CN111891249A - Hydraulic hexapod robot and walking gait control method based on centroid fluctuation - Google Patents

Hydraulic hexapod robot and walking gait control method based on centroid fluctuation Download PDF

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CN111891249A
CN111891249A CN202010566960.XA CN202010566960A CN111891249A CN 111891249 A CN111891249 A CN 111891249A CN 202010566960 A CN202010566960 A CN 202010566960A CN 111891249 A CN111891249 A CN 111891249A
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foot end
centroid
robot
joint
hydraulic
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CN111891249B (en
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金波
董峻魁
刘子祺
翟硕
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Zhejiang University ZJU
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
    • B62D—MOTOR VEHICLES; TRAILERS
    • B62D57/00—Vehicles characterised by having other propulsion or other ground- engaging means than wheels or endless track, alone or in addition to wheels or endless track
    • B62D57/02—Vehicles characterised by having other propulsion or other ground- engaging means than wheels or endless track, alone or in addition to wheels or endless track with ground-engaging propulsion means, e.g. walking members
    • B62D57/032—Vehicles characterised by having other propulsion or other ground- engaging means than wheels or endless track, alone or in addition to wheels or endless track with ground-engaging propulsion means, e.g. walking members with alternately or sequentially lifted supporting base and legs; with alternately or sequentially lifted feet or skid

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Abstract

The invention relates to a hydraulic hexapod robot and a walking gait control method based on centroid fluctuation, and belongs to the technical field of robots. The robot comprises a body and three hydraulic mechanical legs which are respectively arranged on two sides of the body, wherein each hydraulic mechanical leg comprises a root joint, a hip joint, a thigh rod, a knee joint, a shank rod and a foot end fixedly arranged on the shank rod; specifically, under a heel joint coordinate system, the components of the foot end track in the advancing and vertical directions are sextic polynomials and the displacement, the speed and the acceleration are continuous. Compared with the control method for keeping the height of the mass center approximately unchanged in the prior art, the gait with fluctuating mass center can effectively reduce the average flow and the average power of the robot within one gait cycle, thereby effectively improving the utilization rate of energy and being widely applied to the technical field of robots.

Description

Hydraulic hexapod robot and walking gait control method based on centroid fluctuation
Technical Field
The invention relates to the technical field of robots, in particular to a hydraulic hexapod robot and a walking gait control method of the robot based on centroid fluctuation.
Background
The mobile robot is widely applied to the fields with high dangerousness and high labor intensity, such as military industry, emergency rescue and disaster relief, and the like, not only can reduce the working intensity of human beings, but also can finish dangerous work for the human beings; among the existing mobile robots, the multi-legged walking robot adopting hydraulic pressure as a driving mode has the characteristics of high power density, high load, high bandwidth, fast response, strong disturbance resistance and the like, and is particularly suitable for heavy multi-legged walking robots.
As for a specific structure of the hexapod walking robot, as disclosed in patent document No. CN102556198A, the hexapod walking robot includes a body and six hydraulic mechanical legs uniformly arranged on both sides of the body; the six hydraulic mechanical legs are the same in structure, and all comprise root joints, buttocks, hip joints, thigh rods, knee joints and shank rods, and all have three degrees of freedom, and six robot legs; since the hexapod robot can provide stable support based on three feet and can be adapted to various walking environments better, for example, a walking robot suitable for a submarine environment is disclosed in patent document CN 106926995A.
In the walking process of the hexapod robot constructed on the basis of the hydraulic mechanical legs, the used gait plan is generally a three-foot gait state for keeping the centroid height of the robot unchanged, and the hexapod robot has better adaptability to the walking environment on the basis of three-foot support; however, in the walking process, a constant-speed pump source is generally adopted to supply hydraulic oil, namely the pressure of the supplied oil is constant, and when the robot walks in a supporting phase, the robot needs a high-pressure oil source due to the self weight and the load of the robot, and the required flow is small due to the short moving distance of a foot end; in the swing phase, low pressure oil source pressure is needed, and the required flow is larger because the moving distance of the foot end is longer. The problem that a large amount of throttling loss exists in a valve port of a constant-pressure hydraulic system, a large amount of energy is wasted easily, namely, the problem that the six-legged walking robot is high in average power and low in energy utilization rate in the walking motion process exists.
