Control Method for Parallel Four-Legged Robot

Abstract

The object of the present invention is to provide a control method for a parallel four-wheel-legged robot. Based on a 12-degree-of-freedom four-wheel-legged robot with a symmetric parallel mechanism, a corresponding control method is proposed. During the swing phase of the robot, a wheel dynamics compensation method based on the principle of virtual work is proposed in combination with the decomposed virtual model control to improve the model control accuracy. At the same time, in order to achieve attitude decoupling, the present invention also proposes a corresponding attitude control strategy and a ramp adaptive strategy. Combining the dual advantages of wheels and legs, a rolling control method and an attitude control strategy in the wheel-leg mode are proposed to enable the robot to pass multiple wavy obstacles with a height of 0.15 m and a slope of 41.41° unilaterally at a speed of 3.2 m / s in the simulation.

Description

Technical Field

[0001] The present invention relates to the technical field of wheeled-legged robot control, and particularly relates to a control method for a parallel four-wheeled-legged robot. Background Art

[0002] Wheeled-legged robots have both the advantages of discrete foot landing points of legged robots, which is beneficial for crossing obstacles and deep pits, and the advantages of high efficiency of wheeled robots. At the same time, the parallel leg mechanism has a larger load-bearing capacity compared to the serial leg mechanism. Power line inspection, goods delivery, blind guidance, education, and companionship are all future application scopes of wheeled-legged robots.

[0003] Traditional legged quadruped robots generally reduce the leg mass to minimize the impact on the movement of the robot body, while the leg mass of wheeled robots is a non-negligible factor. When adding wheels to the decomposed virtual model control, the swing phase trajectory is prone to the phenomenon of lag in the first half and lead in the second half of the swing phase, and the process of re-adjusting parameters is cumbersome.

[0004] In addition, in the control of the roll angle of quadruped robots, a twelve-degree-of-freedom serial quadruped robot generally decouples the side swing joint and the front swing joint, and constructs a virtual spring damper acting on the side swing joint to offset the reaction torque of flipping around the diagonal line of the support caused by the front swing joint. The parallel four-wheeled-legged robot has a larger load-bearing capacity compared to the serial four-wheeled-legged robot, but the eight-degree-of-freedom parallel quadruped robot does not have a side swing joint. Summary of the Invention

[0005] Aiming at the defects and deficiencies existing in the prior art, the present invention proposes a corresponding control method for a twelve-degree-of-freedom four-wheeled-legged robot based on a symmetric parallel mechanism. In the swing phase of the robot, a wheel dynamics compensation method based on the principle of virtual work is proposed in combination with the decomposed virtual model control to improve the model control accuracy.

[0006] At the same time, in order to achieve attitude decoupling, the present invention also proposes a corresponding attitude control strategy and a ramp adaptive strategy. Combining the dual advantages of wheels and legs, a rolling control method and an attitude control strategy in the wheel-leg mode are proposed to achieve the ability to pass a plurality of wavy obstacles with a height of 0.15 m and a slope of 41.41° unilaterally at a speed of 3.2 m / s in simulation.

[0007] The technical solution specifically adopted by the present invention to solve its technical problems is as follows:

[0008] A control method for a parallel four-wheeled-legged robot, based on a twelve-degree-of-freedom four-wheeled-legged robot with a symmetric parallel mechanism, and its legged control is analyzed and processed on the basis of the decomposed virtual model control method, which is divided into four parts: support phase, swing phase, attitude control, and ramp adaptation:

[0009] For the support phase control:

[0010] Assume that P is a fixed point, i.e., there is no relative sliding between the wheel and the ground; the model is described as follows:

[0011]

[0012] where f x st , f z st is the virtual force of the foot tip relative to the coordinate system in the support phase, K x st , K z st , D x st , D z st are the elastic and damping coefficients of two virtual spring dampers respectively, is the actual and desired centroid velocities in the forward direction of the robot, z st , z d st , are the actual displacement, actual velocity, desired displacement and desired velocity of the foot tip relative to point p in the z direction of the coordinate system respectively;

