Selection and calculation of stepper motors for cnc.

31.03.2019

Stepper motors are brushless devices. They are made with several windings. The main parameters of the devices can be called the threshold voltage and the number of poles. Also, the models differ in terms of winding resistance. Single-phase modifications are made with toothed stators. Magnets are most commonly used cylindrical type.

For CNC stepper motors are ideal. However, in this case a lot depends on the equipment. In particular, modifications are installed on printers, machine tools and laser cutters. They can also be found on drives. However, this applies only to linear configurations. It costs an average of a high-quality stepper motor in the region of 4500 rubles.

How to choose an engine?

How to choose for CNC? First of all, you should decide on the type of modification. If we consider options for machines, then two-phase models are often used on them. Their magnetic cores are installed with good current conductivity. Directly rotors are applied from steel. Cups for stators are made with a ledge.

In this case, the windings are used from a magnetically soft material. The stators in the presented devices are used with teeth. The retention rate must be at least 3 kg/cm. The winding resistance parameter depends on the CNC type. If we talk about modifications with a controller, then the above indicator must be equal to 7 ohms.

Devices for machine tools

How to choose for If we consider a conventional milling model, then first of all it is important to pay attention to the type of shaft. On average, it is installed with a diameter of 5 mm. In this case, the stator must be above the rotor in the cup, and the winding current itself must be 2 A. For more stable operation The motor uses magnetic circuits with high conductivity.

Also, before buying, you should evaluate the inductance of the winding. The indicated parameter for engines fluctuates around 6 mH. In this case, the device drivers must be of the bipolar type. An average stepper motor for a CNC machine costs around 3 thousand rubles.

Drive Models

How to choose a stepper motor for CNC drive? In this case, many consumers prefer two-phase modifications. Their stators are most often toothed. By the type of rotor, the models are quite different. Often they are made from charge steel. The average shaft diameter is 5.5 mm. The pitch angle of the drive models is 1.2 degrees. The winding current in this case should be at least 3 A. If we consider single-phase modifications, then the driver for motors is suitable for a unipolar type.

Winding resistance on average fluctuates around 5 ohms. It is also important to pay attention to the threshold voltage of motors. This parameter, as a rule, does not exceed 6 V. However, there are more powerful models On the market. The maximum winding inductance they have is 10 mH. At the same time, the current overload indicator is at the level of 4 A. A high-quality stepper motor for the drive will cost around 4500 rubles.

Engines for printers

The choice of a stepper motor for a CNC printer is made only among three-phase modifications. It is more expedient to select stators of gear type. Magnetic circuits must have high current conductivity. Thanks to them, the engine will pick up speed smoothly. If we talk about the parameters, then the holding moment of modifications for printers is on average 4 kg / cm. The threshold voltage itself fluctuates around 10 V.

The minimum winding inductance must be 8.5 mH. The step angle of the device should be at the level of 1.3 degrees. Magnets in the presented modifications are often used permanent and are cylindrical in shape. devices depends on the type of rotor. For unipolar drivers, models on the market are quite rare. Buy good engine for a printer, the user is capable at a price of 3 thousand rubles.

Modifications for laser cutters

Which motor to choose for Many experts in this situation prefer 10 V models. Most often they are made with gear-type stators. Their magnetic cores have a fairly high conductivity. Directly, the rotors in the engines are located in special bowls. Modifications of the bipolar type are rare on the market.

On average, the step angle for models does not exceed 2 degrees. The maximum current load of the device is maintained at 5 A. The maximum inductance of the winding depends on the number of steps per revolution. The shaft diameter in the motor must be 5.5 mm. To date, high-quality devices for cutters are sold at a price of 4 thousand rubles.

Single phase modifications

Single-phase models are best suited for. On average, their pitch angle is 2.5 degrees. The maximum inductance of the device is maintained at 7 mH. In terms of the number of steps per revolution, the models are quite different. There are many modifications on the market for 5 and 10 V. Gear ratio they have approximately 1:54.

Bipolar modifications are able to boast of high current conductivity. Rotors are most often installed from charge steel. Cups under them are made with protrusions of different lengths. Buy a set in stores stepper motors for CNC at 5 V it is possible for 4500 rubles.

