A cutaway two-phase stepper drives an indexing table. Commanded steps advance the stator field while a mechanical rotor model responds to magnetic torque, inertia, damping and a constant opposing load. Open-loop commands do not guarantee actual position.
• A two-phase stator with coils A and B, a permanent-magnet rotor and shaft, an indexing table with work fixtures, a phase-current driver and a pulse and direction generator. • Controls for step pulse rate (5-300 full steps/s), constant opposing load torque (0-0.6 N·m), rotor and table inertia (0.001-0.006 kg·m²) and direction. • Readouts of commanded angle, actual rotor angle, following error, magnetic torque, command pulses and rotor speed. • Experiments: low-rate indexing, excess external torque, and a high pulse rate with inertia.
The command is θcommand = direction × floor(rate × t) × 1.8°, so 200 full steps command one mechanical revolution. Magnetic torque is τmag = 0.5 sin[50(θcommand − θ)] N·m, and the rotor follows J dω/dt = τmag − 0.04ω − direction × load. Phase currents are IA = cos(kπ/2) and IB = sin(kπ/2).
This is an ideal sinusoidal permanent-magnet stepper teaching model with 50 electrical periods per revolution and fixed holding torque. It has no current-rise limitation, detent torque, microstepping or manufacturer torque-speed curve, and the enlarged cutaway does not reproduce every rotor tooth.
No. Open-loop stepping does not measure actual shaft position; the table follows the actual shaft angle, not the pulse counter.
No. Maximum magnetic torque is only 0.5 N·m, so a 0.6 N·m load exceeds it and synchronism cannot be maintained.
200 full steps command one mechanical revolution, at 1.8° per step.
The commanded field outruns the rotor, and the unwrapped angle error grows; an increasing error exposes loss of synchronism.