In this article, we'll take a closer look at two types of stepper motors: high-resolution and encoder types, and how they can enhance precision in critical laboratory automation applications like autosamplers.
If you scroll down, you’ll find a table with quick links:
- What is an autosampler?
- Examples of Autosamplers
- How to Improve Positioning Precision of Stepper Motors?
An autosampler is essentially an automated device that feeds samples to an analytical instrument for testing. These machines are widely used in laboratory automation, especially when dealing with large batches of samples. They can either collect samples from a large source and bring them to a sampling station or move a sampling tool to the samples on a carousel. A practical example might be analyzing blood samples from patients for viral infections.
Positioning accuracy is crucial in these applications because the motors need to move samples to specific locations repeatedly. Servo motors and stepper motors are commonly used for this purpose. The precise control and positioning accuracy of stepper motors make them ideal for tasks like sample injection and syringe movements. For more demanding applications that require higher throughput, servo motors may be a better option due to their ability to provide higher torque and speed. Regardless of the motor type chosen, these motors are usually paired with mechanisms to convert rotary motion into linear motion, such as belts, ball screws, or rack and pinion systems. This article will focus primarily on stepper motors.
Let’s explore some examples of autosamplers:
- An autosampler for liquid or gaseous samples
- An autosampler for solid samples used in gamma-ray measurements
Both types require high positioning precision, which means the motors must deliver the same level of accuracy.
A standard 2-phase hybrid stepper motor typically steps at 1.8° and can achieve ±0.05° (±3 arc minutes) stop accuracy while running in open-loop. Enhancing the positioning precision of the motor can significantly improve the overall performance of the machine.
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: high-resolution and encoder types.
Option 1: High-Resolution Type Stepper Motor
By replacing a standard 2-phase stepper motor with a high-resolution type 2-phase stepper motor, the resolution doubles due to the tooth pitch being reduced from 7.2° to 3.6° (360° divided by 50 or 100 teeth). This means you can step at 0.9° instead of 1.8°, which improves the precision of movement.
High-resolution stepper motors have double the number of rotor teeth (100 compared to 50 with the standard type). As a result, the tooth pitch is halved, and the basic step angle becomes 0.9°. Higher resolution allows for finer movement, but it doesn’t necessarily increase accuracy. Better angle-torque characteristics help minimize the negative effects of frictional loads, such as those encountered in ball screw applications.
Option 2: Encoder Type Stepper Motor
While standard hybrid stepper motors won’t miss steps if properly sized for the load and speed, modern machine and robot designers demand more reliability. Many are now closing the loop to ensure the motor doesn’t miss steps during operation. For stepper motors, missing steps can have immediate consequences on subsequent motions and other processes.
Adding an encoder to the rear shaft of a stepper motor and closing the feedback loop to the controller allows the motor's travel distance to be monitored and verified. By comparing the number of commanded steps to the number of pulses from the encoder, missed steps can be automatically corrected to prevent delays.
Oriental Motor offers various encoder types that can be preassembled. For the PKP Series, compact incremental encoders of different resolutions, channel counts, output types, and electrical specifications are available, providing maximum flexibility with host controllers or PLCs. For better noise immunity over longer distances, consider using a line driver output type encoder.
Here are the 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 (TTL equivalent) | 0.5 VDC or less | 4.3 VDC or more (no load) | 100 kHz |
| R2F | Incremental| 400 P/R | A-phase, B-phase, Z-phase (3ch) | 45 mA or less | 5 VDC ±10% | Voltage (TTL equivalent) | 0.5 VDC or less | 4.3 VDC or more (no load) | 100 kHz |
| R3J | Incremental| 1000 P/R | A-phase, B-phase, Z-phase (3ch) | 45 mA or less | 5 VDC ±10% | Voltage (TTL equivalent) | 0.5 VDC or less | 4.3 VDC or more (no load) | 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 include both high-resolution and encoder types. These motors are designed to meet the demands of modern automation applications, ensuring reliable and accurate performance.
If you want to learn more about the PKP Series stepper motors, check out the videos below:
- Video 1: Introduction to PKP Series High-Resolution Type Stepper Motors
- Video 2: Overview of PKP Series Encoder Type Stepper Motors
The PKP Series offers three types of stepper motors: 2-phase bipolar (4-wire), 2-phase unipolar (6-wire), and 5-phase bipolar (5-wire) to connect to your preferred driver. Use a 5-phase motor for applications requiring lower vibration or noise.
For further information or assistance, feel free to reach out to our knowledgeable technical support team.
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