Development and Challenges of Hydraulic Foot – driven Robots

1. Electro-hydraulic servo control technology overview
As a bridge connecting modern microelectronic technology, computer technology and hydraulic technology, electro-hydraulic servo control technology has become an important constituent of modern control technology, with good linearity, small dead zone, high sensitivity, dynamic performance, fast response and high precision. Significant advantages. Electro-hydraulic servo control system consists of hydraulic control unit, servo cylinder, power oil Angle Steel Punching Machine three major components. Application of the system summed up in a total of the following ways: valve-cylinder servo system, valve-controlled motor servo system and pump-controlled motor servo system.

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Electro-hydraulic servo control system has the following advantages:
(1) The power-to-weight ratio and the moment-to-inertia ratio (or force-mass ratio) of the hydraulic components are large, and the forces (or moments) and power delivered are large, making it possible to form small, light, fast, Action of the servo system to control high-power or large load.
(2) hydraulic actuator response speed, servo control in the use of hydraulic actuators can increase the loop gain, the band widened.
(3) anti-load rigidity, so high control accuracy.
In addition, there are components of good lubricity, long life, easy to achieve stepless speed regulation, overload protection and easy.
Electro-hydraulic servo control system has the following disadvantages:
(1) as the working medium is oil, prone to leakage Angle Drilling machine, pollution of the environment.
(2) hydraulic servo components, high precision, and therefore expensive.
(3) susceptible to oil pollution.
2. Foot-type robot overview
At present, the common walking robot is applied in two-legged, four-legged and six-legged type. The robot is the most representative in the United States and Japan. Among them, the bigdog robot in the United States Climbing up to 52kg and climbing up to 35 °. Its leg joints resemble the joint structure of the animal’s legs and are equipped with vibration-absorbing and energy-cycling components. At the same time, the legs are connected with a number of sensors, The movement is controlled by the servo motor. The robot has strong maneuverability and reaction ability. The balancing ability is very good. However, because the gasoline generator needs to carry the fuel tank, it is affected by the environment and poor reliability. In addition, Servo control system, so when walking the engine will issue a strange noise. In addition, Japan Chiba University to low-speed walking, not afraid of slope-based comet-tv robot and Japan chukyo universuty to low-speed walking, climbing-based TTTAN XI robot is a typical representative of foot-type robot.
In summary, the foot-type robot has great advantages such as high efficiency in land-propulsion, stability, strong terrain adaptability, best solution in the conventional mobile-inaccessible area, and thus become the future battlefield, industrial production and exploration Mining an important means of one.
The application of electro – hydraulic servo control technology in foot – type robot
In the process of motion, the foot-type robot, as a rigid body mainly made by machinery, produces a considerable impact load with the ground due to the impact, and the size and direction of the load always show irregular changes, the BigDog robot in the United States For example, the hydraulic drive system consists of a variable piston pump driven by a gasoline engine at the same time on the implementation of 16 hydraulic actuators hydraulic output to achieve the purpose of power output, hydraulic transmission has two characteristics: hydraulic system Busbar Processing Machine oil The pressure depends on the size of the external load, the speed of the implementation of components depends on the flow of hydraulic systems, these two points just with the foot-type robot body of the load and the corresponding rotation. The engine controls the rotation speed of the piston according to the load and rotational speed carried by each joint of the robot body, thus controlling the hydraulic output of the piston pump, adapting to the dynamic demand of the robot movement and has the ability of predicting. The faster the movement speed of the robot, The more severe the change, the greater the corresponding hydraulic output, and vice versa, in order to achieve a strong enough to adapt to the foot-type robot terrain changes.
The foot-type robot makes full use of the characteristics of the hydraulic transmission in the dynamics, and transfers the analysis and calculation of the dynamics to the control of the hydraulic system. The force and torque output of the hydraulic system mainly depend on the load of the terminal actuator. Size and changes, adjust the engine speed to achieve the total hydraulic pressure on the hydraulic control, and then through the electro-hydraulic servo valve control into a single actuator of the oil pressure, flow and flow rate and other parameters to achieve the output load according to the corresponding balance Of the force and torque, including acceleration and deceleration of the situation.
However, the foot-type robot with motor control needs to predict the load of each joint in the next period and set the output of the motor, but this output can not achieve the fast output and load balance of the hydraulic output. Motor output or greater than the terminal load, or less than the terminal load, only in a few cases the two just balance, which is the common motor-driven foot-type robot in the walk, the body will appear the majority of shaking reasons, Unbalanced, and hydraulically actuated foot-type robots, unless subjected to sudden drilling equipment manufacturers external forces, in most cases can be in a dynamic balance, the key is the adaptability of its hydraulic system play a decisive role, when the hydraulic-driven foot When the robot accelerates, the output torque needs to be greater than the current load, which is the use of the servo valve control flow rate function, when an actuator where the limb load suddenly increases, can also use the servo valve pressurization function, To achieve in the actuator oil pressure is greater than the performance of the total road oil pressure.

