CN112987769A - Active leg adjusting method for stable transition of quadruped robot in variable-rigidity terrain - Google Patents
Active leg adjusting method for stable transition of quadruped robot in variable-rigidity terrain Download PDFInfo
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Abstract
The invention provides a leg active adjusting method for a quadruped robot in variable-rigidity terrain stable transition, which comprises the following steps: when the robot lands with diagonal gait, the equivalent length of diagonal legs of the robot is adjusted according to the deviation angle of the robot body, so that the robot body is balanced; in the soaring state, the swing angle of the leg is controlled by planning the position of a foot falling point of the robot to realize the control of the forward speed; when the robot is in the air and lands, compensating the equivalent stiffness of diagonal legs of the robot into the active variable stiffness calculation of the legs to adjust the equivalent leg length, thereby realizing the correction of the pitching attitude of the body; the landing phase posture is subjected to feedback control, and the change of the virtual spring stiffness of the robot is adjusted in real time according to the change of the landing body of the robot, so that a better balance effect is obtained; additional energy compensation is provided for robot jumping by increasing robot leg motor power at the beginning of the next jump cycle. The invention simply and effectively solves the problem that the robot is not easy to fall down when walking on the ground with different hardness.
Description
Technical Field
The invention belongs to the technical field of quadruped robot motion research, and particularly relates to a leg active adjusting method for quadruped robot in variable-rigidity terrain stable transition.
Background
Compared with most of wheeled and crawler-type mobile robots, the foot-type bionic robot has stronger adaptability in a non-structural environment. The quadruped robot has obvious advantages in the aspect of comprehensive evaluation factors such as stability, dynamic performance, control difficulty and the like, so that the quadruped robot has wide attention paid by researchers in the fields of home service, disaster relief and the like
However, the ground surface conditions are complex and various, and the stable transition of the quadruped robot on various grounds under the environment is not easy to realize. Will Bosworth et al found that real-time ground characteristic measurements and controller adaptation are required for transition from hard to soft surfaces through dynamic jumping experiments between soft and hard ground by a Super Mini Cheetah robot and in-situ measurements of ground impedance and friction to improve dynamic motion performance in unknown variable terrain. Meanwhile, the rigidity and the damping under different environmental conditions are not consistent, when the front legs of the four-legged robot step on soft ground (such as grassland), the rear legs are positioned on hard road (such as asphalt road), the rigidity difference of the ground where the front and rear feet are positioned is obvious, and if proper adjustment is not carried out, the robot can cause the self posture to incline or even overturn due to the difference.
The following three methods are commonly adopted in academia for the problem of how to ensure the stable posture of the quadruped robot on the complex terrain. One is based on the zero moment point (abbreviated as ZMP). Zhou Kun et al planned the gait of crawling based on ZMP's steady state criterion, through the height and the slope parameter information of the unknown topography of perception that falls to the ground of swing leg, adjusted each supporting leg length in real time and be used for adjusting barycenter height and fuselage gesture, realized the self-adaptation to the walking of unknown complicated topography steadily. However, when the quadruped robot travels with a high-speed gait such as a rapid diagonal sprint, there may be a case where only two legs land or even the quadruped soaks simultaneously and cannot satisfy the support polygon. The second is a method using a Central Pattern Generator (CPG) to reference the rhythmic movement of the quadruped. Werwell and the like use a bionic spine structure to provide a diagonal running motion control strategy suitable for rough variable terrain, and sense the body state and the foot end contact force of the robot to adjust the planned gait based on the principle of CPG. However, the CPG-based method is usually too highly dependent on parameters, the controller design is complicated, and the CPG-based method is mostly applied to static gait. The third is to adopt a flexible leg joint mechanism to deal with the change of the external environment. Experiments prove that the passive variable-stiffness leg compliance can improve the moving speed and efficiency of the autonomous dynamic operation robot to adapt to the change of terrain and effective load for the first time. Edin Koco et al designed a quadruped robotic variable leg passive compliance unit (VPC) for variable stiffness terrain that varied the leg stiffness in a closed-loop manner to accommodate varying terrain characteristics, ensuring constant frequency hopping over a wide range of terrain stiffness variations. (Christie M D, Sun S, Ning D H, et al. A high viscous-adjustable robot leg for enhancing the comfort of human beings. mechanical Systems and Signal Processing,2019,126(JUL.1):458) adopts the method of rolling spring loading inverted pendulum (R-SLIP) morphology, and proposes a variable stiffness leg of a magneto-rheological fluid center (MRF) and a flexible joint (apVSJ) based on active and passive variable stiffness designed by Zhang et al. However, the method using the variable-stiffness flexible joint tends to cause the leg inertia and the overall structure size to be larger, and the dynamic response performance of the robot is affected.
