A simple bipolar stepper engine with your own hands. Stepper motor control. Software and controller management

I have a lot of different office equipment, which failed. I do not decide to throw it out, but suddenly it will be useful. From its parts it is possible to do something useful.
For example: a stepper motor that is so common is usually used by self-dealers as a mini generator for a flashlight or something else. But I almost never seen it to be used precisely as an engine for transformation of electrical energy into mechanical. It is clear: to control a stepper engine you need electronics. You just do not connect it to the voltage.
And as it turned out - I was mistaken. Stepper motor from the printer or from which device is quite easy to run from alternating current.
I took this engine.

Scheme of stepper engine

• Capacitor with a capacity of 470-3300 μF.
• AC source 12 V.

Delay video

For almost all electrical appliances, special drive mechanisms are needed. We suggest to consider what stepper engine, its design, the principle of operation and the connection scheme.

What is a stepper motor?

The stepping motor is an electrical machine intended for the transformation of the electrical energy of the network into mechanical energy. Constructively consists of stator and magnetic or magnetic solid rotor windings. A distinctive feature stepper Engine It is a discrete rotation at which a specified number of pulses corresponds to a certain number of steps performed. Such devices have the greatest application in CNC machines, robotics, storage devices and reading information.

Unlike other types of machines, the stepper motor makes rotation not continuously, but by steps, from which the device name occurs. Each such step is only part of its total turnover. The number of necessary steps for complete rotation of the shaft will differ, depending on the circuit of the connection, the engine brand and the control method.

Advantages and disadvantages of a stepper electric motor

The benefits of operation of the stepper motor can be attributed:

• In stepper electric motors, the rotation angle corresponds to the number of connected electrical signals, and after stopping the rotation, the full moment and fixation is preserved;
• Accurate positioning - provides 3 - 5% of the set step, which does not accumulate from step to step;
• Provides high start speed, reverse, stop;
• It is distinguished by high reliability due to the lack of driving components for the current collector, unlike collector engines;
• To position the stepping motor, feedback is not required;
• Can produce low revs for directly loaded load without any gearboxes;
• Relatively lower cost relative to the same;
• A wide range of rotation speed control is provided by changing the frequency of electrical pulses.

The disadvantages of the use of the stepper motor include:

• There may be a resonant effect and slipping of the stepper unit;
• There is a probability of loss of control due to the lack of feedback;
• The amount of electricity consumed does not depend on the presence or absence of a load;
• Control complex due to the characteristics of the scheme

Device and principle of operation

Figure 1 shows 4 windings that belong to the engine statist, and their location is arranged so that they are at an angle of 90º relative to each other. What follows that such a machine is characterized by a step in 90º.

At the time of supplying the voltage U1 to the first winding, the rotor is moving on the same 90º. In the event of an alternate supply of voltage U2, U3, U4 to the corresponding windings, the shaft will continue to rotate until the complete circle is completed. After that, the cycle is repeated again. To change the direction of rotation, it is sufficient to change the sequence of feeding the pulses to the corresponding windings.

Types of stepper engines

To ensure various parameters of work, both the step is important to which the shaft and the moment attached to move. Variations of these parameters are achieved by the design of the rotor itself, the method of connecting and designing the windings.

By the design of the Rotor

The rotatable element provides magnetic interaction with the electromagnetic field of the stator. Therefore, its design and technical features Directly determine the operation mode and the parameters of rotation of the stepping unit. In order for in practice to determine the type of step motor, with a de-energized network, you need to turn the shaft if you feel the resistance, this indicates the presence of a magnet, otherwise, this is a design without magnetic resistance.

Reactive

The jet stepping motor is not equipped with a magnet on the rotor, and is performed from magnetic alloys, as a rule, it is typed from the plates to reduce losses to induction. The cross section design resembles a gear with teeth. Poles of stator windings are powered by opposite couples and create magnetic power to move the rotor, which moves from the alternate flow of electric current in the winding pairs.

A significant advantage of this design of the stepper actuator is the lack of a stopping point formed by the field relative to the reinforcement. In fact, this is the same in which the rotor rotor goes in accordance with the Stator field. The disadvantage is to reduce the magnitude of the torque. Step for jet Engine ranges from 5 to 15 °.

