Technical Guide Line

Comparison of Hybrid and Permanent Magnet Linear Stepper Motor

The average efficiency of hybrid motors is about 65%, while the efficiency of permanent magnet motors is about 25%. The main reasons for the difference in efficiency are the following two reasons :

The first reason is that the hybrid motor uses a silicon steel laminated stator assembly (see Figure 1), Compared with the stator assembly formed by stamping and forming of mild steel of permanent magnet motor, the laminated stator of hybrid motor has smaller eddy current loss and the silicon steel material in the laminated structure can reduce hysteresis error ; Therefore, the overall iron loss of the hybrid linear motor is smaller than that of the permanent magnet motor, so the efficiency of the hybrid motor is higher. At the same time, the step angle of the hybrid motor is 1.8 degrees or 0.9 degrees, compared with the step angle of 15 degrees or 7.5 degrees of the permanent magnet motor, and the resolution of each step is increased to 0.000060 inches [0.001524mm]. At 0.00025 inches [0.00635mm], hybrid motors have better positioning performance.

Figure 1: Silicon steel laminated stator assembly and low carbon steel stamping and forming assembly

The second reason is the magnetic circuit of the motor. The structure of the hybrid motor makes the air gap of the stator and rotor about 1/2 of that of the permanent magnet motor. The design air gap of a typical hybrid motor is 0.003~0.004 inches (0.0762~0.01016mm), compared to the permanent magnet motor's air gap of 0.007~0.008 inches (0.1778~0.2032mm). Smaller air gap provides more efficient magnetic coupling, resulting in higher torque. See Figure 2. Size 14 (35) single-stack hybrid motor and 35PM permanent magnet motor, the corresponding input power, the same screw, the same linear speed performance comparison curve, the hybrid motor is higher.

Figure 2. Air gap comparison of hybrid and permanent magnet motors

In addition to the above efficiency advantages, compared to permanent magnet motors, hybrid motors have other advantages as follows :

1, The linear stepper motor is particularly advantageous in positioning applications, because every time the controller sends a pulse, the motor rotates one step. The resolution of motion depends on the lead of the screw and the step angle of the motor. The 1.8 degree or 0.9 degree step angle of the hybrid motor (vs. the 15 degree or 7.5 degree step angle of a typical permanent magnet motor) increases the resolution to a full step of 0.000060 inches [0.001524mm], compared with permanent magnet motors full step of 0.00025 inches [0.00635mm], the hybrid motor has better positioning performance.

2, In many applications, motor installation plays an important role in the performance of the overall system. The front-end cover of the hybrid motor has a positioning boss concentric with the motor bearing to better center the motor to the mechanism during installation. See Figure 3

Figure 3: The concentricity of the positioning is helpful to the installation

3,The hybrid motor can install the encoder more conveniently, so as to achieve the purpose of closed-loop control. Because the metal rotor shaft used in the hybrid motor can be processed to more precise dimensional tolerances, it can be better installed with the encoder code disc, reduce runout and can use higher resolution code discs.

4, Improving the output performance without changing the size of the motor is a requirement for many applications. Hybrid motors with the same flange size can provide several different output powers by changing the overall motor thickness. The permanent magnet motor needs to re-adjust and design the entire mold, which requires a relatively large mold cost investment.

In summary, compared to permanent magnet motors, hybrid motors have higher efficiency due to their smaller iron loss, smaller stator and rotor air gaps, and higher output power density. These performance characteristics also really affect the cost; under the requirements of adaptive thrust, speed and resolution, permanent magnet motors are a feasible low-cost solution.

If your application requires high repeatability, high resolution, high-speed stability, or customized high-efficiency modules, DINGS’ hybrid motor is an ideal solution to meet your requirements.