In the research on the quadruped robot, a plurality of problem academic circles in many aspects provide solutions to various problems, so that the quadruped robot is more and more mature. Nevertheless, the quadruped robot itself still has many problems to be solved, for example, most studies on quadruped robots are now based on the premise of flat ground, and less studies on walking control in a non-flat ground state are performed. In addition, most of previous researches on walking of the robot under different ground rigidity conditions rely on a camera, a radar, ground imaging and the like, so that the complexity of the robot is increased, the cost is increased, and the large-scale popularization is not facilitated. Moreover, many current research methods are good, but are too complex, and the cost is high regardless of calculation or principle. Therefore, how to simply solve the problem that the quadruped robot is difficult to fall down when walking under different situations with different surface softness and hardness is a urgent need to solve at present.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides the active leg adjusting method for the quadruped robot in variable-rigidity terrain stable transition, the method is simple in calculation and low in cost, and the problem that the quadruped robot is not easy to fall down when walking under the condition of different ground hardness is solved.
In order to solve the technical problems, the invention adopts the following technical scheme:
a leg active adjusting method of a quadruped robot in stable transition on variable-rigidity terrain is characterized by comprising the following steps:
s1: when the quadruped robot lands on the ground with diagonal gait, analyzing the body posture of the robot under the diagonal gait, calculating the body offset angle, and adjusting the equivalent length of diagonal legs of the robot according to the body offset angle of the robot to balance the body;
s2: under the soaring state of the robot, the swing angle of the leg is controlled by planning the position of a foot falling point of the robot in the soaring stage to realize the control of the forward speed;
s3: when the robot is in the air and lands on the ground, compensating the equivalent stiffness of diagonal legs of the robot into the active variable stiffness calculation of the legs to adjust the equivalent leg length, thereby realizing the correction of the pitching attitude of the body;
s4: the landing phase attitude of the quadruped robot is subjected to feedback control, the change of the robot body is obtained in real time, and the change of the virtual spring stiffness of the robot is adjusted in real time according to the change of the robot landing body, so that a better balance effect is obtained;
s5: additional energy compensation is provided for robot jumping by increasing robot leg motor power at the beginning of the next robot jump cycle.
Further, in step S1, an angular rate gyro on the robot body receives a signal that the body has deflected, the angular rate gyro changes its own deflection angular rate in accordance with the received deflection signal, and the angular rate w at which the gyro deflectscThe following relationships exist with the robot fuselage deflection angle:
diagonal velocity wcCalculating integral to obtain the body offset angle thetabodyThe main control equipment deviates the angle theta according to the received machine bodybodyAnd angular velocity wcThe pulse signals required by the leg motor of the robot are determined, and the rotation angle of the leg motor of the robot is controlled through the number of the pulse signals, so that the equivalent length of diagonal legs is changed, and the machine body is balanced.
Further, in step S2, forward speed control is implemented by planning the flight phase foot position, which is specifically controlled by the following formula:
in the formula, xf,dFor the desired forward footfall point position of the virtual spring leg,
is the actual horizontal velocity of the fuselage and,
is the desired horizontal speed of the fuselage, KpFor feedback of error gain, TsIs the landing time;
a state machine is introduced into the motion of four legs to judge the flight position, the swing angle of the legs is planned through a polynomial based on position control, corresponding expected joint angles are obtained through inverse kinematics calculation, the difference values are converted into corresponding joint moments through a PD controller through comparison with real-time joint angles to be used for driving the joints of the robot to rotate, so that a pair of diagonal legs touch the ground according to an appropriate ground contact angle, the robot obtains appropriate net forward acceleration, and the robot body accelerates or decelerates to reach an expected horizontal velocity value.
Further, in step S2, the corresponding desired joint angles are obtained by inverse kinematics solution specifically using the following format:
in the formula, L0Virtual leg length, L1Is the length of the thigh, L2Is the length of the lower leg, θ1For a side swing hip joint angle, theta2Angle of anterior swing of hip joint, theta3Angle of knee joint, xf,dFor the expected forward foot-drop position, X, of the virtual spring legsThe vertical distance traveled by the leg end side;
and calculating the angle of each joint at the expected foot drop point according to the formula, and comparing the real-time angle with the calculated angle so as to adjust the rotation angle of the motor at each joint.
