Report....555ic and Stepper Motor

8/3/2019 Report....555ic and Stepper Motor

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Polytechnic University of the Philippines

College of Engineering

Electronics and Communications Engineering3rd Floor CEA Bldg., NDC Compound, Sta. Mesa, Manila

555 TIMER IC AND STEPPER MOTOR

Submitted by:

Cruz, Krizelle Anne

Facunla, Cynthia

Galicia, John Carlin

Loyola, Kareen Kay

Lubi, Kelvin Dennis

Mamonong, Ma. Carmella

Naga, Mark Bennil

Osial, AntonioRamos, Roentgen

Saddi, Jerome

Victoria, Angela

Submitted to:

Engr. Ben Andres


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555 IC TIMER

IntroductionThe 8-pin 555 timer must be one of the mostuseful ICs ever made and it is used in manyprojects. With just a few external components itcan be used to build many circuits, not all ofthem involve timing!

A popular version is the NE555 and this issuitable in most cases where a '555 timer' isspecified. The 556 is a dual version of the 555housed in a 14-pin package, the two timers (Aand B) share the same power supply pins. Thecircuit diagrams on this page show a 555, butthey could all be adapted to use one half of a556.

Low power versions of the 555 are made, suchas the ICM7555, but these should only be usedwhen specified (to increase battery life) becausetheir maximum output current of about 20mA(with a 9V supply) is too low for many standard555 circuits. The ICM7555 has the same pinarrangement as a standard 555.

The circuit symbol for a 555 (and 556) is a box with the pins arranged to suit the circuitdiagram: for example 555 pin 8 at the top for the +Vs supply, 555 pin 3 outputs on theright. Usually just the pin numbers are used and they are not labeled with their function.

The 555 and 556 can be used with a supply voltage (Vs) in the range 4.5 to 15V (18Vabsolute maximum).

Standard 555 and 556 ICs create a significant 'glitch' on the supply when their outputchanges state. This is rarely a problem in simple circuits with no other ICs, but in morecomplex circuits a smoothing capacitor (eg.100F) should be connected across the +Vsand 0V supply near the 555 or 556.

Example circuit symbol (above)

Actual pin arrangements (below)


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The 555 is an integrated circuit (chip) implementing a variety of timer and multivibratorapplications.

Description

NE555 fromSignetics in dual-in-line package

History

The IC was designed and invented by Hans R. Camenzind. It was designed in1970 andintroduced in 1971 by Signetics (later acquired by Philips). The original name was theSE555/NE555 and was called "The IC Time Machine". It is still in wide use, thanks to itsease of use, low price and good stability. Even today, Samsung in Korea manufacturesover 1 billion units per year (2003). The 555 timer is one of the most popular andversatile integrated circuits ever produced. It includes 23 transistors, 2 diodes and 16resistors on a silicon chip installed in an 8-pin mini dual-in-line package (DIP).

The 555 has three operating modes:

Monostable mode: in this mode, the 555 functions as a "one-shot". Applicationsinclude timers, missing pulse detection, bounce free switches, touch switches,etc.

Astable mode: the 555 can operate as an oscillator. Uses include LED and lampflashers, pulse generation, logic clocks, tone generation, security alarms, PulseWidth Modulation (PWM) etc.

Bistable mode: the 555 can operate as a flip-flop, if the DIS pin is not connectedand no capacitor is used. Uses include bounce free latched switches, etc.
http://peswiki.com/index.php?title=Multivibrator&action=edithttp://peswiki.com/index.php?title=Signetics&action=edithttp://peswiki.com/index.php?title=Signetics&action=edithttp://peswiki.com/index.php?title=Hans_R._Camenzind&action=edithttp://peswiki.com/index.php?title=1970&action=edithttp://peswiki.com/index.php?title=1970&action=edithttp://peswiki.com/index.php?title=1971&action=edithttp://peswiki.com/index.php?title=Signetics&action=edithttp://peswiki.com/index.php?title=Philips&action=edithttp://peswiki.com/index.php?title=Samsung&action=edithttp://peswiki.com/index.php?title=Korea&action=edithttp://peswiki.com/index.php?title=1000000000_(number)&action=edithttp://peswiki.com/index.php?title=As_of_2003&action=edithttp://peswiki.com/index.php?title=Transistor&action=edithttp://peswiki.com/index.php?title=Transistor&action=edithttp://peswiki.com/index.php?title=Diode&action=edithttp://peswiki.com/index.php?title=Resistor&action=edithttp://peswiki.com/index.php?title=Dual_in-line_package&action=edithttp://peswiki.com/index.php?title=Monostable&action=edithttp://peswiki.com/index.php?title=Astable&action=edithttp://peswiki.com/index.php?title=Oscillator&action=edithttp://peswiki.com/index.php?title=Oscillator&action=edithttp://peswiki.com/index.php?title=LED&action=edithttp://peswiki.com/index.php?title=Pulse-width_modulation&action=edithttp://peswiki.com/index.php?title=Pulse-width_modulation&action=edithttp://peswiki.com/index.php?title=Bistable&action=edithttp://peswiki.com/index.php?title=Flip-flop_(electronics)&action=edithttp://peswiki.com/index.php/Image:779px-Signetics_NE555N.JPGhttp://peswiki.com/index.php?title=Signetics&action=edithttp://peswiki.com/index.php?title=Hans_R._Camenzind&action=edithttp://peswiki.com/index.php?title=1970&action=edithttp://peswiki.com/index.php?title=1971&action=edithttp://peswiki.com/index.php?title=Signetics&action=edithttp://peswiki.com/index.php?title=Philips&action=edithttp://peswiki.com/index.php?title=Samsung&action=edithttp://peswiki.com/index.php?title=Korea&action=edithttp://peswiki.com/index.php?title=1000000000_(number)&action=edithttp://peswiki.com/index.php?title=As_of_2003&action=edithttp://peswiki.com/index.php?title=Transistor&action=edithttp://peswiki.com/index.php?title=Diode&action=edithttp://peswiki.com/index.php?title=Resistor&action=edithttp://peswiki.com/index.php?title=Dual_in-line_package&action=edithttp://peswiki.com/index.php?title=Monostable&action=edithttp://peswiki.com/index.php?title=Astable&action=edithttp://peswiki.com/index.php?title=Oscillator&action=edithttp://peswiki.com/index.php?title=LED&action=edithttp://peswiki.com/index.php?title=Pulse-width_modulation&action=edithttp://peswiki.com/index.php?title=Pulse-width_modulation&action=edithttp://peswiki.com/index.php?title=Bistable&action=edithttp://peswiki.com/index.php?title=Flip-flop_(electronics)&action=edithttp://peswiki.com/index.php?title=Multivibrator&action=edit


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Specifications

Schematic symbol of the 555 timer

Pins of the 555 timer are as follows: Gnd. Ground connection for chip

Trigger 555 timer triggers when this pin transitions from voltage at Vcc to 33%voltage at Vcc.

Output. Output pin of 555 timer

Reset Resets 555 timer when low

Vcc 5V to 15 V supply input

Discharge Used to discharge a capacitor Threshold Used to detect when the capacitor has charged. The Output pin goes

low when capacitor has charged to 66.6% of Vcc.

Control Voltage Used to change Threshold and Trigger set point voltages and israrely used

These specifications apply to the NE555. Other 555 timers can have betterspecifications depending on the grade (military, medical, etc).

Supply voltage (VCC) 4.5 to 15 V

Supply current (VCC = +5 V) 3 to 6 mA

Supply current (VCC = +15 V) 12 to 15 mA

Output current (maximum) 200 mA

Power dissipation 600 mW

Operating temperature 0 to 70 C


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Applications

The 555 timer integrated circuit is one of the most popular and useful integrated circuitsof all time. It has been used in hundreds or thousands of applications, for example to:

Mark space adjustment.

Pulse width modulation.


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Inductive current detection.