[0013] For the swing phase control:

[0014] The model is described as:

[0015]

[0016] where f x sw , f z sw is the virtual force of the foot tip relative to the coordinate system in the swing phase, K x sw , K z sw , D x sw , D z sw are the elastic and damping coefficients of two virtual spring dampers respectively, is the actual and desired centroid velocities in the forward direction of the robot, x sw , x d sw , z sw , z d sw , z d swThey are the actual displacement, actual velocity, desired displacement, desired velocity, and desired acceleration of the foot end relative to p in the x and z directions of the coordinate system respectively; after calculating the virtual forces in the swing phase and support phase, the virtual forces on the robot leg are mapped into equivalent joint torques through the transpose of the Jacobian matrix to calculate the corresponding joint target torques.

[0017] For attitude control, the magnitude of the virtual force to be compensated is:

[0018]

[0019] Where K roll , K pitch , K yaw , D roll , D pitch , D yaw They are the roll elastic coefficient, pitch elastic coefficient, yaw elastic coefficient, roll damping coefficient, pitch damping coefficient, and yaw damping coefficient in attitude control respectively, ψ d , φ d , They are the desired roll angle, pitch angle, and yaw angle respectively, ψ, φ, They are the actual roll angle, pitch angle, and yaw angle respectively, They are the desired roll angular velocity, pitch angular velocity, and yaw angular velocity respectively, They are the actual roll angular velocity, pitch angular velocity, and yaw angular velocity respectively, B and L are the wheelbase and track width; the virtual force f z roll and f z pitch compensates for f z st , the virtual force f x yaw compensates for f x st ;

[0020] For ramp adaptive control, the angle of the ramp is obtained by the following formula:

[0021]

[0022] Where θ, z f , z h They are the estimated ramp angle, the actual front leg height and hind leg height in the support phase respectively, and the pitch angle coefficient k is used to suppress the angle fluctuations caused during the robot's walking.

[0023] Furthermore, its wheel-foot control part adopts a wheel-leg hybrid control model:

[0024] Establish the following rolling control method:

[0025]

[0026] where τ i represents the wheel input torque, k i p , n di , n i , k di , e i now , e i last respectively represent the proportional coefficient, the desired wheel speed, the actual speed, the differential coefficient, the current speed error, and the previous speed error;

[0027] To adapt to non-rugged ground, establish the following attitude control strategy:

[0028]

[0029] where h zi leg represents the desired height of the single-leg direction, h di leg , pdout roll , pdout pitch , pdout yaw , u i roll , u i pitch , u i yaw respectively represent the initial desired body height, the Euler angle pd calculation result, and the Euler angle coefficient; limit the Euler angle pd calculation result to avoid the instability state or even tipping over that may occur due to excessive Euler angles during the movement; by detecting the joint motor feedback current, determine whether the single leg is suspended, and if suspended, use the position control mode to keep the leg in the current state;

[0030] To achieve skid-steering, establish the following simple kinematic equation:

[0031]

[0032] where n, r, w respectively represent the wheel speed, the turning radius, and the angular velocity.

[0033] And, a control system for a parallel four-wheel-foot robot, constructed according to the control method of the parallel four-wheel-foot robot described above, includes: a mode selection module for selecting the legged mode or the wheel-foot mode; among them, the legged mode includes a support phase control module and a swing phase control module, and the initial parameters required to be input in the legged mode include: the step length s, the center-of-mass height h comAnd the height w of the leg lift during the swing phase, and different leg sequences and corresponding control strategies are selected through the phase switching state machine; the initial parameters required in the wheel-leg mode include: wheel acceleration Wheel speed n di , turning angular velocity w, and the desired leg height Thereby entering the wheel and body attitude control method.

