A legged robot

Abstract

This application discloses a legged robot for improving the stability of a legged robot performing a forward somersault. The legged robot provided in this application includes: at least one processor; and at least one storage medium storing instructions, which, when executed by the at least one processor, cause the legged robot to: in response to a forward somersault trigger instruction, execute a forward somersault sequence, the forward somersault sequence sequentially including a support and somersault phase, an aerial somersault phase, and a lower limb support phase; the support and somersault phase includes: controlling the head to move towards a contact surface, the lower limb tip of the first of the two lower limbs maintaining support contact with the contact surface, and the lower limb tip of the second of the two lower limbs swinging away from the contact surface relative to the hip; the aerial somersault phase includes: controlling the lower limb tip of the first lower limb to detach from the contact surface and swing away from the contact surface, and controlling the legged robot to perform an aerial somersault.

Description

Technical Field

[0001] This application relates to the field of robot control technology, and in particular to a legged robot. Background Technology

[0002] With the development of legged robot control technology, robots are now capable of performing various dynamic movements such as walking, running, jumping, and obstacle crossing. To improve the robot's mobility in complex scenarios, some research has begun to explore enabling robots to perform highly dynamic movements involving overall body rotation, such as a front flip. These types of movements typically require the robot to complete significant changes in body posture within a short period of time and maintain good posture stability upon landing.

[0003] In existing technologies, when robots perform a forward somersault, they typically rely on joint driving force, limb swing inertia, and takeoff speed to obtain the momentum needed for body rotation. For humans, the waist and spine can generate significant folding and unfolding amplitudes during movement, thus coordinating with lower limb extension and swinging to create a forward flipping motion. However, for legged robots, their torsos typically employ a rigid structure, unable to fold and generate force during a flip like the human spine and abdomen. Furthermore, factors such as joint output capacity, body size, and mass limit the robot's available airtime and angular momentum. If the robot fails to complete sufficient posture adjustments during the air phase, it may fall upon landing. Summary of the Invention

[0004] This application provides a legged robot for improving the stability of a legged robot performing a forward somersault.

[0005] This application provides a legged robot, comprising:

[0006] The torso, including the hips; The head, two upper limbs and their corresponding ends, and two lower limbs and their corresponding ends are respectively connected to the torso, wherein the two lower limbs are respectively connected to the hip. At least one processor; And, at least one storage medium storing instructions that, when executed by the at least one processor, cause the legged robot to: In response to a forward somersault trigger command, a forward somersault sequence is executed, which includes a support and flip phase, an airborne flip phase, and a lower limb support phase in sequence. The support and flipping phase includes: controlling the head to move towards the contact surface, the lower limb end of the first lower limb of the two lower limbs maintaining support contact with the contact surface, and the lower limb end of the second lower limb of the two lower limbs swinging away from the contact surface relative to the hip. The aerial flipping phase includes: controlling the lower limb end of the first lower limb to detach from the contact surface and swing away from the contact surface, and controlling the legged robot to flip in the air; The lower limb support phase includes: controlling at least one of the two lower limbs to establish support contact with the contact surface; The moment when the distal end of the first lower limb detaches from the contact surface is recorded as the first moment, and the moment when at least one of the two lower limbs establishes supporting contact with the contact surface is recorded as the second moment. The airborne flipping phase includes the time period from the first moment to the second moment. At the first moment, the first distance between the head and the contact surface is less than the second distance between the hip and the contact surface. The angle of the torso flipping at the second moment is greater than 200° compared to the position at the first moment. The knee joint angle of the first lower limb at the first moment is greater than the knee joint angle of the first lower limb at the second moment. The knee joint angle of the second lower limb at the first moment is greater than the knee joint angle of the second lower limb at the second moment. The distance between the head and the contact surface at the first moment is less than the distance between the head and the contact surface at the second moment. At the first moment, the knee joint angle of the first lower limb is between 135° and 180°, and the knee joint angle of the second lower limb is between 135° and 180°.

[0007] As can be seen from the above technical solutions, this application has the following advantages: When the first lower limb leaves the contact surface, the head is already relatively close to the contact surface; specifically, the distance between the head and the contact surface is less than the distance between the hips and the contact surface. Therefore, the legged robot has already rotated forward at a significant angle before entering the aerial somersault phase, which helps reduce the required rotation angle after takeoff. This allows the robot to complete posture adjustments based on relatively limited takeoff time and rotational angular momentum during the aerial somersault phase, performing a forward somersault and landing smoothly. During the aerial somersault phase, the distal end of the first lower limb detaches from the contact surface and swings away from it, initiating the aerial somersault. The torso's posture at the second moment is rotated by more than 200° compared to the first moment, allowing the legged robot to complete posture adjustments before landing, thus ensuring a smooth landing. Simultaneously, the knee angles of both the first and second lower limbs are between 135° and 180° at the first moment, and the knee angles of both lower limbs at the second moment are smaller than those at the first moment. This allows the two lower limbs to maintain a relatively extended state when entering the airborne flip phase to coordinate with lifting off the ground and flipping. As they approach re-establish support with the contact surface, the knees flex to retract the lower limbs into a support-friendly posture. Through this coordinated action, the likelihood of the legged robot falling due to insufficient flipping during the airborne phase and resulting in a deviated landing posture can be reduced, thus improving the stability of the legged robot performing a forward somersault. Attached Figure Description

[0008] To more clearly illustrate the technical solutions in this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0009] Figure 1 A schematic diagram of the overall structure of a humanoid robot provided as an example of a legged robot for this application; Figure 2 A schematic diagram of the stages of an embodiment of the forward somersault sequence of the legged robot provided in this application; Figure 3 A schematic diagram of the posture of the legged robot provided in this application at the first moment of approach; Figure 4 A schematic diagram of a legged robot provided in this application in a posture approaching the second moment; Figure 5 A planar schematic diagram of the legged robot provided in this application forming a supporting polygon during the force unloading and support phase; Figure 6 A schematic diagram of a posture of the legged robot provided in this application during the airborne flipping phase 202. Detailed Implementation

[0010] This application provides a legged robot for improving the stability of a legged robot performing a forward somersault.

[0011] The legged robot provided in this application includes a torso, a head, two upper limbs, two lower limbs, at least one processor, and at least one storage medium. In some embodiments, the legged robot can be a humanoid robot, which is a specific implementation of the legged robot. For ease of description, the following description mainly uses a humanoid robot as an example. Please refer to... Figure 1 The torso 3 includes an upper torso 31 and a hip 32, which are rotatably connected. The head 4 is connected to the upper torso 31 via the neck. Two upper limbs 1 are connected to the upper torso 31, and two lower limbs 2 are connected to the hip 32. For ease of description, the two upper limbs can be referred to as the first upper limb and the second upper limb, and the two lower limbs can be referred to as the first lower limb and the second lower limb. It should be noted that the terms "first upper limb," "second upper limb," "first lower limb," and "second lower limb" are only used to distinguish different limb structures and do not constitute a limitation on specific left and right positions.

