Stepper motors aren’t any different in their design, but their preferred applications classify them as an entirely separate category. It’s important to understand the way they operate and what differentiates them as at times, at first glance, they may appear to be a twinned version of motors of different types.
The stepper motor is an electric motor that converts the energy flowing through it into circular motion. It operates on direct current and is able to have virtually any size or torque. The term “stepper motor” refers to a stepper motor, as the name implies, is when it is powered by the windings it will take one “step” instead of rotating in a continuous manner. Every step represents a single rotation of a precisely defined angle by the manufacturer of the motor like 1.2deg. This stepper motor has no brushes which is why it is part of the class of DC brushless motors.
It is possible that the stepper motor will not start spinning when you connect the power source to it. It’s necessary to turn the power supply’s windings in the proper sequence. Each switch will trigger a specific angle (the previously mentioned step).
What can an stepper motor built?
Contrary to the brushed DC motors In this stepper motor the ferromagnetic was located in the rotor and the windings in the stator. This allowed it to completely eliminate the mechanical commutator. Moving the motor can be accomplished by alternating the power supply between successive windings.
For permanent magnets, winds directly contact those poles on the rotor made up of magnets. If one of the windings is energized by the generated magnetic field exerts force on the rotor and causes it to spin in a narrow angle. Following this you can ignite the next winding, and then spin the shaft once more. A lot of times, the repulsion between the poles of the rotor is utilized simultaneously because of the reverse direction of the power supply. That is, some winds “attract” and others “push” the rotor’s rotation.
A magnet is always able to create one pair of poles. For stepper motors, there may be additional magnets inside the rotor. Also, the number of magnetic pairs within the rotor is a different factor that the manufacturer defines its motor.
Variable reluctance motors where the rotor is made of an iron cylinder with notched grooves in place of a magnet, operate differently. The operation involves altering the rotor in so that the reluctance, also known as “resistance” to the magnetic field, is as minimal as it is possible. This will happen when the protruding portions of the rotor (in the shape as “teeth”) coincide with the protruding portions of the stator.
Permanent magnet motors are more powerful and have greater torque and variable reluctance motors have higher speeds, and are less expensive and more quiet. Unsurprisingly, a blend of these two technologies is also being tested. hybrid motors have been developed that combine the benefits of both options, but they’re more expensive than their counterparts.
What are the advantages of stepper motors
Stepper motors offer a significant advantage over brushes in situations which require precise movement of the shaft at an angle that is set and maintained to ensure the greatest torque possible. One illustration of such a machine is the CNC milling device, where motors must rotate through the spinning wheel (or the material being milled) with incredible precision, while simultaneously applying the pressure from the cutter rotating towards the object being milled.
There are, of course, options to use brush motors to accomplish this. However, this will require the use of shaft positioning sensors (encoders) as well as advanced controllers that can measure current that significantly increase the cost. It’s more efficient to employ the stepper motor, in which the movement of the shaft can be controlled precisely even without the addition of sensors. This is known as open-loop control, which is with no feedback regarding the direction that the shaft is in.
The result of this solution isn’t just the ability to rotate to an angle of a specific degree however, it also allows for maintaining very low speeds with no additional mechanical gears.
It is possible to construct the clock with a pointer attached to the motor’s shaft stepper motor and rotates at one revolution every day, and then begin to count the seconds with a speed of 1.25 revolutions per minute. If you have other motors, this an idea may be difficult to build.
The most significant benefit is that it does not have wear-prone components (except in the case of bearings). Also, there is no sparking in commutation and it is able to be utilized without worry for instance, in environments that contain explosive gases that could cause explosion.
What are the disadvantages of stepper motors
The main drawback of stepper motors is that they are more difficult to control, i.e. to manage the proper electronic commutation. While off-the-shelf controllers are able to be utilized, their use isn’t as simple than wiring power directly to brush motor’s wires. A wrong control leads to an uncontrolled motion of the rotating shaft and may end up causing permanent damage to the motor.
Stepper motors operate like a stop-blow motor. They allow as they allow as much current to flow through the wires as it can be drawn from a particular power source. This is why it is essential to keep an eye on the current flowing through it, and limit it to the maximum value , or else you’ll cause the windings to burn.
Another issue is the severely restricted maximum speed. Although speeds of tens or thousands of rotations per minute are typical in brush motors that exceed 1,000 aren’t often utilized in stepper motors. In addition, increasing the speed can render the rotor ineffective to keep pace with the electromagnetic field that is rotating which causes it to stop producing torque and to stand to oscillate at a slight. Microstep control can further limit this by limiting the maximum speed.
