Pacific Scientific POWERMAX II stepper motor

Pacific Scientific POWERMAX II Stepper Motor: Performance Benchmark and Flexible Customization for NEMA 23 Framework

Product Overview and Industry Status

In the field of industrial automation, stepper motors, as the core executing components of open-loop positioning systems, directly affect the production efficiency and operating costs of equipment in terms of torque density, dynamic response, and long-term reliability. The POWERMAX II series hybrid stepper motors launched by Pacific Scientific (now a brand under Danaher Motion) have become a global performance benchmark in the NEMA 23 (2.3-inch base) size class due to their excellent torque output, innovative magnetic circuit design, and highly flexible customization capabilities. The maximum holding torque of this series of motors can reach 253 oz in (approximately 1.79 Nm), ranking among the top in the same size class. At the same time, the unity of economy and high performance is achieved through design for manufacturability (DFM). POWERMAX II not only offers standard models, but also supports various customization options such as low inertia rotors, integrated screws, special windings, etc. It is widely used in fields such as electronic assembly, medical equipment, packaging machinery, laboratory automation, and CNC machine tools.

Core Technology: Sigmax ®  Patent magnetic circuit

The core technological advantage of the POWERMAX II series lies in its patented Sigmax ®  Magnetic circuit design (US Patent No. 4712028, 4713470, 4763034, 4827164). During excitation of traditional hybrid stepper motors, some magnetic flux leaks from between the stator teeth and does not participate in torque generation, resulting in a decrease in efficiency. Sigmax technology embeds samarium cobalt (SmCo) rare earth permanent magnets in the stator teeth to focus the magnetic flux on the most effective working air gap position between the rotor and stator, thereby significantly suppressing magnetic leakage and increasing the torque generated per ampere of current. Compared with traditional hybrid design, Sigmax technology enables the motor to output larger holding torque and dynamic torque at the same current, while achieving higher current utilization and lower heat generation.

According to the different magnetic circuit structures, POWERMAX II is divided into two sub series:

P series (standard hybrid): adopts traditional hybrid rotor and stator structure, without rare earth magnet insertion. Provide cost-effective solutions suitable for most general positioning applications. Its step angle accuracy is ± 3% (non cumulative) of each step when there is no load, maintaining a torque range of 42-253 oz in.

M series (enhanced hybrid): Adopting Sigmax technology, samarium cobalt magnets are embedded in the stator teeth. Compared to the P series of the same size, the M series can provide higher torque output and better current utilization. Its step angle accuracy has been improved to ± 1.5% per step, making it suitable for situations with higher requirements for dynamic performance and positioning accuracy.

Rotor structure and inertia options

POWERMAX II offers two rotor structure options to accommodate different motion profile requirements:

L-type rotor (standard laminated rotor): using traditional silicon steel sheet laminated structure, with moderate rotational inertia. Suitable for most general motion controls, providing smooth operating characteristics.

J-shaped rotor (low inertia rotor): By optimizing the rotor geometry and material, the rotational inertia is reduced. A low inertia rotor can generate higher angular acceleration under the same electromagnetic torque, thereby achieving faster start stop and shorter positioning time. Especially suitable for applications that require frequent acceleration, deceleration, and fast positioning, such as surface mount machines, picking and placing mechanisms, etc.

Taking a double stack motor as an example, the standard rotor inertia is 3.57 × 10 ⁻³ oz in · s ² (0.022 × 10 ⁻³ kg · m ²), while the low inertia rotor is 2.59 × 10 ⁻³ oz in · s ² (0.016 × 10 ⁻³ kg · m ²), a decrease of about 27%. Theoretical normalized acceleration comparison shows that P22 series motors with low inertia rotors can increase acceleration by 30%, while M22 series motors can increase acceleration by 63%. It should be noted that the half stack model does not offer a low inertia rotor option.

Model Code and Selection Guide

The complete model code of POWERMAX II includes multiple information bits such as motor type, size, stack length, rotor type, winding, shaft options, connectors, etc. Taking the example model P21NRXS-LNN-NS-00 as an example for analysis (please refer to the original factory selection guide for the actual model code format, and here we will explain the general rules in conjunction with the document content):

The first character (series): P=POWERMAX II

Second character (stack length/machine base): 2=NEMA 23 frame; The following numbers indicate the stack length (1=half stack, 2=single stack, 3=double stack? P2H (half stack), P21, P22, etc. appear in the document, need to be compared).