Abstract:
An attachment to a standard measuring rule includes a body with a three point mount for stably and securely supporting the measuring rule. Within the body a vernier is provided. In one embodiment the vernier is entirely co-planar with the rule, while in other embodiments the vernier is co-planar except for a zero-point marker. Additionally, the vernier is disclosed as an integral part of the body, or, alternatively, as a separate insert into the body. The vernier divides twenty-four one-eighth inch divisions into twenty-five equal parts, enabling vernier measurements in units of thousandths of an inch. Additional attachments including further bodies and verniers enable the standard rule to measure a wide variety of dimensions, while also enabling the use of either fractional or decimal representation on an easy to read scale.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention pertains generally to geometrical instruments, and more specifically to straight-edge rules that include an index for subdividing the scale, commonly referred to as a vernier. 
     2. Description of the Related Art 
     Devices for measuring distances and geometries of objects are quite old, dating back to prehistoric times. The early devices were designed to measure using units associated with commonly available objects, such as forearms, hands and feet. Distances were generally defined in whole units and fractions were used only infrequently, being more difficult to calculate and determine. Commonly available objects were identified that could be used for smaller and larger measurements, which reduced the need for fractions or large values. Eventually, whole unit measurements gave way to fractional divisions of existing units, such as the division of one foot into twelve equal inches. Inches were further divided into fractions by halves, into one-half inch, one-quarter inch, one-eighth inch and smaller divisions. For the purposes of this disclosure, fractional units are defined as this division of whole units by multiples of two, and will be specifically understood to include these units of half, quarter, eighth, and so forth. 
     As time has passed from those early days, so has the development of technology. Advances in technology requiring smaller, more durable, longer life devices have been accepted as commonplace, yet the foundation required for these advances is often misunderstood or taken for granted. 
     To manufacture smaller components, components at greater yield and lower prices, or components capable of special performance or reliability requires the ability to introduce precision into the tools, machines and processes are used to produce the resulting components. These tools, machines and processes must have the same or better precision than that of the finished component. Yet, determining the precision of the tools, machines and processes requires the use of measuring devices capable of measuring widely diverse devices and objects. The measuring devices must, once again, have precision equal or greater than the precision required of the tools. The precision must start with the instruments used to measure other devices and objects. 
     In modern production, these measurements are often more precise than would be readily identified by fractions of an inch, even though many measurements are still specified based upon the fractional system. For example, a hole might be identified as having a one-half inch diameter, but precision may be specified to the nearest hundredth of an inch. Another dimension may be specified as having an outside diameter of 0.625 inches, which is five-eighths of an inch, with a tolerance of plus or minus five thousandths of an inch. These types of mixed fractional and decimal dimensions are commonplace in a manufacturing environment today. 
     Unfortunately, the development of instruments that readily measure and evaluate these fractional and decimal dimensions has not kept pace with the changing needs of the manufacturing environment. Calculators have been developed that will perform conversions between decimal and fractional formats. However, these calculators are not well suited to a manufacturing environment, and are prone to being destroyed by contamination, spills or accidental impact with tools, equipment or the shop floor. They must also be carried about to be of any real use on the shop floor, therefore requiring yet another pocket or pouch. Furthermore, the use of a separate device from the measuring instrument requires a separate step of keying information into the calculator, taking valuable time and introducing the possibility of keying errors. Since there is no direct visual feedback of proportions or relationships between the units of measure, these mistakes may easily go unnoticed until a later time, when the cost of the error is amplified by production of many bad parts. 
     In the prior art, measuring devices frequently have fairly well developed attachments which allow the measurement of a wide and diverse set of components. Typically, these measurements will include inside and outside diameters, elevations, thickness, gap and other similar measurements. Unfortunately, and in spite of their flexibility at measuring diverse components, these instruments are calibrated to either fractional or decimal measuring, but do not provide the ready ability to convert from one format to another. 