With permanent magnets

In this case, the movable element of the stepper motor is collected from permanent magnetin which there may be two and more poles. The rotation of the rotor is ensured by attraction or repelling magnetic poles by an electric field when the voltage is applied to the corresponding windings. For this design, the angular pitch is 45-90 °.

Hybrid

It was designed to combine the best qualities of the two previous models, due to which the unit has a smaller angle and step. Its rotor is made in the form of a cylindrical permanent magnet, which is magnetized along the longitudinal axis. Structurally, it looks like two round poles, on the surface of which the rotor teeth are located from a magnetic material. Such a decision made it possible to provide an excellent holding and torque.

The advantages of the hybrid stepper motor consist in its high accuracy, smoothness and movement speed, with a small step - from 0.9 to 5 °. They are used for high-class CNC machines, computer and office devices and modern robotics. The only drawback is considered a relatively high cost.

For example, we will analyze the option of hybrid shds for 200 steps of the shaft positioning. Accordingly, each of the cylinders will have 50 teeth, one of them is a positive pole, the second negative. At the same time, each positive tooth is located opposite the groove in the negative cylinder and vice versa. Structurally it looks like this:

Because of what a stepper motor shaft is 100 intermittent poles with excellent polarity. The stator also has teeth, as shown in Figure 6 below, except for the gaps between its components.

Due to such a design, you can achieve displacement of the same southern pole relative to the stator in 50 different positions. Due to the differences in the semi-position between the Northern and South Pole, the possibility of moving in 100 positions is achieved, and the phase shift to a quarter of division provides the ability to increase the number of steps due to the sequential excitation, even twice, that is, up to 200 steps of the angular shaft for 1 turnover.

Note Figure 6, the principle of operation of such a stepper motor lies in the fact that with pairwise flow of current in opposite windings, there is tightening of the rotor's variance poles located behind the stator's teeth and the repulsion of the same names going to them along the rotation.

By type of windings

In practice, the stepping motor is a multiphase motor. The smoothness of the work in which directly depends on the number of windings - than them more, the smooth rotation, but also above the cost. At the same time, the torque from the number of phases does not increase, although for normal operation their minimum number on the stator of the electric motor should be at least two. The number of phases does not define the number of windings, so a two-phase stepper motor can have four or more windings.

Unipolar

The unipolar stepper motor is characterized in that there is a branch from the midpoint in the winding circuit. Thanks to which the magnetic poles are changed. The disadvantage of such a design is to use only one half of the available turns, which is why a smaller torque is achieved. Therefore, they are distinguished by large dimensions.

To use the entire power of the coil, the middle output is not connected. Consider the designs of unipolar aggregates, they may contain 5 and 6 conclusions. Their amount will depend on whether the median wire is output separately from each engine winding or they are connected together.

Bipolar

The bipolar stepper motor is connected to the controller after 4 outputs. In this case, the windings can be connected inside both sequentially and in parallel. Consider an example of its work in the picture.

In the design scheme of such an engine, you see with one excitation winding in each phase. Because of this, the change of current requires to use in electronic scheme Special drivers (electronic chips designed to control). It is possible to achieve a similar effect by incorporating a n-bridge. In comparison with the previous, the bipolar device provides the same moment with much smaller dimensions.

Connecting a stepper engine

To power the windings, the device can be able to disperse the control pulse or a series of pulses in a specific sequence. As such blocks, semiconductor devices are served to connect a stepper motor, microprocessor drivers. In which there is a set of output terminals, each of them defines the power method and operation mode.

Depending on the connection scheme, those or other conclusions of the stepping unit should be applied. For different options Summing out those or other terminals to the DC output signal obtains a certain speed of rotation, a step or microsgg of linear movement in the plane. Since there is a low frequency for some tasks, and for others is high, the same engine can specify the parameter at the expense of the driver.

