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A stepper motor, also known as step motor or stepping motor, is a
brushless DC electric motor A brushless DC electric motor (BLDC motor or BL motor), also known as an electronically commutated motor (ECM or EC motor) or synchronous DC motor, is a synchronous motor using a direct current (DC) electric power supply. It uses an electronic ...
that divides a full rotation into a number of equal steps. The motor's position can be commanded to move and hold at one of these steps without any
position sensor A position sensor is a sensor that detects an object's position. A position sensor may indicate the absolute position of the object (its location) or its relative position (displacement) in terms of linear travel, rotational angle or three-dimensio ...
for
feedback Feedback occurs when outputs of a system are routed back as inputs as part of a chain of cause-and-effect that forms a circuit or loop. The system can then be said to ''feed back'' into itself. The notion of cause-and-effect has to be handled ...
(an
open-loop controller In control theory, an open-loop controller, also called a non-feedback controller, is a control system in which the control action is independent of the "process output", which is the process variable that is being controlled."Feedback and cont ...
), as long as the motor is correctly sized to the application in respect to
torque In physics and mechanics, torque is the rotational equivalent of linear force. It is also referred to as the moment of force (also abbreviated to moment). It represents the capability of a force to produce change in the rotational motion of th ...
and speed. Switched reluctance motors are very large stepping motors with a reduced pole count, and generally are closed-loop commutated.


Mechanism

Brushed DC motors rotate continuously when DC voltage is applied to their terminals. The stepper motor is known for its property of converting a train of input pulses (typically square waves) into a precisely defined increment in the shaft’s rotational position. Each pulse rotates the shaft through a fixed angle. Stepper motors effectively have multiple "toothed" electromagnets arranged as a stator around a central rotor, a gear-shaped piece of iron. The electromagnets are energized by an external
driver circuit In electronics, a driver is a circuit or component used to control another circuit or component, such as a high-power transistor, liquid crystal display (LCD), stepper motors, SRAM memory, and numerous others. They are usually used to regul ...
or a
micro controller A microcontroller (MCU for ''microcontroller unit'', often also MC, UC, or μC) is a small computer on a single VLSI integrated circuit (IC) chip. A microcontroller contains one or more Central processing unit, CPUs (processor cores) along with ...
. To make the motor shaft turn, first, one electromagnet is given power, which magnetically attracts the gear's teeth. When the gear's teeth are aligned to the first electromagnet, they are slightly offset from the next electromagnet. This means that when the next electromagnet is turned on and the first is turned off, the gear rotates slightly to align with the next one. From there the process is repeated. Each of the partial rotations is called a "step", with an
integer number An integer is the number zero (), a positive natural number (, , , etc.) or a negative integer with a minus sign (−1, −2, −3, etc.). The negative numbers are the additive inverses of the corresponding positive numbers. In the language ...
of steps making a full rotation. In that way, the motor can be turned by a precise angle. The circular arrangement of electromagnets is divided into groups, each group called a phase, and there is an equal number of electromagnets per group. The number of groups is chosen by the designer of the stepper motor. The electromagnets of each group are interleaved with the electromagnets of other groups to form a uniform pattern of arrangement. For example, if the stepper motor has two groups identified as A or B, and ten electromagnets in total, then the grouping pattern would be ABABABABAB. Electromagnets within the same group are all energized together. Because of this, stepper motors with more phases typically have more wires (or leads) to control the motor.


