Written by : Aliya Hammad & Amr Alaa
Servo motors
Servomotors – A motor with a "feedback" device. Electronic packages control speed and position
accuracy.
Open/closed loops
An open loop drive is one in which the signal goes "in one direction only". . . from the control to the motor. There is no signal returning from the motor/load to inform the control that action/motion has occurred.
If a signal is returned to provide information that motion has occurred, then the system is described as having a signal which goes in "two directions": The command signal goes out (to move the motor), and a signal is returned (the feedback) to the control to inform the control of what has occurred. The information flows back, or returns. This is an example of a "closed loop" drive.
WHAT IS A SERVO?
What is a servo? This is not easily defined nor self-explanatory since a servomechanism, or servo drive, does not apply to any particular device. It is a term which applies to a function or a task.
The function, or task, of a servo can be described as follows. A command signal which is issued from the user's interface panel comes into the servo's "positioning controller". The positioning controller is the device which stores information about various jobs or tasks. It has been programmed to activate the motor/load, i.e. change speed/position.
The signal then passes into the servo control or "amplifier" section. The servo control takes this low power level signal and increases, or amplifies, the power up to appropriate levels to actually result in movement of the servo motor/load.
These low power level signals must be amplified: Higher voltage levels are needed to rotate the servo motor at appropriate higher speeds.
This power is supplied to the servo control (amplifier) from the "power supply" which simply converts AC power into the required DC level. It also supplies any low level voltage required for operation of integrated circuits.
As power is applied onto the servo motor, the load begins to move . . . speed and position changes.
As the load moves, so does some other "device" move. This other "device" is either a tachometer, resolver or encoder (providing a signal which is "sent back" to the controller). This "feedback" sig-nal is informing the positioning controller whether the motor is doing the proper job.
The positioning controller looks at this feedback signal and determines if the load is being moved properly by the servo motor; and, if not, then the controller makes appropriate corrections.
How is the servo motor constructed?
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 picture. The gear mechanism will take high input speed of the motor (fast) and at the output, we will get a output speed which is slower than original input speed but more practical and widely applicable.
How Servo motor works
Say at initial position of servo motor shaft, the position of the potentiometer knob is such that there is no electrical signal generated at the output port of the potentiometer . This output port of the potentiometer is connected with one of the input terminals of the error detector amplifier. Now an electrical signal is given to another input terminal of the error detector amplifier. Now difference between these two signals, one comes frompotentiometer and another comes from external source, will be amplified in the error detector amplifier and feeds the DC motor. This amplified error signal acts as the input power of the dc motor and the motor starts rotating in desired direction. As the motor shaft progresses the potentiometer knob also rotates as it is coupled with motor shaft with help of gear arrangement. As the position of the potentiometer knob changes there will be an electrical signal produced at the potentiometer port. As the angular position of the potentiometer knob progresses the output or feedback signal increases. After desired angular position of motor shaft the potentiometer knob is reaches at such position the electrical signal generated in the potentiometer becomes same as of external electrical signal given to amplifier. At this condition, there will be no output signal from the amplifier to the motor input as there is no difference between external applied signal and the signal generated at potentiometer . As the input signal to the motor is nil at that position, the motor stops rotating. This is how a simple conceptual servo motor works.
Applications
Servo Motor in Robotics
One of the most popular servo motor applications is robotic. Consider a simple pick and place robot. Pick and place robot is such a robotic machine which is used to pick an object from one position and place the object at different position. Now, in order to pick an object from position A and place it in position B the motors which are used to actuate the joints are servo motors. This is because; we have to plan the angular movement of each and every joint to complete this task of pick and place. Once this data is fed to the robot controller, the robot will continuously do its job. The controller will send PWM data to the individual motors of the robot. This gives precise angular control of the arm which is not possible with a regular DC motor.
