സത്യം പറയാം എഴുതാൻ അറിയില്ല...

           വെറുതെ എന്തേലും കുത്തി കുറിക്കുന്നു ,ആരേലും വായിക്കാൻ; ഇല്ലേലും വിരോധം ഇല്ല.ജീവിതത്തിൽ കണ്ടത്, പറയാൻ ആഗ്രഹികുനത് മറ്റുള്ളവരും  അറിയേണ്ടത്

         എന്താണ് ജീവിതത്തിലെ ഏറ്റവും വല്ലിയ പരീക്ഷ എന്ന് ഓരോ കുട്ടിയോടും ചോദിച്ചാൽ..????? ജീവിതത്തിൽ പല പരീക്ഷകളും കണ്ടവർ, എഴുതിയവർ ആണ് നമ്മൾ എല്ലാവരും,ചില വിധ്യാര്തികള്ക് അവര് എഴുതിയ ജയിച്ചേ മതി ആകുള്ളൂ എന്ന് കരുതിയ പരീക്ഷകൾ  ഓടിവരും  മനസിലേക്ക് ...മറ്റു ചിലർക്ക്ആകട്ടെ   ലഭിച്ചേ മതി ആകൂ എന്ന് കരുതിയ ഉദ്യോഗ ഇന്റർവ്യുകലും..എന്നാൽ ഇതിൽ എല്ലാം ഒരു ഖടകം വിധി നിർണയിക്കും ഒരു പരുധി വരെ എങ്കിലും .എന്ത്.??.നമ്മുടെ കഠിനാദ്ധ്വാനം...പക്ഷെ വേറെ ചില പരീക്ഷകൾ അനാവശ്യം ആയി നമ്മൾ നേരിടേണ്ടി വരും..ചിലപ്പോൾ തോല്ക്കും ജയിക്കും...ജയിക്കാൻ മനം ഉരുകി കരയും ഇഷ്ട ദൈവത്തോട്...
     
        ഏതാണ്ട് 6 മാസം മുമ്പാണ്‌ ആദ്യമായി കൊച്ചിയിലെ ആസ്റ്റെർ മെഡിസിറ്റിയിൽ അച്ഛന്റെ കൂടെ ചില ടെസ്റ്റുകൾക്ക് ചെല്ലു്നത് ആദ്യമായിട്ട് ആണ് ഒരു കാൻസർ പരിശോധന ലാബിനു മുന്നില് നിക്കുനതും ..കേട്ട് പരിചയം മാത്രം ഉള്ള വിഷമിപികുന രോഗത്തിനെ  മല്ലടികുനവരെ കാണുനതും.psa പോലുള്ള ടെസ്റ്റുകൾക്ക് ഉള്ള നീണ്ട ക്യു അതിന്റെ വ്യാപ്തിയും വേദനയോടെ   തിരിച്ചറിയിച്ചു ...

        ഒരു കോണിൽ ഏകദേശം 10 വയസ് മാത്രം പ്രായം തോനികുന്ന ഒരു വായാടി പെണ്കുട്ടിയെ അവിടെ തങ്ങി നിന്ന നിശബ്ദത കണ്ണ്അടുപിച്ചു...ചന്ദന കുറി തൊട്ടു റാ കൊണ്ട് വകഞ്ഞ മുടിയും ആയി ഒരു സ്ക്കൂൾ യുണിഫോര്മിൽ ഇരിക്കുന്ന സുന്ദരി കുട്ടി ,തൊടരുകിൽ  ഇരിക്കുന്ന അമ്മയോട് കല പില ബഹളം ഉണ്ടാകുന്നു..തെല്ല് ദേഷ്യത്തോടെ ആ കുട്ടിയെ ശ്രദ്ധിക്കാൻ തുടങ്ങിയത് എന്റെ മനസിന്റെ ഭാരം കാരണം ആണ്.അമ്മേ വേദന കാണുമോ കഴിഞ്ഞ പ്രാവശ്യത്തെ പോലെ ??? എനിക്ക് പേടിയ...ആ സിസ്റ്റർ ആന്റിയോട്‌ പറയാമോ വേദനിപികല്ല്‌ എന്ന്..? ഇനി വേദന ഉണ്ടാകില്ല  എന്നും അടങ്ങി ഇരിക്ക് എന്നും ആ അമ്മ  പാതി കരച്ചിലും ദേഷ്യവും ആയി പറഞ്ഞപോൾ തെല്ലൊരു വിങ്ങലു മാത്രം ഉണ്ടായുള്ളൂ...തുണ്ട ഇടറി പക്ഷെ സംസാരികേണ്ട അവസരം അല്ലാത്ത കൊണ്ട് സ്വയം അടക്കാൻ പറ്റി...
   
