Views: 1 Author: Site Editor Publish Time: 2022-08-18 Origin: Site
Stepper motors are often misconceived as the lesser of servo motors, but as a matter of fact, they are highly reliable just like servo motors. Featuring high torque and low vibration at low-speeds, the custom stepper motor operates by accurately synchronizing with the pulse signal output from the controller to the driver, and achieving highly accurate positioning and speed control. A stepper motor can be divided into open loop stepper motor and closed loop stepper motor. Here Leili Motor will talk about these two types of stepper motors and five major advantages of closed loop stepper motors.
Open loop stepper motor
Open loop stepper motors are the motors that convert electrical pulse signals into angular displacements and are used in an extremely wide range of applications. In the case of non-overload, the speed and stop position of the motor only depends on the frequency of the pulse signal and the number of pulses, and is not affected by changes in the load. When receiving a pulse signal, the stepper driver drives the stepper motor to rotate a fixed angle step by step, called the “step angle”. The rotation is run step by step at a fixed angle.
The amount of angular displacements can be controlled through controlling the number of pulses, so as to achieve accurate positioning; meanwhile, the speed and acceleration of motor rotation can be controlled by controlling the pulse frequency, so as to achieve speed regulation.
A stepper motor is an induction motor that works by using an electronic circuit, a driver, to turn DC power into a time-sharing powered multi-phase timing control current. Although stepper motors are powered by DC current, they cannot be understood as DC motors, which are power motors that convert DC electrical energy into mechanical energy, while stepper motors are open-loop control motors that convert electrical pulse signals into angular displacement.
Seven differences between stepper motor and servo motor
It is worth noting that stepper motors are used in low speed applications - up to 1,000r/min per minute, and the best working range is 150~500r/min, but the best working range of a closed loop stepper motor can be 1500r/min. 2-phase stepper motors at 60~70r/min are prone to low speed resonance, generating vibration and noise, which needs to be avoided by changing the reduction ratio, increasing the subdivision, and adding magnetic dampers, etc. If the accuracy of the step angle can not be guaranteed when the subdivision level is greater than 4, you’d better replace with the stepper motor with more phases (i.e., smaller step angle) or closed-loop stepper motor or servo motor.
● Control accuracy
The control accuracy of the servo motor can be set according to the encoder for higher accuracy.
● Low frequency characteristics
The stepper motor is prone to vibration at low frequencies, while the servo motor will not vibrate.
● Torque-frequency characteristics
The torque of the stepper motor becomes smaller as the speed increases, so its maximum operating speed is generally less than 1,000r/min. The servo motor within the rated speed (generally 3,000r/min) can output the rated torque at constant power at the rated speed, and its maximum speed can be 5,000 r/min.
● Overload capacity
The custom stepper motor cannot be overloaded, but the servo motors can be overloaded by 3 times the maximum torque.
● Operational performance
The stepper motor adopts open-loop control and the servo motor employs closed-loop control.
● Speed response
The stepper motor can start within 0.15~0.5s, but it only takes 0.15~0.5s to start the servo motor, and the servo motor can reach rated 3,000r/min in just 0.01s.
● Efficiency indicator
The stepper motor has an efficiency of about 60% and the servo motor has an efficiency of about 80%.
You will also find in actual use that the servo motor is much more expensive than the stepper motor, so the stepper motor is more widely used, especially in the applications with low positioning accuracy requirements.
Six advantages of closed-loop stepper motors
A closed loop stepper motor is the stepper motor with an encoder added to the end of the motor, allowing for closed-loop control. Closed-loop control of the stepper motor is a servo system that uses position feedback and/or velocity feedback to determine the phase transition that is compatible with the rotor position, which can greatly improve the performance of stepper motors without the phenomenon of lost steps. Here six major benefits of a closed-loop stepper motor are explained to help you better understand its characteristics.
1. High speed response.
Compared to the servo motor, the closed-loop stepper motor can strongly follow the positioning commands, resulting in extremely short positioning time. In applications with frequent starts and stops, the positioning time can be significantly reduced.
2. More torque produced than the servo motor
The closed-loop stepper motor can make up for the drawbacks of an ordinary stepper motor such as out of step and insufficient vibration at low speed.
3. High-torque and out-of-step operation can be achieved even under 100% load, eliminating the need to consider torque loss as is the case with ordinary stepper systems.
4. Closed-loop drive can increase the efficiency to 7.8 times, including output power increased to 3.3 times, and speed increased to 3.6 times. The closed loop stepper motor can obtain higher operating speed, more stable and smoother speed than open-loop control.
5. The closed-loop stepper motor will be completely stationary when it stops, without the micro-vibration of the ordinary servo motor. It can replace the application of general-purpose servo system when low cost and high precision positioning is required.
6. Heat and vibration of the closed-loop stepper motor is less than the open-loop stepper motor. Encoder feedback allows it to have higher accuracy than that of the ordinary stepper motor.
To conclude, the closed-loop stepper motor has the characteristics of low cost, high efficiency, no micro-vibration when stopping, high rigidity, no rectification, high speed, and high dynamic response, etc. Therefore, it has become the most cost-effective solution to replace high-cost servo systems and low-end open-loop stepper systems.
For more information about closed-loop stepper motor, just contact Leili Motor, one of top 10 China nema 23 stepper motor manufacturers.