An adaptive variable impedance algorithm for hydraulic quadruped support unloading

Abstract

The application discloses a kind of self-adapting variable impedance algorithms for hydraulic four-foot support unloading, specific steps include the following: step 1, single cycle variable impedance control, in single step cycle, introduce variable impedance control strategy, when detecting that force sensor detects that force variation rate is larger, judge that robot is impacted by larger, at this moment, the expected force is adjusted quickly to realize unloading, to reduce the impact damage to structural member;Step 2, dynamic impedance coefficient adjustment, when detecting that impact force variation rate exceeds preset threshold or speed increases, dynamically reduce impedance coefficient to reduce rigidity, improve compliance, help to realize quick unloading;Step 3, impact detection and real-time response.The application can dynamically adapt to complex trajectory and stress change, realize compliance control and stable operation throughout, not only improve unloading efficiency and structural reliability, but also take into account compliance and movement ability, provide reliable support for efficient walking of hydraulic four-foot robot in complex environment.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of robot algorithm, and particularly relates to a self-adaptive variable impedance algorithm for hydraulic quadruped support unloading. BACKGROUND

[0002] The self-adaptive variable impedance algorithm for hydraulic quadruped support unloading refers to a control algorithm used in a hydraulic system such as a quadruped robot, which is used to adjust the support force of the robot's legs to adapt to changes in the external environment and achieve stable support. This algorithm is usually based on variable impedance control theory and combines the characteristics of the hydraulic system to achieve dynamic adjustment of the support force. In this algorithm, the support force of the robot's legs can be adaptively adjusted according to the changes in external forces to maintain a stable support state. By monitoring the changes in external forces and combining the state information of the robot itself, the algorithm can adjust the parameters of the hydraulic system in real time to control the size and direction of the leg support force to ensure that the robot maintains balance and stability when moving or standing. This self-adaptive variable impedance algorithm usually needs to combine sensor feedback and real-time control strategies to dynamically adjust impedance parameters and support force size to adapt to different terrains, external forces, and motion requirements. Through this algorithm, the hydraulic quadruped support system can better adapt to complex environments and task requirements, improving the stability and flexibility of the robot.

[0003] Traditional impedance control algorithms are mainly applicable to multi-rigid body systems with fixed bases and exhibit compliant characteristics under constant system forces. However, for a hydraulic-driven quadruped robot, its model is a floating base, and the external force it receives will dynamically change with the change of the motion trajectory. In this case, the traditional impedance control method cannot meet the needs of the hydraulic quadruped robot to achieve instant unloading and maintain compliance during rapid motion.

[0004] Hydraulic actuators can output large forces, and if they cannot achieve rapid unloading during landing, they will cause a large impact on mechanical structural components. If the impedance coefficient is set too small, the robot may not be able to provide enough driving force to complete the leg lifting action when the support phase is converted to the swing phase. Therefore, in order to achieve the compliant control requirements of the hydraulic quadruped robot during rapid walking, an adaptive variable impedance algorithm that can combine the robot's motion trajectory and real-time force information needs to be designed. SUMMARY

[0005] (I) Technical problems solved

[0006] To address the deficiencies in the prior art, the present application provides a self-adaptive variable impedance algorithm for hydraulic quadruped support unloading, which solves the problem that traditional impedance control methods cannot meet the needs of the hydraulic quadruped robot to achieve instant unloading and maintain compliance during rapid walking.

[0007] (II) Technical Solution

[0008] The technical solution of the present application is: an adaptive variable impedance algorithm for hydraulic quadruped support unloading, the specific steps include the following:

[0009] Step 1, single cycle variable impedance control, in a single step cycle, introduce variable impedance control strategy, when the force change rate detected by the force sensor is large, it is judged that the robot is subjected to a large impact, at this time the expected force value is quickly adjusted to realize unloading, thereby reducing the impact damage to the structure;

[0010] Step 2, dynamic impedance coefficient adjustment, when a large impact force change rate exceeds a preset threshold and speed increases, the impedance coefficient is dynamically reduced to reduce rigidity and improve flexibility to assist in achieving rapid unloading;

[0011] Step 3, impact detection and real-time response, by real-time monitoring of the change rate of the force at the foot end of the robot and the movement speed, when the change rate exceeds the preset threshold or the speed changes, the adjustment of the impedance coefficient and the expected force is triggered immediately to adapt to the external force impact and complete the unloading operation.