Types

There are three main types of stepper motors: # Permanent magnet stepper # Variable reluctance stepper #
Hybrid synchronous stepper Hybrid may refer to: Science * Hybrid (biology), an offspring resulting from cross-breeding ** Hybrid grape, grape varieties produced by cross-breeding two ''Vitis'' species ** Hybridity, the property of a hybrid plant which is a union of two di ...
Permanent magnet motor A permanent magnet motor is a type of electric motor that uses permanent magnets in addition to windings on its field, rather than windings only. Use in electric vehicles This type of motor is used in GM's Chevrolet Bolt and Volt, and the rear ...
s use a
permanent magnet A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, steel, nickel, ...
(PM) in the rotor and operate on the attraction or repulsion between the rotor PM and the
stator The stator is the stationary part of a rotary system, found in electric generators, electric motors, sirens, mud motors or biological rotors. Energy flows through a stator to or from the rotating component of the system. In an electric mot ...
electromagnets. Pulses move the rotor in discrete steps, CW or CCW. If left powered at a final step a strong
detent A detent is a mechanical or magnetic means to resist or arrest the movement of a mechanical device. Such a device can be anything ranging from a simple metal pin to a machine. The term is also used for the method involved. Magnetic detents are ...
remains at that shaft location. This detent has a predictable spring rate and specified torque limit; slippage occurs if the limit is exceeded. If current is removed a lesser
detent A detent is a mechanical or magnetic means to resist or arrest the movement of a mechanical device. Such a device can be anything ranging from a simple metal pin to a machine. The term is also used for the method involved. Magnetic detents are ...
still remains, therefore holding shaft position against spring or other torque influences. Stepping can then be resumed while reliably being synchronized with control electronics.
Variable reluctance Variable may refer to: * Variable (computer science), a symbolic name associated with a value and whose associated value may be changed * Variable (mathematics), a symbol that represents a quantity in a mathematical expression, as used in many ...
(VR) motors have a plain
iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...
rotor and operate based on the principle that minimum
reluctance Magnetic reluctance, or magnetic resistance, is a concept used in the analysis of magnetic circuits. It is defined as the ratio of magnetomotive force (mmf) to magnetic flux. It represents the opposition to magnetic flux, and depends on the ge ...
occurs with minimum gap, hence the rotor points are attracted toward the stator magnet poles. Whereas hybrid synchronous are a combination of the permanent magnet and variable reluctance types, to maximize power in a small size. VR motors have power on detents but do not have power off detents.


Two-phase stepper motors

There are two basic winding arrangements for the
electromagnetic coil An electromagnetic coil is an electrical Electrical conductivity, conductor such as a wire in the shape of a wiktionary:coil, coil (spiral or helix). Electromagnetic coils are used in electrical engineering, in applications where electric curre ...
s in a two phase stepper motor: bipolar and unipolar.


Unipolar motors

A unipolar stepper motor has one winding with
center tap In electronics, a center tap (CT) is a contact made to a point halfway along a winding of a transformer or inductor, or along the element of a resistor or a potentiometer. Taps are sometimes used on inductors for the coupling of signals, and ...
per phase. Each section of windings is switched on for each direction of magnetic field. Since in this arrangement a magnetic pole can be reversed without switching the polarity of the common wire, the
commutation Commute, commutation or commutative may refer to: * Commuting, the process of travelling between a place of residence and a place of work Mathematics * Commutative property, a property of a mathematical operation whose result is insensitive to th ...
circuit can be simply a single switching transistor for each half winding. Typically, given a phase, the center tap of each winding is made common: three leads per phase and six leads for a typical two phase motor. Often, these two phase commons are internally joined, so the motor has only five leads. A
microcontroller A microcontroller (MCU for ''microcontroller unit'', often also MC, UC, or μC) is a small computer on a single VLSI integrated circuit (IC) chip. A microcontroller contains one or more CPUs (processor cores) along with memory and programmable i ...
or stepper motor controller can be used to activate the drive
transistor upright=1.4, gate (G), body (B), source (S) and drain (D) terminals. The gate is separated from the body by an insulating layer (pink). A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch e ...
s in the right order, and this ease of operation makes unipolar motors popular with hobbyists; they are probably the cheapest way to get precise angular movements. For the experimenter, the windings can be identified by touching the terminal wires together in PM motors. If the terminals of a coil are connected, the shaft becomes harder to turn. One way to distinguish the center tap (common wire) from a coil-end wire is by measuring the resistance. Resistance between common wire and coil-end wire is always half of the resistance between coil-end wires. This is because there is twice the length of coil between the ends and only half from center (common wire) to the end. A quick way to determine if the stepper motor is working is to short circuit every two pairs and try turning the shaft. Whenever a higher-than-normal resistance is felt, it indicates that the circuit to the particular winding is closed and that the phase is working.


