Servo Motor Technical Parameters
The technical parameters of servo motor are the core indexes to measure its performance and adaptability, covering basic specifications, performance characteristics, control accuracy and other dimensions, the following is a detailed analysis of the key parameters.
First, the basic specifications parameters
rated power (P)
unit for the watts (W) or kilowatts (kW), indicating that the motor long-term stable operation of the output power, the common range from a few tens of watts (such as 60W small servo) to tens of kilowatts (such as 30kW industrial servo). Need to match the load power requirements to ensure that the rated power ≥ 1.2 times the peak power of the load (to avoid overload burnout).
Rated speed (n)
in revolutions / minutes (r / min), refers to the stable speed of the rated power, the mainstream range of 1000-6000r / min. High-speed servo motors (such as 10,000r / min) is suitable for the need for rapid response scenarios (such as mounter), while low-speed and high-torque models (such as 500r / min) is suitable for direct-drive loads (without reducer). loads (no reducer required).
Rated torque (T)
is in Nm, derived from rated power and speed (T=9550 x P/n), and represents the torque continuously output by the motor. Need to meet the load rated torque of more than 1.5 times, in order to cope with transient impact (such as starting, emergency stop).
Performance Characteristics
Peak Torque
The maximum torque that the motor can output in a short period of time (usually 1-3 seconds), which is 2-3 times the rated torque, is used to overcome the inertia of the load at startup or sudden resistance (e.g., when the machine tool cuts instantaneously). Insufficient peak torque can result in startup stall or overload alarms.
Speed Fluctuation Rate
refers to the deviation rate between the actual speed and the set speed of the motor under the rated speed, which can be controlled within ±0.1% for high precision servo. This parameter directly affects the speed control accuracy and is especially critical in uniform speed drive scenarios (e.g. film printing machines).
Blocking torque
The torque output when the motor rotor is locked (usually 1.5 times the rated torque) needs to be greater than the load static friction torque, to avoid burning when the motor is jammed (used in conjunction with the drive overcurrent protection).
Third, the control accuracy parameters
encoder resolution
unit for the number of lines / revolutions (ppr) or bit (bit), indicating the number of pulses output per revolution of the motor. Common values are 1024ppr (basic), 2048ppr (precision), high-end models use 17-bit (131072ppr) or higher resolution encoder, positioning accuracy of up to ± 0.001 °, to meet the needs of semiconductor packaging and other nanometer positioning.
Positioning Accuracy and Repeat Positioning Accuracy
Positioning Accuracy: The maximum deviation between the actual stop position of the motor and the commanded position, usually ≤ ±0.01mm (when combined with ball screw drive).
Repeat Positioning Accuracy: The deviation fluctuation of the same position for several times can be controlled at ±0.0005mm by high precision servo, which ensures the consistency of mass production (e.g. cell phone shell processing).
Response time
motor from receiving instructions to reach the target speed time, high-speed response model (such as within 0.1ms) is suitable for dynamic tracking scenarios (such as robotic welding track following), the response is too slow will lead to track lag.
Electrical parameters
Rated voltage (U)
DC (such as 24V, 48V, for small servo) and AC (such as 220V single-phase, 380V three-phase, industrial mainstream). Voltage stability affects the torque output: voltage fluctuations ± 10%, the torque deviation should be ≤ 5%, otherwise it is necessary to equip a voltage regulator.
Rated current (I)
The operating current at rated power is directly related to motor heating. The drive needs to match the current capacity (usually 1.5 times the rated current) to avoid overload tripping.
Insulation class and protection class
Insulation class: commonly class F (maximum allowable temperature 155℃), class H (180℃) for high temperature environments (e.g., drives in ovens).
Protection class: IP65 (dustproof and waterproof spray) for wet workshop, IP20 (basic dustproof) for clean room (e.g. semiconductor workshop).
Five, mechanical parameters
rotational inertia (J)
unit for kg・m², affecting the motor acceleration performance: the smaller the rotational inertia, the faster the acceleration response (such as 0.01kg・m² servo can realize 1000r/min/ms acceleration). Need to match with the load inertia (load inertia ≤ 10 times the motor inertia), otherwise it is easy to oscillate.
Dimensions and mounting
Includes housing number (e.g., 40mm, 60mm, 130mm series), shaft diameter (8mm-30mm), and type of mounting flange (round, square), which needs to be adapted to the space of the equipment (e.g., servo under 60mm is used for the joints of small robots).
Weight
Lightweight models (e.g. aluminum alloy housing, weight ≤ 1kg) are suitable for mobile equipment (e.g. AGV trolley), while heavy-duty servos (cast iron housing, more than 5kg) are used for stationary equipment (e.g. spindle for CNC machine tools).
The parameters of servo motors need to be selected according to load characteristics (power, inertia), control accuracy (resolution, response speed) and environmental conditions (temperature, protection), for example, high-speed sorting equipment in the 3C industry needs to focus on high speed and response time, while heavy machine tools need to prioritize the matching of high torque and low inertia characteristics.
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