Pen Design Example Web

This knowledgebase uses the MOKA ontology and has been produced from:

  • Fictional knowledge acquisition sessions with an entirely "fictional" subject matter expert
  • Real knowledge modelling work validated by the "fictional" expert

So I guess the end result, too, is a work of fiction.

One of the "interviews" is shown at the end of this page. It has been marked-up using the Protocol tool in PCPACK to import certain key elements into the Pen knowledgebase.

To view the published web click on the links below:

The book Knowledge-Based Systems Example Transformation on this site shows how the KB might be transformed for use with a KBS system (ICAD).

Interview with an expert in pen design

I am John Smith, working in WriteStuff Company for 10 years, responsible for design of new products. I have been in charge of several projects during my career, the last one was our revolutionary ink pen to celebrate the millennium.

Can you describe the product to be designed ?

We have got different types of pen for a start. Pencil pen , ball point pen and ink pen (also called the fountain pen).

Each of them, has different possible configurations. For example, the ink pen is different depending on which ink reservoir you consider. You can have standard disposable ink cartridge (or pre-filled cartridge ), or a permanent one which is a converter that is built for refilling from bottled ink. You can also have a pump system so the body of the pen becomes the reservoir itself, and if you do so, the body has to be wide enough so it can fit the pump mechanism and contain enough ink for you to write a letter. Whichever method is preferred, it must be leak-proof. The entrance to the reservoir allows air in to replace the ink as it leaves the reservoir on its way to the paper.

Talking about size of the body, you have to take into account that men and women haven€™t got the same hand size, neither the same strength. So we have criteria to measure the comfort of use and to make the nib hard enough.

But what is a pump mechanism for ?

Imagine that the body of your pen is completely sealed. So to re-fill with ink, you put the nib into a bottled ink and you will use your pen as a syringe to aspire the ink, using the retractable end of the body.

A bit of history€¦

A significant advance was made in 1832 by John Jacob Parker with the first self-filling fountain pen . Until this time the devices were filled with funnels or eyedroppers. Parker's pen is filled by putting the point in ink and turning the end of the case to raise an internal piston. The tube of the pen was lined with glass or gold to protect against corrosive inks, and the cap had a wire which entered and sealed the feed when replaced for carrying.

Talking about this aspect of ink refilling, the permanent reservoir looks like a metallic cartridge. To refill it, the reservoir is squeezed flat by an internal plate, then the pen's nib is inserted into a bottle of ink and the pressure on the internal plate is released so that the ink sac fills up drawing fresh supply of ink.

So what are the different elements that compose a pen, say an ink pen for example ?

It composes of a body , a cap , a reservoir and a nib . There are nine standard ink pen nib-sizes, with three different nib-tip cuts: straight, oblique and italic. There is as well a kind of capillary system attached to the nib to drain the ink towards the tip of it. It is called a feedbar . The feedbar is directly connected to the reservoir, so depending on which type has been chosen the connection to the reservoir is not the same. The end diameter has to be compliant to some standards when using disposable cartridge otherwise you have got to provide specific ones when selling the pen.

The nib has got a slit and is split into halves. The slit in the nib creates a capillary action, which causes the ink to travel down the nib to its tip. The two halves of the split nib are called tines , and can splay apart under hand pressure. The nib must be positioned on the feedbar so that the capillary groove in the feedbar is directly under the slit in the nib. If the two are not aligned the pen won't work.

So to summarise, the main mechanism is composed of three main parts. The nib, which has the contact with the paper. The feedbar or black part under the nib controls the ink flow from the reservoir to the nib. The round barrel that holds the nib and feed on the writing end protects the ink reservoir internally (this is the part that you grip while writing).

How does this "feedbar" work ?

As the ink leaves the reservoir it moves into the feedbar through a narrow opening. The feedbar is usually made of a special type of high quality plastic.

Feedbars fulfil a number of jobs.

1.   They must channel the ink to the nib through an ink groove .

2.   They must allow ink to flow easily over their surface , and not cause the ink to separate into little globules.

3.   They must incorporate in their structure an 'expansion chamber' that will hold any ink forced out of the reservoir by expanding air . This prevents leaks. Any air in the reservoir heated merely by holding the pen, will expand and force ink into the expansion chamber. The expansion chamber is not usually visible. It is positioned inside the pen beneath the place where your thumb and finger would grip the pen when you write.

4.   The feedbar must also provide a way of allowing the air through into the reservoir to replace the ink as it is used .

5.   Finally, the feedbar has to support the nib .

I remember that for one project we had to review completely our draining system because we had several complaints from our customers in Australia. All of our ink pen products were leaking heavily without any obvious explanation. We found out that the hot temperature had a strong effect on the fluid properties. So we had to change the feedbar characteristics. It is actually really important to analyse and control completely the properties of the ink. The early inks used in ink pens caused steel nibs to quickly corrode. So we had to change and use gold material as it held up to the corrosion.

It sounds to me really complex to design an ink pen.

Yes it is. Some say that building an ink pen is like making a machine that manages a precisely controlled leak.

The ink must be drawn from the reservoir in precisely the right amounts, flowing at exactly the right rate, on a variety of paper surfaces. It is the ability of this type of pen to do just that, and to reflect handwriting character.

You mentioned earlier pressure onto the nib to transfer the ink onto the paper, but how does it work ?

The ability to create the 'light and shade' of thick and thin written lines is produced by the nib tines splaying out when under increased downward pressure, according to the individual style of the writer. The feature is more reliably delivered by better quality fountain pens.

