The conversion of rotary motion into linear motion in a stepper motor can be accomplished using several mechanical methods, including rack and pinion drives, belt drives, and other mechanical linkages. All these designs require various mechanical parts. The most efficient way to achieve this conversion is within the motor itself. A basic stepper motor generates rotation through the interaction of a magnetic rotor core with a pulsating electromagnetic field generated by the stator. A linear motor converts rotary motion into linear motion; the precision of this conversion depends on the rotor's step angle and the chosen method. The linear stepper motor, or linear stepper motor, first appeared in patent number 3,402,308 in 1968, granted to William Henschke. Since then, linear stepper motors have been used in many demanding fields, including manufacturing, precision alignment, and precision fluid measurement. The precision of a threaded linear motor depends on its thread pitch. A nut is installed at the center of the linear motor rotor, and a screw engages with this nut. To allow axial movement of the screw, a method must be used to prevent the screw from rotating with the rotor assembly. Because the screw's rotation is constrained, it achieves linear motion when the rotor rotates. Typical methods for achieving rotational constraint include using a fixed threaded shaft assembly inside the motor or a non-rotating but axially movable nut on an external threaded shaft. To simplify design, implementing linear transformation within the motor is meaningful. This method greatly simplifies design, enabling precise linear movement using linear motors directly without external mechanical linkages in many applications. Early linear motors used a combination of a ball screw and a ball nut. Ball screws offer efficiency improvements of over 90%, while trapezoidal threads provide only 20%-70% efficiency depending on the thread conditions. Although ball screws are an efficient method for converting rotary motion to linear motion, ball nuts require high calibration, are bulky, and expensive. Therefore, ball screws are not a practical solution in most applications. Most equipment designers are familiar with linear motors based on hybrid stepper motors. This product has been around for many years and, like other equipment, has its own strengths and limitations. The inherent advantages of linear motors include their simple, compact design, brushless operation (and therefore no sparks), remarkable mechanical benefits, practicality, and reliability. However, in some situations, linear motors cannot be used in certain devices because their durability cannot be guaranteed without routine maintenance. Several methods have been developed to overcome this limitation, enabling linear motors to achieve greater durability and maintenance-free operation. Due to the brushless design of stepper motors, the only components prone to wear are the rotor bearings and the threaded engagement consisting of a lead screw/nut. Recent improvements in ball bearings have provided long-life products suitable for linear motion. The lifespan and durability of the lead screw and nut combination have also been improved recently. Improving Durability First, it is necessary to understand the basic structure of the motor. A good example is the Size 17 motor, which belongs to the smaller size family of hybrid stepper motors. Conventionally, linear motors use a hollow shaft machined from a bearing-grade metal material (such as bronze), which has internal threads and connects to a threaded guide rod. The hollow shaft is mounted along the rotor axis. The guide rod material is typically stainless steel, which offers considerable corrosion resistance. Most parts use machined threads (such as #10-32), which can be single-start or multi-start, depending on the required precision and speed of the motor. Machined threads are generally chosen as "V" threads because they are easy to machine and can be rolled. While this is more suitable for machining, it is disadvantageous for power transmission. Acme threads are more suitable in comparison, mainly for the following reasons: Acme threads are designed to be more efficient. From a usage perspective, low loss (including friction) means less wear and longer service life. The reason is easy to understand from the basic geometry of threads. The angle between the opposite faces of a "V" thread is 60 degrees, while that of an Acme thread is only 29 degrees. Assuming the same friction, torque and thread angle, a "V" thread can transmit about 85% of the force of a trapezoidal thread. The efficiency can be calculated using equations (1) and (2) because the thread used is V-shaped, depending on the load direction. The ratio can be calculated by dividing the efficiency of a 60-degree thread by the efficiency of a 29-degree thread. The efficiency calculation here does not take into account the additional losses caused by the high pressure on the surface of the "V" thread. Acme threaded guide rods are generally manufactured for power transmission, so their surface finish, pitch accuracy, and tolerances are strictly guaranteed. "V" threads are primarily used for fastening, so their surface finish and straightness are not strictly controlled. Meanwhile, the nut driving the screw becomes even more important, as it is typically embedded in the motor rotor. Traditional nut materials use bearing-grade bronze with internal threads, a balancing act between physical stability and lubrication. Of course, it's described as a balancing act because it's not particularly excellent in either aspect. A better material for the drive nut in linear motors is a self-lubricating thermoplastic. This is because using new engineering plastics reduces the coefficient of friction in the screw-nut motion. Figure 3 compares the frictional properties of different internal thread rotor materials. The results are obvious, but why not use a plastic drive nut? Plastic is good for threads, but unfortunately, engineering plastics are unstable for the rotor journals in hybrid motors. Since motor temperatures can rise to 167°F during operation, plastic can expand by 0.004 inches, while brass expands only 0.001 inches under the same thermal conditions. As shown in Figure 4, the bearing journal is crucial in hybrid motor structures. To achieve optimal performance, hybrid motors must maintain a clearance of a few thousandths of an inch between the rotor core outer diameter and the stator inner diameter during design. If the rotor assembly is misaligned, it will rub against the stator inner wall. Designers aim to achieve good results in both thread life and bearing journal stability by selecting appropriate materials, and an injection-molded metal rotor structure with internal threads is an ideal choice. (Figure 5) This structure significantly improves motor life and efficiency while reducing operating noise. The motor life is longer than that of conventional bronze nut structures used in other motors, and it requires no maintenance. (Figure 6)