Currently, among the four major types of power transmission (mechanical, electrical, hydraulic, and pneumatic), none is perfect. They each have their strengths and weaknesses. So, which of the four transmission methods truly reigns supreme? Let's take a look at their comparisons!
I. Mechanical Transmission
1. Gear transmission
1) Classification: planar gear transmission, spatial gear transmission.
2) Features:
Advantages: Wide range of applicable circumferential speeds and power; accurate, stable, and efficient transmission ratio; high reliability and long service life; can realize transmission between parallel shafts, shafts intersecting at any angle, and shafts crossing at any angle.
Disadvantages: Requires high manufacturing and installation precision, and has high cost; not suitable for long-distance transmission between two shafts.
3) The basic dimensions of involute standard gears include: addendum circle, dedendum circle, pitch circle, module, pressure angle, etc.
2. Worm Gear Drive
It is applicable to motion and dynamics between two axes that are perpendicular to each other in space but do not intersect.
1) Features:
Advantages: Large transmission ratio; compact structure.
Disadvantages: High axial force, prone to overheating, low efficiency; can only transmit in one direction.
The main parameters of worm gear drives include: module, pressure angle, worm wheel pitch circle, worm pitch circle, lead, number of worm wheel teeth, number of worm threads, and transmission ratio.
3. Belt drive
It includes the driving pulley, the driven pulley, and the annular belt.
1) When two axes rotate in the same direction while parallel, it is called open motion, and the concepts of center distance and wrap angle are used.
2) Belts can be classified into three main categories according to their cross-sectional shape: flat belts, V-belts, and special belts.
3) The key points in application are: calculation of transmission ratio; stress analysis and calculation of belt; allowable power of a single V-belt.
4) Characteristics of belt drives:
Advantages: Suitable for transmissions with a large center distance between two shafts; the belt has good flexibility, which can mitigate impact and absorb vibration; it slips under overload to prevent damage to other parts; it has a simple structure and low cost.
Disadvantages: The transmission has a large overall size; a tensioning device is required; due to slippage, a constant transmission ratio cannot be guaranteed; the belt has a short lifespan; and the transmission efficiency is low.
4. Chain drive
Including: active chain, passive chain, and circular chain.
Compared with gear drives, chain drives have the following main characteristics: lower requirements for manufacturing and installation precision; simpler transmission structure when the center distance is large; and poorer transmission smoothness due to the non-constant instantaneous chain speed and instantaneous transmission ratio.
5. Gear train
1) Gear trains are divided into two types: fixed-axis gear trains and planetary gear trains.
2) The ratio of the angular velocity (or rotational speed) of the input shaft to the output shaft in a 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 a planetary gear train, the gear whose axis position changes, that is, the gear that both rotates on its own axis and revolves around the sun, is called a planetary gear, while the gear whose axis position is fixed is called a central gear or sun gear.
4) The transmission ratio of an planetary gear train cannot be calculated directly using the method for solving the transmission ratio of a fixed-axis gear train. It is necessary to use the principle of relative motion and the relative velocity method (or the reversal method) to transform the planetary gear train into a hypothetical fixed-axis gear train for calculation.
5) Main characteristics of gear trains:
It is suitable for transmission between two shafts that are far apart; it can be used as a gearbox to achieve speed change; it can obtain a large transmission ratio; and it can realize the synthesis and decomposition of motion.
II. Electrical Drive
advantage:
1. High accuracy
The servo motor , as the power source, consists of a simple yet highly efficient transmission mechanism composed of ball screws and synchronous belts. Its repeatability error is 0.01%.
2. Save energy
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 by setting parameters. With the support of high-precision sensors , metering devices, and computer technology, the control accuracy can be greatly exceeded that of other control methods.
4. Improve environmental protection standards
The reduction in energy types and their optimized performance have led to fewer pollution sources and lower noise levels, providing a better guarantee for the factory's environmental protection efforts.
5. Reduce noise
Its operating noise level is below 70 decibels, which is about 2/3 of the noise level of a hydraulically driven injection molding machine.
