TechArchive

Original article date: January 2000

Alan Quinn reviews Flender Power Transmission’s new technical handbook. Will it become an industry benchmark?

Covering a wide variety of calculations and useful data through 12 sections running over 150 detailed pages, the Flender Power Transmission technical handbook has a place on any design engineer’s bookshelf.

The pages cover almost any topic which a designer of power transmission is likely to need. There are sections on SI units, maths, physics and geometry and the mechanical properties of materials – surprisingly extensive in scope. These are in addition to the more predictable sections on the geometry and load-carrying capacities of involute gears and the properties of cylindrical gear units, shaft couplings and vibration – a highly mathematical treatment listing formulae for the calculation of stiffness and thereby of vibrations.

Flender’s extensive product range includes geared motors and gear units, as well as couplings and clutches, electronics and special design geared motors.

Indeed, Flender might have done itself a slight disservice in that because the handbook attempts to cover such a wide range of topics, the coverage of the company’s own products is actually briefer than you might have expected!

Technical merits

Another minor criticism is that there is also a commercial price to pay in the introductory 16-page colour section – in fact, the only colour section in the publication – which provides all the corporate information, which seems rather out of place in a publication which is otherwise so comprehensive in its technical content. Maybe more space devoted instead to worked examples might have earned the company more credit.

Those criticisms aside, there is no doubt that the handbook will find a place on many shelves – including my own, as a likely source of those elusive formulae and engineering facts which should be on the tip of one’s tongue but never seem to be! An example of this is the set of tables on explosion protection of electrical switchgear.

Highlight of the handbook for this non-practising engineer is from the heart of the company’s core material and covers the geometry of involute gears. The section contains two tables of the most important formulae used for the determination of sizes of a cylindrical gear and a cylindrical gear pair, and this for both internal and external gear pairs. A further table lists the derived quantities which are used in the calculation of load carrying capacity.

• Flender Power Transmission

January 2000

Original article date: February 2000

Audi is now well placed to record real-time corrosion effects, thanks to Weiss Technik’s all-plastic environmental testing chamber

Asked by Audi to build an all-plastic corrosion test chamber, Weiss Technik’s construction is a two-chamber facility which can record corrosion patterns of car suspensions under mechanical stress (with temperature, torsion, vibration and spray). The chamber was also required to include a dynamic road simulation system with active, moveable actuators.

The objective was to test complete vehicle suspensions under real conditions. The call for an entirely plastic chamber was been dictated by the need for a neutral system in which there is no possibility of false readings resulting from the corrosion of, or other chemical reactions with, the chamber itself.

With the completion and installation of the chamber, Audi is now well placed to record real-time corrosion effects that occur while a mechanical stress is applied. These corrosive effects were previously unknown. New designs can now be undertaken with full data detailing the results of higher corrosion levels of cars and components under test, which ultimately results in a better product for the consumer.

All chamber inner test space is constructed from a special plastic able to withstand temperatures from -30 to +130degC. All internal components, such as fans and spray devices, are made of plastics, while the conventional internal units, such as the air handling unit, are now all external.

Metal heat exchanger

One of the largest problems to be overcome was the construction of the metal heat exchanger. Of course, metal has superior thermal properties, but traditional construction elements, such as aluminium, copper and stainless steel, are the highest contributors to secondary corrosion effects. And so a pumped, indirect conditioning system was developed to remove the need for an evaporator and refrigeration system. Another departure from current practice in the new chamber is the use of real-time testing incorporating high and low temperature tests with humidity. Historically, tests have been accelerated at high temperatures, but real-time testing is required to combine correctly all effects for all parameters.

A lightning conductor is required inside the facility to cope with the high voltage discharge caused by static.

The facility comprises two chambers of 10 and 14m?, for which Weiss Technik developed special seals to allow positioning of the moveable actuators of the dynamic road simulation system.

• Weiss Technik

February 2000

Original article date: November 1999

Advertising feature: The speed of a Festo Premier Stockist’s new cylinder delivery service is going to cause shock waves.