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Generate a single pulse

Debounce a switch i.e. create a clean pulse when a noisy switch ispressed

Generate a time delay Measure time elapsed between events

Measure time duration of events

Measure frequency of a pulse train

Generate a pulse train of specified duty cycle and frequency

Create a variable-frequency train of pulses

Create a fixed-frequency train of pulses having varying width (called pulsewidth modulation)

Create a fixed-frequency train of pulses having varying position (called pulseposition modulation)

Create a pulse train of half the frequency of the incoming pulse train(frequency division)

Generate a voltage which rises linearly (a linear ramp)

Generate a sawtooth voltage (repetitive linear ramps)

Detect a condition (e.g. light on or off, switch open or closed, etc.) and soundan alarm

Generate interesting sounds (sirens, two-tone alternation, dial tone, busysignal, etc.)

The timing intervals available in such applications can be as short as microseconds oras long as months.


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Modes of Operations

All of the timing calculations for circuits using the 555 timer are based on the responseof a series R-C circuit with a step or constant voltage input, and exponential outputtaken across the capacitor. You should understand that standard response very well in

order to understand how to use the timer.

The two basic modes of operation of the timer are (1) monostable operation, in whichthe timer wakes up and generates a single pulse, then goes back to sleep, and (2)astable operation, in which the timer is trapped in an endless cycle generate a pulse,sleep, generate a pulse, sleep, on and on forever. The control voltage, usually but notalways 2/3 of the power supply voltage, determines the limits of a capacitor voltage inthe operations described below.

The monostable (one-pulse) operation can be understood as consisting of these eventsin sequence:

0. (up to t = 0) A closed switch keeps the C uncharged: Vc = 0, Vout is low.

1. (at t = 0) A triggering event occurs: V triggerdrops below Vcontrol/2, very briefly.This causes the switch to open.

2. (0 < t < t1) Vc(t) rises exponentially toward Vcc with time constant RC. Vout ishigh.

3. (at t = t1) Vc reaches Vcontrol. This causes the switch to close, which instantlydischarges the C.

4. (from t = t1 on) A closed switch keeps the C uncharged: Vc = 0, Vout is low.


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Monostable operation showing current flows, pin numbers, charging, and output.


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555/556 Monostable

A monostable circuit produces a singleoutput pulse when triggered. It is called amonostable because it is stable in just

one state: 'output low'. The 'output high'state is temporary.

The duration of the pulse is called thetime period (T) and this is determined byresistor R1 and capacitor C1:

time period, T = 1.1 R1 C1

T = time period in seconds (s)

R1 = resistance in ohms ( )C1 = capacitance in farads (F)The maximum reliable time period is about 10 minutes.

555 monostable output, a single pulse

555 monostable circuit with manual trigger


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The astable (pulse train) operation can be understood as consisting of these events,starting at a point where Vc = Vcontrol/2:

1. (at t = 0) Vc = Vcontrol/2, and the switch opens.

2. (0 < t < t1) Vc(t) rises exponentially toward Vcc with time constant (R1+R2)C. Voutis high.

3. (at t = t1) Vc reaches Vcontrol. This causes the switch to close.

4. (t1 < t < t1 + t2) Vc(t) falls exponentially toward zero with time constant R2C. Voutis low.

5. (at t = t1 + t2 = T) Vc reaches Vcontrol/2. This causes the switch to open. Theseconditions are the same as at step 1, so the cycle repeats every T seconds. (Goto step 2.)


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Astable operation, showing currents, pin numbers, charge/discharge cycle, and output

Notice that in both modes, the output is high only when the C is charging.

Other details:

There is a reset pin (#4); whenever the voltage on that pin is below 0.7volts, the output is forced low. This pin is usually connected to Vcc toprevent accidental resets.

The negative trigger pulse used in the monostable mode (step #1) mustrise back to a voltage higher than Vcontrol/2 before the monostable pulseends, oranotherpulse will be generated.

Usually, Vcontrol is obtained internally from a voltage divider in the 555 and

is constant at (2/3)Vcc. In this case a capacitor is connected between pin 5and ground, to keep Vcontrol at that voltage. The Vc(t) in this case rangesbetween the limits of (1/3)Vcc and (2/3)Vcc.

The Vcc and Ground pins are often connected by a 0.01uF capacitor (adespiking capacitor) to avoid problems from imperfect power suppliesand circuit wiring.

The Vcontrol can be usefully varied from about 2 volts to about 1 volt lessthan Vcc, but not much outside of that range.

The discharge of the C in monostable mode is not truly instantaneous butrequires a few microseconds. Because of this and other factors, the 555cannot reliably generate pulses shorter than about 10 microseconds, and

cannot generate a pulse train with a frequency higher than about 100 KHz. The resistors R1 and R2 in the circuits shown must be greater than 1K and

smaller than 3.3Megohm.

The capacitor C in the circuits shown must be greater than 0.001 uF, or 1nF.


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The input and output pin functions aredescribed briefly below and there are fullerexplanations covering the various circuits:

Astable - producing a square wave

555/556 Astable An astable circuit produces a 'square

wave', this is a digital waveform withsharp transitions between low (0V) andhigh (+Vs). Note that the durations ofthe low and high states may bedifferent. The circuit is called an astablebecause it is not stable in any state: theoutput is continually changing between'low' and 'high'.

The time period (T) of the square wave

is the time for one complete cycle, but itis usually better to considerfrequency (f) which is the number of cycles persecond.

T = 0.7 (R1 + 2R2) C1 and f =1.4

(R1 + 2R2) C1

T = time period in seconds (s)f = frequency in hertz (Hz)R1 = resistance in ohms ( )R2 = resistance in ohms ( )C1 = capacitance in farads (F)

The time period can be split into two parts: T = Tm + TsMark time (output high): Tm = 0.7 (R1 + R2) C1Space time (output low): Ts = 0.7 R2 C1

Many circuits require Tm and Ts to be almost equal; this is achieved if R2 ismuch larger than R1.

555 astable output, a square wave(Tm and Ts may be different)

555 astable circuit
http://www.kpsec.freeuk.com/acdc.htm#propshttp://www.kpsec.freeuk.com/acdc.htm#propshttp://www.kpsec.freeuk.com/acdc.htm#propshttp://www.kpsec.freeuk.com/acdc.htm#props


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Bistable - a simple memory whichcan be set and reset

555/556 Bistable (flip-flop) - amemory circuit

The circuit is called a bistable because it isstable in two states: output high andoutput low. It is also known as a 'flip-flop'.

It has two inputs:

Trigger (555 pin 2) makes the output high.Trigger is 'active low', it functions when < 1/3 Vs.

Reset (555 pin 4) makes the output low.Reset is 'active low', it resets when < 0.7V.

The power-on reset, power-on trigger and edge-triggering circuits can all be usedas described above for the monostable.

Buffer- an inverting buffer (Schmitt trigger)

555/556 Inverting Buffer (Schmitt trigger) or NOT gate

555 bistable circuit
http://www.kpsec.freeuk.com/555timer.htm#bistablehttp://www.kpsec.freeuk.com/555timer.htm#monostablehttp://www.kpsec.freeuk.com/555timer.htm#bufferhttp://www.kpsec.freeuk.com/555timer.htm#bistablehttp://www.kpsec.freeuk.com/555timer.htm#monostablehttp://www.kpsec.freeuk.com/555timer.htm#buffer


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The buffer circuit's input has a very high impedance(about 1M ) so it requires only a few A, but theoutput can sink or source up to 200mA. Thisenables a high impedance signal source (such as anLDR) to switch a low impedance output transducer

(such as a lamp).

It is an inverting buffer orNOT gate because theoutput logic state (low/high) is the inverse of theinput state:

Input low (< 1/3 Vs) makes output high, +Vs Input high (> 2/3 Vs) makes output low, 0V

When the input voltage is between 1/3 and2/3 Vs the output remains in its present state.

This intermediate input region is a dead space where there is no response, a property

called hysteresis, it is like backlash in a mechanical linkage. This type of circuit is calleda Schmitt trigger.

If high sensitivity is required the hysteresis is a problem, but in many circuits it is ahelpful property. It gives the input a high immunity to noise because once the circuitoutput has switched high or low the input must change back by at least 1/3 Vs to makethe output switch back.

