Stepper Motor Selection:
Stepper Motor Selection- When Choosing the Precise stepper motor for a specific use can be confusing for anybody without main information in the field. There are some stepper motor fundamentals. i have already been using stepper motors in different projects.
- Unipolar and bipolar stepper motors
- Arduino CNC Shield with Bipolar Stepper Motors
- CD Rom Stepper Motor control
- Salvage Stepper Motors from LaserJet Printer
In this article, we will look upon such stepper motor types, and then we will discuss the parameters that one needs to focus on to select the best stepper motor fit for his job.
Stepper motors have a number of features that make them the motor of choice for an extensive range of applications mainly in measurement and control. There are low cost highly reliable produce high torque at low speeds and benefit from a simple structure. The advantage of operating in open loop mode is that as long as the motor runs within its definite torque the position of the shaft is known at all times without the need for a feedback loop.
Types of Stepper Motors:-
Permanent magnet Stepper motors:-
The widely used non industrial motor used in applications computer peripherals .These devices have low cost, torque, and speed devices. There structure show that their step angles are relatively large but the simplicity lends itself to high volume production at low cost.
Variable reluctance Stepper motors:-
The motors without permanent magnets providing them a good torque to inertia ratio. For applications such as micro positioning tables these motors are frequently used in small sizes. Though they require a different driving procedure from the other 2 types and are rarely used in industrial applications.
Hybrid Stepper motors:-
These combine the operating principles of the previous 2 types which enables them to provide higher torques. Experience shows that these are by far the most widely used stepper motors in industrial applications for that reason we will consider only this type here.
Making the right choice
There are several factors affecting the choice of stepper motors for particular applications like the type of motor, the torque requirement of the system, complexity of the controller, and the physical features of the motor, etc. Decide on the right stepper motor depends upon the application.
IMPORTANT PARAMETERS FOR STEPPER MOTOR SELECTION
Stepper Motors are a typical component in numerous frameworks. To function appropriately, their selection requires a cautious bit by bit measure that depends vigorously on the expected operation of the Stepper motor. While planning your framework, it is worthwhile in any case the end at the top of the priority list. Subsequently, before the Stepper motor selection can start, it is valuable to characterize what the Stepper motor should do, the performance objectives of the Stepper motor. Understanding these parameters will enable the selection to measure by maintaining the emphasis on what your framework must achieve, and thusly can assist you with bettering characterize Stepper motor specialized necessities. This page will assist you with focusing in on your plan objectives and revive the way toward buying the correct Stepper motor from a list. Start by characterizing the function of the Stepper motor and its performance necessities.
The advancement of manufacturing modern innovation is indivisible from stepper motors. The Stepper motor selection is a monotonous errand. The architect has to think about machine information as well as has to know a great deal of electronic and computer information. In the event that the stepper motor is chosen simply by the drive current, it is unquestionably not reasonable. Subsequently, you should comprehend the significance of some essential parameters before the selection, for example, static torque, drive method, drive voltage, and drive current so on.
Static torque is the holding torque when the rated current passed the Stepper motor two-phase coil and the rotor doesn’t turn. It additionally mirrors the capacity of the venturing motor, which is like the “power” of the traditional motor. Obviously, there is additionally a key contrast between the two kinds of motors: the physical structure of the stepper motor is totally not the same as that of the AC and DC motors, and the output power of the stepper motor is variable. It is normally conceivable to pick which frame size to utilize contingent upon the measure of torque required. As a rule, the torque is below 0.8N.m, and the motor with the frame size NEMA8-NEMA17 can be chosen. For the torque of about 1N.m, it is more appropriate to choose the NEMA23 motor. For larger torque motors, pick NEMA34, NEMA42 and other stepper motors.
Notwithstanding the motor body, the performance of the stepper motor is enormously influenced relying upon the drive method. While choosing a stepper motor and a driver, it is imperative to think about the drive method. The driving method is normally separated into constant voltage and constant current drive, unipolar and bipolar drive.