Servo Motor in Conveyors
Conveyors are used in Industrial manufacturing and assembling units to pass an object from one assembly station to another. Let’s consider an example of bottle filling process, in the process the bottle needs to be filled with the liquid and moved to the next stage which is mainly the packaging stage. So in order to achieve this conveyor belts are used with servo motors so that the bottle moves precisely to the desired location and stops so that the liquid can be poured into it and then it is guided to the next stage. This process continues until stopped. Hence the precise position control ability of the servo shaft comes in handy.
Servo Motor Applications AS Camera Auto Focus
Today’s modern digital cameras are very advanced. One of the advanced features is its ability to auto focus on the object to be captured. When the image of the object is created within the digital signal processor of the camera, it is checked for sharpness. Basically, if the focal length (measured from camera lens) is not proper, the image appears to be blurred. The corrective action to position the lens precisely so that the sharpest image is captured is done using a highly precise servo motor fitted within the camera. This is another important example of servo motor applications.
Servo Motor in Solar Tracking System
Solar power generation and usage is gaining importance as people move towards clean and renewable energy regime. Earlier, Solar panels that were installed were static and remained in one position for the entire duration of the day. General Science dictates that the Sun is not always facing in one direction and that its position relative to the Solar panel will change. This implies that we are not fully utilizing the power of the sun to extract maximum energy out of it. But, if we attach servo motors to the solar panel s in such a way that we are able to precisely control its angle of movement so that it closely follows the Sun, then the overall efficiency of the system vastly increases. This is another application of servo where angle
control is critical and achievable by a servo motor.
These are some of many Servo Motor Applications.
Principle strengths:
1. High performance
2. Small size
3. Wide variety of components
4. High speeds available
with specialized controls
5. If a heavy load is placed on the motor, the driver will increase the current to the motor coil as it
attempts to rotate the motor. Basically, there is no out-of-step condition. (However, too heavy a load
may cause an error.)
Principle weaknesses:
1. Slightly higher cost
2. High performance limited by controls
Servo motor controlled by IC 555
· WWW.Electrical4u.com
· rookieelectronics.com
· Servo control facts – Baldor electric company
· http://www.bpesolutions.com/
Servo motors
Servomotors – A motor with a "feedback" device. Electronic packages control speed and position
accuracy.
Open/closed loops
An open loop drive is one in which the signal goes "in one direction only". . . from the control to the motor. There is no signal returning from the motor/load to inform the control that action/motion has occurred.
If a signal is returned to provide information that motion has occurred, then the system is described as having a signal which goes in "two directions": The command signal goes out (to move the motor), and a signal is returned (the feedback) to the control to inform the control of what has occurred. The information flows back, or returns. This is an example of a "closed loop" drive.
WHAT IS A SERVO?
What is a servo? This is not easily defined nor self-explanatory since a servomechanism, or servo drive, does not apply to any particular device. It is a term which applies to a function or a task.
The function, or task, of a servo can be described as follows. A command signal which is issued from the user's interface panel comes into the servo's "positioning controller". The positioning controller is the device which stores information about various jobs or tasks. It has been programmed to activate the motor/load, i.e. change speed/position.
The signal then passes into the servo control or "amplifier" section. The servo control takes this low power level signal and increases, or amplifies, the power up to appropriate levels to actually result in movement of the servo motor/load.
These low power level signals must be amplified: Higher voltage levels are needed to rotate the servo motor at appropriate higher speeds.
This power is supplied to the servo control (amplifier) from the "power supply" which simply converts AC power into the required DC level. It also supplies any low level voltage required for operation of integrated circuits.
As power is applied onto the servo motor, the load begins to move . . . speed and position changes.
As the load moves, so does some other "device" move. This other "device" is either a tachometer, resolver or encoder (providing a signal which is "sent back" to the controller). This "feedback" sig-nal is informing the positioning controller whether the motor is doing the proper job.
The positioning controller looks at this feedback signal and determines if the load is being moved properly by the servo motor; and, if not, then the controller makes appropriate corrections.
How is the servo motor constructed?
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 picture. The gear mechanism will take high input speed of the motor (fast) and at the output, we will get a output speed which is slower than original input speed but more practical and widely applicable.