       എന്റെ കൂടെ വന്ന അമ്മയുടെ  എന്ത് പറ്റിയതാണ് കുഞ്ഞിനു എന്നാ ചോദ്യത്തിന് കുറച് ആഴ്ചകൾ മുമ്ബ് തോളിൽ വന്ന മുഴ ആണ് ഇവിടെ എത്തിച്ചത് 3 ടെസ്റ്റ്‌ ചെയാൻ പറഞ്ഞു ഇപ്രാവശ്യം അറിയാം എന്ന് മുഖം നോകാതെ പറഞ്ഞപോൾ ആ കണ്ണുകൾ  നിറഞ്ഞിരുന്നു...ഏറ്റവും വലിയ ഞെട്ടലൊടെ  കുട്ടിയുടെ നിഷ്കളങ്കമായ ചോദ്യം വന്നു അമ്മ കരയുക ആണോ???എന്റെ ജീവിതത്തിൽ ഞാൻ നേരിട്ട എല്ലാ പരീക്ഷയും ഒന്നും അല്ല എന്ന് തിരിച്ചറിഞ്ഞ നിമിഷം!! ജീവിതം തുടക്കം മാത്രം എന്ന് അറിഞ്ഞ സമയം...അമ്മ കരയണ്ടാട്ടോ എന്ന് കൊഞ്ചി പറഞ്ഞപോൾ ഓരോന്ന് വരുത്തി വച്ചു എന്ന് ശാപ വാകുകൾ ആരോടോ കല്ല്‌ പോലും ഉരുക്കി കളയുന്ന വേദനയോടെ പറഞ്ഞു...ഇതൊന്നും ശ്രദ്ധികാതെ ചോക്ലാറ്റ് ചോക്ലാറ്റ് എന്ന് വാശി പിടിച്ച കുട്ടിക്ക് മുന്നില് ഒതുക്കി വച്ചിരുന്ന പേർസ്‌ തുറന്നപ്പോൾ മുന്നാലു സ്വര്ണ വളകൾ...

    പെട്ടന്നു ഒരു നര്സു ഇറങ്ങി വന്നു കുട്ടിയുടെ പേര് വിളിച്ചു...അമ്മ്മേ എനിക്ക് പേടി ആകുന്നു അമ്മയും വാ കുട്ടി വീണ്ടും അമ്മയുടെ കയ്യിൽ പിടിച്ചു...ഇപ്രാവശ്യം വേദനികില്ല അമ്മയും അകത് വന്നോളു എന്ന് പറഞ്ഞു സമാദാനിപിച്ച ആ നുര്സിനു നന്ദി പറഞ്ഞു ഇരുവരും അകത്തേക്...വാതിൽ പുറത്ത് നിന്ന് അടച്ച അവര് കുട്ടിക്ക് നല്ല വേദന ഉണ്ടാകും സെല്ൽ എടുകുമ്പോൾ സൂജി നല്ല നീളം ഉളത പാവം എന്ന് പറഞ്ഞപോൾ എന്നും ഇതുപോലെ 100 കണകിനു കാണുന്ന അവര്ക് പോലും ഉള്ള വിഷമം ആണ് കണ്ടത്..
     
     ആ കുട്ടി പരീക്ഷ ജയിച്ചു കാണുമോ..??? ആ അമ്മ സന്തോഷിച്ചു കാണുമോ അറിയില്ല...ജയികട്ടെ ജയിക്കാൻ പ്രാര്തിച്ചു കൊണ്ട് ഞാനും അച്ഛന്റെ ചെകപ് കഴിഞ്ഞ് മടങ്ങി..കാറിൽ ഇരുന്നപോളും ആ കുഞ്ഞ് മുഖം മായാതെ നിന്നു..ഇപോളും....
    


