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