Causes of hydraulic system creep

In the hydraulic transmission system, when the actuator moves at a low speed, the phenomenon of intermittent and uneven speed movement occurs, which is called crawling. Its essence is that when an object moves relatively at a low speed on the East China surface, it is a kind of discontinuous vibration in which the sudden jump and the stop want to alternate under certain conditions.

In hydraulic transmission, the crawling of the actuator is very harmful. In metal cutting machine tools, it will affect the machining accuracy, surface roughness, and shorten the service life of the tool and mechanism.

Reasons for hydraulic crawling:

After research, the crawling phenomenon of moving parts is because of the friction drop characteristic in the transition from static state to moving state. As shown in the figure, it is a double-rod hydraulic cylinder, which drives the worktable with mass m to move on the guide rail. When the left chamber of the hydraulic cylinder is connected to the pressure oil, the piston will not move immediately, and the static friction of each motion pair must be overcome (regardless of the Work load) can drive the table movement.

During this process, the working oil in the left cavity and the air mixed in the oil are continuously compressed and squeezed, the pressure in the left cavity is gradually increased and energy is accumulated, and the workbench will not move until the total pressure can overcome the static friction resistance. Once the table moves, the static friction suddenly becomes the kinetic friction.

Under the action of the difference between the dynamic and static friction forces, the piston is suddenly accelerated, that is, the worktable rushes forward rapidly, and the pressure of the oil in the left chamber also suddenly decreases, and the previously compressed oil and gas expand to release the stored energy, enabling the work The table moves forward more quickly. Due to the forward stroke of the worktable, on the one hand, the oil in the right chamber of the hydraulic cylinder and the air mixed into it are suddenly compressed, which increases the oil discharge resistance, and as a result, the pressure in the right chamber of the hydraulic cylinder rises.

The comprehensive result is that after the workbench rushes forward, it is quickly braked. If this is repeated, the workbench will suddenly stop and continue to circulate, that is, the creeping phenomenon of the workbench will occur.