STEPPERCHINA

It is important to know how to calculate the steps per Revolution for your stepper motor because only then you can program it effectively.

In Arduino we will be operating the stepping motor in 4-step sequence so the stride angle will be 11.25° since it is 5.625°(given in datasheet) for 8 step sequence it will be 11.25° (5.625*2=11.25).

Steps per revolution = 360/step angle

Here, 360/11.25 = 32 steps per revolution.

Why so we need Driver modules for Stepper motors?

Most stepper motors will operate only with the help of a driver module. This is because the controller module (In our case Arduino) will not be able to provide enough current from its I/O pins for the motor to operate. So we will use an external module like ULN2003 module as stepper motor driver. There are a many types of driver module and the rating of one will change based on the type of motor used. The primary principle for all driver modules will be to source/sink enough current for the motor to operate.

Arduino Stepper Motor Control Circuit Diagram and Explanation

The circuit Diagram for the arduino stepper motor control project is shown above. We have used the 28BYJ-48 Stepper motor and the ULN2003 Driver module. To energise the four coils of the stepper motor we are using the digital pins 8,9,10 and 11. The driver module is powered by the 5V pin of the Arduino Board.

But, power the stepping driver with External Power supply when you are connecting some load to the steppe motor. Since I am just using the motor for demonstration purpose I have used the +5V rail of the Arduino Board. Also remember to connect the Ground of the Arduino with the ground of the Diver module.

The voltage of your cnc power supply should be greater than or equal to the rated voltage of your stepper motor. Otherwise, the motor will not receive its full rated current and you will not get the full performance that the motor is capable of. It is OK for the power supply voltage to be higher than the rated voltage of the motor because the Tic has active current limiting. (It rapidly switches the power to the motor on and off while measuring the current to make sure it does not go too high.)

A higher power supply voltage is usually desirable since it allows higher speed and torque. However, if the power supply voltage is extremely high compared to the stepper motor’s rated voltage and you want to use microstepping, you might experience skipped steps.

The voltage of your power supply should be within the operating voltage range of the Tic. Otherwise, the Tic could malfunction or (in the case of high voltages) be damaged.

The continuous current per phase of the Tic should be greater than or equal to the rated current of the stepper motor. Otherwise, the Tic will not be able to deliver the full rated current to the motor and you will not get the full performance that your motor is capable of.

We generally recommend you choose a power supply with a current limit that is at least at least twice the current limit you are planning to use on the Tic as that amount of current should always be safely beyond what the Tic will draw. The current limit you configure on the Tic should generally not exceed the stepper motor’s rated current and should not exceed the continuous current per phase of the Tic.

It is worth noting again that since the Tic actively limits current through the motor coils, you can safely use power supplies with voltages above the rated voltage of the stepper motor as long as you set the current limit to not exceed the best stepper motor’s rated current.

What are the advantages and disadvantages of the different functionalities?

Solution
In general, 2-phase stepper motors can have 4, 6 or 8-wire leads (not including any optional encoder lines).
Some hybrid  step motors have a motor case ground that can be tied to the ground of the system. It is usually a black wire, and it will add one additional wire to the overall count (4 coil wires + 1 casing ground = 5 wires total).

The best solution is to obtain the pinout from the motor manufacturer. If you do not have access to the pinout, then the following procedure will help you in wiring the 2-phases.

If you have four coil wires from the stepper motor:
Approach 1 (using a multimeter)
Each of the two phases should have the same resistance when measured with a multimeter. When measuring the resistance across one wire from each of the two phases, the resistance should be infinite because the circuit is open. Locate the two pairs of wires that represent the two phases; both pairs of wires will have similar internal resistance.
Connect each phase to the amplifier and ignore the polarity (+ / -), for now. You have a 50 percent chance of guessing right.
Send a command to move the motor. If the motor rotates in the wrong direction, then switch either phase A and A- or B and B- (effectively reversing directions).

Approach 2 (without a multimeter)
Connect the four coil wires to the amplifier in any arbitrary pattern. Send a command to move the motor.
If the motor moves erratically or not at all, then switch one wire from phase A with one wire from phase B.
If the motor is rotating in the wrong direction, then switch either phase A and A- or B and B- (effectively reversing directions).

If you have six coil wires, then each phase has a center tap wire:
The center tap wire should have half the internal resistance of the full phase. The easiest option is to use a multimeter to find the two pairs of wires that have the maximum resistance.
Connect each phase to the amplifier, and ignore the polarity (+ / -) for now. You have a 50 percent chance of guessing right. The stepping motor should rotate, and if it is in the opposite direction, then switch either phase A and A- or B and B- (effectively reversing directions).
If you have eight coil wires, then it is highly recommended you find the exact pinout for the motor.
The eight wires represent four pairs of wires, and each pair has the same resistance. It is not easy to find what two pairs represent phase A and phase B without dismantling the motor.

