GB2331342A - Screw adjustment lock mechanism - Google Patents

Abstract

A screw arrangement comprising a female threaded member 13 and a mating male threaded member 12 permitting adjustment of the relative axial position of the members within an operating range has a locking element selectively and axially engageable in the members in any of a number of independent incremental angular positions. In the preferred embodiment, the male member has a socket (36, figure 6 not shown) with a hexagonal cross-section and the locking element has a projection (41, figure 8 not shown) with a similar hexagonal cross-section such that it can be axially inserted into the socket at a particular relative angular position. The locking element is also provided with a plurality of longitudinal splines (55) and the female member is provided with a plurality of longitudinal parallel grooves (25, figure 3 not shown) to receive the splines and to allow the locking element to be moved axially with respect to the second member. A retaining member 15 is arranged such that the axial position of the locking element may be fixed with respect to the members, and a knob 14 facilitates disengagement of the locking element.

Description

SCREW ADJUSTMENT LOCK MECHANISM 2331342

The present invention relates generally to the field of mechanisms for locking the adjustment of threaded members, and, more particularly, to an improved device for locking the threaded adjustment mechanisms of instrumentation devices, such as position transducers.

A variety of methods have been used in the past to secure threaded connections, particularly in situations where the threaded connection serves as an adjustment mechanism. Threaded adjustments are commonly used for the precise positioning of instrumentation devices. A typical example is found in a position transducer known as a linear variable differential transformer (LVDT). This type of transducer is used most often to determine the position or velocity of a first body with respect to a second body. The LVDT is provided with a magnetically permeable core which is connected to a first body and an electrical coil which is connected to the second body. The position of the core with respect to the electrical coil results in the production of an electrical signal which indicates the position or velocity of the first body with respect to the second body. Such transducers are often used in hydraulic servoactuators or other devices requiring accurate position feedback.

When used in connection with hydraulic servoactuators, the core is concentrically received within the electrical coil, and is attached by means of an extension rod to the piston of the hydraulic actuator. Positioning of the core is critical so that an electrical center, or "null" position of the actuator, may be determined. This is necessary for accurate dynamic control of the servoactuator system. Prior to operation of the servoactuator, the transducer core is precisely positioned by adjusting a threaded connection between the extension rod and the actuator piston such that the transducer is nulled at a desired actuation position. It is critical that this adjustment not shift or otherwise vary in operation on account of vibration, shock or thermal effects, as such movement would result in erroneous position measurements and potential loss of accurate system control. Thus, the threaded adjustment must be locked.

In the past. jam nuts. or lock nuts. have been used to lock the LVDT threaded adjustment. However. jam nuts have many problems associated with them. The nuts may cause the adjustment to shift as they are tightened, and hence disturb the precise position of the transducer core. In addition, lock nuts may loosen with time or require special tools for access and adjustment. As such, they are considered unreliable in the trade.

Other methods have been proposed to securely fasten threaded connections. One such method is the use of a mechanical friction device in conjunction with a threaded member, such a nut. Such systems typically use nylon or some other type of deformable insert mounted on either the male or female screw thread. The insert produces a resulting friction when threaded to a mating part, which opposes motion caused by vibration or shock.

Similar devices include a locking insert, such as those produced under the trademark "Helicoi10" manufactured by Ernhart Fastening Teknologies. The locking insert is used to lock threaded connections by the use of a non-standard thread insert with a deformable member which creates mechanical interference between the male and female threads of a threaded connection. Locking inserts, while easy to use, are subject to certain problems. For instance, deformable members such as the nylon insert may wear out with use such that threads may become loose and adjustments may vary. This is especially a problem when numerous adjustments may be made. In addition, because locking inserts are in fact a separate element, situations may arise where an entire insert itself becomes loose, thus compromising the adjustment of the threaded connection.

Other methods for locking threaded connections include the use of liquid locking compounds. Such compounds are typically applied to the threads of the members of a threaded assembly, and serve as a bonding agent once the threaded connection is made. The disadvantage of such fastening techniques is that adjustments may not be readily made without destroying the bonded connection. In addition, use of such compounds often requires extremely clean threaded surfaces typically not found under field conditions.

