Are all servo motors equipped with planetary reducers? What is the possibility of not having a planetary reducer? Please be more specific.

How to understand the reducer and what is it used for? How to classify? If it is used in low-speed occasions, what is the relationship between ordinary motor, reducer, frequency converter, servo driver and servo motor? How to choose servo motor and reducer? Can you tell me more about it?

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The reply is as follows: (after finishing)

First, the general understanding of the reducer:

The simplest understanding is that the reducer changes speed, outputs torque, provides large torque and low speed. Speed ratio of reducer = input speed/output speed. If the speed ratio is 100, the output torque is about 100 times of the input torque. (Slow speed, increase torque)

The reducer is also a gearbox, but the gearbox is usually used to slow down, so it is used to being called a reducer. Generally, the speed reducer has a fixed transmission ratio, which can be adjusted, but it is generally step-by-step speed regulation.

It is easy to think that the car has an adjustable reducer, so the car has several gears. Gasoline engine (diesel engine), like electric motor, can change the throttle speed, but the change range is not big.

Of course, the clutch and the reducer are not the same thing, but generally speaking of the reducer, people can easily think of the speed change of the car, which is the credit of the clutch. In fact, every shift is completed after pulling the shift lever. Generally, the adjustable gearbox cannot be loaded when shifting gears, so the output of the reducer should be separated from the car through the clutch and then connected after shifting gears. Clutch is only a kind of coupling (only separable).

The law of conservation of energy tells us that the output power of a motor cannot be changed for no reason, but can only be changed into heat energy due to various losses. If the power is constant and the speed decreases, the force (torque) will increase; Under the same output power, the (angular) speed is inversely proportional to the force (torque), and the general reducer also has energy loss, and the efficiency is between 70% and 99%.

Second, the general classification, characteristics and general use of common reducers

■ General classification of common reducers

General reducers include helical gear reducers (including parallel axis helical gear reducers, worm gear reducers, bevel gear reducers, etc.). ), planetary gear reducer, cycloidal pin wheel reducer, worm gear reducer, planetary friction mechanical continuously variable transmission, etc. Under normal circumstances, the reduction ratio is fixed, and only planetary friction mechanical CVT can adjust the speed (there is a continuously adjustable operating knob on the reducer).

The name of the reducer can also be called: reducer, gearbox and gearheads (this name is relatively rare, but it is called in Singapore, Malaysia and Taiwan Province Province).

■ Features of common reducers

1) The main feature of the worm gear reducer is that it has reverse self-locking function and can have a large reduction ratio. The input shaft and the output shaft are not on the same axis or plane. (Shenzhen Zhongzheng Precision Electromechanical Co., Ltd.) But it is generally large in size and has low transmission efficiency and accuracy.

2) Harmonic drive of harmonic reducer uses the controllable elastic deformation of flexible components to transmit motion and power, which is small in size and high in accuracy, but it has the disadvantages of limited life of flexspline, impact resistance, poor rigidity compared with metal parts, low input speed and high price.

3) The planetary reducer has the advantages of compact structure, small return clearance, high precision, long service life and high rated output torque, but it is a little expensive. In addition, there are two kinds of planetary reducer: flat tooth and oblique tooth, which have different precision and price.

Performance comparison:

Worm gear reducer, harmonic reducer and planetary reducer

Large and small

Low backlash and high backlash.

High rigidity and low rigidity.

Medium and short life

Low efficiency and high efficiency

■ General purpose and calculation method of common reducers

1) and increase the output torque. The torque output ratio is multiplied by the reduction ratio according to the motor output, but be careful not to exceed the rated torque of the gearbox.

2) Deceleration reduces the inertia of the load at the same time, and the reduction of inertia is the square of the deceleration ratio; The purpose is to achieve matching inertia, which is also the real reason why frequency converters are not used in some places even if the torque is enough. You can look at the inertia data of a torque rotor of GM.

3) If the input and output are switched, it can also be used as a speed-increasing mechanism.

AC servo motors or stepping motors need positive and negative positioning, so more attention is paid to the accuracy of the gearbox, which is generally divided into arcs (an arc is divided into 1/60 degrees).

