Motors & Drives Information

The new Allen-Bradley Ultra-3000 family of high performance, digital servo drives from Rockwell Automation offers a wide choice of easy to install, easy to commission motion control solutions. A typical servo drive has in the order of 120 wiring points and at 5 minutes per connection, the cost of installation can be £300 or more. Five years ago, this would only have represented 5 or 6% of the cost of the drive, but with today's lower hardware costs, it is more like 30%.

So a reduction in installation cost was one of the key goals given to the Rockwell automation engineers when they set out to design the Ultra 3000.

They identified three key areas where these savings could be made: * Connection of the servo drive to the controller, where they chose to use Sercos, a single fibre optic connection.

* Connection of the servo drive to the motor by using pre-configured power and feedback cables.

* A drive that automatically configures itself with the help of a smart feedback facility.

With Sercos, command signal and all position feedback information is routed over the fibre optic network, enabling the user to control, commission and monitor the drive.

The 20 wires that would previously have been required between the controller and servo drive are reduced to a single fibre optic cable.

The pre-configured power and feedback cables are designed to connect the servo drive to all current Allen-Bradley motors.

They are available in various lengths and take only seconds to plug in, compared to several hours needed to connect a conventional system.

With smart feedback technology, the drive can not only read the motor part number and so automatically configure itself, but also support absolute and high-resolution encoders.

This ensures that position is not lost if the power is cut, eliminating time-consuming machine homing cycles.

It delivers resolution down to millionths of a revolution, providing extreme accuracy.

For simple applications where complex multi-axis control is not required, the Ultra 3000 has a built in indexing function, allowing it to carry out a series of moves without an external controller.

This makes it perfect for applications such as pneumatic or clutch/brake replacement.

However, when connected to a modern controller such as the Allen-Bradley ControlLogix, it is capable of handling the most sophisticated requirements.

The power range is 0.5 to 22kW, 100 to 240V single phase or 380 to 500V three-phase AC.

There are eight general-purpose digital inputs assignable to multiple functions, four general-purpose digital and one relay output and a choice of multiple operating modes.

Such versatility is truly amazing, and with easy connectivity and commissioning it can be up and running and saving money in less time than it takes your accountant to do the sums.

With the new FZ 38, Zimmermann-Boko is presenting a CNC portal milling machine with linear drive. The impressive dynamism of this machine bears witness to the highest level of compe-tency in the field of demanding drive technology. The aim Zimmermann is to offer optimum drive concepts for the specific requirements of their customers.

Towards this end, Zimmermann is making use of decades of experience at the peak of technological developments.

Current drive tech-nologies, such as linear motors, rack and pinion drive and ball screws are assessed objectively and customers profit from this: the result is comprehensive machine concepts with optimum drive for precisely defined employment pur-poses - an example of this is the FZ 38 with pure linear drive technology.

This is further proof that Zimmerman assimilate the individual requirements of each customer and focus their solutions accordingly - customer orientation of the highest quality.

F.

Zimmermann - the innovative company from Denkendorf near Stuttgart, Germany - offers state-of-the-art constructions for large-scale CNC portal milling machines and CNC plano-milling machines with high-speed technologies.

This year, the experts from Zimmerman will once again impress their target group at the trade show.

With the FZ 38, Zimmermann is pre-senting a CNC portal milling machine driven by linear motors that points the way to the future with its special qualities.

* Dynamism dimension 1 - exceptional efficiency - the most important aim when using linear drives is the increase in productivity.

The FZ 38 achieves extremely high time / chip volumes of up to 4500cm3/min (aluminium).

Feed rates on linear axes of up to 60m/min and spindle speeds of up to 35,000 rev/min make genuine HSC processing possible.

Just as im-pressive are the torque motors on rotational axes with feed rates of up to 150 deg/s.

The accuracy and surface quality realised in this way are decisive for this outstanding performance data.

And it is precisely in this point that the FZ 38 sets standards.

The linear drives achieve a very high level of standard control with a large Kv factor which also makes a low trailing distance and high po-sitioning accuracy possible even at high feed rates.

* Dynamism dimension 2 - well-established technical know-how - a prerequisite for the performance and accuracy values achieved with the FZ 38 lies primarily in a machine designed especially for using linear drives.

Zimmerman customers can profit here from exceptional empirical val-ues in the development of structurally stiff machines.

The solution lies in the combination of optimized lateral stands and torsion-free portal on the one hand and intelligent arrangement of the interfaces, i e, the drives on the other hand.

* Dynamism dimension 3 - high degree of economic efficiency - the overall economic efficiency of the FZ 38 is a result of the interplay of different aspects.

The high accuracy of the machine reduces manual work on finishing surfaces as far as possible or even avoids them entirely.

