What is a servo hydraulic cylinder
Electro-hydraulic servo system refers to a hydraulic control system with a servo component (servo valve or servo pump) as the control core, which is usually composed of an instruction device, a controller, an amplifier, a hydraulic source, a servo component, an actuator, a feedback sensor and a load. The servo hydraulic cylinder is an executive element in the electro-hydraulic servo system, which can control the direction, position, speed or deformation of the object by applying controllable pushing, pulling, pressing, twisting and other forces to an object.
In the servo hydraulic system, the hydraulic cylinder and the servo valve need to cooperate with each other to achieve the normal operation of the servo system, and there is a combination relationship and direct feedback relationship between each other. In order to simplify the mechanism, shorten the connection distance of the pipeline and improve the control sensitivity, the signal detection and feedback device, servo valve or proportional valve and other components of the system are generally installed directly on the servo hydraulic cylinder.
Servo hydraulic cylinder structure and classification
Servo hydraulic cylinder is generally composed of end cover, cylinder, piston rod, piston assembly, servo module, sensing assembly, base and other main parts.
The performance indicators of the servo hydraulic cylinder will directly affect the accuracy and quality of the electro-hydraulic servo system, and its performance parameters, shape structure, installation and connection form need to be determined with the performance indicators and functions of the servo system and the model of the selected servo valve and feedback sensor.
Compared with ordinary hydraulic cylinders, the focus of servo hydraulic cylinders is on control, and the key point to solve is to ensure a low damping coefficient, that is, to minimize friction. According to the different methods of reducing friction, it is divided into ordinary servo hydraulic cylinder and static pressure support servo hydraulic cylinder.
Ordinary servo hydraulic cylinder is often through the design of the cylinder block, improve the precision of processing and manufacturing, the surface process of the piston rod, and choose a low friction coefficient of seals to reduce the friction.
The static pressure support servo hydraulic cylinder forms a closed chamber through a special mechanism inside the front end cover of the piston rod. A certain pressure of hydraulic oil is driven into the closed chamber to form an oil film before the piston rod and the cylinder, which plays a certain supporting role. Due to the realization of the lubrication of the hydraulic oil, the friction resistance of the hydraulic cylinder is minimal. Its dynamic response and position accuracy are better than ordinary servo hydraulic cylinder, but the cost is higher.
The difference with traditional hydraulic cylinder
Servo hydraulic cylinder is one of the key components in servo hydraulic system, its structure and dynamic characteristics directly affect the performance and service life of the system. Therefore, compared with the traditional hydraulic cylinder, the servo hydraulic cylinder has higher requirements.
01 High stability
The servo hydraulic cylinder is used to drive the negative work load at high frequency, to achieve high precision and high response servo control, and to meet the requirements of high stability of the pressure rod.
02 High strength and stiffness
In order to meet the requirements of working pressure and high frequency impact pressure, for the sake of insurance, the thickness of the servo hydraulic cylinder generally exceeds the calculated value of the normal strength design. At the same time, the stiffness requirements of the servo hydraulic cylinder are high, that is, the slender ratio of the piston rod (the ratio of the length of the piston rod and the cross-sectional area) is smaller, otherwise the frequency of the actuator will be greatly reduced, and the base of the cylinder must not only meet the force requirements of the supporting cylinder, but also have a "solid" foundation.
03 Low friction
The servo hydraulic cylinder does not allow external leakage, requiring small internal leakage.
04 Low leakage
The servo hydraulic cylinder is required to minimize the friction starting resistance and the whole friction resistance, otherwise it is easy to produce limit cycle vibration, and produce static dead zone and dynamic dead zone. Therefore, measures such as the selection of seals with low friction coefficient must be taken to minimize static and dynamic friction resistance.
05 High cleanliness
Ordinary hydraulic cylinders require higher cleanliness, and servo hydraulic cylinders require high cleanliness.