             

ans4:adding zero

(A) THE ZERO S = –Z1 IS NOT PRESENT.
FOR DIFFERENT VALUES OF K, THE SYSTEM CAN HAVE TWO REAL POLES OR A PAIR OF COMPLEX
CONJUGATE POLES. THIS MEANS THAT WE CAN CHOOSE K FOR THE SYSTEM TO BE OVERDAMPED,
CRITICALLY DAMPED OR UNDERDAMPED.
(B) THE ZERO S = –Z1 IS LOCATED TO THE RIGHT OF BOTH POLES, S = – P2 AND S = –P1.
IN THIS CASE, THE SYSTEM CAN HAVE ONLY REAL POLES AND HENCE WE CAN ONLY FIND A VALUE
FOR K TO MAKE THE SYSTEM OVERDAMPED. THUS THE POLE–ZERO CONFIGURATION IS EVEN MORE
RESTRICTED THAN IN CASE (A). THEREFORE THIS MAY NOT BE A GOOD LOCATION FOR OUR ZERO,
SINCE THE TIME RESPONSE WILL BECOME SLOWER.
(C) THE ZERO S = –Z1 IS LOCATED BETWEEN S = –P2 AND S = –P1.
THIS CASE PROVIDES A ROOT LOCUS ON THE REAL AXIS. THE RESPONSES ARE THEREFORE LIMITED TO
OVERDAMPED RESPONSES. IT IS A SLIGHTLY BETTER LOCATION THAN (B), SINCE FASTER RESPONSES
ARE POSSIBLE DUE TO THE DOMINANT POLE (POLE NEAREST TO JAXIS) LYING FURTHER FROM THE J
AXIS THAN THE DOMINANT POLE IN (B).
(D) THE ZERO S = –Z1 IS LOCATED TO THE LEFT OF S = –P2.
THIS IS THE MOST INTERESTING CASE. NOTE THAT BY PLACING THE ZERO TO THE LEFT OF BOTH
POLES, THE VERTICAL BRANCHES OF CASE (A) ARE BENT BACKWARD AND ONE END APPROACHES THE
ZERO AND THE OTHER MOVES TO INFINITY ON THE REAL AXIS. WITH THIS CONFIGURATION, WE CAN
NOW CHANGE THE DAMPING RATIO AND THE NATURAL FREQUENCY (TO SOME EXTENT). THE
CLOSED-LOOP POLE LOCATIONS CAN LIE FURTHER TO THE LEFT THAN S = –P2, WHICH WILL PROVIDE
FASTER TIME RESPONSES. THIS STRUCTURE THEREFORE GIVES A MORE FLEXIBLE CONFIGURATION FOR
CONTROL DESIGN.
WE CAN SEE THAT THE RESULTING CLOSED-LOOP POLE POSITIONS ARE CONSIDERABLY INFLUENCED BY
THE POSITION OF THIS ZERO. SINCE THERE IS A RELATIONSHIP BETWEEN THE POSITION OF CLOSED-LOOP
POLES AND THE SYSTEM TIME DOMAIN PERFORMANCE, WE CAN THEREFORE MODIFY THE BEHAVIOUR OF
CLOSED-LOOP SYSTEM BY INTRODUCING APPROPRIATE ZEROS IN THE CONTROLLER.

REFERENCE:
WEB.MIT.EDU
WWW.WIKIPEDIA.COM

ans3:

Poles and Zeros of a transfer function are the frequencies for which the value of the transfer function becomes infinity or zero respectively. The values of the poles and the zeros of a system determine whether the system is stable, and how well the system performs.Let the polynomial be:
H(s)=N(s)/D(s).

Effects of Poles and Zeros

As s approaches a zero, the numerator of the transfer function (and therefore the transfer function itself) approaches the value 0. When s approaches a pole, the denominator of the transfer function approaches zero, and the value of the transfer function approaches infinity. An output value of infinity should raise an alarm bell for people who are familiar with BIBO stability. Tthe locations of the poles, and the values of the real and imaginary parts of the pole determine the response of the system. Real parts correspond to exponentials, and imaginary parts correspond to sinusoidal values.

The stability of a linear system may be determined directly from its transfer function. An nth order linear system is asymptotically stable only if all of the components in the homogeneous response from a finite set of initial conditions decay to zero as time increases.In order for a linear system to be stable, all of its poles must have negative real parts.

Reference:

Web.mit.edu

INCREMENTAL ENCODERS
INCREMENTAL ENCODER PRODUCE AN OUTPUT WHICH IS A PULSE FOR EACH INCREMENT OF RESOLUTION BUT THESE MAKE NO DISTINCTION BETWEEN INCREMENTS.AN INCREMENTAL ENCODER TYPICALLY HAS FOUR PARTS:
A LIGHT SOURCE(LED)
A ROTARY(OR TRANSLATOR )DISC
A STATIONARY MASK
A SENSOR (PHOTODIODE
An incremental rotary encoder, also known as a quadrature encoder or a relative rotary encoder, has two outputs called quadrature outputs. They can be either mechanical or optical. In the optical type there are two gray coded tracks, while the mechanical type has two contacts that are actuated by cams on the rotating shaft. Due to the fact the mechanical switches require debouncing, the mechanical type are limited in the rotational speeds they can handle. The incremental rotary encoder is the most widely used of all rotary encoders due to its low cost: only two sensors are required. The fact that incremental encoders use only two sensors does not compromise their accuracy. One can find in the market incremental encoders with up to 10,000 counts per revolution, or more.

