IMPROVED SPIRIT-LEVEL INCLINOMETER
This invention relates to devices for measuring inclina¬ tion or level and, more particularly, to such devices of the type that employ liquids in transparent tubes. That is, this invention relates to inclinometers of the Nspirit level1 type.
BACKGROUND TO THE INVENTION
Spirit levels which use bubbles in curved transparent tubes are well known, as are inclinometers that measure the difference in level between two points by the use of a transparent liquid-filled tube connecting the two points. Similarly, it is well known to measure the inclination of a plane or the relative level of two points by the use of an extended ϋ-tube terminating in liquid containing tubes or vessels of diameters chosen to provide appropriate sensitivity. A variety of systems for obtaining electronic read-outs from such levels and inclinometers is also known, some of which allow level measurements and inclination readings to be recorded for later use.
However, while such electronically-fitted devices may function as levels with memories, they are complex and not well suited for use as carpenter's or bricklayer's hand levels.
It is also well known to make carpenter's or bricklayer's hand levels where the bubble tubes are incorporated in a rotatable sub-assembly with graduated angles. This allows the straight-edge of the level to be put in place and the sub-assembly rotated to bring the bubble into its central position. In this way, the inclination of the straight-edge is 'recorded' and the level can be removed without disturbing the setting. However, the sub- assembly is often difficult to adjust accurately when in use and it demands clear sight of the bubble as well as
the use of both hands. Also the sub-assembly is prone to stick under field conditions where water and cement are in use.
OBJECTIVE OF THE INVENTION
It is the objective of the present invention to provide a simple spirit level inclinometer which has a 'memory*; that is, which can retain or recall an angular setting.
OUTLINE OF THE INVENTION
The present invention is based upon the realisation that a ϋ-tube type of level indicator will retain its level setting provided a valve is included in the tube between the arms. When such an inclinometer is being offered to a surface, the valve is opened to let the liquid find its level; before it is removed from the surface, the valve is closed to prevent further exchange of liquid between the arms of the ϋ-tube; and, after it is removed, the earlier inclination of the level can be read - without much regard for the subsequent disposition of the level.
It is preferable, in accordance with the present inven¬ tion, to prevent the loss of liquid which might otherwise occur from an open U-tube, by forming a double ϋ-tube (that is, an 0-tube) and placing one valve between the arms of the tube at the bottom (to prevent exchange of liquid) and another at the top (to prevent exchange of air or gas between the arms). Such an 0-tube can be turned upside-down and operated in exactly the same way but without danger of liquid loss or the ingress of dirt.
It is also preferable, in accordance with the present invention, to arrange for the two valves of the single O- tube to be operated in unison from a single point. Moreover, and again non-essentially, the two interlinked valves of such a configuration can either be biased to
one (usually the closed) position, or they may be switchable between a stable open and a stable closed position.
The 0-tube may be of a generally rectangular shape (with straight arms or sides), of circular shape, or of a D- shape (ie with one straight arm and one semi-circular arm). Since use of straight arms has the advantage of compactness and use of circular arms or sides has the advantage of scale-linearity, the D-shape offers a useful compromise.