Stepper Motor

Introduction

555 inverting buffer circuit(a NOT gate)

NOT gate symbol
http://www.kpsec.freeuk.com/gates.htm#nothttp://www.kpsec.freeuk.com/gates.htm#not


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A stepper motor is a digital version of the electric motor. The rotor moves in discrete

steps as commanded, rather than rotating continuously like a conventional motor. When

stopped but energized, a stepper (short for stepper motor) holds its load steady with a

holding torque. Wide spread acceptance of the stepper motorwithin the last two

decades was driven by the ascendancy of digital electronics. Modern solid state driver

electronics was a key to its success. And, microprocessors readily interface to stepper

motordriver circuits.

Application wise, the predecessor of the stepper motorwas the servo motor. Today this

is a higher cost solution to high performance motion control applications. The expense

and complexity of a servomotor is due to the additional system components: position

sensor and error amplifier. It is still the way to position heavy loads beyond the grasp of

lower power steppers. High acceleration or unusually high accuracy still requires a

servo motor. Otherwise, the default is the stepper due to low cost, simple drive

electronics, good accuracy, good torque, moderate speed, and low cost.

Stepper motor vs. servo motor.

A stepper motorpositions the read-write heads in a floppy drive. They were once used

for the same purpose in hard drives. However, the high speed and accuracy required of

modern hard drive head positioning dictates the use of a linear servomotor (voice coil).

The servo amplifier is a linear amplifier with some difficult to integrate discrete

components. A considerable design effort is required to optimize the servo amplifier

gain vs. phase response to the mechanical components. The stepper motordrivers are

less complex solid state switches, being either on or off. Thus, a stepper motor

controller is less complex and costly than a servo motorcontroller.

Slo-syn synchronous motors can run from AC line voltage like a single-phase

permanent-capacitor induction motor. The capacitor generates a 90o second phase.

With the direct line voltage, we have a 2-phase drive. Drive waveforms ofbipolar()

square waves of 2-24V are more common these days. The bipolar magnetic fields may

also be generated from unipolar (one polarity) voltages applied to alternate ends of a


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center tapped winding. In other words, DC can be switched to the motorso that it sees

AC. As the windings are energized in sequence, the rotor synchronizes with the

consequent stator magnetic field. Thus, we treat steppermotors as a class of AC

synchronous motor.

Unipolar drive of center tapped coil at (b), emulates AC current in single coil at (a).

Characteristics

Steppermotors are rugged and inexpensive because the rotor contains no winding slip

rings, or commutator. The rotor is a cylindrical solid, which may also have either salient

poles or fine teeth. More often than not the rotor is a permanent magnet. Determine that

the rotor is a permanent magnet by unpowered hand rotation showing detent torque,

torque pulsations. Stepper motorcoils are wound within a laminated stator, except for

can stackconstruction. There may be as few as two winding phases or as many as five.

These phases are frequently split into pairs. Thus, a 4-pole stepper motormay have two

phases composed of in-line pairs of poles spaced 90o apart. There may also be multiple

pole pairs per phase. For example a 12-pole stepperhas 6-pairs of poles, three pairs

per phase.

Since steppermotors do not necessarily rotate continuously, there is no horsepower

rating. If they do rotate continuously, they do not even approach a sub-fractional hp

rated capability. They are truly small low power devices compared to other motors. They

have torque ratings to a thousand in-oz (inch-ounces) or ten n-m (newton-meters) for a

4 kg size unit. A small dime size stepperhas a torque of a hundredth of a newton-

meter or a few inch-ounces. Most steppers are a few inches in diameter with a fraction

of a n-m or a few in-oz torque. The torque available is a function ofmotorspeed, load

inertia, load torque, and drive electronics as illustrated on the speed vs torque curve. An

energized, holding stepperhas a relatively high holding torque rating. There is less

torque available for a running motor, decreasing to zero at some high speed. This

speed is frequently not attainable due to mechanical resonance of the motorload

combination.


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Stepperspeedcharacteristics.

Steppermotors move one step at a time, the step angle, when the drive waveforms are

changed. The step angle is related to motorconstruction details: number of coils,

number of poles, and number of teeth. It can be from 90o to 0.75o, corresponding to 4 to

500 steps per revolution. Drive electronics may halve the step angle by moving the rotor

in half-steps.

Steppers cannot achieve the speeds on the speed torque curve instantaneously. The

maximum start frequency is the highest rate at which a stopped and unloaded stepper

can be started. Any load will make this parameter unattainable. In practice, the step rate

is ramped up during starting from well below the maximum start frequency. When

stopping a stepper motor, the step rate may be decreased before stopping.

The maximum torque at which a steppercan start and stop is the pull-in torque. Thistorque load on the stepperis due to frictional (brake) and inertial (flywheel) loads on the

motorshaft. Once the motoris up to speed, pull-out torque is the maximum sustainable

torque without losing steps.

There are three types ofsteppermotors in order of increasing complexity: variable

reluctance, permanent magnet, and hybrid. The variable reluctance stepperhas s solid

soft steel rotor with salient poles. The permanent magnet stepperhas a cylindrical

permanent magnet rotor. The hybrid stepperhas soft steel teeth added to the

permanent magnet rotor for a smaller step angle.

Stepper Motor Glossary


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Absolute Positioning Refers to a motion control system employing positionfeedback devices (absolute encoders) to maintain a given mechanical location.

Absolute Programming A positioning coordinate reference wherein all positionsare specified relative to some reference, or home, position. This is differentfrom incremental programming, where distances are specified relative to thecurrent position.

Acceleration Acceleration is the time rate of change of velocity with respect to afixed reference frame. Angular acceleration is the time rate of change of angulardisplacement with respect to a fixed rotational reference axis. The commandedstep rate is started at a base velocity and accelerated to the slew velocity at a

defined and controlled rate or rate of changes.

Acceleration (Linear) Linear acceleration is the most commonly utilized form ofaccelerating the commanded pulse rate, and is expressed mathematically as:

a = dv/dt (constant)

For rotating bodies, the angular acceleration is the ratio of torque to inertia, andis expressed mathematically as:

a = dw/dt = Torque/Jsystem (constant)

Acceleration (Nonlinear) Nonlinear acceleration is a constantly changingacceleration of the commanded step rate and can be customized to reflect an S-Curve acceleration or any other required shape to provide control of the steppermotor system. The Optimal Nonlinear acceleration technique utilized in somecontroller designs, allow for the high acceleration rates at low commanded pulserates where stepper motors exhibit high torque capabilities, and a reduced

acceleration rate as the slew speed commanded pulse rate is achieved. Optimalnonlinear ramping techniques allow for greater torque utilization and a fasterpoint-to-point positioning than for linear acceleration techniques.


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Accuracy A measure of the difference between expected position and actualposition of a motor or mechanical system. Stepper motor accuracy is usuallyspecified an angle representing the maximum deviation from expected position.

Ambient Temperature The temperature of the cooling medium, usually air,immediately surrounding the motor or another device.

ASCII (American Standard Code for Information Interchange) This code assignsa number to each numeral and letter of the alphabet. In this manner,alphanumeric information can be transmitted between machines as a series ofbinary numbers.

Automation The implementation of processes by automatic means. The theory,art, or technique of making a process more automatic. The investigation, design,development and application of methods of rendering processes automatic, self-moving or self-controlling.

Axial Play (End Play) The shaft displacement axially, due to a reversal of anaxial force.

Back (End of Motor) This is considered the output end, the end which drives theload.

Bandwidth The frequency range in which the magnitude of the system gainexpressed in dB is greater than -3dB.

Baud A unit of signaling speed equal to the number of code elements persecond.

BCD (Binary Coded Decimal) An encoding technique used to describe thenumbers 0 through 9 with four digital (on or off) signal lines. Popular in machine


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tool equipment, BCD interfaces are now giving way to interfaces requiring fewerwires, such as RS232C.

