Thursday, May 17, 2018

Using way of the micro step motor


A stepper motor is a special type of brushless DC motor.  Electromagnetic coils are arranged around the outside of the motor. The center of the motor contains an iron or magnetic core attached to a shaft. By sequencing the voltage of the coils precise rotational control can be achieved at relatively low cost. The drawback is, the control is generally open loop, so the system does not know if the motor stalls or gets out of sync with the controller. How do you know if your stepper motor is a unipolar or a bipolar stepper motor just by looking at it? There are three main ways (yes, stepper motors do have a lot of variation) that a stepper motor can be driven. These three driving styles are full-step drive, half-step drive, and micro stepper motor for sale. Full-step drive always has two electromagnets (or at least two different current flows) energized at the same time. In most cases, the motor you are looking at is both. Unipolar and bipolar are just modes that you can use to run the stepper motor. 
Nema 23 Stepper Motor Drive 24-50VDC 1.5A-4.5A 256 Microstep M542T
The only time a stepper motor is not able to be run in either mode is when there are only four wires coming out of the stepper motor, corresponding to the both ends of the two coils and no central tap wire. If you do have more than four wires, (whether five, six, or even eight wires) at least one of those wires is a center tap wire. You can figure out which wire is which by either looking up the datasheet for your motor or measuring the resistance between two wires at a time with a multi-meter. If one particular wire always measures half of the resistance that other pairs of wires report, then you know that wire must be tapped in the middle (hence half the resistance) of a coil. Despite all of this information, we haven’t actually learned how we can run our motors. To rotate the central shaft, one of the current flows is shut off, “turning off” the electromagnet, and a different current flow is started “turning on” another electromagnet. This driving style has the most torque because two electromagnets are always energized but also has the largest step size. The half-step drive is similar to the full-step drive, but switches between having one or two electromagnets energized. 

One electromagnet will start out energized and then a second one will be “turned on”. Next, the first electromagnet will be “turned off” while leaving the second electromagnet energized. A new current flow will then be started to energize the “third” electromagnet in addition to the second electromagnet being “turned on”. This driving style results in half of the step size of the full-step drive, allowing for more precision, but also results in less torque because there are not always two electromagnets that are energized. Microstepping, such as the nema 42 stepper motors for sale that must have a stronger power than nema 8 stepper motor for sale that you probably suspect, has the smallest step size out of these driving styles. 
Dual Shaft Nema 42 CNC Stepper Motor 30Nm (4248oz.in) 8A 110x201mm 4 Wires
The way it works is by applying a variable amount of voltage to each of the coils in a sinusoidal fashion. The smaller voltage (and thus current flow) increments you are able to produce, the smaller the step size. However, this also results in a variable amount of torque that the stepper motor exhibits, depending on where you are in the step sequence. Most drivers have a thermal protection feature that disables the driver for a brief period of time to allow it to cool.  If you are loosing steps or hear a ticking or pulsing sound from your motors, it could be due to thermal shutdown.

1 comment:

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