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| Solenoids in Card Readers |
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A manufacturer of credit card-operated equipment required an interlock system on their card reader units for use in car parking equipment, ticket issuing machines, pay phones, etc. The interlock was required to prevent the credit card from entering the actuation section of the unit until the card had been validated.
The solution to this application was achieved by using a push type tubular solenoid acting on a gate assembly. The solenoid used is a standard design, with a special push rod fitted with a circlip. This gives the stroke control because the assembly has a spring return in the de-energized position. The gate is located inside the reader entrance slot so that when a credit card is inserted, it comes to a stop position against the gate. A sensor scans the code on the card and, if acceptable, a signal is presented to the solenoid. When energized, the solenoid pushes open the gate and allows the card to move on the internal transport system to the fully home position to complete the necessary transaction. This system was introduced as a standard on all basic card reader units by this manufacturer and has been in production for a number of years.
More recently, a major UK manufacturer of telephone equipment was using these basic card readers together with pre-payment cash cards in the public pay phones of motorway service areas, hotels, airports and more. He received a request for a special feature from one export customer. The normal pay phone using a cash card reader is linked to a
display system on the telephone box which gives details of the amount of credit remaining on the cash card after each call. The new requirement was to provide a facility to advise sight impaired people of the amount of credit remaining on the cash card after each call. In order to meet this requirement it was necessary to devise a mark on the card that sight impaired people could feel-a series of raised protrusions indicating the amount of credit remaining.
A new design of card reader was considered, but rejected because this special unit would require development and tooling by the credit card equipment manufacturer and represented only 10% of the total card readers used by the telephone company. It was decided that the telephone equipment manufacturing company would work with Ledex to develop a modification that could be made to the standard card reader to provide a solution to the new requirement.
Several items challenged the design team. Space restrictions with in the card reader made it difficult to fit a suitable solenoid which could be used to punch indentation in the card. There were additional concerns in developing the necessary solenoid force and correct punch design to give indentation to the card without complete hole penetration or racking of the card, preventing further use. The problem was resolved by fitting a special design of a size 3EF, low profile solenoid fitted with a punch tip on its shaft. The solenoid has a reduced case length of only 11mm to overcome the space problem. The solenoid base is extended to provide location in the card reader track and also to take extended bearings to support the shaft. The shaft is fitted with a circlip to control the return stroke to 4mm, again, to assist in the space restriction. A special coil has been designed to fit the shorter case length and to give correct performance requirements. A special wave washer spring is fitted between the base and armature hub to break any solenoid residual magnetism and to prevent the punch tip, a unique shape constructed of tempered steel, was developed by the pay phone manufacturer, then made and fitted to the solenoid shaft by Saia-Burgess.
The telephone equipment manufacturer now purchases standard card readers incorporating the Size 50 tubular solenoids. On those orders requiring the additional sight impaired feature, the special 3EF solenoids are purchased directly from Saia-Burgess and are fit as an in-house modification. In the mean time, the credit card equipment manufacturer is considering whether it is commercially viable to have a similar modification as a standard feature on card readers.
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