Bipolar motors

Bipolar motors have a pair of single winding connections per phase. The current in a winding needs to be reversed in order to reverse a magnetic pole, so the driving circuit must be more complicated, typically with an
H-bridge A H-bridge is an electronic circuit that switches the polarity of a voltage applied to a load. These circuits are often used in robotics and other applications to allow DC motors to run forwards or backwards. The name is derived from its common sch ...
arrangement (however there are several off-the-shelf driver chips available to make this a simple affair). There are two leads per phase, none is common. A typical driving pattern for a two coil bipolar stepper motor would be: A+ B+ A− B−. I.e. drive coil A with positive current, then remove current from coil A; then drive coil B with positive current, then remove current from coil B; then drive coil A with negative current (flipping polarity by switching the wires e.g. with an H bridge), then remove current from coil A; then drive coil B with negative current (again flipping polarity same as coil A); the cycle is complete and begins anew. Static friction effects using an H-bridge have been observed with certain drive topologies. Dithering the stepper signal at a higher frequency than the motor can respond to will reduce this "static friction" effect. Because windings are better utilized, they are more powerful than a unipolar motor of the same weight. This is due to the physical space occupied by the windings. A unipolar motor has twice the amount of wire in the same space, but only half used at any point in time, hence is 50% efficient (or approximately 70% of the torque output available). Though a bipolar stepper motor is more complicated to drive, the abundance of driver chips means this is much less difficult to achieve. An 8-lead stepper is like a unipolar stepper, but the leads are not joined to common internally to the motor. This kind of motor can be wired in several configurations: * Unipolar. * Bipolar with series windings. This gives higher inductance but lower current per winding. * Bipolar with parallel windings. This requires higher current but can perform better as the winding inductance is reduced. * Bipolar with a single winding per phase. This method will run the motor on only half the available windings, which will reduce the available low speed torque but require less current


Higher-phase count stepper motors

Multi-phase stepper motors with many phases tend to have much lower levels of vibration. While they are more expensive, they do have a higher
power density Power density is the amount of power (time rate of energy transfer) per unit volume. In energy transformers including batteries, fuel cells, motors, power supply units etc., power density refers to a volume, where it is often called volume p ...
and with the appropriate drive electronics are often better suited to the application.


Driver circuits

Stepper motor performance is strongly dependent on the
driver circuit In electronics, a driver is a circuit or component used to control another circuit or component, such as a high-power transistor, liquid crystal display (LCD), stepper motors, SRAM memory, and numerous others. They are usually used to regul ...
.
Torque curve In physics and mechanics, torque is the rotational equivalent of linear force. It is also referred to as the moment of force (also abbreviated to moment). It represents the capability of a force to produce change in the rotational motion of the ...
s may be extended to greater speeds if the stator poles can be reversed more quickly, the limiting factor being a combination of the winding inductance. To overcome the inductance and switch the windings quickly, one must increase the drive voltage. This leads further to the necessity of limiting the current that these high voltages may otherwise induce. An additional limitation, often comparable to the effects of inductance, is the back-EMF of the motor. As the motor's rotor turns, a sinusoidal voltage is generated proportional to the speed (step rate). This AC voltage is subtracted from the voltage waveform available to induce a change in the current.