Festo Premier Stockists exclusively offer a SURCHARGE FREE same day and next day emergency breakdown manufacture service on ISO and VDMA cylinders on any stroke length from 8mm to 125mm bore.

Add to this access to over 40 cylinder types, and diameters from 2.5mm to 320mm, being in the Premier League means we can guarantee the fastest delivery across the widest range of cylinders in the UK.

You’ll find in most instances that when we talk days or even hours, our competitors are talking weeks.

You can rely on your local Festo Premier Stockist for a cylinder service with maximum velocity. 

Our cylinder service in action

Here is an example of an emergency where, without Festo’s impressive same day turnaround, the customer would have incurred huge downtime costs.

At 8.00am a fault is found on a main cylinder of a food packaging machine. Immediately a telephone call straight through to the local Festo Premier Stockist puts the frequently used process in motion. The stockist understands the problem straight away – it’s a non-standard stroke length, non-Festo cylinder that has failed. He recommends to the customer to use Festo and their unique surcharge free same day cylinder service for this emergency breakdown.

Stockist checks the availability of production kits using their ISDN direct electronic interface and communicates the urgent order to Festo. The essential information from the stockist is transmitted to the flexible small batch cylinder manufacturing cell. At 8.45am the CNC program is downloaded to the machine tools which are governed by the meticulous ISO 9002 specifications. The quality procedure demands build inspection at each stage of the assembly. The final test ensures the product’s integrity for its outstanding life expectancy of 10,000km of operation.

By 10.15am it is ready and a motorbike courier picks up the critical cylinder for the 200 mile journey to the customer’s factory. At 2.00pm stockist arrives at factory to ensure that all goes well and assists with the installation. The machine is back up and running, problem solved in just 6 hours and customer extremely satisfied. Festo aim to provide the fastest emergency cylinder service in the UK.

For more information contact:

• Festo Ltd,
  Automation House,
  Harvest Crescent,
  Ancells Business Park,
  Fleet, Hampshire
  GU13 8XP

• Tel: 01252 775000
• Fax: 01252 775001

November 1999

Original article date: September 1998

An innovative approach to sealing or potting electromechanical components comes from US company Multi-Seals – solid pre-forms that melt when heated to form a seal

Precision epoxy preforms are one-part resins that offer a no mix no mess solution to the problem of sealing and potting small parts such as electromechanical components. Solid at room temperature when heated they melt and cure forming a consistent seal that protects components from dust moisture oil solder flux and conformal coatings. They can withstand high soldering temperatures and all of the most common industrial cleaning solvents.

The heat is applied for a specified time depending on the shape size and material used first to melt then to flow and finally to cure the material which is always an electrical grade epoxy or epoxy-phenolic. This method eliminates mixing and metering of two-part liquid epoxies as well as the viscosity variations that can occur. Available shaped include rings rectangles ovals ellipses and triangles. Custom preforms can also be designed and manufactured to suit specific application requirements.

Best curing results are obtained using a forced convection oven preheated to the appropriate cure temperature. A mechanical convection (air circulating) oven allows for the fastest recovery and the most consistent means of heat transfer. The oven should be calibrated at least once a year.

Typically 150 is a good starting point. Adequate cure for most applications will take between 30 minutes and two hours depending upon the grade. Allowances should be made for oven recovery time and component mass including loading trays.

For production purposes adequate cure schedules should be determined experimentally and then strictly adhered to. This is done by placing thermocouples throughout the oven to determine the effects of component mass. The longest time it takes for any of the thermocouples to reach cure temperature should be added to the listed cure times in the data sheets. Adding an additional 5-10 minutes is also recommended.

Preforms need to be stored in a cool dry area and in closed containers when not in use. An air-conditioned office is best but not absolutely necessary. Refrigeration can cause condensation of improperly handled.

The preforms can be dispensed at rates of 200 to 600 using automatic or semi-automatic equipment though they can of course be applied manually as well. Templates pick and place machines and bowl-fed gravity tracks are all viable loading methods for dispensing epoxy preforms.