[0034] Compared with the prior art, the present invention and its preferred solutions propose corresponding control methods for a 12-degree-of-freedom four-wheel-leg robot based on a symmetric parallel mechanism. During the swing phase of the robot, a wheel dynamics compensation method based on the principle of virtual work is proposed in combination with the decomposed virtual model control to improve the model control accuracy.

[0035] At the same time, to achieve attitude decoupling, the present invention also proposes corresponding attitude control strategies and ramp adaptive strategies. Combining the dual advantages of the wheels and legs, a rolling control method and an attitude control strategy in the wheel-leg mode are proposed to enable the robot to pass through multiple wavy obstacles with a height of 0.15 m and a slope of 41.41° unilaterally at a speed of 3.2 m / s in the simulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The present invention will be further described in detail below in conjunction with the drawings and specific embodiments:

[0037] Figure 1 It is an external engineering schematic diagram of the robot targeted by the embodiment of the present invention;

[0038] Figure 2 It is an internal engineering schematic diagram of the robot targeted by the embodiment of the present invention;

[0039] Figure 3 It is a single-leg structure schematic diagram of the robot targeted by the embodiment of the present invention;

[0040] Figure 4 It is a virtual model schematic diagram of the support phase of the embodiment of the present invention;

[0041] Figure 5 It is a control model schematic diagram of the swing phase of the embodiment of the present invention;

[0042] Figure 6 It is a control block diagram of the parallel wheel-leg robot of the embodiment of the present invention;

[0043] Figure 7 It is a comparison diagram of dynamic compensation under different wheel masses of a single leg in the embodiment of the present invention;

[0044] Figure 8 It is a schematic diagram of the instantaneous speed of the fuselage in different directions in the embodiment of the present invention;

[0045] Figure 9Schematic diagrams of the robot postures at different instantaneous speeds in the embodiments of the present invention;

[0046] Figure 10 Schematic diagram of the obstacle size in the embodiments of the present invention;

[0047] Figure 11 Schematic diagram of the comparison of the pitching angles of the robot passing through the obstacle in the embodiments of the present invention;

[0048] Figure 12 Schematic diagram of the simulation environment of the robot passing through a single obstacle in the embodiments of the present invention;

[0049] Figure 13 Schematic diagram of the comparison of the z-direction displacements of the centroids of the robot passing through multiple obstacles in the embodiments of the present invention;

[0050] Figure 14 Schematic diagram of the simulation environment of the robot passing through multiple obstacles in the embodiments of the present invention. Detailed implementation manners

[0051] To make the features and advantages of this patent more obvious and understandable, specific embodiments are given below and described in detail as follows:

[0052] It should be noted that the following detailed descriptions are all illustrative and are intended to provide further explanations for the present application. Unless otherwise specified, all technical and scientific terms used in this specification have the same meanings as those commonly understood by those of ordinary skill in the technical field to which the present application belongs.

[0053] It should be noted that the terms used here are only for describing specific implementation manners and are not intended to limit the exemplary implementation manners according to the present application. As used here, unless the context clearly indicates otherwise, the singular forms are also intended to include the plural forms. In addition, it should also be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or their combinations.

[0054] The present invention proposes corresponding control methods and systems based on a twelve-degree-of-freedom four-wheel-legged robot with a symmetric parallel mechanism. The specific structure of the twelve-degree-of-freedom four-wheel-legged robot with a symmetric parallel mechanism is as Figure 1 and Figure 2As shown, the mechanism consists of four wheeled legs and a fuselage. Among them, the wheel hub 1 is fixed on the wheel motor, and the tire is installed on the wheel hub, forming an active drive wheel. The drive wheel and the calf 4 form a passive rotating pair, the calf 4 and the thigh 5 form a passive rotating pair, and the thigh 5, the motor bracket 14 and the motor 13 form an active rotating pair. Since this is a symmetric parallel mechanism, the other half has the same structure. Through the calculation of the degrees of freedom of the planar mechanism, it can be obtained that a single leg of the robot has three degrees of freedom. The emergency stop switch 7 is fixed on the emergency stop switch cover 8, and the whole is fixed on the machine cover 6. The control core board 11 and the power and signal expansion board 10 are installed in the battery compartment 12, and the bottom plate 9 supports the whole body of the robot.

