BIPOLAR STEPPER MOTOR CONTROL CIRCUIT

         In this circuit, a potentiometer controls both the speed and direction of a small bipolar stepping motor like those found in many 5 1/4" floppy disk drives. Note that the bipolar motors are distinguished from "unipolar" types, in that bipolar units have two coils instead of four, and four wires instead of five. With the potentiometer at the extreme counterclockwise position, the motor runs counterclockwise at the maximum speed. Rotating the potentiometer toward the center slows the motor, until it stops. Continuing potentiometer rotation clockwise, the motor starts to run clockwise, increasing in speed to the maximum clockwise position.
Operational amplifiers U1A and U1B and their associated components form an absolute value circuit with a reference of one half the supply voltage (+4.5 volts). With the potentiometer slider at either extreme position, the output at U1B is about 6 volts, decreasing linearly to +4.5 volts as the slider is moved to the center position.
         Operational amplifier U1D is configured as an integrator, and U2B as a voltage comparator. Together, they form an oscillator. U1C, with its diode, is a voltage-controlled clamp that permits voltage control of the oscillator's frequency from the output of the U1A-U1B absolute-value circuit. The threshold of oscillation depends on the voltage present at U1D's positive input, approximately 4.7 volts. Oscillation will not occur below this level, corresponding to the central segment of the potentiometer's control arc, for which the motor is stopped.
The output pulses from U2B are fed to the clock input of the U3 up-down counter. Comparitor U2A detects which side the potentiometer slider is located with respect to center, and it controls the counter's direction. U3's Q1 and Q2 outputs are decoded into a one-of-four sequence by U4, that in turn drives the inputs of "or" gates U5A through D. A quadrature wave pattern, required for motor rotation, results at the four gate outputs. The eight MOSFET power transistors, configured as two "H" bridges, serve as current amplifiers to drive the motor's coils.
       The values shown in the U1D and U2B oscillator section provide a frequency range of approximately 1 to 100 Hertz, corresponding to a motor speed of 0.6 to 60 RPM. Although 9 volts is indicated, the circuit will operate from 6 to 12 volts, with higher voltages providing greater torque. The circuit's speed range will be the same for any given supply voltage within the specified limits, due to the circuit's ratiometeric reference. The Matsushita KP39HM4-016 motor is rated 12 volts, 80 milliamperes per coil, and rotates 3.6 degrees per step.

Stepper Motor Driver (74194)

       Probably the simplest, reversible drive circuit is the H-Bridge. Some BEAMbots use H-bridge motor drivers; many more use an H-bridge variant of some sort. Here's a simple conceptual schematic: Image Based on the SN74LS194 - Bidirectional Universal Shift Register the circuit is designed to drive UNIPOLAR type stepper motors and provides only basic control functions - Forward, Reverse, Stop and Speed adjustment. The only step angle for this driver is the design step angle for the motor. The circuit is not complex and is cheaper than many dedicated driver/controller devices and the parts are easy to find.

This page links to UNIPOLAR and BIPOLAR stepper motor driver pages. The drivers are designed for simple requirement applications and are made with parts that are available from a variety of sources.

Both of the stepper drivers are use a 74194 - Bidirectional Universal Shift Register from the 74LS or 74HC - TTL families of logic devices to produce the stepping function. A diagram at the bottom of this page shows the difference between the 74194 - UNIPOLAR and BIPOLAR stepping pattern generation.

The UNIPOLAR driver uses a ULN2003 - eight segment, darlington IC as its output device.

The BIPOLAR driver uses a SN74410 - four segment, Quad - 1/2 H-Bridge IC as its output device.

These stepper drivers have only basic control functions: Forward, Reverse and Stop and Step rate adjustment. The calculated Step rate adjustment range of the drivers is 0.72 (1.39 sec) to 145 steps per second. (Lower and higher step rates are also possible.)

The only step angle for these drivers is the design step angle of the motor itself. 'Half-stepping' is not possible with either of the driver circuits.

