A new multiaxis distributed controller has adopted the FireWire comms link, bringing faster data transfer rates that traditional buses

Motion controllers often have to operate in less than ideal industrial environments. The production or manufacturing floor can be tough on the controller, both physically and in terms of the demands on its systems.

National Instruments reckons it has addressed both of these issues with the FW7344 multiaxis distributed controller. For one, it’s a sturdy, self contained device more than able to cope with the physical rigours. And importantly, it is the first product of its type to adopt FireWire as a communications bus.

With FireWire, the host PC monitors motion at a much faster rate than is possible with other serial buses. Once programmed, the controller monitors motion independently from its host PC. And because of this independence, and the use of FireWire, it performs exceptionally well at high speeds.

“Fast communication is especially important when your motion is tightly coupled to other processes on your PC,” says Mike Darden, motion control product manager at National Instruments. “The FireWire interface on the FW-7344 has the speed to integrate the controller into a high performance computer-based data acquisition or industrial automation system.

The FireWire bus transfers data and 400Mbps, which is markedly faster than the current Universal Serial Bus, which transfers data at 12Mbps, or RS485 which bottoms out at just 10Mbps. With the Firewire interface, you can daisy chain as many as 32 FW-7344 controllers together. PCs lacking FireWire ports can be easily equipped via conversion boards.

• National Instruments

June 2000

An encoder with millions of variants from a single disc is on offer from Stegmann. Alan Quinn considers the implications for encoder users

Perhaps the greatest problem with the development of encoders has been that all manufacturers have needed a large number of etched discs – one for each number of incremental lines – to accommodate the resolution requirements of all of their users.

In conventional designs, the etched discs have to be cemented to the shaft, which means that the shaft type and its profile have to be determined before the product can be made. The natural result of this, along with fact that an enormously wide and varied range of components have to be connected around the shaft/disc assembly, is that an extremely large number of different mechanical procedures are required.

This has resulted in obvious difficulties, both for the manufacturer and the end user. Only order-specific production is possible, with the inevitable consequences on delivery lead times.

Now, with an encoder system called Coretech, Stegmann claims to have changed all this. Coretech uses a disc with an electronically applied line pattern which is imposed as part of the manufacturing process itself. This means that only one type of disc needs to be held in stock and – it sounds silly to say it – any one of 10 million possible versions can be generated, with only 100 individual components.

Stegmann isn’t saying too much about the actual production process itself but, in particular, the discs can be despatched within 48 hours, way in advance of the current industry benchmark. The user can choose from a very wide range with much improved quality and reliability. And there is no price premium, whether the customer requires a solid or hollow shaft, servo or face mount, absolute or incremental.

• Stegmann

April 2000

An innovative positioning unit has the motor and drive close-coupled. WAYNE BROWN finds out the implications

On the face of it the Icla positioning drives look like a motor of some sort, having a shaft, a body and a cable entry. But take a closer look and you will see that SIG Positec has squeezed a gearbox, motor, encoder, power stage, microprocessor and fieldbus interface into a single unit.

What this means is that, given a fieldbus and central controller, you can download an instruction to the Icla drive and it will then move to the required position and stay there until it receives the next instruction. Indeed, you will notice that there is no mention of a brake so far, and that is because the high holding torque of the brushless DC motor is sufficient to maintain the position under normal conditions. However, if there should be a disturbance, the drive’s real-time position correction will come into play and bring the drive back into position.

One of the most obvious advantages of this all-in-one configuration is that you no longer need to find cabinet space for the motor controller. Time and money can also be saved because of the simplicity with which the integrated unit is mounted. In terms of electrical connections, all that is required is a bus link and a suitable power supply.

Of course, the bus link is bidirectional so, as well as sending instructions to the drive, the central controller can also receive diagnostic data. SIG Positec supplies a software package with the Icla units so that configuration, operation and remote diagnostics are made as quick and simple as possible.

Despite the innovative configuration, there have been no compromises on accuracy or torque – either running torque or holding torque. Four different gearbox options are being launched, giving nominal speeds of 30 to 220rpm and nominal torques from 3.5 to 12Nm.

Typical applications are anticipated to be in the fields of printing, packaging, and the wood, metal and plastics processing industries where ‘push-button’ format adjustments are frequently required on machines.

We have already seen several motors introduced with inverters mounted on their bodies, but we certainly like the look of this fully integrated positioning drive.