Due to the high feed rates, the ancillary times, e g, for reposi-tioning, tool orientation or tool change can be reduced.

The FZ 38 achieves very high levels of availability.

This is not least due to the contact-free, play- and wear-free and there-fore low-maintenance direct drives.

* Some technical details - construction method - as with all high-quality CNC portal milling machines from Zimmerman, with the FZ 38 we are dealing with a modularly constructed machine concept which allows different work areas, milling spindles and con-trol systems to be combined.

The machine has permanent lateral walls, a clamping table perma-nently connected to the foundation and an upper portal which moves in X-direction and is driven on both sides.

The workpiece is not moved.

The constantly moved masses (portal slide, cross slide and z-slide, milling head) ensure consistently dynamic behaviour - a prerequisite for optimum surface quality and the use of linear drives.

* Machine frame and guides - the machine bed is constructed from grey cast steel; lateral walls, portal and Z-slides are welded steel constructions.

The lateral walls are filled with a special compound material for dampening vibrations and stabilizing temperature.

The guides, drive and measuring systems on the X-, Y- and Z-axes are extensively protected against contamination or penetration by chips.

* Axis drive - irrespective of the make of the control system, all linear axes are equipped with the latest generation of Siemens digital linear motors.

At standstill, the machine is held in position by brake shoes on tes X- and Y-axes.

* Safety concept - if electricity fails, the Z-slide is effectively secured by powerful clamping heads and all axes are braked by the backfeed of the poten-tial energy through the effect of the generator.

* Cooling - the linear drives are uncoupled effectively from the machine by precision coolers with separate cooling cycles for magnet and motor ele-ments.

* Accuracy - the dynamism of the machine and the extreme inherent stiffness enable high levels of accuracy, in particular when finishing with high speeds and feed rates.

* The new VH 6 milling head with MuST technology - the new VH 6 milling head is especially designed for the HSC technology.

The drive of both rotation axes is carried out by backlash free torque motors.

With the high driving power the rotation axes can be used for simultaneous operations or they can be electronically fixed in position.

In addition, the two axes can be clamped hydraulically.

Both axes drives are designed following the Thermosandwichprinzip, and are equipped with a power and a supplementary precision cooling unit.

This drive technology enables a combination of precision, high driving power and increased dynamics.

In general two different spindles with various specifications are available for all application areas such as roughing, finishing and fine finishing.

* Universal spindle for all kinds of machining of aluminium, composites and light machining of cast iron and steel.

* Finishing spindle - high frequency spindle designed for finishing, for milling of fine contours and for fine finishing with highest surface quality.

Concerning flexibility Zimmermann came up with even more ideas.

Due to its modular design, the MuST system enables different configurations.

1 - One spindle is fixed in the milling head - however this can be changed manually as well.

2 - Semi-automatic spindle change system.

3 - Full automatic spindle change system - enables unmanned shifting * Areas of application - thanks to high stability and stiffness, constantly moved masses and highly dynamic linear drives as well as the spindle changing concept MuST, the FZ 38 is suitable for HSC work on all common materials in making tools, moulds and models as well as in the aircraft industry.

* Aluminium chipping with extreme feed rates.

* Compound materials.

* Overall processing of heavyweight materials such as steel, cast products and even titanium.

Conclusion - Zimmermann's strength is to offer efficient combinations of different machine concepts, drives, milling heads and spindle types.

Zimmermann is consistently enlarging its machine program and with its latest innovation, the FZ 38, it is now enriched by the ultimate high speed type dynamics and speed directly turn into benefit for our cus-tomers.

Rolf Roehm, Zimmermann sales and marketing director resumed: 'The perfect combination of machine design, tools, tool and work piece clamping devices, material technology parameters, the applica-tion know-how as well as the so called C-techniques has highest pri-ority when consulting our customers'.

'The development of the FZ 38 contributes a further option to the drive technique which is of great advantage to our customers.' * F Zimmermann will be exhibiting at IMTS 2006, Chicago, USA, September 6-13, Booth A-8568.

The Allen-Bradley PowerFlex 7000 medium-voltage AC drive, with new Direct-to-Drive technology, was developed by Rockwell Automation to eliminate the disadvantages associated with using a drive isolation transformer. The new technology connects the supply power directly to the MV drive. It is a strategic advantage for industries where control room space is at a premium or for example, at high altitudes in mining applications.

Direct-to-Drive technology can also benefit the oil and gas industry, sugar mills, water/wastewater, power plants and cement plants.

The need for a better drive is universal.

When the PowerFlex 7000 AC drives were first introduced in 1999, Rockwell Automation sold in countries around the world, including China, India, Australia and Korea.

Today, in Latin America, there is immediate potential.