A4983 Stepper Motor Driver Carrier

Overview

This product is a carrier board or breakout board for Allegro’s A4983 DMOS Microstepping Driver with Translator; we therefore recommend careful reading of the A4983 datasheet (368k pdf) before using this product. This stepper motor driver lets you control one bipolar stepper motor at up to 2 A output current per coil (see the Power Dissipation Considerations section below for more information). Here are some of the driver’s key features:

• Simple step and direction control interface
• Five different step resolutions: full-step, half-step, quarter-step, eighth-step, and sixteenth-step
• Adjustable current control lets you set the maximum current output with a potentiometer, which lets you use voltages above your stepper motor’s rated voltage to achieve higher step rates
• Intelligent chopping control that automatically selects the correct current decay mode (fast decay or slow decay)
• Over-temperature thermal shutdown, under-voltage lockout, and crossover-current protection

Like nearly all our other carrier boards, this product ships with all surface-mount components—including the A4983 driver IC—installed as shown in the product picture.

We also sell a larger version of the A4983 carrier that has reverse power protection on the main power input and built-in 5 V and 3.3 V voltage regulators that eliminate the need for separate logic and motor supplies.

Included hardware

The A4983 stepper motor driver carrier comes with one 1×16-pin breakaway 0.1" male header. The headers can be soldered in for use with solderless breadboards or 0.1" female connectors. You can also solder your motor leads and other connections directly to the board.

Using the driver

Minimal wiring diagram for connecting a microcontroller to an A4983 stepper motor driver carrier (full-step mode).

Power connections

The driver requires a logic supply voltage (3 – 5.5 V) to be connected across the VDD and GND pins and a motor supply voltage of (8 – 35 V) to be connected across VMOT and GND. These supplies should have appropriate decoupling capacitors close to the board, and they should be capable of delivering the expected currents (peaks up to 4 A for the motor supply). We also sell a version of the A4983 carrier with 5 V or 3.3 V voltage regulators eliminating the need for separate logic and motor supplies.

Motor connections

Four, six, and eight-wire stepper motors can be driven by the A4983 if they are properly connected; a FAQ answer explains the proper wirings in detail.

Warning: Connecting or disconnecting a stepper motor while the driver is powered can destroy the driver. (More generally, rewiring anything while it is powered is asking for trouble.)

Step (and microstep) size

Stepper motors typically have a step size specification (e.g. 1.8° or 200 steps per revolution), which applies to full steps. A microstepping driver such as the A4983 allows higher resolutions by allowing intermediate step locations, which are achieved by energizing the coils with intermediate current levels. For instance, driving a motor in quarter-step mode will give the 200-step-per-revolution motor 800 microsteps per revolution by using four different current levels.

The resolution (step size) selector inputs (MS1, MS2, MS3) enable selection from the five step resolutions according to the table below. MS2 and MS3 have internal 100kΩ pull-down resistors, but MS1 does not, so it must be connected externally. For the microstep modes to function correctly, the current limit must be set low enough (see below) so that current limiting gets engaged. Otherwise, the intermediate current levels will not be correctly maintained, and the motor will effectively operate in a full-step mode.

MS1	MS2	MS3	Microstep Resolution
Low	Low	Low	Full step
High	Low	Low	Half step
Low	High	Low	Quarter step
High	High	Low	Eighth step
High	High	High	Sixteenth step

Control inputs

Each pulse to the STEP input corresponds to one microstep of the stepper motor in the direction selected by the DIR pin. Note that the STEP and DIR pins are not pulled to any particular voltage internally, so you should not leave either of these pins floating in your application. If you just want rotation in a single direction, you can tie DIR directly to VCC or GND. The chip has three different inputs for controlling its many power states: RST, SLP, and EN. For details about these power states, see the datasheet. Please note that the RST pin is floating; if you are not using the pin, you can connect it to the adjacent SLP pin on the PCB.