[0012] Each upper limb includes an end effector for establishing supporting contact with a contact surface. Each upper limb may also include an upper arm and a forearm, with the upper arm connected to the upper torso and the forearm connected to the end effector. The upper arm and forearm are connected via an elbow joint. Each lower limb includes an end effector for establishing supporting contact with a contact surface. Each lower limb may also include a thigh and a lower leg, with the thigh connected to the hip and the lower leg connected to the end effector. The thigh and lower leg are connected via a knee joint, allowing the lower limb to adjust its posture between different support states. It should be noted that the contact surface can be the ground, a platform surface, or other load-bearing surface that can provide support for the legged robot; the end effector of the upper limb can be a hand, a robotic hand, or other end structure capable of establishing supporting contact with the contact surface; the end effector of the lower limb can be a foot, a foot actuator, or other end structure capable of establishing supporting contact with the contact surface. This application does not limit the specific end effector.

[0013] It should be noted that, in the embodiments of this application, "contact" refers to the state in which the limbs, torso, or other body parts of the legged robot are in physical contact with the contact surface; "supporting contact" refers to the state in which the above-mentioned contact provides support to the legged robot, enabling the corresponding part to bear part of the load from the body. Specifically, when a part of the legged robot only makes slight contact, rubbing, or non-load-bearing contact with the contact surface, that part can be understood as having ordinary contact with the contact surface; when there is a contact between that part and the contact surface that can bear the weight of the body or participate in posture stability, that part can be understood as establishing supporting contact with the contact surface. Whether supporting contact is established can be determined by force sensors, tactile sensors, joint torque, motor current, contact pressure distribution, or posture changes.

[0014] At least one of the aforementioned storage media stores instructions that, when executed by at least one processor, control the coordinated operation of the various drive components of the legged robot to enable the legged robot to execute a forward somersault sequence in response to a forward somersault trigger command. The forward somersault trigger command can be input by a user or automatically generated by the legged robot based on preset tasks, environmental conditions, or motion planning results.

[0015] Please see Figure 2 , Figure 2 This is a schematic diagram of the stages of a forward somersault sequence for a legged robot. In this embodiment, the forward somersault sequence includes at least the following sequentially executed stages: a support and flip stage 201, a mid-air flip stage 202, and a lower limb support stage 203. Each stage is described in detail below.

[0016] In this embodiment, the support-flipping phase 201 performed by the processor-controlled legged robot includes: Control the head to move closer to the contact surface, keep the end of the first lower limb in supporting contact with the contact surface, and swing the end of the second lower limb away from the contact surface relative to the hip.

[0017] In the support-flipping phase 201, the distal end of the first lower limb, as the main support component, maintains support contact with the contact surface. The processor controls the joint movement between the torso and the first lower limb, causing the torso to rotate in a first direction and the head to gradually approach the contact surface as the torso rotates. The first direction can be understood as the direction in which the legged robot flips forward along its facing side. During the torso's rotation in the first direction, the processor also controls the distal end of the second lower limb to swing relative to the hip in a second direction, which is opposite to the first direction. That is, when the torso tilts forward and flips towards the facing side of the legged robot, the distal end of the second lower limb swings backward away from the contact surface, causing the second lower limb to swing in the opposite direction relative to the torso. Through this reverse swing, on the one hand, the distal end of the second lower limb can gradually move away from the contact surface, preventing the second lower limb from touching the ground prematurely during the support-flipping phase and hindering the body's flipping; on the other hand, the swinging inertia of the second lower limb can participate in driving the torso to rotate in the first direction, thereby enhancing the forward flipping tendency of the legged robot before entering the airborne flipping phase. The first direction and the second direction can be determined as either clockwise or counterclockwise depending on the viewing side of the legged robot. For example, when viewed from one side of the legged robot, rotation of the torso in the first direction can be displayed as clockwise rotation, and the swinging of the lower limb tip in the second direction can be displayed as clockwise swinging; when viewed from the other side of the legged robot, rotation of the torso in the first direction can be displayed as counterclockwise rotation, and the swinging of the lower limb tip in the second direction can be displayed as counterclockwise swinging.

[0018] The effect of the support flipping phase 201 is that the lower limb of the first lower limb maintains support, the torso tilts forward toward the side facing the legged robot, and the lower limb of the second lower limb swings away from the contact surface relative to the hip, so that the legged robot forms a forward flipping posture and forward flipping momentum before entering the air flipping phase.

[0019] In this embodiment, the airborne flipping phase 202, which is controlled by the processor to be performed by the legged robot, includes: Control the lower limb of the first lower limb to detach from the contact surface and swing away from the contact surface, and control the legged robot to flip in the air.

[0020] In the support and flip phase 201, the distal end of the first lower limb maintains support contact with the contact surface, the torso of the legged robot has rotated in the first direction, the head gradually approaches the contact surface, and the distal end of the second lower limb swings away from the contact surface relative to the hip. When the legged robot meets the conditions to enter the aerial flip phase 202, the processor controls the distal end of the first lower limb to detach from the contact surface and swing away from the contact surface, causing the first lower limb to flip forward with the legged robot as a whole, and controls the legged robot to continue flipping in the air to complete the forward somersault.

[0021] In some implementations, the disengagement of the distal end of the first lower limb from the contact surface can be achieved based on the forward roll momentum already generated by the legged robot during the support and rollover phase 201. That is, when the torso rotates to a preset posture in the first direction, and the swinging of the second lower limb enables the legged robot to obtain the angular momentum required for take-off and rollover, as the center of mass and torso of the legged robot continue to move in the forward rollover direction, the distal end of the first lower limb can transition from a support contact state to a state of disengagement from the contact surface.

[0022] In other embodiments, the support flipping phase 201 further includes: after the first distance is less than the second distance, controlling the lower limb end of the first lower limb to output a thrust towards the contact surface, and the reaction force of the contact surface acting on the lower limb end of the first lower limb is used to drive the legged robot into the air flipping phase.

[0023] The detachment of the distal end of the first lower limb from the contact surface can also be achieved by the first lower limb outputting a thrust towards the contact surface. The first distance can be the minimum distance between the head and the contact surface along the direction of gravity, and the second distance can be the minimum distance between the hip and the contact surface along the direction of gravity. Specifically, the processor can control the distal end of the first lower limb to output a thrust towards the contact surface after the first distance between the head and the contact surface is less than the second distance between the hip and the contact surface. The reaction force generated by the contact surface on the distal end of the first lower limb can drive the center of mass of the legged robot away from the contact surface, and enable the legged robot to enter the airborne flipping stage 202 based on the forward tilting and flipping posture it has already formed.

