The invention relates to a device for releasably securing a read and/or write head to other apparatus. The invention relates particularly, though not exclusively, to magnetic read and write heads associated with card or ticket transport apparatus in a card or ticket reading system. The nature of ticket or card reading systems (for example in access control systems having many parallel channels in particular) is such that during busy periods it is essential that channels are not taken out of service for maintenance or repair. This results in queues developing which may give rise to safety problems in the event of an evacuation, or security problems associated with ticket theft or pick-pockets. In addition, repair personnel may be unwilling to spend long periods of time in areas such as subway turnstiles because of the threat of assault. Providing more channels than are strictly necessary to allow for breakdowns is an unpopular solution to this problem with the system operating authorities who wish to purchase the minimum number of turnstiles or access control barriers for a given location to minimize capital expenditure. To help reconcile these conflicting demands it is desirable to design ticket transport systems which can be maintained quickly and easily in-situ without using special tools or relying on skilled maintenance personnel who have to work for long periods at the card or ticket transport apparatus.

In card or ticket reading systems, read and/or write heads (generally optical or magnetic) are usually attached to a card or ticket transport apparatus adjacent a train of rollers, wheels or belts which guide and drive the card or ticket through the apparatus and past the heads in use. In such systems using magnetic coding, it is important that the magnetic head can be urged into contact with the card or ticket whilst it moves past It is important to be able to set the force urging the head into contact with the ticket accurately to the minimum required to give reliable reading, thereby minimizing factional wear of the head and prolong its useful life. A further requirement of card or ticket reading systems is to limit movement of the read or write head in the direction of ticket or card transport. In a magnetic read/write system, if the ticket is magnetically coded with a coding density of (for example) 75 bits per inch, a normal design tolerance for lateral movement of the magnetic head in the direction of ticket motion of 8% of the code

pitch translates to a maximum movement in this direction of approximately plus or minus 25 microns.

In a known device disclosed in US 4,377,828, a fixed magnetic head housing is coupled to an adjustable pressure pad which is used to bias the ticket towards a further opposing read and/or write head. The size of the gap between the pad and the further head is adjusted by means of a screw.

The present invention provides a device for releasably securing a read and/or write head to a card or ticket transport system, the device comprising a frame attachable to the system, a carriage for the head, and mounting means for mounting the carriage on the frame, at least one of the carriage and the frame being resilient, the mounting means comprising a pair of rolling element bearings being loaded axially by the restoring force of the resilient frame and/or carriage when the carriage is mounted on the frame, the carriage being moveable in a direction substantially normal to a major surface of any card or ticket in said card or ticket transport system in use.

This arrangement can provide a minimum and consistent resistance to movement perpendicular to the direction of ticket or card transport to ensure that additional frictional force components do not result in accelerated head wear. Manual setting of the bearing load can be eliminated using this arrangement. Such manual load setting is a time consuming task which requires a technician with considerable practical experience.

The carriage and the frame are preferably a snap-fit. This can enable devices to be replaced easily and quickly for maintenance or repair without the need for hand tools or a particularly skilled technician working on the ticket transport equipment.

The device preferably further comprises a magnetic read or write head, a resilient housing for the head and further mounting means for mounting the housing on the carriage, the said head being pivotable about at least one axis substantially parallel to the said direction of transport. This can enable the reading of and/or writing to tickets or cards having a wide range of thicknesses or to enable the magnetic head to move in a direction substantially normal to a major surface of the card or ticket to cope with warped or creased cards or tickets or uneven surfaces whilst maintaining low friction movement and the advantages of quick and easy changing of a device for maintenance or repair or replacement.

The further mounting means preferably comprises a pair of rolling element bearings being loaded axially when the housing is mounted on the carriage. The housing and further mounting means are preferably a snap-fit

The device advantageously includes biasing means being arranged such that the carriage and/or magnetic head is biased towards any card or ticket present in the transport system in operation. This can result in more reproducible reading and writing to warped or creased cards or tickets or to uneven surfaces. The biasing means can conveniently comprises a resilient member provided between the carriage and the frame. The biasing means is preferably constituted by a spring. In a preferred embodiment, the carriage and/or head movement is limited by the mounting means in the plane of the direction of transport of the card.

The carriage is preferably substantially rigid whilst the frame is resilient

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, in which Figure 1 shows a front and an end elevation of a device according to the invention, Figure 2 shows a front and an end elevation of the magnetic head and housing portion of the device of Figure 1, Figure 3 shows a front elevation of the carriage portion of the device of Figure 1,

Figure 4 shows a plan view of the carriage of Figure 3 without the mounting means, and Figure 5 shows an oblique view of the carriage of Figure 3.

In these Figures, to avoid ambiguity corresponding component parts are given the same reference numerals in all the Figures.

