Material handling machine

Abstract

A material grabber includes: a main unit; a hopper having two or more lobes, capable of digging and grabbing material by changing from an open state to a closed state; a hopper drive and holding mechanism, one end of which is connected to the top of the hopper and the other end fixed to the main unit, capable of moving the hopper and holding it in a fixed position; and a material grabbing control system, the material grabbing control system controlling the movement of the hopper and the drive and holding mechanism, the hopper drive and holding mechanism having an obstacle avoidance buffer device, the obstacle avoidance buffer device being configured such that when the bottom of the hopper is subjected to an upward force during material grabbing, the obstacle avoidance buffer device allows the top of the hopper to move upward for buffering, and the material grabbing control system is capable of controlling the damping magnitude of the obstacle avoidance buffer device.

Description

Technical Field

[0001] This invention relates to a material grabber, and more particularly to a material grabber capable of automatically grabbing materials and preventing the grabber's hopper from tearing the bottom plate of the carrier loaded with materials during the grabbing process. Background Technology

[0002] A material grabber is a type of engineering machinery widely used in mines, steel plants, ports, railway freight stations, etc., to grab materials from and transfer them from carriers such as cargo ships, train cars, or trucks. Typically, a material grabber includes a turntable mounted on a track frame and a material grabbing mechanism mounted on the turntable. The grabbing mechanism includes a boom, a stick, and a bucket. One end of the boom is hinged to the turntable, and the other end is hinged to one end of the stick. A boom cylinder is installed between the boom and the turntable. The other end of the stick is hinged to the bucket, and a stick cylinder is installed between the stick and the boom. A bucket cylinder is installed on the bucket. In operation, the boom cylinder controls the raising and lowering of the boom, the stick cylinder controls the extension and retraction of the stick, and the bucket cylinder controls the opening and closing of the bucket, thus achieving the grabbing and transfer of materials.

[0003] However, existing material grabbers have the following problems: When grabbing material, if the material to be grabbed is close to the bottom plate of the cargo box of a vehicle such as a train, ship, or truck, the hopper is prone to colliding with the bottom plate (hereinafter referred to as "bottom biting"), posing a risk of breaking the bottom plate. In particular, during ship unloading, breaking the bottom of the hull would cause greater losses and greater dangers. In order to grab material without breaking the bottom plate, the operator needs to constantly adjust the height and degree of closure of the hopper, which requires a high level of skill from the operator. When repeated grabbing is required, the labor intensity of the operator is very high. When grabbing material, whether the hopper is fully closed needs to be judged by the operator visually or based on experience. There is a possibility of operator misjudgment. If the material is transferred when the hopper is not fully closed, the material will fall, causing property damage, and more seriously, it may endanger the safety of personnel. Summary of the Invention

[0004] The present invention was made in view of the above problems, and its purpose is to provide a material grabber that, when grabbing material close to the bottom plate of the carrier (hereinafter referred to as "near-bottom operation"), can prevent the hopper from tearing the bottom plate of the carrier, and does not require the operator to frequently perform hopper lifting and closing operations, can grab materials smoothly and reliably, effectively improves work efficiency and reduces the labor intensity of the operator.

[0005] To achieve the above objectives, the material grabber of the first aspect of the present invention comprises: a main unit; a hopper having two or more hopper flaps, capable of digging and grabbing material by changing from an open state to a closed state; a hopper drive and holding mechanism, one end of which is connected to the top of the hopper and the other end is fixed to the main unit, capable of moving the hopper and holding it in a fixed position; and a material grabbing control system, which controls the movement of the hopper and the drive and holding mechanism, wherein the hopper drive and holding mechanism has an obstacle avoidance buffer device, the obstacle avoidance buffer device being configured such that when the bottom of the hopper is subjected to an upward force during material grabbing, the obstacle avoidance buffer device allows the top of the hopper to move upward for buffering, and the material grabbing control system is capable of controlling the damping magnitude of the obstacle avoidance buffer device.

[0006] According to a first aspect of the present invention, the material grabber has an obstacle avoidance and buffer device. When the bottom of the hopper is subjected to an upward force, the top of the hopper can move upward to buffer the impact. The damping of the obstacle avoidance and buffer device can be adjusted to a suitable value by the material grabbing control system, thereby preventing the hopper from tearing the bottom plate of the carrier. In addition, as the top of the hopper gradually moves upward, the bottom of the hopper gradually closes along the bottom plate of the carrier, enabling smooth and reliable material grabbing. This also avoids the need for operators to frequently perform hopper lifting and closing operations, effectively improving work efficiency and reducing labor intensity.

