There are various types of mechanical equipment, and their functions and modes of movement are also different. Some mechanisms are relatively small and flexible, and some mechanisms are thick and clumsy, but they remain the same. In the structure of machinery, power transmission has evolved step by step from ancient mechanical methods to today's extensive use of motors, pneumatics, and hydraulic transmissions. This not only brings about changes in power efficiency, but also enables precise control of mechanical structure movements during processing, making ideal digital and automated processing methods become possible. Among the four major categories of transmission methods (mechanical, electrical, hydraulic and pneumatic) that are currently widely used, today I would like to share with you a comparison of the pros and cons of the four transmission methods.
Mechanical Transmission
Gear transmission
Gear transmission is the most widely used form of transmission in mechanical transmission. It's transmission is relatively accurate, high efficiency, compact structure, reliable operation and long life. Gear transmissions can be divided into many different types according to different standards.
Advantages:
Compact structure, suitable for short-distance transmission, wide range of applicable circumferential speed and power, accurate, stable and efficient transmission ratio, high working reliability and long life, parallel axes, intersecting axes at any angle and staggered at any angle can be realized transmission between shafts.
Disadvantages:
Requires high manufacturing and installation accuracy and high cost, is not suitable for transmission between two axes at long distances, has no overload protection function.
Turbine worm drive
Applicable to motion and dynamics between two axes that are vertical but not intersecting in space.
Advantages:
Large transmission ratio, compact structure and size.
Disadvantages:
Large axial force, easy to generate heat, low efficiency, and can only drive in one direction. The main parameters of the turbine worm drive are: module, pressure angle, worm gear pitch circle, worm pitch circle, lead, number of worm gear teeth, number of worm heads; transmission ratio, etc.
Belt drive
A belt drive is a mechanical transmission that uses a flexible belt tensioned on a pulley to transmit movement or power. Belt transmission usually consists of a driving pulley, a driven pulley and an endless belt tensioned on the two pulleys.
Advantages:
It is suitable for transmissions with a large center distance between two axes. The belt has good flexibility, which can alleviate impact and absorb vibration. It slips to prevent damage to other parts when overloaded. It has a simple structure and low cost.
Disadvantages:
The outer size of the transmission is large, a tensioning device is required, a fixed transmission ratio cannot be guaranteed due to slippage, the belt life is short, the transmission efficiency is low.
Chain drive
Chain drive is a transmission method that transmits the movement and power of a driving sprocket with a special tooth shape to a driven sprocket with a special tooth shape through a chain. Including active chain, driven chain, and ring chain.
Advantages:
Compared with belt drive, there is no elastic sliding and slipping phenomenon, the average transmission ratio is accurate, the operation is reliable, and the efficiency is high. The transmission power is large, the overload capacity is strong, the transmission size is small under the same working conditions, the required tension force is small. The pressure acting on the shaft is small, it can work in harsh environments such as high temperature, humidity, dust, and pollution. Compared with gear transmission, chain transmission has lower manufacturing and installation accuracy requirements, when the center distance is large, its transmission structure is simple.
Disadvantages:
Can only be used for transmission between two parallel shafts, high cost, easy to wear, easy to stretch, poor transmission stability, additional dynamic load, vibration, impact and noise will be generated during operation, so it is not suitable for use in rapid reverse transmission .
Gear train
A transmission consisting of two or more gears is called a gear train. Gear transmission can be divided into ordinary gear transmission and planetary gear transmission according to whether there are gears with axial movement in the gear train. Gears with axial movement in the gear train are called planetary gears.
1) The gear train is divided into two types: fixed axis gear train and epicyclic gear train.
2) The ratio of the angular velocity (or rotational speed) of the input shaft and the output shaft in the gear train is called the transmission ratio of the gear train. It is equal to the ratio of the product of the number of teeth of all driven gears in each pair of meshing gears to the product of the number of teeth of all driving gears.
3) In the epicyclic gear system, the gears whose axis position changes, that is, the gears that rotate and revolve, are called planetary gears, and the gears whose axis position is fixed are called sun gears.
4) The transmission ratio of the epicyclic gear train cannot be calculated directly by the method of solving the transmission ratio of the fixed-axis gear train. The principle of relative motion must be used and the relative speed method (or called the inversion method) is used to convert the epicyclic gear train into a hypothetical one. Fixed axis gear train calculation.
5) Main features of the gear train:It is suitable for transmission between two shafts that are far apart; it can be used as a transmission to achieve variable speed transmission; it can obtain a larger transmission ratio; it can realize the synthesis and decomposition of motion.
Electric Transmission
Electric transmission refers to the use of electric motors to convert electrical energy into mechanical energy to drive various types of production machinery, transportation vehicles, and items that need to move in life.
The main characteristics of electric transmission are:
1) High precision: The servo motor is used as the power source and consists of a ball screw and a synchronous belt to form a transmission mechanism with a simple structure and high efficiency. Its repeatability error is 0.01%.