[0055] Based on this, the control method and control system are designed in this embodiment to achieve the invention purpose, that is, to achieve attitude decoupling, and the corresponding attitude control strategy and ramp adaptive strategy are proposed.

[0056] The control method proposed in this embodiment is mainly divided into two parts: namely, the legged control part and the wheel-legged control part. Among them, the legged control is analyzed and processed based on the decomposed virtual model control method, and is divided into four small parts: the support phase, the swing phase, the attitude control and the ramp adaptation.

[0057] First, the basic principle of legged is analyzed:

[0058] In order to realize the basic movement of the wheeled-leg robot, the kinematic equation of the robot must be obtained. As Figure 3 shown, it is the structural schematic diagram of a single leg of the robot. The {X0Z} coordinate system is established as shown in the figure, and the coordinate origin O is located at the center of the two joint rotation centers A and E. The coordinates (x, z) of the foot end C point can be expressed in the coordinate system as:

[0059]

[0060] where β = γ2 - γ1;

[0061]

[0062]

[0063] Taking the partial derivative of equation (1) can obtain the Jacobian matrix in the corresponding coordinate system:

[0064]

[0065] where

[0066]

[0067]

[0068]

[0069]

[0070] σ5 = l3 + l1cos(q1) - l1cos(q2)

[0071] σ6 = l1sin(q1) - l1sin(q2)

[0072] According to the principle of virtual work, the transpose of the Jacobian matrix maps the virtual forces on the robot leg into equivalent joint torques. Therefore, we have:

[0073] τ = λJ T f (3)

[0074] where f = (f x , f z ) T , τ = (τ0, τ1). During the stance phase, the virtual force F exerted by the ground on the foot end and the virtual force exerted by the foot end on the ground are equal in magnitude and opposite in direction, so λ = -1. During the swing phase, the direction of the force is the same as the direction of the virtual force exerted by the ground on the foot end, so f = 1. It is easy to obtain the inverse kinematic equation as follows:

[0075]

[0076] where

[0077] For the stance phase control model, as shown in Figure 4 :

[0078] The movement of the robot mainly depends on the stance phase, and the control objectives are mainly the height, walking speed, and posture of the robot body. Different from wheeled robots, before performing stance phase control, it is necessary to assume that P is a fixed point, that is, there is no relative sliding between the wheel and the ground. The model can be described as follows:

[0079]

[0080] where f x st , f z st are the virtual forces of the foot end relative to the {H} coordinate system, K x st , K z st , D x st , D z st are the elastic and damping coefficients of the two virtual spring-dampers respectively, is the actual and desired centroid velocity of the robot in the forward (x) direction, z st , z d st , They are respectively the actual displacement, actual velocity, expected displacement and expected velocity of the foot end relative to point p in the z direction in the {H} coordinate system.

[0081] For the swing phase control model, such as Figure 5 As shown:

[0082] The swing phase of the decomposed virtual model assumes that P is a fixed point. At each moment of the swing, the virtual component is used to pull the foot end to track the swing trajectory of the quadruped robot. Its control targets are mainly the leg lifting height and the foot landing point.