Back EMF (Back Electro-Motive Force) A reversed bias generated by rotation ofthe magnetic field (rotor of a hybrid motor), across a stators windings.

Base Speed Response range of a motor to commanded pulses over which theunloaded motor can accelerate to command pulse rate from standstill, deceleratefrom command pulse rate to standstill, and reverse direction (on command)without loss of synchronism.

Bifilar Winding Refers to the winding configuration of a stepper motor whereeach stator pole has a pair of windings, (4 electrical phases), the motor will haveeither 4, 6 or 8 lead wires depending on termination. This winding configurationcan be driven from a unipolar or bipolar driver design.

Bipolar Drive Refers to specific type driver that is connected to a stepper motorconfigured for a 2 phase operation. The 4 electrical cycles required for operationare generated when the direction of current is reversed in each motor phase. A

bipolar driver can be utilized with a 4, 6 or 8 lead motor.

Bit An abbreviation of binary digit. A single character in a binary number. Asingle pulse in a group of pulses. A unit of information capacity of a storagedevice.

Block Diagram A simplified schematic representing components and signal flowthrough a system.

Bode Plot A graph of system gain and phase versus input frequency, whichgraphically illustrates the steady state characteristics of the system.


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Break Frequency Frequency(ies) at which the gain changes slope on a BodePlot. Break Frequencies correspond to the poles and zeros of the system.

BufferA storage device used to compensate for a difference in rate of flow ofdata, or time of occurrence of events, when transmitting data from one device toanother.

Bus A circuit over which data or power is transmitted. Often one which acts as acommon connection among a number of locations. Synonymous with trunk. Acommunications path between two switching points.

Byte A group of eight bits treated as a whole, with 256 possible combinations ofones and zeros, each combination representing a unique piece of information.

Clock A pulse generator, which controls the timing of switching circuits thatcontrol the speed of the stepper motor.

Closed Loop System A stepper motor system can be operated in a closed loopapplication where the output is measured and compared to the input. The outputis then adjusted to reach the desired input condition. In motion control, this termis used to describe a system wherein a velocity or position sensor is used togenerate signals for comparison to desired parameters. For cases where loadsare not predictable, the closed loop feedback from an external encoder to thecontroller may be used for stall detection, position verification or positionmaintenance.

Command An electronic pulse, signal, or set of signals to start, stop, or continuesome operation.

Compliant Coupling Complying, yielding. Limited motion of one shaft withoutmotion of coupled shaft. Does not permit permanent displacement of one shaftwith respect to the other.


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Constant Current Drive Device or control for adjusting the voltage to force andmaintain design current in the winding when switching from one winding toanother.

Controller (stepper motor) A regulating mechanism, essentially a DC powersupply, plus power switching and circuits for controlling the proper stepsequence.

Counter A device capable of changing states in a specified sequence uponreceiving appropriate input signals. The output of the counter indicates the

number of pulses that have been applied.

Critical Damping A system is critically damped when the response to anincremental change in desired velocity or position is achieved in a minimumpossible time with little or no overshoot.

Crossover Frequency The frequency at which the gain intercepts the 0dB point

on a Bode plot. Used in reference to the open-loop gain plot.

Cycle (Incremental Motion) One of a sequence or series of identical events.Includes starting, moving and stopping of the mechanism.

Daisychain The term daisychain is used to describe the linking of several RS-232/422/485 devices in sequence, such that a single data stream flows through

one device and on to the next. The devices are usually distinguished by deviceaddresses which serve to indicate the desired destination for the data in thestream.

DamperA device that attaches to the stepper motor shaft to absorb energy. It isuseful in damping step oscillations and preventing resonances.


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Damping An indication of the rate of decay of a signal to its steady state value.Related to settling time. Suppression of oscillations at the end of motion or duringmotion.

Damping Ratio Ratio of actual damping to critical damping. Less than one is anunder-damped system and greater than one is an over-damped system.

Dead Range or Dead Band The Dead Band window is the range of input signalsfor which there is no system response.

The angle between clockwise and counterclockwise limits to which the rotor of an

energized stepper motor can stop due to internal and external friction.

Deadbeat (Response) Critically damped. Moving from one step position toanother without overshoot or oscillation.

Decibel A logarithmic measurement of gain. If G is a systems gain (ratio ofoutput to input) then 20LogG = gain in decibels (dB).

Decimal, Binary Coded A decimal notation in which each individual decimaldigit is represented by a pattern of ones and zeros; e.g. in the 8-4-2-1 codeddecimal notation the number twelve is represented as 0001 0010 for one and 2respectively; whereas, in pure or straight binary notation, 12 is represented by1100.

Detent Position This position is the static angular position in which the shaft of

an unloaded and unenergized stepper motor comes to rest.

Detent Torque Sometimes noted as Cogging Torque, is the periodic torqueripple resulting from the tendency of the magnetic rotor poles and stator poles toalign themselves to positions of minimal reluctance. The measurement is takenwith all phases de-energized.


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Digital Means to operate in the manner of a switch, meaning in one of twostates, either on or off. Could also be two distinct states or levels.

Diode A device used to permit current flow in one direction in a circuit and toinhibit current flow in the other.

Direction of Rotation The direction the shaft rotates when viewed from themounting shaft end. The standard (positive) direction is defined ascounterclockwise.

Driver (stepper motor) Often referred to as a translator. Drives a stepper motorbased on pulses from a clock source, pulse generator, or computer. Translatesthe train of pulses and applies power to the appropriate stepper motor windings.

Duty Cycle For a repetitive cycle, the ratio of on time to total cycle time.

Duty Cycle = On Time

On Time + Off Time

Dynamic Energy in motion, effective action; active, such as in dynamic torque,which indicates the torque while the stepper motor is producing motion.

Dynamic Torque The torque developed by a motor at low stepping rates.

Efficiency The ratio of power output to power input, expressed in like units;watts, for example.


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Electronic Damping A means of suppressing oscillation of the stepper motoroutput by switching the motor winding in sequence such that the motor and loadhave come to rest when the final step position has been reached.

Encoder An encoder is an electromechanical device which translatesmechanical motion into electronic signals utilized by the system controller formonitoring position or velocity, (examples: position maintenance, stall detect andhome on encoder Z channel). Sometimes called a pulse generator. It consists ofa disc, vane or reflector attached to a stepper motor shaft to provide digitalpulses to the system controller and or counters.

End Play (Axial Play) The axial shaft displacement, due to reversal of an axial

force.

Excitation Current or voltage applied to the stepper motor in order to providemotive power or to hold the rotor in a particular place.

Feedback (Loops, Systems/Transducers) In a closed-loop system, a devicethat detects the condition being controlled and relates the information back

(feedback) to the controlling device or system for comparison with the inputvalues.

Friction (Drag or Coulomb) Friction is defined as the resistance to motioncaused by surfaces rubbing together. Friction can be a constant with varyingspeed (Coulomb) or proportional to speed (Viscous). Limits top speed of steppermotor, slows down acceleration, increases positional error, but enables the motorto stop in less time with minimal oscillations.

Friction Torque In a stepper motor, the bearing friction, usually called coulombor drag friction, is a representative friction torque component. In a permanentmagnet stepper motor, a cog friction torque is also present and is caused by themagnetic drag between the permanent magnet in the rotor assembly and thestator lamination teeth. A viscous friction torque is also possible and is a functionof drag torque, proportional to changing rotor speeds.


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Friction (Viscous) A resistance to motion, proportional to velocity.

Gain The ratio of system output signal to system input signal.

Gate A circuit whose output signal is dependent on some function of its inputsignals.

Holding Torque The maximum torque that can be externally applied to the

stepper motor shaft without causing continuous rotation when one or morephases of the motor are energized.

Home A reference position in a motion control system, usuallyfrom a mechanicaldatum. Often designated as the zero point.

Hysteresis The difference in response of a system to an increasing or

decreasing input signal.

IEEE-488 A digital data communications standard popular in instrumentationelectronics. This parallel interface is also known as GPIB, or Generic PurposeInterface Bus.

