BASIC LINKAGE CONCEPTS

Kinematic Elements A linkage is composed of rigid-body members, or links, connected to one another by rigid kinematic elements, or pairs. The nature of those connections as well as the shape of the links determines the kinematic properties of the linkage. Although many kinematic pairs are conceivable and most do physically exist, only four have general practical use for linkages. In Fig. 3.1, the four cases are seen to include two with one degree of freedom (f = 1), one with f = 2, and one with f = 3. Single-degree-of-freedom pairs constitute joints in planar linkages or spatial linkages. The cylindrical and spherical joints are useful only in spatial linkages. The links which connect these kinematic pairs are usually binary (two connections) but may be tertiary (three connections) or even more.A commonly used tertiary link is the bell crank familiar to most machine designers. Since our primary interest in most linkages is to provide a particular output for a prescribed input, we deal with closed kinematic chains, examples of which are depicted in Fig. 3.2. Considerable work is now under way on robotics, which are basically open chains. Here we restrict ourselves to the closed-loop type. Note that many complex linkages can be created by compounding the simple four-bar linkage.This may not always be necessary once the design concepts of this chapter are applied. 

Richard E. Gustavson

Technical Staff Member
The Charles Stark Draper Laboratory, Inc.
Cambridge,Massachusetts
Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com)

 

Standard Test Method for Water and Sediment in Crude Oil by Centrifuge Method

This standard is issued under the fixed designation D 96; the number immediately following the designation indicates the year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript epsilon (e) indicates an editorial change since the last revision or reapproval. This method has been approved by the sponsoring committees and accepted by the Cooperating Societies in accordance with established procedures. This test method has been adopted for use by government agencies to replace Method 3003 of Federal Test Method Standard No. 791b. Annex A1 is under revision and will be included in subsequent revisions to this standard. 1. Scope 1.1 This test method covers the centrifuge method for determining sediment and water in crude oil during field custody transfers. This test method may not always provide the most accurate results, but it is considered the most practical method for field determination of sediment and water. When a higher degree of accuracy is required, the laboratory procedure described in Test Methods D 4006, D 4377 or D 473 should be used. NOTE 1—Water by distillation and sediment by extraction are considered the most accurate methods of determining sediment and water in crude oils. As such, these methods should be employed to resolve differences in results from variations of this procedure or between this procedure and other methods, or in the case of a dispute between parties. 1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. 2. Referenced Documents 2.1 ASTM Standards: D 235 Specification for Mineral Spirits (Petroleum Spirits) (Hydrocarbon Drycleaning Spirits)2 D 362 Specification for Industrial Grade Toluene2 D 473 Test Method for Sediment in Crude Oils and Fuel Oils by the Extraction Method3 D 846 Specification for Ten-Degree Xylene2 D 1209 Test Method for Color of Clear Liquids (Platinum- Cobalt Scale)2 D 3699 Specification for Kerosine4 D 4006 Test Method for Water in Crude Oil by Distillation4 D 4057 Practice for Manual Sampling of Petroleum and Petroleum Products4 D 4177 Practice for Automatic Sampling of Petroleum and Petroleum Products4 D 4377 Test Method for Water in Crude Oils by Potentiometric Karl Fischer Titration4 E 1 Specification for ASTM Thermometers5 E 542 Practice for Calibration of Volumetric Ware6 2.2 API Standards:7 Manual of Petroleum Measurement Standards Chapter 8, Sampling Petroleum and Petroleum Products Chapter 10, Sediment and Water 3. Summary of Test Method 3.1 Known volumes of crude oil and solvent (water saturated if required) are placed in a centrifuge tube and heated to 60°C 6 3°C (140°F 6 5°F). After centrifugation, the volume of the sediment-and-water layer at the bottom of the tube is read. NOTE 2—It has been observed that for some waxy crude oils, temperatures of 71°C (160°F) or higher may be required to melt the wax crystals completely so that they are not measured as sediment. If temperatures higher than 60°C (140°F) are necessary to eliminate this problem, they may be used with the consent of the parties involved. If water saturation of the solvent is required, it must be done at the same temperature. 4. Significance and Use 4.1 A determination of sediment and water content is required to determine accurately the net volumes of crude oil involved in sales, taxation, exchanges, inventories, and custody transfers. An excessive amount of sediment and water in crud.

---------------------
1 This test method is under the jurisdiction of Committee D-2 on Petroleum
Products and Lubricants and is the direct responsibility of Subcommittee
D02.02.OB on Sediment and Water (Joint ASTM-JP).
Current edition approved March 25, 1988. Published December 1988. Originally
published as D 96 – 63T. Last previous edition D 96 – 73 (1984).e1
2 Annual Book of ASTM Standards, Vol 06.04.
3 Annual Book of ASTM Standards, Vol 05.01.
4 Annual Book of ASTM Standards, Vol 05.02.
5 Annual Book of ASTM Standards, Vol 14.03.
6 Annual Book of ASTM Standards, Vol 14.02.
7 Available from American Petroleum Institute, 1220 L St., Northwest, Washington,
DC 20005.