[0083] The legged quadruped robot needs a set of corresponding swing phase PD parameters in the swing phase, and adding wheels requires adjusting another set of parameters. The process of re-tuning the PD parameters is cumbersome and the control accuracy is not high. If the PD parameters are directly adjusted by adding wheels, it is easy to lag in the first half of the swing phase and advance in the second half. Therefore, a wheel dynamics compensation method based on the principle of virtual work is proposed. After adding wheels, the torque of the joint motor can be given by the following formula:

[0084]

[0085] The above formula can be combined to describe the model as follows:

[0086]

[0087] where f x sw ,f z sw is the virtual force of the foot end relative to the {H} coordinate system, K x sw ,K z sw ,D x sw ,D z sw are the elastic and damping coefficients of the two virtual spring dampers, is the actual center of mass velocity and expected center of mass velocity of the robot in the forward (x) direction, x sw ,x d sw , z sw , z d sw , z d swThey are respectively the actual displacement, actual velocity, desired displacement, desired velocity, and desired acceleration of the foot end relative to p in the {H} coordinate system in the x and z directions. After calculating the virtual forces in the swing phase and support phase, the corresponding joint target torques are calculated through Equation (3).

[0088] In this embodiment, for the attitude control model part, specifically:[[]]END]]

[0089] In the control of the roll angle, a twelve-degree-of-freedom series quadruped robot generally decouples the side-swing joint and the front-swing joint to construct a virtual spring damper acting on the side-swing joint to offset the reaction torque of flipping around the diagonal line of the support phase caused by the front-swing joint. An eight-degree-of-freedom parallel quadruped robot does not have a side-swing joint. To achieve attitude decoupling, from Equation (6), we can get T x = r y f z st The roll angle can be controlled by changing the virtual force f z st in the z direction, and then generate the torque T x . T y = r z f x st - r x f z st The yaw angle can be jointly controlled by the virtual forces f x st , f z st and then generate the torque T y , but this will also affect the yaw angle and roll angle at the same time. Directly compensating for the leg height, the anti-interference ability and instability recovery ability of the system are poor. Therefore, considering that f z st has a greater influence in the pitch direction (i.e., the y direction) than f x st , so a virtual spring damper is constructed in this direction to generate a combined compensation of the pitch virtual force and the roll virtual force for f z st . Similarly, we can get T z = - r y f x st The yaw angle can be controlled by the virtual force f x st and then generate the torque T z . In summary, the magnitude of the virtual force to be compensated is:[[]]END]]

[0090]

[0091] where K roll , K pitch, K yaw , D roll , D pitch , D yaw are the elastic coefficient and damping coefficient in attitude control, ψ d , ψ, φ d , φ, are the desired, actual Euler angles and the corresponding actual and desired angular velocities respectively. Usually, the desired angles and angular velocities are set to zero. B and L are the track width and wheelbase respectively. The virtual forces f z roll and f z pitch compensate for f z st , and the virtual force f x yaw compensate for f x st .

[0092] In this embodiment, the design for slope adaption is specifically as follows:

[0093] Slope adaption is very crucial for improving the robot's motion ability. The two major factors affecting the robot going uphill are: one is that the projection of the robot's center of mass in the vertical direction needs to be at the midpoint of the contact line of the legs during the support phase; the other is that virtual forces should be compensated on the slope. Based on these two factors, the slope angle needs to be estimated, which can be obtained from the following formula:

[0094]

[0095] where θ, z f , z h are the estimated slope angle, the actual front leg height and the rear leg height during the support phase respectively. The pitch angle coefficient k is used to suppress the angle fluctuations caused during the robot's walking. For the center of mass control and virtual force compensation, the methods provided in the reference document "Research on the Intuitive Control Method of the Virtual Model of the Diagonal Trot Gait of a Quadruped Robot" can be adopted.

[0096] The wheel-foot control part adopts a wheel-leg hybrid control model:

[0097] The robot mainly operates in three modes: legged, wheeled, and wheel-leg. A state selector can be used to represent different control modes. The steering ability is a very important factor in the wheeled control mode. According to the reference document [2] it can be known that

[0098] The wheel-foot control part adopts a wheel-leg hybrid control model:

[0099] The robot mainly operates in three modes: legged, wheeled, and wheel-legged, and a state selector can be used to represent different control modes. Steering ability is a very important factor in the wheeled control mode. According to the reference "Research on Skid Steer Control of Small Four-Wheel Independent Drive Vehicles",