There can be an optional third output: reference, which happens once every turn. This is used when there is the need of an absolute reference, such as positioning systems.

The optical type is used when higher RPMs are encountered or a higher degree of precision is required.

Incremental encoders are used to track motion and can be used to determine position and velocity. This can be either linear or rotary motion.
They employ two outputs called A & B which are called quadrature outputs as they are 90 degrees out of phase.

ans1:synchro

A synchro or "selsyn" is a type of rotary electrical transformer that is used for measuring the angle of a rotating machine such as an antenna platform. The primary winding of the transformer, fixed to the rotor, is excited by a sinusoidal electric current (AC), which by electromagnetic induction causes currents to flow in three star-connected secondary windings fixed at 120 degrees to each other on the stator. The relative magnitudes of secondary currents are measured and used to determine the angle of the rotor relative to the stator, or the currents can be used to directly drive a receiver synchro that will rotate in unison with the synchro transmitter. In the latter case, the whole device (in some applications) is also called a selsyn (a portmanteau of self and synchronizing).

Synchro systems were first used in the control system of the Panama Canal, to transmit lock gate and valve stem positions, and water levels, to the control desks.
Selsyn motors were widely used in motion picture equipment to synchronize movie cameras and sound recording equipment, before the advent of crystal oscillators and microelectronics.

On a practical level, synchros resemble motors, in that there is a rotor, stator, and a shaft. Ordinarily, slip rings and brushes connect the rotor to external power. A synchro transmitter's shaft is rotated by the mechanism that sends information, while the synchro receiver's shaft rotates a dial, or operates a light mechanical load. Single and three-phase units are common in use, and will follow the other's rotation when connected properly. One transmitter can turn several receivers; if torque is a factor, the transmitter must be physically larger to source the additional current.

In all cases, the mains excitation voltage sources must match in voltage and phase. The safest approach is to bus the five or six lines from transmitters and receivers at a common point.

A different type of receiver, called a control transformer (CT), is part of a position servo that includes a servo amplifier and servo motor. The motor is geared to the CT rotor, and when the transmitter's rotor moves, the servo motor turns the CT's rotor and the mechanical load to match the new position. CTs have high-impedance stators and draw much less current than ordinary synchro receivers when not correctly positioned.

If we need to operate the stepper motor in closed loop(positional feedback)mode,we need to use synchros for error detection.Here the motor is used like conventional servomotor.A signal from the output is fed back and is used to operate a gate controlling the pulses from a pulse generator

CINCINATI MILACRON T3 ROBOTIC ARM

CINCINATI MILACRON T3 ROBOTIC ARM

Cincinnati Milacron built large industrial robots primarily for welding industry. It was one of the first companies to change from hydraulic to electric robots. Milacron pioneered the first computerized numerical control (CNC) robot with improved wrists and the tool centre point (TCP) concepts. The first hydraulic machine, the introduced in 1978. It closely resembled the General Electric Man-mate, ITT arm, and other predecessors (Sullivan 1971). Constructed of cast aluminium, it is available in two models of 6-axes revolute jointed arms. The largest, the T3-776, uses ballscrew electric drives to power the shoulder and elbow pitch. The ballscrews replaced the hydraulic cylinders originally used on the T3 robots. The elbow is a classical example of intermediate drive elbow. The same techniques, only upside down, appear in the shoulder. Shoulder yaw is provided by the standard bullgear on a base mounted motor drive. End users have discovered that ballscrews are not sufficiently reliable and are pressuring for an alternators. The eventual disappearance of ballscrews in industrial robots seems inevitable.

