Difference Between Stepper Motor and Servo Motor

The significant factor of differentiation between the stepper motor and servo motor lies in the way the two are constructed and controlled. Servomotors are regarded as an alternative to stepper motor when high performance is considered.

One of the crucial differences between a stepper motor and a servo motor is that a stepper motor possesses quite a simple structure with a low operating speed in comparison to a servo motor.

Before understanding more differences between the stepper motor and servo motor. Let us first see –

What is Motor?

A motor is regarded as an electromechanical device designed to change electrical energy into equivalent mechanical energy. The electrical energy used is generally supplied by the battery and the converted mechanical energy is usually rotational motion which the motor provides.

More simply, we can say that a motor is an electrical device that generates rotational force. Thus, the main aim of the stepper and servo motor is to change the applied electrical signal into angular velocity or movement of the shaft.

Content: Stepper Vs Servo Motor

  1. Comparison Chart
  2. Definition
  3. Key Differences
  4. Conclusion

Comparison Chart

Basis for Comparison Stepper MotorServo Motor
BasicStepper motor operates in steps.It is continuous operating machine.
System configurationOpen loopClosed loop
Power requirementMore Comparatively less
DesignSimpleComplex
Ability to response High Comparatively low
CostInexpensiveExpensive
ReliabilityMore Less
Noise and vibrationHighComparatively less
Operating speedSlowFast
Feedback mechanismNot existExist
Heat generationMoreComparatively less
Number of polesGenerally 50 to 150Around 4 to 12
Life spanMoreLess
Damage due to overloadLess prone to get damaged.Comparatively more prone to get damaged.
Torque producedHighLow
EfficiencyLessMore
Tolerance towards moment of inertiaHighLow
ApplicationsIn gaming, textile, welding machineries, medical and 3D printing equipments, etc.In robotics, antenna positioning systems, automatic doors, cameras, remote controlled equipments, etc.

Definition of Stepper Motor

A stepper motor is a brushless motor designed to operate in a number of steps without using a feedback mechanism. Its basic principle of operation is such that it has a rotor (which is generally a permanent magnet) that rotates discretely when the stator (winding) which is surrounded by the rotor is energized externally. The rotation is the result of magnetic interaction between poles of rotor and poles of stator winding which is provided sequential excitation.stepper motor

Thus, we can say, that there is no electrical winding present in the rotor of the stepper motor but it takes the energization provided to the stator winding as input thereby generating output as discrete angular rotation. This is done in a way that, on activating the winding, sequentially step by step current flows through them thereby magnetizing the stator. This resultantly develops electromagnetic poles thus the propulsion within the motor takes place.

Due to such ability, it finds applications as actuators in computer control systems, digital control systems, etc.

Definition of Servo Motor

A servo motor is based on the principle of servomechanism and is a closed-loop system consisting of various units in order to rotate machine parts with high precision. Unlike stepper motor, it uses the feedback mechanism that offers angular precision because of which we can get the desired rotation according to the applied input signal.

Basically, it is constructed in a way that, its output shaft can be moved to a particular angle, a position with a specific velocity that is not offered by any regular motor.

Here the applied electrical signal can be either analog or digital in nature and this applied signal corresponds to the amount of movement required to position the shaft. As a feedback unit, either encoder or resolver is used which provides the speed and position-related information to the controller. The speed of the motor varies in proportion to the applied input voltage.

Key Differences Between Stepper and Servo Motor

  1. The key factor of differentiation between stepper and servo motor lies in the way the two are constructed and operated. A stepper motor uses an open-loop configuration thus has no feedback mechanism involved. As against, a servo motor is based on a closed-loop configuration in which a feedback mechanism is involved.
  2. Generally, there are around 50 to 150 poles exist in the stepper motor. While the number of poles in servo motor is nearly around 4 to 12.
  3. The torque produced in the stepper motor is comparatively more than in the servo motor. But in a stepper motor, with an increase in speed, torque reduces while even in high-speed operation, the produced torque does not vary significantly in servos.
  4. During operation, the amount of heat generation is more in the stepper motor than in the servo motor.
  5. The life span of the servo motor is less than that of the stepper motor. The reason behind this is that the stepper motor has only bearing as its movable part thus, wear and tear are less while the brushes of servomotor require replacement after around 2000 hours of use.
  6. The occurrence of damage to the motor due to mechanical overload is less in the case of a stepper motor while the servo motor possesses severe malfunctioning due to mechanical overload.
  7. For the same operation, a servo motor requires less power than a stepper motor.
  8. Stepper motors are considered to be comparatively more reliable than servo motors due to the fact that the open-loop configuration permits fewer chances of operation failure than the closed-loop configuration of the servo motor.
  9. The operating speed possessed by a stepper motor is nearly around 1000 to 2000 rpm while that of the servo motor is 3000 to 5000 rpm which is quite fast.
  10. A Stepper motor is a low-cost machine than a servo motor.
  11. The noise and vibration associated with the stepper motor are more than the servo motor.
  12. The absence of a feedback mechanism makes the design of the stepper motor quite simple in comparison to the servo motor which is somewhat complex design-wise because of the involvement of a feedback mechanism.

Conclusion

This discussion concludes that the servo motor offers more efficient operation than the stepper motor. One of the major reasons for this is the closed-loop configuration of the servo motor that makes use of error signals to provide accurate positioning and angular displacement.

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