A variety of mechanical methods exist for locking threaded connections. Examples of these devices are representatively disclosed in U.S. Patent Nos. 2,352,585, 3,436,973, 3,640,139 and 752,524. While these patents disclose methods for locking threaded connections, none disclose a mechanism for achieving precise axial posation adjustments through the use of a locking element where axial adjustment is a function of two independent features, and the locking element controls the magnitude of the minimum angular adjustment as a function of a first and second number of angular positions.

The present invention provides an improved position adjustment mechanism that broadly comprises a first member provided with a male thread, a second member provided with a female thread, said threads being configured and arranged so as to be in mating engagement to selectively allow adjustment of the relative axial position of the first member with respect to the second member within an operating range, and a locking element for preventing rotation of the first member with respect to the second member, said locking element being selectively and axially engageable with the first member in any of a first number of incremental angular positions and being selectively and independently axially engageable with the second member in any of a second number of incremental angular positions. This arrangement enables the members to be locked at any of a third number of incremental angular positions, the magnitude of the minimum angular increment of the third number of incremental angular positions being a function of the first and second number of incremental angular positions.

The first member is preferably provided with a socket having a polygonal transverse cross-section, and the locking element is provided with a projection having a transverse crosssection that corresponds to the polygonal cross-section of the socket so that the projection of the locking element may be axially inserted into the socket of the first member when the locking element is in an appropriate angular position relative to the first member. In this case the first number of incremental angular positions is a function of the number of sides of the polygonal cross-section of the socket.

The locking element is preferably also provided with a plurality of longitudinal splines, and the second member is provided with a corresponding plurality of longitudinal grooves having a geometry complementary to the splines to allow the longitudinal splines to be received within the longitudinal grooves and the locking element to be moved axially relative to the second member, the second number of incremental angular positions being a function of the number of longitudinal splines.

At the point the projection of the locking element engages the socket of the first member, and the splines of the locking element engage the grooves of the second member, the first member is locked with respect to the second member so as to prevent any motion between the members.

In the preferred embodiment, the first number of incremental angular positions is six and the second number of incremental angular positions is seven. The first number is thus equivalent to the number of surfaces of the polygonal cross-section, and the second number is equivalent to the number of splines. Also in the preferred embodiment, either of the first or second number is an even number, and the other number is an odd number. In this situation, the magnitude of the minimum angular increment of the third number of incremental angular positions at which the first and second members may be locked is in an inverse proportion to the product of the first and second numbers. In the preferred embodiment, the third number of incremental angular positions is 42, which is equal to the product of the first and second numbers.

The position adjustment mechanism preferably further includes a retaining member operatively arranged such that the axial position of the locking element may be substantially fixed with respect to both first and second members. To accommodate the retaining member, the locking element may have a first annular groove extending radially inwardly and the second member may have a second annular groove extending radially outwardly, the retaining member being disposed between the groove in the locking element and the groove in the second member such that the axial position of the locking element is substantially fixed with respect to the first and second members.

In certain embodiments, the retaining member has an outer cam surface to displace the retaining member inwardly as the locking element is inserted into the second member. In the preferred embodiment, the retaining member is in the form of a split toroidal ring.

The projection of the locking element is of substantially solid construction in the preferred embodiment. In addition, the locking element preferably includes a knob positioned opposite the projection to facilitate disengagement of the locking element from the members.

Accordingly, the present invention provides an improved position adjustment mechanism which may be axially and angularly locked to prevent relative movement between two members in threaded engagement, which is not susceptible to vibration, shock, or thermal expansion, and which may be precisely and threadably adjusted and locked in a particular desired position.

The position adjustment mechanism is particularly suitable for securing and adjusting a position transducer, such as a linear variable differential transformer (LVDT), in connection with a hydraulic servoactuator.

A further advantage of the improved position adjustment mechanism of the invention -5is that it is easily re-adjusted during operation, is readily modifiable, economical to manufacture, reliable, rugged, and may be utilized with a variety of servoactuator and servoyalve designs.

