Stepper Drive Modes

This chapter has explained how to operate steppers by energizing one or two winding pairs at a tiem, but tere are a number of different ways to drive a stepper, and this discussion touches on four of them:

* Full-step (one phase on) mode - Each control signal energizes on winding.
* Full-step (two phases on) mode - Each control signal energizes two windings.
* Half-step mode - Each control signal alternates between energizing one and two windings.
* Microstep mode - The controller delivers sinusoidal signals to the stepper's windings.

Full-Step (One Phase On) Mode

The simplest way to control a stepper is to energize one winding at a time. This is the method discussed at the start of this chapter. Figure 4.15 shows what the signaling sequence looks lide when controlling a stepper in this mode.

With each control signal, the rotor truns to align itself with the energized winding. The rotor always turns through the stepper's rated step angle. That is, if a PM motor is rated for 7.5, each control signal causes it to turn 7.5.

Full-Step (Two Phase On) Mode

In the full-step (two phase on) mode, the controller energizes two windings at once. This turns the rotor through the stepper's rated angle, and the rotor always aligns itself between two windings. Figure 4.16 illustrates one rotation of a stepper motor driven in this mode.

Figure 4.17 shows what the corresponding drive sequence looks like.

The main advantage of this mode over full-step (one phase on) is that it improves the motor's torque. Because two windings are always on, torque increases by approximately 30%-40%. The disadvantage is that the power supply has to provide twice as much current to turn the stepper.

Half-Step Mode

The half-step mode is like a combination of the two full-step modes. That is, the controller alternates between energizing one winding and two windings. Figure 4.18 depicts three rotations of a stepper in half-step mode.

Figure 4.19 illustrates a control signal for a stepper motor driven in half-step mode.

In this mode, the rotor aligns itself with windings (when one winding is energized) and between windings (when two windings are energized). This effectively reduces the motor's step angle by half. That is, if the stepper's step angle is 1.8, it will trun at 0.9 in half-step mode.

The disadvantage of this mode is that, when a single winding is energized, the rotor turns with approximately 20% less toruqe. This can be compenstated for by increasing the current.

Microstep Mode

The purpose of microstep mode is to have the stepper turn as smoothly as possible. This requires dividing the energizing pulse into potentially hundreds of control signals. Common numbers of division are 8,64,and 256. If the energizing pulse is divided into 256 signals, a 1.8 stepper will turn at 1.8/256=0.007 per control signal.

In this mode, the controller delivers current in a sinusoidal pattern. Successive windings receive a delayed version of this sinusoid. Figure 4.20 gives an idea of what this looks like.

Using this mode reduces torque by nearly 30%， but another disadvantage involes speed. As the width of a control signal decrease, the ability of the motor to respond also decrease. Therefore, if the controller delivers rapid pulses to the stepper in microstep mode, the motor may not turn in a reliable fashion.

DSP-BASED Control of Stepper Motors

A stepper motor is an electric machine that rotates in discrete angular increments or steps. Stepper motors are operated by applying current pulses of a specific frequency to the inputs of the motor. Each pulse applied to the motor causes its shaft to the motor causes its shaft to move a certain angle of rotation, called a stepping angle. Since the input signal is converted directly into a requested shaft position without any rotor position sensors or feedback, the stepper motor has the following advantages:

• Rotational speed proportional to the frequency of input pulses
• Digital control of speed and position
• No need of feedback sensor for open loop control Excellent acceleration and deceleration responses to step commands 

Leadshine 57HS09 Stepper Motor

The stepper motor has salient poles on both the stator and the rotor, andnormally only the stator poles hold the poly-phase windings called the controlwindings. Usually stepper motors are classified as:

• Active rotor (permanent magnet rotor)
• Reactive rotor (reluctance type) 
• Hybrid motors (combining the operating principles of the permanentmagnet (PM) and reluctance stepper motor)

While each of these types of stepper motors has merit, hybrid stepper motorsare becoming more popular in industrial applications.  In this chapter, we focus onthe principles and implementation of a hybrid stepper motor control system usingthe LF2407 DSP controller.

The operation of the stepper motor relies on the simple principle of magneticattraction.  This principle states that opposite magnetic poles attract while like polesrepel each other. If the windings are excited in the correct sequence, the rotor will rotate following a certain direction. The basic operation of a stepper motor can beclassified generally as either full step mode or half step mode. These modes are discussed in detail in the following section using the simplified stepper motorconstruction shown in Fig. 8.1.

