Performance Analysis of Rotary Electromagnetic Micromotors Across Different Size and Weight Scales

Currently, REM micromotors are in a progressive stage of development and research. While the technical literature in this field may not be extensive, REM technology has shown immense promise in revolutionizing microelectromechanical systems (MEMS) and enabling precise motion control in miniaturized devices. REMs are finding various applications in robotics, medical instruments, and other fields due to advancements in micromachining technology [1, 2]. REMs are classified as small, medium, big, and micromotors, with the latter being a result of advanced technology. REMs are microelectromechanical device which is mainly used for energy conversion between mechanical and electrical Domains [3]. They generate mechanical energy through an electromagnetic actuator by producing a force from a magnetic field or varying reluctivity of the magnetic circuit [4].

The smallest commercial REMs, as defined in 1977, have a weight of 30 g and a size of 25×20mm. Miniaturization of REMs progressed with MicroElectroMechanical Systems (MEMS) processes in the 1990s [5, 6] and have become crucial components in minimal-invasive surgery, datacom, and positioning drives [3]. In 1999, High-precision motors in the millimeter range are key elements of micro-scanners in minimally invasive diagnostics and surgery as well as in data communication or positioning drives [7, 8]. In 2002, the external dimensions of the actuator using the electromagnetic principle are in the order of a few millimeters [4]. Another definition, the REM is a very small electromechanical device (1 μm to 1 cm) [9], The overall size of a microactuator system is typically in the range of a few centimeters, while important structures are in the micrometer range [10]. In 2020, The term "micromotor" actually includes relatively small motors ranging in size from microns to millimeters or larger [2]. The total size of a REM system ranges from several centimeters, with essential structures in the micrometer range. The definition of a REM can vary due to the existence of different types, and the length of a REM is not fixed.

The global micromotors market size was valued at USD 38.79 billion in 2021 [11], reflecting the high demand for miniaturized electromagnetism motors [8, 12] in various industries such as consumption, office, computer, home appliance, medical treatment, and industrial control. The market has grown thanks to the miniaturization processes that have led to the production of these motors with small volume, high efficiency, high torque, convenient control, and low cost [13]. The micro motor market is also driven by the established silicon manufacturing, and development infrastructure, and expertise in the field of MEMS (Micro Electro Mechanical Systems) [9].

Life processes span over 27 orders of magnitude on the mass scale, from molecules to whales. The identified scaling laws are related to several different mass processes. Recent findings describe a scaling law for the peak specific force of both biological and engineering actuators, where motor force scales either allometrically with the motor cross section or isometrically with the motor mass [12].

On the other hand, the electromagnetic structure of micro-actuators is significantly different from traditional motors [10]. Its being very necessary to present an analysis of a sample micromotors manufactured in series, because the technical literature is not very rich in this area of research.

A comparative study is conducted among several micromotors from manufacturers Faulhaber and Maxon. The aim is to analyze and compare the technologies, particularly through the implementation of regression models. The objective is to estimate the influence of motor mass, efficiency, and mass-to-power ratio on power and torque requirements, with the goal of assisting in the selection of a mass-to-power ratio.

The purpose of the micromotor selection criteria is to provide guidelines and criteria for choosing the most suitable micromotor for a specific application. These criteria consider factors such as power requirements, torque output, efficiency, size, weight, and other performance parameters. By using these selection criteria, engineers and designers can make informed decisions to ensure optimal performance and efficiency of the micromotor in their intended application.

The main criteria that define micromotor selection in electric microsystems design is: output power (P_out) or torque required as calculated by the maximum of operated loading devices. A motor converts an electrical input power (P_in):

$P_{\text {in }}=\mathrm{V}^* I_a$      (1)

$I_a$ the armature current, and V the terminal (input) voltage. In addition, a mechanical output power is:

$P_{\text {out }}=\Omega^* T_{\text {sh }}=\eta^* P_{\text {in }}$        (2)

where, T_sh is the shaft (output) torque, and η is the efficiency.

The data included in this study consists of 84 motors covering 19 weight scales (from 0.35 g to 16.1 g) and diameter scales (from 4 mm to 26 mm). The specific micromotors data chosen for the analysis were sourced from the catalogs of Maxon and Faulhaber, which are renowned and highly regarded manufacturers in the field of micromotors.

Tables 2 and 3 summarize the output power, stall torque, mass, and diameter of the RE, DCX, and ECX ranges of micromotors from Maxon and DCM, FDC, and BDC ranges of micromotors from Faulhaber. The values were taken from specifications provided by the two companies and cover a range of weight and diameter scales.

The motors chosen from Maxon include DCX and RE range (brush commutator micromotors) and ECX range (brushless DC micromotors). The ranges from Faulhaber include dc motors (DCM) with precious metal commutation, flat dc micromotors (FDC) with ironless rotor, and brushless dc micromotor (BDC) with NdeFeB magnet. The tables provide a useful summary of the different types of micromotors available and can be used in electric microsystems design to determine the best fit based on the required output power or torque.

Table 2. Three ranges of motors manufactured by Maxon

Table 3. Three ranges of motors manufactured by Faulhaber

The data collected from the micromotors will be used in the analysis to evaluate and compare various performance parameters such as efficiency, mass, mass-to-power ratio, and torque. By analyzing this data, we aim to gain insights into the characteristics. Additionally, the data will be utilized in regression models and statistical analysis techniques to derive meaningful conclusions and draw comparisons between different micromotors.