2) Energy saving: The energy released during the deceleration phase of the working cycle can be converted into electrical energy for reuse, thereby reducing operating costs. The connected electrical equipment is only 25% of the electrical equipment required for hydraulic drive.
3) Precision control: Precise control is achieved based on set parameters. With the support of high-precision sensors, measuring devices, and computer technology, it can greatly exceed the control accuracy achieved by other control methods.
4) Improve the level of environmental protection: Due to the reduction of energy types and its optimized performance, pollution sources are reduced and noise is reduced, providing a better guarantee for the environmental protection work of the factory.
5) Reduce noise: Its operating noise value is less than 70 decibels, which is about 2/3 of the noise value of a hydraulically driven injection molding machine.
6) Cost saving: This machine eliminates the cost and trouble caused by hydraulic oil. There are no hard pipes or soft pipes, no need to cool the hydraulic oil, and the cost of cooling water is greatly reduced.
Pneumatic Transmission
Pneumatic transmission uses compressed gas as the working medium and relies on the pressure of the gas to transmit power or information to the fluid transmission.
Advantages:
1) Using air as the working medium, it is relatively easy to obtain the working medium. The used air is discharged into the atmosphere and is easy to handle. Compared with hydraulic transmission, there is no need to set up recycled oil tanks and pipelines.
2) Since the viscosity of air is very small (about one ten thousandth of the dynamic viscosity of hydraulic oil), its loss is also very small, so it is convenient for centralized air supply and long-distance transportation. External leakage will not pollute the environment as seriously as hydraulic transmission.
3) Compared with hydraulic transmission, pneumatic transmission has fast action, quick response, simple maintenance, clean working medium, and no problems such as medium deterioration.
4) It has good adaptability to the working environment, especially in harsh working environments such as flammable, explosive, dusty, strong magnetism, radiation, vibration, etc. It is superior to hydraulic, electronic and electrical controls.
5) Low cost, automatic overload protection.
Disadvantages:
1) Since air is compressible, the working speed stability is slightly worse. However, the use of gas-liquid linkage device will achieve more satisfactory results.
2) Because the working pressure is low (generally 0.31MPa) and the structural size should not be too large, the total output force should not be greater than 10~40kN.
3) The noise is loud, so a muffler must be added when exhausting at high speed.
4) The transmission speed of gas signals in pneumatic devices is slower than the speed of electrons and light within the speed of sound. Therefore, pneumatic control systems should not be used in complex circuits with too many component levels.
Hydraulic Transmission
Hydraulic transmission is a transmission method that uses liquid as a working medium to transmit energy and control.
Advantage:
1) From a structural point of view, its output power per unit weight and output power per unit size are the best among the four types of transmission methods. It has a large moment-to-inertia ratio. When transmitting the same power, the hydraulic transmission device is Small size, light weight, small inertia, compact structure and flexible layout.
2) From the perspective of working performance, the speed, torque and power can be adjusted steplessly, the action is responsive, the direction can be changed and speed changed quickly, the speed adjustment range is wide, and the speed adjustment range can reach 100:1 to 2000:1; action It has good speed, relatively simple control and adjustment, convenient and labor-saving operation, and is easy to cooperate with electrical control and connect to CPU (computer) to facilitate automation.
3) From the perspective of use and maintenance, the components have good self-lubricating properties, are easy to achieve overload protection and pressure maintenance, and are safe and reliable; the components are easy to achieve serialization, standardization, and generalization.
4) All equipment using hydraulic technology has good safety and reliability.
5) Economy: Hydraulic technology has strong plasticity and variability, which can increase the flexibility of flexible production and make it easy to change and adjust production procedures. The manufacturing cost of hydraulic components is relatively low, and the adaptability is relatively strong.
6) Hydraulics can be easily combined with new technologies such as microcomputer control to form "mechanical-electronic-hydraulic-optical" integration, which has become a trend of world development and facilitates digitalization.
Disadvantages:
1) Hydraulic transmission inevitably leaks due to relatively moving surfaces. At the same time, the oil is not absolutely incompressible. Coupled with the elastic deformation of oil pipes, etc., hydraulic transmission cannot obtain a strict transmission ratio, so it cannot be used for machine tools such as threaded gear processing. in the inline transmission chain.
2) There are edge losses, local losses and leakage losses during the oil flow process. The transmission efficiency is low and is not suitable for long-distance transmission.
3) There are certain difficulties in using hydraulic transmission under high and low temperature conditions.
4) In order to prevent oil leakage and meet certain performance requirements, hydraulic components require high manufacturing precision, which brings certain difficulties to use and maintenance.
5) It is difficult to check when a fault occurs, especially in units where hydraulic technology is not widely used. This contradiction often hinders the further promotion and application of hydraulic technology. Hydraulic equipment maintenance requires a certain amount of experience, and training hydraulic technicians takes a long time.
