GB2288492A - Electrical device addressing arrangement - Google Patents

Abstract

An address module 20 for providing an electronically readable address for a device comprises a plurality of elongate contacts 21 and a printed circuit board 22. The contacts 21 have one end for insertion into corresponding address cavities (13, Fig. 7) of a connector housing and are mounted to the printed circuit board 22 at their other ends. The printed circuit of the printed circuit board 22 is arranged to electrically connect together various contacts 21 to determine the address. Insulating bushes 23 may be included around the contacts 21 and a plastic coating 24 may be applied to cover the printed circuit board 22 and part of the insulating bushes 23. The contacts 21 may also include spring clip releasable locking means 25 to secure the module 20 to the connector housing. An extraction tool (70, Fig. 8) may be used to separate the address module 20 from the connector housing. <IMAGE>

Description

IMPROVEMENTS RELATING TO ELECTRICAL DEVICE ADDRESSING ARRANGEMENTS Field of the Invention This invention concerns improvements relating to electrical device addressing arrangements and particularly, though not exclusively, to an address module for addressing a specific device in a system comprising many such devices.

Background to the Invention In the field of railway signalling, communications networks comprising many remote devices are known wherein specific signalling information can be sent to a particular device via a common communications link. Each device has a unique digital address which enables it to identify and download its specific signalling information from the communications link.

Referring now to Figure 1, there is shown therein a typical prior art arrangement which is used in the UK rail system to determine the address of a signalling device. The arrangement comprises a connector housing 10 which has a plurality of contact receiving cavities 11, the majority of which are used to connect to terminals (not shown) of the common communications link 12. The other contact receiving cavities (address cavities) 13 of the connector housing 10 are used for the location of a plurality of address terminals 14. In use, each address terminal 14 is releasably locked within a respective address cavity 13 and has a pin termination 15 protruding therefrom to allow selected wire-wrapping interconnections 16 to be made between the different address terminals 14 as is shown. A given address is thus determined by the particular interconnections made between various address terminals.

The construction of the above address determining arrangement is complex, time consuming and labour intensive. For example, as can be seen from Figure 1, most of the pin terminations 15 require two wires to be wire-wrapped to them and then an electrically insulating sleeve 17 has to be placed over each wirewrapped pin termination. In addition, to prevent rotation of the terminals within their cavities 13 during the wire-wrapping operation, there has to be force fitted onto each pin termination 15 a squareshaped electrically insulating anti-rotation bush 18, which, in combination with other anti-rotation bushes 18, acts to stop the pin terminations from rotating.

Furthermore, errors can easily be made during the wire-wrapping procedure which are not easily rectifiable at a later stage.

Another problem with this arrangement is that it provides very little protection from the environment.

This is particularly important in the field of railway signalling where signalling devices can be exposed to very severe climatic conditions, and the safety of train passengers may depend on the correct functioning of the device.

Another disadvantage of using the above address determining arrangement is that the cost of its manufacture is high which is due, in the most part, to the high labour costs involved in assembling and then checking the arrangement.

Summarv of the Invention The present invention in its broadest aspect resides in the appreciation that at least some of the above described problems can be overcome or at least substantially reduced by arranging for the selected address terminals to be interconnected using a printed circuit board.

More particularly, according to the present invention there is provided an address module comprising: a plurality of elongate contacts for insertion into respective contact-receiving cavities of a connector housing; and a printed circuit board supporting said contacts and electrically connecting together various ones of the contacts; the arrangement being such that, in use of the address module with said plurality of elongate contacts received in respective contact-receiving cavities of a said connector housing, the address for a device having terminals connected to said elongate contacts will be established by the interconnections between the elongate contacts that are provided by the printed circuit board.

One of the advantages of using the address module of the present invention is that the labour intensive processes hitherto involved in wiring connections between pins, checking to see if the connections are correct and correcting any mistakes, are not now required. Rather, a predetermined set of printed circuit boards, each having a particular configuration for a particular address, can be manufactured and used to assemble a set of address modules having the required range of addresses. This represents a significant saving in manufacturing costs and greatly simplifies the assembly procedure of the addressing arrangement.

Furthermore, replacing the wire-wrapped connections of the prior art solution with the printed circuit board of the present invention is particularly advantageous as it provides a significant improvement in the reliability of the addressing arrangement. As the mechanical strength of the interconnections is increased, the address module is for more durable and electrically reliable than the wire-wrapped addressing arrangement of the prior art.

