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

Fire-control system designs developed during World War II used synchros extensively, to transmit angular information from guns and sights to an analog fire control computer, and to transmit the desired gun position back to the gun location. Early systems just moved indicator dials, but with the advent of the amplidyne, as well as motor-driven high-powered hydraulic servos, the fire control system could directly control the positions of heavy guns. [2]

Smaller synchros are still used to remotely drive indicator gauges and as rotary position sensors for aircraft control surfaces, where the reliability of these rugged devices is needed. Digital devices such as the rotary encoder have replaced synchros in most other applications.

Synchros designed for terrestrial use tend to be driven at 50 – 60 hertz , while those for marine or aeronautical use tend to operate at 400 hertz

RELATION TO STEPPER MOTOR

A Selsyn is an indicating device which shows the direction in which an object is oriented.it consists of a transmitting and a receiving unit. The stepper motor which is the shaft of  receiving unit rotates along with shaft of the transmitting unit.It finds application in the  direction indicator of a wind vane.  when the wind vane rotates both the indicator and transmitting unit shafts cover equal degrees.

A synchro is a selsyn used for control of mechanical devices .They can be used as remote controllers as they are programmable.

The encoding used to store the common prefix length itself varies from application to application. Typical techniques are storing the value as a single byte; delta encoding, which store only the change in the common prefix length; and various universal codes. It may be combined with other general lossless data compression techniques such as entropy encoding and dictionary coders to compress the remaining suffixes.

Applications

Incremental encoding is widely used in information retrieval to compress the lexicons used in search indexes; these list all the words found in all the documents and a pointer for each one to a list of locations. Typically, it compresses these indexes by about 40%.

As one example, incremental encoding is used as a starting point by the GNU locate utility, in an index of filenames and directories. The GNU locate utility further uses bigram encoding to further shorten popular filepath prefixes.

In general, a rational transfer function for a discrete LTI system has the form:
X(Z)=P(Z)/Q(Z)

where
zi such that P(zi) = 0 are the zeros of the system
zj such that Q(zj) = 0 are the poles of the system

In the plot, the poles of the system are indicated by an ‘X’ while the zeroes are indicated by an ‘o’.

Example

If P(z) and Q(z) are completely factored, their solution can be easily plotted in the Z-Plane. For example, given the following transfer function:

X(z)=(z+2)/(z^2+.25)

The only zero is located at: − 2 The two poles are located at  -i/2,+i/2.

Interpretation

The region of convergence (ROC) for a given transfer function is a disk or annulus which contains no poles.
If the disc includes the unit circle, then the system is BIBO stable.
If the region of convergence extends outward from the largest pole (not at infinity), then the system is right-sided.
If the region of convergence extends inward from the smallest nonzero pole, then the system is left-sided.

It should be noted that the choice of ROC is not unique, however the ROC is usually chosen to include the unit circle since it is important for most practical systems to have Bounded Input, Bounded Output (BIBO) stability.

G(s) =1/(s + p1)(s + p2)      p1 > 0,    p2 > 0

The poles are given by s = –p1 and s = –p2 . When we add a zero at s = –z1 to the controller, the open-loop transfer function will change to:

G1(s) =k(s+z1)/(s+p1)(s+p2)      z1>0

We can put the zero at three different positions with respect to the poles:

1. right of s = –p1

2. Between s = –p2 and s = –p1

3. left of s = –p2

(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. The system can have only real poles and hence we can only find a value for K to make the system overdamped.  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. Faster responses are possible due to the dominant pole  lying further from the jw axis than the dominant pole in (b).

(d) The zero s = –z1 is located to the left of s = –p2. .We can now change the damping ratio and the natural frequency . The closed-loop pole locations can lie further to the left than s = –p2, which will provide faster time responses. It gives a more flexible configuration for control design.

 This robot is a more classically designed  industrial  robot.   Designed as a healthy  compromise between dexterity and strength this robot was one of the ground breakers, in terms of success, in factory environments.  However, while this robot was a success in industry its inflexible interfacing system makes it difficult to use in research. 