Current limiting

To achieve high step rates, the motor supply is typically much higher than would be permissible without active current limiting. For instance, a typical stepper motor might have a maximum current rating of 1 A with a 5Ω coil resistance, which would indicate a maximum motor supply of 5 V. Using such a motor with 12 V would allow higher step rates, but the current must actively be limited to under 1 A to prevent damage to the motor.

The A4983 supports such active current limiting, and the trimmer potentiometer on the board can be used to set the current limit. One way to set the current limit is to put the driver into full-step mode and to measure the current running through a single motor coil without clocking the STEP input. The measured current will be 0.7 times the current limit (since both coils are always on and limited to 70% in full-step mode). Please note that the current limit is dependent on the Vdd voltage.

Another way to set the current limit is to measure the voltage on the “ref” pin and to calculate the resulting current limit (the current sense resistors are 0.05Ω). The ref pin voltage is accessible on a via that is circled on the bottom silkscreen of the circuit board. See the A4983 datasheet for more information.

Power dissipation considerations

The A4983 driver IC has a maximum current rating of 2 A per coil, but the actual current you can deliver depends on how well you can keep the IC cool. The carrier’s printed circuit board is designed to draw heat out of the IC, but to supply more than approximately 1 A per coil, a heat sink or other cooling method is required.

This product can get hot enough to burn you long before the chip overheats. Take care when handling this product and other components connected to it.

Please note that measuring the current draw at the power supply does not necessarily provide an accurate measure of the coil current. Since the input voltage to the driver can be significantly higher than the coil voltage, the measured current on the power supply can be quite a bit lower than the coil current (the driver and coil basically act like a switching step-down power supply). Also, if the supply voltage is very high compared to what the motor needs to achieve the set current, the duty cycle will be very low, which also leads to significant differences between average and RMS currents.

Schematic diagram

Schematic diagram of the md09b A4983 stepper motor driver carrier.

Stepper motor controller circuit

Description.

Here is the circuit diagram of a simple stepper motor controller using only elementary parts. The driver circuit uses, four transistor (SL100) to drive the motor windings, two NOT gates and one XOR gate to decode the two bit control logic to drive the four windings of the motor. The diodes D1 to D4 protects the corresponding transistors from transients generated during the switching of motor windings. d0 and d1 are the control logics which determines the direction of rotation as well as speed.

Circuit diagram with Parts list.

Notes.

• The control logic for the circuit can be obtained from a 2 bit up/down counter clocked by a 555 astable multivibrator.The direction of count determines the direction of rotation and the frequency of astable multivibrator determines the speed of rotation.
• As shown in the schematic above, IC1a IC1b belongs to same IC 7404.
• Pin 14 and pin 7 of both IC1 and IC2 must be connected to +5 V and ground respectively, though it is not shown in circuit diagram.
• The 5V can be obtained from a 7805 based power supply circuit.
• 5V power supply using IC 7805.Click Here.
• Vcc is the voltage required for the stepper motor. It varies from motor to motor. Here we can use up to 24V stepper motors. For higher operating voltages and power the SL100 transistors must be replaced with higher power transistors like 2N3055.

Truth table for clockwise rotation.

Stepper Motors & Drivers

Stepper Motors & Drivers

A stepper motor is used to achieve precise positioning via digital control. The motor operates by accurately synchronizing with the pulse signal output from the controller to the driver. Stepper motors, with their ability to produce high torque at a low speed while minimizing vibration, are ideal for applications requiring quick positioning over a short distance.

• Stepper motors enable accurate positioning with ease. They are used in various types of equipment for accurate rotation angle and speed control using pulse signals. Stepper motors generate high torque with a compact body, and are ideal for quick acceleration and response. Stepper motors also hold their position at stop, due to their mechanical design. Stepper motor solutions consist of a driver (takes pulse signals in and converts them to motor motion) and a stepper motor. Oriental Motor offers many solutions for a wide variety of applications.

Accurate Positioning in Fine Steps

A stepper motor rotates with a fixed step angle, just like the second hand of a clock. This angle is called "basic step angle". Oriental Motor offers stepper motors with a basic step angle of 0.36°, 0.72°, 0.9° and 1.8°.