Two-phase devices

The two-phase motor suits well for printers. The power of the models is quite different. Modifications for unipolar drivers are distinguished by increased current conductivity. The threshold voltage indicator for them is on average 5 V. The rotor is standardly located in the cup. Shafts for models are installed with a diameter of 5 mm. The step angle in the presented configurations does not exceed 2 degrees.

The winding current in this case is 4.5 A. The moment of holding the engine directly depends on the magnetic circuit. If we consider models with high voltage winding, then this parameter averages 3 kg/cm. The gear ratio of the devices does not exceed 1:60. The winding resistance is on average 8 ohms. On the stator in the presented modifications, four outputs are provided for connection. The stepper motor controller for CNC is only found in the bipolar type. A good two-phase modification costs about 5 thousand rubles.

Three-phase models

The three-phase motor is often used for linear actuators. Its threshold voltage indicator fluctuates around 5 V. Modifications with toothed stators come across on the market quite often. The magnetic cores of these models have an indicator of current conductivity at the level of 6 microns. Rotors are made, as a rule, from charge steel. The step angle of the models does not exceed 2.4 degrees. The holding moment in this case depends on the conductivity of the magnetic circuit. On average, this parameter fluctuates around 4 kg / cm.

The gear ratio of the models is 1:63. In terms of winding resistance, the devices differ greatly. The minimum inductance of the motors is 8.5 mH. Devices are manufactured for four and six pins. You can buy a three-phase modification on the market for only 5 thousand rubles.

Motors with ULN2003 driver

Stepper motor for CNC of this type used for its rotor is made of charge steel. The rotor cup itself is made with a high protrusion. The magnetic circuit is installed with a current conductivity of 4 microns. The stator in the device is of a gear type, and the winding on it is provided for low-voltage. The step angle in this case is 2.3 degrees. There are many modifications of the two-phase type on the market. Their winding resistance index does not exceed 8 ohms. The minimum inductance parameter is 10 mH. You can buy a model of this type for 3500 rubles.

5 V modifications

The 5V CNC stepper motor can be manufactured with unipolar and bipolar drivers. Various magnetic circuits are used in devices. Their current conductivity index is on average 5.5 microns. Stator cups are most often made with ledges. Thus, the shaft is gaining momentum smoothly. The step angle of the models does not exceed 1.2 degrees on average.

The limiting current of the winding of the device is maintained at a level of 6 A. The holding torque of the motors is on average 2 kg / cm. In this case, the minimum winding inductance does not exceed 6 mH. There is a good stepper motor for CNC at 5 in the region of 4200 rubles.

10V motors

A 10V CNC stepper motor is often selected for printers that run on unipolar drivers. In this case, there are four outputs in the devices. Directly current conductivity fluctuates around 6 microns. Max Angle step in devices is 2.5 degrees. The winding inductance is at least 8 mH.

It should also be noted that the presented configurations can be used to work with linear actuators. Stators in devices are used cup type. Magnets are only suitable for permanent magnets. They are cylindrical in shape. The holding torque of 10 V motors is on average 4.5 kg/cm. Buy good model for a printer in specialized stores, you can at a price of 5 thousand rubles.

When selecting a stepper motor for CNC, it is necessary to build on the planned scope of the machine and specifications. Below are the selection criteria, the classification of the most popular engines and calculation examples.

How to choose a stepper motor for CNC: criteria

Inductance. The square root of the winding inductance should be calculated and multiplied by 32. The resulting value should be compared with the power supply voltage for the driver. The differences between these numbers should not be much different. If the supply voltage is 30% or more higher than the value obtained, then the motor will heat up and make noise. If less, then the torque will decrease too quickly with speed. Large inductance potentially provide room for more torque. However, this will require a driver with a large supply voltage.
Torque versus speed graph. Allows you to determine whether the selected engine satisfies the conditions in the terms of reference.
Geometric parameters. The motor length, flange and shaft diameter are important.

Advice: you should also pay attention to the ohmic resistance of the phases, the rated current in the phase, the moment of inertia of the rotor, the maximum static synchronizing torque.

engine's type

An important criterion is the type of stepper motor for the CNC machine. Bipolar, unipolar and three-phase models are widely used. Each of them has its own characteristics:

bipolar ones are most often used for CNC due to the simple selection of a new driver when the old one fails, high resistivity at low speeds;
three-phase ones are faster than bipolar ones of the same size. Suitable for when required high speed rotation;
unipolar are several types of bipolar motors, depending on the connection of the windings.

