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To: Subscribers PLCopen Newsletter
Subject: PLCopen newsletter Issue December 2007

Welcome to the PLCopen electronic newsletter.

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PLCopen Newsletter - Issue December 2007 - headlines


1. The PLC is 40 years young
2. PLCopen XML - accepted by AutomationML
3. Safety Part 2 - User Guidelines near completion
4. Logic, Motion, Safety - work under construction
5. Motion Control part 4 well on its way with a new name

1. The PLC is 40 years young

The PLC gets 40 at the turn of this year. To quote the father of the PLC, Dick Morley: “It was New Year’s Day 1968, and I knew I was going to have a hangover”. So he was in a rush. However, the PLC was not invented in one day, since he was building on the years of practical experience. It was all in the head already – now it had to be converted into a product and an architecture.

The PLC was not an instant success. Due to the culture clash it took years to be accepted. And the original company Modicon was transferred several times till this date, also resulting in many other companies in the same market. And that is the market that we know nowadays: under attack several times but healthier then ever before. 40 years of the PLC and it still dominates.  

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2. PLCopen XML - accepted by AutomationML

The AutomationML group, supported by Daimler, has accepted the PLCopen XML as format for the description of the behaviour of the control sequences.
AutomationML, seee , will close the gaps between production design (virtual factory) and shopfloor (meaning production). For this it will use several formats for exchange.
I see this as a major step forward for the acceptance of our work at PLCopen. The definition of the XML schemas provided an interface towards the engineering tools, and as such also to higher level software tools like those for simulation of the factory. Via this implementation and resulting experience, this group will additionally provide feedback on the existing schemas. Based on this feedback, a next meeting for XML will be planned.  

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3. Safety Part 2 - User Guidelines near completion

In February 2006 the independent association PLCopen released their original safety technical specification as Part 1 – Concepts and Functions Blocks. With this PLCopen merged the engineering activities for Logic, Motion and Safety on a common development platform. With this Part 1, and the corresponding corrigendum, the safety aspects can be transferred to a software tool, which is integrated into the software development tools. This helps developers and users to integrate safety-related functionality into their systems right from the beginning of the development cycle. Also, it contributes to the overall understanding of safety aspects, as well as certification and approval from independent safety-related organizations.

This Safety Part 1 is more focused to the implementers of the functionalities. PLCopen realized it needed to help OEMs to add the safety functionality to their machines’ application software. For this reason the PLCopen TC5 Safety group continued with a Part 2 – User Guidelines. The document Part 2 is focused to the users of the PLCopen functionalities and demonstrates the ease of use of the defined function blocks in real life applications. The PLCopen safety functionalities are focused to the machine building industry, as well as related system integrators.

The provided examples show possible, but simplified application programs of typical safety functions. However, the selection of the right safety hardware components, the wiring and coupling to the safety software function blocks in accordance with the risk analysis is required. Furthermore, the user has the responsibility to take additional measures to comply with the safety requirements.

The PLCopen Safety Specification is a milestone on the way to the standardization of safety-relevant application software. The PLCopen compliance logo allows users to easily identify software which fulfills the requirements defined by the safety standard. This kind of software is characterized by a high standard of quality.

The release of Part 2 is planned for beginning next year. We will keep you informed.

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4. Logic, Motion, Safety - work under construction

The combination of logic, motion, and safety in one environment provides the user with a harmonized view to the overall application in one software environment, including the safety and functional applications.

In practice this offers less educational efforts and simpler transfer of knowledge and application software between different controls. Also, it tackles the ‘not-invented-here syndrome’, which is often a cause of errors and additional costs, in particular in the safety application. By using pre-defined and tested functionality, combined with support in the programming environment, including language definition with subsets of functionality, one is able to add the safety related aspects to the application programs for easy commissioning.

With the safety environment and related function blocks defined, and even the first products available on the market, there is a need to clarify the combination of motion and safety.

Safety functionalities like mode selector, safely reduced speed, and several stop functionalities, have a direct link to the motion control.

This new activity wants to provide examples of this combination, making it easier and more natural for the user to integrate safety in their motion and logic application. This is a daunting task, since decomposition of a whole production line in several machine functionalities is foreseen, which again need to be handled per function on logic, motion and safety. However, the benefit is clear: guidance at this level is the basis for a smoother acceptance and usages, and moreover all suppliers need to create these examples anyhow, so a joint effort is effective.

User and educational institutes are invited to help specifying the examples as well as the decomposition of a practical machine in all its aspects.

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5. Motion Control Part 4 well on its way with a new name

Part 4 of the PLCopen suite of specifications is focused to the coordinated multi-axes motion in 3D space. This part used to be called Interpolation – however this is only a part of the specification, and so during the last meeting in November it was decided to change the name in “Coordinated Motion”.

Part 1 and Part 2 of the PLCopen Motion Control suite deal with master / slave motion control, a type of coordinated motion control where the master axis position is used to generate one or more slave axis position commands. For three dimensional movements, one goes beyond this point via a grouping of a set of axes, without a master axis.

In order to work in 3D, one has to use several coordinate systems, as well as a kinematic model of the mechanics involved. The coordinate systems include the axes coordinate system, the machine coordinate system and the product related system.

The current Master/Slave axes have the problem that if an error occurs, the other axes have no knowledge about this, and continue their movement. By combining axes in a group one knows upfront which axes are involved and has the basis for a better error behavior.

The level of the PLCopen Motion Control Function Blocks are specified at the user level: the PLC programmer quickly recognizes the functionality of the function block and what happens if it is activated or connected to other blocks in a sequence of motion commands. Path oriented movements are programmed either with specific robot oriented programming languages, or “G-code” (for instance cf. DIN 66025) as used in the CNC world. Both consist of a relative small number of users. But without a doubt, the movements which can be described in these languages are applicable to a broader area of use. This PLCopen initiative transforms the functionalities as known in the CNC and Robotic world to the PLC world. With this, an additional part is added to the range of PLCopen Motion Control specifications.

The release for comments, version 0.99, of this Part 4 is expected at the Hanover Fair in April 2008.

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Kind regards,
Eelco van der Wal
Managing Director PLCopen

PO Box 3009
NL 4200 EA Gorinchem, the Netherlands
tel.: +31-183-660261
fax: +31-183-664821
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