In view of the above technical problems, a common solution is to add an energy recovery system, but the whole hydraulic system is complex and the energy recovery efficiency is generally low.
Disclosure of Invention
The invention mainly aims to provide a walking gait control method of a hydraulic hexapod walking robot, which can save walking energy consumption;
another object of the present invention is to provide a hydraulic hexapod walking robot that can save walking energy consumption.
In order to achieve the main object, the control method provided by the invention is used for controlling a six-legged walking robot, the six-legged walking robot comprises a body and three hydraulic mechanical legs which are respectively arranged on two sides of the body, and each hydraulic mechanical leg comprises a root joint, a hip joint, a thigh rod, a knee joint, a shank rod and a foot end fixedly arranged on the shank rod; the control method comprises the step of controlling the hydraulic mechanical legs to walk according to the three-foot gait according to the planned foot end track so as to enable the centroid track P of the six-foot walking robotcom,z(t) is a cosine curve trajectory; under the coordinate system of the heel joint, the component of the foot end track in the advancing direction is Px(t) and the component in the vertical direction is Pz(t)＝-Pcom,z(t)+PG,z(t); wherein, Pcom,z(t) is a centroid trace curve in the geodetic coordinate system, PG,z(t) is a foot end trajectory curve under a geodetic coordinate system;
(1) within the swing phase 0< T/2,
Px(t)＝(a0+a1t+a2t2+a3t3+a4t4+a5t5+a6t6)S+si；
wherein, the constraint condition of the track parameter is Px(0)＝-S/2+si，Px(T/4)＝si，Px(T/2)＝S/2+si(ii) a Velocity Vx(0)＝-2S/T，Vx(T/2) ═ -2S/T; acceleration Ax(0)＝0，Ax(T/2)＝0；siThe position deviation of the projection of the hip joint on the horizontal plane and the centers of two extreme positions of the foot end before and after the same gait is shown, and 2S is the step length;
PG,z(t)＝b0+b1t+b2t2+b3t3+b4t4+b5t5+b6t6；
wherein, the constraint condition of the track parameter is PG,z(0)＝0，PG,z(T/4)＝h，PG,z(T/2) ═ 0; velocity VG,z(0)＝0，VG,z(T/2) ═ 0; acceleration AG,z(0)＝0，AG,z(T/2) ═ 0; h is step height;
(2) within the support phase T/2< T,
Figure BDA0002547953060000031
PG,z(t)＝0。
compared with the control method for keeping the height of the mass center approximately unchanged in the prior art, the gait with the fluctuating mass center can effectively reduce the average flow and the average power of the robot in one gait cycle, thereby effectively improving the utilization rate of energy.
The concrete scheme is that the locus of the mass center is
Figure BDA0002547953060000032
Wherein,
Figure BDA0002547953060000033
is the phase of a periodic function, HaIs the middle height of the centroid trace, hfThe undulation height of the robot centroid.
The preferred scheme is that the component of the foot end track in the transverse direction under the heel joint coordinate system is Py(t) 0, the transverse direction is perpendicular to both the advancing direction and the vertical direction. The technical scheme effectively reduces energy connection loss caused by transverse swinging.
The preferred solution is that in six hydro-mechanical legs, the hydraulic cylinder area of the middle leg is twice as large as the hydraulic cylinder area of the remaining four hydro-mechanical legs.