[0012] As a further preferred mode of the present application, it also includes a hydraulic cylinder variable impedance expected force calibration method, which allows the hydraulic quadruped to run in a trot gait without falling to the ground, records the upper and lower limits of the force fluctuation received by the knee joint tension and compression force sensor, sets the upper and lower limit values as (x1, x2), if the sensor value becomes larger when the compression cylinder, the current force sensor value is y1, the expected force is e1, if y1>x2, e1=x1, otherwise e1=x2, if the sensor value becomes larger when the stretching cylinder, then if y1<x2, e1=x2, otherwise e1=x1.

[0013] As a further preferred mode of the present application, it also includes a hydraulic quadruped foot end trajectory planning method, swing phase trajectory: Support phase trajectory:

[0014] X=-sv.a+X1, Z=Z0, X is the X-direction foot end trajectory, Z is the Z-direction foot end trajectory, S is half of the step length, A5=S*2 / T 2 / 25.13, ω l =π / T, ω h =2π / T / 2.86, φ=0.218979522475626, a is the discrete time.

[0015] As a further preferred mode of the present application, the hydraulic cylinder impedance parameter adaptive tuning method is also included, the impedance coefficient is mainly composed of M mass, B damping and K stiffness, the foot end trajectory planning of the electro-hydraulic quadruped is uniform motion, that is, the acceleration is 0, M is set to 0, the size of B depends on the speed of the quadruped robot motion, the size of K depends on the current force, the current speed of the hydraulic robot is v, B(v)=B0e av , B0 mainly depends on the discretization impedance formula (M+BT+KT 2 )Δx(k)=T 2 ΔF(k)+(2M+BT)x(k-1)-MΔx(k-2), T is a discrete time, which depends on the time of the upper computer to do a force control closed loop operation, Δx(k) is the current displacement compensation value, Δx(k-1) is the displacement compensation value of the last period, Δx(k-2) is the displacement compensation value of the last period, ΔF(k)=F(k)-e1, F(k) is the force value received by the current force sensor, the total stroke of the hydraulic cylinder is X, all the above values are substituted, when ΔF(k)=X / 15, the value of B0 is obtained;

[0016] K is the elastic coefficient, if F(k-1) is the last period force sensor value, F(k-2) is the last period force sensor value. The smaller the value of K is, the larger the value of Δx(k) is, that is, the larger the displacement compensation value is, when the hydraulic quadruped enters the support phase, if it just lands, a larger displacement compensation is needed, then the value of K needs to be smaller, if it enters the support phase to swing phase stage, a smaller displacement compensation is needed to ensure that there is enough force to lift, then the value of K needs to be larger. Therefore, K=a*K0e -(F(k)-F(k-1)) , if Z=z1, Z is the Z direction foot end trajectory value, z1 is the minimum value of the Z direction foot end trajectory, when Z=z1, the hydraulic quadruped enters the support phase, then a=60 / m, m is the mass of the hydraulic quadruped, otherwise a=1, to ensure that the elastic coefficient of the swing phase is larger than that of the support phase, the quadruped is in the support phase only to bear a larger force, K0 also depends on the displacement compensation value Δx(k), when K0 is substituted into the discretization impedance formula, Δx(k) should be ≤X / 15, when K0 is equal to 1, K=K0e -(F(k)-F(k-1)) .