CONTROL SYSTEM

The T3 robotic arms is controlled using a Hierarchical Control System.A Hierarchical control system is partitioned vertically into levels of control. The basic comand and control structure is a tree, configured such that each computational module has a single superior, and one or more subordinate modules. The top module is where the highest level decisions are made and the longest planning horizon exists. Goals and plans generated at this highest level are transmitted as commands to the next lower level where they are decomposed into sequences of subgoals. These subgoals are in turn transmitted to the next lower control decision level as sequences of less complex but more frequent commands. In general,the decisions and corresponding decompositions at each level take into account: (a) conrmands from the level above, (b) processed sensory feedback information appropriate to that control decision level, and (c) status reports from decision control modules at the next lower control level.

The figure shown above depicts the schematic block diagram of the integrated control structure as configured on the Cincinnati Milacron T3 Robot. The system is configured in the hierarchical manner and includes five major subsystems:
(1) The Real-Time Control System (RCS)
(2) The commercial. T3 Robot equipment
( 3 ) the End-Effector System
(4) The Vision System
(5) The Watchdog Safety System

The Real-Time Control System as shown in figure is composed of four levels:
(1) The Task Level
(2)The Elemental-Move Level
(3) The Primitive Level
(4)The T3 Level.

The Task, Elemental-Move and Primitive levels of the controller are considered to be Generic Control Levels. That is, these levels would remain essentially the same regardless of the particular robot (commercial or otherwise) being used. The T3 Level, however ,uses information and parameters particular to the T3 Robot and is, therefore, unique to the T3 Robot. The Joystick shown provides an alternate source of commands to the Primitive Level for manual control of the robot and is not used in conjunction with the higher control levels .The T3 Controller shown in figure is part of the T3 Robot equipment as purchased from Cincinnati Milacron. This controller is subordinate to the T3 Level of the RCS and communicates through a special interface.
The End-Effector System consists of a two fingered gripper equipped with position and force sensing .The gripper is pneumatically actuated and servo controlled by a controller which is subordinate to the Primitive Level of the RCS. There are three sensory systems on the robot:

1. The finger force and position sensors on the gripper which report data to the End Effector Controller
2. The 3 point Angle Acquisition System which reports data to the T3 Controller, the T3 Level of the RCS and to the Watchdog Safety System
3. The Vision System which reports data to the Elemental-Move Level of the RCS.
4. Of the sensor systems, the vision system is obviously the most complex. It performs
sophisticated image processing which requires substantial computational time.

The Watchdog Safety System does not fit directly into the hierarchical control structure. It is an independent system which monitors robot motions and compares them to previously defined limits in position, velocity and acceleration. The Watchdog System has the power to stop the robot if any limits are exceeded and consequently monitors both the mechanical and control systems of the robot.

PARTS OF THE REAL TIME CONTROL SYSTEM
(1)Task Level
The Task Level interfaces with the Workstation Level above it and the Elemental-Move Level below it. In the current configuration, the Task Level has no direct interfaces with sensory systems. The Task Level receives commands from the Workstation Level in terms of objects to be handled and named places in the workstation.
For example, the task might be to find a certain part on the tray at the load/unload station, pick it up and put it in the fixture on the machine tool. This task could be issued as one command from the Workstation Level to the Task Level of the RCS.

(2)Elemental-Move Level
The E-Move Level interfaces with the Task Level above it and the Primitive Level below it. In addition, the E-Move Level interfaces with the Vision System from which it acquires part position and orientation data. The E-Move Level receives commands from the Task Level which are elemental segments of the Task Level command under execution. These are generally single moves from one named location to another. If a part acquisition is involved, data from the Vision System is requested to determine the exact location of the next goal point. The E-Move Level then develops a trajectory between the new goal point and its current position. A trajectory maybe simply a straight line move to the goal point or a more complex move, involving departure, intermediate and approach trajectories. These trajectories can be constructed using pre-stored trajectory segments or data acquired from the Vision System. If no pre-stored segments are found for the desired move and the use of vision data is not appropriate, then a straight line path to the new goal point is calculated.

(3)Primitive Level
The Primitive Level interfaces with the E-Move Level above it and the T3 Level and End-Effector Controller below it. The Primitive Level is the lowest level in the RCS
which is robot or device independent. Subsystems subordinate to the Primitive Level are considered to be at the device level in the control hierarchy. In this system, these subsystems or devices are the robot and the end-effector. T3 The Level shown in figure is not a true control decision level by itself and could be logically combined with the T3 Controller at the device level. The robot and end-effector are, therefore, at the same control decision level subordinate to the Primitive Level. Additionally, the Primitive Level interfaces with the Joystick. The Joystick is a peripheral device which is used for manual operation of the robot. Using the Joystick, the operator can control robot motion in several coordinate systems (world, tool or individual joint motions). Under Joystick control the human operator assumes the higher level planning and control duties normally handled by the E-Move and Task Levels when the robot is operating automatically. The actual Joystick unit has groups of small joysticks, rotory and rocker switches dedicated to each coordinate system. These are configured such t hat the robot will move basically the way the lever is pushed or the switch turned that the robot will move basically the way the lever is pushed or the switch turned, giving the operator a relatively feel for the motion produced ’The Primitive Level receives commands from the E-Move L e v e l in terms of goal points in Cartesian space.These points differ from those received by the E-Move Level from the Task Level in that they are not named locations and therefore assume no knowledge of the Workstation layout. These points are typically more closely spaced than those at the higher Levels although this is not necessarily the case.