• Multi-Seals
• Kenneth Harvill
• 00 1 860 643 7188

September 1998

Original article date: November 1999

A new standard for electrical and fluid power installations on machines seems to be emerging. Tommy Miller investigates

Desina is described as a fully comprehensive system to bring standardisation and decentralisation to the field of fluid power and electrical installations on machinery and equipment; the word itself is an abbreviation of Decentralised and Standardised Installation technology. Backed by the VDW (the Association of German Machine Tool Manufacturers), Desina is expected to become widely accepted in the machine tool, automotive manufacturing and wider engineering markets. Already there are well known manufacturers – such as Igus, Siemens and Balluff – who have introduced Desina-compatible product ranges.

One of the main advantages of Desina is that it builds on current standards for communications and connections, rather than starting from scratch; so, for example, Profibus-DP and Canbus and Interbus-S are all supported. Furthermore, by defining standard components, interfaces and connection elements, different fieldbus systems can be made compatible on a common physical basis.

Through developing Desina, the intention is to encourage machine builders and system integrators to implement decentralised installation techniques and to use standard components. There should therefore be savings to be made in planning, installing and operating the equipment.

Standards have been proposed by Desina for components such as inductive proximity switches, hydraulic valves, I/O modules motor feeders and cabling (including plugs and sockets). It is then down to individual manufacturers to check the compatibility of their existing products or to develop new or enhanced products if necessary.

One company that has taken the Desina approach on board is Igus. This company, well-known for its ‘energy chain’ cable conduits and compatible Chainflex flexible cables, has developed a range of cables that are recognised as conforming to the Desina standard. These recently introduced products are:

• Servo cables, shielded (orange)
• Measuring system cables, shielded (green)
• Fieldbus cable (violet)
• Sensor/actuator cable, unshielded (yellow)
• Control cable, unshielded (grey)
• Power cable, unshielded (black)

The violet fieldbus cable is particularly noteworthy because, to make it compatible with the relevant fieldbus standards, it carries four copper conductors and two optical fibres.

 The Desina web site can be found athttp:// desina.arkaden.net/english/flyer_e.htm 

• D esina

November 1999

Original article date: March 1998

The European Sealing Association says that with the advent of asbestos-free sealing materials engineers need guidance about the new approaches required. Consequently it has published a technical glossary relating to flange and gasket sealing terminology aimed at end users OEMs and contractors.

The publication contains descriptions of all the common terms used in sealing and includes layouts for typical flange and gasket systems of which there are many in common use described below. Units of common usage in flange gasket terminology are listed with conversion factors. Relevant standards are listed together with the details of the organisations which issue them. Common abbreviations complete the lineup.

Flat face flanges contain a full face gasket. This is a non-confined gasket with both flange contact surfaces flat. This type of flange is normally used where the flange material is relatively fragile.

In the raised face flange flange contact surfaces are raised although the gasket is non-confined. Normally the gasket covers up to the inside of the bolts. This type of flange allows assembly and removal of the gasket without having to separate the complete flange system thereby making maintenance work easier. It is used commonly in pipework systems.

The tongue and groove flange has a totally confined gasket. The groove depth is equal to or greater than the tongue height. Normally the gasket has the same width as the tongue. In this design it is necessary to separate the flanges completely to change the gasket. This flange system exerts high seating pressure on the gasket and is not usually recommended for non-metallic gasket types.

The spigot flange also known as the male and female flange contains a semi-confined gasket. This can appear in a wide variety of forms. The depth of the female flange is equal to or less than the height of the male in order to avoid the possibility of direct contact between the flanges when the gasket is compressed. The flange system must be separated in order to change the gasket.

The flat face and groove flange system has a totally confined gasket. The external face of one of the flanges is plain and the other has a groove where the gasket is assembled. They are used in applications where the distance between the flanges must be precise. When the gasket is seated the flanges are usually in contract with each other. Only resilient gaskets should be used in this system.

The ring joint flange is also called an API ring. Both flanges have channels to accept the gasket which is normally made of solid metal.

• European Sealing Association
• 01524 844222

March 1998

Original article date: June 2000

Put these guidelines into practice when using enclosures and cases, and you’ll be OK with OKW!