Further, in step S3, a robot leg active variable stiffness adjustment formula is established to realize adjustment control of the robot leg virtual spring stiffness, where the formula is specifically as follows:
maz+mg＝(k1+Δk)x4cos(θ4(t))+k1x1cos(θ1(t))
where Δ k is the equivalent stiffness change amount, k1Is the coupling stiffness, x, of one of a pair of diagonal legs in contact with soft ground1One of a pair of diagonal legs has an equivalent compression amount, x, with the ground4The equivalent amount of compression of the other of a pair of diagonal legs with the ground, azAcceleration in the vertical direction of the fuselage, g is gravity acceleration, and a is pitch angle accelerationyIs a pitch angle thetapitchPerforming secondary differentiation on time, wherein theta 1(t) is an equivalent swing angle of one leg of a pair of diagonal legs, theta 4(t) is an equivalent swing angle of the other leg of the pair of diagonal legs, m and J are the mass and the moment of inertia of the airplane body respectively, and L is the length of the airplane body;
the two formulas are simultaneously solved to obtain the virtual equivalent stiffness variation delta k:
adding delta k into the rigidity calculation of the leg to be compensated, realizing the adjustment of the rigidity value of the leg through a main controller program, and further converting the rigidity value into the knee joint moment tau3So as to adjust the equivalent leg length and further realize the correction of the pitching attitude of the body.
Further, in step S4, for the attitude offsets generated during the motion of the four sets of robots, the robot virtual spring rate variation is adjusted by the following formula:
in the formula taupitchFor adjusting the pitch angle of the fuselage, τrollFor adjusting the roll angle of the fuselage, Kp_pitchPosition feedback gain for fuselage pitch angle, Kp_rollPosition feedback gain of fuselage roll angle, Kv_pitchSpeed feedback gain of fuselage pitch angle, Kv_rollSpeed feedback gain of fuselage roll angle, θpitchIs made into a machineBody pitch angle θrollAs the roll angle of the fuselage, the pitch angle,
is the angular velocity of the pitch angle of the fuselage,
angular velocity, θ, being the roll angle of the fuselagepitch_desireTo a desired pitch angle, θroll_desireAt a desired roll angle, wherein θpitch_desire、θroll_desireTypically set to 0.
In the formula thetapitch、θroll、
The pitch angle and the roll angle of the body and the corresponding pitch angle speed and roll angle speed are obtained by integrating corresponding data measured by a gyroscope, the adjusting torque of each leg joint is calculated according to the two formulas, the adjusting torque is converted into the torque and the rotating speed of the motor through a program and acts on the motor to be adjusted, and corresponding pulse signals are applied to different motors.
Compared with the prior art, the invention has the beneficial effects that: the leg active variable stiffness adjusting strategy based on motion equation derivation provided by the invention has the advantages that the adjusting method combining the strategy and the attitude feedback enables the pitching attitude of the robot body to obtain a better control effect, the problem that the quadruped robot is not easy to fall down when walking under the condition of different ground hardness is simply and effectively solved, and compared with other complicated methods, the control method is simple and can ensure that the lateral rolling attitude of the robot body is kept within a certain error range; in addition, the method does not need to change the joints of the robot, reduces the overall redundancy, and can realize the self-adaptation of the adjustment process for the walking gaits such as diagonal jogging.
Drawings
FIG. 1 is a schematic diagram of attitude deviation of a quadruped robot on a variable-stiffness ground according to an embodiment of the invention;
FIG. 2 is a schematic diagram illustrating the serial numbers of the legs of the robot according to the embodiment of the present invention;
FIG. 3 is a schematic diagram of a single-leg analysis of a quadruped robot according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of the control of the flight phase of the quadruped robot according to the embodiment of the present invention;
FIG. 5 is a schematic diagram of a control scheme of a four-legged robot landing phase according to an embodiment of the present invention;
FIG. 6 is a diagram of a three-dimensional mockup of a robot according to an embodiment of the invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the following embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict.
The present invention is further illustrated by the following examples, which are not to be construed as limiting the invention.