How Servo motor works
Say at initial position of servo motor shaft, the position of the potentiometer knob is such that there is no electrical signal generated at the output port of the potentiometer . This output port of the potentiometer is connected with one of the input terminals of the error detector amplifier. Now an electrical signal is given to another input terminal of the error detector amplifier. Now difference between these two signals, one comes frompotentiometer and another comes from external source, will be amplified in the error detector amplifier and feeds the DC motor. This amplified error signal acts as the input power of the dc motor and the motor starts rotating in desired direction. As the motor shaft progresses the potentiometer knob also rotates as it is coupled with motor shaft with help of gear arrangement. As the position of the potentiometer knob changes there will be an electrical signal produced at the potentiometer port. As the angular position of the potentiometer knob progresses the output or feedback signal increases. After desired angular position of motor shaft the potentiometer knob is reaches at such position the electrical signal generated in the potentiometer becomes same as of external electrical signal given to amplifier. At this condition, there will be no output signal from the amplifier to the motor input as there is no difference between external applied signal and the signal generated at potentiometer . As the input signal to the motor is nil at that position, the motor stops rotating. This is how a simple conceptual servo motor works.
Applications
Servo Motor in Robotics
One of the most popular servo motor applications is robotic. Consider a simple pick and place robot. Pick and place robot is such a robotic machine which is used to pick an object from one position and place the object at different position. Now, in order to pick an object from position A and place it in position B the motors which are used to actuate the joints are servo motors. This is because; we have to plan the angular movement of each and every joint to complete this task of pick and place. Once this data is fed to the robot controller, the robot will continuously do its job. The controller will send PWM data to the individual motors of the robot. This gives precise angular control of the arm which is not possible with a regular DC motor.
Servo Motor in Conveyors
Conveyors are used in Industrial manufacturing and assembling units to pass an object from one assembly station to another. Let’s consider an example of bottle filling process, in the process the bottle needs to be filled with the liquid and moved to the next stage which is mainly the packaging stage. So in order to achieve this conveyor belts are used with servo motors so that the bottle moves precisely to the desired location and stops so that the liquid can be poured into it and then it is guided to the next stage. This process continues until stopped. Hence the precise position control ability of the servo shaft comes in handy.
Servo Motor Applications AS Camera Auto Focus
Today’s modern digital cameras are very advanced. One of the advanced features is its ability to auto focus on the object to be captured. When the image of the object is created within the digital signal processor of the camera, it is checked for sharpness. Basically, if the focal length (measured from camera lens) is not proper, the image appears to be blurred. The corrective action to position the lens precisely so that the sharpest image is captured is done using a highly precise servo motor fitted within the camera. This is another important example of servo motor applications.
Servo Motor in Solar Tracking System
Solar power generation and usage is gaining importance as people move towards clean and renewable energy regime. Earlier, Solar panels that were installed were static and remained in one position for the entire duration of the day. General Science dictates that the Sun is not always facing in one direction and that its position relative to the Solar panel will change. This implies that we are not fully utilizing the power of the sun to extract maximum energy out of it. But, if we attach servo motors to the solar panel s in such a way that we are able to precisely control its angle of movement so that it closely follows the Sun, then the overall efficiency of the system vastly increases. This is another application of servo where angle
control is critical and achievable by a servo motor.
These are some of many Servo Motor Applications.
Principle strengths:
1. High performance
2. Small size
3. Wide variety of components
4. High speeds available
with specialized controls
5. If a heavy load is placed on the motor, the driver will increase the current to the motor coil as it
attempts to rotate the motor. Basically, there is no out-of-step condition. (However, too heavy a load
may cause an error.)
Principle weaknesses:
1. Slightly higher cost
2. High performance limited by controls
Servo motor controlled by IC 555
· WWW.Electrical4u.com
· rookieelectronics.com
· Servo control facts – Baldor electric company
· http://www.bpesolutions.com/
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