[0024] The lower limb support phase 203, which is controlled by the processor to perform on the legged robot, includes: Control at least one of the two lower limbs to establish supporting contact with the contact surface.

[0025] The moment when the distal end of the first lower limb leaves the contact surface is recorded as the first moment, and the moment when at least one of the two lower limbs establishes supporting contact with the contact surface is recorded as the second moment. The airborne flipping phase includes the time period from the first moment to the second moment. At the first moment, the first distance between the head and the contact surface is less than the second distance between the hip and the contact surface. The angle of the torso flipping at the second moment is greater than 200° compared to the position at the first moment. The knee joint angle of the first lower limb at the first moment is greater than the knee joint angle of the first lower limb at the second moment. The knee joint angle of the second lower limb at the first moment is greater than the knee joint angle of the second lower limb at the second moment. The distance between the head and the contact surface at the first moment is less than the distance between the head and the contact surface at the second moment. At the first moment, the knee joint angle of the first lower limb is between 135° and 180°, and the knee joint angle of the second lower limb is between 135° and 180°.

[0026] After the legged robot completes its aerial flip, its torso is in a near-upright position. It can establish a supporting contact with the contact surface through the lower limb ends of the first and second lower limbs, or through the lower limb ends of both lower limbs, thereby absorbing the landing load generated when the legged robot returns to the contact surface from the aerial state.

[0027] For ease of description, the moment when the distal end of the first lower limb detaches from the contact surface is designated as the first moment, and the moment when at least one of the two lower limbs establishes supporting contact with the contact surface is designated as the second moment. The aerial flipping phase 202 includes the time period from the first moment to the second moment. The first moment can be understood as the initial boundary of the legged robot entering the aerial flipping phase 202 from the supporting flipping phase 201, and the second moment can be understood as the initial boundary of the legged robot entering the lower limb supporting phase 203 from the aerial flipping phase 202.

[0028] At the first instant, the first distance between the head and the contact surface is less than the second distance between the hip and the contact surface. The first distance can be the minimum distance between the head and the contact surface along the direction of gravity, and the second distance can be the minimum distance between the hip and the contact surface along the direction of gravity. Thus, when the lower limb of the first lower limb leaves the contact surface, the legged robot has already flipped forward at a large angle, forming a forward-leaning flip posture with the head lower than the hip before entering the airborne flip phase 202. By pre-forming the above-mentioned forward-leaning flip posture before leaving the ground, the flip angle required by the legged robot in the airborne flip phase 202 can be reduced, lowering the requirements for airborne time and instantaneous joint output capability. It should be noted that in some embodiments, the head of the legged robot can be connected to the upper torso through the neck, and the neck can serve as an intermediate connecting structure between the head and the upper torso. That is, when describing the first distance between the head and the contact surface, the movement of the head towards the contact surface, and the posture changes of the head during the forward somersault, the head refers to the head structure on the side of the neck away from the upper torso, i.e., the head itself does not include the neck.

[0029] At the second moment, the torso's pose has rotated by more than 200° compared to the pose at the first moment. Therefore, before re-establishing support contact with the contact surface, the legged robot positions its torso in a suitable landing posture. The distance between the head and the contact surface at the first moment is less than the distance at the second moment, indicating that the legged robot was in a forward-leaning state with its head close to the contact surface at the first moment, but had completed its rotation and gradually moved its head away from the contact surface at the second moment, thus reducing the risk of collision between the head or the front of the torso and the contact surface during landing.

[0030] At the first moment, the knee joint angle of the first lower limb is between 135° and 180°, and the knee joint angle of the second lower limb is also between 135° and 180°. The knee joint angle is the internal angle formed between the thigh and lower leg of the corresponding lower limb. For example, at the first moment, the knee joint angle of the first lower limb can be 145°, 150°, 160°, 170°, or 180°, and the knee joint angle of the second lower limb can be 140°, 155°, 165°, 175°, or 180°. These angle ranges indicate that the two lower limbs are in a relatively extended state at the first moment. For the first lower limb, controlling the knee joint angle to between 135° and 180° at the first moment allows the first lower limb to maintain a larger effective support length before disengaging from contact. This facilitates the output of thrust to the contact surface through the lower limb's distal end, and utilizes the reaction force from the contact surface acting on the lower limb's distal end to drive the body into the takeoff and flipping phase. For the second lower limb, controlling the knee joint angle between 135° and 180° at the first moment can enable the second lower limb to form a larger swing radius during the support and roll phase, allowing the lower limb end to participate more fully in forming forward roll momentum when swinging away from the contact surface relative to the hip.

[0031] During the aerial flip phase 202, the processor controls the first and second lower limbs to increase their flexion, making the knee angle of the first lower limb at the first moment greater than that at the second moment, and the knee angle of the second lower limb at the first moment greater than that at the second moment. Thus, as the legged robot flips from the first moment to the second moment, the two lower limbs gradually switch from a relatively extended state to a flexed state, pre-forming a bending angle between the thigh and lower leg, and bringing the lower limb ends back to a position closer to the landing support posture relative to the hip. By reducing the knee angle of the two lower limbs during the aerial flip, the lower limb ends can complete the pre-adjustment of the landing posture before the second moment, making it easier for the foot area to approach the contact surface in a preset posture, thereby reducing the possibility of the toes or heels impacting the contact surface first. Simultaneously, since the two lower limbs have already formed a flexed posture before the second moment, they can continue to absorb the landing load through the flexion and extension changes of the knee and ankle joints during the lower limb support phase 203, avoiding the lower limbs directly bearing the impact in a near-extended state.

[0032] Please see Figure 3 and Figure 4 , Figure 3 This is a schematic diagram of a legged robot's posture during the first moment of approach. Figure 4 This is a schematic diagram of a legged robot's posture near the second moment. Figure 3As shown, near the first moment, the distal end of the first lower limb is in a state of about to detach from or has already detached from the contact surface. The head is closer to the contact surface than the hip. The minimum distance between the head and the contact surface along the direction of gravity is the first distance d1, and the minimum distance between the hip and the contact surface along the direction of gravity is the second distance d2, where d1 is less than d2. At this time, the torso has completed a forward roll at a certain angle along the first direction. Before entering the aerial roll phase 202, the legged robot forms a forward-tilting roll posture with the head lower than the hip. The distal end of the second lower limb swings away from the contact surface relative to the hip. Figure 4 As shown, near the second moment, the legged robot has completed the main flipping motion in the aerial flipping phase 202, and at least one of its two lower limbs is about to establish supporting contact with the contact surface. Relative to... Figure 3 The first moment shown, Figure 4 The mid-torso has rotated more than 200°, increasing the distance between the head and the contact surface. The knee angle between the two lower limbs has decreased compared to the initial moment, causing the two lower limbs to switch from a relatively extended state to a flexed state. It should be noted that... Figure 3 and Figure 4 This is only used to illustrate the relative posture of the underfoot robot at the first and second moments, and does not constitute a limitation on the specific forward somersault action process.

