BECKHOFF EL7037 - Manual (Page 19)

Product overview
Today, the most widely used type in industry is the hybrid stepper motor type. In this type of motor the rotor
consists of a toothed iron core with one or a few permanent magnets in the rotor core. The rotor is designed
such that the polarity of successive teeth is inverse. This enables the production of motors with a high
number of steps, which is essential for positioning accuracy, combined with a relatively high torque. The
electrical behaviour of such a hybrid stepper motor is comparable with a multipole synchronous servomotor.
However, thanks to the synchronous toothing of stator and rotor, hybrid stepper motors offer a significantly
higher cogging torque.
Hybrid stepper motors with two or more phases are available on the market. Since the terminals described
here are designed for two-phase motors, the description focuses on the two-phase type, with the phases
referred as A and B in this documentation.
The development of the EL70x7 EtherCAT Terminals for the Beckhoff EtherCAT Terminal system opens up
new fields of application. The use of microstepping, the latest semiconductor technology and field-oriented
control (only with Beckhoff motors) offers many advantages:
• smoother operation
• avoidance of resonance
• reduced energy consumption
• lower thermal load on the motor
• minimum electromagnetic emissions
• long cable lengths
• simpler handling
• reduced size of the power electronics
• simple integration into higher-level systems
• integrated feedback system
Stepper motor parameters
• Mechanical system
Irrespective of the drive and the stepper motor itself, the configuration of the mechanism attached to the
motor shaft has significant influence on the achievable control quality.
Natural resonances, load resonances, gear backlash (loose) and static friction have negative affect on the
controllability of the drive system. This often requires "softer" controller parameterisation, which in turn leads
to a higher position lag in the system. Sliding friction can result in reduced efficiency (due to increased
energy demand), but on the other hand it can have a positive effect on the control stability, due to its
dampening effect.
As a general rule, the "stiffer" the mechanics of a drive system, the easier it is to control, which is beneficial
for achieving a small position lag in the drive system.
• Speed
Stepper motors have low maximum speed, which is usually specified as a maximum step frequency.
• Number of phases
Motors with 2 to 5 phases are common. The EL70x7 EtherCAT Terminals support 2-phase motors. 4-phase
motors are basically 2-phase motors with separate winding ends. They can be connected directly to the
EtherCAT Terminal.
• Torque
Refers to the maximum motor torque at different speeds. This parameter is usually represented by a
characteristic curve. Stepper motors have comparatively high torque in the lower speed range. In many
applications, this enables them to be used directly without gearing. Compared with other motors, stepper
motors can quite easily provide a holding moment of the same order of magnitude as the torque.
EL70x7 19 Version 1.0