TechArchive

Original article date: July 2000

What’s the best compression limiter for your application, and what points should you bear in mind? Here are a few simple guidelines

Compression limiters protect the plastic components of an assembly from compressive loads generated by bolt tightening. The objective is to keep compressive stresses below the elastic limit of the plastic, preventing unwanted distortion and cracking. In practice, as the bolt is tightened, the plastic compresses and the stress in the plastic increases until the head of the bolt (or washer if one is used) comes into contact with the compression limiter. Thereafter, the compression limiter and plastic will compress at the same rate. The compression limiter will absorb additional clamping loads without further significant compression and increased stress in the plastic material.

There are two basic types of standard compression limiter: split seam and solid knurled. The split seam type is produced from carbon steel in heat-treated and non-heat-treated versions. In the Spirol Industries range, these are designated Series CL250 and Series CL200 respectively. The solid knurled type is produced from brass in symmetrical and headed versions, Series CL100 and CL110 respectively. Since these compression limiters are designed to meet specified proof loads, the dimensional specifications are different. The split seam design has a lead to aid insertion. The solid design has a pilot, allowing it to stand freely in the hole prior to complete installation.

A properly designed bolted joint must meet the following criteria:

• The head of the bolt (or washer) should always seat against the compression limiter under load. This will prevent deterioration of the bolted joint resulting from diminishing clamping load due to plastic creep

• The compression in the plastic component should not exceed its elastic limit, when compressed to seat the bolt against the compression limiter in the worst-case tolerance condition of the assembly

• To ensure that the compression limiter will not yield prior to the bolt under excessive clamping loads, the proof load of the compression limiter should be equal to or greater than the proof load of the bolt

• The clearance between the maximum bolt diameter and the minimum installed inside diameter of the compression limiter should be sufficient to compensate for normal misalignment.

The Inserts and Tubular Products Divisions of Spirol Industries have joined forces to produce a 12-page design guide to assist design engineers in the selection of compression limiters for their plastics components applications.

The recommended maximum length of the compression limiter is the minimum thickness of the plastic component. The compression of the limiter at the recommended tightening torque assures that there will always be some compression on the plastic component.

The recommended minimum length of the compression limiter is the maximum thickness of the plastic component, minus the maximum allowable compression of the plastic component, plus the compression of the compression limiter at the proof load.

A further determination needs to be made to verify that, at the recommended clamping load, the head of the bolt (or washer if one is used) will seat itself against the compression limiter at the maximum tolerance condition.

• Spirol

July 2000

Original article date: February 1998

The IP ratings for enclosures are well documented. But what is the IK Code for mechanical impact? Alan Quinn went to find out.

The IP Code defined in the standard BS EN 60529:1992 degrees of protection provided by enclosures (IP Code) provides a means of specifying the ability of an enclosure to protect its contents from external objects. The standard applies to enclosures for electrical equipment with a rated voltage not exceeding 72.5kV.

Perhaps less well known is the IK Code, which deals with mechanical impacts. It is defined in the standard BS EN 50102: 1995 Degrees of protection provided by enclosures for electrical equipment against external mechanical impacts (IK Code). It provides a means of specifying the capacity of an enclosure to protect its contents from external impacts.

Before the advent of EN 50102, a third numeral used to be added to the IP Code to indicate the level of impact protection – eg IP66(9). Non-standard use of this system was one of the factors leading to the development of the standard, which uses a separate two numeral code to distinguish it from the old differing systems. The standard came into effect in October 1991 and conflicting standards were supposed to have been withdrawn by April of last year.

EN 50102 specifies the way enclosures should be mounted when tests are carried out, the atmospheric conditions that should prevail, the number of impacts (5) and their (even) distribution, as well as the size, style, material and dimensions of the various types of hammer, designed to produce the energy levels required.

* GAMBICA, the association for the instrumentation, control and automation industry in the UK, has published a new colour handbook as a guide to specifiers and users of enclosures for electrical and electronic systems. The handbook covers every aspect of application, materials, standards, ratings and safety. It also details environmental considerations and hazardous areas. A useful list of enclosure suppliers and their individual services is also included.

Table 1: IK Code and impact energy

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Table 2 Impact test characteristics

Note: R is the radius of the striking element

February 1998

Original article date: February 2000

There’s an age old problem that simply never goes away. Your hard disk always fills up. If you can remember the days when you had a 20MB hard disk, the thought of having a 4GB disk and still filling was probably shocking. But it still happens.

