2-Phase Stepper Motor: Types, Working Principles, and Uses

A stepper motor, also referred to as a step motor, operates by rotating in a sequence of small angular steps rather than continuous rotation. It is a brushless synchronous DC motor, distinguishing itself from standard electric motors that rotate continuously until the DC voltage is cut off.

Stepper motors function as digital input-output devices, offering precise control over initiation and cessation. Their versatility, reliability, cost-effectiveness, and accuracy make them invaluable for controlling exact motor movements. This capability enhances the precision and efficiency of programmed motions across diverse applications and industries. Notably, the 2-phase stepper motor is recognized for its efficiency and accuracy.

In this article, we will delve into the 2-phase stepper motor, exploring its working principles, types, applications, and the factors to consider when choosing it.

What is a 2-phase Stepper Motor?

A 2-phase stepper motor is a variant distinguished by having two phases, conventionally named "A" and "B." The stator of a 2-phase motor comprises 8 magnetic poles with small teeth. This design is widely embraced due to its cost-effectiveness, the prevalence of compatible drives, and a well-balanced blend of speed, torque, and accuracy.

Comprising two bipolar coil windings carrying current, the motor designates the vertical coil phase as "V" and the horizontal one as "H." The bipolar coils alternate in polarity, signifying that when the V phase's polarity changes, the subsequent change occurs in the H phase.

In driving a 2-phase stepper motor, full current energizes its windings, prompting the motor to move in full-step increments. This motion is achieved as the drive executes one complete step.

Regarding construction and operational principles, a 2-phase stepper motor shares similarities with a single-phase motor. The primary difference lies in the absence of a starting winding, a feature in single-phase motors. Instead, a winding symmetrical to the main one, shifted by 90 degrees, assumes the role of the starting winding.

Notably, a 2-phase stepper motor demands twice the power compared to a single-phase counterpart. However, it compensates by delivering 41.4% more torque at the rotating shaft. This enhanced torque renders 2-phase stepper motors suitable for diverse applications where precise control and positioning are imperative.

2-phase Stepper Motors Types

There are two main types of 2-phase stepper motors: unipolar and bipolar.

Bipolar Stepper Motors

A bipolar stepper motor is distinguished by the absence of a center tap and the presence of one winding per phase. Typically furnished with four wires representing the two ends of each winding, this stepper motor operates uniquely. Bipolar stepper motors have two coils per phase, and each coil is equipped with its own positive and negative leads. This specific setup facilitates a more intricate energization process, resulting in the ability to generate increased torque and achieve higher rotational speeds.

One notable advantage of bipolar stepper motors is their capacity to produce more torque than unipolar stepper motors of equivalent size. This is accomplished by fully utilizing the winding instead of only half during operation. However, it's essential to acknowledge that this enhanced performance comes at the expense of necessitating a more complex driver circuit. The driver circuit must be able to reverse the current direction in each winding, introducing an added layer of complexity to the control system. Despite the requirement for a sophisticated driver, the bipolar stepper motor's ability to deliver higher torque makes it the preferred choice in applications where power and precision are paramount considerations.

Unipolar Stepper Motors

A stepper motor of the unipolar variety operates with a unique setup featuring a single winding with a central point per phase. This design involves activating each winding segment for every magnetic field orientation. The commutation circuit streamlines the process, allowing the magnetic pole to reverse without changing the direction of the current flow. In a standard 2-phase stepper motor, the shared central point for each winding typically incorporates six connections.

Unipolar stepper motors are identified by one coil per phase, with each coil including a central point. This configuration permits the coils to be connected in a way that enables them to be energized with either a positive or negative voltage. The simplicity of wiring and control is a significant advantage of unipolar motors. However, it's crucial to recognize that they generally exhibit lower efficiency compared to their bipolar counterparts. Despite this efficiency compromise, the straightforward wiring and control make unipolar stepper motors a pragmatic choice in applications where simplicity and user-friendliness take precedence over maximizing torque or rotational speed.

2-phase Working Principle

Here's an overview of the working principle of 2-phase stepper motors, complemented by visuals for clarity:

1. Motor Structure:

• Stator: Houses a series of electromagnets arranged in two phases (A and B).

• Rotor: A toothed wheel crafted from magnetic material aligns with the stator's magnetic field.

2. Coils Activation:

• Controlling Rotation: The motor's rotation is managed by selectively activating coils in a specific sequence.
• Sequence Example: A straightforward full-step sequence for a 2-phase motor could be: A+, B-, A-, B+.

3. Incremental Movement:

• Discrete Steps: When a coil is activated, the rotor aligns with the new magnetic field, resulting in a distinct rotational step.
• Precise Positioning: This enables accurate positioning and control of the motor's motion.

4. Synchronized Transition:

• Smooth Rotation: To achieve seamless rotation, coils switch synchronously, ensuring a continuous magnetic field for the rotor.

5. Torque Generation:

• Magnetic Interaction: Motor torque results from the stator and rotor magnetic fields interplay.
• Torque Influencing Factors: Design, coil current, and motor load impact the produced torque.

6. Key Points Recap:

• Discrete Steps: 2-phase stepper motors move precisely in distinct steps.
• Sequential Coil Activation: Rotation follows a predefined sequence of coil activation.
• Synchronized Transition: Coordinated coil switching is vital for smooth rotation.
• Magnetic Interaction: Torque emerges from the magnetic field interplay.

Applications of 2-Phase Stepper Motor

3D Printing:

Accurate Motion Management: 2-phase steppers propel the X, Y, and Z axes, ensuring meticulous layer-by-layer printing precision.

Computer Numerical Control (CNC) Machines:

Regulated Milling and Cutting: Steppers govern the movement of cutting tools in CNC machines, facilitating intricate designs and exact cuts.