In addition, the address module of the present invention enables the address of a device to be changed simply by replacing the existing address module by another having the desired new address. In the previous arrangement, the changing of an address was difficult as it involved the rewiring of several interconnections between pin terminations to reconfigure the arrangement to the new address.

The address module may further comprise insulating means, other than the circuit board itself, for electrically isolating from each other contacts which are not interconnected by the printed circuit on the printed circuit board. This insulation means helps to prevent electrical shorts from occurring between adjacent contacts and is particularly important where the contacts are densely packed within a small space. In particular, the insulating means may comprise a plurality of insulating bushes through which the contacts are threaded and connected to the printed circuit board. The bushes may be adhered to the printed circuit board so as to transmit to the printed circuit board any axial loading of a corresponding contact arising during insertion or extraction of the module from the connector housing of the device.

To further reduce the possibility of electrical shorts occurring, the address module may comprise a plastics coating covering the printed circuit board.

This coating seals the printed circuit board, thereby providing protection from the detrimental effects of the environment, and additionally may be extended to cover at least part of the insulating means to strengthen the structure of the module.

The address module may further comprise releasable locking means for locking the module to the connector housing. In an exemplary embodiment of the invention which will be described hereinafter, the locking means comprises at least one spring retention clip which is provided on a respective contact and is arranged to engage with a constriction that is provided in a corresponding cavity of the connector housing to effect locking.

A locked address module may be released by use of an extraction tool which can be inserted into the connector housing to engage and disable the locking means to allow subsequent removal of the address module. When a plurality of contacts have associated locking means, then a special extraction tool is required.

Therefore, according to another aspect of the present invention there is provided an extraction tool for releasing a plurality of locked elongate contacts of an address module from a plurality of corresponding cavities of a connector, said extraction tool comprising: a plurality of tubes for insertion into said cavities to release said locked contacts; and a tool body supporting said tubes; wherein said plurality of tubes are positioned to correspond with the positions of the cavities retaining said locked contacts and are arranged to release all of said contacts simultaneously in a single insertion operation.

The extraction tool according to the invention may comprise a plurality of ejection pins each of which is provided coaxially within a corresponding release tube and is axially drivable to engage the released contacts thereby assisting in the ejection of the address module from the connector housing. The pins may advantageously be driven simultaneously by a drive member which is connected to all the pins. The drive member may for example comprise a spring-biassed push-button.

The extraction tool 70 may comprise means for locating the plurality of release tubes accurately in line with the cavities of the connector housing and may also comprise means for providing protection of the release tubes. In an embodiment of the invention, the locating means and the protection means are provided for by a plurality of walls extending from three sides of the tool body.

The above and further features of the present invention are set out with particularity in the appended claims and, together with the advantages thereof, will become apparent to those skilled in the art from consideration of the following detailed description of an exemplary embodiment of the invention which is given with reference to the accompanying drawings.

Brief Description of the Drawings Figure 1 is a perspective view of a connector housing incorporating a prior art address arrangement; Figure 2 is a perspective view of an address module embodying the present invention; Figure 3 is a schematic front elevation view to a greatly enlarged scale of an elongate contact of the address module of Figure 2; Figures 4A, 4B and 4C are respective front, side and rear elevation views of an exemplary printed circuit board of an address module as shown in Figure 2; Figure 5 is a perspective view of a special location jig used to assemble the address module; Figures 6A and 6B are respective plan and front elevation views of the address module being assembled in the location jig of Figure 5; Figure 7 is a schematic cut away view of a single elongate contact of the address module locked in a contact receiving cavity of the connector housing and a release tube of an extraction tool for releasing the contact; Figure 8 is a perspective schematic view of an extraction tool incorporating a plurality of release tubes; Figure 9A is a sectional view taken on the line X-X of Figure 8; and Figures 9B and 9C are respective schematic top and bottom plan views of the extraction tool of Figure 8.

Detailed Description of the Embodiment Hereinafter described is an address module 20 (see Figure 2) for providing an electrically readable address for a railway signalling device. The module essentially comprises eighteen cylindrical elongate contacts 21 mounted on and soldered to a double sided printed circuit board (PCB) 22. The circuit of the PCB 22 is configured to electrically connect together various contacts 21 to define a unique device address.