There are a few basic tricks that you can use, however, to reclaim valuable disk space.

Let’s start with disk partitions. Some people are not even aware that they have multiple partitions. It’s worth understanding why you have multiple partitions, because it affects how you make the most of your disk drive. A disk is divided into clusters, and clusters are divided into sectors. Prior to Windows 98 there was a restriction on how many of each there could be, and hence how big one drive could be. Therefore, while computers were shipped with, say, a single 3GB hard drive, it would be divided into a 2GB C:drive and a 1GB D: drive.

Furthermore, because there was a limitation on the total number of clusters – approximately 65,500 – and the number of sectors per cluster – 64 – the size of a sector increased if the size of a drive increased. For example, under Windows 95 my 2GB drive has 32K per sector, 64 sectors per cluster, and 65,510 clusters. And here’s the point:: all files, however small, take up at least a whole sector. On my machine, then, all files take up at least 32K. That means if I have 1000 files, each of only 12 bytes, they will still take up some 32MB. If you were to compress those files into one, using something like PKZIP or WinZip, you’d find that they took less than 12K . That’s a big saving! You could also re-partition your disk into smaller chunks: each will have smaller sectors and hence ensure smaller usage per file. This is often thought of as risky, but with a (UK pounds)40 utility called ‘Partition magic’ which you can rapidly locate on the net you’ll find it can be almost totally safe.

There are other ways to save space. Think about deleting all the stuff that you don’t really need. Choose the add/remove programs option from ‘Control panels’ and remove any programs that you simply never use – you’d be surprised just how much you might save. And what about all those things that got installed when you tried out that ‘free’ CD? Or you might have a whole office suite in addition to the one you actually use, just sat there taking up space. Or that stuff filed away under ‘Must have a look at it sometime’. Get real, life’s too short – you’ll never find the time. Bin it now.

Go to a DOS prompt and type del c:\windows\temp\*.* which chucks away any temporary files that are not currently in use by a program – the inevitable ‘access denied’ message will tell you that some of the files there are still in use, but that’s okay, they’ll be left alone. Often this will remove large forgotten files from ages ago when you crashed the PC while editing a huge document or something. Finally, look for programs that generate loads of small files that are not needed. For example, I know of a fax program that generates a 20K file per page it sends, plus a small text file as well. After a few weeks, these get seriously out of hand. You could delete these manually, or use a simple DOS batch file (del c:\faxprog\*.fax) and put a shortcut to it in your ’startup’ folder. A word of advice though – don’t put the ‘del c:\windows\temp\*.*’ command in a startup batch file, or you will probably delete on bootup the ‘rescue files’ that you rely on after a crash.

February 2000

This article was originally written in the period 1995-2000

The selection of the right pump for the job is primarily a matter of matching the required performance range against the capability of each product type, as shown in the accompanying charts.

With over one million pump units sold into more than 35 countries, ASF Thomas supplies a broad product range of air compressors and vacuum pumps that fall into a number of major product groups. The operating principle of each product group is described and illustrated. Any special features which may influence its suitability or unsuitability for a particular application are also mentioned.

A peristaltic pump is required where integrity of the pumped medium is paramount and no leakage can be tolerated. This is achieved by enclosing the medium in a continuous tube which is mounted in a cylindrical casing. Within the cylinder is an eccentrically-mounted shaft, carrying a set of freely rotating rollers fixed on a pair of plates and these rollers are in near-continuous contact with the tube.

As the pump shaft rotates, the eccentric shaft initially causes the pumped medium in the tube to be t rapped against the casing and between adjacent rollers. It is then moved around the cylindrical casing until it exits the pump as the rollers release it. Flow rates can be closely controlled and fiarly aggressive materials can be handled.

In a diaphragm pump, reciprocating motion in a connecting rod is produced by an eccentric bearing on the pump’s drive shaft. Attached to the con rod is a diaphragm which is flexed in a closed chamber, alternately compressing and expanding the contents of the chamber, with inlet and outlet flapper valves controlling the direction of flow.

Whilst similar in concept to a piston pump, there is no sliding seal between moving parts, so integrity of the medium being pumped is preserved, making this the preferred pump when contamination is to be avoided. The chamber is fully exhausted during compression and while the stroke is much shorter than a piston pump, similar vacuum levels are achieved.

