For this or that electric device to work, it requires a special drive mechanism. One of these mechanisms is a stepper motor. In this article you will learn what it is, what is the principle of its work and what categories it is divided into.
- 1 What is a stepper motor?
- 2 Principle of operation of the drive
3 Types of stepper motors
- 3.1 Two phase stepper motors
- 3.2 Reactive stepper motors: features and principle of operation
- 3.3 Synchronous linear stepping motors
- 4 In what modes is the synchronous stepping motor capable to work?
- 5 Stepping motor connection features
- 6 Key engine specifications
- 7 Average cost of a stepper drive in large cities of Russia and Ukraine
What is a stepper motor?
A stepper motor can be unipolar or bipolar. It is electric and brushless. constant current motorcapable of dividing a full turn into several identical steps. It includes such details:
- special controller for stepper;
- magnetic parts;
- dashboard (it also acts as a control unit);
- signaling devices.
The stepper motor is mainly used for the following purposes:
- works of the milling machine;
- grinding machine;
- ensures the operation of various household appliances;
- work of mechanical production;
- provides the work of transport.
Principle of operation of the drive
The principle of operation of this drive is as follows. When voltage is applied to the terminals, the brushes on the stepping motor itself begin to move constantly. The idle has a unique feature: converts incoming pulses, having mainly rectangular orientation, in in advance designated position of the applied drive shaft.
Each of the incoming pulse is able to move the shaft at a certain angle. Instruments that are equipped with a similar gearbox have maximum efficiency, subject to availability several toothed electromagnets that are located around a central iron piece having gear shape. An external control circuit energizes an electromagnet. If necessary, turn the motor shaft, the electromagnet, to which energy is applied, attracts the teeth of the wheel. When they are aligned with the electromagnet, they are offset with respect to the subsequent magnetic part of the engine.
The first electromagnet turns off, and then the second turns on, after which the gear begins to rotate, aligning with the previous wheel. Then this action is repeated the required number of times. Each of these rotations is called a constant step, and the rotational speed of a stepper motor can be calculated by counting the number of steps needed for its complete rotation.
To control the operation of a stepper motor, a special driver is used. This is necessary in those cases, if you configure the drive for the operation of the machine or use it to run the wind generator.
Types of stepper motors
Stepper motors are classified into the following types:
- with the presence of a permanent magnet;
- synchronous hybrid drive;
- variable motor
All of them are somewhat different from each other, including in the principles of their work.
For example, permanent magnet drives are equipped with a special magnetic part in the rotor. Such engines operate on the principle of attraction or repulsion stator and rotor of the motor on the basis of an electromagnet.
Variable engine has an ordinary iron rotor and its work is based on the principle of fundamentality. When a minimum level of repulsion is allowed with the smallest gap, the rotor points have an attraction to the stator poles.
But the hybrid drive can combine both principles of operation, it is considered the most expensive model of stepper motors.
Two phase stepper motors
The two-phase motor is very simple, it can be installed to a person without special experience. Regardless of whether you assembled it yourself or purchased it as a finished product, it has two types of winding for the coils:
If a stepper motor has one winding with a central magnetic valve affecting each phase, then this is a unipolar drive. Each winding section should be included in order to ensure the desired direction of the magnetic field. In this drive, the magnetic pole is able to function without the need for additional switching, therefore current directions and circuit switching are very simple, using one transistor for each winding. This takes into account phase switching:
- three wires per phase;
- six per output.
The microcontroller of the motor drive can be used to activate the transistor in one sequence or another.
And the windings can also be connected by touching the connection wires together with the drive permanent magnets. When connecting the coil terminals, it will be difficult to turn the shaft. Resistance between coil end and common wire equal to half the resistance Reel and wire ends. This is because the common wire is longer than the half part used to connect the coils.
Bipolar stepper motors have one phase winding, in which the current flows through a turning point using a magnetic pole. In this case, the control system will be complicated using a connecting bridge. There are two wires per phase, but they are not common. By mixing a stepper motor signal at high frequencies, the friction effect of the system can be reduced.
In addition, another type of stepper motor is three-phase, but its scope is too narrow:
- during the operation of CNC milling machines;
- on some cars where the throttle is used;
- on the drive and printers of some brands.
Reactive stepper motors: features and principle of operation
It is worth noting that active stepper drives have a big disadvantage: it is a major step, reaching several tens of degrees. In contrast, reactive stepper motors are able to reduce the rotor frequency, thanks to which the step becomes angular less than a degree.
The main feature of the jet drive is that the teeth are placed on the stator poles. The synchronizing moment in it is provided by the difference of magnetic resistances along the transverse and longitudinal axis of the drive.
Jet stepper motor has one key flaw: it has missing sync momentif the stator windings are de-energized.
It is possible to increase the degree of reduction of the engine, regardless of which, active or reactive, using multi-packet constructions, when the stator teeth are shifted on each other by part of the division, and the rotors of each package do not move and the axes of their poles the same. Similar the design is very complicated in terms of creating and it is expensive in the finished form, it also requires a complex switch.
To date, the sale can find a huge number of various designs of engines that differ in parameters such as:
- number of phases;
- type of winding placement;
- ways of fixing the rotor, etc.
In inductor stepper motors, the torque is created by the interaction of the magnetic field, which is created by the stator windings and a permanent magnet located in the gear part of the gap.
