By Mike Webb, Managing Director of Quin Systems Ltd
Automation magazine, November 2004

When machine controls are purchased there is often little thought given to the accumulation of costs associated with the selection of a mixture of products from different vendors. This can lead to loss of profitability and on-going extra costs for support. More careful consideration to the choice of controls that deliver a single-point integrated solution will remove these costs, deliver better performance, provide long term benefits and improved customer satisfaction. A machine builder will always want his machine to be the one that his customer is most satisfied with, lending itself to future business and lower service costs.

At the heart of all modern automated machinery with moving axes is a motion controller. This controller deals with motion path control and gives a machine its basic operational functionality. Software allows flexibility in application and the use of demanding motion paths (using splines for example).

The benefit to the builder in this is that the machine can accommodate different customer manufacturing requirements, and at the same time deliver a single core solution that can be used for many differing machine designs or adaptations. This allows a single investment in training to become a tool for standard solution to divergent customer requirements. The machines themselves will utilise many software functions to deliver quality production with lower cycle times even though the tasks may be demanding or the control task mathematically complex.

The relationship between the controlled parts of a machine requires each motion axis to be closely synchronised within the whole scheme. Stated simply, if the synchronisation and motion are not optimised, then the machine will not produce as much per hour and cycle Time will be lost in an accumulation of delays.

The architecture of the Motion Control system can critically affect this performance issue. When a centralised system is overloaded, pauses will be experienced to the sequencing of the machine's movements - adding to accumulated delay.

The other aspect of machine control is the sequencing of the other parts of themachine. This will usually be undertaken by a Programmable Logic Controller (PLC) that will handle all the switches, solenoids, relays and lights and will provide access to the machine by SCADA and other PC-based applications. When used in a "motion controlled machine" the PLC will interact with the Motion Controller and thereby deliver a complete solution.

It is here that the machine builder can provide a solution that will deliver the advantages for the builder, and for the end-user.

The Motion Controller and PLC combination are at the heart of the machine's performance and reliability. If these items are purchased from different vendors then the motion controller will have its own programming language, as will the PLC. The effect to the builder may initially appear to be minimal; one simply connects the two together by hard wiring or by a bus-based technology. The two units are programmed with due regard to the particular requirements of both systems. During the initial commissioning of the machine the two programmes will be adapted to meet unforeseen requirements.

This will necessitate changes are made within the motion controller and within the PLC - two changes in two differing products with two differing programming languages - and it all has to be tested and debugged before the machine can be quality control tested and delivered.

An additional and consequential complication of this is the use of the control software to diagnose why a machine is faulty or not working optimally. Again the service engineer will require two separate training courses and be faced with two controllers in which to make deductions about the potential cause of the problem.

Recognising the aforesaid problems, Quin Systems has launched a fully integrated solution that delivers both Motion and PLC control functionality. This has been a carefully considered development that retains their fully distributed motion control architecture whilst also having a software PLC for the machine's (or line's) basic sequencing.

At the heart of Quin's offer are the Q-Manager and Q-Drives, which run Quin's feature-rich PTS (Programmable Transmission System) motion software package and are connected together via the ServoNet network. The Q-Manager holds all the various programmes for motion and logic control, the per-axis motion control being performed by the Q-Drives (axis motion controllers) themselves. This distributed architecture has the effect of relieving the central controller of the per-axis computing load, the drives themselves being responsible for this. The non-motion machine devices are connected through integrated inputs and outputs that are accessed by the QManager's Software PLC - "QLC".

Rather than developing a bespoke PLC language for the QManager's software PLC, Quin adopted IEC 61131-3 programming as its soft PLC function. This international standard is widely used and reduces the learning-curve for maintenance departments and commissioning engineers.

Quin has thus overcome the initial builder "deployment" and service problems that were outlined earlier. However, Quin was keen to deliver long term ease-of-use for the user and builder's service team. This has been done by making the motion programming fully interactive. This interactivity allows an engineer to operate the machine through the software in real-time, greatly facilitating commissioning, machine re-configuration and maintenance diagnosis. All these functions can be accessed remotely, allowing specialist support to be rapidly delivered.

With the integration of the soft PLC, Quin's motion and sequencing control system delivers measurable benefits to the builder that will help to fully reduce both machine building and support costs; and deliver a machine that will be the benchmark for customer satisfaction for many years.