(4) T3 Level
The T3 Level interfaces with the Primitive Level above it and the commercial Cincinnati Milacron T3 Robot Controller below it. In addition there is a sensory interface which supplies the six individual joint angles. The T3 Level is so named because elements of it are peculiar to the T3 Robot. From a control hierarchy point of view the T3 Level does not constitute a logical control decision level but is infact a “gray box” necessary to transform command and feedback formats between the Primitive level and T3 controller.

SERVOMECHANISM

Automatic device used to correct the performance of a mechanism by means of an error-sensing feedback. The term servomechanism properly applies only to systems in which the feedback and error-correction signals control mechanical position or one of its derivatives such as velocity or acceleration.

A servomechanism is unique from other control systems because it controls a parameter by commanding the time-based derivative of that parameter. For example a servomechanism controlling position must be capable of changing the velocity of the system because the time-based derivative (rate change) of position is velocity. A hydraulic actuator controlled by a spool valve and a position sensor is a good example because the velocity of the actuator is proportional to the error signal of the position sensor.

All servomechanisms have at least these basic components: a controlled device, a command device, an error detector, an error-signal amplifier
, and a device to perform any necessary error corrections (the servomotor). In the controlled device, that which is being regulated is usually position. This device must, therefore, have some means of generating a signal (such as a voltage), called the feedback signal, that represents its current position. This signal is sent to an error-detecting device. The command device receives information, usually from outside the system, that represents the desired position of the controlled device. This information is converted to a form usable by the system (such as a voltage) and is fed to the same error detector as is the signal from the controlled device. The error detector compares the feedback signal (representing actual position) with the command signal (representing desired position). Any discrepancy results in an error signal that represents the correction necessary to bring the controlled device to its desired position. The error-correction signal is sent to an amplifier, and the amplified voltage is used to drive the servomotor, which repositions the controlled device.

This is just a brief introduction on servo mechanism...

So now lets see the application of servo mechanism

SERVO MOTOR!!!

















A servomotor (servo) is an electromechanical device in which an electrical input determines the position of the armature of a motor. Servos are used extensively in robotics and radio-controlled cars, airplanes, and boats.

So, how does a servo work? The servo motor has some control circuits and a potentiometer (a variable resistor, aka pot) that is connected to the output shaft. In the picture above, the pot can be seen on the right side of the circuit board. This pot allows the control circuitry to monitor the current angle of the servo motor. If the shaft is at the correct angle, then the motor shuts off. If the circuit finds that the angle is not correct, it will turn the motor the correct direction until the angle is correct. The output shaft of the servo is capable of travelling somewhere around 180 degrees. Usually, its somewhere in the 210 degree range, but it varies by manufacturer. A normal servo is used to control an angular motion of between 0 and 180 degrees. A normal servo is mechanically not capable of turning any farther due to a mechanical stop built on to the main output gear.

The amount of power applied to the motor is proportional to the distance it needs to travel. So, if the shaft needs to turn a large distance, the motor will run at full speed. If it needs to turn only a small amount, the motor will run at a slower speed. This is called proportional control.

How do you communicate the angle at which the servo should turn? The control wire is used to communicate the angle. The angle is determined by the duration of a pulse that is applied to the control wire. This is called Pulse Coded Modulation. The servo expects to see a pulse every 20 milliseconds (.02 seconds). The length of the pulse will determine how far the motor turns. A 1.5 millisecond pulse, for example, will make the motor turn to the 90 degree position (often called the neutral position). If the pulse is shorter than 1.5 ms, then the motor will turn the shaft to closer to 0 degress. If the pulse is longer than 1.5ms, the shaft turns closer to 180 degress.

This is one of the best application of servo mechanism. This motor is highly usable in areas of robotics where you are making a humaniod robot where u need things to at a particular position.