Analysis of a Hybrid Step Motor - Part One

Hybrid stepper motors wholesale are used as actuators for equipment where position detection accuracy is required, such as the joints of robots or rotary tables for machine tools. The rotor has a construction that sandwiches a magnet that is magnetized in the axial direction between two rotor cores that have serrated teeth to create salient poles, and the tips of the stator core’s teeth are shaped like gears as well. Because the rotation resolution is determined by the number of rotor teeth and the number of phases for the drive coil, the design uses large number of teeth, such as 50 or 100, so the angle resolution can be increased .The most important characteristics for a stepper motor are the controllability, the detent torque, which is a non-excitation holding torque, and the stiffness torque, which is an excitation holding torque, and not the motor’s output.



The two-plated rotor core of a stepper motor has an N pole on one side and an S pole on the other, so a multipole magnet is achieved by deviating the saliency of the gear condition by 1/2 pitch. Consequently, the magnetic circuit is 3D. There are also times when the division pitch geometry of the teeth is complicated, so it is necessary to carry out a 3D electromagnetic field analysis using the finite element method (FEM) to proceed with an accurate preliminary study.



This document introduces how the detent torque and stiffness torque can be calculated for a hybrid nema 34 stepper motor.


The detent torque is shown in fig. 1, and the magnetic flux distribution in the XY-plane at the rotation position of 0.45 degrees is shown in fig. 2. A closer view to show the flux distribution in the gap is shown in fig. 3. These results reveal that the flux in both the rotor and stator is saturated even with no excitation. The flux leakage around the tips of the teeth, due to saturation, can be expected to have a large effect on the detent torque.



Fig. 4 shows the stiffness torque with one-phase excited and fig. 5 shows the stiffness torque with two-phase excited. The flux distribution in the gap of the XY-plane with one-phase excited is shown in fig. 6, and the flux distribution in the gap of the XY-plane with two-phase excited is shown in fig. 7. As with the detent torque, the magnetic flux around the teeth is saturated. The flux leakage caused by the saturation can be expected to also have a large effect on the stiffness torque.

What’s the difference between detent torque and holding torque?

How to set a stepping motor’s current limit

 Stepper-motor current limiting serves a few functions. Stepper-motor overcurrent can cause overheating as detailed in FAQ: Aren’t heat and noise common stepper motor problems? At its most extreme, overcurrent can cause rotor demagnetization. Recall that current effects acceleration — as in FAQ: What are the requirements for stepper motor acceleration? So any design that uses microstepping needs current limiting, as different windings require different current levels.

Options for current limiting abound. The simplest to use a resistor. This option is easy to implement but has drawbacks. It causes significant heating and (because factors such as motor inductance change with rotor position and frequently go undocumented) can be difficult to implement.



Another option — linear motor current limiters — employ a pair of power resistors. They offer better performance than simple limiters using a single resistor. Instead of limiting current linearly as resistor circuits, they limit current asymptotically … and usually the limit is far above a motor’s rated current. Both types of current limiters are automatic. However, they generate heat.

Still other methods exist to set current limit as part of open-loop systems.

One is to use a voltage boost at the beginning of startup. The controller delivers almost the entire supply voltage early. At the target current, the voltage drops down to only what’s necessary to maintain target current. Use of a dual-voltage supply is also possible. Here the drive applies high voltage until the current reaches the target level, then it switches to operating voltage and the high voltage switches off.

One caveat: This scheme can pose a problem if the drive applies the high voltage applies too long — as that can risk of burning out the motor or demagnetizing it. If the design uses software control to run this circuit and the programmer is unfamiliar with the application, the software may not prevent this situation.

Pulse-width modulation or chopping is another option. Here as current increases, the controller holds supply input to 100% duty cycle.

At target current, duty cycle drops to whatever is necessary to maintain operation. While effective, this method’s drawback is torque ripple. This can cause high-pitched noise in smaller motors. In larger motors, this can create ac voltages on nearby lines. To reduce ripple, designs will often increase the chopper frequency … but this can only go so far before losses are excessively high.

BASICS OF STEPPER MOTORS YOU SHOLD KNOW

Stepper Motor Driver Circuit You Shold Know

Technically stepper motor driver circuit is a Decade Binary Counter circuit. The advantage of this circuit is, it can be used to drive stepper motors having 2-10 steps. Before going any further let’s discuss more about the basics of stepper motor.


The name of this motor is given so because the rotation of shaft is in step form which is different from DC or any other motor. In other motors the speed of rotation, the stop angle are not in complete control unless necessary circuit is inserted. This non-control is present because moment of inertia, which is simply a character to start and stop on command without delay. Consider a DC motor, once its powered the speed of motor increases slowly until it catches the rated speed.

The step motor hybrid does not work on constant supply. It can only be worked on controlled and ordered power pulses. Before going any further we need to talk about UNIPOLAR and BIPOLAR stepper motorS. As shown in figure in a UNIPOLAR stepper motor we can take the center tapping of both the phase windings for a common ground or for a common power. In first case we can take black and white for a common ground or power. In case 2 black is take for a common. In case3 orange black red yellow all come together for a common ground or power.



In BIPOLAR stepper motor we have phase ends and no center taps and so we will have only four terminals. The driving of this type of stepper motor is different and complex and also the driving circuit cannot be easily designed without a microcontroller.

The circuit which we designed here can only be used for stepper motors of UNIPOLAR type.

The power pulsing of UNIPOLAR stepper motor wholesale price will be discussed in circuit explanation.


Circuit Components
+9 to +12 supply voltage
555 IC
1KΩ, 2K2Ω resistors
220KΩ pot or variable resistor
1µF capacitor, 100µF capacitor (not a compulsory, connected in parallel to power)
2N3904 or 2N2222 (no. of pieces depend on type of stepper if it’s a 2 stage we need 2 if it’s a four stage we need four)
1N4007 (no. of diodes is equal to no. of transistors)
CD4017 IC, .

Why do you use a stepper motor?