•  SIG Positec

October 1999

A new drive server has been launched promising to save programming and commissioning time for drive systems. Tommy Miller reports

Imagine a situation where there is an inverter drive, a machine interface and a PC linked to the drive so that data can be collected for analysis in, say, Microsoft Excel. The PC can easily be used to write the PLC program for operating the drive, and for programming the machine interface to display the desired screens and to react to the user inputs.

Easy, so far. However, the machine interface and the drive both need to communicate with each other, which might not be so easy to achieve, especially if the two come from different manufacturers. Also, there is a need to define the data sets separately for the drive and the machine interface, and errors can occur here that may take some considerable time to find and resolve.

“There must be a better way,” came the cry from the engineers at Lenze (formerly known in the UK as Simplatroll). So now the company has launched the drive server and this new software tool should make life far easier. Similar in concept to a printer server, the Lenze drive server is an OPC-based interface that is installed on a Windows NT-based PC and instructed as to which fieldbus protocol to use. The drive server then recognises which drives are present and configures itself accordingly, building up a database of all the drive information. Parameter groups can then be arranged and named.

The main advantages of this alternative approach are that the data sets have to be declared once only, and that different fieldbus systems – perhaps serving different types of hardware – can access the database and communicate with each other, whether they are Can, Profibus, Devicenet or almost any other. Because the data sets are only declared once, there is a significant saving in programming time. Furthermore, the opportunity for making errors is vastly reduced, so the time taken up with debugging is also cut.

Lenze estimates that 30-40% of a typical drive project is spent on engineering the interfaces between the various items of hardware, and that a large portion of this time could be saved by using the drive server. After commissioning, further savings should also be possible due to simplified maintenance and upgrading.

• Lenze

April 2000

By only having to control one axis at a time, this new controller benefits from exceptional performance, as David Norris has been finding out

Some clever technology has gone into the new PM600 digiloop motion controller which Mclennan Servo Supplies is launching. In particular, a new development of Mclennan’s control algorithm enables high positional accuracy to be achieved, but with zero deadband, even if remotely-mounted encoders are used for the positional feedback.

To enhance system stability, a dual encoder feedback technique has been used. Furthermore, the PM600 is equipped with three encoder inputs so as to allow this feedback technique to be used when one axis is to be slaved to another. In order to give the PM600 good repeatability, high-speed registration hardware has been used so that reference signals can be detected with zero error.

For cost-sensitive applications where motion is required in two axes, but not simultaneously, a single PM600 can be used to control both – hence the reference to a one-and-a-half axis controller. Nevertheless, with the PM600 priced at around (UK pounds)400, there will be many applications where it will be very cost-effective simply to install one unit per axis. Also, because the units are compact, there is not a significant requirement for cabinet space if multiple controllers are installed.

Despite its low price, the new controller is an extremely versatile device. For example, it provides both analogue and digital output signals, so it is suitable for use with either servo or stepper motors. And, in addition to bi-directional limit and datum inputs, there are 16 user-definable digital I/O and analogue inputs are provided to enable interfacing with other machine functions. Meanwhile, with operating speeds of up to one million counts per second and a positioning range of +/-2billion counts, the PM600 is a truly high performance motion controller. In many respects the exceptional performance and smooth motion result from the fact that the PM600 is a single-axis controller and the processor therefore does not have to supervise multiple axes. Loop control is therefore tighter, which results in zero error.

Apart from straightforward positioning, other standard control functions include electronic gearbox, flying shears and electronic cams.

•  McLennan

October 1999

We heard about an intriguing terminal box inverter that does not have to be mounted on the motor. Tommy Miller investigated further

Simplatroll believes that a typical application of the Lenze 8200 Motec terminal box inverter will have a payback period of under two years. There are several compelling reasons why this should be the case, in addition to the fact that an inverter will usually save energy costs if the motor speed requirement is not constant.

For an inverter that is mounted on or near a motor, rather than in a control cabinet, there can be an initial saving due to the reduction in cabinet space required. Then, because of the relatively high cost of shielded motor cables, there is another saving in hardware costs. Other savings result from the use of standard motor starter contactors (no chokes required) and local safety isolators (no electrolytic DC bus capacitors required).

There will be occasions where it is not desirable to mount the inverter directly on the motor, perhaps because of space restrictions. Nevertheless, the advantages of an inverter close to the motor are still attractive. Lenze has tackled this dilemma by supplying 8200 Motec inverters separately from the motors such that they can be wall-mounted if you prefer. The design of the heatsink means that the inverter will operate reliably in ambient temperatures as high as 60degC, with no need for forced airflow.

