Closed loop control drive has the advantages of servomotors and steppers

The SERS and WSERS drives from Stogra can by using closed loop control of the stepper motor, always be operated at maximum torque with the result of high dynamic performance and maximum motor acceleration

Closed LoopThis gives high response in case of short positioning movements, no hunting at ‘stand still’, no gain tuning is necessary and having the small load angle, has an advantages over servomotors. This means the motor does not loose its synchronism and therefore no more loosing steps! Furthermore when sizing a stepper motor system the usual torque safety calculated can be reduced or maybe even skipped, and therefore for many applications a smaller motor can be selected. The SERS are rack mountable drives with control board and encoder interface option and the WSERS is a packaged drive, both for use with 2-phase stepping motors.

When comparing the stepper motor in open loop with closed loop control as long as the load angle is less than 1.8°, the stepper motor can be operated in open loop mode. If however the load angle is greater than 1.8° the motor would loose its position in open loop mode. Closed loop mode will automatically prevent this loss of steps.

The communication with the position control is via a serial interface RS232C, RS485, Profibus-DP, PROFIdrive and CANopen (DSP 402) are all supported. The SERS drives guarantees optimal, vibration free, true running motion due to its micro-stepping operation with 12800 steps/rev and the ability to select different phase current characteristics to match the characteristics of the motor type. The rough step by step performance of conventional stepper drives at low speed ranges has been greatly improved with the SERS resulting in very smooth running easily comparable with servo motors. In the standard versions they can be operated in four different modes, serial, stand-alone, parallel and master/slave operation.


Comparing stepper motor in closed loop control with a servomotor

Using the SERS the stepper motor follows its position command values immediately, but a servomotor can only start and stop with a delay/settling time due to its inherent operation that needs to continuously monitor position error. When at motor ‘stand-still’ the stepper motor is completely stationary while a servomotor is slightly moving forwards an backwards around its stand still position, known as hunting.

Micromech is Stogra’s UK distributor for stepper motors, drives and controls products. If you want to know more about these robust and reliable products then contact Alan Spinks on 01376 333333 or email


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