A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Fig. 1 is a fragmentary cross-sectional perspective view showing the screw adjustment lock mechanism, elongated along axis x-x; Fig. 2 is a fragmentary unhatched vertical view, partly in section and partly in elevation, of the improved position adjustment mechanism, showing the assembly of the various parts and components; Fig. 3 is a vertical sectional view of the second member shown in Fig. 2; Fig. 4 is a right end elevation of the second member shown in Fig. 3; Fig. 5 is a vertical view of the first member shown in Fig. 2; Fig. 6 is a vertical sectional view of the first member shown in Fig. 5; Fig. 7 is a right end elevation of the first member shown in Fig. 5; Fig. 8 is a vertical view of the locking element and retaining member shown in Fig. 2; Fig. 9 is a vertical sectional view of the locking element and retaining member shown in Fig. 8; Fig. 10 is a right end elevation of the locking element and retaining member shown in Fig. 8.

At the outset, it should be clearly understood that like reference numerals are intended to identify the same structural elements, portions or surfaces consistently throughout the several drawing figures, as such elements. portions or surfaces may be further described or explained by the entire written specification, of which this detailed description is an integral part. Unless otherwise indicated, the drawings are intended to be read (e.g.. cross-hatching. arrangement of parts, proportion, degree. etc.) together with the specification. and are io be considered a portion of the entire written description of this invention. As used in the following description. the terms "horizontal". vertical". "left". "right". "up" and "down", as well as adjectival and adverbial derivatives thereof (e.g.. "horizontally- rightwardly", "upwardly", etc.), simply refer to the orientation of the illustrated structure as the particular drawing figure faces the reader. Similarly, the terms "inwardly" and "outwardly" generally refer to the orientation of a surface relative to its axis of elongation, or axis of rotation, as appropriate.

The present invention is particularly intended for use in connection with the precise adjustments necessary for positioning various instruments, such as transducers. A typical transducer which requires precise adjustment is the linear variable differential transformer (LVDT). These transducers comprise two parts, namely a core, and an electrical sensing coil. The coil is concentric with the core, and the core is received within the coil to measure the position of a first body with respect to a second body. In the case of the LVDT, the coil is often attached to the body of a hydraulic actuator, and the core is often attached to the piston of the actuator. Hence, the position of the actuator piston with respect to the actuator body may be determined and controlled with great accuracy through feedback control using the output of the LVDT. In practice, the LVDT core is secured to the actuator piston through the use of an extension rod. The extension rod typically contains threads at both ends, with one end being threaded into the core, and the other end being threaded into a reference part, namely the piston.

Referring now to the drawings, and more particularly, to Figs. 1-2 thereof, this invention provides an improved screw adjustment lock mechanism, of which the presently preferred embodiment is generally indicated at 11. The screw adjustment lock mechanism is shown as broadly including: a first member 12, horizontal ly-elongated along axis x-x and having a portion of its outer surface configured as a male thread; a second member 13, horizontal ly-elongated along axis x-x and having a female threaded inner bore in mating engagement with first member 12; a locking element 14 arranged to coaxially engage first and second members 12, 13 so as to prevent rotation of first member 12 with respect to second member 13 thereby locking members 12, 13 both rotationally and translationally; and a retaining member 15 disposed between locking element 14 and second member 13 so as to prevent axial movement of locking element 14 with respect to members 12, 13.

Referring now to Fig. 2, first member 12 may be viewed as being representative of the aforementioned extension rod, and second member 13 may be viewed as being representative of the reference part, i.e. the actuator piston. Hence, first member 12 is adjusted with respect to second member 13 and the adjustment is locked by engagement of locking member 14 with first and second members 12, 13.

As best shown in Fig. 3, second member 13 is a special]v-configured member. axial ly-elongated along axis x-x. Second member 13 has an outer surface that is sequentially bounded by leftwardly-facing vertical annular surface 16. outwardly-facing horizontal cylin- drical surface 18, and rightward ly-faci rig vertical annular surface 19. Second member 13 has a stepped axial through-bore, elongated along axis x- x, that is sequentially bounded, in pertinent part, by an inwardly-facing cylindrical horizontal threaded surface 20 extending rightwardly from the inner margin of annular surface 16, a rightwardly-facing vertical annular surface 24, a leftwardly and inwardly-facing frusto-conical annular surface 23, an inwardly-facing horizontal cylindrical surface 21, and inwardly- and rightwardly-facing frustoconical surface 26 continuing rightwardly therefrom to join the inner margin of annular surface 19. A multi-toothed female spline is formed in the end bore 21, creating a plurality of longitudinal parallel axial grooves, severally indicated at 25, which extend radially into second member 13 from bore surface 21. In the preferred embodiment, seven longitudinal grooves 25 are provided and are configured to receive seven corresponding splines (not shown). An annular groove 22 is counterbored into second member 13, to a diameter best shown in Fig. 4 equal to that of the spline teeth, to receive and accommodate retaining member 15 (not shown).