For constant voltage drive, regardless of whether the drive voltage is 12V or 24V, the proper resistance value must be chosen. For the most part, the resistance value of the motor is several ohms. Something else, the current will be too large to even think about burning the chip of the driver. For constant current drive, it is normally utilized for motors with little resistance and high rated current. The rated current is normally 1-3A. In the event that you need more current, you have to pick some extraordinary driver chips, yet the cost will be marginally more costly.
Contrasted with unipolar and bipolar drive circuits, a unipolar drive circuit requires four power tubes, and current flows a solitary way inside the coil. The quantity of power tubes of the bipolar drive circuit is twice that of the unipolar, and the current flows on the other hand in the positive and negative directions in the coil. Short-term synchronous conduction causes a short circuit of the power supply and creates a solid current, so it is important to forestall the short circuit. The bipolar drive circuit is more convoluted than the unipolar case. For the most part, low-speed, high-torque loads utilize bipolar drives, while fast drive applications are more reasonable for unipolar drives.
The drive voltage alludes to the input voltage of the driver. This is identified with the working climate of the machine. It very well may be selected from DC 12V, 24V, 48V, and so on It can likewise be AC 24V, 36V, 50V, 60V, 110V, 220V, etc. The impact of voltage selection on the performance of the Stepper motor is: the higher the voltage, the better the performance of the stepper motor, particularly the higher speed performance of the Stepper motor.
The drive current alludes to the current passes the single-phase winding of the stepper motor, additionally called the phase current. Some Stepper motors have similar dimensions and a similar static torque, yet the resistance and rated current are different. Why? For instance Different series motors are accessible in an assortment of resistant and current values. These motors with various current ratings are intended to coordinate the client’s various functions and diverse cost drivers: the current is little, the driver get together is straightforward and low expense, and the current is large so the expense of each component of the drive is high. Select a motor with a rated RMS current that is not exactly or equivalent to the current capacity of the stepper drive that will be utilized. Current produces torque. In the event that the drive can’t convey the full rated current of the motor, at that point the motor will create not exactly the rated torque. There is no issue with this as long as the motor produces the necessary torque for the application.
Torque Frequency Characteristic
The value of the torque prerequisite will be somewhat more hard to accurately foresee than the ideal working wheel speed. During steady state constant velocity operation, the motor expects torque to conquer the friction in the framework, for example, between motor heading, gears or other contacting surfaces and any longitudinal component of the weight vector, for example, going up/down a grade. In light of the trouble of getting a large number of these values, a few presumptions will be needed to get the motor selection measure began.
The curve of the output torque got by the motor during operation is known as the running torque frequency characteristic curve, which is one of the main dynamic curves of the motor. The dynamic torque of the motor relies upon the average current when the motor is running. The larger the average current, the larger the output torque of the motor. The output torque of the motor is inversely proportional to the speed. In other words the stepping motor has a large output torque at a low speed and a little torque at a fast. On the off chance that some working conditions require a rapid stepper motor the drive voltage resistance and inductance of the stepper motor must be changed. Expanding the info voltage of the driver and utilizing a little inductor and little resistance motor can achieve a large output torque at rapid.
Torque is regularly at the foundation of numerous stepper-related issues. Two moderately regular events include:
Insufficient torque at speed:
Most advance motors are wound and worked to perform at their ideal level at a specific speed range. In the event that a rapid motor is utilized in a low-speed application, you will without a doubt be pumping in loads of power but the motor will at present stall because of lack of torque. Utilizing a low-speed motor for a fast application will yield comparable outcomes.
Stepper Motors can’t accelerate rapidly with an inertia mismatch among motor and load. The key is to select a Stepper motor size that intently coordinates load size. Something else, the Stepper motor will struggle accelerating a substantial, unsteady load and the framework could without much of a stretch stall whenever accelerated excessively fast. Then again, the framework may resonate and cause noisy commotion, nervous movement, or inaccurate steps, whenever associated with a motor with an excess of torque. At the point when the load isn’t sufficiently substantial to account for the high-torque motor, everything is intensified through the motor’s resonance.