     U.S. Pat. No. 897,437 to Watson is representative of early versions of measuring instruments having both coarse and fine measurement which are capable of measuring a variety of dimensions. A straight rule is provided that has standard graduations marked thereon. Onto the rule there are clamped several arms which extend perpendicularly from the rule. These arms enable the measurement of diverse dimensions by allowing a part to be placed between the arms, to measure thickness or outside diameter, or allowing the arms to be placed within the part, such as for inside diameter. While these types of instruments have met with great success in the trade because of their tremendous versatility in taking measurements of many different types, several deficiencies are noteworthy. In particular, one or both of the adjustable arms cover a large number of graduations on the rule. Since most rules use larger and smaller marks to distinguish different graduations, covering up adjacent marks makes it much more difficult to discern quickly and accurately the particular graduation that is exposed. In addition, the precision of these devices is limited to the smaller sizes of graduations that may be placed upon the scale. While in theory a very large number of such graduations are possible, attempting to place them on the scale and still remain legible and useful is not practically possible. In practice, even scales divided to a sixteenth of an inch become visually “busy”, and these finer scales require more time to accurately discern the measurement. 
     A second limitation is in the ability to quickly convert from fractions to decimals, such as when the part is specified by a combination of fractional and decimal units. 
     A third limitation arises from the fact that the alignment for measuring must occur between two perpendicular planes. The vertical edge of a movable body must be visually aligned with a horizontal Graduation mark. Because the vertical edge and horizontal mark are not co-planar. and are furthermore not of similar width and dimension, accurate correlation between the two different structures is difficult. As a result, any precision beyond the usual sixteenth of an inch is increasingly difficult. 
     In order to overcome the human visual limitation of reading closely spaced graduations, vernier scales were developed such as disclosed by Homan in U.S. Pat. 1,602,490; Berger in U.S. Pat. No. 1,888,305; and Huffman in U.S. Pat. No. 1,888,597. The graduations on the vernier align with the main scale only at the appropriate fractional point of measurement. For example, in the decimal system of measurement, a vernier will divide into ten equal spaces the distance occupied by nine spaces on the scale. When the first vernier graduation mark aligns with a graduation mark on the main decimal scale, the vernier will indicate one-tenth the smallest main scale division. So, carrying this example further, if the main scale is divided into tenths of an inch, the vernier will be calibrated to identify hundredths of an inch without visually cluttering the main scale. This concept has also been widely adapted into the measuring instruments of the prior art, since they quickly advanced the resolution of these versatile instruments. 
     Alternatives to the vernier have been proposed, such as the sawtooth line of Clay in U.S. Pat. No. 4,607,436. However, these alternatives have not proven to offer sufficient benefit in reading the scale with precision for most applications. Furthermore, these scales are more difficult to produce with the intended accuracy. 
     There is a definite need to convert readily between fractional and decimal units, without the need for resorting to special calculators or extremely expensive and complicated devices. This need has not been satisfied by existing instruments. 
     SUMMARY OF THE INVENTION 
     In a first manifestation, the invention is an instrument for measuring distances. A rule is provided having primary fractional graduations. An adjustable body which is movable with respect to the rule has vernier index graduations adjacent to the rule&#39;s fractional graduations for subdividing the rule. Alignment of one vernier index graduation with an adjacent rule fractional graduation designates a decimal division of the rule&#39;s fractional graduation. 
     In a second manifestation, the invention is a rule for measuring a distance accurately to eighths of an inch precision and a first vernier for measuring distance accurately to five-thousandths of an inch precision. A zero point on the rule represents a magnitude of distance equal to zero. One-eighth inch graduations on the rule extend from the zero point and represent increasing distance. Twenty-five equally spaced graduations arc provided within a three inch space on the vernier. The twenty-five vernier graduations are compared with one-eighth inch graduations on the rule for correspondence therebetween, such that when one of said twenty-five vernier graduations is more closely aligned with an adjacent one of the one-eighth inch graduations than any other of the twenty-five vernier graduations to other ones of one-eighth inch graduations, the relative position of the closest one of the twenty-five graduations relative to the first one of the twenty five graduations may be multiplied by five thousandths of an inch. The result is subsequently added to a one-eighth inch fractional distance measurement from the zero point, which has also been converted to decimal format, to thereby calculate a measurement with five-thousandths of an inch precision without interpolation. 