[0007] The second aspect of the material handling machine of the present invention is that, in the first aspect of the material handling machine, the material handling control system enables the hopper to switch between a non-buffered material handling mode and an obstacle avoidance buffered material handling mode. In the non-buffered material handling mode, the material handling control system maximizes the damping of the obstacle avoidance buffer device. In the obstacle avoidance buffered material handling mode, the damping of the obstacle avoidance buffer device is reduced compared to the non-buffered material handling mode.

[0008] The material handling machine according to the second aspect of the present invention can meet different material handling requirements when the material layer is thick and when the material layer is thin.

[0009] The third-party material handling machine of the present invention is, in the second type of material handling machine, the control system includes an instruction input device, through which the operator can switch between a non-buffered material handling mode and an obstacle avoidance buffered material handling mode.

[0010] The third-party material handling machine according to the present invention allows operators to conveniently select different material handling modes according to the situation.

[0011] The fourth embodiment of the material handling machine of the present invention is as follows: In the third-generation material handling machine, when the operator can activate the unbuffered material handling mode or the obstacle avoidance buffered material handling mode through the command input device, the control system causes the hopper to change from an open state to a closed state. According to the fourth embodiment of the present invention, the material handling machine can complete the mode switching and material handling operation in a single operation.

[0012] The fifth aspect of the material gripper of the present invention is as follows: In the second aspect of the material gripper, in the unbuffered material gripping mode, the material gripping control system detects the upward force acting on the bottom of the hopper. When the magnitude of this force exceeds a certain threshold, the material gripping control system causes the hopper drive holding mechanism to drive the hopper to move upward. The fifth aspect of the material gripper according to the present invention can more reliably prevent the hopper from tearing the bottom plate.

[0013] The sixth embodiment of the material handling machine of the present invention, in which the material handling control system detects whether the hopper is fully closed, and provides a prompt to the operator via an information output device when the hopper is detected to be fully closed, is an improvement over the first to fifth embodiments of the material handling machine. The sixth embodiment of the material handling machine of the present invention can prevent material from falling due to the operator transferring material when the hopper is not fully closed.

[0014] The seventh embodiment of the material gripper of the present invention is as follows: In the sixth embodiment, the hopper has a hopper cylinder connected to two or more hopper segments respectively, and the material gripping control system detects whether the hopper is fully closed by signal feedback from the limit switch at the end of the hopper cylinder. The seventh embodiment of the material gripper of the present invention can reliably detect whether the hopper is fully closed.

[0015] The eighth embodiment of the material grabber of the present invention, in which the bucket drive and holding mechanism has a boom and a hydraulic circuit including a boom cylinder, is provided, wherein one end of the boom is hinged to the top of the bucket, and one end of the boom cylinder is connected to the boom to support it. The material grabbing control system controls the hydraulic circuit to make the boom cylinder function as the obstacle avoidance buffer device. The eighth embodiment of the material grabber of the present invention utilizes the boom cylinder as an obstacle avoidance buffer device, resulting in a simple and reliable structure.

[0016] The ninth embodiment of the material grabber of the present invention, in the material grabber of the eighth embodiment, includes a boom cylinder pressure sensor for detecting the pressure of the boom cylinder, and a hydraulic circuit with a proportional relief valve and an accumulator. The accumulator is connected to one of the large or small chambers of the boom cylinder. When switching to the obstacle avoidance and buffering material grabbing mode, the material grabbing control system controls the proportional relief valve to make the pressure of the accumulator equal to the weight of the boom, and connects the other of the large or small chambers to the oil tank of the hydraulic circuit. The material grabber of the ninth embodiment of the present invention utilizes a hydraulic circuit to prevent bottom biting, and has a simple and reliable structure.