Lenze has spent a great deal of effort designing these new inverters to be high performance products. For instance, with a speed range of 1:50, the units are capable of driving a motor at its full rated torque as low as 1Hz. Speed control is achieved by means of sensorless vector technology.

Three-phase models are available in powers ratings from 0.55 to 2.2kW, but higher power versions are likely to be introduced soon, and single-phase models are also understood to be under consideration.

A few other features and options are also worth mentioning: first, an optional on/off switch and potentiometer can be fitted to the base of the Motec unit; second, there is an integrated PID function for process control; third, a built-in braking transistor removes the requirement for a separate brake chopper. Simplatroll can supply standalone Motec inverters, inverter motors and inverter gearmotors.

•  Simplatroll

October 1999

The stepper and servo options provided on modern PLCs make networkable motion control a possibility without ever leaving the PLC rack. Robert Brooks from Omron explains.

While most of the servo applications that catch the headlines tend to be demanding tasks with extremely stringent dynamic requirements at the same time motion control is being adopted for simpler motion systems built around stepper and servo motors perhaps providing point-to-point or indexing control.

What is required in this instance is not necessarily a full blown stand-alone motion control architecture but rather one which is built around a much more user-friendly strategy based on existing hardware with a familiar software front end.

By adding stepper and servo control options to PLCs even the smallest PLCs can now be equipped with a pulse train control output suitable both for controlling stepper drives and – increasingly – servo drives.

Omron’s UE series servo drive is an example of the modern breed of servo which offers good dynamic performance without the cost and complexity traditionally associated with servo drives. Controlled via a pulse train input the UE range is ideally suited to applications such as point-to-point and indexing.

The pulse train output is becoming more common on PLCs. On Omron’s compact and micro PLCs such as the CQM1 pulse output for stepper and servo control is a standard function while on the mid-range C200H series of PLCs it is provided via an NC position control card.

Using the PLC in this way can make it very simple to develop motion control programs since motion-specific instructions have already been included in the standard instruction set. Fig 1 shows a section of an indexing program written for Omron’s CQM1 compact modular PLC. The program instructs the motor to move 25 0 pulses initially at a speed of 1kHz but slowing to 200Hz when a limit switch is actuated.

Combining with the ability of the CQM1 to link directly with any Omron Sysdrive inverter the stepper and servo options extend the capabilities of PLCs to allow complete highly functional machine control architectures to be built up simply around a single compact PLC.

PLCs of this size are also designed to link directly to man-machine interface products without the need for interfacing software making it easy to implement powerful control and diagnostics strategies. PLCs such as the CQM1 are also designed with communications in mind: an I/O card allows it to be connected to networks such as Omron’s Sysmac bus or to open fieldbus systems providing integration into a bigger factory automation network.

• Omron
• Robert Brooks
• 0181 450 4646

February 1999

What is the best way to connect up that motor? Tommy Miller dips into the new wiring manual from Klockner-Moeller

Anybody who works with low-voltage switchgear is likely to find Klockner-Moeller’s new book extremely useful, whether they’re a trainee or an experienced electrical engineer. And because it’s free, there’s no reason not to have a copy!

The book, simply called the Wiring Manual, covers most of the important circuits used in automation and power distribution applications, but it is particularly good for anybody configuring and operating electric motors. Indeed, at the heart of the book is a substantial section called All About Motors.

This key chapter runs to 122 pages (yes, really!) and discusses everything from motor protection and the incoming supply, to various methods of starting motors and controlling motor speeds. Many standard and sample circuits are included, together with tabulated and graphical data where this is appropriate. As well as circuits for direct-on-line starting and star-delta circuits, there are also examples of multi-speed and other miscellaneous circuits

The text is written in straightforward, no-nonsense language, and often comes in a question and answer format. For example: ‘What causes destruction of the overload relay? Destruction will take place only in the event of a short circuit on the load side of the relay when the back-up fuse is rated too high. In most cases this will also endanger the contactor and motor. Therefore, always adhere to the maximum fuse rating specified on every relay.’

Besides the main section on motors, the Wiring Manual also deals with many other related matters. For instance, comprehensive information is included on standards and specifications, there is a comparison of European and North American circuit symbols, units of measurement are tabulated, formulae are reproduced and there is even a table of cable entry and grommet sizes.

Another valuable section within the book considers how motors and control gear should be wired when there is a guard interlock with a mechanical securing action. This will be especially useful for those engineers who are responsible for original equipment or refurbished equipment where CE-marking is an issue. Lists of approvals bodies for different countries, together with marking requirements, will help engineers to target the products for any market world-wide.