And analyzing the transition situation of the quadruped robot under the variable-rigidity ground. When the quadruped robot lands, because the front supporting leg foot-falling point is positioned on the ground with smaller rigidity and the rear supporting leg foot-falling point is positioned on the other ground with larger rigidity, when the two virtual spring legs on the ground have the same rigidity and the contact forces of the foot ends are different, the compression amount of the two legs is different, and then the robot body connected with the leg parts is overturned to a larger extent. If the robot is not adjusted in time, the attitude offset of the robot is accumulated, and when the accumulated amount reaches a certain degree, the robot body collides with the ground, so that a mechanical structure and electronic equipment are damaged. In view of the existing problems, the invention provides a leg active adjustment method of a quadruped robot in stable transition on variable-stiffness terrain, which aims to solve the problem of fuselage balance caused by transition on variable-stiffness terrain, and comprises the following steps:
s1: when the quadruped robot lands on the ground with diagonal gait, analyzing the body posture of the robot under the diagonal gait, calculating the body offset angle, and adjusting the equivalent length of diagonal legs of the robot according to the body offset angle of the robot to balance the body;
when the quadruped robot lands on the ground with a diagonal gait, the motion of the robot is analyzed, and the motion equation of the robot is given, wherein the equation is as follows:
maz＝k4x4 cos(θ4(t))+k1x1 cos(θ1(t))-mg (1)
in the formula, k1Is the coupling stiffness, k, of one of a pair of diagonal legs when in contact with the ground4Is the coupling stiffness, x, of the other of a pair of diagonal legs in contact with the ground1One of a pair of diagonal legs has an equivalent compression amount, x, with the ground4The equivalent amount of compression of the other of a pair of diagonal legs with the ground, azAcceleration in the vertical direction of the fuselage, g is gravity acceleration, and a is pitch angle accelerationyIs a pitch angle thetapitchPerforming secondary differentiation on time, wherein theta 1(t) is an equivalent swing angle of one leg of a pair of diagonal legs, theta 4(t) is an equivalent swing angle of the other leg of the pair of diagonal legs, m and J are the mass and the moment of inertia of the airplane body respectively, and L is the length of the airplane body;
with reference to fig. 1, the coordinate system { G } is a global coordinate system fixed on the ground, the positive direction of the coordinate axis X is the horizontal advancing direction of the quadruped robot, the negative direction of the coordinate axis Z is the direction of the gravitational acceleration, L is the length of the robot body, and the mass and the moment of inertia of the robot body are m, J, k, respectivelyhardGround stiffness, k, for hard (hard) groundsoftGround stiffness for soft (soft) ground, chardDamping value for hard (hard) ground, csoftRespectively, the damping values of soft (soft) ground. The contact between the ground and the virtual spring leg is equivalent to the series connection of two springs, so that the grounding leg (i) can be in contact with the soft groundStiffness k of coupling1And the coupling stiffness k when the leg comes into contact with a hard floor4Calculating according to hardware configuration of a robot body (a motor between a lower leg and a thigh of the robot and a motor in two directions of a shoulder of the robot), namely, the product of the number of frontal pulses emitted by the motor and the equivalent of the pulses can obtain three angles of one leg: the calf angle, the thigh angle, and the shoulder angle. The equivalent length l of the thigh is obtained according to the trigonometric theorem by the shank corner and the thigh corner*Namely:
l*＝lcosθ (3)
the equivalent length of the shank is obtained by the law of trigonometry, theta is the angle turned by the thigh motor, and l is the length of the thigh. The sum of the equivalent lengths of the lower leg and the thigh is the equivalent length of the whole leg (namely the vertical distance from the shoulder of the robot to the ground), the difference between the equivalent length of the lower leg and the equivalent length of the diagonal leg is delta l, and then the triangle theorem is calculated, namely:
l is the length of the fuselage, namely the vertical distance of the diagonal legs, and theta is obtained by the formula (4)pitchAnd (4) the pitch angle of the fuselage.
Due to the difference in stiffness of the coupling of the legs to the ground, i.e. k1And k is4Not equal, specifically, k can be calculated by the calculation formula of the coupling stiffness when the landing leg is in contact with the ground1And k is4The calculation formulas are respectively as follows:
in the formula, the number kleg、khard、ksoftGround of equivalent stiffness, hard (hard) ground and soft (soft) ground of robot leg respectivelyFace stiffness.