[0017] The tenth embodiment of the material grabber of the present invention, in the material grabber of the eighth embodiment, further includes a boom in the bucket drive and holding mechanism, and the hydraulic circuit further includes a boom cylinder. One end of the boom is hinged to the other end of the stick, and one end of the boom cylinder is connected to the boom and can drive the boom to move by extension and retraction. The material grabbing control system controls the hydraulic circuit, causing the boom cylinder to function as the obstacle avoidance and buffer device. The material grabber of the tenth embodiment of the present invention utilizes a boom cylinder as an obstacle avoidance and buffer device, resulting in a simple and reliable structure.

[0018] The eleventh embodiment of the material grabber of the present invention, in the tenth embodiment, includes a material grabbing control system with a boom cylinder pressure sensor for detecting the pressure of the boom cylinder. The hydraulic circuit has a proportional relief valve and an accumulator. The accumulator is connected to one of the large or small chambers of the boom cylinder. When switching to the obstacle avoidance and buffering material grabbing mode, the material grabbing control system controls the proportional relief valve to make the pressure of the accumulator equal to the weight of the boom, and connects the other of the large or small chambers to the oil tank of the hydraulic circuit. The material grabber of the eleventh embodiment of the present invention utilizes a hydraulic circuit to prevent bottom-biting, and has a simple and reliable structure. Attached Figure Description

[0019] Figure 1 This is a front view showing the structure of the material handling machine of the present invention.

[0020] Figure 2 is a drawing showing the structure of the hopper of the material handling machine of the present invention. Figure 2A This is an attached diagram showing the closed state of the hopper. Figure 2B This is an attached diagram showing the state of the hopper when it is operating near the bottom.

[0021] Figure 3 This is a drawing showing the structure of the hydraulic circuit of the material handling machine of the present invention.

[0022] Explanation of reference numerals in the attached figures

[0023] 1. Main unit, 2. Boom cylinder, 3. Boom, 4. Stick cylinder, 5. Stick, 6. Bucket, 7. Left bucket flap, 8. Left bucket cylinder, 9. Right bucket cylinder, 10. Right bucket flap, 11. Material, 12. Base plate, 13. Proportional relief valve, 14. Accumulator, 15. Switching valve, 16. Piping, 17. Explosion-proof valve, 18. Switching valve, 19. Switching valve, 20. Shuttle valve, 21. Pilot control valve, 22. Main pump, 23. Pilot pump, 100. Grab Implementation

[0024] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. It should be noted that in all the drawings, the same reference numerals denote the same elements. Furthermore, the drawings are schematic diagrams illustrating the general structure of the material handling machine involved in this disclosure, and the material handling machine involved in this disclosure is not limited to the structure shown in the drawings. The terminology used in the specification is only used to describe specific embodiments and is not intended to limit the present disclosure. All terms used in the specification, unless otherwise defined, have the meaning commonly understood by those skilled in the art. For the sake of brevity and clarity, well-known functions or structures may not be described in detail. In the description of the present invention, the terms "upper," "lower," "inner," "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship conventionally set when the product of the invention is used. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0025] [Implementation Method 1]

[0026] like Figure 1 As shown, a material handling machine 100 according to one embodiment of the present invention includes a main unit 1, a boom cylinder 2, a boom 3, a stick cylinder 4, a stick 5, and a bucket 6. The main unit 1 is the part that provides power to the material handling machine 100 and performs operation control, including a cab, an equipment compartment, and a track frame. The boom cylinder 2, boom 3, stick cylinder 4, and stick 5 constitute a bucket drive and holding mechanism, wherein one end of the boom 3 is hinged to the turntable of the track frame, and the other end is hinged to one end of the stick 5. The boom cylinder 2 is installed between the boom 3 and the turntable, and the other end of the stick 5 is hinged to the top of the bucket 6. The stick cylinder 4 is installed between the stick 5 and the boom 3. The boom cylinder 2 drives the boom 3 to rise and fall by extending and retracting, and the stick cylinder 4 drives the stick 5 to rise and fall by extending and retracting.

[0027] like Figure 2A and Figure 2BAs shown, the hopper 6 is a shell hopper composed of two hopper petals, having a left hopper petal 7, a left hopper petal cylinder 8, a right hopper petal cylinder 9, and a right hopper petal 10. When grabbing material 11 on the bottom plate 12 of a vehicle such as a truck, the left hopper petal 7 and the right hopper petal 10 are driven to move by the left hopper petal cylinder 8 and the right hopper petal cylinder 9, so that the left hopper petal 7 and the right hopper petal 10 change from the open state to the closed state, thus completing the material grabbing.