Typical SCD Connection Schemes

Depending on how the number of conclusions are presented on a specific step motor: 4, 6 or 8 of the conclusions, it will be different and the possibility of using a particular connection circuit will look into the pictures, here are typical options for connecting a step mechanism:

Subject to the main poles of the stepper from the same driver, according to these schemes, the following distinctive features of the work can be noted:

• The conclusions are uniquely summed up to the appropriate terminals of the device. With a serial connection of the windings increases the inductance of the windings, but lowers the current.
• Provides passport value electrical characteristics. With a parallel diagram, the current increases and the inductance decreases.
• When connected one phase on the winding, the moment will decrease on low revs and reduces the current values.
• When connected, all electrical and dynamic characteristics According to the passport, rated currents. Significantly simplifies the control scheme.
• Gives a much larger point and is used for high rotational frequencies;
• As the previous one is designed to increase the moment, but is used for low speed.

Stepper motor control

Performing operations by a stepping unit can be carried out by several methods. Each of which is characterized by the method of feeding signals to pairs of poles. Total identification of the Activation method of the windings.

Wave - In this mode, only one winding is excited, to which rotary poles are attracted. In this case, the stepper motor is not capable of pulling out a large load, as it gives only half of the moment.

Full-step - In this mode, there are simultaneous switching phases, that is, both are excited immediately. Because of which the maximum moment is ensured, in the case of a parallel connection or sequential turning on the windings, the maximum voltage or current will be created.

Hemisphan - is a combination of two previous switting methods of windings. During the implementation of which in the step motor, an alternate voltage flow occurs first into one coil, and then at once in two. Thereby ensuring the best fixation on maximum speeds And more steps.

For softer control and overcoming the inertia of the rotor, microshop control is used when the signal sinusoid is carried out by microstable pulses. Due to which the power of the interaction of magnetic circuits in the stepping motor receive a smoother change and, as a result, moving the rotor between poles. Allows you to largely reduce stepping engine junction.

Without controller

For driving incattle engines The H-bridge system is used. Which allows you to switch polarity for a stepping motor reverse. Can be performed on transistors or chips that create a logical chain to move the keys.

As you can see, the voltage is served from the power source V. When pairwise activate contacts S1 - S4 or S3 - S2, current will occur through the engine winding. What causes the rotation in one direction or another.

With controller

The controller device allows you to control the stepping motor in various modes. The controller is based on the electronic unit, Forming a group of signals and their sequence sent to the coil of the stator. To prevent the possibility of damage in the event of a short circuit or other emergency on the engine itself, each conclusion is protected by a diode that does not miss the impulse in the opposite direction.

Popular SCD Schemes

It is one of the most obstacle ways of work. In this case, the direct and inverse signal directly connects to the corresponding poles. This scheme should apply the screening of the signal conductor. Perfectly suitable for load with low power.

In this diagram, there is a combination of positive inputs of the controller, which are connected to the positive pole. In the case of power above, 9V requires inclusion in a special resistor scheme to limit the current. Allows you to set the required number of steps with a strictly installed speed, determine acceleration, etc.

The simplest stepping motor driver do it yourself

To assemble the driver scheme at home, some elements from old printers, computers and other equipment can be useful. You will need transistors, diodes, resistors (R) and chip (RG).

To build a program, follow the following principle: when applying to one of the outputs D logical unit (the remaining zero signals), the transistor is opening and the signal passes to the engine coil. Thus, one step is performed.

Based on the diagram, the printed circuit board is drawn up, which can be treated to make independently or to undergo. After that, the corresponding details are sold on the board. The device can control the step device from the home computer by connecting to the usual USB port.

Useful video

In this article, I will describe the entire cycle of the stepping electromotor driver for experiments. This is not a final option, it is designed to manage one electromotor and is necessary only for research, the scheme of the end-driver stepper driver will be presented in a separate article.

In order to make a stepping motor controller, it is necessary to understand the principle of operation of the stepping electrical machines themselves and what they differ from other types of electric motors. And the varieties of electrical machines there are a huge set: DC, AC. AC electric motors are divided into simultaneous and asynchronous. I will not describe each type of electric motors, I will not become so, as it goes beyond the scope of this article, I will only say that each type of engine has its advantages and disadvantages. What is a stepper electric motor and how to manage?