Advice: Another way to select an engine is to analyze finished machines on the market that are close in size and other characteristics to the one being developed.

Examples of calculations for stepper motors for CNC

We determine the forces acting in the system

It is necessary to determine the friction force in the guides, which depends on the materials used. For example, the friction coefficient is 0.2, the weight of the part is 300 kgf, the weight of the table is 100 kgf, the required acceleration is 2 m / s 2, the cutting force is 3,000 N.

To calculate the friction force, you need to multiply the coefficient of friction by the weight of the moving system. For example: 0.2 x 9.81 (100 kgf + 300 kgf). It turns out 785 N.
To calculate the force of inertia, it is necessary to multiply the mass of the table with the part by the required acceleration. For example: 400 x 2 = 800 N.
To calculate full force resistance must be added to the forces of friction, inertia and cutting. For example: 785 + 800 + 3,000. It turns out 4,585 N.

Reference: the resistance force must be developed by the table drive on the ball screw nut.

We calculate the power

The formulas below are presented without taking into account the inertia of the shaft of the stepper motor itself and other rotating mechanisms. Therefore, for greater accuracy, it is recommended to increase or decrease the acceleration requirements by 10%.

To calculate the power of a stepper motor, use the formula F=ma, where:

F is the force in Newtons required to set the body in motion;
m - body weight in kg;
a is the required acceleration m/c 2 .

For determining mechanical power it is necessary to multiply the force of resistance to movement by speed.

Calculate the turnover reduction

It is determined based on the nominal speed of the servo and the maximum speed of the table. For example, the travel speed is 1,000 mm/min, the ball screw pitch is 10 mm. Then the rotation speed of the ball screw should be (1 000 / 10) 100 rpm.

To calculate the reduction factor, take into account the nominal speed of the servo drive. For example, they are equal to 5,000 rpm. Then the reduction will be equal to (5 000 / 100) 50.

Machine tools often use inductor-type stepper motors made in the USSR. We are talking about the models DSHI-200-2 and DSHI-200-3. They have the following characteristics:

Parameter	DSHI-200-2	DSHI-200-3
Power consumption	11.8 W	16.7 W
Step processing error	3%	3%
Maximum static moment	0.46 nt	0.84 nt
Maximum Injection Cleanliness	1000 Hz	1000 Hz
Supply voltage	30 V	30 V
Supply current per phase	1.5 A	1.5 A
single step	1.8 deg	1.8 deg
Weight	0.54 kg	0.91 kg

The calculation examples given are applicable not only to stepper motors, but also to other types of motors. When taking into account the speed, it must be borne in mind that for stepper motors, the frequency is indicated - steps / sec.

Choosing a stepper motor for lifting installation

Choosing a stepper motor for a transport trolley

Determining the torque of a stepper motor in device using screw gears

Torque required from the stepper drive in rotating cylinder system

Determining the moment in mechanisms with rack and pinion

Features of the operation of stepper motors impose very stringent requirements on matching the parameters of the selected motor with a given load. This is especially true in open-loop discrete drive systems, when the passage of at least one control pulse by the engine leads to an error in converting the electrical control signal into an angle that the system is unable to correct. Stepper motors are usually not checked for heating, since they are designed for a long mode of passage of current pulses through the control windings.

When choosing a stepper motor, first of all, you should focus on the power consumed by the drive (motor + control unit) from the network, the supply voltage, the required torque on the output shaft, the shaft rotation speed and the moment of inertia of the load. For the same drive different values supply voltage, the power consumption of the drive P=U*I (voltage*current) is different. For example, the D5779 drive consumes 150W from the network at a supply voltage of 50V, and 90W at a supply voltage of 30V. The efficiency of stepper drives in the frequency range 1 - 5 kHz, as well as the efficiency synchronous motors With permanent magnets is 80-90%.

Drive output power P=M*ω (torque*angular speed). Obviously, the power on the output shaft cannot exceed the power consumed from the network.

