Beckhoff EL7037 User Manual download pdf (Page 18)

Product overview

2.3 Technology

The EL70x7 stepper motor terminal integrates a compact Motion Control solution for stepper motors in a

very compact design.

The user can control stepper motors in the low to medium performance range. With an output current of up

to 5 A, the EL7047 can achieve a considerable torque of e.g. 5 Nm at a standard stepper motor. The supply

voltage of up to 50 V

allows high speeds with good torque and thus high mechanical performance. The

stepper motor and an incremental encoder can be connected directly to the EL70x7.

The stepper motor terminal provides three basic modes of operation.

In standard mode [}22] all unipolar and bipolar stepper motors that comply with the specifications of the

corresponding EL70x7 can be controlled. Two currents with sine/cosine curve are provided. The current is

clocked with 64 kHz and resolved with up to 64-fold microstepping to achieve a smooth current.

Extended mode [}23] is based on field-oriented control. This mode can only be used for stepper motors

from Beckhoff. The current is not only provided, but controlled in a comprehensive manner. Typical stepper

motor problems such as pronounced resonance are therefore finally a thing of the past. Furthermore, the

current is adjusted depending on the load, thereby enabling considerable energy savings and lower thermal

loads at the stepper motor.

In sensorless mode [}25] stepper motors from Beckhoff can be controlled load-dependent without a

feedback system.

Realisation of more demanding positioning tasks

More demanding positioning tasks can be realised via the TwinCAT automation software from Beckhoff. Like

other axes, the stepper motor terminals are integrated via the TwinCAT System Manager and can be used

like standard servo axes. Special stepper motor features, such as speed reduction in the event of large

following errors, are automatically taken into account via the stepper motor axis option. The effort for

changing from a servomotor to a stepper motor - and back - is no greater than changing from one fieldbus to

another one under TwinCAT.

The output stages of the stepper motor terminals have an overload protection in the form of an

overtemperature warning and switch-off. Together with short circuit detection, diagnostic data are accessible

in the process image of the controller. In addition, this status is displayed by the Bus Terminal LEDs, along

with other information. The output stage is switched on via an Enable-Bit. The motor current can be set and

reduced via a parameter value.

Optimum adaptation to the motor and the implementation of energy-saving features require minimum

programming effort. Since all data are set in the form of parameters in the CoE register, it is easily possible

to replace an EtherCAT Terminal or store certain parameters for transfer to the next project. It is therefore no

longer necessary to transfer certain potentiometer settings or to document DIP switch settings.

2.3.1 Stepper motor

Stepper motors are electric motors and are comparable with synchronous motors. The rotor is designed as a

permanent magnet, while the stator consists of a coil package. The frequency of the stator rotary field is

always in a fixed ratio relative to the rotor speed. In contrast to synchronous motors, stepper motors have a

large number of pole pairs. In a minimum control configuration, the stepper motor is moved from pole to pole,

or from step to step.

Stepper motors have been around for many years. They are robust, easy to control, and provide high torque.

In many applications, the step counting facility saves expensive feedback systems. Even with the

increasingly widespread use of synchronous servomotors, stepper motors are by no means "getting long in

the tooth". They are considered to represent mature technology and continue to be developed further in

order to reduce costs and physical size, increase torque and improve reliability. For a standard stepper

motor with 200 full steps, the best possible positioning accuracy is approx. 1.8°.

EL70x718 Version 1.0

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Beckhoff EL7037 User Manual Page 18

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Beckhoff EL7037 User Manual Page 18

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