Easy Control with Pulse Signals

A system configuration for high accuracy positioning is shown below. The rotation angle and speed of the stepper motor can be controlled with precise accuracy by using pulse signals from the controller.

What is a Pulse Signal?

A pulse signal is an electrical signal whose voltage level changes repeatedly between ON and OFF. Each ON/OFF cycle is counted as one pulse. A command with one pulse causes the motor output shaft to turn by one step. The signal levels corresponding to voltage ON and OFF conditions are referred to as "H" and "L" respectively.

The Amount of Rotation is Proportional to the Number of Pulses

The amount the stepper motor rotates is proportional to the number of pulse signals (pulse number) given to the driver. The relationship of the stepper motor's rotation (rotation angle of the motor output shaft) and pulse number is expressed as follows:

The Speed is Proportional to the Pulse Speed

The speed of the stepper motor is proportional to the speed of pulse signals (pulse frequency) given to the driver. The relationship of the pulse speed [Hz] and motor speed [r/min] is expressed as follows:

Generating High Torque with a Compact Body

Stepper motors generate high torque with a compact body. These features give them excellent acceleration and response, which in turn makes these motors well-suited for torque-demanding applications where the motor must start and stop frequently. To meet the need for greater torque at low speed, Oriental Motor also has geared motors combining compact design and high torque.

The Motor Holds Itself at a Stopped Positioning

Stepper motors continue to generate holding torque even at standstill. This means that the motor can be held at a stopped position without using a mechanical brake.

Once the power is cut off, the self-holding torque of the motor is lost and the motor can no longer be held at the stopped position in vertical operations or when an external force is applied. In lift and similar applications, use an electromagnetic brake type.

Closed Loop Stepper Motor and Driver Package - AlphaStep

The AlphaStep consists of package products designed to draw out the maximum features of a stepper motor. These packages normally operate synchronously with pulse commands, but when a sudden acceleration or load change occurs, a unique control mode maintains positioning operation. AlphaStep models can also output positioning completion and alarm signals, which increase the reliability of the equipment which they operate.

Types of Operation Systems

Each stepper motor and driver package combines a stepper motor selected from various types, with a dedicated driver. Drivers that operate in the pulse input mode and built-in controller mode are available. You can select a desired combination according to the required operation system.

Pulse Input Package

The motor can be controlled using a pulse generator provided by the user. Operation data is input to the pulse generator beforehand. The user then selects the operation data on the host programmable controller, then inputs the operation command.

Built-in Controller Package

The built-in pulse generation function allows the motor to be driven via a directly connected personal computer or programmable controller. Since no separate pulse generator is required, drivers of this type save space and simplify wiring.

Difference Between AC Input and DC Input Characteristics

A stepper motor is driven by a DC voltage applied through a driver. In Oriental Motor's 24 VDC input motor and driver systems, 24 VDC is applied to the motor. In the 100-115 VAC motor and driver systems, the input is rectified to DC and then approximately 140 VDC is applied to the motor (certain products are exceptions to this.)

This difference in voltage applied to the motors appears as a difference in torque characteristics at high speeds. This is due to the fact that the higher the applied voltage is, the faster the current rise through the motor windings will be, facilitating the application of rated current at higher speeds. Thus, the AC input motor and driver system has superior torque characteristics over a wide speed range, from low to high speeds, offering a large speed ratio.

It is recommended that AC input motor and driver systems, which are compatible over a wider range of operating conditions than DC input systems, be considered for your application.

Unipolar stepper motor

Unipolar motors

A unipolar stepper motor has one winding with center tap 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 direction of current, the commutation circuit can be made very simple (e.g., a single transistor) for each winding. Typically, given a phase, the center tap of each winding is made common: giving 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 or stepper motor controller can be used to activate the drive transistors 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.

Unipolar stepper motor coils

(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 what it is between coil-end and 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.

[edit]Bipolar motor

Bipolar motors have a single winding 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 arrangement (however there are several off-the-shelf driver chips available to make this a simple affair). There are two leads per phase, none are common.

