A Brief Discussion on the Causes of Unstable Lifting of Hydraulic Lifting Platforms

When the hydraulic lift meets the feeding conditions, the electromagnetic coil is energized, and the clamping arm of the fixture clamps the smoke box tightly, reaching the set value of the pressure relay. The pressure relay sends a signal to lift the smoke box to the position, then the low-level conveying part of the dual-position shuttle car moves under the hydraulic lift, the clamping arm descends, placing the smoke box onto the low-level conveyor. At this time, the clamping arm of the fixture rises to the highest point, and after reaching the position, the dual-position shuttle car sends the smoke box to the next level conveyor in front, and the high-level conveyor moves to the bottom of the hydraulic lift. A signal is sent by the photoelectric switch, and the lifting oil cylinder lowers the fixture to the middle position, waiting for the next cycle to begin.

Analysis and countermeasures for the unstable lifting speed of the hydraulic lift. After the hydraulic lift is put into use, it can meet the basic functional requirements. From the on-site usage, there are frequent occurrences of smoke packages slipping, difficulty in detecting the rising position, inability to find the middle position, impact noise during rising, and oil leakage from the hydraulic cylinder. On-site inspection shows that the main reason is that the lifting speed of the hydraulic cylinder is too fast, leading to an increased failure rate, which severely affects production efficiency. Analysis of the reasons for the unstable lifting speed of the hydraulic cylinder. The reasons for the unstable lifting speed of the hydraulic cylinder are many, including design, manufacturing, and usage aspects.

For the faults existing in this hydraulic system, using the speed stiffness theory, analyze the reasons for the unstable lifting speed of the hydraulic cylinder:

(1) Composition of the lifting hydraulic circuit. Oil pump overflow valve, reversing valve, reversing valve, one-way throttle valve (no throttling), lifting oil cylinder.

(2) Establishing the speed stiffness analysis formula for the lifting circuit. The flow into the hydraulic cylinder, that is, the flow through the one-way throttle valve, is the flow through the throttle valve; the shape of the throttle valve's throttling port and the viscosity of the hydraulic oil are related coefficients; AT is the flow area of the throttling port (lifting without throttling); the outlet pressure of the hydraulic pump; P1 is the pressure in the oil chamber of the hydraulic cylinder, which is the area of the lifting hydraulic cylinder piston; the index determined by the shape of the throttling port shows that when the area of the throttle valve opening remains unchanged, the output speed of the hydraulic cylinder will change with the load. The degree of influence of load changes on speed is represented by speed stiffness T: as the load increases, the output speed of the hydraulic cylinder decreases negatively; to make it a positive number, a negative sign is added in the formula. Substituting into the hydraulic lift, it can be seen that the larger the input throttling speed stiffness value, the better the stability of the hydraulic circuit speed.

From the analysis, the following can be concluded:

(1) When the load remains unchanged, the smaller the throttle valve opening, the higher the system speed stiffness; conversely, if the throttle valve opening area is larger, the stiffness decreases.

(2) When the load remains unchanged, the speed stiffness is good at low speeds, and when the load changes, the speed stiffness is good at low loads.

(3) Increasing the oil supply pressure to enlarge the effective area of the hydraulic cylinder can improve speed stiffness.

In summary, the main reason for the failure of the hydraulic lift is the unreasonable design of the hydraulic system's lifting speed control circuit.