This robot is used most heavily by students taking Dr. Delbert Tesar’s “Robotics and Automation” course (ME 372J) from the Mechanical Engineering Department of the University of Texas at Austin.

Robot Cincinnati Milacron T3 726

Load capacity: 14 lbs

Axes: 6

 Drive system: DC Motor

 Horizontal reach: 41 inches

 Power requirement: 460 VAC 3 PH    

 Hours on meter: 7900

 This unit was working as a welding robot and developed trip out problem. All cables are with the unit.

 Price: $ 1,000.0

The word robot originated from the Czech word robota, meaning work. Webster’s dictionary defines robot as “an automatic device that performs functions ordinarily ascribed to human beings.” A definition used by the Robot Institute of America gives a more precise description of industrial robots: “A robot is a reprogrammable multi-functional manipulator designed to move materials, parts, tools, or special-variety of tasks.” In short, a robot is a programmable general-purpose manipulator with external sensors that can perform various assembly tasks. With this defination, a robot must possess intelligence, which is normally due to computer algorithms associated with its control and sening systems. (Robotics: Control, Sensing, Vision, and Intelligence page1)

Robots are the general-purpose, computer-controlled manipulator consisting of several rigid links connected by joints into an open kinematic chain. Joints are typically rotary (revolute) or linear (prismatic). A revolute joint is like a hinge and allows relative rotation between two links. A prismatic joint allows a linear relative motion between two links. The convention (R) is used to represent revolute joint and convention (P) is used to denote prismatic joints. The joints are shown in the figure. Each joint represents the interconnection between two links, l_i l_i+1. Similarly, the axis of rotation of a revolute joint, or the axis along which a prismatic joint slides is represented by z_i if the joint is the interconnection of links i and i+1. The joint variables, denoted by (theta)_i for a revolute and ‘d’ for a prismatic joint, represent the relative displacement between adjacent links.The number of joints of a manipulator determnes the degrees-of-freedom (DEO) of the manipulator. Typically manipulator should possess at least six DOF: three for positioning and three for orientation. A manipulator having more than six links is referred to as a kinematically redundant manipulator.

The workspace of a manipulator is the total volume swept out by the end-effector as the manipulator executes all possible. There are two types of workspace: a reachable workspace and a dextrous workspace.

Wrist and End-Effectors:

 Cincinnati Milacron T³ robot arm. (b) PUMA 560 series robot arm

Mechanically, a robot is composed of an arm (or mainframe) and a wrist subassembly plus a tool. It is designed to reach a workpiece located within its work volume. The work volume is the sphere of influence of a robot whose arm can deliver the wrist subassembly unit to any point within the sphere. The arm subassembly generally can move with three degrees of freedom. The combination of the movements positions the wrist unit at the workpiece. The wrist subassembly unit usually consists of three rotary motions. The combination of these motions orients the tool according to the configuration of the object for ease in pickup. These last three motions are often called pitch, yaw, and roll; as shown in the figure. Hence, for a six-jointed robot, the arm subassembly is the position mechanism, while the wrist subassembly is the orientation mechanism. These concepts are illustrated by the Cincinnati Milacron T robot and the Unimation PUMA robot arm as shown in the figure.

 Conclusion:

Robots are expensive insturment and complicated design. It is very important for every individual to take maximum efficiency out of each robot. Singularity is one of the major porblems in the movement of robot manipulators. Once robot reach singularity configuration, it stops its movement and the system should be started again. This will result in waste of time and energy, and expence as well. So, determination of singularity configuration in robot movement and its avoidance is of importance in robotic industry. If we encounter singularity configuration then immediately we can choose the alternative path for robot movement.This project also gives a basis to the fact that any robot can be controlled by the users from any part of the world through the means of today’s growing technology of Internet and World-Wide-Web, with the condition that both user and robot are connected with server / system.

This project also provieds basis to rapidly growing and popular distance-learning program in the field of Robotics thrgouth the Internet.

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.