K can be calculated by the above formula1And k is4Inequality, the diagonal angle shank is to the inequality of the reaction force of fuselage promptly, then can lead to the fuselage to rotate, and the transform can appear in the fuselage gesture, and the fuselage appears the unbalance and will make the angular rate gyroscope signal on the organism change to obtain the angular rate that the gyroscope takes place to deflect, calculate by following formula:
diagonal velocity wcCalculating integral to obtain the body offset angle thetabodyAccording to the calculated body offset angle thetabodyThe main control equipment determines pulse signals required by a leg motor of the robot through a program, controls the size of a motor corner through the number of the pulse signals, and then changes the equivalent length of a diagonal leg according to a triangular law, so that the machine body is balanced.
S2: under the soaring state of the robot, the swing angle of the leg is controlled by planning the position of a foot falling point of the robot in the soaring stage to realize the control of the forward speed;
when the robot is adjusted during jumping, the description will be given with reference to the schematic distribution diagram of each leg of the robot in fig. 2. The sequence numbers of the legs are (i), (ii), (iii), (iv), and (iii) are opposite-angle legs and (iii) are another pair.
With regard to the forward speed, the position of the foot end of the robot that touches down after the end of the flight directly affects the acceleration in the subsequent landing state. In order to achieve the purpose of accelerating or decelerating the robot, the control system introduces asymmetry to adjust the magnitude of the forward speed so that the forward speed can be changed from one forward speed to another forward speed, namely the rotation speed and the torque of the motor are indirectly changed by adjusting a pulse signal input into the motor through the main control device. Control of forward speed by planning the position of the foot-falling point during the flight phase, i.e.
In the formula (6), xf,dFor the desired forward footfall point position of the virtual spring leg,
actual and desired horizontal speeds of the fuselage, KpFor feedback of error gain, TsIs the landing time.
The motion of four legs is introduced into a state machine to judge the soaring state, the swing angle of the legs is planned through a polynomial based on position control, corresponding expected joint angles are obtained through inverse kinematics calculation, and the following formula is provided by combining with the graph 3:
in the above formula, L0The virtual leg length is a constant value, L1Is the length of the thigh, L2Is the length of the lower leg, θ1For a side swing hip joint angle, theta2Angle of anterior swing of hip joint, theta3Angle of knee joint, xf,dPosition of forward foot-drop point desired for virtual spring leg, xsThe vertical distance traveled by the leg end side, i.e., the vertical distance of the planned landing point.
Comparing the obtained angle with the real-time motor rotation position angle, landing a pair of diagonal legs (taking the legs I and II as examples) according to a proper ground contact angle, enabling the foot landing points to be far away from or close to a neutral point, enabling the robot to obtain proper net forward acceleration, and accelerating or decelerating the robot body so as to achieve a desired horizontal speed value. While the other pair of diagonal legs is swung into position to prepare for touchdown for the next cycle of touchdown.
As shown in FIG. 3, τ1、τ2、τ3The drive moments of the side swing hip joint, the front swing hip joint and the knee joint respectively, and L1, L2 and r (t) are the lengths of the thigh, the shank and the equivalent spring leg respectively. Theta1、θ2、θ3And theta (t) is a side swing hip joint angle, a front swing hip joint angle, a knee joint angle and an equivalent swing angle respectively. The real-time anterior swing hip joint and knee joint angle information can be obtained by calculating the geometric relation, and the actual lateral swing hip joint angle theta1The rotation angle is obtained by measuring by an angle sensor arranged at the position of the side-sway joint, after the rotation angle is obtained, the angle which needs to be rotated by the corresponding motor at each joint can be obtained by the product of the pulse number of the motor and the stepping angle of the motor, and the specific control flow of the four-footed robot emptying phase is shown in figure 4.
