US3058219A

US3058219A - Uni-axial pantograph

Info

Publication number: US3058219A
Application number: US58282A
Authority: US
Inventors: James C Barnes
Original assignee: National Research Council of Canada
Current assignee: National Research Council of Canada
Priority date: 1960-09-26
Filing date: 1960-09-26
Publication date: 1962-10-16
Anticipated expiration: 1979-10-16

Description

J..C. BARNES UNI-AXIAL PANTOGRAPH Filed Sept. 26, 1960 Oct. 16, 1962 United States This invention relates to a uni-axial pantograph.

It has heretofore been proposed to provide a drafting instrument of the pantograph type which is adapted to retrace a drawing in such a manner that its dimensions are changed in one direction only. However, such prior instruments are usually of complicated structure and consequently costly to produce and difficult to operate.

It is an object of this invention to provide a uni-axial pantograph which is of simple structure, which is subject to convenient and inexpensive manufacture, which is of compact form, which is capable of easy assembly and disassembly, which may be operated in a ready and rapid manner, and which produces results of an adequately satisfactory nature.

The invention will be described with reference to the accompanying drawing, in which FIGURE 1 is a plan View of the instrument of the present invention,

FIGURE 2 is a section on line 2-2 of FIGURE l,

FIGURE 3 is a section on line 3-3 of FIGURE l,

FIGURE 4 is a section on line 4 4 of `FIGURE l,

FIGURE 5 is a section on line 5-5 of FIGURE l,

FIGURE 6 is a sectional view of the tracing point carrying portion,

FIGURE 7 is a sectional view on line 9-9 of FIGURE 1 of an interchangeable tracing viewer,

FIGURE 8 is a diagram illustrative of the functional calculations pertaining to the instrument, and

FIGURE 9 is a side elevation, partly in section, of an ellipse drawing attachment.

In the draiwng, a pair of guide brackets 1 are adapted to be clamped, in spaced relation to each other, to a drafting table 2 as by means of clamps 3. Each bracket comprises a metal or like plate having a portion 4 arranged to overlie the table in spaced relation thereto and with its depending edge portion 5 also slightly spaced from the table to enable `a chart, such as indicated at 6, to be slipped thereunder. Thus, it is unnecessary to cut such a chart should it be of a size greater than the spacing between the brackets. It Will be understood, however, that the spacing between the inner edges of the brackets will be chosen to suit the chart to be traced. Since the guide brackets are clamped to the front edge of the table, they are thereby automatically aligned. Each bracket has a slot 7 therein, such slots 7 being aligned and thus parallel to the front edge of the drafting table.

A slide S is mounted in each bracket for free reciprocal movement in slot 7. One end of a link 9 is pivoted to one slide 8 as by pin 10 and one end of a link 11 is pivoted to the other slide 8 as by pin 12. Links 9 and 11 are preferably formed of a transparent plastic composition material such as that known under the trade name Lucite. Link 9 has a scale 13 thereon and link 11 has a scale 14 thereon. Preferably, the pivot pins 10 and 12 are fixed to the respective links 9 and 11 and are freely seated in the slides 8 for ease of mounting therein and removal therefrom.

A cursor 15 is slidably mounted on link 9 and is provided with a pointer 16 for association with scale 13 as Well as a clamp 17 for xing the cursor in selected position. A cursor 1S is slidably mounted on link 11 and is provided with a pointer 19 for association with scale 14 as well as a clamp 20 for fixing the cursor in selected position.

" atent O y ICC 'Ihe other end of link 11 is pivoted to cursor 15, preferably for convenient mounting and dismounting therefrom, as by means of -a bearing bushing 21 mounted on post 22 carried by an ear 23 on the cursor. A bearing ring 24 fixed to link 11 is engageable with bushing 21 and a nut 25 has screw-threaded engagement with post 22 to secure the pivotal assembly in position.

A stylus or tracer point 26 is removably mounted on the free end of link 9. As shown, such stylus is seated in an opening in an arm 27 fixed to the end portion of link 9 and extending laterally therefrom. A flat spring 28 fixed to arm 27 releasably holds the stylus in seated position.

A pencil 29 is removably mounted on cursor 18, being freely seated in an opening in an ear 30 on cursor 18 and releasably held in position by a flat spring 31.

An operating arm 32 having a knob -33 is xed to link 9 adjacent its free end.

The effective lengths of links 9 and 11 are equal, i.e. the distance between pivot 10 and stylus 26 is equal to the distance between

pivots

12 and 22. It will be apparent that pivots 10 and 12 are constrained to slide in the same straight line.

In operation, it will be understood that the tracer stylus 26 is employed to trace over the original chart and that the pencil 29 will draw the final single axis reduction.

Referring to FIGURE 2:

L=elective length of each link 9 and 11, a=distance between pivot 12 and pencil 29, b=distance between pivots 10 and 22.

Since the product of the reductions produced by the two links must be the overall reduction required, then:

rxr-t (l) where nis the desired overall reduction.

It will be apparent that the error produced by the link 11 must cancel that produced by link 9 and thus:

(L-a)|:l-cos (sin-l -2- sin 0 ]==(Lb) (l-eos 0) where 0 has been arbitrarily chosen as 12.

