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Common basic concepts in servo control (1)
Release Date : 2021-07-08 17:16:32

Connection diagram of traditional servo motor

Schematic diagram of NIMOTION integrated servo motor connection

Main features of PMM series integrated servo motors:

1. Modular high-integration design, rapid site layout and installation, eliminating the need for matching process between driver and motor, reducing the cost of fieldbus and reducing the cost of use.
2. It is connected to the controller through the EtherCAT/CANOpen protocol (DS402), and each node directly uses hardware to implement calculations without software participation, which greatly reduces the message delay time. Transmission rate: 2x100Mbps (full duplex) The hardware delay of a servo axis is only 1us.
3. The control accuracy reaches ±1rpm and ±1pulse, with a real-time response period of 1ms, with excellent control performance and good positioning accuracy.

Common noun explanation


Static friction torque

When the motor winding is open, it rotates the resistance torque that needs to be overcome to start rotating at any position.

Cogging moment

When the motor winding is open, the cyclic torque is generated due to the slotting of the armature core within one revolution of the motor, which tends to tend to the minimum reluctance position.

Continuous locked-rotor current

In continuous work, the current of the winding corresponding to the continuous locked-rotor torque. The square wave drive motor current is the peak value, and the sine wave drive motor current is the effective value.

Continuous locked-rotor torque

In the continuous working area, the maximum continuous torque output by the motor.

Peak locked rotor torque

The motor exceeds the continuous working area and allows the maximum torque output in a short time.
Selection of several common pulse control methods (can be achieved through the parameter setting of the servo)
The pulse + direction mode is the most used. (Almost all small PLCs on the market support simple motion control pulse + direction mode)

1. Pulse + direction


3.Encoder A/B


I/O point

When discussing control systems, I/O point is the term most often heard. It refers to the input/output point, I stands for INPUT, which refers to input, and O stands for OUTPUT, which refers to output.
Input/output are all for the control system. Input refers to the measured parameter entered from the instrument into the control system, and output refers to the parameter output from the control system to the actuator. A parameter is called a point. The scale of a control system is sometimes determined according to the maximum number of I/O points it can control.

Analog quantity and switch quantity

In the control system, a common term is analog quantity and switch quantity. Regardless of input or output, a parameter is either an analog or a switch.
The analog quantity refers to the size of the control system quantity is a continuous value that changes within a certain range, such as temperature from 0 to 100 degrees, pressure from 0 to 10 MPA, liquid level from 1 to 5 meters, and electric valve opening from 0 to 100 %, etc. These quantities are all analog quantities.
Analog quantity is a continuously changing physical quantity, such as voltage, temperature, pressure and speed. The PLC cannot directly process the analog quantity. It needs the A/D converter in the analog input module to convert the analog quantity into a digital quantity proportional to the input signal for use by external actuators (such as electric control valves or inverters).
The switch value includes binary input and binary output. It is a digital signal and only has two states of "0" and "1".
The binary input comes from a contact outside the protection device for use by the protection device. The opening amount is the contact provided by the protection device to the outside, which is supplied to the external equipment, such as the on/off state of the switch, the closing/opening of the relay, the on/off of the solenoid valve, and so on. PLC can directly input and output switch signals.

Control loop

Usually for the control of analog quantities, a controller determines an output quantity according to an input quantity and according to certain rules and algorithms. In this way, the input and output form a control loop.
The control loop has the difference between open loop and closed loop.
Open-loop control loop means that the output is based on a reference quantity, and there is no direct relationship between input and output.
The closed loop loop feeds back the output of the control loop as the loop input, and compares it with the set value or the expected output value of the quantity. Closed loop control, also called feedback control, is the most common control method in control systems.


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