[0028] Figure 3 This is a diagram illustrating the hydraulic circuit of the material handling machine 100 according to this embodiment. Figure 3 As shown, the hydraulic circuit includes a proportional relief valve 13, an accumulator 14, a switching valve 15, a pipeline 16, an explosion-proof valve 17, a switching valve 18, a switching valve 19, a shuttle valve 20, a pilot control valve 21, a main pump 22, and a pilot pump 23.

[0029] The material handling machine 100 has a material handling control system, which consists of sensors including a cylinder pressure sensor and a cylinder end-stroke switch, a command input device for the operator to input commands, a controller, and an information output device for outputting prompt information. In this embodiment, the command input device includes a joystick and a material handling mode switching button mounted on the joystick. However, the material handling mode switching button may not be mounted on the joystick; it can be located in a position easily accessible to the operator. Alternatively, a switch or a touchscreen can be used instead of the material handling mode switching button. Furthermore, in this embodiment, a display screen is provided as the information output device; however, a speaker can also be used, as long as the operator can receive information.

[0030] Next, the working process of the material gripper in this embodiment during material gripping will be described.

[0031] First, the material handling action when the material layer is relatively thick will be explained.

[0032] like Figure 2A As shown, when the material layer is thick, hopper 6 will not grip the bottom plate 12. The operator places hopper 600 above the material 11 and activates the unbuffered gripping mode via the gripping mode switch button. In unbuffered gripping mode, the controller energizes the switching valve 19, which in turn controls the left and right hopper cylinders 8 and 9 to extend until hopper 6 closes via shuttle valve 20. When the piston rods of the left and right hopper cylinders 8 and 9 are fully extended, the limit switch at the end of the cylinder sends a signal to the controller, which stops the hopper closing operation and notifies the operator that the hopper is "fully closed" via the display screen. At this point, the operator can perform lifting operations and transfer the gripped material. If the hopper fails to close completely due to an abnormal situation, the limit switch at the end of the cylinder will not send a "fully closed" signal. In this case, even if the operator wants to transfer the material, the controller will not perform the operation.

[0033] Next, we will explain the material handling action when the material layer is relatively thin.

[0034] When the material layer is thin, the hopper 6 may scrape the bottom plate 12 when grabbing the material 11. In this case, after placing the hopper 6 above the material 11, the operator activates the obstacle avoidance buffer grabbing mode via the grabbing mode switching button. In this mode, the controller charges the accumulator 14 with liquid through the switching valve 15 and collects the pressure of the large chamber of the boom cylinder 2 when the boom 3 is stationary through the cylinder pressure sensor. The controller controls the proportional relief valve 13. At this time, the pressure of the accumulator 14 just overcomes the weight of the boom 3. Then, the proportional relief valve 13 and the switching valve 18 are energized simultaneously, connecting the small chamber of the boom cylinder 2 to the oil tank. The weight of the boom 3 is overcome by the pressure of the accumulator 14. When the hopper closes and a "bottom-biting" phenomenon occurs, such as... Figure 2B As shown, the hopper 6 is subjected to an upward force F, which acts on the boom cylinder 2 through the boom 5 and boom 3. At this time, the piston rod of the boom cylinder 2 extends, and the boom cylinder 2 functions as an obstacle avoidance buffer device. The boom 3 rises upward, thereby preventing the hopper 6 from damaging the base plate 12 of the carrier. As the boom 3 rises, the hopper 6 obtains the space required to close and continues to close, thereby grabbing the material. The boom 3 will continue to rise until the hopper 6 is completely closed. When the hopper 6 is completely closed, the controller will display a "fully closed" prompt message on the display screen based on the signal feedback from the limit switches at the end of the left and right bucket cylinders 8 and 9. At this time, the operator can carry out the lifting operation and transfer the grabbed material.

[0035] [Implementation Plan 2]

[0036] In Embodiment 1, the "bottom-biting" phenomenon is eliminated by raising the boom 3. Unlike Embodiment 1, in Embodiment 2, the "bottom-biting" phenomenon is eliminated by raising the stick 5. Embodiment 2 of the present invention will be described below. When the material layer is thick, Embodiment 2 also employs the same unbuffered material-grabbing mode as Embodiment 1. Therefore, the following description mainly focuses on the material-grabbing operation when the material layer is thin.

