Unipolar stepper motors

Summary

This video covers the fundamentals of unipolar stepper motors, explaining their construction, operation, and key differences from bipolar stepper motors. It highlights common wiring configurations, such as the six-wire and five-wire setups, and discusses how unipolar motors can be driven with low-side FETs. The video also explores methods for adapting unipolar motors to work with bipolar drivers, offering insights into torque, speed, and inductance considerations. Additionally, it provides guidance on using half-bridge drivers and different step modes for optimal motor performance in various applications.

Takeaways

• 😀 Unipolar stepper motors are commonly used in textile machines, industrial printers, pachinko machines, and slot machines.
• 😀 Unipolar and bipolar stepper motors differ in their construction: unipolar motors have a center tap, while bipolar motors do not.
• 😀 A unipolar stepper motor typically uses a six-wire configuration with two VM taps and four wires connected to the motor windings.
• 😀 Bipolar stepper motors use H-bridges to allow current to flow in both directions, delivering higher torque compared to unipolar motors.
• 😀 Unipolar motors can drive a motor in both directions without needing to reverse the current, making them simpler to control.
• 😀 Unipolar stepper motors require only low-side FETs to operate, simplifying the drive circuitry.
• 😀 To operate a unipolar stepper motor as a bipolar motor, you can either ignore the center tap or use half of the winding.
• 😀 Ignoring the center tap on a six-wire unipolar motor allows for bipolar current flow and higher torque, but with limitations on maximum speed.
• 😀 Using half of the winding from a unipolar motor allows for higher available torque at high speeds but results in lower torque at lower speeds and noisier waveforms.
• 😀 TI offers integrated low-side drivers that can easily drive unipolar stepper motors, and these can be adapted for bipolar use with minor reconfiguration.
• 😀 Unipolar motors can be driven using four-channel half-bridge drivers in full-step or half-step modes, with PWM inputs controlling the MOSFETs.

Q & A

What is the key difference between unipolar and bipolar stepper motors?

The key difference between unipolar and bipolar stepper motors lies in their wiring and the direction of current flow. Unipolar motors have two windings per phase with a center tap, and current flows in one direction only. Bipolar motors have a single winding per phase, and current can flow in both directions, allowing for more torque production.

What are common applications of unipolar stepper motors?

Unipolar stepper motors are commonly used in textile machines, industrial printers, pachinko machines, and slot machines, due to their simplicity and ease of use with drivers.

How are unipolar stepper motors typically wired?

Unipolar stepper motors are typically wired in a six-wire or five-wire configuration. In a six-wire setup, there are two center taps connected to the motor voltage supply (VM), and four wires control the motor windings at phases A, B, C, and D.

How does the current flow in a unipolar stepper motor?

In a unipolar stepper motor, the current flows in one direction through the windings, with each phase energized individually. The current direction is always the same, which is why it's called 'unipolar'.

What is the advantage of using bipolar stepper motors?

Bipolar stepper motors offer more torque than unipolar motors because they use full copper windings, and the current can flow in both directions, creating a stronger magnetic field. This results in better performance, particularly for high-torque applications.

How do bipolar stepper motors differ in terms of wiring?

Bipolar stepper motors have only a single winding per phase and require four wires. There is no center tap, and the current flows in both directions through the winding, which is controlled by an H-bridge circuit.

What methods can be used to drive unipolar motors with bipolar drivers?

There are two main methods: Method 1 is to ignore the center tap and disconnect it, allowing bipolar current flow through the motor windings. Method 2 is to use only half of the winding by isolating the center tap, allowing for bipolar current flow while reducing inductance at higher speeds.

What are the advantages and drawbacks of using Method 1 to drive a unipolar motor with a bipolar driver?

Using Method 1 (ignoring the center tap) increases torque at low speeds by utilizing the full winding. However, the increased inductance results in a faster drop in torque at higher speeds, which limits the motor's maximum speed.

What are the advantages and drawbacks of using Method 2 (half-winding configuration) to drive a unipolar motor?

Method 2 (half-winding configuration) reduces coil inductance, allowing for higher available torque at high speeds. However, this method results in lower torque at low speeds and produces noisier voltage and current waveforms.

How can unipolar stepper motors be controlled using PWM inputs?

Unipolar stepper motors can be controlled using four-channel half-bridge drivers, which are controlled by Pulse Width Modulation (PWM) inputs. The PWM controls the low-side MOSFETs in succession, allowing the motor to be driven in full-step or half-step mode, providing finer control over the motor's movement.