Full-step Mode

If none of the stator windings are excited, an attraction between the stator polesand rotor teeth still exists because the PM rotor is trying to minimize the reluctanceof the magnetic flux path from one end to the other.  As a result, the rotor will tend to rest at one of the rest equilibrium positions. From Fig. 8.1, a rest position existswhen a pair of rotor teeth are aligned with two of the stator poles. In the case ofFig. 8.1, the rotor is aligned with pole 1 and pole 3 on the stator. There are a total of12 possible equilibrium positions for a 4-phase, 6-pole stepper motor. The force ortorque that holds the rotor in one of these positions is called the detent torque. The value of the detent torque is usually small because no current flows through thestator windings.

Half-Step Mode

The stepper motor operation discussed rotates 300 per step.  In the half step mode, alternately exciting one winding, then exciting two windings, will cause therotor to move through only 15 degree per step. Though there is a slight loss of thetorque while the single winding is being excited, half-step operation allows forsmoother operation at lower speeds and less overshoot at the end of each step.  The excitation sequence of the stator windings in half-step mode is given in Table 8.3.During this operation, each switch between the two nearest modes will cause a 450 shift of stator field which results in a 150 rotation of the rotor. A total of 24steps are required for a complete revolution, double of what is required for full stepmodes.

Micro Step Mode

For the operating modes discussed previously, the same amount of current flows through the energized stator windings. However, if the currents are not equal, the rotor will be shifted towards the stator pole with the higher current. The amount of deviation is proportionate to the values of the currents in each winding. This principle is utilized in the microstep mode. During this mode, each basic full mode step can be divided into as many as 500 microsteps, providing the proper current profile is applied.

How to Wire Your Stepper

A stepper motor can come with assortment of wire configurations. The type of motor you’ve selected will determine the wire setup. Most commonly stepper motors come with four, five, six, or eight wires.

To begin, if your stepper motor only has four wires, this means it can only be used with a bipolar driver. You will notice each of the two phase windings has a pair of wires, use your meter to identify the wires.

4 Wire Stepper Motors

W numerous motors make the most of 6- and 8-wire configurations, the majority of bipolar (1 winding per phase) stepper motors offer 4 wires to connect towards the motor windings. A fundamental 4-wire stepper motor is shown in Figure 1. Connecting this motor kind is extremely simple and merely demands connecting the A and A' results in the corresponding phase outputs in your motor drive.

There's not a lot detailing right here. The 4 wire stepper denotes a single feasible configuration and that's of a bipolar stepper motor. We don't have to bore us with particulars like whether or not this motor is variably reluctance, permanent magnet or hybrid as that only relates to building. What we have to understand is the fact that two wires are for PHASE A and also the other two wires are for PHASE B. Which 1 is PHASE A and which 1 is PHASE B is type of arbitrary.

If you have the motor datasheet then you know which wires represent which. But if you do not have this document, just do a quick continuity test and determine which two wires are connected together through an inductor. You can also use a simple BACK EMF test in which you short two leads together. If it is harder to move the rotor, then those two wires form one of the phases. If the rotor moves as easy as with no wires crossed over, then those two wires are not connected through a winding. Keep on going until you find both phases.

The Five Wire Stepper

This motor is also equally easy to deal with as it can only be wired as an unipolar stepper motor. There is really no way to use this motor in a bipolar configuration as all the center taps have been shorted together. Do note this motor style is quite rare. I think these motors were more common a few years ago when unipolar motors were much more cost effective. Today, however, since driving bipolar motors is not a superbly expensive endeavor, the five wire stepper motor is not as common as it used to be. Instead, the six wire stepper motor has replaced the five wire stepper motor because of what we will see next. If you do happen to get your hands on a five wire stepper motor, here is how you wire it:

The Six Wire Stepper

We can now start to complicate things. As it turns out, the six wire stepper is optimized to operate as a unipolar stepper motor but it is rather doable to use it as a bipolar stepper motor as well. The trick, however, is that there are multiple ways of wiring the motor as bipolar and it all depends on what you will want to achieve. For example, do you want speed, or do you want torque? Maybe you want both? Well, I can only promise one or the other by utilizing conventional drive technology. If you want both (torque and speed) you will need to resort to some highly advanced drive technology, which although available out there, is not in the$5.00 range.

So lets first see how to wire the six wire stepper as a unipolar motor:

A bipolar driver will require you use only one end wire and one center tap of each winding. With a five wire stepper motor the wire setup is very similar to the six wire driver, the main difference being the center taps are connected together internally, bringing it out as one wire. This will make the motor only function as a unipolar driver. Also, the windings will be impossible to identify without trial and error, the best you can do is try to identify the center tap wire since it has half the resistance.