S3: when the robot is in the air and lands on the ground, compensating the equivalent stiffness of diagonal legs of the robot into the active variable stiffness calculation of the legs to adjust the equivalent leg length, thereby realizing the correction of the pitching attitude of the body;
in the step, the active stiffness-changing adjusting process is to indirectly control the virtual spring stiffness control of the robot leg by controlling the motor power of the robot leg, and the following calculation formula is specifically given:
maz+mg＝(k1+Δk)x4 cos(θ4(t))+k1x1 cos(θ1(t)) (13)
where Δ k is the equivalent stiffness change amount, k1Is the coupling stiffness, x, of one of the diagonal legs (i) when in contact with the soft ground1Is the equivalent compression of the legs (i) in the diagonal legs with the groundAmount, x4The equivalent compression amount of the leg (a) of the pair of diagonal legs to the groundzAcceleration in the vertical direction of the fuselage, g is gravity acceleration, and a is pitch angle accelerationyIs a pitch angle thetapitchThe second differentiation of time, theta 1(t) is the equivalent swing angle of a leg (I) in the diagonal legs, theta 4(t) is the equivalent swing angle of the leg (II) in the diagonal legs, m and J are the mass and the moment of inertia of the airplane body respectively, and L is the length of the airplane body;
the virtual equivalent stiffness variation Δ k can be obtained by simultaneous solution of the above equations (8) and (9):
equivalent compression x in the above equation1、x4Are respectively as
In the above formula, V0The vertical speed of the robot when the current gait cycle lands on the ground, the initial time of the integral time t is the time when the robot body falls to the lowest point, and the termination time is the time when the robot body leaves the ground under the current gait cycle
wyIs the pitch angle velocity of the fuselage, azIs the acceleration of the fuselage in one vertical direction resulting from the ground reaction force.
In combination with the above formula in this step, a vertical velocity formula when the robot lands on the ground in the current gait cycle is given here, that is:
V0the vertical speed of the robot during landing in the current gait cycle can be estimated by adopting the speed during landing in the previous cycle, the time from falling to the lowest point to foot end to ground is taken as the lower integration limit, the time from falling to the lowest point to ground is taken as the upper integration limit, the time at the moment of flying to ground is taken as the upper integration limit, the upper control system time limit and the lower control system time limit are obtained by state conversion calculation of a state machine, and the vertical speed during landing in the previous state cycle can be obtained by integrating the acceleration. After the robot is emptied from the ground, the action of external factors such as air resistance and the like is ignored, and the whole robot is only influenced by self gravity at the moment, so that the speed variation between the grounding time of the current period and the grounding time of the previous period can be obtained by the product of the time difference between the ground leaving of the previous period and the grounding of the current period and the acceleration of gravity, and V can be obtained0The calculation formula of (2).
Calculating V0In the formula (a) of (b),
respectively the ground-off time and the ground-on time of the previous step-state period,
g is the gravitational acceleration as the landing time of the current cycle.
Finally, x obtained by calculation1、x4Substituting other measured values into a formula (15) to obtain the equivalent stiffness delta k, adding the delta k into the calculation of the stiffness k of the leg to be compensated, realizing the adjustment of the stiffness value of the leg through a main controller program, and converting the stiffness value into the knee joint moment tau3Here, the following conversion formula is given:
k＝k0+Δk
F＝k(L0-L)
wherein k is0To leg equivalent stiffness, L0The length of the virtual leg at the time of starting to touch the ground, and L is the length of the virtual leg compressed by the contact with the ground. Here, with reference to FIG. three in step 2, the parameter L can be found1,L2,θ3And then adjusting the rotating angle and speed of the corresponding motor according to the calculated joint torque adjustment pulse input so as to indirectly adjust the equivalent leg length, thereby realizing the correction of the pitching attitude of the body.
S4: the landing phase attitude of the quadruped robot is subjected to feedback control, the change of the robot body is obtained in real time, and the change of the virtual spring stiffness of the robot is adjusted in real time according to the change of the robot landing body, so that a better balance effect is obtained;
most of the work of controlling the robot body is finished at the moment, and finally feedback adjustment of the robot body in the walking process of the robot is added, so that the robot body is controlled more accurately by combining with a graph 5. The control of the robot body is mainly embodied in the pitch angle of the robot body and the offset and angle change of the robot body on two sides in the walking process of the robot, and the intuitive embodiment of the changes can cause the difference between the gyroscope and the ideally set state angle.
For attitude deviation generated during the motion of four groups of robots, the conventional solution is to apply reaction force to the fuselage by using legs when landing, namely:
in the formula taupitchFor adjusting the pitch angle of the fuselage, τrollFor adjusting the roll angle of the fuselage, Kp_pitchPosition feedback gain for fuselage pitch angle, Kp_rollPosition feedback gain of fuselage roll angle, Kv_pitchSpeed feedback for fuselage pitch angleGain, Kv_rollSpeed feedback gain of fuselage roll angle, θpitchAt fuselage pitch angle, θrollAs the roll angle of the fuselage, the pitch angle,
is the angular velocity of the pitch angle of the fuselage,
angular velocity, θ, being the roll angle of the fuselagepitch_desireTo a desired pitch angle, θroll_desireAt a desired roll angle, wherein θpitch_desire、θroll_desireTypically set to 0.