[0033] In this embodiment, when the first lower limb leaves the contact surface, the head is already in a position relatively close to the contact surface; specifically, the distance between the head and the contact surface is less than the distance between the hip and the contact surface. Therefore, the legged robot has already flipped forward at a significant angle before entering the aerial somersault phase, which helps reduce the required flip angle after takeoff. This allows the robot to complete posture adjustment based on a relatively limited takeoff time and flip angular momentum during the aerial somersault phase, completing the forward somersault and landing smoothly. During the aerial somersault phase, the distal end of the first lower limb detaches from the contact surface and swings away from it, causing the legged robot to somersault. The torso's posture at the second moment is flipped by an angle greater than 200° compared to the posture at the first moment, allowing the legged robot to complete posture adjustment before landing, thus ensuring a smooth landing. Simultaneously, the knee angles of both the first and second lower limbs are between 135° and 180° at the first moment, and the knee angles of both lower limbs at the second moment are smaller than those at the first moment. This allows the two lower limbs to maintain a relatively extended state when entering the airborne flip phase to coordinate with lifting off the ground and flipping. As they approach re-establish support with the contact surface, the knees flex to retract the lower limbs into a support-friendly posture. Through this coordinated action, the likelihood of the legged robot falling due to insufficient flipping during the airborne phase and resulting in a deviated landing posture can be reduced, thus improving the stability of the legged robot performing a forward somersault.

[0034] In some embodiments, at a first moment, the ratio of the first distance to the second distance is 0.3 to 0.8.

[0035] In this embodiment, the first distance can be the minimum distance between the head and the contact surface along the direction of gravity, and the second distance can be the minimum distance between the hip and the contact surface along the direction of gravity. The ratio of the first distance to the second distance is used to represent the degree of forward tilt of the legged robot before entering the airborne flipping stage 202. The smaller the ratio, the closer the head is to the contact surface relative to the hip, and the more fully the legged robot has completed forward rotation before the end of the first lower limb leaves the contact surface. When the ratio of the first distance to the second distance is greater than 0.8, the distance between the head and the contact surface is close to or equal to the distance between the hip and the contact surface. The degree of forward tilt of the legged robot at the first moment is small. After entering the airborne flipping stage 202, it still needs to complete a large flipping angle within a limited airborne time, which increases the requirements for airborne time and flipping angular momentum. When the ratio of the first distance to the second distance is less than 0.3, the head is too close to the contact surface, and the risk of interference or collision between the head, upper limbs, or torso and the contact surface before leaving the ground increases. It may also compress the movement space for body posture adjustment. Therefore, by controlling the ratio of the first distance to the second distance at the first moment to be between 0.3 and 0.8, for example, 0.3, 0.4, 0.5, 0.6, 0.7 or 0.8, it is possible to ensure that the head is sufficiently close to the contact surface relative to the hips, while reserving the necessary motion space for the first lower limb to detach from the contact surface, the second lower limb to swing, and the torso to continue to rotate, so that the legged robot can smoothly transition from the support and rotation stage 201 to the airborne rotation stage 202.

[0036] In some embodiments, at the second moment, the knee joint angle of the first lower limb is 30° to 120°, and the knee joint angle of the second lower limb is 30° to 120°.

[0037] In this embodiment, the second moment is the starting moment when at least one of the two lower limbs establishes supporting contact with the contact surface. Therefore, the knee joint angle at the second moment can represent the lower limb flexion posture of the legged robot when it enters the lower limb support phase 203 from the air-flipping phase 202. By controlling the knee joint angle of the two lower limbs at the second moment, the lower limb end can complete the pre-adjustment of the landing posture before the second moment, making it easier for the foot area to approach the contact surface in a preset posture, thereby reducing the possibility of the toes or heels impacting the contact surface first. At the same time, since the two lower limbs have already formed a flexion posture before the second moment, they can continue to reduce the landing impact through the flexion and extension changes of the knee and ankle joints in the lower limb support phase 203, avoiding the lower limbs directly establishing supporting contact with the contact surface in a near-extended state.

[0038] When the knee angle of the corresponding lower limb is greater than 120° at the second moment, the lower limb is close to an extended state, and the distal end of the lower limb extends a large distance relative to the hip. While the legged robot still possesses forward flipping and descent speeds, the distal end of the lower limb is prone to prematurely contacting the contact surface before the robot's posture has fully adjusted to a landing support position. When the knee angle of the corresponding lower limb is less than 30° at the second moment, the lower limb is excessively flexed, and the distal end of the lower limb is overly retracted relative to the hip, resulting in a shorter overall support length. In this case, after the distal end of the lower limb establishes support contact with the contact surface, the knee angle may further decrease under the impact of the contact surface, thus approaching the mechanical limit position of the knee joint and increasing the possibility of knee joint injury. Furthermore, an excessively flexed lower limb usually requires extension or posture adjustment before the distal end can stably support the weight of the robot, which can easily affect the continuity of the transition from the aerial flipping phase 202 to the lower limb support phase 203.

[0039] Therefore, controlling the knee joint angle between the first and second lower limbs at the second moment to be between 30° and 120° allows the legged robot to achieve a moderate knee flexion state when entering the lower limb support phase. For example, at the second moment, the knee joint angle of the first lower limb can be 45°, 60°, 80°, 100°, or 115°, and the knee joint angle of the second lower limb can be 40°, 70°, 90°, 105°, or 120°. Within the above angle range, the two lower limbs can maintain sufficient support length, allowing the lower limb ends to reliably approach the contact surface, while also forming a flexion posture suitable for landing cushioning, enabling the legged robot to smoothly transition from the airborne flipping phase 202 to the lower limb support phase 203.

[0040] In some embodiments, at the second moment, the knee joint angle of the first lower limb is 60° to 120°, and the knee joint angle of the second lower limb is 60° to 120°. This angle range allows the lower limbs to retain a more reliable support length in the initial stage of landing and reduces the possibility of the knee joint further flexing to near the mechanical limit under the impact of the contact surface, thereby improving the stability and safety of the lower limb support phase 203.

