Lifting unit is one of the most common mechanisms in mechanical equipment, especially in conveying-related mechanical equipment and production lines, it can be seen everywhere, and it can also be flexibly used in AGV body or related equipment. In terms of structure, it can be mainly divided into screw type, gear type, chain drive type, scissor type, timing belt type, hydraulic type, cam type, worm gear type, connecting rod type, etc., covering almost all mechanical transmission structures.
1. Main structure types, characteristics and application scenarios of lifting units
|
structure type |
usability
|
Schematic
|
advantage
|
shortcoming
|
Application scenarios
|
| gear drive | high | 
|
Wide range of use speed and power, accurate transmission ratio, good stability, high transmission efficiency and long service life. | High manufacturing precision and high manufacturing cost, not suitable for occasions with large wheelbase or long-distance transmission | Commonly used in machine tools, automobile gearboxes, motor reducers, etc. |
| chain drive | high | 
|
Long transmission distance, simple structure, low manufacturing precision requirements | Low transmission accuracy, instantaneous transmission speed and transmission ratio are not constant | Commonly used in forklifts, vertical warehouses, bicycles, etc. |
| Timing belt type | high | 
|
Accurate transmission ratio, high transmission efficiency and low cost. Elastic and shock-resistant, with little noise | Compared with chain drive and gear drive, the transmission torque is small, and it is easy to age, break or become longer in contact with liquids such as lubricating oil or at higher temperatures. | Usually used in conjunction with a motor |
| Screw drive type | high | 
|
Low friction, stable movement, high transmission efficiency, high positioning accuracy, good accuracy retention, sensitive transmission, low noise, and high synchronization | The cost is high, the installation accuracy is high, and sometimes it needs to be used in conjunction with the guide mechanism. The use environment needs to be waterproof and dustproof | Suitable for machine tools, automated production lines, etc. |
| scissor | middle | 
|
It can be folded and takes up little space. The lifting action is relatively stable and the cost is low | High requirements for power source, not conducive to low-carbon environmental protection and cost reduction | Commonly used in retractable doors and lifts |
| Cam drive type | high | 
|
The structure is relatively simple, and the follower can obtain various expected motion laws only by reasonably designing the contour curve of the cam, and the design is relatively easy | Due to point or line contact, in the process of interaction force and relative motion, large friction and wear will occur, and the transmission distance is small. | Mostly used in automated production lines, food machinery or packaging machinery |
| Worm gear drive type | Low | 
|
The transmission ratio is large, the structure size is compact, and the transmission torque is also large. | The axial force is large, the friction contact is easy to generate heat, and the transmission efficiency is low. | Usually used in reducers |
2. Calculation of lifting force and speed
The following is a brief introduction to the calculation of some main parameters of gear drive, chain drive, synchronous belt drive and screw drive. In actual application, due to different specific use conditions, appropriate adjustments can be made on the basis of the following calculations. The calculation methods of several other transmission modes will be quite different due to different specific structural details, so this article will not introduce them.
2.1 Gear drive, chain drive, synchronous belt drive
Since the transmission principles of gear drive, chain drive, and synchronous belt drive are similar, this paper will take gear drive as an example to list the parameter calculation formulas that are highly concerned in design. Usually, in the design, the higher calculation frequency includes lifting speed, lifting force and motor power. The calculation formulas of these three parameters are listed below. If you need to check other parameters, you can also use the following formulas to change according to your needs.
·v=n*2πr
·F=T/r
·P=T*n/(9550*i)
Where n: motor speed (r/s)
T: Motor torque (N・m)
P: Motor power (kw)
r: gear indexing circle radius (m)
i: gear ratio
2.2 Screw drive
The lead screw drive is a transmission method that converts the rotary motion of the lead screw into the linear motion of the lead screw nut, thereby driving the load to move in a straight line. The calculation formulas of the three main parameters are as follows.
·v=n*2πr=nPh
·F=2π*T/Ph
·P=T*n/(9550*i)
Where n: motor speed (r/s)
Ph: lead screw (m)
T: Motor torque (N・m)
P: Motor power (kw)
i: gear ratio
In order to ensure that the designed mechanism can work normally within the set parameter range, and at the same time has the ability to resist shock and other special conditions within a certain range, it is necessary to consider a certain margin in the actual design process. In addition, the transmission efficiency of the energy in the transmission process should also be considered. The transmission efficiency of various structures can be found in the mechanical transmission efficiency of Volume 1 of “Mechanical Design Handbook”.
3. Precautions in design or use
3.1 Gear type transmission
At high speed, heavy load or high precision, harder (quenched or carburized, etc.) gears should be used, on the contrary, softer (normalized or quenched and tempered) gears can be used. Gears made of cast iron or non-metallic materials can also be selected according to different conditions of use. In terms of structure selection, if the transmission shaft is parallel, a spur gear or a helical gear is generally used, and when the transmission shaft has a certain angle, a bevel gear or a helical gear is used. Bearing the effect of axial force, the design should consider eliminating the effect of axial force as much as possible.
3.2 Chain drive
After a period of use, the chain will loosen and become longer, and an anti-loosening mechanism should be properly set up, such as shortening the chain and adding tensioning wheels. Chains and sprockets should be cleaned or lubricated regularly to increase their service life.
3.3 Synchronous belt drive
When using the synchronous belt, pay attention to adjusting the spacing between the pulleys (or increase the tensioning pulley) to keep the synchronous belt at an appropriate tension. The pulley should maintain a good parallelism to prevent the timing belt from deviating or belt skipping. Timing belts should be replaced regularly. When multiple timing belts are used at the same time, they should be replaced in the same batch as much as possible to avoid using old and new belts at the same time. It is not allowed to use sharp tools when installing the timing belt, so as to avoid damage to the belt body and cause it to break during transmission.
3.4 Screw drive
When the lead screw is driven, it is necessary to ensure sufficient lubrication to prevent the occurrence of impact. In addition, dustproof measures should be taken (installation of lead screw sheath, etc.) to avoid excessive friction and accelerated lead screw wear. When the lead screw is applied, it is usually used in conjunction with parts such as linear guides to avoid the lead screw being subjected to radial force, resulting in abnormal wear and shortened life.