In the formula thetapitch、θroll、
The pitch angle and the roll angle of the body and the corresponding pitch angle speed and roll angle speed are obtained by integrating corresponding data measured by a gyroscope, the adjusting torque tau of each leg joint is calculated according to the two formulas, the adjusting torque tau is converted into the torque and the rotating speed of the motor through a program and acts on the motor needing to be adjusted, and corresponding pulse signals are applied to different motors. The step applies a reaction force to the body by using the moment change of the motor of the leg part of the robot, and the force generated by the leg part is reacted to the body, thereby offsetting the deviation of the body posture.
S5: additional energy compensation is provided for robot jumping by increasing robot leg motor power at the beginning of the next robot jump cycle.
In the above step S3, it is already explained that the robot has energy loss during jumping, so to make the robot follow an expected trajectory, energy compensation needs to be performed on the robot, and the energy compensation directly embodies the control of the controller on the motors of the robot, that is, after the robot jumps up, the state machine detects that the robot has emptied, the controller controls the motors to rotate to the set corresponding positions, and waits for the robot to land. After the robot lands on the ground, the equivalent spring of the leg of the robot can be compressed to a corresponding position by the aid of the conversion of the gravitational potential energy under the guidance of the controller, namely, when jumping next time, the leg motor of the robot is rotated to a program value of the last jumping, corresponding pulse quantity and pulse speed are given to the motor, and the same parameters are used in each jumping process, so that error accumulation in the jumping process is reduced.
In order to verify the method, a robot simulation model is established, and the whole four-legged robot has 12 joints, wherein 3 joints are arranged on a single leg, namely a side swing hip joint, a front swing hip joint and a knee joint. The body of the solid model is a cuboid, the side swing joints are spherical, the front swing hip joints and the knee joints are cuboid, and the foot ends are spherical, and as shown in fig. 6, the important parameters of the robot model are shown in table 1.
TABLE 1 important parameters of the robot model
By analyzing the simulation result of the robot, the effect that the attitude of the fuselage is difficult to control and adjust to an ideal state only by a conventional attitude feedback method under the environment with larger difference of ground rigidity of the opposite corners and feet can be obtained, and by utilizing the active variable stiffness strategy of the legs and adding the conventional attitude feedback as a compensation method, the balance control of the pitching attitude achieves a better experimental effect on the premise that the lateral rolling attitude is stable.
While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.
Claims (6)
1. A leg active adjusting method of a quadruped robot in stable transition on variable-rigidity terrain is characterized by comprising the following steps:
s1: when the quadruped robot lands on the ground with diagonal gait, analyzing the body posture of the robot under the diagonal gait, calculating the body offset angle, and adjusting the equivalent length of diagonal legs of the robot according to the body offset angle of the robot to balance the body;
s2: under the soaring state of the robot, the swing angle of the leg is controlled by planning the position of a foot falling point of the robot in the soaring stage to realize the control of the forward speed;
s3: when the robot is in the air and lands on the ground, compensating the equivalent stiffness of diagonal legs of the robot into the active variable stiffness calculation of the legs to adjust the equivalent leg length, thereby realizing the correction of the pitching attitude of the body;
s4: the landing phase attitude of the quadruped robot is subjected to feedback control, the change of the robot body is obtained in real time, and the change of the virtual spring stiffness of the robot is adjusted in real time according to the change of the robot landing body, so that a better balance effect is obtained;
s5: additional energy compensation is provided for robot jumping by increasing robot leg motor power at the beginning of the next robot jump cycle.
2. The active leg adjustment method for a quadruped robot in a terrain stable transition with variable stiffness according to claim 1, wherein in step S1, an angular rate gyroscope on the robot body receives a signal indicating that the robot body is deflected, the angular rate gyroscope changes its own deflection angle speed according to the received deflection signal, and the gyroscope deflects an angular rate wcThe following relationships exist with the robot fuselage deflection angle:
diagonal velocity wcCalculating integral to obtain the body offset angle thetabodyThe master device receivingBody offset angle thetabodyAnd angular velocity wcThe pulse signals required by the leg motor of the robot are determined, and the rotation angle of the leg motor of the robot is controlled through the number of the pulse signals, so that the equivalent length of diagonal legs is changed, and the machine body is balanced.