In order to achieve the other object, the invention provides a hexapod walking robot bagThe robot comprises a body, a control unit and three hydraulic mechanical legs which are respectively arranged on two sides of the body, wherein each hydraulic mechanical leg comprises a root joint, a hip joint, a thigh rod, a knee joint, a shank rod and a foot end fixedly arranged on the shank rod; the computer program when executed by the processor implements the steps of a control method comprising controlling the hydromechanical leg to walk in a tripodal gait according to the planned foot end trajectory such that the centroid trajectory P of the hexapod walking robotcom,z(t) is a cosine curve trajectory; under the coordinate system of the heel joint, the component of the foot end track in the advancing direction is Px(t) and the component in the vertical direction is Pz(t)＝-Pcom,z(t)+PG,z(t); wherein, Pcom,z(t) is a centroid trace curve in the geodetic coordinate system, PG,z(t) is a foot end trajectory curve under a geodetic coordinate system;
(1) within the swing phase 0< T/2,
Px(t)＝(a0+a1t+a2t2+a3t3+a4t4+a5t5+a6t6)S+si；
wherein, the constraint condition of the track parameter is Px(0)＝-S/2+si，Px(T/4)＝si，Px(T/2)＝S/2+si(ii) a Velocity Vx(0)＝-2S/T，Vx(T/2) ═ -2S/T; acceleration Ax(0)＝0，Ax(T/2)＝0；siThe position deviation of the projection of the hip joint on the horizontal plane and the centers of two extreme positions of the foot end before and after the same gait is shown, and 2S is the step length;
PG,z(t)＝b0+b1t+b2t2+b3t3+b4t4+b5t5+b6t6；
wherein, the constraint condition of the track parameter is PG,z(0)＝0，PG,z(T/4)＝h，PG,z(T/2) ═ 0; velocity VG,z(0)＝0，VG,z(T/2) ═ 0; acceleration AG,z(0)＝0，AG,z(T/2) ═ 0; h is step height;
(2) within the support phase T/2< T,
Figure BDA0002547953060000041
PG,z(t)＝0。
the concrete scheme is that the locus of the mass center is
Figure BDA0002547953060000051
Wherein,
Figure BDA0002547953060000052
is the phase of a periodic function, HaIs the middle height of the centroid trace, hfThe undulation height of the robot centroid.
The preferable proposal is that under the coordinate system of the heel joint, the component of the foot end track in the transverse direction is Py(t) 0, the transverse direction is perpendicular to both the advancing direction and the vertical direction.
The preferred solution is that in six hydro-mechanical legs, the hydraulic cylinder area of the middle leg is twice as large as the hydraulic cylinder area of the remaining four hydro-mechanical legs.
The preferred solution is that the centroid position is coplanar with the root joint position.
Drawings
FIG. 1 is a schematic structural diagram of a six-legged hydraulic robot according to an embodiment of the invention;
FIG. 2 is a schematic structural diagram of a hydromechanical leg according to an embodiment of the present invention;
FIG. 3 is a schematic structural diagram of a foot end trajectory, a root coordinate system and a geodetic coordinate system in an embodiment of the present invention;
FIG. 4 is a graph of the forward component of the foot end trajectory in a geodetic coordinate system in an embodiment of the present invention;
FIG. 5 is a graph of a centroid trace in an embodiment of the present invention;
FIG. 6 is a plot of the vertical direction component of the foot end trajectory in a geodetic coordinate system in an embodiment of the present invention;
FIG. 7 is a graph of the vertical direction component of the foot end trajectory in the root joint coordinate system in an embodiment of the present invention;
FIG. 8 is a graph of the foot end trajectory in the root joint coordinate system in an embodiment of the present invention;
FIG. 9 is a relationship between the heave height and the robot average power in the energy-saving gait with fluctuating center of mass in the embodiment of the present invention, in which the dotted line is the robot average power of the three-legged gait with unchanged centroid height, and the solid line is the robot average power of the energy-saving gait with fluctuating center of mass with different heave heights;
FIG. 10 is a graph of the comparison of the system flow of the energy-saving gait with fluctuating centroid with a constant height of centroid with the system flow of the three-legged gait with constant height of centroid in the embodiment of the invention, wherein the curve is the system flow of the robot with constant height of centroid and the solid line is the system flow of the energy-saving gait with fluctuating centroid with different heights of centroid;
FIG. 11 is an exemplary configuration and exemplary parameters of a hydromechanical leg in calculating average power and average flow in an embodiment of the present invention;
FIG. 12 illustrates exemplary structures and exemplary parameters of a root joint perimeter structure in calculating average power and average flow in an embodiment of the present invention.
Detailed Description
The invention is further illustrated by the following examples and figures.