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The kinematic efficiency of the foot-type robot depends on three aspects: internal friction caused by the motion mode, the transmission efficiency of the mechanical structure and the internal friction caused by the control. The internal friction of the movement mode includes the barying of the center of gravity, the swing of the leg relative to the fuselage and so on. The mechanical part mainly includes each active joint and the hydraulic actuator internal and output end movement conversion mechanism. Thereby requiring energy-efficient driving, compliant adaptation, and adaptable terrain switching control. Although the electro-hydraulic servo control technology can meet the requirements of the latter two, the low efficiency of the hydraulic system becomes the soft rib of the further development of cnc punch machine the foot-type robot, which leads directly to the low efficiency, large volume and high input power of the foot-type robot. As well as the significant shortcomings of poor endurance. In addition, due to the hydraulic system has a lot of noise, but also directly lead to the foot-type robot in the work of the noise is not conducive to the implementation of tasks on the battlefield and the implementation of exploration, which is currently foot-type robot is not widely used important reason one.
In summary, the foot-type robot drive requires high power density ratio and for strong terrain adaptability, it also needs position and force rapid response and precise control and switching, so the electro-hydraulic control system has become a foot-driven robot The best not to replace the program.
Development and Challenges of Hydraulic-driven Foot-type Robots
1. Research on foot-type robot
With the deep research and development of foot-type robot, the performance of foot-type robot in speed, stability, flexibility and adaptability to the ground will continue to improve, the autonomy and intelligence will be gradually realized, comprehensive analysis, The future development, foot-type robot has the following trends:
(1) to achieve high-energy, high-efficiency legs
Animal tendon muscles are highly efficient energy storage and energy saving components to solve the problem of high speed and stable walking and energy efficiency, and foot-type robot robot joints and rigid joints are rigid, not only can not be stored, and because of the touchdown Impact, to consume a lot of energy, and high power and has a buffer energy storage measures of the leg body is a hot issue for future research.
(2) foot-type mobile technology and wheel technology
The combination of foot-type movement and wheel-type technology can not only control the efficiency of movement through wheel-type control, but also use leg mechanism to achieve obstacle avoidance and obstacle avoidance. At present, the combination of wheel and foot Research, in the future research work in wheel, foot combined research will be further increased.
(3) miniaturization of walking robots
Micro-walking robot has a broad application prospects, it can be widely used in various scientific exploration, industrial operations, such as in a small space such as pipe walking, operation and maintenance.
(4) to enhance the foot-type robot load capacity
At present, the research of foot-type robot is mainly focused on small-scale and light-weight, easy to control and so on. It has a certain gap from the low energy consumption and high load requirement. In practical field work, the usability is poor, The research of foot-type robot with low energy consumption of walking mechanism is also an important direction for future research.
(5) robot bionic to further deepen
Foot-type robot can not only be limited to the imitation of institutions, but also should imitate the biological functions, such as the bat’s hearing, dog’s sense of smell, dragonfly’s vision.
In summary, although the foot-type robot technology has made great progress, but constraints of further development of foot-based robot theory has not been fundamentally solved, many of the robot also failed to simple biological movement speed and stability , The key technology of the foot-type robot still needs to be further developed energetically.
Electro-hydraulic servo control foot-type robot technology challenges
Because the electro-hydraulic servo system is a serious uncertain nonlinear system, the environment and characters are complex, and there are many parameters such as external disturbance and cross-coupling interference. In addition, electro-hydraulic servo system has high requirements on frequency band and tracking accuracy. In the application of foot-type robot, because it is in the high-precision fast tracking conditions, the nonlinear effect of electro-hydraulic servo system can not be ignored, so it can be said that electro-hydraulic servo system is a typical unknown uncertain nonlinear system, This kind of system has large disturbance, wide working range, many time-varying parameters and difficult to be modeled accurately. These characteristics will have serious influence on the stability CNC H-Beam Drilling Machine, dynamic characteristics and precision of the system. Especially, the control precision is affected by the load characteristics. It is predicted that the application of computer control in the electro-hydraulic servo system makes the realization of the complex control strategy possible, thus improving the robustness and control precision of the system and playing an active role in solving many engineering problems. In the environment of robot, due to the large disturbance and serious uncertainty of environment, the adaptive algorithm is required to be complicated and difficult to be realized. In addition, its processing ability to nonlinear factors is unsatisfactory. In recent years, , The development of control subjects also contributed to the intelligent control of electro-hydraulic servo control system.
In summary, the hydraulically driven foot-type robot has a wide application prospect and research value because of its many significant advantages, but because of the hydraulic system itself, there are some major flaws also limit the further development of hydraulic drive robots, Therefore, it is necessary to study and solve the problems of electro-hydraulic servo control technology such as low efficiency, high noise and nonlinearity. Only by breaking these technical difficulties, can the development of foot-type robot take a higher level .

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