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Choose the servo system, you must refer to these 9 factors!

Last Updated on 2018-07-27 Hits:2792

There are many factors to consider when choosing the right servo system for a particular application. In order to achieve the optimal performance of the entire servo system, there are 9 aspects that need to be considered.
1, the choice of motor specifications
When the motor starts, there are three most important criteria: speed, torque and moment of inertia.
The first two standards are obvious and, in general, can be calculated using the “selection” software provided by the manufacturer. When using these programs, enter the type of motion required in the application. The software automatically calculates the required torque and speed based on the load and the type of drive (transmission, belt, rack and pinion, ball screw, etc.).
Although the moment of inertia is not so intuitive, it is equally important. Since there is some degree of compliance between most of the couplings and the mechanical transmissions to which they are connected, it is essential that the reflection inertia of the load is not too large compared to the rotational inertia of the motor.
As the ratio of the two increases, it will lead to a significant increase in the difficulty of adjustment. With the development of the adjustment algorithm and the increase of the microprocessor speed, the allowable ratio also increases, but the traditional 10:1 load-motor inertia ratio is a safer choice.
2, load connection
Should the motor be connected directly? Some servos allow the load to be connected directly to the rotor of the motor. In the case of minimum compliance and a low acceleration/deceleration rate, an inertia ratio exceeding 100:1 can be achieved. The selection software provided by the manufacturer is the best tool to adjust these design guidelines to limit the inertia ratio of the system to an appropriate range.
3. Energy recycling
Another factor that servo systems need to consider in many applications is the ability to handle the reusable energy generated by the motor and load. What is involved here is the amplifier of the servo system. When the torque of the motor is in a certain direction and the direction of motion of the motor is opposite, the motor will return the regenerative energy back to the amplifier. This is because the basic design of the motor and generator is the same.
Passing energy to the windings of the motor creates an electromagnetic field that causes the rotor and permanent magnets of the motor to rotate. Similarly, permanent magnet excitation transfers energy to the windings as the rotor of the motor rotates. There are many different ways to drive renewable energy. Some small drives use bus capacitors to absorb this energy, while larger drivers use internal resistors to generate heat. The selection software provided by the manufacturer generally gives an indication of whether an energy regeneration process is required.


4, effective line regeneration
For some large systems, a converter is usually provided so that energy can be transferred back to the power circuit that supplies the system. When choosing a servo system, if the inertia of the design is not matched between the motor and the load, another factor to consider is the amount of renewable energy that the drive can handle.
When dealing with excess regenerative energy applications, an external power resistor is typically connected to the amplifier. These applications are generally vertically arranged when gravity is a consideration and a large inertia load needs to be quickly reduced. Obviously, in addition to the regenerative function, the amplifier needs to supply the motor with the appropriate voltage and current to achieve the required speed and torque. Choosing the right power requirements for the motor and amplifier is just the beginning.
5, control system requirements
Next, you need to deal with the control needs. Let's go back to the motor first. By definition, the servo system always requires a feedback device. Currently, feedback devices are typically high resolution decoders or resolvers. In order to ensure that the required positioning accuracy is met, the feedback device must have the appropriate resolution to achieve repeatability and accuracy. The amplifier must also be compatible with the type of signal from the feedback device mounted on the motor.
6, positioning accuracy
Conventionally, the decoder passes position and speed information through a pulse train on two channels and passes it back to the amplifier. However, as the accuracy of these decoders has greatly increased, some manufacturers have begun to use serial decoders with higher transmission rates instead of pulse sequences to deliver these information packets. These serial decoders are capable of delivering signals with higher resolution, which is more immune to noise and provides other types of signals. This additional information includes the motor temperature and even the part number of the motor.
In servo systems, when the motor and amplifier are supplied by the same manufacturer, the feedback device recognizes the motor and passes it to the amplifier, allowing it to automatically set internal parameters for optimal operation and motor protection.
7, communication connection performance
When the motor and amplifier with drive and feedback devices are matched to each other and have the resolution required for the application, the command signal between the amplifier and the motion controller can be considered. For single-axis applications, it is more common to embed or attach the controller to one side of the amplifier. Some applications integrate it into a higher level control system. A programmable logic controller (PLC) or programmable automation controller (PAC) can control the entire unit or production line and pass these through digital input/output (I/O) or communication protocols such as EtherNet/IP or ModbusTCP/IP. Information is passed to the single motion axis controller.
8, control interface selection
In multi-axis applications, the controllers are generally independent. Traditionally, the commands issued by the controller are typically +10V signals, representing speed or torque. Today, most manufacturers offer network-based solutions. These network-based solutions have less wiring and can handle higher resolution feedback and collect more diagnostic information from the amplifier. There are many types of sports networks available, each with its strengths and weaknesses.
9, the choice of motion control network
Many of the newer motion control networks are based on Ethernet hardware and take advantage of their ever-increasing rates and gradual reductions in cost. However, it cannot be considered to be compatible with the relevant controller or other parts of the network because of the RJ-45 interface on the amplifier.
The protocols running on these networks will determine the compatibility of the system. EtherCAT, Mechatrolink III and Powerlink are several high-speed deterministic networks for motion control based on Ethernet protocols.
Network-based servo systems are typically configured with Ethernet ports that can use common industrial protocols such as Modbus TCP/IP and EtherNet/IP to report diagnostic and product information to the monitoring network.

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