In addition, Australia expects that 80% of its MV drive customers will use the new Direct-to-Drive technology.

'In Europe, customers are requesting quotes and changing their specifications from transformer-fed drives to Direct-to-Drive technology', explains Bruce Ingram, Rockwell Automation's Marketing Manager in Switzerland.

The PowerFlex 7000 medium-voltage AC drive with new Direct-to-Drive technology provides many benefits including common mode voltage (CMV) elimination, reduced harmonics, reduced drive system size and minimal drive complexity.

Reduced capital cost, lower transportation and installation expenses, and increased operating efficiency all contribute to a lower total cost of ownership.

The PowerFlex 7000 Direct-to-Drive technology is the combination of three innovations: new CMV stress protection, the active front end (AFE) rectifier and the symmetrical gate commutated thyristor (SGCT).

Until the development of Direct-to-Drive technology, most MV drive manufacturers used multiple-winding isolation transformers to protect motors from CMV stress.

Transformers are used to isolate the supply system ground from the drive system earth, which allows the motor neutral point to be earthed.

Although the motor is protected from CMV using this method, the high-level CMV stress that would have been imposed on the motor is now imposed on the transformer and the cable insulation.

This requires extra transformer insulation and cable insulation to withstand the CMV stress, adding extra engineering requirements and extra costs.

'Instead of using the transformer method, the PowerFlex 7000 Direct-to-Drive technology uses zero sequence impedance to virtually eliminate the CMV on the motor neutral', explains John Kwarta, Product Manager of Medium-Voltage Drives at the Rockwell Automation Medium-Voltage headquarters in Canada.

'The MV drive is now capable of using standard motor and cable designs with no isolation transformer'.

Manufacturers use different methods to reduce harmonics, so there is a wide range in the complexity of drive designs.

Isolation transformers phase-shift the transformer secondary windings to help reduce harmonics.

'The more secondary windings', says Kwarta, 'the higher the 'pulse number' and the better the harmonic elimination level'.

'But with up to 15 sets of secondary windings, complexity and high component count are major disadvantages'.

'In addition, this method requires a perfectly balanced three-phase distribution system for optimum harmonic elimination'.

Instead of an isolation transformer, the PowerFlex 7000's Direct-to-Drive AFE rectifier uses semiconductor switching to reduce line current harmonics to levels that comply with the world's most accepted harmonic standards.

The AFE rectifier, also known as the pulsewidth modulated (PWM) rectifier, uses the SGCT to produce a PWM switching pattern that prevents the drive from producing high levels of line current harmonics while avoiding the use of a phase-shifting isolation transformer.

Industries are always looking for ways to save control room space.

An isolation transformer can represent 30-50% of a drive system's size and 50-70% of the system's weight.

The PowerFlex 7000 with Direct-to-Drive technology is typically smaller and lighter than drive technologies using isolation transformers.

The typical volume of space required for a 950kW (1250hp) drive with isolation transformer is 13m3, and typical weight is 4200kg.

The transformer-less PowerFlex 7000 of the same voltage and power is 60% smaller at 5.4m3 and 65% lighter at 1350kg.

A smaller and lighter drive system means there are no shipping splits to connect and no interwiring between drive and transformer.

A transformer-less MV drive is perfect for retrofit projects with existing motors, switches and control rooms, where space is often limited or at a premium.

'Control room space is very expensive on oil and gas platforms and in small European cities', says Ingram.

'Customers always ask for small frame solutions'.

'The transformer-less option also improves system efficiency and reliability'.

Reliability is one of the most important factors in the drive and motor system.

The PowerFlex 7000 medium-voltage drive has already earned a reputation for reliability since its introduction in 1999, due to its high fault withstand capability and low component count.

It uses the DC link inductor and line reactor to limit fault currents to levels that are less likely to damage the drive system or connected equipment.

Also, it eliminates the need for fuse protection in the drive.

By using components with high voltage ratings, the PowerFlex 7000 medium-voltage drive reduces the component count to the lowest level in the industry.

In a typical 4160V, 750kW (1000 hp) motor application, an average MV drive can have up to 385 components in its power circuit.

The PowerFlex 7000 with Direct-to-Drive technology has less than 30 components at 4160V.

Capital costs, operating costs and service costs can all be reduced using Direct-to-Drive technology.

The simplicity of its design reduces initial capital investment because it not only eliminates the need to purchase an isolation transformer but also eliminates the need for an isolation transformer protection relay, a DV/DT filter, sine filter or motor terminator and special cables.

Installing an isolation transformer adds to total project costs because of extra cabling, air conditioning, civil engineering, concrete pad construction for outdoor transformers and overall installation.

By purchasing a transformer-less drive, costs for isolation transformer crating, handling and transportation are also eliminated.