Referring now to Figs. 5-7, first member 12 is shown as having a left end portion 34 connected to a transducer core (not shown), and a right end portion 35 provided with a male thread. First member 12 is shown as being a stepped cylindrical member. axially elongated axis x-x, and having an outwardly-facing horizontal cylindrical surface 30 beginning at left end 34 and continuing rightwardly therefrom, a leftwardly-facing vertical annular surface 31, an outwardly- and leftwardly-facing frusto-conical surface 37, an outwardly-facing horizontal cylindrical threaded surface 32, an outwardly- and rightwardlyfacing frusto-conical surface 38, and a rightwardly-facing vertical circular surface 33. First member 12 is provided with an axial hexagonal female socket 36 which extends inwardly from surface 33 into right end portion 35 to a depth substantially equal to right end 35.

As best seen in Fig. 7, socket 36 has six sides and is of a regular planar crosssection. Socket 36 is provided with a regular hexagonal transverse cross section throughout.

Referring now to Figs. 8-10, locking element 14 is a specially-configured member, horizontally-elongated along axis x-x, and having an outer surface bounded by, in pertinent part, a leftward ly-faci rig vertical hexagonal surface 41, a plurality of outwardlyfacing horizontal planar surfaces. severally indicated at 53, a leftwardly-facing vertical surface 49, an outwardly-facing horizontal cylindrical surface 48, an outwardly- facing horizontal cylindrical surface 46, a rightward ly-faci rig vertical annular surface 45, an outwardlyfacing horizontal cylindrical surface 51, a leftwardly-and outwardly-facing frusto-conical surface 47. an outwardly-facing horizontal cylindrical surface 44, an outwardly- and rightwardly-facing frusto-conical surface 43, and a rightward ly- facing vertical circular surface 42. An annular groove 50 extends radially inwardly from surface 48 into locking element 14. Surfaces 53 are arranged in a fashion to create a regular hexagonal projection 40 at the left end of locking element 14. Projection 40 has a cross-section substantially similar to that of socket 36. Surfaces 47, 44, 43, and 42 generally define a knob 54 located at the right end of locking element 14.

Cylindrical surfaces 46, 48 are provided with a plurality of 1 ' ongitudinal spl ines, severally indicated at 55, which extend the length of surfaces 46, 48, parallel to axis x-x and in equal circumferential placement. As best seen in Fig. 10, seven longitudinal splines 55 are provided. Splines 55 are separated by a plurality of grooves, severally indi cated at 52, extending radially and inwardly into locking element 14 from surfaces 46, 48.

The depth of grooves 52 is approximately equal to the depth of annular groove 50.

As best seen in Figs. 8-10, retaining member 15 is a toroidal-shaped ring. Retaining member 15 has a radial split and possesses spring like characteristics such that its at-rest outer diameter is greater than the diameter of cylindrical surface 46. This is best seen in Fig. 9.

Adverting to Fig. 2, it is seen that longitudinal splines 55 of locking element 14 are so configured and arranged so as to engage and mate with longitudinal grooves 25 of second member 13. In this manner, locking element 14 may be axially inserted into second member 13, and rotation between element 14 and second member 13 is prohibited.

Operation of the Invention The present invention serves to lock the threaded engagement of first member 12 with second member 13 by preventing rotation between the members. This locking may be done at a number of different incremental angular positions. Referring again to Fig. 2, it is seen that first member 12 is coaxially threaded into second member 13. Projection 40 of locking element 14 extends longitudinally and axially into socket 36 of first member 12. The hexagonal transverse cross-section of projection 40 is similar to the hexagonal transverse cross-section of socket 36, thereby serving to completely engage socket 36 and prevent rotation of locking element 14 with respect to first member 12. This engagement is similar to that achieved by the use of an allen-type wrench. Locking element 14 may be further inserted into socket 36 until longitudinal splines 55 of locking element 14 then engage longitudinal grooves 25 of second member 13.