L/R driver circuits

L/R driver circuits are also referred to as constant voltage drives because a constant positive or negative voltage is applied to each winding to set the step positions. However, it is winding current, not voltage that applies torque to the stepper motor shaft. The current I in each winding is related to the applied voltage V by the winding inductance L and the winding resistance R. The resistance R determines the maximum current according to
Ohm's law Ohm's law states that the current through a conductor between two points is directly proportional to the voltage across the two points. Introducing the constant of proportionality, the resistance, one arrives at the usual mathematical equat ...
I=V/R. The inductance L determines the maximum rate of change of the current in the winding according to the formula for an
inductor An inductor, also called a coil, choke, or reactor, is a passive two-terminal electrical component that stores energy in a magnetic field when electric current flows through it. An inductor typically consists of an insulated wire wound into a c ...
dI/dt = V/L. The resulting current for a voltage pulse is a quickly increasing current as a function of inductance. This reaches the V/R value and holds for the remainder of the pulse. Thus when controlled by a constant voltage drive, the maximum speed of a stepper motor is limited by its inductance since at some speed, the voltage U will be changing faster than the current I can keep up. In simple terms the rate of change of current is L / R (e.g. a 10 mH inductance with 2 ohms resistance will take 5 ms to reach approx 2/3 of maximum torque or around 24 ms to reach 99% of max torque). To obtain high torque at high speeds requires a large drive voltage with a low resistance and low inductance. With an L/R drive it is possible to control a low voltage resistive motor with a higher voltage drive simply by adding an external resistor in series with each winding. This will waste power in the resistors, and generate heat. It is therefore considered a low performing option, albeit simple and cheap. Modern voltage-mode drivers overcome some of these limitations by approximating a sinusoidal voltage waveform to the motor phases. The amplitude of the voltage waveform is set up to increase with step rate. If properly tuned, this compensates the effects of inductance and back-EMF, allowing decent performance relative to current-mode drivers, but at the expense of design effort (tuning procedures) that are simpler for current-mode drivers.


Chopper drive circuits

Chopper drive circuits are referred to as controlled current drives because they generate a controlled current in each winding rather than applying a constant voltage. Chopper drive circuits are most often used with two-winding bipolar motors, the two windings being driven independently to provide a specific motor torque CW or CCW. On each winding, a "supply" voltage is applied to the winding as a square wave voltage; example 8 kHz. The winding inductance smooths the current which reaches a level according to the square wave
duty cycle A duty cycle or power cycle is the fraction of one period in which a signal or system is active. Duty cycle is commonly expressed as a percentage or a ratio. A period is the time it takes for a signal to complete an on-and-off cycle. As a formu ...
. Most often bipolar supply (+ and - ) voltages are supplied to the controller relative to the winding return. So 50% duty cycle results in zero current. 0% results in full V/R current in one direction. 100% results in full current in the opposite direction. This current level is monitored by the controller by measuring the voltage across a small sense resistor in series with the winding. This requires additional electronics to sense winding currents, and control the switching, but it allows stepper motors to be driven with higher torque at higher speeds than L/R drives. It also allows the controller to output predetermined current levels rather than fixed. Integrated electronics for this purpose are widely available.


Phase current waveforms

A stepper motor is a polyphase AC synchronous motor (see Theory below), and it is ideally driven by sinusoidal current. A full-step waveform is a gross approximation of a sinusoid, and is the reason why the motor exhibits so much vibration. Various drive techniques have been developed to better approximate a sinusoidal drive waveform: these are half stepping and microstepping.


Wave drive (one phase on)

In this drive method only a single phase is activated at a time. It has the same number of steps as the full-step drive, but the motor will have significantly less torque than rated. It is rarely used. The animated figure shown above is a wave drive motor. In the animation, rotor has 25 teeth and it takes 4 steps to rotate by one tooth position. So there will be = 100 steps per full rotation and each step will be = .


Full-step drive (two phases on)

This is the usual method for full-step driving the motor. Two phases are always on so the motor will provide its maximum rated torque. As soon as one phase is turned off, another one is turned on. Wave drive and single phase full step are both one and the same, with same number of steps but difference in torque.


