ADVERTISEMENT FEATURE PLCS & INDUSTRIAL PCS ADDED STRENGTH, ADDED FEATURES
For many years, there has been a trend towards standardisation of bus systems for drive technology. Although many manufacturers rely on Profinet and, especially for drives, EtherCAT, there is a multitude of other partly proprietary bus systems available which enjoy growing popularity in some market segments and regions. Panasonic explain further
T
here is a trend towards global standards, especially towards
Profinet, but in some regions such as Asia there is a preference for classic systems for drive control. What are the reasons for these preferences? For the answer to this question we will concentrate on RTEX (Realtime Express) from Panasonic. As is often the case in automation a solution must meet core demands. For multi-axis drive solutions transmission speed is of utmost importance and should show as little jitter as possible. Further important factors are data integrity and transmission security. An evaluation of the different needs of typical users, for example from the packaging industry, shows that a standardised bus system is not always a ‘must’. What is far more important to potential users is that all components of the drive system match perfectly.
PANASONIC RTEX Apart from Panasonic’s positioning units for PLCs from the FP- (FP-Sigma) or FP2/SH series, it is also possible to use motion controllers from other manufacturers. For example, the motion controller MC464 from Trio Motion
offers the following features: l
Expandable to control up to 64 axes. l IEC 61131-3 PLC programming. l Multi-tasking BASIC programming. l Supports RTEX, Sercos and EtherCAT. l Flexible and expandable with bus units. l Supports Anybus units from HMS (this
means currently 19 different industrial bus systems are supported). With Panasonic’s proprietary RTEX, you keep it within the family, so to speak, as only the physical layer corresponds to classic 100baseTX. All other protocol layers have been optimised for efficiency which means that, unlike Profinet, they are no longer compatible with other protocols such as UDP or TCP/IP. While the classic transmission is
bidirectional, RTEX needs a ring topology as the one-way system helps to achieve another increase in speed. Now let’s take a closer look at the somewhat overworked term ‘real time’. With RTEX, a command to control a
30 NOVEMBER 2014 | AUTOMATION
motion axis is transmitted to up to five axes within 83 microseconds (0.083ms). The axis responds within 166 microseconds (0.166ms). The speed of the RTEX Realtime Express protocol, already not one of the slowest bus systems, has been increased six-fold compared to the earlier Panasonic RTEX system version 1. In theory, it is possible to send
commands in 100 microseconds to 100 axes with EtherCAT SoE, but in reality it is only eight to 32 axes in typical machinery. What makes RTEX so attractive is that with a similar speed (0.5ms) 32 axes can be controlled and monitored. In the meantime, numerous
manufacturers have implemented RTEX, which is easily done by sending a request to Panasonic and by buying an ASIC.
COST CRITERIA Other criteria for deciding on a bus system are the costs for the bus units and compatible network components and gateways, and the cost for cables, especially if it is not possible to use standard Ethernet cables. Another requirement for real time buses is the ability to transmit a great variety of data and signals. Furthermore, fast and easy commissioning is usually an essential element and so choosing the wrong system may turn out to be an expensive mistake. Panasonic Electric Works offers a modular system of motion controllers and PLCs, which can be acquired separately. With this bus system and a
ring network it is possible to control even large machines with up to 32 axes simultaneously with one master. There is only a gradual increase in transmission time when more than five axes are controlled. For example, for ten axes it takes 166 microseconds (including response) and 0.5 milliseconds for 32 axes. The time needed for the response does not influence the time needed for sending the command. This performance can be
achieved with inexpensive, standardised Ethernet cables and transmission distances of up to 100m between servo systems. The high speed combined with
maximum reliability and noise resistance according to IEC61000-4-41 is made possible by a ring network and a specific Ethernet protocol which because it is already on the lower communication layer proves to be highly efficient. RTEX transmits a multitude of
information effectively in real time. This includes 33 different pieces of status information - for example warnings or alarm codes, current position, speed, torque, position deviations, mechanical and electric rotor angle, inputs and outputs and many more.
Below: comparison of real-time Ethernet systems for drives
SUMMARY It is certainly advantageous for users to choose open systems and standards that are supported by several manufacturers. The large market share of real time Ethernet systems, especially Profinet, speaks for itself. However, a proprietary protocol such as RTEX also offers advantages as proven by the many practical cases where the performance of multi- functional motion controllers like the MC464 from Trio Motion convinced users of their suitability. There is little point
in trying to solve all applications with standard Ethernet because the specific requirements of real time applications also limit the selection of
components offered by market leaders. One size fits all - this may be true for
clothes. However, in the automation industry a niche product can be just as efficient as the standard solution and may be even more attractive as far as handling and costs are concerned.
Panasonic
www.panasonic-electric-works.co.uk T: 01908 231 555
Enter 214 /AUTOMATION
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64