'Shipping large transformers can add extra costs you don't see a return on', says Ingram.

'The transformers are too large for container storage and have to be specially crated and shipped on the deck, which can cost the customer thousands of dollars'.

This 'breakbulk' shipment method requires prebooking space on a vessel and longer shipment times due to limited availability of breakbulk vessels.

For example, a recent isolation transformer shipment to Argentina added costs of US $18,700 when no vessels were available to take breakbulk cargo.

The transformers had to be sent to a New York port to be shipped, for a total of 25 days transit time.

In a typical situation, shipping the transformer will add more than US $4,000.

For example, an isolation transformer on a 950kW 1250 hp drive traveling from Los Angeles to Chile would cost about US $2200 for crating and US $1,875 for shipping, plus additional handling and duty costs.

Typical transport time can be three or four weeks.

If a transformer fails, this transportation time for the replacement equipment represents significant downtime and potential lost revenue.

Direct-to-Drive technology reduces operating costs through greater system efficiency because there are no isolation transformer losses and DV/DT or sine filter losses.

And, there is no need for extra air conditioning to cool the transformer.

Lower operating costs result from the PowerFlex 7000 medium-voltage drive's high efficiency and inherent regenerative capability that converts the variable frequency power generated to a signal that can be sold back to the utility.

The drive can provide 100% continuous full current regenerative braking capability without putting thermal stress on the motor.

With the lowest component count of any MV drive manufacturers, there are fewer parts to maintain or replace.

Since its introduction to the market, Rockwell Automation has seen an overwhelming demand for PowerFlex 7000 medium-voltage drives with Direct-to-Drive technology.

Standard and specialty industrial and commercial applications range from fans, pumps and compressors to extruders and conveyors.

Customers worldwide now have the ability to specify a smaller, lighter, more efficient and highly reliable MV drive that will use less control room space, save initial costs and continue to save money in the long term.

As part of a modernisation project, the chemical company Brunner Mond, based in north-west England, is now using variable-speed drives, instead of steam turbines to drive its centrifugal gas compressors. The 50-year old compressors, now fitted with state-of-the-art drive technology, will remain to become an energy-saving, low-maintenance system with a high availability. This has all been made possible by combining special high-speed motors, gearless couplings and medium-voltage drive converters with intelligent HV IGBT (Insulated Gate Bipolar Transistor) power semiconductors.

In addition to supplying the drive system, Siemens carried-out the computer-based vibration analysis, system integration, training of the operating personnel, commissioning and after sales service.

Brunner Mond Group plc.

is one of the leading European producers of alkaline chemicals.

The Company has a total of four plants in Europe and Africa with its head office located in Northwich, in north-west England.

The company produces mainly soda ash, a basic material for use in the glass industry and the production of washing powders, as well as industrial minerals.

Until September 2000 Brunner Mond owned and operated coal, oil and gas -fired boilers in the production facilities at Winnington and Lostock, close to Northwich.

The boilers kept the plants supplied with process steam as well as high-pressure steam for the steam turbines driving the compressors.

Brunner Mond now have all of their steam raising carried out by Powergen Combined Heat and Power via a combination of five new gas boilers.

These central, gas-fired, boilers supply low-pressure steam, to the two facilities at Winnington and Lostock.

This can be used as process steam, but is not suitable for driving the compressors.

Brunner Mond therefore decided to keep the fifty-year old compressors, which were still fully operational, and replace the steam turbines with variable-speed electric drives.

At Lostock, this involved four units.

Compared with steam turbines, electric drives are distinguished by their high reliability and low service requirements.

As deposits continually reduce their efficiency, steam turbines have to be stripped down completely twice a year, cleaned and the seals replaced.

Modern electric drives, however, operate almost maintenance-free with the added advantages of significantly lower noise levels and cooler operation.

The speed of the motor is continually adapted to actual operational requirements, which guarantees accurate process control.

Energy is also saved because the system takes only the amount of power, which it actually requires.

In order to gain the advantages of variable-speed drive technology for the existing Brunner Mond compressors, Siemens selected a system comprising special high-speed motors, gearless couplings and water-cooled medium-voltage Simostart MV drive converters.

The drive converters are equipped with intelligent HV IGBT (Insulated Gate Bipolar Transistor) modules, which are optimally harmonised with each other.

These drives guarantee optimum reliable compressor operation over the complete speed range.

The motors, which have an operating range from 3800 to 6400 RPM, are an individually customised design from the Siemens special drives centre in Berlin.

Induction motors with laminated squirrel-cage rotors are used for the four drives, two machines require 1.5 MW of absorbed power at the coupling and two smaller machines of 1.3 MW, so that the motor dimensions allow the two existing compressors to be used without modification.