On a rotary vane pump, the pumping action is produced by a set of flat vanes fitted on a rotor eccentrically mounted in a cylindrical casing, thus producing a set of unequal swept volumes between vanes. As the rotor rotates on the pump shaft, these swept volumes gradually increase to a maximum, then decreases, with each cycle.

Inlet and outlet ports are carefully positioned in the casing so that the pumped medium is drawn into the expanding swept volumes during the suction half of the cycle, then compressed in the contracting swept volumes during the discharge half. This action produces relatively pulse-free flows from a compact, vibration-free unit.

WOB-L piston pumps operate on the same principle as conventional piston pumps, but with one essential difference: there is no bearing between piston head and connecting rod. This eliminates the need for piston rings. Instead, a rugged, flexible cup is fitted to the piston head.

With no small end bearing, the balanced eccentric cam on the pump shaft causes the integral rod and piston to wobble in operation. Resistance by the pumped medium during the compression stroke expands the cup during the compression stroke, compensating for the wobble and providing a highly efficient seal for consistent performance.

• ASF Thomas
• Tel: 01420 544184
• Fax: 01420 544183
• Contact: Warren Bease, Managing Director

Original article date: June 2000

How has turning a ball-and-socket joint back-to-front led to significant performance improvements in hydraulic pumps and motors?  Tommy Miller explains

Hydraulics is often perceived as an engineering discipline with plenty of rugged, dependable, powerful solutions for problems of motion or high loads, but little innovation. One type of product, however, has just benefited from some lateral thinking combined with up-to-date design and manufacturing methodologies.

Axial piston pumps and motors have been with us for many years and have proved to be particularly suitable for hydraulic transmissions; Linde started using such components in its fork lift trucks in the 1950s. But now the company has come up with a concept that results in pumps and motors that are more compact, have a higher power density, and are cost-effective.

At the heart of the new products is a design of piston and slipper pad that is the reverse of the norm: whereas the ball end of the ball-and-socket joint is usually on the piston and the socket is on the slipper pad, the New Generation Series 02 units have the ball on the slipper pad and the socket on the piston end. This may not sound like a leap forward, but the results speak for themselves.

One of the main advantages of this arrangement is that the swash angle may be increased from the normal 18deg to 21deg. For the same overall size of pump or motor, the swept volume is thus increased. And because fluid power is directly proportional to the displacement per revolution, the power density increases. A secondary benefit of this alternative arrangement is that the piston can now be hollow, which reduces the weight of the rotating components and improves lubrication.

From the outset, one of the objectives for the 02 pumps and motors was to use common parts for both types of product. This has indeed been achieved and the rotating groups – as well as many other components – are common to both. Other elements of the design have also been made modular so that even models of different capacity share common parts. The result of this approach is that Linde can streamline its manufacturing and reduce its stock holding, thereby making cost savings that can be passed on to customers.

Manufacturing technology

Additional investments in dedicated machine tools, automatic manufacturing systems and new machining techniques, together with improved materials specifications, have led to better surface finishes being achieved on the critical components. Running clearances between the dynamic components can therefore be reduced, so there are lower frictional losses, higher volumetric efficiencies and, consequently, an improved overall mechanical efficiency. There are four model ranges that benefit from the new developments: variable pumps for closed circuit operation; variable pumps for open circuit operation; fixed motors for open and closed circuit operation; and variable motors for open and closed circuit operation.

Linde claims that every type provides high performance, high efficiency and low noise, all from a compact, cost-effective package.

And for noise-sensitive environments, there is a special version of the variable pumps for open-circuit operation that feature an accumulator on the high pressure side. This acts as a silencer because it reduces pressure pulsations from 38.7bar to 11.3bar – which gives a useful 2 to 4dB(A) noise reduction.

• Linde Hydraulics

June 2000

Original article date: October 1998

The justification for buying capital equipment is all a question of arithmetic says WILL BOURN sales manager of Modular Automation. Or is it?

The cost of automation can be quite high particularly when it employs the latest robotics vision systems and welding technology. There is often a chicken-and-egg decision to make when considering automation. With insufficient market share the volumes are too low to necessitate automation But without automation the unit cost will remain too high and perhaps the quality too.

By applying a simple discounted cash flow forecast even the lowliest accounts clerk should be able to make a reasonable assessment of the financial sense of capital investment.

But is it always so simple? Rarely. And many of the criteria by which we judge the practicality of major automation projects have little or nothing to do with money – at least not at first sight. So what are the practical factors that decide the viability of any automation project?