     In a third manifestation, the invention is a method of measuring a first distance between a first point and a second point with a fractionally graduated rule and converting the distance measurement into a decimal distance measurement. The method comprises the steps of: aligning a measuring structure coupled to the fractional rule to one extreme of the distance to be measured; moving a block, carrying a zero-point marker and a vernier having vernier graduations therewith, relative to the fractional rule to align a second measuring structure to the other extreme of the distance to be measured; calculating the smallest fractional distance between a zero measurement position on the fractional rule and the zero-point marker on the block, whereby when the distance is zero the zero-point marker aligns with the zero measurement position on the fractional rule; converting the smallest fractional distance to a first decimal value; identifying the closest vernier graduation to a fractional graduation; multiplying by a decimal amount the number of vernier graduations the closest vernier graduation is from the zero point marker to produce a second decimal value; and adding the first decimal value and second decimal value together to produce a sum equal to the decimal distance measurement. 
     In a fourth manifestation, the invention is a measuring attachment for a fractional rule with fractional graduations on a first surface, a second surface opposite the first surface, and third and fourth surfaces perpendicular and interconnecting the first and second surfaces, comprising: a block for supporting a vernier adjacent and co-planar to the first surface, the block further having a groove therein for supporting the second surface of the fractional rule; a means for repeatably and releasably compressing the third surface of the fractional rule against a generally parallel surface within the groove; wherein the rule and measuring attachment may be adjusted relative to each other and the compressing means may be activated to compress the third surface against the generally parallel groove surface, to thereby prevent further movement therebetween and allow co-planar calculation of distance and vernier. 
     OBJECTS OF THE INVENTION 
     A first object of the invention is to provide a vernier for use with a common fractional rule which converts the fractional rule into decimal measurements. A further object of the invention is to provide decimal precision in thousandths of an inch from an eighth-inch rule scale. Another object of the invention is to provide thc vernier as part of an assembly which adapts a standard rule to the measuring of many diverse dimensions. Yet another object of the invention is the provision of a vernier on the same plane as the rule graduations, which further only minimally or more preferably does not at all block the adjacent rule graduations. Another object of the invention is the provision of both fractional and decimal verniers on the same device, most preferably both co-planar with the standard rule. These and other objects of the invention are accomplished in the preferred embodiment, which will be best understood when considered with the accompanying drawings. 
    
    
     BRIER DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a first embodiment of the invention by exploded assembly view. 
     FIG. 2 illustrates a second embodiment of the invention by top plan view. 
     FIG. 3 illustrates a third embodiment of the invention by top plan view. 
     FIG. 4 a  illustrates the exact alignment of a set of graduations of the first three embodiments, while FIG. 4 b  illustrates interpolation which results from equidistant spacing between two adjacent graduations. 
     FIG. 5 illustrates a preferred method for conversion of fractional measurements to decimal values in accord with the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates a first embodiment of the invention which incorporates the teachings of the invention into a compact, portable, rugged and versatile instrument  100  which finds utility in measuring a variety of dimensions. Instrument  100  has a base  110  which acts as a primary substrate about which other components may be assembled. Within base  110  is a longitudinal groove  120  having slightly elevated edges  121 ,  122 . Groove  120  with edges  121 ,  122  acts as a receiver into which a standard rule  160  may be placed. T he actual length of rule  160  is irrelevant to the invention, though a typical one-foot rule is shown in this illustration. By providing slight edges  121  and  122  within groove  120 , rule  160  will be more securely held with less tendency towards wobble, in the event either rule  160  or base  110  are not perfectly planar. Base  110  additionally has a hole  123  extending transverse through body  120 , and hole  123  passes through a perpendicular opening  124 . Into hole  123  may be inserted a hand or thumb screw  130  having a small head  132  and threads  134 . Into hole  124  a generally cylindrical rod  140  may be inserted. Rod  140  has a threaded hole  142  therein which is designed to mate with threads  134 . In view of the cylindrical nature of hole  124  and rod  140 , rod  140  will not be able to spin in the direction of thread rotation. Therefore, when thumb screw  130  is rotated, rod  140  will be drawn by threads  134  towards head  132 . With rule  160  placed within groove  120 , the small elevated region  144  of rod  140  will be drawn against edge  164  of rule  160 , which will in turn push rule  160  towards vernier  152 . Most preferably, vernier  152  will be slightly elevated at ends  150 ,  154  thereon ensuring a two point contact between vernier  152  and edge  162 . By so designing the interface between rule  160  and body  120 , several advantages may be attained. First, a three-point anchor is provided at region  144  and ends  150  and  154  which is very secure and free from wobbling which would otherwise make precise and repeatable measurements difficult or impossible. Second, surface graduation marks upon rule  160  are co-planar with surface graduation marks on body  110 , making the comparison of marks much easier than was known in the prior art. Since graduation marks may be typically depressed slightly into the surface or alternatively raised therefrom, light reflecting from the differences in graduation mark elevation may be reflected and optically determined from rule to vernier, allowing a person to more easily visually determine alignment of marks to great precision. 