Half-stepping

When half-stepping, the drive alternates between two phases on and a single phase on. This increases the angular resolution. The motor also has less torque (approx 70%) at the full-step position (where only a single phase is on). This may be mitigated by increasing the current in the active winding to compensate. The advantage of half stepping is that the drive electronics need not change to support it. In animated figure shown above, if we change it to half-stepping, then it will take 8 steps to rotate by 1 tooth position. So there will be 25×8 = 200 steps per full rotation and each step will be 360/200 = 1.8°. Its angle per step is half of the full step.


Microstepping

What is commonly referred to as microstepping is often ''sine–cosine microstepping'' in which the winding current approximates a sinusoidal AC waveform. The common way to achieve sine-cosine current is with chopper-drive circuits. Sine–cosine microstepping is the most common form, but other waveforms can be used. Regardless of the waveform used, as the microsteps become smaller, motor operation becomes more smooth, thereby greatly reducing resonance in any parts the motor may be connected to, as well as the motor itself. Resolution will be limited by the mechanical
stiction Stiction is the static friction that needs to be overcome to enable relative motion of stationary objects in contact. The term is a portmanteau of the words ''static'' and ''friction'', and is perhaps also influenced by the verb '' to stick''. Any ...
,
backlash Backlash may refer to: Literature * '' Backlash: The Undeclared War Against American Women'', a 1991 book by Susan Faludi * ''Backlash'' (Star Wars novel), a 2010 novel by Aaron Allston * Backlash (Marc Slayton), comic book character * ''Backla ...
, and other sources of error between the motor and the end device. Gear reducers may be used to increase resolution of positioning. Step size reduction is an important step motor feature and a fundamental reason for their use in positioning. Example: many modern hybrid step motors are rated such that the travel of every full step (example 1.8 degrees per full step or 200 full steps per revolution) will be within 3% or 5% of the travel of every other full step, as long as the motor is operated within its specified operating ranges. Several manufacturers show that their motors can easily maintain the 3% or 5% equality of step travel size as step size is reduced from full stepping down to 1/10 stepping. Then, as the microstepping divisor number grows, step size repeatability degrades. At large step size reductions it is possible to issue many microstep commands before any motion occurs at all and then the motion can be a "jump" to a new position. Some stepper controller ICs use increased current to minimise such missed steps, especially when the peak current pulses in one phase would otherwise be very brief.


Theory

A step motor can be viewed as a synchronous AC motor with the number of poles (on both rotor and stator) increased, taking care that they have no common denominator. Additionally, soft magnetic material with many teeth on the rotor and stator cheaply multiplies the number of poles (reluctance motor). Modern steppers are of hybrid design, having both permanent magnets and soft iron cores. To achieve full rated torque, the coils in a stepper motor must reach their full rated
current Currents, Current or The Current may refer to: Science and technology * Current (fluid), the flow of a liquid or a gas ** Air current, a flow of air ** Ocean current, a current in the ocean *** Rip current, a kind of water current ** Current (stre ...
during each step. Winding inductance and counter-EMF generated by a moving rotor tend to resist changes in drive current, so that as the motor speeds up, less and less time is spent at full current—thus reducing motor torque. As speeds further increase, the current will not reach the rated value, and eventually the motor will cease to produce torque.


Pull-in torque

This is the measure of the torque produced by a stepper motor when it is operated without an acceleration state. At low speeds the stepper motor can synchronize itself with an applied step frequency, and this pull-in torque must overcome friction and inertia. It is important to make sure that the load on the motor is frictional rather than inertial as the friction reduces any unwanted oscillations. The pull-in curve defines an area called the start/stop region. Into this region, the motor can be started/stopped instantaneously with a load applied and without loss of synchronism.


Pull-out torque

The stepper motor pull-out torque is measured by accelerating the motor to the desired speed and then increasing the torque loading until the motor stalls or misses steps. This measurement is taken across a wide range of speeds and the results are used to generate the stepper motor's dynamic performance curve. As noted below this curve is affected by drive voltage, drive current and current switching techniques. A designer may include a safety factor between the rated torque and the estimated full load torque required for the application.