Finally there is the eight wire stepper motor, which is much like the six wire. The difference being that the two phases are split into two separate windings. When this is done it allows for the stepper motor to be connected as a unipolar motor, as well as three different bipolar combinations.

Stepper Motor in Cllosed Loop Mode

Due to the limitations of open loop contorl, a closed loop control of stepper motors is used in practice. In a closed loop control, the input controller gets the information about the output through the feedback element. Hence the driver circuit receives the control signal which is based on the feedback information. So switching of the motor takes place by means of train of input pulses, which is generated on the basis of feedback from rotor. Such a switching of the motor is called as closed loop mode of operation of the stepper motor. The block diagram shown in the Fig.A.17 illustrates the closed loop operation of the stepper motor.

Let us consider a closed loop temperature control system. The temperature of the tank is required to be kept constant with the help of controlling the steam flow. There exists a valve whose position is controlled by a stepper motor, to control the steam flow. The actual temperature is sensed by using temperature sensor and feedback is given to the input controller. The input contorller has the reference information corresponding to the desired ideal temperature. It compare the feedback with this reference to generate the appropriate contorl signal. This control signal inturn is given to the driver circuit. The driver circuit control the excitation and logical sequence of the excitation of the phases. This drives the stepper motor and hence valve opening gets controlled appropriately so that steam flow gets controlled. This maintains the temperature of the tank constant. The logical operation of the system is illustrated in the block diagram shown in the Fig. A.18.

In a speed and position control systems, optical encoders coupled to the rotor shaft are used. Simlarly use of microprocessors as an input controller for better accuracy is very commen now a days. The Fig. A.19 shows the use of microprocessor in the closed loop control of the stepper motor.

What are the functionalities of these closed-loop stepper systems?

Closed-loop stepper with step-loss compensation will be the most typical kind of closed-loop stepper manage. The stepper drive operates as a micro-stepping drive and usually receives pulse and path commands to move towards the preferred position. An encoder tracks shaft or load position. If lost actions are detected, a compensation algorithm inserts extra actions to ensure that the motor shaft (or load) arrives in the preferred position. Usually, the stepper-motor drive has settings for two currents: The motor gets operating present when in motion and gets resting present when stopped.

In closed-loop stepper with load-position manage, the stepper drive operates as a typical microstepping drive and usually receives pulse and path commands to move towards the preferred position. The encoder (usually mounted around the load) monitors the load's position. The closed-loop algorithm dynamically tracks the load position and compensates all through the move profile. Usually, the motor gets operating present when in motion and gets resting present when stopped.

Closed-loop stepper servo manage treats the stepper motor like a high-pole-count brushless motor, turning it into a servomotor. A shaft-mounted encoder detects shaft position to figure out the correct present vector. A pulse and path interface might be provided within this kind of drive, however the position controller does not use actions to obtain towards the preferred position. Rather, closed-loop algorithms manage motor torque to servo the shaft into position utilizing a position manage loop (a PID loop for instance). Within this mode, the present setting is dynamic. The stepper drive delivers only the quantity of present required to move the motor shaft and load into position.

How to measure stepper motor

It's hard to stay up to date when you are floating in a sea of technical jargon. However, it's imperative that engineers know the terminology associated with the areas in which they work. And that's especially true if their assignments take them outside their engineering discipline. For example, a mechanical engineer specifying a stepmotor should understand the associated mechanical and electrical terms.
Stepper motors need the right current if they are to work correctly. Without it, the motors can overheat, miss steps, and even freeze in their tracks. Yet the one electrical specification that most confuses all engineers, from the recent graduate through seasoned veteran, is the rating for stepmotor current. No doubt this happens because stepmotor-current ratings come in many forms such as amps/phase, amps RMS, average current, and even amps peak current.

Basics of stepper motor torque

Stepper motor holding torque is one of the main specs of any stepper motor. It is a simple indication of the "strength" of the nema 23 stepper motors.

Stepper motor torque is usually measured in oz/in or ounces per inch. The picture above shows what that measurement means, and a method of actually measuring it. If the motor can HOLD a weight of 100oz on a 1 inch radius pulley it is said to have a stationary "holding torque" of 100oz/in and is therefore sold as a 100oz/in motor.

The picture above shows the same 100oz/in motor but with a more sensible measuring system. Increasing the pulley radius gives greater leverage for the weight, so we can use a smaller weight, and also gives a lever length (10") that is easier to make and will measure more accurately.

