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Basic Drives    

ED-DRIVE / Informazioni Tecniche / Basic Drives
 
 
 
 
 
 
 



A simple way to choose a stepper drive is to look for four things —  voltage, current (rated), microstepping, and control mode. Ensure that the drive can handle a wide range of current so that you can test the system at different voltage levels to fit your application. Factors to be considered when choosing a BLDC driver are; is the motor sensorless or sensored, what is the rated voltage and current and what functionality is needed, velocity and direction or is a more intelligent drive functionality required.

Once the power range of the driver has been chosen, it is important to know that there are different types of drivers on the market according to control methods and performances:


 Typology Performances
 Clock & Direction
These are still the most common type of drivers today. Their operation takes place via a PLC capable of generating a pulse sequence signal via two digital outputs which frequency defines the speed of rotation, besides the number of steps and a high or low signal that provides the driver with the direction where to execute the movement. The limit of this type of drivers is mostly given by the ability of the PLC to generate a precise sequence of pulses. With this type of control, it is difficult to precisely synchronize the movement of two or more motors.
Analogue reference
These drivers are controlled via the analogue input they are equipped with. The analogue reference signal can be generated by a PLC or more simply by a potentiometer; the rotation speed is proportional to the value of the input voltage. A digital input is almost always used to define the direction of rotation of the motor.            The limit of this type of driver depends on the resolution of the analogue input which defines the number of speed levels and this is the reason why their use is indicated in applications where high precision is not required.
 FieldBusThese drivers are controlled via fieldbus networks; the most common are: Serial RS485 Modbus-RTU, CANopen (DS402), EtherCAT CoE (DS402) and Ethernet Modbus TCP.
A master (PLC, PC, HMI etc.) sends the command to be executed to the driver via the fieldbus network.       This type of drivers is well suited for the integration into multi-axis or complex networks.
A fieldbus solution has a greater robustness to disturbances and can achieve higher performances than one realized by clock and direction drivers. Moreover, the higher cost initially sustained is often justified by a reduction in the wirings and the assembly/maintenance time of the machine.
 
 ProgrammableThey are intelligent drivers, programmable from computers via a serial or a USB port and a specific software Editor.
These drivers are equipped with digital/analogue inputs and outputs and fieldbus networks available to the user; they can work even without an external PLC by controlling all the machine functions.
They are often used in addition to a PLC with the task of simplifying the function of the master, which can for example limit itself to prove instructions, via digital I/O or field bus, for starting a specific cycle in the driver. They are advisable drivers for medium/low complexity applications in stand-alone mode (without external controller) allowing savings in terms of wiring reduction and component saving. They can be very useful in complex machines to simplify programmers’ work and making it easy to replace one PLC model with another.


FieldBus Systems

A fieldbus is a serial bus (communication) system used in machines and systems to connect a number of
sensors and actuators (motors) to each other and to one or multiple masters (IPCs, PACs, PLCs). Fieldbuses make it possible to exchange data between different system components over long distances and under high external load. They operate in master-slave mode: While the master is responsible for controlling processes, the slave handles single subtasks.

Fieldbuses differ in the "physical layer" they use, i.e. the hardware level (e.g. CAN, RS485, Ethernet), and in the protocol level that defines the form of the exchanged information.
There are fieldbuses, such as CANopen and DeviceNet, that use the same physical medium (CAN) but operate with different protocols. Equally, there are protocols that can be implemented on varying types of hardware for example Modbus /TCPon Ethernet and as Modbus on RS232.

The hardware i.e. cable lengths and transmission capacity often determines the fundamental bus properties. The protocol level determines which standardized messages and functions are available between the master and slave.

Depending on the application, each of the established fieldbuses has its strengths and weaknesses. Often it is the availability of fieldbus interface components that determines the selection of the specific fieldbus.


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CANopen (Controller Area Network) is a communication protocol and device profile specification for embedded systems used in automation, healthcare, agricultural and automotive systems. In terms of the Open Systems Interconnection (OSI) model, CANopen implements the layers above and including the network layer. The
CANopen standard consists of an addressing scheme, several small communication protocols and an application layer defined by a device profile. The communication protocols have support for network management, device monitoring and communication between nodes, including a simple transport layer for message segmentation/desegmentation. The lower level protocol implementing the data link and physical layers is usually Controller Area Network (CAN), although devices using some other means of communication (such as Ethernet Powerlink, EtherCAT) can also implement the CANopen device profile.


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Modbus is a serial communications protocol originally published by US company Gould-Modicon (now Schneider Electric) in 1979 for use with its programmable logic controllers (PLCs). Using Modbus, a master can exchange data with multiple slaves. In principle, each node can send messages via the bus but communication is usually initiated by the master. Modbus has become a de facto standard communication protocol and is now a commonly available means of connecting industrial electronic devices.

In general, there are three Modbus variants:

  • Modbus RTU
  • Modbus ASCII
  • Modbus TCP
Modbus RTU and ASCII use a serial interface (RS485 or RS232) as physical transmission layer; Modbus TCP uses Ethernet (TCP/IP).
Modbus TCP/IP uses Transmission Control Protocol and Internet Protocol for the transmission of messages from Modbus between compatible devices over various systems. That is, Modbus TCP/IP uses a physical network (Ethernet), with a networking standard (TCP/IP), and itself offers a method of representing data (Modbus as the application protocol). A Modbus TCP/IP message is basically just a Modbus communication data message compressed in an Ethernet TCP/IP cover. TCP/IP is simply a transport layer protocol and does not change the way data is stored or interpreted inside the message.
The main reasons for the use of Modbus in a variety of many market segments are:

  • It was developed with industrial applications in mind, but has expanded to others.
  • It is openly published and royalty-free giving freedom of its use
  • It is easy to deploy and maintain,
  • It moves raw bits or words without placing many restrictions on vendors.
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Ethernet for Control Automation Technology (EtherCAT) was developed by Beckhoff. It’s based on the CANopen protocol and on Ethernet but differs from internet communication or network communications in being specifically optimized for industrial automation control. The standards are defined and maintained by the EtherCAT technology group. EtherCAT is a fast and deterministic network, and processes data using dedicated hardware and software. It uses a full duplex, master-slave configuration, and accommodates any topology. It can process 1,000 I/O points in 30 microseconds and communicate with 100 servo axes in 100 microseconds. The axes receive set values and control data and report actual position and status. Axes are synchronized using a distributed clock technique that’s a simple version of IEEE 1588 and reduce jitter to less than 1 microsecond.
Advantages of EtherCAT:

  • Very high communication speeds
  • Synchronization of multiple units possible
  • Real-time capable
  • Standardized protocol (CiA)