Incremental Motion A motion control term that is used to describe a device thatproduces on step of motion for each step command (usually a pulse) received.Motion made up of starts, moves, and stops. Motion caused by pulses. A smallenvelope or program of steps.

Incremental Programming A coordinate system where positions or distancesare specified relative to the current position.


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Inductance (Mutual) Mutual inductance is the property that exists between twocurrent-carrying conductors or coils when magnetic lines of force from oneconductor or coil are linked with those of the other.

Inductance (Self) The self-inductance of a coil is the constant by which the timerate of change of the current in the coil must be multiplied to give the self-inducedcounter EMF.

Inertia A measure of an objects resistance to a change in velocity. The largeran objects inertia, the greater the torque required to accelerate or decelerate it.

Inertia is a function of an objects mass and shape. For the most efficientoperation, the system coupling ratio should be selected so that the reflectedinertia of the load is equal to or no greater than 10 times the rotor inertia of thestepper motor.

Inertia (Reflected) Inertia as seen by the stepper motor when driving through aspeed change, reducer or gear train.

Input-Output The equipment used to communicate with a computer. Also, thedata involved in the communication. Synonymous with (I/O).

LCD Digital instruments employ LCD (Liquid Crystal Display) readouts becausethey utilize minuscule amounts of power, thereby making them excellent forbattery-operated instruments. LCDs are best in high ambient light levels, as theydo not wash out but instead gain greater contrast in bright light.

Lead(1) A wire or terminal of the stepper motor internally connected to the motorphase windings and externally connected to the driver output(s) terminals.


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Lead(2) The axial distance a nut on a leadscrew travels during one revolution ofthe lead screw, e.g. in./rev. The inverse of pitch.

Lead Compensation Algorithm A mathematical equation implemented by acomputer to decrease the delay between the input and output of a system.

LED Light pipe LED (Light Emitting Diode) displays provide a bright, clearnumeric presentation of readings in digital instruments. They generally are bestfor indoor environments, and can be viewed from a greater distance in normallighting conditions. Most LED displays are red, but are also available in yellowand green.

Limits A properly designed stepper motor system has sensors called limits thatalert the control electronics that a physical end-of-travel is being approached andthat the motion is not allowed in a specific direction.

LinearMotion in a straight line.

Load Any external static or dynamic resistance to motion that is applied to themotor. The characteristics of the load can be defined as: Coulomb Friction,Viscous Friction, Inertial, etc.

Static Load Angle Static Load Angle is the angle through which the rotor isdisplaced from its energized stable equilibrium position by a given appliedtorque at a specified current.

Dynamic Load Angle The Dynamic Load Angle is the angle between the loaded

and unloaded position (theoretical zero) of the rotor at a given instant underotherwise identical conditions at a specified command pulse rate, mode ofwinding excitation and phase current.

Logic Ground The logic ground is the reference zero voltage to which a group


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Maximum Running Torque The maximum torque load that the motor can drivewithout missing a step. This typically occurs when the windings are sequentiallyenergized at approximately 5 pulses-per-second.

Maximum Slew Rate The maximum slew rate is the maximum velocity at whichthe unloaded stepper motor can remain synchronous with the command pulsesunder the specified drive conditions. This velocity is usually defined in the FullStep Mode of 1.8 steps or as shaft speed in revolutions per second.

Maximum Safe Operating Temperature The maximum temp-erature the

stepper motor, either continuously or intermittently rated, may safely be allowedto achieve (measured by the change of winding resistance method). They maybear little or no relation to the class on insulation needed in the construction ofthe motor, but may be dictated by considerations such as bearing lubricant, etc.

Maximum Start-Stop Rate The maximum switching rate at which an unloadedstepper motor can start and run without losing sychronism (missing steps) or stopwithout taking more steps than pulses.

Microsecond One millionth of a second.

Microstepping Microstepping refers to a control technique that proportions thecurrent in a stepper motors windings to provide additional intermediate positionsbetween poles. The advantages of microstepping is the smooth rotation with areduction of system resonances over a wide speed range and semi-highpositional resolution.

Millisecond One thousandth of a second.

Mode A particular sequence of excitation defined by the drive circuit, which,when applied to a stepper motor, will energize certain windings or phases.


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Multi-Level Drive (See Bilevel Drive)

Nanosecond One billionth of a second.

Noncumulative ErrorAn error that does not repeat or accumulate for multiplesteps or increments.

Open CollectorA term used to describe a signal output that is performed with a

transistor. An open collector output acts like a switch closure with one end of theswitch at ground potential and the other end of the switch accessible. Also calledOpen Drain.

Open Loop System An open loop stepper motor system refers to a systemwhere no external sensors are used to provide position or velocity feedbacksignals, such as encoder feedback of position. When an application is selectedthat consists of loads without discontinuity and the proper motor and drive isutilized for positional accuracy, the motor will remain in synchronism with the

command pulse rate and the expected results will occur.

Opto-Isolated A method of sending a signal from one piece of equipment toanother without the usual requirement of common ground potentials. The signalis transmitted optically with a light source (usually a Light Emitting Diode) and alight sensor (usually a photosensitive transistor). These optical componentsprovide electrical isolation.

Overshoot (Permanent) The amount (in degrees) that the shaft of a steppermotor remains beyond the commanded position.


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Overshoot (Transient) The Overshoot (transient) is the peak angular distancethe shaft of the stepper motor rotates beyond the actual final position under thespecified drive and load conditions.

Parallel Refers to a data communication format wherein many signal lines areused to communicate more than one piece of data at the same time.

Permanent Magnet stepper motorA stepper motor having permanent-magnetpoles.

Permeance Conducting power of a magnetic circuit for magnetic flux.

Phase Angle The angle at which the steady state input signal to a system leadsthe output signal.

Phase Angle Rotor-StatorThe angle of lag of the rotor to the axis of the statormagnetic field under load. The angle of lag between rotor and stator teeth underload.

Phase Margin The difference between 180 degrees and the phase angle of asystem at its crossover frequency.

Phase (stepper motor) A motor phase is a set of electrically excited statorpoles, consisting of one or more pairs of oppositely polarized poles. steppermotor manufacturers provide 4 lead motors with bifilar ratings and 6 or 8 lead

motors with unifilar ratings. (See the section on Speed/Torque Relation- shipsfor benefits on driving a motor with a unifilar or bifilar winding configuration).

Positional ErrorPosition error (sometimes designated Absolute Accuracy) isthe deviation from the theoretically correct angular position of any step position ina complete revolution. The zero position used in determining the theoretically


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correct angular position shall be the midpoint between the two extremes ofposition error. It is expressed as either percentage of the nominal full step or asan angular measure and is noncumulative. It is measured under rated motorconditions.

Pole That part of the magnetic circuit where a magnetic pole is generated eitherby a permanent magnet or by windings. A frequency at which the transferfunction of a system goes to infinity.

Power (Motor Heat Dissipation) The heat generated by a stepper motor duringstandstill operation or while responding to a command pulse rate is expressed bythe mathematical equation:

P (watts) = I2 R for single phase operation

P (watts) = (I2 R)2 for dual phase or microstep operation

Where the square of the drive output current (I) times the motor resistance(R) is the dissipated heat generated in the motor.

Power (RMS) The Root Mean Square power of a stepper motor is the effectivevalue of time varying power consumption of the stepper motor.

Pull-In Step Rate The pull-in step rate or error-free start speed is the maximumcommand pulse rate (constant) at which the energized stepper motor canaccelerate an applied load from standstill to command pulse rate, and runsynchronously without missing any steps.

Pull-In Torque The pull-in torque is the maximum positive coulomb friction

torque which an energized stepper motor will accelerate to command pulse rateand run synchronously without missing any steps.

Pull-Out Step Rate The pull-out step rate is the maximum command pulse rate(constant) at which the energized stepper motor can run in synchronism.


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Pull-Out Torque Pull-out torque is the maximum positive coulomb friction torquewhich can be applied to the rotating shaft of a stepper motor (already running atSlew Speed) at a given pulse rate without missing any steps.