Automation:

Articulated Robot Joints: Steppers in robotic joints provide controlled movement and precise positioning for diverse actions and tasks.

Medical Equipment:

Diagnostic Instruments: Steppers in medical devices, such as syringes and pumps, guarantee precise dosage control and seamless operation.

Surveillance Systems:

Camera Pan-Tilt Mechanisms: Steppers in surveillance cameras facilitate controlled pan and tilt movements for comprehensive monitoring.

Office Technology:

Paper Feeders and Scanners: Steppers precisely manage paper movement in printers, scanners, and other office apparatus.

DIY and Recreational Projects:

3D Printer Enhancements and DIY Robotics: Enthusiasts leverage 2-phase steppers for customized ventures like 3D printer upgrades and DIY robotic creations.

Music Instruments:

Electronic Drum Pads and Synthesizers: Steppers integrated into electronic drums and synthesizers offer tactile feedback and accurate control, enhancing the authenticity of playing experiences.

Automotive Sector:

Mirror Adjustment and Valve Control: Automobile steppers regulate functions such as mirror adjustment and valve timing with precision and dependability.

How to Choose the Right 2-Phase Stepper Motor?

Choosing the most suitable 2-phase stepper motor for your project involves thoroughly assessing several crucial factors. Here's a detailed breakdown to assist you in navigating the selection process:

1. Define your application's requirements:

• Torque Requirement: Evaluate the necessary torque considering factors like load weight, friction, and acceleration.
• Speed Requirement: Specify the desired rotational speed or travel distance per unit of time.
• Accuracy and Resolution: Clearly define the required precision in positioning and the number of steps per revolution.
• Environmental Conditions: Consider operating temperature, humidity, and vibration tolerance.

2. Explore motor specifications:

• NEMA Size: Determine the motor's physical size and footprint using the NEMA standard, with common sizes ranging from Nema 8 (small) to Nema 17 (larger).
• Holding Torque: Consider the motor's ability to maintain position against an applied load when not energized, ensuring it exceeds the required operating torque.
• Step Angle: Understand the angular displacement per step; smaller step angles offer finer positioning, potentially requiring micro stepping drivers for smoother operation.
• Phase Current and Voltage: Match the motor's current and voltage requirements with your driver's capabilities.

3. Popular Models in the Market:

• Comparative Analysis: Analyze popular 2-phase stepper motor models to uncover their features, benefits, and limitations. TMC2208 and TMC2209 are among the most popular 2-phase stepper motors, and we offer a comprehensive comparison of both in the previous article that How to Choose the Right Stepper Motor Drivers between TMC2208 and TMC2209.
• Customer Reviews and Recommendations: Gain insights from real-world experiences shared through customer reviews on specific models' practical performance and reliability.

4. Additional considerations:

• Motor Type: Consider the trade-offs between unipolar and bipolar motors, weighing simplicity against efficiency and torque.
• Driver Selection: Choose a driver compatible with your motor's specifications, offering features like micro stepping and protection circuits.
• Noise and Vibration: Assess the impact of motor-generated noise and vibration, especially in sensitive applications.
• Cost and Availability: Compare prices and lead times to find the most valuable option for your project.

Remember, your project's ideal 2-phase stepper motor hinges on a unique combination of factors. By meticulously assessing your application needs and exploring available options, you can make an informed decision that ensures the success and efficiency of your operation.

How to Drive 2-Phase Bipolar Stepping Motors

A fundamental block diagram illustrating a sample 2-phase bipolar driving circuit.

The 2-phase bipolar stepper motor can be effectively controlled using a 2-channel H-bridge drive circuit. The block diagram exemplifies a circuit employing Pulse Width Modulation (PWM) for consistent current control, operating like "Driving Brushed DC Motors Using PWM Output."

Two current regeneration modes, namely Slow Decay and Fast Decay, lead to the attenuation of motor current. In certain modes, suboptimal current tracking may induce vibrations and noise. To address this, certain drivers feature a mixed decay function, allowing external adjustment of the Slow Decay to Fast Decay ratio. A more in-depth exploration of current regeneration modes will be provided in Part 2.

The accompanying waveforms illustrate the drive scenarios for a 2-phase bipolar stepper motor, encompassing two-phase excitation (Slow Decay), 1-2 phase excitation (2-phase full torque, Slow Decay), 1-2 phase excitation (2-phase torque = single-phase torque, Slow Decay), and 1/4-step excitation (Slow Decay). The correlations between input signals (INxx), output voltages (OUTxx), output currents, and the number of steps are noteworthy. Utilizing 1/4-step excitation allows for finer steps and more gradual current changes, facilitating smooth motor rotation.

2-Phase vs. 5-Phase Hybrid Stepper Motor

Two key differences exist between 2-phase and 5-phase stepper motors. The initial contrast is in their mechanical structure. A stepper motor comprises a stator and a rotor. The rotor consists of three elements: rotor cup 1, rotor cup 2, and a permanent magnet. In a 2-phase motor, the stator features 8 magnetic poles with small teeth, whereas the stator of a 5-phase motor comprises 10 magnetic poles, with each pole having its winding.

The second disparity lies in the number of phases. A 2-phase motor has two phases, denoted "A" and "B," whereas a 5-phase motor encompasses five phases. Fundamentally, the term "phases" refers to the diverse combinations of poles that are sequentially energized to attract the rotor.

Conclusion

In conclusion, the 2-phase stepper motor emerges as a powerful and versatile component in motion control. Its precision, energy efficiency, and adaptability make it indispensable in various industries. Whether you're involved in robotics, CNC machining, or DIY projects, understanding the dynamics and considerations of 2-phase stepper motors empowers you to make informed decisions and harness the full potential of this technology. Encourage exploration and implementation to embrace the future of motion control.

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