted on the support frame 9 via a first lifter and a second lifter. The reducer pressure head has a through hole 10 at its center, with its axis perpendicular to the conveying surface of the conveying device. The bearing pressure head is coaxial with the through hole 10, and the projection of the bearing pressure head onto the conveying surface of the conveying device lies within the projection of the through hole 10 onto the conveying surface of the conveying device. The through hole 10 is designed to prevent the bearing pressure head from pressing the bearing into the reducer after the reducer pressure head presses down on the reducer. The reducer pressure head is designed to prevent the reducer from moving during bearing installation, thus stabilizing the reducer's position.

[0041] In a preferred embodiment, the first lifting device includes a pneumatic telescopic rod 11, and the reducer pressure head is a horizontal plate 12 parallel to the conveying surface of the conveying device. The horizontal plate 12 is fixedly connected to one end of the pneumatic telescopic rod 11, and the other end of the pneumatic telescopic rod 11 is fixedly connected to the support frame 9. The large area of ​​the horizontal plate 12 ensures that the pressure on the reducer is concentrated on a single surface during the fixing process, reducing the pressure exerted by the reducer pressure head on the reducer and preventing localized deformation of the reducer surface.

[0042] In a preferred embodiment, the second price increaser includes a telescopic pressure rod 13, and the bearing pressure head includes a pressure head body 14. The telescopic pressure rod 13 is fixedly mounted on the support frame 9, and the telescopic pressure rod 13 is perpendicular to the conveying surface of the conveying device. The output end of the telescopic pressure rod 13 is fixedly connected to the top end of the pressure head body 14. The projection of the telescopic pressure rod 13 on the conveying surface of the conveying device is located within the projection of the through hole 10 on the conveying surface of the conveying device, and the projection of the pressure head body 14 on the conveying surface of the conveying device is located within the projection of the through hole 10 on the conveying surface of the conveying device.

[0043] As a preferred embodiment, a pressure tongue is coaxially provided on the lower surface of the pressure head body 14. The projection of the pressure tongue onto the conveying surface of the conveying device is within the projection of the pressure head body 14 onto the conveying surface of the conveying device. A plurality of radially inner support members are radially provided on the outer side wall of the pressure tongue. By providing radially inner support members, after the clamping hand 2 clamps the bearing, it can place the bearing onto the pressure tongue of the pressure head body 14. In this way, the bearing can move with the movement of the pressure head body 14, preventing the bearing from falling off the pressure tongue of the pressure head body 14.

[0044] In a preferred embodiment, the radial inner support includes an inner support shell 15 with an opening at one end. The size and shape of the opening are smaller than the size and shape of the inner cross-section of the middle section of the inner support shell 15. A spring 16 and a ball bearing 17 are disposed within the inner support shell 15. One side of the ball bearing 17 contacts the spring 16, and the other side contacts the opening. The axis of the spring 16 is parallel to the axis of the inner support shell 15. The opening end of the inner support shell 15 faces away from the central axis of the pressure head body 14, and the size and shape of the opening are smaller than the diameter of the ball bearing 17. Through the arrangement of the inner support shell 15, the spring 16, and the ball bearing 17, during the downward pressing of the pressure head body 14, the inner ring of the bearing compresses the ball bearing 17, causing the ball bearing 17 to compress the spring 16. The elastic force of the spring 16, by compressing the ball bearing 17, supports the bearing. The separate design of the radial inner support and the pressure tongue allows for easy separation of the radial inner support and the pressure tongue during inspection and maintenance, thus avoiding the situation where the entire pressure tongue or pressure head body 14 has to be replaced if the radial inner support is damaged.

[0045] A tray 18 is provided to cooperate with the aforementioned automatic bearing pressing device for a speed reducer. The tray 18 has a speed reducer placement area and a bearing placement area, with a preset distance between them. The lower surface of the tray 18 has a limiting part that cooperates with the aforementioned limiting device. By providing the tray 18 for cooperation with the automatic bearing pressing device for a speed reducer, this application can be used directly without requiring the user to collect the tray 18 separately.

[0046] As a preferred embodiment, the reducer placement area includes four pillars 21, which are respectively located at the four corners of a virtual rectangle 20 on the upper surface of the tray 18. The bearing placement area is located outside the virtual rectangle 20. The four pillars 21 restrict the position of the reducer on the tray 18, preventing it from sliding. The shape and size of the virtual rectangle 20 are the same as the outer contour of the reducer; that is, this application supports bearing assembly on reducers whose outer contours are the same as the shape of the virtual rectangle in this application. Because the pillars 21 are only placed at the four corners of the virtual rectangle 20, manufacturing costs are saved, allowing the reducer's position on the tray 18 to be restricted with a minimal number of components.

[0047] As a preferred embodiment, the bearing placement area includes positioning posts 22 disposed on the surface of the tray 18. The positioning posts 22 are located outside the virtual rectangle 20 and are perpendicular to the upper surface of the tray 18. The bearing is placed by providing the positioning posts 22.