[0100] To achieve skid steering with different radii, the wheelbase of the robot should be greater than the track width. An overly wide body will increase the steady-state error of the robot, so most wheel-legged robots do not meet the above conditions. The wheel-legged robot can be regarded as a four-wheel independent suspension system. Therefore, by changing the front and rear wheel spacing, the conditions can be met to achieve turning with different radii. To increase the stability of turning, the center of gravity can be lowered or the height on both sides can be changed to increase the centripetal force for turning. In the wheel-legged mode, the leg height control still uses the support phase control scheme. To prevent the wheels from slipping, the following rolling control method is established:

[0101]

[0102] where τ i represents the wheel input torque, k i p , n di , n i , k di , e i now , e i last represent the proportional coefficient, the desired wheel speed, the actual speed, the differential coefficient, the current speed error, and the previous speed error. To adapt to non-rough terrain, the following attitude control strategy is established:

[0103]

[0104] where h zi leg represents the desired height of a single leg in the z direction, h di leg , pdout roll , pdout pitch , pdout yaw , u i roll , u i pitch , u i yawThey respectively represent the initial expected body height, the Euler angle pd calculation result, and the Euler angle coefficient. Limiting the Euler angle pd calculation result can appropriately avoid the unstable state or even tipping situation that may occur due to excessive Euler angles during the movement. When the robot passes through some obstacles with relatively high heights, a single leg may be in a suspended state, which does not conform to the control direction of the virtual force of the leg during the support phase. Therefore, by detecting the feedback current of the joint motor (configuring a sole contact sensor in the simulation), it can be determined whether a single leg is suspended. If it is suspended, the position control mode is used to keep the leg in the current state. To achieve skid-steering, the following simple kinematic equation is established:

[0105]

[0106] Where n, r, and w respectively represent the wheel speed, turning radius, and angular velocity.

[0107] The wheel-legged robot is a complex mechanical system, and the control scheme determines the motion performance of the robot. As Figure 6 shown, the control block diagram of the parallel wheel-legged robot designed based on the above control method is provided. The contents of the short dashed line and the long dashed line are respectively the support phase and the swing phase of the legged mode, and the dotted line belongs to the content of the wheel-foot control mode. First, mode selection is required. In the legged mode, the step length s, the center-of-mass height h com and the swing-phase leg-lifting height w are input, and different leg sequences and corresponding control strategies are selected through the phase-switching state machine. In the wheel-foot mode, the wheel acceleration the wheel speed n di , the turning angular velocity w, and the expected leg height are input, and then enter the wheel and body attitude control methods.

[0108] To verify the above control method, in this embodiment, the solidworks 3D model is imported into the simulation software webots, and the corresponding control code is written in C language. Through simulation analysis, the following experimental results are obtained:

[0109] 1. Analysis of the motion trajectory of a single leg

[0110] Table 1 Single-leg motion trajectory parameters

[0111] Lifting height Swing step length Initial wheel mass 0.06m 0.053m 0.18 kg

[0112] As Figure 7As shown, it is a comparison diagram of dynamic compensation under different wheel masses for a single leg. The swing phase trajectory adopts a Bezier curve, and the motion trajectory refers to Table 1. In the diagram without dynamic compensation, the swing phase conforms to the above analysis. In the support phase, as the wheel weight increases, the deviation from the target trajectory becomes more serious, and there is an overshoot at the beginning of the support phase. In the diagram with dynamic compensation, it is significantly better than without dynamic compensation under different masses, and there is no need to re-tune the elastic and damping coefficients, which proves that the wheel dynamic compensation method based on the principle of virtual work proposed on the basis of the decomposed virtual model is feasible.

