Electromagnetic design, analysis, and optimization of an interior permanent magnet motor for robotic application

Abstract

Robotic grippers typically demand two competing capabilities from their actuator: rapid closing motion for effective manipulation and high jaw force once contact occurs. Because most compact grippers employ a fixed transmission (e.g., a gear stage driving a lead screw or linkage), actuator selection should be based on torque-speed capability under electrical limits rather than torque at a single low-speed point. This thesis evaluates the potential of an interior permanent-magnet synchronous motor (IPM) for gripper actuation and benchmarks it against surface-mounted PM (SPM) solutions. A preliminary IPM motor design is first established using a geometry-driven sizing analysis to determine feasible rotor and stator dimensions, followed by the calculation and adoption of an appropriate winding configuration. After this baseline design is defined, the stator geometry, winding arrangement, stack length, air gap, and electrical constraints (48 V DC bus and a maximum phase current limit of 5 A) are held fixed throughout the entire investigation to isolate the influence of rotor topology and rotor geometric parameters. Candidate rotor designs are evaluated using ANSYS Maxwell two-dimensional finite-element analysis (2-D FEA), which provides electromagnetic torque predictions and saturation-dependent inductances Ld and Lq. Using these electromagnetic quantities, optimal operating points are obtained by solving the maximum-torque-per-ampere (MTPA) condition across the speed range and extending into the voltage-limited field-weakening region to generate complete torque–speed envelopes for performance comparison. Rotor development proceeds in two stages. First, a Taguchi design-of-experiments screening study is conducted to quantify the relative influence of selected rotor geometric parameters on key electromagnetic performance metrics (e.g., torque and saliency) and to identify which factors warrant emphasis in the subsequent optimization. Second, a feasibility-constrained, discrete optimization is executed as a batch-wise, surrogate-assisted search implemented in MATLAB: candidate rotor designs are systematically proposed within the constrained design space and evaluated through Maxwell 2-D FEA simulations, and the accumulated electromagnetic data are used to train a surrogate model that iteratively refines the search toward improved designs. In total, 270 rotor configurations are assessed (comprising an initial seed set plus sequential exploration batches) ultimately yielding a final optimized IPM rotor that satisfies all geometric, magnetic, and mechanical constraints. The optimized IPM design is benchmarked against two references: (i) a magnet-budget matched SPM baseline simulated using the same stator and identical electrical limits, and (ii) a commercial 48 V Maxon EC frameless SPM motor of comparable size. To compare candidates in a gripper-relevant way, each torque-speed envelope is translated through an idealized “virtual transmission” that normalizes all designs to the same required closing speed. Under this common-speed basis, the optimized IPM achieves the highest equivalent output torque, providing approximately 13% higher normalized torque than the SPM baseline and approximately 80% higher than the commercial Maxon SPM reference. This outcome reflects the greater geometric adjustability of the IPM rotor, which enables tuning the saliency and field-weakening behavior toward a gripper-oriented torque-speed profile.

Date	25 Mar 2026
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Vincent Duchaine (Supervisor)