Pulse Width Modulation (PWM) Refers to a technique of con-trolling theaverage current in a motor winding by varying the duty cycle of an appliedvoltage.

Resonance Since a stepper motor system is a discrete incremental positioningsystem, it is subject to the effects of resonance, where the system is operated atthis given frequency, it may begin to oscillate. Primary resonance frequencyoccurs at about one revolution per second. This oscillating will cause a loss ofeffective torque and may result in loss of synchronism. When an application isbeing considered, the design should allow for working outside the primaryresonance frequency or by utilizing half-step or microstep techniques to reduceor shift the resonance frequency. The resonance frequency may also be shiftedby changing the system friction or inertia.

Ringing Refers to the oscillation resulting in a system following a suddenchange in velocity or position state.

Settling Time Refers to the total time from the application of the last pulse signaluntil the amplitude of the oscillatory motion of the rotor has diminished to aspecified level under certain conditions.

Slew Refers to the position of a move profile where the motor is operating at aconstant velocity.

Static Torque This is the peak torque that can be applied to the shaft of anenergized motor at standstill, also called holding torque. The mode of windingexcitation and applied current shall be specified.


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Stepper motorA stepper motor is a polyphase synchronous inductor motor, therotor of which rotates in discrete angular increments when the stator windingsthereof are energized in a programmed manner either by appropriately timed DC

states or by polyphase AC states. Rotation occurs because of the magneticinteraction between the rotor poles and the poles of the sequentially energizedstator phases.

Variable Reluctance (VR) A variable reluctance stepper motor utilizes a rotorwhich has pole salients (soft iron) without magnetic bias in the de-energizedstate.

Permanent Magnetic (PM) A permanent magnet stepper motor utilizes a rotorwhich has magnetized poles.

Hybrid (HY) A hybrid stepper motor utilizes a permanent magnet to polarize softiron pole pieces.

Stiffness (Sometimes called Torque Gradient) is the derivative (slope) of thetorque-verse-angle curve. The curve is the sum of the stiffness due to holdingtorque and detent torque.

Synchronism Synchronism exists when the motors output is correctlycorresponding to the systems input signals. Load torques exceeding the motorscapabilities will cause loss of synchronism. This condition will not damage thestepper motor.

Thermal Resistance Thermal resistance is the opposition to the flow of heat inthe materials of which the motor is constructed. It is expressed as degreesCelsius per watt. All measurements are taken after steady state conditions havebeen achieved and without heatsinking in still air.


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Thermal Resistance (Winding to Frame) This is the measured difference intemperature between the winding and the specified point on the surface of themotor divided by the total electrical Power input to the motor.

Thermal Resistance (Frame to Air) This is the same as Thermal Resistance

(Winding to Frame), except that the temperature difference is the temperature ata specified point on the surface of the motor and the ambient air surrounding themotor.

Thermal Time Constant This is the time required for the winding temperature ofa motor to reach 63% of its steady state temperature rise with constant powerapplied to the motor. It is measured by allowing the motor to reach steady statetemperature and then disconnecting the electrical power input. The windingtemperature is recorded as a function of time; zero time being the time at which

the power source is disconnected. The time required to drop 37% of the steady-state temperature rise is the thermal time constant. Usually expressed inseconds, conditions will be specified.

Translator Logic Translator logic (Driver Logic) converts the signal channelpulse train-into multichannel states to be applied to the power amplifier (Driver)which energizes the motor.

Unifilar Winding The term Unifilar winding refers to the winding configuration ofa stepper motor where each stator pole has one set of windings, (4 electricalphases), the motor will have only 4 lead wires. This winding configuration canonly be driven from a bipolar driver design.

Unipolar Drive The term Unipolar refers to specific type driver that is connectedto a stepper motor configured for 4 phase operation. A unipolar driver can only

be utilized with a bifilar wound motor, 6 or 8 leads.

Winding Inductance The winding inductance of a stepper motor winding variesboth with rotor position and with excitation current. Measurements can also beeffected by the rate of change of current; thus, when a figure for inductance isgiven, the conditions under which the measurements were taken must be quoted.


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Winding Inductance, Incremental Unenergized An inductance bridge having atest frequency of 1KHz 1 volt RMS open circuit voltage is used to make thismeasurement. The inductance is measured with the rotor locked in the aligned

or unaligned position, with no DC current applied to any of the windings, theconditions will be stated.

Winding Resistance Winding resistance is the lead-to-lead (terminal-to-terminal) ohmic resistance measured with the windings at 25C.

Unipolar Drive Excitation applied such that torque generating current in each

winding occurs in one direction only. The polarity of voltage to each winding isalways the same.

Viscous Damping A damping that provides a retarding torque during motion. Atzero velocity there is no retarding torque. The higher the velocity, the higher theretarding torque.

Zero A frequency at which the transfer function of a system goes to zero.

Stepper Motors

5V Stepper Motor

ST-02:

Rated Voltage: 5 VDCRated Current: .1 amps (100 mA)Phase Resistance: 50 ohmsWeight: 135 gUnipolar 6 wire5 Degrees per stepShaft Size: 1/8 dia. X 9/16 length


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12V Stepper Motor

ST-03:Rated Voltage: 12 VDCRated Current: .16 amps (160 mA)Size: 1.70" D x 1.125" HWeight: 235 g

Unipolar 5 wire3.6 degrees per step


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Stepper Motor Control Information

Step A B A' B' Common

1 - - +

2 - - +

3 - - +

4 - - +

5 - - +


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Basic theory of Stepping Motors

Construction

Variable reluctance Permanent Magnet

Hybrid

Stepping motor resolution and step angle

Flux vectors

Operation

Phase switching sequences

Stepping motor characteristics

Static or holding torque - displacement characteristic Static load angle Friction torque Systematic angle tolerance Resonance Torque ripple Defining the start / stop frequency
http://www.sapiensman.com/step_motor/index.htm#constructionhttp://www.sapiensman.com/step_motor/index.htm#vrhttp://www.sapiensman.com/step_motor/index.htm#pmhttp://www.sapiensman.com/step_motor/index.htm#pmhttp://www.sapiensman.com/step_motor/index.htm#hbhttp://www.sapiensman.com/step_motor/index.htm#operationhttp://www.sapiensman.com/step_motor/index.htm#fluxhttp://www.sapiensman.com/step_motor/index.htm#operationhttp://www.sapiensman.com/step_motor/index.htm#switchinghttp://www.sapiensman.com/step_motor/index.htm#characterhttp://www.sapiensman.com/step_motor/index.htm#holdinghttp://www.sapiensman.com/step_motor/index.htm#load_anglehttp://www.sapiensman.com/step_motor/stepping%20motors.htm#frictionhttp://www.sapiensman.com/step_motor/stepping%20motors.htm#tolerancehttp://www.sapiensman.com/step_motor/stepping%20motors.htm#resonancehttp://www.sapiensman.com/step_motor/stepping%20motors.htm#ripplehttp://www.sapiensman.com/step_motor/stepping%20motors.htm#start_stophttp://www.sapiensman.com/step_motor/index.htm#constructionhttp://www.sapiensman.com/step_motor/index.htm#vrhttp://www.sapiensman.com/step_motor/index.htm#pmhttp://www.sapiensman.com/step_motor/index.htm#hbhttp://www.sapiensman.com/step_motor/index.htm#operationhttp://www.sapiensman.com/step_motor/index.htm#fluxhttp://www.sapiensman.com/step_motor/index.htm#operationhttp://www.sapiensman.com/step_motor/index.htm#switchinghttp://www.sapiensman.com/step_motor/index.htm#characterhttp://www.sapiensman.com/step_motor/index.htm#holdinghttp://www.sapiensman.com/step_motor/index.htm#load_anglehttp://www.sapiensman.com/step_motor/stepping%20motors.htm#frictionhttp://www.sapiensman.com/step_motor/stepping%20motors.htm#tolerancehttp://www.sapiensman.com/step_motor/stepping%20motors.htm#resonancehttp://www.sapiensman.com/step_motor/stepping%20motors.htm#ripplehttp://www.sapiensman.com/step_motor/stepping%20motors.htm#start_stop


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Construction

Stepping motors are electromagnetic, rotary, incremental devices which convert

digital pulses into mechanical rotation. The amount of rotation is directly

proportional to the number of pulses and the speed of rotation is relative to the

frequency of those pulses.