Detent torque

Synchronous electric motors using permanent magnets have a resonant position holding torque (called detent torque or cogging, and sometimes included in the specifications) when not driven electrically. Soft iron reluctance cores do not exhibit this behavior.


Ringing and resonance

When the motor moves a single step it overshoots the final resting point and oscillates round this point as it comes to rest. This undesirable ringing is experienced as motor rotor vibration and is more pronounced in unloaded motors. An unloaded or under loaded motor may, and often will, stall if the vibration experienced is enough to cause loss of synchronisation. Stepper motors have a
natural frequency Natural frequency, also known as eigenfrequency, is the frequency at which a system tends to oscillate in the absence of any driving force. The motion pattern of a system oscillating at its natural frequency is called the normal mode (if all par ...
of operation. When the excitation frequency matches this resonance the ringing is more pronounced, steps may be missed, and stalling is more likely. Motor resonance frequency can be calculated from the formula: : f=\frac \sqrt ::;: Holding torque N·m ::; : Number of pole pairs ::; : Rotor inertia kg·m² The magnitude of the undesirable ringing is dependent on the
back EMF Counter-electromotive force (counter EMF, CEMF, back EMF),Graf, "counterelectromotive force", Dictionary of Electronics is the electromotive force (EMF) manifesting as a voltage that opposes the change in current which induced it. CEMF is the EMF c ...
resulting from rotor velocity. The resultant current promotes damping, so the drive circuit characteristics are important. The rotor ringing can be described in terms of
damping factor Damping is an influence within or upon an oscillatory system that has the effect of reducing or preventing its oscillation. In physical systems, damping is produced by processes that dissipate the energy stored in the oscillation. Examples inc ...
.


Ratings and specifications

Stepper motors' nameplates typically give only the winding current and occasionally the voltage and winding resistance. The rated
voltage Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to m ...
will produce the rated winding current at DC: but this is mostly a meaningless rating, as all modern drivers are current limiting and the drive voltages greatly exceed the motor rated voltage. Datasheets from the manufacturer often indicate Inductance. Back-EMF is equally relevant, but seldom listed (it is straightforward to measure with an oscilloscope). These figures can be helpful for more in-depth electronics design, when deviating from standard supply voltages, adapting third party driver electronics, or gaining insight when choosing between motor models with otherwise similar size, voltage, and torque specifications. A stepper's low-speed torque will vary directly with current. How quickly the torque falls off at faster speeds depends on the winding inductance and the drive circuitry it is attached to, especially the driving voltage. Steppers should be sized according to published
torque curve In physics and mechanics, torque is the rotational equivalent of linear force. It is also referred to as the moment of force (also abbreviated to moment). It represents the capability of a force to produce change in the rotational motion of the ...
, which is specified by the manufacturer at particular drive voltages or using their own drive circuitry. Dips in the torque curve suggest possible resonances, whose impact on the application should be understood by designers. Step motors adapted to harsh environments are often referred to as
IP65 The IP code or ingress protection code indicates how well a device is protected against water and dust. It defined by the International Electrotechnical Commission (IEC) under the international standard IEC 60529 which classifies and p ...
rated.


NEMA stepper motors

The US National Electrical Manufacturers Association (NEMA) standardises various dimensions, marking and other aspects of stepper motors, in NEMA standard (NEMA ICS 16-2001). NEMA stepper motors are labeled by faceplate size, NEMA 17 being a stepper motor with a faceplate and dimensions given in inches. The standard also lists motors with faceplate dimensions given in metric units. These motors are typically referred with NEMA DD, where DD is the diameter of the faceplate in inches multiplied by 10 (e.g., NEMA 17 has a diameter of 1.7 inches). There are further specifiers to describe stepper motors, and such details may be found in the ICS 16-2001 standard.