The main idea of the present invention is to improve a control method of a hexapod walking robot to reduce energy consumption and improve energy saving, and to design a hexapod walking robot structure with reference to an existing product.
Examples
As shown in fig. 1, the six-legged walking robot 1 of the present invention includes a control unit, a body 10, a hydraulic system, a hydro-mechanical leg 11, a hydro-mechanical leg 12, a hydro-mechanical leg 13, a hydro-mechanical leg 14, a hydro-mechanical leg 15, and a hydro-mechanical leg 16, three hydro-mechanical legs are respectively disposed on two sides of the body 10, and the hydro-mechanical legs on the two sides are symmetrically arranged; in this embodiment, the structures of the six hydraulic mechanical legs are completely the same, except that the area of the hydraulic cylinder of the middle leg is twice that of the hydraulic cylinders of the other hydraulic mechanical legs, that is, the areas of the hydraulic cylinders of the hydraulic mechanical legs 13 and 14 are twice that of the hydraulic cylinders of the other hydraulic mechanical legs; the structure of the hydraulic mechanical leg is shown in fig. 2, specifically, a root joint 20, a root joint rod 27, a hip joint 21, a thigh rod 22, a knee joint 23, a shank rod 24 and a foot end 25 fixedly arranged on the shank rod 24; the hydraulic system comprises an oil liquid supply unit and a control valve assembly; the control unit comprises a processor and a memory, a computer program is stored in the memory, and when the computer program is executed by the processor, the computer program can control the hydraulic system to work based on received control instructions and detection data sent by sensors arranged on the body and the hydraulic mechanical legs, so as to drive the hydraulic actuator to perform telescopic action, control the leg rod assembly to switch the position between a supporting state and a swinging state, control the hydraulic mechanical legs to walk according to the planned foot end track, and realize the walking of the three-foot gait.
As shown in fig. 3, the single hydraulic mechanical leg is specifically divided into a support phase and a swing phase during the movement process; in the swing phase, the single leg swings forward, and the foot end 25 swings from the rear limit position PEP to the front limit position AEP; while in the support phase the legs swing back and the foot end moves from the front limit position AEP to the rear limit position PEP.
The gait planning method of the six-foot walking robot, namely the foot end track planning method, mainly comprises the following steps:
step (1), determining a moving target, a moving parameter and a moving constraint of the six-legged walking robot 1; the advancing direction of the six-legged walking robot 1 is taken as the x direction, and the height of the center of mass of the robot and the root joints of six legs of the robot are in the same horizontal plane; undulation height of robot centroid (h)f) Is the maximum height of the center of mass (H) of the robotmax) And minimum centroid height (H)min) The difference between the two; average robot height (H)a) Is the maximum height of the center of mass (H) of the robotmax) And minimum centroid height (H)min) Mean, i.e. midpoint, of; the gait cycle of the robot is T, and the time of the swing phase and the time of the support phase are both T/2; the step size is 2S and the step height is h. For better adjustment of the force distribution of the legs, the foot ends of the legs have different deviations SiDeviation S ofiIs a hip joint21 the position deviation of the projection on the horizontal plane and the center of the front limit position and the rear limit position of the foot end in the same gait, namely the deviation of the projection on the horizontal plane and the center position between the rear limit position PEP and the front limit position AEP; root joint coordinate system X of a single leg0Y0Z0And the geodetic coordinate system XGYGZGAs shown in fig. 3.
And (2) determining the track component of the foot end 25 in the x direction under the single leg root joint coordinate system:
in this step, to ensure robot stability and reduce touchdown impact, the foot end trajectory should be continuous and the velocity and acceleration should also be continuous.
(2.1) swing phase planning (0< T < T/2)
The foot end 25 of the swing phase is planned in the x-direction trajectory using a method of a sextic polynomial fit.
Let the sixth order polynomial be:
Px(t)＝(a0+a1t+a2t2+a3t3+a4t4+a5t5+a6t6)S+si
the six-term parameter constraints are shown in table 1 below:
TABLE 1 swing phase end trajectory parameter constraint table
Figure BDA0002547953060000081
(2.2) support phase planning (T/2< T < T)
Since the robot makes uniform linear motion, the foot end trajectory can be expressed as:
Figure BDA0002547953060000082
so that the trajectory of the foot end trajectory in the forward direction throughout the gait cycle T is as shown in figure 4.
