Designing and Manufacturing Miniature Stepper Motors

In a world where devices are getting smaller, but must still perform like their larger counterparts, designing hybrid stepper motors to be flexible and accurate takes some design expertise.

Miniaturization is a continual concern for many industries and one of the major trends over recent years. In everything from hand tools to desktop and factory equipment—whether for production, testing, or everyday laboratory use—smaller and more powerful motors are needed for motion and positioning systems. As equipment gets exponentially smaller, the challenges of designing devices to fit this equipment grows.

Lin Engineering, miniature motors, stepper motors

The 106 Series hybrid stepper motor provides micro-stepping capabilities in a small package that also offers high holding torque and high accuracy. (Image source: Lin Engineering)

Of course, companies have been designing and manufacturing small stepper motors for a long time. Yet small enough motors still don’t exist for many applications, which forces buyers into a corner and causes designs to be larger than necessary—ultimately affecting user satisfaction.

On the occasion when motors can be located that are small enough, these products lack the critical specifications needed for the application to perform properly. For instance, they may not have the torque or speed needed for the device to be competitive in the market. The sad option is to use a large-framed stepper motor and shrink all of the components around it, often requiring special brackets and mounting hardware. You can see that motion control in this small a scale is the challenging bottleneck that forces engineers to compromise on the footprint of their devices.

Making Miniature Motors

The miniaturization of stepper motors is challenging because the performance of the motor is directly related to its size. As the size of the frame decreases, so does the room for rotor magnets and windings. This affects the maximum torque output available as well as the speed at which the motor can operate. Of the manufacturers that have tried to create a NEMA 6 size hybrid stepper motor in the past, most have failed, suggesting that the NEMA 6 frame size was too small to provide any useful performance.

To tackle this issue, Lin Engineering increased the step angle from a typical 1.8 degrees to 3.46 degrees. This allowed nearly four times more holding torque—at up to 2.1 oz-in compared to a conventional permanent magnet stepper motor of similar size (which tops out at 0.5 oz-in).

Lin Engineering, miniature motors, stepper motors

Mounted and ready for use, the 106 Series hybrid stepper motor combines compact size with high precision. (Image source: Lin Engineering)

A typical PM motor delivers about 20 steps per revolution—a step angle of 18 degrees. With the 3.46 degree motor, it is able to deliver 5.7 times higher resolution than a typical PM motor. This resolution translates directly into higher precision by providing the benefits of a hybrid stepper with none of the drawbacks of a PM motor. To this change in step angle, add a low inertia rotor design and the motor can achieve over 1 oz-in of dynamic torque at nearly 8,000 rpm, delivering similar speed performance as that of a standard brushless DC motor.

Application Focus in Medical

Miniature stepper motors might be the solution to many small footprint applications. They can be used in a broad variety of industries that require compact size while maintaining high levels of accuracy. The medical industry, in particular, benefits from the cost-efficiency of miniature stepper motors for equipment from the emergency room to the patient’s bedside and the laboratory.

Presently, there is a lot of interest in handheld pipettes, where miniature motors provide the high resolution needed for accurate dispensing of chemicals. These motors provide higher torque and quality for their size when compared to other products on the market used for these purposes.

Mini Steppers for the Lab

For the laboratory, small linear stages that provide the benefits of a miniature stepper motor have become a baseline for quality. Such stages are the hallmark of other industries as well. Anywhere compact size is an issue, such motors become the solution. Whether robotic arms or simple XYZ stages, stepper motors are easy to interface and provide open- or closed-loop functionality.

However, miniature stepper motors are difficult to design and manufacture and often fail to compete with larger motors for applications. With a unique design approach, a hybrid stepper motor can be created that is well suited for many applications requiring tiny motors. This is especially true in the field of medical devices and laboratory automation.

Overall, applications that require a high degree of precision, such as miniature pumps, fluid metering and control, pinch valves, and optical sensor controls, can take advantage of this technology. The product can even be incorporated into motorized hand tools like electronic pipettes, where hybrid stepper motors were previously impossible to integrate.

Terry Persun spent six years in the Air Force as an airborne navigations technology specialist, worked as an engineer in military, medical, and commercial applications, and has been a freelance technology writer for over twenty-five years. 

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