     Body  110  may further include various surfaces useful in measuring special dimensions or shapes, such as inside diameter or height measuring lip  125 , arms such as arms  127  and  128 , and an outside diameter or thickness or height measuring face  126 . In addition, as shown in this embodiment, several different verniers  152  and  156  may be provided adjacent on opposite edges of rule  160 , so that measurements may be taken in the standard fractional scale through vernier  156 , or through the decimal vernier  152  which will be described in greater detail hereinbelow. 
     A cover  170  is preferably provided which serves as a fourth enclosing surface to help retain and guide rule  160  within groove  120 . Cover  170  has holes  172  formed therein through which threaded or other fasteners may pass, preferably extending into threaded holes  129  within body  110 . Cover  170  may take a variety of shapes, but most preferably the “L” shape illustrated in FIG. 1 offers significantly improved visibility to each of the verniers  152 ,  156 . Cover  170  will not block graduation marks which may be needed to quickly ascertain a measurement, where, as aforementioned in the prior art, these adjacent marks were covered. 
     FIG. 2 illustrates an instrument  200  of similar embodiment to instrument  100  from a top plan view, with cover  170  removed therefrom. In the instrument  200 , an additional arm structure  180  is provided at one end of  160 . Arm structure  180  may be permanently affixed, or may be removable therefrom. In the most preferred construction of instrument  200 , arm structure  180  is one-inch wide adjacent to rule  160 . Furthermore, arms  181 ,  182  and  127 ,  128  are each exactly one-half inch wide. By so dimensioning the arms, an inside diameter measurement may be taken and read directly from rule side  162 , using point  150  as the zero marker point. In other words, as shown by the position of body  110  in FIG. 2, an inside diameter measurement of this position would equal exactly three inches. An outside diameter measurement or thickness would equal one inch less, or exactly two inches. Those skilled in the art will readily recognize that other dimensions may be used. Nevertheless, these particular dimensions have been found to be most preferred. 
     FIG. 3 illustrates a third embodiment of the invention which has special vernier inserts  352  and  356  which may be formed separately from body  310  and then attached thereto by, for illustration purposes, screws  357 ,  358 . These separate verniers  352 ,  356  may be made very precisely, and separately from body  310 , thereby saving the special treatments for only those components that truly require them. In the event of any distortions during heat treatment, the verniers  352 ,  356  may be adjusted by loosening screws  357  and  358  to ensure proper alignment with body  310 . In practice, these verniers  352 ,  356  are most preferably exactly one-half inch offset from leading edge  126 . This placement does not alter the operation of the vernier in any way. 
     Instruments  100 ,  200  and  300  each have a fractional vernier adjacent edge  164  of rule  160 . This vernier is most preferred, but not essential. Adding this fractional vernier allows the single instrument to be used for more diverse measurements. Each instrument  100 ,  200 ,  300  also has a decimal vernier  152 ,  352  adjacent edge  162  of rule  160 . This decimal vernier is formed by dividing three inches into twenty-five equal spaces. These spaces, center-to-center, are then equal to 0.120 inches. On the standard rule, the eighth-inch spacings are equal to 0.125 inches, which means that each vernier increment represents exactly 0.005 inches. This allows the fractional rule to be used to take measurements in thousandths of an inch. Furthermore, the eighth-inch graduations are readily converted by a table, which might, for example be printed directly on the back side of body  110 , into the decimal equivalents of 0.125, 0.250, 0.375, 0.500, 0.626, 0.750, and 0.825 inches. By adding the correct numbers of 0.005 inches, based upon the vernier reading, to the decimal equivalent of the eighth-inch scale, an operator can readily determine measurements in thousandths units. 