[0113] 2. Flat ground diagonal gait test

[0114] As Figure 8 shown, it is the instantaneous velocity of the fuselage in different directions. The initial velocity of the robot is 0.2 m / s, and it increases by 0.2 m / s every 15 seconds. It can be seen that the robot changes according to the corresponding velocity in the x direction. The main reason for the up and down fluctuation of its velocity is that the decomposed virtual model scheme is adopted in the support phase. When the current velocity is greater than the desired velocity, the robot will accelerate, and when it is less, it will decelerate. In the z direction, the error is relatively small, with a maximum of about 0.2 m / s. The impact of the wheel on the ground during the robot's downward step will have an impact on it. Due to the limitation of the robot's degrees of freedom, the velocity fluctuation in the y direction increases as the velocity increases.

[0115] As Figure 9 shown, it is the robot's attitude at different instantaneous velocities. It can be seen that the largest attitude change occurs during the velocity change process. The maximum error of the pitch axis is only about 0.07 rad, and the deviation of the roll axis is about 0.19 rad. The main reason for its deviation being greater than that of the pitch axis is that the control outputs of the pitch axis and the roll axis in this control method jointly compensate the virtual force in the z direction. The deviation of the yaw axis is still due to the limitation of the robot's degrees of freedom. Nevertheless, its control accuracy is still acceptable.

[0116] 3. Wheel-foot mode test

[0117] 3.1 Crossing a single obstacle

[0118] It can be seen from Figures 10 - 12 that the fluctuation amplitude of the pitch axis with the rolling control method is smaller than that without the rolling control method.

[0119] 3.2 Crossing multiple obstacles

[0120] Figures 13 - 14 In the simulation environment where the robot passes through 4 obstacles with a distance of 1.5 m apart at a speed of 3.2 m / s, it can be seen from Figure 13 the comparison of the centroid z-direction displacement of crossing multiple obstacles that the attitude control strategy can successfully pass through and maintain the initial height, while without the attitude control, it fails.

[0121] Those skilled in the art should understand that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

[0122] The present application is described with reference to the flowcharts and / or block diagrams of methods, apparatuses (systems), and computer program products according to the embodiments of the present application. It should be understood that each flow and / or block in the flowchart and / or block diagram, as well as the combination of flows and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, such that the instructions executed by the processor of the computer or other programmable data processing devices generate means for implementing the functions specified in Figure 1 one or more of the processes or multiple processes and / or blocks Figure 1 one or more of the blocks or multiple blocks.

[0123] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, such that the instructions stored in the computer-readable memory generate a manufactured article including instruction means that implement the functions specified in Figure 1 one or more of the processes or multiple processes and / or blocks Figure 1 one or more of the blocks or multiple blocks.

[0124] These computer program instructions can also be loaded onto a computer or other programmable data processing device, such that a series of operation steps are executed on the computer or other programmable device to generate a computer-implemented process, so that the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in Figure 1 one or more of the processes or multiple processes and / or blocks Figure 1 one or more of the blocks or multiple blocks.

[0125] As mentioned above, it is only the preferred embodiment of the present invention, and it is not a limitation of the present invention in other forms. Any person skilled in the art may use the disclosed technical content to make changes or modifications into equivalent embodiments with equivalent changes. However, any simple modification, equivalent change, and modification made to the above embodiments based on the technical essence of the present invention without departing from the technical content of the present invention still fall within the protection scope of the technical solution of the present invention.

[0126] This patent is not limited to the above-mentioned best implementation mode. Anyone can derive control methods for other various forms of parallel four-wheel legged robots under the inspiration of this patent. All equal changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope covered by this patent.