The motors have air-to-water heat exchangers, the internal cooling circuit using separately-driven fans with counter current cooling at both ends.

The rotor has a ribbed surface for good cooling characteristics.

In order to eliminate vibration problems from the very beginning, the usual bending and torsion analysis of the rotor was supplemented by investigations into the strength and stiffness of the motor frame, which was optimised by computing the natural frequency.

In order to optimise the dynamic performance of the rotors, Siemens used special tilting-pad bearings.

Four additional balancing planes permit modal balancing and therefore a specific reduction in the bending vibrations in all of the natural forms.

In spite of the wide range of speeds, the application of each of these measures made it possible to locate all of the natural frequencies outside the speed control range.

Full-load system tests were carried out in the Berlin Dynamowerk factory, prior to installation, to ensure that all of the specifications were fulfilled.

For the Brunner Mond application, the motors are coupled to the compressors without using gearboxes.

This configuration has the advantages of a higher overall efficiency, low wear, and increased availability due to the elimination of all problems associated with gearboxes.

In order to guarantee the smooth running properties of the new motors, they were perfectly harmonised with the 50-year old compressors.

Siemens carried-out a torsion and vibration analysis for the complete mechanical transmission using a specially generated three-dimensional finite element model of the old compressor and the new motor.

The moment of inertia for the compressor was determined from documents, which were about 40 years old and using the FEM model, all possible operating situations and mutual interactions were simulated by computer.

From the information gained, optimum smooth running characteristics were obtained for the mechanical transmission up, to a maximum speed of 6400/min.

A Simovert MV medium-voltage converter is used to control the speed.

This unit has an output of 2300 kVA at a motor voltage of 3.3kV and an output frequency of 107 Hertz.

As a result of its unique design, Simovert MV requires little maintenance and has a high availability.

This is particularly due to the fact that it is the first drive converter in the medium-voltage range, which uses HV-IGBT (Insulated Gate Bipolar Transistor) power semiconductors.

In conjunction with a three level voltage DC link, the HV-IGBT modules permit a clearly structured, modular and space-saving design, which is both extremely reliable as well as service-friendly.

This could not be achieved when using other power semiconductors because the HV-IGBT is the only semiconductor element of its class which requires absolutely no snubber circuitry.

Together with the gating system, the IGBT modules form an intelligent switching unit which allows switching, independent of the load, and as a result unnecessary current peaks are eliminated.

In conjunction with the three-level technology and the high-performance transvector control, this guarantees sinusoidal motor currents.

This, in turn, reduces the motor losses and minimises the torque fluctuations, which reduces overstressing of the motor, mechanical transmission and especially the driven load.

Although Simovert MV units can be either water-cooled or air-cooled, it was only possible to use the water-cooled version for the Brunner Mond drives.

The ambient air was far too aggressive for air-cooled converter technology, which is frequently the case in the chemical industry.

Rockwell Automation has extended the Allen-Bradley PowerFlex 700H power range to 500kW, and now offers the popular IP21 enclosure drive in two additional versions of IP54 dust tight enclosure and open-frame IP00 option. More flexible than ever, the PowerFlex 700H is the ideal choice in an even wider variety of open-loop speed control applications. Since its introduction last year, the PowerFlex 700H has proved a popular choice in applications requiring accurate open-loop speed regulation and excellent low-speed torque, such as fans, pumps, conveyors, mixers, crushers, bark strippers, centrifuges, stamping presses and extruders.

With the addition of the new IP54 enclosure option, it can now be employed in an even wider range of applications, in all but the harshest industrial environments.

Along with the existing IP21 enclosure and new IP54 enclosure, Rockwell Automation has also added an IP00 option to the PowerFlex 700H.

The open frame design makes the PowerFlex 700H more accessible than ever to OEMs and machine builders requiring precise, reliable and cost-effective motor control for their high-power applications.

Open frame access and 'pull-apart' control terminal blocks simplify the task of wiring, and the optimised global voltage settings make the drive quick and easy to configure for applications anywhere in the world.

The power range of PowerFlex 700H has now been extended to offer 160kW to 500kW at voltages from 380 to 690V.

Users can configure the PowerFlex 700H for either V/Hz or sensorless vector control.

Standard I/O options include 24V or 115V digital I/O plus analogue I/O for added flexibility.

The extensive communications options available allow the user to easily integrate the drive into a manufacturing process or machine application using Rockwell Automation NetLinxTM, DeviceNetTM, ControlNetTM and EtherNet/IP networks as well as other industrial networks such as Profibus.

The built-in LCD display is multi-line and multi-lingual, and the on-board start and assisted start routines allow for easy configuration and tuning of the drive.