As with all leverage ratios increasing the lever length means decreasing the weight accordingly, so instead of 100oz/1" we use 10oz/10" at 10:1, (the result is still 100oz/in).

Measuring stepper motor torque

To measure the holding torque the leadshine m542 does not need to rotate, so the pulley can be replaced with any simple lever.

I used a plastic ruler. The lever distance was 25cm and used the hole that was already on the plastic ruler. Balancing the lever with a simple counterweight can be done using a piece of string. This also compensates for the weight of the measuring cup. I used a flat plastic food cup and 3 strands of fine wire. Everything was glued together in seconds using hot melt glue which can be easily "broken apart" afterwards.

Maximum Speed of Stepper motor

At 12 V the speed will quickly be zero because some thing will overheat and break. That is if this A4988 factor can even provide the essential 7.five A per phase. If not, then it'll most likely get hot and break. Either way, this isn't a great concept.

There's 1 exception to this, that is when the 12 V is only applied for brief periods of time for you to overcome the inductance from the windings, using the voltage then rapidly brought back down to spec prior to the present exceeds spec. That kind of drive may be helpful for steppers simply because the present within the coils switches quicker, which enables the motor to run quicker. Nevertheless, care should be taken to not exceed the rated present. Unless this A4988 factor is particularly developed to complete this and also you can set a present limit in the 1.78 A maximum the Leadshine servo motor is rated at, the points within the initial paragraph apply.

A4988 Adiquiri a drive with voltage regulator to create my college project. The concept would be to make use of the arduino to create some moves having a shaft on a table. I produced the circuit from the assembly and also the engine worked nicely and produced the move I planned, however the issue and in relation to speed, simply because he's as well slow. Currently attempted every thing i couldn't make it rotate quicker. Currently study the datasheet from the drive and attempted combinations of connections but not worked. I'm utilizing an engine "Minebea 23km-C051-07V Step Motor Hybrid 1.8DEG 56 NEMA23 size of 9.9 kgf / cm" having a supply "12V, 3A" and an Arduino Mega 2560. I truly require assist from you guys simply because my project is currently as well late. I'm in the disposal for any clarification.

The speed of rotation and to possess about 120 RPM. I don't understand how a lot till I improve, nevertheless would like much more, some thing in 1000 or 2000 RPM. I understand that when I shed the speed improve torque, but has no issue simply because the torque doesn't interest me. Currently attempted setting the MS1, MS2 and MS3 based on the table on web page six from the A4988 datasheet, currently produced ??a number of modifications within the arduino code shown beneath, currently utilized a font adjustable to supply a greater voltage, but not obtaining achievement. I'm presently utilizing a supply of 12V, 3A.

Usually speaking, you most likely aren't going to obtain greater than a couple of hundred RPM out of your stepper motor, but you need to have the ability to do much better than 120 RPM. There are some primary methods to improve your maximum step speed:

1) Use a higher voltage. This lets the current ramp up faster every time you step and allows for a higher average current at high step rates.
2) Set the current limit to the maximum allowed by your stepper motor. Unfortunately, you are using a stepper motor rated at 2 A per coil, but the driver you are using can only deliver around 1 A per coil without overheating. Adding a heat sink would let you get a little more current out of it, but I don't expect you can get the full 2 A per coil out of it.
3) Ramp the stepper speed up slowly. You can get the stepper motor to a much higher speed if you gradually increase your speed over time rather than trying to start at the maximum speed from rest.
4) Decrease the external load on the stepper. The more torque your stepper motor needs to deliver, the lower it's maximum step speed will be.

Increasing the motor supply voltage while using current limiting like the leadshine m542 provides does increase maximum pulses per second a stepper motor can handle because a higher voltage causes the coil current to ramp up more quickly. There isn't an easy way to know how well your stepper motor will respond to an increased voltage because it depends on the construction of your particular motor.

How Fast Can Stepper Motors Run

Stepper motors are fairly simple to manage having a microcontroller. But if you are seeking to run then at a higher quantity of revolutions per second issues get difficult fairly rapidly. We've been studying about and developing stepper drivers for many years, and lately he decided to develop a high-performance driver according to a MicroChip reference style.

1200 rpms could be extremely higher for many motors and like Rugged says there could be extremely small torque accessible and could be susceptible to missing actions. Bear in mind also that to attain greater speeds with any substantial load your controller should be in a position to accelerate smoothly to that speed or you'll miss actions and therefore position. Because you do not describe your project I've no concept what your specifications are but motion manage projects do  need a little of preparing to become effective.