Lastly there is, of course, a list of Klockner-Moeller’s sales offices around the world, so you can always be sure of getting hold of the hardware and assistance that you need. Meanwhile, the book itself is highly recommended.

• Klockner-Moeller

September 1999

Drives are now more sophisticated than ever before, but what is the best way to program them? Tommy Miller reports on a new toolset based on function blocks

For run-of-the-mill drives applications (no pun intended), engineers are now almost spoilt for choice in terms of the number of frequency converters available. Even for more complex tasks, perhaps where many more parameters need to be set, there is a wide range from which to choose. So for some people, one of the most important selection criteria is not the performance, size, cost, or after-sales support, but the programming tools that are offered by the drive supplier.

Although a great deal can be achieved with modern hand-held control panels (and even the popular detachable-front-panel type), engineers are understandably more comfortable working on complex programs at a PC, whether a desktop or laptop machine.

Whilst huge advances have been made in the user-friendliness of PC-based tools for programming PLCs – especially when compared with the traditional ladder logic systems – it is arguable that programmers of variable speed drives have not been as well served. That is, until recently, with the introduction of a function block programming tool from Vacon. Furthermore, the latest version has seen some significant changes to enhance the graphical editor. The FC1131-3 Engineering Toolset is, as the name suggests, based on the IEC 1131-3 standard for PLC programming software, so any engineers familiar with many of the current crop of PLC tools should feel at home with this drive programming software. Vacon has designed the toolset to be used with its CX, CXL and CXS frequency converters, which have current ratings in the range 0.75kW to 1.5MW and voltages from 230V to 690V.

PLC-type functions

Among the PLC-type functions that can be programmed, there are boolean logic functions, timers, counters, comparators and flip-flops. It is also possible to work with analogue signal processing and scaling, ramp control, PI-controllers, filters and integrators. Indeed, the toolset gives the user very easy access to the control logic and parameters of a frequency converter, so is said to be particularly suitable for system engineers or OEMs with requirements that are out-of-the-ordinary.

Users can readily create applications using Vacon’s standard applications as a starting point. This makes it even easier and quicker to develop specialist applications than it would be if starting from scratch. In addition, the software package includes tools for downloading, debugging and commissioning applications. Oh yes, and to make sure that you get up to speed as quickly as possible with this powerful package, Vacon is throwing in two days of free training!

• Vacon

June 2000

Is it possible to have an efficient drive that provides multiple control modes? It seems so, as Tommy Miller has been finding out

System developers often want one unit that will do many tasks. This can reduce the time it takes to get up the learning curve as well as reducing stock holding. Meiden is now launching the VT230S, which is a five-in-one vector drive that can provide an effective means control for a very wide range of applications. It also enables motors to run much quieter.

The five operating modes are as follows:

1. Variable frequency control for variable torque loads with ‘advanced torque control’. This mode uses auto tuning to give voltage vector control in open loop.

2. Variable frequency control for constant torque loads with advanced torque control. This mode again uses auto tuning to give voltage vector control in open loop but, in this case, withoutthe higher constant current rating associated with the above type.

3. Sensorless vector control. In Meiden’s case, this refers strictly to flux vector control without use of an encoder. Becaus ethere are two current loops – to control the magnetising and driving currents independently – it is possible to achive torque at zero speed, which is claimed to be an industry first.

4. Closed loop vector control, where an encoder is required. However, if the encoder signal is lost, the drive will switch automatically to sensorless vector control and will also send an alarm output.

5 Permanent magnet motor control. Although Meiden has provided this facility in the VT230S architecture, the company has not yet launched its range of dedicated permanent magnet motors.

It can be seen that the range of applications for which the VT230S will be suitable is far greater than would be the case for a conventional drive – whatever its operating mode.

Quieter motors

Apart from the VT230S being very versatile, its other notable feature is how much more quietly it makes motors run. The characteristic whine of an AC motor under inverter control can be effectivley reduced by means of the ’soft sound’ technology which randomly changes the VT230S drive’s switching frequencies.

Following tests, the development team found that there was no single set of frequncies through which the inverter could be switched randomly to have a satisfactory effect on all motors. This is due to the root cause of the noise: resonances in the motor laminations, whcih will be different for every motor. It is therefore necessary for the commissioning enginer to alter certain parameters to reduce the noise levels. However, this is relatively simple because adjustments can be made with the motor running, which allows the results to be heard immediately.

• Meiden

October 1999