Naturally, PowerFlex 700H is also fully compatible with Allen-Bradley DriveExplorer, DriveExecutive and DriveTools SP software tools, making complex programming and system configuration easy and quick.

The new PowerFlex 700H IP54 enclosure and IP00 open-frame options are just the latest additions to the comprehensive PowerFlex range of AC drives, available from 0.25kW to 6700kW.

Like all products within the PowerFlex family, the 700H meets worldwide power ratings, packaging requirements and electromagnetic compatibility (EMC) criteria.

All the drives include AC-chokes and EMC filters compliant with EN 61800-3, and are CSA/cUL Certified, UL-listed and CE-marked.

The modular design and worldwide availability of spares makes the PowerFlex range easy to maintain in the field.

With the power range extension and addition of IP54 and IP00 variants, PowerFlex 700H is the ideal choice for both OEMs and end-users requiring the best possible combination of features and cost-effectiveness.

A novel design of generator for wind turbines is based on permanent-magnet technology. Compared with a traditional machine, the new generator offers high output relative to the frame size, making for instance a 3.6MW unit a full frame size smaller. The new generator can be operated in a wide speed range with a maximum output of 3.6MW from a 500mm frame.

The efficiency is better than 98%.

The design is based on ABB's low speed permanent magnet generator technology, launched last year.

This has now been further developed with a more robust rotor suitable for higher speeds.

The permanent magnet generator is a synchronous machine where the rotor windings have been replaced with permanent magnets.

This eliminates the excitation losses in the rotor, which otherwise typically represent 20 to 30% of the total generator losses.

The reduced losses also give a lower temperature rise in the generator, which means that a smaller and simpler cooling system can be used.

The temperature reduction in the rotor also reduces the temperature in the bearings, improving reliability by increasing the lifetime of the bearings and the bearing grease.

The high efficiency of the generator means better utilisation of the wind energy, producing more electrical power.

The reduction in size and weight also makes the construction of the windmill easier as smaller lifting equipment can be used.

Recent developments in permanent magnet generator technology have been made possible by a significant improvement of the magnetic materials during the past decade.

A piece of neodymium boron iron (NeFeB) material can have a magnetic force more than 10 times stronger than a traditional ferrite magnet.

The CNC machining centre is for the machining of the ends of various types of components simultaneously and is the most recent evolution of the classical end-working machine for the machining of the extremities of bars, forgings, tubes, etc. Thanks to this evolution, this machine-tool is making a 'technological impact' placing itself at the level of the most advanced machine-tool products and, being able to solve the most different applications of more demanding companies. The machine concept is a reply to those companies who require the availability of the modern engineering manufacturing processes.

Machining both ends without moving the component - the MC 650 machining centre, produced by CAORLE, is a CNC machine with 6 controlled axis (3 + 3): the longitudinal 'Z' (Z1-Z2), the transversal 'X' (X1-X2) and the vertical 'Y' (Y1-Y2).

It works by means of two operating units and two tool-changer facilities and it was conceived and designed for the machining of the extremities.

The MC 650 - said Alberto Caorle, managing director of the Company, 'Has to be considered the evolution of the concept of the simple end-working machine, a type of machine which was always considered as a secondary machine but now, thanks to this new advanced project, it has become a true machining centre qualified for any kind of machining on the extremities of the most varied types of components and for the most different types of industrial sectors.

Using MC 650 it is possible to complete finished-machining and complex machining by interpolation (threading, facing, drilling, routing, execution of keys, etc.) without having to move the work piece.

Different examples of applications, from the machining of finished extremities (threads, chamfers, 'little channels') on the bodies of sunken pumps, which are polished pipes of stainless steel, to the machining of finished extremities (facing, drilling, tapping of the various holes on the end, execution of 'channels' and keys) of camshafts: for both there is not a need of a further machining on a lathe.

In particular, for one of our important customers involved in the 'automotive field', we have supplied machines equipped with customized facilities able to execute facing and centering with reference to the cams, in order to share the stock metal in a balanced way for a better off execution of the following machining.

Tooling breakage control devices (for drills and taps) are also present.' A double machining centre - the bed is an electro-welded and normalized structure made of a thick section heavy duty steel plate, strategically reinforced for obtaining a maximum stiffness and rigidity; the longitudinal guideways (flat guideways with a 'T' shape of 100mm surface) mounted on the bed are made of a hardened steel.

The two cast iron saddles units slide above these guideways and on the same guideways are located the self-centering jaws.

The saddles are driven and positioned by precision ball-screws and AC brushless servo motors Siemens.

The two longitudinal box-type guideways and the spindle unit are made of cast iron, the vertical upright is an electro-welded structure.

'We have developed a machine-tool,' continued Caorle 'that has to be extremely rigid in order to assure the maximum machining quality, so that we have used cast iron for the production of all those components with a need of high rigidity and also for the absorption of the vibrations'.