Stepping motors are simple to drive in an open loop configuration and for their

size provide excellent torque at low speed.

The benefits offered by stepping motors include:

a simple and cost effective design high reliability

maintenance free (no brushes) open loop (no feed back device required) known limit to the 'dynamic position error'

Although various types of stepping motor have been developed, they all fall into

three basic categories.

1. variable reluctance (V.R)2. permanent magnet (tin can)3. hybrid

The variable reluctance or V.R. motor consist of a rotor and stator each with a

different number of teeth. As the rotor does not have a permanent magnet it

spins freely i.e. it has no detent torque. Although the torque to inertia ratio is

good, the rated torque for a given frame size is restricted. Therefore small frame

sizes are generally used and then very seldom for industrial applications.


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Figure 1. cross section through a variable reluctance stepping motor

The permanent magnet (PM) or tin can (fig. 2) motor is perhaps the most widely

used stepping motor in non-industrial applications. In it's simplest form the motor

consists of a radially magnetized permanent magnet rotor and a stator similar to

the V.R. motor. Due to the manufacturing techniques used in constructing the

stator they are also sometimes known as 'claw pole' motors.

Figure 2. cross section through a permanent magnet

The Hybrid is probably the most widely used of all stepping motors. Originally

developed as a slow speed synchronous PM motor it's construction is a

combination of the V.R. and tin can designs. The Hybrid consists of a multi-

phased toothed stator and a three part rotor (single stack). The single stack rotor

contains two toothed pole pieces separated by an axially magnetized permanent

magnet, with the opposing teeth off-set by half of one tooth pitch (fig. 3) to enable

a high resolution of steps.


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Figure 3. exploded drawing illustrating the tooth pitch off-set

The increasing demands on the modern stepping motor system of reducing

acoustic noise, improving drive performance while at the same time reducing

costs were satisfied in the past with two main types of Hybrid stepping motor.

The 2(4) phase which has generally been implemented in simple applications

and the 5 phase which has proven to be ideal for more the demanding of tasks.

The advantages offered by the 5 phase included:

higher resolution lower acoustic noise lower operational resonance lower detent torque

Although the characteristics of the 5 phase offered many benefits; especially

when micro stepping, the increased number of power switches and the additional

wiring required could have an adverse affect on a system's cost. With advances

in electronics allowing circuits with ever higher degrees of integration and ever

more features to be realized, SIG Positec saw an opportunity and took the

initiative in their ground breaking development in stepping motor technology.


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Figure 4. Sections illustrating laminations and rotors for 2-, 3- and 5-phase

stepping motors

The 3 phase Hybrid stepping motor

Although similar in construction to other Hybrid stepping motors (see fig. 4),

implementing 3-phase sine drive technology made it possible for the number of

motor phases to be reduced leaving the number of rotor pole pairs and the driveelectronics to determine the resolution (steps per revolution).


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Figure 5. Cross section through a Hybrid stepping motor (3 phase)

As 3-phase technology has been used for decades as a cost effective method of

generating rotating fields, the advantages of this system are self evident. The 3-

phase stepping motor was therefore a natural progression incorporating all the

best features from the 5-phase system at a significant cost reduction.

Stepping motor resolution and step angle

As already mentioned, the resolution (number of steps) and step angle of a

stepping motor is dependent on:

the number of rotor pole pairs

the number of motor phases

the drive mode (full or half step)

The resolution can be calculated using the formula:

The step angle can then be calculated by dividing one rotation (360) by the

number of steps.


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Flux vectors

Flux vectors are used to illustrate the natural step angles of stepping motors

Figure 6. Flux vector diagrams for 2-, 3- and 5 phase stepping motors

If the phase currents are switched in small increments, these field vectors can

point in virtually any direction.


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Operation

Phase switching sequences

To enable rotation the magnetic field generated by the stator windings needs to

move. This is achieved by switching the direction of current flow through each

winding.

Full step: Using a simple two phase stepping motor with one pole pair as an

example the phase switching sequence when driven in full step mode is as

follows:

Start = Step angle 0 - Windings W1 and W2 are energized producing a north andsouth pole which attracts the rotor's respective poles and holds the rotor in

position.

Step 1 = Step angle 90 - Winding W1 remains the same but the current flow in

winding W2 is switched (reversed). This results in a movement of the stator's

magnetic field which the rotor follows until it is held at the new position.


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Step 2 = Step angle 180 - This time the current flow in Winding W1 is switched

(reversed) and W2 stays the same. Again, the stator's magnetic field moves, the

rotor follows and is held in the new position.

Step 3 = Step angle 270 - Winding W1 stays as before, the current flow in W2 is

switched (reversed) and the rotor follows the stator field to it's new position.


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Switching phases further can then either return the rotor to the starting position or

the switching sequence can be reversed. Current traces can also be used to

illustrate switching sequences as follows:


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Current trace for a 2 phase stepping motor driven in full step mode

Half step: Using the same stepping motor driven in half step mode doubles the

resolution (steps per rotation). Although the switching sequence is similar,

instead of just reversing the flow of current through a phase, a phase is switched

off, allowing the rotor to follow and take up even more positions. The sequence

for one rotation is as follows:


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Rotation sequence for a 2 phase stepping motor driven in half step


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Current trace for a 2 phase stepping motor driven in half step

Current trace for a 2 phase stepping motor driven in half step

By using these simplified models, we have demonstrated the operational principle of the

2 phase stepping motor. This step by step switching of current results in a 'virtual'

rotating field which the permanent magnet rotor then follows.


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Illustrates this step by step switching of current for a 3 phase motor in half step mode

and its corresponding current trace. Full step operation occurs when only the even (t)

numbers are used in the step sequence.

Figure 11 Step sequence and current trace of a 3 phase stepping motor


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Figure 13 Pendulum effect of static torque verses rotor position

Depending on the number of phases, the cycle in figures 11 and 12 would be

equivalent to the following number of full steps:

2 phase 4 steps

3 phase 6 steps 5 phase 10 steps

The torque required to deflect the shaft by a given angle can be calculated using

the formula:

Although this static torque characteristic is not a great deal of use on it's own, it

does explain some of the effects we observe. For example, it dictates the static

stiffness of the system, in other words; how the shaft position changes when a

load is applied to a stationary motor. The shaft must deflect until the torquegenerated matches the applied load. Therefore, the static position varies with the

load.


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Static load angle

The static load angle is defined as, the angle between the actual rotor position

and the stable end position for a given load. Figure 14 illustrates (whether for full

or half step) that as the torque increases so does the shaft deflection from the

stable position.

Figure 14

The static load :angle can be calculated using the formula


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Friction torque

Friction torque is the load implemented on the shaft through mechanical

tolerances in the application.

Figure 14 illustrates how that for a given load the friction torque alsoneeds to be considered if accurate positioning is required.

This phenomenon can also be explained using the mountain model (fig 13).

Although the ball tries to find it's natural place of rest, friction on the surface

prevents it from doing so.

Figure 15 The mountain model

Systematic angle tolerance

'Systematic angle tolerance' is the deviation from the theoretically correct position

of any angle stepped. Also know as 'absolute accuracy', it can either be


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expressed as a percentage of a full step or as an angular measure. It is also non-

cumulative as it remains constant for any angle stepped.

'Systematic angle tolerance' is caused by manufacturing tolerances in the motor

(i.e. differing winding resistances or turns, unequally magnetized magnets, air

gaps etc.) and drive electronics. Although with modern manufacturing techniques

these tolerances are negligible, for extreme accuracy they may need to be

considered.

The 'static load angle curve' (fig. 14) illustrated what happens to a stationary

stepping motor under load. Therefore, if it is producing torque the motor must be

lagging behind the stator field under dynamic conditions i.e. motor running.