Another issue is called lost steps. That is, when motors aren’t capable of performing a move with a fixed angle, as an example, with too much stress. This is a serious issue in the case of relying solely on open loop control. A controller for a 3D printer could “think” that the head is moving by 1 cm but in reality it was in a still position. If it begins its job and again, the rest portion of the printing will shift by one centimeter along one direction.
The problem can be resolved by three different ways. You can increase the size of the motor you’re making use of, i.e. pick a motor with an adequate reserve of torque. Also, you can utilize negative feedback for the controlling, i.e. include an encoder, as an instance. Additionally modern controllers come with an integrated system to detect the lost steps. So even if this issue can’t be avoided, at the very least it is possible to react such as by suspending the device’s operation or informing users of the problem.
Stepper motor controller
When looking at the properties of a stepping engine, it is essential to consider not just the characteristics that result from the structure of the motor and also the motor and the control system in its entirety. The sole focus on the motor provides a non-complete image. The control system plays significant function in shaping the features for stepper motors.
The basic advancement of stepper motors is in the direction of increasing the amount of strokes that can be performed,
efficiency and torque, while reducing the mechanical inertia. The steps of the stepper drive are defined by the design and mechanical characteristics of the object and the motor, as well as the magnetic and electrical components of the motor, the method of providing its windings andthen, lastly control algorithm.
Bipolar and unipolar control of stepper motors
Among stepper motors, there are two basic types: unipolar and bipolar.
A bipolar motor that has two phases has one winding for each phase, whereas a unipolar motor has only one winding per phase, Winding, with a tapping on the center. There are motors that feature two windings each phase. They are able to be operated in unipolar as well as bipolar modes. When bipolar control is enabled, all of the winding band participates in the operation, while when using unipolar control, half of the band is active simultaneously.
In a bipolar drive, the use of a two-position switch or two transistors which are turned on in a cycle can alter the magnetic field inside the center. In a single-phase motor one transistor per phase is enough to control the current.
Unipolar control allows that current flows in a winding only in one direction while bipolar control guarantees that current flows across two different directions. The benefit of the unipolar alternative is that it is simpler and a lesser amount of transistors. the drawback can be that it only works for half the winding is operating at once, which means the full force of torque isn’t produced.
The benefit of bipolar controls is a high torque utilization because the entire winding is in its condition it is in whenever a pulse is received.
In general, bipolar motors require a more elaborate control system. This issue was resolved with the introduction of special power ICs that contain two transistor bridges that can key important currents.
In wave control otherwise known as single-phase control, one phase is energized at any given time. The order of their operation is A-B-A’-B’. The result of this type of control is the execution of a full step.
Wave motors are referred to as unipolar motors. This is due to the quantity of motor phases being used at once. For motors that have unipolar and bipolar windings and identical winding parameters, this type of powering causes the same mechanical motion.
The downside of this type in controlling is that motors using unipolar windings consume only 25%, while motors that have bipolar windings consume 50 percent of the motor’s total winding at any time.
That means the torque at its maximum of the motor isn’t employed.
Full step control
When using two phases a.k.a. full-step control two phases are activated at the same time. The sequence of operations is described as AB-A’B’. The result of this form of control is identical actions as those in single-phase controls, with the exception that the rotor’s position is changed by a half step.
However, due having two motors operate simultaneously this motor can achieve twice the torque as compared to single-phase control, which is equivalent to 50 percent of the total winding.
With full-step control, rotor movements are the same as with wave control.
Half step control
Half-step controls are more complicated than the other two kinds. Half-step control is an amalgamation of control with two phases and one phase. It feeds the stator to one phase before switching to two phases. This leads to a process which is twice as short.
This is largely removing the largest drawback of the two other types of operation, which is the effects of mechanical resonance on the motor while it is in use. The scheme of half-step operation is described sequentially AB-B-A’B-A’-A’B’-B’-AB’-A.
Microstep controls are where the voltages in the windings are changed rapidly, breaking the entire step into smaller steps. Microstep control involves turning the magnet field in the stator faster than half-step or full-step control, which results in less noise and permitting the motor to move without noise down to the 0Hz frequency.
The cause of the motor’s resonance lies in the pulsed energy supply. The remedy for this may be the use of a microstep. It is a stepper motor is a synchronous motor. That means the constant stop position for the rotor is in sync by the magnet field in the stator. Rotor rotation is achieved through rotating the field. the rotor is then moved to a stable position. The torque produced through the motor dependent on the torque at rest (holding the torque) Ms, as well as that distance between stator’s magnetic field as well as the rotor’s position Qr.
Where: Qs and Qr angular distance expressed in electric degrees.
