We turn our attention to belt-drive scissor lift tables in the second article of our series on Lift table types and their advantages and disadvantages .
Modern belt-drive scissor lift tables primarily rely on the use of flat belts. However, many of the positive as well as negative properties listed here can also be transferred to other types of lift tables with traction devices.
The belt of this type of lift table is connected at one end to the electric motor via a gearbox and at the other end to the scissor lift mechanism or a lift carriage.
Put simply, the scissor lift is retracted and extended by rolling the belt on and off a shaft. By 'shortening' the length of the belt, the scissor lift becomes steeper and the platform is raised with the load. Conversely, unrolling the belt will 'lengthen' the belt and lower the load.
The fact that it does not use hydraulic oil as a pressure medium can be associated with some advantages. For example, there is no risk of leaks due to improperly laid hydraulic lines or material failure. Belt-drive scissor lift tables can therefore be used in food processing areas without having to take special measures because of the hydraulic oil.
The drive unit of spindle lift tables must be installed inside the lift platform. This disadvantage does not apply to belt-drive scissor lift tables, as the traction traction device can be easily guided outside by a deflection pulley. However, the positioning of the power unit cannot be quite as discretionary as is usual with a hydraulic scissor lift table, for example.
If a force peak occurs during the lifting or lowering process, this is dampened by the elasticity of the belt. The same positive effect also manifests itself in any vibrations, which greatly reduces the risk of natural vibration. This dampening effect of the flat belt protects the drive from unwanted force effects.
Earlier designs used a single belt for power transmission. Bystanders would be exposed to great danger if this single belt were to be damaged. For this reason, up to six belts are used in modern lift tables, depending on the load capacity.
However, this new design has created a new problem. Due to the existing elongation slip, the individual belts are loaded unevenly during the lifting process and are subject to constant tension changes.
The composition of the material of the belts prevents them from being used in higher temperature ranges. Although high temperatures are also not unproblematic in other types of lift tables, appropriate aids such as oil coolers can be used. Unfortunately, this is not possible with belt-drive scissor lift tables, so that either other lift table designs must be used or suitable ambient conditions must be created.
The belts are particularly sensitive to external influences when they are under load. This applies to both external forces and to contamination of the belt through oil, petrol, water, dirt or dust. Theoretically, the belt could be protected by encapsulation, but the movement of the shears makes this option difficult to implement.
The continuous stretching of the traction device during lifting and lowering of the lift table necessitates the re-tensioning of the belts throughout their service life.
In a hydraulic lift table, the energy balance sheet is often improved by the fact that the electric motor only has to be operated during the lifting process. All the energy needed to lower the scissor lift is provided by the potential energy of the load and the dead weight of the lift table.
In a belt-drive scissor lift table, the electric motor is usually needed both for rolling the traction device on and off. In principle, the belt could also be unrolled using the lift table’s dead weight, but this would make it more difficult to fix the load at a certain height.