Similarly there will be a lead situation during deceleration.

From the static torque curve, it is clear that the lag or lead can not exceed the

maximum holding torque if the motor is to maintain it's synchronism. Therefore,for a Hybrid (50 pole pair) stepping motor the maximum lead or lag angle is 3.6

or, depending on the number of phases 2, 3 or 5 full steps. Figure 16 illustrates

the maximum lag which occurs under dynamic load conditions.

Figure 16 Dynamic load curve

Resonance

The phenomenon of 'resonance' is suffered by all stepping motors, to some

degree or other. Resonance is the term used for the effect which occurs when a


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stepping motor is stepped at it's natural oscillating frequency. Stepping at this

natural frequency can result in the stepping motor desynchronizing or even

stalling.

For a Hybrid stepping motor under no load conditions this resonance occurs

between 80 and 200 Hz i.e. 80 to 200 steps per second. A stepping motor's

resonance can be calculated using the formula:

For ease of use and so that the values can be used directly from SIG Positec'

'Complete Catalogue', the formula can be altered as follows:

Resonance can be overcome by operating outside the resonance range, through

half-step or micro-stepping, shifting the resonance frequency through changes in

the system's inertia or electrical or mechanical friction. Increasing the systemsinertia or friction generally known as damping.

Torque ripple

If, a motor is driven close to it's maximum run torque, torque ripple can have a

resonance effect. Torque ripple is illustrated on 'dynamic torque diagrams' (figs.

17 & 18) and the improvements gained through higher resolution and micro

stepping are clearly visible.


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Figure 17 Dynamic torque diagram for a 2-phase stepping motor


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Figure 18 Dynamic torque diagram for a 5-phase stepping motor

As previously discussed, the phase currents of the 3-phase motor are controlled

with a sine wave. Although this switching technique is more demanding than the

straight forward block commutation used for 2- and 5-phase stepping motors, itdoes offer considerable benefits in the operating characteristics.

The higher the resolution, the lower the current change per step, i.e. the greater

the approximation to a sine function. This ensures the motor has a lower current

ripple and subsequently a lower torque ripple. As only the fundamental

component of the wave form generates torque, any ripple only has a heating

effect on the motor. Which is easily dissipated through the motor body.

This lower tendency to ripple also has a positive effect in reducing acoustic

noise.


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Figure 19 Sine wave commutation of a 3-phase stepping motor

Defining the start / stop frequency

For the simplest of positioning requirements, driving a stepping motor in it's start /

stop mode is the least time consuming method. The maximum no load starting

frequency (fAom) is always given by manufacturers and it will obviously be reduced

when the motor is subjected to a load ML and it's subsequent load inertia JL.

The starting frequency's load dependence is also illustrated on two logarithmic

curves (fig. 20).


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Figure 20

These curves are used as follows:

1. Starting with the inertia curve, the load inertia (JL) is plotted and transposed to

the torque curve.

2. From this point, and parallel to the maximum no load start frequency curve, a

new start frequency curve which accounts for the load inertia is drawn.

3. From the known load torque and the new start frequency curve, the maximum

start / stop frequency can be found .

Calculate the following:

Using the performance curve (fig 21) from SIG Positec's 'Complete Catalogue',

find the maximum start / stop frequency of the motor for an application where:


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Inertia 13.5 kgcm

Torque 210 Ncm

Figure 21

The difference between Stepper motors, Stepper Motors, Servos,

and RC Servos

A stepper motor's shaft has permanent magnets attached to it,

together called the rotor. Around the body of the motor is a series ofcoils that create a magnetic field that interacts with the permanent


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magnets. When these coils are turned on and off the magnetic fieldcauses the rotor to move. As the coils are turned on and off in a

certain sequence the motor will rotate forward or reverse. This iscalled the phase pattern and there are several types that will cause the

motor to turn. Common types are full-double phase, full-single phase,

and half step.To make a stepper motor rotate, you must constantly turn on and off

the coils. If you simply energize one coil the motor will just jump tothat position and stay there resisting change. This energized coil pulls

full current even though the motor is not turning. This is the main way

steppers generate heat, when at standstill. This ability to stay put atone position rigidly is often an advantage of stepper motors. The

torque at standstill is called the holding torque.Because steppers can be controlled by turning on and off coils, they

are easy to control using digital computers. The computer simply

energizes the coils in a certain pattern and the motor will moveaccordingly. At any given time the computer will know the position of

the motor since the number of steps given can be stored. This is trueonly if some outside force of greater strength than the motor has not

interfered with the motion. An optical encoder could be attached to themotor to verify its position but this is not necessary.

A stepper motor can be run in "open-loop" mode (without feedback of

an encoder or other device). Most stepper motor control systems willhave a home switch associated with each motor that will allow the

software to determine the starting or reference "home" position.Servo motors:

There are several types of servo motors but I'll just deal with a simpleDC type here. If you take a normal DC motor that can be bought atRadio Shack it has one coil (2 wires). If you attach a battery to those

wires the motor will spin (see, very different from a stepper already!).Reversing the polarity will reverse the direction. Attach that motor to

the wheel of a robot and watch the robot move noting the speed. Now

add a heavier payload to the robot, what happens? The robot will slowdown due to the increased load. The computer inside of the robot

would not know this happened unless there was an encoder on themotor keeping track of its position.

So, in a DC servo, the speed and current draw is affected by the load.For applications that the exact position of the motor must be known, afeedback device like an encoder MUST be used (not optional like a

stepper).The control circuitry to perform good servoing of a DC motor is MUCH

more complex than the circuitry that controls a stepper motor.RC Servos:

Often when talking about robots the word "servo" really means an RC


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(remote control) servo motor. This is a small box designed for use inhobby airplanes and cars.

Inside this box is a complete servo system including: motor, gearbox,feedback device (pot), servo control circuitry, and drive circuit. It's

really amazing that they can stick all of that in such a small package.

RC servos normally have 3 wires: +v, ground, control. The controlsignal is a pulse that occurs at about 50hz. The width of the pulse

determines the position of the servo motors output. As you can see,this would be pretty easy to control with a digital controller such as a

Basic Stamp. Most will run on 5-6 volts and draw 100-500ma

depending on size.

QUESTION EXERCISES

Give the three operating modes of the 555 timer IC.


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o Monostable, Astable, Bistable

One of the operation of timer IC in which the timer wakes up and generates or

produces a single pulse, then goes back to sleep.

o Monostable operation

An operation of timer IC that is considered unstable because the output is

continually changing between low and high; also produces a square wave.

o Astable operation

It is the duration of pulse.

o Time period

It is the digital version of the electric motor.

o Stepper motor

The predecessor of the stepper motor.

o Servo motor

It is used to illustrate the natural angles of stepping motors.

o Flux vectors


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The angle between the actual rotor position and the stable end position for a

given load.

o Static load angle

The load implemented on the shaft through mechanical tolerances.

o Friction torque

It is the term used for the effect which occurs when a stepping motor is stepped

at its natural oscillating frequency.

o Resonance

How does stepper motor differ from a conventional motor?

o A stepper motor is a digital version of the electric motor. The rotor moves

in discrete steps as commanded, rather than rotating continuously like a

conventional motor.

How does servo motor precedes stepper motor?

o Application wise, the predecessor of the stepper motor was the servo

motor. Today this is a higher cost solution to high performance motion

control applications. The expense and complexity of a servomotor is due

to the additional system components: position sensor and error amplifier.


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It is still the way to position heavy loads beyond the grasp of lower power

steppers.

What are the three types of stepper motor in order of increasing complexity?

Describe each type.

o There are three types of stepper motors in order of increasing complexity:

variable reluctance, permanent magnet, and hybrid. The variable

reluctance stepper has s solid soft steel rotor with salient poles. The

permanent magnet stepper has a cylindrical permanent magnet rotor. The

hybrid stepper has soft steel teeth added to the permanent magnet rotor

for a smaller step angle.

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Report....555ic and Stepper Motor