How to equip a servo motor with a reducer?

Gearbox selection is a compulsory course for every mechanical design engineer. Therefore, we will now introduce the selection precautions for reducers based on the sample selection of reducers.

In fact, during the selection process of the gearbox, we need to pay special attention to the selection and calculation of the following parameters:

A、 Calculation of output shaft torque of reducer;

B、 Calculation of the maximum speed of the transmission mechanism;

C、 Selection of installation method for transmission mechanism;

D、 Selection of gearbox transmission accuracy;

F、 Configuration of gearbox interface;

Next, we will provide a detailed introduction to the selection criteria and methods in the gearbox process from the above aspects.

 

1、 Calculation of output shaft torque of reducer

 

The output torque of the gearbox is the required torque calculated by us for the transmission mechanism. The purpose of choosing a gearbox is to:

Minimizing the rated torque of the motor (i.e. minimizing cost)+reducing the gearbox (increasing torque)=obtaining a larger torque output.

In fact, there are many benefits to the application of reducers in mechanical structures, such as increasing torque, reducing inertia, reducing the impact of transmission mechanisms on servo motors, self-locking transmission mechanisms, and so on.

Of course, its core value lies in increasing torque. So when you confirm the torque required by your transmission mechanism, then compare the torque of the servo motor you have selected, and the ratio of these two torques is the reduction ratio of the gearbox torque you want to choose. Of course, we usually make the final torque of the mechanism redundant, so the transmission ratio should be slightly larger.

So in this process, there are two very important parameters, namely the final torque you need and the rated torque of the servo motor. Only by knowing these two parameters can you confirm the reduction ratio of the deceleration motor you have chosen.

For example, in the sample shown in the above figure, the model of the reducer is SDH-42-L1. When choosing, we need to pay attention to several aspects. Firstly, we need to look at the appearance of the reducer. For example, 42 in the above formula actually has an external dimension of 44 * 44mm. At this time, we need to compare it with the appearance of your servo motor. Usually, we can choose a reducer with a similar appearance.

 

2、 Calculation of maximum speed of transmission mechanism

 

For the maximum speed of the transmission mechanism, mechanical design engineers must confirm it themselves, because this parameter involves the selection of the reduction ratio of the gearbox. When we choose the reduction ratio, it does not mean that we can infinitely increase it, because the larger the reduction ratio, although the torque will be greater, it also means that the output speed will decrease, which leads to a decrease in the operating speed of the entire transmission mechanism.

So, we need to strike a balance between torque and speed, and increase the reduction ratio as much as possible to enhance the transmission torque while meeting the transmission speed of the mechanical mechanism. This is the reasonable choice.

Of course, the transmission speed of a transmission mechanism is not entirely determined by the reducer. The speed of the servo motor, the pitch of the transmission screw, the size of the gear, and so on are all determining factors. Therefore, when designing the structure, we need to consider comprehensively. However, the size of the reduction ratio is also a determining factor that we need to pay attention to.

 

3、 Selection of installation method for transmission mechanism

 

For the selection of a reducer, in addition to the parameter selection mentioned above, it is also necessary to choose the type and installation method of the reducer, such as whether the reducer you choose is a planetary reducer, a worm gear reducer, a coaxial direct connection type, or a 90 degree vertical installation, etc.

Especially for the selection of worm gear reducers, there are specific application scenarios, such as requiring the entire motion mechanism to have self-locking function. We often have such design requirements, such as when the transmission mechanism is installed vertically, in order to avoid the mechanism from falling down after the motor is powered off, we usually choose worm gear reducers.

Of course, many people may argue that it is possible to choose a servo motor with a brake. In theory, this is possible, and we usually choose a brake motor for vertical servo motors. However, in practical applications, we will find that many mechanisms of the servo motor will experience a slight drop when powered on. If you choose a worm gear reducer at this time, you can avoid this phenomenon very well, because the worm gear reducer has a self-locking function.

Of course, this self-locking has a prerequisite. The transmission ratio must be greater than a certain ratio in order for the worm gear reducer to truly function as a self-locking device. A reduction ratio that is too small is still unreliable, and I have forgotten the specific ratio (it seems to exceed 30, uncertain). When using it, you can communicate with the reducer manufacturer carefully, as they have relevant parameters.

So it is also important to choose the type of installation method, and it is not a matter of making arbitrary choices.

 

4、 Selection of Transmission Accuracy for Reducer

 

The transmission accuracy of the reducer depends entirely on the accuracy requirements of the transmission mechanism you design. As long as the corresponding parameters are matched according to your function, it is sufficient. Of course, this is a real cost. The higher the accuracy, the higher the cost, and often it is so high that you cannot accept it, especially for some good brands, which you cannot afford to play with.

In the above figure, there are special annotations for transmission accuracy. You only need to choose according to the explained accuracy. If it does not meet the requirements, change the model. If it still does not meet the requirements, change the brand.

 

5、 Configuration of gearbox interface

 

In the process of selecting a reducer, we need to clarify the interfaces of two reducers through drawings.

At the same time, it is also required that the structural form and external dimensions of the reducer can meet the equipment requirements and be connected to the selected servo motor.