[0041] In some embodiments, the lower limb support phase includes: controlling the lower limb tip of the first lower limb and the lower limb tip of the second lower limb to establish support contact with the contact surface respectively; wherein the time difference between the lower limb tip of the first lower limb and the lower limb tip of the second lower limb establishing support contact is 0s to 1s.

[0042] In this embodiment, a time difference of 0 seconds indicates that the distal ends of the first and second lower limbs simultaneously establish supporting contact with the contact surface; a time difference greater than 0 seconds indicates that the distal end of one lower limb establishes supporting contact with the contact surface first, followed by the distal end of the other lower limb. For example, the time difference between the distal ends of the first and second lower limbs establishing supporting contact can be 0 seconds, 0.1 seconds, 0.2 seconds, 0.3 seconds, 0.5 seconds, 0.8 seconds, or 1 second.

[0043] When the legged robot transitions from the airborne flipping phase 202 to the lower limb support phase 203, it still maintains its descent and forward flipping speeds. By controlling the distal ends of the two lower limbs to establish support contact with the contact surface within a time difference of 0 to 1 second, the landing load can be shared by both lower limbs in a shorter time, reducing the situation where a single lower limb independently bears the impact for a long period of time, thereby reducing the impact force on one side of the lower limb. By controlling this time difference to within 1 second, the lower limb that lands first can immediately participate in the support after absorbing the initial impact, thus expanding the lower limb support area and improving the posture stability of the lower limb support phase 203.

[0044] Based on the premise that the distal ends of the two lower limbs establish supporting contact with the contact surface within a preset time difference, in some embodiments, the landing order of the two lower limbs and the change in the contact area of ​​the lower limb that lands first during the subsequent support process can be further controlled. This allows the lower limb that lands first to receive and transfer part of the landing load, thereby providing a buffer condition for the other lower limb to subsequently establish supporting contact. A detailed explanation follows.

[0045] In some embodiments, during the lower limb support phase, controlling the lower limb ends of the first lower limb and the second lower limb to establish support contact with the contact surface includes: controlling the lower limb ends of the second lower limb to establish support contact with the contact surface before the lower limb ends of the first lower limb; and controlling the lower limb ends of the first lower limb to establish support contact with the contact surface after the lower limb ends of the second lower limb have established support contact with the contact surface.

[0046] In this embodiment, the second lower limb is the limb that swings away from the contact surface relative to the hip during the support-flipping phase 201. Since the second lower limb participates in forming a forward flipping posture during both the support-flipping phase 201 and the airborne flipping phase 202, and completes the posture flipping along with the entire legged robot during the airborne flipping phase 202, the distal end of the second lower limb can be adjusted to a position close to the contact surface as the legged robot approaches the second moment. Therefore, the processor can control the distal end of the second lower limb to first establish support contact with the contact surface, allowing the legged robot to transition from an airborne state to a single-leg support state, and adjust the initial landing posture through the support contact between the second lower limb and the contact surface. After the distal end of the second lower limb establishes support contact with the contact surface, the processor continues to control the distal end of the first lower limb to move towards the contact surface, and also establish support contact between the distal end of the first lower limb and the contact surface. After the first lower limb subsequently participates in the support, the legged robot transitions from a single-leg support state to a double-leg support state, the support area on the contact surface increases accordingly, and the support of the legged robot on the contact surface becomes more stable.

[0047] By establishing support contact sequentially in this embodiment, the legged robot can gradually establish a lower limb support relationship after completing the aerial flip, avoiding sudden changes in robot posture caused by the lower limb ends rigidly contacting the contact surface at the same time, and improving the support stability in the lower limb support stage 203.

[0048] In some embodiments, during the lower limb support phase, after the lower limb tip of the second lower limb establishes support contact with the contact surface, controlling the lower limb tip of the first lower limb to establish support contact with the contact surface includes: after the foot area of ​​the lower limb tip of the second lower limb establishes support contact with the contact surface, controlling the lower limb tip of the second lower limb to output a thrust towards the contact surface, and shifting the contact area between the lower limb tip of the second lower limb and the contact surface from the foot area to the toe area of ​​the lower limb tip of the second lower limb to buffer the impact force received by the knee joint of the first lower limb when establishing support contact with the contact surface; during the process from the lower limb tip of the second lower limb establishing support contact with the contact surface to the lower limb tip of the first lower limb establishing support contact with the contact surface, controlling the knee joint angle of the first lower limb to increase.

[0049] In this embodiment, when the distal end of the second lower limb first establishes supporting contact with the contact surface, the distal end of the second lower limb can first form contact with the contact surface through the foot area. Subsequently, the processor controls the distal end of the second lower limb to output a thrust towards the contact surface, causing the distal end of the second lower limb to produce a supporting action relative to the contact surface, transitioning from the foot area to the toe area. This supporting action can be understood as a pushing or rolling supporting action performed by the second lower limb in the initial stage of landing. Through the continuous transfer of the contact area, the supporting contact position between the distal end of the second lower limb and the contact surface gradually shifts from the foot area to the toe area. Through this contact transfer, the second lower limb can form supporting contact with the contact surface before the first lower limb lands, and use the reaction force provided by the contact surface to assist the legged robot in continuing to complete the landing posture adjustment. As a result, when the distal end of the first lower limb subsequently establishes supporting contact with the contact surface, the relative impact between the distal end of the first lower limb and the contact surface is reduced, and the impact force on the knee joint of the first lower limb at the moment of contact is correspondingly reduced, which helps to reduce the possibility of damage to the knee joint of the first lower limb.

[0050] During the process from the second lower limb establishing supporting contact with the contact surface to the first lower limb establishing supporting contact with the contact surface, the processor also controls the increase of the knee joint angle of the first lower limb. Since the first lower limb has already flexed during the airborne flip phase 202 to prepare for landing, if the first lower limb remains excessively flexed before landing, the extension distance of the lower limb end relative to the hip will be short, easily affecting the timely arrival of the first lower limb end at the contact surface and the formation of stable support. Therefore, appropriately increasing the knee joint angle of the first lower limb before landing allows the lower limb end to extend towards the contact surface and aligns the first lower limb in a posture suitable for establishing supporting contact. Simultaneously, after the knee joint angle of the first lower limb is increased before landing, the first lower limb can still cushion the impact in the subsequent phase after establishing supporting contact with the contact surface through further knee flexion. In other words, the first lower limb prepares for contact with the ground by increasing the knee joint angle before landing, and reduces the impact at the moment of contact by flexing the knee joint after landing, thereby reserving a landing buffer space for the knee joint of the first lower limb and reducing the impact on the knee joint of the first lower limb at the moment of contact.