The law of conservation of energy for a system consisting of a motor and a load on the shaft rotated by one half step is as follows:

M motor *φ=0.5*J*ω 2 + M load *φ + M magn *φ +M friction *φ

where φ is the angle of rotation

J is the moment of inertia of the system reduced to the shaft

ω - angular velocity

M load - load moment

Mmag is the moment of resistance created by the permanent magnets of the motor, approximately 5% of the M value of the motor

M friction - the moment of friction in the system

Hence the maximum speed with which the stepper motor can take the first step in the system with the moment of inertia J reduced to the shaft and loaded with the load moment M:

ω =(2*φ*(M motor - M load - M magnet - M friction)/J) 1/2

In practice, it is also necessary to take into account the electrical transients in the motor phases, which depend both on the supply voltage and inductance of the motor phases, and on the way the motor is controlled. The most dynamic are the motors with the minimum inductance. Usually starting frequencies are in the range of 800-1000Hz (2-2.5 rpm in half step mode). Based on this, for a stepper motor operating in a half-step mode, the acceleration value should not exceed 4 rad/sec 2 .

When the required torque is determined, the choice of a stepper motor depends on the preferred dimensions, connecting dimensions, the price of the motor and the control unit for it.

If a control unit is already present (or selected), it is necessary that the phase current of the stepper motor does not exceed the capacity of the control unit. You also need to keep in mind the number of pins that can be connected to an existing control unit.

The article contains basic information about the operation of a stepper motor and recommendations on the selection method.

A stepper motor is a constant power device when power is defined as torque times speed. This means that torque is inversely proportional to speed. To understand why motor power is independent of speed, imagine an ideal stepper motor.

Currently, the market is filled with offers of a wide variety of motors for a wide variety of applications, which is not surprising when choosing a stepper motor, even if you have prepared and studied the properties of stepper motors, learned their main property to lose torque with increasing rotational speed and, having estimated the moment of inertia of the load reduced to the shaft, approximately determined what torque at what speeds you need to get from the stepper. So how do you choose a stepper motor and what should you first look at when buying?

1. Motor type - bipolar, unipolar, 3-phase, etc.

None of the types of engines has any radical advantages over others. But each of them has its own small features. So, 3-phase motors are faster - they have less torque than bipolar motors of the same size, but they retain it better, thus they are good to use with gearboxes, in high-speed transmissions. Bipolar - the most common, give a high specific at low speeds, for them it is easy to buy a driver to replace a failed one. Unipolar - are a flexible solution, in fact they contain several types of bipolar motors (depending on how to connect the windings), as well as the actual unipolar 6-pin motor. In the vast majority, bipolar is enough, and if you need a high rotation speed, it makes sense to use a 3-phase motor.

2. Graph of torque versus speed

Main feature. You can refer to this graph and see if this stepper motor can even meet the conditions of your specification.

3. Inductance

Calculate the square root of the winding inductance and multiply by 32, compare the resulting number with the voltage of your driver power supply. These numbers should not differ much - if the supply voltage greatly (30% or more) exceeds the received number, the engine will make noise and heat up; if it falls far short, the torque will decrease with speed too quickly.

4. Geometric parameters

Flange, shaft diameter - important as connecting dimensions. The flange, coupled with the length of the motor, also outlines the "power" of the stepper motor.

Theoretical information about the operating modes of the stepper motor

In an ideal motor, there is no friction, its torque is proportional to the ampere-turns of the windings and the only electrical characteristic is the inductance. Inductance L characterizes the ability of the winding to store energy in a magnetic field. Inductances have the property of inductive reactance, i.e. resistance alternating current, which is the greater, the faster the current changes, which means that inductive reactance increases with engine speed. According to Ohm's law, the current is directly proportional to the voltage and inversely proportional to the impedance, which implies that the winding current decreases with increasing rotational speed. Because torque is proportional to ampere-turns, and current is inversely proportional to speed, then torque will also be inversely proportional to speed. Those. at zero speed, the torque tends to infinity, as the speed increases, the torque (and current) begins to tend to zero.

electrically, real engine differs from the ideal mainly in non-zero winding resistance, as well as ferromagnetic components, which tend to saturate with a magnetic field, which leads to hysteresis losses and eddy current losses. Saturation limits the torque, while eddy currents and hysteresis losses cause the motor to heat up. Consider the stepper motor torque versus speed curve.