Each one of the two machining units (MC 650 is equipped with two independent powered and horizontally opposed machining units) consists of: a longitudinal saddle unit made of cast iron with the surface in contact covered with a special antifriction material; a transversal saddle unit mounted above strong and dimensioned rollers re-circulation slide-shoes (on this saddle is also mounted the tooling stock group); a vertical saddle unit is mounted above strong and dimensioned rollers re-circulation slide-shoes and there is also installed the support for the ISO50 spindle (the spindle is equipped with a fast hydraulic unclamping device) together with its motor; an oil-dynamic balancing device for the vertical saddle.

The two spindle units are designed for the axial flow of the coolant through the spindle, in addition to the external one on the machining area.

'The two operating units,' said Caorle, 'Are located exact opposite each other so that the spindles are horizontally positioned, facing one to the other one; these two groups are positioned on the same guideways of the steel-bed, which means that the two operating units are displaced on the same longitudinal axis.

On these guideways is mounted a pair of self centering jaws for blocking the workpieces: bars, pipes, forges, crankshafts, camshafts, ranks, axle shafts and so on.' The vice-jaws customize the machine - the self centering blocking jaws are mounted on the longitudinal guide ways and they work by means of an hydraulic device; the related positioning is made by an hydraulic hooking up (hydraulic blocking/de-blocking system on the guide ways); a system of automatic hooking up of the jaws to the working unit allows to move them to the desired position and, by means of an automatic de-blocking procedure, the unit leaves the jaws which block itself to the guideways of the steel bed.

The structure of the jaws is made of a cast iron body, on which are mounted the hardened steel sliding guide ways and where the blocking vices move themselves.

All the movements are automatically lubricated by means of a centralized systems; the positioning of the jaws is carried out by means of the operating units; hydraulic is the blocking systems device.

The precision heavy duty hardened and ground vice jaws allow to block large components thanks also to the possibility of specific set of jaws.

'An interesting application which has required a customisation of the jaws,' said Caorle, 'It was when we had to machine the extremities (drilling and tapping) of different types of racks (from a size of 25/30mm of side up to a maximum of 250mm) and we had to consider that, each machined piece, was going to be connected to the following one in order to obtain very long racks.

In fact, whereas the classical concept of end-machining consider the use of jaws for clamping round pieces, having to machine racks (of squared or rectangular shape) is necessary to use flat jaws, with reference to the tooth angular shape.

Thanks to the achievement of a clamping system for the workpieces with reference to their teeth, the required machining have been carried out by means of only one positioning of the piece into the machine- tool and obtaining in this way a really short cycle time, but above all with the great advantage of the results obtained in terms of quality.

Going back to basics in bearing selection provides opportunities for improved product performance and competitiveness, says Charles Reed, of NSK's European Technology Centre. When most engineering designers embark upon the task of specifying rolling bearings the chances are that they will not start with a clean piece of paper. In fact, in most cases, their selection will be based on what has gone before: the references provided by successful applications in pumps, gearboxes, machine tool spindles, compressors, etc being too strong to ignore.

Any variances from the norm will usually be of a peripheral nature, typically concerning whether grease or oil is the best lubricant to be used, and what type of sealing best suits the application.

This approach to selection is well proven but it fails to take into account the substantial developments in materials, mechanical design, lubrication and sealing that have occurred in bearing design over the last decade.

The results of these changes are evident in the downsizing of bearings that is taking place right across industry, with the objectives of reducing costs and weight, without, at the same time, impairing performance.

The results are evident, too, in the replacement of bearing sets by single bearing units, as exemplified by the replacement of pairs of angular contact bearings with single cylindrical roller bearings some machine tool applications.

Everywhere there is change, and with this change comes the opportunity to do things better.

In terms of bearing selection this could mean that going back to basics and starting with a clean sheet of paper might provide more dividends than adopting a derivative approach.

A warning is appropriate, however.

The number of applications for rolling bearings is, of course, almost limitless, and the operating conditions and environments where they are used vary greatly.

For these reasons it is necessary to study bearings carefully from many angles to select the best type and size from the many that are available.

In general, a bearing type is chosen provisionally after considering such parameters as: operating conditions, mounting configuration, ease of fitting and replacement, allowable space, cost and availability.

Then the size of the bearing is chosen to satisfy the desired life requirement.

Intrinsic to the overall process are a number of factors such as fatigue life, grease life, noise and vibration, operating speeds and wear.

The allowable space for a rolling bearing and its adjacent parts is generally limited by the housing design, so the type and size of the bearing must be selected within such limits.

In most cases, the shaft diameter is fixed first by the machine design; therefore, the bearing is often selected based on its bore size.

