What is power transmission?
The transmission method is an engineering method that matches the power machine and the working part of the machine in terms of energy configuration, movement speed and motion form.
Types of power transmission
There are four types of power transmission methods, including mechanical power transmission, electrical power transmission, hydraulic power transmission and pneumatic power transmission.
Of the four major types of transmissions (mechanical, electrical, hydraulic, and pneumatic) that are currently in use, none of the power transmissions are perfect.
Today I would like to share with you the advantages and disadvantages of the four transmission methods.
Type 1: Mechanical Transmission
What is mechanical power transmission?
Mechanical power transmission refers to products used for moving parts systems, not systems used for electric power supply.
These products include couplings, chains and sprockets, belts and pulleys, and drive components.
Mechanical transmission system:
It is an important part of the machine tool.
It is mainly driven by the ball screw.
The ball screw and the moving shaft are integrated in the transmission process.
The machine tool is driven by the motor.
The function of mechanical transmission is to transmit motion and force.
The commonly used mechanical transmission types include gear transmission, worm gear transmission, belt transmission, chain transmission and gear train.
The role of mechanical transmission:
The role of mechanical transmission is to transmit motion and force
Types of mechanical power transmission
The most common mechanical power transmission mainly includes: gear drive, turbo vortex drive, belt drive, chain drive, gear train etc.
01 Gear Drive
Gear transmission is the most widely used form of transmission in mechanical transmission.
Its transmission is more accurate, high efficiency, compact structure, reliable operation and long service life.
Gear drives can be divided into many different types according to different standards.
- Compact structure, suitable for short-distance transmission;
- Wide range of applicable peripheral speeds and powers;
- The transmission ratio is accurate, stable and efficient;
- High reliability and long life;
- It can realize the transmission between the parallel axis, the intersecting axis of any angle and the staggered axis of any angle.
- High manufacturing and installation accuracy and high cost;
- Not suitable for transmission between two axes at a long distance;
- No overload protection.
02 Turbo Vortex Drive
Suitable for motion and power between two axes with vertical and non-intersecting spaces.
- Large transmission ratio;
- The structure is compact.
- Large axial force
- Easy to heat
- Low efficiency
- Only one-way transmission.
The main parameters of the turbine drive are:
- Pressure angle
- Worm gear indexing circle
- Worm indexing circle
- Lead stroke
- Worm gear number
- Number of worm heads
- Transmission ratio
03 Belt Drive
A belt drive is a mechanical transmission that utilizes a flexible belt that is tensioned on a pulley for motion or power transmission.
The belt drive usually consists of a drive wheel, a driven wheel and an endless belt that is tensioned on the two wheels.
1) For the case where the direction of the parallel rotation of two axes is the same, it is called the concept of opening motion, center distance and wrap angle.
2) The type of belt can be divided into three categories according to the cross-sectional shape: flat belt, V belt and special belt.
3) The application focus is:
- the calculation of the transmission ratio;
- the stress analysis calculation of the belt;
- the allowable power of the single V-belt.
Pros and cons of belt driving：
- Applicable to the transmission with a large center distance between the two shafts, the belt has good flexibility, can mitigate the impact and absorb vibration;
- Slip during overload to prevent damage to other parts;
- Simple structure and low cost.
- The outer dimensions of the transmission are large;
- The tensioning device is required;
- Due to slippage, a fixed gear ratio cannot be guaranteed;
- The belt has a short life span;
- The transmission efficiency is low.
04 Chain Drive
The chain drive is a transmission method in which the movement and power of a drive sprocket having a special tooth shape are transmitted to a driven sprocket having a special tooth shape through a chain.
- active chain
- driven chain
- circular chain
Chain drives have many advantages, compared to belt drives,
- Inelastic sliding and slipping phenomenon, accurate average transmission ratio, reliable operation and high efficiency;
- The transmission power is large, the overload capability is strong, and the transmission size under the same working condition is small;
- The required tension is small, and the pressure acting on the shaft is small;
- It can work in harsh environments such as high temperatures, humidity, dust, and pollution.
Compared with gear transmission, chain drive featured:
- Low manufacturing and installation requirements;
- When the center distance is large, the transmission structure is simple;
- The instantaneous chain speed and instantaneous gear ratio are not constant, and the transmission is less stable.
The main disadvantages of the chain drive are:
- Can only be used for transmission between two parallel shafts
- High cost
- Easy to wear, easy to stretch, poor transmission stability
- Additional dynamic loads, vibration, shock and noise are generated during operation
- It should not be used in a fast reverse drive.
05 Gear Train
A transmission consisting of more than two gears is called gear train.
According to whether there is axis movement in the gear train, the gear transmission can be divided into ordinary gear transmission and planetary gear transmission.
A gear that has an axis motion in a gear train is called a planetary gear.
1) The gear train is divided into two types: fixed axle train and epicyclic train.
2) The ratio of the angular velocity (or rotational speed) of the input shaft to the output shaft in the train is called the gear ratio of the train.
It is equal to the ratio of the product of the number of teeth of all the follower gears in each pair of meshing gears to the number of teeth of all the driving gears.
3) In the epicyclic gear train, the gear whose axis position changes, that is, the gear that is both rotated and revolved, is called a planetary gear, and the gear with a fixed axial position is called a center gear or a sun gear.