[0017] (Three) beneficial effects

[0018] The present application provides a kind of for hydraulic quadruped support unloading adaptive variable impedance algorithm.It has the following beneficial effects:

[0019] The adaptive variable impedance algorithm can dynamically combine the motion trajectory and real-time force information of the hydraulic quadruped robot, adapt to complex working condition requirements, and effectively compensate for the limitations of traditional impedance control methods in dynamic environments. The adaptive variable impedance algorithm can improve the unloading efficiency and reduce the impact. By detecting the force change rate and adjusting the expected force value in real time, the robot can quickly unload when landing, significantly reduce the impact of large force output by the hydraulic actuator on mechanical structural parts, prolong the service life of the equipment, and improve the running stability. The dynamic impedance coefficient adjustment strategy is adopted to ensure the support and leg lifting performance. The dynamic impedance coefficient adjustment strategy can maintain sufficient rigidity during support to provide driving force for leg lifting, and quickly reduce the impedance coefficient during impact to achieve soft unloading. The dynamic impedance coefficient adjustment strategy can balance the robot flexibility and motion ability, and ensure the stable realization of fast walking performance. The algorithm fully considers the floating base characteristics of the hydraulic quadruped robot and the characteristics of the force changing with the motion trajectory, and can continuously adapt to the force requirements of different trajectories in dynamic environments, ensuring efficient motion control ability. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a shape diagram of the trot gait during motion;

[0021] Figure 2 is an X-direction trajectory and Z-direction trajectory diagram;

[0022] Figure 3 is B(v) = B0e av is a curve diagram;

[0023] Figure 4 is K = K0e when K0 is equal to 1; -(F(k)-F(k-1)) is an image;

[0024] Figure 5 is an actual force curve diagram of a common impedance hydraulic quadruped single leg;

[0025] Figure 6 is a single leg actual force curve diagram after adding the adaptive variable impedance. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0027] Please refer to Figures 1-6The embodiment of the application provides a technical scheme: an adaptive variable impedance algorithm for hydraulic quadruped support and unloading, comprising single-cycle variable impedance control, in a single-step cycle, a variable impedance control strategy is introduced. When a large force change rate is detected by a force sensor, it is judged that the robot is subjected to a large impact, at which time the expected force value is quickly adjusted to achieve unloading, thereby reducing the impact damage to the structure.

[0028] Dynamic impedance coefficient adjustment, considering the influence of impedance coefficient setting on the flexibility and motion ability of the robot, maintaining a moderate impedance coefficient in the normal support condition, ensuring that the robot can provide sufficient leg lifting force in the support phase; when a large impact (the force change rate exceeds the preset threshold) is detected, the impedance coefficient is dynamically reduced to reduce the rigidity and improve the flexibility, assisting in achieving rapid unloading.

[0029] Impact detection and real-time response, by monitoring the force change rate and motion speed of the robot foot end in real time, when the change rate exceeds the preset threshold or the speed changes, the adjustment of the impedance coefficient and the expected force is triggered immediately to adapt to the external force impact and complete the unloading operation, thereby guaranteeing the running stability and walking efficiency of the robot in complex terrain.

[0030] Hydraulic cylinder variable impedance expected force calibration method

[0031] Let the hydraulic quadruped run in the trot gait without falling to the ground, record the upper and lower limits of the force fluctuation received by the knee joint tension and compression force sensor, set the upper and lower limit values as (x1, x2). If the sensor value becomes large when the compression cylinder, the current force sensor value is y1, the expected force is e1, if y1>x2, e1=x1, otherwise e1=x2. If the sensor value becomes large when the stretching cylinder, then if y1<x2, e1=x2, otherwise e1=x1.

[0032] Hydraulic quadruped foot end trajectory planning method

[0033] The core of impedance control is to establish the expected force-position relationship. If virtual inertia is introduced, the dynamic behavior of the system will become more "slow" or "lag", which is not conducive to rapid response. Therefore, the hydraulic quadruped should move at a constant speed, so that the inertia of the object will not have too much impact. When moving, the gait is trot gait, and the shape is steamed bun-shaped, as shown in Figure 1 .