As you can see from the graph, at speeds below a certain limit, the torque, and hence the current, increases very quickly, up to levels that damage the motor. To avoid this, the driver must limit the current rise to a certain value. Since the torque is proportional to the current, the torque will be constant from the moment of holding up to the speed threshold, and above the speed threshold, the current will be limited by the inductance of the windings.

As a result, the speed-torque characteristic ideal engine will start from a segment where the torque is constant, to the point when the motor stops generating and consuming reactive power. A real stepper motor has losses that change the ideal speed-torque characteristic. The contribution of the moment from the tooth harmonics is especially large magnetic field(it is sometimes indicated in the documentation for the engine). There are always losses in the motor, and the faster the shaft of the stepper motor rotates, the more loss, and they must also be subtracted from the ideal characteristic

Notice how real power decreases along with an increase in speed, including in the segment of "constant power". The rounding at the transition point is due to the transient process in the circuit - the driver gradually turns from a current source to a voltage source.

Resonance at mid frequencies

A stepper motor is highly susceptible to resonance, being in fact an analogue of a "load suspended on a spring" pendulum, where the rotor is the load, and the magnetic field is the spring, and has a natural oscillation frequency that depends on the current strength and rotor inertia. At the moment when the phase difference of the moment and speed reaches 180 degrees, a resonance occurs - the change in the magnetic field begins to coincide with the speed, and the speed of the rotor when positioning on new step becomes too large. At resonance, a significant part of the energy of the magnetic field is spent on overcoming the inertia of the rotor when it oscillates around the equilibrium position, which is expressed in a significant drop in torque on the shaft. The accumulated kinetic energy of the rotor is consumed when resonance occurs in about 1-10 seconds, so you can accelerate the engine by passing the resonance zone without consequences, but you won’t be able to work for any long time - the shaft will stop. To eliminate this phenomenon, various anti-resonance algorithms are used in drivers.

Engine power

The motor output (speed×torque) is proportional to the voltage divided by the square root of the inductance. If we double the PWM voltage, we get a different CMX curve, which lies higher, and the power in the constant power section will double. Current is a different picture. The figure below shows what will happen when the driver is set to 2 times the nominal current for the motor. The motor begins to generate 4 times more heat, and the moment low revs increases by less than 2 times due to saturation of the winding cores.

As you can see, the power does not increase at all. It is always recommended to set the current on the driver to the nominal value for the motor. This will also reduce vibration at low frequencies, improve the performance of the stroke in microstepping mode.

Supply voltage and motor heating

The main causes of motor heating are winding resistance losses and ferromagnetic losses. The first part is familiar to everyone - this is the thermal energy released on active resistance winding wires, equal to I2R. The contribution of this term is large only when the engine is in the hold mode, and decreases sharply with increasing engine speed. Ferromagnetic losses are called losses due to Foucault currents and hysteresis losses. They depend on the change in current and therefore on the supply voltage, and are released as heat. As mentioned above, the motor power grows in direct proportion to the voltage, however, ferromagnetic losses also grow, and, unlike power, non-linearly, which limits the maximum voltage that can be used for the driver. We can say that the maximum useful power of a stepper motor is determined by the amount of heat that can be safely generated on it. Therefore, you should not try to squeeze half a kilowatt out of a 57 series motor by connecting the driver to a 10 kV source - the voltage has reasonable limits. They can be counted different ways. Empirically, several upper bounds have been obtained for the maximum supply voltage of a PWM driver: it should not exceed the nominal voltage of the windings by more than 25 times, or a value of 32√ L, where L is the winding inductance.

For clarity, below is a graph showing the ferromagnetic losses for a motor with ratings 4 A, 3 V.

Briefly about the power of the stepper motor

The choice of motor and supply voltage depends entirely on the tasks. Ideally, the motor should produce sufficient torque at the maximum intended speed. It is necessary to distinguish between torque and engine power: big moment on low speeds does not mean that the engine is powerful. Output power - different, more important parameter, it can be roughly estimated from the velocity-torque curve. In theory, maximum power, which can be obtained stably from a driver powered by 80 V and a current output of 7 A of about 250 watts (1/3 hp), in reality this would require 2 or 3 NEMA 34 motors. NEMA 23 motors are too small to dissipate heat, and NEMA 42 motors due to size do not fit impedance: if their current rating is less than 7 A, then the voltage will be more than 80 V , and vice versa. The torque from the cog harmonics in NEMA 42 motors is much larger than in small motors and must be taken into account when calculating the output power. In other words, the power output of NEMA 42 motors drops faster than smaller motors. NEMA 42 should be used if high torque is required at low speeds and there is no point in using a geared motor.