DESCRIPTION OF EXAMPLES
Having broadly portrayed the nature of the present invention, a number of particular examples or embodiments of the present invention will now be described by way of example and illustration only. In the following descrip¬ tion, reference will be made to the accompanying drawings in which:
Figure 1 is a front elevation of a settable spirit level formed in accordance with the present invention employing a single valve and a fluid container in the form of an open ϋ-tube;
Figure 1A is a cross-sectional end elevation of the inclinometer of Figure 1 taken on section A-A of Figure 1;
Figure 2 is a schematic front elevation of a settable inclinometer in which the fluid container is in the form of a closed an 0-tube of generally rectangular shape also employing a single valve;
Figure 3 is a schematic front elevation of a settable inclinometer having an 0-tube fluid container of generally circular shape and employing two valves;
Figure 4 is an exploded sectional elevation of a practical configuration of an inclinometer in which the side arms are linear and wherein two valves are employed which are operable in unison, but biased to the closed position;
Figure 5 is a front, part sectional elevation of an inclinometer having a D-shape fluid container incor¬ porating dual rotary valves;
Figure 5A is an sectional side elevation of the inclinometer of Figure 5 taken along section B-B of Figure 5;
Figure 6 iβ a partial front elevation (in part section) of an inclinometer like that of Figure 5 but incorporating dual slide valves;
Figure 7 is also a partial front elevation (in part section) of an inclinometer like that of Figure 5 but incorporating a tube valve;
The inclinometer of the embodiment of Figures 1 and 1A comprises a fluid container in from of an open ϋ-tube 10 mounted in a straight edge (which is formed from a length of aluminium I-section extrusion 12) so that its upper open ends 14 open out into the upper face 16 of extrusion 12 and are held in place by rubber bushes 17. The tube 10 is, of course, formed from transparent material such as glass or plastic. Slots 18 are cut in the web 20 of the I-extrusion 12 so that the two arms 22 of the ϋ-tube are visible from both sides. Graduations 24 are marked on the edges of slots 18 (on both sides of web 20) to signify angles of slope or the amount of rise or fall per unit length. A stop valve 26 is placed in the bottom run of the ϋ-tube 10 so as to be able to isolate or connect the liquid (21) in each arm 22 at will. Valve 26 and the
two halves of U-tube 10 are held in place by screws 28 which pass through lower face 30 of the straight-edge 12.
In use, a suitable liquid 21 is added to the U-tube 10 to bring the surface in each arm to the corresponding zero graduation when the straight edge is set level and the valve 26 is open. Either the upper face 16 or the lower face 30 of straight edge 12 is then offered up to the surface or line which needs to be checked for slope, the liquid 21 is allowed to come to its own level and valve 26 is closed to prevent further flow of liquid between arms 22. The straight edge is then removed to a con¬ venient place where the retained setting of the liquid 21 in the U-tube 10 may be read.
The embodiment of Figure 2 is substantially the same as that of Figure 1, except that the fluid container is in the form of a closed 0-tube 10a of generally rectangular shape. It is filled (prior to sealing) with the right amount of liquid 21, adjusted in the straight edge (not shown in Figure 2 or in subsequent Figures) so as to bring the liquid level in each arm to the corresponding zero or reference mark (23) and, then, fixed permanently in position. Again a single valve 26 is employed in the lower run (32) of the 0-tube 10a. The inclinometer of this embodiment is used exactly as described with respect to the embodiment of Figure 1 but, since the O-tube is sealed, it does not need to be cleaned or have its liquid level adjusted.
One disadvantage of the embodiments of Figures 1 and 2 is that some care must be taken when handling the level (after the valve has been closed) to ensure that liquid is not lost from the arms of the U-tube container 10 (Figure 1), or exchanged between the arms of the 0-tube container 10a (Figure 2) by transfer through the top run (34) of the tube. These embodiments also have the disad¬ vantages that the scale (for degrees of angle, say) will
not be linear and that the straight-edge must have a top and a bottom edge and must be offered up to the work with that orientation. Nevertheless, these inclinometers levels are simple and have practical value.
The embodiment of Figure 3 is substantially the same as that of Figure 2, having a tubular fluid container formed as an 0-tube 10b, except that the arms of the 0-tube are arcuate rather than linear and that a second valve 26a is provided in the upper run (34) of the 0-tube 10b - that is, opposite valve 26 in the lower run (32). These features remove the disadvantages mentioned in the preceding paragraph. However, as the two valves are not interlinked they must each be set manually in order to effect proper operation of the settable level.
Figure 4 shows an exploded cross-section of a practical arrangement of an inclinometer having a rectangular-form, 0-tube fluid-container with two valves operable in unison and biased to their closed positions. Here, the con¬ tainer is not a continuous tube of plastic or glass but is formed by two straight transparent side tubes 40a and 40b linked by an upper run comprising channels 42a and 42b formed in a moulded plastic end piece 44 and by a lower run comprising channels 46a and 46b formed in the lower end of a moulded centre section 48. However, channels 42a and 42b do not communicate directly with one another in end piece 44; nor do channels 46a and 46b communicate directly with one another in centre piece 48. Channels 42 can be connected by the movement of valve disc 50 and channels 46 can be interconnected by the movement of a second valve disc 52, as will be explained below.