If you control the motor in a full-step or half-step manner the magnetic field in the stator is rotated between 90° and 45 degrees in each phase of the motor. Microstep control requires that the currents flowing through the windings need to change quickly, thereby breaking down the whole step into smaller steps. In microstep motor operation the control system needs to generate signals with intermediate levels that are between the highest and lowest value of the current source. The motor’s currents bands create an electromagnetic flux vector which’s position on the earth is determined by magnitude of the currents.
Utilizing microsteps, better positioning is possible. A standard step is divided by 2-32 times. In the real world, with the division of 8 and 16 results are achieved by reducing the effects from motor resonance.
If you are using the microstep controller, it is important to be noted that the ratio of excitation energy per microstep reduces when you divide the step.
Can bus stepper motor controller
Each slave has a limit for allowed following errors before going the overspeed. If the following errors of that slave is greater than the threshold then the slave speed to catch up with the network.The master will receive the following errors for every slave. If the slave that has the highest number of errors exceeds the threshold set by the master, the master is able to slow down the whole network. The slave that has the following error, which is higher than its own threshold, is running at a slower speed to catch the master.
If the masters resulting from error is greater than the threshold of overspeed the master will only increase speed so that it can catch up.
If an error in the following of a slave exceeds the maximum amount of error that can be attributed to following the slave will stop due to a follow-up error and the master distributes stops to all the networks.
Geared stepper motor
Gear selection for stepper motor
An appropriately selected gearbox is crucial to the effective and efficient operation of our equipment. It is because only the correct gearbox will enable us to increase the performance of a specific stepper motor by achieving the most precise positioning resolution and growing torque.
The choice of the best gearbox to use with a stepper motor should depend primarily on the reason we intend to utilize the motor for robotics, CNC machines as well as automation devices or measurement equipment. The gearbox must allow us that the motor be moved as precisely as is possible while at the same time keep high torque even at a low speed.
Gearbox for a stepper motor There are various types of them?
The most commonly used gears for stepper motors are:
- Planetary gearboxes,
- worm gearboxes,
- hypoid gearboxes and helical-bevel gearboxes.
A gearbox designed for the stepper motor changes both torque and RPM in precise proportions, decreasing RPM, for instance and increasing torque. This is why it’s recommended to select the correct gearbox that meets your requirements and calculate the parameters you need.
A planetary gear is made up of two concentric gears which are the sun wheel (central) with an outer toothing and a ring (outer) with an inner toothing. Between them are tiny satellites of gears linked through an chain (chief). The satellites turn of each one around its individual axis, while all together are able to circle the axis the whole mechanism.
Planetary gearboxes appear to be particularly beneficial to stepper motors. They are able to increase the torque of the motor shaft, and also provide extremely precise motions (individual step) in that stepper motor, i.e. quick starting, braking, as well as changing directions.
How a planetary gearbox works
How does a planetary gearbox work? sun wheel shaft and satellite cage tube shaft and crown wheel are all referred to as the central shafts. If one of these shafts fails then the others will assume all the power through the transmission. It is important to note that the distinctions between sun wheel and the satellites, and sun wheels, in both the circumference and their number of teeth result in these elements rotating at different speeds.
The advantages of planetary gearboxes are:
- High Efficiency
- Small clearances
- Possibility of determining the axis of the gear from the direction of the motor’s axis,
- High transferable torques can be achieved
- Coaxial alignment between shafts for input and output
- Load distribution across several planetary gears
- High efficiency because of low rolling power
- Unlimitless gearbox possibilities because of the combination of multiple different planetary stages
- -It is possible to use it as master gearbox
- Quiet operation
- It is suitable for a broad variety of applications
- Simple design, small size and yet the ability to reach big gear ratios at short switching times.
A worm gear is a type of gear with perpendicular axes lying in two different planes. A gearbox consisting of a worm (threaded helical rotor) meshing with a worm gear (helical cylindrical wheel with a specially shaped rim) set perpendicular to it.
Power transfer in such a gearbox is carried out with friction. The direction of power flow is of vital importance. If the driving element is a worm, the efficiency of the gearbox η is expressed by the relation:
η = tg γ / tg (γ + ς )
γ is the thread pitch angle
ς is a “friction angle” such that the coefficient of friction μ = tg ς.
Similarly, when the driving element is a worm gear, the efficiency of the gearbox η is expressed by due:
η = tg (γ – ς ) / tg γ
It is easy to see here that γ < ς, the efficiency of the gearbox is less than zero, and this means the inability to transmit in this direction, i.e. self-braking.