An American National Standard
British Standard 4385
American Association State
Highway Transportation Standard
AASHTO No. T55

AMERICAN SOCIETY FOR TESTING AND MATERIALS
100 Barr Harbor Dr., West Conshohocken, PA 19428
Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
 

Three dimensional illustrations using isometric and oblique projection

Isometric projection
Figure 6.1 shows three views of a cube in orthographic
projection; the phantom line indicates the original
position of the cube, and the full line indicates the
position after rotation about the diagonal AB. The cube
has been rotated so that the angle of 45° between side
AC1 and diagonal AB now appears to be 30° in the
front elevation, C1 having been rotated to position C.
It can clearly be seen in the end view that to obtain
this result the angle of rotation is greater than 30°.
Also, note that, although DF in the front elevation
appears to be vertical, a cross check with the end
elevation will confirm that the line slopes, and that
point F lies to the rear of point D. However, the front
elevation now shows a three dimensional view, and
when taken in isolation it is known as an isometric
projection.
This type of view is commonly used in pictorial
presentations, for example in car and motor-cycle service
manuals and model kits, where an assembly has been
‘exploded’ to indicate the correct order and position of
the component parts.
It will be noted that, in the isometric cube, line AC1
is drawn as line AC, and the length of the line is reduced.
Figure 6.2 shows an isometric scale which in principle
is obtained from lines at 45° and 30° to a horizontal
axis. The 45° line XY is calibrated in millimetres
commencing from point X, and the dimensions are
projected vertically on to the line XZ. By similar
triangles, all dimensions are reduced by the same
amount, and isometric lengths can be measured from
point X when required. The reduction in length is in
the ratio
isometric length
true length
= cos 45
cos 30
= 0.7071
0.8660
= 0.8165 °°
Now, to reduce the length of each line by the use of an
isometric scale is an interesting academic exercise,
but commercially an isometric projection would be
drawn using the true dimensions and would then be
enlarged or reduced to the size required.
Note that, in the isometric projection, lines AE and
DB are equal in length to line AD; hence an equal
reduction in length takes place along the apparent
vertical and the two axes at 30° to the horizontal. Note
also that the length of the diagonal AB does not change
from orthographic to isometric, but that of diagonal
C1D1 clearly does. When setting out an isometric
projection, therefore, measurements must be made only
along the isometric axes EF, DF, and GF.
Figure 6.3 shows a wedge which has been produced
from a solid cylinder, and dimensions A, B, and C
indicate typical measurements to be taken along the
principal axes when setting out the isometric projection.
Any curve can be produced by plotting a succession of
points in space after taking ordinates from the X, Y,
and Z axes.
Figure 6.4(a) shows a cross-section through an extruded
alloy bar: the views (b), (c), and (d) give alternative
isometric presentations drawn in the three principal
planes of projection. In every case, the lengths of
ordinates OP, OQ, P1, and Q2, etc. are the same, but
are positioned either vertically or inclined at 30° to
the horizontal.
Figure 6.5 shows an approximate method for the
construction of isometric circles in each of the three
major planes. Note the position of the points of
intersection of radii RA and RB.
The construction shown in Fig. 6.5 can be used
partly for producing corner radii. Fig. 6.6 shows a
small block with radiused corners together with
isometric projection which emphasises the construction
to find the centres for the corner radii; this should be
the first part of the drawing to be attempted. The
thickness of the block is obtained from projecting back
these radii a distance equal to the block thickness and
at 30°. Line in those parts of the corners visible behind
the front face, and complete the pictorial view by adding
the connecting straight lines for the outside of the profile.
In the approximate construction shown, a small
inaccuracy occurs along the major axis of the ellipse,
and Fig. 6.7 shows the extent of the error in conjunction
with a plotted circle. In the vast majority of applications
where complete but small circles are used, for example
spindles, pins, parts of nuts, bolts, and fixing holes,
this error is of little importance and can be neglected.

Manual of
Engineering Drawing
Second edition
Colin H Simmons
I.Eng, FIED, Mem ASME.
Engineering Standards Consultant
Member of BS. & ISO Committees dealing with
Technical Product Documentation specifications
Formerly Standards Engineer, Lucas CAV.
Dennis E Maguire
CEng. MIMechE, Mem ASME, R.Eng.Des, MIED
Design Consultant
Formerly Senior Lecturer, Mechanical and
Production Engineering Department, Southall College
of Technology
City & Guilds International Chief Examiner in
Engineering Drawing

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