In operation, adjustment of first and second members 12, 13 is performed as follows. First member 12 is initially adjusted to a desired axial position with respect to second member 13. This may. for instance. correspond to a "nulV position of a hydraulic actuator. The amount of rotational motion required is a function of the thread pitch of the mating threads of members12, 13. Projection 40 of locking element 14 can engage socket 36 before longitudinal splines 55 engage longitudinal grooves 25 due to the relative length of projection 40 with respect to the position of grooves 25 and splines 55. Thus, locking element 14 may be partially inserted into second member 13 so as to engage socket 36 of first member 12, effectively enabling it to be used as a wrench to turn member 12. Knob 54, which may be knurled or hexagonally shaped, can be used to facilitate this function.

After the desired adjustment is achieved, male spline 55 on the locking element must be engaged with female spline grooves 25 in member 13 to provide a positive lock. Since there are six possible positions for inserting projection 40 into socket 36 in the preferred embodiment, it is possible to observe which of the six possible engagements should be used to bring splines 55 most nearly in alignment with grooves 25 with the least amount of angular displacement of member 12 with respect to member 13. Once such determination is made, projection 40 is inserted into socket 36 at the appropriate position and first member 12 is rotated slightly with respect to second member 13 until splines 55 are aligned with grooves 25. By using this method, the desired angular, and hence axial, position of first member 12 with respect to second member 13 is most nearly maintained during the locking process.

As splines 55 are inserted into longitudinal grooves 25, the outer marginal circumference of retaining member 15 engages surface 26 of second member 13. As locking element 14 is further inserted into socket 36, the outer surface of retaining member 15 acts as a cam surface and is compressed inwardly such that it collapses inwardly to engage cylindrical surface 21. Locking element 14 continues to be inserted into socket 36 until the point retaining member 15 is axially aligned with annular groove 22, at which time retaining member 15 springs radially and outwardly to engage groove 22. Thus, retaining member 15 serves as a retaining ring to maintain the axial position of locking element 14 with respect to member 13.

In the event it becomes necessary to further adjust first member 12 with respect to second member 13, knob 54 may be used to facilitate disengagement of locking element 14 from first and second members 12, 13. By axially pulling locking element 14 rightwardly out of second member 13, retaining member 15 is compressed within groove 50 and slides axially along surface 21 to allow locking element 14 to be withdrawn. Locking element 14 is withdrawn until longitudinal splines 55 are no longer engaged with longitudinal grooves 25. First member 12 may then be rotated about axis x-x with respect to second member 13 to achieve a new axial position. and locking element 14 may then be reinserted at a different angular position.

The present invention allows first member 12 to be selectively and angularly adjusted with respect to second member 13 to attain a particular axial position within a given operating range. In the preferred embodiment, locking element 14 is selectively and axially engageable with first member 12 in a first number of incremental angular positions, namely six, and is selectively and independently axially engageable with second member 13 in a second number of incremental angular positions, namely seven. Thus, members 12 and 13 may be locked in a third number of incremental angular positions. The magnitude of the minimum angular increment of the third number of incremental angular positions where locking may occur is generally a function of the first and second numbers Of independent incremental angular positions. In this instance, the magnitude of the minimum angular increment at which the first and second members may be locked is in an inverse proportion to the product of the first number (six) and the second number (seven). Hence, a third number, equal to 42, of possible angular engagements, approximately 8.6o apart, is provided by the product of six and seven independent positions divided into 360o. The function will be the product of the first and second numbers only when one of the first or second numbers is even and the other number is odd. Hence, the instant invention serves as a Overnier" type of adjustment, allowing very fine axial and angular adjustments to be performed.

Modifications The present invention contemplates that many modifications may be made. The particular materials of which the various body parts and components are formed are not deemed critical, and may be readily varied.

Further, the various parts and components may take the form shown, or may have some other form, as desired. In addition, while a particular embodiment of a locking element has been shown and described, numerous variations thereof may be implemented to selectively engage the first and second members as described above.

For instance, the first and second members are currently shown as having male and female threads respectively. This could be easily modified such that the first member has female threads and the second member has male threads. Further, while the present invention discloses an axial locking element with axial engagement means, such means could easily extend radially from either the First or second members.

