In this article, we’re delving deeper into two types of stepper motors—high-resolution and encoder types—and exploring how they can enhance precision in critical laboratory automation applications like autosamplers.
Jump to sections:
- What is an autosampler?
- Examples of Autosamplers
- How to Improve the Positioning Precision of Stepper Motors?
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**What is an Autosampler?**
An autosampler is an automated device designed to deliver samples to an analytical instrument for examination. Commonly used in laboratory automation, autosamplers can handle the testing of large batches of samples efficiently. They either collect samples periodically from a larger source and transport them to a sampling station, or move a sampling tool to the samples located on a carousel. A practical example is testing blood samples for viral diseases.
Positioning precision and accuracy are vital for repetitive sample movements, making stepper motors and servo motors essential components. Stepper motors are particularly advantageous for tasks involving sample injection and syringe movement due to their precise control and positioning capabilities. For more demanding applications requiring higher throughput, servo motors can provide greater torque and speed. Both types of motors are often paired with mechanisms like belts, screws, or racks to convert rotational motion into linear motion. Here, we’ll focus on stepper motors.
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**Examples of Autosamplers**
Autosamplers come in various forms depending on the type of samples they handle. For instance, there are models designed for liquid or gaseous samples and others tailored for solid samples, such as those used in gamma-ray measurements. These machines rely heavily on precise positioning, meaning the motors powering them must exhibit similar levels of accuracy.
A typical 2-phase hybrid stepper motor usually steps at 1.8° and achieves ±0.05° (±3 arc minutes) stop accuracy when operating in open-loop mode. Enhancing the positioning precision of the motor can significantly improve the overall performance of the machine.
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**How to Improve the Positioning Precision of Stepper Motors?**
To boost positioning precision, you can either increase the motor’s resolution or add an encoder—or both. In this article, we’ll focus on two types of stepper motors that can help achieve this: the high-resolution type and the encoder type.
**Option 1: High-Resolution Type Stepper Motor**
Switching to a high-resolution type stepper motor doubles the motor’s resolution because the tooth pitch is halved from 7.2° to 3.6° (360° divided by 50 or 100 teeth). This allows stepping at 0.9° instead of 1.8°, leading to finer resolution and improved movement precision.
In a high-resolution stepper motor, the number of rotor teeth increases to 100 compared to 50 in the standard type, reducing the tooth pitch by half and making the basic step angle 0.9°. Better angle-torque characteristics also minimize the negative effects of frictional loads, such as those encountered in ball screw applications.
**Option 2: Encoder Type Stepper Motor**
While a standard hybrid stepper motor won’t miss steps if sized correctly for the load and speed, modern designers of automated machinery and robots require higher reliability. Many are now using closed-loop systems to ensure the motor doesn’t miss steps during operation. Missing steps can disrupt subsequent motions and processes, so preventing this issue is crucial for stepper motors.
Adding an encoder to the motor’s rear shaft and closing the feedback loop to the controller allows the system to monitor and verify the motor’s travel distance. By comparing the number of commanded steps to the encoder’s pulse count, missed steps can be automatically corrected to avoid delays.
Oriental Motor offers various pre-assembled encoder options for the PKP Series. Compact incremental encoders with different resolutions, channel numbers, output types, and electrical specifications provide maximum flexibility when working with host controllers or PLCs. For better noise immunity over longer distances, consider using a line driver output type encoder.
**Encoder Specifications**
| Encoder Code | Type | Resolution | Output | Input Current | Input Voltage | Output Type | Output Voltage (Low) | Output Voltage (High) | Response Frequency |
|--------------|--------------|------------|----------------------|---------------|---------------|---------------|-----------------------|------------------------|--------------------|
| R2E | Incremental | 200 P/R | A-phase, B-phase, Z-phase (3ch) | 45 mA or less | 5 VDC ±10% | Voltage | 0.5 VDC or less | 4.3 VDC or more | 100 kHz |
| R2F | Incremental | 400 P/R | A-phase, B-phase, Z-phase (3ch) | 45 mA or less | 5 VDC ±10% | Voltage | 0.5 VDC or less | 4.3 VDC or more | 100 kHz |
| R3J | Incremental | 1000 P/R | A-phase, B-phase, Z-phase (3ch) | 45 mA or less | 5 VDC ±10% | Voltage | 0.5 VDC or less | 4.3 VDC or more | 100 kHz |
| R2EL | Incremental | 200 P/R | Line Driver | 30 mA or less | 5 VDC ±10% | Line Driver | 0.5 VDC or less | 2.5 VDC or more | 200 kHz |
| R2FL | Incremental | 400 P/R | Line Driver | 30 mA or less | 5 VDC ±10% | Line Driver | 0.5 VDC or less | 2.5 VDC or more | 200 kHz |
| R3JL | Incremental | 1000 P/R | Line Driver | 30 mA or less | 5 VDC ±10% | Line Driver | 0.5 VDC or less | 2.5 VDC or more | 200 kHz |
Oriental Motor’s PKP Series stepper motors are renowned for their quality and versatility, offering both high-resolution and encoder types. The series includes 2-phase bipolar (4-wire), 2-phase unipolar (6-wire), and 5-phase bipolar (5-wire) options to suit your preferred driver. Opt for a 5-phase motor if your application demands lower vibration or noise.
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**Conclusion**
For precision-driven applications like autosamplers, choosing the right stepper motor is critical. Whether you opt for a high-resolution stepper motor or one equipped with an encoder, both solutions can significantly enhance the accuracy and reliability of your system. Always feel free to reach out to our knowledgeable technical support team for assistance with our products.
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This article aims to provide a comprehensive overview of how stepper motors can improve positioning precision in laboratory automation. If you have further questions or need tailored advice, don’t hesitate to get in touch!
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