How to identify four-wire stepper motor coil pairs with a multimeter

Over the years there have been discussions about the 1.8 degree step angle versus 0.9 degree stepper motor. Most stepper motors today have the standard step angle of 1.8 degrees, resulting in a 200 step per revolution. However, in the early days of stepper motors, before microstepping, low end resonance played a significant role in many applications. Most application engineers suggested either increasing the load, to lower the bandwidth frequency, or simply avoiding this low end resonance region altogether.

For some stepper motor designs the idea of a smaller step angle was created to lessen the ringing around each tooth. The result was a mechanical change, which reduced the step angle from 1.8 degree to 0.9 degree resulting in a 400 steps per revolution stepper motor.

This did reduce the ringing and in some cases allowed for smoother operation accelerating through the low end resonance region. However, the reduction to such a small step angle resulted in higher saturation of the lamination steel around the tooth. This resulted in lower torque due to the core losses. As the current increased, the losses became more significant and the anticipated gains lost due to saturation.

 
0.9 Degree Step Angle 1.8 Degree Step Angle

In the early years, most of the motors utilizing this 0.9 step angle were Nema 23 or single stack Nema 34 frame motors, which had lower currents. The lower currents produced lower saturation in the steel laminations and therefore were successful in some applications.

While there is still a place for 0.9 degree step angle steppers, the introduction of microstepping and the expanded higher end filtering of today’s stepper drives, low end resonance found in 1.8 degree steppers can be successfully accelerated through and perform within this region.

Closed loop-capable stepper motors merge the benefits of stepper and servo motor technology. They run more quietly and have a lower resonance than stepper motors, provide position feedback and control, feature short settling times, and exhibit no step loss at all. They are an alternative to stepper motors if energy efficiency, smooth running and a high load tolerance are required.Compared to servo motors, they have advantages due to their high torque at low speeds, short settling times, correct positioning without back swing and a lower price for sizes that are often smaller.

The closed-loop method is also referred to as a sinusoidal commutation via an encoder with a field-oriented control. The heart of closed-loop technology is power-adjusted current control and feedback of control signals. Through the encoder, the rotor position is recorded and sinusoidal phase currents are generated in the motor coils. Vector control of the magnetic field ensures that the magnetic field of the stator is always perpendicular to that of the rotor and that the field strength corresponds precisely to the required torque. The current level thus controlled in the windings provides a uniform motor force and results in an especially smooth-running motor that can be precisely regulated.

 

True/pseudo closed loop

There are stepping motors that dress themselves up as being closed loops and work with encoders but do not provide any field-oriented control with sinusoidally commutated current control. They only check the step position, and cannot correct step angle errors during operation. True closed loop with field-oriented control compensates step angle errors during a run and corrects load angle errors within a full step.

linear stepping motor linear actuator is essentially rotary stepper motor “unwrapped” to operate in straight line. Linear motor operates on electromagnetic principle and consists of moving “forcer” and stationary platen. The platen is passive toothed steel bar (stainless is available) extending over desired length of travel. Forcer incorporates electromagnetic modules and bearings and moves bi-directionally along the platen.

linear stepper motor is an turn-key linear actuator available with either mechanical roller bearing or air bearings.

Side and bottom mechanical bearings are built into forcer and do not require any adjustments by the user over the lifetime of the motor. They are permanently lubricated and exhibit very little friction.

Air bearing operates by floating the forcer on high pressure air introduced through orifices in the forcer. Air bearing motors can operate continuously at high speed without wear. Air bearing permit smaller air gap resulting in larger motor forces.

linear stepping motor linear actuators are micro-stepped by proportioning currents in two phases of the forcer, much same as in rotary stepper motors. When micro-stepper linear stepper motors following benefits are achieved:

– higher resolution for positioning

– smoothness at slow speeds

– wider speed range

Manufacturers apply the term “closed-loop stepper” to a wide array of controls. Here, we’ll spell out how the three most common closed-loop stepper control schemes work and highlight their advantages and disadvantages.

Are all closed-loop stepper systems created equal?
No. Some manufacturers give the closed-loop stepper motor systems similar-sounding descriptions, which confuses the marketplace. As proof of the confusion, it’s not uncommon that a designer requests one capability and actually needs another.

What are the most common closed-loop stepper systems?
There are three common types: Closed-loop stepper with step-loss compensation; closed-loop stepper with load position control; and closed-loop stepper servo control. Stepper-drive manufacturers call them all “closed loop” but the three have distinct functionalities.

What are the functionalities of these closed-loop stepper systems?
Closed-loop stepper with step-loss compensation is the most common type of closed-loop stepper control. The stepper drive operates as a micro-stepping drive and typically receives pulse and direction commands to move to the desired position. An encoder tracks shaft or load position. If lost steps are detected, a compensation algorithm inserts additional steps so that the motor shaft (or load) arrives at the desired position. Typically, the Closed-loop stepper-motor driver has settings for two currents: The motor gets running current when in motion and gets resting current when stopped.

Like servo motors, china stepper motors are available in both rotary and linear designs. When an application requires force (rather than torque) output and can operate in open loop control, a linear stepper motor is often the preferred solution. Although linear stepper motors are available in both variable reluctance and hybrid designs, the more common version is hybrid linear stepper motors.