Determine load prerequisites
To begin with, determine the load type. Is it an inertial or frictional load? In the event that absolutely inertial, utilize some sort of transmission to coordinate load torque to motor torque. Utilize a gadget to quantify the force needed to move the load at the ideal speed and acceleration. For instance, you can utilize a spring scale to quantify the force on a linear axis or a torque watch to gauge rotary force.
Second, determine the application supply voltage. At that point select a Stepper motor with at any rate twice as much torque as needed at the objective working speed, and utilize a Stepper motor rated at about ¼ supply voltage. Next, take a gander at the driver current needed to get target motor torque. Select a stepper driver dependent on that number.
The alleged “phase number” is the number of coil groups of the Stepper motor, and the two-phase stepping motor has two sets of coils. Numerous clients give little consideration to the number of phases when buying motors, and the majority of them are bought freely. In fact, in various phases of the motor, the work impact is extraordinary. The 2-phase Stepper motor gives a stage angle of 0.9° and 1.8°, and the 3-phase Stepper motor gives a stage angle of 1.2°. The more modest the progression angle, the smoother the motor runs. As a rule, there are more two-phase Stepper motors. In the fast and high-torque working climate, it is more practical to select a three-phase stepping motor.
No-load Starting Frequency
Stepper motor no-load starting frequency generally called “empty frequency”. This is a significant marker of buying a motor. On the off chance that it is needed to start and stop regularly in an instant and the turn speed is around 1000 rpm (or higher) “accelerated start” is generally required. In the event that you have to start legitimately to achieve fast operation it is ideal to pick reactive or permanent magnet motors these machines have a moderately high no-load starting frequency.
Stepper Motor Inductance:
Select a motor with winding inductance that falls inside the allowable inductance scope of the drive that will be utilized. In the event that the Stepper motor inductance is not exactly the drive’s base inductance, at that point the output stage of the drive will overheat and fizzle. In the event that the motor inductance is more noteworthy than the drive’s inductance range, at that point the motor will have not exactly ideal performance.
For most applications, search for the following stepper motor information:
Torque – take a look at rated holding torque and performance curve
Current – take a look at rated RMS current per phase (coordinate with drive)
Inductance – see line-to-line phase inductance (coordinate with drive)
Speed – see performance curve dependent on voltage
Mounting dimensions – take a look at catalogue drawings
Other motor choices, for example, shaft seal, connectors, rear shaft, and so on.
Use steppers to save money, but do it wisely.
Stepper drives consistently offer the least expensive arrangement, so utilize a stepper Motor any place suitable. Recall these significant contemplations: First, does the framework require position affirmation? Second: some unacceptable stepper drive can cause ringing, resonance, and helpless low-speed performance. Third, during high speeds, stepper motors can cry. Since stepper drives have a high shaft check, hysteresis and vortex current misfortunes are likewise basic at fast; thus, a stepper motor isn’t suggested for nonstop operation over 2,000 rpm. At long last, since full current is expected to create holding torque, step motors can get hot at a stop.
As a general guideline, the torque-to-inertia proportion diminishes by a factor of two with each expansion in frame size. An unloaded 34-size motor can accelerate twice as quick as a 42-size motor, paying little mind to the number of stacks.
In the manufacture of stepper motors, the rotor is magnetized after get together to create the most elevated conceivable Flux density. This implies that stepper motors ought not be destroyed, since this motion will be largely demolished if the rotor is eliminated. Not at all like with DC servo motors, it isn’t commonly conceivable to demagnetize stepper motors by applying overabundance current.
Notwithstanding, too high a current can harm the motor in different manners: abundance warming may liquefy the protection or the winding transformers, and may relax the holding material holding the rotor overlays. On the off chance that the overlays are displaced, the impacts can be equivalent to if the rotor was demagnetized.
Note that constant operation at high speeds can prompt overheating of the rotor, however high speeds can be utilized successfully for situating
Since the shaft of a hybrid stepper motor passes through the center point of the permanent magnet, it must be made of non magnetic material to stay away from a magnetic short circuit. Stepper motor shafts are subsequently made of tempered steel stainless steal, and this ought to be borne at the top of the priority list when taking care of the motor.