A 64 stepper motor will spin quicker, because every step is much more distant, it's much more most likely to skip or loose actions. Because you are able to send step signals towards the motor extremely rapidly (computer systems are truly quick in comparison to motors) I do not believe there's any genuine benefit to utilizing the 64 step motor more than the 200 step motor. Just step the 200 step motor quicker. The trick is obtaining a motor and driver that may spin fast sufficient.

Is it possible to drive a stepper motor greater than 1000 rpm?

A 200 step per revolution motor, running at 1,000 RPM must have a stepper drive capable of doing full steps at 3.4kHz, which is well within the range of most motor drive circuits. Here we can recommend you, Leadshine DM542, The DM542 is a fully digital stepper drive developed with advanced DSP control algorithm based on the latest motion control technology. It has achieved a unique level of system smoothness, providing optimal torque and nulls mid-range instability.
However, keep in mind that if you start out the motor at 3.4kHz, it will merely vibrate due to inertia - you don't start a car at 60 miles per hour, you start at 0 and ramp up to 60 MPH, otherwise you just spin your tires.

So you have to design your circuit to ramp the frequency up from 0 to 3.4kHz slowly enough that the motor can keep up. This means you'll also have to take into account the whole drive train - stepper motor, gears, belts, and anything else the stepper motor is moving. This may be a large platform if you're doing CNC, and the inertia may require a very slow ramp up to avoid skipping steps.

Lastly, if the motor isn't powerful enough to move the load at 1,000RPM, then you'll need a more powerful stepper motor. Torque falls as speed increases due to internal motor losses.

Conclusion

If you're trying to drive a stepper motor at high speed, you should really use a constant-current driver circuit, since the voltage required to operate at high speeds will be much greater than that required at low speeds, and since driving enough voltage for high-speed operation into a stalled motor would quickly destroy it if the current weren't limited. If a current-limited supply is used, the motor should continue to supply the expected torque until it's running fast enough that the compliance voltage of the supply is reached.

Step Motor Excitation Modes

Stepper motor drivers often have different modes of operation. These different modes determine in what sequence the coils are energized to make the motor shaft move appropriately. There are four types of these stepping modes. However, only three of the excitation modes are common in most stepper drivers.

Full-step excitation

In full step operation, the motor step through the normal step angle e.g.200 step/revolution motors take 1.8" steps while in half step operation, 0.9" step are taken. There are two kinds of full-step modes. Single phase full-step excitaion is where the motor is operated with only one phase energized at-a-time. This mode should only be used where torque and speed performance are not important, e.g. where the motor is operated at a fixed speed and load conditions are well defined. Problems with resonance can preclude operation at some speeds. This mode requries the least amount of power from the drive power supply of any of the excitation modes. Dual phase full-step excitation is where the motor is operated with two phases energized at-a-time. This mode provides good torque and speed performance with a minimum of resonance problems. Dual excitation, provides about 30 to 40 percent more torque than single excitation, but does require twice the power from the drive power supply.


Half-step excitation

The Half step mode energizes a single coil then two coils then one again. Alternating between energizing a single phase and both phases together gives the motor its higher resolution. A 200 step Step motor driver operating in half step mode would have 400 positions, twice the normal resolution. However, the torque will vary depending on the step position because at times a single phase will be energizes while at other times both phases will be energized. Higher end drivers compensate by increasing the current through the single coil when a single coil is energized. This makes up for the loss in torque, making the half step mode very stable.

Half step excitation is alternating single and dual phase operation resulting in steps that are half the basic step angle. Due to the smaller step angle, this mode provides twice the resolution and smoother operation. Half stepping produces roughly 15% less torque than dual phase full stepping. Modified half stepping eliminates this torque decrease by increasing the current applied to the motor when a single phase is energized.

Micro-step drive

In the micro-step mode, a motor's natural step angle can be divided into much smaller angles. For example, a standard 1.8" degree motor has 200 steps/revolution. If the motor is micro-stepped with a "divide-by-10"). The micro-steps are produced by proportioning the current in the two windings according to sine and cosine functions. This mode is only used where smoother motion or more resolution is required.

It is important to take into consideration the step modes and how best to utilize them when designing the CNC router drive system. It is also very important when choosing a stepper motor driver. Some drivers will micro-step more smoothly than others. In the next section we will cover the ins and outs of buying a stepper driver and what features to look for.

We Fasttobuy Co.,Ltd is a professional manufacturer of automation control. Currently, our company specialized in the production of linear actuator, hybrid stepper motor, screw and nut.For more details, please feel free to contact us!