[0037] When the material layer is thin, after placing the hopper 6 above the material 11, the operator activates the obstacle avoidance and buffer grabbing mode via the grabbing mode switch button. In this mode, the controller charges the accumulator 14 with liquid through the switching valve 15 and collects the pressure of the large chamber of the boom cylinder 4 when the boom 5 is stationary via the cylinder pressure sensor. The controller then controls the proportional relief valve 13. At this point, the pressure of the accumulator 14 just overcomes the weight of the boom 5. Then, the proportional relief valve 13 and the switching valve 18 are simultaneously energized, connecting the small chamber of the boom cylinder 4 to the oil tank. The weight of the boom 5 is then overcome by the pressure of the accumulator 14. When the hopper closes and a "bottom-biting" phenomenon occurs, such as... Figure 2B As shown, the hopper 6 is subjected to an upward force F, which is transmitted to the boom cylinder 4 through the boom 5. At this time, the piston rod of the boom cylinder 4 extends, and the boom cylinder 4 functions as an obstacle avoidance buffer device. The boom 5 rises upward, thereby preventing the hopper 6 from damaging the base plate 12 of the carrier. As the boom 5 rises, the hopper 6 obtains the space required to close and will continue to close to grab the material. The boom 5 will continue to rise until the hopper 6 is completely closed. When the hopper 6 is completely closed, the controller will display a "fully closed" prompt message on the display screen based on the signal feedback from the limit switches at the end of the left and right boom cylinders 8 and 9. At this time, the operator can perform the lifting operation and transfer the grabbed material.

[0038] [Implementation Method 3]

[0039] The above describes Embodiment 1 and Embodiment 2 of the present invention. In Embodiment 1 and Embodiment 2, the boom 3 or stick 5 is raised by the upward force F acting on the hopper 6 during "bottom biting". In this Embodiment 3, the material grabbing control system also has a hopper pressure sensor that detects the pressure on the hopper. The controller determines whether "bottom biting" has occurred based on the detection result of the hopper pressure sensor. When "bottom biting" is determined to have occurred, the boom 3 or stick 5 is raised by the hydraulic cylinder. Embodiment 3 will be described below.

[0040] The material grabber 1 in Embodiment 3 of the present invention has a hopper pressure sensor. When the hopper 6 is closed, the hopper pressure sensor detects the upward force F on the bottom of the hopper 6 and feeds it back to the controller. When the magnitude of the force F exceeds a certain threshold, the controller determines that "bottom biting" has occurred. When "bottom biting" is determined to have occurred, the controller controls the boom cylinder 4 to drive the boom 5 to rise, or drives the boom 3 to rise through the boom cylinder 2, thereby causing the hopper 6 to move upward while closing to grab the material. When the hopper 6 is fully closed, the controller will display a "fully closed" prompt message on the display screen based on the signal feedback from the limit switches at the end of the left and right hopper cylinders 8 and 9. At this time, the operator can perform lifting operations and transfer the grabbed material.

[0041] [Other variations]

[0042] The embodiments 1-3 of the present invention have been described above. However, the present invention can be presented in many different ways and is not limited to the embodiments described above.

[0043] For example, in embodiments 1-3, the grabber has a two-section boom structure consisting of a boom and a lifting arm; however, it can also be a single-section boom structure or a multi-section boom structure.

[0044] In embodiments 1-3, the hydraulic circuit includes a proportional relief valve 13, an accumulator 14, a switching valve 15, a pipeline 16, an explosion-proof valve 17, a switching valve 18, a switching valve 19, a shuttle valve 20, a pilot control valve 21, a main pump 22, and a pilot pump 23. However, the hydraulic circuit can also be configured in other ways as long as the corresponding functions can be achieved.

[0045] In embodiments 1-3, the hopper 6 is a shell hopper with two lobes; however, the hopper 6 may also be a multi-lobed grab bucket with more than two lobes.

[0046] In embodiments 1-3, the material grabber is a tracked material grabber. However, the material grabber may not be equipped with a tracked frame, but may be mounted on the hull of a ship or the body of a truck.

[0047] In embodiments 1-3, the stick cylinder or boom cylinder is used as an obstacle avoidance buffer device. However, other types of buffers can also be provided as obstacle avoidance buffer devices.