The end section 44 is preferably moulded from plastics material to include sockets 54a and 54b for upper ends 56a and 56b of tubes 40a and 40b which interconnect with channels 42a and 42b. The other ends (58a and 58b) of
channels 42a and 42b open out into the lower face of end piece 44 and are normally blocked by valve disc 50 which is pressed against the lower face of end piece 44 by a spring 60. The valve disc 50 and spring 60 are housed in a recess 62 formed in the top of centre piece 48 so that the valve disc can be moved downwards (against the pressure of the spring) and away from and the lower face of end piece 44 to allow luid to low between channel ends 58a and 58b. This movement is effected by the action of an operating pin 63 which can be moved by finger pressure on a flexible membrane seal 64 fitted in the top face of end piece 44. To ensure that fluid does not leak from the 0-tube around pin 63, a compression seal 68 is compressed by a threaded plug 70 which is screwed into a threaded hole formed in the end piece 44 around pin 60.
A somewhat similar arrangement allows controlled com¬ munication between channels 46a and 46b which open out into the lower face of centre piece 48 through openings 72a and 72b. These openings are normally blocked by valve disc 52 under pressure of a compression spring 74, valve disc 52 and spring 74 being located in a cavity 76 formed in the top of a lower end piece 78. The valve disc 52 can be moved away from the lower face of centre piece 48 to allow fluid to flow between channel ends 72a and 72b by means of a second actuator pin 80 which abuts the under face of valve disc 50 and is moved therewith by finger pressure on pin 63.
It may be seen from an inspection of Figure 4 that ends 82a and 82b of tubes 40a and 40b fit within sockets 84a and 84b of end piece 78 and, when end piece 78 is assembled with the centre piece 48, holes 86a and 86b in sockets 82a and 82b provide a fluid connection between the tubes 40a and 40b and the channels 46a and 46b. Thus, when end pieces 44 and 78 are pressed home onto the ends of centre piece 48, a fluid-tight tubular container
is created in the from of a circular passageway or loop. The desired amount of liquid is poured into the ends 56a or 56b of tubes 40a and 40b after end piece 78 has been pressed into place and before end piece 44 is added.
Though not shown in Figure 4, the valve discs 50 and 52 (conveniently made from nylon or neoprene rubber) have a number of peripheral grooves formed in their edges to allow liquid to flow into and out of cavities 62 and 76. This ensures that the valve discs can always move in their cavities under finger pressure, even if the cavities should fill with liquid.
In the embodiments of the invention shown in Figures 5 to 8, the 0-tube fluid container is formed by sandwiching two sheets of plastics material together, the mating face of at least one of the sheets having been first grooved in the shape of the container. In each of the em¬ bodiments of Figures 5 to 7 the container is D-shape and has two valves on a common spindle set into the straight arm of the "D". The valves are therefore operable jointly and in unison. In the embodiment of Figures 5 and 5A the spindle rotates to operate the valves, while in the embodiments of Figures 6 and 7, the spindle slides to operate the valves. In describing these embodiments similar parts will be referenced by the same numbers.
The inclinometers of Figures 5 to 7 are formed by sticking two rigid, transparent, rectangular methacrylate plastic sheets 100 and 100a together face-to-face, after D-shape grooves have been (respectively) machined in the mating surfaces of each, the grooves coinciding and com¬ bining to form a D-shape tubular fluid container made up of a semi-circular arm 102 and a straight arm 104 for the liquid 106.
To avoid parallax errors, a scale 108 (conveniently marked in degrees, as shown) is printed or inscribed on
the mating face of one of the two sheets (100 or 100a) so as to appear in close proximity to the semi-circular arm 102 of the D-shape container (when sheets 100 and 100a are stuck together). In the embodiments illustrated, the normal position of the inclinometer is with the straight arm 104 of the D-shape container horizontal (as indicated by the scale markings shown). However, the inclinometers can be readily marked and arranged so that the normal position is with the straight arm 104 vertical.