4) The gear ratio of the epicyclic gear train cannot be directly calculated by the method of solving the fixed axle train ratio.
The relative motion method (or inversion method) must be used to convert the epicyclic gear train into a hypothetical fixed axle train using the principle of relative motion.
Features of gear train:
- Suitable for transmission between two axes that are far apart;
- Can be used as a transmission to achieve variable speed transmission;
- A larger gear ratio can be obtained;
- Achieve the synthesis and decomposition of motion.
Type 2: Electric Drive
Electric drive 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 be moved in life.
High precision: Servo motor is used as the power source, and the ball screw and timing belt are composed of a simple and efficient transmission mechanism. Its repeatability error is 0.01%. The press brake machine is using this transmission method.
Energy-saving: The energy released in the deceleration phase of the work cycle can be converted into electrical energy for reuse, thus reducing operating costs, and the connected electrical equipment is only 25% of the power equipment required for hydraulic driving.
Precise control: Accurate control according to set parameters, with the support of high-precision sensors, measuring devices, computer technology, can greatly exceed the control accuracy that can be achieved by other control methods.
Environmental protection: Due to the reduction of energy use and its optimized performance, the pollution source is reduced and the noise is reduced, which provides a better guarantee for the environmental protection work of the factory.
Noise reduction: The operating noise value is less than 70 decibels, which is about 2/3 of the noise value of the hydraulically driven injection molding machine.
Cost-saving: the cost of hydraulic oil and the trouble caused are removed. There is no hard pipe or soft pipe, no need to cool the hydraulic oil, and the cooling water cost is greatly reduced.
Type 3: Pneumatic Transmission
The pneumatic transmission uses compressed gas as the working medium, and the fluid transmission of the power or information by the pressure of the gas.
- With air as the working medium, the working medium is relatively easy to obtain, and the used air is discharged to the atmosphere, which is convenient to handle, and it is not necessary to provide a recovered fuel tank and pipeline compared with the hydraulic transmission.
- Because the viscosity of air is very small (about one ten-thousandth of the viscosity of hydraulic oil), its loss is also small, so it is convenient to concentrate gas supply and long-distance transportation. External leaks do not pollute the environment as much as hydraulic drives.
- Compared with the hydraulic transmission, the pneumatic transmission has a quick action, fast response, simple maintenance, clean working medium, and no deterioration of the medium.
- The working environment has good adaptability, especially in the harsh working environment such as flammable, explosive, dusty, strong magnetic, radiation, vibration, etc., superior to hydraulic, electronic and electrical control.
- The cost is low and the overload can be automatically protected.
- Due to the compressibility of the air, the working speed is less stable. However, the use of a gas-liquid linkage device will get satisfactory results.
- Due to low working pressure (generally 0.31 MPa), and because the structure size should not be too large, the total output force should not be greater than 10 ~ 40kN.
- The noise is large, and a muffler is added at the time of high-speed exhaust.
- The gas signal transmission speed in the pneumatic device is slower than the electron and light speed within the sound velocity. Therefore, the pneumatic control system should not be used in complex circuits with too many component stages.
Type 4: Hydraulic Transmission
Hydraulic transmission is a transmission method that uses liquid as a working medium to transfer energy and control.
- From the structural point of view, the output power per unit weight and the output power per unit size is force-compressed in the four types of transmission modes, and have a large moment inertia ratio. The volume of the hydraulic transmission is small when the same power is transmitted. Light weight, low inertia, compact structure and flexible layout.
- From the performance point of view, speed, torque, power can be steplessly adjusted, fast response, fast commutation and shifting, wide speed range, speed range up to 100:1 to 2000:1; fast action, the control and adjustment are relatively simple, the operation is convenient and labor-saving, and it is convenient to cooperate with the electrical control, and the connection with the CPU (computer) to facilitate automation.
- From the point of view of use and maintenance, the components have good self-lubricating properties, easy to achieve overload protection and pressure keeping, safe and reliable; components are easy to achieve serialization, standardization and generalization.
- All equipment with hydraulic technology is safe and reliable.
- Economy: The plasticity and variability of hydraulic technology are very strong, which can increase the flexibility of flexible production, and easy to change and adjust the production process. Hydraulic components are relatively inexpensive to manufacture and have relatively high adaptability.
- Easy combination of hydraulic technology with new technologies such as microcomputer control constitutes the “machine-electric-hydraulic-light” integration, which has become the trend of world development and is easy to realize digitalization.
Everything has two sides, there are advantages and disadvantages. Hydraulic drives are no exception:
- The hydraulic transmission is inevitably leaked due to the relative moving surface, and the oil is not absolutely incompressible. In addition, the hydraulic transmission can not obtain a strict transmission ratio, and thus cannot be used in the transmission chain of machine tools such as threaded gears.
- There are losses such as along loss, local loss and leakage during the flow of oil, and the transmission efficiency is low, which is not suitable for long-distance transmission.
- Under high temperature and low-temperature conditions, the hydraulic transmission has certain difficulties.
- In order to prevent oil leakage and to meet certain performance requirements, hydraulic components are manufactured with high precision requirements, which poses certain difficulties for use and maintenance.
- It is difficult to check for faults, especially for units where hydraulic technology is not popular. This contradiction often hinders the further promotion and application of hydraulic technology. Hydraulic equipment maintenance requires a certain amount of experience and the training for hydraulic technicians needs a longer period of time.