[0048] As a preferred embodiment, the limiting portion is a recessed portion 19 that mates with the top end of the limiting device, and the recessed portion 19 is located on the lower surface of the tray 18. The recessed portion 19 facilitates the lifting of the tray 18 during the upward movement of the limiting device, preventing slippage between the lower surface of the tray 18 and the top end of the limiting device during the limiting process.

Claims

1. A speed reducer automatic bearing pressing apparatus characterized by, The rack (1) is provided with a conveying device, a limiting device, a clamping hand, a servo pressure head and a sensor (3). The limiting device is located between the beginning and end of the conveying device. The clamping hand is arranged above one side of the conveying device. The servo pressure head is located above the limiting device. The limiting device and the servo pressure head are within the stroke range of the clamping hand. The sensor (3) is signal connected with the limiting device, the clamping hand and the servo pressure head. The sensing surface of the sensor (3) faces the conveying device and the servo pressure head. The sensor (3) and the conveying surface of the conveying device are provided with a preset distance. The conveying device comprises two parallel conveying belts (4). The limiting device is located below the two conveying belts (4). The limiting device comprises a lifting cylinder (5) and a support table (6). The lifting cylinder (5) is vertically arranged on the rack (1). The lower end of the lifting cylinder (5) is fixedly connected with the rack (1). The free end of the lifting cylinder (5) is fixedly connected with the support table (6). The limiting device further comprises a support block (7) and a horizontal cylinder (8). The horizontal cylinder (8) is arranged on the rack (1). The horizontal cylinder (8) is parallel to the conveying direction of the conveying device. The output end of the horizontal cylinder (8) is fixedly connected with the support block (7). When the horizontal cylinder (8) is contracted, the projection of the upper surface of the rack (1) and the projection of the support table (6) on the upper surface of the rack (1) are provided with a preset distance. The projection of the support table (6) on the upper surface of the rack (1) is within the stroke range of the horizontal cylinder (8). The lower surface of the support block (7) is in sliding contact with the rack (1).

2. A speed reducer automatic bearing pressing apparatus according to claim 1, wherein The clamping hand (2) comprises a clamping jaw (2-1), an X-axis driver (2-2) and a Z-axis driver (2-3). The X-axis driver (2-2) is fixedly arranged on the rack (1). The output end of the X-axis driver (2-2) is fixedly provided with the Z-axis driver (2-3). The output end of the Z-axis driver (2-3) is fixedly provided with the clamping jaw (2-1).

3. A speed reducer automatic bearing pressing apparatus according to claim 1, wherein The servo pressure head comprises a support frame (9), a speed reducer pressure head and a bearing pressure head. The support frame (9) is fixedly arranged on the rack (1). The support frame (9) is located on one side of the conveying device. The speed reducer pressure head and the bearing pressure head are arranged on the support frame (9) through first and second lifters respectively. The central part of the speed reducer pressure head is provided with a through hole (10) whose axis is perpendicular to the conveying surface of the conveying device. The bearing pressure head is coaxial with the through hole (10). The projection of the bearing pressure head on the conveying surface of the conveying device is located within the projection of the through hole (10) on the conveying surface of the conveying device.

4. A speed reducer automatic bearing pressing apparatus according to claim 3, wherein The first lifting device comprises a pneumatic telescopic rod (11), the reducer pressure head is a horizontal plate (12) parallel to the conveying surface of the conveying device, the horizontal plate (12) is fixedly connected with one end of the pneumatic telescopic rod (11), and the other end of the pneumatic telescopic rod (11) is fixedly connected with the support frame (9).

5. A speed reducer automatic bearing pressing apparatus according to claim 3, wherein The second lifting device comprises a telescopic pressure rod (13), the bearing pressure head comprises a pressure head body (14), the telescopic pressure rod (13) is fixedly arranged on the support frame (9), the telescopic pressure rod (13) is perpendicular to the conveying surface of the conveying device, the output end of the telescopic pressure rod (13) is fixedly connected with the top end of the pressure head body (14), the projection of the telescopic pressure rod (13) on the conveying surface of the conveying device is located in the projection of the through hole (10) on the conveying surface of the conveying device, and the projection of the pressure head body (14) on the conveying surface of the conveying device is located in the projection of the through hole (10) on the conveying surface of the conveying device.

6. A tray characterized in that, The tray is matched with the reducer automatic bearing pressing equipment in claim 1, the tray (18) is provided with a reducer placing area and a bearing placing area, a predetermined distance is arranged between the reducer placing area and the bearing placing area, and a limiting portion matched with the limiting device is arranged on the lower surface of the tray (18).

7. A pallet according to claim 6, wherein, The reducer placing area comprises four stand columns (21), the four stand columns (21) are respectively arranged at four corners of a virtual rectangle (20) on the upper surface of the tray (18), and the bearing placing area is located outside the virtual rectangle (20).

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