Claims

1. A control method for a parallel four-wheel-legged robot, characterized in that, A 12-degree-of-freedom four-wheel-legged robot based on a symmetric parallel mechanism, whose leg control is analyzed and processed based on the decomposed virtual model control method, is divided into four small parts: the support phase, the swing phase, the attitude control, and the ramp adaptation: For the support phase control: Assume that P is a fixed point, that is, there is no relative sliding between the wheel and the ground; the model is described as follows: where f x st , f z st is the virtual force of the foot tip relative to the coordinate system in the support phase, K x st , K z st , D x st , D z st are the elasticity and damping coefficients of two virtual spring dampers respectively, is the actual and desired centroid velocities in the forward direction of the robot, z st , z d st , are the actual displacement, actual velocity, desired displacement and desired velocity of the foot tip relative to point p in the z direction of the coordinate system respectively; For the swing phase control: The model is described as: where f x sw , f z sw is the virtual force of the foot tip relative to the coordinate system in the swing phase, K x sw , K z sw , D x sw , D z sw are the elasticity and damping coefficients of the two virtual spring dampers respectively, are the actual and desired centroid velocities in the forward direction of the robot, x sw , x d sw , z sw , z d sw , z d sw are the actual displacement, actual velocity, desired displacement, desired velocity and desired acceleration of the foot tip relative to p in the x and z directions of the coordinate system respectively; After calculating the virtual forces in the swing phase and the support phase, the virtual forces on the robot leg are mapped into equivalent joint torques through the transpose of the Jacobian matrix to calculate the corresponding joint target torques; For the attitude control, the magnitude of the virtual force to be compensated is: Among which K roll , K pitch , K yaw , D roll , D pitch , D yaw are respectively the roll angle elastic coefficient, pitch angle elastic coefficient, yaw angle elastic coefficient, roll angle damping coefficient, pitch angle damping coefficient and yaw angle damping coefficient in attitude control, ψ d , φ d , are respectively the desired roll angle, pitch angle and yaw angle, ψ, φ, are respectively the actual roll angle, pitch angle and yaw angle, are respectively the desired roll angular velocity, pitch angular velocity and yaw angular velocity, are respectively the actual roll angular velocity, pitch angular velocity and yaw angular velocity, B and L are respectively the track width and wheelbase; the virtual forces f z roll and f z pitch compensate for f z st , the virtual force f x yaw compensate for f x st ; For the ramp adaptation control, the angle of the ramp is obtained by the following formula: where θ, z f , z h are the estimated ramp angle, the actual front leg height and the hind leg height during the stance phase, respectively. The pitch angle coefficient k is used to suppress the angular fluctuations caused during the robot's walking.

2. The control method of the parallel four-wheel foot robot according to claim 1, characterized in that: Its wheel-leg control part adopts a wheel-leg hybrid control model: Establish the following rolling control method: where τ i represents the wheel input torque, k i p , n di , n i , k di , e i now , e i last represent the proportionality coefficient, the desired wheel speed, the actual speed, the differential coefficient, the current speed error, and the previous speed error, respectively; To adapt to non-rugged ground, establish the following attitude control strategy: where h zi leg represents the desired height in the single-leg direction, h di leg , pdout roll , pdout pitch , pdout yaw , u i roll , u i pitch , u i yaw respectively represent the initial desired body height, the calculation result of the Euler angle pd, and the Euler angle coefficient; limit the calculation result of the Euler angle pd to avoid the unstable state or even tipping that may occur due to excessive Euler angles during the movement process; by detecting the feedback current of the joint motor, determine whether the single leg is suspended, and if it is suspended, use the position control mode to keep the leg in the current state; To achieve skid steering, establish the following simple kinematic equation: Where n, r, and w represent the wheel speed, turning radius, and angular velocity respectively.

3. A control system for a parallel four-wheel-foot robot, characterized in that; Constructed according to the control method of the parallel four-wheel-legged robot as described in claim 2, including: a mode selection module for selecting a legged mode or a wheel-legged mode; wherein, the legged mode includes a support phase control module and a swing phase control module, and the initial parameters required to be input in the legged mode include: step length s, center-of-mass height h com and swing phase leg lift height w, and different leg sequences and corresponding control strategies are selected through a phase switching state machine; the initial parameters required to be input in the wheel-legged mode include: wheel acceleration wheel speed n di , turning angular velocity w and expected leg height and thus enter the wheel and body attitude control method.

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