Let’s tackle the tricky one first. People are one of the most significant costs in any manufacturing process. Therefore reducing the number of people in any one project will have a dramatic effect on its feasibility. You can easily make a rough approximation of the cost savings by costing one person working a single shift at (UK pounds)15 000 per annum. By that calculation if automating a continuous process would save two people then the cost saving is six person-shifts or (UK pounds)90 000 per annum. If you require a two-year payback period it’s worth spending up to (UK pounds)180 0 on the automation. Simple? No not quite that simple.

This assumes that the people who are replaced are found “gainful and acceptable employment” elsewhere within the factory. If not additional payments will be required. There is of course also a social element to be considered and not least the effect on morale of the remaining workforce.

And there’s much more to consider. The problem might not be how to deploy your workforce but how to recruit one. Some geographical areas have a chronic shortage of skilled and semi-skilled labour. In areas where this is a problem increasing levels of automation might be the only sensible option even if the strict application of a cost analysis doesn’t justify it.

The working environment is also a major factor when considering automation. Whether the application requires clean room hygiene or is such a hostile environment that manual intervention is impossible automation may be the only answer almost irrespective of costs. Semiconductor manufacture for instance requires a very high level of automation to avoid contamination. Conversely applications using heating or pressing could be dangerous to the operator. So too applications where the actual environment itself is too hazardous (heat dust etc.) such as foundries and nuclear establishments.

But probably the greatest and most irresistible reason for automation is quality control. Many companies recognise that automation or semi-automation is the only practical way of ensuring the quality of their products eliminating failures and costly returns or recalls. In the automotive industry for example first-tier suppliers are generally only considered for contracts if they employ automated processes. Here however high the cost of automating the cost of not automating when it really should be necessary can be quite devastating.

• Modular Automation
• Tel: 0121 766 7979
• Will Bourn

October 1998

This article was originally written in the period 1995-2000

Flexible membrane couplers exploit the tensile and flexural properties of membranes (discs) pressed from cold-rolled stainless spring steel. Attached alternately to the driver and driven members, the membranes transmit torque in tension, while flexing readily in bending mode to comply with alignment errors.

These heat-treated membranes can sustain an almost infinite number of flexural (misalignment) cycles. Huco-Flex M couplers are rates for continuous unidirectional and bidirectional rotation up to 15,000 rpm and are typically specified for high resolution measurement devices, high gain velocity or motion control systems, position-critical frictional loads and dynamometers.

Typically, Flex M couplers conduct the transmission through two complementary angles when compensating for radial shaft errors. The greater the distance between the membranes, the larger the radial error than can be accommodated. To cater for the differing levels of radial error, Flex M are made in two standard lengths.

Being pivotal devices, membrane couplers are also available in single-stage form. When linked by an intermediate shaft, these make up into “whirl-free” cardans (floating shafts) that extend the coupler’s reach and accommodate larger offsets. Cardans de-mount into three parts and, in this form, Flex M can be fitted or removed without disturbing pre-aligned shafts.

Misalignment

The maximum radial error should be determined under the worst case tolerance accumulations before selecting a short or long coupling. If correct shaft alignment relies on setting-up by skilled factory personnel, it must be able to be replicated by service engineers. Should the predicted radial error exceed the capacity of standard two-stage couplers, single-stage versions should be used linked by an appropriate intermediate shaft.

Resonance

Excitation frequencies of closed-loop position or velocity control systems can give rise to resonance when the loads are predominantly inertial and the load inertia exceeds that of the motor. In these conditions, the coupler’s torsional stiffness should be such that the natural resonance frequency exceeds 300-600Hz, depending on the dynamics.

Torque

Permissible torque varies according to the nature of the duty. One of the following torque definitions should best approximate to any application.

Peak torque:the maximum load torque sustainable for a minimum of 10<6>static torque reversal cycles at maximum compliance
Application: Periodic operation of valves, switches or other incrementally-operated loads.

Nominal torque:the maximum non-reversing load torque sustainable at maximum compliance.
Application: Unidirectional drives, typically pumps, fans and dynamometers.

Reversing torque:the maximum reversing load torque sustainable at maximum compliance.
Application: Predominantly inertial loads associated with position or velocity control. Typical direct loads: encoders, resolvers and tachogenerators. Typical reflected loads: slide tables, linear positioning systems.