In a hybrid linear stepper motor, the base, or platen, is a passive steel or stainless steel plate with slots milled into it. The forcer contains motor windings, permanent magnets, and laminations with slotted teeth that serve to concentrate the flux that’s created when current is applied to the coils. The teeth of the forcer and the platen are staggered by ¼ tooth pitch in relation to one another to ensure that constant attraction is maintained and that the next set of teeth will come into alignment as current is switched in the coils. This means that for each full step of the motor, the forcer moves along the platen by ¼ tooth pitch.

Whereas variable reluctance linear stepper motors for sale can only operate in full step mode, hybrid versions can operate in either full step or microstepping modes. Microstepping, which divides the step angle into smaller increments, enables higher resolution motion and better control of speed and force. Because each phase of the motor is driven with (theoretically) ideal sine waves, 90 degrees apart, microstepping also allows the current to increase in one winding as it decreases in the other, providing smoother operation at low speeds than can be achieved with full- or half-step operation.

For guiding the load on hybrid linear stepper motors, either mechanical roller bearings or air bearings are typically used. (Because the platen in a hybrid linear stepper motor is passive, it can serve as the air bearing surface.) The magnetic flux between the forcer and platen creates a strong magnetic attraction, so these support bearings actually serve two purposes – to guide and support the load and to maintain the correct air gap between the forcer and the platen.

Like other linear motor designs, hybrid linear stepper motors can incorporate multiple forcers onto one platen, with each forcer moving independently. In addition to smooth low-speed operation (obtained with microstepping control), they are also able to achieve very high speeds and accelerations with high resolution and low to moderate force generation.

With simple mechanical construction and easy setup (no servo tuning required), hybrid linear stepper motors are ideal for applications that can operate in open-loop mode and that require either high speed with low force production or very smooth motion at low speed.

 

When the stepper motor receives the final pulse signal, (either one or from a continuous train), it will stop rotating. However, complete rest will not occur until all the oscillations have stopped. The time it takes from the application of the last pulse received until the stepper motor comes to a complete rest is known as settling time. (See graph below). Resonance occurs when the stepper motor suddenly makes large oscillations, or the output torque suddenly drops at one certain pulse rate or numerous small regions of pulse rates. The stepper motor will stop (stall), may miss steps or reverse direction from the commanded direction. This phenomenon occurs when the natural frequency of the stepper motor coincides with the frequency of the input pulse rate. This generally occurs around 100 – 200 pulses per second in a full-step operation, and also at higher pulse rates. Microstepping half-step operation, or electrical or mechanical damping, can reduce resonance issues. Microstepping has a large effect on settling time and resonance due to the smaller angular displacement taken per pulse. See Figure below.

Resonance Characteristics
Since a hybrid stepper motor system is a discreet increment positioning system, it is subject to the effect of resonance. Where the system is operated at this given frequency, it may begin oscillating. The primary resonance frequency occurs at about one revolution per second. Oscillating will cause a loss of effective torque and may result in a loss of synchronism. Settling time and resonance can be best dealt with by dampening the stepper motor’s oscillations through mechanical means. Mechanically, a friction or viscous damper may be mounted on the stepper motor to smooth out the desired motion.

Methods for Changing or Reducing Resonance Points:
• Use of Gearboxes or Pulley Ratios
• Utilize Microstep Drive Techniques
• Change System Inertia
• Accelerate Through Resonance Speed Ranges
• Correct Coupling Compliance

General Stepper Motor Driver Safety Considerations

In this post, I’ll describe the process I use for sizing gearboxes and geared stepper motors.

To make the selection, I am using KEB’s software sizing program called KEB-DRIVE. KEB-DRIVE is free and easy to use. If interested to follow along, you can download a copy of the software.

2. Select the correct gear technology for the application
Configurations in KEB-Drive start at the top left. On the left, you’ll see drop-downs to select different gear types and sizes.

3.Motor Selection (Size, voltage, frequency)
Working to the right, I then select the size of the motor I want. Options for both Induction motors and AC Servo motors are listed. Here is a comparison of the advantages between servo and induction motors.

4.Adjust the Torque/Speed selection
Is it a speed reducer? Or a torque Increaser? It’s both – higher gear ratios will provide lower output speeds and higher torques. Use the drop down to see all the different possible configurations with the selected gearbox/motor combo.

5. What is the gearing Service Factor and why is it important?
The gearing service factor (SF) is the ratio between the:
A SF of 1.0 means the gears will have a nominal output torque equal to that of their rating. Selecting a motor/gear configuration with a SF of less than 1.0 is not advised. This means the gears will be undersized when operated at the nominal point. This could also indicate that the motor selected is too large.

6.Select gearmotor options (mounting style)
This section allows a user to select how the geared motor will be mounted. The flexibility of mounting is one reason that the KEB integral gearmotor solution has been so popular. Users can select a unit with an output shaft. Or a shaft mounted unit with a hollow bore. Mounting feet and mounting flanges can also be selected.