In Figure 1, a device for releasably securing a magnetic read and/or write head to a card or ticket transport system is shown in a front elevation 18 and in an end elevation 19 looking along the direction of transport of the card or ticket. The device comprises a resilient frame 1, a carriage 2 for the head 3, and mounting means (which cannot be seen in this Figure, but are shown in Figure 3 as elements 4 and 5) for mounting the carriage on the frame. The mounting means 4 and 5 in the present example both comprise rolling

element bearings - in the present example commercial quality steel ball bearings being loaded axially in operation by the restoring force of the resilient frame such that the carriage is moveable about a first axis 6 (shown in Figure 3) substantially parallel to the direction of transport of any card or ticket in said ticket transport system in operation. The arrangement of the mounting means is such that the carriage is limited from being pivotally moveable in the plane of the paper of the front elevation 18 of Figure 1, i.e. in a plane substantially parallel to the direction of transport. The figure also shows electrically conductive wire 23 and a connector 24 for connecting the head to control means (not shown). The type of bearings used in the device possess both radial and axial internal clearances which are completely removed in the design of the bearing mountings by axially loading the bearings. The type of bearing chosen and the low axial loading provided permits consistently low rotational resistance to be obtained at the same time as removing the clearances as noted above. This limits lateral movement of the magnetic head in the direction of ticket travel to plus or minus 25 microns. The actual range of movement permitted and the amount of axial loading provided can be easily changed by changing the design (for example the material and or the dimensions) of the frame or of the carriage or both. The figure of plus or minus 25 microns given for the present example is purely illustrative and does not limit the scope of the invention. Smaller or larger distances may be chosen.

In the example shown in Figure 1, the carriage is made of a rigid material such as aluminium and the resilient frame is made from a thermoplastic material. Although either the frame or the carriage or both could be made from a resilient material such as a thermoplastic to produce the restoring force to axially load the rolling element bearing mount or mounts, for the most accurate and reproducible reading of magnetically encoded tickets the use of a rigid carriage and resilient frame is preferred. This minimizes head motion in the direction of transport of the ticket or card.

In the example of Figure 1 the device includes a magnetic read head 3 and further mounting means (8, 9 shown in Figure 3) for mounting the said head on the carriage, the said head being rotatable about a second axis 7 (shown in Figure 3) substantially parallel to the first axis 6. The mounting means 8 and 9 are again axially loaded rolling element

bearings as described above. The device includes a housing 12 which carries the magnetic head.

The housing 12 and the magnetic read head 3 are shown in greater detail in Figure 2. The housing has been designed to be resilient and a snap-fit over the cylindrical outer race of the bearing such that during snap fitting the correct axial loading of the bearing is automatically obtained through the restoring force of the deforming housing. Figure 4 shows a view from below of the carriage of Figure 3 with the rolling element bearings 4, 5, 8 and 9 removed. The rolling element bearings are a push fit onto the pins 20 attached to the carriage. Each pin is provided with a shoulder 21 which engages with the inner races of the corresponding bearing. When assembled the outer race of each bearing is arranged to abut a shoulder provided on either the housing or the frame, thereby providing the axial loading. The head and housing assembly can thus be easily removed for replacement without the need for tools of any kind. The arrangement also eliminates the need for a skilled technician to set the loading force of the rolling element bearings using for example a screw thread.

The device of Figure 1 further includes biasing means 11 being arranged such that the carriage and magnetic head is biased towards any card or ticket present in the transport system in operation. In the present example this biasing means comprises a compression spring situated between the frame and the carriage. However, other biasing means such as a weight (the magnetic head plus the housing could be used as at least part of this weight if the axes 6 and 7 are not in vertical alignment), or a resilient member such as a rubber rod or a leaf or helical spring placed between the carriage and another body may be used alternatively or in addition. The oblique view of the carriage 2 shown in Figure 5 illustrates the presence of a notch 14 which is used to locate one end of the spring or resilient member in use.

The housing 12 need not substantially surround the magnetic head, the housing carries the head and enables the head to be easily mounted onto the carriage. Magnetic heads each in a housing would typically be kept as integral replaceable units for use as spare parts. Magnetic read heads and magnetic write heads may be mounted in the system using a device according to the invention. Heads which do not use magnetism to read or write may be used as an alternative falling within the scope of the present invention. For example optical or electronic heads may be provided if desired.

The present invention can provide accurately controllable limitation of the movement of the head in a plane substantially parallel to the direction of movement of the card or ticket, whilst simultaneously providing a minimum and consistent resistance to movement orthogonal to the direction of ticket or card transport so that additional frictional force components do not result in accelerated head wear. Manual setting of the bearing load is not necessary using this arrangement. The device is simple to manufacture. The axial loading is designed to be achieved by the restoring force of the resilient components. When the carriage and the frame and/or the carriage and the housing are a snap-fit, the carriage unit and/or the housing and head unit can be replaced very easily and quickly for maintenance or repair without hand tools or a skilled technician working on the ticket transport equipment. In practice, such devices are usually mounted on pivotable bodies which are releasably secured to the ticket reading system such that they can be swung out of the line of the card or ticket transport for access during maintenance.

In summary, a device for releasably securing a magnetic, electronic or optical read and/or write head to a card or ticket transport system, comprises a resilient frame (1), a carriage (2) for the head, and mounting means (4, 5) for mounting the carriage on the frame, the mounting means comprising a pair of rolling element bearing axially loaded by the restoring force of the resilient frame. The carriage is pivotally moveable about a first axis parallel to the direction of transport of any ticket and not pivotally moveable in the direction of transport. The device may further comprise a magnetic head (3) in a resilient housing (12) and biasing means (11), the head being pivotally moveable about a second axis substantially parallel to the first axis. In operation, the biasing means biases the magnetic head towards any card or ticket.