Fixed and floating shafts

Fixed shafts:Couplers with radial flexibility are required when both shafts are conventionally located by two bearings.

Floating shafts:Floating shafts self-align and make a true angle with the adjoining shafts. Radial location is provided by the coupler. Only angular flexibility is required, or desirable, in the coupler.

Huco Engineering
• Tel: 01992 509888
• Fax: 01992 509890
• Contact: Ray Buttifant

Original article date: May 1998

Won the lottery?

No, nor have I, but in common with most of the population I’ve wondered what I’d do if it happened. Actually, I reckon the answers are divided into two key areas.

Firstly, there are the things I’d change to cope with the fact that time was now the most precious thing of all, so I would spend whatever it took to save it. Secondly, there are the things I’d do because I always wanted to do them.

Here then are the things I’d like to have which would save me time.

1. Something in my car which could read my new email to me as I drove to work. And allow me to verbally mark ones for further attention. Hands free.

2. A special phone to cope with annoying menu systems (usually belonging to people who I actually want to buy things from). This would allow me to record a brief message saying what I want to talk about, then the phone would automatically call the company, wait until a real operator arrives at the end of the menu, and then repeat my message to them so they get the message and call me back.

3. A mobile phone which, when it receives an incoming call from a number it doesn’t know, says at the end of the call “Would you like that number added to your address book?” and when I say yes, it asks me for the name and nickname (which I speak) and someone at the exchange types the data in and it’s added to my phone automatically.

4. A car that not only knows its service status, but recognises my patterns of work and decides one day that I’ll be parked here for another three hours, calls the service guy, gives a GPS location and a password, then when the guy arrives, unlocks the door so he can service the car. Or MOT it. (What, and your Morris Minor doesn’t do this already? ­ Ed)

5. A small number of pre-programmed buttons on the steering wheel such as:

“Passing Tesco in five mins, do we need anything?” (which would call home), or

“Pint of the usual Dave, I’ll be there in five minutes” (which would initiate a message to my local).

6. A standardised international laptop so all I need to travel with a computer is a removeable hard drive, allowing me to use it on trains, planes, in hotels etc. which all have the rest of the PC fitted and waiting for me.

7. A standardised international pint of the usual so I know how drunk I am

8. A hands-free kebab

9. All junk mail sent to me electronically, allowing me to apply certain filters and not disappear in a mountain of paper. With a hard coded block on double glazing and new Visa cards.

10. Oh, and un-loseable keys.

And now, the things I’ve always wanted to do, which I could if I won the lottery, and hang the consequences.

1. Use one of those PLC ‘digital sound modules’ and build a machine control system that responded to error signals with sound samples of Father Jack (if you don’t know, you don’t want to ­ Ed).

2. Tell the client from hell what I really think

3. Turn down work

4. Mount a ‘fitness for purpose’ legal challenge against the supplier of any operating system that gives me serious grief.

5. Take a course in any technology that currently makes me feel stupid because I don’t understand it. Examples include Windows programming, marketing hype, how to explain fuzzy logic without any arm-waving whatsoever, and how you can charge all that money for a BA tail fin graphic. Oh, and cricket.

6. Make a list where the numbering wasn’t consecutive.

10. Move to Tibet and escape all the Millennium bug hype forever.

May 1998

Original article date: February 2000

For 78-year-old Howard Arneson, who invented the famous Arneson surface drive propulsion system, slicing through ocean swells at over 100mph is just a piece of cake.

The Arneson drive, now made under license by US-based transmission systems manufacturer Twin Disc, is probably the most popular propulsion system in high speed boating. It is used widely on racing boats, cruisers, patrol boats and yachts of all sizes. A variation of the drive is even used in military applications, including US Army tanks.

This is a surface drive that can be steered and trimmed in the water while the craft is moving. It runs with the propeller partly out of the water. This design reduces appendage drag (such as a dragging gearcase) and cavitation, which detrimentally affects efficient propeller performance.

The Arneson drive pivots port and starboard like a stern drive, working without a rudder. This pivoting controls the direction of propeller thrust, thus improving steering response. A boat with this drive can be trimmed while moving to get the right degree of submersion for the load and condition of the water.

With a surface drive like the Arneson, the propeller and drive train extend aft, not down in the water. This positioning reduces draft, along with the noise and vibration usually conducted from below through the hull. It also improves propeller bite. With the drive behind the transom, the designer of a high performance boat can place the engine as far aft as desired.