Step (3), planning the fluctuation track of the center of mass of the robot:
adding mass center fluctuation in the Z direction in the motion of the robot, wherein a cos curve is used as a robot mass center curve track; the trajectory may be expressed as:
Figure BDA0002547953060000091
wherein,
Figure BDA0002547953060000092
is the phase of a periodic function.
So that the centroid trace is as shown in figure 5 throughout the gait cycle T.
And (4) determining the track component of the foot end 25 in the z direction under the geodetic coordinate system:
(4.1) swing phase planning (0< T < T/2)
The trajectory of the foot 25 in the z-direction of the geodetic coordinate system is planned using a method of fitting a sixth order polynomial, such that the sixth order polynomial is:
PG,z(t)＝b0+b1t+b2t2+b3t3+b4t4+b5t5+b6t6
the polynomial parameter constraints are shown in table 2 below.
TABLE 2 swing phase end trajectory parameter constraint table
Figure BDA0002547953060000093
Figure BDA0002547953060000101
(4.2) support phase planning (T/2< T < T)
Since the robot makes uniform linear motion, the foot end trajectory can be expressed as:
PG,z(t)＝0
so that the trace of the foot end trace in the vertical direction in the whole gait cycle T is shown in figure 6.
And (5) determining the track component of the foot end 25 in the z direction under the single-leg root joint coordinate system:
from the coordinate system relationship shown in fig. 2, the locus of the foot end in the z direction of the coordinate system of the single-leg root joint can be obtained, and the formula can be expressed as follows:
Pz(t)＝-Pcom,z(t)+PG,z(t)
i.e. in the wobble phase (0< T/2) can be expressed as:
Figure BDA0002547953060000102
and in the support phase (T/2< T) can be expressed as:
Figure BDA0002547953060000103
the vertical component of the foot end trajectory over the gait cycle T is thus shown in figure 7.
And (6) determining the track component of the foot end 25 in the y direction under the single-leg root joint coordinate system:
since the robot makes a uniform linear motion, there is no motion in the y direction, and the component in this direction can be expressed as:
Py(t)＝0
thus, the foot end trajectory is shown in fig. 8 throughout the gait cycle T.
Based on the gait plan, the control method of the hexapod walking robot comprises the following steps, namely when a processor executes a computer program stored in a memory, the following steps can be realized:
controlling the hydraulic mechanical legs to walk according to the planned foot end track and the three-foot gait so as to enable the mass center track P of the six-foot walking robotcom,z(t) is a cosine curve track, and the component of the track at the foot end in the advancing direction is P under a heel joint coordinate systemx(t) the component in the vertical direction is Pz(t)＝-Pcom,z(t)+PG,z(t) and the component in the transverse direction is Py(t) of (d). Wherein:
(1) within the swing phase 0< T/2,
Px(t)＝(a0+a1t+a2t2+a3t3+a4t4+a5t5+a6t6)S+si；
wherein, the constraint condition of the track parameter is Px(0)＝-S/2+si，Px(T/4)＝si，Px(T/2)＝S/2+si(ii) a Velocity Vx(0)＝-2S/T，Vx(T/2) ═ -2S/T; acceleration Ax(0)＝0，Ax(T/2)＝0；siThe position deviation between the projection of the hip joint on the horizontal plane and the centers of two extreme positions of the foot end before and after the same gait is shown, and 2S is the step length.
PG,z(t)＝b0+b1t+b2t2+b3t3+b4t4+b5t5+b6t6；
Wherein, the constraint condition of the track parameter is PG,z(0)＝0，PG,z(T/4)＝h，PG,z(T/2) ═ 0; velocity VG,z(0)＝0，VG,z(T/2) ═ 0; acceleration AG,z(0)＝0，AG,z(T/2) ═ 0; h is step height.