WHAT THE CHARACTERISTICS OF THE STEP MOTOR TALK ABOUT

If you omitted everything written above, or read, but did not understand much, this chapter will help you figure out how to move on to the practical part. A few words about the size of the engine. The development of the stepper motor industry has made great strides, and now the stepper motors are one size different manufacturers have very similar characteristics. It is the size of the engine that sets the framework within which it can change main characteristic- speed-torque curve. Inductance windings shows how steep the CMX curve will be with the same supply voltage of the PWM driver: if we take 2 motors of the same size with different inductances, and drive them with one driver with the same supply voltage, the resulting CMX curves will differ in steepness:

More inductance potentially gives you more torque, but to make this conversion, you need a driver with a higher supply voltage - then the CMX curve will rise in proportion to the increase in voltage. In practice, almost all companies produce motors of the same size in two versions - "slow" and "fast", with large and small inductance. Moreover, "fast" models are more popular - for them on high revs less voltage is required, which means cheaper drivers and power supply. And if suddenly there is not enough power - you can take a bigger engine. "Slow" models remain for specific applications - in cases where the stepper drive is not required high speeds, a large holding torque is needed, etc.

Current winding is indirectly related to torque, but basically it tells what kind of driver will need to be selected for this motor - it must be able to deliver exactly this level of current.

Winding supply voltage shows what DC (not PWM) voltage can be applied to the winding - this is the voltage value used by the drivers constant voltage. It is useful when calculating the maximum allowable supply voltage of a PWM driver, and is also indirectly related to the maximum torque.

STEP MOTOR SELECTION ALGORITHM

So how do you choose an engine? Depends on what data you have. By by and large, motor selection comes down to choosing 5 things - manufacturer, motor type, size, phase current and inductance. The first parameter is difficult to assess - few people have a representative sample of samples from different suppliers. As for the type of motor, we recommend whenever there is uncertainty in the choice to use bipolar stepper motors with 4 leads and low inductance. Those. the choice mainly consists in choosing the size of the motor (within the same size, the characteristics of motors with the same inductance of almost all manufacturers are practically the same). For selection specific model you can use the following algorithm:

Calculate top speed rotation V in rev / s that you want to get from the drive, and the moment M that you need to get from it at this speed (put a margin of 25-40% in this value).
Convert the rotation speed to PPS full stride rate, for standard engine in 1.8 deg increments PPS = 200 * V.
Select an engine size that is approximately suitable at first glance, from among available models For this size, choose a motor with a smaller inductance.
Use the manufacturer's CMX curve and find your PPS value on it. Check if the torque indicated on the curve is sufficient.
If the torque indicated on the curve is too small, consider a larger motor, if too large, consider a smaller motor.

However, this method often gives incorrect results due to a large number factors and assumptions in the calculation of the moment. You can easily get that to control a small portal router with a portal weighing 15 kg, ST86-114 motors will suddenly be required. More often, empirical methods are used, and they turn out to be more accurate. One of these methods is to determine the engines by the weight of the portal and the size of the working field. For example, the choice of a stepper motor for a horizontal gear (X and Y axes) can be made based on the weight of the moving part, gear, guides and materials planned for processing. For classic gantry machines, with ball screw transmission, pitch 5 mm per revolution, for processing wood and plastic, speed idle move up to 4000 mm/min, assuming that the steering axles are not preloaded and adjusted so that the moving part runs on them without any resistance, the following values can be recommended:

Another common approach is to analyze off-the-shelf machines on the market that are close to the designed one in terms of dimensions and performance - a proven design means that the motors are already optimally matched and their characteristics can be taken as a basis.

Stepper motors can be found in the device of automotive dashboards, printers, CD-ROM drives, electric tools, in general - everywhere where increased positioning accuracy is required. But the most famous SD received in CNC machines.