Cases have quite an influence on the electromagnetic compatibility of a product. The main reasons for EMC interference are:

• Conductive – within low frequency range below 100MHz
• Radiation from Cables – within medium frequency range (30-300MHz)
• Penetration through material and openings – high frequency range > 300MHz.

Hence, in order to reduce interference radiation, shielding of cases for ranges exceeding 100MHz is of vital importance. Shielding is defined as the ratio of field intensity in front of and behind the shielding wall. The effect of electromagnetic shields is based on a combination of several effects: if an electromagnetic wave hits metal, part of the wave is reflected. Another part of the wave penetrates the metal layer and is transformed into heat. The remaining part penetrates the metal layer and finally represents the source of interference.

As almost every case is provided with openings and cable connections which reduce the shielding effect, it is important to observe the following recommendations. The interference energy which is released through the opening largely depends on the following factors:

• Maximum linear size
• Frequency of the interference energy
• Polarisation of the wave
• Distance from radiation
• Field type.

Experience suggests that an opening should have an attenuation performance of at least 20dB. This means:

In order to achieve a shielding effect of approximately 40dB, OKW applies an aluminium layer which is exclusively attached to the inside of the case. Gaskets made of silver and silicone are also recommended, though these are unsuitable for humid conditions. Display windows should be provided with a conductive foil and should have a terminal lugs for connection to the case shield. To reduce the radiation between cable, plug and case, good design practice is to:

• Reduce the number of contacts
• Remove lacquer, colours and oxides
• Ensure direct and complete contact between cable shield and case
• Use shielded cables.

In order to maintain the protection class of the case and to improve the cable radiation, a suitable screw fitting for the cables is necessary. The use of external accessories may influence the protection class and can cause corrosion. For this reason, do consult the supplier before use.

• OKW

June 2000

Original article date: February 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

Original article date: September 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

Original article date: November 1999

ROBERT WORRALL of Encoder Technology explains tells us why the Inductcoder sensor enjoys hostile environments

Based on the principle of magnetic induction, Inductcoder from Encoder Technology is a totally original sensor which offers significant benefits. Excellent repeatability, high resolution, high accuracy and quick response are the principal characteristics of this non-contact sensor, which could prove a particularly popular choice for applications in hostile environments. it is also exceptionally compact, light and attractively priced – indeed, it is now on special offer!

The development has resulted from sponsorship and support from the Government and from major names in the engineering industry. Now available in the UK, Inductcoder offers a serious challenge to existing position sensor technology and has already been adopted by some of the world’s leading machinery and systems manufacturers.

Typically, an absolute resolution of 220 (ie 20 bit) can be achieved with an ultra-small rotary Inductcoder sensor of only 10mm diameter! Such a device is not only extremely rugged, but is also highly effective.

Inductcoder is a digital absolute system which comprises a detecting element – a combination of magnetic coil and ferromagnetic material – and a conversion element. This converts mechanical deviation to the phase difference between the input and output signals and establishes position by measuring time.

This position data output is refreshed at every scan

(10-4s) and is interpolated further up to 10-4s x 1/128 to provide an even faster response.

Thanks to the phase difference detecting system, the relationship between amplitude and cable length does not need to be considered. Accordingly, Inductcoder has good repeatability. Minimal temperature drift is assured as compensation for any fluctuation is automatic and as the sensor uses an AC magnetic circuit, there is no hysteresis.

This unique device may be specified to suit a wide range of applications, including the control of hydraulic and pneumatic systems. Automated semiconductor production is also a prime market for the new sensor. As its detecting element consists only of magnetic coils, Inductcoder is highly resistant to vibration, shock, oil, dust and extremes of temperature.

Options include rotary, linear, wire, stroke detection, linear gauge and strain gauge types. There is an analogue output (0 to 10V, 4 to 20mA) and digital output, including parallel and series – RS232C, RS422 and Canbus. An incremental and absolute encoder high resolution signal is also available. Intelligent outputs for velocity, acceleration, multi-switch and diagnostic signal may also be specified.

• Encoder Technology

November 1999