Why is the lifting speed and deceleration of the scissor lift unstable?
When we use scissor lifts, we sometimes encounter the phenomenon of unstable speed during lifting. What is the specific reason for this phenomenon? Everyone knows the composition and working principle of the hydraulic system. The hydraulic system is an important part of the scissor lift, which is mainly composed of motor oil pump, valve plate, overflow valve, safety valve, hydraulic cylinder, hydraulic pipeline and so on. When the scissor lift has the feeding condition, the solenoid coil is energized and the attachment arm clamps the smoke box to reach the setting value of the pressure relay. The pressure relay sends a signal to raise the smoke box into position, and the double station The low conveying part of the shuttle car is under the hydraulic elevator, the clamp arm is lowered, so that the cigarette box is placed on the low conveyor. At this time, the attachment clamp arm rises to the highest point. After it is in place, the double-station shuttle car sends the cigarette box to the next Before the high-level conveyor, the high-level conveyor is under the hydraulic elevator, and the photoelectric switch sends out a signal, and the lifting cylinder will lower the attachment to the neutral position, and wait for the beginning of the next cycle.
Analysis and countermeasures of unstable lifting speed of scissor lifts. After being put into use, scissor lifts can meet the basic functional requirements. From the point of view of on-site use, the cigarette packs often fall and the rising position is difficult to detect. The neutral position and rising are difficult to detect There are phenomena such as impact noise and oil seepage in hydraulic cylinders from time to time. According to on-site inspection, the main reason is that the lifting speed of the lifting hydraulic cylinder is too fast, which increases the failure rate and seriously affects the production efficiency. Analysis of the reasons for the unstable lifting speed of the lifting hydraulic cylinder. There are many reasons for the unstable lifting speed of the lifting hydraulic cylinder, including design, manufacturing and use.
In view of the failure of the hydraulic system, industry experts from Guangzhou Oulite Machinery Equipment Co., Ltd. have drawn some application conclusions and analyzed the reasons for the unstable lifting speed of the scissor lift:
(1) The composition of the lifting hydraulic circuit. Oil pump relief valve, reversing valve, reversing valve, one-way throttle valve (no throttle), lifting cylinder.
(2) Establish a speed rigidity analysis formula for the lifting circuit. The flow into the hydraulic cylinder, that is, the flow through the one-way throttle valve. In the formula, it is the flow through the throttle valve; the throttle orifice shape of the throttle valve and the coefficients related to the viscosity of the hydraulic oil; AT inlet is the orifice flow Area (lift without throttling); outlet pressure of the hydraulic pump; P1 is the pressure of the hydraulic cylinder's inlet cavity to increase the area of the plunger of the hydraulic cylinder; the index determined by the shape of the orifice, the speed of the speed control circuit can be known , When the throttle valve port area is constant, the output speed of the hydraulic cylinder will change with the change of the load. The degree of influence of load change on speed is expressed by speed stiffness T: As the load increases, the output speed of the hydraulic cylinder of the elevator actuator decreases by a negative number; in order to make the advance a positive number, a negative sign is added to the formula. Substituting a scissor elevator, the greater the speed stiffness of the imported throttle speed control circuit, the better the speed stability of the hydraulic circuit.
According to the above analysis, the reasons for the unstable lifting speed of the scissor lift are as follows:
(1) When the load is constant, the smaller the throttle valve inlet, the higher the system speed rigidity; on the contrary, the larger the throttle valve opening area, the lower the inlet.
(2) When the load is constant, the speed stiffness at low speed is good, when the load changes, the speed stiffness is good when the load is small.
(3) Increasing the oil supply pressure increases the effective area of the hydraulic cylinder, which can increase the speed rigidity.
In summary, the main reason for the failure of the scissor lift is the unreasonable design of the hydraulic system's lifting speed control circuit.
