Technical Knowledge

Common basic concepts in servo control (2)
Release Date : 2021-07-08 17:34:57

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


Operating area

The working area is represented by two-dimensional plane coordinates composed of speed and torque (see the figure below).


In the figure:

2TN—2 times the rated torque (peak locked-rotor torque);
TN—rated torque;
Tnmax—Maximum torque at maximum speed;
nTmax—the maximum speed under 2 times the rated torque;
nN—rated speed;
nmax—the maximum speed of the motor;
The temperature rise of the motor does not exceed the specified value, and the area that can work for a long time is the continuous working area. The shaded part in the above figure is the continuous working area, beyond the continuous working area, the area that allows the motor to run under short-term overload is the intermittent working area.

DC bus voltage

The DC voltage at the input terminal of the AC servo drive inverter (ie, the power supply voltage is 48V or 24V);

Rated power

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

Rated speed

In the continuous working area, the speed of the rated power point of the motor.

Rated torque

The output torque of the motor at rated power and rated speed.

Torque constant

Under specified conditions, the average electromagnetic torque produced when the motor passes unit line current.

Back EMF constant

Under specified conditions, when the armature winding of the motor is open, the linear induced electromotive force generated in the armature winding per unit angular velocity. The back EMF of the square wave drive motor is the peak value, and the back EMF of the sine wave drive motor is the effective value.
Ideally, when using international units, the torque constant Kt and the back-EMF constant Ke have the following relationship:
Square wave drive motor, Kt=Ke;
For sine wave drive motor, Kt=√3Ke;

Static friction torque

When the motor winding is open, the resistance torque that needs to be overcome to make the rotor start to rotate at any position.

Thermal resistance of motor

The resistance to heat flow from the heat source (winding, core, etc.) in the motor to the cooling medium.


The inductance between the two phase wires of the motor.

Inductance of d-axis(direct axis)

The inductance exhibited by the stator when the axis of the rotating magnetic field of the stator coincides with the direct axis of the rotor.

Inductance of q-axis(quadrature axis)

The inductance exhibited by the stator when the axis of the rotating magnetic field of the stator coincides with the quadrature axis of the rotor.

Electrical time constant

Under step input voltage and specified conditions, it takes time for a locked-rotor motor to make the winding current reach 63.2% of its final value.

Thermal time constant

Under constant power consumption and specified conditions, it takes time for the temperature rise of the motor windings to reach 63.2% of the stable value.

Maximum permitted speed

Under the conditions of ensuring the dielectric strength and mechanical strength of the electrical insulation, the maximum design speed of the motor.

Equivalent torque r.m.s torque

In non-constant torque applications, the root mean square value of the torque in a complete working cycle is calculated as follows:

In the formula:
Trms ----------Equivalent torque;
T(t)------------Torque as a function of time t
Tti-------------Torque value within Δti
Δti-------------Duration of torque Tti
Ttot------------The time of a complete work cycle


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