Since Equation 2 is not readily usable in the form shown, series approximations are used to give the form:

b 2 2 2 (E) (cos 0/ It is then possible to use Equations 1 and 3 as a simultaneous pair and solve for (a) and (b). While the series approximations introduce a small unknown error, this is not of practical moment. A number of tests has shown this error to be approximately .00116 inch.

To recapitulate briefly, the links are connected together in such a manner that the product of the Y-axis reduction produced by each is the overall reduction required, and the error (ellipse) produced by one link is cancelled by the error of the other. The result is obviously a straight line of the correct reduced length of the Y-axis. Obviously, a limited range of motion is provided which, -for instance, may be arbitrarily set at 112 relative to the horizontal axis. This angle, together with an eective link length of 24 inches, gives adequate coverage for a paper of 81/2" x ll" size.

It will be obvious that the pencil and stylus may be interchanged to provide an enlargement rather than a reduction.

Instead of the stylus 26, a transparent pin 34 may be provided for interchange therewith as desired. The pin 34, which has a head 35 for engagement by spring 28, is

of a transparent material such as Lucite whereby the chart details are visible therethrough.

i An attachment may be provided for drawing an ellipse, indicated at 36, rfrom a'circle 37. Such attachment is illustrated at 38 and, as shown, may comprise a longitudinally extensible arm 39 having parts 40 and 41 slidable with respect to each other. A pin and slot connection 42, 43 may be provided lto lock the parts in adjusted position. One part 40 has a. hole 44 to receive the stylus point and the part 41 has a hole 45 to receive a pin 46 which is lixed at Vthe center of the circle 37. It will be apparent that as the stylus describes the circumference of the circle, the pencil 29 will draw the ellipse 36.

I claim:

1. A uni-axial pantograph comprising first and second links each having a first pivot at one end thereof, a pair of brackets each arranged to slidably support one of said ffrst pivots along a common straight line, a scale on each link, a cursor on each link arranged for adjustment on one of said scales, said iirst link cursor having means pivotally supporting the other end of said second link about a second pivot yforming an interconnecting pivot for said links, a tracer point carried by the other end of said first link and having a fixed and unvarying position thereon, the distance between said tirst pivot of said first link and said tracer point being equal to the distance between said first and second pivots of said second link, and a marking point carried by said second link cursor at selected distances from said interconnecting pivot continuously exceeding the spacing from said tracer point to said interconnecting pivot.

2. A uni-axial pantograph comprising irst and second links each having a rst pivot at one end thereof, a pair of brackets spaced from each other along a selected rectilinear axis, a slide slidably carried by each said bracket for rectilinear movement along said selected rectilinear axis, each said pivot being mounted in one of said slides, a scale on each link, a cursor on each link arranged for adjustment on one of said scales adapted to be disposed at selected positions intermediate the ends of said links, said first link cursor having means pivotally supporting the other end of said second link about a second pivot and providing an interconnecting pivot for said links at the end of said second link adapted to be disposed at selected locations intermediate the ends of said first link, `a tracer point carried by the other end of said first link and having a xed Yand unvarying position thereon, and a marking member carried by said second link cursor at selected locations along said second link intermediate the ends thereof, the distance between said first pivot of said first link and said tracer point being equal to the distance between said first and second pivots of said second link, said tracer point and marking member being disposed at selected positions which are dissimilar distances from said interconnecting pivot.

3. A uni-axial pantograph as defined in claim 2, including an ellipse drawing attachment comprising an adjustably extensible arm, and means pivotally connecting one end of said arm to said tracing point.

4. A uni-axial pantograph comprising first and second links having distal and proximal ends, said links each having a first pivot at said proximal end, a pair of guide brackets having means for removably clamping the same in spaced relation to each other along an edge of a drafting table or the like, said brackets having rectilinear slots therein aligned along a rectilinear guide axis spaced inwardly from and in parallelism with said edge, means slidably connecting said first pivots of said links with said slots for guiding the same along said rectilinear guide axis, a scale on each of said links, a cursor slidably mounted on each of said links for adjustment along said scales including clamping means for releasably fixing the cursor at selected positions intermediate the ends of the associated link, the cursor on said first link having a pivotal connection with the distal end of said second link forming an interconnecting pivot for said links adapted to be disposed at selected locations intermediate :the ends of said first link, a tracing stylus carried by the distal end of said iirst link occupying a fixed and unvarying position thereon, the distance between said first pivot of said first link and said 'tracing stylus being equal to the distance between said rst pivot and said connection at the distal end of said second link, and a marker carried by the cursor on said second link at a selected distance from said interconnecting pivot Vcontinuously exceeding the distance between said tracing stylus and said interconnecting pivot.

References Cited in the le of this patent UNITED STATES PATENTS 364,043 Riche May 31, 1887 503,934 Braastad Aug. 22, 1893 2,553,026 Williams et al May 15, 1951 2,699,606 Breau Ian. 18, 1955 2,835,974 Wilkinson et al May 27, 1958 FOREIGN PATENTS 63,721 Germany Aug. 11, 1892 661,980 Great Britain Nov. 28, 1951