The stepping motor is a synchronous brushless motor with several windings (usually with four), in which the current supplied to one of the stator windings causes the rotor fixation. Sequential activation of the engine windings causes discrete angular movements (steps) of the rotor. The conceptual electrical circuit of a stepper motor gives an idea of \u200b\u200bits device.

I applied as strength keys The IRF634B transistors are the maximum voltage source-flow 250V, flow current 8,1A, this is more than enough for my case. With the scheme less figured out we will draw pCB. Painted in the built-in Paint editor, I will say this is not the best idea, next time I will use some specialized and simple editor of printed circuit boards. Below is a drawing of a finished circuit board.

Next, this image in the mirror reflection is printed on paper using a laser printer. The brightness of the print is best to make the maximum, and the paper needs to use not the usual office and glossy, conventional glossy magazines are suitable. We take a leaf and typing over an existing image. Next, the resulting picture apply to a predetermined piece of foil fiberglass and a good stroke in the iron for 20 minutes. Iron need to heat up to maximum temperature.
How to prepare Textolol? Firstly, it needs to be cut into the size of the image of the printed circuit board (with the help of metal scissors or hacking for metal), secondly sanding the edges of small emery paper so that there are no burrs. It is also necessary to walk the sandpaper on the surface of the foil, remove oxides, the foil will acquire a smooth reddish tint. Next, the surface treated with emery paper should be wiped with a cottage moistened to the solvent (use 646 solvent it also stinks).
After warming up the iron, the toner from paper is baked on the surface of the foil glassstolite as an image of contact tracks. After this operation, the paper fee must be cooled to room temperature and put in the bath with water for about 30 minutes. During this time, the paper will rays and it needs to be carefully rolling with the pillows of the fingers from the surface of the textolite. On the surface will remain smooth black traces in the form of contact tracks. If you did not manage to transfer the image from paper and you have flaws, then the toner should be flushed from the surface of the textolite with a solvent and repeat everything again. I did everything from the first time.
After receiving the high-quality image of the tracks, it is necessary to raise the extra copper, for this we will need the etching solution that we will prepare themselves. Previously, for etching printed circuit boards, I used a copper vigorous and a conventional cook salt in a ratio of 0.5 liters of hot water 2 tablespoons with a slide of copper mood and a cook salt. All this was carefully stirred in water and the solution is ready. But this time I tried a different recipe, very cheap and affordable.
Recommended method for the preparation of the pools:
In 100 ml of pharmacy 3% of hydrogen peroxide dissolves 30 g citric acid and 2 teaspoons of a cook salt. This solution should be enough to etch the area of \u200b\u200b100 cm2. Salt in the preparation of the solution can not be sorry. Since it plays the role of the catalyst and in the etching process is practically not consumed.
After the preparation of the solution, the printed circuit board must be omitted into the container with the solution and observe the process of etching, the main thing is not to reveal. The solution will eat uncovered toner surface of copper as soon as this will take place to get and rinsed with cold water, then it needs to dry and remove the toner from the surface of the tracks using the rolling and solvent. If your board provides holes for fastening radio components or fasteners, it's time to drill them. I lowered this operation due to the fact that it is just a stepper motor dye intended for the development of new technologies for me.
We proceed to the luggage of the tracks. It must be done to make it easier for soldering. I used to be thin with solder and rosin, but I will say this "dirty" way. From rosin a lot of smoke and slag on the board that will need to wash off the solvent. I applied another method, the lentation of glycerin. Glycerin is sold in pharmacies and worth a penny. The surface of the board must be wiped with a mock-moistened in glycerin and apply fine smears with a solder. The surface of the tracks is covered with a thin layer of solder and remains clean, excess glycerin can be removed with a rut or rinse in water with soap. Unfortunately, I do not have a photo of the result obtained, after the meadow, but the resulting quality is impressive.
Next, you need to solder all radio components on a fee, I used tweezers for soldering SMD components. Glycerin used the flux. It turned out very carefully.
The result is obvious. Of course, after the manufacture, the board looked better, in the photo it is already after numerous experiments (for this it was created).

This control program makes one full turn of the stepping motor shaft, after a break lasting in one second, repeated to infinity. It is possible to experiment with the speed of rotation, the direction of rotation as well as corners of turns.