But why is this mechanism called that way - "stepper motor"? If you describe it in a nutshell, then it is a brushless synchronous motor with several wire windings. Electricity is fed into one of the windings of the stator (fixed element) and thus fixes the rotor (moving part) in a certain position. Then the current enters the other winding and the rotor makes a new movement. Such a sequential change of position is called a "step". And it is thanks to this principle of operation that the Stepper Motor got its name.

Device and types of SD

Today, there are three main types of stepper motors:

It should be noted that microstepping is possible only in hybrid stepper motors. Each microstep is carried out through independent control of the windings. By controlling the ratio of currents, the rotor can even be fixed in the intermediate section between two adjacent steps. This improves the smoothness of rotation of the movable element and achieves optimum positioning accuracy. The number of steps in this mode can even reach 51,200 per revolution.

Many amateurs are wondering: why was the gear shape of the rotor chosen? The answer is simple: in order to obtain a periodic dependence of the stator winding on the angular position of the rotor. The gap between the grooves is made much larger than between the teeth. This makes it possible to provide a lower magnetic conductivity of the gaps relative to the specific conductivity of the teeth. Otherwise, the stepper motor simply would not be able to function. Obviously, it is the totality of all its design features, as well as the shapes and composition of the elements, allow the stepper motor to be a full-fledged mechanism, and not just a piece of metal.

In addition, depending on the type of windings, stepper motors are divided into:

bipolar. They have one winding for each phase. Changing the direction of the magnetic field in them is provided by reversing the driver - a bipolar half-bridge or bridge;
unipolar. Such a stepper motor also has one winding in each of the phases, but at the same time, a tap is made from the middle of any individual winding. The direction of the field can thus be changed by switching the half winding used. The driver only needs to contain four keys, so it's simpler than a bipolar motor.

Stepper motor characteristics

In the technical documentation for stepper motors, you can find the following list of characteristics:

Torque or Torque. It is measured in kilogram-force-centimetres. Often a graph is attached to this item, which expresses the dependence of torque on speed. The higher this figure, the faster the motor picks up speed when turned on.
holding moment. It shows with what force the stator can block the rotor when the motor is on but not running. That is, it is the torque parameter at zero speed. According to the graph, it decreases in direct proportion to the increase in rotational speed. This is measured in ounces per inch. The holding torque in the measure specified by the manufacturer, the motor can only demonstrate in static mode, provided that the full current is supplied immediately to two phases.
Braking torque. This is the amount of force that keeps the rotor from rotating in the absence of current supply. That is, the locking force of the rotor when turned off. It is also called the stop moment. In hybrid stepper motors, it is no more than a tenth of the force that keeps the rotor from turning when the current is fully applied. This characteristic measured in the same units as the holding moment.
Rated voltage. This indicator directly depends on the inductance of the windings and allows you to determine the optimal voltage that should be supplied to the motor. The best voltage suitable for your stepper motor is between 4 and 25 times the nominal voltage. If you exceed the applied current, the motor will overheat, which will lead to its failure. And if the voltage is not enough, then it simply will not start. This characteristic is indicated in Volts. To calculate optimal strength current, a special formula is used U = 32 x√ L, where L is the inductance of the winding, and U is the desired value.
Separately, the result of dielectric tests is indicated, during which the maximum voltage that the winding can withstand for a certain period of time was determined. This indicator determines the strength of the engine, how successfully it can resist overloads.
Moment of inertia of the moving part of the motor. Determines the speed of stepper motor acceleration. This value is measured in gram-square centimeters.
Number of steps per revolution(only full steps are taken into account, half values are not taken into account). The more steps, the more powerful and faster the engine.
Length and weight. This refers to the length of the body, excluding the shaft. But in the parameter "weight" is indicated total weight products. The dimensions and weight determine the conditions in which the engine can be used. In some cases, you need a compact motor, while in others only a larger and more powerful one will do.

Consider the nema stepper motor as an example. Engine PL57H41, which means the width-height (diameter) of the square flange 57mm - PL57. Engine length, without shaft 41mm - H41. Torque, holding and other moments of the engine depend more on the diameter than on the length of the engine.