Three, frequency converter and servo driver roughly classified.

■■ General classification of frequency converters: Shenzhen Zhongzheng Precision Electromechanical Co., Ltd.

Universal, you can choose to use it in any occasion;

Fan and water pump are special types, and this kind of frequency converter has limitations and can only be used on the load of fan and water pump;

Special type for injection molding machine, this frequency converter is specially designed for injection molding machine;

When choosing, just set it according to the above contents, and then you need to pay attention to the power of the motor and choose the appropriate frequency converter according to the power of the motor. (Shenzhen Zhongzheng Precision Electromechanical Co., Ltd.) The power of general frequency converters should be the same as or higher than that of ordinary motors. For example, 1 1KW motor, you should choose 1KW or 65438.

■ Servo drives are roughly classified as follows:

The previous sections have been introduced in detail, so I won't repeat them here. (Friends who need to see it can go back to the front.)

Four, the best operation of ordinary motor

The optimum working frequency of common motor design is 50-60Hz. Long-term low-speed operation is harmful to the life of the motor itself, and the heat dissipation of the motor itself is also a problem.

Sometimes in order to get a lower speed, it is really impossible without a reducer. Someone used to drive with a 400: 1 reducer. It seems that the low-speed end is slower than the snail. The reducer is rigid, and the frequency converter alone sometimes can't meet the requirements. At the same time, it is not conducive to the long-term operation of the inverter at 20Hz to obtain low speed.

Why should we prevent the inverter from working below 20 Hz for a long time? (1) Because the rotating speed is too low, the heat dissipation effect of the fan is poor, and the variable frequency speed regulation needs to maintain a constant flow (Shenzhen Zhongzheng Precision Electromechanical Co., Ltd.). When the frequency is very low, the voltage will be very low, the constant torque current will be very large, and the heat generation will be very large, but the heat dissipation is very poor, which is extremely unfavorable to the motor and inverter. (2) The price ratio of speed reducer and frequency converter is quite different. The reducer is generally calculated at 100 yuan per kilowatt, while the inverter is almost calculated at 2000 yuan per kilowatt, so unless it is particularly necessary, the inverter cannot be used instead of the reducer.

Generally, frequency converter is used to control the flow of liquid and gas instead of flow valve, which can save the huge loss of valve and recover the investment within half a year, which is worth popularizing. Then there are machines that need speed regulation, such as spindle frequency conversion speed regulation for machine tools (spindle stepless speed regulation). If speed regulation is not needed, there is no need to use a frequency converter.

There is a company. There are about 100 motors in the whole plant. Except one DC motor (about 300KW), the others are all variable frequency. The small one is 30KW, the medium one is 900Kw, the second one is 2,000 Kw, and the largest one is more than 6,000 Kw, all of which are variable frequency, but almost no one does not need a gearbox, and the gearbox is generally larger than the motor. At this time, compared with servo, inverter has obvious cost-effective advantages in high-power applications.

5. If it is used in low-speed situations, is it enough to use only one ordinary low-speed motor? Or use a servo motor?

Only use ordinary low-speed motors, of course not, because:

The speed of 1) is generally not reached: in general, the number ratio of the reducer can be as low as 3: 1 or even smaller, or higher than 180: 1 or even larger.

That is to say, when the speed of a common motor is 1380 rpm (4-pole motor), the output speed of the reducer can be as high as 460 rpm or even higher, or as low as 7.6 rpm or even lower. And ordinary motors can achieve such a large speed range? Even if it is a multi-pole variable speed motor, the fastest 2-pole motor is about 2880-2970 rpm, and the lowest 12-pole motor is about 480-490 rpm. If only tens of revolutions per minute are needed, the ordinary motor is even worse.

2) Generally, the torque of ordinary motors can't be reached: generally speaking, the load that needs to run at a low speed needs a relatively large torque (for example, hoists, elevators, production lines, winding machines, etc.). ). Even if the speed of ordinary motor meets the requirements, the torque often can't just meet the requirements. Note that the mechanical guide rail is easy to "crawl" at low speed.

Can only one AC servo motor be used at low speed? It also scores specific different situations:

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It is no problem to use AC servo motor to run at low speed (the servo driver has built-in electronic gear, which can be set at will, but the recommended reduction ratio is 1/50≤50). However, there are also cases where the speed meets the requirements and the torque does not necessarily meet the requirements. If the torque also meets the requirements, it is of course the best solution in the first place.

If the torque does not meet the requirements, it can be subdivided into two different configuration schemes: a) high-power AC servo device (AC servo driver+servo motor) scheme; B) Low-power AC servo device+reducer scheme.

A) When there is no special requirement for position accuracy, choose the scheme of high-power AC servo device because of its high cost. Compared with the scheme of low-power AC servo device+reducer, the cost-performance advantage is not obvious.

(We have a customer who is installed on a large vertical lathe and feeds up and down, left and right, all of which adopt the scheme of AC servo device+reducer. )

B) However, if there is a high position accuracy requirement, the position accuracy requirement is guaranteed, although the cost of using high-power AC server is higher; However, the low-power AC servo device+reducer scheme has to make some sacrifices in position accuracy because of the backlash of mechanical gears in the reducer. The final scheme should be determined according to the specific equipment, design objectives, technical indicators, accuracy requirements and other factors. Shenzhen zhongzheng precision mechanical and electrical co., ltd

C) In addition, the torque of the motor and the inertia of the rotor must be considered.

Six, servo motor and reducer is how to choose? For example, how to choose a motor with a medium inertia of 750W and a reducer with a reduction ratio of about 60?

Attention should be paid to when choosing:

1) Make sure that the rated torque of your load is less than >; Rated output torque of reducer.

2) rated torque of servo motor (multiplied by) x reduction ratio is greater than >; Load rated torque.

3) The moment of inertia of the load converted to the servo motor through the reducer shall be within the allowable range of the servo motor.

4) Confirm that the accuracy of the reducer can meet your control requirements.

5) The structure and size of the reducer can meet the equipment requirements and can be connected with the selected servo motor.

Besides the transmission ratio of the reducer, the output torque, axial force and radial force of the output shaft; It also depends on the transmission accuracy of the reducer and is selected according to the working conditions. Because the transmission precision is high and the price is high, as long as the motor and reducer meet your requirements (function and performance), there is no problem.

Technical indicators should meet the requirements, and the cost and price of materials are moderate, which is a good plan.

Seven, the relationship between ordinary motor, reducer and frequency converter (servo driver).

Generally, ordinary motors provide appropriate power, that is, appropriate rotational speed and torque, while motors with small torque are small in size and have high power factor and efficiency, so high-speed motors with 1400 to more than 2800 are generally built. If low speed and large torque are needed, a reducer is equipped, but the efficiency of the reducer is very low at a large reduction ratio, so a low-speed motor is needed.

Generally speaking, the speed ratio of the reducer is fixed, and the reducer with bevel gear can also adjust the speed, but it can only be fixed manually, and its performance is different from that of the inverter; In short, the role of the reducer is to achieve appropriate speed and torque while pursuing high efficiency.

The function of frequency converter is frequency conversion speed regulation, which can adjust speed dynamically and quickly in a wide range. Constant torque speed regulation below power frequency, and constant power speed regulation above power frequency, which can not completely replace the reducer.

If the transmission system needs to be simple, with large torque, high efficiency, large speed regulation ratio and insensitive to volume, the torque motor with frequency converter can also be used. If you don't care much about efficiency, but about volume, torque and speed regulation ratio, you can also use hydraulic drive with frequency converter (constant pressure control).

Take an inappropriate analogy: the motor is like a human being and is the power source; The reducer is a lever [the speed ratio is the ratio of the power arm and the resistance arm of the lever]; The frequency converter (servo driver) is like a pulley block. In all walks of life and the actual use process, we should comprehensively consider the parameters, working conditions, load properties and use characteristics of the equipment to achieve careful design and accurate calculation, and then select the motor, reducer and frequency converter (servo driver) to form a relatively coordinated overall device, so as to maximize its working efficiency.

735745370@qq.com Liu Xiaohu zhongzheng precision mechanical and electrical co., ltd.