     FIGS. 4 a  and  4   b  illustrate another feature of the preferred embodiment, wherein rule graduation marks  410 ,  420  and  420  are adjacent decimal vernier graduation marks  440 ,  450 ,  460 . As shown in FIG. 4 a , vernier mark  450  is aligned exactly with rule graduation  420 . If each of the graduations on the rule and vernier are exactly 0.005 inches in width, the 0.120 inch center to center spacing between marks  440  and  450 , when added to the 0.005 inches width of mark  440 , will bring mark  440  just to the edge of mark  410 , which is 0.125 inches on center from mark  420 . As a result, the edges of marks  440  and  460  will align with the edges of marks  410 ,  430 , as shown therein. 
     As can be seen in FIG. 4 b , an interpolation feature is also possible when each of the graduation marks  410 - 460  are equal to the difference in center to center spacings between the rule and vernier. As seen therein, when none of the marks exactly align, but two adjacent marks are equidistant between vernier and rule, such as adjacent marks  410 ,  420  which are, in FIG. 4 b  equidistant to marks  440 ,  450  of the vernier scale, the actual vernier calculation is the average of the two adjacent marks. In other words, the actual vernier distance will be the sum of vernier amounts calculated for mark  440  and  450 , the sum then divided by two. In effect, this allows relatively precise interpolation to 0.0025 inches with consistency. 
     Important is the process for determining the actual graduation mark width. The graduation marks are most preferably exactly equal to the difference in spacing between the vernier and the rule. As long as this is true, this phenomenon of FIG. 4 will then apply to other dimensions besides the eighth-inch rule and five-thousandths vernier of the preferred embodiment. Nevertheless, the eighth-inch unit is the only unit which converts to the desired thousandths precision, so this combination is the most preferred of the present invention. 
     FIG. 5 illustrates by flow chart the process  500  of calculating the decimal vernier in more detail. Therein, the first step  510  is to position the rule relative to one extreme of the distance being measured. This is typically accomplished by placing either an end of the rule or arms such as arms  181 ,  182  against the first extreme edge to be measured. Next, in step  520 , block  110  or  310  will be moved relative to rule  160  until the appropriate feature of the block is adjacent the other extreme edge to be measured. In step  530  the fractional rule is read, making sure that if a measurement is between two fractions, the smaller amount is used as the fractional amount. In other words, if the value is between one-eighth and one quarter of and inch, the one-eight inch value is the one that should be used. That fractional measurement, which will also include whole numbers for the total number of full inches, will be converted to a decimal value in step  540 . This will most preferably be accomplished using a look-up table or chart for each of the seven discrete fractions, though other techniques may be used. 
     The next steps  550  and  560  are listed in sequential order following steps  530  and  540 , but it is important to note that the actual order of these steps is not critical and that steps  550  and  560  could, in fact, come before steps  530  and  540 . In steps  550  and  560 , the vernier marks are compared to the rule fractional graduation marks to find the closest ones. Once that is done, an operator will count from the zero mark vernier graduation the number of vernier graduation marks to the closest mark. This number is multiplied in step  560  by  0 . 005  to calculate a second decimal value which represents the vernier offset from the fractional distance of step  530 . Once that is done, the first decimal value of step  540  is added to the second decimal value of step  560 , to obtain the full measured distance in decimal format. In the event two marks are equidistant at step  550 , then the average of the two marks must be used to get an accurate measure, as was previously discussed in reference to FIG. 4 b.    
     By placing the graduation marks upon the top surface of the rule and vernier, and keeping these marks closely adjacent, optical alignment and visual determination of precision approaching one-thousandth of an inch are viable. However, the inventors recognize that the principles of this feature of the invention, dividing a fractional rule with a decimal vernier, may be implemented by other methods besides optical and visual discrimination. Other methods may be considered by those skilled in the art, such as electrical or electromagnetic interpolations and digital displays, the use of microprocessors to perform the basic computations illustrated herein for the calculation of the actual distances, and so on. Nevertheless, the preferred embodiment offers the advantages of durability and simplicity, making this construction optimal for a harsh production environment. 
     While the foregoing details what is felt to be the preferred embodiment of the invention, no material limitations to the scope of the claimed invention are intended. Further, features and design alternatives that would be obvious to one of ordinary skill in the art are considered to be incorporated herein. The scope of the invention is set forth and particularly described in the claims hereinbelow.