It is also not essential that retaining member 15 be a separate element. For instance, locking element 14 could be designed in a "clothespin" type arrangement whereby protrusion 40 is provided with a number of fingers extending radially outwardly from the locking element in the direction of (he socket. Each Finger could be provided with a cam surface on its distal marginal end portion to displace the associated fineer radially and inwardly as the fingers are inserted into the socket. The first member could be provided with a recess extending radially into the member wherein a finger of the locking element could engage the recess when the locking element is in a particular angular position with respect to the first member. Hence, a variety of different methods for retaining the locking element axially with respect to first and second members may be used without departing from the spirit of the instant invention.

Similarly, the geometry and configuration of the locking element may vary so as to facilitate the locking of the first member to the second member. The particular configuration of such locking element may be varied by any person having ordinary skill in the art. For instance, while the instant invention discloses a locking element which has a protrusion 40 engaging first member 12, one skilled in the art could easily envision an embodiment wherein protrusion 40 engages second member 13.

Another embodiment for locking element 14 would be a functionally equivalent locking means operating on theface of either the first or second element. For example, a mating "poker-chip" pattern may be provided on the first member, and a complimentary.poker-chip" pattern may be provided on the locking element. Further, the detent mechanism holdingthe locking element in engagement with both the first and second members could act between the first member and locking element or between the second member and locking element.

In addition, the current invention is provided with a locking element having six potential engagement positions with the first member and seven potential engagement positions with the second member. These numbers may be varied to achieve much finer resolutions of the magnitude of the axial position of the first member with respect to the second member. For instance, the numbers may be increased, or may be varied such that the first and second numbers are both odd or both even, or are equal to one another. In addition, where coarser resolution is required, the first and second numbers may be varied to, say, two and seven positions.

Therefore, while the presently-preferred form of the screw adjustment lock mechanism has been shown and described, and several modifications thereof discussed, persons skilled in this art will readily appreciate that various additional changes and modifications may be made without departing from the scope of the invention, as defined and differentiated by the following claims.

Claims (12)

Claims

1. In a position adjustment mechanism having a first member provided with a male thread and having a second member provided with a female thread, said threads being in mating engagement to selectively allow adjustment of the relative axial position of said members within an operating range, the improvement which comprises:

a locking element selectively and axially engageable with said first member in any of a first number. of incremental angular positions and selectively and independently axially engageable with said second member in any of a second number of incremental angular positions such that said members may be locked at any of a third number of incremental angular positions, the magnitude of the minimum angular increment of said third number of incremental angular positions being a function of said first and second numbers.

2. The improvement as set forth in claim 1 wherein said first member has a sock et provided with a polygonal transverse cross-section, and wherein said locking element has a projection having a transverse cross-section that simulates said polygonal cross-section such that said projection may be axially inserted into said socket when said locking element is in a particular angular position relative to said first member, and wherein said first num ber is a function of the number of sides of said polygonal cross-section.

The improvement as set forth in claim 1 wherein one of said locking element and said second member is provided with a plurality of longitudinal splines, and wherein the other of said locking element and said second member is provided with a plurality of longitudinal grooves to receive said spfines, and to allow said locking element to be moved axially relative to said second member, and wherein said second number is a function of the number of said longitudinal splines.

4. The improvement as set forth in claim 1 wherein said first number is six and said second number is seven.

5. The improvement as set forth in claim 1 wherein the magnitude of the mini mum angular Increment of said third number of Incremental angular positions is in an in verse proportion to the product of said First and second numbers and wherein either one of said First or second numbers is even and the other of said First or second numbers is odd.

6. The improvement as set forth in claim 1 and further comprising a retaining member operatively arranged such that the axial position of said locking element may be substantially fixed with respect to either of said members.

7. The improvement as set forth in claim 6 wherein said locking element has a first groove extending radially inwardly, and wherein said second member has a second groove extending radially outwardly and wherein said retaining member is disposed between said first groove of said locking element and said second groove of said second member.

8. The improvement as set forth in claim 6 wherein said retaining member has an outer cam surface to displace said retaining member inwardly as said locking element is inserted into said second member.

9. The improvement as set forth in claim 6 wherein said retaining member is a split toroidal ring.

10. The improvement as set forth in claim 2 wherein said projection is of substantially solid construction.

11. The improvement as set forth in claim 2 wherein said locking element includes a knob opposite said projection for facilitating disengagement of said locking element from said members.

12. A position adjustment mechanism according to clairn 1, substantially as described with reference to the accompanying drawings.