The contacts 21 are distributed on the PCB 22 in a 3 x 6 staggered array so as to be aligned with the eighteen address cavities 13 of the connector housing 10 shown in Figure 1. Each contact 21 is mounted to the PCB 22 through a nylon bush 23 and the module 20 is coated with a protective epoxy coating 24 which covers the PCB 22 and the nylon bushes 23. In addition, six of the eighteen contacts 21 have spring retention clips 25 mounted to their bodies for engaging with constriction portions (see Figure 7) in corresponding address cavities 13 of the connector housing 10, to releasably lock the address module 20 thereto.

As will be described in detail hereinafter, the design of the address module 20 is such that the contacts 21 have to be inserted into and extracted from the connector housing 10 collectively. By providing spring retention clips 25 on only six of the eighteen contacts 21, the overall force required for insertion or extraction is greatly reduced. Insertion of the module 20 is carried out manually, but extraction requires the use of a special extraction tool 70 to release the locked retention clips 25. The construction and operation of the extraction tool will also be described in detail hereinafter, as will the assembly of the address module 20 which requires the use of a special location jig 50.

Referring now to Figure 3, each cylindrical contact 21 is of a known design which comprises an engaging portion 30 for engaging a respective address cavity 13 and a solder tail 31 for soldering the contact 21 onto the PCB 22. The engaging portion 30 comprises a main body 32 which has an abutment shoulder 33 that determines the correct depth of insertion of the contact 21 within the address cavity 13. Also the contact has a head end 34 which comprises a female contact for making an electrical connection with a male (pin) contact of a complementary connector and which defines an ejector pin receiving bore 35 and a recessed portion 36 for locating the spring retention clip 25.

The spring retention clip 25 is also known and is designed to collapse its arms 37 during insertion through the constriction portion of the cavity 13 and to open them out thereafter. This allows the contact 21 to be securely locked in the cavity 13 with the constriction portion being held between the abutment shoulder 33 and the opened out retention clip arms 37.

Release of the contact 21 from the cavity 13 is simply achieved by inserting a release tube (see Figure 7) from the other end of the cavity, to refold the arms 37 of the retention clip 25 thereby allowing the contact 21 to be extracted (as discussed in detail hereinafter).

The solder tail 31 of the contact 21 locates the nylon bush 23 against the main body 32 and passes through the PCB 22 where it is electrically connected to copper tracks 38 on the solder side 39 of the PCB 22 by a solder joint 40. The nylon bush 23 serves to transmit some of the axial load present on the contact 21 during its insertion or extraction, to the PCB 22.

If the nylon bush 23 was not used, the contact 21 could only withstand a maximum axial force equivalent to that of the adhesion between the board 22 and the copper tracks 38 of the PCB, before breaking free. In addition, the nylon bush 23 is adhered to the nonsolder side 41 of the PCB 22 to provide radial as well as axial support for the contact 21.

Another function of the nylon bushes 23 is to electrically insulate the contacts 21 from each other so that the only interconnections between the contacts are provided by the printed copper tracks 38 of the PCB 22. Use of the nylon bushes 23 prevents electrical shorts from occurring at the non-solder side surface 41 of the PCB 22, for example, which may otherwise be caused by moisture forming between adjacent contacts 21. Also, they enable the use of a double sided PCB 22 as the solder tail 31 does not interfere with any copper tracks (not shown) on the non-soldering side 41 of the PCB.

In order to further electrically insulate the contacts 21 from each other, the address module 20 is coated with the protective plastics coating 24 comprised of an epoxy resin. As shown in Figure 3, the protective coating 24 covers the entire PCB 22 and extends up to level A of the nylon bush 23.

Alternatively, the protective coating 24 could just coat the PCB 22 and not the nylon bush 23. The coating thus encapsulates the PCB 22 and provides both environmental protection for the address module 20, for example sealing against moisture and corrosion of copper tracks of the PCB, and additional strength for the PCB/contact connections.

As discussed earlier, each contact 21 has a recessed portion 36 for locating a spring retention clip 25 and so a maximum of eighteen retention clips can be used for this address module 20. Any number of retention clips (1 to 18) could be used for the module 20 to be lockable to the connector housing 10. In practice, the use of too few clips provides too low an effective locking force, whereas the use of too many clips increases the cost, complicates the design of the extraction tool 70 and makes the forces required for insertion and extraction of the module 20 undesirably large. Therefore, it has been found that by using six retention clips 25, one in each of six predetermined positions, a compromise solution is obtained. The selected positions for the 3 x 6 array of contacts 21, shown in Figure 2, are at the four corners of the array and at the third and fourth columns of the first and third rows respectively.

Referring to Figures 4A to 4C, there are shown various views of the double-sided PCB 22 including plan views of the non-solder and solder sides 41 and 39 (Figures 4A and 4C) respectively. The PCB 22 has a through hole 42 and a solder pad 43 for each of the contacts 21 to be connected and four printed circuit tracks 44 connecting together various solder pads 43.

The PCB 22 is shaped on three of its sides to match the contour of the connector housing 10 and incorporates chamfered corners 45. In addition, to allow access to the cavities 11 for communications link terminals adjacent to the address cavities 13, the remaining side 46 of the PCB 22 incorporates three semi-circular notches 47.

The communications system within which the address module 20 is used requires each device to have a 2 x 6 bit address so that a maximum of 128 (2 x 26) devices can be connected to the common communications link 12 at any one time. The printed circuits 44 shown in Figure 4A and 4C define one such address for the module 20. However, the address module 20 can provide any one of the remaining 127 addresses by simply using a PCB 22 where predetermined interconnections, i.e. printed circuit tracks, have been made which define that address. This presents many significant advantages over the previously used wire-wrapped arrangement, for example, removing the need for a skilled worker to wire up the different connections 16 between selected pin terminations 15 for each of the different addresses. In addition, the reliability of the device is greatly improved whilst the cost is reduced.

Referring now to Figures 5, 6A and 6B, a special location jig 50 for assembling the address module 20 is shown. The jig 50 has a main body 51 which is made from an insulating plastics material and has a plurality of contact locating apertures 52 formed therein. The apertures 52 are located at positions which correspond exactly with the positions of the cavities 11,13 of the connector housing 10. Each aperture 52 has a diameter fractionally larger than the outer diameter of a pin contact 21 and has a depth equivalent to that of the engaging portion 30 of the pin contact 21. Six of the eighteen apertures 52 at one end of the main body 51 have identification marks 53 on them. This is to allow the assembler to know which positions require pin contacts 21 having spring retention clips 25. Although not shown in Figure 5, other groups of eighteen sockets in the main body may also have similar markings on them to enable several address modules 20 to be assembled at the same time.

To assemble an address module 20, eighteen contacts 21 are inserted into the apertures 52 at one end of the main body 51 with their respective solder tails 31 facing upwardly. Six of these contacts 21 have spring retention clips 25 and these six contacts are inserted into the marked apertures. A nylon bush 23 is then threaded onto the solder tail 31 of each contact 21 and the PCB 22 mounted to the ends of the contacts 21, with its non-solder side 41 being adhered to each of the nylon bushes 23. The solder tails 31 of the contacts, which extend through the through holes 42 of the PCB 22 to its solder side 39, are then soldered to the solder pads 43. A reference position 54 (see Figure 6A) is established on the 3 x 6 array of positions for the contacts 21, from which each of the other positions can be defined. The thus assembled address module 20 is then taken out of the location jig 50 and dip coated in the protective plastics material 24 up to the level "A" as previously described and shown in Figure 3.

A particularly important feature of the location jig 50 is that it enables all of the contacts 21 of an address module 20 to be located perpendicularly to the PCB 22 and with their equivalent parts, for example their abutment shoulders 33, all located in the same plane. This ensures that during insertion and removal of the address module 20 from the address cavities 13 of the connector housing 10, the spring retention clips 25 lock and unlock the address module 20 to the connector housing 10 all at the same time, and that all electrical connections to the complementary connector can readily be made/broken effectively at the same time.

Referring now to Figure 7, a contact 21 of the address module 20 is shown inserted within a corresponding address cavity 13 in a locked condition.

As mentioned previously, the contact 21 is locked to the connector housing 10 by virtue of the constriction portion 60 of the address cavity 13 being secured between the abutment shoulder 33 of the contact 21 and the arms 37 of the retention clip 25. Also shown is a release tube 71 of the extraction tool 70 which is used to release the contact 21 from its locked condition.

The release tube 71 has an internal diameter which is equivalent to the diameter of the constriction portion 60 of the cavity 13. When the closure tube 71 is inserted into a release end 61 of the cavity 13 and pushed up against the constriction portion 60, the flared arms 37 of the spring retention clip 25 are collapsed and the contact 21 can be withdrawn. To assist with the removal of the released contact 21, the tube 71 is provided internally with an axially drivable ejector pin 72 which when driven against the contact 21 forces the contact to be pushed part of the way out of the cavity 13.

The ejector pin 72 has an external diameter which is smaller than the internal diameter of the receiving bore 35 of the contact 21. During removal of the contact, the ejector pin 72 is axially driven into the receiving bore 35 of the contact until it abuts against the end of the bore and then it is further driven to push out the contact 21 from the 13. This acts to channel the axial force being applied from the ejector pin 72 to the contact 21.

The extraction tool 70 (shown in Figures 8, 9A to 9C) comprises a tool body 73 having three locating walls 74 extending therefrom to locate the tool 70 accurately over the release end 61 of the connector housing 10. Six tubes 71 are provided on an engaging face 75 of the tool body 73 for insertion into selected ones of the address cavities 13. Each tube 71 has a corresponding ejector pin 72 as previously described which is connected to an ejector mechanism.

The ejector mechanism is located within a chamber 76 in the tool body 73 and comprises a spring-biassed push button 77 connected to the six ejector pins 72.

Referring to Figures 8, 9A to 9C in more detail, the locating walls 74 of the tool body 73 are dimensioned to fit around the release end 61 of the connector housing 10 such that the extraction tool 70 can always be located accurately over the connector housing 10. Once correctly located, the extraction tool 70 is push fitted to the connector housing 10 so that the closure tubes 71 are pushed into their respective address cavities 13 to release the locked contacts 21 of the address module 20. Thus, the provision of the locating walls 74 prevents insertion of the extraction tool 70 into incorrect address cavities 13 and also allows a user to engage the extraction tool 70 with the correct address cavities 13 without requiring a great deal of manual dexterity.

The latter of these points is especially important where the connector housing 10 is positioned awkwardly such that it is difficult to see how to locate the extraction tool 70 correctly. In addition, as the locating walls 74 recess the tubes 71 within the tool body 73, some degree of protection is provided for the tubes 71, which otherwise, in use, may be susceptible to damage if the extraction tool is dropped, for example.

The tool body 73 includes a recessed portion 78 in its engaging surface 75. This recessed portion 78 provides a clearance for accommodating jack pins and guide screws (not shown) which are used to secure a cover 19 (see Figure 1) to the connector housing 10.

Thus, it is possible to flush mount the engaging surface 75 of the tool body 73 to the release end 61 of the connector housing 10.

Each of the tubes 71 is formed of phosphor bronze to provide a high degree of resilience in a thin walled structure and this enables each tube 71 to be splayed within the tool body 73 to resiliently anchor the tube 71 to the tool body 73. The positioning of the tubes 71 is determined to correspond to the locations of those address cavities 13 which will receive the six pin connectors 21 having the spring retention clips 25.

The spring-biassed push button 77 of the ejector system (see Figure 9A) is securely connected to the ends of the six ejector pins 72. Each ejector pin 72 has a spring 79 provided around the pin and between the bottom of the chamber 76 and the push button 77.

This biasses the button 77 against the top surface of the chamber 76 and in this position the ejector pins 72 are retracted within the tubes 71. The exertion of a downward force on the button 77 causes all six ejector pins 72 to slide along the centres and extend from the ends of the tubes 71 so that, in use, they can push out the contacts 21 from the address sockets 13.

The most significant features of this push button ejector mechanism are that it allows an even force to be applied to each ejector pin 72 and that it makes the six ejector pins 72 move in unison with their contact engaging ends 80 all located in the same plane. Thus, all the ejector pins 72 engage the contacts 21 at the same time and the force required to push the address module 20 out of the address cavities 13 is distributed evenly between the ejector pins.

The number and positioning of tubes 71 employed in the extraction tool 70 is dependent upon the predetermined number of retention clips 25 that are to be used in the address module 20 and which of the contacts 21 are to have these retention clips 25. In this embodiment, six retention clips 25 and thus six closure tubes 71 have been used as they provide a balanced solution with consideration to the factors of cost, force required to eject the address module 20 and locking force provided by the address module 20.

Having thus described the invention with reference to a particular embodiment it is to be appreciated that the described embodiment is exemplary only and is susceptible to modification and variation without departure from the spirit and scope of the invention as determined by the appended claims. For example, the use of the address module is not limited to railway signalling applications and could be incorporated into any communications network requiring discretely addressed devices.

Claims (21)

CLAIMS:

1. An address module comprising: a plurality of elongate contacts for insertion into respective contact-receiving cavities of a connector housing; and a printed circuit board supporting said contacts and electrically connecting together various ones of the contacts; the arrangement being such that, in use of the address module with said plurality of elongate contacts received in respective contact-receiving cavities of a said connector housing, the address for a device having terminals connected to said elongate contacts will be established by the interconnections between the elongate contacts that are provided by the printed circuit board.

2. An address module according to claim 1, further comprising insulation means for electrically insulating said contacts from each other at said printed circuit board other than where they are interconnected via said printed circuit.

3. An address module according to claim 2, wherein said insulation means comprises a plurality of insulating bushes, each bush being adhered to said printed circuit board for transmitting an axial load applied to a corresponding contact to a surface of the printed circuit board during insertion or withdrawal of said module from said connector housing.

4. An address module according to any preceding claim, further comprising a plastics coating covering the printed circuit board for sealing the same and protecting it against detrimental effects of the environment.

5. An address module according to claim 4, as dependent from claim 2 or 3, wherein said plastics coating also covers at least part of said insulating means.

6. An address module according to any preceding claim, further comprising releasable locking means for locking said module to said connector housing.

7. An address module according to claim 6, wherein said locking means comprises at least one spring retention clip, said at least one clip being provided on a respective contact for engaging a constriction in a corresponding cavity of said connector housing for locking said module thereto.

8. An address module according to any preceding claim, wherein said printed circuit board comprises a double-sided printed circuit board.

9. An address module according to any preceding claim, wherein said printed circuit board is shaped to allow access to adjacent cavities of said connector housing when said module is in use.

10. An address module according to any preceding claim, wherein said contacts are arranged such that their ends for insertion into said cavities lie substantially within the same plane, said plane being parallel to the plane of the printed circuit board.

11. An assembly jig for assembling an address module according to any preceding claim, said jig comprising a plurality of receptacles, each receptacle being arranged to receive one of said plurality of contacts and being positioned with respect to the other receptacles so as to arrange said contacts to correspond to the arrangement of said cavities of said connector housing, said receptacles being further arranged to locate ends of said contacts for insertion into said cavities substantially within the same plane.

12. An extraction tool for releasing a plurality of locked elongate contacts of an address module from a plurality of corresponding cavities of a connector housing, said extraction tool comprising: a plurality of tubes for insertion into said cavities to release said locked contacts; and a tool body supporting said tubes; wherein said plurality of tubes are positioned to correspond with the positions of the cavities retaining said locked contacts and are arranged to release all of said contacts simultaneously in a single insertion operation.

13. An extraction tool according to claim 12, further comprising a plurality of ejection pins, each ejection pin being provided coaxially within a corresponding tube and being arranged to be axially drivable for engaging said released contacts to assist in the ejection of the same from said cavities.

14. An extraction tool according to claim 13, further comprising a drive member, said member being connected to said ejection pins and being arranged to axially drive the same simultaneously upon operation of the member.

15. An extraction tool according to claim 14, wherein said drive member comprises a spring-biassed push button.

16. An extraction tool according to any of claims 12 to 15, further comprising means for locating the plurality of tubes accurately in line with said cavities of said connector housing.

17. An extraction tool according to any of claims 12 to 16, further comprising means for providing protection for said tubes.

18. An extraction tool according to claim 16 or 17, wherein said locating means or said protection means comprises a plurality of walls extending from three sides of said tool body to an extent such that said tubes are recessed within said walls.

19. A railway signalling device comprising an address module according to any of claims 1 to 10.

20. A communications system for a railway signalling application, said system comprising a plurality of devices connected to a common communications link, wherein each device comprises an address module according to any of claims 1 to 10.

21. An address module or extraction tool substantially as described herein with reference to Figures 2 to 9C of the accompanying drawings.