For rolling bearings, there are numerous standardized dimension series and types and the selection of the optimum bearing from among them is necessary.

This can be achieved using manufacturers' standard catalogues.

The operating environment for a bearing extends beyond ambient conditions, such as temperature, humidity, corrosiveness etc.

These are important factors which must be taken into account in any selection process, but other questions also need to be asked regarding quality of lubrication and, in certain applications, the facility of the bearing material to provide high levels of seizure resistance and its life in combinations of such conditions as extreme heat, and insufficient or contaminated lubrication.

Recent developments in bearing technology mean that these problems can now be largely overcome using a synergetic approach, bringing together materials, design, lubrication and sealing technologies.

The role of bearings, even in difficult environments, can evolve from one of pure support and load carrying to that of a full performance enhancer.

A fundamental question when considering bearing load rating is how high are the axial and radial forces?

In fact, they are closely related in a manner that depends on the bearing design.

When bearings of the same dimension series are compared, roller bearings have a higher load capacity than ball bearings and are superior if shock loads exist.

Therefore, before designing a bearing arrangement the size and proportions of the radial and axial loads and their direction need to be quantified.

Procedures exist for calculating the equivalent loadings to cyclical load patterns.

The maximum speed of rolling bearings varies depending not only on the type of bearing but also on its size, type of cage, loads, lubricating method and facility for heat dissipation.

Generally, bearing speed is limited by the allowable operating temperature, which is a combination of friction within the bearing and heat input, possibly from adjoining structures.

Low-friction, single-row, deep-groove ball bearings and angular contact bearings achieve the highest speeds, the latter units being widely used in machine tool spindles.

When specifying bearings consideration must be given to the levels of misalignment the bearing is likely to see.

This condition occurs due to a combination of three factors: deflection of a system caused by applied loads: dimensional or geometrical errors of the shaft or housing and mounting errors.

The permissible level of misalignment varies depending on the bearing type and operating condition, but is usually a small angle, less than 0.0012 radians.

When a "large" misalignment is expected, bearings with an aligning feature, such as self-aligning ball bearings, spherical roller bearings or mounted ball bearing units should be selected.

Another major consideration is bearing rigidity.

When loads are imposed on a rolling bearing some elastic deformation occurs in the contact areas between the rolling elements and raceways.

The rigidity of the bearing is determined by the ratio of bearing load to the amount of elastic deformation of the inner and outer rings and rolling elements.

Roller bearings are deflected less than ball bearings and, if the application allows it, can be selected for a more rigid setup.

When extra high rigidity is required, bearings are given a preload, which means that they have a negative clearance.

This must be very carefully assessed; consult with your bearing supplier for advice.

Angular contact ball bearings and tapered roller bearings are two types of bearings that are often supplied in this condition.

Much of today's machinery and equipment have designs optimised for lower thicknesses and weights of materials.

These give the sought after space and weight savings.

This also results in greater potential for noise generation and transmission.

Fortunately, as rolling bearings are manufactured with very high precision, noise generation is minimal.

International Rectifier has introduced the IR3103 motor drive IC, expanding its motion control integrated design platform offerings. The new device is a half-bridge FredFET with gate driver IC that does not require a heatsink for electronic motor drive applications up to 180W. Packaged in a sleek 11-pin mini SIP, the IR3103 simplifies the design of extremely compact, high performance two- and three-phase half-bridge inverter motor drives for appliances such as fans and refrigerator compressors.

'The transition away from noisy and inefficient motor controls based on triacs to quieter, more efficient and compact controls are made possible with the IR3103'.

'Our latest solution simplifies the transition to more efficient, variable speed driver designs for low power appliance products and shrinks the footprint', said David Tam, Vice President of International Rectifier's Consumer and Industrial Group.

Propagation delays for the high- and low-side power FredFET devices are matched for better synchronisation of switching characteristics and lower power dissipation.

The device can operate up to a maximum input voltage rating of 500V up to 150C.

The package features isolation ratings up to 1500V RMS for 1min, and enables shorter component interconnections, reducing unwanted EMI emissions.
ESD protection is included on all leads, and a bootstrap diode for the high-side driver section is integrated into the IR3103.

In addition, a single-polarity power supply is all that is needed to drive the internal circuitry, simplifying module use.

To accelerate the design process and demonstrate the features of the IC, the IRADK31 demo kit is available.

The kit includes a complete three-phase 250W motor drive system controlled by easy-to-use graphical user interface software.

The software can compare several motor control drive strategies for traditional AC induction motors as well as advanced brushless DC (BLDC) motors.

The IR3103 is available immediately.

Pricing is US $1.25 each in 10,000-unit quantities.

Prices are subject to change.