The synchronizing moment in the inductor motor itself is reactive, which results in a stator winding, and a permanent magnet is able to create a moment of fixation, so that the rotor is held in the desired position with no current.
Unlike the jet stepper motor, the inductor, with a similar step, has a greater synchronizing moment, as well as more improved technical characteristics.
Synchronous linear stepping motors
In order to automate some production processes in an enterprise, sometimes it becomes necessary to move objects in the plane. To do this need to use a special converter rotational motion in translational, which is achieved by applying kinematics.
With the help of linear stepper motors, you can convert a pulse command directly into a linear displacement, which greatly simplifies the kinematic scheme of various electric drives.
The stator in this drive is presented in the form of a magnetically soft plate, and the wires are magnetized by the operation of a permanent magnet.
Tooth divisions in the stator and the movable part are the same, while they can be shifted by half division within one rotor wire. The bias flux and its magnetic resistance, in this case, do not depend on where the moving part of the engine is located.
To move an object in a plane according to two coordinates, two-coordinate engines are used.
Also in the linear motors used magnetic air suspension. Due to the strength of the magnetic attraction, the rotor is attracted to the stator. Further air is forced through the nozzles under the rotor in a compressed form, as a result, a force appears that repels the rotor from the stator. So between them there is an air cushion and the rotor hangs above the stator with the presence of a minimum gap. This provides a minimum of rotor movement resistance and high-precision positioning.
In what modes is the synchronous stepping motor capable to work?
The drive is able to work steadily in the absence of loss of steps during the development of the angle when applying to the control windings a pulse series. When working out each step the rotor has a steady balance in relation to the vector of magnetic induction relating to the magnetic field of the stator.
The mode of testing each step should correspond to the number of control pulses that are fed to the drive winding, and he, at the same time, before the arrival of the next pulse, must work out the angle given to him rotation. At the beginning of each step, the angular motor speed should be zero.
Allowed oscillations of the angular drive shaft with respect to the steady-state value. They are caused by the presence of kinetic energy, which is accumulated by the motor shaft during corner mining. At the same time, energy is able to transform into losses:
The greater their value, the faster the process of transition of one-step working out by a drive ends.
When starting, the rotor may lag the stator flow a step or even more, resulting in a discrepancy between the number of rotor steps and the stator flow.
The key characteristics of a stepper motor are:
- ultimate mechanical performance;
The limiting characteristic is the dependence of the maximum possible synchronizing moment on the frequencies of the control pulses.
And the pickup rate is the frequency of these pulses, which eliminates the possibility of losses or step additions during processing. Intake considered a key indicator mode of transition in the engine. It is able to grow with the synchronizing moment, the decrease of the step, the inertial moment of linearly moved or rotated particles, as well as the static moment of resistance.
Stepping motor connection features
A stepping motor can be connected according to one or another scheme, which depends on the number of wires and methods of starting.
Engines may have four to eight wires. If there are only four of them, then the engine can only be used with a bipolar device. Each phase winding, which is only two, is equipped with two wires. Determine the wired pairs should be using a meter, then the driver is connected step by step.
The motor, equipped with six wires, includes two wires for each winding and a central crane, also for each of them. It can be connected to both unipolar and bipolar devices. To separate the drive a special device should be used for measuring. A drive can be connected to a unipolar device using all six wires, and to a unipolar device there will be enough one end and one central tap from each winding.
The five-wire motor practically does not differ from the previous one, however, its central terminals are internally connected as one solid cable and have one output to one of the wires. Do not separate the windings from each other, otherwise you can break them. Instead, it is better to determine the center of the wire and connect it to other conductors, this will be the most efficient connection solution. After that, you can connect the device itself and check it for operability.
Key engine specifications
The primary winding at a constant current creates a rated voltage. And the initial speed of the drive torque varies with the current. From what the motor circuit and from the inductance of its windings depends on the time of reduction of the linear moment at higher speeds. Some engine brands with IP65 protection are able to work in the most difficult conditions.
If you want to choose a ready-made model of a domestic-made stepper motor, pay attention to the main specifications most famous models:
- SD-1 - degree step is equal to 15, 4 phases, torque is 40 Nt;
- LH-0.04A - degree of pitch 22.5, 4 phases, torque 100 Nt;
- DSHI 200 - degree of pitch 1.8, 4 phases, torque 0.25 Nt;
- LH-6 - degree step - 18, 4 phases, torque 2300 Nt.
Also among the buyers in demand are such models as:
- four-phase DSR-40;
- Purelogic R & D with encoder;
- NEMA 23;
When selecting the right engine, it is necessary to calculate the parameters of power, voltage and torque.
One of the problems with the operation of a stepper motor is the control of instruments in the absence of a controller. To cope with this, should take a special block of logical connection, helping to control the engine in the absence of an appropriate microcircuit. However, it is best to control the operation of stepper motors using a special controller.
Average cost of a stepper drive in large cities of Russia and Ukraine
The cost of this device depends directly on indicators such as:
- engine's type;
- construction power;
The average cost of a unipolar stepper motor is:
- Moscow - 3000 cu.
- St. Petersburg - 3500 cu.
- Kiev - 3500 cu.
- Kharkiv - 4000 USD
So, we told what a stepping motor is, what principle it works in, which categories it is divided into and which properties it differs from. We hope that this will facilitate your choice if you need to purchase this device.