(2) Within the support phase T/2< T,
Figure BDA0002547953060000121
PG,z(t)＝0。
the transverse component is P during the whole gait cycley(t)＝0。
(3) The centroid trajectory is:
Figure BDA0002547953060000122
wherein,
Figure BDA0002547953060000123
is the phase of a periodic function, HaIs the middle height of the centroid trace, hfThe undulation height of the robot centroid.
Based on the foregoing control method, the dimensional parameters of the hydraulic robot according to the example are: root joint rod length L0 ═ 0.1m, thigh rod length L1 ═ 0.4m, shank rod length L2 ═ 0.448m, front and rear leg hydraulic cylinder piston diameters: 0.02m, the diameter of a piston rod is 0.014m, the diameter of a piston of a middle-leg hydraulic cylinder is as follows: 0.04m, and the diameter of the piston rod is 0.028 m; the gait parameters of the curve shown in fig. 9 are s-0.24 m, T-1 s, h-0.1 m, s 1-s 2-0.17 m, s 3-s 4-0.09, s 5-s 6-0.13 m, and Ha-0.75 m; and the gait parameters of the curve shown in fig. 10 are: s-0.24 m, T-1 s, h-0.1 m, s 1-0.17 m, s 3-0.09, s 5-0.82-0.13 m, Ha-0.75 m, hf-0.02 m,
Figure BDA0002547953060000124
(the pressure of the hydraulic system is 30MPa) is calculated based on an experimental model, and the relation between the fluctuation height and the robot average power in the energy-saving gait with fluctuation of the mass center is obtained as shown in figure 9, wherein the dotted line in the figure is the robot average power of the three-legged gait with unchanged height of the mass center, and the solid line is the robot average power of the energy-saving gait with fluctuation of the mass center with different fluctuation heights. Fig. 10 is a comparison graph of the system flow of the energy-saving gait with fluctuating centroid and the tripodal gait with constant height centroid in the embodiment of the invention, wherein the curve is the system flow of the robot with the tripodal gait with constant height centroid, and the solid line is the system flow of the energy-saving gait with fluctuating centroid with different height centroid.
In the above calculation, as shown in fig. 11 and 12, specific exemplary parameters in the calculation process are shown in table 3 below:
TABLE 3 calculation of example parameters
Figure BDA0002547953060000131
Wherein, CiIs a hydraulic cylinder, ai、biIs the connector length.
From fig. 9 and fig. 10, it can be found that the energy-saving gait with fluctuating centroid can effectively reduce the average flow and average power of the robot in one period, so as to achieve the energy-saving effect, and the maximum energy-saving efficiency can reach more than 10%.

Claims (10)

1. A control method of a hexapod walking robot comprises a body and three hydraulic mechanical legs which are respectively arranged on two sides of the body, wherein each hydraulic mechanical leg comprises a root joint, a hip joint, a thigh rod, a knee joint, a shank rod and a foot end fixedly arranged on the shank rod; the method is characterized in that:
the control method comprises the step of controlling the hydraulic mechanical legs to walk according to the planned foot end track and the three-foot gait so as to enable the mass center track P of the six-foot walking robotcom,z(t) is a cosine curve trajectory; under a heel joint coordinate system, the component of the foot end track in the advancing direction is Px(t) and the component in the vertical direction is Pz(t)＝-Pcom,z(t)+PG,z(t); wherein, Pcom,z(t) is a centroid trace curve in the geodetic coordinate system, PG,z(t) is a foot end trajectory curve under a geodetic coordinate system;
(1) within the swing phase 0< T/2,
Px(t)＝(a0+a1t+a2t2+a3t3+a4t4+a5t5+a6t6)S+si；
wherein, the constraint condition of the track parameter is Px(0)＝-S/2+si，Px(T/4)＝si，Px(T/2)＝S/2+si(ii) a Velocity Vx(0)＝-2S/T，Vx(T/2) ═ -2S/T; acceleration Ax(0)＝0，Ax(T/2)＝0；siThe position deviation of the projection of the hip joint on the horizontal plane and the centers of two extreme positions of the foot end before and after the same gait is shown, and 2S is the step length;
PG,z(t)＝b0+b1t+b2t2+b3t3+b4t4+b5t5+b6t6；
wherein, the constraint condition of the track parameter is PG,z(0)＝0，PG,z(T/4)＝h，PG,z(T/2) ═ 0; velocity VG,z(0)＝0，VG,z(T/2) ═ 0; acceleration AG,z(0)＝0，AG,z(T/2) ═ 0; h is step height;
(2) within the support phase T/2< T,
Figure FDA0002547953050000011
PG,z(t)＝0。
2. the control method of claim 1, wherein the centroid trajectory is:
Figure FDA0002547953050000012
wherein,
Figure FDA0002547953050000021
is the phase of a periodic function, HaIs the middle height of the centroid trace, hfThe undulation height of the robot centroid.