[0034] Swing phase trajectory: Support phase trajectory:

[0035] X=-sv.a+X1, Z=Z0. X is the X-direction foot end trajectory, Z is the Z-direction foot end trajectory, S is half of the step length, and A5=S*2 / T 2 / 25.13, ω l= pi / T, w h = 2 pi / T / 2.86, phi = 0.218979522475626, a is the discrete time.X direction trajectory and Z direction trajectory are shown as Figure 2

[0036] Hydraulic cylinder impedance parameter adaptive tuning method

[0037] Impedance coefficient is mainly composed of M mass, B damping and K stiffness. Since the foot trajectory planning of electro-hydraulic quadruped is uniform motion, that is, the acceleration is 0, M is generally set to 0, the size of B depends on the speed of the quadruped robot, and the size of K depends on the current force received.

[0038] Let the current speed of the hydraulic robot be v, B(v) = B0e av , B0 mainly depends on the discretization impedance formula (M + BT + KT 2 ) Delta x(k) = T 2 Delta F(k) + (2M + BT) Delta x(k-1) - M Delta x(k-2), T is the discrete time, which depends on the time of one force control closed loop operation of the host computer, Delta x(k) is the current displacement compensation value, Delta x(k-1) is the displacement compensation value of the last period, Delta x(k-2) is the displacement compensation value of the last period, Delta F(k) = F(k) - e1, F(k) is the force value received by the current force sensor. Let the total stroke of the hydraulic cylinder be X. Substitute all the values above, and when Delta F(k) = X / 15, B0 value is obtained. a e (0, 1). B(v) = B0e av The curve is shown as Figure 3

[0039] K is the elastic coefficient, F(k-1) is the force sensor value of the last period, F(k-2) is the force sensor value of the last period, if the value of K is smaller, the value of Delta x(k) is larger, that is, the displacement compensation value is larger. When the hydraulic quadruped enters the support phase, if it just lands, a larger displacement compensation is needed, then the value of K needs to be smaller, if it enters the support phase to swing phase stage, a smaller displacement compensation is needed to ensure enough force to lift, then the value of K needs to be larger. Therefore, K = a * K0e -(F(k)-F(k-1)) . If Z = z1, Z is the Z direction foot trajectory value, z1 is the minimum value of Z direction foot trajectory, when Z = z1, the hydraulic quadruped enters the support phase, then a = 60 / m, m is the mass of the hydraulic quadruped, otherwise a = 1. This is to ensure that the elastic coefficient of the swing phase is larger than that of the support phase, because the quadruped is in the support phase only when it receives a larger force.

[0040] K0 also depends on the displacement compensation value Delta x(k), when K0 is substituted into the discretization impedance formula, x(k) should be less than or equal to X / 15. When K0 is equal to 1, K = K0e -(F(k)-F(k-1)) The image is as Figure 4 ​As shown.

[0041] The magnitude of B0 and K0 mainly depends on the magnitude of the cylinder displacement sensor and the magnitude of the force sensor, when B0 and K0 are temporarily determined, Δx(k) and X should be of the same order of magnitude, and Δx(k) should be as small as possible X / 15, if the compensation displacement is too large, it will affect the trot gait of the walking.

[0042] The single leg structure of the hydraulic quadruped robot usually includes three degrees of freedom, which are the swing joint, the hip joint and the knee joint. The swing joint is mainly used to realize the steering function, so the swing hydraulic cylinder does not need displacement compensation during the regular walking process. In contrast, during the landing stage, the main load bearing part is the knee joint hydraulic cylinder, so displacement compensation usually only needs to be designed and optimized for the knee joint hydraulic cylinder.