After the sheets 100 and 100a have been assembled in forming the inclinometer of Figures 5 and 5a, a valve chamber 110 is bored from one edge in parallel spaced relation to straight arm 104 to intersect the ends of the semi-circular arm 102. A rotary valve spindle 112a is then inserted in the chamber 110 and the open end of the chamber is closed by plug 114 to retain the spindle in place. To allow addition of indicator liquid 106 to container 104 after assembly, a threaded hole 116 is formed in one edge of the inclinometer coaxial with (and opening into) the straight arm 104 of the "D-'-shape container. This hole (116) is closed by plug 117 that also serves as a zero-adjustment by varying the effective volume of the straight arm 104.
Referring again to Figures 5 and 5A, the rotary spindle 112a has end and central portions (118 and 120, respec¬ tively) of enlarged diameter, the end portions 118 being cross-drilled with holes 122 that can be brought into or out of line with the ends of the semi-circular arm 102 of the fluid container. 0-rings 124 are provided inwards of each end portion 118 to prevent loss liquid along the spindle towards its centre. The enlarged central portion 120 of spindle 112a has gear teeth 126 machined or moulded into its surface to engage with a transversely mounted rack 128, which serves to operate the valves by rotating the spindle 112a to bring the cross holes 120 in its ends 118 into and out of line with the corresponding
end portions of the semi-circular arm 102 of the fluid container.
In the embodiment of Figure 6, the spindle chamber 110 is formed by appropriate recesses moulded into the sheets 100 and 100a which are assembled around the slidable spindle 112b which, like spindle 112 of Figure 5, has enlarged central and end portions. Spindle 112a is a cylindrical metal rod which carries loose rectangular valve blocks 130 that are held against corresponding valve faces by means of springs 132. The ends 134 of the spindle 112a project from the edges of the blocks 100 and 100a so that it can be moved to and fro axially by finger pressure. Loss of liquid from the container along end portions 134 is prevented by 0-rings 136.
Though not illustrated, indicator liquid can be introduc¬ ed into the fluid container by means of a threaded hole and plug fitted in the front or rear face of the inclino- meter. While such a plug could be used as a zero- adjustment as above described, the use of a metal spindle in the embodiment of Figure 6 can mitigate the need for such a zero adjustment. This is because of the differen¬ tial thermal expansion of the metal, liquid and plastics material.
The embodiment of Figure 7, is similar to that of Figure 6, except that the slidable spindle 112c is tubular and itself forms the straight arm of the D-shape fluid container. 0-rings 136 are again used to prevent loss of liquid along the end portions of the spindle, the ends of the tube which forms the spindle 112c being plugged by plugs 140. The spindle tube is drilled transversely to form holes 142 which can be brought into and out of line with corresponding ends of the semi-circular arm 102.
The final embodiment shown in Figure 8 is a precision, limited-range inclinometer formed by the sandwich
technique describedwith respect to Figures 5 - 7 but, as will be seen, the fluid container 10c is of an elongate rectangular shape. As this inclinometer is generally similar to that of Figure 3, the reference numerals employed correspond generally to those employed in Figure 3. In this embodiment the upper and lower runs (34 and 32) are of a length sufficient to confer the desired sensitivity. Independently adjustable valves 26 and 26b are fitted in the upper and lower runs 32 and 34. The left hand arm 150 is linear while the right hand arm 152 is arcuate and subtends a few degrees of arc (in this case, 4°). An opaque coating is applied to most of the surface of the plastics sheets which form the inclino¬ meter so as to obscure most of the container 10c. This helps to highlight the arcuate arm 152.
It will be appreciated by those skilled in the art that a simple, non-electronic settable spirit level has been provided which has many useful applications in building, cabinet making and engineering. It will be of particular value for those who must read the inclination of sur aces which may not be easily accessible or visible. Never¬ theless, it will also be appreciated that many varia¬ tions, additions and modifications can be made to the selected embodiments without departing from the scope and principles of the present invention as set out in the following claims.