Stepper Engine Driver on Transistors

I present to your attention a bipolar stepping motor driver on bipolar transistors of the "CT" series.

The driver works on the principle of the emitter repeater. The control signal enters the stage of gain assembled on the CT315 transistor. After that, it will fall on the bridge from the complementary pair of KT815 and CT 814.

Strengthening cascade is necessary because current power output from the microcontroller is not enough for opening of power transistors. After power transistors, self-induction diodes are installed.

Also in the diagram there is provided interference in the form of condensers by 3 by 0.1 μF and 1 per 100 μF. Since the driver was designed to work with a 150 watt drive CD engine, cooling on transistors

Stepper motor from CD drive connected to the driver on transistors

it was established, but the maximum current of the emitter of transistors KT814 and KT815 is 1.5 A, making the drivers and more powerful. To do this, you need to install cooling plates on power transistors.

The article provides fundamental schemes of options for a simple, inexpensive stepping motor controller and resident software (firmware) for it.

General description.

The stepping motor controller is designed on PIC PIC12F629 controller. This is 8 output microcontroller worth a total of $ 0.5. Despite the simple scheme and low cost of components, the controller provides fairly high characteristics and broad functionality.

• The controller has options for controlling both unipolar and bipolar stepper motor.
• Provides engine speed adjustment over wide range.
• It has two steps control modes:
  • full-step;
  • hemisphan.
• Provides rotation in direct and reversing directions.
• Setting modes, parameters, controller control is carried out by two buttons and ON (inclusion) signal.
• When the power is turned off, all modes and parameters are saved in the non-volatile memory of the controller and do not require reinstallation when turned on.

The controller does not have protection against short-circuits of engine windings. But the implementation of this function complicates significantly complicates the scheme, and the closure of the windings is the case is extremely rare. I did not come across such. In addition, the mechanical stop of the stepping motor shaft during rotation does not cause dangerous currents and the driver protection does not require.

About modes and methods for managing a stepper motor can be read about divers.

The diagram of the unipolar stepper motor controller with the driver on bipolar transistors.

Explain in the scheme especially nothing. To the PIC controller connected:

• buttons "+" and "-" (through analog input of the comparator);
• oN signal (engine power on);
• driver (VT1-VT4 transistors, VD2-VD9 protective diodes).

PIC uses an internal tact generator. Modes and parameters are stored in the internal EEPROM.

The driver diagram on bipolar transistors KT972 provides a switching current up to 2 A, the voltage of the windings up to 24 V.

I saved the controller on the sizes with dimensions of 45 x 20 mm.

If the switching current does not exceed 0.5 A, the transistors of the BC817 series can be used in SOT-23 enclosures. The device will turn out quite miniature.

Software and controller control.

Resident software is written on an assembler with a cyclic reinstalling of all registers. The program will not depend in principle. Download Software (firmware) for PIC12F629.

Controller control is sufficient.

• With the active signal "ON" (closed on the ground) the engine is spinning, with inactive (cut off from the Earth) - stopped.
• When the engine is running (the ON signal is active), the "+" and "-" button changes the speed of rotation.
  • Each pressing on the "+" button increases the speed to minimal discreteness.
  • Pressing the "-" button - reduces speed.
  • When holding the "+" or "-" buttons, the rotation speed increases smoothly or decreases, by 15 discreteness values \u200b\u200bin sec.
• When the engine is stopped (the ON signal is not active).
  • Pressing the "+" button sets the rotation mode in the forward direction.
  • Pressing the "-" button translates the controller to reversible rotation mode.
• To select the mode, a full-step or semi-step needed when power is applied to the controller, hold the "-" button is pressed. Motor control mode will be changed to another (inverted). It is enough to withstand the button - pressed for 0.5 seconds.

A diagram of the unipolar stepper motor controller with a driver on MOSFET transistors.

Low-threshold MOSFET transistors allow you to create a driver with higher parameters. Application in the MOSFET transistors driver, for example, IRF7341 gives the following advantages.

