Servo is a power transmission device that provides control for the movement operation required by electromechanical equipment. Therefore, the design and selection of servo system is actually the process of selecting appropriate power and control components for the electromechanical motion control system of the equipment. It involves The products received mainly include:
The automatic controller used to control the movement posture of each axis in the system;
Servo drive that converts AC or DC power with fixed voltage and frequency into the controlled power supply required by the servo motor;
Servo motor that converts the alternating power output from the driver into mechanical energy;
The mechanical transmission mechanism that transmits the mechanical kinetic energy to the final load;
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Considering that there are many martial arts series of industrial servo products on the market, before entering the specific product selection, we still need to first according to the basic needs of the equipment motion control application we have learned, including controllers, drives, motors Preliminary screening is carried out with servo products such as reducers…etc.
On the one hand, this screening is based on the industry attributes, application habits and functional characteristics of the equipment to find some potentially available product series and program combinations from many brands. For example, the servo in the wind power variable pitch application is mainly the position control of the blade angle, but the products used need to be able to adapt to the harsh and harsh working environment; the servo application in the printing equipment uses the phase synchronization control between multiple axes At the same time, it is more inclined to use a motion control system with high-precision registration function; tire equipment pays more attention to the comprehensive application of a variety of hybrid motion control and general automation systems; plastic machine equipment requires the system to be used in the product processing process. Torque and position control provide special function options and parameter algorithms….
On the other hand, from the perspective of equipment positioning, according to the performance level and economic requirements of the equipment, select the product series of the corresponding gear from each brand. For example: if you don’t have too high requirements for equipment performance, and you want to save your budget, you can choose economical products; conversely, if you have high performance requirements for equipment operation in terms of accuracy, speed, dynamic response, etc., then naturally It is necessary to increase budget input for it.
In addition, it is also necessary to take into account the application environment factors including temperature and humidity, dust, protection level, heat dissipation conditions, electricity standards, safety levels, and compatibility with existing production lines/systems…etc.
It can be seen that the primary selection of motion control products is largely based on the performance of each brand series in the industry. At the same time, the iterative upgrade of application requirements, the entry of new brands and new products will also have a certain impact on it. . Therefore, to do a good job in the design and selection of motion control systems, daily industry technical information reserves are still very necessary.
After preliminary screening of the available brand series, we can further carry out the design and selection of the motion control system for them.
At this time, it is necessary to determine the control platform and overall architecture of the system according to the number of motion axes in the equipment and the complexity of the functional actions. Generally speaking, the number of axes determines the size of the system. The more the number of axes, the higher the requirement for controller capacity. At the same time, it is also necessary to use bus technology in the system to simplify and reduce the controller and drives. The number of connections between the lines. The complexity of the motion function will affect the choice of controller performance level and bus type. Simple real-time speed and position control only need to use ordinary automation controller and field bus; high-performance real-time synchronization between multiple axes (such as electronic gears and electronic cams) requires both controller and field bus It has high-precision clock synchronization function, that is, it needs to use the controller and industrial bus that can perform real-time motion control; and if the device needs to complete the plane or space interpolation between multiple axes or even integrate the robot control, then the performance level of the controller The requirements are even higher.
Based on the above principles, we have basically been able to select the available controllers from the products previously selected and implement them to more specific models; then based on the compatibility of the fieldbus, we can select the controllers that can be used with them. The matching driver and the corresponding servo motor options, but this is only at the stage of the product series. Next, we need to further determine the specific model of the drive and motor according to the power demand of the system.
According to the load inertia and motion curve of each axis in the application requirements, through simple physics formula F = m · a or T = J · α, it is not difficult to calculate their torque demand at each time point in the motion cycle. We can convert the torque and speed requirements of each motion axis at the load end to the motor side according to the preset transmission ratio, and on this basis, add appropriate margins, calculate the drive and motor models one by one, and quickly draw up the system draft for Before entering a large number of meticulous and tedious selection work, perform a cost-effective evaluation of the alternative product series in advance, thereby reducing the number of alternatives.
However, we cannot take this configuration estimated from the load torque, speed demand and preset transmission ratio as the final solution for the power system. Because the torque and speed requirements of the motor will be affected by the mechanical transmission mode of the power system and its speed ratio relationship; at the same time, the inertia of the motor itself is also part of the load for the transmission system, and the motor is driven during the operation of the equipment. It is the entire transmission system including load, transmission mechanism and its own inertia.
In this sense, the selection of the servo power system is not only based on the calculation of the torque and speed of each motion axis…etc. Each axis of motion is matched with a suitable power unit. In principle, it is actually based on the mass/inertia of the load, the operating curve, and possible mechanical transmission models, substituting the inertia values and driving parameters (moment-frequency characteristics) of various alternative motors into it, and comparing its torque (or force) with The occupancy of the speed in the characteristic curve, the process of finding the optimal combination. Generally speaking, you need to go through the following steps:
Based on various transmission options, map the speed curve and inertia of the load and each mechanical transmission component to the motor side;
The inertia of each candidate motor is superimposed with the inertia of the load and the transmission mechanism mapped to the motor side, and the torque demand curve is obtained by combining the speed curve on the motor side;
Compare the proportion and inertia matching of the motor speed and torque curve under various conditions, and find the optimal combination of drive, motor, transmission mode and speed ratio.
Since the work in the above stages needs to be carried out for each axis in the system, the workload of power selection of servo products is actually very huge, and most of the time in the design of the motion control system is usually consumed here. Place. As mentioned earlier, it is necessary to estimate the model through torque demand to reduce the number of alternatives, and this is the meaning.
After completing this part of the work, we should also determine some important auxiliary options of the drive and motor as needed to finalize their models. These auxiliary options include:
If a common DC bus drive is selected, the types of rectifier units, filters, reactors and DC bus connection components (such as bus backplane) should be determined according to the distribution of the cabinet;
Equip a certain axis(s) or the entire drive system with braking resistors or regenerative braking units as needed;
Whether the output shaft of the rotating motor is a keyway or an optical shaft, and whether it has a brake;
The linear motor needs to determine the number of stator modules according to the stroke length;
Servo feedback protocol and resolution, incremental or absolute, single-turn or multi-turn;
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At this point, we have determined the key parameters of the various alternative brand series in the motion control system from the controller to the servo drives of each motion axis, the model of the motor and the related mechanical transmission mechanism.
Finally, we also need to select some necessary functional components for the motion control system, such as:
Auxiliary (spindle) encoders that help certain axis(s) or the entire system to synchronize with other non-servo motion components;
High-speed I/O module for realizing high-speed cam input or output;
Various electrical connection cables, including: servo motor power cables, feedback and brake cables, bus communication cables between the driver and the controller…;
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In this way, the selection of the entire equipment servo motion control system is basically completed.
Post time: Sep-28-2021