Servomechanism may or may not use a servomotor. For example a household furnace controlled by thermostat is a servomechanism, yet there is no motor being controlled directly by the servomechanism.

A common type of servo provides position control. Servos are commonly electrical or partially electronic in nature, using an electric motor as the primary means of creating mechanical force. Other types of servos use hydraulics, pneumatics, or magnetic principles. Usually, servos operate on the principle of negative feedback, where the control input is compared to the actual position of the mechanical system as measured by some sort of transducer at the output. Any difference between the actual and wanted values (an “error signal”) is amplified and used to drive the system in the direction necessary to reduce or eliminate the error. An entire science known as control theory has been developed on this type of system.

Servomechanisms were first used in military fire-control and marine navigation equipment. Today servomechanisms are used in automatic machine tools, satellite-tracking antennas, remote control airplanes, automatic navigation systems on boats and planes, and antiaircraft-gun control systems. Other examples are fly-by-wire systems in aircraft  which use servos to actuate the aircraft’s control surfaces, and radio-controlled models which use RC servos for the same purpose. Many autofocus cameras also use a servomechanism to accurately move the lens, and thus adjust the focus. A modern hard disk drivehas a magnetic servo system with sub-micrometre positioning accuracy.

Typical servos give a rotary (angular) output. Linear types are common as well, using a screw thread or a linear motor to give linear motion.

Another device commonly referred to as a servo is used in automobiles to amplify the steering or braking force applied by the driver. However, these devices are not true servos, but rather mechanical amplifiers.

In industrial machines, servos are used to perform complex motion.

History

James Watt ‘s steam engine governor is generally considered the first powered feedback system. The windmill fantail is an earlier example of automatic control, but since it does not have an amplifier or gain, it is not usually considered a servomechanism.

The first feedback position control device was the ship steering engine, used to position the rudder of large ships based on the position of ship’s wheel. This technology was first used on the SS Great Eastern in 1866. Steam steering engines had the characteristics of a modern servomechanism: an input, an output, an error signal, and a means for amplifying the error signal used for negative feedback to drive the error towards zero.

Electrical servomechanisms require a power amplifier. World War II saw the development of electrical fire-control servomechanisms, using an amplidyne as the power amplifier. Vacuum tube amplifiers were used in the UNISERVO tape drive for the UNIVAC I computer.

Modern servomechanisms use solid state power amplifiers, usually built from MOSFET or thyristor devices. Small servos may use power transistors

The origin of the word is believed to come from the French “Le Servomoteur” or the slavemotor, first used by J. J. L. Farcot in 1868 to describe hydraulic and steam engines for use in ship steering.

^APPLICATIONS

1 . RC servos                                                                                        

 

Small R/C servo mechanism
1. electric motor
2. position feedback potentiometer
3. reduction gear
4. actuator arm

RC servos are hobbyist remote control devices servos typically employed in radio-controlled models, where they are used to provide actuation for various mechanical systems such as the steering of a car, the flaps on a plane, or the rudder of a boat.

RC servos are composed of an electric motor mechanically linked to a potentiometer. Pulse-width modulation (PWM) signals sent to the servo are translated into position commands by electronics inside the servo. When the servo is commanded to rotate, the motor is powered until the potentiometer reaches the value corresponding to the commanded position.

Due to their affordability, reliability, and simplicity of control by microprocessors, RC servos are often used in small-scale robotics applications.

2. Stepper motor 

Computer-controlled stepper motors are one of the most versatile forms of positioning systems. They are typically digitally controlled as part of an open loop system, and are simpler and more rugged than closed loop servo systems.

Industrial applications are in high speed pick and place equipment and multi-axis machine.  In the field of lasers and optics they are frequently used in precision positioning equipment such as linear actuators, linear stages, rotation stages, goniometers, and mirror mounts. Other uses are in packaging machinery, and positioning of valve pilot stages for fluid control systems.

Commercially, stepper motors are used in floppy disk drives, flatbed scanners , computer printers, plotters and many more devices.