[0043] Actual effect comparison:

[0044] Figure 5 For the actual force curve of the ordinary impedance hydraulic quadruped single leg, Figure 6 For the actual force curve of the ordinary impedance hydraulic quadruped single leg,

[0045] The above shows and describes the basic principles and main features of the present application and the advantages of the present application, for those skilled in the art, it is obvious that the present application is not limited to the details of the above exemplary embodiments, and the present application can be realized in other specific forms without departing from the spirit or essential characteristics of the present application. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting, the scope of the present application is defined by the appended claims rather than the above description, therefore all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present application. Any reference signs in the claims should not be regarded as limiting the claims involved.

[0046] In addition, it should be understood that although the present specification is described in terms of embodiments, not every embodiment contains only one independent technical solution, and the description manner of the specification is only for the sake of clarity, those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be combined to form other embodiments which can be understood by those skilled in the art.

Claims

1. An adaptive variable impedance algorithm for hydraulic quadruped support unloading, characterized by: The specific steps include The following: Step 1, single period variable impedance control, in a single step period, introduce variable impedance control strategy, when the force sensor detects that the rate of change of force is large, it is judged that the robot is subjected to a large impact, at this time the expected force value is quickly adjusted to realize force unloading, thereby reducing the impact damage to the structure; Step 2, dynamic impedance coefficient adjustment, when the impact force change rate exceeds the preset threshold and the speed increases, the coefficient is dynamically reduced to reduce the rigidity and improve the compliance, which helps to realize fast force unloading; Step 3, impact detection and real-time response, by real-time monitoring of the change rate of the force at the foot of the robot and the movement speed, when the change rate exceeds the preset threshold or the speed changes, the adjustment of the impedance coefficient and the expected force is triggered immediately to adapt to the external force impact and complete the force unloading operation; Also include, hydraulic cylinder impedance parameter adaptive adjustment method, impedance coefficient mainly by mass damping stiffness, the foot end trajectory planning of electro-hydraulic quadruped is uniform velocity motion, i.e. acceleration is 0, Set to 0, The size depends on the speed of the quadruped robot movement, The size depends on the current force, the current speed of the hydraulic robot is , , Mainly depends on the discretization impedance formula , Discrete time, depends on the time of the host computer to do a force control closed loop operation, The current displacement compensation value is The last cycle displacement compensation value is The last cycle displacement compensation value is , The current force sensor received force value is the total stroke of the hydraulic cylinder , all the above values are substituted, when , the value of is obtained; is the elastic coefficient, is the force sensor value of the last cycle, is the force sensor value of the second last cycle, if is smaller, is larger, i.e. the displacement value of compensation is larger, when the hydraulic quadruped enters the support phase, if just landing, a larger displacement compensation is needed, then the value of needs to be smaller, if entering the support phase to swing phase stage, a smaller displacement compensation is needed to ensure enough force to lift, then the value of needs to be larger, so , if , is the Z direction foot end trajectory value, is the minimum value of the Z direction foot end trajectory, when the hydraulic quadruped enters the support phase, then , is the mass of the hydraulic quadruped, otherwise , to ensure that the elastic coefficient of the swing phase is larger than the elastic coefficient of the support phase, the quadruped is in the support phase only to bear a larger force, also depends on the displacement compensation value , when is substituted into the discretization impedance formula, when is equal to 1, .

2. The self-adaptive variable impedance algorithm for hydraulic quadruped support and load relief of claim 1, wherein: Also included is a hydraulic cylinder variable impedance desired force calibration method, which makes the hydraulic quadruped swing freely in trot gait, records the upper and lower limits of the force fluctuation received by the knee joint tension and compression force sensor, sets the upper and lower limit values as , if the sensor value becomes large when the compression cylinder is compressed, the current force sensor value is , the desired force is , if > , , otherwise , if the sensor value becomes large when the stretching cylinder is stretched, if < , , otherwise .

3. The self-adaptive variable impedance algorithm for hydraulic quadruped support and load relief of claim 1, wherein: Also included are hydraulic quadruped foot trajectory planning methods, swing phase trajectory: , , support phase trajectory: , , is the X-direction foot-end trajectory, is the Z-direction foot-end trajectory, is a half step length, , , , , , is a discrete time.

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