• Resistance to transistors in open state no more than 0.05 ohms. It means a small voltage drop (0.1 V at a current 2 A), transistors do not heat, do not require cooling radiators.
• Transistor current up to 4 A.
• Voltage up to 55 V.
• In one 8, the output case SOIC-8 placed 2 transistors. Those. The execution of the driver will require 2 miniature buildings.

Such parameters cannot be achieved on bipolar transistors. With switching current, over 1, I highly recommend the versions of the MOSFET transistors.

Connecting to the controller of unipolar stepper motors.

In unipolar mode, engines with winding configurations 5, 6 and 8 wires can operate.

Connection diagram of a unipolar stepper motor with 5 and 6 wires (outputs).

For FL20STH, FL28STH, FL35ST, FL39ST, FL42STH, FL57ST, FL57STH, FL57STH with configuration of windings 6 wires, the conclusions are marked with the following colors.

Configuration with 5 wires is an option in which the shared winding wires are connected inside the engine. Such engines are. For example, PM35S-048.

Documentation on the PM35S-048 stepping motor in PDF format can be downloaded.

Connection diagram of unipolar stepper motor with 8 wires (outputs).

The same as for the previous version, only all connections of the windings occur outside the engine.

How to choose a voltage for a stepper motor.

According to the Ohm's law through the winding resistance and the permissible phase current.

U \u003d Iphazy * Robs

DC winding resistance can be measured, and the current must be signed in reference data.

We emphasize that we are talking about simple drivers that do not provide a complex current and voltage form. Such modes are used at high speeds of rotation.

How to determine the windings of stepper motors if there is no reference data.

In unipolar engines with 5 and 6 conclusions, the average output can be determined, measuring, resistance to windings. Between the phases, the resistance will be twice as large as between the middle conclusion and phase. Average conclusions are connected to the power supply plus.

Further, any of the phase conclusions can be assigned to phase A. 8 There will be 8 options for plotting. You can go through them. If we consider that the winding of the phase B has a different average wire, then options becomes even less. Forehead of the windings of the phase does not lead to the failure of the driver or engine. The engine rattles and does not spin.

It is only necessary to remember that the speed of rotation is too high to the same effect (output from synchronization). Those. It is necessary to install the speed of rotation.

Bipolar stepping motor controller circuit with L298N integrated driver.

Bipolar regime gives two advantages:

• an engine can be used with almost any configuration of windings;
• about 40% increases torque.

Create a Bipolar Driver Scheme on Discrete Elements - Ungrateful Cause. It is easier to use the L298N integral driver. The description in Russian is.

The controller circuit with the L298N bipolar driver looks like this.

The L298N driver is included in the standard diagram. Such an option of the controller provides phase currents up to 2 A, voltage up to 30 V.

Connecting to the controller of bipolar stepping motors.

In this mode, an engine can be connected with any configuration of windings 4, 6, 8 wires.

Connection diagram of bipolar stepping motor with 4 wires (outputs).

For engines FL20STH, FL28STH, FL35ST, FL39ST, FL42STH, FL57ST, FL57STH with the configuration of windings 4 wires, the conclusions are marked with the following colors.

Connection diagram of a bipolar stepping motor with 6 wires (outputs).

For ENGINES FL20STH, FL28STH, FL35ST, FL39ST, FL42STH, FL57ST, FL57STH with such a configuration of windings, the conclusions are marked with the following colors.

Such a scheme requires supply voltage twice as compared to unipolar inclusion, because The resistance of the windings is twice as much. Most likely, the controller must be connected to 24 V.

Connection diagram of a bipolar stepping motor with 8 wires (outputs).

There may be two options:

• with successive inclusion
• with parallel inclusion.

Scheme of serial inclusion of windings.

The scheme with sequential turning on the windings requires two times more voltage of the windings. But the phase current does not increase.

Diagram of parallel inclusion of windings.

The scheme with parallel turning on the windings increases 2 times phase currents. The advantages of this scheme can be attributed, low inductance of phase windings. This is important at high speed rates.

Those. The choice between the sequential and parallel inclusion of a bipolar stepper engine with 8 leads is determined by the criteria:

• maximum drive current;
• maximum driver voltage;
• engine rotation speed.

Software (firmware) for PIC12F629 can be downloaded.