Static friction effects using an H-bridge have been observed with certain drive topologies.^[2]

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 wound 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

[edit]Higher-phase count stepper motors

Multi-phase stepper motors with many phases tend to have much lower levels of vibration,^[3] although the cost of manufacture is higher. These motors tend to be called 'hybrid' and have more expensive machined parts, but also higher quality bearings. Though they are more expensive, they do have a higher power density and with the appropriate drive electronics are actually better suited to the application^{[citation needed]}, however price is always an important factor. Computer printers may use hybrid designs.

[edit]Stepper motor drive circuits

Stepper motor with Adafruit Motor Shield drive circuit on Arduino

Stepper motor performance is strongly dependent on the drive circuit. Torque curves may be extended to greater speeds if the stator poles can be reversed more quickly, the limiting factor being 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.

[edit]L/R drive circuits

L/R drive 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 lawI=V/R. The inductance L determines the maximum rate of change of the current in the winding according to the formula for an Inductor dI/dt = V/L. Thus when controlled by an L/R 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 10mH inductance with 2 ohms resistance will take 5 ms to reach approx 2/3 of maximum torque or around 24 msec 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.

[edit]Chopper drive circuits

Chopper drive circuits are referred to as constant current drives because they generate a somewhat constant current in each winding rather than applying a constant voltage. On each new step, a very high voltage is applied to the winding initially. This causes the current in the winding to rise quickly since dI/dt = V/L where V is very large. The current in each winding is monitored by the controller, usually by measuring the voltage across a small sense resistor in series with each winding. When the current exceeds a specified current limit, the voltage is turned off or "chopped", typically using power transistors. When the winding current drops below the specified limit, the voltage is turned on again. In this way, the current is held relatively constant for a particular step position. 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. Integrated electronics for this purpose are widely available.

[edit]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.

Different drive modes showing coil current on a 4-phase unipolar stepper motor

[edit]Wave drive

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 than rated torque. It is rarely used.

[edit]Full step drive (two phases on)

This is the usual method for full step driving the motor. Two phases are always on. The motor will have full rated torque.

[edit]Half stepping

When half stepping, the drive alternates between two phases on and a single phase on. This increases the angular resolution, but the motor also has less torque (approx 70%) at the half 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.

[edit]Microstepping

What is commonly referred to as microstepping is often "sine cosine microstepping" in which the winding current approximates a sinusoidal AC waveform. Sine cosine microstepping is the most common form, but other waveforms can be used [2]. 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, backlash, and other sources of error between the motor and the end device. Gear reducers may be used to increase resolution of positioning.

Step size repeatability 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.^{[citation needed]}

[edit]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 during each step. Winding inductance and reverse 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.

[edit]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.

[edit]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.

[edit]Detent torque

Synchronous electric motors using permanent magnets have a remnant 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.

[edit]Stepper motor ratings and specifications

Stepper motors nameplates typically give only the winding current and occasionally the voltage and winding resistance. The rated voltage 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.

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, which is specified by the manufacturer at particular drive voltages or using their own drive circuitry.

[edit]Applications

Computer-controlled stepper motors are a type of motion-control positioning system. They are typically digitally controlled as part of an open loop system for use in holding or positioning applications.

In the field of lasers and optics they are frequently used in precision positioning equipment such as linear actuators, linear stages, rotation stages, goniometers, and mirror mounts. Other uses are in packaging machinery, and positioning of valve pilot stages for fluid control systems.

Commercially, stepper motors are used in floppy disk drives, flatbed scanners, computer printers, plotters, slot machines, image scanners, compact disc drives, intelligent lighting.

[edit]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 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 of step motors are low cost, high reliability, high torque at low speeds and a simple, rugged construction that operates in almost any environment. The main disadvantages in using a stepper motor is the resonance effect often exhibited at low speeds and decreasing torque with increasing speed.^[4]

stepping motor calculation

His section covers all types of motors, from the elementary circuitry needed to control a variable reluctance. H-bridge circuitry needed to control a bipolar permanent magnet motor. Each class of drive circuit illustrated with practical examples. However, these examples are not intended to be a comprehensive catalog of commercially available control circuits, nor is it a substitute for the component data sheets by the manufacturers of these items are found.