[0051] Through the above control method, the second lower limb lands first, and then the contact area is transferred from the sole area to the toe area. Combined with the control of increasing the knee joint angle before the first lower limb lands, the legged robot can first establish support contact with the contact surface through the second lower limb and complete the posture adjustment, and then the first lower limb participates in the support, thus forming a double lower limb support state, thereby improving the landing continuity and support stability in the lower limb support stage 203.

[0052] In some embodiments, the forward somersault sequence further includes a stress-relieving support phase following the lower limb support phase 203. The stress-relieving support phase is used to further reduce the body's posture height after the legged robot has established lower limb support, and to establish a stable support relationship through the joint action of the lower and upper limbs. The stress-relieving support phase includes: controlling the legged robot's center of mass to move towards the contact surface; the knee joint of the second lower limb establishing support contact with the contact surface; and the distal end of the first upper limb establishing support contact with the contact surface. The first upper limb and the second lower limb are located on the same side of the torso. The knee joint of the second lower limb, the distal end of the first upper limb, and the distal end of the first lower limb together form a support polygon on the contact surface, and the projection point of the center of mass along the direction of gravity on the contact surface is located within the support polygon.

[0053] After a legged robot completes a mid-air flip, if multiple support areas, such as the lower limbs, knee joints, and upper limbs, are simultaneously controlled to establish support contact with the contact surface, these areas will be subjected to the reaction force of the contact surface within a short period of time. This can easily cause the legged robot to rebound or cause a sudden change in its posture, affecting its stability after landing. Therefore, based on the aforementioned principle that the lower limb of the second leg first establishes support contact with the contact surface, and the contact area between the lower limb of the second leg and the contact surface shifts from the foot area to the toe area, and the lower limb of the first leg subsequently establishes support contact with the contact surface, in this embodiment, the processor controls the center of mass of the legged robot to move towards the contact surface, controls the knee joint of the second lower limb to establish support contact with the contact surface, and simultaneously controls the upper limb of the first of the two upper limbs to establish support contact with the contact surface. The first upper limb and the second lower limb are located on the same side of the torso. Therefore, after the legged robot supports itself with both lower limbs, it can further increase the support contact points with the contact surface through the knee joint of the second lower limb and the tip of the first upper limb, allowing the body to transition from a lower limb-supported state to a multi-point support state. The knee joint of the second lower limb, the tip of the first upper limb, and the tip of the first lower limb together form a support polygon on the contact surface, and the projection point of the legged robot's center of mass along the direction of gravity on the contact surface is located within this support polygon. By ensuring that the projection point of the center of mass is within the support polygon, the legged robot can achieve a stable support posture during the unloading support phase, reducing the risk of continuing to lean forward, tilt to the side, or bounce back after completing a forward somersault.

[0054] Please see Figure 5 , Figure 5 This is a planar schematic diagram illustrating the formation of a support polygon by a legged robot during the unloading and support phase. Figure 5In the illustrated embodiment, the knee joint of the second lower limb and the contact surface form a second lower limb knee joint support region 501, the distal end of the first upper limb and the contact surface form a first upper limb distal end support region 502, and the distal end of the first lower limb and the contact surface form a first lower limb distal end support region 503. The second lower limb knee joint support region 501, the first upper limb distal end support region 502, and the first lower limb distal end support region 503 together define a support polygon 500.

[0055] Taking the understanding that the supporting polygon 500 is jointly determined by the supporting regions as an example, convex hull calculations can be performed on the outer boundaries of the second lower limb knee joint supporting region 501, the first upper limb distal end supporting region 502, and the first lower limb distal end supporting region 503. The smallest convex hull closed polygon including the aforementioned supporting regions is taken, and the outer contour region obtained from the convex hull calculation is used as the supporting polygon 500. At this time, the supporting polygon 500 covers the second lower limb knee joint supporting region 501, the first upper limb distal end supporting region 502, the first lower limb distal end supporting region 503, and the area enclosed by the outer boundaries of the convex hulls between the supporting regions. When the center of mass of the legged robot is projected onto the contact surface along the direction of gravity within the supporting polygon 500, it can be considered that the center of mass of the legged robot falls within the stable support range jointly defined by the aforementioned three supporting regions.

[0056] Taking the understanding that the supporting polygon 500 is constructed from supporting points in the supporting regions as an example, at least one supporting point can be selected from the second lower limb knee joint supporting region 501, the first upper limb distal support region 502, and the first lower limb distal support region 503, and the supporting polygon 500 can be constructed based on the selected supporting points. For example, a first supporting point can be selected from the second lower limb knee joint supporting region 501, a second supporting point can be selected from the first upper limb distal support region 502, and a third supporting point can be selected from the first lower limb distal support region 503. After connecting the first, second, and third supporting points in sequence, a triangular supporting region can be formed, and this triangular supporting region can be used as the supporting polygon 500. In other embodiments, multiple supporting points can also be selected from any supporting region to form a convex-sided supporting polygon with more sides.

[0057] In some embodiments, the centroid projection point is considered to be within the support polygon 500 calculated from the outer boundary convex hull of the second lower limb knee joint support region 501, the first upper limb distal support region 502, and the first lower limb distal support region 503. In other embodiments, the centroid projection point is also considered to be within the support polygon 500 when it is located within any convex-edge support polygon constructed from selected support points.

[0058] The unloading support phase is a continuous action with the aforementioned lower limb support phase 203. In the lower limb support phase 203, the distal end of the second lower limb first establishes support contact with the contact surface through the foot area, and under the action of thrust, the contact area is transferred to the toe area. Subsequently, the distal end of the first lower limb establishes support contact with the contact surface. After this, the unloading support phase further controls the descent of the center of gravity, gradually involving the knee joint of the second lower limb and the distal end of the first upper limb in the support. Through this continuous control method, the legged robot can first complete the landing support with the distal end of the lower limb, and then gradually introduce the knee joint and the distal end of the upper limb for support, reducing the overall rebound caused by multiple support areas simultaneously contacting the contact surface after takeoff, making the posture change after landing smoother.

[0059] In some embodiments, the support flip phase further includes: controlling the ends of the two upper limbs to swing away from the contact surface; wherein, at the first moment, the minimum distance between the end of the second lower limb and the end of the upper limb is less than the minimum distance between the end of the second lower limb and the ends of the two upper limbs at the second moment; the forward somersault sequence further includes a power-accumulating phase prior to the support flip phase, the power-accumulating phase including: controlling the ends of the two upper limbs to swing away from the contact surface, and the swing direction is opposite to the swing direction of the two upper limbs in the support flip phase; controlling the end of the second lower limb to swing away from the contact surface relative to the hip, and the swing direction is opposite to the swing direction of the second lower limb in the support flip phase; and controlling the knee joint of the first lower limb to bend to accumulate power.