6. Cost savings
This machine eliminates the cost and hassle of hydraulic oil, has no rigid pipes or flexible hoses, does not require hydraulic oil cooling, and significantly reduces cooling water costs.
shortcoming:
1. Mechanical properties: low hardness, poor stability;
2. Low power transmission;
3. Only suitable for situations where speed regulation requirements are not high.
III. Hydraulic Transmission
advantage:
1. Structurally, its output power per unit weight and output power per unit size are superior among the four types of transmission methods. It has a large torque-to-inertia ratio. When transmitting the same power, the hydraulic transmission device is small in size, light in weight, has low inertia, compact structure, and flexible layout.
2. In terms of performance, speed, torque and power can be steplessly adjusted, the action response is fast, it can quickly change direction and speed, the speed adjustment range is wide, the speed adjustment range can reach 100:1 to 2000:1; the action is fast, the control and adjustment are relatively simple, the operation is convenient and labor-saving, it is easy to cooperate with electrical control, and it is easy to connect with CPU (computer) to realize automation.
3. From the perspective of use and maintenance, the components have good self-lubricating properties, are easy to achieve overload protection and pressure holding, and are safe and reliable; the components are easy to serialize, standardize and generalize.
4. All equipment using hydraulic technology is safe and reliable.
5. Economy: Hydraulic technology is highly adaptable and variable, which can increase the flexibility of flexible production and make it easy to change and adjust the production process. Hydraulic components are relatively inexpensive to manufacture and have strong adaptability.
6. Hydraulics can be easily combined with new technologies such as microcomputer control to form an integrated "mechanical-electrical-hydraulic-optical" system, which has become a global trend and facilitates digitalization.
shortcoming:
Everything has two sides, and hydraulic transmission is no exception.
1. Due to the inevitable leakage caused by the relatively moving surfaces in hydraulic transmission, and the fact that the oil is not absolutely incompressible, coupled with the elastic deformation of oil pipes, hydraulic transmission cannot achieve a strict transmission ratio. Therefore, it cannot be used in the internal transmission chain of machine tools such as those used for machining threaded gears.
2. During the oil flow process, there are losses along the flow path, local losses, and leakage losses, resulting in low transmission efficiency and making it unsuitable for long-distance transmission.
3. Under high and low temperature conditions, it is difficult to use hydraulic transmission.
4. To prevent oil leakage and to meet certain performance requirements, hydraulic components require high manufacturing precision, which brings certain difficulties to their use, maintenance and repair.
5. Faults are difficult to diagnose, especially in units where hydraulic technology is not widely adopted. This contradiction often hinders the further promotion and application of hydraulic technology. Hydraulic equipment maintenance relies on experience, and training hydraulic technicians takes a considerable amount of time.
IV. Pneumatic Transmission
advantage:
1. It uses air as the working medium, which is relatively easy to obtain. The air is discharged into the atmosphere after use, making it easy to handle. Compared with hydraulic transmission, it does not require the installation of a recovery tank and pipeline.
2. Because air has a very low viscosity (approximately one ten-thousandth the dynamic viscosity of hydraulic oil), its loss is also very small, making it easy to centrally supply air and transport it over long distances. External leakage will not cause as much environmental pollution as hydraulic transmission.
3. Compared with hydraulic transmission, pneumatic transmission is faster, more responsive, easier to maintain, and uses a cleaner working medium, eliminating problems such as medium deterioration.
4. It has good adaptability to working environment, especially in harsh working environments such as flammable, explosive, dusty, strong magnetic, radiation, and vibration environments, where it is superior to hydraulic, electronic, and electrical control.
5. Low cost, with automatic overload protection.
shortcoming:
1. Because air is compressible, its operating speed stability is slightly poor. However, using a pneumatic-hydraulic linkage device will yield more satisfactory results.
2. Due to the low working pressure (generally 0.3-1.0 MPa) and the fact that the structural dimensions should not be too large, the total output force should not exceed 10-40 kN.
3. The noise level is relatively high, so a muffler should be added when the exhaust is at high speed.
4. The speed of air signal transmission in pneumatic devices is slower than that of electrons and light, which is within the speed of sound. Therefore, pneumatic control systems are not suitable for complex circuits with too many component stages.
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