3. The active leg adjustment method of a quadruped robot in a variable-stiffness terrain stable transition as claimed in claim 1, wherein in step S2, the forward velocity control is realized by planning the flight phase foot point position, which is specifically controlled by the following formula:
in the formula, xf,dFor the desired forward footfall point position of the virtual spring leg,
is the actual horizontal velocity of the fuselage and,
is the desired horizontal speed of the fuselage, KpFor feedback of error gain, TsIs the landing time;
a state machine is introduced into the motion of four legs to judge the flight position, the swing angle of the legs is planned through a polynomial based on position control, corresponding expected joint angles are obtained through inverse kinematics calculation, the difference values are converted into corresponding joint moments through a PD controller through comparison with real-time joint angles to be used for driving the joints of the robot to rotate, so that a pair of diagonal legs touch the ground according to an appropriate ground contact angle, the robot obtains appropriate net forward acceleration, and the robot body accelerates or decelerates to reach an expected horizontal velocity value.
4. The active leg adjustment method for a quadruped robot in variable-stiffness terrain stable transition according to claim 3, characterized in that in step S2, the corresponding each desired joint angle is obtained by inverse kinematics calculation specifically using the following format:
in the formula, L0Virtual leg length, L1Is the length of the thigh, L2Is the length of the lower leg, θ1For a side swing hip joint angle, theta2Angle of anterior swing of hip joint, theta3Angle of knee joint, xf,dFor the expected forward foot-drop position, X, of the virtual spring legsThe vertical distance traveled by the leg end side;
and calculating the angle of each joint at the expected foot drop point according to the formula, and comparing the real-time angle with the calculated angle so as to adjust the rotation angle of the motor at each joint.
5. The active leg adjustment method for the quadruped robot in the variable stiffness terrain stable transition according to claim 1, wherein in step S3, an active variable stiffness adjustment formula of the robot leg is established to realize the adjustment control of the virtual spring stiffness of the robot leg, and the formula is specifically as follows:
maz+mg＝(k1+Δk)x4 cos(θ4(t))+k1x1 cos(θ1(t))
where Δ k is the equivalent stiffness change amount, k1Is the coupling stiffness, x, of one of a pair of diagonal legs in contact with soft ground1One of a pair of diagonal legs has an equivalent compression amount, x, with the ground4The equivalent amount of compression of the other of a pair of diagonal legs with the ground, azAcceleration in the vertical direction of the fuselage, g is gravity acceleration, and a is pitch angle accelerationyIs a pitch angle thetapitchPerforming secondary differentiation on time, wherein theta 1(t) is an equivalent swing angle of one leg of a pair of diagonal legs, theta 4(t) is an equivalent swing angle of the other leg of the pair of diagonal legs, m and J are the mass and the moment of inertia of the airplane body respectively, and L is the length of the airplane body;
the two formulas are simultaneously solved to obtain the virtual equivalent stiffness variation delta k:
adding delta k into the rigidity calculation of the leg to be compensated, realizing the adjustment of the rigidity value of the leg through a main controller program, and further converting the rigidity value into the knee joint moment tau3So as to adjust the equivalent leg length and further realize the correction of the pitching attitude of the body.
6. The active leg adjustment method for a quadruped robot in a variable-stiffness terrain stable transition according to claim 1, wherein in step S4, for the attitude offsets generated in the four groups of robot motions, the virtual spring stiffness change of the robot is adjusted by the following formula:
in the formula taupitchFor adjusting the pitch angle of the fuselage, τrollFor adjusting the roll angle of the fuselage, Kp_pitchPosition feedback gain for fuselage pitch angle, Kp_rollPosition feedback gain of fuselage roll angle, Kv_pitchSpeed feedback gain of fuselage pitch angle, Kv_rollSpeed feedback gain of fuselage roll angle, θpitchAt fuselage pitch angle, θrollAs the roll angle of the fuselage, the pitch angle,
is the angular velocity of the pitch angle of the fuselage,
angular velocity, θ, being the roll angle of the fuselagepitch_desireTo a desired pitch angle, θroll_desireAt a desired roll angle, wherein θpitch_desire、θroll_desireTypically set to 0.
In the formula thetapitch、θroll、
The pitch angle and the roll angle of the body and the corresponding pitch angle speed and roll angle speed are obtained by integrating corresponding data measured by a gyroscope, the adjusting torque of each leg joint is calculated according to the two formulas, the adjusting torque is converted into the torque and the rotating speed of the motor through a program and acts on the motor to be adjusted, and corresponding pulse signals are applied to different motors.
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