The worm gear in certain conditions can be self-braking. This is both a disadvantage as an benefit. Self-braking is a possibility depending on the circumstances. for instance, a lack of grease the coefficient of friction is higher than the acceptable limit, and the gearbox falls within the self-braking category.
This can also be desired, in this the worm mechanism functions as an gear in one direction, and also as brake in the other. The mechanism can be found for example in worm jacks, and also in the mechanism to tighten guitar strings.
However, the self-braking capability of the worm drive cannot be considered to be brakes within the system, specifically with winches or jacks when safety considerations are crucial, since when the drive system that has an unsupported load is increased and the drive is disengaged in unfavourable conditions, the load won’t stop but instead cause the system to be driven, which will accelerate it.
Application of worm gearboxes
Gears are beneficial to use when you need to transfer torque at 90 degrees. They are suitable to propel, which is the transfer of energy from an active shaft onto a passive and also in devices for dividing, like an divider, or driving on the machine’s table or driving the table of an envelope milling machine. They can also be utilized in devices that allow manual turning or steering. Worm gears are a great choice for stepper motors.
Helical bevel gears can also possess characteristics similar to those of worm gears.
Helical bevel gearboxes can be described as gearboxes that have at minimum two stages of reduction (depending upon the proportion ), and there are four- and three-stage gearboxes). In these gears, the first phase is bevel gears while the next stages are cylindrical. The helical cone gear permits an angular torque transmission. So, gears, constructed with two wheels, can be used to alter how transmission is transmitted theoretically within between 0-180deg and more often in the 30deg-to 150deg. Dimensions of wheels vary between a few millimeters all the way to 2.5 meters.
Helical bevel gearboxes are distinguished by high efficiency, reaching as high as 97 percent. One of the advantages of crowning gearboxes with helical bevels is the superior inflexibility of their teeth and their silent operation. If needed combinations of the mentioned gear types may also be employed.
In the search to find a compromise between performance and efficiency of a bevel-roller gearbox as well as its simple design and the beneficial ratio of power transmitted from the active shaft to an inactive shaft one could look into the possibility of hypoid gearbox. The compromise to be considered with hypoid gearbox is the combination of function and efficiency, a simple structure and a low cost.
Hybrid stepper motor
Hybrid motors are typically employed in the industrial sector, due to reasons that they combine the two stepper motor technologies mentioned above and have superior features, and higher performance. The resolution of this motor is significantly greater, and the rotation angle ranges between 0.9 degree up to 3.6 degrees, giving 100-400 steps per rotation. The motor’s rotor (rotor) of the motor is constructed of permanent magnets. However, unlike PW motors they aren’t put in radially but magnetized in an axial direction. The rotor of this type of motor is comprised of two ring magnetized in a differential manner and superimposed over the motor’s axis.
Each ring is made up of small channels (grooves) which provide teeth to the rotor. the more grooves, the greater the resolution of the motor (smaller pitch of the rotor and more steps) As I said earlier, hybrid motors can have the ability to move between 100-400 times per turn. A smaller pitch is a benefit in this regard, as it allows the motor to be placed more precisely. The rotor teeth offer an improved path for magnetic flow that improves motor’s performance, and the dynamic and resting torque is greater than motors with PM and VR. Furthermore each rotor ring is separated from the other by half one tooth.
The stator of a motor is usually made up of two windings and eight poles but four poles can work in tandem with a single winding i.e. by feeding each of the windings in the motor two poles that are not identical appear on the stator and are placed along the radial axis, in unison.
The basic principle of operation that is the basis of hybrid motors rests upon magnetic interaction . A permanent magnet that is placed on the rotor produces an unipolar magnetic flux which is closed by the magnetic circuit that is: stator – air gap and the rotor. When the winding of the stator is activated, the magnetic flux that is generated under one side of the stator will be added to flux of permanent magnets and under the other , it is subtracted. The rotor is put in motion in order that the axes of teeth of the stator and the rotor coincide.
It could be stated with a simple explanation that teeth in the one “ring” of the rotor match those of the stator then the teeth in the other rings of the rotor aren’t in agreement with the stator’s teeth and are in the grooves of the energized coil , and mesh half a tooth to the coil that is not energized. It’s like they’re “waiting” for the coil with the teeth that match to stop and for the coil that has been energized to mesh a half tooth in order to move and move from a half teeth of the stator to a complete one. This is the interaction between the magnetic field.
The concept behind an hybrid motor’s design is identical to that of the VR motor. The hybrid motor is similar to a VR motor, but it has a numerous poles and teeth for the rotor. Hybrid motors are typically used in industries because of their superior performance than PM motors, even though they are more costly.