Servomotor
A servomotor is a rotary actuator or linear actuator that allows for precise control of angular or linear position, velocity and acceleration.it consists of a suitable motor coupled to a sensor for position feedback. It also requires a relatively sophisticated controller, often a dedicated module designed specifically for use with servomotors.
servomotors are not a specific class of motor although the term servomotor is often used to refer to a motor suitable for use in a closed-loop control system.
A stepper motor or step motor or stepping motor is a brush less DC electric motor that divides a full rotation into a number of equal steps. The motor's position can then be commanded to move and hold at one of these steps without any feedback sensor (an open-loop controller), as long as the motor are very large stepping motors with a reduced pole count and generally are closed-loop com mutated.
Advantages
1.Low Cost for control archived
2.high torque at startup and low speeds
3.Ruggedness
4.simplicity of construction
5.can operate in an open loop control system
6.low maintenance
7.less likely to stall or slip
8.Will work in any environment
9.Can be used in robotics in a wide scale.
2.high torque at startup and low speeds
3.Ruggedness
4.simplicity of construction
5.can operate in an open loop control system
6.low maintenance
7.less likely to stall or slip
8.Will work in any environment
9.Can be used in robotics in a wide scale.
Disadvantages
1.Require a dedicated control circuit
2.Use more current then D.C Motors
3.Torque Reduces at higher speeds
2.Use more current then D.C Motors
3.Torque Reduces at higher speeds
Servomotors Vs. Stepper Motors
A servomotor consumes power as it rotates to the commanded position but then The servomotor rests. Stepper motors run warm to the touch because they continue to consume power to lock in and hold the commanded position.
servomotors are generally used as a high performance alternative to the stepper motor. Stepper motors have some inherent ability to control position, as they have built-in output steps. This often allows them to be used as an open-loop position control, without any feedback encoder, as they drive signal specifies the number of steps of movement to rotate, but for this the controller needs to 'know' the position of the stepper motor on power up. therefore, on first power up, the controller will have to activate the stepper motor and turn it to a known position, e.g. until it activates an end limit switch. This can be observed when switching on an inkjet printer: the controller will move the ink jet carrier to the extreme left and right to establish the end positions. A servomotor will immediately turn to whatever angle the controller instructs it to, regardless of the initial position at power up.
The lack of feedback of a stepper motor limits its performance, as the stepper motor can only drive a load that is well within its capacity, otherwise missed steps under load may lead to positioning errors and the system may have to be restarted or re-calibrated. The encoder and controller of a servomotor are an additional cost, but they optimist the performance of the overall system (for all of speed , power and accuracy) relative to the capacity of the basic motor. with larger systems, where a powerful motor represents an increasing proportion of the system cost, servomotors have the advantage.
There has been increasing popularity in closed loop stepper motors in recent years.They act like servomotors but have some differences in their software control to get smooth motion. the top 3 manufacturers of closed loop stepper motor system employ magnetic encoders as their feedback device of choice due to low cost, and resistance to vibration the main benefit of a closed loop stepper motor is the cost to performance ratio. There is also no need to turn the PID controller on a closed loop stepper system saving time
Many application, such as laser cutting machines, may be offered in two ranges the low-priced range using stepper motors and the high-performance range using servomotors.
Control
Most modern servomotors are designed and supplied around a dedicated controller module from the same manufacturer. Controllers may also be developed around Micro controllers in order to reduce cost for large volume applications.
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Post By : Irfan khan
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