What are the Types of Servo Motor?

Servo Motor
There are some special types of application of electrical motor where rotation of the motor is required for just a certain angle not continuously for long period of time. For these applications, some special types of motor are required with some special arrangement which makes the motor to rotate a certain angle for a given electrical input (signal). This is normally a simple motor which is controlled for specific angular rotation with the help of additional servomechanism (a typical closed loop feedback control system). Servo motor is a special type of motor which is automatically operated up to certain limit for a given command with help of error-sensing feedback to correct the performance.

Servomechanism
A servo system mainly consists of three basic components that is a controlled device, an output sensor and a feedback system.
This is an automatic closed loop control system. Here instead of controlling a device by applying the variable input signal, the device is controlled by a feedback signal generated by comparing output signal and reference input signal. When reference input signal or command signal is applied to the system, it is compared with output reference signal of the system produced by  output sensor, and a third signal produced by a feedback system. This third signal acts as an input signal of controlled device. This input signal to the device presents if there is a logical difference between reference input signal and the output signal of the system. After the device achieves its desired output, there will be no longer the logical difference between reference input signal and reference output signal of the system. Then, the third signal produced by comparing theses above said signals will not remain enough to operate the device further and to produce a further output of the system until  the next reference input signal or command signal is applied to the system. Hence, the primary task of a servomechanism is to maintain the output of a system at the desired value in the presence of disturbances.

Working Principle of Servo Motor
A servo motor is basically a DC motor (in some special cases it is AC motor) along with some other special purpose components that make a DC motor a servo. In a servo unit, you will find a small DC motor, a potentiometer, gear arrangement and an intelligent circuitry. The intelligent circuitry along with the potentiometer makes the servo to rotate according to our wishes. As  we know, a small DC motor will rotate with high speed but the torque generated by its rotation will not be enough to move even a light load. This is where the gear system inside a servomechanism comes into the picture. The gear mechanism will take high input speed of the motor (fast) and at the output, we will get an output speed which is slower than original input speed but more practical and widely applicable.

Types of Servo Motor
Servo motors are classified into different types based on their application,

• AC servo motor
• DC servo motor
• brushless DC servo motor
• positional rotation
• continuous rotation
• linear servo motor

Typical servo motors comprise of three wires namely, power control and ground. The shape and size of these motors depend on their applications. RC servo motor is the most common type of servo motor used in hobby applications, robotics due to their simplicity, affordability and reliability of control by microprocessors.

AC Servo Motor
AC servo motor is an AC motor that includes encoder is used with controllers for giving closed  loop control and feedback. This motor can be placed to high accuracy and also controlled precisely as compulsory for the applications. Frequently these motors have higher designs of tolerance or better bearings and some simple designs also use higher voltages in order to  accomplish greater torque. Motor mainly involve in automation, robotics, CNC machinery, and other applications a high level of precision and needful versatility.

DC Servo Motor
The motor which is used as a DC servo motor generally have a separate DC source in the field of winding & armature winding. The control can be archived either by controlling the armature  current or field current. Field control includes some advantages over armature control. In the same way armature control includes some advantages over field control. Based on the applications the control should be applied to the DC servo motor. DC servo motor provides very  accurate and fast respond to start or stop command signals due to the low armature inductive  reactance. DC servo motors are used in similar equipments and computerized numerically controlled machines.

Positional Rotation Servo Motor
Positional rotation servo motor is a most common type of servo motor. The shaft’s o/p rotates in  about 1800. It includes physical stops located in the gear mechanism to stop turning outside  these limits to guard the rotation sensor. These common servos involve in radio controlled water, radio controlled cars, aircraft, robots, toys and many other applications.

Continuous Rotation Servo Motor
Continuous rotation servo motor is quite related to the common positional rotation servo motor, but it can go in any direction indefinitely. The control signal, rather than set the static position  of the servo, is understood as the speed and direction of rotation. The range of potential commands sources the servo to rotate clockwise or anticlockwise as preferred, at changing speed, depending on the command signal. This type of motor is used in a radar dish if you are riding one on a robot or you can use one as a drive motor on a mobile robot.

Linear Servo Motor
Linear servo motor is also similar the positional rotation servo motor is discussed above, but with an extra gear to alter the o/p from circular to back-and-forth. These servo motors are not simple to find, but sometimes you can find them at hobby stores where they are used as actuators in higher model airplanes.