Because the point is constantly being moved over the paper in a 'rubbing' motion, the nib tip must be very hard. To give the nib its required durability, a small pellet , usually of very hard metals like Iridium or Ruthenium, is welded to the point. Iridium has replaced gold because it was too soft. The pellet also has to be slit just like the rest of the nib.

So coming back to the elements constitutive of the pen, when there is a pump system, what are the differences ?

When you design a pen with cartridges, the body has nothing special, the internal diameter has to be wider and longer than the cartridge , thick enough to be structurally strong enough.  Concerning the pump system, it is composed of a piston connected to a stick , itself commanded by the retractable tip end of the body. So the body itself is made of two main parts screwed together. There is a spring as well pressuring the piston. So we are making calculations to optimise the diameter of the piston together with the body, related to volume of ink, length of the screw thread.

Did you consider using another technical solution to embody the pump system ?

In the past we have explored different solutions to avoid having a screw thread between the actionable end and the body because it's expensive from a manufacturing point of view. We tried to design a simple flush fitting of the 2 parts together which is feasible as the pressure is fairly low. So we reproduced the simple mechanism of a syringe. But the system is not completely reliable and the stick tends to break easily, which is not acceptable for such a range of product.

And how do you choose which configuration to use ?

The price and which marketing product we target at a time. The pump pen is a luxury product, expensive to produce .

And for the ball point pen, I guess it's somehow less complex ?

Ball point pens transfer their thick oil-based ink from ball to paper as the ball is rolled across the writing surface. Ball pens are robust and can withstand harsh working conditions.

But for this type, we just design the structure because we get the ball point sticks from a supplier. There are 2 possible configurations : the retractable and the classic ball point pen with cap . The classic one is composed of a body that can be cylindrical or square, it can be opened or sealed at the bottom end, it can be split in half with a screwed joint. If it's opened there is a closing cap in addition. The retractable ball point is more complex. The retraction mechanism is realised by an actionable button that pushes the ball point stick out, and the release or retraction is eased by a spring. There are several possible technical solutions to embody this function at different costs and reliability level . The cheapest is the classic pen configuration.

So how would you choose one ?

It depends on the targeting market. But as well on what the supplier has got available in stock. Because the ball point sticks are different regarding the configuration. If you have a classic one sealed at the bottom end, you need a particular ball point stick to fit in through the top end.

If we were to talk about how do you design a pen ?

A new design starts each time there is a new product to launch. The marketing department decides what should be the high level specifications , such as the type, the configuration in the type, the target range, the level of price/cost, the palette of colours/decoration, the final external aspect, and the material€¦. I didn't mention to you the material and the colours.  Depending on the material and the manufacturing constraints related, the shape of the body may differ slightly, as well as the choice of configuration/technical solution. For example, for a ball point pen with screw joint, if you choose to make it with a plastic material, it needs to have specific properties to prevent structural cracks in the screw thread. Or, if you need a glazing as a finish cover for your pen, this needs to be applied once all components are completely finished, and it can't be applied on all kind of plastic materials. Or, you can't make a pump pen in plastic, because the quality of the finished surface won't be sufficient to be completely hermetic so it's going to leak.

But, coming back to the process you would use to design a pen, let say a classic ball point pen.

Everything starts from the profile of the pen, given by the new product style department. Each new product has got an external profile €œall dressed€, meaning €œcap on€ and this gives you the boundaries for your design.

First of all, you will design the overall lay-up of the pen . Start from a cylinder shape, decide what are the proportions between the head and the body - if it is a 2 parts ball point pen. Then depending on the dimensions of the chosen ball point stick, you give the minimum value for the internal diameter . You have got then to check if the thickness is big enough . You have got to check this value against the manufacturing constraints to know if the hole is feasible. Then you design the screw thread , which is usually internal. When I say €œusually€ it is because it can seem not a good choice as it is expensive to manufacture. Actually, it is more difficult to cut a screw thread inside a long cylinder sealed at the other end, which is our actual configuration. But it seems to be the "way it's done" for a long time now !! There are some generic rules to follow to calculate the length of the screw thread .

Then, you design the head . Made of a cylinder finishing in a conic shape, the head has to fit inside the overall boundaries given by the cap . You have got to respect some clearances between the head and the internal diameter of the cap . It gives 1st values for the main dimensions, length, external diameter,etc. Then, you give values for the internal diameters . It depends on the stick dimensions. Same checks applied. There are some clearance rules to respect, especially for the tip end of the pen. To allow rolling of the ball, as well as for writing comfort, the minimum distance has to be of 0.05 mm . Then add/design the shape for the screw thread that goes in addition to the initial shape.  Then you can refine the values to relax some of the constraints coming from manufacturing , or to improve the style.

Then you finish by the cap .



Additional information : ink pen design

          



Additional information : Classic Ball point pen drawings

Additional Information about the Ball point stick

                  

The ball in a ball-point pen actually prints its ink onto the paper as it rolls over the paper. The ink that is used in ball pens is very thick. Even thicker than treacle or syrup, and is made from oils and dyes.

Ballpoints write for a very long time. If all the writing from one Parker ball pen refill was made as a straight line, it would be more than five kilometres long.

In making that line, the little ball in the point could have rolled round more than 3 million times.

Gravity makes the ink in the pen fall onto the ball as it sits in its socket. As the pen is moved across the paper the ball turns, and the ink is transferred onto the paper.

The ball at the tip is sometimes only half a millimetre in diameter.