[0048] In embodiments 1-3, the material grabber is a tracked material grabber. However, the material grabber may not be equipped with a tracked frame, but may be mounted on the hull of a ship or the body of a truck.

[0049] The above embodiments are intended to make the disclosure of the present invention more complete and to fully illustrate the scope of protection of the present invention to those skilled in the art. Without changing the spirit of the present invention, the technical features of the embodiments described herein can be modified and combined in various ways to provide more additional embodiments.

Claims

1. A material handling machine, comprising: Host; A hopper having two or more hopper flaps, capable of digging and grabbing materials by changing from an open state to a closed state; A hopper drive and holding mechanism, one end of which is connected to the top of the hopper and the other end to the main unit, enables the hopper to move and hold it in a fixed position; and The material handling control system controls the movement of the hopper and the drive holding mechanism. Its features are, The hopper drive holding mechanism includes an obstacle avoidance and buffer device. This device is configured such that, when the bottom of the hopper is subjected to an upward force during hopper gripping material, the top of the hopper can move upward to provide cushioning. The material handling control system can control the damping magnitude of the obstacle avoidance buffer device. The material handling control system enables the hopper to switch between a non-buffered material handling mode and an obstacle avoidance buffered material handling mode. In the non-buffered material handling mode, the material handling control system maximizes the damping of the obstacle avoidance buffer device. In the obstacle avoidance buffered material handling mode, the damping of the obstacle avoidance buffer device is reduced compared to the non-buffered material handling mode.

2. The material handling machine according to claim 1, characterized in that, The control system has a command input device, through which the operator can switch between unbuffered material handling mode and obstacle avoidance buffered material handling mode.

3. The material handling machine according to claim 2, characterized in that, When the operator activates the unbuffered material grabbing mode or the obstacle avoidance buffered material grabbing mode through the command input device, the control system changes the hopper from the open state to the closed state.

4. The material handling machine according to claim 1, characterized in that, In the unbuffered material gripping mode, the material gripping control system detects the upward force on the bottom of the hopper. When the magnitude of the force exceeds a certain threshold, the material gripping control system causes the hopper drive holding mechanism to drive the hopper to move upward.

5. The material handling machine according to any one of claims 1-4, characterized in that, The material handling control system detects whether the hopper is fully closed. If the hopper is fully closed, the system prompts the operator through an information output device.

6. The material handling machine according to claim 5, characterized in that, The hopper has a hopper cylinder that is connected to two or more hopper segments respectively. The material gripping control system detects whether the hopper is fully closed by signal feedback from the limit switch at the end of the hopper cylinder.

7. The material handling machine according to any one of claims 1-4, characterized in that, The bucket drive and holding mechanism has a stick and a hydraulic circuit including a stick cylinder. One end of the stick is hinged to the top of the bucket, and one end of the stick cylinder is connected to the stick to support it. The material gripping control system controls the hydraulic circuit so that the stick cylinder functions as the obstacle avoidance buffer device.

8. The material handling machine according to claim 7, characterized in that, The material handling control system has a boom cylinder pressure sensor for detecting the pressure of the boom cylinder. The hydraulic circuit has a proportional relief valve and an accumulator. The accumulator is connected to one of the large or small chambers of the boom cylinder. When switching to the obstacle avoidance and buffer material handling mode, the material handling control system controls the proportional relief valve to make the pressure of the accumulator equal to the weight of the boom to support the boom, and connects the other of the large or small chambers to the oil tank of the hydraulic circuit.

9. The material handling machine according to claim 7, characterized in that, The bucket drive and holding mechanism also includes a boom and a boom cylinder. One end of the boom is hinged to the other end of the stick, and one end of the boom cylinder is connected to the boom to support it. The material handling control system controls the hydraulic circuit so that the boom cylinder also functions as the obstacle avoidance buffer device.

10. The material handling machine according to claim 9, characterized in that, The material handling control system has a boom cylinder pressure sensor for detecting the pressure of the boom cylinder. The hydraulic circuit has a proportional relief valve and an accumulator. The accumulator is connected to one of the large or small chambers of the boom cylinder. When switching to the obstacle avoidance and buffer material handling mode, the material handling control system controls the proportional relief valve to make the pressure of the accumulator equal to the weight of the boom to support the boom, and connects the other of the large or small chambers to the oil tank of the hydraulic circuit.

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