[0060] In this embodiment, the fact that the minimum distance between the lower limb tip of the second lower limb and the upper limb tip of the upper limb at the first moment is less than the minimum distance between the lower limb tip of the second lower limb and the upper limb tip of the upper limb at the second moment indicates that: when the lower limb tip of the first lower limb just leaves the contact surface, the lower limb tip of the second lower limb and the upper limb tip of at least one upper limb are relatively close in space, so that the upper limb and the second lower limb form a relatively contracted swinging posture at the end of the support and flipping stage 201; at the second moment, as the legged robot completes the aerial flip and prepares to enter the lower limb support stage 203, the distance between the lower limb tip of the second lower limb and the upper limb tip of the upper limb increases, so that the upper limb and the lower limb gradually switch to a posture suitable for landing support and stability.

[0061] Both the upper limbs can have motion components away from the contact surface during the power-accumulation phase and the support-flipping phase 201, but their swing directions relative to the torso or shoulder joint are opposite. For example, during the power-accumulation phase, the processor can control the distal ends of both upper limbs to swing towards the facing side of the legged robot and away from the contact surface; during the support-flipping phase 201, the processor further controls the distal ends of both upper limbs to swing towards the side away from the facing side and away from the contact surface. Through the upper limb swing during the power-accumulation phase, the upper limbs can accumulate power, thereby generating a larger swing amplitude during the support-flipping phase 201, coordinating with the torso's rotation in the first direction. Similarly, both the second lower limbs can have motion components away from the contact surface during the power-accumulation phase and the support-flipping phase 201, but their swing directions relative to the hip are opposite. For example, during the power-accumulation phase, the processor controls the distal ends of the second lower limbs to swing towards the facing side of the legged robot relative to the hip and away from the contact surface; during the support-flipping phase 201, the processor further controls the distal ends of the second lower limbs to swing towards the side away from the facing side relative to the hip and away from the contact surface. By swinging the second lower limb in this way, the second lower limb can form a larger swing amplitude during the support and flipping phase 201, thereby enhancing the tendency of the trunk to rotate in the first direction.

[0062] During the power-accumulation phase, the processor also controls the knee flexion of the first lower limb to give the first lower limb room to continue extending and output thrust during the support-flipping phase 201. Subsequently, during the support-flipping phase 201, the lower limb tip of the first lower limb maintains support contact with the contact surface, and the extension movement of the first lower limb can assist the legged robot in entering the airborne flipping phase 202.

[0063] It should be noted that during the power-accumulation phase, controlling the swinging of the upper limbs, the swinging of the lower limbs, and the bending of the knee of the first lower limb can be performed in a preset sequence, or at least partially synchronously or overlappingly. For example, in some embodiments, the processor can first control the upper limbs to swing away from the contact surface, then control the lower limbs to swing away from the contact surface relative to the hip, and then control the knee of the first lower limb to bend. In other embodiments, the processor can first control the lower limbs to swing relative to the hip, then control the upper limbs to swing, and then control the knee of the first lower limb to bend. In still other embodiments, the processor can first control the lower limbs to swing relative to the hip, then control the upper limbs to swing, and then control the knee of the first lower limb to bend. In yet another embodiment, the processor can first control the knee of the first lower limb to bend, and then control the upper limbs and the second lower limb to swing. In still another embodiment, the processor can control the upper limbs and the lower limbs to swing synchronously, and control the knee of the first lower limb to gradually bend during the swinging process.

[0064] Through the above control method, a continuous action relationship is formed between the power accumulation phase and the support and flip phase 201: the power accumulation phase prepares for action by swinging the upper limbs and the second lower limbs and bending the first lower limbs; the support and flip phase 201 enables the legged robot to form a forward flip posture and forward flip momentum before the first moment by swinging the upper limbs and the second lower limbs in opposite directions, tilting the torso forward and rotating, and supporting the first lower limbs, thereby improving the action continuity of the legged robot when it enters the airborne flip phase 202.

[0065] In some embodiments, during the support and flipping phase, controlling the lower limb end of the second lower limb of the two lower limbs to swing away from the contact surface relative to the hip includes: during the process of controlling the lower limb end of the second lower limb to swing away from the contact surface relative to the hip until a first moment is reached, controlling the knee joint angle of the second lower limb to first decrease and then increase, so as to increase the rotational angular momentum of the trunk.

[0066] In this embodiment, in the initial stage of the support and flipping phase 201, the processor can first control the knee joint angle of the second lower limb to decrease, causing the second lower limb to switch from a relatively extended state to a relatively flexed state. After the second lower limb is flexed, the lower leg can form a larger swing adjustment space relative to the thigh, allowing the second lower limb to participate in adjusting its overall posture through the rapid swing of the lower leg relative to the thigh when swinging away from the contact surface. At the same time, the distance between the lower limb end and the hip decreases, reducing the rotational inertia that the second lower limb needs to overcome in the initial swing, which is beneficial for the second lower limb to complete the swing relative to the hip more quickly and reduces the possibility of interference between the second lower limb and the contact surface in the initial swing. After the second lower limb completes the swing, the processor then controls the knee joint angle of the second lower limb to increase, causing the second lower limb to gradually switch from a relatively flexed state to a relatively extended state. As the knee joint angle increases, the distance between the lower limb end and the hip increases, and the swing radius of the second lower limb increases accordingly. At this time, the lower limb of the second lower limb continues to swing away from the contact surface. The swinging effect generated by the extension of the lower leg can enhance the driving effect of the second lower limb on the forward flipping of the body, and cooperate with the torso to rotate in the first direction, so that the legged robot can form a more complete forward flipping tendency before reaching the first moment.

[0067] Please see Figure 6 , Figure 6 This is a schematic diagram of a legged robot in a flipping phase during the airborne phase. Figure 6As shown, after the distal end of the first lower limb detaches from the contact surface, the legged robot enters the aerial flipping phase 202. At this time, the distal end of the first lower limb has left the contact surface and is swinging away from it, while the head remains close to the contact surface. The torso continues to flip along the first direction, and the distal end of the second lower limb swings away from the contact surface relative to the hip, with the knee joint angle of the second lower limb at a relatively large angle. Figure 6 In the posture shown, during the support and flipping phase 201, the processor can control the knee joint angle of the second lower limb to first decrease and then increase as it swings the lower limb tip away from the hip relative to the contact surface until the first moment is reached. Near the first moment, the lower limb tip is already positioned away from the contact surface, and the knee joint angle is relatively large, resulting in a large swing radius for the second lower limb as a whole. That is, by participating in the forward flipping motion of the legged robot in the first direction through a large knee joint angle and swing radius, the rotational angular momentum of the torso in the first direction is increased.