Finally, the hydraulic rams which are key to the Arneson drive are positioned outside the boat, freeing up space inside. Propeller depth is controlled by a vertical trim cylinder permitting 15deg of up/down motion. A horizontal steering cylinder allows 40deg of port-starboard trim.

Arneson has now reached 175mph piloting the 46ft Skater, a new generation catamaran powered by a 4500hp Lycoming gas turbine similar to that giving flight to a Chinook helicopter. The initial propeller shaft for the Skater was made by Ziegler Industries from 17Cr-4Ni precipitation hardening stainless steel, known for its good combination of high strength, high hardness and corrosion resistance. The finished shaft measures 40in long by 2.5in diameter in the centre, tapering down to 1.875in at both ends. The shaft is installed using a double cardon joint with a front-end drive, propeller at the other end and bearings at both ends.

But after 50 hours of running time at speeds of around 100mph, the shaft broke off, dropping to the bottom of the sea with its propeller. Up to then, the shaft had not been subjected to the shear forces of the severe acceleration or sustained, record-setting high speeds which Arneson anticipated. The President of Zieger – Don Zieger – suggested making the propeller shaft from Custom 465 stainless – a premium-melted, martensitic, age-hardenable alloy made by Carpenter Technology. This alloy can reach a 260ksi UTS when peak aged (H900 condition). In this condition, it has excellent notch tensile strength and fracture toughness.

When over-aged in the H1000 condition, Carpenter’s Custom 465 stainless provides a superior combination of strength, toughness and stress corrosion cracking resistance when compared with other high-strength PH stainless alloys.

Condition H1050 was selected from the heat treatment schedule to get a hardness of RC45-46 and maintain essential straightness. Test have shown successful performance of the shaft at speeds of 175mph, sustained for several hours.

• Carpenter Specialty Alloys

February 2000

Original article date: March 1999

Two methods of detecting contrasting colour for production systems are described in detail in a new technical guide from OMRON.

Colour mark sensors are a type of diffuse sensor designed to detect a mark by the contrast between the mark and the background.

A diffuse sensor incorporates emitter and receiver in the same body much like a retro-reflective sensor but without the reflector to return the beam to the receiver. Instead the target itself reflects the light back to the sensor and the target object is detected. This principle has the advantage of only requiring wiring and fitting in one place making it especially useful for applications where there is only access to one side.

The lens arrangement of colour mark sensors is slightly different to that of a standard diffuse type in that they are focused The amplifier is also more sensitive to changes of colour. The sensitivity or mark sensors is also influenced by the light source used. A red light source (which is the normal light source for most diffuse sensors) provides reasonable sensing distances but is more limited in its response to colour combinations and in particular red on white as the red content is reflected.

If a green LED is used it means a smaller sensing distance but it is much more sensitive across the colour range. It is more suitable for like colours (those with less of a contrast between mark and background).

Which colour light sources should be considered when wishing to detect a mark? If the marks (such as shades of the same colour) are to be detected then sensitivity adjustment can be difficult if not almost impossible if the shades have minute differences. If this is the case a different type of sensor called the RGB sensor can be used.

An RGB sensor works not on the amount of light received but on what the light actually consists of recognising that light is actually made up of many different parts visible light being only a small part.

So to detect colours accurately it is possible to analyse the content of the light which is reflected. Firstly it is necessary to know the exact nature of light that is transmitted. Omron’s E3MC sensor has three light sources which are red green and blue LEDs. They emit lens via the same lens and this is reflected from the target object. Depending upon the colour of the target object different quantities of light are absorbed and reflected.

The reflected light is detected by a photodiode and is then analysed by the sensor for the content of R (red) G (green) and B (blue) . The operation of the sensor is then dependent upon which of the two operation modes the user has selected.

If C mode has been used the ration between R G and B is analysed. Regardless of the sensing distance the colour ratio of the light will not change although the intensity will. This gives the advantage of stable detection if the target is mechanically fluctuating.

In I mode the detection of minute colour differences is possible. This mode uses the intensity of the RGB reflected light. Using this method the detection of minute colour differences is achievable but unlike the C mode the sensor is influenced by the mechanical position of the target.

Whichever method is used a teach function is used to teach the sensor the target colour required. The light received is indicated by a bar graph and the threshold level can be set to determine the operation point.

• Omron
• Tel: 0181 450 4646
• Web:http://www.omron.co.uk

March 1999