Applications

Computer controlled stepper motors are a type of motion-control
positioning system A positioning system is a system for determining the position of an object in space. One of the most well-known and commonly used positioning systems is the Global Positioning System (GPS). Positioning system technologies exist ranging from world ...
. They are typically digitally controlled as part of an
open loop Open or OPEN may refer to: Music * Open (band), Australian pop/rock band * The Open (band), English indie rock band * ''Open'' (Blues Image album), 1969 * ''Open'' (Gotthard album), 1999 * ''Open'' (Cowboy Junkies album), 2001 * ''Open'' (YF ...
system for use in holding or positioning applications. In the field of
laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The fir ...
s and
optics Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultraviole ...
they are frequently used in precision positioning equipment such as
linear actuator A linear actuator is an actuator that creates motion in a straight line, in contrast to the circular motion of a conventional electric motor. Linear actuators are used in machine tools and industrial machinery, in computer Peripheral, periphera ...
s,
linear stage A linear stage or translation stage is a component of a precise motion system used to restrict an object to a single axis of motion. The term linear slide is often used interchangeably with "linear stage", though technically "linear slide" refe ...
s, rotation stages, goniometers, and
mirror mount A mirror mount is a device that holds a mirror. In optics research, these can be quite sophisticated devices, due to the need to be able to tip and tilt the mirror by controlled amounts, while still holding it in a precise position when it is n ...
s. 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 A floppy disk or floppy diskette (casually referred to as a floppy, or a diskette) is an obsolescent type of disk storage composed of a thin and flexible disk of a magnetic storage medium in a square or nearly square plastic enclosure lined w ...
,
flatbed scanner An image scanner—often abbreviated to just scanner—is a device that optically scans images, printed text, handwriting or an object and converts it to a digital image. Commonly used in offices are variations of the desktop ''flatbed scanner'' w ...
s,
computer printer In computing, a printer is a peripheral machine which makes a persistent representation of graphics or text, usually on paper. While most output is human-readable, bar code printers are an example of an expanded use for printers. Differ ...
s,
plotter A plotter is a machine that produces vector graphics drawings. Plotters draw lines on paper using a pen, or in some applications, use a knife to cut a material like vinyl or leather. In the latter case, they are sometimes known as a cutting pl ...
s,
slot machine A slot machine (American English), fruit machine (British English) or poker machine (Australian English and New Zealand English) is a gambling machine that creates a game of chance for its customers. Slot machines are also known pejoratively a ...
s,
image scanner An image scanner—often abbreviated to just scanner—is a device that optically scans images, printed text, handwriting or an object and converts it to a digital image. Commonly used in offices are variations of the desktop ''flatbed scanner'' ...
s,
compact disc The compact disc (CD) is a Digital media, digital optical disc data storage format that was co-developed by Philips and Sony to store and play digital audio recordings. In August 1982, the first compact disc was manufactured. It was then rele ...
drives,
intelligent lighting Intelligent lighting refers to lighting that has automated or mechanical abilities beyond those of traditional, stationary illumination. Although the most advanced intelligent lights can produce extraordinarily complex effects, the intelligence l ...
,
camera lens A camera lens (also known as photographic lens or photographic objective) is an optical lens or assembly of lenses used in conjunction with a camera body and mechanism to make images of objects either on photographic film or on other media capab ...
es, CNC machines, and
3D printer 3D printing or additive manufacturing is the Manufacturing, construction of a three-dimensional object from a computer-aided design, CAD model or a digital 3D modeling, 3D model. It can be done in a variety of processes in which material is ...
s.