3. The control method according to claim 1 or 2, characterized in that:
under the heel joint coordinate system, the component of the foot end track in the transverse direction is Py(t) 0, the transverse direction being perpendicular to both the advancing direction and the vertical direction.
4. The control method according to any one of claims 1 to 3, characterized in that:
in the six hydro-mechanical legs, the hydraulic cylinder area of the middle leg is twice as large as the hydraulic cylinder area of the remaining four hydro-mechanical legs.
5. The control method according to any one of claims 1 to 4, characterized in that:
the centroid position is coplanar with the root joint position.
6. A six-foot walking robot comprises a body, a control unit and three hydraulic mechanical legs which are respectively arranged on two sides of the body, wherein each hydraulic mechanical leg comprises a root joint, a hip joint, a thigh rod, a knee joint, a shank rod and a foot end fixedly arranged on the shank rod; the method is characterized in that:
the computer program, when executed by the processor, performs the steps of a control method comprising controlling the hydromechanical leg to walk in a tripodal gait according to the planned foot end trajectory such that the centroid trajectory P of the hexapod walking robotcom,z(t) is a cosine curve trajectory; under a heel joint coordinate system, the component of the foot end track in the advancing direction is Px(t) and the component in the vertical direction is Pz(t)＝-Pcom,z(t)+PG,z(t); wherein, Pcom,z(t) is a centroid trace curve in the geodetic coordinate system, PG,z(t) is a foot end trajectory curve under a geodetic coordinate system;
(1) within the swing phase 0< T/2,
Px(t)＝(a0+a1t+a2t2+a3t3+a4t4+a5t5+a6t6)S+si；
wherein, the constraint condition of the track parameter is Px(0)＝-S/2+si，Px(T/4)＝si，Px(T/2)＝S/2+si(ii) a Velocity Vx(0)＝-2S/T，Vx(T/2) ═ -2S/T; acceleration Ax(0)＝0，Ax(T/2)＝0；siThe position deviation of the projection of the hip joint on the horizontal plane and the centers of two extreme positions of the foot end before and after the same gait is shown, and 2S is the step length;
PG,z(t)＝b0+b1t+b2t2+b3t3+b4t4+b5t5+b6t6；
wherein, the constraint condition of the track parameter is PG,z(0)＝0，PG,z(T/4)＝h，PG,z(T/2) ═ 0; velocity VG,z(0)＝0，VG,z(T/2) ═ 0; acceleration AG,z(0)＝0，AG,z(T/2) ═ 0; h is step height;
(2) within the support phase T/2< T,
Figure FDA0002547953050000031
PG,z(t)＝0。
7. the hexapod walking robot of claim 6, wherein the centroid trajectory is:
Figure FDA0002547953050000032
wherein,
Figure FDA0002547953050000033
is the phase of a periodic function, HaIs the middle height of the centroid trace, hfThe undulation height of the robot centroid.
8. The hexapod walking robot according to claim 6 or 7, wherein:
under the heel joint coordinate system, the component of the foot end track in the transverse direction is Py(t) 0, the transverse direction being perpendicular to both the advancing direction and the vertical direction.
9. A hexapod walking robot according to any of claims 6-8 wherein:
in the six hydro-mechanical legs, the hydraulic cylinder area of the middle leg is twice as large as the hydraulic cylinder area of the remaining four hydro-mechanical legs.
10. A hexapod walking robot according to any one of claims 6 to 9 wherein:
the centroid position is coplanar with the root joint position.
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