Related Articles.
Analyze operational mechanism and step sequence of stepper motor drive.
More about step motor.
This section covers the most elementary control circuitry for each class of vehicles. All of these circuits assume that the motor drive voltage is the voltage of the motor, and this is a significant performance Motor Co., the next in the drive circuit, current limiting coverage of operational efficiency. high drive circuit.

Variable reluctance motor.

General controller for variable reluctance stepping motors are variations on the outline shown in Figure 3.1.

Figure 3.1.

Figure 3.1 boxes are used to represent switches; controller, not shown, is responsible for the control signals for opening and closing the switch at the right time to turn on the engine. In many cases, the control unit is connected to a computer or controller interface directly with software generating the outputs required to control the switches. But in other cases, an additional control circuit is introduced, sometimes not!

Motor windings, solenoids and similar devices are all inductive loads. The current through the motor winding is not on or off, without immediately with endless tensions! When the switch controlling a motor winding is closed, allowing current to flow results of this is to slowly increase the current. If the switch for a motor winding is the result of the voltage spike that can seriously damage the switch unless care in order to treat it properly.

There are two basic ways of dealing with this voltage spike. One is to bridge the motor winding with a diode, and the other is to bridge the motor winding capacitor with Figure 3.2 shows the two methods.

Figure 3.2.

Diodes, as shown in Figure 3.2, to be able to carry the full current through the motor winding. It will be executed in a short period of closed switches, the current through the winding decreases. If such relatively slow diode typically used family 1N400X rapidly in conjunction with the switch, it may be necessary to provide a small capacitor, the book parallel with a diode.

Capacitor in Figure 3.2 is more complex design problems! If the switch is closed, the capacitor to discharge to ground through the switch and the switch must be able to handle these short spike discharge. Resistor in series with the capacitor or in series with the power supply to limit the current when the switch will be stored energy in the motor winding turn on the capacitor to a voltage higher than the voltage, and. need to withstand this voltage. To achieve the size of the capacitor, we equate the two formulas for the energy stored in the resonant circuit.

C P = V2 / 2

P = L I2 / 2

Location:.

P - stored energy in watt seconds or coulomb volts.

C - capacitance in farads.

V - voltage across the capacitor.

L - inductance of motor winding in Henry.

I - current through the motor winding.

The solution for the minimum size of capacitor required to prevent overvoltage switch easily.

C> I2 L / (VB - Vs) 2

Location:.

VB - the breakdown voltage of the switch.

Vs - pressure.

Variable reluctance motors have variable inductance which depends on the angular shaft. So in the worst case would be used to select a capacitor motor inductances are frequently poorly documented, if at all.

Motor winding and capacitor form a resonance circuit in combination. If the drive motor at frequencies near the resonant frequency of this circuit, the current through the motor windings and the motor torque exerted by the engine is quite different from the steady state voltages less! The resonance frequency.

f = 1 / (2 (L C) 0.5).

Again, the electrical resonant frequency of the variable reluctance angle from the shaft. When a variable reluctance motor with the excitation square wave current pulses near the motor winding is operable to cause the magnetic field at the resonant frequency is zero and the greatly reduce the torque available!

Unipolar and hybrid permanent magnet motors.

Joint inspections for unipolar stepping motors are variations on the scheme shown in Figure 3.3.

Figure 3.3.

In Figure 3.3, Figure 3.1 boxes are used to represent switches, control unit, not shown, is responsible for the control signals for opening and closing the switch at the right time to turn on the engine. The control unit is the interface to computer applications or software directly generating the outputs needed to control the switches.

As with drive circuitry for variable reluctance motors, we have created with the inductive kick when each of these switches is turned off deal. Again, we may shunt the inductive kick using diodes, but now, 4 diodes are required, as shown in Figure 3.4.