[0068] Through the aforementioned control method, the second lower limb can first reduce the knee joint angle to provide movement space for lower leg swinging and lower limb posture switching, and then increase the knee joint angle to form a larger swing radius and swing amplitude. Therefore, the swinging of the second lower limb can more effectively participate in the legged robot's forward roll in the first direction, thereby increasing the rotational angular momentum of the torso in the first direction and improving the continuity of the transition from the support rollover phase 201 to the airborne rollover phase 202.

[0069] In the embodiments of this application, multiple control actions are described for the same action stage. Unless one control action is explicitly specified to be executed before or after another control action, the multiple control actions can be executed in a preset order, or at least partially synchronously or overlappingly.

[0070] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0071] In the several embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces, or indirect coupling or communication connection between apparatuses or units, and may be electrical, mechanical, or other forms.

[0072] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0073] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0074] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods of the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

Claims

1. A legged robot, characterized in that, include: The torso, including the hips; The head, two upper limbs and their corresponding ends, and two lower limbs and their corresponding ends are respectively connected to the torso, wherein the two lower limbs are respectively connected to the hip. At least one processor; And, at least one storage medium storing instructions that, when executed by the at least one processor, cause the legged robot to: In response to a forward somersault trigger command, a forward somersault sequence is executed, which includes a support and flip phase, an airborne flip phase, and a lower limb support phase in sequence. The support and flipping phase includes: controlling the head to move towards the contact surface, the lower limb end of the first lower limb of the two lower limbs maintaining support contact with the contact surface, and the lower limb end of the second lower limb of the two lower limbs swinging away from the contact surface relative to the hip. The aerial flipping phase includes: controlling the lower limb end of the first lower limb to detach from the contact surface and swing away from the contact surface, and controlling the legged robot to flip in the air; The lower limb support phase includes: controlling at least one of the two lower limbs to establish support contact with the contact surface; The moment when the distal end of the first lower limb detaches from the contact surface is recorded as the first moment, and the moment when at least one of the two lower limbs establishes supporting contact with the contact surface is recorded as the second moment. The airborne flipping phase includes the time period from the first moment to the second moment. At the first moment, the first distance between the head and the contact surface is less than the second distance between the hip and the contact surface. The angle of the torso flipping at the second moment is greater than 200° compared to the position at the first moment. The knee joint angle of the first lower limb at the first moment is greater than the knee joint angle of the first lower limb at the second moment. The knee joint angle of the second lower limb at the first moment is greater than the knee joint angle of the second lower limb at the second moment. The distance between the head and the contact surface at the first moment is less than the distance between the head and the contact surface at the second moment. At the first moment, the knee joint angle of the first lower limb is between 135° and 180°, and the knee joint angle of the second lower limb is between 135° and 180°.

2. The legged robot according to claim 1, characterized in that, At the first moment, the ratio of the first distance to the second distance is between 0.3 and 0.

8.

3. The legged robot according to claim 1, characterized in that, The support and flipping phase further includes: after the first distance is less than the second distance, controlling the lower limb end of the first lower limb to output a thrust towards the contact surface, and the reaction force of the contact surface acting on the lower limb end of the first lower limb is used to drive the legged robot into the air flipping phase.

4. The legged robot according to claim 1, characterized in that, At the second moment, the knee joint angle of the first lower limb is 30° to 120°, and the knee joint angle of the second lower limb is 30° to 120°.

5. The legged robot according to claim 1, characterized in that, The lower limb support phase includes: Control the lower limb ends of the first lower limb and the second lower limb to establish supporting contact with the contact surface respectively; The time difference between the establishment of supporting contact between the lower limb tip of the first lower limb and the lower limb tip of the second lower limb is 0s to 1s.

6. The legged robot according to claim 5, characterized in that, During the lower limb support phase, controlling the distal ends of the first and second lower limbs to establish supporting contact with the contact surface includes: Control the lower limb tip of the second lower limb to establish a supporting contact with the contact surface before the lower limb tip of the first lower limb; After the lower limb tip of the second lower limb establishes supporting contact with the contact surface, the lower limb tip of the first lower limb is controlled to establish supporting contact with the contact surface.

7. The legged robot according to claim 6, characterized in that, In the lower limb support phase, after the lower limb tip of the second lower limb establishes support contact with the contact surface, controlling the lower limb tip of the first lower limb to establish support contact with the contact surface includes: After the foot area of ​​the lower limb of the second lower limb establishes supporting contact with the contact surface, the lower limb of the second lower limb is controlled to output a thrust to the contact surface. The contact area between the lower limb of the second lower limb and the contact surface is transferred from the foot area to the toe area of ​​the lower limb of the second lower limb, so as to buffer the impact force on the knee joint of the first lower limb when it establishes supporting contact with the contact surface. During the process of the lower limb end of the second lower limb establishing a supporting contact with the contact surface to the lower limb end of the first lower limb establishing a supporting contact with the contact surface, the knee joint angle of the first lower limb is controlled to increase.

8. The legged robot according to claim 7, characterized in that, The forward somersault sequence also includes a stress relief phase following the lower limb support phase, which includes: The center of mass of the legged robot is controlled to move towards the contact surface. The knee joint of the second lower limb establishes a supporting contact with the contact surface. The end of the first upper limb of the two upper limbs establishes a supporting contact with the contact surface. The first upper limb and the second lower limb are located on the same side of the torso. The knee joint of the second lower limb, the end of the first upper limb, and the end of the first lower limb together form a supporting polygon on the contact surface. The projection point of the center of mass on the contact surface along the direction of gravity is located within the supporting polygon.

9. The legged robot according to claim 1, characterized in that, The support and flipping phase further includes: controlling the ends of the two upper limbs to swing away from the contact surface; wherein, at the first moment, the minimum distance between the end of the second lower limb and the ends of the two upper limbs is less than the minimum distance between the end of the second lower limb and the ends of the upper limbs at the second moment. The forward somersault sequence also includes a power-building phase preceding the support and flip phase. The power-building phase includes: controlling the ends of the two upper limbs to swing away from the contact surface in a direction opposite to the swing direction of the two upper limbs in the support and flip phase; controlling the end of the second lower limb to swing away from the contact surface relative to the hip in a direction opposite to the swing direction of the second lower limb in the support and flip phase; and controlling the knee joint of the first lower limb to bend in order to build up power.

10. The legged robot according to claim 1, characterized in that, During the support and flipping phase, controlling the distal end of the second lower limb of the two lower limbs to swing away from the contact surface relative to the hip includes: During the process of controlling the lower limb end of the second lower limb to swing away from the contact surface relative to the hip until reaching the first moment, the knee joint angle of the second lower limb is controlled to first decrease and then increase in order to increase the rotational angular momentum of the trunk.

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