AZ Series closed loop stepper motors

A conventional stepper counts pulses and assumes the rotor followed them. If the load jams or the acceleration is too steep, the rotor slips, the count is wrong and nothing tells the PLC. The AZ Series closes that gap in two ways: the ABZO sensor always knows the true shaft position, and the driver uses that information to correct errors itself.

In normal running the AZ behaves like an open-loop stepper, so it responds instantly to short moves and holds position at standstill without the small back-and-forth hunting a servo can show on a flexible belt or low-rigidity mechanism. When the deviation between command and actual position reaches about ±1.8°, the driver switches to closed-loop mode and drives the windings to generate torque based on the real rotor position, bringing the load back in line. A continuous overload produces an alarm output, and an END signal confirms each completed move.

Because the ABZO sensor is mechanical, it keeps the absolute position without a battery or power, which is the main practical difference from servo systems that use battery-backed multi-turn encoders.

• No home or limit sensors needed for return-to-home in most machines
• Home is set with a switch on the driver, MEXE02 software or an input signal
• Position survives power loss and a disconnected motor cable
• Set home again after replacing a motor

Start from the mechanism, not the catalogue. Work out the load inertia, the required move distance and time, and any thrust or gravity load, then use Oriental Motor's sizing tools or send the data to us. As a rule of thumb from Oriental Motor, an open-loop stepper handles roughly 10 times its rotor inertia, a closed-loop stepper around 30 times, and a servo about 100 times. If your inertia ratio is high, a geared AZ motor is often the answer because the gear ratio divides the reflected inertia and multiplies torque.

Next pick the supply. DC input (24/48 VDC) suits compact machines, battery-powered AGVs and panels with an SMPS already fitted, and it gives access to the smallest frames, mini drivers and multi-axis drivers. AC input (100–120 VAC or 200–240 VAC) gives the larger 85/90 mm frames and more high-speed torque, and plugs straight into a typical Indian 230 VAC control panel.

Finally choose how the PLC will talk to the driver. This choice matters more than the motor for commissioning time.

• Pulse input: use with a PLC positioning module or motion controller that already generates pulses (line driver up to 1 MHz, open collector up to 250 kHz)
• Pulse input with RS-485: same pulse control plus Modbus monitoring of position, speed, load factor, temperature and alarms
• Built-in controller: store up to 256 moves in the driver and trigger them by I/O or Modbus RTU; up to 31 drivers on one RS-485 line
• EtherCAT, EtherNet/IP or PROFINET: direct connection to the machine network, no pulse module needed
• Mini drivers and 2–4 axis drivers: DC input only, for tight panels or mounting near the motor
• Add a brake motor for vertical axes so the load cannot drop on power loss

A conventional open-loop stepper such as the PKP Series is the most economical option when the load is steady, the move profile is conservative and a missed step would only cost a re-home. It needs no feedback and no tuning, but it cannot tell you if it has lost position, and it typically has to be derated to keep temperature in check.

An AC servo is the right tool for continuous high-speed motion, very high inertia ratios and applications that need strong torque across a wide speed range. It needs tuning, and a multi-turn absolute servo encoder usually depends on a backup battery.

The AZ Series sits between the two. It gives the stepper's strong low-speed torque, quick short moves and hunting-free standstill, adds feedback, overload alarms and battery-free absolute position, and does not need gain tuning. Oriental Motor's own comparison on an index table showed the AZ positioning faster for short moves, while the servo was quicker once the travel went beyond roughly four motor revolutions. That is a useful rule when you are deciding for an indexing table, a pick-and-place axis or a feeder.

• Short, frequent moves on belts, cams or index tables: AZ Series
• Steady light loads and lowest cost: open-loop PKP + CVD
• Long, fast continuous moves or very high inertia: AC servo

The motors are not interchangeable between the two families: an AC input AZ motor runs with an AC input AZD driver, and a DC input motor with a DC input driver. Both families use the same ABZO sensor, the same MEXE02 software and very similar operating functions, so the choice is mainly about power, size and panel design.

Choose DC input when the machine is compact, runs from 24 V or 48 V, or is battery powered (AGVs, mobile robots). You also get the 20 mm and 28 mm frames, the mini drivers that fit near the motor, and 2–4 axis EtherCAT drivers. Choose AC input for larger frames up to 85/90 mm, higher torque at speed and when you want to run directly from single-phase or three-phase mains without a separate DC supply. AC input drivers also offer a Safe Torque Off (STO) function for machine safety circuits.

Most AZ installations we see in Gujarat are on machines that already have a Mitsubishi, Siemens, Omron or Delta PLC. With a pulse-input driver the AZ drops into an existing positioning module as a replacement for a stepper or servo drive. With a built-in controller driver you can store the moves in the driver and let the PLC trigger them over I/O or Modbus RTU, which suits small special-purpose machines where adding a motion module is not worth the cost.

Oriental Motor's MEXE02 software is a free download and lets you set parameters, test moves, and watch waveforms, load factor and temperature. For machines that restart after every shift change or power cut, as is common in textile and packaging units running on unstable supply, set the home position once with the switch on the driver and the machine can resume from where it stopped without a homing run.