Features PL57H110

PL57H110	L, mm	131	Phase inductance, mH	6.0±20%
	Angular step, °	1.8±5%	Phase resistance, Ohm	1.0±10%
	Number of phases	2	Holding moment, kgxcm	28
	Insulation resistance, MOhm	100	Moment of inertia, g x cm 2	405
	Ambient temperature environment, °С	-20~40	Weight, kg	1.7
	Working temperature, °С	110max	Number of shafts	1
	Phase current, A	4	Type
			Keyway size, mm

Features PL86H113

PL86H113	L1 ±1, mm	113	Phase resistance, Ohm	1.0±10%
	L2±1, mm	35	Holding moment, kg x cm	1"
	L3, mm	148	2	2700
	Angular step, °	1.8±5%	Number of shafts	1
	Number of phases	2	Weight, kg	3.5
	Insulation resistance, MOhm	100	Radial runout of the motor shaft (load 450g.)
	Ambient temperature environment, °С	-20-40	Radial runout of the motor shaft (load 450g.)
	Working temperature, °С	110max	Phase inductance, mH	6.3±20%
	Phase current, A	4.2

Connection, drivers and encoders

As a rule, stepper motors are controlled by means of special drivers connected to the computer's LTP port. The driver receives the signals generated by the program and transforms them into commands to the motor, transmitted by applying current to the windings. The software can adjust the trajectory, amount, speed and amount of movement.

The driver is a stepper motor control unit. In CNC machines, control signals are generated on CNC controllers, so 4 stepper motor outputs, control wires from the CNC controller (usually 4 wires) and power + and - from the power supply are connected to the driver. Signals from the controller enter the driver, where they already control the switching of keys power circuit supply voltage coming from the power supply through these keys to the engine.

The driver should be selected according to the maximum output current of the required voltage to the terminals for the motor windings. The current output by the driver must be either the same as the motor will consume, or higher. There are switches on the driver with which you can set the desired output voltage parameters and not burn the engine.

How you connect a stepper motor to a common circuit depends on how many wires you have in your drive and how exactly you want to use the stepper motor. There are a lot of models and each of them has its own connection scheme. The number of wires in the motor can vary from four to six. Four-wire motors are used exclusively with bipolar mechanisms.

Each two windings corresponds to two wires. To determine the necessary pairs and the relationship between them, you will need a meter. The most powerful are six-wire motors. They have a center tap and two wires for each individual winding. Such a stepper motor can be connected to both bipolar and unipolar devices. You will need a special measuring device to separate the wires. For unipolar devices, use all six wires. For bipolar, one central tap and wire for one winding are enough.

The center tap is an ordinary wire, which is also called "middle" or "central". It is found in some types of stepper motors. IN unipolar motors There are three wires for each winding. Two of them are designed to connect to transistors. And the middle one, that is, the center tap, must be connected to a voltage source. That is, if you do not need to connect transistors, you can simply ignore the two side wires.

Five-wire stepper motors are similar to six-wire ones, however, in them the central wires are brought out into one common cable, along with the others. Without breaks, you will not be able to separate the windings among themselves. It is best to find the middle wire and connect it to other conductors - this will be an effective and most not dangerous option.

Encoders are often used with stepper motors. They are simply sensors whose job it is to give signals to the software. Many experts believe that in most cases, combining a stepper motor with encoders does not make sense and is an inefficient waste of money. But if there is a non-linear dependence of movement on the number of steps, when it is necessary to build the fifth coordinate, the encoder will be indispensable. It will make it easier to track the angles of the table, which will save time by eliminating the need for more complex methods.

Applications, pros and cons

ShDs are especially widespread in high-tech and heavy industries. Due to the fact that they are very inexpensive, and they are quite simple, the demand for them does not fade away even in the 21st century. Often you can find them in CNC machines, robotics, automation devices (feeding, dosing, mechanisms automatic welding and assembly, etc.).

Stepper motors are especially popular in the design of coordinating tables and CNC machines. Thanks to the low cost software necessary for their functioning, SDs are indispensable in the manufacturing sector, in control panels, programming and setting tasks, and in other elements of mechanisms.

Stepper motors are often used in computer peripherals, printing machines and devices, milling machines and drawing machines, monitoring and control systems, perforators, tape readers.

Stepper motors compete in popularity with servo motors that can perform similar functions under the same conditions as stepper motors.

Advantages of stepper motors in comparison with servo motors: