GB1603820A

GB1603820A - Electric switches

Info

Publication number: GB1603820A
Application number: GB46667/77A
Authority: GB
Original assignee: Hoover Ltd
Current assignee: Hoover Ltd
Priority date: 1977-11-09
Filing date: 1977-11-09
Publication date: 1981-12-02
Also published as: ZA786162B; AU528674B2; SE7811547L; TR20756A; DE2847772A1; FR2408903A1; FR2408903B3; AU4134878A

Description

(54) ELECTRIC SWITCHES (71) We, HOOVER LIMITED, a Company registered under the laws of England, of Perivale, Greenford, Middlesex, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to electric switches and is concerned with the design of an extremely simple and inexpensive construction which nevertheless has excellent characteristics particularly from the points of view of compactness, current capacity and maintaining corrosion-free contacts.

A review of the prior art indicates that in general the constructions are relatively complex involving a considerable number of moving parts. Where simplicity has been obtained, it generally involves a restriction to purely rocking movements with the consequent disadvantages.

According to one aspect of the present invention an electric switch includes at least two contact elements, a bridging piece of shallow V-form the limbs of which on one side subtend an angle of less than 1800 facing away from the contact elements whilst regions of the opposite surface of the bridging piece contact two of the contact elements in an operative position of the bridging piece, and an actuator to move the bridging piece to and from its operative position, the actuator including a rocker member which is interconnected with the bridging piece by means of a coil spring one end of which is carried by the rocker member, the other end of the spring directly engaging an intergral part of the bridging piece.

Preferably the integral part has a pair of vertical faces and the angles subtended between these faces and the limbs of the V of the bridging piece are substantially identical.

In a particularly simple embodiment the bridging piece is manufactured from sheet metal and the integral part comprises a struckout portion of the sheet metal and the integral part may be of generally inverted T-shape, the head of the T being disposed at the centre of the one side of the bridging piece and the head affording, on each side of the stem of the T, a substantially horizontal surface upon which a portion of the spring bears.

Preferably the actuator is arranged to cause separation of the bridging piece form one contact element by a rotary movement of the bridging piece and the separation is followed by a combined translatory and rotary movement of the bridging piece. The rotary movement may be preceded by a translatory movement, and may or may not be accompanied by a translatory movement.

Moveover the actuator may be arranged to cause closing contact of the bridging piece with the one contact element by a rotary movement of the bridging piece followed by a translatory sliding movement of the bridging piece with respect to the contact element whilst in engagement with the contact element.

The invention may be carried into practice in a number of ways but certain specific embodiments will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a sectional side elevation through a rocker-type changeover switch according to the invention; Figure 2 is a view similar to Figure 1 showing the switch being operated from one position to the other; Figure 3 shows the switch of Figures 1 and 2 at a slightly later stage of movement than in Figure 2; Figure 4 is a perspective view of a bridging piece incorporated in the switch of Figure 1 to 3; Figure 5 is a sectional side elevation of a second embodiment comprising a rocker-type onoff switch which is biased to the on position; Figure 6 is a sectional side elevation of a third embodiment of a push-push type switch.

Figure 7 is a sectional side elevation through a rocker-type changeover switch according to a further embodiment of the invention; Figure 8 is a vertical sectional side elevation on the median line of Figure 7 when the parts are all centrally positioned; Figure 9 is a plan view of a bridging piece incorporated in the switch of Figure 7 and 8; Figure 10 is a side elevation of the bridging piece of Figure 9; Figure 11 is a sectional side elevation on the line 11-11 of Figure 10; Figure 12 is a sectional side elevation on the line 12-l2ofFigure 10; Figure 13 is a sectional side elevation of part of the switch of Figures 7 to 12, showing the parts in a position in which the bridging piece is about to move away from a contact; Figure 14 is a sectional side elevation similar to Figure 13 but showing the bridging piece further moved; and Figure 15 is a sectional side elevation similar to Figures 13 and 14 showing the bridging piece in its alternative operative position.

Referring firstly to the embodiment of Figures 1 to 4, the switch shown in these Figures includes a moulded plastics housing 10 having a side wall 11 terminating at its upper end in an outward flange 12. The moulding includes a base 14 and a pair of side flaps 16 which, in their relaxed position shown in the drawings, project laterally beyond the flange 12 but which can be pressed towards the side wall 11 when the switch as a whole is inserted into a socket in a machine. At this time the flaps bend around their lower ends 18 and it is to be noted that the flaps taper downwards and merge with the base 14 at a point 20 which is inboard of the lower end 22 of the side wall 11.

This defines a space 24 extending the length of the side wall 11. By turning the flap 16 under the base 14 to the point 20 a longer and more resilient flap is provided than would otherwise be the case if the flap were connected to the lower end of the side wall 11 , assuming that this extended down to the level of the lower face of the base 14. In this way it is found practicable to shorten the overall depth of the moulding and yet obtain the same resilience of flaps as has been obtained with longer or deeper flaps associated with deeper housing mouldings.

In the embodiment of Figures 1 to 4 the base 14 has extending through it three metallic plates 26, 28 and 30. These plates pass through vertical apertures 32 formed in the moulding, these apertures each having an enlarged lower end 34 to receive a sprag 36 struck-out from the associated plate.

It will be observed that each of the outer plates 26 and 30 projects to a small extent above the inner face of the base 14 whilst central plate 28 projects at its upper end into the space 40 within the moulding to a level higher than the plates 26 and 30.

Located in the space 40, and journalled to rock about a horizontal pivot 42, is a rocker 44 having on its upper side a pair of operative faces 46 and 48, and on its under side, a central downwardly projecting stem 50. The lower end of the stem 50 has a counter-bore 52 the upper end of which has located within it a stud 54, which is integral with the stem 50, for retaining the upper end of a coil spring 56 during assembly. It is to be observed that the spring has minimum working clearance in the bore 52 and the last 2-3 coils of the spring 56 normally project below the lower end 58 of the stem 50.

The underside of the lowermost coil of the spring is ground substantially flat.

Figure 4 illustrates the particular form of a bridging piece 60 made of brass or copper which is incorporated within the switch as shown in Figure 1. The bridging piece 60 is of shallow V form having two limbs 61, 62 the upper faces of which, in this embodiment, subtend an angle between them of approximately 1600. This angle can vary according to requirements but preferably is between 140 and 175" The main sides 63 are parallel and end portions 64 are stepped inwardly at 65 in order to clear vertically extending pillars 66 of the housing 10.

Struckout from the central portion of the bridging piece 60 is a vertically upstanding inverted T-shaped tab 68. The stem 70 of the T extends into the lower end of the coil spring 56 as shown in Figures 1 to 3, whilst the lower coil of the spring rests on upwardly facing shoulders 72 on the head of the T.

The bridging piece 60 has two operative positions one of which is shown in Figure 1, in which it bridges the upper ends of the plates 28 and 30. In the other of the two operative positions, not shown, the bridging piece bridges the two plates 26 and 28 in a similar manner.

As illustrated in Figure 1 between two and three coils of the spring 56 extend beyond the counterbore 52 and these coils are therefore capable of deflecting out of the general axial line of the spring as shown in Figure 1. In the stable position of Figure 1 the spring 56 is exerting a downward force on the tab 68 via the shoulders 72. This maintains the underside of the right hand limb 61 of the bridging piece firmly in engagement with the upper end of the plate 30.

It will be observed that the right hand end 76 of the bridging piece 60 overhangs to the right the upper end of the plate 30 and abuts the inner side of the wall 11 of the housing.

At this time the radiused upper end of the central plate 28 engages a region 78 of the left hand limb 62 of the bridging piece slightly to the left of the apex 69 of the bridging piece.

Since movement of the bridging piece to the left from the position of Figure 1 involves a compression of the spring 56 it is ensured that the spring maintains the bridging piece firmly in its stable position of Figure 1 until the rocker is moved in a manner now to be described.

The rocker 44 has a skirt 82 the lower end of which engages one or other of two shoulders 84 within the housing 10 to limit the movement of the rocker from one position to the other.

When it is described to move the bridging piece 60 to its other stable position, in which it bridges the upper ends of the plates 26 and 28, pressure is applied to the upper face 46 of the rocker to move it downwards about the pivot 42. This in tum rotates the spring 56 bodily about the pivot 42, and since the relative dimensions of the interior of the spring and the tab 68 provide for slight lost motion between these parts, the spring engages the right-hand side of the tab 68 of the bridging piece to rotate it antibclockwise about the region 78 on the upper end of the central plate 28. Accordingly between the positions of Figure 1 and Figure 2 the first angular movement of the rocker causes the bridging piece to rotate away from the upper end of the plate 30 so breaking electrical continuity between the plates 28 and 30 and opening the switch. This is essentially a rotary movement due to the friction between the region 78 of the bridging piece and the upper end of the plate 28, but very shortly afterwards the continued movement of the spring 56 in a clockwise direction causes the bridging piece to be shifted laterally, first to the position of Figure 2, and then to the position of Figure 3. In other words the bridging piece is physically lifted as the contact between the upper end of the central plate 28 moves from the region 78 shown in Figures 1 and 2 to the apex 69 as shown in Figure 3.

The movement of the rocker in a clockwise direction from Figures 1 to 3 and onwards in a continuous rotary movement and as a consequence, immediately the rocker moves slightly further clockwise from the Figure 3 position, the spring 56 will impart first a further anticlockwise rotation to the bridging piece 60 so that its left hand end 85 sharply contacts the upper end of the plate 26 to provide electrical continuity between the plates 28 and 26. The movement of the bridging piece does not finish here however since the spring continues to impart a lateral movement to the bridging piece until the left hand end 85 of the bridging piece contacts the left hand inside surface of the inner wall 11. Accordingly the bridging piece first carries out a rotary movement and then a wiping movement with respect to the upper end of the plate 26 which is an ideal method of making contact since any deposits on or corrosion of either the contact or the under side of the bridging piece adjacent its end 84 tend to be wiped away by means of this method.

Despite the asymmetry of the bridging piece it is effectively symmetrical from the point of view of its reverse operation and anti-clockwise rotation of the rocker shifts the bridging piece in an identical reverse manner, i.e. it carries out a rotary breaking movement followed by a sliding lateral movement, a further rotary movement into contact and a further sliding wiping movement.

Referring to Figure 1 it is to be particularly noted that the portion of the lower coil of the spring 56 which is acting on the tab 68 is slightly to the left of the centre line of the spring, so that, as shown, the last coil of the spring is slightly tilted from a radial plane, the spring being slightly opened on its right hand side and slightly closed on its left hand side in Figure 1. Only in the position of Figure 3 is the spring axis in line with the tab 68.

This embodiment of the switch is extremely compact and compares extremely favourably with all known prior constructions since it provides for direct communication between a tag struck out from the bridging piece to cooperate directly with the end of a spring of the rocker.

The switch is found to have a generally higher current capacity than any known switches of comparable size. The V-form of the bridging piece provides good clearance between it and the plates when in the open position which is enhanced by the upper end of the central plate being higher than either of the other plates.

Furthermore the mode of operation is such that the bridging piece carries out the sequence of operations outlined above giving good breaking contact and excellent making contact.

Referring now to Figure 5 this shows an alternative embodiment having only two plates 90 and 91 bridged by a similar bridging piece 60A in the position of Figure 5. The bridging piece 60A can be shifted to an open position in the same manner as in Figures 1 to 4 by clockwise rotation of a rocker 44A, the movement of the bridging piece being limited by engagement of its left hand end 84A with an inner surface 92 of the housing. As shown in Figures 5 the rocker is biased in an anti-clockwise direction by means of a return spring 94 so that normally the rocker and the bridging piece 60A maintain the position of Figure 5 and the switch is only opened by maintaining a closwise rotation of the rocker. The lower end of the spring 94 surrounds a projecting stud 96 on a horizontally extending plate 98 which is supported by the pillars 66. The plate 98 is incorporated when the switch is to be used in environments such as washing machines in order to protect the contacts from splashes of water.

Figure 6 illustrates a third embodiment incorporating a pair of contact plates 90B and 91 B together with a bridging piece 60B of the same form as in the previous two embodiments and which is actuated by means of a coil spring 56B carried in a counter-bore 52B of a rocker member 102 which rotates about a pivot 104 between two positions limited by engagement of the ends of arms 106 of the rocker with housing shoulders 84B. The housing 1 0B in this case has a cap 108 of generally top-hat form having an upper aperture 110 which receives a plunger 112. Mounted within a bore 114 of the plunger is a tapered pin 116 which is biased to an upper position by means of a coil spring 118.

Depression of the plunger 112 causes the lower end 120 of the pin 116 to slide down one or other of two sloping surfaces 122 on the upper side of the rocker 102 to cause rotation of the rocker from one position to the other. In this way the switch constitutes a push-push switch.

The switch shown in Figures 7 to 15 incorporates a housing 200 which is generally similar to the housing of the first embodiment of Figures 1 to 4. Mounted in the housing 200 is a rocker 201. The base of the housing has extending through it two metallic plates 202 and 203 and may optionally have a further plate 204 shown in dotted lines if the switch is to be of a changeover type. These plates pass through vertical apertures formed in the housing as with previous embodiments. It will be observed in this embodiment that each of the plates projects at its upper end into a space 206 within the housing 200. In this embodiment the plates project upwards to the same extent.

The rocker 201 has a central stem 208, the lower end of which has a counter bore 209 in which is mounted a coil spring 210. It is to be observed that the spring has minimum working clearance in the bore 209 and the last 2 to 3 coils of the spring 210 normally project below the lower end of the stem 208.

Figure 9 to 12 illustrate the particular form of a bridging piece 220 incorporated in this embodiment and which is made of bronze or copper. The bridging piece is again of shallow V form having two limbs 222 and 224, the upper faces of which, in this embodiment, subtend at an angle between them of approximately 1 soy. The main portions 226 and 227 are parallel whilst end portions 229 and 230 are formed with a shallow transverse curve as shown in Figure 12.

Struck out from the central portion of bridging piece 220 is a vertically upstanding tab 234. The lower part of the tab has substantially vertical sides 236 while the upper part of the tab 234 has inclined faces 238 merging with a rounded top 240. Also struck out from the body of the bridging piece 220 on each side of the tab 234 is an inverted V shaped fulcrum 244, the apex 246 of the fulcrum in each case lying on a medial line through the centre of the bridging piece 220.

Referring to Figures 7 and 15, the bridging piece 220 has two operative positions shown one in each figure. In Figure 7, the bridging piece bridges the upper ends of the plates 202 and 203. In the other of the operative positions shown in Figure 15, the bridging piece bridges the upper ends of the plates 203 and 204 (where the plate 204 is included).

The lower coil of the spring 210, which is cut as shown in Figure 7, is received as a firm fit around the vertical faces 236 of the tab 234 and the coil also rests on the apex 246 of the inverted V shaped fulcrum 244. It is to be observed by making a comparison between this embodiment and first embodiment, that the lower end of the spring 210 is engaging the apex 246 at a point nearer the bridging piece than in the case of the first embodiment. As a result of this different positioning of the engagement of the spring with the bridging piece, the movement of the rocker 201 and the spring 210 to the position shown in Figure 13 initially produces a translatory movement of the bridging piece 220 leftwards in Figure 13 whilst still maintaining contact with the plates 202 and 203. This is in contrast to the first embodiment where the first movement of the bridging piece was essentially a rotary movement. Figure 13 shows the position of the bridging piece at the limit of its initial translatory movement to the left and just before it will separate from the plate 202 by means of an anticlockwise rotary movement. It is thus to be observed that the bridging piece will separate from the plate 202 at a region 250 of the bridging piece 220 which is displaced from the region 252 shown in Figure 7 where contact is normally maintained during use of the switch after contact has been made. The virtue of this embodiment is that the arcing caused at the point of separation of the bridging piece 220 from the plate 202 is at a different region of the bridging piece than at which contact is normally made during use. As will be seen, the region 250 is also a different region from that at which contact is made during a reverse movement.

Referring to Figure 14, this shows a further position of the bridging piece 220 at which time the rocker is symmetrically positioned and the bridging piece is symmetrically disposed about the centre plate 203. Thus comparing Figures 13 and 14, it will be seen that there has been a combined rotary and leftward translatory movement of the bridging piece between these two figures. Referring to Figure 15, it will be seen that between Figures 14 and 15 the movement is essentially a rotary movement of the bridging piece 220 and that contact will be made, where a plate 204 is included at a region 254 near the end of the limb of the bridging piece. Thereafter, the continued rocking movement of the rocker will shift the bridging piece laterally until it attains a position which is a mirror image of the position shown in Figure 7. At this time, the end 256 of the bridging piece abuts the wall of the housing 200.

It is found with this embodiment, apart from the distribution of the regions of making, breaking and normal operation of the bridging piece that the provision of a fairly sharp falcrum for the end of the spring provides for cleaner and more consistent operation of the switch as a whole.

The fact that the coil spring is a tight fit on the tag 234 enables the bridging piece to be fitted onto an inverted rocker-spring assembly without fear of falling off before final insertion into the body which is presented upside down and pressed over the rocker-spring-bridging piece assembly. Furthermore, with the embodiment, of Figure 15 contact between the tag 234 and the spring is avoided and the force of the spring acting on the bridging piece now occurs essentially at the fulcrum points provided on the inverted V shaped fulcrum 244.

WHAT WE CLAIM IS:

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. to the housing of the first embodiment of Figures 1 to 4. Mounted in the housing 200 is a rocker 201. The base of the housing has extending through it two metallic plates 202 and 203 and may optionally have a further plate 204 shown in dotted lines if the switch is to be of a changeover type. These plates pass through vertical apertures formed in the housing as with previous embodiments. It will be observed in this embodiment that each of the plates projects at its upper end into a space 206 within the housing 200. In this embodiment the plates project upwards to the same extent. The rocker 201 has a central stem 208, the lower end of which has a counter bore 209 in which is mounted a coil spring 210. It is to be observed that the spring has minimum working clearance in the bore 209 and the last 2 to 3 coils of the spring 210 normally project below the lower end of the stem 208. Figure 9 to 12 illustrate the particular form of a bridging piece 220 incorporated in this embodiment and which is made of bronze or copper. The bridging piece is again of shallow V form having two limbs 222 and 224, the upper faces of which, in this embodiment, subtend at an angle between them of approximately 1 soy. The main portions 226 and 227 are parallel whilst end portions 229 and 230 are formed with a shallow transverse curve as shown in Figure 12. Struck out from the central portion of bridging piece 220 is a vertically upstanding tab 234. The lower part of the tab has substantially vertical sides 236 while the upper part of the tab 234 has inclined faces 238 merging with a rounded top 240. Also struck out from the body of the bridging piece 220 on each side of the tab 234 is an inverted V shaped fulcrum 244, the apex 246 of the fulcrum in each case lying on a medial line through the centre of the bridging piece 220. Referring to Figures 7 and 15, the bridging piece 220 has two operative positions shown one in each figure. In Figure 7, the bridging piece bridges the upper ends of the plates 202 and 203. In the other of the operative positions shown in Figure 15, the bridging piece bridges the upper ends of the plates 203 and 204 (where the plate 204 is included). The lower coil of the spring 210, which is cut as shown in Figure 7, is received as a firm fit around the vertical faces 236 of the tab 234 and the coil also rests on the apex 246 of the inverted V shaped fulcrum 244. It is to be observed by making a comparison between this embodiment and first embodiment, that the lower end of the spring 210 is engaging the apex 246 at a point nearer the bridging piece than in the case of the first embodiment. As a result of this different positioning of the engagement of the spring with the bridging piece, the movement of the rocker 201 and the spring 210 to the position shown in Figure 13 initially produces a translatory movement of the bridging piece 220 leftwards in Figure 13 whilst still maintaining contact with the plates 202 and 203. This is in contrast to the first embodiment where the first movement of the bridging piece was essentially a rotary movement. Figure 13 shows the position of the bridging piece at the limit of its initial translatory movement to the left and just before it will separate from the plate 202 by means of an anticlockwise rotary movement. It is thus to be observed that the bridging piece will separate from the plate 202 at a region 250 of the bridging piece 220 which is displaced from the region 252 shown in Figure 7 where contact is normally maintained during use of the switch after contact has been made. The virtue of this embodiment is that the arcing caused at the point of separation of the bridging piece 220 from the plate 202 is at a different region of the bridging piece than at which contact is normally made during use. As will be seen, the region 250 is also a different region from that at which contact is made during a reverse movement. Referring to Figure 14, this shows a further position of the bridging piece 220 at which time the rocker is symmetrically positioned and the bridging piece is symmetrically disposed about the centre plate 203. Thus comparing Figures 13 and 14, it will be seen that there has been a combined rotary and leftward translatory movement of the bridging piece between these two figures. Referring to Figure 15, it will be seen that between Figures 14 and 15 the movement is essentially a rotary movement of the bridging piece 220 and that contact will be made, where a plate 204 is included at a region 254 near the end of the limb of the bridging piece. Thereafter, the continued rocking movement of the rocker will shift the bridging piece laterally until it attains a position which is a mirror image of the position shown in Figure 7. At this time, the end 256 of the bridging piece abuts the wall of the housing 200. It is found with this embodiment, apart from the distribution of the regions of making, breaking and normal operation of the bridging piece that the provision of a fairly sharp falcrum for the end of the spring provides for cleaner and more consistent operation of the switch as a whole. The fact that the coil spring is a tight fit on the tag 234 enables the bridging piece to be fitted onto an inverted rocker-spring assembly without fear of falling off before final insertion into the body which is presented upside down and pressed over the rocker-spring-bridging piece assembly. Furthermore, with the embodiment, of Figure 15 contact between the tag 234 and the spring is avoided and the force of the spring acting on the bridging piece now occurs essentially at the fulcrum points provided on the inverted V shaped fulcrum 244. WHAT WE CLAIM IS:

1. An electric switch including at least two contact elements, a bridging piece of shallow Vform the limbs of which on one side subtend an angle of less than 1 80o facing away from the contact elements whilst regions of the opposite surface of the bridging piece contact two of the contact elements in an operative position of the bridging piece, and an actuator to move the bridging piece to and from its operative position, the actuator including a rocker member which is interconnected with the bridging piece by means of a coil spring one end of which is carried by the rocker member, the other end of the spring directly engaging an integral part of the bridging piece.

2. A switch as claimed in Claim 1 in which the integral part has a pair of vertical faces and the angles subtended between these faces and the limbs of the V of the bridging piece are sub stantially identical.

3. An electric switch as claimed in Claim 1 or Claim 2 in which the bridging piece is manufactured from sheet metal and the integral part comprises a struckout portion of the sheet metal.

4. An electric switch as claimed in any one of the preceding Claims in which the integral part is of generally inverted T-shape, the head of the T being disposed at the centre of the one side of the bridging piece and the head affording, on each side of the stem of the T, a substantially horizontal surface upon which a portion of the spring bears.

5. An electric switch as claimed in Claim 1 in which the actuator is arranged to cause separation of the bridging piece from one contact element by a rotary movement of the bridging piece and the separation is followed by a combined translatory and rotary movement of the bridging piece.

6. An electric switch as claimed in Claim 5 in which the rotary movement is preceded by a translatory movement.

7. An electric switch as claimed in Claim 5 or Claim 6 in which the rotary movement is accompanied by a translatory movement.

8. An electric switch as claimed in Claim 5 in which the actuator is arranged to cause closing contact of the bridging piece with the one contact element by a rotary movement of the bridging piece followed by a translatory sliding movement of the bridging piece with respect to the one contact element whilst in engagement with the one contact element.

9. An electric switch as claimed in Claim 8 in which the closing contact is accompanied by a translatory movement.

10. An electric switch as claimed in any one of Claims 1 to 4 in which one contact element in an operative position of the bridging piece contacts the opposite side of the bridging piece adjacent one end of one limb, the other contact element contacting the same side of the other limb at a contact point positioned a short distance from the apex of the V, initial movement of the bridging piece by the actuator causing translatory movement of the bridging piece to bring a different contact point, nearer the V, into contact with the other contact element, further movement of the actuator causing movement of the bridging piece about said different contact point to separate the bridging piece from the one contact element, the bridging piece then sliding in a direction away from the one contact element until the other contact element is in engagement with the apex of the V, the actuator then causing further rotary movement of the bridging piece further away from the one contact element.

11. An electric switch as claimed in Claim 10 in which said further rotary movement of the bridging piece continues until the other limb of the bridging piece contacts an abutment (which may be another contact element) whereafter the actuator causes sliding movement of the bridging piece with respect to that abutment.

12. An electric switch substantially as specifically described herein with reference to Figures 1 to 5; or Figure 6; or Figures 7 to 15 of the accompany drawings.