Stepper motor system

A stepper motor system consists of three basic elements, often combined with some type of user interface (host computer, PLC or dumb terminal): ;Indexers: The indexer (or controller) is a
microprocessor A microprocessor is a computer processor where the data processing logic and control is included on a single integrated circuit, or a small number of integrated circuits. The microprocessor contains the arithmetic, logic, and control circu ...
capable of generating step pulses and direction signals for the driver. In addition, the indexer is typically required to perform many other sophisticated command functions. ;Drivers: The driver (or amplifier) converts the indexer command signals into the power necessary to energize the motor windings. There are numerous types of drivers, with different voltage and current ratings and construction technology. Not all drivers are suitable to run all motors, so when designing a motion control system, the driver selection process is critical. ;Stepper motors: The stepper motor is an electromagnetic device that converts digital pulses into mechanical shaft rotation.


Advantages

*Low cost for control achieved *High torque at startup and low speeds *Ruggedness *Simplicity of construction *Can operate in an open loop control system *Low maintenance (high reliability) *Less likely to stall or slip *Will work in any environment *Can be used in robotics in a wide scale. *High reliability *The rotation angle of the motor is proportional to the input pulse. *The motor has full torque at standstill (if the windings are energized) *Precise positioning and repeatability of movement, since good stepper motors have an accuracy of 3–5% of a step and this error is non-cumulative from one step to the next. *Excellent response to starting/stopping/reversing. *Very reliable since there are no contact brushes in the motor. Therefore, the life of the motor is simply dependent on the life of the bearing. *The motor's response to digital input pulses provides open-loop control, making the motor simpler and less costly to control. *It is possible to achieve very low-speed synchronous rotation with a load that is directly coupled to the shaft. *A wide range of rotational speeds can be realized, as the speed is proportional to the frequency of the input pulses.


Disadvantages

*Resonance effect often exhibited at low speeds and decreasing torque with increasing speed.


See also

*
Brushed DC electric motor A brushed DC electric motor is an internally commutated electric motor designed to be run from a direct current power source and utilizing an electric brush for contact. Brushed motors were the first commercially important application of electri ...
*
Brushless DC electric motor A brushless DC electric motor (BLDC motor or BL motor), also known as an electronically commutated motor (ECM or EC motor) or synchronous DC motor, is a synchronous motor using a direct current (DC) electric power supply. It uses an electronic ...
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Flange A flange is a protruded ridge, lip or rim (wheel), rim, either external or internal, that serves to increase shear strength, strength (as the flange of an iron beam (structure), beam such as an I-beam or a T-beam); for easy attachment/transfer of ...
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Fractional horsepower motors A fractional-horsepower motor (FHP) is an electric motor with a rated output power of less than (the term 'fractional' indicates less than one unit). There is no defined minimum output, however, it is generally accepted that a motor with a frame ...
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Servo motor A servomotor (or servo motor) is a rotary actuator or linear actuator that allows for precise control of angular or linear position, velocity and acceleration. It consists of a suitable motor coupled to a sensor for position feedback. It also r ...
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Solenoid upright=1.20, An illustration of a solenoid upright=1.20, Magnetic field created by a seven-loop solenoid (cross-sectional view) described using field lines A solenoid () is a type of electromagnet formed by a helix, helical coil of wire whose ...
* Three-phase AC synchronous motors *
ULN2003A The ULN2003A is an integrated circuit produced by Texas Instruments. It consists of an array of seven NPN Darlington transistors capable of 500 mA, 50 V output. It features common-cathode flyback diodes for switching inductive loads ...
(stepper motor) driver IC


References


External links


Controlling a stepper motor without microcontrollerZaber Microstepping Tutorial
Retrieved on 2007-11-15.
Stepper System Overview
Retrieved on 2012-3-01.
Control of Stepping Motors - A Tutorial
Douglas W. Jones Douglas W. Jones is an American computer scientist at the University of Iowa. His research focuses primarily on computer security, particularly electronic voting. Jones received a Bachelor of Science, B.S. in physics from Carnegie Mellon Univer ...
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The University of Iowa The University of Iowa (UI, U of I, UIowa, or simply Iowa) is a public university, public research university in Iowa City, Iowa, United States. Founded in 1847, it is the oldest and largest university in the state. The University of Iowa is org ...

Stepping 101NEMA motor
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